Method for realizing effective separation of polyurethane foam degradation product

Abstract

The invention provides a method for effectively separating a polyurethane foam degradation product, which comprises the following steps: adding a polyazacyclo quaternary ammonium salt flocculant into a suspension obtained by degrading polyurethane flexible foam, heating and stirring at 40-60 DEG C, and standing and layering after stirring to obtain a polyol product recovered at the upper layer and isocyanate condensed at the lower layer. The method is a method for effectively separating the degradation product of the polyurethane flexible foam by adding a flocculating agent, the separated product can be directly used as original polyhydric alcohol, and the problem that the recycling of the polyhydric alcohol is influenced due to the fact that the polyhydric alcohol and the isocyanate part of the degradation product of the polyurethane flexible foam are difficult to effectively separate is solved. According to the invention, the existing polyurethane waste foam degradation technology is deepened, the polyazacyclo quaternary ammonium salt flocculant is synthesized on the basis of an inorganic flocculant and a composite flocculant, and efficient separation of soft and hard segments of a polyurethane degradation product is realized.

Description

Technical Field

[0001] This invention relates to the field of polyurethane foam recycling, and in particular to a method for effectively separating degradation products of polyurethane flexible foam using flocculants. Background Technology

[0002] Polyurethane (PU) is short for polyurethane, a polymer formed by the condensation polymerization of polyisocyanates and polyhydroxy polymers. It is a high molecular weight compound containing many repeating urethane segments (-NHCOO-) in its main molecular chain. Polyurethane materials possess excellent properties such as wear resistance, high mechanical strength, high elasticity, aging resistance, and corrosion resistance. These excellent properties are closely related to the molecular structure of polyurethane materials: the main chain of polyurethane molecules is composed of flexible long-chain polyols and rigid isocyanate blocks, which can effectively disperse stress. The coexistence of polar and non-polar segments also improves the chemical stability of polyurethane. Simultaneously, the widespread hydrogen bonding within the polymer further enhances the mechanical properties of the material. Furthermore, the -NCO groups of isocyanates are highly reactive and can react rapidly with alcohols, water, organic amines, etc., resulting in good processability. By controlling the reaction conditions and catalysts, various polyurethane products with different hardnesses and structures can be obtained, such as rubber- or plastic-like elastomers, open-cell sponges, closed-cell rigid foams, adhesives, coatings, sealants, etc., which are widely used in various fields of national production and daily life.

[0003] Foam materials constitute the largest category of polyurethane products by production volume, encompassing both rigid and flexible foams. Rigid foams are primarily used for insulation and filling, such as pipe insulation, building exterior wall insulation, and refrigerator insulation layers; as fillers, they can be used for waterproofing, leak sealing, and filling in goaf areas such as coal mines. Flexible foams are mainly used in automobiles and furniture, such as sofa foam and car seat fillings. Flexible foams account for the highest production volume among all polyurethane products. With the increasing production of polyurethane year by year, polyurethane waste is also increasing annually. However, polyurethane waste is typically disposed of through incineration or landfill, which not only wastes resources but also pollutes the environment.

[0004] Polyurethane flexible foam can be recycled through physical, chemical, and energy recovery methods. However, physical and energy recovery, currently the main methods for treating polyurethane waste, run counter to the current trend of resource recycling and environmental governance. Chemical recycling involves chemically degrading waste polyurethane into reusable polyols, which are then used to reprocess polyurethane products, achieving high-value recycling of materials. Polyurethane is typically recycled through acid hydrolysis, alcohol hydrolysis, and amino hydrolysis, and the recovered polyols can be used to reprocess foam. However, the products from polyurethane acid hydrolysis, amino hydrolysis, and alcohol hydrolysis are suspensions. The lower-layer products from these processes are mainly isocyanate derivatives. These isocyanate derivatives mix with the polyols, making effective separation impossible and affecting subsequent polyol recycling, significantly increasing the cost of separation and purification. Therefore, post-treatment of the degradation products of polyurethane flexible foam is necessary to achieve effective separation of the soft and hard segments of the polyurethane.

[0005] Flocculants are chemical substances used to treat water pollution. They cause suspended solid particles in water to quickly aggregate into larger particles, which can then be removed from the water through sedimentation or filtration, thus purifying the water. Therefore, flocculants are widely used in the following fields: In wastewater treatment, flocculants promote the aggregation of solid matter in wastewater, making it easier to filter or settle and ensuring that the treated wastewater meets discharge standards. Currently, they are mainly used in industrial and mining wastewater treatment and urban sewage treatment. Flocculants are also widely used in drinking water treatment. By adding flocculants to raw water, they can help coagulate and remove suspended solids, turbidity, humic acid, and other particulate matter, thereby purifying the water. In industries such as papermaking, food, beverage, printing and dyeing, and electroplating, large amounts of water pollutants are often generated during production. Flocculants can help purify the water in these industries to meet national discharge standards and internal company requirements. Other fields: Flocculants can also be applied in other fields, such as oilfield wastewater treatment, water pollution control in metallurgical production, environmental remediation, and seawater desalination, making important contributions to the protection and sustainable use of water resources in production and human life.

[0006] The mechanism of action of flocculants is based on disrupting the stability of colloidal particles in water and causing them to aggregate into easily separable particles. Specifically, after being added to water, flocculants undergo hydrolysis, forming charged colloids. These colloids, together with ions in the water, form micelles with an electric double layer structure. Rapid stirring promotes collisions between colloidal impurities in the water and the micelles formed by the flocculant hydrolysis, causing them to lose stability and aggregate into larger particles. The flocculation process typically consists of three consecutive stages: mixing, coagulation, and flocculation. Mixing first takes place in a mixing tank, followed by coagulation and flocculation in a reaction tank.

[0007] Adding flocculants promotes the coagulation of isocyanate derivatives in suspension, achieving effective separation of soft and hard segments. There are many types of flocculants, each with its own characteristics. Inorganic flocculants, such as aluminum sulfate and ferric sulfate, while convenient to use, inexpensive, and non-toxic, also have disadvantages such as unstable quality, high impurity content, difficulty in hydrolysis at low water temperatures, and relatively loose flocs. These problems increase the complexity of chemical solution preparation and waste residue treatment. Organic polymeric flocculants, due to their numerous active groups and high molecular weight, have the advantages of low dosage, low scum production, and strong flocculation ability, facilitating floc separation and performing well in oil and suspended solids removal. However, most organic polymeric flocculants themselves hydrolyze, their degradation products are toxic, and they are costly. In contrast, inorganic polymeric flocculants are highly efficient, adaptable, non-toxic, and inexpensive; they are developed based on traditional aluminum and iron salts. Composite flocculants combine the advantages of inorganic and polymeric flocculants, improving flocculation efficiency through a synergistic effect. Summary of the Invention

[0008] To address the problem that the polyol and isocyanate components of polyurethane flexible foam degradation products are difficult to separate effectively in existing technologies, thus affecting the utilization of recycled polyols, this invention provides a method for effectively separating polyurethane foam degradation products. This method involves adding a flocculant to achieve effective separation of polyurethane flexible foam degradation products, and the separated products can be directly used as the original polyols.

[0009] The present invention adopts the following technical solution: A method for effectively separating degradation products of polyurethane flexible foam by adding a flocculant, the method comprising: Add 0.05–0.1 wt% flocculant to the suspension obtained from degradation, 45 o Heat and stir for 20-30 minutes at a stirring speed not exceeding 200 rpm. After stirring, allow the mixture to stand and separate into layers to obtain the upper layer of recovered polyol product and the lower layer of condensed isocyanate derivative.

[0010] The flocculant is a composite flocculant, and the mass of the composite flocculant is 0.05 to 0.1% of the mass of the polyurethane flexible foam degradation products. The composite flocculant is a mixture of polyaluminum chloride (PAC, PACL), polyaluminum sulfate (PAS), polyferric chloride (PFC), polyacrylamide (PACM), and chitin (PAPCh).

[0011] The composite flocculant is a solid, granular, or flake flocculant.

[0012] The flocculant is a polynitrogen heterocyclic quaternary ammonium salt flocculant, and the polynitrogen heterocyclic quaternary ammonium salt flocculant accounts for 0.05 to 0.08% of the mass of the polyurethane flexible foam degradation products; The total mass of the polynitrogen heterocyclic quaternary ammonium salt flocculant solution is 3-5% of the mass of the polyurethane flexible foam degradation products; A method for effectively separating polyurethane flexible foam degradation products by adding a flocculant includes the following steps: Polyazo-heterocyclic quaternary ammonium salt flocculant was added to the suspension obtained from the degradation of polyurethane flexible foam, heated and stirred at 40~60℃, and after stirring was completed, it was allowed to stand and separate into layers to obtain the upper layer of recovered polyol product and the lower layer of condensed isocyanate.

[0013] The structure of the polynitrogen heterocyclic quaternary ammonium salt flocculant is as follows: .

[0014] Polynitrogen heterocyclic quaternary ammonium salts achieve flocculation primarily through three pathways: charge neutralization, adsorption bridging, and mesh sweeping. Firstly, the molecular chains of polynitrogen heterocyclic quaternary ammonium salts are rich in positively charged quaternary ammonium groups (—N). + R3), the positively charged groups of quaternary ammonium salts adsorb negatively charged colloids in the suspension, neutralizing the surface charge of the colloids, disrupting their stability, and promoting particle destabilization and aggregation to form micro-flocs. Furthermore, the nitrogen heterocyclic structure and quaternary ammonium groups possess strong adsorption activity, capable of simultaneously adsorbing multiple destabilized colloidal particles in the suspension. These particles are then "bridging" each other through long molecular chains, forming larger flocs. Finally, the polynitrogen heterocyclic quaternary ammonium salt cross-links in water to form a three-dimensional network structure, sweeping and encapsulating the colloidal particles to form dense flocs, thereby achieving the flocculation effect.

[0015] The preparation of the polynitrogen heterocyclic quaternary ammonium salt flocculant specifically includes: Hexamethylenediamine and methanol were added to a reactor, and epichlorohydrin was added under stirring. The synthesis reaction yielded the quaternary ammonium salt primary product. The quaternary ammonium salt primary product and methanol were added to the reactor, and a nitrogen heterocyclic compound was added and stirred under reflux. The polynitrogen heterocyclic quaternary ammonium salt flocculant was obtained by rotary evaporation and washing.

[0016] The synthesis reaction conditions are: stirring at 45~80℃ for 8~13h.

[0017] Add nitrogen heterocyclic compounds and stir under reflux at 70-90°C for 9-13 hours.

[0018] The nitrogen heterocyclic compound is one of pyridine, quinoline, imidazole, and piperidine.

[0019] The mass ratio of the polyazo-heterocyclic quaternary ammonium salt flocculant to the suspension is 0.0005-0.001:1.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention deepens the existing polyurethane waste foam degradation technology. Based on inorganic flocculants and composite flocculants, a polynitrogen heterocyclic quaternary ammonium salt flocculant was synthesized to achieve efficient separation of soft and hard segments of polyurethane degradation products.

[0021] (2) It simplifies the subsequent recycling of polyols and isocyanate derivatives.

[0022] (3) Recycled polyols can be directly reused, which increases the commercial potential of polyurethane foam degradation.

[0023] (4) The recovered isocyanate derivatives can be used as flame retardants, which not only improves the utilization rate and commercial value of polyurethane degradation products.

[0024] (5) This method does not require a flocculant separation step. The flocculant component and the lower isocyanate derivative component are in the same phase, which does not affect the quality of the upper polyol component. It is more efficient and will not cause environmental pollution. Attached Figure Description

[0025] Figure 1 These are degradation products resulting from acidolysis, alcohololysis, and aminolysis. Figure 2 These are the degradation products after the addition of flocculants; Figure 3 NMR spectrum of polynitrogen heterocyclic quaternary ammonium salt flocculant; Figure 4 These are the degradation products after the addition of flocculants; Figure 5 These are the degradation products after the addition of flocculants; Figure 6 These are the degradation products after the addition of flocculants; Figure 7 These are the degradation products after the addition of flocculants; Figure 8 These are the degradation products after the addition of flocculants; Figure 9 These are the degradation products after the addition of flocculants; Figure 10 These are degradation products after centrifugation; Figure 11 The images show the morphology and structure of recycled polyurethane foam, including (a) the morphology of 5wt% recycled foam, (b) the structure of 5wt% recycled foam, (c) the morphology of 6wt% recycled foam, and (d) the structure of 6wt% recycled foam. Detailed Implementation

[0026] The present invention is further described below through specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0027] Unless otherwise specified, the raw materials and equipment used in this invention can be purchased from the market or are commonly used in the field. Unless otherwise specified, the methods in the embodiments are conventional methods in the field.

[0028] Preparation Example 1 The synthesis steps of polynitrogen heterocyclic quaternary ammonium salt flocculants are as follows: Add 13.36g hexamethylenediamine and 50ml methanol to a 250ml single-necked flask. While stirring, add 23.13g epichlorohydrin dropwise. o After stirring at C for 12 hours, 35.63 g of the initial quaternary ammonium salt product was obtained; Add the above primary product and 50 ml of methanol to a 250 ml single-necked flask, and add an appropriate amount of pyridine (n(intermediate):n(pyridine) = 1:1.2). o After stirring under reflux for 12 hours, 20.32 g of polynitrogen heterocyclic (pyridine) quaternary ammonium salt flocculant was obtained by rotary evaporation and washing.

[0029] Add 0.1g of polyazocyclic (pyridine) quaternary ammonium salt flocculant to the suspension obtained from degradation, 45 o Heat and stir for 20-30 minutes at a stirring speed not exceeding 200 rpm. After stirring, allow the mixture to stand and separate into layers to obtain the upper layer of recovered polyol product and the lower layer of condensed isocyanate derivative.

[0030] The synthesized polynitrogen heterocyclic (pyridine) quaternary ammonium salt flocculant NMR spectroscopy results are as follows: Figure 3 As shown.

[0031] Example 1 (as a comparison) 200.0 g of the degradation suspension was placed in a 250 mL three-necked flask, and then 1.0 g (0.5 wt% of the suspension mass) of polyaluminum chloride (PAC) powder was accurately weighed and heated at 45 °C. o Under constant temperature water bath conditions (C) and mechanical stirring at 200 rpm / min, the substance was slowly added to the suspension, and timing was started. This heating and stirring process continued for 30 minutes, after which stirring and heating were stopped, and the system was allowed to stand for flocculation and sedimentation. The sedimentation time was strictly controlled to 30 minutes. After complete separation, a clear phase interface was observed, with a volume ratio of approximately 1:9 between the upper and lower layers. The supernatant was then carefully aspirated using decantation and a dropper; this was the recovered polyol product, while the lower precipitate was the isocyanate derivative. Both were collected and weighed. (e.g.) Figure 4 (As shown).

[0032] Example 2 (as a comparison) 200.0 g of the degradation suspension was placed in a 500 mL three-necked flask, and then 0.6 g (0.3 wt% of the suspension mass) of polyaluminum sulfate (PAS) powder was accurately weighed and heated at 45 °C. o Under constant temperature water bath conditions (C) and mechanical stirring at 200 rpm / min, the mixture was slowly added to the suspension and the timer was started. This heating and stirring process continued for 30 minutes, after which stirring and heating were stopped, and the system was allowed to stand for flocculation and sedimentation. The sedimentation time was strictly controlled to 20 minutes. After complete separation, a clear phase interface was observed, with a volume ratio of approximately 3:7 between the upper and lower layers. The supernatant was then carefully aspirated using decantation and a dropper; this was the recovered polyol product, while the lower precipitate was an isocyanate derivative (such as...). Figure 5 (As shown).

[0033] Example 3 (as a comparison) 200.0 g of the degradation suspension was placed in a 500 mL three-necked flask, and then 0.6 g (0.3 wt% of the suspension mass) of polyferric chloride (PFC) powder was accurately weighed and heated at 45 °C. o Under constant temperature water bath conditions (C) and mechanical stirring at 200 rpm / min, the mixture was slowly added to the suspension and the timer was started. This heating and stirring process continued for 30 minutes, after which stirring and heating were stopped, and the system was allowed to stand for flocculation and sedimentation. The sedimentation time was strictly controlled to 23 minutes. After complete separation, a clear phase interface was observed, with an upper and lower layer volume ratio of approximately 3:7. Subsequently, the supernatant was carefully aspirated using decantation and a dropper; this portion is the recovered polyol product, while the lower precipitate is an isocyanate derivative (such as...). Figure 6 (As shown).

[0034] Example 4 (as a comparison) 200.0 g of the degradation suspension was placed in a 500 mL three-necked flask. Then, 0.2 g (0.1 wt% of the suspension mass) of polyferric chloride (PFC) powder and 0.1 g of polyacrylamide (PACM) were accurately weighed and heated at 45 °C. o Under constant temperature water bath conditions (C) and mechanical stirring at 200 rpm / min, the mixture was slowly added to the suspension sequentially, and the timing was started. This heating and stirring process continued for 30 minutes, after which stirring and heating were stopped, and the system was allowed to stand for flocculation and sedimentation. The sedimentation time was strictly controlled to 35 minutes. After complete separation, a clear phase interface was observed, with an upper and lower layer volume ratio of approximately 6:4. Subsequently, the supernatant was carefully aspirated using decantation and a dropper; this portion is the recovered polyol product, while the lower precipitate is an isocyanate derivative (such as...). Figure 7 (As shown).

[0035] Example 5 (as a comparison) 200.0 g of the degradation suspension was placed in a 500 mL three-necked flask. Then, 0.2 g (0.1 wt% of the suspension mass) of polyferric chloride (PFC) powder and 0.2 g (0.1 wt% of the suspension mass) of chitosan (PAPCh) were accurately weighed and heated to 45 °C. o Under constant temperature water bath conditions (C) and mechanical stirring at 200 rpm / min, the mixture was slowly added to the suspension sequentially, and the timing was started. This heating and stirring process continued for 30 minutes, after which stirring and heating were stopped, and the system was allowed to stand for flocculation and sedimentation. The sedimentation time was strictly controlled to 40 minutes. After complete separation, a clear phase interface was observed, with an upper and lower layer volume ratio of approximately 8:2. Subsequently, the supernatant was carefully aspirated using decantation and a dropper; this portion is the recovered polyol product, while the lower precipitate is an isocyanate derivative (such as...). Figure 8 (As shown).

[0036] Example 6 200.0 g of the degradation suspension was placed in a 500 mL three-necked flask, and then 0.2 g (0.1 wt% of the suspension mass) of the polyazo-heterocyclic (pyridine) quaternary ammonium salt flocculant prepared in Preparation Example 1 was accurately weighed and heated to 45 °C. o Under constant temperature water bath conditions (C) and mechanical stirring at 200 rpm / min, the mixture was slowly added to the suspension and the timer was started. This heating and stirring process continued for 30 minutes, after which stirring and heating were stopped, and the system was allowed to stand for flocculation and sedimentation. The sedimentation time was strictly controlled to 15 minutes. After complete separation, a clear phase interface was observed, with an upper and lower layer volume ratio of approximately 4:6. Subsequently, the supernatant was carefully aspirated using decantation and a dropper; this portion is the recovered polyol product, while the lower precipitate is an isocyanate derivative (such as...). Figure 9 (As shown).

[0037] Comparative Example 1 The suspension of 200.0g of degraded polyurethane flexible foam was centrifuged at 1000rpm / min for 15min. A small amount of loose flocs and a large number of suspended particles were found in the suspension, making it difficult to separate and recover the polyol.

[0038] Comparing Examples 1-6 with Comparative Example 1, it was found that the system without flocculant could not effectively separate the hard and soft segments, and the recovered polyol contained a large number of suspended particles, making it unusable directly. In contrast, the systems with added inorganic flocculants and composite flocculants showed obvious stratification, and the recovered polyol and isocyanate derivatives could be used directly. The polyol separated in Example 6 was used for re-foaming, resulting in regenerated polyurethane foam as shown in Example 6. Figure 11 The mechanical properties of recycled polyurethane foam are shown in Table 1.

[0039] Table 1. Mechanical properties of commercial polyurethane foam (Pure), recycled polyurethane foam (5%), and recycled polyurethane foam (6%) Table 1 shows that the mechanical properties of recycled polyurethane foam are not significantly different from those of original polyurethane foam. However, adding too much recycled polyol will affect its mechanical properties. Overall, the performance of recycled polyurethane foam is better.

[0040] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention are all within the scope of the present invention.

Claims

1. A method for effecting efficient separation of polyurethane foam degradation products, characterized by, It comprises the following steps: The polyazacyclic quaternary ammonium salt flocculant is added to the suspension obtained by degrading the polyurethane soft foam, heated and stirred at 40-60 DEG C, and after the stirring is completed, the upper layer is recovered and the lower layer is condensed to obtain the polyol product and the isocyanate.

2. The method of effecting the efficient separation of polyurethane foam degradation products according to claim 1, wherein, The polyazacyclic quaternary ammonium salt flocculant has the following structure: ； ； ； 。 3. The method of effecting efficient separation of polyurethane foam degradation products according to claim 2, wherein, The preparation of the polyazacyclic quaternary ammonium salt flocculant specifically comprises: Hexanediamine and methanol are added to a reactor, and epichlorohydrin is added under stirring to obtain a quaternary ammonium salt primary product after a synthesis reaction; The quaternary ammonium salt primary product and methanol are added to a reactor, and an azacyclic compound is added under stirring to obtain the polyazacyclic quaternary ammonium salt flocculant after condensation reflux and washing.

4. The method of effecting efficient separation of polyurethane foam degradation products according to claim 3, wherein, The synthesis reaction is performed under stirring at 45-80 DEG C for 8-13 h.

5. The method of effecting efficient separation of polyurethane foam degradation products according to claim 3, wherein, The azacyclic compound is added under stirring at 70-90 DEG C for 9-13 h.

6. The method of effecting efficient separation of polyurethane foam degradation products according to claim 3, wherein, The azacyclic compound is one of pyridine, quinoline, imidazole and piperidine.

7. The method of effecting efficient separation of polyurethane foam degradation products according to claim 3, wherein, The mass ratio of the polyazacyclic quaternary ammonium salt flocculant to the suspension is 0.003-0.005:1.

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