Thermal Decomposition of COS to CO and Sulfur: Byproducts of Flue Gas Scrubbing

Sulfur dioxide in flue gas from coal-fired power plants presents both ecological and health hazards. Scrubbing dilute, sulfurous flue gas with carbonate eutectic melt at 823K can mitigate these hazards, but for an efficient and economical process, the melt must be regenerated and any resulting contaminants, in particular carbonyl sulfide gas (COS), a known neurotoxin, eliminated. In order to characterize this final stage in the recycling process, the thermal decomposition of COS was studied. A laboratory-scale, quartz flow reactor operating in the temperature range 773-1123 K was selected, with the optional addition of one of three potential catalysts to promote decomposition: an untreated or aqua regia-treated catalytic convertor, gamma-alumina powder and charcoal. The extent of decomposition and the reaction products were monitored via gas chromatography as a function of reactor temperature and gas residence time. The feed gas concentration of COS was generally held constant at 30 mol%, the remainder being N-2. Under the conditions of our study, 7-44 min residence time, catalytic effects on the kinetics of the COS decomposition reaction were not observed. AddingCO(2), thereby lowering the feed COS concentration to 20 mol%, resulted in increased COS decomposition for T < 923 K. Reducing the flow rate from 60 to10 ml/min led to marked increase in the extent of COS thermal decomposition : gas chromatography evaluated COS decomposition at approximate to 76% following 44 min residence time in the reactor at 823 K. Under no conditions of time or temperature, were reaction products other than CO and sulfur detected.

Automated summary

Sulfur dioxide in the flue gas from coal-fired power plants poses ecological and health hazards. A study was conducted to investigate the thermal decomposition of carbonyl sulfide gas (COS) for the final stage of the recycling process. The study found that the addition of catalysts did not affect the kinetics of the COS decomposition reaction. Lowering the COS concentration and reducing the flow rate led to increased COS decomposition.