Page 210 - Elements of Chemical Reaction Engineering 3rd Edition

182 Isothermal Reactor Design Chap. 4

I Equations (E4-9.15) and (E4-9.16) solve to
FA, = 1.34 mol/min
F,, = 17.32 mol/min

We note from Figure E4-9.1 that the molar flow rates begin to approach the equilib-
rium values near the end of the reactor.,

4.6.2 Membrane Reactors

Catalytic membrane reactors can be used to increase the yield of reactions
that are highly reversible over the temperature range of interest. (Some refer to
this type of reaction as being thermodynamically limited.) The term membrane
reactor describes a number of different types of reactor configurations that con-
tain a membrane. The membrane can either provide a barrier to certain compo-
nents, while being permeable to others, prevent certain components such as
particulates from contacting the catalyst., or contain reactive sites and be a cat-
By having one of [he alyst in Itself. Like reactive distillation, the membrane reactor is another tech-
products pass nique for driving reversible reactions to the right in order to achieve very high
throughout the conversions. These high conversions can be achieved by having ene of the reac-
membrane we
drive the rea;tion tion products diffuse out of a semipermeable membrane surrounding the react-
towards completion ing mixture.s As a result, the reaction will continue to proceed to the right
toward completion.
Two of the main types of catalytic membrane reactors are shown in Fig-
ure 4- 12. The reactor in the middle is called an inert membrane reactor with
cura/yst pe//ets on the feed side (IMRCF). Here the membrane is inert and
serves as a barrier to the reactants and some of the products. The reactor on the
bottom is a carn/jfic membrane reactor (CMR). The catalyst is deposited
directly on the membrane and only specific reaction products are able to'exit
the permeate side. For example, in the reversible reaction

C,HI, - + 3H2
C,H,
t---
H2 diffuses through the hydrogen molecule is small enough to diffuse through the small pores of the
the membrane membrane while C,H and CbH6 cannot. Consequently, the reaction continues
while C6H, does to proceed to the right even for a small value of the equilibrium constant.
not
Detailed modeling of the transport and reaction steps in membrane reac-
tors is beyond the scope of this text but can be found in Membrane Reactor
Technology.5 The salient features, however, can be illustrated by the following
example. When analyzing membrane reactors, it is much more convenient to
use molar flow rates rather than conversion.

R. Govind, and N. Itoh, eds., Membrane Reactor Technology, AIChE Symposium
Series No. 268, Vol. 85 (1989). T. Sun and S. Khang, Ind. Eng. Chem. Res., 27, 1136
(1988).