The simplest hydrocarbon , methane is a gas with a chemical formula of CH4.
The carbon atom central to the methane molecule has 4 valence electrons and thus needs 4 more electrons from four hydrogen atoms to complete its octet. The hydrogen atoms have a 109 degree bond angle giving the molecule a tetrahedral geometry .
A principal component of natural gas, methane is significant . Burning one molecule of methane in the presence of oxygen releases one molecule of CO2[carbon dioxide) and two molecules of H2O (water):
- CH4 + 2O2 ---> CO2 + 2H2O
The strength of the carbon hydrogen covalent bond in the methane molecule is among the strongest in all hydrocarbons, and thus its use as a chemical feedstock is limited. The search for which one can facilitate C-H bond activation in methane and other low alkanes is an area of research with considerable industrial significance.
Pure methane is odorless, but when used as a fuel it is usually mixed with small quantities of strongly-smelling sulfur compounds such as ethyl mercaptan to enable the detection of leaks.
Methane is a greenhouse gas with a global warming potential of 22 (meaning that it has 22 times the warming ability of carbon dioxide).
Methane results from the decomposition of certain organic matters in the absence of oxygen. It is therefore also classified as a biogas.
The U.S. Geological Survey has estimated that the United States has 320,000 trillion cubic feet of gas hydrates, some 200 times conventional natural gas resources and reserves in the country. If only 1 percent of the methane hydrate resource could be made recoverable, the United States could more than double its domestic natural gas resource base
Principal sources are
- decomposition of organic wastes ;
- natural sources (;marshes) : 23 %
- fossil fuel extraction : 20 % Coal bed methane extraction
- the processes of digestion of animals (cattle) : 17 %
- bacteria found in rice plantations : 12 %
- biomass anaerobic heating or combustion
80% of the world emissions are of human source. They come primarily from agricultural and other human activities. During the past 200 years, the concentration of this gas in the atmosphere doubled, passing from 0.8 to 1.7 ppm.
Methane as a Fuel
Methane is important for electrical generation by burning it as a fuel in a gas turbine or steam generator. Compared to other hydrocarbon fuels, burning methane produces less carbon dioxide for each unit of heat released. At about 891 kJ/mol, methane's heat of combustion is lower than any other hydrocarbon but the ratio of the heat of combustion (891 kJ/mol) to the molecular mass (16.0 g/mol, of which 12.0 g/mol is carbon) shows that methane, being the simplest hydrocarbon, produces more heat per mass unit (55.7 kJ/g) than other complex hydrocarbons. In many cities, methane is piped into homes for domestic heating and cooking purposes. In this context it is usually known as natural gas, which is considered to have an energy content of 39 megajoules per cubic meter, or 1,000 BTU per standard cubic foot.
Methane in the form of compressed natural gas is used as a vehicle fuel and is claimed to be more environmentally friendly than other fossil fuels such as gasoline/petrol and diesel. Research into adsorption methods of methane storage for use as an automotive fuel has been conducted.
Liquefied natural gas (LNG) is natural gas (predominantly methane, CH4) that has been converted to liquid form for ease of storage or transport.
Liquefied natural gas takes up about 1/600th the volume of natural gas in the gaseous state. It is odorless, colorless, non-toxic and non-corrosive. Hazards include flammability after vaporization into a gaseous state, freezing and asphyxia.
The liquefaction process involves removal of certain components, such as dust, acid gases, helium, water, and heavy hydrocarbons, which could cause difficulty downstream. The natural gas is then condensed into a liquid at close to atmospheric pressure (maximum transport pressure set at around 25 kPa or 3.6 psi) by cooling it to approximately −162 °C (−260 °F).
LNG achieves a higher reduction in volume than compressed natural gas (CNG) so that the energy density of LNG is 2.4 times greater than that of CNG or 60% of that of diesel fuel. This makes LNG cost efficient to transport over long distances where pipelines do not exist. Specially designed cryogenic sea vessels (LNG carriers) or cryogenic road tankers are used for its transport.
LNG, when it is not highly refined for special uses, is principally used for transporting natural gas to markets, where it is regasified and distributed as pipeline natural gas. It is also beginning to be used in LNG-fueled road vehicles. For example, trucks in commercial operation have been achieving payback periods of approximately four years on the higher initial investment required in LNG equipment on the trucks and LNG infrastructure to support fueling. However, it remains more common to design vehicles to use compressed natural gas. As of 2002, the relatively higher cost of LNG production and the need to store LNG in more expensive cryogenic tanks had slowed widespread commercial use.
Power to gas
Power to gas is a technology which converts electrical power to a gas fuel. The method is used to convert carbon dioxide and water to methane, (see natural gas) using electrolysis and the Sabatier reaction.[clarification needed] The excess power or off peak power generated by wind generators or solar arrays could theoretically be used for load balancing in the energy grid.
Liquid methane rocket fuel
In a highly refined form, liquid methane is used as a rocket fuel.
While investigations of methane use have existed for decades, no production methane engines have yet been used on orbital spaceflights. This is changing, and liquid methane has recently been selected for the active development of a variety of bipropellant rocket engines.
Since the 1990s, a number of Russian rockets have been proposed to use liquid methane. One 1990s Russian engine proposal was the RD-192, a methane/LOX variant of the RD-191.
In 2005, US companies, Orbitech and XCOR Aerospace, developed a demonstration liquid oxygen/liquid methane rocket engine and a larger 7,500 pounds-force (33 kN)-thrust engine in 2007 for potential use as the CEV lunar return engine, before the CEV program was later cancelled.
More recently the American private space company SpaceX announced in 2012 an initiative to develop liquid methane rocket engines,] including, initially, the very large Raptor rocket engine. Raptor is being designed to produce 4.4 meganewtons (1,000,000 lbf) of thrust with a vacuum specific impulse (Isp) of 363 seconds and a sea-level Isp of 321 seconds, and is expected to begin component-level testing in 2014. In February 2014, the Raptor engine design was revealed to be of the highly efficient and theoretically more reliable full-flow staged combustion cycle type, where both propellant streams—oxidizer and fuel—will be completely in the gas phase before they enter the combustion chamber. Prior to 2014, only two full-flow rocket engines have ever progressed sufficiently to be tested on test stands, but neither engine completed development or flew on a flight vehicle.
In October 2013, the China Aerospace Science and Technology Corporation, a state-owned contractor for the Chinese space program, announced that it had completed a first ignition test on a new LOX methane rocket engine. No engine size was provided.
In September 2014, another American private space company—Blue Origin— publically announced that they were into their third year of development work on a large methane rocket engine. The new engine, the Blue Engine 4, or BE-4, has been designed to produce 2,400 kilonewtons (550,000 lbf) of thrust. While initially planned to be used exclusively on a Blue Origin proprietary launch vehicle, it will now be used on a new United Launch Alliance (ULA) engine on an new launch vehicle that is a successor to the Atlas V. ULA indicated in 2014 that they will make the maiden flight of the new launch vehicle no earlier than 2019.
it is abundant in many parts of the solar system and it could potentially be harvested on the surface of another solar-system body (in particular, using methane production from local materials found on Mars or Titan), providing fuel for a return journey.
By 2013, NASA's Project Morpheus had developed a small restartable LOX methane rocket engine with 5,000 pounds-force (22 kN) thrust and a specific impulse of 321 seconds suitable for inspace applications including landers. Small LOX methane thrusters 5–15 pounds-force (22–67 N) were also developed suitable for use in a Reaction Control System (RCS).
SpaceNews is reporting in early 2015 that the French space agency CNES is working with Germany and a few other governments and will propose a LOX/methane engine on a reusable launch vehicle by mid-2015, with flight testing unlikely before approximately 2026.
What is the geometry of the methane molecule? An interactive activity which includes a jmol applet of methane.