Extractive-Catalytic Oxidative Desulfurization with Graphene Oxide-Based Heteropolyacid Catalysts: Investigation of Affective Parameters and Kinetic Modeling

Abstract

Different tungsten and molybdenum containing heteropolyacid (HPA) catalysts (H3PMo12O40:Mo12, H3PMo8W4O40:Mo8W4, H3PMo6W6O40:Mo6W6, H3PW12O40:W12) were immobilized on graphene oxide (GO) to obtain HPA–GO heterogeneous catalysts (Mo12–GO, Mo8W4–GO, Mo6W6–GO, and W12–GO). The synthesized catalysts were applied in removal of sulfur containing compounds [benzothiophene (BT), dibenzothiophene (DBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT)] with combined extraction–oxidation process using a batch reactor. The sulfur removal efficiency was gradually increased with increasing the ratio of molybdenum ions in the HPAs and complete sulfur removal efficiency for DBT was obtained for Mo12–GO. The roles of affecting parameters such as extracting solvent, catalyst calcination, and feed concentration were also investigated. Among different extracting solvents including acetonitrile, DMF, NMP, methanol, water, and ethylene glycol, acetonitrile represented the best ECOD performance as the extracting solvent. The performance of non-calcined catalyst for sulfur removal was slightly better than that by the calcined one. It was also found that the high sulfur removal activity of the extractive-catalytic oxidative process (ECOD) was retained even at high feed concentration. The kinetic model was evaluated considering mass transfer coupled with chemical reaction, in which the catalytic oxidation reaction was recognized as the rate-controlling step. The kinetic parameters such as rate constants and apparent activation energy were determined.