(606d) Batch to Continuous (B2C) Reactor Intensification through a First-Principles-Based Optimization Framework

The conversion of existing batch processes to novel, intensified continuous flow processes has been the subject of a significant research effort in the last two decades. Continuous flow processes generally promise a smaller physical footprint, while offering many technical advantages such as better heat and material management, established process control principles, and simpler (and faster) scale-up from the bench to the industrial scale [1].

Among the main challenges involved in making the B2C transition for chemical reactors is determining whether this transition is feasible. For example, chemical processes involving slow reactions are often conducted in batch reactors, since an equivalent continuous flow reactor (CFR) at the same operating conditions would be unreasonably long. Nevertheless, the B2C switch under these circumstances is not necessarily impossible, if changes in operating conditions (e.g., temperature, temperature profile) are considered. Therefore, assessing the feasibility of the switch must take the specific constraints on the different equipment involved in the two processing modes into account.

For this reason, feasibility studies that focus on assessing the possibility of making the B2C reactor switch often involve testing a particular reaction (experimentally or computationally) in batch and CFRs independently, then comparing their performances. General approaches (applicable to any chemical reaction scheme) to assess feasibility are scarce, and are mostly based on heuristics (see, for example, [2]).

Motivated by the above, in this work, we develop a general, optimization-based framework that utilizes existing batch reactor information to assess B2C feasibility. We begin by assuming that a reference batch process exists, and that it is optimal with respect to some defined metric. Then, starting with first-principle models, we define dimensionless performance metrics that are applicable for the two reactor types, and show the equivalence between the evolution (trajectory) of these metrics in time (for the batch reactor) and space (for the continuous flow reactor). This then allows us to use concepts from optimal control to assess the feasibility of designing CFRs whose performance (defined in terms of said “trajectories”) are equivalent to the reference batch system. Multiple case studies are presented to illustrate the theoretical developments.

References

[1] Hessel, V. Novel Process Windows – Gate to Maximizing Process Intensification via Flow Chemistry, Chemical Engineering Technology, 32, 1655-1681, 2009

[2] Plouffe, P, Macchi, A, Roberge, D. From Batch to Continuous Chemical Synthesis – A Toolbox Approach, Organic Process Research & Development, 18, 1286-1294,2014