Adsorption and separation of CH 4/CO 2/N 2/H 2/CO mixtures in hexagonally ordered carbon nanopipes CMK-5

Abstract

Adsorption and separation of N 2, CH 4, CO 2, H 2 and CO mixtures in CMK-5 material at room temperature have been extensively investigated by a hybrid method of grand canonical Monte Carlo (GCMC) simulation and adsorption theory. The GCMC simulations show that the excess uptakes of pure CH 4 and CO 2 at 6.0 MPa and 298 K can reach 13.18 and 37.56 mmol/g, respectively. The dual-site Langmuir–Freundlich (DSLF) model was also utilized to fit the absolute adsorption isotherms of pure gases from molecular simulations. By using the fitted DSLF model parameters and ideal adsorption solution theory (IAST), we further predicted the adsorption separation of N 2–CH 4, CH 4–CO 2, N 2–CO 2, H 2–CO, H 2–CH 4 and H 2–CO 2 binary mixtures. The effect of the bulk gas composition on the selectivity of these gases is also studied. To improve the storage and separation performance, we finally tailor the structural parameters of CMK-5 material by using the hybrid method. It is found that the uptakes of pure gases, especially for CO 2, can be enhanced with the increase of pore diameter D i , while the separation efficiency is apparently favored in the CMK-5 material with a smaller D i . The selectivity at D i =3.0 nm and 6.0 MPa gives the greatest value of 8.91, 7.28 and 27.52 for S CO 2 / N 2 , S CH 4 / H 2 and S CO 2 / H 2 , respectively. Our study shows that CMK-5 material is not only a promising candidate for gas storage, but also suitable for gas separation.