CS277264B6 - Process for producing alkyl esters - Google Patents

Abstract

A method of producing alkyl esters by reacting triacylglycerols with a monohydric alcohol in the presence of an alkaline catalyst, the essence of which is that sodium, potassium, calcium, magnesium or aluminum salts and/or dihydroxypropyl esters and/or hydroxypropyl diesters of aliphatic carboxylic acids with a number of carbon atoms of 8 to 22 are added to the reaction mixture as emulsifiers. The advantage of this process is that the emulsifier homogenizes the reaction mixture, so that a less powerful mixer and shorter time are sufficient to achieve the desired conversion of triacylglycerols.

Description

The invention relates to a process for the preparation of alkyl esters by reacting triacylglycerols with a monohydric alcohol in the presence of an alkaline catalyst.

Alkyl esters, especially methyl esters of aliphatic acids, have now become a key raw material in the field of oleochemistry. Methyl esters are mainly used for the production of fatty alcohols, which are further chemically modified either by oxyethylenation to nonionic surfactants or by oxyethylenation and subsequent sulfation to anionic surfactants. Methyl esters of saturated fatty acids (e.g. stearic acid) can be sulfonated and the resulting product, i.e. alpha-sulfoesters of aliphatic carboxylic acids, can be applied to powder detergents as an anionic surfactant. Thus, alpha-sulphoesters can be used as a substitute for alkylbenzenesulfonates, and alpha-sulphoesters, in contrast to alkylbenzenesulfonates, are well biodegradable. In addition, methyl esters have recently been used as an environmentally friendly fuel for diesel engines.

Alkyl esters of aliphatic carboxylic acids, i.e. fatty acid esters, can be prepared either by esterification of the acids with an alcohol under acid catalysis or by transesterification. At present, the transesterification of triacylglycerols is clearly preferred, since in this way the ester can be obtained directly in one step, whereas in esterification the triacylglycerol must first be cleaved into fatty acids and distilled and then esterified.

Transesterification of triacylglycerols with a monohydric alcohol such as methanol is usually performed as follows. A mixture of triacylglycerols and methanol with a small amount of alkaline catalyst, usually sodium methoxide, sodium hydroxide, potassium carbonate, or magnesium or calcium oxide, is heated under reflux for 1 to 6 hours. The reaction mixture initially consists of two phases, upper methanolic and lower triacylglycerol (oil). . After some time with stirring, the reaction begins, and when the desired conversion of triacylglycerols to methyl ester is achieved, the stirrer is turned off, and the reaction mixture is divided into two phases, the lower glycerol and the upper ester. The disadvantage of this simple procedure is that, especially from the beginning of the reaction, intensive stirring is necessary so that the area of the interfacial interface is as large as possible and the reaction has a reasonable rate.

The above disadvantages are solved by a process for the preparation of alkyl esters by reacting triacylglycerols with a monohydric alcohol in the presence of an alkaline catalyst, the essence of which is added 0.01 to 4% by weight of sodium, potassium, calcium, magnesium or aluminum salt and / or dihydroxypropyl ester and / or and hydroxypropyl diester of an aliphatic carboxylic acid having 8 to 22 carbon atoms.

The advantage of the above process is that the above additives act as emulsifiers, so that the reaction mixture is emulsified from the beginning, so that a powerful stirrer is not necessary and, in addition, a shorter time is sufficient to achieve the desired conversion of triacylglycerols. Table 1 compares the time course of the conversion of triacylglycerol to ester without emulsifier and in the presence of the emulsifier according to the invention. Obviously, to achieve a balanced composition

reaction mixture (i.e. 97%) of ester is required under the conditions of Example 1 without emulsifier 6 h in the presence of emulsifier only 4 h, according to Example 2 it is 4 h versus 2 h. in Example 3, which describes a continuous device the conversion to ester is compared under the same conditions without and with emulsifier it is 95 compared to 97%. In addition to the fact that it is possible to increase the performance of the production unit according to the amount of emulsifier added by (80 to 100%), the ester prepared in this way, especially unsaturated acids, has better parameters because the reaction takes less time and therefore undesired side degradations cannot occur. in particular polymerization reactions. Since the glycerol phase contains the fatty acid salt formed from the catalyst and the monoacyl- and diacylglycerol, i.e. the dihydroxypropyl ester and the hydroxydipropyl ester of the fatty acid, the glycerol phase from the previous reaction can also be used for emulsification.

All percentages given in the text are% by weight. The production method according to the invention is illustrated in the following examples, which, however, do not limit the scope of the invention in any way.

Table 1

Time dependence of conversion of triacylglycerol to methyl ester

time (h) Example 1 emulsifier content Example 2 emulsifier content 0 0.02% 0 0.1% 0 0 0. 0 0 1 88 90 91 94 2 91 93 94 97 3 93 95 96 97 4 95 97 97 97 5 96 97 97 97 6 97 97 97 97

Example 1

^{9.52 kg (14 mol) of coconut oil (Cat. No. 0.4 mg KOH.g -1} ) was poured into a 25 L reactor equipped with a reflux condenser, mechanical stirrer, hopper, temperature control and heating jacket.

2.69 kg (84 mol) of methanol and stirring and heating switched on, and then 95 g of potassium carbonate and 2.4 g of stearic acid dihydroxypropyl ester were added. After 4 h, stirring and heating were turned off, and the mixture was allowed to stand for 1 h. The glycerol phase was separated. After evaporation of the methanol, 9.38 kg (98% of theory) of an ester containing 98.99% of methyl ester were obtained.

0.91% monoacylglycerol

0.06% glycerol

0.04% soap (sodium carboxylic acid).

Example 2

12.47 kg (14 mol) of rapeseed oil (No. 0.6 mg KOH.g ^-1 ), 2.69 kg (84 mol) of methanol were poured into the reactor described in Example 1, stirring was switched on, heating and then 62 g of sodium hydroxide and 62 g of the glycerol phase from the previous reaction containing 25% sodium oleate, 5% dihydroxypropyl oleic acid ester, 1% hydroxypropyl oleic acid ester and 69% glycerol were added. After 2 h, stirring and heating were turned off and the mixture was allowed to stand for 1 h. The glycerol phase (of the above composition) was separated. Methanol was evaporated from the ester phase to give 12.2 kg (97%) of methyl ester containing:

98.91% methyl ester

0.95% monoacylglycerol

0.09% glycerol

0.05% soap (sodium carboxylic acid)

Example 3

12.47 kg (14 mol) of partially hydrogenated rapeseed oil (preheated to 75 ° C), 2 kg of methanol (preheated to 55 ° C), a solution of 62 g of methoxide were metered into an cascade of 3 stirred reactors (10 l each). of sodium in 0.7 kg of methanol (preheated to 55 ° C) and 0.5 kg of glycerol phase (preheated to 75 ° C - composition see Example 2) at 75 ° C. An exchanger is arranged downstream of the reactor, the reaction mixture is cooled, fed to a separator, the glycerol phase is separated from the ester, which has the following composition:

98.72% methyl ester

1.08% monoacylglycerol

0.14% glycerol

0.06% soap (sodium carboxylic acid)

Claims (1)

PATENT CLAIMS Process for the preparation of alkyl esters by reacting triacylglycerols with a monohydric alcohol in the presence of an alkaline catalyst, characterized in that 0.01 to 4% by weight of sodium, potassium, calcium, magnesium and / or aluminum salts and / or dihydroxypropyl ester and / or aliphatic hydroxypropyl ester are added to the reaction mixture. carboxylic acids having 8 to 22 carbon atoms.