Vapour pressure data

The vapour pressure of a flammable substanee also provides an indieation of how easily the material will volatilize to produee flammable vapours the higher the vapour pressure, the greater the risk. Lists of vapour pressures usually eontain data obtained under differing eonditions but inspeetion of boiling points (when the vapour pressure equals atmospherie pressure) gives a first approximation of the ease with whieh substanees volatilize. Table 6.1 therefore ineludes both boiling point and vapour pressure data. 

Equation (18) was applied by Margules (1895) to calculate the heats of admixture of water and alcohol from the vapour-pressure data of Regnault the results agreed with the direct determinations of Winkelmann (1873). 

The environmental behaviour of organotins is strongly influeneed by partition eoeffieients. Based upon the water solubihty and vapour pressure data, BUSES estimates the dimensionless Henry s law eonstant (the air/water partition eoeffieient). As indieated in Table 1, there is a wide variability in the air/water partition eoeffieients for the six substanees. 

Ohe, S. (1976) Computer Aided Data Book of Vapour Pressure (Data Book Publishing Co., Japan). 

Some vapour pressure data at 20°C are reported in Table 1.3. In Fig. 1.1, the temperature dependence of vapour pressure of some substances is reported. A special attention is to be devoted to water vapour pressure which is very high. 

Ashby also constructed sintering maps in which x/a is plotted versus the homologous temperature T/Tm where Tm is the melting point. These maps, which must be drawn for a given initial radius of the sintering particles, use the relevant diffusion and vapour pressure data. Isochrones connect values of x/a which can be achieved in a fixed time of annealing as a function of the homologous temperature. 

The vapour pressure data and the equilibrium data are plotted in Figures llu and llv. (a) Using aPH = Pp/P ... 

Of special interest in stable isotope geochemistry are evaporation-condensation processes, because differences in the vapour pressures of isotopic compounds lead to significant isotope fractionations. For example, from the vapour pressure data for water given in Table 1.2, it is evident that the lighter molecnlar species are preferentially enriched in the vaponr phase, the extent depending upon the temperature. Such an isotopic separation process can be treated theoretically in terms of fractional distillation or condensation under equilibrium conditions as is expressed by the Rayleigh (1896) equation. For a condensation process, this equation is... 

The r, N curve for the adsorption of pyridine from an aqueous solution at a water-uncharged mercury interface. The surface tension measurements employed are those found by Gouy Ann. de Ghimie et de Physique, vill. ix. 130, 1906), whilst the pyridine activities are derived from the vapour pressure data of Zadwiski... 

The average value of q can be calculated using equations (6.2) or (6.3) above and adiabatic experimental data which should be corrected to a thermal inertia of 1 (see Annex 2). The temperatures corresponding to the relief pressure and maximum accumulated pressure are obtained from vapour pressure data. The temperature difference between the relief pressure and the maximum pressure, , can also be obtained from experimental data, as described in A2.4. 

The vapour pressure data (from a physical properties database capable of carrying out multi-component estimations) has been plotted as a straight line on Figure 6.4. This allows the temperatures at the relief pressure and maximum pressure to be read off. The rates of temperature rise at these pressures can also be read off. These values are given in Table 6.2. 

It is also important to correct the raw vapour pressure data for any pad gas which was present in the test cell. This can be done by subtracting the partial pressure of any non-condensible pad gas which was present in the test cell, to obtain the vapour pressure (see A2.7.1). Because pressure transducers may not be very accurate at the bottom end of their range, it is advisable to vent the test cell to atmosphere, once it is filledand before sealing it and heating to the initial runaway temperature, so that a reliable initial pad gas pressure is known. (This may not always be compatible with the desire to simulate the runaway scenario within the test.) An alternative is to evacuate both test cell and containment vessel before the reactants are added so that there is no pad gas and no correction is needed,... 

This section presents a method for correcting pressure data measured in closed system tests to remove the partial pressure of pad gas. The method is required for vapour pressure systems. Vapour pressure data obtained during tempering in an open test do not require to be corrected for pad gas. 

Note that, if the reacting system has a wide boiling range, the measured vapour pressure data will be different to that for the relieving reactor. The composition for the relieving reactor will change due to the preferential vaporisation of the most volatile component(s), but this will not be the case for the closed calorimetric test. 

A plot of vapour pressure data on log pressure versus 1 /temperature axes. This gives a straight line for vapour pressure systems. 

From vapour pressure data, the vapour temperature = 338 K and the molecular weight of xylene = 106 kg/kmol. 

The above equations are variously labelled as Clausius-Clapeyron equations. Subject to the satisfactory nature of the assumptions made, a plot (Figure 26.1(a)) of the variation of the natural logarithm of the vapour pressure, In(P/P°), over a liquid measured at various temperatures against the reciprocal of temperature (1 /T) should be linear and have a gradient equal to — Avap H°/R so provides a means of measuring Avap H° for a variety of liquids (Figure 26.1(b)). Also from vapour pressure data for solids at two or more different temperatures one can measure AsubH°. 

As was pointed out earlier, molecular distillation is normally used to fractionate mixtures of components of very low volatility. It is proposed that a supercritical fractionation process, as schematically shown in figure 6, can be used to produce fractions superior to that of molecular distillation. In order to test this, a molecular distillation model must be used. As a first approximation, the molecular distillation of high molecular weight alkanes is viewed as a simple flash. The vapour pressure data of Kudchadker et al[10] was used in the flash calculations. 

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