Method for recycling solvent-free base-solubilized polymeric aromatic liquid crystal polyester

Abstract

The application provides a method for recycling and reusing solvent-free alkali fusion of poly (aromatic liquid crystal polyester), and belongs to the field of chemical depolymerization recycling of liquid crystal polymers. The method uniformly dry-mixes aromatic liquid crystal polyester and inorganic alkali, then performs heating, and obtains an intermediate product containing aromatic hydroxyl carboxylic acid salt by using alkali to depolymerize the liquid crystal polymer under stirring; subsequently, the intermediate product is dissolved in water, and an acid solution is added, so that the aromatic hydroxyl carboxylic acid salt is subjected to a neutralization reaction with the acid, is converted into corresponding aromatic hydroxyl carboxylic acid, and is precipitated from the aqueous solution, so that the recycling of the aromatic hydroxyl carboxylic acid monomer is realized after solid-liquid separation. The reaction process of the application does not use organic solvents, has low cost, fast depolymerization speed, moderate reaction temperature, high yield, and is performed under normal pressure, and does not need a protective gas.

Description

Technical Field

[0001] This invention relates to the field of chemical depolymerization and recycling of liquid crystal polymers, and specifically to a solvent-free alkali melting method for recycling and reusing aromatic liquid crystal polyesters. Background Technology

[0002] Aromatic liquid crystal polyesters (LCPs) are a class of high-performance thermoplastic engineering plastics whose molecular backbone contains a large number of rigid aromatic benzene ring structures. They combine the orientational order of liquid crystals with the processability of polymers, exhibiting excellent mechanical properties, heat resistance, chemical resistance, self-flame retardancy, and low dielectric properties, earning them the reputation of "super engineering materials." They are widely used in high-end fields such as electronics, 5G communications, and aerospace. However, in stark contrast to the rapid development of the LCPs industry, the recycling rate of waste LCPs is extremely low, with large quantities of waste LCPs scattered in the natural environment, causing irreversible impacts on the ecological environment and human health.

[0003] LCPs (Liquid Polyesters) molecules have a backbone composed of numerous rigid aromatic structures, exhibiting extremely high chemical stability and making them very difficult to decompose in the natural environment. Currently, the chemical recycling of polyesters typically employs strong alkaline hydrolysis or aminolysis to degrade them into monomers or oligomers. While high-temperature pyrolysis can achieve degradation, it is energy-intensive, produces a wide distribution of products, and makes it difficult to obtain high-purity monomers. Traditional acid-base hydrolysis methods result in severe equipment corrosion and high post-processing costs. Alcohololysis and aminolysis require large amounts of organic solvents and expensive reagents, making them uneconomical. Enzymatic hydrolysis is almost ineffective for LCPs.

[0004] The high chemical stability, high melting point, and complex monomer composition of LCPs often necessitate stringent conditions for their chemical depolymerization. An ideal controlled catalytic depolymerization technology for LCPs requires the following conditions: no organic solvents required, moderate reaction temperature, no need for protective gases such as nitrogen or hydrogen, readily available, inexpensive, non-toxic catalyst feedstock, and stability during the reaction. Furthermore, the entire process must have low overall operating costs to ensure its feasibility for commercial application. However, currently, no technology reports have been found that simultaneously meets all of these conditions for the chemical recovery of waste LCPs.

[0005] Therefore, there is an urgent need for a green and environmentally friendly chemical recycling method for waste LCPs that does not use organic solvents, is low in cost, has a short depolymerization time, low temperature, high yield, simple post-processing, and operates at atmospheric pressure throughout the entire process. This method would promote the high-value-added conversion and reuse of a large number of urban and industrial waste LCPs, and achieve the green and sustainable development of the LCPs industry. Summary of the Invention

[0006] The purpose of this application is to provide a solvent-free alkali melting method for recycling and reusing aromatic liquid crystal polyesters. This method utilizes inorganic alkali to catalyze the mild and controllable depolymerization of waste LCPs to prepare aromatic hydroxycarboxylic acid monomers, overcoming the problem of harsh reaction conditions in existing methods, and has the advantages of being green, environmentally friendly, and sustainable.

[0007] In a first aspect, embodiments of this application provide a method for recycling and reusing solvent-free alkali-melting polyaromatic liquid crystal polyester, comprising the following steps: S1, without adding solvent, the fragments of aromatic liquid crystal polyester are dry-mixed with an inorganic alkali to obtain a mixture; S2, Under stirring conditions, the mixture obtained in step S1 is heated at 160 ℃~360 ℃ for 5-200 min to obtain an intermediate product containing aromatic hydroxycarboxylate. S3, the obtained solid mixture is dissolved in water and the solid and liquid are separated; under continuous stirring in an ice-water bath, an acid solution is added to the filtrate to neutralize the aromatic hydroxycarboxylate salt with the acid, converting it into the corresponding aromatic hydroxycarboxylic acid and precipitating it from the aqueous solution to obtain a suspension; after standing overnight, the suspension crystallizes at 0°C, and the solid and liquid are separated to obtain the depolymerized monomer.

[0008] Furthermore, the inorganic base is one or a mixture of several of the following: sodium hydroxide, lithium hydroxide, potassium hydroxide, zinc hydroxide, barium hydroxide, and calcium hydroxide.

[0009] Furthermore, in the mixture, the mass ratio of the aromatic liquid crystal polyester to the inorganic alkali is 1:(0.1~10).

[0010] Furthermore, the repeating unit of the aromatic liquid crystal polyester includes at least one of hydroxybenzoic acid structural units and hydroxynaphthoic acid structural units; when the repeating unit of the aromatic liquid crystal polyester includes hydroxybenzoic acid structural units, the obtained depolymerization monomer includes hydroxybenzoic acid; when the repeating unit of the aromatic liquid crystal polyester includes hydroxynaphthoic acid structural units, the obtained depolymerization monomer includes hydroxynaphthoic acid.

[0011] Furthermore, the aromatic liquid crystal polyester is a waste liquid crystal polyester, and its structural formula is shown in Formula I: I; Where m ranges from 0 to 10000, n ranges from 0 to 10000, and m+n≥20.

[0012] Furthermore, the waste liquid crystal polyester is fragments, granules, or powder that have been crushed or ground.

[0013] Furthermore, the acid solution is one of hydrochloric acid solution, sulfuric acid solution, nitric acid solution, acetic acid solution, and phosphoric acid solution.

[0014] Furthermore, in step S3, an acid solution is added to adjust the pH of the system to less than 7.

[0015] The beneficial effects of this invention are: (1) This application uses an inorganic alkali as an alkaline melting polymerizing agent to generate aromatic hydroxycarboxylic acid salts by activating the RCOOR′ bond (i.e., ester bond, activating the O in the C=O double bond and CO single bond in the ester bond) in the LCP polymer chain. Subsequently, acidification is used to prepare aromatic hydroxycarboxylic acid monomers with high yield and high purity. This method solves the problem of recycling and reusing industrial and urban waste LCPs, providing a new green route for the recycling and reuse of large quantities of waste LCPs. It also provides a new and simple method for preparing important chemical raw materials, which is of great significance for environmental protection, resource recycling and sustainable development.

[0016] (2) This application uses waste LCPs as raw materials, which not only simplifies the operation process of depolymerizing and recovering products from waste LCPs, but also makes the degradation process green and environmentally friendly. No organic solvents are used in the reaction and purification process, and only harmless waste brine is produced. Compared with traditional catalytic depolymerization, which often requires high temperature and high pressure or a large amount of organic solvents, this application can achieve efficient catalytic depolymerization of waste LCPs under normal air pressure, without the generation of oligomer byproducts such as dimers or polymers, and obtains high-purity and high-yield aromatic hydroxycarboxylic acids. This application turns waste LCPs into treasure, fundamentally realizing the permanent closed-loop recycling of LCPs, which will generate huge social and economic benefits and has a very obvious industrialization prospect.

[0017] (3) The reaction process of this application does not use organic solvents, has low cost, fast depolymerization speed, moderate reaction temperature, high yield, and the whole reaction is carried out in an atmospheric pressure air atmosphere without the need for protective gas (such as nitrogen and helium).

[0018] (4) This application fully meets the needs of recycling waste LCPs, and can realize the ecological and commercial development of the industry, providing strong support for the operation of the current waste LCPs recycling industry. This application can transform waste LCPs and other high-value inert polymers into high-value-added, high-purity monomers, thereby obtaining a very high input-output ratio (i.e., a high revenue-to-variable operating cost ratio), providing a truly commercially viable industrial feasibility for the sustainable circular management of high-value polymers.

[0019] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0021] Figure 1 The liquid chromatograms are those of 4-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid prepared in Example 1.

[0022] Figure 2 The infrared spectra of 4-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid prepared in Example 1 are shown.

[0023] Figure 3 The image shows a comparison of the infrared spectra of 4-hydroxybenzoic acid prepared in Example 1 and commercial 4-hydroxybenzoic acid.

[0024] Figure 4 The image shows a comparison of the infrared spectra of 6-hydroxy-2-naphthoic acid prepared in Example 1 and commercial 6-hydroxy-2-naphthoic acid.

[0025] Figure 5 The image shows the 1H NMR spectrum of the mixture of 4-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, the depolymerization products obtained in Example 1.

[0026] Figure 6 The images show the 1H NMR spectra of 4-hydroxybenzoic acid prepared in Example 1 and commercial 4-hydroxybenzoic acid.

[0027] Figure 7 The images show the 1H NMR spectra of 6-hydroxy-2-naphthoic acid prepared in Example 1 and commercial 6-hydroxy-2-naphthoic acid.

[0028] Figure 8 This is the mass spectrum of 4-hydroxybenzoic acid prepared in Example 9.

[0029] Figure 9 The image shows the 1H NMR spectrum of 4-hydroxybenzoic acid obtained in Example 9.

[0030] Figure 10 This is the mass spectrum of 6-hydroxy-2-naphthoic acid prepared in Example 10.

[0031] Figure 11 The image shows the 1H NMR spectrum of 6-hydroxy-2-naphthoic acid obtained in Example 10. Detailed Implementation

[0032] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0034] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0035] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0036] Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application according to the specific circumstances.

[0037] Please see Figures 1 to 11 As shown, this application provides a solvent-free alkali-melting method for recycling and reusing aromatic liquid crystal polyesters, which uses inorganic alkali as an alkali melting polymerizing agent to catalyze the controlled depolymerization of waste LCPs to prepare aromatic hydroxycarboxylic acid monomers.

[0038] The general reaction formula is as follows: The specific process steps are as follows: S1, without adding solvent, the fragments of aromatic liquid crystal polyester are dry-mixed with an inorganic alkali to obtain a mixture; Inorganic bases are one or a mixture of several of the following: sodium hydroxide, lithium hydroxide, potassium hydroxide, zinc hydroxide, barium hydroxide, and calcium hydroxide.

[0039] The repeating units of the aromatic liquid crystal polyester include at least one of hydroxybenzoic acid structural units and hydroxynaphthoic acid structural units.

[0040] In some embodiments, the aromatic liquid crystal polyester is a waste liquid crystal polyester, and its structural formula is shown in Formula I: I; Where m ranges from 0 to 10000, n ranges from 0 to 10000, and m+n≥20.

[0041] Waste liquid crystal polyester refers to fragments, granules, or powder that have been crushed or ground.

[0042] In the mixture, the mass ratio of aromatic liquid crystal polyester to inorganic alkali is 1:(0.1~10).

[0043] S2, Under stirring conditions, the mixture obtained in step S1 is heated at 160 ℃~360 ℃ for 5-200 min to obtain an intermediate product containing aromatic hydroxycarboxylate. S3, the obtained solid mixture is dissolved in water and the solid and liquid are separated; under continuous stirring in an ice-water bath, an acid solution is added to the filtrate to neutralize the aromatic hydroxycarboxylic acid salt with the acid, converting it into the corresponding aromatic hydroxycarboxylic acid and precipitating it from the aqueous solution to obtain a suspension; after standing overnight, the suspension is crystallized at 0 °C, and the solid and liquid are separated to obtain the aromatic hydroxycarboxylic acid monomer.

[0044] When the repeating unit of the aromatic liquid crystal polyester includes a hydroxybenzoic acid structural unit, the resulting depolymerization monomer includes hydroxybenzoic acid; when the repeating unit of the aromatic liquid crystal polyester includes a hydroxynaphthoic acid structural unit, the resulting depolymerization monomer includes hydroxynaphthoic acid.

[0045] The pH of the system is adjusted to less than 7 by adding an acid solution; the acid solution is one of hydrochloric acid solution, sulfuric acid solution, nitric acid solution, acetic acid solution, and phosphoric acid solution.

[0046] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0047] Example 1 This embodiment provides a method for recycling and reusing solvent-free alkali melting polyaromatic liquid crystal polyester, including the following steps: S1, without adding solvent, aromatic liquid crystal polyesters (LCPs) (1.00 g) are dry-mixed with NaOH (2.00 g) to obtain a mixture; wherein, the repeating units of the aromatic liquid crystal polyester include hydroxybenzoic acid structural units and hydroxynaphthoic acid structural units, and its structural formula is shown in Formula I: I; Where n is 365, m is 135, and the molar ratio of hydroxybenzoic acid structural units to hydroxynaphthoic acid structural units is 73:27.

[0048] S2, the resulting homogeneous solid mixture was transferred to a ceramic crucible and heated in a muffle furnace at 290 °C for 50 minutes in air atmosphere. After the reaction was completed, the crucible was cooled to room temperature to obtain a light yellow crude solid product (a solid mixture of 4-hydroxybenzoate and 6-hydroxy-2-naphthoate).

[0049] S3. The crude product was dissolved in 5 mL of distilled water under magnetic stirring to obtain an alkaline solution. Solid-liquid separation was performed to obtain an alkaline filtrate. Insoluble residues were removed by vacuum filtration and washed with a small amount of distilled water. The alkaline filtrates were combined. Hydrochloric acid solution was added dropwise to the alkaline filtrate with continuous stirring in an ice-water bath to acidify to pH = 2. During this process, a large amount of solid precipitated, forming a suspension. The resulting suspension was then placed in an ice-water bath and allowed to stand overnight for further crystallization. The precipitate was collected by vacuum filtration, washed with cold distilled water (0 °C), and dried under vacuum at 60 °C to obtain a mixture of depolymerized monomers (4-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid) in a yield of 90.11% (0.9011 g).

[0050] Figure 1 The liquid chromatograms are those of 4-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid prepared in Example 1.

[0051] As can be seen, the liquid chromatogram (LC) shows two extremely sharp and isolated elution peaks with retention times of 4.908 min and 5.860 min, respectively; the baseline is relatively flat, indicating that only two substances are present.

[0052] Figure 2 The infrared spectra of 4-hydroxybenzoic acid (4-HBA) and 6-hydroxy-2-naphthoic acid (2,6-HNA) prepared in Example 1 are shown. The mixed product refers to the mixture of 4-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid obtained when LCPs contain hydroxybenzoic acid structural units and hydroxynaphthoic acid structural units.

[0053] Figure 3 This is a comparison of the infrared spectra of 4-hydroxybenzoic acid prepared in Example 1 and commercial 4-hydroxybenzoic acid.

[0054] Figure 4 The image shows a comparison of the infrared spectra of 6-hydroxy-2-naphthoic acid prepared in Example 1 and commercial 6-hydroxy-2-naphthoic acid.

[0055] Figure 2 FTIR spectroscopy confirmed that the LCPs had successfully depolymerized into a monomer mixture. The ester group C=O peak (1735 cm⁻¹) was observed. -1 The carboxyl group C=O (1677 cm) completely disappeared, while the carboxyl group C=O (1677 cm) -1 ) and -OH (3000-3500 cm -1 The presence of the band confirms that the LCP backbone has been completely broken. Simultaneously, the infrared spectra of the mixed product and the two monomers completely overlap.

[0056] Depend on Figure 3 , Figure 4 It can be seen that the infrared spectrum of the separated product completely overlaps with that of commercially available high-purity 4-HBA and 2,6-HNA.

[0057] Examples 2-8 and Comparative Examples 1-3 Compared with Example 1, the difference lies in the change of the mass ratio of aromatic liquid crystal polyester to inorganic alkali, heating temperature, heating time, and type of inorganic alkali, as shown in Table 1 below. The rest is roughly the same as Example 1, and will not be repeated here.

[0058] Example 9 Compared to Example 1, the difference lies in the alteration of the unit structure of the aromatic liquid crystal polyester, which now contains only hydroxybenzoic acid structural units, specifically poly(4-hydroxybenzoic acid) homopolymer. The rest is largely the same as in Example 1 and will not be repeated here.

[0059] Example 10 Compared to Example 1, the difference lies in the alteration of the unit structure of the aromatic liquid crystal polyester, which now contains only hydroxynaphthoic acid structural units, specifically poly(6-hydroxy-2-naphthoic acid) homopolymer. The rest is largely the same as in Example 1 and will not be repeated here.

[0060] Table 1 Figure 5 The image shows the 1H NMR spectrum of the mixture of 4-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, the depolymerization products obtained in Example 1.

[0061] Figure 6 The images show the 1H NMR spectra of 4-hydroxybenzoic acid prepared in Example 1 and commercial 4-hydroxybenzoic acid.

[0062] Figure 7 The images show the 1H NMR spectra of 6-hydroxy-2-naphthoic acid prepared in Example 1 and commercial 6-hydroxy-2-naphthoic acid.

[0063] Figure 8 This is the mass spectrum of 4-hydroxybenzoic acid prepared in Example 9.

[0064] Figure 9 The image shows the 1H NMR spectrum of 4-hydroxybenzoic acid obtained in Example 9.

[0065] Figure 10 This is the mass spectrum of 6-hydroxy-2-naphthoic acid prepared in Example 10.

[0066] Figure 11 The image shows the 1H NMR spectrum of 6-hydroxy-2-naphthoic acid obtained in Example 10.

[0067] like Figure 8 As shown, this substance exhibits a very strong parent ion peak [MH]. - The m / z value is 137, which perfectly matches the mass of 4-HBA after losing a proton (M = 138). Furthermore, a high-abundance fragment ion (m / z = 93) was clearly detected in the mass spectrum, which is consistent with the phenolic anion fragments produced when the 4-HBA molecule loses its carboxyl group (-COOH, mass loss of 44) under bombardment. Simultaneously, a significant ion peak at m / z = 275 was observed. This is not an impurity or an incompletely fragmented covalent dimer, but rather a non-covalent dimer formed by the strong intermolecular hydrogen bond self-assembly of 4-HBA molecules containing both carboxyl and phenolic hydroxyl groups during ESI. This peak is consistent with [2M-H]. - (2 × 138 - 1 = 275) A perfect match.

[0068] same, Figure 10 In the [MH] spectrum, a molecular ion peak ([MH]) is observed at m / z = 187. - This is completely consistent with the theoretical value (M = 188) for 2,6-HNA. Simultaneously, the mass spectrum shows a characteristic decarboxylation fragment ion at m / z = 143 and a dimer peak at m / z = 375, corresponding to the [2M-H] peak of 2,6-HNA. -Species (2 × 188 - 1 = 375). The formation of this dimer under strong intermolecular hydrogen bonding strongly demonstrates that both carboxyl and hydroxyl functional groups are completely retained in the degradation products. These precise mass spectrometry data clearly indicate that the separated products are precisely the depolymerized monomers 4-HBA and 2,6-HNA.

[0069] As can be seen, in high-resolution nuclear magnetic resonance (NMR) spectroscopy analysis (400 MHz, DMSO- d 6 In ), the mixed products 1 The H NMR spectrum completely overlaps with the spectra of 4-HBA and 2,6-HNA. Meanwhile, the entire... 1 The 1H NMR spectrum showed a smooth baseline, with no impurity peaks due to residual ester bond protons, incomplete depolymerization, or unknown side reactions. The purified monomer also resembled that of commercial products. 1 The HNMR spectra match perfectly.

[0070] In summary, the solvent-free alkali-melting method for recycling and reusing polyaromatic liquid crystal polyesters provided in this application can significantly improve the depolymerization yield of waste LCPs within a specific process parameter window, and different process conditions have a decisive impact on the yield, as detailed below: (1) Critical effect of inorganic base dosage: Comparing Examples 1-4 with Comparative Examples 1-2, it can be seen that the mass ratio of raw materials to inorganic base is crucial to the reaction yield. When the amount of base is too high (Comparative Example 1), the yield decreases significantly (33.22%), which may be due to the excess solid base in the system hindering mass and heat transfer, or triggering other side reactions. When the amount of base is too low (Comparative Example 2), the ester bond cannot be effectively catalyzed to break down, forming monomers.

[0071] (2) The important role of reaction temperature: As can be seen from Comparative Examples 2-3, both excessively high and excessively low temperatures will lead to a significant decrease in yield. Excessively high temperatures may produce a large number of side reactions, including carbonization, decomposition, and mineralization. On the other hand, excessively low temperatures may not be able to activate the alkali, resulting in a slower depolymerization reaction kinetics.

[0072] (3) Effect of mixed alkali system: Comparing Example 1 and Example 7, it can be seen that when a mixed inorganic alkali (equal amounts of NaOH and KOH) is used, the process conditions are optimized. In Example 7, an excellent yield of 80.75% was maintained even at an extremely low heating temperature of only 160 °C. This indicates that the combination of NaOH and KOH produces a significant synergistic and eutectic effect, greatly reducing the activation energy and operating temperature required for the depolymerization reaction.

[0073] In summary, the types, mass ratios, and temperature conditions of inorganic alkalis specified in this application are not conventional choices for those skilled in the art, but rather optimal combinations derived through creative exploration, enabling efficient and low-energy-consumption depolymerization and recovery of waste LCPs.

[0074] It should be noted that the inorganic base can be one or a mixture of several of the following: sodium hydroxide, lithium hydroxide, potassium hydroxide, zinc hydroxide, barium hydroxide, and calcium hydroxide.

[0075] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for recycling and reusing solvent-free alkali-melting polyaromatic liquid crystal polyester, characterized in that, Includes the following steps: S1, without adding solvent, the fragments of aromatic liquid crystal polyester are dry-mixed with an inorganic base to obtain a mixture; the inorganic base is one or a mixture of several of sodium hydroxide, lithium hydroxide, potassium hydroxide, zinc hydroxide, barium hydroxide, and calcium hydroxide; the repeating unit of the aromatic liquid crystal polyester is at least one of hydroxybenzoic acid and hydroxynaphthoic acid. S2, Under stirring conditions, the mixture obtained in step S1 is heated at 160 ℃~360 ℃ for 5-200 min to obtain an intermediate product containing aromatic hydroxycarboxylate. S3, the obtained intermediate product is dissolved in water and the solid and liquid are separated; under continuous stirring in an ice-water bath, an acid solution is added to the filtrate to neutralize the aromatic hydroxycarboxylate salt with the acid, converting it into the corresponding aromatic hydroxycarboxylic acid and precipitating it from the aqueous solution to obtain a suspension; after standing overnight, the suspension crystallizes at 0°C, and the solid and liquid are separated to obtain the depolymerized monomer.

2. The method for recycling and reusing solvent-free alkali-melting polyaromatic liquid crystal polyester according to claim 1, characterized in that, The inorganic base is one or a mixture of two of sodium hydroxide and potassium hydroxide.

3. The method for recycling and reusing solvent-free alkali-melting polyaromatic liquid crystal polyester according to claim 1, characterized in that, In the mixture, the mass ratio of the aromatic liquid crystal polyester to the inorganic alkali is 1:(0.1~10).

4. The method for recycling and reusing solvent-free alkali-melting polyaromatic liquid crystal polyester according to claim 1, characterized in that, When the repeating unit of the aromatic liquid crystal polyester includes hydroxybenzoic acid, the resulting depolymerization monomer includes hydroxybenzoic acid; when the repeating unit of the aromatic liquid crystal polyester includes hydroxynaphthoic acid, the resulting depolymerization monomer includes hydroxynaphthoic acid.

5. The method for recycling and reusing solvent-free alkali-melting polyaromatic liquid crystal polyester according to claim 1, characterized in that, The aromatic liquid crystal polyester is a waste liquid crystal polyester, and its structural formula is shown in Formula I: I； Where m ranges from 0 to 10000, n ranges from 0 to 10000, and m+n≥20.

6. The method for recycling and reusing solvent-free alkali-melting polyaromatic liquid crystal polyester according to claim 5, characterized in that, The waste liquid crystal polyester is fragments, granules, or powder that have been crushed or ground.

7. The method for recycling and reusing solvent-free alkali-melting polyaromatic liquid crystal polyester according to claim 1, characterized in that, The acid solution is one of hydrochloric acid solution, sulfuric acid solution, nitric acid solution, acetic acid solution, and phosphoric acid solution.

8. The method for recycling and reusing solvent-free alkali-melting polyaromatic liquid crystal polyester according to claim 1, characterized in that, In step S3, an acid solution is added to adjust the pH of the system to less than 7.

Images