Study On Synthesis,optimization And VOCs Adsorption Properties Of Fly Ash Based Zeolite

Coal accounts for the largest part of energy consumption in China.Coal combustion produces a large amount of fly ash,which not only pollutes the soil,water and atmospheric environment,but also seriously endangers human health.On the other hand,fly ash has good hydration activity,large specific surface area and adsorption performance.It is a recyclable resource,which is often used for landfill,road making and building materials production.Zeolite is an ore with cage structure.Because of its excellent adsorption performance,it is widely used in the fields of sewage treatment,waste gas adsorption and soil improvement.Commercial high-quality zeolite is mainly synthesized by reagent,and the preparation cost is high.The synthesis of zeolite from fly ash can reduce its preparation cost,which is a promising high-value utilization way.In order to optimize the synthesis of fly ash zeolite,X-type fly ash zeolite was synthesized in this paper.The effects of initial concentration,adsorption temperature and space velocity on the adsorption of acetone by X-type fly ash zeolite were studied.The adsorption mechanism of acetone by X-type fly ash zeolite was clarified through kinetic analysis,and then high silicon content biomass ash was added to modify the doping of fly ash,The physicochemical method of alkali ball milling destroyed the physical structure of fly ash and biomass ash and improved the extraction rate of silicon and aluminum.ZSM-5 zeolite with adjustable Si/Al ratio was synthesized by alkali melting hydrothermal method.Combined with characterization technology,the effect of Si/Al ratio on the properties of ZSM-5 zeolite was studied.On this basis,the effects of Si/Al ratio on the VOCs adsorption performance and hydrophobicity of ZSM-5 zeolite were studied,and the thermal stability of ZSM-5 zeolite was investigated.Finally,the adsorption mechanism of ZSM-5 zeolite was revealed through kinetic and thermodynamic studies,and the economy of the resource utilization of biomass ash and fly ash to synthesize zeolite was evaluated.The main work of this paper is as follows:1,Preparation of fly ash X-zeolite and its adsorption mechanism for acetone.X zeolite was synthesized from fly ash.The properties of zeolite were analyzed combined with characterization technology.The characterization results of XRF,XRD and SEM show that the synthesized zeolite has less impurities,high crystallinity,single crystal phase,and the particle surface morphology presents a standard octahedral structure of X-type zeolite.Therefore,the synthesized zeolite is a high-quality X-type zeolite.At the same time,the results of nitrogen absorption and desorption showed that the average particle size of zeolite was 0.83μm.The average pore size of zeolite is3.2 nm,the specific surface area is 165.8 m²·g^-1,and the total pore volume is 0.13 cm³·g^-1.The effects of initial concentration,adsorption temperature and space velocity on the adsorption of acetone by X-type fly ash zeolite were studied.It was found that the higher the initial concentration,space velocity and temperature,the faster the adsorption penetration and saturation;In the experimental range,temperature and space velocity are negatively correlated with the adsorption capacity,while the initial concentration is positively correlated with the adsorption capacity.Finally,the adsorption mechanism of fly ash X-type zeolite is studied by kinetic model fitting.The results show that Bangham model and quasi first-order model can better fit the adsorption process of acetone on X-type fly ash zeolite,and the adsorption mechanism of acetone on X-type fly ash zeolite is more in line with the pore adsorption dominated by physical adsorption.2,Study on the synthesis of high quality ZSM-5 zeolite by modifying fly ash with biomass ash.Adding biomass ash with high silicon content to modify fly ash,and using the mechanochemical method of alkali ball milling to destroy the physical structure of fly ash and biomass ash,the chemical bond is destroyed by alkali melting method,and the extraction rate of silicon and aluminum is improved.Combined with ICP and XRD,it is found that the optimal ball milling time under activation conditions is 2 hours,and the optimal alkali ash ratio is 1.2:1.Five kinds of zeolites with different Si/Al ratio were synthesized by adjusting the ratio of fly ash to biomass ash in raw materials.Combined with characterization experiments,the effects of Si/Al ratio on the properties of zeolites were studied.The XRF results show that the synthetic zeolite has less impurities and high purity,and the Si/Al ratio is basically consistent with the Si/Al ratio of the raw material;SEM results show that when the Si/Al ratio is 400 and 800,the surface compactness and dispersion of zeolite particles are the highest,and the surface morphology of zeolite is the best;XRD and nitrogen adsorption/desorption experiments show that when the Si/Al ratio of zeolite is between 50 and 400,the crystallinity,specific surface area and pore volume of ZSM-5 zeolite increase with the increase of Si/Al ratio.When the Si/Al ratio reaches 800,the zeolite skeleton collapses,resulting in the decrease of crystallinity,specific surface area and pore volume;The results of NH₃-TPD and FITR experiments show that the amount of Lewis acid sites on the surface of ZSM-5 zeolite is inversely proportional to the Si/Al ratio,and the amount of Br?nsted acid sites is not affected by the Si/Al ratio.Finally,the economy of preparing ZSM-5zeolite from fly ash and biomass ash is evaluated.It is found that compared with commercial ZSM-5 zeolite,the total cost per ton of zeolite can be reduced by 1200 yuan by synthesizing ZSM-5 zeolite from fly ash and biomass ash.3,Study on adsorption performance and adsorption mechanism of ZSM-5 zeolite for VOCs.The adsorption properties of ZSM-5 zeolite with different Si/Al ratio for toluene,acetone and dichloromethane were compared.It was found that ZSM-5（400）had the best adsorption performance for three VOCs among the five zeolites;Among the three VOCs,ZSM-5 zeolite has the best adsorption performance for acetone.The effect of Si/Al ratio on the hydrophobicity of ZSM-5 zeolite was studied.The results showed that the higher the Si/Al ratio,the better the hydrophobicity of ZSM-5 zeolite.The effect of thermal desorption regeneration times on the adsorption performance of ZSM-5 zeolite was investigated.It was found that the adsorption performance of ZSM-5（400）did not decrease significantly after multiple thermal desorption regeneration,and ZSM-5 zeolite had good thermal stability.Finally,the adsorption mechanism of ZSM-5 zeolite is revealed through kinetic and thermodynamic analysis.It is found that the quasi first-order model,Bangham thermodynamic model and Freundlich thermodynamic model can better fit the adsorption process of ZSM-5 zeolite for three VOCs,and the adsorption mechanism of three VOCs on ZSM-5 zeolite is closer to the multi-layer pore adsorption dominated by physical adsorption.