Page 473 - Elements of Chemical Reaction Engineering Ebook

444 Steady-State Nonisothermal Reactor Design 'Chap. 8

and used to design CSTRs (i.e., to obtain the reactor volume or operating tem-
perature). If necessary, the CSTR is either heated or cooled by a heating or
cooling jacket as shown in Figure 8-2, or by a coil placed inside the reactor.
Reactions are frequently carried out adiabatically, often with heating or
cooling provided upstream or downstream of the reaction vessel. With the
exception of processes involving highly viscous materials such as in Problem
P8-4, the work done by the stirrer can usually be neglected. After substituting
Equation (8-42) for Q , the energy balance can be written as

CSTR with heat
exchange

Under conditions of adiabatic operation and negligible stimng work, both Q
and wS are zero, and the energy balance becomes

Adiabatic operation
of a CSTR

The procedure for nonisothermal reactor design can be illustrated by con-
sidering the first-order irreversible liquid-phase reaction shown in Table 8-1.
The algorithm for working through either case A or B is summarized in Figure
8-4. Its application is illustrated in the following example.
From here on, for the sake of brevity we will let

unless otherwise specified.

I Example 8-4 Production of Propylene Glycol in an Adiabatic CSTR
I Propylene glycol is produced by the hydrolysis of propylene oxide:

CH2-CH-CH3 + H20 CH CH-CH3
\/ I I-1
0 OH OH
Over 800 million pounds of propylene glycol were produced in 1997 and the selling
Production, uses, price was approximately $0.67 per pound. Propylene glycol makes up about 25% of
and economics the major derivatives of propylene oxide. The reaction takes place readily at room
temperature when catalyzed by sulfuric acid.
You are the engineer in charge of an adiabatic CSTR producing propylene
glycol by this method. Unfortunately, the reactor is beginning to leak, and you must
replace it. (You told your boss several times that sulfuric acid was corrosive and that
mild steel was a poor material for construction.) There is a nice overflow CSTR of
33-gal capacity standing idle; it is glass-lined and you would like to use it.