Phase Behavior in the Methane-ethane-n-pentane System

Abstract

Abstract The composition of the coexisting phases in the methane-ethane-n-pentane systemwas determined at 100'F. This was accomplished by withdrawing samples of thecoexisting phases under isobaric-isothermal conditions. The relative amount ofeach of the components present in the liquid and gas phases was determined byconventional analytical fractionation methods. The phase behavior of thissystem approximates that estimated from generalized correlations which takeinto account the influence of the nature and amount of each of the componentspresent upon the equilibrium. It was found that for particular pressures andtemperatures the equilibrium constant of each of the components was influencedsignificantly by the composition of the system and this effect was morepronounced at the lower pressures for methane than for the components ofgreater molecular weight. However, at the higher pressures approaching themaximum two-phase pressure for the system at this temperature the compositionmarkedly influences the equilibrium constants of all the components at aparticular pressure and temperature. The results of this study are presented ingraphical and tabular form. Introduction The phase behavior of many of the binary systems containing paraffinhydrocarbon components from methane through n-pentane has been investigatedduring recent years. In addition the compositions of the coexisting phases inmixtures of crude oil and natural gas have been studied. However, these results do not establish the influence of the nature and amountof the other substances making up a multicomponent system upon the gas-liquidequilibrium constant of anyone component. A preliminary correlation on thebasis of values for binary systems was made utilizing such experimentalinformation as was available. However, there is need for much additionalinformation regarding behavior in systems containing more than twocomponents. Study of the phase behavior of ternary systems offers a feasible attack uponthe determination of the influence of composition as well as of pressure andtemperature upon the several equilibrium constants concerned. An investigationof the phase behavior of the methane-propane-n-pentane system at 100?, 160?, and 220'F was reported. This work served to illustrate the marked influence ofconcentration of the other components upon the equilibrium constants.Variations of as much as $0 pet in the equilibrium constants for methane forfixed temperature and pressure were observed in regions remote from thecritical state. Likewise there was a marked variation in the equilibriumconstants of propane and n-pentane as a result of changes in the composition.These results indicated the desirability of investigating additional ternarysystems. The present paper deals with a study of the methane-ethane-n- pentanesystem at 100'F, which is similar in many respects to the work upon themethane-propane-n-pentane system cited above. T.P. 2232