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Kneader Processor The List Kneader Processor Is a Unique Solution for Working in the Concentrated Phase

| Editor: Dr. Jörg Kempf

Industry is under pressure to develop sustainable processing methods. With this in mind, the List kneader processor provides an alternative to the stirred-tank reactor for the production of polymers, allowing solvents to be eliminated from the reaction step. The kneader processor is also an alternative to the extruder for polymer devolatilization.

Kneader devolatilizer processing a polymer melt at up to 8 t/h. This customized process incorporates compounding within the devolatilization step. (Pictures: LIST)
Kneader devolatilizer processing a polymer melt at up to 8 t/h. This customized process incorporates compounding within the devolatilization step. (Pictures: LIST)

The conventional stirred-tank reactor has long been the standard equipment for polymerization reactions. To allow effective mixing and control of the heat of reaction, however, the stirred tank requires large amounts of solvent to dilute and cool the polymer solution.

Another well-established technology in the polymer industry is the extruder, which is used for operations such as compounding and devolatilization. The basic function of the extruder is forced conveying at high shear rates (1000 s–1), first melting and then conveying the product, with a simultaneous buildup of pressure. The extruder was developed in the 1960s by Rudolf Erdmenger, and subsequently manufactured by Werner & Pfleiderer as the so called “Zwei Schnecken Kneter” (ZSK).

Heinz List, who founded List AG in 1965, had a different vision: to develop unit operations working in the concentrated phase. His first reactor was the All Phase Processor — the famous “AP”. This twin-shaft kneader reactor is still used in the polyurethane industry to recover toluene di-isocyanate (TDI) from tars.

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