Semi-batch operation emulsion polymerization

In a common semi-batch operation mode (sometimes called semi-continuous mode), some fraction of reactants, i.e. the initial charge, are initially charged into the reactor, and the rest of the formulation is continuously provided to feed over some period of time. In a fully semi-batch emulsion process, the polymerization starts with an aqueous solution only containing a surfactant and an initiator (micellar solution), and then the monomer feed is provided in very small drops with a given rate. 

Emulsion polymerization studies reported in the scientific literature are usually based on experiments with batch or semibatch reactor systems. Since most workers in the field are familiar with such reactors, the thrust of this discussion will be to compare continuous reactors with batch and semi-batch operations. The particular areas to be reviewed include (i) inhibitor effects, (ii) particle age distributions, (iii) particle nucleation, (iv) copolymerization, (v) particle morphology, (vi) temperature control and heat removal and (vii) polymerization kinetic models. 

A semi-batch reactor has the same disadvantages as the batch reactor. However, it has the advantages of good temperature control and the capability of minimizing unwanted side reactions by maintaining a low concentration of one of the reactants. Semi-batch reactors are also of value when parallel reactions of different orders occur, where it may be more profitable to use semi-batch rather than batch operations. In many applications semi-batch reactors involve a substantial increase in the volume of reaction mixture during a processing cycle (i.e., emulsion polymerization). 

Industrial chemical processes are categorized as batch, semi-batch or continuous, and the manufacture of emulsion polymers is carried out in aU these process types. The processes differ not only in equipment type and economics of operation but also in the specific properties imparted to the polymer and the emulsion. In a batch emulsion polymerization, all ingredients are added to a vessel, polymerization is initiated and the reaction proceeds to completion over a period of time. Thus, conditions in the reactor gradually change from monomer -i- water —> polymer -i- water, passing through all intermediate ratios of monomer/polymer. 

---