SK155491A3 - Method of preparation of methylesters of higher aliphatic acids by preestherification of triacylglycerols - Google Patents

Abstract

Mixture methylesters of high aliphatic acids are prepared by preestherification of natural triacylglycerols creating the main component of vegetable or animal oils and greases by methanol in presence of alkaline catalyst. Methanol with dissolved alkaline catalyst is added into triacylglycerole in two degrees, in first degree with hole ratio acyl triacylglycerol: :methanol 1:0,9 to 1:1,1 and in second degree with ratio 1:0,3 to 1:0,5 reacting mixture is in every degree shortly intensive mixed and next holded for 105 to 240 minutes at temperature 50 to 70 degrees of Celsius. After first and second degree is precipitated glycerol layer separed from reacting mixture. Mixture methylesthers of higher aliphatic acids are directly applicable as fuel for diesel engines or as raw material for oleochemie.

Description

Technical field

The invention relates to a process for the preparation of mixed methyl esters of higher fatty acids by the transesterification of triacylglycerols of vegetable or animal oils and fats.

The state of the art

According to the known processes for the preparation of alkyl esters, in particular methyl esters of higher fatty acids, in the presence of basic catalysts in the form of alkali metal alcoholates, hydroxides, oxides or carbonates, the aliphatic lower alcohol, especially methanol, is contacted with the dissolved alkali catalyst. oil, in particular rapeseed, sunflower, castor, palm and the like, optionally with ointment, tallow, fish oil and the like, at temperatures of 20 to 100 ° C. An excess of alcohol is used with an amount of 1.1 to 2 times the equimolar amount, which is preferably concentrated in the heavier glycerol phase and less in the lighter ester phase. The glycerol phase is separated, the excess alcohol from the ester phase is removed by vacuum distillation, the ester is washed several times with water to remove the catalyst, dried and filtered. The disadvantage of these processes is that, with a small excess of alcohol, the relatively low conversion of triacylglycerols to alkyl esters is about 70%, and on the other hand, at a higher excess, the cost of alcohol recovery is increased and the separation of the glycerol phase from the ester phase is more difficult. The amount of catalyst used is relatively high, although the catalyst concentrates predominantly in the glycerol phase, it also remains in the ester phase and must be removed therefrom, for example by washing with water. This operation results in stable emulsions and partial hydrolysis of the ester. The process described in Austrian Patent 386 2228 employs an increased amount of catalyst KOU of 1.3 to 1.7% by weight. with respect to the oil phase, the stoichiometric ratio of alcohol to triacylglycerols, the reaction is carried out at ambient temperature after briefly stirring the reaction mixture without further stirring, and an ion exchanger is used to remove the alkali from the ester phase. The disadvantage of this process is higher catalyst consumption and reduced conversion of triacylglycerols to methyl esters by about 80% due to the equimolar amount of alcohol only.

The process of U.S. Pat. No. 4,652,406 employs a two-step process, but in the first step an acid catalyst is used to esterify the free fatty acids, and in the second step an alkaline catalyst is used for the transesterification.

SUMMARY OF THE INVENTION

The process according to the invention is characterized in that a methanolic solution of alkaline hydroxide at a concentration of 2 to 5% is mixed with triacylglycerols in a molar ratio of acyl triacylglycerol: methanol of 1: 1.2 to 1: 1.6 in two stages so that in the first stage using a ratio of 1: 0.9 to 1: 1, and in a second stage a ratio of 1: 0.3 to 1: 0.5, while maintaining the reaction mixture at 50 to 70 ° C for both stages after intensive stirring for 5 to 15 minutes. The glycerol phase is separated from the reaction mixture for 105 to 240 minutes and after the first step, and the reaction mixture is treated with fresh methanolic alkali catalyst solution.

The process according to the invention has several advantages over the known processes for the preparation of alkyl esters. It uses a reduced catalyst content, 2 to 3 times lower, in addition to the most preferred catalyst, cheap NaOH is recommended. In addition to the economic effect, this catalyst means

has the further advantage that its solubility in the ester phase is substantially lower compared to the solubility of KOH. Its residual content in the ester phase is negligible and therefore no additional treatment of the ester in this direction is required, eliminating the need for ion exchangers or the disadvantageous operation of washing the esters with water. A two-stage addition of methanol with dissolved catalyst while depleting the glycerol layer after the first step provides an advantageous shift of equilibrium in the product formation direction, thereby achieving a high conversion of triacylglycerols to methyl esters of about 98%. The glycerol layer dissolves the methanol together with the catalyst, and as the reaction progresses, there is a methanol and catalyst deficiency in the mixed ester and triacylglycerol phases and the reaction is stopped. A second-stage addition of fresh methanol with the catalyst, while in the absence of the glycerol phase, brings about a recovery of the reaction and a further increase in conversion. Excess alcohol in the reaction system has little effect on the ester phase, the alcohol preferably dissolves in the glycerol phase and its residues from the ester phase are removed by a simple stripping operation. Unrefined vegetable and animal oils and fats with an acid number of up to 6 mg KOH / g can be used in the process of the invention.

Solution of an alkali hydroxide, preferably sodium hydroxide, NaOH, mol.

in methanol at a concentration of 2 to 5% is mixed with a vegetable oil, e.g. rapeseed, sunflower, rope and the like; animal fat or oil, for example, ointment, tallow, fish oil and the like, at a molar ratio of acyl triacylglycerol: methanol of 1: 0.9 to 1: 1.1, which at an average molar mass of triacylglycerol of 880 g / mol represents a triacylglycerol: methanol weight ratio 1: 0.098 to 1: 0.120, and after briefly vigorous stirring for 5 to 15 minutes, it is maintained at 50 to 70 ° C for 105 to 240 minutes. Then, the first-stage operation is terminated by removing the settled heavier glycerol phase from the reaction mixture. In the second step of the reaction, the mixed es, and pow- der triacylglycf.íroio _t-zej second phase of the methanol; with the catalyst in the same concentration as in the first step in the moles out. the ratio of acyl triacylglycerol: methanol 1: 0.3 to 1: 0.5; in a weight ratio of triacylglycerol: methanol of 1: 0.032 to 1: 0.054, and the reaction mixture is again stirred for 5 to 15 minutes and held at 50 to 70 ° C (105 to 240 minutes). After this time, the precipitated lower glycerol phase is drained and excess methanol is stripped off with air and collected on a low temperature cooler. The mixed methyl esters are pumped into a sedimentation tank, where it gradually settles out of the finely dispersed glyeerol flow along with the remainder of the alkaline catalyst which is precipitated from the ester phase due to the temperature drop and the removal of methanol as solvent. The total weight ratio of triacylglycerol: methanol used in both steps of the reaction is 1: 0.131 to 1: 0.375, and the proportion of NaOH catalyst used, based on the starting triacylglycerols, is 0.4 to 1.13% by weight.

The composition of the mixture of methyl esters resulting from the transesterification of triacylglycroles depends on the representation of the individual fatty acids in the triacylglycerols. In vegetable oils, unsaturated fatty acids predominate, in particular oleic (18 carbons, including double bond - 18: 1), linoleum (18: 2) and linolenic (18: 3), and palmitooleate (16: 1), myristol (14: 1), erucous (22: 1) and others. Saturated fatty acids such as stearic (18; 0), palmitic (16: 0), myristic (14: 0), lauric (12: 0), arachic (20: 0), behenic (22: 0) and others are in plant oils, while in animal oils their proportion is higher. For example, in a reduced rapeseed oil, erucic acid in the total amount of fatty acids, the individual acids contribute as follows: oleic about 60%, oleic 20%, linolenic 10, palmitic 4, stearic 1%.

Lard. contains about 24?. palmitic acid, 13 stearic acid, myristic, 40% oleic, 9 linoleic.

Examples of Rea-Ino. invention

Example 1

10.72 kg of unrefined rapeseed oil with an average molar mass of 880 g.mol with an acid number of 2.4 mg KOH / g was heated to 55 ° C and mixed with 1.09 kg of methanol in the first stage of the reaction, in which it was dissolved 46 g of NaOH catalyst, representing 4% by weight. % relative to methanol and 0.42 wt. with respect to oil. The molar ratio of acyl triacylglycerol: methanol is 1: 0.932. After the addition of methanol, the reaction mixture was stirred vigorously for 10 minutes and then kept at 55-60 ° C for 180 minutes. After this time, the lower glycerol layer of 1.33 kg was removed. The methyl ester content of the ester layer was determined by GLC and represented 68.7% by weight. In the second step of the reaction, 0.44 kg of methanol with dissolved 20 g of NaOH was added to the ester-oil phase, the mixture was stirred for 10 minutes and kept at 55-60 ° C for 180 minutes. The molar ratio of acyl triacylglycerol: methanol for the second step is 1: 0.376. The total weight of methanol used in the reaction was 1.53 kg, which means a molar ratio of acyl triacylglycerol: methanol of 1: 1.308, respectively. weight ratio tr'dcylglycerol: methanol 1: 0.142, total catalyst amount 0.6% w / w. with respect to triacylglycerols. After the glycerol phase settled, it was pumped off with a weight of 0.65 kg. The ester phase containing 0.9% methanol was stripped with air. 10.30 kg of mixed methyl esters with the following characteristics were obtained: methyl ester content 98.8% by weight, monoacylglycerols 0.9% by weight, diacylglycerols 0.3% by weight, flash point in a closed crucible 8 ° C, kinematic viscosity at 20 ° C 7.3 mm 2 s ash content 0.02% by weight, acid number 0.46 mg KOI / g, pour point -13 ° C.

Example 2

830 g of cracked pork ointment with an average molar mass of 855 g.mol ¹ g with an acid number of 0.81 mg KOH / g was heated to 60 ° C and mixed with 106 g of methanolic NaOH solution to carry out the first reaction step. The molar ratio of acyl triacylglycerol-: methanol was 1: 1.09, the weight ratio tr / acylglycerol: methanol 1: 0.122, the catalyst to fat phase ratio was 0.50% by mass The reaction mixture was stirred vigorously for 5 minutes and maintained at 68-70 ° C for 120 minutes. Excluded excluded glycerol phase from the first. The conversion of triacylglycerols to methyl esters was 78% by weight. In the second step of the reaction, 27 g of methanolic NaOH solution was added, which represents a molar ratio of acyl triacylglycerol: methanol of 1: 0.278, a weight ratio of triacylglycerol: methanol of 1: 0.278:

0.032, catalyst content to fat 0.14 wt. The total methanol weight used in the reaction was 129 g, representing a 1: 0.154 triacylglycerol: methanol 1: 0.154 weight ratio, a 1: 1.371 molar acyl triacylglycerol: methanol ratio, the proportion of catalyst used relative to the starting fat of 0.64% by mass. minutes and then held at 68-70 ° C for 120 minutes. The glycerol phase taken from the second reaction stage was 31 g. 826 g of crude methyl esters were obtained, containing about 1% methanol. After the methanol was stripped off with air, the following parameters were determined for the mixed methyl esters: methyl ester content 98.2% by mass, flash point in a closed crucible 122 ° C, kinematic viscosity at 20 ° C 8.26 mm s, ash content 0.022% mass, acid number 0.69 mg KOH / g, pour point 9 ° C.

Industrial usability

The process according to the invention can be used in the preparation of mixed methyl esters as non-traditional fuel for internal combustion engines, where these methyl esters can be used immediately without modification of the motor. Mixed methyl esters can also be used to prepare other biodegradable products, such as hydraulic oils, chainsaw oils and the like, that are environmentally friendly. Mixed methyl esters are the preferred starting material for oleochemistry.

Claims (2)

PATENT CLAIMS Process for the preparation of methyl esters of higher fatty acids having a carbon number of 12 to 22 by the transesterification of triacylglycerols of fats with methanol in the presence of an alkali catalyst in an amount of 2 to 5 mol%, relative to methanol, in two steps. of an alkali catalyst in a molar ratio of acyl triacylglycerol: methanol of 1: 0.9 to 1.1, characterized in that the treatment is carried out for 5 to 15 minutes with vigorous stirring and subsequently maintaining the reaction mixture at a temperature of 50 to 70 ° C for 105 to 240 minutes to form two layers, methyl ester and glycerol, and after separation of the glycerol layer, the methyl ester layer is treated with fresh methanolic alkali catalyst solution at a molar ratio of acyl triacylglycerol: methanol of 1: 0.3 to 0.5 under the same physical conditions as in first stage. 2. The process according to claim 1, wherein the alkali catalyst is sodium hydroxide.