Classifications

• • C—CHEMISTRY; METALLURGY
  • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
  • C11C—FATTY ACIDS FROM FATS, OILS OR WAXES; CANDLES; FATS, OILS OR FATTY ACIDS BY CHEMICAL MODIFICATION OF FATS, OILS, OR FATTY ACIDS OBTAINED THEREFROM
  • C11C3/00—Fats, oils, or fatty acids by chemical modification of fats, oils, or fatty acids obtained therefrom
  • C11C3/003—Fats, oils, or fatty acids by chemical modification of fats, oils, or fatty acids obtained therefrom by esterification of fatty acids with alcohols
• • C—CHEMISTRY; METALLURGY
  • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
  • C11C—FATTY ACIDS FROM FATS, OILS OR WAXES; CANDLES; FATS, OILS OR FATTY ACIDS BY CHEMICAL MODIFICATION OF FATS, OILS, OR FATTY ACIDS OBTAINED THEREFROM
  • C11C3/00—Fats, oils, or fatty acids by chemical modification of fats, oils, or fatty acids obtained therefrom
  • C11C3/04—Fats, oils, or fatty acids by chemical modification of fats, oils, or fatty acids obtained therefrom by esterification of fats or fatty oils

Definitions

• the invention relates to a process for the preparation of fatty acid methyl ester mixtures by catalytic transesterification from natural fats and oils which contain free fatty acids.
• Fatty acid methyl esters are of great technical importance as a starting material for the production of fatty alcohols and other oleochemical products such as ester sulfonates, fatty acid alkanolamides and soaps.
• the industrial production of the fatty acid methyl esters takes place predominantly by catalytic transesterification (alcoholysis) of fatty acid triglyceride mixtures as they are present in the fats and oils of vegetable and animal origin.
• fats and oils can be transesterified at 25 to 100 ° C. with a 0.5 to 1.0 molar excess of alcohol under normal pressure to give the corresponding fatty acid ester mixtures.
• a corresponding method is described as the first stage of soap production in US Pat. No. 2,360,844. This alkali-catalyzed, pressure-free transesterification can be carried out without problems as long as fats and oils are used which are largely anhydrous and whose free fatty acid content is below 0.5% by weight (corresponding to an acid number of about 1).
• fats and oils with a higher content of free fatty acids in the presence of alkali or zinc catalysts at 240 ° C. under a pressure of about 100 bar with a 7- to 8-molar excess of methanol can be added to the corresponding ones Fatty acid methyl esters are transesterified (Ullmann, Encyclopedia of Industrial Chemistry, 4th edition, Volume 11 (1976), page 432).
• the unpressurized transesterification is characterized by a significantly lower methanol requirement and - because of the lower reaction temperatures - by a lower energy consumption.
• the transesterification works under normal pressure without expensive pressure reactors. Due to the fact that there are almost always larger amounts of water and fatty acids in technical fats and oils, the unpressurized transesterification results in drying and a reduction in the acid number - for example by prior conversion of the free fatty acids into the corresponding alkyl or glycerol esters in the course of a pre-esterification reaction - in advance.
• the pre-esterification of the acidic fats and oils can be carried out in the presence of alkaline catalysts at 240 ° C and 20 bar (Ullmann, Encyclopedia of Industrial Chemistry, 4th edition, Volume 11 (1976), page 432). This type of pre-esterification with methanol in turn requires the use of expensive pressure reactors.
• the invention had for its object to facilitate the production of fatty acid methyl esters from such triglyceride starting materials that contain large amounts of water and free fatty acids.
• both process stages should be able to be carried out at comparatively low temperatures and without the use of pressure reactors.
• the excess alcohol required for the transesterification should be kept as low as possible, taking into account the necessary processing and cleaning steps.
• it should enable the production of fatty acid methyl esters in an energy-saving and cost-effective manner, especially with starting materials of the type obtained as fats and oils of vegetable or animal origin.
• stage a) of the process according to the invention the proportion of free fatty acids present in the triglyceride mixtures of the starting material is esterified with excess methanol in the presence of acidic esterification catalysts.
• comparatively mild reaction conditions are chosen so that a transesterification of the triglycerides with methanol does not take place or does not take place to a significant extent.
• the ratio between triglyceride and methanol is expediently chosen so that on the one hand there is a clear excess of methanol over the free acid to be esterified, and on the other hand a clean separation into an oil and a methanol phase is ensured at the end of the reaction.
• 20 to 50 parts by volume of methanol are normally used per 100 parts by volume of starting material.
• stage a The pre-esterification of stage a) is usually carried out at normal pressure.
• Working with low overpressure can be advantageous in various cases. In this case, however, only pressures up to 5 bar come into consideration, for which no special pressure reactors are required.
• all acidic, non-volatile esterification catalysts are suitable as catalysts for stage a), for example the corresponding systems based on Lewis acids, low-volatility inorganic acids and their acidic partial esters and heteropolyacids.
• Alkyl, aryl or alkarylsulfonic acids such as e.g. Methanesulfonic acid, naphthalenesulfonic acid and dodecylbenzenesulfonic acid.
• Sulfuric acid and glycerol monosulfuric acid may be mentioned as an example of low volatile inorganic acids and their partial esters.
• Suitable heteropolyacids are the tungstic and molybdate phosphoric acids. These catalysts are generally used in amounts of 0.5 to 5 parts by weight per 100 parts by weight of starting material.
• the reactants were heated together with the catalyst to the intended reaction temperature with vigorous stirring and then held at this temperature until the acid number of the oil phase had dropped to the desired value.
• the acid number of the oil phase is preferably reduced to values below 1 in step a).
• Process step a) can be carried out batchwise or continuously.
• the components alcohol and oil can be carried out in cocurrent and in countercurrent.
• reaction mixture is left at temperatures between 40 and 60 ° C. without further stirring.
• a separation into an oil and a methanol phase occurs.
• the two liquid phases are separated in a known manner.
• the methanol phase which contains most of the water of reaction and practically all of the amount of catalyst, is worked up by distillation to recover the catalyst and the methanol.
• the catalyst remains in the distillation residue, which can be used again as a catalyst additive in stage a) of the process according to the invention without further purification steps.
• the oil phase resulting from step a) is mixed with the intended amount of glycerol-methanol mixture and the mixture obtained is stirred vigorously for 1 to 5 minutes. The mixture is then left to stand still until phase separation and the extracted oil phase is separated off. In order to separate the water of reaction and catalyst residues still present as far as possible, it has proven to be advantageous not to carry out the entire extraction in stage b) at normal temperature, but at 40 to 60.degree.
• Step b) can be carried out in batch mode in a simple stirred tank.
• erfi nd ungsgemä- SEN method are realized in a stirred tank cascade or in a equipped with static mixing elements column. It is also possible to continuously pass the oil phase and the glycerol-methanol mixture in countercurrent through an extraction column.
• the deacidified and largely anhydrous triglycerides are subjected to the pressure-free alkali-catalyzed transesterification with methanol in a manner known per se.
• the following conditions are expediently observed:
• the transesterification is carried out with essentially anhydrous methanol.
• the methanol is used in a 50 to 150 percent excess over the stoichiometric amount required for the transesterification.
• Alkali metal hydroxides, in particular sodium and potassium hydroxide, and alkali metal alcoholates, in particular sodium methylate, are particularly suitable as catalysts.
• the catalysts are used in amounts of 0.05 to 0.2 parts by weight per 100 parts by weight of triglyceride.
• the mixture of triglyceride (oil phase), methanol and catalyst is heated to the intended reaction temperature with stirring.
• the transesterification reaction takes place at sufficient speed even at 25 to 30 ° C. In general, however, it is preferred to carry out the transesterification reaction at a temperature of 5 0 to 100 ° C, in particular at reflux temperature.
• the reaction mixture is allowed to stand without further stirring until the phases have separated.
• the phases are then separated in a known manner.
• the glycerol phase containing methanol is generally used as an extracting agent in stage b) of the process according to the invention before it is worked up to glycerol and methanol in a manner known per se.
• the methyl ester phase is further processed in a manner known per se via appropriate purification and distillation steps to give the desired starting materials for organic syntheses.
• the separated oil phase (204 kg; acid number 0.8; water content 0.34 percent by weight; methanol content 14.1 percent by weight) was 40.8 kg glycerol-methanol mixture from the alkali-catalyzed unpressurized transesterification (59, 0 percent by weight glycerol ; 28 , 1 percent by weight methanol; 12.8 percent by weight fat derivatives; 0.1 percent by weight free alkali) added.
• the two-phase mixture was stirred for 10 minutes. After the stirring process had ended, the two phases were clearly separated in a few minutes. After draining off the glycerol phase, 196 kg of oil phase remained (acid number 0.4; water content 0.08 percent by weight; methanol content 10.6 percent by weight).
• the extracted oil phase was refluxed with 35 liters (27.7 kg) of methanol and 0.3 kg of sodium methylate as the transesterification catalyst with stirring for 30 minutes.
• the reaction mixture was then cooled to 50 ° C.
• the methanol-containing glycerol phase which separated out was separated off.
• the remaining crude coconut fatty acid methyl ester (188 kg) contained 0.4 weight percent bound glycerol, 0.02 weight percent water and 8.1 weight percent methanol; its acid number was 0.04.
• Example 2 200 liters (174 kg) of coconut oil (acid number 15.1) were reacted with 60 liters (47.4 kg) of methanol in the presence of 1.6 kg of p-toluenesulfonic acid with stirring at 65 ° C.
• the oil phase obtained (204 kg; acid number 0.8; water content 0.34 percent by weight) was fed directly to the unpressurized transesterification. To this end, the oil phase was heated to reflux with 36.51 (288 kg) of methanol and 0.3 kg of Na methylate with stirring for 30 minutes. After cooling to 50 ° C., the lower phase containing methanol and glycerol was separated off.
• the crude coconut fatty acid methyl ester (18 6 kg) contained 2.3 weight percent bound glycerol, 0.09 weight percent water and 7.9 weight percent methanol; its acid number was 0.04.
• This example shows that the catalyst used can be easily recovered from the methanol phase by pre-esterification by distilling off the methanol and the water of reaction. When the catalyst is reused, there is no appreciable impairment in activity.
• Example 2 The methanol phase obtained in Example 2 was again evaporated and the residue was used for a further pre-esterification. Almost the same results as in Example 2 were obtained.
• the following analytical values were determined for the oil phase: 0.33 percent by weight water; 15.5 weight percent methanol; Acid number 0.9.
• the separated oil phase (204 kg) was at 50 to 55 ° C with 40.8 kg glycerol-methanol mixture from the alkali-catalyzed unpressurized transesterification (55.0 weight percent glycerol; 33.7 weight percent methanol; 11.2 weight percent fat derivatives; 0, 1 weight percent free alkali) stirred for 10 minutes. After renewed phase separation, the oil phase had an acid number of 0.5.
• the oil phase (195 kg) was transesterified at 65 ° C. with the addition of 35 l (27.7 kg) of methanol and 0.3 kg of sodium methylate.
• the raw coconut fatty acid methyl ester obtained (185 kg) contained 0.5 percent by weight glycerol, 0.02 percent by weight water and 7.6 percent by weight methanol; its acid number was 0.04.
• Example 2 Analogously to Example 1, 200 liters (174 kg) of beef tallow (acid number 21) were pre-esterified with 60 liters (47.4 kg) of methanol in the presence of 1.6 kg of p-toluenesulfonic acid. The oil phase separated from the reaction mixture was extracted with 40.8 kg of glycerol-methanol mixture from a previous alkali-catalyzed pressure-free transesterification. The pre-esterified tallow had an acid number of 0.6 after separation from the glycerol-methanol phase.
• Example 2 Analogously to Example 1, 200 liters (174 kg) of coconut oil (acid number 15.1) were reacted with 60 liters (47.4 kg) of methanol in the presence of 0.4 kg of 98% strength by weight sulfuric acid at 65 ° C. for 15 minutes.
• the separated oil phase (206 kg; acid number 0.7; water content of 0.31 percent by weight; methanol content 11.3 weight percent) was added at 50 - 55 ° C 41.2 kg of glycerol-methanol mixture from the alkali-transesterification (57, 1 percent by weight Glycerin; 33.0 weight percent methanol; 9.8 weight percent fat derivatives; 0.1 weight percent free alkali) stirred for 10 minutes. After phase separation, 0.13% by weight of water and 11.6% by weight of methanol were found in the oil phase; the acid number was 0.2.
• the oil phase (197 kg) was transesterified at 65 ° C. with the addition of 35 l (27.7 kg) of methanol and 0.3 kg of sodium methylate.
• the thus obtained Kokosfettchuremethylester (188 kg) contained 0.5 weight percent glycerol, 0.2 percent by weight water, and 6, 1 weight percent methanol; the acid number was 0.04.
• Example 6 was repeated with the modification that the oil phase obtained from the pre-esterification was fed directly to the alkali-catalyzed unpressurized transesterification without intermediate extraction with a glycerol-methanol mixture. In this procedure, a Obtained coconut fatty acid methyl ester containing 2 percent by weight bound glycerin.
• Example 6 shows that the degree of conversion in the transesterification of the pre-esterified oil can be considerably improved if the pre-esterified oil is extracted with a glycerol-methanol mixture before the transesterification.

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• 1984
  • 1984-12-08 DE DE19843444893 patent/DE3444893A1/de not_active Withdrawn
• 1985
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  • 1985-11-30 EP EP85115217A patent/EP0184740B1/fr not_active Expired - Lifetime
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