Ferric sulfate modified bifunctional catalyst for methyl esters production from microwave-assisted intensification of Delonix regia and waste cooking oil mixture

Abstract

Intensification of synergistic active sites of a bifunctional catalyst promotes process efficiency in biodiesel production. In this study, a bifunctional solid catalyst was developed from waste eggshells and ferric sulfate in the presence of ammonium molybdate solution. The developed catalyst was applied in a microwave-aided process for simultaneous esterification-transesterification of Delonix regia seed oil and waste cooking oil mixture. Several analytical methods were utilized to examine the characteristics of the synthesized catalyst. The findings reveal that the catalyst is mainly composed of mesoporous particles featuring medium to strong acidic and basic sites, essential for its dual catalytic activity. The synthesized catalyst has a surface area of 52.38 m2/g and a pore diameter of 8.34 nm. Crystalline phase of the catalyst was dominated by both acidic (CaSO4 and Fe2O3) and basic (CaO) compounds. Optimal conditions for methyl esters production in the single-step process were: MeOH/oil molar ratio of 15:1, reaction time of 5 min, and catalyst amount of 1 wt%, with a corresponding methyl esters yield of 98.52 %. Estimated specific energy consumption of 1.9 kWh/kg and specific CO2 emissions of 1.52 kg/kg of biodiesel indicate efficient microwave energy usage in driving the reaction process while contributing to a reduced carbon footprint. The biodiesel produced has physicochemical and fuel properties that fall within ASTM D6751 and EN 14214 stipulated standards. This strategy could help improve the process economics of biodiesel production by using eggshell waste as support, leading to less reduction in ecotoxicity.