Methane gas (CH4)

Jun 24, 2020 | Methane (CH4) | 0 comments

Ms.Rozita Dehbasteh

Ms.Rozita Dehbasteh

Bachelor of applied Chemistry
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Methane is a colorless odorless gas. It is also known as marsh gas or methyl hydride. It is easily ignited. The vapors are lighter than air. Under prolonged exposure to fire or intense heat the containers may rupture violently and rocket. CH4 is a gas produced by a group of colonic anaerobes, absorbed from the colon, and excreted in expired air. All CH4 produced in human beings is a metabolic product of intestinal bacteria, and about 50% of CH4 produced in the gut is absorbed and excreted in expired air. It could seem likely that the intracolonic activity of a variety of bacteria similarly might be assessed quantitatively via analysis of expired air.

Figure 1: Methane structure

Methane is a one-Carbon compound in which the carbon is attached by single bonds to four Hydrogen atoms. It is a colorless, odorless, non-toxic but flammable gas (b.p: -161℃). It has a role as a fossil fuel, a member of greenhouse gas and a bacterial metabolite. It is a mononuclear parent hydride, a one-carbon compound, a gas molecular entity and an alkane. It is a conjugate acid of a methanide.[1] , [2]

CH4 cycle

Most people have heard of the water cycle, in which water evaporates into the air, returns to Earth and then evaporates again. Many other substances, including methane, cycle this way too. There are many sources that release methane (CH4) into the atmosphere. There are also sinks or ways that methane is trapped or destroyed. 

 The methane cycle begins in the soil where methane gas is created by microbes. Soil methane is consumed by methanotrophs, microorganisms that feed on methane. Methanogens make more methane that methanotrophs consume.

Methanotrophs live in drier soil layers above the deep, wet oxygen poor soils of swamps. Their “food” bubbles past them on its way to the surface, releasing methane into the atmosphere. This methane joins methane from other sources, such as landfills, livestock and exploitation of fossil fuels.[3]

Physical properties

Table 1: Physical properties of Methane

[4]

Chemical properties

Combustion

When methane is burned in the presence of oxygen, the reaction—called a combustion reaction—produces carbon dioxide, water, and a large amount of heat. In molecular terms, the chemical reaction can be represented as follows:

CH4 + 2O2 → CO2 + 2H2O + heat

Hydrogen activation

In methane, the Carbon-Hydrogen covalent bond is among the strongest in all hydrocarbons. In chemical terms, there is a high “activation barrier” to break this C-H bond—in other words, considerable energy is required to break it. Nonetheless, methane is still the principal starting material for the manufacture of hydrogen. The search for Catalysts that can lower the activation barrier and other small-molecule alkanes is an area of research with considerable industrial significance.

Reactions with halogens

Under the proper conditions, methane reacts with all the halogens. The general reaction can be represented as follows:

CH4 + X2 → CH3X + HX

Here, X is either (F), (Cl), (Br), or sometimes (I). [5]

Table (2): Methane oxidation reactions

[6]

Production

The Earth’s mantle is the main reservoir of methane, and large quantities of this gas have been found in geological deposits known as natural gas fields. It occurs in association with other hydrocarbons and sometimes also Helium and Nitrogen. In general, natural gas is present in sediments buried deeper and at higher temperatures than those that contain petroleum. Natural gas fields are currently the main source from which methane is extracted for human use.

Biogas, produced by wetlands and landfills, is another source of methane. Biogas is a mixture of methane, carbon dioxide, and small amounts of other gases. It is generated by the microbial matter—including manure, wastewater sludge, municipal solid waste, or other biodegradable feedstock—under anaerobic conditions. Biogas is also called swamp gas, landfill gas, or marsh gas, depending on where it is produced. Also, methane is produced by the digestive systems of ruminants, termites, rice paddies, and oceans. [7]

Sources

Wetlands

Natural wetlands are responsible for approximately 80% of global methane emissions from natural sources. Wetlands, such as bogs, marshes, fens and permafrost provide a habitat favorable to microbes that produce methane during the decomposition of organic material.

These microbes require environments with no oxygen and plentiful organic matter, both of which are present in wetland conditions. Wetlands contribute approximately 140-280 Tg (million metric tons) to the global methane budget each year.

Termites

  They are estimated to be about 11% of the global methane emissions from natural sources or about 2-20 Tg per year. Microbes in the guts of termites produce methane as part of their normal digestive process, and the amount generated varies among different species. The emissions contributed by termites depend largely on the population of these insects, which varies significantly in different regions.

Landfills

Methane is generated in landfills and open dumps as waste decomposes under anaerobic conditions (oxygen-free). The amount of methane created depends on the quantity and moisture content of the waste and the design and management practices at the site. Landfills in regions with dry conditions are not as productive as those in area with high moisture content. In 2012, landfills contributed 102.8 Tg of methane to the atmosphere.

Human activities

Human activities that produce methane include fossil fuel production, the livestock industry, rice cultivation, biomass burning, and waste management. These activities release significant quantities of methane to the atmosphere.[8] , [9]

New tool for tracking oil and gas-related methane emissions worldwide

The concentration of Methane in the atmosphere is currently greater than pre-industrial levels and increasing steadily. This rise has important implications for climate change as methane is a potent greenhouse gas. The energy sector is one of the largest sources of methane emissions originating from human activity. The new “Methane tracker” offers the most comprehensive global picture of methane emissions, covering eight industry areas across more than seventy countries.

This new and unique tool provides the most up-to-date estimates of current oil and gas methane emissions, drawing on the best available data. It also sets out the reductions that are possible using existing technology and sheds light on this underexplored component of energy transitions. Analysis has highlighted that global methane emissions from the oil and gas sectors could be reduced by nearly half at no net cost.[10]

Table 3 : Methane cylinder color code

[11]

Applications

Hydrogen production from CH4 dry reforming over bimetallic Ni–Co/Al2O3 catalyst

The 5%Ni-10%Co/Al2O3 catalyst was evaluated for dry reforming of methane at varying reaction temperature of 923-973 K and atmospheric pressure. TPC and XRD measurements identified the presence of NiO, Co3O4, NiCo2O4, CoAl2O4 and NiAl2O4 phases on γ-Al2O3 support surface. The fine dispersion of both NiO and Co3O4 phases was observed by SEM morphology. 5%Ni-10%Co/Al2O3 catalyst exhibited stable catalytic performance with 4 h on stream and the conversions of CH4 and CO2 were about 67-71% at 973 K whilst H2 yield was superior to 50%. The activation energy estimated from Arrhenius plots for reactants and gaseous products varied from 40 to 63 kJ/mol. The reverse water-gas shift reaction simultaneously occurred during methane dry reforming reaction over Ni-Co catalyst. Raman spectroscopy and SEM measurements observed the existence of both whisker-like and graphitic carbons. However the amorphous carbon seemed to be dominant on spent catalyst surface explaining the catalytic stability with TOS.[12]

CH4→C+2H2

 Methane sensor

A methane gas sensor is a device used as an integral part of a fixed gas detection system for the purposes of monitoring and detecting levels of methane in air in %LEL (Lower Explosive Limit) levels or in percent by volume levels. There are two technologies used for this, Catalytic Bead and Infrared Sensor technologies.

As a methane sensor, Infrared sensor has now become the dominate sensor in a fixed gas detection system for combustible detection of hazardous levels of methane in air; because this method does not require Oxygen to operate. However, some users prefer to use Catalytic Bead due to their lower cost. Specially where there could be other combustible solvent vapors preset that the Catalytic Bead will detect, while an Infrared would not.[13]

The Use of Methane in Practical Solutions of Environmental Engineering

Methane can be extracted from hydrogen fuel which is dedicated to low-temperature fuel cells, generators or electric current and heat. Because of its physicochemical properties, methane can respond to the increasing demand for electricity in the world; the use of methane for energy purposes leads to its reduction in the atmosphere, which is a measurable benefit in terms of counteracting climate change. An interesting technological proposal is the use of methane derived from waste to produce hydrogen for low temperature cells.

 Also, the production of hydrogen produced from the waste fermentation (methane) product can lead to the reclassification of low temperature cells to unconventional renewable generators of electricity and heat. And with the use of renewable fuel (waste), serial fuel cell production can be introduced.[14]

Carbon Black

Methane gas can be burned incompletely leading to unusual carbon deposits. These deposits are known as carbon black and are used to strengthen rubber which is used to make vehicle tires. This same carbon black is used to make paints and printing ink.

Rocket fuels

Its gaseous state translates to less carbon deposits when combusted, making it ideal for rocket fuel. It also leaves no residue. Other forms of fuel such as kerosene emit a lot of carbon, making the rocket combustion chamber faulty.

Cooking

Methane is a hydrocarbon and lighter than air. Therefore, it produces more energy per unit weight in comparison to oil and coal. It is also preferred for cooking since it does not have any smell and does not leave soot on the cooking utensils. [15]

Industrial Uses

Some productions that might be obtained from CH4 are hydrogen for ammonia synthesis, acetylene by exposure to an electric arc, methyl chloride by chlorination, hydrogen sulfide by reaction with sulfur, oxidation products such as methanol, formaldehyde and formic acid and nitro methane.[16] For example about production of Methanol;

Single Step Oxidation of Methane to Methanol–Towards Better Understanding

Currently it is being produced by a conventional process which is expensive and energy intensive. Conversion of methane to a liquid fuel is a more desirable alternative to compressed natural gas due to ease of storage. The two-step process produces liquid methanol by the steam reforming of methane to synthesis gas followed by the high-pressure catalytic conversion of the synthesis gas of methanol. The single step performs at lower temperature, however there are some side reactions.

But improved catalyst and novel reactor design and operation can enhance methanol selectivity.[17]

Electricity from methane by reversing methanogenesis

Given vast methane reserves and the difficulty in transporting methane without substantial leaks, the conversion of methane directly into electricity would be beneficial. Microbial fuel cells harness electrical power from a wide variety of substrates through biological means; however, the greenhouse gas methane has not been used with much success previously as a substrate in microbial fuel cells to generate electrical current.

MFCs were first inoculated with the air-adapted M. acetivorans that produces ANME Mcr via pES1-MATmcr3, so that methane could be converted to acetate30. Although the air-adapted strain can tolerate oxygen and oxidize methane to produce acetate, the whole apparatus was operated anaerobically to eliminate oxygen as a terminal electron acceptor that competes with the generation of an electrical current.

 Methane consumption followed the voltage generation trends in that MFCs with the air-adapted M. acetivorans producing Mcr paired with G. sulfurreducens and sludge having the highest methane consumption. Methane consumption in MFCs with the air-adapted M. acetivorans strain producing Mcr but without both G. sulfurreducens and sludge had little methane consumption; hence, electricity is generated as a means to remove the excess electrons from the process for methane oxidation to occur, and the sludge and G. sulfurreducens provide a means to conduct the electrons to the anode. Methane losses were not due to leaks, since no oxygen was detected. In MFCs including G. sulfurreducens and sludge, production of Mcr from ANME allowed for greater consumption of the methane substrate.[18]

CH4 gasin pipelines

Assessing fugitive emissions of CH4 from high-pressure gas pipelines in the UK

Natural gas pipelines are an important source of fugitive methane emissions in lifecycle greenhouse gas assessments, but limited monitoring has taken place of UK pipelines to quantify fugitive emissions. For the pipeline routes, there were 26 peaks above 2.1 ppmv CH4 at 0.23 peaks/km, compared with 12 peaks at 0.11 peaks/km on control routes. Three distinct thermogenic emissions were identified based on the isotopic signal from these elevated concentrations with a peak rate of 0.03 peaks/km. A further three thermogenic emissions on pipeline routes were associated with pipeline infrastructure.

Figure 3: Map of pipelines

 Methane fluxes from control routes were statistically significantly lower than the fluxes measured on pipeline routes, with an overall pipeline flux of 627 (241–1123 interquartile range) tones CH4/km/yr. Soil gas CH4 measurements indicated a total flux of 62.6 kt CH4/yr, which equates to 2.9% of total annual CH4 emissions in the UK.

While little research has been conducted in recent years on distribution pipeline emissions, beyond industry surveys. This study has re-ported potential emissions from transmission stations and distribution pipelines and would recommend further work to better quantify their impact on GHG emissions.[19]

CH4 emission

As you can see in the graph below, Methane level has been increasing bouncy in recent years.[20]

Safety

FIRST AID MEASURES The conscious person who becomes aware of nausea and pressure on the forehead and eyes should go promptly to an uncontaminated area and inhale fresh air or oxygen.  However, in the event of a massive exposure the victim may become unconscious or symptoms of asphyxiation may persist.  In that case the person should be removed to an uncontaminated area, and given artificial respiration and then oxygen, after breathing has been restored. Treat symptomatically thereafter.[21] , [22]

Dangerous effects of Methane gas in atmosphere

Figure 3: MSDS of Methane

Global emission of methane in 2000 is 352 million tons. This calculation would accurately be applied for a fifteen-year period (1995-2010).

Hence in 15 years total emissions of methane = 32 million×15 tons = 35 billion tons. The total cost of 15 years global methane emissions is $ 600 billion. So that the mean benefit = 600 billion ÷ 5.3 billion = $110 per ton of methane reduction.

All values are calculated in 1990 dollars. Only 5% of the benefits are in the EU,  and  8%  in  the  USA;  the  rest  are  benefited  the  developing countries. As like methane, ozone (O3) is also a greenhouse gas. Tropospheric O3 is formed from photochemical reactions involving nitrogen oxides (NOx) and volatile organic compound in the global troposphere.  So that CH4 mitigation reduces O3 concentration in the troposphere. Tropospheric O3 damages agriculture, ecosystems, health.

Methane mitigation provides opportunity to improve air quality globally, which can be a cost-effective component of international ozone management, bringing multiple benefits for air quality, climate, agriculture and human health.[23]

[1]: https://pubchem.ncbi.nlm.nih.gov/compound/Methane#section=2D-Structure

[2]: https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.memorangapp.com%2Fflashcards%2F253097%2F2%2BBonding%2Band%2BStructure%2F&psig=AOvVaw0lYX_QqXFG2c2919eihFwM&ust=1590654342586000&source=images&cd=vfe&ved=0CA0QjhxqFwoTCJj-nbLP0-kCFQAAAAAdAAAAABAO

[3] , [8]: https://www.esrl.noaa.gov/gmd

[4]: http://www.airproducts.com/Products/Gases/gas-facts/physical-properties/physical-properties-methane.aspx

[5] , [7]: https://www.newworldencyclopedia.org/entry/Methane

[6]: https://www.airgas.com/msds/001033

[9]: https://earthobservatory.nasa.gov/images/5270/atmospheric-methane

[10]: https://www.iea.org/news/iea-launches-new-tool-for-tracking-oil-and-gas-related-methane-emissions-worldwide

[11]: INDUSTRIAL GAS CYLINDERS COLOR CODING TD 08/15/E. MIDDLE EAST GASES ASSOCIATION (MEGA)   European Business Center, Office BC – 25   Dubai Investments Park, PO Box: 166 Dubai-UAE

[12]: Journal of the Energy Institute. Volume 91.Issue 5. October 2018.Pages 683-694. Author links open overlay panelTan JiSiangaSharanjitSinghaOsazeOmoregbeaLong GiangBachbNguyen Huu HuyPhuccDai-Viet N.Voad

[13]: https://www.gdscorp.com/methane-sensor

[14]: Journal of Ecological engineering. Volume 19, Issue 2, 2018. Aneta Skorek

Renata Włodarczyk.

[15]: https://www.conserve-energy-future.com/sources-uses-effects-methane-gas.php

[16]: Nature 159, 670 (1947). Issue Date17 May 1947

[17]: Procedia engineering. Volume 51. 2013. Pages 409-415. PriyankKhirsariyaRaju K.Mewada

[18]: Nature communication. Article number 15419.2017. Michael J. McAnulty, Venkata G. Poosarla, Kyoung-Yeol Kim, Ricardo Jasso-Chávez, Bruce E. Logan & Thomas K. Wood 

[19]: Science of the total environment. 631-632 · March 2018. Ian Bothroyd. Sam Almond .Fred Worrall. Rosemary K.Davies

[20]: https://www.methanelevels.org

[21]: Afrox. Date: January 2017. Version2 Ref. no.: MS042

[22]: https://www.airgas.com/msds

[23]: Haradhan Kumar Mohajan. Premier University.June 2012.


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