Experimental study of pure and mixtures of CO2 and CH4 adsorption on modified carbon nanotubes

In this work 3-[2-(2-aminoethylamino)ethylamino]propyl trimethoxysilane (TRI) was employed to functionalize MWCNT containing hydroxyl groups (OH-MWCNT), and the XRD, FTIR, TGA and CHNS elemental analysis techniques were used to characterize the resulted adsorbents. The characterization results for amineMWCNT showed amine groups effectively attached to the surface of the MWCNT. The equilibrium adsorption capacity of pure CO₂ and CH₄ and their binary mixture on the pristine MWCNT, OH-MWCNT and amine-MWCNT was measured through a set of equilibrium adsorption experiments at 303.2 and 318.2 K. Capacities of all three types of adsorbents for CO₂ adsorption were higher than those for methane adsorption. Also, amine-MWCNT demonstrated better performance on CO₂ adsorption than the other two adsorbents, especially at low partial pressures. The capacity of amine-MWCNT for pure CO₂ adsorption was 2.5 and 4 times as much as those for pristine MWCNT and OH-MWCNT, respectively, at the temperature of 303.2 K and the pressure of 0.2 bar. The binary adsorption experiment revealed that CO₂/CH₄ selectivity for pristine MWCNT and amine-MWCNT in all molar fractions of CO₂ is about 1.77 and 7, respectively.

Keywords
Adsorption; Carbon dioxide; Carbon nanotube; Functionalization; Methane; Natural gas