Value Chain Return Process for Spent Polyamides by Hydrogenation

Abstract

Spent polyamides are returned to the value chain by hydrogenating the spent polyamide in a hydrogen atmosphere in the presence of at least one homogeneous transition metal catalyst complex, wherein the transition metal is selected from metals of groups 7, 8, 9 and 10 of the periodic table of elements according to IUPAC, to obtain a polyamine and a polyol. The hydrogenation is carried out at a reaction temperature of at least 160° C. in a non-reducible solvent having a dipole moment in the range of 1.Math.10.sup.−30 to 10.Math.10.sup.−30 C.Math.m.

Claims

1. A value chain return process for spent polyamides, comprising hydrogenating the spent polyamide in a hydrogen atmosphere in the presence of at least one homogeneous transition metal catalyst complex, wherein the transition metal is selected from metals of groups 7, 8, 9 and 10 of the periodic table of elements according to IUPAC, to obtain a polyamine and a polyol, wherein the hydrogenation is carried out at a reaction temperature of at least 160° C. in a non-reducible solvent having a dipole moment in the range of 1.Math.10.sup.−30 to 10.Math.10.sup.−30 C.Math.m.

2. The process according to claim 1, wherein the non-reducible solvent comprises at least one electron pair donor.

3. The process according to claim 1, wherein the non-reducible solvent is selected from ethers, alcohols and amines.

4. The process according to claim 1, wherein the hydrogenation reaction is carried out in the essential absence of DMSO.

5. The process according to claim 1, wherein the reaction temperature is from 170 to 220° C.

6. The process according to claim 1, wherein the spent polyamide is polyamide 66.

7. The process according to claim 1, wherein the homogeneous transition metal catalyst complex comprises a transition metal selected from rhenium, ruthenium, iridium, nickel, palladium or platinum.

8. The process according to claim 1, wherein the homogeneous transition metal catalyst complex comprises at least one polydentate ligand having at least one nitrogen atom and at least one phosphorous atom which are capable of coordinating to the transition metal.

9. The process according to claim 8, wherein the at least one polydentate ligand conforms to general formula (I) ##STR00010## in which each R′ is independently H or C.sub.1-C.sub.4-alkyl, R.sup.1 and R.sup.2, independently of one another, are C.sub.1-C.sub.12-alkyl, cycloalkyl or aryl, which alkyl is unsubstituted or carries 1, 2, 3, 4 or 5 identical or different substituents R.sup.7, and which cycloalkyl and aryl are unsubstituted or carry 1, 2, 3, 4 or 5 identical or different substituents R.sup.8, R.sup.3 and R.sup.4, independently of one another, are H or C.sub.1-C.sub.12-alkyl, which is unsubstituted or carries 1, 2, 3, 4 or 5 identical or different substituents selected from alkoxy, cycloalkoxy, heterocycloalkoxy, aryloxy, hetaryloxy, hydroxyl, NE.sup.1E.sup.2 and PR.sup.1R.sup.2, R.sup.5 is H or C.sub.1-C.sub.12-alkyl, which is unsubstituted or carries 1, 2, 3, 4 or 5 identical or different substituents R.sup.7, R.sup.6 is H or C.sub.1-C.sub.4-alkyl, or R.sup.4 and R.sup.6 are absent and R.sup.3 and R.sup.5, together with the nitrogen atom to which R.sup.3 is bonded and the carbon atom to which R.sup.5 is bonded, form a 6-membered heteroaromatic ring, which is unsubstituted or carries 1, 2, 3, 4 or 5 identical or different substituents which are selected from C.sub.1-C.sub.12-alkyl, cycloalkyl, aryl and hetaryl, which alkyl is unsubstituted or carries 1, 2, 3, 4 or 5 identical or different substituents R.sup.7, and which cycloalkyl, aryl and hetaryl are unsubstituted or carry an alkyl substituent which is unsubstituted or carries a substituent selected from alkoxy, cycloalkoxy, heterocycloalkoxy, aryloxy, hetaryloxy, hydroxyl, NE.sup.1E.sup.2 and PR.sup.1R.sup.2, each R.sup.7 is independently cycloalkyl, heterocycloalkyl, aryl, hetaryl, alkoxy, cycloalkoxy, heterocycloalkoxy, aryloxy, hetaryloxy, hydroxyl or NE.sup.1E.sup.2, each R.sup.8 is independently C.sub.1-C.sub.4-alkyl, cycloalkyl, heterocycloalkyl, aryl, hetaryl, alkoxy, cycloalkoxy, heterocycloalkoxy, aryloxy, hetaryloxy, hydroxyl or NE.sup.1E.sup.2, and E.sup.1 and E.sup.2, independently of one another and independently of each occurrence, are radicals selected from H, C.sub.1-C.sub.12-alkyl, cycloalkyl and aryl.

10. The process according to claim 9, wherein the at least one polydentate ligand conforms to general formula (II) ##STR00011## in which D is H, C.sub.1-C.sub.12-alkyl, cycloalkyl, aryl or hetaryl, which alkyl is unsubstituted or carries 1, 2, 3, 4 or 5 identical or different substituents R.sup.7, and cycloalkyl, aryl or hetaryl are unsubstituted or carry an alkyl substituent which is unsubstituted or carries a substituent selected from alkoxy, cycloalkoxy, heterocycloalkoxy, aryloxy, hetaryloxy, hydroxyl, NE.sup.1E.sup.2 and PR.sup.1R.sup.2, preferably NE.sup.1E.sup.2 and PR.sup.1R.sup.2.

11. The process according to claim 1, wherein the at least one polydentate ligand is selected from compounds A to G, wherein Et is ethyl, iPr is isopropyl, tBu is tert-butyl, Cy is cyclohexyl, Ph is phenyl: ##STR00012##

12. The process according to claim 1, wherein the hydrogenation reaction is carried out at a pressure of 50 to 500 bar absolute.

13. The process according to claim 1, wherein the hydrogenation reaction is carried out in the presence of a base.

Description

EXAMPLES

[0096] The present invention can be further explained and illustrated on the basis of the following examples. However, it will be understood that these examples are included merely for purposes of illustration and are not intended to limit the scope of the invention in any way.

[0097] All chemicals and solvents were purchased from Sigma-Aldrich or ABCR and used without further purification, unless otherwise specified. .sup.1H-, .sup.13C- and .sup.31P NMR spectra were recorded on Bruker Avance 200 or 400 MHz spectrometer and were referenced to the residual proton (.sup.1H) or carbon (.sup.13C) resonance peaks of the solvent. Chemical shifts (δ) are reported in ppm. .sup.31P NMR spectra were referred to an external standard (ample of D.sub.3PO.sub.4).

[0098] Hydrogenation catalysts P and Q were prepared according literature protocols: E. Balaraman, J. Am. Chem. Soc. 2010, 132, 16756-16758 and D. Srimani, Adv. Synth. Catal. 2013, 355, 2525-2530.

Reference Example 1: Synthesis of Hydrogenation Catalyst H

[0099] ##STR00007##

[0100] First step: In a 50 mL Schlenk tube, 6-methyl-2,2′-bipyridine (511 mg, 3.00 mmol) was dissolved in 15 mL Et.sub.2O, cooled to 0° C. and LDA (3.50 mL, 1 M in THE/hexanes) was added dropwise. After stirring at 0° C. for 1 h, the system was cooled to −80° C. by iPrOH/liquid N.sub.2 and CIPCy.sub.2 (815 g, 3.50 mmol) in 5 mL Et.sub.2O was added slowly. The cooling bath was removed after 1 h and the mixture was recovered to r.t. gradually and stirred overnight. The reaction mixture was quenched by adding 10 mL of degassed water to the yellow slurry. The organic phase was separated and the aqueous phase was extracted with ether (2×5 mL). The combined organic phase was dried over Na.sub.2SO.sub.4, filtered and the solvent was removed to give the crude ligand as a sticky orange oil. 52% purity based on .sup.31P NMR. It was used directly for the next step without further purification.

[0101] Second step: The ligand obtained in the first step was dissolved in 20 mL THF. RuHCl(CO)(PPh.sub.3).sub.3 (952 mg, 1.00 mmol) was added, the mixture was stirred at 70° C. for 5 hours and then cooled to r.t. The solvent was reduced to ca. 10 mL under vacuum and 20 mL of Et.sub.2O were added to the remaining red-orange dispersion. The solution was removed via cannula and the solid was washed with Et.sub.2O (2×10 mL) and dried under vacuum to give 465.2 mg of the orange product (87% yield based on Ru).

[0102] .sup.31P {.sup.1H} NMR (122 MHz, CD.sub.2Cl.sub.2) δ 83.68.

[0103] .sup.1H NMR (301 MHz, CD.sub.2Cl.sub.2) δ 9.22-9.13 (m, 1H), 8.07-7.97 (m, 1H), 7.93 (d, J=8.0 Hz, 1H), 7.86 (td, J=8.0, 1.6 Hz, 1H), 7.82 (td, J=8.0, 0.9 Hz, 1H), 7.49 (d, J=7.7 Hz, 1H), 7.45-7.39 (m, 1H), 3.82-3.56 (m, 2H), 2.46-2.27 (m, 2H), 2.08-0.99 (m, 20H), −14.83 (d, J=23.6 Hz, 1H).

[0104] .sup.13C {.sup.1H} NMR (126 MHz, CD.sub.2Cl.sub.2) δ 207.71 (d, J=14.9 Hz), 161.70 (d, J=5.1 Hz), 156.38, 154.78 (d, J=2.7 Hz), 153.51 (d, J=1.7 Hz), 137.30, 136.51, 126.42 (d, J=1.9 Hz), 123.13 (d, J=9.6 Hz), 122.76 (d, J=1.6 Hz), 119.73, 40.59 (d, J=22.2 Hz), 38.59 (d, J=23.4 Hz), 35.76 (d, J=28.9 Hz), 31.01 (d, J=2.9 Hz), 29.60 (d, J=4.2 Hz), 28.61 (d, J=4.5 Hz), 28.20 (d, J=13.6 Hz), 27.73, 27.56 (d, J=9.2 Hz), 26.82 (d, J=4.4 Hz), 26.74 (d, J=3.5 Hz), 26.71 (d, J=2.0 Hz), 26.35 (d, J=1.5 Hz).

[0105] HRMS (ESI): m/z calcd. for C.sub.24H.sub.32N.sub.2OPRu [M-Cl].sup.+: 497.1296, found: 497.1291.

Example 1: Hydrogenation of a Polyamide Sample

[0106] ##STR00008##

[0107] Under argon, a 60 mL Premex autoclave equipped with a Teflon insert was charged with 0.3 g (1.25 mmol calculated as the repeating unit) polyamide 66 (obtained by reacting adipic acid and a 15% excess of 1,6-hexamethylenediamine; MW=8240 g/mol; amino end group content=1748 mmol/kg; acid end group content=14 mmol/kg). The ruthenium complex as indicated in table 1 (0.01 mmol), KO.sup.tBu and solvent were added as shown above. The autoclave was closed, charged with H.sub.2 to the pressure given in table 1 outside the glovebox and put in an aluminum block (preheated to the reaction temperature as shown in table 1). After the reaction was finished (20 h), the autoclave was taken out of the heating block and cooled to r.t. in a water bath. The internal pressure was carefully released. The autoclave was opened and mesitylene was added to the mixture as internal standard for GC analysis. The amounts of diamine and diol were obtained according to calibrated GC results, see table 1.

TABLE-US-00001 TABLE 1 T p (H.sub.2) diamine diamine diol diol solvent [° C.] [bar] [mmol] [yield] [mmol] [yield] TON .sup.[a] catalyst THF 200 100 0.98 78% 0.78 62% 98 H THF 180 100 0.75 60% 0.44 35% 75 H THF* 150 70 0.15 12% <0.06 <5% 15 H THF 200 80 0.88 70% 0.59 47% 88 H dimethoxy- 200 100 0.88 70% 0.58 46% 88 H ethane toluene 200 100 0.74 59% 0.40 32% 74 H anisole 200 100 0.86 69% 0.58 49% 86 H *comparative example. .sup.[a] turn-over-number = moles of diamine per mole of catalyst.

[0108] The results in table 1 show that the diol and diamine yields increase with an increase of the reaction temperature. Higher yields are obtained in solvent THE in comparison to anisole.

Example 2: Hydrogenation of a Polyamide Sample

[0109] Under argon, a 60 mL Premex autoclave equipped with a Teflon insert was charged with 0.5 g (2.08 mmol according to the repeating unit) polyamide 66 (Ultramide A27 obtainable from BASF SE; 1:1 polyamide from adipic acid and 1,6-hexamethylenediamine). Ruthenium complex H (0.01 mmol), KO.sup.tBu (0.04 mmol) and THE (5 mL) were added. The autoclave was closed, charged with H.sub.2 (100 bar absolute) outside the glovebox and put in an aluminum block (preheated to the reaction temperature of 200° C.). After the reaction was finished (20 h), the autoclave was taken out of the heating block and cooled to r.t. in a water bath. The internal pressure was carefully released. The autoclave was opened and mesitylene was added to the mixture as internal standard for GC analysis. The amounts of diamine and diol were obtained according to calibrated GC results. Yield diamine: 19% (39 mmol); yield diol 18% (37 mmol); turn-over-number according to the diamine: 39.

Comparative Example 1: Runs 1 to 3 Using Heterogeneous Catalysts

[0110] ##STR00009##

[0111] Example 1 was repeated except that the ruthenium catalysts as shown in table 2 were used instead of catalyst H. THE was used as the solvent. The autoclave was sealed and flushed with H.sub.2 several times before charging with H.sub.2. Afterwards, the autoclave was put into a preheated aluminum block (200° C.). After the reaction was finished, the autoclave was taken out of the heating block and cooled to r.t. in a water bath. The internal pressure was carefully released. Then, the autoclave was opened and mesitylene was added to the mixture as internal standard for GC analysis. The amounts of diamine and diol were obtained according to calibrated GC results, see table 2.

TABLE-US-00002 TABLE 2 # catalyst diamine [mmol] diol [mmol] 1 Ru/C not detected not detected 2 Raney Co not detected not detected 3 Ru@SiO.sub.2 0.56 not detected

[0112] The results in table 2 show that heterogeneous catalysts are not suitable for the hydrogenation of polyamide 66. No hydrogenation occurs in runs 1 and 2. In run 3, only diamine was detected.

Comparative Example 2: Conversion of 1,6-Hexanediol Using a Heterogeneous Catalyst

[0113] A 60 mL Premex autoclave equipped with a Teflon insert was charged with 0.5 mmol 1,6-hexanediol dissolved in 5 mL of THF. 100 mg of the heterogeneous catalyst Ruthenium on silica was added. The autoclave was sealed and flushed with H.sub.2 several times before charging with H.sub.2 (100 bar). Afterwards, the autoclave was put into a preheated aluminum block (200° C.). After the reaction was finished, the autoclave was taken out of the heating block and cooled to r.t. in a water bath. The internal pressure was carefully released. Then, the autoclave was opened and mesitylene was added to the mixture as internal standard for GC analysis. After 29 h, no 1,6-hexanediol was detected. The diol was consumed during the reaction. No reaction product could be identified. Conceivably, 1,6-hexanediol underwent deoxygenation to give hexane.

Example 3: Conversion of 1,6-Hexanediol Using a Homogeneous Catalyst

[0114] Comparative example 2 was repeated except that catalyst Q was used instead of the heterogeneous catalyst. In this experiment, no hydrogenation or deoxygenation of 1,6-hexanediol occurred. This observation underlines the importance of the use of a homogeneous catalyst.