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High-Pressure Multiphase Behavior of the Ternary Systems (Ethene + Water + Acetone) and (Ethane + Water + Acetone)

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journal contribution
posted on 14.10.2010, 00:00 by Tatiana Ulanova, Dirk Tuma, Gerd Maurer
The high-pressure phase equilibrium of two ternary systems(ethene + water + acetone) and (ethane + water + acetone)was investigated by a static−analytical method. Both systems exhibit the “salting-out” phenomenon upon pressurization by the gaseous compound. The composition of the two coexisting liquid phases L1 and L2 of the high-pressure liquid−liquid−vapor (L1L2V) equilibrium was determined at (293, 313, and 333) K over the entire pressure range that spans from about (2.9 to 8.0) MPa for (ethene + water + acetone) and from about (2.3 to 5.8) MPa for (ethane + water + acetone), respectively. Additionally, the coordinates of both critical end point lines (i.e., the lower ((L1 = L2)V) and the upper (L1(L2 = V)), respectively) bordering the L1L2V equilibrium were recorded between (278 and 353) K. For both systems, it was found that, at constant temperature, increasing the pressure has a stronger impact on the L2 phase (resulting in higher contents of the gas), whereas the composition of the water-rich L1 phase is only slightly changed. Furthermore, for both systems, increasing the temperature enlarged the pressure region in which the three-phase L1L2V equilibrium is observed, and the corresponding pressures of both critical end point lines were shifted to higher values. In the second part of the work, an approach based on the Peng−Robinson equation of state was employed to model the phase equilibrium data of both ternary systems. Two different mixing rules (that developed by Panagiotopoulos and Reid as well as the mixing rule proposed by Huron and Vidal) were applied. The first procedure resorted to fitting the binary interaction parameters required by the mixing rules to vapor−liquid equilibrium data for the corresponding binary subsystems that were taken from the literature. The calculation results only agreed qualitatively with the experimental data but predicted the main characteristics correctly. In a second procedure, binary interaction parameters were directly fitted to the ternary phase equilibrium data of the experiment instead. A quantitative description of the experimental data could be achieved for both the coordinates of the critical end point lines and the compositions of the coexisting liquid phases L1 and L2 at L1L2V equilibrium. The maximum mean relative deviations between experimental data and calculation results from that method amount to 19 % for the water mole fraction in the organic phase L2 of the system (ethene + water + acetone) at 313 K and to 25 % for the gas mole fraction in the aqueous phase L1 of the system (ethane + water + acetone) at 293 K, respectively. There was no significant difference in the results from the choice of the mixing rule, but a slightly better performance was accomplished by the Panagiotopoulos−Reid mixing rule with a temperature-dependent set of binary interaction parameters.