MEASUREMENT OF THE HIGH-PRESSURE-HIGH-TEMPERATURE FLUID-PHASE BEHAVIOR OF THE SYSTEMS CF4+H2O, CF4+H2O+NACL, CHF3+H2O, AND CHF3+H2O+NACL

The high-pressure-high-temperature fluid phase behavior of model syste ms encountered in supercritical water oxidation processes (SCWO) for t he destruction of CFCs has been determined experimentally. For that pu rpose, the following systems have been selected: CF4 + H2O, CF4 + H2O + NaCl, CHF3 + H2O, and CHF3 + H2O + NaCl. The experiments were conduc ted in the temperature range of 580 < T (K) < 673 and in the pressure range of 20 < p (MPa) < 200. Gas-gas equilibria were measured for vari ous water-rich mixtures in a high-temperature autoclave, which was equ ipped with sapphire windows to enable visual observation of the phase transitions. As salts are formed during the destruction of organics co mprising hetero-atoms by SCWO, the influence of addition of small amou nts of NaCl on the fluid phase behavior of the binaries was also inves tigated. Unfortunately, due to limitations of the experimental equipme nt with respect to the maximum allowable temperature (673 K), the comp lete composition ranges of CF4 and CHF3 could not be covered. The expe rimental results revealed that both binary systems exhibit type-m flui d phase behavior according to the classification of Van Konynenburg an d Scott [P.H. van Konynenburg, R.L. Scott, Philos. Trans. A 298 (1442) (1980) 495-540]. Although only two mixture critical points could be m easured in the system CF4 + H2O, the path of the critical locus sugges ts that this system exhibits gas-gas immiscibility of the second kind. In comparison with the binary system CF4 + H2O, the immiscibility reg ion of the binary system CHF3 + H2O is located at significantly lower temperatures. Addition of NaCl shifts the immiscibility regions toward s higher temperatures compared to the corresponding binary systems. (C ) 1998 Elsevier Science B.V. All rights reserved.