Synthesis and feasibility for reaction and separation systems with recycles
In this dissertation, we have developed systematic feasibility analysis and process synthesis methods that can be used to address these issues. The new methodologies can be used to determine process alternatives based on reactive distillation alone, and most importantly for reactive distillation coupled with conventional separations. The multicomponent mixtures considered in this research typically have heterogeneous and/or homogeneous azeotropic behavior.
In the first part, feasible splits for azeotropic mixtures with or without chemical reactions are predicted from the generalized fixed point structure of the mixture. Each distillation region is decomposed into one or more sub-regions based on the fixed point structures. The procedure provides a global view of generating sharp (direct and indirect) splits and non-sharp splits (one or more fixed point distributing in both products).
In the second part, a systematic generation of process alternatives for multi-component heterogeneous or homogeneous distillation systems is developed. Alternatives based on distillation and decanting alone must generally be expanded by mixing and occasionally by recycle to provide high purity products. The recycle of pure components is also pointed out as a useful and sometimes essential feature in developing alternatives. When chemical reactions are considered in generating flowsheet alternatives, the feasible region methodology is studied for evaluating reactors with high yields and selectivity. Both simultaneous reactive separation and sequential reaction followed by separation are considered for developing the overall flowsheets.
Systematic considerations of recycle further expands those alternatives to meet the additional goal of high recoveries. Therefore, the third part of the work generates many potential alternatives, and new necessary conditions eliminate as many as 90% of the infeasible alternatives without the need for a complete converged material balance simulation. This “Recycle Reachability Rule” ensures that there is an exit point for each component not only for the entire process system, but also within each recycle loop.
The methods developed here are applicable to multicomponent mixtures with general number of reactions, and are not restricted to distillation, decantation or reactive distillation. (Abstract shortened by UMI.)