Chemical Reaction Engineering Asynchronous Video Series Chapter 3, Part 4: Reaction Stoichiometry...

Chemical Reaction Engineering

Asynchronous Video Series

Chapter 3, Part 4:

Reaction Stoichiometry

Measures Other Than Conversion

H. Scott Fogler, Ph.D.


Uses: A. Membrane reactors

B. Multiple reaction

Liquids: Use concentrations, i.e., CA

€

C A =FA

υ0





1. For the elementary liquid phase reaction carried out in a CSTR, where V, vo,CAo,k, and Kc are given and the feed is pure A, the combined

mole balance, rate laws, and stoichiometry are:

€

C A =FA

υ0

€

A ⇔ B

€

−rA = k C A −CB

K C

⎡

⎣ ⎢ ⎢

⎤

⎦ ⎥ ⎥





1. For the elementary liquid phase reaction carried out in a CSTR, where V, vo,CAo,k, and Kc are given and the feed is pure A, the

combined mole balance, rate laws, and stoichiometry are:

€

C A =FA

υ0

€

A ⇔ B

€

C A0 − CA

−rA=

€

V =FA0 − FA

−rA=

υ 0 C A 0 −C A[ ]

−rA

€

−rA = k C A −CB

K C

⎡

⎣ ⎢ ⎢

⎤

⎦ ⎥ ⎥







€

C A =FA

υ0

€

A ⇔ B

€

C A0 − CA

−rA=

€

V =FA0 − FA

−rA=

υ 0 C A 0 −C A[ ]

−rA

€

τ =CA 0 − C A

k CA −CB

K C

⎡

⎣ ⎢

⎤

⎦ ⎥

€

−rA = k C A −CB

K C

⎡

⎣ ⎢ ⎢

⎤

⎦ ⎥ ⎥







€

C A =FA

υ0

€

A ⇔ B

€

C A0 − CA

−rA=

€

V =FA0 − FA

−rA=

υ 0 C A 0 −C A[ ]

−rA

€

τ =CA 0 − C A

k CA −CB

K C

⎡

⎣ ⎢

⎤

⎦ ⎥

€

V =FB 0 − FB

−rB

=υ 0 C B 0 − C B[ ]

−rB

€

−rA = k C A −CB

K C

⎡

⎣ ⎢ ⎢

⎤

⎦ ⎥ ⎥


€

τ =3s, C A 0 = 2 mol dm3 , K C =10, k = 0.1s −1


€

τ=C B0 − CB

−rB=

0− CB

−rB=

−C B

rA=

C B

−rA=

C B

k CA −C B

KC

⎡

⎣ ⎢ ⎢

⎤

⎦ ⎥ ⎥

€

τ =C B

k CA −CB

K C

⎡

⎣ ⎢

⎤

⎦ ⎥

€

τ =3s, C A 0 = 2 mol dm3 , K C =10, k = 0.1s −1


€

τ=C B0 − CB

−rB=

0− CB

−rB=

−C B

rA=

C B

−rA=

C B

k CA −C B

KC

⎡

⎣ ⎢ ⎢

⎤

⎦ ⎥ ⎥

2. There are two equations, two unknowns, CA and CB

€

τ =3s, C A 0 = 2 mol dm3 , K C =10, k = 0.1s −1

€

τ =C B

k CA −CB

K C

⎡

⎣ ⎢

⎤

⎦ ⎥


• Gases: Use molar flow rates, i.e., FI

€

C T =FT

υ=

PRT

, CT 0 =FT 0

υ 0

=P

RT0



€

C A = C T0

FA

FT

⎛

⎝ ⎜

⎞

⎠ ⎟PP0

T0

T , CT 0 =P0

RT0

€

C T =FT

υ=

PRT

, CT 0 =FT 0

υ 0

=P

RT0



If the above reaction, ,carried out in the gas phase in a PFR, where V, vo,CAo,k, and Kc are given and the feed is pure A, the combined

mole balance, rate laws, and stoichiometry yield, for isothermal operation (T=To) and no pressure drop (P=0) are:

€

C A = C T0

FA

FT

⎛

⎝ ⎜

⎞

⎠ ⎟PP0

T0

T , CT 0 =P0

RT0

€

C T =FT

υ=

PRT

, CT 0 =FT 0

υ 0

=P

RT0

€

−rA = k C A −CB

K C

⎡

⎣ ⎢ ⎢

⎤

⎦ ⎥ ⎥



If the above reaction, ,carried out in the gas phase in a PFR, where V, vo,CAo,k, and Kc are given and the feed is pure A, the combined mole

balance, rate laws, and stoichiometry yield, for isothermal operation (T=To) and no pressure drop (P=0) are:

€

C A = C T0

FA

FT

⎛

⎝ ⎜

⎞

⎠ ⎟PP0

T0

T , CT 0 =P0

RT0

€

C T =FT

υ=

PRT

, CT 0 =FT 0

υ 0

=P

RT0

Use Polymath to plot FA and FB down the length of the reactor.

€

−rA = k C A −CB

K C

⎡

⎣ ⎢ ⎢

⎤

⎦ ⎥ ⎥



Given:

€

V0 = 30 dm 3 , υ 0 = 10 dm 3 s, K C = 10, k = 0.1s −1



Given:

€

V0 = 30 dm 3 , υ 0 = 10 dm 3 s, K C = 10, k = 0.1s −1

V

FA

FB

Summary

At the start of the chapter we saw we needed -rA=f(X). This result is achieved in two steps.

Summary


1. Rate Laws

– -rA=k f(Ci)

– 1st order A--> B or 1st order

-rA=kCA

€

−rA = k C A −C B

KC

⎡

⎣ ⎢ ⎢

⎤

⎦ ⎥ ⎥

Summary


1. Rate Laws

– -rA=k f(Ci)


– 2nd order A+B --> C

– Rate laws are found by experiment

-rA=kCA

€


KC

⎡

⎣ ⎢ ⎢

⎤

⎦ ⎥ ⎥

-rA=kACACB

Summary


1. Rate Laws

– -rA=k f(Ci)


– 2nd order A+B --> C

– Rate laws are found by experiment

2. Stoichiometry

– Liquid:

– Gas:

-rA=kCA

€


KC

⎡

⎣ ⎢ ⎢

⎤

⎦ ⎥ ⎥

-rA=kACACB

€

C A = CA 0 1− X( )

€

C A =CA 0 1− X( )

1+ εX( )PP0

T0

T

€

C A = CT 0

FA

FT

PP0

T0

T

Chemical Reaction Engineering Asynchronous Video Series Chapter 3, Part 4: Reaction Stoichiometry...

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Transcript of Chemical Reaction Engineering Asynchronous Video Series Chapter 3, Part 4: Reaction Stoichiometry...