Liquid-liquid phase equilibrium (LLE) data are essential for the proper design, operation, and simulation of many chemical processes. Processes such as distillation, adsorption, and liquid-liquid extraction are examples of the more prevalent applications. Additionally, the development of environmental impact studies, such as the potential contamination of a body of water by a liquid hydrocarbon, is dependent on phase equilibrium data.

When experimental data are unavailable, thermodynamic models for LLE are used to predict the phase equilibrium. The accuracy of these models is dependent on the quality, as well as the quantity, of the experimental data used in the model development. While sufficient literature data are available on LLE for select hydrocarbon-water systems at ambient or near ambient temperatures, a deficiency exists for data at elevated temperatures. The objectives of this work were to (a) evaluate existing mutual hydrocarbon-water liquid-liquid equilibrium (LLE) data, and (b) develop an experimental apparatus capable of measuring accurately the hydrocarbon-water (LLE) mutual solubilities. The hydrocarbon-water systems studied included benzene-water, toluene-water, and 3-methylpentane-water.

A continuous flow apparatus was utilized to measure the LLE mutual solubilities at temperatures ranging from ambient to 500 K, which is near the three-phase critical end point of the benzene-water and toluene-water systems. The well-documented benzene-water system was used to validate the reliability of the sampling and analytical techniques employed. Generally, adequate agreement was observed for the benzene-water, toluene-water, and 3-methylpentane-water systems with literature data. An error propagation analysis for the three systems indicated maximum expected uncertainties of 4% and 8% in the water phase and organic phase solubility measurements, respectively. This study provides valuable LLE mutual solubility data and demonstrates the efficacy of the experimental apparatus in making accurate measurements.