Molecular Sieve Hydrophobic Modification-optimization Of Dispersant

At present,China has entered a new stage of coordinated control of ozone（O₃）and fine particulate matter(PM_2.5,mainly including secondary organic aerosols,SOA).Volatile organic compounds（VOCs）are the key precursors of PM_2.5and O₃in atmospheric environment.Therefore,the control of VOCs pollution has become an important work of air pollution prevention and control in China.The end treatment and control measures are very critical for the treatment of VOCs waste gas discharged from industrial sources.Adsorption method is one of the most widely used technologies for the treatment of VOCs waste gas at present,and adsorption materials become the key.Molecular sieve as a kind of adsorption material with excellent performance is affected by its hydrophilicity,in the treatment of organic waste gas under high humidity conditions is limited,so in order to meet the needs of industrial production,hydrophobic modification of molecular sieve is one of the important research topics at present.At present,the commonly used modification method is liquid deposition method.Although some researches have made some achievements in graft modification,few researches have been made on the selection of dispersant.Based on this problem,this paper modified ZSM-5 and Na Y molecular sieves with trimethylchlorosilane（TMCS）by liquid phase deposition（CLD）method,respectively,to explore the effects of different reaction temperature,reaction time and reactant ratio on the hydrophobicity of modified molecular sieves when different dispersants（toluene and anhydrous ethanol）were used.It was characterized by means of SEM、FTIR、XRD、nitrogen desorption、water contact Angle and thermogravimetric analysis,etc.to explore the influence of dispersant on the modified results from the perspective of structure and performance.The adsorption performance of modified molecular sieve to toluene and ethyl acetate under different humidity conditions was tested,and the reuse rate and regeneration conditions were evaluated through the exploration of regeneration means and regeneration temperature,then the adsorption isothermal model is fitted.The experimental results show that ZSM-5 molecular sieve is more suitable for this method.Using anhydrous ethanol as dispersant,the organic group-Si（CH₃）₃can be grafted to ZSM-5 molecular sieve,which significantly improves its hydrophobicity,and the modification effect is significantly better than that of the sample with toluene as dispersant due to the relationship between like dissolves like and kinetic diameter.When the modification temperature was 40℃,the reaction time was controlled at 24 h,and the ratio of raw materials was ZSM-5（g）:anhydric ethanol（m L）:silane coupling agent（m L）=1:10:0.4,the modification effect was the best,and the static water adsorption rate could be as low as1.13%.To evaluate the adsorption performance of ZSM-5 zeolite to toluene and ethyl acetate under different humidity before and after modification.The results showed that the saturation adsorption capacity of sample ZSM-5-E modified by anhydric ethanol to toluene under 90%humidity could reach 81.9 mg/g,which was nearly three times that of the sample modified by toluene。Through the dynamic adsorption experiment,the dynamic saturation adsorption amount of toluene with ZSM-5-E with anhydrous ethanol as dispersant is better than that with toluene as dispersant,and the adsorption amount of ethyl acetate is larger than that of toluene.This is because ethyl acetate has small molecular weight,small steric resistance,large effective adsorption surface area and pore volume,which can quickly enter the micropores of molecular sieve to complete the adsorption process,resulting in fast adsorption rate and large saturated adsorption capacity.The mechanical stability and thermal stability were achieved after hydrophobic modification.By using hot air desorption and vacuum thermal desorption to investigate the regeneration performance of the selected ZSM-5-E₀at different temperatures.Under the same temperature,the recycling efficiency of vacuum thermal desorption is1.3 times of hot air desorption.