We next compare the results of the new method with results obtained with Aspen Plus R and an optimization in an external loop. As described before there are 5 degrees of freedom left, which can be chosen as optimization variables. We chose the flow rates of the product streams A and B (both ranging from 0.5 to 1.5 kmol/h), the reboiler duty (25 to 200 kW) and the two split ratios l s (0.2 to 0.9) and v s (0.15 to 0.9) as optimization variables. The objective was again to minimize the reboiler duty QR and we demanded the same purities of 0.95 mol/mol in each product stream. The optimization routine needed 18 iterations which took 534.74 seconds. This is about 39 times more time than the new approach needed. Both results, the one obtained with the new approach and with Aspen Plus R as simulation software, are shown in Table . Again we list the product streams, the heat duties and the split ratios.