Modified molecular sieve catalyst, method of preparation and use thereof in the degradation of polyurethanes

Abstract

This invention discloses a modified molecular sieve catalyst, its preparation method, and its application in the degradation of polyurethane, belonging to the interdisciplinary technical field of catalytic materials and solid waste resource utilization. Addressing the technical pain points of existing polyurethane degradation products—low added value, high separation cost of catalytic systems, and high reaction energy consumption—this invention modifies the molecular sieve catalyst by controlling the hydroxyl content on the molecular sieve surface through preheating treatment and grafting boron-containing halide reagents. This catalyst enables the direct preparation of isocyanate monomers from polyurethane through heterogeneous catalytic degradation under mild conditions. Simultaneously, the weak Lewis acidity of the molecular sieve and the synergistic catalytic effect of boron sites enhance the degradation efficiency, while the abundant pore structure of the molecular sieve simultaneously adsorbs degradation byproducts, protecting active sites and promoting the forward reaction. The catalyst preparation process of this invention is simple, easy to separate, and has low energy consumption, providing a solution for the direct preparation of isocyanates from polyurethane through heterogeneous catalytic degradation.

Description

Technical Field

[0001] This invention relates to the interdisciplinary field of catalytic materials and solid waste resource utilization, specifically to the technical field of multiphase catalytic degradation of polyurethane using modified molecular sieve catalysts to prepare isocyanate monomers. Background Technology

[0002] Polyurethane (PU) is a widely distributed polymer composed of isocyanates, polyols / diols, and short-chain diol chain extenders, and is widely used in everyday consumer products. Statistics show that over ten million tons of PU waste are generated globally each year, most of which is landfilled or incinerated, causing environmental and health problems. Furthermore, the high price of the core raw material isocyanate, the reliance on highly toxic phosgene in the synthesis process, and the carcinogenic risks posed by the monomers themselves all contribute to safety and environmental hazards. Therefore, recycling this waste into high-value products and achieving closed-loop reuse and green production of polyurethane raw materials has become a core direction for the industry's development.

[0003] Currently, PU recycling strategies mainly include mechanical recycling and chemical recycling. Mechanical recycling involves crushing waste materials and using them directly with the addition of adhesives. Although low-cost, the performance of the recycled products is limited, severely restricting their application scenarios. Compared to mechanical recycling, chemical recycling can degrade PU into monomers or other small molecules. The most commonly used methods include alcoholysis, hydrolysis, ammonolysis, acidolysis, and pyrolysis. The products of these methods are mainly polyols, amines, and small-molecule polyurethanes, but they have limitations in isocyanate recovery.

[0004] In related technologies, Chinese patent application CN120005276A discloses a method for recovering polyols from polyurethane waste. This method utilizes amine compounds, alcohol compounds, or alkanolamine compounds as degrading agents, effectively converting waste into polyols. However, isocyanates are irreversibly converted into amine compounds during the alcoholysis reaction, failing to achieve isocyanate regeneration. In another related technology, European patent application EP4372024A1 discloses a method for hydrolyzing polyisocyanurate. This method involves contacting polyisocyanurate with water and hydrolyzing it in the presence of an alkali or a combination of alkali catalysts to produce carboxylic acids, corresponding alcohols, and organic amines / polyamines. However, some amines can only be rechlorinated or phosgenated to obtain isocyanates, failing to achieve direct isocyanate regeneration. Summary of the Invention

[0005] To achieve efficient recovery of isocyanate monomers, heterogeneous catalysis has become a research hotspot due to the ease of catalyst separation and recovery. Among these, molecular sieves, with their regular pore structure, abundant hydroxyl sites, and excellent thermal stability, hold great potential in active component design. However, to date, there are no reports of modified molecular sieve catalysts serving as active sites in the field of polyurethane degradation. Therefore, developing a modified molecular sieve catalyst synthesized by controlling the acid strength and active sites of the molecular sieve to match the requirements of polyurethane degradation to isocyanate will provide the most direct and effective solution for the high-value utilization and closed-loop recycling of polyurethane.

[0006] An embodiment of the present invention describes the preparation of isocyanate monomers from polyurethane using a modified molecular sieve catalyst for heterogeneous catalytic degradation. This modified molecular sieve catalyst enables the degradation of polyurethane into isocyanates under mild conditions. In this modified molecular sieve catalyst, the hydroxyl content on the molecular sieve surface is controlled by preheating treatment, thereby allowing for sufficient grafting of boron-containing halide reagents. With boron atoms as the active center and connected to one or two halogen atoms, the boron atoms exhibit strong Lewis acidity and strong electronegativity, possessing excellent electrophilic catalytic activity. They can form stable coordination bonds with oxygen atoms in the urethane bonds of polyurethane, causing the polyurethane to directionally break down into isocyanate monomers.

[0007] In this type of modified molecular sieve catalyst, the molecular sieve itself possesses weak Lewis acidity. Through the adsorption of polyurethane reactants and synergistic catalysis with boron sites, the degradation efficiency of the modified molecular sieve catalyst can be further improved. Furthermore, the modified molecular sieve catalyst inherently possesses a rich pore structure, simultaneously adsorbing degradation byproducts HX (such as HF, HCl, HBr, or HI), thus protecting the active sites of the catalyst while promoting the forward degradation reaction. The catalyst in the embodiments of this invention features a simple preparation process, easy separation, and low energy consumption, providing a solution for the direct preparation of isocyanates from polyurethane through heterogeneous catalytic degradation.

[0008] According to one aspect of the present invention, a method for preparing a modified molecular sieve catalyst is provided, the method comprising:

[0009] The molecular sieve was calcined for 1-3 h under a first inert gas atmosphere and a first heating condition, and then calcined for 2-6 h under a second heating condition by introducing an air mixture containing water vapor. After cooling, the hydroxylated molecular sieve was obtained.

[0010] The hydroxylated molecular sieve was placed in an anhydrous solvent to form a slurry. A boron-containing halide reagent was added under a second inert gas atmosphere and reacted at 20-50 °C for 1-6 h. The solvent was then removed by rotary evaporation at 40-70 °C and dried under vacuum at 50-120 °C to obtain the modified molecular sieve catalyst.

[0011] In some embodiments, the first heating condition includes heating to 300-400 °C at a first heating rate, and the second heating condition includes heating to 450-600 °C at a second heating rate lower than the first heating rate, wherein the second heating rate is 0.5-5.0 °C / min, or

[0012] The first heating conditions are the same as the second heating conditions, and include heating to 450-600 °C at the second heating rate.

[0013] In some embodiments, the volume fraction φ(H2O) of the water vapor in the water vapor-containing air mixture is 5-10%.

[0014] In some embodiments, the surface hydroxyl content of the hydroxylated molecular sieve is 0.5-3.5 mmol / g.

[0015] In some embodiments, the molar ratio of the boron-containing halide reagent to the hydroxyl groups on the molecular sieve surface is 1.1-1.3:1.

[0016] In some embodiments, the first inert gas and the second inert gas are at least one of nitrogen, argon, and helium.

[0017] In some embodiments, the boron-containing halide is at least one selected from boron trifluoride dihydrate, boron trifluoride ethylamine complex, boron trifluoride dimethyl ether, boron trifluoride diethyl ether, boron trifluoride dibutyl ether, boron trichloride, dichloroborane, boron tribromide, dibromoborane, and iodoborane.

[0018] In some embodiments, the anhydrous solvent is at least one selected from methanol, n-pentane, hexane, dichloromethane, chloroform, and acetone.

[0019] In some embodiments, the molecular sieve is at least one of H-ZSM-5, H-Beta, H-MCM-41, H-MCM-22, H-SBA-15, HY, H-MOR, and H-USY.

[0020] According to another aspect of the present invention, a modified molecular sieve catalyst is provided, wherein the modified molecular sieve catalyst is Z-OBX. n Type Z-OBX catalyst, wherein Z is a molecular sieve, O is an oxygen atom, B is a boron atom, X is a halogen atom, and n is 1 or 2. n The modified molecular sieve catalyst has -ZOB- bonds. The modified molecular sieve catalyst was prepared according to the preparation method of the modified molecular sieve catalyst described in the foregoing examples.

[0021] In some embodiments, the halogen atom includes at least one of fluorine, chlorine, bromine, and iodine.

[0022] According to another aspect of the present invention, there is provided the use of a modified molecular sieve catalyst in the degradation of polyurethane. In the presence of a solvent, the modified molecular sieve catalyst is used to degrade polyurethane via a heterogeneous catalytic reaction to prepare isocyanate. The modified molecular sieve catalyst is prepared according to the modified molecular sieve catalyst described in the foregoing embodiments, or according to the preparation method of the modified molecular sieve catalyst described in the foregoing embodiments.

[0023] In some embodiments, the degradation of polyurethane by catalytic reaction comprises: mixing polyurethane and the solvent to form a mixture; adding the modified molecular sieve catalyst to the mixture under an inert gas atmosphere at a temperature of 50-90 °C, a stirring rate of 200-1000 rpm, and a reaction pressure of 0.1-1.0 MPa; and after reacting for 0.3-2.0 h, filtering the reaction mixture and removing the reaction solvent by rotary evaporation at 40-90 °C to prepare isocyanate.

[0024] In some embodiments, the solvent is at least one selected from tetrahydrofuran, methyltetrahydrofuran, tetrahydropyran, 2-methyltetrahydropyran, butyl acetate, ethyl acetate, 1,4-dioxane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and dimethyl carbonate.

[0025] In some embodiments, polyurethane is a polymer containing urethane bonds, including at least one of flexible polyurethane elastomers, rigid polyurethane foams, flexible polyurethane foams, polyurethane coatings, polyurethane adhesives, polyurethane leather resins, and polyurethane elastic fibers.

[0026] According to another aspect of the present invention, a method for catalytic degradation of polyurethane is provided, the method comprising: mixing polyurethane and a solvent to form a mixture; adding a modified molecular sieve catalyst to the mixture under an inert gas atmosphere at a temperature of 50-90 °C, a stirring rate of 200-1000 rpm, and a reaction pressure of 0.1-1.0 MPa; and after reacting for 0.3-2.0 h, filtering the reaction mixture and removing the reaction solvent by rotary evaporation at 40-90 °C to prepare isocyanate, wherein the modified molecular sieve catalyst is the modified molecular sieve catalyst according to the foregoing embodiments, or prepared according to the preparation method of the modified molecular sieve catalyst according to the foregoing embodiments.

[0027] The modified molecular sieve catalyst, preparation method, and use in the degradation of polyurethane according to the present invention have at least one of the following advantages:

[0028] (1) The modified molecular sieve catalyst, preparation method and its use in the degradation of polyurethane of the present invention utilizes molecular sieve as a carrier to graft boron-containing halide reagents, utilizes the hydroxyl structure on the surface of molecular sieve to chemically bond boron-containing halide reagents, introduces strong Lewis acid centers, and matches the acid strength requirements of urethane bond breaking during the degradation of polyurethane.

[0029] (2) The modified molecular sieve catalyst, preparation method and its use in the degradation of polyurethane of the present invention utilize the molecular sieve pore structure to exert adsorption effect, and simultaneously adsorb polyurethane degradation byproducts. While avoiding the poisoning of boron active centers by byproducts, it effectively promotes the forward process of polyurethane degradation reaction and improves degradation efficiency.

[0030] (3) The modified molecular sieve catalyst, preparation method and its use in the degradation of polyurethane of the present invention utilize the controllable hydroxyl structure on the surface of molecular sieves to optimize the hydroxyl content on the surface of molecular sieves through preheating treatment, providing sufficient and uniformly active reaction sites for grafting boron-containing halide reagents.

[0031] (4) The modified molecular sieve catalyst, preparation method and its use in the degradation of polyurethane of the present invention utilize a two-stage heating process for preheating treatment, and stepwise control the dehydration process and hydroxylation reaction of the molecular sieve to achieve uniform distribution of active hydroxyl groups on the surface of the molecular sieve and complete preservation of the pore structure, thereby ensuring the efficient and directional degradation of polyurethane.

[0032] (5) The modified molecular sieve catalyst, preparation method and its use in the degradation of polyurethane of the present invention utilizes a boron-containing halogenated reagent as a grafting reagent. Due to the strong electronegativity of the halogen atom, the boron atom becomes a strongly electron-deficient center. Its empty p orbital forms a stable coordination with the carbonyl oxygen of the urethane bond, thereby realizing the directional breaking of the urethane bond.

[0033] (6) The modified molecular sieve catalyst, preparation method and its use in the degradation of polyurethane of the present invention utilize the weak Lewis acidity of molecular sieve to adsorb polyurethane reactants, enrich polyurethane in the catalytic active region on the surface of molecular sieve, and synergistically catalyze with boron centers to improve the utilization rate of boron active centers, shorten the mass transfer path of reactants and improve the degradation efficiency.

[0034] (7) The modified molecular sieve catalyst, preparation method and its use in the degradation of polyurethane of the present invention utilizes molecular sieve grafted with boron-containing halide reagent to form a solid catalyst. In the presence of solvent, it reacts with polyurethane to form a multiphase reaction system, which has the characteristics of easy separation, low energy consumption and high product yield in the degradation process. Attached Figure Description

[0035] Figure 1 This is a TEM (transmission electron microscope) image of the hydroxylated molecular sieve prepared in Example 1.

[0036] Figure 2 This is a TEM image of the modified molecular sieve catalyst prepared in Example 1.

[0037] Figure 3 The images show ATR-FTIR (attenuated total reflectance-Fourier transform infrared) spectra of pure MDI (4,4'-diphenylmethane diisocyanate), the reaction products of Examples 1 and 5.

[0038] Figure 4 The polyurethane degradation conversion rate and isocyanate yield are those of Examples 1 and 5. Detailed Implementation

[0039] The technical solution of the present invention will be further described in detail below with reference to the embodiments. The following embodiments are only used to explain the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0040] In this embodiment, a modified molecular sieve catalyst, namely Z-OBX, is provided. n Type Z-OBX catalyst, where Z is a molecular sieve, O is an oxygen atom, B is a boron atom, X is a halogen atom, and n is 1 or 2. n The catalyst has -ZOB- bonds.

[0041] Modified molecular sieve catalysts can be used for the heterogeneous catalytic degradation of polyurethane. In these modified molecular sieve catalysts, boron atoms act as electron-deficient active centers, exhibiting strong Lewis acidity. When using these catalysts to degrade polyurethane, boron atoms attack the oxygen atoms of the urethane bonds, forming stable coordination bonds with the oxygen atoms. Electron clouds are transferred from the CN and CO bonds, reducing the bond energies of the CO and CN bonds and promoting the directional breaking of the urethane bonds to form isocyanate monomers.

[0042] The modified molecular sieve catalyst of this invention not only exhibits high catalytic efficiency but also possesses synergistic advantages. On one hand, the weak Lewis acidity of the molecular sieve itself can adsorb reactants, forming a synergistic effect with boron sites and improving catalytic degradation efficiency. On the other hand, the modified molecular sieve catalyst retains a rich pore structure, which can simultaneously adsorb degradation byproducts HX (HF, HCl, HBr, or HI, etc.), protecting the active sites of the catalyst and further promoting the forward degradation reaction. The modified molecular sieve catalyst of this invention provides a highly efficient technical solution for the direct preparation of isocyanates from polyurethane through multiphase catalytic degradation.

[0043] In the embodiments, the halogen atom includes at least one of fluorine, chlorine, bromine, and iodine.

[0044] In this embodiment, a method for preparing a modified molecular sieve catalyst is also provided. This preparation method can be used to prepare the molecular sieve catalyst described in the above embodiments. The preparation method includes:

[0045] The molecular sieve is calcined for 1-3 h (e.g., 1.5-2.5 h) under a first inert gas atmosphere and a first heating condition, and then calcined for 2-6 h (e.g., 3-5 h) under a second heating condition by introducing an air mixture containing water vapor. After cooling, the hydroxylated molecular sieve is obtained.

[0046] The hydroxylated molecular sieve is placed in an anhydrous solvent to form a slurry, and a boron-containing halide reagent is added under a second inert gas atmosphere, and then heated at 20-50 °C (e.g., 30-40 °C). React at ℃) for 1-6 h (e.g., 2-4 h), then at 40-70 ℃ (e.g., 50-60 ℃) for 1-6 h (e.g., 2-4 h), and then at 40-70 ℃ (e.g., 50-60 ℃). The solvent is removed by rotary evaporation at 50-120 °C (e.g., 60-100 °C) and then dried under vacuum to obtain the modified molecular sieve catalyst.

[0047] In embodiments of the present invention, a hydroxylated molecular sieve is obtained by preheating the molecular sieve, and a modified molecular sieve catalyst is prepared by grafting boron-containing halide reagents onto the hydroxyl groups (-Si / Al-OH) on the molecular sieve surface. During the modification process, the content of hydroxyl groups (-Si / Al-OH) on the molecular sieve surface is controlled by preheating. These hydroxyl groups, grafted with boron-containing halide reagents, provide active centers for the degradation of polyurethane, exhibiting strong Lewis acidity. When the modified molecular sieve catalyst is used to degrade polyurethane, boron atoms attack the oxygen atoms of the urethane bonds in the polyurethane, causing the boron atoms to form stable coordination bonds with the oxygen atoms. The electron cloud is transferred from the CN and CO bonds, reducing the bond energies of the CO and CN bonds, and promoting the directional breaking of the urethane bonds to form isocyanate monomers.

[0048] Furthermore, the modified molecular sieve catalyst of the present invention has a simple preparation process and, as a solid catalyst, is easy to separate in the reaction system, thereby reducing the energy consumption of the entire degradation process.

[0049] In an embodiment of the present invention, the molecular sieve is first preheated to obtain a hydroxylated molecular sieve. The preheating process can be a two-stage heating process. The first stage of low-temperature preheating removes physically adsorbed water and retains the hydroxyl groups on the surface of the molecular sieve under the protection of an inert gas atmosphere. The second stage of higher-temperature preheating utilizes water vapor to react with the silicon-oxygen-aluminum bonds in the molecular sieve framework to generate highly active surface isolated hydroxyl bonds, which facilitate the grafting of boron-containing halide reagents.

[0050] Specifically, the first heating conditions include heating to 300-400 °C (e.g., 320-360 °C) at a first heating rate. (℃). For example, the first heating rate is 5.0-10.0 ℃ / min, preferably 5.0-8.0 ℃ / min. ℃ / min.

[0051] The second heating condition includes heating to 450-600 °C (e.g., 500-550 °C) at a second heating rate slower than the first heating rate. (℃). The second heating rate is 0.5-5.0 ℃ / min, preferably 1.0-2.0 ℃ / min. ℃ / min.

[0052] In embodiments of the present invention, the preheating process may also employ a single-stage heating process.

[0053] Specifically, the first heating conditions and the second heating conditions are the same, and include heating to 450-600 °C (e.g., 500-550 °C) at a second heating rate. (℃). The second heating rate is 0.5-5.0 ℃ / min, preferably 1.0-2.0 ℃ / min. ℃ / min.

[0054] Compared to a single-stage heating process, a two-stage heating process can generate more hydroxyl sites on the molecular sieve surface during preheating. This is because the first stage (e.g., 300-400 °C) removes water or residual small molecules from the template agent adsorbed in the molecular sieve channels, exposing potential hydroxyl sites and cleaning the channels. This ensures that the water vapor pressure within the molecular sieve channels is controllable during the second high-temperature treatment (450-600 °C), preventing hydroxyl loss due to high-temperature condensation. This promotes the hydrolysis of water vapor with the silica-alumina bonds in the molecular sieve framework, generating new surface hydroxyl bonds. Simultaneously, the two-stage heating process reduces the temperature gradient inside and outside the molecular sieve, effectively minimizing hydroxyl loss due to channel collapse. In contrast, a single-stage heating process generates fewer hydroxyl sites because adsorbed water and template agents cannot be completely removed. At high temperatures, excessively high water vapor partial pressure within the channels leads to excessive hydrolysis of the silica-alumina bonds in the framework, triggering condensation reactions between adjacent hydroxyl groups and resulting in surface hydroxyl loss.

[0055] The heating rate (especially the second heating rate) is set to 0.5-5 ℃ / min to ensure uniform heating inside and outside the molecular sieve, prevent structural collapse, and thus preserve the complete pore structure of the molecular sieve, ensuring the subsequent generation of hydroxyl groups and improving the mass transfer of reactants / products. If the heating rate is too high, uneven heating inside and outside the molecular sieve will cause local thermal stress concentration, resulting in pore shrinkage or collapse, affecting the mass transfer process of reactants / products, and leading to a reduction in the outer surface area of ​​the molecular sieve and a decrease in the surface hydroxyl content, which in turn limits the amount of boron grafting, ultimately leading to a decrease in the degradation efficiency of polyurethane.

[0056] In the embodiments, the volume fraction φ(H2O) of water vapor in the water vapor-containing air mixture is 5-10% (e.g., 6-8%).

[0057] Using an air mixture with a φ(H2O) content of 5-10% can ensure the bonding between water molecules and the silicon-aluminum bonds [Si] in the molecular sieve framework. x Al y O] - The hydrolysis reaction forms a sufficient amount of surface hydroxyl groups [Si / Al-OH], which can avoid insufficient hydroxyl generation due to too low a concentration or loss of hydroxyl groups due to water vapor condensation in the pores due to too high a concentration. This effectively increases the hydroxyl content on the surface of the molecular sieve, thereby increasing the grafting amount of boron-containing halide reagents.

[0058] In the examples, the surface hydroxyl content of the hydroxylated molecular sieve is 0.5-3.5 mmol / g (e.g., 1.0-2.5 mmol / g).

[0059] In the embodiments, during the grafting process, by controlling the type, concentration, or grafting temperature of the boron-containing halide reagent, the boron-containing halide reagent is uniformly grafted onto the hydroxyl groups on the surface of the molecular sieve, forming highly dispersed strong Lewis acid active sites without blocking the pore structure of the molecular sieve itself; and other hydroxyl structures in the molecular sieve structure, such as bridging hydroxyl groups and hydroxyl pockets, are retained. These hydroxyl structures simultaneously adsorb degradation byproducts HX (HF, HCl, HBr, or HI, etc.), which promotes the forward degradation reaction while avoiding activity poisoning caused by competitive binding between byproducts and boron Lewis acid active sites, thus maintaining the high activity of the catalyst.

[0060] Specifically, the molar ratio of the boron-containing halide reagent to the hydroxyl groups on the molecular sieve surface is 1.1-1.3:1 (e.g., 1.2:1).

[0061] In the embodiments, an inert gas atmosphere is used during the preheating process to prevent the hydroxyl groups in the molecular sieve structure from being contaminated or damaged, thus protecting the original hydroxyl structure.

[0062] The first inert gas is at least one of nitrogen, argon, and helium.

[0063] The second inert gas is at least one of nitrogen, argon, and helium.

[0064] The first inert gas and the second inert gas can be the same or different. For example, the first inert gas can be argon and the second inert gas can be helium.

[0065] In the examples, the boron-containing halide is at least one of boron trifluoride dihydrate, boron trifluoride ethylamine complex, boron trifluoride dimethyl ether, boron trifluoride diethyl ether, boron trifluoride dibutyl ether, boron trichloride, dichloroborane, boron tribromide, dibromoborane, and iodoborane.

[0066] In the examples, placing the hydroxylated molecular sieve in an anhydrous solvent ensures that the surface of the molecular sieve is uniformly grafted with boron-containing halide reagents. The anhydrous solvent is at least one selected from methanol, n-pentane, hexane, dichloromethane, chloroform, and acetone.

[0067] In the embodiments, the molecular sieve is at least one of H-ZSM-5, H-Beta, H-MCM-41, H-MCM-22, H-SBA-15, HY, H-MOR, and H-USY.

[0068] In the embodiments, the use of a modified molecular sieve catalyst in the degradation of polyurethane is also provided. Specifically, in the presence of a solvent, the modified molecular sieve catalyst of the foregoing embodiments is used to degrade polyurethane via a heterogeneous catalytic reaction to prepare isocyanate.

[0069] This invention utilizes the weak Lewis acidity of molecular sieves to adsorb polyurethane reactants, enriching the polyurethane in the catalytically active region on the molecular sieve surface. This shortens the mass transfer path of the reactants and improves the catalytic degradation efficiency. Boron atoms in the modified molecular sieve catalyst, due to the strong electronegativity of halogen atoms, become strongly electron-deficient centers. Their empty p orbitals form stable coordination with the carbonyl oxygen of the urethane bond, achieving directional breaking of the urethane bond. The molecular sieve's pore structure is used for adsorption, simultaneously adsorbing polyurethane degradation byproducts. This avoids the byproducts poisoning the boron active centers while effectively promoting the forward reaction of polyurethane degradation. Furthermore, the modified molecular sieve catalyst constitutes a solid catalyst. In the presence of a solvent, it forms a heterogeneous reaction system with the polyurethane degradation reaction, exhibiting easy separation characteristics. The degradation process has low energy consumption and high product yield, thus realizing the direct preparation of isocyanate monomers from polyurethane under mild conditions through heterogeneous catalytic degradation.

[0070] In an embodiment, the degradation of polyurethane by catalytic reaction includes: mixing polyurethane and a solvent to form a mixture, and then, under an inert gas atmosphere, at a temperature of 50-90 °C (e.g., 60-80 °C). The modified molecular sieve catalyst was added to the mixture at a stirring speed of 200-1000 rpm (e.g., 300-800 rpm) and a reaction pressure of 0.1-1.0 MPa (e.g., 0.3-0.8 MPa). After reacting for 0.3-2.0 h (e.g., 0.5-1.5 h), the reaction mixture was filtered and then reacted at 40-90 °C (e.g., 50-80 °C). The reaction solvent was removed by rotary evaporation at ℃ to prepare isocyanate.

[0071] In the examples, the solvent is at least one selected from tetrahydrofuran, methyltetrahydrofuran, tetrahydropyran, 2-methyltetrahydropyran, butyl acetate, ethyl acetate, 1,4-dioxane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and dimethyl carbonate.

[0072] In the embodiments, polyurethane is a polymer containing urethane bonds (-NHCOO-), including at least one of flexible polyurethane elastomer (TPU), rigid polyurethane foam, flexible polyurethane foam, polyurethane coating, polyurethane adhesive, polyurethane leather resin, and polyurethane elastic fiber (spandex).

[0073] In the embodiments, the inert gas is at least one of nitrogen, argon, and helium.

[0074] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings. Those skilled in the art should understand that the present invention is not limited to the specific embodiments described, and reasonable modifications can be made after understanding the concept of the present invention.

[0075] raw material:

[0076] TPU (thermoplastic polyurethane) elastomer: 0.4 mmol / g urethane bonds, MDI type, BASF;

[0077] TPU elastomer waste: TPU substrate from discarded mobile phone cases, midsole elastomers from discarded sports shoes, and TPU shock-absorbing cushioning pads;

[0078] MDI-type rigid insulation waste: rigid insulation layer of the inner liner of used freezers, polyurethane insulation layer of scrapped cold chain refrigerated boxes, waste polyurethane insulation board for exterior walls, and waste MDI rigid insulation board.

[0079] TDI (toluene diisocyanate) type soft polyurethane foam waste: waste soft foam for cushions, waste mattress sponge padding, and TDI soft foam trimming waste;

[0080] 4,4'-Diphenylmethane diisocyanate (MDI-100), Wanhua Chemical;

[0081] Beta molecular sieve, ZSM-5 molecular sieve, Nankai University;

[0082] Methanol, boron trifluoride dihydrate, 1 M boron trichloride dichloromethane solution, tetrahydrofuran, Maclean, AR.

[0083] Example 1

[0084] (1) Preparation of modified Beta molecular sieve

[0085] 10 g of Beta molecular sieve was placed in a tube furnace and heated to 320 °C at a rate of 5 °C / min under a nitrogen atmosphere, and calcined at 320 °C for 2 h. Then, the temperature was increased to 550 °C at a rate of 1 °C / min, while simultaneously introducing an air mixture containing 6% water vapor at a flow rate of 15 mL / min, and calcined for 3 h. The mixture was then allowed to cool naturally to room temperature to obtain hydroxylated Beta molecular sieve with a surface hydroxyl content of 2.0 mmol / g. The obtained product was placed in a round-bottom flask, purged with nitrogen, and 40 mL of anhydrous methanol was added dropwise. A slurry was formed by stirring, and then 2.1 g of boron trifluoride dihydrate was added dropwise. After stirring and reacting at room temperature for 2 h, the methanol solvent was removed by rotary evaporation at 50 °C. Finally, the mixture was dried in a vacuum drying oven at 60 °C to obtain the modified Beta molecular sieve catalyst with a boron grafting amount of 2.0 mmol / g. TEM images of the prepared hydroxylated molecular sieve are shown below. Figure 1 As shown, the TEM image of the prepared modified molecular sieve catalyst is as follows. Figure 2 As shown, by Figure 1 and Figure 2 It can be seen that grafting boron-containing halide reagents onto the surface of molecular sieves forms -O-BX. n After structural modification, no obvious boron species aggregates were observed, and the original morphology of the molecular sieve was not affected.

[0086] (2) Degradation reaction of polyurethane

[0087] 50 g of TPU elastomer was added to a reactor, followed by 1.2 L of anhydrous tetrahydrofuran. Nitrogen gas was introduced, and the mixture was stirred at 500 rpm for 0.5 h at 60 °C. Then, 10 g of the modified Beta molecular sieve catalyst prepared in step (1) was added, and stirring was continued for another 0.5 h. After the reaction was completed, the reaction mixture was filtered, and the reaction solvent was removed by rotary evaporation at 50 °C. All the TPU elastomer was converted, and the isocyanate monomer yield was 95%.

[0088] Example 2

[0089] (1) Preparation of modified Beta molecular sieve

[0090] 10 g of Beta molecular sieve was placed in a tube furnace and heated to 550 °C at a rate of 1 °C / min under a nitrogen atmosphere. It was calcined for 2 h, followed by calcination for 3 h with an air mixture containing 6% water vapor at a flow rate of 15 mL / min. The mixture was then allowed to cool naturally to room temperature to obtain hydroxylated Beta molecular sieve with a surface hydroxyl content of 1.4 mmol / g. The resulting product was placed in a round-bottom flask, purged with nitrogen, and 40 mL of anhydrous methanol was added dropwise. The mixture was stirred to form a slurry, and then 2.1 g of boron trifluoride dihydrate was added dropwise. After stirring and reacting for 2 h at room temperature, the methanol solvent was removed by rotary evaporation at 50 °C. Finally, the mixture was dried in a vacuum drying oven at 60 °C to obtain the modified Beta molecular sieve catalyst with a boron grafting amount of 1.4 mmol / g.

[0091] (2) Degradation reaction of polyurethane

[0092] The same polyurethane degradation reaction as in Example 1 was used, with the only difference being that the TPU elastomer conversion rate was 75% and the isocyanate monomer yield was 72%.

[0093] Compared with the two-stage heating process in Example 1, in the single-stage heating process of this example, the hydroxyl content on the molecular sieve surface decreased from 2.0 mmol / g to 1.4 mmol / g. The reduction of hydroxyl sites directly limited the grafting efficiency of boron-containing halide reagents, resulting in a decrease in the amount of boron grafted from 2.0 mmol / g to 1.4 mmol / g. Since the boron center is the active center for catalyzing the directional breaking of polyurethane urethane bonds, the reduction in its grafting amount led to a decrease in the conversion rate of TPU elastomer from 100% to 75%, and a decrease in the yield of isocyanate monomer from 95% to 72%.

[0094] Example 3

[0095] (1) Preparation of modified Beta molecular sieve

[0096] The preparation method was the same as in Example 1, except that 40 mL of anhydrous methanol was replaced with 20 mL of dichloromethane, and boron trifluoride dihydrate was replaced with 28.9 g of a 1.0 mol / L boron trichloride dichloromethane solution. The grafting amount of boron was 2.0 mmol / g.

[0097] (2) Degradation reaction of polyurethane

[0098] 50 g of TPU elastomer was added to a reactor, followed by 1.2 L of anhydrous tetrahydrofuran. Nitrogen gas was introduced, and the mixture was stirred at 500 rpm for 0.5 h at 60 °C. Then, 10 g of the modified Beta molecular sieve catalyst prepared in step (1) was added, and stirring was continued for another 0.5 h. After the reaction was completed, the reaction mixture was filtered, and the reaction solvent was removed by rotary evaporation at 50 °C. The TPU elastomer was completely converted, and the isocyanate monomer yield was 93%.

[0099] Example 4

[0100] (1) Preparation of modified ZSM-5 molecular sieve

[0101] ZSM-5 molecular sieves were placed in a tube furnace and heated to 320 °C at a rate of 5 °C / min under a nitrogen atmosphere, and calcined at 320 °C for 2 h. The temperature was then increased to 550 °C at a rate of 1 °C / min, while simultaneously introducing an air mixture containing 6% water vapor at a flow rate of 15 mL / min, and calcined for 3 h. The mixture was then allowed to cool naturally to room temperature to obtain hydroxylated ZSM-5 molecular sieves with a surface hydroxyl content of 1.7 mmol / g. The obtained product was placed in a round-bottom flask, purged with nitrogen, and 40 mL of anhydrous methanol was added dropwise. A slurry was formed by stirring, followed by the addition of 1.8 g of boron trifluoride dihydrate. The mixture was stirred and reacted at room temperature for 2 h. The methanol solvent was removed by rotary evaporation at 50 °C, and the mixture was finally dried in a vacuum drying oven at 60 °C to obtain the modified ZSM-5 molecular sieve catalyst with a boron grafting amount of 1.7 mmol / g.

[0102] (2) Degradation reaction of polyurethane

[0103] 42 g of TPU elastomer was added to a reactor, followed by 720 mL of anhydrous tetrahydrofuran. Nitrogen gas was introduced, and the mixture was stirred at 500 rpm for 0.5 h at 60 °C. Then, 10 g of the modified ZSM-5 molecular sieve catalyst prepared in step (1) was added, and stirring was continued for another 0.5 h. After the reaction was complete, the reaction mixture was filtered, and the reaction solvent was removed by rotary evaporation at 50 °C. The TPU elastomer was completely converted, and the isocyanate monomer yield was 93%.

[0104] Example 5

[0105] (1) Treatment of TPU elastomer waste: The TPU elastomer waste was cut into 5*5 mm particles, and then ultrasonically cleaned with deionized water and anhydrous ethanol for 30 min respectively. After cleaning, it was placed in a drying oven and dried at 80 ℃.

[0106] (2) Degradation reaction of TPU elastomer waste

[0107] Using the catalyst (10 g) from Example 1, 50 g of TPU elastomer waste was added to a reactor, followed by 1.2 L of anhydrous tetrahydrofuran. Nitrogen gas was introduced, and the mixture was stirred at 500 rpm for 0.5 h at 60 °C, followed by a reaction time of 1.0 h. After the reaction was complete, the reaction mixture was filtered, and the reaction solvent was removed by rotary evaporation at 50 °C. The TPU elastomer waste was almost completely converted, and the isocyanate monomer yield was 91%.

[0108] Figure 3 ATR-FTIR spectra of pure MDI chemical and the reaction products of Examples 1 and 5. Figure 3 It can be seen that the TPU elastomer is completely degraded, and 4,4'-diphenylmethane diisocyanate (MDI) is the main product after the reaction, exhibiting high selectivity. Figure 4 The graph shows the polyurethane degradation conversion rate and isocyanate yield results for Examples 1 and 5. Figure 4 It can be seen that the catalyst prepared in Example 1 can efficiently and with high yield degrade both high-purity TPU elastomer chemicals and TPU elastomer waste generated in daily life into isocyanate monomers.

[0109] Example 6

[0110] (1) Treatment of waste material of MDI type rigid insulation layer: cut the waste material of MDI type rigid insulation layer into 5*5 mm particles, and then ultrasonically clean it with deionized water and anhydrous ethanol for 30 min respectively. After cleaning, place it in a drying oven and dry it at 80℃.

[0111] (2) Degradation reaction of MDI-type rigid insulation layer waste

[0112] Using the catalyst (10 g) from Example 1, 50 g of MDI-type rigid insulation waste was added to a reactor, followed by 1.2 L of anhydrous tetrahydrofuran. Nitrogen gas was introduced, and the mixture was stirred at 500 rpm for 0.5 h at 60 °C, followed by a reaction time of 1.0 h. After the reaction was complete, the reaction mixture was filtered, and the reaction solvent was removed by rotary evaporation at 50 °C. The MDI-type rigid insulation waste was almost completely converted, and the isocyanate monomer yield was 89%.

[0113] Example 7

[0114] (1) Treatment of TDI type flexible polyurethane foam waste

[0115] TDI-type flexible polyurethane foam waste was cut into 5*5 mm particles, and then ultrasonically cleaned with deionized water and anhydrous ethanol for 30 min each. After cleaning, it was placed in a drying oven and dried at 80 ℃.

[0116] (2) Degradation reaction of TDI type flexible polyurethane foam waste

[0117] Using the catalyst (10 g) from Example 1, 50 g of TDI-type flexible polyurethane foam waste was added to a reactor, followed by 1.2 L of anhydrous tetrahydrofuran. Nitrogen gas was introduced, and the mixture was stirred at 500 rpm for 0.5 h at 60 °C, followed by a reaction time of 1.0 h. After the reaction was complete, the reaction mixture was filtered, and the reaction solvent was removed by rotary evaporation at 50 °C. The TDI-type flexible polyurethane foam waste was almost completely converted, and the isocyanate monomer yield was 90%.

[0118] The above-described embodiments are merely preferred embodiments of the present invention, used to explain and illustrate the technical solutions of the present invention. Those skilled in the art should understand that improvements or combinations can be made to the embodiments without departing from the principles of the present invention. The scope of protection of the present invention is defined by the claims and their equivalents.

Claims

1. The use of a modified molecular sieve catalyst in the degradation of polyurethane, characterized in that, In the presence of a solvent, the modified molecular sieve catalyst is used to degrade polyurethane via a heterogeneous catalytic reaction to prepare isocyanate. The modified molecular sieve catalyst is prepared according to the following preparation method, which includes: The molecular sieve was calcined for 1-3 h under a first inert gas atmosphere and a first heating condition, and then calcined for 2-6 h under a second heating condition by introducing an air mixture containing water vapor. After cooling, the hydroxylated molecular sieve was obtained. The hydroxylated molecular sieve was placed in an anhydrous solvent to form a slurry, and a boron-containing halide reagent was added under a second inert gas atmosphere. The mixture was then heated to 20-50 °C. o React at C for 1-6 hours, then at 40-70°C. o Solvent is removed by rotary evaporation at C, followed by evaporation at 50-120°C. o The modified molecular sieve catalyst was obtained by drying under vacuum at C. The first heating conditions include heating to 300-400 at a first heating rate. o C, and the second heating conditions include heating to 450-600 at a second heating rate slower than the first heating rate. o C, the second heating rate is 0.5-5.

0. o C / min, or The first heating conditions and the second heating conditions are the same, and include heating to 450-600 at the second heating rate. o C, The boron-containing halide is at least one selected from boron trifluoride dihydrate, boron trifluoride ethylamine complex, boron trifluoride dimethyl ether, boron trifluoride diethyl ether, boron trifluoride dibutyl ether, boron trichloride, dichloroborane, boron tribromide, dibromoborane, and iodoborane. The molecular sieve is at least one of H-ZSM-5, H-Beta, H-MCM-41, H-MCM-22, H-SBA-15, HY, H-MOR, and H-USY.

2. The use according to claim 1, characterized in that, The volume fraction φ(H2O) of the water vapor in the water vapor-containing air mixture is 5-10%.

3. The use according to claim 2, characterized in that, The surface hydroxyl content of the hydroxylated molecular sieve is 0.5-3.5 mmol / g.

4. The use according to any one of claims 1-3, characterized in that, The molar ratio of the boron-containing halide reagent to the hydroxyl groups on the molecular sieve surface is 1.1-1.3:

1.

5. The use according to claim 4, characterized in that, The first inert gas and the second inert gas are at least one of nitrogen, argon, and helium, respectively; The anhydrous solvent is at least one of methanol, n-pentane, hexane, dichloromethane, chloroform, and acetone.

6. The use according to any one of claims 1-3, characterized in that, The modified molecular sieve catalyst is Z-OBX. n Type Z-OBX catalyst, wherein Z is a molecular sieve, O is an oxygen atom, B is a boron atom, X is a halogen atom, and n is 1 or 2. n The catalyst has -ZOB- bonds.

7. The use according to claim 6, characterized in that, The halogen atom includes at least one of fluorine, chlorine, bromine, and iodine.

8. The use according to claim 6, characterized in that, The degradation of polyurethane via catalytic reaction includes: mixing polyurethane and the solvent to form a mixture, and then, under an inert gas atmosphere, at a temperature of 50-90°C. o C. At a stirring speed of 200-1000 rpm and a reaction pressure of 0.1-1.0 MPa, the modified molecular sieve catalyst is added to the mixture. After reacting for 0.3-2.0 h, the reaction mixture is filtered and then subjected to a reaction at 40-90 °C. o The reaction solvent was removed by rotary evaporation at C to prepare isocyanate.

9. The use according to claim 8, characterized in that, The solvent is at least one of tetrahydrofuran, methyltetrahydrofuran, tetrahydropyran, 2-methyltetrahydropyran, butyl acetate, ethyl acetate, 1,4-dioxane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and dimethyl carbonate.

10. The use according to claim 9, characterized in that, The polyurethane is a polymer containing urethane bonds, including at least one of flexible polyurethane elastomers, rigid polyurethane foams, flexible polyurethane foams, polyurethane coatings, polyurethane adhesives, polyurethane leather resins, and polyurethane elastic fibers.

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