Method for producing hydrogen through pyrolysis and gasification of nonmetal part of waste circuit board

Abstract

The invention discloses a method for producing hydrogen through pyrolysis and gasification of a nonmetal part of a waste circuit board, and belongs to the technical field of solid waste resource recycling and solid waste gasification and pyrolysis. The method comprises the following steps: mixing a non-metal part of the waste circuit board with a catalyst, introducing nitrogen to remove air in a reaction cavity, carrying out gasification and pyrolysis, introducing water vapor, keeping the temperature, and collecting to prepare hydrogen-rich gas. The hydrogen content in the prepared hydrogen-rich gas is high, solid-gas phase reaction and gas-gas phase reaction are promoted through introduction of the alkaline metal oxide catalyst and the water vapor atmosphere, more fuel gas is generated, the form and components of a solid product are improved, and the recovery difficulty of subsequent treatment is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of solid waste resource recycling and solid waste gasification and pyrolysis, and in particular relates to a method for producing hydrogen by pyrolysis and gasification of non-metallic parts of waste circuit boards. Background Art

[0002] Waste printed circuit boards (WPCB) are the main component of waste electronic appliances, accounting for about 10-30% (by weight) of waste electronic appliances, of which valuable metals such as copper and gold account for 30-40%, and 60-70% of non-metallic materials are composed of glass fiber, epoxy resin and brominated flame retardants. The current treatment process of waste printed circuit boards often focuses on the metal part with higher recycling value, and there are furans, bromides and other potential health and environmental risk pollutants, while the non-metallic resources are ignored.

[0003] At present, the recycling technologies of waste circuit boards mainly include incineration, landfill, pyrometallurgy, mechanical separation, wet acid-base leaching, pyrolysis, biological metabolism leaching and supercritical fluid method. However, these methods can only recycle the metal resources therein, and there are some threats. Studies have shown that incineration will produce toxic emissions, such as heavy metals Cd, Cu, Pd, etc. evaporated at high temperature and released into the atmosphere. The presence of halogen flame retardants will also cause dioxins and furans to be released into the atmosphere. The landfill treatment method will cause the land and water resources in the landfill area to be polluted by the leachate of heavy metals and brominated flame retardants, and will also form multi-directional diffusion pollution through the earth's water cycle system. The landfill and incineration treatment methods only play a role in elimination, and do not play a role in recycling the valuable resources therein, and have caused serious resource pollution. Although other recycling methods have been explored by researchers at home and abroad, and have achieved relatively significant breakthroughs in different methods. However, in the face of expanded industrial production and environmental health, it still faces severe challenges. The working conditions of smelting waste circuit boards are complicated, and toxic and harmful substances (such as dioxins and HBr) will be produced during the recycling process. Mechanical separation treatment performs well in the separation and recovery of metals and non-metals, but the purity of the separated metal concentrate is unstable. The wet acid-base leaching method is difficult to effectively extract the encapsulated metals, and involves a variety of chemical reagents, which produces a lot of wastewater. Problems such as the long test cycle of the biological metabolic leaching method and the need for specific bacterial colonies cannot be changed at present. Compared with the above methods, the pyrolysis method for treating waste circuit boards is carried out under anaerobic conditions to produce valuable liquid and gas products, effectively avoiding the problem of low resource recovery and utilization rate. However, the small molecular bromine-containing substances after the pyrolysis of bromine-containing flame retardants cannot be ignored, and pose a threat to the composition of liquid and gas products.

[0004] The existing recycling technologies for the non-metallic part of waste circuit boards are mainly physical, chemical and pyrolysis. Most of the non-metallic recycled products obtained by physical and chemical methods are then used in the building materials and plastics industries. The non-metallic part of waste circuit boards contains a large amount of organic polymers, such as tetrabromobisphenol A epoxy resin, polyacrylonitrile-butadiene styrene and high-impact polystyrene (HIPS). Pyrolysis not only realizes the resource utilization value of the non-metallic part of waste circuit boards (NMF-WPCB), but also obtains hydrogen-rich fuel gas. This will contribute to the energy reserve problem faced. Hydrogen production can be achieved through various primary energy sources and different methods. Most of the hydrogen produced now comes from the reforming of natural gas, oil and coal gasification. The strategy of converting solid waste resources into hydrogen has received attention in recent years. Waste circuit boards are an important part of urban solid waste. With the significant increase in urban solid waste production, resource shortages and the current situation of energy recycling, if waste circuit boards are not effectively utilized, it will not only cause resource waste, but also seriously pollute the environment. Summary of the invention

[0005] In order to realize the resource utilization value of the non-metallic parts of waste circuit boards and promote the development of non-fossil energy, the purpose of the present invention is to provide a method for producing hydrogen by pyrolysis and gasification of the non-metallic parts of waste circuit boards.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for producing hydrogen by pyrolysis and gasification of non-metallic parts of waste circuit boards comprises the following steps: mixing the non-metallic parts of waste circuit boards with a catalyst, heating them to a gasification and pyrolysis temperature in an oxygen-free environment, then introducing water vapor for gasification and pyrolysis, and collecting hydrogen-rich gas.

[0008] The present invention introduces water vapor as a gasifying agent to perform a gasification hydrogen production reaction while pyrolyzing the non-metallic part of the waste circuit board and the catalyst. The addition of the catalyst improves the yield and collection amount of the gas phase product and reduces the difficulty of recovering the solid phase product; on the other hand, it plays a role in the fixation of the brominated organic matter in the raw material and the conversion to inorganic bromine. The introduction of water vapor separates the inorganic bromide salt in the solid product and enters the liquid in the form of inorganic bromide, avoiding the influence on the subsequent hydrogen production reaction, thereby affecting the hydrogen yield and purity.

[0009] Furthermore, the molar ratio of bromine in the non-metallic part of the waste circuit board to the catalyst is 1:(0.5-3).

[0010] Furthermore, the particle size of the non-metallic part of the waste circuit board is 80 mesh.

[0011] Furthermore, the catalyst is an alkali metal oxide. The added alkali metal oxide catalyst not only plays a role in supporting the skeleton of the solid phase product, but also plays a catalytic role in the gasification process.

[0012] Furthermore, the alkali metal oxide is calcium oxide.

[0013] Calcium oxides have the effect of fixing bromine and converting organic bromine during the pyrolysis of WPCB, which will help obtain safe hydrogen-rich fuel gas. Water vapor passes through the porous structure formed by the pyrolysis of the catalyst calcium oxide and the raw material, and a variety of solid-gas phase reactions and gas-gas phase reactions occur in this process to complete the gas phase reforming reaction, thereby increasing the yield and collection amount of the collected gas phase products, and greatly increasing the volume fraction of hydrogen in the collected gas.

[0014] Furthermore, the gasification pyrolysis temperature is 750-950°C.

[0015] Furthermore, the water vapor has an inlet flow rate of 1-5 mL / min.

[0016] Furthermore, the gasification and pyrolysis time is 30-70 minutes.

[0017] Furthermore, further, the oxygen-free environment is an inert gas atmosphere environment.

[0018] Preferably, the inert gas is nitrogen.

[0019] Compared with the prior art, the present invention has the following advantages and technical effects:

[0020] The present invention provides a method for producing hydrogen by pyrolysis and gasification of the non-metallic part of waste circuit boards, which contributes a promising process direction for the recycling and reuse of the non-metallic part of waste circuit boards and has strong compatibility. The volume content of hydrogen can reach 85.92%, which is 34.9% and 34.43% higher than that of pyrolysis without water vapor and catalytic pyrolysis without water vapor, respectively.

[0021] The catalyst calcium oxide and water vapor atmosphere used in the present invention are low-priced, widely available, closer to the main elements in the waste circuit board raw materials, will not bring new impurities to the solid phase product after pyrolysis, and are conducive to the subsequent reuse of the solid phase product. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0023] Figure 1 It is a process flow chart of the present invention;

[0024] Figure 2 The figure is a comparison chart of the yield (a) and gas content (b) of the solid phase product, liquid phase product and gas phase product obtained after the reaction of Example 1, Comparative Example 1 and Comparative Example 2;

[0025] Figure 3 This is a comparison chart of XRD of the non-metallic part of the waste circuit board, the solid phase products of Example 1, Comparative Example 1 and Comparative Example 2. DETAILED DESCRIPTION

[0026] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0027] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0028] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0029] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to the skilled artisan. The present invention description and examples are exemplary only.

[0030] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0031] The embodiment of the present invention provides a method for producing hydrogen by pyrolysis and gasification of the non-metallic part of a waste circuit board, comprising the following steps: mixing the non-metallic part of the waste circuit board (80 mesh) after crushing and sorting with a catalyst calcium oxide (the molar ratio of calcium oxide to bromine is 0.5-3) to obtain a pyrolysis raw material. The quartz crucible containing the pyrolysis raw material is placed in the center of the reaction chamber, sealed and connected to a steam generating device, a condensing device and a gas collecting device, and an inert gas (nitrogen) is introduced for 8-10 minutes to create an oxygen-free environment required for pyrolysis. The pyrolysis temperature program is set (750-950°C). Stop the introduction of nitrogen and start pyrolysis. When the final pyrolysis temperature is reached, open the water vapor introduction valve (the water vapor flow rate is 1-5mL / min), start gasification pyrolysis, and maintain the temperature (30-70min). The volume of the obtained gas phase product is measured by the water drainage gas collection method, and the component content is analyzed by a gas chromatograph (GC).

[0032] In some embodiments of the present invention, the molar ratio of bromine in the non-metallic part of the waste circuit board to the catalyst can be selected as 1:0.5, 1:1, 1:1.5, 1:2 or 1:3, preferably 1:1.5.

[0033] In some embodiments of the present invention, the temperature of the gasification pyrolysis may be 750°C, 800°C, 850°C, 900°C or 950°C, preferably 900°C.

[0034] In some embodiments of the present invention, the water vapor introduction flow rate can be selected from 1 mL / min, 2 mL / min, 3 mL / min, 4 mL / min or 5 mL / min, preferably 3 mL / min.

[0035] In some embodiments of the present invention, the temperature maintaining time may be selected from 30 min, 40 min, 50 min, 60 min or 70 min, preferably 60 min.

[0036] After high-temperature pyrolysis, the long-chain macromolecular organic matter in the non-metallic part of the waste circuit board breaks the chain bonds, the types and quantities of small molecular substances are increased, and the amorphous carbon produced by pyrolysis reacts with water vapor as a gasifier to form carbon vapor. In addition, the Boudouard reaction, water gas shift reaction (WGS), methane dry reforming reaction (DR), methane steam reforming reaction (SMR) and hydrocarbon reforming reactions occur simultaneously. Under the joint action of these reactions, hydrogen-rich gas is obtained.

[0037] The specific reactions are as follows:

[0038] C+H2O( g )=CO+H2 (1)

[0039] CH4+H2O(g )=CO+3H2 (2)

[0040] CO+H2O( g )=CO2+H2 (3)

[0041] CH4+CO2=2CO+2H2 (4)

[0042] CO + 3H2 = CH4 + H2O ( g ) (5)

[0043] H2+CO2=CO+H2O( g ) (6)

[0044] C+CO2=2CO (7)

[0045] C n H m +nH2O (g) =nCO+(n+m / 2)H2 (8)

[0046] Formula (1) is the steam reaction of carbon, formula (2) is the methane steam reforming reaction, formula (3) is the water gas shift reaction, formula (4) is the methane dry reforming reaction, formula (5) is the methanation reaction, formula (6) is the reverse water gas shift reaction, formula (7) is the boudouard reaction, and formula (8) is the hydrocarbon steam reforming reaction.

[0047] The initial raw material of the non-metallic part of the waste circuit board used in the present invention is the waste circuit board, which is disassembled to obtain the waste circuit board substrate and the waste circuit board non-metallic device. The waste circuit board substrate is detinned and then crushed and sorted together with the waste circuit board non-metallic device to obtain metal particles and non-metal particles respectively. The non-metallic particles are the non-metallic part of the waste circuit board used in the present invention. The part is mixed with a catalyst and the like to react as above. For a specific flow chart, see Figure 1 The preliminary treatment process of the non-metallic part of the waste circuit board is a conventional operation and can be carried out by conventional methods in the art, so as to obtain the target raw materials.

[0048] The "room temperature" in the present invention refers to 20-30°C unless otherwise specified.

[0049] The raw materials used in the present invention are all purchased from the market.

[0050] The technical solution of the present invention is further illustrated by the following embodiments.

[0051] Example 1

[0052] A method for producing hydrogen by pyrolysis and gasification of non-metallic parts of waste circuit boards, comprising the following steps: weighing 10g of non-metallic parts of 80-mesh waste circuit boards, mixing them according to the molar ratio of bromine and calcium oxide in the non-metallic parts of the waste circuit boards of 1:1.5, introducing nitrogen for 8-10 minutes to create an oxygen-free environment required for pyrolysis, heating to 900°C, stopping the introduction of nitrogen and starting pyrolysis, introducing water vapor with a flow rate of 3mL / min and keeping the temperature for 60 minutes, and obtaining solid phase products, liquid phase products and gas phase products after the reaction is completed. The gas components in the mixed gas obtained by GC detection are: the volume content of hydrogen (excluding the influence of nitrogen) H2: 85.92%, CO: 4.9%, CH4: 1.35%, CO2: 7.03%.

[0053] Example 2

[0054] Same as Example 1, except that the gasification and pyrolysis temperatures were set to 750° C., 800° C., 850° C. and 950° C. respectively. The results are shown in Table 1.

[0055] Table 1 Effect of temperature on the mass percentage of pyrolysis products and the content of mixed gas components

[0056]

[0057] Note: The mass percentage of pyrolysis solid phase products is the mass percentage of pyrolysis solid phase products in the total amount of products, wt.%; the mass percentage of pyrolysis liquid phase products is the mass percentage of pyrolysis oil in the total amount of products, wt.%; the mass percentage of pyrolysis gas phase products is the mass percentage of pyrolysis gas phase products in the total amount of products, wt.%. The content of mixed gas components is the content of other components in the pyrolysis gas phase products excluding nitrogen components, vol%. The same below.

[0058] As can be seen from Table 1, with the continuous increase of temperature, the solid phase yield and liquid phase yield gradually decrease, while the gas phase yield gradually increases and the three product yields reach stability after 900°C, which indicates that the pyrolysis reaction of NMF-WPCB has been completed. Since most of the hydrogen remains in the tar composed of hydrocarbons and heteroatom compounds, higher temperatures effectively promote the dehydrogenation of heavy hydrocarbons, break CH bonds, and generate hydrogen and carbon.

[0059] As the temperature increases to 850°C, the light hydrocarbon content decreases significantly due to the enhanced generation of hydrogen by the breaking of the CH bond. At this time, the hydrogen content increases by 8.14% to 79.36% compared with 800°C. This is because the pyrolysis oil formed after the condensation of the volatile matter undergoes a large amount of secondary cracking reaction. The gradual decrease in CH4 content is mainly due to the occurrence of methane dry reforming reaction (Formula 4) and methane steam reforming reaction (Formula 2), which increases the H2 and CO content. WGS is affected by the presence of water vapor that is beneficial to the reaction, and generates more H2 and CO2 by consuming CO. The CO content decreases with increasing temperature.

[0060] Example 3

[0061] The same as Example 1, except that the molar ratios of bromine and calcium oxide in the non-metallic waste circuit boards were set to 1:0.5, 1:1, 1:2 and 1:3 respectively. The results are shown in Table 2.

[0062] Table 2 Effect of calcium oxide addition ratio on mass percentage of pyrolysis products and content of mixed gas components

[0063]

[0064] As can be seen from Table 2, NMF-WPCB is mainly composed of organic polymers and calcium aluminum silicate. With the continuous increase of the catalyst ratio, the solid yield gradually increases, showing a positive correlation with the addition ratio. This is because the added CaO is retained in the solid phase product and supports the morphology and structure of the material, and the total weight of the solid phase product increases. When less CaO is added, there is not enough effect of escaping the retained volatiles. At this time, the pyrolysis reaction is violent, and a large amount of volatiles are blown out of the test tube reaction zone by water vapor.

[0065] The continuous removal of CO2 by CaO continuously promotes the WGS reaction limited by the forward equilibrium, promotes the reaction of water vapor with carbon in the solid residue (Formula 1) and WGS (Formula 3), thereby ensuring the increase of H2 content. As the proportion of additives continues to increase, the H2 content gradually decreases, and the CO and CO2 contents slowly increase, which may be due to some CaO blocking the reaction channel, causing H2 and CO2 to undergo a reverse water-gas shift reaction (Formula 6).

[0066] Example 4

[0067] The same as Example 1, except that the flow rate of water vapor was set to 1 mL / min, 2 mL / min, 4 mL / min and 5 mL / min respectively. The results are shown in Table 3.

[0068] Table 3 Effect of water vapor flow rate on mass percentage of pyrolysis products and content of mixed gas components

[0069]

[0070] It can be seen from Table 3 that when the water vapor flow rate is 1 ml / min, the volatile matter stays in the high temperature reaction zone for the longest time, and the maximum gas product yield is 45.36%. When the water vapor flow rate is 3 ml / min, the gas product yield is 44.86%, which is 0.5% lower than that of 1 ml / min. However, the reason why the H2 content in the gas component is at a disadvantage may be due to the insufficient water vapor in formula (3) and the reduced reactant content in formula (1). The CO concentration decreases with the increase of the water vapor flow rate, which is the result of promoting formula (3).

[0071] Example 5

[0072] Same as Example 1, except that the holding time was set to 30 min, 40 min, 50 min and 70 min respectively. The results are shown in Table 4.

[0073] Table 4 Effect of holding time on mass percentage of pyrolysis products and content of mixed gas components

[0074]

[0075] As can be seen from Table 4, the increase in the holding time is conducive to heat transfer and makes the reaction of the raw materials more complete. The liquid product continues to break chemical bonds at high temperatures, and the number of monomer small molecules increases. Under the influence of the above two factors, the gas product gradually increases and the H2 content gradually increases. The extension of the holding time increases the reaction time between the particles, which affects the gas-solid phase reaction and the gas phase reaction. Changes in the content of gas components: The continuous decrease in the content of CO, CH4, and light hydrocarbons and the increase in the content of CO2 and H2 indicate that the extension of time promotes the implementation of formulas (1-3) and (8).

[0076] Comparative Example 1

[0077] The same as Example 1, except that no catalyst is added and no water vapor is introduced.

[0078] The gas components in the mixed gas were obtained by GC detection: H2: 51.02%, CO: 12.69%, CH4: 15.77%, CO2: 15.28%. This result shows that the H2 content is low after pyrolysis of raw materials without catalyst and water vapor.

[0079] Comparative Example 2

[0080] Same as Example 1, except that water vapor is not introduced.

[0081] The gas components in the mixed gas were obtained by GC detection: H2: 51.49%, CO: 33.83%, CH4: 9.7%, CO2: 0.54%. The results show that the H2 content does not change significantly after the water vapor-free raw material and the catalyst are co-pyrolyzed, the CO content is greatly increased, and the CO2 content is greatly reduced, which may be related to the Boudouard reaction of formula (7).

[0082] Figure 2 The graph is a comparison of the yield (a) and gas content (b) of the solid product, liquid product and gas product obtained after the reaction of Example 1 (SS1), Comparative Example 1 (DB1) and Comparative Example 2 (DB2).

[0083] Figure 3 The XRD comparison diagrams of the non-metallic part of the waste circuit board (NMF-WPCB), the solid phase products of Example 1 (SS1), Comparative Example 1 (DB1) and Comparative Example 2 (DB2) are shown in FIG. Figure 3 It can be seen that the diffraction peak distribution in Comparative Example 1 is relatively clear. CaSiO3, Sb2O3, etc. react at high temperature to increase the content of Ca2SiO4·3H2O, CaSb2O4, and Sb and make the structure more prominent. The diffraction peak distribution of Comparative Example 2 after adding calcium oxide is relatively complex, among which the diffraction peak with a lower peak value is mainly CaSiO3. The addition of calcium oxide makes the reaction between the solid phases complicated and increases the product, such as Ca5MgSi3O 12 、Ca2SiO4、Ca3Al6Si2O 16 This helps improve the morphology of the solid phase product, forms numerous micropores, and promotes the gas-solid phase reaction, thereby increasing the gas yield and hydrogen content.

[0084] The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for producing hydrogen by pyrolysis and gasification of the non-metallic part of waste circuit boards, characterized in that: The following steps are involved: The non-metallic part of the waste circuit board is mixed with a catalyst, heated to the gasification and pyrolysis temperature in an oxygen-free environment, and then water vapor is introduced for gasification and pyrolysis, and hydrogen-rich gas is collected.

2. The method for producing hydrogen by pyrolysis and gasification of the non-metallic part of waste circuit boards according to claim 1, characterized in that: The molar ratio of bromine in the non-metallic part of the waste circuit board to the catalyst is 1:(0.5-3).

3. The method for producing hydrogen by pyrolysis and gasification of the non-metallic part of waste circuit boards according to claim 2, characterized in that: The particle size of the non-metallic part of the waste circuit board is 80 meshes.

4. The method for producing hydrogen by pyrolysis and gasification of the non-metallic part of waste circuit boards according to claim 2, characterized in that: The catalyst is an alkali metal oxide.

5. The method for producing hydrogen by pyrolysis and gasification of the non-metallic part of waste circuit boards according to claim 4, characterized in that: The alkali metal oxide is calcium oxide.

6. The method for producing hydrogen by pyrolysis and gasification of the non-metallic part of waste circuit boards according to claim 1, characterized in that: The temperature of the gasification and pyrolysis is 750-950°C.

7. The method for producing hydrogen by pyrolysis and gasification of the non-metallic part of waste circuit boards according to claim 1, characterized in that: The water vapor introduction rate is 1-5 mL / min.

8. The method for producing hydrogen by pyrolysis and gasification of the non-metallic part of waste circuit boards according to claim 1, characterized in that: The time of gasification and pyrolysis is 30-70 minutes.

9. The method for producing hydrogen by pyrolysis and gasification of the non-metallic part of waste circuit boards according to claim 1, characterized in that: The oxygen-free environment is an inert gas atmosphere environment.

10. The method for producing hydrogen by pyrolysis and gasification of the non-metallic part of waste circuit boards according to claim 9, characterized in that: The inert gas is nitrogen.

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