A nitrogen-doped sludge-based carbon catalytic material, its preparation method and application

Abstract

The present invention discloses a nitrogen-doped sludge-based catalytic material, its preparation method and application, which includes grinding and sieving the dried sludge to obtain the first sludge powder; soaking the first sludge powder in a dilute acid solution for sufficient reaction, filtering and separating the mixture to obtain the filtered sludge and the first filtrate; adding an oxalic acid solution to the first filtrate, filtering after sufficient reaction to obtain the second filtrate; mixing the second filtrate and the filtered sludge, and the product after the reaction is successively washed, dehydrated, dried, ground and sieved to obtain the second sludge powder; finally, mixing the second sludge powder with melamine and pyrolyzing it under an inert atmosphere, and obtaining the nitrogen-doped sludge-based catalytic material after cooling. The present invention obtains an environmentally friendly material prepared from sludge, which has remarkable catalytic effect and excellent stability in the process of organic wastewater treatment, and has great application potential in the fields of sewage treatment and resource recovery.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment and resource utilization, and particularly relates to a nitrogen-doped sludge-based catalytic material, a preparation method thereof, and an application thereof. Background Art

[0002] Excess sludge, which is often regarded as waste, has attracted attention in the field of catalytic applications due to its rich resources. Excess sludge is one of the main by-products of sewage treatment, which is rich in non-metallic and metallic elements such as carbon, nitrogen, oxygen, and iron. Currently, the mainstream sludge resource utilization technologies include using sludge as building materials after drying and pressing, etc. There are problems such as high treatment costs but low benefits, complex treatment processes, and small treatment volumes in sludge pyrolysis to produce bio-oil and sludge to produce adsorption materials. There is still a lack of high-value recovery paths for sludge, and it is an urgent problem to develop methods for safe disposal of sludge and realize high-value resource utilization.

[0003] Using excess sludge as an effective precursor to prepare heteroatom-doped porous carbon materials is a very promising sludge resource utilization approach. Sludge carbon has been used as a catalyst in different systems such as photocatalysis, ozonation, hydrogen peroxide oxidation, and sulfate peroxide oxidation to remove organic pollutants. The removal mechanism is mainly physical and chemical adsorption and hydroxyl radical oxidation. Although using sludge as a raw material to prepare biochar has the advantage of waste utilization, sludge carbon still has problems such as small specific surface area, low heteroatom doping amount, and low catalytic performance. Therefore, it is urgent to develop heteroatom-doped sludge carbon catalysts with high activity, high performance, and good stability to promote the development of high-value resource recovery of sludge and the degradation technology of organic pollutants in water. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects in the prior art and provide a nitrogen-doped sludge-based catalytic material, a preparation method thereof, and an application thereof. The nitrogen-doped sludge-based catalytic material obtained by the preparation method of the present invention has a high nitrogen doping amount, rich pores and non-metallic catalytic sites, and metal catalytic sites that are not agglomerated but uniformly dispersed, showing characteristics such as high catalytic activity, wide pH response range, high stability, and low metal leaching risk in actual organic wastewater treatment.

[0005] The specific technical solutions adopted by the present invention are as follows:

[0006] In the first aspect, the present invention provides a preparation method of a nitrogen-doped sludge-based catalytic material, specifically as follows:

[0007] S1: Grind and screen the dried sludge to obtain a first sludge powder. Immerse the first sludge powder in a dilute acid solution and shake it at room temperature to make it react fully. Filter and separate the mixture of the first sludge powder and the dilute acid solution to obtain the filtered sludge and the first filtrate.

[0008] S2: Add an oxalic acid solution to the first filtrate, stir well for reaction to produce calcium oxalate precipitate, and obtain a second filtrate after filtration.

[0009] S3: Mix the second filtrate with the filtered sludge, oscillate at room temperature to make them react fully, and after the obtained product is successively washed, dehydrated, dried, and ground and sieved, obtain a second sludge powder.

[0010] S4: Mix the second sludge powder with melamine and pyrolyze it under an inert atmosphere, and obtain a nitrogen-doped sludge carbon-based catalytic material after cooling.

[0011] Preferably, the temperature of the drying treatment in S1 is 60 - 85 °C, and the time is 15 - 30 h. The mesh number of the grinding and sieving is 100 - 200 meshes.

[0012] Preferably, the above-mentioned dilute acid solution is a dilute hydrochloric acid solution with a concentration of 0.5 - 2 M, and the mixing solid-liquid ratio of the first sludge powder to the dilute acid solution is 1:(4 - 20).

[0013] Preferably, the oscillation time of the dilute acid solution and the first sludge powder in S1 is 24 - 36 h, and the oscillation rate is 150 - 300 rpm. The oscillation time of the second filtrate and the filtered sludge in S3 is 24 - 36 h, and the oscillation rate is 150 - 300 rpm.

[0014] Preferably, the concentration of the above-mentioned oxalic acid solution is 50 - 200 g / L, and the reaction time of the first filtrate and the oxalic acid solution in S2 is 2 - 5 min.

[0015] Preferably, centrifugal dehydration is used for dehydration in S3, the centrifugal speed is 3000 - 8000 r / min, and the centrifugal time is 2 - 10 min. The temperature of drying in S3 is 60 - 85 °C, and the drying time is 15 - 30 h.

[0016] Preferably, the mixing mass ratio of the above-mentioned second sludge powder and melamine is 1:(0.5 - 5).

[0017] Preferably, the above-mentioned pyrolysis temperature is 800 - 1000 °C, the heating rate is 5 - 15 °C / min, and the pyrolysis time is 2 - 5 h.

[0018] In a second aspect, the present invention provides a nitrogen-doped sludge carbon-based catalytic material prepared by the preparation method described in the first aspect.

[0019] In a third aspect, the present invention provides an application of the nitrogen-doped sludge carbon-based catalytic material described in the second aspect in treating organic wastewater.

[0020] The present invention has the following beneficial effects compared with the prior art:

[0021] The present invention provides a method for preparing a nitrogen-doped sludge carbon-based catalytic material. The method comprises the following steps: pre-treating the sludge with a dilute acid solution to dissolve metals and calcium elements in the sludge, thereby generating vacant sites in the sludge, which is beneficial for subsequent doping with nitrogen elements; reacting an acid filtrate (a first filtrate) with an oxalic acid solution and then filtering the sludge, thereby removing the calcium elements in the acid filtrate while retaining the metal elements in the acid filtrate; then mixing the acid filtrate (a second filtrate) from which the calcium elements have been removed with the filtered sludge, thereby allowing the metal elements to adhere to the sludge surface again, thereby facilitating the formation of metal catalytic sites in subsequent sludge carbon products. Oxalic acid can also introduce more oxygen-containing catalytic sites into the sludge carbon; and co-pyrolysis with melamine results in a high nitrogen doping level in the sludge carbon product, while fixing the metal elements to prevent them from agglomerating at high temperatures.

[0022] The nitrogen-doped sludge carbon-based catalytic material prepared by the method of the present invention can significantly improve the catalytic degradation performance of organic matter in organic wastewater, and has a wide pH response range, high stability and low heavy metal dissolution risk, and has great application potential in the field of wastewater treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The figure shows the removal effect of the nitrogen-doped sludge carbon-based catalytic material on perfluorooctanoic acid prepared in the embodiment of the present invention;

[0024] Figure 2 The figure shows the removal effect of perfluorooctanoic acid by the nitrogen-doped sludge carbon-based catalytic material prepared in the examples of the present invention under different pH conditions. DETAILED DESCRIPTION

[0025] The present invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention may be combined accordingly, provided that there is no conflict between them.

[0026] Example

[0027] This example uses dried municipal sludge from a sewage treatment plant in Hangzhou as raw material. The specific method for preparing nitrogen self-doped sludge carbon-based catalytic material is as follows:

[0028] Step 1: Dry the raw sludge at 60° C. for 20 h to complete the drying treatment, grind it through a 200-mesh sieve, and obtain the first sludge powder.

[0029] Step 2: Soak the first sludge powder obtained in step 1 in a dilute hydrochloric acid solution with a concentration of 1 M at a solid-liquid ratio of 1:5, and oscillate at room temperature for 24 hours to allow it to fully react at an oscillation rate of 180 rpm; filter and separate the mixture of the first sludge powder and the dilute hydrochloric acid solution to obtain filtered sludge and a first filtrate.

[0030] Step 3: Add oxalic acid solution with a concentration of 100 g / L to the first filtrate obtained in Step 2, stir and react for 3 min to make it fully react, generating white calcium oxalate precipitate; after filtration, a second filtrate is obtained.

[0031] Step 4: Mix the second filtrate obtained in Step 3 with the filtered sludge obtained in Step 2, oscillate at room temperature for 24 h to make it fully react, and the oscillation rate is 180 rpm.

[0032] Step 5: Rinse the product after being treated in Step 4, then centrifuge for dehydration, the centrifuge rate is 8000 r / min, the centrifuge time is 5 min, then dry at 60 °C for 20 h, and finally grind through a 200-mesh sieve to obtain the second sludge powder.

[0033] Step 6: Mix the second sludge powder obtained in Step 5 with melamine at a mass ratio of 1:3, pyrolyze at 800 °C for 2 h under a nitrogen atmosphere, the initial heating rate is 5 °C / min, and after the reaction, it is naturally cooled to room temperature to obtain a nitrogen-doped sludge carbon-based catalytic material.

[0034] The specific surface area of the finally obtained nitrogen-doped sludge carbon-based catalytic material prepared in this example is 79.5 m 2 / g, the pore volume is 0.29 cm 3 / g, the nitrogen doping amount is 21.3 at%, the oxygen doping amount is 9.3 at%, and the iron loading amount is 1.2 at%. This shows that the prepared sludge carbon has successfully achieved high nitrogen and oxygen loading and relatively rich pores, and metallic iron is also stably and evenly dispersed on the surface of the sludge carbon.

[0035] In order to further verify the catalytic degradation effect of the nitrogen-doped sludge carbon-based catalytic material prepared in this example on organic matter in wastewater, the nitrogen-doped sludge carbon-based catalytic material is added to the activated persulfate system. The dosage of the nitrogen-doped sludge carbon-based catalytic material is 1 g / L, the initial concentration of persulfate is 5 mM, and the initial concentration of the refractory organic pollutant perfluorooctanoic acid is 2 mg / L. The reaction is carried out for 60 min in a system with an initial pH of 6.5.

[0036] The results are as Figure 1 shown. As can be seen from Figure 1 , the degradation rate of perfluorooctanoic acid after 60 min of reaction is as high as 99.9%, and the degradation rate still reaches 94.2% after 4 cycles of operation, proving that the nitrogen-doped sludge carbon-based catalytic material has high catalytic performance and stability.

[0037] In addition, in the range of pH = 3 - 9, the degradation rate of perfluorooctanoic acid after 60 min is above 96%, as shown in Figure 2As shown. It can be seen that the nitrogen-doped sludge-based catalytic material synthesized by the present invention has a wide pH adaptation range and can maintain a relatively stable catalytic degradation efficiency of organic matter under different pH conditions. At the same time, after operation under different pH conditions, no heavy metals are leached out as detected by ICP-MS.

[0038] In the present invention, the dried sludge is crushed and ground, the metals and calcium elements in the sludge powder are leached out by using a dilute acid solution, the calcium elements in the leaching solution are removed by using an oxalic acid solution, the leaching solution is remixed with the sludge, and then the sludge is washed, dried, ground and mixed with melamine, and pyrolyzed to obtain nitrogen-doped sludge carbon.

[0039] The pretreatment step of the present invention creates vacant sites in the sludge, which is conducive to achieving a high nitrogen doping amount in the subsequent pyrolysis process; more oxygen-containing catalytic sites are introduced into the sludge carbon by using oxalic acid; at the same time, the metals are stably and uniformly dispersed on the surface of the sludge-based carrier. The nitrogen-doped sludge-based material prepared by the present invention is a green and environment-friendly material, which has a significant catalytic effect and excellent stability in the process of organic wastewater treatment, and has great application potential in the fields of sewage treatment and resource recovery, providing a new solution for achieving the sustainable development goal.

[0040] The above-described embodiments are only a preferred solution of the present invention, but they are not intended to limit the present invention. Those of ordinary skill in the relevant technical fields can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all technical solutions obtained by adopting equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A preparation method of a nitrogen-doped sludge-based catalytic material, characterized in that, The details are as follows: S1: Grinding and sieving the dried sludge to obtain a first sludge powder; soaking the first sludge powder in a dilute acid solution and shaking at room temperature to allow it to fully react; filtering and separating the mixture of the first sludge powder and the dilute acid solution to obtain filtered sludge and a first filtrate; S2: adding oxalic acid solution to the first filtrate, stirring thoroughly to react to produce calcium oxalate precipitate, and filtering to obtain a second filtrate; S3: mixing the second filtrate with the filtered sludge, shaking at room temperature to allow them to fully react, and washing, dehydrating, drying, grinding and sieving the obtained product in sequence to obtain a second sludge powder; S4: mixing the second sludge powder with melamine and pyrolyzing the mixture under an inert atmosphere, and obtaining a nitrogen-doped sludge carbon-based catalytic material after cooling.

2. The preparation method according to claim 1, characterized in that, The drying treatment in S1 is carried out at a temperature of 60 to 85° C. for 15 to 30 hours; and the grinding and sieving process has a mesh size of 100 to 200 meshes.

3. The preparation method according to claim 1, characterized in that, The dilute acid solution is a dilute hydrochloric acid solution with a concentration of 0.5 to 2 M, and the solid-liquid ratio of the first sludge powder to the dilute acid solution is 1:(4 to 20).

4. The preparation method according to claim 1, wherein The oscillation time of the dilute acid solution and the first sludge powder in S1 is 24 to 36 hours, and the oscillation rate is 150 to 300 rpm; the oscillation time of the second filtrate and the filtered sludge in S3 is 24 to 36 hours, and the oscillation rate is 150 to 300 rpm.

5. The preparation method according to claim 1, wherein The concentration of the oxalic acid solution is 50-200 g / L, and the reaction time of the first filtrate and the oxalic acid solution in S2 is 2-5 minutes.

6. The preparation method according to claim 1, wherein The dehydration in S3 is performed by centrifugal dehydration, the centrifugal speed is 3000-8000 r / min, and the centrifugal time is 2-10 min; the drying temperature in S3 is 60-85° C., and the drying time is 15-30 h.

7. The preparation method according to claim 1, characterized in that, The mixing mass ratio of the second sludge powder to melamine is 1:(0.5-5).

8. The preparation method according to claim 1, wherein, The pyrolysis temperature is 800-1000° C., the heating rate is 5-15° C. / min, and the pyrolysis time is 2-5 hours.

9. A nitrogen-doped sludge carbon-based catalytic material prepared according to the preparation method according to any one of claims 1 to 8.

10. Use of the nitrogen-doped sludge carbon-based catalytic material according to claim 9 in treating organic wastewater.

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