Impregnation of nanoclay montmorillonite by choline chloride-urea for selective CO2, N2, and O2 adsorption: Experimental and modeling

In this study, we successfully utilized a green chemistry approach to prepare an adsorbent by functionalizing Montmorillonite with Choline Chlroride: Urea (a Deep Eutectic Solvent) to compare CO2, O2, and N2 adsorption. We conducted studies on the adsorption mechanism using a volumetric system at temperatures ranging from 25 to 55 °C under pressures of up to 9 bar. We assessed the effects of acid activation concentration, solvent concentration, and adsorbent mass on the CO2/O2 and CO2/N2 adsorption ratios (mg/mg). Characterization analyses confirmed that modification of interlayer spaces, ion exchange content, and Al/Si occurred through acid treatment and solvent impregnation. The CO2 adsorption mechanism demonstrated a heterogeneous multilayer and chemophysical sorption nature, which was in agreement with the Hill isotherm and Ellovich kinetic model. In contrast, the O2 and N2 mechanisms were in agreement with a monolayer nature, which matched the Langmuir isotherm and first-order kinetic model. We achieved the optimum adsorption ratio of CO2/O2 and CO2/N2 at 35 °C, while the highest individual adsorption for all three gases was obtained at 25 °C. At 35 °C, 5 bar, and 0.5 g, the highest uptake adsorption was 208.6 mg/g for CO2, 72.6 mg/g for O2, and 39.3 mg/g for N2. Thermodynamic parameters showed that the adsorption nature of CO2, O2, and N2 was exothermic (ΔH < 0) with values of −14.49 Kj/mol, −7.74 Kj/mol, and −4.09Kj/mol, respectively. The study's experimental and modeling results showed a corresponding interpretation, which was remarkable. The adsorbent exhibited desirable renewability at adsorption/desorption cycles with remarkable uptake capacity, making it a highly potential adsorbent for CO2 capture from flue gases. The selectivity of CO2 towards O2 and N2 was almost 2.1 and 3.9, respectively.