Vapor-Liquid Equilibrium at Atmospheric Pressure: Systems Containing Ethyl Alcohol, n-Hexane, Benzene, and Methylcyclopentane.

Abstract

VAPOR-LIQUID equilibrium relationships at atmospheric pressure for the ternary system n-hexane-benzenemethylcyclopentane and the quaternary system ethyl alcohol-n-hexane-benzene-methylcyclopentane were determined. The latter system was investigated at n-hexane concentrations of approximately 35 and mole 70 in the liquid phase. This is a continuation of the work of Sinor and Weber (IO) and means that two of the possible four ternary systems which can be made with the four compounds have been investigated and additional quaternary data are available. The six binary systems have been investigated by Myers (7-9), Wehe and Coates (II), and Ehrett and Weber (3). The experimental results show that the ternary hydrocarbon system deviated to some extent from ideal liquid phase behavior, the maximum value of the activity coefficients being approximately 1.40. No ternary azeotrope was found. Concerning the quaternary system, qualitatively, as the concentration of n-hexane was increased in the liquid phase, the relative volatility of n-hexane tended to change from a value greater than 1 to a value less than 1. The quaternary system also exhibited large deviations from ideal liquid phase behavior. EXPERIMENTAL Purity of Compounds. The n-hexane, benzene, and methylcyclopentane were pure grade materials of 99 mole 7'0 (minimum) purity (Phillips Petroleum Co.). The ethyl alcohol (U. S. Industrial Chemicals Co.) and the hydrocarbons were not purified further. When these materials were run, singly, through the Vapor Fractometer no small peaks appeared, indicating the purity of the compounds was in all probability considerably higher than the minimum claimed value. Physical constants for the materials are shown in Table I. Procedure. Vapor-liquid equilibrium data were obtained using a Braun still as described by Hipkin and Myers (4), and the experimental technique outlined by these authors was followed. Nitrogen was bled into the still to maintain the operating pressure of 760 =k 0.5 mm. of Hg. The pressure was controlled by a manostat and measured on an absolute mercury manometer. Temperatures were measured by copper-constantan thermocouples used with a Leeds and Northrup Type K potentiometer. Temperatures are believed to be accurate within * 0.1 C. n-Heptane was used as the jacket fluid. The pressure in the jacket was regulated so that the boiling temperature of the n-heptane was 0.1 C., or less, greater than the boiling temperature of the test sample. Ternary and quaternary samples were analyzed by gas chromatography, using a Perkin-Elmer Model 154-C Vapor Fractometer. Helium was the carrier gas. To separate the components of the ternary mixture, a 2-meter column packed with Perkin-Elmer Type A column material was used. This packing is finely powdered diatomaceous earth with diisodecyl phthalate as the adsorbed liquid. PerkinElmer Type F packing was used to separate the components of the quaternary mixture. This packing is diatomaceous earth with tetraethylene glycol dimethyl ether as the adsorbed liquid phase. To analyze the ternary mixtures, the Fractometer was operated at 50 C. with a column pressure of 15 p.s.i.g. and a detector voltage of 8 volts. The helium flow rate was 164 cc. per minute measured at 22 C. Twenty-four minuteswere required to run one sample. The peak areas were well spaced and completely separated. To analyze the quaternary mixtures, the Fractometer was operated as given above. except the column pressure was 11.5 p.s.i.g. and the helium flow rate was 116 cc. per minute and the time required for the analysis of one sample was 30 minutes. The peaks were well spaced and completely separated. In both cases, the peak areas were measured with a planimeter and the final compositions are believed to be accurate within i= 0.5 mole %.