CB/EB 76 Mellapak 500Y 30。5 27。9 27。9 22。4 22。98

i-C4/n-C4 8533 Mellapak 250Y 11。9 31。8 25。4 24。1 21。6–3110

C6/n-C7 1241 Flexipac 250Y 21。8 40。6 35。6 30。5 38–4110

cis-/trans-Decalin 304 Mellapak 250Y 24。1 41。9 39。4 38。1 33–35。68

TEG/H2O/CH4 31,030 Flexipac 250Y 472。4 348。0 1193。8 140 167。612

In all cases, the countercurrent flow model was used。 All experiments at total reflux。 HETPs are reported in cm。 CB, chlorobenzene; EB, ethylbenzene; TEG, triethylene   glycol。

Figure 1。 Diagram showing the changing driving force for mass transfer between the operating line and the equilibrium curve。

Consider the diagrams in Figure 1。 Note that there is a con- tinuously changing overall driving force  for  mass transfer。 Where it is possible to assume that the equilibrium curve is lin- ear over the range in which  it is to  be used,  it can  be shown that the logarithmic mean  of  the  terminal  potentials  accounts for the continuously changing driving  force    exactly。13,15

Substituting

G ¼ ðKOyamÞjnHETPn

 1 —  mn G!

ln。mn G。

(5)

The amount of the more volatile component (referred to as component ‘‘A’’)  transferred from the vapor to the liquid     phase

Further, if we define kn  ¼ mnG/L,   then

per unit area (i。e。, the flux of the more volatile component) is

NA  ¼ Gðyn  — ynþ1Þ (1)

HETPn ¼

G

ðKOyaÞjn

。 ln kn 。

kn — 1

(6)

where G is the molar flux of vapor in the column (assumed constant in the packed section because of constant molal overflow)。

With the assumption that the equilibrium curve is   straight

This is the final expression for the HETP at stage ‘‘n’’— HETPn。 kn can be considered a sort of stripping factor。 The notation above—HETPn, KOya|n, and kn—implies that these quantities are dependent on the stage number, n, whereas G is  not  (because  of  the  assumption  of  constant  molal  over-

0 1 flow)。 Figure 2 shows how ln(k)/(k—1) varies with k。