During the last decade, several parallel reactors have been developed (16 parallels Amtec Germany, 16 parallel Flowrence, hte). The possible system of flow stream can be divided into three concepts based on the position of the Multi-Position Valves (MVs) as shown in the following Figure 3.5.
Figure 3.5 Schematic flow-sheet of (a) MV‘s at both sides (b) one downstream MV, and (c) one upstream MV
The high-throughput instrument requires a good user interface, be fast and relatively inexpensive. Obviously, using two multi-position valves (figure 3.5, example a) fails to meet the last criterion. Although implementing MVs both upstream and downstream probably produces the most accurate
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results, the application of one MV installed downstream (b) is general sufficient for the development of parallel reactors.
However, the concept of installing one MV downstream leads to another problem:
while a specific channel is measured, all other channels remain under continuous flow. This creates two drawbacks. First, to observe the activation or deactivation of catalytic material accurately, the designed structure of the reactor should be tested, so that the total flow rate is equally distributed through all channels and have the same pressure drop. Furthermore, supplying a continuous flow to all channels simultaneously significantly increases expenses due to feed-gas consumption.
Installing MV either upstream or downstream of the catalyst bed is of importance to establish ‗flow concept‘ in the parallel reactor. An upstream MV (c) causes a high risk that effluent gas analyzed can be contaminated by gases from the rest of the operating channel. Because of this, so far, the parallel reactor development has generally used to set up MV‘s positioned downstream (b). Disadvantages connected with the upstream positioned MV could be avoided using a splitting module. Here, it will be elucidated how this system works to neglect the contamination of effluent gas in each channel.
3.5.1 Design of splitting module
Figure 3.6 Effluent gas splitting module downstream
To solve the gas contamination problem in the case of installing the MV upstream, a gas splitting module was invented and designed by the mechanical engineer R. Richter as shown in Figure 3.6,
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which has the function of minimizing or eliminating the influence of gas contamination between online and offline columns. It is comprised of three parts such as upper plate (height = 20 mm, diameter = 20 mm), middle plate (height = 18 mm, diameter = 20 mm) and bottom plate (height = 20 mm, diameter = 20 mm). In order to avoid corrosion, plates were made of stainless steel (X6CrNiMTi17-12-2). To avoid gas leakage they are enclosed in polished planes by tightening screws
and sealing with 23 gaskets (2 sealing rings, 11 sealing O-rings, 11 sealing ellipses). The heating rod (height = 38.1 mm, diameter = 9.6 mm, 100W) in the center of the module allows to keep the temperature above 100 °C. The effluent gas from the online column is passed through a capillary line connected to the Micro-GC.
Figure 3.7 Function of module for splitting effluent gas
Our specific technique compared to other high-throughput reactors is the gas splitting module as shown in Figure 3.7. State-of-the-art technology for avoiding gas contamination between on-line and off-line results in the application of fine flow lines (width 2.5 mm) associated with the function of the stainless balls (diameter 3 mm).
Each ball accomplishes opening or shutting each channel by moving its position up and down by overcoming the force of gravity associated with the weight of the ball. The ball in the online channel
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is raised by the convection force derived by the flow as shown in the top left of Figure 3.7. In contrast, when one channel is open for flow of flue-gas, the other 10 offline channels remain close by pushing the ball based on the gravity force itself and the convection force of feed-gas as shown in the top right of Figure 3.7.
Although contamination can occur through the narrow gap between the ball and channel based on diffusion effects, this influence may be small enough to be ignored. The extent of error in this regard will be shown in the following chapter on the validation of the reactor performance. The entire design of the splitting module can be seen in the appendix.
3.5.2 Comparison of two methods
Figure 3.8 Stage robot reactor vs. 10-fold parallel reactor
The so-called ‗multichannel fixed bed reactor‘ or ‗10-fold parallel reactor‘ was developed for the secondary screening and hit validation. In this chapter the performance of this reactor will be compared with the stage robot reactor (SRR). Both high-throughput methods are used with the Micro-GC as analysis instruments and were automated with temperature control and the pretreatment of catalyst. Despite the fact that the new reactor can carry out tests with a maximum of 10 catalysts compared to 207 in the stage robot reactor, the accuracy is high, which makes it suitable for the optimization of catalysts or scale-enlargements. However, it is unclear which reactor is more suitable for high-throughput experimentation since each reactor has specific advantages and
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drawbacks. Ideally, the combination of two high-throughput methods is the best choice for discovering new catalysts in a set of large variables.
To summarize, the stage robot reactor as a primary screening method has to meet the following challenges: tests should be simple, fast and scalable; large variety of catalysts can be tested under steady-state conditions and continuous flow; analysis has to provide a reliable estimate of conversion and selectivity of catalyst; the test results have to be reproducible; all tasks have to be automated under systematic workflow[81].
It is also necessary to confirm promising results in secondary screening methods, which is used to scale up a certain conversion to production scale or screen conditions under conventional test[100]. Therefore, the 10-fold parallel reactor developed by in-house workshop is suitable to take this role as the instrument in secondary screening process.
Evidently, there is a difference between two high-throughput reactors and each reactor has specific criteria to extrapolate catalyst properties in primary screening and secondary screening stages. After all, using both reactors can both enhance the rate of the catalyst testing and harvest on the synergy effect of getting reliable data.