Aqueous hydrocarbon systems: Experimental measurements and quantitative structure-property relationship modeling

Scope and method of study. The experimental 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. The modeling efforts in this study focused on developing quantitative structure-property relationship (QSPR) models for the prediction of infinite-dilution activity coefficient values ( ginfinityi ) of hydrocarbon-water systems. Specifically, case studies were constructed to investigate the efficacy of (a) QSPR models using multiple linear regression analyses and non-linear neural networks; and (b) theory-based QSPR model, where the Bader-Gasem activity coefficient model derived from a modified Peng-Robinson equation of state (EOS) is used to model the phase behavior, and QSPR neural networks are used to generalize the EOS binary interaction parameters. The database used in the modeling efforts consisted of 1400 infinite-dilution activity coefficients at temperatures ranging from 283 K to 373 K.; Findings and conclusions. 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. In general, the use of non-linear QSPR models developed in this work were satisfactory and compared favorably to the majority of predictive models found in literature; however, these model did not account for temperature dependence. The Bader-Gasem activity coefficient model fitted with QSPR generalized binary interactions was capable of providing accurate predictions for the infinite-dilution activity coefficients of hydrocarbons in water. Careful validation of the model predictions over the full temperature range of the data considered yielded absolute average deviations of 3.4% in ln ginfinityi and 15% in ginfinityi , which is about twice the estimated experimental uncertainty. This study provides valuable LLE mutual solubility data and further demonstrates the effectiveness of theory-framed QSPR modeling of thermophysical properties.