Siloxane adsorption on activated carbons: Role of the surface chemistry on sorption properties in humid atmosphere and regenerability issues

Commercial activated carbons (ACs) have been studied in dynamic adsorption of octamethylcyclotetrasiloxane (D4) in both dry and wet conditions. 1000 ppm (v/ v) D4 with N-2 as carrier gas and relative humidity (RH) up to 70% were used. Samples were characterized by physicochemical techniques such as N-2 and H2O adsorption/desorption at -196 and 20 degrees C, respectively, XPS, Boehm titration, chemical and elemental analysis, thermogravimetric measurements. No correlation between adsorption capacity in dry conditions and textural properties could be established. In wet conditions, the presence of hydrophilic sites preferentially adsorbing H2O strongly decreases the ability of ACs to adsorb D4. The regenerability by thermal treatment after D4 adsorption in dry conditions was also addressed and followed by gas chromatography and in situ DRIFTS. The D4 polymerization into polysiloxanolate/PDMS was found to proceed on ACs containing alkali metals (K, Na) as revealed by the observed release of their decomposition products during the thermodesorption treatment. This property is detrimental to the regenerability of the AC by blockage of its porosity. The eventual formation of polysiloxanalolate type species during the adsorption could also be responsible for limiting the D4 uptake by partial blockage of the AC porosity.