Equilibrium and Dynamic CO2 Adsorption on Activated Carbon Honeycomb Monoliths

In this work, CO2 adsorption tests from simulated flue gas are carried out in a laboratory-scale fixed-bed reactor, at different temperatures (303 and 353 K) and CO2 concentrations (3−25%), in order to investigate both the kinetics and thermodynamics. To this purpose, two different activated carbon (AC) monoliths were synthesized starting from an African Palm stone (Elaeis guineensis), activated either with H3PO4 (48% w/v) or with a combination of H3PO4 (32% w/v) + CaCl2 (2% w/ v), respectively. In order to increase the affinity toward CO2, the AC monoliths were subjected to the same surface modification postprocess, conducted with a 30% (w/w) aqueous ammonia solution. The textural characterization of the AC monoliths was carried out by N2 and pure CO2 adsorption at 77 and 273 K, respectively, allowing determination of the micro- and mesopore volumes as well as pore-size distributions. The adsorption tests show a maximum CO2 adsorption capacity for the sample with the greatest ultramicropore volume, while the adsorption rate increases in the presence of mesopores and for higher temperature. Moreover, dedicated regeneration studies demonstrate that both of the AC monoliths can be fully regenerated at each investigated adsorption temperature and their CO2 adsorption capacity remains almost constant in five consecutive cycles of adsorption−desorption. It can be concluded that AC monoliths can be a good alternative to granular or powdered AC for CO2 capture in fixed-bed adsorption columns.