50% Cyclohexane, 50% n-Heptane Feed
Change in Vapor Concentration
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
0
5
10
15
20
25
30
35
40
45
50
XD .9993-.9990
(yn+1-yn-1)/2
Theoretical Stage No. from Bottom
Figure 4.1 Vapor concentration response from concentration gradient per theoretical stage and from increased D/F.
Distillate/Feed Material Balance Split ◾  27
calculated as the difference between the last two stages. This
shows that the largest temperature gradient per theoretical
stage is 7.6% of 17.7°C, that is, 1.3°C, at stage number 15 or 16
from the bottom.
For example, if at theoretical stage 15, temperature is 1.35°C
hotter than Stage 16, and Stage 17 is 1.25°C cooler than Tray
16, the average response would be a shift of 1.30°C from the
nearest tray.
4.3 Temperature Change from D/F Shift
The method reported by Tolliver and McCune 1 for finding
the most responsive temperature point was also used for this
cyclohexane/n-heptane system. A second computer simulation was run using the same reflux/feed ratio for the separation power base while shifting the D/F (distillate/feed) ratio
up. The heavy key impurity concentration in the distillate was