Influence of CO and H₂ concentrations on coal gas dechlorination by supported manganese oxide sorbent

The Mn₂O₃/SiO₂ sorbent prepared by incipient wetness impregnation was investigated for the elimination of chlorine species produced from coal gasification. The experiments were conducted in a fixed-bed reactor at 673 K with the Mn₂O₃/SiO₂ sorbent at various CO and H₂ concentrations to evaluate their influences on the dechlorination performance. It was observed that the absence of inlet H₂ led to a drastic decrease in the sorbent capacity; i.e., the presence of H₂ was essential for achieving dechlorination. Furthermore, the concentration of CO seemed to have no obvious effect on the HCl removal. Through the breakthrough experiments, X-ray powder diffractometer, and Fourier transform infrared spectroscopy analysis, the overall dechlorination mechanism of the Mn₂O₃/SiO₂ sorbent in a chlorine-containing coal gas system was successfully described in this study. The mechanism consisted of three major routes: (a) Mn₂O₃ reacted with HCl to form MnCl₂, (b) Mn₂O₃ was first reduced into Mn₃O₄ and then reacted with HCl to produce MnCl₂, and (c) without the involvement of HCl in the dechlorination experiments, the Mn₂O₃ contained in the fresh sorbent was first reduced to Mn₃O₄ and then to MnO under the strong reducing atmosphere provided by CO and/or H₂.