METHANE

Description

Methane is a colorless, odorless, flammable hydrocarbon gas that is the simplest alkane. The root word, met, in methane is derived from the Greek root word methe meaning wine. Methylene was used in the early 19th century as the name for methanol, which is wood alcohol, CH3OH. Methylene comes from methe + hydē, the latter being the Greek word for wood, so methylene would mean wine from wood. Methanol got the names methylene and wood alcohol because it was discovered by Robert Boyle (1627–1691) in the 17th century by the destruction distillation of wood. Destructive distillation involves heating in the absence of air.

Methane is the first alkane and carries the suffix“ane” denoting an alkane, thus methe z + ane = methane. The carbon is at the center of the tetrahedron, which can be assumed to be an equilateral pyramid, with a hydrogen atom at each of the four corners of the tetrahedron.
Methane is the principal component of natural gas, with most sources containing at least 75% methane. Methane production occurs naturally through a process called methanogenesis. Methanogenesis involves anaerobic respiration by single-cell microbes collectively called methanogens.

Chemical properties

Methane is a natural, colorless, odorless, and tasteless gas. It is used primarily as fuel to make heat and light. It is also used to manufacture organic chemicals. Methane can be formed by the decay of natural materials and is common in landfi lls, marshes, septic systems, and sewers. It is soluble in alcohol, ether, benzene, and organic solvents. Methane is incompatible with halogens, oxidizing materials, and combustible materials. Methane evaporates quickly. Methane gas is present in coal mines, marsh gas, and in sludge degradations. Methane can also be found in coal gas. Pockets of methane exist naturally underground. In homes, methane may be used to fuel a water heater, stove, and clothes dryer. Incomplete combustion of gas also produces carbon monoxide. Methane gas is flammable and may cause fl ash fi re. Methane forms an explosive mixture in air at levels as low as 5%. Electrostatic charges may be generated by fl ow and agitation.

History

Methane has been used as a fossilfuel for thousands of years. The discovery of methane is attributed to the Italian physicist Alessandro Volta (1745–1827). Volta, known primarily for his discoveries in electricity, investigated reports of a flammable gas found in marshes. In November 1776, Volta, while visiting the Lake Maggiore region of northern Italy, noticed that gas bubbles emanated from disturbed sediments in marshes. Volta collected the gas and began investigations on its nature. He discovered that the gas was highly flammable when mixed with air. He developed an instrument termed Volta’s pistol (also called a spark eudiometer) that fired metal balls like a miniature cannon to conduct combustion experiments with methane. He also developed a lamp fueled by methane.

The Uses of METHANE

Methane is used primarily as a fuel to make heat and light. It is also used to manufacture organic chemicals. Methane can be formed by the decay of natural materials and is common in landfills, marshes, septic systems, and sewers. It is soluble in alcohol, ether, benzene, and organic solvents. Methane is incompatible with halogens, oxidising materials, and combustible materials. Methane evaporates quickly. Methane gas is present in coal mines, marsh gas, and sludge degradations. Methane can also be found in coal gas. Pockets of methane exist naturally underground. In homes, methane may be used to fuel a water heater, stove, and clothes dryer. Also, incomplete combustion of gas also produces carbon monoxide. Methane gas is flammable and may cause flash fire. Methane forms an explosive mixture in air at levels as low as 5%. Electrostatic charges may be generated by flow and agitation.

The Uses of METHANE

Methane is widely distributed in nature. As adeep earth gas, it is outgassing from earth’scrust. It is also present in the atmosphere(0.00022% by volume). It is the prime constituentof natural gas (85–95% concentration).It is formed from petroleum crackingand decay of animal and plant remains. It isfound in marshy pools and muds. Methaneis used as a common heating fuel in naturalgas; in the production of hydrogen, acetylene,ammonia, and formaldehyde; and as acarrier gas in GC analysis.

The Uses of METHANE

Methane is an important starting material for numerous other chemicals. The most important of these are ammonia, methanol, acetylene, synthesis gas, formaldehyde, chlorinated methanes, and chlorofl uorocarbons. Methane is used in the petrochemical industry to produce synthesis gas or syn gas, which is then used as a feedstock in other reactions. Synthesis gas is a mixture of hydrogen and carbon monoxide. It is produced through steam-methane reforming by reacting methane with steam at approximately 900 C in the presence of a metal catalyst: CH4 + H2O→CO + 3H2. Alternately, methane is partially oxidized and the energy from its partial combustion is used to produce syn gas:
CH4 + 2O2→ CO2 + 2H2O
CH4 + CO2→2CO + 2H2
CH4 + H2O→CO + 3H
Hydrogen from syn gas reacts with nitrogen to produce ammonia: N2 + 3H2→2NH3. Carbon monoxide and hydrogen from syn gas can be combined to produce methanol: CO + 2H2→CH3OH.
Methanol is primarily used for the production of formaldehyde through an oxidation process: 2CH3OH + O2→CH2O + H2O or an oxidation-dehydrogenation process: CH3OH CH2O + H2.
Chlorination of methane, in which chlorine is substituted for one to all four of the hydrogens in methane, produces methyl chloride (CH3Cl), methylene chloride (CH2Cl2), chloroform (CHCl3), and carbon tetrachloride (CCl4). The substitution of chlorines and fluorines in methane results in chlorofl uorocarbons. Methane is a fossil fuel that acts as a greenhouse gas, making it a subject of widespread interest in global warming research.

Definition

A gaseous alkane. Natural gas is about 99% methane and this provides an important starting material for the organic-chemicals industry. Methane can be chlorinated directly to produce the more reactive chloromethanes, or it can be ‘reformed’ by partial oxidation or using steam to give mixtures of carbon oxides and hydrogen. Methane is the first member of the homologous series of alkanes.

Definition

methane: A colourless odourless gas, CH₄; m.p.–182.5°C; b.p.–164°C.Methane is the simplest hydrocarbon,being the first member of thealkane series. It is the main constituentof natural gas (～99%) and as such is an important raw material forproducing other organic compounds.It can be converted into methanol by catalytic oxidation.

Definition

natural gas: A naturally occurringmixture of gaseous hydrocarbonsthat is found in porous sedimentaryrocks in the earth’s crust, usually inassociation with petroleum deposits.It consists chiefly of methane(about 85%), ethane (up to about10%), propane (about 3%), and butane.Carbon dioxide, nitrogen, oxygen,hydrogen sulphide, and sometimeshelium may also be present. Naturalgas, like petroleum, originates in thedecomposition of organic matter. It iswidely used as a fuel and also to producecarbon black and some organicchemicals. Natural gas occurs onevery continent, the major reservesoccurring in the USA, Russia, Kazakhstan,Turkmenistan, Ukraine, Algeria,Canada, and the Middle East. Seealso liquefied petroleum gas.

Production Methods

Methane is the end product of anaerobic decay. It is the major constituent of natural gas, present at concentrations between 600,000 and 800,000 ppm 60 to 80% of natural gas. Methane collects in coal mines or geologically similar earth deposit sites, evolves as marsh gas, and forms during certain fermentation and sludge degradation processes. Methane is also produced by decomposition in municipal landfills; concentrations can be as high as 250,000 ppm. It is often accompanied by other low molecular weight hydrocarbons.

Definition

The first member of the paraffin (alkane) hydrocarbon series.

General Description

METHANE is a colorless odorless gas. METHANE is also known as marsh gas or methyl hydride. METHANE is easily ignited. The vapors are lighter than air. Under prolonged exposure to fire or intense heat the containers may rupture violently and rocket. METHANE is used in making other chemicals and as a constituent of the fuel, natural gas.

Air & Water Reactions

Highly flammable.

Reactivity Profile

METHANE is a reducing agent, METHANE is involved in many explosions when combined with especially powerful oxidizers such as bromine pentafluoride, chlorine trifluoride, chlorine, iodine, heptafluoride, dioxygenyl tetrafluoroborate, dioxygen difluoride, trioxygen difluoride and liquid oxygen. Other violent reactions include, chlorine dioxide and nitrogen trifluoride. Liquid oxygen gives an explosive mixture when combined with liquid METHANE [NFPA 1991]. Contact of very cold liquefied gas with water may result in vigorous or violent boiling of the product and extremely rapid vaporization due to the large temperature differences involved. If the water is hot, there is the possibility that a liquid "superheat" explosion may occur. Pressures may build to dangerous levels if liquid gas contacts water in a closed container [Handling Chemicals Safely 1980].

Hazard

Severe fire and explosion hazard, forms explosive mixture with air (5–15% by volume). An asphyxiant gas.

Health Hazard

Methane is a relatively potent gas. It is the simplest alkane and the principal component of natural gas. Exposures to methane gas cause toxicity and adverse health effects. The signs and symptoms of toxicity include, but are not limited to, nausea, vomiting, diffi culty breathing, irregular heart beat, headache, drowsiness, fatigue, dizziness, disorientation, mood swings, tingling sensation, loss of coordination, suffocation, convulsions, unconsciousness, and coma. While at low concentrations methane causes no toxicity, high doses lead to asphyxiation in animals and humans. Displacement of air by methane gas is known to cause shortness of breath, unconsciousness, and death from hypoxemia. Methane gas does not pass readily through intact skin. However, in its extremely cold liquefi ed form, methane can cause burns to the skin and eyes. No long-term health effects are currently associated with exposure to methane.

Health Hazard

Methane is a nonpoisonous gas. It is anasphyxiate. Thus exposure to its atmospherecan cause suffocation.

Fire Hazard

Special Hazards of Combustion Products: None

Agricultural Uses

Biogas, a gaseous fuel, is produced by the fermentation of organic matter by methane-forming bacteria (methanogens). Biogas consists of a mixture of methane, carbon dioxide and hydrogen.
A mixture of methane and carbon dioxide, or even methane alone, formed in the deep layers of organic material in swamp bottoms or landfills, is sometimes called swamp gas or marsh gas.
Acetoclastic bacteria form methane exclusively from acetic acid in anaerobic digestion. They grow slowly and have a doubling time of several days, which is the rate-limiting step in biogas production. Bacteria that ferment fatty acids (mainly propionic acid and butyric acid) to acetic acid are called acetogenic bacteria.
Animal dung and plant residues are used to produce biogas in a fermenter. The residual biogas slurry containing 1.4 to 1.8 % nitrogen, 1.1 to 1.7 % phosphorus (as P₂O₅)an d 0.8 to 1.3 % potassium (as K₂O) is used as organic manure. Animal manure used for biogas production does not lose its fertilizer nutrient value. Biogas is usually made by the decomposition of domestic, industrial and agricultural sewage wastes. Methane, its major component, can be harvested and used as a pollution-free renewable resource and a derived source of domestic energy. Biogas, produced in special biogas digesters, is widely used in China and India.

Agricultural Uses

Methane (CH₄) is a colorless gas produced from a highly reduced paddy field. This odorless gas is also produced by decomposing organic matter in sewage and marshes. It is the chief constituent of natural gas. It occurs in coal gas and water gas and is produced in petroleum refining.
There is now enough evidence to suggest that rice cultivation results in increased methane emission to the atmosphere. The reasons for interest in methane are that it is an important energy source, which has a global warming potential of about 24.5% (carbon dioxide being loo%), and is responsible for approximately 25% of the anticipated warming.
Atmospheric methane originates mainly from biogenic sources, such as rice paddies and natural wetlands. Rice paddies account for 15 to 20% of the world's total anthropogenic methane emission. In addition to the role of rice plant in methane emission, it also plays a significant role in methane oxidation because oxygen transported below the ground by plants, leaks out of the rhizosphere into the sediments, stimulating the methane oxidizing activity. Most of the methane emitted from rice fields is expected to be from the Asian region as it has 90% of the total world rice harvested area. Several investigations have demonstrated that methane flux in rice fields is dependent on the variety of rice [dryland, imgated or deep ponded water], water level, fertilizer application and crop phenology
Strategies to mitigate methane emission from paddy soils of the world have been identified, which include (a) a form and dose of nitrogen and other chemical fertilizers, (b) the mode of fertilizer application, (c) water management, and (d) cultivation practices. Recent studies have indicated that methane emission decreased by about 50% after the application of an ammonium based fertilizer, due to oxidation of methane. The various options to mitigate methane emission are (a) direct seediig of paddy crop, (b) intermittent irrigation, (c) soil amendment with sulphate containing fertilizers, and (d) compost addition in place of fresh organic matter.

Agricultural Uses

Natural gas is the feedstock for 78% of the world's ammonia produced. It is a naturally occurring mixture of gaseous hydrocarbons found in porous sedimentary rocks in the earth's crust, usually in association with petroleum deposits. It is a colorless, odorless, flammable gas or liquid.
Natural gas contains methane (about 85%), hydrogen sulphide and carbon dioxide in varying percentages, and a small percentage of ethane and higher hydrocarbons.

Materials Uses

Methane is noncorrosive and may be contained by any common, commercially available metals, with the exception of cryogenic liquid applications. Handling equipment must, however, be designed to safely withstand the temperatures and pressures to be encountered.
At the temperature of liquid methane, ordinary carbon steels and most alloy steels lose their ductility and are considered unsafe for liquid methane service. Satisfactory materials for use with liquid methane include Type 18-8 stainless steel and other austenitic nickel-chromium alloys, copper, Monel, brass, and aluminum.

Safety Profile

A simple asphyxiant. Very dangerous fire and explosion hazard when exposed to heat or flame. Reacts violently with powerful oxidzers (e.g., bromine pentafluoride, chlorine trifluoride, chlorine, fluorine, iodine heptafluoride, dioxygenyl tetrafluoroborate, dioxygen difluoride, trioxygen difluoride, liquid oxygen, ClO2, NF3,OF2). Incompatible with halogens or interhalogens in air (forms explosive mixtures). Explosive in the form of vapor when exposed to heat or flame. To fight fire, stop flow of gas. See also ARGON for a description of asphyxiants.

Potential Exposure

Methane is used as a fuel and in the manufacture of organic chemicals, acetylene, hydrogen cyanide, and hydrogen. It may also be a cold liquid. Natural gas is used principally as a heating fuel. It is transported as a liquid under pressure. It is also used in the manufacture of various chemicals including acetaldehyde, acetylene, ammonia, carbon black; ethyl alcohol; formaldehyde, hydrocarbon fuels; hydrogenated oils; methyl alcohol; nitric acid; synthesis gas; and vinyl chloride. Helium can be extracted from certain types of natural gas.

Physiological effects

Methane is generally considered nontoxic. Exposures to concentrations of up to 9 percent methane have been reported without apparent ill effects; inhalation of higher concentrations eventually causes a feeling of pressure on the forehead and eyes, but the sensation ends after returning to fresh air. Methane is a simple asphyxiant.

First aid

If this chemical gets into the eyes, remove any contact lenses at once and irrigate immediately for at least 15 min, occasionally lifting upper and lower lids. Seek medical attention immediately. If this chemical contacts the skin, remove contaminated clothing and wash immediately with soap and water. Seek medical attention immediately. If this chemical has been inhaled, remove from exposure, begin rescue breathing (using universal precautions, including resuscitation mask) if breathing has stopped and CPR if heart action has stopped. Transfer promptly to a medical Methane 1725 facility. When this chemical has been swallowed, get medical attention. Give large quantities of water and induce vomiting. Do not make an unconscious person vomit. If frostbite has occurred, seek medical attention immediately; do NOT rub the affected areas or flush them with water. In order to prevent further tissue damage, do NOT attempt to remove frozen clothing from frostbitten areas. If frostbite has NOT occurred, immediately and thoroughly wash contaminated skin with soap and water.

Environmental Fate

Methane is a relatively potent greenhouse gas. The concentration of methane in the Earth’s atmosphere in 1998, expressed as a mole fraction, was 1745 ppb, up from 700 ppb in 1750. By 2008, however, global methane levels, which had stayed mostly flat since 1998, had risen to 1800 ppb. Methane has a molecular weight of 16.04 gmol^-1. At 25 ℃, methane has solubility in water of 22 mg l^-1, an estimated vapor pressure of 466 000 mmHg, and a Henry’s law constant of 0.66 atm-m³ mol^-1 (HSDB, 2011). The log octanol/ water partition coefficient is 1.09. Conversion factors for methane in air are as follows: 1mgm^-3 = 1.52 ppm; and 1 ppm= 0.66 mgm^-3.
If released into air, the very low boiling point (^-161 ℃) and high vapor pressure predict that methane will exist solely as a vapor in the ambient atmosphere. Vapor-phase methane will be degraded in the atmosphere by a reaction with photochemically produced hydroxyl radicals; the halflife for this reaction in air is estimated to be 6 years (HSDB, 2011).
If released into water, liquid methane would boil off. Any residual methane would only moderately adsorb to suspended solids and sediment based on an estimated Koc (organic carbon partition coefficient) of 90. Volatilization from water surfaces is expected to be the dominant fate process based on the estimated Henry’s law constant. Estimated volatilization half-lives for both a model river and a model lake are 2 h (US EPA, 2011). Utilization of methane by soil microorganisms has been detected from five soil samples collected from sites near Adelaide, South Australia. The biodegradation half-life of methane was estimated to be 70 days to infinity based on gas exchange biodegradation experiments conducted in model estuarine ecosystems (HSDB, 2011).
If released to soil, methane would be expected to rapidly volatilize. Anymethane thatmigrated to the subsurface would have high to moderate mobility in the subsurface based on the relatively low Koc value. Volatilization of methane from moist soil surfaces is expected to be an important fate process (HSDB, 2011).
Using a measured log Kow (octanol water partition coefficient) of 1.09, the US Environmental Protection Agency’s (USEPA) EPI Suite computer program estimates both a bioconcentration factor (BCF) and a bioaccumulation factor (BAF) of 2. This predicts that bioaccumulation and/or biomagnification would be insignificant. Methane would therefore not be expected to be found in the tissues of fish or wildlife as methane contains no persistent functional groups (e.g., chlorine, bromine) and exposure would be expected to be low.

storage

Occupational workers should store methane gas containers away from incompatible substances and handle in accordance with standard set regulations and grounding and bonding if required.

Shipping

UN1971 Methane, compressed or Natural gas, compressed (with high methane content), Hazard Class: 2.1; Labels: 2.1-Flammable gas. UN1972 Methane, refrigerated liquid (cryogenic liquid) or Natural gas, refrigerated liquid (cryogenic liquid), with high methane content), Hazard Class: 2.1; Labels: 2.1-Flammable gas. Cylinders must be transported in a secure upright position, in a wellventilated truck. Protect cylinder and labels from physical damage. The owner of the compressed gas cylinder is the only entity allowed by federal law (49CFR) to transport and refill them. It is a violation of transportation regulations to refill compressed gas cylinders without the express written permission of the owner

Purification Methods

Dry methane by passing over CaCl2 and P2O5, then through a Dry-ice trap and fractionally distil it from a liquid-nitrogen trap. Oxygen can be removed by prior passage in a stream of hydrogen over reduced copper oxide at 500o, and higher hydrocarbons can be removed by chlorinating about 10% of the sample: the hydrocarbons, chlorides and HCl are readily separated from the methane by condensing the sample in the liquid-nitrogen trap and fractionally distilling it. Methane has also been washed with conc H2SO4, then solid NaOH and then 30% NaOH solution. It is dried with CaCl2, then P2O5, and condensed in a trap at liquid air temperature, then transferred to another trap cooled in liquid nitrogen. CO2, O2, N2 and higher hydrocarbons can be removed from methane by adsorption on charcoal. [Eiseman & Potter J Res Nat Bur Stand 58 213 1957, Beilstein 1 IV 3.] HIGHLY FLAMMABLE.

Toxicity evaluation

Methane acts as an asphyxiant at concentrations that are high enough to displace oxygen.

Incompatibilities

May form explosive mixture with air. A strong reducing agent. Incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, fluorine, etc.); contact may cause fires or explosions. Keep away from alkaline materials, strong bases, strong acids, oxoacids, epoxides. Reacts violently with bromine pentafluoride, chlorine dioxide, nitrogen trifluoride, oxygen difluoride and liquid oxygen. In general, avoid contact with all oxidizers

Waste Disposal

Return refillable compressed gas cylinders to supplier. Incineration (flaring)

Precautions

Occupational workers should be careful during handling and management of methane gas because of its severe fi re and explosion hazard, particularly with pressurized containers. The containers may rupture or explode if exposed to suffi cient heat. Workers should avoid heat, flames, sparks, and other sources of ignition, and stop any leak if possible without personal risk. Workers should wear appropriate chemical-resistant gloves. Also, vapors should be reduced with water spray and keep unnecessary workers/people away from the place of chemical hazard. The closed spaces should be well ventilated before the workers enter. Methane is not toxic; however, it is highly flammable and may form explosive mixtures with air. Methane is violently reactive with oxidizers, halogens, and some halogen-containing compounds. Methane is also an asphyxiant and in enclosed areas displaces oxygen. Septic tanks, cesspools, and drywells present serious hazards, including septic cave-in or collapse, methane gas explosion hazards, and asphyxiation hazards. Occupational workers/work area supervisor should note the indications of methane gas poisoning: Soon after exposure to oxygen levels of less than 15% in air, if the workers feel symptoms of dizziness, headache, and tiredness, medical advice should be provided.

GRADES AVAILABLE

Methane is typically available for commercial and industrial purposes in a c.P. Grade (minimum purity of 99 mole percent), a technical grade (minimum purity of 98.0 mole percent), and a commercial grade that is actually natural gas as it is received from the pipeline. (There is no guaranteed purity, but methane content usually runs about 93 percent or better.)