大孔对ZnO/SiO_(2)复合脱硫剂常温脱硫性能的影响机制

Influence mechanism of macropores on the room temperature desulfurization performance of ZnO/SiO_(2)adsorbent

煤化工行业作为我国主要的碳排放源,在双碳目标的约束下将面临巨大挑战。煤制气体精脱硫是煤炭高效清洁利用的重要组成部分,对于碳减排意义重大。氧化锌是目前普遍使用的干法精脱硫剂,但受动力学的限制,其在常温下的脱硫活性非常低,无法满足工业应用要求。孔扩散是氧化锌与H_(2)S反应发生的前提,但目前鲜有报道研究孔径,特别是大孔对脱硫性能的影响及影响机制。基于此,采用溶胶凝胶法和胶晶模板法分别制备了以介孔为主和以大孔为主的ZnO/SiO_(2)复合脱硫剂,探究了大孔结构的引入对其常温脱硫性能的影响。研究表明,尽管大孔的引入会增加脱硫剂的比表面积、强化表面碱性、提高氧化锌的分散性以及增加脱硫剂中氧空位浓度,但会导致脱硫剂脱硫性能大幅下降。介孔脱硫剂的穿透硫容为151.9 mg/g,是大孔脱硫剂的脱硫性能的2.3倍。这是因为大孔结构不稳定,在脱硫过程中易坍塌,阻碍了氧化锌反应位点的获取。气氛中的水汽在大孔表面不利于凝聚成水膜,进而抑制了脱硫反应的发生。更为重要的是,大孔制备过程中由于模板剂的燃烧会释放大量热,致使SiO_(2)网络发生深度交联,从而减小了脱硫剂中的介孔孔径。较小的介孔孔径导致其表面物理吸附水的量过多,进而抑制了氧化锌与H_(2)S的反应。

The coal chemical industry,as the main source of carbon emissions in China,will face great challenges under the constraints of the dual carbon goals.Coal derived gas deep desulfurization is an important component for highly efficient and clean utilization of coal,which is of great significance for carbon reduction.Zinc oxide is a commonly used adsorbent for desulfurization,but due to kinetic limitations,its room temperature desulfurization reactivity is very low,and this cannot meet the requirements of industrial application.Pore diffusion is a prerequisite for the reaction between ZnO and H_(2)S,and is crucial for desulfurization performance.However,the influence of pore size,especially macropores,on the desulfurization performance and its mechanism have been rarely reported.For this reason,two ZnO/SiO_(2)adsorbents with mesopores and macropores in this study were prepared using a sol-gel method and a colloidal crystal template method,respectively,and the influence of macropores on their room temperature desulfurization performance was explored.It is found that although the introduction of macropores increases the specific surface area of the adsorbent,strengthens its surface alkalinity,improves the dispersion of ZnO,and increases the concentration of oxygen vacancies in the adsorbent,its introduction leads to a remarkable decrease in the desulfurization performance of adsorbent.The breakthrough sulfur capacity of mesoporous adsorbent is 151.9 mg/g,2.3 times than that of macroporous adsorbent.This is because the macroporous structure is unstable and prone to collapse during the desulfurization process,which hinders the accessibility of reaction sites of ZnO;Secondly,the water vapor in the atmosphere is not conducive to the formation of a water film on the surface of macropores,thereby inhibiting the occurrence of desulfurization reactions.More importantly,the combustion of the template releases a large amount of heat during the preparation of macropores,which leads to a deep crosslinking of the SiO_(2)network and a decrease in the mesoporous pore size of adsorbent.The smaller mesoporous pore size results in an excessive amount of water physically adsorbed on its surface,inhibiting the reaction between ZnO and H_(2)S.