Alkanes: Sources
Contents
What are alkanes?
Alkanes are saturated hydrocarbons, which means they are made of only carbon and hydrogen atoms and the carbon atoms are connected by single bonds only.
Where can we find alkanes?
Alkanes are found not just in our planet but also elsewhere in the universe.
Alkanes in other celestial bodies
| Celestial body | Alkanes |
|---|---|
| Mars | Methane1 |
| Jupiter | Methane, Ethane2 |
| Saturn | Methane, Ethane, Propane3 |
| Titan | Methane4, Ethane, Propane5 |
| Enceladus | Methane, Ethane, Propane6 |
| Uranus | Methane7 |
| Neptune | Methane8 |
| Triton | Methane9 |
| Pluto | Methane10, Ethane11 |
| Comet C/1996 B2 | Methane, Ethane12 |
| HD 189733b | Methane13 |
Alkanes in the earth
Methane in the earth’s atmosphere is formed mainly due to anaerobic respiration of microbes. The main source of alkanes are petroleum and natural gas found in the crust of earth. They are formed by high temperature and pressure and under anaerobic conditions from the plants and organisms that were buried long time back. This is why petroleum and natural gas are known as fossil fuels.
Methanogenesis
About two thirds of methane produced in nature comes from reduction of acetate groups and about one third comes from reduction of CO2 and very little amount comes from the reduction of methanol and methylamines. These processes can be achieved by microbes, generically known as archaea. Therefore the essential processes14 are:
- Conversion of acetate groups to methane and carbon dioxide
- Reduction of carbon dioxide to methane
- Disproportionation of methanol or methylamine to carbon dioxide and methane
Petroleum and Natural Gas
Crude oil can be fractionally distilled to obtain various products varying in the length of alkyl chain. Higher fractions can also contain cycloalkanes. The usage of alkanes will be discussed further in details.
Fractional distillation of crude oil
| Fraction Name | Boiling point (celsius) | Approx. carbon number | Usage |
|---|---|---|---|
| Light petrol | 20-100 | 5-7 | solvent |
| Petroleum ether | 70-90 | 6-7 | dry cleaning |
| Ligroin | 80-120 | 6-8 | solvent |
| Petrol (gasoline) | 70-200 | 6-11 | motor fuel |
| Kerosene (paraffin oil) | 200-300 | 12-16 | lighting |
| Heavy oil (Diesel) | > 300 | 13-18 | fuel |
| Lubricating oil | Non-volatile liquids | 16-20 | lubricants |
| Grease, vaseline, petrolatum | Non-volatile liquids | 18-22 | pharmaceuticals |
| Paraffin wax (hard wax) | Non-volatile liquids | 20-30 | candles, waxed paper |
| Residue | Non-volatile liquids | 30-40 | Asphalt tar, petroleum coke |
Alkanes in natural gas
Only smaller alkanes are found in natural gas.15
| Alkane | Number of carbons | Composition |
|---|---|---|
| Methane | 1 | 70-90% |
| Ethane | 2 | 0-20%` |
| Propane | 3 | 0-20%` |
| Butane | 4 | 0-20% |
Further Studies
References
- ESA Mars Express report [↩]
- Alkanes in Jupiter [↩]
- Alkanes in Saturn [↩]
- Alkanes in Titan, Reference 1 [↩]
- Alkanes in Titan, Reference 2 [↩]
- Alkanes in Enceladus [↩]
- Methane in Uranus [↩]
- Methane in Neptune [↩]
- Methane in Triton [↩]
- Methane in Pluto [↩]
- Ethane in Pluto [↩]
- Alkanes in comets [↩]
- Alkanes in extrasolar plantets [↩]
- Biochemistry of methanogenesis [↩]
- Natural gas composition [↩]
