Molecular Simulation And Experiment Study On The Influence Of Zeolite Structure And Chemical Modification On VOCs Adsorption

In recent years,people have gradually realized the great harm of Volatile Organic Compounds（VOCs）.As one of the most important air pollutants,VOCs not only induces canceration and distortion of human body,but also forms photochemical smog and PM_2.5 under certain conditions.With the rapid development of economy,the total emission amount of VOCs has increased year by year and the composition of VOCs emission has become more and more complicated.Therefore,effective VOCs controlling is urgent.The adsorption method has many advantages,such as mature technology,high purification efficiency,low energy consumption,recyclable desorbed adsorbent.So it has been widely used in purification of VOCs waste in low contration and high flow rate.Adsorbent is the core that determines the adsorption performance.Zeolite is one of the important choices of VOCs adsorbent because of its flexiblility and stability.Due to the variety of VOCs and zeolites,it needs to take a lot of time and cost to complete the matching of VOCs and zeolites by experiment.In this study,firstly,molecular simulation and experiment were applied to investigate adsorption behavior of VOCs in pure silica zeolites.The purpose is to screen appropriate zeolites for different kinds of VOCs.After that,we could modify these zeolites with advanced method to improve adsorption capacity of VOCs.Above work could give guidance for optimizing the formula of adsorbents.Chapter one is the background review.Firstly,the harm of VOCs,the trend of emission and current controlling technologies were indrucuced.Secondly,the reaearch status of zeolites for VOCs adsorption was highlighted.Finally,in view of existing proploms,the research approach of screening matching zeolites for VOCs and optimizing formula of adsorbents by molecular simulation and experimental means was proposed.Chapter two introduced the materials and instruments used in the experiment and the theoretical algorithm adopted in the molecular simulation.It not only concluded the preparation methods for adsorbents and fixed-bed adsorption facility,but also concluded the basic theory and software modules for molecular simulation.Chapter three is on the researchs of VOCs adsorption preformance in pure silica zeolites.Firstly,Grand Canonical Monte Carlo method was applied to investigate the single component adsorption behavior of seven VOCs in twelve zeolites.We achieved the adsorption isotherms and adsorption site information of VOCs,thus completing the selection of zeolites and expliciting the adsorption mechanism of VOCs.At the same time,the effect of the effective porosity of zeolites on the VOCs adsorption was also studied.Then theoretical calculation results were verified by the adsorption experiment.The main conclusions were as follows:（1）many factors,such as topology structures of zeolites,the relative size of VOCs and aperture of zeolites,and polarity of adsorbates,colud influence the VOCs adsorption process;（2）the higher the effective porosity of zeolites was,the more VOCs the zeolites accommodated;（3）the adsorption capacity of polar VOCs is higher than non-polar ones.For non-polar molecules,with the adsorbate molar volume increased,adsorption capacity gradually decreased.Chapter four is on the researchs of VOCs adsorption preformance in modified zeolites.Firstly,Density Functional Theory was applied to calculate the adsorption energy of VOCs in different modified ionic zeolites.Then theoretical calculations were verified by adsorption experiments.The main conclusions were as follows:（1）compared with pure silica zeolites,zeolites would improve adsorption capacity of VOCs when introducing midified ion;（2）as for hydrogen zeolites,with the Si/Al ration decreased,increased acid sites in zeolites gradually enhanced adsorption capacity of VOCs;（3）when adsorbed in modified zeolites,VOCs adsorption characteristics were closely related to the existence of the modified ions in zeolites.In this paper,when copper existed in the form of[Cu-OH]⁺and Cu²⁺in MFI and BETA zeolites,the promotion for VOCs adsorption of Cu²⁺was better than that of[Cu-OH]⁺.Similarly,when La was in the presence of[La（OH）₂]⁺and La³⁺forms in the zeolites,the existence of La³⁺had more advantages to enhance VOCs adsorption.Chapter five is a summary of the full study.