Biogas upgrading by selective adsorption onto CO2 activated carbon from wood pellets

Abstract

An activated carbon from commercial pine wood pellets was obtained by means of physical activation with carbon dioxide. Carbonized sample was also prepared in order to compare both samples. Carbonization lead to a material with very low micropore volume, which was increased when physical activation was performed (W-0(N-2) from 0.00 to 0.22 cm(3)g (1) and W-0(CO2) from 0.21 to 0.31 cm(3) g (1)). After characterizing their porous texture, samples were tested as CO2 selective adsorbent in a mixture of CH4 and CO2; at first high pressure isotherms of both compounds were obtained at different temperatures to calculate the adsorbed amount of each compound at given pressure and temperature (for PINPEL20: CO2, q(sat) = 6.66 mol kg (1) and Delta H-ads = 28.4 kJ mol (1); CH4, q(sat) = 3.36 mol kg (1) and Delta H-ads = 19.0 kJ mol (1)). Variations on isosteric heat of adsorption with uptake were also analysed (it was increased with uptake in the case of CO2 and the opposite tendency was found for CH4). Selectivity resulted larger for the activated sample (2.9 versus 1.9 at 1 bar and 30 degrees C), so this one was chosen to perform dynamic adsorption experiments. Breakthrough curves demonstrated the outstanding performance of sample as CO2 selective adsorbent in both single component experiments (Breakthrough time 995 s for CH4 and 1545 s for CO2) and competitive adsorption (950 s for CH4 and 1373 s for CO2). Activated sample showed an excellent behaviour as CO2 selective adsorbent for biogas upgrading.