Reactor operating modes

Two limiting modes of operating chemical reactors employ (a) a vessel so well stirred that the composition and temperature are the same throughout (b) a vessel typified by a tube without mixing in which all molecules have the same residence time, and in which gradients of composition and temperature exist. Material and heat balances on these devices utilize the conservation law, 

Various such balances will be made. They also are summarized in Tables 2.3 to 

The balances are written in terms of volumetric flow rates, concentrations and a power law rate equation, rc = kCn. The sink term is rcVr the rate of reaction in a reference volume. Vr is the instantaneous volume occupied by the fluid in the vessel and Vrt is the capacity of the vessel. 

The last equation indicates a way of measuring a rate of reaction by relatively simple means. 

This may be solved together with Q, the material balance and the rate equation 

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It is evident, that in any membrane reactor operation mode there are important parameters which determine the performance of the process (Shah, Remmen and Chiang 1970). These are (1) the total and partial pressures on both sides of the membrane, (2) the total and partial pressure differences across the membrane, (3) the diffusion mechanism through the support and the membrane layer (membrane structure), (4) the thickness of the membrane, (5) the reactant configuration (i.e. whether the reactants are supplied from the same or from opposite sides of the membrane, in counter or co-current flow) and (6) the catalyst distribution. 

Thus, development of the investigations in this branch is not an extensive process. Interest in this problem is regularly kept alive by new theoretical ideas. All currently known elementary reactions proceeding in the Fenton system are shown by the overall sketch in Figure 6.1 which presents the whole variety of highly active intermediate particles, synthesized in seemingly simple reactions. However, it should be noted that the fate of free radicals and charged particles in the mechanism is determined by the process kinetics, where the basic factors are the reactor operation mode and physicochemical parameters of the catalyst. 

The DCC has two reactor operating modes DCC-I (Riser-plus fluidized dense-bed reactor, maximum propylene mode) and DCC-II (Riser reactor, maximum iso-olefins mode). The DCC can process different heavy feeds— VGO, DAO, coker gasoil, atmospheric residue, VR, etc. Paraffinic feedstocks are the best feeds for DCC. In DCC maximum propylene operation mode, over 20 wt% propylene yield can be obtained from paraffinic feedstocks. The naphtha and middle distillates streams from the DCC unit can be used as blending components for high-octane, commercial gasoline and fuel oil, respectively. 

Most polymers produced by emulsion polymerization are copolymers therefore, it is important to consider the effect of the reactor operation mode on copolymer composition. Moreover, because of the heterogeneous nature of the system, partition of the monomers between the phases during the polymerization as well as monomer reactivities have to be taken into account. 

Table 4.4. General definition of rates in different reactor operation modes.

Select the most suitable reactor operation mode, that is, batch, continuous, or semibatch, to improve selectivity and yield. 

Several modes of waste management are available. The simplest is to dilute and disperse. This practice is adequate for the release of small amounts of radioactive material to the atmosphere or to a large body of water. Noble gases and slightly contaminated water from reactor operation are eligible for such treatment. A second technique is to hold the material for decay. This is appHcable to radionucHdes of short half-life such as the medical isotope technetium-9 9m = 6 h), the concentration of which becomes negligible in a week s holding period. The third and most common approach to waste... 

All the mentioned precautions do not make the operating mode of these tubular reactors close to that of large-scale reactors. The outside observer... 

In the case of thermodynamics, the designer can investigate the nature of the reaction heat and whether the reaction is reversible. If these exothermic reactions are irreversible, attention may be focused on the influence of reactor design on conversion and with heat transfer control. An objective of reactor design is to determine the size and type of reactor and mode of operation for the required job. The choice... 

Whether the reactor operates in batch or semi-batch mode... 

The fact that the worker normally operated reactor B, and he reverted to this operating mode when distracted, indicates that the internal error mechanism was a Stereotype Takeover. 

For catastrophic demand-related pump failures, the variability is explained by the following factors listed in their order of importance system application, pump driver, operating mode, reactor type, pump type, and unidentified plant-specific influences. Quantitative failure rate adjustments are provided for the effects of these factors. In the case of catastrophic time-dependent pump failures, the failure rate variability is explained by three factors reactor type, pump driver, and unidentified plant-specific Influences. Point and confidence interval failure rate estimates are provided for each selected pump by considering the influential factors. Both types of estimates represent an improvement over the estimates computed exclusively from the data on each pump. The coded IPRDS data used in the analysis is provided in an appendix. A similar treatment applies to the valve data. 

This work particularly emphasizes the importance of selecting the initiator system for optimum reactor operation and reveals general concepts which specify the desired properties and operational modes of an optimum initiator system. In addition, the effects of the system heat transfer and the CTA (chain transfer agent) level on the conversion-molecular weights relationships are presented. 

One of the first published microwave-assisted synthesis of benzothiazoles is the condensation of a dinucleophile such as 2-aminothiophenol, with an ortho-ester (neat) in the presence of KSF clay in a mono-mode microwave reactor operating at 60 W under a nitrogene atmosphere [ 12] (Scheme 12). Traditional heating (oil bath, toluene as solvent and KSF clay) gave the expected products in similar yields compared to the microwave experiments but more than 12 h were required for completion. Solvent-free microwave-assisted syntheses of benzothiazoles was also described by attack of the dinucleophiles cited above on benzaldehydes and benzaldoximines [13] (Scheme 12). This methodology was performed in a dedicated monomode microwave reactor... 

Many industrial reactors operate in the fed-batch mode. It is also called the semibatch mode. In this mode of operation, reactants are charged to the system at various times, and products are removed at various times. Occasionally, a heel of material from a previous batch is retained to start the new batch. 

Multiphase reactors can be batch, fed-batch, or continuous. Most of the design equations derived in this chapter are general and apply to any of the operating modes. Unsteady operation of nominally continuous processes is treated in Chapter 14. 

The typical bioreactor is a two-phase stirred tank. It is a three-phase stirred tank if the cells are counted as a separate phase, but they are usually lumped with the aqueous phase that contains the microbes, dissolved nutrients, and soluble products. The gas phase supplies oxygen and removes by-product CO2. The most common operating mode is batch with respect to biomass, batch or fed-batch with respect to nutrients, and fed-batch with respect to oxygen. Reactor aeration is discussed in Chapter 11. This present section concentrates on reaction models for the liquid phase. 

The physical picture of emulsion polymerization is complex due to the presence of multiple phases, multiple monomers, radical species, and other ingredients, an extensive reaction and particle formation mechanism, and the possibility of many modes of reactor operation. 

In case of exothermic reactions, the heat-exchange capacities of the reactor allow to rapidly evacuate the heat generated by the reaction and therefore to perform a transposition of a pure batch operating mode into a continuous one. The main point is the ability to avoid, as far as possible, an initial increase of the temperature as soon as the reactants are mixed. 

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