Plug flow reactor batch recycle

Tubular Reactors. The simplest model of a tubular reactor, the plug-flow reactor at steady state is kinetically identical to a batch reactor. The time variable in the batch reactor is transformed into the distance variable by the velocity. An axial temperature gradient can be imposed on the tubular reactor as indicated by Gilles and Schuchmann (22) to obtain the same effects as a temperature program with time in a batch reactor. Even recycle with a plug flow reactor, treated by Kilkson (35) for stepwise addition without termination and condensation, could be duplicated in a batch reactor with holdback between batches. 

Reactions orders and rate coefficients can be established with methods that use either rate or concentration data. Batch, tubular plug-flow, and differential recycle reactors yield concentrations as directly measured quantities, and calculation of rates... 

Reactions orders and rate coefficients can be established with methods that use either rate or concentration data. Batch, tubular plug-flow, and differential recycle reactors yield concentrations as directly measured quantities, and calculation of rates requires finite-difference approximations. To avoid these, concentration methods should be used. In contrast, continuous stirred-tank reactors allow rates to be calculated from material balances without approximation. Here, evaluation based on rates is equally suited. 

Models for a continuous reactor without recycle will be identical with those developed for the batch reactor. We will therefore confine ourselves to a continuous reactor with recycle. Although the low conversion per pass make the hydrodynamic classification of the reactor of little significance, it will still be convenient to develop the continuous reactor model on the basis of a plug-flow reactor. 

Several bioreactor designs are used to produce bioproducts, and include, but are not limited to batch reactors, fed-batch reactors, continuous cultivation reactors, plug flow reactors, recycle bioreactor systems, immobilized cell reactors, biofilm reactors, packed bed reactors, fluidized-bed reactors, and dialysis cultivation reactors (Williams 2002). These reactor types can contain either mixed or pure cultures, and can stimulate heterotrophic and/or phototrophic cellular functions depending on the specific reactor design. Additionally, these reactor schemes can be used to produce products directly, or to harvest biomass or other products for downstream processes. Due to the complex nature of bioreactors, particularly anaerobic digesters, the use of metagenomics is helpful to understand the physiology of such systems. 

Although the system could have been operated in a continuous mode, it was decided to operate it in a batch mode. In the batch high-recycle mode the reactor mass balance is that for a stlrred-tank batch reactor and thus over a period of time is analogous to the mass balance for a plug flow reactor over a distance along... 

For example, different fermentation schemes have been developed for the production of ethanol. Conventional batch, continuous, cell recycle and immobilized cell processes, as well as membrane, extraction and vacuum processes, which selectively remove ethanol from the fermentation medium as it is formed, were compared on identical bases using a consistent model for yeast metabolism (Maiorella et al., 1984). The continuous flow stirred tank reactor (CSTR) with cell recycle, tower and plug flow reactors all showed similar cost savings of about 10% compared to batch fermentation. Cell recycle increases cell density inside the fermentor, which is important in reducing fermentation cost. 

Finally, some remarks on the operation of mechanically agitated gas-liquid reactors are worth mentioning. The mode of operation (i.e., batch, semibatch, continuous, periodic, etc.) depends on the specific need of the system. For example, the level of liquid-phase backmixing can be controlled to any desired level by operating the gas-liquid reactor in a periodic or semibatch manner. This provides an alternative to the tanks in series or plug flow with recycle system and provides a potential method of increasing the yield of the desired intermediate in complex reaction schemes. In some cases of industrial importance, the mode of operation needs to be such that the concentration of the solute gas (such as Cl2, H2S, etc.) as the reactor outlet is kept at a specific value. As shown by Joshi et al. (1982), this can be achieved by a number of different operational and control strategies. 

For elucidation of mechanisms, rate data at very low conversions may be highly desirable. They can be obtained more easily from a batch reactor than from a CSTR or plug-flow tubular reactor. A standard CSTR would have to be operated at very high flow rates apt to cause fluid-dynamic and control problems. The same is true for a standard tubular reactor unless equipped with a sampling port near its inlet, a mechanical complication apt to perturb the flow pattern. If the problem of confining the reaction to a very small flow reactor can be solved—as is possible, for example, for radiation-induced reactions—a differential reactor operated once-through or with recycle may be the best choice. 

Bench-scale kinetic experiments can be conducted in batch, continuous stirred-tank, tubular plug-flow, or differential reactors. The last of these can be operated with once-through flow or recycle. The advantages and disadvantages of the various types are discussed in Section 3.1. 

The flows in PFR and MFR can be precisely deflned by simple mathematical eqnations, and the batch reactor is simply the batch version of the PFR. A reactor is now considered where the flow is between plug and fnlly mixed, i.e., a nonideal reactor. Two common examples of such partially mixed reactors are the recycle reactor and the tanks-in-series reactor. In the recycle reactor, part of the outlet from a reactor is recycled at the inlet, thns establishing some mixing between the downstream and the upstream fluids. In the tanks-in-series reactor, several mixed-flow reactors are operated in series. A single MFR is fully mixed, whereas an inflnite nnmber of MFRs (or a... 

Bench-scale kinetic experiments can be conducted in batch, continuous stirred-tank (CSTR), tubular plug-flow, or differential reactors. The last of these can be operated with once-through flow or recycle. Advantages and disadvantages of the various types are discussed. In particular Batch reactors are inexpensive, but require attention to rapid attainment of reaction conditions at start CSTRs are excellent for gas-liquid, but less so for gas-phase reactions tubular reactors are especially suited for reactions of heterogeneous catalysis and differential reactors operated "once through" are best for measurement of initial rates. 

The factors in Tabic 2.5 may be reviewed briefly. The mode of operation may involve a batch (simple batch or batch recycle) or a continuous (plug flow stirred tank or cascade) reactor, with respect to electrolysis (as detailed in section 2,4). The mode of operation must also be considered with regard to product extraction from the cell, which may be batch or continuous. In the simplest case, the products are removed via the exit flow from the reactor... 

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