Effect of methanol concentration

Which reaction channel is followed depends on the availability of neighboring free places. This could explain the effect of methanol concentration on adsorbate composition. It has been observed that the initial rate of adsorption is strongly enhanced by increasing methanol concentration [14]. From the adsorption steps given above, the first one, Eq. (2.7), is directly affected by the bulk concentration. At high methanol concentrations the Pt surface becomes very quickly covered with species like CH2OH or CHOH. Further reaction to a more stable state such as COH is inhibited because of the lack of free adjacent sites. Under these conditions CO should be formed with a greater probability. 

Figure 2. Effect of Methanol concentration on reaction rate. Catalyst Nil2 Bu3P,LiI. Pressure 1000 psig. T=180°, Solvents AcOH and AcOMe as indicated.

TABLE 4 Effect of Methanol Concentration on the Chiral Resolution of Amino Acids on Cu(II)-L-Hydroxypropyl)methyl-Silica Gel... 

FIGURE 5 Effect of methanol concentration on the chiral resolution of ergot alkaloid on terguride-based CSP using 0.05 M ammonium acetate as the mobile phase at pH 7.2 (A),... 

Figure 6.6 Effect of methanol concentration in the mobile phase on the retention time of metformin and phenformin using varied concentrations of methanol with 40 mM HFBA [46].

Table 6 Effect of Methanol Concentration on the Esterification of Racemic 3-Benzoylthio-2-Methylpropionic Acid (19)...

Smith and Sanagi reported the packed-column SFC of benzodiazepines (diazepam, lorazepam, lormetazepam, nordazepam, temazepam, es-trazolam, chlordiazepoxide, triazolam, cloxazolam, ketazolam, and lopra-zolam) with methanol-modified carbon dioxide as the mobile phase [29]. The effect of methanol concentration on separation was studied on three columns polystyrene-divinylbenzene, octadecylsilane, and cyanopropyl-bonded silica columns. They concluded that proportion of methanol has marked effect on the selectivity of compounds containing different functional groups. 

Fig. 7. Effect of methanol concentration on polymerization of propene by a-TiCl3/ AlEt3 (initial rates) [109],...

The methanol extract of soil is diluted with water to increase the affinity of the solute for the C-18 sorbent. Figure 7.6 shows the effect of methanol concentration on the sorption capacity of atrazine and other triazine herbicides for C-18. At concentrations of methanol less than 10%, the capacity of the sorbent is more than adequate to isolate the atrazine and alachlor from the methanol/water phase. This procedure is many times simpler than evaporating the methanol however, methanol evaporation may be necessary if more water-soluble compounds are present. 

Pigure 7.6. Effect of methanol concentration on capacity of atrazine, deethylatrazine, and deisopropylatrazine for a C-18 sorbent for a 100-mL sample. [Mills and Thurman (1992) published with permission.]... 

Distilled water. Isooctane, and methanol were used as aging media. Isooctane and methanol were reagent grade and were used as received without further purification. Isooctane was selected as a relatively Inert fluid to study the effect of methanol concentration. 

The effects of methanol concentration were also evaluated upon the performance of this sample, as illustrated in Fig. 1.77. It is evident that better... 

Fig. 1.77 Effect of methanol concentration upon the performance of a 1 x 1 size direct methanol fuel cell (USC-MEA 7) containing a PSSA-PVDF membrane in a direct methanol fuel cell.

The effects of methanol concentration upon the performance was also investigated at the larger cell size, as illustrated in Fig. 1.99. and displayed trends similar to that observed with the smaller cell sizes. It is evident that better performance can be realized at higher current densities when greater methanol concentration is used, and is explained by enhanced mass transfer of the methanol to the electrode surface. The inferiority of the 2.0 M methanol solution at lower current densities can be ascribed to increased methanoP crossover compared to 1.0 M methanol. 

Fig. 1.99 Effect of methanol concentration (1.0 M and 2.0 M Methanol) upon the performance of a direct methanol fuel utilizing a PSSA-PVDF membrane at 60 °C (12 L min." and 20 psig oxygen).

Dohle et al. presented a one-dimensional model for the vapor-feed DMFC, including a description of the methanol crossover [158]. The effects of methanol concentration on the cell performance were studied. Scott et al. also developed several simplified single-phase models to study transport and electrochemical processes in liquid-feed DMFC and showed that the cell performance is limited by the slow diffusion of methanol in the liquid [13, 159-171]. Siebke et al. presented a ID mathematical model and a numerical simulation to explore the influence of different physical and electrochemical phenomena in the MEA of the liquid feed DMFC [162]. Dohle et al. presented a model to describe the heat and the power management of a DMFC system [163]. 

FIGURE 19.4 Effect of methanol concentration on the digestion of myoglobin in human plasma (w = 3). [Reprinted from Li et al. (2009) with permission of Rapid... 

Hg.3. Effect of methanol concentration on acyltransferase activity of lipolytic acyl hydrolase. Amounts of free fatty acids (circles) and fatty acid methyl esters formed (triangles) or lyso-phosphatidylcholine deacylated (squares) in 10-min incubations at 2S°C are given as percentage of substrate (lysophosphatidylcholine) added. (Reproduced from Galliard and Dennis, 1974, by permission.)... 

Effect of Methanol Concentration by Using Air as Oxidant 1.1. Single Cell Results... 

Figure 10. Effect of methanol concentration on fuel energy density for a DMFC single cell at 60 C using air as oxidant and methanol as fuel with various concentrations.

Figure 9 Effect of methanol concentration of the eluent on the retention of proteins on silica-bound Fe(lll)-IDA. Eluent, 25 mM phosphate buffer pH 6.0, containing 0.15 M ammonium sulfate and methanol at different concentrations. Symbols are as in Fig. 4. (From Ref. 31.)...

Figure 9.6 The effect of methanol concentration on the chiral resolution of phenoxy acid herbicides, using 200 mM sodium phosphate sodium acetate buffers (pH 6.5) containing...

The fuel feed to the anode is controlled, as mentioned in Section 6.2.4 above, so that at times of low current there is no excess of methanol. Clearly, the lower the methanol concentration at the anode, the lower it will be in the electrolyte, and hence at the cathode. See Figure 6.4. The effect of methanol concentration on DMFC fuel cell performance has been extensively studied, for example, in Scott et al., 1999b and Dohle et al., 2002. Mathematical models have also been developed, as in, for example, Dohle et al., 2000. The conclusion is that the concentration should always be about 1M, though a more accurate optimum will need to be found for every type of ceU under all conditions. 

The effect of methanol concentration was initially probed using complexes 3 and 6 (26). In the presence of 1.41 M methanol, current efficiencies of approximately 74% were obtained for both catalysts. This value was significantly higher than the 43% obtained at a methanol concentration of 0.35 M. This increase in current efficiency was attributed to improved electron... 

Fig. 14.6 The effect of methanol concentration and membrane thickness on DMFC performance curves. Methanol crossover fluxes are given relative to Nafion 117 (215 um) at 1.0 M and 60°C. Crossover is expressed as a relative fraction of the methanol flux observed for a Nafion 117 membrane at the fuel cell operation conditions with Nafion 117 and 1.0 M methanol...

Fig. 16.5 Comparison between the porefilling membrane (CLPE-ATBS) and the Nafion 117 membrane effect of methanol concentration on change in membrane area ratio at 25 °C...

The effect of methanol concentration on the initial rate of reaction showed that the rate decreases with increase in methanol concentration as shown in Fig 2.11. However, in these experiments, a change in methanol concentration resulted in a change in acetic acid concentration as the volume of liquid phase was kept constant. Since, the densities of methanol and acetic acid are different, a decrease in the molar concentration of acetic acid was more significant and not linearly proportional to increase in methanol concentration. Therefore, the rate was found to decrease as a result of changes in both methanol and acetic acid concentration (see data in Table 2.4). 

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