Aspen Plus R as simulation software: The calculations presented in the following are compared with results obtained using Aspen Plus R , version 11 2019. In these calculations the software Aspen Plus R is considered as a black box simulator solving all MESH equations. The simulation was optimized in an outer loop. This means that in each iteration the optimizer sets all specifications which serve as optimization variables and the simulation is evaluated for these specifications. After a converged simulation the objective function (reboiler duty) and the constraints (purity demands) can be evaluated. Depending on their values the specifications are modified until a satisfying result is found. The procedure is explained in more detail in the works by In the present work we used the reboiler duty, the flowrates of the top stream and side product streams as well as the ratio of the splits at the dividing walls as specifications. We again used sequential quadratic programming to solve the optimization problems. Here we worked with two implementations from the Schittkowski optimization suite. Namely the solvers and MISQP Exler and Schittkowski 2007. The demanded final accuracy was set to 10 -3 . Unfortunately the simulation software Aspen Plus R does not provide derivatives which is why we used derivatives obtained using finite differences. The calculations with Aspen Plus R have been performed on a 64-Bit Windows computer with 16GB of RAM and an Intel R Core TM i5-6500 processor.