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 present application relates to the technical field of polymer material recycling, and particularly relates to a PVC high volatile hydrocarbon conversion rate recycling method. BACKGROUND

[0002] The information disclosed in this Background section is for the purpose of providing an overall understanding of the application and is not intended to be taken as an acknowledgement or any form of suggestion that this information forms part of the prior art.

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

[0004] The unsolved reasons include: existing catalytic technology cannot regulate the important role of polymer chains in the reaction, making it difficult to inhibit intermolecular reactions. The cascade upgrading and recycling of PVC plastics requires selective conversion into certain organic intermediates, but the selectivity and yield of this process are difficult to control, making it difficult to establish the basis for upgrading and recycling.

[0005] The polyacetylene structure generated after PVC dechlorination has extremely high reactivity and is prone to cross-linking and carbonization, resulting in serious carbon deposition problems. It is necessary to use porous and high specific surface area materials to effectively constrain the PVC molecular chain to inhibit intermolecular reactions and reduce carbon yield. SUMMARY

[0006] The purpose of the present application is to provide a PVC high volatile hydrocarbon conversion rate recycling method based on porous metal organic framework material MOFs, which adsorbs PVC into MOF or on the surface and pyrolyzes in an isolated environment, solving the following problems in the prior art: (1) Too many side reactions: By constraining the degrees of freedom of PVC molecular chains, intermolecular reactions are inhibited, and the generation of coke and macromolecular byproducts is reduced. (2) Low volatile hydrocarbon yield: Optimizing the reaction conditions significantly improves the conversion rate of volatile hydrocarbons, providing a basis for the upgrading and recycling of PVC. In summary, the present application aims to provide an efficient and environmentally friendly PVC recycling method, solving the problem of high carbon yield in traditional methods, and providing a chemical path from PVC to volatile hydrocarbons, making downstream chemical conversion possible, which has important environmental and economic value.

[0007] The technical solutions adopted by the present application are as follows: In the first aspect of the present application, the application of a porous metal organic framework material (MOFs) in obtaining high volatile hydrocarbons from pyrolysis of PVC is provided.

[0008] In one or some embodiments of the present application, the high specific surface area and regular pore channel of the MOFs and the constraint effect of the pore channel structure of the catalytic sites on 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 application, the adsorption method of the porous uniform site catalyst is used to adsorb PVC into UiO-66, and the pyrolysis of the PVC-UiO-66 composite material is performed, wherein the uniform pore size and the distribution of the catalytic sites of the UiO-66 are realized by the coordination polymerization of the metal sites and the organic ligand.

[0011] In the second aspect of the present application, a method for recovering high volatile hydrocarbons of PVC is provided, the adsorption method of the porous uniform site catalyst is used to adsorb PVC into MOFs, and the pyrolysis of the adsorbed composite material is performed, wherein the uniform pore size and the distribution of the catalytic sites of the catalyst are realized by the coordination polymerization of the metal sites and the organic ligand, and the catalyst is MOFs.

[0012] In one or some embodiments of the present application, the specific method comprises: (1) The adsorption method of liquid phase is used to adsorb PVC into MOFs, and through separation and drying treatment, the adsorbed composite material is obtained; (2) The pyrolysis of the adsorbed composite material is performed in an isolated environment to obtain a cracking product.

[0013] Further, after step (2), step (3) is further included, and the cracking product is collected by using an absorbent. The absorbent is deuterated chloroform or a liquid nitrogen cold trap. The present application uses deuterated chloroform or a liquid nitrogen cold trap as an absorbent to perform high-efficiency separation and recovery on the cracking product.

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

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

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

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

[0018] Preferably, the solution adsorption method used employs THF, acetone, butanone, chloroform, DMF or other organic solvents as the solvent.

[0019] Preferably, the melt adsorption method used has a melting temperature of 120-200°C and is protected by inert gas. In one or some embodiments of the present application, the MOFs are UiO-66, ZIF-8, MIL-101, HKUST-1, DUT-52 or UiO-67.

[0020] Further preferably, the MOFs are UiO-66.

[0021] In one or some embodiments of the present application, the pyrolysis temperature is 280-320°C.

[0022] Compared with the related art known to the present inventors, one technical solution of the present application has the following beneficial effects: (1) The regular porous material structure constrains the PVC molecular chains: the porous metal organic framework material is used to effectively constrain the PVC molecular chains, limit their degrees of freedom, suppress intermolecular reactions and reduce the generation of coke and large molecular byproducts.

[0023] (2) Filling the gap in the industry: the present application first proposes to constrain the PVC molecular chains by porous materials, studies the effect of the pores on the intermolecular reactions of PVC, thereby reducing the carbon yield and obtaining high-value products. Based on the above theoretical research, the present application first proposes a PVC recycling method with high carbon hydrogen utilization rate (low carbon yield).

[0024] (3) Originality: the present application is the first method for high-conversion-rate recycling of PVC, solves the problems of low yield of volatile hydrocarbons and complex side reactions in the prior art, and has important international leading significance. BRIEF DESCRIPTION OF DRAWINGS

[0025] The accompanying drawings, which form a part of the present application, are used to provide further understanding of the present application, and the illustrative embodiments of the present application and their description serve to explain the present application, and do not constitute an improper limitation of the present application.

[0026] Figure 1 It is a schematic diagram of the pyrolysis reactor device.

[0027] Figure 2For 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.

[0028] Figure 3 For BET of Example 1, (a) adsorption kinetics of PVC on UiO-66; (b) BET curves before and after loading; (c) pore size distribution curves before and after loading.

[0029] Figure 4 For TGA thermogravimetric analysis results of Example 1, (a) thermogravimetric curves of PVC and PVC-UiO-66; (b) pyrolysis carbon yield of PVC-UiO-66 and PVC.

[0030] Figure 5 For NMR nuclear magnetic hydrogen spectrum analysis results of Example 1, nuclear magnetic resonance hydrogen spectrum of PVC, PVC-UiO-66 and UiO-66 pyrolysis products and deuterated chloroform and tert-butyl chloride. DETAILED DESCRIPTION

[0031] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0032] It is also to be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0033] The present application relates to a MOFs-based recovery method for the preparation of high volatile hydrocarbons with high selectivity and yield by catalytic decomposition of PVC (polyvinyl chloride), and the specific structure comprises the following components: Metal-Organic Frameworks (MOFs) are a class of porous crystalline materials formed by the self-assembly of metal ions or clusters with organic ligands through coordination bonds. MOFs have high specific surface area, adjustable pore structure, and functionalized pore surfaces, thus have wide application potential in gas adsorption, catalysis, separation, drug delivery, etc. Characteristics: High specific surface area: The specific surface area of MOFs is usually up to thousands of square meters per gram, far exceeding traditional porous materials (such as zeolites and activated carbon); adjustable pore structure: by selecting different metal ions and organic ligands, the pore size, shape and function of MOFs can be precisely controlled; functionalized pores: the pore surface of MOFs can be modified by introducing functional groups, thus realizing selective adsorption and catalysis of specific molecules or reactions; good thermal and chemical stability: some MOFs (such as UiO series) exhibit excellent stability at high temperature and in chemical environment. Typical MOF materials include UiO-66, ZIF-8, MIL-101 and HKUST-1. Among them, UiO-66 is a classic zirconium-based MOF material formed by zirconium ions (Zr 6+ ) and terephthalic acid ligands through coordination bonds. UiO-66 has a highly ordered three-dimensional pore structure, exhibits excellent thermal and chemical stability, and is widely used in catalysis, gas adsorption and separation, etc. 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 maintain structural stability at high temperature (up to 500°C) and in acidic environment, suitable for applications under harsh conditions; (3) functionalizable pores: by introducing functional ligands (such as amino, nitro, etc.), the adsorption and catalytic properties of UiO-66 can be further regulated.

[0034] In a typical embodiment of the present application, taking UiO-66 as an example, the method of MOF catalytic selective decomposition of PVC is described as follows.

[0035] UiO-66 is a zirconium-based MOF material that can effectively adsorb PVC molecular chains to form PVC-UiO-66 composite materials. Characterized by powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM), the morphology of UiO-66 does not change significantly before and after adsorbing PVC, proving that PVC is mainly adsorbed in the pores rather than just on the surface (as shown in Figure 2 ). PVC is loaded into the pores of UiO-66 by adsorption method, with a loading capacity of 0.12 g / g. After loading, the specific surface area of UiO-66 decreases to 666.1134 m² / g, and the total pore volume decreases to 0.3841 ml / g, proving that PVC is successfully adsorbed in the pores (as shown in Figure 3as shown).

[0036] The technical solution of the present application comprises the following steps: (1) PVC loading to UiO-66: PVC powder was added into THF solution, heated and stirred until completely dissolved, obtaining a transparent PVC solution. Alternatively, PVC powder was placed in a beaker and heated to complete melting at 150℃, obtaining a PVC melt. Subsequently, UiO-66 was immersed in the PVC solution / melt, and the PVC molecular chain was introduced into the UiO-66 pore by liquid phase adsorption method. By centrifugal separation and drying treatment, PVC-UiO-66 composite material was obtained.

[0037] (2) Pyrolysis experiment: PVC-UiO-66 composite material was added to the left flask of the pyrolysis reactor, and pyrolysis was carried out at 280-320℃, while inert gas was introduced to create an isolated environment. The pyrolysis products were introduced into the right absorption device by inert gas flow, and deuterated chloroform or liquid nitrogen cold trap was used as the absorption device to absorb and collect the pyrolysis products (reactor device as shown in Figure 1 ).

[0038] (3) Product analysis: The selectivity of the product was determined by nuclear magnetic resonance (NMR) analysis of the pyrolysis products (as shown in Figure 5 ).

[0039] In order to enable those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below in conjunction with specific examples.

[0040] Material source: 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), and then 55 μL of hydrochloric acid (HCl) was added. The mixed solution was transferred to a high-pressure reaction kettle and reacted at 120℃ for 48 hours. After the reaction was completed, the solid product was collected by centrifugal separation, and washed with DMF and methanol for three days, and finally dried to obtain UiO-66.

[0041] 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.

[0042] (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.

[0043] 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 ).

[0044] Example 1 significantly improves the yield of C9 and C10 hydrocarbons and reduces carbon yield by adsorbing PVC into UiO-66 and pyrolyzing in an isolated environment, achieving the recovery of high-value products. This method has important environmental and economic value, fills the gap in the industry, and is the first method for high-conversion recovery of PVC.

[0045] Example 2 The difference between this example and Example 1 is only that the selectivity of the decomposition reaction products is adjusted by adjusting the pore size of the MOF. In this example, DUT-52 is used to decompose PVC, and DUT-52 has a smaller pore size and higher selectivity for short chains.

[0046] DUT-52 is immersed in a PVC solution, and the PVC molecular chain is introduced into the DUT-52 channel through liquid-phase adsorption, followed by centrifugal separation and drying treatment to obtain a PVC-DUT-52 composite material; the PVC-DUT-52 sample is added to a pyrolysis reactor, and pyrolysis is carried out at 320°C while introducing inert gas to create an isolated environment, and the gas produced by pyrolysis is introduced into an absorption device through inert gas flow, and deuterated chloroform is used as an absorbent to collect the cracking products; the thermal stability and carbon yield of PVC-DUT-52 are verified by thermogravimetric analysis (TGA), and the cracking products are analyzed by nuclear magnetic resonance (NMR) to determine the selectivity of high-value products. Through NMR analysis, it is found that when PVC-DUT-52 is used to catalyze the decomposition of PVC, the conversion rate of CH elements in PVC to coke is about 15%, and the yield of C8 hydrocarbons in PVC-DUT-52 cracking products is significantly increased, with the following specific data: C8 hydrocarbon yield is 43%, and C9 hydrocarbon yield is 32%.

[0047] Example 3 The difference between this example and Example 1 is only that UiO-67 is used to decompose PVC, and UiO-67 has a pore size of about 1 nm, which is larger. Specifically: PVC-UiO-67 composite material was obtained by immersing PVC in a solution of UiO-67, followed by centrifugation and drying. The PVC-UiO-67 sample was added to a pyrolysis reactor and pyrolysis was performed at 320°C with the introduction of inert gas to create an isolated environment. The gases produced by pyrolysis were introduced into an absorption device through the flow of inert gas, and the pyrolysis 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 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 PVC-UiO-67 was 8%, indicating that the pore constraint effect of UiO-67 effectively inhibited the carbonization reaction of PVC. Through NMR analysis, the yield of C11 hydrocarbons in the pyrolysis products of PVC-UiO-67 increased significantly, and the carbon number distribution of the products was wider. The specific data are as follows: the yield of C11 hydrocarbons was 31%, the yield of C9 hydrocarbons was 12%, and the yield of C10 hydrocarbons was 34%; the conversion of benzene increased to 16%.

[0048] Comparative Example 1 The experimental method of this comparative example is the same as that of Example 1, except that no MOF catalyst is used. Under the same reaction equivalent, about 85% of CH in the pyrolysis products of pure PVC is converted into coke, and the selectivity of other high-value products (such as benzene) is less than 20%.

[0049] Comparative Example 2 The only difference between this comparative example and Example 1 is that activated carbon material is used to decompose PVC, specifically: The PVC-activated carbon composite material was obtained by immersing activated carbon material in a PVC solution, followed by centrifugation and drying. The PVC-activated carbon sample was added to a pyrolysis reactor and pyrolysis was performed at 320°C with the introduction of inert gas to create an isolated environment. The gases produced by pyrolysis were introduced into an absorption device through the flow of inert gas, and deuterated chloroform was used as an absorbent to collect the pyrolysis products. The thermal stability and carbon yield of 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 the carbon yield of PVC-activated carbon was 35.8%, a decrease of 0.2%, indicating that the pore constraint effect of activated carbon material had limited inhibition effect on the carbonization reaction of PVC. Through NMR analysis, the yield of C7 and C8 hydrocarbons in the pyrolysis products of PVC-activated carbon increased significantly, and the specific data are as follows: the yield of C7 hydrocarbons was 16.8%, and the yield of C8 hydrocarbons was 14.5%.

[0050] Comparative Example 3 The only difference between this comparative example and Example 1 is that a random carbon material is used to support zirconium metal to decompose PVC, specifically: The random carbon material is immersed in a PVC solution, and the PVC molecular chains enter the pore channels of the random carbon material through liquid phase adsorption, followed by centrifugal separation and drying treatment to obtain a PVC-random carbon material composite. The PVC-random carbon material sample is added to a decomposition reactor, pyrolysis is carried out at 320°C, and inert gas is introduced to create an isolated environment. The gas produced by pyrolysis is introduced into an absorption device through the flow of inert gas, and deuterated chloroform is used as an absorbent to collect the decomposition products. The thermal stability of the PVC-random carbon material and the carbon yield are verified by thermogravimetric analysis (TGA), and the decomposition products are analyzed by nuclear magnetic resonance (NMR) to determine the selectivity of high-value products. The experimental results show that the carbon yield of the PVC-random carbon material is 90%, which proves that the constraining effect of the random carbon material and the random catalytic site alone cannot effectively inhibit the carbonization reaction of PVC.

[0051] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited by the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application should be equivalent replacement methods, and are all included in the protection scope of the present application.

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: PVC is adsorbed into MOFs 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 between 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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