Nafion beads

Nafion beads, Nafion—Si02, and Aciplex-Si02 were tested by Okuhara and coworkers923 924 in the Ritter reaction between 1-adamantanol and acrylonitrile [Eq. 

Looking at the schematic representation of the flow profile within the fiber shown in Fig. 3-39, it becomes apparent that a further sensitivity increase can be accomplished by changing the parabolic flow profile. When the fiber is packed with inert Nafion beads, the translational diffusion of ions is favored over longitudinal diffusion. This, in turn, improves the mass-transfer across the membrane which leads to a further increase in sensitivity, particularly pronounced in the case of orthophosphate as the salt of a weak acid. 

In contrast with conventional acid resins, sulfonated perfluorocarbon-based Nafion polymers can withstand temperatures up to 200 °C and have superacid sites. Nafion beads, however, have an extremely low surface area (< 0.02 m ... 

Different alkylation reactions have been investigated with Nafion as a catalyst. An example is the propylation of benzene to cumene. Large rate enhancements were observed on use of Nafion-silica composites, compared with bulk polymeric catalysts such as pure Nafion NR50 and Amberlyst-15. The activity of the composite was ca 6-7 times higher than that of pure Nafion beads on the basis of the total amount of catalyst. If this correlation were made on the basis of the total number of acid sites on Nafion, the activity would be ca 50 times higher. Amberlyst-15 was about twice as active as the Nafion NR50 particles (on the basis of the total amount of catalyst) [7]. 

In a similar study, Nafion-H beads, 10% Nafion-H on silica, and 13% Nafion-silica were compared in the adamantylation of toluene with 1-bromoadamantane.239 13% Nafion-silica nanocomposite exhibited the highest activity and showed achangeinthe isomeric ratio of the two alkylated products the para/me ta ratio shifted to lower values in prolonged reaction (Table 5.20). Acidity is known to exert a significant influence on... 

A U-tube filled with a GC sorbent (e.g. polymethoxysilane coated silica beads) and maintained in liquid nitrogen (where hydrides are trapped) allows the product to be concentrated prior to insertion, either into the detector or onto the column. A thermal desorption system is mandatory for proper, fast removal of retained, preconcentrated species. A water trap (another U-tube maintained at — 15°C or filled with anhydrous CaCl,), a Nafion tube and various other devices are often placed in between the separator and detector. 

The Claisen rearrangement of allyl phenyl ethers proceeds in the presence of the Nafion-H and silica/Nafion-H nanocomposites. The 2-methyldihydrobenzofuran is formed as a major product (75%) in the presence of the Nafion-H beads the minor product is the orf/zo-allylphenol (25%) (equation 10). However, the ortto-allylphenol is formed as the major product in the presence of the Nafion/H-silica nanocomposites. 

New and up to-date materials have been developed in our laboratory to carry out Fenton photo-assisted processes efficient in the decoloration/degradation of organic pollutants that show stability against radical attack, do not allow the leaching of Fe-ions into the solution and intervene with suitable kinetics in the degradation processes. These new materials comprise Fe-ions supported on Nation membranes, Nafion-glass mats composites, alginate beads, amorphous polycrystalline fused copolymers and silica woven fabrics. 

The preparation of the supported catalytic Fe-clusters have been recently reported by our laboratory for Fe/Nafion membranes [1,2,3] for Fe/Nafion/glass-mats [4,5] micro-encapsulated Fe-alginate beads [6] Fe-amorphous polycrystalline thin film fused copolymers [7] and finally Fe/silica woven fabrics [8]. Experiments were conducted with Nafion perfluorinated cation transfer membrane. Photolysis experiments were carried out by means of a Hanau Suntest Lamp with tunable light intensity equipped with an IR filter to remove infrared radiation. Light... 

Nafion is commercially available as Nafion NR50 (DuPont) in the form of relatively large (2-3 mm) beads. A disadvantage of these beads is the low surface area (typically < 0.02 m g ) [8]. Water-selective Perma Pure membranes also consist of the polymer Nafion and were especially developed for removal of water from gas-phase streams [9]. Nafion is also available as a 5 % solution in a mixture of lower aliphatie alcohols and water [10]. 

To overcome the disadvantage of the low surface area (< 0.02 m g ) of pure Nafion NR50 beads, researchers at DuPont developed Nafion-silica composites, in which small (20-60 nm) Nafion resin particles are embedded in a porous silica matrix [7]. The composites, available under the trade name SAC 13 (containing 13 % (w/w) Nafion) are prepared by a sol-gel technique. Because of the higher surface area and accessibility of the active sites the application of this material as a solid-acid catalyst has become attractive. 

Recently, Yamamoto and Hyodo have employed the DPD method for studying Nafion membranes [20]. The systems considered in this study were built using two distinct molecular species, denoted comb-shaped polymer ip) and water (w). The polymer was presented as a branched sequence of beads. It consisted of a main chain (backbone) of iV = 20 effective monomer units (-CF2CF2CF2CF2 ) linked with rig = 5 short side chains of = 2 units [-0CF2C(CF3)F0 and F2CF2S03H] the total number of interaction sites in the macromolecule was Np= N/, + n xn = 30. A water-like particle was modeled as the same size as the units of the Nafion fragment (<7 = 6.1 A) and represented four water molecules. The x parameters were found using an atomistic calculation. The DPD simulation was performed for water volume... 

Related Reagents. p-Toluenesulfonic Acid Amberlyst 15 (20-60 mesh beads) Amberllte IR-120 (8% cross-linked beads) Dowex 50 (2% cross-linked mesh (dry) 50-100 mesh beads) Nafion-H NR50 (10-35 mesh beads 97% purity). 

Multiscale Modeling, Fig. 10 Spontaneous microstructure formation snapshots along the trajectory and during microstmcture formation at (a) t) 100 ps, annealed configuration, (b) t) 40 ns, and (c) t) 320 ns, final equilibrated configuration. The gray spheres show the carbon particles. Nafion backbones correspond to red beads, while green beads show the side chains. Small blue beads represent hydronium ions inside the pore network. Water beads are... 

FIGURE 2.11 A snapshot of a the microstructure of Nafion at A. = 9 obtained form DPD simulation. Nafion backbone is shown in dark and the first sidechain bead in light. The second sidechain bead, water and hydronium ions are shown in medium grey, defining the ionic cluster region. (Reprinted with permission from Malek, K. et al. 2008. J. Chem. Phys., 129, 204702, Figures 1,2,5,6,9,10. Copyright (2008), American Institute of Physics.)... 

Malek et al. (2008) employed a typical coarse-grained parameterization of hydrated Nafion. Clusters of four water molecules are represented by polar beads. Clusters of three water molecules and a hydronium ion correspond to charged beads. An ionomer sidechain is represented by a single charged bead. A four-monomeric unit of PTFE (-[-CF2-CF2-CF2-CF2-CF2-CF2-CF2-CF2-]- on the backbone, corresponds to a nonpolar bead. All beads are assigned a radius 0.43 nm and a volume of 0.333 nm ... 

The simulation box considered in Malek et al. (2008) had a size of (25 x 25 x 25) nm. It contained 72 coarse-grained Nafion chains, as depicted and described in Figure 2.12. 1440 CG hydronium ions were added for electroneutrality. A varying number of water beads was added to simulate systems with varying water contents, corresponding to A. = 4,9,15. 

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