Biodiesel: using renewable resourcesIntroductionOne of ways in which processes can be made ‘greener’ is to use renewable resources to replace non-renewable starting materials. Chemical processes that rely on materials that cannot be supplied in a sustainable fashion are harmful since such processes can eventually deplete a resource. It makes little sense to become dependent on any resource that exists in finite quantities. However, many processes are in this very position because, although the resources they use are finite, they are also vast. Petroleum is a good example. Because it is so plentiful, little thought has been given to finding a renewable alternative. This is despite the fact that our petroleum reserves are sure to run out eventually. If an alternative can be found that would convert plant material to useable fuel, it would demonstrate the green chemistry principle of using renewable resources. This involves finding ways to use renewable starting materials, such as substances derived from growing plants, rather than materials like the Earth’s petroleum and natural gas supplies that are irreplaceable in the short term. One such process is the manufacture of ‘biodiesel’ – an alternative to diesel fuel – from vegetable oils. Activity 1: Making biodieselBiodiesel is a mixture of methyl esters of fatty acids (long chain carboxylic acids). It has similar properties to the diesel fuel made from crude oil that is used to fuel many vehicles. It can be made easily from vegetable cooking oil that contains compounds of fatty acids. Enough fuel can be produced in this activity to burn in a later activity, although it is not pure enough to actually be used as fuel in a car or lorry. The synthesis is a simple chemical reaction that produces biodiesel and propane-1,2,3-triol (glycerol). Cooking oil is mixed with methanol and 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. What you will need
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Q 1. What changes did you see between the starting materials (cooking oil, methanol and potassium hydroxide solution) and the final products (biodiesel and propane-1,2,3-triol (glycerol)? Q 2. What signs did you observe that a chemical reaction had taken place? Q 3. What is the purpose of the washing in step 7 above? Q 4. In the commercial production of biodiesel, 1200 kg of vegetable oil produces 1100 kg of crude biodiesel. How does your yield compare to this? Activity 2: Testing biodieselHow does biodiesel compare to 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 properties of an alternative fuel should equal or exceed those of the traditional product. But how are fuels evaluated in the first place. In this activity, biodiesel and some other fuels are tested and compared for sootiness and acidity. What you will need
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Figure 1 Apparatus for testing biodiesel Q 1. Compare how long it took to change the colour of the universal indicator in each test. Try to explain any differences you observed. Q 2. Compare the amount of soot collected at the funnel and in the tube containing the mineral wool in each of the experiments. Activity 3: Potential for biofuels for the futureAssuming we wanted to replace petroleum diesel with biodiesel, a key question is ‘how much biodiesel could we make’? An obvious limit is the amount of land available for growing. The United States of America (US) uses approximately 30 billion gallons of diesel annually. At the same time they produce some 225 million metric tons of oilseeds (this includes soybean, cottonseed, peanut, sunflower seeds, and rape seeds). Soybeans are about 18% oil, the others vary. Some additional data is given below. Use whatever data you need to calculate your answer to the question. You will find some of the units used unfamiliar because they are ones used by farmers in the US. You should find this useful practice in converting units. There is no point in calculating a precise answer – a ‘ballpark’ figure will do, so it would be good practice to round off some of the figures. Quantities in the US41 pounds of soybeans to make 1 gallon of soydiesel. 1 ton of soybeans makes 47.33 gallons of oil. 1 bushel of soybeans is 60 pounds. By weight soybeans are about 20% oil. 60 pounds of soybeans yields 1.42 gallons of oil. 38.1 bushels average in 1 acre (2000 data). 53.4 gallons of soybean oil per acre in 2000. Agriculture in the US2.2 million farms and nearly 990 million acres (47.3% crops, 52.6% livestock/other). 74 million acres are in surplus. Energy in the USSoydiesel 117 093 BTU per gallon, gasoline 114 264 BTU per gallon. Soydiesel requires 23,620 BTU per gallon to make. Diesel requires about an equal amount of BTU to make. * BTU stands for British Thermal Unit – a unit measuring the energy content of the fuel. Volume used in the US30 billion gallons of diesel used per year. 18 million barrels of petroleum used per day (about 6.6 billion barrels per year). 42 gallons of petroleum per barrel. 277 billion gallons of petroleum per year. Q 1. Given the data above, could the US expect to grow enough soybeans to replace fossil diesel with biodiesel? Show your calculations. Q 2. Use the Web and other resources to research the annual use of diesel and oil seed production in the United Kingdom and in Germany. Compare the feasibility of replacing fossil diesel with biodiesel in each of these counties. Q 3. What are the similarities and differences among the three counties relating to their use of diesel and potential for sustainable biodiesel programs? Q 4. 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. Background Information on biodiesel: using renewable resourcesDiesel is a common fuel used to power many large vehicles and heavy equipment (such as tractors). It is made from crude oil that was formed millions of years ago by the decomposition of prehistoric plants and animals. In an oil well, crude oil is pumped out of the ground, and is transferred (often by large ocean tankers) to oil refineries. Crude oil contains widely varying organic (carbon-based) chemicals which range in size from small molecules with only 1 carbon atom (C1) to very large molecules with over 20 carbon atoms (>C20). By using a distillation tower, crude oil is broken into various fractions (or components) based on the size of the molecule. Distillation towers operate on the principle that smaller carbon compounds have lower boiling points, while larger ones have higher boiling points. A distillation tower works much like a distillation apparatus you might use in the laboratory. Crude oil is heated as it enters the distillation tower so that it boils. The vapour is then gradually cooled as rises up the tower. Since less-volatile compounds condense at higher temperatures they are separated low down the tower. The more-volatile compounds rise higher in the tower before they start to condense. Thus, fractions of crude oil can be separated by the decreasing temperature as they move up the tower. Chemists have created a substitute for diesel - biodiesel - by chemically changing various fats and oils. Fats and oils can be burned without any chemical alteration (old whaling ships used to burn the ‘blubber’ or fat from whales in their oil lamps). By using a chemical technique called transesterification chemists can turn oils from various crops (such as rapeseed 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. Diesel comes from crude oil, which takes millions of years to form. While, over the course of the next few million years, more underground pools of crude oil will be formed; it is consumed at a rate which is drastically faster than the rate at which it is forming. Most experts believe that at current production, crude oil will be economically (and thus essentially) exhausted in the next 40 years. Biodiesel, however, is made from renewable resources; oils derived from farm crops, such as soybeans. One major focus of green chemistry is to develop new chemical processes and products which eliminate the need for using non-renewable starting materials, by replacing them with renewable starting materials. Biodiesel also creates less sulfur emissions when it is burned which helps reduce acid rain and it also breaks down more quickly in the environment; thus lessening the consequences of an accidental spill when compared to crude oil. Finally, while combustion of a hydrocarbon always creates carbon dioxide (CO2), biodiesel is made from crops that need carbon dioxide to grow. Thus, much of the carbon dioxide released from burning bio-diesel, is absorbed by the crops growing to make the fuel and no excess carbon dioxide is produced to contribute to global warming (http://www1.eere.energy.gov/biomass/, accessed September 2002).
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