Thermodynamic Modeling of the Sulfuric Acid – Water – Sulfur Trioxide System with Symmetric Electrolyte NRTL Model

Properties and phase Equilibria of the sulfuric acid – water – sulfur trioxide system is of great interest to the industry. Two recent application examples are dew point calculations of flue gas in oxyfuel combustion and process design for Sulfur-Iodine Cycle thermal chemical decomposition of water for hydrogen production. Recently developed symmetric electrolyte NRTL activity coefficient model is utilized to investigate the thermodynamics of the sulfuric acid – water – sulfur trioxide system. Partial dissociations of sulfuric acid and bisulfate ion in aqueous phase are considered. Hydrations of proton from the partial dissociations of sulfuric acid are assumed in the form of mono-hydrate and di-hydrate. Decomposition of sulfuric acid to water and sulfur trioxide is also accounted for. Excellent match between model predictions and available literature data are achieved for osmotic coefficient, liquid phase speciation, heat of solution, liquid phase heat capacity, and vapor-liquid equilibrium of the sulfuric acid – water – sulfur trioxide system over the whole concentration range.