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Supercooling of liquids leads to peculiarities which are scarcely studied under high-pressure conditions. Here, we report the surface tension, solubility, diffusivity, and partial molar volume for normal and supercooled liquid solutions of methane with p-xylene. Liquid bodies of perdeuterated p-xylene (p-C8D10), and, for comparison, o-xylene (o-C8D10), were exposed to pressurized methane (CH4, up to 101 bar) at temperatures ranging 7.0–30.0 °C and observed at high spatial resolution (pixel size 20.3 μm) using a non-tactile neutron imaging method. Supercooling led to the increase of diffusivity and partial molar volume of methane. Solubility and surface tension were insensitive to supercooling, the latter substantially depended on methane pressure. Overall, neutron imaging enabled to reveal and quantify multiple phenomena occurring in supercooled liquid p-xylene solutions of methane under pressures relevant to the freeze-out in the production of liquefied natural gas.

The gas and organic vapour permeation of integrally skinned asymmetric poly(vinylidene fluoride) (PVDF) hollow fibre membranes with an effective skin thickness of ca. 0.2 ?m was studied. Methanol, dichloromethane and acetone showed fundamentally different behaviour related to their interaction with the polymer phase. Strong plasticization by acetone led to a very pronounced increase in permeance as a function of the vapour activity. In contrast, the permeance of methanol was virtually independent of the vapour activity. Dichloromethane showed intermediate behaviour. The data were supported by vapour and liquid phase sorption measurements and liquid phase dilation measurements on 38.5 ?m thick flat sheet reference samples. X-ray diffraction analysis revealed a significant decrease in crystallinity upon swelling by acetone, whereas none of the liquids caused a notable change in the crystal polymorphs. In addition, differential scanning calorimetry revealed no irreversible changes in crystallinity or crystal polymorphs. A considerable discrepancy between liquid phase sorption and vapour phase sorption at high activity, known as Schröder's paradox, was observed for C-C alcohols. The anomalous transport properties were investigated in detail and were explained in terms of the ENSIC model for polymer-vapour interactions. The results were discussed in light of the potential use of asymmetric PVDF membranes in gas/vapour separation, vapour/vapour separation or pervaporation.

We report on synthesis, preparation and characterization of newly prepared hyperbranched polyimide (HBPI) based on 4,4´-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 4,4′,´´-triaminotriphenylmethane (TTM). HBPI material was synthesized via the amine-terminated hyperbranched polyamic acid (HBPAA) precursor and the absence of corresponding HBPAA amide band at 1670 cm−1 in IR spectra indicated complete imidization. TGA analysis of 6FDA-TTM proved the excellent thermal stability up to ca. 500 °C. Gas permeation measurements (H2, CH4, and CO2) revealed the excellent separation properties for the CO2/CH4 gas pair, with the best-reached selectivity value of 137 and 27.4 Barrer of CO2 permeability that exceeds the Robeson 2008 upper bound. The 6FDA-TTM based-analogs containing 5 and 20 mol% of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane (DMQ) were prepared for comparison to investigate the effects of reduced HBPI branching on material properties. 6FDA-TTM-DMQ displayed lower CO2 sorption in the whole pressure interval (1–15 bar) while for CH4 only at higher pressures, presumably due to reduced chains mobility to accommodate excessive amounts of CO2. Similarly, 6FDA-TTM-DMQ with increasing of DMQ content exhibited lower H2 and CO2 permeabilities and lower corresponding CO2/CH4 selectivities. However, in the case of H2/CO2 were selectivities higher (2.3 and 2.1, respectively) compared to a neat polymer (1.5). Simultaneously, the effect of mesoporous hollow and solid silica spheres with diameters 600 and 400 nm, respectively, in amounts of 1, 5 and 10 wt % embedded in 6FDA-TTM and 6FDA-TTM-DMQ membranes was studied too. Prepared mixed matrix membranes exhibited rather enhanced permeability due to the introduction of the additional free volume, but without clear trend with respect to the silica morphology and loading, and, in most cases, it reduced corresponding selectivities compared to a neat polymer. Consistent with that, experimental permeabilities were comparable or higher than those obtained by Maxwell model due to the mesoporosity of the silica particles and, to some extent, due to probably the non-homogeneous distribution of filler within the matrix. However, our work proves the concept of 6FDA-TTM materials for effective gas separation and outlined the possibilities for further tailoring the material properties.

We report on the characterization of blends of polybutylene succinate (PBS) with cellulose triacetate (CTA) with focus on their mass transport properties and physical structure. Blends containing 0–30 wt% of PBS were tested using gas permeation, vapour permeation, pervaporation and vapour sorption. Permeability for gases (CO2, H2, etc.) decreased with increasing PBS content in a fixed ratio. In contrast to that, permeability for vapours (methanol, dimethyl carbonate) decreased compound-specifically, thus rendering the blends more selective towards methanol than pure CTA. Interestingly, higher separation factors were observed for the permeation of vapours than for the pervaporation of liquids. The influence of the PBS content on the physical structure and thermal properties of the blends were studied using XRD, SEM, FTIR-ATR, DSC, TGA and DMA techniques. Overall, the blends of PBS and CTA were homogenous, thermally stable and had enhanced barrier properties compared to pure CTA.

Nafion®, a highly hydrophilic polymer, is potentially usable for water - organic and hydrophilic organic - hydrophobic organic membrane separations. Since Nafion has accessible sulfo groups in its structure, we propose modifying it with primary amines and did so with aniline, benzylamine and ethanolamine. The resulting modifications contained ionic and sulfonamide bonds, as these were detected using Fourier transform infrared (FTIR) spectrometry. To quantify the separation characteristics of the amine-modified Nafion membranes, vapour sorption microgravimetry and pervaporation experiments were made. The vapour sorption tests showed that amine-modified Nafions sorb ca. 2–4 times less methanol, water and dimethyl carbonate vapours than pure Nafion. Importantly, pervaporation experiments made with methanol-dimethyl carbonate mixtures showed that Nafion modified with ethanolamine is approximately twice as selective to methanol as pure Nafion, the sodium salt of Nafion and Nafion modified with benzylamine.

The separation of the individual xylene isomers remains challenging and energy intensive. Since the utilization of membrane separations could bring an improvement, we compare the efficacy of two related membrane methods, pervaporation and perstraction, for the separation of p‑xylene/m‑xylene mixtures using membranes from polydimethylsiloxane (PDMS) and cellulose triacetate (CTA) at 40 °C. Methanol was used as the receiving liquid in perstraction and as a membrane entrainer; feeds containing 0–80 mol.% of methanol were studied. While PDMS showed almost no selectivity to p‑xylene over m‑xylene during pervaporation, the selectivity reached up to 1.40 when operated in the perstraction mode with the feed enriched with methanol. CTA performed better than PDMS for all studied mixtures, the highest selectivity of 1.93 was observed for the perstraction of the molten eutectic mixture with no methanol in the feed. The likely reason for the enhancement of the selectivity are the isomer-specific interactions with the polar moieties in the polymer plasticized by methanol. Overall, it was demonstrated that a simple change in the mode of operation from pervaporation to perstraction and the use of a membrane entrainer can appreciably enhance the p‑xylene to m‑xylene selectivity of the common and reliable membrane materials.

This work presents densities, dynamic viscosities, surface tensions, and refractive indices of three methyl ethereal solvents: cyclopentyl methyl ether (CPME), tert-amyl methyl ether (TAME), and tert-butyl methyl ether (MTBE). CPME and TAME were chosen as methyl alternatives of the common but environmentally problematic MTBE. The highest density, viscosity, surface tension, and refractive index were observed for CPME and the lowest for MTBE. The results are in good agreement with other authors’ data. Based on the experiments, the critical temperature and the critical pressure of CPME were estimated. The parachor, molar refraction, and critical compressibility factor were calculated from experimental data. Parameterisations of the experimental data using corresponding correlative models are presented.

This work reports on new method for description of sorption and swelling phenomena in liquid + polymer systems. An innovative approach to description of polymer-solvent interactions combines swelling and sorption properties of polymeric membranes in liquid media. It stems from gravimetric (material mass change) and dilatometric (material volume change) experiments. Further, we introduced a new parameter, a product of the dilatation interaction factor and the solubility of the organic liquid in the swollen polymer, which can describe the “moving ability” of polymer chains of swollen polymer. The approach was developed on the basis of the data determined for low density semicrystalline polyethylene (LDPE) with benzene and cyclohexane derivates. The obtained results are presented as functions of temperature, number of C-atoms in the side chain of liquid cyclic molecules, and as a function of van der Waals volume of liquid penetrants. The moving ability of polymer chains increases with increasing temperature, but decreases with increasing number of C-atoms in the side chain of penetrants. The new parameter was determined also for rubbery polydimethylsiloxane (PDMS), Lukopren, modified Lukopren with embedded montmorillonite and on polyvinylidene fluoride (PVDF) membrane samples.

Sorption of liquids in polymers is an important factor for any application where polymers come into contact with an organic solvent. We report on sorption properties of hydrophobic poly(ethylene chlorotrifluoroethylene) Halar®901 in view of its potential application as a membrane material. For the first time, the liquid phase sorption of 34 common organic liquids such as linear C6 C10 alkanes, methyl-, ethyl- and propyl-derivates of benzene and cyclohexane and of linear-, branched- and cyclic-ethers, ketones, acetates and chloroderivates in the 1:1 alternating copolymer of ethylene and chlorotrifluoroethylene (ECTFE) is presented. The effects of solvent molecular structure and its physico-chemical properties on the total mass uptake are discussed in detail. Furthermore, two sorption-predictive methods developed from determined data allows to anticipate the behavior of solvents in Halar®901 based exclusively on three type of structural units (C-bone, functional groups, molecular geometry) or four (molar mass, surface tension, boiling temperature and Van der Waals volume) parameters only. A successful verification of our methods proved their versatility in predicting organic liquid sorption in ECTFE material Halar®901.

The CO2/CH4 separation performance under humidified mixed feed conditions relevant to biogas separation is reported for supported, epoxy-amine-based ion gel membranes containing fixed-site amine facilitated CO2 transport carriers. The chemical composition of the ion gel membranes consists of combination of the bis(epoxide)-IL monomer and trifunctional amine monomer in a mole ratio 3:2 plus either 50 or 75 wt% free [EMIM][Tf2N], impregnated into a Omnipore™ support film. Prepared samples were examined for fundamental structure/property relationships via permeation and sorption methods. Gas sorption confirmed specific gas interactions, showing elevated CO2 sorption compared to CH4 with increasing equilibrium feed pressure. Single gas permeation demonstrated almost a three-fold increase in CO2 permeability from 195 barrer for 50 wt% of free [EMIM][Tf2N] to 525 barrer for 75 wt% of ionic liquid while the ideal selectivity α(CO2/CH4) stayed almost the same (20 and 18, respectively). The effects of feed composition, feed pressure, and relative humidity (32% and 54%) on the CO2/CH4 separation performance were elucidated for mixed-gas feeds. Under simulated biogas processing conditions, an increase of CO2/CH4 separation factor from 25 to 35 with increasing humidity and low feed pressure was observed. Such behavior indicates that the fixed-site-carrier facilitated CO2 transport mechanism enhances also the CO2/CH4 separation performance of studied membranes, as observed for the CO2/N2 mixtures studied previously. This feature also enables them to reach a performance level close to the 2008 Robeson plot upper bound.

In this work, we report on the permeation of methanol and dimethyl carbonate (DMC) vapour mixtures through dense membranes made from cross-linked polydimethylsiloxane (PDMS) and from poly[(trimethylsilyl)propyne] (PTMSP). Since methanol forms a methanol-rich pressure-maximum azeotrope with dimethyl carbonate, vapour permeation through hydrophobic (DMC selective) membranes is presumably a favourable method of azeotrope breaking. Permeation of vapours of pure compounds and of binary vapour mixtures was measured at 40 °C for a series of feed mixture compositions. Both membranes showed practically constant permeabilities of both studied compounds, thus indicating that no significant coupling of fluxes occurred. The membrane prepared from PTMSP was ca. 2–5 times more permeable and showed higher separation factors (αDMC ⩽ 4.2) than the one prepared from PDMS (αDMC ⩽ 2.8). In the case of the PDMS, the separation factors decreased with the increasing dilution of the feed mixtures with inert gas (hydrogen). Conversely, the separation factors increased with increasing feed mixture dilution in the case of PTMSP. The highest separation factors were observed near the azeotrope composition for both polymers (ca. 82 mol.% of methanol), thus enabling the development of effective hybrid processes combining rectification columns and vapour permeation units.

This manuscript describes the gas separation performance of PIM-2, a partially fluorinated linear copolymer synthesized from 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethylspirobisindane (TTSBI) and decafluorobiphenyl (DFBP). As one of the early members of the family of polymers of intrinsic microporosity, it had never been tested as a gas separation membrane because of insufficient mechanical resistance. This has been solved only recently, allowing the preparation of robust self-standing films. Molecular modelling studies demonstrated a high fractional free volume (34%) and an elevated surface area (642 m2 g-1), and the latter is in good agreement with experimental BET results. Pure gas permeabilities measured on a fixed-volume time-lag instrument at 1 bar compare well with the results of mixed separation tests on a variable volume setup from 1-6 bar(a). Molecular modelling and independent sorption measurements on a gravimetric sorption balance both show strong dual-mode sorption behaviour, especially for CO2 and to a lesser extent for CH4. Temperature-dependent pure gas permeation measurements show typical Arrhenius behaviour, with a clear increase in the activation energy for diffusion with the increasing molecular size of the gas, indicating high size-selectivity. This is in agreement with the highly rigid PIM structure, determined by AFM force spectroscopy measurements. The dual-mode behaviour results in a moderate pressure dependence of the CO2 permeability and the CO2/N2 and CO2/CH4 selectivity, all slightly decreasing with increasing pressure. The presence of humidity in the gas stream has a remarkable small effect on the membrane performance, which is probably due to the high fluorine content and the consequently low water vapour solubility in the polymer, as confirmed by gravimetric sorption measurements. The manuscript describes an extensive study on the structure-property relationships in PIM-2. © 2019 Elsevier B.V. European Commission, EC Grantová Agentura Ceské Republiky, GA Ä?R: 18-05484S --Research on biogas upgrading presented in this work was supported by EU structural funding in the frame of Operational Programme Research, Development and Education, project No. CZ.02.1.01./0.0/0.0/17_049/0008419 “COOPERATION”. This work was further supported by the CNR-CAS bilateral agreement 2016–2018 “Innovative polymeric membranes for pervaporation and advanced gas and vapour separations” and by the Czech Science Foundation (grant no. 18-05484S ). Appendix A

Membranes from PIM-1 represent a promising tool for the efficient recovery of organic components from their vapour mixtures with water or alcohols. To understand the phenomena governing the separation, sorption, swelling and mechanical characteristics were systematically studied for thick PIM-1 films exposed to vapour mixtures of methanol and dimethyl carbonate (DMC). The studied binary vapour mixtures contained 30, 55, 82 and 90 mol.% of methanol and reached 28, 49 and 63% of the dew point pressure at 40 °C. The separation factor for sorption of vapour mixtures ranged 4.0–7.5, peaked for the azeotropic mixture (82 mol% of methanol) at low saturation (28% of the dew point pressure), and was significantly contributed by competitive sorption. Furthermore, the tested PIM-1 films exhibited anomalously low volume swelling while their storage modulus remained comparable to that of the pure polymer until exposed to the highly saturated vapours (63% of the dew point pressure). Raman spectroscopy analysis of PIM-1 swollen by liquid methanol and DMC revealed the pronounced frequency shifts of the C–C vibrations in the aromatic rings and the C–H vibrations in the pentacyclic units. These centres presumably triggered the relaxation of the polymer backbone occurring at high saturations of the vapours. In conclusion, PIM-1 remains highly rigid and selective to DMC in wide ranges of saturation and composition for vapour mixtures of methanol with DMC and is a candidate for effective inversely selective vapour separation membranes.

The individual solubility of CH 4 and CO 2 from binary gas mixtures was measured at 35 °C and up to 35 bar in a polymer of intrinsic microporosity (PIM-1), at different compositions of the gas phase (from 0 to 50 mol% of CO 2 ). The experiments were conducted on a pressure-decay apparatus equipped with a gas chromatograph, allowing a highly flexible measuring procedure. The gas solubility was plotted versus gas phase composition, total pressure, gas fugacity and second gas concentration. The mixed gas solubility of both species, CH 4 and CO 2 , is lower than the pure gas value at the same fugacity, but the reduction of methane solubility due to the presence of CO 2 is generally more significant. Such behavior is due to the fact that CO 2 has normally higher solubility than methane: indeed the depression of the solubility coefficient with respect to the pure gas value is similar for both gases, when reported at the same concentration of the second gas. The real, mixed gas solubility selectivity is in general higher than the ideal value calculated from pure gas behavior. The ratio between real and ideal solubility selectivity increases with CO 2 concentration in the membrane, according to a single mastercurve, reaching a maximum value of 4, and it also increases with the ratio between CO 2 and CH 4 concentration in the membrane. In particular, as in the case of other glassy polymers, the real solubility selectivity of CO 2 over CH 4 is higher than the ideal value if c (CO 2 )> c (CH 4 ), and it is lower than the ideal value if the opposite condition holds true. Such behavior occurs because the competition for sorption is normally less effective on the more abundant penetrant in the polymer. A selectivity–solubility performance plot can be drawn for this system.

The separation of dimethyl carbonate (DMC) from its mixtures with methanol was studied using pervaporation (PV) and vapour permeation (VP) through thick (∼0.5 mm) PIM-1 membranes; PV characteristics of PDMS and PTMSP membranes are provided for comparison. DMC is a “green” chemical with numerous applications in chemistry, but its production is energy- and cost-intensive. As their azeotrope contains 82 mol.% of methanol at 40 °C, DMC-selective rather than common methanol-selective membranes can allow for energy efficient separation and thus production of this “green chemical”. PV of the azeotropic mixture through the PIM-1 membrane showed a separation factor of 2.3, which is comparable to that observed for PV through the PDMS membrane; the PTMSP membrane showed practically no separation. The total PV fluxes followed the order: PTMSP ≫ PIM-1 > PDMS. When the PIM-1 membrane was operated in the VP mode, a separation factor of up to 5.1 was reached for the vapours having the azeotropic composition, while total fluxes dropped ca 50-times compared to PV. The highest observed separation factor of 6.5 was found for VP of DMC-rich vapour mixtures highly diluted with inert gas. To our knowledge, VP through PIM-1 membranes enables to date the most selective membrane-based removal of DMC from its azeotrope with methanol.

An understanding of gas transport in polymers of intrinsic microporosity (PIMs) is limited by a lack of directly determined (experimental) sorption data and by quantitative inaccuracies in solubilities calculated indirectly from permeation time-lag analysis. To address this, we provide a detailed gas sorption analysis for seven different PIMs and assess the influence of the non-linear steady-state CO2 concentration profiles on the apparent solubilities obtained from permeation experiments. Equilibrium sorption was analysed with dual-mode sorption (DMS) and Guggenheim, Anderson and De Boer (GAB) models, which provided accurate descriptions of the data. The non-linear steady-state CO2 concentration profiles were calculated using the thermodynamic Fick’s law based on the DMS or GAB model coefficients. Once the thermodynamic term was incorporated into the model for permeation, better agreement between directly (gravimetric sorption) and indirectly (time-lag analysis) determined solubility was observed for most membranes. The monolayer capacities were found to be linearly dependent between the models and could be used for a qualitative comparison of the apparent surface area of PIM materials. Diffusivities determined from time-lag analysis were higher (e.g., PIM-Trip-TB, CO2, 111∙10-8 m2 s-1) than those from sorption measurements (24∙10-8 m2 s-1), probably due to substantially low mass uptake in Henry mode (11 % of total sorption capacity). Thus, a careful gas sorption analysis in combination with time lag experiments provides a deeper insight into the transport behavior of gases in PIMs than when only time lag measurements are performed.

The aim of this work is to study in detail the sorption of binary gas mixtures containing methane into polymers suitable for membrane separations. A novel measuring procedure has been developed and validated by performing mixed gas sorption tests on the n -C 4 /CH 4 mixture in films of poly(1-trimethylsilyl-1-propyne) (PTMSP), for which literature data are available. Then, individual uptakes of CH 4 and CO 2 from binary gas mixtures were measured at 35 °C and up to 35 bar in PTMSP, in the whole gas composition range. The experiments were conducted on a pressure-decay apparatus equipped with a gas chromatographic device. The novel experimental procedure was set up in order to obtain data either at constant partial pressure of one gas, as done by previous authors, or at constant gas composition and variable total pressure. The latter protocol allows to mimic more closely the real membrane separation processes, where only the total pressure of the mixture can be varied arbitrarily. It was observed that the presence of CH 4 does not alter significantly the sorption of CO 2 and of n -C 4 in PTMSP, while the mixed gas solubility of CH 4 is lower than the pure gas value at the same CH 4 fugacity. In particular, the CH 4 solubility coefficient, as well as the mixed gas solubility selectivity are univocal functions of CO 2 fugacity (or concentration) and are otherwise independent of the gas phase composition. The real CO 2 /CH 4 solubility-selectivity of PTMSP is similar to the ideal value at low CO 2 fugacity but it becomes significantly higher, up to 4.5 times, at 25 bar of CO 2 fugacity. A quantitative rule can be drawn using data of several binary gas mixtures in glassy polymers, based on which the ratio between actual mixed gas and pure ideal solubility selectivity of CO 2 over CH 4 is a single, monotonously increasing function of the ratio between the concentration of the two components, c (CO 2 )/ c (CH 4 ), which becomes higher than unity as c (CO 2 )> c (CH 4 ). In other words, the competition effects depress more significantly the less abundant penetrant in the polymer, that is usually CH 4 .

Equilibrium sorption of vapour mixtures of methanol and dimethyl carbonate in poly[(trimethylsilyl)propyne], PTMSP, is reported. The experiments were conducted at 40 °C and at atmospheric pressure using an apparatus that combined the sorption gravimetry in a carrier gas and the analysis of the desorbate by Fourier transform infrared spectroscopy (FT-IR). An unusual combination of competitive and cooperative sorption effects of dimethyl carbonate on methanol was observed. The cooperative sorption occurred at small methanol vapour activities, at which the sorption of pure methanol vapour is anomalously, and advantageously, small. The sorption isotherms of pure vapours and vapour mixtures were plausibly parameterized using Guggenheim, Anderson, De Boer (GAB) model and its semi-empirical extension for vapour mixtures, respectively. While the ideal separation factor of sorption, observable from the pure component sorption data, ranged 2–248, the real separation factor was significantly lowered by the co-sorption effects to 1–20. Overall, the highest real separation factors were observed for the higher dilutions of the binary feed mixtures with the inert gas and, advantageously, for methanol rich feed mixtures ( i.e . in the vicinity of the composition of the azeotropic mixture).

We report an original experimental method for the characterization of the sorption of binary vapour mixtures in polymers. Measurements of sorption of vapour mixtures can reliably identify and quantify the cooperative and competitive sorption, which can limitedly be predicted from the data on sorption of pure components, and on which scarce data are available. The method combined the sorption gravimetry and the analysis of sorbate using Fourier-transform infrared spectroscopy. The sorption of binary vapour mixtures of methanol and dimethyl carbonate in cross-linked poly (dimethylsiloxane), PDMS, was measured at 40 °C. A clear cooperative sorption effect of dimethyl carbonate on methanol was observed. To effectively parameterize the sorption of the vapour mixtures in the polymer, an extension of Guggenheim Anderson de Boer (GAB) model was derived. Overall, the proposed method represents a feasible way of measuring the sorption of mixtures of vapours in polymers.

The removal of aroma compounds from packaged food items - aroma scalping – can be primarily controlled by the choice of packaging materials. Although the utilization of biodegradable polymers as packaging materials can greatly contribute to the sustainability of the packaging industry, only limited data on their aroma scalping properties are available. In this work, the aroma scalping characteristics of a series of films made from biodegradable polybutylene succinate (PBS) and polybutylene succinate-co-addipate (PBSA) for common aroma compounds in foods (ethyl acetate, ethyl butyrate, ethyl hexanoate, hexan-1-ol, heptanal and (R)-(+)-limonene) are reported. The aroma scalping characteristics of a film made from poorly biodegradable low density polyethylene (LDPE) are reported for comparison. The aroma scalping characteristics, namely sorption and diffusion coefficients, of the tested aroma compounds were determined at 23 °C by means of sorption microgravimetry, and the permeability coefficients were estimated using the solution-diffusion model. The permeability coefficients for the films made from PBS, PBSA and LDPE were comparable for the more polar compounds: hexan-1-ol, ethyl acetate and ethyl butyrate. Conversely, the permeability coefficients of the less polar aroma compounds (ethyl hexanoate, heptanal and (R)-(+)-limonene) in PBS and PBSA-based films were by one to two orders of magnitude lower than those of the LDPE. In addition, a new mathematical model was proposed for the kinetics of the transient sorption of aroma compounds of low volatility (psat

This study reports on the sorption and permeation of ethanol vapors in the ionic liquid polymer gel membrane. The gel membrane was based on poly(vinylidene fluoride-co-hexafluoropropylene), which contained 80 wt.% of the imidazolium-based ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Ethanol sorption in ionic liquid membrane was compared with that in the neat polymer. Further, from experimental data followed that the diffusion coefficient of ethanol was 3 orders of magnitude higher in ionic liquid membrane in comparison with neat polymer membrane. Interestingly, ethanol permeability was found immeasurably low in neat polymer membrane while ethanol permeability reached approximately 25,000 Barrer in the ionic liquid membrane at the highest ethanol vapor activity. The values of the activation energy of diffusion and permeation were determined from the temperature dependences of the sorption and permeation experimental data.

The preparation and gas-separation performance of self-standing, high-flux, graphene oxide (GO) membranes is reported. Defect-free, 15-20 μm thick, mechanically stable, unsupported GO membranes exhibited outstanding gas-separation performance towards H2 /CO2 that far exceeded the corresponding 2008 Robeson upper bound. Remarkable separation efficiency of GO membranes for H2 and bulky C3 or C4 hydrocarbons was achieved with high flux and good selectivity at the same time. On the contrary, N2 and CH4 molecules, with larger kinetic diameter and simultaneously lower molecular weight, relative to that of CO2 , remained far from the corresponding H2 /N2 or H2 /CH4 upper bounds. Pore size distribution analysis revealed that the most abundant pores in GO material were those with an effective pore diameter of 4 nm; therefore, gas transport is not exclusively governed by size sieving and/or Knudsen diffusion, but in the case of CO2 was supplemented by specific interactions through 1) hydrogen bonding with carboxyl or hydroxyl functional groups and 2) the quadrupole moment. The self-standing GO membranes presented herein demonstrate a promising route towards the large-scale fabrication of high-flux, hydrogen-selective gas membranes intended for the separation of H2 /CO2 or H2 /alkanes.

The swelling and plasticization of polydimethylsiloxane (PDMS), a rubbery polymeric network, and poly[(trimethylsilyl)propyne] (PTMSP), a glassy polymer, in methanol and dimethyl carbonate (DMC) vapors (a) and liquids (b) was studied using visible-light microscopy (ad a), dynamic mechanical analysis (DMA, ad a) and confocal Raman microscopy (ad b). The properties of swollen PDMS were found to be as expected: Volume swelling followed volume additivity and swelling in mixed vapors was predictable from single component swelling data, elastic moduli followed the scaling law and Raman spectra of pure and swollen PDMS were indistinguishable. On the contrary, swollen PTMSP showed pronouncedly lower volume changes than those expected from volume additivity and non-predictable swelling in mixed vapors, preferential saturation of the nonequilibrium packing defects of the polymer, an initial plateau for the storage modulus and pronounced spectral changes when swollen with the liquids. The initially rigid physical structure of PTMSP was found to be relaxed when the concentration of the volatile compound in the polymer exceeded the capacity of the first adsorption layer, which is one of the parameters of the Guggenheim, Anderson, de Boer (GAB) model of multilayer adsorption. Hence, the general mechanism for sorption of volatile compounds in glassy polymers is likely adsorption and gradual physical relaxation.

Novel data on the sorption of vapours and liquids in cross-linked poly(dimethylsiloxane) (PDMS) elastomer at 25–40 °C are reported together with the accurate and original way of parameterising the sorption isotherms by using the GAB (Guggenheim, Anderson and De Boer) model of multilayer adsorption. The GAB model has been found to provide a comparable or better representation of sorption isotherms than the Flory–Huggins model with a concentration-dependent interaction parameter and better than the ENSIC (Engaged Species Induced Clustering) model. This comparison holds true for poor solvents of PDMS (water, methanol), mild solvents (acetone, methyl acetate, dimethyl carbonate) and good solvents ( tert -butyl methyl ether, tert -amyl methyl ether, cyclopentyl methyl ether). The GAB model provided a noticeably good assessment of the sorption of liquids and highly saturated vapours, which makes the model applicable within the entire activity range.

The suitability of the Guggenheim–Anderson–De Boer (GAB) model for the parameterization of gas sorption isotherms and their dependences on temperature is explored. The GAB model implies that molecules adsorb on inner surfaces of the polymer in multilayers, which contrasts with the assumptions of the classical Dual Mode Sorption (DMS) model which implies the simultaneous occurrence of Henry-like dissolution and Langmuir's case I adsorption. The GAB model shows similar efficacy of the parameterization of the gas sorption isotherms in polymers as the DMS model. The isosteric heat of adsorption shows clear dependence on relative surface coverage for carbon dioxide sorption in cellulose acetate, polyethylene terephthalate, and the first polymer of intrinsic microporosity (PIM-1), thus allowing for the occurrence of adsorption multilayers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 1490–1495

Understanding of the properties over long time scales is a key requirement for the successful application of novel polymers as membrane materials. In this light, the physical aging of dense PIM-1 films with different previous histories was monitored for more than 4 years via parallel gas sorption and permeability measurements. The effect of aging on the individual transport parameters, permeability, solubility and diffusivity, was studied on alcohol treated membranes with high excess free volume. Thermal conditioning of these membranes led to accelerated aging and a reduction of the initial gas permeability and diffusivity of the membranes. A long-term CO2 sorption analysis showed aging affected the sorption kinetics much more than the total equilibrium sorption. This was confirmed by permeation studies with six different gases, showing that the reduction of the permeability coefficient of the samples as a function of time is almost entirely due to a reduction of the diffusion coefficient. A renewed alcohol treatment of the aged membrane led to significant rejuvenation of the membrane. To the best of our knowledge, this is the first systematic long term aging study on PIM-1 via simultaneous analysis of sorption and permeation kinetics. Mixed gas permeation measurements with a CO2/CH4 mixture and an N2/O2/CO2 mixture confirm the excellent permselective properties of the PIM-1 membranes even after long aging.

This article is designated for anybody, who is interested in the membrane process, for example, learners, young researchers, or practitioners. Existing knowledge from the literature was summarized in order (i) to provide a comprehensive overview of existing methods for characterization of polymeric membranes and (ii) to serve as the suitable additional study source. For selected cases, the detailed analysis of related theoretical roots is presented and thoroughly discussed from the physical chemistry point of view.

The experimental study of transport properties of mixed matrix membranes (MMMs) based on PEBA-4033 with two types of zeolites is reported. Gas (CO2, O2, N2) and vapor (benzene, toluene, methanol, water) permeation measurements were performed using the differential flow permeameter at temperature of 298.15 K and at atmospheric pressure. Gas/vapor permeation was monitored by measuring the changes of the thermal conductivity of carrier gas (H2). Sorption experiments were performed gravimetrically. Determined values of the transport parameters (permeability, diffusion and sorption coefficients) of all studied vapors revealed expected high-order permeability of PEBA based membranes for vapors in comparison with gases whereas increasing of zeolite-filler content up to 30 wt.% in polymer matrix led to higher values of permeability and gas/gas and vapor/gas selectivity in comparison with pure polymer.

In this paper, two methods for measuring the equilibrium vapor sorption in polymers are critically compared and data on sorption of toluene, p-xylene, hexane, cyclohexane, and heptane in low density polyethylene are reported. The vapor phase calibration method (VPC) was used to measure vapor sorption at low vapor activities in air (below 0.01), and the gravimetric method was used to measure sorption over wide range of activities of pure vapors (0.1–0.9). The Flory-Huggins interaction parameter (in amorphous phase) varied between 1.00 for cyclohexane and 1.19 for toluene. The resulting confidence intervals are conjunctive, indicating that both methods provide consistent results.

We propose a method of measuring the transient diffusion of vapor mixtures through flat dense membranes. The experimental setup consists of a self-developed differential permeation cell and a real-time analyzer to monitor the permeate–sweep gas mixture. The selectivity and the low sampling period of the real-time analysis are ensured by combining a quadrupole mass spectrometer and a gas chromatograph equipped with an inert capillary column. The proposed method is demonstrated at 298 K on the following binary mixtures of vapors: p -xylene–octane and toluene–octane permeating through low density polyethylene, and propan-1-ol–butan-1-ol vapors permeating through polydimethylsiloxane and through polydimethylsiloxane filled with montmorillonite. Based on extended Fick’s laws, we evaluate parameters describing cross-diffusion effects, using the Gauss–Newton method and finite difference modeling. In contrast to the transient diffusion of pure compounds, the simultaneous diffusion of a binary mixture of vapors is influenced by the dynamics of each diffusing compound. The effect on the transient diffusion of each vapor can be either positive or negative, depending on the type of membrane and on the actual mixture of vapors. Moreover, this cross-effect is mitigated by the presence of a filler, specifically of montmorillonite in polydimethylsiloxane in this particular case.

A mass transport of organic compounds (benzene, hexane, cyclohexane and methanol) and their binary mixtures at wide activity range through dense semicrystalline low density polyethylene membranes is presented. Single and binary vapour permeation measurements were performed at 25°C and at 35°C by the differential flow permeation apparatus method connected with GCMS device. Determined values of steady-state molar fluxes revealed the differences between single and binary permeation as well as the mutual coupling effect of second component in mixture on permeation flux of the first one.

The non-porous, flat membranes were prepared from the novel hyperbranched polyimide based on 4,4’,4”-triaminotriphenylmethane (MTA) and 4,4’-oxydiphthalic anhydride (ODPA) and also from the linear polyimide (LPI) based on 4,4’-methylenedianiline (MDA) and ODPA. The permeability coefficients of hydrogen, carbon dioxide, oxygen, nitrogen and methane in the membrane prepared from hyperbranched polyimide were 2–3.7 times higher than those in the membrane from LPI at comparable selectivities.

This paper is focused on modeling of sorption and desorption kinetics as well as on equilibrium butan-1-ol vapor sorption in blended poly(dimethylsiloxane)–benzyl-3-butylimidazolium tetrafluoroborate membranes. Based on the generalized Fick’s second law, on time-dependent boundary conditions and on two models of equilibrium sorption, the diffusion coefficients of butan-1-ol were calculated from the experimental data using the finite difference modeling. Although anomalous sorption occurred at higher concentrations of butan-1-ol, the diffusion coefficients calculated from the data on sorption and desorption kinetics were in a good agreement. The increase of the ionic liquid content in poly(dimethylsiloxane) elevated the butan-1-ol equilibrium concentration in the membrane, and, at the same time, decreased the values of butan-1-ol diffusion coefficient.

This paper describes an improvement to the method used for the calculation of diffusion coefficients from data obtained by the measurement of vapor sorption kinetics in a flat, non-porous polymeric membrane. The advantage of our corrected model is that it can be applied to systems displaying both fast and slow sorption kinetics, as is demonstrated using cellulose myristate – hexane and cellulose acetovalerate – ethanol systems at a temperature of 298 K. Experiments were conducted on a specially developed sorption apparatus equipped with McBain’s spiral quartz balances. Sorption kinetics are generally described by the solution of Fick’s second law, the solution of which assumes relative pressure in the form of the unit step function. Our correction involves modifying this solution so that a more realistic relative pressure increase is assumed in terms of the Laplace transform.

In this work, we show that the latter interpretation can efficiently represent the solubility of several gases and vapors in such polymer. Indeed, the Non Equilibrium Thermodynamic model for Glassy Polymer (NET-GP), which assumes that the polymeric phase is a dense and homogeneous one, can be applied successfully to evaluate the solubility in PIM-1 at room temperature.

The sorption of gases (CO2, N2, CH4, O2) and vapors of different nature (n-butane, n-pentane, i-pentane, n-hexane, n-heptane, methanol, ethanol, 1-propanol, 1-butanol, water, chloroform, toluene, 1,4-dioxane, tetrahydrofurane) in films of a polymer of intrinsic microporosity (PIM-1) was studied at room temperature and various pressures. For the first time, the solubility properties of PIM are studied with a rigorous macroscopic model based on the Lattice Fluid (LF) theory; the LF parameters, not available for PIM-1, were obtained from independent gas sorption data at low pressure. The solubility of gases and water vapor follows the typical concave trend of dense glassy polymers and is described accurately by the Non Equilibrium Lattice Fluid (NELF) model, given the dry polymer density value and a slight adjustment of the binary parameter kij. The organic vapor solubility isotherm in PIM-1 can reach very high values and even exhibit a positive concavity at high penetrant contents, that is typical of sorption in rubbery phases. Such portion of the solubility isotherm was thus modeled with the equilibrium LF Equation of State (EoS) and one adjustable parameter kij, while at lower activities the sorption was described with the same value of kij and the NELF model. The value of PIM-1 density in the swollen glassy state required by the NELF model is estimated with an a priori scheme, based on pure penetrant liquid volume. The present work shows that, despite its peculiar microscopic structure, the solubility of PIM-1 can be estimated successfully with the same thermodynamic tools used for dense homogeneous phases and a limited number of parameters.