Calculation of phase behavior and chemical transformations in H2O-NH3-CO2 system using a modified hole quasichemical model

A technique for calculation of phase equilibria over a wide range of temperatures and pressures for fluid systems, where chemical interactions lead to the formation of ionic species, was developed. A hole quasichemical model was modified to account for chemical reactions and electrostatic interactions in the liquid phase. The densities and dielectric permittivity as function of a solution composition was taken into account in describing the electrostatic contribution to the Gibbs energy (Pitzer approximation) and Born contribution, that is required for thermodynamic consistency of simulation results. A method of assessing the appropriate relationships for mixtures of ammonia-water and ternary solutions was suggested. Calculations of the phase behavior of the H2O-NH3 system in the entire range of concentrations in the temperature interval 373-588 K at pressures up to 200 bar, and also of H2O-NH3-CO2 system containing NH3 to 30 mol% and CO2 up to 14 mol% in the temperature range 373-473 K at pressures to 88 bar gave satisfactory agreement with experimental data. Concentrations of the molecular and ionic individuals in the liquid phase, depending on the overall composition of the mixture were evaluated.