CO₂ adsorption capacity of zeolites synthesized from coal fly ashes

Given the increase in CO2 emissions, the adsorption process using zeolites are proposed to remove this compound from combustion gases in pulverized coal power plants. Besides it, these materials can also be synthesized using coal fly ash to reconcile environmental and economic concerns. The aim of this study was to measure the adsorption capacity of zeolites synthesized from coal fly ash compared with commercial zeolites and assess their performance in temperature swing adsorption processes. Two pelletized synthetic zeolites were selected, one NaX type (SZX) and one NaA type (SZA), and two commercial zeolites, one NaX (CZX) and one NaA (CZA). Zeolites were characterized by XRF, XRD and textural analysis (BET). Adsorption capacity tests were performed by thermogravimetric analysis using similar CO2 concentrations to those found in pulverized carbon combustion gases, without moisture. Isotherms were also obtained for synthetic and commercial zeolites type X. The XRD results showed substantial similarity between the commercial and synthesized zeolites, indicating a good degree of crystallinity. The CO2 adsorption capacity at 303 K for both samples showed values similar to those reported in the literature (1.97 mmol/g for SZX and 1.37 mmol/g for SZA), demonstrating their potential in commercial applications. After five cycles, the adsorption capacity of all samples remained practically unchanged, indicating the possibility of application in TSA processes. In the adsorption tests at different temperatures and in the isotherms, adsorption capacity declined as temperature increased for both samples, being similar to benchmark commercial 13X and 4A zeolite adsorbents.