(431a) Dynamic Intensification: Periodic Operation of Intensified Process Units

Richard Pattison, Austin Dulaney, Michael Baldea

McKetta Department of Chemical Engineering

The University of Texas at Austin, 1 University Station C0400, Austin, TX 78712

email: mbaldea@che.utexas.edu

One of the core tenets of process intensification is to â??do more with less.â? This includes carrying out more operations in fewer units (integration) and replacing conventional units with equal throughput units with smaller physical dimensions (miniaturization).

In a different vein, periodic operation of process units, particularly chemical reactors, was shown to increase throughput for many reaction schemes in comparison to steady state operation of a plant of the same capacity [1]. However, the potential benefits of periodic operation are often limited by material and energy transport constraints. Intensified units with small physical dimensions that combine both reaction and separation can eliminate some of these physical constraints by increasing heat and mass transfer rates through high surface area to volume ratios.

In this paper, we focus on the broad class of intensified processes that feature reaction and separation, such as reactive distillation columns and membrane reactors. We develop a prototype system representation under the assumption on unconstrained inlet and outlet material fluxes [2] (i.e., the reacting system is not limited by transport phenomena, which provides a design target for intensified unit operations). On this basis, we utilize the Pi criterion to define conditions under which imposing an oscillatory behavior (e.g., by periodically varying the manipulated variables) results in superior productivity compared to steady state operation. Our results are based on analytical solutions for several common reaction schemes, including reversible, consecutive and higher-order reactions.

We illustrate our theoretical framework with several detailed case studies. Moreover, we use numerical analysis to tackle the more complex cases whereby the material fluxes to the intensified unit are constrained. Our simulation results show that intensified reaction-separation systems can benefit from periodic operation for most reaction schemes, proving that dynamic intensification is a highly promising avenue for advancing the state of the art in the process intensification realm.

We will present the framework for a general reaction scheme and provide analytical conclusions for specific cases, then present results of detailed and optimized case studies, where we no longer assume that the material flux is unconstrained.

[1] Sterman, L.E.; Ydstie, B.E. Periodic forcing of the CSTR: An Application of the generalized II�criterion. AIChE J., 1991, 37, 986-996.

[2] Peschel, A.; Freund, H.; Sundmacher, K. Methodology for the design of optimal chemical reactors based on the concept of elementary process functions. Ind. Eng. Chem. Res., 2010, 49, 10535-10548.