CN107902655A - A kind of method for preparing nitrating activated carbon using discarded activated carbon - Google Patents

Abstract

The invention discloses a method for preparing a nitrogen-doped carbon material by using waste activated carbon. The waste carbon is used as a raw material, and the nitrogen-containing organic matter saturated and adsorbed by the waste carbon, such as amino acid, acetaminophen or protein, is used as a nitrogen source. After the two-step carbonization, the nitrogen-doped carbon material can be obtained. The invention greatly reduces the treatment cost of high-risk waste such as industrial waste carbon, realizes resource utilization, and can obtain nitrogen-modified activated carbon with high added value in one step. The preparation method is simple and easy to operate, can directly utilize the existing activated carbon production process, and the recovered carbon material can be directly used as a catalyst to catalyze the hydrochlorination of acetylene to prepare vinyl chloride monomer, which greatly improves the added value of waste activated carbon.

Description

A method for preparing nitrogen-doped activated carbon by using waste activated carbon

technical field

The invention belongs to the field of recovery and regeneration of waste activated carbon to prepare new materials, and in particular relates to a nitrogen-doped carbon material prepared from waste activated carbon produced in the refining and decolorization process of the food industry and its application.

Background technique

my country's grain transformation industry, such as fermentation industry, has developed rapidly. Among them, the output of starch sugar is about 2 million tons/year, citric acid is 400,000 tons/year, and monosodium glutamate is 1 million tons. These products are bound to be used in the production and refining process. to activated carbon. According to rough statistics, only 35,000 to 40,000 tons of charcoal is used in the refining process of monosodium glutamate per year. In addition, the annual consumption of sorbic acid, citric acid, pharmaceutical intermediates, food additives and dye intermediates, etc., requires wood activated carbon. About 30,000 to 35,000 tons. Most of these adsorbed activated carbons are directly discarded or incinerated or landfilled as waste, which not only increases the production cost but also causes great pollution to the environment, and the adsorbed organic substances have not been properly treated and recycled. It also causes a waste of resources.

As a material with high specific surface area and developed pores, activated carbon has the advantages of acid and alkali corrosion resistance and low price. In the fields of industrial production of food and medicine, the decolorization process is an essential link, and activated carbon is widely used as an adsorbent with high adsorption capacity. For example, in the field of monosodium glutamate production, activated carbon is often used for adsorption. Pigments, iron ions, and nitrogen-containing substances such as sodium glutamate, protein, and amino acids can be adsorbed on the surface; Activated carbon) is used for decolorization and adsorption removal; L-tryptophan is an essential amino acid for humans and animals, which plays an important role in the growth, development and metabolism of humans and animals. At present, the extraction process of tryptophan includes microfiltration, ion Exchange, decolorization, evaporation, and crystallization, among which the decolorization process mostly uses activated carbon adsorption for decolorization. Most of these adsorbed activated carbons are directly discarded as waste or incinerated or landfilled, which not only increases the production cost but also causes great pollution to the environment, and the adsorbed nitrogen-containing substances have not been properly treated and recycled. , but also caused a waste of resources.

The way to regenerate the waste activated carbon that has adsorbed organic matter is to leaching, decomposing or in-situ carbonization of organic matter. At present, the commonly used regeneration methods of this kind of waste carbon are high temperature method, acid-base washing method, oxidation regeneration method, microwave irradiation method, solvent regeneration method, biological regeneration method, etc. These methods can make waste carbon to a certain extent Regeneration, but there are also certain problems, such as the regeneration rate of the high temperature method is not high, the acid-base washing method has certain corrosion problems on the equipment, the solvent regeneration method will produce a large amount of waste liquid at the same time, and the microwave regeneration method is difficult to achieve industrial production. The regeneration method also has disadvantages such as remaining organic matter on the surface of activated carbon. In addition, the high-temperature method and acid-base washing method cannot fundamentally solve the problem of "dangerous solid", but only transform it into "dangerous gas" and "dangerous liquid". At present, there is still a lack of an effective treatment of industrial decolorization waste. Activated charcoal means. The components adsorbed on the activated carbon are complex, requiring a large amount of organic solvents and complex processes to purify, which greatly increases energy consumption and environmental protection costs. If the waste activated carbon can be directly converted into functionalized activated carbon, on the one hand, the skeleton structure of the activated carbon can be restored; on the other hand, the activated carbon can be modified during the regeneration process to increase its added value, such as as a catalyst carrier, This can also greatly reduce production costs and realize the reuse of resources.

As a new type of basic carbon material, nitrogen-doped carbon material has shown excellent performance in the field of adsorption and catalysis. At present, nitrogen-doped carbon material has not yet achieved industrial production. There are many preparation methods for nitrogen-doped carbon material in the literature, but Most of them are obtained by modifying the synthesized carbon materials by impregnating additional organic or inorganic nitrogen sources such as ammonia water, urea, ammonium bicarbonate, melamine, etc. These methods require additional consumption of nitrogen-containing reagents, such as the invention patent [ Application Publication No. CN106115698A] Use waste carbon as carbon source, ammonium oxalate as nitrogen source, and prepare nitrogen-doped carbon material through mechanical grinding and carbonization. Invention patent [Application Publication No. CN105819443A] chooses waste plant-based biomass as raw material, mixes impregnation with activator and nitrogen-containing phosphate, and prepares nitrogen-doped carbon material through drying and carbonization. Invention patent [Application Publication No. CN103922306A] selects biomass raw material as the carbon source, conducts carbonization under an inert atmosphere, and then conducts secondary carbonization treatment under an ammonia atmosphere to obtain a modified porous carbon material with high nitrogen doping content. Invention patent [Application Publication No. CN105948045A] uses starch as a carbon source and an external nitrogen source after hydrothermal activation and high-temperature carbonization to obtain nitrogen-doped activated carbon nanospheres. These methods all have disadvantages such as high cost, complex process, and additional consumption of a large amount of organic raw materials to a certain extent, and at the same time, there are certain corrosion problems to the reactor, making it difficult to realize industrial production.

In view of the above problems, the present invention proposes an idea of turning waste into treasure to prepare nitrogen-doped alkaline activated carbon, using organic matter (glutamic acid, glycine, acetaminophen, distiller's grains, etc.) adsorbed in waste activated carbon as a nitrogen source , nitrogen-containing organic matter is cracked by heat treatment under oxygen-deficient conditions, and nitrogen-doped activated carbon is obtained in one step. The present invention realizes the modification of activated carbon while recycling resources of waste, and introduces nitrogen element into the surface of activated carbon while restoring the pore structure of activated carbon to obtain nitrogen-doped alkaline activated carbon.

A method of using waste activated carbon to prepare nitrogen-doped activated carbon in the present invention can kill three birds with one stone. While treating waste carbon, the pore structure is restored, and active centers are introduced at the same time, so that resource utilization of waste carbon can be realized in one step; cost can be saved, Reducing the discharge of three wastes and turning waste into treasure is a new way of green and environmentally friendly solid waste resource utilization.

Contents of the invention

The invention discloses a method for preparing a nitrogen-doped carbon material by using waste activated carbon adsorbed with nitrogen-containing compounds, using activated carbon adsorbed with nitrogen-containing substances in the refining process of the food industry as a raw material, and using nitrogen-containing compounds in waste carbon as a nitrogen source , impregnated with a carbonization catalyst, and then carbonized in an inert atmosphere after drying to obtain the nitrogen-doped carbon material.

The invention also provides a method for regenerating industrial decolorized waste activated carbon to obtain functionalized nitrogen-doped carbon materials in situ, which greatly reduces the treatment cost of high-risk waste such as industrial decolorized waste carbon. The preparation method is simple and easy to operate, and can directly use the existing activated carbon production process, and the recovered carbon material not only exhibits excellent adsorption performance in the adsorption of dye wastewater, but also can be directly used as a catalyst to catalyze the hydrochlorination of acetylene, greatly improving Increased the added value of waste activated carbon.

The present invention adopts following technical scheme:

A method for preparing nitrogen-doped activated carbon by using waste activated carbon, the method comprising: drying the waste activated carbon at a drying temperature of 80-110°C and a drying time of 12-24 hours, adding a carbonization catalyst dropwise on the dried waste activated carbon, Stand still, the standing temperature is 25-50°C, the standing time is 8-24h, and then pre-carbonize in an inert gas atmosphere, the temperature is controlled between 150-350°C, the holding time is 1-10h, and then the temperature Raise the temperature to 400-850°C and keep it for 1-20 hours to obtain the nitrogen-doped activated carbon; the waste activated carbon is waste activated carbon that adsorbs nitrogen-containing organic matter, and the carbonization catalyst is concentrated sulfuric acid or oxalic acid solution.

In the above method, the mass of the carbonization catalyst is 1-5% of the mass of the waste activated carbon. The mass fraction of the oxalic acid solution is 10-30wt%. Concentrated sulfuric acid refers to an aqueous solution of pure _H2SO4 with a mass fraction greater than or _equal to 70%.

In the above method, the waste activated carbon of the nitrogen-containing organic matter, the nitrogen-containing organic matter is one or more of amino acids, acetaminophen or protein.

In the above method, the amino acid is one or more of glutamic acid, alanine, arginine, aspartic acid, histidine, lysine, tryptophan or L-glycine.

In the above method, the waste activated carbon is selected from one or more types of waste activated carbon produced in the fields of food and pharmaceutical synthesis.

In the above method, the waste activated carbon in the food industry is selected from waste decolorized activated carbon produced in monosodium glutamate production industry, waste activated carbon produced in glycine production, waste activated carbon produced in starch sugar industry, and waste activated carbon produced in soy sauce brewing industry. Or one or more of the waste activated carbon produced in the wine brewing industry.

In the above method, the inert gas is nitrogen or argon.

In the above method, through two-step carbonization, the nitrogen-containing organic matter adsorbed on the surface of the activated carbon is cracked and surface reacted. The first step of carbonization is "adding a carbonization catalyst dropwise on the dried waste activated carbon, standing, and the standing temperature is 25 ~50°C, the standing time is 8~24h, and then pre-carbonization is carried out under an inert gas atmosphere, the temperature is controlled between 150~350°C, and the holding time is 1~10h", the second step of carbonization is "increasing the temperature to 400 ~ 850 ° C, holding time 1 ~ 20h", you can get the modified activated carbon, that is, nitrogen-doped activated carbon.

The process described above is preferably carried out in a tube furnace.

Further, the nitrogen-doped activated carbon prepared by the present invention can be directly used as a catalyst for acetylene hydrochlorination, and can also be used as a carrier for a mercury-free catalyst. The prepared nitrogen-doped activated carbon is introduced into the active component by impregnation or other conventional catalyst preparation methods, and dried to obtain the modified activated carbon supported catalyst. The activated carbon components described here may be RuCl ₃ , HAuCl ₄ , HgCl ₂ and the like.

The present invention also provides the application of the nitrogen-doped activated carbon as a catalyst in the hydrochlorination of acetylene. The hydrochlorination of acetylene adopts conventional operations, for example, by following operations:

Acetylene hydrochlorination is carried out in a glass fixed-bed reactor with an inner diameter of 20mm, the catalyst loading is 1-4mL, the pressure of acetylene and hydrogen chloride is both 0.1MPa, V(C ₂ H ₂ ):V(HCl)=1:1.05 ~1.2, control the acetylene flow space velocity at 30h ^-1 , and the reaction temperature at 180°C. The acetylene gas is first purified by concentrated sulfuric acid to remove impurities such as H ₂ S and H ₃ P, and the HCl gas is used to remove moisture in a silica gel dryer. Before the reaction, the moisture and air in the system were purged with N ₂ , and then HCl gas was passed through for activation for 0.5h, and then acetylene gas was passed through for reaction. The gas flow is controlled with a mass flow meter. The reaction product was analyzed by gas chromatography after absorbing HCl gas with NaOH solution, and the content of each component was determined by the area normalization method.

Compared with the prior art, the present invention has the following advantages:

1. The present invention uses industrial decolorization waste activated carbon as a raw material, and uses adsorbed nitrogen-rich substances as a nitrogen source, and realizes one-step in-situ synthesis of nitrogen-doped carbon materials without adding additional nitrogen sources;

2. The raw material of the present invention is waste activated carbon from the food industry. Compared with the production of activated carbon using wood, coconut shells and coal as raw materials, it has the characteristics of low cost and simple process. The prepared activated carbon contains nitrogen element, and does not require pre-treatment when used for catalyst preparation.

3. The catalyst prepared by the present invention can be used as a catalyst for the hydrochlorination of acetylene, showing high catalytic activity and stability, and can also be used as a carrier for a mercury-free catalyst, and other components can be prepared by impregnation After that, a mercury-free catalyst can be obtained.

4. The method for producing modified alkaline activated carbon proposed by the present invention can not only turn waste into treasure, but also has a simple production process, no liquid waste and solid waste discharge, is a green and environmentally friendly technology, and meets the national regulations on waste resource The policy orientation of utilization has good industrialization prospects.

5. The alkaline activated carbon produced by the present invention also has a wide range of applications in water fields such as capacitors, electrode materials and adsorption materials. It is not limited to the field of catalysis described in the present invention.

Description of drawings

Fig. 1 is the nitrogen adsorption-desorption curve (left) and the pore size distribution diagram (right) of the regenerated activated carbon prepared in Example 1 and the fresh activated carbon as a comparison sample

Fig. 2 is the acetylene conversion rate graph of the regenerated nitrogen-doped activated carbon material sample of Example 1 and the fresh activated carbon catalyzed acetylene hydrochlorination as a comparative sample.

Detailed ways

The present invention will be further described below in conjunction with specific examples, but the protection scope of the present invention is not limited thereto. Concentrated sulfuric acid was purchased from Quzhou Juhua Group, with a mass fraction greater than or equal to 70%.

Example 1

Weigh 20g of waste activated carbon used in the decolorization section in the production process of monosodium glutamate, dry it at 110°C for 24h, add 2g of concentrated sulfuric acid to the surface of the activated carbon dropwise by dipping, let it stand at 25°C for 10h, and transfer the sample to a porcelain boat. Carbonization is then carried out in a tube furnace. The carbonization conditions are: the nitrogen flow rate is 30mL/min, the temperature is raised from 30°C at 3.4°C/min to 250°C for 2 hours, 850°C for 3 hours, and naturally cooled to room temperature to obtain the nitrogen-doped regenerated carbon material. .

Example 2

Weigh 20g of waste activated carbon used in the decolorization section in the production process of monosodium glutamate, dry it at 110°C for 24h, add 2g of concentrated sulfuric acid to the surface of the activated carbon dropwise by dipping, let it stand at 25°C for 10h, and transfer the sample to a porcelain boat. Carbonization is then carried out in a tube furnace. The carbonization conditions are as follows: the nitrogen flow rate is 30mL/min, the temperature is raised from 30°C at 3.4°C/min to 250°C for 2 hours, 850°C for 10 hours, and naturally cooled to room temperature to obtain the nitrogen-doped carbon material.

Example 3

Take by weighing 20g of waste activated carbon used in the decolorization section in the monosodium glutamate production process, dry 24h at 110°C, drop 2g of oxalic acid solution (15wt%) on the surface of the activated carbon by dipping, leave it at 30°C for 10h, and transfer the sample to in a porcelain boat, followed by carbonization in a tube furnace. The carbonization conditions are as follows: the nitrogen flow rate is 30mL/min, the temperature is raised from 30°C at 3.4°C/min to 250°C for 2 hours, 400°C for 3 hours, and naturally cooled to room temperature to obtain the nitrogen-doped carbon material.

Example 4

Weigh 20g of waste activated carbon produced in the production of glycine, dry it at 110°C for 24h, add 2g of concentrated sulfuric acid dropwise to the surface of the activated carbon by dipping, let it stand at 30°C for 15h, transfer the sample to a porcelain boat, and then place it in a tube carbonization in a furnace. The carbonization conditions are as follows: the nitrogen flow rate is 30mL/min, the temperature is raised from 30°C at 3.4°C/min to 250°C for 2 hours, 850°C for 3 hours, and naturally cooled to room temperature to obtain the nitrogen-doped carbon material.

Example 5

Weigh 100g of waste activated carbon produced in the brewing process of soy sauce, dry it at 110°C for 24h, add 2g of concentrated sulfuric acid dropwise to the surface of the activated carbon by dipping, let it stand at 50°C for 15h, transfer the sample to a porcelain boat, and then Carbonization was performed in a tube furnace. The carbonization conditions are as follows: the nitrogen flow rate is 30mL/min, the temperature is raised from 30°C at 3.4°C/min to 250°C for 2 hours, 850°C for 3 hours, and naturally cooled to room temperature to obtain the nitrogen-doped carbon material.

Table 1 Physical parameters and nitrogen content of various carbon materials

Table 1 lists the nitrogen element content in the waste activated carbon used as raw material in the above-mentioned examples and the product prepared in Examples 1-5. It can be seen from the specific surface area, pore volume and nitrogen content values of fresh activated carbon, waste activated carbon and regenerated activated carbon given in Table 1 that the specific surface area and pore volume of waste activated carbon are greatly reduced compared with fresh activated carbon, and most of the pores of activated carbon Blocked by adsorbed substances, after treatment and regeneration by the method of the present invention, the specific surface area returns to more than 1000m ² /g, and the pore volume returns to 0.97cm ³ /g, which shows that the method provided by the present invention can not only realize the regeneration of activated carbon, At the same time, the nitrogen modification of activated carbon has been realized, and nitrogen element has been successfully introduced into activated carbon.

Figure 1 shows the nitrogen adsorption-desorption curve (left) and pore size distribution curve (right) of the nitrogen-doped carbon material prepared in Example 1, and provides the fresh activated carbon nitrogen adsorption-desorption curve and pore size distribution curve without decolorization process As a comparison. It can be seen from the figure that the nitrogen-doped carbon material prepared in this example has a large specific surface area, contains both micropores and mesopores, and can basically recover to the pore structure of fresh activated carbon after high-temperature carbonization.

Example 6

The fresh activated carbon in Example 1 and the nitrogen-doped carbon material obtained after regeneration of waste activated carbon were crushed, sieved with 40-80 mesh, dried at 110°C for 2 hours, sampled 4mL, and loaded into a stainless steel fixed-bed reactor with an inner diameter of 10mm The acetylene hydrochlorination reaction is carried out in the middle, the pressure of acetylene and hydrogen chloride is 0.1MPa, n(C ₂ H ₂ ):n(HCl)=1:1.2, the flow space velocity of acetylene is controlled at 30h ^-1 , the reaction temperature is 220°C, the acetylene The gas is first purified by concentrated sulfuric acid to remove impurities such as H ₂ S and H ₃ P, and the hydrogen chloride gas is dehydrated in a silica gel dryer. Before the reaction, purge with nitrogen gas to remove moisture and air in the system, then pass through hydrogen chloride gas for activation for 0.5h, and then pass through acetylene gas for reaction. The gas flow is controlled with a mass flow meter. The reaction product was analyzed by gas chromatography after absorbing hydrogen chloride gas with sodium hydroxide solution, and the content of each component was determined by the area normalization method. Fig. 2 is the conversion ratio figure of acetylene catalyzed by acetylene hydrochlorination with fresh activated carbon and nitrogen-doped carbon material in Example 1. As can be seen from Figure 2, the acetylene conversion rate of fresh activated carbon is only about 15%, while the acetylene conversion rate of the nitrogen-doped carbon material regenerated in Example 1 reaches more than 60%, indicating that the regenerated nitrogen-doped carbon material is compared with fresh activated carbon material. The conversion rate of acetylene is greatly improved. The above results prove that the regeneration of activated carbon and the simultaneous introduction of nitrogen-doped active centers can be realized by using this technology, which has good innovation.

Claims (8)

1. A kind of 1. method for preparing nitrating activated carbon using discarded activated carbon, it is characterised in that the method is：By discarded activity Charcoal is dried, and drying temperature is 80~110 DEG C, and drying time is 12~24h, and charcoal is added dropwise on discarded activated carbon after the drying Change catalyst, stand, dwell temperature is 25~50 DEG C, and time of repose is 8~24h, is then carried out under atmosphere of inert gases pre- Charing, for temperature control between 150~350 DEG C, the retention time is 1~10h, then temperature is warming up to 400~850 DEG C, is kept Time is 1~20h, up to the nitrating activated carbon；The discarded activated carbon is the discarded activated carbon of absorption itrogenous organic substance, The charing catalyst is the concentrated sulfuric acid or oxalic acid solution.
2. 2. the method as described in claim 1, it is characterised in that：The quality of the charing catalyst is the discarded active carbonaceous The 1~5% of amount.
3. 3. the method as described in claim 1, it is characterised in that：The oxalic acid solution mass fraction is 10-30wt%.
4. 4. the method as described in claim 1, it is characterised in that：The discarded activated carbon of the absorption itrogenous organic substance, it is described Itrogenous organic substance is the one or more in amino acid, paracetamol or protein.
5. 5. method as claimed in claim 4, it is characterised in that：The amino acid is glutamic acid, alanine, arginine, winter One or more in propylhomoserin, histidine, lysine, tryptophan or L glycine.
6. 6. the method as described in claim 1, it is characterised in that：The discarded activated carbon is selected from food, medical synthesis field row The one or more in activated carbon are discarded caused by industry.
7. 7. method as claimed in claim 6, it is characterised in that：Activated carbon is discarded caused by the food service industry and is selected from taste Waste active carbon, starch sugaring industry institute caused by the decoloration active carbon discarded caused by smart production industry, glycine production In waste active carbon caused by the waste active carbon of generation, soy sauce brewing industry or drinks brewing industry in caused waste active carbon One or more.
8. 8. the method as described in claim 1, it is characterised in that：The inert gas is nitrogen or argon gas.