Dynamic studies on carbon dioxide capture using lignocellulosic based activated carbons

In this work, CO2 adsorption tests are carried out in a lab-scale fixed-bed reactor from a simulated flue-gas,at four temperature levels (30, 45, 60 and 80 °C) and different CO2 concentrations (3–30 %). Three different activated carbons (AC) derived by agricultural raw materials, namely peach stones, olive stones and apricot stones, were synthesized by a combination of pyrolysis and activation by water vapour. The textural characterization of the AC samples by N2 adsorption at -196 °C shows that the AC derived from apricot stones has the highest micropore volume, almost shifted toward ultramicropores, while the AC derived from olive stones shows the highest contribution of meso and macropores. Adsorption tests show that the AC derived from apricot stones has the highest CO2 adsorption capacity at 30 °C, due to its microstructural properties. Differently, at higher temperatures, the AC derived from apricot and peach show similar performances, due to their similar content of basic functional groups and pHPZC values. In all the cases, the Freundlich model provides very good data interpretation. The kinetic patterns reveal that the adsorption rate is mainly related to the mean Sauter particle diameter of the AC samples and, at less extent, to their meso and macropore content. Finally, a modelling analysis allowed individuating the intraparticle diffusion as the adsorption rate-limiting step.