Computational Study on Purification of CO2 from Natural Gas by C60 Intercalated Graphite

By combining grand canonical Monte Carlo (GCMC) simulations with adsorption theory, we perform a computational study on adsorption of CH4 and CO2 gases and purification of CO2 from the CH4-CO2 and N-2-CO2 binary mixtures by the C-60 intercalated graphite. The adsorption isotherms, isosteric heats and snapshots of pure gases have been examined extensively. It is found that the maximum excess uptakes at 298 K are relatively low, only giving 4.04 and 4.96 mmol/g for CH4 and CO2, respectively, due to a low porosity of 0.45 and a large crystal density of 1.57 g/cm(3) of this material. It indicates that the pristine material is not suitable for gas storage. However, this material provides excellent selectivity for CO2, and the selectivity at ambient condition can reach 8 and 50 for the CH4-CO2 and N-2-CO2 mixture, respectively. Furthermore, the selectivity of CO2 is almost independent of the bulk gas composition for P > 0.1 MPa. The dual-site Langmuir-Freundlich (DSLF) equation is used to fit the adsorption isotherms of pure gases from GCMC simulations, and the corresponding parameters are obtained. Moreover, we further predicted the adsorption behavior of binary mixtures by the DSLF-based ideal adsorption solution theory (IAST). Although the IAST theory slightly overestimates the selectivity, compared to GCMC results, the uptakes and selectivity from both methods are basically consistent. To improve the adsorption capacities, we further tailor the structural parameter g of the C-60 intercalated graphite by GCMC simulations. For equimolar gas composition, at the condition of g = 1.4 nm and 6 MPa, the CO2 uptakes could be raised by 200%, approaching 12 mmol/g for both mixtures, without loss of the selectivity for CO2. In summary, this work demonstrates that the C-60 intercalated graphite is an excellent material for CO2 purification, especially for N-2-CO2 system at room temperature.