Page 224 - Separation process principles 2

Exercises 189

Essentially
impurities
1 atm pressure
throughout
system
Pasteurizing{
section
Distillate

Steam -
k- Bottoms
Figure 5.30 Conditions for Exercise 5.38.
Figure 5.32 Conditions for Exercise 5.40.

5.38 When the feed to a distillation column contains a small
amount of impurities that are much more volatile than the desired
distillate, it is possible to separate the volatile impurities from +
the distillate by removing the distillate as a liquid sidestream from
a stage located several stages below the top stage. As shown in 99.95 mot% benzene
Figure 5.30, this additional top section of stages is referred to as a
pasteurizing section.
(a) Determine the number of degrees of freedom for the unit
(b) Determine a reasonable set of design variables kmollh
Benzene 261.5 87.2 kg mollh
5.39 A system for separating a mixture into three products is Toluene 1% of benzene in the feed
shown in Figure 5.31. For it, determine Biphenyl 5.1
(a) The number of variables.
(b) The number of equations relating the variables.
(c) The number of degrees of freedom and propose.
(d) A reasonable set of design variables.

Figure 5.33 Conditions for Exercise 5.41.
Total
condenser
Product 1 5.40 A system for separating a binary mixture by extractive dis-
tillation, followed by ordinary distillation for recovery and recycle
of the solvent, is shown in Figure 5.32. Are the design variables
shown sufficient to specify the problem completely? If not, what
2 , Partial
F
Feed , additional design variables(s) would you select?
c
5.41 A single distillation column for separating a three-
component mixture into three products is shown in Figure 5.33. Are
the design variables shown sufficient to specify the problem
completely? If not, what additional design variable(s) would you
h
select?
Product 3
Cooler
Figure 5.31 Conditions for Exercise 5.39.