Transesterification

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: www.biodiesel.org

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 , 2008. Biodiesel Handling and Use Guide

6. Emissions Impact of Biodiesel Source: NREL , 2008. 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 , 2008. 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 , 2008. Biodiesel Handling and Use Guide

11. Source: NREL , 2008. 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 , 2008. Biodiesel Handling and Use Guide

14. Source: NREL , 2008. Biodiesel Handling and Use Guide Variation in Biodiesel Properties • Feedstocks and Processes

15. Source: NREL , 2008. Biodiesel Handling and Use Guide Fuel Properties as a Function of Feedstocks

16. Heating Value of Fuel Source: NREL , 2008. Biodiesel Handling and Use Guide

17. Cetane Number Source: NREL , 2008. 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 , 2008. Biodiesel Handling and Use Guide, pp.21

19. Long-Term Storage Stability Source: NREL , 2008. 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 = 35.06 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 35.06 x 106 lb = 350.6 x 103 lb

22. Further Reading • Fangrui Ma and Milford A. Hanna, 1999. Biodiesel production: a review. Bioresource Technology, vol. 70, pp. 1-15

23. Chemical Properties of Biodiesel Source: Singh, 2008. 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: www.ndsu.edu. 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. Source: Singh, 2008. 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., 2004. Biodiesel Production Technology

31. Hydrolysis of Triglycerides • At high temperature, water can hydrolyze triglycerides and form free fatty acids (FFAs). Source: Gerpen et al., 2004. 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., 2004. 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, 2008. 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., 2004. Biodiesel Production Technology