Carbon Dioxide Capture in a Fixed Bed of Coconut Shell Activated Carbon Impregnated With Sodium Hydroxide: Effects of Carbon Pore Texture and Alkali Loading

Abstract

Performance of CO₂ adsorption was investigated in a fixed bed of coconut shell activated carbon impregnated with sodium hydroxide with emphasis on the effect of alkali loading and carbon pore texture. CO₂ adsorption capacity increased with the increase of NaOH loading and passed through a maximum value at the optimum loading of 180 g NaOH/g carbon. This optimum loading appeared to be the same, independent of the surface area of activated carbon in the range of 766-1052 m²/g. A pore blocking phenomenon was proposed to account for the effect of alkali loading on the CO₂ adsorption behavior. Empirical equations were also developed to correlate the breakthrough time, the adsorption capacity at breakthrough time and the equilibrium adsorption capacity with alkali loading and surface area of activated carbon. The breakthrough equation based on the LDF model was found to describe the experimental breakthrough data reasonably well. The transport of CO₂ molecules in the pore structure of activated carbon to the adsorption sites is governed by the mechanism of surface diffusion and the surface diffusivity is about two orders of magnitude larger than the pore diffusivity.