Use of sulfonic acid-functionalized silica as catalyst for esterification of free fatty acids (FFA) in acid oil for biodiesel production: an optimization study

Abstract

This paper deals with esterification of free fatty acids (FFAs) in acid oil (a byproduct of oil refining) to obtain biodiesel. Sulfonic acid-functionalized silica (SiO2–Pr–SO3H) was used as promising solid-acid catalyst. The conditions affecting conversion to fatty acid methyl esters (FAME), for example reaction temperature, reaction time, catalyst concentration, and methanol-to-oil molar ratio, were investigated and optimized by use of the Taguchi method. The highest conversion obtained under the optimized conditions was 96.78 % after 8 h. Analysis of variance revealed that temperature was the most significant factor effecting conversion among the four conditions studied. The experimental results were found to fit a pseudo first-order kinetic law. SiO2–Pr–SO3H is a highly effective, reusable, and environmentally benign catalyst for biodiesel production from waste low-cost oil feedstock with a high FFA content.