Fabrication Of Ceramic Microreactor And Study Of High Temperature Catalytic Microreaction

Materials normally used in Micro-electromechanical Systems(MEMS)are metals, silicon,glass and polymers.However,these materials can not meet our demand under the conditions of high temperature and corrosion environments.Ceramic,especially alumina,has several advantages over other materials in MEMS,such as heat resistance,hardness,chemical inertness,corrosion and oxidation resistively,and working even in harsh environments.Thus,the application of ceramic will be prospective in the field of aerospace,micro detectors,microreactors and biological engineering.The ceramic is very hard so that it is difficult to fabricate the ceramic micro-structure.Hence,it is necessary to develop a suitable ceramic microstructure fabrication process.For this purpose,the ceramic microstructure fabrication process had been investigated.Combined a novel extended lost mold technology with LIGA technique,ceramic microstructure had been fabricated successfully using synchrotron radiation.Ceramics is a more excellent catalytic support than metals and silicon in microreactor.A novel ceramic microreactor had been designed and fabricated.And the steam reforming of ethanol has been investigated in the ceramic microreactor.The higher H₂ selectivity and longer lifetime were gotten in the microreactors compared to the traditional reactor.The main work and innovations are described as the following:1 Study of ceramic micro-structure fabrication processDue to the high hardness of the ceramic,especially alumina,in the sintered state, it is difficult to fabricate the ceramic micro-structures and to depart the green body from the mould insert without micro-structure fracturing.To solve these problems, various lost mold techniques have been applied to fabricate ceramic microstructure. In this paper,a new method of producing ceramic micro-device was presented.The PMMA micro moulding inserts were fabricated by using synchrotron X-ray lithography..The green bodies of the ceramic microstructures were formed through embossing process,under the condition of vacuum and high pressure circumstances. After the lost mold process,the formed ceramic microstructures were sintered at 1550-1700℃in furnace.The micro ceramic structure with a width of 30μm and height of 400μm could be fabricated through this method.The effect of the size of the powder grain,the content of the adhesive and heating rate were discussed.2 Design of micro-reactorDifferent from traditional design of micro-reactor,the design of micro-reactor in this paper was based on two different functional module parts.One is a catalytic micro tunnel module.Another is a peripheral equipment module.Based on the analysis of the shape and size of micro tunnel,the optimized cross-sectional area of 400×400μm² was finally chosen.The ceramic peripheral equipment module was designed and fabricated based on simulation of the possible flow mix of fluid.The ceramic microreactor was sealed by pressing polished ceramic lid to the polished ceramic peripheral equipment module.However,the ceramic material is so hard that this seal method can only be effective at low pressure.In order to obtain better seal effect,the stainless steel material was used for making the peripheral equipment module.After gas seal experiment,the results show that the micro-reactor can be sealed very well even at 20 times atmospheric pressure.3 Study of steam reforming of ethanol in ceramic micro-reactorIn recent years,producing clean electricity in fuel cells has been an increased interest.Ethanol is a very good renewable resource which can be produced by corn or other biomass.Hence,the study of hydrogen production from ethanol is very significative.In the paper,the catalyst metal of Pt and Ni was directly coated on the surface of the ceramic microchannels by sputtering technique.The XRD experiment results indicate that the catalysts on the microreactor are NiO/α-Al₂O₃ and Pt/α-Al₂O₃.The hydrogen production by steam reforming of ethanol at the temperature range of 450℃-700℃was studied in the microreactor.The performance of the microreactor was characterized by the conversion of C₂H₆O,selectivity of H₂,and other products composition as a function of the temperature.That life time of Pt catalyst is longer than that of NiO catalyst can be explained by the carbon information.It may indicate that the kinetic process is quite different for the two catalysts.