An ultra-low ash food-grade activated carbon and its preparation method

Abstract

The present invention relates to an ultra-low ash food-grade activated carbon and a preparation method thereof, belonging to the technical field of activated carbon production. The activated carbon comprises the following raw materials: broken material of Pteris vittata, activator, polyvinylidene chloride, polyvinyl butyral resin, sodium silicate and ammonium persulfate. In the present invention, polyvinylidene chloride and polyvinyl butyral resin are added, effectively increasing the strength and adsorption of the finished activated carbon; in addition, in the present invention, the ash is fixed by a solution formed by sodium silicate and deionized water, and then the activated carbon is oxidized and removed by a solution formed by ammonium persulfate and deionized water, and the two can play a complementary role, so that the prepared activated carbon has the advantage of low ash. At the same time, phosphoric acid is used as the activator in this article, and the T-62MP de-aluminum resin exchange column is used for the recovery and purification of phosphoric acid, and then it is regenerated by hydrochloric acid and backwashed with soft water or tap water for recycling.

Description

Technical Field

[0001] The present invention belongs to the technical field of activated carbon production, and specifically relates to an ultra-low ash food-grade activated carbon and a preparation method thereof. Background Art

[0002] Activated carbon is a porous carbon-containing material with a very developed pore structure and a large specific surface area inside, and surface functional groups with special functions containing elements such as oxygen on the surface. It is often widely used as a catalyst, adsorption material, and energy storage material in important fields such as food processing, chemical industry, medicine, and military. At the same time, activated carbon is easy to regenerate and reuse, and has received extensive attention in today's society. Currently, the commercially available food-grade activated carbon has a relatively high ash content during the preparation process, which limits its application in the field of water purification for foods such as sugar production, pharmaceutical production, beverages, wine, and water. Therefore, it is necessary to research and develop a food-grade activated carbon with a low ash content. Summary of the Invention

[0003] The purpose of the present invention is to provide an ultra-low ash food-grade activated carbon and a preparation method thereof. The present invention adds polyvinylidene chloride and polyvinyl butyral resin, effectively increasing the strength and adsorption of the activated carbon product. In addition, the present invention first fixes the ash with a solution formed by sodium silicate and deionized water, and then oxidizes and removes the activated carbon with a solution formed by ammonium persulfate and deionized water. The two can play a complementary role, making the prepared activated carbon have the advantage of low ash, and solving the problem of high ash content of the activated carbon existing in the prior art.

[0004] The purpose of the present invention can be achieved by the following technical solutions:

[0005] An ultra-low ash food-grade activated carbon, the activated carbon comprises the following raw materials in parts by mass:

[0006] Fragmented material of Pteris vittata 60 - 90g

[0007] Activating agent 23 - 52g

[0008] Polyvinylidene chloride 12 - 33g

[0009] Polyvinyl butyral resin 13 - 37g

[0010] Sodium silicate 3 - 8g

[0011] Ammonium persulfate 7 - 15g.

[0012] Centipede Pteris is a perennial evergreen herb belonging to the Pteridaceae family and the terrestrial fern genus Pteris. It is widely distributed in tropical and subtropical areas of my country and has the characteristics of rich resources and high yield. Its rhizome is upright with a drill-shaped leaf at the top. It is more drought-resistant when planted in soil. It is commonly seen in sandy loam or rocks, step gaps and wall brick gaps in the wild. It is rough and grows rapidly. The raw materials are very easy to obtain. In addition, the rhizome of centipede pteris contains a high carbon content and adsorption performance, so it is a preferred product for preparing activated carbon raw materials.

[0013] As a preferred embodiment of the present invention, the preparation method of the centipede pteris fern crushed material is: the centipede pteris fern rhizome raw material is naturally dried for 1-2 days, then crushed and passed through a 50-60 mesh sieve, and after screening, the temperature is controlled at 100-110°C and dried for 0.5-1h to obtain the centipede pteris fern crushed material.

[0014] As a preferred embodiment of the present invention, the activator is a phosphoric acid solution with a mass fraction of 65-70%.

[0015] As a preferred embodiment of the present invention, the method for preparing activated carbon comprises the following steps:

[0016] S1. Mix the centipede pteris fern crushed material, sodium silicate and ammonium persulfate with deionized water to obtain a mixed material, a mixed solution A and a mixed solution B respectively;

[0017] S2, adding an activator to the mixture and reacting it under the assistance of ultrasound, and vacuum filtering after the reaction is completed to obtain a filter residue and a filtrate A;

[0018] S3, adding polyvinylidene chloride and polyvinyl butyral resin to the filter residue and kneading them evenly, controlling the temperature and activating them under nitrogen protection to obtain the material to be flushed;

[0019] S4. Cool the material to be rinsed to room temperature, then rinse it once with mixed solution A, rinse it twice with mixed solution B, and rinse it with deionized water to obtain material to be dried. Dry the material to be dried under controlled temperature to obtain a finished activated carbon product.

[0020] As a preferred embodiment of the present invention, in step S1, the mass ratio of the centipede fern crushed material to deionized water is 1:4-4.5; the mass ratio of the sodium silicate to deionized water is 4-4.5:6-7; and the mass ratio of the ammonium persulfate to deionized water is 1:1-1.3.

[0021] As a preferred embodiment of the present invention, the filtrate A in step S2 is also recovered and purified. The method for recovery and purification is as follows: The filtrate A in step S2 is passed through a filter to remove the residual solid impurities therein, obtaining filtrate B. The filtrate B is passed through a Tulsimer ® T-62MP aluminum-removing resin exchange column at a controlled rate of 8-10 BV / h to obtain purified phosphoric acid.

[0022] As a preferred embodiment of the present invention, the Tulsimer ® T-62MP aluminum-removing resin exchange column is recycled by the following method: The Tulsimer ® T-62MP aluminum-removing resin exchange column is regenerated with hydrochloric acid, and then backwashed with soft water or tap water at a controlled rate to wash the Tulsimer ® T-62MP aluminum-removing resin exchange column, and then it can be recycled.

[0023] As a preferred embodiment of the present invention, the mass fraction of the hydrochloric acid is 5-7%, the flow rate is 4-5 BV / h, and the regeneration time is 30-35 min; the flow rate of the soft water or tap water is 5-10 BV / h, and the time for backwashing the Tulsimer ® T-62MP aluminum-removing resin exchange column is 30-40 min.

[0024] As a preferred embodiment of the present invention, the power of the ultrasonic wave in step S2 is 60-80 kW, and the reaction time is 30-70 min.

[0025] As a preferred embodiment of the present invention, the temperature for temperature-controlled activation in step S3 is 300-450 °C, and the time is 30-80 min.

[0026] As a preferred embodiment of the present invention, the number of times of the first flushing in step S4 is 4-6 times, the number of times of the second flushing is 4-5 times, the degree of flushing with deionized water is to flush until the pH value is 6-7, the temperature for temperature-controlled drying is 120-130 °C, and the time is 2-3 h.

[0027] As a preferred embodiment of the present invention, the application of the ultra-low ash food-grade activated carbon prepared by the present invention is for water purification in foods such as sugar production, pharmaceutical production, beverages, wine, and water.

[0028] Advantages of the present invention:

[0029] (1) The present invention adds polyvinylidene chloride and polyvinyl butyral resin, effectively increasing the strength and adsorption of the activated carbon product. This is because, under high-temperature conditions, the carbon-carbon skeleton of the polyvinyl butyral resin can still be retained, providing a skeletal structure for the activated carbon raw material to a certain extent and enhancing the strength of the prepared activated carbon. Polyvinylidene chloride can interact with the activated carbon raw material and polyvinyl butyral resin to form chemical bonds, which make the bonding between the raw materials in the system closer, thus assisting the polyvinyl butyral resin to prepare activated carbon with higher strength. In addition, during the pyrolysis process, polyvinylidene chloride itself can generate pores, so it can effectively reduce the macropore volume of the high specific surface area activated carbon and is more conducive to improving the adsorption of the prepared activated carbon.

[0030] (2) The present invention first uses a solution formed by sodium silicate and deionized water, and then uses a solution formed by ammonium persulfate and deionized water to treat the activated carbon, making the prepared activated carbon have the advantage of low ash content. This is because sodium silicate can react chemically with the ash substances on the surface of the activated carbon to form water-insoluble silicate, making the ash easy to be fixed on the surface of the activated carbon and facilitating removal, creating conditions for the ash removal work of ammonium persulfate; ammonium persulfate has strong oxidizing properties and can remove the silicate fixed on the surface of the activated carbon and further effectively remove the residual ash in the activated carbon. That is, the present invention first fixes the ash with sodium silicate and then oxidizes and removes it with ammonium persulfate, and the two can play a complementary role and synergistically improve the ash removal effect of the activated carbon.

[0031] (3) In this article, phosphoric acid, which is economical and less polluting, is used as the activator, and a method for recycling and purifying phosphoric acid using a Tulsimer ® T-62MP de-aluminum resin exchange column is provided. Under this method, the purity of phosphoric acid reaches more than 95%. In addition, the used Tulsimer ® T-62MP de-aluminum resin exchange column of the present invention is regenerated with hydrochloric acid and backwashed with soft water or tap water, providing a method for the recyclable use of the Tulsimer ® T-62MP de-aluminum resin exchange column. Both of these methods save more than 7% of the acid consumption cost and have actual economic benefits. Detailed implementation manners

[0032] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0033] The Tulsimer described in the present invention ®The T-62MP aluminum removal resin exchange column was purchased from Clean Science & Technology (Beijing) Co., Ltd.

[0034] Example 1

[0035] An ultra-low ash food-grade activated carbon, the activated carbon comprising the following raw materials in parts by mass:

[0036] Crushed material of Pteris vittata 90 g

[0037] Phosphoric acid solution with a mass fraction of 65% 23 g

[0038] Polyvinylidene chloride 12 g

[0039] Polyvinyl butyral resin 25 g

[0040] Sodium silicate 8 g

[0041] Ammonium persulfate 7 g.

[0042] The preparation method of the crushed material of Pteris vittata is as follows: The rhizome raw material of Pteris vittata is naturally dried for 2 days, then crushed and sieved through a 55-mesh sieve, and after sieving, it is dried at a controlled temperature of 100 °C for 1 h to obtain the crushed material of Pteris vittata.

[0043] The preparation method of the activated carbon comprises the following steps:

[0044] S1. Mix the crushed material of Pteris vittata and deionized water evenly according to a mass ratio of 1:4.5 to obtain a mixture; mix sodium silicate and deionized water evenly according to a mass ratio of 4:6.5 to obtain a mixed solution A; mix the ammonium persulfate and deionized water evenly according to a mass ratio of 1:1 to obtain a mixed solution B;

[0045] S2. Add the phosphoric acid solution with a mass fraction of 65% to the mixture and react for 70 min under ultrasonic assistance with a power of 60 kW. After the reaction is completed, vacuum filtration is carried out to obtain a filter residue and a filtrate A;

[0046] S3. Add polyvinylidene chloride and polyvinyl butyral resin to the filter residue and knead evenly, activate at a controlled temperature of 300 °C for 55 min under nitrogen protection to obtain a material to be rinsed;

[0047] S4. Cool the material to be rinsed to room temperature, then rinse the material to be rinsed 4 times with the mixed solution A, then rinse 4 times with the mixed solution B after rinsing is completed, and continue to rinse with deionized water until the pH value is 6 to obtain a material to be dried. Dry the material to be dried at a controlled temperature of 130 °C for 2 h to obtain the finished activated carbon product.

[0048] Among them, the filtrate A in step S2 is purified in the following manner:

[0049] Filter the filtrate A from step S2 through a filter to remove the residual solid impurities therein, obtaining filtrate B. Pass filtrate B through a Tulsimer ® T-62MP aluminum-removing resin exchange column at a rate of 9 BV / h to obtain purified phosphoric acid, and return the purified phosphoric acid to step S2 for continued use;

[0050] Among them, the Tulsimer ® T-62MP aluminum-removing resin exchange column is recycled by the following method: The Tulsimer ® T-62MP aluminum-removing resin exchange column is regenerated with 5% hydrochloric acid by mass at a rate of 5 BV / h for 33 minutes, and then backwashed with soft water or tap water at a rate of 10 BV / h for ® 30 minutes for the T-62MP aluminum-removing resin exchange column. The Tulsimer ® T-62MP aluminum-removing resin exchange column can then be recycled.

[0051] After testing, the purity of the purified phosphoric acid obtained in this example is 95.8%, and the acid consumption cost of phosphoric acid is saved by 7%.

[0052] Example 2

[0053] An ultra-low ash food-grade activated carbon, the activated carbon comprising the following raw materials in parts by mass:

[0054] Crushed material of Pteris vittata 75 g

[0055] Phosphoric acid solution with a mass fraction of 70% 52 g

[0056] Polyvinylidene chloride 22 g

[0057] Polyvinyl butyral resin 37 g

[0058] Sodium silicate 5 g

[0059] Ammonium persulfate 11 g.

[0060] The preparation method of the crushed material of Pteris vittata is as follows: Naturally dry the rhizome raw material of Pteris vittata for 2 days, then crush it and pass it through a 60-mesh sieve. After sieving, dry it at a temperature of 105 °C for 0.5 h to obtain the crushed material of Pteris vittata.

[0061] The preparation method of the activated carbon comprises the following steps:

[0062] S1. Mix the crushed material of Pteris vittata and deionized water evenly according to a mass ratio of 1:4 to obtain a mixture; Mix sodium silicate and deionized water evenly according to a mass ratio of 4.3:7 to obtain mixture A; Mix the above ammonium persulfate and deionized water evenly according to a mass ratio of 1:1.3 to obtain mixture B;

[0063] S2. Add a phosphoric acid solution with a mass fraction of 70% to the mixture and react for 50 min under ultrasonic assistance with a power of 80 kW. After the reaction is completed, perform vacuum filtration to obtain a filter residue and filtrate A;

[0064] S3. Add polyvinylidene chloride and polyvinyl butyral resin to the filter residue and knead evenly. Activate at 375 °C for 30 min under nitrogen protection to obtain the material to be rinsed;

[0065] S4. Cool the material to be rinsed to room temperature, then rinse the material to be rinsed 5 times with mixture A, then rinse 5 times with mixture B after the rinsing is completed, and continue to rinse with deionized water until the pH value is 6.5 to obtain the material to be dried. Dry the material to be dried at 125 °C for 3 h to obtain the finished activated carbon product.

[0066] Among them, the filtrate A in step S2 is purified in the following manner:

[0067] Filter the filtrate A in step S2 through a filter to remove the residual solid impurities therein to obtain filtrate B. Control the speed of filtrate B at 10 BV / h and pass it through the Tulsimer ® T-62MP aluminum removal resin exchange column to obtain purified phosphoric acid, and the purified phosphoric acid is returned to step S2 for continued use;

[0068] Among them, the Tulsimer ® T-62MP aluminum removal resin exchange column is recycled by the following method: The Tulsimer ® T-62MP aluminum removal resin exchange column after purified phosphoric acid is regenerated with hydrochloric acid with a mass fraction of 6% at a speed of 4 BV / h for 30 min, and then backwashed with soft water or tap water at a speed of 8 BV / h for 35 min for the Tulsimer ® T-62MP aluminum removal resin exchange column. The Tulsimer ® T-62MP aluminum removal resin exchange column can be recycled.

[0069] After testing, the purity of the purified phosphoric acid obtained in this example is 95.9%, and the acid consumption cost of phosphoric acid is saved by 9%.

[0070] Example 3

[0071] An ultra-low ash food-grade activated carbon, and the activated carbon comprises the following raw materials in parts by mass:

[0072] Crushed material of Pteris vittata 60 g

[0073] Phosphoric acid solution with a mass fraction of 68% 38 g

[0074] Polyvinylidene chloride 33 g

[0075] 13 g of polyvinyl butyral resin

[0076] 3 g of sodium silicate

[0077] 15 g of ammonium persulfate.

[0078] The preparation method of the broken material of Pteris vittata L. is as follows: naturally air-dry the rhizome raw material of Pteris vittata L. for 1 day, then crush it and pass through a 50-mesh sieve. After sieving, dry it at a controlled temperature of 110 °C for 0.5 h to obtain the broken material of Pteris vittata L.

[0079] The preparation method of the activated carbon includes the following steps:

[0080] S1. Mix the broken material of Pteris vittata L. and deionized water evenly according to a mass ratio of 1:4.3 to obtain a mixed material; mix sodium silicate and deionized water evenly according to a mass ratio of 4.5:6 to obtain a mixed solution A; mix the above-mentioned ammonium persulfate and deionized water evenly according to a mass ratio of 1:1.2 to obtain a mixed solution B;

[0081] S2. Add a phosphoric acid solution with a mass fraction of 68% to the mixed material and react for 30 min under ultrasonic assistance with a power of 70 kW. After the reaction is completed, perform vacuum filtration to obtain a filter residue and a filtrate A;

[0082] S3. Add polyvinylidene chloride and polyvinyl butyral resin to the filter residue and knead evenly. Activate at a controlled temperature of 450 °C for 80 min under nitrogen protection to obtain a material to be rinsed;

[0083] S4. Cool the material to be rinsed to room temperature, then rinse the material to be rinsed 6 times with the mixed solution A. After rinsing is completed, then rinse it 4 times with the mixed solution B. After rinsing is completed, continue to rinse with deionized water until the pH value is 7 to obtain a material to be dried. Dry the material to be dried at a controlled temperature of 120 °C for 2.5 h to obtain the finished activated carbon product.

[0084] Among them, the filtrate A in step S2 is purified in the following way:

[0085] Filter the filtrate A in step S2 through a filter to remove the residual solid impurities therein to obtain a filtrate B. Pass the filtrate B through a Tulsimer ® T-62MP aluminum removal resin exchange column at a controlled speed of 8 BV / h to obtain purified phosphoric acid. The purified phosphoric acid is returned to step S2 for continued use;

[0086] Among them, the ® T-62MP aluminum removal resin exchange column is recycled by the following method: the Tulsimer after the purified phosphoric acid ®The T-62MP aluminum removal resin exchange column is regenerated with 7% hydrochloric acid at a controlled speed of 4.5 BV / h for 35 minutes, and then backwashed with soft water or tap water at a controlled speed of 5 BV / h for 40 minutes. After that, the T-62MP aluminum removal resin exchange column can be recycled. ® T-62MP aluminum removal resin exchange column for 40 minutes, Tulsimer ® T-62MP aluminum removal resin exchange column can be recycled.

[0087] After testing, the purity of the purified phosphoric acid obtained in this example is 96.2%, and the acid consumption cost of phosphoric acid is saved by 10%.

[0088] Comparative Example 1

[0089] Compared with Example 3, the difference in Comparative Example 1 is that polyvinylidene chloride is not added, and the rest of the operation steps and raw materials are the same.

[0090] Comparative Example 2

[0091] Compared with Example 3, the difference in Comparative Example 2 is that polyvinyl butyral resin is not added, and the rest of the operation steps and raw materials are the same.

[0092] Comparative Example 3

[0093] Compared with Example 3, in Comparative Example 3, the activated carbon includes the following raw materials in parts by mass:

[0094] Broken material of Pteris vittata 60 g

[0095] Phosphoric acid with a mass fraction of 68% 38 g

[0096] Polyvinylidene chloride 33 g

[0097] Polyvinyl butyral resin 13 g

[0098] Sodium silicate 18 g.

[0099] The preparation method of the activated carbon includes the following steps:

[0100] S1. Mix the broken material of Pteris vittata and deionized water evenly according to a mass ratio of 1:4.3 to obtain a mixture; mix sodium silicate and deionized water evenly according to a mass ratio of 4.5:6 to obtain a mixed solution A;

[0101] S2. Add phosphoric acid with a mass fraction of 68% to the mixture and react for 30 minutes under ultrasonic assistance at a power of 70 kW. After the reaction is completed, vacuum filtration is carried out to obtain a filter residue and filtrate A;

[0102] S3. Add polyvinylidene chloride and polyvinyl butyral resin to the filter residue and knead evenly. Activate at 450 °C for 80 minutes under nitrogen protection to obtain the material to be rinsed;

[0103] S4. Cool the material to be rinsed to room temperature, then rinse the material to be rinsed 6 times with mixture A. After rinsing, continue to rinse with deionized water until the pH value is 7 to obtain the material to be dried. Control the temperature of the material to be dried at 120 °C and dry it for 2.5 h to obtain the finished activated carbon product.

[0104] Keep the other operation steps and parameters unchanged.

[0105] Comparative Example 4

[0106] Compared with Example 3, in Comparative Example 4, the activated carbon comprises the following raw materials in parts by mass:

[0107] Fragmented material of Pteris vittata 60 g

[0108] Phosphoric acid with a mass fraction of 68% 38 g

[0109] Polyvinylidene chloride 33 g

[0110] Polyvinyl butyral resin 13 g

[0111] Ammonium persulfate 18 g.

[0112] The preparation method of the activated carbon comprises the following steps:

[0113] S1. Mix the fragmented material of Pteris vittata and deionized water evenly according to a mass ratio of 1:4.3 to obtain a mixed material; mix the ammonium persulfate and deionized water evenly according to a mass ratio of 1:1.2 to obtain a mixed solution B;

[0114] S2. Add phosphoric acid with a mass fraction of 68% to the mixed material and react for 30 min under ultrasonic assistance with a power of 70 kW. After the reaction is completed, perform vacuum filtration to obtain a filter residue and filtrate A;

[0115] S3. Add polyvinylidene chloride and polyvinyl butyral resin to the filter residue and knead evenly. Activate at 450 °C for 80 min under nitrogen protection to obtain the material to be rinsed;

[0116] S4. Cool the material to be rinsed to room temperature, then rinse the material to be rinsed 4 times with mixed solution B. After rinsing, continue to rinse with deionized water until the pH value is 7 to obtain the material to be dried. Control the temperature of the material to be dried at 120 °C and dry it for 2.5 h to obtain the finished activated carbon product.

[0117] Performance detection

[0118] (1) According to the standard GB / T 12496.6-1999, the strength of the activated carbon prepared in Examples 1-3 and Comparative Examples 1-2 was tested, and the results are shown in Table 1.

[0119] (2)According to the standard GB / T 12496.8-1999, the iodine adsorption value of the activated carbon prepared in Examples 1-3 and Comparative Examples 1-2 was tested, and the results are shown in Table 1.

[0120] (3)According to the standard GB / T 12496.3-1999, the ash content of the activated carbon prepared in Examples 1-3 and Comparative Examples 3-4 was tested, and the results are shown in Table 1.

[0121]

[0122] As can be seen from the strength and iodine adsorption value data of Examples 1-3 and Comparative Examples 1-2 in Table 1, the activated carbon prepared by the present invention has excellent strength and adsorption properties. This is because the present invention adds polyvinylidene chloride and polyvinyl butyral resin. Under high-temperature conditions, the carbon-carbon skeleton of the polyvinyl butyral resin can still be retained, providing a skeletal structure for the activated carbon raw materials to a certain extent and enhancing the strength of the prepared activated carbon. Polyvinylidene chloride can interact with the activated carbon raw materials and polyvinyl butyral resin to form chemical bonds, which make the bonding between the system raw materials closer, thus assisting the polyvinyl butyral resin to prepare activated carbon with higher strength. In addition, during the pyrolysis process, polyvinylidene chloride itself can generate pores, so it can effectively reduce the macropore volume of high specific surface area activated carbon and is more conducive to improving the adsorption properties of the prepared activated carbon.

[0123] As can be seen from the ash content data of Examples 1-3 and Comparative Examples 3-4 in Table 1, the activated carbon prepared by the present invention has the advantage of ultra-low ash content. This is because the present invention first fixes the ash with a solution formed by sodium silicate and deionized water, and then oxidizes and removes it with a solution formed by ammonium persulfate and deionized water. The two can play a complementary role and synergistically improve the ash removal effect of the activated carbon.

[0124] In the description of the specification, the description with reference to terms such as "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0125] The above content is only an example and illustration of the present invention. Those skilled in the art of the present technology can make various modifications or supplements to the described specific embodiments or use similar methods for substitution, as long as they do not deviate from the invention or exceed the scope defined by the claims of the present invention, they should fall within the protection scope of the present invention.

Claims

1. An ultra-low ash food-grade activated carbon, characterized in that, the activated carbon comprises the following raw materials in parts by mass: Fragmented material of Pteris vittata 60 - 90g Activating agent 23 - 52g Polyvinylidene chloride 12 - 33g Polyvinyl butyral resin 13 - 37g Sodium silicate 3 - 8g Ammonium persulfate 7 - 15g; The preparation method of the activated carbon comprises the following steps: S1. Mix the fragmented material of Pteris vittata, sodium silicate and ammonium persulfate with deionized water respectively and uniformly to obtain a mixed material, a mixed solution A and a mixed solution B respectively; S2. Add the activating agent to the mixed material and react under ultrasonic assistance. After the reaction is completed, perform vacuum filtration to obtain a filter residue and a filtrate A; S3. Add polyvinylidene chloride and polyvinyl butyral resin to the filter residue and knead evenly, and carry out temperature-controlled activation under nitrogen protection to obtain a material to be rinsed; S4. Cool the material to be rinsed to room temperature, then use the mixed solution A to perform a first rinse on the material to be rinsed. After the first rinse is completed, then use the mixed solution B to perform a second rinse. After the second rinse is completed, continue to rinse with deionized water to obtain a material to be dried. Dry the material to be dried under temperature control to obtain the finished product of activated carbon.

2. An ultra-low ash food-grade activated carbon according to claim 1, characterized in that, the preparation method of the fragmented material of Pteris vittata is: naturally air-dry the rhizome raw material of Pteris vittata for 1 - 2 days, then crush it and pass through a 50 - 60 mesh sieve. After passing through the sieve, dry it at 100 - 110°C for 0.5 - 1h under temperature control to obtain the fragmented material of Pteris vittata.

3. An ultra-low ash food-grade activated carbon according to claim 1, characterized in that, the activating agent is a phosphoric acid solution with a mass fraction of 65 - 70%.

4. An ultra-low ash food-grade activated carbon according to claim 1, characterized in that, in step S1, the mass ratio of the fragmented material of Pteris vittata to deionized water is 1:4 - 4.5; the mass ratio of sodium silicate to deionized water is 4 - 4.5:6 - 7; the mass ratio of ammonium persulfate to deionized water is 1:1 - 1.

3.

5. An ultra-low ash food-grade activated carbon according to claim 1, characterized in that, the recovery and purification method of the activating agent in step S2 is: filter the filtrate A in step S2 through a filter to remove the residual solid impurities therein to obtain a filtrate B, and pass the filtrate B through a Tulsimer® T-62MP de-aluminum resin exchange column at a controlled speed of 8 - 10BV / h to obtain purified phosphoric acid.

6. An ultra-low ash food-grade activated carbon according to claim 5, characterized in that, the Tulsimer® T-62MP de-aluminum resin exchange column is recycled by the following method: regenerate the Tulsimer® T-62MP de-aluminum resin exchange column with hydrochloric acid, and then backwash the Tulsimer® T-62MP de-aluminum resin exchange column at a controlled speed with soft water or tap water, and then it can be recycled.

7. An ultra-low ash food-grade activated carbon according to claim 6, characterized in that, The mass fraction of the hydrochloric acid is 5-7%, the flow rate is 4-5 BV / h, and the regeneration time is 30-35 min; the flow rate of the soft water or tap water is 5-10 BV / h, and the backwashing time of the Tulsimer® T-62MP de-aluminum resin exchange column is 30-40 min.

8. An ultra-low ash food-grade activated carbon according to claim 1, characterized in that the power of the ultrasonic wave in step S2 is 60-80 kW, and the reaction time is 30-70 min; the temperature of the temperature-controlled activation in step S3 is 300-450 °C, and the time is 30-80 min.

9. An ultra-low ash food-grade activated carbon according to claim 1, characterized in that the number of times of the first flushing in step S4 is 4-6 times, the number of times of the second flushing is 4-5 times, the degree of flushing with deionized water is to flush until the pH value is 6-7, the temperature of the temperature-controlled drying is 120-130 °C, and the time is 2-3 h.

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