Functionalized Zn-based desulfurizer with ordered mesoporous structure based on insights into sulfur-release mechanism during hot coal gas desulfurization

Abstract

Sulfur-release effect impedes the engineering application of hot coal gas desulfurization. However, the related mechanism is not clear. This study aims to clarify the aforementioned effects and directionally design/fabricate ordered mesoporous Zn-based sorbents with function of inhibiting sulfur-release behavior. The results reveal that COS is mainly formed via R-1 (reaction between CO and H2S) before the reaction gas contacts Zn-based sorbents. R-2 (reaction between CO2 and H2S) catalyzed by ZnS is more kinetically favorable than its non-catalytic process. Furthermore, R-1 and R-2 contribute almost equally to the overall amount of released COS during desulfurization process. Then, considering the composition of coal gas, the strategy of promoter (with function of catalytic hydrogenolysis of COS) modification was proposed to inhibit sulfur-release behavior. A series of functionalized sorbents with four Zn/Me (Me: Mo, Ni) molar ratios (88:12–97:3) were constructed. The sorbents exhibit ordered pore-arrangement structure. Compared to unmodified sorbents, Mo- and Ni-doping both result in significant decline (by 98 %−99 %) in the amount of released COS before H2S-breakthrough. Moreover, the doping of Mo/Ni into ZnO generally produces positive effects on H2S-uptake activity. However, regeneration leads to notable deterioration of performance for Mo-doped sorbents. It is ascribed to the inadequate conversion of ZnS and structure destruction of sorbents. On the contrast, Ni-doped sorbents with Zn/Ni molar ratio of 90:10 could not only greatly suppress the sulfur-release effect and but also maintain 92 %−95 % of initial sulfur capacity during five sulfidation-regeneration cycles.