Methanol transportation

Ren, X., Springer, T. E., Zawodzinski, T. A. and Gottesfeld, S. 2000. Methanol transport through Nafion membranes— Electro-osmotic drag effects on potential step measurements. Journal of the Electrochemical Society 147 466-474. 

Tricoli, V., Carretta, N. and Bartolozzi, M. 2000. A comparative investigation of proton and methanol transport in fluorinated ionomeric membranes. Journal of the Electrochemical Society 147 1286-1290. 

Bello, M., Javaid Zaidi, S.M., and Rahman, S.U. (2008) Proton and methanol transport behavior of SPEEK/ TPA/MCM-41 composite membranes for fuel cell application. /. Membr. Sd., ill (1), 218-224. 

Mechanisms of Solvent (Water, Methanol) Transport. The following types of transport are considered in this section (i) self-diffusion or tracer diffusion of solvent molecules, which is the unidirec-... 

There are actually no experimental measurements of protonic streaming currents (Lu) and coupled water and methanol transport (L23 = L32) however, the first may be related to the hydrodynamic component of the electro-osmotic drag L /Ln, Lis/Lu) (see discussion in Section 3.2.1.1). The second is expected to be qualitatively related to the ratio of the electro-osmotic drag coefficient of water and methanol (L12/Z.13). In the following, the directly accessible transport coefficients o (Do), FH2O, MvieOH,... 

Ion transport is also often coupled with cellular energy production and with nutrient and product membrane transport. Aside from Papoutsakis work on the influence of methanol transport on growth of methanol-consuming bacteria, the importance of membrane control of nutrient and product fluxes into the cell has been largely ignored by biochemical engineers [25]. Better methods for measuring the pH and electrical potential differences across cell membranes are needed, as is more careful consideration of membrane-mediated processes in cell kinetics models. 

The crossover of methanol has caused problems in finding a suitable membrane material. On the positive electrode side, methanol combines with oxygen to form CO2. Among the alternatives to pure Nafion are Nafion filled with zirconium phosphate or grafted with styrene to inhibit methanol transport (Bauer and Willert-Porada, 2003 Sauk et al., 2004), as well as non-Nafion membrane materials such as sulfonated polyimide (Woo et al., 2003). None have achieved performance as good as the one shown in Fig. 3.53, which, however, has a substantial methanol crossover rate. 

It is favorable for fuel cell operation when reduced methanol transport across the membrane is accompanied by proper water management. In particular, a low water crossover from the anode to the cathode is necessary to avoid flooding of the cathode. The dependence of water permeation on the membrane thickness is weak. Only a small decrease in water permeation is observed for the commercial Nafion membranes, whereas the thickness of the recast membranes has no significant influence on the water transport rate. In contrast, the effect of temperature on water permeation is strong. At 65°C, the rates are higher by a factor of 5 compared to those at 25°C. 

X. Ren, T.A. Zawodzinski, and S. Gottesfeld. Water and methanol transport in membranes for direct methanol fuel cells. Abstracts of Papers of the American Chemical Society 217, U490 1999. 

The CO2 is emitted from plantation, methanol plant construction, methanol transport, natural gas power plant and the total CO2 emitted is 2.88 x 10 tons per annum. The effect of CO2 mitigation by replacing natural gas with biomass is estimated to be 1.68 X 10 tons per aimum. Therefore, their difference is the net mitigation of CO2, which is 1.39 X 10 ton per annum. This means a reduction of about 2.4 tons of carbon per hectare a year. It indicates that about 2.4 tons of carbon can be substituted for natural gas by energy plantation using biomass with a fixation ability of about 5 tons carbon per hectare per annum. In other words, about 379,000 t-C (on carbon basis) can be avoided as an alternative of natural gas per annum. 

Even more important is the fact that most PEM materials (see below) are also quite permeable for water and methanol. Thus, thin membranes lead to substantial transport of these molecules from the anode side to the cathode (e. g., [25-29]). The permeation of methanol in the DMFC is undesirable for the obvious reason that it reduces the cell power ( mixed potential formation ), because no electrical work is generated in a cathodic oxidation reaction. Furthermore methanol on the cathode is unfavorable because it can block adsorption sites needed for the oxygen reduction reaction. The presence of methanol may even alter the rate constant of the oxygen reduction reaction. A typical solution to the problem of methanol transport is the use of dilute aqueous solutions of methanol, which assures almost complete oxidation when the anodic catalyst loading is high enough [30],... 

Finally, the nse of Pt-Rn catalysts snpported on a carbon aerogel as an anode for DMFC has been reported by Dn and co-workers [90]. The total metal loading was fixed to 20 wt%, and the Pt/Rn atomic ratio varied from 3 1 to 1 1. Metal particles were dispersed on the snpport nniformly, with a mean size of 3 nm. These anthors fonnd that with mnch less metal loading on the carbon aerogel, the membrane electrode assemblies had the same power density as that of commercial catalysts. This was attributed to the mesopore texture of the carbon aerogel, which facilitated methanol transportation in the electrode. 

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... 

Whereas uniform distribution of water within the membrane is desired, the permeability of the material to reactants (i.e., hydrogen or methanol and oxygen) has to be low to prevent direct chemical reaction between fuel and oxidant, which may lead to hotspots and, eventually, pinhole formation. Methanol permeability is a major challenge in the direct methanol fuel cell (DMFC), largely because methanol transport is strongly correlated with water transport, leading to significant penalties in fuel efficiency and poor cathode performance [189]. 

Xu F, Innocenti C, Bonnet B, Jones DJ, Roziere J (2005) Chemical modification of perfluor-osulfonated membranes with pyrrole for fuel cell application preparation, characterization and methanol transport. Fuel Cells 5 398—405... 

Tiicoli V (1998) Proton and methanol transport in poly(perfluorosulfonate) membranes containing Cs and H cations. J Electrochem Soc 145 3798-3801... 

Kim DS, Park HB, Rhim JW, Lee YM (2005) Proton ctmdnctivity and methanol transport behavior of cross-linked PVA/PAA/silica hybrid mtanbranes. Solid State Ion 176 117-126... 

Kim DS, Park IC, Cho HI, Kim DH, Moon GY, Lee HK, Rhim JW (2009) Effect of organo clay content on proton conductivity and methanol transport through crosslinked PVA hybrid membrane for direct methanol fuel cell. J Ind Eng Chem 15 265-269... 

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