Preparation of activated carbon by hydrothermal nitridation with nitrogen-rich hydrolysate and its application in room-temperature desulfurization

Abstract

The application belongs to the field of activated carbon preparation, and discloses a kind of nitrogen-rich hydrolysate reinforced hydrothermal nitrogen-doped preparation activated carbon and its room temperature desulfurization application, and the preparation method comprises the following steps: (1) high water content nitrogen-rich organic solid waste is mixed with liquid water, and heat hydrolysis reaction is carried out to obtain nitrogen-rich hydrolysate;(2) the nitrogen-rich hydrolysate is mixed with high water content organic solid waste, and then hydrothermal reaction is carried out to obtain nitrogen-containing hydrothermal coke;(3) nitrogen-containing hydrothermal coke is activated to obtain nitrogen-doped activated carbon.The application uses high water content nitrogen-rich organic solid waste as raw material, first obtains nitrogen-rich hydrolysate through heat hydrolysis reaction, then uses nitrogen-rich hydrolysate and other high water content organic solid waste to carry out hydrothermal reaction to obtain nitrogen-containing hydrothermal coke, and finally carries out activation treatment, which not only realizes harmless, reduction and resource utilization of solid waste, but also solves the problem of high preparation cost of current carbon-based catalyst, and the method can prepare carbon-based catalyst with high specific surface area, and has high practical value.

Description

Technical Field

[0001] This invention belongs to the field of activated carbon preparation, and more specifically, relates to a method for preparing activated carbon by hydrothermal doping with nitrogen-rich hydrolysate and its application in room temperature desulfurization. The nitrogen-doped activated carbon prepared by the nitrogen-rich hydrolysate and activation can be used as a catalyst for the removal of hydrogen sulfide at room temperature. Background Technology

[0002] Hydrogen sulfide is a common, toxic, and harmful acidic gas with an extremely low odor threshold (0.41 ppbv). It is prevalent in many industrial processes, such as wastewater treatment plants, landfills, oil or gas production processes, and petrochemical processing plants, as well as other hydrocarbon processes. Hydrogen sulfide can corrode some equipment and pipelines and can be converted into sulfur dioxide, causing acid rain and severe air pollution. Piped natural gas in the United States and Denmark requires hydrogen sulfide levels to be below 4 ppmv, while reformers and fuel cell applications must maintain levels below 1 ppmv. Therefore, deep desulfurization in industrial production is crucial for pollution control and safe operation. There are many desulfurization methods, including chemical scrubbing, biological filtration, and adsorption. Adsorption is the most promising room-temperature desulfurization method due to its high desulfurization precision, moderate operating conditions, and lack of secondary pollution. Activated carbon is widely used for room-temperature desulfurization due to its abundant pore structure, high specific surface area, and tunable surface properties.

[0003] Currently, the key factor limiting the large-scale application of activated carbon is cost, especially carbon precursors, which include organometallic compounds, polymers, and biomass. Urban household waste, with its abundant sources and large volume, holds potential value for large-scale activated carbon production. High-moisture solid waste (generally 5%–65% moisture content; moisture content refers to the percentage of water mass in solid waste relative to its total mass; in developed countries, the average moisture content of kitchen waste is 25%) constitutes the largest proportion of urban household waste. However, the traditional activated carbon preparation method—pyrolysis and reactivation of raw materials—is not suitable for high-moisture raw materials.

[0004] In recent years, the direct conversion of high-moisture-content solid waste into hydrothermal coke using hydrothermal carbonization has attracted widespread attention, realizing the concept of energy conservation and environmental protection to a certain extent. Hydrothermal carbonization is a thermochemical process that occurs in subcritical water at medium temperatures (180–250℃) and medium pressures (1.0–2.5 MPa). Hydrothermal coke contains abundant functional groups, giving it great activation potential and making it suitable for producing highly active porous carbon. For example, CN111841495A discloses a method for preparing porous tea residue biochar with a high specific surface area. The method involves hydrothermally treating tea residue, then impregnating and mixing the dried tea residue hydrothermal carbon with potassium bicarbonate, followed by pyrolysis to obtain biochar with a well-developed pore structure and a specific surface area as high as 1405 m². 2 / g. Activated carbon prepared by hydrothermal activation of organic solid waste with high water content not only has cost advantages but also yields activated carbon with high porosity. However, activated carbon prepared using hydrothermal coke currently suffers from insufficient active sites, poor performance, and difficulty in applying it to actual industrial desulfurization.

[0005] The surface chemistry of activated carbon is a key factor affecting its desulfurization performance. Heteroatom doping can alter the chemical properties of porous carbon surfaces, thereby enhancing its adsorption capacity for specific adsorbates. Nitrogen doping, in particular, can increase the content and defects of basic functional groups, thus promoting the adsorption and dissociation of hydrogen sulfide or the chemisorption of oxygen. Under aerobic conditions and a certain humidity, activated carbon can also act directly as a catalyst, catalyzing the reaction of hydrogen sulfide with oxygen to produce elemental sulfur. For example, under room temperature pre-humidification conditions, nitrogen doping can increase the breakthrough sulfur capacity from 54.0 mg / g to 90.5 mg / g (meaning that under the same conditions, each gram of undoped activated carbon can adsorb 54.0 mg of hydrogen sulfide; after nitrogen doping, each gram of nitrogen-doped activated carbon can adsorb 90.5 mg of hydrogen sulfide). The introduction of nitrogen can increase the adsorption capacity and oxidation degree of hydrogen sulfide by increasing the size and volume of micropores. The large-scale application of nitrogen-rich activated carbon is limited not only by the cost of carbon precursors but also by the cost of nitrogen precursors. Currently, nitrogen-doped porous carbon is usually produced by thermally treating a physical mixture of nitrogen dopant and carbon precursor. However, Xiao has demonstrated that, compared to the physical mixing method, nitrogen-doped assisted hydrothermal processes can achieve sufficient contact and interaction between the nitrogen dopant and the raw material. CN110342512A describes the preparation of nitrogen-doped hydrothermal carbon using a hydrothermal nitrogen doping method on organic solid waste. The hydrothermal carbon is then mixed with potassium carbonate, potassium bicarbonate, or potassium hydroxide activators and activated to produce porous nitrogen-containing porous carbon. This method uses any one of melamine, urea, or dicyandiamide as the nitrogen dopant. This method is cumbersome and the nitrogen dopant is expensive. CN112456488A discloses a nitrogen-containing hierarchical porous biochar, its preparation method, and its application. Biomass and hydrogen peroxide solution undergo a hydrothermal reaction to obtain hydrothermal carbon, which is then pyrolyzed to obtain hierarchical porous biochar with well-developed micropores and mesopores, containing abundant nitrogen functional groups and exhibiting excellent acid gas removal performance. This method uses at least one nitrogen doping agent selected from urea, melamine, or dicyandiamide. However, this method also suffers from the high cost of the nitrogen doping agent. CN108483442A discloses a method for synthesizing high-mesoporous nitrogen-doped carbon, which involves hydrothermal reaction of bamboo shoot shells to obtain a hydrothermal carbon precursor, followed by low-temperature carbonization of the hydrothermal carbon precursor with a nitrogen source to obtain a carbide; finally, the carbide is activated with an activator to obtain a high-mesoporous nitrogen-doped carbon. This method uses at least one nitrogen doping agent selected from urea, ethylenediamine, melamine, polyphenylene, pyridine, and pyrrole. In these disclosed patents, the use of nitrogen-doping chemical reagents significantly increases the cost of activated carbon. Therefore, developing a low-cost, mild, and environmentally friendly porous biochar has become a current research focus. Summary of the Invention

[0006] To address the aforementioned deficiencies or improvement needs of existing technologies, the present invention aims to provide a method for preparing activated carbon using nitrogen-rich hydrolysate-enhanced hydrothermal nitrogen doping and its application in room temperature desulfurization. This method involves improving the overall design of the process flow, using high-moisture-content nitrogen-rich organic solid waste as raw material. First, a nitrogen-rich hydrolysate is obtained through a hot hydrolysis reaction. Then, the nitrogen-rich hydrolysate is used in a hydrothermal reaction with other high-moisture-content organic solid waste to obtain nitrogen-containing hydrothermal coke. Finally, activation treatment yields nitrogen-doped activated carbon. This method not only achieves the harmlessness, reduction, and resource recovery of solid waste but also solves the problem of high preparation costs for carbon-based catalysts. Furthermore, this method can prepare carbon-based catalysts with high specific surface area, demonstrating high practical value in the preparation and application of carbon-based catalysts.

[0007] To achieve the above objectives, according to one aspect of the present invention, a method for preparing activated carbon by hydrothermal doping with nitrogen-rich hydrolysate is provided, characterized by comprising the following steps:

[0008] (1) Mix high-moisture nitrogen-rich organic solid waste with liquid water and carry out hot hydrolysis reaction; after the reaction is completed, cool to room temperature, separate solid and liquid, retain the supernatant to obtain nitrogen-rich hydrolysate; wherein, the moisture content of the high-moisture nitrogen-rich organic solid waste is 5wt.% to 88wt.%, and the nitrogen content under dry basis is not less than 4wt.%.

[0009] (2) The nitrogen-rich hydrolysate is mixed with organic solid waste with high water content and then subjected to hydrothermal reaction; after the reaction is completed, the solid product is collected, washed and dried to obtain nitrogen-containing hydrothermal coke; wherein, the water content of the organic solid waste with high water content is 5 wt.% to 88 wt.%.

[0010] (3) The nitrogen-containing hydrothermal coke is mixed with a solid activator and then heated under a protective atmosphere to carry out an activation reaction. After the reaction is completed, the nitrogen-doped activated carbon is obtained by washing and drying. The solid activator is a solid potassium-containing activator.

[0011] As a further preferred embodiment of the present invention, in step (1), the high water content nitrogen-rich organic solid waste is selected from any one or any combination of two of municipal sludge, Chlorella, and pork kitchen waste;

[0012] The mixing of high-moisture-content nitrogen-rich organic solid waste and liquid water satisfies the following ratio: (dry basis mass of high-moisture-content nitrogen-rich organic solid waste): (mass of water contained in high-moisture-content nitrogen-rich organic solid waste + mass of liquid water) = 1:3 to 1:10.

[0013] As a further preferred embodiment of the present invention, in step (1), the reaction temperature of the hot water hydrolysis reaction is 120-200°C, and the reaction time is 0.5-1.5h;

[0014] Preferably, in step (1), the nitrogen-rich hydrolysate is further concentrated to achieve a total nitrogen concentration of 2000–10000 ppm.

[0015] As a further preferred embodiment of the present invention, in step (2), the high moisture content organic solid waste is one or more of rice kitchen waste, melon rind kitchen waste, and waste paper pulp;

[0016] The nitrogen-rich hydrolysate is mixed with high-moisture organic solid waste in a ratio of 1:3 to 1:10 (dry basis mass of high-moisture organic solid waste): (mass of water contained in high-moisture organic solid waste + mass of nitrogen-rich hydrolysate).

[0017] As a further preferred embodiment of the present invention, in step (2), the reaction temperature of the hydrothermal reaction is 180-250°C and the reaction time is 0.5-3h.

[0018] As a further preferred embodiment of the present invention, in step (2), the cleaning is specifically performed by alternating washing with distilled water and ethanol for a total of 3 to 10 times; the drying is specifically performed by drying in an oven at 60 to 100°C for 6 to 24 hours until constant weight.

[0019] As a further preferred embodiment of the present invention, in step (3), the nitrogen-containing hydrothermal coke and the activator are mixed in a mass ratio of 1:(1-6);

[0020] The activation reaction is carried out at a temperature of 600–900°C, with a heating rate of 3–10°C / min and a reaction time of 0.5–3 h.

[0021] The solid potassium-containing activator is selected from potassium hydroxide, potassium carbonate, potassium nitrate, potassium bicarbonate, potassium oxalate, potassium formate, potassium acetate, potassium citrate, potassium tartrate, and potassium lactate.

[0022] The protective atmosphere is nitrogen or argon.

[0023] As a further preferred embodiment of the present invention, in step (3), the washing specifically involves washing with acid and water respectively, preferably washing with dilute hydrochloric acid and distilled water 3 to 10 times each until the supernatant is neutral; wherein, the dilute hydrochloric acid is dilute hydrochloric acid with a concentration of 0.5 to 4M;

[0024] The drying process specifically involves drying in an oven at 60–100°C for 6–24 hours until constant weight is achieved.

[0025] According to another aspect of the present invention, the present invention provides nitrogen-doped activated carbon obtained by the above method.

[0026] According to another aspect of the present invention, the present invention provides the application of nitrogen-doped activated carbon obtained by the above method as a catalyst in the removal of hydrogen sulfide at a temperature of 20-30°C.

[0027] Compared with the prior art, the above technical solution conceived by this invention uses high-moisture-content nitrogen-rich organic solid waste as raw material. First, a nitrogen-rich hydrolysate is obtained through a hot hydrolysis reaction. Then, the nitrogen-rich hydrolysate is used to carry out a hydrothermal reaction with other high-moisture-content organic solid waste to obtain nitrogen-containing hydrothermal coke. Finally, the activated carbon is obtained through activation treatment. It can be used for room temperature removal of hydrogen sulfide at 25±5℃, and is suitable for industrial room temperature desulfurization.

[0028] This invention utilizes nitrogen-rich organic solid waste with high water content as a nitrogen-containing raw material, ensuring a high nitrogen content in the hydrolysate and reducing raw material costs. Through hot hydrolysis, proteins in the organic solid waste are hydrolyzed, promoting the conversion of large organic molecules into smaller molecules. The separated hydrolysate provides a better nitrogen source. The hydrothermal reaction between the organic solid waste and the nitrogen-rich hydrolysate retains high levels of heterocyclic nitrogen (pyridine-N, pyrrole-N) in the hydrothermal coke. These heterocyclic nitrogens significantly promote the adsorption, ionization, and oxidation of hydrogen sulfide, especially under humid and aerobic conditions (the efficiency of hydrogen sulfide removal at room temperature decreases under anaerobic and humidity-free conditions, but since industrial waste gases generally contain oxygen and water vapor, the application prospects are still very good even considering only industrial waste gas treatment). Furthermore, the concentration of the nitrogen-rich hydrolysate allows for the synthesis of carbon-based catalysts with varying nitrogen contents. Activation reactions can significantly enhance the porosity of carbon-based catalysts, increase specific surface area, and increase the number of micropores and mesopores. The increase in micropores can increase the number of reactive sites, while mesopores and macropores can provide abundant mass transfer channels, which is beneficial for the deposition of elemental sulfur in the product.

[0029] This invention utilizes nitrogen-rich hydrolysate wastewater obtained from hot water hydrolysis. After hydrothermal carbonization and activation, a nitrogen-doped carbon-based catalyst is obtained, which can be used for hydrogen sulfide removal at room temperature. The nitrogen dopant is inexpensive, the process is simple, and it achieves high-value application of wastewater, thus improving the overall application value of the process. Under the same nitrogen addition conditions, compared with inorganic nitrogen sources, the nitrogen on the surface of the activated carbon obtained by this invention is more conducive to hydrogen sulfide removal. The disposal of large amounts of hydrolysate generated from the pretreatment of organic solid waste by hot hydrolysis has always been a bottleneck problem hindering the development of this technology. This invention utilizes the nitrogen-rich hydrolysate obtained from the hot hydrolysis reaction of high-moisture-content nitrogen-rich organic solid waste as a nitrogen source. The hot hydrolysis reaction can destroy cell tissue structure and promote the transformation of organic macromolecules into small molecules, enhancing the dissolution of organic matter. Thus, a large amount of energy / polluting elements (carbon, nitrogen, etc.) will be transferred to the liquid phase. Through hydrolysis-assisted hydrothermal method, nitrogen doping and hydrothermal coke production can be realized simultaneously. After activation, nitrogen-doped activated carbon is obtained, which can realize the resource utilization of hydrolysate and solve the problem of high cost in the current preparation of carbon-based catalysts. It can be especially applied to the deep removal of hydrogen sulfide in industry.

[0030] High-moisture-content organic solid waste is difficult to dispose of conventionally due to its complex composition and high moisture content. This invention first utilizes hot water hydrolysis to obtain a nitrogen-rich hydrolysate from the nitrogen-rich organic solid waste. This hydrolysate is then reacted with the organic solid waste in a hydrothermal process to obtain nitrogen-containing hydrothermal coke. Finally, the nitrogen-containing hydrothermal coke is activated with an activator to obtain a carbon-based catalyst. The resulting carbon-based catalyst has a highly developed pore structure. This carbon-based catalyst is particularly suitable for room-temperature desulfurization, exhibiting excellent desulfurization efficiency and catalytic performance. The nitrogen sources in the nitrogen-rich hydrolysate include organic and inorganic nitrogen. To investigate the influence of nitrogen species on room-temperature desulfurization performance, using Comparative Examples 2 and 3 as examples, this invention further verifies the effect of nitrogen species in the liquid phase on desulfurization performance through experiments involving the addition of organic and inorganic nitrogen. It was found that activated carbon formed by adding organic nitrogen, due to its heterocyclic nitrogen structure, exhibits superior room-temperature hydrogen sulfide removal performance compared to activated carbon formed by adding inorganic nitrogen, which has a higher specific surface area. The low-temperature process of hydrolysis allows for product diversity, with smaller organic molecules (including sugars and amino acids) being more readily utilized for high-value applications. This invention utilizes hydrolysis to treat high-moisture solid waste to obtain a nitrogen-rich hydrothermal fluid with high organic nitrogen content, which is then used in a hydrothermal process to obtain high-performance nitrogen-containing activated carbon. Under the same nitrogen addition conditions, compared to inorganic nitrogen sources, the nitrogen-containing activated carbon obtained using the method of this invention is more effective in removing hydrogen sulfide.

[0031] The carbon-based catalyst prepared by the above-described method of this invention uses nitrogen-rich organic solid waste with high water content as a nitrogen source. Through hot hydrolysis, a nitrogen-rich hydrothermal fluid is obtained. Furthermore, by introducing heterocyclic nitrogen basic catalytic sites, the surface acid-base or redox chemical properties are improved, thereby increasing the room-temperature sulfur penetration capacity and the generation of elemental sulfur. The hydrothermal coke is rich in nitrogen-containing functional groups, which, upon activation, can increase porosity and the specific surface area of ​​the carbon-based catalyst. Therefore, the large specific surface area of ​​the desulfurization catalyst enables deep desulfurization at room temperature. The room-temperature hydrogen sulfide removal catalyst obtained by the method of this invention can achieve deep removal of hydrogen sulfide, high room-temperature sulfur penetration capacity, and high content of elemental sulfur generation. For example, in the embodiments described below, under room-temperature conditions, with 1 vol.% oxygen, a relative humidity of 30%, and an activation temperature of 900℃, the sulfur penetration capacity can reach 176.3 mg / g.

[0032] In summary, this invention achieves the effective utilization of nitrogen sources in hydrolysate, enabling the efficient preparation of room-temperature hydrogen sulfide removal catalysts. The entire process achieves the harmlessness, reduction, and resource recovery of solid waste. The preparation method of this invention is simple to operate, has universal applicability to solid waste, and can achieve the harmlessness, reduction, and resource recovery of solid waste. This invention utilizes the resource recovery based on the compositional characteristics of nitrogen-rich hydrolysate, with simple and safe procedures, low cost, and suitability for continuous production and large-scale industrial application, possessing good economic and social benefits. Attached Figure Description

[0033] Figure 1 This is a process flow diagram of the preparation of a room temperature hydrogen sulfide removal catalyst by enhancing hydrothermal nitrogen doping with nitrogen-rich hydrolysate according to an embodiment of the present invention.

[0034] Figure 2 These are comparative field emission scanning electron microscope (FESQS) images of the carbon catalysts prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of this invention; wherein, Figure 2 (a) in the text corresponds to Example 1. Figure 2 (b) corresponds to a ratio of 1. Figure 2 (c) corresponds to ratio 2. Figure 2 (d) in the figure corresponds to scale 3, and the size scale represents 10μm (magnification is 10k).

[0035] Figure 3 These are the nitrogen adsorption-desorption curves of the carbon catalysts prepared in Examples 1, 1, 2, and 3 of this invention. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0037] The present invention describes a method for preparing carbon-based catalysts by adding nitrogen-rich hydrolysate to enhance nitrogen doping during the hydrothermal process of high-moisture-content organic solid waste. The process flow is as follows: Figure 1 As shown:

[0038] Step 1. Mix the high-moisture-content nitrogen-rich organic solid waste with liquid water (e.g., ultrapure water) evenly and carry out a hot hydrolysis reaction (the reaction temperature can be 120-200℃). After solid-liquid separation (e.g., solid-liquid pressing separation used in industry), a nitrogen-rich hydrolysate is obtained. The solid can be treated by off-site incineration.

[0039] Step 2. Mix the high-moisture organic solid waste with the nitrogen-rich hydrolysate evenly and carry out a hydrothermal reaction (the reaction temperature can be 180-250℃). After solid-liquid separation (such as solid-liquid pressing separation), the solid is obtained, which is nitrogen-containing hydrothermal coke. The liquid can be discharged to the sewage treatment plant for treatment.

[0040] Step 3. Grind the nitrogen-containing hydrothermal coke and the solid potassium-containing activator until they are evenly mixed, perform high-temperature activation, and obtain a carbon-based catalyst after washing and drying.

[0041] In step 1, the high-moisture-content nitrogen-rich organic solid waste can be any one or a combination of two of the following: municipal sludge, pork waste, Chlorella, and distiller's grains. The ratio of the high-moisture-content nitrogen-rich organic solid waste to liquid water can be 1:3 to 1:10 (mass of water in the high-moisture-content nitrogen-rich organic solid waste + mass of liquid water). The hydrolysis reaction temperature can be 120–200℃, and the reaction time can be 0.5–1.5 h. The resulting nitrogen-rich hydrolysate can be concentrated to different concentrations through evaporation, distillation, condensation, and ion exchange to prepare carbon-based catalysts with different nitrogen contents.

[0042] In step 2, the main components of the high-moisture-content organic solid waste can be one or more of amylopectin, amylose, cellulose, and lignin, such as rice waste, melon rind waste, waste paper pulp, and biogas residue. The mixture is prepared according to a ratio of (dry weight of the high-moisture-content organic solid waste) to (weight of water in the high-moisture-content organic solid waste + weight of nitrogen-rich hydrolysate) of 1:3 to 1:10. The hydrothermal carbonization reaction temperature can be 180–250℃, and the reaction time can be 0.5–3 hours.

[0043] In step 3, the solid potassium-containing activator can be any one of potassium hydroxide, potassium carbonate, potassium nitrate, potassium bicarbonate, potassium oxalate, potassium formate, potassium acetate, potassium citrate, potassium tartrate, or potassium lactate. The nitrogen-containing hydrothermal coke and the solid activator can be mixed in a mass ratio of 1:(1-6). The activation treatment can be carried out in a nitrogen or argon atmosphere at atmospheric or slightly positive pressure, at an activation temperature of 600-900℃, a heating rate of 3-10℃ / min, and an activation time of 0.5-3h. Washing can be performed using acid and water separately, for example, washing 3-10 times each with dilute hydrochloric acid and distilled water until the supernatant is neutral. The dilute hydrochloric acid can be 0.5-4M. Drying can be performed in an oven at 60-100℃ for 6-24h until constant weight.

[0044] Taking the preparation of a room-temperature hydrogen sulfide removal catalyst using a specific nitrogen-rich hydrolysate-enhanced hydrothermal nitrogen doping method as an example, the technical solution of this invention will be further described in detail on a laboratory scale. For ease of laboratory research, the raw materials used in the following examples and comparative examples—high-moisture-content nitrogen-rich organic solid waste (e.g., municipal sludge, Chlorella, pork waste, etc.) and high-moisture-content organic solid waste (e.g., rice waste, melon rind waste, waste paper pulp, etc.)—are all in a dry-basis state (that is, the organic solid waste raw materials have undergone pre-drying treatment; the water contained in wet organic solid waste, typically including free water, interstitial water, surface water, and bound water, has all been dried and removed). Of course, in practical applications, the moisture content of various organic solid wastes can be measured first, and then the amount of liquid water to be added to the wet high-moisture-content nitrogen-rich organic solid waste during hot hydrolysis can be calculated based on the mass ratio of dry-based nitrogen-rich organic solid waste to water (including: newly added liquid water + water contained in wet high-moisture-content nitrogen-rich organic solid waste). Additionally, the amount of nitrogen-rich hydrolysate to be added to the wet high-moisture-content organic solid waste during hydrothermal reaction can be calculated based on the solid-liquid mass ratio of dry-based organic solid waste to nitrogen-rich hydrolysate (where "solid" refers to dry-based organic solid waste; "liquid" includes: water contained in wet high-moisture-content organic solid waste + nitrogen-rich hydrolysate). (If necessary, the nitrogen-rich hydrolysate can be concentrated.)

[0045] Example 1

[0046] Step 1. Select municipal sludge (nitrogen content ~4wt.%) as the raw material for hot hydrolysis, and then mix municipal sludge (dry basis) with ultrapure water at a mass ratio of 1:4. The hot hydrolysis reaction is carried out at a hydrolysis temperature of 160℃ and a reaction time of 1h. After the reaction is completed, centrifuge to obtain nitrogen-rich hydrolysate. The total nitrogen concentration was measured to be 7120ppm by a total organic carbon analyzer (Vario TOC cube, Germany).

[0047] Step 2. Mix rice waste (dry basis) and nitrogen-rich hydrolysate at a mass ratio of 1:7 and carry out hydrothermal carbonization reaction. The hydrothermal reaction temperature is 205℃ and the reaction time is 1h. After the reaction is completed, cool to room temperature, centrifuge, wash and dry the solid product to obtain nitrogen-containing hydrothermal coke.

[0048] Step 3. Nitrogen-containing hydrothermal coke and solid KOH were ground and mixed evenly at a mass ratio of 1:2, and then activated at high temperature under a nitrogen atmosphere. The heating rate was 5℃ / min, the activation temperature was 700℃, and the activation time was 2 hours. After the reaction, the mixture was cooled to room temperature under an inert atmosphere. The solid product was washed and dried to obtain the carbon-based catalyst. The prepared carbon-based catalyst had a nitrogen content of 4.2 wt.% and a BET specific surface area of ​​1913 m². 2 / g, with a microporous specific surface area of ​​1730m² 2 / g.

[0049] The carbon-based catalyst prepared in Example 1 was subjected to a room temperature hydrogen sulfide removal test (the room temperature hydrogen sulfide removal test conditions in subsequent examples and comparative examples remained unchanged). 100 mg of carbon catalyst was placed in a fixed-bed reactor. The carrier gas was argon, the oxygen concentration was 1 vol.%, the relative humidity was 30%, the adsorption temperature was 25 °C, the carrier gas flow rate was 150 mL / min, and the hydrogen sulfide concentration was 1000 ppm. The hydrogen sulfide concentration at the reactor tail was detected using a hydrogen sulfide analyzer (WOST B1010, CHN). The experiment was stopped when the outlet hydrogen sulfide concentration reached 20 ppm. The measured adsorption capacity of the carbon-based catalyst for hydrogen sulfide was 120.7 mg / g.

[0050] Example 2

[0051] The main difference between this embodiment and Embodiment 1 is that:

[0052] In step 1, a mixture of municipal sludge and pork kitchen waste (nitrogen content ~14wt.%) of equal mass was selected as the raw material for hot water hydrolysis. The raw material was then uniformly mixed with ultrapure water at a mass ratio of 1:8 and subjected to hot water hydrolysis reaction at a hydrolysis temperature of 180℃ for 0.5h. After the reaction was completed, the mixture was centrifuged to obtain a nitrogen-rich hydrolysate.

[0053] In step 2, a mixture of rice waste (dry basis) and melon peel waste (dry basis) was selected as the organic solid waste raw material. The organic solid waste and nitrogen-rich hydrolysate were mixed evenly at a mass ratio of 1:10. The hydrothermal temperature was 240℃, the reaction time was 1.5h, centrifuged, and dried to obtain nitrogen-containing hydrothermal coke.

[0054] In step 3, nitrogen-containing hydrothermal coke, solid K₂CO₃, and KHCO₃ were uniformly mixed in a mass ratio of 2:1:1 and activated at high temperature under a nitrogen atmosphere. The heating rate was 8℃ / min, the activation temperature was 750℃, and the activation time was 3h. The prepared carbon-based catalyst had a nitrogen content of 3.6 wt.% and a BET specific surface area of ​​2375 m². 2 / g, with a microporous specific surface area of ​​1926m² 2 / g.

[0055] The carbon-based catalyst prepared in Example 2 was tested for hydrogen sulfide removal at room temperature, and the measured hydrogen sulfide adsorption capacity reached 147.5 mg / g.

[0056] Example 3

[0057] The main difference between this embodiment and embodiment 2 is that:

[0058] In step 1, Chlorella (nitrogen content ~5wt.%) was selected as the raw material for hot water hydrolysis. The raw material (dry basis) was then uniformly mixed with ultrapure water at a mass ratio of 1:6, and the hot water hydrolysis reaction was carried out at a hydrolysis temperature of 120℃ for 1.5h. After the reaction was completed, the mixture was centrifuged to obtain a nitrogen-rich hydrolysate.

[0059] In step 2, melon rinds and kitchen waste are selected as organic solid waste raw materials. The organic solid waste (dry basis) and nitrogen-rich hydrolysate are mixed evenly at a mass ratio of 1:10. The hydrothermal temperature is 200℃, the reaction time is 1h, centrifuged, and dried to obtain nitrogen-containing hydrothermal coke.

[0060] In step 3, nitrogen-containing hydrothermal coke, solid KOH, and K₂CO₃ were uniformly mixed in a 1:1:1 mass ratio and activated at high temperature under a nitrogen atmosphere. The heating rate was 3℃ / min, the activation temperature was 900℃, and the activation time was 0.5h. The prepared carbon-based catalyst had a nitrogen content of 2.1 wt.% and a BET specific surface area of ​​2705 m². 2 / g, with a microporous specific surface area of ​​2432m² 2 / g.

[0061] The carbon-based catalyst prepared in Example 3 was tested for hydrogen sulfide removal at room temperature, and the measured hydrogen sulfide adsorption capacity reached 176.3 mg / g.

[0062] Example 4

[0063] The main difference between this embodiment and embodiment 3 is that:

[0064] In step 1, a mixture of municipal sludge and dry Chlorella was selected as the raw material for hot hydrolysis. The raw material (dry basis) was then uniformly mixed with ultrapure water at a mass ratio of 1:3, and the hot hydrolysis reaction was carried out at a hydrolysis temperature of 140℃ for 1 hour. After the reaction was completed, the mixture was centrifuged to obtain a nitrogen-rich hydrolysate.

[0065] In step 2, waste paper pulp is selected as organic solid waste raw material. The organic solid waste (dry basis) and nitrogen-rich hydrolysate are mixed evenly at a mass ratio of 1:5. The hydrothermal temperature is 180℃, the reaction time is 2h, centrifuged, and dried to obtain nitrogen-containing hydrothermal coke.

[0066] In step 3, nitrogen-containing hydrothermal coke and solid KHCO3 were uniformly mixed at a mass ratio of 1:5 and then activated at high temperature in a nitrogen atmosphere. The heating rate was 10℃ / min, the activation temperature was 600℃, and the activation time was 1h. The prepared carbon-based catalyst had a nitrogen content of 4.9 wt.% and a BET specific surface area of ​​1626 m². 2 / g, with a microporous specific surface area of ​​1395m² 2 / g.

[0067] The carbon-based catalyst prepared in Example 4 was tested for hydrogen sulfide removal at room temperature, and the measured hydrogen sulfide adsorption capacity reached 109.2 mg / g.

[0068] Example 5

[0069] The main difference between this embodiment and embodiment 4 is that:

[0070] In step 1, pork kitchen waste was selected as the raw material for hot hydrolysis. The raw material (dry basis) was then uniformly mixed with ultrapure water at a mass ratio of 1:10 and the hot hydrolysis reaction was carried out at a hydrolysis temperature of 200℃ for 0.5h. After the reaction was completed, the mixture was centrifuged to obtain a nitrogen-rich hydrolysate.

[0071] In step 2, a mixture of biogas residue and waste paper pulp dry basis is selected as organic solid waste raw material. The organic solid waste (dry basis) and nitrogen-rich hydrolysate are mixed evenly at a mass ratio of 1:3. The hydrothermal temperature is 220℃, the reaction time is 0.5h, centrifuged, and dried to obtain nitrogen-containing hydrothermal coke.

[0072] In step 3, nitrogen-containing hydrothermal coke, solid KOH, and K₂CO₃ were uniformly mixed in a mass ratio of 2:3:3 and activated at high temperature under a nitrogen atmosphere. The heating rate was 5℃ / min, the activation temperature was 850℃, and the activation time was 1 h. The prepared carbon-based catalyst had a nitrogen content of 3.2 wt.% and a BET specific surface area of ​​2598 m². 2 / g, with a microporous specific surface area of ​​2169m² 2 / g.

[0073] The carbon-based catalyst prepared in Example 5 was tested for hydrogen sulfide removal at room temperature, and the measured hydrogen sulfide adsorption capacity reached 168.9 mg / g.

[0074] Example 6

[0075] The main difference between this embodiment and embodiment 5 is that:

[0076] In step 1, distiller's grains (nitrogen content ~4wt.%) were selected as the raw material for hot hydrolysis. The raw material (dry basis) was then uniformly mixed with ultrapure water at a mass ratio of 1:7 and hot hydrolysis was carried out at a hydrolysis temperature of 150℃ for 1 hour. After the reaction was completed, the mixture was centrifuged to obtain a nitrogen-rich hydrolysate.

[0077] In step 2, biogas residue is selected as organic solid waste raw material. The organic solid waste (dry basis) and nitrogen-rich hydrolysate are mixed evenly at a mass ratio of 1:8. The hydrothermal temperature is 250℃, the reaction time is 2.5h, centrifuged, and dried to obtain nitrogen-containing hydrothermal coke.

[0078] In step 3, nitrogen-containing hydrothermal coke and solid K2CO3 were uniformly mixed at a mass ratio of 1:6 and then activated at high temperature in a nitrogen atmosphere. The heating rate was 6℃ / min, the activation temperature was 700℃, and the activation time was 2h. The prepared carbon-based catalyst had a nitrogen content of 4.3 wt.% and a BET specific surface area of ​​1974 m². 2 / g, with a microporous specific surface area of ​​1672m² 2 / g.

[0079] The carbon-based catalyst prepared in Example 6 was tested for hydrogen sulfide removal at room temperature, and the measured hydrogen sulfide adsorption capacity reached 139.1 mg / g.

[0080] Example 7

[0081] The main difference between this embodiment and embodiment 6 is that:

[0082] In step 1, a mixture of pork kitchen waste and dry distillers' grains was selected as the raw material for hot hydrolysis. The raw material was then mixed with ultrapure water at a mass ratio of 1:9 and the mixture was subjected to hot hydrolysis at a temperature of 170°C for 0.5 hours. After the reaction was completed, the mixture was centrifuged to obtain a nitrogen-rich hydrolysate.

[0083] In step 2, a mixture of biogas residue, melon peel and kitchen waste dry base, etc., is selected as organic solid waste raw material. The organic solid waste and nitrogen-rich hydrolysate are mixed evenly at a mass ratio of 1:9. The hydrothermal temperature is 220℃, the reaction time is 3h, centrifuged, and dried to obtain nitrogen-containing hydrothermal coke.

[0084] In step 3, nitrogen-containing hydrothermal coke, solid KOH, and KHCO3 were uniformly mixed in a mass ratio of 1:2:2 and activated at high temperature under a nitrogen atmosphere. The heating rate was 9℃ / min, the activation temperature was 800℃, and the activation time was 1.5h. The prepared carbon-based catalyst had a nitrogen content of 5.4 wt.% and a BET specific surface area of ​​2190 m². 2 / g, with a microporous specific surface area of ​​1796m² 2 / g.

[0085] The carbon-based catalyst prepared in Example 7 was tested for hydrogen sulfide removal at room temperature, and the measured hydrogen sulfide adsorption capacity reached 155.7 mg / g.

[0086] Comparative Example 1

[0087] The main difference between this comparative example and Example 1 is:

[0088] Step 1 is not included.

[0089] Step 2. Mix rice waste (dry basis) and ultrapure water evenly at a mass ratio of 1:7, and carry out a hydrothermal carbonization reaction at a temperature of 205℃ for 1 hour. After the reaction is completed, cool to room temperature, centrifuge, wash and dry the solid product to obtain hydrothermal coke;

[0090] Step 3. Grind and mix the obtained hydrothermal coke and solid KOH at a mass ratio of 1:2 until homogeneous, then perform high-temperature activation. The activation atmosphere is nitrogen, the heating rate is 5℃ / min, the activation temperature is 700℃, and the activation time is 2h. The prepared carbon-based catalyst has a nitrogen content of 1.2wt.% and a BET specific surface area of ​​1566m². 2 / g, with a microporous specific surface area of ​​1478m² 2 / g.

[0091] The carbon-based catalyst prepared in Comparative Example 1 was tested for hydrogen sulfide removal at room temperature, and the measured hydrogen sulfide adsorption capacity reached 29.5 mg / g.

[0092] Comparative Example 2

[0093] The main difference between this comparative example and Example 1 is:

[0094] Step 1 is not included.

[0095] Step 2. During hydrothermal treatment, the amount of nitrogen added was kept consistent with the nitrogen content in the hydrolysate obtained in Example 1. Therefore, rice waste (dry basis), inorganic nitrogen additive (25% ammonia water), and ultrapure water were mixed evenly in a mass ratio of 17:2:117, and a hydrothermal carbonization reaction was carried out. The hydrothermal reaction temperature was 205°C, and the reaction time was 1 hour. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, and the solid product was washed and dried to obtain nitrogen-containing hydrothermal coke.

[0096] Step 3. Nitrogen-containing hydrothermal coke and solid KOH are ground and mixed evenly at a mass ratio of 1:2, and then activated at high temperature in a nitrogen atmosphere. The heating rate is 5℃ / min, the activation temperature is 700℃, and the activation time is 2h. The prepared carbon-based catalyst has a nitrogen content of 4.0 wt.% and a BET specific surface area of ​​2188 m². 2 / g, with a microporous specific surface area of ​​1906m² 2 / g.

[0097] The carbon-based catalyst prepared in Comparative Example 2 was tested for hydrogen sulfide removal at room temperature, and the measured hydrogen sulfide adsorption capacity reached 50.2 mg / g.

[0098] Comparative Example 3

[0099] The main difference between this comparative example and Example 1 is:

[0100] Step 1 is not included.

[0101] Step 2. During hydrothermal treatment, the amount of nitrogen added was kept consistent with the nitrogen content in the hydrolysate obtained in Example 1. Therefore, rice waste (dry basis), organic nitrogen additive (alanine), and ultrapure water were mixed evenly at a mass ratio of 6.4:1:44, and a hydrothermal carbonization reaction was carried out at a temperature of 205°C for 1 hour. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, and the solid product was washed and dried to obtain nitrogen-containing hydrothermal coke.

[0102] Step 3. Nitrogen-containing hydrothermal coke and solid KOH are ground and mixed evenly at a mass ratio of 1:2, and then activated at high temperature in a nitrogen atmosphere. The heating rate is 5℃ / min, the activation temperature is 700℃, and the activation time is 2h. The prepared carbon-based catalyst has a nitrogen content of 5.4 wt.% and a BET specific surface area of ​​1280 m². 2 / g, with a microporous specific surface area of ​​1184m² 2 / g.

[0103] The carbon-based catalyst prepared in Comparative Example 3 was tested for hydrogen sulfide removal at room temperature, and the measured hydrogen sulfide adsorption capacity reached 132.2 mg / g.

[0104] It can be observed that in the above embodiments and comparative examples, the addition of organic nitrogen in step 2 (Comparative Example 3) significantly improves the removal performance of hydrogen sulfide by carbon-based catalysts compared to inorganic nitrogen (Comparative Example 2). Under the same nitrogen addition amount, the desulfurization performance of activated carbon added to nitrogen-rich hydrolysate is between that of organic nitrogen and inorganic nitrogen. Although it is slightly lower than that of organic nitrogen, the utilization of hydrolysate not only achieves the harmlessness, reduction and resource utilization of solid waste, but also solves the problem of high cost of nitrogen doping agents for nitrogen-containing catalysts, and has high practical application value.

[0105] Table 1 shows the pore structure parameters of the carbon catalysts prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3. Table 2 shows the relative XPS surface element content of the carbon catalysts prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0106] Table 1. Pore structure parameters of the carbon catalysts prepared in Example 1 and Comparative Examples 1-3.

[0107]

[0108] Table 2. Relative elemental content of XPS surface of carbon catalysts prepared in Example 1 and Comparative Examples 1-3

[0109] Sample Name C N O S Example 1 85.50 4.20 10.02 0.28 Comparative Example 1 86.06 1.24 12.50 0.20 Comparative Example 2 85.40 4.03 10.42 0.15 Comparative Example 3 82.76 5.40 11.67 0.17

[0110] In addition, the carbon catalysts prepared in Examples 1, 1, 2, and 3 were subjected to nitrogen adsorption tests. The specific surface area and pore size were measured at 77 K using a nitrogen specific surface area and pore size analyzer (Micromeritics ASAP2020, USA), and the specific surface area was calculated using the BET (Brunauer-Emmett-Teller) method. The N2 adsorption-desorption curves of the nitrogen-containing activated carbon are shown below. Figure 3 As shown in Table 1, the specific parameters are as follows. The addition of inorganic nitrogen (Comparative Example 2) and nitrogen-rich hydrolysate (Example 1) can significantly increase the surface area of ​​activated carbon, which may be due to the transformation of certain thermally unstable nitrogen-containing structures during KOH activation. These structures are consumed and react with K2CO3 produced by KOH activation, releasing a large amount of gas, which greatly benefits the development of micropores and mesopores. Although Comparative Example 2 has the best specific surface area data, the measured hydrogen sulfide adsorption capacity of Comparative Example 2 is lower than that of Example 1 and Comparative Example 3. It can be seen that the removal of H2S is not only related to the specific surface area, but also to the nitrogen on the surface of activated carbon. The heterocyclic nitrogen on the surface of activated carbon synthesized from organic nitrogen (alanine) is more conducive to the adsorption, oxidation, and dissociation of H2S, while the nitrogen-rich hydrolysate in this invention is less effective.

[0111] In the above embodiments and comparative examples, the hydrothermal reactions were all carried out in a hydrothermal reactor. The above embodiments are merely examples; for instance, besides centrifugation as a solid-liquid separation process, other solid-liquid separation processes such as solid-liquid pressing can also be used. Furthermore, in addition to nitrogen, inert gases such as argon can be used as the protective atmosphere. Additionally, the nitrogen-rich hydrolysate can be concentrated to different gradient concentrations (e.g., total nitrogen concentration of 2000–10000 ppm) to prepare carbon-based catalysts with different nitrogen contents (e.g., nitrogen doping of 2–10 wt.%). This invention is applicable to both room temperature hydrogen sulfide removal under aerobic humid conditions and room temperature hydrogen sulfide removal under anaerobic humid conditions (of course, room temperature hydrogen sulfide removal can also be achieved under anaerobic and humid conditions, although the catalytic reaction rate will decrease). The room temperature can be 20°C–30°C.

[0112] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. The application of nitrogen-doped activated carbon as a catalyst in the removal of hydrogen sulfide at a temperature of 20–30 °C under humid and aerobic conditions; wherein the nitrogen-doped activated carbon can promote the adsorption, ionization, and oxidation processes of hydrogen sulfide through pyridine-N and pyrrole-N therein, and wherein the nitrogen-doped activated carbon is prepared by a method of preparing activated carbon by hydrothermal doping enhanced by nitrogen-rich hydrolysate, the method of preparing activated carbon by hydrothermal doping enhanced by nitrogen-rich hydrolysate comprising the following steps: (1) Mix high-moisture nitrogen-rich organic solid waste with liquid water and carry out a hot hydrolysis reaction; after the reaction is completed, cool to room temperature, separate solid and liquid, retain the supernatant to obtain nitrogen-rich hydrolysate; wherein, the moisture content of the high-moisture nitrogen-rich organic solid waste is 5 wt.% to 88 wt.%, and the nitrogen content under dry basis is not less than 4 wt.%; the high-moisture nitrogen-rich organic solid waste is selected from any one or any combination of two of municipal sludge, Chlorella, and pork kitchen waste; (2) The nitrogen-rich hydrolysate is mixed with organic solid waste with high water content and then subjected to a hydrothermal reaction; after the reaction is completed, the solid product is collected, washed, and dried to obtain nitrogen-containing hydrothermal coke; wherein the water content of the organic solid waste with high water content is 5 wt.% to 88 wt.%; (3) The nitrogen-containing hydrothermal coke is mixed with a solid activator, and then heated under a protective atmosphere to carry out an activation reaction. After the reaction is completed, the carbon is washed and dried to obtain nitrogen-doped activated carbon. The solid activator is a solid potassium-containing activator.

2. The application as described in claim 1, characterized in that, In step (1), the high-moisture-content nitrogen-rich organic solid waste is mixed with liquid water to satisfy the following ratio: (dry basis mass of high-moisture-content nitrogen-rich organic solid waste): (mass of water contained in high-moisture-content nitrogen-rich organic solid waste + mass of liquid water) is 1:3 to 1:

10.

3. The application as described in claim 1, characterized in that, In step (1), the reaction temperature of the hot water hydrolysis reaction is 120-200 °C and the reaction time is 0.5-1.5 h.

4. The application as described in claim 3, characterized in that, In step (1), the nitrogen-rich hydrolysate is further concentrated to achieve a total nitrogen concentration of 2000-10000 ppm.

5. The application as described in claim 1, characterized in that, In step (2), the high moisture content organic solid waste is one or more of rice kitchen waste, melon peel kitchen waste, and waste paper pulp; The nitrogen-rich hydrolysate is mixed with high-moisture organic solid waste in a ratio of 1:3 to 1:10 (dry basis mass of high-moisture organic solid waste): (mass of water contained in high-moisture organic solid waste + mass of nitrogen-rich hydrolysate).

6. The application as described in claim 1, characterized in that, In step (2), the hydrothermal reaction temperature is 180–250 °C and the reaction time is 0.5–3 h.

7. The application as described in claim 1, characterized in that, In step (2), the cleaning is specifically performed by alternating washing with distilled water and ethanol for a total of 3 to 10 times; the drying is specifically performed by drying in an oven at 60 to 100 ℃ for 6 to 24 hours until constant weight.

8. The application as described in claim 1, characterized in that, In step (3), the nitrogen-containing hydrothermal coke and the activator are mixed in a mass ratio of 1:(1-6); The activation reaction is carried out at a temperature of 600–900 °C, with a heating rate of 3–10 °C / min and a reaction time of 0.5–3 h. The solid potassium-containing activator is selected from potassium hydroxide, potassium carbonate, potassium nitrate, potassium bicarbonate, potassium oxalate, potassium formate, potassium acetate, potassium citrate, potassium tartrate, and potassium lactate. The protective atmosphere is nitrogen or argon.

9. The application as described in claim 1, characterized in that, In step (3), the washing specifically involves washing with acid and water respectively; The drying process specifically involves drying in an oven at 60–100 °C for 6–24 hours until constant weight is achieved.

10. The application as described in claim 9, characterized in that, In step (3), the washing involves washing with dilute hydrochloric acid and distilled water 3 to 10 times each until the supernatant is neutral; wherein the dilute hydrochloric acid is dilute hydrochloric acid with a concentration of 0.5 to 4 M.

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