Process Study On The Synthesis Of ZSM-5 Zeolite For VOCs Adsorption Using Desilication Solution Of Coal Gasification Slag

ZSM-5 zeolite is an aluminosilicate porous zeolite.It has good thermal stability,water vapor stability,non-flammability,and renewability due to its unique pore structure.It has the potential to be an effective adsorbent for the removal of volatile organic compounds（VOCs）in environmental protection.Coal gasification slag is a typical bulk coal-based solid waste with an annual output of over 33 million tons.Because the gasification slag is rich in Si O₂,it can be used to synthesize high value-added materials such as ZSM-5 zeolite.The methods of synthesizing ZSM-5 zeolite currently have some drawbacks,such as high cost of raw materials,long processing durations.It is very important to study the synthesis of ZSM-5 zeolite with high efficiency and low cost.ZSM-5 zeolite was synthesized utilizing hydrothermal and microwave methods using coal gasification slag desilication solution as the main raw material in this study,respectively.The process settings were optimized,and the adsorption effect of ZSM-5 zeolite on VOCs was further evaluated under the optimal conditions.The following are the main contents and conclusions of the study:（1）The hydrothermal synthesis of ZSM-5 zeolite for VOCs adsorption was studied with coal gasification slag desilication solution as the main Si source and Na source.The desilication solution of coal gasification slag was mixed with aluminum source,template and ZSM-5 zeolite without aging step.The effects of reaction time,reaction temperature,Na₂O/Si O₂ molar ratio and Si O₂/Al₂O₃ molar ratio on the relative crystallinity and specific surface area of ZSM-5 zeolite were investigated and optimized.The optimum reaction conditions were as follows:12 h,170℃,Na₂O/Si O₂ molar ratio of 0.2,Si O₂/Al₂O₃ molar ratio of 200.The ZSM-5 zeolite synthesized under these conditions was hexagonal,with regular grains,relative crystallinity of 101.48%,specific surface area of 337.48 mg·g^-1 and pore volume of 0.190 cm³·g^-1.In the adsorption evaluation of ZSM-5 zeolite,the static saturation adsorption capacities of p-xylene,benzene,toluene and butyl acetate were 118.85,69.98,68.74 and 95.85 mg·g^-1,respectively,showing that the ZSM-5 zeolite produced by hydrothermal technique may achieve effective adsorption.The approach has the advantages of a quick synthesis time and a straightforward preparation process.Simultaneously,the high value utilization of the silicon component in the coal gasification slag was realized,which is simple to produce on a wide scale and has the potential for industrial application.（2）The one-step microwave synthesis of ZSM-5 zeolite from coal gasification slag desilication solution and the adsorption evaluation of VOCs were carried out to shorten reaction time.ZSM-5 zeolite was rapidly crystallized by microwave after the desilication solution,aluminum source,template and crystal seed were combined uniformly according to the feed ratio.On the relative crystallinity and specific surface area of ZSM-5 zeolite,the effects of microwave reaction time,reaction temperature,Na₂O/Si O₂ molar ratio and Si O₂/Al₂O₃ molar ratio were examined and adjusted.The optimum reaction conditions were as follows:4 h,180℃,Na₂O/Si O₂ molar ratio of 0.2 and Si O₂/Al₂O₃ molar ratio of 200.The ZSM-5 zeolite synthesized under these conditions was hexagonal,with smooth crystal surface and uniform grain size.The relative crystallinity was 103.5%,specific surface area of 344.27 mg·g^-1 and the pore volume of0.196 cm³·g^-1.The experimental results of the adsorption evaluation of VOCs showed that the static saturation adsorption amounts of ZSM-5 zeolite were 106.84,63.83,58.85 and 115.47mg·g^-1 for p-xylene,benzene,toluene and butyl acetate,respectively;and the dynamic adsorption capacities of p-xylene and butyl acetate were 81.44 and 176.14 mg·g^-1,respectively.The adsorption of p-xylene and butyl acetate on the ZSM-5 zeolite followed a pseudo first-order kinetic model,with physical adsorption playing a significant role in the adsorption process.The crystallization of zeolite by microwave method significantly reduced the reaction time,and the ZSM-5 zeolite product had excellent physical and chemical properties.Meanwhile,utilizing coal gasification slag desilication solution,it established a green and practical process pathway for the short procedure and rapid manufacture of ZSM-5 zeolite for VOCs adsorption.