In the presented approach the optimization variables describe the streams connecting the different sections of the distillation column. Analogous to the previous example we chose the following process variables: the flow rates of each component in the streams 3-6 and 9-16; the flow rates in the product streams A and D; the reboiler and the condenser duty and the percentage withdrawn in the side streams B and C. In total with the new approach we obtain an optimization problem with 60 optimization variables and 52 equality constraints that remain to be solved. As an comparison the original simulation problem has around 1600 process variables and MESH equations.