In order to assist in detecting leaks, a minute amount of odorant is added to the otherwise colorless and almost odorless gas used by consumers.
Particular importance is the odorization of natural gas distributed to homes and industries: a substance called odorant that gives the gas the characteristic garlic odor; that allows you to feel in the air smell the presence of gas before they create dangerous conditions for explosiveness and toxicity.
For the odorizing gas numerous qualities are required, including high odorosity, highly recognizable smell, high miscibility in gas, low chemical reactivity with the pipe, low chemical reactivity with the gas and smell disappearing with burning.
Among the various substances made available by industrial chemistry, mercaptans have proven very effective; especially Ter-butyl mercaptan with a very intense and characteristic smell. 10 mg / Stm³ are enough, though it must be used in a mixture with other mercaptans to prevent freezing.
Very used is also a second substance of the chemical family of organic sulphides called tetrahydrothiophene, despite being classified as a toxic gas by current legislation: in this case it is sufficient 35 ÷ 40 mg for scenting effectively 1 Stm³ of methane.
The final years of the last decade got under way in Germany the use of sulfur-free odorants in order to address the problem of acid rain, composed essentially of methyl acrylate and ethyl acrylate, but to date the use in Italy is not permitted by law force.
The odorant is normally done at the sites where the gas is delivered by the company making the distribution conveyor; in such sites, before odorization, gas is filtered, preheated if necessary, decompressed and measured. However, they may be present installations of re-odorizing downstream of these sites, in order to achieve a level of odorization satisfactory.
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