Matrimid®5218/AO-PIM-1 Blend Membranes for Gas Separation

Document Type : VSI: Honoring Prof. Yampolskii

Authors

1 Institute on Membrane Technology, CNR-ITM, Via P. Bucci 17/C, 87036 Rende (CS), Italy

2 Institute of Sustainable Processes, University of Valladolid, Dr. Mergelina s/n., 47011 Valladolid, Spain

3 University of Edinburgh Joseph Black Building David Brewster Road Edinburgh EH9 3FJ

Abstract

In the search for more efficient gas separation membranes, blends offer a compromise between costly high-performance  polymers and low-cost commercial polymers. Here, blends of the polymer of intrinsic microporosity, AO-PIM-1, and  commercial Matrimid® 5218 polyimide are used to prepare dense films by solution casting. The morphology of the pure polymers and their blends with 20, 40, 60 and 80 wt% of AO-PIM-1 in Matrimid® are studied by scanning electron  microscopy (SEM), and their pure gas permeability is studied as a function of the blend composition with H2, He, O2, N2,  CH4 and CO2. The polymers were found only partially miscible and a two-phase structure was formed with large  domains of each polymer. When necessary, the films were coated with a thin silicone layer to heal possible pinhole  defects. Even small amounts of Matrimid® in AO-PIM-1 resulted in an unexpectedly strong decrease in the permeability  of the PIM, whereas a small amount of the PIM led to a modest increase in permeability of Matrimid®. Due to the two-hase structure, the Maxwell model was more suitable to describe the gas permeability as a function of the blend  composition than the model for miscible blends. At low Matrimid® concentrations in AO-PIM-1, all models fail to describe the experimental data due to an unexpectedly strong depression of the permeability of the PIM by Matrimid®.  Time lag measurements reveal that the changes in permeability as a function of the blend composition are mostly due to  changes in the diffusion coefficient. 

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