DMD-2 «ODORANT» process

The process was developed for treating gas condensates and light hydrocarbon fractions for hydrogen sulfide and low molecular weight С₁−С₄ mercaptans with production of a mixture of natural mercaptans as a sales product – an odorant for natural and liquefied gases.

Feedstock at a temperature of 30−40^oС and gauge pressure of 0.6 MPa is supplied to the bottom of extractor K-1. To the top of the extractor a 5−20 % aqueous solution of alkali, pre-cooled in cooler С-1 to a temperature of 30−40^oС, is supplied with pump P-1. Extraction of С₁−С₄ mercaptans with formation of mercaptides takes place in column K-1. The demercaptanized feedstock is sent from the top of column K-1 to separator-settler V-1 and then to a tank farm.

The alkaline solution, containing the mercaptides, is discharged from the bottom of extractor K-1, passes recuperative heat-exchanger H-2, where it is heated to a temperature of 80−90^оС and then it is sent to the top of regenerator K-2. At the bottom of regenerator K-2 the mercaptide-alkaline solution is heated to 110−125^оС. Sodium mercaptides hydrolysis with production of С₂−С₄ mercaptans takes place in regenerator K-2.

The desorbed mercaptans together with steam pass from the top of regenerator K-2 to cooler С-3 to be cooled to 10−20^о С and then to separator-settler V-2, where separation of mercaptan and water layers takes place. The mercaptans are discharged from the top of settler V-2 to storage facilities and the water from the bottom of settler       V-2 is sent to the top of regenerator K-2.

The regenerated sodium hydroxide solution is sent from the bottom of K-2 with pump P-2 to cooler С-4 to be cooled to 50−60^оС and then to regenerator K-3 for catalytic oxidation of methyl mercaptides with air oxygen to a corresponding disulfide. Sodium sulfide in this case is oxidized to sodium thiosulfate and sulfate. A required quantity of process air is supplied to the bottom of regenerator K-3. The spent air from the top of K-3 is sent via separator-demister V-3 to a nearest incinerator for burning.

The regenerated alkaline solution from the bottom of K-3 flows to disulfide separator V-4. The alkaline solution from the bottom of separator V-4 is pumped with pump P-1 to extractor K-1. The disulfides (dimethyl disulfide – 90 %) from the top of separator V-4 are discharged to storage facilities. As sodium thiosulfate and sulfate accumulate in the alkaline solution, some of the solution is discharged from the system from time to time.

The process was implemented on Orenburg GPZ (1983) and in Iran (2018).

THE DMD-2 «ODORANT» process flow diagram