Isotherm and Thermodynamic Studies on the Removal of Sulfur from Diesel Fuel by Mixing-Assisted Oxidative–Adsorptive Desulfurization Technology

Abstract

In recent years, fuel modifications, such as the production of ultralow sulfur diesel, have been mandated by international agencies to limit gaseous sulfur emissions and reduce atmospheric pollution. In this study, raw diesel fuel was subjected to sequential (1) high shear mixing-assisted oxidative desulfurization and (2) adsorptive desulfurization. A detailed study on the isotherm and thermodynamics of sulfur removal was carried out using powdered activated carbon (PAC) and powdered alumina in batch adsorption experiments. Results showed that sulfur adsorption by PAC and powdered alumina followed the Langmuir (R2 = 0.9020) and the Freundlich (R2 = 0.8626) isotherm models, respectively. Adsorption of sulfur by powdered alumina was controlled solely by chemisorption, whereas adsorption by PAC was controlled by a combination of a chemical reaction and diffusion process. For both powdered alumina and PAC, the positive values of the enthalpy of activation (ΔH) indicate that the adsorption process was endothermic. Negative ΔS and increasing ΔG values with increase in temperature indicates that lower temperatures favored sulfur adsorption by powdered alumina, whereas positive ΔS and decreasing ΔG values with increase in temperature indicate that sulfur adsorption by PAC was more favorable at high temperature.