WO2008075003A1

WO2008075003A1 - Glycerol fuel

Info

Publication number: WO2008075003A1
Application number: PCT/GB2007/004811
Authority: WO
Inventors: Paul Day; Felix Sirovski; Sergej Daut; John A. Mcneil
Original assignee: Aquafuel Research Limited
Priority date: 2006-12-16
Filing date: 2007-12-14
Publication date: 2008-06-26
Also published as: GB0625248D0; GB0910294D0; GB2457404A

Abstract

A fuel composition comprises glycerol and a combustion improving agent. The glycerol may be obtained from a renewable biological source and before mixing with the combustion improving agent may be treated by mixing with an inorganic acid and removing water and methanol under normal or reduced pressure, and removing solid material. Other aspects of the invention provide a method of making a fuel composition and methods of combusting glycerol fuel compositions.

Description

GLYCEROL FUEL

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to glycerol fuels and their combustion. Crude glycerol containing waste streams may be derived from manufacture of biodiesel. Biodiesel, an alternative diesel fuel, is made from renewable biological sources, such as vegetable oils and animal fats. It is biodegradable and nontoxic, has low emission profiles and so is environmentally beneficial (Krawczyk, T., 1996. Biodiesel - Alternative fuel makes inroads but hurdles remain. INFORM 7, 801- 829). It is produced by transesterification with alcohol, for example methanol, to form esters (biodiesel), and crude glycerol as a by-product. Per 1 MT of biodiesel produced, about 150 kg of crude glycerol is obtained as a by-product. This crude glycerol may contain any or all of the following: metals, soaps, fatty acids, alcohol^', water and unconverted fatty acid triglycerides.

The crude glycerol is derived from the renewable raw material and is itself a renewable resource. An aspect of the present invention relates to a process for preparing a composition suitable for combustion and a method for its combustion. In particular, aspects of the present invention relate to a process for converting crude glycerol into a fuel composition and to methods for its combustion.

2. Description of the Prior Art

US2006199970 describes a process for the preparation of a fuel oil (diesel fuel or heating oil) composition which is a mixture of an alkanol tranesterified fatty acid ester triglyceride and an acetal of glycerol. The process preferably provides a prestep of Jtie formation oXatieaslsome of the-alkanol transesterified ^"triglyceride containing the glycerol for use in the formation of the acetal of glycerol. The composition can also be formed from a reaction of 1 ,1- dimethoxy- or 1,1- diethoxyethane and glycerol to form the acetal in the alkanol transesterified triglyceride. A difficulty for this use of crude glycerol is that there are standards applied to bodiesel (for example BS EN14214) in the biggest markets which exclude such fuels from use in the road vehicle markets.

U.S. Pat. No. 6,890,364 B2 and US2004/0025417 A1 to Delfort et al describe a process for producing glycerol acetals for use in diesel fuels, and they are incorporated herein by reference in their entireties. U.S. published application 2003/0167681 A1, which is also incorporated by reference in its entirely, describes a similar two step process. The process conditions enable the formation of the acetals, with filtration of the solid and catalyst from the composition produced, which is a mixture of acetals. The acetal mixture is added in an amount between 1 to 40%, preferably 1 to 20% by volume to diesel fuel and is soluble in the heating or diesel fuel oils which is important for preventing separation on storage. The acetal additive reduces particulate emissions, particularly from diesel engines and functions like an oxygenate.

U.S. Pat. No. 5,917,059 to Bruchmann relates to a process for forming acetals. Also U.S. Pat. Nos. 6,713,640 and 6,548,681 to Miller et al relate to a process for preparing acetals. These acetal additives need to compete with conventional diesel fuel additives in cost and performance; substantial market uptake would be needed for there to be any impact on the volume of crude glycerol produced from biodiesel production. There is no evidence to suggest these acetals are gaining commercial acceptance.

3. SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a method of preparing crude glycerol for use in fuel compositions comprising: i) Adding a least one inorganic acid for example sulphuric, hydrochloric or nitric acid, to crude glycerol at 40-90 degrees C and mixing with removal of water and methanol under normal or reduced pressure and ii) Removing solid material.

According to a second aspect of the present invention there is provided a fuel composition comprising glycerol and at least one combustion improving agent. The glycerol may be crude glycerol which has been processed according to the first aspect of the present invention.

According to a third aspect of the present invention there is provided a combustion improving agent made by nitration of crude glycerol.

According to a fourth aspect of the present invention there is provided a method of combustion comprising combusting glycerol in a combustion apparatus with oxygen enrichment of the combustion air.

In a preferred embodiment the glycerol is crude glycerol which has been processed according to the first aspect of the invention.

According to a fifth aspect of the present invention there is provided a composition and method of combustion comprising; i) a fuel composition including a fuel composition according to the second aspect of the present invention and ii) combusting said composition in a combustion apparatus with oxygen enrichment of the combustion air

3. Detailed Description

According to a first aspect of the present invention there is provided a method of processing crude glycerol for use in fuel compositions comprising: iii) Adding a least one inorganic acid for example sulphuric, hydrochloric or nitric acid, to crude glycerol at 40-90 degrees C and mixing with removal of water and methanol under normal or reduced pressure and iv) Removing solid material.

The process can be carried out in batch or continues reactors. Removal of solid material can be achieved by processes well known in the art including, for example by centrifuge or filtration.

Example 1 4I of raw glycerol was placed in a three neck flask, equipped with a cooler and receiver for methanol collection. The flask was heated to 80⁰C. 20ml of concentrated HCI was poured to the glycerol mass. The reaction was allowed to proceed for 5 minutes. 340ml of 10% HCI was added slowly over a period of 1 hour. During the reaction the methanol vapours pass through the condenser and liquid methanol was collected in the receiver. The solid material was removed by centrifugation. The final product was a viscous brown mixture. Ash content in the crude glycerol before processing was 4.88%; after processing ash content was 0.25%.

The step of adding acid may be carried out as part of any of the present processes or it may be a part of the normal operation of a biodiesel plant from which the crude glycerol may be obtained.

This product of example 1 was combusted as a 50% weight mixture composition with heavy fuel oil, in a 2-cylinder Lister Petter direct injection diesel engine.

According to a second aspect of the present invention there is provided a fuel composition comprising: ^" i) crude glycerol processed according to the first aspect of the present invention and ii) at least one combustion improving agent

Preferred combustion improving agents include those known in the art as cetane improvers, combustion catalysts and materials which generate oxygen on decomposition, for example, ammonium nitrate. The combustion improving agents may be soluble or dispersed in the processed crude glycerol.

Fuel ignition in diesel engines is achieved through the heat generated by air compression, as a piston in the cylinder moves to reduce the cylinder volume during the compression stroke. In the engine, the air is first compressed, then the fuel is injected into the cylinder; as the fuel contacts the heated air, it vaporizes and finally begins to burn as the self-ignition temperature is reached. Additional fuel is injected during the compression stroke and the fuel burns almost instantaneously, once the initial flame has been established. Thus, a period of time elapses between the beginning of fuel injection and the appearance of a flame in the cylinder. This period is commonly called "ignition delay" and must be relatively short in order to avoid "diesel knock". A major contributing factor to diesel fuel performance and the avoidance of "diesel knock" is the cetane number of the diesel fuel. Diesel fuels of higher cetane number exhibit a shorter ignition delay than do diesel fuels of a lower cetane number. Therefore, higher cetane number diesel fuels are desirable to avoid diesel knock. A good correlation between ignition delay and cetane number has been reported in "How Do Diesel Fuel Ignition Improvers Work" Clothier, et al., Chem. Soc. Rev, 1993, pg. 101-108 in the region 3<t_igni<8 m sec using the equation CN=91-6.4 t_igni, which reflects contributions by engine timing and levels of additives in the fuels. Correcting the equation to remove the influences .of. timing and -additives-results -in-the equation- CN=85-6.0 tigni.

Cetane improvers have been used for many years to improve the ignition quality of diesel fuels. Many types of additives have been prepared and evaluated to raise the cetane number of diesel fuel. Such additives include peroxides, nitrates, nitrites, azo compounds and the like.

When using a combustion improver such as dimethyl ether (DME), the DME may be added as a gas through the air intake.

Alkyl nitrates such as amyl nitrate, hexyl nitrate and mixed octyl nitrates have been used commercially with good results. Other nitrates such as 2-methyl-2-nitropropyl nitrate (U.S. Pat. No. 4,536,190) have been suggested as cetane improvers but were found to be shock sensitive. However, it is generally accepted that organic nitrates, more specifically the commercial 2-ethylhexyl nitrate (2-EHN), are the most cost-effective additives to improve cetane number of diesels. Because of its relatively low cost, and environmentally friendly nature (ashless), there has been limited work done in this area to replace the 2-ethylhexyl nitrate.

' W093/08244 discloses cetane improving additives comprising 13-25 carbon alkyl nitrates. The nitrates are obtained by nitration of oxo process alcohols. The fuel contains, in addition to the alkyl nitrate, an ashless dispersant, preferably a macrocyclic polyamine dispersant.

EP157,684 discloses nitrates of alkyoxylated alcohol or phenol added to diesel fuels to improve cetane index and keep fuel injector systems clean by detergent action. The organic nitrate is of the formula

R (OCH₂ CHX)_n ONO₂ . ^ wherein R is a C₆ to C₂₀ alkoxy or aryl substituted by a C₄ -Ci₈ alkyl chain, X is hydrogen or methyl and n is 1 to 15, R is a radical derived from an aliphatic monoalcohol of natural or synthetic origin -such- as hexanol; -octanol^~nnyristvrdr^~ stearyl alcohol or alcohols from the oxo-process.

G. B. Patent 2,227,752A teaches that cetane number of a hydrocarbon-based fuel is increased by the addition of a minor amount of a parketal of the formula R₂ R3 C(OORi)₂ wherein Ri is a C₄ -Ci₀ tertiary alkyl group and R₂ and R₃ together with the attached C atom form a cycloalkane ring optionally substituted by one or more Ci -C₄ alkyl radicals or other essentially inert substituents. The perketal is not used in combination with an alkyl nitrate,

Patent EP0537931 discloses a fuel composition for reducing emissions on combustion consisting of a middle distillate fuel, organic nitrate combustion improver and a tert-alkyl peroxyalkanoate or peroxybenzoate.

U.S. Pat. No. 5,114,433 describes a process for improving the cetane number of a directly distilled diesel fuel by intimately contacting same with hydrogen peroxide in the presence of carboxylic acid or with a percarboxylic acid in the presence or absence of hydrogen peroxide.

G. B. Patent 2,227,751A discloses a hydrocarbon-based fuel to which has been added a minor amount, sufficient to increase the cetane value of the fuel, of a perester of the formula RiCOOOR₂ where R-i is a C₅ -C₂o secondary or tertiary alkyl group and R₂ is a C₄ -C₁0 tertiary alkyl group.

U.S. Pat. No. 4,365,973 discloses a middle distillate fuel additive composition to improve cold flow properties, cetane, pour point, wax formation and anti-icing characteristics and comprising a cold flow improver, preferably vinyl acetate- ethylene copolymer, a cetane improver comprising paraffinic nitrate or a mixture of nitrates and an anti-icer comprising an aliphatic alcohol or cyclic aliphatic alcohol having from 1 to 6 carbon atoms.

EP 467,628 discloses a middle distillate composition to reduce atmospheric pollutants (NOx, CO and/or hydrocarbons), the fuels incorporate a peroxy ester combustion improver of the formula (R-~Q--O,--(CO))_π R¹-where-R and R¹ -are both hydrocarbyl groups. Suitable peroxy esters include tert-butyl peroxydodecanoate, di-(tert-butyldiperoxy) phthalate and 1,1-dimethylpropylperoxy benzoate. The peroxy ester is used in combination with an organic nitrate ester such as 2- ethylhexyl nitrate. U.S. Pat. No. 4,330,304 discloses a fuel additive for improving the combustion efficiency of fuels for diesel engines, jet engines, boilers and other apparatus. The additive comprises a hydroperoxide such as cumene hydroperoxide, a nitroparaffin and propylene oxide.

EP 293,069 discloses a cetane improver comprising tetralin hydroperoxide. The cetane improver is produced by partially hydrogenating a naphthalene or alkyl naphthalene-containing hydrocarbon oil to obtain tetralins, which are then partially oxidized to produce a hydrocarbon oil containing tetraline hydroperoxides.

U.S. Pat. No. 5,258,049 discloses a diesel fuel containing the nitric acid ester of 1- phenyl ethanol as cetane improver.

U.S. Pat. No. 5,454,842 discloses a cetane improver composition containing 0.01 - 2 wt % of a fatty alcohol nitrate ester. The cetane improver composition is produced by nitration of tall oil fatty alcohols, vegetable oil fatty alcohol and mixtures thereof.

Example 2

A mixture of 3,380 g of glycerol, 60 g of Span-80 and 560 g of 2-EHN were mixed for 5-10 minutes in a 5L beaker until an opalescent (milky) emulsion was formed. The preferred concentration of surfactant is 1.5-2%. Preferred surfactants are Span-80 and Twin-20. However, it will be understood that other surfactants may be used and the emulsion may be prepared by any known method.

A wide variety of compounds are known in the art as combustion catalysts, including, without limitation, compounds containing metals. Preferred compounds contain: i) alkali and alkaline earth metals, comprised of group Ia and Ha metals of the periodic table, including barium, strontium, sodium and calcium, ii) transition metals of groups three to twelve of the periodic table, including iron, copper, platinum, manganese, nickel, cobalt and palladium iii) rare earth metals of the lanthanide and actinide series of the periodic table, including cerium. Mixtures of metals or metal compounds may be employed.

The composition can also include further fuel components, for example, ethyl alcohol and hydrocarbon fuel. The term "hydrocarbon fuel" is used herein to refer to hydrocarbonaceous petroleum distillate fuels (for example petrol (gasoline), diesel, and gas oil) and mixtures thereof. The term also refers to non- hydrocarbonaceous materials that include but are not limited to oils, fuels derived from vegetables (for example olive, corn, rapeseed, alfalfa), fuels derived from animal material (for example tallow), fuels derived from minerals (for example from shale, coal, anthracite and the like) and mixtures thereof and combinations thereof. The hydrocarbon fuel may include mixtures of one or more hydrocarbonaceous and one or more non-hydrocarbonaceous materials, for example diesel and corn oil. The hydrocarbon fuel may optionally be admixed with other additives, for example ethanol, acetone or ether.

The compositions of the invention may be used in combination with one or more co-additives known in the art, for example the following : detergents, antioxidants, corrosion inhibitors, dehazers, demulsifiers, metal deactivators, antifoaming agents, co-solvents, package compatibilisers, cold flow improvers, lubricity additives, static dissipators, stabilisers, biocides, re-odorants, dyes and markers.

The term "cold flow improvers" comprises the following: wax anti-settling additives (WASA), wax anti-settling flow improvers (WAFI), pour point depressants (PPD), cloud point depressants (CPD) and cold filter plugging point additives (CFPP).

This aspect of the present invention is further illustrated by the following example:

Example 3

5 parts of ammonium nitrate was added with mechanical stirring to 95 parts of product material from Example 1. The applicants have surprisingly discovered that despite the apparently favourable combustion characteristics of glycerol (ETSU report B/M3/00388/40/REP herein incorporated in its entirety) crude glycerol will not combust in a high speed diesel ^' engine even when processed according to the first aspect of the present invention which makes it suitable for introduction into a diesel engine. By contrast the material according to the second aspect exemplified in example 2 was combusted in a 2-cylnder Lister -Petter direct injection engine.

According to a third aspect of the present invention there is provided a combustion - improving agent made by nitration of crude glycerol. This aspect of the present invention is illustrated by the following example.

Example 4 To a 3 I round bottom flask equipped with an agitator and dropping funnel was placed 400 g of crude glycerol biodiesel by-product. To this mixture at temperature 0- +5 ⁰C is added 880 g of fuming nitric acid (d=1.5 g/ml) for 1.5 hour. After the addition, the mixture is stirred for 1 h and quenched with 400 ml of water. The remaining acid is neutralised with CaCO3. After the separation of layers about 600 g of organic nitration product is obtained.

Example 5

The 5L three-necked jacketed flask equipped with a mechanical stirrer, dropping funnel and a thermometer is charged with 630 g of glycerol. The content of the flask is cooled to -10-12⁰C. To this content 1056 g of concentrated sulphuric acid is added keeping the temperature below 5 C. After addition of all sulphuric acid the flask is charged with.a nitrating mixture consisting of 456 g -of fuming 100% nitric^" acid and 1056 g concentrated sulphuric acid. The addition proceeds at temperature below 5-8°C. The nitrating mixture is prepared in a separate flask under cooling. After the addition of nitrating mixture is completed the reaction mixture is poured on 8 kg of ice and neutralised with 2 .8 kg of sodium carbonate and extracted with 1.5 litres of ethyl acetate. The precipitated salt is washed several times with 1.5 litres of ethyl acetate. Ethyl acetate is removed from combined extracts under vacuum using standard rotary evaporator. The yield of nitrated product (mostly glycerol mono nitrate) is 180 g.

In another embodiment of this aspect of the present invention the product after nitration is not neutralised or solid material separated. This material can be used as the inorganic acid source in an embodiment of the first aspect of the present invention.

The cetane improver composition comprises nitration products of biodiesel crude glycerol by-product. Such nitration products include mixture of mono- and di- glycerol nitrate esters, and fatty acid nitration products.

The cetane improver action of example 2 was confirmed by addition of 5 % wt to the Heavy fuel oil cetane number 22.2. The results of combustion test according to FIA 100/3 procedure showed that the cetane number increased to 26.2

According to a fourth aspect of the present invention there is provided a composition and method of combustion comprising; iii) a fuel composition including crude glycerol processed according to the first aspect of the present invention and iv) combusting said composition in a combustion apparatus with oxygen enrichment of the combustion air

According to this aspect of the present invention compositions including glycerol processed according to the first aspect are combusted with oxygen enrichment of the combustion air. The applicants have discovered that despite the favourable stoichiometry with respect to oxygen content of mixtures containing glycerol, full combustion is only realised with oxygen enrichment of.the combustion^air,

According to a fifth aspect of the present invention there is provided a composition and method of combustion comprising; v) a fuel composition including a fuel composition according to the second aspect of the present invention and vi) combusting said composition in a combustion apparatus with oxygen enrichment of the combustion air

According to this aspect of the present invention compositions including compositions according to the second aspect of the present invention are combusted with oxygen enrichment of the combustion air. The applicants have discovered that despite the favourable stoichiometry with respect to oxygen content of compositions including compositions according to the second aspect of the present invenion, full combustion is only realised with oxygen enrichment of the combustion air.

Example 6

Material from Example 3 was combusted in a 2-cylnder Lister -Petter direct injection diesel engine. When the combustion air was enriched with 5% oxygen power output rose from 6.83 to 7.56KW.

Experimental data from various combustion experiments are given in Tables 1-5, as follows.

Tables 1&2: Attainment of stable running on glycerol and 2-EHN at 20%.

Table 3: Glycerol + 10%2-EHN and 8% ethanol.

Table 4: DME fumigation starting with 2-EHN mixtures and then without. The table also includes results for combustion with and without oxygen enrichment and the effect on DME dosage and knock.

Table 5: Stable operation with DME and results for a small sample of nitrated glycerol. Glycerol Running / Base fuel = 98.5% pure Glycerol 1 Stable Running on Glycerol + 20% 2EHN

ω

TABLE 1

2. Stable running on Glycerol + 20% 2EHN

σi

TABLE 2 (CONTINUED)

3. Stable running on Glycerol + 10% 2EHN + 8% Ethanol

σ>

4. First trial of Glycerol + DME gas fumigated into engine air iniet + various oxygen enrichment observations

9°

TABLE 4 (CONTINUED)

5. Stable running of developed system for Glycerol + DME gas. Also succesful trial sample of nitrated pure glycerol.

CD

TABLE 5

Claims

1. A fuel composition comprising glycerol and a combustion improving agent.

2. A fuel composition according to claim 1 , wherein the combustion improving agent is selected from a group comprising nitrated glycerol, ammonium nitrate, peroxides, nitrates, nitrites, azo-compounds, perketals, ethers, or a mixture thereof.

3. A fuel composition according to claim 1 , wherein the combustion improving agent is nitrated glycerol.

4. A fuel composition according to claim 1 , wherein the combustion improving agent is ammonium nitrate or an alky! nitrate.

5. A fuel composition according to claim 4 wherein the combustion improving agent is 2-EHN.

6. A fuel composition according to claim 1 , wherein the combustion improving agent is DME.

7. A method of making the fuel composition of claim 1 , comprising mixing glycerol and a combustion improving agent.

8. A method according to claim 7, wherein the glycerol is obtained from a renewable biological source and before mixing with the combustion improving agent is treated by mixing with an inorganic acid and removing water and methanol under normal or reduced pressure, and removing solid material.^"

9. A method according to claim 8, wherein the glycerol and acid mixture is maintained at a temperature in the range 40-90⁰C during removal of water and methanol.

10. A method of combustion comprising combusting a fuel composition according to any of claims 1-6 in a combustion apparatus.

11. A method according to claim 10, wherein the combustion apparatus is a diesel-cycle engine.

12. A method according to claim 10 or claim 11 , wherein the combustion is carried out with oxygen enrichment.

13, A method of combustion comprising combusting glycerol in a combustion apparatus with an air intake, and introducing DME into the combustion apparatus with intake air through the air intake.

14. Use of nitrated glycerol as a combustion improvement agent.

15. Use according to claim 14, wherein the glycerol is substantially mononitrated.

16. A method of combustion comprising combusting glycerol in a combustion apparatus with oxygen enrichment of the combustion air.

17. A method according to claim 16, wherein the glycerol is obtained from a renewable biological source and treated by mixing with an inorganic acid and removing water and methanol under normal or reduced pressure, and removing solid material.

18. A method of preparing crude glycerol for use in fuel compositions or combustion, the method comprising: i) adding a least one inorganic acid for example sulphuric, hydrochloric or nitric acid, to crude glycerol at 40-90 degrees C and mixing with removal of water and methanol under normal or reduced pressure and ii) removing solid material.

19. A method according to claim 18, wherein the crude glycerol is obtained as a by-product in the manufacture of biodiesel.