High‐temperature mutual solubilities of hydrocarbons and water. Part I: Benzene, cyclohexane andn‐hexane

Abstract

The mutual solubilities at the three-phase equilibrium pressure of three C6 hydrocarbons (benzene, cyclohexane and n-hexane) and water have been experimentally investigated up to 482 K. A thermodynamic analysis of these new measurements and of critically selected literature data has been carried out up to the three-phase critical end point. Information is also provided on the two-phase critical locus, The solubility of hydrocarbons in water has been used to calculate Henry's constants, while the solubility of water in the hydrocarbons has been correlated with a modified version of the Redlich-Kwong equation of state. Consideration is also given to the effect of pressure on the mutual solubilities. CONSTANTINE TSONOPOULOS SCOPEKnowledge of the hydrocarbon/water mutual solubilities is frequently of importance to the design and operation of process equipment in refineries and petrochemical plants. Hydrocarbons, like other pollutants, must be removed from refinery and petrochemical plant wastewater streams. Accordingly, the solubility and volatility of the hydrocarbons are needed to trace their phase distribution through the entire process sequence and to design separation equipment (such as sour water strippers) for their removal.If the water present in a hydrocarbon mixture exceeds its solubility limit, a second liquid phase will form, the "free" water phase, that can affect product specifications and equipment operation. Perhaps the most common adverse process effect is corrosion. Even when a free-water phase does not form, the solubility of water in hydrocarbons at 470 K and above is so high that the phase distribution of water can affect both the operation of the equipment, say, a distillation tower, and the product quality. Sometimes, however, a water-rich phase is formed intentionally, for example, to remove salts that would otherwise deposit out. This case also requires the accurate prediction of the solubility limits.The maximum temperature of interest in water pollution abatement is about 420 K, or even 470 K in certain cases, which can be reached in sour water strippers. On the hydrocarbon-rich side, the maximum temperature of interest can be much higher. Generally, it is the maximum temperature at which the hydrocarbon-rich liquid phase can exist. This is somewhat below the critical temperature of the hydrocarbon.The process conditions at which hydrocarbon streams are contacted with water and lead to the formation of a second liquid phase need to be predicted reliably. The solution of water in hydrocarbons can be predicted accurately with an equation of state, using only a temperature-independent binary interaction parameter. The same procedure can then be used to predict the distribution of water between the vapor and hydrocarbonrich liquid phases. On the other hand, the solubility of hydrocarbons in water is not predictable by such a procedure, unless the binary interaction parameter is made a strong function of temperature. The solubility of hydrocarbons in water is so low, however, that Henry's law i...

Prediction of Phase Behavior for the System Methane-Carbon Dioxide- Hydrogen Sulfide-Water with the PR and PC-SAFT Equations of State

“…Nonetheless, even if these contributions could be included in the model in an explicit way, we did not do that because the purpose of this work was focused on the capability of this equation of state in its original form to represent the experimentally observed complex phase behavior developed by this mixture and compare its performance against another thermodynamic model. In this context, it should be mentioned that all phase equilibrium predictions with this equation were obtained using binary interaction parameters taken from the literature, which had previously been fitted from binary vapor-liquid equilibrium data, instead of using other interaction parameters fitted from three phase equilibrium data, as done, for instance, by Nutakki [31] to modeling the three-phase binary water-hydrocarbon systems data of Brady et al [32] and Tsonopoulos and Wilson [33] with the Schmidt-Wenzel EoS in order to determine the interaction parameters between the hydrocarbon and water in the hydrocarbon liquid and aqueous phases. The latter is important because once the interaction parameters have been fitted at three phase equilibrium conditions, there is a risk to use them to predict the phase behavior of a given system at different conditions at which the interaction parameters were determined, so that the prediction may fail and/or give physical meaningless results.…”

Feasibility study of material-balance assessment of petroleum from the New Albany Shale in the Illinois Basin

“…Lewan (1992) suggests that the enhancement of yield under hydrous conditions relative to anhydrous closed conditions is a result of dissolved H20 in the bitumen network acting as a source of hydrogen. It has been experimentally established that the solubility of water in hydrocarbons is two orders of magnitude higher than the solubility of hydrocarbons in water (Tsonopoulos and Wilson, 1983;Heidman and others, 1985;Skripka and Boksha, 1976;Guerrant, 1964;Griswold and Kasch, 1942). However, this high solubility of water in hydrocarbons is strongly dependent on temperature, with water solubilities being more than one order of magnitude higher at temperatures used in hydrous pyrolysis (300°C to 365°C) than at temperatures encountered in subsiding sedimentary basins ( 1 00°C to 200°C).…”

Guidelines for reporting of phase equilibrium measurements (IUPAC Recommendations 2012)

“…Models can also be used to compare the new experimental data with literature values obtained at other conditions, and can reveal data quality issues related to composition or temperature dependence that, otherwise, would remain undetected (see [56]). Nonetheless, successful application of these consistency tests should be considered necessary, but not sufficient, tests of data quality.…”