Silicon-technology based microreactors for high-temperature heterogeneous partial oxidation reactions

In this thesis the results of a study into the feasibility of silicon-technology based microreactors for fast oxidation reactions have been discussed. When designed properly, silicon microreactors are suitable for studying heterogeneous gas phase reactions, such as reaction kinetics of direct catalytic partial oxidation of methane into synthesis gas. This thesis focused on the design and realization of silicon-technology based micro flow reactors that are to be used for research on high-temperature heterogeneous gas phase reactions. A variety of design aspects that these microreactors have to fulfill are treated and discriminated, such as the concept of the reactor, materials that can be used at high temperatures, possible catalytic materials, the dimensions of the flow channel and the integration of actuators (i.e. heating filaments) and sensors (i.e. temperature sensors) for starting up and control of gas phase reactions. Thermal and mechanical analyses of ‘flat-membrane’ microreactors were done to obtain insight in and verify the behaviour of the membrane at high temperatures. The influences of several parameter variations were calculated for a composite membrane consisting of 850 nm heavily boron-doped mono-crystalline silicon (p++-Si) and 150 nm low stress silicon-rich nitride (SiRN). It was found that small variations in the thickness of the p++-Si-part and/or its thermal conductivity lead to significant deviations in the temperature profile and maximum temperature of the membrane that can be reached with a certain heating power. Therefore the thickness of the silicon part of the membrane has to be uniform. Furthermore, by implementation of a membrane with the mentioned composition, control of exothermic reactions seems possible, since the calculated time constants for heating up and cooling down are sufficiently small (ca. 1 millisecond). Mechanical analyses of the microreactor showed that problems due to pressure fluctuations and/or thermally induced stresses were not expected for temperatures up to 700 ºC. Well-defined tracks of catalytic material can be deposited in the flow channel of the microreactor with a shadow mask micromachined in Si (110): by means of a 3D, self-aligning shadow mask 2 patches of rhodium were deposited in the flow