Preparation and C3H8/Gas Separation Properties of a Synthesized Single Layer PDMS Membrane

In this paper, a new polydimethylsiloxane (PDMS) membrane was synthesized and its ability for separation of heavier gases from lighter ones was examined. Sorption, diffusion, and permeation of H₂, N₂, O₂, CH₄, CO_2, and C₃H₈ in the synthesized membrane were investigated as a function of pressure at 35°C. PDMS was confirmed to be more permeable to more condensable gases such as C₃H₈. This result was attributed to very high solubility of larger gas molecules in hydrocarbon?based PDMS in spite of their low diffusion coefficients relative to small molecules. The synthesized membrane showed much better gas permeation performance than others reported in the literature. Increasing upstream pressure increased solubility, permeability and diffusion coefficients of C₃H₈, while these values decreased slightly or stayed constant for other gases. Local effective diffusion coefficient of C₃H₈ and CO₂ increased with increasing penetrant concentration which indicated plasticization effect of these gases over the range of penetrant concentration studied. C₃H₈/gas solubility, diffusivity and overall selectivities also increased with increasing feed pressure. Ideal selectivity values of 4, 13, 18, 20, and 36 for C₃H₈ over CO₂, CH₄, H₂, O_2, and N₂, respectively, at upstream pressure of 7 atm, confirmed the outstanding separation performance of the synthesized mebrane.     

Properties of cold lake bitumen saturated with pure gases and gas mixtures

This paper presents new data for the viscosity, density and gas solubility of Cold Lake bitumen saturated with light gases and gas mixtures over a temperature range of 15 to 103°C at up to 10 MPa pressure. Specifically, the gases whose effects on the bitumen properties were measured are N₂, CH₄, CO₂ and C₂H₆, and two mixtures of CO₂ and CH₄. With CO₂ and C₂H₆, experiments were also performed in the liquid-liquid region, and the results of these experiments generally agree with the previously published predictions. The viscosity of the gas-free Cold Lake bitumen is comparable to that of a Marguerite Lake bitumen that was tested previously. Due to the large solubilities of C0₂ and C₂H₆, the reduction in gas-saturated bitumen viscosity is quite dramatic. The density of the gas-saturated bitumen decreases with increased amounts of the dissolved CH₄ and C₂H₆ gases, but no such trends are evident for the N₂ and CO₂ gases. The results of the experiments with two binary gas mixtures (i.e., CO₂ and CH₄) indicate that the bitumen properties are affected largely by the major gas constituent.     

The gas permeation properties of 6FDA-2, 4, 6-trimethyl-1, 3-phenylenediamine (TMPDA)/1, 3-phenylenediamine (mPDA) copolyimides

Summary The gas permeation behavior of 2, 2’-bis (3, 4’dicarboxyphenyl) hexafluoropropane dianhydride(6FDA)- 2, 4, 6-Trimethyl-1, 3-phenylenediamine (TMPDA)/1,3-phenylenediamine (mPDA) polyimides was investigated by systematically varying the diamine ratios. The physical properties of the copolyimides were characterized by IR, DSC and TGA. All the copolyimides were soluble in most of the common solvents. The gas permeabilities and diffusion coefficients decreased with increasing mPDA content; however, the permselectivity of gas pairs such as H₂/N₂, O₂/N₂, CO₂/CH₄ was enhanced with the incorporation of mPDA moiety. The permeability coefficients of H₂, O₂, N₂, CO₂ and CH₄ were found to decrease with the increasing order of kinetic diameters of the penetrant gases. Moreover, all of the copolyimides studied in this work exhibited performance near, lying on or above the existing upper bound trade-off line between permselectivity and permeability.     

Synthesis and gas permeation properties of a single layer PDMS membrane

In this work, a new polydimethylsiloxane (PDMS) membrane was synthesized and its sorption, diffusion, and permeation properties were investigated using H₂, N₂, O₂, CH₄, CO₂, and C₃H₈ as a function of pressure at 35°C. PDMS, as a rubbery membrane, was confirmed to be more permeable to more condensable gases such as C₃H₈. The synthesized PDMS membrane showed much better gas permeation performance than others reported in the literature. Based on the sorption data of this study and other researchers' works, some valuable parameters such as Flory‐Huggins (FH) interaction parameters, χ, etc., were calculated and discussed. The concentration‐averaged FH interaction parameters of H₂, N₂, O₂, CH₄, CO₂, and C₃H₈ in the synthesized PDMS membrane were estimated to be 2.196, 0.678, 0.165, 0.139, 0.418, and 0.247, respectively. Chemical similarity of O₂, CH₄, and C₃H₈ with backbone structure of PDMS led to lower χ values or more favorable interactions with polymer matrix, particularly for CH₄. Regular solution theory was applied to verify correctness of evaluated interaction parameters. Local effective diffusion coefficient of C₃H₈ and CO₂ increased with increasing penetrant concentration, which indicated the plasticization effect of these gases over the range of penetrant concentration studied. According to high C₃H₈/gas ideal selectivity values, the synthesized PDMS membrane is recommended as an efficient membrane for the separation of organic vapors from noncondensable gases. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Permeation of H2, N2, CH4, C2H6, and C3H8 through asymmetric polyetherimide hollow‐fiber membranes

Permeation properties of pure H₂, N₂, CH₄, C₂H₆, and C₃H₈ through asymmetric polyetherimide (PEI) hollow‐fiber membranes were studied as a function of pressure and temperature. The PEI asymmetric hollow‐fiber membrane was spun from a N‐methyl‐2‐pyrrolidone/ethanol solvent system via a dry‐wet phase‐inversion method, with water as the external coagulant and 50 wt % ethanol in water as the internal coagulant. The prepared asymmetric membrane exhibited sufficiently high selectivity (H₂/N₂ selectivity >50 at 25°C). H₂ permeation through the PEI hollow fiber was dominated by the solution‐diffusion mechanism in the nonporous part. For CH₄ and N₂, the transport mechanism for gas permeation was a combination of Knudsen flow and viscous flow in the porous part and solution diffusion in the nonporous part. In our analysis, operating pressure had little effect on the permeation of H₂, CH₄, and N₂. For C₂H₆ and C₃H₈, however, capillary condensation may have occurred at higher pressures, resulting in an increase in gas permeability. As far as the effect of operating temperature was concerned, H₂ permeability increased greatly with increasing temperature. Meanwhile, a slight permeability increment with increasing temperature was noted for N₂ and CH₄, whereas the permeability of C₂H₆ and C₃H₈ decreased with increasing temperature. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 698–702, 2002     

Gas transport properties of polyaniline membranes

The transport properties of He, H₂, CO₂, O₂, N₂, and CH₄ gases in solvent cast, HCl doped, and undoped polyaniline (PANi) membranes were determined. Measurements were carried out at 40 psi pressure from 19°C to 60°C. An excellent correlation was found between the diffusion coefficients and the molecular diameters of gases. The solubility coefficients of gases were found to correlate with their boiling points or critical temperatures. The sepa-ration factors for CO₂/N₂ and CO₂/CH₄ are dominated by the high solubility of CO₂. These correlations enable us to predict the permeability, diffusion, and solubility coefficients of other gases. After the doping-undoping process, the fluxes of gases with kinetic diameters smaller than 3.5 Å increased but those of larger gases decreased. This results in a higher separation factor for a gas pair involving a small gas molecule and a larger one. © 1996 John Wiley & Sons, Inc.     

Transport properties of gases through integrally skinned asymmetric composite membranes prepared from date pit powder and polysulfone

Studies were conducted on transport properties and separation performance of date pit/polysulfone composite membranes for CO₂, CH₄, N₂, He, and H₂ gases. Date seeds were obtained and processed into powder. Asymmetric flat sheet membrane was prepared by solvent casting method with 2–10 wt % date pit powder. Membrane characterization was done using high pressure gas permeation, X‐ray diffraction, thermogravimetric, and scanning electron microscope analyses. The separation performance and the plasticization resistance property were evaluated in terms of gas permeability, selectivity, and plasticization pressure, respectively. Time dependent performance properties were evaluated up to a pressure of 40 bar for 75 days. Results obtained showed the highest selectivity values of 1.54 (He/H₂), 3.637 (He/N₂), 2.538 (He/CO₂), 2.779 (He/CH₄), 3.179 (H₂/N₂), 3.907 (H₂/CO₂), 1.519 (CH₄/N₂), 1.650 (CO₂/N₂), and 1.261 (CO₂/CH₄) at 10 bar and 35 °C feed pressure and temperature, respectively. The resulting composite membrane showed about 39.50 and 66.94% increase in the selectivity of He/N₂ and CO₂/CH₄, respectively, as compared to the pure polysulfone membrane. Thus, the membrane composites possess some potentials in membrane gas separation. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43606.     

Microstructure relaxation process of polyhexafluoropropylene after swelling in supercritical carbon dioxide

This paper studies the process of relaxation of a polymer after swelling in supercritical carbon dioxide. Polyhexafluoropropylene (PHFP) was chosen as the object for investigation. The relaxation process was monitored by a change of the permeability coefficients for a number of gases. Thin polymeric films of PHFP were modified by different treatments: drying to a constant weight, annealing at a temperature slightly higher than the glass‐transition temperature, and swelling in supercritical carbon dioxide. The permeability coefficients of six gases, He, H₂, O₂ N_2, CO₂, and CH₄, were measured after each stage of the treatment. It was shown that the permeability coefficients in the films were increased by 2.4 times for He, 3.6 for H₂, 5.9 for O₂, 8.1 for N₂, 6.7 for CO₂, and 10.9 for methane. The permeability coefficients of the same gases were measured 50 days later after swelling in supercritical carbon dioxide. A decrease in the permeability coefficient demonstrated that the relaxation process had taken place. Nevertheless, the values exceeded the initial ones for annealed samples by 2.0 times for He, 2.4 for H₂, 1.8 for O₂, 1.7 for N₂, 1.7 for CO₂, and 1.3 for methane. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43105.     

Mixed matrix membranes based on 6FDA polyimide with silica and zeolite microsphere dispersed phases

Mixed matrix membranes (MMMs) prepared with 6FDA‐DAM polymer using ordered mesoporous silica MCM‐41 spheres (MSSs), Grignard surface functionalized MSSs (Mg‐MSSs) and hollow zeolite spheres are studied to evaluate the effects of surface modification on performance. Performance near or above the so‐called permeability‐selectivity trade‐off curve was achieved for the H₂/CH₄, CO₂/N₂, CO₂/CH_4, and O₂/N₂ systems. Two loadings (8 wt % and 16 wt %) of MSSs were tested using both constant volume and Wicke–Kallenbach sweep gas permeation systems. Besides single gas H₂, CO₂, O₂, N₂, and CH₄ tests, mixed gas (50/50 vol %) selectivities were obtained for H₂/CH₄, CO₂/N₂, CO₂/CH₄, and O₂/N₂ and found to show enhancements vs. single gases for CO₂ including cases. Mg‐MSS/6FDA‐DAM was the best performing MMM with H₂/CH₄, CO₂/N₂, CO₂/CH₄, and O₂/N₂ separation selectivities of 21.8 (794 Barrer of H₂), 24.4 (1214 Barrer of CO₂), 31.5 (1245 Barrer of CO₂), and 4.3 (178 Barrer of O₂), respectively. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4481–4490, 2015     

Calculation of the solubilities of gases in paraffin hydrocarbons

A semiempirical equation is proposed to calculate the solubilities of gas systems containing H₂, CO, CO₂, N₂, Ar, CH₄, C₂H₆, and C₃H₈ in normal paraffin hydrocarbons from C₅ to C₂₀ and higher over wide temperature and pressure ranges. The applicability of the equation proposed is evaluated.     

Adsorption of CO2 from dry gases on MCM-41 silica at ambient temperature and high pressure. 2: Adsorption of CO2/N2, CO2/CH4 and CO2/H2 binary mixtures

Adsorption equilibrium capacity of CO₂, CH₄, N₂, H₂ and O₂ on periodic mesoporous MCM-41 silica was measured gravimetrically at room temperature and pressure up to 25 bar. The ideal adsorption solution theory (IAST) was validated and used for the prediction of CO₂/N₂, CO₂/CH₄, CO₂/H₂ binary mixture adsorption equilibria on MCM-41 using single components adsorption data. In all cases, MCM-41 showed preferential CO₂ adsorption in comparison to the other gases, in agreement with CO₂/N₂, CO₂/CH₄, CO₂/H₂ selectivity determined using IAST. In comparison to well known benchmark CO₂ adsorbents like activated carbons, zeolites and metal-organic frameworks (MOFs), MCM-41 showed good CO₂ separation performances from CO₂/N₂, CO₂/CH₄ and CO₂/H₂ binary mixtures at high pressure, via pressure swing adsorption by utilizing a medium pressure desorption process (PSA-H/M). The working CO₂ capacity of MCM-41 in the aforementioned binary mixtures using PSA-H/M is generally higher than 13X zeolite and comparable to different activated carbons.     

Evaluation of pure‐component adsorption properties of silicalite based on the Langmuir and Sips models

The Langmuir and Sips models parameters were estimated for the adsorption of several light gases and hydrocarbons (H₂, CH₄, CO₂, CO, N₂, C₂H₆, C₃H₈, n‐C₄H₁₀) in silicalite along with their functionality with temperature. This is a scientific attempt to resume and reconcile the number of available experimental data and supply scientists and other operators with the adsorption properties of silicalite within a wider range of temperature and pressure. Furthermore, to provide readers with more detailed information on where each of the two models work better, the analysis is divided into three temperature ranges: low‐temperature, high‐temperature, and whole temperature range. As a result, it is found that the Langmuir model works well in the whole temperature range for the light gases considered but not for the other hydrocarbons, for which it is better to use the Sips model by splitting calculation over low‐ and high‐temperature range. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3911–3922, 2015     

Gas permeation and separation properties of sulfonated polyimide membranes

Permeability and selectivity of pure gas H₂, CO₂, O₂, N₂ and CH₄ as well as a mixture of CO₂/N₂ for sulfonated homopolyimides prepared from 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA) and 2,2-bis[4-(4-aminophenoxy)phenyl] hexafluoro propane disulfonic acid (BAPHFDS) were measured and compared to those of the non-sulfonated homopolyimide having the same polymer backbone. The polyimide in a proton form (NTDA-BAPHFDS(H)) displayed higher selectivity of H₂ over CH₄ without loss of H₂ permeability. Strong intermolecular interaction induced by sulfonic acid groups decreased diffusivity of the larger molecules. The CO₂/N₂ (19/81) mixed gas permeation was investigated as a function of humidity. With increasing relative humidity from 0% RH to 90% RH, the CO₂ permeability for NTDA-BAPHFDS(H) polyimide increased by more than one order of magnitude, and the selectivity of CO₂/N₂ also increased twice or more. On the other hand, the gas permeability for the non-sulfonated polyimide slightly decreased with increasing humidity. NTDA-BAPHFDS(H) polyimide displayed a CO₂ permeability of 290×10⁻¹⁰ cm³ (STP) cm/(cm² s cmHg) and a separation factor of CO₂/N₂ of 51 at 96% RH, 50 °C and total pressure of 1 atm.     

Comparative investigations of coal pyrolysis under inert gas and H2 at low and high heating rates and pressures up to 10 MPa

Five German hard coals of 6–36 wt% volatile matter yield (maf) were pyrolysed at pressures up to 10 MPa, using two different apparatuses, which mainly differ in the heating rates. One consists of a thermobalance where a coal sample of ≈ 1.5 g is heated at a rate of 3 K min ^?1 under a gas flow of 3 I min^?1. The other apparatus is constructed for rapid heating (10²?10³ K s^?1) of a small sample of ≈10 mg of finely-ground coal distributed as a layer between the folded halfs of a stainless-steel screen, heated by an electric current. The product gas composition was determined by quantitatively analysing for H₂, CH₄, C₂H₄, C₂H₆, CO, CO₂ and H₂O. The amounts of tar and char were measured by weighing. The heating rate, pressure and gas atmosphere were varied. Under an inert gas atmosphere, high heating rates result in slightly higher yields of liquid products, e.g. tar. The yields of light hydrocarbon gases remain the same. With increasing pressure, the thermal cracking of tar is intensified resulting in high yields of char and light hydrocarbon gases. Under H₂, pyrolysis is influenced strongly at elevated pressure. Additional amounts of highly aromatic products are released by hydrogenation of the coal itself, particularly between 500 and 700°C. This reaction is less effective at higher heating rates because of the shorter residence time and diffusion problems of H₂. The yield of light gaseous compounds CH₄ and C₂H₆ increases markedly under either heating condition owing to gasification of the reactive char.     

Effect of doping treatment on gas transport properties and on separation factors of polyaniline memebranes

Gas permeation experiments of H₂, O₂, CO₂, N₂, and CH₂ were carried out with freestanding films of the conjugated polymer polyaniline (PANi). At first annealed to remove residual solvent, PANi membranes were doped (i.e., protonated) in a strongly acidic medium (HCl 4M), undoped in a basic medium (NH₄OH 1M), and redoped in a slightly acidic medium (HCl 10^?2M). Protonation and deprotonation kinetics were studied by elementary analysis Gas permeation experiments were performed with the annealed, doped, undoped, and redoped PANi films. The gas transport mechanism was clearly influenced by the diffusivity factor and it obeyed a Fickian diffusion model. From the variations in permeability coefficients with the doping treatment, gases could be divided in two subgroups comprising H₂, O₂, and CO₂ on one hand and N₂ and CH₄ on the other. After the doping–undoping–redoping process, gas fluxes were increased by 15% for the smaller gases and were decreased by 45% for the larger gases. As a consequence gas separation factors were approximately doubled for a gas pair involving the two subgroups and these were unchanged for a gas pair involving only one subgroup. The highest O₂/N₂ and CO₂/CH₄ selectivity coefficients were, respectively, equal to 14 and 78. © 1995 John Wiley & Sons, Inc.     

Hydrogen production from coal by separating carbon dioxide during gasification

Hydrogen generation during the reaction of a coal/CaO mixture with high pressure steam was investigated using a flow-type reactor. Coal, CaO and CO reactions with steam, and CO₂ absorption by Ca(OH)₂ or CaO occurred simultaneously in the experiment. It was found that H₂ was the primary resultant gas, comprising about 85% of the reaction products. CO₂ was fixed into CaCO₃ and CO was completely converted to H₂. Pyrolysis of the coal/CaO mixture carried out in N₂ was also examined. The pyrolysis gases were compared with gases produced by general coal pyrolysis. While general coal pyrolysis produced about 14.7% H₂, 50.5% CH₄, 12.0% CO and 12.0% CO₂, the gases produced from coal/CaO mixture pyrolysis were 84.8% H₂, 9.6% CH₄, 1.6% CO₂ and 1.1% CO.     

Gas Permeation Properties of Copolyimides from 1,4-Bis(3,4-dicarboxyphenoxy)benzene Dianhydride and 2,2-Bis(3,4- dicarboxyphenyl)hexafluoroisopropane Dianhydride

A series of aromatic copolyimides was prepared from 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride (HQDPA) and 2,2-bis(3,4-dicarboxy-phenyl)hexafluoroisopropane dianhydride (6FDA) with 3,3′-dimethyl-4,4′-methyl-ene dianiline (DMMDA) by a chemical imidization. The gas permeability coefficients of the copolyimides to H₂, CO₂, O₂, N₂ and CH₄ were measured under 7atm. pressure. The fractional free volume of 6FDA–DMMDA is larger than that of HQDPA–DMMDA, while the chain segmental mobility of 6FDA–DMMDA is lower than that of HQDPA–DMMDA. The gas permeability of 6FDA–DMMDA is much higher than that of HQDPA–DMMDA but the perm-selectivity of 6FDA–DMMDA for H₂, CO₂, O₂, N₂ over CH₄ is lower than that of HQDPA–DMMDA. The experimental values of the gas permeability coefficients of the copolyimides are in satisfactory agreement with the values estimated from the gas permeability coefficients of the constituent homopolyimides and their weight fractions. © of SCI.     

Oxidative coupling of methane. The effect of alkali chlorides on molybdate based catalyst leading to high selectivity in C3-product formation

LiCl-Na₂MoO₄ was found to be an active catalyst for oxidative coupling of methane at temperatures around 620 °C. In these systems, the selectivity for the formation of C₃-products exceeds the selectivity for the formation of C₂-products. While the homogeneous reaction of CH₄ and O₂ leads to C₃H₆ as C₃-product, the 50% LiCl-50% Na₂MoO₄ catalyst leads to C₃H₈ as the predominant C₃-product, indicating that in the latter case the reaction cannot be purely homogeneous. The dependency of the product distribution on temperature, gas composition, reactor dimensions, flow rate, CH₄/O₂ ratio and type of catalyst has been studied. The reaction was studied by co-feeding CH₄, O₂ and a diluent gas at atmospheric pressure continuously in a conventional flow reactor containing the catalyst. The reaction products observed were: C₂H₄, C₂H₆, C₃H₆, C₃H₈, H₂O and CO + CO₂. The two latter gases were the main oxidation products observed. Characterization of the catalysts used was carried out by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD).     

Pure gas and vapor permeation properties of poly[1-phenyl-2-[p-(trimethylsilyl)phenyl]acetylene] (PTMSDPA) and its desilylated analog, poly[diphenylacetylene] (PDPA)

The permeabilities of He, H₂, N₂, O₂, CO₂, CH₄, C₂H₆, C₃H₈, and n-C₄H₁₀ in poly[1-phenyl-2-[p-(trimethylsilyl)phenyl]acetylene] (PTMSDPA) and poly[diphenylacetylene] (PDPA) are presented and compared to those of poly(1-trimethylsilyl-1-propyne) (PTMSP), poly(1-phenyl-1-propyne) (PPP), and polysulfone. Like PTMSP, PTMSDPA, a disubstituted glassy acetylene-based polymer, exhibits higher permeabilities to organic vapors than to permanent gases due to its rigid polyacetylene backbone and bulky side groups, which provide a relatively high fractional free volume (FFV) value of 0.26. Desilylation was performed on PTMSDPA. The resulting material, PDPA, is totally insoluble in common organic solvents, so it has much higher chemical resistance than PTMSDPA. Additionally, due to its insolubility in polymerization solvents, desilylation provides the only known route to high molar mass PDPA. The FFV of the resulting membrane (PDPA) is reduced by approximately 12% relative to that of PTMSDPA. This leads to a decrease in gas permeability values and selectivity of organic vapors relative to nitrogen. For example, the oxygen permeability is reduced from 1200 to 500 Barrers upon desilylation. The pure gas selectivities decrease from 9 to 3 for n-C₄H₁₀/N₂ and from 26 to 9 for C₃H₈/N₂.