Energy-efficient sulfone separation process for the production of ultralow sulfur diesel by two-step adsorption

A three-step process for producing ultralow sulfur diesel (S concentration < 10 ppm) is experimentally investigated, consisting of (1) the separation of sulfone in diesel (S concentration > 150 ppm) by adsorption on silica and the subsequent regeneration of silica using a polar solvent, (2) the separation of sulfone in methanol by adsorption on activated carbon and the subsequent regeneration of activated carbon using a nonpolar solvent, and (3) the distillation for the recovery of a nonpolar solvent. Various polar solvents (i.e., acetone and methanol) and nonpolar solvents (i.e., n-butane, n-pentane, and n-hexane) were considered. Methanol and n-butane were found to be good solvents for regenerating sulfone-adsorbed silica and sulfone-adsorbed activated carbon, respectively. The two-step adsorption process was able to substantially reduce the energy consumption during the distillation because the heat of vaporization (320 kJ/kg) of n-butane is much lower than that (1104 kJ/kg) of methanol. This study showed the potential to produce ultralow sulfur diesel with low energy consumption in a continuous separation process.