Natural gas
Natural gas (also called fossil gas, methane gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane (97%)[1] in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbon dioxide, nitrogen, hydrogen sulfide, and helium are also usually present.[2] Methane is colorless and odorless, and the second largest greenhouse gas contributor to global climate change after carbon dioxide.[3] Because natural gas is odorless, odorizers such as mercaptan (which smells like sulfur or rotten eggs) are commonly added to it for safety so that leaks can be readily detected.[4]
Not to be confused with gasoline, biogas, or liquefied petroleum gas.
Natural gas is a fossil fuel and non-renewable resource that is formed when layers of organic matter (primarily marine microorganisms)[5] decompose under anaerobic conditions and are subjected to intense heat and pressure underground over millions of years.[6] The energy that the decayed organisms originally obtained from the sun via photosynthesis is stored as chemical energy within the molecules of methane and other hydrocarbons.[7]
Natural gas can be burned for heating, cooking,[8] and electricity generation. It is also used as a chemical feedstock in the manufacture of plastics and other commercially important organic chemicals and less commonly used as a fuel for vehicles.
The extraction and consumption of natural gas is a major and growing contributor to climate change.[9][10][11] Both the gas itself (specifically methane) and carbon dioxide, which is released when natural gas is burned, are greenhouse gases.[12][13] When burned for heat or electricity, natural gas emits fewer toxic air pollutants, less carbon dioxide, and almost no particulate matter compared to other fossil and biomass fuels.[14] However, gas venting and unintended fugitive emissions throughout the supply chain can result in natural gas having a similar carbon footprint to other fossil fuels overall.[15]
Natural gas can be found in underground geological formations, often alongside other fossil fuels like coal and oil (petroleum). Most natural gas has been created through either biogenic or thermogenic processes. Biogenic gas is formed when methanogenic organisms in marshes, bogs, landfills, and shallow sediments anaerobically decompose but are not subjected to high temperatures and pressures. Thermogenic gas takes a much longer period of time to form and is created when organic matter is heated and compressed deep underground.[16][6]
During petroleum production, natural gas is sometimes flared rather than being collected and used. Before natural gas can be burned as a fuel or used in manufacturing processes, it almost always has to be processed to remove impurities such as water. The byproducts of this processing include ethane, propane, butanes, pentanes, and higher molecular weight hydrocarbons. Hydrogen sulfide (which may be converted into pure sulfur), carbon dioxide, water vapor, and sometimes helium and nitrogen must also be removed.
Natural gas is sometimes informally referred to simply as "gas", especially when it is being compared to other energy sources, such as oil, coal or renewables. However, it is not to be confused with gasoline, which is also shortened in colloquial usage to "gas", especially in North America.[17]
Natural gas is measured in standard cubic meters or standard cubic feet. The density compared to air ranges from 0.58 (16.8 g/mole, 0.71 kg per standard cubic meter) to as high as 0.79 (22.9 g/mole, 0.97 kg per scm), but generally less than 0.64 (18.5 g/mole, 0.78 kg per scm).[18] For comparison, pure methane (16.0425 g/mole) has a density 0.5539 times that of air (0.678 kg per standard cubic meter).
Name[edit]
In the early 1800s, natural gas became known as "natural" to distinguish it from the dominant gas fuel at the time, coal gas.[19] Unlike coal gas, which is manufactured by heating coal, natural gas can be extracted from the ground in its native gaseous form. When the use of natural gas overtook the use of coal gas in English speaking countries in the 20th century, it was increasingly referred to as simply "gas."[20] In order to highlight its role in exacerbating the climate crisis, however, many organizations have criticized the continued use of the word "natural" in referring to the gas. These advocates prefer the term "fossil gas" or "methane gas" as better conveying to the public its climate threat.[21][22][23] A 2020 study of Americans' perceptions of the fuel found that, across political identifications, the term "methane gas" led to better estimates of its harms and risks.[24]
Adsorbed natural gas (ANG)[edit]
Natural gas may be stored by adsorbing it to the porous solids called sorbents. The optimal condition for methane storage is at room temperature and atmospheric pressure. Pressures up to 4 MPa (about 40 times atmospheric pressure) will yield greater storage capacity. The most common sorbent used for ANG is activated carbon (AC), primarily in three forms: Activated Carbon Fiber (ACF), Powdered Activated Carbon (PAC), and activated carbon monolith.[167]