High performance membrane materials for gas separation

The use of membranes in various gas separations has increased significantly in recent times. This review presents some of the recent noteworthy advances in the field of membranes materials for these applications. A description of the most promising groups of high free volume polymers, including polyimides, thermally rearranged (TR) polymers, substituted polyacetylenes, perfluoropolymers, and polymers with intrinsic microporosity (PIM) is provided. High performance, rubbery, polyethers and polyether based copolymers are shown as another important class of polymer membrane materials.  The development of inorganic membranes, which are not bound to the trade-off limitations between permeability and selectivity exhibited by polymers is also presented. The attention is focused on zeolitic materials, metal organic frameworks (MOF), and carbon molecular sieves (CMS). The field of mixed matrix membranes composed of inorganic particles embedded in a polymer matrix is also briefly outlined

Polyimide-Based Membrane Materials for CO2 Separation: A Comparison of Segmented and Aromatic (Co)polyimides

A series of new poly(ethylene oxide) (PEO)-based copolyimides varying in hard segment structure are reported in this work as CO2 selective separation membranes. Their structural diversity was achieved by using different aromatic dianhydrides (4,4′-oxydiphthalic anhydride (ODPA), 4,4’-(hexafluoroisopropylidene)diphthalic anhydride (6FDA)) and diamines (4,4′-oxydianiline (ODA), 4,4′-(4,4′-isopropylidene-diphenyl-1,1′- diyldioxy)dianiline (IPrDA), 2,3,5,6-tetramethyl-1,4-phenylenediamine (4MPD)), while keeping the content of PEO (2000 g/mol) constant (around 50%). To get a better insight into the effects of hard segment structure on gas transport properties, a series of aromatic polyimides with the same chemistry was also studied. Both series of polymers were characterized by 1HNMR, FTIR, WAXD, DSC, TGA, and AFM. Permeabilities for pure He, O2, N2, and CO2 were determined at 6 bar and at 30 °C, and for CO2 for pressures ranging from 1 to 10 bar. The results show that OPDA-ODA-PEO is the most permeable copolyimide, with CO2 permeability of 52 Barrer and CO2/N2 selectivity of 63, in contrast to its fully aromatic analogue, which was the least permeable among polyimides. 6FDA-4MPD-PEO ranks second, with a two times lower CO2 permeability and slightly lower selectivity, although 6FDA-4MPD was over 900 times more permeable than OPDA-ODA. As an explanation, partial filling of hard domain free voids by PEO segments and imperfect phase separation were proposed