Adsorption of octamethylcyclotetrasiloxane (D4) on silica gel (SG): Retention mechanism

Silica gel (SG) is an efficient adsorbent for the removal of octamethylcyclotetrasiloxane (D4) – a volatile organic silicon compound present in biogas. Complementary physicochemical characterizations of SG before and after D4 adsorption were performed: specific surface area, porosity, pH measurements, infrared spectroscopy, thermodesorption, thermogravimetry and differential scanning calorimetry. A retention mechanism, based on a combination of hydrogen bonding (at low uptake) and polymerization (at higher uptake) is proposed. This mechanism is able to explain the difficulties of siloxane thermal desorption.