Once the basic performance of the design has been evaluated, changes can be made to improve the performance; the process is optimized. These changes might involve the synthesis of alternative structures, that is, structural optimization. Thus, the process is simulated and evaluated again, and so on, optimizing the structure. Each structure can be subjected to parameter optimization by changing operating conditions within that structure. From the project definition an initial design is synthesized. This can then be simulated and evaluated. Once evaluated, the design can be optimized in a parameter optimization through changing the continuous parameters of flowrate, composition, temperature and pressure to improve the evaluation. However, this parameter optimization only optimizes the initial design configuration, which might not be an optimal configuration. So the design team might return to the synthesis stage to explore other configurations in a structural optimization. Also, if the parameter optimization adjusts the settings of the conditions to be significantly different from the original assumptions, then the design team might return to the synthesis stage to consider other configurations in the structural optimization. In the context of process design and optimization, the problems can be considered multi-objective or multi criteria. The problems are implemented in whether sequential-modular or equation-oriented manners.