Chemical thermodynamics of aqueous electrolyte systems for industrial and environmental applications

Abstract

This thesis consists of studies of chemical thermodynamics of aqueous electrolytes for industrial and environmental applications. Calculations have been used to represent vapor-liquid-solid equilibria and chemical equilibria for aqueous systems including solubility of gases. Modern simulation methods combined with experiments provide a useful tool for the research and design of new processes as well as evaluating changes in the operational conditions of chemical processes. The Gibbs energy minimization methods ChemSage, and ChemSheet have been used along with activity coefficient models including Pitzer ion interaction model. The calculated results were compared if possible with experiments or with reference data. Further this work consists of studies on oxygen-pressurized peroxide bleaching, which is an important sequence of total chlorine free (TCF) bleaching for environmental reasons. The solution properties like pH have been measured and modelled both in pure H2O2-NaOH-H2O system and in bleaching conditions. Further, the thermodynamic multicomponent model was used with kinetic constraints for pH calculations in reactive solution. The knowledge of the pulp- and solution properties along with the results of the model calculations could be used for optimisation of the bleaching process with respect to reaction time and temperature. Thermodynamics provides a practical tool for the estimation of the chemical states of pulp and paper solutions as well as in hydrometallurgical applications. Such a fundamental approach relates to the chemical energy, chemical reactions, solubility of gases and salts, and an important online process parameter pH. The Gibbs energy approach was further applied to equilibrium and reaction dynamic studies of multiphase CO2-CaCO3-H2O system.