01 Teknik Reaksi Kimia Lanjut

1Teknik Reaksi Kimia LanjutAdvanced in Reaction Engineering

Dr.-Eng. IGBN MakertiharthaLab. Teknik Reaksi Kimia dan Katalisis

2Reaksi Kompleks padaReaktor Ideal

Kinetika kompleks Reaksi Kompleks pada Reaktor-

Reaktor Ideal

3Kinetika Reaksi Kompleks

Dalam sebuah Reaktor Aliran Sumbat (RAS): Pada sebuah sistem reaksi kimia yang melibatkan

komponen A, B, C, , neraca massa masing-masingkomponen dapat digambarkan oleh sistem persamaandiferensial:

,...),,(

,...),,(

,...),,(

CBACC

CBABB

CBAAA

CCCrdz

dCu

CCCrdz

dCu

CCCrdz

dCu

=

=

=


Dalam sebuah Reaktor Tangki Ideal Kontinyu(RTIK):

1

2

3

( , , ,...) 0( , , ,...) 0( , , ,...) 0

A B C

A B C

A B C

f C C Cf C C Cf C C C

===


Suku rA, rB, rC identik dengan laju reaksi kimia untuk sistemdalam reaktor partaian.

Suku-suku ini akan lebih representatif jika juga merupakanfungsi dari temperatur yang merupakan operator utamapada besarnya laju reaksi spesifik atau tetapan laju reaksi.

Pada kasus realistik, sistem persamaan diferensial di atasharus diselesaikan secara numerik karena hampir dapatdipastikan bahwa penyelesaian analitik sebuah sistempersamaan diferensial tak linier tidak terdefinisi.

6Model Kinetika Reaksi Kompleks

Pada prinsipnya, proses penentuan parameter kinetika pada sebuah model kinetika kompleksadalah mencari parameter-parameter kinetika yang menyebabkan akumulasi kesalahan yang diakibatkanperbedaan nilai antara data kinetika dengan nilaihasil perhitungan dengan model sekecil mungkin.

( ),untuk 1: dan , ,...

j ik C

j n i A B

== =

r f

7Perkiraan Parameter Kinetika Kompleks

Fungsi obyektif yang harus diminimalkan:

= i dataimi CC ,,E

( ) = i dataimi CC 2,,2E

8Algoritma

Evaluasi fungsi obyektif optimasiFOBJ berdasarkan harga k

terbaru

Evaluasi Ci,m denganmenyelesaikan sistempersamaan diferensial

Hitung FOBJ

FOBJ min?

Yes

No

Parameterkinetika k

Selesai

Masukkan:1. Data kinetika CA,data2. Model kinetika3. Tebakan awal ko4. Parameter optimasi

Perkirakan harga kbaru dengan metoda

optimasi

( ) = i dataimi CC 2,,2E

9Contoh 1Kinetika Reaksi Kompleks Tentukan harga parameter kinetika (m, n, ki) dari

reaksi kompleks berikut yang terjadi dalam sebuahreaktor RAS:

DCmB

nAC

mB

nAA

k

CkCkCCkrDC

CCkrCBAk

k 321

11

2

3+=

=+

10

Data Kinetika

(jam) C A (mol/m3)

C C (mol/m3)

(jam) C A (mol/m3)

C C (mol/m3)

(jam) C A (mol/m3)

C C (mol/m3)

0.000 50.00 0.00 0.230 25.56 21.22 1.665 3.42 32.420.001 49.79 0.21 0.294 21.99 23.58 1.962 2.68 32.810.006 48.94 1.06 0.372 18.53 25.61 2.306 2.09 33.140.016 47.29 2.68 0.463 15.46 27.21 2.705 1.62 33.410.031 45.08 4.82 0.568 12.77 28.45 3.168 1.26 33.640.049 42.45 7.30 0.691 10.45 29.43 3.668 0.98 33.810.072 39.46 10.04 0.833 8.48 30.22 4.168 0.79 33.930.101 36.20 12.91 0.997 6.83 30.88 4.668 0.65 34.020.136 32.76 15.79 1.188 5.46 31.46 5.000 0.58 34.060.178 29.18 18.60 1.409 4.33 31.97

11

Persamaan Kinetika

DCmB

nA

C

mB

nA

A

CkCkCCkd

dC

CCkd

dC

321

1

+=

=

Neraca Massa( )( ) ( )CCoAAoDoD

AAoBoB

CCCCCCCCCC

++==

12

Metoda Optimasi untuk KinetikaKompleks Fungsi Obyektif

( )=

=CAi

dataimi CCFOBJ,

2,,

Metoda Numerik fminsearch : peminimum fungsi obyektif ode23 : integrasi (sistem) persamaan diferensial

13

Program MATLAB

Program utama:% tebakan awalk = [.5 1 3 1 .5];%eksekusi optimisasiKonstanta =

fminsearch('kinetics',k)

Program persamaankinetika:

function dYdt = laju(t,Y,FLAG,Co,k)A = Y(1);B = Co(2) - (Co(1) - A);C = Y(2);D = Co(5) + Co(4)+(Co(1) - A) - C;dYdt = [ -k(1)*A.^k(4)*B.^k(5)

k(1)*A.^k(4)*B.^k(5) - k(2)*C + k(3)*D];

14

Program MATLAB

B. Program menghitungfungsi obyektif:

function minimize = kinetics(k)tdat = [ 0

0.00020.0012

:

4.66795.0000 ];

Ydat =[ 50.00 0 49.96 0.03 49.79 0.20 48.93 1.05 47.29 2.67 45.08 4.81

:0.65 34.01

0.57 34.06 ];

15

Program MATLABLanjutan% Parameter ODECo = [Ydat(1,1) 50 Ydat(1,2) 0];[t,Y] = ode23('laju',tdat',[Co(1) Co(3)],[ ],Co,k);% Plot hasil parsial dari estimasi kplot(t,Y,'black-',tdat,Ydat,'blacko')title('Plot estimasi parameter kinetika')xlabel('t [detik]')ylabel('Konsentrasi')gridpause(.05)% Akumulasi kesalahan FOBJminimize = sum(sum(Y-Ydat).^2);

16

Hasil Estimasi Parameter

Dengan tebakan awal k1=0,5, k2=1, k3=3, n=1, m=0,5, diperoleh harga parameter kinetika sebagai berikut:

k1 = 0.4975 k2 = 1.1141 k3 =2.3440 n = 0.9899 m = 0.5035

17

Simulasi Kinetika

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50

5

10

15

20

25

30

35

40

45

50Plot estimasi parameter kinetika

t [jam]

K

o

n

s

e

n

t

r

a

s

i

[

m

o

l

/

m

3

]

18

Complex Kinetics of Ethanol Oxidation on the Ag Gauzed Catalyst

IGBN MakertiharthaDepartment of Chemical EngineeringInstitut Teknologi BandungJalan Ganesha 10, Bandung 40132Indonesia

19

Acetaldehyde

Important intermediate aliphatic chemicals for producing acetic acid, acetic anhydride, pentaerythritol, pyridine, etc

Process: Metal oxide catalysed process Ag catalysed process

20

Acetaldehyde Production Routes

Hydration of acetylene Oxidation of Ethylene Oxidation of saturated HC Oxidation of Ethanol Dehydrogenation of Ethanol

21

Silver vs Metal-Oxide CatalystVariables Silver Catalysed Process Metal-Oxide Catalyst

Catalyst metal (silver) Fe/Mo Oxide

Conversion 85 95 % > 99 %

MeOH/air ratio Higher than flammability limit of mixture (> 36 %-vol)Lower than flammability limit of mixture (< 6,7 %-vol)

Opr. Pressure 1 atm 1 atm

Opr.Temperature 600 650 C 330 380 C

Tolerance to contaminant Low High

Reaction Oxidative and non-oxidative pathway (dehydrogenation) Direct oxidation

22

Problem Definition

Very active catalyst. Low selectivity compared with the metal

oxide catalyst process. Catalyst development Modification of Ag catalyst active site

Stability and kinetics study of complex reaction of Ethanol Oxidation.

23

Research Destination

to suggest some plausible mechanisms for building model for complex kinetics of ethanol conversion to acetaldehyde over silver catalyst

24

Form metalWeight 0.038-0.042 grThick 0.05 cmDiameter 2-2.3 cmColor-fresh off-white

spent dark grey/blackUseful life 3-12 monthsPoisoned by transition metals

(Fe, S, etc)

Silver Catalyst Data

25

Operating Variables

Operation Pressure 1 atmEthanol to Air Ratio 1.2 % (vol)

Reaction Temperature 475 550 CSpace Time (Wcat/Ffeed) 0.034 0.674 gr.hr/mole

26

Apparatus Set-Up

300

b

u

b

l

e

s

o

a

p

f

l

o

w

m

e

t

e

r

o

x

y

g

e

n

t

a

i

l

g

a

s thermocouple

thermocoupledisplay

tail gas nickelinwire

air

furnacereactor

heaterset upacetaldehyde

tail gas

termolyneN2 O2

n

i

t

r

o

g

e

n

syringe pump

ethanol

27

Possible Reactions ETHANOL OXIDATION

C2H5OH + O2 CH3CHO + H2O ETHANOL DEHYDROGENATION

C2H5OH CH3CHO + H2, EXCESSIVE OXIDATION OF H2

H2 + O2 H2O, OXIDATION OF ACETALDEHYDE

CH3CHO + 5/2 O2 2 CO2 + 2 H2O, DEHYDRATION OF ETHANOL

C2H5OH C2H5OC2H5 + H2O

28

Kinetic Model

)pKpKpKpK(ppKkr

CCWWAA/

OO

/OEOsr

221

211

1 1 ++++=

22225

254

4 1 )pKpKpKpK(pKpKkr

WWCC/

OOAA

/OOAAsr

++++=

r5 = kdee pEn

Ethanol oxidation

Acetaldehyde oxidation

Ethanol dehydration

29

Ethanol Conversion

0.88

0.9

0.92

0.94

0.96

0.98

1

0 0.2 0.4 0.6 0.8

W/F [gr cat.hr/mole EtOH]

E

t

h

a

n

o

l

C

o

n

v

e

r

s

i

o

n

T = 475 oC

T = 525 oC

T = 550 oC

30

CO2 and (C2H5)2O Selectivity

0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0.018

0.02

space time [gr.hr/mole etOH]

C

O

2

S

e

l

e

c

t

i

v

i

t

y

T=475 oCT=525 oCT=550 oC

0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

space time [gr.hr/mole etOH]

d

i

e

t

h

y

l

e

t

h

e

r

s

e

l

e

c

t

i

v

i

t

y

T=475 oCT=525 oCT=550 oC

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Kinetic Model

Kinetic Rate Constants :

ksrI = 1.914x104 exp (-11447.66/RT)

ksrII = 1.918x104 exp(-12374.49/RT)

kIII = 3.830x103 exp(-2818.64/RT)

32

Kinetic Model

214472 .78 12 .608ln OK R T R

=

R861.15

RT72.15630Kln A =

R818.20

RT98.16117Kln 2CO =

R336.23

RT44.16823Kln W =

33

Parity Plot T = 475 C

0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

0.02

0.04

0.06

0.08

0.1

0.12T = 475oC

space time

p

a

r

t

i

a

l

p

r

e

s

s

u

r

e

pE exp pE model pA exp pA model pCO2 exp pCO2 modelpDEEexp pDEE model

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.180

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18data vs model at T=475oC

[partial pressure] data

[

p

a

r

t

i

a

l

p

r

e

s

s

u

r

e

]

m

o

d

e

l

pE pA pCO2pDEE

34


0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

0.02

0.04

0.06

0.08

0.1

0.12T = 525oC

space time

p

a

r

t

i

a

l

p

r

e

s

s

u

r

e


0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.180

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16



[

p

a

r

t

i

a

l

p

r

e

s

s

u

r

e

]

m

o

d

e

l

pE pA pCO2pDee

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

0.02

0.04

0.06

0.08

0.1

0.12T = 550oC

space time

p

a

r

t

i

a

l

p

r

e

s

s

u

r

e


0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.180

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16



[

p

a

r

t

i

a

l

p

r

e

s

s

u

r

e

]

m

o

d

e

l

pE pA pCO2pDee

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Consistency

Statistical Consistency!!

37

Consistency

Thermodynamic Consistency (Boudarts Rule) Boudarts rule (1), Sao < 0 for all components

there is a reduction in entropy caused by a changed in dimensional phase when a gaseous molecule (3-D phase) is adsorbed on the surface of catalyst (2-D phase) Boudarts rule (2), -Sao < Sgo for all components

a molecule cannot lose more entropy than it has Boudarts rule (3), -Sao > 41.84 J/mole.K [9.9998

cal/mole.K] for all componentsas a conservative guideline which is based on the change in volume that occurs

when a gaseous molecule is adsorbed Boudarts rule (4), -Sao < 51.05+0.0014(- Hao)J/mole.K

based on empirical work of Everett

38

Conclusion

Hougen-Watson formalism is excellent tool to model the heterogeneous catalytic reactions

It is statistically and thermodynamically consistent

Teknik Reaksi Kimia LanjutAdvanced in Reaction EngineeringReaksi Kompleks padaReaktor IdealKinetika Reaksi KompleksKinetika Reaksi KompleksKinetika Reaksi KompleksModel Kinetika Reaksi KompleksPerkiraan Parameter Kinetika KompleksAlgoritmaContoh 1Kinetika Reaksi KompleksData KinetikaPersamaan KinetikaMetoda Optimasi untuk Kinetika KompleksProgram MATLABProgram MATLABProgram MATLABLanjutanHasil Estimasi ParameterSimulasi KinetikaComplex Kinetics of Ethanol Oxidation on the Ag Gauzed CatalystAcetaldehydeAcetaldehyde Production RoutesProblem DefinitionResearch DestinationConsistencyConsistencyConclusion

01 Teknik Reaksi Kimia Lanjut

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