METHOD FOR RECYCLING A POLYAMIDE UNDER ACIDIC CONDITIONS

1 . A method of recovery of the monomers from a polyamide (PA) of the AABB type comprising the following steps:

a) a product (P) comprising the polyamide (PA) is optionally comminuted;

b) an aqueous medium comprising water, the product (P) and an acid (Ac) having at least one pKa lower than 0 and selected in the group consisting of the nitrogen-free inorganic acids, methanesulfonic acid and combinations of two or more of these acids, is heated to induce the dissolution and the hydrolysis of the polyamide (PA);

c) a stream (S) comprising the diacid (A) and the diamine (B) in the form of a salt with the acid (Ac), recovered at the end of step b) is further processed in order to either separate and recover the diacid (A) and the diamine (B) (embodiment E1) or collect the salt formed by the diacid (A) and the diamine (B) (embodiment E2);

wherein step b) is performed with the following conditions:

(i) the initial proportions in the aqueous medium are the following:

proportion of polyamide (PA): at least 15.0 wt. %;

proportion of water: between 20.0 and 70.0 wt. %;

the remainder as acid (Ac) with the condition that the proportion of acid (Ac) is at least 2.0 wt. %,

these proportions being based on the total weight of polyamide (PA), water and acid (Ac);

the molar ratio (H/N) representing the amount of H from the acid (Ac) over the amount of N from the amide bonds of the polyamide (PA) between 1.1 and 7.0;

(ii) the temperature is between 80° C. and 150° C.;

wherein after step b), the method optionally comprises a total or partial removal of the unreacted acid (Ac) from the reaction mixture;

wherein:

according to embodiment (E1), step c) comprises a separation substep c1), wherein the diacid (A) and the salt of the diamine (B) are separated and a neutralisation substep c2), wherein the salt of diamine (B) separated from the diacid (A) is neutralised with at least one inorganic base of formula XOH, X being Li, Na, K or a combination of two or more of these cations to release the diamine (B);

according to embodiment (E2), step c) comprises a neutralisation substep c2) in which the salt of diamine (B) is neutralised with an inorganic base of formula XOH to release the diamine (B);

and wherein the α ratio is less than or equal to 7.0, this ratio being defined as the molar ratio=[salt of the acid (Ac) with XOH released by the method]/[amide bonds of the polyamide (PA)].

2 . The method according to claim 1 , wherein the polyamide (PA) of the AABB type is prepared by polycondensation of:

at least one diacid (A) selected in the group of C 3 -C 18 aliphatic diacids, isophthalic acid and terephthalic acid; and

at least one diamine (B) selected in the group consisting of C 2 -C 18 aliphatic diamines, C 4 -C 18 cycloaliphatic diamines and diamines of formula (IV):

 (IV) wherein Alk is a C 1 -C 6 linear or branched alkylene group.

3 . The method according to claim 1 , wherein the polyamide (PA) is selected in the group consisting of polyamide 6.6, polyamide 6.9, polyamide 6.10, polyamide 6.12, polyamide 10.10, polyamide 4.6, polyamide 4.9, polyamide 4.10, polyamide 12.12, polyamide 10.12, polyamide MXD6, polyamide MXD6/PXD6, polyamide MXD6/MXDI, polyamide 6T/66, polyamide 6T/6I/66, PA 6T/6I and mixtures thereof.

4 . (canceled)

5 . (canceled)

6 . (canceled)

7 . The method according to claim 1 , wherein the acid (Ac) is selected in the group consisting of HCl, HBr, H 2 SO 4 , methane sulfonic acid and combinations of two or more of these acids.

8 . (canceled)

9 . The method according to claim 1 , wherein the initial proportions in the liquid medium are the following:

proportion of polyamide (PA): between 15.0 and 55.0 wt. %;

proportion of water: between 20.0 and 70.0 wt. %;

proportion of acid (Ac): between 10.0 and 55.0 wt. %;

H/N between 2.0 and 7.0, or

the following:

proportion of polyamide (PA): between 15.0 and 35.0 wt. %;

proportion of water: between 20.0 and 55.0 wt. %;

proportion of acid (Ac): between 12.0 and 50.0 wt. %;

H/N between 2.5 and 3.5, or

the following:

proportion of polyamide (PA): between 15.0 and 30.0 wt. %;

proportion of water: between 30.0 and 45.0 wt. %;

proportion of acid (Ac): between 12.0 and 50.0 wt. %;

H/N between 2.5 and 3.5.

10 . (canceled)

11 . (canceled)

12 . The method according to claim 1 , wherein the proportion of water in the aqueous medium is between 30.0 wt. % and 70.0 wt. % or between 35.0 wt. % and 65.0 wt. %.

13 . (canceled)

14 . (canceled)

15 . (canceled)

16 . The method according to claim 1 wherein the initial molar ratio (H/N) is at least 2.0, or between 2.5 and 7.0.

17 . (canceled)

18 . The method according to claim 1 , wherein the temperature at which step b) is performed is between 100° C. and 130° C.

19 . (canceled)

20 . The method according to claim 1 , wherein the degree of hydrolysis R achieved at the end of step b) is at least 90.0 mol %, this ratio corresponding to the degree of conversion of the hydrolysis of the polyamide (PA).

21 . The method according to claim 20 , wherein a degree of hydrolysis R of at least 90.0 mol %, is achieved for a duration of step b) of less than 9.0 hours.

22 . The method according to claim 1 wherein a productivity ratio R* of at least 20.0%, is achieved for a duration of step b), the productivity ratio being defined for a degree of hydrolysis R of at least 90.0% as: initial proportion in wt. % of polyamide (PA)×R (%)/(initial proportion in wt. % of water+initial proportion in wt. % of acid)×100.

23 . (canceled)

24 . (canceled)

25 . The method according to claim 1 , wherein the solid materials that may be present in the stream (S) are partly or totally removed by filtration of stream (S) prior to step c).

26 . The method according to claim 1 wherein, notably where the method comprises after step b), a total or partial removal of the unreacted acid (Ac) from the reaction mixture, α is less than or equal to 2.0 (≤2.0).

27 . (canceled)

28 . (canceled)

29 . The method according to claim 1 , wherein the duration of the hydrolysis from a degree of hydrolysis of R=0 to R=90.0% is between 6.0 and 10.0 hours.

30 . (canceled)

31 . The method according to claim 1 , wherein the total or partial removal of the unreacted acid (Ac) from the reaction mixture is performed by heating and/or applying vacuum to the reaction mixture.