Abstract
Global warming by greenhouse gas emissions is one of the main threats of our modern society, and efficient CO2 capture processes are needed to solve this problem. Membrane separation processes have been identified among the most promising technologies for CO2 capture, and these require the development of highly efficient membrane materials which, in turn, requires detailed understanding of their operation mechanism. In the last decades, molecular modeling studies have become an extremely powerful tool to understand and anticipate the gas transport properties of polymeric membranes. This work presents a study on the correlation of the structural features of different membrane materials, analyzed by means of molecular dynamics simulation, and their gas diffusivity/selectivity. We propose a simplified method to determine the void size distribution via an automatic image recognition tool, along with a consolidated Connolly probe sensing of space, without the need of demanding computational procedures. Based on a picture of the void shape and width, automatic image recognition tests the dimensions of the void elements, reducing them to ellipses. Comparison of the minor axis of the obtained ellipses with the diameters of the gases yields a qualitative estimation of non-accessible paths in the geometrical arrangement of polymeric chains. A second tool, the Connolly probe sensing of space, gives more details on the complexity of voids. The combination of the two proposed tools can be used for a qualitative and rapid screening of material models and for an estimation of the trend in their diffusivity selectivity. The main differences in the structural features of three different classes of polymers are investigated in this work (glassy polymers, superglassy perfluoropolymers and high free volume polymers of intrinsic microporosity), and the results show how the proposed computationally less demanding analysis can be linked with their selectivities.
Highlights
Efficient gas separations may limit pollution by reducing both gas emission and energy consumption, and many of the relevant industrial separations can be optimized by using membrane-based processes
Molecular simulations have reached an impressive development in membrane science, due to their use both in the research of new materials and in the study of the transport and sorption phenomena [3,4,5,6,7,8,9]
Molecular dynamics (MD) simulations can be considered as a chemical engineering tool, being that MD is part of the “molecular processes–product–process
Summary
Efficient gas separations may limit pollution by reducing both gas emission and energy consumption, and many of the relevant industrial separations can be optimized by using membrane-based processes. Together with gas separation process engineering, a crucial role is played by the design of new materials with improved properties. A good understanding of the correlations between the materials properties and their transport mechanisms is required, along with the realization of innovative functional materials with improved properties. In this context, molecular modeling is a Membranes 2020, 10, 328; doi:10.3390/membranes10110328 www.mdpi.com/journal/membranes. Membranes 2020, 10, 328 valuable tool for understanding the relationship between the chemical structure and the functional properties of a material. Molecular dynamics (MD) simulations can be considered as a chemical engineering tool, being that MD is part of the “molecular processes–product–process (3PE)” integrated multiscale approach [10]
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