Pulse Reactors

At higher total flow rates, particularly when the Hquid is prone to foaming, the reactor is a pulsed column. This designation arises from the observation that the pressure drop within the catalyst bed cycles at a constant frequency as a result of Hquid temporarily blocking gas or vapor pathways. The pulsed column is not to be confused with the pulse reactor used to obtain kinetic data ia which a pulse of reactant is introduced into a tube containing a small amount of catalyst. 

Figure 4-24. Pulse reactors. (Source V. W. Weekman, Laboratory Reactors and Their Limitations," A ChEJ, Vol. 20, p. 833, 1974. Used with permission of the AlChEJ.)...

Experiments were carried out in a pulse reactor system based on the TAP-2 reactor described by Cleaves et al. [3]. This consists of a small tubular reactor and a detector housed in a vacujun system pumped by a 1,500 Is" turbomolecular pump to a base pressure of... 

A pulse reactor system similar to that described by Brazdll, et al( ) was used to obtain the kinetic data. The reactor was a stainless-steel U-tube, composed of a l/S" x 6 preheat zone and a 3/8" X 6 reactor zone with a maximum catalyst volume of about 5.0 cm. The reactor was Immersed In a temperature controlled molten salt bath. 

We thank K. S. Patel and D. M. DiCicco for providing the dynamometer-aged catalysts and sweep evaluation data. E. Gulari and C. Sze (U. of Michigan) assisted with the design of the pulsed reactor system. 

In order to investigate whether COj reacts in a concerted way with surface carbon or whether it dissociates first to CO and adsorbed oxygen and the adsorbed oxygen reacts, infrared spectroscopy, pulse reactor studies and XANES measuremerrts were used. The i.r. spectrum of a prereduced (Ihour at 675K in S /oHj/Nj) Pt/ZrOj catalyst in contact with CO2 at 775K is shown in Fig 6 The spectrum shows the presence of linearly bound CO on Pt at 2053 cm [15]. Additionally, bands of carbonate type species appeared in the region between 1375 and 1540 cm . Over pure supports (in the absence of Pt) the CO band was not seen, but peaks in the carbonate region were observed... 

Fig. 7 Cumene cracking over H-ZSM5 and the physical mixture of Pt/Si02 and H-ZSM-5 at 423K in a pulse reactor.

The pulse technique may also be conveniently extended to include stages of reactant preparation. Figure 9 shows a schematic representation of a pulse reactor system recently used by Gault et al. (81), which includes stages for alcohol (the reactant precursor) dehydration and subsequent olefin hydrogenation, the resulting saturated hydrocarbon being the material of catalytic interest. A method has been described (82) which allows the use of a pulse reactor at above atmospheric pressure. 

In a first scale-up to an air pulsed reactor of 1.5 L, it can be seen how at lower concentrations (250 pg/L) the removal of both studied benzophenones is also very high. In the case of 4-MBC, as well as other highly hydrophobic compounds, those kinds of studies in bioreactor are not suitable to perform because it is totally necessary a complete solubilization of the compound for a reliable quantification. Therefore, liquid samples cannot be taken at different time course because they would not be representative. That fact, at different scale, would be what happen with those compounds in the WWTP (and to extension in the environment) the more soluble compounds, like benzophenones, are those found in a higher proportion in the liquid effluent, while the UV filters with a higher log Kow (such as 4-MBC and OC) are mainly found adsorbed onto the sludge. 

Finally, experimental procedures differing from that described in the preceding examples could also be employed for studying catalytic reactions by means of heat-flow calorimetry. In order to assess, at least qualitatively, but rapidly, the decay of the activity of a catalyst in the course of its action, the reaction mixture could be, for instance, either diluted in a carrier gas and fed continuously to the catalyst placed in the calorimeter, or injected as successive slugs in the stream of carrier gas. Calorimetric and kinetic data could therefore be recorded simultaneously, at least in favorable cases, by using flow or pulse reactors equipped with heat-flow calorimeters in place of the usual furnaces. 

Takeuchi, H., S. Takaiwa, S. Hodoshima, and Y. Saito, Hydrogen formation with use of a flow-type pulse reactor for catalytic decalin dehydrogenation. /. Hydrogen Energy Syst. Soc. Jpn., 28(1), 61-66 (2003). 

Development of a Pulse Reactor with On-Line MS Analysis to Study the Oxidation of Methanol... 

Initial tests using the pulse reactor described in this paper have been done on the selective oxidation of methanol to formaldehyde using molybdate catalysts. 

Catalytic titration, 27 114-118 gas-liquid chromatography, 27 115, 116 pulse reactors, 27 115, 116 Catalyzed reactions, mechanisms, 38 234-236 Catenanes, 24 135 Cathodes... 

The disproportionation and isomerization of trimethylbenzene(TrMB) were studied at 200°C using a continuous fixed bed reactor. The reactant TrMB was diluted with nitrogen in a molar ratio of 1 9. The cracking of cumene was carried out at 400 C using a pulse reactor. The catalyst was treated in a stream of nitrogen for 1 h at a desired temperature in the range 400-600°C prior... 

Table m. Influence of the Gas Phase Oxygen on the Products Formation in Methane Partial Oxidation over Si02> 4% Mo03/Si02 and 5% V205/Si02 Catalysts. Pulse Reactor Data ... 

These two samples were then tested for the oxidation of butane in a pulse reactor. In these studies, pulses of butane (0.05 ml at 1 atm) were passed in a He carrier over 0.05 g of 8.2 V/nm catalyst or 0.75 g of 2.9 V/nm catalyst [17]. The products were collected in a trap at 77 K and later flashed into a gas chromatograph for analysis. Since no gaseous oxygen was present, the oxygen consumed by the reaction had to be originated from the lattice. Therefore, from the product selectivities and conversions of the butane pulses, the degrees of reduction of the catalysts could be calculated. 

See Ref. 5. Catalysts supported metals, 0.8-5%. Apparatus pulse reactor, at atmospheric pressure of H2. Multiple splitting hydrocarbon is split off into C, pieces (CHJ before it leaves the catalyst surface. Terminal splitting always one C, fragment is split off during one adsorption sojourn on the surface. 

---