SUSTAINABLE ENERGY INITIATIVE PROJECT
Module 1: How to make Biodiesel?
Part 3: Analysis of the Biodiesel
PURPOSE:
 Develop the procedures for washing and drying the biodiesel sample prior to
characterization
 Assessment to quality of biodiesel with chromatographic and spectroscopic methods.
THEORY:
Biodiesel is an alternative fuel for diesel engines that is receiving great attention worldwide.
Although it attracts the most attention because it is renewable, it can be used either pure or in
blends with diesel fuel in unmodified diesel engines, and it reduces some exhaust pollutants. It
is also of interest to the students because it can be produced easily from commonly available
feedstocks such as recycled cooking oil. However, the relative simplicity of biodiesel production
can mask the importance of maintaining high quality standards for any fuel supplied to a
modern diesel engine. It is essential to the growth of the biodiesel industry that all fuel
produced and sold meet these quality standards1.
The term biodiesel is defined as a mixture of simple alkyl esters of long-chain fatty acids that can
be produced from vegetable oils, animal fats or recycled cooking oils and used as fuels for diesel
engines, either neat or when blended with petroleum diesel. Biodiesel is typically produced
from oils or greases by transesterification with an alcohol in the presence of a catalyst, usually
alkaline. This alternative fuel to petrodiesel is environmentally friendly with little or no sulphur
(flash point above 110°C) and has superior lubrication properties, providing appropriate motor
performance and a low emission profile upon combustion in compression ignition engines2.
The fuel properties of biodiesel are determined by the amounts of each fatty acid in the
feedstock used to produce the esters. Fatty acids are designated by two numbers: the first
number denotes the total number of carbon atoms in the fatty acid chain and the second is the
number of double bonds present in the chain. For example, 18:1 designates oleic acid, which has
18 carbon atoms and one double bond. The most common fatty acids (and their methyl esters)
are listed in the following Table. There are numerous other fatty acids, but, the ones given here
comprise the vast majority of those contained in biodiesel1.
Different methods are used for analyzing Biodiesel. Some of them are included in international
standards governing the quality of biofuels. Among these, in the United States the ASTM 675108 publishes new specifications for biodiesel blends and in Europe the EN 14214 which applies
only to FAME. This standard exists in three versions, English, French and German. The most
recent version is the November 2008 and replaces the version of 2003. The DIN 51606 is the
latest German standard. The following link contains specifications of these standards:
http://www.biodiesel-fuel.co.uk/biodiesel-standards (Este link es para poder ser consultado al
momento de leer el texto, para esto debo consultar al Dr. Cruz cuando lo postee en la página)
Fatty Acid
(trivial name/rational name)
Myristic Acid/
Tetradecanoic Acid
Palmitic Acid/
Hexadecanoic Acid
Structure
R-(CH2)12-CH3
Common
acronym
C14:0
R-(CH2)14-CH3
C16:0
R-(CH2)16-CH3
C18:0
Oleic Acid/
9(Z)-Octadecenoic Acid
R-(CH2)7-CH=CH(CH2)7 -CH3
C18:1
Linoleic Acid/
9(Z), 12(Z)- Octadecadienoic Acid
R-(CH2)7-CH=CHCH2-CH=CH(CH2)4 -CH3
C18:2
Linolenic Acid/
9(Z), 12(Z), 15(Z)- Octadecatrienoic
Acid
R-(CH2)7-(CH=CHCH2)3 -CH3
C18:3
Stearic Acid/
Octadecanoic Acid
Methyl Ester
(trivial name/rational name)
Methyl Myristate/
Methyl Tetradecanoate
Methyl Palmitate/
Methyl Hexadecanoate
Methyl Stearate/
Methyl Octadecanoate
Methyl Oleate/
Methyl 9(Z)-Octadecenoate
Methyl Linoleate/
Methyl 9(Z), 12(Z)Octadecadienoate
Methyl Linolenate/
Methyl 9(Z)Octadecatrienoate
Generally, the analytical methods can be divided into three categories: chromatographic methods,
spectroscopic methods, and physical-property based methods. Chromatographic and spectroscopic
methods provide insight into the chemical properties of biodiesel. However, physical property methods
are also very important especially for the commercial and industrial sectors. Excellent references are
available1,2. In general, the fuel quality of biodiesel can be influenced by several factors, including the
quality of the feedstock, the fatty acid composition of the parent vegetable oil or animal fat, the
production process, the other materials used in this process, and postproduction parameters.
MATERIALS:
REAGENTS:







MgSO4 or Na2SO4
125 ml Separatory funnel
100 ml Graduated cylinder
250 ml Beaker
Filter funnel
Filter paper
pH paper
Hotplate
Assessing the biodiesel
A key visual indicator during the synthesis of biodiesel is the formation of two distinct layers
after settling. The layer at the bottom is a crude glycerine byproduct, and the layer on top is
biodiesel. By shaking the bottle slightly from side to side, you can observe that the lower layer is
thicker and more viscous than the biodiesel top layer. The higher viscosity of glycerine is one of
the reasons that it isn’t suitable for use in a diesel engine at room temperatures. It is common to
see a whitish third layer floating between glycerine and the biodiesel. This soap like material is a
result of adding too much NaOH, or having water in the oil. It should be discarded with the
glycerine.
Washing the Biodiesel
The bottle now contains biodiesel, glycerin, mono-and di-glycerides, soap, methanol, NaOH, and
possibly a little leftover oil (triglycerides). The glycerides are all oil-soluble, so they’ll reside
predominantly in the upper, biodiesel layer. The thin layer of glycerin, which is water soluble,
will sink. Depending on the oil and catalyst used, it might be either liquid or solid. Soap,
methanol, and NaOH, which are also water-soluble, will be mixed throughout both layers –
although some of the soap can sometimes form its own thin layer between the biodiesel and
glycerin.
If the bottle has more than two layers, or only one, then something is wrong – possibly excessive
soap or monoglyceride formation. These are both emulsifiers, and in sufficient quantities they
will prevent separation. Repeat the procedure of preparation. Module 1 Part 2.
PROCEDURE STEPS:
1. Measure the biodiesel with a graduated cylinder
2. Transfer the biodiesel into a separatory funnel
3. Gently add the same volume warm distilled water to the biodiesel
4. Rotate the separatory funnel until slight soap foam is formed. This may take a few minutes.
Do not shake the separatory funnel! The biodiesel contains soap, and vigorous agitation will
produce a stable emulsion difficult to separate.
5. Drain out the soapy water of the separatory funnel.
6. Add more warm water and keep repeating the draining process. Each time there will be less
soap allowing for mixing more vigorously. Repeat this procedure until the water becomes
clear and pH of wash water reaches 7. Record the pH of wash water in the lab notebook.
Note: If the emulsification layer persists, try applying heat, adding salt, and adding vinegar, in
that order.
7. Dry the biodiesel with MgSO4 or Na2SO4. Filter.
8. Characterize the sample with GC-MS, NIR, and HPLC
Notes:
1. Pressures can build up in the separatory funnel. Safety Goggles must be worn at all times.
2. Make sure the stopcock of your separatory funnel is CLOSED before adding liquids!
3. Biodiesel can be discarded with other chemical wastes from the chemistry laboratory.
REFERENCES:
1. J. Van Gerpen. B. Shanks. D. Clements. G. Knote. Biodiesel Analytical Methods. 2002-2004.
National Renewable Energy Laboratory NREL
2. M.F. Pimentel. G. Ribeiro. R. Da Cruz et all. Determination of biodiesel content when blended
with mineral diesel fuel using infrared spectroscopy and multivariate calibration. 2006.
Microchemical Journal. 82. 201 – 206.
3. G. Knothe. J. Van Gerpen. J. Krahl. The Biodiesel Handbook. 2005 AOCS Press. Champaign,
Illinois.