Method and device for treating nitroso compound

A method for recovering carbon dioxide in a gas to be treated, comprising:

• a step (I) of bringing the gas to be treated that contains carbon dioxide into contact with a CO2 lean absorption liquid containing amines for absorbing the carbon dioxide into the CO2 lean absorption liquid to obtain a CO2 rich absorption liquid;
• a step (II) of heating the CO2 rich absorption liquid for releasing the carbon dioxide to regenerate the CO2 lean absorption liquid;
• a step (IIIa) of adding an aqueous solution containing hydrogen halide to part of the CO2 lean absorption liquid regenerated in the step (II) in such a manner that the hydrogen halide is present in an amount of 2 mol or more and 20 mol or less per mol of a nitroso group in a nitroso compound contained in the CO2 lean absorption liquid, and subsequently heating the CO2 lean absorption liquid at a temperature of not lower than 75° C. and not higher than a boiling point of water under ordinary pressure;
• and
• a step (IV) of providing, to the step (I), another of the CO2 lean absorption liquid regenerated in the step (II) and or the CO2 lean absorption liquid heated in the step (IIIa).

A method for recovering carbon dioxide in a gas to be treated, comprising:

• a step (I) of bringing the gas to be treated that contains carbon dioxide into contact with a CO2 lean absorption liquid containing amines for absorbing the carbon dioxide into the CO2 lean absorption liquid to obtain a CO2 rich absorption liquid;
• a step (II) of healing the CO2 rich absorption liquid for releasing the carbon dioxide to regenerate the CO2 lean absorption liquid;
• a step (V) of reclaiming part of the CO2 lean absorption liquid regenerated in the step (II) to remove a heat stable salt;
• a step (IIIb) of adding an aqueous solution containing hydrogen halide to a remaining liquid obtained in the step (V) in such a manner that the hydrogen halide is present in an amount of 2 mol or more and 20 mol or less per mol of a nitroso group in a nitroso compound contained in the remaining liquid, and subsequently heating the remaining liquid at a temperature of not lower than 75° C. and not higher than a boiling point of water under ordinary pressure to recover amines;
• and
• a step (IV) of providing, to the step (I), another of the CO2 lean absorption liquid regenerated in the step (II) and/or the amines recovered in the step (IIIb).

A processing apparatus for decomposing a nitroso compound, comprising:

• a reaction vessel for heating a liquid to be treated that contains the nitroso compound at a temperature of not lower than 75° C. and not higher than a boiling point of water under ordinary pressure in the presence of hydrogen halide in an amount of 2 mol or more and 20 mol or less per mol of a nitroso group in the nitroso compound so as to decompose the nitroso compound;
• a gas passage for discharging a decomposition gas produced in the decomposition from the reaction vessel by introducing a carrier gas into a gas-phase portion of the reaction vessel;
• a condenser for cooling the decomposition gas to condense water vapor;
• and
• a halogen recovery apparatus for recovering a halogen gas in the decomposition gas.