Ideal Flow Reactors - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 225

Butene production (monomer for polymer production);

C 3 H 8 % C 3 H 6 þ H 2 (5.90)

Propylene production (monomer for polymer production).
These gas phase reactions can also be simplified to

A % B þ C (5.91)

with one of the product that is significantly smaller in size. The small molecules can permeate
through membranes that larger molecules could not. Although these reactions are thermody-
namically unfavorable, the removal of H 2 from the reaction mixture can shift the thermody-
namic equilibrium that favors the production of alkenes, which are valuable as they are
monomers for polymer production.
Figure 5.18 shows an idealization of membrane reactors. From Fig. 5.18 , one can conclude
that membrane reactor problem can easily be solved just as other reactors. In most situations
though, an automatic integrator is needed.
Mole balance of species B in the reactive stream yields:

d F B þ r B d V aJ B d V ¼ 0 (5.92)

where a is the specific mass transfer area (surface area of the membrane divided by reaction
mixture volume), F B is the molar flow rate of species B in the reactive stream, r B is the rate of

V V + d V

(a)

C A0 Q 0

f Ae

Q ,

C B

C Ae , C B

C OBe

Q OBe

F OB , C OB

(b)

J

d Q B

Q -d Q

Q

C A + dC A

C A , C

B

V V+ d V

FIGURE 5.18 A schematic of membrane reactor. (a) Some components are allowed to permeate through the
membrane and removed from the reaction mixture. (b) Blowout of a differential volume (section) of the membrane
reactor.