A8 Practice For Conversion Of Observed Vapor Temperature To Atmospheric Equivalent


A8.1 Scope

A8.1.1 This practice is for conversion of the actual distillation temperature obtained at sub-ambient pressure to AET corresponding to the equivalent boiling point at atmospheric pressure, 101.3 kPa (760 mm Hg), by means of equations derived by Maxwell and Bonnell.10

A8.2 Significance and Use

A8.2.1 Final data on atmospheric equivalent temperatures are to be obtained by computation. Tables 3-5 are provided only as a guide in estimating the AET during distillation.

A8.3 Calculation

A8.3.1 Convert observed vapor temperature to atmospheric equivalent temperature using Eq A8.1:

10 Maxwell and Bonnell, Industrial Engineering Chemistry, Vol 49, 1957, p. 1187.


AET = atmospheric equivalent temperature, °C, and T = observed vapor temperature, °C.

= 5.143222 - 0.972546 log10 P A = 2579.329 - 95.76 log10 P (A8.2)


P = operating pressure, kPa, (operating pressure $0.266 kPa), or

= 5.994295 - 0.972546 log10 P A = 2663.129 - 95.76 log10 P (A8.3)


P = operating pressure, mm Hg (operating pressure $2 mm

A8.3.2 The equations are correct only for fractions that have a Watson ^-factor of 12.0 ± 0.2. The ^-factor shall be assumed to be 12 and any effect of ^-factor ignored unless there is mutual agreement to the contrary.

A8.3.3 If correction is required, calculate the ^-factor using Eq A8.4:


B = mean average boiling point, °C, and D = relative density at 15°C.

A8.3.3.1 By custom, either the mid vapor temperature of the fraction or the mid-point of a gas chromatographic distillation of the fraction can be used for the mean average boiling point. In either case the method must be specified.

A8.3.3.2 An estimate of the ^-factor can be made using Fig. A8.1.

A8.3.4 Calculate the correction to be applied to the AET using Eq A8.5:


Pa = atmospheric pressure, kPa (mm Hg), and Po = observed pressure, kPa (mm Hg).

A8.3.4.1 An estimate of the correction can be made using Fig. A8.2.

Watson Uop Factor
FIG. A8.1 Watson Characterization Factor of Petroleum Fractions

Observed vapor pressure

FIG. A8.2 Boiling Point Corrections for K-Factor

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