Degradation and recovery method of polyethylene glycol terephthalate

Abstract

The invention relates to the technical field of high-molecular polymer recovery, in particular to a degradation and recovery method of polyethylene glycol terephthalate. The invention provides a degradation and recovery method of polyethylene glycol terephthalate, which comprises the following steps: mixing polyethylene glycol terephthalate, a catalyst and a cocatalyst, and carrying out ball milling to obtain a polyethylene glycol terephthalate degradation product. The degradation and recovery method is mild in condition, low in energy consumption, efficient and green.

Description

Technical Field

[0001] The invention relates to the technical field of high molecular polymer recovery, in particular to a degradation recovery method for polyethylene terephthalate. Background Art

[0002] In recent years, with the deterioration of the environment, people pay more and more attention to the ecological environment. Polyethylene terephthalate (PET), as a common polymer plastic, is widely used in textiles, packaging, electronics and electrical, and medical and health fields. Although PET is one of the most recycled plastics, only about 6% is recycled into new plastics. The remaining PET is either downgraded and recycled, and is regarded as waste after being used once, or is directly landfilled or incinerated, becoming an important part of solid waste pollution. Secondly, among the PET recycling and treatment schemes currently used, chemical recycling (degradation through the action of catalysts under high temperature and high pressure) is the main method, which generates monomers with certain reaction activity by changing the structure of its polymer chain and using them as chemical raw materials. However, chemical recycling has problems such as high energy consumption, high cost and low degradation efficiency. Therefore, the efficient and green degradation and recycling of PET is still a problem that needs to be solved urgently. Summary of the invention

[0003] The object of the present invention is to provide a degradation and recovery method for polyethylene terephthalate, which has mild conditions, low energy consumption, high recovery efficiency and is environmentally friendly.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides a degradation and recovery method for polyethylene terephthalate, comprising the following steps:

[0006] The polyethylene terephthalate, the catalyst and the co-catalyst are mixed and ball-milled to obtain a polyethylene terephthalate degradation product.

[0007] Preferably, the catalyst is one or more of sodium hydroxide, potassium hydroxide and sodium carbonate.

[0008] Preferably, the co-catalyst is one or more of a metal, a metal chloride and a metal bromide;

[0009] The metal, the metal element in the metal chloride and the metal element in the metal bromide are independently one or more of copper, iron and zinc.

[0010] Preferably, the mass ratio of the polyethylene terephthalate to the catalyst is (0.5-5):1.

[0011] Preferably, the mass ratio of the polyethylene terephthalate to the co-catalyst is (15-40):1.

[0012] Preferably, the ball milling speed is 400 to 1400 rpm, and the time is 2 to 40 hours.

[0013] Preferably, the material of the ball milling medium used in the ball milling is stainless steel, silica, steel, ceramic or agate;

[0014] The mass ratio of the ball milling medium to polyethylene terephthalate is (20-100):1.

[0015] Preferably, after the ball milling, separation is also included;

[0016] The separation comprises first mixing the product obtained by ball milling with a washing liquid, separating the mixture, and second mixing the obtained filtrate with an acidic solution, followed by sedimentation.

[0017] Preferably, the washing liquid comprises one or more of deionized water, ethanol and methanol;

[0018] The acidic solution includes one or more of hydrochloric acid, sulfuric acid, formic acid and acetic acid.

[0019] Preferably, the pH of the mixed solution obtained after the second mixing is 1.0 to 7.0;

[0020] The sedimentation time is 1 to 20 hours.

[0021] The invention provides a degradation and recovery method for polyethylene terephthalate, comprising the following steps: mixing polyethylene terephthalate, a catalyst and a co-catalyst, and ball milling to obtain a polyethylene terephthalate degradation product.

[0022] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0023] 1) Compared with the prior art, the degradation recovery method of the present invention does not require pre-separation, and does not require additional hydrogen supply solvent or atmosphere during the degradation process, so it has significant economy and high efficiency, is simple and efficient, realizes efficient degradation of PET, significantly improves the specificity of the product, and significantly reduces the process cost;

[0024] 2) The degradation and recycling method of the present invention uses a one-pot method to achieve efficient degradation of PET. Compared with the chemical degradation method in the prior art, it has a low reaction temperature (no additional heating is required) and a simple process. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the MS spectrum of the polyethylene terephthalate degradation product described in Example 1. DETAILED DESCRIPTION

[0026] The present invention provides a degradation and recovery method for polyethylene terephthalate, comprising the following steps:

[0027] The polyethylene terephthalate, the catalyst and the co-catalyst are mixed and ball-milled to obtain a polyethylene terephthalate degradation product.

[0028] In the present invention, the particle size of the polyethylene terephthalate is preferably less than 40 meshes. When the particle size of the polyethylene terephthalate does not meet the above requirements, the polyethylene terephthalate is preferably crushed and sieved in sequence. The present invention does not have any special limitation on the crushing and sieving process, and the process well known to those skilled in the art can be used.

[0029] In the present invention, the catalyst is preferably one or more of sodium hydroxide, potassium hydroxide and sodium carbonate. When the catalyst is two or more of the above specific selections, the present invention has no special restrictions on the ratio of the above specific substances, and they can be mixed in any ratio. In an embodiment of the present invention, the catalyst can be sodium hydroxide or potassium hydroxide.

[0030] In the present invention, the mass ratio of the polyethylene terephthalate to the catalyst is preferably (0.5-5):1, more preferably (2-4):1. In an embodiment of the present invention, the mass ratio of the polyethylene terephthalate to the catalyst may be 5:1 or 4:1.

[0031] In the present invention, the catalytic principle of the catalyst is that under the action of mechanical force, NaOH attacks the ester groups in PET in a directional manner, causing chain scission.

[0032] In the present invention, the co-catalyst is preferably one or more of metal, metal chloride and metal bromide; the metal, metal element in the metal chloride and metal element in the metal bromide are independently preferably one or more of copper, iron and zinc. When the co-catalyst is ferric chloride and ferric bromide, the present invention has no special restrictions on the ratio of the ferric chloride and ferric bromide, and they can be mixed in any ratio. In an embodiment of the present invention, the co-catalyst can be ferric chloride or cupric chloride.

[0033] In the present invention, the mass ratio of the polyterephthalate to the co-catalyst is preferably (15-40):1, more preferably (20-30):1. In an embodiment of the present invention, the mass ratio of the polyterephthalate to the co-catalyst may be 15:1 or 20:1.

[0034] In the present invention, the working principle of the co-catalyst is that the metal salt ions promote the OH- Selectivity for ester groups.

[0035] The present invention does not have any special limitation on the mixing process, and the mixing process may be carried out by a process well known to those skilled in the art and ensured to be uniform.

[0036] In the present invention, the ball milling speed is preferably 400-1400 rpm, more preferably 600-1000 rpm; the ball milling time is preferably 2-40 hours, more preferably 10-30 hours. In an embodiment of the present invention, the ball milling speed can be 1400 rpm or 700 rpm, and the time can be 5 hours or 15 hours.

[0037] In the present invention, the materials of the ball milling jar and the ball milling medium used in the ball milling are preferably stainless steel, silica, steel, ceramic or agate. The mass ratio of the ball milling medium to the polyethylene terephthalate is preferably (20-100):1, more preferably (40-80):1. In an embodiment of the present invention, the mass ratio of the ball milling medium to the polyethylene terephthalate can be 50:1 or 80:1.

[0038] In the present invention, the role of the ball mill is to strengthen the disturbance of the reaction components through mechanical force, increase the reaction activity, and make the sodium hydroxide attack the ester bonds in the PET.

[0039] In the present invention, the components of the product obtained after ball milling preferably include terephthalic acid (TPA, main product) and trace impurities, and the trace impurities include ethylene terephthalate and its corresponding oligomers.

[0040] After the ball milling, the present invention preferably further comprises separation; the separation preferably comprises first mixing the product obtained by the ball milling with a washing liquid, separating, and second mixing the obtained filtrate with an acidic solution for sedimentation.

[0041] In the present invention, the washing liquid preferably includes one or more of deionized water, ethanol and methanol. When the washing liquid is two or more of the above specific selections, the present invention has no special restrictions on the ratio of the above specific substances, and they can be mixed in any ratio. In an embodiment of the present invention, the washing liquid can be water or ethanol.

[0042] The present invention does not have any special limitation on the first mixing process, and the process well known to those skilled in the art may be used to ensure that the product obtained by the ball milling is fully dissolved in the washing liquid.

[0043] In the present invention, the separation method is preferably one or more of distillation, filtration and centrifugation. The present invention does not have any special limitation on the separation process, and the separation process can be carried out using a process well known to those skilled in the art.

[0044] In the present invention, the acidic solution preferably includes one or more of hydrochloric acid, sulfuric acid, formic acid and acetic acid. When the acidic solution is two or more of the above specific selections, the present invention has no special restrictions on the ratio of the above specific substances, and they can be mixed in any ratio. The present invention has no special restrictions on the concentration of the acidic solution, and a concentration well known to those skilled in the art can be used to ensure that TPA can be precipitated.

[0045] The present invention does not have any special limitation on the second mixing process, and the second mixing process may be carried out using a process well known to those skilled in the art.

[0046] In the present invention, the pH of the mixed solution obtained after the second mixing is preferably 1.0 to 7.0, more preferably 5.0 to 7.0. In an embodiment of the present invention, the pH of the mixed solution obtained after the second mixing may be 4.0 or 6.0.

[0047] In the present invention, the sedimentation time is preferably 1 to 20 hours, more preferably 10 to 15 hours. In an embodiment of the present invention, the sedimentation time can be 10 hours or 15 hours.

[0048] After the sedimentation is completed, the present invention also preferably includes separation and drying performed in sequence; the present invention has no special limitation on the separation and drying process, and the mixture can be mixed in any ratio.

[0049] The degradation and recovery method of polyethylene terephthalate provided by the present invention is described in detail below in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0050] Example 1

[0051] After the waste PET is crushed by a crusher, it is screened by a vibrating screen to obtain PET particles with a particle size of less than 40 mesh;

[0052] The PET particles, a sodium hydroxide catalyst (the mass ratio of the sodium hydroxide catalyst to the PET particles is 1:5) and a ferric chloride co-catalyst (the mass ratio of the ferric chloride co-catalyst to the PET particles is 1:15) are mixed, added to a ball mill made of agate, and ball milled (the ball milling medium is agate balls, the mass ratio of the ball milling medium to the PET particles is 80:1, the rotation speed is 1400 rpm, and the time is 5 hours). The product obtained by ball milling is added to deionized water, filtered to obtain a filtrate and a filter residue, and hydrochloric acid is added to the filtrate to a pH of 6.0 and precipitated for 10 hours to obtain a polyethylene terephthalate degradation product; wherein the PET degradation rate and the TPA yield are 100% and 95%, respectively.

[0053] Figure 1 is the MS spectrum of the polyethylene terephthalate degradation product, Figure 1 It can be seen that the peak of the decomposition product is mainly 165.15, corresponding to the nucleus-to-mass ratio of terephthalic acid.

[0054] Example 2

[0055] After the waste PET is crushed by a crusher, it is screened by a vibrating screen to obtain PET particles with a particle size of less than 40 mesh;

[0056] The PET particles, potassium hydroxide catalyst (the mass ratio of sodium hydroxide catalyst to PET particles is 1:4) and cupric chloride co-catalyst (the mass ratio of cupric chloride co-catalyst to PET particles is 1:20) are mixed and added to a ball mill made of zirconium oxide, and ball milled (the ball milling medium is zirconium oxide, the mass ratio of the ball milling medium to the PET particles is 50:1, the rotation speed is 700rpm, and the time is 15h), and the product obtained by ball milling is added to deionized water, and after filtering to obtain a filtrate and a filter residue, hydrochloric acid is added to the filtrate to a pH of 4.0 and precipitated for 15h to obtain a polyethylene terephthalate degradation product; wherein the PET degradation rate and TPA yield are 100% and 94% respectively. The polyethylene terephthalate degradation product is subjected to MS detection, and the test result is similar to that of Example 1.

[0057] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for the degradation and recovery of polyethylene terephthalate, characterized in that: The following steps are involved: The polyethylene terephthalate, the catalyst and the co-catalyst are mixed and ball-milled to obtain a polyethylene terephthalate degradation product.

2. The degradation and recovery method according to claim 1, characterized in that: The catalyst is one or more of sodium hydroxide, potassium hydroxide and sodium carbonate.

3. The degradation and recovery method according to claim 1, characterized in that: The co-catalyst is one or more of metal, metal chloride and metal bromide; The metal, the metal element in the metal chloride and the metal element in the metal bromide are independently one or more of copper, iron and zinc.

4. The degradation and recovery method according to claim 1 or 2, characterized in that: The mass ratio of the polyethylene terephthalate to the catalyst is (0.5-5):

1.

5. The degradation and recovery method according to claim 1 or 3, characterized in that: The mass ratio of the polyterephthalate to the co-catalyst is (15-40):

1.

6. The degradation and recovery method according to claim 1, characterized in that: The ball mill has a rotation speed of 400 to 1400 rpm and a milling time of 2 to 40 hours.

7. The degradation and recovery method according to claim 1 or 6, characterized in that: The ball milling medium used in the ball milling is made of stainless steel, silica, steel, ceramic or agate; The mass ratio of the ball milling medium to polyethylene terephthalate is (20-100):

1.

8. The degradation and recovery method according to claim 7, characterized in that: After the ball milling, separation is also included; The separation comprises first mixing the product obtained by ball milling with a washing liquid, separating the mixture, and second mixing the obtained filtrate with an acidic solution, followed by sedimentation.

9. The degradation and recovery method according to claim 8, characterized in that: The washing liquid includes one or more of deionized water, ethanol and methanol; The acidic solution includes one or more of hydrochloric acid, sulfuric acid, formic acid and acetic acid.

10. The degradation and recovery method according to claim 8, characterized in that: The pH of the mixed solution obtained after the second mixing is 1.0 to 7.0; The sedimentation time is 1 to 20 hours.

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