Oil desulfurization
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Oil desulfurization is a widely used process for removing sulfur from petroleum products (gasoline, diesel fuel, fuel oil, etc.) so that sulfur dioxide emissions are reduced from automobiles, trucks and other internal combustion engines and oil-burning power plants. Typically, those petroleum products are desulfurized in refineries using a process, referred to as Hydrodesulfurization (HDS). HDS involves the chemical reaction of hydrogen with petroleum products in the presence of a catalyst at high temperature, resulting in the removal of sulfur in the form of hydrogen sulfide gas.
The effectiveness of HDS is determined by the type of catalyst employed and by the severity of the operating conditions. HDS typically uses a catalyst containing transition metals such as cobalt and molybdenum. The desired amount of sulfur reduction is attained by controlling the severity of the reactor conditions, notably, temperature, hydrogen pressure, and residence time. In general, the better the catalyst and the more severe the conditions the more desulfurization occurs in a given time period.
An alternative to conventional HDS has been developed using the enzymes of microorganisms as the catalysts for sulfur removal, referred to as biological desulfurization or BDS. Interestingly, dibenzothiophene sulfur compounds are typically the most susceptible to BDS, yet, in contrast, are the most resistant to HDS. The removal of sulfur from these molecules can add significantly to refinery costs for the production of the low sulfur fuels mandated by current and pending EPA regulations.
The BDS process has not yet been commercially practiced largely to due to process cost issues arising from low catalytic rate and longevity. Energy BioSystems (now Enchira) was a company dedicated to the development of this technology. Research in this area continues in various locations around the world.
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