Batch reactor residence time distribution

Two-Phase Liquid-Liquid Systems. Mhdng times for both liquid phases and the overall liquid-liquid mass-transfer rate are the most important issues for two-phase liquid-liquid homogeneous catalytic batch reactors. Residence time distributions and overall liquid-liquid mass transfer are the most important issues for two-phase liquid-liquid homogeneous catalytic CSTRs. 

The concept of a well-stirred segregated reactor which also has an exponential residence time distribution function was introduced by Dankwerts (16, 17) and was elaborated upon by Zweitering (18). In a totally segregated, stirred tank reactor, the feed stream is envisioned to enter the reactor in the form of macro-molecular capsules which do not exchange their contents with other capsules in the feed stream or in the reactor volume. The capsules act as batch reactors with reaction times equal to their residence time in the reactor. The reactor product is thus found by calculating the weighted sum of a series of batch reactor products with reaction times from zero to infinity. The weighting factor is determined by the residence time distribution function of the constant flow stirred tank reactor. 

To run the residence time distribution experiments under conditions which would simulate the conditions occurring during chemical reaction, solutions of 15 weight percent and 30 percent polystyrene in benzene as well as pure benzene were used as the fluid medium. The polystyrene used in the RTD experiment was prepared in a batch reactor and had a number average degree of polymerization of 320 and a polydispersity index, DI, of 1.17. 

Chemical Kinetics, Tank and Tubular Reactor Fundamentals, Residence Time Distributions, Multiphase Reaction Systems, Basic Reactor Types, Batch Reactor Dynamics, Semi-batch Reactors, Control and Stability of Nonisotheimal Reactors. Complex Reactions with Feeding Strategies, Liquid Phase Tubular Reactors, Gas Phase Tubular Reactors, Axial Dispersion, Unsteady State Tubular Reactor Models... 

The Residence Time Distribution. All fluid elements have the same residence time in a batch reactor, but there will be a wide spread in residence times in a CSTR. 

For cases where the growth period is the same as the residence time in the reactor, as in polycondensation processes, the residence time distribution is the dominant factor influencing the molecular weight distribution. In this case one obtains a broader molecular weight distribution from a CSTR than from a batch reactor. Figure 9.12 [also taken from Denbigh (11)] indicates the type of behavior expected for systems of this type. 

The integral for a batch reaction is tabulated in the first two columns. A potential reactor has the residence time distribution E(t) given in column 3. Find the outlet concentration in segregated flow. 

Continuous Multicomponent Distillation Column 501 Gas Separation by Membrane Permeation 475 Transport of Heavy Metals in Water and Sediment 565 Residence Time Distribution Studies 381 Nitrification in a Fluidised Bed Reactor 547 Conversion of Nitrobenzene to Aniline 329 Non-Ideal Stirred-Tank Reactor 374 Oscillating Tank Reactor Behaviour 290 Oxidation Reaction in an Aerated Tank 250 Classic Streeter-Phelps Oxygen Sag Curves 569 Auto-Refrigerated Reactor 295 Batch Reactor of Luyben 253 Reversible Reaction with Temperature Effects 305 Reversible Reaction with Variable Heat Capacities 299 Reaction with Integrated Extraction of Inhibitory Product 280... 

In industrial reactors, the full equilibration of the chain length distribution is prevented by incomplete mixing, as well as by the residence time distribution, thus resulting in considerable deviations from the equilibrium polydispersity index. These deviations are generally higher for continuous plants than for batch plants and increase with increasing plant capacity as demonstrated in Figure 2.2. 

Generally, alkoxide-derived monodisperse oxide particles have been produced by batch processes on a beaker scale. However, on an industrial scale, the batch process is not suitable. Therefore, a continuous process is required for mass production. The stirred tank reactors (46) used in industrial process usually lead to the formation of spherical, oxide powders with a broad particle size distribution, because the residence time distribution in reactor is broad. It is necessary to design a novel apparatus for a continuous production system of monodispersed, spherical oxide particles. So far, the continuous production system of monodisperse particles by the forced hydrolysis... 

The SSE is an important and practical LCFR. We discussed the flow fields in SSEs in Section 6.3 and showed that the helical shape of the screw channel induces a cross-channel velocity profile that leads to a rather narrow residence time distribution (RTD) with crosschannel mixing such that a small axial increment that moves down-channel can be viewed as a reasonably mixed differential batch reactor. In addition, this configuration provides self-wiping between barrel and screw flight surfaces, which reduces material holdback to an acceptable minimum, thus rendering it an almost ideal TFR. 

Mayer et al. [358] investigated the performance of a PPC reactor in the continuous emulsion polymerization of St. They found that the number of polymer particles produced in the PPC reactor depended strongly on the residence time distribution (RTD) - in other words, on the pulsation conditions - and that it had a value between those recorded for the batch and the CSTR processes. 

The polymerization time in continuous processes depends on the time the reactants spend in the reactor. The contents of a batch reactor will all have the same residence time, since they are introduced and removed from the vessel at the same times. The continuous flow tubular reactor has the next narrowest residence time distribution, if flow in the reactor is truly plug-like (i.e., not laminar). These two reactors are best adapted for achieving high conversions, while a CSTR cannot provide high conversion, by definition of its operation. The residence time distribution of the CSTR contents is broader than those of the former types. A cascade of CSTR s will approach the behavior of a plug flow continuous reactor. 

The performance of a single CSTR can he quite different from that of a batch reactor for a number of reasons. First, the distribution of reactor residence times in a CSTR is quite broad. This leads to broad size and age distributions of the latex particles. By contrast, the polymer particles in a batch reactor are usually all formed near the h< inning of the reaction and the particle size and age distrihutions of the product latex are narrow. 

The reactor in which chemical reactions lake place is fhe mosl imporlanl piece of equipmenl in each chemical planl. A variety of reactors are used in induslry, bul all of Ihem can be assigned to cerlain basic types or a combination of fhese ideal reactors [53] (1) bafch slirred-lank reactor, (2) continuous slirred-lank reactor, and (3) lubular reactor. The ideal slirred-lank bafch reactor is characterized by complete mixing, while in the ideal tubular reactor, plug flow is assumed. In contrast to the stirred-tank batch reactor with well-defined residence time, the continuous stirred-tank reactor has a very broad residence-time distribution. In... 

The PFR and CSTR models encompass the extremes of the residence-time distributions shown in Figure 4.3 however the batch reactor and the laminar-flow reactor, both of which we have already mentioned in this chapter, are also types exhibiting a well-defined mixing behavior. The batch reactor is straightforward, since it is simply represented by the perfect mixing model with no flow into or out of the system, and has been treated extensively in Chapter 1. 

Clearly, space-time Vr/V in the ideal tubular reactor is the same as residence time in the ideal batch reactor but this is true, even in the case of ideal operation, only if the reaction is not accompanied by a volume change. Otherwise, the space-time calculated with volumetric flow rate at entrance is not equal to residence time. The latter depends on degree of conversion and is therefore not a useful concept. In general, with flow reactors, residence times should be used with caution since there may be a distribution of them or they may depend on conversion. 

These are identical for the limiting values for the batch reactor, except that they require only the assumption of perfect mixing. Thus, while polydispersi-ties of 2.0 and 1.5 for termination by disproportionation and combination respectively represent unattainable minima for batch polymerization, these same values represent feasible operation in a well-mixed CSTR. Thus, the CSTR will give a narrower dead polymer number chain length distribution since it is possible to maintain a constant reaction environment at steady state. The effect of residence time distribution on the polydispersity is negligible since the lifetime of a single radical is far less than the average residence time. Likewise, for a copolymerization in a CSTR at steady state, the constancy of... 

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