Measurement of the high-pressure-high-temperature fluid phase behavior of the systems CF4+H2O, CF4+H2O+NaCl, CHF3+H2O, and CHF3+H2O+NaCl

摘要

The high-pressure-high-temperature fluid phase behavior of model systems encountered in supercritical water oxidation processes (SCWO) for the destruction of CFCs has been determined experimentally. For that purpose, the following systems have been selected: CF4 + H2O, CF4 + H2O + NaCl, CHF3 + H2O, and CHF3 + H2O + NaCl. The experiments were conducted 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 various water-rich mixtures in a high-temperature autoclave, which was equipped with sapphire windows to enable visual observation of the phase transitions. As salts are formed during the destruction of organics comprising hetero-atoms by SCWO, the influence of addition of small amounts of NaCl on the fluid phase behavior of the binaries was also investigated. Unfortunately, due to limitations of the experimental equipment with respect to the maximum allowable temperature (673 K), the complete composition ranges of CF4 and CHF3 could not be covered. The experimental results revealed that both binary systems exhibit type-m fluid phase behavior according to the classification of Van Konynenburg and Scott [P.H. van Konynenburg, R.L. Scott, Philos. Trans. A 298 (1442) (1980) 495-540]. Although only two mixture critical points could be measured in the system CF4 + H2O, the path of the critical locus suggests that this system exhibits gas-gas immiscibility of the second kind. In comparison with the binary system CF4 + H2O, the immiscibility region of the binary system CHF3 + H2O is located at significantly lower temperatures. Addition of NaCl shifts the immiscibility regions towards higher temperatures compared to the corresponding binary systems. (C) 1998 Elsevier Science B.V. All rights reserved. [References: 17]