Thermodynamics in the treatment of vapor/liquid equilibrium (VLE) data

Abstract

The Rossini lecture affords the lecturer an opportunity to review his contributions to a subject and to reflect on them from the perspective of an extended career. The subject here is vapor/liquid equilibrium, and the topics reviewed include property relations, experimental measurements, consistency tests, and data reduction and correlation.In the first of these lectures Dr. Rossini remarked that the sponsoring group was named the Commission on Thermodynamics rather than the Commission on Chemical Thermodynamics so that engineering thermodynamics could be included. I am, however, the first engineer to give this lecture, a possible exception being Dr. Rossini himself. His B.S. degree was in fact in chemical engineering; however, he immediately turned to graduate work in chemistry, and certainly considered himself a chemist during his professional career. So it would seem that all of my predecessors have been chemists, very distinguished chemists, who have set a high standard indeed for this lecture. As the tenth Rossini lecturer I am expected to draw upon contributions I have made to thermodynamics. Of greatest practical interest no doubt are those relating to vapor/liquid equilibrium (VLE). I propose therefore to expound on the thermodynamic treatment of VLE data, with consideration limited to binary systems at low to moderate pressures, a scope suited to the occasion. This topic is more complex and less widely understood than might be supposed. PROPERTY RELATIONSCentral to the correlation of VLE data are the thermodynamic excess properties, which describe the behavior of the liquid phase. These properties, introduced during the mid-l930's, express the differences between actual property values of a solution and the values which would be exhibited by an ideal solution at the same temperature, pressure, and composition. The equation interrelating these properties was derived in one of my earliest papers on thermodynamics (1). Now known as the fundamental excess-property relation, it is an integral part of the thermodynamic structure that we lay before undergraduate students (2):where yi is the activity coefficient of species a in solution and g = GE/RT Implicit in Eq. (1) is the relation,

Isobaric vapor–liquid equilibria for mixtures of acetone, ethanol, and 2,2,4-trimethylpentane at 101.3kPa

“…The thermodynamic consistency of three binary systems was treated using the direct test proposed by Van Ness [18]. According to the Van Ness's method, a consistency index associated with the test characterizes the degree of departure of a data set from consistency.…”

Isothermal v.l.e. and excess molar Gibbs energy of binary and ternary mixtures containing diisopropyl ether,n -heptane and isopropanol at T= 313.15 K

“…Thus, the vapour phase needs not to be sampled and the resulting data are thermodynamically consistent per se. (16)(17)(18) The data reduction of the binary and ternary mixtures has been performed using Barker's method (19) according to well established procedures. (20,21) …”

Excess thermodynamic properties of binary and ternary mixtures containing methyl 1,1-dimethylethyl ether (MTBE), -heptane, and methanol at= 313.15 K

“…Thus, the vapour phase need not be sampled, and the resulting data are thermodynamically consistent per se. (12)(13)(14) The data reduction of the binary and ternary mixtures has been performed using Barker's method (15) according to well-established procedures. (16,17) A developed computer program described elsewhere (1) has been used to implement the technique.…”