The last six cycles of a 25-cycle sorbent durability test were completed, final installation of the flame photometric detector was accomplished, and fifteen tests whose aim was to determine the minimum prebreakthrough H{sub 2}S concentration over reduced CeO{sub 2} were performed. There was little, if any, evidence of sorbent deterioration in the durability test. During the durability test the author confirmed that, when using pre-reduced sorbent and a clean system, the prebreakthrough H{sub 2}S concentration was less than 100 ppmv, the detection limit of the thermal conductivity detector (TCD). Consequently, a more sensitive flame photometric detector (FPD) which permitted measurements of H{sub 2}S concentrations of 1 ppmv or less was installed. The FPD and TCD were connected in parallel so that, when desired, the entire H{sub 2}S breakthrough curve could be measured. Most of the quarter was devoted to conducting reduction-sulfidation tests to determine the minimum prebreakthrough H{sub 2}S concentrations which could be achieved using prereduced CeO{sub 2}. Fifteen runs involving variations in reduction-sulfidation temperature, H{sub 2}S concentration in the feed gas, and feed gas volumetric flow rate were completed. In all tests the prebreakthrough H{sub 2}S concentration was less than 10 ppmv, and in many of the tests the H{sub 2}S concentration was equal to or less than 1 ppmv for an extended time period.
