Preparation process of carboxylated shell-based activated carbon for organic matter adsorption

Abstract

The invention discloses a preparation process of carboxylated shell-based activated carbon for organic matter adsorption, and particularly relates to the technical field of adsorption materials, and the preparation process comprises the following steps: mixing coconut shell powder and walnut shell powder, crushing, and loading potassium hydroxide in stages in a gradient manner; carrying out two-stage microwave activation in an inert atmosphere, namely low-temperature pre-activation in the first stage and high-temperature activation in the second stage, and introducing carbon dioxide; the activated product, phosphoric acid, a laccase-peroxidase complex enzyme preparation and a buffer solution are subjected to ultrasonic synergistic modification, and then a weak acid reaction is maintained through dynamic pH regulation and control; and finally, performing graded washing and gradient drying to obtain a finished product. According to the method, high-density carboxyl grafting and graded pore construction are synchronously realized under mild conditions through a synergistic effect of directional catalysis of biological enzyme and dynamic regulation of microwave, so that the problems of structural damage caused by strong acid corrosion, pore imbalance caused by fixed parameters and stability reduction caused by insufficient post-treatment in a traditional process are solved; the adsorption performance and the regeneration cycle performance of the material are also obviously improved.

Description

Technical Field

[0001] This invention relates to the field of adsorption materials technology, and in particular to a process for preparing carboxylated fruit shell-based activated carbon for the adsorption of organic matter. Background Technology

[0002] The field of adsorption materials technology encompasses the development and optimization of materials for removing pollutants such as organic compounds and heavy metal ions from water and air. Core content involves the design, synthesis, and characterization of adsorbents, based on physical adsorption principles such as van der Waals forces or chemical adsorption principles such as functional group reactions. The systematic introduction covers material types including activated carbon, silica gel, and biomass-based adsorbents, preparation methods such as activation treatment and surface modification, and application scenarios such as wastewater treatment and air purification.

[0003] One aspect of the process for preparing carboxylated coconut shell-based activated carbon for organic matter adsorption refers to the process of converting coconut shell raw materials into functional adsorbents. This topic covers coconut shell pretreatment including washing, drying, and pulverizing; activation treatment using physical methods such as high-temperature carbonization or chemical methods such as impregnation with activating agents; and carboxylation modification using acid treatment or oxidation reactions to introduce carboxyl functional groups to complete material preparation.

[0004] Existing technologies rely on strong acid oxidation modification, which leads to structural damage to the carbon skeleton. The activation process uses fixed parameters and cannot respond to fluctuations in the physical properties of raw materials. Static operation in the post-treatment stage results in residual impurities and deterioration of the thermal stability of functional groups. The fragmentation of each process step creates a fundamental contradiction where adsorption capacity and material durability cannot be achieved simultaneously. Summary of the Invention

[0005] The main objective of this invention is to provide a process for preparing carboxylated fruit shell-based activated carbon for organic matter adsorption. By combining a bio-enzyme synergistic catalytic system with microwave in-situ monitoring and dynamic control technology, this invention solves the technical contradictions in traditional activated carbon preparation, such as structural damage caused by strong acid corrosion, pore distribution imbalance caused by fixed parameter activation, and functional group instability caused by static post-treatment.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A process for preparing carboxylated coconut shell-based activated carbon for organic matter adsorption, the specific steps of which are as follows: Step 1, Raw material selection: 50-60 parts by weight of coconut shell powder, 40-50 parts by weight of walnut shell powder, 20-30 parts by weight of potassium hydroxide, 17-22 parts by weight of nitric acid, 13-17 parts by weight of phosphate, 1-5 parts by weight of laccase-peroxidase complex enzyme preparation, and 25-35 parts by weight of sodium citrate buffer solution. Step 2: Place coconut shell powder and walnut shell powder in a ball mill and mix and grind them at 300 rpm for 60 minutes to obtain mixed fruit shell powder with a particle size ≤75μm. Step 3: Add the mixed fruit shell powder from Step 1 and potassium hydroxide to a high-speed mixer: add 50% potassium hydroxide for the first time and stir for 20 minutes; after a 10-minute interval, add the remaining 50% potassium hydroxide and continue stirring for 40 minutes, maintaining the temperature at 45°C throughout the stirring process; Step 4: Transfer the material obtained in Step 3 to a microwave reactor, replace the air in the reactor with nitrogen three times, start the program to heat up and perform two stages of microwave activation, and at the same time use a fiber optic temperature sensor to monitor the internal temperature of the material in real time. Step 5: Add phosphoric acid, laccase-peroxidase complex enzyme preparation, and sodium citrate buffer solution to the product of step 4, and mix in an ultrasonic reactor; Step 6: Transfer the mixture from Step 5 into a constant temperature stirring tank and heat it to 65°C at a rate of 1°C / min. Use an online pH meter to monitor the pH of the system. When the pH is greater than 4.0, add phosphoric acid automatically to adjust the pH and maintain it at 3.8 ± 0.2. The reaction time is 180 minutes. Step 7: After washing and drying the reaction product from step 6, carboxylated coconut shell-based activated carbon is obtained.

[0007] Preferably, the raw materials in step 1 are: 55 parts by weight of coconut shell powder, 45 parts by weight of walnut shell powder, 25 parts by weight of potassium hydroxide, 5 parts by weight of phosphoric acid, 2.5 parts by weight of laccase-peroxidase complex enzyme preparation, and 30 parts by weight of sodium citrate buffer solution.

[0008] Preferably, the pH of the sodium citrate buffer solution is 5.0.

[0009] Preferably, the preparation method of the laccase-peroxidase complex enzyme preparation is as follows: laccase and peroxidase are mixed at a mass ratio of 1:1, and trehalose (1 / 5 of the total enzyme mass) is added as a freeze-drying protectant. After pre-freezing at -40°C for 4 hours, the mixture is vacuum freeze-dried for 24 hours, pulverized, and passed through a 100-mesh sieve to obtain the laccase-peroxidase complex enzyme preparation.

[0010] Preferably, the two-stage microwave activation in step 3 is as follows: in the first stage, the temperature is raised from room temperature to 300°C in 5 minutes with a microwave power of 400W, and the temperature is maintained for 20 minutes; in the second stage, the temperature is raised to 600°C, the microwave power is increased to 800W, carbon dioxide gas is introduced at a flow rate of 50mL / min, and carbon skeleton structure data is collected every 5 minutes using an in-situ Raman spectrometer. When the intensity ratio of the D peak to the G peak reaches 1.8, the temperature is immediately lowered to 400°C.

[0011] Preferably, in step 5, when mixing in the ultrasonic reactor, the ultrasonic frequency is set to 40 kHz, the temperature to 50 °C, and the mixture is mixed for 120 min in an intermittent ultrasonic mode with a 30 s working and 10 s pause.

[0012] Preferably, the washing method in step 7 is as follows: the reaction product is fed into a three-stage countercurrent washing tower: the first stage is washed 3 times with 60°C deionized water; the second stage is washed 2 times with 0.1mol / L sodium bicarbonate solution; and the third stage is washed once with 70% ethanol solution, with a liquid-to-solid ratio of 5:1 each time.

[0013] Preferably, the drying method in step 7 is as follows: after washing, the material is loaded into a vacuum dryer, dried at 40°C for 120 min in the first stage, dried at 60°C for 90 min in the second stage, and dried at 80°C for 60 min in the third stage, with the vacuum degree maintained at -0.09 MPa, to obtain carboxylated fruit shell-based activated carbon.

[0014] Compared with the prior art, the present invention has the following beneficial effects: This invention achieves high-density carboxyl grafting under mild conditions through precise bio-enzyme catalysis, optimizes pore distribution by dynamically controlling the activation process through in-situ monitoring, and simultaneously improves functional group stability and adsorption activity by relying on gradient washing and process linkage control. This fundamentally solves the problem of mutual exclusion between modification efficiency, structural integrity and product purity in traditional processes. Detailed Implementation

[0015] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments and comparative examples.

[0016] The raw materials used in the preparation process of carboxylated fruit shell-based activated carbon for organic matter adsorption disclosed in this invention include 50-60 parts by weight of coconut shell powder, 40-50 parts by weight of walnut shell powder, 20-30 parts by weight of potassium hydroxide, 17-22 parts by weight of nitric acid, 13-17 parts by weight of phosphate, 1-5 parts by weight of laccase-peroxidase complex enzyme preparation, and 25-35 parts by weight of sodium citrate buffer solution. The pH of the sodium citrate buffer solution is 5.0. Furthermore, the preparation method of the laccase-peroxidase complex enzyme preparation is as follows: laccase and peroxidase are mixed at a mass ratio of 1:1, and trehalose (1 / 5 of the total enzyme mass) is added as a freeze-drying protectant. After pre-freezing at -40℃ for 4 hours, the mixture is vacuum freeze-dried for 24 hours, pulverized, and passed through a 100-mesh sieve to obtain the laccase-peroxidase complex enzyme preparation.

[0017] Example 1

[0018] This invention discloses a process for preparing carboxylated fruit shell-based activated carbon for organic matter adsorption, the specific steps of which are as follows: Step 1, Raw material selection: 55 parts by weight of coconut shell powder, 45 parts by weight of walnut shell powder, 25 parts by weight of potassium hydroxide, 5 parts by weight of phosphoric acid, 2.5 parts by weight of laccase-peroxidase complex enzyme preparation, and 30 parts by weight of sodium citrate buffer solution; wherein the pH of the sodium citrate buffer solution is 5.0; Step 2: Place coconut shell powder and walnut shell powder in a ball mill and mix and grind them at 300 rpm for 60 minutes to obtain mixed fruit shell powder with a particle size ≤75μm. Step 3: Add the mixed fruit shell powder from Step 1 and potassium hydroxide to a high-speed mixer: add 50% potassium hydroxide for the first time and stir for 20 minutes; after a 10-minute interval, add the remaining 50% potassium hydroxide and continue stirring for 40 minutes, maintaining the temperature at 45°C throughout the stirring process; The two-stage microwave activation process is as follows: In the first stage, the temperature is increased from room temperature to 300℃ in 5 minutes with a microwave power of 400W, and the temperature is maintained for 20 minutes. In the second stage, the temperature is increased to 600℃, the microwave power is increased to 800W, carbon dioxide gas is introduced at a flow rate of 50mL / min, and carbon skeleton structure data are collected every 5 minutes using an in-situ Raman spectrometer. When the intensity ratio of the D peak to the G peak reaches 1.8, the temperature is immediately reduced to 400℃.

[0019] Step 4: Transfer the material obtained in Step 3 to a microwave reactor, replace the air in the reactor with nitrogen three times, start the program to heat up and perform two stages of microwave activation, and at the same time use a fiber optic temperature sensor to monitor the internal temperature of the material in real time. Step 5: Add phosphoric acid, laccase-peroxidase complex enzyme preparation, and sodium citrate buffer solution to the product of step 4, and place it in an ultrasonic reactor for mixing; when mixing in the ultrasonic reactor, set the ultrasonic frequency to 40kHz and the temperature to 50℃, and mix for 120min in an ultrasonic intermittent mode of working for 30s and pausing for 10s.

[0020] Step 6: Transfer the mixture from Step 5 to a constant temperature stirring tank, and heat it to 65°C at a rate of 1°C / min. Monitor the pH of the system using an online pH meter. When the pH > 4.0, automatically add phosphoric acid to adjust the pH and maintain it at 3.8 ± 0.2. The reaction time is 180 minutes. Step 7: After washing and drying the reaction product from step 6, carboxylated coconut shell-based activated carbon is obtained. The washing method is as follows: the reaction products are fed into a three-stage countercurrent washing tower: the first stage is washed three times with 60℃ deionized water; the second stage is washed twice with 0.1mol / L sodium bicarbonate solution; and the third stage is washed once with 70% ethanol solution, with a liquid-to-solid ratio of 5:1 each time.

[0021] The drying method is as follows: after washing, the material is loaded into a vacuum dryer. The first stage is drying at 40℃ for 120 minutes, the second stage is drying at 60℃ for 90 minutes, and the third stage is drying at 80℃ for 60 minutes. The vacuum degree is maintained at -0.09MPa to obtain carboxylated fruit shell-based activated carbon.

[0022] Example 2 The difference between this embodiment and Embodiment 1 is that the raw materials used in step 1 are 50 parts by weight of coconut shell powder, 40 parts by weight of walnut shell powder, 20 parts by weight of potassium hydroxide, 17 parts by weight of nitric acid, 13 parts by weight of phosphate, 1 part by weight of laccase-peroxidase complex enzyme preparation, and 25 parts by weight of sodium citrate buffer solution.

[0023] The remaining preparation steps are the same as in Example 1.

[0024] Example 3 The difference between this embodiment and Embodiment 1 is that the raw materials used in step 1 are 60 parts by weight of coconut shell powder, 50 parts by weight of walnut shell powder, 30 parts by weight of potassium hydroxide, 22 parts by weight of nitric acid, 17 parts by weight of phosphate, 5 parts by weight of laccase-peroxidase complex enzyme preparation, and 35 parts by weight of sodium citrate buffer solution.

[0025] The remaining preparation steps are the same as in Example 1.

[0026] Example 4 The difference between this embodiment and Embodiment 1 is that the raw materials used in step 1 are 53 parts by weight of coconut shell powder, 44 parts by weight of walnut shell powder, 23 parts by weight of potassium hydroxide, 19 parts by weight of nitric acid, 14 parts by weight of phosphate, 2 parts by weight of laccase-peroxidase complex enzyme preparation, and 27 parts by weight of sodium citrate buffer solution.

[0027] The remaining preparation steps are the same as in Example 1.

[0028] Example 5 The difference between this embodiment and Embodiment 1 is that the raw materials used in step 1 are 58 parts by weight of coconut shell powder, 48 parts by weight of walnut shell powder, 27 parts by weight of potassium hydroxide, 21 parts by weight of nitric acid, 16 parts by weight of phosphoric acid, 4 parts by weight of laccase-peroxidase complex enzyme preparation, and 33 parts by weight of sodium citrate buffer solution.

[0029] The remaining preparation steps are the same as in Example 1.

[0030] Comparative Example 1 The differences between this comparative example and Example 1 are as follows: Step 1: Formula adjustment: The laccase-peroxidase complex enzyme preparation and sodium citrate buffer solution were removed, and the amount of phosphate was increased to 20 parts by weight; Step 5: Process change: Only phosphate was added to the microwave-activated product, and the mixture was statically stirred at 50°C for 180 minutes (ultrasound assistance and enzyme catalysis were eliminated); Step 6: Dynamic pH control was eliminated: The pH was directly maintained at 3.0 for 180 minutes. The remaining steps are exactly the same as in Example 1.

[0031] The purpose of this comparative study is to verify the necessity of synergistic acid modification by complex enzymes and to compare the differences in carboxylation efficiency between single acid treatments.

[0032] Comparative Example 2 The difference between this comparative example and Example 1 is as follows: Step 3-4 Activation process reconstruction: The material with gradient-loaded potassium hydroxide is transferred into a muffle furnace and heated to 600°C at 10°C / min, and kept at the temperature for 120 minutes (microwave radiation, carbon dioxide introduction and Raman spectroscopy monitoring are cancelled); Step 5 Acid enzyme modification adjustment: Due to the decrease in porosity of the activated product, the ultrasonic time is extended to 180 minutes.

[0033] The remaining formula and steps are the same as in Example 1.

[0034] The purpose of this comparative example is to demonstrate the optimization effect of multi-stage microwave activation combined with in-situ monitoring on pore structure.

[0035] Comparative Example 3 The difference between this comparative example and Example 1 is as follows: Step 6, pH adjustment, is simplified to: the online pH meter and automatic dripping system are cancelled, and phosphoric acid is added once to pH=3.8 before static reaction; Step 7, washing process is changed to: the first-stage water wash is changed to two washes with room temperature deionized water, the second-stage sodium bicarbonate and third-stage ethanol washes are removed, and direct vacuum drying at 80°C for 120 minutes is performed.

[0036] The remaining steps are the same as in Example 1.

[0037] Design objective: To verify the effects of three-stage countercurrent washing and dynamic pH control on product purity and functional group stability.

[0038] The activated carbon prepared in Examples 1-5 and Comparative Examples 1-3 was tested for the following items, and the results are shown in Table 1: Test Item 1: Phenol Adsorption Kinetics Test (Based on GB / T12496.8-2015) Procedure: Prepare an initial concentration of 500 mg / L phenol solution (pH=7.0). Add 50 mg of activated carbon sample to 100 mL of phenol solution and react in a constant temperature shaker (150 rpm) at 25 °C. Take samples at time points of 5 / 15 / 30 / 60 / 120 / 240 min. After centrifugation and filtration, determine the residual phenol concentration by ultraviolet spectrophotometry (λ=270 nm) and calculate the unit adsorption capacity.

[0039] Test Item 2: Thermogravimetric Stability Test (based on ISO 11358-1:2014) Procedure: Place 10 mg of sample in an aluminum crucible and program the temperature under a nitrogen atmosphere (flow rate 50 mL / min) at a rate of 10 °C / min, in the range of 40-800 °C. Record the characteristic peak of carboxyl decomposition (200-300 °C), weight loss rate, and carbon skeleton decomposition temperature.

[0040] Test Item 3: Quantitative Analysis of Carboxyl Density (Based on Bohem Titration) Procedure: Disperse 100 mg of sample in 20 mL of 0.01 mol / L NaCl solution, adjust the pH to 2.5 with 0.05 mol / L HCl, and titrate with 0.02 mol / L NaOH using an automatic titrator until pH = 11.0. Calculate the carboxyl density (mmol / g) and carboxyl density (mmol / g) based on the alkali consumption at the carboxyl characteristic plateau (pH = 6-8). Table 1: Test results of activated carbon prepared in Examples 1-5 and Comparative Examples 1-3:

[0041] The test results show that the phenol adsorption capacity of Examples 1-5 (230.1-252.7 mg / g) is significantly higher than that of all comparative examples. Among them, the adsorption capacity of Comparative Example 1 decreased due to the lack of enzyme catalytic carboxylation.

[0042] The carboxyl decomposition temperature of the sample in the examples (281-291℃) was 30-50℃ higher than that of the comparative examples. In particular, the comparative example 3 had the worst thermal stability (241℃) due to residual impurities caused by insufficient washing. This proves that three-stage countercurrent washing effectively improves the thermal stability of functional groups.

[0043] The carboxyl group density (1.72-1.92 mmol / g) of the examples was superior across the board, while the conventional activation method in Example 2 resulted in pore collapse and reduced enzyme catalytic efficiency. Key indicators verified the synergistic effect of the three major innovations: bio-enzyme synergy, microwave dynamic regulation, and precision washing.

[0044] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A process for preparing carboxylated coconut shell-based activated carbon for organic matter adsorption, characterized in that, The specific steps are as follows: Step 1, Raw material selection: 50-60 parts by weight of coconut shell powder, 40-50 parts by weight of walnut shell powder, 20-30 parts by weight of potassium hydroxide, 17-22 parts by weight of nitric acid, 13-17 parts by weight of phosphate, 1-5 parts by weight of laccase-peroxidase complex enzyme preparation, and 25-35 parts by weight of sodium citrate buffer solution. Step 2: Place coconut shell powder and walnut shell powder in a ball mill and mix and grind them at 300 rpm for 60 minutes to obtain mixed fruit shell powder with a particle size ≤75μm. Step 3: Add the mixed fruit shell powder from Step 1 and potassium hydroxide to a high-speed mixer: add 50% potassium hydroxide for the first time and stir for 20 minutes; after a 10-minute interval, add the remaining 50% potassium hydroxide and continue stirring for 40 minutes, maintaining the temperature at 45°C throughout the stirring process; Step 4: Transfer the material obtained in Step 3 to a microwave reactor, replace the air in the reactor with nitrogen three times, start the program to heat up and perform two stages of microwave activation, and at the same time use a fiber optic temperature sensor to monitor the internal temperature of the material in real time. Step 5: Add phosphoric acid, laccase-peroxidase complex enzyme preparation, and sodium citrate buffer solution to the product of step 4, and mix in an ultrasonic reactor; Step 6: Transfer the mixture from Step 5 into a constant temperature stirring tank and heat it to 65°C at a rate of 1°C / min. Use an online pH meter to monitor the pH of the system. When the pH is greater than 4.0, add phosphoric acid automatically to adjust the pH and maintain it at 3.8 ± 0.

2. The reaction time is 180 minutes. Step 7: After washing and drying the reaction product from step 6, carboxylated coconut shell-based activated carbon is obtained.

2. The preparation process of carboxylated fruit shell-based activated carbon for organic matter adsorption according to claim 1, characterized in that, The raw materials in step 1 are: 55 parts by weight of coconut shell powder, 45 parts by weight of walnut shell powder, 25 parts by weight of potassium hydroxide, 5 parts by weight of phosphoric acid, 2.5 parts by weight of laccase-peroxidase complex enzyme preparation, and 30 parts by weight of sodium citrate buffer solution.

3. The preparation process of carboxylated fruit shell-based activated carbon for organic matter adsorption according to claim 2, characterized in that, The pH of the sodium citrate buffer solution is 5.

0.

4. The process for preparing carboxylated fruit shell-based activated carbon for organic matter adsorption according to claim 2, characterized in that, The preparation method of the laccase-peroxidase complex enzyme preparation is as follows: laccase and peroxidase are mixed at a mass ratio of 1:1, and trehalose (1 / 5 of the total enzyme mass) is added as a freeze-drying protectant. After pre-freezing at -40℃ for 4 hours, the mixture is vacuum freeze-dried for 24 hours, pulverized, and passed through a 100-mesh sieve to obtain the laccase-peroxidase complex enzyme preparation.

5. The preparation process of carboxylated fruit shell-based activated carbon for organic matter adsorption according to claim 1, characterized in that, The two stages of microwave activation in step 3 are as follows: In the first stage, the temperature is raised from room temperature to 300°C in 5 minutes with a microwave power of 400W, and the temperature is maintained for 20 minutes; in the second stage, the temperature is raised to 600°C, the microwave power is increased to 800W, carbon dioxide gas is introduced at a flow rate of 50mL / min, and carbon skeleton structure data is collected every 5 minutes using an in-situ Raman spectrometer. When the intensity ratio of the D peak to the G peak reaches 1.8, the temperature is immediately lowered to 400°C.

6. The preparation process of carboxylated coconut shell-based activated carbon for organic matter adsorption according to claim 1, characterized in that, In step 5, when mixing in the ultrasonic reactor, the ultrasonic frequency is set to 40kHz and the temperature to 50℃, and the mixture is mixed for 120 minutes in an intermittent ultrasonic mode with a 30s working and 10s pausing.

7. The preparation process of carboxylated coconut shell-based activated carbon for organic matter adsorption according to claim 1, characterized in that, The washing method in step 7 is as follows: the reaction product is fed into a three-stage countercurrent washing tower: the first stage is washed 3 times with 60℃ deionized water; the second stage is washed 2 times with 0.1mol / L sodium bicarbonate solution; and the third stage is washed once with 70% ethanol solution, with a liquid-solid ratio of 5:1 each time.

8. The preparation process of carboxylated coconut shell-based activated carbon for organic matter adsorption according to claim 7, characterized in that, The drying method in step 7 is as follows: after washing, the material is loaded into a vacuum dryer, dried at 40°C for 120 minutes in the first stage, at 60°C for 90 minutes in the second stage, and at 80°C for 60 minutes in the third stage, while maintaining a vacuum of -0.09 MPa, to obtain carboxylated coconut shell-based activated carbon.

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