Continuous stirred-tank reactor latex from

Although the early literature described the application of a tubular reactor for the production of SBR latexes(1), the standard continuous emulsion polymerization processes for SBR polymerization still consist of continuous stirred tank reactors(CSTR s) and all of the recipe ingredients are normally fed into the first reactor and a latex is removed from the last one, as shown in Figure 1. However, it is doubtful whether this conventional reactor combination and operation method is the most efficient in continuous emulsion polymerization. As is well known, the kinetic behavior of continuous emulsion polymerization differs very much according to the kind of monomers. In this paper, therefore, the discussion about the present subject will be advanced using the... 

While vinyl acetate is normally polymerized in batch or continuous stirred tank reactors, continuous reactors offer the possibility of better heat transfer and more uniform quality. Tubular reactors have been used to produce polystyrene by a mass process (1, 2), and to produce emulsion polymers from styrene and styrene-butadiene (3 -6). The use of mixed emulsifiers to produce mono-disperse latexes has been applied to polyvinyl toluene (5). Dunn and Taylor have proposed that nucleation in seeded vinyl acetate emulsion is prevented by entrapment of oligomeric radicals by the seed particles (6j. Because of the solubility of vinyl acetate in water, Smith -Ewart kinetics (case 2) does not seem to apply, but the kinetic models developed by Ugelstad (7J and Friis (8 ) seem to be more appropriate. 

The vector c in Eq. (5) describes the creation in, and/or removal of latex particles from, the system. The creation component may arise from in situ particle formation in Interval I) or from the flow behavior in a continuous stirred-tank reactor system (CSTR) with an arbitrary number of reaction vessels. Particle removal terms may be required if coagulation occurs or in the context of CSTR operation. 

In continuous operation mode, both feed and effluent streams flow continuously. The main characteristic of a continuous stirred tank reactor (CSTR) is the broad residence time distribution (RTD), which is characterized by a decreasing exponential function. The same behavior describes the age of the particles in the reactor and hence the particle size distribution (PSD) at the exit. Therefore, it is not possible to obtain narrow monodisperse latexes using a single CSTR. In addition, CSTRs are hable to suffer intermittent nucleations [89, 90) that lead to multimodal PSDs. This may be alleviated by using a tubular reactor before the CSTR, in which polymer particles are formed in a smooth way [91]. On the other hand, the copolymer composition is quite constant, even though it is different from that of the feed. 

A number of studies endeavored to experimentally determine the values of the desorption rate constant. It is also interesting to note that Lee and Poehlein [46,48,49] modified the approach of Ugelstad et al. [8,9] and applied it to emulsion polymerization carried out in a single continuous stirred tank reactor (CSTR) system. The resultant latex particle size distribution data were then used to determine the value of A des. The k data obtained from other literature are summarized in Table 4.4. Significant variations in the values of k isi for the emulsion polymerizations of styrene at 60 °C are observed. 

It is not straightforward to successfully manufacture a particular latex product, which is generally developed in a laboratory batch or semibatch reactor, in a commercial continuous emulsion polymerization system (e.g., a continuous stirred tank reactor). This is simply because the characteristics of continuous stirred tank reactors are dramatically different from those of batch and semibatch reactors. As a consequence, the particle nucleation process and kinetics experienced in batch or semibatch emulsion polymerization systems cannot be directly applied to continuous systems consisting of stirred tank reactors. 

When stirred-tank reactors are operated in the batch mode, all ingredients are added at or near the beginning of the reaction cycle, the reaction is allowed to proceed to a desired end point, and the product latex is removed for further processing. Strict batch operation has a number of disadvantages. First, the heat load on the cooling system can be very nonuniform. The production rates from such reactors can be limited by the capability of the heat removal system during the peak in the exotherm. The use of mixed initiator systems (fast and slow) and the continuous addition of a fast initiator are two ways of trying to deal with this problem. 

Continuous Reactors. A variety of continuous reactor systems are used commercially, but the most common are comprised of a number of stirred-tank reactors (CSTR) connected in series. Operation normally Involves pumping all ingredients into the first CSTR and removing the partially converted latex from the final reactor. Intermediate feed streams can also be employed. Detailed reviews... 

Most commercial continuous emulsion polymerization processes consist of a series of stirred-tank reactors (CSTR s) (1,2). Early SBR systems were comprised of 10 to 15 equal-sized reactors in series. All of the recipe ingredients were fed into the first reactor and a partially converted latex was removed from the last reactor for monomer stripping and further processing. More recent processes involve fewer reactors perhaps 3 to 5. 

Polymer production technology involves a diversity of products produced from even a single monomer. Polymerizations are carried out in a variety of reactor types batch, semi-batch and continuous flow stirred tank or tubular reactors. However, very few commercial or fundamental polymer or latex properties can be measured on-line. Therefore, if one aims to develop and apply control strategies to achieve desired polymer (or latex) property trajectories under such a variety of conditions, it is important to have a valid mechanistic model capable of predicting at least the major effects of the process variables. 

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