DECOS-1: Carbonyl sulfide removal



Application area

The technology is used for post-treatment of propane-propylene fraction (PPF) from carbonyl sulphide (COS) to a residual content of 1.0 ppm.


Hydrolysis of carbonyl sulphide in PPF with an aqueous solution of KOH saturated with water-soluble polar organic compounds 50-70 °C.

Concentration of carbonyl sulfide in the feed LPG is up to 0.01% by weight, the residual content of carbonyl sulphide is not more than 0.0001% by weight.

Technology description

Schematic diagram of PPF treatment from carbonyl sulphide:

Treated from hydrogen sulfide and mercaptans, LPG is sent to the LPG depropanization column. In the depropanization column, the treated liquefied gas is separated into PPF and BBF. PPF, saturated with carbonyl sulfide, enters the bottom of the T-101 alkaline hydrolysis column, equipped with cap trays. A potassium hydroxide solution heated in the E-101 heat exchanger to a temperature of 60-70°C is fed over the plates of the T-101 column.

When PPF interacts with an aqueous solution of potassium hydroxide at a temperature of 50-70 ° C, the carbonyl sulfide contained in the raw material is hydrolyzed and the hydrogen sulfide and carbon dioxide released during this process are chemisorbed by alkali to form potassium sulfide and carbonate according to reactions (1 – 3):

COS + H2O → H2S + СО2    (1)
H2S + 2KOH → KSS + 2H2O   (2)
СО2 + 2KOH → K2CO3 + H2O   (3)

From the top of the T-101, the PPF enters the horizontal settling tank V-101 and then goes to the boundary of the installation.

An aqueous solution of potassium hydroxide, saturated with salts, is removed from the bottom of column T-101, settling tank V-101 and, under its own pressure, is sent to the degassing tank V-102, where, due to pressure reduction, PPF dissolved in the alkaline solution is released, which is sent to the flare collector . Due to the accumulation of the ballast amount of salts in the alkaline solution, at the exit from the bottom of the T-101 column, it is planned to install filters to trap crystallized inorganic salts.

The degassed aqueous solution of potassium hydroxide from V-102 is sent by pump P-101A/B through heat exchanger E-102 to oxidizing column R-101. Air is introduced into the aqueous potassium hydroxide line before the R-101 column. In column R-101, on the surface of a heterogeneous catalyst, potassium sulfide is oxidized to thiosulfate and potassium sulfate according to reaction (4):

9K2S + 9O2 + 4Н2O → 4K2S2O3 + K2SO4 + 8KOH (4)

The exhaust air mixture with the regenerated potassium hydroxide solution is discharged from the top of the column R-101 to the exhaust air separator V-103. Exhaust air is removed from the top of the V-103 separator and directed to the furnace.

The regenerated solution from the bottom of the V-103 separator and again fed to the T-101 column by the P-102A / B pump.


The resulting sulfurous-alkaline effluents do not contain toxic sulfide-hydrosulfide compounds.

Alkaline hydrolysis of carbonyl sulfide proceeds at 50-70°C

Minimization of SBS by filtering precipitated potassium thiosulfate, sulfate and carbonate.