Hydrogen sulfide a useful gas for human being as it finds its application in many chemical and industrial applications. The most common characteristics of H2S that links everyday experiences is its rotten-egg like foul odor at low concentrations (Holleman, Wiberg and Wiberg). It is a colorless and dense gas. However, at certain conditions, the gas might be very harmful for human and other animals. For example, at higher concentrations, it becomes highly toxic, corrosive and explosive (ACS). The threshold level for H2S is 10 ppm. Any concentration over 10 ppm can create problem for human health. The molar mas of the gas is 34.0809 grams/ mole. Its melting point is –82° C and boiling point is –60°C.
It has a chemical formula of ‘H2S’, which is why it is referred to as dihydrogen monosulfide, sour gas, sewer gas, stink damp or simply sulfureted hydrogen. It shows acidic and reducing properties. In analytical chemistry, it is used as a group reagent where it precipitates certain sulfides of metals in acidic medium (Mazumdar).
The sources of and Production of Hydrogen Sulfide H2S
Hydrogen sulfide may be produced arbitrarily in chemical laboratory and research and development labs. The laboratory production of hydrogen sulfide is done through the chemical reaction between the diluted sulfuric acid and the ferrous sulfide. The chemical reaction may be written as:
FeS + H2SO4 = FeSO4 + H2S
One mole of ferrous sulfide reacts with one mole of sulfuric acid to produce one mole of ferrous sulfate and one mole of hydrogen sulfide gas. Similarly, it may be produced through the chemical reaction of zinc sulfide and sulfuric acid or sodium by-hydrogen sulfide and hydrochloric acid. Chemical formulae are given below:
ZnS + H2SO4 = ZnSO4 + H2S
NaHS + HCL= NaCl+ H2S
Hydrogen sulfide is produced naturally in abundance, which is why it is almost unnecessary to produce in the industry. Any decaying organic matter can produce hydrogen sulfide through anaerobic digestion. Human activities also release large amount of hydrogen sulfide in the environment. Anaerobic and non-specific bacterial reduction from sulfate containing organic compounds and sulfates (Bhomick and Rao).
Crude petroleum, natural gases, hot springs of sulfur and volcanic gases are natural sources of hydrogen sulfide. Ground water is also a large source of hydrogen sulfide. Manure, coal pits and stagnant polluted waters are also natural sources of hydrogen sulfide gas. Sewerage sludge can produce hydrogen sulfide gas if they are left for a certain period of time. Human body also produces a small amount of the gas naturally and use it as a signaling molecule in the body. Hydrogen sulfide used in human body for signaling is also referred as the gasotransmitter (Bos, Goor and Joles). Only three gases including nitric oxide (NO) and carbon monoxide (CO) are used as the gasotransmitter in human body. However, the amount required to facilitate signaling activity is extremely low.
Many commercially available methods are present for producing hydrogen sulfide gas. Petroleum refineries produces a large amount hydrogen sulfide as a byproduct because they refine crude petroleum, a natural source of hydrogen sulfide (Skrtic). Purification of natural gases also releases a large amount of hydrogen sulfide gas. As a byproduct of Kraft pulp, paper manufacturing and carbon disulfide production process hydrogen sulfide is produced largely. Again, in the production of inorganic sulfides as well as sulfuric acid, huge amount of this gas is released as an intermediate product. It is evident that almost all types of industries that uses heating or boiling or distillation, produce hydrogen sulfide gas.
The gas is a byproduct in the agricultural and mining industry. In agriculture, the gas finds its application as a disinfectant, which is why it is produced in insecticide industry. In the mining industry, hydrogen sulfide is produced as a product of decomposition of xanthates. Xanthates starts decomposing when it comes in contact with the water. For this, mining laborer often suffer from hydrogen sulfide related toxicity. The reduction of sulfate and organo sulfur compounds releases hydrogen sulfide gas when they are reduced by the bacterium Desulphovibrio desulphurican. Furthermore, it is related to carboxyl sulfate (COS), dimethyl disulfide (CH3.S.S.CH3) and methane thiol (CH3SH).
As a natural and industrial byproduct, hydrogen sulfide finds its application in many production and manufacturing processes, but it possesses larger threats than it does goods to human and nature. To avoid hydrogen sulfide related toxicity and pollution, careful monitoring of industrial processes is essential. Control of natural processes like sewerage sludge production etc. can also help in reducing its harmful effect to the environment.
ACS. Hydrogen sulfide. 06 July 2015. <https://www.acs.org/content/acs/en/molecule-of-the-week/archive/h/hydrogen-sulfide.html>.
Bhomick, Parimal Chandra and Kaza Somasekhara Rao. “Sources And Effects of Hydrogen Sulfide.” Journal of Appliecable Chmeistry (2014): 914-918.
Bos, Eelke M, et al. “Hydrogen sulfide: physiological properties and therapeutic potential in ischaemia.” British Journal of Pharmacology (2015): 1479-1493.
Holleman, A. F., Egon Wiberg and Nils Wiberg. Inorganic Chemistry. Academic Press, 2001.
Mazumdar, Manik. Rudiments of Chemistry. Academic Publishers, 2006.
Skrtic, Lana. Hydrogen Sulfide, Oil and Gas, and People’s Health. Berkeley: Unversity of California, 2006.