chemical engineering research and design 92 (2014) 2283–2293 Contents lists available at ScienceDirect Chemical Engineering Research and Design journal homepage: www.elsevier.com/locate/cherd Thermodynamic modeling of the dissociation conditions of hydrogen sulfide clathrate hydrate in the presence of aqueous solution of inhibitor (alcohol, salt or ethylene glycol) Abolfazl Mohammadi a , Mehrdad Manteghian b,∗ , Amir H. Mohammadi c,d , Arash Kamran-Pirzaman e a Faculty of Engineering, University of Bojnord, Bojnord, Iran b Department of Chemical Engineering, Tarbiat Modares University, Tehran, Iran c Institut de Recherche en Génie Chimique et Pétrolier (IRGCP), Paris Cedex, France d Thermodynamics Research Unit, School of Chemical Engineering, University of KwaZulu-Natal, Howard College Campus, King George V Avenue, Durban, South Africa e Chemical Engineering Department, Mazandaran University of Science and Technology, Behshahr, Iran abstract Hydrate dissociation conditions of hydrogen sulfide in the presence of aqueous solution of thermodynamic inhibitor (methanol, ethanol, ethylene glycol, NaCl, KCl and CaCl 2 ) is modeled in this communication. A thermodynamic model is developed to correlate the hydrate dissociation conditions for the systems of H 2 S + water + salt (single and mixed salts of NaCl, KCl and CaCl 2 ), H 2 S + water + alcohol (methanol or ethanol), H 2 S + water + ethylene glycol and H 2 S + water + mixed salt, and methanol/ethylene glycol. Extended-UNIQUAC (e-UNIQUAC) approach is used for modeling of the activity coefficient of water in aqueous phase. The structural parameters of e-UNIQUAC model are extracted from literature but interaction parameters of this model are obtained by fitting the model with experimental data. The results of the present model are in satisfactory agreement with experimental data. © 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. Keywords: Gas hydrates; Hydrogen sulfide; Thermodynamic inhibitor; Thermodynamic modeling; Phase equilibria 1. Introduction Clathrate hydrates or gas hydrates are crystalline compounds formed by contacting the small molecules (typically gases and volatile liquids) as guests with water as host at low tempera- tures and high pressures. The hydrate structures are stabilized because of the physical forces between water/guest molecules. There is no chemical interaction between guest and water in hydrate formation process. The van der Waals forces are the only interaction between host/guest molecules (Sloan and Koh, 2008). Three typical types of hydrate crystalline struc- tures are I, II and H with different numbers and sizes of cavities in each type (Sloan and Koh, 2008). Since 1934 when Ham- merschmid found that hydrate formation causes plugging in ∗ Corresponding author at: P.O. Box 14115-311, Iran. Tel.: +98 21 82883333. E-mail address: manteghi@modares.ac.ir (M. Manteghian). Received 15 May 2013; Received in revised form 6 January 2014; Accepted 7 January 2014 Available online 13 January 2014 natural gas pipelines (Hammerschmidt, 1934), many scien- tists have directed their research toward hydrate formation process and they have investigated the pressure/temperature (P/T) condition of this process (Bond and Russell, 1948; Cady, 1981; Carroll, 1990; Carroll and Mather, 1989; Javanmardi and Moshfeghian, 2000; Javanmardi et al., 2000, 2001; Mahadev and Bishnoi, 1999; Mahmoodaghdam, 2001; Majumdar et al., 2000; Mohammadi and Richon, 2009, 2010, 2012a,b; Ng and Robinson, 1983; Ng et al., 1985; Platteeuw and Van der Waals, 1959; Selleck et al., 1952; Von Stackelberg, 1949). Increasing the temperature, decreasing the pressure, and using the inhibitors in the system are traditionally considered for preventing the hydrate formation. Thermodynamic inhibitors (such as alco- hol, glycol and salt) are compounds that decrease the hydrate 0263-8762/$ – see front matter © 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cherd.2014.01.010