MX2008004046A - Production of high-cetane diesel fuel from low-quality biomass-derived feedstocks - Google Patents

Abstract

A method is taught for producing diesel fuels of high cetane value from a triglyceride feedstock, comprising pretreating the triglyceride feedstock by thermal cracking to partially convert the triglycerides and produce a middle distillates stream, and catalytically hydrotreating the middle distillate fraction to produce high cetane value diesel fuels. A biomass-derived diesel fuel is also taught having sulphur content below 10 ppm, a cetane-value of at least 70, a cloud point below 0oC and a pour point of less than -4 oC. A blended diesel fuel is also taught comprising 5 to 20 vol.%of the biomass-derived diesel fuel of the present invention and 80 to 95 vol.%of a petroleum diesel, based on total volume of the blended diesel fuel.

Description

PRODUCTION OF DIESEL FUEL WITH GREAT CONTENT OF CETAN WITH ORIGIN IN BIOMASS DERIVED FEEDS The present invention deals with a two-step method for producing diesel fuel with high cetane value from feeds derived from low quality biomass. In recent years, the area of diesel fuels derived from biomass has attracted a lot of attention. These fuels originate in plants and animals and are produced from sources such as cañola, corn, soy, etc. Fuels derived from biomass are generally less environmentally damaging to use than traditional fossil fuels. Another potential source for diesel fuels derived from biomass is waste fats from facilities that service animals and residual edible oils, such as those found as restaurant greases. However, these waste fats and oils tend to contain contaminants that must be removed effectively before processing. In the past, catalytic hydrotreating was don triglyceride feeds in an attempt to produce diesel fuels with high cetane content. Examples of such processes can be seen in U.S. Patent Nos. 5,705,722 and 4,992,605. The cetane value of a diesel fuel is a measure of how easy the fuel will self-ignite at predetermined pressure and temperature and is often used to determine fuel quality. However, large quantities of hydrogen are needed for this process, which is a major operating cost in the production of diesel fuel derived from biomass by catalytic hydrotreating. Reducing the volume of hydrogen consumed in the process would further benefit the economy of the process. Likewise, it was discovered that hydrotreatment works best for very high quality feeds, such as tallow, vegetable oils (Canola oil, soybean oil, etc.) and yellow fat. It was discovered that lower quality feeds, such as restaurant collector fats, are difficult to convert by catalytic hydrotreating, due to their heterogeneous nature and the presence of contaminants. These contaminants quickly deactivate the catalyst, thereby reducing the time of the hydrotreating reactor in the stream, requiring the use of large amounts of catalyst, and increasing operating costs. Therefore, there is a great need to find efficient methods to produce a product with high cetane value from low quality waste triglyceride feeds, such as restaurant collector fats and other waste fats, which can be used as a diesel fuel or a mix reserve for diesel fuel. There is also a need to find efficient methods to reduce hydrogen consumption in the catalytic hydrotreating stage. The present invention thus provides a method for producing high-cetane diesel fuels from triglyceride feeds, which comprises pre-treating the triglyceride feeds by thermal cracking to partially convert the triglycerides and produce a stream of intermediate distillates and hydrotreat catalytically. the fraction of intermediate distillates to produce diesel fuels of high cetane value. The present invention also provides a diesel fuel derived from biomass having sulfur content below 10 ppm, a cetane value of at least 70, an opacity point below 0 ° C and a runoff temperature below -4 ° C. In yet another embodiment, the present invention provides a mixed diesel fuel comprising 5 to 20 vol. % of diesel fuel derived from biomass of the present invention and 80 to 95 vol. % of an oil diesel, based on the total volume of the mixed diesel fuel. The present invention will now be described in greater detail with reference to the following drawings, wherein: Figure 1 is a flow diagram of a preferred process for carrying out the present invention. Diesel fuel derived from biomass - a diesel fuel produced by catalytic hydrotreatment of biomass feeds and that practically does not contain oxygen. Biodiesel - a diesel fuel produced from the transesterification of oils derived from biomass with alcohol and containing oxygen. Cetane number - measurement of the ignition quality of the diesel fuel obtained by comparing it to the reference fuel or reference fuel mixtures of known cetane number in a standardized engine test. The reference fuels are n-cetane, which has a good quality of inflammation (CN = 100) and heptamethylnonano, which has poor quality of inflammation (CN = 15). High Cetane Value - for the purposes of the present invention a high cetane value is defined as a value of at least 70. Feed of waste triglycerides - a triglyceride from waste sources such as restaurant collector fats, waste facilities that care for animals and other sources of oil and waste fats, which usually have at least some contaminants. Catalytic hydrotreating - a refinery process to convert and catalytically remove sulfur, nitrogen and oxygen from fuel and fuel feeds at high hydrogen pressures and appropriate temperatures. Intermediate distillates - encompass a range of petroleum fractions from kerosene to lubricating oil and include light fuel oils, which generally have a boiling temperature ranging from 150 to 345 ° C. Thermal cracking - the process of breaking down large hydrocarbon molecules into smaller molecules under high temperature and pressure. Opacity point - a measure of the capacity of a diesel fuel to operate under cold weather conditions. It is defined as the temperature at which the wax begins to be seen when the diesel fuel is cooled under standardized test conditions. Runoff temperature - the lowest temperature at which a fuel flows when cooled under standardized test conditions. Usually taken to be 3 ° C (5.4 ° F) or 1 ° C (1.8 ° F) (depending on the selected temperature range) above the temperature of the point of no flow in which a test container The fuel does not show movement when a burst of nitrogen gas is applied to the surface of the specimen (ASTM D 5949). The present process employs a novel combination of thermal cracking followed by catalytic hydrotreating to convert the feed of low quality triglycerides to diesel fuel derived from usable biomass. In the present process, thermal cracking is used as a preliminary treatment step prior to catalytic hydrotreating, to partially break down triglycerides into lower molecular weight components and fatty acids, which can then be hydrotreated easily to produce a diesel fuel with large Cetane value and low sulfur content. A flowchart of the process steps and streams of an embodiment of the present invention is shown in Figure 1. A feed 18 of low quality triglycerides is fed to the thermal cracking unit 10. The feed 18 may be a variety of waste biomass, including restaurant collector fats, waste fats from facilities that service animals and other forms of waste oils and fats and low quality vegetable oils. Preferably, the feed 18 is restaurant collector grease and other low quality feed. The feed stream 18 can have a homogeneous nature and can contain water, carbon particles and have an oxygen content of up to 14% weight or more. In the thermal cracking unit 10, the feed 18 is partially converted into a mixture of fatty acids and hydrocarbons of very low molecular weight. The thermal cracking is preferably carried out under light cracking conditions which are preferably defined as an operating temperature ranging between 390 and 460 ° C, more preferably between 410 and 430 ° C, and preferably an operating pressure of between 0 and 415 kPa, more preferably between 205 and 275 kPa. Thermal cracking produces several fractions including gas 24, naphtha plus water 26, intermediate distillate 22 and residue 20. In an optional embodiment (not shown), the triglyceride feed can be filtered to remove any gross contaminant particles. The intermediate distillate stream 22 comprises more than half of the thermally cracked product and has been found to have suitable characteristics for further hydrotreating. Intermediate distillates typically comprise a variety of equivalent fractions of petroleum from kerosene to lubricating oil and include light fuel oils and diesel fuel. In an embodiment of the present invention it was found that the intermediate distillates have a boiling temperature ranging from 150 to 345 ° C., and more preferably between 165 and 345 ° C. It was found that the middle distillate fraction contains up to 40% less oxygen than the initial triglyceride feed 18, resulting in less need for hydrogen in the next hydrotreating step. The intermediate distillate stream 22 is fed to a catalytic hydrotreating unit 12 containing a catalyst to facilitate and improve the hydrotreating process. This catalyst is a commercial hydrotreating catalyst such as, for example, nickel-molybdenum, cobalt-molybdenum or nickel-tungsten in a catalytic support. Preferably it is a catalyst supported with nickel-molybdenum. Known methods can be used to maintain catalyst activation, thus increasing the useful life of the catalyst. Hydrogen 28 is also fed into the hydrotreating unit 12. The present inventors have discovered that, by partially removing the oxygen from the charge in the preliminary thermal cracking treatment step, the consumption of hydrogen in the hydrotreating step is considerably reduced. The typical consumption of hydrogen for hydrotreatment of high quality clean biomass feed, without thermal cracking, varies between 2.3 and 3.0 kg H2 per 100 kg of feed. In contrast, the hydrogen consumption during the hydrotreating of the stream of thermally cracked intermediate distillates 22 is only between 1.5 and 2.0 kg H2 per 100 kg of intermediate distillate charge 22 for the hydrotreating unit 12. It has also been observed that, When thermally cracked waste triglycerides are processed, hydrotreating can be conducted at lower temperatures than those needed for high quality, clean biomass feed. Hydrotreating temperatures of between 330 and 400 ° C, and more preferably between 350 and 390 ° C, are used in the present invention, as compared to at least 375 ° C typically required for clean, uncracked biomass feeds. with hydrotreating. The hydrotreated product 30 can then optionally be fed to a separator 14 in which the product 30 is separated in a gas stream 35, a stream of water 36 and a stream of liquid organic product 38. The gas stream 35 can be recycled from new in the hydrotreating unit 12 as a hydrogen recycle stream 32, or can form a fuel gas by-product stream 34. In a preferred embodiment, the separate liquid organic product stream 38 is fed to a column of distillation 16 to further separate the diesel fuel 40 from any paraffin residue 42. Optionally the naphtha 26 and gases 24 from the thermal cracking unit 10 and the fuel gas 34 coming from the hydrotreating step can be sold as products valuable secondary The waste streams 20 and 42 are small and can be removed by means well known in the art. Stream 42 is much cleaner than stream 20 and it is also possible that it can be used as feed for petrochemical applications. The catalytic hydrotreating of the middle distillate stream 22 produces a mass-derived diesel fuel with a cetane value ranging between 75 and 80 and a sulfur content below 10 ppm. The oxygen content of the resulting diesel fuel, an indication of the extent of feed conversion to diesel fuel, was found to be in the limit of 0.09% by weight or less, based on the weight of the diesel product. The diesel fuel derived from biomass of the present invention also shows excellent cold flow properties. The opacity point of the fuel is as low as -1.4 to -2.5 ° C and the runoff temperature is -4 ° C or less. In another embodiment, the diesel fuel derived from biomass of the present invention can be used by mixing the stock to produce a mixed diesel fuel with high cetane value. Preferably, the mixed diesel fuel comprises 5 to 20% vol. of diesel fuel derived from biomass of the present invention and 80 to 95% vol. of diesel oil, based on a total volume of mixed diesel fuel. More preferably, the mixed diesel fuel comprises 10 vol%. of diesel fuel derived from biomass of the present invention and 90% vol. of diesel oil, based on a total volume of mixed diesel fuel. It was discovered that the cetane value of the mixed diesel fuel is proportional to the amounts of diesel derived from biomass and diesel oil used in the mixture and was generally higher than the typical values of 40 to 50 for diesel oil. The cold flow properties of such mixed diesel fuel are improved by the addition of diesel oil and are superior to those of diesel fuel derived from biomass alone. The following examples better illustrate the process of the present invention: Example 1: Conversion of restaurant collector grease into diesel derived from biomass The restaurant collector grease with an average density of 0.925 g / mL, and an oxygen content of 13.72. % weight was fed to the thermal cracking unit where it was exposed to cracking at a temperature of 418.5 ° C and a pressure of 300 kPa for 40 minutes. The thermal cracking produced a gas stream, a stream of naphtha, an intermediate distillate stream having a boiling temperature in the range of 165 to 345 ° C, water and residue. The intermediate distillate stream comprised 63.0% by weight of the total cracked product and its oxygen content was 7.99% by weight. The intermediate distillate stream was then fed to a catalytic hydrotreating unit. The hydrotreatment produced a diesel fuel derived from biomass with a cetane value of 75.4, a runoff temperature of -6.0 ° C and an opacity point of -2.5 ° C. Diesel was found to have less than 10 ppm sulfur content, which is perfectly within tolerable commercial limits. Example 2: Conversion of yellow fat into diesel derived from biomass Yellow fat is waste fat resulting from melting animal fat. In this case, the yellow fat, which has a density of 0.918 g / mL and an oxygen content of 11.56% weight was fed to a thermal cracking unit in which it was cracked at 411 ° C and 100 kPa for 40 minutes. The thermal cracking produced a product with content of 68.6% by weight of intermediate distillates (165 ° C-345 ° C), 7.0% by weight of naphtha and the rest of gas, water and waste. The intermediate distillate stream, which was discovered to have 8.29% oxygen weight, was then fed to a catalytic hydrotreating unit. The resulting biomass diesel stream had a cetane value of 79.2, a runoff temperature of -4.0 ° C and an opacity point of -1.4 ° C. The sulfur content of the diesel was found to be less than 10 ppm. The detailed description of the process and methods is used to illustrate an embodiment of the present invention. Those skilled in the art will be able to see that various modifications can be made in the present process and methods and that various alternative embodiments can be used. Therefore, it will be recognized that various modifications can also be made to the applications to which the process and methods are applied without departing from the spirit of the invention, which is limited only by the appended claims.

CLAIMS 1. A method for producing high-value cetane diesel fuels from a triglyceride feed, comprising: a. pre-treat the triglyceride feed by thermal cracking to partially convert the triglycerides and produce a fraction of intermediate distillates; e b. catalytically hydrotreat the fraction of intermediate distillates to produce high-value cetane diesel fuel. The method of claim 1 characterized in that the triglyceride feed is selected from the group consisting of restaurant greaser fat, animal fats, waste fats, low quality vegetable oils and combinations thereof. 3. The method of claim 1 or 2 characterized in that the fraction of intermediate distillates has a boiling temperature ranging from 160 ° C to 345 ° C. The method of one of claims 1 to 3, characterized in that the thermal cracking is conducted at a temperature of 390 ° C to 460 ° C. 5. The method of claim 4 characterized in that the thermal cracking is conducted at a temperature of

Claims (1)

1. 410 ° C at 430 ° C. 6. The method of any of claims 1 to 5 characterized in that the catalytic hydrotreatment consumes less than 2.0 kg of hydrogen per 100 kg of the intermediate distillate fraction fed to the hydrotreating step. 7. The method of any of claims 1 to 6 characterized in that the catalytic hydrotreating is conducted at a temperature of 30 ° C to 400 ° C. The method of claim 7 characterized in that the catalytic hydrotreating is conducted at a temperature of 350 ° C to 390 ° C. The method of any of claims 1 to 8 characterized in that the catalytic hydrotreating is conducted using a commercial hydrotreating catalyst. The method of claim 7 characterized in that the commercial hydrotreating catalyst is nickel-molybdenum, cobalt-molybdenum or nickel-tungsten in a catalytic support. The method of any of claims 1 to 10 further comprising filtering the triglyceride feed to remove the macroscopic contaminant particles prior to thermal cracking 12. The method of any of claims 1 to 11 further comprising conducting the subsequent separation to the catalytic hydrotreating to produce a gas stream, a water stream and a liquid organic product stream. The method of claim 12, further comprising distilling the liquid organic product stream to also separate the diesel fuels from the paraffin residues. The method of claim 12 or 13, further comprising the step of recycling the gas stream as hydrogen recycling during catalytic hydrotreating. 15. A mixture feed of biomass-derived diesel for use in increasing the cetane values of mixed diesel fuels, where the mixing stock has a cetane value of at least 70, an opacity point below 0 ° C and a runoff temperature of less than -4 ° C. 16. The biomass-derived diesel mixture feed of claim 15, which has a sulfur content below 10 ppm. 17. The biomass-derived diesel mixture feed of claim 15 or 16, produced by the method of claim 1. 18. A mixed diesel fuel comprising 5 to 20% by weight weight of biomass-derived diesel mixture stock. as described in claim 15 and 80 to 95 vol.%. diesel oil, based on a total volume of mixed diesel fuel. 19. The mixed diesel fuel of claim 18 comprising 10 vol. of the stock of diesel mixture derived from biomass as described in claim 15 and 90% vol. of diesel oil, based on a total volume of mixed diesel fuel.