CHEMICAL ENGINEERING TRANSACTIONS VOL. 45, 2015 A publication of The Italian Association of Chemical Engineering www.aidic.it/cet Guest Editors: Petar Sabev Varbanov, Jiří Jaromír Klemeš, Sharifah Rafidah Wan Alwi, Jun Yow Yong, Xia Liu Copyright © 2015, AIDIC Servizi S.r.l., ISBN 978-88-95608-36-5; ISSN 2283-9216 DOI: 10.3303/CET1545099 Please cite this article as: Suleman H., Nasir Q., Maulud A.S., Man Z., 2015, Comparative study of electrolyte thermodynamic models for carbon dioxide solubility in water at high pressure, Chemical Engineering Transactions, 45, 589- 594 DOI:10.3303/CET1545099 589 Comparative Study of Electrolyte Thermodynamic Models for Carbon Dioxide Solubility in Water at High Pressure Humbul Suleman, Qazi Nasir, Abdulhalim S. Maulud*, Zakaria Man Department of Chemical Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750, Tronoh, Perak, Malaysia halims@petronas.com.my The electrolyte thermodynamic models have been extensively studied for carbon dioxide – water system for the prediction of vapour liquid equilibrium at low pressures. However, no guidelines are available for selection of electrolytic models which are applicable at high pressure for prediction of thermodynamic properties. In this study, solubility prediction of limited Debye Huckel (DH), Pitzer Debye Huckel (PDH) and modified Three Characteristic Parameter Correlation (mTCPC) electrolyte models have been tested for a wide range of temperature (273 – 453 K) and pressure (0.1 – 7.2 MPa).The comparative study shows that introduction of electrolyte model improves the prediction accuracy when physical solubility of gas is low, either in high temperature or low pressure region. The mTCPC model gives improved prediction than non- electrolyte model but requires additional parameters and complex calculations. New values for binary interaction parameters of UNIFAC for carbon dioxide – water system are also optimized. 1. Introduction Absorption of carbon dioxide in water has found extensive applications in chemical process industries such as beverages, enhanced oil recovery, carboxylic acids, etc. Moreover, the recent developments in carbon capture have focused on solubility of carbon dioxide in water based solvents. The knowledge of vapour- liquid equilibrium (VLE) of the CO2 – H2O system is a key factor in the design of such chemical processes (Kohl, 1997) and associated process development, like oil and gas sector (Nguyen et al., 2014). Since CO2 slightly dissociates into ionic species upon dissolution in water, a lot of research has been channelled to discuss the effect of ionic equilibria at low pressures and temperatures (Edwards et al., 1978), but has limited information at high pressures. Chapoy et al. (2004) applied equation of state / excess Gibbs energy model (EoS/G E ) to predict VLE for CO2 – H2O system for medium pressure range and low temperatures. Valtz et al. (2004) compared semi-empirical, EoS/G E and statistical thermodynamic modelling techniques for limited pressure and temperature. Both studies neglected the ionic equilibria in liquid phase. The importance of ionic equilibria in modelling has been detailed by Li Yuen Fong et al. (2014). The purpose of this study is to analyze the effect of electrolytic correction on prediction of carbon dioxide solubility in water. The study encompasses a large data with range of pressures (0.1 – 7.2 MPa) and temperatures (273 – 453 K). 2. Experimental Data The experimental data was taken from published literature and is given in Table 1. 3. Determination of Liquid Phase Ionic Equilibria The dissociation of carbon dioxide in water is represented by following reactions (Edwards et al., 1978), where k1, k2 and k3 represents the equilibrium constants for reactions given in Eq(1) to Eq(3).         1 1 2 2 2 3 3 [ ] [ ] [ ] k k CO CO HO HCO H HCO H (1)