Valorization of alkaline hydroxide modified coal fly ash to efficient adsorbents for enhanced carbon capture

Abstract

High carbon content coal fly ash was used in this study to synthesize an adsorbent using two step fusion hydrothermal method. Both KOH and NaOH were used in the fusion to observe deviations from the usual NaOH method. They were compared in terms of their physico-chemical attributes. The SEM micrographs showed that coal fly ash lost its geoid structures after fusion with the alkalis. XRD diffractograms showed that both K/Na/CFA-Heavy adsorbent and K/Na/CFA-Light adsorbent were highly amorphous. The K/Na/CFA-Light adsorbent had inferior morphology but better BET than K/Na/CFA-Heavy adsorbent. Even in terms of CO2 uptake capacity, at room temperature K/Na/CFA-Light adsorbent (1.48 mmol/g) outperformed K/Na/CFA-Heavy adsorbent (1.13 mmol/g). A maximum value CO2 uptake value of 1.48 mmol/g was observed for K/Na/CFA-Light adsorbent at 298 K. Kinetic studies displayed that the adsorption process was best explained by the Avrami model with an R2 value of 0.99. Cyclic stability studies were performed at 298 K and they showed that that K/Na/CFA-Light adsorbent showed a cyclic retention capacity of 80% at the end of five cycles.