Process for the manufacture of a solution of salts of diacids/diamine(s)

A process for manufacturing an aqueous solution comprising salts of diacids and at least one diamine, the process comprising:

• producing an aqueous solution (A′) of diamine(s) and diacid(s) having a diacid/diamine molar ratio of less than 1, by feeding into a reactor (a) a liquid comprising water and diamine at a temperature from 55° C. to 95° C., (b) a stream (B′) comprising an aliphatic or cycloaliphatic diacid comprising a number of carbon atoms of greater than 10 or an aromatic diacid, optionally (c) a stream comprising diamine, and optionally (d) a stream comprising water;
• wherein the flow rates of the feed stream or streams are controlled to always have a temperature of the solution in the reactor less than the boiling point of the solution under operating pressure;
• and the amounts of the water and diamine in the liquid and flow rates of the feed streams being controlled in order to always have a diacid(s)/diamine(s) molar ratio of less than 1;
• mixing the aqueous solution (A′) resulting from the first stage with a stream (B″) comprising at least one diacid, the diacid being an aliphatic or cycloaliphatic diacid comprising a number of carbon atoms of less than or equal to 10, and optionally supplementary water and/or supplementary diamine;
• and obtaining an aqueous solution (resulting from the mixing of (A′) and (B″)) having a diacids/diamine(s) molar ratio of between 0.9 and 1.1;
• bringing the solution to a temperature at most equal to the boiling point of the solution at operating pressure by at least a release of heat of reaction between the diamine(s) and the diacids;
• and
• obtaining an aqueous solution (A) comprising salts of diacids and diamine(s) having a concentration by weight of salt of between 40 and 70%.