Thermally rearranged semi-interpenetrating polymer network (TR-SIPN) membranes for gas and olefin/paraffin separation

Phthalide-containing poly(ether-imide)s based thermal rearrangement membranes for gas separation application

The diamine monomer 3,3-bis[4-(3-hydroxy-4-amino-phenoxy)phenyl]phthalide (BHAPPP) was firstly synthesized by the nucleophilic substitution of 5-fluoro-2-nitrophenol and phenolphthalein, followed by a reduction reaction. A series of phthalide-containing poly(ether imide)s (PEI) were then prepared through the polycondensation of BHAPPP with six kinds of dianhydrides, including 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 3,3',4,4'-biphenyl tetracarboxylic dianhydride (BPDA), 4,4'-oxydiphthalic dianhydride (ODPA), 1,2,3,4-cyclobutane tetracarboxylic dianhydride (CBDA) and pyromellitic dianhydride (PMDA), as well as thermal imidization. After further thermal treatment, the corresponding thermal rearrangement (TR) membranes were obtained. Due to the existence of the phthalide lactone ring, the PEIs probably underwent TR and crosslinking simultaneously. With the increase of thermal treatment temperature, the mechanical properties of the TR membranes dramatically decreased, but the gas separation properties obviously increased. When the PEIs were treated at 450 °C for 1 h, the CO2, H2, O2, N2 and CH4 permeability of TR(BHAPPP-6FDA) reached 258.5, 190.5, 38.35, 4.25 and 2.15 Barrers, respectively. Meanwhile, the CO2/CH4 selectivity of 120.2 sharply exceeded the 2008 Robeson limit, and O2/N2 selectivity was 9.02, close to the 2015 upper limit. Therefore, the TR membranes derived from phthalide-containing PEIs exhibit superior gas separation performance, andare expected to be applied in the field of gas separation.

Microporous polymers with cascaded cavities for controlled transport of small gas molecules

In membrane-based separation, molecular size differences relative to membrane pore sizes govern mass flux and separation efficiency. In applications requiring complex molecular differentiation, such as in natural gas processing, cascaded pore size distributions in membranes allow different permeate molecules to be separated without a reduction in throughput. Here, we report the decoration of microporous polymer membrane surfaces with molecular fluorine. Molecular fluorine penetrates through the microporous interface and reacts with rigid polymeric backbones, resulting in membrane micropores with multimodal pore size distributions. The fluorine acts as angstrom-scale apertures that can be controlled for molecular transport. We achieved a highly effective gas separation performance in several industrially relevant hollow-fibrous modular platform with stable responses over 1 year.