Adsorption of octamethylcyclotetrasiloxane on silica gel for biogas purification

Biogas can be used as a fuel for electricity conversion. However, volatile organic silicon compounds (including siloxanes) in biogas severely damage combustion engines or solid oxide fuel cells. Three adsorbents of different nature were tested for octamethylcyclotetrasiloxane (D4) removal and silica gel (SG) proved to be the most efficient. It was shown that SG adsorption capacity is in the order of 250 mgD4/gSG and the adsorbent bed height has little influence on this adsorption capacity. In the presence of water (relative humidity of 70%), the adsorption capacity was lowered by 90% due to competitive effects and preferential adsorption of water. An increase of the temperature of roughly 20 °C also lowered the adsorption capacity but the decrease was less than 15%. Moreover, SG regeneration by heating was only partial, probably due to siloxane polymerization on SG.