Page 219 - Elements of Chemical Reaction Engineering Ebook

190 Isothermal Reactor Design Chap. 4

4.7.2 Semibatch Reactors
\
Of the two types of semibatch reactors described earlier, we focus atten-
tion primarily on the one with constant molar feed. A schematic diagram of
this semibatch reactor is shown in Figure 4-14. We shall consider the elemen-
tary liquid-phase reaction

A+B-+C

Figure 4-14 Semibatch reactor.

in which reactant B is slowly added to a vat containing reactant A. A mole.
balance on species A yields
- r rate of 1
-
1 accumulation (4-5 1)

There are three variables that can be used to formulate and solve semi-
batch reactor problems: the concentration, Cj, the number of moles, Nj, and the
conversion. X.

Writing the Semibatch Reactor Equations in Terms of Concentrations.
Recalling that the number of moles of A is just the product of concentration of
A, CA, and the volume % we can rewrite Equation (4-51) as

(4-52)

We note that since the reactor is being filled, the volume, % varies with time.
The reactor volume at any time t can be found from an overall mass balance
of all species:
generation. =[ accumulation rateof I
+ [ rate of
[r;;] - (4-5.3)
- d(PV)
POUO - 0 + 0 - dt

For a constant-density system, po = p , and