The Low-Cost Dolomite Catalyst for Sustainable Biodiesel Production from Kapok Seed Oil

Abstract

This study investigated dolomite as a low-cost heterogeneous catalyst for microwave-assisted biodiesel production from kapok seed oil (KSO). Dolomite was thermally activated at 900 °C for 4 h to convert carbonate phases into catalytically active CaO–MgO oxides. Catalyst characterization using XRD, nitrogen adsorption–desorption, EDS, and Hammett indicators confirmed the formation of crystalline oxide phases, mesoporous characteristics, and an increased surface area from 0.7190 to 1.2676 m²/g. Calcination increased total basicity from 3.23 to 9.90 mmol/g. Transesterification was performed under microwave irradiation by varying reaction temperature, methanol-to-oil molar ratio, and catalyst loading. The highest biodiesel yield (89%) was obtained at 60 °C, a methanol-to-oil molar ratio of 12:1, and a catalyst concentration of 7.5 wt%. The GC–MS analysis confirmed the formation of fatty acid methyl esters dominated by methyl linoleate, methyl palmitate, methyl oleate, and methyl stearate. The biodiesel produced from KSO exhibited physicochemical properties that met the standards of SNI 7182 and ASTM D6751 for measured parameters. However, catalyst reusability decreased from 89% to 65% after four cycles, indicating progressive deactivation.