Abstract: One of the drawbacks common to many currently available low-temperature gas mixture separation techniques is that known systems and methods that embody the techniques are inefficient. In contrast to known systems and methods for low-temperature gas mixture separation, some embodiments of the present invention provide a system for low-temperature gas mixture separation that recycles energy and reduces power consumption by re-circulating heated and/or cooled flows (e.g. gas, liquid and mixed-phase flows) within the system. Accordingly, in some embodiments efficiency is somewhat improved, as compared to comparable systems that do not include the re-circulation of heat energy. In some embodiments the heat energy that is re-circulated is a combination of heat added to the system (i.e. inputs to the system) and heat released within the system (i.e. byproducts from within the system) that are subsequently recovered.