INDUSTRIAL AND ENGINEERING CHEMISTRY
964
Vol. 48, No. 5
Vapor-Liquid Equilibria for ystem Car on Tetrach oride-Furfural DEARSIR: Testing of vapor-liquid equilibrium data for thermodynamic consistency is a pomerful tool, but under certain circumstances misunderstanding and confusion can develop through the use of such procedures. I n the paper, “Vapor-Liquid Equilibria for the System Carbon Tetrachloride-Furfural” [R. E. V’ingard, TT’. S. Durant, H. E. Tubbs, and W.0. Brown, IND.ENG.CHEX 47, 1757 (1955)], it should be noted by readers t h a t in the graphical method for obtaining the van Laar constants A and B, the authors have used In y and not Tln y as is correctly recommended by Robinson and Gilliland. The components boil 85’ C. apart. T h e use of Tln y gives A = 0.569 and B = 490 from component 1 data, and A = 0.541 and B = 230 from component 2 data. The lack of agreement between the two values of B does not arise from nonideality of the system, but is caused by lack of thermodynamic consistency between the 2-1~ and 2-t data. Incidentally, the incorrect use of In y fortuitously also leads to the same conclusion since in this case A = 1.232 and B = 2.66 from component 1 data as reported in the paper but A = 0.645 and B = 1.00 from component 2 data. However, the latter are not explicitly given in the paper. The method of measuring temperatures used in the work is very likely to lead to uncertainty and error since subjective judgments are required in adjusting the heating jackets. With the very great relative volatilities and temperature differences that are involved, there would also seem t o be a likelihood of condensation on the walls of the equilibrium vessel. Thus, absence of thermodynamic consistency in the results is not surprising. General experience with mixtures and equipment such as those used by Wingard and coworkers suggest that the data are probably adequate for preliminary engineering purposes, but the thermodynamic analysis and discussion at the end of the paper does not confirm the accuracy or precision of the data. PENNSYLVANIA STATEUNIVERSITY UNIVERSITY PARK, PA.
ARTHURROSE
DEARSIR: I n reference to Dr. Arthur Rose’s comments on the paper “Vapor-Liquid Equilibria for the System Carbon TetrachlorideFurfural,” the folloving points should be noted: The purpose of the investigation was to obtain the necessary t-x and y-x data for the construction of the vapor-liquid equilibrium diagram. The diagram would then be used in the design of distillation equipment. Such a diagram suitable for engineering purposes was presented. Therefore, the mission has been accomplished. No claim was made in the paper for thermodynamic consistency of the data. Certain minimum criteria relating t o vapor-liquid equilibrium data were applied to the satisfaction of the authors vs. 21/22 plot of the raw data yielded and reviewers. The a straight line with no forcing. This would indicate little or no heat of mixing and certainly indicate consistent experimental data. The log y us. z plot also obeys certain minimum criteria again indicating that the unsmoothed data are reasonably good. Those familiar with the behavior of the carbon tetrachloridefurfural system in high furfural concentrations will readily recognize t h a t many things chemical may happen to preclude the existence of a n ideal solution. The claim is made in the paper t h a t certain modifications t o the Othmer still, as suggested in the literature by Othmer, improve the operation of the still. The data in our paper represent, a t present, the best and only data no17 available on the system. ALABAWA P O L Y T E C H h I C INSPITUTE
AURCRN.A L A .
R. E. WINGARD
