LOWER ALKYL ESTER RECYCLING SYNTHESIS

Abstract: Process for synthesizing and purifying polyol fatty acids polyesters or other nondigestible fats selected from the group of esterified linked alkoxylated polyols and esterified epoxide extended polyols, in which unreacted lower alkyl ester is recovered from a reaction mixture and recycled for use in the synthesis of the nondigestible fat. The process includes the steps of reacting an excess of lower alkyl ester with polyol to esterify hydroxyl groups thereof and form polyol fatty acid polyester, separating at least a portion of the unreacted lower alkyl ester from the polyol fatty acid polyester, and recycling the separated unreacted lower alkyl ester for further reaction with polyol or partially esterified polyol. The recycled lower alkyl ester is substantially free of lower alkyl ester degradation reaction products, such as carbonyls and free fatty acids.

Description: LOWER ALKYL ESTER RECYCLING SYNTHESIS TECHNICAL FIELD This application cross-references and incorporates by reference U.S. Patent Application 08/797,018, "Lower Alkyl Ester Recycling in Polyol Fatty Acid Polyester Synthesis", filed February 7, 1997, in the name of enneally et al. This invention relates to a process for synthesizing and purifying polyol fatty acids polyesters or other nondigestible fats selected from the group of esterified linked alkoxylated polyols (such as esterified linked alkoxylated glycerins) and esterified epoxide extended polyols, in which unreacted lower alkyl ester is recovered from a reaction mixture and recycled for use in the synthesis of the nondigestible fat. More particularly, this invention relates to such a process wherein good product quality of polyol polyester synthesized with the recycle ester is maintained by minimizing alkyl ester degradation reactions such as oxidation, hydrolysis, pyrolysis, and saponification. BACKGROUND The food industry has recently focused attention on polyol polyesters for use as low- calorie fats in food products. Triglycerides (triacylglycerols) constitute about 90% of the total fat consumed in the average diet. One method by which the caloric value of edible fat can be lowered is to decrease the amount of triglycerides that is consumed, since the usual edible triglyceride fats are almost completely absorbed in the human system (see Lipids, 2, H. J. Deuel, Interscience Publishers, Inc., New York, 1955, page 215). Low calorie fats which can replace triglycerides are described in Mattson, et al., U.S. Patent No. 3,600,186. Mattson, et al. disclose low calorie, fat-containing food compositions in which at least a portion of the triglyceride content is replaced with a polyol fatty acid polyester having at least four fatty acid ester groups, with each fatty acid having from eight to twenty-two carbon atoms. Rizzi and Taylor, U.S. Patent No. 3,963,699, disclose a solvent-free transesterification process in which a mixture of polyol (such as sucrose), a fatty acid lower alkyl ester (such as a fatty acid methyl ester), an alkali metal fatty acid soap (emulsifier), and a basic catalyst is heated to form a homogenous melt. Excess fatty acid lower alkyl ester is added to the melt to form the higher polyol fatty acid polyesters. The polyesters are then separated from the reaction mixture using various separation procedures; distillation or solvent extraction are preferred. Volpenhein, U.S. Patent No. 4,517,360 and U.S. Patent No. 4,518,772, discloses a solvent-free transesterification process in which a mixture of polyol (such as sucrose), fatty acid ester selected from the group consisting of methyl esters, 2-methoxy ethyl esters, and benzyl esters, an alkali metal fatty acid soap, and a basic catalyst is heated to form a homogenous melt, to which is added excess fatty acid ester to form the higher polyol fatty acid polyesters. The polyesters are then separated from the reaction mixture using various separation procedures; distillation, water washing, conventional refining techniques or solvent extraction are preferred. Bossier (III) U.S. Patent No. 4,334, 061, discloses a process in which a mixture of polyol, fatty acid ester, alkali metal fatty acid soap, and basic catalyst is heated to form a homogenous melt, to which is added excess fatty acid ester to form the polyol fatty acid polyesters. The polyesters are then recovered by contacting the crude reaction product with an aqueous washing medium while maintaining the resulting mixture at a pH of from 7 to about 12, in the presence of an emulsion decreasing organic solvent. The alkali metal fatty acid soaps and the color-forming bodies are dissolved in the aqueous phase. The polyol fatty acid polyester is recovered from the organic phase by solvent extraction to remove excess fatty acid lower alkyl esters and steam stripping to remove trace amounts of residual fatty acid lower alkyl esters and solvent. Additionally, the following patent documents provide description related to esterified propoxylated glycerins, esterified linked alkoxylated glycerins, and/or esterified epoxide extended polyols: U.S. Patents 4,861,613 to Pollard; 4,983,329 to Cooper; 5,175,323 to Cooper; 5,273,772 to Cooper; 5,304,665 to Cooper; 5,399,728 to Cooper; 5,512,213 to Cooper; 5,603,978 to White; 5,641,534 to White; EPO Patent Documents 325,010 published July 26, 1989 in the name of White et al.; 667,105 published August 16, 1995 in the name ofZiegert et al.; PCT Publication WO 97/222260; U.S. Patents 5,273,772 to Cooper; 5,362,894 to Handweker; 5,374,446 to Ferenz; 5,427,815 to Ferenz; 5,516,544 to Sekula; EPO Patent Document 571,219 published November 24, 1993 in the name of Masten. Virtually all of the polyol fatty acid polyester synthesis processes require that the polyol fatty acid polyester be separated from a reaction mixture comprising products, by-products, and unreacted ingredients. Additionally, many polyol polyester synthesis processes require the use of excess lower alkyl ester, in particular excess methyl ester, so that a significant amount of unreacted lower alkyl ester is contained in the reaction mixture from which the polyol polyester product is recovered. The polyol fatty acid polyester synthesis would therefore be more economically efficient if the excess methyl esters could be reused in the polyol fatty acid polyester synthesis. However, because significant degradation of the lower alkyl esters can occur in conventional processing steps employed to separate and purify the polyol polyester product or in separation of the unreacted lower alkyl ester from the reaction mixture, reuse of the degraded lower alkyl ester can result in the synthesis of inferior polyol polyester product. Consequently, there remains a need to develop a process which can recycle the excess lower alkyl ester from a polyol fatty acid polyester synthesis without adversely affecting product quality of polyesters synthesized from the recycled ester. SUMMARY OF INVENTION Accordingly, it would be desirable to obviate problems encountered in the prior art and provide improved processes for synthesis of nondigestible and partially digestible fats including esterified linked alkoxylated polyols (such as esterified linked alkoxylated glycerins), esterified epoxide-extended polyols and mixtures thereof. It would also be desirable to minimize the side reactions which degrade lower alkyl esters during such processes to allow the recycle of excess lower alkyl ester without adversely impacting the quality of the nondigestible or partially digestible fat produced therefrom. It would also be desirable to provide a novel process for the production of nondigestible and partially digestible fats including esterified linked alkoxylated polyols, esterified epoxide- extended polyols and mixtures thereof, which process recycles unreacted ingredients and improves the economics of the polyol synthesis. In accordance with one aspect of the present invention, there is provided a novel process for synthesizing a nondigestible or partially digestible fat, such as a polyol fatty acid polyester, which includes esterified linked alkoxylated polyols, esterified epoxide-extended polyols and mixtures thereof. The process comprises the steps of reacting excess lower alkyl ester and polyol, partially esterified polyol or mixtures thereof to esterify hydroxyl groups thereof and form polyol fatty acid polyester comprising partially and/or fully esterified polyol in admixture with unreacted lower alkyl ester; separating at least a portion of the unreacted lower alkyl ester from the polyol fatty acid polyester; and recycling the separated unreacted lower alkyl ester for further reaction with polyol or partially esterified polyol, wherein the recycled lower alkyl ester is substantially free of lower alkyl ester degradation reaction products. Such processes can be batch or continuous processes, and can eliminate the need to dispose of significant amounts of unused excess reactants. The process can comprise the steps of heating a mixture of polyol, excess fatty acid lower alkyl ester, and basic reaction catalyst; reacting a portion of said fatty acid lower alkyl ester with polyol to obtain a product mixture; separating unreacted fatty acid lower alkyl ester from the product mixture; and recycling the separated unreacted fatty acid lower alkyl ester for further reaction, wherein the recycled lower alkyl ester is substantially free of degradation reaction products. In one embodiment, the unreacted fatty acid lower alkyl ester is directly recycled to the reaction mixture comprising polyol after separation to reduce the level of degredation reaction products. Unreacted lower alkyl esters can be recovered from the product mixture of product, byproducts and unreacted ingredients, and recycled for use in the polyol fatty acid polyester synthesis with no adverse impact on the polyol fatty acid polyester reaction or on the quality of the polyester produced. Potential degradation reactions, such as oxidation, hydrolysis, pyrolysis, and saponification, can be minimized so as to recycle directly back to the synthesis reactor the unreacted lower alkyl ester which is substantially free of degradation reaction products. The recycling of unreacted lower alkyl esters according to the invention can improve the economics of the synthesis reaction, since separated unreacted fatty acid lower alkyl esters which contain high levels of degradation product would need to be further processed to remove substantial amounts of the degradation products from the ester recycle, or otherwise would need to be discarded, either of which can be expensive. Additionally, basic compounds which are used to catalyze the polyol fatty acid polyester synthesis can also be used to neutralize fatty acids in the recycled ester, thereby further improving the economical aspects of the synthesis processes employing ester recycle. After the methyl esters are removed, the reaction product (e.g. an esterified propoxylated glycerin) preferably has a peroxide value of less than 100 ppm, a carbonyl value less than 200 pp , free fatty acid less than 0.4%, residual soap less than 2000 ppm and final color (Lovibond red) of less than 4.0. The peroxide value, carbonyl value, free fatty acid level, soap level, and color are determined in the test methods set forth below. The distillate methyl esters from the evaporator can be used in subsequent reactions. These and additional advantages will be more fully apparent in view of the following detailed description. DETAILED DESCRIPTION OF THE INVENTION The present invention encompasses processes for recycling lower alkyl esters in the synthesis of nondigestible fats, such as polyol fatty acid polyesters, which nondigestible fats include esterified linked alkoxylated glycerins, esterified epoxide-extended polyols and mixtures thereof. Polyol fatty acid polyester synthesis methods, including those which utilizes lower alkyl esters, are disclosed generally in U.S. Patents Nos. 3,963,699; 4,517,360; 4,518,772; 4,806,632 and 5,491,226; U.S. Patents 4,861,613 to Pollard; 4,983,329 to Cooper; 5,175,323 to Cooper; 5,273,772 to Cooper; 5,304,665 to Cooper; 5,399,728 to Cooper; 5,512,213 to Cooper; 5,603,978 to White; 5,641,534 to White; EPO Patent Documents 325,010 published July 26, 1989 in the name of White et al.; 667,105 published August 16, 1995 in the name of Ziegert et al.; PCT Publication WO 97/222260; U.S. Patents 5,273,772 to Cooper; 5,362,894 to Handweker; 5,374,446 to Ferenz; 5,427,815 to Ferenz; 5,516,544 to Sekula; EPO Patent Document 571,219 published November 24, 1993 in the name of Masten; all incorporated herein by reference. The present invention encompasses processes which can be either batch processes or continuous processes. As used herein, the term "nondigestible fats" is intended to include fats substitutes that are not digested by animals or humans. Preferably at least 75% of the material is undigested. Such nondigestible fats include polyol polyesters, silicone esters, and related compositions. As used herein, the term "polyol" is intended to include any aliphatic or aromatic compound containing at least two free hydroxyl groups. Suitable polyols can be selected from the following classes: saturated and unsaturated straight and branch chain linear aliphatics that contain more than one hydroxy group; saturated and unsaturated cyclic compounds, including heterocyclic compounds, that contain more than one hydroxy group; and mononuclear or polynuclear aromatics, including heterocyclic aromatics, that contain more than one hydroxy group. Carbohydrates and non-toxic glycols are preferred polyols. Monosaccharides suitable for use herein include, for example, mannose, glucose, galactose, arabinose, xylose, ribose, apiose, rhamnose, psicose, fructose, sorbose, tagatose, ribulose, xylulose, and erythrulose. Oligosaccharides suitable for use herein include, for example, maltose, kojibiose, nigerose, cellobiose, lactose, melibiose, gentiobiose, turanose, rutinose, trehalose, sucrose and raffinose. Polysaccharides suitable for use herein include, for example, amylose, glycogen, cellulose, chitin, inulin, agarose, zylans, mannan and galactans. Although sugar alcohols are not carbohydrates in a strict sense, the naturally occurring sugar alcohols are so closely related to the carbohydrates that they are also preferred for use herein. The sugar alcohols most widely distributed in nature and suitable for use herein are sorbitol, mannitol, and galactitol. Preferred unesterified polyols include alkoxylated polyols. Suitable alkoxylated polyols include alkoxylated glycerol, alkoxylated polyglycerols, alkoxylated sorbitols and sorbitans, alkoxylated polysaccharides, and linked alkoxylated polyols such as linked alkoxylated glycerins. Polyols may be alkoxylated with C3-C6 epoxides, such as propylene oxide, butylene oxide, isobutylene oxide, and pentene oxide, to produce epoxide-extended polyols having an epoxylation index minimum of at least about 2, preferably in the range of from about 2 to about 8, as described in U. S. Patent No. 4,816,613, incorporated herein by reference. Polyols may be also alkoxylated with an epoxide, preferably a C3-C10 1,2-alkylene oxide, in the presence of a ring-opening polymerization catalyst, as described in U. S. Patent Nos. 5,399,729 and 5,512,313, incorporated herein by reference. Suitable alkoxylated polyols are also described in U. S. Patent Nos. 4,983,329; 5,175,323; 5,288,884; 5,298,637; 5,362,894; 5,387,429; 5,446,843; 5,589,217; 5,597,605; 5,603,978 and 5,641,534, all incorporated herein by reference. Suitable alkoxylated polyols include alkoxylated sugar alcohols, alkoxylated monosaccharides, alkoxylated disaccharides, alkoxylated polysaccharides, alkoxylated C2 - C J aliphatic diols, and alkoxylated C3 -C j 2 aliphatic triols. Preferred alkoxylated C3 -C ] 2 aliphatic triols are alkoxylated glycerols, more preferred are propoxylated glycerols, and particularly preferred are propoxylated glycerols having from about 3 to about 21 moles of propylene oxide per mole glycerol. Preferred alkoxylated polysaccharides are alkoxylated polysaccharides containing anhydromonosaccharide units, more preferred are propoxylated polysaccharides containing anhydromonosaccharide units, as described in U. S. Patent No. 5,273,772, incorporated herein by reference. Preferred linked alkoxylated glycerins include those comprising polyether glycol linking segments, as described in U.S. Patent No. 5,374,446, incorporated herein by reference, and those comprising polycarboxylate linking segments, as described in U. S. Patent Nos. 5,427,815 and 5,516,544, incorporated herein by reference; more preferred are those described in U. S. Patent No. 5,516,544. As used herein, the term "polyol fatty acid polyesters " is intended to include fatty acid esters of polyols, in which the hydroxyl groups are esterified with fatty acids. Suitable fatty acid esters can be derived from either saturated or unsaturated fatty acids. Suitable preferred fatty acids include, for example, capric, lauric, palmitic, stearic, behenic, isomyristic, isomargaric, myristic, caprylic, and anteisoarachadic. Suitable preferred unsaturated fatty acids include, for example, maleic, linoleic, licanic, oleic, elaidic, linolenic, erythrogenic acids. In a preferred embodiment of the invention the fatty acid chains of the esterified polyols have from about two to about twenty-four carbon atoms. Polyol fatty acid polyesters obtained from naturally occurring oil such as soybean oil, cottonseed oil, palm kernel oil, palm oil, coconut oil, sunflower oil, safflower oil, rapeseed oil, high erucic acid rapeseed oil, canola oil, tallow oil, peanut oil and corn oil are preferred. The oils can be fully hydrogenated oils, partially hydrogenated oils, non-hydrogenated oils, and/or mixtures thereof. Preferred polyol fatty acid polyesters are those in which the fatty acid chains have from about eight to about twenty-four carbon atoms. Suitable polyol fatty acid polyesters are esterified linked alkoxylated glycerins, including those comprising polyether glycol linking segments, as described in U.S. Patent No. 5,374,446, incorporated herein by reference, and those comprising polycarboxylate linking segments, as described in U. S. Patent Nos. 5,427,815 and 5,516,544, incorporated herein by reference; more preferred are those described in U. S. Patent No. 5,516,544. Additional suitable polyol fatty acid polyesters are esterified epoxide-extended polyols of the general formula P(OH)A+C (EPO)^ (FE)β wherein P(OH) is a polyol, A is from 2 to about 8 primary hydroxyls, C is from about 0 to about 8 total secondary and tertiary hydroxyls, A + C is from about 3 to about 8, EPO is a CyCfr epoxide, N is a minimum epoxylation index average number, FE is a fatty acid acyl moiety and b is an average number is the range of greater than 2 and no greater than A + C, as described in U. S. Patent No. 4,861,613 and EP 0324010 Al, incorporated herein by reference. The minimum epoxylation index average number has a value generally equal to or greater than A and is a number sufficient so that greater than 95% of the primary hydroxyls of the polyol are converted to secondary or tertiary hydroxyls. Preferably the fatty acid acyl moiety has a C7-C23 alkyl chain. Preferred esterified epoxide-extended polyols include esterified propoxylated glycerols prepared by reacting a propoxylated glycerol having from 2 to 100 oxypropylene units per glycerol with C10-C24 fatty acids or with C] Q-C24 fatty acid esters, as described in U. S. Patent Nos. 4,983,329 and 5,175,323, respectively, both incorporated herein by reference. Also preferred are esterified propoxylated glycerols prepared by reacting an epoxide and a triglyceride with an aliphatic polyalcohol, as described in U. S. Patent No. 5,304,665, incorporated herein by reference, or with an alkali metal or alkaline earth salt of an aliphatic alcohol, as described in U. S. Patent No. 5,399,728, incorporated herein by reference. More preferred are acylated propylene oxide-extended glycerols having a propoxylation index of above about 2, preferably in the range of from about 2 to about 8, more preferably about 5 or above, wherein the acyl groups are Cg-C24 , preferably C j 4-C ] g , compounds, as described in U. S. Patent Nos. 5,603,978 and 5,641,534, both incorporated herein by reference. Particularly preferred are fatty acid-esterified propoxylated glycerols which exhibit a sharp melt point before about 92 F (33 C) and have a dilatomeric solid fat index at 92 F (33 C) of less than about 30, as described in WO 97/2260, or which have a dilatomeric solid fat index of at least about 50 at 70 F (21 C) and at least about 10 at 98.6 F (37 C), as described in U. S. Patent Nos. 5,589,217 and 5,597,605, both incorporated herein by reference. Other suitable esterified epoxide-extended polyols include esterified alkoxylated polysaccharides. Preferred esterified alkoxylated polysaccharides are esterified alkoxylated polysaccharides containing anhydromonosaccharide units, more preferred are esterified propoxylated polysaccharides containing anhydromonosaccharide units, as described in U. S. Patent No. 5,273,772, incorporated herein by reference In the processes of the present invention, polyol fatty acid polyester is synthesized and unreacted lower alkyl ester is recycled. In particular, a polyol fatty acid polyester is synthesized by a process comprising the steps of (a) reacting excess lower alkyl ester with polyol, partially esterified polyol, or mixtures thereof to esterify hydroxyl groups thereof and form polyol fatty acid polyester, the polyol fatty acid polyester comprising partially esterified polyol, fully esterified polyol, or mixtures thereof, and being in admixture with unreacted lower alkyl ester, (b) separating at least a portion of the unreacted lower alkyl ester from the polyol fatty acid polyester, and (c) recycling the separated unreacted lower alkyl ester for further reaction with polyol or partially esterified polyol, wherein the lower alkyl ester which is recycled for further reaction is substantially free of lower alkyl ester degradation reaction products. In one preferred embodiment, the step of recycling the separated unreacted lower alkyl ester comprises directly recycling the unreacted lower alkyl ester to the reaction mixture comprising polyol. Such direct recycling can be desirable to reduce the level of degradation reaction products. As used herein, "substantially free" of lower alkyl degradation reaction products means that the use of the recycled lower alkyl ester will not adversely effect the quality of the polyol polyester product formed from the recycled lower alkyl ester. Degradation reaction products of the lower alkyl ester will be apparent to those skilled in the art and comprise products of oxidation, hydrolysis, pyrolysis, saponification and the like. These degradation reaction products should be minimized or eliminated to permit direct recycling of the lower alkyl ester to the polyol polyester reaction, without resorting to extra cleanup or purification steps for the recycled esters. EXCESS METHYL ESTER RECYCLING a) Oxidation Oxidation of lower alkyl esters can result in the formation of carbonyls and other double-bonded structures, which can directly lead to off-color in the lower alkyl ester material as well as in the polyol polyester product produced therefrom. Oxidation can be minimized or substantially prevented by eliminating exposure of the lower alkyl esters to sources of oxygen (e.g., air) such as by performing the synthesis reaction, separation processing and recycle under a blanket of an inert gas so that the unreacted lower alkyl ester is maintained in the inert gas atmosphere. Suitable inert gases include nitrogen, carbon dioxide and helium. Oxidation can also be minimized by using a vacuum in order to exclude sources of air from synthesis reactions and separation and recycle processes. Further, eliminating or reducing light exposure of the lower alkyl ester reactant and minimizing the trace metal content of the lower alkyl ester and other reactants will also reduce oxidation degradation reactions. The processes according to the present invention are therefore preferably conducted in these manners in order to minimize oxidation reactions whereby the lower alkyl ester which is recycled for further reaction is substantially free of oxidation degradation reaction products. Preferably, the recycled lower alkyl ester has a carbonyl value of less than 200 ppm and a peroxide value of less than about 100 ppm. Additionally, the trace metal content of the alkyl ester is preferably reduced to less than about 0.2 ppm Fe and less than about 0.1 ppm Cu in order to further minimize any oxidative reactions in the alkyl ester reactant which is recycled. b) Hydrolysis Hydrolysis reactions are minimized by avoiding or substantially preventing exposure of the unreacted lower alkyl ester to acidic conditions and/or elevated temperatures, for example temperatures greater than about 85°C, particularly in the presence of water, as such exposures lead to the conversion of the fatty acid lower alkyl ester to fatty acid. Free fatty acid is to be avoided in the recycled lower alkyl ester, since it will stoichiometrically be neutralized by, and thereby consume, the basic catalyst used to catalyze the polyol polyester esterification reaction. The neutralization of the free fatty acid by the basic catalyst forms soap. Excessive amounts of soap in the polyol polyester reaction are to be avoided, since they can lead to an increase in viscosity of the polyol polyester reaction mixture. At the later stage of the esterification reaction, it is important to remove by-product methanol from the reaction mixture to drive the reaction toward completion. Inert gas sparging and/or vacuum are commonly used to carry away methanol that has been formed and which migrates to the liquid-gas interface. Consequently, highly viscous reaction mixtures slow the methanol mass transfer rate and hence, its removal rate from the reaction mixture, thereby directly affecting the reaction rate and degree of completion. The pH of the polyol fatty acid polyester synthesis reaction preferably is no less than about 7. Preferably any fatty acid which is formed is neutralized. During subsequent steps of refining and finishing of the polyol fatty acid polyester, the pH preferably is no less than 5.5. Using a sufficiently strong base to neutralize any fatty acid present in the recycle ester, without saponifying the alkyl esters to an excessive degree, will minimize any negative effects on the polyol polyester esterification reaction. Preferably, the hydrolysis reactions are minimized so that the lower alkyl ester is substantially free of fatty acid, whereby direct recycle of the lower alkyl ester to the polyol polyester reaction will not adversely affect the quality of the polyol polyester product formed therefrom. The free fatty acid content of the recycled alkyl ester should be, by weight percent, preferably less than about 0.4, more preferably less than about 0.2, and most preferably less than about 0.1. Generally, the extent of the hydrolysis reaction which occurs in the lower alkyl ester reactant depends on the level of water present, the temperature of the lower alkyl ester and the contact time with water. As discussed supra, water is used to wash the polyol polyester reaction products of impurities and byproducts, whereby the excess alkyl ester is exposed to the wash water. The usage level of water is selected by color removal requirements, with 2 to 20 percent water by weight of the polyol polyester oil generally being suitable. The temperature of the lower alkyl ester is preferably maintained at less than about 85°C during water processing, and the contact time of the lower alkyl ester with water is preferably less than about 30 minutes, more preferably less than about 15 minutes, even more preferably less than about 10 minutes, and most preferably less than about 5 minutes. The water can be separated from the reaction product by gravity settling or centrifugation. Gravity settling may require up to about 2 hours. A preferred embodiment uses centrifugation of less than about 20 minutes, preferably less than about 10 minutes. As discussed above, fatty acid neutralization in the recycle ester is conducted without saponifying the alkyl ester to an excessive degree. The maximum level of saponification products which can be present in the lower alkyl ester recycle is preferably not greater than about 1.0 percent by weight, and more preferably not greater than about 0.5 percent by weight, and even more preferably not greater than about 0.2 percent by weight. Most preferably, the saponification products will be non-detectable; i.e., about 0 percent. Preferably, the same basic material can be used to both catalyze the polyol fatty acid polyester synthesis reaction and neutralize any fatty acid in the recycled lower alkyl ester. Suitable basic compounds to be used as basic reaction catalysts and as fatty acid neutralizers include alkali metals such as sodium, lithium and potassium; alloys of two or more alkali metals such as sodium-lithium and sodium-potassium alloys; alkali metal hydrides, such as sodium, lithium and potassium hydride; alkali metal lower (C1-C4) alkyls such as butyl-lithium; and alkaline metal alkoxides of lower (C1-C4) alcohols, such as lithium methoxide, potassium t- butoxide, potassium methoxide, and/or sodium methoxide. Other suitable basic compounds include carbonates and bicarbonates of alkali metals or alkaline earth metals. A preferred class of basic catalysts include potassium carbonate, sodium carbonate, barium carbonate, or mixtures of these compounds having particle sizes that are less than about 100 microns, preferably less than about 50 microns. It has been found that when these specific compounds are used as catalysts, increased yields of light-colored higher polyol polyesters are obtained when compared to essentially identical reactions carried out using more conventional catalysts, such as sodium hydride, potassium hydride, soap, or sodium methoxide. These preferred catalysts can be used in admixture with the more conventional basic catalysts, described above. Potassium carbonate and/or potassium methoxide are also preferred catalysts. The use of these catalysts is further disclosed in U.S. Patent No. 4,517,360 (Volpenhein), which is incorporated by reference. In one embodiment, the basic compound used as both a basic reaction catalyst and a fatty acid neutralizer is potassium carbonate. The level of basic catalyst is typically from about 0.01 to about 0.5, preferably from about 0.01 to about 0.2, more preferably from about 0.02 to about 0.15 moles of catalyst per mole polyol. If the basic catalyst is also used to neutralize fatty acids in the recycle ester, the level will be adjusted to an amount effective for neutralizing the acids without excessively saponifying the methyl esters, as discussed above. To minimize saponification of the alkyl esters, the amount of base catalyst which is employed is preferably limited to one to two times the stoichiometric amount of base required to neutralize the free fatty acid content of the lower alkyl ester reactant. Preferably, when the excess lower alkyl ester reactant is recycled for further polyol polyester production, the catalyst level is typically increased, if at all, by an amount of up to about 20% above the level of catalyst employed for production when only fresh lower alkyl ester is employed and no lower alkyl ester is recycled. c) Pyrolysis It is also desirable to minimize pyrolysis degradation reaction products in the lower alkyl ester reactant. Generally, pyrolysis of the polyol polyester can occur in evaporation and/or stripping processes which can be used to separate the excess lower alkyl ester reactant from the polyol fatty acid polyester product. Free fatty acid is one of the primary pyrolysis products. If pyrolysis of the polyol polyester occurs, the pyrolysis products are carried off with the lower alkyl ester material during removal. Additionally, pyrolysis generally is a time-dependent reaction. Pyrolysis tends to become significant at increased temperatures. Accordingly, process conditions for the evaporation and stripping steps are controlled in order to avoid degradation reactions of the polyol polyester. Preferably, the evaporation and stripping processes are conducted at temperatures of from about 190°C to about 260°C, more preferably from about 200°C to about 250°C and even more preferably, from about 215°C to about 240°C, and at pressures of from about 0.01 to 10 mm Hg, more preferably from about 0.05 to about 5 mm Hg, and even more preferably from about 0.1 to about 1.0 mm Hg. Without being limited by theory, it is believed that the process of the present invention can be used to reduce the level of certain undesirable components (degredation, decomposition products) that may be otherwise present during synthesis and/or heating of polyol polyesters of the type described herein. In particular, typical processes for synthesizing such polyol polyesters can result in the production of certain volatile compounds not typically found in heated fats and oils. Such undesirable volatile compounds are described in "Volatile Compounds in Heated Oleic Acid-Esterified Propoxylated Glycerol" by Mahungu et al., Journal of American Oil Chemists, page 683-690, Vol. 75, No. 6 (1998), which article is incorporated herein by reference. It is believed that synthesizing esterified linked alkoxylated polyols and esterified epoxide-extended polyols according to the process of the present invention can help reduce the level of undesirable volatile compounds described in the above referenced article. Separation of lower alkyl ester from the polyol fatty acid polyester product can be effected with many different reactor designs; batch, continuous, and column reactors, inter alia, can all be utilized. For example, fatty acid methyl esters can be distilled by batch (single stage or multi stage) distillation or by continuous distillation. For batch distillation, residence times typically range from about four hours to about thirty hours, preferably from about six hours to about eighteen hours, more preferably from about eight hours to about twelve hours. For continuous distillation, residence times typically range from about 0.1 to about ten minutes, preferably, from about 0.5 to about 5 minutes. Pressures of from about 0.005 to about 30 mm, preferably from about 1 to about 5 mm, of mercury are used in the distillation process. Temperatures typically range from about 120°C to about 260°C. The lower alkyl esters can also be recovered from the reaction mixture by solvent extraction, using suitable known techniques, with the provision that the extraction conditions are controlled so as to substantially prevent degradation reactions of the lower alkyl ester as discussed above. In a preferred embodiment, the lower alkyl esters are removed from the polyol fatty acid polyester product using a two-step process. Generally, the crude polyol fatty acid polyester product will contain from about 10 to about 90 weight percent of the lower alkyl ester, i.e., methyl ester, reactant. In the first step of the preferred separation process, the lower alkyl ester concentration is reduced to a range of from about 0.5 weight percent to about 5 weight percent using an evaporation device, for example, a flash tank, a falling film or rising film evaporator, a wiped film evaporator, any combination thereof, or the like. This step of the separation process is typically limited by heat transfer. The vapor fraction from the vessel is the lower alkyl ester recycle stream. The liquid fraction is the polyol polyester product stream. In the second step of the preferred separation method, the lower alkyl ester concentration in the polyol fatty acid polyester product stream is further reduced from the about 0.5 weight percent to about 5 weight percent content resulting from the evaporation step, to less than about 0.1 weight percent using a multi-stage mass transfer device, for example, packed columns or tray columns, together with gas stripping. Steam or nitrogen can suitably be employed as the stripping gas. The second step of the separation process is typically limited by mass transfer. As used herein, all ratios are molar ratios unless otherwise specified, and all percentages are by weight unless otherwise specified. In general, the heterogeneous reaction mixture comprises from about 5% to about 90%, preferably from about 10% to about 60%, more preferably from about 15% to about 30% by weight of the polyol; from about 10% to about 90%, preferably from about 20% to about 80%, by weight of the fatty acid esters; and from about 0.01%) to about 0.5%, preferably from about 0.01% to about 0.2%, more preferably from about 0.05% to about 0.15%, by weight of the basic catalyst. The ratio of the fatty acid chains of the lower alkyl ester to the hydroxyl groups of the polyol is typically in the range of about 0.5: 1 to about 1.5: 1. The ratio of catalyst to polyol typically ranges from about 0.01 : 1 to about 0.5:1. In the transesterification process, excess fatty acid lower alkyl ester is included in the reaction mixture. The transesterification process is preferably carried out in a single reaction stage. As used herein, the term "excess" is intended to be an amount beyond that required to form lower polyol fatty acid polyesters. When fatty acid methyl esters are used, it is preferred that all the methyl ester (including excess methyl ester) is present in an initial, single reaction stage to avoid the need for multiple reaction stages. The reaction mixture is heated to a temperature of from about 120°C to about 160°C, preferably at about 135°C, at a pressure from about 0.01 to about 2500 mm Hg, preferably from about 0.1 to about 1500 mm Hg. The reaction time is preferably less than about 10 hours, and generally is between about 2 to about 8 hours. During the reaction, partially esterified polyol is further esterified to provide highly esterified polyol fatty acid polyesters. As used herein, the term "highly esterified polyol fatty acid polyester" refers to a polyol wherein at least about 50%o, preferably at least about 70%, and most preferably at least about 96%, of the hydroxy groups are esterified. The transesterification reaction can be conducted in any of the reactors conventionally employed, including, but not limited to batch, semi-batch and continuous reactors. Continuous stirred tank reactors (single or in series) and column reactors (packed or multi-stage) are suitable for use in the transesterification reaction. Plug flow column reactors can be suitable in one or more embodiments. As the transesterification reaction proceeds, a lower alcohol is formed as a by-product. In order to promote the reaction, the alcohol by-product is preferably removed. Many removal techniques are known in the art and can be used to effectively and efficiently remove the lower alkyl alcohol. Vacuum removal, with and without an inert gas sparging, can be used to promote the reaction. Alternatively, inert gas sparging can be used at atmospheric or greater pressures to promote methanol and other alcohol removal. The polyol fatty acid polyesters are separated from the reaction mixture containing polyesters, by-products, and unreacted starting materials. Separation can be accomplished with any of the separation procedures routinely used in the art. Distillation, water washing, and conventional refining techniques or solvent extractions are preferred, with the provision that the steps noted above be taken to prevent substantial degradation of lower alkyl ester which is to be recycled. In the final step, the unreacted fatty acid lower alkyl esters recovered from the reaction mixture are recycled, for use as ingredients in the transesterification reaction mixture. EXAMPLES: The processes of the present invention are further understood in view of the following examples in which all parts and percentages are by weight, unless otherwise specified. Example 1. Synthesis Of A Liquid EPG. Glycerin, 992 parts, is heated with 80 parts of 85% potassium hydroxide solution at 1 10°C and 10 mm Hg in a reactor with a dry ice trap for water removal until no further water is evolved. The reactor is pressurized with nitrogen and cooled to 92°C, and 3126 parts of propylene oxide is added on a pressure demand basis maintaining a reactor pressure of 55 psi. After the propylene oxide has been added the reaction is continued for an additional 5 hours. The reactor is then cooled and purged with nitrogen. A propoxylated glycerin with a molar ratio of propylene oxide to glycerin of 5: 1 is obtained. The propoxylated glycerin and soybean methyl esters are mixed in a molar ratio of methyl esters to propoxylated glycerin of 5: 1. Sodium methylate, 0.13 mole sodium methylate/mole propoxylated glycerin, is added as additional basic catalyst. The propoxylated glycerin, soybean methyl esters and catalyst are heated at 150°C for 3 hours at a pressure of 10 mm Hg in a reaction flask equipped with a distilling head for removing methanol. At this time the reaction mix is recatalyzed with another 0.13 mole sodium methylate/mole propoxylated glycerin and heated at 150°C for an additional 3 hours at a pressure of 10 mm Hg. All through the purification steps, the crude reaction mix is maintained at a temperature of 80-100 C unless otherwise noted. The crude reaction mix is hydrated with 0.3% by weight water and the soap is removed by filtration. After removing the soap, the reaction mixture is washed with an 18% by weight water solution, the water solution containing 2.8%> tripotassium citrate. The water phase is separated by centrifugation. The reaction mix is then washed a second time with 340% by weight water and the water phase is separated by centrifugation. The mixture is then dried under vacuum, bleached with 1% silica gel and filtered. The excess methyl esters are removed on a Pope® wiped film evaporator operating at 230° C and 0.1 mm Hg pressure. Steam stripping of the polyol polyester is used to complete the methyl ester removal. Steam stripping is performed with a packed column with countercurrent flow of steam and polyol polyester operating under a pressure of about 4.0 mm Hg and a temperature of about 218 Centigrade. The finished esterified propoxylated glycerin has a peroxide value of less than 100, a carbonyl value less than 200, free fatty acid less than 0.4%, residual soap less than 2000 ppm and final color (Lovibond red) of less than 4.0. The distillate methyl esters from the evaporator can be used in subsequent reactions. Example 2. Synthesis Of A Liquid EPG Using Recycled Methyl Esters. Example 1 is repeated except that the soybean methyl esters comprise 38% of the methyl ester recycled from the distillate off the Pope® evaporator from Example 1 and 62% fresh methyl esters. The final esterified propoxylated glycerin has peroxide value of less than 100, carbonyl value less than 200, free fatty acid less than 0.4%, residual soap less than 2000ppm and final color (Lovibond red) of less than 4.0. Example 3. Synthesis Of An Esterified, Linked Alkoxylated Polyol. A propoxylated glycerin with a molar ratio of propylene oxide to glycerin of 4:1 is prepared by the method of Example 1. The residual catalyst is not removed. The propoxylated glycerin and catalyst (324 parts) is mixed with of methyl behenate (708 parts giving a 2/1 mole ratio methyl behenate to propoxylated glycerin). Sodium methylate, 0.13 mole sodium methylate/mole propoxylated glycerin, is added as additional basic catalyst. The propoxylated glycerin, methyl behenate and catalyst are heated at 150°C at a pressure of 10 mm Hg in a reaction flask equipped with a distilling head for removing methanol until at least 95% conversion of the methyl behenate has occurred. Dimethyl adipate (87 parts) is added and heating continued at a pressure of 100 mm HG until at least 95% conversion of the original hydroxyl groups of initial propoxylated glycerin has occurred. The distillate comprising methanol and unreacted dimethyl adipate is periodically collected and the methanol removed on a rotovap. The unreacted dimethyl adipate is recycled to the reaction. At the end of the reaction, any excess dimethyl adipate is removed on a rotovap and can be used in subsequent reactions. All through the purification steps, the crude reaction mix is maintained at a temperature of 80-100 C unless otherwise noted. The crude reaction mix is hydrated with 0.3% by weight water and the soap is removed by filtration. After removing the soap, the reaction mixture is washed with an 18% by weight water solution, the water solution containing 2.8% tripotassium citrate. The water phase is separated by centrifugation. The reaction mix is then washed a second time with 340% by weight water and the water phase is separated by centrifugation. The mixture is then dried under vacuum, bleached with 1%> silica gel and filtered. The excess methyl esters are removed on a Pope® wiped film evaporator operating at 240 C at a pressure of 0.1 mm Hg. Steam stripping of the polyol polyester is used to complete the methyl ester removal. Steam stripping is performed with a packed column with countercurrent flow of steam and polyol polyester operating under a pressure of about 4.0 mm Hg and a temperature of about 218 Centigrade. The resulting esterified, linked, alkoxylated glycerin has a peroxide value of less than 100, a carbonyl value less than 200, free fatty acid less than 0.4%, residual soap less than 2000 ppm and final color (Lovibond red) of less than 4.0. The distillate methyl esters from the evaporator can be used in subsequent reactions. Example 4. Synthesis Of An Esterified, Linked Alkoxylated Polyol Using Recycled Methyl Esters. Example 3 is repeated except that the methyl behenate comprises 30% of the methyl ester recycled from the distillate off the Pope® evaporator from Example 3 and 70% fresh methyl behenate. The final esterified propoxylated glycerin has a peroxide value of less than 100, carbonyl value less than 200, free fatty acid less than 0.4%, residual soap less than 2000ppm and final color (Lovibond red) of less than 4.0. TEST METHODS: Peroxide Value: The peroxide value is determined by thiosulfate titration. Peroxides reduce the KI to I2, and I2 can complex with starch indicator to create a blue color. A thiosulfate titrant oxides the I2, causing the blue color to disappear; 0.5 mole of I2 is consumed per mole thiosulfate. A potassium iodide solution of 15 grams KI in 10 ml deionized water and a 0.0 IN thiosulfate solution is prepared. Samples are prepared by dissolving 20 grams of sample with 30 ml of a 60:40 v:v glacial acetic acid/1, 1,2-trichlorotrifluoroethane solution, adding 1 ml of the KI solution, agitating for 1 minute, adding 100 ml of distilled water, mixing, and adding 2 ml of a starch indicator solution (Fisher Scientific, #SS408-1). The samples are then titrated with the thiosulfate to a colorless endpoint. The peroxide value was calculated using the equation: ppm H 2 0 2 = (34 g/mole H θ2 (moles thiosulfate titrant)(0.5 thio/hXI O 6 ppm/g) ~ - sample weight (g) ~ Preferably, the peroxide value is less than about 85 ppm. Free Fatty Acid Level: The free fatty acid level is determined by phenolphthalein titration. One milliliter of phenolphthalein indicator, 50 ± 0.2 grams of sample and 100 ml of warm neutral denatured alcohol are mixed. The solution is titrated to a phenolphthalein endpoint using 0.0 IN NaOH. The percent free fatty acid (%FFA) is reported as % oleic acid, and is calculated according to the equation: %FFA as Oleic = Kml of NaOH) x (Normality of NaOH) x 28.211 Sample Weight (g) Preferably, the percentage of free fatty acid is less than about 0.4%, more preferably less than about 0.3%. Carbonyl Value: The carbonyl value is determined based upon reacting fatty acid lower alkyl ester with an ethanolic solution of 2,4-dinitrophenylhydrazine (2,4-DNPH) and hydrochloric acid to form 2,4-dinitrophenylhydrazones, which in the presence of a base produce red color. A 2,4-DNPH stock solution is prepared by dissolving 0.8 ± 0.02 g of 2,4-DNPH in 200 ml of 200 proof (100%>) undenaturated ethanol, and then adding 10 ml of concentrated HC1. A KOH solution is prepared by dissolving 1 18 g of KOH in 500 ml of distilled water, and diluting to 2000 ml with 200 proof undenaturated ethanol. A dodecanal stock solution is prepared by diluting 0.200 ± 0.001 g of dodecanal to 50 ml with 200 proof undenaturated ethanol. The carbonyl concentration is calculated as: ppm C=0 = ug C=Q in stock = weight of dodecanal (g) x 28 x F x 10" ug ; ml 50 ml 184 g F = % purity of dodecanal/100. The dodecanal stock is diluted 50-fold with 200 proof undenaturated ethanol to form a working solution; the working solution is used to make calibration standards. Fatty acid lower alkyl ester samples are prepared by diluting 0.1 ± 0.0100 g of sample with 4 ml of ethanol. Each of the samples, standards, and ethanol blanks are placed in a 25-ml volumetric flask, and 2 ml of the 2,4-DNPH solution is added to each flask. Stoppered flasks are placed in a 75 ± 1 °C water bath for 20 ± 0.5 minutes, cooled to room temperature, diluted to 25 ml with the KOH solution, and mixed well with shaking. After standing at room temperature for 20 ± 0.5 minutes, the absorbance is read at 480 nm using quartz cells. A calibration curve is constructed from the absorbance values of the calibration standards. Preferably, the carbonyl value is less than 200 ppm. Color: Color is determined using a Lovibond Automatic Tintometer with a red/yellow calibration standard (2.9 red/12.0 yellow). The color is reported in AOCS red and yellow units. Preferably, the color is less than about 3.7 Lovibond red units. Level of Soap: The level of soap remaining in the polyol polyester reaction product after centrifuging is preferably less than 2000ppm. The level of soap remaining is determined by acid tritiation. Samples are prepared by mixing 0.5 ± 0.01 grams of sample with 50 ml of a 1 : 1 v:v isopropanol/ deionized water solution. The sample is titrated with 0.0 IN HC1 using an automatic titrator. One equivalence point is observed. Residual potassium soap is calculated using the equation: % K soap = (ml HCl) (Normality HC1) X 32.0** sample weight (g) **32.0 = Molecular Weight K Soap (g/mol) * 0.001 1/ml * 100 Having described the preferred embodiments of the present invention, further adaptations of the processes described herein can be accomplished by appropriate modifications by one of ordinary skill in the art without departing from the scope of the present invention. A number of alternatives and modifications have been described herein, and others will be apparent to those skilled in the art. Accordingly, the scope of the present invention should be considered in terms of the following claims, and is understood not to be limited to the details of the processes described in the specification.

Claims: WHAT IS CLAIMED IS: 1. A process for synthesizing and purifying a nondigestible or partially digestible fat, the process characterized by the the steps of: (a) reacting lower alkyl ester with polyol, partially esterified polyol, or mixtures thereof to esterify hydroxyl groups thereof and form a reaction product comprising a member selected from the group consisting of esterified linked alkoxylated polyols, esterified epoxide extended polyols, and mixtures thereof; wherein said reaction product is in admixture with unreacted lower alkyl ester; (b) separating at least a portion of the unreacted lower alkyl ester from the reaction product, wherein the separated unreacted lower alkyl ester is substantially free of degradation reaction products; and (c) recycling the separated unreacted lower alkyl ester to step (a) for further reaction with polyol or partially esterified polyol. 2. A process according to Claim 1 further characterized by a cleaning step, after separating at least a portion of the unreacted lower alkyl ester from the reaction product, wherein degradation reaction products are further removed from the separated unreacted lower alkyl esters. 3. A process according to Claim 1 or 2 further characterized by the step of water- washing the reaction product in admixture with unreacted lower alkyl ester prior to separating the unreacted lower alkyl ester from the reaction product, wherein the water-washing temperature is less than 85°C, and the unreacted lower alkyl ester has a contact time with water of preferably less than 30 minutes, more preferably less than 15 minutes. 4. A process according to any one of the preceding claims, wherein the separated unreacted lower alkyl ester has a carbonyl value of less than 200 ppm. 5. A process according to any one of the preceding claims, wherein the separated unreacted lower alkyl ester has a peroxide value of less than 100 ppm. 6. A process according to any one of the preceding claims, wherein the separated unreacted lower alkyl ester comprises less than about 0.4 weight percent free fatty acid. 7. A process according to any one of the preceding claims, wherein the separated unreacted lower alkyl ester comprises less than 2000 ppm soap. 8. A process according to any one of the preceding claims, wherein unreacted lower alkyl ester is separated from the reaction product by evaporating the unreacted lower alkyl ester at a temperature at which degradation reaction of the reaction product is substantially prevented. 9. A process according to any one of the preceding claims, comprising the step of refining the reaction product in the presence of a base, wherein the base is included in an amount sufficient to neutralize fatty acids present therein without saponifying the lower alkyl esters. 10. A process according to any one of the preceding claims, wherein a base is included in the unreacted lower alkyl ester in an amount sufficient to neutralize fatty acids present therein without saponifying the lower alkyl esters.

Inventors: HOWIE JOHN KEENEY, KENNEALLY COREY JAMES, SARAMA ROBERT JOSEPH, TROUT JAMES EARL, HOWIE, JOHN, KEENEY, KENNEALLY, COREY, JAMES, SARAMA, ROBERT, JOSEPH, TROUT, JAMES, EARL
Applicants: HOWIE JOHN KEENEY, KENNEALLY COREY JAMES, PROCTER & GAMBLE, SARAMA ROBERT JOSEPH, TROUT JAMES EARL, HOWIE, JOHN, KEENEY, KENNEALLY, COREY, JAMES, SARAMA, ROBERT, JOSEPH, THE PROCTER & GAMBLE COMPANY, TROUT, JAMES, EARL
Application year: 1999
Main classification: C07H13
IPC codes: C07H13