Characterization of novel geopolymer - Zeolite composites as solid adsorbents for CO2 capture

The article reports on the application of novel composite materials formed by Na13X zeolite embedded in a geopolymer matrix for low temperature CO2 capture applications. The formulation of the composite sorbent was varied (K and Na silicates), taking into account the chemical affinity between the two constituents and the need to produce materials in suitable shapes for application in real processes. In this respect, the sorbents were produced in forms of monoliths. The morphological characterization showed the presence of geopolymer nanoprecipitates covering zeolite particles for the K+-based composite, whereas the Na+-based composite exhibited the formation of NaA zeolite phase and partial modification of the Na13X grains. The surface area analysis showed that the geopolymer-zeolite composites have characteristics of Type I isotherms of microporous solids. The process performances were determined in a dedicated pressure-decay apparatus and by thermogravimetric analysis. The CO2 capacity of Na+-based composite resulted significantly larger (2-3 times) than sorbents based on K, approaching the values obtained for pure Na13X zeolite. A synergistic effect was also noted, the CO2 capacity being approximately 20% larger that the value expected by averaging those of the constituents; such effect is mainly related to the large interaction among the phases obtained by the effective chemical mixing achieved during the geopolymerization reaction.