(28a) Ternary Vapor-Liquid Equilibrium at 1 Atm - the Simplest Case: A Tutorial Using Literature Data

Ternary Vapor-Liquid Equilibrium at 1 Atm – The Simplest Case:
A Tutorial Using Literature Data    

Robert G. Kunz

RGK Environmental Consulting, L.L.C.

Hillsborough, North Carolina

Paper Proposed for Presentation at

2015 AIChE Spring Meeting 

April, 2015

Austin, TX

Abstract

            In making the transition from two-component (binary) to three-component (ternary) distillation, it appears that an important stepping stone in the learning process has often been left out.  While it may be more interesting to move directly to analyze ternary systems with unusual properties, much can be gained from a brief study of ternary distillation for cases exhibiting ideal or nearly ideal behavior.  At the very least, these provide a standard for the treatment of non-ideal systems in regard to technique and presentation.            It is instructive to predict idealized vapor-liquid equilibrium (VLE) of the resulting ternary system, starting with the three constituent binaries, each assumed to follow Raoult’s Law in the liquid phase with an ideal-gas vapor phase.  Typical graphical presentation of numerical results for a ternary system is also explored.            Since it is unlikely that any real VLE system would ever be perfectly ideal, it is even more fruitful to evaluate any deviations between the idealized calculations and experimental data.          To illustrate the principles involved, binary and related ternary VLE data at atmospheric pressure are considered for mixtures of benzene, toluene, and para-xylene and for mixtures of methanol, ethanol, and the propanols, where experimental VLE data are available for comparison.  Relatively low-boiling components and low pressure have been selected to keep things as simple as possible in this tutorial.  The minor deviations in both x-y and temperature values compare favorably with both the original investigators’ raw data and their more complicated calculations using experimentally determined activity coefficients. 

The methodology can be extended to multi-component (quaternary and higher) systems and forms the basis for empirical distillation-column design methods involving families of similar molecules.  These techniques are explored briefly.

Keywords.     Antoine Equation; Binary and Ternary Systems; Dalton’s Law; Ideal-Gas Vapor Phase; Liquid-Phase Activity Coefficients; Multi-Component Systems; Ideal Systems; Raoult’s Law; Specific Systems:  Benzene–Toluene, Toluene–Ethylene Dichloride (EDC), Methanol–Water, Benzene–Toluene–p-Xylene, Methanol–Ethanol–1-Propanol, and Methanol–Ethanol–2-Propanol, Butanols with Methanol, Ethanol and 1-Propanol; Vapor Pressure; Vapor-Liquid Equilibrium (VLE).