Activated carbons prepared from hydrothermally carbonized waste biomass used as adsorbents for CO_2

摘要

Activated carbons prepared from hydrothermally carbonized (HTC) waste biomass were studied with respect to the adsorption of carbon dioxide. The physically activated carbons (PAC) exhibited a large adsorption of CO_2 of 1.45 mmol/g at a small partial pressure of CO_2 (10kPa and a temperature of 0℃). These PACs were prepared by activation in a stream of CO_2 and had significant amounts of ultramicrop-ores, which were established by analyzing the adsorption of CO_2 with a density functional theory. The uptake at such low pressures of CO_2 is of most importance for an adsorption-driven CO_2 capture from flue gas at large power stations, as it is difficult to imagine a pressurization of the flue gas. The capacities to adsorb CO_2 of the different activated carbons were compared with both the micropore volumes as established by N_2 adsorption, and the ultramicropore volumes as established by CO_2 adsorption. The ultrami-cropore volume is of crucial importance for the capture of CO_2 from flue gas. PAC from HTC grass cuttings and from horse manure had the largest ultramicropore volumes. In general, the PAC showed excellent cyclability of adsorption/desorption of CO_2 and a minimal capacity loss after subsequent cycles. In addition, the PAC showed a rapid adsorption of CO_2. Both characteristics are essential for the eventual use of such PACs in the adsorption driven separation of CO_2 from flue gas. A chemically activated carbon (CAC) was prepared by treating hydrothermally carbonized beer waste with H_3PO_4 and a heat treatment in a flow of N_2. This CAC showed a significant amount of mesopores in the range of 5 nm, in addition to micropores. The apparent selectivity for the activated carbons for CO_2-over-N_2 adsorption was determined at 0 ℃ and 10 kPa.