US-12624187-B2 - Method for recovering raw materials from polyurethane products

US12624187B2US 12624187 B2US12624187 B2US 12624187B2US-12624187-B2

Abstract

The invention relates to a method for recovering raw materials from polyurethane products, having the steps of: (A) providing a polyurethane product based on an isocyanate component and a polyol component; (B) reacting the polyurethane product with an alcohol in the presence of a catalyst, wherein a first product mixture containing alcohol, polyols, carbamates, and optionally water is obtained; (C) preparing the first product mixture, having the steps of: (C.I.) mixing the first product mixture obtained in step (B) with an organic solvent, which can be mixed with the alcohol used in step (B), optionally followed by a separation of solid components, thereby obtaining a second product mixture; (C.II) washing the second product mixture obtained in step (C.I) using an aqueous washing fluid, wherein carbamates contained in the second product mixture are hydrogenated partly while releasing amines and alcohol, and carrying out a phase separation into a first solvent phase, containing the organic solvent used in step (C.I) and polyols, and a first aqueous phase, containing water, alcohol, carbamates, and amines; and (C.III) processing the first solvent phase, thereby obtaining the polyols; and optionally (D) processing the first aqueous phase, thereby obtaining an amine which corresponds to an isocyanate of the isocyanate component.

Inventors

Friedhelm Steffens
Sebastian Pohl
Shabnam Majidi Salehi
Jonas Krause

Assignees

COVESTRO DEUTSCHLAND AG

Dates

Publication Date: 20260512
Application Date: 20210921
Priority Date: 20200923

Claims (17)

1 . A method for recovering raw materials from a polyurethane product, comprising: (A) providing a polyurethane product that is based on an isocyanate component and a polyol component; (B) reacting the polyurethane product with an alcohol in the presence of a catalyst, to give a first product mixture containing alcohol, polyols and carbamates, and optionally water; (C) working up the first product mixture by a process comprising: (C.I) mixing the first product mixture obtained in step (B) with an organic solvent which is miscible with the alcohol used in step (B), optionally followed by a removal of solid constituents, to obtain a second product mixture; (C.II) washing the second product mixture obtained in step (C.I) with an aqueous wash liquid, whereby carbamates present in the second product mixture are partially hydrolyzed to release amines and alcohol, and phase separation into (a) a first solvent phase containing organic solvent used in step (C.I) and polyols, and (b) a first aqueous phase containing water, alcohol, carbamates and amines; (C.III) working up the first solvent phase to obtain the polyols; and optionally (D) working up the first aqueous phase to obtain an amine corresponding to an isocyanate from the isocyanate component.
2 . The method as claimed in claim 1 , in which step (D) is conducted and comprises: (D.I) mixing the first aqueous phase with an organic solvent and phase separation into (c) a second solvent phase containing organic solvent used in step (D.I) and polyols, and (d) a second aqueous phase containing alcohol, carbamates and amines.
3 . The method as claimed in claim 1 , in which step (D) is conducted and comprises: (D.IIa) hydrolyzing the carbamates present in the first aqueous phase to obtain a third product mixture containing water, alcohol and amines; (D.III.a) evaporating water out of the third product mixture to leave an amine-alcohol mixture; (D.IV.a) evaporating an alcohol fraction from the amine-alcohol mixture to leave an amine phase; and (D.V) recovering from the amine phase an amine corresponding to an isocyanate from the isocyanate component.
4 . The method as claimed in claim 3 , in which the water evaporated in step (D.III.a) is recycled into step (C.II) as a constituent of the aqueous wash liquid.
5 . The method as claimed in claim 3 , in which the alcohol fraction evaporated in step (D.IV.a) is recycled into step (B).
6 . The method as claimed in claim 1 , in which step (D) is conducted and comprises: (D.II.b) evaporating a water-alcohol fraction from the first aqueous phase leaving a carbamate phase; (D.III.b) hydrolyzing the carbamates present in the carbamate phase to obtain a third product mixture containing water, alcohol and amines; (D.IV.b) evaporating an alcohol fraction from the third product mixture to obtain an amine phase; and (D.V) recovering from the amine phase an amine corresponding to an isocyanate from the isocyanate component.
7 . The method as claimed in claim 6 , in which the water-alcohol fraction evaporated in step (D.II.b) is recycled into step (C.II) as a constituent of the aqueous wash liquid.
8 . The method as claimed in claim 6 , in which the alcohol fraction evaporated in step (D.IV.b) is recycled into step (B).
9 . The method as claimed in claim 3 , further comprising (E) providing a crude product fraction of an amine, which is the same amine which is recovered in step (D.V), where the crude product fraction comprises, in addition to the amine present in the crude product fraction, organic impurities boiling at a higher point than the amine present in the crude product fraction; and where step (D.V) comprises: (D.V.1) mixing the amine phase with the crude product fraction and working up the resulting mixture, to give the amine contained in the crude product fraction together with the amine recovered from the amine phase.
10 . The method as claimed in claim 9 , in which the crude product fraction is taken from a bottom fraction of a distillation to purify the amine contained in the crude product fraction, where in step (D.V.1) additionally a solid residue is obtained which comprises the organic impurities boiling at a higher point than the amine present in the crude product fraction; or in which the crude product fraction is taken from a crude product of a process for producing the amine contained in the crude product fraction, and comprises organic impurities boiling at a lower point than the amine present in the crude product fraction, and water, and is supplied to a distillation to remove water, in which a bottom fraction comprising the amine present in the crude product fraction, organic impurities boiling at a lower point than the amine present in the crude product fraction and organic impurities boiling at a higher point than the amine present in the crude product fraction, and a top fraction comprising removed water.
11 . The method as claimed in claim 10 , in which step (E) comprises: (E.I) catalytically hydrogenating the nitro compound corresponding to the amine present in the crude product fraction, optionally in the presence of a solvent, to give a crude product comprising, in addition to the amine present in the crude product fraction, organic impurities boiling at a higher point than the amine present in the crude product fraction, organic impurities boiling at a lower point than the amine present in the crude product fraction, and water; (E.II) removing water from the crude product, to give a water-depleted process product; and (E.III) distilling the water-depleted process product, to give a distillate fraction of the amine present in the crude product fraction, and a bottom fraction containing, in addition to the amine present in the crude product fraction, organic impurities boiling at a higher point than the amine present in the crude product fraction.
12 . The method as claimed in claim 1 , in which the isocyanate component contains an isocyanate comprising tolylene diisocyanate, a di- and/or polyisocyanate of the diphenylmethane series, pentane 1,5-diisocyanate, hexamethylene 1,6-diisocyanate, isophorone diisocyanate, xylylene diisocyanate, or a mixture of any two or more thereof, and/or in which the polyol component contains a polyol comprising a polyether polyol, a polyester polyol, a polyetherester polyol, a polyethercarbonate polyol, or a mixture of any two or more thereof.
13 . The method as claimed in claim 1 , in which the organic solvent in step (C.I) comprises a halogen-substituted aliphatic hydrocarbon, a halogen-substituted alicyclic hydrocarbon, a halogen-substituted aromatic hydrocarbon, or a mixture of any two or more thereof, and the alcohol in step (B) comprises methanol, ethanol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, methylglycol, triethylene glycol, glycerol, 2-methylpropane-1,3-diol, or a mixture of any two or more thereof.
14 . The method as claimed in claim 1 , in which the polyurethane product is a polyurethane foam, a polyurethane elastomer, a polyurethane adhesive or a polyurethane coating.
15 . The method as claimed in claim 1 , in which water is supplied to the reaction in step (B), if at all, in an amount such that the mass fraction of water, based on the total mass of polyurethane product in step (B), catalyst, alcohol and water, is in a range from 0% to 5.0%, with no further water being added after commencement of the reaction of the polyurethane product with the alcohol in the presence of the catalyst.
16 . The method as claimed in claim 2 , in which step (D) comprises: (D.IIa) hydrolyzing the carbamates present in the second aqueous phase to obtain a third product mixture containing water, alcohol and amines; (D.III.a) evaporating water out of the third product mixture to leave an amine-alcohol mixture; (D.IV.a) evaporating an alcohol fraction from the amine-alcohol mixture to leave an amine phase; and (D.V) recovering from the amine phase an amine corresponding to an isocyanate from the isocyanate component.
17 . The method as claimed in claim 2 , in which step (D) comprises: (D.II.b) evaporating a water-alcohol fraction from the second aqueous phase, leaving a carbamate phase; (D.III.b) hydrolyzing the carbamates present in the carbamate phase to obtain a third product mixture containing water, alcohol and amines; (D.IV.b) evaporating an alcohol fraction from the third product mixture to obtain an amine phase; and (D.V) recovering from the amine phase an amine corresponding to an isocyanate from the isocyanate component.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a national stage application under 35 U.S.C. § 371 of PCT/EP2021/075916, filed Sep. 21, 2021, which claims the benefit of European Application No. 20197639.6, filed Sep. 23, 2020, each of which is incorporated herein by reference. The project leading to the present application received funding under Grant Agreement No. 814543 as part of the European Union's Horizon 2020 research and innovation programme. FIELD The present invention relates to a method for recovering raw materials (i.e. polyols and optionally additional amines) from polyurethane products, comprising the steps of: (A) providing a polyurethane product based on an isocyanate component and a polyol component; (B) reacting the polyurethane product with an alcohol in the presence of a catalyst, to give a first product mixture containing alcohol, polyols and carbamates, and optionally water; (C) working up the first product mixture, comprising: (C.I) mixing the first product mixture obtained in step (B) with an organic solvent which is miscible with the alcohol used in step (B), optionally followed by a removal of solid constituents, to obtain a second product mixture; (C.II) washing the second product mixture obtained in step (C.I) with an aqueous wash liquid, whereby carbamates present in the second product mixture are partially hydrolyzed to release amines and alcohol, and phase separation into a first solvent phase containing organic solvent used in step (C.I) and polyols, and a first aqueous phase containing water, alcohol, carbamates and amines; and (C.III) working up the first solvent phase to obtain the polyols; and optionally (D) working up the first aqueous phase to obtain an amine corresponding to an isocyanate from the isocyanate component. BACKGROUND Polyurethane products enjoy a diversity of applications in industry and in everyday life. Distinctions are typically made between polyurethane foams and what are known as “CASE” products, with “CASE” being a collective term for polyurethane coatings (e.g., paints), adhesives, sealants and elastomers. The polyurethane foams are typically divided into rigid foams and flexible foams. Common to all of these products in spite of their heterogeneity is the basic polyurethane structure, which is formed by the polyaddition reaction of a polyfunctional isocyanate and of a polyol and which in the case, for example, of a polyurethane based on a diisocyanate O═C═N—R—N═C═O and a diol H—O—R′—O—H (where R and R′ denote organic radicals) may be represented as ~~~[O⁢‐⁢R⁢‘‐⁢O⁢‐⁢(O=C)⁢‐⁢HN⁢‐⁢R⁢‐⁢NH⁢‐⁢(C=O)]~~~ It is the great economic success of the polyurethane products that means that there are large quantities of polyurethane waste arising (from old mattresses or seated furniture, for example) that must be sent for rational use. The mode of reuse that is the easiest to implement technically is that of incineration, with the heat of combustion released being utilized for other processes, examples being industrial processes. However, this does not allow the raw materials loops to be completed. Another mode of use is that referred to as “physical recycling”, which sees polyurethane wastes mechanically comminuted and used in the manufacture of new products. The obvious limits to this mode of recycling mean that there has been no lack of attempts to recover the raw materials underlying polyurethane production by rebreaking the polyurethane linkages (referred to as “chemical recycling”). These raw materials to be won back comprise primarily polyols (i.e., in the example above, H—O—R′—O—H). In addition it is possible through hydrolytic cleavage of the urethane bonding to recover amines as well (i.e., in the example above, H2N—R—NH2), which after workup can be phosgenated to form isocyanates (in the example above, to form O═C═N—R—N═C═O). A variety of chemical recycling approaches have been developed in the past. The three foremost are briefly summarized as follows: 1. Hydrolysis of urethanes by reaction with water to recover amines and polyols with formation of carbon dioxide.2. Glycolysis of urethanes by reaction with alcohols, where the polyols incorporated in the urethane groups are released by being replaced with the alcohol used. This process is commonly referred to in the literature as transesterification (more accurately: transurethanization). Regardless of the exact nature of the alcohol used, this mode of chemical recycling is dubbed glycolysis in the literature, a term that really applies only for glycol. In the present invention, therefore, the term used generally is alcoholysis. The glycolysis may be followed by a hydrolysis. If the hydrolysis is conducted in the presence of the as yet unchanged glycolysis mixture, this is called a3. Hydroglycolysis of urethane compounds by reaction with alcohols and water. It is of course likewise possible to add alcohol and water from the start, in which case the above-described processes of glycolysis and