Molecular Dynamics Simulation of Methane and Carbon Dioxide Permeation Through A Layered Inorganic Membrane

Introduction

A lot of efforts to address problems in environment and industrial process rely on gas separation techniques. Methane and carbon dioxide gases have been a long-time subject of research interest due to their industrial importance and environmental impact as greenhouse gases. Methane is the primary component of natural gas, but its mining is often contaminated with carbon dioxide that forms acid in the presence of water vapor, causing pipe corrosion during the gas transportation through the pipeline. The rising of methane and carbon dioxide level in the atmosphere is mainly from anthropogenic emission and it is projected to increase due to economic growth and industrial development. Therefore, the need for a reliable gas separation methods to remove carbon dioxide will see an increasing demand with the continuous effort to upgrade the quality of natural gas, biogas, landfill gas, and atmospheric environment.^1–3

There is a vast amount of reports on separation technologies for methane and carbon dioxide. These include chemical absorption,⁴ pressure swing adsorption (PSA),^3,5,6 solid-phase adsorption, and membrane separation. Separation using membrane is widely utilized in the laboratory and industrial scale because of the reusability, low cost, high efficiency, low pollution, and simple in operation. Commercial membranes are mostly built from the organic polymer which can be easily functionalized by attaching a particular functional group of interests. However, the poor thermal and chemical resistance of the organic membranes restrict their use to moderate condition only. On the contrary, the inorganic membrane is known to have a higher thermal and mechanical stability that enables a continuous separation to be carried at high temperature and pressure.⁷ The latter situation is considered to be advantageous for gas separation since the kinetic of permeation can be expected to be proportional to both temperature and pressure. A wide array of solid material for selective carbon dioxide removal has been reported such as metal-organic framework (MOF),^8–13 zeolite,^14–17 graphene,^18,19 and clay.²⁰

Regardless of the abundant information on the potential materials that can be used for methane and carbon dioxide separation, a systematic study to investigate the influence of membrane structure to the permeation of both gases at the microscopic level is scarcely reported.²¹ In particular, pore size and shape are the...