Design and fabrication of microreactors for high temperature applications.

摘要

This work focuses on the design and fabrication of microreactors composed of a ceramic housing and a ceramic catalyst support for the carrying out of high temperature reactions, such as the steam reforming of hydrocarbons for the production of hydrogen for portable electrical power generation. Microreactors show great promise for high temperature reactions because of phenomena encountered at the microscale that are not typically encountered in conventional scale reactors. These phenomena include the larger surface area-to-volume ratios, which reduce overall reactor volumes for heterogeneous catalysis, and higher heat and mass transfer rates due to the smaller characteristic lengths, which allow for higher operating temperatures and higher rates of chemical production.; This thesis first describes yet another phenomenon, laminar flow at the microscale, and the underlying fundamentals of multistream laminar flow, including diffusion; the position of the fluid-fluid interface; and methods to introduce advection at the microscale. Applications of multistream laminar flow in micro-total analysis systems, microreactors, and enabling tools are reviewed, and a study of the effect of density differences on the reorientation of fluid-fluid interfaces is presented.; Microreactors show promise because of the phenomenon of higher heat and mass transfer rates as the length scale decreases. This thesis describes the fabrication and characterization of SiC and SiCN inverted beaded catalyst supports, which have high chemical and thermal stability (are stable to 1200°C in air), are highly porous (have a void fraction of 0.74) to reduce the pressure drop across the reactor, and have a high surface area-to-volume ratio. Because these catalyst supports are monolithic, they also eliminate the channeling that typically occurs with packed particles. This thesis then describes the integration of SiC catalyst supports with alumina housings and the characterization of these integrated reactors for the decomposition of ammonia to form hydrogen. Different approaches to generate hydrogen, including the steam reforming of hydrocarbons and the decomposition of NH3, are also evaluated on the basis of the energy density and availability of the fuel, the size of the reactor, the complexity of the fuel processing system, and heat transfer.