Thermodynamics of aqueous solutions containing volatile weak electrolytes

Abstract

AbstractA thermodynamic framework has been established to calculate equilibrium vapor‐liquid compositions for dilute aqueous solutions of one or more volatile weak electrolytes: ammonia, carbon dioxide, hydrogen sulfide, sulfur dioxide, and hydrogen cyanide, in the temperature range 0° to 100°C and for liquid‐phase concentrations from 10−4 to 1 or 2 molal.Binary electrolyte‐water parameters are obtained from reduction of experimental data for single‐solute solutions. Additional parameters required for multi‐solute systems are estimated from correlations. These parameters, coupled with chemical equilibria, are used to predict multicomponent vapor‐liquid equilibria. At a fixed temperature, either liquid‐phase or vapor‐phase compositions may be calculated if the composition of the other phase is known. Although the framework has no adjustable parameters for multisolute systems, predicted and observed equilibria are in good agreement for two ternary systems: ammonia‐hydrogen sulfide‐water and ammonia‐carbon dioxide‐water.