Reduction of SO2 to elemental sulfur with H2 and mixed H2/CO gas in an activated carbon bed

Experiments and thermodynamic equilibrium calculations were carried out on a H2-SO2 system. The effects of temperature, H2/SO2 ratio, and retention time on SO2 reduction in an activated carbon bed were studied. The equilibrium calculations showed elemental sulfur to be the major S-containing product of SO2 reduction at low H2/SO2 ratios. However, when the H2/SO2 ratio was greater than three, the calculations predicted that SO2 would be completely reduced to H2S with elemental sulfur completely absent from the reduction products. The experimental results showed that the starting temperature for reduction of SO2 with H2 is 600 °C. In the presence of activated carbon, the starting temperature decreased and an obvious increase in the SO2 conversion and S yield was achieved at temperatures below 800 °C. The experimental results showed a lower SO2 conversion and higher S selectivity than those predicted by the equilibrium calculations because equilibrium was not achieved under the experimental conditions. Higher H2/SO2 ratios and longer retention times were beneficial to SO2 conversion. They also improved the S yield initially; however, subsequently, the yield decreased because an increase in S-containing byproduct formation after complete SO2 conversion was achieved. The activity of mixed H2/CO gas for SO2 reduction was also probed. CO displayed a higher SO2 reduction activity in comparison with H2. COS was the major S-containing byproduct at lower temperatures, while H2S was the main byproduct at 800 °C. At a H2/CO ratio of 1, the optimum SO2 conversion and S yield achieved were 99.3% and 79.3%, respectively, at 700 °C with a (H2 + CO)/SO2 ratio of 2.5.