Process for reducing caprolactam and its oligomers in nylon-6 pre-polymer
View Patent ↗Disclosed is a process for reducing low molecular weight impurities, namely caprolactam and its oligomers, from Nylon-6 pre-polymer during the preparation of Nylon-6 polymer.
1. A process for removing caprolactam and its oligomers from a pre-polymer mixture comprising caprolactam, oligomers of caprolactam, and nylon-6 pre-polymer, said process comprising:
(a) subjecting the pre-polymer mixture in a molten state to a sudden pressure drop discharge;
(b) contacting the discharged pre-polymer mixture from step (a) with water to produce a pre-polymer phase and a water phase for a time sufficient for at least a portion of caprolactam and oligomers of caprolactam to be extracted into the water phase, wherein the temperature of the water used is from about 10° C. to about 50° C.; and
(c) separating the pre-polymer phase from the water phase.
2. The process of claim 1 , wherein the pre-polymer discharge from step (a) is allowed to solidify prior to contacting the water in step (b).
3. The process of claim 2 , wherein the time that the solidified pre-polymer mixture is in contact with the water does not exceed about 60 minutes.
4. The process of claim 1 , wherein the pressure drop in step (a) is at least about 50 psi.
5. The process of claim 1 , wherein the pressure drop discharge in step (a) is accomplished through a nozzle.