Carbon dioxide adsorption on nitrogen-enriched gel beads from calcined eggshell/sodium alginate natural composite

Bio-degradable calcined egg-shell/sodium alginate (CES/SA) beads were prepared and functionalized using aqueous ammonia (33%). The tailor-made beads were then used as adsorbent for CO 2 capture in a fixed-bed reactor. The performance of the prepared beads was evaluated under various experimental conditions ( i.e. 1 2 concentration between 20 to 45 vol%). Modification with ammonia could successfully introduce additional functional groups containing nitrogen onto the surface of the CES/SA (up to 10.56 wt%). The results showed an increase in CO 2 adsorption with ammonia-impregnated CES/SA, compared to the non-impregnated CES/SA. A maximum CO 2 adsorption capacity of 0.2380 mmol/g was obtained for the gel beads with 45% CO 2 concentration at 1 bar and 30 °C. The adsorption capacity decreased with an increase in temperature and increased with an elevation in the inlet CO 2 concentration, pressure and flow rate. Among the investigated isotherm models ( i.e. Sips, Freundlich and Toth), the Toth isotherm model best described the adsorption data. The thermodynamic properties using the adsorption isotherm data revealed the entropy change (ΔS > 0) reflected the affinity of the adsorbent with the CO 2 molecules. The CO 2 adsorption/desorption process indicated a drop in the CO 2 adsorption capacity of the gel beads in the second cycle; however, this almost remained constant in the subsequent cycles. This observation pointed out to a chemisorption process for the fresh adsorbent and a physical adsorption mechanism for the subsequent adsorption cycles.