Cycles batch/semibatch reactors

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. 

The second type of semibatch reactor is when some material is removed from the reactor during the batch. The material is typically one of the products of the reaction. A common example is in fermentors producing ethanol in which the byproduct carbon dioxide is vented off during the batch cycle. 

PE = polyethylene PP = polypropylene PS = polystyrene ASR = automobile shredder residue VGO = vacuum gas oil LCO = light cycle oil. SA = Si02/ AI2O3 MOR = mordenite. TD/CD = thermal degradation followed by catalytic degradation COMB = mixed polymer and catalyst in a batch reactor COMS = mixed polymer and catalyst in a semibatch reactor FB = fixed bed flow reactor BIRR = Berty internal recycle reactor. 

A semibatch system will be influenced differently by the presence of inhibitor. If inhibitor is present in the recipe ingredients of a batch reactor it will delay the start of polymerization, after which the reaction will proceed in a normal manner. Inhibitor in the delayed feed stream(s) to a semibatch system will reduce the effective rate of initiation. This reduction may require the use of more initiator, and because the inhibitor reacts rapidly, the polymerization rate may increase dramatically when the delayed-feed part of the cycle is finished. 

The differences between a single CSTR and a batch reactor are similar to those between semibatch and batch reactors, except that they are usually more pronounced. The addition of more reactors to a series system tends to reduce some of the observed performance differences. A typical example of different behavior is the heat release profile. An advantage often cited for continuous reactor systems is a constant heat load with fully used reactor volume. Batch reactors are not usually operated full, and the heat load is nonuniform. In addition, portions of the batch reaction cycle are devoted to charging and emptying the reactor and sometimes for heating the reagents to polymerization temperature. Thus, the production rate per unit volume can be higher in a continuous system. 

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