# 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 bodyAlkanes
MarsMethane1
JupiterMethane, Ethane2
SaturnMethane, Ethane, Propane3
TitanMethane4, Ethane, Propane5
UranusMethane7
NeptuneMethane8
TritonMethane9
PlutoMethane10, Ethane11
Comet C/1996 B2Methane, Ethane12
HD 189733bMethane13

## 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 NameBoiling point (celsius)Approx. carbon numberUsage
Light petrol20-1005-7solvent
Petroleum ether70-906-7dry cleaning
Ligroin80-1206-8solvent
Petrol (gasoline)70-2006-11motor fuel
Kerosene (paraffin oil)200-30012-16lighting
Heavy oil (Diesel) > 30013-18fuel
Lubricating oilNon-volatile liquids16-20lubricants
Grease, vaseline, petrolatumNon-volatile liquids18-22pharmaceuticals
Paraffin wax (hard wax)Non-volatile liquids20-30candles, waxed paper
ResidueNon-volatile liquids30-40Asphalt tar, petroleum coke

#### Alkanes in natural gas

Only smaller alkanes are found in natural gas.15

AlkaneNumber of carbonsComposition
Methane170-90%
Ethane20-20%
Propane30-20%
Butane40-20%