Cross‐linked Copolyimide Membranes for the Separation of Gaseous and Liquid Mixtures

Abstract

Cross-linked polymer structures gain increasing attention as membrane materials because they can fullfill the demands for industrial applications. Thereby, not only good separation characteristics but also high temperature stability and chemical resistancy are required. Furthermore, it is important that the membrane materials be plasticization resistant, because it is found that this causes strong increasing permeability with a drastic loss in selectivity. Plasticization effects occur with polyimide membranes in the presence of high CO 2 concentrations, hydrocarbons as propylene, propane, or aromatics. Unfortunately, these components are present in mixtures with high relevance being separated economically by membrane units or hybrid processes. In this article, the advantages of cross-linked 6FDA (4,4'hexafluoro isopropylidene diphthalic acid anhydride)-copolyimides are discussed based on experimental results for the separation of propylene/propane, benzene/cyclohexane, and high-pressure CO 2 /CH 4 mixtures. Additionally, opportunities for implementing the membrane units in conventional separation processes are discussed.

Gas Separation Performance of Carbon Molecular Sieve Membranes Based on 6FDA‐mPDA/DABA (3:2) Polyimide

“…As a result, they consist of almost-pure carbon materials with a resulting "turbostatic" structure that comprises disordered, sp 2 -hybridized, condensed carbon sheets [33] with pores formed from packing imperfections. The pore structure is described as a "slit-like" structure comprising both micropores (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) and smaller ultra-micropores (< 7 ), with a special bi-nodal pore-size distribution. [34] The specific combination of micropores and ultra-micropores provides both high flux and high separation efficiency in gas separations through a molecular sieving function in the CMS membranes.…”

“…[3][4][5][6][7][8][9] Furthermore, 6FDA-based polyimides can be dissolved in several common solvents, which allows easy fabrication of the polymer into a working device. [6,8,9,[12][13][14][15][16][17][18] Our group first investigated ester bond crosslinking of 3,5-diaminobenzoic acid (DABA)-based polyimide membranes by using a diol to form the ester bonds among the polyimide chains. [3,6,10,11] This disadvantage can be overcome through crosslinking of the membranes.…”

“…However, one drawback in using polyimides is that they are plasticized under aggressive feed conditions (e.g., high pressure or high CO 2 content), which causes selectivity loss and thus separation efficiency loss. [3,6,9,15,17,[19][20][21][22][23] More recently, we also developed a new decarboxylation-induced thermal crosslinking approach to afford a DABA-based 6FDA family of polyimides, [8,12] and subsequently, elaborated that approach to a sub-T g (T g = glass transition temperature) thermal-crosslinking method. [6,8,9,[12][13][14][15][16][17][18] Our group first investigated ester bond crosslinking of 3,5-diaminobenzoic acid (DABA)-based polyimide membranes by using a diol to form the ester bonds among the polyimide chains.…”

“…[6,8,9,[12][13][14][15][16][17][18] Our group first investigated ester bond crosslinking of 3,5-diaminobenzoic acid (DABA)-based polyimide membranes by using a diol to form the ester bonds among the polyimide chains. [3,6,9,15,17,[19][20][21][22][23] More recently, we also developed a new decarboxylation-induced thermal crosslinking approach to afford a DABA-based 6FDA family of polyimides, [8,12] and subsequently, elaborated that approach to a sub-T g (T g = glass transition temperature) thermal-crosslinking method. [12] Unexpectedly, the decarboxylation-induced thermal crosslinking mechanism caused a significant increase in permeability for different gases, including He, O 2 , N 2 , CH 4 , and CO 2 , and only a slight decrease in CO 2 /CH 4 selectivity, which was presumably due to reduced segmental packing.…”

Copolyimide mixed matrix membranes with oriented microporous titanosilicate JDF-L1 sheet particles

“…Secondly, 6FDA-based polyimides show improved separation characteristics in comparison to polyimides using other dianhydrides like pyromellitic dianhydride. This is due to the fact that the bulky -CF 3 -side groups improve the free volume of the polymer which increases the permeability but simultaneously the -CF 3 -groups reduce the chain mobility which leads to an increase in selectivity [34].…”