WO2007027669A1 - Improved biodiesel fuel, additives, and lubbricants - Google Patents

Abstract

Compositions and methods for forming hydrocarbon products from triglycerides are disclosed. In one aspect, the methods involve the Fischer-Tropsch synthesis of syngas derived in whole or in part from glycerol. In another aspect, the methods involve the Kolbe electrolysis of fatty acids derived from the hydrolysis of triglycerides. The Kolbe electrolysis products and/or the Fischer-Tropsch synthesis products can be subjected to molecular averaging reactions, hydrocracking reactions, isomerization reactions, and the like, to form products in the distillate fuel range, and/or products in the lube base oil range. Thus, vegetable oils and/or animal fats can be converted using water, electricity, catalysts, and heat, into conventional products in the distillate fuel range virtually indistinguishable from those commercially available today. Indeed, the main distinguishing feature is that the products will have virtually no sulfur, nitrogen or aromatic content.

Description

IMPROVED BIODIESEL FUEL, ADDITIVES AND LUBRICANTS

FIELD OF THE INVENTION

The present invention relates to biodiesel fuels derived in whole or in part from biological, renewable sources.

BACKGROUND OF THE INVENTION

Diesel fuel is a refined petroleum product which is burned in the engines powering most of the world's trains, ships, and large trucks. Petroleum is, of course, a non-renewable resource of finite supply. Accordingly, extensive research effort is now being directed toward replacing some or all petroleum-based diesel fuel with a fuel derived from a renewable source such as farm crops.

Vegetable oils have been directly added to diesel fuel in an attempt to replace at least a portion of the diesel fuel. However, when pure vegetable oils are used as a fuel source in diesel engines, they often cause excessive engine wear and fuel injector coking, and have high smoke values. Further, their viscosity is much higher than petroleum based diesel fuel.

Vegetable oils are mostly comprised of triglycerides, esters of glycerol, CH₂ (OH)CH(OH)CH₂ (OH), and three fatty acids. Fatty acids are, in turn, aliphatic compounds containing 4 to 24 carbon atoms and having a terminal carboxyl group.

Diglycerides are esters of glycerol and two fatty acids, and monoglycerides are esters of glycerol and one fatty acid. Naturally occurring fatty acids, with only minor exceptions, have an even number of carbon atoms and, if any unsaturation is present, the first double bond is generally located between the ninth and tenth carbon atoms. The characteristics of the triglyceride are influenced by the nature of their fatty acid residues.

In an effort to overcome some of the problems associated with using pure vegetable oils, several attempts have been made to use fatty acid ethyl and/or methyl esters. These esters are typically prepared by transesterifying triglycerides, the major component in fats and oils, with ethanol and/or methanol, in the presence of an acid or base catalyst.

The glycerol by-product of this reaction is immiscible with the ethyl/methyl esters and is separated. The fatty acid ethyl/methyl ester-rich stream ("biodiesel") is washed with water and then blended with diesel fuel at varying ratios. Biodiesel fuels are associated with some limitations. For example, some research indicates that they cause higher emissions of nitrogen oxides (NOx), increased wear on engine components, and fuel injector coking ("Progress in Diesel Fuel from Crop Oils," AgBiotechnology, (1988)). Also, biodiesel does not provide as much power as petroleum-based diesel is burned (See, for example, Jori, et al, "Comparative test with different biodiesel fuels in tractor engine," Hungarian Agricultural Engineering, 6:7, 27- 28 (1993)), and the diesel engines may need to be retuned in order to run efficiently on biodiesel. However, perhaps the largest drawback of biodiesel fuel is the significance of the glycerol by-product. The crude glycerol volume is about twenty (20%) percent of the source triglyceride volume. Known large scale processes for production of biodiesel fuel largely downplay the significance of the economic loss caused by by-product crude glycerol production as something which can be simply discarded, or sold for whatever the market will pay. Because it is relatively expensive to purify the crude glycerol to prepare it for third party usage, the crude glycerol from biodiesel production typically has a low value. Accordingly, it would be beneficial to provide processes for producing biodiesel fuel that use the glycerol, ideally in a manner which improves the resulting biodiesel fuel.

There have been a few attempts in the prior art to make use of the crude glycerol, and these attempts were largely focused on forming glycerol ethers and adding them to the ethyl/methyl fatty acid esters. For example, U.S. Patent No. 5,578,090 to Bradin disclosed a fuel additive composition including fatty acid alkyl esters and glyceryl ethers, and an alternative fuel composition that includes the fuel additive composition. In one embodiment, Bradin esterified free fatty acids and etherified glycerol with one or more olefins in the presence of an acid catalyst. U.S. Patent No. 5,476,971 to Gupta disclosed reacting glycerol with isobutylene in the presence of an acid catalyst to produce mono-, di- and tri-tertiary butyl ethers of glycerol. U.S. Patent No. 5,308,365 to Kessling disclosed using glycerol ethers mixed with biodiesel fuels to improve emissions content, and U.S. Patent No. 6,015,440 described using glycerol ethers to reduce the cloud point and viscosity of biodiesel fuels.

As olefinic feedstocks are derived mainly from crude oil, it would be advantageous to develop other feedstocks for the olefins needed to convert the glycerol to glycerol ethers. It would also be advantageous to provide other uses for the glycerol resulting from biodiesel fuel production. Also, most car engines in use in the United States today run on gasoline rather than diesel. Much focus has been placed on biodiesel fuel, but little focus has been made on converting vegetable oils and/or animal fats to gasoline. It would be advantageous to provide a renewable source for gasoline ("biogasoline") in addition to diesel fuel. The present invention provides such olefinic feedstocks, biogasoline, and methods for producing same.

SUMMARY OF THE INVENTION

Biodiesel and biogasoline compositions, and methods for their preparation and use directly as fuels, or as blends with conventional diesel fuel and/or gasoline, are disclosed. The biodiesel fuels can include alkyl esters of fatty acids, but ideally include linear and/or branched hydrocarbons that do not include ester, carboxylic acid or hydroxyl group functionality.

In one embodiment, the biodiesel fuel additive composition and/or alternative fuel composition containing the additive include one or more fatty acid alkyl esters, which can be prepared by transesterifieation, or by the reaction of one or more fatty acids with a stream of mixed olefins, such as that derived from Fischer-Tropsch synthesis using an iron catalyst, where the Fischer-Tropsch synthesis can be performed on syngas derived from the glycerol produced from hydrolysis and/or transesterification of triglycerides. In one embodiment, triglycerides are the starting material for the biodiesel fuel described herein. In other embodiments, the free fatty acids are derived from fermentation of biomass, although these tend to be of relatively low molecular weight compared to those derived from animal fats or vegetable oils.

Any triglyceride can be used that provides a fuel additive composition with desired properties. Preferred sources of triglycerides include vegetable oils and fats, as well as animal oils and fats. Any vegetable oil can be used. Animal fats are preferably used. Preferably, animal fats comprise between approximately 1 and 50 percent by weight of the triglycerides. If animal fats comprise more than 50 percent of the triglycerides, the viscosity of the fuel additive composition may be too high for use at low temperatures. The triglycerides can either be converted to free fatty acids and glycerol, or transesterified to form alkyl esters of the fatty acids and glycerol. If an alcohol is used to transesterify the triglyceride, the alcohol is preferably ethanol, methanol, or a mixture of the two. Alternatively, the alcohol can be any C_1-6 straight, branched, or cyclic alcohol. The triglycerides can be converted to glycerol and free fatty acids, for example, by hydrolysis, saponification (followed by re-acidification of the resulting fatty acid salts), enzymatic hydrolysis, or reaction with water under conditions of high temperature and pressure. At least a portion of the glycerol can be converted to syngas, and subjected to

Fischer-Tropsch synthesis. The Fischer-Tropsch synthesis can be performed under conditions which provide a mostly C_2-8 olefin-rich stream (iron catalysts), or under conditions which provide a mostly paraffinic stream (cobalt catalysts).

Olefins produced by Fischer Tropsch synthesis can be used in the fuel production process. They can be used, for example, to esterify fatty acids, and/or to etherify glycerol. The olefins can further be used in an olefin metathesis reaction with paraffins derived from Kolbe electrolysis of fatty acids, optionally with high molecular weight paraffins derived from a separate Fischer Tropsch synthesis using a cobalt catalyst, or other catalyst in which paraffins are the predominant product. The olefins can also be used as a solvent to extract oil from vegetable sources, for example, extracting soybean oil from soybeans. The olefins can also be oligomerized to form higher molecular weight products.

In one embodiment, a portion of the glycerol is combined with the olefinic stream from the Fischer-Tropsch synthesis to form glycerol ethers. These ethers, when combined with conventional diesel fuel, biodiesel fuel, or conventional gasoline products, provide advantageous properties similar to those provided by methyl t-butyl ether (MTBE). The glyceryl ethers lower the viscosity of the fuel additive composition, relative to pure vegetable oils. Also, hydroxy groups on partially etherifϊed glycerol may help to incorporate a small amount of water into the fuel, which can lower NOx emissions.

In another embodiment, both fatty acid alkyl esters and glyceryl ethers are prepared, by reacting free fatty acids and glycerol with olefins in the presence of an acid catalyst. While glycerol and fatty acid alkyl esters are immiscible, the glycerol ethers and fatty acid alkyl esters are miscible, leading to a product stream that makes use of both the glycerol and fatty acid portions of the triglycerides, as opposed to conventional biodiesel processes which only use the fatty acid portion.

The acid catalyst can be a proton source, such as hydrochloric acid, sulfuric acid, and hydrobromic acid, or can be a Lewis acid, for example, aluminum chloride, ferrous chloride, and zeolites. The olefins can be derived, in whole or in part, by Fischer-Tropsch synthesis on syngas formed using glycerol as a starting material. The esterifϊcation and etherification reactions can be run in separate reactors, or in one reactor. The etherification and/or esterification, when performed using an olefin, are preferably run at room temperature, to avoid excessive polymerization of the olefin. Use of ferrous chloride can be preferred, since this catalyst is known to minimize the polymerization of olefins. If the etherification and esterification are run at temperatures in excess of 70⁰C, a large degree of olefin dimerization, trimerization, and polymerization would be expected.

The fatty acids can be treated to remove the carboxylic acid functionality, for example, by enzymatic decarboxylation and/or Kolbe electrolysis. Enzymatic decarboxylation yields one product (i.e., RCO₂H -^ RH + CO₂), whereas Kolbe electrolysis yields a different product (i.e., (i.e., RCO₂H -> RR + CO₂). These alkanes can be used directly in or as lube base stock oil.

A portion of the fatty acids can be esterified using the olefin stream formed by Fischer-Tropsch synthesis on the glycerol to form biodiesel fuel (i.e., RCO₂H + R³HC=CH₂ -> RCO₂CH₂CH₂R'). In these reactions, it is to be understood that the value for R is the alkane chain in the fatty acid present in the triglyceride(s) to be subjected to the processes described herein, which will vary depending on the particular triglycerides used, and R' is H when the olefin is ethylene, and various carbon lengths if the olefin is larger. It can be desired, in certain embodiments, to lower the molecular weight of the alkane products (i.e., of RH and/or RR), and to isomerize the alkane products, to better serve in or as gasoline, jet fuel and/or diesel fuel compositions. The molecular weight of the alkane products can be lowered by hydrocracking/hydrofinishing, and the alkanes can be isomerized using conventional isomerization catalysts. Olefin metathesis can also be used to lower the molecular weight of the products produced from the fatty acids and/or raise the molecular weight of the olefin-rich stream produced by Fischer-Tropsch synthesis of the glycerol.

Olefin metathesis can be performed on the products of decarboxylation (RH) or Kolbe electrolysis (RR) by first dehydrogenating the products to form olefins, and then combining the relatively long chain olefins with a relatively short chain olefins, such as those formed via Fischer-Tropsch synthesis on glycerol, in the presence of suitable olefin metathesis catalysts. The resulting product stream has an averaged molecular weight, and a product stream in the gasoline, jet fuel and/or diesel fuel range can be isolated, for example, by distillation. The relatively low molecular weight product stream from Fischer-Tropsch synthesis of the glycerol (itself resulting from hydrolysis or transesterification of triglycerides) can similarly be combined with any relatively higher molecular weight olefin stream and subjected to olefin metathesis. The olefin metathesis products can be further treated, via hydrogenation, isomerization, and other known process steps, to produce desired end-products.

In one embodiment, ionic liquids are used to conduct one or more of the transesterification, hydrolysis, and Kolbe electrolysis steps. The use of ionic liquids can make it easier to separate the products relative to when water or alcohol is used as a solvent, and potentially reduce the amount of water or alcohol needed for hydrolysis or transesterification. When the ionic liquid is itself acidic, an acid catalyst need not be added, or can be added in lesser concentrations.

The molecular weight of the hydrocarbons can be lowered by hydrocracking, by a combination of dehydrogenation to form relatively high molecular weight olefins, which can then be subjected to olefin metathesis to form olefins with a lower molecular weight distribution. Once the molecular weight of the olefins/paraffms is reduced to the gasoline range, they can be isomerized to a biogasoline composition.

In one embodiment, the fuel additive composition is heated to a temperature of between approximately 100 and 500°F, and contacted with a Lewis acid catalyst, to thermally crack the hydrocarbon chains in the fatty acid alkyl esters. The Lewis acid can be any Lewis acid that is effective for cracking hydrocarbons, including but not limited to zeolites, clay montmorrilite, aluminum chloride, aluminum bromide, ferrous chloride and ferrous bromide. The catalyst preferably is a fixed-bed catalyst. Suitable hydrocarbon cracking catalysts are known to those of ordinary skill in the art.

In another embodiment, the fuel additive composition is hydrocracked. Hydrocracking conditions for hydrocarbons are well known to those of skill in the art.

In another embodiment the fuel additive composition is pyrolyzed. Conditions for pyrolyzing vegetable oils are known to those of skill in the art.

An alternative diesel fuel containing the fuel additive composition can be prepared by blending the fuel additive composition with diesel fuel. In one embodiment, the resulting alternative fuel contains between approximately 25 and 95 percent petroleum- based diesel fuel and between approximately 5 and 75 percent of the fuel additive composition. The resulting alternative fuel is derived, in part, from renewable resources. By using olefins rather than alcohols to prepare the fuel additive composition, the method should be less expensive than existing biodiesel fuel preparations.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a process flow chart showing the hydrolysis of triglycerides to form fatty acids and glycerol, the conversion of glycerol to syngas and resulting Fischer- Tropsch products, the conversion of the fatty acids to hydrocarbons via Kolbe electrolysis, the hydrotreatment of the resulting hydrocarbons, and the production of glycerol ethers from the Fischer-Tropsch olefins.

DETAILED DESCRIPTION

Fuel compositions, and methods for their production, are disclosed. In one embodiment, the fuel composition includes fatty acid alkyl esters and glyceryl ethers. In another embodiment, the fuel composition hydrocarbons in the gasoline, jet, or diesel range. In the latter embodiment, fatty acids can be enzymatically decarboxylated, or subjected to Kolbe electrolysis, to form hydrocarbons. These hydrocarbons can be subjected to hydrocracking to lower the molecular weight, or to olefin metathesis with a low molecular weight (i.e., C_2-8, ideally C_2-4) olefin fraction, where the average molecular weight of the olefin metathesis product is in the gasoline, jet or diesel range. The products of the olefin metathesis can be subjected to isomerization and/or hydrotreatment to form desirable fuel products. Such products can be used directly as fuel, or added to gasoline, jet fuel, and/or diesel fuel to provide alternative gasoline, jet fuel and/or diesel fuel compositions.

In some embodiments, the processes described herein are integrated processes. As used herein, the term "integrated process" refers to a process which involves a sequence of steps, some of which may be parallel to other steps in the process, but which are interrelated or somehow dependent upon either earlier or later steps in the total process.

An advantage of the present process is the effectiveness and relatively inexpensive processing costs with which the present process may be used to prepare high quality fuels, and particularly with feedstocks which are not conventionally recognized as suitable sources for such fuels. An additional advantage is that the resulting fuel is highly paraffinic, and has relatively low levels of sulfur, nitrogen and polynuclear aromatic impurities.

The following definitions will further define the invention: The term "alkyl", as used herein, unless otherwise specified, refers to a saturated straight, branched, or cyclic hydrocarbon OfC₁^, and specifically includes methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, cyclopentyl, isopentyl, neopentyl, hexyl, isohexyl, cyclohexyl, 3-methylpentyl, 2,2-dimethylbutyl, and 2,3-dimethylbutyl.

The term "olefin" refers to an unsaturated straight, branched or cyclic hydrocarbon OfC_2-10, and specifically includes ethylene, propylene, butylene, isobutylene, pentene, cyclopentene, isopentene, hexene, cyclohexene, 3-methylpentene, 2,2-dimethylbutene, 2,3-dimethylbutene, 1-heptene, 2-heptene, 3-heptene, 1-octene, 2-octene, 3-octene, 4- octene, 1-nonene, 2-nonene, 3-nonene, 4-nonene, 1-decene, 2-decene, 3-decene, 4- decene, and 5-decene. Ethylene, propylene and isobutylene can be preferred due to their relatively low cost, and C_2-8 olefins can be preferred as they are produced as the major products in Fischer-Tropsch synthesis when an iron catalyst is used.

Highly substituted olefins are preferred because they can stabilize a carbocation intermediate more readily than unsubstituted olefins.

I. Fuel Composition

The fuel prepared according to the process described herein typically has an average molecular weight in the C₅-₂0 range. The molecular weight can be controlled by adjusting the molecular weight and proportions of the decarboxylated fatty acid fraction and the low molecular weight olefin fraction. Fuel compositions with boiling points in the range of between about 68-450° F, more preferably between about 250-370° F, are preferred. The currently most preferred average molecular weight is around Cs-2o, which has a boiling point in the range of roughly 345° F, depending on the degree of branching. Specifications for the most commonly used diesel fuel (No. 2) are disclosed in ASTM D 975 (See, for example, p. 34 of 1998 Chevron Products Company Diesel Fuels Tech

Review). The minimum flash point for diesel fuel is 52° C (125° F). Specifications for jet fuel are disclosed in ASTMD 1655, standard Specification for Aviation Turbine Fuels. The minimum flash point for jet fuel is typically 38° C.

The process is adaptable to generate higher molecular weight fuels, for example, those in the C_15-20 range, or lower molecular weight fuels, for example, those in the C_5-S range. Preferably, the majority of the composition includes compounds within about 8, and more preferably, within about 5 carbons of the average. Another important property for the fuel is that it has a relatively high flash point for safety reasons. Preferably, the flash point is above 90°C, more preferably above 110°C, still more preferably greater than 175°C, and most preferably between 175°C and 300⁰C.

The fuel can be used, for example, in diesel automobiles and trucks. The high paraffinic nature of the fuel gives it high oxidation and thermal stability. The fuel can also be used as a blending component with other fuels. For example, the fuel can be used as a blending component with fuels derived from crude oil or other sources. The fuel composition can include alkanes and/or alkenes in the gasoline, jet fuel and diesel fuel ranges, and can optionally also include fatty acid alkyl esters and/or glyceryl ethers. Glyceryl ethers are defined as compounds in which one, two or three of the hydroxy groups (OH) in glycerol has been etherified (O-alkyl). These components can reduce the smoke points, enhance the cetane value of diesel fuels, remove water that might condense in fuel tanks and fuel lines during the winter, and provide other useful benefits. The glycerol ethers can be prepared using the glycerol derived from the hydrolysis of triglycerides.

π. Components Used to Prepare the Fuel Composition

A. Triglycerides

Any source of triglycerides can be used to prepare the fatty acid ester derivatives, as long as it provides a fuel additive composition with the desired properties. Preferred sources of triglycerides include, but are not limited to, vegetable oils and fats, as well as animal oils and fats. Examples of suitable vegetable oils include, but are not limited to, crude or refined soybean, corn, coconut (including copra), palm, rapeseed, cotton and oils. Examples of suitable animal fats include, but are not limited to, tallow, lard, butter, bacon grease and yellow grease. Naturally-occurring fats and oils are the preferred source of triglycerides because of their abundance and renewability. Oils with a higher boiling point are preferred over oils with a lower boiling point.

If cost is not considered, the preferred source of vegetable oil is refined soybean oil, because of its abundance, purity, and high percentage of longchain fatty acids. However, a blend of soybean oil and tallow produces a satisfactory crop oil at a substantially reduced cost (the current price of tallow in the U. S. A is less than one-half that of refined soybean oil). A blend of soybean oil with tallow generally contains at least about 50 percent soybean oil, and preferably contains at least about 70 percent soybean oil. Similarly, plants/biomass comprising triglycerides can be used without purification/extraction to provide the triglycerides used in the process. When animal fats are used, the water content of the fuel additive composition and the resulting alternative fuel composition can be adjusted to between approximately 600 and 1000 ppm, preferably between approximately 700 and 900 ppm. For reasons that are as yet not completely understood, a fuel additive composition with this small amount of water has reduced NOx emissions. For this reason, a preferred fuel additive composition contains at least an effective amount of animal fat and fatty acid ester derivatives derived from animal fat such that the water content of the resulting alternative fuel composition is between approximately 600 and 1000 ppm, more preferably between approximately 700 and 900 ppm. A preferred fuel composition is prepared in which between approximately 1 and 50% of the products are derived from animal fats. B. Alcohols

Any alcohol that provides a fuel additive composition with the desired properties can be used to prepare the fatty acid alkyl esters. Suitable alcohols for use in the present invention include, but are not limited to, saturated straight, branched, or cyclic alcohols of C 1-6, and specifically include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, t-butanol, pentanol, cyclopentanol, isopentanol, neopentanol, hexanol, isohexanol, cyclohexanol, 3-methylpentanol, 2,2-dimethylbutanol, and 2,3- dimethylbutanol. Methanol and ethanol are preferred alcohols. Ethanol is generally available commercially in a denatured form. A preferred form of denatured ethanol is grade 3 A which contains minor amounts of methanol and water. Ethanol is produced commercially from ethylene and by fermentation of grains.

It is preferred that any alcohol used in the present invention contains less than five percent water, preferably less than approximately one percent water, to avoid saponification or hydrolysis of the triglycerides.

C. Olefins

Olefins suitable for the etherification and esterification include C_1-10 straight, branched, or cyclic olefins. It is preferred that these olefins contain only hydrogen and carbon. Suitable olefins for use in the present invention include, but are not limited to, ethylene, propylene, butylene, isobutylene, pentene, cyclopentene, isopentene, hexene, cyclohexene, 3-methylpentene, 2,2-dimethylbutene, 2,3-dimethylbutene, 1-heptene, 2- heptene, 3-heptene, 1-octene, 2-octene, 3-octene, 4-octene, 1-nonene, 2-nonene, 3- nonene, 4-nonene, 1-decene, 2-decene, 3-decene, 4-decene, and 5-decene. Ethylene, propylene and isobutylene are preferred olefins due to their relatively low cost. Highly substituted olefins are preferred because they can stabilize a carbocation intermediate more readily than unsubstituted olefins.

In one embodiment, the olefins are a mixture of olefins, in unpurified form, obtained by the cracking of crude oil. Since virtually any olefin will form a combustible product (an ester or an ether), it is unnecessary to form fatty acid esters or glyceryl ethers from pure olefins.

D. Catalysts Any acid catalyst that is suitable for performing glycerol etherification, triglyceride hydrolysis, and/or alkyl chain isomerization, can be used, as appropriate for each individual reaction, and in any effective amount and any effective concentration. Examples of suitable acids include, but are not limited to, hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, and solid catalysts such as Dowex 50®. Strong acids are preferred catalysts. The most preferred acid catalyst for triglyceride hydrolysis and etherification is sulfuric acid. In one embodiment of triglyceride hydrolysis, approximately one cup of concentrated sulfuric acid is added per ten gallons of oil.

The presence of sulfur in downstream Fischer-Tropsch synthesis is not preferred. Accordingly, if sulfuric acid is used to form glycerol/water mixtures that are to be converted to Fischer-Tropsch products, desulfurization may be required.

In one embodiment, the olefins are a mixture of olefins, in unpurified form, obtained by the cracking of crude oil or from Fischer-Tropsch synthesis. Since virtually any olefin will form a combustible product when reacted with an acid to form an ester or an alcohol to form an ether, it is unnecessary to form fatty acid esters or glyceryl ethers from pure olefins. However, the reactions proceed at a faster rate when the olefins are branched relative to unbranched.

The composition is preferably derived from one or more triglycerides and one or more olefins. Preferably, the fuel composition is combined with conventional gasoline, jet fuel or diesel fuel to form an alternative fuel composition. The resulting alternative fuel preferably has a viscosity substantially similar to the conventional gasoline, jet fuel or diesel fuel at a temperature range of between approximately -10⁰F and 110°F. An appropriate viscosity can be achieved, for example, by adjusting the amounts of the individual components in the fuel composition or in an alternative fuel composition that includes the fuel composition. The viscosity of the fuel composition and the alternative fuel composition can be measured by means known to those of ordinary skill in the art, for example, using a viscometer.

When the fuel includes a fatty acid ester-based biodiesel formed by transesterification of a triglyceride, the fatty acid alkyl esters are preferably methyl esters, ethyl esters, or combinations thereof. Blends of ethyl and methyl esters are slightly less expensive and can perform nearly as well in biodiesel fuel as pure ethyl esters, and have lower melting points, albeit with the limitation of additional toxicity. Fuel additive compositions that include fatty acid butyl esters can also be preferred. The presence of glyceryl ethers in the fuel composition can help lower the gel temperature of the fuel, i.e., the temperature at which the fuel becomes so viscous that it cannot be used. The presence of hydroxy groups on partially etherifϊed glycerol derivatives may also improve nitrogen oxide emissions and particulate emissions.

E. Additional Components

The fuel composition can include various additives, such as lubricants, emulsifiers, wetting agents, densifϊers, fluid-loss additives, corrosion inhibitors, oxidation inhibitors, friction modifiers, demulsifϊers, anti-wear agents, anti-foaming agents, detergents, rust inhibitors and the like. Other hydrocarbons, such as those described in U.S. Pat. No. 5,096,883 and/or U.S. Pat. No. 5,189,012, may be blended with the fuel, provided that the final blend has the necessary octanelcetane values, pour, cloud and freeze points, kinematic viscosity, flash point, and toxicity properties. The total amount of additives is preferably between 50-100 ppm by weight for 4-stroke engine fuel, and for 2- stroke engine fuel, additional lubricant oil may be added.

Diesel fuel additives are used for a wide variety of purposes; however, they can be grouped into four major categories: engine performance, fuel stability, fuel handling, and contaminant control additives.

Engine performance additives can be added to improve engine performance. Cetane number improvers (diesel ignition improvers) can be added to reduce combustion noise and smoke. 2-Ethylhexyl nitrate (EHN) is the most widely used cetane number improver. It is sometimes also called octyl nitrate. EBDST typically is used in the concentration range of 0.05% mass to 0.4% mass and may yield a 3 to 8 cetane number benefit. Other alkyl nitrates, ether nitrates some nitroso compounds, and di-tertiary butyl peroxide can also be used.

Fuel and/or crankcase lubricant can form deposits in the nozzle area of injectors-- the area exposed to high cylinder temperatures. Injector cleanliness additives can be added to minimize these problems. Ashless polymeric detergent additives can be added to clean up fuel injector deposits and/or keep injectors clean. These additives include a polar group that bonds to deposits and deposit precursors and a non-polar group that dissolves in the fuel. Detergent additives are typically used in the concentration range of 50 ppm to 300 ppm. Examples of detergents and metal rust inhibitors include the metal salts of sulfonic acids, alkylphenols, sulfurized alkylphenols, alkyl salicylates, naphthenates and other oil soluble mono and dicarboxylic acids such as tetrapropyl succinic anhydride. Neutral or highly basic metal salts such as highly basic alkaline earth metal sulfonates (especially calcium and magnesium salts) are frequently used as such detergents. Also useful is nonylphenol sulfide. Similar materials made by reacting an alkylphenol with commercial sulfur dichlorides. Suitable alkylphenol sulfides can also be prepared by reacting alkylphenols with elemental sulfur. Also suitable as detergents are neutral and basic salts of phenols, generally known as phenates, wherein the phenol is generally an alkyl substituted phenolic group, where the substituent is an aliphatic hydrocarbon group having about 4 to 400 carbon atoms.

Lubricity additives can also be added. Lubricity additives are typically fatty acids and/or fatty esters. Examples of suitable lubricants include polyol esters of C 12-28 acids. The fatty acids are typically used in the concentration range of 10 ppm to 50 ppm, and the esters are typically used in the range of 50 ppm to 250 ppm.

Some organometallic compounds, for example, barium organometallics, act as combustion catalysts, and can be used as smoke suppressants. Adding these compounds to fuel can reduce the black smoke emissions that result from incomplete combustion. Smoke suppressants based on other metals, e.g., iron, cerium, or platinum, can also be used.

Anti-foaming additives such as organosilicone compounds can be used, typically at concentrations of 10 ppm or less. Examples of anti-foaming agents include polysiloxanes such as silicone oil and polydimethyl siloxane; acrylate polymers are also suitable.

Low molecular weight alcohols or glycols can be added to diesel fuel to prevent ice formation.

Additional additives are used to lower a diesel fuel's pour point (gel point) or cloud point, or improve its cold flow properties. Most of these additives are polymers that interact with the wax crystals that form in diesel fuel when it is cooled below the cloud point.

Drag reducing additives can also be added to increase the volume of the product that can be delivered. Drag reducing additives are typically used in concentrations below 15 ppm.

Antioxidants can be added to the fuel to neutralize or minimize degradation chemistry. Suitable antioxidants include, for example, hindered phenols and certain amines, such as phenylenediamine. They are typically used in the concentration range of 10 ppm to 80 ppm. Examples of antioxidants include those described in U.S. Pat. No. 5,200,101, which discloses certain amine/hindered phenol, acid anhydride and thiol ester- derived products.

Acid-base reactions are another mode of fuel instability. Stabilizers such as strongly basic amines can be added, typically in the concentration range of 50 ppm to 150 ppm, to counteract these effects.

Metal deactivators can be used to tie up (chelate) various metal impurities, neutralizing their catalytic effects on fuel performance. They are typically used in the concentration range of 1 ppm to 15 ppm.

Multi-component fuel stabilizer packages may contain a dispersant. Dispersants are typically used in the concentration range of 15 ppm to 100 ppm.

Biocides can be used when contamination by microorganisms reaches problem levels. Preferred biocides dissolve in both the fuel and water and can attack the microbes in both phases. Biocides are typically used in the concentration range of 200 ppm to 600 ppm. Demulsifϊers are surfactants that break up emulsions and allow fuel and water phases to separate. Demulsifiers typically are used in the concentration range of 5 ppm to 30 ppm.

Dispersants are well known in the lubricating oil field and include high molecular weight alkyl succinimides being the reaction products of oil soluble polyisobutylene succinic anhydride with ethylene amines such as tetraethylene pentamine and borated salts thereof.

Corrosion inhibitors are compounds that attach to metal surfaces and form a barrier that prevents attack by corrosive agents. They typically are used in the concentration range of 5 ppm to 15 ppm. Examples of suitable corrosion inhibitors include phosphosulfurized hydrocarbons and the products obtained by reacting a phosphosulfurized hydrocarbon with an alkaline earth metal oxide or hydroxide.

Examples of oxidation inhibitors include antioxidants such as alkaline earth metal salts of alkylphenol thioesters having preferably C5-12 alkyl side chain such as calcium nonylphenol sulfide, barium t-octylphenol sulfide, dioctylphenylamine as well as sulfurized or phosphosulfurized hydrocarbons. Additional examples include oil soluble antioxidant copper compounds such as copper salts of C 10- 18 oil soluble fatty acids.

Examples of friction modifiers include fatty acid esters and amides, glycerol esters of dimerized fatty acids and succinate esters or metal salts thereof. Pour point depressants such as C8-18 dialkyl fumarate vinyl acetate copolymers, polymethacrylates and wax naphthalene are well known to those of skill in the art.

Examples of anti-wear agents include zinc dialkyldithiophosphate, zinc diary diphosphate, and sulfurized isobutylene. Additional additives are described in U.S. Pat. No. 5,898,023 to Francisco et al., the contents of which are hereby incorporated by reference.

HL Alternative Fuel Composition

The fuel additive composition prepared as described above can be used directly in a diesel engine, or can be blended with petroleum-based diesel fuel at a ratio such that the resulting alternative fuel composition contains between approximately 25 to 95 percent diesel fuel and between approximately 5 to 75 percent of the fuel additive composition. The components can be mixed in any suitable manner.

IV. Methods for Preparing the Fuel Composition

A. Transesterification/Hydrolysis

Starting with triglycerides, the first step in the process involves either hydrolysis (or saponification) of the triglyceride to form free fatty acids and glycerol, or transesterification of the triglyceride to form fatty acid esters and glycerol. The hydrolysis or transesterification reaction can be conducted in an ionic liquid, which can minimize the need for added water/alcohol to approximately stoichiometric levels and/or facilitate product separation/purification.

Ionic liquids are organic compounds that are liquid at room temperature. They differ from most salts, in that they have very low melting points. They tend to be liquid over a wide temperature range, are not soluble in non-polar hydrocarbons, are immiscible with water, depending on the anion, and are highly ionizing (but have a low dielectric strength). Ionic liquids have essentially no vapor pressure. Most are air and water stable, and they are used herein to solubilize olefin-complexing metal salts. The properties of the ionic liquids can be tailored by varying the cation and anion. Examples of ionic liquids are described, for example, in J. Chem. Tech. Biotechnol., 68:351-356 (1997); Chem. Ind., 68:249-263 (1996); and J. Phys. Condensed Matter, 5 :(supρ 34B):B99-B106 (1993), Chemical and Engineering News, Mar. 30, 1998, 32-37; J. Mater. Chem., 8:2627- 2636 (1998); and Chem. Rev., 99:2071-2084 (1999), the contents of which are hereby incorporated by reference. Many ionic liquids are formed by reacting a nitrogen-containing heterocyclic ring, preferably a heteroaromatic ring, with an alkylating agent (for example, an alkyl halide) to form a quaternary ammonium salt, and performing ion exchange or other suitable reactions with various Lewis acids or their conjugate bases to form ionic liquids. Examples of suitable heteroaromatic rings include substituted pyridines, imidazole, substituted imidazole, pyrrole and substituted pyrroles. These rings can be alkylated with virtually any straight, branched or cyclic C 1-20 alkyl group, but preferably, the alkyl groups are Cl-16 groups, since groups larger than this tend to produce low melting solids rather than ionic liquids. Various triarylphosphines, thioethers and cyclic and non-cyclic quaternary ammonium salts have also been used. Counterions which have been used include chloroaluminate, bromoaluminate, gallium chloride, tetrafluoroborate, tetrachloroborate, hexafluorophosphate, nitrate, trifluoromethane sulfonate, methylsulfonate, p- toluenesulfonate, hexa fluoroantimonate, hexa fiuoroarsenate, tetrachloroaluminate, tetrabromoaluminate, perchlorate, hydroxide anion, copper dichloride anion, iron trichloride anion, zinc trichloride anion, as well as various lanthanum, potassium, lithium, nickel, cobalt, manganese, and other metal-containing anions.

Certain low melting solids can also be used in place of ionic liquids, depending on the particular separation to be effected. Low melting solids are generally similar to ionic liquids but have melting points between room temperature and about 212° F or are liquid under the process conditions.

The ionic liquids can either be neutral, acidic or basic. Neutral ionic liquids should be used if the desired olefins are not to be isomerized. If it does not matter whether the olefins are isomerized (and if the olefins and/or non-olefms are not acid-sensitive), either neutral or acidic ionic liquids can be used. Examples of appropriate uses of acidic ionic liquids include where the desired goal is to remove olefins and provide a paraffϊnic hydrocarbon stream, or where the olefins are already isomerized.

In one embodiment, a library, i.e., a combinatorial library, of ionic liquids is prepared, for example, by preparing various alkyl derivatives of the quaternary ammonium cation, and varying the associated anions. The acidity of the ionic liquids can be adjusted by varying the molar equivalents and type and combinations of Lewis acids. In place of ionic liquids, the transesterification and/or hydrolysis reactions can be performed in a single critical phase medium is disclosed. The critical phase medium provides increased reaction rates, decreases the loss of catalyst or catalyst activity and improves the overall yield of desired product. The process involves the steps of dissolving an input glyceride- or free fatty acid-containing substance with an alcohol or water into a critical fluid medium; reacting the glyceride- or free fatty acid-containing substance with the alcohol or water input over either a solid or liquid acidic or basic catalyst and sequentially separating the products from each other and from the critical fluid medium, which critical fluid medium can then be recycled back in the process.

B. Conversion of Free Fatty Acids to Alkanes

Free fatty acids can be converted to alkanes via Kolbe electrolysis or enzymatic decarboxylation. Suitable enzymes and reaction conditions for enzymatic hydrolysis are known in the art (see, for example, http://arginme.chem.cornell.edu/Publications/Abstracts/Absl49.html). Decarboxylation reactions are widespread in biochemical pathways. The main feature of a decarboxylase is its ability to stabilize the developing carbanion, most often through derealization of the negative charge. Three suitable enzymes are S-adenosylmethionine decarboxylase, phosphoribosyl carboxyaminoimidazole mutase and orotidine-5 '-monophosphate decarboxylase.

Kolbe electrolysis is an anodic oxidation process of a carboxylate anion. A radical is formed, which then decarboxylates. The resulting radical combines with another to form a dimer. For example, acetic acid will lose a mole of carbon dioxide to produce a methyl radical, two of which will combine to form ethane. The efficiency of Kolbe electrolysis is sensitive to water. It can therefore be preferred to run the reaction in (almost) water free conditions. For this reason, it can be preferred to hydrolyze the triglyceride into free fatty acids in an ionic liquid, and also to perform the Kolbe electrolysis in an ionic liquid. Anion exchange membranes can be used as solid polymer electrolytes (http://www.pca-gmbh.com/appli/spe.htm).

In addition to, or in place of, the free fatty acids derived from triglycerides, carboxylic acids derived from biomass fermentation (i.e., C_4-8 fatty acids), can also be used in the processes described herein. In one aspect, the electricity used to perform the Kolbe electrolysis is derived from coal.

The hydrocarbon products can be subjected to molecular averaging conditions (olefin metathesis) using lower molecular weight olefins. If the hydrocarbons do not include carbon-carbon double bonds, these can be introduced by dehydrogenation. The molecular averaging averages the molecular weight between the decarboxylated fatty acids from enzymatic decarboxylation or Kolbe electrolysis, and the low molecular weight olefins. Ideally, the average molecular weight is centered around desirable range, such as the gasoline, jet and/or diesel ranges. In one embodiment, the lower molecular weight olefins used in a molecular averaging reaction with the Kolbe electrolysis products are derived, in whole or in part, from Fisher Tropsch synthesis using coal, natural gas, or glycerol as all or part of the feedstock.

Using the chemistry described herein, one can use vegetable oil and coal and/or natural gas, as well as fatty acids derived from the fermentation of biomass, to synthesize enough fuel to replace a substantial portion of the amount consumed in the United States that is presently derived from crude oil.

C. Fischer-Tropsch Synthesis i. Synthesis Gas (Syngas) Production

In one embodiment, Fischer-Tropsch synthesis is performed using coal, natural gas, methanol, ethanol, or lignin as a starting material to form synthesis gas. In another embodiment, glycerol is used to form synthesis gas. Fischer-Tropsch synthesis is then performed using the syngas. Where the Fischer-Tropsch synthesis uses an iron catalyst, the products tend to be relatively low molecular weight olefins. These relatively low molecular weight olefins can be used in a molecular averaging reaction with the hydrocarbons produced by the thermal decarboxylation of the fatty acids.

It is known in the art to convert glycerol to synthesis gas (see, for example, http://www.biocap.ca/files/biodiesel/dalai.pdf). The addition of water to the glycerol, as is the case when triglycerides are hydrolyzed with water to form free fatty acids and glycerol, can be beneficial to syngas production. It can help enhance gasification and hydrogen production. The water-gas-shift reaction plays an important role in the conversion of glycerol to hydrogen via steam gasification and pyrolysis. Catalytic steam gasification can give high yields of syngas at relatively low temperatures. The resulting syngas, optionally combined with syngas from other sources, such as that derived from natural gas, can be used in Fischer-Tropsch Synthesis. The syngas is converted to a range of hydrocarbon products, collectively referred to as syncrude, via Fischer-Tropsch synthesis. ii. Fischer-Tropsch Chemistry

In one embodiment, low molecular weight olefin and or wax/heavy fractions are obtained via Fischer-Tropsch chemistry using syngas derived from glycerol. The Fischer- Tropsch products can be combined with the products of the Kolbe electrolysis of fatty acids and/or carboxylic acids produced by fermentation of biomass and subjected to olefin metathesis conditions. It can be preferred to form low molecular weight olefins as the Fischer-Tropsch product when the olefin metathesis is to be performed.

Fischer-Tropsch chemistry tends to provide a wide range of products from methane and other light hydrocarbons to heavy wax. Syngas is converted to liquid hydrocarbons by contact with a Fischer-Tropsch catalyst under reactive conditions.

Depending on the quality of the syngas, it may be desirable to purify the syngas prior to the Fischer-Tropsch reactor to remove carbon dioxide produced during the syngas reaction and any sulfur compounds, if they have not already been removed. This can be accomplished by contacting the syngas with a mildly alkaline solution (e.g., aqueous potassium carbonate) in a packed column.

In general, Fischer-Tropsch catalysts contain a Group VHI transition metal on a metal oxide support. The catalyst may also contain a noble metal promoters) and/or crystalline molecular sieves. Pragmatically, the two transition metals that are most commonly used in commercial Fischer-Tropsch processes are cobalt or iron. Ruthenium is also an effective Fischer-Tropsch catalyst but is more expensive than cobalt or iron. Where a noble metal is used, platinum and palladium are generally preferred. Suitable metal oxide supports or matrices which can be used include alumina, titania, silica, magnesium oxide, silica-alumina, and the like, and mixtures thereof.

Although Fischer-Tropsch processes produce a hydrocarbon product having a wide range of molecular sizes, the selectivity of the process toward a given molecular size range as the primary product can be controlled to some extent by the particular catalyst used. In the present process, one can form low molecular weight olefins using an iron catalyst, and use the olefins in a molecular averaging reaction with the decarboxylated fatty acids, or one can produce C₂o-so paraffins as the primary product using a cobalt catalyst. One suitable catalyst that can be used is described in U.S. Pat. No. 4,579,986 as satisfying the relationship:

(3+4R)>L/S>(0.3+0.4R), wherein: L=the total quantity of cobalt present on the catalyst, expressed as mg Co/ml catalyst,

S=the surface area of the catalyst, expressed as m2 /ml catalyst, and weight ratio of the quantity of cobalt deposited on the catalyst by kneading to the total quantity of cobalt present on the catalyst.

Preferably, the catalyst contains about 3-60 ppw cobalt, 0.1-100 ppw of at least one of zirconium, titanium or chromium per 100 ppw of silica, alumina, or silica-alumina and mixtures thereof. Typically, the synthesis gas will contain hydrogen, carbon monoxide and carbon dioxide in a relative mole ratio of about from 0.25 to 2 moles of carbon monoxide and 0.01 to 0.05 moles of carbon dioxide per mole of hydrogen. It is preferred to use a mole ratio of carbon monoxide to hydrogen of about 0.4 to 1, more preferably 0.5 to 0.7 moles of carbon monoxide per mole of hydrogen with only minimal amounts of carbon dioxide; preferably less than 0.5 mole percent carbon dioxide. The Fischer-Tropsch reaction is typically conducted at temperatures between about 300° F and 700° F (149° C to 371° C), preferably, between about 400° F and 550° F (204° C to 228° C). The pressures are typically between about 10 and 500 psia (0.7 to 34 bars), preferably between about 30 and 300 psia (2 to 21 bars). The catalyst space velocities are typically between about from 100 and 10,000 cc/g/hr, preferably between about 300 and 3,000 cc/g/hr.

The reaction can be conducted in a variety of reactors for example, fixed bed reactors containing one or more catalyst beds, slurry reactors, fluidized bed reactors, or a combination of different type reactors.

In a preferred embodiment, the Fischer-Tropsch reaction is conducted in a bubble column slurry reactor. In this type of reactor synthesis gas is bubbled through a slurry that includes catalyst particles in a suspending liquid. Typically, the catalyst has a particle size of between 10 and 110 microns, preferably between 20 and 80 microns, more preferably between 25 and 65 microns, and a density of between 0.25 and 0.9 g/cc, preferably between 0.3 and 0.75 g/cc. The catalyst typically includes one of the aforementioned catalytic metals, preferably cobalt on one of the aforementioned catalyst supports when formation of C₂₀+ wax fractions is desired. Preferably, such a catalyst comprises about 10 to 14 percent cobalt on a low density fluid support, for example alumina, silica and the like having a density within the ranges set forth above for the catalyst. Since the catalyst metal may be present in the catalyst as oxides, the catalyst is typically reduced with hydrogen prior to contact with the slurry liquid. The starting slurry liquid is typically a heavy hydrocarbon with a viscosity (typically a viscosity between 4-100 centistokes at 100°C) sufficient to keep the catalyst particles suspended. The slurry liquid also has a low enough volatility to avoid vaporization during operation (typically an initial boiling point range of between about 350°C and 550°C). The slurry liquid is preferably essentially free of contaminants such as sulfur, phosphorous or chlorine compounds. Initially, it may be desirable to use a synthetic hydrocarbon fluid such as a synthetic olefin oligomer as the slurry fluid.

The slurry typically has a catalyst concentration of between about 2 and 40 percent catalyst, preferably between about 5 and 20 percent, and more preferably between about 7 and 15 percent catalyst based on the total weight of the catalyst, i.e., metal plus support. The syngas feed typically has a hydrogen to carbon monoxide mole ratio of between about 0.5 and 4 moles of hydrogen per mole of carbon monoxide, preferably between about 1 and 2.5 moles, and more preferably between about 1.5 and 2 moles. The bubble slurry reactor is typically operated at temperatures within the range of between about 15O⁰C and 300°C, preferably between about 185°C and 265°C, and more preferably between about 21°C and 230°C. The pressures are within the range of between about 1 and 70 bar, preferably between about 6 and 35 bar, and most preferably between about 10 and 30 bar (1 bar=14.5 psia). Typical synthesis gas linear velocity ranges in the reactor are from about 2 to 40 cm per sec, preferably from about 6 to 10 cm per sec.

Additional details regarding bubble column slurry reactors can be found, for example, in Y. T. Shah et al., "Design Parameters Estimations for Bubble Column Reactors", AIChE Journal, 28 No. 3, pp. 353-379 (May 1982); Ramachandran et al., "Bubble Column Slurry Reactor, Three-Phase Catalytic Reactors", Chapter 10, pp. 308-332, Gordon and Broch Science Publishers (1983); Deckwer et al., "Modeling the Fischer-Tropsch Synthesis in the Slurry Phase", Ind. Eng. Chem. Process Des. Dev., v 21, No. 2, pp. 231-241 (1982); Kolbel et al., "The Fischer-Tropsch Synthesis in the Liquid Phase", Catal. Rev.-Sci. Eng., v. 21(n), pp. 225-274 (1980); and U.S. Pat. No. 5,348,982, the contents of each of which are hereby incorporated by reference in their entirety. The relatively high (for example, C₂₀₊) and relatively low (for example, C2-6) molecular weight fractions which are to be molecularly averaged are described herein in terms of a Fischer-Tropsch reaction product. However, these fractions can also be obtained through various modifications of the literal Fischer-Tropsch process by which hydrogen (or water) and carbon monoxide (or carbon dioxide) are converted to hydrocarbons (e.g., paraffins, ethers, etc.) and to the products of such processes. Thus, the term Fischer-Tropsch type product or process is intended to apply to Fischer-Tropsch processes and products and the various modifications thereof and the products thereof. For example, the term is intended to apply to the Kolbel-Engelhardt process typically described by the reaction:

3CO+H₂O -» CH₂ - +2CO₂

The molecular averaging process described combines a low molecular weight olefmic fraction (C_2-6, light gas/naphtha) and a high molecular weight decarboxylated fatty acid fraction, which can be dehydrogenated if necessary to form a relatively high molecular weight olefinic fraction prior to molecular averaging.

Suitable catalysts, supports and promoters for separately forming the low and high molecular weight fractions are described in detail below.

iii. Catalysts With Low Chain Growth Probabilities

Suitable catalysts that provide relatively low (alpha values of between 0.600 and 0.700) to moderate (alpha values of between 0.700 and 0.800) chain growth probabilities tend to provide high yields of light (C_2-S) alpha olefins. Such catalysts are well known to those of skill in the art. Preferably, the catalyst used in the first stage is an iron-containing catalyst. Iron itself can be used and, when iron oxides are formed, can be reduced with hydrogen back to iron. However, because the presence of iron fines in the product stream is not preferred, and because iron oxides (rust) decrease the surface area of the catalyst available for reaction, other iron-containing catalysts are preferred. Examples of suitable iron-containing catalysts include those described in U.S. Pat. No. 4,544,674 to Fiato et al. In a preferred embodiment, the iron catalysts include at least about 10 to about 60 weight percent iron. More preferably, they include between about 20 to about 60 weight percent iron, and most preferably about 30 to about 50 weight percent iron. These catalysts can be unsupported, but are preferably promoted with a refractory metal oxide (SiO₂, A1₂O₃3, etc.), alkali (K, Na, Rb) and/or Group IB metals (Cu, Ag). These catalysts are usually calcined, but usually not reduced, rather they are brought up to reaction temperature directly in the COZH₂ feed.

Co-precipitated iron-based catalysts, including those containing cobalt, can be used. High levels of cobalt in an iron-cobalt alloy are known to produce enhanced selectivity to olefϊnic products, as described in Stud. Surf. Sci. Catal. 7, Pt/A, pg. 432

(1981).

Examples of co-precipitated iron-cobalt catalysts and/or alloys include those described in U.S. Pat. Nos. 2,850,515, 2,686,195, 2,662,090, and 2,735,862; AICHE 1981 Summer Nat'l Meeting Preprint No. 408, "The Synthesis of Light Hydrocarbons from CO and H2 Mixtures over Selected Metal Catalysts" ACS 173rd Symposium, Fuel Division,

New Orleans, March 1977; J. Catalysis 1981, No. 72(1), pp. 37-50; Adv. Chem. Ser.

1981, 194, 573-88; Physics Reports (Section C of Physics Letters) 12 No. 5 (1974) pp.

335-374; UK patent application No. 2050859A; J. Catalysis 72, 95-110 (1981); Gmelins Handbuch der Anorganische Chemie 8, Auflage (1959), pg. 59; Hydrocarbon Processing,

May 1983, pp. 88-96; and Chem. Ing. Tech. 49 (1977) No. 6, pp. 463-468.

Methods for producing high surface area metal oxides are described, for example, in the French article, "C. R. Acad. Sc. Paris", p. 268 (May 28, 1969) by P. Courte and B.

Delmon. Metal oxides with a high surface area are prepared by evaporating to dryness aqueous solutions of the corresponding gly colic acid, lactic acid, malic or tartaric acid metal salts. One oxide that was prepared was CoFe₂O₄.

Iron-cobalt spinels which contain low levels of cobalt, in an iron/cobalt atomic ratio of 7:1 to 35:1, are converted to Fischer-Tropsch catalysts upon reduction and carbiding (see, for example, U.S. Pat. No. 4,544,674 to Fiato et al.). These catalysts tend to exhibit high activity and selectivity to C_2-6 olefins and low methane production.

iv. Catalysts with High Chain Growth Probabilities

Catalysts that provide relatively high chain growth probabilities (alpha values of between 0.800 and 0.900) can be used to form a product that mostly includes C₂₀₊ waxes. Any catalyst that provides relatively high chain growth probabilities can be used. Preferably, the catalyst used in the second stage is a cobalt-containing catalyst. Ruthenium is also an effective Fischer-Tropsch catalyst but is more expensive.

One suitable cobalt catalyst that can be used is described in U.S. Pat. No. 4,579,986, as satisfying the relationship:

(3+4R)>L/S>(0.3+0.4R),

wherein: L=the total quantity of cobalt present on the catalyst, expressed as mg Co/ml catalyst;

S=the surface area of the catalyst, expressed as m2 /ml catalyst; and R=the weight ratio of the quantity of cobalt deposited on the catalyst by kneading to the total quantity of cobalt present on the catalyst.

Other suitable catalysts include those described in U.S. Pat. Nos. 4,077,995,

4,039,302, 4,151,190, 4,088,671, 4,042,614 and 4,171,320. U.S. Pat. No. 4,077,995 discloses a catalyst that includes a sulfϊded mixture of CoO, Al₂O₃ and ZnO. U.S. Pat. No. 4,039,302 discloses a mixture of the oxides of Co, Al, Zn and Mo. U.S. Pat. No.

4,151,190 discloses a metal oxide or sulfide of Mo, W, Re, Ru, Ni or Pt, plus an alkali or alkaline earth metal, with Mo-K on carbon being preferred.

U.S. Pat. No. 4,088,671 discloses minimizing methane production by using a small amount of Ru on a cobalt catalyst. Examples of supported ruthenium catalysts suitable for hydrocarbon synthesis via Fischer-Tropsch reactions are disclosed, for example, in U.S. Pat. Nos. 4,042,614 and 4,171,320.

In general, the amount of cobalt catalytic metal present is about 1 to about 50 weight percent of the total catalyst composition, more preferably from about 10.0 to about

25 weight percent. Preferably, the catalyst which provides high chain growth probabilities contains about 3-60 ppw cobalt, 0.1-100 ppw of at least one of zirconium, titanium or chromium per 100 ppw of silica, alumina, or silica-alumina and mixtures thereof.

v. Catalyst Supports The type of support used can influence methane production, which should be minimized regardless of whether the catalyst used promotes high or low chain growth probabilities. Suitable metal oxide supports or matrices which can be used to minimize methane production include alumina, titania, silica, magnesium oxide, silica-alumina, and the like, and mixtures thereof. Examples include titania, zirconium titanate, mixtures of titania and alumina, mixtures of titania and silica, alkaline earth titanates, alkali titanates, rare earth titanates and mixtures of any one of the foregoing with supports selected from the group consisting of vanadia, niobia, tantala, alumina, silica and mixtures thereof.

In the case of supported ruthenium catalysts, the use of a titania ortitania- containing support will result in lower methane production than, for example, a silica, alumina or manganese oxide support. Accordingly, titania and titania-containing supports are preferred.

Typically, the catalysts have a particle size of between 10 and 110 microns, preferably between 20 and 80 microns, more preferably between 25 and 65 microns, and have a density of between 0.25 and 0.9 g/cc, preferably between 0.3 and 0.75 g/cc. The catalysts typically include one of the above-mentioned catalytic metals, preferably including iron for low molecular weight olefin production and cobalt for C20+ wax production, on one of the above-mentioned catalyst supports. Preferably, the cobalt- containing catalysts include about 10 to 14 percent cobalt on a low density fluid support, for example, alumina, silica and the like, having a density within the ranges set forth above for the catalyst.

vi. Promoters and Noble Metals

Methane selectivity is also influenced by the choice of promoter. Alkali metal promoters are known for reducing the methane selectivities of iron catalysts. Noble metals, such as ruthenium, supported on inorganic refractory oxide supports, exhibit superior hydrocarbon synthesis characteristics with relatively low methane production. Where a noble metal is used, platinum and palladium are generally preferred. Accordingly, alkali metal promoters and/or noble metals can be included in the catalyst bed of the first stage provided that they do not significantly alter the reaction kinetics from slow chain growth probabilities to fast chain growth probabilities.

The disclosures of each of the patents discussed above are incorporated herein by reference in their entirety.

vii. The Separation of Product from the Fischer-Tropsch Reaction

The products from Fischer-Tropsch reactions generally include a gaseous reaction product and a liquid reaction product. The gaseous reaction product includes hydrocarbons boiling below about 650° F (e.g., tail gases through middle distillates). The liquid reaction product (the condensate fraction) includes hydrocarbons boiling above about 650° F (e.g., vacuum gas oil through heavy paraffins).

The product that boils below 650°F can be separated into a tail gas fraction and a condensate fraction, i.e., about C_5-20 normal paraffins and higher boiling hydrocarbons, using, for example, a high pressure and/or lower temperature vapor-liquid separator or low pressure separators or a combination of separators. The preferred fractions for preparing the fuel composition via molecular averaging generally include C_2-5 and C₂₀₊ paraffins and olefins.

After removing the particulate catalyst, the fraction boiling above about 650° F. (the condensate fraction) can be separated into a wax fraction boiling in the range of about 650° F-1200°F, primarily about containing C_20-S₀ linear paraffins with relatively small amounts of higher boiling branched paraffins, and one or more fractions boiling above about 1200°F. However, both fractions are preferably combined for molecular averaging.

Products in the desired range (for example, C_25-20, preferably around C_8-12) are preferably isolated and used directly to prepare fuel compositions. Products in the relatively low molecular weight fraction (for example, C_2-63 light gas/naphtha) and the relatively high molecular weight fraction (for example, C₂₀₊, wax/heavy fractions) can be isolated and combined for molecular redistribution/averaging to arrive at a desired fraction. The product of the molecular averaging reaction can be distilled to provide a desired C_5-20 fraction, and also relatively low and high molecular weight fractions, which can be reprocessed in the molecular averaging stage.

It is generally possible to isolate various fractions from a Fischer-Tropsch reaction, for example, by distillation. The fractions include a gasoline fraction (B.P. about 68-450° F/20-232°C), a middle distillate fraction (B.P. about 250-750° F/121-399°C), a wax fraction (B.P. about 650-1200° F/343-649°C) primarily containing C_20-50 normal paraffins with a small amount of branched paraffins and a heavy fraction (B.P. above about 1200° F/649°C) and tail gases.

An advantage of using fuels prepared from syngas is that they do not contain significant amounts of nitrogen or sulfur and generally do not contain aromatic compounds. Accordingly, they have minimal health and environmental impact.

However, a limitation associated with Fisher-Tropsch chemistry is that it tends to produce a broad spectrum of products, ranging from methane to wax. While the product stream includes a fraction useful as fuel, it is not the major product.

Fischer-Tropsch products tend to have appreciable amounts of olefins in the light fractions (i.e., the naphtha and fuel fractions), but less so in the heavy fractions.

Depending on the specifics of the Fischer-Tropsch process, the naphtha can be expected to include more than 50% olefins, most of which are alpha olefins. The fuels will also contain some level of olefins (typically between 10 and 30%) and the waxy fractions can contain smaller quantities. One approach for preparing fuels is to perform Fischer-Tropsch synthesis at high alpha values that minimize the yield of light gases, and maximize the yield of heavier products such as waxes. The wax from the Fischer-Tropsch process typically causes the entire syncrude to be a solid even at high temperatures, which is not preferred. The waxes are then hydrotreated and hydrocracked to form fuels. Since hydrocracking is performed at relatively high temperatures and pressures, it is relatively expensive. In those embodiments where the starting material is glycerol (converted to syngas), and the resulting products can be combined with products from the conversion of fatty acids, both portions of the triglyceride can be converted to fuel products.

D. Olefin Metathesis/Molecular Averaging

As used herein, the terms "molecular redistribution" and olefin metathesis are used to refer to a process in which a mixture of olefins with a relatively wide size distribution is converted into an olefin stream with a relatively narrow size distribution. The terms "molecular averaging" and "disproportionation" are also used.

Fuel compositions can be prepared from a relatively low molecular weight olefinic fraction, such as a C_2-6 olefinic fraction, such as that derived from Fischer- Tropsch synthesis, and a relatively high molecular weight olefinic fraction, such as a C₂₀₊ fraction formed from the enzymatic decarboxylation of fatty acids or Kolbe electrolysis of fatty acids, via molecular averaging, as described in U. S. Patent No. 6,369,286 to Dennis O 'Rear, the contents of which are hereby incorporated by reference.

More products in the desired range are produced when the reactants have molecular weights closer to the target molecular weight. Of course, following fractional distillation and isolation of the product of the molecular averaging reaction, the other fractions can be isolated and re-subjected to molecular averaging conditions.

In the process described herein, a high molecular weight paraffinic fraction is partially dehydrogenated and combined with low molecular weight olefins. The combined olefins are then subjected to olefin metathesis conditions.

i. Catalysts for Molecular Redistribution/Averaging

A typical dehydrogenation/hydrogenation catalyst includes a platinum component and a typical metathesis catalyst includes a tungsten component. Examples of suitable catalysts are described in U.S. Pat. No. 3,856,876, the entire disclosure of which is herein incorporated by reference. The individual steps in the overall molecular averaging reaction are discussed in detail below.

ii. Dehydrogenation The catalyst used to dehydrogenate the relatively high molecular weight paraffin fraction must have dehydrogenation activity. It is necessary to convert at least a portion of the paraffins in the relatively high molecular weight feed to olefins, which are believed to be the actual species that undergo olefin metathesis.

Platinum and palladium or the compounds thereof are preferred for inclusion in the dehydrogenation/hydrogenation component, with platinum or a compound thereof being especially preferred. As noted previously, when referring to a particular metal in this disclosure as being useful in the present invention, the metal may be present as elemental metal or as a compound of the metal. As discussed above, reference to a particular metal in this disclosure is not intended to limit the invention to any particular form of the metal unless the specific name of the compound is given, as in the examples in which specific compounds are named as being used in the preparations.

The dehydrogenation step can be conducted by passing the linear paraffin feed over a dehydrogenation catalyst under dehydrogenating reaction conditions. The dehydrogenation is typically conducted in the presence of hydrogen and correspondingly a certain percentage of oxygenates, e.g., linear alcohols, will be hydrogenated to the corresponding paraffins and then dehydrogenated to the corresponding internal olefins. Thus, the linear hydrocarbon feed may contain a substantial amount of linear oxygenates. On a mole percent basis, this may be up to about 50 mol. % linear oxygenates although it is preferably less than 30 mol. %. On a weight percent basis of oxygen, this will generally be much less, because the linear hydrocarbons are typically made up of only one or two oxygen atoms per molecule.

In order to reduce or eliminate the amount of diolefms produced or other undesired by-products, the reaction conversion to internal olefins should preferably not exceed 50% and more preferably should not exceed 30% based on the linear hydrocarbon content of the feed. Preferably, the minimum conversion should be at least 15 wt. % and more preferably at least 20 wt. %.

Because of the low dehydrogenation conversions, feedstocks with a higher proportion of linear hydrocarbons having carbon atom numbers in the upper range of the desired normal alpha olefin (NAO) products are preferred to facilitate separation of the desired NAO's based on boiling point differences between the NAO and unreacted paraffins. Preferably, the final carbon numbers in the NAO product are within 50 carbon atoms of the initial carbon numbers in the linear paraffinic hydrocarbon feed. More preferably, the final carbon numbers are within 25 carbon atoms, and most preferably within 10 carbon atoms.

The dehydrogenation is typically conducted at temperatures between about 500°F and 1000° F (260°C and 538°C), preferably between about 600°F and 800° F (316°C and 427° C). The pressures are preferably between about 0.1 and 10 atms, more preferably between about 0.5 and 4 atms absolute pressure (about 0.5 to 4 bars). The LHSV (liquid hourly space velocity) is preferably between about 1 and 50 hr^"1, preferably between about 20 and 40 hr^'1. The products generally and preferably include internal olefins.

Since longer chained paraffins are easier to dehydrogenate than shorter chained paraffins, more rigorous conditions, e.g., higher temperatures and/or lower space velocities, within these ranges are typically used where shorter chain paraffins are dehydrogenated. Conversely, lower temperatures and/or higher space velocities, within these ranges, are typically used where longer chained paraffins are dehydrogenated. The dehydrogenation is also typically conducted in the presence of a gaseous diluent, typically and preferably hydrogen. Although hydrogen is the preferred diluent, other art-recognized diluents may also be used, either individually or in admixture with hydrogen or each other, such as steam, methane, ethane, carbon dioxide, and the like. Hydrogen is preferred because it serves the dual-function of not only lowering the partial pressure of the dehydrogenatable hydrocarbon, but also of suppressing the formation of hydrogen- deficient, carbonaceous deposits on the catalytic composite. Hydrogen is typically used in amounts sufficient to insure a hydrogen to hydrocarbon feed mole ratio of about from 2: 1 to 40 : 1 , preferably in the range of about from 5 : 1 to 20 : 1.

Suitable dehydrogenation catalysts which can be used include Group VIE noble metals, e.g., iron, cobalt, nickel, palladium, platinum, rhodium, ruthenium, osmium, and iridium, preferably on an oxide support.

Less desirably, combinations of Group Vm non-noble and Group VIB metals or their oxides, e.g., chromium oxide, may also be used. Suitable catalyst supports include, for example, silica, silicalite, zeolites, molecular sieves, activated carbon alumina, silica- alumina, silica-magnesia, silica-thoria, silicaberylia, silica-titania, silica-aluminum-thora, silica-alumina-zirconia kaolin clays, montmorillonite clays and the like. In general, platinum on alumina or silicalite afford very good results in this reaction. Typically, the catalyst contains about from 0.01 to 5 wt. %, preferably 0.1 to 1 wt. % of the dehydrogenation metal (e.g., platinum). Combination metal catalysts, such as those described in U.S. Patent Nos. 4,013,733; 4,101,593 and 4,148,833, the contents of which are hereby incorporated by reference in their entirety, can also be used. Preferably, hydrogen and any light gases, such as water vapor formed by the hydrogenation of oxygenates, or hydrogen sulfide formed by the hydrogenation of organic sulfur are removed from the reaction product prior to olefin metathesis, for example, by using one or more vapor/liquid separators. In general, where the feedstock is hydrotreated prior to the dehydrogenation, these gases will be removed by gas/liquid phase separation following the hydrotreatment. Since dehydrogenation produces a net gain in hydrogen, the hydrogen may be taken off for other plant uses or as is typically the case, where the dehydrogenation is conducted in the presence of hydrogen, a portion of the recovered hydrogen can be recycled back to the dehydrogenation reactor. Further information regarding dehydrogenation and dehydrogenation catalysts can, for example, be found in U.S. Pat. Nos. 4,046,715; 4, 101,593; and 4, 124,649, the contents of which are hereby incorporated by reference in their entirety. A variety of commercial processes also incorporate dehydrogenation processes, in their overall process scheme, which dehydrogenation processes may also be used in the present process to dehydrogen the paraffinic hydrocarbons. Examples of such processes include the dehydrogenation process portion of the Pacol process for manufacturing linear alkylbenzenes, described in Vora et al., Chemistry and Industry, 187-191 (1990); Schulz R. C. et ai, Second World Conference on Detergents, Montreaux, Switzerland (October 1986); and Vora et al., Second World Surfactants Congress, Paris France (May 1988), hereby incorporated by reference in their entirety. If desired, diolefins produced during the dehydrogenation step may be removed by known adsorption processes or selective hydrogenation processes which selectively hydrogenate diolefins to monoolefins without significantly hydrogenating monoolefins. One such selective hydrogenation process known as the DeFine process is described in the Vora et al. Chemistry and Industry publication cited above. If desired, branched hydrocarbons may be removed before or after the dehydrogenation process or after the olefin metathesis process described below by any suitable process, typically by adsorption. One commercial adsorption process for removing branched hydrocarbons and aromatics from linear paraffins is known as the Molex or Sorbex process described in McPhee, Petroleum Technology Quarterly, pages 127-131, (Winter 1999/2000) which description is hereby incorporated by reference.

iii. Olefin Metathesis The relatively low molecular weight fractions (i.e., C_2-6) and the decarboxylated fatty acids can be subjected to olefin metathesis to form a desired fraction in the range of around C5-20, for example, a gasoline fraction around C5-9, more preferably around C_6-8, a jet fuel fraction of from C_5-15 or C_8-16, or a diesel fraction of from C₁O_-20- This involves using an appropriate olefin metathesis catalyst under conditions selected to convert a significant portion of the decarboxylated fatty acids and low molecular weight olefins to a desired fraction.

The low molecular weight olefin fraction can be used directly in the olefin metathesis reaction. As discussed above, if there are not sufficient olefins in the decarboxylated fatty acids to carry out olefin metathesis, the decarboxylated fatty acids must be converted into olefins in a process known as dehydrogenation or unsaturation before they can participate in the reaction. The resulting olefins are combined with the low molecular weight olefins and the reaction mixture is subjected to olefin metathesis conditions. The metathesized olefins are then optionally converted into paraffins in a process known as hydrogenation or saturation, although they can be used in fuel compositions without first having been hydrogenated.

Various catalysts are known to catalyze the olefin metathesis reaction. The catalyst mass used in the olefin metathesis reaction must have olefin metathesis activity. Olefin metathesis typically uses conventional catalysts, such as WZSiO₂ (or inexpensive variations). Usually, the olefin metathesis catalyst will include one or more of a metal or the compound of a metal from Group VIB or Group VQB of the Periodic Table of the Elements, which include chromium, manganese, molybdenum, rhenium and tungsten. Preferred for inclusion in the olefin metathesis component are molybdenum, rhenium, tungsten, and the compounds thereof. Particularly preferred for use in the olefin metathesis component is tungsten or a compound thereof. As discussed, the metals described above may be present as elemental metals or as compounds of the metals, such as, for example, as an oxide of the metal. It is also understood that the metals may be present on the catalyst component either alone or in combination with other metals.

The chemistry does not require using hydrogen gas, and therefore does not require relatively expensive recycle gas compressors. The chemistry is typically performed at mild pressures (100-5000 psig). The chemistry is typically thermoneutral and, therefore, there is no need for additional equipment to control the temperature.

Depending on the nature of the catalysts, olefin metathesis (and dehydrogenation) may be sensitive to impurities in the feedstock, such as sulfur- and nitrogen-containing compounds and moisture, and these must be removed prior to the reaction. Typically, if the paraffins being metathesized result from a Fischer-Tropsch reaction, they do not include an appreciable amount of sulfur. However, if the paraffins resulted from another process, for example, distillation of crude oil, they may contain sufficient sulfur impurities to adversely affect the olefin metathesis chemistry. The presence of excess hydrogen in the olefin metathesis zone can affect the equilibrium of the olefin metathesis reaction and to deactivate the catalyst.

Since the composition of the fractions may vary, some routine experimentation will be necessary to identify the contaminants that are present and identify the optimal processing scheme and catalyst to use in carrying out the invention. The process conditions selected for carrying out the olefin metathesis step will depend upon the olefin metathesis catalyst used. In general, the temperature in the reaction zone will be within the range of from about 400°F to about 1000°F, with temperatures in the range of from about 500°F to about 850°F usually being preferred. In general, the conversion of the olefins by olefin metathesis increases with an increase in pressure. Therefore, the selection of the optimal pressure for carrying out the process will usually be at the highest practical pressure under the circumstances. Accordingly, the pressure in the reaction zone should be maintained above 100 psig, and preferably the pressure should be maintained above 500 psig. The maximum practical pressure for the practice of the invention is about 5000 psig. More typically, the practical operating pressure will below about 3000 psig. The feedstock to the olefin metathesis reactor should contain a minimum of olefins, and preferably should contain no added hydrogen.

Saturated and partially saturated cyclic hydrocarbons (cycloparaffins, aromatic- cycloparaffms, and alkyl derivatives of these species) can form hydrogen during the molecular averaging reaction. This hydrogen can inhibit the reaction, thus these species should be substantially excluded from the feed. The desired paraffins can be separated from the saturated and partially saturated cyclic hydrocarbons by deoiling or by use of molecular sieve adsorbents, or by deoiling or by extraction with urea. These techniques are well known in the industry. Separation with urea is described by Hepp, Box and Ray in lnd. Eng. Chem., 45: 112 (1953). Fully aromatic cyclic hydrocarbons do not form hydrogen and can be tolerated. Polycyclic aromatics can form carbon deposits, and these species should also be substantially excluded from the feed. This can be done by use of hydrotreating and hydrocracking.

Tungsten catalysts are particularly preferred for carrying out the molecular averaging step, because the molecular averaging reaction will proceed under relatively mild conditions. When using the tungsten catalysts, the temperature should be maintained within the range of from about 400°F (200⁰C) to about 1000°F (540°C), with temperatures above about 500° F (260°C) and below about 800⁰F being particularly desirable. The olefin metathesis reaction described above is reversible, which means that the reaction proceeds toward a roughly thermodynamic equilibrium limit. Therefore, since the feed to the olefin metathesis zone has two streams of paraffins at different molecular weights, equilibrium will drive the reaction to produce a product stream having a molecular weight between that of the two streams. The zone in which the olefin metathesis occurs is referred to herein as an olefin metathesis zone. It is desirable to reduce the concentration of the desired products in the olefin metathesis zone to as low a concentration as possible to favor the reactions in the desired direction. As such, some routine experimentation may be necessary to find the optimal conditions for conducting the process. In the event the catalyst deactivates with the time-on-stream, specific processes that are well known to those skilled in art are available for the regeneration of the catalysts.

Any number of reactors can be used, such as fixed bed, fluidized bed, ebulated bed, and the like. An example of a suitable reactor is a catalytic distillation reactor. When the decarboxylated fatty acid and low molecular weight olefin fractions are combined, it may be advantageous to take representative samples of each fraction and subject them to olefin metathesis, while adjusting the relative amounts of the fractions until a product with desired properties is obtained. Then, the reaction can be scaled up using the relative ratios of each of the fractions that resulted in the desired product. Using this method, one can "dial in" a molecular weight distribution which can be roughly standardized between batches and result in a reasonably consistent product.

Following olefin metathesis, the olefins are optionally converted back into paraffins using a hydrogenation catalyst and hydrogen. While it is not intended that the present invention be limited to any particular mechanism, it may be helpful in explaining the choice of catalysts to further discuss the sequence of chemical reactions which are believed to be responsible for molecular averaging of the paraffins.

As an example, the following is the general sequence of reactions for ethylene and a C20 paraffin, where the C₂₀ paraffin is first dehydrogenated to form an olefin and combined with ethylene, the two olefins are molecularly averaged, and, in this example, the resulting metathesized olefins are hydrogenated to form paraffins:

iv. Refractory Materials

In most cases, the metals in the catalyst mass (dehydrogenation and olefin metathesis) will be supported on a refractory material. Refractory materials suitable for use as a support for the metals include conventional refractory materials used in the manufacture of catalysts for use in the refining industry. Such materials include, but are not necessarily limited to, alumina, zirconia, silica, boria, magnesia, titania and other refractory oxide material or mixtures of two or more of any of the materials. The support may be a naturally occurring material, such as clay, or synthetic materials, such as silica- alumina and borosilicates. Molecular sieves, such as zeolites, also have been used as supports for the metals used in carrying out the dual functions of the catalyst mass. See, for example, U.S. Pat. No. 3,668,268. Mesoporous materials such as MCM-41 and MCM48, such as described in Kresge, C. T., et al., Nature (Vol. 359) pp. 710-712, 1992, may also be used as a refractory support. Other known refractory supports, such as carbon, may also serve as a support for the active form of the metals in certain embodiments. The support is preferably non-acidic, i.e., having few or no free acid sites on the molecule. Free acid sites on the support may be neutralized by means of alkali metal salts, such as those of lithium. Alumina, particularly alumina on which the acid sites have been neutralized by an alkali salt, such as lithium nitrate, is usually preferred as a support for the dehydrogenation/hydrogenation component, and silica is usually preferred as the support for the metathesis component. The preferred catalyst/support for the dehydrogenation step is Pt'silicalite, as this combination is believed to show the best resistance to fouling. The amount of active metal present on the support may vary, but it must be at least a catalytically active amount, i.e., a sufficient amount to catalyze the desired reaction. In the case of the dehydrogenation/hydrogenation component, the active metal content will usually fall within the range from about 0.01 weight percent to about 50 weight percent on an elemental basis, with the range of from about 0.1 weight percent to about 20 weight percent being preferred. For the olefin metathesis component, the active metals content will usually fall within the range of from about 0.01 weight percent to about 50 weight percent on an elemental basis, with the range of from about 0.1 weight percent to about 25 weight percent being preferred. If only the decarboxylated fatty acid fraction is subjected to dehydrogenation conditions, the dehydrogenation catalyst and the olefin metathesis catalyst can be present in separate reactors. However, for olefin metathesis catalysts which can tolerate the presence of the hydrogen generated in the dehydrogenation step, it may be possible to perform both steps in a single reactor. In a reactor having a layered fixed catalyst bed, the two components may, in such an embodiment, be separated in different layers within the bed.

If it is desirable to hydrogenate the olefins from the molecular averaging chemistry, it may be necessary to include an additional hydrogenation step in the process, since the hydrogenation of the olefins must take place after the molecular averaging step.

iv. Feedstocks for the Molecular Averaging Reaction Examples of preferred feedstocks for the molecular averaging reaction include feedstocks with an average molecular weight of C_2-8 (low molecular weight fraction) and either C_10-20 hydrocarbons, derived from enzymatic decarboxylation of fatty acids, or C_2O-4o hydrocarbons, derived from Kolbe electrolysis of fatty acids.

Most preferably, the low molecular weight fraction is obtained from Fischer-Tropsch synthesis, for example, using syngas derived from coal, natural gas, or glycerol and/or the high molecular weight fraction is obtained from the Kolbe electrolysis of free fatty acids. However, numerous petroleum feedstocks, for example, those derived from crude oil, are suitable for use, so long as one of the above feedstocks is also used. Examples include gas oils and vacuum gas oils, residuum fractions from an atmospheric pressure distillation process, solvent-deasphalted petroleum residues, shale oils, cycle oils, petroleum and slack wax, waxy petroleum feedstocks, NAO wax, and waxes produced in chemical plant processes. Straight chain n-paraffins either alone or with only slightly branched chain paraffins having 20 or more carbon atoms are sometimes referred to herein as waxes.

Depending on the olefin metathesis catalysts, the feedstocks may need to exclude appreciable amounts of heteroatoms, diolefins, alkynes or saturated C₆ cyclic compounds. If any heteroatoms or saturated C₆ cyclic compounds are present in the feedstock, they may have to be removed before the molecular averaging reaction. Heteroatoms, diolefins and alkynes can be removed by hydrotreating. Saturated cyclic hydrocarbons can be separated from the desired feedstock paraffins by adsorption with molecular sieves or by deoiling or by complexing with urea. Preferred petroleum distillates for use in the relatively low molecular weight (Cs-6 or less) fraction boil in the normal boiling point range of about 80° C or less. Suitable feedstocks for use in the high molecular weight fraction include any highly paraffinic stream, such as waxes and partially refined waxes (slack waxes). The feedstock may have been subjected to a hydrotreating and/or hydrocracking process before being supplied to the present process. Alternatively, or in addition, the feedstock may be treated in a solvent extraction process to remove aromatics and sulfur- and nitrogen-containing molecules before being dewaxed.

As used herein, the term "waxy petroleum feedstocks" includes petroleum waxes. The feedstock employed in the process of the invention can be a waxy feed which contains greater than about 50% wax, and in some embodiments, even greater than about 90% wax. Such feeds can contain greater than about 70% paraffinic carbon, and in some embodiments, even greater than about 90% paraffinic carbon.

Examples of additional suitable feeds include waxy distillate stocks such as gas oils, lubricating oil stocks, synthetic oils and waxes such as those produced by Fischer- Tropsch synthesis, high pour point polyalphaolefins, foots oils, synthetic waxes such as normal alpha-olefin waxes, slack waxes, deoiled waxes and microcrystalline waxes. Foots oil is prepared by separating oil from the wax, where the isolated oil is referred to as foots oil.

The olefinic fraction is ideally obtained from the Fischer-Tropsch reaction of syngas produced from glycerol, which in turn is derived from the formation of biodiesel from triglycerides or the hydrolysis of triglycerides to form free fatty acids. Molecular averaging converts the fractions to a product that includes a significant fraction in the Cs- 20 range that can be used for preparing a fuel composition. If the fraction is used to form gasoline, it is preferably isomerized to increase the octane value and lower the pour, cloud and smoke point. The product can also be hydrotreated and/or blended with suitable additives for use as a fuel composition.

In its broadest aspect, the present invention is directed to an integrated process for producing fuels, including jet fuel, gasoline and diesel. The process involves the enzymatic decarboxylation of fatty acids or the Kolbe electrolysis of fatty acids to form olefins, which are combined with a low molecular weight olefin fraction and subjected to olefin metathesis conditions. The wax fraction and/or heavy fraction of a Fischer- Tropsch reaction, such as that formed when glycerol is converted to syngas and a cobalt catalyst is used in the Fischer-Tropsch synthesis, can be added to the reaction mixture. The resulting product has an average molecular weight between the molecular weight of the low molecular weight fraction and the molecular weight of the decarboxylated fatty acid fraction.

Fractions in the distillate fuel range can be isolated from the reaction mixture, for example, via fractional distillation. The product of the molecular averaging reaction tends to be highly linear, and is preferably subjected to catalytic isomerization to improve the octane values and lower the pour, cloud and freeze points. The resulting composition has relatively low sulfur values, and relatively high octane values, and can be used in fuel compositions.

In one embodiment, one or both of the feeds to the molecular averaging reaction is isomerized before the molecular averaging reaction. Incorporation of isoparaffins into the molecular averaging reaction provides a product stream that includes isoparaffins in the distillate fuel range which have relatively high octane values. When these isoparaffins are formed from renewable resources such as triglycerides, they form "biogasoline."

In another embodiment, the alpha olefins in the light naphtha and gas are converted into internal olefins (either normal internal or iso-internal olefins). When these materials are averaged against the internal olefins derived from dehydrogenation of the wax, the yield of intermediate fuels is increased.

In one embodiment, the light naphtha and gas fractions may contain impurities such as alcohols and acids. These oxygenates can be converted to additional olefins by dehydration and decarboxylation. Traces of other impurities should be reduced to acceptable levels by use of adsorbents and/or extractants.

Preferably, after performing Fischer-Tropsch synthesis on syngas, and before performing the molecular averaging reaction (olefin metathesis), hydrocarbons in the fuel range are separately isolated, for example, via fractional distillation. The wax and/or heavy fraction are then dehydrogenated, the naphtha and/or light gas fractions are added to the resulting olefϊnic mixture, and reaction mixture is molecularly averaged by subjecting the olefins to olefin metathesis conditions.

It is preferred that at least a portion of the decarboxylated fatty acids are isolated from Kolbe electrolysis, and the low molecular weight fraction is derived from Fischer- Tropsch synthesis, for example, using glycerol derived from the hydrolysis and/or transesterifϊcation of triglycerides. However, at least a portion of the low molecular weight olefin fraction can be derived from a source other than Fischer-Tropsch synthesis. Due to the nature of the molecular averaging chemistry, the reactants cannot include appreciable amounts (i.e., amounts that would adversely affect the catalyst used for molecular averaging) of thiols, amines, or cycloparaffins.

It may be advantageous to take representative samples of each fraction and subject them to molecular averaging reactions, adjusting the relative proportions of the fractions until a product with desired properties is obtained. Then, the reaction can be scaled up using the relative ratios of each of the fractions that resulted in the desired product. Using this method, one can "dial in" a molecular weight distribution which can be roughly standardized between batches and result in a reasonably consistent product.

E. Conversion of Free Fatty Acids to Fatty Acid Esters Any method for preparing fatty acid alkyl esters from free fatty acids can be used.

Fatty acid alkyl esters can be prepared by reacting a fatty acid with one or more alcohols or olefins or in the presence of an acid catalyst. Olefins can be preferred, they are relatively inexpensive reagents as compared to alcohols. Further, when alcohols are used to esterify free fatty acids, water is formed as a by-product. This water can dilute or destroy the acid catalyst. The resulting water layer can also separate to the bottom of the reaction mixture. When olefins are used to esterify free fatty acids, no water is produced as a by-product, and therefore, no water layer forms. A potential downside to using olefins is that they can dimerize, trimerize, or polymerize under acidic conditions. However, these derivatives also bum, and can even be desirable in some applications. Side reactions such as dimerization, trimerization, and polymerization can be controlled to some extent by adjusting the reaction conditions. For example, if the concentration of olefin is kept relatively low (and the concentration of free fatty acids and glycerol relatively high), side reactions are minimized. Low temperatures also disfavor side reactions. The esterification reactions generally go to completion in approximately six to twenty four hours, and can be run in both batch-type and continuous reactors. Reaction conditions for esterification reactions are known to those of skill in the art.

Glycerol can also be converted to glycerol ethers by etherification, in the presence of olefins, using an acid catalyst. The reaction conditions are substantially the same as for conversion of free fatty acids to fatty acid esters, so these reactions can be run simultaneously in the same reactor if desired. If the free fatty acids and glycerol are obtained from the saponification or hydrolysis of triglycerides, the molar ratio of free fatty acids to glycerol is 3:1. Glycerol has up to three hydroxy groups to etherify, and the free fatty acids have only one carboxylic acid to esterify. Therefore, a mole ratio of free fatty acids/glycerol/olefins is at least 1:1:2, and can be as high as to 1 : 1 :4, although excess olefin can be required due to undesirable side reactions. The preferred ratio is between approximately 1 : 1 :2 to 1:1:3, since it is preferable to have glyceryl ethers with one or more hydroxy groups remaining. The olefins used to etherify the glycerol can be derived by the conversion of part of the glycerol product resulting from the hydrolysis of triglycerides into syngas, and the Fischer-Tropsch synthesis using the resulting syngas using an iron or other suitable catalyst that produces low molecular weight (C_2-S, preferably mostly C_2-4) olefins.

The extent of esterification and etherification can be followed by means known to those of skill in the art, including high performance liquid chromatography and gas chromatography. Representative chromatography conditions for following the degree of esterification of fatty acids are described, for example, in Christopolou and Perkins, "High Performance Size Exclusion Chromatography of Fatty Acids, Mono-, Di- and Triglyceride Mixtures." The esterification and etherification are preferably run until the desired range of components, as discussed above, is obtained.

The resulting fatty acid esters and/or glycerol ethers can be directly blended with diesel fuel, or washed with water or other aqueous solutions to remove various impurities, including the catalysts, before blending.

It is possible to neutralize acid catalysts with base. However, this process produces salt. To avoid engine corrosion, it is preferable to minimize the salt concentration in the fuel composition. Salts can be substantially removed from the fuel additive composition, for example, by washing the composition with water.

In another embodiment, the composition is dried after it is washed, for example, by passing the composition through a drying agent such as calcium sulfate. In yet another embodiment, a neutral fuel additive is obtained without producing salts or using a washing step, by using a polymeric acid, such as Dowex 50®, which is a resin that contains sulfonic acid groups. The catalyst is easily removed by filtration after the esterification and etherification reactions are complete.

V. Optional Method Steps

A. Isomerization Chemistry

Optionally, the fractions being molecularly averaged or the products of the molecular averaging chemistry are isomerized, so that the products have more branched paraffins, thus improving their pour, cloud and freeze points. Isomerization processes are generally carried out at a temperature between 200° F and 700° F, preferably 300° F. to 550° F, with a liquid hourly space velocity between 0.1 and 2, preferably between 0.25 and 0.50. The hydrogen content is adjusted such that the hydrogen to hydrocarbon mole ratio is between 1 : 1 and 5:1. Catalysts useful for isomerization are generally bifunctional catalysts comprising a hydrogenation component (preferably selected from the Group Viπ metals of the Periodic Table of the Elements, and more preferably selected from the group consisting of nickel, platinum, palladium and mixtures thereof) and an acid component. Examples of an acid component useful in the preferred isomerization catalyst include a crystalline zeolite, a halogenated alumina component, or a silica-alumina component. Such paraffin isomerization catalysts are well known in the art.

Optionally, but preferably, the resulting product is hydrogenated. The hydrogen can come from a separate hydrogen plant, can be derived from syngas, or made directly from methane and other light hydrocarbons. After hydrogenation, which typically is a mild hydrofinishing step, the resulting fuel product is highly paraffinic. Hydrofinishing is done after isomerization. Hydrofinishing is well known in the art and can be conducted at temperatures between about 190°C to about 340°C, pressures between about 400 psig to about 3000 psig, space velocities (LHSV) between about 0.1 to about 20, and hydrogen recycle rates between about 400 and 1500 SCF/bbl.

The hydrofinishing step is beneficial in preparing an acceptably stable fuel. Fuels that do not receive the hydrofinishing step may be unstable in air and light due to olefin polymerization. To counter this, they may require higher than typical levels of stability additives and antioxidants. B. Thermal Cracking

In some embodiments, after the esterification and etherification reactions, or Kolbe electrolysis, the viscosity of the products is slightly higher than that of diesel fuel. The viscosity can be lowered by thermally cracking, hydrocracking, or pyrolyzing the composition, preferably in the presence of a Lewis acid catalyst. These conditions provide lower molecular weight products, such as alkanes and aromatic, which have lower viscosities than the higher molecular weight fatty acid ester derivatives.

Methods for thermally cracking or hydrocracking hydrocarbons are known to those of skill in the art. Representative Lewis acid catalysts and reactions conditions are described, for example, in Fluid Catalytic Cracking DL, Concepts in Catalyst Design, ACS Symposium Series 452, Mario Occelli, editor, American Chemical Society, Washington, D. C, 1991, the contents of which are hereby incorporated by reference. The pyrolysis of vegetable oils is described in Alencar, et al., Pyrolysis of Tropical Vegetable Oils, J. Ag. Food Chem., 31 : 1268-1270 (1983), the contents of which are hereby incorporated by reference. The hydrocracking of vegetable oils is described in U.S. Pat. No. 4,992,605 to Craig et al., the contents of which are hereby incorporated by reference. The methods described above for thermally cracking, pyrolyzing, and hydrocracking vegetable oils are also effective with the fuel additive composition of the present invention. In one embodiment, the fuel additive composition is heated to a temperature of between approximately 100° and 500⁰F, preferably to between approximately 100° and 200°F, and more preferably to between approximately 150° and 180⁰F, and then passed through a Lewis acid catalyst. Any Lewis acid catalyst that is effective for thermally cracking hydrocarbons can be used. Suitable catalysts for use in the present invention include, but are not limited to, zeolites, clay montmorrilite, aluminum chloride, aluminum bromide, ferrous chloride and ferrous bromide. Preferably, the catalyst is a fixed-bed catalyst.

A preferred catalyst is prepared by coating a ceramic monolithic support with lithium metal. Supports of this type are manufactured, for example, by Dow-Corning. Lithium is coated on the support by first etching the support with zinc chloride, then brushing lithium onto the support, and then baking the support.

The retention time through the Lewis acid catalyst can be as little as one second, although longer retention times do not adversely affect the product. After passing through the Lewis acid catalyst, the derivative stream is then preferably heated to a temperature of between approximately 200° and 600°F, preferably between approximately 200° and 230⁰F, to thermally crack the product. The resulting product is suitable for blending with diesel fuel to form an alternative fuel composition.

C. Hydrotreating and/or Hydrocracking Chemistry

Fractions used in the molecular averaging chemistry may include heteroatoms such as sulfur or nitrogen, diolefms and alkynes that may adversely affect the catalysts used in the molecular averaging reaction. If sulfur impurities are present in the starting materials, they can be removed using means well known to those of skill in the art, for example, extractive Merox, hydrotreating, adsorption, etc. Nitrogen-containing impurities can also be removed using means well known to those of skill in the art. Hydrotreating and hydrocracking are preferred means for removing these and other impurities from the heavy wax feed component. Removal of these components from the light naphtha and gas streams must use techniques that minimize the saturation of the olefins in these streams. Extractive Merox is suitable for removing sulfur compounds and acids from the light streams. The other compounds can be removed, for example, by adsorption, dehydration of alcohols, and selective hydrogenation. Selective hydrogenation of diolefms, for example, is well known in the art. One example of a selective hydrogenation of diolefins in the presence of olefins is UOP's DeFine process.

Accordingly, it is preferred that the heavy wax fractions be hydrotreated and/or hydrocracked to remove the heteroatoms before performing the molecular averaging process described herein. Hydrogenation catalysts can be used to hydrotreat the products resulting from the Fischer-Tropsch, molecular averaging and/or isomerization reactions, although it is preferred not to hydrotreat the products from the Fischer-Tropsch reaction, since the olefins necessary for the molecular averaging step would be hydrogenated. As used herein, the terms "hydrotreating" and "hydrocracking" are given their conventional meaning and describe processes that are well known to those skilled in the art. Hydrotreating refers to a catalytic process, usually carried out in the presence of free hydrogen, in which the primary purpose is the desulfurization and/or denitrification of the feedstock. Generally, in hydrotreating operations, cracking of the hydrocarbon molecules, i.e., breaking the larger hydrocarbon molecules into smaller hydrocarbon molecules, is minimized and the unsaturated hydrocarbons are either fully or partially hydrogenated. Hydrocracking refers to a catalytic process, usually carried out in the presence of free hydrogen, in which the cracking of the larger hydrocarbon molecules is a primary purpose of the operation. Desulfurization and/or denitrifϊcation of the feed stock usually will also occur. Catalysts used in carrying out hydrotreating and hydrocracking operations are well known in the art. See, for example, U.S. Pat. Nos. 4,347,121 and 4,810,357 for general descriptions of hydrotreating, hydrocracking, and typical catalysts used in each process.

Suitable catalysts include noble metals from Group VHIA, such as platinum or palladium on an alumina or siliceous matrix, and unsulfided Group VIIIA and Group VBB, such as nickel-molybdenum or nickel-tin on an alumina or siliceous matrix. U.S. Pat. No. 3,852,207 describes suitable noble metal catalysts and mild hydrotreating conditions. Other suitable catalysts are described, for example, in U.S. Pat. Nos. 4,157,294 and 3,904,513. The non-noble metal (such as nickel-molybdenum) hydrogenation metal are usually present in the final catalyst composition as oxides, or more preferably or possibly, as sulfides when such compounds are readily formed from the particular metal involved. Preferred non-noble metal catalyst compositions contain in excess of about 5 weight percent, preferably about 5 to about 40 weight percent molybdenum and/or tungsten, and at least about 0.5, and generally about 1 to about 15 weight percent of nickel and/or cobalt determined as the corresponding oxides. The noble metal (such as platinum) catalyst contains in excess of 0.01 percent metal, preferably between 0.1 and 1.0 percent metal. Combinations of noble metals may also be used, such as mixtures of platinum and palladium.

The hydrogenation components can be incorporated into the overall catalyst composition by any one of numerous procedures. The hydrogenation components can be added to matrix component by co-mulling, impregnation, or ion exchange and the Group VI components, i.e., molybdenum and tungsten can be combined with the refractory oxide by impregnation, co-mulling or co-precipitation. Although these components can be combined with the catalyst matrix as the sulfides, that may not be preferred, as the sulfur compounds may interfere with some molecular averaging or Fischer-Tropsch catalysts. The matrix component can be of many types including some that have acidic catalytic activity. Ones that have activity include amorphous silica-alumina or may be a zeolitic or non-zeolitic crystalline molecular sieve. Examples of suitable matrix molecular sieves include zeolite Y, zeolite X and the so-called ultra stable zeolite Y and high structural silica: alumina ratio zeolite Y such as that described in U.S. Pat. Nos. 4,401,556, 4,820,402 and 5,059,567. Small crystal size zeolite Y, such as that described in U.S. Pat. No. 5,073,530, can also be used. Non-zeolitic molecular sieves which can be used include, for example, silicoaluminophosphates (SAPO), ferroaluminophosphate, titanium aluminophosphate, and the various ELAPO molecular sieves described in U.S. Pat. No. 4,913,799 and the references cited therein. Details regarding the preparation of various non-zeolite molecular sieves can be found in U.S. Pat. Nos. 5,114,563 (SAPO); U.S. Pat. No. 4,913,799 and the various references cited in U.S. Pat. No. 4,913,799. Mesoporous molecular sieves can also be used, for example, the M41S family of materials (J. Am. Chem. Soc. 1992, 114, 10834-10843), MCM-41 (U.S. Pat. Nos. 5,246,689, 5,198,203 and 5,334,368), and MCM-48 (Kresge et al., Nature 359 (1992) 710).

Suitable matrix materials may also include synthetic or natural substances as well as inorganic materials such as clay, silica and/or metal oxides such as silica-alumina, silica-magnesia, silica-zirconia, silica-thoria, silica-berylia, silica-titania as well as ternary compositions, such as silica-alumina-thoria, silica-alumina-zirconia, silica-alumina- magnesia, and silica-magnesia zirconia. The latter may be either naturally occurring or in the form of gelatinous precipitates or gels including mixtures of silica and metal oxides. Naturally occurring clays which can be composited with the catalyst include those of the montmorillonite and kaolin families. These clays can be used in the raw state as originally mined or initially subjected to calumniation, acid treatment or chemical modification. Furthermore, more than one catalyst type may be used in the reactor. The different catalyst types can be separated into layers or mixed. Typical hydrotreating conditions vary over a wide range. In general, the overall LHSV is about 0.25 to 2.0, preferably about 0.5 to 1.0. The hydrogen partial pressure is greater than 200 psia, preferably ranging from about 500 psia to about 2000 psia. Hydrogen recirculation rates are typically greater than 50 SCF/Bbl, and are preferably between 1000 and 5000 SCF/Bbl.

Temperatures range from about 300°F to about 750⁰F, preferably ranging from 450° F to 600°F.

D. Oligomerization Heavy products, especially lubricating base oils and diesel, can be formed by oligomerizing the olefins in the Fischer-Tropsch condensate formed from synthesis gas derived from glycerol. During oligomerization, the lighter olefins are converted into heavier products. The carbon backbone of the oligomers will also display branching at the points of molecular addition. Due to the introduction of branching into the molecule, the pour point of the products are reduced making the final products of the oligomerization operation excellent products themselves or excellent candidates for blending components to upgrade lower quality conventional petroleum-derived products to meet market specifications. In the event the pour point is too high, the oligomerization product may be sent to a catalytic dewaxing unit or, alternatively, the boiling range of the second intermediate effluent from the thermal cracker may be adjusted prior to going to the oligomerization operation to make a lower pour point and lower cloud point product. By lowering the upper boiling point of the thermal cracker effluent, the average molecular weight of the feed to the oligomerization unit will be lowered. Lower molecular weight molecules will yield increased branching in the oligomerization mixture which will translate into a lower pour point and cloud point in the final product. The higher boiling fractions may be recycled to the thermal cracker for further processing. As already noted above, the selection of the Fischer-Tropsch catalyst, such as by use of an iron-based catalyst, may also be used to increase branching in the molecules of the final products. The oligomerization of olefins has been well reported in the literature, and a number of commercial processes are available. See, for example, U.S. Pat. Nos. 4,417,088; 4,434,308, 4,827,064; 4,827,073; and 4,990,709. Various types of reactor configurations may be employed, with the fixed catalyst bed reactor being used commercially. More recently, performing the oligomerization in an ionic liquids media has been proposed, since the contact between the catalyst and the reactants is efficient and the separation of the catalyst from the oligomerization products is facilitated. Preferably, the oligomerized product will have an average molecular weight at least 10 percent higher than the initial feedstock, more preferably at least 20 percent higher. The oligomerization reaction will proceed over a wide range of conditions. Typical temperatures for carrying out the reaction are between about 32° F (0° C) and about 800° F (425° C). Other conditions include a space velocity from 0.1 to 3 LHSV and a pressure from 0 to 2000 psig. Catalysts for the oligomerization reaction can be virtually any acidic material, such as, for example, zeolites, clays, resins, BF3 complexes, HF, H2SO4, A1C13, ionic liquids (preferably ionic liquids containing a Bronsted or Lewis acidic component or a combination of Bronsted and Lewis acid components), transition metal-based catalysts (such as Cr/SiO2), superacids, and the like. In addition, non-acidic oligomerization catalysts including certain organometallic or transition metal oligomerization catalysts may be used, such as, for example, zirconocenes. E. Filtration of the Fuel Composition

In one embodiment, the fuel composition is filtered, preferably through a filter with a pore size of between approximately 5 and 50 microns, more preferably, between approximately 10 and 20 microns, to remove solid impurities. This can be especially important when animal fats are used, since rendering processes can inadvertently place small pieces of bone and other particulate matter in the animal fat that needs to be removed.

VL Representative Processes Figure 1 is a representative process flow diagram illustrating the production of both biogasoline and biodiesel from Kolbe electrolysis, and the etherification of glycerol using primarily existing MTBE (methyl tert butyl ether) technology.

As shown in Figure 1, 10 is a source of triglycerides. The triglycerides are hydrolyzed (20) to form glycerol and free fatty acids. The fatty acids are subjected to IColbe electrolysis (30), and the glycerol is converted to syngas in a syngas generator (40). The syngas is sent to a Fischer-Tropsch reactor (50) and converted to either low molecular weight olefins or high molecular weight paraffins.

The low molecular weight olefins from Fischer-Tropsch, as shown in the diagram, come from glycerol, but these can include Fischer-Tropsch products from other sources, and need not include Fischer-Tropsch from glycerol. These olefins are combined with the products of the Kolbe electrolysis and subjected to molecular averaging (60) to form products in the distillate fuel range, ideally, in the gasoline, jet, or diesel range.

The olefins from Fischer-Tropsch synthesis can be combined with glycerol and subjected to etherification conditions (70), and the resulting products optionally subjected to fractional distillation (80) if desired, with the residual glycerol and/or olefins, if any, recycled to the etherification tank (70). The glycerol ethers, which can include, for example, a blend of glycerol ethers, monoethers, diethers, ortriethers, can then be stored (100) for future use, for example, as a solvent and/or for blending with gasoline, jet, and/or diesel fuel compositions. An embodiment is blending at a molar ratio of olefins to glycerol and is at least 1.5/1. Additionally, the molar ratio of olefins to glycerol is at least 2/1.

In some embodiments, it can be preferred to use mono-ethers, diethers, or blends thereof. Modifications and variations of the present invention relating to a fuel additive composition and an alternative fuel derived from the composition will be obvious to those skilled in the art from the foregoing detailed description of the invention.

Claims

1. A method for preparing a hydrocarbon product, comprising the steps of: a) performing Kolbe electrolysis on a Ci_O-2o fatty acid, to form a Kolbe electrolysis product, b) combining the Kolbe electrolysis product with an olefin-containing material substantially in the C_2-16 range to form a reaction mixture, and c) subjecting the reaction mixture to molecular averaging to form a hydrocarbon product, wherein, if the fatty acid is saturated, a dehydrogenation step is performed on either the fatty acid or the Kolbe electrolysis product before the molecular averaging step is performed.

2. The method of claim 1, wherein the fatty acid is obtained by hydrogenating a vegetable oil or animal fat.

3. The method of claim 1, wherein the hydrocarbon product of the molecular averaging step is fractionated, and a product in the distillate fuel range is obtained.

4. The method of claim 3, wherein the product is in the diesel fuel range.

5. The method of claim 3, wherein the product is in the Cs-I₂ range.

6. The method of claim 5, wherein the product in the C_5-12 range is isomerized to provide branched hydrocarbons.

7. The method of claim 1, wherein the olefin-containing material substantially in the C_2-16 range is obtained by Fisher-Tropsch synthesis.

8. The method of claim 7, wherein the Fisher-Tropsch synthesis was performed using syngas derived in whole or in part from coal or natural gas.

9. The method of claim 7, wherein the Fisher-Tropsch synthesis was performed using syngas derived in whole or in part from glycerol.

10. The method of claim 9, wherein the glycerol was derived from the hydrolysis of a triglyceride.

11. A method of forming a fuel product comprising the steps of: a) performing Kolbe electrolysis on a C_10-20 fatty acid to form a Kolbe electrolysis product, b) combining the Kolbe electrolysis product with an olefin-containing material substantially in the C_2-8 range derived from Fischer-Tropsch synthesis to form a reaction mixture, and subjecting the reaction mixture to molecular averaging to form a hydrocarbon product, wherein, if the fatty acid is saturated, a dehydrogenation step is performed on either the fatty acid or the Kolbe electrolysis product before the molecular averaging step is performed.

12. The method of claim 11, wherein the C₁O_-20 fatty acid is obtained by hydrogenating a vegetable oil or animal fat.

13. The method of claim 11 , wherein the hydrocarbon product of the molecular averaging step is fractionated, and a product in the distillate fuel range is obtained.

14. The method of claim 13, wherein the product in the distillate fuel range is in the diesel fuel range.

15. The method of claim 13, wherein the product in the distillate fuel range is in the C_5-I2 range.

16. The method of claim 15, wherein the product in the C_5-I₂ range is isomerized to provide branched C_5-12 hydrocarbons.

17. The method of claim 11 , wherein the Fisher-Tropsch synthesis was performed using syngas derived in whole or in part from natural gas.

18. The method of claim 11 , wherein the Fisher-Tropsch synthesis was performed using syngas derived in whole or in part from glycerol.

19. The method of claim 18, wherein the glycerol was derived from the hydrolysis of a triglyceride.

20. A method of forming a hydrocarbon product comprising the step of performing Kolbe electrolysis on a reaction mixture comprising fatty acids and an ionic liquid.

21. The method of claim 20, further comprising the step of combining the Kolbe electrolysis products with a source of olefins in the C_2-15 range and performing a molecular averaging reaction.

22. The method of claim 21, further comprising the step of isolating a hydrocarbon product in the distillate fuel range.

23. The method of claim 22, further comprising performing an isomerization step to form an isomerized hydrocarbon product in the distillate fuel range.

24. A method of hydrolyzing one or more triglycerides to form a mixture of fatty acids and glycerol, comprising the steps of: a) adding one or more triglycerides and at least a stoichiometric amount of water to an ionic liquid, where the ionic liquid is and/or includes an acid catalyst, and b) hydrolyzing the triglycerides to form a reaction mixture comprising fatty acids and glycerol.

25. The method of claim 24, further comprising the step of separating a fraction comprising water and glycerol from the reaction mixture.

26. The method of claim 25, further comprising the step of performing Kolbe electrolysis on the fatty acids.

27. The method of claim 26, further comprising the steps of isolating the reaction products from the Kolbe electrolysis step, combining the products with an olefln- containing material substantially in the C_2-^ range to form a reaction mixture, and c) subjecting the reaction mixture to molecular averaging to form a hydrocarbon product, wherein, if the fatty acid is saturated, a dehydrogenation step is performed on either the fatty acid or the Kolbe electrolysis product before the molecular averaging step is performed.

28. The method of claim 27, wherein the olefϊn-containing material substantially in the C_2-16 range is derived from Fischer-Tropsch synthesis.

29. The method of claim 28, wherein the Fischer-Tropsch synthesis was performed using syngas derived in whole or in part from glycerol.

30. The method of claim 28, wherein the Fischer-Tropsch synthesis was performed using syngas derived in whole or in part from natural gas.

31. A process for forming a hydrocarbon product comprising the steps of: a) converting glycerol to syngas, b) optionally combining the syngas derived from the glycerol with syngas derived from natural gas, and c) subjecting the syngas to Fischer-Tropsch synthesis.

32. The method of claim 31 , wherein the glycerol is obtained by hydrogenating a vegetable oil or animal fat.

33. The method of claim 31 , wherein the Fischer-Tropsch synthesis is performed using an iron catalyst, and the reaction product comprises C_2-8 olefins.

34. The method of claim 33, wherein the reaction product comprising C_2-8 olefins is reacted with glycerol to form glycerol ethers.

35. The method of claim 34, wherein the glycerol ethers are combined with fatty acid ethyl and/or methyl esters and/or with a hydrocarbon product in the diesel fuel range derived from Fischer-Tropsch synthesis.

36. The method of claim 33, wherein the reaction product comprising C_2-S olefins is combined with a hydrocarbon stream containing olefins in the molecular weight range OfC_18-5O to form a reaction mixture, and the reaction mixture is subjected to a molecular averaging reaction to form a hydrocarbon product.

37. The method of claim 36, wherein hydrocarbon product of the molecular averaging step is fractionated, and a product in the distillate fuel range is obtained.

38. The method of claim 37, wherein the product in the distillate fuel range is in the diesel fuel range.

39. The method of claim 37, wherein the product in the distillate fuel range is in the C5-12 range.

40. The method of claim 39, wherein the product in the C_5-12 range is isomerized to provide branched C_5-12 hydrocarbons.

41. The method of claim 36, wherein the hydrocarbon stream containing olefins in the molecular weight range of Ci_<s_-5o is derived in whole or in part from the Kolbe electrolysis of fatty acids.

42. A method of forming a hydrocarbon product, comprising the steps of: a) performing Kolbe electrolysis on fatty acids, b) hydrocracking the reaction products from the Kolbe electrolysis step, and c) isolating a product in the distillate fuel range.

43. The method of claim 42, wherein the fatty acids are derived from the hydrolysis of vegetable oil and/or animal fat.

44. The method of claim 43, wherein the hydrolysis and/or the Kolbe electrolysis is performed in an ionic liquid.

45. The method of claim 42, wherein the product in the distillate fuel range is in the diesel fuel range.

46. The method of claim 42, wherein the product in the distillate fuel range is in the C_5-12 range.

47. The method of claim 46, wherein the product in the C_5-12 range is isomerized to provide branched C_5-12 hydrocarbons.

48. The methods of any of claim 1-47, further comprising a hydrofinishing and/or hydrogenation step to hydrogenate all or a portion of any olefins that may be present.

49. A hydrocarbon product produced by the methods of any of claim 1-48.

50. The hydrocarbon product of claim 49, wherein the product is in the C_16-38 range, and is used as lubricating oil.

51. A method of preparing glycerol ethers, comprising the steps of: a) hydrolyzing triglycerides to form glycerol, b) converting a portion of the glycerol to syngas, c) performing Fischer-Tropsch synthesis on the glycerol, d) isolating a C_2-4 olefmic fraction, and e) reacting the resulting C_2-4 olefmic fraction with glycerol under conditions which provide glycerol ethers.

52. The method of claim 51, wherein the molar ratio of olefins to glycerol is at least 1.5/1.

53. The method of claim 51, wherein the molar ratio of olefins to glycerol is at least 2/1.