メタノール-水, イソプロパノール-水系の混合熱, 液熱容量およびエンタルピー

濃度線図

抄録

The measurements of heat of mixing and liquid heat capacity at various tempratures and concentrations were performed for the systems, methanol-water and iso-propanol-water, at 1 atm. The object of the experiments was to obtain the basic data available for constructing enthalpyconcentration charts and for checking thermodynamic consistency of vapor-liquid equilibrium data at various pressures which will be reported in another paper.
New methods were adopted for the measurements, especially for the measurement of exothemic mixing and heat capacity. Experimental data obtaind are given in Figures 4, 5, 7 and 8, and Tables 1, 2, 5 and 6, and smoothed values, in Tables 3, 4, 7 and 8. The values of heat of mixing for iso-propanol-water system at temperatures other than 20°C, given in Table 8, were calculated from the values of heat of mixing at 20°C and the smoothed values of heat capacity for the system. The values of heat capacity of pure alcohols were somewhat higher than those of I.C.T., but the value for iso-propanol at 50°C was lower. The plots of expansion factor vs. heat capacity were made to check the applicability of Eq.(1), derived by Chow and Bright as a general correlation for liquid of a pure component. Figure 6 shows that the equation mostly holds good not only for pure alcohols but also for the mixtures of alcohols and water at high alcohol concentration, especially at higher temperatures. The poor correlation of Eq.(1) at low concentration may be due to some peculiar properties of water.
Enthalpy-concentration charts for the two systems at 1atm. were constructed on molal units by the use of the data obtained from this experiment and of other properties from the literature. Figures 10 and 11 show the charts, and Tables 10 and 11 give the calculated values, the datum level for the enthalpies being chosen as pure liquids at 0°C and 1 atm.
Using these charts, comparison was made between the numbers of the theoretical plates of a distillation column by the Ponchon and the McCabe methods, and the effect of heat loss from column wall on the number of theoretical plates of the Ponchon method was studied. For alcoholwater systems the McCabe method always gives fewer number of plates than the Ponchon method. Figure 11 shows the comparison between the results by these two methods applied to the methanolwater system.