GB634411A - Method of treating low-grade fatty stock to form alkyl esters therefrom - Google Patents

Abstract

Low grade fatty material, such as renderer's tallow or grease, which contains free fatty acid, is subjected to treatment with the vapour of alkanol containing not more than six carbon atoms in the molecule so that the free fatty acid is converted to alkyl esters by esterification and these esters are thereupon removed. The treatment is carried out at a temperature above 150 DEG C., but below the decomposition temperature of the alkanol vapour, and in the presence of an insoluble inorganic esterification catalyst. Suitable alkanols are methanol, ethanol and propanol, while suitable esterification catalysts are insoluble oxides of the elements of Groups III-VIII of the Periodic Table, particularly alumina, silica, thoria and zirconia. Other esterification catalysts which may be employed are magnesia, calcium oxide, bauxite, clays, salts. Mixtures of catalysts, for example a mixture of alumina and silica, may be employed and they may be supported on silica gel or alumina. The reaction conditions may be chosen so that the alkanol, in addition to esterifying the free fatty acid, alcoholyses a part of the glyceride in the fatty material. In this case alkyl esters, glycerol, mono-glycerides and diglycerides may be recovered from the reaction mixture. Whatever the reaction conditions for the esterification reaction, however, the reaction mixture may be subjected to further treatment with lower alkanol. This treatment may be (a) treatment with the lower alkanol vapour at a temperature above 150 DEG C. but below the decomposition temperature of the alkanol vapour, and in the presence of an insoluble alcoholysis catalyst; (b) treatment with the liquid lower alkanol in the presence of a soluble alcoholysis catalyst; or (c) treatment (a) followed by treatment (b). This treatment converts the glycerides to alkyl esters and glycerol. The alcoholysis catalyst for treatment (a) may be an insoluble oxide of Groups II-VIII of the Periodic Table or a mixture of alumina and silica, while the alcoholysis catalyst for treatment (b) may be an alkaline material such as caustic alkali or an alkali metal alcoholate, particularly sodium methoxide. Treatments with alkanol vapour may be carried out by allowing a stream of the fatty material to flow down a vertical tower in countercurrent to a stream of alkanol vapour and such treatments may be carried out at a pressure greater than atmospheric pressure. Removal of alkyl esters from any reaction mixture may be effected by distillation or, in the case of an alcoholysis reaction, by allowing the reaction mixture to separate first into an upper layer consisting predominantly of alkyl esters and a lower layer consisting predominantly of glycerol. In the examples: (1) grease containing free fatty acid is treated with methanol vapour in the presence of bauxite using the counter-current technique in a vertical column, if desired with recycling of the reaction products to produce alcoholysis of the glycerides; and (ii) the reaction products of (1) are treated with liquid methanol in the presence of sodium, which latter reacts with the methanol to form sodium methoxide; alkyl esters and glycerol are recovered, any remaining glycerides are returned for p re-working, and unsaponifiables treated to obtain sterols.ALSO:Low grade fatty material, such as renderer's tallow or grease, which contains free fatty acid, is subjected to treatment with the vapour of an alkanol containing not more than six carbon atoms in the molecule so that the free fatty acid is converted to alkyl esters by esterification and these esters are thereupon removed. The treatment is carried out at a temperature above 150 DEG C. but below the decomposition temperature of the alkanol vapour, and in the presence of an insoluble inorganic esterification catalyst. Suitable alkanols are methanol, ethanol and propanol, while suitable esterification catalysts are insoluble oxides of the elements of Groups III-VIII of the Periodic Table, particularly alumina, silica, thoria and zirconia. Other esterification catalysts which may be employed are magnesia, calcium oxide, bauxite, clays, salts. Mixtures of catalysts, for example a mixture of alumina and silica, may be employed and they may be supported on silica gel or alumina. The reaction conditions may be chosen so that the alkanol, in addition to esterifying the free fatty acid, alcoholyses a part of the glyceride in the fatty material. In this case alkyl esters, glycerol, mono-glycerides and di-glycerides may be recovered from the reaction mixture. Whatever the reaction conditions for the esterification reaction, however, the reaction mixture may be subjected to further treatment with lower alkanol. This treatment may be (a) treatment with the lower alkanol vapour at a temperature above 150 DEG C. but below the decomposition temperature of the alkanol vapour, and in the presence of an insoluble alcoholysis catalyst; (b) treatment with the liquid lower alkanol in the presence of a soluble alcoholysis catalyst, or (c) treatment (a) followed by treatment (b). This treatment converts the glycerides to alkyl esters and glycerol. The alcoholysis catalyst for treatment (a) may be an insoluble oxide of Groups II-VIII of the Periodic Table or a mixture of alumina and silica, while the alcoholysis catalyst for treatment (b) may be an alkaline material such as caustic alkali or an alkali metal alcoholate, particularly sodium methoxide. Treatments with alkanol vapour may be carried out by allowing a stream of the fatty material to flow down a vertical tower in countercurrent to a stream of alkanol vapour and such treatments may be carried out at a pressure greater than atmospheric pressure. Removal of alkyl esters from any reaction mixture may be effected by distillation or, in the case of an alcoholysis reaction, by allowing the reaction mixture to separate first into an upper layer consisting predominantly of alkyl esters and a lower layer consisting predominantly of glycerol. In the examples (i) grease containing free fatty acid is treated with methanol vapour in the presence of bauxite using the countercurrent technique in a vertical column, if desired with recycling of the reaction products to produce alcoholysis of the glycerides, and (ii) the reaction products of (i) are treated with liquid methanol in the presence of sodium, which latter reacts with the methanol to form sodium methoxide; alkyl esters and glycerol are recovered, any remaining glycerides are returned for reworking and unsaponifiables treated to obtain sterols.