Microchannel reactors, heat control

Aligned multiwall CNT arrays were synthesized as a basis for a microstructured catalyst, which was then tested in the Fischer-Tropsch reaction in a microchannel reactor [269]. Fabrication of such a structured catalyst first involved MOCVD of a thin but dense A1203 film on a FeCrAlY foam to enhance the adhesion between the catalyst and the metal substrate. Then, multiwall CNTs were deposited uniformly on the substrate by controlled catalytic decomposition of ethene. Coating the outer surfaces of the nanotube bundles with an active catalyst layer results in a unique hierarchical structure with small interstitial spaces between the carbon bundles. The microstructured catalyst was characterized by the excellent thermal conductivity inherent to CNTs, and heat could be efficiently removed from the catalytically active sites during the exothermic Fischer-Tropsch synthesis. 

Pacific Northwest National Labs (PNNL) designed their microchannel Prox reactor in which reactors are interlayered with the microchannel heat exchanger, so reaction temperature was precisely controlled and high selectivity could be reached. 

The internal heating technique incorporates heating elements in microfluidic devices to control temperature of fluids. A widely used technique is direct fabrication of a heater or reactor [5] inside of a microchannel or chamber. This requires a microfabricating process to manufacture the microheater system to fit in the microscaled container. 

Microstructured reactors (microreactors) represent a new type of reaction equipment for applications in chemistry. Small dimensions of microchannels provide a short diffusion time, better temperature and pressure control, large specific surface area, high heat exchanging efficiency, and a higher level of safety [1]. 

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