Pulsed-flow reactor

The catalytic activity for the dehydrofluorination of CF3CH2CI was measured at 320°C, under atmospheric pressure, in a pulse flow reactor [9]. Pulses of pure CF3CH2CI were injected into a helium stream ev ten minutes. The amount of chlorocompound was adjusted (40.9 pmol) in order to obtain a converaon ca 10 %. 

The transformation of CF3CH2CI was studied at 320 C in a pulse flow reactor. Indeed, in a dynamic reactor, the agnificant alkene formation leads to a rapid deactivation of the catalyst. The reaction is carried out in absence of HF in order to favour the dehydrofluorination reaction. Products distribution is shown in Fig. 1. 

Figure 1. Products of CF3CH2CI transformation without HF over chromium oxide versus the time (T = 320°C,pulse flow reactor, 1 pulse = 40.9nmol CF3CH2CI)...

Continuous reactors have traditionally been used for reactions with fast kinetics [10]. Solutions to this limitation are being developed, such as recycling or pulsed flow reactors [11]. However, an alternative solution to this limitation is simply to avoid it by re-thinking the chemical route to the target molecule. 

No detailed kinetic study of thiol or sulphide dehydrosulphidation has been reported, but first-order kinetics have been assumed for measurements with a pulse flow reactor and found acceptable [248,249]. 

Oxidation of ethene on silver catalysts to yield ethene oxide is a good example of an industrial catalytic process with a high selectivity. In order to confirm a possible correlation between the catalysts affinity towards oxygen and their activity in ethene epoxidation, a heat-flow microcalorimeter equipped with a pulse flow reactor has been used to study the reaction of oxygen at 473 K with a series of silica-supported silver catalysts [71]. At 473 K, adsorption of oxygen at the surface of silver is a fast process incorporation of oxygen into deeper metal layers, though present, is a slow process. 

The stoicheiometric number concept has been applied to butane dehydrogenation, the isobutane-isobutene-H2 system, SO2 oxidation and ethanol dehydrogenation. Experimentally it is desirable to operate in a differential mode, using a reactor either of the recirculating or once-through continuous flow type. Since the method is based on the assumption that a steady state exists as regards the concentration of surface intermediates, pulsed flow reactors are not suitable for this type of experiment. 

Belmant C, Cognet P, Berlan J, Lacoste G, Fabie P-L, Jud J-M (1998) Application of an electrochemical pulsed flow reactor to electroorganic synthesis. Part I Reduction of acetophenone. J Appl Electrochem 28 185-191... 

Most ion-molecule techniques study reactivity at pressures below 1000 Pa however, several techniques now exist for studying reactions above this pressure range. These include time-resolved, atmospheric-pressure, mass spectrometry optical spectroscopy in a pulsed discharge ion-mobility spectrometry [108] and the turbulent flow reactor [109]. 

In the continuous hydrovinylation experiments, the ionic catalyst solution was placed in the reactor R, where it was in intimate contact with the continuous reaction phase entering from the bottom (no stirring was used in these experiments). The reaction phase was made up in the mixer from a pulsed flow of ethylene and a continuous flow of styrene and compressed CO2. 

Fig. 5.2.1 Flow regimes in a trickle-bed reactor (after Sie and Krishna [2]). Typical conditions for research and industrial reactor operation are indicated. The black line indicates the boundary between the pulsed flow regime and the spray, trickle and bubble flow regimes.

The responses of this system to ideal step and pulse inputs are shown in Figure 11.3. Because the flow patterns in real tubular reactors will always involve some axial mixing and boundary layer flow near the walls of the vessels, they will distort the response curves for the ideal plug flow reactor. Consequently, the responses of a real tubular reactor to these inputs may look like those shown in Figure 11.3. 

Pulse operation (80) is an alternative mode with a flow reactor, and is particularly convenient for use with reactants which are only available in very small quantities (e.g. 13C-labeled substances). It also has the advantage that the pulse of reaction products may, if desired, be passed directly to a GPC column for analysis. 

The decolorization of Orange II by immobilized P. chrysosporium in a continuous packed-bed reactor (PBR) was investigated [50]. Nearly complete decolorization (95%) with immobilized fungus on PuF was obtained when working at optimal conditions [dye load rate of 0.2 g/l/d, temperature of 37°C, a hydraulic retention time (HRT) of 24 h], and also oxygen gas in a pulsed flow was applied. A correlation between residual MnP activity and decolorization was observed, but no laccase and LiP enzyme activities were detected. 

Fig. 8. CH4 conversion as a function of the number of CH4/O2 pulses for partial oxidation of CH4 catalyzed by Ni/La203. Reaction conditions temperature, 873 K catalyst, 20 mg of 20 wt% Ni/La203 loaded in a fixed-bed flow reactor feed gas, 0.9 mL CH4/02 (molar ratio 2/1) in each pulse carrier gas, helium (flow rate, 100 mL min-1) (134).

There are several preparative methods for the production of bare metal clusters including the fast flow reactor (PER), the fast flow tube reactor (FTR), the SIDT (24), the GIB (23), and a supersonic cluster beam source (SCBS) (198). Essentially, all of these methods are similar. The first process is to vaporize the metal sample producing atoms, clusters, and ions. Laser vaporization is generally favored although FAB or FIB may be used. The sample is located in a chamber or a tube and so vaporization generally takes place in a confined environment. An inert gas such as helium may be present in the vaporization source or may be pulsed in after the ionization process. 

For a conservative tracer with an unsteady input, a plug flow reactor simply acts as a time lag, where the input comes out of the reactor later, precisely as it went in. The examples of a pulse input and a front input at time t = 0 are given in Figure 6.7. The only difference between the inflow and the outflow are the times at which the... 

Figure 6.7. Response of a plug flow reactor to a pulse and to a front in concentration at f = 0. (Top) Front. (Bottom) Pulse.

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