Process for recovering raw materials from polyurethane waste

Abstract

The invention relates to a process for recycling polyurethanes, in particular polyurethane foams, in which urea is used as the sole and cheap reagent to solve the problem of inverse proportionality between the efficiency and selectivity of the degradation of urethane groups in the PU foam structure. In this respect, urea acts simultaneously as a cleavage agent for the urethane groups and as a scavenger of free aromatic amine. The reaction mixtures consisting of polyurethane foam scraps and urea reagent can be heated by microwave irradiation or by conventional means.

Description

[0001] Process for recovering raw materials from polyurethane waste

[0002] Abstract

[0003] The invention relates to a process for recycling polyurethanes, in particular polyurethane foams, in which urea is used as the sole and cheap reagent to solve the problem of inverse proportionality between the efficiency and selectivity of the degradation of urethane groups in the Pll foam structure. In this respect, urea acts simultaneously as a cleavage agent for the urethane groups and as a scavenger of free aromatic amine. The reaction mixtures consisting of polyurethane foam scraps and urea reagent can be heated by microwave irradiation or by conventional means.

[0004] Background

[0005] Polyurethane (Pll) foams are bulky, thermoset materials for which incineration, landfill and mechanical recycling are not the most suitable methods for dealing with this type of polymer waste. For this reason, many efforts have been focused on their chemical recycling. To this end, various methods have been developed to degrade the urethane groups in the Pll foam structure, such as hydrolysis, glycolysis / alcoholysis, acidolysis, aminolysis and phosphorolysis. Ammonolysis, on the other hand, although mentioned as early as in 1955 in patent DE 967601C1, is one of the less studied methods for Pll degradation.2In the ammonolysis of Pll, ammonia is used as a cleavage reagent for the urethane groups. Ammonia can be used either as a single reagent in the form of gas3’4or under supercritical conditions5or as one component of a multi-component reagent system, e.g. ammonia in combination with alcohol / glycol3 4or ammonia in combination with water3 4.

[0006] US patent application US 4162995A3and German patent DE 2721724B24describe the degradation of rigid or flexible PU foams with gaseous or aqueous ammonia (30% by weight ammonia solution) at elevated temperatures of 100 - 250 °C and ambient or elevated pressure (approx. 7 bar) in the presence or absence of alcohols or polyols with molecular weights from 100 to 5000 Da. As a preferred method, they describe the continuous bubbling of ammonia gas through an alcohol or polyol with a high boiling point (above 100 °C), followed by the addition of PU foam scraps, with reaction times of up to 3 hours or more. Since water, glycols and / or polyols present in the system can also act as reagent, the mechanism of urethane group degradation is a combination of ammonolysis and glycolysis / hydrolysis. Without additional purification, the products of these processes are viscous, dark-colored oils with a high hydroxyl number (of about 500). Subsequent purification of the resulting degradation products using vacuum distillation yields a light yellow or light brown viscous oil with a hydroxyl number of 56. Recycled products were mainly used to synthesize new rigid Pll foams with good mechanical properties. On the other hand, flexible Pll foams made partly from the recycled polyols obtained in this way from waste flexible Pll foams are stiffer than Pll foams synthesized from virgin polyols.

[0007] Patent application DE 4217524A16describes a process for Pll hydrolysis at ambient pressure and a temperature range of 120 - 250 °C by adding an amino compound, e.g. ammonia, which is reported to act as a catalyst for the hydrolysis of the urethane groups. During the reaction, water is introduced drop-wise into the system. The resulting product is a low-viscosity oil that is particularly suitable for reaction injection molding (RIM).

[0008] Patent application US 4511680A7describes ammonia as one of the possible base catalysts in a continuous glycolysis degradation process of rigid or flexible PU foams in a multishaft screw machine reactor. The product obtained was used for the synthesis of new rigid PU foams.

[0009] The ammonolysis process of PU with ammonia as the sole reagent was studied by Lentz et. al.5In this case, supercritical ammonia was used as the reaction medium and reagent for the degradation of methylene diphenyl diisocyanate (MDI)-based elastomers and MDI- based flexible PU foams. The process is carried out at supercritical conditions of 139 °C and 140 bar with a reaction time of 120 minutes. Supercritical ammonia is capable of extracting 1 ,4-butanediol chain extender, 4,4'-methylenedianiline (MDA) and other side products originating from PU oligourea hard segments. The extraction is carried out over a period of 90 minutes. The extracted material can be subjected to further separation processes in which urea is removed by washing with water and the remaining side products such as MDA and 1 ,4- butanediol are isolated by distillation.

[0010] Another approach to perform PU ammonolysis is by using a compound that serves as an ammonia precursor, e.g., ammonium carbonate, ammonium bicarbonate, ammonium carbamate, or urea, all of which generate ammonia under the reaction conditions used.8-12Patent applications GB 2062660A8, JP S5653128A9and DE 3037545C210describe the use of ammonia precursors such as ammonium carbonate, ammonium bicarbonate and urea for the degradation of rigid or flexible PU foams. The typical process using conventional heating takes place at elevated temperature (between 50 - 200 °C), pressure (between 5 - 7 bar) and a reaction time of up to 7 hours. The amount of reagent used is typically 30 - 150 parts per 100 parts by weight of PU with simultaneous use of the solvent (e.g. water or methanol) in an amount of 20 - 100 parts per 100 parts by weight of Pll. Water or methanol acts also as a reagent, resulting in a mixed mechanism of degradation of the urethane groups (hydrolysis or alcoholysis in combination with ammonolysis). Under optimal reaction conditions for urethane group degradation in the PU foam structure, about 50% of the diisocyanate used for PU synthesis converts to aromatic diamine, which is a disadvantage of the described methods. The reaction products are viscous, dark liquids. The recovered polyols were used in combination with virgin polyol (up to 25 wt.% recycled polyol) for the synthesis of new less- demanding rigid PU foams.

[0011] Patent application WO 2022112581 A211uses aqueous urea (1 - 10 wt.% solution) for PU degradation in an amount of 0.5 - 2.5 mL per 1 g of PU foam. The process is carried out at elevated temperatures of 190 - 250 °C, a pressure of preferably 10 - 45 bar and a reaction time of 20 to 240 min. Since the water in the system is present in a high molar excess per urethane groups in the PU foam structure, hydrolysis is the predominant mechanism of the urethane group degradation, which leads to significant amount of undesired carcinogenic aromatic diamine side product.

[0012] In patent application US 5508312A,12urea was identified as a scavenger for aromatic diamines formed in the process of PU foam or polyurea glycolysis. The process can be carried out in a separate two-step or in a combined one-step process of glycolysis of PU or polyurea waste in combination with a low molecular weight urea or carbamic acid ester. In the case of a two-step process, the first step comprises the degradation of PU or polyurea waste by glycolysis using a low molecular weight diol (< 350 Da) and / or a high molecular weight polyol (350 - 4000 Da) at elevated temperatures of 100 -260 °C and ambient pressure. In the second step, the glycolysate products obtained in the first step are reacted with a low molecular weight urea or carbamic acid ester at temperatures of 50 - 200 °C, ambient pressure, and reaction time of up to 90 min. In a one-step process, the reaction conditions are similar to the first step of a two-step process, with the exception that the low molecular weight urea or carbamic acid ester is introduced into the system together with the PU or polyurea waste and the diol / polyol. The mass ratio between reagents and PU (or polyurea) waste is between 1 : 1 and 20 : 1 for high molecular weight diols / polyols and between 5 : 1 and 1 : 3 for low molecular weight d iols / polyo Is. The low molecular weight urea or carbamic acid ester is generally used in a molar ratio of 1 : 2 - 3 : 1 in relation to the amino groups of aromatic diamine side products formed in the process. The authors report that the homogeneous single-phase glycolysis products obtained by a one-step glycolysis process contain about 0.6 wt.% of free aromatic diamines, whereas in the process carried out under the same conditions with added urea, the content of aromatic diamines decreases below 0.1 wt.%. In addition, urea is also used as a catalyst for rigid Pll foam alcoholysis, as described by Li et. al.13The reactions are performed in an autoclave with reaction temperatures of 140 - 190 °C and a mass ratio of Pll foam to ethanol to urea of 1 : 10 : 0.5. Complete degradation of the urethane groups in the foam structure was achieved at reaction times of 3 h and temperatures above 180 °C.

[0013] Summary of the invention

[0014] The present invention provides a method for efficiently degrading the urethane groups in the Pll structure using urea as the sole reagent, acting simultaneously as a degradation agent for urethane groups and as an amine scavenger. The reaction is preferably carried out in bulk, without additional reagent and / or solvent / medium. Urea as a degradation reagent is non-toxic, inexpensive and can be used in small quantities of 3 to less than 30 wt.% per PU foam (i.e., 1 - 8 molar equivalents of urea per urethane group), making the degradation process cost-effective and sustainable. By choosing the optimal experimental conditions, the amount of free aromatic diamine in the final degradation mixture can be reduced to -0.1 % by weight. The reaction mixtures can be heated by microwave irradiation or by conventional means. Heating the reaction mixtures by microwaves alone or in combination with conventional heating allows a significant reduction in reaction time while improving energy efficiency. In addition, the process can be carried out as a one- or two-step process in which the heating methods can be combined.

[0015] The crude polyol can be used without additional purification, or it can be further purified depending on the quality requirements of the final product. If purification is required, a low-cost purification method is preferred. One such method is extraction of the recovered polyol in cyclohexane, which can be used in a closed-loop system, so that there is no economic or environmental impact. If necessary, purification with an acidic aqueous solution (HCI / water) can also be performed.

[0016] The disclosed process is characterized by an efficient degradation of the urethane groups in the PU foam structure with concomitant low amount of aromatic diamine formed, which results in the recovery of recycled polyols containing predominantly the hydroxyl end group functionality. Recycled polyols can be used as a feedstock for the synthesis of new flexible PU foams or other polymer products. The process of the invention makes it possible to obtain high-quality recycled polyols that are structurally good equivalent to the corresponding virgin polyols. Recycled polyols obtained by the process described in the present invention are therefore suitable for the production of new flexible Pll foams (even when 100 wt% recycled polyol is used) whose quality (density, morphology and mechanical properties) is comparable to the flexible Pll foams produced from the corresponding virgin polyols, as shown by our results.

[0017] Description of the invention

[0018] The present invention discloses a cost-effective process for degrading the urethane groups in the Pll structure to recover high quality recycled polyether polyols. A first aspect of the invention is a process for decomposing polyurethane (Pll) which comprises treating said Pll with urea as the sole reagent at a temperature in a range of 134°C - 260°C.

[0019] The method utilizes a urea reagent that is readily available, non-toxic and inexpensive. At high temperature, the urea reagent undergoes a thermal decomposition reaction to form ammonia and isocyanic acid. The ammonia formed acts as a cleavage agent for the urethane groups in the Pll structure, while the isocyanic acid acts as an amine scavenger through the reaction of its isocyanate group with the amino group of a diamine formed by hydrolysis or thermal degradation of the urethane and / or aromatic urea group of Pll foam hard segments, which leads to the formation of a urea bond (Fig.1). In this way, the amount of undesirable, toxic aromatic diamine side products resulting from the degradation of oligourea hard segments in the Pll foam structure can be reduced to ~0.1 % by weight or more. The recovered polyols can be used with or without additional purification steps for the synthesis of new flexible / rigid Pll foams or for the synthesis of other products.

[0020] Thermal degradation of urea reagent

[0021] The present invention utilizes the decomposition products of urea formed during thermal degradation. Urea starts to decompose thermally above its melting point (133 °C) and in particularly above 152 °C.14Thus, the reaction temperature in the process of the invention is preferably at least 200°C or higher, more preferably in a range of 200°C to 260°C or 210 to 250°C. The decomposition consists of a complex set of non-equilibrium and equilibrium reactions that take place in (and between) solid, liquid, and gaseous phases. In a simplified reaction, the urea decomposes to ammonia and isocyanic acid.

[0022] H2N-CO-NH2 NH3+ HNCO urea ammonia + isocyanic acid Isocyanic acid can further react with (i) the water present in the system to form another ammonia molecule and carbon dioxide. Alternatively, it can (ii) react with urea to form a biuret, or it can (iii) trimerize to form a cyanuric acid. In the reaction system with Pll, isocyanic acid (iv) reacts with the diamines formed by hydrolysis or thermal degradation of oligourea hard segments in the Pll structure, which is the preferred reaction of the present invention.

[0023] (i) HNCO + H2O NH3+ CO2

[0024] (ii) HNCO + H2N-CO-NH2 H2N-CO-NH-CO-NH2

[0025] (iii) 3 HNCO [CONH]3

[0026] (iv) HNCO + H2N-R-NH2 H2N-R-NH-CO-NH2

[0027] R is a diamine residue formed by the degradation of Pll hard segments.

[0028] Degradation of polyurethane with ammonia

[0029] In the disclosed method, the urethane groups in the Pll structure are degraded by ammonolysis with ammonia generated in-situ by thermal degradation of urea. The mechanism of urethane group degradation involves either (i) direct reaction of ammonia with the urethane groups or (ii) ammonia reacts with the isocyanate group formed in thermal degradation of the urethane group, thus preventing the recombination of the hydroxyl and isocyanate precursors back into the urethane bond. Both reaction pathways lead to the same reaction product, i.e. , a ureido-functionalized derivative, and a hydroxyl-functionalized polyol (diol).

[0030] (i) RNHCOOR’ + NH3RNHCONH2+ HOR’ (direct reaction)

[0031] (ii) RNHCOOR’ RNCO + HOR’ (reversible thermal degradation)

[0032] RNCO + NH3— > RNHCONH2 (indirect reaction)

[0033] R and R’ are the diisocyanate and polyol / diol residue, respectively.

[0034] Reaction of isocyanic acid and (di)amines and formation of ureido-functionalized (di)amine derivatives and benzoylene urea derivatives

[0035] The challenge in Pll recycling is to carry out the chemical degradation process in such a way that an efficient and selective degradation of the urethane groups in the Pll structure is achieved in order to obtain preferably hydroxyl-functionalized polyols and oligourea hard segments functionalized with the selected degradation reagent. However, prior art results on acidolyis,15glycolysis16and aminolysis17show that the selectivity of degradation of urethane groups is lower with improved degradation efficiency. In such cases, the urea bonds of the oligourea hard segments in the Pll foam structure are also chemically and / or thermally degraded, leading to the formation of toxic, carcinogenic and therefore undesirable aromatic diamine by-products, e.g. toluene diamine (TDA), methylene dianiline (MDA). Since the efficiency and selectivity of the degradation of the urethane groups in the Pll foam structure are inversely proportional, we use the latent reagent urea, which thermally decomposes into two components, of which ammonia serves as the reagent for the degradation of the urethane group, while the isocyanic acid formed in-situ reacts with the amino groups of the aromatic (di)amines and thus acts as a scavenger of the amino groups. Under suitable reaction conditions, the amount of TDA formed can be reduced to below 0.1 % by weight as a result of an irreversible reaction of isocyanic acid with TDA and / or TDA derivatives, during which thermally stable and in the polyol insoluble benzoylene urea derivatives are formed. In this way, the content of aromatic diamines in the degradation products can be reduced below 0.1 % by weight.

[0036] As already described in detail in Japanese patent application JP 2012017279A18and European patent EP 2592069B119, TDA reacts with urea and biuret to form disubstituted benzoyleneurea (1 ,2,3,4-tetrahydroquinazoline-2,4-dione).

[0037] According to the present invention, the reaction between TDA and isocyanic acid can be carried out irreversibly to form thermally stable benzoyleneurea derivatives, which are insoluble in the recovered polyols. The benzoyleneurea derivatives are useful in well- established applications such as fire retardants, raw materials for the pharmaceutical industry, semiconductor industry, etc.18

[0038] Formation of a polyol by-product

[0039] Isocyanic acid can also react to a certain extent with the hydroxyl end-groups of the polyol, which is an undesirable side reaction and leads to the formation of a carbamoyl end- functionalized polyol.

[0040] ROH + HNCO ROCONH2 (R is the polyol residue)

[0041] The formation of the said by-product can be minimized by a suitable selection of experimental conditions, particularly the ratio between the reagent and PU, the reaction temperature and the time. Reaction conditions of the disclosed method for the degradation of PU foams

[0042] According to the present invention, the process is suitable for the degradation of flexible or rigid Pll foams from various diisocyanates or various homo- or copolyether polyols. It is also suitable for degradation of other types of polyurethanes or other polymers that contain chemically labile bonds such as ester, amide, urea or carbonate bonds, in the backbone. The PU-based waste can be pre-sorted depending on the planned application of the final recycled product. If the recovery of high-quality recycled polyether polyols with defined molecular weights is preferred, the Pll waste should be subjected to a pre-sorting treatment process. It is advantageous to use uniformly composed PU-based feedstock, i.e. PU made from the same di- or polyols. The PU-based feedstock can be shredded or cryogenically ground, or, if necessary, subjected to another particle size reduction technique.

[0043] The aim of the invention is to present a process that allows complete degradation of the urethane groups in the PU foam structure with minimal formation of undesirable aromatic diamines in the process and minimal carbamoyl functionalization of the hydroxyl groups of the recovered polyol (side reaction between polyol hydroxyl groups and HNCO, which is formed during the urea thermal decomposition). At moderate temperatures (up to 200°C as is the case in GB 2062660A), the oligourea hard segments are largely converted into aromatic mono- and di-ureido derivatives by reaction of aromatic amine and isocyanic acid. Since the formation of ureido-aromatic derivatives is a reversible reaction, this reaction mechanism inevitably leads to a certain amount of aromatic diamine formed in the process. At temperatures above 200 °C, ureido-aromatic derivatives further react with isocyanic acid into the thermally stable benzoyleneurea derivatives. The extent of this reaction increasingly predominates with increasing temperature. Since this reaction mechanism is irreversible, it results in a lower formation of free aromatic amines compared to the process performed at lower temperatures below 200 °C, where the reversible reaction mechanism to ureido-aromatic derivatives is more pronounced.

[0044] The degradation of PU can be carried out in a medium or preferably in bulk without an additional medium. If a medium is used, it is generally chosen to match the diol / polyol type used in the synthesis of the PU / PU foam so that the final quality of the recycled polyol is not compromised. Preferably, the medium consists of the di- or polyol(s) the PU-based feedstock is made of. Both virgin and recycled di- or polyol can be used as a medium. The process can be carried out in one or two steps as indicated below. The foam scraps and the urea reagent can be added to the reactor all at once, in portions or continuously. The urea reagent is added in an amount of 1 - 30 % or 1 less than 30 % by weight based on the PU scrap (the PU-based feedstock), preferably 1 - 28 %, 2 - 25 % or 3 - 20 % by weight based on the PU-based feedstock.

[0045] As the amount of urea increases, so does the proportion of carbamoyl end- functionalized polyol. Since the reactivity of the carbamoyl end groups for the reaction with the isocyanate groups of the diisocyanate during Pll formation is much lower than that of the polyol hydroxyl end groups, the goal is to minimize this side reaction. Therefore, according to the invention, the use of urea amounts greater than 30% by weight is avoided. Carbamoyl- functionalized polyol is thermally less stable at temperatures above 200°C and decomposes into hydroxyl-functionalized polyol and isocyanic acid, which subsequently among others trimerizes into thermally stable cyanuric acid. This is the reason why hydroxyl end- functionalized polyol is predominantly formed at temperatures above 200 °C. In addition, the use of excessive amounts of urea reagent inhibits the formation of benzoylene urea derivatives - the mechanism that is a driving force for the reduced formation of aromatic diamines and for achieving very high degrees of degradation of the urethane groups in the foam structure. In GB 2062660A, the authors claim the use of 30-150 parts by weight of urea per 100 parts by weight of polyurethane. With such an amount of urea together with reaction temperatures below 200 °C, the reversible reaction mechanism leading to the ureido-aromatic derivatives proceeds. A final product besides ureido-aromatic derivatives contains larger amounts of aromatic amines, while the hydroxyl groups of the polyol are functionalized to a large extent by carbamoyl groups that are poorly reactive with isocyanate groups of diisocyanate in Pll foam synthesis. In contrast, the present invention describes the reaction conditions under which the polyurethane irreversible reacts with urea into thermally stable benzoylene urea derivatives, which is a driving force for the high degree of degradation of the urethane groups, the low formation of aromatic diamine and the low extent of carbamoyl end-group functionalization of the polyol.

[0046] According to the present invention, Pll degradation is carried out at elevated temperatures, generally up to about 260 °C and preferably from 200 °C to 250°C. Temperatures above 200°C are preferred, i.e., more than 200 to 260°C, such as 205 - 260°C, or 210 - 250°C. The reaction mixtures may be heated by microwave irradiation or by conventional means. The process is generally carried out at autogenous pressures from 2 to 100 bar, preferably from 2 to 20 bar. Extra pressures, in addition to the autogenous pressures resulting from the decomposition of the urea, can be provided if necessary by introducing additional ammonia gas or other ammonia precursors (e.g. ammonium carbonate, ammonium bicarbonate) into the system. The reaction time depends largely on other reaction parameters, e.g. the treatment temperature, the pressure, the polyurethane composition and the urea concentration in the reaction mixture. In the case of microwave heating, the reaction time is typically between 5 minutes and 2 hours, but preferably between 10 minutes and about 1 hour. If the reaction mixture is heated by conventional means, the reaction time should be extended to up to 24 hours or longer. In general, excessively long reaction times are avoided, so that the reaction times are preferably between 1 and 6 hours.

[0047] The type of the final reaction product depends on the reaction conditions used. Under milder reaction conditions (temperature and time), the final product is generally a homogeneous mixture with a low aromatic diamine content (up to 1.5 wt.%) and largely preserved hard segments when heated conventionally. At harsher reaction conditions (up to 250 °C) in combination with microwave heating, a phase separation of the reaction mixtures (solid-liquid two-phase system) occurs as a result of the immiscibility between the polyol and the resulting derivatives of oligourea hard segments. The degree of degradation of the urethane groups in the PU foam structure is typically above 90% and the resulting polyols contain about 90% or more hydroxyl end-groups and about 10% or less aromatic-amino end- groups. The content of aromatic diamine in the polyols obtained is typically less than 1.5% by weight. With longer reaction times (> 40 min) and even harsher reaction conditions (temperature above 240 °C), complete degradation of the urethane bonds is achieved, resulting in recycled polyols that are predominantly functionalized with hydroxyl end-groups and contain less than 0.1 wt.% TDA, since under these conditions benzoylene urea derivatives are predominantly formed in an irreversible reaction.

[0048] Isolation and purification of recovered polyether polyols

[0049] If the purpose of PU foam recycling is to recover polyether polyol as raw material, it can be isolated from the two-phase reaction mixture by extraction with solvents with low boiling point, low heat of vaporization and high specific evaporation rate, e.g. C4 - C12 alkanes and / or cycloalkanes or mixtures thereof with cyclohexane as preferred solvent. After polyol extraction, the removal of insoluble by-products can be facilitated by centrifugation or filtration. Finally, the solvent is removed from the polyol by evaporation and can thus be used in a closed-loop system. This purification method removes most of the remaining urea reagent and almost all by-products originating from the hard segments of the PU foam, with the exception of the remaining aromatic diamine. In cases where the amount of aromatic diamine formed during PU foam degradation is low, this isolation / purification process results in a high-quality recycled polyether polyol without the need for subsequent removal of the residual aromatic diamine.

[0050] Alternatively, and if necessary, side products containing amino group(s) in the structure can be removed from the isolated di- or polyol(s) by adsorption on a solid support (such as silica gel or activated charcoal) or by washing the di- or polyol(s) with an acidic aqueous solution, preferably aqueous HCI. Before purification, the recycled di- or polyol(s) can be dissolved in appropriate solvent, such as ethyl acetate for extraction and cyclohexane for adsorption of side products on solid support. The extraction of aromatic diamine in acidified water can be performed without additional solvent by heating the recovered polyol to 60 °C to minimize losses during extraction. Alternatively, the polyol can be previously dissolved in solvents such as ethyl acetate.

[0051] The invention will be further described by reference to the following figures and examples which are not intended to be understood as limiting the scope of the invention.

[0052] Figures

[0053] Fig. 11H NMR spectra of the recovered polyol from Example 1 (red) and the corresponding virgin polyol (black) recorded in DMSO-cfe. The residual DMSO solvent signal is marked with an asterisk.

[0054] Fig. 2 SEC / RI-UV chromatograms of the recovered polyol from Example 1 [B] and the corresponding virgin polyol [A], The black solid curves and the red dotted curves represent the responses of the Rl and UV detectors, respectively. The solvent peak in the chromatograms recorded with the Rl detector is marked with an asterisk. The UV chromatogram of the recycled polyol (red curve) shows a low intensity UV response under the polyol peak due to traces of aromatic amino end-groups in the polyol as a result of incomplete degradation of the urethane groups in the PU foam structure, and the low intensity peaks between the elution time of 25 - 23 mL as a result of the presence of a trace amount of side products (TDA derivatives) in the recycled polyol.

[0055] Fig. 3 FTIR spectra of the recovered polyol from Example 1 (red) and the corresponding virgin polyol (black).

[0056] Fig. 4 Scheme illustrating the reaction mechanism of degradation of PU foam with urea reagent.

[0057] Fig. 5 Photograph of flexible polyurethane foams synthesized by formulation described in Fehler! Verweisquelle konnte nicht gefunden werden. using 100% recycled polyol obtained by the process of the present invention (right) and the 100% corresponding virgin polyol (left). Examples

[0058] The examples described below relate to degradation of flexible Pll foams synthesized from TDI diisocyanate and either polypropylene oxide-based homopolyether polyol with a molecular weight of 3 kDa or polypropylene oxide-co-ethylene oxide) copolyether polyol with a molecular weight of 3.5 kDa. In the cases where the polyol medium was used to facilitate mixing of the reaction mixture with magnetic stirrer, its chemical composition was the same as that of the polyol used to synthesize the flexible Pll foam, which was degraded. The degradation products were comprehensively characterized by a combination of different characterization techniques; i.e., NMR, SEC / UV-MALS-RI, MALDI-TOF MS, FTIR, determination of hydroxyl number, and water content.

[0059] Example 1

[0060] 6 g of copolyether-based flexible Pll foam and 1 .031 g of urea (corresponding to 5 molar equivalents of urea per urethane group in the Pll foam structure) are mixed and preheated to 175 °C over a period of 3 minutes to ensure partial liquefaction of the Pll foam. The main reaction cycle is carried out at 250 °C for 60 minutes under microwave irradiation. A two-phase (solid, liquid) system is formed, with the liquid phase being a light-yellow oil. Analysis of the crude polyol phase shows complete degradation of the urethane groups and a TDA content of 0.07 wt.% per polyol. The polyol is separated from the reaction mixture by extraction in cyclohexane. The yield of the recovered polyol is 92%, based on the theoretical content of the polyol soft segments in the Pll foam (66.9% by weight). The recovered polyol consists of 98 mol% hydroxyl end-groups and 2 mol% carbamoyl end-groups, while the aromatic amino end- group content is below the detection limit of1H NMR spectroscopy. The recovered polyol contains 0.21 wt.% TDA and has a hydroxyl number of 58 mg KOH / g.

[0061] Example 2

[0062] 6 g of homopolyether-based Pll foam is mixed with 3 g of homopolyether polyol as reaction medium to facilitate stirring of the reaction mixture and 0.477 g of urea (2 molar equivalents per urethane group in the Pll foam structure). The reaction mixture is preheated to 175 °C over a period of 3 minutes to ensure partial liquefaction of the Pll foam. The main reaction cycle is performed at 230 °C for 40 minutes reaction time under microwave irradiation. A two- phase (solid, liquid) system is formed. The liquid phase is composed of a yellow oil. Analysis of the liquid polyol phase reveals 94 % degradation of the urethane groups. The crude polyol consists of 89 mol% hydroxyl end-groups, 6 mol% aromatic amino end-groups, and 4.7 mol% carbamoyl end-groups, and it contains 1.45 wt.% TDA.

[0063] Example 3

[0064] 6 g of homopolyether Pll foam is mixed with 3 g of homopolyether polyol as reaction medium and 1.428 g of urea, which corresponds to 6 molar equivalents of urea per urethane group in the Pll foam structure. The reaction mixture is preheated to 175 °C over a period of 3 minutes to ensure partial liquefaction of the Pll foam. In the main reaction cycle, the mixture is heated to 250 °C for 120 minutes under microwave irradiation. The result is a two-phase (solid, liquid) system comprising of a light-yellow liquid phase. The analysis of the liquid phase shows complete degradation of urethane groups. The crude polyol consists of 98 mol% hydroxyl end- groups, 2 mol% carbamoyl end-groups, while the aromatic amino end-group content is below the detection limit of1H NMR spectroscopy. The crude polyol contains 0.08 wt.% TDA.

[0065] Example 4

[0066] 6 g of copolyether Pll foam is mixed with 3 g of copolyether polyol medium and 1 .236 g of urea (6 molar equivalents of urea per urethane group in the Pll foam structure). The mixture is transferred to an autoclave and heated conventionally at 190 °C for 240 minutes in a laboratory oven. The obtained reaction mixture is a brown paste. Analysis of the reaction mixture reveals 91 - 92 % degree of degradation of the urethane groups in the Pll foam structure and it contains 0.54 wt.% TDA. The polyol is separated from the reaction mixture by extraction with cyclohexane. The obtained polyol is a light-yellow oil with 86 mol% hydroxyl, 8 mol% carbamoyl and 6 mol% aromatic amino end-groups, and it contains 0.39 wt.% TDA.

[0067] Example 5

[0068] 6 g of copolyether Pll foam scraps are mixed with 3 g of copolyether polyol medium and 1 .236 g of urea (6 molar equivalents of urea per urethane group in the Pll foam structure). The mixture is heated to 175 °C over a period of 3 minutes to ensure partial liquefaction of the Pll foam. The main reaction cycle is carried out at 190 °C for 60 minutes under microwave irradiation. A heterogeneous, semi-liquid reaction product is obtained. Analysis of the reaction mixture obtained shows a degree of degradation of the urethane groups of 82 - 83 % and a TDA content of 0.82 % by weight. The polyol is extracted from the reaction mixture with cyclohexane. The polyol obtained is a yellow-colored viscous liquid containing 80 mol% hydroxyl, 15 mol% aromatic amino and 5 mol% carbamoyl end-groups, and 0.65 wt.% TDA.

[0069] A comparison of the two reaction products from Example 4 and Example 5 shows that that the oligourea hard segments of the Pll foam of the same type are much better preserved when the reaction mixtures are heated conventionally, although the degree of degradation of the urethane groups is higher than in the product obtained by heating the reaction mixture with microwave irradiation. These results show that conventional heating of the reaction mixtures enables a higher selectivity of degradation of the urethane groups in the Pll foam structure than microwave irradiation, which also degrades the urea groups in the Pll foam hard segments to a high degree.

[0070] Example 6

[0071] Flexible Pll foams synthesized exclusively from recycled polyol obtained by the process of the present invention are compared with the corresponding virgin polyol without changing the formulation and synthetic procedure. The structural characteristics of the recycled polyol are given in Table 1 and Fig. 1 to 3.

[0072] Table 1. Comparison of the properties of recycled polyol obtained by the process of the present invention and the corresponding virgin polyol.

[0073] The flexible Pll foams were synthesized according to the formulation shown in Table 2.

[0074] Table 2. Formulations used for flexible polyurethane foam synthesis form 100% recycled polyol obtained by the process of the present invention and from the corresponding virgin polyol. Values are given as parts by weight.

[0075] The results of the evaluation of the properties of the synthesized flexible foams (Fig. 5, Table 3) show comparable density and mechanical properties, regardless of the type of polyol used for the synthesis (virgin or recycled polyol). This is a successful example of the synthesis of flexible Pll foams exclusively from recycled polyol, which has not been previously reported.

[0076] Table 3. Comparison of mechanical properties of flexible polyurethane foams synthesized from 100% recycled polyol obtained by the process of the present invention and the corresponding virgin polyol.

[0077] References

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[0083] 6. Liman, U. D.; Meckel, W. D.; Muenzmay, T. D.; Nefzger, H. D.; Quiring, B. D.; Rashofer, W. D. Recovering isocyanate-reactive components from polyurethane(s) and polyurea(s) - by heating with water, amine(s) and opt. mono, di or poly:hydric alcohol(s), and distilling to recover prod, and amine etc. . DE4217524A1, 1993.

[0084] 7. Niederdellmann, G.; Grigat, E. Process for the continuous high temperature glycolytic cleavage of polyurethane plastics waste in screw machines. US4511680A, 1985.

[0085] 8. Yukuta, T.; Ishiwaka, T.; Usiu, K.; Akoh, M. Method of recovering and reproducing raw materials from polyurethanes. GB2062660A, 1981.

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[0090] 13. Li, H.; Hou, X.; Chai, L.; Cui, X.; Wang, Y.; Deng, T., Efficient and green catalytic degradation of high crosslinked rigid PU foam and recovery value-added products via selective cleavage of C-0 and C-N bonds. Polymer Degradation and Stability 2020, 18 , 10.1016 / j.polymdegradstab.2020.109262 Schaber, P. M.; Colson, J.; Higgins, S.; Thielen, D.; Anspach, B.; Brauer, J., Thermal decomposition (pyrolysis) of urea in an open reaction vessel. Thermochimica Acta 2004, 424 (1-2), 131-142; 10.1016 / j.tca.2004.05.018 Grdadolnik, M.; Drincic, A.; Oreski, A.; Onder, O. C.; lltrosa, P.; Pahovnik, D.; Zagar, E., Insight into Chemical Recycling of Flexible Polyurethane Foams by Acidolysis. ACS Sustain Chem Eng 2022, 10 (3), 1323-1332; 10.1021 / acssuschemeng.1c07911 Vanbergen, T.; Verlent, I.; De Geeter, J.; Haelterman, B.; Claes, L.; De Vos, D., Recycling of Flexible Polyurethane Foam by Split-Phase Alcoholysis: Identification of Additives and Alcoholyzing Agents to Reach Higher Efficiencies. ChemSusChem 2020, 73 (15), 3835-3843; 10.1002 / cssc.202000949 Grdadolnik, M.; Zdovc, B.; Drincic, A.; Onder, O. C.; lltrosa, P.; Ramos, S. G.; Ramos, E. D.; Pahovnik, D.; Zagar, E., Chemical Recycling of Flexible Polyurethane Foams by Aminolysis to Recover High-Quality Polyols. ACS Sustain Chem Eng 2023, 11 (29), 10864-10873; 10.1021 / acssuschemeng.3c02311 Murayama, K.; Shimokawadoko, S.; Sugano, T.; Takamatsu, K.; Takeuchi, H.; Sasaki, S. Method of producing benzoyleneurea or its derivative, and compound thereof JP2012017279A, 2014. Murayama, K.; Shimokawatoko, Y.; Kanno, T.; Takamatsu, K.; Takeuchi, H.; Sasaki, M.; Kotaki, Y. Method of producing toluenedicarbamate and method of producing toluenediisocyanate EP2592069B1 , 2019.

Claims

Claims1. A process for decomposing polyurethane (Pll) which comprises a step of reacting PU- based feedstock with urea as the sole reagent at a temperature in a range of 200°C - 260°C, preferably 200°C - 250°C, more preferably 210°C - 250°C, to yield a product mixture comprising di- and / or polyol, wherein urea is used in an amount of 1 to 30 % by weight based on the PU-based feedstock, preferably less than 30 % by weight of urea.

2. The process according to claim 1 , wherein the PU-based feedstock comprises PU waste, such as flexible or rigid PU foam, or mixtures of PU and other polymers that contain chemically labile bonds such as ester, amide, urea or carbonate bonds, in the backbone.

3. The process according to claim 1 or 2, comprising preceding steps of size reduction of the PU-based feedstock and / or pre-sorting PU-based feedstock according to the di- or polyols and / or the diisocyanates it is made of.

4. The process according to any one of the preceding claims, wherein the reaction of the PU-based feedstock with urea is carried out (i) in the absence of any other reagent (water, alcohol, glycol, amine, etc.) and / or solvent or medium, or (ii) in the presence of a di- or polyol corresponding to the di-or polyol the PU-based feedstock is made of.

5. The process according to any one of the preceding claims, wherein the urea is used in an amount of 1 - 28 %, 2 - 25 %, or 3 - 20 % by weight based on the PU-based feedstock,6. The process according to any one of the preceding claims, wherein the reaction is carried out under heating by microwave irradiation, preferably for a term in a range of 5 min to 2 h, more preferably between 10 min and 1 h.

7. The process according to any one of claims 1-5, wherein the reaction is carried out under heating by conventional means, preferably for a term in a range of 1 to 24 h or longer, more preferably between 1 and 6 h.

8. The process according to any one of the preceding claims, wherein the reaction is carried out at pressures in a range of 2 to 100 bar, preferably from 2 to 20 bar.

9. The process according to any one of the preceding claims, further comprising steps of isolating di- or polyol(s) from the product mixture.

10. The process according to claim 9, wherein the di- or polyol(s) are extracted from the product mixture by solvent extraction using a solvent that has a low boiling point, low heat of vaporization and high specific evaporation rate, e.g. C4 - C12 alkanes and / or cycloalkanes or mixtures thereof, preferably cyclohexane.

11. The process of claim 10, further comprising solvent removal by evaporation and optionally recycling the solvent for further use in solvent extraction.

12. The process of any one of claims 9-11, further comprising removal of insoluble byproducts by centrifugation or filtration.

13. The process of any one of claims 9-12, further comprising removal of side products containing amino group(s) in the structure from the isolated di- or polyol(s) by absorption on a solid support, such as silica gel or activated charcoal, or washing the di- or polyol(s) with an acidic aqueous solution, preferably aqueous HCI.

14. The process of claim 13, wherein the recycled di- or polyol(s) is / are dissolved in a solvent before the removal of side products, in particular in ethyl acetate for extraction and in cyclohexane for adsorption of side products on solid support.

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