Performance Stability And Kinetics Of Zinc-based Ordered Mesoporous Sorbent For High Temperature Coal Gas

H₂S existed in coal gas will cause serious pollution to product and environment,which requires to be removed for further utilization.During the desulfurization process of high temperature coal gas,the sorbents employed are prone to sintering and pulverization,and thus the desulfurization performance will be restricted by the poor stability and low repeating utilization rate.Hence,improving the stability and performance of sorbents in multiple desulfurization-regeneration cycles are of great significance for developing coal gas desulfurization technology.In this paper,zinc acetate was used as raw material,modified MCM-41 was selected as supporter,the effects of factors on the construction of multistage pore structure were investigated.Zn-based ordered mesoporous high temperature gas sorbent was prepared through in-situ oxidation method and the textures and desulfurization properties of sorbent were optimized.The structure-activity relationship between the microstructure construction of sorbent and properties was clarified.The enhancement of mass transfer and interfacial effects based on thermal and non-thermal effects of microwave heating during preparation and regeneration process were investigated to reveal the mechanism of microwave heating on microstructure and properties of sorbent.The influences of sorbent textures on activity and stability were also analyzed from the perspective of kinetics.Specific research results are as follows:(1)In preparation process,the pore structure regularity of sorbent decreased with the increase of aluminium content.When the ratio of Si/Al was 30:1,the sulfur capacity was largest,9.14 g S/100 g sorbent.The ability for H₂S removal of sorbent increased firstly and then decreased with the increase of crystallization p H.When the p H value was 10.0,the desulfurization performance of sorbent achieved the optimal value.The structure performance of sorbent improved with the increasing of sulfur source addition.The specific surface area and pore volume of sorbent reached the maximum at the ratio of Zn to S was 1:3.The desulfurization performance of sorbent significantly improved with the increasing of active component,and it reached the optimal when the ratio of Zn to Si reached0.32:1.Based on the results above,the optimal preparation conditions of sorbent were ratio of Si/Al 30:1,crystallization pH 10.0,ratio of Zn/S 1:3 and ratio Zn/Si0.32:1.(2)During in-situ oxidation process,when the oxidation temperature was650°C,the oxidation rate of the precursor reached the highest,and the desulfurization performance of sorbent was the best.The sorbent had largest sulfur capacity when the space velocity was 3000 h^-1.The desulfurization performance of sorbent reached the optimal at 6 vol%oxygen concentration.Therefore,the optimal conditions of in-situ oxidation process were:650°C for oxidation temperature,3000 h^-1 for space velocity,6 vol%for oxygen concentration.In the desulfurization performance test,the initial sulfur capacity of Al-doped sorbent decreased,while in the process of multiple desulfurization-regeneration cycles,the supporter of Al-doped sorbent showed high stability in structure,the sulfur capacity retention rate increased from 51 to 81%.(3)Compared to the conventional method,microwave oxidization-regeneration reduced the binding energy of active components of sorbent,which improved the adsorption capacity of sorbent to H₂S.Meanwhile,it promoted the active components migrated to the surface of sorbent,which resulted in an increase of the active sites for desulfurization and improved the desulfurization activity,the initial sulfur capacity of sorbent prepared by microwave increased to10.30 g S/100 g sorbent.The characteristic of microwave reduced the influence of high temperature on sorbent supporter,which maintained the regularity of pore structure during desulfurization-regeneration cycles and improved the desulfurization performance stability of sorbent.The sulfur retention rate of sorbent obtained by microwave oxidization-regeneration method increased to 88%after five times desulfurization-regeneration cycles.(4)Reaction kinetics showed that the desulfurization and regeneration reaction of sorbent were all first-order reaction.In desulfurization reaction,the introduction of aluminium increased the surface chemical reaction activation energy and reduced the product layer diffusion activation energy,which was triggered by enhancement of surface acidity and improvement of structure stability caused by doping of aluminium.The surface chemical reaction activation energy and product layer diffusion activation energy decreased for sorbent oxidized by microwave,which indicated that microwave enhanced the micro mass transfer and elevated the desulfurization activity of sorbent.In the study of sorbent regeneration kinetics,it was found that the surface chemical reaction activation energy and product layer diffusion activation energy of sorbent which doped with aluminium were reduced,and further decreased after microwave oxidation.It indicated that improving the structure stability of sorbent can reduce the reaction resistance in desulfurization-regeneration process and promote the performance of sorbent in the process of multiple desulfurization-regeneration cycles.