High temperature gas desulfurization with elemental sulfur production

Preliminary results on the use of cerium oxide as a high-temperature desulfurization sorbent are presented. The primary advantage of cerium over current zinc-based sorbents is the potential to produce elemental sulfur during the regeneration phase of the process. Although CeO2 is less effective for H2S removal during sulfidation, the sulfided product, Ce2O2S, will react with SO2 to produce elemental sulfur directly. Rapid and complete regeneration is possible over the range of 500 to 700 degrees C, and only elemental sulfur is formed. Elemental sulfur concentrations (considered as S-2) as large as 20 mol% have been produced in the regeneration product. The sorbent has been subjected to ten sulfidation-regeneration cycles using a laboratory-scale fixed-bed reactor with negligible activity loss. Effectively complete conversion of CeO2 to Ce2O2S during sulfidation and subsequent regeneration to CeO2 was achieved in each cycle. A two-stage desulfurization process using CeO2 for bulk H2S removal followed by a zinc sorbent polishing step has been proposed to meet specifications of the integrated gasification combined cycle (IGCC) process. Economic comparison with a single-stage desulfurization process using zinc sorbent followed by elemental sulfur recovery using the direct sulfur recovery process (DSRP) shows that the two-stage cerium process may be less costly if the cerium sorbent is sufficiently durable. (C) 1999 Elsevier Science Ltd. All rights reserved.