Hydrocarbon and fluorocarbon solubility and dilation in poly(dimethylsiloxane): Comparison of experimental data with predictions of the Sanchez–Lacombe equation of state

Sorption and dilation isotherms are reported for a series of gases (N₂, O₂, CO₂), hydrocarbon vapors (CH₄, C₂H₆, C₃H₈), and their fluorocarbon analogs (CF₄, C₂F₆, C₃F₈) in poly(dimethylsiloxane) (PDMS) at 35°C and pressures up to 27 atmospheres. The hydrocarbons are significantly more soluble in hydrocarbon-based PDMS than their fluorocarbon analogs. Infinite dilution partial molar volumes of both hydrocarbons and fluorocarbons in PDMS were similar to their partial molar volumes in other hydrocarbon polymers and in organic liquids. Except for C₂H₆ and C₃H₈, partial molar volume was independent of penetrant concentration. For these penetrants, partial molar volume increased with increasing concentration. The Sanchez–Lacombe equation of state is used to predict gas solubility and polymer dilation. If the Sanchez–Lacombe model is used with no adjustable parameters, solubility is always overpredicted. The extent of overprediction is more substantial for fluorocarbon penetrants than for hydrocarbons. Very good fits of the model to the experimental sorption and dilation data are obtained when the mixture interaction parameter is treated as an adjustable parameter. For the hydrocarbons, the interaction parameter is approximately 0.96, and for the fluorocarbons, it is approximately 0.87. These values suggest less favorable interactions between the hydrocarbon-based PDMS matrix and the fluorocarbon penetrants than between PDMS and hydrocarbons. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3011–3026, 1999     

Sorption and partial molar volume of gases in poly (dimethyl siloxane)

Sorption of N₂, O₂, Ar, CH₄, CO₂, C₂H₄, and C₂H₆ in poly (dimethyl siloxane) liquid and rubber and the dilation of the polymers due to sorption of the gases are studied at 25°C under pressures up to 50 atm. In the liquid, the sorption isotherms for low-solubility and high-solubility gases are described by Henry's law and the Flory–Huggins equation, respectively. Gas sorption in the rubber, which contains a 29 wt % silica filler, follows the dual-mode sorption model, though marked hysteresis is observed in the sorption of O₂ and CH₄. The dilation isotherms increase linearly or exponentially in both polymers with increasing pressure. Considering that gas molecules adsorbed into micropores of the filler particles do not participate in the dilation, partial molar volumes of the dissolved gases in the rubber are determined from data of sorption and dilation. The values are nearly equal to the partial molar volumes in the liquid (48–60 cm³/mol).     

Effect of penetrant-induced isothermal glass transition on sorption,dilation, and diffusion behavior of polybenzylmethacrylate/CO2

The effect of a penetrant-induced isothermal glass transition on sorption, dilation, and diffusion behavior was studied in a single experimental run for CO₂ in cast polybenzylmethacrylate films. The dual-mode type sorption isotherms below the glass transition temperature of the polymer changed to linear ones above a certain concentration. Meanwhile, partial molar volume of CO₂ determined from the dilation of the films above the concentration gave a value very close to the one reported for rubbery polymers, and diffusion coefficients became less concentration-dependent. The results were conformable to the concept of unrelaxed volume in glassy polymers. © 1996 John Wiley & Sons, Inc.     

Sorption and partial molar volume of gases in polybutadiene

Sorption of He, H₂, N₂, O₂, Ar, CH₄, C₂H₆, and C₂H₆ in polybutadiene and the dilation of the polymer due to sorption of the gases are investigated over the pressure range 0-50 atm at 25°C. For CO₂ the measurements are made at temperatures ranging from 15 to 80°C. Partial molar volumes of the gases in the polymer are determined. The temperature dependence of partial molar volume is discussed on the basis of the data for CO₂. The Flory-Huggins interaction parameters of CO₂, C₂H₄, and C₂H₆ are also estimated.     

Dilation and plasticization of polystyrene by carbon dioxide

We have used an optical interference technique to measure the dilation of polystyrene films in the presence of carbon dioxide or helium at pressures up to 20 atm. Dilation isotherms (plots of dilation versus gas pressure at constant temperature) were obtained for three samples of polystyrene which had widely differing molecular weights. The dilation isotherms have the same general shape as sorption isotherms, which means that all of the sorbed gas molecules contribute to volume dilation and non can be thought of as occupying molecular-sized voids in the polymer. Using sorption results from the literature we show that the partial molar volume of CO₂ at 35°C is about 39 cm³ mol^?1 and appears to be independent of polystyrene molecular weight. For a polystyrene sample with M_n = 3600, the partial molar volume of sorbed CO₂ increases to 44 and 50 cm³ mol^?1 at 45 and 55°C, respectively. The sorption of CO₂ in polystyrene is shown to depress the glass transition temperature of the mixture, consistent with theoretical predictions. The shape of the dilation and sorption isotherms are consistent with the depression of the glass transition temperature.     

Sorption and partial molar volumes of gases in poly(ethylene-co-vinyl acetate)

Sorption and dilation properties of polymer-gas systems involving poly(ethylene-co-vinyl acetate) and N₂, CH₄, or CO₂, have been investigated at pressures up to 50 atm at temperatures of 10–40°C. Sorption isotherms for low-solubility gases (i.e., CH₄ and N₂) can be described by Henry's law, and those for high-solubility gas (i.e., CO₂) by Flory-Huggins dissolution equation. Dilation isotherms are similar in contour to the corresponding sorption isotherms. From the obtained sorption and dilation data, partial molar volumes of the gases in the polymer were determined as a function of temperature. Thermal expansivity of dissolved CO₂ molecules was estimated at ca. 2.4 × 10^?3°C^?1 from the temperature dependence of partial molar volume. The expansivity is smaller than that of liquid CO₂ and larger than those of the polymer and organic liquids. © 1994 John Wiley & Sons, Inc.     

Dilation of polyethylene by sorption of carbon dioxide

The dilation of low-density polyethylene accompanied by the sorption of CO₂ was measured by microscopy under pressures up to 50 atm at temperatures from 25 to 55°C. The dilatometry measurement, which is also applied to the determination of the thermal expansion coefficient, is directly performed by a cathetometer. The dilation of LDPE by sorbed CO₂ is linear with concentration. The buoyancy correction is described for the CO₂ sorption isotherms in LDPE. The partial molar volume of CO₂ in LDPE, calculated from the dilation and the sorption isotherms, is almost independent of temperature.     

Dilation of polycarbonate by carbon dioxide

A new technique is described for dilatometry under high pressure. The technique is based on optical interferometry and is analogous to measuring the thickness of thin, nonabsorbing films and coatings. The procedure is demonstrated for the well-characterized system of n-pentane sorption by polyisobutylene, and then results for the dilation of polycarbonate by the sorption of carbon dioxide are presented. The dilation of polycarbonate by CO₂ is nearly linear with concentration; the partial molar volume of CO₂ decreases slightly with increasing pressure. This result indicates that all sorbed CO₂ molecules contribute equally to the dilation of the polymer matrix and that none reside in microvoids or in preexisting free-volume elements which do not contribute to volume expansion of the polymer.     

Thermodynamic interactions in rubbery polymer/gas systems

The Flory–Huggins interaction parameters χ for 23 gases (He, Ne, Ar, Kr, Xe, H₂, N₂, O₂, N₂O, CO₂, CH₄, C₂H₄, C₂H₆, C₃H₆, C₃H₈, 1,3-C₄H₆, four C₄H₈'s, n-C₄H₁₀, iso-C₄H₁₀, and n-C₅H₁₂) in five rubbery polymers (1,2-polybutadiene (PB), poly(ethylene-co-vinyl acetate)) (EVAc), polyethylene (PE), polypropylene (PP), and poly(dimethyl siloxane) (PDMS) were determined from either literature data on Henry's law coefficient and partial molar volume or those on sorptive dilation for each polymer/gas system. Values of χ for the gases increased in the order of PDMS < PP ≡ PB < EVAc ≡ PE. Among the gases except He and H₂ whose χ values are not reliable, Ne and Xe have respectively the highest and the lowest values of χ for the polyolefins. The χ values of the hydrocarbons were compared together with previously reported χ values of n-alkanes C₃-C₁₀. The dependencies of χ upon concentration and temperature were discussed on the basis of the literature data. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1049–1053, 1997     

Argon sorption and partial molar volume in poly(ethyl methacrylate) above and below the glass transition temperature

Sorption and dilation isotherms for argon in poly(ethyl methacrylate) (PEMA) are reported for pressures up to 50 atm over the temperature range 5–85°C. At temperatures below the glass transition (T_g=61°C), sorption isotherms are well described by the dual-mode sorption model; and isotherms above T_g follow Henry's law. However, isotherms for dilation due to sorption are linear in pressure at all temperatures over the range investigated. Partial molar volumes of Ar in PEMA are obtained from these isotherms. The volumes are approximately constant above T_g (about 40 cm³/mol), whereas the volumes below T_g are smaller and dependent on both temperature and concentration (19–26 cm³/mol). By analyzing the experimental data according to the dual-mode sorption and dilation model, the volume occupied by a dissolved Ar molecule and the mean size of microvoid in the glass are estimated to be 67 129 ų, respectively. The cohesive energy density of the polymer is also estimated as 61 cal/cm³ from the temperature dependence of the dual-mode parameters.     

GAS SORPTION,DIFFUSION AND PERMEATION OF ORDERED POLYMERIC MEMBRANES

He, CO_2, O_2, N_2, CH_4, C_3H_8, and t-C_4H_(10) gas permeability coefficients and diffusion coefficients of poly(4-methylpentene-1) (PMP) with various degrees of crystallization were plotted against the degree of crystallization. The plotdemonstrated a linear relationship. The gas permeability coefficient and diffusion coefficient of pure amorphous and purecrystalline PMPs were evaluated by a linear extrapolation to zero and 100% crystallinity, respectively. The relationshipbetween the diffusion coefficient of crystalline parts of PMP and the kinetic diameter of penetrant gases was discussed.Syndiotactic polystyrene (SPS) could exist as δ form crystals complexed with organic solvents such as benzene, toluene,xylene, and ethylbenzene. The mesophase of SPS is prepared by annealing the δ form of crystalline complexes at a certaintemperature for 1 h. The desorption of solvent during annealing almost does not result in changes of both the conformation ofbackbone chains and the crystal lattice. We could prepare the mesophase containing molecular cavities with the size andshape of the organic solvent molecules. The mesophase could sorb the same solvent after the manner of Langmuir sorption atlow vapor pressure range while this would not be the case for solvents of different size and shape. This suggests a molecularrecognition of organic solvent, and mesophase SPS might be useful for separation membrane and adsorptive material.     

Sorption and Swelling of Poly(D,L-lactic acid) and Poly(lactic-co-glycolic acid) in Supercritical CO2

Summary: The equilibrium sorption and swelling behavior in supercritical CO₂ of poly(D,L-lactic acid) and poly(lactic-co-glycolic acid) has been studied at a temperature of 35 °C and at pressures up to 200 bar. Sorption was measured through a gravimetric technique and swelling by visualization. From these data, the behavior of the different polymers can be compared. In terms of partial molar volume of CO₂ in the polymer matrix, all the polymers exhibit a behavior typical of rubbery systems. The experimental results have been modeled using the Sanchez-Lacombe equation of state, which is able to represent the actual behavior of the polymer-CO₂ systems with reasonable accuracy.     

Sorption and swelling of semicrystalline polymers in supercritical CO2

The equilibrium sorption and swelling behavior of four different polymers—poly(methyl methacrylate), poly(tetrafluoroethylene), poly(vinylidene fluoride), and the random copolymer tetrafluoroethylene–perfluoromethylvinylether–in supercritical CO₂—are studied at different temperatures (from 40 to 80 °C) and pressures (up to 200 bar). Swelling is measured by visualization, and sorption through a gravimetric technique. From these data, the behavior of amorphous and semicrystalline polymers can be compared, particularly in terms of partial molar volume of CO₂ in the polymer matrix. Both poly(methyl methacrylate) and the copolymer of tetrafluoroethylene exhibit a behavior typical of rubbery systems. On the contrary, polymers with a considerable degree of crystallinity, such as poly(tetrafluoroethylene) and poly (vinylidene fluoride), show larger values of partial molar volume. These can be related to the limited mobility of the polymer chains in a semicrystalline matrix, which causes the structure to “freeze” during the sorption process into a nonequilibrium state that can differ significantly from the actual thermodynamic equilibrium. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1531–1546, 2006     

Preparation and characterization of a composite PDMS membrane on CA support

Polydimethylsiloxane (PDMS) is the most commonly used membrane material for the separation of condensable vapors from lighter gases. In this study, a composite PDMS membrane was prepared and its gas permeation properties were investigated at various upstream pressures. A microporous cellulose acetate (CA) support was initially prepared and characterized. Then, PDMS solution, containing crosslinker and catalyst, was cast over the support. Sorption and permeation of C₃H₈, CO₂, CH₄, and H₂ in the prepared composite membrane were measured. Using sorption and permeation data of gases, diffusion coefficients were calculated based on solution‐diffusion mechanism. Similar to other rubbery membranes, the prepared PDMS membrane advantageously exhibited less resistance to permeation of heavier gases, such as C₃H₈, compared to the lighter ones, such as CO₂, CH₄, and H₂. This result was attributed to the very high solubility of larger gas molecules in the hydrocarbon‐based PDMS membrane in spite of their lower diffusion coefficients relative to smaller molecules. Increasing feed pressure increased permeability, solubility, and diffusion coefficients of the heavier gases while decreased those of the lighter ones. At constant temperature (25°C), empirical linear relations were proposed for permeability, solubility, and diffusion coefficients as a function of transmembrane pressure. C₃H₈/gas solubility, diffusivity, and overall selectivities were found to increase with increasing feed pressure. Ideal selectivity values of 9, 30, and 82 for C₃H₈ over CO₂, CH₄, and H₂, respectively, at an upstream pressure of 8 atm, confirmed the outstanding separation performance of the prepared membrane. Copyright © 2009 John Wiley & Sons, Ltd.     

Gas sorption,diffusion, and permeation in poly(dimethylsiloxane)

The permeability of poly(dimethylsiloxane) [PDMS] to H₂, O₂, N₂, CO₂, CH₄, C₂H₆, C₃H₈, CF₄, C₂F₆, and C₃F₈, and solubility of these penetrants were determined as a function of pressure at 35 °C. Permeability coefficients of perfluorinated penetrants (CF₄, C₂F₆, and C₃F₈) are approximately an order of magnitude lower than those of their hydrocarbon analogs (CH₄, C₂H₆, and C₃H₈), and the perfluorocarbon permeabilities are significantly lower than even permanent gas permeability coefficients. This result is ascribed to very low perfluorocarbon solubilities in hydrocarbon‐based PDMS coupled with low diffusion coefficients relative to those of their hydrocarbon analogs. The perfluorocarbons are sparingly soluble in PDMS and exhibit linear sorption isotherms. The Flory–Huggins interaction parameters for perfluorocarbon penetrants are substantially greater than those of their hydrocarbon analogs, indicating less favorable energetics of mixing perfluorocarbons with PDMS. Based on the sorption results and conventional lattice solution theory with a coordination number of 10, the formation of a single C₃F₈/PDMS segment pair requires 460 J/mol more energy than the formation of a C₃H₈/PDMS pair. A breakdown in the geometric mean approximation of the interaction energy between fluorocarbons and hydrocarbons was observed. These results are consistent with the solubility behavior of hydrocarbon–fluorocarbon liquid mixtures and hydrocarbon and fluorocarbon gas solubility in hydrocarbon liquids. From the permeability and sorption data, diffusion coefficients were determined as a function of penetrant concentration. Perfluorocarbon diffusion coefficients are lower than those of their hydrocarbon analogs, consistent with the larger size of the fluorocarbons. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 415–434, 2000     

Combined Reforming and Partial Oxidation of CO<Subscript>2</Subscript>-Containing Natural Gas Using an AC Multistage Gliding Arc Discharge System: Effect of Stage Number of Plasma Reactors

The effect of stage number of multistage AC gliding arc discharge reactors on the process performance of the combined reforming and partial oxidation of simulated CO₂-containing natural gas having a CH₄:C₂H₆:C₃H₈:CO₂ molar ratio of 70:5:5:20 was investigated. For the experiments with partial oxidation, either pure oxygen or air was used as the oxygen source with a fixed hydrocarbon-to-oxygen molar ratio of 2/1. Without partial oxidation at a constant feed flow rate, all conversions of hydrocarbons, except CO₂, greatly increased with increasing number of stages from 1 to 3; but beyond 3 stages, the reactant conversions remained almost unchanged. However, for a constant residence time, only C₃H₈ conversion gradually increased, whereas the conversions of the other reactants remained almost unchanged. The addition of oxygen was found to significantly enhance the process performance of natural gas reforming. The utilization of air as an oxygen source showed a superior process performance to pure oxygen in terms of reactant conversion and desired product selectivity. The optimum energy consumption of 12.05 × 10²⁴ eV per mole of reactants converted and 9.65 × 10²⁴ eV per mole of hydrogen produced was obtained using air as an oxygen source and 3 stages of plasma reactors at a constant residence time of 4.38 s.     

Crosslinking and stabilization of nanoparticle filled PMP nanocomposite membranes for gas separations

Poly(4-methyl-2-pentyne) (PMP) has been crosslinked using 4,4′-(hexafluoroisopropylidene) diphenyl azide (HFBAA) to improve its chemical and physical stability over time. Crosslinking PMP renders it insoluble in good solvents for the uncrosslinked polymer. Gas permeability and fractional free volume (FFV) decreased as crosslinker content increased, while gas sorption was unaffected by crosslinking. Therefore, the reduction in permeability upon crosslinking PMP was due to decrease in diffusion coefficient. Compared to the pure PMP membrane, the permeability of the crosslinked membrane is initially reduced for all gases tested due to the crosslinking. By adding nanoparticles (FS, TiO₂), the permeability is again increased; permeability reductions due to crosslinking could be offset by adding nanoparticles to the membranes. Increased selectivity is documented for the gas pairs O₂/N₂, H₂/N₂, CO₂/N₂, CO₂/CH₄ and H₂/CH₄ using crosslinking and addition of nanoparticles. Crosslinking is successful in maintaining the permeability and selectivity of PMP membranes and PMP/filler nanocomposites over time.     

Gas sorption and characterization of poly(ether‐b‐amide) segmented block copolymers

The solubilities of He, H₂, N₂, O₂, CO₂, CH₄, C₂H₆, C₃H₈, and n‐C₄H₁₀ were determined at 35°C and pressures up to 27 atmospheres in a systematic series of phase separated polyether–polyamide segmented block copolymers containing either poly(ethylene oxide) [PEO] or poly(tetramethylene oxide) [PTMEO] as the rubbery polyether phase and nylon 6 [PA6] or nylon 12 [PA12] as the hard polyamide phase. Sorption isotherms are linear for the least soluble gases (He, H₂, N₂, O₂, and CH₄), convex to the pressure axis for more soluble penetrants (CO₂, C₃H₈, and n‐C₄H₁₀) and slightly concave to the pressure axis for ethane. These polymers exhibit high CO₂/N₂ and CO₂/H₂ solubility selectivity. This property appears to derive mainly from high carbon dioxide solubility, which is ascribed to the strong affinity of the polar ether linkages for CO₂. As the amount of the polyether phase in the copolymers increases, gas solubility increases. The solubility of all gases is higher in polymers with less polar constituents, PTMEO and PA12, than in polymers with more polar PEO and PA6 units. CO₂/N₂ and CO₂/H₂ solubility selectivity, however, are higher in polymers with higher concentrations of polar repeat units. The sorption data are complemented with physical characterization (differential scanning calorimetry, elemental analysis, and wide angle X‐ray diffraction) of the various block copolymers. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2463–2475, 1999     

A Microporous Metal‐Organic Framework Supramolecularly Assembled from a CuII Dodecaborate Cluster Complex for Selective Gas Separation

A novel 3D metal‐organic framework BSF‐1 based on the closo‐dodecaborate cluster [B₁₂H₁₂]^2? was readily prepared at room temperature by supramolecular assembly of CuB₁₂H₁₂ and 1,2‐bis(4‐pyridyl)acetylene. The permanent microporous structure was studied by X‐ray crystallography, powder X‐ray diffraction, IR spectroscopy, thermogravimetric analysis, and gas sorption. The experimental and theoretical study of the gas sorption behavior of BSF‐1 for N₂, C₂H₂, C₂H₄, CO₂, C₃H₈, C₂H₆, and CH₄ indicated excellent separation selectivities for C₃H₈/CH₄, C₂H₆/CH₄, and C₂H₂/CH₄ as well as moderately high separation selectivities for C₂H₂/C₂H₄, C₂H₂/CO₂, and CO₂/CH₄. Moreover, the practical separation performance of C₃H₈/CH₄ and C₂H₆/CH₄ was confirmed by dynamic breakthrough experiments. The good cyclability and high water/thermal stability render it suitable for real industrial applications.     

Tests of a free-volume model for the permeation of gas mixtures through polymer membranes. CO2-C2H4, CO2-C3H8, and C2H4-C3H8 mixtures in polyethylene

Steady-state permeability coefficients have been measured for equimolar mixtures of CO₂-C₂H₄, CO₂-C₃H₈, and C₂H₄-C₃H₈, as well as for a mixture of 74.9 mol % CO₂ and 25.1 mol % C₂H₄ in polyethylene membranes. The measurements were made at 20, 35, and 50°C and at pressures of up to 28 atm. Each component of the permeating mixtures studied had the effect of increasing the permeability coefficient for the other component. Furthermore, at equal partial pressures and at the same temperature, the component exhibiting the highest solubility in the polymer had the largest effect in increasing the permeability coefficient of the other component. This behavior is in agreement with the predictions of a free-volume model for the permeation of gas mixtures proposed by Fang, Stern, and Frisch. From a quantitative viewpoint, the permeability coefficients for the components of the mixtures agreed, on the average, to better than 25% with the predicted values. The theoretical permeability coefficients can be estimated from the model by using parameters determined with the pure components only.