Desulfurization of Heavy Oil with Iron Oxide-based Catalysts Using Steam

Petroleum refineries utilize thermal cracking, catalytic cracking and hydrogenation processes to produce high quality oil products. Hydrodesulfurization is one of the most important methods to remove sulfur from petroleum fractions. Heavy oil contains various types of sulfur compound. The structure of the sulfur compounds affects the ease of sulfur removal1). Acyclic sulfur compounds including thiols and disulfides can be easily removed. In contrast, cyclic sulfur compounds containing a thiophene ring have lower reactivity, which decreases with a higher number of aromatic rings. The ease of sulfur removal follows the order: acyclic sulfur compounds>thiophene>benzothiophene> dibenzothiophene (DBT). The cost of sulfur removal in heavy oil upgrading may be reduced by the use of water as an alternative hydrogen source. Several studies have reported desulfurization of heavy oil using water2)~5). Benzothiophene and DBT were decomposed by hydrothermal reaction with alkali2). Upgrading of oil sand bitumen using supercritical water showed similar trends in sulfur content as upgrading in high-pressure nitrogen3), but addition of MoS2 catalysts improved the sulfur removal from Arabian Heavy crude oil in supercritical water4). Hematite nanoparticles were catalytically active to desulfurize thiophene in aquathermolysis5). We previously reported that catalytic cracking of atmospheric residual oil (AR) with iron oxide-based catalysts containing zirconia and alumina produced light oil using the oxygen and hydrogen species derived from steam6),7). The oxygen species were incorporated from steam into the iron oxide lattice, and reacted with heavy hydrocarbons. The oxygen species were transferred from steam to carbon dioxide and a small amount of oxygen-containing compounds6). This reaction produced the hydrogen species from steam. Some of the hydrogen species were added to product hydrocarbons, suppressing alkene generation6). The present study investigated desulfurization of heavy oil with iron oxide-based catalyst using hydrogen and oxygen species derived from steam, and examined desulfurization of AR and reactivity of cyclic sulfur compounds using DBT as a model compound.