Preparation Of Opal Shale Mesoporous Material And Its Adsorption Properties To Toluene And Acetone

Most of the exhaust of volatile organic compounds?VOCs?emitted from industrial production plants are caused by the volatilization of organic solvents during the production process.They have characteristics of large air volume,low concentration,and high humidity.The use of an adsorption method to treat this type of industrial exhaust gas has the advantage of high removal rate and the possibility of organic material recovery.MCM-41 is a type of mesoporous molecular sieve with ordered hexagonal mesopores,which has the advantages of adjustable pore size and functional modification.Therefore,the adsorption and purification treatment of industrial VOCs exhaust gas can be realized by hydrophobing the MCM-41.In this paper,toluene and acetone were selected as typical VOCs and opal shale was used as the silicon source to prepare opal shale mesoporous materials for the adsorption efficiency of toluene and acetone and multiple cycle adsorption.In this study,acid activated pretreatment was used to deal with the natural opal shale,determining 2.0 mol/L sulfuric acid activated natural opal shale as the source of silicon for synthetic opal mesoporous materials.The effect of different synthesis conditions on the opal mesoporous ordering was investigated using X-ray diffraction?SXRD?within a small range of angles.It was found that the optimal synthesis conditions for opal shale mesoporous materials were SiO₂:CTAB:H₂O?molar ratio?=1:0.3:70,pH=11.0,stirring time 12 h,crystallization temperature 110°C,crystallization at 48 h,the characteristics of opal mesoporous materials were characterized in various ways,and the key technical advantages of the adsorption of VOCs by opal mesoporous materials were identified.The effects of single component toluene,acetone gas flow rate,initial inlet gas concentration,and adsorption temperature on the adsorption of toluene and acetone on the opal shale mesoporous materials were investigated.It was found that the saturated adsorption capacity of toluene and acetone increase first and then decrease with the increase of gas flow rate,reaching the maximum when the gas flow rate was 0.20L/min.And the saturated adsorption capacity increases with the increase of the initial concentration of VOCs and the amplitude decreases gradually.The saturated adsorption capacity decreases with increasing temperature and reaches the maximum at 20°C,and the dynamic saturated adsorption capacity is 137mg/g and 239mg/g respectively.In the two-component adsorption experiment of toluene/acetone,the role of the polar index plays a dominant role,as the acetone molecules displace the toluene adsorbed in the material.Adsorption kinetics results show that the adsorption results of toluene and acetone by opal mesoporous materials are in good agreement with the Langmuir adsorption equation.Freundlich adsorption fitting results show that the adsorption type is physical adsorption and acetone is more easily adsorbed than toluene.The results of the Yoon-Nelson model fitting curve show that the model has good applicability to adsorption of toluene and acetone on opal mesoporous materials,and the correlation coefficient is greater than 0.92.After the methyl/silanization,amino/silanization,and mercapto/silanization,the opal shale mesoporous materials was used to characterize the mesoporous order,specific surface area,functional group grafting,and hydrophobicity of the materials.Explore the adsorption efficiency of different silanized modified materials for moisture content of 60%VOCs.The steam desorption method was used to desorption and regeneration of the materials before and after the modification,and the change trend and rate of change of desorption rate over time were explored.The results showed that the order of the modified materials was good.The specific surface area and pore volume decreased to varying degrees with the specific surface area decreased by 11.9%,13.8%,and 14.19%,respectively,and the pore volume decreased by 22.6%,26.19%,and 25.0%,respectively.Si-OH,NH₂,and SH groups have been successfully grafted onto mesoporous surfaces and the hydrophobicity of the contact angle has been improved.The saturation adsorption capacities of the modified materials to toluene and acetone increased 3.5-fold and 3-fold,respectively.The modification effects of thiol/silanization and amino/silanization were better than that of methyl/silanization.The desorption rates of toluene in unmodified,methyl/silanized,amino/silanized,and mercapto/silylated opal shale mesoporous materials reached 96.72%,93.68%,91.5%,and 91.62%respectively,and the desorption of acetone.The rates were 89.23%,85.71%,81.65%,and 80.33%respectively.At the same temperature,the desorption rate of acetone was smaller than that of toluene.After five cycles of adsorption-desorption for opal shale mesoporous materials,the saturated adsorption capacities for toluene and acetone decreased by54.0%and 68.2%respectively.