GB845711A - Process for the treatment of granular polyamide materials with gaseous agents - Google Patents

Abstract

In a process for drying and after-condensation of granular polyamides with a hot inert gas, the gas stream is divided, one part being used to entrain the granules, and to circulate a stream thereof in counter flow with the other part of the gas. In a vessel (2), Fig. 1, containing a downwardly moving bed of the granules, fed in from a <PICT:0845711/IV(a)/1> hopper 10, a vertical pipe 1 is mounted with the lower end above the bottom of the vessel. Hot gas enters a pipe S and entrains granules which are carried up the pipe, and are thrown on to the bed by a deflector plate 4. Part of the treating gas also passes upwards through the bed. The used gas passes to an exit 3, filter 8, condenser 9, cooler 19, to a re-heater 6 and circulating pump 7. The gas used is preferably oxygen-free nitrogen heated at 80 DEG to 250 DEG C. In examples, moist granular polyhexamethylene diammonium adipate or poly-e -caprolactam of mean grain size 2-4 mm., are treated for several hours with nitrogen at 186 DEG C. Water content is reduced from 10-11% to 1-2%, intrinsic viscosity increased from 1,5 to 2,5, and molecular weight from 12,000 to 40,000.ALSO:In a process for drying and after-condensation of granular polyamides with a hot inert gas, the gas stream is divided, one part being used to entrain the granules and to circulate the stream thereof in counterflow with the other part of the gas. In a vessel 2 Fig. 1, containing a downwardly moving bed of the granules fed in from a hopper 10, a vertical pipe 1 is mounted with the lower end above the bottom of the vessel. Gas enters a pipe S <FORM:0845711/III/1> and entrains granules which are carried up the tube 1 and are thrown on to the bed by a deflector plate 4. Part of the treating gas also passes upwards through the bed. The used gas passes through an exit 3 to filter 8, condenser 9, and cooler 19 to re-heater 6 and pump 7. In modifications the deflector plate may be replaced by a large diameter tube open at the base, or by a pipe through which a downward jet of air passes. The gas used is preferably oxygen-free nitrogen heated at 80 DEG to 250 DEG C. In examples, moist granular polyhexamethylene diammonium adipate, or poly-e -caprolactam of mean grain size 2-4 mm. are treated for several hours. Water content is reduced from 10 to 11% to 2%, intrinsic viscosity increased from 1.5 to 2.5, and molecular weight from 12,000 to 40,000.