A znal-f-lhd catalyst, a preparation method thereof and application thereof in degrading plastics

Abstract

The application discloses a ZnAl-F-LDH catalyst and a preparation method and application thereof in degrading plastics, and belongs to the technical field of plastic chemical recycling. The ZnAl-F-LDH catalyst with excellent photo-thermal catalytic conversion plastic PET performance is constructed by using fluorine atoms to replace part of oxygen atoms with LDH as a template. The catalyst can realize efficient catalytic conversion of PET waste plastics at a lower temperature. Compared with traditional chemical recycling technology, the method has the advantages of high catalytic efficiency, green environmental protection and the like, and the ZnAl-F-LDH catalyst is easy to mass-produce, and has broad commercial application value.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of plastic chemical recycling, and more particularly relates to a ZnAl-F-LDH catalyst, a preparation method thereof and application of the ZnAl-F-LDH catalyst in degradation of plastics. BACKGROUND

[0002] With the development of society, plastics have become an indispensable part of daily life. Due to the many advantages of plastics, such as light weight, low cost, long durability, and wide chemical use, they have been widely used in fields such as agriculture, construction, and electronics. However, the recycling of waste plastics is very difficult. Currently, the treatment methods for waste plastics can be divided into physical recycling and chemical recycling. Physical recycling mainly includes incineration, landfill, mechanical recycling, etc. However, incineration of waste plastics releases environmental pollution gases such as nitrogen oxides; landfill pollutes groundwater, occupies land resources, and makes the soil lose fertility, directly affecting human daily life; mechanical recycling consumes a large amount of manpower and material resources, and is high in cost, which is not conducive to popularization and operation. Compared with traditional plastic recycling strategies, chemical recycling can achieve efficient catalytic conversion of waste plastics.

[0003] In terms of chemical upgrading and recycling of plastic waste, various approaches such as thermal catalysis, photocatalysis, electrocatalysis, and enzyme catalysis have made significant progress. Among them, thermal catalysis technology can depolymerize waste plastics into monomers, and the monomers can be repolymerized into plastic products after purification. This recycling strategy can realize resource recycling, but the pyrolysis process of plastic waste usually requires harsh reaction conditions and expensive metal catalysts. Unlike pyrolysis, photocatalysis has received widespread attention in recent years due to its lack of high temperature and high pressure. However, low solar energy capture efficiency and recombination of photo-generated carriers limit its catalytic performance. Photothermal catalysis emerged as a technology that combines the advantages of photocatalysis and pyrolysis by synergistically utilizing thermal and light energy. Compared with energy-intensive thermal catalysis, renewable solar-driven photothermal catalysis provides a green and sustainable way to drive catalytic reactions. Therefore, photothermal catalysis can exhibit excellent catalytic performance even under mild conditions.

[0004] However, due to the introduction of thermal effects in the conversion of plastics by photothermal catalysis, the selectivity of the products is difficult to control compared to photocatalysis, and the study of the mechanism of plastic conversion under the synergistic action of light and heat is still in its infancy, which restricts the directional design and performance optimization of the catalyst. Therefore, it is of great significance to construct a photothermal catalyst with high light-heat conversion efficiency and high product selectivity. SUMMARY

[0005] The purpose of the present application is to provide a ZnAl-F-LDH catalyst, a preparation method thereof and application of the ZnAl-F-LDH catalyst in degradation of plastics, in order to solve the problems existing in the prior art and achieve efficient photothermal catalytic conversion of waste plastics.

[0006] To achieve the above object, the present application provides the following scheme:

[0007] One of the technical schemes of the present application: a preparation method of a ZnAl-F-LDH catalyst is provided, comprising the following steps:

[0008] Mixing a zinc source, an aluminum source and a fluorine source to obtain a mixed salt solution;

[0009] Mixing the mixed salt solution, a sodium hydroxide solution and a sodium carbonate solution, and reacting to obtain the ZnAl-F-LDH catalyst.

[0010] Preferably, the zinc source is zinc nitrate hexahydrate; the aluminum source is aluminum nitrate nonahydrate; and the fluorine source is sodium hexafluoroaluminate.

[0011] Preferably, the molar ratio of the fluorine source to the total metal ions in the mixed salt solution is 0.5-2:1.

[0012] Preferably, the volume ratio of the sodium hydroxide solution to the sodium carbonate solution is 1:1.

[0013] Preferably, the concentration of the sodium hydroxide solution is 0.1-1 mol / L; and the molar ratio of carbonate in the sodium carbonate solution to aluminum ions in the mixed salt solution is 0.5-2:1.

[0014] Preferably, the reaction temperature is 60-120℃, the pH value is 9-11, and the reaction time is 10-24h.

[0015] The present application uses LDH as a template, and uses fluorine atoms to replace part of the oxygen atoms to construct a ZnAl-F-LDH catalyst with excellent photo-thermal catalytic conversion of plastic PET performance. Since fluorine atoms have high electronegativity, the interaction between the catalyst and the solvent is enhanced, which makes the oxygen atoms in the solvent more electron-rich, which is conducive to the occurrence of nucleophilic addition-elimination reaction, thereby enhancing the efficiency of photo-thermal catalytic conversion of PET.

[0016] The catalyst prepared by the present application maintains the original skeleton structure characteristics of LDH, and has a sheet structure. Compared with conventional LDH, the separation efficiency of electron-hole pairs is improved, and the efficiency of photo-thermal catalytic conversion of PET is enhanced.

[0017] The second technical scheme of the present application: a ZnAl-F-LDH catalyst prepared according to the above preparation method is provided.

[0018] The third technical scheme of the present application: the above ZnAl-F-LDH catalyst is applied in photo-thermal catalytic conversion of plastics.

[0019] Preferably, the plastic includes PET waste plastic.

[0020] The fourth aspect of the present application provides a method for photo-thermal catalytic conversion of plastics, comprising the following steps:

[0021] After mixing the ZnAl-F-LDH catalyst, the plastic and the ethylene glycol, the photo-thermal catalytic reaction is carried out, and the photo-thermal catalytic conversion of the plastic is completed.

[0022] Preferably, the amount of the ZnAl-F-LDH catalyst added is 0-100% of the mass of the plastic, excluding 0; the photo-catalytic reaction includes: using a 0-300w xenon lamp as a light source, excluding 0, controlling the temperature of the photo-thermal catalytic reaction to be 130-170℃, and the time to be 1-6h.

[0023] The present application discloses the following technical effects:

[0024] In order to design and develop a photo-thermal catalyst with high performance, stable structure and low cost for efficient and high-selectivity chemical recycling of plastics, the present application constructs a fluorine-substituted ZnAl-F-LDH photo-thermal catalyst based on a ZnAl-LDH template, and uses the catalyst for efficient catalytic conversion of PET waste plastics to generate BHET.

[0025] Compared with the simple ZnAl-LDH catalyst, the photo-thermal catalyst constructed in the present application improves the electron-hole separation ability. Moreover, the fluorine atom has high electronegativity, which enhances the interaction between the catalyst and the solvent, promotes the electron-rich of the oxygen atom in the solvent, and is beneficial to the occurrence of the nucleophilic addition-elimination reaction, thereby enhancing the efficiency of the photo-thermal catalytic conversion of PET. In addition, the photo-thermal catalyst prepared in the present application can realize efficient catalytic conversion of PET waste plastics, compared with the traditional chemical recycling technology, has the advantages of simple operation, low price, high catalytic efficiency, green environmental protection, etc., is easy to mass produce, and shows broad commercial application value. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 X-ray diffraction pattern of the ZnAl-F-LDH catalyst prepared in Example 1;

[0027] Figure 2 X-ray diffraction pattern of the ZnAl-LDH catalyst prepared in Comparative Example 1;

[0028] Figure 3 Scanning electron microscope image of the ZnAl-F-LDH catalyst prepared in Example 1;

[0029] Figure 4 Scanning electron microscope image of the ZnAl-LDH catalyst prepared in Comparative Example 1;

[0030] Figure 5This is a scanning electron microscope energy spectrum of the ZnAl-F-LDH catalyst prepared in Example 1;

[0031] Figure 6 This is a photoelectrochemical test diagram of the ZnAl-F-LDH catalyst prepared in Example 1;

[0032] Figure 7 This is a photoelectrochemical test diagram of the ZnAl-LDH catalyst prepared in Comparative Example 1;

[0033] Figure 8 This is the infrared spectrum of the ZnAl-F-LDH catalyst prepared in Example 1;

[0034] Figure 9 This is the infrared spectrum of the ZnAl-LDH catalyst prepared in Comparative Example 1;

[0035] Figure 10 This is the infrared spectrum of the photothermal catalytic product BHET of the ZnAl-F-LDH catalyst prepared in Example 1;

[0036] Figure 11 This is the infrared spectrum of the photothermal catalytic product BHET of the ZnAl-LDH catalyst prepared in Comparative Example 1;

[0037] Figure 12 This is the nuclear magnetic resonance spectrum of the photothermal catalytic product BHET of the ZnAl-F-LDH catalyst prepared in Example 1;

[0038] Figure 13 This is the nuclear magnetic resonance spectrum of the photothermal catalytic product BHET of the ZnAl-LDH catalyst prepared in Comparative Example 1;

[0039] Figure 14 This is a graph showing the photothermal catalytic conversion performance of ZnAl-F-LDH catalyst prepared in Example 1 for PET waste plastics at different temperatures;

[0040] Figure 15 This is a graph showing the photothermal catalytic conversion performance of ZnAl-F-LDH catalyst prepared in Example 1 for PET waste plastics at different times;

[0041] Figure 16 This is a graph showing the photothermal catalytic conversion performance of ZnAl-LDH catalyst prepared in Comparative Example 1 for PET waste plastics at different times;

[0042] Figure 17 The catalytic conversion effect of the ZnAl-F-LDH catalyst prepared in Example 1 on different PET waste plastics. DETAILED DESCRIPTION

[0043] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0044] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0045] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0046] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0047] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0048] It should be pointed out that the matters not described in detail in the present invention are conventional operating means in this field and are not the focus of the present invention.

[0049] Unless otherwise specified, the raw materials used in the following examples and comparative examples of the present invention are all commercially available products, and the sources of the commercially available products do not affect the technical effects of the present invention.

[0050] Example 1

[0051] Preparation of ZnAl-F-LDH catalyst:

[0052] Weigh 5.95g of zinc nitrate hexahydrate, 1.875g of aluminum nitrate nonahydrate and 1.049g of sodium hexafluoroaluminate and dissolve them in 100mL of deionized water (Zn in the mixed solution is 0.01%). 2+ and Al 3+The molar ratio of the mixture is 2:1), and the solution is mixed uniformly by ultrasonic shaking; 100 mL of 0.1 mol / L sodium hydroxide aqueous solution is prepared; 100 mL of sodium carbonate aqueous solution is prepared; the mixed salt solution and sodium hydroxide solution are simultaneously dropped into the sodium carbonate solution (CO3 2- and Al 3+ The molar ratio of the two catalysts was 0.5:1, and the pH value of the obtained mixed solution was controlled to be 10. ZnAl-F-LDH was synthesized by a co-precipitation method, wherein the reaction conditions were controlled at 80°C and the constant temperature was maintained for 12 hours. Finally, the obtained precipitate was washed with deionized water and dried at 60°C for 12 hours to obtain a ZnAl-F-LDH catalyst.

[0053] Figure 1 The X-ray diffraction pattern of the ZnAl-F-LDH catalyst prepared in Example 1;

[0054] Figure 3 This is a scanning electron microscope image of the ZnAl-F-LDH catalyst prepared in Example 1;

[0055] Figure 5 This is a scanning electron microscope energy spectrum of the ZnAl-F-LDH catalyst prepared in Example 1;

[0056] Figure 6 This is a photoelectric test image of the ZnAl-F-LDH catalyst prepared in Example 1;

[0057] Figure 8 This is the infrared spectrum of the ZnAl-F-LDH catalyst prepared in Example 1.

[0058] Depend on Figure 3 It can be seen that the ZnAl-F-LDH catalyst prepared in Example 1 maintains the original skeleton structure characteristics of LDH and presents a sheet-like structure. Figure 5 It can be seen that the present invention uses LDH as a template and utilizes fluorine atoms to replace some oxygen atoms to construct a ZnAl-F-LDH catalyst.

[0059] The process of photothermal degradation of PET waste plastics to produce BHET (bis(hydroxyethyl) terephthalate)) using ZnAl-F-LDH catalyst is as follows:

[0060] The prepared ZnAl-F-LDH catalyst (0.5 g) and commercial PET plastic (5 g) were mixed evenly and placed in 30 mL of ethylene glycol. The reaction temperature was controlled at 160°C, and a 300 W xenon lamp was used as the light source for the photothermal catalytic experiment. A photothermal catalytic conversion experiment was carried out. After 6 hours, the product was collected and the results were analyzed using infrared and nuclear magnetic resonance spectroscopy.

[0061] Figure 10The infrared spectrum of the photo-thermal catalytic product BHET of the ZnAl-F-LDH catalyst prepared in Example 1;

[0062] Figure 12 The nuclear magnetic resonance spectrum of the photo-thermal catalytic product BHET of the ZnAl-F-LDH catalyst prepared in Example 1.

[0063] It can be seen from Figure 10 and Figure 12 that the ZnAl-F-LDH catalyst prepared in Example 1 can convert PET plastic into high-purity BHET.

[0064] Verify the conversion performance of the prepared ZnAl-F-LDH catalyst for photo-thermal catalytic conversion of PET waste plastic at different temperatures:

[0065] The prepared ZnAl-F-LDH catalyst (0.5 g) and commercial PET plastic (5 g) were mixed uniformly and placed in 30 mL of ethylene glycol, and the reaction temperature was controlled at 130℃, 140℃, 150℃, 160℃ and 170℃, respectively, and a 300W xenon lamp was used as the light source for photo-thermal catalytic experiment. The photo-thermal catalytic conversion experiment was carried out for 6h; the conversion rate of commercial PET waste plastic was analyzed, and the results are shown in Figure 14 .

[0066] Figure 14 The conversion performance of the ZnAl-F-LDH catalyst prepared in Example 1 for photo-thermal catalytic conversion of PET waste plastic at different temperatures.

[0067] Verify the conversion performance of the prepared ZnAl-F-LDH catalyst for photo-thermal catalytic conversion of PET waste plastic at different times:

[0068] The prepared ZnAl-F-LDH catalyst (0.5 g) and commercial PET plastic (5 g) were mixed uniformly and placed in 30 mL of ethylene glycol, and the reaction temperature was controlled at 160℃, and a 300W xenon lamp was used as the light source for photo-thermal catalytic experiment. The photo-thermal catalytic conversion experiment was carried out for 1h, 2h, 3h, 4h, 5h and 6h, respectively; the conversion rate of commercial PET waste plastic was analyzed, and the results are shown in Figure 15 .

[0069] Figure 15 The conversion performance of the ZnAl-F-LDH catalyst prepared in Example 1 for photo-thermal catalytic conversion of PET waste plastic at different times.

[0070] It can be seen from Figure 14 and Figure 15 that the ZnAl-F-LDH catalyst prepared in Example 1 can convert PET plastic into high-purity BHET.

[0071] Comparative Example 1

[0072] Preparation of ZnAl-LDH catalyst:

[0073] Weigh 5.95 g of zinc nitrate hexahydrate and 3.82 g of aluminum nitrate nonahydrate into 100 mL of deionized water (the molar ratio of Zn 2+ and Al 3+ in the mixed solution is 2:1), mix the solution uniformly by ultrasonic agitation; prepare 100 mL of 0.1 mol / L sodium hydroxide aqueous solution; prepare 100 mL of sodium carbonate aqueous solution; simultaneously drop the mixed salt solution and the sodium hydroxide solution into the sodium carbonate solution (the molar ratio of CO3 2- and Al 3+ in the mixed solution is 0.5:1), and control the pH value of the obtained mixed solution to be 10, and use the coprecipitation method to synthesize and prepare ZnAl-LDH, wherein the reaction condition is controlled at 80°C, and the constant temperature is 12 h; finally, wash the obtained precipitate with deionized water and dry it at 60°C for 12 h to obtain the ZnAl-LDH catalyst.

[0074] Figure 2 X-ray diffraction pattern of the ZnAl-LDH catalyst prepared in Comparative Example 1;

[0075] Figure 4 Scanning electron microscope image of the ZnAl-LDH catalyst prepared in Comparative Example 1;

[0076] Figure 7 Photoelectric test image of the ZnAl-LDH catalyst prepared in Comparative Example 1;

[0077] Figure 9 Infrared spectrum of the ZnAl-LDH catalyst prepared in Comparative Example 1.

[0078] The process of the photo-thermal catalytic degradation of PET waste plastics to generate BHET (bis-hydroxyethyl terephthalate) by the ZnAl-LDH catalyst is as follows:

[0079] Mix the prepared ZnAl-LDH catalyst (0.5 g) and commercial PET plastic (5 g) uniformly and place them in 30 mL of ethylene glycol, control the reaction temperature to be 160°C, use a 300 W xenon lamp as the light source for the photo-thermal catalytic experiment, and perform the photo-thermal catalytic conversion experiment; collect the product, and use infrared and nuclear magnetic resonance spectrum analysis results.

[0080] Figure 11 Infrared spectrum of the photo-thermal catalytic product BHET of the ZnAl-LDH catalyst prepared in Comparative Example 1;

[0081] Figure 13This is the nuclear magnetic resonance spectrum of the photothermal catalytic product BHET of the ZnAl-LDH catalyst prepared in Comparative Example 1.

[0082] Verify the photothermal catalytic conversion performance of PET waste plastics prepared by ZnAl-LDH catalyst at different times:

[0083] The prepared ZnAl-LDH catalyst (0.5 g) and commercial PET plastic (5 g) were mixed evenly and placed in 30 mL of ethylene glycol. The reaction temperature was controlled at 160 ° C. A 300 W xenon lamp was used as the light source for the photothermal catalytic experiment. The photothermal catalytic conversion experiments were carried out for 1 h, 2 h, 3 h, 4 h, 5 h and 6 h respectively. The conversion rate of commercial PET waste plastic was analyzed. The results are as follows: Figure 15 shown.

[0084] Figure 16 This is a diagram showing the photothermal catalytic conversion performance of ZnAl-LDH catalyst prepared in Comparative Example 1 for PET waste plastics at different times.

[0085] contrast Figure 15 and Figure 16 The data show that the conversion effect of the ZnAl-F-LDH catalyst prepared in Example 1 on commercial PET plastics is significantly better than that in Comparative Example 1.

[0086] Figure 17 This is the conversion effect of the ZnAl-F-LDH catalyst prepared in Example 1 on PET plastics in daily life.

[0087] Depend on Figure 17 It can be seen that the ZnAl-F-LDH catalyst prepared in Example 1 can realize the catalytic conversion of waste plastics generated in real life, and achieve efficient catalytic conversion of PET waste plastics within 6 hours.

[0088] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0089] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A process for the preparation of a ZnAl-F-LDH catalyst, characterized in that, The method comprises the following steps: mixing a zinc source, an aluminum source and a fluorine source to obtain a mixed salt solution; mixing the mixed salt solution, a sodium hydroxide solution and a sodium carbonate solution, and reacting to obtain the ZnAl-F-LDH catalyst; the zinc source is zinc nitrate hexahydrate; the aluminum source is aluminum nitrate nonahydrate; and the fluorine source is sodium hexafluoroaluminate; the molar ratio of the fluorine source to the total metal ions in the mixed salt solution is 0.5-2:1; the volume ratio of the sodium hydroxide solution to the sodium carbonate solution is 1:1; the concentration of the sodium hydroxide solution is 0.1-1 mol / L; and the molar ratio of carbonate in the sodium carbonate solution to aluminum ions in the mixed salt solution is 0.5-2:1; the reaction temperature is 60-120℃, the pH value is 9-11, and the reaction time is 10-24 h. 2.A ZnAl-F-LDH catalyst prepared by the preparation method in claim 1. 3.Use of the ZnAl-F-LDH catalyst in claim 2 in the photo-thermal catalytic conversion of plastics.

4. A method of photo-thermal catalytic degradation of plastics, characterized by, The method comprises the following steps: mixing the ZnAl-F-LDH catalyst in claim 2, plastics and a solvent, and then performing a photo-thermal catalytic reaction to complete the photo-thermal catalytic conversion of the plastics.

5. The method of claim 4, wherein, The amount of the ZnAl-F-LDH catalyst added is 0-100% of the mass of the plastics, and 0 is not included; the photo-thermal catalytic reaction comprises: using a 0-300-w xenon lamp as a light source, 0 is not included, controlling the temperature of the photo-thermal catalytic reaction to be 130-170℃, and controlling the time of the photo-thermal catalytic reaction to be 1-6 h.

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