90
40
GHSV = 11 , 000 h -1 at 650˚C
35
80
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0
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Time on stream (h) 150
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Figure 3 Performance stability of the Fe-based catalyst operated at 11,000 h -1 and 650°C within the same experiment as shown in Figure 2 using hte’s advanced high throughput technology (95% NH₃, 5,000 ppm H₂O, 4.5 % Ar, 15 and 40 barg).
a constant conversion level at 64-65% was approached. This experiment shows strong run- in behaviour of the catalyst during the start-up phase of the process. Thus, a stabilisation phase should be considered when testing catalysts for NH₃ cracking at elevated temperature and pressure. Please note that this catalyst was a catalyst for unit validation prepared in-house and not tuned for this kind of chemistry. An Arrhenius plot using the H₂ formation rate from the reactors operated at 100,000 h -1 (see Figure 4 ) revealed an apparent activation energy of approximately 160 kJ/mol of the catalyst in its equilibrated state (second run 110-250 h TOS, slightly lower activity) and approximately 140 kJ/mol during the initial
activity (0-110 h TOS). These values are in line with literature studies reporting 150 kJ/mol for Fe-based catalyst (Zhang, et al., 2008). Screening As the fitness of the technology and equipment was proven regarding NH₃ cracking at elevated pressure combined with high temperature, the high throughput unit was used to support and accelerate hte’s customer’s catalyst and process R&D. Typical projects address the screening of newly developed or optimised materials, process optimisation, accelerated ageing tests, generation of data sets for kinetic modelling, commercial catalyst benchmarking, quality control of different catalyst batches, or (co-)feed studies. This section introduces an extract of a customer project investigating the performance of four different catalysts under a broad range of process parameters (see Figure 5 ). The catalyst materials were loaded into the parallel reactors in three to four different bed lengths to realise GHSV variation for each experiment and to allow the best possible catalyst ranking. During the four weeks of screening time, 72-96 different process conditions were screened for each of the four catalysts, which emphasised the potential of a high throughput unit in accelerating catalyst R&D, as well as speeding up time to market. The reactor temperature applied for the catalysts was chosen individually according to the requirements of the different material groups. Some catalysts were already
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100 , 000 h -1 , 15 barg 100 , 000 h -1 , 40 barg
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F(x) = -19.1308 x + 18.6104 F(x) = -20.0418 x + 19.1892
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1
1000/Temperature (K -1 ) 1.15 1.1 1.05
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Figure 4 Arrhenius plot of the reactors operated at 100,000 h -1 in equilibrated state (second temperature cycle, 95% NH₃, 5,000 ppm H₂O, 4.5% Ar, 550-750°C, 15 and 40 barg)
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