AIChE 2018 Annual Meeting, Pittsburgh, United States Of America, 28 October - 02 November 2018, pp.1
Membrane plasticization has been a major concern over years in the industrial application of gas separation membranes. At elevated gas pressures, condensable gases such as CO2, induce swelling of polymeric membranes resulting reduced selectivity hence loss of separation performance. Prediction of the plasticization pressure requires elaborate high-pressure experiments. While molecular simulation is a powerful tool to predict materials performances, modelling gas separation performances of polymeric structures is proven to be challenging due to the complex and flexible structures. In this work, CO2-induced plasticization of promising PIM-1 membranes were investigated using a complete molecular simulation approach.
A detailed study on modeling of PIM-1 was accomplished for accurate simulations of the material to be performed. Quantum-level charge calculations were integrated wih all-atom force fields for PIM-1 model. Molecular Dynamics (MD) and Monte-Carlo (MC) simulations were integrated in order to mimic PIM-1 chain behaviors with and without CO2 presence and also CO2 sorption on the membrane. The methodology was validated in previous studies , where plasticization pressure of several polyimides were predicted. CO2 sorption simulations up to 40 bar were carried out using integrated MD-MC simulation and validated using experimental data.
Plasticizing effect of CO2 was then investigated using specific fractional free volume (FFV) analysis that evaluates interconnected CO2-accessible free volume. Experimental physical properties of PIM-1 such as density, FFV and glass transition temperature, were successfully reproduced via simulations. Accurate modeling of rigid PIM-1 chains were accomplished and structural analyses on plasticization were performed.
This work was supported by the Scientific and Technological Research Council of Turkey - TUBITAK (Grant# 217M630) ) and the Scientific Projects Unit of Istanbul Technical University (Grant# MDK-2018-41400).
 Balcik M., Ahunbay M.G., Prediction of CO2-induced plasticization pressure in
polyimides via atomistic simulations, J. Memb. Sci. 547 (2017) 146-155.