Glycerine esterification with free fatty acids: Homogeneous catalysis

Abstract

The esterification of glycerine with free fatty acids using sulfuric, p-toluenesulfonic, and methanesulfonic acids as catalysts is studied in detail analyzing the effect of different variables. These catalysts resulted to be much more active than the heterogeneous catalysts, which require very high temperatures in order to convert high fractions of free fatty acids. The differences in activities among these homogeneous catalysts are explained based on their surface tensions. This parameter plays a key role in the kinetic behavior, affecting the interface area. An inductive period in the reaction was observed and explained on the basis of the surface tension changes that occur during the reaction due to the formation of monoglycerides, which are compounds that decrease the interfacial tension. In this reacting system there is a formation of important amount of secondary products with a darkening of the reaction media. In this work these products have been quantified under different reaction conditions, showing the best way of conducting this reaction in order to minimize this loss of yield. Using methanesulfonic acid at a low concentration of 0.35 equiv/L and low temperature (100 °C) complete conversion is obtained with a yield of 95% without darkening of the product.