METHOD FOR THE DEMOCTION OF PLASTICS

Description

[0001] The present invention relates to a method for the catalytic degradation of at least one plastic, wherein the at least one plastic is polyurethane.

[0002] The resulting mixtures can be used as raw materials, e.g. for the production of plastics (plastic recycling).

[0003] Plastics are ubiquitous materials and are used extensively as packaging materials, fibers, insulation, components of paints and adhesives, foams, and construction materials, for example in vehicle manufacturing. Plastics are typically based largely on petrochemical raw materials. Especially in times of increasing resource scarcity, but also in light of the problem of rising environmental pollution, recycling processes are becoming increasingly important.

[0004] Recycling plastics encompasses the mechanical, thermal, or chemical degradation of plastics. In mechanical degradation, the starting material is finely ground and then shaped into a new form using common processing techniques such as extrusion and injection molding. This is the most common method of plastic recycling, but it has the disadvantage that only clean, single-type plastics can be processed. Furthermore, the recycling possibilities are tied to the starting material and are therefore limited.

[0005] In thermal degradation, for example through pyrolysis, plastics are broken down at high temperatures of approximately 400–900 °C in the absence of oxygen. By recovering the low-molecular-weight degradation products of the plastic, thermal recycling is more versatile than purely mechanical processes. However, the disadvantages associated with these high degradation temperatures include the immense energy expenditure and the increased occurrence of side reactions, which reduces product purity. Furthermore, the production of temperature-sensitive monomers is not possible using thermal processes.

[0006] In chemical degradation, plastics are broken down into their monomers through chemical reactions. These monomers can then be reused as starting materials in a variety of chemical processes. However, the economic significance of chemical recycling is often limited by the complexity of the process and the associated costs.

[0007] Asani et al. (Polym. Degrad. Stab. 2004, 86, 147) describe the chemical degradation of polyurethanes (PUs) in methanol. For an acceptable degradation rate of more than 90%, the reaction must be carried out at a temperature of at least 200 °C and a pressure of 2–15 MPa.

[0008] Liu et al. (Polym. Degrad. Stab. 2013, 98, 2520) describe the mechanism of the chemical degradation of PU in methanol. For reaction conditions of 220-260°C and 3-13 MPa, a conversion rate of more than 90% is revealed.

[0009] Disadvantages of the PU methanolysis processes listed above include the high reaction temperatures and pressures required to generate acceptable conversion rates. Increasing temperatures promote unwanted side reactions, which significantly impair the purity and yield of the decomposition products and necessitate additional purification steps. Economic efficiency may also be reduced by the use of expensive catalysts. Furthermore, the use of catalysts typically requires a complex separation step.

[0010] Liu et al. (J. Polym. Res. 2015, 22, 135) disclose the catalytic methanolysis of pure polylactic acid (PLA). Maximum conversion of PLA is described at reaction temperatures of at least 130 °C, with the addition of 0.01 mol of iron(III) chloride catalyst per mol of PLA for 4 hours. Complete depolymerization is not achieved.

[0011] DE 25 41 100 A1 discloses a process for the decomposition of polyurethanes in the presence of an alcoholate catalyst at temperatures from 50 °C to 180 °C.

[0012] Despite the high relevance of processes for the degradation of plastics, there is currently a lack of processes that enable the regeneration of various monomers from sometimes contaminated and / or post-consumer plastics, such as discarded mattresses, packaging or bulky waste, under economic conditions.

[0013] The aim of the present invention is therefore to provide a process that enables the degradation of various types of plastics using simple means. Of particular interest is a reduction in production costs, for example through short reaction times, relatively low reaction temperatures and pressures, and cost-effective starting materials (e.g., inexpensive catalysts). Furthermore, the process according to the invention aims at complete depolymerization, thereby enabling improved further processing of the recovered degradation products and increasing the associated added value.

[0014] A first aspect of the present invention relates to a method for the degradation of plastics comprising the steps of: (i) Providing at least one plastic in at least one solvent in a reactor; (ii) Adding at least one catalyst selected from alkoxide; (iii) Treating the mixture obtained in step (ii) at an elevated temperature of 30-250°C and / or an elevated pressure of >1-100 bar; and (iv) optionally separating the mixture obtained in step (iii), wherein the at least one plastic is polyurethane, and wherein the solvent is methanol or ethanol, in particular methanol.

[0015] The method according to the invention relates to the degradation and thus, in a first step (i), the provision of at least one plastic, wherein the at least one plastic is polyurethane.

[0016] It is known to those skilled in the art that polyurethanes are produced by reacting polyisocyanates with polyols.

[0017] The term "polyol" refers to compounds with at least two, that is, two, three, four or more, preferably two or three hydroxyl groups. A polyol within the meaning of the invention is preferably a polyether polyol, in particular an aliphatic polyether polyol, e.g., polyethylene glycol or polypropylene glycol, or an aromatic polyether polyol; a polyester polyol, in particular an aliphatic or aromatic polyester polyol; diethylene glycol; a C1-6 alkylene glycol, in particular hexanediol, butanediol, ethylene glycol, and neopentyl glycol; a C1-8 alkylene polyol, in particular trimethylolpropane and glycerol; or a mixture thereof. Preferred polyols have a weight-average molecular weight of 50–10,000 g / mol, more preferably of 300–6,000 g / mol. Preferred polyols have an OH number of 10–900, more preferably of 20–500.

[0018] A polyisocyanate according to the invention can, for example, comprise an aromatic or aliphatic polyisocyanate, in particular toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polymeric MDI, isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HMDI), naphthylene-1,5-diisocyanate (NDI), or a mixture thereof. Preferred polyisocyanates have a weight-average molecular weight of 100–800 g / mol, more preferably 150–600 g / mol. In a preferred embodiment, the polyisocyanate has an NCO content of 5–70%, more preferably 15–55%.

[0019] The plastic provided in process step (i) can be provided as granules, powder or cut material.

[0020] In step (i) the at least one plastic is provided in at least one solvent, wherein the solvent is methanol or ethanol, preferably methanol.

[0021] The weight ratio of plastic to solvent in step (i) may be 1:1 to 1:40, preferably 1:5 to 1:20 and more preferably 1:5 to 1:10.

[0022] The at least one plastic in at least one solvent is provided in a reactor. Preferably, the reactor includes an agitator. The agitator can, for example, convey axially or radially and stir in one or more stages. Furthermore, the reactor can optionally be sealed gas-tight.

[0023] In process step (ii), at least one catalyst selected from an alcoholate is added to the mixture from step (i). The catalyst is preferably a methoxide, more preferably an alkali methoxide, such as potassium methoxide or sodium methoxide. Alcoholates are readily available and preferred for the process according to the invention because they are inexpensive and can be easily separated from the reaction mixture, e.g., after hydrolysis.

[0024] In one embodiment, the weight ratio of plastic to catalyst is preferably between 40:1 and 5:1, more preferably between 25:1 and 5:1. In a preferred embodiment, the weight ratio of plastic to catalyst is optionally between 40:1 and 10:1, and particularly between 30:1 and 20:1.

[0025] At the end of the process according to the invention, the catalyst can be recovered by suitable means known to those skilled in the art, such as filtration, and reused in the process. If catalyst regeneration is not desired, the catalyst can be converted at the end of the plastic degradation by suitable means, such as hydrolysis, into readily separable compounds, e.g., carbonates and / or sulfates. The latter can be easily separated, for example, by filtration. Alternatively, the product obtained at the end of the process, comprising the catalyst and the at least one solvent, can optionally be added as a catalyst in step (ii) of a new plastic degradation cycle.

[0026] Surprisingly, it was demonstrated that the use of methoxides significantly improves the reaction conditions compared to prior art processes. Thus, the process according to the invention can be carried out at lower reaction temperatures, lower reaction pressures, and / or shorter reaction times compared to established processes. Furthermore, it has been shown that high yields and excellent product qualities can be achieved with the process according to the invention. The high conversion rates are particularly attributable to the polyurethane-to-catalyst ratio according to the invention.Furthermore, alcoholate catalysts, and in particular methoxide catalysts, have the advantage that they do not interfere with a later application of the plastic degradation products and can, if necessary, be converted into easily separable compounds, such as carbonates and / or sulfates, by a suitable reaction, such as hydrolysis.

[0027] In one embodiment, the mixture obtained in (ii) is treated at elevated temperature in process step (iii). In another embodiment, the mixture obtained in (ii) is treated at elevated pressure in step (iii). In a preferred embodiment, the mixture obtained in (ii) is treated at both elevated temperature and elevated pressure.

[0028] An elevated temperature according to the invention is 30-250°C, more preferably 50-200°C, and even more preferably 80-180°C. An elevated pressure according to the invention is > 1 to 100 bar, preferably 1.5-30 bar, more preferably 1.5-25 bar, more preferably 1.5-20 bar, more preferably 2-20 bar, more preferably 5-20 bar, and most preferably 15-20 bar. Optionally, the reactor is gas-tightly sealed in step (iii). In one embodiment, an oxygen-reduced or oxygen-free atmosphere may be present in the reactor. Optionally, an inert gas atmosphere may be present in the reactor. Examples of suitable inert gases are nitrogen and noble gases, such as argon.

[0029] The treatment duration in step (iii) is preferably 5-800 minutes and preferably 10-600 minutes. In a preferred embodiment, the treatment duration is optionally 10-300 minutes and preferably 10-180 minutes.

[0030] According to the present invention, the mixture obtained after the end of step (iii) typically contains polyamines, polyols, carbamates, polycarboxylic acids and / or polycarboxylic acid esters.

[0031] In process step (iv), the mixture obtained in step (iii) is optionally separated. The separation may be carried out by distillation, filtration, in particular membrane filtration, precipitation, chromatography, or centrifugation. Optionally, the separation may comprise more than one separation step and / or more than one separation method, for example, separation by filtration and distillation, filtration and chromatography, precipitation, filtration and distillation, or precipitation, filtration, and chromatography.

[0032] Another aspect of the present invention is the provision of a mixture obtainable by a method according to steps (i), (ii) and (iii) described above.

[0033] Another aspect of the present invention is the use of the mixture obtained in step (iii) for the production of plastics. In a preferred embodiment, the mixture is used for the production of polyurethanes. The mixture can preferably be used without further intermediate steps, e.g., as a monomer for the production of plastics. In another embodiment, the mixture is used for the production of plastics after at least one separation step.

[0034] Another aspect of the present invention is the use of the mixture obtained according to the invention, after step (iii), for the production of lubricants. In one embodiment, the mixture for the production of lubricants optionally comprises carboxylic acid esters, dicarboxylic acid esters such as phthalic acid esters, and / or hydroxy-functionalized carboxylic acid esters.

[0035] Another aspect of the present invention is the use of the mixture obtained according to the invention in step (iii) for the production of solvents or basic chemicals. In one embodiment, the mixture for the production of solvents or basic chemicals optionally comprises an amine and / or a polyamine such as diaminotoluene. In another embodiment, the mixture for the production of solvents or basic chemicals optionally comprises a dicarboxylic acid or a dicarboxylic acid ester such as adipic acid or adipic acid esters. In yet another embodiment, the mixture for the production of solvents or basic chemicals optionally comprises a polyol such as hexanediol or trimethylolpropane.

[0036] Furthermore, the present invention will be explained by the following examples. Example 1

[0037] 4270 g of polyurethane flexible foam (high-resilience (HR) foam from mattress manufacturing), based on polyether polyol and toluene diisocyanate, were prepared in 34300 g of methanol in a reactor with an agitator. After adding 1420 g of sodium methoxide solution (30% in methanol, NM30 from Evonik), the reactor was sealed and inerted with nitrogen. The mixture was then stirred in the reactor for 5 hours at 158 ​​°C and 15 bar.

[0038] The resulting clear solution was analyzed by GC (FID detector, ZB-WAXplus column from Phenomex) at an injector temperature of 250 °C, a heating rate of 60 °C / min, and a temperature profile of: 20 min at 200 °C, 5 min at 210 °C, 5 min at 220 °C. The detected degradation products were 31.5 mg / ml of 2,4-toluenediamine and 8.3 mg / ml of 2,6-toluenediamine.

[0039] GPC analysis (eluent THF, phenogel 5µm 100A column) detected an ether polyol (3500 g / mol). The plastic degradation was quantitative; no polyurethane derivative was detected in the mixture.

[0040] The mixture resulting from the plastic degradation was separated by distillation at normal pressure for the quantitative separation of methanol and by distillation in a vacuum for the separation of diamines. Example 2

[0041] 4270 g of polyurethane flexible foam (high-resilience (HR) foam from mattress manufacturing), based on polyether polyol and toluene diisocyanate, were prepared in 34300 g of methanol in a reactor with an agitator. After adding 1420 g of sodium methoxide solution (30% in methanol, NM30 from Evonik), the reactor was sealed and inerted with nitrogen. The mixture was then stirred in the reactor for 5 hours at 168 °C and 19 bar.

[0042] The resulting clear solution was analyzed by GC as described in Example 1. The detected degradation products were 28.1 mg / ml of 2,4-toluenediamine and 7.9 mg / ml of 2,6-toluenediamine.

[0043] GPC analysis (eluent THF, phenogel 5µm 100A column) detected an ether polyol (3500 g / mol). The plastic degradation was quantitative; no polyurethane derivative was detected in the mixture.

[0044] The mixture resulting from the plastic degradation was separated by distillation at normal pressure for the quantitative separation of methanol and by distillation in a vacuum for the separation of diamines. Example 3 (comparative example)

[0045] 4270 g of polyurethane flexible foam (high-resilience (HR) foam from mattress manufacturing), based on polyether polyol and toluene diisocyanate, were prepared in 34300 g of methanol in a reactor equipped with an agitator. After adding 1% tetrabutyl titanate relative to the amount of flexible foam to be degraded, the reactor was sealed and inerted with nitrogen. The mixture was then stirred in the reactor for 5 hours at 158 ​​°C and 15 bar.

[0046] The resulting turbid solution was analyzed by GC as described in Example 1. The degradation products detected were 16.5 mg / ml of 2,4-toluenediamine and 4.1 mg / ml of 2,6-toluenediamine. The plastic degradation was incomplete; undissolved polyurethane was detected in the mixture. Example 4

[0047] 4270 g of polyurethane flexible foam from mattress manufacturing, based on polyester polyol and toluene diisocyanate, were prepared in 34300 g of methanol in a reactor with an agitator. After adding 1420 g of sodium methoxide solution (30% in methanol, NM30 from Evonik), the reactor was sealed and inerted with nitrogen. The mixture was then stirred in the reactor for 5 hours at 158 ​​°C and 15 bar.

[0048] The resulting brownish solution was analyzed by GC-MS. The degradation products detected were methanol, 2,4-toluenediamine, 2,6-toluenediamine, methyl adipic acid ester, diethylene glycol, trimethylolpropane, and trace amounts of carbamates. The plastic degradation was quantitative; no polyurethane derivative could be detected in the mixture.

[0049] The mixture resulting from the plastic degradation was separated by distillation at normal pressure for the quantitative separation of methanol and by fractional distillation under vacuum for the separation of diethylene glycol, adipic acid methyl ester and toluenediamine.

Claims

1. Method for degradation of plastics comprising the steps: (i) provision of at least one plastic in at least one solvent in a reactor; (ii) addition of at least one catalyst, selected from alcoholate; (iii) treatment of the mixture obtained in step (ii) at elevated temperatures of 30-250 °C and / or at elevated pressures from > 1 to 100 bar; and (iv) optionally separation of the mixture obtained in step (iii), wherein the at least one plastic is polyurethane, and wherein the solvent is methanol or ethanol.

2. Method according to claim 1, wherein the plastic in step (i) is provided as granules, powder or chopped material.

3. Method according to any one of the preceding claims, wherein the solvent is methanol.

4. Method according to any one of the preceding claims, wherein the catalyst in step (ii) is selected from methanolate, more preferably alkali methanolate, e.g. potassium methanolate or sodium methanolate.

5. Method according to any one of the preceding claims, wherein step (iii) is carried out at temperatures of 50-200 °C, preferably 80-180 °C and preferably at pressures of >1-30 bar, more preferably >1-25 bar.

6. Method according to any one of the preceding claims, wherein the weight ratio of plastic to solvent in step (i) is 1:1 to 1:40, preferably 1:5 to 1:20, more preferably 1:5 to 1:10.

7. Method according to any one of the preceding claims, wherein the weight ratio of plastic to catalyst is between 40:1 to 5:1, preferably between 40:1 to 10:1, more preferably between 30:1 to 20:1.

8. Method according to any one of the preceding claims, wherein the separation in step (iv) is achieved through distillation, filtration, in particular membrane filtration, precipitation and / or chromatography.

9. Mixture obtainable using a method according to claim 1 (i), (ii) and (iii).

10. Use of the mixture according to claim 9 for the manufacture of plastics, in particular polyurethanes, lubricants, in particular ester-based lubricants, base chemicals or solvents.