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CAS No.: 7783-06-4
Registry name: Hydrogen sulphide
Chemical name: Dihydrogen sulphide
Synonyms, Trade names: Sulphuretted hydrogen, hydrogen sulphide
Chemical name (German): Schwefelwasserstoff, Hydrothionsäure
Chemical name (French): Acide sulfhydrique, gaz sulfhydrique, hydrogène sulfuré
Appearance: colourless, sweetish gas with offensive odour
BASIC CHEMICAL AND PHYSICAL DATA
Empirical formula: H2S
Rel. molecular mass: 34.08 g
Density: 1.54 g/l (gaseous)
Relative gas density: 1.19
Boiling point: -60°C
Melting point: -86°C
Vapour pressure: 18.1 bar at 20°C, 36.5 bar at 50 °C
Flash point: inflammable
Ignition temperature: 270°C
Explosion limits: 4.3 - 45.5 Vol%
Odour threshold: 0.01 ppm
Solvolysis/solubility: in water: 4.0 g/l at 20°C; 2.5 g/l at 40°C (approx.)
1 mg/m3 = 0.706 ppm
1 ppm = 1.416 mg/m3
ORIGIN AND USE
Technical H2S is usually subjected to further processing to form sulphur or sulphur dioxide which is required in large quantities in the production of sulphuric acid. Further uses are the production of metal sulphides, flotation processes, catalyst activation and poisoning.
Small quantities of H2S are quite common in the environment, e.g. dissolved in mineral springs, bodies of water, waste water and above all in natural gases. H2S is produced during the decomposition of sulphurous protein amino acids due to the influence of putrifactive and sulphur bacteria, for example in marshes, standing water and sewage treatment plants. It is encountered in various production processes in industry such as in the manufacture of chemical fibres, or in coking plants and refineries. The hydrogen sulphide resulting from the purification of natural gas is generally processed immediately to form sulphur.
Worldwide (1986) 14 x 106 t (as sulphur from H2S) [ULLMANN, 1989]
|Humans:||1.2-2.8 mg/l air (immediately lethal)||acc. Tab. Chemie, 1980|
|0.6 mg/l air (0.5-1 h, lethal)||acc. Tab. Chemie, 1980|
|0.1-0.15 mg/l air (several hours inhalation, poisonous)||acc. Tab. Chemie, 1980|
|Mouse||LD50 53 mg/kg, (sodium sulphide)||acc. DVGW, 1988|
|Fish||0.86 mg/l (toxic)||acc. HOMMEL, 1973|
|Char||LC 0.86 mg/l (24 h)||acc. DVGW, 1988|
|Carp||LC 6.3 mg/l (24 h)||acc. DVGW, 1988|
|Tench||LC 10 mg/l||acc. DVGW, 1988|
|Fish prey||1 mg/l (lethal)||acc. HOMMEL, 1973|
Humans/mammals: H2S is an irritant and a nerve and cell toxin. It may cause irritation of the eyes and respiratory organs, bronchial catarrh, nausea, malfunction of olfactory nerves at large concentrations, spasms, numbness and finally death due to respiratory paralysis. Hypersensitivity to H2S , once established, may remain for a long time. Illness caused by hydrogen sulphide at the workplace must be reported.
Plants: There is only slight damage to plants. The most sensitive edible plants are radishes, tomatoes, cucumbers, and soya beans.
H2S dissolves in water. The air over such solutions may be explosive. If H2S infiltrates into groundwater (bank filtrate) it becomes undrinkable.
When the gas expands, large quantities of cold mist rapidly form in addition to extremely poisonous, explosive mixtures. The mists are denser than air, creep along the ground and, when ignited, they may flash back over long distances.
The occurrence of hydrogen sulphide in soil is not so much the result of the application of sulphurous fertilisers, but rather a consequence of inexpert soil cultivation. Under anaerobic conditions, e.g. due to saturation and compaction of the soil, and in the presence of organic material (e.g. stubble) which is subject to rapid microbial decomposition, the reduction of sulphate and the mineralisation of organic sulphur compounds may cause the formation of hydrogen sulphide.
Degradation, decomposition products, half-life:
H2S is rapidly oxidised in the organism to form sulphate which is excreted.
|Medium/ acceptor||Sector||Country/ organ.||Status||Value||Cat.||Remarks||Source|
|Water:||Drinkw||CDN||0.05 mg/l||acc. DVGW, 1988|
|1)||DIN 2000||acc. DVGW, 1988|
|0.05 mg/l||acc. DVGW, 1988|
|5 mg/m3||mass flow > 50 g/h||acc. TA Luft, 1986|
|0.005 mg/m3||IW1||Long-time value||acc. KÜHN, BIRETT, 1983|
|0.01 mg/m3||IW2||Short-time value||acc. KÜHN, BIRETT, 1983|
|10 ml/m3||MAK||DFG, 1989|
|15 mg/m3||acc. TAB. CHEMIE, 1980|
|7 ml/m3||Skin resorption||acc. SORBE, 1988|
|10 mg/m3||Skin resorption||acc. SORBE, 1988|
|10 ml/m3||TWA||acc. SORBE, 1988|
|15 mg/m3||TWA||acc. SORBE, 1988|
|15 ml/m3||STEL||acc. SORBE, 1988|
|27 mg/m3||STEL||acc. SORBE, 1988|
1) The hydrogen-sulphide concentration level must be below the odour threshold.
|Haltern||D||10 µg/l||acc. DVGW, 1988|
The presence of hydrogen sulphide can be immediately noticed by its offensive odour. Nevertheless, chronic symptoms often occur (occupational disease). Therefore, the air at the workplace has to be monitored on a continuous basis.
Hydrogen sulphide must be kept away from waters since any water which comes into contact with it will be spoiled. Any emission of hydrogen sulphide into the atmosphere should be avoided.
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