Simultaneous phase behaviour, elemental composition and density measurement using X-ray imaging

Over the past 10 years, we have been developing an X-ray view cell apparatus to observe the phase behaviour of complex organic fluids, and to determine individual phase densities and compositions, without sampling, over a broad range of temperatures and pressures. Earlier this year we achieved our goal of duplicating the key features of the now classical Cailletet cell where volume, pressure and temperature can be varied independently. The new apparatus makes use of transmitted X-rays instead of visible light, as the basis for phase detection and a stainless steel bellows rather than a mercury column is used to vary cell volume. Thus, the new apparatus is not restricted to fluids that are transparent to visible light, and it can operate over a broader temperature range than the classical technique. Another feature of the cell is that gas can be added continually while an experiment is in progress. With the current configuration, the upper operating bounds for pressure and temperature are 28 MPa and 725 K, respectively and volume can be varied within the interval 10 cm3 to 175 cm3. Phase boundaries are resolved to within ±2 K and ±0.02 MPa at these extreme conditions. The standard derivations of the elemental composition and density measurements are ±1 wt.% for carbon and hydrogen, ±0.3 wt.% for sulfur and ±12 kg/m3 for density, respectively. The success of this approach relies upon the coupling of state of the art apparatus construction techniques with video image processing technology.