Methane: A tidbit

In an age of global warming/ heating/ boiling it is important to have a basic understanding of a few chemicals. Methane is one of them.

A chemical compound is a substance made of many identical molecules containing atoms from more than one chemical element, held together by chemical bonds. There are several different types of chemical bonds, but those will not be discussed here, but the next time a chemical is presented.

Atmospheric oxygen = O2 is not a compound because there are atoms of only one element present, two atoms of oxygen joined together. Water = H20 is a chemical compound. It consists of two hydrogen atoms and one oxygen atom. A compound can be transformed into a different substance by a chemical reaction, typically involving interactions with other substances, and where bonds between atoms may be broken and/or new bonds formed.

Natural gas is not a compound, but a naturally occurring mixture of gaseous hydrocarbons consisting primarily (typically 97%) of methane. The chemical formula for methane, CH4, indicates that it is a compound, with one carbon atom bonding with four hydrogen atoms to create a methane compound. Natural gas/ methane used to be considered a clean-burning bridge fuel, an intermediate step between coal and renewables, to reduce emissions. Such a pleasant fantasy.

Atmospheric methane concentration has increased by about 160% since 1750, with the overwhelming percentage caused by human activity. It accounts for 20% of the total radiative forcing from all of the long-lived and globally mixed greenhouse gases, according to the 2021 Intergovernmental Panel on Climate Change report.

Radiative forcing = climate forcing = a climate science concept to quantify the change in energy balance in the Earth’s atmosphere caused by various factors, such as concentrations of greenhouse gases, aerosols, and changes in solar radiation. Technically, it is the change in the net = downward minus upward = radiative flux (expressed in W/m2) due to a change in an external driver of climate change. Both carbon dioxide (CO2) and methane (CH4) are examples of external drivers. Most of the atmosphere is made up of nitrogen (N2) in addition to about 21% oxygen (O2).

The International Energy Agency 2024 methane tracker chart (below) shows the countries with the worst methane emissions from their oil and gas industries. At the far end of the chart is Norway which releases 0.01% well to end use emissions.

Worst in class is the United States, which is also the world’s largest producer of gas and oil by volume. USA produces 943.2 Gm3 of natural gas, compared to second-place Russia’s 701.7 Gm3. Canada’s sixth-place produces 172.3 Gm3, and Norway’s 11th place produces 11.43 Gm3. The natural gas figures are from The CIA World Factbook, 2021. From the same source, one can read that USA produces considerably more oil than than second-place Russia, and third-place Saudi Arabia. Part of the reason for United States’ position is its unconventional oil and gas extraction with shale oil and fracking. Both lead to high methane emissions.

For over fifty years, I have been one of those lummoxes who refuses to use non-metric units. For example, most days I refuse to use figures like 13.5 million tons, or even the quasi-metric equivalent expressed in tonnes. 1 ton = ca. 907 kg. Instead, I convert the original quantity to something metric. In this case 12.25 Tg.

The use of metric prefixes dates back to the definition of kilogram after the French Revolution. Currently there are 24 prefixes in use, ranging from quecto- (q) = 10 -30 to quetta- (Q) = 1030. Quecto, ronto (10-27), ronna (1027) and quetta were added in 2022. Wikipedia has an enjoyable (at least for some of us) article about metric prefixes.

Methane is a gas, so it is necessary to understand how gasses are measured. It begins with pressure. The standard atmosphere (atm) is an American unit of pressure defined as 101325 Pa = 101.325 kPa. While the Pascal is an SI unit, most metric users will call the standard atmosphere 1 bar, more accurately 1.01325 bar. Both of these units refer to a standard pressure, approximately equal to Earth’s average atmospheric pressure at sea level.

Methane is a colourless and transparent gas. It has a boiling point of −161.5 °C = -258.7 °F (read: deadly cold) at a pressure = 1 atm. As a gas, it is flammable over a range of concentrations (5.4%–17%) in air at 1 atm.

Methane is also odorless. The smell of natural gas some people experience at various locations is caused by the addition of an odorant for safety purposes. Usually the odorant is tert-butylthiol = tert-butyl mercaptan (TBM) = (CH3)3CSH often abbreviated t-BuSH. Given a choice, most people prefer to smell an odorant, alerting them to a gas leakage, than to die in an unannounced gas explosion.

Methane does more damage in the atmosphere than carbon dioxide. Thus the twenty year global warming potential (GWP-20) = 81.2. That second number is used to convert the pollutant into a CO2 equivalent. In the case of methane, GWP-100 = 27.9, is significantly less because methane has a much shorter atmospheric lifetime than carbon dioxide. Thus, 12.25 Tg of methane has the effect of 994.7 Tg GWP-20 of CO2. Despite it not being totally correct, I am going to refer to this as its 1 Pg GWP-20 C02 equivalent. The GWP-100 value is 340 Tg. The world’s total carbon dioxide emissions are about 40 billion tons a year = ca 3.6 Pg/ year.

The most common chemical reactions of methane are combustion, steam reformation of synthetic gas and halogenation.

Combustion, is an exothermic redox chemical reaction between a fuel = reductant and an oxidant = most often atmospheric oxygen, that produces oxidized, often gaseous products. Redox = reduction–oxidation = chemical reaction where oxidation results in the loss of electrons while reduction results in a gain of electrons. Exothermic means the reaction releases energy from the system to its surroundings, usually in the form of heat.

CH4 + 2O2 → CO2 + 2H2O

Steam reforming to synthetic gas (syngas) is an endothermic process = a chemical/ physical process that requires/ absorbs heat from its surroundings. Endothermic is the opposite of exothermic. In this case, there is a need for energy ( 206 kJ/mol of methane) for the reaction to take place:

CH4 + H2O → CO + 3 H2

Halogenation is a chemical reaction that entails the introduction of one or more halogens into a compound. Halogens form a group (#17) a column of elements with similar characteristics, in the periodic table. They consist of five (or six) chemically related elements from top = lightest, to bottom = heaviest, atomic mass. Their symbols, atomic number = position and approximate atomic mass/ weight are: fluorine (F #9, 18.998), chlorine (Cl #17, 35.45), bromine (Br #35, 79.904), iodine (I #53, 126.9), and the radioactive elements astatine (At #85, 210) and tennessine (Ts #117, 294). Not all chemists accept tennessine as a halogen. The word halogen = salt former = salt maker. When halogens react with metals, they produce salts. Think: NaCl (sodium chloride) or common table salt. Sodium (Na) is a metal, chlorine (Cl) is a halogen.

CH4 + Cl2 → CH3Cl + HCl

Note: This is not the first chemical I have written about. Earlier, I wrote a weblog post about silicone.