CO2 capture performance of bi-functional activated bleaching earth modified with basic-alcoholic solution and functionalization with monoethanolamine: isotherms, kinetics and thermodynamics

CO₂ capture performance of bifunctional activated bleaching earth (ABE) was investigated at atmospheric pressure. The sorbents were characterized by means of X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Caron-Hydrogen-Nitrogen analysis (CHN), Fourier transform infrared (FT-IR) and thermal gravimetric analysis (TGA). The CO₂ capacity was enhanced via basic-modification and monoethanolamine (MEA) loading of the ABE sorbent to obtain a bifunctional surface property. Here, basic-modified calcined ABE with a 30 wt.% MEA loading (SAB-30) showed the highest CO₂ capture capacity, but this was decreased with excess MEA loading (> 30 wt.%). At a 10% (V/V) initial CO₂ concentration feed, the maximum capacity of SAB-30 increased from 2.71 mmol/g at 30°C (without adding moisture to the feed) to 3.3 mmol/g at 50°C when adding 10% (V/V) moisture to the feed. Increasing the moisture concentration further reduced the maximum CO₂ capacity due to the blocking effect of the excess moisture on the sorbent surface. However, SAB-30 could completely capture CO₂ even in a 100% (V/V) initial CO₂ concentration feed. A maximum CO₂ capacity of 5.7 mmol/g for SAB-30 was achieved at 30°C. Varying the ratio of sorbent weight to total flow rate of the gas stream had no discernible effect on the equilibrium CO₂ capture capacity. Avrami''s equation and Toth''s isotherm model provided a good fitting for the data and suggested the presence of more than one reaction pathway in the CO₂ capture process and the heterogeneous adsorption surface of SAB-30. Thermodynamics studies revealed that CO₂ capture on the bifunctional SAB-30 is feasible, spontaneous and exothermic in nature.