Fuel Composition Derived from Biodiesel

Info

Publication number: 20110016776
Type: Application
Filed: Jul 22, 2010
Publication Date: Jan 27, 2011
Inventor: Chandrashekhar H. Joshi (Bedford, MA)
Application Number: 12/841,483

Abstract

The present invention relates to a fuel composition and method for the preparation thereof. The fuel composition is particularly useful as an aviation fuel and as a ground transportation fuel in cold weather environments. The fuel composition includes oil derived from a biological source such as vegetable oil and/or animal fat. Further, the fuel composition can be based on biodiesel. Moreover, the fuel composition of the present invention includes a reduced amount of oxygen as compared to the biodiesel or substantially no oxygen.

Description

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/227,583, filed Jul. 22, 2009, and entitled “Conversion and Purification of Biodiesel to Aviation Fuel.”

FIELD OF THE INVENTION

The present invention relates to a fuel composition and a method of producing the fuel composition. In particular, the fuel composition can be useful in cold temperature environments and as aviation fuel.

BACKGROUND OF THE INVENTION

Global climate change is causing a shift in the sources of energy from fossil fuels to more sustainable and renewable resources, such as biodiesel. For ground transportation, there is a significant development effort to use electricity from non-fossil primary fuel to power cars, trucks and rail systems. However, in cold climates, such as in temperate or polar regions of the world (including a significant portion of the United States, Canada, northern Europe and northern Asia), biodiesel fuels tend to solidify rendering inoperable engines that use it.

Furthermore, for aircraft, the energy densities available from batteries, fuel cells and other portable sources are not sufficient. Aviation fuel, such as jet fuel, is generally a specialized type of petroleum-based fuel used to power an aircraft and is generally of a higher quality than fuel used for ground transportation. Aviation fuel is designed to remain liquid at cold temperatures as found in the upper atmosphere where aircraft fly. Aviation fuels can include hydrocarbons, such as paraffins; olefins; naphthenes and aromatics; antioxidants; and metal deactivators. Known aviation fuels include jet fuels, such as JP-5, JP 8, Jet A, Jet A-1, and Jet B. Aviation requires a high energy dense liquid fuel to achieve the speeds and distances airplanes can deliver today. Jet fuel has the highest volumetric energy density of liquid fuels, such as ethanol, butanol, bio-kerosene, and biodiesel.

There is a need in the art to develop a fuel composition that does not solidify in cold temperature environments for use as ground transportation fuel, that satisfies the specified standard requirements for use as aviation fuel, and is based on sustainable and renewable resources, such as biodiesel.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a fuel composition including oil derived from a biological source and alcohol. The fuel composition is at least substantially free of oxygen and oxygen-containing compounds.

The oil may be selected from the group of biological sources including vegetable oil, crop seed oil, animal oil, animal fat, and combinations thereof.

The alcohol may be selected from the group consisting of methanol, ethanol, propanol, isopropanol, butanol, and mixtures thereof.

The fuel composition may be oxygen free. In another embodiment, the fuel composition may have a level of oxygen that is less than the level of oxygen in biodiesel. In yet another embodiment, the fuel composition may have a level of oxygen that is less than 2000 parts per million oxygen based on the fuel composition.

The fuel composition includes molecules and each of the molecules may have a carbon chain length of from 12 to 14 carbon atoms.

The fuel composition may be used for aviation fuel. In another embodiment, the fuel composition may be used for ground transportation fuel in a cold climate.

The fuel composition may include an alkane.

The fuel composition may further include a catalyst. The catalyst may be selected from the group consisting of calcium hydroxide, potassium hydroxide and mixtures thereof.

In another aspect, the present invention provides a method for preparing a fuel composition. The method includes reacting oil derived from a biological source and alcohol to produce an alkyl ester-containing product; and removing at least a portion of oxygen from the alkyl ester-containing product to produce a fuel composition which is at least substantially free of oxygen and oxygen-containing compounds.

In an embodiment, the alkyl ester-containing product may include an alkyl ester selected from the group consisting of methyl ester, ethyl ester, propyl ester, isopropyl ester, butyl ester and mixtures thereof.

In another embodiment, the alkyl ester-containing product may include biodiesel.

In the method, the reacting step may be conducted in accordance with a transesterification reaction.

In the method, the removing step may be conducted in accordance with a nucleophilic acyl reaction.

In an embodiment, the cloud point of the fuel composition may be lower than the cloud point of the alkyl ester-containing product.

In the method, the removing step may further include removing a portion of carbon atoms from the alkyl ester-containing product.

In the method, the fuel composition includes molecules and each of the molecules may have a carbon chain length of from 12 to 14 carbon atoms.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention as set forth in the claims will become more apparent from the following detailed description of certain preferred practices thereof illustrated, by way of example only, and the accompanying drawings, wherein

FIG. 1 is a schematic showing a reaction process for reducing an ethyl ester to ethanol in accordance with an embodiment of the present invention; and

FIG. 2 is a schematic showing a process for chemoselectively reducing secondary and tertiary alcohols (e.g., 2-decanol) to alkanes (e.g., decane) in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a fuel composition and method thereof. The fuel composition can be used in various applications. In particular, the fuel composition can be employed as a cold weather fuel for use in ground transportation vehicles, such as trucks, automobiles, railroads, and the like, and as an aviation fuel for use in aircrafts, such as airplanes, helicopters, and the like. Further, the fuel composition of the present invention can be prepared based on biodiesel. For example, biodiesel can be produced and converted to a fuel composition that is suitable for use as cold weather ground transportation and aviation fuel. Biodiesel is derived from plant oils, algae oils, and animal fats, and therefore, the present invention provides a fuel composition which is grown and produced using standard agricultural and chemical processing methods. The biodiesel can be converted to a fuel composition including an alkane or a mixture of alkanes.

Biodiesel has various characteristics and properties that make it unattractive for use in cold weather environments and as aviation fuel. For example, biodiesel has an energy density that is lower than required for aviation fuel. Further, at low temperatures, certain molecules within biodiesel begin to agglomerate into solid particles causing the normally translucent biodiesel to appear cloudy. The highest temperature at which the biodiesel begins to agglomerate or cloud is called the cloud point. The cloud point is an important characteristic of fuels used in internal combustion engines and jet engines because the presence of solid or agglomerated particles causes fuel pumps and injectors to clog rendering the engines inoperable. The cloud point for some common biodiesel products are as follows: 0° C. for canola; 1° C. for soybean; −6° C. for safflower; 1° C. for sunflower; −2° C. for rapeseed; 13° C. for jatropha; and 15° C. for palm. The cloud points of various fossil fuels are as follows: 0° C. for ULS diesel; −40° C. for Jet A; −47° C. for JP-8; and −40° C. for ULS kerosene. Aviation fuels have very low cloud points. For aviation fuels, the low cloud point is important because the fuel must remain liquid at high altitude where temperatures are well below zero. For ground transportation fuels, a low cloud point is important because the fuel must remain liquid in cold weather environments where ground vehicles are used.

The cloud point of fuel is a function of its chemical composition. Most fossil fuels include numerous compounds in the form of linear or branched chains of carbon atoms with one or more oxygen and hydrogen atoms bound to each carbon atom. For example, a general composition of conventional aviation fuel is C_mH_n, where _mis an integer from 12-14, and _nis an integer from 20 to 30, and a general composition of conventional biodiesel is C_jH_kCO₂CH₃, where _jis an integer from 14 to 16, and _kis an integer from 26 to 33. Jet A and synthetic aviation fuel are both composed of alkanes, which are compounds of carbon and hydrogen only. Biodiesel is a vegetable oil or animal fat-based diesel fuel composed of long-chain alkyl esters. The differences between aviation fuels and biodiesel include (i) the size of the molecules (biodiesel molecules are larger and include more carbon atoms per molecule) and (ii) the presence of oxygen (biodiesel contains oxygen, whereas aviation fuel is at least substantially oxygen free).

The presence of the oxygen in the biodiesel molecule causes it to have a degree of polarity (an electrostatic charge separation). This polarity results in an attraction between oxygen in one molecule to hydrogen atoms bound in an adjacent molecule through van der Waal's forces. This attractive force among biodiesel molecules causes solidification at higher temperatures than a similar molecule without oxygen. For example, Table 1 shows a comparison of the solidification temperature for various alkanes, i.e., oxygen-free molecules, and corresponding alcohols, i.e., oxygen-containing molecules. As shown below, the alcohols have a single oxygen atom in addition to the corresponding alkane. The alcohol has a higher solidification point than the corresponding alkane. The presence of additional oxygen atoms would result in a greater difference in solidification points as compared to the alkane.

TABLE 1 Solidifi- Solidifi- cation cation Alkane Composition (C) Alcohol Composition (C) Methane CH₄ −183 Methanol CH₄O −97 Ethane C₂H₆ −183 Ethanol C₂H₆O −115 Propane C₃H₈ −190 Propanol C₃H₈O −127 Butane C₄H₁₀ −138 Butanol C₄H₁₀O −90 Hexane C₆H₁₄ −95 Hexanol C₆H₁₄O −47 Octane C₈H₁₈ −57 Octanol C₈H₁₈O −16 Dodecane C₁₂H₂₆ −10 Dodecanol C₁₂H₂₆O 24 Eicosane C₂₀H₄₂ 37 Eicosanol C₂₀H₄₂O 66

Thus, it is contemplated by the present invention that the reduction in or removal of oxygen from the biodiesel, i.e., long-chain alkyl esters, will result in a product, i.e., an alkane, having a lower solidification temperature or cloud point.

In addition, it is contemplated by the present invention that reducing the length of the carbon chain in the biodiesel molecule from 16-18 carbons to 12-14 carbons will further reduce the solidification temperature or the cloud point of the resultant fuel composition.

The reduction or removal of oxygen or oxygen-containing components from biodiesel can be accomplished by employing a variety of chemical or thermal processes that result in a hydrocarbon, e.g., alkane, having less or no oxygen. The resulting hydrocarbon (e.g., fuel) will have a lower solidification temperature or cloud point than the starting biodiesel. The process used for the reduction in or removal of oxygen from biodiesel can include the reaction of an ester group, e.g., alkyl ester, with other chemicals either catalytically or electrically. In addition to removing oxygen atoms from the ester group, this ester reaction may also remove carbon atoms such that the overall carbon chain length of the biodiesel molecule is reduced. In one embodiment, the fuel composition of the present invention is substantially free of oxygen and has a carbon chain length of from 12 to 14 carbon atoms. This embodiment produces a fuel composition that is essentially comparable to aviation fuel (and compatible with aviation fuels to produce a mixture thereof) and can be used as a fuel for ground transportation vehicles in cold climates. In another embodiment, the produced fuel contains a reduced oxygen content and has a carbon chain length of 12-14 atoms. In a further embodiment, the fuel composition of the present invention contains less than 2000 parts per million of oxygen based on the fuel composition.

Biodiesel can be produced by a variety of conventional processes that are known in the art. Biodiesel is an oil-based diesel fuel, wherein the oil is obtained from a biological source, such as, but not limited to, a vegetable oil or animal fat. Oils suitable for use in producing biodiesel can be oils obtained from a wide variety of biological sources. Suitable oils from a biological source can include, but are not limited to, crop seed oils, vegetables oils, animal oils, animal fats, and combinations thereof. The crop seed oils can be isolated from biological sources, such as, but not limited to, rapeseed oil, sunflower oil, mustard oil, canola oil, peanut oil, palm oil, coconut oil, soybean oil, and mixtures thereof. Additional examples of suitable oils include, but are not limited to, waste vegetable oil; animal fats, including tallow, lard, yellow grease, chicken fat, by-products of the production of Omega-3 fatty acids from fish oil, and mixtures thereof; algae; oil from halophytes, such as salicornia bigelovii; and mixtures thereof. In alternative embodiments, the oil from a biological source can be distilled, separated, or at least partially purified to increase or decrease the content of a particular component of the oil, such as, but not limited to, triglycerides, diglycerides, monoglycerides, saturated fatty acids, unsaturated fatty acids, trilaurin, erucic acid, lauric acid, oleic acid, linoleic acid, linolenic acid, stearic acid, palmitic acid, and mixtures thereof.

In an embodiment, the oil from a biological source can be hydrocracked in accordance with conventional processes known in the art to yield smaller molecular weight species.

Biodiesel includes long-chain alkyl esters, such as, but not limited to, methyl ester, ethyl ester, propyl ester, isopropyl ester, butyl ester, and mixtures thereof. Biodiesel can be prepared by a transesterification process, wherein lipids are chemically reacted with alcohol. Suitable lipids include the oils derived from biological sources (such as, but not limited to, vegetable oils and animal fats) described herein. Suitable alcohols include, but are not limited to, ethanol, methanol, propanol, isopropanol, butanol, and mixtures thereof. In addition, the transesterification process can include the presence of catalyst. The catalyst can be selected from a wide variety of materials known in the art to facilitate the reaction between lipids and alcohols. Suitable catalysts include, but are not limited to, calcium hydroxide, potassium hydroxide, and mixtures thereof. The transesterification reaction can be carried out using a variety of conventional processes known in the art. Suitable processes include, but are not limited to, common batch processes, supercritical processes, and ultrasonic methods. In general, the transesterification reaction converts base oil in the vegetable or animal starting materials to the desired esters, e.g., alkyl esters, in the biodiesel product. The transesterification process can produce by-products. For example, free fatty acids present in the base oil are typically converted to soap and removed from the process or they are esterified using an acidic catalyst. Further, glycerol can be produced as a by-product of the transesterification process. Typically, this crude glycerol is purified by employing a conventional purification process known in the art, such as, but not limited to, vacuum distillation. The refined, purified glycerol then can be utilized directly or converted into other products.

In one embodiment, biodiesel is made by reacting animal fat or vegetable oil with methanol by transesterification. The process yields two products: (i) methyl esters, i.e., biodiesel, and (ii) glycerin, i.e., a by-product that can be used for the production of soap. In alternate embodiments, this process can be conducted on any scale, e.g., in a mason jar or in a large-scale production facility.

In another embodiment, vegetable oil or animal fat reacts with ethanol or methanol or mixtures thereof, and a catalyst, such as calcium hydroxide or potassium hydroxide or a mixture thereof. In a further embodiment, the initial oil or fat is relatively low in free fatty acids in order to reduce or prevent the formation of soap. The reactants are mixed thoroughly for about an hour at room temperature or slightly-elevated temperature. In one embodiment, the temperature is from about 20° C. to about 50° C. After about one hour of mixing, the solution is allowed to settle.

During the settling time, the heavy glycerin (glycerol) settles to the bottom of the solution and biodiesel is formed on top. The glycerin is then separated by, for example, draining it from the bottom of a settling tank. In an alternate embodiment, separation can be accomplished by using a centrifuge which is typically employed in large scale production of biodiesel to reduce the time needed to carry out the process.

The final steps in the process include washing and drying the biodiesel using conventional methods known in the art. In one embodiment, a fine mist of water is applied to the biodiesel to absorb any trace amounts of the catalyst remaining in the biodiesel. This is separated from the biodiesel, for example, in the same manner as the glycerin separation. A subsequent bubbling of air through the biodiesel removes any remaining water to ensure a high purity biodiesel product for use in diesel engines.

In another embodiment, wherein the starting material contains a significant amount of free fatty acids (as is typical in vegetable oil after it is used for cooking or animal fat), a pretreatment of the free fatty acid can be conducted using conventional methods known in the art. For example, the vegetable oil or animal fat can be reacted with hydrochloric acid and methanol. This pretreatment converts the free fatty acids into biodiesel. After washing and drying the hydrochloric acid from the resulting solution using a conventional method known in the art, the remaining vegetable oil can be converted to biodiesel using the transesterification process described herein.

The following table gives approximate amounts of the reactants needed to produce one gallon of biodiesel in accordance with an embodiment of the invention. The amounts can depend on the level of free fatty acid and water in the feedstock vegetable oil or animal fat.

TABLE 2 Feedstock (veg. oil or animal fat) 1 gal Methanol 0.1667 gal Potassium hydroxide 0.0435 kg Hydrochloric Acid 0.001 Gal Water 0.4 Gal Electric Power 0.6667 kW/Gal/hr

In one embodiment of the present invention, multiple reactions may be necessary to reduce or remove the oxygen and/or oxygen-containing compounds from biodiesel to produce a fuel having a low solidification temperature or cloud point for use in cold climates or as aviation fuel. For example, an ester, such as an alkyl ester in biodiesel, can be reduced to two alcohols through a reaction with lithium aluminum hydride (LiA1H₄). This nucleophilic acyl substitution reaction is generally conducted as follows:

FIG. 1 shows a four-step reaction process for reducing an ethyl ester (I) to ethanol (V). In FIG. 1, the nucleophilic hydrogen atom (H) from the hydride reagent (LiA1H₄) adds to the electrophilic carbon (C) in the polar carbonyl group of the ester (I). Electrons from the carbon and oxygen double bond (C═O) move to the electronegative oxygen atom (O) creating an intermediate metal alkoxide complex (II).

The tetrahedral intermediate collapses and displaces the alcohol portion of the ester as a leaving group, which produces a ketone as an intermediate (III).

The nucleophilic H from the hydride reagent adds to the electrophilic C in the polar carbonyl group of the aldehyde. Electrons from the C═O move to the electronegative O creating an intermediate metal alkoxide complex (IV).

The final step is a simple acid/base reaction. Protonation (H+) of the alkoxide oxygen creates the primary alcohol product (V) from the intermediate complex.

Reduction of the resultant alcohol to alkane can be accomplished by a variety of chemical processes. FIG. 2 shows a process for chemoselectively reducing secondary and tertiary alcohols to alkanes. This direct pathway shows selective reduction of the hydroxyl (OH) moiety without affecting other functional groups. In FIG. 2, 2-decanol (compound 1a) is reduced to decane (compound 2a) using this process. The reducing system in FIG. 2 includes dissolving 2-decanol in a CH₂ClCH₂Cl solvent with hydrosilane and indium chloride (InCl₃) catalyst, at a temperature of about 80° C. for about 4 hours.

The fuel composition of the present invention can provide at least one of the following benefits:

- Reduced solidification temperature or cloud point; and
- Agricultural-based starting materials.

In one embodiment, wherein the fuel composition of the present invention includes the conversion of biodiesel fuel to ground transportation fuel or aviation fuel, the cloud point of the fuel composition is less than the cloud point of the biodiesel. In another embodiment, wherein the fuel composition of the present invention is used as aviation fuel, the cloud point can be less than or equal to about −40° C. In another embodiment, wherein the fuel composition of the present invention is used as ground transportation fuel in cold temperature conditions, the cloud point can be less than about −20° C. Cold climate conditions can vary and in one embodiment, cold climate temperatures can be less than or equal to about 0° C.

While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the breadth of the appended claims and any and all equivalents thereof.

Claims

1. A fuel composition, comprising:

oil derived from a biological source; and

alcohol,

wherein the fuel composition is at least substantially free of oxygen and oxygen-containing compounds.

2. The fuel composition of claim 1, where the oil is selected from the group of biological sources consisting of vegetable oil, crop seed oil, animal oil, animal fat and combinations thereof.

3. The fuel composition of claim 1, wherein the alcohol is selected from the group consisting of methanol, ethanol, propanol, isopropanol, butanol and mixtures thereof.

4. The fuel composition of claim 1, wherein the fuel composition is oxygen-free.

5. The fuel composition of claim 1, wherein the fuel composition has a level of oxygen that is less than the level of oxygen in biodiesel.

6. The fuel composition of claim 1, wherein the fuel composition has a level of oxygen that is less than 2000 parts per million oxygen based on the fuel composition.

7. The fuel composition of claim 1, wherein the fuel composition includes molecules and each of the molecules has a carbon chain length of from 12 to 14 carbons atoms.

8. The fuel composition of claim 1, wherein the fuel composition is used for aviation fuel.

9. The fuel composition of claim 1, wherein the fuel composition is used for ground transportation fuel in a cold climate.

10. The fuel composition of claim 1, wherein the fuel composition comprises an alkane.

11. The fuel composition of claim 1, wherein the fuel composition further comprises catalyst.

12. The fuel composition of claim 11, wherein the catalyst is selected from the group consisting of calcium hydroxide, potassium hydroxide and mixtures thereof.

13. A method for preparing a fuel composition, the method comprising:

reacting oil derived from a biological source and alcohol to produce an alkyl ester-containing product,

removing at least a portion of oxygen from the alkyl ester-containing product to produce a fuel composition which is at least substantially free of oxygen and oxygen-containing compounds.

14. The method of claim 13, wherein the alkyl ester-containing product comprises alkyl ester selected from the group consisting of methyl ester, ethyl ester, propyl ester, isopropyl ester, butyl ester and mixtures thereof.

15. The method of claim 13, wherein the alkyl ester-containing product comprises biodiesel.

16. The method of claim 13, wherein the reacting step is conducted in accordance with a transesterification reaction.

17. The method of claim 13, wherein the removing step is conducted in accordance with a nucleophilic acyl reaction.

18. The method of claim 13, wherein the cloud point of the fuel composition is lower than the cloud point of the alkyl ester-containing product.

19. The method of claim 13, wherein the removing step further comprises removing a portion of carbon atoms from the alkyl ester-containing product.

20. The method of claim 13, wherein the fuel composition comprises molecules and each of the molecules has a carbon chain length of from 12 to 14 carbon atoms.