Surface Modification Of Porous Material And Its Performance In Polar VOCs Adsorption

Volatile organic compounds（VOCs）are one of the important sources of air pollution,which not only has a potential impact on the atmospheric environment,as well as causing serious harm to indoor air quality and human health.Adsorption is an effective end-of-pipe treatment measure to control the pollution of industrial emissions of VOCs waste gas.The performance of adsorbent is the key factor affecting the treatment efficiency.The adsorption performance of currently available adsorbent materials for polar VOCs such as methanol,methylene chloride and acetonitrile is not satisfactory due to the low number of polar groups on the surface and low adsorption rate,which makes it necessary to develop porous adsorbent materials with higher adsorption activity for these polar components.In consideration of the widespread use of activated carbon and molecular sieve in the adsorption of industrial VOCs-containing tail gas,the relatively inexpensive columnar activated carbon and ZSM-5 molecular sieve,which is rich in surface polar groups,were selected in this paper,and to their surfaces were modified to improve their surface polarity,and the performance after modification were investigated as well.Finally,the porous adsorption material with better adsorption effect was selected for the fixed bed adsorption process design.The main studies are as follows:The activated carbons were modified by acid modification and oxidation modification,and then characterized by scanning electron microscopy（SEM）,specific surface determination（BET）,Fourier infrared spectroscopy（FTIR）and Boehm titration.The results showed that both approaches could increase the content of oxygen-containing functional groups on the surface of activated carbons,and the most significant increase in the content of oxygen-containing functional groups was achieved with hydrogen peroxide modification.The results of dynamic adsorption tests showed that the hydrogen peroxide-modified activated carbon had the highest adsorption capacities for the three adsorbents,with the maximum adsorption capacities of 122.5 mg·cm^-3,164 mg·cm^-3 and128 mg·cm^-3 for the polar VOCs methanol,methylene chloride and acetonitrile,respectively.The molecular sieves of ZSM-5 with different silica-alumina ratios were synthesized by hydrothermal method and modified by doping with metal ions.The results indicate that among ZSM-5 molecular sieves with different silicon aluminum ratios,ZSM-5 molecular sieve with a silicon aluminum ratio of 120 has the largest pore volume,and among different metal doping modifications,Ca-ZSM-5 molecular sieve has the largest pore volume.The static adsorption test results show that the metal doping modification can improve the adsorption capacity of ZSM-5 molecular sieve.Ca-ZSM-5 molecular sieve has the largest static adsorption capacity to methanol,dichloromethane and acetonitrile,which were 472 mg·cm^-3,712 mg·cm^-3 and 484 mg·cm^-3,respectively.For the two adsorbents with the best adsorption effect,the correlation coefficients wer all above 0.995 when the dynamic adsorption curve was fitted by Yoon-Nelson model.For the Freundlich and Langmuir adsorption isotherm models,the Langmuir isotherm adsorption model gave the best simulation result for both adsorbents,indicating that the adsorption of methanol,dichloromethane and acetonitrile on the two adsorbents were mnonlayer adsorption.The initial concentration and temperature affect the length of the mass transfer zone and the total mass transfer coefficient of the substances in the adsorption experiments,and the high temperature was found to be unfavorable for the adsorption to proceed.The recycling performance of Ca-ZSM-5 molecular sieve was found to be better than that of the modified activated carbon material in the recycling adsorption experiments..For the high-concentration organic waste gas(40 000 m³·h^-1,1400 mg·m^-3)mainly containing methanol component generated by a glycine manufacturer,Ca-ZSM-5molecular sieve as the adsorbent,and the process of concentration by the fixed-bed adsorption and condensation by heat-exchanger was designed and calculated.At a cycle period of 24 h,three adsorption beds were used,each with an adsorbent loading volume of4.418 m³,and the methanol fraction was recovered by condensation heat exchange with a heat exchanger condensation area of 14.09 m².The results can provide a basis for calculations for the industrial adsorption of methanol,a polar component of VOCs,by Ca-ZSM-5 molecular sieve.