(376aw) The Transport Mechanism of CO2/CH4 Mixtures in Ionic Polyimides and Ionic Liquid Composite Membranes – MD Simulation Studies

The reduction and control of greenhouse gases emission is one of the most challenging problem that the society is struggling with nowadays. Greenhouse gases, like CO₂ and CH₄, are produced in many industrial processes and to limit their emission several pre- and post-combustion techniques have been applied [1]. However, these processes still face some limitations, like corrosion or volatility and toxicity of solvents used, i.e. monoethanolamine (MEA). Because of this, new materials or membranes are needed.

Ionic polyimides (i-PI) are a new class of polymers that are very promising as membranes to capture CO₂ [2,3]. This novel class of polymers contains ionic liquids species in the backbone separated by organic linker, which provides an additional degree of structural variety in the polymer system. Additionally to neat i-PI, significant attention is attracted by the composite membranes, which contain different ionic liquids (ILs) combined inside the neat polymer.

In our studies, the transport mechanism of two gases: CO₂ and CH₄ in neat and composite membranes were analyzed. For both gases, the diffusion in the neat i-PI is significantly slower that in the composite membranes with significant amount of ionic liquids added. This behavior results from plasticization effect of the ionic liquids on the rigid neat i-PI. However, addition of small, around 10 %, of IL to the system decreases the diffusion coefficient. This decrease in the gas diffusivity depends on the blocking effects of the gas diffusion route induced by the dispersed IL in the i-PI matrices rather than the plasticization effect.

References:

1. Martín, C. F.; Stöckel, E.; Clowes, R.; Adams, D. J.; Cooper, A. I.; Pis, J. J.; Rubiera, F.; Pevida, C. Hypercrosslinked organic polymer networks as potential adsorbents for pre-combustion CO₂Journal of Materials Chemistry 2011, 21, 5475.
2. Abedini, A.; Crabtree, E.; Bara, J. E.; Turner, C. H. Molecular Simulation of Ionic Polyimides and Composites with Ionic Liquids as Gas-Separation Membranes. Langmuir2017, 33, 11377-11389.
3. Abedini, A.; Crabtree, E.; Bara, J. E.; Turner, C. H. Molecular analysis of selective gas adsorption within composites of ionic polyimides and ionic liquids as gas separation membranes, Phys. 2019, 516, 71-83.