BIODIESEL-Using Renewable Resources

BIODIESEL-Using renewable resources

2007 Science Outreach Workshop

Introduction:One of the ways in which processes can be made “greener” is to use renewable resources to replace nonrenewable starting materials. Chemical processes that rely on materials that cannot be supplied in a sustainable fashion are fundamentally harmful to the environment. Such processes can eventually deplete a resource. While it makes little sense to become dependent on any resource that exists in finite quantities, many processes are in this very position because although they are finite, they are also vast. Petroleum is a good example. Because it is presently so plentiful, too little regard has been given to finding a renewable alternative. Yet our petroleum reserves are sure to run out, possibly in a matter of decades. The conversion of plant material into usable fuel is one approach that could be part of a larger alternative to the use of petroleum. In this experiment, we explore the making of fuel from vegetable oil as a demonstration of the green chemistry principle of using renewable resources, such as substances derived from growing plants, rather than irreplaceable materials like the earth’s petroleum and natural gas supplies.

Reference:This experiment, taken from the American Chemical Society’s Introduction to Green Chemistry, is adapted from The Royal Society of Chemistry, Learning about Materials; The Royal Society of Chemistry: London, 1998.

Background information:

Diesel is a common fuel used to power many large trucks (like the 18-wheel rigs commonly found on interstate highways) and heavy equipment (such as tractors and backhoes). Diesel fuel is made from crude oil that was formed over millions of years by the decomposition of prehistoric plants and animals. Through the use of an oil well, crude oil is pumped out of the ground and transferred (often by large ocean tankers) to oil distillation units. Crude oil contains widely varying organic chemicals that range in size from small molecules with only 1 carbon atom to very large molecules with more than 20 carbon atoms that can be separated into various fractions (or components) based on the size with a distillation tower.

Chemists have created a substitute for diesel by chemically changing various fats and oils. By using a chemical technique called transesterification, chemists can turn oils from various crops (most commonly canola and soy) into a viable diesel substitute. One of the major advantages of using biodiesel instead of diesel is that biodiesel is derived from a renewable resource. As mentioned before, diesel comes from crude oil, which takes millions of years to form. During the next few million years, more underground pools of crude oil will be formed; however, it is consumed at a rate that is drastically faster than that at which it is forming. Most experts believe that at current production, crude oil will be economically exhausted in the next 40 years ( Conversely, biodiesel is made from renewable resources, namely, oils derived from farm crops, such as soybeans.

Biodiesel also creates lower sulfur emissions when it is burned, which helps reduce acid rain. It also breaks down more quickly in the environment, thus lessening the severity of an accidental spill compared with crude oil. Finally, unlike fossil fuels such as gasoline, biodiesel does not cause an overall increase in the amount of CO2 (a greenhouse gas) in the atmosphere when the fuel is burned. Soybeans and other plants that produce oils for making biodiesel take up CO2 from the atmosphere as they grow. When oil is extracted from the mature plants and burned, and the remainder of the plant material decomposes, CO2 is returned to the atmosphere. Thus there is a balance between the amount of CO2 removed from the atmosphere by growing plants and returned to the atmosphere by the same plants. No excess CO2 is produced to contribute to global climate change (

Part 1. Making biodiesel

Biodiesel is a mixture of methyl esters of fatty acids. It can be made very easily from vegetable cooking oil. Enough fuel can be produced from this lab to burn in a later activity, although it is not pure enough to actually be used as fuel in a car or truck. The synthesis is a simple chemical reaction that produces biodiesel and glycerol. Cooking oil is mixed with methanol, while potassium hydroxide is added as a catalyst. The products separate into two layers, with the biodiesel on the top. The biodiesel is separated and washed and is then ready for further experimentation.

Biodiesel consists of three principal feed stocks:

Oil: Glycerides are commonly known as oils or fats, chemically speaking these are long chain fatty acids joined by a glycerin backbone.

2. Alcohol: Methanol is one of the most common industrial alcohols; because of its

abundant supply it’s most often the least expensive alcohol as well.

Catalyst: the third reactant needed is a catalyst that initiates the reaction and allows the

oils to break. The strong base solutions typically used are sodium hydroxide (NaOH) and

potassium hydroxide (KOH). This experiment will be using KOH as catalyst.

Procedure:

Safety:You must wear goggles and an apron.Methanol is flammable and poisonous. Sodium hydroxide is corrosive.

1. Record your starting observations (color, viscosity, odor) in a data table and any changes that take

place. (Data to include observations before, during and after the reaction.)

2. Measure 3 mL of methanol into a large test tube.

3. Using a graduated pipette, carefully add 0.5 mL of 9M KOH to the alcohol. (Sodium hydroxide is

corrosive) Swirl gently.

4. Use a graduated cylinder to measure 12 mL of warm cooking oil into your test tube.

5. Swirl and shake the mixture for 10 minutes. Occasionally release any pressure.

6. Wash the product using 1 mL of salt water. Invert gently a few times and let stand.

7. Allow the mixture to sit and separate. A few drips of salt water to help the separation process.

8. Carefully remove the top layer (biodiesel) using a pipette and put into a clean test tube.

9. Add a small scoop of anhydrous sodium sulfate and swirl gently. Stopper and store in your drawer

for the next lab day.

Observations (part 1):

Starting Observations / Interim Observations / Final Observation
Color
Viscosity
Other

Part 2. Testing biodiesel

How does biodiesel compare with other fuels? Just because we can produce a fuel from an alternative source, does that mean it is a good idea? There are many factors that go into the decision to use alternative fuels. Ideally, the physical characteristics of an alternative fuel meet or exceed those of the traditional product

Procedure:

Safety: This procedure involves the burning of liquid fuel. Know the location of fire extinguisher and how to smother a small fire with a wet paper towel.

Measure the amount of biodiesel you have collected and compare it to the amount of vegetable oil you started with. Also record the characteristics of your biodiesel (color, viscosity, odor) and compare them to those of the original oil.

Pour 125 mL of tap water into the filter flask and add 20 drops of universal indicator. The solution should be violet or at the most basic end of the universal indicator color range.

3. Pour 10 mL of solution prepared in step 1

into a small beaker labeled control. Set this

control aside for later comparisons.

4. Assemble the apparatus illustrated in the

figure at right.

5. Then turn on the water tap so the aspirator

pulls air through the flask. Mark or note the position of the faucet handle so you can run the

aspirator at the same flow rate later in the experiment. You should see gas bubbles coming from

the tube into the universal indicator.

6. Without anything burning, allow the setup to run until the solution turns yellow or for two minutes

(whichever occurs first). Record the time and what happens in the funnel(point A), the tube(point B),

and the universal indicator. Record the results in the data table below.

7. Refresh the universal indicator solution and repeat the experiment withaburner filled withtraditional

diesel fuel. Placed a fluffed piece of steel wool into a dry evaporating dish. Add 40 drips of fuel on to

the surface of the steel wool.

8. Turn on the water and ignite the fuel away from the funnel. Position the lit burner directly under the

funnel so as to capture the fumes from the burning fuel. Start your timing and allow the apparatus to

run until the universal indicator turns yellow.

9. Record the time required for a color change and the amount of soot in the funnel (point A), the

amount of water vapor in the glass tube (point B).

10. Refresh the apparatus with clean water and indicator, use a dry paper towel to wipe any soot

from the funneland repeat the experiment using a burner filled with biodiesel. Light the burner and

adjust the flame to match the height of the previous trial before placing it under the funnel.

11. Record the time and what happens in the funnel (point A), the tube (point B), and the universal

indicator.

12. Dismantle and clean the funnel with a dry paper towel. Dispose of the steel wool and wipe up.

Observations: Part 2

Trial Tested / Time of color changes (minutes) / Observations of Universal Indicator / Observations at Point A (funnel) / Observations at Point B (glass tube)
No Fuel
Trad.
Diesel
Biodiesel

Questions:

1. What changes did you see between the characteristics of the starting materials (cooking oil,

methanol, and potassium hydroxide solution) and the final products (biodiesel and glycerol)? What

evidence is there that a chemical reaction has occurred? [4]

2. In the commercial production of biodiesel, 1200 kg of vegetable oil produces 1100 kg of crude

biodiesel. Calculate the percent yield of the commercial process and for your process in the lab.

How does your yield compare? Suggest reasons for any differences. [3]

3. What is the purpose of ‘washing’ the biodiesel mixture with salt water? [1]

4. After burning both fuels, compare the time it took to change the color of the universal indicator in each test. Explain reasons for any differences you observed. [3]

5. What was the purpose of the ‘No Fuel’ test? What did it show? [2]

6. Compare the amount of soot collected in the funnel (point A) and in the water vapor in the tube (point B) in each of the experimental runs. [3]

7. Is biodiesel really green? Explain at least two arguments in support of the idea that biodiesel is a “greener” fuel. Also present one argument that biodiesel is not a “greener” fuel. Reference your lab data when appropriate. [4]

Sources:

Optional Activity

Part 3. Measuring the Heat of Combustion of Biodiesel

Procedure:

Safety: This procedure involves the burning of liquid fuel. Know the location of fire extinguisher and how to smother a small fire with a wet paper towel.

1. Use a disposable pipette and rubber bulb to transfer ~2 mL of your biodiesel product to a porcelain

crucible. Add a piece of candle wicking approximately 1” long. One end of wick should be in the

biodiesel and the other above the surface. Re-weigh the crucible and record the total mass.

2. Place 75.0 mL cold water in an empty soda can. Assemble

the apparatus shown by hanging the soda can from a stirring

rod supported by an iron ring. Place a thermometer in the can

and allow it to sit for 5 minutes. Replace the sample holder in

the image to the left with your crucible of biodiesel. Adjust

the height of the can so that it hangs just over the crucible.

3. Record the starting temperature of the water in the can.

Light the wick and let it burn for 5 minutes before gently

blowing out the flame. Remember that the crucible will be

hot! Record the final temperature of the water.

4. After the crucible has cooled, obtain its final mass. Pour all

remaining biodiesel into the waste bottle in the hood. Empty

your can down the drain and clean up your lab bench.

5. For this part of the lab you must determine the heat of

combustion of biodiesel in kJ/g. Determine the mass of

biodiesel that burned. Assume that all heat release by the

combustion was absorbed by the water in the can. Use the

following equation to determine the heat of combustion for

your biodiesel.

ΔE = s x m x ΔT

where s = 4.184 J/g oC

m = mass of water in can

ΔT = Tfinal - Tinitial

Mass of Empty Crucible (g) / Starting Temp of Water (°C)
Mass of Crucible + Fuel / Final Temp of Water (°C)
Final Mass of Crucible / Change in Temp of Water (°C)
Mass of Fuel Burned / Starting Temp of Water (°C)

Data Table:

Questions:

1. Compare the heat of combustion of biodiesel to that of octane (48.23 kJ/g).

2. Describe any sources of error that could affect this experiment. Indicate if each error would raise

or lower the final value for the experimental value for the heat of combustion.

Instructional notes

Instructional notes on activity 1: Making biodiesel

In this activity, students make biodiesel from cooking oil. The cooking oil is mixed with methanol and a catalyst (potassium hydroxide). Cooking oil is a lipid called a triglyceride or triacyglycerol. The structure of this type of lipid is characteristic of all animal and plant fats. It consists of a glycerol attached to three fatty acids. Differences among the fats are due to the different fatty acids connected to the glycerol. In making biodiesel, the reaction breaks the bond between the glycerol and the fatty acids. A methyl group is added to the end of the fatty acid, which is what we call biodiesel, and the other products are glycerol and the remaining sodium hydroxide catalyst. If any water is present, the reaction will yield soap, not biodiesel. Tell students to use dry glassware, and keep reagent bottles capped. It takes awhile to get the NaOH to dissolve in methanol. Cooling with an ice bath will speed dissolution.

Instructional notes on activity 2: Testing biodiesel

This activity is designed to test the characteristics of the biodiesel prepared by students with a semiquantitative measure. The idea is that the waste products that are given off by the combustion of the biodiesel include CO2and soot. A rough measure of the amount of CO2is gained by bubbling the waste gas through a universal indicator. Because CO2forms an acid when it dissolves in water (carbonic acid), the rate of change in color of the universal indicator is proportional to the amount of CO2in the combustion products. Students are also asked to compare the amount of soot that collects. Soot is uncombusted carbon and represents incomplete combustion of the fuel. Less efficient fuel generally produces more soot.

Answers to questions:

1. What changes did you see between the characteristics of the starting materials (cooking oil, methanol, and potassium hydroxide solution) and the final products (biodiesel and glycerol)? Cooking oil is nonpolar, greasy, and slippery. Methanol is a colorless liquid that may have an odor and evaporates quickly. The potassium hydroxide solution is colorless and odorless, and it may be slippery when touched (not recommended, because it is very caustic). Glycerol is a slightly viscous liquid that is colorless and odorless. The biodiesel appearance will vary but may have some slight color and odor. What signs did you observe that a chemical reaction had taken place? The mixture separates into two layers, the biodiesel and the glycerol.

2. In the commercial production of biodiesel, 1200 kg of vegetable oil produces 1100 kg of crude biodiesel. How does your yield compare to this? Student answers will vary. In the example given, it is approximately a 90% yield.

3. What is the purpose of the washing with distilled water? The washing removes the potassium hydroxide catalyst.

4. Compare the time it took to change the color of the universal indicator in each test. Explain any differences you observed. Gas mixtures with a high concentration of CO2will cause a faster color change in the universal indicator. The amount of CO2and SO2 released from combustion is an indication of the efficiency of the combustion reaction. If biodiesel is a fair substitute for petrodiesel, you would expect it to perform similarly. Traditional diesel does contain sulfur and should produce a somewhat faster color change.

5. What was the purpose of the ‘No fuel’ test? What did it show? This trial acts as a control and provides a baseline for comparison. Air should not change the color of the indicator very much which shows that combustion products do pollute the water.

6. Compare the amount of soot collected in the funnel and in the tube (point B) in each of

the experimental runs. Soot occurs when a combustion reaction is not complete. The more soot, the less efficient the combustion process. Again, we would expect the biodiesel and petrodiesel to be similar.

7. Is biodiesel really green? Explain at least one argument in support of the idea that biodiesel is a “greener” fuel. Also present one argument that biodiesel is not a greener fuel.

One green feature of biodiesel is that it does use renewable resources. It is also lower in sulfur content and produces fewer particulates. It is much less toxic than fossil diesel and is more biodegradable. Some “not so green” features are that it is still a combustion reaction that releases the same types of exhaust emissions (nitrogen oxides, carbon monoxide, hydrocarbons, soot, etc.) as those released into the atmosphere by diesel fuel; however, biodiesel releases lower quantities of these. A slightly lower energy content of biodiesel may result in having to use more to get equivalent results. Approximately 1.1 gallons of biodiesel give the energy equivalent to 1.0 gallons of diesel fuel.