Production of solutions of diacid/diamine salts

A process for the production of an aqueous solution of salts of diamines and diacids, comprising:

• (a) producing an aqueous solution of diamine and diacid having a diacid/diamine molar ratio from 1.5 to 5 and a concentration of dissolved reactants comprising diamine and diacid in water from 40% to 75% by weight, in a first reaction zone containing either (i) at least 5% by volume of aqueous solution of diamine and diacid with a molar ratio ranging from 1.5 to 5, or (ii) water constituting at least 10% of the total amount of water to be introduced into said reaction zone, a stream comprising diacid, by feeding into said reaction zone a stream comprising diamine and, optionally, a stream of water, the flow rates of the feed stream comprising diacid and of the feed stream comprising diamine being controlled such that the temperature of the solution in said reaction zone is constantly below the boiling point at the operating pressure in said reaction zone and such that the diacid/diamine molar ratio is constantly greater than 1.1, the amount of acid introduced corresponding to at least 90% by weight of the total mass of the acid required to produce the desired amount of aqueous salt solution, the amount of water introduced constituting at least 75% by weight of the total mass of water required to produce the desired amount of the aqueous salt solution;
• (b) transferring the aqueous solution obtained in the first reaction zone into a second reaction zone equipped with a condenser;
• and
• (c) introducing into the second reaction zone a stream comprising diamine to provide a diacid/diamine molar ratio ranging from 0.9 to 1.1, the temperature of the solution being adjusted to at most 110° C. and, optionally, introducing amounts of additional water and/or diacid such as to provide the salt solution with the desired concentration and with the desired diacid/diamine ratio,
• thereby, obtaining an aqueous solution of salts of diamines and diacids at a salt concentration ranging from 50% to 80% by weight.