Process optimization for enhanced carbon capture and cyclic stability using adsorbents derived from coal fly ash

Zeolites and metal-organic frameworks (MOFs) are popular adsorbents when it comes to capturing CO2 from the gaseous feed stream. In this study, a hybrid of zeolite and ZIF-8 adsorbent was synthesized from coal fly ash via fusion-hydrothermal process and then in-situ aqueous ZIF-8 synthesis technique. This technique of in-situ synthesis is highly cost-effective as it is done at room temperature. The hybrid adsorbent showed an enhanced microporosity as compared to zeolites synthesized from coal fly ash due to the in-situ synthesis of ZIF-8 upon coal fly ash zeolite. It was designated as CFAZ/ZIF-8. At 298 K, a maximum CO2 uptake value of 2.83 mmol/g was observed with a constant decrease with an increase in temperature. BET surface area value of 426 m2/g was obtained for this adsorbent. Kinetics fit for the best uptake value was performed with the Avrami model kinetics, describing the adsorption well at an R2 value of 0.997 for the fit. The adsorbent also showed impressive cyclic stability after five cycles of carbonation and decarbonation. The cyclic stability studies show that the as-synthesized hybrid adsorbent shows promise in CO2 uptake studies.