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EP-4504827-B1 - VALUE CHAIN RETURN PROCESS FOR THE RECOVERY OF PHOSPHOROUS ESTER-BASED FLAME RETARDANTS FROM POLYURETHANE RIGID FOAMS

EP4504827B1EP 4504827 B1EP4504827 B1EP 4504827B1EP-4504827-B1

Inventors

  • SCHAUB, THOMAS
  • SCHUETTE, MARKUS
  • HASHMI, A. STEPHEN K.
  • ZUBAR, Viktoriia
  • KLEIN, PHILIPPE

Dates

Publication Date
20260506
Application Date
20230328

Claims (15)

  1. A value chain return process for polyurethane rigid foams containing at least one phosphorous ester-based flame retardant, comprising hydrogenating the polyurethane rigid foam - in an organic aprotic solvent, - 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, and - at a reaction temperature of at least 120 °C, to obtain a hydrogenation product containing a polyamine and a polyol from the polyurethane rigid foam, and recovering the flame retardant from the hydrogenation product.
  2. The process according to claim 1, wherein the polyamine is recovered from the hydrogenation product via distillation.
  3. The process according to claim 1 or 2, wherein the flame retardant is recovered via distillation from the hydrogenation product, or from a distillation bottoms thereof.
  4. The process according to any one of the preceding claims, wherein the polyol is recovered by extraction from the hydrogenation product, or from a distillation bottoms thereof, or is recovered as a distillation bottoms after removal of volatile components.
  5. The process according to any one of the preceding claims, wherein the polyurethane rigid foams are selected from aromatic isocyanate-based polyurethane rigid foams, preferably from methylenedi(phenylisocyanate)-based polyurethane rigid foams, polymeric methylenedi(phenylisocyanate)-based polyurethane rigid foams and 1,5-naphthyldiisocyanate-based polyurethane rigid foams.
  6. The process according to any one of the preceding claims, wherein the at least one phosphorous ester-based flame retardant is selected from tris(2-chloroethyl)phosphate, tris(chloroisopropyl)phosphate, tris(1,3-dichloro-2-propyl)phosphate, tris(2-ethylhexyl)phosphate, tricresylphosphate, tris-(2,3-dibromo)phosphate, tetrakis-(2-chlorethyl)-ethylenediphosphate, dimethylphosphonate, dimethylpropylphosphonate, diphenylcresylphosphate, triethylphosphate, and mixtures thereof.
  7. The process according to any one of the preceding claims, wherein the organic aprotic solvent is selected from ethers, aromatic hydrocarbons, and mixtures thereof.
  8. The process according to claim 7, wherein the ether is selected from tetrahydrofuran, 1,4-dioxane, and anisole; the aromatic hydrocarbon is selected from benzene, toluene, xylene, and mesitylene.
  9. The process according to any one of the preceding claims, wherein the homogeneous transition metal catalyst complex comprises a transition metal selected from manganese, rhenium, ruthenium, iridium, nickel, palladium and platinum, preferably manganese, ruthenium, and iridium.
  10. The process according to any one of the preceding claims, 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.
  11. The process according to claim 10, wherein the at least one polydentate ligand conforms to general formula (I) in which each R' is independently H or C 1 -C 4 -alkyl, R 1 and R 2 , independently of one another, are C 1 -C 12 -alkyl, cycloalkyl or aryl, which alkyl is unsubstituted or carries 1, 2, 3, 4 or 5 identical or different substituents R 7 , and which cycloalkyl and aryl are unsubstituted or carry 1, 2, 3, 4 or 5 identical or different substituents R 8 , R 3 and R 4 , independently of one another, are H or C 1 -C 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 1 E 2 and PR 1 R 2 , R 5 is H or C 1 -C 12 -alkyl, which is unsubstituted or carries 1, 2, 3, 4 or 5 identical or different substituents R 7 , R 6 is H or C 1 -C 4 -alkyl, or R 4 and R 6 are absent and R 3 and R 5 , together with the nitrogen atom to which R 3 is bonded and the carbon atom to which R 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 1 -C 12 -alkyl, cycloalkyl, aryl and hetaryl, which alkyl is unsubstituted or carries 1, 2, 3, 4 or 5 identical or different substituents R 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 1 E 2 and PR 1 R 2 , each R 7 is independently cycloalkyl, heterocycloalkyl, aryl, hetaryl, alkoxy, cycloalkoxy, heterocycloalkoxy, aryloxy, hetaryloxy, hydroxyl or NE 1 E 2 , each R 8 is independently C 1 -C 4 -alkyl, cycloalkyl, heterocycloalkyl, aryl, hetaryl, alkoxy, cycloalkoxy, heterocycloalkoxy, aryloxy, hetaryloxy, hydroxyl or NE 1 E 2 , and E 1 and E 2 , independently of one another and independently of each occurrence, are radicals selected from H, C 1 -C 12 -alkyl, cycloalkyl and aryl.
  12. The process according to claim 11, wherein the at least one polydentate ligand conforms to general formula (II) in which D is H, C 1 -C 12 -alkyl, cycloalkyl, aryl or hetaryl, which alkyl is unsubstituted or carries 1, 2, 3, 4 or 5 identical or different substituents R 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 1 E 2 and PR 1 R 2 , preferably NE 1 E 2 and PR 1 R 2 .
  13. The process according to any one of the preceding claims, wherein the at least one polydentate ligand is selected from compounds A to L, wherein Et is ethyl, i Pr is isopropyl, t Bu is tert-butyl, Cy is cyclohexyl, Ph is phenyl:
  14. The process according to any one of the preceding claims, wherein the hydrogenation reaction is carried out at a pressure of 30 to 500 bar absolute, preferably 40 to 300 bar absolute, more preferably 50 to 200 bar absolute.
  15. The process according to any one of the preceding claims, wherein the hydrogenation reaction is carried out in the presence of a base, preferably an alkali metal or alkaline earth metal carbonate, an alkali metal or alkaline earth metal hydroxide or an alkali metal or alkaline earth metal alcoholate, more preferably an alkali metal tert-butoxide.

Description

The present invention relates to a value chain return process for polyurethane rigid foams which allows for the recovery of phosphorous ester-based flame retardants contained therein. In the last three decades, there has been an enormous increase in worldwide plastics demand. For example, in the last 10 years, the amount of plastics produced worldwide has increased by almost 50%. Within 30 years, it has even almost quadrupled reaching an amount of 359 million metric tons in 2018. From these facts, it becomes clear that production of said huge amounts of plastics is followed by a need to dispose or recycle spent plastics. Preference should be given to recycling as thereby valuable materials, e.g. compounds which can act as monomers, can be added back to the value chain, e.g. by direct re-use in plastics production. Plastics are used with additive components incorporated for the purpose of imparting various functions to the resins. For example, as resins have high combustibility by themselves, the resins are mixed with flame retardants in a proportion of up to 25% by weight from the viewpoint of preventing the spread of fire. The possibility of returning flame retardants into the industrial cycle appears to be promising both with respect to saving of resources and from an economic point of view. In addition, in the industrial production of polyurethane rigid foams, polyurethane (PU) rigid foam wastes are incurred. For example, such waste of PU rigid foam is obtained upon casting blocks of PU rigid foam, followed by cutting, trimming or sizing said blocks to obtain the desired PU workpiece. Additionally, rejects of PU rigid foams such as off-spec products are incurred. Thus, there is a need to develop processing techniques to recover materials from plastic waste. The recycling process should reduce both the waste of material and the carbon footprint. Further, it should be an economical and energy efficient process delivering valuable materials which comprise high technical features. In contrast, disposal, e.g. by combustion, has a negative impact on the environment as well as on the carbon footprint. Among the plastics mentioned above, polyurethanes (PU) are important representatives. Generally, polyurethanes are produced by polyaddition of (poly)isocyanates with polyol. The characteristic chain link is the urethane group. Polyurethane exists in many types, e.g. as foams, elastomers, or thermosets, among which foams are especially important. The polyaddition of (poly)isocyanates with polyol results in the formation of linear, branched, or cross-linked polyurethanes. As an alternative to alcohols, the most important group of NCO-reactive compounds are amines resulting in the formation of di- or trisubstituted ureas. Ureas are also formed by the reaction of water with isocyanates, in which the carbamic acid formed in the first step of the reaction spontaneously decomposes to an amine with elimination of carbon dioxide. This amine then reacts with excess isocyanate to yield symmetrically substituted ureas. This reaction is the basic reaction leading to polyurethane foams. These foams may be formed in wide range of densities and may be of flexible, or rigid foam structures. Generally speaking, "flexible foams" are those that recover their shape after deformation. In addition to being reversibly deformable, flexible foams tend to have limited resistance to applied load and tend to have mostly open cells. "Rigid foams" are those that generally retain the deformed shape without significant recovery after deformation. Rigid foams tend to have mostly closed cells. Whether PU soft foams or PU rigid foams are formed during polyaddition mainly depends on the types of polyisocyanate and polyol components used. For example, the starting materials may influence the crosslinking of the polymers meaning that the polymer consists of a three-dimensional network. Long, flexible segments, contributed by the polyol, result in the formation of PU soft foams. PU rigid foams are obtained from short chains with many crosslinks. More details for the polyurethane rigid foams suitable to be used according the invention can be found in: Kunststoffhandbuch, Band 7, Polyurethane, Carl-Hanser-Verlag, 3. Auflage, 1993, Kapitel 6. Polyurethane rigid foams provide excellent insulation properties. Thus, they are of great importance in the construction sector and commonly used as insulation materials, e.g. for buildings insulations. However, for application of polyurethane rigid foams as insulation material in buildings, the addition of flame retardants is necessary for fire protection reasons. For this purpose, flame retardants are added in the production process of the polyurethane rigid foams. Nowadays, mainly phosphorous esters, such as tris(2-chloroethyl)phosphate, tris(chloroisopropyl)phosphate, tris(1,3-dichloro-2-propyl)phosphate, tris(2-ethylhexyl)phosphate, triethylphosphate, tricresylphosphate, tris-(2,3-dibromo)phosphate, tetrakis-(2-c