What is natural gas?
Natural gas is a mixture of small organic molecules that are all gasses at normal temperatures. Methane is the most abundant constituent of natural gas, while ethane, propane, and helium are also present. Natural gas also includes trace amounts of other organic gases. While the term “organic” is popularly used to describe foods that are made with no added chemicals, to chemists the word refers to molecules that include carbon – and often hydrogen – atoms.
One molecule of methane contains one carbon atom and four hydrogen atoms. In contrast, a molecule of ethane contains two carbons and six hydrogens, while propane contains three carbons and eight hydrogens. Another molecule called butane contains four carbons and ten hydrogens.
Methane, ethane, and propane belong to a subgroup of organic molecules called “hydrocarbons”, which means that molecules of methane are made of only atoms of hydrogen and carbon. Hydrocarbons are well-known for their use as energy sources because the chemical bonds between carbon and hydrogen store much energy. In fact, even if your home is not heated with natural gas, you likely use hydrocarbons every day in other ways. The propane that provides fuel for the fire in your grill is a hydrocarbon, and butane (which has four carbons) is found in small lighters. And if you drive anywhere in a vehicle, you are probably using combinations of hydrocarbons like octane to fuel your travels.
Because hydrocarbons are an excellent source of heat and energy, natural gas is frequently used as a fuel for home heating. Most of the natural gas that we use is called "dry." It generally consists of 95% methane, 3% ethane, propane, and butane, and 2% non-hydrocarbon gases such as carbon dioxide, nitrogen, or helium (EPA 2010). On the other hand, some forms of natural gas - called “wet” - contain up to 20% of ethane, propane, and butane. These components have to be removed or converted to methane to produce dry natural gas that is piped to customers.
However, when large amounts of methane escape into the air, its flammability may prove dangerous. Methane has no odor to warn of danger, and so companies add small amounts of unpleasant smelling chemicals like mercaptan to natural gas so that people are aware of leaks. Mercaptan is very similar to methane; it has one carbon atom, four hydrogen atoms, and one sulfur atom. It gives off an odor like rotten eggs, thus allowing people to know when a natural gas leak is occurring in their home.
Methane is produced when organic material is fermented in environments that lack oxygen. It emanates comes from many common sources, including livestock and even humans. Many microorganisms produce methane, including many found in swamps and marshy areas. Methane is also produced by landfills, and some landfills are starting to harvest the methane using new technology.
You may have heard of methane as a gas that contributes to global warming. Methane is a greenhouse gas, and is capable of trapping much more heat in earth’s atmosphere than carbon dioxide. It may be considered beneficial to burn methane because it results in carbon dioxide. Therefore, though carbon dioxide is also a greenhouse gas, carbon dioxide that is the result of the combustion of methane has replaced a more dangerous gas in the atmosphere.
You can learn more about natural gas and methane here:
EPA. 2010. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2008. ANNEX 2, Methodology and Data for Estimating CO2 Emissions from Fossil Fuel Combustion. (http://www.epa.gov/climatechange/emissions/downloads10/US-GHG-Inventory-2010-Annex-2-CO2-Fossil-Fuel-Combustion.pdf)
Primary Author: Rachel Curtis ---- First posted: 14 January 2011 ---- Version: First revision, posted 29 April 2011.
Suggested citation style: Curtis, R. 2011. What is natural gas? Institute for Energy and Environmental Research of Northeastern Pennsylvania Clearinghouse website. http:energy.wilkes.edu/148.asp. Posted 14 January 2011, revised 29 April 2011.