Dynamic separation of ultradilute CO2 with a nanoporous amine-based sorbent

Abstract

An alternative amine-based sorbent (RFAS) was developed in this work. RFAS was assessed under various conditions. Studies show that the CO2 sorption capacities of RFAS increase considerably with N loading, slowly with increasing temperature (apparently contrary to the prediction with the isothermal equation of exothermic sorption), and gradually with the decease of gas flow rate in the tested range. In addition, CO2 sorption capacity increases and then decreases as the H2O:CO2 mole ratio increases, and the stoichiometric ratio 1:1 is the turning point. The CO2 sorption capacities achieved by RFAS with 8.07mmolN/g for air with 400ppm CO2 and the CO2–N2 gas mixtures containing 1 vol% CO2 are 1.78mmol CO2/g and 1.92mmol CO2/g, respectively, higher than those reported in the most recent literature. A kinetic model corresponding to three proposed pathways is derived and expected to quantitatively predict the CO2 sorption characteristics given that the involved parameters can be established in the future. The half-CO2-adsorption and desorption times of RFAS along with temperatures are used to evaluate the dynamics of the sorbent. The adsorbed CO2 can be completely desorbed at only 80°C within as short as 30min. Low temperature desorption not only leads to the decrease in energy consumption but also benefits the structure stability of RFAS. The CO2 sorption capacities of RFAS within 10 sorption–desorption cycles are repeatable. All the results confirm that RFAS is a highly adsorptive, reversibly dynamic, and regenerable sorbent for capture of ultradilute CO2 from gas mixtures.