From Chemical Engineers' Portable Handbook
Binary Distillation; the McCabe-Thiele Method
In the case of a continuous distillation column (see Figure 5-8) a method used to determine the number of ideal stages is the McCabe-Thiele.
Figure 5-8: Schematic of continuous distillation column. Section above feed is enriching or rectifying; below feed is stripping section. (Reproduced with permission from reference 38. Copyright 1997 American Chemical Society.)
The stages in a distillation column can be of various configurations. Two systems are shown in Figure 5-9.
Figure 5-9: Bubble cap ( a and b) and sieve plate ( c). Adapted from 36, 37.
The enthalpy balance for the McCabe-Thiele in the rectifying section essentially reduces to the vapor streams entering and leaving a stage V in moles/time and ?, the enthalpy of vaporization.
For chemically similar materials,
This gives a condition known as constant molal overflow (i.e., all the V's in the rectifying section including V a are equal; the same holds true for all the L's including L a). The same condition holds for the stripping section (all vapor streams including V b are equal and all L streams are equal to each other).
A mass balance for the rectifying section gives
Likewise, the mass balance for the stripping section is
Equations 5-16 through 5-19 are straight lines because of constant molal overflow.
The junction of the rectifying and stripping mass balances is fixed by the feed...
Products & Services
Topics of Interest
Binary Distillation; Additional Cases; Enthalpy-Equilibrium Approach The McCabe-Thiele method can be used for a variety of special cases. Figure 5-14 illustrates the situation if two feeds are used.
Absorption in Plate Columns Plate or stage columns can be used as absorbers. In such cases (Figure 5-27) the liquid (absorbing) stream and the gas streams move countercurrently. Figure 5-27:...
A multistage membrane operation can be represented in similar fashion to a multistage, plate-to-plate, stepwise or stagewise distillation column or operation, although at first glance this may not...
13.9. SEPARATIONS IN PACKED TOWERS Continuous changes in compositions of phases flowing in contact with each other are characteristic of packed towers, spray or wetted wall columns. The theory of...
Overview M. F. Doherty, Ph.D. Professor of Chemical Engineering, University of California Santa Barbara (Section Editor) Z. T. Fidkowski, Ph.D. Process Engineer, Air Products and Chemicals Inc.