Mercaptan sulfur – term used in determining mercaptans concentration and based on counting elemental sulfur. Mercaptan sulfur is present across the entire spectrum of hydrocarbons: natural gas, liquefied petroleum gas, gasoline fraction, kerosene fraction, etc.
In natural and liquefied petroleum gases concentration of mercaptan sulfur is determined by chromatography or potentiometric titration. In liquid hydrocarbons mercaptan sulfur is determined mainly by potentiometric titration.
The only mercaptan sulfur in natural gas is methyl mercaptan (methanethiol) – CH3SH, in liquefied petroleum gases – methyl and ethyl mercaptans (CH3SH and C2H5SH). Increasing molecular weight of hydrocarbons (gasoline, kerosene, diesel fractions, etc.) the molecular weight of mercaptan sulfur increases accordingly.
Mercaptans are corrosive compounds with a specific unpleasant smell. The maximum permissible concentration (MPC) of methyl mercaptan is 1,0 • 10-4 mg/m3, ethyl mercaptan is 3 • 10-5 mg/m3. Therefore, to detect gas leakage as an odorant mainly used light (C1-C3) mercaptans.
In Russia, light mercaptans are produced at the Gas processing plant in Orenburg. The content of mercaptan sulfur in gases is limited. For propane, butane or a mixture thereof mercaptan sulfur concentration in accordance with GOST 22985 must not exceed 0.01%wt.