Modified activated carbon and method for preparing the same

Abstract

This invention provides a modified activated carbon and its preparation method. The modified activated carbon has oxygen-containing functional groups on its surface, a porous structure, and a specific surface area of ​​1000 m². 2 / g~1600 m 2 / g, total pore volume is 0.65 cm³ 3 / g~0.95 cm 3 / g. The modified activated carbon provided by this invention can significantly improve the adsorption selectivity and adsorption capacity of activated carbon through the synergistic effect of porous structure, oxygen-containing functional groups, and specific specific surface area and total pore volume, while taking into account excellent decolorization effect and good regeneration performance. When applied to the decolorization process of diethylene terephthalate, a product of polyester raw material alcoholysis, it helps to improve the recovery rate of diethylene terephthalate and makes it easier to control the loss rate of diethylene terephthalate at a low level.

Description

Technical Field

[0001] This invention relates to the field of chemical recycling, and more particularly to a modified activated carbon and its preparation method. Background Technology

[0002] The resource utilization of waste textiles is a key measure to implement the concept of green development and alleviate resource and environmental pressures. As the world's largest producer and consumer of textiles and apparel, China generates more than 20 million tons of waste textiles annually, but its overall recycling rate is only about 21%. A large amount of waste textiles are incinerated or landfilled, causing serious resource waste and environmental pollution. Among them, polyester (polyester fiber), as the chemical fiber with the highest usage in textiles, has made efficient recycling a core issue and key direction in the field of waste textile resource utilization.

[0003] Currently, waste polyester recycling technologies are mainly divided into two categories: physical methods and chemical methods. Physical methods are characterized by short processes and low initial investment costs, but they suffer from problems such as decreased regeneration performance and difficulty in removing dyes. They are typically only reused in blended forms or downgraded for recycling, limiting their application scope and preventing high-value utilization. In contrast, chemical methods depolymerize polyester polymers into monomers, which are then purified and repolymerized to prepare recycled products. This approach maximizes the preservation of the original properties of the raw materials, achieving a closed-loop high-value utilization of waste polyester and representing a more promising recycling technology path.

[0004] Among numerous chemical depolymerization methods, ethylene glycol alcoholysis stands out as the most promising industrial solution due to its mature technology, high product purity, and mild reaction conditions. The core of this method is to depolymerize polyester into bis(2-hydroxyethyl) terephthalate (BHET) monomers through ethylene glycol alcoholysis. After purification and decolorization, BHET can be directly used for repolymerization and dyeing to prepare new polyester products, thus completing the entire polyester recycling chain. However, waste polyester comes from a wide range of sources, including dyed and printed fabrics, waste clothing, and industrial scraps, containing a diverse range of dyes. Some dyes form stable binding states with BHET monomers during alcoholysis, making the decolorization and purification of BHET monomers extremely difficult. This problem directly restricts the industrial-scale promotion of ethylene glycol alcoholysis and has become a core bottleneck that urgently needs to be overcome in the industry. Adsorption methods, due to their simple operation, controllable operating costs, and lack of secondary pollution, are currently the mainstream technology for BHET decolorization. In existing technologies, most improvements focus on adsorbent modification, but significant drawbacks remain. For example, Chinese patent CN117680204A discloses a method for alcohol decolorization of waste polyester textiles, using Fe... 3+ Fe 2+ Zn 2+ Al 3+Metal cations were modified by ion exchange with quaternary ammonium salt styrene resins for BHET adsorption and decolorization. Although it was claimed that this could reduce product loss, the actual measured BHET loss rate was still as high as 3.88%, which is difficult to meet the stringent cost control requirements of industrial production.

[0005] In existing technologies, adsorbents used for BHET decolorization suffer from the problem of difficulty in simultaneously achieving decolorization efficiency and product recovery rate. Therefore, developing a highly efficient adsorbent with a low loss rate has become a breakthrough in overcoming existing technological bottlenecks and meeting the needs of waste polyester alcoholysis recovery. Summary of the Invention

[0006] This invention provides a modified activated carbon and its preparation method. The modified activated carbon provided by this invention can significantly improve the adsorption selectivity and adsorption capacity of activated carbon through the synergistic effect of porous structure, oxygen-containing functional groups, and specific specific surface area and total pore volume, while taking into account excellent decolorization effect and good regeneration performance. When applied to the decolorization process of diethylene terephthalate, a product of polyester raw material alcoholysis, it helps to improve the recovery rate of diethylene terephthalate and makes it easier to control the loss rate of diethylene terephthalate at a low level.

[0007] This invention provides a modified activated carbon, wherein the surface of the modified activated carbon contains oxygen-containing functional groups, the modified activated carbon has a porous structure, and the specific surface area of ​​the modified activated carbon is 1000 m². 2 / g~1600 m 2 / g, total pore volume is 0.65 cm³ 3 / g~0.95 cm 3 / g.

[0008] According to one embodiment of the present invention, the oxygen-containing functional group includes a carboxylic acid group and / or a phenolic hydroxyl group.

[0009] In another aspect, the present invention provides a method for preparing modified activated carbon, comprising the following steps: mixing activated carbon with a solution containing an acidic oxidant to obtain a mixture; subjecting the mixture to a dynamic modification reaction and a static modification reaction in sequence, and then filtering to obtain a solid product; wherein the temperature of the dynamic modification reaction and the static modification reaction are each independently 40°C to 70°C; washing the solid product with water until the pH value of the washing solution is 6.5 to 7.5, and then drying the washed solid product to obtain the modified activated carbon.

[0010] According to one embodiment of the present invention, the mass ratio of the activated carbon to the acidic oxidant is 1:(80~120).

[0011] According to one embodiment of the present invention, the acidic oxidant includes nitric acid.

[0012] According to one embodiment of the present invention, the solution containing the acidic oxidant is an aqueous solution of the acidic oxidant.

[0013] According to one embodiment of the present invention, in the solution containing the acidic oxidant, the concentration of the acidic oxidant is 0.03 mol / L to 1.5 mol / L.

[0014] According to one embodiment of the present invention, the dynamic modification reaction is carried out under oscillating conditions.

[0015] According to one embodiment of the present invention, the time for the dynamic modification reaction is 1 h to 4 h.

[0016] According to one embodiment of the present invention, the static modification reaction time is 6 h to 12 h.

[0017] In another aspect, the present invention provides a method for decolorizing diethylene terephthalate, comprising the following steps: using an adsorbent to adsorb and decolorize the diethylene terephthalate to be purified, thereby obtaining decolorized diethylene terephthalate; wherein the adsorbent comprises the modified activated carbon or modified activated carbon prepared by the method described above.

[0018] According to one embodiment of the present invention, the diethylene terephthalate to be purified includes crude diethylene terephthalate obtained from polyester raw material by alcoholysis.

[0019] According to one embodiment of the present invention, the mass ratio of the adsorbent to the diethylene terephthalate to be purified is 1:(20~60).

[0020] According to one embodiment of the present invention, the process of using an adsorbent to adsorb and decolorize the diethylene terephthalate to be purified includes: adding the adsorbent to an aqueous solution containing the diethylene terephthalate to be purified to perform the adsorption and decolorization treatment; wherein, in the aqueous solution containing the diethylene terephthalate to be purified, the mass concentration of the diethylene terephthalate is 5% to 10%.

[0021] According to one embodiment of the present invention, the temperature of the adsorption decolorization treatment is 75℃~90℃, and the time is 6 h~10 h.

[0022] The implementation of this invention has at least the following beneficial effects: The modified activated carbon provided by this invention can significantly improve the adsorption selectivity and adsorption capacity of activated carbon through the synergistic effect of porous structure, oxygen-containing functional groups and specific specific surface area and total pore volume, while taking into account excellent decolorization effect and good regeneration performance; when applied to the decolorization process of diethylene terephthalate, a product of polyester raw material alcoholysis, it helps to improve the recovery rate of diethylene terephthalate and can control the loss rate of diethylene terephthalate at a low level of 2%~3%. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. The specific embodiments listed below are merely descriptions of the principles and features of this invention, and the examples given are only for explaining this invention and are not intended to limit the scope of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0024] This invention provides a modified activated carbon. The surface of the modified activated carbon contains oxygen-containing functional groups, the modified activated carbon has a porous structure, and the specific surface area of ​​the modified activated carbon is 1000 m². 2 / g~1600 m 2 / g, total pore volume is 0.65 cm³ 3 / g~0.95 cm 3 / g.

[0025] According to the inventors' research, the modified activated carbon described above can be applied to the decolorization and adsorption of crude diethylene terephthalate (BHET) obtained from the alcoholysis of polyester raw materials. Specifically, the surface of the modified activated carbon contains oxygen-containing functional groups, which possess polarity and active adsorption sites. Through specific interactions such as hydrogen bonding and electrostatic interactions, the adsorption selectivity of the modified activated carbon for dye impurities in the crude product is significantly enhanced. Furthermore, its porous structure provides ample physical adsorption space, enhancing the adsorption capacity. Simultaneously, the porous structure serves as a transport channel for dye impurities, allowing dye molecules to rapidly diffuse into the micropores and contact the adsorption sites, achieving a synergistic effect of physical and chemical adsorption. Meanwhile, the specific surface area of ​​the modified activated carbon is controlled at 1000 m². 2 / g~1600 m 2 / g, total pore volume controlled at 0.65cm³ 3 / g~0.95 cm 3Within a specific range of / g, the specific surface area can provide a high density of adsorption sites, enhancing the adsorption capacity for dye impurities; the total pore volume can balance adsorption capacity and structural stability, and the two work together to further improve the adsorption capacity and structural stability of modified activated carbon.

[0026] The modified activated carbon provided by this invention, through the synergistic effect of porous structure, oxygen-containing functional groups and specific total pore volume, can improve the adsorption selectivity and adsorption capacity of dye impurities, while balancing the decolorization effect and the recovery rate of crude BHET, so that the loss rate of BHET can be controlled at a low level of 2% to 3%.

[0027] The specific surface area of ​​the modified activated carbon can be 1000 m². 2 / g~1600 m 2 / g, for example, 1000 m 2 / g、1100 m 2 / g、1200 m 2 / g、1300 m 2 / g、1400 m 2 / g, 1500 m 2 / g、1600 m 2 / g or a range consisting of any two of them. Specific surface area not less than 1000 m² 2 / g helps improve the adsorption efficiency of dye impurities and shorten the adsorption reaction time; specific surface area not higher than 1600 m² 2 / g helps reduce the adsorption loss of the target product while enhancing the structural stability of the modified activated carbon.

[0028] The total pore volume of the modified activated carbon can be 0.65 cm³. 3 / g, 0.70 cm 3 / g, 0.75 cm 3 / g, 0.80 cm 3 / g, 0.85 cm 3 / g, 0.90 cm 3 / g, 0.95 cm 3 / g or a range consisting of any two of these. The total pore volume mentioned above refers to the sum of the volumes of all pores in a unit mass of modified activated carbon. The total pore volume is not less than 0.65 cm³. 3 / g helps improve the adsorption capacity for dye impurities and avoids incomplete decolorization; the total pore volume is no higher than 0.95 cm³. 3 / g helps to suppress non-selective adsorption of the target product and reduce the loss rate of the target product.

[0029] In some embodiments, the oxygen-containing functional groups include carboxylic acid groups and / or phenolic hydroxyl groups. Carboxylic acid groups (-COOH) are highly polar and acidic, and can form hydrogen bonds or ionic bonds with amino or hydroxyl groups in dye impurity molecules. Simultaneously, the presence of carboxylic acid groups gives the activated carbon surface a negative charge, allowing it to adsorb positively charged dye molecules through electrostatic attraction, while the interaction between the target product and the carboxylic acid group is relatively weak. Phenolic hydroxyl groups (-OH) have a certain degree of polarity and activity, and can bind to dye impurity molecules through hydrogen bonding. Furthermore, the presence of phenolic hydroxyl groups can regulate the electron distribution on the activated carbon surface, enhancing the physical adsorption of dye molecules. Moreover, the interaction between phenolic hydroxyl groups and the target product is mild and does not increase the adsorption loss of the target product.

[0030] Specifically, the modified activated carbon described above contains oxygen-containing functional groups on its surface, including carboxylic acid groups and / or phenolic hydroxyl groups. These oxygen-containing functional groups are formed by oxidizing and etching the carbon-hydrogen bonds on the activated carbon surface with an acidic oxidant to generate a porous structure, while simultaneously oxidizing the non-polar carbon-hydrogen bonds on the activated carbon surface into oxygen-containing functional groups. That is, the acidic oxidant first attacks the carbon-hydrogen bonds of the aromatic ring carbon sites on the activated carbon skeleton surface, introducing oxygen atoms through oxidation modification to form phenolic hydroxyl groups; at the same time, the acidic oxidant performs stepwise deep oxidation on the active aliphatic carbon sites at the edge defect sites and the inner walls of the pores of the activated carbon, first forming hydroxyl intermediates, and then further oxidizing them into carboxylic acid groups, thereby achieving the directional generation of carboxylic acid groups and / or phenolic hydroxyl groups on the activated carbon surface.

[0031] The modified activated carbon provided by this invention can significantly improve the adsorption selectivity and adsorption capacity of activated carbon through the synergistic effect of porous structure, oxygen-containing functional groups and specific specific surface area and total pore volume, while taking into account excellent decolorization effect and good regeneration performance.

[0032] This invention also provides a method for preparing the modified activated carbon, comprising the following steps: mixing activated carbon with a solution containing an acidic oxidant to obtain a mixture; subjecting the mixture to a dynamic modification reaction and a static modification reaction in sequence, and then filtering to obtain a solid product; wherein the temperatures of the dynamic modification reaction and the static modification reaction are each independently 40℃~70℃; washing the solid product with water until the pH value of the washing solution is 6.5~7.5, and then drying the washed solid product to obtain the modified activated carbon.

[0033] According to the inventors' research, thoroughly mixing activated carbon with a solution containing an acidic oxidant allows the acidic oxidant molecules to uniformly contact the surface and pore entrances of the activated carbon particles, laying the foundation for the uniformity of subsequent modification reactions. A dynamic modification reaction is performed first, using dynamic disturbance to encourage the acidic oxidant to fully penetrate the pores of the activated carbon, achieving uniform oxidation etching on the surface and within the pores. A static modification reaction is then performed, promoting deeper oxidation reactions, forming sufficient oxygen-containing functional groups on the activated carbon surface, and optimizing the etching of the pore structure.

[0034] In some embodiments, the mass ratio of the activated carbon to the acidic oxidant can be 1:(80~120), for example, 1:80, 1:90, 1:100, 1:110, 1:120, or any combination thereof. A mass ratio of not less than 1:80 helps ensure sufficient use of the acidic oxidant, allowing the activated carbon surface to undergo a full oxidation reaction and avoiding incomplete modification due to insufficient oxidant. A mass ratio of not more than 1:120 helps reduce production costs, avoids waste caused by excessive acidic oxidant, and reduces the wastewater treatment pressure in subsequent washing steps. Controlling the mass ratio within the above range is beneficial for achieving a balance between modification effect, cost, and environmental protection.

[0035] In some embodiments, the acidic oxidant includes nitric acid. Nitric acid solution has oxidizing properties and can selectively oxidize nonpolar carbon-hydrogen bonds on the surface of activated carbon to form oxygen-containing functional groups; simultaneously, its acidity can assist in etching pores, achieving pore structure optimization; furthermore, nitrate ions are easily removed in subsequent washing steps, reducing the risk of impurity residue.

[0036] In some embodiments, the solution containing the acidic oxidant is an aqueous solution of the acidic oxidant. The concentration of the acidic oxidant in the solution can be from 0.03 mol / L to 1.5 mol / L, for example, 0.03 mol / L, 0.2 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, 1.2 mol / L, 1.5 mol / L, or any combination thereof. A concentration not less than 0.03 mol / L helps provide sufficient oxidizing active material to form adequate oxygen-containing functional groups on the activated carbon surface, while simultaneously achieving effective etching of the pores, thereby enhancing the decolorization performance of the activated carbon. A concentration not higher than 1.5 mol / L helps maintain the integrity of the activated carbon's pore structure. Controlling the nitric acid concentration within the above range is beneficial for balancing the modification effect with the structural stability of the activated carbon, resulting in a modified adsorbent with excellent performance.

[0037] In some embodiments, the dynamic modification reaction is carried out under oscillation. The duration of the dynamic modification reaction can be 1 h to 4 h, for example, a range of 1 h, 2 h, 3 h, 4 h, or any combination thereof; the duration of the static modification reaction can be 6 h to 12 h, for example, a range of 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, or any combination thereof. Limiting the modification reaction to the above ranges can synergistically control the uniformity and sufficiency of the modification reaction: a dynamic reaction of 1 h to 4 h can promote the rapid penetration of the acidic oxidant into the deep pores of the activated carbon, resulting in uniform modification of all parts of the particles, while avoiding incomplete modification due to too short a reaction time and energy waste due to too long a reaction time; a static reaction of 6 h to 12 h provides sufficient time for oxidation etching, which helps to achieve sufficient generation of oxygen-containing functional groups and precise optimization of pore structure, while preventing excessive oxidation caused by reaction overtime and damage to the activated carbon skeleton structure.

[0038] Specifically, in the process of drying the washed solid product, the drying temperature can be 95℃~115℃, for example, 95℃, 100℃, 105℃, 110℃, 115℃ or any combination thereof.

[0039] In practice, activated carbon is mixed with a solution containing an acidic oxidant to obtain a mixed solution; a dynamic modification reaction is carried out at 40℃~70℃ with shaking for 1 h~4 h; the reaction system is then allowed to stand at 40℃~70℃ for 6 h~12 h to obtain a modified activated carbon intermediate solution; the modified activated carbon intermediate solution is filtered to obtain a solid product; the solid product is washed with deionized water until the pH of the washing solution is 6.5~7.5; the washed solid product is dried to obtain modified activated carbon.

[0040] The modified activated carbon preparation method provided by this invention utilizes the oxidative etching effect of an acidic oxidant to optimize the porous structure parameters of the activated carbon. Simultaneously, it transforms the nonpolar carbon-hydrogen bonds on the carbon surface into oxygen-containing functional groups, thereby controlling the pore structure and surface chemical properties to obtain modified activated carbon with both a specific pore structure and high adsorption selectivity. This preparation process is simple and controllable, requires no complex equipment, helps reduce industrial production costs, and is suitable for large-scale mass production needs.

[0041] This invention also provides a method for decolorizing diethylene terephthalate (BHET), comprising the following steps: using an adsorbent to adsorb and decolorize the diethylene terephthalate to be purified, thereby obtaining decolorized diethylene terephthalate; wherein the adsorbent comprises the modified activated carbon described above or modified activated carbon prepared according to the modified activated carbon preparation method described above.

[0042] According to the inventors' research, this modified activated carbon possesses both an optimized porous structure and oxygen-containing functional groups. Through the synergistic effect of physical adsorption (pore trapping, van der Waals forces) and chemical adsorption (hydrogen bonding, electrostatic interactions), it selectively adsorbs dye impurities in BHET to be purified. Its non-selective adsorption of BHET is weak, avoiding the problem of excessively high BHET loss rates in existing decolorization methods. Decolorization using modified activated carbon results in a BHET loss rate of 1.9%~2.8%, with an L value ≥ 93, an absolute a value ≤ 0.5, and an absolute b value ≤ 2.0 for the decolorized BHET solid crystals.

[0043] In some embodiments, the diethylene terephthalate (BHET) to be purified includes crude BHET obtained from polyester raw materials through alcoholysis. The main impurities in the crude BHET obtained from the alcoholysis of polyester raw materials are various dye molecules introduced during polyester dyeing and a small amount of alcoholysis byproducts. The modified activated carbon of this invention exhibits excellent selective adsorption performance for these polar dye impurities, which is beneficial for realizing the resource-based regeneration of waste polyester and improving the environmental friendliness and economy of the process.

[0044] In some embodiments, the mass ratio of the adsorbent to the diethylene terephthalate to be purified can be 1:(20~60), for example, 1:20, 1:30, 1:40, 1:50, 1:60, or any combination thereof. A mass ratio of not less than 1:20 provides sufficient adsorbent, which is beneficial for the full adsorption of dye impurities and avoids incomplete decolorization due to insufficient adsorbent. A mass ratio of not more than 1:60 helps to avoid the waste of raw materials caused by excessive adsorbent, while reducing the difficulty and cost of subsequent filtration and separation operations. Controlling the mass ratio within the above range helps to achieve a balance between decolorization effect and economic cost, thereby improving the economic efficiency of the decolorization process.

[0045] Specifically, the mass ratio of the modified activated carbon to the aqueous solution containing the diethylene terephthalate to be purified can be 1:(400~600), for example, 1:400, 1:450, 1:500, 1:550, 1:600 ​​or any combination thereof.

[0046] In some embodiments, the process of adsorbing and decolorizing the diethylene terephthalate to be purified using an adsorbent includes: adding the adsorbent to an aqueous solution containing the diethylene terephthalate to be purified for the adsorption and decolorization treatment; wherein, the mass concentration of the diethylene terephthalate in the aqueous solution containing the diethylene terephthalate to be purified can be 5% to 10%, for example, 5%, 6%, 7%, 8%, 9%, 10%, or any combination thereof. A mass concentration of not less than 5% helps to improve industrial processing efficiency and reduce energy consumption and processing costs per unit product; a mass concentration of not more than 10% helps to prevent BHET molecules from agglomerating and encapsulating dye impurities, ensuring that the adsorbent can fully contact the impurities and exert its adsorption effect; controlling the concentration within the above range is beneficial for balancing processing efficiency and decolorization effect, while reducing product loss caused by BHET agglomeration.

[0047] In some embodiments, the temperature of the above-mentioned adsorption decolorization treatment can be 75℃~90℃, for example, a range of 75℃, 78℃, 82℃, 85℃, 90℃ or any combination thereof; the time can be 6 h~10 h, for example, a range of 6 h, 7 h, 8 h, 9 h, 10 h or any combination thereof. A temperature not lower than 75℃ and a time not lower than 6 h help to increase the adsorption reaction rate and improve treatment efficiency; a temperature not higher than 90℃ and a time not exceeding 10 h help to reduce the hydrolysis rate of BHET while maintaining the adsorption performance of the adsorbent; controlling the temperature within the above range is beneficial for balancing the adsorption rate and BHET recovery rate, ensuring the efficient and stable operation of the decolorization process.

[0048] In practice, the modified activated carbon is added to an aqueous solution containing BHET to be purified for the above-mentioned adsorption and decolorization treatment for 6 h to 10 h to obtain a reaction solution containing decolorized BHET; the reaction solution is then filtered, cooled and crystallized to obtain decolorized BHET.

[0049] The decolorization method for BHET provided by this invention utilizes modified activated carbon, which possesses both an optimized porous structure and oxygen-containing functional groups. Through the synergistic effect of physical and chemical adsorption, it can selectively adsorb dye impurities in the BHET to be purified. Its non-selective adsorption of BHET is relatively weak, which can remove impurities while retaining most of the target product, thus contributing to the efficient decolorization and purification of BHET.

[0050] The present invention will be further described below through specific embodiments.

[0051] Example 1

[0052] S1. Preparation of modified activated carbon

[0053] Weigh 1 g of activated carbon and mix it with 100 g of nitric acid solution (0.1 mol / L) to obtain a mixture; carry out a dynamic modification reaction at 40 °C with shaking for 4 h; then let the reaction system stand at 40 °C for 12 h to obtain a modified activated carbon intermediate solution.

[0054] The modified activated carbon intermediate solution was filtered to obtain a solid product.

[0055] The solid product was washed multiple times with deionized water until the pH of the washing solution was 6.5.

[0056] The washed solid product was dried at 105°C to obtain modified activated carbon.

[0057] S2, modified activated carbon adsorption and decolorization BHET

[0058] Take 100 g of an aqueous solution (5% by mass) containing the BHET to be purified and place it in a screw-top conical flask. Add 0.2 g of nitric acid-modified activated carbon and mix. Perform adsorption and decolorization treatment at 85 °C for 8 h to obtain a reaction solution containing decolorized BHET. After filtering, cooling and crystallizing the reaction solution, obtain decolorized BHET.

[0059] The modified activated carbon prepared in Example 1 had a specific surface area of ​​1412.54 m². 2 / g, total pore volume is 0.80 cm³ 3 / g; the L value of the decolorized BHET solid crystals was 94.04, the a value was -0.2, the b value was -1.2, and the BHET loss rate was 2.7%.

[0060] The properties of the decolorized BHET solid crystals prepared in the examples and comparative examples were determined using the following methods:

[0061] (1) Method for determining BHET loss rate after decolorization

[0062] Samples were taken and the BHET content in the solution before adsorption was determined by high performance liquid chromatography (Agilent 1260 Infinity II), denoted as w1. After the adsorption and decolorization reaction was completed, samples were taken and the BHET content in the solution after adsorption was determined, denoted as w2. BHET loss rate = (w1- w2) / w1×100%.

[0063] (2) Methods for determining the L value, a value, and b value of decolorized BHET solid crystals

[0064] The colorimeter (ColorFlex EZ) was calibrated; the BHET solid powder obtained after decolorization, crystallization and drying was placed into the sample chamber of the colorimeter for color value detection, and the measured L value, a value and b value were recorded.

[0065] The difference between Examples 2 to 4 and Example 1 is that the concentration of the nitric acid solution, the total pore volume and specific surface area of ​​the modified activated carbon are different, while other reaction conditions remain the same.

[0066] Example 5

[0067] S1. Preparation of modified activated carbon

[0068] Weigh 1 g of activated carbon and mix it with 100 g of nitric acid solution (the concentration of nitric acid solution is 1.2 mol / L) to obtain a mixed solution; carry out a dynamic modification reaction at 40 ℃ and shake the reaction for 4 h; then let the reaction system stand at 40 ℃ for 12 h to obtain a modified activated carbon intermediate solution.

[0069] The modified activated carbon intermediate solution was filtered to obtain a solid product.

[0070] The solid product was washed multiple times with deionized water until the pH of the washing solution was 6.5.

[0071] The washed solid product was dried at 105°C to obtain modified activated carbon.

[0072] The modified activated carbon prepared in Example 5 had a specific surface area of ​​1125.36 m². 2 / g, total pore volume is 0.71 cm³ 3 / g.

[0073] Other reaction conditions remain unchanged.

[0074] Example 6

[0075] S1. Preparation of modified activated carbon

[0076] Weigh 1 g of activated carbon and mix it with 100 g of nitric acid solution (0.05 mol / L) to obtain a mixture; carry out a dynamic modification reaction at 40 ℃ and shake the reaction for 4 h; then let the reaction system stand at 40 ℃ for 12 h to obtain a modified activated carbon intermediate solution.

[0077] The modified activated carbon intermediate solution was filtered to obtain a solid product.

[0078] The solid product was washed multiple times with deionized water until the pH of the washing solution was 6.5.

[0079] The washed solid product was dried at 105°C to obtain modified activated carbon.

[0080] The modified activated carbon prepared in Example 6 had a specific surface area of ​​1584.27 m². 2 / g, total pore volume is 0.91 cm³ 3 / g.

[0081] Other reaction conditions remain unchanged.

[0082] Example 7

[0083] S1. Preparation of modified activated carbon

[0084] Weigh 1 g of activated carbon and mix it with 100 g of nitric acid solution (the concentration of nitric acid solution is 1.5 mol / L) to obtain a mixed solution; carry out a dynamic modification reaction at 40 ℃ and shake the reaction for 4 h; then let the reaction system stand at 40 ℃ for 12 h to obtain a modified activated carbon intermediate solution.

[0085] The modified activated carbon intermediate solution was filtered to obtain a solid product.

[0086] The solid product was washed multiple times with deionized water until the pH of the washing solution was 6.5.

[0087] The washed solid product was dried at 105°C to obtain modified activated carbon.

[0088] The modified activated carbon prepared in Example 7 had a specific surface area of ​​1033.45 m². 2 / g, total pore volume is 0.68 cm³. 3 / g.

[0089] Other reaction conditions remain unchanged.

[0090] Example 8

[0091] S1. Preparation of modified activated carbon

[0092] Weigh 1 g of activated carbon and mix it with 100 g of nitric acid solution (0.03 mol / L) to obtain a mixture; carry out a dynamic modification reaction at 40 ℃ and shake the reaction for 4 h; then let the reaction system stand at 40 ℃ for 12 h to obtain a modified activated carbon intermediate solution.

[0093] The modified activated carbon intermediate solution was filtered to obtain a solid product.

[0094] The solid product was washed multiple times with deionized water until the pH of the washing solution was 6.5.

[0095] The washed solid product was dried at 105°C to obtain modified activated carbon.

[0096] The modified activated carbon prepared in Example 8 had a specific surface area of ​​1562.14 m². 2 / g, total pore volume is 0.90 cm³. 3 / g.

[0097] Other reaction conditions remain unchanged.

[0098] The difference between Examples 9-12 and Example 2 is that the mass ratio of activated carbon to acidic oxidant, the total pore volume and specific surface area of ​​the modified activated carbon are different, while other reaction conditions remain unchanged.

[0099] The difference between Examples 13-16 and Example 2 is that the mass ratio of modified activated carbon to crude BHET is different, while other reaction conditions remain the same.

[0100] The difference between Example 17 and Example 1 is that the concentration of the nitric acid solution, the total pore volume and specific surface area of ​​the modified activated carbon are different, while other reaction conditions remain the same.

[0101] The difference between Example 18 and Example 1 is that the acidic oxidant in Example 18 is peracetic acid, and the total pore volume and specific surface area of ​​the modified activated carbon are different, while other reaction conditions remain the same.

[0102] Comparative Example 1

[0103] S1. Preparation of modified activated carbon

[0104] Weigh 1 g of activated carbon and mix it with 100 g of nitric acid solution (the concentration of nitric acid solution is 1.8 mol / L) to obtain a mixed solution; carry out a dynamic modification reaction at 40 ℃ and shake the reaction for 4 h; then let the reaction system stand at 40 ℃ for 12 h to obtain a modified activated carbon intermediate solution.

[0105] The modified activated carbon intermediate solution was filtered to obtain a solid product.

[0106] The solid product was washed multiple times with deionized water until the pH of the washing solution was 6.5.

[0107] The washed solid product was dried at 105°C to obtain modified activated carbon.

[0108] The modified activated carbon prepared in Comparative Example 1 had a specific surface area of ​​0.62 m². 2 / g, total pore volume is 1054.25 cm³. 3 / g.

[0109] Other reaction conditions remain unchanged.

[0110] Comparative Example 2

[0111] S1. Preparation of modified activated carbon

[0112] Weigh 1 g of activated carbon and mix it with 100 g of nitric acid solution (0.02 mol / L) to obtain a mixture; carry out a dynamic modification reaction at 40 ℃ and shake the reaction for 4 h; then let the reaction system stand at 40 ℃ for 12 h to obtain a modified activated carbon intermediate solution.

[0113] The modified activated carbon intermediate solution was filtered to obtain a solid product.

[0114] The solid product was washed multiple times with deionized water until the pH of the washing solution was 6.5.

[0115] The washed solid product was dried at 105°C to obtain modified activated carbon.

[0116] The modified activated carbon prepared in Comparative Example 2 had a specific surface area of ​​1591.82 m². 2 / g, total pore volume is

[0117] 0.96 cm 3 / g.

[0118] Other reaction conditions remain unchanged.

[0119] Comparative Example 3

[0120] S1. Preparation of modified activated carbon

[0121] Weigh 1 g of activated carbon and mix it with 100 g of nitric acid solution (the concentration of nitric acid solution is 2.0 mol / L) to obtain a mixed solution; carry out a dynamic modification reaction at 40 ℃ and shake the reaction for 4 h; then let the reaction system stand at 40 ℃ for 12 h to obtain a modified activated carbon intermediate solution.

[0122] The modified activated carbon intermediate solution was filtered to obtain a solid product.

[0123] The solid product was washed multiple times with deionized water until the pH of the washing solution was 6.5.

[0124] The washed solid product was dried at 105°C to obtain modified activated carbon.

[0125] The modified activated carbon prepared in Comparative Example 3 had a specific surface area of ​​0.61 m². 2 / g, total pore volume is

[0126] 946.77 cm 3 / g.

[0127] Other reaction conditions remain unchanged.

[0128] Comparative Example 4

[0129] S1. Preparation of modified activated carbon

[0130] Weigh 1 g of activated carbon and mix it with 100 g of nitric acid solution (0.01 mol / L) to obtain a mixture; carry out a dynamic modification reaction at 40 ℃ and shake the reaction for 4 h; then let the reaction system stand at 40 ℃ for 12 h to obtain a modified activated carbon intermediate solution.

[0131] The modified activated carbon intermediate solution was filtered to obtain a solid product.

[0132] The solid product was washed multiple times with deionized water until the pH of the washing solution was 6.5.

[0133] The washed solid product was dried at 105°C to obtain modified activated carbon.

[0134] The modified activated carbon prepared in Comparative Example 4 had a specific surface area of ​​1632.65 m². 2 / g, total pore volume is 0.96 cm³ 3 / g.

[0135] Other reaction conditions remain unchanged.

[0136] The difference between Comparative Example 5 and Example 1 is that the activated carbon was not modified, i.e., step S1 was omitted. Step S2 was carried out using unmodified activated carbon, while other reaction conditions remained unchanged.

[0137] The difference between Comparative Example 6 and Example 1 is that the ferrous ion modified activated carbon prepared in Example 4 of patent CN119465612A was used for step S2, while other reaction conditions remained unchanged.

[0138] Table 1

[0139]

[0140] Table 2

[0141]

[0142] As shown in Table 2, the modified activated carbon provided by this invention can significantly improve the adsorption selectivity and adsorption capacity of activated carbon, while also achieving excellent decolorization effect and good regeneration performance. When applied to the decolorization process of diethylene terephthalate (DTH), a product of polyester raw material alcoholysis, it helps to improve the recovery rate of DTH and makes it easier to control the loss rate of DTH at a low level. When the modified activated carbon provided by this invention is applied to the decolorization process of DTH, a product of polyester raw material alcoholysis, its BHET loss rate is only 1.75%~2.80%, and the L value of the BHET solid crystals after decolorization is ≥93.09. The absolute values ​​of a and b both meet the industrial application standards.

[0143] The BHET samples prepared in Comparative Examples 1 to 4 failed to meet the color standard. Comparative Examples 5 and 6, using unmodified or traditional ferrous ion-modified activated carbon, all exhibited BHET loss rates exceeding 4% and significantly low L values. The data demonstrate that the modified activated carbon provided by this invention possesses significant technical advantages compared to existing adsorbents.

[0144] The data from the examples further demonstrate that controlling the process conditions within a reasonable range can result in a more balanced and stable decolorization effect and product retention rate. When the nitric acid concentration is 0.1 mol / L to 0.6 mol / L, the product loss rate is low and the color performance is optimal. Examples 5 to 8, which deviate from this range, show a decrease in decolorization or product retention performance. When the mass ratio of activated carbon to acidic oxidant is 1:(80~120) and the mass ratio of modified activated carbon to crude BHET is 1:(20~60), the decolorization effect and product retention rate are more balanced. Examples 11 to 12 and 16, which exceed this range, show a slight decrease in performance. This indicates that reasonable control of reaction and mixing conditions can significantly improve the adsorbent performance and process adaptability.

[0145] In summary, the modified activated carbon provided by this invention can significantly improve the adsorption selectivity and adsorption capacity of activated carbon through the synergistic effect of porous structure, oxygen-containing functional groups, and specific specific surface area and total pore volume, while also taking into account excellent decolorization effect and good regeneration performance. When applied to the decolorization process of diethylene terephthalate, a product of polyester raw material alcoholysis, it helps to improve the recovery rate of diethylene terephthalate and makes it easier to control the loss rate of diethylene terephthalate at a low level.

[0146] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing modified activated carbon, characterized in that, Includes the following steps: Activated carbon is mixed with a solution containing an acidic oxidant to obtain a mixture; wherein the concentration of the acidic oxidant in the solution is 0.03 mol / L to 1.2 mol / L. The mixture is subjected to dynamic modification reaction and static modification reaction in sequence, and then filtered to obtain a solid product; wherein the temperature of the dynamic modification reaction and the static modification reaction are each independently 40℃~70℃, the time of the dynamic modification reaction is 1 h~4 h, and the time of the static modification reaction is 6 h~12 h. The solid product was washed with water until the pH of the washing solution reached 6.5-7.

5. The washed solid product was then dried to obtain the modified activated carbon; the specific surface area of ​​the modified activated carbon was 1000 m². 2 / g~1600 m 2 / g, total pore volume is 0.65 cm³ 3 / g~0.95 cm 3 / g.

2. The method for preparing modified activated carbon according to claim 1, characterized in that, The modified activated carbon has oxygen-containing functional groups on its surface and a porous structure.

3. The method for preparing modified activated carbon according to claim 2, characterized in that, The oxygen-containing functional groups include carboxylic acid groups and / or phenolic hydroxyl groups.

4. The method for preparing modified activated carbon according to claim 1, characterized in that, The mass ratio of activated carbon to acidic oxidant is 1:(80~120).

5. The method for preparing modified activated carbon according to claim 1 or 4, characterized in that, The acidic oxidizing agent includes nitric acid; And / or, the solution containing the acidic oxidant is an aqueous solution of the acidic oxidant.

6. The method for preparing modified activated carbon according to claim 1, characterized in that, The dynamic modification reaction is carried out under oscillation.

7. A method for decolorizing diethylene terephthalate, characterized in that, Includes the following steps: The diethylene terephthalate to be purified is subjected to adsorption and decolorization treatment using an adsorbent to obtain decolorized diethylene terephthalate; wherein the adsorbent includes modified activated carbon prepared by the method of any one of claims 1-6.

8. The decolorization method for diethylene terephthalate according to claim 7, characterized in that, The diethylene terephthalate to be purified includes crude diethylene terephthalate obtained from polyester raw materials through alcoholysis.

9. The decolorization method for diethylene terephthalate according to claim 7 or 8, characterized in that, The mass ratio of the adsorbent to the diethylene terephthalate to be purified is 1:(20~60).

10. The decolorization method for diethylene terephthalate according to claim 9, characterized in that, The process of using an adsorbent to adsorb and decolorize the diethylene terephthalate to be purified includes: adding the adsorbent to an aqueous solution containing the diethylene terephthalate to be purified to perform the adsorption and decolorization treatment; wherein, the mass concentration of the diethylene terephthalate in the aqueous solution containing the diethylene terephthalate to be purified is 5%~10%; And / or, the temperature of the adsorption decolorization treatment is 75℃~90℃, and the time is 6 h~10 h.

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