SK16402002A3 - Process of production of methylesters of higher fatty acids - Google Patents

Abstract

Methylesters of higher fatty acids from vegetable oils and/or animal fats with increased content of free fat acids are prepared by acid catalytic esterification and subsequently by alkaline catalytic transesterification with methanol. After mixing oil and/or fat with methanol and an acid catalyst at an increased temperature the reaction mixture is separated into a water-methanol layer and an ester layer. The ester layer is dried up and subjected to alkaline catalytic transesterification with methanol.

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 vegetable oils and / or animal fats with an increased content of free fatty acids. Higher fatty acid methyl esters are used as an alternative fuel in diesel engines.

BACKGROUND OF THE INVENTION

According to the known processes for the preparation of methyl esters of higher fatty acids from natural triacylglycerols, in particular, the alkali-catalyzed transesterification of oils and / or fats with methanol, for example according to the patent specification SK 277 860, is used in a preferred two-step operation. The glycerol formed in the reaction forms a separate liquid phase, thereby shifting the chemical equilibrium of the reaction significantly in the product direction and achieving a high conversion of acylglycerols to methyl esters above 96%. However, if the starting triacylglycerols contain an increased proportion of free fatty acids, resulting in an increased acid number above 3.0 mg KOH / g, these free fatty acids react preferentially with an alkaline catalyst to form alkaline soaps. Alkaline soaps are good emulsifiers and, when transesterified, emulsify glycerol in the reaction medium and make it impossible to go into a separate phase. Alkaline catalysed transesterification under these conditions takes place only to a small extent, or does not take place at all. On the other hand, the occurrence of oils and / or fats with an increased acid value of 3.0 to 50 mg KOH / g is common at a favorable price ratio as compared to low acid triacylglycerols. The ever-increasing demand for methyl esters as prospective alternative fuels for diesel engines and the high price of high-quality oils and fats make it necessary to use these sources with increased acidity. For example, palm oil naturally has a high acidity of about 20 mg KOH / g. The acid number of worn frying oils is around 10 mg KOH / g as a result of especially hydrolytic processes in use. Rendering fats from the killing of dead animals show an acid number of about 40 mg KOH / g as a result of enzymatic and hydrolytic processes. The treatment of such sources of triacylglycerols with increased acidity into methyl esters is, for example, carried out by vacuum distillation to remove free fatty acids in the form of a distillate from the oil and / or fat and the distillation residue is a neutral or low acid oil and / or fat. . The disadvantage of this process is the sophisticated technological equipment and the formation of a distillate fraction of free fatty acids, which must be used in an appropriate manner. Also known is U.S. Pat. No. 4,652,406, in which in the primary operation free fatty acids are esterified with methanol in the presence of an acid catalyst, after subsequent separation of the alcohol and ester phases, the ester phase is extracted with a mixture of glycerol, methanol and alkali. alkaline catalysed transesterification. A disadvantage of this process is the complicated extraction treatment of the reaction mixture after acidic esterification with large volumes of extraction agent.

SUMMARY OF THE INVENTION

The above disadvantages are eliminated in the process for preparing the higher fatty acid methyl esters of the invention, which comprises mixing a mixture of triacylglycerols and free higher fatty acids with methanol and an acid catalyst at 50 to 120 ° C for 1 to 10 hours; the layer is separated and the lower layer, after drying, is subjected to alkaline catalyzed transesterification with methanol

The process of the invention has several advantages. The free fatty acids, which are detrimental to alkaline catalysed transesterification, are purposefully removed and disposed of in the preparatory operation so that, without the need for isolation, they are converted to the target methyl esters in a single step. This increases the yield of methyl esters with respect to feed oil and / or fat. To remove residual reaction water from esterification, the presence of which makes alkaline catalysed transesterification difficult, it is sufficient to dry the ester layer under reduced pressure and elevated temperature in a standard operation, which is also used in the final treatment of methyl esters after transesterification. The aqueous-methanol layer, which contains the bulk of the reaction water and virtually all of the acid catalyst introduced, can be separated and regenerated by pure methods, as well as the acid catalyst, usable in the esterification directly without further treatment. Non-volatile mineral acids such as sulfuric or phosphoric acid, but preferably also alkyl-, aryl-, or alkylarylsulfonic acids, such as ptoluenesulfonic acid, can be used as the acid catalyst. Since the weights of methanol used in the acid esterification in the preparation operation are small, the weights of the hydro-methanol phase for regeneration are also small. For undisturbed alkaline transesterification, the acid number of the ester phase of up to 3.0 mg KOH / g is suitable, especially if the ester phase is intensively dried after separation of the aqueous-methanol phase. The pre-esterification as well as the subsequent transesterification take place at moderately elevated temperatures and at atmospheric pressure, or at a pressure slightly elevated to 5 bar, so that expensive pressure equipment is not required. The process may be continuous or discontinuous. In addition to methanol, another C2-C4 lower alcohol may be used in the esterification operation, but preferably methanol is preferred, which is then exclusively used in the transesterification operation.

The vegetable oil and / or animal fat having an acid number of 2 to 50 mg KOH / g, usually between 10 and 40 mg KOH / g, is mixed with cream so that the molar ratio of free acid: methanol is 1: 5 to 1:40, usually 1:10 to 1:30. For lower acidity of the oil, a lower acid: methanol molar ratio is generally used. The proportion of acid catalyst to the triacylglycerol feeds is 0.1 to 3 wt%, usually 0.5 to 1.0 wt%. Conventional acid catalysts such as sulfuric acid, p-toluenesulfonic acid and the like are used. The reaction mixture is stirred and kept at 50 to 120 ° C under reflux at atmospheric pressure or at a slight positive pressure to 5 bar, usually at 50 to 70 ° C at atmospheric pressure. The reaction time is 1 to 10 hours, usually 2 to 4 hours. After this time, stirring is stopped and the reaction mixture is allowed to sediment. The upper aqueous-methanol phase, which consists mainly of methanol, reaction water and a catalyst, is separated from the lower ester phase. The lower ester phase is subjected to drying under reduced pressure of 1 to 50 kPa at a temperature of 60 to 120 ° C, preferably in a film apparatus. The dried ester phase has an acid number of 1.0 to 3.0 mg KOH / g and is used in alkaline catalyzed transesterification with methanol, for example according to the method described in SK 277 860. The total molar ratio of triacylglycerols: methanol is 1: 4.3, 79 wt. % methanol and 21% wt. methanol. The catalyst is 4 to 6 wt. solution of alkaline lye in methanol. The ester layer at 50-70 ° C is vigorously mixed in each step with an appropriate amount of catalyst and methanol and allowed to settle for 90-120 minutes. The formed bottom glycerol phase in each of the two steps is removed and the crude methyl esters are subjected to a final treatment. The aim of the finish is to remove free methanol, free glycerol and alkaline soaps from the methyl esters.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

150 g of rapeseed oil with an acid number of 13.6 mg KOH / g were mixed with 17.1 g of methanol to obtain a molar ratio of free acid: methanol of 1:15. The sulfuric acid catalyst was present with 0.5 wt. against oil. The mixture was heated to 65 ° C with stirring and maintained at this temperature for 2 hours. After this time stirring was stopped and the mixture was allowed to sediment. The aqueous-methanol phase formed had a mass of 14.3 g and an acid number of 49.6 mg KOH / g. The lower ester phase after drying had an acid number of 1.0 mg KOH / g. The dried ester layer was used in standard alkaline catalysed transesterification in two steps with conversion of acylglycerols to methyl esters of 98.0%.

Example 2

172.2 g of rendered fat with an acid number of 32.2 mg KOH / g was mixed with 79 g of methanol, which represents a molar ratio of free acid: methanol of 1:25. The sulfuric acid catalyst content was 0.5% by weight. against fat. The mixture was heated to 65 ° C with stirring and maintained at this temperature for 2 hours. After this time stirring was stopped and the mixture was allowed to sediment. The aqueous-methanol phase formed had a weight of 52 g and an acid number of 9.9 mg KOH / g. The lower ester phase after drying had an acid number of 2.6 mg KOH / g. The dried ester layer was used in standard two-stage alkaline catalyzed transesterification with conversion of acylglycerols to methyl esters of 97.1%.

Industrial usability

The invention is useful in the preparation of higher fatty acid methyl esters from vegetable oils and / or animal fats with an increased content of free fatty acids. The process according to the invention makes it possible to make full use of the low-quality and inexpensive sources of natural triglycerides. Higher fatty acid methyl esters are used as an alternative fuel in diesel engines.

Claims (1)

Process for preparing higher fatty acid methyl esters from vegetable oils and / or animal fats with a higher content of free fatty acids, characterized in that the mixture of triacylglycerols and free fatty acids with an acid number of 2 to 50 mg KOH / g is mixed with methanol in a molar acid ratio: methanol 1: 5 to 1:40 in the presence of an acid catalyst of 0.1 to 3 wt. based on the weight of the starting oil and / or fat at 50 to 120 ° C for 1 to 10 hours, after sedimentation, the upper layer is separated and the lower layer with an acid number of up to 3 mg KOH / g is transesterified with methanol after drying.