1. Reaction Kinetics of Soybean Oil Transesterification at High Temperature
Present at AICHe Meeting
Nov. 16, 2008
Shuli Yan, Manhoe Kim, Steve O. Salley, John Wilson, and K. Y. Simon Ng
National Biofuels Energy Laboratory
NextEnergy/Wayne State University
Detroit, MI 48202
Good afternoon, today my presentation is about Transesterification of triglyceride with methanol at different temperature.

2. Outline Introduction Experiment Catalyst structure Kinetic Parameters
Kinetics of soybean oil to methyl esters
Homogenous catalysis
Heterogeneous catalysis

3. Introduction
Transesterification of vegetable oil with alcohol for biodiesel production
Homogeneous catalysis
Heterogeneous catalysis
Nowadays, most industrial applications are performed in batch reactors using homogenoeus catalyst, such as alkaline hydroxides or metal alkoxides. However, the use of homogeneous base catalysts requires neutralization and separation from the reaction mixture leading to a series of environmental
problems related to the use of high amounts of solvents and energy. Heterogeneous solid base catalysts, able to catalyze the transesterification of alkyl esters could solve these issues; they can be easily separated from the reaction mixture without any solvent, show easy regeneration and have a less corrosive character, leading to safer, cheaper and more environment-friendly operation.
Therefore, it is of interest to investigate the possibility to replace the homogeneous base catalysts by solid base catalysts in transesterification reactions, and in particular, to study the kinetics of the heterogeneously base-catalyzed process in order to evaluate its industrial applicability.
Although several authors investigated the kinetics of transesterification catalyzed by homogeneous base catalysts, there is very little information concerning the kinetics of heterogeneous base-catalyzed transesterification.

4. 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. 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 of transesterication.
Dufek studied the acid-catalyzed transesterication of 9(10)-carboxystearic acid and its mono- and di-methyl esters. Freedman et al. 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 applied the effects of mixing of soybean oil with methanol on its kinetics of transesterication.
Although several authors investigated the kinetics of transesterification catalyzed by homogeneous base catalysts, there is very little information concerning the kinetics of heterogeneously catalytic transesterification.

5. Solid Base Catalysts Catalyst T Time(h) Conv.(%) Ref. ZnO 120°C 24 80
HT (Mg-Al)
180°C 1 92 3
SO42-/ZrO2
200°C 4
95.7
1. Catalytic activities of most of them are much lower than homogeneous catalysts such as NaOH.
2. Most of them were conducted at elevated temperature and pressure
3. there is little information regarding their catalytic durability.
Goal

6. Introduction
Kinetics of transesterification catalyzed by heterogonous catalysts
very little information concerning the kinetics of heterogeneously catalytic transesterification at high temperature
Our goal:
studying the use of the heterogeneously ZnxLayOz catalyzed transesterification reaction in batch stirred tank reactors for biodiesel production
developing a kinetic model based on the three step ‘Eley–Rideal’ type mechanism to simulate the transesetrification process.
Although several authors investigated the kinetics of transesterification catalyzed by homogeneous base catalysts, there is very little information concerning the kinetics of heterogeneously catalytic transesterification.

7. Experiments Catalyst preparation and characterization
Homogeneous-coprecipitation method using urea as precipitant
Prepare a mixture solution of Zn(NO3)2 , La(NO3)3 and urea
Heat to 100 oC and hold for 6 hr
Stirred with magnetic stirrer
Filter/unfilter
Dry at 150 oC for 8 hr
Use step-rise calcination method at 250 (2hr), 300 (2hr), 350 (2hr), 400 (2hr), 450 oC (8hr),
Here is the catalyst preparation process.
SEM/EDS

8. Experiments Transesterification
Molar ratio of methanol to soybean oil :1
Catalyst dosage %(wt)
Stir speed rpm
Catalytic transesterifications were conducted in a 500 ml stainless stirred reactor. In each test, 120 g of oil, 180 g of methanol and 2.3 % of catalyst were used. Stir speed is controlled about 490 rpm.

9. Catalyst structure
SEM/EDS

10. Catalyst structure
SEM/EDS

11. Effect of mixing
A picture

12. Effect of temperature on 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
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

13. Effect of temperature on 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.
Fig. 6 Effect the temperature on the methyl esters formation

14. Effect of catalyst concentration
A picture

15. Kinetic model Assumptions:
Only methanol molecule adsorb on the surface of catalyst
Surface chemical reaction is the rate-determing step
pKa (Methanol: Natural oil: 3.55 )
Molecular size (Methanol: 0.33 nm Natural oil: 2 nm)
Heterolytically dissociate

16. Kinetic model Eley-Rideal bimolecular surface reactionsCA QA
fast
RDS
khet A AB B CB
An adsorbed molecule may react directly with an impinging molecule by a collisional mechanism
To correlate experimental data and to quantify the temperature and reaction time effects observed above, the experimental results were analyzed further in terms of the kinetics of rapeseed oil to methyl esters.
Fig. 9 Eley-Rideal mechanism

17. Kinetic model Elementary reactions based on Eley-Rideal-type mechanism
Adsorption
Where A is methanol molecule and S is an adsorption site on the surface
（1）
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.

18. Kinetic model Elementary reactions based on Eley-Rideal-type mechanism
2. Surface reaction
Where B is tri-, di-, and mono-glyceride molecule, DS is an adsorpted di-, and mono-glyceride molecule on catalyst surface,
（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-Rideal-type mechanism
3. Desorption
Di-, mono-glyceride and glycerin desorb from catalyst surface
（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 .

20. Kinetic model According to steps 1 , 2 and 3, we can get Because of
（4）
Because of
Then
（5）

21. Kinetic model
（6）
Where
>>
Because tri-, di- mono-glyceride and glycerin have low adsorption,
Then
（7）

22. Kinetic model
Because the final product glycerine will separate from reaction mixture, we assume that step 2 is unreversible.
（8）
When methanol concentration is kept constant,
（9） Kr
为表观速度常数，与甲醇的浓度、不同温度下甲醇的吸附常数、催化剂表面活性位等有关
Where

23. Table 1 the reaction rate constant of transesetrification
Kinetic model
The rate constant of transesterification reaction
Table 1 the reaction rate constant of transesetrification
Reaction condition
k(s-1)
Temperature oC
Pressure Psi
180
~ 330
190
~ 410
200
~ 450
210
~ 580

24. Kinetic model Arrhenius equation E = 16.4 KJ/mol
Fig. 10 The temperature dependency of the reaction rate constants

25. Fig. 11 Mechanism of ZnO-catalyzed transesterification of triglyceride with methanol
（1）
（2）
（3）
（4）
（5）

26. Conclusion A multiporous catalyst
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. Acknowledgement
Financial support from the Department of Energy (DE ) and Michigan’s 21st Century Job Fund is gratefully acknowledged.

29. Thank you!