Emulsion tubular reactor

Classification of the many different encapsulation processes is usehil. Previous schemes employing the categories chemical or physical are unsatisfactory because many so-called chemical processes involve exclusively physical phenomena, whereas so-called physical processes can utilize chemical phenomena. An alternative approach is to classify all encapsulation processes as either Type A or Type B processes. Type A processes are defined as those in which capsule formation occurs entirely in a Hquid-filled stirred tank or tubular reactor. Emulsion and dispersion stabiUty play a key role in determining the success of such processes. Type B processes are processes in which capsule formation occurs because a coating is sprayed or deposited in some manner onto the surface of a Hquid or soHd core material dispersed in a gas phase or vacuum. This category also includes processes in which Hquid droplets containing core material are sprayed into a gas phase and subsequentiy solidified to produce microcapsules. Emulsion and dispersion stabilization can play a key role in the success of Type B processes also. 

Continuous-Emulsion Polymerization of Styrene in a Tubular Reactor... 

The advantages of continuous tubular reactors are well known. They include the elimination of batch to batch variations, a large heat transfer area and minimal handling of chemical products. Despite these advantages there are no reported commercial instances of emulsion polymerizations done in a tubular reactor instead the continuous emulsion process has been realized in series-connected stirred tank reactors (1, . ... 

A few workers have examined the continuous emulsion polymerization process in a tubular reactor (, 5,, the initial work... 

A summary of the nine batch reactor emulsion polymerizations and fifteen tubular reactor emulsion polymerizations are presented in Tables III IV. Also, many tubular reactor pressure drop measurements were performed at different Reynolds numbers using distilled water to determined the laminar-turbulent transitional flow regime. 

Figure 10. Monomer conversion rates as a function of emulsion Reynolds number for straight and helical tubular reactors...

The work reported here is part of a continuing program on the emulsion polymerization of styrene in a tubular reactor. It is now evident that the reactor construction is of primary importance in avoiding the problem of reactor plugging. The plugging is associated with a wall effect so that both the reactor dimensions and the nature of the wall surface are important. 

The Effect of Flow Regime on the Continuous Emulsion Polymerisation of Styrene in a Tubular Reactor , Can. J. of Chem. 25, 565 (1977)... 

There are many variations on this theme. Fed-batch and continuous emulsion polymerizations are common. Continuous polymerization in a CSTR is dynamically unstable when free emulsifier is present. Oscillations with periods of several hours will result, but these can be avoided by feeding the CSTR with seed particles made in a batch or tubular reactor. 

Loop A continuous process for polymerizing aqueous emulsions of olefinic compounds such as vinyl acetate. Polymerization takes place in a tubular reactor (the loop) with recycle. Invented by Gulf Oil Canada in 1971 and further developed by several United Kingdom paint companies. It is now used for making copolymers of vinyl acetate with ethylene, used in solvent-free paints and adhesives. 

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 objective of this study was to investigate the feasibility of using a tubular reactor for the seeded emulsion polymerization of vinyl acetate, and to study the effect of process variables on conversion rate and latex properties. 

Reflecting the importance of continuous emulsion polymerization processes, numerous investigations have been carried out to date, which are categorized into three groups (1) studies on the reactor configuration (stirred-tank reactors, tubular type reactors such as a simple tubular reactors, pulsed tubular reactors... 

The stirred-tank reactor and the tubular reactor are two basic reactors used for continuous processes, so much of the experimental and theoretical studies pubhshed to date on continuous emulsion polymerization have been conducted using these reactors. The most important elements in the theory of continuous emulsion polymerization in a stirred-tank reactor or in stirred-tank reactor trains were presented by Gershberg and Longfleld [330]. They started with the S-E theory for particle formation (Case B), employing the same assumptions as stated in Sect. 3.3, and proposed the balance equation describing the steady-state number of polymer particles produced as ... 

The data on particle size distributions for both PVA and PMMA emulsions suggest that small particles could be quite important in the kinetic scheme, and that the larger particles probably grow by internal polymerization and by flocculation with smaller particles. The experiments with the tubular reactor installed upstream of the CSTR demonstrate a practical way to eliminate uncontrolled transients with continuous systems. We believe that the particles generated in the tube prevent CSTR oscillations by avoiding the unstable particle formation reactions in the CSTR. Berrens (8 ) accomplished the same results by using a particle seed in the feed stream to a CSTR with PVC emulsion polymerizations. 

Polystyrene can be easily prepared by emulsion or suspension techniques. Harkins (1 ), Smith and Ewart(2) and Garden ( ) have described the mechanisms of emulsTon polymerization in batch reactors, and the results have been extended to a series of continuous stirred tank reactors (CSTR)( o Much information on continuous emulsion reactors Ts documented in the patent literature, with such innovations as use of a seed latex (5), use of pulsatile flow to reduce plugging of the tube ( ), and turbulent flow to reduce plugging (7 ). Feldon (8) discusses the tubular polymerization of SBR rubber wTth laminar flow (at Reynolds numbers of 660). There have been recent studies on continuous stirred tank reactors utilizing Smith-Ewart kinetics in a single CSTR ( ) as well as predictions of particle size distribution (10). Continuous tubular reactors have been examined for non-polymeric reactions (1 1 ) and polymeric reactions (12.1 31 The objective of this study was to develop a model for the continuous emulsion polymerization of styrene in a tubular reactor, and to verify the model with experimental data. 

Figure 1 shows the equipment used. The tubular reactor was 240 ft (73m) long, 0.5 inch (1.27cm) OD, Type 316 stainless steel. The reactor was placed in an agitated, constant temperature water bath. Two gear pumps were used to give metered flow of the two feed streams-an emulsion of styrene in an equal volume of water, and a solution of potassium persulfate in water. Table 1 shows the recipe used for polymerization. 

The objective was to develop a model for continuous emulsion polymerization of styrene in tubular reactors which predicts the radial and axial profiles of temperature and concentration, and to verify the model using a 240 ft. long, 1/2 in. OD Stainless Steel Tubular reactor. The mathematical model (solved by numerical techniques on a digital computer and based on Smith-Ewart kinetics) accurately predicts the experimental conversion, except at low conversions. Hiqh soap level (1.0%) and low temperature (less than 70°C) permitted the reactor to perform without plugging, giving a uniform latex of 30% solids and up to 90% conversion, with a particle size of about 1000 K and a molecular weight of about 2 X 10 . 

Continuous tubular reactors can also he used to produce emulsion polymers. Such reactors have been used in series with CSTRs (Gonzalez, 1974), as how-through reactors (Rollins et nl., 1979 Ghosh and Forsyth, 1976) and in a ccaitinuous loop process (Lanthier, 1970) in which material is fed and removed from a tubidar loop with a circulating flow greater than the throughput. 

Microwaves should be well suited for continuous tubular reactors, where they might reduce the amount of energy needed, reduce costs, and increase the output of a plant. If water were inert, it might be used to absorb the microwave radiation, the reagents being in solution or in an emulsion. Further research will undoubtedly find many more applications for this technique. 

Emulsion polymerization reactions have also been studied in reactors consisting only of tubes. Such reactors offer the potential advantage of a large area for heat transfer per unit volume and hence a high polymerization rate. One potential problem with tubular reactors, namely plugging, has discouraged commercial use. A number of studies have been reported on once-through continuous tubular reactors but commercial reactors of this type have not been publicized. 

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