Methane and other compounds from the series of alkanes

Danilo Anton

Methane is by far the most abundant hydrocarbon both on Earth and on the various planetary bodies in the solar system. According to the abiogenic theory, methane forms at high pressures and temperatures in the mantle.
The basic formula is CH4. It is a gas that liquefies at very low temperatures (-161.6 degrees Celsius at 1 atmosphere pressure).
There are other members of the same series (alkanes) that include three compounds that are gaseous at ordinary temperature and pressure with formulas C2H6 (ethane), C3H8 (propane) and C4H10 (butane) . These four lower molecular weight alkanes (methante, ethane, propane and butane) which are gaseous on the Earth surface liquefy at low temperatures. 
The boiling point of methane at the Earth’s surface atmospheric pressure is -161.6  C, solidifying at very cold temperatures -182  C.
Ethane, propane and butane liquify relatively easily when subjected to high pressure (they are put into containers for use as cooking gas). Methane requires much higher pressures and therefore is impractical for this purpose.
Mixed with this gas there are several hydrocarbonaceous sulfurs, nitrogen compounds and organic oxygenates including metals (metal porphyrins with nickel, vanadium and iron).
The geological mixture of these gases is called “natural gas”. 
The relative proportions of methane, ethane, propane and butane in natural gas varies, but methane largely dominates (approximately with 70 to 90% of the mixture). 
Ethane, propane and butane are less than 20% and usually much less i.e.10%). In addition to the alkanes there are various amounts of other gases (carbon dioxide, oxygen, nitrogen, hydrogen sulfide, helium and rare gases).

Typical composition of natural gas                                          
Methane             CH4               70-90%               
Ethane                C2H6                                                            
 Propane             C3H8            * 0-20%
 Butane               C4H10                            
 Carbon dioxide  CO2               0-8%                 
oxygen                O2                  0-0.2%                             
nitrogen              N2                  0-5%
Hydrogen sulfide  H2S             0-5%  
Helium                He               approx. 1.5-7% 
rare gases          A, Ne, Xe       traces              
* + Ethane + propane butane              
Reference: naturalgas.org - http://www.naturalgas.org/overview/background.asp                                          
 The following alkanes (pentane, hexane, heptane, octane) are liquids at atmospheric conditions, with boiling temperatures ranging from 36.1 to 125.5 Co, solidifying (melting point) at temperatures between -57 Co -129.8 Co.