Aqueous Solubility of Hydrocarbon Mixtures J. C. de Hemptinne, H. Delepine, C. Jose, J. Jose To cite this version: J. C. de Hemptinne, H. Delepine, C. Jose, J. Jose. Aqueous Solubility of Hydrocarbon Mixtures. Revue de l’Institut Français du Pétrole, EDP Sciences, 1998, 53 (4), pp.409-419. 10.2516/ogst:1998035. hal-02079003 HAL Id: hal-02079003 https://hal-ifp.archives-ouvertes.fr/hal-02079003 Submitted on 25 Mar 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Distributed under a Creative Commons Attribution| 4.0 International License AQUEOUS SOLUBILITY OF HYDROCARBON MIXTURES J.-C. de HEMPTINNE* SOLUBILITÉ DANS L’EAU DE MÉLANGES D’HYDROCARBURES Institut français du pétrole1 La solubilité de composés hydrocarbonés dans l'eau est d'une importance cruciale pour les sciences environnementales. Sa H. DELEPINE, C. JOSE and J. JOSE prévision est généralement basée sur la solubilité des constituants purs et de leur fraction molaire en mélange. La solubilité des 2 Université Claude Bernard composés purs est généralement bien connue, mais peu de don- nées ont été publiées concernant les mélanges. L’utilisation d’une relation simple conduit à une sous-estimation de la solubilité réelle. Cet article présente quelques données nouvelles de solubilités de mélanges hydrocarbonés simples. Une analyse thermodynamique rigoureuse permet de décrire la solubilité observée, aussi bien pour des mélanges modèles que pour des kérosènes. Les modèles de coefficient d'activité utilisés dans ce but sont NRTL, UNIQUAC et UNIFAC. Étant donné la faible concentration de cer- tains constituants dans l'huile, leurs coefficients d'activité peut devenir important. Ceci explique une augmentation de la solubilité par rapport à celle proposée par le modèle simple d'un facteur supérieur à deux. AQUEOUS SOLUBILITY OF HYDROCARBON MIXTURES The solubility of hydrocarbon components in water is of great importance for the environmental sciences. Its prediction is usually based on using the pure component solubilities and the mole fraction of the components in the mixture. While the pure component solubilities are generally well known, few data exist on the solubility of mixtures. Using a simple relationship leads to an underestimation of the true solubility. This paper presents some new data on the aqueous solubility of binary hydrocarbon mixtures. Using a rigorous thermodynamic analysis, we explain the observed behavior, as well as other data from the literature, including the solubility of jet fuel mixtures in water. The activity coefficient models used for this purpose are NRTL, UNIQUAC and UNIFAC. Considering the small concentration in oil of some very soluble substances, the activity coefficient can become significant and thus explain the fact that solubilities of some component may be as much as twice as large as expected. SOLUBILIDAD EN EL AGUA DE LAS MEZCLAS DE HIDROCARBUROS La solubilidad de los compuestos hidrocarbonados en el (1) 1 et 4 , avenue de Bois-Préau, 92852 Rueil-Malmaison Cedex - France agua representa una importancia esencial para las ciencias medioambientales. Su predicción se funda, por lo general, en la (2) 43, boulevard du 11 novembre 1918, solubilidad de los componentes puros y de sus fracciones molares 69622 Villeurbanne Cedex - France en mezcla. La solubilidad de los componentes puros es * To whom correspondence should be addressed. perfectamente conocida pero se han publicado muy pocos datos REVUE DE L’INSTITUT FRANÇAIS DU PÉTROLE VOL. 53, N° 4, JUILLET-AOÛT 1998 409 AQUEOUS SOLUBILITY OF HYDROCARBON MIXTURES acerca de las mezclas. La utilización de una relación simplificada INTRODUCTION conduce a subestimar la solubilidad real. En este artículo se presentan algunos nuevos datos de solubilidades de mezclas Largely for environmental reasons, a great amount of hidrocarbonadas simples. Un análisis termodinámico riguroso permite describir la solubilidad observada, tanto de las mezclas work has been performed in order to determine modelo como de los querosenos. Los modelos de coeficiente de the solubility of hydrocarbons in water at various actividad utilizados con este objeto son NRTL, UNIQUAC y temperatures. These solubility data have been compiled UNIFAC. Habida cuenta de la reducida concentración de ciertos (Kertes, 1989a and 1989b) and correlated (Yaws, 1990, componentes en el petróleo, su coeficiente de actividad puede 1993a, 1993b, 1995). llegar a ser importante. Esto permite explicar un aumento de la solubilidad con respecto a aquella propuesta por el modelo simple In most cases, however, the water is in contact with a de un factor superior a dos. mixture of hydrocarbons, and the saturated water solubility must be corrected with the mole fraction of the component in the mixture. This is often taken for granted and very few experimental results have been published concerning water solubilities of hydrocarbon mixtures. Leinonen (1972) first observed that the true concentration in water is larger than that predicted from binary data. A more detailed study of this effect has been presented by Leinonen and Mackay (1973). They analyze their results using an activity coefficient in the hydrocarbon phase, but conclude that it may be insufficient for explaining the increase in solubility. Burris and MacIntyre (1984) have similarly presented solubility measurements of two synthetic jet fuel mixtures, and related the increased solubility to the activity coefficient in the hydrocarbon phase. More recently, Dhima et al. (1998) have discussed the water solubility of binary hydrocarbon gas mixtures under high pressure conditions. They use an equation of state (Peng-Robinson) for describing the hydrocarbon phase non-idealities. The goal of the work presented in this paper is to contribute to the understanding and the modeling of the water solubility behavior of mixtures. To that end, additional experimental measurements have been performed to determine the solubility of a mixture of hydrocarbons in pure water. A rigorous thermodynamic treatment of the results and of other literature data including jet fuel mixtures indicates that the molar fraction approach may not be sufficient if accurate predictions are needed. On the contrary, the use of an activity coefficient model is required for that purpose. 1 EXPERIMENTAL SETUP The hydrocarbon + water two-phase mixture was stirred during two days using a magnetic stirrer. The cell, sketched in Figure 1, had a volume of 250 cm3. A water + glycol mixture was circulated through the REVUE DE L’INSTITUT FRANÇAIS DU PÉTROLE VOL. 53, N° 4, JUILLET-AOÛT 1998 410 AQUEOUS SOLUBILITY OF HYDROCARBON MIXTURES Solubilities of both benzene and cyclohexane in water, at different temperatures, are reported in Tables 1 and 2, and in Figures 2 and 3. Good agreement is observed with data found in the literature. TABLE 1 Experimental solubility of benzene in water (mole fraction x 106) Thermostatted at different temperatures, comparison with data found in the literature fluid (Sorensen et al., 1980) Temperature (°C) x aq aq exp xlit 15.6 397 * Figure 1 10.1 387 378.9 Experimental setup. 20.0 379 366.6 30.0 402 392.5 40.3 422 410.2 external envelope providing a temperature control to 50.1 446 434.4 ± 0.1°C. A pipe at the bottom of the cell relied on * No data have been found. gravity to draw off the aqueous phase. TABLE 2 Aqueous phase sampling is carried out as follows: Experimental solubility of cyclohexane in water (mole fraction x 106) – the hydrocarbon + water mixture is allowed to stand at different temperatures, comparison with data found in the literature for 24 hours; (Kertes et al., 1989a) – 4 ml of a paraxylene + n-octane mixture at 500 mass Temperature (°C) x aq aq ppm of n-octane, providing the internal standard, are exp xlit introduced into a 10 ml volumetric flask; 11.1 13.5 * – the liquid level is brought to the mark by adding the 16.1 13.0 13.2 aqueous phase drawn from the experimental cell; 21.1 12.6 14.9; 21.4 25.6 12.8 12.4 – the mixture is vigorously shaken during 2 minutes; 29.1 13.0 * – the emulsion is let stand for 12 hours; 35.0 14.1 19.0 – finally, the organic phase is analyzed by gas phase 40.2 14.0 * 50.0 15.4 * chromatography (GPC) using a semi-capillary column (stationary phase: OV1, 0.15 µm film, 0.53 * No data have been found. mm ID, 25 m length). Solubilities of the organic compounds in the aqueous We have verified that a single liquid-liquid extraction phase, at various temperatures, are reported in Tables 3 allows a quantitative recovery of benzene and through 6, and in the Figures 4 through 8, for the ternary cyclohexane dissolved in water. The paraxylene used as mixture benzene-cyclohexane-water. an extracting solvent has been purified on a 40 plate adiabatic column in order to remove the traces of TABLE 3 volatile impurities that could possibly interfere with Experimental solubility of benzene and cyclohexane in water benzene, cyclohexane or n-octane during the gas (mole fraction x 106) at different temperatures for organic phase: chromatographic analysis. xorg (benzene) = 0.3281 aq aq Temperature (°C) xexp (benzene) xexp (cyclohexane) 2 EXPERIMENTAL RESULTS 29.8 168 9.0 21.5 169 8.4 The uncertainty in the solubility in the aqueous 30.0 169 8.5 phase is estimated to be ± 4 molar ppm for benzene and 41.3 174 8.8 ± 0.2 molar ppm for cyclohexane. 49.7 178 9.5 REVUE DE L’INSTITUT FRANÇAIS DU PÉTROLE VOL.