Activated carbon-supported sulfuric acid as an adsorbent/polymerization catalyst for decamethylcyclopentasiloxane removal

Siloxanes are detrimental trace impurities that can severely impair the performance and operational efficiency of biogas combustion systems, making their effective removal essential. Given the relatively high concentration of cyclic siloxanes and their susceptibility to acid-catalyzed ring-opening polymerization, a combined adsorption–polymerization approach on a solid acid adsorbent may offer higher removal efficiency compared to conventional adsorption methods. In this work, we employed activated carbon as a support and fabricated sulfuric acid-supported activated carbon (CSA) via a simple impregnation method. This study represents the first systematic investigation of the synergistic adsorption and acid-catalyzed polymerization of decamethylcyclopentasiloxane (D5) using this material. The activated carbon function as an adsorbent, providing mass transfer channels for D5, whereas the supported sulfuric acid serves as a catalyst to promote its ring-opening polymerization. Dynamic adsorption tests showed that CSA exhibited a high D5 removal capacity, with a theoretical maximum capacity ( Q m, th ) of 3219.7 mg g −1 at 0 °C. A series of characterizations, kinetic interpretation, mass balance analysis and density functional theory (DFT) calculations were also conducted to elucidate the potential adsorption/polymerization mechanisms responsible for D5 removal. The results confirmed that the formation of highe-molecular-weight polysiloxane structures on the CSA surface imparted a high degree of hydrophobicity to the spent CSA material. These findings highlight the potential of CSA as a cost-effective and practical solution for siloxane removal.