Batch Reactors Polymerization Reactor

The polymerization of MMA is a radical-based polymerization, similar to the production of PVC or PE. It requires the use of initializers. We assume that the small amount needed to initialize the reaction does not affect the volume of the liquid phase. The reaction mechanism proposed is as follows  

Termination by combination Termination by disproportion Transfer to monomer 

R represents the active radicals M is the monomer P is the polymer in formation D is the dead polymer 

The subindexes n and m correspond to the number of monomeric units The different constants and definitions are taken from the papers mentioned earlier  

Based on the literature, we assume that the propagation rate constants are independent of the chain length, kj = kp, [9]. It is also considered that the transfer to the monomer is small kj = 0 [9], 

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Flexible batch. Both the formula and the processing instructions can change from batch to batch. Emulsion polymerization reactors are a good example of a flexible batch facility. The recipe for each produc t must detail Both the raw materials required and how conditions within the reac tor must be sequenced in order to make the desired product. 

Kiparissides, C., Daskalakis, G., Achilias, D.D., Sidiropoulou, Dynamic simulation of industrial poly(vinyl chloride) batch suspension polymerization reactors, Ind. Eng. Chem. Res., 1997, 36,1253-1267... 

An example of the use of the population balance method to predict reaction in particulate systems is presented in the work of Min and Ray (M16, M17). The authors developed a computational algorithm for a batch emulsion polymerization reactor. The model combines general balances, individual particle balances, and particle size distribution balances. The individual particle balances were formulated using the population balance... 

Types of Reactor Processes Batch Reactors Semibatch Reactors Continuous Reactors Emulsion Polymerization Kinetics Other Preparation Methods... 

Figure 2.3.5 shows the conversion-time data for the batch reactor polymerization of styrene in ether and acetone under FRRPP conditions (80°C). The half-life of the V501 initiator used in the ether system is about 130 min (Wako Chemicals, 1987). It is evident that there is a sharp rise in conversion at the beginning, followed by a period of reduced conversion rate. The onset of reduced conversion rate occurs at around 25%. 

Min, K.W., W.H. Ray, The computer simulation of batch emulsion polymerization reactors through a detailed mathematical model. J. Appl. Polym. Sci. 22, (1978), 89-112. 

Computer Aided Design of Styrene Batch Suspension Polymerization Reactors... 

The model for the batch suspension polymerization reactor was developed using in the gPROMS simulator. A windows based interface developed in Delphi programming language was employed to build, modify and run the reactor model. The model can predict the monomer conversion, initiator(s) and blow agent (pentane) concentrations, polymerization rate, molecular weight distribution of polystyrene, external jacket inlet/outlet temperatures, and the reactor temperature and pressure. 

Hvalaa N, Aller F, Mitevaa T, Kukanjab D. Modelling, simulation and control of an industrial, semi-batch, emulsion-polymerization reactor. Comp Chem Eng 2011 35 2066-2080. 

The simplest experimental arrangement is the constant volume batch reactor. Polymerization is accompanied by a pressure drc which must be related to conversion and to the reacticm rate. In a bulk polymerization carried cmt isothermally in a 1-phase S3 em the following basic thermodynamic equation applies... 

PVDE is manufactured using radical initiated batch polymerization processes in aqueous emulsion or suspension operating pressures may range from 1 to 20 MPa (10—200 atm) and temperatures from 10 to 130°C. Polymerization method, temperature, pressure, recipe ingredients, the manner in which they are added to the reactor, the reactor design, and post-reactor processing are variables that influence product characteristics and quaUty. 

Soap-starved recipes have been developed that yield 60 wt % soHds low viscosity polymer emulsions without concentrating. It is possible to make latices for appHcation as membranes and similar products via emulsion polymerization at even higher soHds (79). SoHds levels of 70—80 wt % are possible. The paste-like material is made in batch reactors and extmded as product. 

The manufacture of siHcone polymers via anionic polymerization is widely used in the siHcone industry. The anionic polymerization of cycHc siloxanes can be conducted in a single-batch reactor or in a continuously stirred reactor (94,95). The viscosity of the polymer and type of end groups are easily controUed by the amount of added water or triorganosUyl chain-terminating groups. 

A factor in addition to the RTD and temperature distribution that affects the molecular weight distribution (MWD) is the nature of the chemical reaciion. If the period during which the molecule is growing is short compared with the residence time in the reactor, the MWD in a batch reactor is broader than in a CSTR. This situation holds for many free radical and ionic polymerization processes where the reaction intermediates are very short hved. In cases where the growth period is the same as the residence time in the reactor, the MWD is narrower in batch than in CSTR. Polymerizations that have no termination step—for instance, polycondensations—are of this type. This topic is treated by Denbigh (J. Applied Chem., 1, 227 [1951]). 

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). 

In order to be economically viable, a continuous emulsion polymerization process must be able to produce a latex which satisfies application requirements at high rates without frequent disruptions. Since most latex products are developed in batch equipment, the problems associated with converting to continuous systems can be significant. Making such a change requires an understanding of the differences between batch and continuous reactors and how these differences influence product properties and reactor performance. 

Inhibitors can be present in most reaction ingredients. They are deliberately added to monomers to prevent premature polymerization. Ingredient streams such as monomers are cleaned and handled carefully to avoid inhibition in fundamental studies, especially in most academic laboratories. Commercial processes, however, are usually operated with inhibitors present in the feed streams, particularly in the monomer. When such ingredients are used in a batch reactor, a dead time is observed before the reaction starts. 

Continuous stirred-tank reactors can behave very differently from batch reactors with regard to the number of particles formed and polymerization rate. These differences are probably most extreme for styrene, a monomer which closely follows Smith-Ewart Case 2 kinetics. Rate and number of particles in a batch reactor follows the relationship expressed by Equation 13. 

The rate of polymerization with styrene-type monomers is directly proportional to the number of particles formed. In batch reactors most of the particles are nucleated early in the reaction and the number formed depends on the emulsifier available to stabilize these small particles. In a CSTR operating at steady-state the rate of nucleation of new particles depends on the concentration of free emulsifier, i.e. the emulsifier not adsorbed on other surfaces. Since the average particle size in a CSTR is larger than the average size at the end of the batch nucleation period, fewer particles are formed in a CSTR than if the same recipe were used in a batch reactor. Since rate is proportional to the number of particles for styrene-type monomers, the rate per unit volume in a CSTR will be less than the interval-two rate in a batch reactor. In fact, the maximum CSTR rate will be about 60 to 70 percent the batch rate for such monomers. Monomers for which the rate is not as strongly dependent on the number of particles will display less of a difference between batch and continuous reactors. Also, continuous reactors with a particle seed in the feed may be capable of higher rates. 

In batch reactors, heat transfer will also limit the rate of heat-up to the required temperatures for initiation of polymerization. Use of a multiple catalyst system to provide lower temperature initiation has been proposed to minimize the time and energy required in heating. 

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