October 05, 2009

TransesterificationTransesterification 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

Source: NREL , 2008. Biodiesel Handling and Use Guide

1.9 – 6.0

ASTM Standards for Biodiesel

Source: NREL , 2008. Biodiesel Handling and Use Guide

Important Properties to Look

Flash Point/Methanol ContentWater ContentSulfated Ash ContentFree Glycerin Total Glycerin Na and K Content Sulfur Content (if H2SO4 is used as catalyst)

B100B100 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 PropertiesFeedstocks and Processes

Source: NREL , 2008. Biodiesel Handling and Use Guide

Fuel Properties as a Function of Feedstocks

Source: NREL , 2008. Biodiesel Handling and Use Guide

Heating Value of Fuel

Source: NREL , 2008. Biodiesel Handling and Use Guide

Cetane Number

Source: NREL , 2008. Biodiesel Handling and Use Guide

Oxidation StabilityFuel 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 1Determine 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 = 292.2Molecular Weight of Methanol = 32.1Molecular weight of Glycerol = 92.1Molecular 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 = 6:1Amount of Methanol = 6 x 40 x 103 lb mol = 240 x 103 lb mol = 7.68 x 106 lbAmount of Glycerol = 40 x 103 lb mol = 3.68 x 106

lbWeight 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 TransesterificationAcid-catalyzed TransesterificationEnzyme-catalyzed TransesterificationSupercritical 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 ExtractionDegumming ProcessDetermine the Amount of Methanol and

CatalystTransesterification ProcessNeutralizationMethanol RecoveryCrude Glycerin and Biodiesel SeparationCrude Biodiesel Purification

Degumming Process

Source: www.ndsu.edu. Small Scale Biodiesel Production

Figure: Degumming Process Figure: Clear Wash

Methanol Vs. EthanolEthanol 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

Formation of SoapFormation of soap inhibits the separation

process and also deactivate the catalyst.

Source: Gerpen et al., 2004. Biodiesel Production Technology

Hydrolysis of TriglyceridesAt high temperature, water can hydrolyze

triglycerides and form free fatty acids (FFAs).

Source: Gerpen et al., 2004. Biodiesel Production Technology

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.

Acid-catalyzed Transesterification

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.

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.

Supercritical Transesterification

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 FeedstocksPut 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