Ethylene purification is called ethylene fractionation, which separates ethylene as a highly pure overhead product, 99.9wt%, free of olefins, acetylenes, dienes, and water. Driers must be used to remove water since it is a poison for the catalyst in the polyethylene reactor. From distillation tower, ethylene can be split from the ethane. However, there would be some light ends that would go with ethylene. Those are let to react with hydrogen to give ethylene. The ethylene fractionator operates at 700-2800 kPa, with an overhead condenser temperature of -40 to -90oC, and a bottom reboiler at -15 to -65oC.