Process for preparing nylon salt and its polymerization

A process for preparing a granular nylon salt material comprising steps of:

• (a) providing in a pressure vessel a concentrated aqueous mixture comprising at least 65 wt. % of salt components and at most 35 wt. % of an aqueous medium, the weight percentages (wt. %) being relative to the total weight of the aqueous mixture;
• (b) controlling temperature of the concentrated aqueous mixture in the pressure vessel so that the concentrated aqueous mixture has a temperature Tp of 150° C. to 230° C.;
• (c) controlling pre-condensation eventually occurring in the concentrated aqueous mixture so that pre-condensation therein remains at a level of at most 15 mole %;
• and
• (d) discharging the concentrated aqueous mixture from the pressure vessel by flashing the concentrated aqueous mixture at the temperature Tp of 150° C. to 230° C. via a flash valve into a flash chamber to evaporate the aqueous medium in an amount sufficient to result in a residual moisture content of at most 7.5 wt. % and thereby directly form a granular nylon salt material, wherein the wt. % of the residual moisture content is relative to the weight of the granular nylon salt material.