Standard rectifying columns have a single vapor feed. The two-enthalpy feed rectifier condenses a portion of this vapor feed to produce a liquid feed of the same composition. With the same total amount of cooling, the two-enthalpy feed rectifier has a smaller diameter but requires more stages than standard rectifiers. Detailed Aspen Plus simulations for 10 mol % argon-90% oxygen producing a 98% argon distillate at an external reflux ratio similar to 1.2 times the minimum show the column volume could be reduced by 12.1% or energy could be reduced by 8.3% compared to the case with a standard rectifier. Savings are lower when simulations are operated closer to the minimum reflux ratio. The feed condensation temperature is 2.2 K higher than the condensation of distillate. Reducing the amount of feed condensed gives the new rectifier design excellent turn-down properties with less energy required per mole of distillate. Methanol water and a ternary hydrocarbon mixture had larger savings than argon-oxygen.