A method for preparing a carbon-based monolithic catalytic material from domestic sewage sludge and its application

Abstract

The present invention discloses a method for preparing a high-performance monolithic carbon-based catalytic material by using the sludge generated from urban domestic sewage treatment plants as raw materials and with the aid of ball milling and 3D printing technology, as well as the application of this material in sewage treatment to achieve "treating pollution with waste". The method includes the following steps: 1. Air-dry the water-containing sludge, add an activator and a metal source (such as cobalt, iron, Cu), ball mill for a certain time, and then add a binder and water to adjust the sludge viscoelasticity. 2. By means of 3D printing, print the above-mentioned sludge into monolithic material precursors with different morphologies, and calcine in a protective atmosphere at 600-1100 °C to obtain a high-performance carbon-based monolithic catalytic material. The preparation process flow of the present invention is easy to control and has good repeatability; the metal content, morphology, and porosity of the prepared material are adjustable, and at the same time, it has high stability; this process follows the principle of sustainable development, not only realizing the resource recycling of sludge, but also being able to efficiently and continuously degrade pollutants, achieving the transformation of waste into treasure.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste treatment and resource utilization, and particularly relates to a preparation method of using sludge to 3D print a high-performance carbon-based monolithic catalytic material. Background Art

[0002] With the improvement of urbanization level, the output of urban sludge has been increasing year by year. Domestic sludge, as a waste urgently needed to be treated, contains a large number of zoogloea formed by microorganisms and organic and inorganic substances adsorbed on its surface. Therefore, it is often used as a raw material for carbon materials after anaerobic carbonization, which can not only reduce the pollution caused by sludge as solid waste, but also prepare high-value-added catalytic materials for use in the sewage treatment process to achieve the purpose of "treating pollution with waste". The sludge carbon material simply prepared by the high-temperature anaerobic carbonization method has problems such as low catalytic activity and unstable catalytic activity of the catalytic material due to its low specific surface area and low binding force between metal and sludge.

[0003] As a rapidly developing manufacturing technology, 3D printing technology has the characteristics of high efficiency, precise processing, and personalized production, and can prepare monolithic materials with controllable morphology, porosity, etc. Monolithic materials can effectively reduce pressure drop and enhance mass transfer, and are widely used in fixed-bed reactors. However, when using 3D printing to prepare carbon-based catalytic materials from urban sludge, due to the very low specific surface area of sludge particles or sludge carbon itself, it is not conducive to the loading of metals. Therefore, it is necessary to activate and create pores in the sludge to provide more sites for the loading of metals. If the sludge is first activated by a chemical method and then ball-milled and printed, it significantly increases the steps of the material preparation process. Therefore, it is necessary to provide a method that can ensure metal loading while simplifying the material preparation steps.

[0004] The ball-milling method realizes the deformation, refinement, and interatomic mutual diffusion of powder under the actions of impact, shear, friction, compression, etc. of grinding balls by inputting mechanical energy. Through the ball-milling method, not only the specific surface area of sludge can be increased, but also the binding force between sludge and metal is increased, thereby improving the stability of active sites on the carrier. Combining the advantages of the above two technologies, this application applies the ball-milling method and 3D printing technology to the preparation of carbon-based monolithic catalytic materials from sludge, and is expected to achieve efficient and continuous treatment of antibiotic wastewater. Therefore, a method of directly ball-milling a chemical activator and sludge simultaneously is designed to increase the binding force among metal active sites, activator, and sludge during the ball-milling process, and then construct a monolithic catalytic material through 3D printing to improve the continuous degradation stability of the carbon-based monolithic catalytic material for antibiotic wastewater after carbonization. Summary of the Invention

[0005] The object of the present invention is to provide a method for simultaneously ball-milling a chemical activator, a metal catalyst, and sludge particles, followed by slurry preparation, printing, and carbonization to prepare a monolithic catalytic material. The whole process is relatively simple, and the prepared material is particularly suitable for treating antibiotic wastewater such as tetracycline or levofloxacin.

[0006] The technical solution of the present invention is as follows:

[0007] A preparation method and application of a carbon-based monolithic catalytic material prepared from municipal domestic sludge. The catalytic material mechanically crushes the air-dried sludge, and then ball-mills the sludge particles, metal source, and activator. The obtained ball-milled product is mixed with a binder, retarder, water reducer, and water, and then undergoes slurry preparation, printing, and carbonization to obtain the carbon-based monolithic catalytic material; wherein, based on the mass of the monolithic catalytic material skeleton, the metal content is 1-10 wt%.

[0008] In the above catalytic material: the metal source is one of iron, cobalt, and copper salts or their reduced powders, the activator is ZnCl2, the binder is clay, the retarder is tartaric acid, and the water reducer is a polycarboxylic acid superplasticizer.

[0009] In the above catalytic material: the mass ratio of the sludge particles, binder, metal source, and activator is (0.05-0.3):0.7-0.9:(0.01-0.1):(0.01-0.1).

[0010] A preparation method of the above catalytic material, and the preparation method of the catalytic material is as follows:

[0011] (1) Preparation of activated metal sludge powder by ball-milling method

[0012] Air-dry the municipal domestic sludge and immerse it in a ZnCl2 solution with a certain concentration for 12-48 h. After drying, mechanically crush and sieve it to obtain activated sludge powder; use the ball-milling method to fully mix the above crushed sludge, metal source, and clay powder to obtain activated metal sludge powder;

[0013] (2) Preparation of carbon-based monolithic material by 3D printing technology

[0014] The obtained activated metal sludge powder is mixed with water, retarder, and water reducer to prepare a slurry with appropriate viscosity and viscoelasticity. Using 3D printing technology, print out monolithic catalytic material precursors with different morphologies, and then obtain high-performance carbon-based monolithic materials through high-temperature carbonization.

[0015] In the above method, by using the ball-milling method and the strong mechanical force generated by ball-milling, the size of the active sites of the sludge and the metal source is greatly reduced, and the active sites of the sludge and the metal source can be effectively combined. The metal source is a metal salt or a reduced metal powder, specifically selected from one of iron, cobalt, and copper salts or their reduced powders.

[0016] In the above method, based on the monolithic catalytic material, the metal loading is 1-10 wt%.

[0017] In the above method, the ball milling time is 1-4 hours, the average particle size of the ball milled product is 0.02 - 0.1 mm, preferably 0.05 mm; in the above method, the activator is ZnCl2, and the activator concentration is 0.5 - 1 mol / L; the mass ratio of sludge powder, clay, metal source and activator is (0.05 - 0.3):0.7 - 0.9:(0.01 - 0.1):(0.01 - 0.1);.

[0018] In the above method, the sludge powder accounts for 5 - 30 wt% of the total mass of the slurry.

[0019] In the above method, the viscosity range of the monolithic catalytic material slurry is 10 mPa·s - 25 mPa·s, the elastic modulus is 10 5 ~10 6 Pa, and the phase angle is below 45°.

[0020] In the above method, the high-temperature carbonization temperature is 600 - 900 °C, and the carbonization time is 4 - 6 h; in the high-temperature carbonization process in step (2), nitrogen is introduced as a protective atmosphere, and the nitrogen flow rate is 30 - 50 mL / min.

[0021] In the technical solution of the present invention: the application of the high-loading cobalt-containing carbonitride nanosheet monolithic catalytic material as a catalyst for degrading organic substances, preferably the application as a catalyst for degrading tetracycline and levofloxacin.

[0022] The catalytic reaction conditions and results of the present invention: The content of tetracycline or levofloxacin was measured using an ultraviolet spectrophotometer. The ultraviolet absorbance of levofloxacin was measured at an excitation wavelength of 290 nm, and the concentration was calculated through a standard curve. The catalytic material was filled in a fixed-bed reactor for activity evaluation. The concentration of each solution was: the initial concentration of levofloxacin was 10 mg / L, the initial concentration of PMS was 0.05 mmol / L, and the catalyst was loaded in the fixed-bed reactor for continuous degradation reaction under normal temperature and pressure.

[0023] The beneficial effects of the present invention are:

[0024] 1. In the present invention, the activator, sludge particles and metal catalyst are simultaneously ball milled by a one-step ball milling method, which solves the problems of low specific surface area of sludge particles themselves and low binding force between the catalyst and sludge. It not only increases the metal stability and reduces metal loss, but also reduces the preparation path, meeting the requirement of using 3D printing to prepare carbon-based monolithic catalytic materials from domestic sewage sludge.

[0025] 2. The monolithic materials prepared by 3D printing have characteristics such as controllable morphology and porosity. By combining the ball milling method and 3D printing technology to prepare monolithic materials, there is a large modulation space for both the metal loading and the material morphology. The obtained monolithic materials can reduce the fluid transmission resistance, improve the mass transfer rate, and are beneficial to efficient continuous degradation.

[0026] 3. The present invention uses the ball milling method to treat Fe 0 powder (ZVI) / FeS to prepare a composite metal source. Utilizing the strong mechanical force of the ball milling method, a ZVI / FeS hybrid powder with high binding force and high activity is obtained, and it is used as a catalyst to improve the catalytic activity of the carbon-based monolithic material.

[0027] 4. The present invention solves the problem that sludge, as a solid waste, urgently needs to be treated. By applying it to the treatment of antibiotic wastewater, an efficient continuous degradation process of PMS is realized, achieving the purpose of "treating pollution with waste". Description of the Drawings

[0028] Figure 1 : Photos of the materials in Example 1 and Comparative Example 1.

[0029] Figure 2 : Elastic modulus and phase change angle of Example 1, Example 2, Example 3 and Comparative Example 1.

[0030] Figure 3 : Continuous degradation effect diagrams of tetracycline of the materials in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2. Detailed Embodiments

[0031] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0032] Example 1

[0033] (1) Preparation of activated metal sludge powder by ball milling method

[0034] Weigh 1 g of Fe 0Powder (ZVI) and 1.56 g of FeS powder were added to the ball milling tank. The rotation speed of the ball mill was set at 400 revolutions per minute, and the ball milling time was 30 minutes to obtain ZVI / FeS mixed metal powder. 1 L of ZnCl₂ solution with a concentration of 1 mol / L was prepared. 200 g of sludge was weighed and added to a beaker, impregnated for 24 h, taken out and dried, and then ground into powder through a 100-mesh sieve with a crusher to obtain activated sludge powder. 12 g of activated sludge powder, 45 g of clay powder, and 3 g of ZVI / FeS mixed powder were weighed and added to the ball milling tank. The rotation speed of the ball mill was 400 revolutions per minute, and the ball milling time was 1 h to obtain activated metal sludge powder.

[0035] (2) 3D printing of integral carbon-based catalytic materials

[0036] The above-mentioned metal sludge powder (60 g), 3 g of retarder and water reducer (weight ratio 2:1) (the mass fraction of sludge powder in all materials is about 20%) were added to 40 ml of pure water, and stirred evenly and fully for 10 min until it became viscous to obtain sludge-clay mixed slurry. It was filled into the filling cylinder, the pressure of the pressure pump was set at 0.4 Pa, the 3D printing moving speed was 12 mm / s, and the pore filling rate was 40% to obtain a 3D printed preliminary sample. After air drying for 24 h, it was carbonized. The carbonization temperature was 800 °C, the heating rate was 10 °C / min, and the heat preservation time was 2 h. After carbonization under nitrogen protection, an integral material was obtained (the photo is as Figure 1 shown).

[0037] (3) Catalytic degradation activity test

[0038] As Figure 3 shown, the content of levofloxacin was tested using an ultraviolet spectrophotometer. The ultraviolet absorbance of levofloxacin was measured at an excitation wavelength of 290 nm, and the concentration was calculated through the standard curve. The integral material was filled in a fixed-bed reactor for continuous degradation reaction. The concentration of each solution was: the initial concentration of levofloxacin was 25 mg / L, the initial concentration of PMS was 0.05 mmol / L, and the continuous degradation efficiency of the catalyst at normal temperature and pressure for 6 h was 80%.

[0039] (4) Application scope

[0040] The integral carbon-based catalytic material prepared by this method is applicable to water antibiotic organic pollutants such as tetracycline and levofloxacin.

[0041] Example 2

[0042] (1) Preparation of activated metal sludge powder by ball milling method

[0043] Weigh 1 g of Fe 01 g of iron powder (ZVI) and 1.56 g of FeS powder were added to a ball milling jar. The rotation speed of the ball mill was set at 400 revolutions per minute, and the ball milling time was 30 minutes to obtain ZVI / FeS mixed metal powder. 1 L of ZnCl₂ solution with a concentration of 1 mol / L was prepared. 200 g of sludge was weighed and added to a beaker, impregnated for 24 h, taken out and dried, and then ground into powder through a 100-mesh sieve by a crusher to obtain activated sludge powder. 6 g of activated sludge powder, 51 g of clay powder, and 3 g of ZVI / FeS mixed powder were weighed and added to the ball milling jar. The rotation speed of the ball mill was 400 revolutions per minute, and the ball milling time was 1 h to obtain activated metal sludge powder.

[0044] (2) Preparation of 3D printed monolithic carbon-based catalytic material

[0045] The above-mentioned metal sludge powder (60 g), 3 g of retarder and water reducer (the mass fraction of sludge powder in all materials was about 10%) were added to 40 ml of pure water, and stirred evenly and fully for 10 min until it became viscous to obtain sludge-clay mixed slurry. It was filled into a filling cylinder, the pressure of the pressure pump was set at 0.4 Pa, the 3D printing moving speed was 12 mm / s, and the pore filling rate was 40% to obtain a 3D printed preliminary sample. After air drying for 24 h, it was carbonized at a carbonization temperature of 800 °C, a heating rate of 10 °C / min, and a heat preservation time of 2 h to obtain a monolithic material under nitrogen protection.

[0046] (3) Catalytic degradation activity test

[0047] As Figure 3 shown, the content of levofloxacin was tested by an ultraviolet spectrophotometer. The ultraviolet absorbance of levofloxacin was measured at an excitation wavelength of 290 nm, and the concentration was calculated through a standard curve. The monolithic material was filled in a fixed-bed reactor for continuous degradation reaction. The concentration of each solution was: the initial concentration of levofloxacin was 25 mg / L, the initial concentration of PMS was 0.05 mmol / L, and the continuous degradation efficiency of the catalyst exceeded 70% at normal temperature and pressure for 6 h.

[0048] (4) Application scope

[0049] The monolithic carbon-based catalytic material prepared by this method is applicable to water antibiotic organic pollutants such as tetracycline and levofloxacin.

[0050] Example 3

[0051] (2) Preparation of activated metal sludge powder by ball milling method

[0052] 1 g of Fe was weighed 0Powder (ZVI) and 1.56 g of FeS powder were added to the ball milling tank. The rotation speed of the ball mill was set at 400 revolutions per minute, and the ball milling time was 30 minutes to obtain the ZVI / FeS mixed metal powder. 1 L of ZnCl₂ solution with a concentration of 1 mol / L was prepared. 200 g of sludge was weighed and added to a beaker, taken out and dried after impregnation for 24 h, and ground into powder through a 100-mesh sieve with a crusher to obtain the activated sludge powder. 18 g of activated sludge powder, 39 g of clay powder, and 3 g of ZVI / FeS mixed powder were weighed and added to the ball milling tank. The rotation speed of the ball mill was 400 revolutions per minute, and the ball milling time was 1 h to obtain the activated metal sludge powder.

[0053] (2) 3D printing of integral carbon-based catalytic materials

[0054] The above-mentioned metal sludge powder (60 g), 3 g of retarder and water reducer (the mass fraction of sludge powder in all materials was about 30%) were added to 40 ml of pure water, and stirred evenly and fully for 10 minutes until it became viscous to obtain the sludge-clay mixed slurry. It was filled into the packing cylinder, the pressure of the pressure pump was set at 0.4 Pa, the 3D printing moving speed was 12 mm / s, and the pore filling rate was 40% to obtain the 3D printed preliminary sample. After air drying for 24 h, it was carbonized. The carbonization temperature was 800 °C, the heating rate was 10 °C / min, and the holding time was 2 h. After carbonization under nitrogen protection, an integral material was obtained.

[0055] (3) Catalytic degradation activity test

[0056] As Figure 3 shown, for the levofloxacin content test, an ultraviolet spectrophotometer was used to measure the ultraviolet absorbance of levofloxacin at an excitation wavelength of 290 nm, and the concentration was calculated through the standard curve. The integral material was filled in a fixed-bed reactor for continuous degradation reaction. The concentration of each solution was: the initial concentration of levofloxacin was 25 mg / L, the initial concentration of PMS was 0.05 mmol / L, and the continuous degradation efficiency of the catalyst exceeded 70% under normal temperature and pressure for 6 h.

[0057] (4) Application scope

[0058] The integral carbon-based catalytic material prepared by this method is applicable to water antibiotic organic pollutants such as tetracycline and levofloxacin.

[0059] Comparative example 1

[0060] (1) Preparation of activated metal sludge powder by ball milling method

[0061] Except that all the sludge was replaced with clay during the preparation of the catalyst, other conditions were the same as in Example 1;

[0062] (2) 3D printing of integral catalytic materials

[0063] Weigh 60 g of metal clay powder and add it to 40 ml of pure water. Stir it evenly and fully for 10 min until it becomes viscous to obtain a clay mixed slurry. Load it into the filler cylinder, set the pressure of the pressure pump to 0.4 Pa, the 3D printing moving speed to 12 mm / s, and the pore filling rate to 40%, to obtain a preliminary 3D printed sample. After air drying for 24 h, carbonize it at a carbonization temperature of 800 °C, a heating rate of 10 °C / min, and a holding time of 2 h. After carbonization under nitrogen protection, an integral material is obtained.

[0064] (3) Catalytic degradation activity test

[0065] As Figure 3 shown, for the levofloxacin content test, a UV spectrophotometer is used to measure the UV absorbance of levofloxacin at an excitation wavelength of 290 nm, and the concentration is calculated through the standard curve. Fill the integral material in a fixed bed reactor for continuous degradation reaction. The concentrations of each solution are as follows: the initial concentration of levofloxacin is 25 mg / L, the initial concentration of PMS is 0.05 mmol / L, and the continuous degradation efficiency of the catalyst at normal temperature and pressure for 6 h is 20%.

[0066] (3) Comparative effect

[0067] It can be seen from the comparison with Example 1 that when all the sludge powder is replaced by clay, the catalytic efficiency significantly decreases.

[0068] In addition, the deformation of the printed structure is mainly related to the static yield stress and viscoelasticity of the material. The higher the elastic modulus, the more deformation the material can resist when subjected to external forces, thus achieving the stability of the material structure after printing. The viscoelasticity and static yield stress of the slurries in Examples 1, 2, 3 and Comparative Example 1 were tested, as Figure 2 shown. It can be seen from Figure 2 that for Examples 1, 2, and 3 with added sludge, their elastic modulus is significantly increased compared to Comparative Example 1 without added sludge, and the elastic modulus of Example 1 has increased by an order of magnitude. This result shows that the addition of sludge increases the elastic modulus of the slurry, which is due to the fact that the introduction of sludge improves the water absorption performance of the slurry. The incorporation of 20% sludge ratio has the best improvement effect on the viscoelasticity of the slurry, indicating that the structure of the material after printing in Example 1 is the most stable. At the same time, it can also be seen from Figure 2 that as the sludge content increases from 0% to 30%, the critical stress of the slurry shows a trend of first decreasing, then increasing, and then decreasing again. Therefore, it shows that after adding sludge, it has higher printability and stability. Under the conditions of Example 1 (the mass fraction of sludge powder in all materials is about 20%), the structure of the material is the most stable. For Examples 1, 2, 3 and Comparative Example 1, the phase angles of all slurries in the LVR are lower than 45°, showing a solid-like state, proving that they all have sufficient hardness.

[0069] Comparative Example 2

[0070] (1) Preparation of catalytic material

[0071] Except that when preparing the catalyst, the ball-milled Fe 0 powder (ZVI) and FeS powder were replaced by mechanical stirring method, and other conditions were the same as those in Example 1;

[0072] (2) 3D printing monolithic carbon-based catalytic material

[0073] Weigh 60 g of metal sludge powder (the sludge powder accounts for 20%) and add it to 40 ml of pure water. After uniformly and fully stirring for 10 min until it becomes viscous, a sludge-clay mixed slurry is obtained. Fill it into the filler cylinder, set the pressure pump pressure to 0.4 Pa, the 3D printing moving speed to 12 mm / s, and the pore filling rate to 40% to obtain a 3D printed preliminary sample. After air drying for 24 h, carbonization is carried out. The carbonization temperature is 800 °C, the heating rate is 10 °C / min, and the holding time is 2 h. After carbonization under nitrogen protection, a monolithic material is obtained.

[0074] (3) Catalytic degradation activity test

[0075] As Figure 2 shown, the content of levofloxacin was tested by an ultraviolet spectrophotometer. The ultraviolet absorbance of levofloxacin was measured at an excitation wavelength of 290 nm, and the concentration was calculated through the standard curve. The monolithic material was filled in a fixed-bed reactor for continuous degradation reaction. The concentrations of each solution were: the initial concentration of levofloxacin was 25 mg / L, the initial concentration of PMS was 0.05 mmol / L, and the continuous degradation efficiency of the catalyst at normal temperature and pressure for 6 h was 12%.

[0076] (3) Comparative effect

[0077] It can be seen from the comparison with Example 2 that replacing the ball-milling method with mechanical stirring significantly reduces the catalytic efficiency.

Claims

1. Application of a carbon-based monolithic catalytic material as a catalyst in the degradation of organic substances, characterized in that, The organic substance is tetracycline or levofloxacin. The preparation method of the carbon-based monolithic catalytic material comprises the following steps: (1) Preparation of activated metal sludge powder by ball milling method: Air-dry the urban domestic sludge and immerse it in an activated agent ZnCl2 solution with a certain concentration for 12 - 48 h. After drying, mechanically crush and screen it to obtain activated sludge powder; use the ball milling method to fully mix the activated sludge powder, metal source, and clay powder to obtain activated metal sludge powder; (2) Preparation of carbon-based monolithic material by 3D printing technology: Mix the obtained activated metal sludge powder with water, retarder, and water reducer to prepare a slurry with appropriate viscosity and viscoelasticity. Use 3D printing technology to print the precursor of the monolithic catalytic material, and obtain the carbon-based monolithic catalytic material through high-temperature carbonization; The metal source is Fe 0 powder and FeS powder; The concentration of the activated agent ZnCl2 solution is 0.5 - 1 mol / L; The mass ratio of the activated sludge powder, clay, metal source, and activated agent ZnCl2 is (0.05 - 0.3):0.7 - 0.9:(0.01 - 0.1):(0.01 - 0.1); based on the monolithic catalytic material, the metal loading is 1 - 10 wt%; The ball milling time is 1 - 4 hours, and the average particle size of the ball milling product is 0.02 - 0.1 mm.

2. The preparation method according to claim 1, characterized in that: The average particle size of the ball milling product is 0.05 mm.

3. The preparation method according to claim 1, characterized in that: In step (2), the sludge powder accounts for 5 - 30 wt% of the total mass of the slurry.

4. The preparation method according to claim 1, characterized in that: In step (2), the viscosity range of the mud is 10 mPa·s - 25 mPa·s, the elastic modulus is 10 5 ~ 10 6 Pa, and the phase angle is less than 45°.

5. The preparation method according to claim 1, wherein: The high-temperature carbonization temperature is 600 - 900 °C, and the carbonization time is 4 - 6 h; in step (2), nitrogen is introduced as a protective atmosphere during the high-temperature carbonization process, and the nitrogen flow rate is 30 - 50 mL / min.

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