A bimetallic catalyst for degrading polyethylene terephthalate and methods of making and using the same

Abstract

The application relates to the technical field of waste resource recycling, in particular to a bimetallic catalyst for degrading polyethylene terephthalate and a preparation and use method thereof, wherein in the preparation process, a metal A salt is first mixed and dispersed with a complexing agent and a carrier, so that the metal A salt can be dispersed on the carrier through complexation first, then a metal B salt is added, mixed uniformly and calcined, and the bimetallic catalyst can be prepared. The bimetallic catalyst comprises an active metal and a carrier, the active metal comprises metal A and metal B, and the metal A and the metal B are any one of transition metals. The application solves the technical problem that the existing catalyst for degrading PET has low catalytic efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of waste resource recycling, and particularly relates to a bimetallic catalyst for degrading polyethylene terephthalate and a preparation and use method thereof. BACKGROUND

[0002] Polyethylene terephthalate (PET) is an important plastic material, which is widely used in beverage bottles, food packaging, clothing fibers, and power transmission and transformation equipment packaging due to its high strength, good heat resistance, and high chemical stability. With the development of China's economy, the demand for polyethylene terephthalate has also increased sharply. Due to the large population base in China, the consumption of polyethylene terephthalate accounts for a large proportion in the world. The large use of polyethylene terephthalate is accompanied by a large amount of waste polyethylene terephthalate generation and discharge. The sources of waste polyethylene terephthalate mainly include two parts: one is the leftover materials and part of the defective products generated in the industrial production and processing process, namely industrial waste; the other part is the consumer goods and engineering plastics after consumption and use, such as beverage bottles, food packaging, etc. Waste polyethylene terephthalate is difficult to degrade in the natural environment due to its high chemical stability, which has brought a large amount of environmental pollution problems.

[0003] At present, the recycling of waste polyethylene terephthalate mainly includes physical recycling and chemical recycling. The physical recycling method mainly uses waste polyethylene terephthalate through washing, crushing, melting, and granulation processes, and is used, such as using food packaging grade polyethylene terephthalate in industrial packaging and other fields. The chemical recycling method mainly uses polyethylene terephthalate through washing, crushing, and chemical degradation processes to obtain the process of polyethylene terephthalate production raw material terephthalic acid and its ester. In recent years, the large consumption of petroleum resources has brought heavy pressure to the environment. In the face of the two challenges of the increasing depletion of non-renewable resources and the regeneration of polyethylene terephthalate waste, developing polyethylene terephthalate degradation and utilization technology and establishing a sound circular economy system have become the best choice.

[0004] In the degradation catalyst of waste polyethylene terephthalate, homogeneous catalysts such as zinc acetate, zinc chloride, ionic liquid, etc. have been widely studied in recent years. Li Yonggui et al. used zinc acetate as a catalyst to depolymerize waste polyethylene terephthalate fibers, and studied the glycolysis process. It is found that the main factors affecting the polyethylene terephthalate alcoholysis are temperature, time and catalyst amount. Under the conditions of reaction temperature 196℃, catalyst amount 2%, and reaction time 2h, the polyethylene terephthalate alcoholysis rate can reach 96.65%. Heterogeneous catalysts, because of their easy separation from solvents and reduction of catalyst cost, are also considered as a very potential catalyst. Researchers directly use zeolite as a catalyst to degrade polyethylene terephthalate alcoholysis, but the monomer yield is low, and the catalytic effect is not ideal. Compared with homogeneous catalysts, heterogeneous catalysts have higher mechanical strength and can continue to play a catalytic role at high temperature.

[0005] In summary, the catalysts in the prior art have high separation cost, complex preparation method, and poor catalytic activity. In view of the economic and industrial application, it is inevitable to develop a catalyst with low cost, simple preparation process and high activity. SUMMARY

[0006] The present application aims to provide a bimetallic catalyst for degrading polyethylene terephthalate and a preparation and use method thereof, so as to solve the technical problem of low catalytic efficiency of the existing PET degradation catalyst.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: a bimetallic catalyst for degrading polyethylene terephthalate, comprising an active metal and a carrier, wherein the active metal comprises metal A and metal B, and the metal A and the metal B are any one of transition metals.

[0008] The beneficial effects of the present application are as follows:

[0009] In the process of long-term research on PET degradation catalysts, the inventors of the present application propose a double-metal-based catalyst for degrading PET, wherein the double-metal catalyst is designed based on a hindered Lewis acid-base pair strategy, two transition metals are anchored on the carrier using a complexing agent, and stable metal-metal, metal-oxygen, metal-sulfur, metal-oxygen vacancy, etc. chemical bonds can be formed after calcination, so that the double-metal catalyst can maintain stability in a wide range of working temperature and pH. At the same time, the double-metal catalyst in the present application utilizes the synergistic effect of two metal sites to improve the catalytic reaction speed and the selectivity of the catalytic reaction, and can degrade PET materials to generate p-toluene dimethyl ester and ethylene glycol, wherein the degradation rate can reach 100%, the reaction selectivity and yield can reach more than 99%. And the double-metal catalyst in the present application can open the ester bond under relatively mild conditions. Compared with the biological catalyst and ionic liquid catalyst used in the current research, the heterogeneous catalyst prepared in the present application can realize complete separation of the product and the catalyst, and when a fixed bed reactor is used, PET can be continuously and continuously degraded.

[0010] Preferably, as an improvement, the metal A and the metal B are any one of Fe, Co, Ni, Mn, Cu, Zn, Mo, V, La, Bi, Ca, Ir, Pt, Au, Ru, Rh, Pd; more preferably, the metal A is any one of Co, Ni, Ru, and the metal B is any one of Co, Ni.

[0011] In the present application, various transition metals can be used as metal A and metal B, wherein different metals can be selected and used according to different purposes, for example, if an economical double-metal catalyst is needed, cheaper metals such as Fe, Mn and Cu can be selected for combination, and if a double-metal catalyst with higher catalytic efficiency is needed, noble metals such as Ru can be selected for combination.

[0012] Preferably, as an improvement, the carrier is any one of zinc oxide, magnesium oxide, cerium oxide, calcium oxide, tungsten trioxide, aluminum hydroxide, magnesium hydroxide, aluminum oxide, silicon dioxide, hydrotalcite, and hydroxyapatite; more preferably, the carrier is any one of zinc oxide and magnesium oxide.

[0013] In the present application, the carrier can be selected according to the characteristics of the active metal, and the carrier can be selected from an acid, a base or a neutral carrier, and the selection range is wide, and the carrier will not be restricted by raw materials in industrial production.

[0014] Preferably, as an improvement, the mass percentage of the active metal in the catalyst is 0.1-20wt%; more preferably, the mass percentage of the active metal in the catalyst is 5-10wt.%; the molar ratio of metal A to metal B in the active metal is 0.3-10, more preferably, the molar ratio of metal A to metal B in the active metal is 0.5-1.5:1.

[0015] In the present application, the proportion of active metal will affect the catalytic effect of the catalyst. When the amount of active metal added is too large, the reaction sites will be occupied due to too much metal loaded on the surface of the carrier, thereby reducing the catalytic effect. In the present application, the molar ratio of metal A and metal B in the catalyst also affects the catalytic effect of the catalyst. If the doping ratio of metal A and B is out of balance, the synergistic effect of the bimetallic catalyst cannot be achieved, thereby reducing the selectivity and catalytic efficiency of the reaction.

[0016] The present application also provides a preparation method of a bimetallic catalyst for degrading polyethylene terephthalate, comprising the following steps:

[0017] S1: dispersing the metal A salt, the complexing agent and the carrier in a solvent, and heating and stirring;

[0018] S2: adding the metal B salt to the mixed solution of S1, and continuously heating and stirring;

[0019] S3: after the solution obtained in S2 is uniformly dispersed, drying, and then heating and calcining in a protective gas atmosphere, and naturally cooling to obtain the bimetallic catalyst.

[0020] The beneficial effects of the present application are as follows:

[0021] In the present application, the metal A salt is first mixed and dispersed with the complexing agent and the carrier, which can ensure that the metal A salt is first dispersed on the carrier through complexation, and then the metal B salt is added, thereby obtaining a bimetallic catalyst with high loading, high dispersity and high stability. At the same time, the preparation method of the present application has simple steps, mild reaction conditions and good repeatability, and is suitable for large-scale production and preparation.

[0022] Preferably, as an improvement, the metal A salt and the metal B salt in step S1 are any one of the nitrate, chloride, sulfate, acetate, acetylacetone salt of metal A and metal B; the complexing agent is one or a combination of several of urea, thiourea, sulfamine, potassium bicarbonate, sodium bicarbonate, benzoic acid, ethanolamine or citric acid; and the solvent is any one of water, ethanol, methanol, dimethyl sulfoxide and N,N-dimethylformamide.

[0023] Preferably, as an improvement, the heating and stirring temperature in steps S1 and S2 is 25-200℃, and the time is 1-32h.

[0024] Preferably, as an improvement, the ratio of the sum of the amounts of substance of the metal A salt and the metal B salt to the amount of substance of the carrier is 0.005-0.5; the ratio of the amount of substance of the complexing agent to the sum of the amounts of substance of the metal A salt and the metal B salt is 0.1:1-20:1, more preferably 3:1-10:1.

[0025] In the present application, the metal A salt and the metal B salt can be completely loaded on the carrier under the action of the complexing agent, and therefore the amount of the complexing agent and the amount of the carrier need to be ensured to be within a suitable range. If the amount of the complexing agent is too large, too much of the surface of the carrier will be occupied, which is not conducive to the sintering loading of the active metal and the carrier.

[0026] Preferably, as an improvement, the temperature for the temperature rising calcination in step S3 is 200-1000℃, and the time is 1-8h; the protective gas is one or more of nitrogen, helium, ammonia or any proportion of oxygen / nitrogen mixed gas.

[0027] Preferably, as an improvement, the temperature rising speed in step S3 is 5-10℃ / min.

[0028] The present application also provides a use method of the bimetallic catalyst for degrading polyethylene terephthalate, comprising the following steps: crushing the polyethylene terephthalate product to be degraded into pieces, then adding the catalyst and methanol thereto, ultrasonic treatment, heating reaction, filtering and recovering the catalyst after the reaction, and obtaining a mixed solution of dimethyl terephthalate and ethylene glycol.

[0029] The beneficial effects of the present application are as follows:

[0030] The use method in the present application is simple and easy to operate, and the use conditions are mild, and the degradation and depolymerization of PET can be realized at a lower temperature. Moreover, the amount of the catalyst used in the method is relatively small, and a high-efficiency PET degradation can be completed with the addition of only about 2% of the catalyst based on the PET raw material. Meanwhile, the catalyst can also be recycled after use, further saving the use of the catalyst.

[0031] Preferably, as an improvement, the addition ratio of the polyethylene terephthalate product (mass) : catalyst (mass) : methanol (volume) is 5000:30:80-100:10:20; the heating reaction temperature is 100-250℃; the reaction time is 0.5-5h; more preferably, the reaction temperature is 150-200℃; and the reaction time is 1-2h. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The XRD pattern of the bimetallic catalyst CoMo@SiO2 in Example 1 of the present application is shown in the following figure:

[0033] Figure 2TEM image of the bimetallic catalyst CoMo@SiO2 in Example 1 of the present application;

[0034] Figure 3 XRD image of the bimetallic catalyst RuNi@HAP in Example 10 of the present application;

[0035] Figure 4 TEM image of the bimetallic catalyst RuNi@HAP in Example 10 of the present application. DETAILED DESCRIPTION

[0036] The following is further described in detail through specific embodiments:

[0037] Example 1

[0038] A bimetallic catalyst for degrading polyethylene terephthalate and a preparation method thereof, wherein the method comprises the following steps:

[0039] 0.243g of Co(NO3)·6H2O, 1g of urea, and 2g of silicon dioxide were weighed, and the above raw materials were dispersed in 100ml of N,N-dimethylformamide and stirred at 50°C for 2h. Then 0.987g of ammonium molybdate was added to the above mixture solution, and the stirring was continued at 50°C for 12h. The solvent in the stirred mixture solution was evaporated, and after the solvent was evaporated, it was placed in an oven at 120°C for drying. The dried solid powder was placed in a tube furnace for pyrolysis treatment, the pyrolysis temperature was 800°C, the pyrolysis time was 1h, the tube furnace was in a nitrogen atmosphere, and the heating rate of the tube furnace was 10°C / min -1 . After pyrolysis treatment, it was naturally cooled and ground to obtain the bimetallic catalyst CoMo@SiO2, the molar ratio of Co to Mo in CoMo@SiO2 was 1:1, and the weight ratio of Co and Mo in the catalyst was 6%.

[0040] The present embodiment also includes a method for using a bimetallic catalyst for degrading polyethylene terephthalate, which specifically comprises the following steps:

[0041] The collected polyethylene terephthalate (PET) waste was mechanically crushed to obtain small particle PET fragments, and the fragments were washed and dried for standby use. 1g of the dried PET fragments, 30mg of the above prepared CoMo@SiO2, and 50ml of methanol were placed in an autoclave, 0.5g of sodium hydroxide was added to adjust the reaction pH, and after ultrasonic treatment, the inner lining was placed in a high-pressure stirred autoclave, and after sealing, it was reacted at 200°C for 1h. After the reaction, the unreacted PET and catalyst were filtered and dried for standby use, and the conversion rate was calculated. A certain amount of filtrate was added to acetonitrile or isopropyl alcohol for gas chromatography analysis, and the selectivity of terephthalic acid dimethyl ester was calculated.

[0042] Example 4

[0043] Take 0.006g of RuCl3, 0.06g of thiourea, 1g of calcined hydroxyapatite (hydroxyapatite is calcined at 400℃ for 12h). The above raw materials are dispersed in 100mL of ethanol, and are placed in an ultrasonic stirrer at 25℃ for 2h. Take 0.012g of Ni(acac)2 and add it to the above mixture, and stir at 40℃ for 2h. The solvent in the stirred mixture is evaporated, and after the solvent is evaporated, it is placed in an oven at 60℃ for drying. The dried solid powder is placed in a tube furnace for pyrolysis treatment, the pyrolysis temperature is 400℃, the pyrolysis time is 2h, the tube furnace is in a helium atmosphere, and the tube furnace is heated at a rate of 5℃ / min -1 . After pyrolysis treatment, the bimetallic catalyst RuNi@HAP is obtained by natural cooling, the molar ratio of Ru to Ni in RuNi@HAP is 0.5:1, and the weight ratio of Ru and Ni in the catalyst is 3%.

[0044] The use method of the bimetallic catalyst for degrading polyethylene terephthalate in the embodiment also includes the following steps:

[0045] The collected polyethylene terephthalate (PET) waste is mechanically crushed to obtain small-particle PET fragments, and the fragments are washed and dried for standby use. Take 1g of the dried PET fragments, 20mg of the above-prepared RuNi@HAP, and 50ml of methanol, and place them in an autoclave. Add 0.5g of sodium hydroxide to adjust the reaction pH, and after ultrasonic treatment, place the inner lining in a high-pressure stirred autoclave. After sealing, react at 200℃ for 1h. After the reaction, filter the unreacted PET and the catalyst, dry and weigh them for standby use, and calculate the conversion rate. Take a certain amount of filtrate and add acetonitrile or isopropyl alcohol for gas chromatography analysis to calculate the terephthalic acid dimethyl ester selectivity.

[0046] Example 10

[0047] Take 0.249g of Co(OAc)2·4H2O, 1g of citric acid, and 1g of zinc oxide, and disperse the above raw materials in 50mL of water, and stir at 60℃ for 2h. Take 0.249g of Ni(OAc)2·4H2O and add it to the above mixture, and continue to stir at 60℃ for 24h. Evaporate the solvent in the stirred mixture, and after the solvent is evaporated, place it in an oven at 60℃ for drying. The dried solid powder is placed in a tube furnace for pyrolysis treatment, the pyrolysis temperature is 800℃, the pyrolysis time is 2h, the tube furnace is in a nitrogen atmosphere, and the tube furnace is heated at a rate of 5℃ / min -1 . After pyrolysis treatment, the bimetallic catalyst CoNi@ZnO is obtained by natural cooling, the molar ratio of Co to Ni in CoNi@ZnO is 1:1, and the weight ratio of Co and Ni in the catalyst is 5%.

[0048] The application also provides a method for using the bimetallic catalyst for degrading polyethylene terephthalate, which comprises the following steps:

[0049] The collected polyethylene terephthalate (PET) waste is mechanically crushed to obtain small-particle PET fragments, and the fragments are washed and dried for standby use. 1 g of the dried PET fragments, 30 mg of the prepared CoNi@ZnO and 50 ml of methanol are placed in an autoclave, 0.5 g of sodium hydroxide is added to adjust the pH of the reaction, and the inner lining is placed in a high-pressure stirred tank after ultrasonic treatment. After sealing the autoclave, the reaction is carried out at 200°C for 1 hour. After the reaction, the unreacted PET and the catalyst are filtered and dried for standby use, and the conversion rate is calculated. A certain amount of filtrate is added to acetonitrile or isopropyl alcohol for gas chromatography analysis, and the selectivity of terephthalic acid dimethyl ester is calculated.

[0050] The difference between Example 2-3 and Comparative Example 1-9 is only the change of experimental condition parameters, the difference between Example 5-8 and Comparative Example 4 is only the change of experimental condition parameters, the difference between Example 9 and 11 and Comparative Example 10 is only the change of experimental condition parameters, and the detailed experimental parameters of the above examples and comparative examples are shown in Table 1, wherein A:B represents the molar ratio of metal A to metal B in the bimetallic catalyst; (A+B) wt.% represents the mass ratio of metal A to metal B in the bimetallic catalyst. The corresponding experimental results are shown in Table 2:

[0051] Table 1: Bimetallic catalyst and its preparation parameters of examples and comparative examples

[0052]

[0053] Table 2: Use conditions and experimental results of examples and comparative examples

[0054] Analysis of experimental results:

[0055] As can be seen from the above examples and comparative examples, the degradation rate of PET can reach more than 90% and the reaction selectivity of the product terephthalic acid dimethyl ester can also reach more than 90% by using the technical scheme of the application for catalytic degradation of PET, and the yield of the product can reach more than 85%.

[0056] Comparative Examples 1-4 change the preparation parameters compared with Example 1, and the catalytic efficiency and selectivity of the bimetallic catalyst decrease obviously. When the molar ratio of the bimetallic A and B changes, the synergistic effect of the bimetallic sites cannot be played, which greatly affects the catalytic efficiency and selectivity of the catalyst.

[0057] Compared with Example 1, the catalytic efficiency and selectivity of the bimetallic catalysts were significantly decreased by changing the use parameters in Comparative Examples 5-9. Among them, when the reaction temperature is too high, it will affect the efficiency of catalytic degradation.

[0058] The above is only the embodiment of the present application, and the specific technical solutions and / or common knowledge of the scheme are not described in detail. It should be pointed out that for those skilled in the art, without departing from the technical solutions of the present application, a number of modifications and improvements can be made, which should also be considered as the protection scope of the present application, which will not affect the effect and practicality of the patent. The protection scope of the present application should be subject to the content of its claims, and the specific implementation mode and the like recorded in the specification can be used to explain the content of the claims.

Claims

1. The application of a bimetallic catalyst for the degradation of polyethylene terephthalate, characterized in that: The preparation method of the bimetallic catalyst includes the following steps: S1: Disperse the metal A salt, complexing agent and support in a solvent, and heat and stir at 25-200℃ for 1-32 hours; S2: Add metal B salt to the mixed solution of S1, and heat and stir at 25-200℃ for 1-32 hours; S3: After the solution obtained from S2 is evenly dispersed, it is dried. After drying, it is pyrolyzed at 200-1000 ℃ for 1-8 hours under a protective gas atmosphere at a rate of 5-10 ℃ / min. After natural cooling, the bimetallic catalyst is obtained. The metal A is any one of Co, Ni, and Ru, and the metal B is any one of Co and Ni; metal A and metal B are different metals; the carrier is any one of zinc oxide, magnesium oxide, cerium oxide, calcium oxide, tungsten trioxide, aluminum hydroxide, magnesium hydroxide, aluminum oxide, silicon dioxide, hydrotalcite, and hydroxyapatite. The catalyst contains 5–10 wt.% active metal; the molar ratio of metal A to metal B in the active metal is 0.5–1.5:

1. The application of the bimetallic catalyst includes the following: the polyethylene terephthalate product to be degraded is crushed into small pieces, then the catalyst and methanol are added, ultrasonically treated and heated to react, and after the reaction is completed, the catalyst is recovered by filtration to obtain a mixed solution of dimethyl terephthalate and ethylene glycol.

2. The application according to claim 1, characterized in that: The carrier can be either zinc oxide or magnesium oxide.

3. The application according to claim 1, characterized in that: In step S1, metal A salt and metal B salt are any one of the following: nitrate, chloride, sulfate, acetate, and acetylacetone salt of metal A and metal B; the complexing agent is one or a combination of several of urea, thiourea, potassium bicarbonate, sodium bicarbonate, ethanolamine, or citric acid; and the solvent is any one of water, ethanol, methanol, dimethyl sulfoxide, and N,N-dimethylformamide.

4. The application according to claim 1, characterized in that: The protective gas is one or both of nitrogen and helium.

5. The application according to claim 1, characterized in that: The ratio of the sum of the amounts of metal A salt and metal B salt to the amount of the carrier is 0.005 to 0.5:1; the ratio of the amount of the complexing agent to the sum of the amounts of metal A salt and metal B salt is 0.1:1 to 20:

1.

6. The application according to claim 5, characterized in that: The ratio of the amount of the complexing agent to the sum of the amounts of metal A salt and metal B salt is 3:1 to 10:

1.

7. The application according to claim 1, characterized in that: The ratio of the added mass of the polyethylene terephthalate product to the added mass of the catalyst and the volume of methanol is 1000mg:30mg:50mL, 1000mg:50mg:30mL, or 5000mg:30mg:80mL; the heating reaction temperature is 100-250℃; and the reaction time is 0.5-5 h.

8. The application according to claim 7, characterized in that: The heating reaction temperature is 150–200°C; the reaction time is 1–2 hours.

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