Patent ID: 7927573

Claim:
A process for treating gaseous carbon dioxide, comprising (A) providing a gaseous feed stream of carbon dioxide that also comprises NOx and sulfur dioxide, and that is at a pressure of at least 2 bar; (B) contacting NOx-rich sulfuric acid with said gaseous feed stream and NO 2 desorbed in step (B) to strip NOx from said NOx-rich sulfuric acid and form NOx-reduced sulfuric acid and NOx-augmented gaseous carbon dioxide that comprises SO 2 and NO 2 ; (C) converting NO in said NOx-reduced sulfuric acid to NO 2 , and desorbing said NO 2 from said NOx-reduced sulfuric acid to form NOx-lean sulfuric acid and desorbed NO 2 ; (D) controlling the amount of desorbed NO 2 contacted with NOx-rich sulfuric acid in step (B) by converting desorbed NO 2 to nitric acid and NO, and recovering said nitric acid; (E) reacting water and oxygen with the NOx-augmented gaseous carbon dioxide to form NOx-rich sulfuric acid and SO 2 -depleted NOx-containing carbon dioxide; (F) absorbing NOx from said SO 2 -depleted NOx-containing carbon dioxide into one or both of said NOx-reduced sulfuric acid and said NOx-lean sulfuric acid to form NOx-rich sulfuric acid and NOx-lean SO 2 -depleted carbon dioxide; (G) subjecting the NOx-lean SO 2 -depleted carbon dioxide to a subambient-temperature recovery process, employing refrigeration provided by expansion of at least one liquid carbon dioxide product stream formed by said recovery process, to produce at least one gaseous carbon dioxide product stream and at least one gaseous carbon dioxide-containing vent stream; (H) separating the vent stream into a carbon dioxide-rich stream and a carbon dioxide-depleted stream, by pressure swing adsorption or by physical or chemical absorption; and (I) recycling said carbon dioxide-rich stream to said carbon dioxide-containing feed stream.