Bilayer thin-film composite membranes for air separation

Bilayer composite membranes suitable for separating air, consisting of poly(4-methylpentene-1) (PMP) thin film as a selective top layer, an ethylcellulose–heptycellulose (ECHC) blend thin film as a selective sublayer, and polysulfone as a porous support, were investigated using a constant pressure–variable volume method. By varying operating temperature, pressure, time, as well as stage cut, the membranes were characterized for their oxygen enriched air (OEA) flux and oxygen concentration in the OEA permeated in a single step. The results show that both the OEA flux and oxygen concentration through the membranes increase with increasing operating pressure. With the increase of operating temperature, the OEA flux increases largely but the oxygen concentration decreases slightly. The oxygen concentration also decreases slightly with the stage cut. On the contrary, the OEA flux decreases and oxygen concentration increases slightly with operating time. It is found that a PMP thin film plays an important role in enhancing the air-separation capability of the membrane. The PMP/ECHC bilayer thin-film composite membrane could enrich the OEA containing 43.6% oxygen at the OEA flux of 5.06 × 10^?4 cm³ (STP)/s cm² with a good performance stability. © 1995 John Wiley & Sons, Inc.     

Air separation characteristics with liquid crystalline alkyl cellulose blend thin-film composite membranes

Composite membranes were made of liquid crystalline triheptyl cellulose (THC)/ethyl cellulose (EC) blends as dense thin films and poly(ether sulfone) (PES) or polysulfone (PSF) as porous support layer. The effects of the composite membrane composition and operating conditions on the air separation characteristics of oxygenenriched air (OEA) permeating through the membranes were studied using a constant pressure-variable volume method. The flux (OEA) through the membranes decreases slightly and the oxygen concentration in the OEA permeated increases with increasing THC content in the thin film from 4 to 15 wt.-%. The OEA flux increases significantly with decreasing thin-film thickness or increasing operating temperature and transmembrane pressure difference. The oxygen concentration in the OEA increases with increasing the thin-film thickness or the pressure difference but decreases slightly with increasing the operating temperature. There is no regular variation in the air separation properties by changing the support from PES to PSF. In long-term tests, the air separation properties remained almost constant for as long as 800 h. An OEA flux of 1.0–1.9·10^-3 cm³ (STP)/s·cm² containing 34.8–39.4 vol.-% oxygen can be attained at 30–55°C and 0.41–0.49 MPa pressure difference in a single pass through the membranes. The OEA flux is much higher for the thin-film composite membranes than for the homogeneous dense membranes made of the same materials.     

Multilayer ultrathin-film composite membranes for oxygen enrichment

Multilayer composite membranes were made of poly(4-methylpentene-1) (PMP), an ethyl cellulose (EC) + heptyl cellulose (HC) blend, polycarbonate (PC), polysulfone, poly(2,6-dimethylphenylene oxide), cellulose triacetate ultrathin films as selective layers, and polysulfone, poly(ether sulfone), and poly(sulfone amide) ultrafiltration membranes with a 10–45 nm pore size and 100–120 μm thickness as porous support layers. The effects of the ultrathin-film type and its casting solution concentration, operating pressure, temperature, as well as time on the oxygen-enriched air (OEA) flux and oxygen concentration in the OEA permeated in a single step through the composite membranes were investigated using a constant pressure—variable volume method. The OEA flux increases significantly with an increasing transmembrane pressure difference and operating temperature. The oxygen concentration in the OEA also increases with an increasing pressure difference but decreases slightly with an increasing operating temperature. In long-term tests, the oxygen-enrichment properties were maintained almost constant for as long as 170 h. The composite membranes consisting of the bilayer ultrathin film cast from a more dilute solution (0.11–0.26 wt %) on the porous support with a smaller pore size combine a higher oxygen-enriching ability and a higher stability than do those of monolayer and tetralayer ultrathin films. The maximum OEA flux and oxygen concentration produced at 20–75°C and a 500 kPa transmembrane pressure difference in a single pass across the PMP/98EC + 2HC bilayer and PC bilayer ultrathin-film composite membranes are 3.1 × 10⁻³ cm³(STP)/s cm² and 50%, respectively. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2139–2147, 1997     

Oxygen enrichment from air through multilayer thin low‐density polyethylene films

Several multilayer thin low‐density polyethylene (LDPE) films were fabricated by blown thin film having a thickness of 7 μm and an area of 130 cm². They were characterized for their oxygen‐enrichment performance from air by a constant pressure–variable volume method in a round permeate cell with an effective area of 73.9 cm². The relationship between oxygen‐enrichment properties, including oxygen‐enriched air (OEA) flux, oxygen concentration, permeability coefficients of OEA, oxygen, nitrogen, as well as separation factor through the multilayer LDPE films, and operating parameters, including transfilm pressure difference, retentate/permeate flux ratio, temperature, as well as layer number, are all discussed in detail. It is found that all of the preceding oxygen‐enrichment parameters increase continuously with an increase of transfilm pressure difference from 0.1 to 0.65 MPa, especially for the trilayer and tetralayer LDPE films. The oxygen concentration and separation factor appear to rapidly increase within the retentate/permeate flux ratio below 200, and then become unchangeable beyond that, whereas the OEA flux and the permeability coefficients of OEA, oxygen, and nitrogen seem to remain nearly constant within the whole retentate/permeate flux ratio investigated, especially for the monolayer and bilayer LDPE films. The selectivity becomes inferior, whereas the permeability becomes superior, as the operating temperature increases from 23 to 31°C. The highest oxygen concentration was found to be 44.8% for monolayer LDPE film in a single step with air containing oxygen of 20.9% as a feed gas and operating pressure of 0.5 MPa at a retentate/permeate flux ratio of 340 and 23°C. The results demonstrate a possibility to prepare an oxygen‐enriching membrane directly from air, based on the easily obtained thin LDPE films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3013–3021, 2002; DOI 10.1002/app.2331     

Actual air separation across multilayer composite membranes

Multilayer composite membranes are fabricated from six types of thin films as selective layers, an ethyl cellulose (EC) thin film as a flexible spacer, and poly(ether sulfone) (PES) with 15–45 nm pore size or 100–120 μm thickness as a porous support layer. The effects of the thin‐film type and its layer number, operating temperature, and transmembrane pressure difference, as well as the operational time on the actual air‐separation properties through the composite membranes, are investigated by a constant pressure‐variable volume method. The results show that a pure polystyrene thin‐film composite membrane exhibits poor actual air‐separation performance due to its brittleness, although it has a higher ideal oxygen over nitrogen separation factor. The oxygen‐enrichment air (OEA) flux through all of the composite membranes tested increases significantly with increasing operating temperature and pressure difference. The oxygen concentration in the OEA increases slightly with an increase in operating temperature, and the oxygen concentration through the polystyrene/cholesteryl oleyl carbonate blend, top layer composite membrane exhibits the maximal value. As the transmembrane pressure difference increases, the oxygen concentration in the OEA also exhibits the maximal value. The maximum oxygen concentration can reach 39.1%, which is achieved by the multilayer composite membrane consisting of a polystyrene/cholesteryl oleyl carbonate (95/5) monolayer, an EC single flexible spacer, and a PES support at 35°C and a transmembrane pressure difference of 550 kPa. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2396–2403, 2000     

Electrochemical preparation of poly(o‐toluidine) film and its application as a permselective membrane

Poly(o‐toluidine) films were electrochemically synthesized on Pt electrodes at a constant potential (0.75 V versus Ag/AgCl) from a deoxygenated aqueous solution of 0.1M toluidine dissolved in 0.1M KCl. To form permselective polymeric film electrodes, poly(o‐toluidine) films at different thicknesses were prepared by varying the amount of charge consumed during electrochemical polymerization. Then, experimental parameters (e.g., concentrations of monomer and electrolyte and pH of the phosphate buffer salt solution) affecting the polymeric film thickness were optimized. Permeation of the various electroactive and nonelectroactive species such as ascorbic acid, oxalic acid, hydrogen peroxide, lactose, sucrose, and urea through the optimized poly(o‐toluidine)‐coated electrodes was investigated using a chronoamperometric technique. From experimental results, it was found that a poly(o‐toluidine)‐coated electrode permitted the oxidation of hydrogen peroxide and prevented the permeation of the mentioned electroactive and nonelectroactive species. In other words, it was seen that this polymeric electrode responded to only hydrogen peroxide selectively. Thus, it has been claimed that a poly(o‐toluidine)‐coated Pt electrode can be used as a permselective polymeric membrane to overcome interference problems occurring in the hydrogen peroxide‐based biosensor applications. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2141–2146, 1999     

Studies on the dielectric properties of poly(o‐toluidine) and poly(o‐toluidine‐aniline) copolymer

Poly(o‐toluidine) (PoT) and poly(o‐toluidine co aniline) were prepared by using ammonium persulfate initiator, in the presence of 1M HCl. It was dried under different conditions: room temperature drying (48 h), oven drying (at 50°C for 12 h), or vacuum drying (under vacuum, at room temperature for 16 h). The dielectric properties, such as dielectric loss, conductivity, dielectric constant, dielectric heating coefficient, loss tangent, etc., were studied at microwave frequencies. A cavity perturbation technique was used for the study. The dielectric properties were found to be related to the frequency and drying conditions. Also, the copolymer showed better properties compared to PoT alone. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 592–598, 2004     

The inhibitive effect of poly(p‐toluidine) on corrosion of iron in 1M HCL solutions

In recent years, polymer amines have been recognized as an excellent corrosion inhibitors for iron in acid solutions. In this work, the inhibitive effect of p‐toluidine and poly(p‐toluidine) on corrosion of iron in 1M HCl has been studied by the electrochemical methods such as impedance, linear polarization, Tafel polarization techniques. The effectiveness of poly(p‐toluidine) was found to be high in comparison with that of monomer. The results showed that p‐toluidine and poly(p‐toluidine) suppressed both cathodic and anodic processes of iron dissolution in 1M HCl. The inhibition efficiency of both p‐toluidine and poly(p‐toluidine) were found to increase with the inhibitor concentrations. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Air Separation through Modified Ethyl Cellulose Thin Film Supported on Porous Polyethersulfone

Abstract

Composite membranes for air separation were prepared from a liquid crystal DYC-modified ethyl cellulose (EC) thin film ranging in thickness from 1 to 7 μm and a porous polyethersulfone support with a thickness of 120 μm. The effects of DYC/EC (9/91) solution concentration, water, and operating parameters such as temperature, pressure, and time on the air-separation properties of the composite membranes were examined by a constant pressure—variable volume method. The permeate flux and oxygen concentration of the oxygen-enriched air (OEA) through the membranes increase significantly with increasing operating pressure difference. With decreasing casting solution concentration, or with increasing humidity around the membranes or operating temperature, the OEA flux increases greatly while the oxygen concentration sometimes decrease slightly. An increase in the operating time leads to an OEA flux decline, but the oxygen concentration rose when the operating time was varied for 70 hours. However, a further increase of the operating time from 70 to 500 hours does not lead to further changes of the OEA flux and oxygen concentrations. A thin-film composite membrane exhibits a slightly lower oxygen concentration accompanied by a very significant enhancement in the OEA flux and membrane stability compared to a homogeneous dense membrane of the same materials.     

Electrochemical preparation of poly(N‐acetylaniline)/poly‐(4‐styrenesulfonic acid‐co‐maleic acid) composite film towards ascorbic acid sensing

Poly(N‐acetylaniline)/poly(4‐styrenesulfonic acid‐co‐maleic acid) (PNAANI/PSSMA) composite film was prepared by cyclic voltammetry (CV), and was characterized by FTIR and X‐ray photoelectron spectrum (XPS). The electroactivity of the composite film was high in neutral and basic solutions, and it had been used for amperometric determination of ascorbic acid (AA). Compared with pure PNAANI film, the catalytic activity of the composite film was much better. AA was detected amperometrically in sodium citrate buffer at a potential of 0.3 V (versus SCE). The response current was proportional to the concentration of ascorbic acid in the range of 4.7 × 10^?6 to 5.0 × 10^?5M and 5.0 × 10^?5 to 2.5 × 10^?3M, respectively, with the detection limit of 1.9 × 10^?6 mol L^?1 at a signal to noise ratio 3. In addition, the stability and reusability of the composite film were performed well, and it was satisfying to be used for determination of AA in real fruit juice samples. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and surface properties of polydimethylsiloxane‐based block copolymers: poly[dimethylsiloxane‐block‐ (ethyl methacrylate)] and poly[dimethylsiloxane‐block‐(hydroxyethyl methacrylate)]

A polydimethylsiloxane (PDMS) macroazoinitiator was synthesized from bis(hydroxyalkyl)‐terminated PDMS and 4,4′‐azobis‐4‐cyanopentanoic acid by a condensation reaction. The bifunctional macroinitiator was used for the block copolymerization of ethyl methacrylate (EMA) and 2‐(trimethylsilyloxy)ethyl methacrylate (TMSHEMA) monomers. The poly(DMS‐block‐EMA) and poly(DMS‐block‐TMSHEMA) copolymers thus obtained were characterized using Fourier transform infrared and ¹H NMR spectroscopy and differential scanning calorimetry. After the deprotection of trimethylsilyl groups, poly(DMS‐block‐HEMA) and poly(DMS‐block‐EMA) copolymer film surfaces were analysed using scanning electron microscopy and X‐ray photoelectron spectroscopy. The effects of the PDMS concentration in the copolymers on both air and glass sides of films were examined. The PDMS segments oriented and moved to the glass side in poly(DMS‐block‐EMA) copolymer film while orientation to the air side became evident with increasing DMS content in poly(DMS‐block‐HEMA) copolymer film. The block copolymerization technique described here is a versatile and economic method and is also applicable to a wide range of monomers. The copolymers obtained have phase‐separated morphologies and the effects of DMS segments on copolymer film surfaces are different at the glass and air sides. Copyright © 2010 Society of Chemical Industry     

Air Separation Properties and Stabilities of Blend Membranes of Liquid Crystals with Ethyl Cellulose

Abstract

Air separation properties and stabilities of four blend membranes, 1–30-μ.m thick, prepared from ethyl cellulose (EC) with a small amount of nematic and cholesteric liquid crystals, such as p-heptyl-p'-cyanobiphenyl (7CB), p-pentylphenol-p'-methoxybenzoate (5PMB), benzoate-containing liquid crystal mixture (DYC), and cholesteryl oleyl carbonate (COC), were investigated by the variable volume method. To provide more significant information guiding membrane-based air separation, air was directly used as the test gas. The membranes showed both higher oxygen permeability, P _O2 , and oxygen over nitrogen separation factor, P _O2 /P _N2 , in the temperature range of the liquid crystalline phase. Oxygen-enriched air (OEA) flux, Q _OEA, and oxygen concentration. Y _O2 increased simultaneously with increasing transmembrane pressure difference. Stability studies revealed that the efficiencies of concentrating oxygen using 1–7-μm thick DYC/EC (9/91) membranes laminated to porous polyethersulfone membranes were almost constant for a 120–510-hour operating time. The membrane possessed a Q _OEA of 9.0 × 10^?4 cm³(STP)/s.cm² and Y_O2 of 40% at 30°C and 0.41 MPa for a single-stage process. The results suggest that the membranes could be used effectively in enriching oxygen from air.     

Copolymers of aniline with o‐ and m‐toluidine: synthesis and characterization

Copolymers of aniline and toluidine were synthesized by oxidative chemical polymerization using different ratios of the monomers in the feed, and characterized by a number of techniques including UV–visible, IR, Raman, ¹H NMR and EPR spectroscopies, as well as by thermogravimetric analysis and conductivity measurements. The properties of the copolymers are influenced by the amount of toluidine in the copolymer. Poly(o‐toluidine) and poly(m‐toluidine) are noticeably different in their solubility and conductivity. The copolymers show better solubilities than polyaniline but have lower conductivities. Differences in the properties of the salt and base forms of the copolymers are pointed out. Copyright © 2003 Society of Chemical Industry     

Chemical grafting of aniline and o‐toluidine onto poly(ethylene terephthalate) fiber

Graft copolymerization of poly(aniline) and poly(o‐toluidine) onto poly(ethylene terephthalate) fiber was conducted by using peroxydisulfate as a lone initiator under nitrogen atmosphere at various experimental conditions in aqueous hydrochloric acid medium. The grafting of poly(aniline) and poly(o‐toluidine) onto poly(ethylene terephthalate) fiber was verified by recording cyclic voltammetry of the grafted fiber, conductivity measurements, and thermal analysis. Graft parameters—such as % grafting, % efficiency, and the rate of grafting—were followed. Grafting was always accompanied by homopolymerization. The rate of homopolymerization was also followed in all experimental conditions. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 121–128, 1999     

Preparation and characterization of sulfonated block‐graft copolyimide/sulfonated polybenzimidazole blend membranes for fuel cell application

Polymer electrolyte blend membranes composed of sulfonated block‐graft polyimide (S‐bg‐PI) and sulfonated polybenzimidazole (sPBI) were prepared and characterized. The proton conductivity and oxygen permeability coefficient of the novel blend membrane S‐bg‐PI/sPBI (7 wt%) were 0.38 S cm^?1 at 90 °C and 98% relative humidity and 7.2 × 10^?13 cm³(STP) cm (cm² s cmHg)^?1 at 35 °C and 76 cmHg, respectively, while those of Nafion^® were 0.15 S cm^?1 and 1.1 × 10^?10 cm³(STP) cm (cm² s cmHg)^?1 under the same conditions. The apparent (proton/oxygen transport) selectivity calculated from the proton conductivity and the oxygen permeability coefficient in the S‐bg‐PI/sPBI (7 wt%) membrane was 300 times larger than that determined in the Nafion membrane. Besides, the excellent gas barrier properties based on an acid ? base interaction in the blend membranes are expected to suppress the generation of hydrogen peroxide and reactive oxygen species, which will degrade fuel cells during operation. The excellent proton conductivity and gas barrier properties of the novel membranes promise their application for future fuel cell membranes. © 2015 Society of Chemical Industry     

Development of thin‐film composite membranes for carbon dioxide and methane separation using sulfonated poly(phenylene oxide)

Novel membranes based on sulfonated poly (phenylene oxide) (SPPO) was developed. SPPO membranes in the hydrogen form were converted to metal ion forms. The effect of exchange with metal ions including monovalent (Li⁺, Na⁺, K⁺), divalent (Mg²⁺, Ba²⁺, Ca²⁺) and trivalent (Al³⁺) ions was investigated in terms of permeation rate and permeation rate ratios for CO₂ and CH₄ gases. Both dense homogeneous membranes and thin‐film composite (TFC) membranes were studied for their gas separation characteristics. The effect of membrane preparation conditions and operating parameters on the membrane performance were also investigated. The selectivity of the TFC membrane increased as the cationic charge density increased as a result of electrostatic cross‐linking. TFC membrane of very high selectivity was achieved by coating a thin layer of SPPO‐Mg on a PES substrate. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 735–742, 2000     

A novel porous‐dense dual‐layer composite membrane reactor with long‐term stability

A porous‐dense dual‐layer composite membrane reactor was proposed. The dual‐layer composite membrane composed of dense 0.5 wt % Nb₂O₅‐doped SrCo_0.8Fe_0.2O_3‐δ (SCFNb) layer and porous Ba_0.3Sr_0.7Fe_0.9Mo_0.1O_3‐δ (BSFM) layer was prepared. The stability of SCFNb membrane reactor was improved significantly by the porous‐dense dual‐layer design philosophy. The porous BSFM surface‐coating layer can effectively reduce the corrosion of the reducing atmosphere to the membrane, whereas the dense SCFNb layer permeated oxygen effectively. Compared with single‐layer dense SCFNb membrane reactor, no degradation of performance was observed in the dual‐layer membrane reactor under partial oxidation of methane during continuously operating for 1500 h at 850°C. At 900°C, oxygen flux of 18.6 mL (STP: Standard Temperature and Pressure) cm^?2 min^?1, hydrogen production of 53.67 mL (STP) cm^?2 min^?1, CH₄ conversion of 99.34% and CO selectivity of about 94% were achieved. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4355–4363, 2013     

Ion‐exchange membranes prepared by blending sulfonated poly(2,6‐dimethyl‐1,4‐phenylene oxide) with polybenzimidazole

New ion‐exchange acid/base‐blend (SPPO/PBI) membranes were prepared by mixing N,N‐dimethylacetamide (DMA) solutions of sulfonated poly(2,6‐dimethyl‐1,4‐phenylene oxide) (SPPO) in the ammonium form and of polybenzimidazole (PBI), casting the solution as a thin film, evaporating the solvent, and treating the membrane with aqueous hydrochloric acid. The resulting membranes were found insoluble in DMA. The preliminary tests of the membranes were carried out in an H₂/O₂ fuel cell at room temperature. Their performance in the fuel cell increased with the increase in the concentration of SPPO sulfonic acid groups in the blend, but the membranes formed with the highly sulfonated SPPO alone or predominanting, which swelled excessively in water, did not give reproducible results, and their performance was usually inferior to that of the membranes having an optimum ratio of both components. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1118–1127, 2002     

Alkyl amine functional dextran macromonomer‐based thin film composite loose nanofiltration membranes for separation of charged and neutral solutes

Thin film composite (TFC) nanofiltration membranes with defined porous structure of the separation layer are desirable for the concentration of neutral solute and separation of salts from a mixture. Herein, we report the formation of TFC membranes composed of polyamide (PA) separation layer by the interfacial polymerization between new dextran‐butyl amine (Dex‐NH₂) macromonomer and trimesoyl chloride on polysulfone support membrane. The membranes prepared with 1%–1.5% (wt/vol) of Dex‐NH₂ exhibited water permeance of 110–116 L m^?2 h^?1 MPa^?1 with 62%–71% rejection of Na₂SO₄ and 12%–14% rejection of MgCl₂. The membranes also showed about 91% rejection of poly(ethylene glycol) of molecular weight 2000 g/mol and about 11% rejection of NaCl. A decrease in permeance and ions selectivity was observed with increasing concentration of Dex‐NH₂. The dextran chains attached to the PA network restrict the diffusion of Dex‐NH₂ toward the interfacial zone and thereby assist the formation of porous and thin PA layer compared to that when free amine (alkyl diamine) was used. These membranes are applicable for the separation of small molecular weight neutral solutes from mixture containing monovalent salts. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45301.     

Engineering design of outer‐selective tribore hollow fiber membranes for forward osmosis and oil‐water separation

Outer‐selective thin‐film composite (TFC) hollow fiber membranes offer advantages like less fiber blockage in the feed stream and high packing density for industrial applications. However, outer‐selective TFC hollow fiber membranes are rarely commercially available due to the lack of effective ways to remove residual reactants from fiber's outer surface during interfacial polymerization and form a defect‐free polyamide film. A new simplified method to fabricate outer‐selective TFC membranes on tribore hollow fiber substrates is reported. Mechanically robust tribore hollow fiber substrates containing three circular‐sector channels were first prepared by spinning a P84/ethylene glycol mixed dope solution with delayed demixing at the fiber lumen. The thin wall tribore hollow fibers have a large pure water permeability up to 300 L m^?2 h^?1 bar^?1. Outer‐selective TFC tribore hollow fiber membranes were then fabricated by interfacial polymerization with the aid of vacuum sucking to ensure the TFC layer well‐attached to the substrate. Under forward osmosis studies, the TFC tribore hollow fiber membrane exhibits a good water flux and a small flux difference between active‐to‐draw (i.e., the active layer facing the draw solution) and active‐to‐feed (i.e., the active layer facing the feed solution) modes due to the small internal concentration polarization. A hyperbranched polyglycerol was further grafted on top of the newly developed TFC tribore hollow fiber membranes for oily wastewater treatment. The membrane displays low fouling propensity and can fully recover its water flux after a simple 20‐min water wash at 0.5 bar from its lumen side, which makes the membrane preferentially suitable for oil‐water separation. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4491–4501, 2015