Anna Lee Y. Tonkovich

Fabrication of Microchannel Chemical Reactors Using a Metal Lamination Process

Incorporation of microchannel arrays into small-scale chemical processing devices offers significant advantages in improving thermal control in the reaction region. Development of methods to produce high aspect ratio microchannels within solid metallic structures is an important step in the evolution of man-portable and other small-scale chemical processing units requiring high temperature and/or high pressure capabilities. Microchannel arrays can be used to facilitate heat removal or addition at the reaction zone or can be used to pre-heat gases prior to reaction. Staff at the Pacific Northwest National Laboratory (PNNL) have developed a method for producing solid metal components incorporating complex microchannel arrays by using a lamination and diffusion bonding process. This method uses metal shims that have been machined such that, when properly stacked, alternating microchannels and fins are produced in the laminated structure. The widths of the microchannels are determined by the thickness of the shim material, and heights and lengths of the channels are determined by the machined areas on the shims forming the channels. Machining of the shims can be accomplished in large quantities at low cost per shim by using photochemical machining or stamping processes. Consolidation of the laminated stack into a solid, leak-tight metal device is accomplished at elevated temperature and pressure by diffusion bonding. Microchannel arrays formed using this process can be produced either on the interior of the finished device or on an exterior surface. Typical microchannel dimensions in chemical processing devices produced at PNNL are 250 microns wide by 5000 microns deep. Application of the lamination process combined with a sheet-flow architecture can be used to produce highly compact chemical processing units. Among the devices produced at PNNL using this method are catalytic fuel processors and fuel vaporizers. Examples of all-metal stainless steel microchannel chemical processing devices produced using the lamination/diffusion bonding process will be presented and discussed.

Microchannel Chemical Reactors for Fuel Processing Applications. II. Compact Fuel Vaporization

A fuel processor is a critical element for the deployment of automotive fuel cell power systems. One component of the fuel processor, the compact gasoline vaporizer, was demonstrated at full-scale using commercial-grade gasoline. The full-scale process volume was less than 0.3 liters; it vaporized nearly 300 mL/min of gasoline, which is sufficient to support a 50-kWe fuel cell. The reduction in hardware volume was made possible using a microchannel reactor-based design; the compact process hardware is roughly an order of magnitude smaller than conventional technology.

Fabrication of a stainless steel microchannel microcombustor using a lamination process

Microscale chemical devices have potential application as fuel processors to produce high purity hydrogen for PEM fuel cells from hydrocarbon fuels such as methane, methanol, ethanol, or gasoline. The fabrication of a novel stainless steel catalytic microcombustor/reactor suitable for use to high temperatures is described. The device consisted of three parts to accommodate catalyst loading: a laminated reactor body, a laminated combustor, and a solid cover plate. The laminated components were produced using stacks of photochemically machined stainless steel shims. When formed into solid leak-tight components using a diffusion bonding process, the laminated parts were designed to contain a complex series of internal gas-flow microchannels that could not be produced in a solid metal block by other fabrication methods. Included within the reactor body was an array of heat exchanger microchannels 250 microns wide and 5000 microns deep that were designed to extract heat from the catalytic reaction region and pre-heat the reactant gases. Catalytic combustion of hydrogen or hydrocarbon fuel occurred in a separate laminated combustor plate. The laminated combustor/reactor design has potential for use in a variety of chemical processing and heat exchanger applications.