Continuous stirred tank reactor CSTR batch recycle

The catalyst components are generally dissolved in methyl acetate which acts as both reactant and solvent. Other solvents may be used and in fact, upon several batch recycles where lower boiling products are distilled off, the solvent is an ethylidene diacetate-acetic acid mixture. Any water introduced in the reaction mixture will be consumed via ester and anhydride hydrolysis, therefore anhydrous conditions are warranted. Typical batch reaction examples are presented in Table 1. There is generally sufficient reactivity when carbon monoxide and hydrogen are present at 200-500 psi. Similar results were obtained from the pilot plant using a continuous stirred tank reactor (CSTR). The reaction can also be run continuously over a supported catalyst with a feed of methyl acetate, methyl iodide, CO, and hydrogen. 

Most chemical processes involve two important operations (reaction and separalion) that are typically carried out in different sections of the plant and use different equipment. The reaction section of the process can use several types of reactors [continuous stirred-tank reactor (CSTR), tubular, or batch] and operate under a wide variety of conditions (catalyzed, adiabatic, cooled or heated, single phase, multiple phases, etc.). The separation section can have several types of operations (distillation, extraction, crystallization, adsorption, etc.), with distillation being by far the most commonly used method. Recycle streams between the two sections of these conventional multiunit flowsheets are often incorporated in the process for a variety of reasons to improve conversion and yield, to minimize the production of undesirable byproducts, to improve energy efficiency, and to improve dynamic controllability. 

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. 

Continuous Stirred Tanks Without Biomass Recycle. The chemostat without biomass recycle is a classic CSTR. The reactor is started in the batch mode. 

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. 

Continuous flow stirred tank reactors are wonderful for kinetic experiments since they allow a direct determination of the reaction rate at known concentrations of the reactants. One other type of reactor allows this in principle. Dijferential reactors have such a small volume that concentrations and temperatures do not change appreciably from their inlet values. However, the small change in concentration makes it very hard to determine an accurate rate. The use of differential reactors is akin to numerical differentiation and is not recommended. If a CSTR cannot be used, a batch or piston flow reactor is preferred over a differential reactor even though the reaction rate is not measured directly but must be inferred from measured outlet concentrations. See also Sections 4.3.3 and 4.5.3, which describe a common technique for converting a differential reactor to a CSTR through the use of recycle. 

A real continuous-flow stirred tank will approximate a perfectly mixed CSTR provided that tmix h/i and tmix i. Mixing time correlations are developed using batch vessels, but they can be applied to flow vessels provided the ratio of throughput to circulatory flow is small. This idea is explored in Section 4.5.3 where a recycle loop reactor is used as a model of an internally agitated vessel. 

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