Removal And Recovery Of O-xylene By Silica Gel Using Pressure Swing Adsorption

Volatile organic compounds(VOCs)are an important component of air pollutants.Their huge emissions seriously affect the lives and health of human.The treatment of VOCs has become an urgent and important environmental task.The use of vacuum swing adsorption on the recovery of VOCs is one of the most promising treatment technologies.Because it possesses the advantages of high removal efficiency,no secondary pollution,VOCs resource utilization,and so on.Furthermore,it could work together with other treatment technologies.In this study,silica gel was used as the adsorbent.O-xylene was selected as the typical VOCs.The systematic research of adsorption and desorption was carried out by vacuum swing adsorption.The results showed that the adsorption isotherms of o-xylene on silica gel conformed to the Langmuir-Freundlich model.Further thermodynamic characterization and interfacial characterization showed that the surface structure of silica gel was heterogeneous.The dynamic adsorption and desorption experiments suggested that increasing the ratio of height to diameter of the adsorbent bed,the feed flow rate or the initial concentration of o-xylene could enhanced the adsorption of o-xylene on the silica gel significantly.However,the desorption of o-xylene from silica gel was found to be improved by the reduction in the ratio of the height to diameter of the adsorbent bed,desorption pressure or increase in purge gas flow rate.After the experimental design and optimization,the optimum technological conditions were determined as: 5:1 for the ratio of height to diameter of the adsorbent bed,5 kPa(absolute pressure)for the desorption pressure,and 0.45 L/min for the purge gas flow rate.The adsorption and desorption kinetics were studied by mathematical model and fitting.The results showed that the adsorption of o-xylene on silica gel was film diffusion control and adsorption process could be enhanced by increasing the feed flow rate and the initial concentration of o-xylene.The adsorption and desorption processes were integrated and conducted with long-term operation to verify the results above.The long-term operation results showed that the removal efficiency of o-xylene was 100% with 87% of the VOCs directly recovered as liquid.Compared with heat treatment and absorption,vacuum swing adsorption showed a significant economic advantage,since it could recover VOCs as a by-product.These results indicate that vacuum swing adsorption using atmospheric air cooling to recover high boiling VOCs is a promising technology.