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Data Update---------------Transesterification of triglyceride with methanol at different temperatures
Shuli Yan
20080205
2
Outline
Introduction
Experiment Catalyst structure Effect of temperature on methyl esters formation Kinetics of soybean oil to methyl esters
Homogenous catalysis
Heterogeneous catalysis
3
Introduction Transesterification of vegetable oil with alcoh
ol for biodiesel production
Homogeneous catalysis
Heterogeneous catalysis
Strong acid or alkaline catalysts such as HCl, NaOH
4
Introduction Kinetics of transesterification catalyzed by ho
mogenous catalysts
Dufek studied the kinetics of acid-catalyzed transesterication of 9(10)-carboxystearic acid and its mono- and di-methyl esters.
Freedman et al. firstly reported transesterication reaction of soybean oil and other vegetable oils with alcohols, and examined in their study were the effects of the type of alcohol, molar ratio, type and amount of catalyst and reaction temperature on rate constants and kinetic order.
Noureddin and Zhu studied the effects of mixing of soybean oil with methanol on its kinetics model of transesterication.
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Introduction Kinetics of transesterification catalyzed by het
erogonous catalysts
Our goal: 1. studying the use of the heterogeneously ZnxLayOz catalyzed trans
esterification reaction in batch stirred tank reactors for biodiesel production
2. developing a kinetic model based on a three step ‘Eley–Rideal’ type mechanism to simulate the transesetrification process.
very little information concerning the kinetics of heterogeneously catalytic transesterification
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Experiments Catalyst preparation and characterization
Homogeneous-coprecipitation method using urea as precipitant
1. Prepare a mixture solution of Zn(NO3)2 , La(NO3)3 and urea
2. Heat to 100 oC and hold for 6 hr
3. Stirred with magnetic stirrer
4. Filter/unfilter
5. Dry at 150 oC for 8 hr
6. Use step-rise calcination method at 250 (2hr), 300 (2hr), 350 (2hr), 400 (2hr), 450 o
C (8hr),
SEM/EDS
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Experiments Transesterification
Molar ratio of methanol to soybean oil-----------------42:1
Catalyst dosage----------------------2.3 %(wt)
Stir speed------------------------------490 rpm
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Catalyst structure SEM/EDS
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Catalyst structure SEM/EDS
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11
Catalyst structure SEM/EDS
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SEM/EDS
Catalyst structure
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Effect of temperature on methyl esters formation
120 140 160 180 200 220 2400
10
20
30
40
50
Blank
ZnxLa
yO
z
Yie
ld o
f FA
ME
%
Temperature oC
Reaction conditions:
ZnxLayOz, catalyst dosage is 2.3% (wt),
Molar ratio of methanol to oil is 42:1,
Stir speed is about 490 rpm
Temperature was raised by step method. And when getting to the at target temperature point, it was hold for 1min
Fig. 5 Methyl esters yield at different temperature
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Effect of temperature on methyl esters formation
0 100 200 300 4000
20
40
60
80
100
200 oC
Time min
210 oC
180 oC
190 oC
Fig. 6 Effect the temperature on the methyl esters formation
Reaction conditions:
ZnxLayOz, catalyst dosage is 2.3% (wt),
Molar ratio of methanol to oil is 42:1,
stir speed is about 490 rpm.
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Kinetic model Assumptions:
1. The slurry batch reactor was perfectly mixed
2. Only methanol molecule adsorb on the surface of catalyst
3. Surface chemical reaction is the rate-determing step
— pKa (Methanol: 15.54 Natural oil: 3.55 )
— Molecular size (Methanol: 0.33 nm Natural oil: 2 nm)
— Heterolytically dissociate
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Kinetic model
Fig. 8 Methanol dissociates heterolytically on acid and base sites of ZnO surface.
Fig. 7 Transesterification reaction
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Kinetic model Eley-Rideal bimolecular surface reactions
CA
fast
RDS
khet
AAB
BCBAn adsorbed molecule may
react directly with an impinging molecule by a collisional mechanism
Fig. 9 Eley-Rideal mechanism
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Kinetic model Elementary reactions based on Eley-Rideal-ty
pe mechanism
ASSA Where A is methanol molecule and S is an adsorption site on the surface
1. Adsorption
( 1) 0NCbN AAA
Where is methanol molecule concentration on the surface of catalyst, bA is the adsorption coefficient, is the fraction of surface empty sites, CA is the concentration of methanol.
AN 0N
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Kinetic model Elementary reactions based on Eley-Rideal-ty
pe mechanism
CDSBAS
Where B is tri-, di-, and mono-glyceride molecule, DS is an adsorpted di-, and mono-glyceride molecule on catalyst surface,
2. Surface reaction
CDBA CNkCNkr 22 ( 2 )
Where k2 and k-2 is the reaction rate constants, Cc is the concentration of FAME
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Kinetic model Elementary reactions based on Eley-Rideal-ty
pe mechanism
SDDS Di-, mono-glyceride and glycerin desorbs from catalyst surface
3. Desorption
0NCbN DDD ( 3 )
Where is di-, mono-glycerie and glycerine molecule concentration on the surface of catalyst, bD is the adsorption coefficient, CD is the concentration of di-, mono-glycerie and glycerine .
DN
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Kinetic modelAccording to steps 1 , 2 and 3, we can get
( 4 ) 0202 NCbCkNCCbkr DDCBAA
DAS NNNN 0Because of
DDAA
S
CbCb
NN
10( 5 )
Then
DDAA
DCDSBAAS
CbCb
CCbNkCCbNkr
122
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Kinetic model
( 6 )DDAA
DCP
BA
CbCb
CCK
CCk
r
1
1
Where
( 7 )AA
DCP
BA
Cb
CCK
CCk
r
1
1
Because tri-, di- mono-glyceride and glycerin have low adsorption,
AACb DDCb>>
Then
AS bNkk 2D
AP bk
bkK
2
2
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Kinetic model
BAA
A CCb
kCr
1
B
AA
AS Cb
C
bNk
12 ( 8 )
Because the final product glycerine will separate from reaction mixture, we assume that step 2 is unreversible.
BrCkr ( 9 )
When methanol concentration is kept constant,
Where
AA
ASr
bC
bNkk
12
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Kinetic model The rate constant of transesterification reaction
Reaction condition k(s-1)
Temperature oC Pressure Psi
180 ~ 330 0.01299
190 ~ 410 0.01806
200 ~ 450 0.05000
210 ~ 580 0.05220
Table 1 the reaction rate constant of transesetrification
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Kinetic model Arrhenius equation
0.0044 0.0046 0.0048 0.0050 0.0052 0.0054 0.0056 0.0058 0.0060-4.5
-4.2
-3.9
-3.6
-3.3
-3.0
-2.7
Ln
k
1/T K-1
ART
Ek lnln
Fig. 10 The temperature dependency of the reaction rate constants
E = 16.4 KJ/mol
26Fig. 11 Mechanism of ZnO-catalyzed transesterification of triglyceride with methanol
O
H2C
HC
H2C
O
O
O
Zn
C R2
C R3
O
O CH3
+O
C O CH3R1
+
O
H2C
HC
H2C
O
O
O
CO
R1
CO
R2
C R3
Zn
O
CH3
O
CH3
O
H2C
HC
H2C
O
O
O
C
O-
C R2
C R3
O
R1
O CH3
Zn O CH3
CH3 OH +O
H2C
HC
H2C
O
O
O
Zn
C R2
C R3
O
O CH3
+O
H2C
HC
H2C
O
O
O
H
C R2
C R3
OZn
O
CH3
O
CH3
ZnOx + Zn(CH3O)2 + OH2CH3OH
+ZnOxZnO O ( 1)
( 2)
( 3)
( 4)
( 5)
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Conclusion
A multiporous catalyst 170 oC A kinetic model was developed based on a thr
ee-step E-R type of mechanism.
First order reaction as a function of the concentration of triglyceride
E = 16.37KJ/mol
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Future work
Investigate the influence of some kinetic parameters on transesterification such as molar rat
io of methanol to oil, catalyst amount
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Thank you!