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

• Physicochemical characterization of SG was performed before and after D4 adsorption.
• After D4 adsorption, SG pores were totally blocked.
• After D4 adsorption, free silanol groups at the SG surface were less abundant.
• After D4 adsorption on SG, no desorption occurred in the range 25–800 °C in nitrogen.
• Retention mechanism is based on hydrogen bonding, ring opening and polymerization.

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.

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