Methanol self-diffusion coefficients

Table 5, Average polymer chain concentration (ape), polymer swellability (S), rotational correlation times of TEMPONE (r) and self-diffusion coefficient of methanol (Zf) in the swollen 2,2% Pd catalysts.

For comparison purposes, the proton mobility. Do (for Nafion solvated with water), which is closely related to the self-diffusion coefficient of water, is also plotted. At low degrees of hydration, where only hydrated protons (e.g., H3O+) are mobile, it has a tendency to fall below the water diffusion coefficient (this effect is even more pronounced in other polymers), which may be due to the stiffening of the water structure within the regions that contain excess protons, as discussed in Section 3.1.1. . Interestingly, the proton mobility in Nafion solvated with methanol (Da(MeOH) in Figure 14a) is even lower than the methanol self-diffusion (Z ieon). This may... 

Typical values of self-diffusion coefficients and mutual diffusion coefficients in aqueous solutions and in molten salt systems such as (K,Ag)N03 are of the order of 10 m s and the coefficients do not usually vary by more than a factor of 10 over the whole composition range [1, 2, 15]. From measurements in pure ionic liquids we have learned that their self-diffusion coefficients are only of the order of 10 m s From this point of view it is interesting to investigate systems of ordinary and ionic liquids. Figure 4.4-3 shows the results of first measurements in the methanol/[BMIM][PF6] system, which can be seen as a prototype for a system in which an organic and an ionic liquid are mixed. 

Figure 4.4-3 Self-diffusion and mutual diffusion coefficients in the methanol/[BMIM][PF5] system. X2 mole fraction of [BMIMjfPFg], D mutual diffusion coefficient, Ds self-diffusion coefficient of methanol, D52+ self-diffusion coefficient of [BMIMj. ...

Self-difFusion coefficients were measured with the NMR spin-echo method and mutual diffusion coefficients by digital image holography. As can be seen from Figure 4.4-3, the diffusion coefficients show the whole bandwidth of diffusion coefficient values, from 10 m s on the methanol-rich side, down to 10 on the [BMIM][PFg]-rich side. The concentration dependence of the diffusion coefficients on the methanol-rich side is extreme, and shows that special care and attention should be paid in the dimensioning of chemical processes with ionic Hquids. 

FlC. 26. Self-diffusion coefficients of methanol (squares) and water (circles) in their binary mixtures sorbed in HZSM-5 for two total loadings 35 mg (H2O + CH3OH) g" (open m-bols) and 50 mg g (filled symbols) at 300 K (725). Comparison with the self-diffusivity in liquid methanol/water mixtures (126,127) dotted line, D(CH30H) dashed lines, D(H20). 

Finally, two more specialized publications The group of Zeidler has developed a modified high-pressure probe in which they were able to measure pressure-dependent self-diffusion coefficients of [bmim]BF4 (neat and in methanol) [35], Kanakubo and coworkers have compared the self-diffusion coefficients of pure and 97% pure [bmim]PF6 [36] and found large differences between the two samples... 

Conclusions about a rate limiting stage of methanol chemisorption on the micropo-rous Xerogel were performed by Mertens and Fripiat [62] from the comparison of a self-diffusion coefficient of physically adsorbed methanol (D = 1.5 10 cm s at 25°C or 1.5 10 cm - s at 150°C) with a range of its reaction rate constants on the... 

Membrane Diffusion in Nonaqueous Solvent Environments. Self-diffusion coefficients of Na+ and Cs+ for 1200 EW Nafion membranes in dilute methanol and acetonitrile solutions have been measured (5). Arrhenius plots of these results are shown in Figure 7 along with corresponding results for aqueous experiments activation energies of diffusion are listed in Table IV. Diffusion coefficients of Na+ in methanol and water-equilibrated membranes are very similar, and the activation energy of diffusion for the methanol system is only slightly higher than the respective value for Na+ in pure methanol solvent, 12.9 kJ mol 1 (27). Thus a solution-like diffusion mechanism is inferred for both solvent systems. Cesium ion diffusion in the methanol equilibrated membrane is much slower than sodium ion diffusion in fact the... 

In the case of systems containing ionic liquids, components and chemical species have to be differentiated. The system methanol/[BMIM][Pp6], for example, consists of two components (methanol and [BMIMJfPPe]) but three chemical species (methanol, [BMIMJ+ and [PPe] ), assuming that [BMIM][Pp6] is completely dissociated. If [BMIM][PFis] is not completely dissociated, one has a fourth species, the undissociated [BMIM][PFis]. From this it follows that the diffusive transport can be described with three and four flux equations, respectively. But the fluxes of [BMIMJ+ and [PFg]" are not independent because of electroneutrality in each volume of the system. Furthermore, the flux of [BMIMJIPFe] is not independent of the flux of the ions because of the dissociation equilibrium. Thus, the number of independent fluxes is reduced to one, and the system can be described with only one mutual diffusion coefficient. In addition, one has four self-diffusion coefficients Ds(methanol), Ds([BMIM]+), Ds([PF6] ), and Ds([BMIM](PF6]), so that five diffusion coefficients are necessary to describe the system completely. 

Sulfonated Pis with a high proton conductivity and low methanol permeability were tested for their performance as proton exchange membranes in direct methanol fuel cells [58]. The proton to methanol transport selectivity of the membranes correlates well with the self-diffusion coefficients of water in the membranes. The membranes show an improved fuel cell device performance, however the high interfacial resistance between the membranes and electrodes... 

Figure 21.38. Data derived from NMR analysis of TMOS-based silica gels prepared at different pH of the starting solution as a function of target density (left Ti relaxation time), right self-diffusion coefficient of methanol in the...

Acetone swells PMMA to a greater extent than methanol, and the self-diffusion coefficients of the system are about two orders of magnitude greater than those of the methanol/PMMA system. This is apparently due to the increased volume available to the acetone molecules. The self-diffusion coefficients decrease by 35% from equilibrium in the outer regions to the region near the glassy core. The decreasing motions of the polymer chains as the core is... 

Figure 4.4-3 Self-diffusion and mutual diffusion coefficients in the methanol/[BMIM][PFg] sys-...

Figure 14. Solvent (water, methanol) diffusion coefficients of (a) Nafion 117 (EW =1100 g/equiv) and (b) sulfonated poly(arylene ether ketone)s, as a function of the solvent volume fraction. Self-diffusion data (AiaO. T eOi-i) are taken from refs 197, 224, 226, 255—263 and unpublished data from the laboratory of one of the authors) chemical diffusion coefficients (Z>h2o) are calculated from self-diffu-sion coefficients (see text), and permeation diffusion coefficients are determined from permeation coefficients. ...

L22 and L33 are related to the self-diffusion and chemical diffusion coefficients of water and methanol ... 

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