Microstructured plates

Figure 2.24 Geometry of the microstructured plates (left) and subdivision of the flow domain into channel segments (right) as considered in [116].

The microstructured plates were made by wet-chemical etching. The platelet stack was bonded by standard welding. The inlet and outlet connectors were also welded. 

This device is a generically simple reactor comprising a micro-channel Y-piece section and an elongated reaction micro channel attached [26, 27]. The microstructures were mechanically fabricated in PMMA using a flat end mill. A top plate was joined with the microstructured plate by baking under vacuum. The reaction temperature was fixed using a hot-plate. 

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. 

Microfabrication involves multiple photolithographic and etch steps, a silicon fusion bond and an anodic bond (see especially [12] for a detailed description, but also [11]). A time-multiplexed inductively coupled plasma etch process was used for making the micro channels. The microstructured plate is covered with a Pyrex wafer by anodic bonding. 

The microstructures are fabricated by photoetching of a specially glass (see Figure 1.79) [20, 124], Such microstructured plates are joined by soldering. The joint plate stack is held in a frame. 

The fluidic network is formed by the assembly of two identically microstructured plates [7]. The horizontal splitting layer is inserted between the two plates as well as seals. A steel housing serves for compression and provides the fluidic connections. 

Mesh Microcontactor A mesh microcontactor contains a microstructured plate with regular circular openings through which separate gas and liquid streams come into contact [270,271]. Stability of the interface and prevention of breakthrough are achieved by adjusting the pressure. Gas-liquid operation requires a low gas flow... 

To achieve an even higher degree ofnumberingup, a modular microbubble column reactor was developed that contains a stack of microstructured plates. The construction encompasses five different assembly groups, a cylindrical inner housing, which... 

Yeong et al. [100,101] used a microstructured film reactor for the hydrogenation of nitrobenzene to give aniline in ethanol at a temperature of 60 °C, a H2 partial pressure of 0.1-0.4 MPa, and residence times of 9-17 s. Palladium catalysts were deposited as films or particles on a microstructured plate. Confocal microscopy was used to measure the liquid film thickness, which increased from 67 to 92 pm as flow rates were increased from 0.5 to 1.0 cm3 min-1. The value of kha characteristic of this system was estimated to be 3-8 s 1 at an interfacial surface area (per reactor volume) of 9000-15000 m2 m 3. Conversion was found to be affected by both liquid flow rate and H2 partial pressure, and the reactor operated between the kinetic and mass transfer-controlled regimes. 

The morphology of the porous oxide layer does not depend solely on the experimental conditions for the anodic oxidation a subsequent hydro-thermal treatment can considerably increase the surface area [155]. An example is shown in Figure 19. Whereas in most cases microstructured plates are oxidized before assembly, Haas-Santo et al. [158] performed... 

Typically, the microstructured plates are coated prior to their assembly. After cleaning and possible thermal treatment of the bare plates, inlet and outlet parts of the structures are protected, for example, with a thin polymer film. The suspension is deposited on the microchannel plates, and any excess suspension is wiped off. Then, the washcoat is dried at room temperature, whereby it shrinks. After cleaning of the top parts of the microchannel fins, the washcoats are calcined at temperatures of 500-600 °C. After calcination, a catalytically active compound can be introduced by impregnation. 

FM5. Corrosion. The positive grid is subject to corrosion. The rate of this debilitating process is influenced by grid composition and microstructure, plate potential, electrolyte composition, temperature. The corrosion product is generally more electrically resistive than the grid and thus diminishes the output of the battery. In extreme cases, corrosion results in disintegration of the grid and collapse of the plate. 

In another reactor carrying microstructured plates, a copper-based low temperature water-gas-shift catalyst was apphed [76]. The reactor took up 20 plates made of FeCr Al alloy with channel size 200 X100 pm. The kinetic measurements were carried out and expressions were determined for both a tubular fixed bed reactor containing 30 mg catalyst particles and the microreactor coated with the... 

The reactors applied for catalyst evaluation are usually laboratory-type devices, which allow the removal of the microstructured plates after testing [2-9]. They are operated with electric power for heating and therefore are still far away from practical application. Therefore, the design of these reactors will not be discussed in detail here, bearing in mind that they are useful tools for catalyst screening and characterization. 

Find et al. [25] developed a nickel-based catalyst for methane steam reforming. As material for the microstructured plates, AluchromY steel, which is an FeCrAl alloy, was applied. This alloy forms a thin layer of alumina on its surface, which is less than 1 tm thick. This layer was used as an adhesion interface for the catalyst, a method which is also used in automotive exhaust systems based on metallic monoliths. Its formation was achieved by thermal treatment of microstructured plates for 4h at 1000 °C. The catalyst itself was based on a nickel spinel (NiAl204), which stabUizes the catalyst structure. The sol-gel technique was then used to coat the plates with the catalyst slurry. Good catalyst adhesion was proven by mechanical stress and thermal shock tests. Catalyst testing was performed in packed beds at a S/C ratio of 3 and reaction temperatures between 527 and 750 °C. The feed was composed of 12.5 vol.% methane and 37.5 vol.% steam balance argon. At a reaction temperature of 700°C and 32 h space velocity, conversion dose to the thermodynamic equilibrium could be achieved. During 96 h of operation the catalyst showed no detectable deactivation, which was not the case for a commercial nickel catalyst serving as a base for comparison. 

Akohol Steam Reforming in Microstructured Plate Heat Exchangers... 

IMM provides two reactors for catalyst screening. The catalyst testing microreactor contains 10 microstructured plates made out of stainless steel, whicii can be coated on demand with various catalysts. Every plate is fed simultaneously by a sub-stream and the reactor can be operated serially or in parallel. The pressure stability of this reactor is 20 bar (100 bar at 400 °C) and a maximum temperature of 800 °C is possible. MicroChannel plates with different channel geometries with specific surface areas around 7300 m m are offered by IMM. 

The volume basis for this simple model is the material of the fins or pillars between the channels or in the slits, respectively. This specific volume is responsible for transport through a stack of several catalytically modified microstructured plates without intermediate cooling or heating. Assumption for this simple solution of the heat transport equation is a temperature constant heat production rate, so that only small predicted gradients fit the experiment. The stack height without intermediate cooling/heating is... 

Microstructured plate heat exchangers are stacked arrangements with a multitude of parallel minichannels and high sur-face-to-volume ratios in the range of 200 m /m . The preferred construction material is stainless steel. Wet chemical etching, initially developed for silicon micromachining, is suited for mass... 

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. 

Find et al. developed a nickel-based catalyst for methane steam reforming in microchannels [218]. AluchromY steel, which is a Fecralloy (see Section 10.2.1), was used as the construction material for the microstructured plates. The catalyst was based upon a nickel spinel support (NiAl204) for stabilisation. The active nickel... 

Figure 5.14 Comparison between conventional fixed-bed technology and a combined microstructured plate heat-exchanger/catalytic afterburner according to Delsman etal. [386] power range, 5 kWe. ...

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