Spatially patterned catalytic reactors

Aaron St. Yves Cote, Purdue University

Abstract

This work deals with the creation of spatially structured reaction networks (“patterns”) in which auxiliary catalysts are introduced into a reaction system to steer a desired reaction around a performance obstacle and toward enhanced performance. Modeling efforts have demonstrated the ability of this pattern approach to circumvent a variety of constraints including those imposed by equilibrium limitations, byproduct inhibition, and the degradation of desired products. Although “traditional” admixed beds can offer advantages in situations that demand rapid switching between reactions, their intimacy of catalyst mixing forbids them from coupling reactions that cannot operate effectively in a common environment. We propose a more universally applicable “layered pattern” strategy in which the catalysts are organized in a discrete distribution alternating between broad layers of the various catalysts, implemented as distinct reactors. Computational work has shown that by integrating inter-reactor heat exchangers into the design and providing each layer with a carefully controlled side feed, one can tune the temperature and concentration profiles so that incompatibilities between the various reactions are mitigated. Concerns about the capital intensity of a layered reactor are addressed by considering the application of a recycle pattern consisting of a single repeat unit of reactors. In this design, effluent recirculation provides the necessary multiple reaction-switching events. Simulation results indicate that the recycle approach can generate performance benefits that are comparable to those offered by the layered pattern while simplifying reactor tuning. These multi-reaction networks displayed very complex multiplicity phenomena. Because the various steady states corresponded to dramatically different levels of performance, the full benefit of the pattern approach was only realized when the system operated on appropriate states. Effluent recycle suppressed multiplicity, further simplifying recycle reactor operation. Experimental work on a system designed to convert methane to benzene in a repeating four-step sequence (oxidative coupling, dehydrogenation, aromatization, dealkylation) has been conducted to confirm the computational discoveries. This effort revealed the need to synthesize novel catalysts tailored specifically for their roles within a complex pattern environment. Overall, the pattern approach demonstrated a remarkable ability to couple diverse reactions in order to circumvent a variety of performance limitations.

Degree

Ph.D.

Advisors

Ramkrishna, Purdue University.

Subject Area

Chemical engineering

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