Is used for treating light C2 ─ С6 hydrocarbons for mercaptans and hydrogen sulfide. The process provides decrease of mercaptan sulfur content in the product to 20 ррm and less. The DMD-2M process is used for simultaneous feedstock treatment for RSH, H2S, COS and CS2.
The feedstock at a temperature of 40–70 оС and a pressure of 0.5–2.0MPa is supplied to the bottom of extractor V-1. The alkaline solution of IVKAZ catalyst (CC) is supplied to the top of the extractor with pump Р-1. Removal of hydrogen sulfide and mercaptans with the alkaline solution with formation of sodium sulfide and mercaptides proceeds in the extractor following the reactions:
H2S + NaOH ® Na2S + H2O
RSH + NaOH ® RSNa + H2O
Removal of carbonyl sulfide and carbon disulfide also takes place in the DMD-2M process in the extractor over an activator following the reactions:
COS + 4 NaOH ® Na2S + Na2CO3 + 2 H2O
CS2 + ROH + NaOH ® S = C – OR + H2O
From the top of the extractor the treated feedstock flows to separator-demister V-2 and then to a storage. From the bottom of the extractor the catalyst complex solution passes to the bottom of regenerator R-1, where an estimated quantity of air is simultaneously injected via disperser from a compressor. Regeneration of the alkali proceeds in apparatus R-1 at a temperature of 40–45 оС and pressure of 0.4–0.5 MPa following the reactions:
2 RSNa + 0.5 O2 + H2O ® RSSR + NaOH
3 Na2S + 4 O2 + H2O ® Na2S2O3 + Na2SO4 + 2NaOH
From the top of R-1 the catalyst complex and air are directed to separator V-3. The spent air from the top of the separator is sent to a nearest incinerator. From the bottom of V-3 the CC with the disulfides enters separator V-4, where the disulfides separate from the CC forming an upper hydrocarbon layer. The disulfides are discharged from the top of V-4 and the regenerated CC is sent with pump Р-1 to extractor V-1.
Beginning from 1974, the DMD-2 process has been commissioned on many Russian oil and gas refineries (Ryazan, Kuibyshev, Astrakhan, etc.)
A license on the DMD-2M process was sold to National Iranian Oil Company (NIOC) for building a propane and butane treating plant for KHARG petrochemical company. The plant start-up is planned for 2007.
DMD-2M process flow diagram