Removal of siloxanes from biogas using acetylated silica gel as adsorbent

Abstract

Biogas can be used as an alternative energy source for producing heat and electricity; however, volatile methylsiloxanes (VOSiC) present in biogas can severely damage heat exchangers, turbines and gas engines. Consequently, efficient removal of VOSiC from biogas that is used as a biofuel is required. In this work, acetylated silica gel (Ac@SG) was synthesized, via treatment of microporous silica gel (SG) with acetic anhydride as an adsorbent, for removal of VOSiC from biogas, and characterized with XRD, SEM–EDS, N2-BET and FT-IR. This Ac@SG adsorbent exhibited a meso-/microporous structure and hydrophobic surface, indicating it was a more efficient adsorbent for removing hexamethyldisiloxane (L2) and octamethylcyclotetrasiloxane (D4) from biogas samples than conventional SG. It was found that the adsorption capacities of Ac@SG reached 304 mg L2/g for hexamethyldisiloxane and 916 mg D4/g for octamethylcyclotetrasiloxane at lower temperatures in the experimental range, and water had no significant effect on its absorption efficiency. The used Ac@SG could be easily regenerated by heating it at 110 °C, and the adsorption capacity of recycled Ac@SG for hexamethyldisiloxane and octamethylcyclotetrasiloxane was kept constant in four recycle adsorption experiments.