Surface modification of activated carbon for siloxane adsorption

The presence of siloxanes challenges the use of landfill gas (LFG) as a fuel for energy recovery, due to the formation of microcrystalline silica deposits during combustion. Activated carbon (AC) is often selected as an adsorbent for removing siloxanes from LFG. In order to find the key characteristics that affect the siloxanes adsorption capacity of AC, this paper studied the effects of AC textural structure and surface chemistry on siloxane adsorption. Anthracite AC was respectively treated by aqua ammonia, hydrochloric acid and heat to obtain modified AC with different surface properties. Adsorption capacities of the original and modified AC for octamethylcyclotetrasiloxane (D4) were measured. Results showed that most of the modified AC had a higher D4 adsorption capacity than the original AC. Several approaches were adopted to characterize the AC. The results obtained by nitrogen adsorption experiment revealed that all the employed modification methods changed the AC pore size distribution to some extent. The narrow mesopores on the AC surface are more desired for the siloxane adsorption. As for the AC surface functional groups, the results obtained by Boehm titration revealed that the alkaline and phenolic groups are favorable for siloxane adsorption, while the carboxylic groups are undesired for siloxane adsorption.