Is used for treating oils and gas condensates for hydrogen sulfide (from 100 tо 5 ppm) and low molecular weight С1-С4 mercaptans (from 4000 tо 50 ppm)
The process is carried out in two stages. On the first stage С1─ С3 mercaptans are extracted with the alkaline solution with subsequent regeneration of the alkaline solution, containing mercaptides. On the second stage high molecular weight mercaptans are oxidized with molecular oxygen to disulfides over a catalyst, dissolved in the alkaline solution.
Stabilized oil or condensate enters the first stage of treatment ─ mixer М-1, where it is mixed with the circulating CC. From the mixer the oil with the CC flows to settler V-1, where it is separated to the oil and alkaline phases. The CC, containing mercaptides, passes from the bottom of V-1 to the bottom of regenerator R-1, where air is also supplied from a compressor. Oxidation of the mercaptides to disulfides takes place in the regenerator at a temperature of 50 0С and a pressure of 0.4–0.5 MPa following reaction:
2 RSNa + 0.5 O2 + H2O RSSR + 2 NaOH
From the top of the regenerator the reaction mixture flows to air separator V-2, where the air is separated from the alkaline solution. If necessary, the disulfides can be separated as a separate phase. From the bottom of the separator the regenerated alkaline solution is returned with pump Р-1 to mixer М-1.
The rich alkaline solution may be regenerated in two ways: with utilization of a homogeneous catalyst, dissolved in an alkaline solution, or with utilization of heterogeneous UVKO catalyst, placed into regenerator R-1 as a fixed packing.
The oil, separated from the alkaline solution, flows from the top of settler V-1 to the second stage of the process ─ mixer М-2 ─ to be mixed with air and circulating alkaline solution, containing the catalyst. The mixture of the oil, the air and the alkaline solution enters the bottom of reactor R-2, where oxidation of mercaptans to disulfides takes place at a temperature of 50─60 0С and a pressure of 0.6─1.0 MPA following the reaction:
2 RSH + 0.5 O2 RSSR + H2O
From the top of the reactor the reaction mixture enters separator V-3, where it is separated to the oil and alkaline phases. The oil from the top of the separator is sent to a storage tank. From the bottom of the separator the CC is sent with pump Р-2 to mixer М-2.
The DMC-3 process was commissioned in 2000 on CJS “Yuzhno-Uralskaya Promyshlennaya kompania”, Orenburg for treating Karachaganak condensate for С1 ─ С3 mercaptans for 2 MM t/yr capacity and on OJS «CNPC Aktobemunaygaz» for treating Zhanazhol oil. In 2002, the process was commissioned on «Mazheiku Nafta» oil refinery for treating 700 000 t/yr of Astrakhan condensate.
DMC-3 process flow diagram