A facile, low-cost route for the preparation of calcined porous calcite and dolomite and their application as heterogeneous catalysts in biodiesel production

Despite their potential for biodiesel synthesis, directly calcined minerals rich in magnesium/calcium carbonates are used at the expense of large amounts of the catalyst, high alcohol loading, long processing times, and severe conditions. We report a facile and low-cost route for preparing calcined porous calcite (CPC) and dolomite (CPD) via simple thermal decomposition of the reaction mixtures of natural calcite and dolomite with stearic acid. CPC and CPD, both of which have porous structures, were compared with previously reported catalysts and examined as promising heterogeneous base catalysts under mild conditions. A 40% increase in conversion through CPC and CDC was achieved compared with that achieved through directly calcined minerals. A systematic understanding of the enhancement and deactivation relationships of the products was established by catalyst characterization, including XRD, BET, CO2-TPD, SEM, TEM, and XPS. The obtained CPC and CPD showed large pore sizes and high active site densities and provided an advantageous environment for transesterification of triglyceride with methanol. CPC and CPD are re-usable and show no loss of activity after regeneration.