Formation of a Third Liquid Layer in the Nitrogen–Methane–Ethane System

Abstract

LIQUID–liquid–vapour equilibrium data for the nitrogen–methane–ethane system have been reported^1,2 between −220° and −255° F. The existence of one pair of partially miscible liquids at low temperatures is interesting, because this system consists of the three major components of natural gases, and the separation of nitrogen from natural gases rich in nitrogen may be facilitated by taking advantage of the composition difference of the two liquid phases. The experimentally determined equilibrium compositions indicate that the bottom liquid layer is rich in ethane and the top liquid layer is rich in nitrogen. The binodal curve obtained² at −255° F is shown in Fig. 1. A forced-recirculation apparatus was used for the determination of equilibrium data. A 100 ml. Jerguson transparent gauge with stainless steel body was used for the equilibrium cell. A Dewar flask of 18 l. capacity was used as the cryostat with isopentane as the bath liquid. The practical grade isopentane has a boiling point of 27°–31° C at 1 atmosphere. Description of the equipment assembly, the equilibrium cell and the cryostat has been given in detail¹.