US 4,376,680 AGranted

Process for demonomerizing polycapronamide

AssigneeSnia Viscosa Societa' Nazionale Industria Applicazioni Viscosa S.p.A.

InventorsEdgardo Horak, Alvaro Casati, Giancarlo Bianucci, Luigi Marafioti, Silvio Notarbartolo

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Abstract

The process and an apparatus for separating and recovering caprolactam moer from polycapronamide are described. A process comprises subjecting a molten capronamide to the action of a vacuum while it flows as a thin layer, extracting therefrom caprolactam as a vapor and condensing the caprolactam vapor by contact with a stream of molten caprolactam, substantially under the same vacuum to which the polymer has been subjected. Preferably the caprolactam vapor and the molten caprolactam flow equicurrently, the molten caprolactam being suitably subdivided. Heat exchange intensifying surfaces are present in the equicurrent flow path. The molten caprolactam is circulated in a closed circuit. The apparatus comprises thin layer evaporator, feed means, a condenser, means for creating a vacuum in the evaporator, and means in the condenser for determining the desired path and subdivision of molten and vapor caprolactam streams, a molten caprolactam circulation circuit and means for drawing off caprolactam from said circuit.

Claims10

Dependent claims

Method for the demonomerization of polycapronamide containing caprolactam monomer, which comprises:

(a) providing a thin layer evaporator for evaporating the caprolactam monomer from the polymer,
means for conveying to said evaporator the polycapronamide to be demonomerized,
a condenser,
means for creating a vacuum in the evaporator through the condenser and for conveying to the condenser the evaporated caprolactam vapor,
the condenser being provided with means for contacting said caprolactam vapor with molten caprolactam whereby said molten caprolactam can absorb said vapor caprolactam and means for determining the desired path and the desired subdivision of the molten and vapor caprolactam,
an external molten caprolactam circulation circuit which feeds the condenser and is fed thereby,
means for drawing off from said circuit a stream of caprolactam corresponding to the amount of vapors which are absorbed,
and means on said circuit for replacing a portion of said stream containing said absorbed vapors with fresh, pure caprolactam,
(b) introducing into said thin layer evaporator said polycapronamide containing caprolactam monomer, and
(c) removing demonomerized caprolactam from said means for drawing off caprolactam.

7 more elements

Dependencies are inferred from the claim text.