Selective adsorption of CO2 on a regenerable amine-bentonite hybrid adsorbent

The ability of magnesium form of bentonite modified by monoethanolammonium cations (MEA(+)-Mg-bentonite) to reversibly and selectively adsorb CO2 over other light gases, such as CH4 and N-2 has gravimetrically been investigated using a Magnetic Suspension Balance (MSB) equipment. Before CO2 adsorption measurements, untreated bentonite and MEA(+)-Mg-bentonite were characterized by XRD, FTIR, TGA and BET techniques to establish their structural characteristics, thermal stability and specific surface area and porosity characteristics. The results showed that MEA(+)-Mg-bentonite adsorbed higher CO2 amount compared to untreated bentonite under similar conditions. The equilibrium isotherms for CO2 adsorption on untreated bentonite and MEA(+)-Mg-bentonite were measured at 25,50 and 75 degrees C and a pressure range of 01.0 bar. It was found that MEA(+)-Mg-bentonite has static CO2 adsorption capacities of 0.79, 0.69 and 0.56 mmol/g, compared to 0.45, 0.36 and 0.30 mmol/g for untreated bentonite at temperatures of 25, 50 and 75 degrees C and a pressure of 1 bar, respectively. The calculated values of the thermodynamic parameters revealed that the process involving CO2 adsorption on MEA(+)-Mg-bentonite adsorbent was a physical, spontaneous and exothermic. Moreover, the results showed moderate and slightly high equilibrium selectivities for CO2 over CH4 on MEA(+)-Mg-bentonite with the values of 1.36, 4.85 and 3.43 at 25, 50 and 75 degrees C, respectively. However, MEA(+)-Mg-bentonite showed equilibrium selectivity for CO2 over N-2 as high as 13.79, 9.91 and 6.32 at 25,50 and 75 degrees C, respectively. Regenerative ability in short runs of isothermal CO2 adsorption-desorption cycles revealed that MEA(+)-Mg-bentonite adsorbent was able to undergo several CO2 adsorption-desorption cycles without noticeable decrease in its adsorption capacity. Clearly, amine-bentonite hybrid adsorbents are promising inexpensive materials for CO2 capture. (C) 2015 Elsevier B.V. All rights reserved.