SK277860B6 - Method of preparation of methylesters of higher aliphatic acids by preestherification of triacylglucerols - 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

Mixed methyl esters of higher fatty acids are prepared by the transesterification of natural triacylglycerols, constituting the major component of vegetable or animal oils and fats, with methanol in the presence of an alkaline catalyst. To do this, methanol with dissolved alkali catalyst is added to the triacylglycerols in two stages, in the first stage with a molar ratio of acyl triacylglycerol: methanol of 1: 0.9 to 1: 1.1 and in the second stage with a ratio of 1: 0.3 Up to 1: 0.5, the reaction mixture is stirred vigorously for a short period at each stage and maintained at 50 to 70 ° C for 105 to 240 minutes. After the first and second steps, the precipitated glycerol layer is separated from the reaction mixture. Mixed methyl esters of higher fatty acids are directly usable as fuel for diesel engines or as a raw material for oleochemistry.

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.

BACKGROUND OF THE INVENTION

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 treated with 1.1 to 2 times the equimolar amount, which is preferably concentrated in the heavier glycerine 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 conversion of triacylglycerols to alkyl esters is about 70% relatively low, and on the other hand, at a higher excess, the cost of alcohol recovery is increased and the separation of the glycroline 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 ester hydrolysis. The process described in Austrian Patent 386 2228 employs an increased amount of KOH of 1.3-1.7% by weight. with respect to the oil phase, the stoichiometric ratio of alcohol and 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 the higher catalyst consumption and, due to only an equimolar amount of alcohol, a reduced conversion of triacylglycerols to methyl esters of about 80%.

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 acids and in the second step an alkaline catalyst is used for the transesterification.

SUMMARY OF THE INVENTION

The essence of the process of the invention is to mix a 2 to 5% methanolic alkaline hydroxide solution 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: 1.1 and in a second stage a ratio of 1: 0.3 to 1: 0.5, the reaction mixture being maintained at 50 to 70 for both stages after intensive initial mixing 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 remainder of the reaction mixture is treated with a 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, cheap NaOH is recommended as the most preferred catalyst. In addition to the economic effect, this catalyst also has the additional 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, methanol and catalyst deficiencies occur in the mixed ester and triacylglycerol phases and the reaction is stopped. The second-stage addition of fresh methanol with the catalyst, in the absence of the glycerol phase, provides a recovery reaction and a further increase in conversion. The excess alcohol in the reaction system is little evident on the ester phase and the alcohol is preferably dissolved 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.

A solution of an alkali hydroxide, preferably sodium hydroxide, NaOH, in methanol at a concentration of 2 to 5 mol%. is mixed with a vegetable oil, e.g. rape, sunflower, flax, etc., or. animal fat or oil, for example, ointment, tallow, fish oil, and the like, in an acyl triacylglycerol: methanol molar ratio of 1: 0.9 to 1: 1.1, which at an average molar mass of triacylglycerol of 880 g / mol is the triacylglycerol: methanol 1: 0.098 to 1: 0.120 and after brief vigorous stirring for 5 to 15 minutes is maintained at 50-70 ° 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, a second portion of methanol with the catalyst at the same concentration as in the first step is added to the mixed ester and triacylglycerol phases at a molar ratio of acyl triacylglycerol: methanol of 1: 0.3 to 1: 0.5, i. in a weight ratio of triacylglycerol: methanol of 1: 0.032 to 1: 0.054 and the reaction mixture is again mixed for 5 to 15 minutes and held at 50 to 70 ° C for 105 to 240 minutes. After this time, the precipitated bottom 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 settling tank, where the remainder of the finely dispersed glycerol is gradually sedimented together with the remainder of the alkali 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: 0.175 and the proportion of NaOH catalyst used with respect to the starting triacylglycerols is 0.34 to 1.13% by weight.

The composition of the mixture of methyl esters formed by the transesterification of triacylglycerols depends on the proportion of individual fatty acids in the triacylglycerols. In vegetable oils, unsaturated fatty acids predominate, mainly oleic (number of carbons 18, one double bond - 18: 1), linoleic (18: 2) and linolenic (18: 3), then palmitooleate (16: 1), myristoleate ( 14: 1), erucous (22: I) 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 erucic acid-reduced rapeseed oil, the total fatty acids contribute as follows: oleic about 60%, linoleic 20%, linolenic 10%, palmitic 4%, stearic 1%. Pork ointment contains about 24% palmitic acid, 13% stearic, 1% myristic, 40% oleic, 9% linoleic.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

10.72 kg of unrefined rapeseed oil with an average molar mass of 880 g.mol ¹ 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. dissolved 46 g of NaOH catalyst, representing 4 wt. % 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 held at 55-60 ° C for 180 minutes. After this time, the lower glycerol layer weighing 1.33 kg was removed. The methyl ester content of the ester layer was determined by GLC by chromatography 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, stirred for 10 minutes and kept at temperature 55-60 ° C for 180 minutes. Mole ratio of acyl triacylglycerol: methanol 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 triacylglycerol: methanol 1: 0.142, total catalyst amount 0.6 wt. 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 having 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 closed crucible 88 C, kinematic viscosity at 20 " C 7.3 miri 's' ^1, the ash content of 0.02 wt.%, acid value 0.46 mg KOH / g, a pour point -13 • C.

Example 2

830 g of cracked pork ointment with an average molar mass of 855 g.min ¹ with an acid number of 0.81 mg KOH / g was poured at 60 ° C and mixed with 106 g of methanolic NaOH solution to effect the first reaction step. The molar ratio of acyl triacylglycerol: methanol was 1: 1.09, the weight ratio of triacylglycerol: methanol 1: 0.122, the catalyst to fat phase ratio was 0.50 wt%. The reaction mixture was vigorously stirred for 5 minutes and held at 68-70 °. C for 120 minutes. The eliminated excreted glycerol phase from the first stage weighed 101 g, the conversion of three cylglycerols to methyl esters was 78% by weight. In the second reaction stage 27 g of methanolic NaOH solution was added, representing 1: 0.278 molar acyl triacylglycerol: methanol molar ratio. The total weight of methanol used in the reaction was 129 g, which represents the weight ratio of triacylglycerol: methanol 1: 0.154, the molar ratio of acyl triacylglycerol: methanol 1: 1.371, the proportion used. The mixture was stirred vigorously for 5 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 stripping methanol with air, the following parameters were determined for the mixed methyl esters: methyl ester content 98.2% by weight, flash point in a closed crucible 122 ° C, kinematic viscosity at 20 ° C 8.26 mm ¹ , ash content 0.022% by weight. 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 engine. 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 an advantageous starting material for olechemia.

Claims (2)

A process for the preparation of higher fatty acid methyl esters having a carbon number of 12 to 22 by the transesterification of fat triglycerides 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 while vigorously stirring and subsequently maintaining the reaction mixture at 50 to 70 ° C for 105 to 70 ° C. 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 the first step . 2. The process according to claim 1, wherein the alkali catalyst is sodium hydroxide.