Sorbents for Desulfurization of Refinery Off-Gases

The off-gases from various refinery operations could be converted into valuable chemicals, such as hydrogen, instead of being sent to flare, where they contribute to energy loses and greenhouse gas emissions. However, refinery off-gases contain large concentrations of sulfur and other impurities. Before these gases can be converted to hydrogen, sulfur and other impurities must be removed to prevent poisoning of the reforming catalysts used in the conversion process. Traditionally, desulfurization has been achieved by a two-step process consisting of hydro desulfurization (HDS) and subsequent removal of H2S with an expendable chemical absorbent. Although this approach has long been used for the desulfurization of natural gas feed stocks (where the sulfur level does not exceed 5-10 ppmv), its utility for use with high sulfur off-gases is cost prohibitive. This project will develop a novel physical adsorbent to desulfurize refinery off-gases. The sorbent, which will be operated either in an expendable or regenerable manner, operates at near ambient temperatures (20-60oC) and reduces the sulfur content of the gas stream to ppb levels, thereby protecting the catalyst used in the downstream conversion process. Unlike conventional sorbents, the material removes not only H2S but also organic sulfur compounds (such as mercaptans, sulfides and thiophenes) with high capacity and higher removal efficiency. Phase I (1) developed low cost, regenerable sorbents that can remove sulfur compounds from refinery off-gases with very high capacity; (2) demonstrated that the regenerable sorbent maintains its capacity for over 20 absorption/regeneration cycles; and (3) established the potential for the cost-effective production of hydrogen from sulfur-contaminated refinery off-gas streams. Phase II will improve sorbent performance, scale-up its production using commercial manufacturing techniques, design and fabricate a prototype test unit, and carry out a detailed system analysis and engineering assessment. Commercial Applications and Other Benefits as described by the awardee: The new sorbent technology should provide U.S. refiners with a cost-effective way to remove sulfur from refinery off-gases. The cost of the process should be low enough to allow the resulting gases to be profitably used as a low cost feedstock for hydrogen production. The sorbent also could be used to desulfurize any light hydrocarbon stream that is used as a feedstock for catalytic chemical conversion or as a feed for a fuel cell.