Microreactors in Organic Chemistry and Catalysis, Second Edition (2013)
3. Microreactors Made of Glass and Silicon
3.4. Other Processes
3.4.1 Sensor Integration
Another important point is the integration of sensors into the microreactor. A full integration is often not economical. This section explains new ways for an appropriate technology. For optimal operation of microreactors, we need to measure
process pressure,
process temperature,
volume flow,
mass flow
and concentration.
This is necessary both for process control as well as the reliability of the system. The integration of sensors into the microreactor or building a multisensor module for the four functions of state is easy for a microreactor made of silicon. For the process pressure, the piezoresistive principle is used often. With differential pressure measurements, the flow rate can be determined. Alternatively, calorimetric principles are used widely. These are easy to implement technically, but a calibration is needed for each new medium. The most robust sensors are the Coriolis mass flow sensors. In process engineering, they are very common, but in terms of micro process engineering, there is still a need for research. In Ref. [26], sensors of this type are described. Ref. [25] is a good summary of other microflow sensors. For measurement of temperature, there are many equivalent principles but will not be discussed here. Substantially, it is more difficult to measure the concentration in the reactor. In addition to optical principles, the impedance spectroscopy is often used. See Ref. [27–31] for more details.
Life of the sensors is increased when the wetted surfaces are passivated with a chemically resistant material, silicon nitride or aluminum nitride.