Microchemical systems for kinetic studies of catalytic processes

Abstract

Silicon microfabrication techniques and scale-up by replication have for decades fueled spectacular advances in the electronics industry. More recently, with the rise of microfluidics, microfabrication has enabled the development of microchemical systems for a variety of chemical and biological applications. This work focuses on the development of these systems for improved gas phase heterogeneous catalysis research. The catalyst development process often requires fundamental information such as reaction rate constants, activation energies, and reaction mechanisms to gauge and understand catalyst performance. To this end, we have examined the ability of microreactors with a variety of geometries to efficiently obtain accurate kinetic information. This work primarily focuses on microfabricated packed-bed reactors that utilize standard catalyst particles and briefly explores the use of membrane based reactors to obtain kinetic information. Initial studies with microfabricated packed-beds led to the development of a microfabricated silicon reactor that incorporates a novel cross-flow design with a short pass multiple flow-channel geometry to reduce the gradients that often confound kinetics in macroscale reactors. The cross-flow geometry minimizes pressure drop though the particle bed and incorporates a passive flow distribution system composed of an array of shallow flow channels. Combined experiments and modeling confirm the even distribution of flow across the wide catalyst bed with a pressure drop [approx.] 1600 times smaller than typical microfabricated packed-bed configurations.

(cont.) Coupled with the inherent heat and mass transfer advantages at the sub-millimeter length scale achievable through microfabrication, the cross-flow microreactor has been shown to operate in near-gradientless conditions and is an advantageous design for catalyst testing. The ability of microfabricated packed-beds to obtain accurate catalytic information has been demonstrated through experiments with phosgene generation over activated carbon, and CO oxidation and acetylene hydrogenation over a variety of noble metals on alumina. The advantages of using microreactors for catalyst testing is quantitatively highlighted throughout this work.