Adsorption of CO_2/CH_4 in shale organic nanoparticles: A molecular simulation study

摘要

Shale gas is a kind of unconventional gas, but it is difficult to exploit because of the low permeability and porosity of shale. In recent years, with the larger emission of CO_2, how to use CO_2 to enhance shale gas recovery(CO_2-ESGR) and sequestrate CO_2 effectively is a topic of common concern. Besides the experiment and theory, Molecular simulation is another research method which can describe the competition adsorption law of CH_4 and CO_2 in a more profound and microscopic way. In the current work, molecular simulations have been carried out using a grand canonical Monte Carlo method and molecular dynamics method to study the competitive adsorption of CH_4 and CO_2 in the carbon-based slit pores of a given width. The burial depth, composition and other factors were studied, and the density distribution of CH_4 and CO_2 in the pore and the adsorption selectivity of CO_2 over CH_4 are also analyzed. The results indicated that adsorption amount of CO_2 is almost constant, while CH_4 sorption is increasing with the increase of buried depth. Furthermore, under the same temperature and pressure, CO_2 has a higher adsorption capacity and isosteric heat. In the case of ratio of CH_4:CO_2=1:1, there is a large proportion of CO_2 in the pore wall. The CO_2 of adsorbate state is parallel to the pore surface. The higher CO_2 ratio, the larger selectivity of graphene for CO_2 relative to CH_4, which reflected the larger CO_2 adsorption capacity.