What makes a good fuel?

There are lots of fuels to choose from.
Some are non-renewable fossil fuels such as oil, kerosene, petrol or gasoline, diesel or petrodiesel, coal, natural gas, coal seam gas (CGS).
Some are renewable biofuels like biodiesel, bioethanol, biogas.
How can chemistry help us decide which fuel to use?
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Biodiesel

What's the difference between diesel and biodiesel?
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Turning Polyethylene Waste into Fuel

Low density polyethylene, LDPE, is used to make many things we use everyday such as plastic milk containers, cling wrap, and plastic bags. LDPE can be recycled quite easily, but a lot of LDPE ends up as rubbish in land fills.
Chemists in India have developed a commercially viable way to turn LDPE into a liquid fuel by heating the LDPE waste to between 400 and 500^oC over a kaolin catalyst which causes the long chain polymer chains to break apart. This process is known as thermo-catalytic degradation: thermo means heat, the catalyst is kaolin, and degradation means breaking apart. This thermo-catalytic degradation of LDPE produces much smaller carbon-based molecules. Gas Chromatography was used to characterise these smaller molecules, and it was found that they were mainly alkanes and alkenes between 10 and 16 carbon atoms long. This makes the mixture very similar to that found in petrochemical fuels. For example, the hydrocarbons in gasoline (petrol) typically have a chain length of between 4 and 12 carbon atoms while diesel fuel typically contains hydrocarbons with a chain length between 8 and 21 carbon atoms.

The catalyst, kaolin, is a layered, aluminosilicate clay mineral with the formula Al₂Si₂O₅(OH)₄. It acts as a catalyst by providing a large surface on which the polymer molecules can sit in an orientation favourable to the degradation under heat.

Using the kaolin catalyst at 450^oC, the thermo-catalytic degradation of 1 kg of LDPE produced 700 g of liquid fuel.

Reference:
Achyut Kumar Panda, Raghubansh Kumar Singh. Thermo-catalytic degradation of low density polyethylene to liquid fuel over kaolin catalyst. International Journal of Environment and Waste Management, 2014; 13 (1): 104 DOI: 10.1504/IJEWM.2014.058803

Further Reading:
Polythene (polyethylene): Properties, Production and Uses 
Gas Chromatography 
Alkanes: properties and uses
Alkenes: properties and uses
Ethene (ethylene): properties and uses
Silicates: structure and formula

Suggested Study Questions:

1. Give the molecular structure for ethene (ethylene).
2. Write an equation showing how ethene (ethylene) molecules can be polymerized to form polythene (polyethylene).
3. Name the type of polymerization reaction being described by the equation in question 2.
4. Explain, using a diagram of the partial structure of polythene (polyethylene), what happens when polyethylene undergoes thermo-catalytic degradation.
5. Describe the differences in the structures of alkanes and alkenes.
6. Draw a straight chain alkane with 10 carbon atoms.
7. Draw a structural isomer of the molecule in question 6.
8. Draw a straight chain alkene with 10 carbon atoms.
9. How many structural isomers of the molecule in question 8 do you think there would be? Support your answer with the structural formula for each of these structural isomers.
10. Why do you not find short carbon chain alkanes, between 1 and 4 carbon atoms long, in the liquid petrochemical fuels like gasoline (petrol) and diesel?

Butanol Biofuel

A team of chemical engineers at the University of Arkansas has developed a method for converting common algae into butanol, a renewable fuel that can be used in existing combustion engines.

Butanol has several significant advantages over ethanol, the current primary additive in petrol (gasoline). Butanol releases more energy per unit mass and can be mixed in higher concentrations than ethanol. It is less corrosive than ethanol and can be shipped through existing pipelines. These attributes are in addition to the advantages gleaned from butanol's source. Unlike corn, algae are not in demand by the food industry. Furthermore, it can be grown virtually anywhere and thus does not require large tracts of valuable farmland.

The team grows algae on "raceways," which are long troughs made out of screens or carpet, usually 2 feet wide and ranging from 5-feet to 80-feet long, depending on the scale of the operation. Algae survive on nitrogen, phosphorus, carbon dioxide and natural sunlight, so the researchers grow algae by running nitrogen- and phosphorus-rich creek water over the surface of the troughs. Excess nitrogen and phosphorus in natural waters is sometimes referred to as "dead zones" because these elements in excess can kill fish and plants.
They enhance this algal growth by delivering high concentrations of carbon dioxide through hollow fiber membranes that look like long strands of spaghetti.

The researchers harvest the algae every five to eight days by vacuuming or scraping it off the screens. After waiting for it to dry, they crush and grind the algae into a fine powder as the means to extract carbohydrates from the plant cells. Carbohydrates are made of sugars and starches. They treat the carbohydrates with acid and then heat them to break apart the starches and convert them into simple, natural sugars. They then begin a unique, two-step fermentation process in which organisms turn the sugars into the organic acids butanoic acid( butyric acid), lactic acid and ethanoic acid (acetic acid).

The second stage of the fermentation process focuses on butanoic acid (butyric acid) and its conversion into butanol. The researchers use a unique process called electrodeionization which involves the use of a special membrane that rapidly and efficiently separates the acids during the application of electrical charges.

Reference:
University of Arkansas, Fayetteville (2011, March 2). Algae converted to butanol; Fuel can be used in automobiles. ScienceDaily. Retrieved March 11, 2011, from http://www.sciencedaily.com­ /releases/2011/03/110301200638.htm

Further Reading
Elements and Compounds
Nomenclature
Alkanols (alcohols)
Functional Groups
Carbohydrates
Carbon Cycle


Study Questions

1. Draw a table with the headings elements and compounds. Place each element and compound mentioned in the article above into the table.
2. Give the formula for each of the following:
   
   • butanol
   • ethanol
   • nitrogen gas
   • carbon dioxide gas
   • butanoic acid
3. Describe what is meant when a Chemist uses the term carbohydrate.
4. What is the difference between a sugar and a starch?
   
5. Give 3 examples of compounds that are carbohydrates.
6. Write an equation to represent the process by which algae produce glucose from carbon dioxide and water.
   
7. Write an equation to represent the fermentation of glucose into ethanol.
8. What are the advantages of using butanol as an additive to petrol (gasoline) rather than ethanol?
   

Spinach Protein Could Help Make Biofuel

Plants use photosynthesis to convert the energy of sunlight into chemical energy. Scientists would love to be able to mimic this process in order to harness the sun's energy for the production of electricity and fuel.

Scientists at the Oak Ridge National Laboratory have been studying the LHC-II protein extracted from spinach. The primary role of the LHC-II protein is as a solar collector, absorbing sunlight and transferring it to the photosynthetic reaction centres, but it can also carry out electron transfer reactions.

When LHC-II is introduced into a liquid environment containing polymers, it interacts with the polymers to form sheets similar to those found in natural photosynthetic membranes. The ability of LHC-II to force the assembly of structural polymers into an ordered, layered state, could make the development of biohybrid photoconversion systems possible. These systems would consist of high surface area, light-collecting panes that use the proteins combined with a catalyst such as platinum to convert the sunlight into hydrogen, which could be used for fuel.

Reference
Mateus B. Cardoso, Dmitriy Smolensky, William T. Heller, Kunlun Hong, Hugh O'Neill. Supramolecular assembly of biohybrid photoconversion systems. Energy & Environmental Science, 2011; 4 (1): 181 DOI: 10.1039/C0EE00369G

Further Reading
Carbon Cycle
Proteins
Oxidation and Reduction
Polymers
Fuel

Study Questions:

1. Describe the process of photosynthesis.
2. Write a chemical equation to demonstrate this process of photosynthesis.
3. What is meant by the term 'electron transfer reaction' used in the article above?
4. Is photosynthesis an example of an electron transfer reaction?
5. Many electron transfer reactions in nature. Describe one example.
6. Describe what Chemists mean when they call something a protein.
7. Explain what is meant by the term 'polymer' as used by Chemists.
8. When Chemists refer to a protein forming sheets, what type of protein structure are they referring to? Explain how this type of structure can form.
9. What is meant by the term 'catalyst'?
10. Why is a catalyst necessary for man-made systems designed to convert sunlight into hydrogen to be used as a fuel?