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Lesson 17. Don't Be Fuelish
Week Four Lessons
15. Methane Investigation Lab
16. Geologic Sequestration
17. Don't be Fuelish
18. Wedge Game
19. Global recommendations

Lab creating biofuels | Personal & Social Perspectives (Ecology)

Links on this page: Don’t Be Fuelish - Background Information
| Don’t Be Fuelish-Lab Procedure | Don’t be Fuelish – Student Sheet | Don’t be Fuelish – Teacher Key | Don’t Be Fuelish-
Information for Upper Level Classes
| Don’t Be Fuelish-Extension Activity Ideas

National Education Standards Met:

science

 

Goal: Introduce students to the characteristics and synthesis of biodiesel as a potential mitigation technique for greenhouse gas emissions.

Objectives:  Students will…

  • Use a chemical reaction to create a biodiesel
  • Examine the materials used to synthesize a biodiesel

Materials (per team of 2-4 students):

  • Lab balance
  • Biodiesel PowerPoint
  • Computer with projection system
  • 1 – plastic soda bottle with cap
  • 1 – 100 ml beakers
  • 1 – 250 ml beaker
  • Plastic stirring stick
  • 1 – 25 ml graduated cylinder
  • 1 – 100 ml graduated cylinder
  • 5 – Beral pipettes
  • Distilled water
  • 100 ml canola or other vegetable oil
  • Safety glasses for each student
  • Apron for each student
  • Fume hood if available
  • 15 ml methanol (Cautionary note: Flammable, dangerous fire risk, toxic by ingestion)
  • 1g 9 M potassium hydroxide (KOH) solution (Cautionary note:  Skin contact causes severe blistering, strongly corrosive, very harmful if swallowed, extremely dangerous to eyes, generates large amounts of heat when solution is prepared.  Consider immersing solution container in ice bath when preparing.)

Time Required: 45-60 minutes

Standards Met: S1, S2, S3, S4, S6, M1, M2, DA1, DA2, DA3

Procedure:

PREP

Prepare a 9 M potassium hydroxide solution. To prepare a specific volume of a specific molar solution from a dry reagent use the formula:

#grams that you will need = desired volume (L) * desired molarity (mole/L in this case 9 mole/L ) * FW (g/mole in this case 56)

IN CLASS

  • Explain that today students will be creating a biodiesel in class.
  • Give students a copy of Don’t Be Fuelish-Background Information and review.
  • Divide students into lab groups of 4
  • Hand out Don’t Be Fuelish-Lab Procedure to each group.
  • Review safety precautions and lab procedures.
  • Allow students time to complete the lab as they follow their lab procedure.
  • Remind them to fill out their observations on the Don’t Be Fuelish-Lab Procedure.
  • Review clean up procedures and give them time to complete a thorough clean up of their lab station.
  • Hand out Don’t Be Fuelish-Student Sheet and give them time to complete.
  • Review the answers together if time allows.

Assessment:
Completed lab procedures
Completed student sheet


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Don’t Be Fuelish
Background Information

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 thermo chemical 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.  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 used to synthesize biodiesel:


BIODIESEL CONSISTS OF THREE PRINCIPLE FEEDSTOCKS:

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 triglycerides.  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 a 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 is 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 KOH 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.

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Don’t Be Fuelish-Lab Procedure

Safety Note:  Always wear safety glasses!  Follow all instructions given by your instructor and only use the quantities suggested!  Use extreme caution!  Materials are extremely corrosive, toxic, and flammable.

Gather the following materials:

  • Lab balance
  • 1 – plastic soda bottle with cap
  • 1 – 100 ml beakers
  • 1 – 250 ml beaker
  • Plastic stirring stick
  • 1 – 25 ml graduated cylinder
  • 1 – 100 ml graduated cylinder
  • 5 – Beral pipettes
  • Distilled water
  • 100 ml canola or other vegetable oil
  • Safety glasses
  • Apron
  • Fume hood if available
  • 15 ml methanol (Cautionary note: Flammable, dangerous fire risk, toxic by ingestion)
  • 1g 9 M potassium hydroxide (KOH) solution (Cautionary note:  Skin contact causes severe blistering, strongly corrosive, very harmful if swallowed, extremely dangerous to eyes, generates large amounts of heat when solution is prepared.  Consider immersing solution container in ice bath when preparing.)

Procedure:

  • Using the 100 ml graduated cylinder, measure out exactly 100 ml of vegetable oil.
  • Pour the 100 ml of vegetable oil into the plastic soda bottle.
  • Using the 25 ml graduated cylinder, measure out 15 ml of methanol.
  • Carefully add the 15 ml of methanol to the soda bottle with the vegetable oil.
  • Record your observations below.

 

 

 

 


  • Measure out 1 ml of 9 M KOH in the 25 ml graduated cylinder.
  • Slowly add the 1 ml of 9 M KOH to the soda bottle.
  • Record your observations below.

 

 


  • Wash out the 25 ml graduated cylinder thoroughly.
  • Cap the soda bottle tightly.
  • Shake the bottle carefully for 5 minutes to thoroughly mix the solutions.
  • Pour the mixture into a 250 ml beaker.
  • Allow the solution to sit and separate for at least 5 minutes.
  • Record your observations below.

 

 


  • Carefully remove the top layer using a plastic pipette, and place it into a clean 100 ml beaker.
  • Wash this product by adding 10 ml of distilled water, stirring for about 2 minutes.
  • Allow the mixture to sit and separate again for at least 5 minutes.
  • Record your observations below.

 

 


  • Carefully remove the top layer from the wash solution and place it into the 25 ml graduated cylinder.  Congratulations!  What you have in you graduated cylinder is biodiesel fuel, ready to burn in any diesel engine.
  • Describe the biodiesel fuel below.

 

 

 

 


  • Clean up all equipment according to the directions given by your instructor.  Be careful not to remove your protective clothing until all equipment has been completely put away.

Note:  Potassium hydroxide is extremely corrosive.  Dispose of excess potassium hydroxide by neutralizing it with 3 M hydrochloric acid and pour neutral solution down the drain with lots of water.

  • Complete Don’t Be Fuelish-Student Sheet.
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Don’t be Fuelish – Student Sheet

 

Name: ___________________________________
Date: ____________________________________

 

Questions for Thought –

 

  1. What changes did you see between the characteristics of the starting materials (cooking oil, methanol, and potassium hydroxide solution) and the fuel products (biodiesel and glycerol)?


  2. Which did you have more of at the end of the reaction, the product or the waste?


  3. What signs did you observe that a chemical reaction had taken place?


  4. What is the purpose of the washing step?


  5. In the commercial production of biodiesel, 1200 kg of vegetable oil produces 1100 kg of crude biodiesel.  How does your yield compare to this?


  6. How would transferring to biodiesel fuels in diesel engines reduce the amount of greenhouse gases in the atmosphere?


  7. Why is it that the CO2 produced during the combustion of biodiesel does not add to the overall greenhouse effect?

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Don’t be Fuelish – Teacher Key

Name:________________________________
Date:_________________________________


  1. What changes did you see between the characteristics of the starting materials (cooking oil, methanol, and potassium hydroxide solution) and the fuel products (biodiesel and glycerol)?

    Some possible answers are color changes, viscosity, and smell.



  2. Which did you have more of at the end of the reaction, the product or the waste?

    If the experiment was done correctly, there should be more biodiesel produced than waste. Your students will have to measure the exact amount to answer question 5 below.

  1. What signs did you observe that a chemical reaction had taken place?

    Evidence of a chemical reaction is color change, new substance formed.

  1. What is the purpose of the washing step?

    Washing the initial product helps eliminate possible impurities in the fuel.

  1. In the commercial production of biodiesel, 1200 kg of vegetable oil produces 1100 kg of crude biodiesel.  How does your yield compare to this?

    Answers will vary.

  1. How would transferring to biodiesel fuels in diesel engines reduce the amount of greenhouse gases in the atmosphere?

    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.  Therefore the CO2 produced during the combustion of biodiesel does not increase the total amount of carbon dioxide in the atmosphere.

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Don’t Be Fuelish-
Information for Upper Level Classes

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).

Alcohol

An alcohol is a molecule in which any carbon atoms has 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 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 (footnote 1)


Fatty Acid

Acronym

Molecular
Weight

Melt
ºC/ºF

Boil
ºC/ºF

Cetane
Number

Heat Combust
(kg-cal/mole)

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

1453.07

Lauric

12:0

200.32

44.0/111.2

131.0/267.8

 

1763.25

Myristic

14:0

228.38

58.0/136.4

250.5/482.9

 

2073.91

Palmitic

16:0

256.43

63.0/145.4

350.0/662.0

 

2384.76

Stearic

18:0

284.43

71.0/159.8

360.0/680.0

 

2696.12

Oleic

18:1

282.47

16.0/60.8

286.0/546.8

 

2657.4

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

 

 


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) 16 COOH.

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 carbon-carbon 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 carboxyl 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:

 

                                 

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 denser 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 were 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 (footnote 1)


Methyl Ester

Acid
Acronym

Molecular
Weight

Melt
ºC/ºF

Boil
ºC/ºF

Cetane
Number

Heat Combust
(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

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 it’s 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.  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. (footnote 3 )

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 materials 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 varieties 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 oils (footnote 2)

 

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

 

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 inadvertently 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-catalyzed 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).

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Don’t Be Fuelish-Extension Activity Ideas

The topic of biodiesel can be introduced in a variety of classes such as 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 to learn how science topics relate to non-scientific fields.

Below is an extensive list of potential Extension Activities to the Don’t Be Fuelish lesson plan.

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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.

1. Carbon Cycle
The carbon cycle is a topic that many students – even a majority of adults – have difficulty understanding. 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 CO
2 in the atmosphere and then convert 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 while 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 + O
2

The glucose can then be converted into other forms by the plant such as other sugars, 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 (CH
4). 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, billions of years ago when the earth was much younger and had much higher levels of atmospheric carbon dioxide, for example. 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. This level 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 this process, we gradually increase the atmospheric carbon level beyond the fairly stable level it has been at for 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 environmental standpoint, this is the most important reason for moving from fossil fuels to renewable biofuels resulting in no net addition to atmospheric carbon levels.

Figure 4 - Anthropogenic carbon emissions  
Figure 5 - Atmospheric Carbon Increase

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2.  Greenhouse Effect

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.


3. 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.  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 a typical MSDS, you will notice it is rated a “0” (the safest score) in the Health category, in the NFPA symbol. This ranking was 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 cannot metabolize 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. 10-Formyl-THF then undergoes oxidation to CO2.  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 that 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 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.

4.  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 that biodiesel researchers are 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.

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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:

1. 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 with 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.  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.

2. 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.

3. 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.  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.  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, 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.  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.

With liquids consisting of molecules of various freezing points, gelling occurs as a result of solid molecules entangling and cross-linking, 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/cross linking 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.  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.

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Physics

1. 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 that is unfortunately often completely overlooked.  A key concept for students to understand here is the conservation of energy.  Energy cannot 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 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 were 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 (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 that 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

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 on biodiesel

Jetta TDI on petroleum diesel

Jetta 2.0L gasoline engine

Toyota Prius on gasoline

Honda Fuel Cell vehicle (hydrogen)

Dodge ESX3 (diesel-hybrid) on biodiesel

Vehicle cost

$19,970

$19,970

$18,790

$21,520

$100,0003

$28,500

Fuel efficiency, miles/gallon

41/48.5

42/50

24/31

52/45

5.74

72

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

???

Cost/mile2

$0.047

$0.040

$0.062

$0.035

$0.195

$0.03

Energy density of fuel (Thousands of BTUs/gal)

127

141

123

123

9

127

Fossil Fuel Energy Balance6

3.2

0.83

0.74

0.74

0.667

3.2

Total fossil energy input/mile8 (Thousand BTU/mile)

0.89

3.7

6.0

3.4

2.4

0.55

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Footnotes

  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
  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 Figure 6. This important analysis shows that the most likely scenario for the hydrogen economy would yield vehicles which would still require considerably more fossil energy input per mile than vehicles available today, running on biodiesel. Unfortunately, such energy analyses are rarely done by the media, or even the panels making recommendations on public energy policy.

2.  Engines, combustion

Lessons focused on various engine designs can lead to a discussion of multiple topics of physics, as well as 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 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).  If we separated hydrogen from water, then used it as a fuel, we would 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.*

*Taken from an article by UNH Biodiesel Group
http://www.unh.edu/p2/biodiesel

Additional Resources:

“Biodiesel: The Use of Vegetable Oils and Their Derivatives as Alternative Diesel Fuels,” Knothe, Dunn, and Bagby, USDA Agricultural Research Services,

“Biodiesel Fuel”, Vern Hofman, NDSU Extension Service, http://www.ext.nodak.edu/extpubs/ageng/machine/ae1240w.htm

“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

“Sinks for Anthropogenic Carbon”, Sarmiento and Gruber, Physics Today, August 2002, http://www.aip.org/pt/vol-55/iss-8/p30.html#bio

“Carbon Dioxide Buildup Acceleration,” CNN, March 20, 2004. http://www.cnn.com/2004/TECH/science/03/20/climate.record.ap/index.html

Burke Oil, http://www.burkeoil.com/pdf/patb1002.pdf  for B100 MSDS. Diesel MSDS available at http://www.burkeoil.com/pdf/diesls2.pdf


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