Application of sludge-based catalyst in phenol degradation

Abstract

The invention discloses an application of a sludge-based catalyst in phenol degradation. The sludge-based catalyst is prepared by the following steps: mixing crushed dry-based sludge with water, reacting at 190-210 DEG C for 20-40 minutes, carrying out solid-liquid separation, drying the solid, and firing the dried material at 700-750 DEG C in a nitrogen atmosphere for 200-250 minutes to obtain sludge carbon; the method comprises the following steps: mixing crushed pyrite slag with a hydrochloric acid solution with the mass concentration of 15-30%, reacting at 60-95 DEG C for 1-4 hours, carrying out solid-liquid separation, and introducing oxygen or air into the liquid to oxidize for 24 hours, so as to prepare an impregnation liquid; adding sludge carbon and oxalic acid into the steeping liquor, stirring and reacting for 4-4.5 hours, carrying out solid-liquid separation, drying a solid, and calcining in a nitrogen atmosphere, according to the method, sewage is purified while sludge is treated, efficient recycling of resources is promoted, and the concept of green and sustainable development is met.

Description

Technical Field

[0001] The present invention relates to the use of a sludge-based catalyst in phenol degradation, belonging to the technical field of solid waste resource utilization. Background Art

[0002] With the advancement of industrialization, municipal sludge, as a by-product of urban sewage treatment, has a huge annual output and complex composition, which can cause harm to the human body and the environment. However, in addition to the pollutants that affect the environment, municipal sludge also contains substances such as proteins, carbohydrates, and lipids, making the sludge have the potential for resource utilization. Moreover, at present, the preparation of biochar from sludge has become a research hotspot.

[0003] Pyrite cinder mainly comes from the roasting process of pyrite extraction. Sulfur dioxide gas will be generated during the roasting of pyrite and is used to manufacture sulfuric acid. The remaining solid residue is pyrite cinder. Pyrite is an important mineral resource and is widely used in fields such as iron and steel, chemical industry, and building materials. A large amount of pyrite cinder will be generated during the mining and processing of pyrite. It not only contains a large amount of sulfur elements, and its main components include iron oxide, silicon dioxide, and oxides of other metal elements. Due to containing certain metal components, pyrite cinder has a certain comprehensive utilization value and can be used for iron extraction, manufacturing building materials, etc. It also contains various metal elements such as copper, iron, and zinc, and has a high comprehensive utilization value.

[0004] Pyrite cinder has significant hazards to the environment and human health. If it is randomly stacked or disposed of, it will not only cause serious pollution to the soil, water source, and air, leading to the acidification of the soil and groundwater and affecting plant growth and the water body ecological environment. At the same time, pyrite cinder contains various valuable metal elements. If not recycled, it will cause waste of resources.

[0005] In recent years, with the increasingly strict environmental protection policies and the continuous improvement of the awareness of comprehensive resource utilization, the treatment and utilization technologies of pyrite cinder have developed rapidly. The main treatment and utilization technologies include ore dressing enrichment technology, acid leaching for impurity removal technology, magnetization treatment, and resource utilization. These technologies have not only improved the resource utilization rate but also realized the resourceization, reduction, and harmless treatment of waste.

[0006] In the past few decades, nanocatalysts have occupied an important position in the field of catalysis. However, there is a major problem in nanocatalysis, which is the low atomic utilization rate, resulting in relatively high catalytic costs (especially for noble metal catalysts). With the development of technology and the improvement of material preparation methods, catalysts have gradually shifted from the nanoscale to the atomic scale. Single-atom catalysts (SACs) have the highest atomic utilization rate and unique electronic structures, showing great promise in realizing the rational utilization of metal resources and improving the economy of catalytic systems. With the development of SACs preparation technology and the in-depth study of catalytic mechanisms, their applications in the field of emerging pollutant treatment have gradually become more diverse.

[0007] Phenol is a toxic and harmful organic compound widely used in industries such as chemical engineering, pharmaceuticals, plastics, and dyes. Once phenol-containing wastewater enters the environment, it will pose a serious threat to the ecosystem and human health. Therefore, the development of efficient and low-cost phenol treatment technologies has become a hot issue in the field of environmental protection. In recent years, the treatment technologies for phenol include: (1) Chemical oxidation method. Although it can degrade phenol completely, with a short residence time and a fast degradation rate, it requires a large amount of oxidants, resulting in high costs and may also generate other pollutants. (2) Adsorption method. Although it is simple to operate and has significant effects, the adsorbent needs to be frequently replaced, leading to relatively high operation costs and difficulties in waste treatment. (3) Biodegradation method. It has good treatment effects, simple equipment, convenient operation, and no secondary pollution. However, it has a long treatment time and relatively high requirements for environmental conditions. (4) Membrane treatment technology. It is efficient, energy-saving, and environmentally friendly, but the cost of membrane materials is relatively high, and they may need to be replaced regularly. (5) Advanced oxidation technology. It has a high degradation efficiency and a wide application range, but the technology is relatively complex and costly. In addition to these technologies for treating phenol in wastewater, there are also many preparation materials for treating phenol, including metal-organic framework materials (MOFs). They have a large specific surface area, adjustable pore structures, and excellent adsorption properties. However, their synthesis is complex, the cost is relatively high, and their adsorption performance is greatly affected by factors such as pH value and temperature. Secondly, tungstate ionic liquids can efficiently degrade high-concentration phenol under mild conditions with simple operations, but their synthesis process is relatively complex and may also cause secondary pollution. There are also heterogeneous Fenton catalysts, which have high catalytic activity, good selectivity, and can be reused, but the preparation and regeneration costs of the catalysts are relatively high. Summary of the Invention

[0008] Aiming at the problems existing in the prior art, the present invention provides a new use of a sludge-based catalyst and its application in phenol degradation. In the present invention, sludge is reacted in a high-pressure reactor and hydrothermal carbon materials are formed by high-temperature calcination. The hydrothermal carbon materials can play an active role in stably loading metal single atoms. Due to their large specific surface area, high porosity and rich organic functional groups, they become a good loading material with stable loading sites. Pyrite slag and hydrochloric acid are mixed and reacted at a certain temperature to prepare an impregnating solution to provide a source of metal single atoms. Sludge carbon and oxalic acid are added to the impregnating solution, stirred and reacted, solid-liquid separated, the solid is dried, and the sludge-based catalyst is obtained by calcination. The metal single atoms are stably loaded on the catalyst carrier of the present invention. When the catalyst is used for degrading phenol, the phenol removal rate is above 85%.

[0009] The specific operation of the method of the present invention is as follows: 1. The sludge-based catalyst is prepared by mixing crushed dry-based sludge with water, reacting at 190 - 210 °C for 20 - 40 min, separating solid and liquid, drying the solid, and calcining the dried product at 700 - 750 °C in a nitrogen atmosphere for 200 - 250 min to obtain sludge carbon; 2. The crushed pyrite slag is mixed with a hydrochloric acid solution with a mass concentration of 15 - 30%, reacted at 60 - 95 °C for 1 - 4 h, separated solid and liquid, and oxygen or air is introduced into the liquid for oxidation for 24 h to obtain an impregnating solution; The mass-volume ratio of the pyrite slag to the hydrochloric acid solution is 1 - 2:3 g:mL 3. Sludge carbon and oxalic acid are added to the impregnating solution, stirred and reacted for 4 - 4.5 h, separated solid and liquid, dried the solid, and calcined in a nitrogen atmosphere to obtain the sludge-based catalyst; The mass-volume ratio of the sludge carbon to the impregnating solution is 1:8 - 11 g:mL, and the mass ratio of the sludge carbon to the oxalic acid is 1:3 - 5; the calcination temperature is 500 - 600 °C.

[0010] Advantages and technical effects of the present invention: 1. In the present invention, sludge is prepared into biochar by the subcritical hydrothermal method, which realizes the low-cost treatment of sludge while preparing a carrier with stable and complete adsorption sites. Compared with the method of preparing biochar by pyrolysis, the subcritical hydrothermal method does not need to be carried out under anaerobic or anoxic conditions and the reaction temperature does not need to be very high. At the same time, this method has low energy consumption, high efficiency, low cost and will not cause secondary pollution to the environment. At the same time, using pyrite slag as the raw material to prepare the experimental materials we need can better realize the resource utilization of solid waste and relieve the pressure of environmental pollution; 2. The catalyst of the present invention, in which active metal single atoms are loaded on the surface of the carrier, is used to treat organic pollutants in sewage. Compared with traditional nanoparticle catalysts, single-atom catalysts have a higher surface atom utilization rate, and each atom is an independent active center that can provide higher selectivity. It also has high stability, and the interaction between single atoms and the carrier is strong, which helps to prevent the aggregation or inactivation of the catalyst. Single-atom catalysts have high efficiency, selectivity, stability, and controllability. At the same time, the present invention uses solid waste to prepare a carrier to load a single-atom catalyst for treating organic pollutants, which reflects the utilization value of solid waste, promotes the concept of circular economy, and promotes the efficient recycling of resources, meeting the concept of green and sustainable development; 3. The present invention prepares sludge into biochar to load a single-atom catalyst for treating organic pollutants in sewage. Compared with traditional sludge disposal technologies, it has higher environmental and economic benefits. Solid waste can be made into environmentally friendly materials, effectively reducing the sludge storage volume and improving the treatment and utilization rate of sludge. Secondly, the prepared product can load a single-atom catalyst to treat sewage, purifying the sewage while treating the sludge, promoting the efficient recycling of resources, and meeting the concept of green and sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is the N2 adsorption - desorption diagram of the sludge-based catalyst; Figure 2 It is the pore size distribution diagram of the sludge-based catalyst; Figure 3 It is the XRD diagram of the sludge-based catalyst. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0012] The present invention will be further described in detail below with reference to the embodiments. However, the protection scope of the present invention is not limited to the content described. The methods used in this embodiment are all conventional methods unless otherwise specified, and the reagents used are all conventional reagents unless otherwise specified; Example 1: Preparation and Application of Sludge-based Catalyst (1) Dry and crush municipal sludge, pass it through a 100-mesh sieve to obtain sludge powder. Mix the sludge powder and water in a mass ratio of 1:10, put it into a high-pressure reactor, react at 200°C for 30 minutes, filter, and after drying the solid, put it into a tubular furnace and heat it to 700°C at a heating rate of 10°C / min, and keep it calcined in a nitrogen atmosphere for 4 hours to obtain sludge-based biochar; (2) Dry pyrite cinder, crush and screen it to a particle size of 80 µm. Mix pyrite cinder with a 20% hydrochloric acid solution in a mass-to-volume ratio of g:mL of 1:3, react at 65°C for 4 hours, filter to obtain the leaching solution, and pass air through the leaching solution to oxidize for 24 hours to prepare an impregnating solution; (3) Add the sludge-based biochar and oxalic acid to the impregnating solution at a mass-to-volume ratio of the sludge-based biochar to the impregnating solution of g:mL = 1:8 and a mass ratio of the sludge carbon to oxalic acid of 1:3.6. Stir and react for 4 h, filter, dry the solid at 60 °C, then place it in a tubular furnace and heat it to 550 °C at a heating rate of 5 °C / min, and keep it at this temperature for 4 h in a nitrogen atmosphere to obtain the sludge-based catalyst. (4) Weigh 30 mg of the sludge-based catalyst and add it to 15 mL of a water sample containing 23.45 mg / L of phenol. Treat it at different temperatures for 4 h, detect the phenol content in the water sample, and calculate the phenol removal rate. The results are shown in Table 1. Table 1

[0013] As can be seen from the table, the catalyst of the present invention can obtain a degradation rate of about 90% when treating phenol at room temperature.

[0014] Example 2: Preparation and application of the sludge-based catalyst (1) Dry and crush the municipal sludge, sieve it through a 100-mesh sieve to obtain sludge powder. Mix the sludge powder and water at a mass ratio of 1:10, put it into a high-pressure reactor, react at 200 °C for 30 min, filter, dry the solid, then place it in a tubular furnace and heat it to 700 °C at a heating rate of 10 °C / min, and keep it calcined for 4 h in a nitrogen atmosphere to obtain the sludge-based biochar. (2) Dry the sulfuric acid slag, crush and screen it to a particle size of 80 µm. Mix the pyrite slag and a 20% hydrochloric acid solution at a mass-to-volume ratio of g:mL = 1:3. React at 65 °C for 4 h, then filter to obtain the leaching solution, and pass air through the leaching solution for oxidation for 24 h to prepare the impregnating solution. (3) Add the sludge-based biochar and oxalic acid to the impregnating solution at a mass-to-volume ratio of the sludge-based biochar to the impregnating solution of g:mL = 1:10 and a mass ratio of the sludge carbon to oxalic acid of 1:3.6. Stir and react for 4 h, filter, dry the solid at 60 °C, then place it in a tubular furnace and heat it to 550 °C at a heating rate of 5 °C / min, and keep it at this temperature for 4 h in a nitrogen atmosphere to obtain the sludge-based catalyst. (4) Weigh 30 mg of the sludge-based metal single-atom catalyst and add it to 15 mL of a water sample containing 23.45 mg / L of phenol. Treat it at different pH values for 4 h, detect the phenol content in the water sample, and calculate the phenol removal rate. The results are shown in Table 2. Table 2

[0015] As can be seen from the table, the catalyst of the present invention can obtain better degradation efficiency under the conditions of pH 6 - 8.

[0016] Example 3: Preparation and Application of Sludge-based Catalyst (1) Dry and crush municipal sludge, pass it through a 100-mesh sieve to obtain sludge powder. Mix the sludge powder and water at a mass ratio of 1:10, put them into a high-pressure reactor, react at 200 °C for 30 min, filter, dry the solid, and then put it into a tube furnace and heat it to 700 °C at a heating rate of 10 °C / min, and keep it calcined in a nitrogen atmosphere for 4 h to obtain sludge-based biochar; (2) Dry the sulfuric acid slag, crush and screen it to a particle size of 80 µm. Mix the pyrite slag and 20% hydrochloric acid solution at a mass-to-volume ratio of g:mL of 1:2.5. React the pyrite slag with the hydrochloric acid solution at 65 °C for 2 h, then filter to obtain the leaching solution, and pass air through the leaching solution for oxidation for 24 h to prepare the impregnation solution; (3) Add the sludge-based biochar and oxalic acid to the impregnation solution at a mass-to-volume ratio of g:mL of 1:10 for the sludge-based biochar and the impregnation solution and a mass ratio of 1:4.75 for the sludge carbon and oxalic acid. Stir and react for 4 h, filter, dry the solid at 60 °C, and then put it into a tube furnace and heat it to 500 °C at a heating rate of 5 °C / min, and keep it in a nitrogen atmosphere for 4 h to prepare the sludge-based catalyst; The N2 adsorption-desorption diagram of the catalyst is shown in Figure 1 , from which it can be calculated that the BET average pore diameter of the sludge-based catalyst is 8.67 nm and the specific surface area is 153.9428 m2 / g; The single-atom catalyst is analyzed by X-ray diffraction, indicating that the catalyst of the present invention has a relatively high specific surface area, good catalytic activity, can provide more active sites for catalytic reactions, and at the same time the catalyst is a mesoporous structure, which is conducive to the diffusion of reactant phenol and degradation products, reduces internal diffusion limitations, improves reaction efficiency, also has good adsorption capacity, can accommodate a large number of molecular active sites, and at the same time the catalyst has a large surface area, contains more active sites, has higher catalytic activity, has a relatively uniform pore structure and a high porosity. The pore size distribution diagram is shown in Figure 2 , from which it can be seen that the pore size of the catalyst is concentrated in the range of 2-50 nm, indicating that the catalyst has a mesoporous structure and excellent physical and chemical properties. The mesoporous structure has a relatively large specific surface area, provides more active sites for catalytic reactions, improves catalytic efficiency, the mesoporous structure is conducive to the diffusion of reactant phenol and degradation products, can reduce diffusion limitations, improve reaction rate, and the mesoporous structure can also improve the thermal stability and mechanical stability of the catalyst, and extend the service life of the catalyst; The XRD of the catalyst Figure 3It can be seen that when 2T = 26.635, the prepared catalyst has the most obvious characteristic peaks, indicating that there is a main metal single-atom crystal phase in the catalyst, and the crystallinity of this metal single atom is relatively high. High crystallinity can enhance the activity and stability of the catalyst, ensuring the efficiency of the catalyst. At the same time, it also shows that the purity of the main metal single-atom crystal phase in the catalyst is relatively high, which can improve the selectivity of the target product. Catalysts with high crystallinity usually have better structural stability and can maintain their activity during the reaction process. Therefore, it can be seen that the catalyst of this invention has high crystallinity and purity, and thus has high activity and stability.

[0017] (4)Weigh 30 mg of the sludge-based catalyst and add it to a 15 mL water sample containing 23.45 mg / L of phenol. Treat it at the optimal temperature and pH for 4 h, detect the phenol content in the water sample, and calculate the phenol removal rate. The removal rate is 96.35%.

[0018] Example 4: Preparation and application of the sludge-based catalyst (1)Dry and crush the municipal sludge, pass it through a 100-mesh sieve to obtain sludge powder. Mix the sludge powder and water at a mass ratio of 1:10, put it into a high-pressure reactor, react at 210 °C for 25 min, filter, dry the solid, then put it into a tube furnace and heat it to 750 °C at a heating rate of 10 °C / min, and keep it calcined in a nitrogen atmosphere for 200 min to obtain the sludge-based biochar; (2)Dry the sulfuric acid slag, crush and screen it to a particle size of 80 µm. Mix the pyrite slag and the hydrochloric acid solution at a mass-to-volume ratio of g:mL of 2:3, mix the pyrite slag with a 30% mass concentration hydrochloric acid solution, react at 90 °C for 1 h, then filter to obtain the leaching solution, and pass air through the leaching solution to oxidize for 24 h to prepare the impregnating solution; (3)Mix the sludge-based biochar and oxalic acid into the impregnating solution at a mass-to-volume ratio of g:mL of 1:11 and a mass ratio of sludge carbon to oxalic acid of 1:5, stir and react for 4 h, filter, dry the solid at 60 °C, then put it into a tube furnace and heat it to 600 °C at a heating rate of 5 °C / min, and keep it in a nitrogen atmosphere for 4 h to obtain the sludge-based catalyst; (4)Weigh 30 mg of the sludge-based catalyst and add it to a 15 mL water sample containing 23.45 mg / L of phenol. Treat it at the optimal temperature and pH value for 4 h, detect the phenol content in the water sample, and calculate the phenol removal rate. The removal rate is 95.4%.

Claims

1. Application of a sludge-based catalyst in phenol degradation; The sludge-based catalyst is prepared by mixing crushed dry sludge with water, reacting at 190-210° C. for 20-40 minutes, separating the solid from the liquid, drying the solid, and calcining the dried product at 700-750° C. in a nitrogen atmosphere for 200-250 minutes to obtain sludge charcoal; The crushed pyrite slag is mixed with a hydrochloric acid solution with a mass concentration of 15-30%, reacted at 60-95°C for 1-4 hours, solid-liquid separation, oxygen or air is introduced into the liquid for oxidation for 24 hours, and an impregnation solution is obtained; Sludge charcoal and oxalic acid were added to the impregnation solution, stirred for reaction for 4-4.5 hours, solid-liquid separation, solid drying, and calcination under nitrogen atmosphere to obtain the sludge-based catalyst.

2. The use according to claim 1, characterized in that: The mass volume ratio of pyrite slag and hydrochloric acid solution is 1~2:3 in g:mL.

3. The use according to claim 1, characterized in that: The mass volume ratio of sludge charcoal to impregnation solution (g:mL) is 1:8~11, and the mass ratio of sludge charcoal to oxalic acid is 1:3~5.

4. The use according to claim 1, characterized in that: The calcination temperature is 500~600℃.

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