Vapor-Liquid Equilibria for N-Hexane—Benzene Mixtures

Abstract

INA PREVIOUS communication (10), while describing the isolation of V-hexane from Pennsylvania petroleum, the abnormal vapor pressure relations of V-hexane and benzene were noted. It was found impossible even after prolonged distillation in very efficient columns to obtain V-hexane containing less than 2.5 per cent by volume of benzene. Other investigators have isolated V-hexane from petroleum [a complete review is given by Bruun and Hicks-Bruun (S, 4) ] but have never obtained it pure unless chemical means were employed to remove the benzene. It has been supposed that V-hexane and benzene form a constant-boiling mixture (12). It is the purpose of the present work to study the binary mixture of V-hexane and benzene, and to determine if V-hexane can be obtained pure from the binary mixture by the addition of a third liquid and by subsequent distillation.Four hundred cc. of the Vhexane-benzene mixture were nitrated, in two separate batches, with a nitration mixture consisting of 58 per cent by weight concentrated sulfuric acid, 25 per cent by weight concentrated nitric acid, and 17 per cent by weight water. Equal volumes of the hydrocarbon and the acid mixture were placed in 500-cc. glass-stoppered bottles which were put on the mechanical shaker for 8 hours. The acid layer was separated, and the hydrocarbon layer washed with concentrated sulfuric acid and then with water.After drying, the hydrocarbon was distilled over sodium in a partial condensing column 12 mm. in diameter, 91 cm. tall, and packed with Lessing rings (5X5 mm.) made of 50-mesh copper screen (11). The distillate after drying over sodium had a boiling point of 67.4°C. (730 mm.) or 68.65°C. (760 mm.), and a refractive index (ro2D°) of 1.3750. The density taken in a Sprengel type pycnometer was 0.6593 (dj°). These physical constants are in close agreement not only with those given above for pure V-hexane, but also with those of synthetic Ar-hexane [boiling point 68.7°C. (760 mm.), refractive index (n\°) 1.3750] prepared in this laboratory.

Separation, by distillation with acetic acid, of the aromatic hydrocarbons from the fraction of a midcontinent petroleum boiling between 154 and 162 C

“…By the formation of binary azeotropic mixtures, the original ratio of the various classes may be materially altered in the vapor phase, and separation becomes possible. This general procedure has been used to separate hydrocarbons by addition of methyl alcohol [21,22], ethyl alcohol [22], tert-butyl alcohol [26], and acetic acid [23,24].…”

Separation of hydrocarbons by azeotropic distillation

“…This difference in the shapes of the liquid-vapor curves for the two kinds of solutions is illustrated in figure 3, which gives the temperature-composition diagrams for the binary system of benzene and n-hexane [13] and for the binary system of benzene and ethyl alcohol [14]. The much greater spread in composition (except for the constant-boiling mixture) between the liquid and vapor phases for the latter system than for the former is readily apparent.…”

“…'i'he scgle of ordinates gives the temperature In degrees centigrade, and the scale of abscissas gives the mole fraction of benzene. The dia~ram for tbe system of ethyl alcohol and henzene was constructed from the data of Fritzweiler and Dietrich 114] and that for the system of n·hex-ane and ben1.ene was constructed from the data 01 Tongberg and Joh nston [13]. …”

“…Tongberg and Johnston [13] have described the separation of benzene from n-hexane by azeotropic distillation with tert-butanol.…”

A Practical Fitting Method Involving a Trade-Off Decision in the Parametrization Procedure of a Thermodynamic Model and Its Repercussion on Distillation Processes

“…In studies related to the thermodynamics of solutions, the experimental information generated by the binary benzene + hexane, for different properties, has been, and still is, used by researchers in that area as a reference of their investigations; therefore, the choice of this system is justified. Twenty-three useful VLE data series were found in the bibliography [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42], 16 iso-p and 7 iso-T. Figure 3 shows important errors in some of the series [29,31,37] at 101 kPa, with data missing the trend observed in the other series. These are propagated to the T vs x,y representations ( Figure 4(a)).…”