Polyvalent-metal Salts of Phosphotungstate as Efficient Heterogeneous Catalysts for the Esterification of Fatty Acids

In this article, polyvalent-metal salts of phosphotungstate were prepared by a double decomposition method. Bismuth phosphotungstate was found to be the most efficient catalyst in the esterification of n-butanol with oleic acid. The physical properties of bismuth phosphotungstate were characterized by X-ray diffraction and thermogravimetry. The molar ratio of alcohol to acid, the dosage of catalyst, reaction time, reaction temperature, and the recycling of the catalyst on the conversion of fatty acids were investigated. The optimized conditions are as follows: molar ratio of alcohol to oil is 1.8:1, the amount of catalysts is 5 wt% (based on the weight of fatty acid), reaction time is 4 h, and reaction temperature is 100°C. Under optimum conditions, the highest conversion of fatty acids is 90.1%. Moreover, this catalyst is easily recovered and can be reused at least five times.