34 coking and catalyst deactivation at 700 and 800c

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Unformatted text preview: : 2nd experiment 95 90 O2 85 0 50 100 150 yieldy [%] 100 C3H8 200 CO 250 H2 90 80 70 60 0 50 100 150 25 H2O 200 CH4 250 CO2 yield [%] 20 15 10 5 0 0 50 100 150 200 time [min] Fig. 35 Catalytic performance and reproducibility with time-on-stream of the reference catalyst at 800°C, 25% O2 surplus, GHSV 900dm3·h-1·g-1, TOS 240min 250 4. Results and discussion - catalytic partial oxidation of propane 115 All the investigated catalysts were found successful in the partial oxidation of C3H8 at 700 and 800°C. Over all catalysts CO and H2 were at both temperatures the main products and H2O, CH4 and CO2 the only considerable side products. This is in contrast to the partial oxidation of propane performed over Pt or Pd containing catalysts [22]. Over Pt the olefins C3H6 and C2H4 were main products and Pd was not suitable due to rapid deactivation by coking. For a higher yield of syngas over the Ni catalysts it is favourable to perform the reaction at 800 instead of 700°C. The catalysts with a low and medium Ni/Mg ratio are superior in the syngas formation compared to the catalysts with a higher ratio or the reference catalyst. At 800°C the highest yield of CO and H2 were achieved over the catalyst Ni10C900, at 700°C the highest yield of CO was observed over Ni30C900 and the highest yield of H2 again over Ni10C900. However, considering both the yields of CO and H 2 also at 700°C Ni10C900 should be regarded as the best of the studied catalyst. No clear connection between the tendency towards coking and the catalyst deactivation with TOS can be found, which is attributed to the fact that different forms of coke can be formed under the reaction conditions, e.g. deactivating pyrolytic coke and non deactivating filamental coke. The observation that the tendency towards coking found for the HT derived Mg containing catalysts does not extent to the pure Ni/Al catalyst is attributed to the fact that the catalysts consist of a different structure. As shown in the investigation of the reduction...
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This document was uploaded on 10/07/2013.

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