Hydrotreating and oxidative desulfurization of heavy fuel oil into low sulfur marine fuel over dual function NiMo/γ–Al2O3 catalyst

Abstract

The recent 0.5 wt% global sulfur cap on marine fuels increases the demand for low-sulfur marine fuels. Currently, marine fuels on the market contain up to 4.5 wt% of sulfur. The existing standalone desulfurization processes including hydrotreatment are not cost-effective for reducing the sulfur level of marine fuel to the mandated level. This study explored a new combination of desulfurization methods for marine fuels, first hydrotreatment under moderate process conditions, followed by oxidative desulfurization (ODS) to reduce the sulfur content to a desirable level of ≤ 0.5 wt%. The heavy fuel oil (HFO) feedstock of this study contains 3.4 wt% of S. Hydrotreating of HFO was performed in a trickle bed reactor using a commercial NiMo/γ–Al2O3 sulfide catalyst. Hydrotreating reduced the sulfur content of HFO to 1.14 wt%. It was further desulfurized by ODS using cumene hydroperoxide as an oxidant over the oxide form of NiMo/γ–Al2O3 catalyst. The FTIR analysis of the ODS product validated oxidation of sulfur compounds into sulfones and sulfoxides. The Box-Behnken design was applied to optimize ODS reaction variables such as temperature, oxidant concentration, and time. NiMo/γ–Al2O3 contains surface oxomolybdenum sites, which are expected to catalyze ODS by transferring oxygen from cumene hydroperoxide to sulfur compounds. The NiMo/γ–Al2O3 catalyst was found to be suitable for both hydrotreating and ODS. The upgraded heavy fuel oil of this two-step desulfurization process meets the IMO 2020 sulfur regulations.