Experimental investigation on different activated carbons as adsorbents for CO2 capture

Abstract

The current research focuses on characterizing and comparing seven commercially available activated carbons (ACs) as adsorbents for CO2 capture in ambient conditions. Various physiochemical properties like BET surface area, pore-volume, pore diameter, surface morphology, and structural characteristics of the ACs are analyzed using the N2 adsorption/desorption technique, FE-SEM, EDAX and XRD. The equilibrium CO2 uptake capacities of the different activated carbons are estimated for sub-atmospheric to 1 bar pressure and 273 to 333 K. The N2 adsorption/desorption analysis revealed that the selected ACs are highly microporous (Microporosity = 50–81%, SBET = 924–1254 m2/g, pore diameter = 16.54–19.21 Å), with some ultra micropores (pore size <10 Å), which play a vital role in post-combustion CO2 capture. At 1 bar pressure and 273 K, AC CARB 6X12 55 showed maximum CO2 uptake of 4.53 mmol/g, whereas Norit RB 4 showed the least uptake of 3.02 mmol/g. Different parameters of Langmuir, Freundlich, Sips and Tóth isotherm models are estimated based on the experimental P-q-T data. In conjunction with the Vant Hoff’s and the Clausius Clapeyron equations, mentioned isotherm models are used to estimate important thermodynamic properties of adsorption such as change in enthalpy of reaction, entropy and Gibb’s free energy, and isosteric heat of adsorption (Qst). The Qst values for all ACs at different surface coverages varied from 15.20 to 43.33 kJ/mol, confirming the physisorption process. The study confirms that the selected ACs will be suitable for various gas sorption applications. Moreover, the estimated properties will be quite valuable for actual system design.