The correlation of vapor‐liquid equilibria of light hydrocarbons in paraffinic and in aromatic solvents at low temperatures and elevated pressures

Abstract

Rice U n i v e r s i t y , H o u s t o n , TexasA correlational procedure was developed to predict the vapor-liquid equilibrium behavior of light hydrocarbons in heavier hydrocorbon solvents at low temperatures and elevated pressures. T h e method i s applicable to paraffinic a s well a s aromatic solvents. The method employed the Benedict-Webb-Rubin equation of state to predict the vapor phase fugacities. Methane liquid fugacities in the various hydrocarbon solvents were based upon Henry's law which included terms to account for compositional and pressure effects. The liquid fugacities for ethane and propane were calculoted using infinite dilution data to modify empirically the Scatchord-Hildebrond equation. Excellent agreement between the correlated and low-temperature data available on this class of systems was obtained.The literature abounds with correlations for vapor-liquid equilibria at elevated pressures. Of particular note are the Chao-Seader correlation ( 4 , correlations in light hydrocarbon systems based on equations of state (11, and convergence pressure correlations such a s those appearing in the NGSMA Data Book (12). The strength of the Chao-Seader correlation lies in i t s generality; that i s , in i t s ability to predict vapor-liquid phase behavior in systems composed of paraffins, napthenes and aromatics, including gases such a s hydrogen, nitrogen, carbon dioxide, and hydrogen sulfide a t low concentrations. T h e application of equations of state and the corresponding s t a t e s methods is usually limited to systems composed of paraffins and nonpolar substances. The purpose of this paper i s to develop a method of predicting phase behavior in systems containing a supercritical component, methane, with intermediates, ethane and propane, and a relatively heavy paraffin or aromatic component, such as heptane or toluene, using basic data which are functions of pressure and temperature only. Temperatures of interest range from 70' to -100OF. and pressures up to 1,500 Ib./sq. in. abs. Other correlations have not been successful for this type of system under these conditions. By definition, the vapor-liquid equilibrium constant, or K value, is the ratio of mole fractions of the component in the vapor and in the liquid. Since the fugacities for components are equal among the equilibrium phases (1) Chao and Seader (4) chose to separate the liquid fugacity

Phase equilibria for chain‐fluid mixtures near to and far from the critical region

“…Although extensive experimental studies have been reported (for a review, see Dohrn and Brunner, 1995), it has been difficult to develop a universal model to describe the thermodynamic properties and phase behavior of fluid mixtures at high pressures over a wide range of conditions, including the critical region. Most previous studies are concerned with empirical or phenomenological correlations for vapor-liquid equilibria (VLE) (such as Chao and Seader, 1961;Dastur and Thodos, 1963;Stevens and Thodos, 1963;Van Horn and Kobayashi, 1968;Reid et al, 1987); these studies use any one of several popular EOSs, such as RK (Redlich and Kwong, 1949), SRK (Soave, 19721, and PR (Peng and Robinson, 1976). These cubic EOSs provide improvement over the original van der Waals EOS (van der Waals, 1873) through modifications of the attraction terms as reviewed by Yelash and Kraska (1999).…”