DMD-2M process

The process is used for treating light hydrocarbon feed (C₁-С₅₊) for RSH, H₂S, COS and CS₂.

The feedstock at a temperature of 40–70^о 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)
                                                 |
                                               SNa

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 40–45^о 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