Abstract
The average boiling point of oil fractions with narrow boiling ranges or pseudo-components is an important parameter in thermodynamic calculations in the fields of process design and environmental protection. The present work provides an experimental approach, involving a method based on the thermogravimetric analysis, for determination of the pressure dependence of average boiling points (or in other words for determination of “the vapour pressure curve corresponding to average boiling points”) of oil fractions with narrow boiling ranges, pre-prepared by distillation. This method can be used for determination of the atmospheric average boiling points (corresponding to atmospheric pressure) of thermally unstable fractions from the pressure dependence curves, obtained from the tests conducted at lower pressures. The method uses the principle of ASTM E1782 “Standard Test Method for Determining Vapor Pressure by Thermal Analysis”, where the material is vaporised at pre-determined pressure from a hermetically sealed capsule through a pinhole using a constant heating rate experiment. The accuracy of the method was evaluated on the basis of the average boiling point values of narrow boiling ranges fractions determined by rectification both at atmospheric pressure and in vacuum (determined as the arithmetic mean of the lower and upper temperature limits of the fraction). The pressure dependence curves of the average boiling points, formed here on the basis of average boiling points obtained in the pressure range from 5 kPa to atmospheric pressure, can be reliably described by the integrated Clausius-Clapeyron equation. To increase the accuracy in determining the atmospheric average boiling points of thermally unstable fractions, obtained in extrapolation from the Clausius-Clapeyron curve of the average boiling points in the tests conducted at lower pressures, a higher number of tests, on the basis of which to conduct the extrapolation, is desirable.
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