A comparative study of the removal of o-xylene from gas streams using mesoporous silicas and their silica supported sulfuric acids

The three types of silica supported sulfuric acids (SSA), with the same sulfuric acid loading of 9.25 mmol g^-1, were prepared by a wet impregnation method from silica gel (SG), SBA-15 and MCM-41. Characterization of the prepared SSA showed that two anchoring states coexisted for sulfuric acid supported on the surface of the silicas: A physiosorbed (P)-state sulfuric acid; and a chemically bonded (C)-state sulfuric acid. Dynamic adsorption results showed that each SSA had a significant removal capacity for o-xylene gas in the reactive temperature regions. The ranges of the reactive regions were 120-220 °C (SSA/SG), 120-230 °C (SSA/SBA-15) and 120-250 °C (SSA/MCM-41), and this could be attributed to the sulfonation reaction between o-xylene and the anchored sulfuric acid. SSA/MCM-41 showed the highest theoretical breakthrough adsorption capacity (Q_{B, th}, 526.71 mg g^-1) compared with SSA/SBA-15 (363.54 mg g^-1) and SSA/SG (239.15 mg g^-1). Q_{B, th} was closely associated with the amount or proportion of the C-state sulfuric acid on the surface of each SSA. Optimum breakthrough time and Q_{B, th} was obtained by increasing the bed height and decreasing flow rate and inlet concentration. The SSA exhibited excellent recyclability and reuse performance over eight consecutive adsorption/desorption/regeneration cycles. The results suggested that the SSA, especially SSA/MCM-41, might have good potential in applications using adsorbents for the removal of BTEX pollutants.