Ideal adsorbed solution theory, two-dimensional equation of state, and molecular simulation for separation of H2/N2/O2/CH4/CO in graphite nanofiber and C60 intercalated graphite

Abstract

We performed grand canonical Monte Carlo (GCMC) simulations to investigate the adsorption separation of H2, N2, O2, CO and CH4 gas mixtures in graphite nanofibers (described by slit pore model), and C60 intercalated graphite (CIG). The presence of C60 molecules between the layers resulted in less than half of the adsorption of O2 and CH4 in CIG, compared to the slit pore. However, the adsorption selectivity of O2/N2, CH4/N2, CH4/H2, and CO/H2 systems in CIG is much higher than that of slit pores. These observations indicate that the slit pore and CIG are suitable for gas storage and gas separation, respectively. We used the two-dimensional Zhou-Gasem-Robinson (2D ZGR) EOS and the dual-site Langmuir-Freundlich (DSLF) to correlate the pure component adsorption isotherms simulated by GCMC method, and further predicted the adsorption of the binary gas mixtures by the ZGR model and ideal adsorbed solution theory (IAST), respectively. We found that neither adsorption model can accurately predict the adsorption properties of the four gas mixtures in the two materials simulated by GCMC method. IAST has a satisfactory predictive effect on the adsorption of N2-O2, N2-CH4 and H2-CO gas mixtures in CIG, while ZGR can accurately predict the gas adsorption of N2-O2, H2-CH4 and H2-CO in CIG. However, both models perform poorly in predicting gas adsorption in the slit pore. Consequently, experimental study or molecular simulation should be carried out for the validation of the results, when using the adsorption theory such as IAST and 2D EOS to predict the adsorption of a gas mixture.