Scientists distinguished between synthetic method and analytical method for high pressure VLE measurement. In the former method, a mixture of known composition prepared and its behaviour is observed as a function of temperature and pressure, the problem of analysing the equilibrium compositions is thereby avoided.
A simpler classification is based on whether either the liquid or vapour, or both, are circulated through equilibrium chamber. If circulation takes place it is classified as dynamic or flow method, otherwise it is a static method.
It consists of the following:
1. An equilibrium cell in which the vapour and liquid phases of the mixture are in equilibrium.
2. An environment that controls the temperature of the equilibrium cell, e.g. air bath, oil or water bath etc.
3. A procedure for agitating and mixing the cell contents, e.g. stirrer.
4. A method for sampling the liquid and vapour phases.
5. A means for accurate analysis of the withdrawn samples.
6. Pressure and temperature measuring devices.