Reactor segregated

Segregation of a catalyst (and cofactor) in a reactor Segregation of enzymes with respect to molecular weight on ultrafiltration membranes... 

Fig. 6-7 Residence-time distribution in a laminar-flow tubular reactor (segregated flow)...

Ideal PFR Ideal CSTR Ideal laminar Row reactor Segregation Maximum mixedness Dispersion Tanks in series... 

We next study the effect of particle size. Figure 8.22 shows ca(6) for particle sizes ranging from 0.1 pm to 1.0 cm. We see that if the stirrer is able to produce A particles of 1.0 pm or less, then the reactor is essentially in the state of maximum mixedness, or, equivalently, operates as an ideally mixed CSTR. At the other extreme, if the A particles are larger than about 1.0 mm, then the reactor operates essentially as a segregated-flow reactor. Segregated flow essentially reduces the reaction rate to zero because the A and B species cannot come into contact. 

Program to calculate conversion of second-order reaction in non-ideal reactor—-segregated flow reactor and laminar flow reactor... 

The oxychlorination reaction is very exothermic and the catalyst is very active, which makes it necessary to mix the catalyst with an inert diluent to avoid overheating in a fixed-bed reactor. A low surface area, spherically- or ring-shaped alumina or chemical porcelain body can be used as a diluent with the ring-shaped catalyst. The density of the inert material should be similar to the catalyst to avoid segregation during loading, and the size should be slightly different to allow separation of the inert material from the spent catalyst. 

Segregated flow Occurs when all molecules that enter together also leave together. A state of aggregation is associated with every RTD. Each aggregate of molecules reacts independently of every other aggregate thus, as an individual batch reactor. 

In contrast to segregated flow, in which the mixing occurs only after each sidestream leaves the vessel, under maximum mixedness mixing of all molecules having a certain period remaining in the vessel (the life expectation) occurs at the time of introduction of fresh material. These two mixing extremes—as late as possible and as soon as possible, both consistent with the same RTD—correspond to performance extremes of the vessel as a chemical reactor. 

The scope of the previously addressed CE case study is now altered to allow for stream segregation, mixing, and recycle within the ethyl chloride plant. There are five sinks the reactor (u = 1), the first scrubber (u = 2), the second scrubber (u = 3), the mixing tank (u = 4) and the biotreatment facility for effluent treatment (m = 5). There are six sources of CE-laden aqueous streams (in = 1-6). There is the potential for segregating two liquid sources (lu = 2, 4). The following process constraints should be considered ... 

These results can be used to construct the solution as shown in Fig. 7.14. The target for minimum CE discharge through segregation, mixing and direct recycle is 0.488 X 10 kg/s (about 15 kg/yr). The solution indicates that the optimal policy is to segregate the effluents of the two scrubbers, pass the effluent of the first scrubber to the reactor, recycle the aqueous effluent of the reactor to the hrst scrubber and dispose of the second scrubber effluent as the terminal wastewater stream. 

In what follows, both macromixing and micromixing models will be introduced and a compartmental mixing model, the segregated feed model (SFM), will be discussed in detail. It will be used in Chapter 8 to model the influence of the hydrodynamics on a meso- and microscale on continuous and semibatch precipitation where using CFD, diffusive and convective mixing parameters in the reactor are determined. 

In the three and four environment (3B and 4B) models (Ritchie and Togby, 1979 Mehta and Tarbell, 1983), the reactor is divided into two segregated entering environments and one or two fully mixed leaving environments. The mixing parameter is the transfer coefficient between the environments. 

Villemiaux, J., 1989. A simple model for partial segregation in a semibatch reactor. American Institute of Chemical Engineers Annual Meeting, San Francisco, Paper 114a. 

Wang, Y.-D. and Mann, R., 1992. Partial segregation in stirred batch reactors effect of scale-up on the yield of a pair of competing reactions. Transactions of the Institution of Chemical Engineers, 70, 282-290. 

A CSTR is a deliberately backmixed reactor and, in principle, its effluent temperature and composition are the same as the reactor contents. With an ideal CSTR, the feed blends instantaneously with the uniform reactor contents. In actual practice, of course, we find that feed blending time may be protracted, and varying degrees of segregation, short circuiting and stagnation exist in the reactor contents. 

There are many interesting reports in the literature where computer simulations have been used to examine not only idealized cases but have also been used in an attempt to explain segregation and viscosity effect in unperturbed polymerization reactors (6). Some experimental work has been reported (7, 8). It is obvious, however, that although there is some change in the MWD with conversion in the batch and tubular reactor cases and that broadening of the MWD occurs as a result of imperfect mixing, there is no effective means available for controlling the MWD of the polymer from unperturbed or steady-state reactors. 

Friis and Hamielec (48) offered some comments on the continuous reactor design problem suggesting that the dispersed particles have the same residence time distribution as the dispersing fluid and the system can be modeled as a segregated CSTR reactor. 

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. 

Calculated Molecular Weight Distributions. The calculated weight fraction distributions for the micro-mixed, segregated, and micro-mixed reactor with dead-polymer models for Runs 2, 5,... 

The effects of micro-mixing on the molecular weight distribution are much more pronounced than those of segregation. According to Patterson (33) only a small increase in micro-mixing over that of total segregation will yield a pol)nner distribution very similar to that of micro-mixed reactor. 

In spite of visual indications of at least partial segregation, the concept of micro-mixing proved to be most useful in modeling the laboratory reactor. 

The completely segregated, continuous-how stirred tank reactor... 

The condition of negligible diffusion means that the reactor is completely segregated. A further generalization of Equation (8.9) applies to any completely segregated reactor ... 

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