Value Chain Return Process for Spent Polyurethanes by Hydrogenation

Abstract

Spent polyurethanes are returned to the value chain by hydrogenating the spent polyurethanes 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 120° C. in a non-reducible solvent having a dipole moment of 10-10.sup.30 C.Math.m or less.

Claims

1. A value chain return process for spent polyurethanes, comprising hydrogenating the spent polyurethanes 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 reaction is carried out at a reaction temperature of at least 120° C. in a non-reducible solvent having a dipole moment of 10.Math.10.sup.−30 C.Math.m or less.

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 non-reducible solvent is selected from aromatic solvents.

5. The process according to claim 4, wherein the aromatic solvent is selected from benzene, toluene, xylene, mesitylene, and anisole.

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

7. The process according to claim 1, wherein the reaction temperature is from 150 to 220° C.

8. The process according to claim 1, wherein the spent polyurethanes are selected from aromatic isocyanate-based polyurethanes.

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

10. The process according to claim 9, wherein the transition metal is manganese and the non-reducible solvent is an aromatic solvent.

11. 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.

12. The process according to claim 11, wherein the at least one polydentate ligand conforms to general formula (I) ##STR00035## 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 heterocycloalkyl, aryl, hetaryl, 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.

13. The process according to claim 12, wherein the at least one polydentate ligand conforms to general formula (II) ##STR00036## 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 which 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.

14. The process according to claim 1, wherein the at least one polydentate ligand is selected from compounds A to L, wherein Et is ethyl, iPr is isopropyl, tBu is tert-butyl, Cy is cyclohexyl, Ph is phenyl: ##STR00037## ##STR00038##

15. The process according to claim 1, wherein the hydrogenation reaction is carried out at a pressure of 30 to 500 bar absolute.

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

Description

EXAMPLES

[0114] 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.

[0115] 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).

[0116] 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

[0117] ##STR00009##

[0118] 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 THF/hexanes) was added dropwise. After stirring at 0° C. for 1 h, the system was cooled to −80° C. by .sup.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.

[0119] 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). .sup.31P {.sup.1H} NMR (122 MHz, CD.sub.2Cl.sub.2) δ 83.68.

[0120] .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).

[0121] .sup.13C {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). HRMS (ESI): m/z calcd. for C.sub.24H.sub.32N.sub.2OPRu [M-Cl].sup.+: 497.1296, found: 497.1291.

Preparation of Reference Material 1: Preparation of a Polyurethane Sample

[0122] 2,4-Toluenediisocyanate (3.48 g, 20.0 mmol) was dissolved in 40 mL DMF. Ethylene glycol (1.24 g, 20.0 mmol) was added dropwise while stirring. The mixture was stirred at r.t. for 2 h and then heated to 60° C. for 2 h. The solution was poured into 100 mL of water to give solid precipitates. The solvent was filtered off and the solid was washed with ether and dried in a 60° C. oven overnight to give the product as a white solid (4.11 g, MW=4476 g/mol).

Preparation of Reference Material 2: Preparation of a Polyurethane Sample

[0123] 2,4-Toluenediisocyanate (3.48 g, 20 mmol) was dissolved in 20 mL of DMF and 1,6-hexandiol (2.36 g, 20 mmol) in 20 mL DMF was added slowly. After the addition, the system was left stirring at room temperature for 2 h and heated to 60° C. for 2 h. The resulting solution was poured into 100 mL of water to give precipitates. The solid residue was washed with water, Et.sub.2O and dried in a 60° C. oven yielding a white solid (5.21 g, MW=2800 g/mol).

Preparation of Reference Material 3: Preparation of a Polyurethane Sample

[0124] Methylenediphenyl isocyanate (5.00 g, 20 mmol) was dissolved in 20 mL DMF and 1,6-hexandiol (2.36 g, 20 mmol) in 20 mL DMF was added slowly. After the addition, the system was left stirring at room temperature for 2 h and heated to 60° C. for 2 h. The resulting solution was poured into 100 mL of water to give precipitates. The solid residue was washed with water, Et.sub.2O and dried in a 60° C. oven yielding a white solid (6.80 g, MW=3290 g/mol).

Example 1: Hydrogenation of Polyurethane Reference Material 2

[0125] ##STR00010##

[0126] Under argon, ruthenium catalyst (see table 1 below, 0.01 mmol), KOBu (0.02 mmol, if applicable), the polyurethane reference material 2 (0.12 g) and 3 mL THF were added to a 10 mL microwave crimp-cap vial, equipped with a magnetic PTFE stirring bar. The vial was closed with the crimp-cap septum with a needle plug through and placed into a HEL CAT-7 autoclave. The autoclave was charged with 50 bar of H.sub.2 outside the glovebox, heated to 120° C. and stirred for 24 h. Afterwards, the autoclave was cooled to r.t. and pressure was released carefully, mesitylene was added as internal standard to each glass vial and the product was determined by GC analysis.

TABLE-US-00001 TABLE 1 hydrogenation cat. 1 2 3 4 5 diamine [mmol] 0.33 0.34 0.24 0.34 0.31 yield [%] 65 67 47 67 61 turn-over-number.sup.[a] 33 34 24 34 31 .sup.[a]moles of diamine per mole of catalyst.

Example 2: Hydrogenation of Polyurethane Reference Material 2

[0127] ##STR00011##

[0128] Under argon, a 60 mL Premex autoclave equipped with a Teflon insert was charged with polyurethane reference material 2 (0.29 g, 1 mmol calculated as the repeating unit of the polyurethane). The ruthenium complex as shown above and KOBu together with 5 mL of THF were added. The autoclave was closed, charged with 50 bar of H.sub.2 outside the glovebox and put into a preheated aluminum block (120° C.). After 20 h, the reaction was stopped by taking the autoclave out of the heating block and cooling to r.t. in water. The internal pressure was carefully released. Afterwards, mesitylene was added as internal standard to each glass vial and the product was determined by GC analysis. According to the yield of diaminotoluene, the turn-over-number is 72.

Example 3: Hydrogenation of Polyurethane Reference Material 3

[0129] ##STR00012##

[0130] Under argon, a 60 mL Premex autoclave equipped with a Teflon insert was charged with polyurethane reference material 3 (0.37 g, 1 mmol calculated as the repeating unit of the polyurethane). The ruthenium complex as shown above and KOBu together with 5 mL of THF were added. The autoclave was closed, charged with 50 bar of H.sub.2 outside the glovebox and put into a preheated aluminum block (120° C.). After 20 h, the reaction was stopped by taking the autoclave out of the heating block and cooling to r.t. in water. The internal pressure was carefully released. Afterwards, mesitylene was added as internal standard to each glass vial and the product was determined by GC analysis. According to the yield of the diamine, the turn-over-number is 76.

Example 4: PU Foam Hydrogenation

[0131] ##STR00013##

[0132] Under argon, a 60 mL Premex autoclave equipped with a Teflon insert was charged with a toluenediisocyanate-based polyurethane and the polyol (Lupranol 2074; trifunctional polyetherol-based on glycerol and propylene oxide; MW 3500 g/mol). The ruthenium complex and KOBu together with 15 mL of THF were added. The autoclave was closed, charged with 100 bar of H.sub.2 outside the glovebox and put into a preheated aluminum block (200° C.). After 20 h, the reaction was stopped by taking the autoclave out of the heating block and cooling to r.t. in water. The internal pressure was carefully released. The mixture was transferred to a 50 mL round bottom flash and the solvent was removed in vacuum. The residue was dissolved in 5 mL CDCl.sub.3, mesitylene was added as internal standard, the diamine product was quantified using .sup.1H NMR (1.87 mmol) and was further isolated via column chromatography (200 mg, 1.64 mmol) as a mixture of 2,4-toluenediisocyanate and 2,6-toluenediisocyanate. According to the yield of diaminotoluene, the turn-over-number is 164. According GPC-analysis of the reaction mixture, the polyol was obtained with an average molecular mass of 3500 g/mol, showing that the polyol can be obtained without degradation.

Example 5: Large Scale PU Foam Hydrogenation

[0133] ##STR00014##

[0134] Under argon, a 60 mL Premex autoclave equipped with a Teflon insert was charged with a toluenediisocyanate-based polyurethane and the polyol (Lupranol 2074; trifunctional polyetherol-based on glycerol and propylene oxide; MW 3500 g/mol). The ruthenium complex and KOBu together with 50 mL of THF were added. The autoclave was closed, charged with 100 bar of H.sub.2 outside the glovebox and put into a preheated aluminum block (200° C.). After 30 h, the reaction was stopped by taking the autoclave out of the heating block and cooling to r.t. in water. The internal pressure was carefully released. The resultant solution was filtered via syringe filter and the solvent was removed on a rotavap. Conversion (96%) was estimated by the weight of remaining solid after filtration and diaminotoluene (1.63 g) and Lupranol® 2074 were separated via column chromatography (4.84 g). According to the yield of diaminotoluene, the turn-over-number is 667. According GPC-analysis of the reaction mixture, the polyol was obtained with an average molecular mass of 3500 g/mol, showing that the polyol can be obtained without degradation.

Example 6: Hydrogenation of a PU Based Commercial Product (Yellow Kitchen Sponge)

[0135] ##STR00015##

[0136] The yellow kitchen sponge was cut off from a household scouring pad and was ground before hydrogenation. 10.0 g of ground kitchen sponge powder was subjected to hydrogenation. The reaction was conducted in a 200 mL Premex autoclave. After the reaction was finished, the solution was filtered via syringe filter and the solvent was removed on a rotavap. Conversion was estimated by the weight of remaining solid after filtration and diaminotoluene was isolated by column chromatography. According to the yield of diaminotoluene, the turn-over-number is 970.

Comparative Example: Runs 1 and 2 Using Heterogeneous Catalysts

[0137] ##STR00016##

[0138] Runs 1 and 2 of the comparative example were carried out in the same way as example 4 (PU foam hydrogenation) except that a heterogeneous SiO.sub.2 supported ruthenium catalyst was used instead of the homogeneous hydrogenation catalyst. Also, the solvent volumes were adapted as shown above.

[0139] The comparative experiments show that the use of a heterogeneous ruthenium-catalyst under the otherwise inventive conditions does not yield toluenediamines. Instead, the aromatic ring is hydrogenated and the undesired saturated monomeric diamine is the main product.

[0140] Hydrogenation catalyst L, or alternatively named Mn-8, was prepared according to the following literature protocol: K. Das, A. Kumar, Y. Ben-David, M. A. Iron, D. Milstein, J. Am. Chem. Soc. 2019, 141, 12962-12966.

##STR00017##

[0141] General protocol for the hydrogenation of polyurethanes with Manganese catalysts: Inside an Ar glove box, a Premex autoclave (30, 60, 100 or 200 mL) was equipped with a Teflon insert and a magnetic stirring bar and was charged with the polymer sample, Mn catalyst, KOtBu and solvent. The sealed autoclave was taken out of the glove box, charged with Hz, and transferred to a preheated aluminum block. The reaction was stirred for the indicated time and cooled to room temperature in an ice bath. Afterwards, the hydrogen pressure was carefully released, mesitylene was added as an internal standard and the crude reaction mixture was submitted for GC analysis. In case of the larger scale hydrogenations shown in schemes 1 and 2, the products were isolated and purified by column chromatography.

Example 7

[0142] Polyurethane reference material 2 was used as the polyurethane.

##STR00018##

Example 8

[0143] Polyurethane reference material 2 was used as the polyurethane.

##STR00019##

Example 9

[0144] Polyurethane reference material 2 was used as the polyurethane.

##STR00020##

Example 10

[0145] Polyurethane reference material 2 was used as the polyurethane.

##STR00021##

Example 11

[0146] Polyurethane reference material 2 was used as the polyurethane.

##STR00022##

Example 12: Solvent Screening

[0147] Polyurethane reference material 2 was used as the polyurethane.

##STR00023##

TABLE-US-00002 # solvent amine (GC yield) [%] diol (GC yield) [%] 1 toluene 33 71 2 ethanol 0 86 3 isopropanol 9 70 4 dioxane 16 57 5 tetrahydrofuran 10 68

Example 13

[0148] In this example, an additive free PU foam was used. It is based on toluenediisocyanate and a trifunctional polyetherol based on glycerol and propylene oxide having a molecular weight of 3500 g/mol.

##STR00024##

Example 14

[0149] The PU foam of example 13 was used.

##STR00025##

Example 15

[0150] The PU foam of example 13 was used.

##STR00026##

Example 16

[0151] Polyurethane reference material 3 was used as the polyurethane.

##STR00027##

Example 17

[0152] A commercial polyurethane kitchen sponge was used. The material was a toluenediisocyanate-based polyurethane with an unspecified polyetherol.

##STR00028##

Example 18

[0153] A polyurethane soft foam from an end-of-life office chair was used. The material was a methylenediphenyl isocyanate-based polyurethane with an unspecified polyetherol.

##STR00029##

Example 19

[0154] An end-of-life black-colored polyurethane soft foam packaging material was used. The material was a toluenediisocyanate-based polyurethane with an unspecified polyetherol.

##STR00030##

Example 20

[0155] A rigid polyurethane foam was used. The material was a methylenediphenyl isocyanate-based polyurethane with an unspecified polyetherol.

##STR00031##

Example 21

[0156] An end-of-life polyurethane soft foam from mattresses (mattress 1) was used. The material was a toluenediisocyanate-based polyurethane with an unspecified polyetherol.

##STR00032##

Example 22

[0157] An end-of-life polyurethane soft foam from mattresses (mattress 2) was used. The material was a toluenediisocyanate-based polyurethane with an unspecified polyetherol.

##STR00033##

Example 23

[0158] An end of life polyurethane soft foam from mattresses (mattress 3) was used. The material was a toluenediisocyanate-based polyurethane with an unspecified polyetherol.

##STR00034##