DEMERUS NAPHTHA: light gasoline treatment
TECHNOLOGY OF LIGHT GASOLINE FRACTIONS TREATMENT FROM MERCAPTANS (process “DEMERUS NAPHTHA”)
The technology is used for regenerative alkaline treatment of light gasoline fraction (LGF) from mercaptan sulfur to a residual content of 10.0 ppm and total sulfur not more than 50.0 ppm.
Schematic diagram of LGF treatment from mercaptans:
LGF is fed into the cube of the T-101 plate absorber. A regenerated aqueous solution of NaOH is supplied to the upper plate of the T-101 absorber from the D-103 disulfide settler to extract mercaptans according to the reversible reaction (1):
RSH + NaOH = RSNa + H2O (1)
Purified from mercaptans LGF from the absorber T-101 is sent to the settling tank D-101 and further for gasoline compounding.
The alkaline solution saturated with mercaptides is removed from the cube of the absorber T-101, heated in the heat exchanger E-101 to 50-70°C and enters the cube of the regenerator R-101. The calculated amount of air under pressure of 0.5-0.7 MPa is also supplied to the cube of the regenerator. In the R-101 regenerator, on the surface of the heterogeneous catalyst, alkali is regenerated according to reactions (2) and (3):
2RSNa + 0.5 O2 + H2O → RSSR + 2NaOH (2)
2RSNa + 1.5 O2 + H2O → RSО2SR+ 2NaOH (3)
The mixture of exhaust air, regenerated alkaline solution and formed disulfides from the top of the R-101 regenerator enters the D-102 separator. The air is removed from the top of the D-102 separator through a mist eliminator and is directed to the furnace for combustion. The regenerated alkali solution with disulfides is withdrawn from the D-102 separator bottom, mixed with the gasoline fraction by pump Р-101А/В, cooled down to 40°С in the E-102 cooler and enters the D-103 disulfide sump.
The gasoline fraction saturated with disulfides is removed from the top of D-103 to the feedstock of catalytic cracking units, AVT or to hydrotreatment, and the regenerated alkali solution from the bottom of the D-103 settler is returned to the T-101 absorber for treatment of LGF from mercaptans.
The technology is designed for mercaptans removal from high-octane gasoline distillates, in which the content of total sulfur minus mercaptan sulfur does not exceed Euro4 standards, and allows reducing the load on the distillate fractions hydrotreatment unit.
The technology increases the period of use of the alkaline solution without replacement up to 1 year, which makes it possible to reduce the consumption of alkali and the volume of alkaline effluents.
The heterogeneous catalyst provides strong retention of catalytically active components on the polymer carrier, increased resistance to catalytic poisons and thermal effects, and stable activity throughout the entire period of commercial operation. There is no need for its periodic or continuous replenishment with expensive compounds of metals of variable valence, which eliminates the ingress of cobalt phthalocyanines and their derivatives, as well as salts of other heavy metals into the wastewater of the enterprise. The warranty period of the catalyst is 8 years.