Phase behavior of light gases in hydrocarbon and aqueous solvents

摘要

Under previous support from the Department of Energy, an experimental facility211u001ehas been established and operated to measure valuable vapor-liquid equilibrium 211u001edata for systems of interest in the production and processing of coal fluids. To 211u001efacilitate the development and testing of models for prediction of the phase 211u001ebehavior for such systems, we have acquired substantial amounts of data on the 211u001eequilibrium phase compositions for binary mixtures of heavy hydrocarbon solvents 211u001ewith a variety of supercritical solutes, including hydrogen, methane, ethane, 211u001ecarbon monoxide, and carbon dioxide. The present project focuses on measuring the 211u001ephase behavior of light gases and water in Fischer-Tropsch (F-T) type solvents at 211u001econditions encountered in indirect liquefaction processes and evaluating and 211u001edeveloping theoretically-based correlating frameworks to predict the phase 211u001ebehavior of such systems. Specific goals of the proposed work include (a) 211u001edeveloping a state-of-the-art experimental facility to permit highly accurate 211u001emeasurements of equilibrium phase compositions (solubilities) of challenging F-T 211u001esystems, (b) measuring these properties for systematically-selected binary, 211u001eternary and molten F-T wax mixtures to provide critically needed input data for 211u001ecorrelation development, (c) developing and testing models suitable for 211u001edescribing the phase behavior of such mixtures, and (d) presenting the modeling 211u001eresults in generalized, practical formats suitable for use in process engineering 211u001ecalculations. During the present period, the Park-Gasem-Robinson (PGR) equation 211u001eof state (EOS) has been modified to improve its volumetric and equilibrium 211u001epredictions. Specifically, the attractive term of the PGR equation was modified 211u001eto enhance the flexibility of the model, and a new expression was developed for 211u001ethe temperature dependence of the attractive term in this segment-segment 211u001einteraction model. The predictive capability of the modified PGR EOS for vapor 211u001epressure, and saturated liquid and vapor densities was evaluated for selected 211u001enormal paraffins, normal alkenes, cyclo-paraffins, light aromatics, argon, carbon 211u001edioxide and water. The generalized EOS constants and substance-specific 211u001echaracteristic parameters in the modified PGR EOS were obtained from the pure 211u001ecomponent vapor pressures, and saturated liquid and vapor molar volumes. The 211u001ecalculated phase properties were compared to those of the Peng-Robinson (PR), the 211u001esimplified-perturbed-hard-chain theory (SPHCT) and the original PGR equations. 211u001eGenerally, the performance of the proposed EOS was better than the PR, SPHCT and 211u001eoriginal PGR equations in predicting the pure fluid properties (%AAD of 1.3, 2.8 211u001eand 3.7 for vapor pressure, saturated liquid and vapor densities, respectively).