Recovery process of bromine in circuit board waste based on multi-stage dissociation

Abstract

The invention discloses a technology for recycling bromine in circuit board waste based on multistage dissociation, which comprises the following steps: 1) after mechanically crushing the circuit board waste, separating to obtain metal crushed aggregates and non-metal crushed aggregates containing bromine; 2) carrying out gradient heating treatment including a first stage and a second stage on the bromine-containing nonmetal crushed material, wherein the heating temperature of the first stage is lower than that of the second stage; after heating treatment is completed, bromine-containing pyrolysis gas is obtained; 3) introducing the bromine-containing pyrolysis gas into the catalytic bed for reaction, introducing an oxidizing agent in the reaction process, and further treating the reacted gas in an adsorption column; after adsorption saturation, the adsorption column is subjected to desorption treatment, and high-concentration bromine steam is obtained; and 4) condensing and refining the high-concentration bromine steam, and drying to obtain a high-purity bromine product. According to the method, chlorine pollution can be avoided, the release efficiency of bromine in the circuit board waste in the processing process is high, no waste gas is generated, the recovery rate of prepared Br2 is high, and the purity reaches up to 99.5%.

Description

Technical Field

[0001] The present invention relates to the technical field of bromine recovery, and particularly to a bromine recovery process from printed circuit board waste based on multi-stage dissociation. Background Art

[0002] In printed circuit board waste, bromine mainly exists in the form of brominated flame retardants, including brominated epoxy resins, tetrabromobisphenol A, etc. These flame retardants can endow the printed circuit board with better fire resistance. In case of high-temperature situations such as fires, these flame retardants can prevent the spread of flames through the action of the gas phase and the condensed phase. However, these brominated flame retardants are dispersed in the plastics and resins of the circuit board waste. If not recovered, bromine elements may gradually be released under natural conditions. Bromine is an element that poses potential hazards to the environment and biological health. It may enter the soil, water bodies, and air, causing environmental pollution. For example, bromides can form bromates under certain conditions, and human intake of bromates may affect thyroid function. Therefore, recovering bromine can effectively reduce the risk of such environmental pollution. In addition, bromine is an important chemical raw material and is widely used in multiple fields such as flame retardants, pharmaceuticals, and pesticides. The social demand for bromine resources is increasing continuously, while the reserves of bromine resources are limited. Recovering bromine from waste printed circuit boards can effectively supplement bromine resources and alleviate the shortage of resources.

[0003] In the prior art, the bromine recovery process from printed circuit board waste mostly adopts pyrolysis combined with wet absorption. In the recovery process, chlorine gas is mostly used for oxidation, resulting in problems such as low bromine release efficiency, low bromine recovery rate, low purity of bromine products, high cost of chlorine gas oxidation, and complex tail gas treatment. Therefore, the present invention aims to develop a bromine recovery process from printed circuit board waste based on multi-stage dissociation to better meet the actual needs. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a bromine recovery process from printed circuit board waste based on multi-stage dissociation to solve the problems of low bromine release efficiency, poor bromine recovery rate and product quality, high cost of chlorine gas oxidation, and complex tail gas treatment existing in the existing bromine recovery technology.

[0005] The technical problem to be solved by the present invention is achieved by the following technical solutions:

[0006] A bromine recovery process from printed circuit board waste based on multi-stage dissociation includes the following steps:

[0007] 1) After mechanically crushing the printed circuit board waste, metal scraps and bromine-containing non-metal scraps are separated;

[0008] 2) Carry out gradient heating treatment on the bromine-containing non-metallic scraps, which includes a first stage and a second stage. The heating temperature in the first stage is lower than that in the second stage. The first-stage heating treatment is used to decompose bromides with low thermal stability; the second-stage heating treatment is used to decompose bromides with high thermal stability; after the heating treatment is completed, bromine-containing pyrolysis gas is obtained; through the gradient heating treatment, brominated flame retardants with different thermal stabilities can be decomposed step by step.

[0009] 3) Pass the bromine-containing pyrolysis gas into the catalytic bed for reaction, and an oxidant is introduced during the reaction. The oxidant is preferably one or more of oxygen, ozone, and nitrogen dioxide. The gas after the reaction enters the adsorption column for further treatment; after the adsorption column is saturated, it is desorbed to obtain high-concentration bromine vapor;

[0010] 4) Condense, refine, and dry the high-concentration bromine vapor to obtain high-purity bromine products.

[0011] Further, in step 3), the residual gas after the adsorption treatment of the adsorption column is passed into the absorption liquid. The absorption liquid is preferably one or more of the mixed liquids of NaOH~H2O2, Na2CO3~H2O2, and NaHCO3~H2O2; a solution with bromide ions is generated by the reaction, and the solution with bromide ions is subjected to electrolysis treatment. The gas generated after the electrolysis treatment enters step 4) for condensation and refinement, and the liquid generated after the electrolysis treatment is used as the absorption liquid for recycling.

[0012] Further, in step 1), the particle size of the circuit board after crushing is <5 mm; the crushed circuit board waste is separated by a high-precision separator with a metal recovery rate >98%. The high-precision separator is a magnetic separator or an eddy current separator or an electrostatic separator.

[0013] Further, in step 2), the heating temperature in the first stage is 300~400 °C, and the time is 20~50 min; the heating temperature in the second stage is 400~600 °C, and the time is 20~50 min.

[0014] Further, in step 2), during the gradient heating treatment, an inert gas with a flow rate of 10~20 L / min is introduced to maintain an anaerobic environment. Maintaining the anaerobic environment can inhibit the formation of dioxins, and the inert gas can be one or more of nitrogen and argon.

[0015] Further, in step 2), during the gradient heating treatment, microwave assistance is used for strengthening. The microwave frequency is 1.45~2.45 GHz, and the power is 5~20 kW. Microwave strengthening can assist in targeted heating of polar molecules, promote the breaking of C~Br bonds, release HBr gas, and ensure that the bromine release rate >95%.

[0016] Further, in step 2), the bromine-containing pyrolysis gas is treated by a condensation system at -20°C to 0°C to separate tar and then enters step 3).

[0017] Further, in step 3), the loading of the catalyst in the catalytic bed is 5-10 wt%, and the catalyst is a transition metal supported catalyst or a composite metal oxide catalyst; the transition metal supported catalyst includes Cu / γ-Al2O3 or Fe / SiO2; the composite metal oxide catalyst includes CuO-CeO2 or MnO2-CeO2.

[0018] During the reaction process, the temperature is 150-300°C; the gas flow rate of the bromine-containing pyrolysis gas introduced into the catalytic bed is controlled at 0.4-1.0 m 3 / h, and the flow rate of the oxidant is controlled at 0.1-0.25 m 3 / h.

[0019] The main reactions in the catalytic bed are as follows:[[]]END]]

[0020]

[0021] Further, the adsorption column is a bromide ion imprinted polymer adsorption column, the adsorption temperature is controlled at 30-45°C, the pore diameter of the adsorption column is 2-5 nm, and the adsorption capacity is 150-220 mg / g.

[0022] Further, in step 4), the condensation and purification include the first-stage condensation and purification and the second-stage condensation and purification. The temperature of the first-stage condensation and purification is 0-4°C, and the temperature of the second-stage condensation and purification is -15 to -25°C; drying is carried out using microporous molecular sieve drying.

[0023] Further, the residual gas after the reaction in step 5) is introduced into the absorption liquid. The absorption liquid is preferably one or more of the mixed liquids of NaOH-H2O2, Na2CO3-H2O2, and NaHCO3-H2O2; a bromide ion-containing solution is generated by the reaction, and the bromide ion-containing solution is subjected to electrolysis treatment. The gas generated after the electrolysis treatment enters step 4) for condensation and purification, and the liquid generated after the electrolysis treatment is used as the absorption liquid for recycling.

[0024] If the absorption liquid is Na2CO3-H2O2, the following reaction occurs:

[0025] Br2 + Na2CO3 + H2O2 → 2NaBr + CO2↑ + H2O + O2↑

[0026] The generated bromide ion-containing solution is a NaBr solution, and the NaBr solution is electrolytically regenerated into Br2 and NaOH to realize the recycling of the absorption liquid, as follows:

[0027]

[0028] Beneficial effects: The bromine recovery process from printed circuit board waste based on multi-stage dissociation according to the present invention decomposes brominated flame retardants with different thermal stabilities step by step during the pyrolysis process. During the catalytic process, the pyrolysis gas passes through a fixed-bed reactor filled with a catalyst to generate bromine vapor, and Br2 in the gas phase is selectively captured by a unique adsorption column. This process can replace the traditional Cl2 oxidation method, avoid chlorine pollution, generate no waste gas during the process, the absorption liquid can be recycled, the bromine recovery rate from printed circuit board waste is as high as 94%, and the purity of the prepared Br2 product is as high as 99.5%.

[0029] In addition, during the pyrolysis process of the present invention, through microwave assistance, selective heating of polar molecules can accelerate the cracking of organic substances, efficiently release bromine elements in the form of HBr, and at the same time reduce the generation of dioxins. During the catalytic reaction process, by regulating the flow rate of the oxidant, HBr is converted into Br2, avoiding the problem of salt pollution in subsequent alkali liquid absorption. Specific embodiments

[0030] In order to make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments.

[0031] Example 1

[0032] The bromine recovery process from printed circuit board waste based on multi-stage dissociation described in this example includes the following steps:

[0033] 1) Mechanically crush the printed circuit board waste to a particle size of <5 mm. The crushed printed circuit board waste is sorted by a high-precision separator with a metal recovery rate >98%. The high-precision separator is a magnetic separator or an eddy current separator or an electrostatic separator. After sorting, ferromagnetic metals such as iron and nickel can be separated from non-metals such as bromine-containing plastics. The sorted crushed materials are further separated by electrostatic separation to separate residual metals such as copper and lead from non-metals with high precision, obtaining metal crushed materials and bromine-containing non-metal crushed materials; the metal crushed materials can be further recycled.

[0034] 2) Perform gradient heating treatment on the bromine-containing non-metal crushed materials, including a first stage and a second stage. The heating temperature in the first stage is 350 °C and the time is 30 min. In this stage, low-thermal-stability bromides such as HBCD are decomposed; the heating temperature in the second stage of the heating treatment is 500 °C and the time is 30 min. In this stage, high-thermal-stability bromides such as TBBPA are mainly further cracked; after the heating treatment, bromine-containing pyrolysis gas is obtained; through gradient heating treatment, brominated flame retardants with different thermal stabilities can be decomposed step by step, reducing tar generation.

[0035] During the heating processes in the first and second stages, nitrogen gas is introduced and enhanced by microwave assistance. The nitrogen gas flow rate is 10 L / min, the microwave frequency is 2.45 GHz, and the power is 10 kW.

[0036] The bromine-containing pyrolysis gas is treated by a condensation system at about 10 °C to separate tar and then enters step 3) for further treatment.

[0037] 3) The bromine-containing pyrolysis gas treated by the condensation system is introduced into a catalytic bed containing MnO2 - CeO2 for reaction. The loading of the catalyst in the catalytic bed is 8 wt%. During the reaction process, the temperature is 200 °C; the gas flow rate of the bromine-containing pyrolysis gas introduced into the catalytic bed is controlled at 0.6 m 3 / h. Oxygen is introduced during the catalytic reaction process, and the oxygen flow rate is 0.15 m 3 / h to oxidize HBr to Br2. The reacted gas enters an adsorption column for further treatment; the adsorption column is a bromide ion-imprinted polymer adsorption column, the adsorption temperature is controlled at 40 °C, the pore diameter of the adsorption column is 5 nm, and the adsorption capacity is 200 mg / g. After the bromide ion-imprinted polymer adsorption column (Br-IIP) is saturated with adsorption, the adsorption column is desorbed, and high-concentration bromine vapor is obtained by heating to 100 °C;

[0038] 4) The high-concentration bromine vapor is subjected to secondary condensation refining and then drying to obtain high-purity bromine products. The temperature of the first-stage condensation refining is 0 °C to remove moisture and high-boiling impurities, and the temperature of the second-stage condensation refining is -20 °C for deep condensation of Br2; drying is carried out using microporous molecular sieve drying, and 3A microporous molecular sieve is used to adsorb trace amounts of H2O.

[0039] The residual gas after the adsorption treatment by the adsorption column in step 3), and the residual gas after the reaction in step 5) contain trace amounts of Br2 and are subjected to regeneration treatment: the residual gas is introduced into a Na2CO3 - H2O2 absorption solution, and a NaBr solution is generated by reaction; the NaBr solution is electrolyzed to be regenerated into Br2 and NaOH; Br2 enters step 4) for recycling, and NaOH enters the absorption solution for recycling; the unreacted gas is discharged up to standard after being adsorbed by activated carbon and washed with alkali solution.

[0040] In the traditional process, the bromine recovery rate is about 80%. Using the process described in this example, the bromine recovery rate is 94%, and the purity of the bromine gas product is 99.5%, meeting the industrial-grade standard for the use of bromine gas.

[0041] Example 2

[0042] The bromine recovery process from printed circuit board waste based on multi-stage dissociation described in this example includes the following steps:

[0043] 1) Mechanically crush the waste circuit boards to a particle size of <5 mm. The crushed waste circuit boards are sorted using a high-precision separator with a metal recovery rate > 98%. The high-precision separator is a magnetic separator, an eddy current separator, or an electrostatic separator. After sorting, ferromagnetic metals such as iron and nickel can be separated from non-metals such as bromine-containing plastics. The sorted shredded materials are further separated by electrostatic separation to obtain high-precision separation of residual metals such as copper and lead from non-metals, resulting in metal shredded materials and bromine-containing non-metal shredded materials; the metal shredded materials can be further recycled.

[0044] 2) Gradient heating treatment of the bromine-containing non-metal shredded materials is carried out, including a first stage and a second stage. The heating temperature in the first stage is 400 °C and the time is 25 min. In this stage, low thermal stability bromides such as HBCD are decomposed. The heating temperature in the second stage of the heating treatment is 600 °C and the time is 20 min. In this stage, high thermal stability bromides such as TBBPA are mainly further cracked. After the heating treatment, bromine-containing pyrolysis gas is obtained. Through gradient heating treatment, brominated flame retardants with different thermal stabilities can be decomposed step by step, reducing tar formation.

[0045] During the heating treatment in the first stage and the second stage, nitrogen is introduced and microwave assistance is used for strengthening. The nitrogen flow rate is 18 L / min, the microwave frequency is 1.85 GHz, and the power is 15 kW.

[0046] The bromine-containing pyrolysis gas is treated by a condensation system at ~20 °C to separate tar and then enters step 3) for further treatment.

[0047] 3) The bromine-containing pyrolysis gas treated by the condensation system is introduced into a catalytic bed containing Fe / SiO2 for reaction. The loading of the catalyst in the catalytic bed is 10 wt%. During the reaction process, the temperature is 250 °C. The gas flow rate of the bromine-containing pyrolysis gas introduced into the catalytic bed is controlled at 0.8 m 3 / h. Oxygen is introduced during the catalytic reaction process, and the flow rate is 0.15 m 3 / h to oxidize HBr to Br2. The reacted gas enters an adsorption column for further treatment; the adsorption column is a bromide ion-imprinted polymer adsorption column. The adsorption temperature is controlled at 35 °C, the pore diameter of the adsorption column is 3 nm, and the adsorption capacity is 180 mg / g. After the bromide ion-imprinted polymer adsorption column (Br-IIP) is saturated with adsorption, the adsorption column is desorbed, and high-concentration bromine vapor is obtained by heating to 100 °C;

[0048] 4) The high-concentration bromine vapor is subjected to secondary condensation refining and then drying to obtain a high-purity bromine product. The temperature of the first-stage condensation refining is 4 °C to remove moisture and high-boiling impurities. The temperature of the second-stage condensation refining is ~25 °C for deep condensation of Br2; drying is carried out using microporous molecular sieve drying, and 3A microporous molecular sieve is used to adsorb trace amounts of H2O.

[0049] The residual gas after the adsorption column treatment in step 3) and the residual gas after the reaction in step 5) contain trace amounts of Br2 and are subjected to regeneration treatment: The residual gas is passed into a Na2CO3-H2O2 absorption solution to react and form a NaBr solution; the NaBr solution is electrolyzed to regenerate Br2 and NaOH; the Br2 enters step 4) for recycling, and the NaOH enters the absorption solution for recycling; the unreacted gas is discharged up to standard after being adsorbed by activated carbon and washed with an alkaline solution.

[0050] Using the process described in this example, the bromine recovery rate is 94%, and the purity of the bromine gas product is 99.5%, meeting the industrial-grade standard for the use of bromine gas.

[0051] Control Example 1

[0052] The bromine recovery process from printed circuit board waste based on multi-stage dissociation described in this control example includes the following steps:

[0053] 1) Mechanically crush the printed circuit board waste to a particle size <5 mm. The crushed printed circuit board waste is sorted using a high-precision separator with a metal recovery rate >98%. The high-precision separator is a magnetic separator, an eddy current separator, or an electrostatic separator. After sorting, ferromagnetic metals such as iron and nickel can be separated from non-metals such as bromine-containing plastics. The sorted shredded materials are further separated by electrostatic separation to separate residual metals such as copper and lead from non-metals to obtain metal shredded materials and bromine-containing non-metal shredded materials; the metal shredded materials can be further recycled.

[0054] 2) Heat-treat the bromine-containing non-metal shredded materials at a constant temperature of 500 °C for 30 min; after the heat-treatment is completed, bromine-containing pyrolysis gas is obtained.

[0055] During the heat-treatment process, nitrogen is introduced throughout, and the nitrogen flow rate is 10 L / min.

[0056] The bromine-containing pyrolysis gas is treated by a condensation system at ~10 °C to separate tar and then enters step 3) for further treatment.

[0057] 3) Pass the bromine-containing pyrolysis gas treated by the condensation system into a catalytic bed containing MnO2-CeO2. The loading of the catalyst in the catalytic bed is 8 wt%. During the reaction process, the temperature is 200 °C; the gas flow rate of the bromine-containing pyrolysis gas passing into the catalytic bed is controlled at 0.6 m 3 / h. Oxygen is introduced during the catalytic reaction process, and the flow rate is 0.15 m 3 / h. The gas after the reaction enters an adsorption column for further treatment; the adsorption column is a bromide ion-imprinted polymer adsorption column, the adsorption temperature is controlled at 40 °C, the pore size of the adsorption column is 5 nm, and the adsorption capacity is 200 mg / g. After the bromide ion-imprinted polymer adsorption column (Br-IIP) is saturated with adsorption, the adsorption column is desorbed, and high-concentration bromine vapor is obtained by heating to 100 °C;

[0058] 4) After condensing, refining, and drying the high-concentration bromine vapor, high-purity bromine products are obtained. The temperature for the first-stage condensation and refining is 0 °C to remove moisture and high-boiling-point impurities. The temperature for the second-stage condensation and refining is -20 °C for deep condensation of Br2. Drying is carried out using microporous molecular sieves, and 3A microporous molecular sieves are used to adsorb trace amounts of H2O.

[0059] The residual gas after adsorption column treatment in step 3) and the residual gas after the reaction in step 5) contain trace amounts of Br2 and are subjected to regeneration treatment: The residual gas is passed into a Na2CO3-H2O2 absorption solution to react and form a NaBr solution; the NaBr solution is electrolyzed to be regenerated into Br2 and NaOH; Br2 enters step 4) for recycling, and NaOH enters the absorption solution for recycling; the unreacted gas is discharged up to standard after activated carbon adsorption + alkali solution washing.

[0060] The process described in this comparative example has no gradient pyrolysis scheme and no microwave enhancement assistance during the pyrolysis process. The bromine recovery rate is 82%, and the purity of the bromine gas product is 92%, which is lower than the industrial-grade standard for bromine gas use. In this process, due to uneven pyrolysis, the release of bromine elements in the raw materials is insufficient, and continuous high temperature results in a dioxin emission concentration of 0.5 ng TEQ / Nm 3 (exceeding the standard. The environmental protection emission requirement for dioxin is <0.1 ng TEQ / Nm 3 )

[0061] Comparative Example 2

[0062] The bromine recovery process from printed circuit board waste based on multi-stage dissociation described in this example includes the following steps:

[0063] 1) Mechanically crush the printed circuit board waste to a particle size <5 mm. The crushed printed circuit board waste is sorted using a high-precision separator with a metal recovery rate >98%. The high-precision separator is a magnetic separator, an eddy current separator, or an electrostatic separator. After sorting, ferromagnetic metals such as iron and nickel can be separated from non-metals such as bromine-containing plastics. The sorted crushed materials are further separated by electrostatic separation to separate residual metals such as copper and lead from non-metals with high precision, obtaining metal crushed materials and bromine-containing non-metal crushed materials; the metal crushed materials can be further recycled.

[0064] 2) Carry out gradient heating treatment on the bromine-containing non-metal crushed materials, including a first stage and a second stage. The heating temperature in the first stage is 350 °C for 30 min; the heating temperature in the second stage of the heating treatment is 500 °C for 30 min; after the heating treatment, bromine-containing pyrolysis gas is obtained.

[0065] During the heating processes of the first and second stages, nitrogen gas is introduced and enhanced by microwave assistance. The nitrogen gas flow rate is 10 L / min, the microwave frequency is 2.45 GHz, and the power is 10 kW.

[0066] The bromine-containing pyrolysis gas is treated by a condensation system at about 10 °C to separate tar and then enters step 3) for further treatment.

[0067] 3) The bromine-containing pyrolysis gas treated by the condensation system is introduced into a catalytic bed containing MnO2 - CeO2 for reaction. The catalyst loading in the catalytic bed is 8 wt%. During the reaction process, the temperature is 200 °C; the gas flow rate of the bromine-containing pyrolysis gas introduced into the catalytic bed is controlled at 0.6 m 3 / h. Chlorine gas is introduced during the catalytic reaction process, and the oxygen gas flow rate is 0.15 m 3 / h to oxidize HBr to Br2. The reacted gas enters an adsorption column for further treatment; the adsorption column is a bromide ion-imprinted polymer adsorption column, the adsorption temperature is controlled at 40 °C, the pore diameter of the adsorption column is 5 nm, and the adsorption capacity is 200 mg / g. After the bromide ion-imprinted polymer adsorption column (Br-IIP) is saturated with adsorption, the adsorption column is desorbed by heating to 100 °C to obtain high-concentration bromine vapor;

[0068] 4) The high-concentration bromine vapor is subjected to condensation refining and then drying to obtain a high-purity bromine product. The temperature of the first-stage condensation refining is 0 °C to remove moisture and high-boiling impurities, and the temperature of the second-stage condensation refining is about -20 °C for deep condensation of Br2; drying is carried out using microporous molecular sieve drying, and 3A microporous molecular sieve is used to adsorb trace amounts of H2O.

[0069] The residual gas after the adsorption treatment of the adsorption column in step 3), and the residual gas after the reaction in step 5) contain trace amounts of Br2 and are subjected to regeneration treatment: the residual gas is introduced into a Na2CO3 - H2O2 absorption solution, and a NaBr solution is generated by reaction; the NaBr solution is electrolyzed to be regenerated into Br2 and NaOH; Br2 enters step 4) for recycling, and NaOH enters the absorption solution for recycling; the unreacted gas is discharged up to standard after being adsorbed by activated carbon and washed with alkali solution.

[0070] Using the process described in this example, the bromine recovery rate is 94.7%, and the purity of the bromine gas product is 93.6%, which is lower than the industrial-grade standard for bromine gas use. In this process, due to the excessive use of Cl2 to ensure complete bromine oxidation, not only is the cost high, but it also causes chlorine gas to be contained in the bromine vapor, resulting in a decrease in the purity of the bromine vapor.

[0071] Comparative Example 3

[0072] In this comparative example, compared with the example, the difference lies in that in step 2), the heating temperature in the first stage of the first stage is 500 °C and the time is 30 min; the heating temperature in the second stage of the heat treatment is 300 °C and the time is 30 min, and the rest is the same as in Example 1. Using the process described in this comparative example, the bromine recovery rate is 89.3%, and the purity of the bromine gas product is 95.6%, which is lower than the industrial standard for the use of bromine gas.

[0073] Comparative Example 4

[0074] In this comparative example, compared with Example 1, the difference lies in that in step 3), the bromine-containing pyrolysis gas treated by the condensation system is directly reacted with oxygen, and the gas after the reaction enters the adsorption column for further treatment, and the rest is the same as in Example 1. Using the process described in this comparative example, the bromine recovery rate is 85.1%, and the purity of the bromine gas product is 83.5%, which is lower than the industrial standard for the use of bromine gas.

[0075] Comparative Example 5

[0076] In this comparative example, compared with Example 1, the difference lies in that in step 3), oxygen is introduced during the catalytic reaction, and the flow rate is 0.10 m 3 / h, and the rest is the same as in Example 1. Using the process described in this comparative example, the bromine recovery rate is 90.7%, and the purity of the bromine gas product is 86.6%. The oxidation efficiency is low and lower than the industrial standard for the use of bromine gas.

[0077] Comparative Example 6

[0078] In this comparative example, compared with Example 1, the difference lies in that in step 4), the high-concentration bromine vapor is subjected to primary condensation and refining, and the temperature of the condensation and refining is ~20 °C, and the rest is the same as in Example 1. Using the process described in this comparative example, the bromine recovery rate is 96.7%, and the purity of the bromine gas product is 89.5%, which is lower than the industrial standard for the use of bromine gas.

[0079] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art of this industry should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A bromine recovery process from printed circuit board waste based on multi-stage dissociation, characterized in that, It includes the following steps: 1) After mechanically crushing the waste circuit boards, metal fragments and bromine-containing non-metal fragments are separated; 2) The bromine-containing non-metal fragments are subjected to gradient heating treatment including a first stage and a second stage, where the heating temperature in the first stage is lower than that in the second stage. The first-stage heating treatment is used to decompose bromides with low thermal stability; the second-stage heating treatment is used to decompose bromides with high thermal stability; after the heating treatment, bromine-containing pyrolysis gas is obtained; 3) The bromine-containing pyrolysis gas is introduced into a catalytic bed for reaction, an oxidant is introduced during the reaction process, and the reacted gas enters an adsorption column for further treatment; after adsorption saturation, the adsorption column is desorbed to obtain high-concentration bromine vapor; 4) The high-concentration bromine vapor is subjected to condensation refining and then drying to obtain a high-purity bromine product.

2. The bromine recovery process from circuit board waste based on multi-stage dissociation according to claim 1, wherein, In step 3), the residual gas after adsorption treatment by the adsorption column is introduced into an absorption liquid, and a solution containing bromide ions is generated by reaction. The solution containing bromide ions is subjected to electrolysis treatment, and the gas generated after electrolysis treatment enters step 4) for condensation refining, and the liquid generated after electrolysis treatment is used as the absorption liquid for recycling.

3. The bromine recovery process from printed circuit board waste based on multi-stage dissociation according to claim 1, wherein, In step 1), the particle size of the circuit boards after crushing is <5 mm; the crushed waste circuit boards are separated by a high-precision separator with a metal recovery rate >98%, and the high-precision separator is a magnetic separator or an eddy current separator or an electrostatic separator.

4. The bromine recovery process from circuit board waste based on multi-stage dissociation according to claim 1, wherein, In step 2), the heating temperature in the first stage is 300 - 400 °C, and the time is 20 - 50 min; the heating temperature in the second stage is 400 - 600 °C, and the time is 20 - 50 min.

5. The bromine recovery process from printed circuit board waste based on multi-stage dissociation according to claim 4, wherein, In step 2), during the gradient heating treatment, an inert gas with a flow rate of 10 - 20 L / min is introduced to maintain an oxygen-free environment.

6. The bromine recovery process from printed circuit board waste based on multi-stage dissociation according to claim 5, wherein, In step 2), during the gradient heating treatment, microwave assistance is used for strengthening, the microwave frequency is 1.45 - 2.45 GHz, and the power is 5 - 20 kW.

7. The bromine recovery process from circuit board waste based on multi-stage dissociation according to claim 1, characterized in that, In step 2), the bromine-containing pyrolysis gas is treated by a condensation system at -20 °C to 0 °C to separate tar and then enters step 3).

8. The bromine recovery process from printed circuit board waste based on multi-stage dissociation according to claim 1, wherein In step 3), the loading amount of the catalyst in the catalytic bed is 5-10 wt%, and the catalyst is a transition metal supported catalyst or a composite metal oxide catalyst; during the reaction process, the temperature is 150-300 °C; the gas flow rate of the bromine-containing pyrolysis gas introduced into the catalytic bed is controlled at 0.4-1.0 m 3 / h, and the flow rate of the oxidant is controlled at 0.1-0.25 m 3 / h.

9. The bromine recovery process from printed circuit board waste based on multi-stage dissociation according to claim 1, characterized in that, The adsorption column is a bromide ion-imprinted polymer adsorption column, the adsorption temperature is controlled at 30 - 45 °C, the pore diameter of the adsorption column is 2 - 5 nm, and the adsorption capacity is 150 - 220 mg / g.

10. The bromine recovery process from printed circuit board waste based on multi-stage dissociation according to claim 1, characterized in that, In step 4), the condensation refining includes a first-stage condensation refining and a second-stage condensation refining. The temperature of the first-stage condensation refining is 0 - 4 °C, and the temperature of the second-stage condensation refining is -15 - -25 °C; drying is carried out using a microporous molecular sieve.

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