The objective of the collinear laser pyrolysis reactor (Figure 1 b) is to significantly increase the residence time of the precursors in the laser interaction zone compared to conventional laser pyrolysis (Figure 1 a). For this, the laser beam is placed collinearly and centered on the same axis as the flow of precursors in the interaction zone. Preferably, this axis is vertical so as to be also collinear with the axis of natural convection. In the collinear configuration, it is possible to adjust the distance and residence time as desired by adjusting the distance Di (Figure 1 a). It is thus possible to extend the reaction zone to several tens of cm. The residence time can therefore be increased by more than an order of magnitude compared to conventional laser pyrolysis.
Figure 1 Laser pyrolysis set-up. a) conventional b) collinear
An analysis of the CFD simulation results are shown in the following figure. In Figure 2 a), the map of volume fractions of sensitizer gas is presented with the example of the use of NH3 as a sensitizer gas. This map allows us to make 2 important observations: First, the distribution of the volume fraction of NH3 is homogeneous over almost the entire area of interaction with the laser; Secondly, we note the total absence of NH3 in the vicinity of the laser windows. This condition is essential to guarantee the integrity of these windows in the long term. This absence of heating of the gases in the vicinity of laser windows is confirmed by the temperature map in Figure 2 b). On this map, we see a heating of the central gas, symmetrical and significant. The velocity map in Figure 2 c) shows a constant gas velocity throughout the area of interaction with the laser. This spatial stability of the flows guarantees uniform interaction throughout the area and allows better control of product properties, as well as better reproducibility of results.
Figure 2: CFD simulations of the collinear laser pyrolysis
Collinear laser pyrolysis is used for Highly Active, High Specific Surface Area Fe/C/N ORR Electrocatalyst synthesis from Liquid Precursors.