INVESTIGATION OF COMPETITIVE ADSORPTION AND DIFFUSION BEHAVIORS OF CO2/CH4/N2/H2O AFFECTED BY COAL RANKS IN SLIT STRUCTURES

Abstract

In this work, different slit structures of coals (brown coal, bituminous coal, and anthracite coal) with various ranks are established at a molecular level. Based on the grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) methods, the effects of coal rank on CO<sub>2</sub>, CH<sub>4</sub>, N<sub>2</sub> and H<sub>2</sub>O multi-component gases adsorption and diffusion in slit structures are investigated. The influence of coal rank on the swelling ratio caused by adsorption and diffusion in different slit structures is discussed for the first time. It is shown that the adsorption capacity of CO<sub>2</sub>, CH<sub>4</sub>, N<sub>2</sub> and H<sub>2</sub>O in different slit structures follows the order of H<sub>2</sub>O > CO<sub>2</sub> > CH<sub>4</sub> > N<sub>2</sub>, whereas the diffusion coefficient follows H<sub>2</sub>O < CO<sub>2</sub> < CH<sub>4</sub> < N<sub>2</sub>. With the growth of coal rank, the adsorption capacity and diffusion coefficients of CO<sub>2</sub>, CH<sub>4</sub>, N<sub>2</sub> and H<sub>2</sub>O increase, meanwhile, the adsorption selectivity coefficients of CH<sub>4</sub>/CO<sub>2</sub>, N<sub>2</sub>/CH<sub>4</sub>, and CO<sub>2</sub>/H<sub>2</sub>O rise, following the order of anthracite coal > bituminous coal > brown coal. In addition, both the adsorption and diffusion swelling ratio reduce with the decrease of coal rank. The present molecular investigation of competitive adsorption and diffusion characteristics of multi-component gases can provide theoretical basis for efficient exploitation of coalbed methane.