Selective adsorption of CO<inf>2</inf> on a regenerable amine-bentonite hybrid adsorbent: Fid-Bau Portal

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

Elkhalifah, Ali E.I. / Azmi Bustam, M. / Shariff, A.M. / Murugesan, T.

Abstract 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 N2 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°C and a pressure range of 01.0bar. It was found that MEA⁺-Mg-bentonite has static CO2 adsorption capacities of 0.79, 0.69 and 0.56mmol/g, compared to 0.45, 0.36 and 0.30mmol/g for untreated bentonite at temperatures of 25, 50 and 75°C and a pressure of 1bar, 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°C, respectively. However, MEA⁺-Mg-bentonite showed equilibrium selectivity for CO2 over N2 as high as 13.79, 9.91 and 6.32 at 25, 50 and 75°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.

Highlights • Amine-bentonite hybrids are promising inexpensive adsorbents for CO2 capture. • MEA⁺-Mg-bentonite showed the highest CO2 loading capacity at 25°C and 1bar. • MEA⁺-Mg-bentonite selectively adsorbed CO2 over CH4 and N2 at different temperatures. • Regeneration of MEA⁺-Mg-bentonite confirmed its suitability for cyclic operations.