Method for catalytically converting plastic into carboxylic acid

Abstract

The invention belongs to the technical field of catalytic oxidation of plastics, and discloses a method for catalytically converting plastics into carboxylic acid. The method comprises the following steps: uniformly dispersing a metal oxide, which is prepared by a dipping drying reduction method and is loaded with metal atoms on the surface, as a catalyst and to-be-treated plastic in water to obtain a mixed solution; carrying out a hydrothermal reaction on the mixed solution in an air atmosphere at 100-150 DEG C so as to convert the to-be-treated plastic into a carboxylic acid product; in the catalyst, the metal oxide is one or more of CeO2, TiO2, SiO2, ZnO, ZrO2 and Al2O3; the metal atoms are one or two of Ni, Cu, Fe, Ru, Ir, Pd and Pt. According to the invention, the plastic can be catalytically converted into the carboxylic acid product without depending on hydrogen; the reaction conditions are milder and more environmentally friendly, the reaction time is shorter, the cost is low, and popularization and large-scale use are facilitated.

Description

Technical Field

[0001] The invention relates to the technical field of catalytic oxidation of plastics, in particular to a method for catalytically converting plastics into carboxylic acid. Background Art

[0002] Plastics have profoundly impacted human life. However, most discarded plastics are disposed of directly in landfills or incineration, which poses a serious threat to the ecological environment and health. This challenge has prompted research on chemical upcycling of plastics into value-added products, which has become a new vision for plastic application and recycling.

[0003] To improve the recycling conversion rate of plastics, heterogeneous catalytic processes have been proposed as a potential strategy to effectively convert plastics into fuels, chemicals, monomers, etc.

[0004] Polyethylene, whose full English name is Polyethylene, is abbreviated as PE. PE has high stability and accounts for the largest proportion of waste plastics. In the existing technology, the catalytic hydrogenolysis process is currently mainly used to realize the recycling of plastics into value-added products, and then to achieve the disposal of waste plastics. Although the above-mentioned catalytic hydrogenolysis process can effectively convert it into low-molecular alkane products to re-enter the energy cycle, the reaction temperature of the catalytic hydrogenolysis process used in the existing technology is usually higher than 200°C, and the reaction process is highly dependent on H2 and must be carried out in a H2 atmosphere of 0.5MPa to 6MPa. At this stage, H2 mainly comes from fossil fuels, resulting in harsh processing conditions and high costs, which is not conducive to promotion for large-scale use. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method for catalytically converting plastic into carboxylic acid.

[0006] The method for catalytically converting plastic into carboxylic acid of the present invention is achieved by the following technical scheme:

[0007] A method for catalytically converting plastic into carboxylic acid comprises the following steps:

[0008] Step 1: Using a metal oxide with metal atoms loaded on its surface prepared by an impregnation drying reduction method as a catalyst, uniformly dispersing the metal oxide and the plastic to be treated in water to obtain a mixed solution.

[0009] Step 2: subjecting the mixed solution to a hydrothermal reaction at 100° C. to 150° C. in an air atmosphere to convert the plastic to be treated into a carboxylic acid product.

[0010] It should be noted that, in the catalyst used in the present invention, the metal oxide is one or more of CeO2, TiO2, SiO2, ZnO, ZrO2 and Al2O3; the metal atom is one or two of Ni, Cu, Fe, Ru, Ir, Pd and Pt.

[0011] In some preferred embodiments of the present invention, in the catalyst, the loading amount of the metal atoms is 0.5% to 2% of the mass of the catalyst.

[0012] In some preferred embodiments of the present invention, the catalyst is obtained by the following steps:

[0013] S1, uniformly dispersing the soluble metal salt corresponding to the metal atom in a solvent to obtain a soluble metal salt solution.

[0014] S2, using metal oxide as a carrier and the soluble metal salt solution as an impregnation solution, adopting an equal volume impregnation method to impregnate the metal oxide into the soluble metal salt solution so that the metal component is loaded on the surface of the metal oxide to obtain a pre-modified metal oxide.

[0015] S3, after drying the pre-modified metal oxide, performing a reduction treatment so that the soluble metal salt is converted into a metal atom form and loaded on the surface of the metal oxide, thus obtaining the catalyst.

[0016] It should be noted that the present invention can select corresponding soluble metal salts according to the actual metal atoms to be loaded to form a soluble metal salt solution. For example, in some preferred embodiments of the present invention, the soluble metal salts used can be selected from one or two of soluble Ni salts, soluble Cu salts, soluble Fe salts, soluble Ru salts, soluble Ir salts, soluble Pd salts and soluble Pt salts. Among them, it should be emphasized that when preparing the soluble metal salt solution, according to the actual mass of the added metal oxide, the corresponding mass of the soluble metal salt is added, only so that the loading amount of metal atoms in the finally formed catalyst is 0.5% to 2% of the mass of the overall catalyst.

[0017] When preparing the catalyst in the present invention, the specific type of solvent used in S1 is not limited, as long as the solvent used has good solubility for the soluble metal salt and good dispersibility for the metal oxide used, so as to ensure that the metal component can be loaded on the surface of the metal oxide in the solvent used. For example, in a preferred embodiment of the present invention, water is preferably used as the solvent in consideration of economic cost.

[0018] In some preferred embodiments of the present invention, when the metal oxide is impregnated in the soluble metal salt solution, the immersion temperature is room temperature and the immersion time is 12 hours to 36 hours, so that the metal salt components in the soluble metal salt solution can be evenly loaded on the surface of the metal oxide, so that through subsequent treatment, the metal atoms are evenly loaded on the surface of the metal oxide.

[0019] In some preferred embodiments of the present invention, in the above S3, the treatment atmosphere of the reduction treatment is H2 atmosphere, the reduction temperature is 220°C to 280°C, and the reduction time is 2h to 4h, so as to convert the soluble metal salt into metal atomic form through reduction treatment.

[0020] In some preferred embodiments of the present invention, the hydrothermal reaction time is 4 h to 36 h.

[0021] In some preferred embodiments of the present invention, the plastic to be disposed of is high-density polyethylene.

[0022] In some preferred embodiments of the present invention, the mass ratio of the plastic to be treated to the catalyst is 1 to 3:1.

[0023] In some preferred embodiments of the present invention, the pressure of the air is 0.5 MPa to 2 MPa.

[0024] In some preferred embodiments of the present invention, the carboxylic acid product is a long-chain monoacid or a long-chain dicarboxylic acid.

[0025] In some preferred embodiments of the present invention, post-processing is also included, and the post-processing is carried out by the following steps:

[0026] The products after the hydrothermal reaction are separated and the carboxylic acid product is collected.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention uses a metal oxide with metal atoms loaded on the surface prepared by an impregnation drying reduction method as a catalyst, so that the catalyst used in the present invention is in powder form and has a regular morphology and a specific exposed crystal face, which can make the metal active species highly dispersed on the surface of the metal oxide, thereby improving the catalyst performance, so that the present invention can achieve catalytic conversion of the plastic to be disposed of by hydrothermal reaction at a temperature of 100°C to 150°C without relying on hydrogen. The reaction temperature of the catalytic conversion of the present invention does not exceed 150°C, does not need to rely on H2, the reaction conditions are milder and more environmentally friendly, the reaction time is shorter, the cost is low, and it is conducive to promotion and large-scale use.

[0029] The present invention converts the plastic to be disposed into a carboxylic acid product, and the yield of the carboxylic acid product obtained by catalytic conversion of the plastic through the method of the present invention can reach more than 61%, or even 75%, with high catalytic conversion efficiency, thus realizing the chemical upgrading and recycling of the plastic into value-added chemicals. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the TEM image of the catalyst prepared in Example 1 at a 20 nm scale.

[0031] Figure 2 This is the TEM image of the catalyst prepared in Example 1 at a 5 nm scale. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present invention will be described clearly and completely below. It should be noted that in the following embodiments of the present invention, the high-density polyethylene used is high-density polyethylene powder.

[0033] Example 1

[0034] This embodiment provides a method for catalytically converting plastic into carboxylic acid, comprising the following steps:

[0035] Step 1, prepare the mixed solution:

[0036] 1.1) Preparation of catalyst:

[0037] S1, 0.0213 g of RuCl3·nH2O is uniformly dispersed in 0.19 mL of deionized water to obtain a soluble metal salt solution.

[0038] S2, using 0.5g of CeO2 carrier and the above-mentioned S1 soluble metal salt solution as the impregnation solution, adopting the equal volume impregnation method, impregnating the metal oxide into the soluble metal salt solution, and impregnating at 25°C for 24h to obtain a pre-modified metal oxide.

[0039] S3, drying the pre-modified metal oxide obtained in the above S2 at 100°C for 12 hours, and then reducing it at 250°C for 3 hours under H2 atmosphere to obtain a catalyst, which is recorded as Ru / CeO2.

[0040] 1.2) Mixing high-density polyethylene and catalyst:

[0041] Using Ru / CeO2 as a catalyst, 100 mg of high-density polyethylene and 50 mg of the catalyst were uniformly dispersed in 20 mL of deionized water to obtain a mixed solution.

[0042] Step 2, transfer the mixed solution obtained in the above step 1.2 to a reactor, set the reaction temperature to 150°C, introduce 1.5MPa air, and the reaction time to 12h.

[0043] Step 3, after the reaction liquid after the hydrothermal reaction in step 2 is cooled to room temperature, an alcohol solution is added, stirred, ultrasonically treated for 15 minutes, solid-liquid separation is performed, and the filtrate is collected; the filtrate is concentrated by vacuum distillation to obtain a carboxylic acid product (long-chain monoacid and long-chain dicarboxylic acid) with a molecular weight of 1240 and a yield of 75%.

[0044] Example 2

[0045] This embodiment provides a method for catalytically converting plastic into carboxylic acid, comprising the following steps:

[0046] Step 1, prepare the mixed solution:

[0047] 1.1) Preparation of catalyst:

[0048] S1, 0.0213 g of RuCl3·nH2O is uniformly dispersed in 2.92 mL of deionized water to obtain a soluble metal salt solution.

[0049] S2, using 0.5g of SiO2 as a carrier and the above-mentioned S1 soluble metal salt solution as an impregnation solution, adopting an equal volume impregnation method, impregnating the metal oxide into the soluble metal salt solution, and impregnating at 25°C for 24h to obtain a pre-modified metal oxide.

[0050] S3, drying the pre-modified metal oxide obtained in the above S2 at 100°C for 12 hours, and then reducing it at 250°C for 3 hours under H2 atmosphere to obtain a catalyst, which is recorded as Ru / SiO2.

[0051] 1.2) Mixing high-density polyethylene and catalyst:

[0052] Using Ru / SiO2 as a catalyst, 100 mg of high-density polyethylene and 50 mg of the catalyst were uniformly dispersed in 20 mL of water to obtain a mixed solution.

[0053] Step 2, transfer the mixed solution obtained in the above step 1.2 to a reactor, set the reaction temperature to 150°C, introduce 1.5MPa air, and the reaction time to 12h.

[0054] Step 3, after the reaction liquid after the hydrothermal reaction in step 2 is cooled to room temperature, an alcohol solution is added, stirred, ultrasonically treated for 15 minutes, solid-liquid separation is performed, and the filtrate is collected; the filtrate is concentrated by vacuum distillation to obtain a carboxylic acid product (long-chain monoacid and long-chain dicarboxylic acid) with a molecular weight of 1150 and a yield of 74%.

[0055] Example 3

[0056] This embodiment provides a method for catalytically converting plastic into carboxylic acid, comprising the following steps:

[0057] Step 1, prepare the mixed solution:

[0058] 1.1) Preparation of catalyst:

[0059] S1, 0.0213 g of RuCl3·nH2O is uniformly dispersed in 0.15 mL of deionized water to obtain a soluble metal salt solution.

[0060] S2, using 0.5 g of Al2O3 as a carrier and the soluble metal salt solution obtained in the above S1 as an impregnation solution, adopting an equal volume impregnation method, impregnating the metal oxide in the soluble metal salt solution, and impregnating at 25°C for 24 hours to obtain a pre-modified metal oxide.

[0061] S3, drying the pre-modified metal oxide obtained in the above S2 at 100°C for 12 hours, and then reducing it at 250°C for 3 hours under H2 atmosphere to obtain a catalyst, which is recorded as Ru / Al2O3.

[0062] 1.2) Mixing high-density polyethylene and catalyst:

[0063] Using Ru / Al2O3 as a catalyst, 100 mg of high-density polyethylene and 50 mg of the catalyst were uniformly dispersed in 20 mL of water to obtain a mixed solution.

[0064] Step 2, transfer the mixed solution obtained in the above step 1.2 to a reactor, set the reaction temperature to 150°C, introduce 1.5MPa air, and the reaction time to 12h.

[0065] Step 3, after the reaction liquid after the hydrothermal reaction in step 2 is cooled to room temperature, an alcohol solution is added, stirred, ultrasonically treated for 15 minutes, solid-liquid separation is performed, and the filtrate is collected; the filtrate is concentrated by vacuum distillation to obtain a carboxylic acid product (long-chain monoacid and long-chain dicarboxylic acid) with a molecular weight of 1220 and a yield of up to 65%.

[0066] Example 4

[0067] This embodiment provides a method for catalytically converting plastic into carboxylic acid, comprising the following steps:

[0068] Step 1, prepare the mixed solution:

[0069] 1.1) Preparation of catalyst:

[0070] S1, 0.0213 g of RuCl3·nH2O is uniformly dispersed in 0.39 mL of deionized water to obtain a soluble metal salt solution.

[0071] S2, using 0.5 g of ZnO as a carrier and the soluble metal salt solution obtained in S1 as an impregnation solution, adopting an equal volume impregnation method, impregnating the metal oxide in the soluble metal salt solution, and immersing at 25° C. for 24 hours to obtain a pre-modified metal oxide.

[0072] S3, drying the pre-modified metal oxide obtained in the above S2 at 100°C for 12 hours, and then reducing it at 250°C for 3 hours under H2 atmosphere to obtain a catalyst, which is recorded as Ru / ZnO.

[0073] 1.2) Mixing high-density polyethylene and catalyst:

[0074] Using Ru / ZnO as a catalyst, 100 mg of high-density polyethylene and 50 mg of the catalyst were uniformly dispersed in 20 mL of water to obtain a mixed solution.

[0075] Step 2, transfer the mixed solution obtained in the above step 1.2 to a reactor, set the reaction temperature to 150°C, introduce 1.5MPa air, and the reaction time to 12h.

[0076] Step 3, after the reaction liquid after the hydrothermal reaction in step 2 is cooled to room temperature, an alcohol solution is added, stirred, ultrasonically treated for 15 minutes, solid-liquid separation is performed, and the filtrate is collected; the filtrate is concentrated by vacuum distillation to obtain a carboxylic acid product (long-chain monoacid and long-chain dicarboxylic acid) with a molecular weight of 1020 and a yield of more than 68%.

[0077] Example 5

[0078] This embodiment provides a method for catalytically converting plastic into carboxylic acid, comprising the following steps:

[0079] Step 1, prepare the mixed solution:

[0080] 1.1) Preparation of catalyst:

[0081] S1, 0.0213 g of RuCl3·nH2O is uniformly dispersed in 0.58 mL of deionized water to obtain a soluble metal salt solution.

[0082] S2, using 0.5 g of TiO2 as a carrier and the soluble metal salt solution obtained in the above S1 as an impregnation solution, adopting an equal volume impregnation method, impregnating the metal oxide in the soluble metal salt solution, and immersing at 25°C for 24 hours to obtain a pre-modified metal oxide.

[0083] S3, drying the pre-modified metal oxide obtained in the above S2 at 100°C for 12 hours, and then reducing it at 250°C for 3 hours under H2 atmosphere to obtain a catalyst, which is recorded as Ru / TiO2.

[0084] 1.2) Mixing high-density polyethylene and catalyst:

[0085] Using Ru / TiO2 as a catalyst, 100 mg of high-density polyethylene and 50 mg of the catalyst were uniformly dispersed in 20 mL of water to obtain a mixed solution.

[0086] Step 2, transfer the mixed solution obtained in the above step 1.2 to a reactor, set the reaction temperature to 150°C, introduce 1.5MPa air, and the reaction time to 12h.

[0087] Step 3, after the reaction liquid after the hydrothermal reaction in step 2 is cooled to room temperature, an alcohol solution is added, stirred, ultrasonically treated for 15 minutes, solid-liquid separation is performed, and the filtrate is collected; the filtrate is concentrated by vacuum distillation to obtain a carboxylic acid product (long-chain monoacid and long-chain dicarboxylic acid) with a molecular weight of 1140 and a yield of up to 61%.

[0088] Example 6

[0089] This embodiment provides a method for catalytically converting plastic into carboxylic acid, comprising the following steps:

[0090] Step 1, prepare the mixed solution:

[0091] 1.1) Preparation of catalyst:

[0092] S1, 0.0213 g of RuCl3·nH2O is uniformly dispersed in 0.35 mL of deionized water to obtain a soluble metal salt solution.

[0093] S2, using 0.5 g of ZrO2 as a carrier and the soluble metal salt solution obtained in the above S1 as an impregnation solution, adopting an equal volume impregnation method, impregnating the metal oxide in the soluble metal salt solution, and impregnating at 25°C for 24 hours to obtain a pre-modified metal oxide.

[0094] S3, drying the pre-modified metal oxide obtained in the above S2 at 100°C for 12 hours, and then reducing it at 250°C for 3 hours under H2 atmosphere to obtain a catalyst, which is recorded as Ru / ZrO2.

[0095] 1.2) Mixing high-density polyethylene and catalyst:

[0096] Using Ru / ZrO2 as a catalyst, 100 mg of high-density polyethylene and 50 mg of the catalyst were uniformly dispersed in 20 mL of water to obtain a mixed solution.

[0097] Step 2, transfer the mixed solution obtained in the above step 1.2 to a reactor, set the reaction temperature to 150°C, introduce 1.5MPa air, and the reaction time to 12h.

[0098] Step 3, after the reaction liquid after the hydrothermal reaction in step 2 is cooled to room temperature, an alcohol solution is added, stirred, ultrasonically treated for 15 minutes, solid-liquid separation is performed, and the filtrate is collected; the filtrate is concentrated by vacuum distillation to obtain a carboxylic acid product (long-chain monoacid and long-chain dicarboxylic acid) with a molecular weight of 1980 and a yield of up to 62%.

[0099] Example 7

[0100] This embodiment provides a method for catalytically converting plastic into carboxylic acid, comprising the following steps:

[0101] Step 1, prepare the mixed solution:

[0102] 1.1) Preparation of catalyst:

[0103] S1, 0.0213 g of H2PtCl6 soluble metal salt is uniformly dispersed in 0.19 mL of deionized water to obtain a soluble metal salt solution.

[0104] S2, using 0.5 g of CeO2 as a carrier and the soluble metal salt solution obtained in the above S1 as an impregnation solution, adopting an equal volume impregnation method, impregnating the metal oxide in the soluble metal salt solution, and immersing at 25°C for 24 hours to obtain a pre-modified metal oxide.

[0105] S3, drying the pre-modified metal oxide obtained in the above S2 at 100°C for 12 hours, and then reducing it at 250°C for 3 hours under H2 atmosphere to obtain a catalyst, which is recorded as Pt / CeO2.

[0106] 1.2) Mixing high-density polyethylene and catalyst:

[0107] Using Pt / CeO2 as a catalyst, 100 mg of high-density polyethylene and 50 mg of the catalyst were uniformly dispersed in 20 mL of water to obtain a mixed solution.

[0108] Step 2, transfer the mixed solution obtained in the above step 1.2 to a reactor, set the reaction temperature to 150°C, introduce 1.5MPa air, and the reaction time to 12h.

[0109] Step 3, after the reaction liquid after the hydrothermal reaction in step 2 is cooled to room temperature, an alcohol solution is added, stirred, ultrasonically treated for 15 minutes, solid-liquid separation is performed, and the filtrate is collected; the filtrate is concentrated by vacuum distillation to obtain a carboxylic acid product (long-chain monoacid and long-chain dicarboxylic acid) with a molecular weight of 1123 and a yield of 66%.

[0110] Example 8

[0111] This embodiment provides a method for catalytically converting plastic into carboxylic acid, comprising the following steps:

[0112] Step 1, prepare the mixed solution:

[0113] 1.1) Preparation of catalyst:

[0114] S1, 0.0153 g of IrCl3·xH2O is uniformly dispersed in 0.19 mL of deionized water to obtain a soluble metal salt solution.

[0115] S2, using 0.5 g of CeO2 as a carrier and the soluble metal salt solution obtained in the above S1 as an impregnation solution, adopting an equal volume impregnation method, impregnating the metal oxide in the soluble metal salt solution, and immersing at 25°C for 24 hours to obtain a pre-modified metal oxide.

[0116] S3, drying the pre-modified metal oxide obtained in the above S2 at 100°C for 12 hours, and then reducing it at 250°C for 3 hours under H2 atmosphere to obtain a catalyst, which is recorded as Ir / CeO2.

[0117] 1.2) Mixing high-density polyethylene and catalyst:

[0118] Using Ir / CeO2 as a catalyst, 100 mg of high-density polyethylene and 50 mg of the catalyst were uniformly dispersed in 20 mL of water to obtain a mixed solution.

[0119] Step 2, transfer the mixed solution obtained in the above step 1.2 to a reactor, set the reaction temperature to 150°C, introduce 1.5MPa air, and the reaction time to 12h.

[0120] Step 3, after the reaction liquid after the hydrothermal reaction in step 2 is cooled to room temperature, an alcohol solution is added, stirred, ultrasonically treated for 15 minutes, solid-liquid separation is performed, and the filtrate is collected; the filtrate is concentrated by vacuum distillation to obtain a carboxylic acid product (long-chain monoacid and long-chain dicarboxylic acid) with a molecular weight of 1440 and a yield of up to 72%.

[0121] Example 9

[0122] This embodiment provides a method for catalytically converting plastic into carboxylic acid, comprising the following steps:

[0123] Step 1, prepare the mixed solution:

[0124] 1.1) Preparation of catalyst:

[0125] S1, 0.0133 g of PdCl2 soluble metal salt is uniformly dispersed in 0.19 mL of deionized water to obtain a soluble metal salt solution.

[0126] S2, using 0.5 g of CeO2 as a carrier and the soluble metal salt solution obtained in the above S1 as an impregnation solution, adopting an equal volume impregnation method, impregnating the metal oxide in the soluble metal salt solution, and immersing at 25°C for 24 hours to obtain a pre-modified metal oxide.

[0127] S3, drying the pre-modified metal oxide obtained in the above S2 at 100°C for 12 hours, and then reducing it at 250°C for 3 hours under H2 atmosphere to obtain a catalyst, which is recorded as Pd / CeO2.

[0128] 1.2) Mixing high-density polyethylene and catalyst:

[0129] Using Pd / CeO2 as a catalyst, 100 mg of high-density polyethylene and 50 mg of the catalyst were uniformly dispersed in 20 mL of water to obtain a mixed solution.

[0130] Step 2, transfer the mixed solution obtained in the above step 1.2 to a reactor, set the reaction temperature to 150°C, introduce 1.5MPa air, and the reaction time to 12h.

[0131] Step 3, after the reaction liquid after the hydrothermal reaction in step 2 is cooled to room temperature, an alcohol solution is added, stirred, ultrasonically treated for 15 minutes, solid-liquid separation is performed, and the filtrate is collected; the filtrate is concentrated by vacuum distillation to obtain a carboxylic acid product (long-chain monoacid and long-chain dicarboxylic acid) with a molecular weight of 1040 and a yield of up to 70%.

[0132] Based on the above, the reaction temperature of the catalytic hydrogenolysis process with technology is usually higher than 200°C, and the reaction process is highly dependent on H2. It must be carried out in an H2 atmosphere of 0.5MPa to 6MPa to achieve catalytic conversion of the rate. According to the catalytic conversion results of the above-mentioned embodiments of the present invention, the present invention can effectively convert high-density polyethylene into carboxylic acid products under mild and environmentally friendly reaction conditions at a reaction temperature not exceeding 150°C without relying on H2. And the yield of the carboxylic acid product obtained by the catalytic conversion of plastics by the method of the present invention can reach more than 61%, or even 75%, with high catalytic conversion efficiency, realizing the chemical upgrading and recycling of plastics into value-added chemicals. In other words, the reaction conditions of the catalytic conversion of the present invention are milder and more environmentally friendly, with a shorter reaction time and low cost, which is conducive to promotion for large-scale use.

[0133] The present invention takes the catalyst prepared in Example 1 as an example, and performs TEM tests on it, and the test results are as follows: Figure 1 and Figure 2 shown.

[0134] Figure 1This is a TEM image of the catalyst prepared in Example 1 at a scale of 20 nm. It can be seen that the catalyst prepared in Example 1 has a nanometer-level size and a regular rod-like structure.

[0135] Figure 2 This is a TEM image of the catalyst prepared in Example 1 at a scale of 5 nm. Figure 2 It can be seen that the catalyst prepared in Example 1 presents a uniformly distributed and regular crystal face structure with specific exposed crystal faces.

[0136] Based on the above test results, it can be seen that the catalyst prepared by the present invention has a nanometer-level size, a regular morphology, and a specific exposed crystal face, so that the catalyst prepared by the present invention is conducive to the high dispersion of metal active species on the surface of the metal oxide, thereby improving the catalyst performance, so that the present invention can achieve improved catalytic conversion through a hydrothermal reaction at a temperature of 100°C to 150°C without relying on hydrogen.

[0137] Obviously, the above embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Claims

1. A method for catalytically converting plastics into carboxylic acids, characterized in that: The following steps are involved: A metal oxide with metal atoms loaded on its surface prepared by an impregnation drying reduction method is used as a catalyst, and the catalyst and the plastic to be treated are uniformly dispersed in water to obtain a mixed solution; The mixed solution is subjected to a hydrothermal reaction at 100° C. to 150° C. in an air atmosphere to convert the plastic to be treated into a carboxylic acid product; In the catalyst, the metal oxide is one or more of CeO2, TiO2, SiO2, ZnO, ZrO2 and Al2O3; The metal atom is one or two of Ni, Cu, Fe, Ru, Ir, Pd and Pt; In the catalyst, the loading amount of the metal atoms is 0.5% to 2% of the mass of the catalyst.

2. The method for catalytic conversion of plastics into carboxylic acids according to claim 1, characterized in that: The catalyst is obtained by the following steps: uniformly dispersing the soluble metal salt corresponding to the metal atom in a solvent to obtain a soluble metal salt solution; Using a metal oxide as a carrier and the soluble metal salt solution as an impregnation solution, an equal volume impregnation method is used to immerse the metal oxide in the soluble metal salt solution so that the metal component is loaded on the surface of the metal oxide to obtain a pre-modified metal oxide; After the pre-modified metal oxide is dried, it is subjected to reduction treatment so that the soluble metal salt is converted into metal atoms and loaded on the surface of the metal oxide, thereby obtaining the catalyst.

3. The method for catalytic conversion of plastic into carboxylic acid according to claim 2, characterized in that: When the metal oxide is impregnated in the soluble metal salt solution, the impregnation temperature is room temperature and the impregnation time is 12 hours to 36 hours.

4. The method for catalytic conversion of plastic into carboxylic acid according to claim 2, characterized in that: The reduction treatment is carried out in a H2 atmosphere, at a temperature of 220°C to 280°C, for a time of 2h to 4h.

5. The method for catalytic conversion of plastics into carboxylic acids according to claim 1, characterized in that: The hydrothermal reaction time is 4h to 36h.

6. The method for catalytic conversion of plastics into carboxylic acids according to claim 1, characterized in that: The plastic to be disposed of is high-density polyethylene.

7. The method for catalytic conversion of plastics into carboxylic acids according to claim 1, characterized in that: The mass ratio of the plastic to be disposed to the catalyst is 1 to 3:

1.

8. The method for catalytic conversion of plastics into carboxylic acids according to claim 1, characterized in that: The pressure of the air is 0.5 MPa to 2 MPa.

9. The method for catalytic conversion of plastics into carboxylic acids according to claim 1, characterized in that: The carboxylic acid product is a long-chain monoacid or a long-chain dicarboxylic acid.

10. The method for catalytic conversion of plastics into carboxylic acids according to claim 1, characterized in that: Post-processing is also included, and the post-processing is performed by the following steps: After the reaction liquid after the hydrothermal reaction is cooled to room temperature, an alcohol solution is added, stirred, ultrasonically treated, solid-liquid separated, and the filtrate is collected; the filtrate is concentrated by vacuum distillation to obtain a carboxylic acid product.

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