(30d) Desulfurization of Refinery off-Gases for Hydrogen Production

Petroleum refining has become the second largest industrial consumer of energy in the U.S, accounting for approximately 10% of the total manufacturing energy use. The petroleum industry was also responsible for 3% of the toxic waste emissions and 17% of the greenhouse gas emissions from manufacturing section. A large fraction of these emissions come from the combustion (in some cases flaring) of various by-product fuel gases. In a typical refinery, these off-gases are generated from various separation units (crude distillation, cracking, hydro-treating) generate off-gasses. Because of the lack of the technologies that could convert these refinery off-gases into valuable products, many of these gases are currently flared. The off-gases from various refinery unit operations could be converted into valuable chemicals such as hydrogen instead of being sent to flare which contributes to energy loses and greenhouse gas emissions. However, the refinery off-gases contain large concentrations of sulfur and other impurities such as arsenic that must be removed to prevent the poisoning catalysts used in hydrogen production. Traditionally, deep desulfurization can be achieved by a two-step process consisting of hydrodesulfurization (HDS) and subsequent removal of H₂S with an expendable chemical absorbent. Although this approach has long been used for desulfurization of natural gas feedstocks (where the sulfur level does not exceed 5-10 ppmv), the one-time use of expendable metal oxide type sorbents for cleanup of the refinery off-gas is not practical due to the high concentration of sulfur and the presence of organic sulfur compounds which are not absorbed at near ambient temperatures.

TDA Research, Inc. (TDA) is developing a novel physical adsorbent, which will be operated in a regenerable manner to desulfurize refinery off-gases. The sorbent operates at near ambient temperatures (20-60^oC) while reducing the sulfur content of the gas stream to less than ppmv levels (and can reduce the sulfur content to ppb levels if needed) to protect the catalyst used in the downstream conversion process. Unlike conventional sorbents, in addition to H₂S, our material removes organic sulfur compounds (such as mercaptans, sulfides and thiophenes) with high capacity and higher removal efficiency. The sorbent can be regenerated by applying a mild temperature swing. In this paper we will demonstrate the performance of the regenerable sorbent under multiple adsorption/regeneration cycles and the economic viability of our desulfurization process for producing hydrogen from sulfur contaminated refinery off-gas streams.