Abstract: Systems and methods for purifying a carbon dioxide gas mixture are disclosed. A carbon dioxide purification and in liquefaction unit integrated with an external hydrocarbon dosing system is used to purify a mixture that includes (1) primarily carbon dioxide and (2) other material including an organic chloride and other organic hydrocarbons. The organic chloride in the mixture may be substantially removed via controlling the amount of the organic chloride reacted in the reactor of the carbon dioxide purification and liquefaction unit. The controlling of the organic chloride content is executed by the external hydrocarbon dosing system. The external hydrocarbon dosing system is configured to maintain a temperature of the effluent from the reactor within a predetermined range via controlling the flow rate of the external hydrocarbon into the mixture.