Regenerable solid sorbents for Claus tailgas cleanup: A treatment process for the catalytic removal of SO2 and H2S

Use of a regenerable solid sorbent can offer advantages over conventional wet scrubbing for Claus tailgas treatment. In this paper, we describe a novel process/catalyst combination for this service. The Mobil Oil SO, Treatment (MOST) process, demonstrated here on the laboratory scale, consists of first combusting the Claus tailgas with air, converting all sulfur species to SO2/SO3. The SOx is then sorbed onto a solid sorbent, and in a separate step, the sulfur is reductively desorbed as a concentrated stream of mainly SO2 and H2S, which can then be recycled to the Claus plant for further processing. Catalyst screening for this application focused on examining alumina and magnesium aluminates, with oxidation promoters including ceria, vanadia, and platinum. The materials with the highest SOx uptake are a commercial FCC SOx transfer additive and a vanadia/ceria-promoted, magnesium aluminate (V/Ce/Mg2Al2O5) spinel (54 and 46 wt% SOx uptake, respectively). During most of the adsorption period, the SO2 level in the effluent from the sorbent bed was below 1 ppmv. When the same base magnesium aluminate was examined with ceria but without vanadia, the SOx uptake was lower (25 wt%), while the base alone had fairly low uptake (5 wt%). Thus, effective SO2 oxidation promoters are necessary for this application. Oxidation of CO to CO2 was also demonstrated over these catalysts. All materials examined were found to be regenerable under hydrogen. The main products observed were SO2, H2O, and H2S. The results indicate that a regenerable solid sorbent-based SOx abatement system can give lower emissions of sulfur species and of CO than current Claus treatment processes and may allow a capacity increase in a hydraulically limited Claus plant.