Data Update
---------------Transesterification of triglyceride
with methanol at different temperatures
Shuli Yan
20080205
1
Outline

Introduction
Homogenous catalysis
Heterogeneous catalysis




Experiment
Catalyst structure
Effect of temperature on methyl esters formation
Kinetics of soybean oil to methyl esters
2
Introduction

Transesterification of vegetable oil with
alcohol for biodiesel production

Homogeneous catalysis
Strong acid or alkaline catalysts such as HCl, NaOH

Heterogeneous catalysis
3
Introduction

Kinetics of transesterification catalyzed by
homogenous 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.
4
Introduction

Kinetics of transesterification catalyzed by
heterogonous catalysts
very little information concerning the kinetics of
heterogeneously catalytic transesterification
Our goal:
1. studying the use of the heterogeneously ZnxLayOz catalyzed
transesterification 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. 5
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 oC (8hr),
 SEM/EDS
6
Experiments

Transesterification
Molar ratio of
methanol to soybean
oil-----------------42:1
Catalyst dosage---------------------2.3 %(wt)
Stir speed-----------------------------490 rpm
7
Catalyst structure

SEM/EDS
8
Catalyst structure

SEM/EDS
9
10
Catalyst structure

SEM/EDS
11
Catalyst structure

SEM/EDS
12
Effect of temperature on methyl esters
formation
Reaction conditions:
50
ZnxLayOz
Yield of FAME %
40
ZnxLayOz, catalyst dosage is
2.3% (wt),
30
20
Blank
10
Molar ratio of methanol to oil is
42:1,
Stir speed is about 490 rpm
0
120
140
160
180
Temperature
200
220
240
o
C
Fig. 5 Methyl esters yield at different temperature
Temperature was raised by step
method. And when getting to
the at target temperature point, it
13
was hold for 1min
Effect of temperature on methyl esters
formation
100
Reaction conditions:
80
ZnxLayOz, catalyst dosage is
2.3% (wt),
60
o
210 C
o
Molar ratio of methanol to oil is
42:1,
200 C
40
o
190 C
o
180 C
20
stir speed is about 490 rpm.
0
0
100
200
300
400
Time min
Fig. 6 Effect the temperature on the methyl esters formation
14
Kinetic model

Assumptions:
1. The slurry batch reactor was perfectly mixed
2. Only methanol molecule adsorb on the surface
of catalyst
— pKa (Methanol: 15.54
Natural oil: 3.55 )
— Molecular size (Methanol: 0.33 nm Natural oil: 2 nm)
3. Surface chemical reaction is the rate-determing
step
— Heterolytically dissociate
15
Kinetic model
Fig. 7 Transesterification reaction
16
Fig. 8 Methanol dissociates heterolytically on acid and base sites of ZnO surface.
Kinetic model

Eley-Rideal bimolecular surface reactions
CA
An adsorbed molecule may
react directly with an
impinging molecule by a
collisional mechanism
A
AB
CB
B
RDS
QA
khet
fast
Fig. 9 Eley-Rideal mechanism
17
Kinetic model

Elementary reactions based on Eley-Ridealtype mechanism
1. Adsorption
A  S  AS
Where A is methanol molecule and S is an adsorption site on the surface
N A   bAC A N0 
（1）
Where N A  is methanol molecule concentration on the surface of catalyst, bA is the
adsorption coefficient, N  is the fraction of surface empty sites, CA is the
concentration of methanol.
0
18
Kinetic model

Elementary reactions based on Eley-Ridealtype mechanism
2. Surface reaction
AS  B  DS  C
Where B is tri-, di-, and mono-glyceride molecule, DS is an adsorpted di-,
and mono-glyceride molecule on catalyst surface,
r  k2 N A CB  k2 N D CC
（2）
Where k2 and k-2 is the reaction rate constants, Cc is the concentration of FAME
19
Kinetic model

Elementary reactions based on Eley-Ridealtype mechanism
3. Desorption
DS  D  S
Di-, mono-glyceride and glycerin desorbs from catalyst surface
N D   bDC D N0 
（3）
Where N D  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 .
20
Kinetic model
According to steps 1 , 2 and 3, we can get
r  k2bAC ACB N 0   k2CC bDCD N 0 
Because of
Then
（4）
N S   N 0   N A   N D 
N 0  
N S 
1  bAC A  bD C D
（5）
k 2 N S bAC AC B  k  2 N S bD CC C D
r
1  bAC A  bD C D
21
Kinetic model


1
k  C AC B 
CC C D 
KP


r
1  bAC A  bD C D
Where
k  k 2 N S bA
（6）
KP
k 2bA

k  2 bD
Because tri-, di- mono-glyceride and glycerin have low adsorption,
bA C A
Then
>>
bD C D


1
k  C AC B 
CC C D 
KP


r
1  bAC A
（7）
22
Kinetic model
Because the final product glycerine will separate from reaction mixture, we
assume that step 2 is unreversible.
r

kCA
CB
1  bAC A
k 2 N S bA
CB
1
 bA
CA
（8）
When methanol concentration is kept constant,
r  k r CB
Where
kr
k 2 N S b A

1
 bA
C
（9）
23
Kinetic model

The rate constant of transesterification reaction
Table 1 the reaction rate constant of transesetrification
Reaction condition
Temperature
oC
k(s-1)
Pressure Psi
180
~ 330
0.01299
190
~ 410
0.01806
200
~ 450
0.05000
210
~ 580
0.05220
24
Kinetic model
Arrhenius equation
E
ln k  
 ln A
RT
-2.7
-3.0
-3.3
Ln k

E = 16.4 KJ/mol
-3.6
-3.9
-4.2
-4.5
0.0044
0.0046
0.0048
0.0050
0.0052
1/T
K
0.0054
0.0056
0.0058
0.0060
-1
Fig. 10 The temperature dependency of the reaction rate constants
25
ZnO
ZnOx
+
ZnOx
+
O
（1）
CH3OH
Zn(CH 3O) 2
+
O
H2C O C R1
O
HC O C R2
O
+
O
H3 C
O CH3
O
O
Zn
CH3
Zn
O
CH3
（3）
HC O C R2
O
H2C O C R3
H2C
O
C
-
H2C O C R1
O
H2C O C R3
R1
（2）
H2O
O
Zn O CH3
（4）
O
O
CH3
+
HC O C R2
O
H2C O C R3
H 2C O H
H2C O Zn O CH3
O
H3C OH
+
HC O C R2
O
H 2C O C R 3
O
H3 C
O
O
Zn
CH3
+
（5）
HC O C R2
O
H 2C O C R 3
Fig. 11 Mechanism of ZnO-catalyzed transesterification
of triglyceride with methanol
26
Conclusion



A multiporous catalyst
170 oC
A kinetic model was developed based on a
three-step E-R type of mechanism.
First order reaction as a function of the concentration of triglyceride
E = 16.37KJ/mol
27
Future work
Investigate the influence of some kinetic
parameters on transesterification such as
molar ratio of methanol to oil, catalyst amount
28
Thank you!
29