Author(s)

N. Azmi, S. Yusup, K. M. Sabil

Abstract

Calcium-based adsorbents produced by biomass material is technically feasible, costly effective and advantageous to a certain extent in capturing CO₂. Since the waste of a cockle shell is found to contain around 98% calcium, it can be a good source for CaCO₃ and yield CaO through the high temperature calcination process. The sorption equilibria of CO₂ on synthesized CaO with different amounts of water were measured experimentally by using a volumetric method at a temperature of 2°C. Under dry conditions, synthesized CaO has a low CO₂ uptake, as the adsorption rate of CO₂ in calcium-based sorbent is high at higher temperatures. While under wet conditions, the large increment of CO₂ adsorption was observed due to formation of CO₂ hydrates which were indicated by inflection of isotherms at a definite pressure of the S-shape. At the inflection point, the highest sorption capacity (5.07 mmol/g) was obtained at a water ratio of 0.55, which is about 30 times higher than dry samples. The trend of FTIR spectra were observed to be similar for raw cockle shells and wet CaO after CO₂ adsorption, in contrast with spectra of CaO before adsorption. The formation of CO₂ hydrate can be further verified by the changes of surface morphology of CaO, before and after adsorption. It can be concluded that calcium-based sorbent with the presence of water has the ability to be further utilized for CO₂ separation.

Keywords

CO₂ emission, sorption equilibria, gas hydrate, cockle shell, calcium oxide