Experimental determination of critical temperatures and pressures of mixtures: The methane‐ethane‐n‐butane system

An experimental unit has been designed and constructed for the study of critical phenomena in multicomponent systems. This unit has been built to utilize a new visual PV̇T cell capable of operating at temperatures up to 300°F. and pressures to 10,000 lb./sq. in. abs. This cell is of the liquid piston type with mercury as the pressurizing fluid and affords unobstructed visual observation of its contents. The dependability of the unit has been tested on two mixtures of ethane and n ‐butane. Phase equilibria data were obtained, which in turn were used to establish the critical temperture and pressure. Critical temperatures and pressures have been determined for six different compositions of the methane‐ethane‐ n ‐butane system. These mixtures consisted of two series, each of three compositions differing only in methane content. The data obtained from them, in conjunction with previously reported critical values for the binaries of this system, have been utilized to generate the complete critical locus for the ternary system. The results for the six mixtures of this study have been compared with critical values predicted by methods available in the literature.