Impact of Impure Gas on CO 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, and O in the flue gas on the adsorption of CO/N mixture in carbon nanotubes (CNTs) and carboxyl doped CNT arrays. In the presence of single impure gas, SO yielded the most inhibitions on CO 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 was found to hardly affect the adsorption and separation of CO. With three impurities in flue gas, SO still played a major role to suppress the adsorption of CO by reducing the adsorption amount significantly. This was mainly because SO had a stronger interaction with carbon walls in comparison with CO. 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 HO occupied the adsorption space outside the tube in the carbon nanotube arrays, and SO produced competitive adsorption for CO in the tube. Both of the two effects inhibited the adsorption of CO, but improved the selectivity of CO/N, and the competition between the two determined the adsorption distribution of CO inside and outside the tube. In addition, it was found that (7, 7) CNT always maintained the best CO/N adsorption and separation performance in the presence of impurity gas, for both the cases of single CNT and CNT array.