Materials for next-generation molecularly selective synthetic membranes

Abstract

Materials research is key to enable synthetic membranes for large-scale, energy-efficient molecular separations. Materials with rigid, engineered pore structures add an additional degree of freedom to create advanced membranes by providing entropically moderated selectivities. Scalability - the capability to efficiently and economically pack membranes into practical modules - is a critical yet often neglected factor to take into account for membrane materials screening. In this Progress Article, we highlight continuing developments and identify future opportunities in scalable membrane materials based on these rigid features, for both gas and liquid phase applications. These advanced materials open the door to a new generation of membrane processes beyond existing materials and approaches.

Highly Compatible Hydroxyl-Functionalized Microporous Polyimide-ZIF-8 Mixed Matrix Membranes for Energy Efficient Propylene/Propane Separation

“…This result implies that that the purecomponent gas transport properties of ZIF-8 and PIM-6FDA-OH were preserved in the MMMs, which is of utmost importance for the estimation of gas permeabilities and selectivities of the MMMs by the Maxwell model (Table S3 and Table S4). 7,18 Interaction between ZIF-8 and PIM-6FDA-OH was qualitatively identified by FT-IR and XPS spectra, as shown in Figure 2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Moreover, high resolution XPS spectrum of N 1s (Figure 2c) in the MMM sample (centered at 400.3 eV) reveals a major shift of 1.7 eV to a higher energy value compared to pure ZIF-8 (398.6 eV, Figure …”

“…3,4 Because of the small difference in relative volatility between propylene and propane (~1.08-1.12), distillation is performed in columns over 200 ft tall containing over 150 trays and operating at reflux ratios > 10, thereby making it one of the most energy-intensive separation processes in the chemical process industry. [5][6][7] Membrane technology offers a potential alternative to the conventional distillation process for propylene/propane separation. The current sales of membrane-based gas separation systems is in the range of US$ 1-1.5 billion per year with a 90% market share for: (i) hydrogen recovery from various off-gas streams, (ii) onsite nitrogen production from air, (iii) carbon dioxide removal from natural gas, and (iv) olefin recovery from nitrogen-containing petrochemical vent gas streams.…”

Molecular sieve membranes for N2/CH4separation

“…20 Specifically, these CMS phases display open micropores connected by rigid slit-like ultramicropores to provide high sorption and diffusion coefficients. 21 Different from the well-defined microporous structures which characterize zeolites and metal organic frameworks, CMS exhibit distributions of micropores and ultramicropores. 21 Koros group reported the synthesis of a CMS membrane obtained from a controlled pyrolysis of a commercial polyimide MatrimidÒ 5218.…”

“…21 Different from the well-defined microporous structures which characterize zeolites and metal organic frameworks, CMS exhibit distributions of micropores and ultramicropores. 21 Koros group reported the synthesis of a CMS membrane obtained from a controlled pyrolysis of a commercial polyimide MatrimidÒ 5218. 19 During the conversion process, (polymer to CMS) scission and reorganization of polymer main chains occur, with small gas molecules released and free radicals formed.…”

The state of flux

“…On page 289 of this issue, William Koros and Chen Zhang provide a detailed report of the membrane materials and technologies that show the most promise in this regard, with a specific emphasis on molecularly selective membranes 1 . Molecular selectivity is the discrimination between similarly sized molecules in gas and liquid mixtures, and is quite unlike a simpler filtration used to separate dissimilar species.…”