Biogas upgrading through CO2 removal by chemical absorption in an amine organic solution. Physical and technical assessment, simulation and experimental validation

An experimental and modelling study of CO2 removal from a simulated biogas feed by chemical absorption in an organic solution of 2-amine-2-methyl-1-propanol in an ethylene glycol and n-propanol solvent is presented. Absorption was carried out under different temperature, feed flow rate, and feed recirculation conditions. Regeneration was carried at different temperatures. Cyclability tests showed that the absorption capacity remained stable starting from the fourth cycle. In the conditions analyzed, higher temperatures and liquid recirculation favor absorption. With all other conditions constant, the CO2 absorption efficiency increased from 72% to 87% when the temperature increased from 23 to 45°C. At 33°C, liquid recirculation enhanced the absorption efficiency from to 93%–97%. A model was developed and validated against experimental results. Absorption and desorption rates are proportional to the carbon dioxide and AMP concentrations and to the alkyl carbonate concentration, respectively. The two rate constants were fitted from the experimental data: their values at 30°C are 0.033 s−1 (kmol/m3)−1 and 1.5 × 10−6 s−1, respectively. The model indicates that the beneficial effect of temperature and liquid recirculation is due to the increased mass transfer coefficient of CO2 from the gas to the liquid solution, which increased from 4 × 10−3 s−1 at 20°C to 1.3 × 10−2 s−1 at 70°C and by a factor of 8.8 as a consequence of feed recirculation. An increase in the biogas flow rate reduced the absorption efficiency by decreasing the contact time. Higher temperatures also increased the rate of CO2 desorption