Reactor recirculation

With a reaction-limited deposition process, the film should have uniform thickness as long as the partial pressures ofreactants do not vary with position. In a tubular reactor, the conversion of reactants must be kept small or the film thickness will depend on the location of the sohd in the reactor, with upstream regions having a greater deposition rate. It is therefore common to use a gas recirculation reactor (a recycle PFTR) so that the composition of the reactants is independent of position in the reactor to assure uniform film thickness. 

A thorough comparative study of the reactivity of O-, OJ, and Oj toward alkanes and alkenes on MgO has been carried out by Lunsford and co-workers (see Sections V and VI in Ref. 1 and Section VI in this article). In these stoichiometric studies, a known concentration of oxygen species on the surface was reacted with a known amount of hydrocarbon in a recirculation reactor and the products were analyzed. In all cases, a 1 1 stoichiometry was observed. 

Lyubarski et al. [192] studied the oxidation of tolualdehyde, phthalic anhydride and maleic anhydride, separately and in mixtures, using a recirculation reactor with a high temperature V2Os catalyst at 400—460° C. o-Tolualdehyde (and o-xylene) were found to stabilize phthalic anhydride, even with a 10 1 excess of the latter. Phthalic anhydride, in turn, appeared to inhibit the maleic anhydride oxidation. Consequently, the tolualdehyde oxidation seemingly follows a parallel scheme... 

Hydrogen oxidation on Pt catalyst in adiabatic recirculating reactor Horak and Jirafcek (45) X X... 

It is interesting to note that the cis-trans ratios obtained by Ghorbel and coworkers (312) on 1-butene isomerization were mostly unaffected by the chemisorption of the different poisons and corresponded to the thermodynamically determined ratio. The same result was obtained by Knozinger and Aounallah (377), when 1-butene was isomerized in a recirculating reactor at 120°C on tj-A1203 (activated at 500°C) that was partially poisoned by pyridine. In micro-catalytic pulse experiments, on the other hand, one observes kinetically determined primary product distributions with cis-trans ratios of about 2 (370). Different types of active sites appear, therefore, to be involved in the doublebond shift and in the cis-trans isomerization, the latter remaining unaffected by pyridine chemisorption. 

The most applied CSTRs are recirculation reactors in heterogeneous catalysis and well stirred vessels in slurry or liquid-phase systems. Injection of a (5-pulse of a tracer should give an exponentially decaying output concentration ... 

In recirculation reactors, a recirculation ratio Rc (ratio of the total flow returned to the inlet and the total outlet flow) larger than 20 is frequently recommended [11, 16]. This criterion is not complete as is apparent from the literature [17-19]. One can demand that the rate over the catalyst bed may not change more than 5%, thus for an nth order isothermal reaction,... 

Key Features of an Internal Recirculation Reactor [After Shah, 1979]... 

It is necessary to consider the mass balances over the electrochemical cell and the reservoir to describe the temporal evolution of COD in the batch recirculation reactor system given in Fig. 1.5. Considering that the volume of the electrochemical reactor Ve (m3) is much smaller than the reservoir volume Vr (m3), we can obtain from the mass balance on COD for the electrochemical cell the following relation ... 

Fig. 8.1 Types of ideal chemical reactors (Levenspiel, 1996). The batch recirculation reactor system consists of a vessel of total volume V and a reactor of a specified volume Vr, CSTR continuously stirred tank reactor.

On the other hand, the treatment of M in a batch recirculation reactor system will generate a completely different concentration profile (Fig. 8-2, situation B). Small fractions of fluid are continuously removed from the batch tank and pumped through the photoreactor module (PR). Here, the same amount of OH... 

The kinetics must be obtained in a reactor that should be as simple as possible with a well-characterized geometry in such a way that the obtained parameters are point value results of position and time. The laboratory device shovm in Figures 4 and 5 is a continuous flow, well-mixed, recirculating reactor. The details are described in Table 2. The reader interested in... 

A specific t)q)e of recirculating reactor is the commercial indoor-air treatment device. The device is characterized by a small operating volume (a few lifers af mosf), which is several orders of magnitude smaller than the reservoir (a room, vehicle, or aircraft, for example). The reactor itself can be eifher free standing or part of a larger system, usually an air-conditioning system, and is supposed to be able to take care of continuous emission of... 

Several reactors are presently used for studying gas-solid reactions. These reactors should, in principle, be useful for studying gas-liquid-solid catalytic reactions. The reactors are the ball-mill reactor (Fig. 5-10), a fluidized-bed reactor with an agitator (Fig. 5-11), a stirred reactor with catalyst impregnated on the reactor walls or placed in an annular basket (Fig. 5-12), a reactor with catalyst placed in a stationary cylindrical basket (Fig. 5-13), an internal recirculation reactor (Fig. 5-14), microreactors (Fig. 5-16), a single-pellet pulse reactor (Fig. 5-17), and a chromatographic-column pulse reactor (Fig. 5-18). The key features of these reactors are listed in Tables 5-3 through 5-9. The pertinent references for these reactors are listed at the end of the chapter. 

Figure 5-14 Internal recirculation reactors, (o) With catalyst at the wall.65 (b) with catalyst at the center.64...

The analytical problems associated with differential reactors can be overcome by the use of the recirculation reactor. A simplified form, called a Schwab reactor, is described by Weisz and Prater . Boreskov.and other Russian workers have described a number of other modifications " . The recirculation reactor is equivalent kinetically to the well-stirred continuous reactor or backmix reactor , which is widely used for homogeneous liquid phase reactions. Fig. 28 illustrates the principle of this system. The reactor consists of a loop containing a volume of catalyst V and a circulating pump which can recycle gas at a much higher rate, G, than the constant feed and, withdrawal rates F. 

One type of reactor which can be useful for kinetic measurements is the continuous stirred tank reactor (CSTR). The kinetic model is identical with that for the recirculation reactor and the designs are based on the reactors used for homogeneous reactions. Carberry et have described a CSTR which... 

Otto et al. at the Ford Motor Company have published two papers ° on the reaction of NO with NH3 over supported platinum at 200—250 °C in a recirculating reactor. Working at total pressures of about lOOTorr they were able to show that the overall stoicheiometry was virtually independent of NH3/NO ratio and temperature. The approximate product distribution was given by... 

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