Uptake methanol

Ren X, Springer TE, Gottesfeld S (2000) Water and methanol uptakes in Nafion membranes and membrane effects on direct methanol cell performance. J Electrochem Soc 147 92-8... 

N. Miyake, J.S. Wainright, and R.F. Savinell. Evaluation of a sol-gel derived Nafion/sihca hybrid membrane for polymer electrol3te membrane fuel cell apphcations. II. Methanol uptake and methanol permeabihty. Journal of the Electrochemical Society 148, A905-A909 2001. 

X. Ren, M.S. Wilson and S. Gottesfeld, High performance direct methanol polymer electrolyte fuel cells, J. Electrochem. Soc., 1996,143, L12-L15 X. Ren, T.E. Springer and S. Gottesfeld, Water and methanol uptakes in Nafion membranes and membrane effect on direct methanol cell performance, J. Electrochem. Soc., 2000,147, 92-98. 

Fig. 44 Surface permeability of the MOF-type crystal under study during methanol uptake as a function of the boundary concentration (mean value during the considered time step) via Eqs. 7 and 8, with the boundary concentration Csurf(t) taken from the margins of the measured concentrations. The polynomial fit to these data is given by the broken line. The full line shows the dependence of the permeability on concentration, which leads to the best fit of the recalculated concentration profiles to the experimental ones (Fig. 45)...

Fig. 45 Comparison of the transient concentration profiles during methanol uptake by the MOF-type crystal as recorded by interference microscopy (symbols) with the corresponding profiles recalculated from the measured diffusivities with surface permeabilities (full line in Fig. 44) which lead to the best fit to the experimental points...

Fig. 55 Correlation between the actual boundary concentration (Csu f) and the relative uptake (m) at the corresponding instants of time for methanol uptake by ferrierite for a pressure step from 0 to 10 mbar...

Some fundamental studies relating to methanol transport in membranes has also been reported. A study of the transport of formaldehyde and ethylene glycol through ion permeable membranes in electrolytic ceils has also been investigated. The water and methanol uptake from methanol-water... 

Figure 6, Methanol uptake of Epon 862/W 1%, 3%, 6% SCI6/Epon 862/W and 1%, 3%, 6% L30E/Epon 862/W nanocomposites, (See page 5 of color insert,)...

The uptake of alcohols by Naflon membranes has been much less studied than the water uptake. Nevertheless, several authors determined the sorption of pure methanol from the liquid and the vapor phase in commercial and recast Naflon membranes [268-282] and the reported results are summarized in Table 6.2, expressed as A, that is, moles of methanol sorbed by sulphonic group. The treatment of the membrane previous to the methanol uptake determination is also indicated. 

The observed scatter in the data is in part due to differences in measurement temperature, which was not well controlled in some of the cases, but it is mainly due to different membrane treatment previous to the alcohol uptake. As in the case of water uptake, methanol uptake from the liquid phase is higher than from the vapor phase when compared for the same membrane under the same treatment. This phenomenon, known as Schroeder s paradox, is related to the thermal history of the adsorbing polymer [90]. 

The expanded form of the Nafion membrane, obtained by boiling the membrane in 3 % H2O2, followed by boiling in water, sulphuric acid and finally in water again (treatment A), tends to uptake more methanol than the non-expanded or cast membrane. At temperatures close to ambient, typical liquid methanol uptake (/I) range from 17 to 27, except for a few studies. These values are similar to that observed for the uptake of water by Nafion. 

It is interesting to analyze the effect of inorganic fillers or blending with other polymers on the methanol uptake of Nafion-based membranes. Kim et al. [46] measured methanol uptake in composite of Nafion with organic modified silica (ORMOSIL) and they observed that the methanol uptake decrease proportionally to the amount of inorganic phase in the membrane, reaching a half of its value in Nafion when the filler content is close to 40 wt%. The connectivity between the... 

In the case of Nafion/zirconium phosphate membranes an increase of the water and a decrease of the methanol uptakes is observed with increasing content of the inorganic phase. 

Park et al. [102] reported a noticeable reduction of the methanol uptake in Nafion/polypyrrole composite membranes, which is accompanied by a similar decrease in the water sorption. A Nafion/polyaniline membrane containing polyanilines with different oxidation states is reported [127] to reduce around 10 % the methanol uptake, particularly the oxidized state, along with a very small reduction of the water uptake. A similar study on Nafion/polyaniline membrane reported a larger reduction (40 %) of the methanol uptake, which reached 50 % when Si02 was added to the composite membrane, without any significant effect on the water uptake [125]. 

The methanol uptake of a grafted Nafion/poly(glycidyl methacrylate) membrane was studied by Mohy Eldin et al. [162]. The membrane, its amine derivate, and the phosphoric acid -doped membrane exhibit an important enhance of the methanol and water uptake with increasing grafting percentages. 

Diaz et al. [280] have recently study the behaviour of the water-methanol uptake from the vapour phase by ultra-thin (thickness < 100 nm) Nafion cast membranes and they observed similarities with the water-methanol uptake from the liquid of thick commercial membranes. As illustrated in Fig. 6.17, the total uptake also exhibits a maximum close to x = 0.5. Moreover, the apparent partition constant increase smoothly isK = 1.20 0.06 for methanol fraction in the vapor between 0.12 and 0.69, indicating a preference for methanol uptake. 

Water-methanol uptake from the vapor phase by PBI was determined in thin membranes (100 nm thick) using the quartz crystal microbalance method [280]. The results, expressed as moles of water plus methanol sorbed per imidazole ring, are shown in Fig. 6.31. It was assumed that the partition constant of methanol is Kx = 1.29, as determined by NMR analysis of a PBI membrane in equilibria with a methanol aqueous solution (20 wt%) [280]. 

The behavior observed in Fig. 6.32 is different from that observed Nafion in Fig. 6.17. In the case of PBI, and also for the modified ABPBI membrane, the pme water sorption almost doubles pure methanol sorption, that is, these membranes have a clear preference for water uptake over methanol, while no differences in the uptake of water and methanol was observed in Nafion. The water-methanol uptake from the liquid phase (methanol 20 wt%) of a thick PBI membrane (50-100 pm) shows the same behavior, that is water uptake (A = 3.48) is much higher than methanol uptake (2 = 0.63), which is desirable behaviour for a membrane which intend to be a good barrier for methanol crossover. 

Fig. 6.32 Water-methanol uptake in FBI and ABPBI membranes at room temperature as a function of the vapor composition...

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