Methanol concentration

Prepare a single multicomponent working standard from the stock standards by making appropriate dilutions with methanol. Concentrations in the working standards should be at such a level that a 20- xL sample added to 100 mL of water gives a calibration standard whose response for each trihalomethane is within 25% of that for the samples to be analyzed. 

Density and refractive index are nearly linear functions of formaldehyde and methanol concentration. Based on available data (16—19), the density may be expressed ia g/cm by the following approximation ... 

In methanol—formaldehyde—water solutions, increasing the concentration of either methanol or formaldehyde reduces the volatility of the other. Vapor-hquid-equihbrium data (8,27) for several methanolic formaldehyde solutions ate given in Table 2. The flash point varies with composition, decreasing from 83 to 60°C as the formaldehyde and methanol concentrations increase (17,18). 

Ethylene glycol can be produced by an electrohydrodimerization of formaldehyde (16). The process has a number of variables necessary for optimum current efficiency including pH, electrolyte, temperature, methanol concentration, electrode materials, and cell design. Other methods include production of valuable oxidized materials at the electrochemical cell s anode simultaneous with formation of glycol at the cathode (17). The compound formed at the anode maybe used for commercial value direcdy, or coupled as an oxidant in a separate process. 

This program helps calculate the rate of methanol formation in mol/m s at any specified temperature, and at different hydrogen, carbon monoxide and methanol concentrations. This simulates the working of a perfectly mixed CSTR specified at discharge condition, which is the same as these conditions are inside the reactor at steady-state operation. Corresponding feed compositions and volumetric rates can be calculated from simple material balances. 

Methanol is frequently used to inhibit hydrate formation in natural gas so we have included information on the effects of methanol on liquid phase equilibria. Shariat, Moshfeghian, and Erbar have used a relatively new equation of state and extensive caleulations to produce interesting results on the effeet of methanol. Their starting assumptions are the gas composition in Table 2, the pipeline pressure/temperature profile in Table 3 and methanol concentrations sufficient to produce a 24°F hydrate-formation-temperature depression. Resulting phase concentrations are shown in Tables 4, 5, and 6. Methanol effects on CO2 and hydrocarbon solubility in liquid water are shown in Figures 3 and 4. 

Gurgel and Grenier s results showed the bed conductivity to increase from 0.14 to 0.17 W/mK as the pressure was raised from 4 mbar (evaporating pressure) to 110 mbar (condensing pressure). The principle reason stated for this small variation is the reduction in the gas conductivity with decreasing pressure (Knudsen effect) in the macropores. The solid grain conductivity varied linearly from 0.61 to 0.65 W/mK as the methanol concentration varied from 0 to 31%. 

In contrast, the alkane chains on the polymeric phase cannot collapse in an environment of water as they are rigidly held in the polymer matrix. Thus, the retention of the solute now continuously falls as the methanol concentration increases as shown in Figure 4. It should be pointed out that if the nature of the solutestationary phase interactions on the surface of a bonded phase is to be examined in a systematic manner with solvents having very high water contents, then a polymeric phase should be used and brush type reversed phases avoided if possible. 

Using the average value for the equilibrium constant, the distribution concentration of the different components of a methanol water mixture were calculated for initial methanol concentrations ranging from zero to 100%v/v. The curves they obtained are shown in Figure 28. The molar refractivities of 11.88 is also in accordance with that expected since the molar refractivity s of water and methanol are 3.72 and 8.28 respectively. The refractive index of the associate of 1.3502 is, as would be expected, higher than that of either water or methanol. 

Katz et al. also plotted the distribution coefficient of n-pentanol, benzonitrile and vinyl acetate against the concentration of unassociated methanol in the solvent mixture and the results are shown in Figure 32. It is seen that the distribution coefficient of all three solutes is predominantly controlled by the amount of unassociated methanol in the aqueous solvent mixture. In addition, the distribution coefficient increases linearly with the concentration of unassociated methanol for all three solutes over the entire concentration range. The same type of curves for anisole and benzene, shown in Figure 33, however, differ considerably. Although the relationship between distribution coefficient and unassociated methanol concentration is approximately linear up to about 50%v/v of unassociated methanol, over the entire range the... 

A low-pressure process has been developed by ICl operating at about 50 atm (700 psi) using a new active copper-based catalyst at 240°C. The synthesis reaction occurs over a bed of heterogeneous catalyst arranged in either sequential adiabatic beds or placed within heat transfer tubes. The reaction is limited by equilibrium, and methanol concentration at the converter s exit rarely exceeds 7%. The converter effluent is cooled to 40°C to condense product methanol, and the unreacted gases are recycled. Crude methanol from the separator contains water and low levels of by-products, which are removed using a two-column distillation system. Figure 5-5 shows the ICl methanol synthesis process. 

Fig. 15. CD-spectra of random (L-Leu0,48, L-Lys0,52) in water-methanol mixtures as a function of methanol concentration at 20 °C and pH 7,0. The insert shows [0]2O8 and —[0]2jo dependent on the methanol content112113 ...

Appropriate. The medium contains a suitable methanol concentration and allows... 

Coelenterazine analogues are easily soluble in methanol like coelenterazine. When methanol is used, however, the methanol concentration in the regeneration mixture should not exceed 5%. If the use of methanol must be avoided, dissolve the coelenterazine analogue in water with the help of a trace amount of 1M NaOH. However, coe-lenterazines in alkaline condition are extremely unstable. Therefore, the solution must be made rapidly in argon atmosphere and added at once to the regeneration mixture containing apoaequorin. 

Fig. 6.3.2 Absorption spectra of Watasenia oxyluciferin (A), coelenterazine (B), and coelenterazine disulfate (C), all in methanol. Concentrations 0.1 mM for B and C undetermined for A.

The solution is illustrated in Fig. 8.15, which shows the equilibrium concentration of methanol for different initial gas mixtures. Note that the maximum methanol concentration occurs for the pure CO + H2 mixture. Hence, in principle, a mixture of just CO and H2 could be used, with minor amounts of CO2, to produce the maximum amount of methanol. However, it is not only the equilibrium constant that matters but also the rate of methanol formation, and one must remember that methanol forms from CO2 not CO. Hence, the rate is proportional to the CO2 pressure and this is why the methanol synthesis is not performed with the simple stoichiometric 3 1 mixture of H2 and CO2 that Eq. (19) suggests. 

Figure 8.15. Outlet equilibrium methanol concentration as function of the inlet mo e fraction ofH2, CO, and COa-Notice that the highest methanol concentration is or a mixture of only Ha and CO at a ratio o...

To extract and evalnate the color pigments from cochineals Dactylopius coccus Costa), a simple method was developed. The procednre is based on the solvent extraction of insect samples nsing methanol and water (65 35, v/v) and a two-level factorial design to optimize the solvent extraction parameters temperature, time, methanol concentration in mixtnre, and yield. For hydrophilic colorants that are more sensitive to temperatnre, water is the solvent of choice. For example, de-aerated water extraction at low temperatnre was applied to separate yellow saffrole and carthamine from saffron (Carthamus tinctorius) florets that contain about 1% yellow saffrole and 0.3% red carthamine. ... 

The exchange current density for methanol oxidation depends on the methanol concentration, i.e. ... 

Without the direct pathway contribution, this equation may either yield an increasing or decreasing current transient, depending on the value of A ox/ dec- If this ratio is larger than 4, i.e., if methanol decomposition is slow compared with CO oxidation, then the current is predicted to increase with time. Experimentally, this simation has been observed for a low methanol concentration and an almost perfect Pt(l 11) electrode [Housmans and Koper, 2003], which both lead to a low methanol decomposition rate. Typically, however, current transients decrease with time, suggesting that the rate... 

Using the colloidal Pt(i t ) + RU c/C catalysts described above, the optimal atomic ratio depends upon methanol concentration, cell temperature, and applied potential, as shown by the Tafel plots recorded with methanol concentrations of 1.0 and 0.1 M at T = 298K (Fig. 11.4) and 318K (Fig. 11.5). Some authors have stated that for potentials between 0.35 and 0.6 V vs. RHE, the slow reaction rate between adsorbed CO and adsorbed OH species must be responsible for the rate of the overall process [Iwasita et al., 2000]. From these results, it can be underlined that, at a given constant potential lower than 0.45-0.5 V vs. RHE, an increase in temperature requires an increase in Ru content to enhance the rate of methanol oxidation, and that, at a given constant potential greater than 0.5 V vs. RHE, an increase in temperature requites a decrease in Ru content to enhance the rate of methanol oxidation. 

Such bimetallic alloys display higher tolerance to the presence of methanol, as shown in Fig. 11.12, where Pt-Cr/C is compared with Pt/C. However, an increase in alcohol concentration leads to a decrease in the tolerance of the catalyst [Koffi et al., 2005 Coutanceau et ah, 2006]. Low power densities are currently obtained in DMFCs working at low temperature [Hogarth and Ralph, 2002] because it is difficult to activate the oxidation reaction of the alcohol and the reduction reaction of molecular oxygen at room temperature. To counterbalance the loss of performance of the cell due to low reaction rates, the membrane thickness can be reduced in order to increase its conductance [Shen et al., 2004]. As a result, methanol crossover is strongly increased. This could be detrimental to the fuel cell s electrical performance, as methanol acts as a poison for conventional Pt-based catalysts present in fuel cell cathodes, especially in the case of mini or micro fuel cell applications, where high methanol concentrations are required (5-10 M). 

Evidently, the increase of methanol concentration in the reaction mixture above the molar ratio MeOH SA = 20 has no effect on the attainable conversions. On the other hand, decrease of the methanol concentration below this level has a very detrimental effect. It is probably connected with the influence of the reaction mixture composition on the polymer catalyst. 

Houpert, Y., Tarallo, P., and Siest, G., Amino acid analysis by ion-exchange chromatography using a lithium elution gradient. Influence of methanol concentration and sample pH, /. Chromatogr., 115, 33, 1975. 

Charge measurements, as mentioned above, were also performed using the porous Pt electrodes required by the on-line MS technique. At low methanol concentrations (10 2 M), the charge ratio QaJQm, near 1 indicates that (C,0, H) must be the predominant adsorbate composition [14,47], This result is in good agreement with that of Heitbaum and co-workers [15] who used Eq. 1.2 to determine the number of electrons, n, per C02 produced from methanol adsorbate. They found for n a value of 3, which would be in agreement with reactions 2.1 or 2.2 for methanol adsorption. 

The ratio QaJQ0X varies between 1 and 2 depending on methanol concentration and degree of coverage. In principle this can be interpreted in terms of a mixture of particles of composition (C, O) and (C, O, H). The nature of the Pt surface seems to influence also the charge ratio. In principle, the following configurations could be expected ... 

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