A method for efficiently producing terephthalate by depolymerizing waste polyester with carbonate

Abstract

The invention belongs to the technical field of polyester recycling, and relates to a method for efficiently producing terephthalate by depolymerizing waste polyester with carbonate, wherein waste polyester, carbonate and catalyst are subjected to depolymerization reaction under nitrogen or inert gas protection and solvent-free conditions, the catalyst is a mixture of A and B with a mass ratio of 10 to 20:1, A is one or more of zinc acetate, sodium acetate, potassium chloride, lithium chloride, potassium carbonate, sodium carbonate, antimony glycol, antimony trioxide, antimony acetate, titanium glycol and titanium dioxide, and B is sodium ethoxide. The invention solves the problems of limited monomer conversion and long production process in chemical recycling of waste polyester in the prior art, significantly improves catalytic efficiency and depolymerization speed by compounding catalysts, simplifies the depolymerization process, reduces energy consumption, and is conducive to industrial application.

Description

Technical Field

[0001] The invention belongs to the technical field of polyester recycling and relates to a method for efficiently producing terephthalate by depolymerizing waste polyester with carbonate. Background Art

[0002] Polyethylene terephthalate (PET for short), as a thermoplastic polymer with excellent performance, is widely used in various fields of life. However, post-consumer polyester is difficult to directly handle because it is non-degradable. Chemical recycling of polyester has become one of the direct ways to recycle waste polyester in large quantities due to its simple and efficient characteristics. Chemical recycling refers to the process in which polyester undergoes an ester exchange reaction with depolymerized molecules under the action of a catalyst, gradually achieving chain scission, and thus obtaining monomer products. Depending on the depolymerized molecules, chemical recycling can be divided into methanol depolymerization, ethylene glycol depolymerization, hydrolysis, aminolysis, etc., and the corresponding end products are monomers such as dimethyl terephthalate (DMT), diethyl terephthalate (BHET), and terephthalic acid (TPA). In particular, ethylene glycol depolymerization of polyester has become the most common polyester chemical recycling method at present because of its simple and mild reaction conditions and relatively easy product separation.

[0003] However, there is a problem of chemical reaction balance in the depolymerization of polyester by ethylene glycol, and the main products are small molecular BHET and partially soluble PET oligomers. In order to promote the depolymerization reaction to proceed in the forward direction, a high dose of ethylene glycol is usually required, which limits the conversion rate and yield of the monomer. For example, patent application CN102875382A discloses a method for the alcoholysis of polyethylene terephthalate catalyzed by metal acetate ion liquid. Under the condition that the molar ratio of polyester segment content to ethylene glycol is 1:20, the monomer product yield is only 88.5%.

[0004] In addition, in order to ensure the stable preparation of subsequent polymers, it is usually necessary to perform a secondary transesterification on the product generated by the depolymerization of ethylene glycol and react it with methanol to generate dimethyl terephthalate (DMT) to ensure batch stability. For example, patent application CN118666683A discloses a solidification extraction process for chemically regenerated dimethyl terephthalate. However, the overall depolymerization process of obtaining monomer DMT under this method is relatively long and has high energy consumption.

[0005] Depolymerization through carbonates is simple and efficient. For example, patent application CN117986114A discloses a method for alkylating polyester materials with the participation of carbonates or carboxylates, which uses carbonates to catalyze the depolymerization of polyesters through ionic liquids under solvent conditions. However, even under solvent-enhanced conditions, waste polyester still requires a long time (4 to 8 hours) to react and degrade, and the catalytic efficiency is insufficient. The problem derived from the strategy of strengthening depolymerization through solvent effects is that the product separation operation is complicated, the equipment requirements are high, and the industrialization is difficult. Summary of the invention

[0006] The purpose of the present invention is to solve the problems existing in the prior art and provide a method for efficiently producing terephthalate by depolymerizing waste polyester with carbonate.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A method for efficiently producing terephthalate by depolymerizing waste polyester with carbonate, comprising the steps of carrying out a depolymerization reaction on waste polyester, carbonate and a catalyst under the protection of nitrogen or inert gas and in the absence of solvent, wherein the catalyst is a mixture of A and B in a mass ratio of 10 to 20:1, wherein A is one or more of zinc acetate, sodium acetate, potassium chloride, lithium chloride, potassium carbonate, sodium carbonate, antimony glycolate, antimony trioxide, antimony acetate, titanium glycolate and titanium dioxide, and B is sodium ethoxide.

[0009] As the preferred technical solution:

[0010] In the method for efficiently producing terephthalate esters by depolymerizing waste polyester with carbonate, the amount of catalyst added is 0.1-5wt% of the mass of the waste polyester.

[0011] In the method for efficiently producing terephthalate by depolymerizing waste polyester with carbonate, the molar ratio of carbonate to waste polyester is 3 to 30:1.

[0012] In the method for efficiently producing terephthalate by depolymerizing waste polyester with carbonate, the carbonate is one or more of dimethyl carbonate, diethyl carbonate and dibutyl carbonate.

[0013] The method for efficiently producing terephthalate by depolymerizing waste polyester with carbonate as described above, the waste polyester is any form of product or waste product made from X or Y, X is polyethylene terephthalate, and Y is a copolyester obtained by copolymerizing polyethylene terephthalate with a dibasic acid and / or a diol, and the specific form can be liquid-dyed fiber containing a pigment / dye, waste polyester fiber dyed with a disperse dye / cationic dye, and its products.

[0014] The above-mentioned method for efficiently producing terephthalate by depolymerizing waste polyester with carbonate has a depolymerization reaction temperature of 160-200°C and a depolymerization reaction time of 30-200min.

[0015] The method for efficiently producing terephthalate by depolymerizing waste polyester with carbonate as described above comprises the following steps: after the depolymerization reaction, firstly performing decompression devolatilization on the depolymerization reaction product at 140-190° C., collecting the removed volatile components to obtain a mixture of terephthalate and carbonate, then performing decompression devolatilization on the mixture of terephthalate and carbonate at 70-100° C., collecting the removed volatile components to obtain carbonate, and collecting residual components to obtain terephthalate (main product).

[0016] The above-mentioned method for efficiently producing terephthalate by depolymerizing waste polyester with carbonate comprises the following steps: after decompressing and devolatilizing the depolymerization reaction product at 140-160° C., collecting the residual components, and washing, separating and filtering the residual components to obtain ethylene carbonate.

[0017] The present invention can also realize efficient separation of products, and can directly separate catalysts, ethylene carbonate, carbonates and terephthalates with high efficiency and high quality through gas-liquid separation.

[0018] According to the method for efficiently producing terephthalate by depolymerizing waste polyester with carbonate, the solid phase conversion rate of the waste polyester is 80-100%, the conversion rate of terephthalate is 80-100%, the purity of terephthalate is 99%-99.9%, and the oligomer content in terephthalate is 0-0.5wt%.

[0019] Principle of the invention:

[0020] The reaction system of the present invention adopts a near-molten system, avoiding the use of other solvents, reducing the difficulty of product separation and the requirements for the device;

[0021] The catalyst of the present invention is compounded by A (conventional metal salt) and B (sodium ethoxide). If the catalyst is only A, the conventional metal salt has insufficient nucleophilic ability, which easily leads to low catalytic efficiency. If the catalyst is only B, the sodium ethoxide has a strong hydrolysis side reaction, which easily leads to difficult control of the depolymerization reaction and inconsistent batch depolymerization. After A and B are compounded, B (as a co-catalyst) can make up for the defect of insufficient nucleophilic ability of A (main catalyst), so that the catalytic efficiency of the catalyst is higher. At the same time, A has extremely excellent stability, which can ensure the excellent high-temperature stability of the catalyst, and then the depolymerization reaction can be carried out in a near-molten system, which significantly improves the depolymerization efficiency.

[0022] In a near-molten system, a strong base catalytic system composed of a metal salt and a co-catalyst sodium ethoxide can enhance the nucleophilic reaction of carbonate. Carbonate attacks the ester group in the polyester molecular chain through nucleophilic reaction, resulting in the breakage of the polyester chain. At the same time, carbonate and the generated ethylene glycol spontaneously form a ring to form ethylene carbonate, thereby promoting the forward movement of the depolymerization reaction equilibrium, and finally efficiently depolymerizing to obtain terephthalate (taking the waste polyester as polyethylene terephthalate as an example, the depolymerization process is as follows Figure 1 As shown in the figure, rapid depolymerization of waste polyester and high conversion rate of monomers were achieved.

[0023] Beneficial Effects

[0024] (1) The present invention adopts a catalyst composed of A (conventional metal salt) and B (sodium ethoxide). B, as a co-catalyst, can make up for the defect of insufficient nucleophilic ability of A, thereby significantly improving the catalytic efficiency of the catalyst.

[0025] (2) Under the protection of nitrogen or inert gas and in the absence of solvent, waste polyester, carbonate and catalyst undergo depolymerization reaction. Due to the efficient catalytic effect of the catalyst, the depolymerization reaction proceeds rapidly, significantly improving the depolymerization efficiency.

[0026] (3) The present invention does not require secondary transesterification of the depolymerization product and directly obtains terephthalate monomer, thereby simplifying the overall depolymerization process and reducing energy consumption.

[0027] (4) The method of the present invention carries out the depolymerization reaction in a near-molten system, has relatively low requirements on the device, does not require complicated product separation operations, and is conducive to industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The mechanism of depolymerization of waste polyester by carbonate;

[0029] Figure 2 This is the DSC melting curve of the terephthalate of Example 1. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0031] The following are the calculation formulas for the relevant performance indicators in each embodiment and comparative example:

[0032] Solid phase conversion rate of waste polyester = ;

[0033] In the formula, is the added mass of waste polyester (g), is the mass (g) of the undepolymerized waste polyester (i.e., the residual solid) after the depolymerization reaction is completed;

[0034] Conversion of terephthalate = ;

[0035] Wherein, m2 is the mass of the collected terephthalate (g), M1 is the molar mass of the collected terephthalate (g / mol), is the added mass of waste polyester (g), M2 is the molar mass of the repeating unit of waste polyester (for example, if the waste polyester is polyethylene terephthalate, M2=192g / mol. Note that when the waste polyester contains two repeating units, the molar mass here is the average of the two repeating units).

[0036] The following are the test methods for the relevant performance indicators in each embodiment:

[0037] Purity of terephthalate esters and oligomer content in terephthalate esters: The purity and oligomer content of the collected terephthalate esters were qualitatively and quantitatively analyzed using Shimadzu Corporation's LC-16 high performance liquid chromatograph (HPLC) equipped with a WondaSil C18-WR (200mm, filling particle size 5μm) chromatographic column and a UV detector. The detection wavelength was 254nm, the detection temperature was 40℃, and a binary gradient test method was used. The mobile phases were methanol and water (3:1, V / V), respectively. The flow rate was 0.8mL / min, and the purity was fitted using the external standard method.

[0038] Melting point: Weigh 5-10 mg of terephthalate in an aluminum crucible and measure the melting point (T m ), the specific process is: heating from 30°C to 250°C at 10°C / min, keeping warm for 5 minutes, and then analyzing with Universal Analysis software to obtain the melting point of the product.

[0039] Example 1

[0040] A method for efficiently producing terephthalate by depolymerizing waste polyester with carbonate, the specific steps are as follows:

[0041] (1) Preparation of raw materials;

[0042] Waste polyester: waste fibers made from polyethylene terephthalate;

[0043] Dimethyl carbonate;

[0044] Catalyst: a mixture of zinc acetate and sodium ethoxide in a mass ratio of 10:1;

[0045] (2) subjecting waste polyester, dimethyl carbonate and a catalyst to a depolymerization reaction at 160° C. for 200 min under nitrogen or inert gas protection and in the absence of a solvent to obtain a depolymerization product, first subjecting the depolymerization product to decompression devolatilization at 140° C., collecting the removed volatile components to obtain a mixture of terephthalate and dimethyl carbonate, collecting the residual components, and washing the residual components with water, separating and filtering to obtain ethylene carbonate, and then subjecting the mixture of terephthalate and dimethyl carbonate to decompression devolatilization at 70° C., collecting the removed volatile components to obtain dimethyl carbonate, and collecting the residual components to obtain terephthalate;

[0046] The amount of the catalyst added is 0.1wt% of the mass of the waste polyester, and the molar ratio of dimethyl carbonate to the waste polyester is 30:1.

[0047] The test shows that the solid phase conversion rate of waste polyester is 100%, the conversion rate of terephthalate is 100%, the purity of terephthalate is 99.9%, and the melting point of terephthalate is 140°C (DSC melting curve is shown in Figure 2 As shown), the oligomer content in terephthalate is 0.01wt%.

[0048] Comparative Example 1

[0049] A method for producing terephthalate esters by depolymerizing waste polyester with carbonate is basically the same as that in Example 1, except that the catalyst is replaced with an equal mass of sodium ethoxide.

[0050] Tests show that the solid phase conversion rate of waste polyester is 80% and the conversion rate of terephthalate is 75%.

[0051] Compared with Example 1, the solid-phase conversion rate of waste polyester and the conversion rate of terephthalate in Comparative Example 1 are significantly reduced. This is because sodium ethoxide is used alone as a catalyst in Comparative Example 1, and sodium ethoxide has a strong hydrolysis side reaction, which easily leads to the difficulty in controlling the depolymerization reaction, and then the batch depolymerization is inconsistent, making it impossible to stably and efficiently carry out the entire depolymerization reaction, resulting in a significant decrease in the solid-phase conversion rate of waste polyester and the conversion rate of terephthalate.

[0052] Comparative Example 2

[0053] A method for producing terephthalate by depolymerizing waste polyester with carbonate is basically the same as that in Example 1, except that the catalyst is replaced by zinc acetate of the same mass.

[0054] Tests show that the solid phase conversion rate of waste polyester is 75% and the conversion rate of terephthalate is 70%.

[0055] Compared with Example 1, the solid-phase conversion rate of waste polyester and the conversion rate of terephthalate in Comparative Example 2 are significantly reduced. This is because zinc acetate is used alone as a catalyst in Comparative Example 2, and its nucleophilic ability is insufficient, which makes it difficult to effectively induce carbonate to attack the ester group in the polyester molecular chain to achieve the breakage of the polyester chain during the depolymerization reaction, thereby causing the entire depolymerization reaction to be unable to proceed efficiently, resulting in a significant decrease in the solid-phase conversion rate of waste polyester and the conversion rate of terephthalate.

[0056] Example 2

[0057] A method for efficiently producing terephthalate by depolymerizing waste polyester with carbonate, the specific steps are as follows:

[0058] (1) Preparation of raw materials;

[0059] Waste polyester: waste colored fibers made from polyethylene terephthalate;

[0060] Diethyl carbonate;

[0061] Catalyst: a mixture of potassium carbonate and sodium ethoxide in a mass ratio of 20:1;

[0062] (2) subjecting waste polyester, diethyl carbonate and a catalyst to a depolymerization reaction at 170° C. for 150 min under nitrogen or inert gas protection and in the absence of a solvent to obtain a depolymerization product, first subjecting the depolymerization product to decompression devolatilization at 150° C., collecting the removed volatile components to obtain a mixture of terephthalate and diethyl carbonate, collecting the residual components, and washing the residual components with water, separating and filtering to obtain ethylene carbonate, and then subjecting the mixture of terephthalate and diethyl carbonate to decompression devolatilization at 80° C., collecting the removed volatile components to obtain diethyl carbonate, and collecting the residual components to obtain terephthalate;

[0063] The amount of catalyst added is 1wt% of the mass of the waste polyester, and the molar ratio of diethyl carbonate to the waste polyester is 20:1.

[0064] Tests show that the solid phase conversion rate of waste polyester is 100%, the conversion rate of terephthalate is 99%, the purity of terephthalate is 99.9%, and the oligomer content in terephthalate is 0.03wt%.

[0065] Example 3.

[0066] A method for efficiently producing terephthalate by depolymerizing waste polyester with carbonate, the specific steps are as follows:

[0067] (1) Preparation of raw materials;

[0068] Waste polyester: waste fiber made from polyethylene terephthalate modified with propylene glycol;

[0069] The structural formula of propylene glycol modified polyethylene terephthalate is as follows:

[0070] ;

[0071] Wherein, x and y are integers ranging from 10 to 100;

[0072] Dibutyl carbonate;

[0073] Catalyst: a mixture of lithium chloride and sodium ethoxide in a mass ratio of 15:1;

[0074] (2) subjecting waste polyester, dibutyl carbonate and a catalyst to a depolymerization reaction at 180° C. for 100 min under nitrogen or inert gas protection and in the absence of a solvent to obtain a depolymerization product, first subjecting the depolymerization product to decompression devolatilization at 190° C., collecting the removed volatile components to obtain a mixture of terephthalate and dibutyl carbonate, collecting the residual components, and washing the residual components with water, separating and filtering to obtain ethylene carbonate, and then subjecting the mixture of terephthalate and dibutyl carbonate to decompression devolatilization at 80° C., collecting the removed volatile components to obtain dibutyl carbonate, and collecting the residual components to obtain terephthalate;

[0075] The amount of the catalyst added is 2wt% of the mass of the waste polyester, and the molar ratio of dibutyl carbonate to the waste polyester is 15:1.

[0076] Tests show that the solid phase conversion rate of waste polyester is 95%, the conversion rate of terephthalate is 92%, the purity of terephthalate is 99.3%, and the oligomer content in terephthalate is 0.1wt%.

[0077] Example 4

[0078] A method for efficiently producing terephthalate by depolymerizing waste polyester with carbonate, the specific steps are as follows:

[0079] (1) Preparation of raw materials;

[0080] Waste polyester: waste fiber made from polyethylene terephthalate-1,4-cyclohexanedimethanol ester;

[0081] The structural formula of polyethylene terephthalate-1,4-cyclohexanedimethanol ester is as follows:

[0082] ;

[0083] Wherein, x and y are integers ranging from 10 to 100;

[0084] Dimethyl carbonate;

[0085] Catalyst: a mixture of antimony glycolate and sodium ethoxide in a mass ratio of 14:1;

[0086] (2) subjecting waste polyester, dimethyl carbonate and a catalyst to a depolymerization reaction at 190° C. for 30 min under nitrogen or inert gas protection and in the absence of a solvent to obtain a depolymerization product, first subjecting the depolymerization product to decompression devolatilization at 160° C., collecting the removed volatile components to obtain a mixture of terephthalate and dimethyl carbonate, collecting the residual components, and washing the residual components with water, separating and filtering to obtain ethylene carbonate, and then subjecting the mixture of terephthalate and dimethyl carbonate to decompression devolatilization at 90° C., collecting the removed volatile components to obtain dimethyl carbonate, and collecting the residual components to obtain terephthalate;

[0087] The amount of catalyst added is 5wt% of the mass of the waste polyester, and the molar ratio of dimethyl carbonate to the waste polyester is 10:1.

[0088] Tests show that the solid phase conversion rate of waste polyester is 90%, the conversion rate of terephthalate is 85%, the purity of terephthalate is 99.2%, and the oligomer content in terephthalate is 0.2wt%.

[0089] Example 5

[0090] A method for efficiently producing terephthalate by depolymerizing waste polyester with carbonate, the specific steps are as follows:

[0091] (1) Preparation of raw materials;

[0092] Waste polyester: waste bottle flakes made from polyethylene terephthalate;

[0093] Dibutyl carbonate;

[0094] Catalyst: a mixture of titanium glycolate and sodium ethoxide in a mass ratio of 18:1;

[0095] (2) subjecting waste polyester, dibutyl carbonate and a catalyst to a depolymerization reaction at 200° C. for 50 min under nitrogen or inert gas protection and in the absence of a solvent to obtain a depolymerization product, first subjecting the depolymerization product to decompression devolatilization at 160° C., collecting the removed volatile components to obtain a mixture of terephthalate and dibutyl carbonate, collecting the residual components, and washing the residual components with water, separating and filtering to obtain ethylene carbonate, and then subjecting the mixture of terephthalate and dibutyl carbonate to decompression devolatilization at 100° C., collecting the removed volatile components to obtain dibutyl carbonate, and collecting the residual components to obtain terephthalate;

[0096] The amount of the catalyst added is 4wt% of the mass of the waste polyester, and the molar ratio of dibutyl carbonate to the waste polyester is 3:1.

[0097] Tests show that the solid phase conversion rate of waste polyester is 80%, the conversion rate of terephthalate is 80%, the purity of terephthalate is 99%, and the oligomer content in terephthalate is 0.5wt%.

Claims

1. A method for efficiently producing terephthalate esters by depolymerizing waste polyester with carbonate, characterized in that: The waste polyester, carbonate and catalyst are subjected to depolymerization reaction under the protection of nitrogen or inert gas and in the absence of solvent. The catalyst is a mixture of A and B in a mass ratio of 10 to 20:1, A is one or more of zinc acetate, sodium acetate, potassium chloride, lithium chloride, potassium carbonate, sodium carbonate, antimony glycolate, antimony acetate and titanium glycolate, and B is sodium ethoxide.

2. The method for efficiently producing terephthalate esters by depolymerizing waste polyester with carbonate according to claim 1, characterized in that: The amount of catalyst added is 0.1 to 5 wt% of the mass of the waste polyester.

3. The method for efficiently producing terephthalate esters by depolymerizing waste polyester with carbonate according to claim 1, characterized in that: The molar ratio of carbonate to waste polyester is 3 to 30:

1.

4. The method for efficiently producing terephthalate esters by depolymerizing waste polyester with carbonate according to claim 3, characterized in that: The carbonate ester is one or more of dimethyl carbonate, diethyl carbonate and dibutyl carbonate.

5. The method for efficiently producing terephthalate esters by depolymerizing waste polyester with carbonate according to claim 1, characterized in that: Waste polyester is any form of product or waste product made from X or Y, X is polyethylene terephthalate, and Y is a copolyester obtained by copolymerizing polyethylene terephthalate with a dibasic acid and / or a diol.

6. The method for efficiently producing terephthalate esters by depolymerizing waste polyester with carbonate according to claim 1, characterized in that: The depolymerization reaction temperature is 160-200° C., and the depolymerization reaction time is 30-200 min.

7. The method for efficiently producing terephthalate esters by depolymerizing waste polyester with carbonate according to claim 1, characterized in that: After the depolymerization reaction, the depolymerization reaction product is first subjected to reduced pressure devolatilization at 140-190° C., and the removed volatile components are collected to obtain a mixture of terephthalate and carbonate. The mixture of terephthalate and carbonate is then subjected to reduced pressure devolatilization at 70-100° C., and the removed volatile components are collected to obtain carbonate. The residual components are collected to obtain terephthalate.

8. The method for efficiently producing terephthalate esters by depolymerizing waste polyester with carbonate according to claim 7, characterized in that: After the depolymerization reaction product is decompressed and devolatilized at 140-160° C., the residual components are collected and washed, separated and filtered to obtain ethylene carbonate.

9. The method for efficiently producing terephthalate esters by depolymerizing waste polyester with carbonate according to claim 1, characterized in that: The solid phase conversion rate of waste polyester is 80-100%, the conversion rate of terephthalate is 80-100%, the purity of terephthalate is 99%-99.9%, and the oligomer content in terephthalate is 0-0.5wt%.

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