High boiling contaminants such as chloro-aromatic compounds are removed from a gas by compressing the gas containing the contaminant, cooling the compressed gas to reduce the temperature of the gas to at least 20° C. above the outlet temperature of a second cooling stage but above the freezing point of the highest melting compound in the first cooling stage, further cooling the gas in a second cooling stage to at least −20° C., returning cooled gas from the second cooling stage to the first cooling stage, and recovering condensate streams which contain the contaminant compound from the first and second cooling stages. An apparatus suitable for carrying out this process is also disclosed. The process of the present invention is particularly useful for removing chloro-aromatic compounds from anhydrous hydrogen chloride gas.