# Membrane separation study for methane-hydrogen gas mixtures by molecular simulations

## TL;DR

This study uses molecular dynamics simulations to analyze methane-hydrogen separation in silica zeolite membranes, revealing that permeation selectivities favor methane and differ from equilibrium adsorption predictions.

## Contribution

It introduces a hybrid non-equilibrium molecular dynamics methodology to simulate gas transport in real zeolite structures, providing detailed insights into permeation selectivities.

## Key findings

- Permeation selectivities favor methane over hydrogen.
- Transport selectivities differ from equilibrium adsorption ratios.
- Selectivity depends on membrane loading and component mobilities.

## Abstract

Direct simulation results for stationary gas transport through pure silica zeolite membranes (MFI, LTA and DDR types) are presented using a hybrid, non-equilibrium molecular dynamics simulation methodology introduced recently. The intermolecular potential models for the investigated CH$_{4}$ and H$_{2}$ gases were taken from literature. For different zeolites, the same atomic (Si and O) interaction parameters were used, and the membranes were constructed according to their real (MFI, LTA, or DDR) crystal structures. A realistic nature of the applied potential parameters was tested by performing equilibrium adsorption simulations and by comparing the calculated results with the data of experimental adsorption isotherms. The results of transport simulations carried out at 25$^0$C and 125$^0$C, and at 2.5, 5 or 10 bar clearly show that the permeation selectivities of CH$_{4}$ are higher than the corresponding permeability ratios of pure components, and significantly differ from the equilibrium selectivities in mixture adsorptions. We experienced a transport selectivity in favor of CH$_{4}$ in only one case. A large discrepancy between different types of selectivity data can be attributed to dissimilar mobilities of the components in a membrane, their dependence on the loading of a membrane, and the unlike adsorption preferences of the gas molecules.