Transcript 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
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
Source: NREL , 2008. Biodiesel Handling and Use Guide
Variation in Biodiesel Properties
 Feedstocks and Processes
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: Degumming Process
Source: www.ndsu.edu. Small Scale Biodiesel Production
Figure: Clear Wash
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.
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