Preparation of composite membranes with polyimides and poly (amide-imide)s skin via interfacial condensation for air separation

Composite membranes were prepared by the interfacial condensation of water-soluble diamines with an organic solvent (dichloromethane)-soluble dicarbo-methoxy terephthaloyl chloride or carbomethoxy terephthaloyl chloride on top of a porous aluminum oxide support. The morphology of skin on the composite membranes is different in the two different procedures. The polyimide composite membranes with 40-times coatings provide a high gas permeation rate of oxygen and good permselectivity [α(O₂/N₂)]. The composite membrane with the polyimides skin at 40-times coatings had a gas permeation rate of oxygen range from 83 × 10⁻⁵ to 130 × 10⁻⁵ cm³(STP) s⁻¹ cm⁻² cmHg⁻¹, and a permselectivity [α(O₂/N₂)] range of 3.57 to 5.60. The composite membrane with poly (amide-imide)s skin at 40-times coatings had a gas permeation rate of oxygen range from 102 × 10⁻⁵ to 146 × 10⁻⁵ cm³(STP) s⁻¹ cm⁻² cmHg⁻¹, and the permselectivity (α(O₂/N₂)) range from 3.20 to 4.96.     

Application of poly(phthalazinone ether sulfone ketone)s to gas membrane separation

A series of poly(phthalazinone ether sulfone ketone) (PPESK) copolymers containing different component ratios of bis(4‐fluorodiphenyl) ketone and bis(4‐chlorodiphenyl)sulfone with respect to a certain amount of 4‐(4‐hydroxyphenyl)‐2,3‐phthalazin‐1‐one were synthesized by polycondensation. Glass transition temperatures of these polymers were adjusted from 263°C to 305°C by changing the ratios of reactants. Gas permeability and selectivity of the dense membranes of the polymers for three kinds of gases (CO₂, O₂, and N₂) were determined at different temperatures. The result indicated that the membrane of PPESK (S/K = 1/1, mol ratio) had an excellent gas separation property. Permeability of the polymer membranes for CO₂, O₂, and N₂ was P = 4.121 barrier, P = 0.674 barrier, and P = 0.0891 barrier, respectively. Separation factors of α and α were 7.6 and 46, respectively. New material was made into a composite membrane with silicone rubber for blocking up leaks and defects on the surface of its nonsymmetrical membrane. As a result of the test, permeability of the composite membrane was J = 7.2 × 10⁻⁶ cm³ (STP) cm⁻² S⁻¹ cm⁻¹ Hg and J = 0.99 × 10⁻⁶ cm³ (STP) cm⁻² S⁻¹ cm⁻¹ Hg, whereas the α was still higher than 7. These showed that PPESKs had a bright prospect as the potential membrane material for high‐temperature gas separation. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2385–2390, 1999     

Gas permeability and permselectivity of polyimides prepared from phenylenediamines with methyl substitution at the ortho position

Polyimides were prepared from diamines: 2,4,6-trimethyl-1,3-phenylenediamine (3MPDA) and 2,3,4,5-tetramethyl-1,4-phenylenediamine (4MPDA). 1,4-Bis(3,4-dicarboxyphenoxy)benzene dianhydride (HQDPA), 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA), 3,3′-4,4′-diphenylsulphone tetracarboxylic dianhydride (SO₂PDA), 3,3′,4,4′-diphenylsulphide tetracarboxylic dianhydride (SPDA), pyromellitic dianhydride (PMDA), and 2,2′-bis(3,4-dicarboxyphenyl)hexafluoroisopropane dianhydride (6FDA) were used as dianhydride. The gas permeabilities of H₂, O₂ and N₂ through the polyimides were measured at temperatures from 30 °C to 90 °C. The results show that as methyl and trifluoromethyl substitution groups densities increase from 7.73 × 10⁻³ mol cm⁻³ to 13.50 × 10⁻³ mol cm⁻³, the peameability of H₂ increases 10-fold at 60% loss of permselectivity of H₂/N₂; however, the permeability of O₂ increases 20-fold at 20% loss of permselectivity of O₂/N₂. For O₂/N₂ separation, PMDA-3MPDA has similar performance to 6FDA-3MPDA and 6FDA-4MPDA; all have higher permeabilities for O₂ than normal polyimides, and the P(O₂)/α(O₂/N₂) trade-off relationships lie on the upper bound line for polymers. © 1999 Society of Chemical Industry     

Membrane transport of organics. II. Permeation of some carboxylic acids through strongly basic polymer membrane

The permeability characteristics of the strongly basic polymer membrane Neosepta® AFN‐7, (Tokuyama Soda) have been studied for acetic, propionic, lactic, tartaric, oxalic, and citric acid. The results were interpreted by using the model of transport in reactive membranes. The specific constants, that is, the maximum flux J_max, the reactivity constant K, and the permeability coefficient (P), were calculated using the experimental quasi‐stationary fluxes and the equation derived as a sum of reaction–diffusion (Michaelis–Menten‐type), and the solution–diffusion transport equation. The constants K and J_max were found to range from 0.1 to 5 dm³ mol⁻¹ and from 0.4 × 10⁻⁷ to 2.5 × 10⁻⁷ mol cm⁻² s⁻¹ depending, on the acid properties. The values of K and J_max were correlated with the dissociation constants K_dis.acid, and the diffusion coefficients D_aq.acid in aqueous media, respectively. It was found that the reaction–diffusion flux is predominating for all acids, except for the lactic one, when the feed concentration is lower than 0.5 mol dm⁻³. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2179–2190, 1999     

Gas permeability and selectivity through asymmetric polyimide membranes

Permeability and selectivity of CO₂, O₂, N₂, and CH₄ were determined for the asymmetric membrane of aromatic polyimide derived from 2,2′-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 3,3′-diaminodiphenylsulfone (m-DDS) at 35°C and at pressure up to 76 cmHg. The average apparent skin layer thickness of all asymmetric membranes measured was 2.6 μm. The selectivities for (O₂/N₂) and (CO₂/CH₄) in the membranes were 11.5 at O₂ permeance of 3.2 × 10⁻⁷ and 153 at CO₂ of 6.3×10⁻⁷ [cm³(STP)/cm² s cmHg], respectively, without the necessity of an additional coating process. The average gas selectivities of the asymmetric memberanes were much larger than those determined for the dense membrances. The effect of the microstructure of polyimide on the gas selectivity is discussed. © 1996 John Wiley & Sons, Inc.     

MMA/TPX homograft membrane for oxygen enrichment

Utilizing the factors of degradation and crosslinking of TPX polymer and high O₂/N₂ selectivity of MMA, the performances of MMA homografted TPX membrane are efficiently improved compared to those of pure TPX membrane. The degradation and crosslinking of TPX polymer solution with or without dissolved oxygen during irradiation were observed and proved in existence by the gas permeability, mechanical, and viscosity change study. High O₂/N₂ permeability ratio of 7.6 and fairly high oxygen permeability of 28 × 10^?10 cm³ cm/cm² s cm Hg of the membrane which was cast from the degassing polymer solution, with 20% degree of MMA grafting, can be obtained. Also the membrane for high oxygen permeability of 63 × 10^?10 cm³ cm/cm² s cm Hg with an O₂/N₂ permeability ratio of 4.5, which was cast from the polymer solution with dissolved oxygen, can be obtained under the condition of 60 h irradiation time and about 7% degree of grafting. O₂/N₂ selectivity of TPX membrane can be improved by homografting method with lower MMA grafting degree than that of heterografting method.     

Gas permeation properties of new type asymmetric membranes

We have developed a new type of asymmetric membranes having a homogeneous hyperthin skin layer, which was used as a polyimide synthesized by 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 2,2-bis(4-amino phenyl) hexafluoro-propane (BAAF). The skin layer thicknesses of the 6FDA-BAAF polyimide asymmetric membranes were 40–60 nm, and the porosity was 10^-6% when a defect size was assumed as 5 nm. The permselectivity of 6FDA-BAAF polyimide asymmetric membranes after silicone coating had α of 40 for CO₂/CH₄ and a flux of 1.0 [Nm³/m²-h-atm] (=3.7 × 10⁻⁴ [cm³(STP)/cm² s cmHg]) for CO₂, α of 4.3 for O₂/N₂ and a flux of 2.0 × 10⁻¹ [Nm³/m²/h/atm] (=7.1 × 10⁻⁵ [cm³(STP)/cm²s cmHg]) for O₂. These values were constant for large-scale manufacturing. © 1996 John Wiley & Sons, Inc.     

Preparation of vinylpyridine irradiation-grafted poly(4-methyl-pentene-1) membrane for oxygen enrichment

By adjusting the casting conditions, the oxygen permeabilities of poly(4-methyl-pentene-1) (TPX) membranes prepared in this study are in the range of 2.91–7.14 × 10^?9 cm³(STP) cm/cm² s cm Hg and permeability ratio of O₂/N₂ between 2.7 and 4.4. To increase O₂? N₂ selectivity, the vinylpyridine is γ-ray irradiation-grafted onto the substrate–TPX membrane. The factors that affect the structure and performance of the grafted membrane considered are: tightness of substrate, kind of solvent for grafting monomers, irradiation conditions, total irradiation dose, and operating temperature and pressure. The O₂/N₂ selectivities of grafted TPX membranes are significantly improved comparing to that of nongrafted TPX membranes. For example, an O₂ permeability of 35.6 × 10^?10 cm³(STP) cm/cm² s cm Hg and an O₂/N₂ permeability ratio of 7.5 for the grafted membrane can be obtained.     

Study of CO2 permeation in Zn2+-modified Al2O3-carbonate membrane

Molten carbonate-based membranes for CO₂ capture have received attentions because of their high CO₂ selectivity, potential energy-saving capability and environmental friendliness. Zn²⁺-modified Al₂O₃/carbonates membranes with the enhanced CO₂ permeability have been developed in this work. Interfaces of LiAlO₂ were formed on the surface of Al₂O₃ due to the carbonates incorporation. Microstructural and interfacial characterisation of the membrane revealed that the outermost LiAlO₂ layer was due to the reactions between Li₂CO₃ and ZnAl₂O₄, resulting in the dissolution of ZnO in the molten carbonate. CO₂ permeability of 0.5% ZnAl₂O₄/Al₂O₃/carbonates reached 9.12 × 10⁻¹² mol.m⁻¹s⁻¹ Pa⁻¹ at 700°C, higher than that of Al₂O₃/carbonates, because of the dissolved ZnO. With the increase of ZnAl₂O₄, CO₂ permeability was decreased. The dissolved ZnO in the molten carbonates could enhance the ionic conductivity, whereas a higher amount of ZnO than its solubility will attenuate its effects on CO₂ permeation.     

Preparation of a thick sponge-like structured amorphous silica ceramic coating on 6061 aluminum alloy by plasma electrolytic oxidation in TEOS solution

Plasma electrolytic oxidation (PEO) was performed on 6061 aluminum alloy in organosilicon electrolyte using a stepwise constant potential control method for 23 min. The resulting coating was a sponge-like structured amorphous silica ceramic with a thickness of about 130 μm. Its exceptional wear resistance was attributed to the high hardness of the silica ceramic and the low elastic modulus of the sponge-like structure. The corrosion resistance was enhanced by a dense layer of approximately 2 μm between the coating and the substrate. Impressively, the indentation depth of the PEO coating during nano-indentation tests was only 50–60% of that of 6061 aluminium alloy under varying loads, while the recovery depth of the PEO coating after unloading was 2.5–3.1 times greater than that of 6061 aluminium alloy. Due to its special composition and structure, the PEO coating caused serious wear to the high hardness Si₃N₄ friction balls during the friction and wear test. In the electrochemical tests, the coating reduced the corrosion current density from 1.056 × 10⁻⁵A·cm⁻² to 1.239 × 10⁻⁷A·cm⁻², while extending the passivation region from 0.322 V to 1.032 V.     

Carbon molecular sieve membranes for natural gas purification: Role of surface flow

Carbon molecular sieve membranes (CMSM) were prepared from the pyrolysis of polyimide films within a temperature range of 600°C-800°C under nitrogen stream. The membrane samples were characterized and tested for the permeation of He, CH₄, CO₂, and N₂ at different pressures and temperatures, respectively. The CMSM700 membrane (pyrolyzed at 700°C) showed an ideal selectivity of ~ 11 for N₂/CH₄ with a permeability of 2.18 × 10⁻¹⁵ mol · m/m² · s · Pa for N₂. The separation mechanism for the N₂/CH₄ pair was shown to be largely molecular sieving rather than surface flow. The membrane showed an ideal selectivity of ~ 500 for the CO₂/CH₄ pair with a CO₂ permeability of 9.72 × 10⁻¹⁴ mol · m/m² · s · Pa. The permeability of He was lower than that of CO₂, suggesting that the surface flow played a significant role in the CO₂ permeation. The updated permeability-selectivity tradeoff curves show that this CMSM membrane compared favourably with other membrane materials reported in the literature for the removal of N₂ and CO₂ from CH₄ for natural gas upgrading.     

Reducing the crystallinity of high molecular weight poly (ethylene oxide) using ultraviolet cross-linking for preparation of gas separation membranes

CO₂-selective cross-linked poly (ethylene oxide) (PEO) membranes were prepared by the UV irradiation of high molecular weight PEO in the presence of benzophenone as photo-initiator, which act as a hydrogen-abstracting agent. The main goal was to study the effects of the cross-linking process on the structural properties of hydrogel films intended for the gas separation applications. It was found that the gel fraction, and cross-link density enhanced, and the crystallinity, and the size of spherulites decreased by the cross-linking process. Moreover, the permeation performances for N₂, O₂, CH₄, and CO₂ and the relationship between the gas permeation performances and physical properties were investigated. The results indicated that the degree of cross-linking and crystallinity could be controlled by changing the initiator concentration, as by increasing the initiator content, the crystallinity percent and gas permeability of the membranes decreased, and the gas pair ideal selectivity of CO₂/N₂, CO₂/CH₄, CH₄/N₂, and O₂/N₂ increased.     

High pyroelectric performance in Pb0.99Nb0.02[(Zr0.57Sn0.43)0.94Ti0.06]0.98O3/Al2O3 composites by design

High pyroelectric performance around human body temperature is essential for ultra-sensitive infrared detectors of medical systems. Herein, toward human health monitoring, composite ceramics (1-x)Pb_0.99Nb_0.02[(Zr_0.57Sn_0.43)_0.94Ti_0.06]_0.98O₃/xAl₂O₃ (x = 0, 0.1, and 0.2) were designed. A metastable ferroelectric (FE) phase was induced in the anti-FE matrix by the Al₂O₃ component-induced internal stress, and in turn FE-anti-FE phase boundary was constructed. The ceramics at x = 0.2 exhibit high pyroelectric coefficient with p = 10.9 × 10⁻⁴ C·m⁻²·K⁻¹ and figures of merit with current responsivity F_i = 6.23 × 10⁻¹⁰ m·V⁻¹, voltage responsivity F_v = 12.71 × 10⁻² m²·C⁻¹, and detectivity F_d = 7.03 × 10⁻⁵ Pa^−1/2 around human body temperature. Moreover, the enhanced pyroelectric coefficients exist in a broad operation temperature range with a large full width at half maximums of 18.5°C and peak value of 29.2 × 10⁻⁴ C·m⁻²·K⁻¹ at 48.2°C. The designed composite ceramic is a promising candidate for infrared thermal imaging technology of noncontact human health monitoring system.     

Controlled synthesis of high performance carbon/zeolite T composite membrane materials for gas separation

A simple approach has been developed to synthesize the carbon/zeolite T composite membrane materials with the high gas separation performance. The precursors of the composite membrane are composed of polyimide matrix and dispersed zeolite T particles. The composite membranes prepared by pyrolysis at 973 K show excellent gas (H₂, CO₂, O₂, N₂, and CH₄) permeability and selectivity (O₂/N₂, CO₂/CH₄) for both single gas and mixed-gas. The gas separation performance of the composite membranes can be controlled in a wide range by only changing the zeolite T particle size. The maximum selectivity of O₂ over N₂ (21/79 mol%) for the composite membranes with the least zeolite T particle (0.5 μm) is 15 with an O₂ permeability of 347 Barrers (1 Barrer = 7.5 × 10⁻¹⁸ m² s⁻¹ Pa⁻¹) and the selectivity of CO₂ over CH₄ (50/50 mol%) reaches a value of 179 with a CO₂ permeability of 1532 Barrers. It is believed that the increase of gas permeability is attributed to the ordered microchannels in the zeolite and the interfacial gaps formed between zeolite and carbon matrix in the composite membranes. And the gas selectivity is tuned by the size of interfacial gaps which are varied with the zeolite particle size. This technique will provide a simple and convenient route to efficiently improve the trade-off relationship between the permeability and the selectivity and enable the construction of carbon-based composite materials with novel functionalities in membrane science.     

Supercritical fluid extraction of walnut kernel oil

The objective of this study was to investigate the effects of the main process parameters on supercritical fluid extraction of walnut (Juglans regia L.) kernel oil. The recovery of walnut kernel oil was performed in a green and high-tech separation process. CO₂ and CO₂ + ethanol mixtures were used as the supercritical solvent. The extraction was carried out at operating pressures of 30, 40 and 50 MPa, operating temperatures of 313, 323 and 333 K, mean particle sizes of 1.78×10⁻⁴, 3.03×10⁻⁴, 4.78×10⁻⁴, 7.00×10⁻⁴ and 9.00×10⁻⁴ m, supercritical CO₂ (SC CO₂) flow rates of 1.67×10⁻⁸, 3.33×10⁻⁸, 6.67×10⁻⁸ and 13.33×10⁻⁸ m³/s and entrainer (ethanol) concentrations of 2, 4, 8 and 12 vol-%. Maximum extraction yield and oil solubility in SC CO₂ obtained at 50 MPa, 333 K, 9.00×10⁻⁴ m, 3.33×10⁻⁴ m³/h were 0.65 kg oil/kg of dry sample and 37.16 g oil/kg CO₂, respectively. The results obtained in this study showed that the crossover pressure effect of walnut kernel oil was at 30 MPa. At 30 MPa and 313 K, the obtained extraction yields above 4 vol-% ethanol reached the organic solvent extraction yield of 68.5 kg oil/kg dry sample. Extraction time was decreased significantly because of the higher solubility of walnut kernel oil in SC CO₂ + ethanol mixtures.     

Synthesis of dual-functionalized mixed matrix membrane with amino-GO-Bent/PVDF for efficient separation of CO2/CH4 and CO2/N2

Mixed matrix membranes (MMMs), which combine the characteristics of inorganic nanofillers and organic matrices, have received wide attention because of their good permeability and selective performance for separating CO₂ from industrial waste gases. In this work, the amino-GO-loaded bentonite (amino GO-Bent) was prepared by loading  NH₂ on the GO surface with a large number of functional sites. Firstly, by introducing  NH₂ on the surface of GO and then interacting with bentonite (Bent) organically modified by silane coupling agents through amide bonding. Mixed matrix membranes (MMMs) with an area of 623.7 cm² and homogeneous texture were prepared using amino-GO-Bent as inorganic filler to improve the membrane selectivity for CO₂/N₂ and CO₂/CH₄ separation. The results show that the introduction of amino GO-Bent in MMMs can greatly improve the CO₂ permeability and obtain high CO₂ permeation performance: 2.67945 × 10⁻⁷ cm³ (STP)·cm/s/cm²/cmHg, and the selectivity of CO₂/N₂ and CO₂/CH₄ can reach 307.28 and 325.97, respectively. The two selective values were 14 and 18 times higher than those of pure PVDF membranes, and the performance of MMMs far exceeded the Robeson upper limit in 2008, respectively.     

Temperature Jump Measurements in Gas Kinetics

The temperature jump relaxation method is applied to kinetic measurements in the gas phase. The system N₂O₄⇄2NO₂ is studied. Fast T-jumps are induced by IR absorption from a TEA CO₂ laser. Temperature jumps of less than 1 K lead to readily detectable concentration changes which are monitored by UV absorption in a simple single shot experiment. k_rec(Ar) is found to be 1.05 × 10¹⁰ cm³ mol⁻¹ s⁻¹ at P_Ar = 1 bar and T = 258 K, in agreement with recent experimental data.     

Fabrication and characterization of poly(vinylidene fluoride)–polytetrafluoroethylene composite membrane for CO2 absorption in gas–liquid contacting process

The wetting resistance of poly(vinylidene fluoride) (PVDF) membrane is a critical factor which determines the carbon dioxide (CO₂) absorption performance of the gas–liquid membrane contactors. In this study, the composite PVDF–polytetrafluoroethylene (PTFE) hollow fiber membranes were fabricated through dry-jet wet phase-inversion method by dispersing PTFE nanoparticles into PVDF solution and adopting phosphoric acid as nonsolvent additive. Compared with the PVDF membrane, the composite membranes presented higher CO₂ absorption flux due to their higher effective surface porosity and surface hydrophobicity. The composite membrane with addition of 5 wt % PTFE in the dope gained the optimum CO₂ absorption flux of 9.84 × 10⁻⁴ and 2.02 × 10⁻³ mol m⁻² s⁻¹ at an inlet gas (CO₂/N₂ = 19/81, v/v) flow rate of 100 mL min⁻¹ by using distilled water and aqueous diethanolamine solution, respectively. Moreover, the 5% PTFE membrane showed better long-term stability than the PVDF membrane regardless of different types of absorbent, indicating that polymer blending demonstrates great potential for gas separation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47767.     

New composite membrane poly(vinyl alcohol)/graphene oxide for direct ethanol–proton exchange membrane fuel cell

This study investigated a simple synthesis of a crosslinked poly(vinyl alcohol)/ graphene oxide composite membrane with lower ethanol permeability membrane for passive direct ethanol–proton exchange membrane fuel cells (DE-PEMFCs). The chemical and physical structure, morphologies, ethanol uptake and permeability, ion exchange capacities, water uptake, and proton conductivities were determined and found that transport properties of the membrane were affected by the GO loading. The composite membrane with optimum GO content (15 wt %) exhibited the highest proton conductivity of 9.5 × 10⁻³ Scm⁻¹ at 30°C, 3.24 × 10⁻² Scm⁻¹ at 60°C, respectively and reduced ethanol permeability until 1.75 × 10⁻⁷ cm² s⁻¹. In the passive DE-PEMFC, the power density at 60°C were obtained as 5.84 mW cm⁻² higher than those by commercial Nafion 117 is 4.52 mW cm⁻². © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46928.     

Syntheses and gas-transport properties of alkylsilane-modified SBS membranes

Alkylsilane-modified styrene-butadiene-styrene (SBS) polymers were prepared via two steps. In the first step, dimethylchlorosilane HSi(CH₃)₂Cl and SBS (Korea Kumho Petrochem. Co.; 35% vinyl content; M_o = 48,000, M_o/M_n = 1.05) were reacted in toluene using H₂PtCl₆ catalyst to produce a hydrosilylated polymer. In the second step, chloride in the silyl group was replaced with alkyl by reaction with RLi (R = Me, n-Bu). Under severe conditions, silylation occurs on all the double bonds of the polymer so that their elastomeric nature disappears. However, under mild conditions, selective hydrosilylation of the pendant vinyl groups of SBS could be accomplished so that the polymer retained its elastomeric properties with two low T_g values. These modified SBS polymers were easily dissolved in THF, and thus could be formed into film-type membranes by solvent casting on teflon plates. From the measurements of their gas permeability for O₂ and N₂, they showed higher selectivity for O₂ compared with the unmodified SBS. The permeability for oxygen was dependent on the size of the alkylsilyl group. Methylsilane and butylsilane-modified SBS membranes showed the higher permeability values of 31.2 and 37.5 barrer (1 barrer = 1 × 10⁻¹⁰ cm³ (STP) cm cm⁻² s⁻¹ cmHg⁻¹) at 30°C, respectively, compared with 2.39 barrer of the unmodified SBS. Furthermore, their selectivities for O₂ over N₂ were increased to 3.0 and 3.2, respectively, from 2.5 of the unmodified SBS case. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1117–1122, 1997