Microstructured Plate Heat-Exchanger Reactors

Ramshaw was one of the first to propose coating catalysts onto the surface of microreactors [466]. 

Nowadays, catalytic microreactors for gas phase reactions have become established as tools for laboratory and pilot scale investigations. The first examples of microreactors becoming established in chemical production have been published, but many other applications are being kept proprietary. Microreactors are heading for 

---

Figure 7.31 shows a microstructured plate heat-exchanger reactor developed by Kolb et al. [312], which was designed for a power equivalent of 2 kW of the corresponding fuel cell. The temperature profile, which was determined experimentally in... 

A microstructured plate heat exchanger for preferential oxidation in the kilowatt size range was developed by Kolb et al. [139]. The reactor had three-stage cross-flow design for the sake of easier fabrication. Platinum catalyst supported by alumina... 

To make a fuel-processing reactor out of a microstructured plate heat exchanger, heterogeneous catalysts need to be introduced into the microchannels, usually by wash-coating, similar to the procedure established for automotive exhaust clean-up. 

Besides microstructured heat exchanger/reactors constructed in the form of plates as shown in Figure 5.1, shell and tube micro heat exchangers are available. An example is shown in Figure 5.6. The heat transfer within the reactor tubes can be estimated with the asymptotic Nu or with Equation 5.12 for short channels. The outer heat transfer coefficient depends on the flow regime, the arrangement of the tubes, and the presence of baffles [8, 13]. For small-scale systems, capillaries submerged in constant temperature baths are commonly used. In this case, the main heat transfer resistance is mostly located at the outer side of the reactor. 

A chip-type micro reactor array comprises parallel mixer units composed of inverse mixing tees, each followed by a micro channel that it is surrounded by heat exchange micro channels (so called channel-by-channel approach similar to the tube-in-tube concept). Such an integrated device was developed as a stack of microstructured plates made of a special glass, termed Foturan (Figure 4.26). The integrated device was attached to PTFE tubes of various lengths. 

Another reactor for fast catalyst testing is a modular microstructured device with up to 10 catalysts applied on titer plates. An advantage of this reactor is the composition of various modules such as flow distribution, reaction heat exchange and gas sampling, which can be interconnected in different ways. The reactor can be operated at maximum pressure and temperature of 30 bar and 600 °C in the reaction module, and flow rates up to 10 mL min are possible. Catalyst deposition can be carried out very rapidly by a sputtering method or by washcoating, which has already been tested for the oxidation of methane [107, 108]. 

The majority of micro-reactors reported in the literature are stiU dedicated to catalyst evaluation. These reactors are usually monolith-type laboratory devices without heat-exchange functions, which allow for the removal of the microstructured plates after testing [26-35]. These are supplied by electrical power for heating and are StiU far away from a practical appUcation. Therefore, the design of these reactors wiU not be discussed in detail below, bearing in mind that they are useful tools for catalyst screening and characterization. 

---