Study On The Surface Structure Regulation Of Y Zeolites And Its Structure-activity Relationship For Adsorption Of Typical Volatile Organic Compounds

Y zeolites have the characteristics of moderate pore size,large specific surface area and good hydrothermal stability.Its VOCs(volatile organic compounds)adsorption characteristics and adsorption capacity are most similar to the commonly activated carbon adsorbents used in industry.In view of the problem of poor performance of Y zeoites adsorption of VOCs under high humidity conditions,conventional Y zeoites was taken as the research object,composite dealumination modification and gas phase silicon-coated modification method were used to adjust its surface structure,and X-ray diffraction(XRD),N2 adsorption-desorption,Fourier infrared(FT-IR),solid nuclear magnetic(NMR)and other modern analysis and characterization methods and typical VOCs static/dynamic adsorption performance evaluation experiment were combined in this thesis.The research on the surface microstructure of Y zeoites,its hydrophobic properties and the structure-activity relationship of typical VOCs adsorption were carried out from the following four aspects:(1)The conventional NaY zeolites was used as primary material to prepare high-silicon hydrophobic Y zeolites by composite dealuminization modification method.The results of the study showed that the oxalic acid-ammonium chloride buffer solution(Oxalic acid:ammonium chloride:water=1:10:50,weight ratio)was used to treat the Y zeoites twice,and the ratio of silicon to aluminum was able to meet the acid leaching requirements,and the crystallinity remained above 80%.Further 0.5 mol/L nitric acid used for acid leaching treatment,the ratio of silicon to aluminum of Y zeoites was increased to 42.7,the crystallinity was 74.5%,the specific surface area was 785 m2·g-1,the hydrophobic coefficient Hn was 3.19,its toluene static saturation adsorption capacity was 32.6%,and water contact angle was increased to 135°.Under the condition that GHSV is 15000 ml·h-1·g-1,T=35?,C0=5000 mg·m-3,RH=60%,its dynamic adsorption capacity for toluene is 0.21 g/g.(2)Organosilane used as modifying agent,gas-phase silicon-coated modification method was used to hydrophobically modify the three silicon-aluminum ratio HY(5),HY(40)and HY(120)zeoites.Optimal preparation conditions are that under O2 atmosphere,the reaction temperature was 250?,trimethylchlorosilane(TMCS)was the modifying reagent,and the modification time was 40 min.The modified three silica-aluminum ratio Y zeoitess have the highest hydrophobic coefficients Hn of 1.92,3.30 and 4.86,and the crystallinity was maintained above 81%.The pore size of zeoites remained basically unchanged,the specific surface area only decreased by 8.1%,5.3%,and 4.1%;and the dynamic adsorption capacity of toluene was 0.15,0.21,and 0.25 g·g-1.The signal peak attributed to the amorphous SiO2 species in the new environment appears at ?=-90.2,indicating that the gas-phase silicon-coated modification successfully covered the surface of zeoites with SiO2.(3)In order to explore the adsorption mechanism and theoretical model of VOCs on hydrophobic Y zeolites,zeolites cluster model was constructed to perform density functional theory calculation and fit the toluene adsorption isotherm.From the results of adsorption energy calculated by density functional theory,the toluene adsorption energies of HY,silicon-coated modified Y zeolites and high silicon Y zeolites were-2.2 kJ/mol,-4.4 kJ/mol and-5.9 kJ/mol.The water adsorption energies were-5.2 kJ/mol,-2.3 kJ/mol and-1.9 kJ/mol,which were in agreement with the experimental data;The adsorption isotherm fitting results showed that the adsorption behavior of toluene adsorption of high-silicon Y zeolites and silicon-coated modified Y zeolites was more in line with Langmuir model and Langmuir-Freundlich mixed model model,respectively.It can be seen that the hydrophobic Y zeolites formed strong interaction with toluene molecules through van der Waals force,and performs single-molecule physical adsorption.The adsorption mechanism was mainly micropore filling.(4)The high-silicon Y and silicon-coated modified Y zeolites prepared by composite dealumination modification have little difference in the adsorption capacity of different VOCs,and have broad spectrum adsorption.After desorption for 15 min under the desorption power of 800 W microwave,four typical VOCs molecules can be completely desorbed on hydrophobic zeolites,and the desorption rate can reach more than 90%.After 30 cycles of regeneration,the desorption rate of dilute materials tended to be stable,maintained at about 91.2%and 90.5%,and the saturated adsorption rate of dilute materials was maintained at about 30.3%and 21.2%.