«DeCOS-2» process

Application area

DEMERUS LPG + COS is used for an additional purification of LPG from carbonyl sulfide impurities to a residual content of 5.0 ppm.


Carbonyl sulfide hydrolysis and chemisorption of its products with aqueous diethanolamine (DEA) solution, with the following regeneration of saturated DEA solution. Carbonyl sulfide concentration may be up to 0.02 wt%, residual content of carbonyl sulfide – not more than 0.0005 wt%.

Technology description

Schematic diagram of carbonyl sulfide removal process from LPG:


LPG purified from hydrogen sulfide is fed to the bottom of column T-101 equipped with plates, where proceeds hydrolysis of carbonyl sulfide and its products removal according to reactions 1-4:

COS + H2O → H2S + СО2  (1)
H2S + (HOCH2CH2)2NH ⇌ (HOCH2CH2)2NH2SH  (2)
(HOCH2CH2)2NH2SH + (HOCH2CH2)2NH ⇌ [(HOCH2CH2)2NH2]2S  (3)
СО2 + H2O + 2(HOCH2CH2)2NH ⇌ [(HOCH2CH2)2NH2]2CO3  (4)

Hydrogen sulfide and carbon dioxide dissolved in aqueous solution of DEA is removed from the bottom of T-101, warmed in heat exchanger E-101 up to 120°С, and supplied through a distributor into regenerator R-101. Regeneration of DEA solution proceeds according to the following reactions:

(HOCH2CH2)2NH2SH ⇌ H2S + (HOCH2CH2)2NH             (5)
[(HOCH2CH2)2NH2]2S ⇌ H2S + 2(HOCH2CH2)2NH             (6)
[(HOCH2CH2)2NH2]2CO3 ⇌ CO2 + 2(HOCH2CH2)2NH + H2O             (7)

Hydrogen sulfide, carbon dioxide and water vapor from the top of R-101 and through condenser-cooler E-103 are supplied to the tank D-101. Regenerated DEA solution precooled in cooler E-104 down to 40 °C is removed from the bottom of R-101 to D-101 as well. DEA regeneration gases are removed from the top of D-101 through a demister and supplied to the oven for calcination.


DEMERUS LPG + COS is comprehensive regenerative technology. It enables to remove hardly removable carbonyl sulfide (COS) along with mercaptans, hydrogen sulfide and carbon dioxide. Absence of toxic sulfide‑containing wastes.