Basic Sorbents for High-pressure CO2-Containing Streams: Experimental Investigations and Energy Evaluations

Current liquid sorbents for CO2 capture in post-combustion gas mixtures are based on aqueous solutions of aliphatic alkanolamines, which react with carbon dioxide by forming carbamates. Regeneration of sorbents is therefore energy intensive. The present work shows that aromatic amines can be used advantageously, because of their lower energy demand. CO2 capture experiments are carried out in batch mode, allowing gas to flow into the headspace of a reactor at various pressures and temperatures. Sorption kinetics by the present liquid sorbents are measured by integrating data from a mass flow meter. Tests were conducted under two different pressures (10-20 bar) and temperatures (10-20 °C) for 4M water-ethanol solutions of the aromatic amines. CO2 sorption profiles show faster capture kinetics as the temperature and pressure, independently, increase. Alkylated derivatives are generally faster at sorbing CO2, while sorption amounts at the equilibrium are comparable for several species. Desorption/regeneration of sorbents occurred at a much lower temperature (30 °C) than with common alkanolamines. 80% saturation of some of the sorbents is very fast, being reached in 1-3 minutes. Loading capacities up to 200 mg CO2/g of sorbent solution (4.5 mol CO2/ kg solvent) were observed. Energy demand calculations show how the present systems are much cheaper than those based on carbamate-forming sorbents. We propose that such energy savings may be invested in pressurization of a post-combustion flue gas, leading to the possibility of application of imidazole-based sorbents to this industrial process. In fact, it is shown that the energy burden added for pressurization is more than overcome by the drastic reduction of the sorption/desorption temperatures. This cooler process also decreases the corrosion potential of the sorbent.