Patent ID: 7819951

Claim:
A method for removing a first contaminant selected from oxygen and carbon monoxide from impure liquid carbon dioxide, said method comprising: separating said impure liquid carbon dioxide in a mass transfer separation column system to produce first contaminant-enriched overhead vapor and carbon dioxide-enriched bottoms liquid; and reboiling a portion of said carbon dioxide-enriched bottoms liquid by indirect heat exchange against crude carbon dioxide fluid to produce carbon dioxide-enriched vapor for said column system and cooled crude carbon dioxide fluid; wherein said impure liquid carbon dioxide has a greater concentration of carbon dioxide than said crude carbon dioxide fluid and is derived from said cooled crude carbon dioxide fluid by: further cooling at least a portion of said cooled crude carbon dioxide fluid by indirect heat exchange to produce partially condensed crude carbon dioxide fluid; and phase separating at least a portion of said partially condensed crude carbon dioxide fluid to produce said impure liquid carbon dioxide and carbon dioxide-depleted vapor, wherein: the entire refrigeration duty required by the method is provided internally by indirect heat exchange between process streams, at least a portion of said refrigeration duty being provided by vaporizing a portion of the carbon dioxide-enriched bottoms liquid or liquid carbon dioxide derived therefrom by indirect heat exchanger, and the operating pressure of said column system is lower than the pressure of said impure liquid carbon dioxide and the pressure of said impure liquid carbon dioxide being reduced to about the operating pressure of said column system without forming solid carbon dioxide prior to feeding said impure liquid carbon dioxide to said column system.