Comparison of hydroxide‐based adsorbents of Mg(OH)₂ and Ca(OH)₂ for CO₂ capture: utilization of response surface methodology, kinetic, and isotherm modeling

Abstract

CO 2 capture using hydroxide-based adsorbents is studied experimentally for two adsorbents of Mg(OH) 2 and Ca(OH) 2. The adsorbents are characterized before and after the adsorption process by X-ray diffraction and Fourier transform infrared spectroscopy analyses. The experiments were carried out in the ranges of 25-65°C, 2-10 bar, and 0.5-2.5 g for temperature, initial pressure, and weight of adsorbent, respectively. Based on the response surface methodology with a central composite design approach, predicted CO 2 adsorption capacities are fitted well with R 2 values of 0.981 and 0.929 for Mg(OH) 2 and Ca(OH) 2 , respectively. The Freundlich isotherm model with R 2 values of 0.985 and 0.994 is the best model for adsorption capacity prediction of Mg(OH) 2 and Ca(OH) 2 , respectively. Also, the pseudo-second-order kinetic model with R 2 values more than 0.98 is selected as the best model for both adsorbents. From the thermodynamic parameters, the reactive adsorption process is found to be exothermic and spontaneous. Due to higher adsorption percentage and capacity at the same conditions, Ca(OH) 2 is more efficient than Mg(OH) 2 for CO 2 capture at studied ranges.

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