To further minimise the total temperature gradient

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Unformatted text preview: eed that the koalinite wool plug is always of the same thickness and shape, both factors that may change the temperature profile and hence the catalytic performance. To further minimise the total temperature gradient over the whole reactor and to improve the isothermal zone especially, the furnace was rebuild using the same electrical heating element (Fig. 9). A wider and longer metal container with a tightly fitting lid was used in which the furnace was placed. The free space between the metal container and the heating element was filled with insulating kaolinite wool enlarging the furnace dimensions and the heated zone. Furthermore a straight quartz tube was inserted between the furnace and the reactor reducing the space through which cold air can circulate. The 3 way T-junction which hold the reactor was placed on the top of the insert. This way the T-junction also plugged the top end of the insert, hence avoiding the need for an additional kaolinite wool plug. This way the reactor could also be placed without any complications in the same position in every experiment. The rebuilding of the furnace improved the temperature profile remarkably (Fig. 9). As the hottest zone was only shifted upstream by 0.3 cm and the temperature gradient in the innermost 1cm of the hottest zone was reduced to 2°C. Also the whole temperature profile was found to be much narrower. Therefore the furnace was regarded as suitable. 2. Experimental 72 The temperature measurements were performed at 800°C in a flow of 50 and 100 ml/min He in order to resemble the reaction conditions as much as possible. Helium was used for the measurements, because of its good thermal conductivity ensuring accurate temperature readings. The actual temperature at different positions was measured by an additional external thermocouple system. Each measurement was performed twice. The reproducibility for each experiment at each point was within ± 1°C. The flow rate had no considerable influence on the temperature (± 2°C) or th...
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