Polyimide composite membrane

Strathmann prepared an all-polyimide composite membrane-both bottom and top layers.97 A microporous asymmetric film of the polyamic acid intermediate was cast by quenching in acetone, then dried and thermally cyclized to the polyimide at 300°C. The microporous polyimide sheet was then overcoated with a dilute solution of the same polymer, which was allowed to evaporate to give a 300-angstrom-thick coating. This was also cyclized to the polyimide to generate a fully solvent resistant reverse osmosis membrane. 

Asymmetric membranes are made from solution in the form of a hollow fiber, but the process used to form a thin, pore free dense layer on these hollow fibers is not disclosed.45 46 However, US patent 4,440,64312 describes a unique process for producing pore-free polyimide composite membranes. An asymmetric polyimide porous substrate is prepared from solution. When fully imi-dized, the substrate is insoluble. The substrate can now be coated with a poly-amic acid from dilute solution (— 1 %). When fully imidized, the resultant polyimide coating becomes the separating layer. This process allows use of the same or different polyimides for the substrate and the separating membrane. While the examples in the reference describe preparation of flat sheet membranes, this process could be used to prepare hollow fiber membranes. 

Yanagishita, H., Kitamoto, D., Haraya, K., Nakane, T., Tsuchiya, T., and Koura, N. 1997. Preparation and pervaporation performance of polyimide composite membrane by vapor deposition and polymerization (VDP). J. Membr. Sci. 136 121-126. 

Munukata H, Yamamoto D, Kanamura K (2008) Three-dimensionally ordered macroporous polyimide composite membrane with controlled pore size for direct methanol fuel cells. J Power Sources 178 596-602... 

C. J. Cornelius, E. Maraud, Hybrid silica-polyimide composite membranes gas transport properties, J. Membr. ScL, 202, 97-118 (2002). 

Kusakabe K, Ichiki K, Hayashi J-I, Maeda H, Morooka S (1996) Preparation and charactCT-ization of silica— polyimide composite membranes coated on porous tubes for CO2 separation. J Membr Sci 115(l) 65-75... 

K. Tadanaga, Y. Michiwaki, T. Tezuka, A. Hayashi, M. Tatsumisago, Structural change and proton conductivity of phosphosilicate gel-polyimide composite membrane for a fuel cell operated at 180 °C, J. Membr. Sci. 324 (1)... 

Pei L, Abbott J, Zufelt K, Davis A, Zappe M, Decker K, Liddiard S, Vanlleet R, Liirfoid MR, Davis R (2011) Processing of thin carbon nanotube-polyimide composite membranes. Nanosci Nanotechnol Lett 3(4) 451 57... 

Lee S-Y, Yasuda T, Watanabe M (2010) Fabrication of protic ionic liquid/sulfonated polyimide composite membranes for non-humidified fuel cells. J Power Sources 195 5909-5914... 

Cornelius CJ, Maraud E (2002) Hybrid silica-polyimide composite membranes gas transport... 

Kulkami, S. and Hasse, D.J. (2007) Novel polyimide based mixed matrix composite membranes. US Patent Application 2007/0199445 Al. 

Salts rejected by the membrane stay in the concentrating stream but are continuously disposed from the membrane module by fresh feed to maintain the separation. Continuous removal of the permeate product enables the production of freshwater. RO membrane-building materials are usually polymers, such as cellulose acetates, polyamides or polyimides. The membranes are semipermeable, made of thin 30-200 nanometer thick layers adhering to a thicker porous support layer. Several types exist, such as symmetric, asymmetric, and thin-film composite membranes, depending on the membrane structure. They are usually built as envelopes made of pairs of long sheets separated by spacers, and are spirally wound around the product tube. In some cases, tubular, capillary, and even hollow-fiber membranes are used. 

According to literary data, the following mixtures of aromatic/aliphatic-aromatic hydrocarbons were separated toluene/ n-hexane, toluene/n-heptane, toluene/n-octane, toluene/f-octane, benzene/w-hexane, benzene/w-heptane, benzene/toluene, and styrene/ethylbenzene [10,82,83,109-129]. As membrane media, various polymers were used polyetherurethane, poly-esterurethane, polyetherimide, sulfonyl-containing polyimide, ionicaUy cross-linked copolymers of methyl, ethyl, n-butyl acrylate with acrilic acid. For example, when a composite polyetherimide-based membrane was used to separate a toluene (50 wt%)/n-octane mixture, the flux Q of 10 kg pm/m h and the separation factor of 70 were achieved [121]. When a composite mebrane based on sulfonyl-containing polyimide was used to separate a toluene (1 wt%)/ -octane mixture, the flux 2 of 1.1 kg pm/m h and the separation factor of 155 were achieved [10]. When a composite membrane based on ionically cross-linked copolymers of methyl, ethyl, w-butyl acrylate with acrilic acid was used to separate toluene (50 wt%)//-octane mixture, the flux Q of 20-1000 kg pm/m h and the separation factor of 2.5-13 were achieved [126,127]. 

The membrane shown in Fig. 4.10 was prepared using this three-dimensionally ordered macroporous polyimide obtained according to the above process with AMPS polymer. The proton conductivity and methanol permeability of the composite membrane are summarized in Table 4.2. The proton conductivity of the composite membrane was higher than that of Nafion and the methanol permeability of the composite membrane was slightly lower than that of Nafion . Both tendencies are good for membrane for direct methanol fuel cell. In this way, three-dimensionally ordered macroporous materials are suitable for matrix of soft proton conductive polymer with higher proton conductivity. 

Fig. 4.10 Photograph and scanning electron micrograph of three-dimensionaUy ordered macro-porous polyimide and composite membrane consisting of macroporous polyimide and proton conductive polymer...

Table 4.2 Proton conductivity and methanol permeability of the composite membrane with three-dimensionally ordered macroporous polyimide matrix. Measurement temperature 30°C, Methanol concentration 10 mol dm ...

Since the pioneering work of Tehennepe et al. [152] in 1987, many efforts have been made filling the polymeric matrix with zeolites in order to improve their stability. There are several companies that offer pervaporation organic membranes and composite membranes such as Sulzer Chemtech [153]. Commercial pervaporation and vapor permeation installations utilize polymeric membranes, like PVA (Sulzer Chemtech), polyimide (Vaperma), per-fiuoropolymers (MTR and Compact Membrane Systems), and polyelectrolytes (GKSS) or ceramic membranes, like zeolite A (Mitsui, Mitsubishi, Inocermic) and silica... 

Several reviews on membranes for DMFC fuel cells have been published in the last decade [1-9], starting with that by Kreuer [1], discussing the differences between Nafion and sulfonated polyether ketone membranes. According to Fig. 6.1, reviews published till 2006 [1 ] cover only one third of the ionomeric membranes currently developed for DAFC. More recent reviews deal with polyimide ionomer membranes [5], composite membranes for high temperature DMFC [6], non-perfluorated sulfonic acid membranes [7], modified Nafion membranes [8], and hybrid membranes [9-11]. 

The acid-base Nafion composite membranes include blends of Nafion with polypyrrole (PPy) [98-104], polybenzimidazole (PBI) [105-107], poly (propyleneoxide) (PPO) [108, 109], polyfurfuryl alcohol (PFA) [110], poly(vinyl alcohol) (PVA) [111-115], sulfonated phenol-formaldehyde (sPF) [116], polyvinylidene fluoride (PVdF) [117-122], poly(p-phenylene vinylene) (PPV) [123], poly(vinyl pyrrolidone) (PVP) [124] polyanifine (PANI) [125-128], polyethylene (PE) [129], poly(ethylene-terephtalate) [130], sulfated p-cyclodextrin (sCD) [131], sulfonated poly(ether ether ketone) (sPEEK) [132-135], sulfonated poly(aryl ether ketone) (sPAEK) [136], poly(arylene ether sulfone) (PAES) [137], poly(vinylimidazole) (PVl) [138], poly(vinyl pyridine) (PVPy) [139], poly (tetrafluoroethylene) (PTFE) [140-142], poly(fluorinated ethylene-propylene) [143], sulfonated polyhedral oligomeric silsesquioxane (sPOSS) [144], poly (3,4-ethylenedioxythiophene) (PEDT) [145, 146], polyrotaxanes (PR) [147], purple membrane [148], sulfonated polystyrene (PSSA) [149, 150], polystyrene-b-poly(ethylene-ran-butylene)-bpolystyrene (SEES) [151], poly(2-acrylamido-2-methyl-l-propanesulphonic acid-co-l,6-hexanediol propoxylate diacrylate-co-ethyl methacrylate) (AMPS) [152], and chitosan [31]. A binary PVA/chitosan [153] and a ternary Nafion composite with PVA, polyimide (PI) and 8-trimethoxy silylpropyl glycerin ether-1,3,6-pyrenetrisulfonic acid (TSPS) has also been reported [154]. 

Nguyen T, Wang X (2010) Multifunctional composite membranes based on a highly porous polyimide matrix for direct methanol fuel cells. J Power Sources 195 1024-1030... 

Polybutadiene/polycarbonate membranes with a pp-ethylenediamine layer had an increased gas permeability (in comparison with the unmodified one) due to surface etching. Their selectivity was closely connected with the chemical composition of the top layer. A high nitrogen content was required for high O2 selectivity (Ruaan et al. 1998). The presence of the amine groups on the membrane surface also enhanced the capacity for CO2/CH4 separation. The plasma-polymerized diisopropylamine on the surface of the composite membrane—porous polyimide (support)/ silicone (skin)— made the separation coefficient as high as 17 for a permeation rate of 4.5 X cmVcm sec cmHg (Matsuyama et al. 1994). 

Figure 20.4 Chemical structures of (a) [dema][TfO] and (b) sulfonated polyimides. (c) Appearance of the composite membrane. Fundamental thermal and electrochemical properties are also shown in (a).

Figure 20.5 Temperature dependence of ionic conductivity of composite membrane based on sulfonated six-membered polyimide with an lEC of 2.15 meqg". Reproduced with permission from Ref. [21).

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