Competitive CO₂/H₂O Adsorption on CALF-20

The equilibrium and breakthrough studies of the H2O adsorption and the competition of CO2/H2O on a physisorbent MOF CALF-20, commercialized for CO2 capture from cement plants, are reported. Volumetric measurements and thermogravimetry were used to measure the water isotherm at various temperatures and relative humidity (RH) values. A Cubic-Langmuir model was used to describe the water isotherms at different temperatures. Both adsorption and desorption dynamic column breakthrough experiments were performed at different RH values to examine different transitions in the isotherm. To quantify the competitive adsorption of CO2 and H2O, both thermogravimetric analysis and dynamic column breakthrough techniques were required. A wide range of relative humidity (RH) values was considered, i.e., 10% to 90% RH. CALF-20 showed high CO2 loadings for RH was smaller than 47%; showing its exceptional capacity to be deployed for CO2 capture from industrial flue gas. Beyond 70% RH, water was strongly adsorbed, resulting in a significant loss of CO2 capacity. In the presence of CO2, CALF-20 showed an unique phenomena where water adsorption was suppressed making it more favourable for practical applications. The modified Langmuir isotherm model was used to describe the competitive CO2 loading as a function of water loadings and temperatures. A one-dimensional column model simulates the water dynamic column breakthrough and competitive CO2/H2O breakthroughs. Both concentration profiles and temperature histories agreed with the experimental results.