The process is used for treating oils and gas condensates for hydrogen sulfide (from 50 tо 5 ppm) and mercaptans (from 5000 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 mercaptide-containing alkaline solution. On the second stage higher 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 catalyst complex (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, wherein 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:
2RSNa + 0,5O2 + H2O → RSSR + 2NaOH
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: using a homogeneous catalyst, dissolved in an alkaline solution, or using 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 MPа following the reaction:
2RSH + 0.5O2 → RSSR + H2O
From the top of the reactor the reaction mixture enters separator V-3, where it is separated to oil and alkaline phases. The oil from the top of the separator is sent to a storage tank. The CC is sent from the bottom of the separator with pump Р-2 to mixer М-2.
The DMC-3 process was commissioned in 2000 on a plant of JSC “Yuzhno-Uralskaya Promyshlennaya kompania”, Orenburg, for treating Karachaganak condensate for С1-С3 mercaptans of 2 MM t/yr capacity and on JS “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