Patent EA-004051-B1 (EA)
Title: Method for producing fatty acid esters of monovalent alkyl alcohol sand use of the same
Inventor: TURCK RALF
IPC: C07C67/03
Filed: 2000-06-07
Abstract: 1. Method for producing fatty acid esters of monovalent alkyl alcohols by base-catalyzed transesterification of triglycerides from natural or synthetic oils and/or fats, which contain free fatty acids as interfering accompanying substances, wherein initially the oils and/or fats are processed with an immiscible basic glycerin phase so as to neutralize the free fatty acids and cause them to pass over into the glycerin phase, and subsequently, following separation of the glycerin phase by means of monovalent alcohols, the triglycerides are subjected to transesterification in an agitator vessel, using a base as a catalyst, to form said fatty acid esters, characterized in that following separation of the fatty acid esters, the basic glycerin phase, produced during transesterification of the triglycerides is used for processing the oils and/or fats for removal of the free fatty acids, with the minimum quantity of catalyst used being calculated, relative to 1,000 g of the oil to be processed, as a function of the acid number of the oil and the mean molar mass of the oil, according to the equations (I) to (III): with an acid number satisfying the inequation (I) SZ<(0.084 mol/1,000 g of oil)*M(KOH)*Y (I) according to equation (II) minimum quantity of cat/1,000 g of oil=0.088 mol/100 g oil*Y (II) or else according to equation (III) minimum quantity of cat/1,000 g of oil=(SZ/M/KOH)*(0.088/0.084) (III) with Y=(880 g/mol)/(mean molar mass of the used oil) and SZ=acid number of the oil used [(g KOH)/(1,000 g of oil)]. 2. Method according to claim 1, wherein a base and an alkyl alcohol are added for transesterification to the triglycerides produced following said step of pre-processing with an immiscible basic glycerin phase, and wherein after transesterification, a fraction rich in fatty acid esters of monovalent alkyl alcohols is separated, with the fraction separated first, which is rich in fatty acid esters of monovalent alkyl alcohols, being mixed with a base and an alkyl alcohol for further transesterification and wherein, following transesterification, a second fraction rich in fatty acid esters of monovalent alcohols is separated. 3. Method according to claim 1, wherein metal hydroxides and/or alcoholates or their alkyl alcoholic solutions are used as the base. 4. Method according to claim 1, wherein the separation of said fractions rich in fatty acid esters of monovalent alkyl alcohols is carried out using phase separation. 5. Method according to claim 1, wherein, prior to the respectively last phase separation, the reaction mixture is washed with 5 or more % by weight of water, relative to the weight of the mixture containing fatty acid esters, which is used in this step. 6. Method according to claim 5, wherein low-boiling components are expelled from said fraction rich in fatty acid esters of monovalent alkyl alcohols following the respectively last phase separation. 7. Method according to any one of claims 4-6, wherein a vessel is used for separating the fractions rich in fatty acid esters of monovalent alkyl alcohols, into which the respective starting mixture is supplied at or below the liquid/liquid phase boundary and from which the fraction to be separated is removed in the upper third of said vessel. 8. Method according to claim 6 or 7, wherein an evaporator is used to expel said low-boiling components, in which the fraction separated last is conducted over a first surface heated to between 90 and 120 degree C and in which said low-boiling components are deposited on a second surface. 9. Method according to any one of the preceding claims, wherein vegetable oils are used as a starting material. 10. Method according to any one of the preceding claims, wherein alkyl alcohols containing 1 to 10 carbon atoms are used. 11. Method according to any one of the preceding claims, wherein said step of pre-processing with said basic glycerin phase is carried out in an agitator vessel for a duration of between 1 and 60 minutes. 12. Method according to claim 11, wherein the duration of said pre-processing step is between 5 and 15 minutes. 13. Method according to claim 1, wherein 5 to 15% of the basic glycerin phase produced during transesterification are used in said pre-processing step. 14. Method according to claim 1, wherein, in addition to said basic glycerin phase produced during transesterification, additional glycerin and/or base is/are used for removing said free fatty acids. 15. Method according to claim 14, wherein additionally industrial glycerin or pharmaceutical glycerin is used, in which KOH, NaOH or sodium ethylate are dissolved. 16. Method according to any one of the preceding claims, wherein the total quantity of basic transesterification catalyst used is between 1 and 4 times greater than the minimum quantity of catalyst according to claim 1. 17. Method according to any one of the preceding claims, wherein the total quantity of alcohol used corresponds to between 1.2 and 1.4 mol per mol of bound fatty acid fractions. 18. Method according to any one of the preceding claims, characterized in that a fraction X of said basic glycerin phase produced during transesterification of the triglycerides is re-used, following separation of said fatty acid esters, for the transesterification reaction, with the acid number satisfying the inequation (IV): SZ<(0.084 mol/1,000 g of oil)*M(KOH)*Y (IV) and with the minimum quantity of catalyst to be used (relative to 1,000 g of the oil to be processed) as well as the fraction X of the basic glycerin phase to be re-used for transesterification being so selected that the equations(V) and (VI) are satisfied at the same time: minimum quantity of cat/1,000 g oil=(0.088 mol/1,000 g of oil-X*0.084 mol/1,000 g of oil))*Y (V) minimum quantity of cat/1,000 g oil=SZ/M/KOH)*(0.088/0.084*(1-X)) (VI) with Y=(880 g/mol)/(mean molar mass of the used oil) SZ=acid number of the used oil [(g KOH)/(1,000 g of oil)] X=fraction of the basic glycerin phase, which is re-used for transesterification. 19. Method according to any one of the preceding claims, characterized in that the free fatty acids or their salts, respectively, which are separated using the basic glycerin phase, are subjected to post-esterification with alkyl alcohol. 20. Use fatty acid esters of monovalent alkyl alcohols produced according to any one of the preceding claims for producing fuel for diesel engines.