Removal and recovery of o-xylene by silica gel using vacuum swing adsorption

Abstract

The removal and recovery of o-xylene (a typical volatile organic compounds, VOCs) by silica gel has been systematically investigated by vacuum swing adsorption (VSA) process. Laboratory scale measurements show that the adsorption of o-xylene on silica gels could be significantly enhanced by increasing the height to diameter ratio (H/D) of adsorption bed, the inlet flowrate and o-xylene initial concentration. However, reducing the H/D and desorption pressure or increasing the amount of purging gas are observed to be favorable for the desorption of o-xylene from the silica gels. The optimized operational conditions are determined at 5:1 for H/D, 5kPa (absolute) of desorption pressure and 0.45L/min of purge gas flowrate. According to further kinetic fitting and analysis, it is found that the adsorption of o-xylene on this silica gel is film-diffusion control, which could be enhanced by increasing gas flowrate or initial o-xylene concentration. In addition, reducing the particle size of the silica gel is also found to increase the saturation of adsorbed o-xylene in silica gels. A scaled-up integrated VSA setup was applied to confirm the above results, leading to a complete o-xylene removal from the gas (100% removed) with 87% of o-xylene recovered directly as liquid. Based on a rough economic calculation, the VSA shows greater merits than those of traditional thermal treatment and absorption methods, due to its recovered VOCs as products. Additional tests by other aromatic VOCs further approved the feasibility of the VSA using silica gels. These findings indicate that the VSA with air cooling at ambient temperature would be a promising and ‘green’ technology for treating high boiling VOCs.