Application of molecular sieve-based catalysts based on cathode materials of waste lithium-ion batteries in microwave catalytic oxidation of VOCs

Abstract

The present invention discloses an application of a molecular sieve-based catalyst based on waste lithium-ion battery positive electrode materials in microwave catalytic oxidation of VOCs. The molecular sieve-based catalyst is prepared by the following method: first, the ternary positive electrode material powder NCM obtained after heat treatment and CuSO4·5H2O are co-roasted in a muffle furnace to obtain a catalyst precursor; then the catalyst precursor is water-leached at room temperature, and the leached residue is loaded on the molecular sieve by an equal volume impregnation method, and then calcined and activated to obtain the catalyst. The present invention uses the leached residue after the selective extraction of Li from waste lithium-ion battery positive electrode materials as a catalyst, and the preparation method is simple. At the same time, transition metal elements such as Ni, Co, Mn, Cu, etc. are introduced into the catalyst, which can significantly improve the catalytic oxidation efficiency of benzene-based organic matter, reduce the cost of waste gas treatment, and achieve the purpose of "treating waste with waste".

Description

Technical Field

[0001] The invention belongs to the technical field of waste gas treatment, and particularly relates to an application of a molecular sieve-based catalyst based on anode materials of waste lithium-ion batteries in microwave catalytic oxidation of VOCs. Background Art

[0002] With the development of industry, the total amount of volatile organic compounds (VOCs) emitted by industrial sources is growing. A variety of technologies such as absorption, adsorption, photocatalysis, low-temperature plasma, condensation, membrane separation, thermal incineration, catalytic oxidation, and biofiltration have been used to control VOCs. Among them, catalytic oxidation has been proven to be one of the most reliable and effective technologies. Compared with direct thermal incineration, catalytic oxidation can achieve complete degradation of VOCs at a relatively low temperature without releasing any undesirable byproducts. However, the traditional catalytic oxidation process uses electric heating or natural gas heating to start. The electric heating temperature rises slowly, while natural gas heating will lead to additional energy consumption. The microwave-assisted heating process has the advantages of fast heating speed, strong penetration ability, low energy consumption, and good selectivity. It can make the reaction materials absorb microwave energy and be heated according to their different properties (wave transmission, reflection and absorption), and effectively reduce the reaction temperature and shorten the reaction time by changing the heat transfer mode. Therefore, microwave catalytic oxidation technology has gradually become a hot topic in current research, and the selection of catalysts is critical to the entire technology.

[0003] Currently, used lithium batteries are widely used and face the problem of being scrapped in large quantities. The positive electrode materials in them contain a large amount of valuable metal elements and have resource recovery value. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide an application of a molecular sieve-based catalyst based on waste lithium-ion battery positive electrode materials in microwave catalytic oxidation of VOCs. While recycling lithium in waste lithium-ion battery positive electrode materials, the present invention prepares a high-efficiency microwave catalytic oxidation catalyst that introduces transition metal elements, such as Ni, Co, Mn, Cu, etc., which can significantly reduce the reaction activation energy of organic oxidation reactions, increase the reaction rate, degrade organic matter into H2O and CO2, reduce the energy consumed by the oxidation system to treat organic waste gas, and increase the degradation rate. The present invention selectively extracts Li from waste ternary electrode materials and applies it to the preparation of catalytic oxidation catalysts, which not only simplifies the recovery procedure of battery positive electrode materials, but also reduces the cost of catalytic oxidation degradation, achieving the purpose of treating waste with waste, and can make catalytic oxidation technology play a more important role in industrial waste gas treatment and have more advantages.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] The present invention provides an application of a molecular sieve-based catalyst based on anode materials of waste lithium-ion batteries in microwave catalytic oxidation of VOCs. The molecular sieve-based catalyst is prepared by the following method:

[0007] Firstly, the ternary cathode material powder NCM and CuSO4·5H2O obtained after heat treatment are co-calcined in a muffle furnace to obtain a catalyst precursor; then the catalyst precursor is water-leached at room temperature, the leaching solution is a solution rich in Li2SO4, and the leached residue is loaded on the molecular sieve by an equal volume impregnation method, and then calcined and activated to obtain a molecular sieve-based catalyst. The catalyst loading in the molecular sieve-based catalyst is 2~12wt%.

[0008] In the present invention, the ternary positive electrode material powder NCM is obtained by heat treating CaO and a ternary positive electrode sheet at a temperature of 290-320°C.

[0009] In the present invention, the molar ratio of the ternary positive electrode material powder NCM and CuSO4·5H2O is 2:1; the calcination temperature is 550-600° C., and the calcination time is 60-90 minutes.

[0010] In the present invention, the catalyst calcination activation temperature is 350-400° C., and the activation time is 60-90 minutes.

[0011] In the present invention, the molecular sieve is selected from any one of 13X molecular sieve, 3A molecular sieve, 4A molecular sieve, 5A molecular sieve or ZSM-5 molecular sieve, and the catalyst loading in the molecular sieve-based catalyst is 7.5-10wt%.

[0012] In the present invention, the leaching solution is purified by precipitation with oxalic acid to remove the Ni, Co, Mn and Cu elements contained therein, and Na2CO3 is added to the purified solution, which is then filtered to obtain a Li2CO3 filter cake.

[0013] In the present invention, the application method is as follows: the molecular sieve-based catalyst is loaded in a quartz tube fixed bed reactor of a microwave reactor, and air containing volatile organic matter enters the microwave reactor for microwave catalytic oxidation to achieve catalytic degradation of the volatile organic matter.

[0014] In the present invention, the catalyst bed thickness is 30-50 mm, the catalyst bed temperature is 350-380°C, and the concentration of volatile organic matter is 950-1050 mg / m 3 The gas flow rate was 1.5-2.5 L / min, and the space velocity in the microwave reactor was 4000-7000 mg / m 3 , the microwave power of the microwave reactor is between 300-500W.

[0015] In the present invention, the volatile organic compounds (VOCs) are benzene-based organic compounds, and the relative humidity of the air containing the volatile organic compounds is between 0% and 8%.

[0016] The present invention makes full use of the high value of waste lithium-ion batteries, uses relatively cheap waste ternary cathode materials that have only undergone simple heat treatment as precursor materials, and uses catalytic oxidation technology to purify organic waste gas, truly realizing the closed-loop idea from waste resource utilization to waste treatment. Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention obtains a microwave catalytic oxidation reaction catalyst for degrading volatile organic compounds (VOCs) such as benzene organic compounds by recycling the positive electrode materials of waste ternary lithium ion batteries. The catalyst introduces transition metal elements such as Ni, Co, Mn, Cu, etc., which can significantly improve the microwave catalytic oxidation efficiency of benzene organic compounds.

[0018] The method of obtaining a microwave catalytic oxidation reaction catalyst from the cathode material of waste ternary lithium-ion batteries is simple, and the valuable metal Li in the cathode material can also be effectively recovered to achieve resource utilization;

[0019] In the present invention, when the catalyst based on the cathode material of waste ternary lithium-ion batteries is used to degrade volatile organic compounds (VOCs) in a microwave reaction cavity, the microwave reaction cavity can further promote the uniformity of catalyst surface temperature, heating stability and improve heating efficiency;

[0020] The catalyst of the present invention has moisture resistance and is suitable for catalytic degradation of VOCs under a certain humidity. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of the organic waste gas catalytic oxidation system.

[0022] Figure 2 It is a schematic diagram of the structure of a microwave reactor.

[0023] Figure 3 It is the electric field intensity distribution cloud diagram of the microwave reactor after structural optimization.

[0024] Figure 4 Morphology and composition characterization of the prepared materials; A-leached residue after Li resource extraction, B-molecular sieve, C-supported composite metal oxide catalyst, D-element distribution analysis on the surface of the prepared catalyst.

[0025] Figure 5 The effect of catalysts prepared under different loading amounts on toluene conversion.

[0026] Numbers in the figure: 1-air inlet, 2-air pump, 3-air purification system, 4-benzene series organic matter generating device, 5-humidity control system, 6-buffer tank, 7-microwave reactor, 8-exhaust gas purification system, 9-air outlet, 10-quartz tube, 11-rectangular waveguide, 12-infrared temperature measuring probe, 13-feed port. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0028] In the embodiment, a molecular sieve-based catalyst for microwave catalytic oxidation of volatile organic compounds is provided, and the preparation method thereof is as follows:

[0029] (1) Since the ternary positive electrode sheet is composed of aluminum foil, positive electrode powder, conductive agent (acetylene black), binder (polyvinylidene fluoride PVDF), etc., the positive electrode material powder must first be separated from other components. The traditional heat treatment method often requires a heat treatment temperature of more than 550°C, which consumes a lot of energy and is not conducive to green environmental protection requirements. CaO, as a cheap and readily available product, can be used as an auxiliary agent for heat treatment to effectively reduce the heat treatment temperature. First, CaO and the ternary positive electrode sheet are co-calcined at a temperature of 300°C. During the heat treatment process, the binder PVDF reacts with CaO to generate CaF2, thereby eliminating the binder in the ternary positive electrode sheet to achieve the separation of the positive electrode powder and the aluminum foil. After the positive electrode powder is analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES), it is found that its composition is lithium nickel cobalt manganese oxide (NCM), and the chemical formula is: Li 1.006 Ni 0.333 Co 0.317 Mn 0.298 O 2-δ ;

[0030] (2) The ternary cathode material powder (NCM) obtained after heat treatment and CuSO4·5H2O were calcined in a muffle furnace at a molar ratio of 2:1 to obtain a catalyst precursor. Since the NCM crystal has a layered structure, during the heat treatment process, the Li embedded in the layered structure will be deintercalated and react with sulfate to form Li2SO4. At the same time, in order to maintain the charge balance, the lattice oxygen on the surface of NCM will overflow and react with Cu ions to form CuO. Due to the water solubility of Li2SO4, it can be efficiently recovered by water leaching, and the leached residue can be used for subsequent catalytic processes. In addition, studies have confirmed the promotion effect of the introduction of Cu on catalytic oxidation. The calcination mechanism of the muffle furnace is: heating at a rate of 80℃ / min to 600℃ and maintaining for 60 minutes;

[0031] (3) The catalyst precursor is immersed in water, and the leached residue is loaded on the molecular sieve by an equal volume impregnation method. The specific operation steps are as follows: first, determine the water absorption rate of the carrier, take a certain mass of the carrier and immerse it in an excess and known volume of water. After the carrier fully absorbs water, take out the excess water and drain it, and then record the remaining water volume. The ratio of the difference between the original water volume and the remaining water volume to the weight of the carrier is the water absorption rate of the carrier. The second step is to prepare the active component impregnation solution according to the water absorption rate of the carrier. Under certain conditions, the active component is infiltrated into the inner surface of the carrier with a porous structure in the form of a solution. Subsequently, it is calcined and activated at a temperature of 380°C for 60 minutes to obtain a supported catalyst for subsequent microwave catalytic oxidation. The leaching solution is a Li2SO4-rich aqueous solution. The leaching solution is purified with an appropriate amount of oxalic acid to remove a small amount of Ni, Co, Mn, Cu and other elements. After adding an appropriate amount of Na2CO3 to the purified solution and filtering, a Li2CO3 filter cake with high purity is obtained, realizing the resource utilization of the leaching solution.

[0032] Figure 4 To characterize the morphology and composition of the prepared materials, it can be seen that the leached residue obtained after leaching presents a clustered structure composed of thin sheets, such as Figure 4 (A) Figure 4 (B) is the morphology analysis of the molecular sieve carrier, which clearly shows the microporous structure on its surface. The unique microporous structure makes the molecular sieve have a large specific surface area, which is conducive to the loading of active components. The surface morphology of the catalyst after loading is shown in Figure 2. Figure 4 (C) Figure 4 (D) is the elemental analysis (energy dispersive X-ray spectroscopy analysis) of the prepared catalyst. It can be seen that the elements on the surface of the prepared catalyst are Ni, Co, Mn, Cu, and O. Due to the low characteristic X-ray output of element Li, the distribution of element Li in the sample cannot be determined by mapping analysis. From the elemental maps, it can be seen that all elements are evenly distributed, which fully demonstrates the effectiveness of the equal volume impregnation method loading.

[0033] In the embodiment, a system for degrading volatile organic compounds (VOCs) using a molecular sieve-based catalyst based on anode materials of waste lithium-ion batteries is further provided, such as Figure 1 As shown, the system includes an air pump 2, an air purification system 3, a benzene-based organic matter generator 4, a buffer tank 6, a microwave reactor 7 and an exhaust gas purification system 8; the system carries the organic matter in the benzene-based organic matter generator 4 out into the buffer tank 6 through the carrier gas purified by the air pump 2, and enters the microwave reactor 7 after stabilization, and then passes through the fixed bed reactor of the composite metal oxide molecular sieve-based catalyst based on the positive electrode material of waste lithium-ion batteries prepared as above, so that the exhaust gas is further degraded.

[0034] In the microwave reactor 7, the cavity is simulated and analyzed using the high-frequency electromagnetic field simulation software High Frequency Structure Simulator (HFSS) to optimize the structure of the microwave reactor. The simulation adopts the eigenmode solution, and the model is constructed in the HFSS environment for simulation. The microwave reactor model is established according to the actual conditions ( Figure 2 ). The length, width and height of the waveguide are 668 mm, 56 mm and 95 mm, the cavity is 320 mm high and 160 mm in diameter. The relative dielectric constant of the cavity in a vacuum environment is 1 and the relative permeability is 1. The quartz tube in the middle is 330 mm high and 30 mm in diameter. The relative dielectric constant of quartz is 3.78 and the relative permeability is 1. Set the operating frequency to 2.45 GHz, and keep the default input power of 1W without changing the input power. The waveguide input is a transverse electric wave (TE mode). The vertical component of the electric field in the propagation direction of the electromagnetic wave is zero, and the longitudinal component of the magnetic field is not zero. The magnetic field has little effect on it, so only the electric field needs to be analyzed. By changing the position of different waveguides, the electric field intensity inside the cavity is simulated, and the simulation results are analyzed and discussed. The microwave reactor after structural optimization can significantly improve the heating uniformity of the catalyst bed. The electric field intensity distribution cloud map of the microwave reactor after structural optimization is shown in the figure Figure 3 shown.

[0035] In the embodiment, the molecular sieve catalyst prepared as above is used in the system of microwave catalytic oxidation of benzene-based organics to remove benzene-based organics. In order to simulate the exhaust gas flow under actual working conditions, the system uses a bubbling method at the air inlet end to control the humidity of the exhaust gas flow. In addition, in the microwave catalytic oxidation system, the microwave reactor 7 after structural optimization can significantly improve the heating uniformity of the catalyst bed. First, according to the actual working conditions, a catalyst with a certain bed thickness is placed in the quartz tube 10, and the catalyst bed thickness is 30~50 mm. The air is pulled by the air pump 2 and passes through the air purification system 3. The purified air is used in conjunction with the benzene-based organics generating device to produce continuous and stable toluene exhaust gas. The air distribution volume of the air pump is 2 L / min, and the air velocity in the microwave reactor 7 is 4000-7000 mg / m 3 Subsequently, the exhaust gas passes through the buffer tank 6 and enters the microwave reactor 7. The concentration of benzene organic matter at the outlet of the buffer tank 6 is 950-1050 mg / m 3 The temperature is monitored by an infrared temperature probe 12. During the catalytic oxidation process, the catalyst bed temperature is 350-380°C. During this process, the organic waste gas is attacked by active oxygen species on the surface of the composite transition metal oxide catalyst, degraded, and the waste gas is purified. The degraded waste gas is treated by the tail gas purification system 8 and then discharged.

[0036] Based on the above conditions, when the catalyst bed thickness was 30 mm, the effects of the catalysts prepared at different loading amounts on the toluene conversion were analyzed. Figure 5 As shown. It can be seen that as the loading increases from 2.2% to 7.5%, the conversion rate of toluene gradually increases due to the increase in catalyst content, reaching 92.3% at 7.5% loading. When the loading is further increased to 10%, the toluene conversion rate does not increase significantly, so 7.5% is selected as the optimal loading condition. In order to further improve the toluene conversion rate, the bed thickness is increased to further increase the residence time. Through analysis, the air intake is controlled at 2L / min, toluene is selected as the target pollutant, and its concentration is controlled at 1000mg / m 3 The time of exhaust gas in the fixed bed reactor was controlled at 1.1s, the catalyst bed thickness was 50mm, the microwave power was 374.5W, and the catalyst loading was 7.5%. The results showed that toluene was completely degraded in 60min, and the water resistance test showed that the catalytic degradation efficiency of the catalyst could also reach more than 90% at a relative humidity of 5.7%, which is suitable for industrial application and promotion.

Claims

1. An application of a molecular sieve-based catalyst based on waste lithium-ion battery cathode material in microwave catalytic oxidation of VOCs, characterized in that: The molecular sieve-based catalyst is prepared by the following method: First, the ternary cathode material powder NCM and CuSO4·5H2O obtained after heat treatment are co-calcined in a muffle furnace to obtain a catalyst precursor; then the catalyst precursor is water-leached at room temperature, the leaching solution is a solution rich in Li2SO4, and the leached residue is loaded on a molecular sieve by an equal volume impregnation method, and then calcined and activated to obtain a molecular sieve-based catalyst, wherein the catalyst loading in the molecular sieve-based catalyst is 2-12wt%; wherein: The molar ratio of the ternary cathode material powder NCM and CuSO4·5H2O is 2:1; the calcination temperature is 550~600℃, and the calcination time is 60~90 minutes; The catalyst calcination activation temperature is 350~400℃, and the activation time is 60~90min.

2. The use according to claim 1, characterized in that: The ternary cathode material powder NCM is obtained by heat treating CaO and a ternary cathode sheet at a temperature of 290-320°C.

3. The use according to claim 1, characterized in that: The molecular sieve is selected from any one of 13X molecular sieve, 3A molecular sieve, 4A molecular sieve, 5A molecular sieve or ZSM-5 molecular sieve, and the catalyst loading in the molecular sieve-based catalyst is 7.5-10wt%.

4. The use according to claim 1, characterized in that: The leaching solution is purified by precipitation with oxalic acid to remove the elements Ni, Co, Mn and Cu therein, and Na2CO3 is added to the purified solution, which is then filtered to obtain a Li2CO3 filter cake.

5. The use according to claim 1, characterized in that: The application method is as follows: the molecular sieve-based catalyst is loaded in a quartz tube fixed bed reactor of a microwave reactor, and air containing volatile organic matter enters the microwave reactor for microwave catalytic oxidation to achieve catalytic degradation of the volatile organic matter.

6. The use according to claim 5, characterized in that: The concentration of volatile organic compounds is 100~1500 mg / m 3 , gas flow rate is 1.5-2.5 L / min, catalyst bed thickness is 30-50 mm, catalyst bed temperature is 350-380 °C, and space velocity in microwave reactor is 4000-7000 mg / m 3 , the microwave power of the microwave reactor is 300-600W.

7. The use according to claim 5, characterized in that: Volatile organic compounds are benzene-based organic compounds, and the relative humidity of air containing volatile organic compounds is between 0% and 8%.

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