Magnetic solid base catalyst and method for directional upgrading of methanolysis of polyester materials

Abstract

The invention discloses a magnetic solid base catalyst and a polyester material methanolysis directional upgrading method, which relates to the comprehensive utilization of waste resources. The method uses a magnetic composite oxide derived from heterogeneous magnesium-iron or magnesium-aluminum-iron hydrotalcite to catalyze the methanolysis reaction of PET. After the reaction, the magnetic catalyst can be directly separated from the system, and the system mixed liquid can be cooled to directly obtain high-purity dimethyl terephthalate crystals. The invention can be used for the depolymerization and upgrading of waste PET materials, and can also be used for other similar polyesters and polycarbonates, such as polyethylene succinate, polyethylene adipate, polycarbonate and polypropylene carbonate, which are also suitable for the recovery strategy of the invention, and the products are corresponding dimethyl adipate, dimethyl succinate, dimethyl carbonate and diols. In addition, the catalyst has high catalytic efficiency in the reaction and can be directly reused, effectively reducing the process processing cost.

Description

Technical Field

[0001] The present invention relates to a method for producing dimethyl terephthalate by methanolysis of PET without distillation, and relates to a technology for comprehensive utilization of waste resources and separation of products. More specifically, the present invention relates to a method for methanolysis of various polyester raw materials including PET and polycarbonate, and obtains dicarboxylic acid esters of high purity. Background Art

[0002] The separation and purification of products plays an important role in ensuring product quality and the economic benefits of the production process. Purification is an important process step, which directly affects the quality and market competitiveness of the product. Therefore, product separation and purification is one of the keys to industrialization. At present, PET chemical solvolysis mainly occurs through hydrolysis, alcoholysis, aminolysis or ammonialysis, and specific nucleophilic reagents are selected to attack the C=O bond of polyester to prepare high-value chemical monomers. With the industrial development of various types of solvolysis technologies, problems such as incomplete reaction depolymerization, poor catalytic efficiency and high product purification costs have become the main limiting factors for further improvement of industrial production capacity. In particular, various chemicals must be distilled to obtain high-purity monomers, which greatly increases the additional separation energy consumption. Therefore, how to solve these limiting factors of PET chemical solvolysis is a key issue in promoting the reuse of waste plastic carbon resources.

[0003] In order to promote the development of this field, it is crucial to simplify the monomer purification procedure and reduce energy consumption. Among various process methods, the methanol decomposition system has a high pollution resistance, making it a cost-effective option for treating complex PET-based waste. However, methanol decomposition generally requires a higher temperature (generally ≥200°C) to promote the slow decomposition of PET depolymerization reaction, and the product DMT yield is only between 80-85%. In order to pursue a high yield of DMT, there are currently a small number of supercritical methanol or microwave-assisted methanol decomposition system research projects, but considering factors such as equipment operation and economic benefits, it is not recommended. In addition, homogeneous acid-base catalysts are used in most reactions, which makes it difficult to separate them from the system, resulting in additional economic costs, which to a certain extent also restricts the industrialization progress of methanol decomposition of PET waste plastics. It can be seen that how to provide an effective PET methanol decomposition catalytic system, a separation technology for high-purity DMT monomers, and a means to reduce the recycling cost of catalysts in the catalytic system are problems that need to be solved by technicians in this field.

[0004] Layered double hydroxides (LDHs, also known as hydrotalcite-like compounds) are widely used in the field of transesterification as a solid base catalyst with excellent performance. This type of material has low cost, simple preparation, high activity and good dispersibility. The alkalinity of the composite metal oxide after calcination is further enhanced, making it more suitable for the transesterification reaction system. By adjusting the ratio of magnesium iron and magnesium aluminum iron in the catalyst, a high-activity magnetic composite metal oxide (Mg-Fe-LDOs or Mg-Al-Fe-LDOs) with excellent performance can be obtained. This type of magnetic solid base catalyst has excellent methanolysis catalytic performance. By precisely controlling the alkalinity and magnetism of the catalyst, two important problems of complete degradation of PET and separation of the catalyst are solved, and high-purity DMT is directly obtained by cooling crystallization. This magnetic catalyst separation and recovery strategy helps to comprehensively utilize PET waste and reduce the energy consumption of product separation. To a certain extent, it helps to alleviate the consumption of petroleum resources and improve the recycling value and process capacity of PET waste. Summary of the invention

[0005] Aiming at the demand for separation of methanolysis products of PET waste plastics and the shortcomings of the prior art, the present invention provides a method for directional upgrading of polyester materials to various dicarboxylic acid esters by methanolysis catalyzed by magnetic solid base. The method uses a composite oxide derived from heterogeneous magnesium-aluminum-iron or magnesium-iron hydrotalcite to catalyze the methanolysis reaction of PET, and the catalyst can be directly separated by magnetism, while the high-purity product DMT is directly obtained by cooling crystallization.

[0006] The specific technical solutions adopted by the present invention are as follows:

[0007] In a first aspect, the present invention provides a magnetic solid base catalyst, wherein the magnetic solid base catalyst is a magnetic composite oxide derived from magnesium iron hydrotalcite or magnesium aluminum iron hydrotalcite after being calcined at 400-600°C.

[0008] In a second aspect, the present invention provides a method for preparing a magnetic solid base catalyst, comprising:

[0009] S1. gradually adding a metal ion solution into an alkaline solution system to prepare a hydrotalcite-like compound by a coprecipitation method; the metal ion solution is a composite solution of magnesium ions, ferrous ions and ferric ions, or a composite solution of magnesium ions, ferric ions and aluminum ions;

[0010] S2. Grind the layered double hydroxide and then calcine it in an inert atmosphere at a temperature of 400 to 600° C. for 4 to 8 hours to finally obtain a magnetic composite oxide derived from a hydrotalcite-like compound.

[0011] As a preference of the second aspect above, the calcination temperature of the heterogeneous catalyst is preferably 500°C.

[0012] As a preferred embodiment of the second aspect, in the co-precipitation method, the metal ion solution is gradually added to water, and the pH of the system is maintained at 9.5-10.5 by simultaneously adding NaOH solution. The final mixed solution is fully reacted at ambient temperature and then heated to 60-80°C with stirring and reflux for 8-16 hours. The precipitate is filtered, washed and dried to obtain a hydrotalcite-like compound.

[0013] As a preferred embodiment of the second aspect, the metal ion solution is a composite solution of magnesium ions, ferrous ions and ferric ions in a molar ratio of (4-3):1:(2-1); further preferably, the molar ratio of magnesium ions, ferrous ions and ferric ions is 4:1:2.

[0014] In a third aspect, the present invention provides a magnetic solid base catalyst prepared by the preparation method described in any one of the schemes of the second aspect above.

[0015] In a fourth aspect, the present invention provides a method for directional upgrading of polyester materials by methanolysis using the magnetic solid base catalyst as described in the first and third aspects above, comprising:

[0016] The crushed polyester material, the magnetic solid base catalyst and the methanol solvent are placed in a reaction kettle, and a depolymerization reaction is carried out at a depolymerization temperature of 160 to 200° C. for 1 to 4 hours. After the reaction is completed, the temperature is cooled to room temperature to obtain a depolymerization product containing dicarboxylic acid ester crystals and diols;

[0017] The polyester materials are polyethylene terephthalate (PET), polyethylene succinate (PES), polyethylene adipate (PEA), polycarbonate (PC) and polypropylene carbonate (PPC).

[0018] Taking PET as an example, the reaction equation of the above depolymerization reaction can be expressed as:

[0019]

[0020] As a preferred embodiment of the fourth aspect, the added amount of the magnetic solid base catalyst is 0.05wt% to 0.5wt% of the polyester material.

[0021] As a preferred embodiment of the fourth aspect, the added amount of the methanol solvent is 3-6 mL / mmol of the polyester material.

[0022] As a preferred embodiment of the fourth aspect, the polyester material is waste made of polyethylene terephthalate (PET), and the waste needs to be pre-crushed into centimeter-level flakes, particles or powder before adding into the reactor; preferably, the waste is in the form of PET waste bottles, PET matrix waste films, PET colored ropes or PET non-woven fabrics.

[0023] As a preference in the fourth aspect, the depolymerization reaction temperature is preferably 180°C.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The heterogeneous magnetic magnesium-aluminum-iron or magnesium-aluminum-hydrotalcite-derived composite oxide catalyst used in the present invention has the advantages of high efficiency, simple recovery, and multiple recycling, and can promote the methanolysis reaction of PET and the recovery of high-purity DMT crystals in a relatively short time.

[0026] (2) The waste plastic PET methanol depolymerization strategy developed by the present invention has the advantages of short reaction time and high catalytic efficiency, and can complete the directional conversion process of PET to DMT and ethylene glycol with a yield of 99% under standard reaction conditions. This strategy has a wide range of applications, and the types of waste PET raw materials are varied. Various types of PET waste materials such as various types of PET waste bottles, PET matrix waste films, PET colored ropes and PET non-woven fabrics can all be efficiently upgraded and converted in a short time.

[0027] (3) The PET waste plastic matrix material of the present invention can be replaced by various polyesters and polycarbonates with similar structures, such as polyethylene succinate, polyethylene adipate, polycarbonate and polypropylene carbonate, which to a certain extent shows the high applicability of the strategy and further broadens the scope of waste plastic treatment materials. Under the premise of ensuring high depolymerization efficiency and rapid reaction time, the corresponding conversion can be completed to obtain dicarboxylic acid esters and diols. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a demonstration of the catalyst recycling effect of the present invention. DETAILED DESCRIPTION

[0029] In order to make the above-mentioned purpose, features and advantages of the present invention more obvious and easy to understand, a detailed description is given below through specific embodiments. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below. The technical features in each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0030] Example 1

[0031] Preparation of Heterogeneous Catalyst Magnetic Mg-Al-Fe or Mg-Al-Hydrotalcite Derived Composite Oxides (LDOs):

[0032] Various types of hydrotalcites were prepared by coprecipitation at a constant pH of 10, and then magnesium-aluminum hydrotalcite-derived composite oxides (LDOs) were prepared by calcination. First, two solutions were prepared as follows: flask A: 20 mL of deionized water was added, beaker B: 12.20 g of MgCl2·6H2O (0.060 mol), 2.34 g of FeSO4 (0.015 mol) and 8.10 g of FeCl3·6H2O (0.030 mol) were dissolved in 50 mL of deionized water. The contents of beaker B were added to flask A in a dropwise manner. During the dropwise addition, the pH value was maintained at 10 using a 1 mol / L NaOH solution. The resulting mixed solution was reacted at ambient temperature for two hours. Subsequently, the mixed solution was heated to 80°C and stirred and refluxed for 12 hours. The resulting precipitate was filtered, washed with hot deionized water, and then dried in a vacuum oven at 80°C for 24 hours to obtain layered double hydroxide (Mg4 2+ -Fe1 2+ -Fe2 3+ -LDH). In the dried Mg4 2+ -Fe1 2+ -Fe2 3+ -LDH is ground into powder and then calcined, specifically by heating to 500°C in an argon flow in a tube furnace and maintaining for 6 hours. The composite oxide obtained after calcination is the magnesium-aluminum hydrotalcite-derived composite oxide (Mg4 2+ -Fe1 2+ -Fe2 3+ For the convenience of description, the final product is named LDO-I catalyst and is used as the heterogeneous catalyst in subsequent Examples 12 to 20.

[0033] Then, 0.192 g of CR-pure PET powder (1 mmol), 0.01 g of catalyst (two groups of experiments were set up for comparison, one group was added with Mg4 2+ -Fe1 2+ -Fe2 3+ -LDH, and the other group added Mg4 2+ -Fe1 2+ -Fe2 3+-LDO) and 5mL methanol, place the autoclave reactor, start stirring and heating. The reaction system is heated to 180°C and reacted at this temperature for 2h. After the reaction is completed, the temperature is cooled to room temperature, and the resulting mixed solution is the product. The resulting mixed solution is diluted with dichloromethane, and the dilution is measured by GC for yield, with mesitylene as the internal standard and Mg4 2+ -Fe1 2+ -Fe2 3+ -LDH and Mg4 2+ -Fe1 2+ -Fe2 3+ The corresponding DMT yields for the -LDO catalysts were 26% and 88%, respectively (Table 1, entries 1 and 2).

[0034] Example 2

[0035] In this example, the raw materials in Example 1 were replaced with 12.20 g MgCl2·6H2O (0.060 mol), 2.34 g FeSO4 (0.015 mol) and 4.05 g FeCl3·6H2O (0.015 mol), and the rest of the process remained the same. The obtained compound was called Mg4 2+ -Fe1 2+ -Fe1 3+ -LDH, then the dried compound is ground and calcined to obtain compound Mg4 2 + -Fe1 2+ -Fe1 3+ -LDO.

[0036] Then, 0.192 g of CR-pure PET powder (1 mmol), 0.01 g of Mg4 2+ -Fe1 2+ -Fe1 3+ -LDO catalyst and 5mL methanol, place the autoclave reactor, start stirring and heating. The reaction system is heated to 180°C and reacted at this temperature for 2h. After the reaction is completed, cool to room temperature, and the resulting mixed solution is the product. The resulting mixed solution is diluted with dichloromethane, and the dilution is measured by GC for yield, with mesitylene as the internal standard, and the DMT yield is 86% (Table 1, entry 3).

[0037] Example 3

[0038] In this example, the raw materials in Example 1 were replaced with 9.15 g MgCl2·6H2O (0.045 mol), 2.34 g FeSO4 (0.015 mol) and 4.05 g FeCl3·6H2O (0.015 mol), and the rest of the process remained the same. The obtained compound was called Mg32+ -Fe1 2+ -Fe1 3+ -LDH, and then the dried compound is ground and calcined to obtain compound Mg3 2+ -Fe1 2 + -Fe1 3+ -LDO.

[0039] Then, 0.192 g of CR-pure PET powder (1 mmol), 0.01 g of Mg3 2+ -Fe1 2+ -Fe1 3+ -LDO catalyst and 5mL methanol, after placing the autoclave reactor, start stirring and heating. The reaction system is heated to 180°C and reacted at this temperature for 2h. After the reaction is completed, it is cooled to room temperature, and the resulting mixed solution is the product. The resulting mixed solution is diluted with dichloromethane, and the diluent is measured by GC for yield, with mesitylene as the internal standard, and the DMT yield is 83% (Table 1, entry 4).

[0040] Example 4

[0041] In this example, the raw materials in Example 1 were replaced with 6.10 g MgCl2·6H2O (0.030 mol), 2.34 g FeSO4 (0.015 mol) and 4.05 g FeCl3·6H2O (0.015 mol), and the rest of the process remained the same. The obtained compound was called Mg2 2+ -Fe1 2+ -Fe1 3+ -LDH, then the dried compound is ground and calcined to obtain compound Mg2 2+ -Fe1 2 + -Fe1 3+ -LDO.

[0042] Then, 0.192 g of CR-pure PET powder (1 mmol), 0.01 g of Mg2 2+ -Fe1 2+ -Fe1 3+ -LDO catalyst and 5mL methanol, after placing the autoclave reactor, start stirring and heating. The reaction system is heated to 180°C and reacted at this temperature for 2h. After the reaction is completed, it is cooled to room temperature, and the resulting mixed solution is the product. The resulting mixed solution is diluted with dichloromethane, and the dilution is measured by GC for yield, with mesitylene as the internal standard, and the DMT yield is 78% (Table 1, entry 5).

[0043] Example 5

[0044] In this example, the raw materials in Example 1 were replaced with 12.20 g MgCl2·6H2O (0.060 mol) and 4.05 g FeCl3·6H2O (0.015 mol), and the rest of the process remained the same. The obtained compound was called Mg4 2+ -Fe1 3+ -LDH, then the dried compound is ground and calcined to obtain compound Mg4 2+ -Fe1 3+ -LDO.

[0045] Then, 0.192 g of CR-pure PET powder (1 mmol), 0.01 g of Mg4 2+ -Fe1 3+ -LDO catalyst and 5mL methanol, after placing the autoclave reactor, start stirring and heating. The reaction system is heated to 180°C and reacted at this temperature for 2h. After the reaction is completed, it is cooled to room temperature, and the resulting mixed solution is the product. The resulting mixed solution is diluted with dichloromethane, and the diluent is measured by GC for yield, with mesitylene as the internal standard, and the DMT yield is 34% (Table 1, entry 6).

[0046] Example 6

[0047] In this example, the raw materials in Example 1 were replaced with 12.20 g MgCl2·6H2O (0.060 mol), 3.62 g AlCl3·6H2O (0.015 mol) and 4.05 g FeCl3·6H2O (0.015 mol), and the rest of the process remained the same. The obtained compound was called Mg4 2+ -Al1 2+ -Fe1 3+ -LDH, then the dried compound is ground and calcined to obtain compound Mg4 2+ -Al1 2+ -Fe1 3+ -LDO.

[0048] Then, 0.192 g of CR-pure PET powder (1 mmol), 0.01 g of Mg4 2+ -Al1 2+ -Fe1 3+-LDO catalyst and 5mL methanol, place the autoclave reactor, start stirring and heating. The reaction system is heated to 180°C and reacted at this temperature for 2h. After the reaction is completed, it is cooled to room temperature, and the resulting mixed solution is the product. The resulting mixed solution is diluted with dichloromethane, and the dilution is measured by GC for yield, with mesitylene as the internal standard, and the DMT yield is 80% (Table 1, entry 7).

[0049] Example 7

[0050] In this example, the raw materials in Example 1 were replaced with 12.20 g MgCl2·6H2O (0.060 mol), 3.62 g AlCl3·6H2O (0.015 mol) and 8.10 g FeCl3·6H2O (0.03 mol), and the rest of the process remained the same. The obtained compound was called Mg4 2+ -Al1 2+ -Fe2 3+ -LDH, then the dried compound is ground and calcined to obtain compound Mg4 2+ -Al1 2+ -Fe2 3+ -LDO.

[0051] Then, 0.192 g of CR-pure PET powder (1 mmol), 0.01 g of Mg4 2+ -Al1 2+ -Fe2 3+ -LDO catalyst and 5mL methanol, place the autoclave reactor, start stirring and heating. The reaction system is heated to 180°C and reacted at this temperature for 2h. After the reaction is completed, it is cooled to room temperature, and the resulting mixed solution is the product. The resulting mixed solution is diluted with dichloromethane, and the dilution is measured by GC to determine the yield, with mesitylene as the internal standard, and the DMT yield is 28% (Table 1, entry 8).

[0052] Example 8

[0053] In this example, the raw materials in Example 1 were replaced with 12.20 g MgCl2·6H2O (0.060 mol), 2.40 g γ-Fe2O3 (0.015 mol) and 4.05 g FeCl3·6H2O (0.015 mol), and the rest of the process remained the same. The obtained compound was called Mg4 2+ -Fe1 3+ -γ-Fe2O3-LDH, and then the dried compound is ground and calcined to obtain compound Mg4 2+ -Fe1 3+ -γ-Fe2O3-LDO.

[0054] Then, 0.192 g of CR-pure PET powder (1 mmol), 0.01 g of Mg4 2+ -Fe1 3+ -γ-Fe2O3-LDH catalyst and 5mL methanol were placed in the autoclave reactor, and stirring and heating were started. The reaction system was heated to 180°C and reacted at this temperature for 2h. After the reaction was completed, the temperature was cooled to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the dilution was measured by GC for yield, with mesitylene as the internal standard, and the DMT yield was 58% (Table 1, entry 9).

[0055] Example 9

[0056] In this example, the raw materials in Example 1 were replaced with 12.20 g MgCl2·6H2O (0.060 mol), 3.47 g Fe4O3 (0.015 mol) and 4.05 g FeCl3·6H2O (0.015 mol), and the rest of the process remained the same. The obtained compound was called Mg4 2+ -Fe1 3+ -Fe4O3-LDH, and then the dried compound is ground and calcined to obtain the compound Mg4 2 + -Fe1 3+ -Fe4O3-LDH.

[0057] Then, 0.192 g of CR-pure PET powder (1 mmol), 0.01 g of Mg4 2+ -Fe1 3+ -Fe4O3-LDH catalyst and 5mL methanol were placed in the autoclave reactor, and stirring and heating were started. The reaction system was heated to 180°C and reacted at this temperature for 2h. After the reaction was completed, the temperature was cooled to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the dilution was measured by GC for yield, with mesitylene as the internal standard, and the DMT yield was 76% (Table 1, entry 10).

[0058] Example 10

[0059] In this example, the raw materials in Example 1 were replaced with 12.20 g MgCl2·6H2O (0.060 mol) and 3.47 g Fe4O3 (0.015 mol), and the rest of the process remained the same. The obtained compound was called Mg4 2+ -Fe4O3-LDH, and then the dried compound is ground and calcined to obtain the compound Mg4 2+-Fe4O3-LDO.

[0060] Then, 0.192 g of CR-pure PET powder (1 mmol), 0.01 g of Mg4 2+ -Fe4O3-LDO catalyst and 5mL methanol were placed in the autoclave reactor, and stirring and heating were started. The reaction system was heated to 180°C and reacted at this temperature for 2h. After the reaction was completed, the temperature was cooled to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the dilution was measured by GC for yield, with mesitylene as the internal standard, and the DMT yield was 80% (Table 1, entry 11).

[0061] Embodiment 11

[0062] In this embodiment, the calcination temperature in Example 1 was adjusted, and the other methods remained the same, that is, the Mg4 2+ -Fe1 2+ -Fe2 3+ -LDH was calcined at 400℃ and 600℃ respectively to obtain Mg4 2+ -Fe1 2+ -Fe2 3 + -LDO 400℃ and Mg4 2+ -Fe1 2+ -Fe2 3+ -LDO 600℃ .

[0063] Then, 0.192 g of CR-pure PET powder (1 mmol), 0.01 g of catalyst (two groups of experiments were set up for comparison, one group of catalysts used Mg4 2+ -Fe1 2 + -Fe2 3+ -LDO 400℃ , another group of catalysts uses Mg4 2+ -Fe1 2+ -Fe2 3+ -LDO 600℃ ) and 5mL methanol, place the autoclave reactor, start stirring and heating. The reaction system is heated to 180°C and reacted at this temperature for 2h. After the reaction is completed, the temperature is cooled to room temperature, and the resulting mixed solution is the product. The resulting mixed solution is diluted with dichloromethane, and the dilution is measured by GC for yield, with mesitylene as the internal standard and Mg4 2+ -Fe1 2+ -Fe2 3+ -LDO400℃ and Mg4 2+ -Fe1 2+ -Fe2 3+ -LDO 600℃ The corresponding DMT yields of the catalysts were 53% and 85%, respectively (Table 1, entries 12-13).

[0064] In the above Examples 1 to 11, the preparation parameters and effects of different catalysts are summarized in Table 1:

[0065] Table 1 is a comparison chart of the catalyst effects of the present invention.

[0066]

[0067]

[0068] The comparison of experimental data in Table 1 shows that adjusting the ratio of divalent magnesium, divalent iron and trivalent iron in the catalyst has a significant effect on the catalytic effect of the reaction, while adjusting the raw material sources of different metals has little effect on the reaction. In addition, the calcined hydrotalcite in the present invention shows better catalytic activity.

[0069] Example 12

[0070] In the present invention, taking PET as an example, the depolymerization process is as follows: crushed PET powder, magnetic solid base catalyst LDO-Ⅰ and methanol solvent are placed in a reactor, and a depolymerization reaction is carried out at a depolymerization temperature of 160 to 200° C. for 1 to 4 hours. After the reaction is completed, the temperature is cooled to room temperature to obtain a depolymerization product containing dicarboxylic acid ester crystals and diols.

[0071] In this example, LDO-Ⅰ prepared in Example 1 was used to optimize and explore different control parameters in the above depolymerization process.

[0072] In this embodiment, the method is as follows:

[0073] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 grams of CR-pure PET powder (1 mmol), catalysts of different amounts m, and 5 mL of methanol were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to T ° C and reacted at this temperature for t hours. After the reaction was completed, it was cooled to room temperature, and the resulting mixed solution was the product. The comparative parameters set in this embodiment are as follows: the reaction time t is adjusted to 2h, 3h and 4h (Table 2, entries 1-3), the catalyst loading m is set to 0.05g, 0.08g and 0.1g (Table 2, entries 4-6), and the reaction temperature T is 160 ° C and 180 ° C (Table 2, entries 7-8), so as to determine the optimal reaction conditions. The resulting mixed solution was diluted with dichloromethane, and the diluent was measured by GC for yield, with mesitylene as the internal standard, and the yield is shown in Table 2.

[0074] Table 2 is the optimization results of the present invention.

[0075]

[0076]

[0077] The experimental data in Table 2 above show that the DMT yield is positively correlated with the reaction time, catalyst loading and reaction temperature. The results show that the optimal reaction conditions are a catalyst loading of 0.03 g, a reaction temperature of 180° C. and a reaction time of 2 h.

[0078] Embodiment 13

[0079] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 g of CR-pure PET powder (1 mmol), 0.03 g of catalyst LDO-Ⅰ, and 5 mL of methanol were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 180°C and reacted at this temperature for 3 hours. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the diluent was measured for yield by GC, with mesitylene as the internal standard. The results showed that the PET decomposition rate of this embodiment was 100%, and the yield of dimethyl terephthalate was 99%.

[0080] In addition, in order to prove the recyclability of the catalyst in the present invention, the catalyst Mg4 2+ -Fe1 2 + -Fe1 3+ -LDO was separated and recovered, and after being rinsed and impurities removed, it was dried at 200℃, and the recovered catalyst was directly recycled to the next reaction. Figure 1As shown, after being reused for 6 times, the yield of dimethyl terephthalate still remains at 99%, indicating that the catalyst of the present invention still maintains excellent catalytic activity after multiple cycles.

[0081] Embodiment 14

[0082] Discarded PET plastic bottles (Coca-Cola, Pepsi and Nongfu Spring brands) were crushed to centimeter level in advance, and then 0.192 grams of PET plastic bottles were crushed to centimeter level (1mmol), 0.05 grams of catalyst LDO-Ⅰ and 5mL methanol were added to an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple and a program temperature controller. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 180°C and reacted at this temperature for 3h. After the reaction was completed, it was cooled to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the diluent was measured for yield by GC, with mesitylene as the internal standard. The results showed that the decomposition rate of this embodiment was 100%, and the yield of dimethyl terephthalate was 99%.

[0083] Embodiment 15

[0084] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 g of PET film (1 mmol), 0.03 g of catalyst LDO-Ⅰ, and 5 mL of methanol were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 180°C and reacted at this temperature for 3 hours. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the diluent was measured for yield by GC, with mesitylene as the internal standard. The results showed that the decomposition rate of this embodiment was 100%, and the yield of dimethyl terephthalate was 99%.

[0085] Example 16

[0086] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 g of PET snakeskin rope (1 mmol), 0.03 g of catalyst LDO-Ⅰ, and 5 mL of methanol were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 180°C and reacted at this temperature for 3 hours. After the reaction was completed, the temperature was cooled to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the diluent was measured for yield by GC, with mesitylene as the internal standard. The results showed that the decomposition rate of this embodiment was 100%, and the yield of dimethyl terephthalate was 99%.

[0087] Embodiment 17

[0088] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.172 g of polyethylene adipate (1 mmol), 0.03 g of catalyst LDO-Ⅰ, and 5 mL of methanol were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 180°C and reacted at this temperature for 3 hours. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The yield was determined by H NMR, with mesitylene as the internal standard. The results showed that the decomposition rate of polyethylene adipate in this embodiment was 100%, the yield of dimethyl adipate was 99%, and the yield of ethylene glycol was 99%.

[0089] Embodiment 18

[0090] 0.144 g of polyethylene succinate (1 mmol), 0.03 g of catalyst LDO-Ⅰ and 5 mL of methanol were added to an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple and a programmable temperature controller. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 180°C and reacted at this temperature for 3 hours. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The yield was determined by H NMR, with mesitylene as the internal standard. The results showed that the decomposition rate of polyethylene succinate in this embodiment was 100%, the yield of dimethyl succinate was 99%, and the yield of ethylene glycol was 99%.

[0091] Embodiment 19

[0092] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.254 g of polycarbonate (1 mmol), 0.03 g of catalyst LDO-Ⅰ, and 5 mL of methanol were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 180°C and reacted at this temperature for 3 hours. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The yield was determined by H NMR method, with mesitylene as the internal standard. The results showed that the decomposition rate of polypropylene carbonate particles in this embodiment was 100%, the yield of dimethyl carbonate was 98%, and the yield of bisphenol A was 97%.

[0093] Embodiment 20

[0094] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.102 g of polypropylene carbonate particles (1 mmol), 0.03 g of catalyst LDO-Ⅰ, and 5 mL of methanol were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 180°C and reacted at this temperature for 3 hours. After the reaction was completed, the temperature was cooled to room temperature, and the resulting mixed solution was the product. The yield was determined by H NMR method, with mesitylene as the internal standard. The results showed that the decomposition rate of polypropylene carbonate particles in this embodiment was 100%, the yield of dimethyl carbonate was 94%, and the yield of propylene glycol was 96%.

[0095] The above-described embodiment is only a preferred solution of the present invention, but it is not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A method for directional upgrading of polyester materials by methanolysis using a magnetic solid base catalyst, characterized in that: include: The crushed polyester material, the magnetic solid base catalyst and the methanol solvent are placed in a reaction kettle, and a depolymerization reaction is carried out at a depolymerization temperature of 160-200° C. for 1-4 hours, and the temperature is cooled to room temperature after the reaction is completed to obtain a depolymerization product containing dicarboxylic acid ester crystals and diols; The polyester material is polyethylene terephthalate (PET), polyethylene succinate (PES), polyethylene adipate (PEA), polycarbonate (PC) or polypropylene carbonate (PPC); The preparation method of the magnetic solid base catalyst is as follows: S1. gradually adding a metal ion solution into an alkaline solution system to prepare a hydrotalcite-like compound by a coprecipitation method; the metal ion solution is a composite solution of magnesium ions, ferrous ions and ferric ions in a molar ratio of (4-3):1:(2-1); S2. Grind the hydrotalcite-like compound and then calcine it in an inert atmosphere at a temperature of 500-600° C. for 4-8 h to finally obtain a magnetic composite oxide derived from the hydrotalcite-like compound.

2. The method for directional upgrading of polyester materials by methanolysis according to claim 1, characterized in that: In the co-precipitation method, a metal ion solution is gradually added to water, and a NaOH solution is simultaneously added to maintain the pH of the system at 9.5-10.

5. The final mixed solution is fully reacted at ambient temperature and then heated to 60-80°C while being stirred and refluxed for 8-16 hours. The precipitate is filtered, washed and dried to obtain a hydrotalcite-like compound.

3. The method for directional upgrading of polyester materials by methanolysis according to claim 1, characterized in that: The metal ion solution is a composite solution of magnesium ions, ferrous ions and ferric ions in a molar ratio of 4:1:

2.

4. The method for directional upgrading of polyester materials by methanolysis according to claim 1, characterized in that: The added amount of the magnetic solid base catalyst is 0.05 wt% to 0.5 wt% of the polyester material.

5. The method for directional upgrading of polyester materials by methanolysis according to claim 1, characterized in that: The amount of the methanol solvent added is 3-6 mL / mmol of the polyester material.

6. The method for directional upgrading of polyester materials by methanolysis according to claim 1, characterized in that: The polyester material is waste made of polyethylene terephthalate (PET), and the waste needs to be pre-crushed into centimeter-level flakes, particles or powder before adding it to the reactor; the waste is in the form of PET waste bottles, PET matrix waste films, PET colored ropes or PET non-woven fabrics.

7. The method for directional upgrading of polyester materials by methanolysis according to claim 1, characterized in that: The depolymerization reaction temperature is 180°C.

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