Reforming in Monolithic Reactors

Homg described the start-up behaviour of their monolithic autothermal methanol reformer [479]. The ceramic monolith was coated with a mixed platinum and copper/ zinc oxide catalyst. The monolith had 117-mm diameter and 50-mm length, while the whole reactor was more than 510-mm long. Glow plugs were used for the start-up. 

The latter is necessary to avoid excessive cooling ofthe air feed through evaporation of the methanol. 

These investigations document the problem of hot spot formation in monoUthic reactors. The temperature of methanol autothermal reforming should not exceed 350 °C to minimise carbon monoxide formation. 

At 290 °C reaction temperature and a feed composition of 9 vol.% methanol and 11% water, which corresponded to S/C 1.2,65% methanol conversion could be achieved at 99% hydrogen selectivity over CuZns samples treated by acid leaching for 20 min. Under autothermal conditions, more than 25% methanol conversion was achieved at S/C 1.2 and 0/C 0.3, while the oxygen was fully converted. Later, Homy et al. improved their catalyst by doping with chromium [482]. At S/C 1.0 and 0/C 0.25, axial temperature profiles were determined over the reactor to determine the hot spot formation. The hot spot did not exceed 3 K due to the high heat conductivity ofthe brass. A fixed catalyst bed showed a hot spot of about 20 K under comparable conditions. 

Catillon et al. reported the application of a copper/zinc oxide catalyst coated onto copper foams for methanol steam reforming [483]. Significant improvement ofthe heat transfer and consequently higher catalyst activity was achieved compared with fixed catalyst beds. 

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