Semibatch reactors unsteady-state operation

Remark 1. Eq.(9) can be used on a CSTR in unsteady state operation or in a semibatch reactor when there is no phase change. 

Equation (9-9) applies to a semibatch reactor as well as unsteady-state operation of a CSTR. 

Equation (13-9) applies to a semibatch reactor, as well as for the unsteady-state operation of a CSTR and is also shown in Table I l-I as Equation (Tl l-I.I). 

A semibatch reactor is a variation of a batch reactor in which one reactant may be added intermittently or continuously to another contained as a batch in a vessel, or a product may be removed intermittently or continuously from the vessel as reaction proceeds. The reaction may be single-phase or multiphase. As in a batch reactor, the operation is inherently unsteady-state and usually characterized by a cycle of operation, although in a more complex manner. 

Up to now we have focused on the steady-state operation of nonisothermal reactors. In this section the unsteady-state energy balance will be developed and then applied to CSTRs, plug-flow reactors, and well-mixed batch and semibatch reactors. 

Case 5 Mixed gas, batch liquid, and unsteady state In this semibatch operation, a batch of liquid is taken in a reactor and a stream of gas is passed through it (Figure 11.4d). The problem here is usually one of calculating the time needed for a given conversion in a reactor of known volume. 

In Chapter 5 we discussed the unsteady operation of one type of reactor, the batch reactor. In this section, we discuss two other aspects of unsteady operation startup of a CSTR and of semibatch reactors. First, the startup of a CSTR is examined to determine the time necessary to reach steady-state operation [see Figure 6-4(a)]. and then semibatch reactors are discussed. In each of these cases, we are interested in predicting the concentration and conversion as a function of time. Closed-form analytical solutions to the differential equations arising from the mole balance of these reaction types can be obtained only for zero- and hrst-order reactions. ODE solvers must be used for other reaction orders. 

Closure. After completing this chapter, the reader should be able to af ly the unsteady-state energy balance to CSTRs, semibatch and batch reactors. The reader should be able to discuss reactor safety using the ONCB and the T2 Laboratories case studies of explosions to help prevent future accidents. Included in the reader s discussion should be how to start up a reactor so as not to exceed the practical stability limit. After studying these examples, the reader should be able to describe how to operate reactors in a safe manner for both single and multiple reactions. 

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