US20090199462A1 - Method for separating saturated and unsaturated fatty acid esters and use of separated fatty acid esters

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US20090199462A1

Publication number: US20090199462A1
Application number: US12/261,806
Authority: US
Inventors: Shailendra Bist; Bernard Y. Tao; Samia Mohtar
Original assignee: Individual
Current assignee: Purdue Research Foundation
Priority date: 2007-03-23
Filing date: 2008-10-30
Publication date: 2009-08-13

The present invention provides a composition comprising methyl esters derived from vegetable oils having less than about 3% by weight of saturated fatty acid methyl esters and a cloud point of less than about −30° C. A method for making the lowered cloud point composition is also disclosed in which vegetable derived methyl esters, urea and alcohol are mixed under sufficient heat to form a homogenous mixture. The mixture is then cooled to a temperature where a solid phase and a liquid phase are formed. The solid phase is enriched in saturated fatty acid methyl esters and the liquid phase is enriched in unsaturated fatty acid methyl esters. The solid phase is separated from the liquid phase. Finally, unused urea and methanol are removed from the liquid phase to form a liquid composition having a cloud point of less than about −30° C. and less than about 3% by weight saturated fatty acid methyl esters.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 11/690,540, filed Mar. 23, 2007, which claims priority to U.S. patent application Ser. No. 11/668,865, filed Jan. 30, 2007, now abandoned, which claims priority to U.S. patent application Ser. No. 11/068,104, filed Feb. 28, 2005, which claims priority to U.S. Provisional Patent Application Ser. No. 60/547,992, filed Feb. 26, 2004, all of which are hereby incorporated by reference in their entirety.

BACKGROUND OF THE DISCLOSURE

The present invention generally relates to fatty acid esters, more particularly, to a method for preparation and separation of fatty acid esters. A multitude of energy crises stemming from supply disruption as well as significantly increasing demand for fossil fuels by industrialized nations in the past few decades have spawned motivation for development of alternative fuel sources. Additionally, since there are finite reserves of crude oil from which petroleum based fuels are derived, there is also motivation to develop renewable fuel sources. A substantial amount of effort has recently been made to develop biodiesel fuels from renewable sources.
Soy methyl ester (SME) or methyl soyate, the chemical description of which is provided below, is a common organic acid ester precursor for producing biodiesel. Organic acids, as the name indicates, are organic compounds with acid-like properties. One common group of organic acids are carboxylic acids, which have a “—COOH tail.” Esters constitute a class of organic acid compounds where at least one —OH member is replaced by an alkoxy group (—O—C_nH₂₊₁). In the case of methyl acetate ester, for example, a methoxy group (—O—CH₃), which is the simplest form of an alkoxy, has replaced the —OH group in acetic acid CH₃COOH. This results in CH₃COOCH₃, or methyl acetate ester. This chemical reaction is commonly termed esterification. Diagram 1, found below, shows the chemical bond structures for these compounds.
Fatty acids consist mainly of carbon chains and hydrogen atoms. These chains can be short with a small number of carbon atoms, e.g., butyric acid (CH₃CH₂CH₂COOH), or long with large number of carbon atoms, e.g., oleic acid CH₃(CH₂)₇CH═CH(CH₂)₇COOH. Fatty acids may include single and double bonds between carbon atoms. A saturated fatty acid has the maximum number of hydrogen atoms covalently bound to each carbon atom in the chain of carbon atoms, i.e., a saturated fatty acid has no double bonds. An unsaturated fatty acid has at least one double bond between two carbon atoms. Diagram 2, found below, shows an example of saturated and unsaturated fatty acids.
SME is produced by the transesterification of soybean oil with methanol in the presence of a catalyst. Transesterification results in a class of organic reactions where one ester is transformed into another ester by interchanging at least one alkoxy. The catalyst is often an acid or base.
SME profile by percent and by molecular weight is given in Table 1, below.

TABLE 1

Typical SME profile

Fatty			Molecular		Percent of
Acid	Carbon		Weight	Melting	SME by
Name	Design	Formula and Structure	(g/mole)	Point (° C.)	Weight

methyl palmi- tate	C16:0		270.5	30.5	10.3

methyl stearate	C18:0		298.5	39.1	4.7

methyl oleate	C18:1		296.5	−19.8	22.5

methyl lino- leate	C18:2		294.5	−34.9	54.1

methyl lino- lenate	C18:3	CH₃(CH₂CH═CH)₃ (CH₂)₇CO₂CH₃	292.5	−57	8.3

Biodiesel produced by typical methods suffers from a crystallization phenomenon when temperatures decrease. Although this crystallization phenomenon is not limited to biodiesel, the temperature at which biodiesel begins to crystallize is substantially higher than petroleum-based diesel fuel. The crystallized constituents can clog fuel filters in vehicles using biodiesel and thereby cut off the fuel supply to the engine. The temperature at which two phases, i.e., the liquid and solid phases start to separate, thus producing a cloudy mixture, is referred to as cloud point (C.P.). Saturated fatty acid esters constituents have a higher C.P. than unsaturated fatty acid esters. To lower the temperature at which crystallization occurs and thereby lower the C.P. of the fuel, several techniques are often used, examples of which include blending with petroleum-based diesel, introducing additives, and winterization. Winterization refers to removal of saturated fatty acids, e.g., C16:0 and C18:0, and in some cases mono-unsaturated fatty acids, e.g., C18:1, that cause the biodiesel product to crystallize at an undesirably high temperature. The removal process is typically by filtration of the crystallized particles of the saturated and in some cases mono-unsaturated fatty acids which leaves a mixture having a greater amount of unsaturated fatty acids compounds with lower C.P., thereby lowering the C.P. of the biodiesel so produced.
The winterization process has gained more interest in recent years. Winterization by itself produces low yields, i.e., a substantial portion of the starting material is lost during the filtration process. Therefore, use of compounds which improve the winterization process, typically referred to as “improvers,” is essential. One process which includes the addition of improvers is referred to as fractionation, which uses the crystallization properties of esterified fatty acids to separate a mixture into low and high melting point liquid fractions. During fractionation, these improvers create inclusion compounds/complexes. This process includes a host constituent having a series of cavities or landing sites for attachment by a second chemical constituent, commonly referred to as the guest. The compound resulting from the combination of the host and the guest is called an “inclusion compound.” The forces that hold the host and the guest constituents together are van der Waals type forces. That is, no covalent bonds form between the guest and the host. Clathrates are one type of inclusion compound in which the spaces in the host constituent are enclosed on all sides, causing a “trapping effect.”
There are three different types of fractionation: dry fractionation, detergent fractionation, and solvent fractionation. Solvent fractionation has received a substantial amount of interest in recent years. It is an efficient process by which one group of esterified fatty acid constituents are separated from another group. The differing solubility of the groups is the key to success with this process. Several advantages are offered by solvent fractionation as compared to dry fractionation. For example, dry fractionation requires a longer crystallization period than solvent based fractionation; and solvent fractionation substantially increases the chance of crystallization in one round rather than multiple stages as may be the case with dry fractionation. Conversely, solvent based fractionation requires more energy and the solvents are costly, although in many cases they are recovered in solvent recovery schemes.
The prior art method of thermal crystallization (winterization) followed by filtration (with or without solvent) utilizes the difference in crystallization temperature of the saturated and unsaturated components of SME. The saturated components crystallize at a higher temperature and can be removed via filtration, centrifugation, etc. However, a significant amount of co-crystallization occurs. Co-crystallization occurs when during the winterization process certain unsaturated components also crystallize and are thus also removed, resulting in high losses of the preferred unsaturated fatty acid methyl esters (FAME). To obtain a C.P. of −16° C., almost 75% of the starting material was removed in the work reported by Dunn et al. See R. O. Dunn, M. W. Shockley, and M. O. Bagby, “Improving the Low-Temperature Properties of Alternative Diesel Fuels: Vegetable Oil-Derived Methyl Esters,” JAOCS, Vol. 73, No. 12 (1996), PP 1720-1721. Additionally, these techniques involve cooling to very low temperatures and require processing times of days.
Also, the amount of saturated or monounsaturated molecules which are extracted from the fatty acid compound has been shown to have an effect on the C.P. For instance, Dunn et al. in two published articles suggest a linear relationship in the depression in C.P. as a function of reduction of saturate constituents. See, Dunn et al. “Improving the low-temperature properties of alternative diesel fuels: Vegetable oil-derived methyl esters” published in 1996, and “Winterized Methyl Esters from Soybean Oil: An Alternative Diesel Fuel with Improved Low-Temperature Flow Properties” published in 1997. In the latter article, Dunn et al. describe a linear relationship between total concentration of saturate constituents and C.P., as described in equation (1), found below:
CP=1.4403*(Total Saturates)−24.8 (1)
FIG. 1 titled as prior art graphically shows the linear relationship described by Dunn's equation (1) between the C.P. and the total saturates.
In the 1996 article, Dunn et al. reported a winterization process resulting in a C.P. of −16° C. having final components of C16:0 (4.3, % by wt), C18:0 (1.3, % by wt), C18:1 (30.3, % by wt), C18:2 (49.6, % by wt), C18:3 (11.9, % by wt), and others (2.6, % by wt). In the same paper, Dunn et al. suggested a laboratory experiment resulting in a C.P. of −23° C. C.P. for a pure solution of unsaturated C18 components, presumably C18:1, C18:2, and C18:3, i.e., a saturate concentration of 0. That is, according to Dunn et al., a drop of 7° C. is to be expected in going from a normal winterization process having a C.P. of −16° C., to −23° C. with zero concentration of saturated components. Extension of the linear relationship, as shown in FIG. 1, or by use of equation (1), places the point at which the line crosses the abscissa, i.e., saturate concentration of 0, at −24.8° C. This confirms that Dunn et al. in both the 1996 and 1997 articles contemplated a further but small depression of C.P. as the concentration of the saturates approaches zero. In fact, immediately after presenting the laboratory data directed at the removal of all saturates, in the 1996 article Dunn et al. stated “[w]interization may prove to be effective in removing nearly all saturated long methyl esters from SME. However, complete removal of saturated methyl esters may not be recommended because doing so would significantly reduce their ignition quality.” P. 1721, JAOCS, Vol. 73 no. 12 (1996). Therefore, in addition to predicting a linear relationship, Dunn et al. concluded that the extra 7° C. of C.P. depression in going from −16° C. at saturate concentration of about 6% by weight (C16:0:4.3% by wt, and C18:0:1.3% by weight) in a typical winterization process to a C.P. of −23° C. for 0% saturate components, experimentally, and −24.8° C. based on equation (1), was not advisable.
In other prior art work, urea, also known as carbamide with the chemical formula (NH₂)₂CO, has been used in the winterization process. Urea is used to form inclusion compounds with long chain organic compounds. This was first discovered and reported by F. Bengen in a German patent filed in 1940. See Bengen, F., German Patent Application 0. Z. 12438, Mar. 18, 1940. Later studies from the late forties to the early fifties reported the selectivity of urea in forming complexes with long chain organic molecules. (See citations in the Reference section.) This selectivity was found to be based on: a) Carbon chain length, b) presence of unsaturation in the molecule, and c) degree of unsaturation. The formation of these complexes was found to be a useful technique for the separation of a mixture of saturated and unsaturated organic compounds, e.g., fractionation of a mixture of free fatty acids. Various techniques for the formation of such complexes were also studied, however, with little or no focus on process parameters. Hayes et al. worked on the fractionation of fatty acids and studied various process parameters that affect the formation of urea inclusion complexes, product yields, and the composition of fractions obtained. U.S. Pat. Nos. 5,106,542 and 5,243,046 to Traitler et al. describe the art of fractionating fatty acid mixtures via urea inclusion. U.S. Pat. No. 5,679,809 to Bertoli et al. (“the '809 patent”) describes the concentration of polyunsaturated fatty acid ethyl esters via urea inclusion.
In solvent fractionation, urea dissolves in ethanol, methanol, or other solvents as an early step in producing inclusion compounds. The goal of solvent-based fractionation, as explained in the '809 patent, is to remove saturated and monounsaturated fatty acid ethyl esters. The '809 patent teaches heating the mixture of ester, urea, and ethanol to a particular temperature until the urea is dissolved. The mixture is then cooled to allow certain molecules to form a solid phase. The solid phase is separated from the liquid phase by filtration or centrifugation. The liquid phase is further processed to partly remove ethanol, and the desired ethyl esters enriched with polyunsaturated fatty acids are then extracted by washing the remaining liquid phase with an acidic liquid.
As cloud points of approximately −20° C. are too high for many cold weather uses of biodiesel, such as in vehicles, there is still a need for an improved process to lower C.P. of biodiesel to an acceptable level.

REFERENCES

1. Bengen, F., German Patent Application 0. Z. 12438, Mar. 18, 1940.
2. Swern, D. “Urea and Thiourea Complexes in Separating Organic Compounds,” Industrial and Engineering Chemistry, Vol. 47, 216-221, 1955.
3. Swern, D., Parker, W. E., “Application of Urea Complexes in the Purification of Fatty Acids, Estes, and Alcohols. 1. Oleic Acid from Inedible Animal Fats,” JAOCS, 431-434, 1952.
4. Newey, H. A., Shokal, E. C., Mueller, A. C., Bradley, T. F., “Industrial and Engineering Chemistry,” Vol. 42, 2538-2540, 1950.
5. Schlenk, H., Holman, R. T., “Separation and Stabilization of Fatty Acids by Urea Complexes,” Journal of American Chemical Society, vol. 72, 5001-5005, 1950.
6. Hayes, D. G., Bengtsson, Y. C., Alstine, J. M. V., Setterwall, F., “Urea Complexation for the Rapid, Ecologically Responsible Fractionation of Fatty Acids from Seed Oil,” vol. 75, JAOCS, 103-1409, 1998.
7. Hayes, D. G., Bengtsson, Y. C., Alstine, J. M. V., Setterwall, F., “Urea-Based Fractionation of Seed Oil Samples Containing Fatty Acids and Acylglycerols of Polyunsaturated and Hydroxy Fatty Acids,” Vol. 77, JAOCS, 207-213, 2000.
8. Hayes, D. G., “Free Fatty Acid Fractionation via Urea Inclusion Compounds,” Vol. 13, INFORM, 832-833, 2002.
9. Hayes, D. G., Alstine, J. M. V., Asplund, A. L., “Triangular Phase Diagrams to Predict the Fractionation of Free Fatty Acid Mixtures via Urea Complex Formation,” Separation Science and Technology, Vol. 36, 45-58, 2001.
10. Lee, L. A. Johnson and E. G. Hammond, “Reducing the Crystallization Temperature of Biodiesel by Winterizing Methyl Soyate,” JAOCS, Vol. 73, No. 5 (1996).
11. R. O. Dunn, M. W. Shockley, and M. O. Bagby, “Improving the Low-Temperature Properties of Alternative Diesel Fuels: Vegetable Oil-Derived Methyl Esters,” JAOCS, Vol. 73, No. 12 (1996).
12. R. O. Dunn, M. W. Shockley, and M. O. Bagby, “Winterized Methyl Esters from Soybean Oil: An Alternative Diesel Fuel With Improved Low-Temperature Flow Properties,” Oil Chemical Research, Society of Automotive Engineers, Inc., 1997.
13. Diks, R. M. M., Lee, M. J., “Production of Very Low Saturate Oil Based on the Specificity of Geotrichum Candidum Lipase,” JAOCS, Vol. 76, No. 4, 1999.
14. Shimada, Y., Maruyama, K., Okazaki, S., Nakamura, M., Sugihara, C., “Enrichment of Polyunsaturated fatty Acids with Geotrichum Candidum Lipase,” JAOCS, Vol. 71, 951-953, 1994.
15. U.S. Pat. No. 5,678,809, “Concentration of Polyunsaturated Fatty Acid Ethyl Esters and Preparation Thereof.”
16. U.S. Pat. No. 5,106,542, “Process for the Continuous Fractionation of a Mixture of Fatty Acids.”
17. U.S. Pat. No. 5,243,046, “Process for the Continuous Fractionation of a Mixture of Fatty Acids.”
18. U.S. Pat. No. 6,444,784 B1, “Wax Crystal Modifiers.”
19. U.S. Pat. No. 6,409,778 B1, “Additive for Biodiesel and Biofuels.”
20. International Publication No. WO 99/62973, “Wax Crystal Modifiers Formed Form Dialkyl Phenyl Fumarate.”
21. International Publication No. WO 00/32720, “Winterized Paraffin Crystal Modifiers.”
22. U.S. Pat. No. 3,961,916, “Middle Distillate Composition with Improved Filterability and Process Thereof.”
23. U.S. Pat. No. 5,726,048, “Mutant of Geotricum Candidum Which Produces Novel Enzyme System to Selectively Hydrolyze Triglycerides.”
24. U.S. Pat. No. 6,537,787, “Enzymatic Methods for Polyunsaturated Fatty Acid Enrichment.”
25. U.S. Pat. No. 5,470,741, “Mutant of Geotrichum Candidum Which Produces Novel Enzyme System to Selectively Hydrolyze Triglycerides.”
26. Kocherginsky et al., “Mass Transfer of Long Chain Fatty Aids Through Liquid-Liquid Interface Stabilized by Porous Membrane,” Separation Purification Technology, Vol. 20, 197-208, 2000.
27. U.S. Pat. No. 4,542,029, “Process for Separating Fatty Acids.”
28. U.S. Pat. No. 4,049,688, “Process for Separating Esters of Fatty Acids by Selective Adsorption.”
29. U.S. Pat. No. 4,129,583, “Process for Separating Crystallizable Fractions from Mixtures Thereof.”
30. Maeda, K., Nomura, Y., Tai K., Uneo, Y., Fukui, K., Hirota, S., “New Crystallization of Fatty Acids From Aqueous Ethanol Solution Combined with Liquid-Liquid Extraction,” Ind. Eng. Chem. Res., Vol. 38, 2428-2433, 1999.

The above references 1-30 are incorporated herein by reference.

SUMMARY OF THE INVENTION

Embodiments of the present teachings are related to lowering cloud point of a vegetable derived composition having methyl esters by fractionating saturated and mono-unsaturated components of methyl esters in the composition.
According to one exemplary embodiment, a composition is disclosed having methyl esters derived from vegetable oils. The methyl esters comprise less than about 3% by weight of saturated fatty acid methyl esters. The composition has a cloud point of less than about −30° C.
The methyl esters in certain embodiments comprise methyl oleate, methyl linoleate and methyl linolenate. The methyl linolenate may comprise less than about 10% by weight of the methyl esters. The methyl stearate comprises less than about 0.1% by weight of the methyl esters. The methyl linoleate comprises at least about 50% or at least about 60% by weight of the methyl esters.
Cloud point of the composition can be selected, but for most cold weather applications envisioned, the composition has a cloud point that is less than about −35° C. In another embodiment, the composition has a cloud point that less than about −40° C. In still another embodiment, the composition has a cloud point less than about −45° C.
In another embodiment, the composition has a cloud point less than about −50° C.
In yet another embodiment, the composition has a cloud point is less than about −55° C.
In one embodiment, the methyl esters in the composition comprise less than about 2% saturated methyl esters. In another embodiment, the methyl esters in the composition comprise less than about 1.5% saturated methyl esters. In another embodiment, the methyl esters in the composition comprise less than about 0.5% saturated methyl esters.
In one embodiment, the vegetable from which the composition is derived comprises soy oil. In another embodiment, the composition includes material comprising a petroleum based component, wherein the petroleum based component comprises fossil fuel derived diesel fuel. In another embodiment, the composition includes material comprising animal fat derived methyl esters.
In one embodiment, the composition comprises less than about 1% methyl stearate. In another embodiment the composition comprises less than about 0.5% methyl stearate. In yet another embodiment the composition comprises less than about 0.1% methyl stearate.
In one exemplary embodiment, a method of lowering the cloud point of methyl esters derived from vegetable oil is disclosed. The method includes mixing vegetable derived methyl esters, urea and alcohol with sufficient heat to form a homogenous mixture. The homogeneous mixture is cooled to a temperature where a solid phase and a liquid phase are formed, the solid phase being enriched in saturated fatty acid methyl esters and the liquid phase being enriched in unsaturated fatty acid methyl esters. The solid phase is separated from the liquid phase, and methanol and unused urea are removed from the liquid phase to form a liquid composition having a cloud point of less than about −30° C. and less than about 3% by weight saturated fatty acid methyl esters.
In one embodiment of the above method, the alcohol comprises methanol. Also, the method further comprises, before the step of forming the homogeneous mixture, the step of mixing vegetable derived oil, sodium hydroxide and methanol to form the vegetable derived methyl esters. In certain embodiments, the homogeneous mixture contains methanol in an amount of about 3 to 10 times by weight of the amount of the fatty acid methyl ester. Excess methanol is provided in the step of mixing the vegetable derived oil, sodium hydroxide and methanol to form the vegetable derived methyl esters. Adding methanol during the step of forming the homogeneous mixture is therefore unnecessary.
In another embodiment, the method further comprises separating glycerin from the vegetable derived methyl esters before the step of forming the homogeneous mixture. In another embodiment of the method, the ratio of urea to methyl esters in the homogeneous mixture is from about 0.9:1 to about 1:1. In another embodiment, the solid phase is separated from the liquid phase by filtration, centrifugation, sedimentation, or decantation of the liquid phase. In yet another embodiment, the liquid composition comprises less than about 2 percent by weight of saturated fatty acid methyl esters. In another embodiment of the method, the liquid composition comprises less than about 1.5 percent by weight of saturated fatty acid methyl esters. In yet another embodiment of the method, the step of removal of methanol is by evaporation. Alternatively, the step of removal of methanol can be by applying vacuum. In another embodiment of the method, unused urea is removed by washing with acidified water, and the washed unused urea can be separated by a liquid-liquid centrifugal extractor or by a gravity separation.
In one embodiment of the method, the yield of the liquid composition is at least 43% by weight of the vegetable-derived methyl esters used to form the homogeneous mixture and the cloud point of the liquid composition is less than −34° C. The cloud point of the liquid composition, however, can be less than −40° C. or less than −50° C.

BRIEF DESCRIPTION OF DRAWINGS

The above-mentioned and other advantages of the present invention and the manner of obtaining them, will become more apparent and the invention itself will be better understood by reference to the following description of the embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a graph showing a linear relationship between saturate concentration and C.P. taught by the prior art;

FIG. 2 a is a schematic showing process steps involved in producing SME;

FIG. 2 b is a schematic showing process steps involved in fractionation of SME in accordance with the current teachings;

FIG. 3 is a graph of fuel flow rate versus power range;

FIG. 4 is a graph of controlled emission of Jet A fuel and soy methyl ester blends for carbon monoxide;

FIG. 5 is a graph of controlled emission of Jet A fuel and soy methyl ester blends for nitrogen dioxide;

FIG. 6 is a graph of controlled emission of Jet A fuel and soy methyl ester blends for nitrogen monoxide;

FIG. 7 is a graph showing cloud point depression as a function of SME:urea:ethanol/methanol and also showing remaining methyl esters in the treated product;

FIG. 8 is a graph of percent extracted SME vs. extracted species;

FIG. 9 a is a graph of C.P. vs. percent saturates illustrating how the current teachings differ from prior art predictions;

FIG. 9 b is a graph of C.P. vs. percent saturated fatty acids, monounsaturated fatty acids, and polyunsaturated fatty acids;

FIG. 10 is a graph of yield vs. C.P.; and

FIG. 11 is a graph of C.P. vs. urea ratio to the starting material.

DETAILED DESCRIPTION

The embodiments of the present invention described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the present invention.
These teachings relate to the fractionation/separation of fatty acid methyl esters, e.g., SME, into saturated fatty acid-rich and unsaturated fatty acid-rich fractions via the use of urea inclusion/urea complexation. Operation of diesel engines using renewable energy sources including triglycerides-derived fuels is known, as is the challenge of overcoming negative properties of these triglycerides-derived fuels, e.g., the gelling of bioderived diesel (biodiesel) at higher temperatures than petroleum derived fuels. The composition of typical un-winterized biodiesel from SME is as given in table 2.

TABLE 2

Composition of SME based biodiesel

	Fatty Acid Methyl Ester	% by Weight

	Methyl Palmitate (C 16:0) ¹	10.3
	Methyl Sterate (C18:0)	4.7
	Methyl Oleate (C18:1)	22.5
	Methyl Linoleate (C 18:2)	54.1
	Methyl Linolenate (C18:3)	8.3

	¹The parenthetical reference (Cnn:n) indicates the number of carbon atoms of the molecule on the left side of the colon followed by the number of carbon-carbon double bonds in the molecule on the right hand side of the colon.

Referring to FIG. 2 a, transesterification of a starting material is shown. Transesterification reactants comprise a fatty acid source, e.g., soy oil, an alcohol, and a catalyst. Methanol is typically chosen as the reactant for SME transesterification, resulting in formation of the methyl ester from triglycerides. A hydroxide catalyst is typically used to accelerate the transesterification, although the reaction also responds to acid catalysis. Generally, mineral acids or mineral bases are selected as transesterification catalysts.
Typically, the transesterification of fatty acids from soy oil is considered “commercially complete” after a reaction time of from one to three hours at reaction conditions. Total time of reactants in the reaction vessel may exceed these times if it is necessary to heat reactants to reaction temperature in situ. In commercial settings, completion of the transesterification occurs when continuation of the transesterification cannot economically be maintained. Commercial completion may be influenced by many factors related to the equipment involved. Examples of these factors are capital cost/depreciation status, operating expense, size, geometry, separation equipment available, raw material cost, labor cost, or even the time of day as it relates to an operator's shift change.
The range of possible fat sources is not limited. Commercial fat sources are generally chosen from oilseeds, often locally produced, such as soybeans and canola. The carbon content of fatty acids from such sources ranges from 16 to 22 carbon atoms per fatty acid molecule.
In one embodiment, transesterification of raw materials of fats is most commonly accomplished by supplying fats and alcohol in the molar ratio of 1 mole fat (triglycerides) to 3 moles alcohol. Although the process is operable outside this ratio, unreacted raw materials result. The reaction is observed to be nearly stoichiometric although it may be advantageous to add excess alcohol to the esterification step as will be discussed below. One percent catalyst by weight of fat is sufficient to facilitate the reaction at a commercially acceptable rate. Insufficient catalyst results in a slowed reaction; excess catalyst is not observed to significantly increase the reaction rate and may require additional separation effort at the completion of the reaction.
An example of the transesterification process is shown in FIG. 2 a. Sodium Hydroxide (NaOH) is mixed with methanol, creating methoxide in methanol. The mixture produces heat. Fatty acids (in this case soy oil), are added to the methoxide mixture. The transesterification reaction generates glycerin and methyl esters. If a period of quiescence is allowed, the glycerin phase will separate from the methyl esters at the completion of the transesterification, forming a liquid phase of methyl ester on top of a liquid phase of glycerin. The phases may then be separated by, e.g., decanting the methyl esters. Other phase separation methods such as a centrifugation may be used to accelerate and enhance the separation of glycerin from the methyl ester. The exemplary technique for the above-described transesterification process is illustrated by the following example.

Transesterification of Soy Oil to Produce Un-Winterized SME Example:

Transesterification of soy oil with methanol in a vessel was completed with 6 molar parts methanol to 2 molar parts refined soy oil. NaOH as a catalyst at the rate of 1% by weight of soy oil was included. The liquid components were heated to 65° C. The condition was maintained for one hour with continuous mixing. The resulting two phases (upper layer—soybean methyl esters, methanol, impurities; bottom layer-glycerol, residual catalyst, impurities) were separated by decantation, using a 1000 ml separatory funnel. Analysis of the methyl ester phase disclosed the composition by weight in Table 3a.

TABLE 3a

Soy Oil Methyl Ester

	Fatty Acid Methyl Ester	% by Weight

	Methyl Palmitate (C 16:0) ¹	10.9
	Methyl Stearate (C18:0)	4.1
	Methyl Oleate (C18:1)	25.9
	Methyl Linoleate (C 18:2)	53.0
	Methyl Linolenate (C 18:3)	6.1
	Others	traces
	Total Saturates	15.0
	C.P. (° C.)	3

For purpose of comparison, compositions of other vegetable oils are listed in table 3b, while compositions of the fats of some land and marine animals are listed in table 3c.

TABLE 3b*

Fatty Acid Composition of Some Vegetable Oils (%)

Oil	C10:0	C12:0	C14:0	C16:0	C18:0	C18:1	C18:2	C18:3

Cocoa butter				26	3.5	37	2.5
Coconut	7	48	17	8	3	6	2
Corn				11	3	27	57
Cottonseed			0.8	25	2	18	53	0.1
Olive			1	15	2.6	67	13	1
Palm			1	46	5	39	9	0.4
Palm kernel	3.6	50	16	8	2	15	1
Peanut				10	3	52	29
Rapeseed				3	1	25	17	8.5
Safflower				6	2	14	74	0.4
Soybean				11	3.5	22	54	8
Sunflower				7	4	17	71	0.3

TABLE 3c*

Fatty Acid Composition of Some Vegetable Oils (%)

	C4:0-
Oil	12:0	C14:0	C16:0	C18:0	C18:1	C18:2	C18:3	C20:5	C22:6

Beef tallow		3	26	22	42	2	0.2
Butter	12	10.8	26	10.3	28	2	1
Chicken		0.9	22	10	41	20	2
Lard		1.3	24	15.5	46	9	0.3
Mackerel		6	16	3	15	2	1	5	9

*Source: Bailey Industrial Oil and Fat Products, 5^thedition, 1996, Vol. 1, Edible Oil and Fat Products: General Applications, Y. H. Hui, editor Wiley Interscience, John Wiley and Sons, Inc.

Biodiesel derived from SME has proven to be an extender, additive, or replacement for petroleum-based diesel fuel and heating oil. Studies are ongoing for using biodiesel as an aviation turbine fuel extender. A challenge posed by biodiesel is its poor cold flow properties. The total content of saturates is about 14-15% (wt/wt) and causes the C.P. to be about 0° C. and pour point to be about −2° C. to −4° C. This limits the use of SME at low temperatures. Various efforts have been made to reduce or depress the C.P. of SME, e.g., 1) removal of saturated components, 2) use of cold flow additives, 3) use of branched chain alcohol esters, and 4) combinations thereof.
The popular method for removal of saturate components is winterizing or cold filtering. Various studies have been conducted; however, these methods have very low yields for any significant reduction in the C.P. Cold flow additives have been successful in lowering the P.P. (Pour Point), but have little or no effect on the C.P.
These teachings disclose a C.P. reduction ranging from about −2° C. to about −57° C. by a controlled removal of the saturated, and in some cases, mono-unsaturated fractions by clathration and subsequent separation. The remaining polyunsaturated fatty acid fractions yields range from 98%-41% of the starting material, i.e., SME. The process parameters of greater significance are: 1) urea/FAME/Alcohol (weight/weight/weight ratio), and 2) the temperature to which the methyl ester clathrate mixture is cooled. The rate of cooling appears to play a lesser role in the formation of urea clathrates and therefore separation of saturated from unsaturated fatty acid methyl ester.
Referring to FIG. 2 b, starting material composed of SME, urea, and solvent in the form of alcohol (methanol or ethanol) is mixed in reactor 100 to start the fractionation process. Although the starting material shown in FIG. 2 b is SME, resulting from the transesterification process whereby glycerol is decanted from the fatty acids, the starting material for the process shown in FIG. 2 b can contain glycerol. The mixture in reactor 100 is heated to 60-65° C. to achieve a homogenous mixture to facilitate formation of clathrates.
Subsequent to heating, the mixture in reactor 100 is cooled to precipitate the clathrates. The mixture is cooled to a final temperature of between 20-25° C. While the rate of cooling does not have an important effect in the final composition of the mixture, the final temperature is a crucial parameter in the process affecting yield and the amount by which saturated components are removed from the mixture. For example, cooling down to 20-25° C. has provided acceptable yields while removing high amounts of saturated compounds. Constant stirring is important throughout the process. The cooling will result in a fractional crystallization of the mixture, giving rise to the formation of two phases: 1) solid phase or precipitate having urea complexes (mainly clathrates of saturated fatty acids and urea); and 2) liquid phase or filtrate having methanol (mainly unsaturated fatty acids and urea). This fractionation process can be repeated in several steps, generally referred to as step fractionation, on the same sample to obtain the desired composition and properties of the final product.
The liquid-solid mixture is transferred to liquid-solid separation station 102 where centrifugation, filtration, or other techniques may be employed to separate liquids from solid clathrates. Extraction and purification of the mixture having mainly unsaturated fatty acids and urea is accomplished by centrifugal separation, vacuum filtration, or by using conical decantation tank to precipitate the solids. The liquid that is separated from the solid clathrates is then transferred to solvent recovery station 104 to remove the solvent. Solvent recovery station 104 is a closed vessel in which the liquid is heated to evaporate and recover the solvent, e.g., methanol 105. Solvent recovery can also be accomplished by applying vacuum to the closed vessel. In one embodiment, an evaporator equipped with an internal detector can be used which stops the heating process whenever the evaporator detects that no more solvent is being evaporated. In another embodiment a rotary evaporator can be used having a water-bath that is at about 60° C., having a vacuum of between 15-25 mm Hg. The recovered methanol 105 is then transferred to reactor 100 to supplement the solvent used in the starting material. The solvent recovered liquid extract is then washed by acidified water in mixer 106 (60° C., pH 3-4) to dissolve the remaining urea (around 100 ml water for each 170 g of urea), before going through liquid-liquid separation station 108 to extract low C.P. SME 124 as well as urea brine 116. Optionally, hexane or another suitable organic solvent can be added to improve the extraction of the remaining unsaturated methyl esters. The water/solvent phases are separated either by a liquid-liquid centrifugal extractor or by gravity separation (decantation) of phases.
Raffinate solids 110 extracted from liquid-solid separation station 102 are mixed with water in mixer 112 and transferred to liquid-liquid separation station 114 to extract urea brine 116 and high C.P. SME 120. The raffinate solids 110 are washed with warm water to dissolve the urea inclusion compounds (UIC). The upper layer containing the methyl esters is decanted or siphoned in liquid-liquid separation station 114. Urea brine 116 coming from liquid-liquid separation stations 108 and 114 is combined and dried in dryer 122 to produce urea 118 that can be re-used in reactor 100. If this results in a hardened form of urea, it is recommended to grind it before recycling it into the process.
Depending upon the desired C.P. reduction, a particular proportion of urea/FAME/Alcohol as starting material is chosen. Affecting the C.P. reduction is also the terminal temperature to which the mixture is cooled in reactor 100. In one embodiment of the current teachings, the mixture is allowed to cool to room temperature. Additionally, the fatty acid starting materials in the transesterification process affect the cloud point. Various combinations of these parameters are possible for the same C.P. reduction. The urea/FAME ratio may range from 0.0:1 to 1:1 wt/wt. The alcohol/FAME ratio may range from 3:1 to 10:1 wt/wt.
Exemplary methods in accordance with these teachings add an alcohol, such as methanol, as a urea solvent and urea for fractionation or clathration. By weight, the ratio of urea to FAME may be in the range from 0.1:1 to 1:1. It is also envisioned that a ratio greater than 1 part urea to 1 part FAME can be used if a very low CP is desired. Urea forms solid phase clathrates with the saturated fatty acid esters.
Sufficient alcohol should be added to dissolve all urea that is added. A sufficient amount of alcohol results in a ratio of alcohol to the methyl ester which ranges from 3:1 to 10:1 wt/wt. Excess alcohol decreases the tendency to produce urea clathrates, thus, decreases the efficiency of the process. Alcohol present after clathrate formation is often separated from the predominantly unsaturated ester by methods utilizing the relative vapor pressures of the two components, for example, distillation or flash evaporation. Economic considerations encourage limiting alcohol to an amount necessary to dissolve the added urea.
Methanol is preferred for esterification. Use of methanol as the solvent for urea in preference to C2-C4 alcohols eliminates the need to store and handle additional reagents for separation of fatty acid methyl esters. After formation of the FAME and glycerin, a convenient manufacturing sequence separates the glycerin phase from the fatty acid ester phase, followed by addition of urea and alcohol to the FAME. The urea and alcohol may be added separately or as a solution of urea dissolved in alcohol. An option afforded by the use of methanol as urea solvent is the convenient continuation of the process by conducting the subsequent clathration step in the same vessel used for the ester formation. By continuing the process in the same vessel with methanol as the solvent, capital investment is reduced by eliminating additional process steps to first remove residual methanol prior to addition of C2-C4 alcohols.
In one embodiment, excess methanol may be provided in the esterification step such that the addition of solvent during the clathration stage can be reduced or eliminated. In another embodiment it is possible to proceed directly from esterification to clathration without removing glycerin. In this embodiment, glycerin is removed as a final stage, as are clathrates.
Dissolution of urea in methyl ester is accomplished by stirring alcohol in the solution at temperatures in the range of 50-75° C. The rate of heating of the mixture has not been observed to have a significant effect on the yield of the product or the C.P. achieved.
It has been observed that the cooling rate has little influence on the C.P. Yields are impacted more significantly by the terminal temperature to which a mixture is cooled. Cooling the mixture of saturated fatty acid esters urea clathrates, unsaturated fatty acid methyl esters, excess/unreacted methyl alcohol, excess/unreacted urea, and optionally, glycerin, to temperatures of 20 to 25° C. provides economically acceptable yields resulting in high clathrate formation of saturated esters compounds and thereby in high removal of saturates without the need for refrigeration.
The solid phase including clathrates of the saturated methyl esters may be separated from the liquid phase comprising unsaturated-methyl-esters, methanol, dissolved urea, and optionally, glycerin by convenient solid-liquid separation means such as filtration or centrifuge, as indicated by liquid-solid separation station 102.
If present, glycerin may be removed from the liquid phase. Alcohol present in the liquid phase that is rich in unsaturated fatty acid esters may be recovered by evaporation at a temperature between 30-50° C. (e.g., in a closed vessel under vacuum, as indicated by solvent recovery station 104). The remaining filtrate is then washed with warm acidic water (60-70° C., pH 3-4) to remove urea and alcohol, as indicated by liquid-liquid separation station 108. The water wash may be carried out in steps, washing the filtrate with warm, acidified water in each step, or in a continuous manner. Suitable purity of filtrate may be achieved with single or multiple step washes with water volumes equal to the filtrate volume. Continuous washing is successful with 3-4 water volumes.
The saturate rich fraction, indicated by high temperature SME 120 in FIG. 2 b, may be obtained from the raffinate by dissolving and washing with warm acidified water (60-70° C., pH 3-4) in the liquid-liquid separation station 114. The warmed saturate rich fraction phase separates from the aqueous phase. The saturate rich fraction has utility such as a hydrocarbon source in chemical manufacturing or additives to heating oil and other heavy oils or fuels where C.P. is not a critical property. Urea can be recovered for re-use by evaporation of the wash water or by thermal dissociation, as indicated by dryer station 122.
The exemplary technique is illustrated by the following examples. A summary of these examples is found in table 4. In Table 4 FAME constituents are listed for each example. Additionally, resulting C.P., cooling rate, % by weight of starting SME and the proportions of SME to urea to ethanol is listed for each example.

Methyl Palmitate (C16:0)	9.2	6.3	1.6	2.3	2.1
Methyl Stearate (C18:0)	3.8	1.4	0	0	0
Methyl Oleate (C 18:1)	23.5	24.6	21.9	22.5	24.0
Methyl Linoleate (C18:2)	55.3	59.6	69.5	68.5	66.0
Methyl Linoleniate (C18:3)	7.6	8.1	7.0	6.8	7.5
Others	0.7	0.02	0.03	0.02	0.01
Total Saturates	12.9	7.7	1.6	2.3	2.1
Cooling rate (° C./min)		1.2	1.2	1.3	10.7
Cooled downed temperature (° C.)		20	20	30	20
% by Wt of starting SME		78.4	66.4	75.9	64.9
SME/Urea/EtOH (g/g/mL)		24.1/	24.1/	24.1/	24.1/
		10.1/	18.0/	16.0/	16.0/
		160	160	160	160
C.P. (° C.)	0	−10	−26	−16	−23

Example 1

Soy methyl ester prepared as described is analyzed for composition. The starting soy methyl ester had the composition and properties according to Table 5:

	TABLE 5

		Percentage by Weight
	Fatty Acid Methyl Ester	Composition

	Methyl Palmitate (C 16:0)	9.2
	Methyl Stearate (C18:0)	3.8
	Methyl Oleate (C18:1)	23.5
	Methyl Linoleate (C18:2)	55.3
	Methyl Linolenate (C 18:3)	7.6
	Others	0.7
	Total Saturates	12.9
	C.P. (° C.)	0

24.1 g of soy methyl ester and 10.1 g of urea were added to 160 mL of ethanol and the mixture was heated to 67° C., with constant stirring. A homogenous mixture was obtained with all the urea dissolving at this temperature. The mixture was then cooled at a rate of 1.2° C./min to a final temperature of 20° C. The urea inclusion compounds (clathrates) formed were separated by filtration. The filtrate was then heated to 30° C. and 70% of the starting volume of ethanol was recovered via evaporation under vacuum. The remaining filtrate was twice washed with equal volumes of water (60° C., pH 3). 18.8 g of fractionated soy methyl ester (78.4% by wt of the starting soy methyl ester) was recovered with the composition and properties according to Table 6. Recovered ethanol is available for re-use in the process.

	TABLE 6

		Percentage by Weight
	Fatty Acid Methyl Ester	Composition

	Methyl Palmitate (C 16:0)	6.3
	Methyl Stearate (C18:0)	1.4
	Methyl Oleate (C18:1)	24.6
	Methyl Linoleate (C18:2)	59.6
	Methyl Linolenate (C 18:3)	8.1
	Others	0.02
	Total Saturates	7.7
	C.P. (° C.)	−10

Example 2

24.1 g of soy methyl ester having the composition according to Table 5 and 18.0 g of urea were added to 160 mL of ethanol and the mixture was heated to 73° C., with constant stirring. A homogenous mixture was obtained with all the urea dissolving at this temperature. The mixture was then cooled at a rate of 1.2° C./min to a final temperature of 20° C. The urea inclusion compounds formed were then separated by filtration. The filtrate was then heated to 30° C. and 52% of the starting volume of ethanol was recovered via evaporation under vacuum. The filtrate was twice washed with equal volumes of water (60° C., pH 3). 16.0 g of fractionated soy methyl ester (66.4% by wt of the starting soy methyl ester) was recovered with the composition and properties according to Table 7.

	TABLE 7

		Percentage by Weight
	Fatty Acid Methyl Ester	Composition

	Methyl Palmitate (C16:0)	1.6
	Methyl Stearate (C18:0)	0.0
	Methyl Oleate (C18:1)	21.9
	Methyl Linoleate (C 18:2)	69.5
	Methyl Linolenate (C 18:3)	7.0
	Others	0.03
	Total Saturates	1.6
	C.P. (° C.)	−26

Example 3

24.1 g of soy methyl ester having the composition according to Table 5 and 16.0 g of urea were added to 160 mL of ethanol and the mixture was heated to 72° C., with constant stirring. A homogenous mixture was obtained with all the urea dissolving at this temperature. The mixture was then cooled at a rate of 1.3° C./min to a final temperature of 30° C. The urea inclusions compounds formed were then separated by filtration. The filtrate was then heated to 30° C. and 63% of the starting volume of ethanol was recovered via evaporation under vacuum. The filtrate was twice washed with equal volumes of water (60° C., pH 3). 18.3 g of fractionated soy methyl ester (75.9% by wt of the starting soy methyl ester) was recovered with the composition and properties according to Table 8.

	TABLE 8

		Percentage by Weight
	Fatty Acid Methyl Ester	Composition

	Methyl Palmitate (C 16:0)	2.3
	Methyl Stearate (C18:0)	0.0
	Methyl Oleate (C18:1)	22.5
	Methyl Linoleate (C18:2)	68.5
	Methyl Linolenate (C 18:3)	6.8
	Others	0.02
	Total Saturates	2.3
	C.P. (° C.)	−16

Example 4

24.1 g of soy methyl ester having the composition according to Table 5 and 16.0 g of urea were added to 160 mL of ethanol and the mixture was heated to 72° C., with constant stirring. A homogenous mixture was obtained with all the urea dissolving at this temperature. The mixture was the cooled at a rate of 10.7° C./min to a final temperature of 20° C. The urea inclusions compounds formed were then separated by filtration. The filtrate was then heated to 30° C. and 63% of the starting volume of ethanol was recovered via evaporation under vacuum. The filtrate was twice washed with equal volumes of water (60° C., pH 3). 15.6 g of fractionated soy methyl ester (64.9% by wt of the starting soy methyl ester) was recovered with the composition and properties in Table 9.

	TABLE 9

		Percentage by Weight
	Fatty Acid Methyl Ester	Composition

	Methyl Palmitate (C 16:0)	2.1
	Methyl Stearate (C18:0)	0.0
	Methyl Oleate (C18:1)	24.0
	Methyl Linoleate (C 18:2)	66.0
	Methyl Linolenate (C 18:3)	7.5
	Others	0.01
	Total Saturates	2.1
	C.P. (° C.)	−23

Examples 5-7

Fuel for turbine engines is specified by ASTM standard D-1655. Plant sourced oils have limited penetration in to the market for turbine fuel.
A commercially sourced soybean oil derived fatty acid methyl ester, the properties of which are described in Table 5, was fractionated as described herein. The “as obtained” fraction analysis and the fraction analysis after processing appears in Table 11. The fractionated soy methyl ester of Examples 5-7 was then blended with the Commercial Jet A fuel to yield the properties which are listed in Table 10.

TABLE 10

Turbine Fuel

		9 Parts Jet A:	7 Parts Jet A:	9 Parts Jet A:
Property-		1 Part	3 Parts	1 Part
Measurement	ASTM D	Fractionated SME	Fractionated SME	Fractionated SME
Units	1655	Example 5	Example 6	Example 7

Density-kg/m³	775-840	817.8	831.4	817.8
Viscosity cSt g-	maximum 8.0	5.5	—	—
20° C.
Freeze Point-	maximum −40° C.	−42° C.	−41° C.	−40° C.
1 ° C.
Net Heat of	minimum 42.8	42.7	41.4	42.6
Combustion-
MJ/kg
Acid Value-	maximum 0.01	0.016	0.028	0.016
mgKOG/g

TABLE 11

Com-	Fractionated	Fractionated	Fractionated
mercial	SME	SME	SME
SME	Example 5	Example 6	Example 7

Component	Percent by Weight

methyl palmitate	9.2	3.5	1.3	6.5
methyl stearate	3.8	0.2	0.1	0.5
methyl oleate	23.5	29.0	28.2	28.7
methyl linoleate	55.3	58.1	60.6	56.0
methyl linolenate	7.6	9.2	9.8	8.3
unknown	0.7	0	0	0

The fractionated soy methyl ester was blended with Jet A fuel in the ratios indicated in Table 10 which yielded the properties that are indicated in Table 10. The blended fuel has demonstrated that the requirements of ASTM D-1655 are attainable with blends including soy methyl ester.
Combustion studies of soy methyl ester blends with commercial Jet A show non-critical deviation from the combustion of commercial Jet A fuel. An Allison stationary 250 turbine having a relatively low compression ratio of 6.2:1 was used for the combustion study. FIG. 3 shows the fuel flow rate over a power range from 40 to 70 RPM % for Jet A fuel, and soy methyl ester blends of 10%, 20% and 30% with Jet A fuel.
Controlled emissions for Jet A and soy methyl ester blends are shown in FIG. 4 for carbon monoxide, FIG. 5 for nitrogen dioxide, and FIG. 6 for nitrogen monoxide.

Example 8

24.0 g of soy methyl esters and 16.8 g of urea were added to 120 mL of methanol and the mixture was heated to 55° C., with constant stirring. The starting SME was prepared according to the example which followed the discussion of transesterification process and which was titled “Transesterification of soy oil to produce un-winterized SME example.” A homogenous mixture was obtained with all the urea dissolving at this temperature. The mixture was then cooled in a water bath to 25° C. The urea clathrates were then separated by filtration. Methanol was recovered from the filtrate by flash evaporation. The filtrate was washed two times with equal volumes of water (60° C., pH of 3). 12.4 g of fractionated soy methyl ester (51.7 by wt of the starting soy methyl ester) was recovered with the composition and properties according to Table 12.

TABLE 12

Fractionated Soy Methyl Ester

		Percentage by Weight
	Fatty Acid Methyl Ester	Composition

	Methyl Palmitate (C16:0)	2.3
	Methyl Stearate (C18:0)	0
	Methyl Oleate (C18:1)	24.4
	Methyl Linoleate (C18:2)	66.0
	Methyl Linolenate (C18:3)	7.3
	Others (>C20)	traces
	Total Saturates	2.3
	C.P. (° C.)	−23

Example 9

24.0 grams of soy methyl esters, prepared according to transesterification of soy oil to produce un-winterized SME example, and 19.2 grams of urea were added to 120 ml of methanol. The mixture was heated to 55° C., with constant stirring. After all components were dissolved, the mixture was cooled down to 25° C. in a water bath; the urea clathrates formed were separated by filtration. The methanol from the filtrate was removed by flash evaporation. The filtrate was then washed twice with equal volume of water (60° C., pH of 3). 10.7 g of fractionated SME (yield=44.6%) was recovered with the composition and properties according to Table 13.

	TABLE 13

		Percentage by Weight
	Fatty Acid Methyl Ester	Composition

	Methyl palmitate (C16:0)	1.7%
	Methyl Stearate (C 18:0)	0%
	Methyl Oleate (C18:1)	24.2%
	Methyl Linoleate (C 18:2)	66.1%
	Methyl Linolenate (C18:3)	8.0%
	Others (>C20)	Traces
	Total saturated fatty acids	1.7%
	C.P. (° C.)	−34

Example 10

24.0 g of soy methyl ester, prepared according to transesterification of soy oil to produce un-winterized SME example, and 24.0 g of urea were added to 120 mL of methanol. The mixture was heated to 55° C., with constant stirring. The homogenous mixture obtained was then cooled in a water bath to 25 to 20° C. The urea clathrates were separated by filtration. Methanol was removed from the filtrate by flash evaporation. The filtrate was washed two times with equal volumes of water (60° C., pH of 3). 10.3 g of fractionated soy methyl ester (42.9% by wt of the starting soy methyl ester) was recovered with the composition and properties according to Table 14.

	TABLE 14

		Percentage by Weight
	Fatty Acid Methyl Ester	Composition

	Methyl Palmitate (C 16:0)	0
	Methyl Stearate (C18:0)	0
	Methyl Oleate (C18:1)	19.2
	Methyl Linoleate (C 18:2)	72.3
	Methyl Linolenate (C 18:3)	8.5
	Others (>C20)	traces
	Total Saturates	0
	C.P. (° C.)	−57

Referring to FIG. 7, a bar graph as shown that illustrates reduction in cloud point achieved by a process in accordance with these teachings as a function of the proportion of SME, urea and methanol starting materials. FIG. 7 represents experiments 8-10 as well as other experiments. Data points corresponding to experiments 8-10 are marked accordingly in FIG. 7. Data points corresponding to the other experiments are marked as 11-15, and data corresponding to these experiments are presented in Table 15.

TABLE 15

Data point	11	12	13	14	15

SME: Urea (120 ml of methanol)	1:0	1:0.2	1:0.3	1:0.4	1:0.5
Methyl Palmitate (C16:0)	10.9	9.9	7.0	5.8	4.3
Methyl Stearate (C18:0)	4.1	4.2	2.0	1.4	0.0
Methyl Oleate (C 18:1)	25.9	25.5	26.8	25.5	27.4
Methyl Linoleate (C18:2)	53.0	54.5	57.6	60.5	60.5
Methyl Linoleniate (C18:3)	6.1	5.9	6.6	6.8	7.8
Total Saturates	15.0	14.1	9.0	7.2	4.3
C.P. (° C.)	5	−1	−7	−8	−13

Each bar in FIG. 7 represents an individual process to achieve cloud point reduction. The height of an individual bar represents the yield at the completion of the process, with higher yields shown on the left hand side of the graph. The relative amounts of starting materials are printed below each bar. As shown, the relative proportion of SME to methanol is the same for all runs, 1 to 5. Moving from left to right on the graph of FIG. 7, however, the amount of urea in the starting material incrementally increases from zero (0) parts (bar on far left) to one (1) part (bar on far right). Finally, the relative proportion of each individual fatty acid, e.g., C16:0, C18:0, etc., is indicated by the different cross-hatched segments of the individual bars. For example, the bar on the far left hand side has about 2.1 g C16:0, 1.2 g C18:0, 5.8 g C:18:1, 13.1 g C:18:2 and 1.8 g C:18:3. Resulting cloud point is plotted on the y-axis as a solid line connected by the data points as shown.
FIG. 7 shows that lower cloud points are achieved as the relative proportion of urea increases. A C.P. data point is shown in the center of each bar, indicating the cloud point associated with the composition of the starting material. For example, the bar on the far left hand side of the graph corresponding to a starting material having a proportion of 1:0:5 of SME, urea and ethanol (or methanol), has a C.P. of 3° C.
A solid line connecting the C.P. data points is shown in FIG. 7. This solid line shows that the corresponding cloud point achieved varies from 3° C. to −57° C. as the proportion of urea to SME is increased from 0 to 1. Specifically, the C.P. decreases from 3° C. to −8.8° C. according to the four consecutive data points on the left hand side of the graph. This drop is associated with a urea increase from 0 to 0.4, in relative proportion, while SME and ethanol (or methanol) proportions are held constant. This decrease of 3° C. to −8.8° C. for the first four data points represents about 20% of the overall decrease in C.P. (decrease of 3° C. to −57° C.). Conversely, the last four data points, corresponding to urea proportions of 0.5 to 1 represent a drop of C.P. from −12° C. to −57° C. This drop represents 75% of the overall decrease in C.P. This data illustrates a significant decrease in C.P. when urea proportion is increased from 0.5 to 1.
Additionally, FIG. 7 shows the relationship between the fatty acid profiles achieved at the end of the process based on the amount of urea used in the starting material. For example, the fatty acid profile of the bar shown on the far left hand side of the graph is given above. As the percentage of saturates (C16:0 and C18:0) in the fatty acid profile decreases, the C.P. decreases accordingly. For example, in the bar on the far left hand side of the graph, associated with a urea to SME ratio of 0, the percentage of saturates (C16:0 and C18:0) is about 14% (about 3.3 g out of the about 24.0 g total fatty acids). The C.P. corresponding to this bar is 3° C. The bar in the center of the graph associated with a urea proportion of 0.5 shows a saturate percentage of about 4%. The C.P. corresponding to this bar is −12° C. The bar on the right hand side of the graph associated with a urea proportion of 0.8 shows a saturate percentage of about 1.9%. The C.P. corresponding to this bar is −34° C. Finally, the bar on the far right hand side of the graph has a saturate percentage of 0% while having a C.P. of −57° C. Therefore, the C.P. decreases significantly as the last of saturates, C16:0, are removed from the fatty acid profile. Specifically, 38% of the overall C.P. decrease occurs as urea proportion is increased from 0.8 to 1.0.
As discussed above, the prior art teachings of Dunn et al., predict a straight line relationship between the amount of saturated components removed and the reduction in cloud point. Dunn et al. predicted that this straight line can be extrapolated to compositions having no saturated components. However, quite surprisingly and remarkably, the inventors of the instant application have found that the reduction in cloud point as the last few percent of saturated components is removed is not linear. In stark contrast to the teachings of Dunn et al., the inventors have found that the cloud point of composition having very low amounts of saturated components is far lower than Dunn et al. predicted. For example, one of skill in the art can readily recognize that the slope of the line extending from left to right in FIG. 7 steepens significantly between the third to the last and last bar, as shown. This dramatic change in slope is unexpected, and directly contradicts the straight line relationship taught by the prior art.
FIG. 7 also shows that C18:0 is removed prior to complete removal of C16:0. This is shown in the bars associated with urea proportions of 0.4 and 0.5. That is, a small amount of C18:0 is found in the fatty acid profile shown in the bar associated with urea proportion of 0.4. However, no C18:0 is found in the bar associated with urea proportion of 0.5. In fact, as urea proportions are increased to 0.7 and 0.8, only a small amount of C16:0 saturates remain in the corresponding fatty acid profiles. The reason C18:0 saturates are removed prior to removal of C16:0 is that the urea inclusion compounds are formed favoring longer straight chain hydrocarbons. Thus, C18:0 is thus preferentially removed, before C16:0.
In addition, it can be observed from FIG. 7 that the amounts of C18:3, polyunsaturated component of the fatty acid profiles, are not significantly affected as the urea proportion is increased from 0 to 1. This is to be contrasted with other unsaturated components, C18:1 and C18:2. Specifically, large portions of the C18:2 polyunsaturated components as well as the C18:1 monounsaturated components are lost as urea proportion is increased from 0 to 1. The loss of unsaturated components is apparently due to the indiscriminate clathration of these components when saturated components are no longer abundantly present in the mixture.
Another observation that can be made from FIG. 7 is that the yield at the lowest C.P., associated with the bar at the far right hand side of the graph, is about 46% of the starting SME, shown in the bar at the far left hand side of the graph. However, the yield does not decrease significantly as the C.P. decreases from −34° C. to −57° C. This can be appreciated from the last two bars on the right hand side of the graph.
Referring to FIG. 8, a graph of % extracted SME vs. extracted species is presented. The graph in FIG. 8 shows the way different constituents of the fatty acid profile change over the range of experiments shown in FIG. 7. All of the constituents start at 100% at the right hand side of the graph. There are 8 data points for each constituent except for C18:0, which only has 4 data points. Each data point corresponds to the percentage of one of the fatty acid constituents in the fatty acid profile of a particular experiment shown in FIG. 7. Different fatty acid constituents are represented with different symbols. For example, C18:0 is represented by solid squares, C16:0 by solid diamonds, C18:1 by solid triangles, C18:2 by hollow diamonds and C18:3 by letter “X”. Vertical bars are included in the graph in order to facilitate reading data points on the graph.
The graph in FIG. 8 demonstrates how constituent of the fatty acid profile reduce as the amount of urea is increased in the starting material. The horizontal axis in FIG. 8 titled “% Ext_SME” represents the percentage of fatty acids extracted at the end of each experiment shown in FIG. 7. The vertical axis in FIG. 8 represents the percentage of the remaining fatty acid constituents in each experiment as compared to the amount of those constituents in the starting material (indicated by the bar on the far left hand side of FIG. 7). The horizontal axis is a representation of the overall yield. For example, a yield of 70%, shown approximately at the center of the horizontal axis in FIG. 8, corresponds to the fifth bar from the left hand side in FIG. 7, having urea proportion of 0.5. The total amount of fatty acids extracted is about 16.5 g. This amount represents about 70% of the starting fatty acids shown in the far left hand bar in FIG. 7, which totals about 24.0 g. Referring to FIG. 7, of the approximate amount of 16.3 g of extracted fatty acids, associated with the bar representing urea proportion of 0.5, about 0.6 g is C16:0 (about 25% of the 2.4 g of starting C16:0), about 4.4 g is C18:1 (about 76% of the 5.8 g of starting C18:1), about 9.9 g is C18:2 (about 76% of the starting 13.0 g of C18:2), and about 1.4 g is C18:3 (about 82% of the starting 1.7 g of C18:3). These values are shown in FIG. 8. For example, the dotted line going through 70% of % Ext_SMEshows no C18:0 (represented by a solid square), about 25% C16:0 (represented by a solid diamond), about 76% C18:1 (represented by a solid triangle), about 76% C18:2 (represented by a hollow diamond), and about 82% C18:3 (represented by a letter “X”). Regression results showing best fit curves are seen as solid lines and curves in FIG. 8. These solid lines and curves assist in determining % Ext_spiciesat any % Ext_SMEbetween about 44% and 100% of % Ext_SME.
It is envisioned that experimental results using different starting material as indicated in FIG. 7 can be provided to a mathematical analysis package, e.g., SAS, for the purpose of fitting a curve to the experimental results. Such a mathematical analysis package can perform a regression analysis and provide a formula relating C.P. to molar or weight fraction of the constituents of a starting material. Such a formula will advantageously provide an analytical tool for predicting C.P. of a particular mixture by knowing the species of a fatty acid profile that make up the mixture. For example, by knowing the molar or weight fractions of C16:0, C18:0, C18:1, C18:2, and C18:3 of a particular mixture, a corresponding C.P. can be calculated.
In addition to the effect of the amount of urea in the urea/FAME/alcohol mixture on the C.P., the starting material in the transesterification process, i.e., the source of starting fatty acid, also affects the C.P. Referring to FIG. 9 a, a graph of C.P. vs. % saturates is provided. In FIG. 9 a the C.P. depression discussed in the prior art is compared with the C.P. depression according to the current teachings. The C.P. depression according to the current teachings is designated by “Tao soybean.” Of particular interest are C.P. depression of “dunn 97 solvent,” “dunn 96,” and “Gomez.” The linear graph of “dunn 97” corresponds to FIG. 1, titled prior art, which shows a C.P. depression from about 0° C. to about −16° C. Similarly, “dunn 97 solvent” represents Dunn et al. (1997 article) winterization using solvents, and “Gomez” indicate C.P. depression in the range of about 0° C. and 2° C. to about −10° C. and −5° C., respectively.
Further referring to FIG. 9 a, the line shown in FIG. 1 is shown again based on the actual data points, designated as “solvent dunn 96.” The line is extrapolated so that it meets the vertical axis at about, −25° C. Dunn used SME in the experiment for which the results are shown in FIG. 9 a.
The amount of saturated fatty acids, i.e., C16:0 and C18:0, that remain at the end of the clathration process controls the cloud point. This concept is shown in FIG. 9 b which shows experimental data from different starting material, examples of which are provided in Table 3b. The experimental data corresponding to FIG. 9 b is presented in Table 16. Each data point corresponding to polyunsaturated, monounsaturated, and saturated fatty acids indicates percent weight of the corresponding constituents as compared to the whole. For example, in experiment number 1, 6%, by weight, are polyunsaturated fatty acids, 25.5% are monounsaturated fatty acids, and 11.5% are saturated fatty acids.

TABLE 16

Exp. No.	1	2	3	4	5	6	7	8	9	10

C.P.	−5	−1	−6	−7	−8	−13	−16	−18	−22	−28
PUFA*	63	60.4	64.3	64.2	67.3	68.4	18.7	69.4	33.7	36.7
MUFA**	25.5	25.5	24.1	26.8	25.5	27.4	78.3	24.9	63.5	61.5
SFA***	11.5	14.1	11.6	9.0	7.2	4.3	3.1	5.7	2.8	1.8

Exp. No.	11	12	13	14	15	16	17	18	19

C.P.	−28	−34	−37	−37	−38	−39	−49	−52	−57
PUFA*	73.3	74.1	41.3	48.4	37.1	39.3	90.9	90.8	80.8
MUFA**	24.4	24.1	58.2	51.6	61.6	59.8	9.1	9.2	19.2
SFA***	2.3	1.7	0.5	0	1.3	1	0	0	0

*PUFA indicates polyunsaturated fatty acids, e.g., C18:2 and C18:3
**MUFA indicates monounsaturated fatty acids, e.g., C18:1
***SFA indicates saturated fatty acids, e.g., 16:0 and C18:0.

In experiments 10 and 15, for example, the amounts of PUFA and MUFA are approximately the same, i.e., 36.7% vs. 37.1, and 61.5% vs. 61.6%. However, the SFA are different by 0.5%, i.e., 1.8% vs. 1.3%. The difference in percent SFA results in a drop in C.P. of 10° C. In contrast to these experiments, experiments 1 and 2 reveal a much smaller lowering of C.P. in the presence of a much larger drop in SFA. For example, a difference of 2.6% in SFA, i.e., 14.1% vs. 11.5%, results in a 5° C. drop in C.P. This observation further strengthens the point that very small amounts of SFA remaining in the end composition could produce ultra low C.P., lower than −30° C. Moreover, as the percent SFA remaining in the end composition reaches about 1-2%, further removing small amounts of SFA, e.g., 0.5%, results in larger drops in C.P., e.g., 10° C. This shows that the relationship between the amount of saturated fatty acids and CP becomes nonlinear after most of the saturated fatty acids are removed. Conversely, where large amounts of SFA remain in the end composition, e.g., about 11-14%, further removing large amounts of SFA, e.g., 2.6%, results in relatively smaller drops in C.P., e.g., 5° C.
In another embodiment, the product from the fractionation process, according to the current teachings, can be used to treat petroleum based fuel to improve cold flow properties of the petroleum based diesel fuel. Two types of diesel fuel are commonly used. Diesel number 2, which contains a higher amount of paraffin, has a cloud point of about −28° C. Diesel number 1 has a cloud point of about −40° C. Traditionally, diesel number 1 is blended with diesel number 2 for cold-weather operation. Adding fractionated esters from the current process, which is rich in polyunsaturated fatty acids, to diesel number 2 will improve C.P. of the blend. This is advantageous since blending fuel with diesel number 1 in large quantities is not desirable for diesel engine operation due to lubricity difference between diesel number 1 and number 2. However, addition of polyunsaturated-rich fractionated esters to diesel number 2 will not have the same lubricity disadvantages. It is well known that addition of polyunsaturated-rich fractionated esters will actually improve lubricity.
Referring to FIG. 10, a graph of yield vs. C.P. is presented. Yield is affected by the processes of the current teachings. In order to lower C.P., relative concentration of saturated molecules are diminished which negatively affects yield. FIG. 10 shows the resulting SME yield as a function of the desired C.P. For example, at −57° C. the yield is at about 46% the starting SME. A substantial portion of the remaining 54% of the starting SME is removed as high temperature SME (see reference numeral 120 in FIG. 2 b). As mentioned above, there are various utilities for high temperature SME such as a hydrocarbon source in chemical manufacturing or additives to heating oil and other heavy oils where C.P. is not a critical property. Therefore, the high temperature SME cannot be viewed as waste.
Referring to FIG. 11 impact of the amount of urea on C.P. used in processing different starting material is shown. This graph shows that an effective starting material from the group of starting material listed in FIG. 11 is SME. Independent of the chosen starting material, the amount of urea generally causes depression of the C.P. with SME showing the largest amount of C.P. depression.
Applicants' method as disclosed enables the fractionation of fatty acid methyl esters based on saturated vs. unsaturated molecules from mixtures of saturated and unsaturated fatty acid methyl esters. Separated fractions may be achieved with the desired unsaturated fraction comprising from 15 to 0% by weight saturated fatty acid methyl esters, from 10 to 45% by weight monounsaturated fatty acid methyl esters, and from 50 to 85% polyunsaturated fatty acid methyl esters.
The C.P. for mixtures of saturated and unsaturated fatty acid methyl esters may be reduced by preferably 10° C., more preferably 25° C. to 60° C. below the C.P. of the unfractionated fatty acid methyl ester mixture.
It is envisioned that for many cold weather uses, biodiesel in accordance with these teachings should have a cloud point that is less than about −30° C. Other cold weather applications may require the biodiesel to have a cloud point less than about −40° C., or less than about −45° C., or even less than about −50° C. These teachings provide a composition having a cloud point of as low as −57° C. (see Example 10) and a method of making the same.
As one of skill in the art can appreciate from the examples above, these surprisingly low cloud points are achieved when almost all of the saturated fatty acid components, i.e., more than about 97%, are removed. In accordance with these teachings, the amount of saturated fatty acid components in the final product should be less than about 3%, more preferably less than about 2%. To achieve cloud points of less than −40° C. or less than about −50° C., the amount of saturated fatty acid components should be less than about 3%, depending on the feedstock.
The experiments above also empirically show that surprisingly low cloud points are achieved in a composition with a small relative amount of C18:3 components. With reference to FIG. 7, the last three bars on the right hand side represent compositions having cloud points of −23° C., −34° C. and −57° C., respectively. The amounts of C18:3 in these compositions range from about 7.3% to about 8.5%. It is thus envisioned that compositions with low cloud points in accordance with these teachings may have C18:3 components of less than about 10%. Indeed, cloud points approaching −40° C. were achieved with pure sunflower oil (see FIG. 10), which has less than 0.5% C18:3 components, but has 71% C18:2 components.
Additionally, empirical data show that very low C.P.'s may be achieved without a significant corresponding sacrifice in yields. For example, to achieve a cloud point of −23° C., yield was about 52% (resulting SME compared to starting SME), whereas for a cloud point of −57° C., yield was about 43%. Surprisingly, yield was substantially unaffected when lowering cloud point from −34° C. to −57° C., as the yield was lowered only by about 2%.
While exemplary embodiments incorporating the principles of the present invention have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

Experiment Number

1. A composition, comprising:

methyl esters derived from vegetable oils, the methyl esters comprising less than about 3% by weight of saturated fatty acid methyl esters; and

the composition having a cloud point of less than about −30° C.

2. The composition of claim 1, wherein the methyl esters consist essentially of methyl oleate, methyl linoleate and methyl linolenate.

3. The composition of claim 2, wherein the methyl linolenate comprises less than about 10% by weight of the methyl esters.

4. The composition of claim 3, wherein the methyl stearate comprises less than about 0.1% by weight of the methyl esters.

5. The composition of claim 3, wherein the methyl linoleate comprises at least about 50% by weight of the methyl esters.

6. The composition of claim 4, wherein the methyl linoleate comprises at least about 60% by weight of the methyl esters.

7. The composition of claim 1, wherein the cloud point is less than about −35° C.

8. The composition of claim 1, wherein the cloud point is less than about −40° C.

9. The composition of claim 1, wherein the cloud point is less than about −45° C.

10. The composition of claim 1, wherein the cloud point is less than about −50° C.

11. The composition of claim 1, wherein the cloud point is less than about −55° C.

12. The composition of claim 1, wherein the methyl esters comprise less than about 2% saturated methyl esters.

13. The composition of claim 1, wherein the methyl esters comprise less than about 1.5% saturated methyl esters.

14. The composition of claim 1, wherein the methyl esters comprise less than about 0.5% saturated methyl esters.

15. The composition of claim 1, wherein the vegetable oils from which the methyl esters are derived comprise soy oil.

16. The composition of claim 1, further comprising a petroleum based component.

17. The composition of claim 16, wherein the petroleum based component comprises fossil fuel derived diesel fuel.

18. The composition of claim 1, comprising less than about 1% methyl stearate.

19. The composition of claim 1, comprising less than about 0.5% methyl stearate.

20. The composition of claim 1, comprising less than about 0.1% methyl stearate.

21. The composition of claim 1, further comprising animal fat derived methyl esters.

22. A method of lowering the cloud point of methyl esters derived from vegetable oil, comprising:

mixing vegetable derived methyl esters, urea and alcohol with sufficient heat to form a homogenous mixture;

cooling the homogeneous mixture to a temperature where a solid phase and a liquid phase are formed, the solid phase being enriched in saturated fatty acid methyl esters and the liquid phase being enriched in unsaturated fatty acid methyl esters;

separating the solid phase from the liquid phase; and

removing alcohol and unused urea from the liquid phase to form a liquid composition having a cloud point of less than about −30° C. and less than about 3% by weight saturated fatty acid methyl esters.

23. The method of claim 22, wherein the alcohol comprises methanol.

24. The method of claim 23, further comprising, before the step of forming the homogeneous mixture, mixing vegetable derived oil, sodium hydroxide and methanol to form the vegetable derived methyl esters.

25. The method of claim 24, wherein the homogeneous mixture contains methanol in an amount of about 3 to 10 times by weight of the amount of the fatty acid methyl ester.

26. The method of claim 25, wherein excess methanol is provided in the step of mixing the vegetable derived oil, sodium hydroxide and methanol to form the vegetable derived methyl esters, whereby adding methanol during the step of forming the homogeneous mixture is unnecessary.

27. The method of claim 23, further comprising separating glycerin from the vegetable derived methyl esters before the step of forming the homogeneous mixture.

28. The method of claim 22, wherein the ratio of urea to methyl esters in the homogeneous mixture is from about 0.9:1 to about 1:1.

29. The method of claim 22, wherein the solid phase is separated from the liquid phase by filtration, centrifugation, sedimentation, or decantation of the liquid phase.

30. The method of claim 22, wherein the liquid composition comprises less than about 2 percent by weight of saturated fatty acid methyl esters.

31. The method of claim 22, wherein the liquid composition comprises less than about 1.5 percent by weight of saturated fatty acid methyl esters.

32. The method of claim 22, wherein the removal of the alcohol is by evaporation.

33. The method of claim 22, wherein the removal of the alcohol is by applying vacuum.

34. The method of claim 22, wherein the removal of unused urea is by washing with acidified water, wherein the washed unused urea is separated by a liquid-liquid centrifugal extractor or by a gravity separation.

35. The method of claim 22, wherein the yield of the liquid composition is at least 43% by weight of the vegetable-derived methyl esters used to form the homogeneous mixture.

36. The method claim of 35, wherein cloud point of the liquid composition is less than −34° C.

37. The method claim of 35, wherein cloud point of the liquid composition is less than −40° C.

38. The method claim of 35, wherein cloud point of the liquid composition is less than −50° C.