Flow pulsing

Rota.ry Lobe Pumps. Rotary lobe pumps are similar to gear pumps in principle. These pumps have an added advantage of noncontacting metal parts by use of external gears, which reduces the wear, but adds complexity. Low wear and improved shear characteristics make these pumps apphcable to the food industry, where cleanliness and absence of contamination are required. These pumps produce a strong pulsing flow that must be addressed. 

Baines, N.A., Hajilouy-Benisi, A., and Yeo, J.H., 1994. The Pulse Flow Performance and Modeling of Radial Inflow Turbines, IMechE, Paper No. a405/017. 

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. 

The centrifugal pump is a versatile unit in the process plant, since its ease of control, non-pulsing flow, pressure limiting operation fits many small and large flow systems. 

Design of oversized piping to overcome the higher pressure drop induced by pulsative flow. 

Some of the later papers referred to have pointed to the existence of distinctly different flow patterns under conditions normally characterized as trickle-flow operation. The pulsing flow pattern observed may be of particular interest, and this mode of operation could be a fertile area for research. 

Weekman and Myers (W3) measured wall-to-bed heat-transfer coefficients for downward cocurrent flow of air and water in the column used in the experiments referred to in Section V,A,4. The transition from homogeneous to pulsing flow corresponds to an increase of several hundred percent of the radial heat-transfer rate. The heat-transfer coefficients are much higher than those observed for single-phase liquid flow. Correlations were developed on the basis of a radial-transport model, and the penetration theory could be applied for the pulsing-flow pattern. 

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)...

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.

Carbon dioxide chemisorptions were carried out on a pulse-flow microreactor system with on-line gas chromatography using a thermal conductivity detector. The catalyst (0.4 g) was heated in flowing helium (40 cm3min ) to 723 K at 10 Kmin"1. The samples were held at this temperature for 2 hours before being cooled to room temperature and maintained in a helium flow. Pulses of gas (—1.53 x 10"5 moles) were introduced to the carrier gas from the sample loop. After passage through the catalyst bed the total contents of the pulse were analysed by GC and mass spectroscopy (ESS MS). 

Rotary splitter (Selves and Barnes, 1993), which can be used to provide up to 36-way splitting. Due to its intermittent operation, the pulsing flow in the branches downstream of the splitter would not be suitable for applications requiring a smooth and regular injection of material. 

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. 

Figure 5. Pulse flow measurement of the conversion of CO over prereduced (top curves reduction in 5% CO in He at 600°C for 1 h at a flow of 100 mL/60 s.) and as received (bottom curves) La2FeMnOe. Duty cycle 30 s pulse length, 10 min interval, 18-23-s sample delay. Conditions t, decreased or increased in steps catalyst weight, 176 mg and flow, 100 mL/60 s of 5% CO and 5% OsinHe.

Figure 7. Pulse flow and continuous flow measurements of the conversion of CO over prereduced (see Fig. 6 for conditions) Sr,tFeMnOs. Flow of 100 mL/60 s of 5% CO and 5% 02 in He over 177 mg of catalyst. Key , points taken during stepwise decrease of temperature and O, A, during stepwise increase.

A square concentration pulse flow technique has been developed to study the kinetics of catalytic reactions over catalysts which change their stoichiometry in response to the reaction conditions. The technique makes it possible to obtain hysteresis-free kinetics data while greatly reducing the time during which the catalyst is exposed to the reaction mixture. 

Fluidized bed (2) Moving beds Microspheres, spheroids Slurries, inclined bed, tumbled beds, vibrated beds, beds with pulsed flow, Raschig rings... 

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. 

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