A pet degradation catalyst, a preparation method and application thereof

Abstract

The application discloses a PET degradation catalyst, a preparation method thereof and application of the PET degradation catalyst in a DMT preparation process based on PET degradation. The preparation method comprises the following steps: fully cleaning industrial waste residues, drying the waste residues, ball-milling and sieving the waste residues, fully mixing the waste residues with organic acid, drying the waste residues, and performing heat treatment on the waste residues under an inert atmosphere to obtain a PET degradation catalyst with calcium oxide / carbon composite. The catalyst is applied to PET methanolysis, and the obtained dimethyl terephthalate has a purity of 98-99% and a yield of 90-95%. In addition, graphite contained in the waste residues can adsorb dyes carried by PET in the degradation process, so that a subsequent decoloring treatment process is omitted. The PET degradation catalyst has high degradation capacity for PET, and the obtained product has high purity and yield, and the process is simple, raw materials are cheap, and the PET degradation catalyst has a good application prospect.

Description

Technical Field

[0001] This invention relates to the field of waste polyester degradation technology, and in particular to a PET degradation catalyst, its preparation method, and its application. Background Technology

[0002] Polyethylene terephthalate (PET) is commonly used in textiles, plastic bottles, and food packaging. However, with the widespread use of PET, the pollution problem caused by waste PET has become increasingly serious. Large quantities of PET plastic are difficult for microorganisms to degrade in nature, thus causing great harm to the environment. How to recycle PET has attracted the attention of researchers worldwide.

[0003] The recycling of waste PET can be divided into physical recycling and chemical recycling. Physical recycling refers to the mechanical crushing, melting, and granulation of used PET for regeneration. Although this method is simple and low-cost, the extrusion and melting during the recycling process reduce the mechanical properties of the polymer, resulting in low-performance products and low economic benefits. Chemical recycling, on the other hand, depolymerizes waste PET into polymer monomers through chemical reactions. The generated monomers can be used to polymerize and regenerate PET with intact physicochemical properties, or further upgraded to produce high-value chemicals or petroleum-derived chemicals, potentially achieving the requirements of a circular polymer economy.

[0004] The main methods for chemical recycling of PET include hydrolysis, methanol hydrolysis, glycolysis, and ammonolysis; among them, the degradation product obtained by methanol hydrolysis is dimethyl terephthalate (DMT).

[0005] Traditional methanol hydrolysis is extremely energy-intensive and requires extensive equipment, involving supercritical conditions at temperatures above 300°C and pressures of 0.5–1.0 MPa. This can lead to structural changes in PET molecular units, including isomerization or pyrolysis. These modified molecules may be toxic or disrupt the production of recycled PET, affecting the quality of the depolymerized products in future applications.

[0006] For example, Chinese patent document CN1413178A discloses a method for separating and recovering dimethyl terephthalate and ethylene glycol from polyester (polyethylene terephthalate (PET)) waste containing inclusions. This method includes the steps of treating the mixture in ethylene glycol containing a depolymerization catalyst at 175-190°C and a pressure of 0.1-0.5 MPa, and removing solid inclusions floating to the surface of the resulting liquid reaction mixture by flotation separation; removing residual solid inclusions from the resulting mixture by solid-liquid separation; and making the resulting solution… The process includes the following steps: distillation and concentration to recover the distilled EG; adding an ester transfer catalyst and methanol to the resulting residual solution to induce an ester transfer reaction between the residual solution and methanol to form DMT and EG; recrystallizing the resulting reaction mixture and then centrifuging it to separate the mixture into a DMT filter cake and a mixed solution; distilling the filter cake to distill off and recover high-purity DMT; distilling the residual mixed solution to recover methanol; and distilling the resulting residue to recover EG.

[0007] In response, Chinese patent document CN116685572A improves upon the traditional methanol alcoholysis method by disclosing an improved method for recovering PET through alcoholysis. The depolymerization step is carried out in the presence of a monohydric alcohol and an organic base having guanidine or amidine units, and a second base; the second base can be an inorganic base or an oxide ether.

[0008] However, existing PET depolymerization processes still generate a significant amount of byproducts and oligomers, resulting in low purity of DMT obtained from depolymerization. Furthermore, most PET production processes involve the addition of dyes, which are carried into the product after depolymerization, necessitating additional dye removal steps. Summary of the Invention

[0009] To address the aforementioned technical problems in the existing technology, the present invention aims to provide a PET degradation catalyst, its preparation method, and its application. The PET degradation catalyst of the present invention can efficiently catalyze the degradation of PET to dimethyl terephthalate, while also exhibiting good decolorization effects. During catalytic PET degradation, it can simultaneously remove dyes and impurities from PET, yielding high-purity dimethyl terephthalate in one step.

[0010] The technical solution of the present invention is as follows:

[0011] A method for preparing a PET degradation catalyst, comprising:

[0012] The industrial waste residue is thoroughly cleaned, dried, ball-milled, and sieved. 100-300 mesh industrial waste residue powder is selected, thoroughly mixed with organic acid, dried, and then heat-treated at 600-900℃ for 2-20 hours under an inert atmosphere to obtain a calcium oxide / carbon composite PET degradation catalyst.

[0013] The industrial waste residue mentioned above is the waste residue generated during the production process of chemicals using calcium cyanamide as a raw material, after the calcium cyanamide is hydrolyzed and then precipitated and filtered by passing carbon dioxide through it.

[0014] The chemicals that use calcium cyanamide as a raw material are cyanamide, dicyandiamide, thiourea, or carbendazim;

[0015] The main components of the waste residue are calcium carbonate and graphite; the calcium carbonate content in the waste residue is 85-95%, and the graphite content is 5-15%.

[0016] The main component of industrial waste residue is calcium carbonate, which is micron- or even nano-sized, possessing excellent specific surface area and small particle size. This allows it to effectively contact PET molecules, entering the PET macromolecular structure for catalytic reactions and improving mass transfer. This, in turn, reduces the formation of byproducts and oligomers, increasing the purity of dimethyl terephthalate (DMT) products. The added organic acid is calcined into carbon at high temperature and under an inert atmosphere, forming a thin film on the calcium oxide surface. This restricts calcium oxide grain growth, increases the catalyst's specific surface area, and further enhances its degradation of PET. Furthermore, the graphite in the waste residue adsorbs dyes carried by the PET itself during degradation, eliminating the need for subsequent decolorization and simplifying the process. Compared to commonly used activated carbon adsorbents, the graphite in the waste residue does not adsorb products, thus not reducing product purity or yield.

[0017] Preferably, the organic acid is at least one selected from citric acid, malic acid, tartaric acid, oxalic acid, and ascorbic acid.

[0018] Further preferably, the mass ratio of industrial waste residue to organic acid is 10-1:1. Too much organic acid will cause the carbon formed during high-temperature, inert atmosphere roasting to completely encapsulate the waste residue, preventing the active sites of the catalyst from being fully exposed. Too little organic acid will prevent the formation of a coating layer, making it difficult to limit the growth of calcium oxide particles. Furthermore, the carbon dioxide and carbon monoxide gases produced during the carbonization and decomposition of organic acid can regulate the decomposition process of calcium carbonate in the waste residue, further limiting the growth of calcium oxide particles during heat treatment.

[0019] The industrial waste residue has a particle size of 100-300 mesh. If the particle size of the industrial waste residue is too large, the binding effect between the waste residue and organic acid will be poor, and the formed carbon will not be effectively coated on the waste residue; if the particle size of the industrial waste residue is too small, the carbon formed by the organic acid may completely coat the waste residue, and the active centers of the catalyst will not be fully exposed, resulting in low catalytic performance.

[0020] The inert atmosphere is a nitrogen and / or argon atmosphere.

[0021] This invention also provides a calcium oxide / carbon composite PET degradation catalyst prepared by the above-described method. This catalyst exhibits excellent catalytic performance in PET degradation, specifically in the degradation of PET to dimethyl terephthalate, and also demonstrates good decolorization effects.

[0022] This invention also provides a process for preparing DMT based on the degradation of PET using a PET degradation catalyst, comprising:

[0023] The PET degradation catalyst and PET fragments were added to methanol and stirred. Under an inert atmosphere, the mixture was heated to the reaction temperature and stirred. After the reaction was completed, the mixture was cooled to room temperature. A solvent to dissolve DMT was added and stirred to dissolve the DMT. The mixture was then filtered, and the filter residue was dried to obtain the recovered PET degradation catalyst. The filtrate was concentrated to remove the solvent, and the target product, dimethyl terephthalate, was obtained.

[0024] Preferably, the mass ratio of PET to PET degradation catalyst is 4-20:1, and the mass ratio of PET to methanol is 1:5-20.

[0025] Preferably, the reaction temperature is 160-200℃ and the reaction time is 1-6h.

[0026] More preferably, the stirring rate of the stirring reaction is 300-1000 r / min.

[0027] Preferably, the solvent for dissolving DMT is at least one of n-butanol, tetrahydrofuran, chloroform, cyclohexanone, ethyl acetate, and acetonitrile.

[0028] Preferably, the diameter of the PET fragments is less than 10 mm.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] This invention uses industrial waste residue as raw material to prepare a calcium oxide / carbon composite catalyst for PET degradation. It not only obtains a highly efficient PET degradation catalyst at a lower production cost, but also solves the environmental hazards of waste PET and industrial waste residue, increases the added value of waste PET and industrial waste residue, and realizes the high-value utilization of industrial waste residue, turning waste into treasure, and provides a new way for the comprehensive utilization of industrial waste residue. Attached Figure Description

[0031] Figure 1 This is a diagram of the products obtained by degrading colored PET using the calcium oxide / carbon composite catalyst prepared in Example 1.

[0032] Figure 2 This is a diagram of the products after the calcium oxide catalyst prepared in Comparative Example 1 degrades colored PET.

[0033] Figure 3 The image shows the products after the catalyst prepared in Comparative Example 3 degraded colored PET.

[0034] Figure 4 The nitrogen adsorption curve of the calcium oxide / carbon composite catalyst prepared in Example 1 is shown. Detailed Implementation

[0035] In the following examples, the PET used is all recycled waste PET.

[0036] Example 1

[0037] Weigh 10g of cyanamide waste residue, soak it in deionized water overnight, and then filter it. Place the washed industrial waste residue in an oven to dry. After drying, place it in a ball mill and ball mill for 30 minutes, repeating twice. Sieve the ball-milled waste residue through a 200-mesh sieve and select the portion larger than 200 mesh. Prepare a citric acid solution of a certain concentration, and measure the citric acid solution according to a certain mass ratio (waste residue: citric acid = 5:1). Then add it to the waste residue, stir evenly, and dry. Place the waste residue combined with citric acid in a tube furnace, introduce nitrogen gas, and raise the temperature of the material in the tube furnace to 800℃ and keep it at that temperature for 5 hours. Then cool down to obtain the calcium oxide / carbon composite catalyst.

[0038] Waste PET was cut into 5mm x 5mm pieces, placed in a beaker, and washed twice in an ultrasonic cleaner with deionized water for 5 minutes each time. After filtration, the pieces were air-dried for later use. 0.1g of the obtained catalyst, 1g of PET, and 10g of anhydrous methanol were added to a reaction vessel. The reaction vessel was assembled, and temperature, pressure, and stirrer were connected. The reaction vessel was purged three times with nitrogen to replace the air, and the mechanical stirring rate was fixed at 800 rpm. -1 The reaction system was kept at 160℃ for 2 hours. After the reaction was complete, the reactor was cooled in a water bath. After cooling, the reactor was opened, and the reaction mixture was dissolved in a certain amount of THF. The mixture was then filtered, and the residue was dried at 80℃ and weighed. The filtrate was added to a 50 / 25mL volumetric flask and diluted to volume with THF. A sample was then taken for gas chromatography analysis. The remaining filtrate was concentrated to remove the solvent, yielding the target product DMT.

[0039] Example 2

[0040] Weigh 10g of cyanamide waste residue, soak it in deionized water overnight, and then filter it. Place the washed industrial waste residue in an oven to dry. After drying, place it in a ball mill and ball mill for 30 minutes, repeating twice. Sieve the ball-milled waste residue through a 200-mesh sieve and select the portion larger than 200 mesh. Prepare a citric acid solution of a certain concentration, and measure the citric acid solution according to a certain mass ratio (waste residue: citric acid = 5:1). Then add it to the waste residue, stir evenly, and dry. Place the waste residue combined with citric acid in a tube furnace, introduce nitrogen gas, and raise the temperature of the material in the tube furnace to 600℃ and keep it at that temperature for 5 hours. Then cool down to obtain the calcium oxide / carbon composite catalyst.

[0041] Waste PET was cut into 5mm x 5mm pieces, placed in a beaker, and washed twice in an ultrasonic cleaner with deionized water for 5 minutes each time. After filtration, the pieces were air-dried for later use. 0.1g of the obtained catalyst, 1g of PET, and 10g of anhydrous methanol were added to a reaction vessel. The reaction vessel was assembled, and temperature, pressure, and stirrer were connected. The reaction vessel was purged three times with nitrogen to replace the air, and the mechanical stirring rate was fixed at 800 rpm. -1 The reaction system was kept at 160℃ for 2 hours. After the reaction was complete, the reactor was cooled in a water bath. After cooling, the reactor was opened, and the reaction mixture was dissolved in a certain amount of THF. The mixture was then filtered, and the residue was dried at 80℃ and weighed. The filtrate was added to a 50 / 25mL volumetric flask and diluted to volume with THF. A sample was then taken for gas chromatography analysis. The remaining filtrate was concentrated to remove the solvent, yielding the target product DMT.

[0042] Example 3

[0043] Weigh 10g of cyanamide waste residue, soak it in deionized water overnight, and then filter it. Place the washed industrial waste residue in an oven to dry. After drying, place it in a ball mill and ball mill for 30 minutes, repeating twice. Sieve the ball-milled waste residue through a 200-mesh sieve and select the portion larger than 200 mesh. Prepare a citric acid solution of a certain concentration, and measure the citric acid solution according to a certain mass ratio (waste residue: citric acid = 5:1). Then add it to the waste residue, stir evenly, and dry. Place the waste residue combined with citric acid in a tube furnace, introduce nitrogen gas, and raise the temperature of the material in the tube furnace to 800℃ and keep it at that temperature for 5 hours. Then cool down to obtain the calcium oxide / carbon composite catalyst.

[0044] Cut waste PET into 5mm x 5mm pieces, place them in a beaker, add deionized water, and clean twice in an ultrasonic cleaner for 5 minutes each time. Filter and air dry for later use. Add 0.1g of the obtained catalyst, 1g of PET, and 10g of anhydrous methanol to the reactor. Install the reactor, connect the temperature and pressure sensors, and the stirrer. Purge the reactor three times with nitrogen to replace the air, and set the mechanical stirring speed to a fixed 700 rpm. -1 The reaction system was kept at 160℃ for 2 hours. After the reaction was complete, the reactor was cooled in a water bath. After cooling, the reactor was opened, and the reaction mixture was dissolved in a certain amount of THF. The mixture was then filtered, and the residue was dried at 80℃ and weighed. The filtrate was added to a 50 / 25mL volumetric flask and diluted to volume with THF. A sample was then taken for gas chromatography analysis. The remaining filtrate was concentrated to remove the solvent, yielding the target product DMT.

[0045] Example 4

[0046] Weigh 10g of cyanamide waste residue, soak it in deionized water overnight, and then filter it. Place the washed industrial waste residue in an oven to dry. After drying, place it in a ball mill and ball mill for 30 minutes, repeating twice. Sieve the ball-milled waste residue through a 200-mesh sieve and select the portion larger than 200 mesh. Prepare a citric acid solution of a certain concentration, and measure the citric acid solution according to a certain mass ratio (waste residue: citric acid = 5:1). Then add it to the waste residue, stir evenly, and dry. Place the waste residue combined with citric acid in a tube furnace, introduce nitrogen gas, and raise the temperature of the material in the tube furnace to 900℃ and keep it at that temperature for 5 hours. Then cool down to obtain the calcium oxide / carbon composite catalyst.

[0047] Waste PET was cut into 5mm x 5mm pieces, placed in a beaker, and washed twice in an ultrasonic cleaner with deionized water for 5 minutes each time. After filtration, the pieces were air-dried for later use. 0.1g of the obtained catalyst, 1g of PET, and 10g of anhydrous methanol were added to a reaction vessel. The reaction vessel was assembled, and temperature, pressure, and stirrer were connected. The reaction vessel was purged three times with nitrogen to replace the air, and the mechanical stirring rate was fixed at 800 rpm. -1 The reaction system was kept at 160℃ for 2 hours. After the reaction was complete, the reactor was cooled in a water bath. After cooling, the reactor was opened, and the reaction mixture was dissolved in a certain amount of THF. The mixture was then filtered, and the residue was dried at 80℃ and weighed. The filtrate was added to a 50 / 25mL volumetric flask and diluted to volume with THF. A sample was then taken for gas chromatography analysis. The remaining filtrate was concentrated to remove the solvent, yielding the target product DMT.

[0048] Example 5

[0049] The method was carried out according to Example 1, except that the organic acid combined with the waste residue was malic acid.

[0050] Example 6

[0051] The method was carried out according to Example 1, except that the organic acid combined with the waste residue was oxalic acid.

[0052] Example 7

[0053] The method was implemented according to Example 1, except that the mass ratio of the sieved waste residue to citric acid was 1:1.

[0054] Example 8

[0055] The method was implemented according to Example 1, except that the mass ratio of the sieved waste residue to citric acid was 10:1.

[0056] Example 9

[0057] The method was carried out according to Example 1, except that the reaction temperature was 180°C.

[0058] Example 10

[0059] The method was carried out according to Example 1, except that the reaction temperature was 200°C.

[0060] Comparative Example 1

[0061] Commercial calcium carbonate was weighed and placed in a tube furnace. Nitrogen gas was introduced to raise the temperature of the material in the tube furnace to 800°C and maintain the temperature for 5 hours. Then the temperature was lowered and the calcium oxide catalyst was obtained.

[0062] Subsequent degradation steps were carried out according to the method in Example 1.

[0063] Comparative Example 2

[0064] The method was carried out according to Example 1, except that commercial calcium oxide was directly used as the catalyst.

[0065] Comparative Example 3

[0066] Weigh 10g of cyanamide waste residue, soak it in deionized water overnight, and then filter it. Place the washed industrial waste residue in an oven to dry. After drying, place it in a ball mill and ball mill for 30 minutes, repeating twice. Use a 200-mesh sieve to sieve the waste residue after ball milling and select the portion larger than 200 mesh. Place 2g of the sieved waste residue in a tube furnace, introduce nitrogen gas, and bring the temperature of the material in the tube furnace to 800℃ and keep it at that temperature for 5 hours. Then cool it down to obtain the PET degradation catalyst.

[0067] Subsequent degradation steps were carried out according to the method in Example 1.

[0068] The specific surface area and pore volume of the catalysts obtained in Examples 1-8 and Comparative Examples 1-3 were tested, and the results are shown in Table 1.

[0069] Table 1

[0070] <![CDATA[S.A.(m 2 / g)]]> <![CDATA[P.V.(cm 3 / g)]]> Example 1 232 0.18 Example 2 198 0.13 Example 3 208 0.13 Example 4 210 0.16 Example 5 182 0.12 Example 6 156 0.11 Example 7 205 0.13 Example 8 211 0.14 Comparative Example 1 60 0.08 Comparative Example 2 20 0.05 Comparative Example 3 150 0.11

[0071] The purity of dimethyl terephthalate (DMT) obtained in Examples 1-10 and Comparative Examples 1-3 was analyzed by gas chromatography, and the results are shown in Table 2.

[0072] Table 2

[0073]

[0074] The yields of dimethyl terephthalate (DMT) in Examples 1-10 and Comparative Examples 1-3 were calculated, and the results are shown in Table 3.

[0075] Table 3

[0076]

[0077] Figure 1-3 The images show the products obtained after degradation of colored PET by the catalysts prepared in Example 1, Comparative Example 1, and Comparative Example 3, respectively. The catalyst prepared in Example 1 has high purity and yield of dimethyl terephthalate after degradation of colored PET, and the decolorization effect is good, with the obtained product being colorless and transparent. In contrast, the products obtained in Comparative Examples 1 and 3 have poor decolorization effects, with almost no decolorization effect.

[0078] Figure 4 The nitrogen adsorption curve of the calcium oxide / carbon composite catalyst prepared in Example 1 shows that the prepared calcium oxide / carbon composite catalyst is a mesoporous material, which is beneficial to the transport of PET molecules in the catalyst.

[0079] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for the preparation of DMT from PET based on the degradation of PET by a catalyst, characterized by, The application relates to a preparation method of a PET degradation catalyst and a preparation method of dimethyl terephthalate. The preparation method of the PET degradation catalyst comprises the following steps: fully cleaning industrial waste residues, drying the industrial waste residues, ball milling and sieving the industrial waste residues, selecting 100-300 mesh industrial waste residue powder, fully mixing the industrial waste residue powder with organic acid, drying the mixture, and heat-treating the mixture at 600-900 DEG C for 2-20 h under an inert atmosphere to obtain the calcium oxide / carbon composite PET degradation catalyst. The industrial waste residues are generated in the production process of chemicals with lime nitrogen as raw material, and are obtained by precipitating, filtering and hydrolyzing lime nitrogen. The chemicals with lime nitrogen as raw material are monocyanoamine, dicyanoamine, thiourea or carbendazim. The main components of the waste residues are calcium carbonate and graphite, and the content of the calcium carbonate is 85-95%, and the content of the graphite is 5-15%. The mass ratio of the industrial waste residues to the organic acid is 10-1:

1. The organic acid is at least one of citric acid, malic acid, tartaric acid, oxalic acid and ascorbic acid.

2. The process for the preparation of DMT from PET based on PET degradation catalysts according to claim 1, characterized in that, The particle size of the industrial waste residues is 100-300 mesh.

3. The process for the preparation of DMT from PET based on PET degradation catalysts according to claim 1, characterized in that, The mass ratio of the PET to the PET degradation catalyst is 4-20:1, and the mass ratio of the PET to the methanol is 1:5-20.

4. The process for the preparation of DMT from PET based on PET degradation catalysts according to claim 1, characterized in that, The reaction temperature is 160-200 DEG C, and the reaction time is 1-6 h.

5. The process for the preparation of DMT from PET based on PET degradation catalysts according to claim 1, characterized in that, The stirring rate of the stirring reaction is 300-1000 r / min.

6. The process for the preparation of DMT from PET based on PET degradation catalysts according to claim 1, characterized in that, ​

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