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 CO 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 CO uptake value of 2.83 mmol/g was observed with a constant decrease with an increase in temperature. BET surface area value of 426 m/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 R 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 CO uptake studies.