Assessment of a three step process using tungsten catalyzed hydrogen peroxide-based oxidative desulfurization for commercial diesel fuels

Abstract

A three-step oxidative desulfurization (ODS) process comprising of oxidation, liquid–liquid extraction, and adsorption was applied to two compositionally very different commercial diesel samples, namely a straight run middle distillate and a blend of primary and secondary refining streams, to assess the ODS process feasibility. The oxidation of sulfur compounds was achieved using hydrogen peroxide as an oxidant in the presence of tungstic acid catalyst. The diesel feedstocks, intermediate and final products were characterized in detail using standard analytical methods along with state-of-the-art speciation techniques. Under mild conditions (ambient pressure and 80 °C), ODS was found to target sulfur species that are refractory to low-severity hydrodesulfurization (HDS), specifically dibenzothiophenes. The ODS process removed 85.3% and 33.5% of the sulfur compounds in the blend and straight run diesel samples, respectively. A comprehensive material balance for the overall process and each process step was also established, revealing that approximately 80% of the initial diesel could be recovered after desulfurization, when accounting for the removed sulfur compounds. However, any extraction based desulfurization approach has an inherent limit for the achievable overall diesel recovery because of the potentially high mass fraction of organosulfur compounds that is removed in the process. Consequently, ODS should be preceded by an HDS process to target the main bulk of sulfur compounds while the ODS process then removes the remaining HDS refractory compounds. Removal of nitrogen species, which are also undesirable in the final product, was a positive side effect of the studied ODS process.