Catalytic reduction of sulfur dioxide using hydrogen or carbon monoxide over Ce_(1-x)Zr_xO2 catalysts for the recovery of elemental sulfur

摘要

This study focuses on the direct sulfur recovery process (DSRP), in which SO2 can be directly converted into elemental sulfur using a variety of reducing agents over Ce_(1-x)Zr_xO2 catalysts. Ce_(1-x)Zr_xO2 catalysts (where x = 0.2,0.5, and 0.8) were prepared by a citric complexation method. The experimental conditions used for SO2 reduction were as follow: the space velocity (GHSV) was 30,000 ml/g_(-cat) h and the ratio of [CO (or H2, H2 + CO)]/[SO2] was 2.0. It was found that the catalyst and reducing agent providing the best performance were the Ce_(0.5)Zr_(0.5)O2 catalyst and CO, respectively. In this case, the SO2 conversion was about 92% and the sulfur yield was about 90% at 550 °C. Also, a higher efficiency of SO2 removal and elemental sulfur recovery was achieved in the reduction of SO2 with CO as a reducing agent than that with H2. In the reduction of SO2 by H2 over the Ce_(0.5)Zr_(0.5)O2 catalyst, SO2 conversion and sulfur yield were about 92.7% and 73%, respectively, at 800 °C. Also, the reduction of SO2 using synthetic gas with various [CO]/[H2] molar ratios over the Ce_(0.5)Zr_(0.5)O2 catalyst was performed, in order to investigate the possibility of using coal-derived gas as a reducing agent in the DSRP. It was found that the reactivity of the SO2 reduction using the synthetic gas with various [CO]/ [H2] molar ratios was increased with increasing CO content of the synthetic gas. Therefore, it was found that the Ce_(1-x)Zr_xO2 catalysts are applicable to the DSRP using coal-derived gas, which contains a larger percentage of CO than H2.