SK16562001A3 - Process for treating methyl esters of higher fatty acids - Google Patents

Abstract

Methylesters of higher fatty acids are prepared by acid catalytic esterification, so that higher fatty acids and/or mixture of their methylesters with an acid number 40 to 200 mg KOH/g are mixed with methanol at an increased temperature in the molar ratio free fatty acid:methanol 1 : 2 to 1 : 10, whereby the acid number 2 to 20 mg KOH/g is achieved, methanol is removed from the reaction mixture and water and the mixture is mixed with glycerol phase in the weight ratio reaction mixture:glycerol phase 1 : 0.05 to 1 : 0.3 and after sedimentation the glycerol layer with higher density is separated from the methylester layer with lower density.

Description

Process for the preparation of methyl esters of higher fatty acids

The invention relates to a process for the preparation of higher fatty acid methyl esters from higher fatty acids and / or from a mixture of their methyl esters by acid-catalyzed esterification with methanol. Higher fatty acid methyl esters are used as an alternative fuel or as a component thereof in diesel engines.

BACKGROUND OF THE INVENTION

According to the hitherto known processes for the preparation of methyl esters of higher fatty acids, the alkali catalysed transesterification of vegetable oils or animal fats with methanol is most used. On the other hand, there are a number of free fatty acid sources useful for preparing the methyl esters by direct esterification with methanol acid catalyzed esterification. These processes are made difficult by the fact that esterification produces water, the presence of which in the reaction mixture prevents the high conversion of the free acids into the methyl esters. The method of distilling off water in the form of an azeotropic mixture in the case of methanol cannot be used since methanol and water do not form an azeotrope. Procedures with the addition of an additional component to create a thematic azeotrope are complicated and poorly effective. Therefore, the known processes utilize high molar excesses of methanol relative to the free acids at concurrently high concentrations of acid catalysts. Despite the large excesses of methanol and high catalyst concentrations, the low acid value of the final methyl esters cannot be achieved.

SUMMARY OF THE INVENTION

These disadvantages are overcome by the process according to the invention, which is based on the fact that higher fatty acids and / or a mixture of their methyl esters with an acid number of 50 to 200 mg KOH / g are mixed with methanol at elevated temperature in a free fatty acid: methanol ratio of 1: 2 to 2. 1:10, while reaching an acid number of 2 to 20 mg KOH / g, remove methanol and water from the reaction mixture and mix the mixture with the glycerol phase in a weight ratio of the reaction mixture: glycerol phase 1: 0.05 to 1: 0.30 and after sedimentation, the higher density glycerol layer is separated from the lower density methyl ester layer.

The process of the invention has several advantages. First of all, the product is methyl esters with an acid number below 0.5 mg KOH / g, which value is required for alternative diesel fuel. The molar ratio of acids to methanol is favorably low so that the amount of methanol to be regenerated is reduced. In addition, a relatively low concentration of acid catalyst is used without adversely affecting the double bonds of the unsaturated acyls present. The process utilizes a glycerol phase, which is formed as a by-product in the production of methyl esters of higher fatty acids by alkaline catalyzed transesterification of natural acylglycerols with methanol, for example according to the method described in U.S. Patent No. 277,860. The methyl esters contain alkali components in the form of hydroxides, methoxides or carbonates, with the free fatty acids forming the corresponding alkaline sodium or potassium soaps which pass from the methyl ester phase to the glycerol phase. Fatty acids can be readily regenerated from the glycerol phase after decomposition with a strong mineral acid such as hydrochloric acid. Upon such decomposition, they form an organic layer over the glycerol layer containing free higher fatty acids and a mixture of their methyl esters. It is this organic layer, as a mixture of free higher fatty acids and methyl esters of higher fatty acids, which is formed even after decomposition of the glycerol phase from the production of methyl esters by transesterification, is the focus of its complete conversion to methyl esters, and the invention is particularly concerned. Thus, unreacted acids are not lost during esterification and are reusable in repeated operations. In some cases, the alkaline reserve of the glycerol phase used for the extraction may not be sufficient, moreover, it must be accepted that the reaction between the alkali and the free fatty acids does not proceed completely by stoichiometry. Therefore, the glycerol phase is fortified with an alkali, for example in the form of a concentrated solution of alkaline lye KOH or NaOH in methanol. The alkaline liquor fortification can also advantageously be carried out by adding the required amount of alkali in the form of a concentrated solution of alkali in methanol to the system of the treated reaction mixture and the glycerol phase prior to extraction. The amount of lye to be fortified is indicatively determined by the acid number of the crude methyl esters which need to be deoxygenated by the glycerol phase.

The higher fatty acids and / or the mixture of their methyl esters with an acid number of 40 to 200 mg KOH / g are mixed with methanol in a molar ratio of free acid: methanol from 1: 2 to 1.10 and with an acid catalyst of 0.5 to 3 wt. relative to the non-alcoholic reactant. As the catalyst, p-toluenesulfonic acid, phosphoric acid, methanolic HCl and the like are used. The reaction mixture is allowed to react under stirring at 60 ° C to about 2 ° C for about 2 to 8 hours. During this time, the acid number of the reaction mixture drops to 2 to 20 mg KOH / g. The reaction mixture is then evaporated to remove unreacted methanol and reaction water to give a modified reaction mixture. This conditioned reaction mixture is mixed at 20 to 80 ° C with the glycerol phase obtained from the alkaline catalyzed transesterification of vegetable oils or animal fats with methanol containing glycerol, methyl esters, methanol, alkaline sodium or potassium soaps according to the alkali catalyst used and also the free alkali in the in the form of hydroxides, methoxides or carbonates. The weight ratio of the adjusted reaction mixture: glycerol phase ranges from 1: 0.05 to 1: 0.30. 0.4 to 4.0 wt.% Are added to the conditioned reaction mixture and glycerol phase prior to extraction. alkaline lye with respect to the weight of the treated reaction mixture, usually in the form of a concentrated solution of potassium hydroxide in methanol. The system is then vigorously stirred for typically 5 to 20 minutes at 20 to 80 ° C. After vigorous stirring, the system is allowed to settle for sedimentation. Unreacted higher fatty acids will form alkali soaps with the alkali, which will pass into the heavier glycerol layer, and neutral methyl esters with an acid number of typically 0.2-0.4 mg KOH / g will form a lighter methyl ester layer. The methyl esters thus prepared are dark after the action of the acid catalyst. After suitable treatment, for example, preferably after distillation in a film vacuum evaporator, they achieve a light yellow to light green color.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

300 g of a mixture of higher fatty acids and their methyl esters, obtained from the decomposition of the glycerol phase from the alkaline catalyzed transesterification of rapeseed oil with methanol and having an acid number of 71 mg KOH / g, were mixed with 49 g of methanol. , and 6.0 g of p-toluenesulfonic acid, 2.0 wt. of the catalyst relative to the non-alcoholic component. The mixture was stirred and refluxed for 75 hours at 75-80 ° C. Then methanol and reaction water were distilled off from the reaction mixture and the mixture was vacuum dried at 110 ° C and pressure.

2.6 kPa. After this operation, a modified reaction mixture was obtained with an acid number of

10.2 mg KOH / g. 100 g of the treated reaction mixture were mixed with 20 g of glycerol phase from an alkali catalyzed transesterification of rapeseed oil with methanol and 2.5 g of KOH in 7 g of methanol. The amount of alkali used is 2.5% by weight. relative to the weight of the treated reaction mixture.

The system was vigorously stirred at 65 ° C. After sedimentation of the layers, 70 g of the methyl ester layer was obtained with an acid number of 0.35 mg KOH / g.

Example 2

320 g of a mixture of higher fatty acids and their methyl esters with an acid number of 71 mg KOH / g were mixed with 79 g of methanol, meaning a 1: 6 molar ratio of acid: methanol, and 3.2 g of p-toluenesulfonic acid, representing 1 % by weight of the non-alcoholic reactant. The mixture was refluxed at 72-78 ° C for 7 hours, then unreacted methanol and reaction water were distilled off, and the mixture was vacuum dried at 110 ° C and 2.6 kPa. The acid number of the treated reaction mixture was 5.4 mg KOH / g. To 100 g of the treated reaction mixture was added 20 g of glycerol phase from the transesterification of rapeseed oil and 0.7 g of KOH dissolved in 2.2 g of methanol. The system, after vigorous stirring at 45 ° C and subsequent sedimentation, gave a 88 g methyl ester layer with an acid number of 0.40 mg KOH / g.

Industrial usability

The invention is useful in the preparation of methyl esters of higher fatty acids in the treatment of a mixture of higher fatty acids and their methyl esters obtained after decomposition of the glycerol phase from the alkaline catalyzed transesterification of vegetable oils and animal fats. . This completes the free fatty acid recycle and increases the economic efficiency of producing alternative fuels for renewable diesel engines.

Claims (4)

PATENT CLAIMS A process for the preparation of methyl esters of higher fatty acids from higher fatty acids and / or a mixture of their methyl esters by acid-catalyzed esterification with methanol, characterized in that the free fatty acids and / or a mixture of their methyl esters with an acid number of 40-200 mg KOH / g are mixed with methanol in a molar ratio of free fatty acid: methanol from 1: 2 to 1:10, after reaching an acid number of 2 to 20 mg KOH / g, remove methanol and water from the reaction mixture and mix the treated reaction mixture with the glycerol phase by weight ratio adjusted reaction mixture: glycerol phase from 1: 0.05 to 1: 0.30 and after sedimentation, the higher density glycerol layer is separated from the lower density methyl ester layer. 2. A process for the preparation of methyl esters of higher fatty acids according to claim 1, characterized in that an alkaline lye is added to the mixture of the treated reaction mixture and the glycerol phase in an amount of 0.4 to 4.0% by weight. based on the weight of the treated reaction mixture. 3. A process for the preparation of higher fatty acid methyl esters according to Claims 1 and 2, characterized in that the mixing of methanol with higher fatty acids and / or a mixture of their methyl esters takes place at a temperature of 60 to 90 [deg.] C. 4. A process for the preparation of methyl esters of higher fatty acids according to claims 1 to 3, characterized in that mixing of the treated reaction mixture with the glycerol phase and the alkaline liquor takes place at a temperature of 20 to 80 ° C.