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Gas permeability data are presented for mixed matrix membranes (MMMs) of few-layer graphene in the polymer of intrinsic microporosity PIM-1, and the results compared with previously reported data for two other nanofillers in PIM-1: multiwalled carbon nanotubes functionalized with poly(ethylene glycol) (f-MWCNTs) and fused silica. For few-layer graphene, a significant enhancement in permeability is observed at very low graphene content (0.05 vol.%), which may be attributed to the effect of the nanofiller on the packing of the polymer chains. At higher graphene content permeability decreases, as expected for the addition of an impermeable filler. Other nanofillers, reported in the literature, also give rise to enhancements in permeability, but at substantially higher loadings, the highest measured permeabilities being at 1 vol.% for f-MWCNTs and 24 vol.% for fused silica. These results are consistent with the hypothesis that packing of the polymer chains is influenced by the curvature of the nanofiller surface at the nanoscale, with an increasingly pronounced effect on moving from a more-or-less spherical nanoparticle morphology (fused silica) to a cylindrical morphology (f-MWCNT) to a planar morphology (graphene). While the permeability of a high-free-volume polymer such as PIM-1 decreases over time through physical ageing, for the PIM-1/graphene MMMs a significant permeability enhancement was retained after eight months storage. [ABSTRACT FROM AUTHOR]

Abstract: Porous asymmetric hydrophobic membranes were prepared from poly(vinylidenefluoride-co-hexafluoropropylene) and polyvinylidenefluoride (PVDF) homopolymer by the phase inversion process induced by a nonsolvent. The effect of pore-forming hydrophilic additives on the membrane morphology and transport properties was investigated. Mean pores size and effective porosity were calculated by the gas permeation method. It was found that membranes made of PVDF copolymer offer a higher resistance to mass transport compared to membranes prepared from PVDF homopolymer under the same experimental conditions. This result is due to lower membrane porosity and pore size and to the presence of a double skin layer (on the upper and bottom surface) for these membranes, reducing the permeate flux. However, membrane morphology and transport properties can be modified by additives in the casting solution. In particular, it was found that polyvinylpyrrolidone improves membrane permeability; LiCl can be used in order to reduce macrovoid formation and increase the mechanical stability of the membranes. [Copyright &y& Elsevier]

A detailed comparison of the gas permeability of four Polymers of Intrinsic Microporosity containing Tröger's base (TB-PIMs) is reported. In particular, we present the results of a systematic study of the differences between four related polymers, highlighting the importance of the role of methyl groups positioned at the bridgehead of ethanoanthracene (EA) and triptycene (Trip) components. The PIMs show BET surface areas between 845–1028 m2 g−1 and complete solubility in chloroform, which allowed for the casting of robust films that provided excellent permselectivities for O2/N2, CO2/N2, CO2/CH4 and H2/CH4 gas pairs so that some data surpass the 2008 Robeson upper bounds. Their interesting gas transport properties were mostly ascribed to a combination of high permeability and very strong size-selectivity of the polymers. Time lag measurements and determination of the gas diffusion coefficient of all polymers revealed that physical ageing strongly increased the size-selectivity, making them suitable for the preparation of thin film composite membranes. [ABSTRACT FROM AUTHOR]

The effect on the gas transport properties of Matrimid®5218 of blending with the polymer of intrinsic microporosity PIM-EA(H2)-TB was studied by pure and mixed gas permeation measurements. Membranes of the two neat polymers and their 50/50 wt % blend were prepared by solution casting from a dilute solution in dichloromethane. The pure gas permeability and diffusion coefficients of H2, He, O2, N2, CO2 and CH4 were determined by the time lag method in a traditional fixed volume gas permeation setup. Mixed gas permeability measurements with a 35/65 vol % CO2/CH4 mixture and a 15/85 vol % CO2/N2 mixture were performed on a novel variable volume setup with on-line mass spectrometric analysis of the permeate composition, with the unique feature that it is also able to determine the mixed gas diffusion coefficients. It was found that the permeability of Matrimid increased approximately 20-fold with the addition of 50 wt % PIM-EA(H2)-TB. Mixed gas permeation measurements showed a slightly stronger pressure dependence for selectivity of separation of the CO2/CH4 mixture as compared to the CO2/N2 mixture, particularly for both the blended membrane and the pure PIM. The mixed gas selectivity was slightly higher than for pure gases, and although N2 and CH4 diffusion coefficients strongly increase in the presence of CO2, their solubility is dramatically reduced as a result of competitive sorption. A full analysis is provided of the difference between the pure and mixed gas transport parameters of PIM-EA(H2)-TB, Matrimid®5218 and their 50:50 wt % blend, including unique mixed gas diffusion coefficients. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the preparation and extensive characterization of polyphenylsulfone (PPSU) hollow fiber membranes (HFM) was carried out. PPSU is a polysulfone with better solvent resistance than Polysulfone (PSf) and poly(ether sulfone) (PES), which makes investigation of its potential use in solvent resistant nanofiltration (SRNF) membranes interesting. The membranes were prepared via the dry wet spinning method with three different concentrations of PPSU (22.5%, 25% and 27.5%W/W) in N-methyl-2-pyrrolidone (NMP) as the dope solution. They were characterized on the basis of their morphology, porosity and permeo-selective properties. In addition, their resistance in different organic solvents was investigated. Scanning electron microscopy (SEM) was used to explore the morphological characteristics and the structure of the cross section. It was found that the fiber has a typical asymmetric structure with a nearly dense skin layer and a porous substructure. An increasing amount of macro-voids in the porous substructure was observed when the polymer concentration decreased. The maximum pore size was estimated by bubble point measurements. Iso-propanol permeability and the dye rejection tests were performed in order to study the permeo-selective properties. An increase in the polymer concentration in the dope produces a decrease in the iso-propanol permeability and an increase in the rejection of dyes. In terms of rejection the membranes offer good potential for successful use in nanofiltration applications, although the permeability is low and needs further optimization. The effect of the membrane exposure to ethyl acetate, n-hexane, toluene, diethyl ether, iso-propanol and acetone was investigated by measuring the change in the length of the fiber before and after solvent treatment for ten days. The membranes were visually stable in most of the solvents except for methyl ethyl ketone. The methanol, ethanol, iso-propanol, n-hexane, n-heptane, acetone and toluene permeability has been tested. Except for the last two solvents, the membranes were stable during the permeation test. Mechanical tests show the loss of mechanical stability of fibers in contact with toluene, while their mechanical strength remains the same in contact with n-hexane and iso-propanol. [Copyright &y& Elsevier]

Abstract: Integrally skinned asymmetric poly(vinylidene fluoride) hollow fibre membranes were prepared and characterized. The effects of phase inversion methods (dry-wet or wet) and spinning conditions, such as the type of solvent (NMP, DMAc), the concentration of polymer in dope solution, temperature of the external coagulation bath and the composition of the inner coagulant on the morphology and on the formation of a dense skin layer were investigated. The structure of the membranes was analyzed by scanning electron microscopy and the gas permeation properties with six different gases (He, H2, N2, O2, CH4 and CO2) were measured at 25°C to confirm the integrity of the selective skin layer. Under the proper conditions highly selective and permeable PVDF hollow fibre membranes were thus obtained by dry-wet spinning of a 30 wt.% PVDF solution in DMAc, using hot water (50°C) as the external coagulant and a bore fluid of pure water as the internal coagulant. The best membrane had a selective outer skin with an effective thickness of approximately 0.2μm. The ideal selectivity of the hollow fibres approached or even exceeded the intrinsic ideal selectivity of a dense PVDF film, for instance the selectivity for He over N2 was 86.2 for the hollow fibre, whereas it was 83.5 for a dense PVDF reference film. DSC and FT-IR/ATR analysis indicated a higher fraction of the β-crystal phase in the selective skin and a high overall crystallinity than in the melt-processed film. The latter explains the relatively high selectivity and low permeability of the membranes. Intrinsic polymer properties make the membranes also suitable for vapour transport than for gas separation. [Copyright &y& Elsevier]

The gas transport properties of mixed matrix membranes (MMMs), prepared by dispersing nanoparticles of MOFs MIL-101(Cr) or MIL-177(Ti) into highly permeable Polymers of Intrinsic Microporosity PIM-EA-TB or PIM-TMN-Trip, were investigated. The homogeneity of the dispersion was confirmed by means of Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray (EDX) mapping analysis. Single gas time-lag measurements provided the permeability and ideal selectivity of different gas pairs, both after treatment of the MMMs with methanol and after natural aging over an extended period (up to 2000 days). This data demonstrated that the gas size-sieving pores of MIL-101(Cr) and MIL-177(Ti) and their good dispersion into the PIM matrix results in MMMs with enhanced gas separation performance, as compared to films composed solely of the polymer. The comparison of actual permeability with the Maxwell model for PIM-EA-TB with both MOFs confirmed the good dispersion and the absence of anomalies, whereas the inconsistency of permeability with prediction data for PIM-TMN-Trip suggests that the MOFs improved the polymer properties, stiffening or occupying the polymer free volume. In particular, the incorporation of MIL-101(Cr) into PIM-EA-TB significantly enhances the H 2 permeability from ∼6000 to 13,000 Barrer, with a concurrent increase of the H 2 /N 2 selectivity from 14 to 21. MIL-177(Ti) also enhances the H 2 /N 2 selectivity to 20 due to a slight reduction of the N 2 permeability. The addition of MIL-101(Cr) and MIL-177(Ti) into the ultra-permeable PIM-TMN-Trip showed more modest increases in H 2 permeability and H 2 /N 2 selectivity from 4.6 to ∼ 10. Hence the data for some of the MMMs surpass the 2008, and even approach the 2015/2019 Robeson's upper bounds, particularly for gas pairs including H 2. [Display omitted] • The MIL-101(Cr) and MIL-177(Ti) were loaded into PIM-EA-TB or PIM-TMN-Trip for fabrication of MMMs. • Smaller MIL-101 particle-size favour better compatibility with polymers than larger MIL-177. • Mixed gas experiments confirm an excellent separation performance under a long aging. • Data for some MMMs break the 2008 upper approaching the 2015/2019 Robeson's upper bounds. [ABSTRACT FROM AUTHOR]

Membrane gas separations requirematerials with high permeabilityand good selectivity. For glassy polymers, the gas transport propertiesdepend strongly on the amount and distribution of free volume, whichmay be enhanced either by engineering the macromolecular backboneto frustrate packing in the solid state or by thermal conversion ofa soluble precursor to a more rigid structure of appropriate topology.The first approach gives polymers of intrinsic microporosity (PIMs),while the second approach is used in thermally rearranged (TR) polymers.Recent research has sought to combine these approaches, and here anew range of thermally rearrangeable PIM-polyimides are reported,derived from dianhydrides incorporating a spiro center. Hydroxyl-functionalizedpolyimides were prepared using two different diamines: 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane(bisAPAF) and 4,6-diaminoresorcinol (DAR). Thermal treatment at 450°C under N2for 1 h yielded polybenzoxazole (PBO)polymers, which showed increased permeability, compared to the precursor,in membrane gas permeation experiments. A polymer based on DAR (PIM-PBO-3)exhibited a CO2/N2selectivity of 30 as prepared,higher than the values of 21–23 obtained for polymers derivedfrom bisAPAF with the same dianhydride (PIM-PBO-1). [ABSTRACT FROM AUTHOR]

Nitrile groups in the polymer ofintrinsic microporosity PIM-1were reduced to primary amines using borane complexes. In adsorptionexperiments, the novel amine–PIM-1 showed higher CO2uptake and higher CO2/N2sorption selectivitythan the parent polymer, with very evident dual-mode sorption behavior.In gas permeation with six light gases, the individual contributionsof solubility and diffusion to the overall permeability was determinedvia time-lag analysis. The high CO2affinity drasticallyrestricts diffusion at low pressures and lowers CO2permeabilitycompared to the parent PIM-1. Furthermore, the size-sieving propertiesof the polymer are increased, which can be attributed to a higherstiffness of the system arising from hydrogen bonding of the aminegroups. Thus, for the H2/CO2gas pair, whereasPIM-1 favors CO2, amine–PIM-1 shows permselectivitytoward H2, breaking the Robeson 2008 upper bound. [ABSTRACT FROM AUTHOR]

Microporous polymers of extreme rigidity are required for gas-separation membranes that combine high permeability with selectivity. We report a shape-persistent ladder polymer consisting of benzene rings fused together by inflexible bridged bicyclic units. The polymer's contorted shape ensures both microporosity--with an internal surface area greater than 1000 square meters per gram--and solubility so that it is readily cast from solution into robust films. These films demonstrate exceptional performance as molecular sieves with high gas permeabilities and good selectivities for smaller gas molecules, such as hydrogen and oxygen, over larger molecules, such as nitrogen and methane. Hence, this polymer has excellent potential for making membranes suitable for large-scale gas separations of commercial and environmental relevance. [ABSTRACT FROM AUTHOR]

Polymer-based membranes have the potential for use in energy efficient gas separations. The successful exploitation of new materials requires accurate knowledge of the transport properties of all gases of interest. Open-source databases of gas permeabilities are of significant potential benefit to the research community. The Membrane Society of Australasia (https://membrane-australasia.org/) hosts a database for experimentally measured and reported polymer gas permeabilities. However, the database is incomplete, limiting its potential use as a research tool. Here, missing values in the database were imputed (filled) using machine learning (ML). The ML model was validated against gas permeability measurements that were not recorded in the database. Through imputing the missing data, it is possible to re-analyse historical polymers and look for potential "missed" candidates with promising gas selectivity. In addition, for systems with limited experimental data, ML using sparse features was performed, and we suggest that once the permeability of CO 2 and/or O 2 for a polymer has been measured, most other gas permeabilities and selectivities, including those for CO 2 /CH 4 and CO 2 /N 2 , can be quantitatively estimated. This early insight into the gas permeability of a new system can be used at an initial stage of experimental measurements to rapidly identify polymer membranes worth further investigation. [Display omitted] • The Polymer Gas Separation Membrane Database was imputed with machine learning. • The machine learning model is robust against different experiment conditions. • Gas permeability data not recorded in the database can be accurately predicted. • Data driven insight can be obtained to rapidly identify gas selective polymers. [ABSTRACT FROM AUTHOR]

• Cellulose acetate derivatised with ionic liquid-like cationic pendants grafted on its backbone. • PEs in the form of thin film composite membranes showed robust performance in CO 2 capture. • Membranes with a combination of IL-like pendants enhanced permeation of CO 2 molecules. Cellulose acetate (CA) is an attractive membrane polymer for CO 2 capture market. However, its low CO 2 permeability hampers its application as part of a membrane for most relevant types of CO 2 containing feeds. This work investigates the enhancement of CA separation performance by incorporating ionic liquid-like pendants (1-methylimidazol, 1-methylpyrrolidine, and 2-hydroxyethyldimethylamine (HEDMA) on the CA backbone. These CA-based polyelectrolytes (PEs), synthesised by covalent grafting of cationic pendants with anion metathesis, were characterised by NMR, FTIR, DSC/TGA, and processed into thin-film composite membranes. The membrane performance in CO 2 /N 2 mixed-gas permeation experiments shows a decrease in CO 2 and N 2 permeability and an initial decrease and then gradual increase in CO 2 /N 2 selectivity with increasing HEDMA content. The amount of HEDMA attached to the CA backbone determines overall separation process in bifunctional PEs. This indicates that the hydroxy-substituted cationic pendants alter interactions between PEs network and permeating CO 2 molecules, suggesting possibilities for further improvements. [ABSTRACT FROM AUTHOR]

The potential of an ultrapermeable benzotriptycene-based polymer of intrinsic microporosity (PIM-TMN-Trip) for the upgrading of biogas is investigated. Permeation experiments were performed using an in-house bespoke permeation unit for pure gases and gas mixtures, and included tests with model mixtures as well as real biogas from a sewage treatment plant, under dry and humid conditions. Permeability and CO 2 /CH 4 selectivity for either pure gases or for real biogas were high and lie close to or on the recently defined 2019 Robeson upper bound based on ideal permselectivities. In addition, a remarkable increase in CO 2 /CH 4 selectivity was observed after two weeks of continuous exposure to CO 2 due to a significant decrease of CH 4 permeability. The constant CO 2 permeability and increased selectivity upon ageing suggest that ageing in the presence of CO 2 causes a rearrangement, rather than a reduction of the fractional free volume. The mixed gas permeability experiments were performed with high stage-cut in order to mimic a real separation process, and the results confirmed the potential of PIM-TMN-Trip membranes for biogas upgrading. Image 1 • PIM-TMN-Trip membrane can excellently separate biogas at small pressure difference. • Model binary mixture represents very well the behaviour of real biogas. • Increasing upstream pressure causes the decrease of mixed gas selectivity. • Pristine membrane had an ideal CO 2 /CH 4 selectivity of about 15. • CO 2 treatment strongly enhances the ideal CO 2 /CH 4 selectivity up to 39. [ABSTRACT FROM AUTHOR]