The standard catalytic test was carried out by

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Unformatted text preview: prior to the reaction first C3H8 was added to the existing flow of He and allowed to stabilise before adding O2 to the feed. The standard catalytic test was carried out by passing continuously 75 ml/min of the reaction mixture over the catalyst resulting in a gas hourly space velocity (GHSV) of 900 dm3· h-1· g(cat)-1 measured at room temperature and atmospheric pressure. The reaction mixture consisted of C3H8, O2 and He in a ratio of 16/30/54. The temperature rise observed at the beginning of the reaction was automatically compensated by decreasing the heating power of the furnace. The reaction temperature had to be stable at the set temperature for at least 5 min before the first analysis. After the stabilisation of the temperature the reaction temperature had to be constant within 2°C of the set temperature otherwise the experiment was rejected. After 240 min on stream the reaction was stopped by switching off first the O2 and then C3H8 flow in order to avoid oxidation of the carbon deposits or of the catalyst. The catalyst was cooled down in a flow of He and separated from the quartz wool bed for further the determination of the amount of coke formed during the reaction. Experiments with different C3H8/O2 ratios were performed by increasing or decreasing the O2 flow. The total flow and hence the GHSV were kept constant by adjusting the helium flow accordingly. Experiments carried out at different GHSVs were performed 2. Experimental 66 ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffyffffffffffffffffffffffffffffff fffffffffff by using the same ratio of the gases as under the standard test reaction but changing the total flow rate while keeping the amount of the catalyst constant. This was done because the length of the catalyst bed can influence the performance of the catalyst even at the same GHSV [121]. The flow rates of the gases were measured using the same bubble flow meter as in the leak checks. The carbon content of the spent catalyst was measured as mas...
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