UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
Biodiesel Processing
Biodiesel is a clean, renewable and domestically produced diesel fuel, which has many
characteristics of a promising alternative energy resource. The most common process for making
biodiesel is known as transesterification. This process involves combining any natural oil (vegetable or
animal) with virtually any alcohol, and a catalyst. There are other thermochemical processes available
for making biodiesel, but transesterification is the most commonly used one due to the simplicity and
high energy efficiency. The high energy efficiency of transesterification is an important aspect of
Biodiesel, which makes it favorable in the competitive energy market. The following is a
transesterification reference guide that can be used to process Biodiesel on an experimental scale. It
can be done with basic equipment and common chemicals. Be sure to use extreme caution when
carrying out this procedure, the methanol and catalyst are toxic, and give off potentially harmful
vapors. Proper personal protection is imperative, including thorough ventilation.
Materials
Biodiesel consists of three principal feed stocks;
1. Oil: Glycerides are commonly known as oils or fats, chemically speaking these are long chain fatty
acids joined by a glycerin backbone. They appear most often with three fatty acid chains connected to
the glycerin, making them trigylcerides. The triglyceride resources most frequently used and specific
to this experiment, are virgin soybean oil, or recycled cooking oil. Used cooking oil when heated
becomes hydrogenated, meaning the double bonds within the ester chains were broken into single
bonds with two more hydrogen’s attached. To counter this, additional catalyst must be added according
to the acidity of the specific oil.
2. Alcohol: Although a variety of alcohols can be used to produce Biodiesel, such as, ethanol or
butanol, this experiment will focus on methanol as it is most readily available, and most frequently
used. Therefore the Biodiesel produced is referred to as methyl esters. Methanol is one of the most
common industrial alcohols; because of its abundant supply it’s most often the least expensive alcohol
as well.
3. Catalyst: the third reactant needed is a catalyst that initiates the reaction and allows the esters to
detach. The strong base solutions typically used are sodium hydroxide (NaOH) and potassium
hydroxide (KOH). This experiment will be using NaOH as catalyst.
Safety:
Extreme caution must be taken when working with methanol and especially with sodium
methoxide. Safety Goggles, Chemical gloves and ventilation apparatus must be used at all times. Have
plenty of water and vinegar (to neutralize the base) on hand.
Processing guidelines;
1. The oil should first be heated to 60º C to help the reaction proceed more quickly. Used
Vegetable oil should be heated to 100º C (to remove water), and filtered to remove particulate
matter (french fries).
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
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UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
2. Approximately .35% NaOH by volume is needed when using virgin oil. However when using
waste oils (which therefore have free fatty acid (FFA) content), the pH must first be determined
(by titration) to calculate the additional amount of NaOH needed.
Titration (for used oils, or older oils that could have degraded some, producing FFAs):
Dissolve one gram of NaOH into 1 liter of distilled water. Dissolve 1ml of the filtered oil into
10ml of isopropyl alcohol and add two drops of phenolphthalein, an acid base indicator. Now
slowly add, by calibrated dropper or pipet, the NaOH(aq) solution to the oil solution, mix
intermittently. When the oil solution turns pink and stays pink for ten seconds the titration is
complete. The volume of NaOH(aq) solution in milliliters necessary to neutralize the free fatty
acids corresponds directly with the number of additional grams per liter of NaOH needed for
transesterification.
3. Methanol makes up approximately 10% of the Biodiesel, but to force the reaction, an excess is
generally added – usually totalling 20% of the volume of the oil. So for a reaction with one liter
of oil; 200 ml of methanol is first mixed with 3.5 grams of NaOH, plus any additional NaOH in
regards to the hydrogenated vegetable oil titration. Ensure the NaOH is completely dissolved;
this reaction creates sodium methoxide. Again, Caution! Sodium methoxide is extremely toxic.
Provide thorough ventilation and wear protective equipment.
4. Add the sodium methoxide to the oil. Mix thoroughly, a blender on a low setting for twenty
minutes is ideal; however, vigorous shaking for a couple minutes will suffice (although if this
method is used, it would be good to re-shake the solution after twenty minutes or so).
5. Allow the solution to sit. After about ten minutes, the beginning of separation can be observed.
However, after about eight hours the glycerin molecules will have settled almost completely to
the bottom of the container and the methyl esters (biodiesel) will be on top.
Analyze results
Possible errors:
Too much lye- soapy residue
Not enough lye- unreacted oil, free glycerin
Not enough alcohol (reaction does not proceed to completion)
Water in oil (results in catalyst being broken apart, and the metal ion from the catalyst joining with
the fatty acids to make soap)
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
2
UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
Biodiesel Chemistry
Biodiesel
Chemically, biodiesel (from transesterification) refers to mono alkyl esters of long chain fatty acids
derived from natural oils. We’ll look a little closer into what exactly that means.
Ester
An ester is the product of combining an acid (abbreviated as R1-COOH) with an alcohol (abbreviated
as R2OH). Esters in general are often abbreviated as R1-COOR2, where R1COO represents the residue
of an oxygen acid (The residue is what’s left when the hydrogen is lost), and R2 represents an alkyl –
from an alcohol that lost its OH group. So, through the combination, an H is lost, and an OH (although
in reality the O could come from either the alcohol or the acid), yielding a water molecule (H2O), and
the ester, made up of everything else remaining of the acid and alcohol except the H2O. Esters vary
depending on the type of acid (R1COOH, often abbreviated as R1 for simplicity) and the type of
alcohol (R2OH, often abbreviated R2).
Vegetable Oil
Vegetable oils are esters of glycerin (an alcohol, aka glycerol) and varying fatty acids. A glycerin
molecule looks like:
CH2OH
|
CHOH
|
CH2OH
Figure 1 – Glycerin (glycerol)
Each vegetable oil molecule is a triglyceride, meaning it consists of three fatty acids (which can be of
different types) connected to a glycerin backbone. So, while some esters consist of just one acid (R1),
vegetable oil molecules have three acids combined with an alcohol. So, when speaking about vegetable
oils in particular, the three acids are often referred to as R1, R2, and R3, and the alcohol as R4. A
triglyceride (vegetable oil) can be drawn as:
CH2OOR1
|
CHOOR2
|
CH2OOR3
Figure 2 – A triglyceride (vegetable oil molecule)
The fatty acids involved would be R1OH, R2OH, and R3OH (the hydrogen atoms are lost when the acid
is combined with the alcohol to make the triglyceride).
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
3
UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
Alcohol
An alcohol is a molecule in which any carbon atoms have the maximum number of hydrogen atoms
attached possible, except for one carbon atom which has an OH group connected. The simplest
alcohol, and the one used most often in biodiesel production, is methanol. Methanol consists of only
one carbon atom, with three hydrogen atoms attached, and one oxygen attached. The oxygen atom also
has a hydrogen atom attached. Thus, methanol is often written as CH3OH. The next simplest alcohol is
ethanol, which has one more carbon atoms, with two hydrogen atoms attached, in between the CH3
group and the OH group. Ethanol is written as either CH3CH2OH, or C2H5OH. The former method is
often used to give more of a description of the structure (since it consists of a carbon with three
hydrogen atoms attached, connected to another carbon with two hydrogens attached, connected to an
oxygen with one hydrogen attached). These alcohols are abbreviated as ROH, where the R is the
hydrocarbon chain (consisting of CnH2n+1), and determines what type of alcohol it is.
Typical Fatty Acids in vegetable oils
Below is a table of typical fatty acids found in alcohol, and some of their properties. The “Acronym” is
a chemical abbreviation for the molecule. The first number refers to the number of carbon atoms in the
chain, and the second number refers to the number of double bonds in the molecule. Thus, Linoleic
acid, for example, is a fatty acid consisting of a chain of 18 carbon atoms, with two double bonds.
Notice that the more double bonds in the acid, the lower the melting point. This is an important issue
regarding the cold weather suitability of the oil or the biodiesel produced from the oil, and will be
discussed further. The double bonds also lower the boiling point, which does not make a significant
difference on the operability of the fuel since all biodiesel molecules have boiling points so high as to
make vaporization not an issue.
Table 1 – Properties of Fatty Acids commonly found in vegetable oils 1
Fatty Acid Acronym Molecular Melt
Boil
Cetane
Weight
ºC/ºF
ºC/ºF
Number
Caprylic
8:0
144.2
16.5/61.7 239.3/462.7
Capric
10:0
172.27
31.5/88.7 270.0/518.0 47.6
Lauric
12:0
200.32
44.0/111.2 131.0/267.8
Myristic
14:0
228.38
58.0/136.4 250.5/482.9
Palmitic
16:0
256.43
63.0/145.4 350.0/662.0
Stearic
18:0
284.43
71.0/159.8 360.0/680.0
Oleic
18:1
282.47
16.0/60.8 286.0/546.8
Linoleic
18:2
280.45
-5.0/23.0
230.0/446.0
Linolenic 18:3
278.44
-11.0/12.2 232.0/449.6
Erucic
22:1
338.58
33.0/91.4 265.0/509.0
Heat Combust
(kg-cal/mole)
1453.07
1763.25
2073.91
2384.76
2696.12
2657.4
Saturated Fatty Acids
A saturated fatty acid is one containing no double bonds. Since fatty acids are acids with a COOH
group at the end, a saturated acid is one in which the rest of the carbon chain is an alkane – i.e., the
carbon atoms in the chain have the maximum number of hydrogen atoms bonded possible (every
bonding location is filled with a hydrogen atom, except for single bonds to neighboring carbon atoms).
Stearic acid (18:0) is an example of a saturated fatty acid, as it has no double bonds. The chemical
formula for stearic acid is CH3(CH2)16COOH.
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
4
UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
Unsaturated Fatty Acids
An unsaturated fatty acid is one containing one or more alkene functional groups – those being
hydrocarbons with double bonds between two carbon atoms. An alkene does not have the maximum
number of hydrogen atoms possible on all of the carbon atoms, as two adjacent carbons have a double
bond between them, and therefore one less hydrogen attached each. Oleic acid is an unsaturated acid of
the same length as stearic acid, but with a double bond between two of the carbon atoms, and therefore
two less hydrogen atoms. Molecules with double bonds are often written using an equals sign (“=”) to
show where the double bond is. For example, oleic acid has its one double bond as the ninth carboncarbon bond, counting from the chain most distant from the carboxyl group (COOH). Thus, oleic acid
would be written as CH3(CH2)7CH=CH(CH2)7COOH. Thus, the molecule has a methyl group (CH3),
then 7 carbons with single bonds between them, each having two hydrogens attached ((CH2)7), then the
carbon that has one end of the double bond (leaving only room left for one hydrogen atom, so it’s a
CH), the double bond connecting to another CH, followed by 7 more CH2 groups, and finally the
carboxyly group (COOH). This molecule is exactly the same as the stearic acid molecule
(CH3(CH2)16COOH, no double bonds), except for the double bond between the 9th and 10th carbon
atoms (so the 9th carbon-carbon bond). Thus, in the middle of the molecule, a set of two CH2 groups is
replaced by CH=CH (double bond between the carbons, only one hydrogen each).
This seemingly minor difference results in a significant change in some of the properties of the
molecule, most notably the melting point. The cold flow properties of the oils, and the resulting
molecules can thus be a nice method for introducing this topic of how minor differences in a molecule
can have large effects, and in particular, double bonds lower the melting point of molecules
(generally).
The oleic acid molecule could have another double bond added, which would turn it into linoleic acid
(18:2). A third double bond would make linolenic acid. Many vegetable oils normally consist of a
significant percentage of these particular 18 carbon acids with double bonds. When the oil is
hydrogenated (usually through high temperatures, such as when oil is used in a fryolator), that is when
some of these double bonds are lost, replacing a CH=CH group with CH2CH2. The acid (or the oil that
the acid is a part of) acquires two more hydrogens, and loses a double bond. The result is an increasing
of the melting temperature of the acid, or oil of which it is part. This is an important consideration as
far as using waste vegetable oils as feedstocks for producing biodiesel. The more heavily used the oil
is, the more hydrogenated it becomes, resulting in higher melting points for the molecules. Therefore,
caution should be taken when using heavily used (hydrogenated) oils for making biodiesel, as the
higher freezing/melting points of the molecules would result in a greater tendency of the fuel to clog
fuel filters, or possibly gel entirely.
Transesterification
Chemically, transesterification is the process of exchanging the alkyl group (from an alcohol)
of an ester with another alkyl, from a different alcohol. In the case of biodiesel, a vegetable oil ester is
combined with a simple alcohol and a catalyst, resulting in the breakup of the triglyceride ester (three
fatty acids connected to a single glycerol (alcohol)), and the joining of the fatty acids with the added
simple alcohols. The glycerin alkyls are replaced with the alkyl of the added alcohol (i.e. methyl for
methanol, ethyl for ethanol, etc.). The separated glycerol is the waste product. This reaction is shown
below:
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
5
UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
CH2OOR1
catalyst
CH2OH
|

|
CHOOR2 + 3CH3OH  3CH3OORx + CHOH
|
|
CH2OOR3
CH2OH
Vegetable oil
3 Methanols
Biodiesel
Glycerin
Figure 3 – Transesterification
Rx is used since the biodiesel produced will consist of different types of mono-alkyl esters,
because of the various fatty acids (R1, R2, R3) in the vegetable oil. The reaction can proceed both ways,
so it is generally necessary to add an excess of methanol to force the reaction to the right. Since it is
not desirable to have free methanol in the biodiesel fuel, it is then necessary to recover the methanol
either by water washing, or a pressure-condensing method. The glycerin is more dense than the
biodiesel, so it will gradually settle to the bottom in the reactor.
Biodiesel – Mono Alkyl Esters
As mentioned previously, biodiesel molecules are referred to as mono-alkyl esters, since they
are esters with one alkyl (from the alcohol) per fatty acid, in contrast to the triglycerides in the
vegetable oil, which had three fatty acids for each glycerol. If the alcohol used in making the biodiesel
was methanol, then the biodiesel is referred to as a methyl ester. If the alcohol was ethanol, the
biodiesel would consist of ethyl esters. Table 2 below shows a list of the methyl esters made from the
fatty acids listed in Table 1, and their properties. Note that the methyl esters of fatty acids with more
double bonds have lower melting points than those without double bonds, just as the fatty acids
themselves do. Also notice that the melting points of the methyl esters are lower than the melting
points of the fatty acids themselves. An interesting point of discussion is that the boiling points are not
all affected similarly, from fatty acids being turned into mono alkyl esters. Note that methyl stearate
has a much higher boiling point than stearic acid, while methyl linolenate has a much lower boiling
point than linolenic acid. Fortunately, the boiling points don’t have any significant affect on the use of
the chemicals as fuels.
Table 2 – Properties of Methyl Esters from Vegetable Oils 1
Methyl Ester
Acid
Molecular Melt
Boil
Cetane Heat Combust
Acronym Weight
ºC/ºF
ºC/ºF
Number (kg-cal/mole)
Methyl Caprylate
8:0
158.24
193.0/379.4 33.6
1313
Methyl Caprate
10:0
186.30
224.0/435.2 47.7
1625
Methyl Laurate
12:0
214.35
5.0/41.0
266.0/510.8 61.4
1940
Methyl Myristate
14:0
242.41
18.5/65.3
295.0/563.0 66.2
2254
Methyl Palmitate
16:0
270.46
30.5/86.9
418.0/784.4 74.5
2550
Methyl Stearate
18:0
298.51
39.1/102.4 443.0/829.4 86.9
2859
Methyl Oleate
18:1
296.49
-20.0/-4.0 218.5/425.3 47.2
2828
Methyl Linoleate
18:2
294.48
-35.0/-31.0 215.0/419.0 28.5
2794
Methyl Linoleneate 18:3
292.46
-57.0/-70.6 109.0/228.2 20.6
2750
Methyl Erucate
22:1
352.60
222.0/431.6 76.0
6454
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
6
UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
Why not use the straight oil?
Biodiesel is intended to replace petroleum diesel as a fuel in Diesel engines. A common
question (which students may have, since much of the public does) is why not just use the straight
vegetable oil (SVO), rather than going to the trouble to convert it into biodiesel. After all, Rudolf
Diesel did initially invent his diesel engine to run on pure vegetable oil. There are a couple of reasons
why SVO isn’t as appealing as biodiesel.
First and foremost, is the fact that modern diesel engines use high tech injection pumps, which
don’t tolerate very viscous fluids. The viscosity of vegetable oil is considerably higher than the
biodiesel made from that oil. Most vegetable oils have viscosities around 30-50 “centistokes”, while
most biodiesel has a viscosity around 5-6 centistokes.2 If a person were to just pour vegetable oil into
their fuel tank, with most diesel vehicles, the fuel pump would fail fairly quickly due to the strain of
pumping the very viscous oil. That problem can be skirted somewhat by using a system to heat the
vegetable oil before it gets to the pump, reducing its viscosity to an acceptable level. In fact, this
approach has been taken by many people as it provides a method for them to run their diesel vehicle on
free waste vegetable oil from restaurants, without having to go to the trouble of turning it into
biodiesel. The most common approach is to put in a second fuel tank for the oil, and use the coolant
system of the vehicle to heat the second tank. The car would be started on either diesel or biodiesel,
and once the engine (and therefore the coolant) has heated up to operating temperature - usually
around 200F on most vehicles – the car can switch to pulling fuel from the auxiliary tank holding
heated vegetable oil. This approach can work, but is not ideal for a few reasons. But, it can present an
interesting project for mechanically inclined students, and at several high schools and colleges around
the country, students have modified older diesel vehicles to run on straight vegetable oil in this
manner.
The main drawbacks of this approach are that most modern fuel injection pumps suffer from
increased wear from the high temperature of the fuel. The pumps simply aren’t designed to tolerate
having 200F liquid flowing through them. Additionally, the straight vegetable oil does not burn as
cleanly as biodiesel (due in large part due to the presence of the glycerin in the SVO), resulting in
worse emissions, and carbon buildup on fuel injectors and inside the engine. Together, the effects to
the injectors, injection pump, and inside the engine make a vehicle running on SVO less reliable, and
more polluting than a vehicle running on biodiesel. A final reason for converting the vegetable oil into
biodiesel can be seen by comparing the melting points for the fatty acids shown in Table 1 to those of
their methyl esters shown in Table 2. The methyl esters all have lower melting points than their
corresponding fatty acids (and henceforth, the triglycerides made of those fatty acids). The result is
that straight vegetable oil would be more difficult to use in cold or even moderate temperatures than
biodiesel.
An important point to notice is that for the most part, the methyl esters with the lower (and
therefore preferable) melting points, unfortunately have lower (and therefore less preferable) cetane
numbers. Modern diesel engines generally require a cetane number of at least 40, preferably 45 or
higher. So, while from looking at Table 2, we might think that the ideal biodiesel would be composed
entirely of methyl linoleneate, due to the extremely low melting/freezing point (-70º F), we should also
notice that the cetane number is far too low (20.6) for a fuel composed entirely of methyl linoleneate to
be acceptable.
Another point of interest is that other alcohols produce biodiesel molecules with lower melting
points. For example, isopropyl stearate has a melting point of 28º C, compared to 39.1º C for methyl
palmitate. 3
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
7
UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
What exactly is cetane number?
Cetane number is an important characteristic of diesel fuels, just as octane is important for
gasoline. Whereas octane measures how well a gasoline fuel resists early detonation (and is not
actually the quantity of octane molecules present in the fuel), cetane number is a measure of how well
suited the fuel is for a diesel engine. Whereas gasoline engines use a spark to ignite the fuel (spark
ignition), diesel engines use compression alone, with no spark. Diesel engines are therefore referred to
as “compression ignition” engines. Cetane number is a measure of how readily the fuel ignites under
compression. The higher the cetane number, the more readily the fuel ignites in the engine. Therefore,
higher cetane is preferable. The best method for measuring cetane number is to use an engine
specifically designed for that purpose – known as a cetane engine. ASTM D 613 (ASTM is the
American Society for Testing and Materials, and establishes specifications for a variety of chemicals
and meterials to meet) is the standard test used for this purpose, and in the test, the fuel being measured
is compared to fuels of known cetane values, and ignited at various compression ratios. Most diesel
fuel in the US has a cetane number ranging from 40-50. Most modern diesel engines are designed for
cetane numbers of at least 45. Diesel Fuel has to meet the specification ASTM D 975, while biodiesel
meets ASTM D 6751.
Differences between various vegetable oils
Looking at the properties of the various methyl esters demonstrates that the properties of
biodiesel – in particular the cold weather properties, could vary considerably depending on what oil it
is made from. Table 3 below lists a few different vegetable oils, and the levels of various fatty acids
they contain (bare in mind, in the oil the fatty acids are bound to glycerin as triglycerides. The table
lists the fatty acids themselves, but is not meant to imply that they exist as free fatty acids in the oil).
The fatty acid profiles are generalities, as various plants (and animal fats, such as the tallow included)
do have variability among them, depending on growing conditions and other factors. A field in
biodiesel research focuses on breeding varities of various plants for ideal fatty acid profiles. The table
also includes the gel point, cloud point (these qualities are explained in section II.c of the Lesson Ideas
portion of this document), and cetane number for methyl ester made from each oil.
Table 3 – Fatty Acid profile, and properties of methyl esters for various oils2
Rapeseed
Canola
Tallow
Soybean
Myristic (14:0
0
0.0
3.0
0.0
Palmitic (16:0
2.2
4.0
23.3
9.9
Stearic (18:0
0.9
2.4
17.9
3.6
Oleic (18:1)
12.6
65.0
38.0
19.1
Linoleic (18:2)
12.1
17.3
0.0
55.6
Linolenic (18:3)
8.0
7.8
0.0
10.2
Elcosenoic (20:1)
7.4
1.3
0.0
0.2
Behenic (22:0)
0.7
0.4
0.0
0.3
Erucic (22:1)
49.9
0.1
0.0
0.0
Properties of Methyl Esters of the oils
Cetane number
61.8
57.9
72.7
54.8
Cloud Point ºC
0
1
16
3
Gel/Pour Point ºC
-15
-9
16
-3
Data taken from http://www.biofuels.fsnet.co.uk/comparison.htm
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
8
UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
Soap Formation
Soap can be made by combining sodium hydroxide (NaOH), water, and vegetable oil. The
water separates the sodium hydroxide, resulting in free Na+ ions. The vegetable oil triglycerides are
broken apart, separating the fatty acids and glycerin. The Na+ ions attach to the fatty acids in the same
place that the alkyl groups attach during transesterification to produce biodiesel. The fatty acids with a
sodium ion attached make a soap.
Since a base is used both for making soap from vegetable oil, and also as the catalyst for
breaking apart the vegetable oil molecule during transesterification, care needs to be taken that one
doesn’t inadvertantly make soap. The NaOH is combined with the alcohol to make sodium methoxide,
which is then added to the vegetable oil. It is imperative that there be no water present in the
methoxide mix, or at least as little as possible. This is because the water would break apart the NaOH
molecule, producing free Na+ ions, which could then combine with fatty acids to produce soap. If the
sodium is bound up in sodium methoxide, when the vegetable oil is broken apart, the methyl groups
will preferentially bond with the fatty acids, rather than sodium – resulting in biodiesel rather than
soap. Using too much NaOH can result in soap formation, due to the excess sodium joining the fatty
acids after the vegetable oil molecules are separated.
With waste vegetable oils, free fatty acids are generally already present. These free fatty acids
will essentially always combine with a sodium ion during the processing, resulting in saponification
(soap formation). Unfortunately, that is an unavoidable result when using this base-catalysed
transesterification process (and is a reason why some groups have developed methods of performing
the reaction without a catalyst). Since these free fatty acids consume the catalyst, when waste
vegetable oils are used, extra catalyst needs to be added to account for that. Otherwise, not enough
catalyst would be left for breaking apart the triglycerides in the oil, as some would be consumed by the
free fatty acids (FFAs). This is the reason for doing the titration when using a waste vegetable oil
feedstock, so that extra catalyst can be added to account for the fact that some catalyst will be
consumed by the FFAs.
When oils with free fatty acids are used, the free fatty acids will be turned into soaps by the
catalyst. As a result, the yield of biodiesel is lower for these oils, and the soap needs to be removed
(usually through water washing).
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
9
UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
Biodiesel – Lesson Ideas
The topic of biodiesel can be introduced in a variety of classes – chemistry, biology, physics,
and even classes focusing on politics and current events. This document will discuss some options for
using the topic of biodiesel as a vehicle for beginning other lesson plans, or discussing topics which
students otherwise may not be interested in. An ideal approach could involve coordinating biodiesel
lessons in the science classroom with relevant discussions in a civics, economics, or current events
classroom. Since scientists and engineers in today’s world need to also focus on issues such as making
their processes and products economical, and looking into related political issues, biodiesel presents an
excellent example for students learning how science topics relate to non-scientific fields.
The goal of this workshop is not necessarily to give you an exact lesson plan which you could
use as-is in your classroom (since there are science teachers here from different branches of science,
and different grade levels), but to teach you more about the topic of biodiesel, and to give you ideas on
how you could incorporate it into your classroom. The UNH Biodiesel Group is always eager to help
out, so if after the workshop you have any questions on biodiesel itself, or ideas for incorporating it
into the classroom, please feel free to contact either Michael Briggs (msbriggs@alberti.unh.edu, 8622828), or Dr. Ihab Farag (ihab.farag@unh.edu, 862-2313).
I. Biology
Being produced from biological matter, there are several options for topics that could be
introduced or elaborated on through a discussion of
biodiesel. The following are a few possibilities.
Figure 3 - Biodiesel's Closed Carbon Cycle
I.a. Carbon Cycle
The carbon cycle is a topic that many students –
even a majority of adults – have difficulty understanding.
Our UNH Biodiesel Group has given many presentations
to legislators, members of the general public, students, and
scientists. We have found that a discussion of how the
carbon cycle works for biodiesel is very successful in
engendering a better understanding of the carbon cycle in
general.
With regard to alternative fuels, the main
importance of the carbon cycle is whether it is a closed or
open cycle. Any fuel produced entirely from biomass
would have a closed carbon cycle – since all of the carbon
within the fuel came from the plants from which it was
produced, and the carbon in the plants came from the
atmosphere. As Figure 1 shows, plants get their carbon
from CO2 in the atmosphere – converting the CO2 to O2
during photosynthesis, with the carbon being stored in the plant (as carbohydrates, oils, starch, etc.).
Photosynthesis is the process by which plants convert carbon dioxide and water into glucose and
oxygen, in the presence of chlorophyll and sunlight (which supplies the energy). In energy terms, the
plants are converting the electromagnetic energy (sunlight) into chemical energy (glucose).
CO2 + water (+sunlight)  glucose + O2
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu 10
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
The glucose can then be converted into other forms by the plant – other sugars, or fats, starches,
proteins (which also requires nitrogen and sometimes sulfur), and so on. Plants can get everything they
need to make sugars, oil, and starches from the air (CO2), sunlight, and water (H2O). That’s because
those molecules are made only of carbon, hydrogen, and water. As far as the carbon cycle, the
important point is that all of the carbon within a plant comes from carbon dioxide in the air.
If the plant decays, much of that carbon finds its way back into the atmosphere as CO2 or
methane (CH4). If the oil is extracted from the plant, and turned into biodiesel (the alcohol used to
make the biodiesel could come from alcohol also made from the plant), all of the carbon in the
biodiesel had to come from CO2 in the air. So, when we burn biodiesel, even though it gives off CO2,
there is no net addition to atmospheric carbon (CO2) levels, since that same carbon we are releasing
was taken from the atmosphere by the plants when they were growing.
Contrast this to the carbon released when we burn any fossil fuels. The carbon in gasoline, for
example, is from the petroleum we extract out of the ground. That carbon itself was likely in the
atmosphere at one point – but billions of years ago, when the earth was much younger, and had much
higher levels of atmospheric carbon dioxide. The bacteria that grew on the young earth took carbon out
of the atmosphere, and over billions of years of dying, not fully decaying, “sequestered” that carbon
within the earth (which resulted in atmospheric carbon dioxide levels dropping to the stable level they
have been at now for millions of years – a level that results in the right amount of infrared insulation
for maintaining a temperature here on earth that is suitable for humans, etc.). By burning a fossil fuel,
we are adding carbon to the atmosphere (as CO2, with the oxygen portion coming from O2 already
present in the atmosphere) that had not been in our atmosphere for billions of years. Through so doing,
we gradually increase the atmospheric carbon level beyond the fairly stable level it has been at for
Figure 4 - Anthropogenic carbon emissions4
Figure 5 - Atmospheric Carbon Increase
millions of years, resulting in more heat
held in through the greenhouse effect
(another issue to be discussed). Figure 5 shows the increase in atmospheric carbon levels over the past
200 years since the Industrial revolution, when we began burning fossil fuels. Figure 4 plots the
anthropogenic (man-made) emissions of carbon to the atmosphere (largely from burning fossil fuels).
Some of this CO2 emitted was taken up by plants and the oceans (the green region), while the rest
remains in the atmosphere, increasing the atmospheric level of CO2, the prime greenhouse gas. The
most recent data point for atmospheric carbon levels was released this month (March, 2004). The
current level is now up to 379 ppm.5
There have been minor fluctuations in the atmospheric carbon levels over the past few million
years, but nothing close to the increase we have caused in the past 200 years alone. From the
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu 11
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
environmental standpoint, this is the most important reason for moving from fossil fuels to renewable
biofuels, which result in no net addition to atmospheric carbon levels.
I.b. Greenhouse Effect
Note – This topic could fall under several categories – biology, chemistry, physics, environmental
science, politics and current events (i.e. Kyoto Protocol)
This is a topic that could be covered in a variety of courses, yet is a topic covered very little in
most current curriculum. The issue could be covered either briefly, or in excruciating detail. Being
such an important topic, particularly as far as an issue with science and political crossover, it would be
very desirable for students to garner a better understanding of the greenhouse effect. There are many
valuable resources on the web providing a thorough discussion of it from a variety of perspectives
(biology, chemistry, physics, public policy, etc.). A few that would be useful references:
http://www.science.gmu.edu/~zli/ghe.html
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/grnhse.html
http://www.whoi.edu/science/MCG/doneylab/papers/doney_schimel_els_2001.pdf
http://oregonstate.edu/instruction/bi301/globclim.htm
http://media.wiley.com/product_data/excerpt/83/04708501/0470850183.pdf
http://www.firstscience.com/site/articles/gribbin.asp
http://www.newscientist.com/hottopics/climate/climatefaq.jsp
One valuable reason for lessons on the greenhouse effect, and global climate change, is for
students to learn that there are ongoing discussions and debates about many topics in science. Students
often get the impression that science is a “finished book”. Learning that there are many questions
scientists are still trying to answer, with many lively debates among scientists helps develop student
interest in the subject.
I.c. Health issues
A biology and chemistry related issue that is often not covered (because it’s not pure biology,
but is something that anyone who ends up working with any form of chemical will encounter) is the
issue of Material Safety Data Sheets (MSDS), which cover the health effects of a particular chemical.
Government environmental groups (EPA, and state Environmental departments (New Hampshire
Department of Environmental Services, NH DES)) and labor groups (OSHA) oversee the use and
development of these. Your packet includes a sample MSDS for biodiesel (this one is from Burke Oil
in Chelsea, MA, who sells biodiesel as “Patriot B100 Biodiesel”)6. The MSDS covers physical
characteristics, fire and explosion data, reactivity data, health hazard data, and handling and control
measure guidelines. A summary of the MSDS is generally included as the NFPA (National Fire
Protection Association) Hazard Symbol, usually at the top of an MSDS. This diamond shaped symbol
summarizes the flammability, reactivity, health, and radioactivity characteristics of the material in
question (radioactivity is left off of most MSDS). Each type of potential risk is ranked from 0 to 4,
with 0 meaning no threat is posed, and 4 indicating a very serious risk.
Since MSDS are used at any workplace that uses any sort of chemical (whether hazardous or
not), it would be valuable for students to become familiar with them. Additionally, the MSDS for
biodiesel presents an interesting lesson in biology. Looking at the included MSDS, you will notice it
was rated a “0” (the safest score) in the Health category, in the NFPA symbol. This ranking was
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu 12
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
awarded based on tests done for the EPA, in which the LD50 (dose at which 50% of the animals used
in the tests die) was evaluated in rats. These tests found that the LD50 for biodiesel is greater than 17.4
g/kg (the tests did not go any higher, but found that that level did not yield an LD50 result). By
comparison, table salt is roughly ten times as toxic, meaning a dose 1/10th as large would yield an
LD50 result. The problem with these tests is that they were done on rats, and humans are not identical
to rats.
Humans and other primates can not metabolyze methanol, while essentially every other animal
(including rats) can. While properly made biodiesel should contain no free methanol, if the fuel is
made with methanol as the alcohol involved, it will contain methyl groups. An enzyme in our digestive
tract separates this methyl group, and adds an OH to it, turning it into a methanol. Methanol is
metabolized into formaldehyde by hepatic alcohol dehydrogenase. Formaldehyde is then quickly
metabolized to formic acid, which can result in metabolic acidosis, as seen in methanol poisoning. The
methanol itself does not cause problems, but a metabolite byproduct does – with formate being the
primary metabolite responsible for the adverse effects.
From http://www.maripoisoncenter.com/ctr/9802methanol.html ,
“Formate is handled primarily by the carbon 1-unit transfer biochemical pathway which utilizes folate
as a co-factor. Formate combines with tetrahydrofolate (THF) through formyl-THF synthetase. 10Formyl-THF then undergoes oxidation to C02. Hepatic THF concentrations dictate the rate of formate
metabolism. If hepatic THF levels are reduced, as in the case of most primates, the formate will
accumulate producing metabolic acidosis.”
Essentially, the metabolization of methanol results in formate. Humans, like most primates,
have low levels of hepatic THF, which prevents quick metabolization and elimination of the formate.
The result is a buildup of formate in humans, resulting in metabolic acidosis. Since most non-primates,
including rats, have higher levels of hepatic THF, they do not suffer the risk of metabolic acidosis from
consumption of methanol, or chemicals containing methyl groups which can be turned into methanol
in their digestive system. This is also the risk associated with extreme consumption of the sweetener
aspartame (L-aspartyl-L-phenylalanine methyl ester), also a methyl ester.
This issue demonstrates an important lesson in biology – one which the EPA apparently has not
yet learned themselves. Most often, human toxicity analysis is done based on testing on other animals,
particularly rats. The case of the EPA’s assessment of the safety of biodiesel made with methanol
presents an example of the problem with this practice. While rats can consume methyl esters with no
adverse effect, humans do not contain the high levels of hepatic THF necessarily to quickly metabolize
the formate that would result from such ingestion. As a result, the EPA’s “0” rating for the health risk
of biodiesel is not entirely correct, since humans should not ingest the fuel.
Fortunately, biodiesel is broken down very rapidly in the environment, so a leaking
underground storage tank, for example, would not pose a significant risk, as the methyl esters – and
then the methanol would be broken down fairly rapidly. But, it would still be preferable if MSDS
sheets, and the EPA’s ratings upon which they were based were correct, so as not to lead people to
believe they could safely drink biodiesel made with methanol.
This also presents a reason why it would be preferable to make biodiesel with ethanol, rather
than methanol, as humans can properly metabolize ethanol and its metabolites, so long as they are not
consumed in extreme amounts. In general terms though, biodiesel is considerably safer than petroleum
fuels. Petroleum diesel has NAFPA ratings of 1, 2, and 0 for health, flammability, and reactivity.
Biodiesel degrades far more quickly than diesel, and is not harmful to most animals (i.e. non-primates).
It is also considerably less flammable, with a flash point over 300º F (compared to 125º F for diesel).
Biodiesel was scored 0, 1, and 0 for Health, Flammability, and Reactivity. The 0 for Health is correct
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu 13
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
for all non-primates, but biodiesel produced with methanol should not be ingested by humans or other
primates. Biodiesel is not considered an acute or chronic hazard (see the MSDS Sheet), while diesel
fuel is.
I.d. Plant Suitability
A key area of research related to biodiesel is finding or developing alternative crops that can be
grown for producing biodiesel – or another alternative fuel. The crop used for producing a fuel is
referred to as the feedstock. Currently, soybeans are the primary feedstock in the US for biodiesel
production. The only reason for this is the fact that the US produces a large amount of surplus soybean
oil as a by-product of the soy industry. Soybeans are growing in the US primarily for their protein
content – with the bulk of that being for animal consumption (animals in the US grown for human
consumption consume ten times as much protein every year as all of the humans in the US). But, other
crops would make far better options for biodiesel production – from the perspective of biology,
chemistry, and physics. One example the UNH Biodiesel Group is working on is hybrids of yellow
mustard, bred to have higher concentrations of glucosinolates. These glucosinolates are broken down
in soil by bacteria, creating isothiocyanates. The isiothiocyanates have strong pesticidal qualities, but
themselves break down within a few days. The result is that the mustard meal (what is left after
extracting the oil) could make an excellent organic pesticide, to replace much more harmful pesticides.
The isiothiocyanates are as effective as pesticides currently used, but due to the fact that they
themselves biodegrade quickly, there would be no concern about pesticidal residue on crops intended
for consumption. The high economic value of the mustard meal then would allow the oil to be sold
much more cheaply, resulting in lower cost biodiesel.
This is an example of understanding the chemistry involved in the glucosinolate breakdown,
understanding the biology of breeding mustard for higher glucosinolate levels, and the effects of those
glucosinolates on plants and animals, and the economics resulting from the same crop producing a very
high value co-product.
II. Chemistry
There are several lessons that can be initiated with a discussion of biodiesel. Many of the lesson
ideas that are also mentioned under biology and physics could be included in the chemistry classroom.
This section will focus on a few ideas that would be specific to chemistry, while the ones that overlap
into other areas are listed in the area of overlap. Some possibilities specific to chemistry include:
II.a. Titration
Vegetable oil becomes hydrogenated and acidic (due to the formation of free fatty acids
(FFAs)) when heated to high temperatures, as is done in fryolators. As a result, when using waste
vegetable oil, extra catalyst (a base) needs to be added. The reason being that the free fatty acids will
consume the catalyst. The metal ion in the catalyst (such as sodium) bonds to the free fatty acid, where
the alkyl group normally bonds during transesterification, forming soap. Since some of the catalyst is
consumed by the FFAs, extra catalyst must be added to make up for that lost to the FFAs. The handout
on making biodiesel discusses the titration itself. Since titrations are important for chemistry students
to learn, biodiesel can provide an interesting example of how titrations are used in the “real world”.
Since most students continually ask themselves (and sometimes the teachers) “why do I need to learn
this”, it is always valuable to show a real world use of what is being taught.
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu 14
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
II.b. Organic Chemistry Terminology
Discussing vegetable oils and transesterification presents a nice opportunity for students to
learn about, or further their knowledge of various chemistry terminology and classification – in
particular, alcohols, alkenes, alkanes, alkyls, acids, esters, and so on. In addition to examining the
reactions involved in making biodiesel, it can also be valuable to examine the properties of the various
types of molecules involved (from different types of oils). In particular, looking at the properties of the
methyl esters of 18 carbon chain fatty acids can demonstrate the effect of double bonds, and why it is
so important to have the many different names in chemistry to distinguish between seemingly minor
differences. Most students would not expect initially that what appears to be a minor difference – one
molecule having a double bond, and two less hydrogen, as compared to an otherwise identical
molecule – would have such a large impact on the properties of the molecule.
II.c. Freezing and Gelling
Most liquid fuels consist of a number of different molecules, with different properties. As a
result, the entire fuel does not have one single freezing point. Looking at Table 3 of the document
“Biodiesel Chemistry”, included in the packet, shows typical profiles of a few different vegetable oils
as well as an animal fat (beef tallow). From this, it can be seen that most potential biodiesel feedstock
oils consist of a variety of fatty acids, anywhere from a few, up to nine or more. As a result, the
properties of the biodiesel will depend on the makeup of the fatty acid profile, as well as the particular
alcohol used in processing (for example, ethyl esters have lower melting points than methyl esters of
the same oil, meaning ethanol would be a preferred alcohol to use for cold weather operation of the
biodiesel. Ethanol has only minor impacts on the cetane number, lubricity, and viscosity of the fuel.
However, producing biodiesel with ethanol is somewhat more finicky than with methanol. With
methanol, the concentration of the reactants can be off slightly, and the reaction will still proceed
successfully. Transesterification with ethanol is less forgiving. The main reason methanol is the prime
alcohol used in the biodiesel industry, however, is the cheaper cost of methanol).
There are a few different important properties for cold weather performance of any fuel. These
include the “Cloud Point” (CP), “Cold Filter Plugging Point” (CFPP), and “Pour Point” (PP), also
referred to as “Gel Point” (GP). The CP is the temperature at which some of the molecules in the fuel
first begin to freeze, resulting in the appearance of crystals in the fuel, which give it a “cloudy”
appearance initially. Since the Cloud Point is the temperature at which the highest freezing point
molecules in the fuel begin to freeze, a casual analysis would leave students to believe that the CP is
simply the freezing point of that biodiesel molecule (methyl ester, ethyl ester, etc.) in the fuel that has
the highest freezing point. But, that is not the case. The molecules in the fuel with lower freezing
points have an anti-freezing effect on the molecules with higher freezing points. This can be observed
by looking closely at Tables 2 and 3 in the Biodiesel Chemistry handout. In soybean oil, ignoring the
behenic acid and erucic acid, which are present in only very small percentages, the fatty acid whose
methyl ester has the highest freezing point is stearic acid, which constitutes 3.6% of soybean oil. The
next highest is palmitic acid, constituting 9.9%. The freezing points of methyl stearate and methyl
palmitate, respectively (from Table 2), are 39.1º C and 30.5º C (102.4º F and 86.9º F). So, at first
glance, we may expect that the “Cloud Point” for soy biodiesel (aka methyl soyate) would be 39.1º C,
the freezing point for methyl stearate. But, looking at Table 3, we see that the CP is actually 3º C,
considerably lower. The reason for this is the freezing point depressing effect of the other molecules in
the fuel, which have considerably lower freezing points. Biodiesel therefore presents an interesting
opportunity for discussion of how freezing point depression works.
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu 15
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
With liquids consisting of molecules of various freezing points, gelling occurs as a result of
solid molecules entangling and crosslinking, to form a semi-rigid structure, even though the majority
of the molecules may still be liquid. A gel, also referred to as a sol, would of course present a serious
problem to a vehicle’s fuel system. Regular petroleum diesel can gel at anywhere from –20º C (-4º F)
to -10º C (14º F), depending on the quality of the fuel. Since atmospheric temperatures can fall below
that, the diesel fuel industry has developed techniques for “winterizing” the fuel, to prevent this gelling
from happening. The temperature at which this gelling occurs is referred to as either the “Gel Point”
(GP), or more commonly, the “Pour Point” (PP). With diesel fuel, in some cases the gelling issue is
dealt with by blending in other liquids with lower freezing points, such as kerosene. This also has a
freezing point depressing effect on the molecules in the diesel fuel, so it also lowers the cloud point.
Another method of winterizing involves the addition of an “antigel additive”. These additives are
generally added in very small quantities (0.1-0.2% by volume), but can significantly lower the PP.
They do so, primarily, by bonding to frozen molecules when the fuel falls below the cloud point, and
preventing those molecules from bonding/crosslinking with other frozen molecules. The molecules of
an antigel additive are generally considerably smaller than the fuel molecules themselves, so 0.1% of
the additive by volume can effectively block a much larger percentage of fuel molecules from having
the ability to gel the fuel. Some additives can lower the PP of diesel fuel by 30ºC (48º F) or more.
These same methods of winterization can also be used with biodiesel. Many of the same antigel
additives that are effective with petroleum diesel are also effective with biodiesel. An issue of critical
importance, however, is that most biodiesel fuels have a greater percentage of the highest freezing
point molecules than most petroleum diesel, so while 0.1% by volume of the additive may be enough
to bond to all of those high-freeze point molecules in petroleum diesel, they may not be enough for
biodiesel. As a result, using the same amount may have no effect on the gel point. But, using a greater
percentage, based on the percentage of high freeze point molecules in the biodiesel, a significant
antigelling effect can be achieved. Most methyl soyate biodiesel has a gel/pour point slightly below
0ºC (-3ºC is the PP of the sample analyzed in the reference used for compiling Table 3). But, in tests
performed by a member of the UNH Biodiesel Group (Michael Briggs), use of antigel additives in the
appropriately higher percentage required successfully lowered the PP of soy biodiesel to below -23ºC.
The cold flow properties of biodiesel present an excellent opportunity for lessons on freezing
point depression as well as sols (gels), and applications of those concepts currently in use in the
automotive fuel sector, as well as how they can be used with an alternative fuel entering the market.
III. Physics
III.a. Thermodynamics, Energy Conservation
An important issue when looking at fuels, and energy “production”, is the energy efficiency of
the processes involved. For an automotive fuel, the more efficiently it can be produced, the less energy
we need to create for the production of the fuel. This is an issue of critical importance in any
discussion of alternative energy or fuel, and is something which is unfortunately often completely
overlooked. A key concept for students to understand here is the conservation of energy. Energy can
not be created or destroyed, it can only be changed from one form to another. When we say we
“produce energy from coal”, for example, we are not actually creating energy, we are instead
converting the chemical energy that was in the coal into electrical energy which we can more readily
use.
There are many different methods of examining the energy efficiency for a process. One of the
most useful is referred to as the EROI – or Energy Return On Investment. Essentially, this means how
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu 16
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
much energy we get back (in the form of a fuel, or usable energy) for each unit of energy we put into
the process. The higher the EROI, the better the process. If the EROI is below one, then we actually
lose energy through the process.
A similar method often used is referred to as an energy balance. Energy balances can be
performed in a number of ways, and at heart are the same as an EROI. But, energy balances are often
done to only include a certain type of energy input. For example, fossil energy balances are often done
to look at how efficiently something uses fossil fuels. A fossil energy balance is done to see how much
energy we get back for each unit of fossil energy expended in the process – including the energy of any
fossil fuel converted to a more usable form. To clarify, for analyzing the use of petroleum to make
gasoline, diesel, etc., the EROI measure tells us how much energy we get in the form of those fuels for
each unit of energy we expend on extracting the petroleum, refining, and transporting it. But, the EROI
does not include the energy in the petroleum itself as an energy input. For the various petroleum
products (gasoline, diesel, etc.), the EROI is generally around 10 to 20, depending on the quality of the
petroleum and amount of processing involved (i.e. Middle Eastern oil is generally lighter, and requires
less processing to get gasoline, than petroleum from the US). An EROI of 10 means that for each unit
of energy we put into the process (including extracting the petroleum, refining it to fuel, transporting it,
etc.), we get back an amount of fuel containing 10 units of energy.
An EROI of 10 is not a violation of the conservation of energy. No energy is “created” in the
process. The reason the EROI can be greater than 1 is that the energy contained in the petroleum itself
is not counted as an energy input for this calculation. This is done since we do not have to put energy
in ourselves to “make” the petroleum. It’s just sitting there, so if we can extract it, we can consider the
petroleum energy “free” – at least for the purpose of an EROI calculation. An EROI of 10 simply
means that all of the additional energy, which we have to put into the process, adds up to only one unit
of energy for each unit of fuel we are able to process from the “free” petroleum (free in energy terms
for this calculation). All of the energy input used for the process is included, even if that energy came
from petroleum itself.
By contrast, a fossil energy balance includes the energy in the petroleum as an input. The
reason for such a calculation is that it’s often useful to know how efficiently we can convert fossil fuels
to more usable fuels, since fossil fuels are after all not unlimited, and not “free”. So, for a fossil energy
balance, the energy within the extracted petroleum is counted as an energy input. If we extract an
amount of petroleum containing 11 units of energy, spend 1 unit of that energy in processing (i.e. burn
some of the petroleum to produce heat and electricity for operating a refinery, etc.), and end up with 10
units of energy in the form of various petroleum fuels, our fossil energy balance would be 10 units of
output energy to 11 units of input energy, 10:11, or a fossil energy balance of 10/11:1, 0.91:1. Such a
fossil energy balance would be abbreviated as just 0.91, meaning we get 0.91 units of energy in the
form of fuels for each unit of fossil energy input – including the energy within the petroleum being
processed. So, while petroleum fuels may have an EROI of 10, they would have a fossil energy
balance of 0.91.
These analyses are useful for comparing other forms of alternative fuels and energy. If an
alternative fuel has an EROI of only 1.4, to make enough fuel-energy to replace all of the petroleum
fuel we currently use, we would have to generate far more energy to be used as input to the process
than we currently do for processing petroleum fuels. Likewise, if the EROI or fossil energy balance is
below 1, we would end up using up a greater amount of energy than we end up with as fuel.
In energy terms, biofuels use the sun as their prime energy input. We may put energy into
planting, fertilizing, harvesting, and processing the crops, but a great deal of energy input also comes
from the sun. Since plants use photosynthesis to convert solar energy into chemical forms of energy
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu 17
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
(carbohydrates, fats, etc.), we can think of plants as “cheap” solar cells. They convert solar energy into
a form more usable as a fuel. So, whereas we might in some ways consider the energy in a fossil fuel
we dig up out of the ground as “free” (except for the additional energy we expend getting it), we can
also consider the energy in the plants free – except for the energy that we put into planting, fertilizing,
and harvesting them. After all, “we” are not responsible for producing the solar energy the plants use
as their prime energy source for making the chemical energy within the plant’s biomass.
The U.S. Department of Energy (US DOE) performed a thorough fossil energy balance
calculation for soybean biodiesel. In this analysis, they assumed that all energy inputs other than the
energy within the soybeans themselves came from fossil fuels. So, for example, the tractors used for
planting and harvesting were assumed to run on petroleum diesel – even though they could be run on
biodiesel, so it would not be a fossil input. This assumption is useful to make, as for a biofuel it results
in the fossil energy balance essentially being an EROI calculation. The reason being that this method
for calculating a fossil energy balance assumes that all energy input (except the energy in the plant) is
from fossil fuels. Therefore, the energy input for the EROI of a biofuel is the same as the energy input
side of the equation for a fossil energy balance, when that assumption is made (since neither analysis
would include the energy in the plant as an input). The fossil energy balance would be better if some
inputs came from biofuels as well, such as running tractors on biodiesel, but it is more useful to know
how much total energy input is required.
The US DOE’s analysis yielded a value of 3.2 for the fossil energy balance (and henceforth
EROI) of soybean biodiesel. This is considerably better than the fossil energy balance for petroleum
fuels, but lower than the EROI of petroleum fuels. Other options for producing biodiesel can yield a
considerably higher EROI, which makes it suitable as a potential wide-scale replacement for
petroleum. This analysis also assumed that the methanol used was derived from natural gas – a
reasonable assumption for now, since that is where most of our methanol comes from. But, there are
many options for producing methanol from biomass, which could be used in the future. So, if those
methods were used, the EROI and fossil energy balance could be increased substantially.
An example of why energy analyses are so important in analyzing alternative fuels can be seen
by looking at the furor over the notion of a “hydrogen economy”. One good example of this is included
in the “Misconceptions” section later in this document. In essence, the relevant issue is that most media
articles, and even many attempts at scientific analysis of hydrogen as a fuel completely ignore this
issue. Deciding upon public energy decisions without including an energy analysis is extremely shortsighted.
Table 4, “Analysis of Prototype and Production Vehicles on Various Fuels”, includes an
example of using a fossil energy balance to examine various fuel options. This analysis includes
vehicles running on gasoline, diesel, biodiesel, and hydrogen. The biodiesel vehicle included is a
Volkswagen Jetta TDI Wagon, a vehicle currently in full-scale production. The hydrogen vehicle
included is Honda’s Fuel Cell Vehicle (FCV) prototype, a vehicle which Honda estimates would sell
for roughly $100,000 if in full-scale production in 2012. For such a cost, we should hope for a very
high fossil energy balance – at least higher than for the Volkswagen available today for around
$20,000, and running on 100% biodiesel.
The most useful means of comparing vehicles on their energy efficiency is the total
fossil energy input per mile. As the table shows, this quantity is a combination of the fossil energy
balance for the fuel itself (FEB), the energy density of the fuel in Btu/gallon (ED), and the fuel
efficiency of the vehicle in miles per gallon (FE). The total fossil energy input per mile then becomes:
Fossil Energy Input per Mile = _____Energy Density_______
Fuel Efficiency * Fossil Energy Balance
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu 18
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
The fossil energy balance is used since it gives a better comparison of how efficiently we use
fossil fuels, and the net CO2 emissions (since those only come from fossil fuels). For biofuels, as
mentioned, the energy inputs could all come from non-fossil sources, but for this analysis, it is more
meaningful to assume they come from fossil sources.
For the hydrogen analysis, the method of generating hydrogen was assumed to be steam
reformation of natural gas – the most common and cost effective method of producing hydrogen, and
likely the primary method that would be used in a “hydrogen economy”. Large quantities of hydrogen
are already produced via this method for various industrial uses. The cost and efficiency of this process
is therefore very well established. A US DOE analysis calculated the fossil energy balance (FEB) for
this process of producing hydrogen to be 0.66, meaning for each unit of fossil energy input, we get
back 0.66 units of energy in the form of hydrogen. Using the specifications for Honda’s Fuel Cell
Vehicle from Table 4 (FE = 5.7 mpg, ED = 9 Btu/gal, FEB = 0.66) , this yielded a fossil energy input
per mile of 2.4 Btu/mile. By comparison, with the Volkswagen already on the market (FE = 44.75 mpg
average between city/highway), running on soybean biodiesel (and assuming all energy inputs
(tractors, etc.) are from fossil fuels, for a FEB of 3.2, and ED of 127 Btu/gal) yields an input of 0.89
Btu/mile. If biodiesel were used in the Dodge Intrepid ESX3, a diesel-electric hybrid prototype
developed by Chrysler in 2000 (and with an expected full-scale production cost of $28,500), the input
would be 0.55 Btu/mile.
Table 4 - Analysis of Prototype and Production Vehicles on Various Fuels
Jetta TDI Jetta TDI
Jetta 2.0L Toyota
Honda
Dodge
on
on
gasoline
Prius on
Fuel Cell
ESX3
biodiesel
petroleum engine
gasoline
vehicle
(dieseldiesel
(hydrogen) hybrid) on
biodiesel
Vehicle cost
$19,970
$19,970
$18,790
$21,520
$100,0003
$28,500
4
Fuel efficiency,
41/48.5
42/50
24/31
52/45
5.7
72
miles/gallon
Vehicle range
609/711
609/711
348/450
619/536
155
???
Power (hp)
90
90
115
70
110
???
Torque (ft-lbs)
155
155
122
82 (EM?)
188
???
2
5
Cost/mile
$0.047
$0.040
$0.062
$0.035
$0.19
$0.03
Energy density of
127
141
123
123
9
127
fuel (Thousands of
BTUs/gal)
Fossil Fuel Energy 3.2
0.83
0.74
0.74
0.667
3.2
6
Balance
Total fossil energy 0.89
3.7
6.0
3.4
2.4
0.55
input/mile8
(Thousand
BTU/mile)
1 Assuming modern catalyst used with the TDI running biodiesel or ULSD.
2 Assuming $1.70/gallon for gasoline, $1.80 for petroleum diesel, and $2.16/gallon for biodiesel,
based on 50/50 average of city/highway
3 Honda’s estimate for the cost of their fuel cell vehicles in mass production in 2012
4 Miles per gallon of hydrogen compressed to 5,000 psi (35 atmospheres), based on maximum range of
Honda’s FCV of 170 miles on a 30 gallon tank
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu 19
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
5 30 gallons at 5,000 psi equals 3.2 kg of hydrogen (hydrogen density at 14.7 psi is 0.0003142 kg/gal,
at 5000 psi it’s 0.1069 kg/gal). Typical cost for very large consumers of compressed hydrogen
expected to be $10/kg. So, $32 for 170 miles.
6 See http://www.mda.state.mn.us/ethanol/balance.html
7 Assumes hydrogen produced from steam reformation of natural gas, fossil energy balance (net
energy ratio) taken from http://www.nrel.gov/docs/fy01osti/27637.pdf
8 Fossil Energy Input calculated based on 50/50 average fuel mileage and fossil energy balance of
creating fuel. Fossil Energy input per mile then equals (energy density of fuel )/[(fuel efficiency
(mpg))*Fossil Energy balance]
The Total Fossil Energy Inputs per mile are shown in 2.5
Ho nd a ' s F ue l
C e l l V e hi c l e
Figure 6. This important analysis shows that the most likely
scenario for the hydrogen economy would yield vehicles which 2
V W , so yb ean
B i o d i esel
would still require considerably more fossil energy input per mile
1.5
than vehicles available today, running on biodiesel.
Dodge
Unfortunately, such energy analyses are rarely done by the media,
I nt r e p i d ,
d i esel - el ect r i c
or even the panels making recommendations on public energy 1
hy b r i d
policy.
0.5
III.b. Engines, combustion
0
FEI, Btu/Mile
Lessons focused on various engine designs can lead
Figure 6 - Total Fossil Energy Input (FEI) per
to a discussion of multiple topics of physics, as well as
mile
chemistry. Engines of useful focus include gasoline (spark
ignition), diesel (compression ignition), and fuel cells. Some valuable web resources for such
discussions include:
http://ibs.howstuffworks.com/ibs/mia/diesel.htm
http://ibs.howstuffworks.com/ibs/mia/engine.htm
http://ibs.howstuffworks.com/ibs/mia/fuel-cell.htm
Misconceptions
In the February 2, 2001 issue of “C2C, Connecting Classroom and Community”, an article appeared
written by James Higgins of The Detroit News. In the article, he wrote:
“Perhaps in about 100 years everything will run on
hydrogen -- cars, electric generation plants, the whole
energy industry. Water will be the basic fuel.
Automobiles will have a device that splits H2O into
hydrogen for combustion and oxygen as a byproduct.
Earth's biggest threat at that time will be oxygen
pollution. Environmentalists will demand that forests,
sources of the noxious gas, be eradicated.”
Sadly, this presents a few common energy and environmental misconceptions held by the general
public, the media, and even some educators. First, there is a misconception that shows a clear lack of
understanding of thermodynamics, in particular as it relates to hydrogen as a “fuel”. There has been
much discussion in the media about hydrogen powered vehicles. Unfortunately, that discussion has left
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu 20
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
out several important scientific points. First, it takes energy to separate hydrogen from water. As a
result, hydrogen produced from water is not an energy source, but an energy storage medium. The
process of electrolysis is most commonly used for this separation, and is only roughly 60% efficient.
That means that for each 1 kWh of energy we put into the process, the hydrogen we get back only
contains about 0.6 kWh of thermal energy. Since automotive hydrogen fuel cells are roughly 50%
thermally efficient, using that hydrogen in the fuel cell would then give us 0.3 kWh of energy for each
1 kWh we put into making the hydrogen. The result is a big net energy loss during the process of
“producing” hydrogen from water, and then using the hydrogen as a fuel. It would make no sense to
separate water onboard a vehicle to get hydrogen, and then use that hydrogen in a fuel cell to run the
vehicle. The reason being that it takes energy to separate the hydrogen – and it would take roughly 3
times as much energy as we would get back. So, if we have some source of energy on the vehicle with
which to electrolyze the water to get hydrogen, we should simply use that energy source directly to
power the vehicle, rather than using that energy to make hydrogen, and then using the hydrogen to
power the vehicle, during the course of which we lose 70% of the energy we started with. For that
reason, we will never have “water powered” cars.
The fact that this misconception is so common demonstrates that we need to educate students
more thoroughly about the issues involved – in this case, primarily thermodynamics. Essentially, the
notion that “there ain’t no free lunch”. The author of the above quote doesn’t seem to realize that it
takes energy to separate the hydrogen from water initially – we can’t do it “for free”.
The second big misconception in the quote is the notion that splitting water into hydrogen
which would then be used as fuel would result in “oxygen pollution”. The problem with this notion is
that when hydrogen is burned or used in a fuel cell (or any other fuel that contains hydrogen, including
biodiesel, gasoline, diesel, etc.), that hydrogen is mostly turned back into water by joining it with
oxygen during the combustion process. With most combustion, the energy produced comes from the
hydrogen in the fuel being combined with oxygen to make water, releasing energy (the reverse of that
process is how we would produce hydrogen from water, which has to have an energy input since
combining the two releases energy). So, if we separated hydrogen from water, then used it as a fuel,
we’d end up with water again. The result being that there would be no net change in either water
levels, or oxygen levels. This misconception lies in a misunderstanding of mass balances, chemistry,
and is a key issue why many people don’t understand the carbon balance.
Footnotes:
1 – “Biodiesel: The Use of Vegetable Oils and Their Derivatives as Alternative Diesel Fuels”, Knothe,
Dunn, and Bagby, USDA Agricultural Research Services,
2 – “Biodiesel Fuel”, Vern Hofman, NDSU Extension Service,
http://www.ext.nodak.edu/extpubs/ageng/machine/ae1240w.htm
3 – “The production of isopropyl esters and their effects on a diesel engine”, Wang, P, Iowa State,
http://www.me.iastate.edu/biodiesel/Technical%20Papers/Wang%20Intro.pdf
4 – “Sinks for Anthropogenic Carbon”, Sarmiento and Gruber, Physics Today, August 2002,
http://www.aip.org/pt/vol-55/iss-8/p30.html#bio
5 - “Carbon Dioxide Buildup Acceleration”, CNN, March 20, 2004.
http://www.cnn.com/2004/TECH/science/03/20/climate.record.ap/index.html
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu 21
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
6 – Burke Oil, http://www.burkeoil.com/pdf/patb1002.pdf for B100 MSDS. Diesel MSDS available at
http://www.burkeoil.com/pdf/diesls2.pdf
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu 22
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu 23
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321
UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel
Michael Briggs, M.S., msbriggs@alberti.unh.edu, 862-2828, Joseph Pearson, jzp2@alberti.unh.edu 24
Dr. Ihab Farag, ihab.farag@unh.edu, 862-2321