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.