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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
=
=
=
4Kinetika Reaksi Kompleks
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
===
5Kinetika Reaksi Kompleks
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
31
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
Parity Plot T = 525 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 = 525oC
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=525oC
[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
35
Parity Plot T = 575 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 = 550oC
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=525oC
[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
36
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