Method for preparing high-strength flaky coal-based activated carbon from coal gasification ash

Abstract

The invention relates to the technical field of solid waste treatment, in particular to a method for preparing high-strength flaky coal-based activated carbon from coal gasification ash, which comprises the steps of modified attapulgite preparation, raw material pretreatment, carbonization treatment, molding treatment and activation treatment. According to the whole process scheme, industrial waste coal gasification ash is used as a main raw material, resource utilization of waste is achieved, the preparation cost of the activated carbon is reduced, and both environmental benefits and economic benefits are taken into account. The parameter design of each process step is matched with each other, for example, the dispersion condition of the composite binder is matched with the forming pressure and the drying temperature, and the activation temperature is matched with the carbonization temperature, so that the continuity and the stability of the whole preparation process are ensured, the production yield is improved, the production period is shortened, and the industrial application prospect is good.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid waste treatment, in particular to a method for preparing high-strength sheet-shaped coal-based activated carbon from coal gasification slag. BACKGROUND

[0002] With the rapid development of coal chemical industry, coal gasification process is increasingly widely used in the field of energy conversion, but the amount of coal gasification slag generated is also increasing. These slags contain a large amount of valuable components such as silicon, aluminum and carbon. If they are directly stored or landfilled, not only a large amount of land resources will be occupied, but also environmental problems such as soil pollution and groundwater pollution may be caused by leakage of harmful substances, and resources will be wasted. Therefore, realizing the resource utilization of coal gasification slag has become an important direction for the sustainable development of coal chemical industry.

[0003] At present, there have been some researches on the recycling of coal gasification slag at home and abroad, mainly focusing on the preparation of building materials, soil conditioners, adsorbent materials and other directions. Among them, preparing coal gasification slag into coal-based activated carbon is one of the effective ways to realize its high-value utilization. Coal-based activated carbon has a wide range of application requirements in many fields such as wastewater treatment, waste gas purification and food processing due to its developed pore structure, large specific surface area and good adsorption performance.

[0004] However, the existing technology for preparing coal-based activated carbon from coal gasification slag still has many shortcomings. On the one hand, coal gasification slag has complex composition and contains many metal oxides and sulfides. These impurities will affect the pore development and adsorption performance of activated carbon. The traditional acid washing pretreatment method is difficult to remove the impurities completely, resulting in poor adsorption capacity of the product. On the other hand, the forming property of the slag itself is poor, and the mechanical strength of the prepared activated carbon product is low and easy to break, which cannot meet the structural stability requirements of sheet-shaped activated carbon in industrial applications.

[0005] In order to solve the above technical problems, it is urgent to develop a preparation method which can fully remove the impurities in coal gasification slag, optimize the forming process and activation effect of activated carbon, and improve the mechanical strength and adsorption performance of the product, so as to realize the efficient and high-value resource utilization of coal gasification slag. SUMMARY

[0006] The purpose of the present application is to overcome the shortcomings of the prior art and provide a method for preparing high-strength sheet-shaped coal-based activated carbon from coal gasification slag.

[0007] The specific technical scheme is as follows: a method for preparing high-strength sheet-shaped coal-based activated carbon from coal gasification slag, comprising the steps of modified attapulgite preparation, raw material pretreatment, carbonization treatment, forming treatment and activation treatment, specifically as follows: (1) The preparation of modified attapulgite includes: ① raw material pretreatment; ② acid activation; ③ composite modification; (2) raw material pretreatment: coal gasification slag is crushed to 100-200 mesh, and is classified by 80 kHz ultrasonic vibration screen; 5% (v / v) HCl solution is added, the solid-liquid ratio is 1:5 (g / ml), and the acid washing is carried out at 65-70°C constant temperature water bath for 3 hours under 200-300 r / min magnetic stirring; 0.5 wt% citric acid is added every 30 min during the acid washing process, and then the acid washing is followed by vacuum filtration, washing with deionized water until the pH is 6.5-7.0, and drying at 105°C for 2 hours to obtain the pretreated slag; (3) carbonization treatment: the pretreated slag is placed in a tube furnace, vacuumed to -0.09 MPa for 30 min, nitrogen is introduced, the temperature is increased to 500°C at a rate of 10°C / min, and then the temperature is kept constant for 1 h, and then the temperature is increased to 900°C for carbonization for 2 h, and the total carbonization time is 3 h; after the carbonization is completed, nitrogen is continuously introduced until the temperature in the furnace is reduced to below 100°C, and then the carbon powder is taken out; (4) forming treatment: 5 wt% composite binder is added to the carbon powder according to the mass ratio of 2:1; the mixture is transferred into a powder tablet press with a mold diameter of 25 mm, and gradient pressing is adopted: pre-pressing at 5 MPa for 1 min, and then increasing to 10-12 MPa for 3-5 min to obtain a sheet-shaped blank with a thickness of 7-9 mm; the blank is placed in an oven, and stepwise drying is adopted: drying at 40°C for 4 h, and then increasing the temperature to 60°C for 6 h, and the total drying time is 10 h to obtain a formed matrix; (5) activation treatment: the formed matrix is placed in a muffle furnace, the temperature is increased to 300°C for 30 min to remove residual air; CO2 gas is introduced, and the activation is carried out at 800°C for 1 h; during the activation process, CO2 is introduced in a pulse mode, the pulse frequency is 30 s / time, and the single pulse amount is 50-80 Nm 3 ; after the activation is completed, the system is naturally cooled to room temperature to obtain high-strength sheet-shaped coal-based activated carbon.

[0008] As a further technical solution, the preparation of the modified attapulgite clay specifically includes: ① raw material pretreatment: natural attapulgite clay is crushed to 200-300 mesh, dried at 105°C for 2 h to remove free water, and refined attapulgite clay is obtained by screening with a 200 mesh standard sieve; ② acid activation: the refined attapulgite clay is added to a 15% by mass hydrochloric acid solution, the solid-liquid ratio is 1:8 (g / ml), and the activation is carried out at 80°C constant temperature water bath for 2 h, during which the stirring is carried out every 30 min for 10 min; then the attapulgite clay is dispersed by 80 kHz ultrasonic wave for 30 min, washed with deionized water until the pH of the filtrate is 6.8-7.0, and vacuum dried at 60°C for 4 h to obtain the activated attapulgite clay; ③ Complex modification: activated attapulgite, gamma-aminopropyl triethoxysilane and chitosan-cerium nitrate composite gel are weighed according to the mass ratio of 1:0.4:1.0, added into anhydrous ethanol to form a suspension; 70 DEG C oil bath reflux stirring reaction 4h, the stirring rate is 500r / min during the reaction; after the reaction, centrifugal 10 min at 8000r / min, the precipitate is washed with anhydrous ethanol for 3 times, and vacuum drying at 60 DEG C for 6h to obtain modified attapulgite.

[0009] As a further technical solution, the vacuum degree of vacuum drying in step 2 is-0.09MPa.

[0010] As a further technical solution, the liquid-solid ratio of anhydrous ethanol to activated attapulgite in step 3 is 10:1 (ml / g).

[0011] As a further technical solution, the chitosan-cerium nitrate composite gel in step 3 is prepared by dissolving chitosan and cerium nitrate in deionized water according to the mass ratio of 1:0.6, and crosslinking for 15 min under 60kHz ultrasonic, and the gel solid content is 15%.

[0012] As a further technical solution, the vacuum degree of vacuum filtration in step (2) is-0.08MPa, and the filtration time is 15min.

[0013] As a further technical solution, the composite binder in step (4) is composed of carboxymethyl cellulose sodium and modified attapulgite according to the mass ratio of 9:1; the composite binder is dispersed by a high-speed shearing machine at 8000r / min for 30min before use.

[0014] As a further technical solution, the heating rate of the muffle furnace in step (5) is 15 DEG C / min, and after heating to 300 DEG C, the heating rate is changed to 5 DEG C / min to the activation temperature.

[0015] As a further technical solution, the citric acid in step (2) is added by dripping, and the dripping rate is 0.5ml / min.

[0016] The high-strength sheet-shaped coal-based activated carbon is prepared by the method.

[0017] Compared with the prior art, the present application has the following beneficial effects: In the preparation process of the modified attapulgite of the application, the raw material pretreatment removes impurities and free water in the natural attapulgite through crushing, drying and screening, providing a pure raw material basis for subsequent activation; the acid activation process expands the interlayer spacing of the attapulgite, increases its specific surface area and surface active sites through the erosion of hydrochloric acid under specific temperature and solid-liquid ratio conditions; the composite modification further modifies the surface structure of the attapulgite through the coupling effect of gamma-aminopropyl triethoxysilane and the cross-linking effect of chitosan-cerium nitrate composite gel, so that the attapulgite not only has stronger bonding properties, but also can form synergistic adsorption sites with the active carbon matrix. The modified attapulgite and sodium carboxymethyl cellulose are compounded as a composite binder, which can uniformly wrap the surface of the carbon powder particles after high-speed shearing and dispersion, and form a stable bonding network during the molding process, significantly enhancing the inter-particle bonding force and improving the structural compactness of the molded body from the micro perspective.

[0018] In the raw material pretreatment link, the coal gasification ash is crushed to a specific fineness and classified and screened by an ultrasonic vibration screen, ensuring uniform particle size distribution of the raw material and avoiding the influence of large particle impurities on the subsequent process; the combination of hydrochloric acid pickling and citric acid dropwise addition removes most of the metal oxide impurities through the strong acidity of hydrochloric acid, while the chelating effect of citric acid can complex the residual metal ions, and then magnetic stirring and vacuum filtration are used to realize deep removal of impurities, so that the purity of the pretreated ash is greatly improved, creating favorable conditions for the formation of carbon skeleton and pore development in the carbonization process.

[0019] The carbonization treatment adopts a process combining stepwise heating and nitrogen protection, first removing the volatile matter and moisture in the raw material at 500 DEG C, and then heating to 900 DEG C for deep carbonization, gradually building a stable carbon skeleton structure; the nitrogen atmosphere effectively prevents the carbon skeleton from being oxidized at high temperature, ensuring the carbon content and structural stability of the carbon powder. In the molding process, the gradient pressure mode first removes the air in the mixture through low-pressure pre-pressing, and then makes the particles tightly bonded through high-pressure pressing, and the segmented drying process avoids cracks in the green body due to rapid evaporation of water during drying, ensuring the structural integrity and dimensional stability of the molded matrix.

[0020] In the activation process, the temperature is raised step by step to the activation temperature and kept for a period of time to remove residual air, avoiding the interference of oxygen in the air on the activation process; the pulse type CO2 inlet mode allows the activation gas to repeatedly penetrate into the interior of the molded matrix, fully contact with the carbon skeleton and react, uniformly etching to form a large number of micropores and mesopores, effectively avoiding the problems of excessive or insufficient local activation compared with the traditional continuous activation, making the pore structure more regular and the specific surface area larger.

[0021] The modified attapulgite is compounded and modified, and the compounded binder is used in combination with the gradient pressure forming process, so that the problems of difficult forming of coal gasification ash and low mechanical strength are solved from the aspects of bonding performance and forming pressure, so that the prepared sheet-shaped activated carbon has excellent compressive strength and bending strength, and meets the structural stability requirements in industrial applications; the deep impurity removal process of raw material pretreatment is coordinated with the step-by-step heating carbonization process, so that the impurities affecting the formation of carbon skeleton are removed, the purity and structural integrity of the carbon powder are ensured, and the uniform development of pores in the subsequent activation process is laid as a foundation; and the pulse CO2 activation process is matched with the carbonization and forming processes in the early stage, so that the developed and regular pore structure is constructed on the basis of the stable carbon skeleton, and the adsorption performance of the product is greatly improved.

[0022] The whole process scheme of the present application takes industrial waste coal gasification ash as the main raw material, realizes the resource utilization of waste, reduces the preparation cost of activated carbon, and takes into account the environmental benefits and economic benefits. The parameter design of each process step is matched, such as the dispersion condition of the composite binder, the forming pressure and the drying temperature, the activation temperature and the carbonization temperature, which ensures the continuity and stability of the whole preparation process, improves the production yield, shortens the production cycle, and has good industrial application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is the SEM diagram of the coal-based activated carbon prepared by the coal gasification ash of the present application embodiment 2. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0025] The present application provides a method for preparing high-strength sheet-shaped coal-based activated carbon from coal gasification ash, which comprises the steps of modified attapulgite preparation, raw material pretreatment, carbonization treatment, forming treatment and activation treatment.

[0026] The present application firstly carries out the preparation of modified attapulgite, which comprises three links of raw material pretreatment, acid activation and composite modification. In the present application, the natural attapulgite can be obtained by using the commercially available goods known to those skilled in the art without special limitation. In the raw material pretreatment, the natural attapulgite is crushed to 200-300 mesh, dried at 105℃ for 2 hours to remove free water, and refined attapulgite is obtained by screening with a 200 mesh standard sieve. In the acid activation stage, the refined attapulgite is added into a hydrochloric acid solution with a mass fraction of 15%, the solid-liquid ratio is controlled to be 1:8 (ml / g), and the attapulgite is activated in a constant temperature water bath at 80℃ for 2 hours, during which it is stirred for 10 minutes every 30 minutes, then dispersed by ultrasonic wave with a frequency of 80 kHz for 30 minutes, washed with deionized water until the pH of the filtrate reaches 6.8-7.0, and vacuum dried at a temperature of 60℃ under a vacuum degree of -0.09 MPa for 4 hours to obtain activated attapulgite. In the composite modification, the activated attapulgite, γ-aminopropyltriethoxysilane and chitosan-cerium nitrate composite gel are weighed according to a mass ratio of 1:0.4:1.0, added into anhydrous ethanol to form a suspension, wherein the liquid-solid ratio of anhydrous ethanol to activated attapulgite is 10:1 (ml / g); the stirring rate is kept at 500 r / min during the reaction process in an oil bath at 70℃ for 4 hours; after the reaction, the precipitate is collected by centrifugation at 8000 r / min for 10 minutes, washed with anhydrous ethanol for 3 times, and vacuum dried at 60℃ for 6 hours to obtain modified attapulgite. The chitosan-cerium nitrate composite gel is prepared by dissolving chitosan and cerium nitrate in deionized water according to a mass ratio of 1:0.6, and cross-linking by ultrasonic wave with a frequency of 60 kHz for 15 minutes, and the solid content of the gel is 15%.

[0027] After the preparation of modified attapulgite is completed, the raw material pretreatment is carried out. In the present application, the coal gasification slag can be obtained by using the industrial waste recovery method known to those skilled in the art or purchased through the market. The coal gasification slag is crushed to 100-200 mesh and screened by an 80 kHz ultrasonic vibration screen; 5% (v / v) HCl solution is added, the solid-liquid ratio is controlled to be 1:5 (g / ml), and the acid washing is carried out in a constant temperature water bath at 65-70℃ for 3 hours, during which the magnetic stirring is carried out at a rate of 200-300 r / min; at the same time, 0.5 wt% citric acid is added at a drop rate of 0.5 ml / min every 30 minutes, after the acid washing, the vacuum filtration is carried out under a vacuum degree of -0.08 MPa for 15 minutes, the pretreated slag is washed with deionized water until the pH reaches 6.5-7.0, and dried at 105℃ for 2 hours to obtain the pretreated slag.

[0028] After the raw material pretreatment is completed, the carbonization treatment step is entered. The pretreated ash is placed in a tube muffle furnace, vacuumized to-0.09 MPa and kept for 30 minutes, nitrogen is introduced, the temperature is increased to 500 DEG C at a rate of 10 DEG C / min, kept for 1 hour, then continuously increased to 900 DEG C for carbonization for 2 hours, the total carbonization time is 3 hours; after the carbonization is completed, nitrogen is continuously introduced until the temperature in the furnace is reduced to below 100 DEG C, and the carbon powder is taken out.

[0029] After the carbonization treatment, the forming treatment is carried out. 5wt% of a composite binder is added to the carbon powder according to the mass ratio of 2:1, the composite binder is composed of sodium carboxymethyl cellulose and modified attapulgite according to the mass ratio of 9:1, and the composite binder is dispersed by a high-speed shearing machine at 8000r / min for 30 minutes before use; the mixture is transferred into a powder tablet press with a mold diameter of 25mm, and a gradient pressure is adopted: first pre-pressing at 5MPa for 1min, then increasing to 10MPa-12MPa for 3min-5min, and a tablet-shaped blank with a thickness of 7mm-9mm is prepared; the blank is placed in an oven, and a staged drying process is adopted: drying at 40 DEG C for 4 hours, then increasing the temperature to 60 DEG C for drying for 6 hours, and the total drying time is 10 hours to obtain a formed matrix.

[0030] Finally, the activation treatment is carried out. The formed matrix is placed in a muffle furnace, the temperature is increased to 300 DEG C at a rate of 15 DEG C / min and kept for 30 minutes to remove residual air, then the rate is changed to 5 DEG C / min to increase to the activation temperature; CO2 gas is introduced, and the activation is carried out at 800 DEG C for 1 hour; during the activation process, the CO2 is introduced in a pulse mode, the pulse frequency is 30s / time, and the single introduction amount is 50Nm 3 -80Nm 3 ; after the activation is completed, the temperature is naturally cooled to room temperature, and a high-strength sheet-shaped coal-based activated carbon is prepared.

[0031] The treatment method and process parameters provided by the application realize the resource utilization of coal gasification ash, reduce the preparation cost of activated carbon, and through the synergistic effect of the composite modification technology of modified attapulgite, the pickling and ultrasonic synergistic process of raw material pretreatment, the gradient pressure forming, and the pulse type CO2 activation, the prepared sheet-shaped coal-based activated carbon has excellent mechanical strength and adsorption performance; at the same time, the process design of staged drying and step-by-step carbonization ensures the dimensional stability of the product, solves the problems of traditional coal-based activated carbon such as difficult forming, low strength and poor adsorption performance, and improves the production yield and product quality.

[0032] In order to further illustrate the application, the following examples and comparative examples are described in detail.

[0033] Example 1: Preparation of modified attapulgite: Raw material pretreatment: The natural attapulgite was crushed to 200 mesh, dried at 105℃ for 2 hours to remove free water, and refined by 200 mesh standard sieve.

[0034] Acid activation: The refined attapulgite was added into a 15% hydrochloric acid solution with a solid-liquid ratio of 1:8 (ml / g), and activated in a constant temperature water bath at 80℃ for 2 hours. During the process, stirring was performed every 30 minutes for 10 minutes. Then, the attapulgite was dispersed by ultrasonic wave at 80 kHz for 30 minutes, washed with deionized water until the pH of the filtrate was 6.8, and vacuum dried at 60℃ under a vacuum degree of -0.09 MPa for 4 hours to obtain activated attapulgite.

[0035] Composite modification: The activated attapulgite, γ-aminopropyl triethoxysilane, and chitosan-cerium nitrate composite gel were weighed according to a mass ratio of 1:0.4:1.0, and added into anhydrous ethanol to form a suspension. The liquid-solid ratio of anhydrous ethanol to activated attapulgite was 10:1 (ml / g). Reflux stirring was performed at 70℃ for 4 hours at a stirring rate of 500 r / min. After the reaction, centrifugation was performed at 8000 r / min for 10 minutes. The precipitate was washed with anhydrous ethanol for 3 times, and vacuum dried at 60℃ for 6 hours to obtain modified attapulgite. The chitosan-cerium nitrate composite gel was prepared by dissolving chitosan and cerium nitrate in deionized water according to a mass ratio of 1:0.6, and cross-linking by ultrasonic wave at 60 kHz for 15 minutes. The solid content of the gel was 15%.

[0036] Raw material pretreatment: The coal gasification slag was crushed to 100 mesh, and classified by 80 kHz ultrasonic vibration screening. Then, 5% (v / v) HCl solution was added, and the solid-liquid ratio was 1:5 (g / ml). Acid washing was performed at 65℃ in a constant temperature water bath for 3 hours with magnetic stirring at 200 r / min. During the acid washing process, 0.5wt% citric acid was added at a drop rate of 0.5 ml / min every 30 minutes. After acid washing, vacuum filtration was performed at a vacuum degree of -0.08 MPa for 15 minutes. The slag was washed with deionized water until the pH was 6.5, and dried at 105℃ for 2 hours to obtain pretreated slag.

[0037] Carbonization treatment: The pretreated slag was placed in a tube furnace, vacuumed to -0.09 MPa for 30 minutes, and then nitrogen was introduced. The temperature was increased to 500℃ at a rate of 10℃ / min, and kept constant for 1 hour. Then, the temperature was increased to 900℃ for carbonization for 2 hours, and the total carbonization time was 3 hours. After carbonization, nitrogen was continuously introduced until the temperature in the furnace decreased to below 100℃, and the carbon powder was taken out.

[0038] Molding process: 5wt% of composite binder was added to the carbon powder in a mass ratio of 2:1, the composite binder was composed of sodium carboxymethyl cellulose and modified attapulgite in a mass ratio of 9:1, and was dispersed by a high-speed shearing machine at 8000 r / min for 30 minutes before use; the mixture was transferred into a powder tablet press with a mold diameter of 25 mm, and gradient pressing was adopted: pre-pressing at 5 MPa for 1 minute, then increasing to 10 MPa for 3 minutes to obtain a sheet-shaped blank with a thickness of 7 mm; the blank was placed in an oven and subjected to staged drying: drying at 40℃ for 4 hours, then increasing the temperature to 60℃ for 6 hours, and the total drying time was 10 hours to obtain a molded matrix.

[0039] Activation process: the molded matrix was placed in a muffle furnace, the temperature was increased to 300℃ at a rate of 15℃ / min and kept for 30 minutes to remove residual air, then the temperature was increased to the activation temperature at a rate of 5℃ / min; CO2 gas was introduced, and the activation was carried out at 800℃ for 1 hour; during the activation process, the CO2 was introduced in a pulse mode, the pulse frequency was 30s / time, and the single pulse amount was 50 Nm 3 ; after the activation was completed, the temperature was naturally cooled to room temperature to obtain a high-strength sheet-shaped coal-based activated carbon.

[0040] Example 2: Preparation of modified attapulgite: Raw material pretreatment: the natural attapulgite was crushed to 250 mesh, dried at 105℃ for 2 hours to remove free water, and refined attapulgite was obtained by screening with a 200 mesh standard sieve.

[0041] Acid activation: the refined attapulgite was added to a hydrochloric acid solution with a mass fraction of 15%, the solid-liquid ratio was 1:8 (ml / g), and the activation was carried out in a constant temperature water bath at 80℃ for 2 hours, during which the stirring was carried out every 30 minutes for 10 minutes, then the ultrasonic dispersion was carried out at 80 kHz for 30 minutes, the attapulgite was washed with deionized water until the pH of the filtrate was 6.9, and the vacuum drying was carried out at a vacuum degree of-0.09 MPa and a temperature of 60℃ for 4 hours to obtain activated attapulgite.

[0042] Composite modification: the activated attapulgite, γ-aminopropyl triethoxysilane, and chitosan-cerium nitrate composite gel were weighed in a mass ratio of 1:0.4:1.0 and added to anhydrous ethanol to form a suspension, the liquid-solid ratio of anhydrous ethanol to activated attapulgite was 10:1 (ml / g); the stirring was carried out at 70℃ oil bath reflux for 4 hours, the stirring rate was 500 r / min; after the reaction was completed, the centrifugation was carried out at 8000 r / min for 10 minutes, the precipitate was washed with anhydrous ethanol for 3 times, and the vacuum drying was carried out at 60℃ for 6 hours to obtain modified attapulgite. The chitosan-cerium nitrate composite gel was prepared by dissolving chitosan and cerium nitrate in deionized water in a mass ratio of 1:0.6, and ultrasonic crosslinking was carried out at 60 kHz for 15 minutes, and the solid content of the gel was 15%.

[0043] Raw material pretreatment: The coal gasification ash was crushed to 150 mesh and classified by 80 kHz ultrasonic vibration screen. 5% (v / v) HC1 solution was added at a solid-liquid ratio of 1:5 (g / ml) and stirred at 250 r / min in a constant temperature water bath at 68°C for 3 hours. During the acid washing process, 0.5wt% citric acid was added at a drop rate of 0.5 ml / min every 30 minutes. After acid washing, the ash was vacuum filtered at a vacuum degree of -0.08 MPa for 15 minutes, washed with deionized water until the pH was 6.8, and dried at 105°C for 2 hours to obtain the pretreated ash.

[0044] Carbonization treatment: The pretreated ash was placed in a tube furnace, vacuumed to -0.09 MPa for 30 minutes, and then nitrogen was introduced. The temperature was raised to 500°C at a rate of 10°C / min, and then maintained for 1 hour. The temperature was then raised to 900°C for carbonization for 2 hours, with a total carbonization time of 3 hours. After carbonization, nitrogen was continuously introduced until the temperature in the furnace dropped below 100°C, and the carbon powder was removed.

[0045] Molding treatment: 5wt% composite binder was added to the carbon powder at a mass ratio of 2:1, and the composite binder was composed of sodium carboxymethyl cellulose and modified attapulgite at a mass ratio of 9:1. The composite binder was dispersed by a high-speed shearing machine at 8000 r / min for 30 minutes before use. The mixture was transferred to a powder tablet press with a mold diameter of 25 mm. Gradient pressure was used: pre-pressing at 5 MPa for 1 minute, and then pressing at 11 MPa for 4 minutes to obtain a tablet-shaped body with a thickness of 8 mm. The body was placed in an oven and dried in stages: 40°C for 4 hours, and then 60°C for 6 hours, with a total drying time of 10 hours to obtain the molded matrix.

[0046] Activation treatment: The molded matrix was placed in a muffle furnace and heated to 300°C at a rate of 15°C / min to remove residual air, and then heated to the activation temperature at a rate of 5°C / min. CO2 gas was introduced, and the matrix was activated at 800°C for 1 hour. During the activation process, CO2 was introduced in a pulse mode with a pulse frequency of 30 s / second and a single pulse volume of 65 Nm 3 After activation, the matrix was naturally cooled to room temperature to obtain high-strength sheet-shaped coal-based activated carbon.

[0047] Example 3: Preparation of modified attapulgite: Raw material pretreatment: The natural attapulgite was crushed to 300 mesh and dried at 105°C for 2 hours to remove free water. The refined attapulgite was obtained by screening with a 200 mesh standard sieve.

[0048] Acid activation: refined palygorskite was added into 15% hydrochloric acid solution with a solid-liquid ratio of 1:8 (ml / g), and activated in a constant temperature water bath at 80℃ for 2 hours. During the process, the mixture was stirred for 10 minutes every 30 minutes. Then, the mixture was dispersed by 80 kHz ultrasonic wave for 30 minutes. The product was washed with deionized water until the pH of the filtrate was 7.0, and then dried in a vacuum dryer at 60℃ for 4 hours under a vacuum degree of -0.09 MPa to obtain activated palygorskite.

[0049] Composite modification: activated palygorskite, γ-aminopropyl triethoxysilane and chitosan-cerium nitrate composite gel were weighed according to a mass ratio of 1:0.4:1.0, and then added into anhydrous ethanol to form a suspension. The liquid-solid ratio of anhydrous ethanol to activated palygorskite was 10:1 (ml / g). The mixture was stirred in an oil bath at 70℃ for 4 hours at a stirring rate of 500 r / min. After the reaction, the mixture was centrifuged at 8000 r / min for 10 minutes. The precipitate was washed with anhydrous ethanol for 3 times, and then dried in a vacuum dryer at 60℃ for 6 hours to obtain modified palygorskite. The chitosan-cerium nitrate composite gel was prepared by dissolving chitosan and cerium nitrate in deionized water according to a mass ratio of 1:0.6, and then cross-linking by 60 kHz ultrasonic wave for 15 minutes. The solid content of the gel was 15%.

[0050] Raw material pretreatment: coal gasification slag was ground to 200 mesh, and then classified and screened by an 80 kHz ultrasonic vibration screen. The slag was added into 5% (v / v) hydrochloric acid solution with a solid-liquid ratio of 1:5 (g / ml), and then acid washed in a constant temperature water bath at 70℃ for 3 hours under magnetic stirring at 300 r / min. During the acid washing process, 0.5 wt% citric acid was added at a drop rate of 0.5 ml / min every 30 minutes. After the acid washing, the slag was vacuum filtered under a vacuum degree of -0.08 MPa for 15 minutes, washed with deionized water until the pH was 7.0, and then dried at 105℃ for 2 hours to obtain pretreated slag.

[0051] Carbonization treatment: the pretreated slag was placed in a tube furnace, vacuumed to -0.09 MPa for 30 minutes, and then nitrogen was introduced. The temperature was increased to 500℃ at a rate of 10℃ / min, and then kept constant for 1 hour. The temperature was further increased to 900℃ for carbonization for 2 hours, and the total carbonization time was 3 hours. After the carbonization, nitrogen was continuously introduced until the temperature in the furnace decreased to below 100℃, and then the carbon powder was taken out.

[0052] Molding treatment: 5 wt% composite binder was added into the carbon powder according to a mass ratio of 2:1. The composite binder was composed of carboxymethyl cellulose sodium and modified palygorskite according to a mass ratio of 9:1, and was dispersed by a high-speed shearing machine at 8000 r / min for 30 minutes before use. The mixture was transferred into a powder tablet press machine with a mold diameter of 25 mm. Gradient pressing was adopted, i.e., pre-pressing at 5 MPa for 1 minute, and then pressing at 12 MPa for 5 minutes to obtain tablet-shaped green bodies with a thickness of 9 mm. The green bodies were placed in an oven, and then dried in stages, i.e., drying at 40℃ for 4 hours, and then increasing the temperature to 60℃ for 6 hours. The total drying time was 10 hours to obtain a molded matrix.

[0053] Activation treatment: put the shaped substrate into a muffle furnace, increase the temperature to 300℃ at a rate of 15℃ / min, keep for 30 minutes to remove residual air, then increase the temperature to the activation temperature at a rate of 5℃ / min; pass in CO2 gas, activate at 800℃ for 1 hour; during the activation process, the CO2 is passed in in a pulse mode, the pulse frequency is 30s / time, and the single-pass amount is 80Nm 3 ; after the activation is completed, naturally cool to room temperature to obtain high-strength sheet-shaped coal-based activated carbon.

[0054] Comparative Example 1 The preparation method of Example 2 is adopted, except that the modified attapulgite is not prepared, and the composite binder is only composed of sodium carboxymethyl cellulose, and the other steps and parameters are completely consistent with Example 2.

[0055] Comparative Example 2 The preparation method of Example 2 is adopted, except that the 80kHz ultrasonic vibration screening is not performed during the raw material pretreatment process, and no citric acid is added during the pickling process, and the other steps and parameters are completely consistent with Example 2.

[0056] Comparative Example 3 The preparation method of Example 2 is adopted, except that the CO2 is continuously passed in during the activation process (the amount of CO2 passed in is consistent with the cumulative amount of Example 2), and the pulse mode is not used, and the other steps and parameters are completely consistent with Example 2.

[0057] Test 1: mechanical strength performance test Sample preparation: cut the sheet-shaped coal-based activated carbon prepared in each example and comparative example into a standard sample of 50mm×25mm×8mm, prepare 5 parallel samples for each group of samples, remove surface impurities and dry to constant weight.

[0058] Compressive strength test: test with a universal material testing machine, the loading rate is 1mm / min, record the maximum compressive load of each sample, and calculate the average value of the compressive strength.

[0059] Flexural strength test: test with a universal material testing machine, the support span is 30mm, the loading rate is 0.5mm / min, record the maximum flexural load of each sample, and calculate the average value of the flexural strength.

[0060] The test results are the average values of 5 parallel samples, and the results are as follows: Table 1 As can be seen from Table 1, the compressive strength and flexural strength of Examples 1-3 show a gradually increasing trend, because as the grinding fineness of the coal gasification ash slag increases, the stirring rate increases, the pressing pressure increases, and the single CO2 input increases, the raw material mixing is more uniform, the internal structure of the shaped body is more compact, and the pore development during the activation process is more reasonable, thereby gradually increasing the mechanical strength.

[0061] The mechanical strength of Comparative Example 1 is significantly lower than that of Example 2, because Comparative Example 1 does not use modified attapulgite, and the composite binder is only sodium carboxymethyl cellulose. The modified attapulgite in the present application is acid-activated and complex-modified, and the surface active groups increase, which can significantly improve the binding performance of the binder and enhance the binding force between carbon powder particles in cooperation with sodium carboxymethyl cellulose. The binding effect of pure sodium carboxymethyl cellulose is limited, the internal porosity of the shaped body is high, and the structure is loose, which leads to a significant decrease in mechanical strength.

[0062] The mechanical strength of Comparative Example 2 is lower than that of Example 2, mainly because the ultrasonic vibration sieve grading screening is missing during the raw material pretreatment process, resulting in uneven particle size distribution of the coal gasification ash slag, and large particles of impurities are not effectively removed. Meanwhile, citric acid is not added during the acid washing process, and the chelating effect of citric acid cannot be exerted, and the metal impurities in the ash slag cannot be fully removed. These impurities and uneven particles form stress concentration points in the shaped body, which reduces the overall mechanical strength.

[0063] The mechanical strength of Comparative Example 3 is lower than that of Example 2, because Comparative Example 3 uses a continuous CO2 activation method, while the pulse input of the present application can make CO2 fully contact with the shaped matrix, and the activation is more uniform, and the pore structure is more regular. When continuously inputting CO2, CO2 is easy to form airflow channels on the surface of the matrix, which leads to insufficient internal activation, uneven pore development, and problems such as excessively large pores or loose structure in some areas, thereby affecting the mechanical strength.

[0064] Test 2: adsorption performance test; Sample preparation: The sheet-shaped coal-based activated carbon prepared in each example and comparative example was crushed to 200 mesh, dried to constant weight, and used as needed.

[0065] Methylene blue adsorption value test: 0.1 g of the sample was accurately weighed, placed in a 250 ml conical flask, 100 ml of methylene blue standard solution with a concentration of 150 mg / L was added, and oscillated in a constant temperature water bath oscillator at 25°C and 150 r / min for 60 minutes. Then it was filtered with a 0.45 μm filter membrane, and the absorbance of the filtrate was measured at a wavelength of 665 nm using a UV-visible spectrophotometer, and the methylene blue adsorption value was calculated.

[0066] Iodine adsorption value test: accurately weigh 0.5 g of the sample, place it in a 250 ml iodine flask, add 100 ml of 0.1 mol / L iodine standard solution, shake for 15 minutes, then stand for 2 minutes, filter with dry filter paper, take 50 ml of the filtrate, titrate with 0.05 mol / L sodium thiosulfate standard solution until light yellow, add 1 ml of starch indicator, continue to titrate until blue disappears, record the volume of sodium thiosulfate standard solution consumed, and calculate the iodine adsorption value.

[0067] Each group of samples was tested in triplicate, and the test results were averaged, as follows: Table 2 As can be seen from Table 2, the methylene blue adsorption value and the iodine adsorption value of Examples 1-3 all show a gradual upward trend, because as the coal gasification ash crushing fineness increases, the specific surface area increases; the stirring rate is increased to make the raw material mixing more uniform, and the binder dispersion is more sufficient; the pressing pressure is increased to make the structure of the formed body more compact, providing a good foundation for the uniform development of pores in the subsequent activation process; the increase in the single CO2 input amount makes the pulse activation effect more significant, and the pore number and specific surface area further increase, thereby improving the adsorption performance.

[0068] The adsorption performance of Comparative Example 1 is much lower than that of Example 2, and the core reason is that modified attapulgite is not used. On the one hand, the binding effect of the composite binder is not good, the internal pore structure of the formed body is chaotic, part of the pores is blocked, and the effective adsorption site is reduced; on the other hand, the modified attapulgite itself has certain adsorption performance, and after composite modification, it can form a synergistic adsorption effect with the activated carbon matrix, and the absence of it leads to a significant decrease in the overall adsorption performance.

[0069] The adsorption performance of Comparative Example 2 is lower than that of Example 2, mainly because the ultrasonic vibration sieve grading screening is missing in the raw material pretreatment process, and the particle size of the ash is not uniform, which affects the normal development of the pores in the subsequent carbonization and activation process; at the same time, citric acid is not added, and the impurities such as metal oxides in the ash cannot be fully removed, which will occupy part of the adsorption sites and may block the pores, leading to a decrease in the adsorption performance.

[0070] The adsorption performance of Comparative Example 3 is lower than that of Example 2, which is due to the continuous input of CO2, the contact between CO2 and the formed matrix is not sufficient during the activation process, part of the area is activated excessively to form large pores, part of the area is not activated enough, and the pore development is not complete, leading to a decrease in the number of effective adsorption pores (micropores and mesopores) and a decrease in the specific surface area, thereby affecting the adsorption capacity of methylene blue and iodine. The pulse input of CO2 can make the CO2 penetrate repeatedly inside the matrix, the activation is more uniform, the number of effective pores is more, and the adsorption performance is better.

[0071] The preferred embodiments of the application disclosed above are only to facilitate the elucidation of the application. The preferred embodiments do not describe all the details of the application, nor limit the application to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of the present specification.

Claims

1. A method for preparing high-strength sheet-like coal-based activated carbon from coal gasification ash, characterized in that, The process includes the preparation of modified attapulgite, raw material pretreatment, carbonization, molding, and activation, as detailed below: (1) The preparation of modified attapulgite includes: ① raw material pretreatment; ② acid activation; ③ composite modification; (2) Raw material pretreatment: The coal gasification ash residue is crushed to 100-200 mesh and screened by an 80kHz ultrasonic vibrating screen; 5% (v / v) HCl solution is added at a material-to-liquid ratio of 1:5 (g / ml), and the mixture is acid-washed in a constant temperature water bath at 65-70℃ for 3 hours with magnetic stirring at 200-300r / min; 0.5wt% citric acid is added every 30 minutes during the acid washing process, and after acid washing, the mixture is vacuum filtered, washed with deionized water until pH 6.5-7.0, and dried at 105℃ for 2 hours to obtain the pretreated ash residue; (3) Carbonization treatment: The pretreated ash residue is placed in a tubular muffle furnace. First, a vacuum is drawn to -0.09MPa and held for 30 minutes. Then, nitrogen is introduced and the temperature is raised to 500℃ at 10℃ / min. The temperature is kept constant for 1 hour. Then, the temperature is raised to 900℃ for carbonization for 2 hours. The total carbonization time is 3 hours. After carbonization, nitrogen is continued to be introduced until the temperature inside the furnace drops below 100℃ and the carbon powder is taken out. (4) Molding process: Add 5wt% composite binder to carbon powder at a mass ratio of 2:1; transfer the mixture into a powder tablet press with a mold diameter of 25mm, and use gradient pressure: pre-press at 5MPa for 1min, then press at 10-12MPa for 3-5min to obtain a sheet blank with a thickness of 7-9mm; put the blank into an oven and dry it in stages: dry at 40℃ for 4h, then heat up to 60℃ for 6h, and dry for a total of 10h to obtain the molded matrix; (5) Activation treatment: Place the molded substrate in a muffle furnace, heat to 300℃ and hold for 30 min to remove residual air; introduce CO2 gas and activate at 800℃ for 1 h; during the activation process, CO2 is introduced in a pulsed manner, with a pulse frequency of 30 s / time and a single introduction amount of 50-80 Nm. 3 After activation, the material is naturally cooled to room temperature to obtain high-strength sheet-like coal-based activated carbon.

2. The method according to claim 1, characterized in that, The preparation of the modified attapulgite specifically includes: ① Raw material pretreatment: Crush natural attapulgite to 200-300 mesh, dry at 105℃ for 2 hours to remove free water, and screen with a 200 mesh standard sieve to obtain refined attapulgite; ② Acid activation: Refined attapulgite was added to a 15% hydrochloric acid solution at a material-to-liquid ratio of 1:8 (g / ml), and activated in a constant temperature water bath at 80℃ for 2 hours, with stirring for 10 minutes every 30 minutes during the process; then it was dispersed by ultrasonication at 80kHz for 30 minutes, washed with deionized water until the pH of the filtrate was 6.8-7.0, and vacuum dried at 60℃ for 4 hours to obtain activated attapulgite; ③ Composite modification: Weigh activated attapulgite, γ-aminopropyltriethoxysilane, and chitosan-cerium nitrate composite gel at a mass ratio of 1:0.4:1.0, and add them to anhydrous ethanol to form a suspension; reflux the mixture in an oil bath at 70℃ for 4 hours with stirring at a rate of 500 r / min during the reaction; after the reaction is completed, centrifuge at 8000 r / min for 10 minutes, collect the precipitate, wash it three times with anhydrous ethanol, and vacuum dry it at 60℃ for 6 hours to obtain modified attapulgite.

3. The method according to claim 2, characterized in that, The vacuum degree of vacuum drying in step ② is -0.09 MPa.

4. The method according to claim 2, characterized in that, In step ③, the liquid-to-solid ratio of anhydrous ethanol to activated attapulgite is 10:1 (ml / g).

5. The method according to claim 2, characterized in that, The chitosan-cerium nitrate composite gel described in step ③ is prepared by dissolving chitosan and cerium nitrate in deionized water at a mass ratio of 1:0.6 and then crosslinking it with ultrasound at 60 kHz for 15 min, with a gel solid content of 15%.

6. The method according to claim 1, characterized in that, In step (2), the vacuum degree of vacuum filtration is -0.08MPa and the filtration time is 15min.

7. The method according to claim 1, characterized in that, The composite binder described in step (4) is composed of sodium carboxymethyl cellulose and modified attapulgite in a mass ratio of 9:1; the composite binder is dispersed for 30 minutes at 8000 r / min using a high-speed shear machine before use.

8. The method according to claim 1, characterized in that, In step (5), the heating rate of the muffle furnace is 15℃ / min, and after heating to 300℃, it is changed to 5℃ / min to reach the activation temperature.

9. The method according to claim 1, characterized in that, In step (2), citric acid is added by dripping at a rate of 0.5 ml / min.

10. High-strength sheet-like coal-based activated carbon prepared by any one of the methods described in claims 1-9.

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