Hydrocarbon-based membranes

The bicontinuous-microemulsion polymerization technique has also been used to develop novel proton exchange membranes (PEM) for fuel cell evaluation [97]. A series of hydrocarbon-based membranes were prepared based on the formulation shown in Fig. 5, with additional ionic vinyl monomers such as VB-SLi or bis-3-sulfopropyl-itaconic acid ester. After polymerization, the membranes were treated with dilute H2SO4 (0.5 M) to convert them to PEM membranes. The good performance of these PEM membranes in a single fuel cell is illustrated in Fig. 9. 

Gross M, Maier G, Fuller T, MacKinnon S and Gittleman C S (2009), Design rules for the improvement of the performance of hydrocarbon-based membranes for proton exchange membrane fuel cells (PEMFC) , in Handbook of Fuel Cells, Vol. 5 (W. Vielstich, H. Yokokawa, and H. A. Gasteiger, eds.),Wiley. 

These membranes ate based on perfluotinated polymers that will withstand oxkforive conditions and high temperatures that would be destructive to hydrocarbon-based membranes. Sulfimic or carboxylic acid groups, or both, are affixed chemically to the perfluotinated polymers to impart catkm-exchange characteristics. 

Krishnan NN, Prabhuram J, Hong YT et al (2010) Fabrication of MEA with hydrocarbon based membranes using low temperature decal method for DMFC. Int J Hydrogen Energy 35 5647-5655... 

Early investigation of PEMELC degradation drew similar conclusions for hydrocarbon-based membranes (LaConti et al. 2(X)5). With use of Aclar-g-polystyrene sulfonic acid as the membrane material, it was found that H, O, and platinum black were necessary for accelerated membrane degradation. 

Very early hydrocarbon-based membranes tested as electrolytes in PEMECs for Gemini space missions, such as sulfonated phenol-formaldehyde resins, sulfonated poly(styrene-divinylbenzene) copolymers, and grafted polystyrene sulfonic acid membranes, were chemically weak, and therefore PEMFCs using these membranes showed poor performance and had only lifetimes of several hundred hours (LaConti et al. 2003). Nafion , a PESA membrane, was developed in the mid-1960s by DuPont (LaConti et al. 2003). It is based on an aliphatic perfluorocarbon sulfonic acid, and exhibited excellent physical properties and oxidative stability in both wet and dry states. A PEMEC stack using Nafion 120 (250- tm thickness, equivalent weight = 1,200) achieved continuous operation for 60,000 h at 43-82°C (LaConti et al. 2003, 2006). A Nafion -based PEMFC was used for the NASA 30-day Biosatellite space mission (LaConti et al. 2003). 

Not only hydrocarbon systems, but also silicon rubbers (Lee 1986), can be pyrolyzed to obtain silicon-based membranes. Details of the pyrolysis are mainly reported for nonmembrane applications. A recent example is the paper of Boutique (1986) for the preparation of carbon fibers used in aeronautical or automobile constructions. 

Dais membranes are reported to be much less expensive to produce than Nation they are also reported to exhibit a rich array of microphase-separated morphologies because of the ability to tailor the block length and composition of the unsulfonated starting polymer. The main drawback of employing hydrocarbon-based materials is their much... 

The membrane potential increased with increasing hydrocarbon chain length. Figure 7 shows the transport rate constants of various phosphonium ions as a function of the membrane potential. The selectivity coefficient of tpp+ has also been determined using a nitrobenzene—based membrane electrode45 a value of log KPot = 8.75 was reported, which is lower than that obtained with the arsenic analogue. 

As with normal hydrocarbon-based surfactants, polymeric micelles have a core-shell structure in aqueous systems (Jones and Leroux, 1999). The shell is responsible for micelle stabilization and interactions with plasma proteins and cell membranes. It usually consists of chains of hydrophilic nonbiodegradable, biocompatible polymers such as PEO. The biodistribution of the carrier is mainly dictated by the nature of the hydrophilic shell (Yokoyama, 1998). PEO forms a dense brush around the micelle core preventing interaction between the micelle and proteins, for example, opsonins, which promote rapid circulatory clearance by the mononuclear phagocyte system (MPS) (Papisov, 1995). Other polymers such as pdty(sopropylacrylamide) (PNIPA) (Cammas etal., 1997 Chung etal., 1999) and poly(alkylacrylicacid) (Chen etal., 1995 Kwon and Kataoka, 1995 Kohorietal., 1998) can impart additional temperature or pH-sensitivity to the micelles, and may eventually be used to confer bioadhesive properties (Inoue et al., 1998). 

PBI (see chemical structure above) is a hydrocarbon membrane that has been commercially available for decades. Free PBI has a very low proton conductivity ( 10 S/cm) and is not suitable for PEM fuel cell applications. However, the proton conductivity can be greatly improved by doping PBI with acids such as phosphoric, sulfuric, nitric, hydrochloric, and perchloric acids. The PA-doped PBI membrane is the most popular one in PEM fuel cell applications because H3PO4 is a nonoxidative acid with very low vapor pressure at elevated temperature. Savinell et al. and Wainright et al. first demonstrated the use of PBI-PA for HT fuel cells in 1994.270 272 since then, there has been a significant amount of research on the PBI-based membrane because of its low cost and good thermal and chemical stabil-... 

The use of Pd-based membrane reactors can increase the hydrogenation rates of several olefins by more than 10 times higher than those in conventional premixed fixed>bed reactors. Furthermore, it has been pointed out that the type and state of the oxygen used to carry out partial oxidation of methane can significantly affect the conversion and selectivity of the reaction. The use of a solid oxide membrane (e.g., a yttria-stabilized zirconia membrane) not only can achieve an industrially acceptable C2 hydrocarbon yield but also may eliminate undesirable gas-phase reactions of oxygen with methane or its intermediates because oxygen first reaches the catalyst through the solid oxide wall [Eng and Stoukides, 1991]. 

Polyether ketones (PEEKs) are studied, but generally do not give performance advantages over Nation, although cost may be lower. Polyphenylene sulphonic acid membranes may improve performance at low humidity, and fluorinated polyarylene ethers may be produced at lower cost, but so far have low conductivity. Also, membranes based on bacterial cellulose with added precious metals have been investigated. Generally, hydrocarbon-based materials have lesser mechanical strength than the C-F based materials (Gil et ah, 2004 Lee et ah, 2004 Evans et ah, 2003). 

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