Originally the problem has around 550 process variables and MESH equations. For a given feed and constant pressure in the column, there remain 5 degrees of freedom. As described in Section 3 the optimization variables need to describe the streams connecting the different sections of the distillation column. For the streams 3, 4 and 7-10 we used the molar flow rates of each component to describe the streams. Instead of describing streams 1, 2 and 5, 6 we considered the molar flow rates of each component of the product streams A and C, the reboiler duty and the condenser duty. From these the streams 1, 2 and 5, 6 can be calculated using the material and enthalpy-balance. Finally, we chose the percentage of product withdrawn at stream B as optimization variable. This way we can also compute the liquid input stream at the top of section C 1,2 from stream 3. Using the new approach the number of variables are reduced to 27 For the optimization starting values are needed. An approximation of the internal flow rates and concentrations of these streams can be obtained using a V min diagram presented by Halvorsen and Skogestad 2003a; Ränger, Preißinger, and Grützner 2018. The initial values used are given in Table . An initial heat and condenser duty can be calculated using the enthalpy-balance around the reboiler and the condenser respectively. As pure components are assumed in the product streams, the flow rate for each product stream must be 1 kmol/h. In the optimization routine we used very rough bounds on the optimization variables. The flow rates for each component of a stream are bounded from below by 0 and from above by 100 kmol/h. Finally, the heat duty and the condenser duty were assumed to lie in the intervals [10 kW, 1000 kW] and [-1000 kW, -10 kW] respectively.