Published: March 30, 2011 r2011 American Chemical Society 1573 dx.doi.org/10.1021/je1012185 | J. Chem. Eng. Data 2011, 56, 1573–1586 ARTICLE pubs.acs.org/jced Thermodynamic Consistency Test for Experimental Solubility Data in Carbon Dioxide/Methane þ Water System Inside and Outside Gas Hydrate Formation Region Ali Eslamimanesh, † Amir H. Mohammadi,* ,†,‡ and Dominique Richon † † MINES ParisTech, CEP/TEP - Centre  Energ etique et Proc  ed es, 35 Rue Saint Honor  e, 77305 Fontainebleau, France ‡ Thermodynamics Research Unit, School of Chemical Engineering, University of KwaZulu-Natal, Howard College Campus, King George V Avenue, Durban 4041, South Africa b S Supporting Information ABSTRACT: Accurate knowledge of solubility in carbon dioxide/methane þ water system over wide ranges of temperatures and pressures is essential for the petroleum industry. However, experimental measurements of such solubilities (especially in gas hydrate formation region) are challenging. For instance, concentrations of these gases in water are low, and furthermore reaching the equilibrium conditions near and inside gas hydrate formation region is a time-consuming process. Those difficulties may consequently result in generation of unreliable experimental data. This work aims at performing a thermodynamic consistency test based on an area approach to study the reliability of such experimental data reported in the literature and points out the suspected inconsistent data. A thermodynamic model based on the Valderrama modification of the Patel-Teja equation of state along with non-density dependent mixing rules is used to model the solubilities in the gas/vapor and liquid water phases. For modeling the solubility of carbon dioxide/methane in water under liquid water-hydrate equilibrium conditions, the van der Waals- Platteeuw model accompanied with Henry’s law approach is employed. The results show that about 23 % of all of the investigated experimental data seem to be thermodynamically consistent, 57 % inconsistent, and 20 % not fully consistent data. ’ INTRODUCTION Carbon dioxide/methane and water systems are one of major systems in the petroleum industry. 1 Such mixtures are often found in oil and gas streams and reservoirs especially as part of enhanced oil recovery (EOR) process. The presence of carbon dioxide/methane and water in these environments may cause complications such as corrosion and gas hydrate formation. 1 On the other hand, CO 2 capture from industrial/flue gases, and CO 2 sequestration are among the novel technologies dealing with mixtures of these compounds. 2,3 Therefore, because of the fact that the aforementioned processes deal with a wide range of pressures and temperatures, accurate knowledge of the solubility in the carbon dioxide/methane þ water system over a wide range of temperatures and pressures are especially necessary to tune adapted thermodynamic models. Figure 1 shows a typical solubility-temperature diagram for a water-pure hydrate former (limiting reactant) system. 2 As can be seen, the temperature and pressure dependencies of the pure hydrate former (e.g., carbon dioxide and methane) solubility in pure water being in the liquid water-gas/vapor (L w -G/V depending on whether the component is in supercritical state or not) equilibrium region are di fferent from the corresponding dependency in the liquid water- hydrate (L w -H) equilibrium region. 2-20 The L w -G/V equilibrium is a strong function of temperature and pressure, while the L w -H equilibrium is a strong function of temperature but a very weak function of pressure. 2-20 On the other hand, the pure hydrate former solubility in pure water in the L w -G/V equilibrium region generally increases with decreasing the temperature at a given pressure, while the corresponding solubility in pure water in the liquid water- hydrate equilibrium region decreases with decreasing the temperature at the same pressure. 2-20 Furthermore, the metastable liquid water- vapor equilibrium may extend well into the gas hydrate formation zone. 2-20 As pointed out earlier, 1 low solubilities of carbon dioxide/ methane gases in water (especially methane) result in some significant experimental measurement difficulties. Although many experimental works have been done to obtain solubilities of carbon dioxide/methane in water in L w -G/V region, the experimental data for describing the L w -H equilibrium are limited mainly due to two factors: the possible extension of the metastable L w -G/V equilibrium into the gas hydrate region and the experimental restraint that the existing analytical methods require modifications. 2-20 Literature surveys reveal the availability of few sets of experimental data for the L w -H equilibrium. 2-20 Consequently, few reliable models are available in the literature for representing the L w -H equilibrium data. 2-20 These models are generally based on cubic equations of state, different mixing rules, and mathematical correlations. To check the existing thermodynamic models or develop new ones, if necessary, for an accurate estimation of the solubility in the carbon dioxide/methane þ water system, reliable experi- mental data sets are required. This communication aims at testing the thermodynamic consistency of such literature solu- bility data in the wide range of available temperatures and Special Issue: John M. Prausnitz Festschrift Received: November 17, 2010 Accepted: February 16, 2011