Study On Preparation Of A Hierarchical Porosity ZSM-5 Zeolite / Polymer Composites Using Coal Fly Ash And Adsorption Of VOCs

In this study,a typical solid waste coal fly ash from coal chemical industry was used as a raw material to prepare a hierarchical porosity ZSM-5 zeolite with excellent adsorption performance,in order to accelerate the mass transfer rate,improve the adsorption efficiency,and achieve efficient adsorption of benzene VOCs.And explore related adsorption mechanisms;We choose a polymer（polyethylene difluoride）with a large pore structure,good compatibility with inorganic materials,and good mechanical properties（combined with the above zeolite）to solve the large pressure drop during the adsorption of powdery zeolite while ensuring the zeolite adsorption efficiency in order to improve its actual use performance,the purpose is to find a new method of efficient and high value-added comprehensive utilization of coal fly ash.Firstly,the coal fly ash is processed by classification to extract the available elements Si and Al;the extracted siliconand aluminum are used to prepare a hierarchical porosity ZSM-5 zeolite using the double template-hydrothermal method.To investigate the effects of crystallization temperature,crystallization time and Na/Si ratio on the crystallization process of ZSM-5zeolite,use orthogonal tables to determine the optimal preparation conditions;compound the prepared hierarchical porosity ZSM-5 with polyethylene difluoride preparation of hierarchical porosity ZSM-5/polymer composites,and use of hierarchical porosity ZSM-5zeolite and hierarchical porosity ZSM-5 zeolite/polymer composites for adsorption studies on typical VOCs such as benzene and xylene adsorption mechanism.XRF,SEM,EDS,XRD,BET and other means were used to perform a series of characterization and analysis on coal fly ash,coal fly ash extract,and prepared ZSM-5 samples,and the hierarchical porosity ZSM-5 zeolite and hierarchical porosity ZSM-5 zeolite/polymer composites for benzene and xylene adsorption kinetics and thermodynamic simulations,the results show that:The SiO₂ content in the selected coal fly ash is 48.52%,the Al₂O₃ content is 33.59%,and it is rich in Fe2O3（5.66%）.Since the sum of the total content of SiO2,Al2O3 and Fe₂O₃ is more than 70%,the selected coal fly ash is classified as Class F.By comparing the amount of sodium carbonate and hydrochloric acid,comprehensively considering the extraction rate and experimental cost,the optimal synthesis conditions are determined as:CFA:Na₂CO₃=1:0.8,CFA:HCl=1:8 after calcination at 900℃for 4h,the extraction rates of SiO₂ and Al（OH）₃ were 94.89%and 87.26%,respectively;Increasing the crystallization temperature can speed up the nucleation and growth of zeolite crystals.If the crystallization temperature is too high,nucleation is inhibited;The characteristic peak increases with the time of synthesis.If the time is insufficient,the crystallization of zeolite is incomplete,and the time is too long,zeolite may be transgranular.Under different hydrothermal conditions,the crystal curve of zsm-5 zeolite is of the"S"type,which is divided into three stages:（1）"induction period";（2）"nucleation period";（3）"crystal growth period";Insufficient sodium ion will affect the crystallization rate.If it is excessive,it will synthesize other types of zeolites（mordenite）;Using the L₉3⁴ orthogonal table to find the best synthesis conditions are:SiO2:Al2O3:Na2O:CTAB:TPABr:H2O=1:0.02:0.5:0.05:0.17:50 crystallization at 160℃for 48h at a molar composition,and its BET analysis showed that it contains micropores and mesoporous structures,which proved the successful synthesis of a hierarchical porosity ZSM-5 zeolite;Hierarchical porosity ZSM-5 zeolite have saturated adsorption of benzene and xylene of 0.264 g/g and0.303 g/g,respectively.The adsorption of benzene and xylene conforms to the Freundlich thermodynamic model and pseudo-first-order kinetic model,respectively.The adsorption of benzene and xylene by hierarchical porosity ZSM-5 zeolite is mainly based on physical adsorption and multi-layer adsorption.The saturated adsorption amounts of benzene and xylene by hierarchical porosity ZSM-5 zeolite/polymer composite molecular sieve are0.134 g/g and 0.162 g/g,respectively.The adsorption of benzene and xylene is a Freundlich thermodynamic model and a pseudo-first-order kinetic model,respectively.The adsorption of benzene and xylene by composite materials is also dominated by physical and multilayer adsorption.