CO₂ capture from the atmosphere and simultaneous concentration using zeolites and amine-grafted SBA-15

CO₂ capture from the atmosphere and concentration by cyclic adsorption-desorption processes are studied for the first time. New high microporosity materials, zeolite types Li-LSX and K-LSX, are compared to zeolite NaX and amine-grafted SBA-15 with low amine content. Breakthrough performance showed low silica type X (LSX) to have the most promise for application in dry conditions and capable of high space velocities of at least 63 000 h ^-1, with minimal spreading of the CO₂ breakthrough curve. Amine-grafted silica was the only adsorbent able to operate in wet conditions, but at a lower space velocity of 1500 h^-1, due to slower uptake rates. The results illustrate that the uptake rate is as important as the equilibrium adsorbed amount in determining the cyclic process performance. Li-LSX was found to have double the capacity of zeolite NaX at atmospheric conditions, also higher than all other reported zeolites. It is further demonstrated that by using a combined temperature and vacuum swing cycle, the CO₂ concentration in the desorption product is >90% for all adsorbents in pellet form. This is the first report of such high CO₂ product concentrations from a single cycle, using atmospheric air.