Process for preparing nylon salt and its polymerization

1. A process for preparing a nylon polymer, wherein the process comprises:

(a) providing a diammonium dicarboxylate salt which is a granular salt material prepared by flash granulation at a temperature Tp of at least 150° C. to 230° C., and

(b) conducting direct solid state polymerization (DSSP) of the diammonium dicarboxylate salt.

2. The process of claim 1 , wherein the granular salt material is a granular nylon salt.

3. The process according to claim 2 , wherein the granular nylon salt is prepared by the steps comprising:

(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 the temperature Tp of at least 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 forming a granular nylon salt material, wherein the wt. % of the residual moisture content is relative to the weight of the granular nylon salt material.

4. The process according to claim 3 , wherein the concentrated aqueous mixture is:

(i) an aqueous solution comprising a diamine, or a mixture of at least two diamines, and a dicarboxylic acid, or a mixture of at least two dicarboxylic acids, all together referred to as salt precursors, dissolved in the aqueous medium; or

(ii) an aqueous slurry comprising a diammonium dicarboxylate salt dispersed in the aqueous medium.

5. The process according to claim 3 , wherein the concentrated aqueous mixture is an aqueous solution prepared by:

dissolving salt precursors in an aqueous medium, using an excess of the aqueous medium, thereby obtaining a diluted solution; and

evaporating the excess of the aqueous medium at elevated temperature and elevated pressure, thereby obtaining a pressurized concentrated solution.

6. The process according to claim 3 , wherein the concentrated aqueous mixture is an aqueous solution prepared by:

providing a slurry comprising salt components dispersed in an aqueous medium in a pressure vessel; and

closing the pressure vessel and heating the slurry in the pressure vessel to elevated temperature thereby increasing the pressure in the pressure vessel, dissolving the salt components and obtaining a pressurized concentrated solution.

7. The process according to claim 3 , wherein the concentrated aqueous mixture is a concentrated aqueous slurry directly obtained from an aqueous solution comprising salt precursors dissolved in the aqueous medium.

8. The process according to claim 7 , wherein the concentrated aqueous slurry is prepared by:

preparing an aqueous solution by dissolving salt precursors in an aqueous medium; and

concentrating the aqueous solution by evaporating the aqueous medium in an amount sufficient to result in partial precipitation of diammonium/dicarboxylate salt, thereby obtaining the concentrated aqueous slurry comprising salt particles dispersed in the aqueous medium.

9. The process according to claim 3 , wherein step (d) is practiced by flashing the concentrated aqueous mixture such that the aqueous medium is evaporated in an amount sufficient to result in a residual moisture content of at most 5.0 wt. %, relative to the weight of the granular nylon salt material.

10. The process according to claim 3 , wherein the aqueous medium consists of water.

11. The process according to claim 3 , wherein the aqueous medium is present in an amount of at most 20 wt. %, relative to the total weight of the aqueous mixture, and wherein the temperature Tp is in a range from 150° C. to 170° C.

12. The process according to claim 3 , wherein the aqueous medium is present in an amount of at most 25 wt. %, relative to the total weight of the aqueous mixture, and wherein the temperature while Tp is in a range from 170° C. to 190° C.

13. The process according to claim 3 , wherein the aqueous medium is present in an amount of at most 30 wt. %, relative to the total weight of the aqueous mixture, and wherein the temperature while Tp is in a range from 190° C. to 210° C.

14. The process according to claim 3 , wherein the aqueous medium is present in an amount of at most 35 wt. %, relative to the total weight of the aqueous mixture, and wherein the temperature while Tp is in a range from 210° C. to 230° C.

15. The process according to claim 3 , wherein the nylon salt is an aliphatic salt, the salt components therein being all aliphatic components, comprising an aliphatic diamine, or a mixture of at least two aliphatic diamines, and an aliphatic dicarboxylic acid, or a mixture of at least two aliphatic dicarboxylic acids, and wherein the aqueous medium is present in an amount of at most 20 wt. %, relative to the total weight of the aqueous mixture, and wherein the temperature Tp is in a the range from 150° C. to 170° C.

16. The process according to claim 3 , wherein the nylon salt is a semi-aromatic salt.

17. The process according to claim 16 , wherein the semi-aromatic salt comprises terephthalic acid.

18. The process according to claim 1 , wherein the granular salt material is in a form of compressed pellets made of the diammonium dicarboxylate salt.