Method for debrominating nonmetal components of waste circuit board

Abstract

The invention belongs to the field of solid waste recovery, and particularly discloses a method for debrominating nonmetal components of a waste circuit board. According to the method, based on the concept of treating waste with waste, the low-temperature pyrolysis debromination rate of the nonmetal components of the waste circuit board is increased by adopting the waste three-way catalyst, collaborative recovery and disposal of two kinds of solid waste can be achieved, the process is low in energy consumption and high in debromination rate, the recovered waste catalyst can be recycled, and the recycling value of the debrominated nonmetal components is high.

Description

Technical Field

[0001] The invention belongs to the field of solid waste recycling, and in particular relates to a method for debrominating non-metallic components of waste circuit boards. Background Art

[0002] According to a report released by the Organization for Economic Cooperation and Development (OECD), the annual global production of waste plastics reaches 353 million tons, and only 9% of waste plastics are recycled. Waste thermosetting plastics account for 18% of the total waste plastics and contain additives such as brominated flame retardants. If improperly disposed of, they will cause harm to the environment. The non-metallic components of waste circuit boards are a typical bromine-containing waste thermosetting plastic, and debromination is the premise and key to its safe recycling.

[0003] At present, mechanochemical, chemical decomposition and high-temperature pyrolysis are mostly used for the debromination of non-metallic components of waste circuit boards. The mechanochemical method requires the consumption of dehalogenating agents and has a small processing volume, while the chemical decomposition method consumes a large amount of reagents and has a large amount of waste liquid discharge. The high-temperature pyrolysis method has high debromination efficiency but has problems such as high energy consumption, difficult product orientation, and high yield of toxic and harmful volatile phases. In previous studies, based on the simulation calculation of the chemical bond breakage characteristics of brominated flame retardants in non-metallic components of waste circuit boards under energy supply conditions, combined with thermal weight loss and pyrolysis product analysis experiments, it was found that the critical temperature for debromination of non-metallic components of waste circuit boards is 260°C, but the vacuum pyrolysis debromination rate of non-metallic components of waste circuit boards at 260°C is only 22.67% (Zhu et al., J. Hazard. Mater., 2022, 421, 126814). Therefore, how to further improve the low-temperature pyrolysis debromination rate of non-metallic components of waste circuit boards is the core issue.

[0004] Three-way catalysts are generally used for automobile exhaust treatment, which can purify carbon monoxide, hydrocarbons and nitrogen oxides in automobile exhaust. Such catalysts generally include a carrier (such as ceramics) and a catalyst coating attached to the carrier containing one or more platinum group metals (commonly used Pt, Pd, Rh) as catalytic active materials. The three-way catalyst has a certain safe life. After the service life is exceeded, the catalyst will be no longer used after failure or catalytic efficiency is reduced. This part of the catalyst is called a waste three-way catalyst. The global reserves of platinum group metals are scarce. According to statistics from the United States Geological Survey, the proven reserves are only 69,000 tons. More than 65% of platinum group metals are used in the production of three-way catalysts. At the same time, the annual output of scrapped three-way catalysts in my country is as high as 200,000 tons. Therefore, waste three-way catalysts are important secondary resources of platinum group metals. At present, the main methods for recovering platinum group metals from waste three-way catalysts are pyrometallurgy, hydrometallurgy and bioleaching. These methods have low recovery rates, long cycles and high costs. The reusability of the recovered waste three-way catalysts needs to be re-evaluated and studied, and their practicality needs to be verified. How to efficiently recycle and reuse waste three-way catalysts still requires further scientific research. Summary of the invention

[0005] In view of the problems of the above-mentioned prior art involving low debromination rate of non-metallic components of waste circuit boards and difficulty in recycling and reusing waste three-way catalysts, the present invention will provide a method for debrominating non-metallic components of waste circuit boards. The method of the present invention is based on the concept of treating waste with waste, and uses waste three-way catalysts to improve the low-temperature thermal debromination rate of non-metallic components of waste circuit boards, so as to achieve coordinated recycling and disposal of the two solid wastes. The process has low energy consumption and high debromination rate, the recovered waste catalyst can be recycled, and the debrominated non-metallic components have high reuse value.

[0006] To achieve the above purpose, the following technical solutions are specifically included:

[0007] The present invention provides a method for debrominating non-metallic components of waste circuit boards, comprising the following steps:

[0008] (1) crushing and ball-milling the waste three-way catalyst containing palladium to obtain waste three-way catalyst powder;

[0009] (2) mixing the waste three-way catalyst powder with non-metallic components of waste circuit boards containing bromine, and pyrolyzing them under vacuum to obtain pyrolysis residue, pyrolysis oil phase components and pyrolysis gas phase components; the pyrolysis temperature is ≥260° C.;

[0010] (3) Screening the pyrolysis residue to obtain debrominated non-metallic components and recovered spent three-way catalyst.

[0011] The three-way catalyst used for automobile exhaust purification contains transition metal Pd, and the reason for its scrapping is not the change of Pd content and morphology. The Pd in ​​the waste three-way catalyst still mainly exists in the form of single metal, but because the Pd atoms gradually migrate to the inside of the three-way catalyst carrier and are wrapped, the three-way catalyst is invalidated and scrapped. In order to expose the active site Pd in ​​the waste three-way catalyst again, the present invention combines crushing and ball milling to mechanically activate it first to obtain a waste three-way catalyst powder with a small particle size. The active site Pd re-exposed by mechanical activation catalyzes the debromination reaction of the brominated flame retardant, and debromination is achieved by participating in oxidative addition reaction and decomposition reaction. After screening and separation, the waste three-way catalyst powder and the debrominated waste circuit board non-metallic components can be recycled and used as a debromination catalyst. The method of the present invention can greatly improve the debromination rate of non-metallic components of waste circuit boards, and even achieves a technical effect of more than four times that of conventional debromination methods.

[0012] Preferably, in step (1), the waste three-way catalyst containing palladium element comprises a carrier and palladium element supported on the carrier; based on the mass of the waste three-way catalyst containing palladium element, the content of palladium element is 100-150 mg / kg.

[0013] Preferably, the carrier is a honeycomb structure.

[0014] Preferably, in step (1), the average particle size of the spent three-way catalyst powder is ≤700 nm.

[0015] Preferably, in step (1), the crushing method includes shear crushing, and the crushing time is 5-30s.

[0016] Preferably, in step (1), in the ball milling, the ratio of balls to materials is (25-40):1, more preferably, (30-48):1.

[0017] Preferably, in step (1), the ball milling time is 2-8 hours, and the ball milling speed is 300-500 rpm.

[0018] More preferably, in step (1), the ball milling time is 4-8 hours, and the ball milling speed is 420-480 rpm.

[0019] Preferably, in step (2), the mass ratio of the waste three-way catalyst powder to the non-metallic components of the waste circuit boards containing bromine is 1:(1-3).

[0020] Preferably, in step (2), the average particle size of the non-metallic components of the waste circuit boards containing bromine is 0.1-2 mm.

[0021] Preferably, in step (2), the vacuum degree of the vacuum is less than 120Pa.

[0022] Preferably, in step (2), the pyrolysis temperature is 260-300°C, the heating rate to the pyrolysis temperature is 8-12°C / min, and the pyrolysis time is 15-45min.

[0023] Preferably, in step (2), the pyrolysis oil phase component also includes water washing. After the pyrolysis oil phase component is washed with water, Br2 and other water-soluble components are separated from water-insoluble organic matter, bromine is extracted from the aqueous solution to obtain Br2; the water-insoluble organic matter is disposed of as hazardous waste.

[0024] Preferably, in step (2), the pyrolysis gas phase component further comprises cooling the pyrolysis gas phase component. The pyrolysis gas phase component is cooled, and a rapid cooling method is generally adopted in the cooling process to obtain condensates such as phenol and non-condensables such as HBr in the pyrolysis gas phase component. The condensates such as phenol are purified by distillation to obtain chemical raw materials such as phenol. The non-condensables such as HBr are absorbed by an alkaline sodium hydroxide solution to separate and obtain NaBr, and the harmless components not absorbed by the alkaline solution are discharged.

[0025] Preferably, in step (3), the screening method includes vibration screening, and the mesh size of the screening is 160-200 mesh.

[0026] Based on the previous crushing and ball milling treatment, the particle size of the waste three-way catalyst powder is relatively small, while the particle size of the conventional waste circuit board non-metallic components is relatively large, which is quite different from the particle size of the waste three-way catalyst powder. The waste three-way catalyst and non-metallic components after pyrolysis can be separated by screening, which is convenient for the recovery and utilization of these two components. Among them, the debrominated non-metallic components after purification can be reused as building materials; the recycled waste three-way catalyst can be recycled in the pyrolysis debromination process of the non-metallic components of the waste circuit board.

[0027] Preferably, in step (3), the debrominated non-metallic components are further purified, and the purification method includes at least one of wind sorting and water washing. The debrominated non-metallic components after purification can be reused as building materials.

[0028] Compared with the prior art, the present invention has the following beneficial effects: the method of the present invention combines crushing and ball milling to mechanically activate the waste three-way catalyst, so that the Pd active sites on the waste three-way catalyst are fully exposed; in the low-temperature co-pyrolysis process of the waste three-way catalyst and the non-metallic components of the waste circuit board, Pd catalyzes the debromination reaction, thereby significantly improving the low-temperature debromination rate of the non-metallic components of the waste circuit board and eliminating its environmental pollution risks; at the same time, the debrominated non-metallic components can still have a resin main body structure and have a high recovery value; the waste three-way catalyst separated from the pyrolysis residue can be recycled. The method of the present invention is based on the concept of treating waste with waste, and uses waste three-way catalysts to improve the low-temperature pyrolysis debromination rate of the non-metallic components of the waste circuit board, which can achieve the coordinated recovery and disposal of the two solid wastes. The process has low energy consumption and high debromination rate. The recovered waste catalyst can be recycled, and the debrominated non-metallic components have high reuse value. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention discloses a method for debrominating non-metallic components of waste circuits and a post-processing flow chart of pyrolysis residues, pyrolysis oil phase components and gas phase components.

[0030] Figure 2 The morphology and particle size distribution of the waste three-way catalysts in Examples 1-4 after mechanical activation: (a) Example 2 was ball-milled for 2 h; (b) Example 3 was ball-milled for 4 h; (c) Example 4 was ball-milled for 6 h; (d) Example 1 was ball-milled for 8 h.

[0031] Figure 3 The valence distribution of Pd in ​​the spent three-way catalyst powder: (a) before low-temperature co-pyrolysis; (b) after low-temperature co-pyrolysis in Example 1.

[0032] Figure 4 It is the debromination rate of the non-metallic components of the waste circuit boards in Examples 1-4 by low-temperature co-pyrolysis.

[0033] Figure 5 It is the infrared spectra of the non-metallic components of waste circuit boards after low-temperature co-pyrolysis in Examples 1-4 and Comparative Example 1 (corresponding to 0h). DETAILED DESCRIPTION

[0034] In order to better illustrate the purpose, technical scheme and advantages of the present invention, the present invention will be further described below through specific examples. The test methods used in the examples and / or comparative examples are conventional methods unless otherwise specified; the materials, reagents, etc. used can be obtained from commercial channels unless otherwise specified.

[0035] The "non-metallic components of waste circuit boards" referred to herein include bromine-containing flame retardants, and may also include non-metallic components such as glass fiber, resin, and some impurities that cannot be excluded, such as impure copper (content less than 5wt.%), solder (content less than 0.5wt.%), etc. The non-metallic components of waste circuit boards used in the following examples and comparative examples are all the same, which are obtained by physically separating the metals from the substrates of the components removed from the waste circuit boards after crushing, and are mainly composed of phenolic resin, epoxy resin, brominated flame retardant, curing agent, and other components. The non-metallic component samples of waste circuit boards used in the following examples and comparative examples are particles with an average particle size of 0.1-2mm and a bromine content of 3.22wt.%.

[0036] The three-way catalyst carrier is usually processed into a honeycomb shape, and then the carrier is filled with a coating containing platinum group metals to obtain it. The common carrier of the three-way catalyst is cordierite (2MgO·2Al2O3·5SiO2). In addition to the main components of cordierite, Mg, Al, Si, and O, the three-way catalyst also contains components such as CeO2 and ZrO2. The "waste three-way catalyst" referred to herein is a discarded, old or scrapped three-way catalyst. The waste three-way catalysts used in the following embodiments and comparative examples are all the same, which are three-way catalysts scrapped from automobile exhaust ports, including a honeycomb cordierite carrier, CeO2, ZrO2 and Pd element components loaded on the carrier, and the Pd element content in the waste three-way catalyst measured by ICP-MS is 154.19 mg / kg.

[0037] Example 1

[0038] A method for debrominating non-metallic components of waste circuit boards, as shown in the attached flow chart Figure 1 , specifically including the following steps:

[0039] S1. Mechanically activate the waste three-way catalyst by combining shear crushing and ball milling, with a crushing time of 15 seconds, a ball-to-material ratio of 36:1, a ball milling time of 8 hours, and a ball milling speed of 480 rpm to obtain waste three-way catalyst powder;

[0040] S2. Add the mechanically activated waste three-way catalyst powder to the non-metallic components of the waste circuit board and mix them thoroughly, wherein the mass ratio of the waste three-way catalyst powder to the non-metallic components of the waste circuit board is 1:2; place the mixture in a vacuum pyrolysis furnace for co-pyrolysis, wherein the vacuum degree during the pyrolysis process is 100 Pa, the heating rate is 10°C / min, the pyrolysis temperature is 260°C, the residence time is 30 min, and after the pyrolysis is completed, pyrolysis residue, pyrolysis oil and pyrolysis gas are obtained;

[0041] S3, after the pyrolysis is completed, the waste three-way catalyst powder in the pyrolysis residue is separated from the debrominated non-metallic components by vibrating screening, and the screen is 170 mesh; the debrominated non-metallic components and the recovered waste three-way catalyst are obtained;

[0042] S4. Use wind power sorting to further purify the debrominated non-metallic components of the remaining small amount of waste three-way catalyst powder; recycle the waste three-way catalyst powder separated and recovered after pyrolysis; and use water washing to safely dispose of the pyrolysis oil, separate Br2 and other water-soluble components from water-insoluble organic matter in the pyrolysis oil, extract bromine from the aqueous solution to obtain Br2, and dispose of the water-insoluble organic matter as hazardous waste; the pyrolysis gas is subjected to rapid cooling treatment to obtain condensates such as phenol and non-condensables such as HBr in the pyrolysis gas phase components, and the condensates such as phenol are purified by distillation to obtain chemical raw materials such as phenol, and the non-condensables such as HBr are absorbed by alkaline sodium hydroxide solution to separate NaBr, and the harmless components not absorbed by the alkaline solution are discharged.

[0043] Example 2

[0044] The difference between this embodiment and embodiment 1 is that in step S1, the ball milling time in this embodiment is 2 hours.

[0045] Example 3

[0046] The difference between this embodiment and embodiment 1 is that in step S1, the ball milling time in this embodiment is 4 hours.

[0047] Example 4

[0048] The difference between this embodiment and embodiment 1 is that in step S1, the ball milling time in this embodiment is 6 hours.

[0049] Example 5

[0050] The difference between this embodiment and embodiment 1 is that in step S1, the ball-to-material ratio during ball milling in this embodiment is 30:1.

[0051] Example 6

[0052] The difference between this embodiment and embodiment 1 is that in step S1, the rotation speed of the ball milling in this embodiment is 420 rpm.

[0053] Example 7

[0054] The difference between this embodiment and embodiment 1 is that in step S1, the crushing time of this embodiment is 10s.

[0055] Example 8

[0056] The present embodiment is different from the embodiment 1 in that, in step S2, the mass ratio of the waste three-way catalyst powder to the non-metallic components of the waste circuit board in the present embodiment is 1:3.

[0057] Example 9

[0058] The difference between this embodiment and embodiment 1 is that in step S2, the pyrolysis temperature of this embodiment is 280°C.

[0059] Example 10

[0060] The difference between this embodiment and embodiment 1 is that in step S2, the residence time at the pyrolysis temperature in this embodiment is 20 minutes.

[0061] Comparative Example 1

[0062] The difference between this comparative example and Example 1 is that in step S1, this comparative example does not perform ball milling, and the specific process is as follows:

[0063] S1, treating the waste three-way catalyst by shearing and crushing, the crushing time is 15s, and obtaining the waste three-way catalyst powder;

[0064] S2. Add the mechanically activated waste three-way catalyst powder to the non-metallic components of the waste circuit board and mix them thoroughly, wherein the mass ratio of the waste three-way catalyst powder to the non-metallic components of the waste circuit board is 1:2; place the mixture in a vacuum pyrolysis furnace for co-pyrolysis, wherein the vacuum degree during the pyrolysis process is 100 Pa, the heating rate is 10°C / min, the pyrolysis temperature is 260°C, the residence time is 30 min, and after the pyrolysis is completed, pyrolysis residue, pyrolysis oil and pyrolysis gas are obtained;

[0065] S3, after the pyrolysis is completed, the waste three-way catalyst powder in the pyrolysis residue is separated from the debrominated non-metallic components by vibrating screening, and the screen is 170 mesh; the debrominated non-metallic components and the recovered waste three-way catalyst are obtained;

[0066] S4. Use wind power sorting to further purify the debrominated non-metallic components of the remaining small amount of waste three-way catalyst powder; recycle the waste three-way catalyst powder separated and recovered after pyrolysis; and use water washing to safely dispose of the pyrolysis oil, separate Br2 and other water-soluble components from water-insoluble organic matter in the pyrolysis oil, extract bromine from the aqueous solution to obtain Br2, and dispose of the water-insoluble organic matter as hazardous waste; the pyrolysis gas is subjected to rapid cooling treatment to obtain condensates such as phenol and non-condensables such as HBr in the pyrolysis gas phase components, and the condensates such as phenol are purified by distillation to obtain chemical raw materials such as phenol, and the non-condensables such as HBr are absorbed by alkaline sodium hydroxide solution to separate NaBr, and the harmless components not absorbed by the alkaline solution are discharged.

[0067] Comparative Example 2

[0068] The difference between this comparative example and Example 1 is that in step S2, the pyrolysis temperature of this comparative example is 250°C.

[0069] The morphology and particle size of the waste three-way catalyst powder obtained in step S1 of the above embodiment and comparative example were tested by scanning electron microscopy (SEM), and the pyrolysis debromination rate of the non-metallic components of the waste circuit board was tested; the Pd valence distribution of the waste three-way catalyst powder before and after pyrolysis was tested by X-ray photoelectron spectroscopy (XPS); and the infrared spectra (IR) of the non-metallic components of the waste circuit board before and after pyrolysis were tested. Some of the results are shown in the attached figure. Figure 2-5 shown.

[0070] Among them, the test method of the debromination rate of the pyrolysis solid phase product sample is: using oxygen bomb combustion (NBSI, Ningbo Saiyin Instrument Co., Ltd.) ion chromatograph to detect and analyze the bromine content. Take 0.2g of the pyrolysis solid phase product sample and place it in the combustion dish of the oxygen bomb combustion device, tie the copper wire in contact with the sample to be tested to the electrodes on both sides of the combustion dish for subsequent ignition, and add 10mL of ultrapure water in the combustion tank as Br ion absorption liquid, seal the combustion tank and fill it with sufficient O2, turn on the power and ignite the sample to be tested to fully burn, open the combustion tank after cooling, pour the absorption liquid into a 50mL volumetric flask, repeatedly wash the combustion dish and rinse the combustion tank wall with ultrapure water, and pour the washing liquid into a 50mL volumetric flask and fix the volume. After taking 10mL of the fixed volume, the solution can be filtered through a 0.22μm filter membrane, and the Br ion concentration can be measured on the machine. The pyrolysis tail gas is passed into the NaOH absorption liquid to absorb the HBr product, so the NaOH absorption liquid can be directly measured on the machine after passing through a 0.22μm filter membrane.

[0071] The debromination rate can be calculated by the following formula:

[0072]

[0073] Where: η is the debromination rate of the sample; m i is the mass of the sample weighed by oxygen bomb combustion (mg); v0 is the volume of the constant volume solution after the sample is burned in the oxygen bomb, which is 0.05L in the present invention; c i is the bromine concentration (mg / L) measured by ion chromatography; ω0 is the bromine content (wt.%) in the sample without any treatment.

[0074] Table 1

[0075]

[0076]

[0077] Table 2

[0078]

[0079] Combination Figure 2-5 As can be seen from Table 1-2, in Examples 1-10, the average particle size of the waste three-way catalyst after mechanical activation is 220-600nm, the valence state of Pd does not change significantly before and after pyrolysis, and the waste three-way catalyst powder separated after pyrolysis can be recycled; the debromination rate of non-metallic components of waste circuit boards is as high as 80%, and the non-metallic components of some examples still retain the resin main structure after debromination, and have a high reuse value.

[0080] It can be seen from Example 1 and Comparative Example 1 that the combination of crushing and ball milling can effectively activate the waste three-way catalyst, which can significantly reduce the particle size of the waste three-way catalyst and improve the debromination rate of the waste three-way catalyst catalytic pyrolysis debromination. It can be seen from Example 1 and Comparative Example 2 that the pyrolysis temperature is too low to effectively debrominate by pyrolysis, and from the infrared spectrum, it can be seen that the structure of Comparative Example 2 before and after pyrolysis is almost the same. It can be seen that only when the pyrolysis temperature is greater than 260°C, the debromination rate of non-metallic components of waste circuit boards can be effectively improved.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for debrominating non-metallic components of waste circuit boards, characterized in that: The steps include: (1) crushing and ball-milling the waste three-way catalyst containing palladium to obtain waste three-way catalyst powder; (2) mixing the waste three-way catalyst powder with non-metallic components of waste circuit boards containing bromine, and pyrolyzing them under vacuum to obtain pyrolysis residue, pyrolysis oil phase components and pyrolysis gas phase components; the pyrolysis temperature is ≥260° C.; (3) Screening the pyrolysis residue to obtain debrominated non-metallic components and recovered waste three-way catalyst.

2. The method for debrominating non-metallic components of waste circuit boards according to claim 1, characterized in that: In step (1), the waste three-way catalyst containing palladium element comprises a carrier and palladium element loaded on the carrier; based on the mass of the waste three-way catalyst containing palladium element, the palladium element content is 100-150 mg / kg, and the average particle size of the waste three-way catalyst powder is ≤700 nm.

3. The method for debrominating non-metallic components of waste circuit boards according to claim 1, characterized in that: In step (1), the ball milling time is 2-8 hours, and the rotation speed of the ball mill is 300-500 rpm.

4. The method for debrominating non-metallic components of waste circuit boards according to claim 1, characterized in that: In step (1), in the ball milling, the ball to material ratio is (25-40):

1.

5. The method for debrominating non-metallic components of waste circuit boards according to claim 1, characterized in that: In step (1), the crushing method includes shear crushing, and the crushing time is 5-30s.

6. The method for debrominating non-metallic components of waste circuit boards according to claim 1, characterized in that: In step (2), the mass ratio of the waste three-way catalyst powder to the non-metallic components of the waste circuit board containing bromine is 1:(1-3).

7. The method for debrominating non-metallic components of waste circuit boards according to claim 1, characterized in that: In step (2), the average particle size of the non-metallic components of the waste circuit boards containing bromine is 0.1-2 mm.

8. The method for debrominating non-metallic components of waste circuit boards according to claim 1, characterized in that: In step (2), the pyrolysis temperature is 260-300°C, the heating rate to the pyrolysis temperature is 8-12°C / min, and the pyrolysis time is 15-45min.

9. The method for debrominating non-metallic components of waste circuit boards according to claim 1, characterized in that: In step (3), the screening method includes vibration screening, and the mesh size of the screening is 160-200 mesh.

10. The method for debrominating non-metallic components of waste circuit boards according to claim 1, characterized in that: Include at least one of the following: In step (2), the vacuum degree of the vacuum is less than 120 Pa; In step (2), the pyrolysis oil phase component further comprises washing it with water; In step (2), the pyrolysis of the gas phase component also includes cooling it; In step (3), the debrominated non-metallic components also include purification treatment, and the purification treatment method includes at least one of wind sorting and water washing.

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