Phase Behavior of Light Gases in Hydrocarbon and Aqueous Solvents

Under previous support from the Department of Energy, an experimental facility has been established and operated to measure valuable vapor-liquid equilibrium data for systems of interest in the production and processing of coal fluids. To facilitate the development and testing of models for prediction of the phase behavior for such systems, we have acquired substantial amounts of data on the equilibrium phase compositions for binary mixtures of heavy hydrocarbon solvents with a variety of supercritical solutes, including hydrogen, methane, ethane, carbon monoxide, and carbon dioxide. The present project focuses on measuring the phase behavior of light gases and water in Fischer-Tropsch (F-T) type solvents at conditions encountered in indirect liquefaction processes and evaluating and developing theoretically-based correlating frameworks to predict the phase behavior of such systems. Specific goals of the proposed work include (a) developing a state-of-the-art experimental facility to permit highly accurate measurements of equilibrium phase compositions (solubilities) of challenging F-T systems, (b) measuring these properties for systematically-selected binary, ternary and molten F-T wax mixtures to provide critically needed input data for correlation development, (c) developing and testing models suitable for describing the phase behavior of such mixtures, and (d) presenting the modeling results in generalized, practical formats suitable for use in process engineering calculations. During the present reporting period, our solubility apparatus was refurbished and restored to full service. To test the experimental apparatus and procedures used, measurements were obtained for the solubility Of C0{sub 2} in benzene at 160{degrees}F. Having confirmed the accuracy of the newly acquired data in comparison with our previous measurements and data reported in the literature for this test system, we have begun to measure the solubility of hydrogen in hexane. The measurements for this system will cover the temperature range from 160 to 280{degrees}F at pressures to 2,500 psia. As part of our model evaluation efforts, we examined the predictive abilities of an alternative approach we have proposed for calculating the phase behavior properties of highly non-ideal systems. Using this approach, the liquid phase fugacities generated from an equation of state (EOS) are augmented by a fugacity deviation function correction. The correlative abilities of this approach are compared with those of an EOS equipped with the recently introduced Wong-Sandler (MWS) mixing rules. These two approaches are compared with the current methods for vapor-liquid equilibrium (VLE) calculations, i.e., the EOS (0/0) approach with the van der Waals mixing rules and the split (y/0) approach. The evaluations were conducted on a database comprised of non-ideal low pressure binary systems as well as asymmetric high pressure binary systems. These systems are of interest in the coal liquefaction and utilization processes. The Peng-Robinson EOS was selected for the purposes of this evaluation