I
n,
Nomenclature
D H
I-
2 I
z
0.2
1
I/
can refer to weight L = most volatile component; can refer to weight N = component of intermediate volatility; can refer to weight W = weight remaining in still pot .yD = weight fraction of more volatile component in distillate xv = weight fraction of more volatile component in still pot aLN = volatility of L relative to N aNR = volatility of N relative to H
’\
Y
,
IO
20
30
I
I
I
I
I
40
50
60
70
80
J
90
WEIGHT % DISTILLED
Figure 4. agree
XDdD
Experimental and calculated results from ternary (L, N, H) distillation
[(L + N ) ( LkN)] L - ( L + N)d ( L ~ N )(L SL N) d(L -d
=
And -d(L
+ N) = dD,
+
N)
SO
the presence of H does not have a large effect on the relation. For example, the top composition a t 27.8% distilled (see Figure 4) is 5% L and 95% N. The per cent H in the bottoms a t this point is
%
=
% H in charge % of charge remaining x
c 2 X 100 72.2 From the above, comes
This is the equation used (L 4- N was taken as the remaining liquid on a n H-free basis, and
L was taken as L + N
~
xw on a n H-free basis). T h e relationship between
-L
XD
and
is not independent of H. Therein I, N lies the only important approximation in the method. However, in most cases
100 =
Wt. 70 5.0 94.9 0.1
Wt. yo 5.0 95.0
L 0.36 N Bottoms composition 70.26
0.43 99.57
N On H-free basis
0.43 99.57
L N Top composition H
H 29.38 L Bottoms composition 0.51
1 690
99.49
...
. ..
Table I V shows the results of a ternary plate-to-plate calculation and a binary calculation for the above top composition. The difference is not significant. I t is interesting to consider the possibility of correcting for the presence of H by a simple trial and error procedure. Thus, the method as outlined here would be used for the first approximation. Based on the approximation, the relationship between xD and x w could be determined on a ternary basis and a corrected curve calculated. This procedure could be repeated if necesssary, but this would seldom be the case.
Conclusions An easy-to-use method for ternary batch distillation calculations without holdup has been described and a n example problem is solved. The method is approximate, but the results are accurate enough for practical use. T h e method requires one necessary and limiting condition-that the distillation must yield, a t some time during its course, a distillate consisting almost entirely of the component of intermediate volatility. Validity of the method is supported by comparison with the results of two actual laboratory rectifications, and by a discussion of the theory involved.
INDUSTRIAL AND ENGINEERING CHEMISTRY
literature Cited (1) Robinson, C. S., Gilliland, E. R., “Elements of Fractional Distillation,” 4th ed., p. 383, McGraw-Hill, New
York, 1950. (2) Scientific Development Co., State College, Pa., Bull. 12. (3) Smoker, E. H., Rose, Arthur, Trans. Am. Znst. Chem. Engrs. 36,285 (1940). (4) Weissberger, A,, ed., “Technique of Organic Chemistry Distillation,” vol. IV, pp. 104-6, Interscience, Yew York, 1951. RECEIVED for review February 28, 1958 ACCEPTEDJuly 24, 1958 Work supported by the Pittsburgh Coke and Chemical Co. and findings published with its cooperation.
= 30.8%
+
Table IV. Difference between Ternary and Binary Calculations for 5% L in Overhead Is Not Significant Ternary, Binary,
= weight of distillate = least volatile component;
Correspondence A N e w Type of Nomogram. Aqueous Ammonium Sulfate Solutions SIR: Since publication of my article [IND. ENG. CHEM. 50, 971 (195S)l Francis W.Winn has called my attention to a nomogram of the same type which was described in his article published in the February 1957 issue of Petroleum R&ner. Attention was also called to the series on how to construct nomograms, which appeared in the Petroleum Rtjinei in October and Sovember 1955 and February and March 1956. I regret that these were unknown to me when my article was published. Dr. Winn has suggested that interpolation of my nomogram would be simpler if the intermediate graduations of the composition, density, and viscosity scales had been graduated in tenths or fifths rather than fourths. The vapor pressure scale, being in fourths and fifths, also seems confusing.
A. M. P. TANS CENTRAL LABORATORY STAATSMIJNEN I N IJMBURG GELEEN, THENETHERLANDS
