Vapor-liquid equilibria of nonelectrolyte solutions in small capillaries. 1. Experimental determination of equilibrium composition

Abstract

The vapor-liquid equilibrium of an ethanol-water solution held in small pores (pore size range, Aim; median pore size, 13.5 µ ) inside a porous sintered stainless steel plate was determined at 50 °C by using a static method. The vapor pressure of ethanol and of water held in these small pores was found to differ greatly from the values obtained from the Antoine equation. By a treatment of the experimental data, it was shown that the ratio of the vapor pressure of pure ethanol to that of pure water in the capillary plate is 3.7876. The ratio of the vapor pressure of pure ethanol and water as predicted from the Antoine equation is 2.3092. Thus, the relative volatility of ethanol and water held in the capillary plate is about 1.58 times the normal relative volatility in the bulk phase. Under the normal vapor-liquid equilibrium in the bulk phase, the value of the relative volatility of the ethanol-water system is unity at Xx = 0.9060 at 50 °C. In the experimental study of the same system in the capillary plate, the relative volatility does not become unity when Xx is less than 0.99. A further treatment of the experimental data by a method suggested by Hirata confirmed the absence of the formation of any azeotrope at Xx < 0.99. The consistency test and thermodynamic test were performed on the experimental data, showing that the data are very consistent and satisfy the rigorous thermodynamic relationships. These tests also displayed the absence of systematic errors in the experiment. In view of the experimental findings made in this study, it is strongly recommended that further experimental studies be conducted on the vapor-liquid equilibrium in small capillaries, for both ideal and nonideal liquid solutions. With the advent of capillary distillation,3,10 these data will be important for the understanding and implementation of the new technique to separate nonideal azeotropic mixtures.

Isothermal Vapor–Liquid Equilibrium of Ethanol–Water Mixtures + Acetone–Ethanol Mixtures Inside Capillary Porous Plates

“…Furthermore, it is clear that the azeotropic point in this case has shifted from x 1 Х 0.90 to the neighborhood of x 1 → 1. These results are similar to those obtained by Yeh et al (4) and Wong (11). In the case of an ethanol-water system in porous carbon or Teflon plates, however, the change in the VLE is insignificant, with no discernible shift in the azeotropic point.…”

“…The apparatus has ports for evacuation, pressure measurement, liquid introduction, and sample withdrawal, and upon charging is placed in a thermostatically controlled constant-temperature air bath. A detailed description of the procedure and the still used to study vapor-liquid equilibria in capillary porous plates can be found elsewhere (4,12).…”

“…An innovative alternative separation method, called capillary distillation, was proposed by Yeh et al (4)(5)(6) and later Abu Al-Rub et al (7) and Abu AlRub and Datta (8)(9)(10) to separate binary mixtures with an azeotropic point. Capillary distillation is a new method that utilizes the surface forces of the solids and the consequent intermolecular interactions between the solid and liquids, which in turn alter the intermolecular interactions among the solution components, thus altering the VLE.…”

“…However, the studies of Yeh et al (4)(5)(6), Abu Al-Rub et al (7), Abu Al-Rub and Datta (8)(9)(10), and Wong (11) show that the Kelvin effect is negligible for pores of radii Ͼ 0.1 m. Abu Al-Rub and Datta (9-10) analyzed the VLE in porous media using a molecular thermodynamics approach. They concluded that the main factor affecting the alteration of VLE in porous media is the intermolecular interaction between the liquids and the solid.…”

Using Simplified Local Density/ Peng-Robinson Equation of State to Study the Effects of Confinement in Shale Formations on Phase Behavior

“…Danesh (1998) claimed that the effect of porous media is significant when the pore size is less than 10 nm. Gas can condense (capillary condensation) inside porous media because of the fluid-wall interactions (Yeh et al (1986) and Sigmund et al (1973)). …”