Upgrading and utilization method of polyester plastic and coupled hydrogen production process

Abstract

The application discloses an upgrading utilization method of polyester plastics and a coupled hydrogen production process. The method comprises the following steps: using a polyoxometalate as a catalyst, and using an organic acid or an inorganic acid and / or a metal ion with oxidizing property as a cocatalyst, and hydrolyzing the polyester plastics into TPA, EG and FA. The method provided by the application can convert the polyester plastics into TPA and EG under mild conditions, and the EG can be further converted into FA. The application further provides an upgrading utilization and coupled hydrogen production process of polyester plastics. The polyester plastics are hydrolyzed in an anode tank, the polyoxometalate with oxidizing property is regenerated through coupling electrolysis, continuous production is realized, and hydrogen is produced through electrolysis in a cathode. The method and the process provided by the application have high degradation rate of the polyester plastics and are green and environment-friendly. Compared with water electrolysis, the hydrogen production in the cathode can save more than 50% of electric energy for producing the same volume of hydrogen.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of waste resource recycling, and more particularly to a method for upgrading and utilizing polyester plastics and a coupled hydrogen production process. BACKGROUND

[0002] Polyester plastics are widely used in packaging, textile fibers, construction, electronics and appliances, and medical fields. Polyethylene terephthalate (PET) is the most representative polyester plastic, with an annual output of over 700 million tons. Currently, plastic waste disposal has become a serious global problem.

[0003] Chemical recycling and high-value utilization of waste plastics is an important research field, and its implementation approaches include alcoholysis, acetic acidysis, ammonolysis, hydrogenolysis, and hydrolysis. Since water is a green and sustainable depolymerization agent, hydrolysis has become an environmentally friendly and clean waste PET recycling approach. However, due to the high hydrophobicity of PET, hydrolysis under neutral conditions needs to be carried out at high temperature (200-300℃) and high pressure (1-4MPa) to overcome the depolymerization kinetics barrier. In order to reduce the reaction conditions, the addition of alkali (such as NaOH or KOH) can effectively accelerate the hydrolysis process of PET. This is because the generated terephthalic acid (TPA) can dissolve to form terephthalate, thereby promoting the reaction kinetics. However, this method has some challenges: the alkali agent is constantly consumed in the reaction, the generated terephthalate product cannot be directly used for PET repolymerization, and the regeneration of TPA requires the consumption of a large amount of acid to neutralize terephthalate. This not only increases chemical consumption, but also generates a large amount of wastewater, causing serious environmental pollution problems. In addition, PET hydrolysis under acidic conditions also faces significant difficulties. For example, PET has high resistance to dilute acid, so high-concentration strong acid (such as 13mol·L -1 of nitric acid or 7mol·L -1 of sulfuric acid) or pure organic acid needs to be used to improve the hydrolysis efficiency. Such high-acidity operating conditions pose dual challenges of safety and environmental impact in industrial applications, further limiting the feasibility of large-scale promotion.

[0004] Chinese patent CN119098218 A reports a method for hydrolyzing PET, using a solid acid modified by an asymmetric double-quaternary ammonium salt surfactant as a catalyst, but the reaction needs to be carried out at 180℃ or above for 24h or more. Therefore, there is an urgent need to develop a method that can efficiently and economically dispose of PET waste, turning waste into treasure and realizing the integrated utilization of resources. SUMMARY

[0005] The application aims to provide a polyester plastic upgrading utilization method and a recycling process.

[0006] In a first aspect, the application provides a polyester plastic upgrading utilization method, which comprises: using a polyoxometalate as a catalyst and water as a solvent to upgrade polyester plastic into terephthalic acid (TPA), formic acid (FA) and ethylene glycol (EG).

[0007] Preferably, the polyoxometalate comprises any one of phosphomolybdic acid, vanadium mono-substituted, di-substituted or tri-substituted phosphomolybdic acid, silicomolybdic acid, or iron, copper, cobalt, chromium or manganese mono-substituted phosphomolybdic acid. -1 .

[0008] Preferably, the method further comprises adding an organic acid or an inorganic acid as a cocatalyst.

[0009] Preferably, the inorganic acid and the organic acid comprise any one of triflic acid, sulfuric acid, hydrochloric acid, nitric acid, perchloric acid, trifluoroacetic acid and trichloroacetic acid; the amount of the organic acid or the inorganic acid is ≤ 2.5 mol·L -1 ; preferably, the amount of the polyoxometalate is 0.05-0.15 mol·L -1 .

[0010] Preferably, the method further comprises using a metal ion with oxidizing property as a cocatalyst; preferably, the metal ion with oxidizing property comprises any one of Cu 2+ , Co 2+ and Fe 3+ .

[0011] Preferably, the temperature of the hydrolysis is 80-120℃.

[0012] Preferably, the temperature of the hydrolysis is 100℃.

[0013] In a second aspect, the application provides a polyester plastic upgrading utilization and coupling hydrogen production process, which comprises: degrading polyester plastic in an anode tank; using a polyoxometalate, or a polyoxometalate and an inorganic acid, or a polyoxometalate, an inorganic acid and a metal ion with oxidizing property as a catalyst to upgrade the polyester plastic into TPA, EG and FA; and electrolyzing hydrogen in a cathode tank.

[0014] The polyoxometalate catalyst can be regenerated in the anode tank by coupling an electrolysis process, so that the process can be continuously produced, and the polyester plastic is almost completely converted (~100%). The cathode produces hydrogen with low energy consumption, and the required energy is only 20.7-50.6% of the energy required for electrolysis of water.

[0015] Preferably, the cathode is Pt / C.

[0016] In a third aspect of the present application, a device for upgrading and utilizing polyester plastic is provided for implementing the upgrading and recycling coupled hydrogen production process described above.

[0017] Compared with the prior art, the technical scheme of the present application has the following beneficial effects:

[0018] (1) The present application can efficiently depolymerize and upgrade PET by using polyoxometalate as a catalyst, or using low-concentration inorganic acid or organic acid and / or metal ions with oxidation as a co-catalyst for synergistic catalysis. Under mild conditions, the polyester plastic can be completely converted into TPA and EG, and a part of the EG can be oxidized into FA, thereby promoting the hydrolysis of the polyester plastic, and the conversion rate is high.

[0019] (2) The upgrading and utilization coupled hydrogen production process of the present application utilizes the catalytic depolymerization ability of polyoxometalate for polyester plastic, efficiently hydrolyzes the polyester plastic, and the polyoxometalate with oxidation can be regenerated by electrolysis. At the same time, hydrogen (H2) is produced at a very low working potential under the catalysis of a Pt / C cathode. Compared with electrolysis of water, the energy consumption for producing the same volume of hydrogen is more than 50% lower. The whole process of conversion and utilization of polyester plastic can realize a green and waste-free process and atomic economy, the conversion rate is close to 100%, and low-energy hydrogen production can be coupled to realize the conversion of hydrogen energy.

[0020] (3) Since the hydrolysis system is acidic, TPA is directly precipitated and can be separated from the reaction system by filtration, avoiding post-neutralization treatment. Compared with the alkaline hydrolysis process, the energy consumption of neutralization and purification is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 FIG. 1 is a schematic diagram of a recycling device in the present application.

[0022] Figure 2 FIG. 4 is an electrolysis curve of the solution after different cycles of reaction.

[0023] Figure 3 FIG. 6 is an XRD spectrum of the product TPA and commercially available TPA in the present application.

[0024] Figure 4 FIG. 7 is an infrared spectrum of the product TPA and commercially available TPA in the present application.

[0025] Figure 5 PET and PMo 12 Reaction solution 1 H NMR. DETAILED DESCRIPTION

[0026] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without the specific details set forth in this description. In other instances, well-known methods have not been described in detail in order to avoid obscuring the present application.

[0027] 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 belongs. The terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting of the application. It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0028] Example 1 Hydrolysis of PET in different kinds of polyoxometalates

[0029] In the PET hydrolysis experiment, the total solution volume was 10 mL, 1.0 g of PET powder and 1 mol L -1 of polyoxometalate were reacted in a glass bottle with a screw cap, the reaction temperature was 100°C, and the reaction time was 10 hours. In order to prevent the influence of oxygen, the air in the container was purified with pure N2 gas before heating. After the reaction was completed, the reaction mixture was poured into about 40 mL of distilled water, and terephthalic acid (TPA) was precipitated and separated.

[0030] In order to calculate the PET conversion rate and TPA yield, the precipitate was redissolved with NaOH aqueous solution (1 mol L -1 ). The unreacted PET that was not dissolved in the alkaline medium was removed by filtration, and the generated TPA was recrystallized with 1 mol L -1 of hydrochloric acid. In all examples, the PET was completely converted. The specific reaction conditions and results are shown in Table 1.

[0031] Table 1 Conversion rate of PET hydrolysis and TPA yield in different kinds of polyoxometalates

[0032]

[0033]

[0034] Example 2 Hydrolysis of PET in different concentrations of PMo 12

[0035] ​Example 1 was repeated with different concentrations (0.5-1 mol·L -1 ) of PMo 12 and PET was reacted at 100℃ for 10 hours. Other operation steps were unchanged. The specific reaction conditions and results are shown in Table 2. With the increase of PMo 12 concentration, the conversion of PET and the yield of TPA also increased.

[0036] Table 2 Conversion of PET hydrolysis and yield of TPA under different PMo 12 concentration conditions

[0037]

[0038] Example 3 Hydrolysis effect of PET in PMo 12 and mixed solution of inorganic acid or organic acid

[0039] Example 1 was repeated, and 0.1 mol·L -1 of PMo 12 was combined with 2.5 mol·L -1 of triflic acid (HTOf), hydrochloric acid (HCl), sulfuric acid (H2SO4), perchloric acid (HClO4), trifluoroacetic acid, and trichloroacetic acid, respectively, and PET was reacted at 100℃ for 10 hours. Other operation steps were unchanged. The specific reaction conditions and results are shown in Table 3.

[0040] Table 3 Conversion of PET hydrolysis and yield of TPA under different types of inorganic acid mixed with PMo 12

[0041]

[0042]

[0043] Example 4 Influence of metal ions as cocatalysts

[0044] Example 1 was repeated, 0.1 mol·L -1 of PMo 12 was combined with 0.1 mol·L -1 of metal ions, and 2.5 mol·L -1 of triflic acid (HTOf) was added, and reacted for 10 hours. Other operation steps were unchanged. The specific reaction conditions and results are shown in Table 4.

[0045] Table 4 Influence of metal ions as cocatalysts on the conversion of PET hydrolysis and the yield of TPA

[0046] Serial number Metal salt PET conversion rate (%) TPA yield (%) Example 4-1 FeCl3 94.65 92.67 Example 4-2 [CuCl2] 92.67 90.25 Example 4-3 CoCl2 92.87 90.45 Example 4-4 Fe(NO)3 95.77 94.09

[0047] Example 5 PMo 12 ​Effect of concentration on PET hydrolysis

[0048] Example 1 was repeated with different concentrations of PMo 12 The total hydrogen ion concentration of triflic acid (HTOf) or perchloric acid (HCIO4) was 2.8 mol-L -1 , and PET was reacted at 100°C for 10 h. PMo 12 As a catalyst, even as low as 0.05 mol-L -1 , PET can be converted by more than 80% in 10 h. Other operating steps were unchanged. The specific reaction conditions and results are shown in Table 5.

[0049] Table 5 PMo 12 Effect of concentration on PET hydrolysis conversion and TPA yield

[0050]

[0051]

[0052] Example 6 Effect of temperature on PET hydrolysis

[0053] Example 1 was repeated with 1 mol-L -1 of PMo 12 or 0.1 mol-L -1 of PMo 12 combined with 2.5 mol-L -1 of triflic acid (HTOf), and PET was reacted at 100°C for 10 h. Other operating steps were unchanged. The specific reaction conditions and results are shown in Table 6.

[0054] Table 6 Effect of temperature on PET hydrolysis conversion and TPA yield

[0055]

[0056] Example 7 Stability of PMo 12 mixed with inorganic acid system and corresponding hydrogen production performance.

[0057] 0.1 mol-L -1 of PMo 12 combined with 2.5 mol-L -1 of triflic acid (HTOf) or perchloric acid (HCIO4), and PET was reacted at 100°C for 10 h. After the reaction was completed, PET and terephthalic acid (TPA) were precipitated and separated. The solution was pumped into the anode of the electrolytic cell for electrolysis and regeneration, the electrolytic cell area was 1 cm 2 , the current density was 50 mA cm -2 , and the cathode used 1 mol-L -1 H3PO4, and record the volume of hydrogen collected. The regenerated solution is used for the depolymerization of PET in the next cycle, which is repeated for 5 times. The schematic diagram of the upgraded utilization device is shown in Figure 1 The electrolysis curve is shown in Figure 2 The specific reaction conditions and results are shown in Table 7. It is illustrated that the upgraded utilization method in the present application can be continuously carried out in the anode tank or anode groove, realizing the regeneration and recycling of the catalyst.

[0058] Table 7 PMo 12 Cyclic stability of PET hydrolysis in the mixed system with inorganic acid

[0059]

[0060] All the solid products TPA obtained in Example 7 are characterized by XRD Figure 3 ) and infrared spectrum Figure 4 ). The IR spectrum and XRD of the TPA prepared in the example are not different, and compared with the commercially available TPA, the characteristic peaks are basically consistent, which illustrates that the polyester plastic is successfully decomposed into TPA in the example of the present application. The PMo 12 The liquid product of hydrolyzed PET is detected by 1 H NMR, as shown in Figure 5 , in addition to the EG signal peak, only one product FA. It is illustrated that the system has good selectivity of polyester hydrolysis.

[0061] The above-described examples only express several embodiments of the present application, which are described in detail and in detail, but cannot be understood as the limitation of the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of variations and improvements can be made, which belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. An upgraded utilization of polyester plastics coupled with a hydrogen production process, characterized in that, The upgrading and utilization of the aforementioned polyester plastics is carried out in the anode cell, and hydrogen is produced by electrolysis in the cathode cell; The upgrading and utilization of polyester plastics includes: using polyoxometalates as catalysts, oxidizing metal ions as co-catalysts, and water as a solvent to degrade polyester plastics into TPA, EG, and FA; the oxidizing metal ions are selected from Cu. 2+ Co 2+ Fe 3+ The reaction mixture comprises any one of the following: phosphomolybdic acid, vanadium mono-, di-, or tri-substituted phosphomolybdic acid, silicomolybdic acid, or mono-substituted phosphomolybdic acid of iron, copper, cobalt, or manganese; it also includes the addition of an inorganic or organic acid as a co-catalyst; the inorganic or organic acid is selected from trifluoromethanesulfonic acid and perchloric acid; the amount of the organic or inorganic acid is ≤2.5 mol·L⁻¹. -1 .

2. The upgraded utilization and coupling hydrogen production process according to claim 1, characterized in that, The dosage of polyoxometalates is 0.05-0.15 mol·L⁻¹. -1 .

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