Transesterification October 05, 2009

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.

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.

Estimated Biodiesel Production in US Source: www.biodiesel.org

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

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

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.

Biodiesel Production Process Source: NREL , 2008. Biodiesel Handling and Use Guide

Commercial Processing Unit for Home Made Biodiesel

Selected Properties of Biodiesel and Diesel 1.9 – 6.0 Source: NREL , 2008. Biodiesel Handling and Use Guide

ASTM Standards for Biodiesel Source: NREL , 2008. Biodiesel Handling and Use Guide ASTM Standards for Biodiesel

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)

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

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

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

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

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

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

Long-Term Storage Stability Source: NREL , 2008. Biodiesel Handling and Use Guide, pp.21

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

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

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

Chemical Properties of Biodiesel Source: Singh, 2008. Ph.D. Dissertation, MSU

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

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.

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

Degumming Process Figure: Clear Wash Figure: Degumming Process Source: www.ndsu.edu. Small Scale Biodiesel Production

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.

Reaction Mechanism of Biodiesel Production Process Source: Singh, 2008. Ph.D. Dissertation, MSU Reaction Mechanism of Biodiesel Production Process

Formation of Soap Formation of soap inhibits the separation process and also deactivate the catalyst. Source: Gerpen et al., 2004. Biodiesel Production Technology

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

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

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.

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.

Effect of Water Content and FFA Source: Ayhan Demirbas, 2008. Biodiesel: a realistic fuel alternative for diesel engines

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

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.

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