Continuous-Row Reactors

All chemical reactions are accompanied by some heat effects so that the temperature will tend to change, a serious result in view of the sensitivity of most reaction rates to temperature. Factors of equipment size, controllability, and possibly unfavorable product distribution of complex reactions often necessitate provision of means of heat transfer to keep the temperature within bounds. In practical operation of nonflow or tubular Row reactors, truly isothermal conditions are not feasible even if they were desirable. Individual continuous stirred tanks, however, do maintain substantially unifonn temperatures at steady state when the mixing is intense enough the level is determined by the heat of reaction as well as the rate of heat transfer provided. 

We call Equation (2-6) the differential form of the design equation for a batch reactor because we have written the mole balance in terms of conversion. The differential forms of the batch reactor mole balances. Equations (2-5) and (2-6), are often used in the interpretation of reaction rate data (Chapter 7) and for reactCHS with heat effects (Chapters 11-13), respectively. Batch reactors are frequently used in industry for both ga.s-phase and liquid-phase reactions. The lidmratory bomb calorimeter reactor is widely used for ol ning reaction rate data Liquid-phase reactions are frequently carried out in batch reactors when small-scale production is desired or operating difficulties rule out the use of continuous Row systems. 

Deans and Lapidus (1960) made use of the analogy between a tubular reactor and a sequence of continuous flow stirred tank reactors for the modelling of heterogeneous reactors. In cell models the reactor is subdivided into small finite elements, the height of each being usually equal to one pellet diameter and each of these elements is considered to be a small CSTR in which the fluid phase is perfectly mixed. In the simple cell model the temperature and concentration conditions of any given cell are dependent only on those of the previous row of cells. 

A/iaiysis One notes that A is consumed more rapidly in the PFR than in the side-fed MR and that more of (he desired product is also fttrmed in the PFR. However, the selectivity is much higher in the MR than the PFR. One also notes, when comparing the molar Row rates, that the rates in the side-fed MR continue to change sig-nihcantly after 30 dm down the reactor, while those in the PFR do not change significantly after 30 dm. ... 

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