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Computer Driven Dynamic Apparatus

Computer Driven Dynamic Apparatus for the Measurement of Vapor-Liquid Equilibrium Data

Distillation is by far the most important industrial separation process. It offers several advantages, e.g. in distillation processes energy is used to create a system of fluid phases (liquid, vapor) that can easily be transported. Finally, distillation is based on vapor-liquid equilibrium (VLE) which can reliably be predicted by group contribution methods such as original UNIFAC and Modified UNIFAC (Dortmund). Since experimental data are often missing or of poor quality, group contribution methods have become increasingly valuable. But the basis for successful fit is formed by a sufficient number of VLE-data.

Measurement of VLE

Starting in 1998/99 a computer - operated dynamic apparatus was developed. It can be used for the measurement of binary VLE data up to atmospheric pressure, activity coefficients at infinite dilution and pure component vapor pressure data.

A scheme of the apparatus is shown in the following Figure.

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Fig. 1 Scheme of the dynamic apparatus for the measurement of VLE-data
(Specifications: temperature range: -20 – 220°C, pressure range: 35 – 1310 mbar)

picture of the device

The temperature is measured with a platinum resistance thermometer (Conatex Pt 100) inside the cell and the pressure is measured at the outlet of the apparatus by a pressure sensor (Druck RPT 301).
The ebulliometer has to be filled manually with purified components. All other operations are automatically performed by the computer.
The measurement is controlled with the help of the Windows program "Computer-Aided-Ebulliometer-Measuring-System 1.0" and an electronic valve control. An automatic pressure program for the measurements of VLE-data up to atmospheric pressure is possible. The control program is connected to the pure component data bank of the Dortmund Data Bank (DDB-PCP).
The directly obtained data are feed composition zi pressure P and temperature T of the system.
Typical results are shown in the figures below.

 

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Fig.2 Directly obtained P,T-curves for the system ethanol (1) + water (2)

 

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Fig. 3 Isobaric T, x-curves for the system ethanol (1) + water (2)

The new VLE-data are used to derive appropriate parameters for the group contribution methods original UNIFAC and mod. UNIFAC (Do). With the help of these data and the DDB - database a revision of parameters for existing groups and the introduction of a new groups is in progress.

The main window of the control program contains the required input data and the current status of the measurement.

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