Improving the extn. of polyamide granules - by counter-current extn. with an upward stream of water, with injection of nitrogen@ gas into the granule-water mixt

摘要

A process for improving the extn. of polyamide granules (I) by passing a countercurrent of water upwards through the granules comprises feeding nitrogen into the granule/water mixt. with a (nitrogen):(water) ratio of 0.01-25 wt.% per unit time. Pref. the nitrogen is injected in several part-streams at different points in the polyamide-water mixt. USE/ADVANTAGE - Used esp. for the purification of polyamide-6 granules by removing oligomers and monomer. Injection of nitrogen improves the extn. process by increasing turbulence, and also prevents back-mixing; the process therefore reduces the consumption of water and increases the final concn. of extract in the water without changing the residence time of (I) in the extractor; the process is also less prone to interference and therefore more user-friendly. The amt. of residual extract in the granules can be reduced to below 0.5%.