Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

26 EXPERIMENTAL METHODS FOR SLOW REACTIONSGAS HANDLINGSYSTEM-FurnaceSUPPLIESNRC 1293M-4Manifold gate ~valveCVC Ambientchevron bafflepre-ampTO NRC HS4-750Diffusion-pump 91.0‘u5Scale in inchesFig. 18. Schematic drawing of the VLPP apparatus. From ref. 87.at a few torr through a variable leak valve and a short length of capillary tubingand from there to the RV. Gases which effuse from the reactor pass to the ionisationchamber of a quadrupole mass spectrometer, which enables the extent of reactionto be determined. A schematic drawing of the apparatus is shown in Fig. 18.(b) Reaction oesselsTypical RV’s are shown in Fig. 19 (thermal systems) and Fig. 20 (photochemicalsystems). They may be subjected to the usual treatments of coating, packing andconditioning (cf. static RV’s). Inherent problems attaching to flow systems areuncertainty of RV volume and residence time in the RV, preheating, pressure dropacross the RV, Poiseuille shearing of flow across the diameter of the RV, andpartial mixing of reactants, products and carrier gas, when “plug” flow is assumed.Gilbert” has shown that partial mixing occurs in the decomposition of hydrazineusing the toluene carrier gas techniqueg0. These difficulties are largely overcomeif a stirred-turbulent or capacity-flow RV is used. This system was devisedby Bodenstein and Wohlgastgl. Since then, it has been used extensively for reactionsin the liquid phase, but not in the gas phase until recentlyg2 -”. In particular,the technique has been reviewed and the theory developed by Denbighg8. Stir-