Hydrogen sulfide is the chemical compound with the formula H
2S. It is a colorless chalcogen hydride gas with the characteristic foul odor of rotten eggs. It is very poisonous, corrosive, and flammable.
Hydrogen sulfide is often produced from the microbial breakdown of organic matter in the absence of oxygen gas, such as in swamps and sewers; this process is commonly known as anaerobic digestion which is done by sulfate-reducing microorganisms. H
2S also occurs in volcanic gases, natural gas, and in some sources of well water. The human body produces small amounts of H
2S and uses it as a signaling molecule.
Swedish chemist Carl Wilhelm Scheele is credited with having discovered hydrogen sulfide in 1777.
The British English spelling of this compound is hydrogen sulphide, but this spelling is not recommended by the International Union of Pure and Applied Chemistry (IUPAC) or the Royal Society of Chemistry.
|Systematic IUPAC name
3D model (JSmol)
|Molar mass||34.08 g·mol−1|
|Odor||Pungent, like that of rotten eggs|
|Density||1.363 g dm−3|
|Melting point||−82 °C (−116 °F; 191 K)|
|Boiling point||−60 °C (−76 °F; 213 K)|
|4 g dm−3 (at 20 °C)|
|Vapor pressure||1740 kPa (at 21 °C)|
Refractive index (nD)
|1.000644 (0 °C)|
Heat capacity (C)
|1.003 J K−1 g−1|
|206 J mol−1 K−1|
Std enthalpy of
|−21 kJ mol−1|
|Main hazards||Flammable and highly toxic|
|F+ T+ N|
|R-phrases (outdated)||R12, R26, R50|
|S-phrases (outdated)||(S1/2), S9, S16, S36, S38, S45, S61|
|Flash point||−82.4 °C (−116.3 °F; 190.8 K) |
|232 °C (450 °F; 505 K)|
|Lethal dose or concentration (LD, LC):|
LC50 (median concentration)
LCLo (lowest published)
|US health exposure limits (NIOSH):|
|C 20 ppm; 50 ppm [10-minute maximum peak]|
|C 10 ppm (15 mg/m3) [10-minute]|
IDLH (Immediate danger)
Related hydrogen chalcogenides
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Hydrogen sulfide is slightly denser than air; a mixture of H
2S and air can be explosive. Hydrogen sulfide burns in oxygen with a blue flame to form sulfur dioxide (SO
2) and water. In general, hydrogen sulfide acts as a reducing agent, especially in the presence of base, which forms SH−.
At high temperatures or in the presence of catalysts, sulfur dioxide reacts with hydrogen sulfide to form elemental sulfur and water. This reaction is exploited in the Claus process, an important industrial method to dispose of hydrogen sulfide.
Hydrogen sulfide is slightly soluble in water and acts as a weak acid (pKa = 6.9 in 0.01–0.1 mol/litre solutions at 18 °C), giving the hydrosulfide ion HS−
(also written SH−
). Hydrogen sulfide and its solutions are colorless. When exposed to air, it slowly oxidizes to form elemental sulfur, which is not soluble in water. The sulfide anion S2−
is not formed in aqueous solution.
Hydrogen sulfide reacts with metal ions to form metal sulfides, which are insoluble, often dark colored solids. Lead(II) acetate paper is used to detect hydrogen sulfide because it readily converts to lead(II) sulfide, which is black. Treating metal sulfides with strong acid often liberates hydrogen sulfide.
At pressures above 90 GPa (gigapascal), hydrogen sulfide becomes a metallic conductor of electricity. When cooled below a critical temperature this high-pressure phase exhibits superconductivity. The critical temperature increases with pressure, ranging from 23 K at 100 GPa to 150 K at 200 GPa. If hydrogen sulfide is pressurized at higher temperatures, then cooled, the critical temperature reaches 203 K (−70 °C), the highest accepted superconducting critical temperature as of 2015. By substituting a small part of sulfur with phosphorus and using even higher pressures, it has been predicted that it may be possible to raise the critical temperature to above 0 °C (273 K) and achieve room-temperature superconductivity.
Hydrogen sulfide is most commonly obtained by its separation from sour gas, which is natural gas with high content of H
2S. It can also be produced by treating hydrogen with molten elemental sulfur at about 450 °C. Hydrocarbons can serve as a source of hydrogen in this process.
Sulfate-reducing (resp. sulfur-reducing) bacteria generate usable energy under low-oxygen conditions by using sulfates (resp. elemental sulfur) to oxidize organic compounds or hydrogen; this produces hydrogen sulfide as a waste product.
This gas is also produced by heating sulfur with solid organic compounds and by reducing sulfurated organic compounds with hydrogen.
Water heaters can aid the conversion of sulfate in water to hydrogen sulfide gas. This is due to providing a warm environment sustainable for sulfur bacteria and maintaining the reaction which interacts between sulfate in the water and the water heater anode, which is usually made from magnesium metal.
Hydrogen sulfide can be generated in cells via enzymatic or non enzymatic pathway. H
2S in the body acts as a gaseous signaling molecule which is known to inhibit Complex IV of the mitochondrial electron transport chain which effectively reduces ATP generation and biochemical activity within cells. Three enzymes are known to synthesize H
2S: cystathionine γ-lyase (CSE), cystathionine β-synthetase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). These enzymes have been identified in a breadth of biological cells and tissues, and their activity has been observed to be induced by a number of disease states. It is becoming increasingly clear that H
2S is an important mediator of a wide range of cell functions in health and in disease. CBS and CSE are the main proponents of H
2S biogenesis, which follows the trans-sulfuration pathway. These enzymes are characterized by the transfer of a sulfur atom from methionine to serine to form a cysteine molecule. 3-MST also contributes to hydrogen sulfide production by way of the cysteine catabolic pathway. Dietary amino acids, such as methionine and cysteine serve as the primary substrates for the transulfuration pathways and in the production of hydrogen sulfide. Hydrogen sulfide can also be synthesized by non-enzymatic pathway, which is derived from proteins such as ferredoxins and Rieske proteins.
2S has been shown to be involved in physiological processes like vasoconstriction in animals, increasing seed germination and stress responses in plants. Hydrogen sulfide signaling is also innately intertwined with physiological processes that are known to be moderated by reactive oxygen species (ROS) and reactive nitrogen species (RNS). H
2S has been shown to interact with NO resulting in several different cellular effects, as well as the formation of a new signal called nitrosothiol. Hydrogen Sulfide is also known to increase the levels of glutathione which acts to reduce or disrupt ROS levels in cells. In these early days in the field of H
2S biochemistry and signaling there are more questions than answers.
The main use of hydrogen sulfide is as a precursor to elemental sulfur. Several organosulfur compounds are produced using hydrogen sulfide. These include methanethiol, ethanethiol, and thioglycolic acid.
Reversibly sodium sulfide in the presence of acids turns into hydrosulfides and hydrogen sulfide; this supplies hydrosulfides in organic solutions and is utilized in the production of thiophenol. 
For well over a century, hydrogen sulfide was important in analytical chemistry, in the qualitative inorganic analysis of metal ions. In these analyses, heavy metal (and nonmetal) ions (e.g., Pb(II), Cu(II), Hg(II), As(III)) are precipitated from solution upon exposure to H
2S. The components of the resulting precipitate redissolve with some selectivity, and are thus identified.
As indicated above, many metal ions react with hydrogen sulfide to give the corresponding metal sulfides. This conversion is widely exploited. For example, gases or waters contaminated by hydrogen sulfide can be cleaned with metals, by forming metal sulfides. In the purification of metal ores by flotation, mineral powders are often treated with hydrogen sulfide to enhance the separation. Metal parts are sometimes passivated with hydrogen sulfide. Catalysts used in hydrodesulfurization are routinely activated with hydrogen sulfide, and the behavior of metallic catalysts used in other parts of a refinery is also modified using hydrogen sulfide.
Scientists from the University of Exeter discovered that cell exposure to small amounts of hydrogen sulfide gas can prevent mitochondrial damage. When the cell is stressed with disease, enzymes are drawn into the cell to produce small amounts of hydrogen sulfide. This study could have further implications on preventing strokes, heart disease and arthritis.
Small amounts of hydrogen sulfide occur in crude petroleum, but natural gas can contain up to 90%. Volcanoes and some hot springs (as well as cold springs) emit some H
2S, where it probably arises via the hydrolysis of sulfide minerals, i.e. MS + H
2O → MO + H
2S. Hydrogen sulfide can be present naturally in well water, often as a result of the action of sulfate-reducing bacteria. Hydrogen sulfide is created by the human body in small doses through bacterial breakdown of proteins containing sulfur in the intestinal tract. It is also produced in the mouth (halitosis).
A portion of global H
2S emissions are due to human activity. By far the largest industrial source of H
2S is petroleum refineries: The hydrodesulfurization process liberates sulfur from petroleum by the action of hydrogen. The resulting H
2S is converted to elemental sulfur by partial combustion via the Claus process, which is a major source of elemental sulfur. Other anthropogenic sources of hydrogen sulfide include coke ovens, paper mills (using the Kraft process), tanneries and sewerage. H
2S arises from virtually anywhere where elemental sulfur comes in contact with organic material, especially at high temperatures. Depending on environmental conditions, it is responsible for deterioration of material through the action of some sulfur oxidizing microorganisms. It is called biogenic sulfide corrosion.
In 2011 it was reported that increased concentration of H
2S, possibly due to oil field practices, was observed in the Bakken formation crude and presented challenges such as "health and environmental risks, corrosion of wellbore, added expense with regard to materials handling and pipeline equipment, and additional refinement requirements".
Besides living near a gas and oil drilling operations, ordinary citizens can be exposed to hydrogen sulfide by being near waste water treatment facilities, landfills and farms with manure storage. Exposure occurs through breathing contaminated air or drinking contaminated water.
Hydrogen sulfide is commonly found in raw natural gas and biogas. It is typically removed by amine gas treating technologies. In such processes, the hydrogen sulfide is first converted to an ammonium salt, whereas the natural gas is unaffected.
The bisulfide anion is subsequently regenerated by heating of the amine sulfide solution. Hydrogen sulfide generated in this process is typically converted to elemental sulfur using the Claus Process.
Hydrogen sulfide is a highly toxic and flammable gas (flammable range: 4.3–46%). Being heavier than air, it tends to accumulate at the bottom of poorly ventilated spaces. Although very pungent at first, it quickly deadens the sense of smell, so victims may be unaware of its presence until it is too late. For safe handling procedures, a hydrogen sulfide safety data sheet (SDS) should be consulted.
Hydrogen sulfide is a broad-spectrum poison, meaning that it can poison several different systems in the body, although the nervous system is most affected. The toxicity of H
2S is comparable with that of carbon monoxide. It binds with iron in the mitochondrial cytochrome enzymes, thus preventing cellular respiration.
Since hydrogen sulfide occurs naturally in the body, the environment, and the gut, enzymes exist to detoxify it. At some threshold level, believed to average around 300–350 ppm, the oxidative enzymes become overwhelmed. Many personal safety gas detectors, such as those used by utility, sewage and petrochemical workers, are set to alarm at as low as 5 to 10 ppm and to go into high alarm at 15 ppm. Detoxification is effected by oxidation to sulfate, which is harmless. Hence, low levels of hydrogen sulfide may be tolerated indefinitely.
Diagnostic of extreme poisoning by H
2S is the discolouration of copper coins in the pockets of the victim. Treatment involves immediate inhalation of amyl nitrite, injections of sodium nitrite, or administration of 4-dimethylaminophenol in combination with inhalation of pure oxygen, administration of bronchodilators to overcome eventual bronchospasm, and in some cases hyperbaric oxygen therapy (HBOT). HBOT has clinical and anecdotal support.
Exposure to lower concentrations can result in eye irritation, a sore throat and cough, nausea, shortness of breath, and fluid in the lungs (pulmonary edema). These effects are believed to be due to the fact that hydrogen sulfide combines with alkali present in moist surface tissues to form sodium sulfide, a caustic. These symptoms usually go away in a few weeks.
Long-term, low-level exposure may result in fatigue, loss of appetite, headaches, irritability, poor memory, and dizziness. Chronic exposure to low level H
2S (around 2 ppm) has been implicated in increased miscarriage and reproductive health issues among Russian and Finnish wood pulp workers, but the reports have not (as of circa 1995) been replicated.
Short-term, high-level exposure can induce immediate collapse, with loss of breathing and a high probability of death. If death does not occur, high exposure to hydrogen sulfide can lead to cortical pseudolaminar necrosis, degeneration of the basal ganglia and cerebral edema. Although respiratory paralysis may be immediate, it can also be delayed up to 72 hours.
Hydrogen sulfide was used by the British Army as a chemical weapon during World War I. It was not considered to be an ideal war gas, but, while other gases were in short supply, it was used on two occasions in 1916.
In 1975, a hydrogen sulfide release from an oil drilling operation in Denver City, Texas, killed nine people and caused the state legislature to focus on the deadly hazards of the gas. State Representative E L Short took the lead in endorsing an investigation by the Texas Railroad Commission and urged that residents be warned "by knocking on doors if necessary" of the imminent danger stemming from the gas. One may die from the second inhalation of the gas, and a warning itself may be too late.
On September 2, 2005, a leak in the propeller room of a Royal Caribbean Cruise Liner docked in Los Angeles resulted in the deaths of 3 crewmen due to a sewage line leak. As a result, all such compartments are now required to have a ventilation system.
In 2014, levels of hydrogen sulfide as high as 83 ppm have been detected at a recently built mall in Thailand called Siam Square One at the Siam Square area. Shop tenants at the mall reported health complications such as sinus inflammation, breathing difficulties and eye irritation. After investigation it was determined that the large amount of gas originated from imperfect treatment and disposal of waste water in the building.
In November 2014, a substantial amount of hydrogen sulfide gas shrouded the central, eastern and southeastern parts of Moscow. Residents living in the area were urged to stay indoors by the emergencies ministry. Although the exact source of the gas was not known, blame had been placed on a Moscow oil refinery.
In June 2016, a mother and her daughter were found deceased in their still-running Porsche Cayenne SUV against a guardrail on Florida's Turnpike, initially thought to be victims of carbon monoxide poisoning. Their deaths remained unexplained as the medical examiner waited for results of toxicology tests on the victims, until urine tests revealed that hydrogen sulfide was the cause of death. A report from the Orange-Osceola Medical Examiner’s Office indicated that toxic fumes came from the Porsche’s battery, located under the front passenger seat.
In January 2017, three utility workers in Key Largo, Florida, died one by one within seconds of descending into a narrow space beneath a manhole cover to check a section of paved street, the hole was filled with hydrogen sulfide and methane gas created from years of rotted vegetation. In an attempt to save the men, a firefighter who entered the hole without his air tank (because he could not fit through the hole with it) collapsed within seconds and had to be rescued by a colleague. The firefighter was airlifted to Jackson Memorial Hospital and later recovered.
The gas, produced by mixing certain household ingredients, was used in a suicide wave in 2008 in Japan. The wave prompted staff at Tokyo's suicide prevention center to set up a special hot line during "Golden Week", as they received an increase in calls from people wanting to kill themselves during the annual May holiday.
As of 2010, this phenomenon has occurred in a number of US cities, prompting warnings to those arriving at the site of the suicide. These first responders, such as emergency services workers or family members are at risk of death from inhaling lethal quantities of the gas, or by fire. Local governments have also initiated campaigns to prevent such suicides.
In the absence of oxygen, sulfur-reducing and sulfate-reducing bacteria derive energy from oxidizing hydrogen or organic molecules by reducing elemental sulfur or sulfate to hydrogen sulfide. Other bacteria liberate hydrogen sulfide from sulfur-containing amino acids; this gives rise to the odor of rotten eggs and contributes to the odor of flatulence.
As organic matter decays under low-oxygen (or hypoxic) conditions (such as in swamps, eutrophic lakes or dead zones of oceans), sulfate-reducing bacteria will use the sulfates present in the water to oxidize the organic matter, producing hydrogen sulfide as waste. Some of the hydrogen sulfide will react with metal ions in the water to produce metal sulfides, which are not water-soluble. These metal sulfides, such as ferrous sulfide FeS, are often black or brown, leading to the dark color of sludge.
Several groups of bacteria can use hydrogen sulfide as fuel, oxidizing it to elemental sulfur or to sulfate by using dissolved oxygen, metal oxides (e.g., Fe oxyhydroxides and Mn oxides), or nitrate as electron acceptors.
The purple sulfur bacteria and the green sulfur bacteria use hydrogen sulfide as an electron donor in photosynthesis, thereby producing elemental sulfur. (In fact, this mode of photosynthesis is older than the mode of cyanobacteria, algae, and plants, which uses water as electron donor and liberates oxygen.)
The biochemistry of hydrogen sulfide is a key part of the chemistry of the iron-sulfur world. In this model of the origin of life on Earth, geologically produced hydrogen sulfide is postulated as an electron donor driving the reduction of carbon dioxide.
In the deep sea, hydrothermal vents and cold seeps with high levels of hydrogen sulfide are home to a number of extremely specialized lifeforms, ranging from bacteria to fish. Because of the absence of light at these depths, these ecosystems rely on chemosynthesis rather than photosynthesis.
Freshwater springs rich in hydrogen sulfide are mainly home to invertebrates, but also include a small number of fish: Cyprinodon bobmilleri (a pupfish from Mexico), Limia sulphurophila (a poeciliid from the Dominican Republic), Gambusia eurystoma (a poeciliid from Mexico), and a few Poecilia (poeciliids from Mexico). Invertebrates and microorganisms in some cave systems, such as Movile Cave, are adapted to high levels of hydrogen sulfide.
Hydrogen sulfide has been implicated in several mass extinctions that have occurred in the Earth's past. In particular, a buildup of hydrogen sulfide in the atmosphere may have caused the Permian-Triassic extinction event 252 million years ago.
Organic residues from these extinction boundaries indicate that the oceans were anoxic (oxygen-depleted) and had species of shallow plankton that metabolized H
2S. The formation of H
2S may have been initiated by massive volcanic eruptions, which emitted carbon dioxide and methane into the atmosphere, which warmed the oceans, lowering their capacity to absorb oxygen that would otherwise oxidize H
2S. The increased levels of hydrogen sulfide could have killed oxygen-generating plants as well as depleted the ozone layer, causing further stress. Small H
2S blooms have been detected in modern times in the Dead Sea and in the Atlantic ocean off the coast of Namibia.
Both had red skin and rash-like symptoms, and had vomited, sources said.
Porsche Cayennes, along with a few other vehicles, have their batteries in the passenger compartment.
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.The term/s acid gas and sour gas are often incorrectly treated as synonyms. Strictly speaking, a sour gas is any gas that specifically contains hydrogen sulfide in significant amounts; an acid gas is any gas that contains significant amounts of acidic gases such as carbon dioxide (CO2) or hydrogen sulfide. Thus, carbon dioxide by itself is an acid gas but not a sour gas.Ammonium hydrosulfide
Ammonium hydrosulfide is the chemical compound with the formula (NH4)HS.Autotroph
An autotroph or primary producer, is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) from simple substances present in its surroundings, generally using energy from light (photosynthesis) or inorganic chemical reactions (chemosynthesis). They are the producers in a food chain, such as plants on land or algae in water (in contrast to heterotrophs as consumers of autotrophs). They do not need a living source of energy or organic carbon. Autotrophs can reduce carbon dioxide to make organic compounds for biosynthesis and also create a store of chemical energy. Most autotrophs use water as the reducing agent, but some can use other hydrogen compounds such as hydrogen sulfide. Some autotrophs, such as green plants and algae, are phototrophs, meaning that they convert electromagnetic energy from sunlight into chemical energy in the form of reduced carbon.
Autotrophs can be photoautotrophs or chemoautotrophs. Phototrophs use light as an energy source, while chemotrophs use electron donors as a source of energy, whether from organic or inorganic sources; however in the case of autotrophs, these electron donors come from inorganic chemical sources. Such chemotrophs are lithotrophs. Lithotrophs use inorganic compounds, such as hydrogen sulfide, elemental sulfur, ammonium and ferrous iron, as reducing agents for biosynthesis and chemical energy storage. Photoautotrophs and lithoautotrophs use a portion of the ATP produced during photosynthesis or the oxidation of inorganic compounds to reduce NADP+ to NADPH to form organic compounds.Biogenic sulfide corrosion
Biogenic sulfide corrosion is a bacterially mediated process of forming hydrogen sulfide gas and the subsequent conversion to sulfuric acid that attacks concrete and steel within wastewater environments. The hydrogen sulfide gas is biochemically oxidized in the presence of moisture to form sulfuric acid. The effect of sulfuric acid on concrete and steel surfaces exposed to severe wastewater environments can be devastating. In the USA alone, corrosion is causing sewer asset losses estimated at
around $14 billion per year. This cost is expected to increase as the aging infrastructure continues to fail.Bismuth sulfite agar
Bismuth sulfite agar is a type of agar media used to isolate Salmonella species. It uses glucose as a primary source of carbon. BLBG and bismuth stop gram-positive growth. Bismuth sulfite agar tests the ability to use ferrous sulfate and convert it to hydrogen sulfide.
Bismuth sulfite agar typically contains (w/v):
1.6% bismuth sulfite Bi2(SO3)3
1.0% pancreatic digest of casein
1.0% pancreatic digest of animal tissue
1.0% beef extract
0.8% dibasic sodium phosphate
0.06% ferrous sulfate • 7 water
pH adjusted to 7.7 at 25 °CThis medium is boiled for sterility, not autoclaved.Chemosynthesis
In biochemistry, chemosynthesis is the biological conversion of one or more carbon-containing molecules (usually carbon dioxide or methane) and nutrients into organic matter using the oxidation of inorganic compounds (e.g., hydrogen gas, hydrogen sulfide) or methane as a source of energy, rather than sunlight, as in photosynthesis. Chemoautotrophs, organisms that obtain carbon through chemosynthesis, are phylogenetically diverse, but also groups that include conspicuous or biogeochemically-important taxa include the sulfur-oxidizing gamma and epsilon proteobacteria, the Aquificae, the methanogenic archaea and the neutrophilic iron-oxidizing bacteria.
Many microorganisms in dark regions of the oceans use chemosynthesis to produce biomass from single carbon molecules. Two categories can be distinguished. In the rare sites at which hydrogen molecules (H2) are available, the energy available from the reaction between CO2 and H2 (leading to production of methane, CH4) can be large enough to drive the production of biomass. Alternatively, in most oceanic environments, energy for chemosynthesis derives from reactions in which substances such as hydrogen sulfide or ammonia are oxidized. This may occur with or without the presence of oxygen.
Many chemosynthetic microorganisms are consumed by other organisms in the ocean, and symbiotic associations between chemosynthesizers and respiring heterotrophs are quite common. Large populations of animals can be supported by chemosynthetic secondary production at hydrothermal vents, methane clathrates, cold seeps, whale falls, and isolated cave water.
It has been hypothesized that chemosynthesis may support life below the surface of Mars, Jupiter's moon Europa, and other planets. Chemosynthesis may have also been the first type of metabolism that evolved on Earth, leading the way for cellular respiration and photosynthesis to develop later.Claus process
The Claus process is the most significant gas desulfurizing process, recovering elemental sulfur from gaseous hydrogen sulfide. First patented in 1883 by the chemist Carl Friedrich Claus, the Claus process has become the industry standard. C. F. Claus was born in Kassel in the German State of Hessen in 1827, and studied chemistry in Marburg before he emigrated to England in 1852. Claus died in London in the year 1900.The multi-step Claus process recovers sulfur from the gaseous hydrogen sulfide found in raw natural gas and from the by-product gases containing hydrogen sulfide derived from refining crude oil and other industrial processes. The by-product gases mainly originate from physical and chemical gas treatment units (Selexol, Rectisol, Purisol and amine scrubbers) in refineries, natural gas processing plants and gasification or synthesis gas plants. These by-product gases may also contain hydrogen cyanide, hydrocarbons, sulfur dioxide or ammonia.
Gases with an H2S content of over 25% are suitable for the recovery of sulfur in straight-through Claus plants while alternate configurations such as a split-flow set up or feed and air preheating can be used to process leaner feeds.Hydrogen sulfide produced, for example, in the hydro-desulfurization of refinery naphthas and other petroleum oils, is converted to sulfur in Claus plants. The reaction proceeds in two steps:
2 H2S +3 O2 → 2 SO2 + 2 H2O
4 H2S +2 SO2 → 3 S2 + 4 H2OThe vast majority of the 64,000,000 tonnes of sulfur produced worldwide in 2005 was byproduct sulfur from refineries and other hydrocarbon processing plants. Sulfur is used for manufacturing sulfuric acid, medicine, cosmetics, fertilizers and rubber products. Elemental sulfur is used as fertilizer and pesticide.Hydrodesulfurization
Hydrodesulfurization (HDS) is a catalytic chemical process widely used to remove sulfur (S) from natural gas and from refined petroleum products, such as gasoline or petrol, jet fuel, kerosene, diesel fuel, and fuel oils. The purpose of removing the sulfur, and creating products such as ultra-low-sulfur diesel, is to reduce the sulfur dioxide (SO2) emissions that result from using those fuels in automotive vehicles, aircraft, railroad locomotives, ships, gas or oil burning power plants, residential and industrial furnaces, and other forms of fuel combustion.
Another important reason for removing sulfur from the naphtha streams within a petroleum refinery is that sulfur, even in extremely low concentrations, poisons the noble metal catalysts (platinum and rhenium) in the catalytic reforming units that are subsequently used to upgrade the octane rating of the naphtha streams.
The industrial hydrodesulfurization processes include facilities for the capture and removal of the resulting hydrogen sulfide (H2S) gas. In petroleum refineries, the hydrogen sulfide gas is then subsequently converted into byproduct elemental sulfur or sulfuric acid (H2SO4). In fact, the vast majority of the 64,000,000 metric tons of sulfur produced worldwide in 2005 was byproduct sulfur from refineries and other hydrocarbon processing plants.An HDS unit in the petroleum refining industry is also often referred to as a hydrotreater.Hydrogen sulfide sensor
A hydrogen sulfide sensor or H2S sensor is a gas sensor for the measurement of hydrogen sulfide.In a laboratory, hydrogen sulphide is prepared by the action of dilute sulphuric acid on iron sulphide.
FeS(s)+H2SO4(aq) = FeSO4(aq) + H2S(g)Concentrated sulphuric acid and nitric acid cannot be used for this process as they oxidise hydrogen sulphide to sulphur. A Woulf's bottle is fitted with a thistle funnel and a delivery tube. Diluted H2SO4 is run down the funnel so as to cover the iron sulphide placed at bottom of the bottle. When iron sulphide reacts with diluted sulphuric acid, hydrogen sulphide is formed which is collected in the gas jar by upward displacement of air.Natural-gas processing
Natural-gas processing is a complex industrial process designed to clean raw natural gas by separating impurities and various non-methane hydrocarbons and fluids to produce what is known as pipeline quality dry natural gas.Natural-gas processing begins at the well head. The composition of the raw natural gas extracted from producing wells depends on the type, depth, and location of the underground deposit and the geology of the area. Oil and natural gas are often found together in the same reservoir. The natural gas produced from oil wells is generally classified as associated-dissolved, meaning that the natural gas is associated with or dissolved in crude oil. Natural gas production absent any association with crude oil is classified as “non-associated.” In 2009, 89 percent of U.S. wellhead production of natural gas was non-associated.Natural-gas processing plants purify raw natural gas by removing common contaminants such as water, carbon dioxide (CO2) and hydrogen sulfide (H2S). Some of the substances which contaminate natural gas have economic value and are further processed or sold. A fully operational plant delivers pipeline-quality dry natural gas that can be used as fuel by residential, commercial and industrial consumers.Potassium hydrosulfide
Potassium hydrosulfide is the inorganic compound with the formula KHS. This colourless salt consists of the cation K+ and the bisulfide anion [SH]−. It is the product of the half-neutralization of hydrogen sulfide with potassium hydroxide. The compound is used in the synthesis of some organosulfur compounds. It is prepared by neutralizing aqueous KOH with H2S. Aqueous solutions of potassium sulfide consist of a mixture of potassium hydrosulfide and potassium hydroxide.
The structure of the potassium hydrosulfide resembles that for potassium chloride. Their structure is however complicated by the non-spherical symmetry of the SH− anions, but these tumble rapidly in the solid high temperatures.Addition of sulfur gives dipotassium pentasulfide.Sodium hydrosulfide
Sodium hydrosulfide is the chemical compound with the formula NaHS. This compound is the product of the half-neutralization of hydrogen sulfide (H2S) with sodium hydroxide. NaHS is a useful reagent for the synthesis of organic and inorganic sulfur compounds, sometimes as a solid reagent, more often as an aqueous solution. Solid NaHS is colorless, and typically smells like H2S owing to hydrolysis by atmospheric moisture. In contrast with sodium sulfide (Na2S), which is insoluble in organic solvents, NaHS, being a 1:1 electrolyte, is more soluble. Alternatively, in place of NaHS, H2S can be treated with an organic amine to generate an ammonium salt. Solutions of HS− are sensitive to oxygen, converting mainly to polysulfides, indicated by the appearance of yellow.Sour gas
Sour gas is natural gas or any other gas containing significant amounts of hydrogen sulfide (H2S).
Natural gas is usually considered sour if there are more than 5.7 milligrams of H2S per cubic meter of natural gas, which is equivalent to approximately 4 ppm by volume under standard temperature and pressure. However, this threshold varies by country, state, or even agency or application. For instance, the Texas Railroad Commission considers a sour gas pipeline one that carries gas over 100 ppm by volume of H2S. However, the Texas Commission on Environmental Quality 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' 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 (CO2) or hydrogen sulfide. Thus, carbon dioxide by itself is an acid gas, not a sour gas. In addition to being toxic, hydrogen sulfide in the presence of water also damages piping and other equipment handling sour gas by sulfide stress cracking. Natural gas typically contains several ppm of volatile sulfur compounds, but gas from one well in Canada is known to contain 90% hydrogen sulfide and others may have H2S contents in the tens of percent range.Sulfanyl
Sulfanyl (HS•), also known as the mercapto radical, hydrosulfide radical, or hydridosulfur, is a simple radical molecule consisting of one hydrogen and one sulfur atom. The radical appears in metabolism in organisms as H2S is detoxified. Sulfanyl is one of the top three sulfur-containing gasses in gas giants such as Jupiter and is very likely to be found in brown dwarfs and cool stars. It was originally discovered by Margaret N. Lewis and John U. White at the University of California in 1939. They observed molecular absorption bands around 325 nm belonging to the system designated by 2Σ+ ← 2Πi. They generated the radical by means of a radio frequency discharge in hydrogen sulfide. HS• is formed during the degradation of hydrogen sulfide in the atmosphere of the Earth. This may be a deliberate action to destroy odours or a natural phenomenon.The organic analogue of sulfanyl is thiyl radical with the formula RS., where R = alkyl or aryl.Sulfide
Sulfide (British English sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. Sulfide also refers to chemical compounds large families of inorganic and organic compounds, e.g. lead sulfide and dimethyl sulfide. Hydrogen sulfide (H2S) and bisulfide (SH-) are the conjugate acids of sulfide.Sulfite reductase
Sulfite reductases (EC 18.104.22.168) are enzymes that participate in sulfur metabolism. They catalyze the reduction of sulfite to hydrogen sulfide and water. Electrons for the reaction are provided by a dissociable molecule of either NADPH, bound flavins, or ferredoxins.
Sulfite reductases, which belong to the oxidoreductase family, are found in archaea, bacteria, fungi, and plants. They are grouped as either assimilatory or dissimilatory sulfite reductases depending on their function, their spectroscopic properties, and their catalytic properties. This enzyme participates in selenoamino acid metabolism and sulfur assimilation. It employs two covalently coupled cofactors - an iron sulfur cluster and a siroheme - which deliver electrons to the substrate via this coupling.
The systematic name of this enzyme class is hydrogen-sulfide:acceptor oxidoreductase. Other names in common use include assimilatory sulfite reductase, assimilatory-type sulfite reductase, and hydrogen-sulfide:(acceptor) oxidoreductase.Sulfur
Sulfur or sulphur is a chemical element with 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 S8. Elemental sulfur is a bright yellow, crystalline solid at room temperature.
Sulfur is the tenth most common element by mass in the universe, and the fifth most common on Earth. Though sometimes found in pure, native form, sulfur on Earth usually occurs as sulfide and sulfate minerals. Being abundant in native form, sulfur was known in ancient times, being mentioned for its uses in ancient India, ancient Greece, China, and Egypt. In the Bible, sulfur is called brimstone, which means "burning stone". Today, almost all elemental sulfur is produced as a byproduct of removing sulfur-containing contaminants from natural gas and petroleum. The greatest commercial use of the element is the production of sulfuric acid for sulfate and phosphate fertilizers, and other chemical processes. The element sulfur is used in matches, insecticides, and fungicides. Many sulfur compounds are odoriferous, and the smells of odorized natural gas, skunk scent, grapefruit, and garlic are due to organosulfur compounds. Hydrogen sulfide gives the characteristic odor to rotting eggs and other biological processes.
Sulfur is an essential element for all life, but almost always in the form of organosulfur compounds or metal sulfides. Three amino acids (cysteine, cystine, and methionine) and two vitamins (biotin and thiamine) are organosulfur compounds. Many cofactors also contain sulfur including glutathione and thioredoxin and iron–sulfur proteins. Disulfides, S–S bonds, confer mechanical strength and insolubility of the protein keratin, found in outer skin, hair, and feathers. Sulfur is one of the core chemical elements needed for biochemical functioning and is an elemental macronutrient for all living organisms.Sulfur cycle
The sulfur cycle is the collection of processes by which sulfur moves to and from rock, waterways and living systems. Such biogeochemical cycles are important in geology because they affect many minerals. Biochemical cycles are also important for life because sulfur is an essential element, being a constituent of many proteins and cofactors.
Steps of the sulfur cycle are:
Mineralization of organic sulfur into inorganic forms, such as hydrogen sulfide (H2S), elemental sulfur, as well as sulfide minerals.
Oxidation of hydrogen sulfide, sulfide, and elemental sulfur (S) to sulfate (SO42−).
Reduction of sulfate to sulfide.
Incorporation of sulfide into organic compounds (including metal-containing derivatives).
These are often termed as follows:
Assimilative sulfate reduction (see also sulfur assimilation) in which sulfate (SO42−) is reduced by plants, fungi and various prokaryotes. The oxidation states of sulfur are +6 in sulfate and –2 in R–SH.
Desulfurization in which organic molecules containing sulfur can be desulfurized, producing hydrogen sulfide gas (H2S, oxidation state = –2). An analogous process for organic nitrogen compounds is deamination.
Oxidation of hydrogen sulfide produces elemental sulfur (S8), oxidation state = 0. This reaction occurs in the photosynthetic green and purple sulfur bacteria and some chemolithotrophs. Often the elemental sulfur is stored as polysulfides.
Oxidation in elemental sulfur by sulfur oxidizers produces sulfate.
Dissimilative sulfur reduction in which elemental sulfur can be reduced to hydrogen sulfide.
Dissimilative sulfate reduction in which sulfate reducers generate hydrogen sulfide from sulfate.Thiosulfuric acid
Thiosulfuric acid is a sulfur oxoacid. The acid cannot be made by acidifying aqueous thiosulfate salt solutions as the acid readily decomposes in water. The decomposition products can include sulfur, sulfur dioxide, hydrogen sulfide, polysulfanes, sulfuric acid and polythionates, depending on the exact reaction conditions. Anhydrous methods of producing the acid were developed by Carol Schmidt:
H2S + SO3 → H2S2O3·n Et2O (in diethyl ether at −78 °C)
Na2S2O3 + 2 HCl → 2 NaCl + H2S2O3·2Et2O (in diethyl ether at −78 °C)
HSO3Cl + H2S → HCl + H2S2O3 (low temperature)The anhydrous acid also decomposes below −5 °C:
H2S2O3 → H2S + SO3The S-acid isomer is believed to be more stable than the O-acid isomer based on Hartree–Fock/ab initio calculations with a 6-311 G** basis set and MP2 to MP4 refinements. There is another isomeric form, a white crystalline adduct of hydrogen sulfide and sulfur trioxide, H2S·SO3, which can also be prepared at low temperature.
|Alkali metal hydrides|
Lithium hydride, LiH
ionic metal hydride
Left (gas phase): BeH2
covalent metal hydride
Right: (BeH2)n (solid phase)
polymeric metal hydride
Borane and diborane
Left: BH3 (special conditions), covalent metalloid hydride
Right: B2H6 (standard conditions), dimeric metalloid hydride
covalent nonmetal hydride
covalent nonmetal hydride
covalent nonmetal hydride
Hydrogen fluoride, HF
covalent nonmetal hydride
|Alkaline earth hydrides|
|Group 13 hydrides|
|Group 14 hydrides|
|Transition metal hydrides|