1. Transesterification
October 05, 2009

2. Transesterification
Transesterification is a chemical reaction where triglyceride is reacted with alcohol in the presence of catalyst to produce alkyl esters. Biodiesel is produced by the transesterification process.
Every 100 gallons of oil produces about 100 gallons of biodiesel and 10 gallons of glycerol.

3. What is Biodiesel?
Biodiesel is a petroleum diesel replacement fuel used in CI engines.
It can be produced from any plant or animal based lipids.
Plant Based Oils:
Soybean oil; cotton seeds oil; sunflower oil.
Animal Fats:
Beef tallow; pork lard; poultry fat.
Recycled Cooking Grease:
Yellow grease.
Note: Raw or refined oil is not biodiesel.

4. Estimated Biodiesel Production in US
Source:

5. Benefits of Biodiesel
High energy return and displace petroleum based fuels.
Biodiesel reduces life-cycle greenhouse gas emissions.
Biodiesel reduces tailpipe emissions except NOx.
Biodiesel improves air quality and has positive impact in human health.
Biodiesel improves engine operation and easy to blend.
Source: NREL , Biodiesel Handling and Use Guide

6. Emissions Impact of Biodiesel
Source: NREL , Biodiesel Handling and Use Guide

7. Other Biodiesel Attributes
Lower Energy Density: 8% less energy per gallon compare to diesel.
Low Temperature Operability: biodiesel freezes at 20 to 30 oF higher than that of petroleum diesel.
Storage Stability: additives should be used if stored more than a few months. Acidity should be measured monthly.
Biodiesel is susceptible to microbial degradation. Minimize water in contact and test for microbial contamination.

8. Biodiesel Production Process
Source: NREL , Biodiesel Handling and Use Guide

9. Commercial Processing Unit for Home Made Biodiesel

10. Selected Properties of Biodiesel and Diesel
1.9 – 6.0
Source: NREL , Biodiesel Handling and Use Guide

11. ASTM Standards for Biodiesel
Source: NREL , Biodiesel Handling and Use Guide
ASTM Standards for Biodiesel

12. Important Properties to Look
Flash Point/Methanol Content
Water Content
Sulfated Ash Content
Free Glycerin
Total Glycerin
Na and K Content
Sulfur Content (if H2SO4 is used as catalyst)

13. B100 B100 refers 100% biodiesel and 0% diesel fuel.
Biodiesel is a very good solvent.
B100 freezes at much higher temperature than conventional diesel.
Biodiesel is not compatible with certain hoses and gaskets.
Biodiesel is not compatible with certain metals and plastics.
Source: NREL , Biodiesel Handling and Use Guide

14. Variation in Biodiesel Properties
Source: NREL , Biodiesel Handling and Use Guide
Variation in Biodiesel Properties
Feedstocks and Processes

15. Fuel Properties as a Function of Feedstocks
Source: NREL , Biodiesel Handling and Use Guide
Fuel Properties as a Function of Feedstocks

16. Heating Value of Fuel
Source: NREL , Biodiesel Handling and Use Guide

17. Cetane Number
Source: NREL , Biodiesel Handling and Use Guide

18. Oxidation Stability
Fuel aging and oxidation can lead to high acid number, high viscosity and formation of sediments.
The higher the level of unsaturation, the more likely that the biodiesel will oxidize.
Heat and sunlight will accelerate oxidation process.
Metals such as copper, brass, bronze, lead, tin, and zinc will accelerate the degradation process.
Keeping oxygen from the biodiesel reduces or eliminates fuel oxidation.
Source: NREL , Biodiesel Handling and Use Guide, pp.21

19. Long-Term Storage Stability
Source: NREL , Biodiesel Handling and Use Guide, pp.21

20. Example 1
Determine the amount of vegetable oil, catalyst and methanol required to produce 35 x106 lb/yr (5 million gallons per year) of biodiesel.
Molecular Weight of FAMEs = 292.2
Molecular Weight of Methanol = 32.1
Molecular weight of Glycerol = 92.1
Molecular weight of soybean oil = 885

21. 35 x 106 lb of FAMEs x (1 lb mol/292.2 lb)
= 120 x 103 lb mol of FAMEs
Amount of VO = 40 x 103 lb mol = x 106 lb
Assuming methanol/oil molar ratio = 6:1
Amount of Methanol = 6 x 40 x 103 lb mol
= 240 x 103 lb mol = 7.68 x 106 lb
Amount of Glycerol = 40 x 103 lb mol = 3.68 x 106 lb
Weight of Catalyst = 0.01 x x 106 lb
= x 103 lb

22. Further Reading
Fangrui Ma and Milford A. Hanna, Biodiesel production: a review. Bioresource Technology, vol. 70, pp. 1-15

23. Chemical Properties of Biodiesel
Source: Singh, Ph.D. Dissertation, MSU

24. Transesterification Process
Base-catalyzed Transesterification
Acid-catalyzed Transesterification
Enzyme-catalyzed Transesterification
Supercritical Transesterification

25. Base-catalyzed Transesterification
This is the most widely used technique to produce biodiesel.
Possibility of formation soap if there is a high free fatty acids (FFAs) content in triglycerides.
Excessive water can hydrolyze to form FFAs.
Recycling of catalyst is challenging and not cost effective.
Glycerol is in the crude form and has very little value.

26. Biodiesel Production Process
Oil Extraction
Degumming Process
Determine the Amount of Methanol and Catalyst
Transesterification Process
Neutralization
Methanol Recovery
Crude Glycerin and Biodiesel Separation
Crude Biodiesel Purification

27. Degumming Process Figure: Clear Wash Figure: Degumming Process
Source: Small Scale Biodiesel Production

28. Methanol Vs. Ethanol Ethanol is more expensive than methanol.
Lower ethyl ester conversion.
Ethanol is difficult to recycle.
Viscosity of the ethyl ester is slightly higher than that of methyl ester.
Cloud and pour points are slightly lower than that of methyl ester.

29. Reaction Mechanism of Biodiesel Production Process
Source: Singh, Ph.D. Dissertation, MSU
Reaction Mechanism of Biodiesel Production Process

30. Formation of Soap
Formation of soap inhibits the separation process and also deactivate the catalyst.
Source: Gerpen et al., Biodiesel Production Technology

31. Hydrolysis of Triglycerides
At high temperature, water can hydrolyze triglycerides and form free fatty acids (FFAs).
Source: Gerpen et al., Biodiesel Production Technology

32. Acid-catalyzed Transesterification
Acid catalyzed transesterification is very slow compared to base-catalyzed transesterification.
Suitable for oil that has higher FFAs.
This process uses strong acid to catalyze esterification of the FFAs and transesterification of triglycerides.
The process does not produce soap with high FFAs because no metal is present.
Esterification of FFAs is generally faster but produces water.
Source: Gerpen et al., Biodiesel Production Technology

33. Enzyme-Catalyzed Transesterification
Use enzymes to produce esters from triglycerides.
Relatively longer period of reaction.
Expensive to produce because of the cost of enzymes.
No commercial plant using enzymes to produce biodiesel.
Catalyst separation issue can be solved easily.

34. Supercritical Transesterification
Liquid is defined as supercritical when its temperature and pressure are above critical points.
Supercritical temperature and pressure for methanol are 240 oC and 1140 psia, respectively.
No Catalyst is required but can be used.

35. Effect of Water Content and FFA
Source: Ayhan Demirbas, Biodiesel: a realistic fuel alternative for diesel engines

36. Biodiesel Production Process
Source: Brent Schulte, University of Arkansas. Biomass Magazine April 2008.

37. High FFAs Feedstocks
Put excess catalyst to form soap and soaps are stripped using centrifuges (“caustic stripping”).
Acid-catalysis followed by base-catalysis process.
Acid catalyzed transesterification.

38. Procedure for High FFA Feedstocks
Measure FFA level.
Add 2.25 g methanol and 0.05 g sulfuric acid for each gram of free fatty acid in the oil or fat.
Agitate for one hour at 60-65ºC.
Let the mixture settle. Methanol-water mixture will rise to the top. Decant the methanol, water, and sulfuric acid layer.
Take bottom fraction and measure new FFA level.
Source: Gerpen et al., Biodiesel Production Technology