Twin screw extruders flow reactors

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.

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. 

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