Liquid/polymer gels

Ionic liquids have already been demonstrated to be effective membrane materials for gas separation when supported within a porous polymer support. However, supported ionic liquid membranes offer another versatile approach by which to perform two-phase catalysis. This technology combines some of the advantages of the ionic liquid as a catalyst solvent with the ruggedness of the ionic liquid-polymer gels. Transition metal complexes based on palladium or rhodium have been incorporated into gas-permeable polymer gels composed of [BMIM][PFg] and poly(vinyli-dene fluoride)-hexafluoropropylene copolymer and have been used to investigate the hydrogenation of propene [21]. 

Many approaches have been developed for the production of ionic liquid-polymer composite membranes. For example, Doyle et al. [165] prepared RTILs/PFSA composite membranes by swelling the Nafion with ionic liquids. When 1-butyl, 3-methyl imidazolium trifluoromethane sulfonate was used as the ionic liquid, the ionic conductivity ofthe composite membrane exceeded 0.1 S cm at 180 °C. A comparison between the ionic liquid-swollen membrane and the liquid itself indicated substantial proton mobility in these composites. Fuller et al. [166] prepared ionic liquid-polymer gel electrolytes by blending hydrophilic RTILs into a poly(vinylidene fiuoridej-hexafluoropropylene copolymer [PVdF(HFP)] matrix. The gel electrolytes prepared with an ionic liquid PVdF(HFP) mass ratio of 2 1 exhibited ionic conductivities >10 Scm at room temperature, and >10 Scm at 100 °C. When Noda and Watanabe [167] investigated the in situ polymerization of vinyl monomers in the RTILs, they produced suitable vinyl monomers that provided transparent, mechanically strong and highly conductive polymer electrolyte films. As an example, a 2-hydroxyethyl methacrylate network polymer in which BPBF4 was dissolved exhibited an ionic conductivity of 10 S cm at 30 °C. 

Chauvin et al. reported the asymmetric hydrogenation of acetamidocinnamic acid to (S)-phenylalanine with a cationic chiral rhodium catalyst in [C4-mim][SbF6] ionic liquid, more recently the 2-arylacryhc acid has been produced with a reasonable 64% yield using a chiral ruthenium catalysts in [C4-mim][BF4] ionic hquids. Palladium catalysts immobilized in an ionic liquid-polymer gel membrane containing either [C2-mim][CF3S03] or [C2-mim][BF4] have also been reported as catalysts for heterogeneous hydrogenation reactions. 

Fuller, J., A.C. Breda, and R.T. Carlin. 1998. Ionic liquid-polymer gel electrolytes fi om hydrophilic and hydrophobic ionic liquids. / Electroanal Chem 459 29-34. 

P. Wang, S. M. Zakeeruddin, I. Exnar, M. Gratzel, (2002) "High efficiency dye-sensitized nanocrystalline solar cells based on ionic liquid polymer gel electrolyte." Chem. Commun., 2972-2973. 

J. Fuller, A. C. Breda, R. T. Carlin, Ionic liquid-polymer gel electrolytes. J. Electrochem. Soc. 1997a, 144(4), L67. 

The use of polymeric catalytic membranes in distributor/contactor-type reactors for hydrogenation or oxidation reactions has been widely described in several former and recent reviews. Mixed-matrix membranes of PDMS hlled with Pd particles, composite membranes of ionic liquid-polymer gels filled with Pd/C, ° ionic liquids containing rhodium complexes and supported in polystyrene sheets in a corrugated configuration, have been used for the selective gas-phase hydrogenation of hydrocarbons in contactor-type membrane reactors. 

Carlin R T and Fuller J (1997), Ionic liquid-polymer gel catalytic membrane , Chem Commun, 1345-1346. 

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