Carbon-based confinement type catalyst as well as preparation method and application thereof

Abstract

The invention discloses a carbon-based confinement type catalyst as well as a preparation method and application thereof. The catalyst comprises a sludge carbon substrate, and carbon nanotubes and active metals covering the surface of the substrate, the active metal comprises Fe and Ni; ni is doped in the carbon nanotube to form a confinement structure; fe is loaded outside the carbon nanotubes. The active metal of the carbon-based confinement type catalyst is confined in a superstructure carbon nanostructure covering the surface of a carbon substrate, so that the hydrothermal oxidation efficiency can be effectively improved, the degree of cracking of sludge extracellular polymeric substances is improved, deep cracking of sludge is realized, and the risk of secondary pollution caused by loss of the active metal is reduced; the catalyst can selectively oxidize macromolecular organic matters released by sludge disintegration, the product selectivity of micromolecular carboxylic acid is improved to be higher than 95% by a confinement structure, the micromolecular carboxylic acid can be further utilized as a carbon source, the treated supernate can be used as a composite carbon source to be applied to the biochemical process of sewage treatment, and resource utilization is realized; the catalyst can realize HTO treatment of sludge at 200 DEG C or below, and does not generate biotoxic by-products in the sludge treatment process, and the treated product can be used as a high-quality carbon source.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of hydrothermal oxidation sludge treatment catalysts, and in particular to a carbon-based confined catalyst and a preparation method and application thereof. Background Art

[0002] The activated sludge method is mainly used in the biological treatment of urban sewage in my country. The mechanism of activated sludge treatment of sewage is as follows: in the sewage treatment process, the bacterial flocs oxidize and decompose various organic matter in the wastewater into carbon dioxide and water, and generate flocs at the same time. At this time, the microbial group of activated sludge is formed. The activated sludge absorbs some pollutants in the sewage and flocculates and settles, producing a large amount of residual sludge.

[0003] Sludge is mainly composed of sludge flocs and water. Sludge flocs are mainly composed of two parts: cell bodies and extracellular polymers. Extracellular polymers are mainly composed of proteins and polysaccharides. Polysaccharide molecules are rich in hydrophilic functional groups such as hydroxyl and carboxyl groups. They can form a stable and elastic network structure through adsorption and bridging, and cross-linking and fixing free cells is beneficial to sludge flocculation. Proteins and lipids can maintain the stability of the floc structure and improve the biological flocculation of sludge accordingly. Polysaccharide molecules, proteins and lipids form a compact and dense network structure through electrostatic forces, hydrogen bonding, ion attraction, biochemistry and other effects, which can serve as a protective layer for microorganisms to resist the invasion of adverse factors such as external heavy metals and toxic compounds. Therefore, the presence of extracellular polymers is also the main reason for the difficulty in sludge degradation. At the same time, the various forces inside / between extracellular polymers make the water in the sludge tightly bound inside / between the sludge flocs through adsorption or chemical bonds, which ultimately leads to a high moisture content in the sludge and is not easy to dehydrate.

[0004] Traditional sludge treatment technologies include anaerobic digestion, dehydration, landfill, incineration, etc. However, traditional sludge treatment technologies have fatal problems such as high cost and secondary pollution, and cannot realize the resource utilization of sludge.

[0005] Hydrothermal Oxidation (HTO) is widely used in the field of organic wastewater and solid waste treatment due to its green and efficient advantages. The reaction with an oxidant in an aqueous solution under high temperature and high pressure conditions in a closed system is a hydrothermal oxidation reaction. Hydrothermal oxidation conditions can effectively release the water component in the sludge, and at the same time break the cell structure in the sludge, thereby releasing the organic matter in it and dissolving it in the liquid phase, thereby achieving sludge stabilization, harmlessness and reduction. In addition, the released organic matter is dissolved in the supernatant, and a large amount of soluble organic matter is oxidized and degraded into volatile fatty acids VFAs and other organic matter such as carbohydrates and proteins under oxygen-rich conditions, which can be used as substrates for the metabolism of various microorganisms. It is a high-quality carbon source and realizes resource utilization. However, the existing HTO technology cannot effectively degrade the extracellular polymers of the sludge, resulting in a low degree of degradation of the extracellular polymers of the sludge, and thus cannot achieve deep decomposition of the sludge, resulting in a high content of organic matter in the treated sludge and incomplete carbon source recovery. Summary of the invention

[0006] The present invention provides a carbon-based confined catalyst and a preparation method and application thereof to solve the above problems.

[0007] In order to achieve the above object, the technical solution of the present invention is:

[0008] A carbon-based confined catalyst, comprising a sludge carbon substrate and carbon nanotubes and active metals covering the surface of the substrate;

[0009] The active metal includes Fe and Ni, wherein Ni is doped inside the carbon nanotube to form a confined structure; and Fe is loaded outside the carbon nanotube.

[0010] Furthermore, the Ni doping amount is 5-25wt%, and the Fe loading amount is 0.5-2.5wt%.

[0011] Another aspect of the present invention provides a method for preparing the carbon-based confined catalyst, comprising the following steps:

[0012] S1: After drying the sludge, the sludge residue is obtained, and the sludge residue is ground and mixed evenly with solid alkali KOH at a mass ratio of 20:1, and then roasted to obtain sludge charcoal;

[0013] S2: The sludge carbon prepared in S1 is placed in a solution containing active metal salts for vacuum impregnation, and then vacuum dried to obtain a dry sample; the calcined sample obtained by high-temperature calcination of the dry sample is placed in a 2 mol / L sulfuric acid solution and stirred at 80°C for 3 to 6 hours, and then rinsed, dried, and pressed to obtain a carbon-based confined HTO catalyst.

[0014] Furthermore, in S1, the calcination conditions are: calcination at 400-500° C. for 2-3 h in an inert atmosphere.

[0015] Furthermore, in S2, the active metal salt includes metal Ni salt and metal Fe salt.

[0016] Furthermore, in S2, the mass ratio of sludge carbon, metal Ni salt and metal Fe salt is 1:0.05-0.25:0.005-0.025; the volume ratio of the mass of sludge carbon to the solution containing active metal salt is 200g:1L.

[0017] Further, in S2, the immersion conditions are: vacuum degree 0.08 MPa, stirring at room temperature for 24 hours;

[0018] The vacuum drying conditions are: vacuum drying at 0.08 MPa and 80°C for 24 hours;

[0019] The high temperature calcination conditions are as follows: calcining the dried sample at 400-500° C. for 2-3 hours in a nitrogen atmosphere, and then calcining at 600-800° C. for another 2-3 hours to obtain a calcined sample.

[0020] In another aspect, the present invention provides the use of a carbon-based confined catalyst described in the above technical solution or a carbon-based confined catalyst prepared by the preparation method described in the above technical solution in treating excess sludge to produce carboxylic acid carbon sources.

[0021] Furthermore, the application is carried out in a device for hydrothermal oxidation of excess sludge, the device for hydrothermal oxidation of excess sludge comprising a raw sludge transmission system, a reaction tower, a heat exchange unit and a solid-liquid separation unit connected in sequence; the reaction tower is also connected to a heat supply unit and an air delivery unit, and the heat exchange unit is connected to the heat supply unit;

[0022] The process steps of the application are as follows:

[0023] Firstly, the residual sludge is transported to the reaction tower by the raw sludge transmission system, and then the carbon-based confined catalyst is added into the reaction tower, an oxidant is introduced into the reaction tower through an air delivery unit, and the reaction tower is heated by a heat supply unit. The carbon-coated dual-active site nitrogen-doped carbon-based catalyst undergoes a hydrothermal oxidation reaction with the residual sludge, and the residual sludge is broken down to generate a carboxylic acid carbon source. The solid-liquid mixture formed after the hydrothermal oxidation reaction is cooled by a heat exchange unit. After cooling, the solid-liquid mixture enters a solid-liquid separation unit for solid-liquid separation, and the separated supernatant and filter cake resources are collected respectively.

[0024] Furthermore, the conditions of the hydrothermal oxidation reaction are: reaction pressure 1.0-5.0 MPa, reaction temperature 140-200°C, volume space velocity 0.5-2.0 h -1 , the oxidant is oxygen in the air.

[0025] The beneficial effects of the present invention are:

[0026] (1) The carbon-based confined catalyst disclosed in the present invention, in which the active metal is confined in the superstructured carbon nanostructure covered on the surface of the carbon substrate, can effectively improve the efficiency of hydrothermal oxidation and at the same time improve the degree of decomposition of extracellular polymers in sludge, so that more organic matter in the sludge enters the sludge liquid phase, thereby improving the efficiency and degree of sludge decomposition and achieving deep decomposition of sludge;

[0027] (2) The confined structure in the catalyst can solve the problems of carbon deposition, agglomeration of active components and loss of active metals during the catalytic process, effectively improve the stability of the catalyst, extend the service life of the catalyst, and reduce the risk of secondary pollution caused by the loss of active metals;

[0028] (3) The catalyst can selectively oxidize the macromolecular organic matter released by sludge decomposition. The confined structure can increase the product selectivity of small molecular carboxylic acids to more than 95%, which is conducive to the further use of the product as a carbon source. The treated supernatant can be used as a composite carbon source in the biochemical process of sewage treatment to achieve resource utilization;

[0029] (4) The catalyst does not use precious metals, is a magnetic catalyst, and uses sludge carbon as a base. While satisfying the resource utilization of sludge, the used catalyst can be effectively recovered through magnetic field treatment and regenerated and recycled, which can greatly save economic costs;

[0030] (5) The catalyst can achieve sludge HTO treatment at temperatures below 200°C, and will not produce biologically toxic byproducts during the sludge treatment process. The treated product can be used as a high-quality carbon source;

[0031] (6) The catalyst promotes the decomposition of sludge and can effectively improve the dewatering performance of sludge. The moisture content of the mud cake after treatment is less than 35%, and can reach a minimum of less than 30%. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 A schematic diagram of the structure of a device for treating excess sludge using the catalyst prepared by the present invention;

[0034] Figure 2 It is a structural schematic diagram of a small test device used when treating excess sludge using the catalyst prepared in an embodiment of the present invention.

[0035] In the figure:

[0036] 1. Heat supply unit; 2. Reaction tower; 3. Heat exchange unit; 4. Solid-liquid separation unit; 5. Carbon source conveying pipeline; 6. Mud cake transfer vehicle; 7. Air pipeline; 8. Raw sludge transmission pipeline; 9. Cold water pipeline; 10. Heat circulation pipeline; 11. Heating furnace; 12. Reactor; 13. Heat exchanger; 14. Sample storage tank; 15. Air conveying pipeline; 16. Air pressure valve; 17. Gas flow meter; 18. Temperature measuring device; 19. Sampling pipeline; 20. Exhaust pipeline; 21. Vent pipeline; 22. Electronic scale. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The principle of the catalyst treatment of sludge in the present invention is:

[0039] The catalyst prepared by the present invention is a superstructure confined HTO catalyst (the surface of the carbon substrate is covered with a large number of coral-like carbon nanotubes, Ni is doped inside the carbon nanotubes, and the outside of the carbon nanotubes is Fe particles), in which the active metal Fe is confined in the carbon nanostructure formed by the active metal Ni, and hydroxyl radicals are generated by electron transfer from the active metal to the oxide (oxygen) during the HTO process, and the released organic matter is selectively degraded into small molecule carboxylic acids through the confined structure, which is conducive to further utilization as a carbon source.

[0040] Embodiment 1:

[0041] A method for preparing a carbon-based confined catalyst Fe (0.5%) Ni (5%) @ sewage sludge comprises the following steps:

[0042] S1: 200 g of sludge residue was obtained by drying the sludge, which was then ground and mixed evenly with 10 g of solid alkali KOH, and calcined at 400 °C for 2 h under nitrogen atmosphere to obtain sludge charcoal;

[0043] S2: Take 200g of the sludge charcoal obtained in S1, 10g of Ni-containing sulfate, and 1g of Fe-containing sulfate, add them to 1L of deionized water and stir evenly, stir and soak them at 0.8MPa vacuum and room temperature for 24h, and then vacuum dry them at 0.8MPa vacuum and 80℃ for 24h to obtain a dry sample; calcine the dry sample at 400℃ for 2h in a nitrogen atmosphere, and then calcine it at 600℃ for 2h to obtain a calcined sample; add the calcined sample to 1L of 2mol / L sulfuric acid solution and stir at 80℃ for 3h, rinse with deionized water, dry, and press to obtain a carbon-based confined catalyst Fe(0.5%)Ni(5%)@sludge charcoal. This carbon-based confined catalyst is a magnetic confined catalyst.

[0044] Embodiment 2:

[0045] A method for preparing a carbon-based confined catalyst Fe(1%)Ni(10%)@sludge charcoal comprises the following steps:

[0046] S1: 200 g of sludge residue was obtained by drying the sludge, which was then ground and mixed evenly with 10 g of solid alkali KOH, and calcined at 400 °C for 2 h under nitrogen atmosphere to obtain sludge charcoal;

[0047] S2: Take 200g of the sludge obtained in S1, 20g of Ni-containing sulfate, and 2g of Fe-containing sulfate, add them into 1L of deionized water and stir evenly, stir and immerse them for 24h under 0.8MPa vacuum and room temperature, and then dry them for 24h under 0.8MPa and 80℃ vacuum to obtain a dry sample; the dry sample is calcined at 500℃ for 2.5h under nitrogen atmosphere, and then calcined at 700℃ for 2.5h to obtain a calcined sample; the calcined sample is added to 1L of 2mol / L sulfuric acid solution and stirred at 80℃ for 3h, and then rinsed with deionized water, dried, and pressed to obtain a carbon-based confined catalyst Fe(1%)Ni(10%)@sludge. This carbon-based confined catalyst is a magnetic confined catalyst.

[0048] Example 3

[0049] A method for preparing a carbon-based confined catalyst Fe(2%)Ni(20%)@sludge charcoal comprises the following steps:

[0050] S1: 200 g of sludge residue was obtained by drying the sludge, which was then ground and mixed evenly with 10 g of solid alkali KOH, and calcined at 400 °C for 2 h under nitrogen atmosphere to obtain sludge charcoal;

[0051] S2: Take 200g of the sludge charcoal obtained in S1, 40g of Ni-containing sulfate, and 4g of Fe-containing sulfate, add them to 1L of deionized water and stir evenly, then stir and immerse them at 0.8MPa vacuum and room temperature for 24h, then dry them at 0.8MPa vacuum and 80℃ for 24h to obtain a dry sample; calcine the dry sample at 500℃ for 3h under nitrogen atmosphere, and then calcine it at 800℃ for 3h to obtain a calcined sample; add the calcined sample to 1L 2mol / L sulfuric acid solution and stir at 80℃ for 3h, rinse with deionized water, dry, and press to obtain a carbon-based confined catalyst Fe(2%)Ni(20%)@sludge charcoal. This carbon-based confined catalyst is a magnetic confined catalyst.

[0052] Example 4

[0053] A method for preparing a carbon-based confined catalyst Fe (2.5%) Ni (25%) @ sewage sludge comprises the following steps:

[0054] S1: 200 g of sludge residue was obtained by drying the sludge, which was then ground and mixed evenly with 10 g of solid alkali KOH, and calcined at 400 °C for 2 h under nitrogen atmosphere to obtain sludge charcoal;

[0055] S2: Take 200g of the sludge obtained in S1, 50g of Ni-containing sulfate, and 5g of Fe-containing sulfate, add them to 1L of deionized water and stir evenly, then stir and immerse them at 0.8MPa vacuum and room temperature for 24h, then dry them at 0.8MPa vacuum and 80℃ for 24h to obtain a dry sample; calcine the dry sample at 500℃ for 3h under nitrogen atmosphere, and then calcine it at 800℃ for 3h to obtain a calcined sample; add the calcined sample to 1L 2mol / L sulfuric acid solution and stir at 80℃ for 3h, rinse with deionized water, dry, and press to obtain a carbon-based confined catalyst Fe(2.5%)Ni(25%)@sludge. This carbon-based confined catalyst is a magnetic confined catalyst.

[0056] 1. Performance test:

[0057] Evaluate catalyst effects and reaction conditions through laboratory tests

[0058] 1. Laboratory test device: Figure 2 The 200 mL fixed bed reactor (model: CWAO-DA480) shown was developed by the Dalian Institute of Chemical Physics, Chinese Academy of Sciences. The process can be scaled up proportionally;

[0059] 2. The pilot test process is as follows: first, the catalyst is put into the reactor, and then the remaining sludge is transported to the fixed bed reactor through a high-pressure sludge pump, air is introduced into the reactor through an air delivery unit (a selection valve, a pressure relief valve, and a gas flow regulating valve are provided on the air delivery pipeline), and the heat source required for the reaction is provided to the reactor through a heating furnace. The catalyst and the remaining sludge undergo hydrolysis and oxidation reactions in the reactor, and the material obtained after the reaction is cooled by a heat exchanger, and the cooled solid-liquid mixture enters a sample storage tank, and finally the solid-liquid mixture in the sample storage tank is separated and filtered by a solid-liquid separation unit, and the supernatant obtained is the carboxylic acid carbon source;

[0060] 3. Catalyst evaluation method: The carbon-based confined HTO catalyst prepared in Examples 1 to 4 was used to treat the residual sludge, and the reaction without adding the catalyst was used as the control group. The catalyst evaluation test was performed in the HTO laboratory test. 200 mL of catalyst was added, and the sludge pump was used for sampling. Air was introduced as an oxidant. The reaction temperature was set to 180°C, the reaction pressure was set to 2.0 MPa, and the reaction contact time was set to 1.0 h (volume space velocity 1.0 h -1 ) After the first 8 hours of sample release, samples were taken every 6 hours. Each condition was sampled 3 times and the results were averaged.

[0061] Catalyst evaluation result analysis method: After the reaction, the sample was filtered, and the supernatant was tested for soluble COD using the national standard method and VFAs using high performance liquid chromatography; the mud cake was tested for moisture content, TS, and VS. The sample was refrigerated and stored at 4°C.

[0062] 4. Catalyst evaluation results:

[0063] The Fe(0.5%)Ni(5%)@sludge carbon catalyst prepared in Example 1 was used to treat residual sludge (water content 99%). The COD of the sludge pyrolysis liquid after HTO treatment was 4915 mg / L, and oxalic acid 255 mg / L (COD 45.3 mg / L), formic acid 68 mg / L (COD 23.6 mg / L), acetic acid 1336 mg / L (COD 1423.7 mg / L), propionic acid 1156 mg / L (COD 1747.6 mg / L), butyric acid 859 mg / L (COD 1559.8 mg / L) were detected in the pyrolysis liquid. The contribution of carboxylic acids to COD accounted for 97.7%. The moisture content of the sludge filter cake after HTO treatment dropped to 33.6%, and VS / TS dropped from 0.45 to 0.16, indicating that the catalyst can improve the degree of decomposition of sludge extracellular polymers, thereby improving the efficiency of the sludge hydrolysis reaction and achieving deep decomposition of the sludge. At the same time, the confined structure of the catalyst will increase the product selectivity of small molecule carboxylic acids to more than 95%. The Fe(1%)Ni(10%)@sludge carbon catalyst prepared in Example 2 was used to treat residual sludge (water content 99%). The COD of the sludge pyrolysis liquid after HTO treatment was 4620 mg / L, and oxalic acid 222 mg / L (COD 39.5 mg / L), formic acid 54 mg / L (COD 18.8 mg / L), acetic acid 1289 mg / L (COD 1373.7 mg / L), propionic acid 1017 mg / L (COD 1537.5 mg / L), butyric acid 870 mg / L (COD 1579.7 mg / L) were detected in the pyrolysis liquid, and the contribution of carboxylic acids to COD accounted for 98.5%. The moisture content of the sludge filter cake after HTO treatment dropped to 32.1%, and VS / TS dropped from 0.45 to 0.15, indicating that the catalyst can improve the degree of decomposition of sludge extracellular polymers, thereby improving the efficiency of the sludge hydrolysis reaction and achieving deep decomposition of the sludge. At the same time, the confined structure of the catalyst will increase the product selectivity of small molecule carboxylic acids to more than 95%.

[0064] The Fe(2%)Ni(20%)@sludge carbon catalyst prepared in Example 3 was used to treat the residual sludge (water content 99%). The COD of the sludge pyrolysis liquid after HTO treatment was 4299 mg / L. Oxalic acid 169 mg / L (COD 30.0 mg / L), formic acid 32 mg / L (COD 11.1 mg / L), acetic acid 999 mg / L (COD 1064.6 mg / L), propionic acid 1061 mg / L (COD 1604.0 mg / L), butyric acid 854 mg / L (COD 1550.7 mg / L) were detected in the pyrolysis liquid, and the contribution of carboxylic acids to COD accounted for 99.1%. The moisture content of the sludge filter cake after HTO treatment dropped to 31.8%, and VS / TS dropped from 0.45 to 0.15, indicating that the catalyst can improve the degree of decomposition of sludge extracellular polymers, thereby improving the efficiency of the sludge hydrolysis reaction and achieving deep decomposition of the sludge. At the same time, the confined structure of the catalyst will increase the product selectivity of small molecule carboxylic acids to more than 95%. The Fe(2.5%)Ni(25%)@sludge carbon catalyst prepared in Example 4 was used to treat the residual sludge (water content 99%). The COD of the sludge pyrolysis liquid after HTO treatment was 4173 mg / L. Oxalic acid 289 mg / L (COD 51.4 mg / L), formic acid 264 mg / L (COD 91.8 mg / L), acetic acid 1869 mg / L (COD1991.7 mg / L), propionic acid 760 mg / L (COD 1149.0 mg / L), butyric acid 432 mg / L (COD 784.4 mg / L) were detected in the pyrolysis liquid, and the contribution of carboxylic acids to COD accounted for 97.5%. The moisture content of the sludge filter cake after HTO treatment dropped to 31.2%, and VS / TS dropped from 0.45 to 0.14, indicating that the catalyst can improve the degree of decomposition of sludge extracellular polymers, thereby improving the efficiency of the sludge hydrolysis reaction and achieving deep decomposition of the sludge. At the same time, the confined structure of the catalyst will increase the product selectivity of small molecule carboxylic acids to more than 95%.

[0065] In the control group, after the 99% water-containing excess sludge crystalline HTO treatment without adding catalyst, the COD of the sludge pyrolysis liquid was 2441 mg / L, and oxalic acid 26 mg / L (COD 4.6 mg / L), maleic acid 87 mg / L (COD 69.5 mg / L), glycolic acid 105 mg / L (COD 66.3 mg / L), formic acid 62 mg / L (COD 21.5 mg / L), acetic acid 567 mg / L (COD 604.2 mg / L), propionic acid 162 mg / L (COD 244.9 mg / L), butyric acid 214 mg / L (COD 388.6 mg / L), valeric acid 117 mg / L (COD 238.3 mg / L) were detected. The contribution of carboxylic acid COD accounted for 67.1%. After the reaction, the sludge VS / TS dropped from 0.45 to 0.49, and the moisture content of the mud cake was 58%.

[0066] Therefore, compared with the control group, the catalysts prepared using Examples 1-4 of the present invention effectively improved the degree of decomposition of extracellular polymers in sludge through dual active metals, achieved deep decomposition of sludge, and effectively reduced the moisture content of the mud cake after treatment; the organic matter released after sludge decomposition passed through the active metal confined superstructure, which improved the selectivity of carboxylic acid products, so that more than 95% of the organic matter was converted into small molecule carboxylic acids, which was convenient for resource utilization.

[0067] 5. Reaction condition evaluation method: The Fe (0.5%) Ni (5%) @ sludge charcoal catalyst prepared in Example 1 was used for HTO test. The HTO test was carried out in the above test device to investigate the reaction temperature (140-200°C), reaction pressure (1.0-5.0 MPa), reaction contact time (volume space velocity 0.5-2.0 h -1 )’s impact.

[0068] Reaction condition evaluation result analysis method: After the reaction, the sample was filtered, and the supernatant was tested for soluble COD using the national standard method and VFAs using high performance liquid chromatography; the mud cake was tested for moisture content, TS, and VS. The sample was refrigerated and stored at 4°C.

[0069] 6. Reaction condition evaluation results:

[0070] (1) Effect of reaction pressure

[0071] Reaction temperature 180℃, reaction contact time 1.0h (volume space velocity 1.0h -1 ), the reaction pressure was set to 1.0MPa, 2.0MPa, 3.0MPa, 4.0MPa, and 5.0MPa, respectively, and the results are as follows:

[0072]

[0073] From the above results, it can be seen that when the reaction pressure is in the range of 1.0-5.0MPa, the sludge is well broken down, the organic matter is well released, and more than 95% of the pollutants are converted into carboxylic acid products, which is beneficial for subsequent application as a carbon source. The increase in reaction pressure is beneficial to the deep breaking of sludge and the removal of organic pollutants, which is beneficial to reducing the VS / TS of sludge after treatment and improving the degree of stabilization. However, with the increase in pressure, the oxidation capacity is enhanced, and the degree of complete mineralization of pollutants becomes higher, resulting in a decrease in the proportion of carboxylic acid COD in the pyrolysis solution.

[0074] (2) Effect of reaction temperature

[0075] Reaction pressure 2.0MPa, volume space velocity 1.0h -1 , the reaction temperatures were set to 140°C, 160°C, 180°C, and 200°C, respectively. The results are as follows:

[0076]

[0077] From the above results, it can be seen that within the range of 140-200°C, the sludge is well broken down, the organic matter is well released, and more than 95% of the pollutants are converted into carboxylic acid products, which is beneficial for subsequent application as a carbon source. The increase in reaction temperature is conducive to the deep breakdown of sludge and the removal of organic pollutants, which is beneficial to reducing the VS / TS of sludge after treatment and improving the degree of stabilization. However, as the temperature increases, the oxidation capacity increases, and the degree of complete mineralization of pollutants increases, resulting in a decrease in the proportion of carboxylic acid COD in the pyrolysis solution.

[0078] (3) Effect of reaction contact time

[0079] The reaction pressure was 2.0 MPa, the reaction temperature was 180°C, and the volumetric space velocity was set to 0.5 h -1 , 1.0h -1 , 2.0h -1 , that is, the reaction contact time is 2.0h, 1.0h, 0.5h, and the results are as follows:

[0080]

[0081] From the above results, it can be seen that within the range of 0.5-2.0h reaction contact time, the sludge is well broken down, the organic matter is well released, and more than 95% of the pollutants are converted into carboxylic acid products, which is beneficial for subsequent application as a carbon source. The extension of the reaction contact time is beneficial to the deep breakdown of the sludge and the removal of organic pollutants, which is beneficial to reduce the VS / TS after sludge treatment and improve the degree of stabilization. However, as the contact time increases, the degree of oxidation becomes deeper, and the degree of complete mineralization of pollutants becomes higher, resulting in a decrease in the proportion of carboxylic acid COD in the pyrolysis solution. Shorter reaction contact time will lead to incomplete sludge breakdown, resulting in higher VS / TS.

[0082] 2. Process testing:

[0083] The process of the process test of using the carbon-based confined HTO catalyst prepared by the present invention to treat excess sludge and simultaneously prepare a carboxylic acid carbon source is as follows:

[0084] like Figure 1The figure shows the structure of the device used when the catalyst prepared by the present invention is used to treat excess sludge. The reaction tower 2 is connected to the heat exchange unit 3, the heat exchange unit is connected to the solid-liquid separation unit 4, the heat supply unit 1 (boiler) is connected to the reaction tower 2, and the heat exchange unit 3 is connected to the heat supply unit 1 (boiler); firstly, the catalyst is put into the reaction tower of the device, the excess sludge is transported to the reaction tower through the biological material transport unit, air is introduced into the reaction tower through the air transport unit, the heat source required for the reaction is provided to the reaction tower through the heat supply unit, and the catalyst and the excess sludge undergo a hydrothermal oxidation reaction. The remaining sludge is effectively broken down. The material obtained after the reaction is cooled by the heat exchange unit. The heat generated by the cooling of the reactants is recovered by the heat exchange unit and transported to the heat supply unit to achieve heat recovery and circulation. The cooled material is separated by the solid-liquid separation unit, and the supernatant obtained is the carboxylic acid carbon source, which can be used as a composite carbon source in the process of sewage treatment to achieve resource utilization. The main inorganic components of the solid mud cake obtained are oxides of silicon, aluminum, calcium, iron, etc. and trace heavy metals, which can be used as inorganic fillers for packaging cardboard, and can also be fired into ceramsite and catalysts for further resource utilization.

[0085] The Fe(0.5%)Ni(5%)@sludge catalyst prepared in Example 1 was selected. Figure 1 In the process shown, the HTO resource treatment process of municipal sludge was tested, the reaction temperature was 180℃, the reaction pressure was 2.0MPa, the reaction contact time was 1.0h, and the sludge from the sewage treatment plant was treated in situ (sludge moisture content 99%±1%). Since the properties of the daily sludge (such as pollution degree, distribution of pollutants contained, etc.) change according to the actual daily sewage treatment conditions, the VS / TS of the treated sludge is between 0.13 and 0.16, the moisture content is 330%±5%, and the pyrolysis liquid COD is 4000-6000mg / L, of which the carboxylic acid products account for more than 95%, and the highest can reach 99%. The catalyst continued to react for 100 days, the catalytic efficiency remained stable, the effluent supernatant index and the mud cake index remained stable, the mud cake moisture content was 30%±5%, and the effluent supernatant small molecule carboxylic acid selectivity exceeded 95%.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A carbon-based confined catalyst, characterized in that: The carbon-based confined catalyst comprises a sludge carbon substrate and carbon nanotubes and active metals covered on the surface of the substrate; The active metal includes Fe and Ni, wherein Ni is doped inside the carbon nanotube to form a confined structure; and Fe is loaded outside the carbon nanotube.

2. A carbon-based confined catalyst according to claim 1, characterized in that: The Ni doping amount is 5-25wt%, and the Fe loading amount is 0.5-2.5wt%.

3. A method for preparing the carbon-based confined catalyst according to any one of claims 1 to 2, characterized in that: The following steps are involved: S1: After drying the sludge, the sludge residue is obtained, and the sludge residue is ground and mixed evenly with solid alkali KOH at a mass ratio of 20:1, and then roasted to obtain sludge charcoal; S2: The sludge carbon prepared in S1 is placed in a solution containing active metal salts for vacuum impregnation, and then vacuum dried to obtain a dry sample; the calcined sample obtained by high-temperature calcination of the dry sample is placed in a 2 mol / L sulfuric acid solution and stirred at 80°C for 3 to 6 hours, and then rinsed, dried, and pressed to obtain a carbon-based confined catalyst.

4. The preparation method according to claim 3, characterized in that: In S1, the calcination conditions are: calcination at 400-500° C. for 2-3 hours in an inert atmosphere.

5. The preparation method according to claim 3, characterized in that: In S2, the active metal salt includes metal Ni salt and metal Fe salt.

6. The preparation method according to claim 3, characterized in that: In S2, the mass ratio of sludge carbon, metal Ni salt and metal Fe salt is 1:0.05-0.25:0.005-0.025; the volume ratio of the mass of sludge carbon to the solution containing active metal salt is 200g:1L.

7. The method according to claim 3, characterized in that In S2, the immersion conditions are: vacuum degree 0.08 MPa, stirring at room temperature for 24 hours; The vacuum drying conditions are: vacuum drying at a vacuum degree of 0.08 MPa and 80° C. for 24 hours; The high temperature calcination conditions are as follows: calcining the dried sample at 400-500° C. for 2-3 hours in a nitrogen atmosphere, and then calcining at 600-800° C. for another 2-3 hours to obtain a calcined sample.

8. Use of a carbon-based confined catalyst as described in any one of claims 1 to 3 or a carbon-based confined catalyst prepared by the preparation method as described in any one of claims 4 to 7 in treating sludge to produce carboxylic acid carbon sources.

9. The use according to claim 8, characterized in that: The application is carried out in a device for hydrothermal oxidation of excess sludge, the device for hydrothermal oxidation of excess sludge comprising a raw sludge transmission system, a reaction tower (2), a heat exchange unit (3) and a solid-liquid separation unit (4) connected in sequence; the reaction tower (2) is also connected to a heat supply unit (1) and an air delivery unit, and the heat exchange unit (3) is connected to the heat supply unit (1); The process steps of the application are as follows: First, the residual sludge is transported to the reaction tower (2) by using a raw sludge transport system, and then the carbon-based confined catalyst is added to the reaction tower (2). An oxidant is introduced into the reaction tower (2) through an air transport unit, and the reaction tower (2) is heated by using a heat supply unit (1). The lattice oxygen-regulated nanocatalyst catalyzes a hydrothermal oxidation reaction of the residual sludge, and the residual sludge is broken down to generate a carboxylic acid carbon source. The solid-liquid mixture formed after the hydrothermal oxidation reaction is cooled by a heat exchange unit (3). After the cooling is completed, the solid-liquid mixture enters a solid-liquid separation unit (4) for solid-liquid separation, and the separated supernatant and filter cake resources are collected respectively.

10. The use according to claim 9, characterized in that: The conditions of the hydrothermal oxidation reaction are: reaction pressure 1.0-5.0 MPa, reaction temperature 140-200°C, volume space velocity 0.5-2.0 h -1 , the oxidant is oxygen in the air.

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