Performance and Plasticization of Polymer-MOF Membranes for Gas Separation At Elevated Pressures

Performance and plasticization of polymer-MOF membranes for gas separation at elevated pressures

 Salman Shahid, Kitty Nijmeijer

Membrane Science & Technology, Mesa+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands. Phone number: +31 53 489 3474, E-mail: s.shahid@utwente.nl

Keywords: Mixed-matrix membranes, Metal-organic frameworks, Matrimid^®, CO₂separation, High pressure, Plasticization

The control of anthropogenic carbon dioxide emission is one of the most important environmental concerns of the current era and is becoming more challenging with the rapid increase in global population, industrialization and energy demands. Therefore, there is significant need for technologies that will reduce the level of carbon dioxide emission. Mixed-matrix membranes (MMMs), filled with inorganic particles, provide an efficient and cost effective mean to improve the gas separation performance of polymeric membranes [1]. However, CO₂ separation applications (e.g., biogas recovery, natural gas sweetening)involve harsh conditions and high pressures. At these high feed pressures CO₂ acts as plasticizer [2]. Conventional methods to prevent plasticization of the membrane are either annealing or crosslinking, which hardly influences the selectivity but decrease the permeability. In this work, MMMs containing the metal organic framework (MOF) Fe(BTC) in Matrimid-PI were characterized in terms of carbon dioxide (CO₂) and methane (CH₄) separation performance and plasticization at high pressures. Physical properties (film density, thermal degradation, glass transition) of Fe(BTC) and prepared MMMs were analyzed. An optimized priming and suspension mixing protocol resulted in a homogeneous distribution of MOF particles in the Matrimid-PI matrix, as observed by scanning electron microscope (SEM). Experimental results show decreased thermal degradation but increased membrane density and glass transition with Fe(BTC) loading, as well as improvement in CO₂ permeability and CO₂/CH₄ selectivity. Native Matrimid-PI membranes showed typical plasticization behavior with pressure in pure gas experiments but upon addition of MOF plasticization seems to be controlled by the MOF particles. In mixed gas experiments, the MMMs showed a decrease in CO₂/CH₄selectivity with pressure but this effect levels off at elevated pressures indicating the suppression of plasticization when MOF particles were added. 

References 

1. P.S. Goh, A.F. Ismail, S.M. Sanip, B.C. Ng, M. Aziz, Recent advances of inorganic fillers in mixed matrix membrane for gas separation, Separation and Purification Technology, 81 (2011) 243-264.
2. A. Bos, I.G.M. Punt, M. Wessling, H. Strathmann, CO2-induced plasticization phenomena in glassy polymers, J. Membr. Sci., 155 (1999) 67-78.