A method of degrading polyphenylene ether plastics

Abstract

The present application relates to the technical field of plastic degradation, in particular to a method for degrading polyphenyl ether plastic. The method for degrading polyphenyl ether plastic comprises the following steps: mixing polyphenyl ether, substituted pyrazole and tetrabutylammonium tetrafluoroborate according to a molar ratio of 1:(4-6):(0.5-1.5), adding a solvent, performing constant current electrolysis for 8-20 hours to obtain a degradation product; the structural formula of the substituted pyrazole is: wherein R 1 , R 2 , R 3 are independently selected from hydrogen, halogen. The present application realizes the reaction route of the polyphenyl ether plastic degradation product under mild conditions by using the method of electrochemistry, converts the polyphenyl ether plastic into the high-value degradation product ketone compound, realizes the recycling of the polyphenyl ether plastic, and is a new path for the degradation and conversion of the polyphenyl ether plastic.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of plastic degradation, and particularly relates to a method for degrading polyphenyl ether plastic. BACKGROUND

[0002] The chemical name of polyphenyl ether is poly 2,6-dimethyl-1,4-phenyl ether, and the chemical formula is C 30 H 22 O4, which is abbreviated as PPO (Polyphenylene Oxide) or PPE (Polypheylene ether). It is a high-strength engineering plastic developed in the 1960s, with an annual output of about 500,000 tons, and is one of the world's five general-purpose engineering plastics. [1] Polyphenyl ether has stable chemical properties, is non-toxic, has excellent comprehensive performance, and the biggest feature is that it has excellent dimensional stability and outstanding electrical insulation under long-term load, and has a wide temperature range. Polyphenyl ether has excellent water and steam resistance, and the finished product has high tensile strength and impact strength, and good creep resistance. In addition, it has good wear resistance and electrical properties. It is widely used in electronic and electrical, automotive, mechanical, chemical and other fields.

[0003] Although polyphenyl ether brings many conveniences, its degradation as waste is a big problem. The main structural unit of polyphenyl ether is a diaryl ether, and the carbon-oxygen bond in it is very stable, with a bond energy of 315 kcal / mol. [2] Therefore, the chemical degradation of polyphenyl ether is very difficult. At present, there are only a few related reports on the degradation of polyphenyl ether. For example, Yan and Wang reported in 2021 that using Ru / Nb2O5 catalyst, under the condition of high temperature (280 degrees Celsius) and high pressure hydrogen gas (5 bar), polyphenyl ether was degraded to produce m-xylene with a yield of 85% [3] . Despite the above reports, how to realize the high-value and efficient conversion of polyphenyl ether plastic under mild conditions (without high temperature and avoiding the use of high-pressure hydrogen gas) has become a scientific and technical problem that needs to be solved by those skilled in the art.

[0004] REFERENCES

[0005] [1] Acute Market Reports. "Global polyphenylene oxide (PPO) resins market size & share, application analysis, regional outlook, growth trends, key players, competitive strategies and forecasts to 2026", 2018.

[0006] [2] K. Lee, Y. Jing, Y. Wang, N. Yan, Nat. Rev. Chem. 2022, 6, 635-652.

[0007] [3] Y. Jing, Y. Wang, S. Furukawa, J. Xia, C. Sun, M. J. Hglsey, H. Wang, Y. Guo, X. Liu, N. Yan, Angew. Chem. Int. Ed. 2021, 60, 5527-5535. SUMMARY

[0008] The present application aims to provide a method for degrading polyphenyl ether plastic under mild conditions to achieve high-value recycling of polyphenyl ether plastic.

[0009] In order to achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0010] A method for degrading polyphenyl ether plastic, comprising the following steps: mixing polyphenyl ether, substituted pyrazole and electrolyte ammonium according to the molar ratio of 1:(4-6):(0.5-1.5), adding a solvent, and performing constant current electrolysis for 8-20h to obtain a degradation product; the structural formula of the substituted pyrazole is:

[0011]

[0012] , R 1 , R 2 , R 3 are independently selected from hydrogen, halogen.

[0013] In one preferred embodiment, the electrolyte is any one or several of tetrabutyl tetrafluoroboric acid, lithium triflate, tetrabutyl ammonium hexafluorophosphate.

[0014] Tetrabutyl tetrafluoroboric acid, lithium triflate, tetrabutyl ammonium hexafluorophosphate are electrolytes that enhance conductivity. In the present application, although similar electrolyte tetrabutyl ammonium acetate can also enhance conductivity, it cannot obtain the product.

[0015] If the amount of substituted pyrazole and electrolyte ammonium is too small, the degradation method is incomplete and the yield is low; if the amount of substituted pyrazole and electrolyte ammonium is too much, the degradation product contains too many impurities.

[0016] In one preferred embodiment, R 1 , R 3 are hydrogen, and R 2 is hydrogen or halogen.

[0017] In one preferred embodiment, R 1 , R 3 are hydrogen, and R2 halogen.

[0018] In one preferred embodiment, R 1 , R 3 is hydrogen, and R 2 is chlorine or fluorine.

[0019] In one preferred embodiment, the solvent is a mixture of toluene and acetonitrile.

[0020] In one preferred embodiment, the volume ratio of toluene and acetonitrile is 2-5:1.

[0021] In one preferred embodiment, the reaction temperature of the constant current electrolysis is 60-100℃.

[0022] In one preferred embodiment, the reaction temperature of the constant current electrolysis is 80-90℃.

[0023] In one preferred embodiment, the anode of the constant current electrolysis is a graphite rod or graphite paper.

[0024] In one preferred embodiment, the diameter of the graphite rod is 4-8mm.

[0025] In one preferred embodiment, the length, width and height of the graphite paper are 1-3cm, 1-2cm and 0.03-0.07cm, respectively.

[0026] In one preferred embodiment, the cathode of the constant current electrolysis is a platinum sheet or graphite paper.

[0027] In one preferred embodiment, the current of the constant current electrolysis is 3-10mA.

[0028] In one preferred embodiment, the current of the constant current electrolysis is 3-7mA.

[0029] In one preferred embodiment, the time of the constant current electrolysis is 12-15h.

[0030] The degradation route of the degraded polyphenyl ether plastic is as follows:

[0031]

[0032] The degradation products are quantitatively analyzed by nuclear magnetic spectrometer hydrogen spectrum, with addition of dibromomethane as an internal standard.

[0033] The present invention utilizes an electrochemical method to realize a reaction route of polyphenylene ether plastic degradation products under mild conditions (below 100°C, without the use of hydrogen), converting polyphenylene ether plastic into high-value degradation product ketone compounds, thereby realizing the recycling of polyphenylene ether plastic and providing a new pathway for the degradation and conversion of polyphenylene ether plastic. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the experimental device for the degradation of polyaniline, (1) is the anode and cathode used in the experiment; (2) is the test tube used for the reaction; (3) is a schematic diagram of the electrodes in the reaction tube; (4) is a schematic diagram of the heating experiment. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the embodiments described are only part of the embodiments of the present application, not all of them. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field based on the present application are within the scope of protection of the present application.

[0036] The present application has no particular restrictions on the types of magnetic stirrers and borosilicate glass test tubes, and those skilled in the art can choose according to actual conditions, as long as the purpose of the present application can be achieved.

[0037] The present application has no particular limitation on the weight average molecular weight of the polyphenylene ether plastic, as long as the purpose of the present application can be achieved.

[0038] In this application, yield refers to the ratio of the actual production output obtained from inputting a unit amount of raw materials (i.e. polyester plastics) to the theoretically calculated product output.

[0039] The present application uses nuclear magnetic resonance spectrometer and mass spectrometer to conduct qualitative and quantitative analysis on the reaction system of each embodiment and comparative example.

[0040] Example 1

[0041] use Figure 1 The device shown in the figure is used to conduct a degradation test of polyaniline. In the figure, (1) is the anode and cathode used in the experiment; (2) is the test tube used for the reaction; (3) is a schematic diagram of the electrodes in the reaction tube; and (4) is a schematic diagram of the heating experiment. The specific degradation test process is as follows:

[0042] Into a 10 mL dry HSG tube with magnetic stirring, polyphenyl ether (25.0 mg, 0.2 mmol, weight average molecular weight 50000), 4-chloropyrazole (102.5 mg, 1.0 mmol), tetrabutylammonium tetrafluoroborate (65.9 mg, 0.2 mmol) were added successively, where the molar ratio of the three reagents was 1:5:1. Then 2.0 mL of toluene and 1.0 mL of acetonitrile were added, and the solution was mixed uniformly. The reaction system used a graphite rod (diameter 6 mm) as the anode and a platinum plate (length x width x thickness = 2 cm x 1 cm x 0.02 cm) as the cathode, and a constant current electrolysis method was used to obtain the degradation product. The reaction temperature was 80°C, the current was 5 mA, and the reaction time was 14 hours. The product was quantified using a nuclear magnetic spectrometer hydrogen spectrum, with the addition of dibromomethane as an internal standard for quantitative analysis, and the yield of the ketone degradation product was 54%.

[0043] The reaction equation is as follows:

[0044]

[0045] The product characterization data are as follows:

[0046] Nuclear magnetic resonance hydrogen spectrum 1 H NMR (400 MHz, CDC13) δ 7.58 (s, 2H), 7.56 (s, 2H), 7.29 (s, 2H), 2.06 (s, 6H).

[0047] Nuclear magnetic resonance carbon spectrum 13 C NMR (101 MHz, CDC13) δ 184.7, 139.6, 137.8, 134.9, 126.0, 111.7, 72.8, 16.1.

[0048] High-resolution mass spectrum ESI HRMS for [C 14 H 12 Cl2N4O + H + ] calculated: 323.0461, found: 323.0464.

[0049] Example 2

[0050] The electrolyte was replaced by lithium trifluoromethanesulfonate (LiOTf) instead of tetrabutylammonium tetrafluoroborate, and the rest was the same as Example 1, and the yield of the ketone degradation product was 37%.

[0051] Example 3

[0052] The electrolyte was replaced by tetrabutylammonium acetate (nBu4OAc) instead of tetrabutylammonium tetrafluoroborate, and the rest was the same as Example 1, and the yield of the ketone degradation product was 0%.

[0053] Example 4

[0054] The electrolyte was changed from tetrabutylammonium tetrafluoroborate to tetrabutylammonium hexafluorophosphate (nBu4PF6), and the rest was the same as Example 1, obtaining a ketone degradation product yield of 48%.

[0055] Comparative Example 1

[0056] No electrolyte was added, and the rest was the same as Example 1, obtaining a ketone degradation product yield of 0%.

[0057] The test results of Examples 1-4 and Comparative Example 1 are shown in Table 1:

[0058] Table 1 Test results of Examples 1-4 and Comparative Example 1

[0059] Electrolyte Yield of degradation product ketone Example 1 Tetrabutylammonium tetrafluoroborate 54％ Example 2 Lithium triflate 37％ Example 3 Tetrabutylammonium acetate 0％ Example 4 Tetrabutylammonium hexafluorophosphate 48％ Comparative Example 1 None 0％

[0060] Example 5

[0061] The equivalent molar ratio was changed from polyphenyl ether: substituted pyrazole: electrolyte = 1:5:1 to 1:4:1, and the rest was the same as Example 1, obtaining a ketone degradation product yield of 43%.

[0062] Example 6

[0063] The equivalent molar ratio was changed from polyphenyl ether: substituted pyrazole: electrolyte = 1:5:1 to 1:6:1, and the rest was the same as Example 1, obtaining a ketone degradation product yield of 52%.

[0064] Example 7

[0065] The equivalent molar ratio was changed from polyphenyl ether: substituted pyrazole: electrolyte = 1:5:1 to 1:5:0.5, and the rest was the same as Example 1, obtaining a ketone degradation product yield of 31%.

[0066] Example 8

[0067] The equivalent molar ratio was changed from polyphenyl ether: substituted pyrazole: electrolyte = 1:5:1 to 1:5:1.5, and the rest was the same as Example 1, obtaining a ketone degradation product yield of 51%.

[0068] Example 9

[0069] The equivalent molar ratio was changed from polyphenyl ether: substituted pyrazole: electrolyte = 1:5:1 to 1:5:2, and the rest was the same as Example 1, obtaining a ketone degradation product yield of 52%.

[0070] The test results of Examples 1, 5-9 are shown in Table 2:

[0071] Table 2 Test results of Examples 1, 5-9

[0072]

[0073]

[0074] Example 10

[0075] The reaction time was adjusted from 14 hours to 8 hours, and the rest was the same as Example 1, and the yield of ketone degradation product was 6%.

[0076] Example 11

[0077] The reaction time was adjusted from 14 hours to 12 hours, and the rest was the same as Example 1, and the yield of ketone degradation product was 25%.

[0078] Example 12

[0079] The reaction time was adjusted from 14 hours to 20 hours, and the rest was the same as Example 1, and the yield of ketone degradation product was 20%.

[0080] The test results of Examples 1, 10-12 are shown in Table 3:

[0081] Table 3 Test results of Examples 1, 10-12

[0082] Reaction time / h Yield of degradation product ketone Example 1 14 54％ Example 10 8 6％ Example 11 12 25％ Example 12 20 20％

[0083] And in Example 10, a new by-product was observed, which was likely an intermediate that reacted with pyrazole again to form ketone, which was likely caused by the shorter reaction time, and the intermediate did not have time to convert.

[0084] The reaction flow of Example 10 is as follows:

[0085]

[0086] Example 13

[0087] The reaction current was adjusted from 5 milliamps to 3 milliamps, and the rest was the same as Example 1, and the yield of ketone degradation product was 29%.

[0088] Example 14

[0089] The reaction current was adjusted from 5 milliamps to 7 milliamps, and the rest was the same as Example 1, and the yield of ketone degradation product was 34%.

[0090] Example 15

[0091] The reaction current was adjusted from 5 milliamps to 10 milliamps, and the rest was the same as Example 1, and the yield of ketone degradation product was 16%.

[0092] Comparative Example 2

[0093] The reaction current was adjusted from 5 mA to 0 mA, and the rest was the same as in Example 1. The yield of ketone degradation products obtained was 0%.

[0094] The test results of Examples 1, 13-15 and Comparative Example 2 are shown in Table 4:

[0095] Table 4 Test results of Examples 1, 13-15 and Comparative Example 2

[0096] Reaction current / mA Yield of degradation product ketone Example 1 5 54％ Example 13 3 29％ Example 14 7 34％ Example 15 10 16％ Comparative Example 2 0 0％

[0097] Example 16

[0098] The reaction temperature was adjusted from 80° C. to 60° C., and the rest was the same as in Example 1. The yield of ketone degradation products was 7%.

[0099] Example 17

[0100] The reaction temperature was adjusted from 80° C. to 70° C., and the rest was the same as in Example 1. The yield of ketone degradation products was 20%.

[0101] Example 18

[0102] The reaction temperature was adjusted from 80° C. to 90° C., and the rest was the same as in Example 1. The yield of ketone degradation products was 43%.

[0103] The test results of Examples 1 and 16-18 are shown in Table 5:

[0104] Table 5 Test results of Examples 1 and 16-18

[0105] Reaction temperature / °C Yield of degradation product ketone Example 1 80 54％ Example 16 60 7％ Example 17 70 20％ Example 18 90 43％

[0106] Example 19

[0107] The electrode anode was changed from graphite rod (diameter 6 mm) to graphite paper (length×width×thickness=2 cm×1 cm×0.05 cm). The rest was the same as in Example 1. The yield of ketone degradation products was 26%.

[0108] Example 20

[0109] The electrode anode was changed from a graphite rod (6 mm in diameter) to a platinum sheet (length×width×thickness=2 cm×1 cm×0.02 cm). The rest was the same as in Example 1. The yield of ketone degradation products was 31%.

[0110] Example 21

[0111] The solvent was adjusted from toluene:acetonitrile (volume ratio 2:1) to 100% toluene. The rest was the same as in Example 1. The yield of ketone degradation products was 0%.

[0112] Example 22

[0113] The solvent was adjusted from toluene:acetonitrile (volume ratio 2:1) to toluene:acetonitrile (volume ratio 5:1), and the rest was the same as in Example 1. The yield of ketone degradation products was 30%.

[0114] Example 23

[0115] The solvent was adjusted from toluene:acetonitrile (volume ratio 2:1) to toluene:acetonitrile (volume ratio 1:1), and the rest was the same as in Example 1. The yield of ketone degradation products was 10%.

[0116] Example 24

[0117] The solvent was adjusted from toluene:acetonitrile (volume ratio 2:1) to toluene:acetonitrile (volume ratio 1:2), and the rest was the same as in Example 1. The yield of ketone degradation products was 6%.

[0118] Example 25

[0119] The solvent was adjusted from toluene:acetonitrile (volume ratio 2:1) to 100% acetonitrile. The rest was the same as in Example 1. The yield of ketone degradation products was 0%.

[0120] The test results of Examples 1 and 21-25 are shown in Table 6:

[0121] Table 6 Test results of Examples 1, 21-25

[0122]

[0123]

[0124] Example 26

[0125] The reaction reagent 4-chloropyrazole was replaced with pyrazole. The rest was the same as in Example 1. The reaction scheme is shown below. The yield of degradation product ketones was 5%.

[0126]

[0127] Example 27

[0128] The reaction reagent 4-chloropyrazole was replaced with 4-fluoropyrazole. The rest of the reaction was the same as in Example 1. The reaction scheme is shown below. The yield of the degradation product ketone was 10%.

[0129]

[0130] Example 28

[0131] The reaction reagent 4-chloropyrazole was replaced with 5-methylpyrazole. The rest was the same as in Example 1. The reaction scheme is shown below. The yield of the degradation product ketone was 0%.

[0132]

[0133] The test results of Examples 1, 26-28 are shown in Table 7:

[0134] Table 7 Test results of Examples 1, 26-28

[0135] Substituted pyrazoles Yield of degradation product ketone Example 1 4-Chloropyrazole 54％ Example 26 Pyrazole 5％ Example 27 4-Fluoropyrazole 10％ Example 28 5-Methylpyrazole 0％

[0136] The above description merely illustrates the embodiments of the present application. The well-known specific structures and characteristics in the scheme are not described in detail. It is obvious for those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and the present application can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be regarded as exemplary and non-limiting, the scope of the present application is defined by the appended claims rather than the above description, and all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application. Any reference signs in the claims should not be regarded as limiting the involved claims.

Claims

1. A method for degrading polyphenylene ether plastic, characterized in that: The following steps are involved: After mixing polyphenylene ether, substituted pyrazole and electrolyte in a molar ratio of 1:(4-6):(0.5-1.5), adding solvent, and performing constant current electrolysis for 8-20 hours to obtain a degradation product; the structural formula of the substituted pyrazole is: Among them, R 1 、R 2 、R 3 are independently selected from: hydrogen, halogen; The electrolyte is any one or more of tetrabutyl tetrafluoroboric acid, lithium trifluoromethanesulfonate, and tetrabutyl ammonium hexafluorophosphate; The solvent is a mixed solution of toluene and acetonitrile; The current of constant current electrolysis is 3-10 mA.

2. The method for degrading polyphenylene ether plastic according to claim 1, characterized in that: R 1 、R 3 is hydrogen, R 2 is hydrogen or halogen.

3. The method for degrading polyphenylene ether plastic according to claim 1, characterized in that: The volume ratio of toluene to acetonitrile is 2-5:

1.

4. The method for degrading polyphenylene ether plastic according to claim 1, characterized in that: The reaction temperature of constant current electrolysis is 60-100°C.

5. The method for degrading polyphenylene ether plastic according to claim 1, characterized in that: The anode of constant current electrolysis is a graphite rod or graphite paper.

6. The method for degrading polyphenylene ether plastic according to claim 1, characterized in that: The cathode of constant current electrolysis is platinum sheet or graphite paper.

7. The method for degrading polyphenylene ether plastic according to claim 1, characterized in that: The constant current electrolysis time is 12-15h.

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