CO2 Absorption in Porous Geopolymers

Alkali bonded ceramics are synthetic and amorphous alkali aluminosilicates, currently known as geopolymers. Since they can be regarded as the amorphous counterpart of zeolites, their application can be potentially extended in the chemical sector of molecular sieves. Geopolymers have a quite good CO2 adsorption capacity and selectivity up to 200 and 100 for CO2/N2 and CO2/CH4 separation, respectively, considerably higher than those of most of the adsorbent materials commonly accounted for such applications. The addition of zeolites or hydrotalcites as fillers can further improve the adsorption capacity for low and intermediate temperature CO2 capture applications. Na-based geopolymer-zeolite composites revealed a synergistic effect, as the CO2 capacity at low temperature was approximately 20% larger than the expected value. As well different types of hydrotalcites with different Mg/Al ratio can be used as fillers in geopolymer matrices for adsorption at intermediate temperature. Upon calcination, the structure of hydrotalcite changes, with loss of interlayered anions and water: the mixed oxide metaphase presents a large surface area and great affinity for CO2.