NOVELTY - A carbon dioxide separating apparatus comprises active heat exchanger (216) for freezing carbon dioxide and regenerating heat exchanger (221), expansion valve (215) and compressor (218) for precooling, expanding and compressing refrigerant (R), respectively. Exchanger (216) contacts mixture of gases maintained at predefined pressure and exchanger (221) contacts R.    USE - For cryogenic purification of biogas, especially methane gas having high carbon dioxide concentration and for separating carbon dioxide from a mixture of gases.    ADVANTAGE - The apparatus utilizes a single stage process to separate carbon dioxide and methane into highly pure product streams without the need for further polishing to enhance the purity of the products. The methane product stream is liquefied to form a high value product in the same stage in which separation of methane and carbon dioxide occurs. The process provides lower capital costs, lower operating costs and reduced complexity and superior gas processing capabilities at large land fills.    DETAILED DESCRIPTION - A separating apparatus for separating carbon dioxide from mixture of gases comprises active heat exchanger, regenerating heat exchanger, expansion valve and compressor. The active heat exchanger freezes carbon dioxide and the heat exchange surface of the exchanger contacts a mixture of gases maintained at predetermined pressure. The heat exchange surface is cooled by a refrigerant, having a temperature lower than the freezing temperature of carbon dioxide. The regenerating heat exchanger pre-cools the refrigerant and the heat exchange surface contacts the refrigerant and layer of frozen carbon dioxide. The refrigerant passes into the regenerating heat exchanger at a temperature above the sublimating temperature of carbon dioxide in the frozen layer. The expansion valve expands the refrigerant after the refrigerant is precooled in the regenerating heat exchanger and before passing into the active heat exchanger. The compressor compresses the refrigerant after the refrigerant discharges from the active heat exchanger. The compressor has an input port for receiving the refrigerant and output port for discharging the compressed refrigerant.    DESCRIPTION OF DRAWING(S) - The figure shows schematic drawing of a portion of biogas purification apparatus.    Heat exchange surface (214)    Expansion valve (215)    Active heat exchanger (216)    Compressor (218)    Regenerating heat exchanger (221)