Biodiesel-Transesterification of Biological Oils with Liquid Catalysts

Catalysts: Thermodynamic Properties of Oil-Methanol-Amine. Mixtures ... procedure results in a conversion higher than 98% in a one-stage operation. By...
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Ind. Eng. Chem. Res. 2005, 44, 9535-9541

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Biodiesel-Transesterification of Biological Oils with Liquid Catalysts: Thermodynamic Properties of Oil-Methanol-Amine Mixtures Tanja C ˇ ercˇ e,† Siegfried Peter,‡ and Eckhard Weidner*,† Ruhr-University Bochum, Chair for Process Technology, Universitaetsstrasse 150, D-44780 Bochum, and Technical Chemistry, University Erlangen, Germany

New catalysts and environmentally benign processes allow generation of biodiesel with improved properties at competitive costs. Different amine-based liquid catalysts are screened with respect to conversion rates. Experimental investigations of the complex phase behavior between methanol, different oils, and catalysts as reactants and methyl ester and glycerol as products are the key to define suitable process conditions for reaction and product recovery. An optimized procedure results in a conversion higher than 98% in a one-stage operation. By using sodiumor potassium-free catalysts, soap formation is avoided and glycerol and methyl ester separate rapidly. Effluents of washing water are minimized or even avoided. 1. Introduction Diesel oil, generated from petroleum by refining, is an important fuel for many engines. Combustion of diesel produces carbon dioxide, which is assumed to contribute to the global warming. Furthermore, mineral fuels contain sulfur, which, if not removed prior to combustion, is a cause of acid rain. The discussion on reduction of CO2 emissions and on high prices for fossil diesel fuel leads to an enforced search for production of fuels from renewable sources. In the announcements of the EU-committee, the intention to replace 5.8% fossil diesel fuel with fuel from biogeneous sources until 2010 was published.1 In the EU and also in southeast Asia, the production of fuel from vegetable oil is favored. Those fuels are biodegradable, nontoxic, and reduce pollution significantly. However, the relative high viscosity and the high melting point of vegetable oils must be reduced to make them compatible with conventional engines and fuel systems. This is achieved by converting the oils with methanol. The common technique for this reaction has been known for about 100 years. Methyl esters of fatty acids are produced by alcoholysis (transesterification with alcohols) of triglycerides with methanol as illustrated in Scheme 1. The reaction rate is so slow that for commercial purposes a catalyst is necessary for accelerating the reaction. The most known alkaline-catalyzed process applies a solution of sodium methylate as catalyst.2 Alternatively, acid-catalyzed processes are used, where fatty acids are converted to methyl ester by means of, for example, benzosulfonic acid.3 Also, enzymatic reactions with lipase as catalyst4 are investigated. Applications of zeolites and basic alkaline-earth metal compounds as solid catalysts have been already investigated.5,6 Performing the reaction with various supercritical alcohols without a catalyst has also been described.7 * To whom correspondence should be addressed. Tel.: +49 234 32 26 680. Fax: +49 234 32 14 277. E-mail: weidner@ vtp.ruhr-uni-bochum.de. † Ruhr-University Bochum. ‡ University Erlangen.

Scheme 1. Transesterification of Triglycerides with Methanol

The use of homogeneous catalysts requires extensive conditioning and purification steps for the reaction products (methyl ester and glycerol) to separate the catalysts. In contrast, heterogeneous catalysts are easily removed from the reaction mixture, making the purification step easier.8 Complete conversion of the triglycerides involves three consecutive reactions with monoglyceride and diglyceride as intermediates.9 In the process of transesterification, two liquid phases are formed. The lower phase mainly consists of glycerol and some catalyst, intermediate products, and may contain water and soap (from residual free fatty acids in the oil). Glycerol as a byproduct of the transesterification reaction has a number of applications in the pharmaceutical, cosmetics, food, and plastics industries, but requires extensive washing and purification from the trace compounds. The upper phase mainly contains methyl ester, which after removing an excess of methanol and washing with water is used as biodiesel. The most widely used vegetable oils for the production of biodiesel are taken from rape seeds, sunflowers, and soybeans. The present research is focused on new, environmentally benign processes for the production of biodiesel from renewable raw materials as vegetable oils or animal fats. To accelerate the reaction, to avoid washing procedures for removing the traditional catalyst, and to produce sodium free methyl esters and glycerol, a series of new catalysts based on solid (heterogeneous)8 or liquid amines (homogeneous) were investigated.

10.1021/ie050252e CCC: $30.25 © 2005 American Chemical Society Published on Web 08/12/2005

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Table 1. Physical and Chemical Properties of Ammonium Catalysts name

M [g/mol]

TB [°C]

pH

DMTMD 4-MP TMAH (25% solution in methanol) DEA TEMED DMAE

102.2 99.18 91.15

132-140 121-127 65

12.7 13 12-13

73.14 116.21 89.14

56 121 132-135

13 8-8.5 12.1

Several vegetable oils, such as rape seed oil, sunflower oil, coconut oil, pig fat, or even used frying fats, were tested. 2. Experimental Section 2.1. Materials. For the investigation of binary fluid phase equilibrium, methanol (MeOH) and several oils, such as rape seed oil, sunflower oil, or mink oil, were used. For investigations on ternary fluid phase equilibrium methyl ester from rape seed oil, glycerol and two catalysts were used beside pure rape seed oil. These catalysts are N,N-dimethyltrimethylenediamine (DMTMD) and 4-methylpiperidine (4-MP). Four more catalysts were used for methanolysis of rape seed oil and methanol, such as diethylamine (DEA), dimethylethanolamine (DMAE), tetramethyldiaminoethane (TEMED), and tetramethylammonium hydroxide as 25% solution in methanol (TMAH). Physical and chemical properties of all catalysts are summarized in Table 1. Refined rape seed oil (Rapso) and sunflower oil (Ja) was bought from the store. Mink oil was delivered by DAKA (Denmark). MeOH (purity 99.8%) and glycerol (purity 99.9%) were purchased from Merck, Darmstadt (Germany). C18-Methyl ester (Edenor ME Ti 05, typical composition: C20-C22: 2.5%, total C18: 81%, C16-0: 11%, C14-0: 3%) was delivered from Cognis, Du¨sseldorf (Germany). 2.2. Apparatus and Methods. 2.2.1. Fluid Phase Equilibrium. Measurements at atmospheric pressure and different temperatures from 20 to 60 °C and above boiling temperature of methanol (64 °C) at the vapor pressure of the reaction mixture were carried out in a phase equilibrium (LLE) apparatus. This apparatus consists of a flask, condenser, thermometer, heater, and a magnetic stirrer. In binary LLE measurements, the first substance was weighed in a flask on two decimals exactly. The flask was then heated in a water bath under reflux, until the designated temperature was achieved. Subsequently, the second substance was added via an analytical syringe under stirring, drop by drop, until a second phase was observed. After achieving phase separation, the syringe with remaining second substance was weighed. The difference between the mass of the syringe before and after the experiment represents the mass of the dosed second substance. All measurements of ternary LLE were performed according to the same principle. The first substance was weighed in a flask on two decimals exactly. A known mass of the second substance was then added, to form a system with two liquid phases. Subsequently, the flask was heated in a water bath to the desired temperature under total reflux. The third substance was weighed in an analytical syringe and subsequently added dropwise

Figure 1. Binary phase equilibrium of different oils and methanol.

to the two-phase system under stirring, until a homogeneous single liquid-phase system was obtained. After the experiment, the syringe with the remaining third substance was weighed again. The difference between both masses of the syringe is the mass of required third substance to get a homogeneous single phase. Selected experiments were repeated three times. The deviations from the average are (1.0 wt %. In addition, some experiments were repeated by a second person at different dates, with different samples of materials. The deviations between the two experiments were lower than 1%. 2.2.2. Methanolysis. The reaction was carried out in a pressure resistant stirred reactor with view glasses. The reactor has a volume of 57 cm3 and is thermostated by electrical heating cartridges. The components were stirred via a cell-integrated propeller stirrer. Oil and methanol were weighed in an analytical syringe and given into the cell. Subsequently, the cell was heated. After the temperature was reached, catalyst was added. During the experiments, the temperature was kept constant. After a certain contact time (10, 15, 30, 45, or 60 min), the reaction was stopped. Depending on the conversion, the product of the methanolysis is obtained either in one or two liquid phases. After the evaporation of excess methanol, two liquid phases were present in any case. The phases were analyzed by gas chromatography using a Hewlett-Packard 5890 chromatograph equipped with flame-ionization detectors on a SGE 12AQZ/HTS 03.1 column with helium as carrier gas. The temperature was raised from 80 °C/3 min ramped at 10 °C/min to 400 °C/10 min. Quantification was made using HP Chem Station Rev. 06.03 software. Peaks were identified by comparison with reference standards. 3. Results and Discussion 3.1. Binary Fluid Phase Equilibrium. The solubility of methanol in oil was tested for rape seed, sunflower, and mink oil. Figure 1shows the phase equilibrium of all analyzed oils with methanol in a temperature-composition plot. The vapor pressure of the reaction mixture above the boiling temperature of methanol (T ) 70 and 75 °C) was between 2 and 3 bar. The maximum solubility of oil in methanol is 2 wt % at temperatures of 70 °C (dots on the right-hand side). With increasing temperature, the weight fraction of oil dissolved in methanol increases slightly. Almost no difference can be observed between the oils. When methanol was added to an excess of oil, a higher solubility was determined. At 20 °C, the solubility of methanol in rape seed oil is approximately 7 wt % and

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Figure 2. Ternary diagram with rape seed oil, methyl ester, and methanol.

at 70 °C approximately 11 wt %. Solubility of methanol in sunflower and mink oil at elevated temperatures is somewhat lower than the solubility in rape seed oil. 3.2. Ternary Fluid Phase Equilibrium. All results are presented in ternary diagrams (concentrations given in weight percent). Below the dots for each temperature, two liquid phases coexist, while only one liquid phase occurs above the dots. 3.2.1. Phase Behavior during the Classical Methanolysis of Triglycerides. The classical methanolysis (catalyzed by sodium-methylate) starts as a two-phase system. The lower phase is rich in triglycerides, while the upper phase contains mainly methanol and the dissolved catalyst. During the reaction, the initial triglyceride phase disappears and methyl ester with good solubility in the methanol phase is formed. Parallel to 3 mol of methyl esters, 1 mol of glycerol is formed, which is almost insoluble in the methyl ester, thus forming a new and small lower phase. For understanding, designing, and optimizing of reaction and product recovery, the knowledge of the complex phase behavior is essential. Therefore, data for the ternary system methanol-triglycerides-methyl esters were measured. Figure 2 shows the results for the system rape seed oilmethanol-methyl ester. From Figure 2 it can be taken that single-phase conditions (area above the dots) depend on temperature and concentration. In general, the single-phase area is reached at lower concentrations of methyl esters when higher temperatures are applied. The influence of the concentration of methanol in the starting mixture is illustrated by means of the straight “mixing” lines in Figure 2. If the starting mixture at T ) 20 °C has a composition of 60 wt % oil and 40 wt % of methanol (O in Figure 2), more than 60 wt % of methyl esters are required before a liquid homogeneous system is reached. If the concentration of oil in the starting mixture is raised (0, 4open triangles), the amount of methyl ester that is needed to reach single phase conditions is decreased. (See intersections of the mixing lines with the binodal curves in Figure 2.) As mentioned above, glycerol is formed simultaneously to methyl esters. The reaction is carried out in excess of methanol. To investigate the thermodynamic boundaries for phase separation after complete conver-

Figure 3. Phase equilibrium of glycerol-methyl ester-methanol.

sion, the LLE equilibrium of the system methyl esterglycerol-methanol was measured. The ternary diagram of that system (Figure 3) shows that the separation of glycerol and methyl ester is temperature dependent. At a temperature T ) 20 °C, the two-phase region is larger than at a temperature of 60 °C. The tie-line in Figure 3 shows that a glycerol phase that is rich in methanol and a methyl ester phase that is poor in methanol are formed. The nonconverted methanol is mostly in the glycerol phase, while, at low temperatures, the methyl ester phase is almost pure. From the thermodynamic point of view, phase separation will be more effective, when the products are cooled. Of course, transport properties have also to be considered in defining suitable conditions for phase separation. In preliminary tests, it was found that different amines are completely miscible with either triglycerides or methyl esters or glycerol or methanol. So, it was concluded that the amines should increase the mutual solubility between methanol and triglycerides (reactants) and eventually also between the products. As several authors describe that multiphase, mass-transfer controlled reactions are strongly influenced by “removing” phase boundaries,9-11 the specific solvent properties of amines in combination with their catalytic activity could have the potential to accelerate the methanolysis.12 To quantify the solubility effect of amines, ternary systems were investigated. 3.2.2. Fluid Phase Equilibrium for Reactants. According to Bocoock,13 a reaction transesterification should perform faster in a homogeneous phase than in a heterogeneous (multiphase) system. To determine the influence of the oil on the amount of amines needed to obtain a homogeneous liquid system, rape seed and sunflower oil were studied. Two different catalysts, DMTMD and 4-MP, were tested. The experiments were made at temperatures between 20 and 80 °C and terminated very fast (approximately in 20 s). As will be shown below, the catalyzed reaction between oil and triglycerides takes some minutes to some 10 min. By performing the phase investigations very rapidly (in some 10 s), the influence of the proceeding reactions on the results of the phase investigations was minimized. The binary systems methanol-catalyst and oilcatalyst are completely miscible, while the binary system oil-methanol is partially miscible. This binary

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Figure 7. Ternary diagram of glycerol, methyl ester, and DMTMD as catalyst. Figure 4. Phase equilibrium of rape seed oil and methanol with DMTMD as catalyst.

Figure 5. Phase equilibrium of sunflower oil and methanol with DMTMD as catalyst.

Figure 6. Phase equilibrium of rape seed oil and methanol with 4-MP as catalyst.

phase behavior is shown on the sides of the triangles in Figure 4-6. In Figure 4, the phase behavior of reactants (rape seed oil and methanol) in the presence of DMTMD is shown. In the shaded gray region (see Figure 4; T ) 20 °C),

the substances form two liquid phases. When the concentration of amine exceeds a certain value (indicated by the dots), a homogeneous mixture of methanol, oil, and amine is obtained. When the ternary system contains more methanol than oil, less amine is needed to attain homogeneous conditions. Less amine is also needed at higher temperature. Similar results were obtained with sunflower oil. The difference between oil is of less significance. At the same temperature and composition, almost the same amount of catalyst is needed. That behavior was already expected from the low difference in solubility between both oils and MeOH. When 4-MP was used as amine, lower mass concentrations are needed to attain homogeneous conditions at all investigated temperatures. 3.2.3. Fluid Phase Equilibrium for Products. The following ternary data were measured to determine the temperature dependency of the amount of amine that still allows phase separation of glycerol and methyl ester. The separation can only be achieved in the twophase region, located below the dots (Figure 7). The diagram of the system methyl ester-glycerolDMTMD (Figure 7) shows that the amount of catalyst needed to achieve phase separation is almost independent from temperature. At higher contents of methyl ester, phase separation between glycerol and methyl ester becomes more difficult at lower DMTMD concentrations. The amount of 4-MP that is needed to obtain one liquid phase is lower than the amount of DMTMD (Figure 8). When 62 wt % of methyl ester and 8 wt % of glycerol are mixed, 30 wt % of 4-MP are sufficient to render phase separation impossible. At similar concentrations of glycerol and methyl ester, the amount of DMTMD is approximately 5 wt % higher. 3.3. Methanolysis. Results of the methanolysis of rape seed oil, coconut oil, and frying fat will be presented. In Figure 9-13, time-composition plots of the esterification with DMTMD as catalyst and rape seed oil are shown at different methanol concentrations and temperatures. At a starting composition (mass ratio) of oil:MeOH: DMTMD ) 46:46:8, the triglycerides were almost completely converted (Figure 9). After a contact time of 45 min, there are approximately 2% of triglycerides left in the reaction mixture. Methyl esters form rather slowly. After 30 min, the amount of methyl ester has reached only 50%. Approximately 18% of diglycerides are present

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Figure 8. Ternary diagram of glycerol, methyl ester, and 4-MP as catalyst.

Figure 9. Methanolysis of rape seed oil catalyzed by DMTMD at T ) 100 °C and high mass concentration of methanol (oil:MeOH: DMTMD ) 46:46:8) corresponding to a molar ratio of oil:MeOH ) 1:25.2.

Figure 11. Methanolysis of rape seed oil catalyzed by DMTMD at T ) 65 °C and low mass concentration of methanol (oil:MeOH: DMTMD ) 77:14:9) corresponding to a molar ratio of oil:MeOH ) 1:4.5.

Figure 12. Methanolysis of rape seed oil catalyzed by DEA at T ) 100 °C (oil:MeOH:DEA ) 79:14:7) corresponding to a molar ratio of oil:MeOH ) 1:4.5.

Figure 13. Methanolysis of rape seed oil catalyzed by 4-MP at T ) 65 °C (oil:MeOH:4-MP ) 66:17:17) corresponding to a molar ratio of oil:MeOH ) 1:6.5. Figure 10. Methanolysis of rape seed oil catalyzed by DMTMD at T ) 100 °C and low mass concentration of methanol (oil:MeOH: DMTMD ) 77:14:9) corresponding to a molar ratio of oil:MeOH ) 1:4.5.

after 15 min, and with longer contact time they were converted further to monoglycerides and methyl esters. Figure 10 shows results of esterification at higher mass ratio between oil and methanol (lower methanol surplus). The triglycerides were converted almost as fast to methyl ester as in case of higher methanol surplus. After 45 min, almost no triglycerides are remaining. The maximum of methyl ester concentration was almost identical to that in the previous reaction. The end product contains a lower amount of monoglycerides and more diglycerides than those obtained at higher methanol surplus. It can also be observed that the amount of diglyceride in the case of lower surplus of methanol after 15 min contact time is higher than that at higher

methanol surplus. Higher methanol concentrations seem to favor the conversion from diglyceride to methyl ester. In addition to the methanol surplus, also the temperature of the reaction was varied (Figure 11). A comparison between Figures 10 and 11 shows only marginal differences in the final composition after 45 min. Furthermore, the curves are more or less identical. It can be concluded that the conversion is almost independent from temperature in the investigated range. This is an indication that the reaction is mass-transfer controlled. In general, it can be concluded that with respect to the formation of biodiesel, the above-described result is not very convincing, as the conversion to methyl ester is rather low. DMTMD seems to be suitable if partial glycerides are the desired product. Nevertheless, the aim of the present work is to generate methylesters (biodiesel) with high effectivity.

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Figure 14. Methanolysis of rape seed oil catalyzed by TMAH at T ) 65 °C (oil:MeOH:TMAH ) 72:25:3) corresponding to a molar ratio of oil:MeOH ) 1:8.7.

Therefore, further catalysts have been screened to achieve a higher yield of methyl esters. In Figures 1214, results are shown. The concentration plot of the products over contact time with 7 wt % of DEA in the starting mixture at T ) 100 °C is presented in Figure 12. After 15 min, the amount of triglycerides is still rather high (approximately 50%). After 45 min, there are still nonconverted tri-, di-, and monoglycerides existing. Higher conversion of rape seed oil is achieved, when the catalyst 4-MP is used (Figure 13). However, for achieving 60% of methyl ester, a rather high concentration of catalyst and longer reaction time are needed. The best result was achieved with TMAH as catalyst and a reaction temperature of 65 °C (Figure 14). As shown in Table 1, TMAH (25 wt %) is delivered as a solution in methanol. For the reaction, 13 wt % of that solution were applied. This corresponds to a concentration of the pure catalyst of only 3 wt % of TMAH in the starting mixture. After 15 min, all triglycerides were converted to methyl ester. In the product, no diglycerides are found and only a very small amount of monoglycerides was detected. With longer contact time, the concentration of monoglycerides can be further reduced below 2 wt %. The reaction mixture contains only catalyst, methyl ester, glycerol, very low concentrations of monoglycerides, and, of course, a surplus of nonconverted methanol, which can easily be removed by distillation.

faster at higher temperatures that this seems to overweigh the better purities at low temperatures. The binary and ternary data form the basis for further investigations on systems involving amines. The phase behaviors of such systems are used both for understanding the processes in the reactor and the product recovery section. It has been demonstrated that transesterification of the oils and fats is catalyzed by all tested liquid amines. The temperature and concentration of methanol are of less influence on the rate of formation of methyl ester. Higher concentration of catalyst causes triglycerides to be converted faster to methyl esters. If the system methanol-oil-catalyst forms a homogeneous liquid phase, mass transfer limitations between the partially miscible reactants methanol and oils will be overcome. Such systems were investigated for two catalysts (DMTMD and 4-MP). 4-MP is the better solvent. Single-phase conditions are reached at lower concentrations. As a result, this catalyst should be better for transesterification. However, the results of methanolysis indicate that higher conversions are achieved with DMTMD, which is a less effective solvent. As mentioned above, during the reaction a new phase is formed (glycerol). This has to be considered in the interpretation of the results of the methanolysis. The amines do not only act as solvents for the reactants, but also for the products. Shifting the chemical equilibrium to the right side is favored, if a solvent is used that has less solvent power for the glycerol and thus facilitates the formation of a separate phase. The highest conversion was achieved with TMAH as catalyst. Here, almost pure methyl esters have been achieved in one reaction stage in a rather short time. The phases separate rapidly (some seconds to minutes). Soap formation is not observed. These are considerable advantages over the classical methods where sodiumor potassium-based alkaline catalysts require a twostage operation with intermediate, time-consuming removal of the glycerol. In addition, the glycerol phase obtained after TMAH catalysis can be purified from the surplus of methanol and catalyst by a sequence of distillations. Washing with water can be avoided. The results have been used to design and operate a pilot plant with a capacity of approximately 1 t/h. For further information, see http://www.daka.dk/page73.asp.

4. Conclusions Acknowledgment Biodiesel is a renewable fuel from natural oils or fats and animal fats. Within the common biodiesel process, the oils or fats, which contain triglycerides, are transesterified with an excess of methanol in the presence of a catalyst. In this work, liquid amines were tested as new catalysts. Several fluid phase equilibria were investigated. The results for the binary system oil-methanol show that the solubility of methanol in oil reaches approximately 10 wt % at a temperature of 70 °C. The solubility of oil in methanol is much lower (2 wt %) at the same temperature. In addition, data on phase behavior in the system glycerol-methyl ester-methanol are provided, which is of importance to design the product purification. From the thermodynamic point of view, the phase diagrams indicate that higher purities of the two phases can be reached at lower temperatures. Nevertheless, in practice, it turned out that phase separation is so much

The results were obtained in the framework of the Daka-Fat Project. We are thankful for the financial support from the Project. Literature Cited (1) Bockey, D. Biodiesel production and marketing in Germany, The situation and perspective, 2002; http://www.ufop.de/2504.htm. (2) Connemann, J. Patent DE 4209779, 1993. (3) Dittmar, T.; Dimmig, T.; Ondruschka, B.; Heyn, B.; Haupt, J.; Lauterbach, M. Herstellung von Fettsa¨uremethylestern aus Rapso¨l und Altfette im diskontinuierlichen Betrieb. Chem.-Ing.Tech. 2003, 75, 595-601. (4) Abigor, R. D.; Uadia, P. O.; Foglia, T. A.; Haas, M. J.; Jones, K. C.; Okpefa, E.; Obibuzor, J. U.; Bafor, M. E. Lipase-catalysed production of biodiesel fuel from some Nigerian lauric oils. Biochem. Soc. 2000, 28, 979-981. (5) Suppes, G. J.; Dasari, M. A.; Doskocil, E. J.; Mankidy, P. J.; Goff, M. J. Transesterification of soybean oil with zeolite and metal catalysts. Appl. Catal., A 2003, 257, 213-223.

Ind. Eng. Chem. Res., Vol. 44, No. 25, 2005 9541 (6) Gryglewicz, S. Rapeseed oil methyl esters preparation using heterogeneous catalysts. Bioresour. Technol. 1999, 70, 249-253. (7) Warabi, Y.; Kusdiana, D.; Saka, S. Reactivity of triglycerides and fatty acids of rapeseed oil in supercritical alcohols. Bioresour. Technol. 2003, 92, 307-310. (8) Peter, S.; Ganswindt, R.; Neuner, H.-P.; Weidner, E. Alcoholysis of triacylglycerols by heterogeneous catalysis. Eur. J. Lipid Sci. Technol. 2002, 104, 324-330. (9) Gru¨n, A.; Wittka, F.; Kunze, E. Zur Kenntnis der Alkoholyse. Chem. Umsch. 1917, 24, 15-20. (10) Ha¨rro¨d, M.; Møller, P. Hydrogenation of Fats and Oils at Supercritical Conditions. High Pressure Chem. Eng. Proceedings of the International Symposium, Zurich, Switzerland, Elsevier Science: Amsterdam, 1996; pp 43-48. (11) Weidner, E.; Brake, C.; Richter, D. Thermo- and fluid dynamic aspects of the hydrogenation of triglycerides and esters

in the presence of supercritical fluids. In Supercritical Fluids as Solvents and Reaction Medium; Brunner, E., Ed., 2004; http://www.elsevier.com/wps/find/bookdescription.cws•home/ 703482/description#description. (12) Peter, S.; Drescher, M.; Ko¨nig, W.; Weidner, E. Deacidification of oils and fats of biological origin by aqueous solutions of tertiary amines. OCL-MONTROUGE 2001, 8, 53-56. (13) Boocock, D. G. B.; Konar, S. K.; Sidi, H. Phase diagrams for oil/methanol/ ether mixture. J. Am. Oil Chem. Soc. 1996, 73, 1247-1251.

Received for review February 25, 2005 Revised manuscript received May 17, 2005 Accepted May 18, 2005 IE050252E