Computer Coupling of Phase Diagrams and Thermochemistry 31 (2007) 281–285 www.elsevier.com/locate/calphad Solubility prediction for the nonelectrolyte urea–hydrogen peroxide–water system and thermodynamic solubility product calculation for CO(NH 2 ) 2 ·H 2 O 2 using the modified Pitzer model Zhao Hongkun ∗ , Tang Cao, Zhang Daosen, Li Rongrong, Wang Yaqiong, Xu Wenlin College of Chemistry & Chemical Engineering, YangZhou University, YangZhou, Jiangsu 225002, PR China Received 31 March 2006; received in revised form 10 October 2006; accepted 5 November 2006 Available online 8 December 2006 Abstract The Pitzer interaction model, which has been applied successfully to the thermodynamic simulation of electrolyte solutions and electrolyte–nonelectrolyte solutions, was extended to nonelectrolyte–nonelectrolyte solution system. In the present work, the modified Pitzer model was used for calculation and correlation of the ternary CO(NH 2 ) 2 –H 2 O 2 –H 2 O system at 283.15 K. The value of the Pitzer interaction parameters for the ternary system and the thermodynamic solubility product of CO(NH 2 ) 2 ·H 2 O 2 were determined using a least-square optimization procedure with coupling activity coefficient and solubility data. The predicted isothermal solubilities agree well with the result obtained from the experiment. The results indicated that the modified Pitzer model could be successfully used to predict the component solubility of the nonelectrolyte–nonelectrolyte system. c  2007 Published by Elsevier Ltd Keywords: Pitzer model; Urea; Hydrogen peroxide; Phase diagram; Prediction 1. Introduction Percarbamide, also named urea hydrogen peroxide with gross formula CO(NH 2 ) 2 ·H 2 O 2 , is an adduct of hydrogen peroxide with urea. It is an important fine chemical that has been used in several oxidation processes [1–3] as well as a safe source for the production of hydrogen peroxide [4]. CO(NH 2 ) 2 ·H 2 O 2 is often produced by reaction of urea with hydrogen peroxide aqueous solution in which stabilizer exists [5,6]. In order to optimize the preparation process, the ternary phase diagram of the CO(NH 2 ) 2 –H 2 O 2 –H 2 O system was constructed [7]. Calculation and correlation of solid–liquid equilibrium phase diagram is of great practical importance for the design of industrial processes. Many thermodynamic models have been proposed to make the simulation and calculation of solid–liquid phase diagram. Pitzer and co-workers [8] have developed a semi-empirical statistical theory of electrolyte solution. In re- cent years, there has been an increasing amount of work ∗ Corresponding author. Tel.: +86 514 7975568; fax: +86 514 7975244. E-mail address: hkzhao@zzu.edu.cn (H. Zhao). concerning Pitzer interaction model in terms of both experi- mental measurements of thermodynamic properties on aque- ous systems and its applications [9–15]. Zhao and co-workers have used extended Pitzer model in calculation and correlation of the electrolyte–nonelectrolyte Na 2 SO 4 –NaCl–H 2 O 2 –H 2 O system [16], however, there is no report on the thermody- namic simulation of nonelectrolyte–nonelectrolyte system us- ing Pitzer model. In this paper, the purpose is to establish a thermodynamic simulation on the basis of Pitzer model in the nonelectrolyte CO(NH 2 ) 2 –H 2 O 2 –H 2 O system. In the first part, a brief description of the thermodynamic model and the model parametrization is introduced. The model parameters are de- termined for binary and ternary systems from saturated vapor pressure and solubility data with least-square analysis. In the second section, the calculation and correlation results in the CO(NH 2 ) 2 –H 2 O 2 –H 2 O system at 283.15 K are presented. 2. Theoretical considerations Here the ternary A–B–H 2 O system is considered. A, represents one nonelectrolyte molecule, and B, another nonelectrolyte molecule. 0364-5916/$ - see front matter c  2007 Published by Elsevier Ltd doi:10.1016/j.calphad.2006.11.001