Study On The Adsorption Performance Of Carbon Silicon-based Adsorbent For VOCs

Gas pollution is an important factor restricting social and economic development,endangering human health and destroying the atmospheric environment,and has attracted more and more people’s attention.In recent years,strict regulations have been imposed on the emission limits of organic gas pollutants（VOCs）and secondary pollutants produced by industry.At present,the main adsorbent of VOCs treatment technology is carbon-based adsorbent material.The key factors of carbon-based adsorbents in industrial applications are adsorption performance,complex operating conditions and recycling performance.Based on this,a novel sol-gel method using multi-walled carbon nanotubes（MWCNTs）loaded with silica（SiO₂）to develop a new type of carbon-silicon-based adsorbent（MWCNTs-SiO₂）.Characterize the adsorbent with transmission electron microscope（TEM）,scanning electron microscope（SEM）,X-ray diffractometer（XRD）,fully automatic physical static analyzer（BET）and Fourier infrared spectroscopy（FTIR）to understand its surface physics Chemical properties.Through the self-created experimental platform,the molar content of MWCNTs（38 mol%,52 mol%and 66 mol%）,adsorption temperature（30℃,40℃,50℃and 60℃）,water vapor（H₂O）volume concentration（1%,3%and 5%）and the number of cycles of regeneration on the adsorption capacity of toluene（C₇H₈）,and compared with the adsorption capacity of activated carbon（AC）.The model analysis of adsorption kinetics and thermodynamics is completed.The following conclusions are drawn:（1）Within 30℃～60℃,the adsorption capacity of MWCNTs-SiO₂adsorbent and AC for C₇H₈ is:AC<CS2（38 mol%）<CS4（52 mol%）<CS6（66 mol%）.Under the best conditions（700 ppm,0%H₂O,30℃and 100ml/min）,CS6 achieves a C₇H₈ adsorption capacity of 50.28 mg/g;for every10℃increase in temperature,the breakthrough time decreases by 10-20minutes;During the adsorption process,the surface active adsorption center is gradually occupied by C₇H₈,at which time the penetration rate of C₇H₈ is the fastest;the penetration rate decreases near the adsorption saturation stage;each time the volume concentration of water vapor increases by 1%,the MWCNTs-SiO₂ adsorbent adsorbs The content dropped by about 3.5%.（2）MWCNTs-SiO₂ adsorbent has good recycling performance.FTIR characterization proves that the type of MWCNTs-SiO₂ adsorbent after regeneration will not change.After 7 regenerations,the adsorption capacity is not less than 73%of the original adsorption.（3）During the whole C₇H₈ adsorption process,the adsorption rate of C₇H₈ by MWCNTs-SiO₂ adsorbent is not completely controlled by the outer surface absorption reaction;CS2,CS4 and CS6 are respectively 170 min～270min,180 min～260 min and 180 min～260 min.The quasi-secondary adsorption kinetic model R² is greater than 0.99 in the 260 min time period,proving that C₇H₈ can be well described by the quasi-secondary adsorption kinetic model at the stage of the fastest mass transfer rate in the sample;When the agent is inside,intragranular diffusion plays a major role;the molar percentage of MWCNTs is in the range of 38%to 66%.When the temperature increases from 10℃to℃～60℃,the absolute value ofΔG decreases by 0.3 k J·mol^-1～0.5 k J·mol^-1,indicating that as the temperature increases,the spontaneous degree of the adsorption process decreases;the adsorption process is exothermic reaction,the adsorption entropy changesΔS to a negative value,and the absolute value ofΔS is between 0.04 J·mol^-1·K～0.05 J·mol^-1·K;MWCNTs-SiO₂ adsorbent adsorbs C₇H₈ during molecular adsorption free Degree decreases,and C₇H₈ is adsorbed on MWCNTs-SiO₂ adsorbent Belonging to the physical adsorption.Above all,MWCNTs-SiO₂ adsorbent has excellent adsorption performance and recycling capacity for C₇H₈,and its adsorption capacity decreases with increasing temperature and water vapor volume concentration;model fitting shows that intragranular diffusion mainly occurs The entire process is exothermic and the spontaneous degree of adsorption decreases with increasing temperature,The MWCNTs-SiO₂ adsorbent can be applied to the complex working conditions of industrial practical applications.The adsorption kinetics and adsorption thermodynamic analysis make the MWCNTs-SiO₂ adsorbent predict the C₇H₈ adsorption model more accurately.