Upgrading utilization method of polyester plastics and coupling hydrogen production process

Abstract

The invention discloses an upgraded utilization method of polyester plastics and a coupling hydrogen production process. The method comprises the following step: hydrolyzing polyester plastics into TPA, EG and FA by taking polyoxometallate as a catalyst and organic acid or inorganic acid and / or metal ions with oxidability as a promoter. According to the method provided by the invention, polyester plastics can be converted into TPA and EG under mild conditions, and EG can be further converted into FA. The invention further provides an upgraded utilization and coupling hydrogen production process of the polyester plastics, the polyester plastics are hydrolyzed in the anode tank, polyoxometallate with oxidability is regenerated through the coupling electrolysis effect, continuous production is achieved, and meanwhile electrolysis hydrogen production is conducted on the cathode. The method and the process provided by the invention have high degradation rate on polyester plastics, and are green and environment-friendly; and when hydrogen is produced at the cathode, compared with electrolyzed water, the power consumption for producing hydrogen with the same volume is reduced by more than 50%.

Description

Technical Field

[0001] The present invention relates to the technical field of waste resource recovery, and more specifically, to an upgrading and utilization method of polyester plastics and a coupled hydrogen production process. Background Art

[0002] Polyester plastics are widely used in packaging, textile fibers, construction, electronics and medical fields. Polyethylene terephthalate (PET) is the most representative polyester plastic, with an annual output of more than 70 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 realization methods include alcoholysis, acetolysis, aminolysis, hydrogenolysis and hydrolysis. Since water is a green and sustainable depolymerization agent, hydrolysis has become an environmentally friendly and clean way to recycle waste PET. However, due to the high hydrophobicity of PET, hydrolysis under neutral conditions needs to be carried out at high temperature (200–300°C) and high pressure (1–4MPa) to overcome its depolymerization kinetic barriers. 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 continuously consumed in the reaction, the generated terephthalate product cannot be directly used for the repolymerization of PET, and the regeneration of TPA requires a large amount of acid to neutralize the terephthalate. This not only increases the consumption of chemicals, but also produces a large amount of wastewater, bringing serious environmental pollution problems. In addition, PET hydrolysis under acidic conditions also faces significant difficulties. For example, PET has a high tolerance to dilute acid, so a high concentration of strong acid (such as 13 mol·L -1 of nitric acid or 7 mol·L -1 Sulfuric acid) or pure organic acid is 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 its large-scale promotion.

[0004] Chinese patent CN119098218 A reports a method for hydrolyzing PET, using a solid acid modified by an asymmetric diquaternary ammonium salt surfactant as a catalyst, but the reaction needs to be carried out at a temperature above 180°C for more than 24 hours. Therefore, it is urgent to develop a method that can efficiently and economically treat PET waste, turn PET waste into treasure, and realize the integrated utilization of resources. Summary of the invention

[0005] The purpose of the present invention is to propose an upgrading and recycling process for polyester plastics. By using polyoxometalate and acid as catalysts and utilizing their synergistic effect, polyester plastics can be upgraded to TPA, FA and EG with high added value under relatively mild conditions. It can also be coupled with electrolytic hydrogen production technology to reduce the energy consumption of hydrogen production and realize the conversion of hydrogen energy.

[0006] The first aspect of the present invention provides a method for upgrading polyester plastics, comprising: using polyoxometalate as a catalyst and water as a solvent to upgrade polyester plastics into terephthalic acid (TPA), formic acid (FA) and ethylene glycol (EG).

[0007] Preferably, the polyoxometalate comprises any one of phosphomolybdic acid, vanadium monosubstituted, disubstituted or trisubstituted phosphomolybdic acid, silicomolybdic acid, or iron, copper, cobalt, chromium or manganese monosubstituted phosphomolybdic acid. Preferably, the amount of the polyoxometalate is 0.5-1 mol·L -1 .

[0008] Preferably, the method further comprises: adding an organic acid or an inorganic acid as a co-catalyst.

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

[0010] Preferably, the invention further comprises: using oxidizing metal ions as co-catalysts; preferably, the oxidizing metal ions include Cu 2+ 、Co 2+ , Fe 3+ Any one of .

[0011] Preferably, the hydrolysis temperature is 80-120°C.

[0012] Preferably, the hydrolysis temperature is 100°C.

[0013] The second aspect of the present invention provides a polyester plastic upgrade and coupled hydrogen production process, in which polyester plastic is degraded in the anode cell, and polyester plastic is upgraded to TPA, EG and FA using polyoxometalates, or polyoxometalates and inorganic acids, or polyoxometalates, inorganic acids and oxidizing metal ions as catalysts; and electrolysis is performed in the cathode cell to produce hydrogen.

[0014] The polyoxometalate catalyst can be regenerated in the anode cell by a coupled electrolysis process, so the process can be continuously produced to achieve almost complete conversion (~100%) of polyester plastics. The cathode produces hydrogen with low energy consumption, requiring only 20.7-50.6% of the energy required for electrolysis of water.

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

[0016] The third aspect of the present invention provides an upgrading and utilization device for polyester plastics, which is used to implement the above-mentioned upgrading and recycling coupled hydrogen production process.

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

[0018] (1) The present invention can efficiently depolymerize and upgrade PET through polyoxometalates, using oxidizing polyoxometalates as catalysts; or using low-concentration inorganic acids or organic acids and / or oxidizing metal ions as co-catalysts for synergistic catalysis. Under mild conditions, polyester plastics can be completely converted to produce TPA and EG, and a portion of EG can be oxidized to FA, thereby promoting the hydrolysis of polyester plastics with a high conversion rate.

[0019] (2) The upgraded utilization and coupled hydrogen production process of the present invention utilizes the catalytic depolymerization ability of polyoxometalates on polyester plastics to efficiently hydrolyze polyester plastics. The oxidizing polyoxometalates can be regenerated by electrolysis. At the same time, hydrogen (H2) is produced at an extremely low working potential under the catalysis of the Pt / C cathode. Compared with the electrolysis of water, the power consumed to produce the same volume of hydrogen is more than 50% lower. The green waste-free process and atomic economy of the entire process of polyester plastic conversion and utilization can be achieved, with a conversion rate of nearly 100%, and can be coupled with low-energy hydrogen production to achieve hydrogen energy conversion.

[0020] (3) Since the hydrolysis system is acidic, TPA is directly precipitated and can be directly 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 THE DRAWINGS

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

[0022] Figure 2 Shows the electrolysis curves of the solution after different cycle reactions.

[0023] Figure 3 The XRD spectra of the product TPA in the present invention and commercially available TPA are shown in FIG.

[0024] Figure 4 The infrared spectra of the product TPA in the present invention and commercially available TPA.

[0025] Figure 5 For PET and PMo 12 After the reaction, the solution 1 H NMR. DETAILED DESCRIPTION

[0026] Many specific details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited to the specific implementation disclosed below.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. It should be noted that the reagents used in the present embodiment are all common commercial products.

[0028] Example 1 Hydrolysis effect of PET in different types of polyoxometalates

[0029] In the PET hydrolysis experiment, the total solution volume was 10 mL, 1.0 g PET powder and 1 mol·L -1 The polyoxometalate was reacted in a glass bottle with a screw cap at 100°C for 10 hours. To prevent the influence of oxygen, the air in the container was purged with pure N2 gas before heating. After the reaction was completed, the reaction mixture was poured into about 40 mL of distilled water for precipitation and separation of terephthalic acid (TPA).

[0030] In order to calculate the PET conversion and TPA yield, the precipitate was treated with NaOH aqueous solution (1 mol·L -1 ) was dissolved again. The unreacted PET insoluble in the alkaline medium was removed by filtration, and the generated TPA was treated with 1 mol·L -1 In all embodiments, PET was completely converted. Specific reaction conditions and results are shown in Table 1.

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

[0032]

[0033]

[0034] Example 2 PET at different concentrations of PMo 12 The hydrolysis effect

[0035] Repeat Example 1, using different concentrations (0.5-1 mol·L -1 ) 12 , reacted with PET at 100°C for 10 hours. The other operation steps remained unchanged. The specific reaction conditions and results are shown in Table 2. 12 With the increase of concentration, the conversion rate of PET and the yield of TPA also increased.

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

[0037]

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

[0039] Repeat Example 1 and add 0.1 mol·L -1 PMo 12 Combined with 2.5 mol·L -1 Trifluoromethanesulfonic acid (HTOf), hydrochloric acid (HCl), sulfuric acid (H2SO4), perchloric acid (HClO4), trifluoroacetic acid, and trichloroacetic acid were reacted with PET at 100°C for 10 hours. The other operation steps remained unchanged. The specific reaction conditions and results are shown in Table 3.

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

[0041]

[0042]

[0043] Example 4 Effect of metal ions as promoters

[0044] Repeat Example 1, using 0.1 mol·L -1 PMo 12 With 0.1 mol·L -1 of metal ions and combined with 2.5 mol·L -1 The reaction was continued for 10 hours with trifluoromethanesulfonic acid (HTOf). The other steps remained unchanged. The specific reaction conditions and results are shown in Table 4.

[0045] Table 4 Effect of metal ions as co-catalysts on the conversion rate and TPA yield of PET hydrolysis

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

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

[0048] Repeat Example 1, using different concentrations of PMo 12 Combined with trifluoromethanesulfonic acid (HTOf) or perchloric acid (HClO4), the total hydrogen ion concentration is 2.8 mol·L -1 , react with PET at 100℃ for 10h. 12 As a catalyst, even as low as 0.05 mol·L -1 PET can also be converted to more than 80% after 10 hours. The other operation steps remain unchanged. The specific reaction conditions and results are shown in Table 5.

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

[0050]

[0051]

[0052] Example 6 Effect of Temperature on PET Hydrolysis

[0053] Repeat Example 1, using 1 mol·L -1 PMo 12 or 0.1 mol·L -1 PMo 12 Combined with 2.5 mol·L -1 Trifluoromethanesulfonic acid (HTOf) was reacted with PET at 100°C for 10 h. The other operation steps remained unchanged. The specific reaction conditions and results are shown in Table 6.

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

[0055]

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

[0057] 0.1 mol·L -1 PMo 12 Combined with 2.5 mol·L -1 Trifluoromethanesulfonic acid (HTOf) or perchloric acid (HClO4) reacts with PET at 100°C for 10 hours. After the reaction is completed, PET and terephthalic acid (TPA) are separated by precipitation. The solution is pumped into the anode of the electrolytic cell for electrolytic regeneration. The electrolytic cell area is 1cm 2 , current density is 50mA cm -2 , the cathode uses 1 mol·L -1 H3PO4, and record the volume of collected hydrogen. The regenerated solution is used for the next PET depolymerization reaction, and repeated 5 times. Figure 1 As shown, the electrolysis curve is Figure 2 The specific reaction conditions and results are shown in Table 7. This shows that the upgrading and utilization method of the present invention can be continuously carried out in the anode pool or anode tank to achieve the regeneration and recycling of the catalyst.

[0058] Table 7 PMo 12 Cyclic stability of PET hydrolysis in mixed systems with inorganic acids

[0059]

[0060] All the solid products TPA obtained in Example 7 were analyzed by XRD ( Figure 3 ) and infrared spectroscopy ( Figure 4 ) were characterized. The IR spectrum and XRD of the TPA prepared in the example were no different. Compared with the commercially available TPA, the characteristic peaks were basically the same, indicating that the polyester plastic was successfully decomposed into TPA in the example of the present invention. 12 The liquid product of PET hydrolysis is used 1 H NMR detection, as Figure 5 As shown in the figure, in addition to the EG signal peak, there is only one product, FA, which indicates that the system has good polyester hydrolysis selectivity.

[0061] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for upgrading polyester plastics, characterized in that: include: Using polyoxometalate as catalyst and water as solvent, polyester plastics are degraded into TPA, EG and FA.

2. The upgrade utilization method according to claim 1, characterized in that: The polyoxometalate includes 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.

3. The upgrade utilization method according to claim 1 or 2, characterized in that: The amount of the polyoxometalate is 0.5-1 mol·L -1 .

4. The upgrade utilization method according to claim 1, characterized in that: Also includes: Inorganic or organic acids are added as co-catalysts.

5. The upgrade utilization method according to claim 4, characterized in that: The inorganic acid or organic acid includes any one of trifluoromethanesulfonic acid, sulfuric acid, hydrochloric acid, nitric acid, perchloric acid, trifluoroacetic acid, and trichloroacetic acid; the amount of the organic acid or inorganic acid is ≤2.5 mol·L -1 Preferably, the amount of polyoxometalate is 0.05-0.15 mol·L -1 .

6. The upgrade utilization method according to claim 1 or 4, characterized in that: Also includes: The oxidizing metal ions are used as co-catalysts; preferably, the oxidizing metal ions include Cu 2+ 、Co 2+ , Fe 3+ Any one of .

7. The upgrade utilization method according to any one of claims 1 to 6, characterized in that: The hydrolysis temperature is 80-120°C.

8. A polyester plastic upgrading and coupled hydrogen production process, characterized in that: The method according to any one of claims 1 to 7 is carried out in the anode cell, and the cathode cell is used for electrolysis to produce hydrogen.

9. An upgrading and utilization device for polyester plastics, used for implementing the coupled hydrogen production process as claimed in claim 8.

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