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 apparatu s to observe the phase behaviour of complex organic fluids, and to determin e individual phase densities and compositions, without sampling, over a bro ad range of temperatures and pressures. Earlier this year we achieved our g oal of duplicating the key features of the now classical. Cailletet cell wh ere volume, pressure and temperature can be varied independently. The new a pparatus makes use of transmitted X-rays instead of visible light, as the b asis for phase detection and a stainless steel bellows rather than a mercur y column is used to vary cell volume. Thus, the new apparatus is not restri cted to fluids that are transparent to visible light, and it can operate ov er a broader temperature range than the classical technique. Another featur e of the cell is that gas can be added continually while an experiment is i n 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 cm(3) to 175 cm(3). Phase boundaries are r esolved to within +/-2 K and +/-0.02 MPa at these extreme conditions. The s tandard derivations of the elemental composition and density measurements a re +/-1 wt% for carbon and hydrogen, +/-0.3 wt.% for sulfur and +/-12 kg/m( 3) for density, respectively. The success of this approach relies upon the coupling of state of the art apparatus construction techniques with video i mage processing technology. (C) 1999 Elsevier Science B.V. All rights reser ved.