Application of Potentiometric Titration in Determination of Mercaptan Sulfur Content in Oil

What is mercaptan sulfur in oil?

Mercaptans are a class of non-aromatic compounds containing sulfhydryl functional groups (-SH). The structure is equivalent to the replacement of oxygen in alcohols by sulfur, such as ethanol (commonly known as alcohol) CH3CH2OH and ethyl mercaptan CH3CH2SH.

There are a small amount of mercaptan compounds in petroleum products. The presence of mercaptan not only causes the oil to have an unpleasant smell, but also transforms into toxic and corrosive sulfur dioxide and sulfur trioxide during combustion, which is harmful to the elastic materials of the fuel system. It also corrodes the components of the fuel system, affecting the life of related machinery, such as automobile engines. Therefore, it is very important to control the mercaptan content in petroleum products.

The sulfur contained in mercaptan in oil is called mercaptan sulfur content. National standards mandate the mercaptan sulfur content in a series of oil products such as gasoline, diesel, kerosene, distillate fuel, and jet fuel.

So how to determine the content of mercaptan sulfur in oil?

Use Potentiometric Titrator to determine mercaptan sulfur content in oil

(1) Instrument: REX ZDJ-5B Automatic Potentiometric Titrator

(2) Electrodes: 216 type silver Electrode and 231-01 type pH glass electrode.

(3) Reagents: ultrapure water, 1-butanethiol, 1-heptanethiol, potassium iodide, concentrated nitric acid, isopropanol, sodium acetate, sodium sulfide, silver nitrate, etc.

(4) Sample: commercial gasoline; butane mercaptan standard solution

(5) The measurement process is as follows:

Electrode pretreatment ----- Standard solution----- Blank titration----- Sample Measurment.