Share NOTE: This project has been completed and all data generated has been added to the 801 Member Database. Any additional experimental work in this area will be undertaken under Project 801. Project Description Critical properties are exceedingly important as they are used to estimate such properties as departure functions, liquid density, viscosity, heat capacity, heat of vaporization, thermal conductivity, diffusion coefficients, and surface tension. Critical properties are also essential for correlation of vapor pressure and liquid density over the entire saturated liquid range. The estimation methods commonly used for critical properties (e.g., Lydersen's method) do not give reliable results for compounds which are unstable or contain multiple function groups. This project was focused on the experimental determination of the critical point (temperature, pressure, density, volume) of pure compounds important to the chemical processing industries for which reliable data were lacking. Since many of these compounds were unstable at their critical temperature the development of new rapid methods of measurement was essential. Project Objective The approach to the critical state is time-dependent and is affected by gravity. However, a close approach can be reached within a few seconds, if an ultra-rapid heating source is employed and gravity becomes less important if a shallow sample can be used. Thus, to measure critical properties of an unstable compound, a small sample in a rapid heating device, with fast temperature and pressure sensors, is needed. To address these requirement project work involved use of a rapidly heated sealed-ampoule apparatus and also a low residence time flow apparatus.