Esterification of oleic acid to biodiesel over a 12-phosphotungstic acid-based solid catalyst

A 12-phosphotungstic acid (PTA)-based esterification catalyst was prepared by modifying PTA with 1,2,3-trizaole-4,5-dicarboxylic acid (TDA). The obtained TDA-PTA sample was characterized with XRD, IR, SEM, TG and potentiometric titration techniques, and its catalytic properties for esterification of oleic acid with methanol were studied. In addition, the effects of reaction conditions, including catalyst amount, oleic acid/alcohol molar ratio, reaction time and reaction temperature, on its catalytic performance were investigated. After modification with TDA, although the Keggin structure of PTA is kept and the sample shows strong acidity, the particle morphology changes to regular spheres. In particular, the sample exhibits high catalytic activity and stability in esterification of oleic acid with methanol. The modification of PTA by TDA effectively prevents PTA from dissolving in the reaction mixture, and thus, the TDA-PTA can be recycled at least six runs without severe loss of catalytic activity, showing that it is a good heterogeneous catalyst for esterification.