Impact of Impure Gas on CO 2 Capture from Flue Gas Using Carbon Nanotubes: A Molecular Simulation Study.

We used a grand canonical Monte Carlo simulation to study the influence of impurities including water vapor, SO 2 , and O 2 in the flue gas on the adsorption of CO 2 /N 2 mixture in carbon nanotubes (CNTs) and carboxyl doped CNT arrays. In the presence of single impure gas, SO 2 yielded the most inhibitions on CO 2 adsorption, while the influence of water only occurred at low pressure limit (0.1 bar), where a one-dimensional chain of hydrogen-bonded molecules was formed. Further, O 2 was found to hardly affect the adsorption and separation of CO 2 . With three impurities in flue gas, SO 2 still played a major role to suppress the adsorption of CO 2 by reducing the adsorption amount significantly. This was mainly because SO 2 had a stronger interaction with carbon walls in comparison with CO 2 . The presence of three impurities in flue gas enhanced the adsorption complexity due to the interactions between different species. Modified by hydrophilic carboxyl groups, a large amount of H 2 O occupied the adsorption space outside the tube in the carbon nanotube arrays, and SO 2 produced competitive adsorption for CO 2 in the tube. Both of the two effects inhibited the adsorption of CO 2 , but improved the selectivity of CO 2 /N 2 , and the competition between the two determined the adsorption distribution of CO 2 inside and outside the tube. In addition, it was found that (7, 7) CNT always maintained the best CO 2 /N 2 adsorption and separation performance in the presence of impurity gas, for both the cases of single CNT and CNT array.