Systematic Optimization-based Synthesis of Hybrid Separation Processes

Hybrid separation processes can offer significant cost-savings over simple distillation processes for close-boiling mixtures. In addition, the separation boundaries of azeotropic mixtures can be overcome. The application of hybrid processes in industry, however, is hindered by the lack of robust and efficient process synthesis tools and methods for these complex and highly integrated processes. In this work, we review an optimization-based framework composed of shortcut and rigorous design steps for the robust and efficient synthesis of separation processes. This synthesis framework is illustrated by an industrial case study for the optimal design of a hybrid process separating a ternary mixture of close-boiling isomers. A multitude of hybrid processes composed of distillation and melt crystallization units are evaluated with powerful shortcut models. A selection of promising process variants is subsequently rigorously optimized by an economic objective function and discrete-continuous optimization techniques. It is shown that the design of the cost-optimal hybrid process within the systematic synthesis framework can be accomplished with paramount robustness and efficiency.