Sour gas is

natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...

or any other gas containing significant amounts of hydrogen sulfide (H₂S). Natural gas is usually considered sour if there are more than 5.7

milligram The kilogram (also kilogramme) is the unit of mass in the International System of Units (SI), having the unit symbol kg. It is a widely used measure in science, engineering and commerce worldwide, and is often simply called a kilo colloquially. ...

s of H₂S per cubic meter of natural gas, which is equivalent to approximately 4 ppm by volume under standard temperature and pressure.NaturalGas.org website page
''Processing Natural Gas'' However, this threshold varies by country, state, or even agency or application. For instance, the

Texas Railroad Commission The Railroad Commission of Texas (RRC; also sometimes called the Texas Railroad Commission, TRC) is the state agency that regulates the oil and gas industry, gas utilities, pipeline safety, safety in the liquefied petroleum gas industry, and sur ...

considers a sour gas pipeline one that carries gas over 100 ppm by volume of H₂S. However, the

Texas Commission on Environmental Quality The Texas Commission on Environmental Quality (TCEQ) is the environmental agency for the state of Texas. The commission's headquarters are located at 12100 Park 35 Circle in Austin. The fourth largest environmental agency in the United States (an ...

has historically defined sour gas for upstream operations – which requires permitting, reporting, and possibly additional emission controls – as gas that contains more than 24 ppm by volume. Natural gas that does not contain significant amounts of hydrogen sulfide is called "sweet gas". Although the terms "

acid gas Acid gas is a particular typology of natural gas or any other gas mixture containing significant quantities of hydrogen sulfide (H2S), carbon dioxide (CO2), or similar acidic gases. A gas is determined to be acidic or not after it is mixed with w ...

" and "sour gas" are sometimes used interchangeably, strictly speaking, a sour gas is any gas that specifically contains hydrogen sulfide in significant amounts, whereas an acid gas is any gas that contains significant amounts of acidic gases such as

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...

(CO₂) or hydrogen sulfide. Thus, carbon dioxide by itself is an acid gas, not a sour gas. In addition to being

toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subs ...

, hydrogen sulfide in the presence of water also damages

piping Within industry, piping is a system of pipes used to convey fluids (liquids and gases) from one location to another. The engineering discipline of piping design studies the efficient transport of fluid. Industrial process piping (and accompa ...

and other equipment handling sour gas by

sulfide stress cracking Sulfide stress cracking (SSC) is a form of hydrogen embrittlement which is a cathodic cracking mechanism. It should not be confused with the term stress corrosion cracking which is an anodic cracking mechanism. Susceptible alloys, especially steel ...

. Natural gas typically contains several ppm of volatile sulfur compounds, but gas from one well in

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

is known to contain 90% hydrogen sulfide and others may have H₂S contents in the tens of percent range.

Methods for sweetening

Within

oil refineries An oil refinery or petroleum refinery is an industrial process plant where petroleum (crude oil) is transformed and refined into useful products such as gasoline (petrol), diesel fuel, asphalt base, fuel oils, heating oil, kerosene, lique ...

or natural gas processing plants, the removal of hydrogen sulfide and other

organosulfur compounds Organosulfur compounds are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur derivatives, e.g., saccharin. Nature abounds with organosulfur compounds—sulfu ...

is referred to as "sweetening". The sweetened products lacks the sour, foul odors of mercaptans and hydrogen sulfide. Before a raw natural gas containing hydrogen sulfide or carbon dioxide can be used, the raw gas must be treated to remove those impurities to acceptable levels, commonly by an amine treatment process.Energy Information Agency website page
''Natural Gas Processing: The Crucial Link Between Natural Gas Production and Its Transportation to Market'' The removed H₂S is most often subsequently converted to by-product elemental

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...

in a Claus process or it can be treated in a

wet sulfuric acid process The wet sulfuric acid process (WSA process) is a gas desulfurization process. After Danish company Haldor Topsoe introduced this technology in 1987, it has been recognized as a process for recovering sulfur from various process gases in the form ...

unit where the by-product is

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...

. Alternatively, the highly H₂S concentrated gas, the by-product of the amine treatment plant, can be recompressed by

gas compressor A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor. Compressors are similar to pumps: both increase the pressure on a fluid and both can tran ...

units specifically designed to handle highly toxic gas and injected back in the reservoir. In addition to utilizing an amine or Claus process, liquid

REDOX Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...

is becoming increasingly popular. Another product removed during sweetening is

carbonyl sulfide Carbonyl sulfide is the chemical compound with the linear formula OCS. It is a colorless flammable gas with an unpleasant odor. It is a linear molecule consisting of a carbonyl group double bonded to a sulfur atom. Carbonyl sulfide can be consi ...

.Georg Hammer, Torsten Lübcke, Roland Kettner, Mark R. Pillarella, Herta Recknagel, Axel Commichau, Hans-Joachim Neumann and Barbara Paczynska-Lahme "Natural Gas" in Ullmann's Encyclopedia of Industrial Chemistry, 2006, Wiley-VCH, Weinheim. {{doi, 10.1002/14356007.a17_073

References

Natural gas de:Saures Gas es:Gas amargo

Methods for sweetening

See also

References