Process optimization of biodiesel production via esterification of oleic acid using sulfonated hierarchical mesoporous ZSM-5 as an efficient heterogeneous catalyst

Abstract

The development of effective heterogeneous catalysts for the production of biodiesel from low-cost feedstocks containing large amounts of free fatty acids has lately become one of the foremost research issues in the energy research area. Herein, hierarchical mesoporous ZSM-5 zeolite containing sulfonic acid groups (SO3H-HM-ZSM-5-3) was prepared via the hard template approach, using soluble starch as a cheap and sustainable mesoporegen, and the subsequent sulfonation using chlorosulfonic acid as a sulfonating agent. The catalytic activity of the synthesized catalyst was evaluated in the esterification of oleic acid with methanol, and the principal process variables were optimized, adopting the response surface methodology. Results revealed that the catalyst amount and reaction temperature seemed to be the most influential variables governing the esterification process. A maximum oleic acid conversion of 100% was achieved under the optimum operating conditions of 18:1 methanol-to-oleic acid molar ratio and 5.2 wt% catalyst amount (based on the mass of oleic acid) at 88 °C, for 10 h. The performance of the developed SO3H-HM-ZSM-5-3 catalyst was comparable to or even outperformed some other reported acidic catalysts. Importantly, the performance of SO3H-HM-ZSM-5-3 for biodiesel production from waste cooking oil doped with 15% of oleic acid was additionally explored, and methyl ester yield as high as 92.45% was achieved through the simultaneous esterification of free fatty acids and the transesterification of triglycerides. Accordingly, SO3H-HM-ZSM-5-3 appears promising as an industrial catalyst for the one-step biodiesel production from low-grade feedstocks containing high levels of FFAs.