Production of Biodiesel by a Two-Step Niobium Oxide Catalyzed Hydrolysis and Esterification

In this work niobium oxide is used as catalyst for both hydrolysis and esterification steps in biodiesel production. Soybean and castor oils were the raw materials and the reactions were conducted in a batch reactor, analyzing the effect of temperature (250-300°C for hydrolysis, 150-200°C for esterification), water/oil and methanol/fatty acid molar ratios (5-20 for hydrolysis, 1.2-3 for esterification) and catalysts concentration (0-20% w/w for both reactions), according to an experimental plan (23). Conversion was measured by acid-base titration and gas chromatography. Molecular modeling was also performed. Cracking was detected as a side reaction, limiting the temperature of hydrolysis. Pseudo-homogeneous kinetic models were more adequate for both reactions and the higher reactivity of unsaturated fatty acids was justified by energy differences of homo and lumo orbitals.