Application of silica gel in removing high concentrations toluene vapor by adsorption and desorption process

Abstract

Abstract An energy-saving set-up of pressure swing adsorption has been designed and applied to remove the high concentrations of toluene vapor (∼12,000 ppm) by silica gel at ambient temperature. It is evident that the adsorption of toluene vapor on silica gel matches the Langmuir–Freundlich model during the whole vapor concentration (up to 3.5 kPa), which is different from that on traditional activated carbon (AC). Results also show that it is much easier and faster for silica gel to adsorb toluene than that of AC. Mechanistic study by microporous characterizations and thermodynamic analysis shows a higher isosteric heat of toluene adsorbed on silica gel (∼55 kJ/mol) compared with that on AC (∼43 kJ/mol) due to a much more significant multilayer adsorption on AC. The vacuum desorption tests show that the desorption capacity of toluene vapor from the silica gel is much higher (61.6% desorbed) than that from AC (46.22% desorbed) at ambient conditions. In addition, an obvious accumulation of toluene has been observed on AC after a five-cycle of dynamic adsorption-desorption tests. Long-time run tests demonstrate that over 75% of the adsorbed toluene could be recovered from the silica gel. Considering the long-time run in future application, the silica gel would be a better candidate for the removal and recovery of high concentrations of toluene vapor from gas stream using the normal adsorption and vacuum desorption combined process at ambient temperature.