Sol-gel derived porous microcomposite of perfluorinated ion-exchange polymer and metal oxide

#This invention relates to porous microcomposites comprising perfluorinated ion-exchange polymers (PFIEP) containing pendant sulfonic acid groups and/or pendant carboxylic acid groups entrapped within and highly dispersed throughout a metal oxide network, prepared using a sol-gel process. Due to their high surface area and acid functionality these microcomposites possess wide utility as improved solid acid catalysts.

#U.S. Pat. No. 5,252,654 discloses polymeric composites comprising an interpenetrating network of an organic polymer and an inorganic glassy polymer and a process for making such composites. The disclosed material is nonporous, and the use of perfluorinated ion-exchange polymers (PFIEP) containing pendant sulfonic acid groups or pendant carboxylic acid groups is not disclosed.

#K. A. Mauritz et al., Polym. Mater. Sci. Eng. 58, 1079-1082(1988), in an article titled “Nafion-based Microcomposites: Silicon Oxide-filled Membranes”, discuss the formation of micro composite membranes by the growth of silicon oxide microclusters or continuous silicon oxide interpenetrating networks in pre-swollen “NAFION®” sulfonic acid films. “NAFION®” is a registered trademark of E. I. du Pont de Nemours and Company.

#FIG. 1 is a graph showing data from Example 58 and Table 4b which shows the effect of contact time at 50° C. and He/1-butene=1.2/1.0 on 1-butene isomerization over a 13 wt % “NAFION®” PFIEP/silica microcomposite prepared as in Example 16.

#The organic-inorganic polymer microcomposites of the present invention are high surface area, porous microcompositions which exhibit excellent catalytic activity. Whereas the surface area of “NAFION®” NR 50 PFIEP, a commercial product, is approximately 0.02 m2 per gram, a preferred embodiment of the present invention comprises microcomposites of PFIEP and silica having a surface area typically of 5 to 500 m2 per gram. The composition of the present invention exists as a particulate solid which is porous and glass-like in nature, typically 0.1-4 mm in size and structurally hard, similar to dried silica gels. The perfluorinated ion exchange polymer (PFIEP) is highly dispersed within and throughout the silica network of the microcomposite of the present invention, and the microstructure is very porous. The porous nature of this material is evident from the high surface areas measured for these glass-like pieces, having typical pore diameters in the range of 1-25 nm. Another preferred embodiment is the use of the present invention in pulverized form.

#In another preferred embodiment, macroporosity (pore sizes about 75 to about 1000 nm) is also introduced into the microcomposite, resulting in a microcomposite having both increased surface area from the micropores and mesopores (0.5-75 nm) and enhanced accessibility resulting from the macropores (75-1000 nm).

#Perfluorinated ion-exchange polymers (PFIEP) containing pendant sulfonic acid, carboxylic acid, or sulfonic acid and carboxylic acid groups used in the present invention are well known compounds. See, for example, Waller et al., Chemtech, Jul., 1987, pp. 438-441, and references therein, and U.S. Pat. No. 5,094,995, incorporated herein by reference. Perfluorinated ion-exchange polymers (PFIEP) containing pendant carboxylic acid groups have been described in U.S. Pat. No. 3,506,635, which is also incorporated by reference herein. Polymers discussed by J. D. Weaver et al., in Catalysis Today, 14 (1992) 195-210, are also useful in the present invention. Polymers that are suitable for use in the present invention have structures that include a substantially fluorinated carbon chain that may have attached to it side chains that are substantially fluorinated. In addition, these polymers contain sulfonic acid groups or derivatives of sulfonic acid groups, carboxylic acid groups or derivatives of carboxylic acid groups and/or mixtures of these groups. For example, copolymers of a first fluorinated vinyl monomer and a second fluorinated vinyl monomer having a pendant cation exchange group or a pendant cation exchange group precursor can be used, e.g., sulfonyl fluoride groups (SO2F) which can be subsequently hydrolyzed to sulfonic acid groups. Possible first monomers include tetrafluoroethylene (TFE), hexafluoropropylene, vinyl fluoride, vinylidine fluoride, trifluoroethylene, chlorotrifluoroethylene, perfluoro (alkyl vinyl ether), and mixtures thereof. Possible second monomers include a variety of fluorinated vinyl ethers with pendant cation exchange groups or precursor groups. Preferably, the polymer contains a sufficient number of acid groups to give an equivalent weight of from about 500 to 20,000, and most preferably from 800 to 2000. Representative of the perfluorinated polymers for use in the present invention are “NAFION®” PFIEP (a family of polymers for use in the manufacture of industrial chemicals, commercially available from E. I. du Pont de Nemours and Company), and polymers, or derivatives of polymers, disclosed in U.S. Pat. Nos. 3,282,875; 4,329,435; 4,330,654; 4,358,545; 4,417,969; 4,610,762; 4,433,082; and 5,094,995. More preferably the polymer comprises a perfluorocarbon backbone and a pendant group represented by the formula —OCF2CF(CF3)OCF2CF2SO3X, wherein X is H, an alkali metal or NH4. Polymers of this type are disclosed in U.S. Pat. No. 3,282,875.