Methane is the main constituent of natural gas. There are also small amounts of ethane (C2
), propane (C3
), butane (C4
), and pentane (C5
) in natural gas.
The methane molecule (CH4
) consists only of one carbon (C) and four hydrogen (H) atoms.
Natural gas is formed when layers of decomposing plant and animal matter are exposed to intense heat and pressure under the surface of the Earth over millions of years. The energy that the plants originally obtained from the sun is stored in the form of chemical bonds in the gas.
Biogas is a mixture of gases produced by the breakdown of organic matter in the absence of oxygen. It consists mostly of methane and CO2
Biogas can be produced from agricultural waste, manure, municipal waste, plant material, sewage, green waste and food waste.
Burning methane creates CO2
emissions. Carbon capture and storage (CCS), or carbon capture and sequestration, could be used to reduce these emissions. CCS is the process of capturing waste CO2
from a single source, for instance from a natural gas power plant. However, CCS technology has so far failed to show cost-effective results.
There are limited opportunities for using captured carbon as CO2
gas or storing the gas permanently, for instance, in oil reservoirs.