The process is used for desulfurization of sulfur-alkaline waste waters and technological water condensates.
The process is based on liquid-phase oxidation of toxic sulfur compounds (hydrogen sulfide, sodium sulfide, hydrosulfide, sulfite and mercaptides) with air oxygen to neutral products (dialkyl disulfides, sodium sulfate and thiosulfate) over homogeneous IVKAZ-W catalyst.
Waste waters, separated from oil products, and mechanical impurities, are supplied from vessel V-1 with pump P-1 via heat exchangers H-1 and H-2 to reactor R-1. Before the reactor IVKAZ catalyst solution is pumped with a dosing pump to the waste water flow. Oxidation of sulfide and mercaptide sulfur takes place in the reactor at a temperature of 40–65 oC and a pressure of 0.4–0.5 MPa over the catalyst with air oxygen, supplied to the bottom of the reactor, following the reactions:
3 Na2S + 4 O2 + H2O → Na2S2O3 + Na2SO4 + 2 NaOH
2 RSNa + 0.5 O2 + H2O → RSSR + 2 NaOH
From the top of R-1 the treated waste waters with air are passed to air separator V-2. From the top of V-2 the spent air is directed to the nearest incinerator; the treated waste waters after cooling in a cooler C-1 to 40–50oC are sent to biological treatment plants. The process provides the degree of sulfide and mercaptide sulfur oxidation up to 99.9%.
Serox-W process has been used since 1990 at Ryazan refinery and since 1995-1996 on Yaroslavl and Kuibyshev refineries for treating sulfur-alkaline waste waters and technological condensate from catalytic cracking units and also for treating sulfur-alkaline waste waters of pyrolysis plant of JS “LUKOIL-Neftokhim” (Burgas, Bulgaria).The capacity of the plants is 30 m3/hr, the residual sodium sulfide content does not exceed 20 mg/l, that of sodium mercaptides does not exceed 5 ppm. At present all Serox plants are designed for use of special homogeneous IVKAZ-W catalyst.
THE SEROX-W process flow diagram