Recovery method for polyvinyl chloride with high volatile hydrocarbon conversion rate

Abstract

The invention particularly relates to a porous metal organic framework material MOFs-based PVC high-volatile hydrocarbon conversion rate recovery method, which comprises the following steps: adsorbing PVC into MOFs by adopting an adsorption method of a porous uniform site catalyst, and pyrolyzing the adsorbed composite material, the uniform aperture and catalytic site distribution of the catalyst are realized by coordination polymerization of metal sites and organic ligands. The invention aims to solve the problems of low volatile hydrocarbon yield, complex side reaction and difficulty in realizing high-value product conversion in the existing PVC cracking method.

Description

Technical Field

[0001] The invention relates to the technical field of polymer material recovery, and in particular to a method for recovering polyvinyl chloride with a high volatile hydrocarbon conversion rate. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance some understanding of the overall background of the invention and should not be necessarily regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Polyvinyl chloride (PVC) is a widely used general-purpose plastic, but its pyrolysis process has the following problems: (1) Complex side reactions: During the PVC cracking process, while the chemical bonds are broken, the polymer chains will participate in intermolecular reactions to generate coke and macromolecular byproducts, resulting in extremely low volatile hydrocarbon production. (2) Low-value conversion: In existing technologies, the C and H elements produced by PVC cracking are usually converted into low-value coke residues, making it difficult to achieve high-value product conversion at lower temperatures. (3) Low recovery efficiency: Traditional methods mainly focus on the breaking of chemical bonds, while ignoring the role of polymer chains in the reaction, resulting in low recovery efficiency.

[0004] The reasons for this unresolved issue include: existing catalytic technologies are unable to control the crucial role of polymer chains in the reaction, making it difficult to inhibit intermolecular reactions. Serial upcycling of PVC plastics requires selective conversion to certain organic intermediates, but the selectivity and yield of this process are difficult to control, resulting in the lack of a foundation for upcycling.

[0005] The polyacetylene structures produced by dechlorination of PVC are highly reactive and prone to crosslinking and carbonization, leading to serious carbonization problems. A porous material with a high specific surface area is needed to effectively constrain the PVC molecular chains, inhibiting intermolecular reactions and reducing carbon yield. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for recovering polyvinyl chloride (PVC) with a high volatile hydrocarbon conversion rate based on porous metal organic framework materials MOFs. By adsorbing PVC into MOF or on the surface and performing pyrolysis in an isolated environment, the following problems existing in the prior art are solved: (1) Excessive side reactions: By constraining the freedom of the PVC molecular chain, intermolecular reactions are inhibited, and the generation of coke and macromolecular byproducts is reduced. (2) Low volatile hydrocarbon production: By optimizing the reaction conditions, the conversion rate of volatile hydrocarbons is significantly improved, providing a basis for the upgrading and recycling of PVC. In summary, the present invention aims to provide an efficient and environmentally friendly PVC recovery method, solve the problem of high carbon yield in traditional methods, provide a chemical pathway from PVC to volatile hydrocarbons, thereby making downstream chemical conversion possible, and has important environmental and economic value.

[0007] The technical solution adopted in the present invention is as follows: In a first aspect of the present invention, there is provided an application of a porous metal organic framework material MOFs in pyrolyzing PVC to obtain highly volatile hydrocarbons.

[0008] In one or some embodiments of the present invention, the high specific surface area and regular pores of MOFs and the pore structure of the catalytic sites constrain the decomposition of PVC molecules.

[0009] Preferably, the MOFs are UiO-66, ZIF-8, MIL-101, HKUST-1, DUT-52 and UiO-67.

[0010] In one or some embodiments of the present invention, PVC is adsorbed into UiO-66 using an adsorption method of a porous uniform site catalyst, and the PVC-UiO-66 composite is pyrolyzed, wherein the uniform pore size and catalytic site distribution of UiO-66 are achieved by coordination polymerization of metal sites and organic ligands.

[0011] In a second aspect of the present invention, a method for recovering polyvinyl chloride with a high volatile hydrocarbon conversion rate is provided, wherein the PVC is adsorbed into the catalyst by an adsorption method using a porous uniform site catalyst, and the adsorbed composite material is pyrolyzed, wherein the uniform pore size and catalytic site distribution of the catalyst are achieved by coordination polymerization of metal sites and organic ligands, and the catalyst is MOFs.

[0012] In one or some embodiments of the present invention, the specific method includes: (1) PVC was adsorbed into MOFs by liquid phase adsorption method, and the adsorbed composite material was obtained by separation and drying; (2) The adsorbed composite material is pyrolyzed in an isolated environment to obtain cracking products.

[0013] Furthermore, step (2) is followed by step (3), wherein the pyrolysis products are absorbed and collected using an absorbent. The absorbent is deuterated chloroform or a liquid nitrogen cold trap. The present invention uses deuterated chloroform or a liquid nitrogen cold trap as an absorbent to efficiently separate and recover the pyrolysis products.

[0014] In one or some embodiments of the present invention, the catalyst pore size is less than 2 nm and the pore size is uniform.

[0015] In one or some embodiments of the present invention, the catalytic site (or coordinated metal center) of the catalyst is a transition metal such as Zr, Cu, Fe, or Zn.

[0016] In one or some embodiments of the present invention, the metal center of the MOFs has exposed catalytic sites for constraining PVC molecular chains.

[0017] In one or some embodiments of the present invention, the adsorption process used is liquid phase adsorption, including solution adsorption and melt adsorption.

[0018] Preferably, the solvent used in the solution adsorption method is an organic solvent such as THF, acetone, butanone, chloroform, DMF, etc.

[0019] Preferably, the melt adsorption method used has a melting temperature of 120-200° C. and is protected by an inert gas.

[0020] In one or some embodiments of the present invention, the MOFs are UiO-66, ZIF-8, MIL-101, HKUST-1, DUT-52 or UiO-67.

[0021] Further preferably, the MOFs is UiO-66.

[0022] In one or some embodiments of the present invention, the pyrolysis temperature is 280-320°C.

[0023] Compared with the related art known to the inventors, one of the technical solutions of the present invention has the following beneficial effects: (1) Regular porous material structure constrains PVC molecular chains: Porous metal organic framework materials are used to effectively constrain PVC molecular chains, limit their degrees of freedom, inhibit intermolecular reactions, and reduce the generation of coke and macromolecular by-products.

[0024] (2) Filling a gap in the industry: This invention proposes, for the first time, the use of porous materials to constrain PVC molecular chains and study the effect of pores on the reaction between PVC molecules, thereby reducing carbon yield and obtaining high-value products. Based on this theoretical research, a PVC recovery method with high carbon-hydrogen utilization (low carbon yield) is proposed for the first time.

[0025] (3) Originality: The present invention is the first method for high-conversion recovery of PVC, which solves the problems of low volatile hydrocarbon production and complex side reactions in the existing technology and has important international leading significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which constitute a part of the specification of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0027] Figure 1 Schematic diagram of the cracking reactor device.

[0028] Figure 2 SEM images and XRD curves of Example 1, (a) XRD curve of UiO-66; (b) SEM image of UiO-66; (c) SEM image of PVC-UiO-66.

[0029] Figure 3 BET of Example 1, (a) adsorption kinetics of PVC on UiO-66; (b) BET curve before and after loading; (c) pore size distribution curve before and after loading.

[0030] Figure 4 TGA thermogravimetric analysis results of Example 1, (a) thermogravimetric curves of PVC and PVC-UiO-66; (b) pyrolysis carbon yields of PVC-UiO-66 and PVC.

[0031] Figure 5 The following are the results of hydrogen NMR analysis of Example 1, the hydrogen NMR spectra of the pyrolysis products of PVC, PVC-UiO-66 and UiO-66, as well as deuterated chloroform and tert-butyl chloride. DETAILED DESCRIPTION

[0032] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0033] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations and / or combinations thereof.

[0034] The present invention relates to a method for recovering highly volatile hydrocarbons by catalytic decomposition of polyvinyl chloride (PVC) based on MOFs with high selectivity and yield. The specific structure includes the following components: Metal-organic frameworks (MOFs) are a class of porous crystalline materials formed by the self-assembly of metal ions or metal clusters with organic ligands through coordination bonds. MOFs possess high surface area, tunable pore structures, and functionalized pore surfaces, offering broad potential for applications in gas adsorption, catalysis, separation, and drug delivery. Key features include: High surface area: MOFs typically have surface areas of thousands of square meters per gram, far exceeding those of traditional porous materials such as zeolites and activated carbon; tunable pore structure: The pore size, shape, and functionality of MOFs can be precisely controlled by selecting different metal ions and organic ligands; functionalized pores: The pore surfaces of MOFs can be modified by introducing functional groups, enabling selective adsorption and catalysis of specific molecules or reactions; and excellent thermal and chemical stability: Some MOFs, such as the UiO series, exhibit exceptional stability at high temperatures and in chemical environments. Typical MOF materials include UiO-66, ZIF-8, MIL-101, and HKUST-1. Among them, UiO-66 is a classic zirconium-based MOF material composed of zirconium ions (Zr 6+ ) is formed by coordination bonds with terephthalic acid ligands. UiO-66 has a highly ordered three-dimensional pore structure and exhibits excellent thermal and chemical stability. It is widely used in catalysis, gas adsorption and separation. Structural characteristics of UiO-66: (1) High specific surface area: The specific surface area of ​​UiO-66 is usually between 1000-1500 m² / g, which can provide a large number of active sites. (2) Excellent stability: UiO-66 can still maintain structural stability at high temperatures (up to 500°C) and in acidic environments, making it suitable for applications under harsh conditions. (3) Functionalizable pores: By introducing functionalized ligands (such as amino groups, nitro groups, etc.), the adsorption and catalytic properties of UiO-66 can be further regulated.

[0035] In a typical embodiment of the present invention, taking UiO-66 as an example, the method of MOF-catalyzed selective decomposition of PVC is described below.

[0036] UiO-66 is a zirconium-based MOF material that can effectively adsorb PVC molecular chains to form PVC-UiO-66 composite materials. Powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM) characterization showed that the morphology of UiO-66 did not change significantly before and after PVC adsorption, proving that PVC is mainly adsorbed inside the pores rather than just on the surface (e.g. Figure 2 PVC was loaded into the UiO-66 pores by adsorption, with a loading amount of 0.12 g / g. After loading, the specific surface area of ​​UiO-66 dropped to 666.1134 m² / g, and the total pore volume dropped to 0.3841 ml / g, proving that PVC was successfully adsorbed into the pores (as shown in Figure 2). Figure 3shown).

[0037] The technical solution of the present invention comprises the following steps: (1) PVC loading to UiO-66: PVC powder is added to a THF solution and heated with stirring until completely dissolved, yielding a transparent PVC solution. Alternatively, PVC powder is placed in a beaker and heated at 150°C until completely melted, yielding a PVC melt. Subsequently, UiO-66 is immersed in the PVC solution / melt, allowing the PVC molecular chains to enter the UiO-66 pores through liquid-phase adsorption. Centrifugal separation and drying yield a PVC-UiO-66 composite.

[0038] (2) Pyrolysis experiment: The PVC-UiO-66 composite material is added to the left flask of the cracking reactor and pyrolyzed at 280-320°C while introducing inert gas to create an isolated environment. The pyrolysis products are introduced into the absorption device on the right through the inert gas flow, and the pyrolysis products are absorbed and collected using deuterated chloroform or liquid nitrogen cold trap as the absorption device (reactor device as shown in Figure 2). Figure 1 shown).

[0039] (3) Product analysis: The cleavage products were analyzed by nuclear magnetic resonance (NMR) spectroscopy ( Figure 5 ), determine the product selectivity.

[0040] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0041] Sources: UiO-66, DUT-52 and UiO-67: Synthesis of UiO-66: ZrCl₄ (77 mg), terephthalic acid (H₂BDC) (52 mg), and benzoic acid (PTA) (61 mg) were dissolved in 6 mL of N,N-dimethylformamide (DMF), followed by the addition of 55 μL of hydrochloric acid (HCl). The mixture was transferred to an autoclave and reacted at 120°C for 48 hours. After completion of the reaction, the solid product was collected by centrifugation, washed with DMF and methanol for three days each, and finally dried to yield UiO-66.

[0042] Synthesis of DUT-52: ZrCl₄ (0.408 g) and 2,6-naphthalene dicarboxylic acid (NDC) (0.378 g) were dissolved in 100 mL of N,N-dimethylformamide (DMF), followed by the addition of 0.5 mL of hydrochloric acid (HCl). The mixture was transferred to an autoclave and reacted at 120°C for 24 hours. After completion of the reaction, the solid product was collected by centrifugation, washed with DMF and methanol for three days each, and finally dried to yield DUT-52.

[0043] (3) Synthesis of UiO-67: ZrCl4 (120 mg), 4,4'-biphenyldicarboxylic acid (BPDC) (125 mg), and benzoic acid (PTA) (1.256 g) were dissolved in 20 mL of N,N-dimethylformamide (DMF), followed by the addition of 0.36 g of hydrochloric acid (HCl). The mixed solution was transferred to an autoclave and reacted at 120°C for 48 hours. After the reaction, the solid product was collected by centrifugation, washed with DMF and methanol for three days each, and finally dried to obtain UiO-67.

[0044] Example 1 The method for decomposing PVC by using solution adsorption and UiO-66 comprises the following steps: (1) PVC loading onto UiO-66: PVC powder was added to THF solution, heated and stirred until completely dissolved to obtain a transparent PVC solution. Subsequently, UiO-66 was immersed in the PVC solution, and the PVC molecular chains were allowed to enter the UiO-66 pores by liquid phase adsorption. PVC-UiO-66 composite materials were obtained by centrifugal separation and drying ( Figure 2 ); (2) Pyrolysis experiment: PVC-UiO-66 composite material was added into the pyrolysis reactor ( Figure 1 ), pyrolysis was carried out at 320 ° C for 4 hours, while argon was introduced to create an isolated environment. The gas produced by pyrolysis was introduced into the absorption device through the flow of inert gas, and deuterated chloroform was used as an absorbent to collect the cracking products; the carbon number of the cracking products was controlled to C9-C11 hydrocarbons by the pore constraint of UiO-66, and efficient separation of the carbon number of the products was achieved. NMR product analysis showed that the conversion rate of CH elements in PVC to C9 hydrocarbons was 56%, C10 hydrocarbons was 13%, C11 hydrocarbons was 11%, the selectivity of other chain hydrocarbons was 6%, and the rest were coke or high-boiling hydrocarbons. There was no aromatic hydrocarbons such as benzene in the product, which proved that the pore constraint effect of UiO-66 effectively inhibited the carbonization reaction of PVC ( Figure 3 、 Figure 4 ), the yields of C9 and C10 hydrocarbons in the cracking products of PVC-UiO-66 increased significantly ( Figure 5 ).

[0045] Example 1, by adsorbing PVC onto UiO-66 and pyrolyzing it in an isolated environment, significantly increased the yield of C9 and C10 hydrocarbons while reducing carbon yield, enabling the recovery of high-value products. This method has significant environmental and economic value, filling a gap in the industry and representing a pioneering approach for high-conversion PVC recovery.

[0046] Example 2 This example differs from Example 1 only in that the selectivity of the decomposition reaction products is adjusted by adjusting the pore size of the MOF. In this example, DUT-52 was used to decompose PVC, as DUT-52 has a smaller pore size and higher selectivity for short chains.

[0047] DUT-52 was immersed in a PVC solution, and the PVC molecular chains were forced into the DUT-52 pores by liquid-phase adsorption. The composite material was then centrifuged and dried to obtain a PVC-DUT-52 composite. The PVC-DUT-52 sample was then placed in a pyrolysis reactor and pyrolyzed at 320°C while introducing an inert gas to create an isolated environment. The pyrolysis gases were then directed into an absorption device using a flow of inert gas, and the pyrolysis products were collected using deuterated chloroform as an absorbent. The thermal stability and carbon yield of the PVC-DUT-52 were verified by thermogravimetric analysis (TGA), and the pyrolysis products were analyzed by nuclear magnetic resonance (NMR) to determine the selectivity of high-value products. NMR analysis revealed that the conversion of CH elements in the PVC to coke was approximately 15% when PVC-DUT-52 was used to catalyze the decomposition of PVC. The yield of C8 hydrocarbons in the PVC-DUT-52 pyrolysis products increased significantly, reaching 43% for C8 hydrocarbons and 32% for C9 hydrocarbons.

[0048] Example 3 The only difference between this embodiment and embodiment 1 is that UiO-67 is used to decompose PVC. The pore size of UiO-67 is about 1 nm, which is larger. Specifically: PVC molecular chains were forced into the pores of UiO-67 through melt adsorption, and then the PVC-UiO-67 composite material was obtained through centrifugal separation and drying. The PVC-UiO-67 sample was added to a cracking reactor and pyrolyzed at 320°C while introducing an inert gas to create an isolated environment. The gases produced by the pyrolysis were introduced into an absorption device through the inert gas flow, and the cracking products were collected using a liquid nitrogen cold trap. The thermal stability and carbon yield of PVC-UiO-67 were verified by thermogravimetric analysis (TGA), and the cracking products were analyzed by nuclear magnetic resonance (NMR) to determine the selectivity of high-value products. Experimental results showed an 8% carbon yield for PVC-UiO-67, demonstrating that the pore-constraining effect of UiO-67 effectively inhibited the carbonization reaction of PVC. NMR analysis revealed a significant increase in the yield of C11 hydrocarbons in the cracking products of PVC-UiO-67, and a wider carbon number distribution. Specific data are as follows: C11 hydrocarbon yield was 31%, C9 hydrocarbon yield was 12%, and C10 hydrocarbon yield was 34%. The benzene conversion rate was also increased by 16%.

[0049] Comparative Example 1 The experimental method for this comparative example was identical to that of Example 1, except that no MOF catalyst was used. Under equivalent reaction conditions, approximately 85% of the CH in the pyrolysis products of pure PVC was converted to coke, while the selectivity for other high-value products (such as benzene) was less than 20%.

[0050] Comparative Example 2 The only difference between this comparative example and Example 1 is that activated carbon material is used to decompose PVC, specifically: Activated carbon was immersed in a PVC solution, and the PVC molecular chains were forced into the pores of the activated carbon material by liquid-phase adsorption. The PVC-activated carbon composite was then obtained by centrifugation and drying. The PVC-activated carbon sample was then pyrolyzed at 320°C in a pyrolysis reactor while an inert gas was introduced to create an isolated environment. The pyrolysis gases were then directed into an absorption device using a deuterated chloroform absorbent. The thermal stability and carbon yield of the PVC-activated carbon were verified by thermogravimetric analysis (TGA), and the pyrolysis products were analyzed by nuclear magnetic resonance (NMR) to determine the selectivity of high-value products. The experimental results showed that the carbon yield of pure PVC was 36%, while that of the PVC-activated carbon was 35.8%, a decrease of 0.2%, demonstrating that the pore confinement of the activated carbon material had limited inhibitory effect on the carbonization reaction of PVC. NMR analysis revealed a significant increase in the yield of C7 and C8 hydrocarbons in the PVC-activated carbon pyrolysis products: 16.8% for C7 hydrocarbons and 14.5% for C8 hydrocarbons.

[0051] Comparative Example 3 The only difference between this comparative example and Example 1 is that random carbon material is used to load zirconium metal to decompose PVC, specifically: The random carbon material was immersed in a PVC solution, and the PVC molecular chains were forced into the pores of the random carbon material by liquid-phase adsorption. The PVC-random carbon material composite was then obtained by centrifugation and drying. The PVC-random carbon material sample was then placed in a pyrolysis reactor and pyrolyzed at 320°C while introducing an inert gas to create an isolated environment. The pyrolysis gases were then introduced into an absorption device using an inert gas flow, and the pyrolysis products were collected using deuterated chloroform as an absorbent. The thermal stability and carbon yield of the PVC-random carbon material were verified by thermogravimetric analysis (TGA), and the pyrolysis products were analyzed by nuclear magnetic resonance (NMR) to determine the selectivity of high-value products. The experimental results showed a carbon yield of 90% for the PVC-random carbon material, demonstrating that the confinement of the random carbon material and random catalytic sites alone cannot effectively inhibit the carbonization of PVC.

[0052] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. Application of porous metal-organic framework materials MOFs in the pyrolysis of PVC to obtain highly volatile hydrocarbons.

2. The use according to claim 1, characterized in that: The high specific surface area and regular pores of MOFs and the catalytic site pore structure constrain the decomposition of PVC molecules; the MOFs are UiO-66, ZIF-8, MIL-101, HKUST-1, DUT-52 and UiO-67.

3. The use according to claim 1, characterized in that: PVC was adsorbed into UiO-66 using the adsorption method of porous uniform site catalyst, and the PVC-UiO-66 composite material was pyrolyzed. The uniform pore size and catalytic site distribution of UiO-66 were achieved by the coordination polymerization of metal sites and organic ligands.

4. A method for recovering high-volatile hydrocarbons from polyvinyl chloride with a high conversion rate, characterized in that: The invention adopts the adsorption method of porous uniform site catalyst, adsorbs PVC into the catalyst, and pyrolyzes the adsorbed composite material, wherein the uniform pore size and catalytic site distribution of the catalyst are achieved by coordination polymerization of metal sites and organic ligands, and the catalyst is MOFs.

5. The method for recovering polyvinyl chloride high volatile hydrocarbons with a conversion rate as claimed in claim 4, wherein: Specific methods include: (1) PVC was adsorbed into MOFs by liquid phase adsorption method, and the adsorbed composite material was obtained by separation and drying; (2) Pyrolyzing the adsorbed composite material in an isolated environment to obtain pyrolysis products; (3) Using an absorbent to absorb and collect the cracking products, the absorbent is deuterated chloroform or a liquid nitrogen cold trap.

6. The method for recovering polyvinyl chloride high volatile hydrocarbons with a conversion rate as claimed in claim 4, wherein: The pore size of the catalyst is less than 2 nm and the pore size is uniform; the catalytic sites of the catalyst are transition metals such as Zr, Cu, Fe, and Zn.

7. The method for recovering polyvinyl chloride high volatile hydrocarbons with a conversion rate as claimed in claim 4 or 5, characterized in that: The adsorption process used is liquid phase adsorption, which includes solution adsorption and melt adsorption; The solution adsorption method used is a solvent such as THF, acetone, butanone, chloroform or DMF; The melt adsorption method used has a melting temperature of 120~200℃ and is protected by inert gas.

8. The method for recovering polyvinyl chloride high volatile hydrocarbons with a conversion rate as claimed in claim 4 or 5, characterized in that: The MOFs are UiO-66, ZIF-8, MIL-101, HKUST-1, DUT-52 or UiO-67.

9. The method for recovering polyvinyl chloride high volatile hydrocarbons with a conversion rate as claimed in claim 4 or 5, characterized in that: The pyrolysis temperature is 280-320℃.

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