Polyester polymer recycling method

Abstract

The invention discloses a polyester polymer recycling method, which comprises the following steps: taking waste polyester polymers and fatty diacid as raw materials, and carrying out transesterification reaction under the action of no additional catalyst and no additional solvent to obtain biodegradable resin and dicarboxylic acid monomer, thereby maximizing the economic benefit of polymer degradation. The dicarboxylic acid monomer in the obtained product can be used as a high-purity monomer for repolymerization of polyester, and the low-molecular-weight saturated polyester resin can be applied to other fields through further separation and purification, so that the economic benefit of polymer degradation is improved to the greatest extent, and the economic benefit of polymer degradation is improved. The method can be regarded as an upgraded recycling method of the waste polyester plastic.

Description

Technical Field

[0001] The invention relates to a polyester polymer recycling method. The method can obtain high-purity dicarboxylic acid monomers and degradable saturated polyester resins, and belongs to the field of organic chemistry. Background Art

[0002] Polyester is a type of polymer made from polyols and polyacids through polycondensation reaction, of which polyethylene terephthalate (PET) is the most representative, and it also includes linear thermoplastic resins such as polybutylene terephthalate (PBT) and polyarylate. These polyester materials are regarded as important engineering plastics due to their excellent performance and wide range of applications. Specific varieties include PET, PBT, polytrimethylene terephthalate (PTT), polyethylene 2,6-naphthalate (PEN), polyethylene furandicarboxylate (PEF) and various modified polyester fibers, among which PET polyester is the most widely used.

[0003] PET polyester occupies a core position in the global plastics industry and is widely used in many important fields such as container manufacturing, packaging materials, film production and engineering plastics. It is gradually becoming a preferred alternative to other synthetic materials. It is worth noting that although the discarded PET material itself is non-toxic, its decomposition rate in the natural environment is extremely low and it is almost difficult to degrade naturally. With the rapid growth of PET polyester production and consumption, discarded PET has become an environmental challenge that needs to be solved urgently. It not only causes serious environmental pollution, but also leads to huge waste of resources. Therefore, the development of efficient PET degradation and recycling technology is of immeasurable value in alleviating environmental pressure and improving the recycling rate of waste plastic resources. Upgrading and recycling PET can not only reduce environmental pollution, but also promote the sustainable use of resources. It is an important part of promoting green development and circular economy.

[0004] Plastic chemical recycling technology, which aims to convert polymers into monomers or oligomers, has become a research focus in the field of waste plastic recycling in recent years. The chemical recycling methods for PET currently mainly include alcoholysis, glycolysis and hydrolysis. In the alcoholysis method, methanolysis can produce dimethyl terephthalate (DMT). However, DMT and ethylene glycol (EG) will form azeotropes during distillation separation, resulting in high separation and purification costs for high-purity DMT and EG. Although glycolysis technology is relatively mature in industry, the separation and purification of the degradation product bis(hydroxyethyl) terephthalate (BHET) is complicated and costly, which limits its application in the recycling of dark / black PET plastics and PET fibers. The alkaline hydrolysis method has relatively mild reaction conditions, but a large amount of acid is required for acidification after the reaction to obtain terephthalic acid (TPA). This process produces a large amount of waste salt and waste liquid, which increases the cost of recycling and reuse. The acid hydrolysis method often uses concentrated sulfuric acid, concentrated nitric acid, etc. as catalysts, but a large amount of waste liquid is generated in this process, and EG is difficult to effectively recover. At the same time, this process is highly corrosive to equipment, which is not conducive to industrial-scale application. In summary, although there are currently a variety of PET chemical recycling methods, each method has its own limitations. Therefore, the development of more efficient, economical and environmentally friendly methods for upgrading and recycling waste polyester plastics is of great significance for promoting the recycling of waste plastic resources.

[0005] In addition, the industrial preparation of terephthalic acid (TPA), the raw material of PET, mainly adopts chemical synthesis methods, including liquid phase oxidation method and gas phase oxidation method. The raw material of TPA, paraxylene, is obtained by reforming oil cracking and gasoline base method. In essence, TPA is a petroleum-based material and a non-renewable resource, so there is an urgent need for a method to efficiently recycle the used TPA. Summary of the invention

[0006] The present invention aims at the deficiencies of the above-mentioned prior art and provides a method for recycling polyester polymers. The present invention conducts an ester exchange reaction between discarded polyester plastics and a series of fatty diacids to finally obtain a degradable resin material and a dicarboxylic acid monomer with high purity, such as TPA. This solves the problem of handling discarded polyester plastics and the problem of industrial demand for non-renewable resources TPA. The method is innovative in method and practical in reality, and has the potential for large-scale application.

[0007] The polyester polymer recycling and reuse method of the present invention uses waste polyester polymers and fatty diacids as raw materials, and obtains biodegradable resins and dicarboxylic acid monomers through an ester exchange reaction without the action of additional catalysts and additional solvents, thereby maximizing the economic benefits of polymer degradation.

[0008] The polyester polymer comprises repeating units of the following structure:

[0009]

[0010] Ar is the aromatic region fragment. In the polymer upgrading and recycling process, the solid dicarboxylic acid monomer product is obtained by ester exchange separation in the aromatic region, while the saturated polyester resin product in the form of paste can be purified and separated from the fat region.

[0011] Ar is preferably the following structure:

[0012] or .

[0013] The polyester polymers include various sources, including commercially available PET powder or granules, and post-consumer PET products widely available in the market, such as transparent mineral water bottles, cola bottles, Sprite bottles, Pocari Sweat bottles, kvass bottles and other colorless or colored PET beverage bottles; preferably, colorless and transparent PET plastic bottles.

[0014] The general structural formula of the fatty diacid is shown below:

[0015]

[0016] Wherein R is a C6-C10 straight chain alkyl, and C6 is the most preferred, i.e. adipic acid is used as the medium for transesterification and the organic acid for degradation.

[0017] The mass ratio of the fatty diacid to the polyester polymer is 10-1:1, preferably 2-4:1.

[0018] The reaction is carried out in a pressure-resistant tube under the protection of an inert gas, the reaction temperature is 230° C. to 290° C., preferably 240° C. to 260° C., and the reaction time is 2 h to 10 h, preferably 4 h to 8 h. The inert gas is nitrogen or argon.

[0019] The reaction route is shown below:

[0020]

[0021] The specific steps include:

[0022] The waste polyester polymer and fatty diacid are added into a pressure-resistant tube, which is protected by an inert gas, and magnetic stirring is started. The temperature is then raised and maintained for a period of time to complete the reaction. After cooling, ethyl acetate is added to dissolve the product, which is filtered to obtain a powdered dicarboxylic acid monomer. The ethyl acetate is removed by rotary evaporation, dissolved in water, and then filtered to obtain a biodegradable resin material.

[0023] The dicarboxylic acid monomer in the product obtained by the present invention can be used as a high-purity monomer for polyester repolymerization, and the low-molecular-weight saturated polyester resin can be applied to other fields through further separation and purification, thereby maximizing the economic benefits of polymer degradation.

[0024]

[0025] The present invention uses organic acid as a solvent for transesterification and a catalyst for degradation to carry out chemical depolymerization of waste polyester materials. This process can extract high-purity dicarboxylic acid monomers from the depolymerization products, and these monomers are ideal raw materials for the polyester repolymerization process. In addition, the small molecule saturated polyester resin produced in the process is a very valuable chemical, which can be widely used in multiple industries through subsequent separation and purification steps, greatly improving the economic and practical value of polyester polymer recovery.

[0026] The upgraded recycling technology of the present invention is simple to operate, has high transesterification efficiency, and has high purity of the product dicarboxylic acid. The separation and purification in the post-processing stage to obtain the saturated polyester resin is simple to operate, and has economical and practical properties. Compared with the industrial method for preparing low-molecular-weight saturated polyester resin, the present invention is upgraded and recycled from waste polyester plastics, which is innovative and novel. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A diagram of the reaction apparatus.

[0028] Figure 2 This is a conceptual diagram of the reaction using adipic acid as the depolymerizing agent and a physical diagram of the product.

[0029] Figure 3 This is the NMR spectrum of terephthalic acid.

[0030] Figure 4 This is the PEA NMR spectrum of Example 4.

[0031] Figure 5 This is the PEA mass spectrum of Example 4. DETAILED DESCRIPTION

[0032] 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.

[0033] The present invention is a new type of waste polyester plastic upgrading and recycling route. Its core technology is to recycle waste polyester plastic by using the transesterification method, and the transesterification product dicarboxylic acid such as TPA can be reused in the polyester industry. The product low molecular weight saturated polyester resin can be used as an additive for products such as dyes, coatings, plastics, synthetic fibers and coatings. The excess dicarboxylic acid can be recycled by purification methods. The final transesterification product is characterized by nuclear magnetic resonance (NMR) and mass spectrometry.

[0034] Embodiment 1~6:

[0035] The aliphatic diacid is preferably adipic acid (AA), the mass ratio of PET to AA is kept at 1:3, the reaction time is 6 hours, and the effect of temperature on the reaction is investigated:

[0036]

[0037]

[0038] The degree of reaction was evaluated by the transesterification rate and TPA yield. 1 The algorithm is calculated by the peak area of ​​the nuclear magnetic hydrogen spectrum:

[0039]

[0040]

[0041] TPA yield 2 = Actual mass of TPA obtained by drying / theoretical mass of all TPA replaced.

[0042] The number average molecular weight of the product PEA of Example 4 is 360.4 g / mol, wherein most of the components are trimers: ethylene glycol diadipate, and some pentamers of PEA also exist.

[0043] Embodiment 7~9:

[0044] The reaction temperature was kept at 240°C, the mass ratio of PET to AA was 1:3, and the effect of reaction time on the results was investigated:

[0045]

[0046] Embodiment 10-12:

[0047] The reaction temperature was kept at 240°C and the reaction time was 8h to investigate the effect of the mass ratio of PET and AA on the results:

[0048]

[0049] Embodiment 13-14:

[0050] According to the physical properties of different aliphatic diacids, the appropriate temperature was selected for implementation. The reaction time was 8h, and the mass ratio of polyester to diacid was 1:3. The effects of different aliphatic diacids on the results were investigated:

[0051] .

Claims

1. A polyester polymer recycling method, characterized in that: Using waste polyester polymers and fatty diacids as raw materials, biodegradable resins and dicarboxylic acid monomers are obtained through ester exchange reaction; The polyester polymer comprises repeating units of the following structure: ； Where Ar is the aromatic region fragment; The general structural formula of the fatty diacid is shown below: ； Wherein R is a C6~C10 straight chain alkyl.

2. The method according to claim 1, characterized in that: Ar is selected from the following structures: or .

3. The method according to claim 1, characterized in that: The fatty diacid is adipic acid.

4. The method according to claim 1, characterized in that: The mass ratio of the fatty diacid to the polyester polymer is 10-1:

1.

5. The method according to claim 4, characterized in that: The mass ratio of the fatty diacid to the polyester polymer is 2-4:

1.

6. The method according to claim 1, characterized in that: The reaction is carried out in a pressure tube under the protection of an inert gas, the reaction temperature is 230°C to 290°C, and the reaction time is 2h to 10h.

7. The method according to claim 6, characterized in that: The reaction temperature is 240℃~260℃, and the reaction time is 4~8h.

8. The method according to any one of claims 1 to 7, characterized in that The steps include: The waste polyester polymer and fatty diacid are added into a pressure-resistant tube, which is protected by an inert gas, and magnetic stirring is started. The temperature is then raised and maintained for a period of time to complete the reaction. After cooling, ethyl acetate is added to dissolve the product, which is filtered to obtain a powdered dicarboxylic acid monomer. The ethyl acetate is removed by rotary evaporation, dissolved in water, and then filtered to obtain a biodegradable resin material.

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