Simulations and experimental investigations of the competitive adsorption of CH and CO on low-rank coal vitrinite.

The mechanism for the competitive adsorption of CH and CO on coal vitrinite (DV-8, maximum vitrinite reflectance R  = 0.58%) was revealed through simulation and experimental methods. A saturated state was reached after absorbing 17 CH or 22 CO molecules per DV-8 molecule. The functional groups (FGs) on the surface of the vitrinite can be ranked in order of decreasing CH and CO adsorption ability as follows: [-CH] > [-C=O] > [-C-O-C-] > [-COOH] and [-C-O-C-] > [-C=O] > [-CH] > [-COOH]. CH and CO distributed as aggregations and they were both adsorbed at the same sites on vitrinite, indicating that CO can replace CH by occupying the main adsorption sites for CH-vitrinite. High temperatures are not conducive to the adsorption of CH and CO on vitrinite. According to the results of density functional theory (DFT) and grand canonical Monte Carlo (GCMC) calculations, vitrinite has a higher adsorption capacity for CO than for CH, regardless of whether a single-component or binary adsorbate is considered. The equivalent adsorption heat (EAH) of CO-vitrinite (23.02-23.17) is higher than that of CH-vitrinite (9.04-9.40 kJ/mol). The EAH of CO-vitrinite decreases more rapidly with increasing temperature than the EAH of CH-vitrinite does, indicating in turn that the CO-vitrinite bond weakens more quickly with increasing temperature than the CH-vitrinite bond does. Simulation data were found to be in good accord with the corresponding experimental results.