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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. Outline.

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reaction kinetics of soybean oil transesterification at high temperature

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

outline
Outline
  • Introduction
  • Experiment
  • Catalyst structure
  • Kinetic Parameters
  • Kinetics of soybean oil to methyl esters
  • Homogenous catalysis
  • Heterogeneous catalysis
introduction
Introduction
  • Transesterification of vegetable oil with alcohol for biodiesel production
  • Homogeneous catalysis
  • Heterogeneous catalysis
introduction1
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.
introduction2
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.
experiments
Experiments
  • Catalyst preparation and characterization
  • Homogeneous-coprecipitation method using urea as precipitant

Prepare a mixture solution of Zn(NO3)2 , La(NO3)3 andurea

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),

  • SEM/EDS
experiments1
Experiments
  • Transesterification

Molar ratio of methanol to soybean oil-----------------38:1

Catalyst dosage----------------------2.3 %(wt)

Stir speed------------------------------490 rpm

effect of temperature on methyl esters formation
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

effect of temperature on methyl esters formation1
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

kinetic model
Kinetic model
  • Assumptions:
  • Only methanol molecule adsorb on the surface of catalyst
  • 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
kinetic model1

CA

A

AB

CB

B

RDS

khet

fast

QA

Kinetic model
  • Eley-Rideal bimolecular surface reactions

An adsorbed molecule may react directly with an impinging molecule by a collisional mechanism

Fig. 9 Eley-Rideal mechanism

kinetic model2

(1)

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

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.

kinetic model3

(2)

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,

Where k2 and k-2 is the reaction rate constants, Cc is the concentration of FAME

kinetic model4

(3)

Kinetic model
  • Elementary reactions based on Eley-Rideal-type mechanism

3. Desorption

Di-, mono-glyceride and glycerin desorb from catalyst surface

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 .

kinetic model5

(4)

(5)

Kinetic model

According to steps 1 , 2 and 3, we can get

Because of

Then

kinetic model6

>>

(6)

(7)

Kinetic model

Where

Because tri-, di- mono-glyceride and glycerin have low adsorption,

Then

kinetic model7

(8)

Kinetic model

Because the final product glycerine will separate from reaction mixture, we assume that step 2 is unreversible.

When methanol concentration is kept constant,

(9)

Where

kinetic model8
Kinetic model
  • The rate constant of transesterification reaction

Table 1 the reaction rate constant of transesetrification

kinetic model9
Kinetic model
  • Arrhenius equation

E = 16.4 KJ/mol

Fig. 10 The temperature dependency of the reaction rate constants

slide25

(1)

(2)

(3)

(4)

(5)

Fig. 11 Mechanism of ZnO-catalyzed transesterification of triglyceride with methanol

conclusion
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
future work
Future work

Investigate the influence of some kinetic parameters on transesterification such as molar ratio of methanol to oil, catalyst amount

acknowledgement
Acknowledgement

Financial support from the Department of Energy (DE12344458) and Michigan’s 21st Century Job Fund is gratefully acknowledged.