Adsorption equilibria and kinetics of silica gel for N2O, O2, N2, and CO2

Abstract

To gain insights into N2O recovery from industrial effluent, adsorption equilibria and kinetics of N2O, O2, N2, and CO2 on silica gels were evaluated at 293, 308, and 323 K under pressures of up to 1000 kPa using a volumetric method. Adsorption characteristics of the adsorbates on silica gel were compared with those on activated carbon. Adsorption isotherms indicated lower adsorption amounts for all of the adsorbates on silica gel, compared to those on activated carbon; both materials adsorbed higher amounts of N2O and CO2 than O2 and N2. In the case of silica gel, CO2 was adsorbed more strongly than N2O, while activated carbon exhibited the opposite. The experimental uptake on silica gel was well fitted by the non-isothermal diffusion model. The adsorption rate on silica gel was slower than that on activated carbon for all the adsorbates, while the order of adsorption rate was the same: N2 > O2 ≫ N2O ≥ CO2. The uptake results of N2O on varying sizes of silica gel indicated that macropore diffusion significantly affected adsorption on silica gel, which was not the case for activated carbon. The adsorption characteristics of N2O and CO2 on silica gel were distinct from those on activated carbon, due to the inherent electrical properties and molecular structural interactions of the adsorbent and adsorbates.