15 barg
40 barg
550˚C, 40 barg
100
10
50
5
*
0
0
Time on stream (h) 120 125 130
550
600
650
700
750
550
600
650
700
750
Temperature (˚C)
32 , 000 h -1
100 , 000 h -1
11 , 000 h -1
Blank
Figure 2 NH₃ cracking using an Fe-based catalyst and hte’s advanced high throughput technology (95% NH₃, 5,000 ppm H₂O, 4.5% Ar, 550-750°C, 15 and 40 barg, 11,000-100,000 h -1 )
to produce a set of performance data while exploring a wide range of process parameters. The experiments were structured by performing a temperature ramp between 550-750°C in 50 K-steps, first at 40 barg followed by a second temperature ramp at 15 barg to investigate the influence of pressure. The temperature curves were generated at a gas hourly space velocity (GHSV) range of 11,000-100,000 h -1 concurrently, enabled by loading different catalyst bed lengths to the parallel reactors. Figure 2 shows the conversion of NH₃ as a function of temperature split by reactor pressure. Starting at 550°C, only little NH₃ conversion between 2-11% was monitored. However, even small conversion levels at 1.7% (100,000 h -1 ) could be resolved with hte’s equipment. The NH₃ conversion increased with temperature and reached >97% at 750°C, operating at 11,000 h -1 . Clear influence of increasing GHSV and reactor pressure could be observed, resulting in reduced conversion of NH₃, which is in accordance with thermodynamics (Ristig, et al., 2022). Productivities of 93,100 mmol(H₂)/min/g(cat) could be reached by applying 100,000 h -1 at 750°C and at the two different pressure levels, respectively. Most studies only report productivities in the low-temperature regime. Here, hte’s Fe-based catalyst reached 4-13 mmol(H₂)/min/g(cat) at 550-600°C, which is comparable with literature reports of the same material group (Ristig, et al., 2022). The blank reactors did not show any significant conversion (<1% at T up to 700°C and 2% at
750°C), demonstrating the suitability and the inert behaviour of hte’s reactor concept under such severe conditions. During the entire study, 5,000 ppm of H₂O was co-fed to simulate commercial-grade NH₃ (Ashcroft & Goddin, 2022) with full recovery at the online GC. Furthermore, the H recovery containing all feed and product components was closed, enabled by a robust and precise analytics workflow. The temperature screening was repeated for both pressures, revealing an activity loss of 1-4% at 15 barg and 4-6% at 40 barg. Finally, scouting experiments up to 50 barg were carried out while varying the feed rate by a factor of four to demonstrate the flexibility of the equipment and extend the covered parameter space to 5,000-200,000 h -1 . The GHSV could have been increased to even higher values (approximately 1,000,000 h -1 ) when reducing the catalyst amount loaded to the reactors at the applied feed rate, which was already demonstrated in an earlier study for reverse water-gas shift (Mutz, et al., 2022). In parallel to the temperature screening shown in Figure 2, a different reactor was kept at a constant temperature of 650°C, serving as a performance stability test within the conducted experiments. It is observed that the catalyst lost a significant share of its initial performance at 40 barg without reaching steady state during the first 60 hours (h) time on stream (TOS). Reduction of the pressure to 15 barg stopped the trend of decreasing performance, and a recovery of the NH₃ conversion to approximately 70% was observed. In the following 40 barg sequence,
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