Lecture 9 Thursday 1/31/08 Membrane Reactors: Used for Thermodynamically Limited Reactions

Balances in Terms of Molar Flow Rates

Block 1: Mole Balances Balance Equation on Every Species Block 2: Rate Laws Relative Rates Transport Laws Block 3: Stoichiometry Block 4: Combine

Multiple Reactions: Selectivety and Yield

Membrane Reactors

Dehydrogenation Reaction:

C3H8 ↔ H2 + C3H6 A ↔ B + C

Thermodynamically Limited:

W = ρbV

ρb = (1-ϕ)ρC

1) Mole Balance: A: In – out + generation = 0

RB = A:

B: In – out – out membrane + generation = 0

B:

reactor of volume

sides through B of moles

000

VrFF AVVAVA

AA r

dV

dF

XCXC

T T

endothermicexothermic

A,B,C

sweep

FA0

B

B

A,C stay behind since they are too big

H2 H2CBS

0

VrVRFF BBVVBVB

)( BBB Rr

dV

dF

)(`BSBCB CCkW DL

DLa

D

4

lumereactor vo

area surface membrane

4

2

BSBCBB CCakaWR ` BSBCB CCkR

Neglected most of the time

Parameters: CTO = 0.2, FA0= 5, k = 4, KC = 0.0004, kC = 8

1)

2)

3)

4)

Relative rates:

5)

6)

7) (isothermal, isobaric)

8)

9)

10)

AA r

dV

dF

BBB Rr

dV

dF

CC r

dV

dF

C

CBAA K

CCCkr

111CBA rrr

T

ATA F

FCC 0

T

BTB F

FCC 0

T

CTC F

FCC 0

CBAT FFFF

CABA rrrr ,

BCB CkR

Multiple Reactions

)(Undesired

(Desired) 2

2

BAUUk

BADDk

CCkrUBA

CCkrDBAU

D

Selectivity Yield

Instantaneous SD/U = rD/rU yD = rD/-rA

Overall ŜD/U = FD/FU ŷD = FD/(FA0-FA)

BU

AD

BAu

BAD

U

DUD Ck

Ck

CCk

CCk

r

rS

2

2

/