An alternative to repeatedly solving the large nonlinear systems of equations with a process simulator is to embed the process simulation into an optimization problem. This can be done by incorporating all MESH equations (Equation ( )) as constraints whereas the process variables x var serve as optimization variables . An objective (eg. minimal energy consumption) and further constraints (eg. purity demands) can be added directly to the optimization problem. The optimization solver finds a solution to the equations describing the simulation that minimizes the objective. The main challenge of this approach is that the resulting optimization problems are large and may be difficult to initialize and to solve.