Simple Niobium Catalysts Applied in Reflux and Ultrasound-Assisted Systems for Biofuel Synthesis

Abstract

Using niobium compounds as heterogeneous catalysts in biodiesel production is a promising methodology from economic and environmental viewpoints. However, the application of niobium catalysts still is a challenge due to the high temperatures and pressures for moderate biofuel yields. Therefore, easily handled and applied materials have been developed to optimize biofuel production, which is the goal of this study. Nb 2 O 5 and ammonium niobium oxalate (AmNO) were activated in reflux and ultrasound-assisted system. Nb 2 O 5 showed better activity under reflux, using methanol. The characterizations conclude that the Lewis-acid sites are determinant for higher conversion rather than surface area. AmNO has better activity also in the reflux system at 70 °C, against 170 °C for Nb 2 O 5 , reaching above 70% conversion. In addition, reactions in ultrasound-assisted systems are also appealing due to the lower time and temperature, with conversion rates above 40%. Both catalysts showed interesting results under milder conditions than those in the literature.

Ammonium Niobium Oxalate (ANO)

“…Conversion of about 90% was observed for ethyl biodiesel from soya bean oil using ANO as the catalyst in a refluxing system, varying the mass ratio (20 and 100% molar ratio catalyst/oil), temperature (25 and 75 °C) in ethanol for 24 h. For the ultrasonic conditions, the best result used soya bean oil for 4 h, at 42 kHz in ethanol at 60 °C, achieving a conversion of about 43%. 8 (E) Amide hydrolysis is a significant reaction in industrial and biochemical processes, due to its applications in peptide and protein modifications. In a preliminary screening, ANO was applied in the hydrolysis of acetamide under reflux in moderate yield (45%) after 20 h. However, the best results of the study were obtained using the heterogeneous catalyst niobium oxide.…”