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...