Total pressure method for vapor‐liquid equilibria at low absolute pressures: Aniline‐nitrobenzene systems

Binary vapor‐liquid equilibrium data for use in the successful design and operation of mass transfer equipment at pressures down to approximately 5 mm. Hg may be advantageously obtained by the method of total pressures. In this method the desired equilibrium data are derived from pressure vs. temperature measurements on a convnient number of made‐up solutions covering the entire composition range. With a modified Smith and Menzies isoteniscope, it is possible to measure accurately the data required for making the equilibrium calculations down to 2 mm. abs. pressure without the “bumping,” supercooling, and superheating encountered with equilibrium stills. The isoteniscope is simple to construct and operate from 1 atm. to 2 mm. abs. The use of the total pressure method and the isoteniscope is illustrated by the determination of the vapor‐liquid equilibrium in the aniline‐nitrobenzene system at 5 and 10 mm. abs. In nineteen out of twenty instances the vapor compositions for a given liquid composition are precise to within ± 0.9% and the relative volatility, which varied between 2.54 and 1.85 over the composition and temperature ranges, is precise within ± 1.5%.