Activated carbon and a method for preparing and using the same

Abstract

The application discloses activated carbon and a preparation method and application thereof, and the preparation of the activated carbon comprises the following steps: performing oxidation pretreatment on enriched carbon to obtain the enriched carbon subjected to the oxidation pretreatment; the enriched carbon is organic residual carbon enrichment obtained by a sorting technology from coal gasification slag; mixing the enriched carbon subjected to the oxidation pretreatment, potassium hydroxide, high-temperature coal tar and water, and uniformly kneading to obtain coal paste; performing shaping and aging on the coal paste to obtain carbonization precursors; performing carbonization on the carbonization precursors, and then performing activation in an activation gas to obtain the activated carbon; and the activation gas comprises air and water vapor. The method is based on the unique physical characteristics and chemical structure features of the enriched carbon, forms the process technology of air pre-oxidation treatment-physical shaping-carbonization-micro-oxidation combined water vapor activation coupling for preparing the activated carbon, and the activated carbon product has good mesopore distribution characteristics, qualified iodine value and qualified methylene blue, and is suitable for being applied to the field of biochemical wastewater deep purification.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of activated carbon, in particular, the present application relates to an activated carbon and its preparation method and application. BACKGROUND

[0002] Coal gasification is the basis for developing processes such as coal-based chemicals, coal-based liquid fuels, IGCC power generation, poly-generation systems, hydrogen production, and fuel cells.

[0003] Coal gasification produces a large amount of solid waste, i.e., gasification slag. The gasification slag is divided into coarse slag and fine slag. The coarse slag is a glass body in the form of a broken block formed by low-melting eutectic substances in the coal ash after water quenching, and is discharged from the gasifier bottom ash lock hopper, accounting for 60-80% of the total amount of gasification ash. The composition of the coarse slag is similar to that of the boiler ash, and the coarse slag can be used as a mixing raw material for building materials and road bridges together with the boiler ash. However, the ignition loss of the coarse slag produced by some furnace types or gasification processes is relatively high, which greatly limits the application of the coarse slag. The fine slag is generated after the flue gas is washed and purified by precipitation, and accounts for 20-40% of the total amount of gasification ash. The ignition loss of the fine slag is as high as 20-30%, and the fine slag cannot be directly used as a building and road material. At present, the fine slag can only be landfilled or stacked, resulting in waste of resources and pollution of the soil and water bodies caused by the leakage of heavy metals.

[0004] The coal gasification slag is mainly composed of a large amount of amorphous substances, a small amount of crystalline minerals, and organic residual carbon, and has a certain surface area and pore structure. The coal gasification slag is a special carbon source for preparing adsorptive materials such as activated carbon, and is cheap and easy to obtain. The structure characteristics of the gasification slag are fully utilized for the preparation of activated carbon, which is beneficial to explore a new way for the high-value conversion and utilization of solid waste gasification slag. SUMMARY

[0005] The present application is based on the discovery and understanding of the inventors of the following facts and problems: At present, the gasification slag can only be landfilled or stacked, resulting in waste of resources and pollution of the soil and water bodies caused by the leakage of heavy metals. It is necessary to explore the high-value conversion and utilization of solid waste gasification slag.

[0006] The present application aims to at least solve one of the technical problems in the related art to some extent. To this end, the embodiments of the present application propose an activated carbon and a preparation method and application thereof. Based on the unique physical characteristics and chemical structure characteristics of the enriched carbon, an air pre-oxidation treatment-physical forming-carbonization-micro-oxidation combined water vapor activation coupling process technology is formed to prepare the activated carbon. The activated carbon product has good mesopore distribution characteristics, a qualified iodine value, and a qualified methylene blue, and is suitable for use in the field of biochemical wastewater deep purification.

[0007] The present application provides a preparation method of activated carbon, including the following steps:

[0008] (1) the enriched carbon is subjected to oxidation pretreatment to obtain an oxidation pretreated enriched carbon; the enriched carbon is an organic residual carbon enrichment obtained by a separation technique from coal gasification slag;

[0009] (2) the oxidation pretreated enriched carbon, potassium hydroxide, high-temperature coal tar and water are mixed and uniformly kneaded to obtain coal paste;

[0010] (3) the coal paste is subjected to shaping and aging to obtain a carbonization precursor;

[0011] (4) the carbonization precursor is subjected to carbonization and then activated in an activation gas to obtain activated carbon; the activation gas includes air and water vapor.

[0012] The preparation method of the activated carbon according to the embodiment of the application has the following advantages and technical effects: the organic residual carbon enrichment-enriched carbon, which is obtained by a separation technique from coal gasification slag, a typical solid waste in coal chemical industry, is used as a raw material, based on the unique physical characteristics and chemical structure features of the enriched carbon, an air pre-oxidation treatment-physical shaping-carbonization-micro-oxidation combined water vapor activation coupling process technology for preparing activated carbon is formed, and the activated carbon product has good mesopore distribution characteristics (for example, mesopore ratio), qualified iodine value and qualified methylene blue, and is suitable for use in the field of biochemical wastewater deep purification.

[0013] In the embodiment of the present application, the gasification slag is obtained after removing ash by sorting, and the enriched carbon has low reactivity, developed pore structure and large specific surface area compared with other activated carbon preparation raw materials, and has the potential to prepare activated carbon and other high value-added carbon materials, and is a cheap and easily available special carbon source. After high temperature refining of the raw material enriched carbon in the gasification furnace, the volatile matter is low, and the activation reaction performance is poor, therefore, the pre-oxidation treatment and micro-oxidation activation technology can improve the activation reaction capacity of the enriched carbon and improve the surface properties of the activated carbon. The pre-oxidation treatment of the enriched carbon selectively oxidizes the fatty structure (such as side chain, bridge bond, etc.) in the enriched carbon to generate more oxygen-containing functional groups, which is beneficial to expand the active sites of the enriched carbon, improve the reactivity of the enriched carbon, and improve the improvement of the surface properties of the enriched carbon by the activating agent in the activation process. After carbonization treatment, the micro-oxidation activation treatment is carried out, and in the gas-solid multiphase micro-oxidation reaction activation process of the enriched carbon, the activation mode of suitable air combined with steam is adopted, and the activating agent potassium hydroxide is matched, the activation gas (steam combined with air) in the system contacts the carbonaceous deposits and coking substances blocking the pores on the surface of the enriched carbon to remove the deposits, exposes the internal polar functional groups, realizes the deep etching of the enriched carbon and improves the pore forming and hole expanding effect, and improves the surface properties and pore structure distribution characteristics of the product. The pre-oxidation treatment and micro-oxidation activation technology combined means improves the reactivity of the enriched carbon, and alleviates the activation temperature. Generally, the gasification slag enriched carbon activation requires a high temperature of 950℃, and after pre-oxidation treatment, the reactivity of the enriched carbon is improved, therefore, the subsequent activation temperature can be reduced to 850℃, and the operation cost is reduced.

[0014] In the embodiment of the present application, the volatile matter of the enriched carbon is low, and the volatile matters such as CO, H2, CH4 and tar generated by carbonization are greatly reduced, and the carbonization tail gas is small, which is beneficial to reduce the tail gas treatment cost. The binder used is high-temperature coal tar, which forms a support skeleton and is easy to solidify during carbonization and activation, and is beneficial to improve the strength of the activated carbon product. The activating agent potassium hydroxide not only can improve the activity of the enriched carbon, is beneficial to the hole expanding reaction, and improve the product index, but also decomposes in the high-temperature activation process and almost does not remain in the product, so the activated carbon product does not need water washing process and does not produce waste water, and the environmental performance of the whole process is improved. Water and the binder jointly act on the enriched carbon to generate interface chemical condensation into paste-like material, the plasticity of the extruded and deformed enriched carbon is improved, and the product strength is easy to be formed and improved. The preparation of activated carbon using the gasification slag sorted enriched carbon as the raw material highlights the structural advantages of the enriched carbon, solves the problems of land resource occupation and serious ecological environment damage caused by gasification slag stacking and landfill, and explores a new way with broad market economic prospects for realizing the resource utilization of coal chemical industry bulk solid waste coal gasification slag.

[0015] In some embodiments, in step (1), the ash content of the enriched carbon is ≤15%;

[0016] And / or, the temperature of the oxidation pretreatment is 280-350℃;

[0017] And / or, the time of the oxidation pretreatment is 3-7h;

[0018] And / or, the oxidation pretreatment is carried out in air;

[0019] And / or, the particle size of the carbon-enriched in the oxidation pretreatment is ≤0.075mm.

[0020] In some embodiments, in the step (2), the mass ratio of the carbon-enriched, the potassium hydroxide, the high-temperature coal tar and the water in the oxidation pretreatment is 1:(0.02-0.05):(0.10-0.30):(0.10-0.20).

[0021] In some embodiments, in the step (2), before mixing, the potassium hydroxide is configured into a potassium hydroxide aqueous solution with a mass fraction of 15-45%;

[0022] And / or, the viscosity E80 of the high-temperature coal tar is ≤5; the relative density d4 20 of the high-temperature coal tar is 1.13-1.22; the mass content of pitch of the high-temperature coal tar is 60%-70%; the mass content of toluene insoluble of the high-temperature coal tar is 3.5%-7.0%; the ash content of the high-temperature coal tar is ≤0.13%; the moisture content of the high-temperature coal tar is ≤4%;

[0023] And / or, the temperature of the kneading uniformity is 70-80℃.

[0024] In some embodiments, in the step (3), the aging includes natural airing for 2-3 days.

[0025] And / or, the mass content of water in the carbonization precursor is 7-9%.

[0026] In some embodiments, in the step (4), the temperature of the carbonization is 500-600℃;

[0027] And / or, the constant temperature time of the carbonization is 30-60min;

[0028] And / or, the carbonization is carried out under an inert atmosphere.

[0029] In some embodiments, in the step (4), the temperature of the activation is 800-900℃;

[0030] And / or, the time of the activation is 90-120min;

[0031] And / or, the volume flow ratio of air to water vapor in the activation gas is 10-20:0.5-1.

[0032] And / or, the activating gas also includes an inert gas, and the inert gas, air and water vapor are introduced in a volume flow rate ratio of 100:10-20:0.5-1.

[0033] This invention provides an activated carbon prepared by the method described in this invention. The activated carbon product exhibits good mesoporous distribution characteristics, meets iodine value and methylene blue standards, and is suitable for applications such as deep purification of biochemical wastewater.

[0034] In some embodiments, the specific surface area of ​​the activated carbon is 500-550 m². 2 ·g -1 ;

[0035] And / or, the iodine value of the activated carbon is 550-620 mg·g. -1 ;

[0036] And / or, the methylene blue value of the activated carbon is 90-100 mg·g. -1 ;

[0037] And / or, the pore volume of the activated carbon is 0.32-0.36 ml·g. -1 ;

[0038] And / or, the mesopore volume of the activated carbon is 0.21-0.23 ml·g. -1 .

[0039] This invention provides an application of activated carbon for wastewater purification. In this embodiment, the activated carbon product exhibits good mesoporous distribution characteristics, meets iodine value and methylene blue standards, and is suitable for wastewater purification, particularly for the deep purification of biochemical wastewater. Attached Figure Description

[0040] Figure 1 These are the FT-IR spectra of the enriched carbon after oxidation pretreatment in Example 1 and the enriched carbon without oxidation pretreatment in Comparative Example 2.

[0041] Figure 2 It is a SEM analysis of the surface morphology of enriched carbon raw materials.

[0042] Figure 3 This is a SEM analysis of the apparent morphology of activated carbon in Example 1. Detailed Implementation

[0043] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0044] An embodiment of the present invention provides a method for preparing activated carbon, comprising the following steps:

[0045] (1) The enriched carbon is subjected to oxidation pretreatment to obtain oxidized pretreated enriched carbon; the enriched carbon is an organic residual carbon enrichment obtained by sorting technology from coal gasification slag.

[0046] (2) Mix the enriched carbon, potassium hydroxide, high-temperature coal tar and water in the oxidation pretreatment, knead evenly, and obtain coal paste;

[0047] (3) The coal paste is shaped and aged to obtain a carbonization precursor;

[0048] (4) The carbonization precursor is carbonized and then activated in an activation gas to obtain activated carbon; the activation gas includes air and water vapor.

[0049] The activated carbon preparation method of this invention uses enriched carbon, an organic residual carbon concentrate obtained by sorting typical solid waste gasification slag from coal chemical industry, as raw material. Based on the unique physical properties and chemical structure characteristics of the enriched carbon, a process technology is formed that couples air pre-oxidation treatment, physical molding, carbonization, and micro-oxidation with steam activation to prepare activated carbon. The activated carbon product has good mesoporous distribution characteristics, qualified iodine value, and qualified methylene blue, and is suitable for use in fields such as deep purification of biochemical wastewater.

[0050] In this embodiment of the invention, enriched carbon is obtained after the gasification slag is sorted and ash is removed. Compared with other raw materials for activated carbon preparation, enriched carbon has low reactivity, a well-developed pore structure, and a large specific surface area, making it a potential source for preparing activated carbon and other high-value-added carbon materials. It is a special carbon source that is inexpensive and readily available. After being subjected to high-temperature processing in a gasifier, the enriched carbon has low volatile matter and poor activation performance. Therefore, pre-oxidation treatment and micro-oxidation activation technology can improve the activation reaction capacity of the enriched carbon and improve its surface properties. Pre-oxidation treatment of the enriched carbon selectively oxidizes the aliphatic structures (such as side chains and bridging bonds) to generate more oxygen-containing functional groups, which is beneficial for increasing the active sites of the enriched carbon, improving its reactivity, and enhancing the effect of the activator on improving the surface properties of the enriched carbon during the activation process. Following carbonization, a micro-oxidation activation treatment is performed. In the gas-solid multiphase micro-oxidation activation process of the enriched carbon, a suitable air-steam combined activation method is employed, using potassium hydroxide as the activator. In this system, the activation gas (steam combined with air) contacts the carbonaceous deposits and coking materials clogging the pores on the enriched carbon surface, causing an oxidation reaction that removes the deposits and exposes the internal polar functional groups. This achieves deep etching of the enriched carbon and enhances pore-forming and expanding effects, improving the surface properties and pore structure distribution characteristics of the product. The combined approach of pre-oxidation treatment and micro-oxidation activation technology enhances the reactivity of the enriched carbon and moderates the activation temperature. Typically, the activation of enriched carbon from gasification slag requires a high temperature of 950℃. After pre-oxidation treatment, the reactivity of the enriched carbon is increased; therefore, the subsequent activation temperature can be reduced to 850℃, lowering operating costs.

[0051] In this embodiment of the invention, the enriched carbon has low volatile content, and the volatiles such as CO, H2, CH4, and tar produced during carbonization are significantly reduced, resulting in less carbonization tail gas and thus lower tail gas treatment costs. The binder used is high-temperature coal tar, which forms a supporting framework during carbonization and activation and is easy to solidify, thus improving the strength of the activated carbon product. The activator potassium hydroxide not only enhances the activity of the enriched carbon, promoting pore-expanding reactions and improving product indicators, but also decomposes during high-temperature activation, leaving almost no residue in the product. Therefore, the activated carbon product does not require a water washing process, generating no wastewater and improving the environmental performance of the entire process. The combined action of water and the binder causes the enriched carbon to undergo interfacial chemical coagulation into a paste-like material, increasing its plasticity for extrusion deformation, facilitating molding, and improving product strength. Using gasification slag-separated enriched carbon as raw material for activated carbon preparation highlights the structural advantages of enriched carbon, solving the problem of gasification slag accumulation and landfill occupying land resources and severely damaging the ecological environment. This explores a new path with broad market economic prospects for the high-value utilization of coal gasification slag, a major solid waste from coal chemical industry.

[0052] In some embodiments, in step (1), the gasification slag includes fine gasification slag. In this embodiment of the invention, the gasification slag escapes in the gasifier as fly ash and is collected outside the furnace. After ash removal by sorting, enriched carbon is obtained.

[0053] In some embodiments, in step (1), the ash content of the enriched carbon is ≤15%; the enriched carbon is an organic residual carbon enrichment obtained by sorting coal gasification slag through sorting technology. The present invention does not have any special restrictions on the sorting technology, as long as the ash is removed by sorting. For example, the sorting technology includes at least one of flotation, gravity separation, electrostatic separation, and combustion, preferably flotation.

[0054] In this embodiment of the invention, carbon in the coal gasification slag produced by coal gasification is sorted, recovered, and dried to obtain enriched carbon. There are no special limitations on the sorting method; enriched carbon with an ash content ≤15% can be obtained using conventional sorting methods in the art. An ash content ≤15% in the enriched carbon is beneficial to improving the liquid-phase adsorption performance of the activated carbon product.

[0055] In some embodiments, there is no special limitation on the particle size of the enriched carbon in step (1). For example, the particle size of the enriched carbon can be ≤0.075mm.

[0056] In some embodiments, in step (1), the temperature of the oxidation pretreatment is 280-350°C, specifically, for example, 280°C, 290°C, 300°C, 310°C, 320°C, 340°C, 350°C; the time of the oxidation pretreatment is 3-7 hours, specifically, for example, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours; the oxidation pretreatment is carried out in air.

[0057] In this embodiment of the invention, the enriched carbon undergoes pre-oxidation treatment. Under suitable oxidation conditions, high-temperature air selectively oxidizes the aliphatic structures (such as side chains and bridging bonds) in the enriched carbon, generating more oxygen-containing functional groups. This is beneficial for increasing the active sites of the enriched carbon, improving its reactivity, and enhancing the effect of the activator on the surface properties of the enriched carbon during the activation process. Furthermore, air pre-oxidation also serves a drying function, and the dried enriched carbon is beneficial for powder production.

[0058] In some embodiments, in step (1), the enriched carbon after oxidation pretreatment is crushed and screened sequentially to obtain the enriched carbon after oxidation pretreatment.

[0059] In some embodiments, in step (1), the particle size of the enriched carbon after oxidation pretreatment is ≤0.075mm; or, the particle size of the powdered enriched carbon after oxidation pretreatment is ≤0.075mm. In this embodiment of the invention, a particle size ≤0.075mm is beneficial to increasing the outer surface area of ​​the enriched carbon after oxidation pretreatment, making it easier to form and improving product strength.

[0060] In some embodiments, in step (2), the mass ratio of the enriched carbon, potassium hydroxide, high-temperature coal tar, and water in the oxidation pretreatment is 1:(0.02-0.05):(0.10-0.30):(0.10-0.20), specifically, 1:0.02-0.05 (e.g., 0.02, 0.03, 0.04, 0.05):0.10-0.30 (e.g., 0.10, 0.12, 0.15, 0.18, 0.20, 0.30):0.10-0.20 (e.g., 0.10, 0.12, 0.15, 0.18, 0.20).

[0061] In this invention embodiment, based on pre-oxidation treatment and micro-oxidation activation technology, a shallow activation method is proposed to treat the activated carbon in a matching manner during the activation process. This ensures that the iodine value and methylene blue content of the product are up to standard. Specifically, this invention only requires the addition of 2-5% KOH to the pre-oxidated activated carbon, while conventional chemical activation methods typically require as much as 200%-300% KOH. When the KOH addition exceeds 10%, the activation process causes the pore walls of the activated carbon to burn off and collapse, resulting in a decrease in surface area, a significant increase in macropores, and a deterioration in surface properties. The combined effect of the shallow activation method, oxidation pre-treatment, and micro-oxidation activation in this invention not only improves the activity of the activated carbon, which is beneficial for pore expansion reactions and improves product indicators, but also ensures that the alkali decomposes during the high-temperature activation process and hardly remains in the product. Therefore, the activated carbon product does not require a water washing process, resulting in no wastewater generation and improving the environmental performance of the entire process.

[0062] In this embodiment of the invention, the binder is selected as high-temperature coal tar with an asphalt content of 60% to 70%, which has good compatibility with the enriched carbon. During carbonization and activation, it is easier to form a supporting skeleton and to solidify, which is beneficial to improving the strength of the activated carbon product. Under the combined action of water and binder, the enriched carbon produces interfacial chemical coagulation into a paste-like material, which improves the plasticity of extrusion deformation, making it easier to form and improve the product strength. By controlling the mass ratio of enriched carbon, potassium hydroxide, high-temperature coal tar and water in the oxidation pretreatment, it is beneficial to the pore expansion reaction and pore development of the carbon matrix in the enriched carbon, which promotes further improvement of adsorption performance.

[0063] In some embodiments, in step (2), before mixing, the potassium hydroxide is prepared into an aqueous solution of potassium hydroxide with a mass fraction of 15-45%, specifically, for example, 15%, 30%, or 45%.

[0064] In some embodiments, in step (2), the viscosity E80 of the high-temperature coal tar is ≤5; the relative density d4 of the high-temperature coal tar is ≤5. 20The content of the high-temperature coal tar is 1.13 to 1.22; the pitch content of the high-temperature coal tar is 60% to 70%, specifically, for example, 60%, 62%, 65%, 68%, or 70%; the toluene-insoluble matter content of the high-temperature coal tar is 3.5% to 7.0%; the ash content of the high-temperature coal tar is ≤0.13%; and the moisture content of the high-temperature coal tar is ≤4%.

[0065] In this embodiment of the invention, the binder used is high-temperature coal tar pitch, which has a higher pitch content (60-70%) than conventional high-temperature coal tar pitch (55-60%). It has good compatibility with enriched carbon, and is easier to form a supporting skeleton and solidify during carbonization and activation, which is beneficial to improving the strength of activated carbon products.

[0066] In some embodiments, in step (2), the mixing includes: first preparing potassium hydroxide into an aqueous solution, and then mixing it with high-temperature coal tar and water in sequence with the enriched carbon after oxidation pretreatment.

[0067] In some embodiments, in step (2), the temperature of the high-temperature coal tar is 70-80°C, that is, the high-temperature coal tar is preheated to 70-80°C, specifically, for example, 70°C, 75°C, or 80°C.

[0068] In some embodiments, in step (2), the water temperature is 60-80°C, specifically, for example, 60°C, 70°C, or 80°C. In this embodiment of the invention, a water temperature of 60-80°C is beneficial for maintaining the fluidity of the binder during the molding process and improving the wetting effect of the binder on the enriched carbon.

[0069] In some embodiments, in step (2), the temperature of kneading is 70-80°C, specifically, for example, 70°C, 75°C, or 80°C; optionally, the kneading is performed using a high-pressure mixer, where the mixture is kneaded vigorously to form coal paste; optionally, the mixture is heated to 70-80°C.

[0070] In some embodiments, there are no special restrictions on the shape of the molding in step (3), for example, it can be cylindrical or spherical; optionally, the molding is performed by extrusion molding; the molding is performed by hydraulic press extrusion molding.

[0071] In some embodiments, in step (3), the aging process includes natural air drying for 2-3 days.

[0072] In some embodiments, in step (3), the water content in the carbonization precursor is 7-9% by mass, specifically, for example, 7%, 8%, or 9%.

[0073] In some embodiments, the carbonization precursor can be cut into carbon strips with a length of about 1-1.5 cm.

[0074] In some embodiments, in step (4), the carbonization temperature is 500-600℃, specifically, for example, 500℃, 520℃, 550℃, 580℃, 600℃; the carbonization heating rate is 5-10℃ / min, specifically, for example, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min; the carbonization isothermal time is 30-60min, specifically, for example, 30min, 40min, 50min, 60min; the carbonization is carried out under an inert atmosphere; optionally, the inert atmosphere includes nitrogen; the nitrogen flow rate in the reaction system is 50-250ml / min; optionally, an inert atmosphere is introduced, and then the temperature is raised to the carbonization temperature for carbonization.

[0075] In some embodiments, in step (4), after carbonization, the temperature is raised to the activation temperature for activation. Optionally, the heating rate is 2-6℃ / min, specifically, for example, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, or 6℃ / min. In this embodiment of the invention, the heating rate is 2-6℃ / min. A lower heating rate means a longer time to reach the target temperature, which is beneficial for the activator to enter the carbon matrix and promote pore development. It also provides more time for the pyrolysis reaction and the escape of pyrolysis gas, forming more pore channels.

[0076] In some embodiments, in step (4), activation is performed in an activation gas;

[0077] The activation temperature is 800-900℃, specifically, for example, 800℃, 820℃, 850℃, 880℃, 890℃, 895℃, 900℃; the activation time is 90-120min, specifically, for example, 90min, 100min, 110min, 120min;

[0078] The volumetric flow rate ratio of air to water vapor in the activation gas is 10-20:0.5-1, specifically, 10-20 (e.g., 10, 12, 14, 16, 18, 20) : 0.5-1 (e.g., 0.5, 0.6, 0.7, 0.8, 0.9, 1);

[0079] Optionally, the air flow rate is 10-40 ml / min, specifically, for example, 10 ml / min, 12 ml / min, 14 ml / min, 16 ml / min, 18 ml / min, 20 ml / min, 30 ml / min, 40 ml / min; the water vapor flow rate is 30-110 ml / h, specifically, for example, 30 ml / h, 35 ml / h, 40 ml / h, 45 ml / h, 50 ml / h, 55 ml / h, 60 ml / h, 70 ml / h, 80 ml / h, 110 ml / h;

[0080] Optionally, activation gas is introduced to begin activation when the temperature is reached.

[0081] Optionally, the activation gas also includes an inert gas, and the volumetric flow rate ratio of the inert gas, air, and water vapor is 100:10-20:0.5-1, specifically, 100:10-20 (e.g., 10, 12, 14, 16, 18, 20):0.5-1 (e.g., 0.5, 0.6, 0.7, 0.8, 0.9, 1); the inert gas includes nitrogen; optionally, during the activation process, after the air and inert gas (nitrogen) are mixed in a gas mixing tank, they are mixed with water vapor in a heated and insulated outlet pipeline and enter the furnace to begin activation. After activation, the flow of water vapor and air is stopped, and the flow of inert gas (nitrogen) continues to cool down until the temperature is below 150°C, at which point the flow of inert gas (nitrogen) is stopped.

[0082] In this embodiment of the invention, after carbonization, a micro-oxidation activation treatment is performed. In the gas-solid multiphase micro-oxidation reaction activation process of enriched carbon, a suitable activation method combining air and water vapor is adopted, with an appropriate amount of potassium hydroxide as the activator. By controlling different activation process parameters and the "appropriate" oxygen content in the activation gas ((air flow rate * oxygen content in air) / (air flow rate + inert gas flow rate)), a suitable activation effect is achieved. In the system, the activation gas (water vapor combined with air) comes into contact with the carbonaceous deposits and coking materials clogging the pores on the surface of the enriched carbon, and an oxidation reaction occurs to remove the deposits, exposing the internal polar functional groups. This achieves deep etching of the enriched carbon and enhances the pore-forming and pore-expanding effects, improving the surface properties and pore structure distribution characteristics of the product. Excessive "oxygen content" will cause pore wall collapse, reduce the distribution and development of pores on the surface, and lead to a decrease in the adsorption performance of activated carbon. Further increases in oxygen content will exacerbate the oxidation and ablation of activated carbon into ash. Using only water vapor without air, or only air without water vapor, lacks the synergistic effect of the two active gases, which is detrimental to the pore-forming and expanding reactions of carbon in low-activity enriched carbon. The optimal volumetric flow rate ratio of air to water vapor is 10-20:0.5-1. The alternating mixing and synergistic effect of air and water vapor with the enriched carbon, along with appropriate oxygen content in the activating gas, is beneficial for the carbon-consuming etching and pore-expanding reactions of low-activity enriched carbon, promoting pore development. However, if the air content is too high, the carbon in the activated carbon will oxidize into ash at high temperatures.

[0083] In this embodiment of the invention, the combined approach of pre-oxidation treatment and micro-oxidation activation technology enhances the reactivity of the enriched carbon and moderates the activation temperature. After pre-oxidation treatment, the reactivity of the enriched carbon is improved, allowing the subsequent activation temperature to be reduced to below 900℃, thus lowering operating costs. Typically, gasification slag enriched carbon that has not undergone pre-oxidation treatment requires a high temperature of 950℃ to achieve similar surface properties and pore structure.

[0084] An activated carbon according to an embodiment of the present invention is prepared by the preparation method described in the embodiment of the present invention. In this embodiment, the activated carbon product has good mesoporous distribution characteristics, meets the required iodine value and methylene blue content, and is suitable for use in fields such as deep purification of biochemical wastewater.

[0085] In some embodiments, the specific surface area of ​​the activated carbon is 500-550 m². 2 ·g -1 The activated carbon has an iodine value of 550-620 mg·g. -1 The activated carbon contains 90-100 mg / g of methylene blue. -1 The activated carbon has a pore volume of 0.32-0.36 ml·g. -1 The mesopore volume of the activated carbon is 0.21-0.23 ml·g. -1 The average pore size of the activated carbon is 3.2-3.5 nm.

[0086] In some embodiments, the activated carbon has good mesopore distribution characteristics, such as a mesopore ratio. Mesopores, also called mesopores, are pores with a diameter range of 2-50 nm. They are channels connecting micropores (<2 nm) and macropores (>50 nm). The mesopore ratio is the mesopore volume / total pore volume. The mesopore ratio of the activated carbon is greater than 50%, and optionally greater than 55% or greater than 60%.

[0087] This invention discloses an application of activated carbon for wastewater purification. In this embodiment, the activated carbon product exhibits good mesoporous distribution characteristics, meets iodine value and methylene blue emission standards, and is suitable for wastewater purification, particularly for the deep purification of biochemical wastewater.

[0088] In some embodiments, it is used for the purification of biochemical wastewater; optionally, it is used for the deep purification of biochemical wastewater; the biochemical wastewater contains organic matter.

[0089] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0090] Example 1

[0091] A method for preparing activated carbon includes the following steps:

[0092] (1) Enriched carbon with 15% ash content was pre-oxidized at 320℃ for 5 hours, and then crushed, ground and sieved to obtain enriched carbon powder with a particle size ≤0.075mm after oxidation pretreatment.

[0093] (2) High-temperature coal tar: viscosity (E80): 2.7, relative density (d4) 20 ): 1.19, bitumen content 65%, toluene-insoluble matter: 4.2%, ash content: 0.1%, moisture content: 2%.

[0094] The enriched carbon powder undergoing oxidation pretreatment is prepared by adding 20% ​​potassium hydroxide solution, high-temperature coal tar, and water in a mass ratio of 1:0.20:0.30:0.15. The 20% potassium hydroxide solution, high-temperature coal tar, and water are added sequentially to the enriched carbon powder undergoing oxidation pretreatment. The high-temperature coal tar is preheated to 80°C, and the water temperature is 60°C. The mixture is then vigorously kneaded in a kneader (heated to 80°C) until homogeneous to form coal paste.

[0095] (3) The coal paste is extruded into a smooth cylindrical shape in a hydraulic press and naturally dried for 2 days. The water content is 8%, forming a carbonization precursor.

[0096] (4) Nitrogen gas is introduced into the system at a rate of 200 ml / min, and the temperature is increased to 550°C at a rate of 7°C / min. The temperature is held for 30 min, and then increased to 850°C at a rate of 3°C / min. When the temperature reaches 850°C, air is introduced at a rate of 20 ml / min. At the same time, water vapor is introduced at a rate of 60 ml / h to start activation. The activation time is 120 min. After activation, the injection of air and water vapor is stopped, and nitrogen gas is continued to be introduced to cool down until the temperature is below 150°C. Nitrogen gas is then stopped and the temperature is allowed to cool down naturally to obtain activated carbon.

[0097] Example 2

[0098] The preparation method is the same as that in Example 1, except that in step (2), the mass ratio of the enriched carbon powder under oxidation pretreatment, 20% potassium hydroxide solution, high-temperature coal tar, and water is 1:0.10:0.20:0.20.

[0099] Example 3

[0100] The preparation method is the same as that in Example 1, except that the activation temperature in step (4) is 800°C.

[0101] Comparative Example 1

[0102] The preparation method is the same as that in Example 1, except that no air is introduced during the activation process in step (4).

[0103] Comparative Example 2

[0104] The preparation method is the same as that in Example 1, except that in step (1), the enriched carbon is not pre-oxidized, that is, the enriched carbon with 15% ash content is crushed, ground and sieved to obtain enriched carbon powder with a particle size of <0.075mm; in step (2), enriched carbon powder is used to replace the enriched carbon powder that has undergone oxidation pretreatment.

[0105] Comparative Example 3

[0106] The preparation method is the same as that in Example 1, except that in step (1), the enriched carbon is not pre-oxidized, that is, the enriched carbon with 15% ash content is crushed, ground and sieved to obtain enriched carbon powder with a particle size of <0.075mm; in step (2), enriched carbon powder is used to replace the enriched carbon powder that has undergone oxidation pretreatment; and in step (4), air is not introduced during the activation process.

[0107] Comparative Example 4

[0108] The preparation method is the same as that in Example 1, except that in step (2), the mass ratio of enriched carbon powder with oxidation pretreatment: 40% potassium hydroxide solution: high-temperature coal tar: water is 1:0.30:0.30:0.15.

[0109] Comparative Example 5

[0110] The preparation method is the same as in Example 1, except that the air flow rate is 200 ml / min.

[0111] Biochemical wastewater purification test: The initial COD content of the biochemical wastewater was 312 mg·L⁻¹. -1 The dosage of activated carbon in the biochemical wastewater is 0.4 g·L. -1 .

[0112] Table 1 Surface property parameters of enriched carbon

[0113]

[0114] Table 2 Activated Carbon

[0115]

[0116]

[0117] The apparent morphology of enriched carbon is as follows Figure 2 As shown, the enriched carbon appears as black, odorless, and non-adhesive sand-like particles. Its surface consists of a large number of irregular porous matrices and a small number of spherical particles. The various morphologies of the substances exhibit a mixed, adhered, and encapsulated state. The presence of a certain number of porous matrices in the microstructure of the enriched carbon initially reflects that it has a certain pore structure, thereby forming a certain specific surface area.

[0118] As can be seen from the surface properties of the enriched carbon in Table 1, the enriched carbon has a certain specific surface area and pore structure, and possesses certain macromolecular liquid adsorption properties. The iodine value of the enriched carbon is 310 mg·g⁻¹. -1 The methylene blue adsorption value was 38 mg·g. -1 None of them met the technical specifications for activated carbon used in industrial water treatment.

[0119] The following points can be observed from Table 2:

[0120] (1) The activated carbon prepared in Example 1 by the coupled method of air pre-oxidation treatment-physical molding-carbonization-micro-oxidation and steam activation is as follows: Figure 3 As shown, the product surface has distinct edges and corners, forming numerous pores of varying sizes. The plate-like carbonaceous components become sparse, with obvious surface pores extending into the interior, evolving into a rich pore structure. This increases the specific surface area, iodine value, methylene blue content, pore volume, and micropore volume of the activated carbon, with a mesopore ratio greater than 60%, which is beneficial for improving liquid adsorption performance. The COD content is 312 mg·L⁻¹. -1 The COD value of the biochemical wastewater was reduced by more than 85%.

[0121] (2) After the enriched carbon was pre-oxidized in air for a period of time, the oxygen-containing functional groups on its surface changed. The FTIR values ​​of the enriched carbon in Comparative Example 2 (without oxidation pretreatment) and the enriched carbon in Example 1 (after oxidation pretreatment) are as follows: Figure 1 As shown.

[0122] Figure 1 The results show that the characteristic peaks of the enriched carbon, before and after oxidation pretreatment, are similar in shape, but differ in intensity, indicating that the composition did not change significantly after pre-oxidation treatment. Under suitable oxidation conditions, high-temperature air selectively oxidizes the aliphatic structures (such as side chains and bridging bonds) in the enriched carbon, generating more oxygen-containing functional groups, which is beneficial to increasing the active sites of the enriched carbon and has a positive effect on improving the surface properties of the activated carbon. As can be seen from Table 2, compared with the activated carbon in Comparative Example 2 that was not pretreated by oxidation, the activated carbon in Example 1 that underwent oxidation pretreatment has a higher specific surface area, iodine value, methylene blue value, etc., and a higher COD removal efficiency from biochemical wastewater.

[0123] (3) As can be seen from Example 1 and Comparative Examples 1 and 3, both steam and air activation are beneficial to improving the surface properties of activated carbon prepared from enriched carbon. The activation reaction of enriched carbon using these two gases belongs to a multiphase reaction of a gas-solid system. The entire process includes the external and internal diffusion of the activation gas on the surface of the enriched carbon, the oxidation-reduction reaction between the activation gas and the surface of the enriched carbon to generate intermediate products, the decomposition of intermediate products into reaction products, the desorption and external diffusion of reaction products, and under high-temperature activation conditions, the activation gas contacts the carbon in the enriched carbon and activates it to generate CO, CO2, H2 and other hydrocarbon gases. The activation gas achieves the effect of pore formation in the carbonization furnace through the ablation of carbon. For enriched carbon, a substance with very low activity, air pre-oxidation increases the active sites on the surface of the enriched carbon and reduces the activation temperature of the enriched carbon jointly activated by steam and air. The specific surface area of ​​the product can be increased at a lower temperature, and the surface properties and pore structure are significantly improved.

[0124] (4) To address the highly inert chemical characteristics of the activated carbon, a combination of air oxidation pretreatment of the raw materials and chemical activation technology using steam and air micro-oxidation was employed. This targeted regulation of the activated carbon's pore structure expanded the pore structure, resulting in a specific surface area comparable to that of ordinary activated carbon. The activated carbon product met the required iodine value and methylene blue standards. The activated carbon prepared by this invention can reduce the COD of biochemical wastewater to 50 mg·L⁻¹. -1 The following water quality meets the Class B requirements of the Integrated Discharge Standard for Water Pollutants (DB11 / 307-2013).

[0125] In Comparative Example 5, when the air flow rate was increased to 200 ml / min, the oxygen content (air flow rate * oxygen content in the air) / (air flow rate + inert gas flow rate) was approximately 10%, and the organic carbon in the enriched carbon was oxidized into ash under high temperature.

[0126] (5) Based on the pre-oxidation treatment and micro-oxidation activation technology, a shallow activation method is proposed to treat the enriched carbon in the activation process to ensure that the iodine value and methylene blue content of the product are qualified. That is, this invention only requires the addition of 2-5% KOH to the enriched carbon after oxidation pretreatment. In Comparative Example 4, when the amount of KOH added exceeded 10%, the activation process caused the pore walls of the enriched carbon to burn off and collapse, the surface area of ​​the enriched carbon decreased after activation, the macropores increased significantly, and the surface properties deteriorated. The combined effect of the shallow activation method, oxidation pretreatment, and micro-oxidation activation in this invention can improve the activity of the enriched carbon, which is conducive to the formation of pore-expanding reactions and improves the product indicators.

[0127] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0128] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A method for preparing activated carbon, characterized in that, Includes the following steps: (1) The enriched carbon is subjected to oxidation pretreatment to obtain oxidized pretreated enriched carbon; the enriched carbon is an organic residual carbon enrichment obtained by coal gasification slag through sorting technology; the temperature of the oxidation pretreatment is 280-350 ℃. (2) The enriched carbon, potassium hydroxide, high-temperature coal tar and water of the oxidation pretreatment are mixed and kneaded evenly to obtain coal paste; the mass ratio of the enriched carbon, potassium hydroxide, high-temperature coal tar and water of the oxidation pretreatment is 1: (0.02~0.05): (0.10~0.30): (0.10~0.20). (3) The coal paste is shaped and aged to obtain a carbonization precursor; (4) The carbonization precursor is carbonized and then activated in an activation gas to obtain activated carbon; the activation gas includes air and water vapor; the volume flow rate ratio of air and water vapor in the activation gas is 10-20:0.5-1.

2. The method for preparing activated carbon according to claim 1, characterized in that, In step (1), the ash content of the enriched carbon is ≤15%; And / or, the oxidation pretreatment time is 3-7 h; And / or, the oxidation pretreatment is carried out in air; And / or, the particle size of the enriched carbon obtained from the oxidation pretreatment is ≤0.075 mm.

3. The method for preparing activated carbon according to claim 1, characterized in that, In step (2), before mixing, the potassium hydroxide is first prepared into a potassium hydroxide aqueous solution with a mass fraction of 15-45%. And / or, the viscosity E80 of the high-temperature coal tar is ≤5; the relative density d4 of the high-temperature coal tar is ≤5. 20 The content of the high-temperature coal tar is 1.13–1.22; the pitch content of the high-temperature coal tar is 60%–70%; the toluene-insoluble matter content of the high-temperature coal tar is 3.5%–7.0%; the ash content of the high-temperature coal tar is ≤0.13%; and the moisture content of the high-temperature coal tar is ≤4%. And / or, the temperature at which the mixture is kneaded evenly is 70-80℃.

4. The method for preparing activated carbon according to claim 1, characterized in that, In step (3), the aging process includes natural air drying for 2-3 days; And / or, the water content in the carbonized precursor is 7-9% by mass.

5. The method for preparing activated carbon according to claim 1, characterized in that, In step (4), the carbonization temperature is 500-600 ℃; And / or, the isothermal time for carbonization is 30-60 min; And / or, the carbonization is carried out under an inert atmosphere.

6. The method for preparing activated carbon according to claim 1, characterized in that, In step (4), the activation temperature is 800-900 ℃; And / or, the activation time is 90-120 min; And / or, the activating gas also includes an inert gas, and the inert gas, air and water vapor are introduced in a volume flow rate ratio of 100:10-20:0.5-1.

7. An activated carbon, characterized in that, It is prepared by the preparation method according to any one of claims 1-6.

8. The activated carbon according to claim 7, characterized in that, The specific surface area of ​​the activated carbon is 500-550 m². 2 •g -1 ; And / or, the iodine value of the activated carbon is 550-620 mg•g. -1 ; And / or, the methylene blue value of the activated carbon is 90-100 mg•g. -1 ; And / or, the activated carbon has a pore volume of 0.32-0.36 ml•g. -1 ; And / or, the mesopore volume of the activated carbon is 0.21-0.23 ml•g. -1 .

9. An application of the activated carbon according to claim 7 or 8, characterized in that, Used for wastewater purification.

Images