Fluorine silica

Normally, a slight excess of sulfuric acid is used to bring the reaction to completion. There are, of course, many side reactions involving siHca and other impurity minerals in the rock. Fluorine—silica reactions are especially important as these affect the nature of the calcium sulfate by-product and of fluorine recovery methods. Thermodynamic and kinetic details of the chemistry have been described (34). 

R. Ciriminna, S. Campestrini and M. Pagliaro, Fluorinated Silica Gels Doped with TPAP as Effective Aerobic Oxidation Catalysts in Dense Phase Carbon Dioxide, Adv. Synth. Catal., 2004, 346, 231. 

H2 and then CO2 pressure were applied, forming a GXL. The fluorinated catalyst then partitioned off of the fluorinated silica support and into the CO2-expanded organic phase. The reaction was assumed to occur in the expanded liquid phase in which reactants (styrene, hydrogen) and catalyst (fluorinated Wilkinson s catalyst) are homogeneously present. After the reaction was completed, the pressure was released and the catalyst then partitioned back onto the silica surface. 

The synthesis of MCM-41 structure in fluoride medium has been reported by Silva and Pastore [10], who used sodium silicate as silica source and carried out crystallization at 150 °C. They suggested the behaviour of Si02-CTMA+-F system was significantly different from that reported previously on the mesophase system. It is known that fluoride ions do influence the nature, activity and polymerizing capacity of silica precursors, and a fluorinated silica surface is much more hydrophobic and more resistant to the attack of water molecules than a silanol silica surface [11]. 

An alkene mixture of industrial source (equal amounts of C9-C13 alkenes and alkanes) was used in the alkylation of benzene on three Nafion-silica catalysts with 5%, 13%, and 20% loadings.195 20% Nafion-silica showed high and stable activity and its performance exceeded that of a Y-zeolite-based material. The selectivity to 2-phenylalkanes (25%) was higher than in the Detal process using fluorinated silica-alumina but decreased somewhat with increasing Nafion content. 

Another elegant technique in fluorous synthesis is the use of reverse-phase fluorinated silica gel as a solid separation phase. Such fluorinated solids allow the separation of fluorous from nonfluorous materials by selective adsorption, and can even be used for chromatographic separations by degree of fluorination (Kainz et al., 1998). These techniques require a considerably lower content of fluorine for efficient separation and have been referred to as light fluorous synthesis (Curran and Luo, 1999). 

Linear alkylbenzenes are made from linear terminal olefins and benzene and are important precursors of biodegradable anionic surfactants (LAS, linear alkylbenzenesulfonates). The conventional catalyst is HF, first to be replaced by a fluorinated silica-alumina in the DETAL process. The DETAL process is safer than the HF process and also more cost-effective because no special metallurgy is required and no calcium fluoride waste stream exists.52 Zeolites such as Beta may come to the fore here because they display a higher selectivity to the desired 2-phenyl isomers.55... 

An interesting effect is seen when FBSs are exposed to pressures of carbon dioxide. Pressures of between 16 and 50 bar can cause many such systems to become monophasic at room temperature and this may have applications in future separations. Related to this is the use of carbon dioxide pressure as a switch for recycling a fluorous catalyst on a fluorinated silica support. 

The use of silica brick in chemical-resistant masonry is limited, because of high cost, to applications requiring a high degree of chemical resistance where traditional acid brick cannot be used, such as concentrated phosphoric acid free of fluorine. Silica brick, however, cannot be used in strong alkaline exposures or any concentrations of hydrofluoric acid. As with acid brick, its main function is to provide a barrier to abrasion and to protect other membranes or structures from chemical attack. Because brick porosity may be as high as 16%, silica brick is backed by an impermeable material and a support structure. 

Figure 5 Schematic representation of the use of fluorinated silica as a trap for fluorous catalysts.

Hsieh C, Chang B, Lin J. Improvement of water and oil repellency on wood substrates by using fluorinated silica nanocoating. Appl Surf Sci 2011 257(18) 7997-8002. 

Fabrication and Superhydrophobic Behavior of Fluorinated Silica Nanosphere Arrays... 

Here we have proposed a modified Cassie-Baxter model to investigate the influence of prirticle size on superhydrophobic behavior of sfiica nanosphere arrays. An assembly technique enabled to prepare well-ordered silica nanosphere arrays, and then the silica arrays were fluorinated by a spin-coating process. Compared with a F-coated flat surface, the contact angle on fluorinated silica nanoarrays reached a value of 152 1.4°. A Cassie-Baxter parameter, surface firaction (4>s), was used to simulate the hydrophobicity. It was found that the nanosphere size played an important role in affecting the hydrophobicity of the sphere arrays. The present work demonstrates that the superhydrophobicity of nanoarrays is well correlated with the modified Cassie-Baxter model. 

Fluorinated silica and alumina have also been used for isobutane alkylation with olefins in a batch reactor at 0°C. The fluorinated alumina was active only when mixed with BF3 H2O, but the fluorinated silica was active by itself The selectivity to trimethylpentanes obtained with these catalysts is much lower than that obtained with H2SO4 as a catalyst (48). At 80°C, however, F/AI2O3 catalysts are active for isobutane/2-butene alkylation, though relatively low butene conversions (27% for the most active catalyst containing 1.3% F) are obtained (49). As expected, octenes are the predominant hydrocarbons in the Cg fraction at such a low conversions. The F/AI2O3 catalysts contained both Bronsted and Lewis acid sites in a proportion that depends on the F loading. A good correlation between... 

Fluorine-19. Despite interesting characteristics (100% abundance, Yf/Yh=0-94), few fluorinated surface compounds have been studied. Fluorine-19 NMR has, however, been used as a powerful complementary technique to silicon-29 NMR to understand the surface sites of fluorinated silica particles (vide supra). " ... 

These fluorinated silica nanocomposites-encapsulated Ar—H can exhibit no weight loss behavior corresponding to the contents of Ar—H even after calcination at 800°C, although fluoroalkyl end-capped acrylic acid oligomer in the nanocomposites decomposed completely under similar conditions [49]. 

Figure 10.6 Fluorinated silica nanoparticles attached to the cellulose fibers rendering them rough and hydrophobic [ 14]. (a) Fiber surface with X 3000 magnification and...

Y.C. Sheen, YC. Huang, C.S. Liao, H.Y Chou and EC. Chang, New approach to fabricate an extremely super-amphiphobic surface based on fluorinated silica nanoparticles, /, Polym. Sci. B, 46,1984-1990 (2008). 

Access to Highly Fluorinated Silica by Direct F2 Fluorination... 

About the Chemical Composition and Morphology of Highly Fluorinated Silica... 

Figure 17.1 Comparison of surface (A.F2-I0CFC XPS, F2-25°C XPS) and bulk (AF2-10CPC global F-titratlon, C>F2-25°Cglobal F-titration) F/Si atomic ratios in fluorinated silica versus F2 dilution. The fluorination has been conducted during two hours at room temperature for all samples. Reproduced by permission j. Phys. Chem. C 2008, 112, pp. 1094310951, American Chemical Society...

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