The process is used for treating light hydrocarbon feed (C1-С5+) for RSH, H2S, COS and CS2.
The feedstock at a temperature of 40–70о С and a pressure of 0.5–2.0 MPa 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 using the alkaline solution with formation of sodium sulfide and mercaptides proceeds in the extractor following the reactions:
H2S + 2 NaOH → Na2S + 2 H2O (1)
RSH + NaOH → RSNa + H2O (2)
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 (3)
CS2 + ROH + NaOH → S = C – OR + H2O (4)
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, wherein 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 40–45о С and a pressure of 0.4–0.5 MPa following the reactions:
3 Na2S + 4 O2 + H2O → Na2S2O3 + Na2SO4 + 2 NaOH (5)
2 RSNa + 0.5 O2 + H2O → RSSR + NaOH (6)
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-4 the CC with the disulfides enters separator V-5, where the disulfides separate from the CC forming an upper hydrocarbon layer. The disulfides are discharged from the top of V-5 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 was put into operation in 2009.
DMD-2M process flow diagram