Facile Synthesis of Ferric-Modified Phosphomolybdic Acid Composite Catalysts for Biodiesel Production with Response Surface Optimization

Abstract

An attempt has been made to optimize the preparation of biodiesel from the transesterification of oleic acid with methanol over iron(III)-doped phosphomolybdic acid (H₃PMo) catalysts. The prepared doped H₃PMo salts were characterized using powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. The detailed characterization results demonstrated that the doped H₃PMo salts have a strong interaction between the iron(III) ions and metal oxygen cluster, well preserving a typical Keggin structure of heteropolyacids and possessing good thermal stability. The effect of esterification reaction parameters was investigated and optimized using single-factor experiments method in combination with response surface methodology (RSM). The doped catalyst exhibited good catalytic activity, affording the oleic acid conversion of 89.2% with single factor optimization and 95.1% with RSM. More importantly, the catalyst was simply separated by decantation and exhibited good stability, with the oleic acid conversion of 70.2% after three consecutive cycles. Besides, this catalyst can also catalyze the esterification of other free fatty acids. Therefore, the doped H₃PMo catalyst is a promising candidate for eco-friendly production of biodiesel in industry.