Biodiesel production via esterification of oleic acid catalyzed by chlorosulfonic acid modified zirconia

Abstract

Biodiesel is a promising renewable alternative to fossil energy. Biodiesel production from low-cost feedstock involves an essential pretreatment step – esterification of free fatty acids (e.g. oleic acid), for avoiding soap formation and catalyst deactivation. Sulfuric acid modified zirconia (H2SO4–ZrO2) is known to be an effective heterogeneous catalyst for this reaction. However, due to rapid SO42- leaching, its reusability is low and its practical use is thus largely hindered. Herein, we report a more stable solid acid analogue for the reaction, chlorosulfonic acid modified zirconia (HClSO3–ZrO2). It was characterized by XRD, SEM, BET, EDX, IR, TGA, and NH3-TPD. Compared with H2SO4–ZrO2, there is over 3 times more sulfur content and nearly 4 times more acid sites amount for HClSO3–ZrO2. More importantly, HClSO3–ZrO2 demonstrates high catalytic activity and long durability in esterification of oleic acid, in which the fatty acid methyl ester yield reaches 100% consecutively for at least 5 cycles under mild conditions.