A method for regenerating waste activated carbon

Abstract

The present invention relates to a method for regenerating waste activated carbon. The waste activated carbon is pretreated by ultrasonic cleaning in water, then pickled with a mixed acid, impregnated in a Cu(II) solution and a solution containing polyols and polyamines for modification, and finally obtained after programmed heating and programmed annealing. The regenerated activated carbon of the present invention restores the adsorption capacity for organic pollutants again, has a high recovery rate, and the regenerated activated carbon has a large adsorption capacity for organic substances in wastewater and a fast adsorption rate, and can effectively complete the preliminary treatment of organic sewage.

Description

Technical Field

[0001] The present invention belongs to the preparation and regeneration technology of activated carbon modified materials, and particularly relates to a method for regenerating waste activated carbon. Background Art

[0002] Due to its strong adsorption capacity, good chemical stability, high mechanical strength and renewable properties, activated carbon is widely used in the fields of sewage treatment, air purification, dye decolorization and gas separation, and has outstanding advantages in removing biorefractory hydrophobic organic compounds in wastewater. However, conventional activated carbon is extremely easy to adsorb a large amount of water under high humidity conditions such as wastewater and humidity. The competitive adsorption of water molecules reduces the adsorption capacity of activated carbon for organic matter. Modifying conventional activated carbon or waste activated carbon materials can enhance the hydrophobicity of the activated carbon material, improve its adsorption capacity for organic matter, and improve the utilization efficiency of activated carbon.

[0003] In addition, after the activated carbon is saturated with adsorption, its adsorption performance drops sharply. Replacing with new carbon has too high treatment costs, and the waste saturated activated carbon is prone to problems such as resource waste and secondary pollution. Removing the pollutants adsorbed by the activated carbon through regeneration and restoring its adsorption capacity not only avoids the pollution caused by treating waste activated carbon, but also saves a large amount of resources and economic costs. Currently, the main methods for regenerating activated carbon include thermal regeneration method, chemical regeneration method, biological regeneration method, wet oxidation regeneration method, vacuum regeneration method; and new regeneration methods in recent years such as ozone regeneration, Fenton regeneration, electrochemical regeneration, etc. Among them, the thermal regeneration method has outstanding advantages such as high efficiency and good regeneration stability, and is the most widely studied and mature method at present. However, when the activated carbon obtained by the thermal regeneration method is used again for wastewater treatment, its adsorption capacity decreases and the adsorption efficiency becomes poor. The possible reason is that the simple thermal regeneration method cannot effectively restore the internal pore volume and pore channels of the activated carbon. The microwave heating regeneration method combines the advantages of thermal regeneration and microwave assistance, and is an important direction in the current research on activated carbon regeneration. However, it also has the defect that the adsorption performance of the regenerated activated carbon decreases. Summary of the Invention

[0004] In order to overcome the problem that the adsorption efficiency of activated carbon decreases after regeneration in the prior art and there is no suitable industrial method for regenerating activated carbon, the present invention provides the following technical solutions:

[0005] A method for regenerating waste activated carbon, comprising the following steps:

[0006] (S1) Pretreatment: After ultrasonic cleaning the waste activated carbon material in water, filtering, and drying;

[0007] Further, the waste activated carbon is the activated carbon that has reached adsorption saturation after being used for industrial wastewater treatment. The industrial wastewater includes printing and dyeing wastewater, chemical pharmaceutical wastewater, municipal sewage, etc. Such waste activated carbon has adsorbed a large amount of organic compounds, and it is difficult to restore its activity by conventional methods such as pyrolysis. The regenerated activated carbon obtained by the method of the present invention has improved adsorption performance, and even better than that of the new activated carbon before use. This is because the present invention combines regeneration and modification of the activated carbon, not only completing the removal of organic pollutants in the pores of the activated carbon, but also completing the modification of the activated carbon at the same time, further improving the adsorption performance of the activated carbon for organic pollutants in wastewater.

[0008] After ultrasonic cleaning, impurities in the pores of the activated carbon can be preliminarily removed, and the pores of the activated carbon can be dredged. The ultrasonic power of the ultrasonic cleaning is 300 - 500W, the ultrasonic frequency is 80 - 120KHz, and the ultrasonic cleaning time is 8 - 12h. The amount of water used is 10 - 15 times the mass of the activated carbon.

[0009] (S2) Pickling: Immerse the activated carbon pretreated in step (S1) in a mixed acid solution including nitric acid, perchloric acid, and sulfuric acid under ultrasonic conditions, filter, wash with water, and dry.

[0010] Further, in step (S2), the ultrasonic conditions are that the power of the ultrasonic instrument is 300 - 500W, and the ultrasonic power is 80 - 120kHz; the mixed acid includes 2 - 5wt% nitric acid, 1.5 - 3wt% perchloric acid, and 3 - 6wt% sulfuric acid; the impregnation time is 10 - 30min.

[0011] After pickling, the internal organic impurities of the activated carbon can be basically removed. However, the number of acidic oxygen-containing groups on the surface of the activated carbon increases after pickling, which is not conducive to the adsorption of low-polarity organic substances. Moreover, the hydrophilicity of the activated carbon increases, and in wastewater treatment and in humid air, it will adsorb a large amount of water. The competitive adsorption of water molecules will reduce the adsorption capacity of the activated carbon for organic substances. Therefore, in the pickling process of the present invention, the concentration of the acid cannot be too high, and the impregnation time cannot be too long. The present invention pickles under ultrasonic conditions, and can complete the pickling process with a lower concentration of acid and a shorter pickling time, without increasing the hydrophilicity of the activated carbon too much while removing the organic impurities of the activated carbon.

[0012] (S3) Modification treatment: The activated carbon pickled in step (S2) is successively immersed in a solution containing Cu(II) ions and a solution containing polyols and polyamines, filtered, and dried.

[0013] Further, in step (S3), the Cu(II)-ion-containing solution is at least one of copper nitrate, copper sulfate, copper chloride, copper acetate, and copper oxalate; the polyol is selected from at least one of sucrose, glucose, and mannitol; the impregnation time of the activated carbon in the Cu(II)-ion-containing solution is 5-10 h, and the impregnation time of the activated carbon in the solution containing polyol and polyamine is 1-2 h; the polyamine is selected from ethylenediamine, diethylenetriamine, and triethylenetetramine; further, the concentration of Cu(II) ions in the Cu(II)-ion-containing solution is 0.2-0.5 M; in the solution containing polyol and polyamine, the solvent is an aqueous alcohol solution of 40-60%, and the alcohol is selected from at least one of methanol, ethanol, and isopropanol; the concentration of the polyol is 0.1-0.2 M, and the concentration of the polyamine is 0.05-0.1 M.

[0014] The inventors unexpectedly found that after the modification treatment in step (S3), the regeneration of the activated carbon can be effectively completed. The activated carbon restores its adsorption capacity for organic pollutants in wastewater, and even its adsorption capacity for some organic substances is enhanced. After the activated carbon is pickled, the content of surface acidic oxygen increases, and its adsorption capacity for metal ions increases. Then it is impregnated in an aqueous solution containing Cu(II). After adsorbing copper ions, it is impregnated in a solution containing polyol and polyamine. The presence of copper ions is beneficial to the anchoring effect of polyol and polyamine on copper ions. After subsequent pyrolysis, the regeneration and modification of the activated carbon are completed.

[0015] (S4) High-temperature activation treatment: The activated carbon after the modification treatment in step (S3) is subjected to programmed heating, programmed annealing treatment, and then naturally cooled to room temperature.

[0016] Further, the programmed heating is carried out at 500°C - 600°C for 15 - 20 h, at 600°C - 700°C for 20 - 30 h, and at 800°C - 900°C for 10 - 15 h; the heating rate during heating is 40 - 70°C / h, during the programmed annealing, it is annealed at 210 - 240°C for 1 - 2 h, and then cooled to 160 - 180°C for annealing for 3 - 5 h, and the cooling rate is 20 - 30°C / h.

[0017] The programmed heating converts the disordered carbon in the activated carbon into a layered structure, greatly improving the order degree of carbon atoms on the surface of the activated carbon, and the content of oxygen-containing functional groups decreases by 70%. At the same time, the substances in the pores of the waste activated carbon are thermally desorbed. Through the above programmed heating, the disorder degree of the activated carbon can be fully and effectively adjusted to complete uniform and stable graphitization. The inventors found that after a suitable annealing procedure, the regenerated activated carbon has a larger adsorption capacity and a faster adsorption rate, and can be more effectively used as an adsorbent for wastewater treatment.

[0018] If the modified treatment in step (S3) is not carried out, the quality of the regenerated activated carbon is poor. The inventor speculates that the reasons are as follows: on the one hand, the activated carbon after pickling has good hydrophilicity, and the competitive adsorption of water reduces the adsorption capacity of the activated carbon for organic substances. The modification with polyamine enhances the hydrophobicity of the activated carbon, and the doping of nitrogen is also helpful for the adsorption capacity of the activated carbon; on the other hand, the presence of copper ions as a catalyst is beneficial to the oxidative degradation of organic substances during the subsequent high-temperature calcination activation process. The inventor speculates that the following reactions may occur: First, copper oxide is generated during the high-temperature calcination of copper salt, and copper oxide and carbon are reduced to copper at high temperature; then copper reacts with combined water to generate carbon dioxide and copper oxide.

[0019] CuO + C=Cu + CO

[0020] Cu + H 2 O=CuO + H 2

[0021] CuO + CO=Cu + CO 2

[0022] Copper plays a role as a catalyst in the catalytic regeneration reaction.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] 1. Through the steps of ultrasonic pretreatment, pickling, modification and high-temperature activation, the adsorption capacity of the waste activated carbon that has reached adsorption saturation for organic pollutants is fully restored, and even better than that of the fresh activated carbon before regeneration.

[0025] 2. Through the cooperation of each step, the regeneration of activated carbon is completed by a simple process. In the high-temperature regeneration process, the temperature is low, the loss of activated carbon is small, and the recovery rate is above 95%.

[0026] 3. The regenerated activated carbon of the present invention has a large adsorption capacity for organic substances in wastewater and a fast adsorption rate, and can effectively complete the preliminary treatment of organic sewage. Detailed implementation mode

[0027] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. The following embodiments are convenient for better understanding of the present invention, but do not limit the present invention. The experimental methods in the following embodiments are all conventional methods unless otherwise specified.

[0028] The waste activated carbon used in the present invention comes from the activated carbon that has reached adsorption saturation during the wastewater treatment of a certain printing and dyeing factory. Its unused fresh activated carbon has a saturated adsorption capacity of 136.2 mg / g for phenol, 427.4 mg / g for methylene blue, and 92.1 mg / g for bisphenol A at 25°C.

[0029] Example 1

[0030] (S1) Pretreatment: The waste activated carbon material is put into 15 times its mass of clear water and ultrasonically cleaned at a ultrasonic power of 300 W and a ultrasonic frequency of 120 KHz for 10 h, then filtered and dried;

[0031] (S2) Pickling: The activated carbon pretreated in step (S1) is impregnated in an aqueous mixed acid solution containing 3 wt% nitric acid, 2 wt% perchloric acid, and 4 wt% sulfuric acid at a ultrasonic power of 300 W and a ultrasonic frequency of 120 KHz for 30 min, then washed with water until the pH of the washing solution is 6.3 - 6.6; filtered and dried;

[0032] (S3) Modification treatment: The activated carbon pickled in step (S2) is impregnated in a 0.2 M copper nitrate solution for 10 h, and then impregnated in a 50% ethanol aqueous solution containing 0.1 M mannitol and 0.05 M triethylenetetramine for 2 h, filtered and dried;

[0033] (S4) High-temperature activation treatment: The activated carbon after the modification treatment in step (S3) is heated at 600 °C for 15 h, 700 °C for 20 h, and 900 °C for 10 h with a heating rate of 40 °C / h during the temperature increase; then cooled at a cooling rate of 20 °C / h to 220 °C, annealed for 1 h, then cooled to 160 °C and annealed for 3 h, and finally naturally cooled to room temperature to obtain the regenerated activated carbon.

[0034] Example 2

[0035] Other conditions and steps are the same as those in Example 1, the difference is that step (S3) is changed to: The activated carbon pickled in step (S2) is impregnated in a 0.3 M copper acetate solution for 8 h, and then impregnated in a 50% ethanol aqueous solution containing 0.2 M sucrose and 0.1 M ethylenediamine for 2 h, filtered and dried.

[0036] Example 3

[0037] Other conditions and steps are the same as those in Example 1, the difference is that step (S4) is changed to: The activated carbon after the modification treatment in step (S3) is heated at 700 °C for 20 h and 900 °C for 15 h with a heating rate of 40 °C / h during the temperature increase; then cooled at a cooling rate of 20 °C / h to 200 °C, annealed for 1 h, then cooled to 160 °C and annealed for 3 h, and finally cooled to room temperature by refrigeration to obtain the regenerated activated carbon.

[0038] Example 4

[0039] Other conditions and steps are the same as those in Example 1, except that step (S4) is changed to: The activated carbon after the modification treatment in step (S3) is heated at 600 °C for 15 h, heated at 700 °C for 20 h, and heated at 900 °C for 10 h with a programmed temperature increase, and the heating rate during the temperature increase is 40 °C / h; then it is cooled at a cooling rate of 20 °C / h to 200 °C, annealed for 3 h, and finally naturally cooled to room temperature to obtain the regenerated activated carbon.

[0040] Comparative Example 1

[0041] Other conditions and steps are the same as those in Example 1, except that step (S3) is changed to: The activated carbon pickled in step (S2) is impregnated in a 50% ethanol aqueous solution containing 0.1 M of mannitol and 0.05 M of triethylenetetramine for 2 h, filtered, and dried; that is, the step of impregnating in the copper nitrate solution is cancelled.

[0042] Comparative Example 2

[0043] Other conditions and steps are the same as those in Example 1, except that step (S3) is changed to: The activated carbon pickled in step (S2) is impregnated in a 0.2 M copper nitrate solution for 10 h, and then impregnated in a 50% ethanol aqueous solution containing 0.1 M of mannitol for 2 h, filtered, and dried; that is, the step of impregnating in the triethylenetetramine solution is cancelled.

[0044] Comparative Example 3

[0045] Other conditions and steps are the same as those in Example 1, except that step (S3) is changed to: The activated carbon pickled in step (S2) is impregnated in a 0.2 M copper nitrate solution for 10 h, and then impregnated in a 50% ethanol aqueous solution containing 0.05 M of triethylenetetramine for 2 h, filtered, and dried; that is, the step of impregnating in the mannitol solution is cancelled.

[0046] Comparative Example 4

[0047] Other conditions and steps are the same as those in Example 1, except that step (S4) is changed to: The activated carbon after the modification treatment in step (S3) is heated at 600 °C for 15 h, heated at 700 °C for 20 h, and heated at 900 °C for 10 h with a programmed temperature increase, and the heating rate during the temperature increase is 40 °C / h; then it is naturally cooled to room temperature. That is, the annealing step is cancelled.

[0048] The regenerated activated carbon of the above examples and comparative examples was tested for the following properties, and the results are shown in Table 1 below:

[0049] 1. Regeneration rate:

[0050] For the activated carbon regeneration rate, three representative pollutants were selected for testing, namely phenol, methylene blue, and bisphenol A. The saturated adsorption capacity of the activated carbon was tested at 25°C.

[0051] 2. Recovery rate:

[0052] Table 1 Test of activated carbon regeneration performance

[0053]

[0054] It can be seen that for the activated carbon regeneration method provided by the present invention, the obtained regenerated activated carbon has good adsorption performance and high regeneration rate for the representative pollutants in wastewater. Even after modification, the adsorption capacity for bisphenol A is better than that of fresh activated carbon. The method of the present invention has a high recovery rate of activated carbon, can recover more than 95% of the activated carbon, and has a simple process and low cost. It is a recovery method suitable for large-scale industrial wastewater, especially for waste activated carbon saturated with organic matter adsorption.

Claims

1. A method for regenerating waste activated carbon, characterized in that, it comprises the following steps: (S1) Pretreatment: After ultrasonic cleaning the waste activated carbon material in water, filtering, and drying; (S2) Pickling: Immerse the activated carbon pretreated in step (S1) in a mixed acid solution including nitric acid, sulfuric acid, and perchloric acid under ultrasonic conditions, filter, wash with water, and dry; the mixed acid includes 2 - 5wt% nitric acid, 1.5 - 3wt% perchloric acid, 3 - 6wt% sulfuric acid; the impregnation time is 10 - 30 min; (S3) Modification treatment: The activated carbon pickled in step (S2) is successively immersed in a solution containing Cu(II) ions, a solution containing polyols and polyamines, filter, and dry; the polyols are selected from at least one of sucrose, glucose, and mannitol; the polyamines are selected from ethylenediamine, diethylenetriamine, and triethylenetetramine; the concentration of Cu(II) ions in the solution containing Cu(II) ions is 0.2 - 0.5 M; in the solution containing polyols and polyamines, the solvent is a 40 - 60% aqueous alcohol solution; the concentration of the polyols is 0.1 - 0.2 M, and the concentration of the polyamines is 0.05 - 0.1 M; (S4) High - temperature activation treatment: The activated carbon after modification treatment in step (S3) undergoes programmed heating, programmed annealing treatment, and natural cooling to room temperature; the programmed heating is heating at 500℃ - 600℃ for 15 - 20 h, 600℃ - 700℃ for 20 - 30 h, 800℃ - 900℃ for 10 - 15 h; the heating rate during heating is 40 - 70℃ / h, the programmed annealing is cooling to 210 - 240℃ for annealing for 1 - 2 h, and then cooling to 160 - 180℃ for annealing for 3 - 5 h, and the cooling rate is 20 - 30℃ / h.

2. The method for regenerating waste activated carbon according to claim 1, characterized in that, in step (S1), the ultrasonic power of the ultrasonic cleaning is 300 - 500 W, the ultrasonic frequency is 80 - 120 KHz, and the ultrasonic cleaning time is 8 - 12 h; the amount of water used is 10 - 15 times the mass of the activated carbon.

3. The method for regenerating waste activated carbon according to claim 1, characterized in that, in step (S3), the solution containing Cu(II) ions is at least one of copper nitrate, copper sulfate, copper chloride, copper acetate, and copper oxalate.

4. The method for regenerating waste activated carbon according to claim 1, characterized in that, in step (S3), the impregnation time of the activated carbon in the solution containing Cu(II) ions is 5 - 10 h, and the impregnation time of the activated carbon in the solution containing polyols and polyamines is 1 - 2 h.

5. The method for regenerating waste activated carbon according to claim 1, characterized in that, in step (S3), in the aqueous alcohol solution, the alcohol is selected from at least one of methanol, ethanol, and isopropanol.

6. Use of the activated carbon prepared by the regeneration method according to any one of claims 1 - 5 in adsorbing organic pollutants in wastewater, wherein the organic pollutants are selected from phenol, methylene blue, or bisphenol A.

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