Structure and properties relationships for aromatic polyimides and their derived carbon membranes: experimental and simulation approaches

Effects on Carbon Molecular Sieve Membrane Properties for a Precursor Polyimide with Simultaneous Flatness and Contortion in the Repeat Unit

Carbon molecular sieve (CMS)-based membrane separation is a promising solution for hydrogen separation due to its great advantages on perm-selectivity, thermal stability, and chemical stability. To prepare high-performance CMS membranes, the molecular structure of polymer precursors and their arrangements should be primarily considered. In this work, a benzimidazole-based 6FDA (2,2'-bis(3,4'-dicarboxyphenyl) hexafluoropropane dianhydride)-type polyimide (PABZ-6FDA-PI) is chosen as precursor to prepare the CMS membrane. Effects of chain flatness and contortion in the polyimide precursor on gas-separation performance of CMS membranes were studied in detail by gas adsorption and permeation experiment. The H₂ permeability of CMS is up to 9500 Barrer and ideal selectivity of gas pairs of H₂ /CH₄ and H₂ /CO₂ is up to 3800 and 13, respectively. The comprehensive performance of hydrogen separation including H₂ /CO₂ , H₂ /N₂ , and H₂ /CH₄ gas pairs is located well above previously reported upper bounds for polymers.

Membrane-Based Olefin/Paraffin Separations

Efficient olefin/paraffin separation is a grand challenge because of their similar molecular sizes and physical properties, and is also a priority in the modern chemical industry. Membrane separation technology has been demonstrated as a promising technology owing to its low energy consumption, mild operation conditions, tunability of membrane materials, as well as the integration of physical and chemical mechanisms. In this work, inspired by the physical mechanism of mass transport in channel proteins and the chemical mechanism of mass transport in carrier proteins, recent progress in channel-based and carrier-based membranes toward olefin/paraffin separations is summarized. Further, channel-based membranes are categorized into membranes with network structures and with framework structures according to the morphology of channels. The separation mechanisms, separation performance, and membrane stability in channel-based and carrier-based membranes are elaborated. Future perspectives toward membrane-based olefin/paraffin separation are proposed.

Olefin–paraffin separation performance of polyimide Matrimid®/silica nanocomposite membranes

In this study, the performance of polyimide Matrimid® membranes in the separation of ethylene/ethane and propylene/propane was improved by silica nanoparticles.