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An upgraded version of the extended UNIQUAC thermodynamic model for the carbon dioxide−ammonia−water system has been developed, on the basis of the original version proposed by Thomsen and Rasmussen (Chem. Eng. Sci. 1999, 54, 1787). The original model was valid in the temperature range 0−110 °C, the pressure range 0−10 MPa, and the concentration range up to 80 m ammonia. In this work, the validity of this model was extended up to 150 °C and the accuracy improved by increasing the number of experimental data points from 2000 to more than 3700. These experimental data consisting of vapor−liquid equilibrium data in various concentration ranges, enthalpy change from partial evaporation measurements, speciation data, heat capacity, enthalpy of solution, and enthalpy of dilution data have been used to refit 43 model parameters and standard-state properties. Henry’s law constant correlations have been used for extrapolating standard-state properties of carbon dioxide and ammonia to supercritical conditions.

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