Classifications

• • C—CHEMISTRY; METALLURGY
  • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
  • C11C—FATTY ACIDS FROM FATS, OILS OR WAXES; CANDLES; FATS, OILS OR FATTY ACIDS BY CHEMICAL MODIFICATION OF FATS, OILS, OR FATTY ACIDS OBTAINED THEREFROM
  • C11C3/00—Fats, oils, or fatty acids by chemical modification of fats, oils, or fatty acids obtained therefrom
  • C11C3/04—Fats, oils, or fatty acids by chemical modification of fats, oils, or fatty acids obtained therefrom by esterification of fats or fatty oils

Definitions

• Fatty acid esters of short-chain aliphatic alcohols are of great technical importance. They are important starting materials for the production of fatty alcohols, for example, but are also used to obtain other oleochemical products such as soaps, surfactants, alkanolamides, etc.
• fatty acid esters of lower alcohols takes place predominantly by alcoholysis of the corresponding fats and / or oils of natural origin, which are known to be fatty acid triglycerides. Vegetable and / or animal fats or oils, however, almost always contain considerable amounts of free fatty acids, and this free acid content can vary within a wide range depending on the origin of the material and its history. The free fatty acid content is almost always above 3 percent by weight.
• the acid number of the commercially available raw coconut oil is normally not more than 10 to 20. For other vegetable oils, the acid number, especially of good qualities, is less than 10, for lower qualities it is, for example, in the range of 20 to 25.
• Technical tallow based on its acid number evaluated and traded, the content of free fatty acids - depending on the quality - between 1 and 15 to 20 percent by weight - corresponding to an acid number of about 30 to 40 - in some cases even higher.
• the acid number of the triglyceride to be used in the transesterification influences the possibilities or process conditions of the transesterification reaction to a considerable extent.
• the BRADSHAW process used in technology uses e.g. B. the alkali-catalyzed transesterification of fats, the SZ of which should not exceed 1.5, with methyl alcohol as the 1st stage of a continuous soap production - see, for example, Ullmann, Encyclopedia of Industrial Chemistry, 3rd edition, volume 7, page 525 ff .; 4th edition, volume 11, page 490 ff.
• the pressure-free transesterification - which is energetically advantageous due to the lower temperatures and the significantly lower methanol requirement and does not require pressure reactors - reduces the SZ - e.g. B. by preceding conversion of the free fatty acids into the corresponding alkyl or glycerol esters - in advance.
• this pre-esterification can be carried out alkali-catalyzed at 240 ° C. and 20 bar. In this case too, expensive pressure reactors must be used for the pre-esterification with methanol and other short-chain alcohols.
• the invention has for its object to facilitate the production of fatty acid esters of lower monoalcohols when using such triglyceride starting materials that contain not inconsiderable amounts of free fatty acids. Based on the combination of a pre-esterification of the free acids with subsequent transesterification, both process stages should be able to be carried out at comparatively low temperatures and without using reactors designed for higher pressures. In addition, it should be possible to reduce the high excess of alcohol required, for example, in pressure transesterification, which is a cost factor that should not be underestimated due to the necessary reprocessing and cleaning steps. Overall, the invention thus aims to realize the production of fatty acid esters of lower alcohols in an energy-saving and cost-effective manner, especially with starting materials such as those obtained in the context of natural, in particular vegetable and / or animal fats and / or oils.
• the invention proposes a process for the preparation of fatty acid esters of short-chain aliphatic alcohols by catalytic transesterification of fats and / or oils containing free fatty acids (oil phase) with the corresponding monoalcohols, which is characterized in that the oil phase in the presence of acidic esterification catalysts Temperatures not exceeding 120 ° C and pressures not exceeding 5 bar and in the presence of a liquid entraining agent which is essentially immiscible with the oil phase are subjected to a pre-esterification with the monoalcohols, then phase separation into an entraining agent phase containing the acidic catalyst and water of reaction and the treated oil phase separates, and this oil phase of the transesterification, while the catalyst-containing entrainer phase is returned to the pre-esterification stage after at least partial drying.
• the acid number of natural, vegetable and / or animal fats and / or oils can vary within a wide range.
• the SZ of commercially available raw coconut oil is normally not more than 10 to 20.
• the SZ is below 10 for good qualities, for example in the range of 20 to 25 for lower qualities, which are evaluated and treated according to the SZ , are in the content of free fatty acids, depending on the quality, between 1 and 15 to 20 weight percent - d. H. with acid numbers up to, for example, 30 to 40 - but sometimes even higher.
• Starting materials with SZ up to 60 or even above can be used in the process according to the invention.
• the first step of the process according to the invention consists in an esterification of the free fatty acids contained in the triglyceride, accelerated by acid catalysts, with the short-chain monoalcohol.
• Preferred monoalcohols are C1 to C4 - mono-alcohols and in particular methanol.
• the monoalcohol, which is also to be used in the subsequent transesterification stage, is expediently already used in this stage of the pre-esterification.
• This pre-esterification stage takes place according to the invention in the presence of the method described conditions liquid entrainer instead, which is essentially immiscible with the oil phase.
• esterification conditions are chosen such that transesterification of the triglycerides with the monoalcohol does not take place or does not occur to any significant extent.
• the pre-esterification can be carried out, for example, at temperatures from 40 to 120.degree. C., preferably at 50 to 100.degree. C., working without pressure or at best with slightly elevated pressures, which are generally not above 5 bar. The use of pressure reactors is therefore not necessary here.
• Suitable entraining agents are in particular sufficiently high-boiling polyfunctional alcohols and / or their ethers or partial ethers which are liquid at 50 ° C. and preferably already at room temperature. Accordingly, suitable liquid entraining agents are, for example, ethylene glycol, propylene glycol, polyethylene glycols, glycol ethers, for example propyl glycol, or diglycol ethers such as methyl diglycol.
• suitable liquid entraining agents are, for example, ethylene glycol, propylene glycol, polyethylene glycols, glycol ethers, for example propyl glycol, or diglycol ethers such as methyl diglycol.
• glycerin is particularly suitable as a liquid entrainer. Glycerin is released anyway in the subsequent stage of the transesterification. The choice of glycerin as an entrainer in the first stage of the process thus brings understandable further process simplifications.
• the entrainer serves in particular as a liquid carrier for the acid catalyst in the first stage (pre-esterification).
• All acidic, non-volatile esterification catalysts are basically suitable, for example So corresponding systems based on Lewis acids, low volatile inorganic acids and / or their acidic partial esters, heteropolyacids and the like.
• a particularly suitable class of acidic catalysts are organic sulfonic acids, which can be described, for example, by the general formula RSO3H, where R represents an alkyl, aryl or alkaryl radical.
• suitable sulfonic acids are methanesulfonic acid, toluenesulfonic acid, naphthalenesulfonic acid or alkylbenzenesulfonic acid.
• sulfuric acid or its half-ester can be used as the non-volatile inorganic acid.
• Suitable heteropolyacids are, for example, the tungstic or the molybdate phosphoric acids.
• the reaction of the free fatty acids with the monoalcohols takes place as the fastest reaction under the conditions of the pre-esterification stage chosen according to the invention, so that not only the transesterification of the triglycerides with the monoalcohol but also the reaction of the free fatty acids with the glycerol used as entrainer does not or not to any appreciable extent entry.
• glycerol is only very slightly soluble in triglycerides under the chosen reaction conditions.
• the acidic esterification catalysts and the reaction formed during the esterification dissolve onswasser much better in glycerin than in triglycerides.
• the result of this is that after the esterification, virtually the entire amount of the esterification catalyst used and the water of reaction formed are in the glycerol phase. Accordingly, the oil phase is practically free of acid catalyst and water of reaction, both of which would interfere with the further reaction in the subsequent alkali-catalyzed reaction.
• the catalyst-containing glycerol phase can be freed from water of reaction and, if desired, from excess alcohol after it has been discharged from the first process stage, so that the catalyst-containing glycerol phase can be recycled to the pre-esterification stage.
• the glycerin - or rather the entrainer which is not miscible with the oil phase - thus serves practically as a liquid carrier substance for the catalyst used and discharges the water of reaction formed in the first process stage from the oil phase.
• the amount of acid catalyst used in the pre-esterification influences the speed of this pre-esterification within certain limits. Because fiction according to which the catalyst can be recovered and recycled practically quantitatively in a simple manner, a restriction of the amount of catalyst is not necessary for reasons of cost. In general, amounts of catalyst in the range from 0.5 to 5.0 percent by weight, based on the oil phase used, will be used. However, the use of smaller or larger quantities is not excluded.
• the amount of entrainer is also hardly influenced by cost considerations, since the entrainer is recovered and recycled practically quantitatively. However, the following point of view is important:
• the amount of entrainer - e.g. glycerin - must be coordinated with the amount of monofunctional alcohol used in the pre-esterification so that after the pre-esterification there is a sufficient difference in density between the oil phase and the entrainer phase for a satisfactory phase separation is present.
• a characteristic density value for the oil phase is, for example, 0.88.
• the density of methanol is 0.79 and that of glycerin is 1.25. Methanol and glycerin are homogeneously miscible, water of reaction and acid catalyst additionally complicate this phase.
• the two-phase reaction product from the pre-esterification will have the oil phase as the upper phase and the entrainer phase as the lower phase.
• simple preliminary tests can be used to determine which mixing ratios of monoalcohol and entrainer, in particular glycerol, are particularly useful to facilitate the phase separation after completion of the pre-esterification.
• the following mixing ratios are preferably used: for 100 parts by volume of oil phase, 5 to 50 parts by volume, in particular 5 to 25 parts by volume of the liquid entraining agent are usually used, while 10 to 50 parts by volume, preferably 15 to 30 parts by volume, of the monoalcohol are used at the same time.
• the amount of monoalcohol used has a positive influence on the speed and completeness of the esterification of the free fatty acids in the first stage of the process, although the solubility of the monoalcohol in the triglyceride is limited and is given as constant for a given reaction temperature. Nevertheless, it has been shown that an increase in the amount of monoalcohol results in a faster and more complete esterification of the free fatty acids. For cost reasons, however, it is advisable to limit the amount of monoalcohol in the pre-esterification, as stated, since the reprocessing of the excess alcohol is a not inconsiderable cost factor.
• the pre-esterification can be carried out batchwise or continuously.
• the starting materials - for example methanol, glycerol and oil phase - can be carried out in cocurrent, but also in countercurrent. If work is carried out in countercurrent, the mixture of monoalcohol and liquid entrainer is expediently counteracted to the oil phase.
• the subsequent phase separation of the reaction product from the pre-esterification is easy to carry out due to the difference in density between the two phases. Normally, a simple settling tank can be used for this.
• the separated oil phase (195 kg) contained 10.2 percent by weight of methanol and had an acid number of 0.8. From the sulfur content of the oil phase (26 ppm) it can be calculated - taking into account the sulfur content of the coconut oil used (12 ppm) - that more than 99% by weight of the p-toluenesulfonic acid used remained in the glycerol phase.
• the separated glycerol phase (45 kg) contained 45 weight percent methanol, 1.3 weight percent water (0.58 kg). The latter corresponds to 92 percent by weight of the water of reaction formed in the reduction of the acid number from 12 to 0.8 by esterification.
• the G lycerinphase was distilled to remove methanol and water. 20 kg of a 2.8 percent by weight water-containing methanol were obtained as the distillate.
• the distillation residue of the glycerol phase (25 kg) had an acid number of 20.6. This corresponds to 99 percent by weight of the p-toluenesulfonic acid used.
• the transesterification of the oil phase to the corresponding methyl esters was carried out with the addition of 0.35 kg sodium methylate (as a 30% solution in methanol) and 2 0 1 methanol at 60-65 ° C. It imagined two-phase reaction mixture (methyl ester phase and glycerol phase). The upper phase (methyl ester phase) was then washed with water. In the raw methyl ester thus freed from methanol and glycerol residues, the degree of conversion was determined via the content of bound glycerol. The degree of conversion of the raw methyl ester was 97%.
• the oil phase obtained in this way had an acid number of 0.7 and a sulfur content of 28 ppm.
• the G lycerinphase was worked up as in Example. 1
• the activity of the recycled p-toluenesulfonic acid in the pre-esterification was still good.
• the p-toluenesulfonic acid was recovered practically quantitatively with the glycerol phase.
• the oil phase obtained in this pre-esterification had an acid number of 0.5. As the acid analysis showed, more than 99 percent by weight of the methanesulfonic acid used was in the glycerol phase obtained.
• Palm oil with an acid number of 14.5 was pre-esterified analogously to Example 1, 40 1 methanol, 2 0 1 glycerol and 1.6 kg of p-toluenesulfonic acid being used per 200 liters of oil.
• the resulting oil phase (acid number 0.7) was transesterified after separation of the glycerol phase with the addition of 0.35 kg of sodium methylate and 15.8 kg of methanol at 65 ° C.
• the crude methyl ester worked up analogously to Example 1 contained 0.4 percent by weight of bound glycerol. The degree of conversion of the triglyceride used was 96%.
• coconut oil with an acid number of 14 was pre-esterified with ethanol analogously to Example 1, using 200 liters of oil, 40 liters of ethanol, 1.6 kg of p-toluenesulfonic acid and instead of glycerol 20 liters of polyethylene glycol with an average molecular weight of 600.
• the mixture was heated to 80 ° C. with stirring for about 30 minutes.
• the acid number of the coconut oil obtained after separation of the glycerol phase was 0.9.
• the coconut oil was then transesterified with ethanol with the addition of 0.2% by weight of KOH, based on the amount of oil used, to give coconut fatty acid ethyl ester at a temperature of 80.degree.
• the content of the crude ethyl ester in bound glycerol was 0.7 percent by weight.
• the conversion of coconut oil to butyl coconut fatty acid was carried out by first reacting 20 liters of coconut oil with 4 liters of butanol and 2 liters of glycerol in the presence of 0.2 kg of p-toluenesulfonic acid with stirring at 120 ° C. After cooling to 80-90 ° C., the glycerol phase was separated off. The oil phase had an acid number of 0.8 and was then transesterified with butanol in the presence of potassium hydroxide as a catalyst to give the corresponding coconut fatty acid ester with an approximately 95% degree of conversion.
• coconut oil with an acid number of 16 was pre-esterified with methanol in such a way that 20 l of coconut oil, 4 l of methanol and 1.8 kg of polyethylene glycol of average molecular weight 3000 in the presence of 160 g of p-toluenesulfonic acid in a closed stirred tank at 100 ° C. and slightly overpressure ( approx. 2 bar) was implemented. After a reaction time of 15 minutes, the acid number of the coconut oil was 0.5. After cooling to 60 ° C, the polyethylene glycol phase was drained. The deacidified coconut oil was transesterified in the presence of 0.2 percent by weight sodium methylate with methanol at 65 ° C. with a 97% degree of conversion.

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• 1983
  • 1983-05-30 DE DE19833319590 patent/DE3319590A1/de not_active Withdrawn
• 1984
  • 1984-04-11 US US06/599,090 patent/US4608202A/en not_active Expired - Fee Related
  • 1984-05-21 EP EP84105794A patent/EP0127104B1/fr not_active Expired
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  • 1984-05-30 JP JP59112195A patent/JPS6035099A/ja active Pending
• 1987
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