Before the toggle valves copper as well as stainless

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Unformatted text preview: er (Supelco). Each individual gas supply line could be opened and closed by a toggle valve placed before the mass flow controllers. Before the toggle valves copper as well as stainless steel tubing was used whereas after the toggle valves only stainless steel tubing, the tube diameter was in all cases  $IWHU WKH mass flow controllers the gases were allowed to mix. A 4 port 3.2 mm (1/8Ž valve allowed choosing whether the gas mixture flew through the reactor or bypassing it. Bypassing the reactor allowed faster calibration and was essential for checking any leaks in the reactor by comparing the flow rates through the reactor and through the bypass. As in the temperature programmed reactions and the test reactions the reactor consisted of a quartz tube, inner diameter 4 mm, outer diameter 6 mm, in which the catalyst was placed on a quartz wool bed, the whole reactor set up is depicted in Figure 7. The quartz wool bed was replaced for each experiment. It was observed that the quartz wool bed and the catalysts could be pushed down the reactor by the flowing gas mixture. To avoid this the quartz wool bed was hold by a quartz capillary from beneath. Otherwise the reactor set up is identical with the one used for the catalytic test reactions and the temperature programmed reactions described above. The temperature of the reactor was controlled by a temperature controller identical to the one used in the temperature programmed reactions. Water was separated from the product stream by a glass condensator at 0°C using a water-ice mixture. 2. Experimental 63 After the condensation of water the gases were analysed by the analytical unit consisting of a gas chromatograph (GC-TCD) (Varian, USA, model Star 3400CX) equipped with thermal conductivity detector and Carboxen 1004 micropacked porous carbon column, 2· 1/16’ in stainless steel (Supelco). Samples were taken automatically using a GC controlled 6 port valve equipped with a sample loop. Helium was used as carrier gas. The comparison of the flow rat...
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