Thermodynamic Modelling of Aqueous Sulfuric Acid

TY - THES

T1 - Thermodynamic Modelling of Aqueous Sulfuric Acid

AU - Sippola, Hannu

PY - 2015

Y1 - 2015

N2 - Aqueous sulfuric acid is an important chemical not only for the industry but also with respect to the environment. A need for a simple thermodynamic model is obvious. The purpose of this thesis was to create a thermodynamic model for aqueous sulfuric acid with a reasonable number of parameters. A key factor in modelling aqueous sulfuric acid is the correct value for the second dissociation constant, K2. In this thesis it was discovered that several equations describing K2, can model aqueous sulfuric acid equally well. The reason for this was identified as the equilibrium between sulfate (SO4[2-]) and bisulfate (HSO4[-]) ions which creates an internal redundancy in the thermodynamic description. Thus, the equation for K2 must be included in the assessment of aqueous sulfuric acid. The thermodynamic properties of aqueous sulfuric acid were modelled with the Pitzer equation. Both the second dissociation constant K2 for sulfuric acid and Pitzer parameters were fitted simultaneously. After variation of the experimental data used and the temperature dependencies of the Pitzer parameters, it was found that only four Pitzer parameters with eight fitted terms are required to cover the thermodynamic properties of aqueous sulfuric acid over a temperature range of 0–170°C. The obtained thermodynamic properties are in good agreement with literature values as well as with other Pitzer based and more complex thermodynamic models for aqueous sulfuric acid. The recent version of Pitzer equation, NPL Pitzer, was also tested. It was found to be capable of predicting activity and osmotic coefficient using only five parameters up to 80w% solution over a wide temperature range.

AB - Aqueous sulfuric acid is an important chemical not only for the industry but also with respect to the environment. A need for a simple thermodynamic model is obvious. The purpose of this thesis was to create a thermodynamic model for aqueous sulfuric acid with a reasonable number of parameters. A key factor in modelling aqueous sulfuric acid is the correct value for the second dissociation constant, K2. In this thesis it was discovered that several equations describing K2, can model aqueous sulfuric acid equally well. The reason for this was identified as the equilibrium between sulfate (SO4[2-]) and bisulfate (HSO4[-]) ions which creates an internal redundancy in the thermodynamic description. Thus, the equation for K2 must be included in the assessment of aqueous sulfuric acid. The thermodynamic properties of aqueous sulfuric acid were modelled with the Pitzer equation. Both the second dissociation constant K2 for sulfuric acid and Pitzer parameters were fitted simultaneously. After variation of the experimental data used and the temperature dependencies of the Pitzer parameters, it was found that only four Pitzer parameters with eight fitted terms are required to cover the thermodynamic properties of aqueous sulfuric acid over a temperature range of 0–170°C. The obtained thermodynamic properties are in good agreement with literature values as well as with other Pitzer based and more complex thermodynamic models for aqueous sulfuric acid. The recent version of Pitzer equation, NPL Pitzer, was also tested. It was found to be capable of predicting activity and osmotic coefficient using only five parameters up to 80w% solution over a wide temperature range.

KW - thermodynamic properties

KW - Pitzer model

KW - activity coefficient

KW - osmotic coefficient

KW - electrochemical cell

KW - termodynaamiset ominaisuudet

KW - Pitzerin yhtälö

KW - aktiivisuuskerroin

KW - osmoottinen kerroin

KW - sähkökemiallinen kenno

KW - thermodynamic properties

KW - Pitzer model

KW - activity coefficient

KW - osmotic coefficient

KW - electrochemical cell

M3 - Doctoral Thesis

SN - 978-952-60-6150-4

T3 - Aalto University publication series DOCTORAL DISSERTATIONS

PB - Aalto University

ER -