Of batch reactors

Figure 13.2 The heat transfer characteristics of batch reactors.

A useful classification of lands of reaclors is in terms of their concentration distributions. The concentration profiles of certain limiting cases are illustrated in Fig. 7-3 namely, of batch reactors, continuously stirred tanks, and tubular flow reactors. Basic types of flow reactors are illustrated in Fig. 7-4. Many others, employing granular catalysts and for multiphase reactions, are illustratea throughout Sec. 23. The present material deals with the sizes, performances and heat effects of these ideal types. They afford standards of comparison. 

Unsteady material and energy balances are formulated with the conservation law, Eq. (7-68). The sink term of a material balance is and the accumulation term is the time derivative of the content of reactant in the vessel, or 3(V C )/3t, where both and depend on the time. An unsteady condition in the sense used in this section always has an accumulation term. This sense of unsteadiness excludes the batch reactor where conditions do change with time but are taken account of in the sink term. Startup and shutdown periods of batch reactors, however, are classified as unsteady their equations are developed in the Batch Reactors subsection. For a semibatch operation in which some of the reactants are preloaded and the others are fed in gradually, equations are developed in Example 11, following. 

Alcorn and Sullivan (1992) faced some specific and difficult problems in connection with coal slurry hydrogenation experiments. Solving these with the falling basket reactor, they also solved the general problem of batch reactors, that is, a good definition of initial conditions. The essence of their... 

From diese various estimates, die total batch cycle time t(, is used in batch reactor design to determine die productivity of die reactor. Batch reactors are used in operations dial are small and when multiproducts are required. Pilot plant trials for sales samples in a new market development are carried out in batch reactors. Use of batch reactors can be seen in pharmaceutical, fine chemicals, biochemical, and dye industries. This is because multi-product, changeable demand often requues a single unit to be used in various production campaigns. However, batch reactors are seldom employed on an industrial scale for gas phase reactions. This is due to die limited quantity produced, aldiough batch reactors can be readily employed for kinetic studies of gas phase reactions. Figure 5-4 illustrates die performance equations for batch reactors. 

Velo, E., C. M. Bosch, and F. Recasens (1996). Thermal Safety of Batch Reactors and Storage Tanks. Development and Validation of Runaway Boundaries. Ind. Eng. Chem. Res. 35, 1288-99. 

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. 

Therefore, consideration of this mass in heat-transfer phenomenon leads to a significant temperature decrease reached after deviation and increases the time to maximum rate. This reveals an intrinsically safer behavior of this apparatus compared to that of batch reactors. 

The fine chemicals business is characterized by a small volume of products manufactured. Therefore, batch production predominates and small-scale reactors are used. The need to implement fine chemistry processes into existing multiproduct plants often forces the choice of batch reactors. However, safety considerations may lead to the choice of continuous processing in spite of the small scale of operation. The inventory of hazardous materials must be kept low and this is achieved only in smaller continuous reactors. Thermal mnaways are less probable in continuous equipment as proven by statistics of accidents in the chemical industries. For short reaction times, continuous or semicontinuous operation is preferred. 

Both flow terms are zero for the case of batch reactor operation, and the outflow term is zero for semi-continuous or semi-batch operation. 

TEMPERATURE OPTIMIZATION OF BATCH REACTOR CONSECUTIVE AND PARALLEL REACTION SEQUENCE... 

It is clear that the use of batch reactors has some serious drawbacks. For the production of larger quantities, mnltiple batch mns have to be performed and this often leads to batch to batch variation in prodnct qnahty and performance. Furthermore, the productivity is often lower than for dedicated continnons reactors and fixed costs are higher cansed by high operator efforts. Therefore, switching to continuons processes holds great appeal, if we can find a device that is snitable for multiple products. 

In the analysis of batch reactors the two flow terms in equation 8.0.1 are omitted. For con-... 

Rylander in Catalytic Hydrogenation Over Platinum Metals (p. 39, Academic Press, New York, 1967). Nitrobenzene in ethanol was hydrogenated at room temperature and 1 atm over various amounts of 5% Pd on carbon. Four loading levels of catalyst were used. At each level, the reduction was carried out in two different types of batch reactor. 

In this chapter, we first consider uses of batch reactors, and their advantages and disadvantages compared with continuous-flow reactors. After considering what the essential features of process design are, we then develop design or performance equations for both isothermal and nonisothermal operation. The latter requires the energy balance, in addition to the material balance. We continue with an example of optimal performance of a batch reactor, and conclude with a discussion of semibatch and semi-continuous operation. We restrict attention to simple systems, deferring treatment of complex systems to Chapter 18. 

The use of batch reactors in the laboratory is described in Section 2.2.2 for the interpretation of rate of reaction, in Section 3.4.1.1 for experimental methodology, and in Chapter 4 and subsequent chapters for numerical treatment of kinetics experimental... 

Semi-Batch Reactor (SBR) a type of batch reactor from which at least one reactant is withheld and then added at a controlled rate, usually to control the rate of heat generation or gas evolution both heat generation and concentrations vary during the reaction process products are removed from the reactor only upon conclusion of the reaction process. 

The participant A is identified by subscript a. Thus the concentration is Ca, the number of mols is na, the fractional conversion is xa, the partial pressure is pa, the rate of decomposition is ra. The capital letter A also is used on occasion instead of Ca. The flow rate in terms of mols is na but the prime ( ) is left off when the meaning is clear, The volumetric flow rate is V, reactor volume is Vr or simply V of batch reactors, the total pressure is... 

Bonvin, D. Optimal Operation of Batch Reactors—A Personal View. J Proc Contr 8 355-368 (1998). 

A large drawback of batch reactors is that a great deal of time is spent not performing chemical transformations a batch process is inherently inefficient in terms of plant usage. Also, as the reaction proceeds and more product is formed, the composition of the batch changes, altering the physical properties of the reaction including viscosity, heat capacity and gas solubilities, all of which... 

Choice of operating conditions favoring the adsorption of the reactant molecules and the desorption of the product molecules fixed-bed reactor instead of batch reactor, high molar substrate/acylating agent ratio, low conversion, high temperature, use of solvents with adequate polarities. 

Batch operation For the design of batch reactors for biphasic conversion the type of stirring device is an essential aspect to generate a narrow distribution with small droplet sizes which is equivalent to high surfaces [36]. Together with the diffusion ability (diffusion coefficient) of the used sol-... 

---