Ferrous sulfide is a product of corrosion between sulfur and its sulfides in oil and iron and its oxides. The sulfur in these oil products mainly comes from crude oil (usually crude oil with a sulfur content below 0.1% is called ultra-low sulfur crude oil, such as Daqing crude oil in China, crude oil with a sulfur content of 0.1-0.5% is called low sulfur crude oil, crude oil with a sulfur content of 0.5-2% is called sulfur-containing crude oil, and crude oil with a sulfur content greater than 2% is called high sulfur crude oil, such as Shengli crude oil and Middle East crude oil), as well as some additives in the crude oil processing process (such as the regeneration process of hydrogenation catalysts such as molybdenum sulfide and cobalt sulfide to produce SO2, which reacts with CO when burning off carbon deposits, producing corrosive elemental sulfur).
According to the action of sulfides on metals, they can be divided into two categories: active sulfur and non active sulfur. This classification method is relative. Active sulfur has high corrosion activity and can directly react with metals to cause corrosion, such as elemental sulfur, hydrogen sulfide (H2S), and mercaptan (R-SH); Non active sulfur refers to sulfides that typically do not directly react with metals, such as sulfides (RSR ′), disulfide compounds (RSSR ′), cyclic sulfides, alkylalunite, thiophene, etc. Non active sulfur as a component
For monomers, they cannot directly react with metals, but in the catalytic cracking reaction of crude oil refining, these so-called non active sulfur organic sulfides will decompose and form active sulfur such as S and H2S. These active sulfur will react with iron or iron compounds under different conditions to form ferrous sulfide or other sulfides of iron.
At present, the solvent used in the device is proprietary to the patent holder, but its main component is still sulfolane, also known as tetrahydrothiophene sulfone, with a molecular formula of C4H8O2S and a molecular weight of 120.17, which belongs to sulfur-containing sulfides.
In daily production, the decomposition rate of sulfolane solvent is relatively slow below 220 ℃, but above 220 ℃, its decomposition rate sharply increases with the increase of temperature. Excessive temperature will promote the decomposition of sulfolane to produce light black polymers (a mixture of polybutadiene and iron oxide) and SO2. There is a local overheating problem on the surface of the heat exchangers in the three towers of the extraction system, with temperatures exceeding 220 ℃, resulting in the decomposition of sulfolane. Therefore, similar domestic devices may experience natural accidents of ferrous sulfide inside the towers.