Critical Properties and Vapor Pressures of Some Ethers and Heterocyclic Compounds.

Abstract

plus remain reasonably constant when the concentration of the heptanes-plus fraction is decreased by a factor of approximately 2. The effect of a decrease in the heptanesplus fraction at the concentrations studied serves mainly to extend the pressure region over which these ratios are defined. This trend could be completely reversed with a continued decrease in the heptanes-plus concentration. Decreasing the amount of the heptanes-plus fraction in this system does have a slight effect on the equilibrium ratios of the intermediate components, ethane through hexanes; the net effect is a small increase at the higher pressures.

Thermodynamic properties of pyridine—I. Vapor pressures, high-temperature heat capacities, densities, critical properties, derived thermodynamic functions, vibrational assignment, and derivation of recommended values

“…The various forms of the Wagner equation all satisfy the Waring criterion, (41) with an inflection point observed in a plot of ln(p/p c ) against (1/T ) near T r =0.86. Differences between vapor pressures calculated with the (2.5, 5) form and the (2, 4) form of the Wagner equation at temperatures above T=430 K reach a maximum of 0.9 per cent near T=570 K. The experimental vapor pressures in this temperature region reported by Kobe et al (4) are not of sufficient precision to determine which form is preferred at high reduced temperatures. This is shown in figure 7, where the values reported by Kobe et al (4) are shown relative to values calculated with the fitted (2.5, 5) and (2, 4) forms.…”

“…(22) where T r =T/T c . The designation (2,4) refers to the exponents of the last two terms in the equation. Previously, the (2.5, 5) form, as recommended by Ambrose, (24) was used exclusively by this research group.…”

“…However, excluding the critical-temperature determinations and relatively low-precision vapor-pressure studies by Kobe et al, (4) none of the measurements was made at temperatures exceeding the normal boiling temperature. The results of the present research provide the information required to derive these properties to near T c , i.e., into the temperature and pressure range typical of petroleum processing conditions.…”

Thermodynamic properties of pyridine—II. Comparisons of new recommended values with the literature

“…(2) Figure 5 shows the deviations of high-temperature vapor pressure values reported by Kobe et al (23) from the values selected in this research. Deviations of the values selected by Das et al (2) and the new ebulliometric values of this research (1) are included in the figure.…”

“…Herington and Martin, (17) and Konakbaeva et al (22) Measurement results by Kobe et al (23) were used for pressures above 0.3 MPa. The fitted Cox equation was not constrained for temperatures outside the experimental ranges.…”