Studies on the CO2 adsorption mechanism of Na-X and Na-Ca-X coal fly ash zeolites

Coal fly ash zeolites (CFAZ) of Na-X and Na-Ca-X types were synthesized using as raw materials fly ashes generated by the combustion of lignite from various deposits with low and medium limestone content. It has been found that CFAZs with higher calcium content superior those containing less calcium with respect to their ability to capture CO2. This provoked our interest to elucidate the role of Ca in the CO2 adsorption process. CFAZs of Na-X and Na-Ca-X types were investigated in dynamic CO2 adsorption cycles, as the thermal regeneration of the adsorbents is carried out at low temperatures at which only the physically adsorbed molecules can be released. Desorption was investigated by thermogravimetric TG-DTG analyses over a wide temperature range.