Pore Structure Control And Hydrophobic Modification Of Zeolites And Their Adsorption Performance For Volatile Organic Compounds

In recent years,air pollution has received widespread attention.Volatile organic pollutants（VOCs）emissions are increasing yearly,and can react with nitrogen oxides to produce secondary pollutants,such as ozone and PM_2.5,and harm to human health.The adsorption technology is an effective technique due to its low cost,high efficiency and simple operation.Zeolites with unique pore structure,large specific surface area and high stability are an ideal adsorbent for VOCs adsorption.It is of great significance to control the pore structure and functional groups of zeolites to improve the adsorption performance of VOCs.In addition,due to the hydrophilicity of the zeolite surface,water competes with VOCs for adsorption,resulting in a decrease in VOCs adsorption capacity.It is important to improve the hydrophobicity of the zeolite and the adsorption capacity of VOCs in a humidity environment.This paper selected zeolites with three-dimensional pore structure and adjusted the specific surface area,pore volume and surface hydroxyl groups of zeolites by adding organic solvent,and explored the effect on the adsorption performance of VOCs.The core-shell structured zeolite/hydrophobic organic polymer composites were synthesized,and explored the VOCs adsorption performance under high humidity conditions.Besides,a one-step molding method was developed to prepare monolithic zeolite spheres with excellent VOCs adsorption performances under high humidity environment.The main results as follows:（1）Y zeolite with high porosity was successfully synthesized by using THF as co-solvent.The effects of different crystallization time,crystallization temperature and THF contents on the crystal structure were investigated,and tested the acetone adsorption performance.THF acted as filler and promoted the template role of cations in the synthesis process.The specific surface area and micropore volume of THF-Y-3increased by 21.4%and 25.7%,while the amount of THF was only 1.3%of the molar mass of water in the synthesis mixture.The obtained Y zeolite had superior acetone adsorption performance（178.9 mg/g）,which was much higher than other zeolites.（2）EMT zeolite with micro-mesoporous structure and rich surface hydroxyl was successfully synthesized by adding polyethylene glycol（PEG400）.The effect of PEG400 amounts on the crystal structure and acetone adsorption performance was investigated.During the synthesis process of zeolite,the silica-alumina gel formed structural units around PEG400,resulting in more mesoporous structures.0.6PEG-EMT zeolite had a higher specific surface area,larger mesopore volume and more hydroxyl groups,which significantly improved the adsorption performance of acetone.0.6PEG-EMT zeolite showed the excellent adsorption capacity for acetone（101.2mg/g）,which was 20.6%higher than pure EMT zeolite.（3）Y@St-DVB composites with hydrophobicity and thermal stability were successfully synthesized using phenylsiloxane as a bridge.The toluene adsorption capacity of Y@St-DVB-12h was 69.9%higher than that of Y zeolite under dry conditions.Under 60%and 90%relative humidity conditions,the toluene adsorption capacity was 1.97 and 1.96 times of that of Y zeolite.This strategy was also applicable to other zeolites（EMT,ZSM-5,Beta zeolite）to modified the hydrophobicity,which can improve the adsorption capacity of toluene under humidity conditions.（4）The Y@P composites with excellent hydrophobicity were synthesized by different crosslinking agents.Y@P-2-80 composite exhibited the better pore structure,excellent hydrophobicity and high toluene adsorption performance when the polymerization temperature was 80℃,and the crosslinking agent was benzaldehyde dimethyl acetal.The toluene adsorption capacity of Y@P-2-80 under 30%,60%,and90%relative humidity were 99.2%,98.8%and 97.2%of adsorption capacity under dry conditions,respectively.Water vapor had little effect on the toluene adsorption capacity.After five regeneration cycles under 60%relative humidity,the adsorption capacity remained above 93%,showing excellent adsorption and desorption performance.（5）This paper adopted the one-step molding method of citric acid to prepare monolithic zeolite spheres,and tested the acetone and toluene adsorption performance under dry and humidity conditions.The results showed that the dealumination of citric acid on the zeolite increased the Si/Al,specific surface area and mesopore volume of the zeolite.In addition,the aluminum species could also act as a“bridge”to increase the force between the zeolite particles.The mechanical strength of the zeolite spheres reached to 15 N,which could maintain the current industrial application requirements.Under 90%relative humidity,the acetone and toluene adsorption capacity of 4M-Y712zeolite spheres reached above 90%of the adsorption capacity under dry conditions,which showed potential in the practical industrial application prospects.