Screw extruder reactors

Brauer, F. Continuous production of polyurethanes on a twin-screw extruder reactor. In PPS Summer Meeting Conference Abstracts, Amherst, MA, August 16-17, 1989 7D. 

Giudici, R. Nascimento, C.A. O. Scherbakoff, N. Modeling of industrial nylon-6,6 polymerization process in a twin screw extruder reactor. I. Phenomenological and parameter adjusting, J. Appl Polym. Sci., 1998, 67, 1583-1587. 

FIGURE 5.4 Twin-screw extruder reactor. (Courtesy of Mack, W. A., and R. Herter, Extruder Reactors for Polymer Production, Werner Pfleiderer Corporation, Waldwick, NJ, 1975.)... 

Fig. 1. Process flow sheet for the continuous conversion of latex in a counterrotating, tangential twin-screw extruder as it might be arranged for the production of acrylonitrile-butadiene-styrene polymer (Nichols and Kheradi, 1982). Polystyrene (or styrene-acrylonitrile) melt is fed upstream of the reactor zone where the coagulation reaction takes place. Washing (countercurrent liquid-liquid extraction) and solids separation are conducted in zones immediately downstream of the reactor zone. The remainii zones are reserved for devolatilization and pumping.

Fig. 2.15. Reactors for producing these materials include batch, continuously vented, tray reactors, twin-screw extruders, and vented single-screw extruders. These production devices will not be covered in this text because they are of more interest to the manufacturing engineer than the extrusion process engineer.

However, some semiaromatic nylons can give problems as a result of the high melt viscosity. A process for producing polymers of hexamethylenediamine, adipic acid, terephthalic acid, and isophthalic acid has been developed, which involves vaporizing the salt mixture in a high temperature dash reactor followed by molecular weight increase in a twin-screw extruder with efficient moisture removal (17). 

Reactive extruders and extrusion dies of different designs can be easily included in standard technological scheme of polymer production plants, such as those for polycaproamide synthesis, as shown in Fig. 4.39. In this case, a reactive material premixed in a tank 1 is fed into a static device 2 for prepolymerization, where part of the polymerization process takes place. Then the reactive mixture enters the extruder-reactor 3. The necessary temperature distribution is maintained along the extruder. Transfer of the reactive mass proceeds by a system of two coaxial screws mounted in series in a common barrel. Controlling the relative rotation speed of both screws provides the necessary residence time for the reactive mass in the extrader, so that the material reaching the outlet section of the die is a finished polymer. 

Recalling the profound differences in the melting mechanisms in SSEs and in corotating twin-screw extruders (Co-TSE) (Chapter 5), we see that the latter one creates all of the melt almost instantaneously, resulting in a very narrow melt age distribution, while in SSE the age distribution is very broad. Thus, Co-TSEs and twin rotor melting devices [e.g., continuous mixers (CMs)] are better suited to be reactors of polymer melts, as is reflected in the current industrial reactive polymer processing practice. 

Fig. 11.15 RTD cumulative functions of a single screw tangential counter-rotating twin-screw extruder (TCTSE) under matched and staggered conditions, and the back-mixed extruder reactor. [Reprinted by permission from Y. Lu, Ph.D Dissertation, Department of Chemical Engineering, Stevens Institute of Technology, Hoboken, NJ, 1993.]...

This study serves to illustrate the methodology of the lamellar model approach and indicate its complexity and limitations. Extension to other mixer-reactors with complicated flow patterns, e.g., static mixers or twin screw extruders is possible with very little conceptual modification. 

Highly viscous polymeric reactions (e.g., the hydrolytic polyamide reaction) are often carried out in a gear-pump reactor (Tadmore and Klein, 1970). This type of reactor is often difficult to operate because the clearance of the gear teeth is increased by wear caused by flow and the reaction process. For smaller viscosity of the melt, a screw reactor or a twin-screw extruder is often used. Sterbecek et al. (1987) used a twin-screw extruder (i.e., Wemer-Pfleiderer extruder ZSK 83) for studying fast ion-catalyzed polymerization (6-caprolactam) in a melt. They indicated that power input and quality of product in such a reactor depends on the slot width between reactor wall and impeller in a twin screw extruder. They provided an optimum design of a twin-screw reactor for a fast ion-catalyzed polymerization in a melt. 

If a linear rubber is used as a feedstock for the mass process (85), the rubber becomes insoluble in the mixture of monomers and SAN polymer which is formed in the reactors, and discrete rubber particles are formed. This is referred to as phase inversion since the continuous phase shifts from rubber to SAN. Grafting of some of the SAN onto the rubber particles occurs as in the emulsion process. Typically, the mass-produced rubber particles are larger (0.5 to 5 JJ.ni) than those of emulsion-based ABS (0.1 to 1 Jim) and contain much larger internal occlusions of SAN polymer. The reaction recipe can include polymerization initiators, chain-transfer agents, and other additives. Diluents are sometimes used to reduce the viscosity of the monomer and polymer mixture to facilitate processing at high conversion. The product from the reactor system is devolatilized to remove the unreacted monomers and is then pelletized. Equipment used for devolatilization includes single- and twin-screw extruders, and flash and thin film evaporators. Unreacted monomers are recovered for recycle to the reactors to improve the process yield. 

In another US patent, [47], polyolefins and tires scrapes mixture is fed to the batch reactor equipped with a special mixer. A screw extruder or other device is used for feed... 

A tubular reactor of special design internal screw mixer has been developed at Wroclaw University of Technology [56, 57]. The melted plastics from a screw extruder are... 

The F curve is another function that has been defined as the normalized response to a particular input. Alternatively, Equation (13-12) has been used as a definition of F(t), and it has been stated that as a result it can be obtained as the response to a positive-step tracer test. Sometimes the F curve is used in the same manner as the RTD in the modeling of chemical reactors. An excellent example is the study of Wolf and White, who investigated the behavior of screw extruders in polymerization processes. 

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