Polymerization static mixer reactor

A number of innovative polymerization reactors using loop reactors, plug-flow and static mixer reactors, and continuous stirred-tank reactors have been reported. For example, Wilkinson and Geddes (15) describe a 50-liter reactor that has the same capacity as a 5000-gallon batch reactor. Extruders, thin-film evaporators, and other devices designed to provide intense mixing for viscous or unstable materials have also been used as reactors. 

Figure 5.11 Radical polymerization of acrylates using a static mixer-reactor without (left) and with (right) a micromixer as premixer. Top molecular weight distribution down appearance ofthe static mixer to illustrate the degree offou ling (by courtesy of Springer) [42],...

A continuous bulk polymerization process with three reaction zones in series has been developed. The degree of polymerization increases from the first reactor to the third reactor. Examples of suitable reactors include continuous stirred tank reactors, stirred tower reactors, axially segregated horizontal reactors, and pipe reactors with static mixers. The continuous stirred tank reactor type is advantageous, because it allows for precise independent control of the residence time in a given reactor by adjusting the level in a given reactor. Thus, the residence time of the polymer mixtures can be independently adjusted and optimized in each of the reactors in series (8). 

VL = 1 Wj), partial inversion. In the first case, N = 0 corresponds to a CSTR and N to a plug-flow reactor. It is shown that the best chemical conversion is obtained with complete flow inversion. The RTD in a Kenics mixer comprising 8 elements could be represented by this model with N = 3 and complete mixing. Static mixers could be used as chemical reactors for specific applications (reactants having large viscosity differences, polymerizations) but the published data are still very scarce and additional information is required for assessing these possibilities. 

In the pre-polymerization vessels, the rubber solution is polymerized to a conversion of 20-30 %. This phase is where the particle structure, the RPS and the RPSD are fixed. In industry, the pre-polymerization is carried out in continuous-flow stirred tank reactors (Shell, Monsanto, Mitsui Toatsu), tower reactors (Dow Chemical), stirred reactor cascades (BASF) or loop reactors with static mixers (Dainippon Ink and Chemicals). 

The effects of mixing in radical polymerization of MMA are interesting [168]. The use of a 5 mm static mixer leads to fouling in the reactor. In contrast, the use of an interdigital multilamination micromixer with 36 lamellae of 25 pm thickness results in a reduction in fouling. This numbering-up approach enables production of 2,000 tons per year without the fouling problem [169]. 

Hirech et al. have described preparation of polyurea microcapsules containing hquid pesticide (e.g., diazinon) suspended in concentrated disinfectant solution, by use of a two-step microencapsulation process [28], The first step is the hquid-hquid dispersion in a Sulzer static mixer (SMX) the second step is microencapsulation by inter-fadal polymerization in a stirred-tank reactor (Fig. 5.4). It has been shown that the... 

The experimental setup, as shown in Fig. 8.6 can also be used for reactive extrusion with prepolymerization (3). In a stirred tank reaetor that can be heated and cooled the mixture is allowed to prepolymerize thermally (without the addition of initiator). This prepolymerization oeeurred batchwise. The contents of the reactor were heated to 135°C, and onee the thermal polymerization started, it was eooled to maintain this temperature. At a conversion of 25% the reactor was cooled to 60°C to stop the reaction. The tubing from this reactor vessel to the extruder was heated to avoid viscosity problems. In another vessel the initiators were dissolved in a small amount of monomer mixture at room temperature. The prepolymer and the monomer-initiator mixture were pumped to the extruder in a ratio of 10 to 1 and mixed in a small statie mixer at the feed port. The volume of the static mixer was chosen such that the residence time in this mixer was in the order of one second to prevent polymerization inside the mixer. 

Craig [312] reports on an investigation of the performance of a large diameter static mixer used as a continuous reactor for styrene polymerization. It was shown the mixer behaved adiabaticaliy. This was confirmed by computer simulation using models that had been verified experimentally. Better results were obtained with a static mixer that carries a heat transfer fluid supplied via manifold connections from external headers. A comparison of different static mixers with respect to thermal homogenization, pressure drop, and mixing efficiency was published by Mueller [313]. 

Block Copolymerization. A polymerization with long chain lives can be used to make block copolsrmers (qv). An important commercial example is styrene/butadiene blocks produced by anionic polymerization (qv). A solution polymerization is done in a batch reactor, starting with one of the two monomers. That monomer is reacted to completion and the second monomer is added while the catalytic sites on the chains remain active. This produces a block copolymer of the AB form. Early addition of the second monomer produces a tapered block. If the second monomer is reacted to completion and replaced by the first monomer, an ABA triblock is obtained. This process is not easily converted to continuous operation because polsrmerizations inside tubes rarely approach the piston-flow environment that is needed to react one monomer to completion before adding the second monomer. Designs using static mixers (also known as motionless mixers) are a possibility. 

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