Phase Behavior of Light Gases in Hydrogen and Aqueous Solvents

Abstract

Under previous support from the U. S. 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-ofthe-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, the solubilities of hydrogen in n-hexane, carbon monoxide in cyclohexane, and nitrogen in phenanthrene and pyrene were measured using a static equilibrium cell over the temperature range from 344.3 to 433.2 K and pressures to 22.8 MPa. The uncertainty in these new solubility measurements is estimated to be less than 0.001 in mole fraction. The data were analyzed using the Peng-Robinson (PR) equation of state (EOS). In general, the PR EOS represents the experimental data well when a single interaction parameter (C ij ) is used for each isotherm.In addition, the predictive capability of the modified Park-Gasem-Robinson (PGR) equation of state (EOS) was evaluated for selected carbon dioxide + normal paraffins, ethane + normal paraffins, and hydrogen + normal paraffins. A set of mixing rules was proposed for the modified EOS to extend its predictive capabilities to mixtures. The predicted bubble point pressures for the ethane + n-paraffin and carbon dioxide + n-paraffin binaries were compared to those of the Peng-Robinson (PR), simplified-perturbed-hard-chain theory (SPHCT) and original PGR equations. The predictive capability of the proposed equation is better or comparable to the PR, SPHCT and original PGR equations of state for the ethane binaries (%AAD of 1.9) and carbon dioxide binaries (%AAD of 2.0). For the hydrogen binaries, the modified PGR EOS showed much better performance (%AAD of 1.7) than the original PGR equation and comparable to the PR equation.A technical report on our rece...