(314f) Modelling of Fluid Transfer in Nanoporous Carbons with Molecular Dynamics Simulation

The separation of CO₂/CH₄ is important in both biogas upgrading and natural gas sweetening. In the past two decades, gas membrane separation technology has become much more advanced due to interest in the technology′s reliability, low-energy consumption, and minimal capital investment. However, most membranes used in industry today are still limited due to an inherent upper bound limitation on their performance, showing a conventional trade-off behaviour between permeability and selectivity^[1].

It is believed that membrane process is a compromise in competition between two dominant mechanisms: the permeability mechanism and the selectivity mechanism^[2]. In essence, the system behaviour is dominated by the complex structure of the membranes and the complex interaction between the gas and the membranes. However, no quantitative results of the permeability and selectivity with the structure structural properties and the interaction were obtained, makes it different to revealed the inherent mechanism to break the Robeson upper bound.

In this work, a novel method based on linear nonequilibrium thermodynamics^[3] and equilibrium molecular simulation was developed to quantitatively predict selectivity and permeability for CO₂/CH₄ mixtures based on the structural properties of materials such as effective contact surface area (S_eff). By adjusting the potential parameters (ε, σ) artificially, different effective contact surface area was obtained and the optimal region to break the Robeson upper bound was obtained.

References:

[1] H. B. Park, J. Kamcev, L. M. Robeson, M. Elimelech, B. D. Freeman, “Maximizing the right stuff: The trade-off between membrane permeability and selectivity”, Science, 2017, 356, 1137.

[2] J. H. Li, “Exploring the Logic and Landscape of the Knowledge System: Multilevel Structures, Each Multiscaled with Complexity at the Mesoscale”, Engineering, 2016, 2, 276-285.

[3] W. L. Xie, X. Y. Ji, X. Feng, X. H. Lu, “Mass-Transfer Rate Enhancement for CO2 Separation by Ionic Liquids: Theoretical Study on the Mechanism”, AIChE Journal, 2015, 61, 4437-4444.