A recent paper studied the separation of ethylene and ethane using several types of distillation systems in which cryogenic cooling is required. The economics of a conventional column using a very low-temperature expensive refrigerant in the condenser were compared with several configurations using process compressors. The alternative configurations involve the pressure in the auxiliary condenser and the fraction of the column overhead vapor sent through the compressor. Low pressure in the condenser requires a very low-temperature expensive refrigerant but has lower compressor costs. The purpose of this paper is to show that all of the vapor from the column should be compressed and then split, with some going to the reboiler and the rest going to an auxiliary condenser that operates at high pressure so that a higher-temperature less-expensive refrigerant can be used. (C) 2019 Elsevier Ltd. All rights reserved.