CN111285371B - Method for extruding activated carbon material by utilizing reactive double-screw extrusion system - Google Patents
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Abstract
The invention relates to a method for extruding an activated carbon material by using a reactive double-screw extrusion system, belongs to the technical field of porous materials, and solves the technical problems that the mass and heat transfer process is limited, continuous production cannot be realized and the preparation process efficiency is low when the existing activated carbon material is prepared. The method of the invention comprises the following steps: step 1, mixing a carbon material raw material with an alkali metal hydroxide to obtain a pretreated carbon material; step 2, injecting the pretreated carbon material into a reactive double-screw extrusion system; step 3, processing the molten mixture of the alkali metal hydroxide and the carbon material raw material by utilizing a reactive double-screw extrusion system; and 4, cooling the solid obtained by the treatment in the step 3 in nitrogen, soaking excessive alkali metal hydroxide by using deionized water, filtering and drying to obtain the activated carbon material. The invention is suitable for various carbon material raw materials such as: petroleum coke, coal, multi-walled carbon nanotubes, nano carbon black, and biomass-based carbonized materials.
Description
Technical Field
The invention relates to the technical field of porous materials, in particular to a method for extruding an activated carbon material by using a reactive double-screw extrusion system.
Background
In the general method for activating and pore-forming the carbon material, the material obtained by activating with sodium hydroxide or potassium hydroxide has large specific surface area and relatively excellent performances in all aspects, but the industrial application of the activation process is less due to higher cost, salt corrosion in the process and a large number of uncontrollable factors, and the method has relatively limited application in producing the super-capacitor carbon material.
Linares-Solano et al have detailed summaries of the related developments of hydroxide activated Carbon materials (Chemistry and physics of Carbon vol.30,2008, p 1-62.). The main mechanism of activating and pore-forming by sodium hydroxide or potassium hydroxide is that the sodium or potassium generated in the heat treatment process intercalates the layered structure in the carbon structure, thereby generating internal pores.
The greatest advantage of this activation process is that it is possible to produce superactive carbon materials with high specific surface area(s) ((>3000m2The specific surface area can reach 5000m under certain conditions2(ii) in terms of/g. The hydroxide base activation process was discovered in 1978 by Wennerberg and O' Grady, Standard Oil Company, USA. Early experimental product PX21 BET nitrogen adsorption specific surface area of 3700m2(iv)/g, total micropore volume of approximately 1.75cm3(ii) in terms of/g. The first commercial alkali-activated super-activated carbon material was AMOCO super-activated carbon AX21 developed by Anderson Development Company and having a BET surface area of 2800-3500m2(ii)/g, the total pore volume of the porous particles is in the range of 1.4 to 2.0cm3(ii) in terms of/g. Further development of the AMOCO process by Kansai Coke and Chemicals Company in Japan has led to the introduction of a series of MaxSORB products having BET surface areas in excess of 3100m2Per g, total pore volume of more than 2.5cm3/g。
The alkali activation process of the hydroxide has some obvious defects, the activation process is generally carried out at the temperature higher than 700 ℃, the hydroxide is in a molten state in the process, and the carbon powder and the molten salt form a high-viscosity high-temperature mixture, so that the heat and mass transfer in the process is greatly limited, the process cannot be continuous, the batch process is less in treatment amount, and the process efficiency is extremely low.
High temperature alkali metal hydroxides are very corrosive, and the high temperature process generates volatile salts and flammable gaseous alkali metals, which place high demands on equipment and operation processes.
Disclosure of Invention
In view of the foregoing analysis, embodiments of the present invention are directed to providing a method for extruding an activated carbon material by using a reactive twin-screw extrusion system, so as to solve the technical problems that the mass and heat transfer process of the existing activated carbon material is limited, the continuous production cannot be performed, and the efficiency of the preparation process is low.
The purpose of the invention is mainly realized by the following technical scheme:
the invention provides a method for extruding an activated carbon material by using a reactive double-screw extrusion system, which comprises the following steps:
step 1, mixing a carbon material raw material with an alkali metal hydroxide to obtain a pretreated carbon material;
and 3, cooling the solid material obtained by the treatment in the step 2 in nitrogen, soaking excessive alkali metal hydroxide by using deionized water, filtering and drying to obtain the activated carbon material.
Further, in the step 2, a feeding rotary inlet and a supplementary feeding hole are arranged at the front end of the reactive double-screw extrusion system, and the reactive double-screw extrusion system is provided with a heating component and a temperature detection component in a propelling zone, a kneading zone and a high-temperature distribution mixing zone;
volatile matter gas discharge ports are correspondingly arranged in the kneading area and the high-temperature distribution mixing area and used for discharging volatile salt and flammable gaseous alkali metal generated in the kneading area and the high-temperature distribution mixing area; the reactive double-screw extrusion system is characterized in that the distance between shafts is 22-30 mm, the diameter of the screw shaft is 28-36 mm, and the total length of the screw shaft is 1100-1300 mm.
Further, in the step 1, the mass ratio of the alkali metal hydroxide to the carbon material raw material is 1: 1-5: 1.
further, in the step 2, the cooled solid material is uniformly mixed with deionized water with the mass of 2-20 times of that of the cooled solid material to form water-carbon slurry, and excess alkali metal hydroxide is impregnated.
Further, in the step 2, ultrasonic treatment is carried out on the water-carbon slurry, and the time of the ultrasonic treatment is 5-30 min.
Further, in the step 1, the alkali metal hydroxide pellets and the pellets of the carbon material raw material are physically mixed, and the alkali metal hydroxide is in a dry state during the mixing.
Further, in the step 1, the carbon material is impregnated with an aqueous alkali metal hydroxide solution.
Further, in the step 1, a pre-melted alkali metal hydroxide is blended with the carbon material raw material.
Further, in the step 1, the alkali metal hydroxide is one of potassium hydroxide and sodium hydroxide or a mixture of the two.
Further, in the step 1, the carbon material raw material is one of petroleum coke, coal, multi-walled carbon nanotubes, nano carbon black and biomass-based carbonized material;
and carrying out heat treatment on the carbon material raw material to enable the content of pure carbon element in the carbon material raw material to reach more than 95%.
Compared with the prior art, the invention can realize at least one of the following beneficial effects:
(1) the invention adopts a reactive double-screw extrusion system to prepare the activated carbon material, and the main principle of the activation process is that sodium or potassium atoms generate intercalation to cause structural expansion to generate structural pores, and the sodium or potassium atoms are generated by hydroxide directly reacting with carbon under the heated condition; the reactive twin-screw extrusion system can realize full contact between hydroxide and carbon and quick mass and heat transfer, thereby realizing efficient intercalation hole making. The traditional heating process is slowly and gradually changed to transfer heat from the outside, so that the pore-forming effect of intercalation is limited to a certain extent; for example, the conventional treatment process for activating a carbon material with an alkali metal hydroxide is to directly heat a mixture of a carbon material raw material and a hydroxide, and there are generally two ways to realize a programmed change in temperature with time: 1) carrying out heat treatment on the raw material mixture by adopting a static heating unit, and carrying out temperature programmed control on the heating unit; 2) the push plate kiln is adopted, and containers filled with raw material mixtures move and advance at different temperature gradient units of the kiln according to a certain speed. Another common mode used in industry is a rotary kiln, but using molten hydroxide as a reactant, the viscosity is too high in the operating state to allow efficient transfer of the material in the reactor. Due to the volatility of hydroxides at high temperatures, rotary kilns require external heating, which is difficult to achieve in rotary kilns. The possibility of a rotary kiln heat treatment regime is substantially eliminated.
(2) The double-screw extrusion system has excellent material conveying capacity, especially for some materials with high viscosity or great performance parameter fluctuation, owing to the rotation of the screw and forced axial periodic vibration. The reactive twin-screw extrusion system can realize continuous treatment of the molten salt activated carbon material of hydroxide, and simultaneously obtain larger treatment flux.
(3) The extrusion process of the twin screw extrusion system of the present invention is a high shear process whereby deep mixing of high viscosity materials can be achieved while devolatilization can also be achieved in the process. The two points are the key points to be solved for activating the carbon material by the hydroxide molten salt, and the deep mixing directly improves the impregnation effect of the hydroxide molten salt on the carbon material and the subsequent intercalation pore-forming process, so that the ideal pore-forming effect can be achieved under the condition of lower hydroxide consumption; the deep mixing process is favorable for devolatilization, and byproducts such as gas molecules, volatile metal salts and the like generated in the intercalation pore-forming process are timely removed from the system, so that negative effects caused by accumulation are avoided.
(4) The twin-screw extrusion system of the present invention has a relatively concentrated core unit (including a propulsion zone, a kneading zone and a high-temperature distribution mixing zone) in view of the equipment structure, which allows the temperature control and discharge system to be greatly simplified in complexity. Therefore, compared with a push plate kiln system, the device occupies small space, the corresponding maintenance and auxiliary system is simple, and the bolt screw extrusion system has obvious advantages from the aspects of economy and environmental protection.
In the invention, the technical schemes can be combined with each other to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and drawings.
Drawings
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout.
FIG. 1 is a schematic diagram of a reactive twin-screw extrusion system according to the present invention.
Reference numerals:
1-a feed swirl inlet; 2-supplement feed inlet; 3-a temperature detection component; 4-discharge of gaseous volatiles; 5-a propulsion zone; 6-kneading zone; 7-high temperature distribution mixing zone.
Detailed Description
The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form a part hereof, and which together with the embodiments of the invention serve to explain the principles of the invention and not to limit its scope.
The invention provides a method for extruding an activated carbon material by using a reactive double-screw extrusion system, which comprises the following steps:
step 1, mixing a carbon material raw material with an alkali metal hydroxide to obtain a pretreated carbon material;
and 3, cooling the solid material obtained by the treatment in the step 2 in nitrogen, soaking excessive alkali metal hydroxide by using deionized water, filtering and drying to obtain the activated carbon material.
The traditional heating process is slowly and gradually changed, and the heat is transferred from the outside, so that the pore-forming effect of intercalation is limited to a certain extent. The invention adopts a reactive double-screw extrusion system to prepare the activated carbon material, and the main principle of the activation process is that sodium or potassium atoms generate intercalation to cause structure expansion to generate structure pores, and the sodium or potassium atoms are generated by hydroxide directly reacting with carbon at the high temperature of 800 ℃; the reactive twin-screw extrusion system can realize full contact between hydroxide and carbon and quick mass and heat transfer, thereby realizing efficient intercalation hole making.
In step 1, the alkali metal hydroxide pellets are physically mixed with the pellets of the carbon material raw material (M1), and the alkali metal hydroxide is in a dry state during the mixing. The physical mixing of the alkali metal hydroxide particles and the particles of the carbon material raw material means that the carbon material raw material (carbon powder) and the hydroxide are mechanically crushed and then mixed, and the hydroxide is prevented from absorbing moisture in the mixing process.
Alternatively, in step 1, the carbon material is impregnated with an aqueous alkali metal hydroxide solution (M2). The hydroxide aqueous solution impregnation is a wet loading process, the carbon material raw material is fully contacted with the solution and then dried, and the dried hydroxide and raw material carbon are mixed into a solid.
Alternatively, in step 1, a pre-melted alkali metal hydroxide is blended with the carbon material raw material (M3). The pre-melting alkali metal hydroxide and carbon material are mixed in an on-line mixing mode, the process is that the hydroxide is heated to the melting temperature in advance to form liquid state, then the liquid state is mixed with the carbon material under the stirring action, and the temperature is kept for a certain time until uniform molten mass is formed.
The mixing method is selected mainly according to the characteristics of the carbon material raw material.
Specifically, the alkali metal hydroxide particles and the particles of the carbon material are physically mixed (M1), and this mixing method is suitable for carbon material materials with small porosity, small polarity and strong hydrophobicity, such as petroleum coke, coal tar and other stone materials. Impregnation of carbon material raw material with alkali metal hydroxide aqueous solution (M2): the mixing mode is suitable for carbon material with larger porosity ratio and good hydrophilicity, and mainly comprises carbon material based on biomass material, such as woody carbon, coconut shell carbon, bamboo charcoal, cellulose derived carbon, carbohydrate generated carbon and the like. Pre-melting alkali metal hydroxide and carbon material raw material blending (M3): the pre-melting alkali metal hydroxide blending method is suitable for nano carbon materials, such as carbon nano tubes, carbon nano belts, carbon nano fibers and the like. The method is a compromise scheme, and the raw material of the carbon nano material has poor hydrophilicity and is not suitable for aqueous solution impregnation. With the physical particle mixing process, the micro morphology of the material is destroyed due to the structural friction and shear effects of the mechanical mixing.
In the step 1, the alkali metal hydroxide is one or a mixture of potassium hydroxide and sodium hydroxide, wherein the mass ratio of the sodium hydroxide to the potassium hydroxide is 1: 1-3: 1. The reactivity of sodium hydroxide and potassium hydroxide varies depending on the structural characteristics of the carbon material, and sodium hydroxide is suitable for activating a carbon material having a less regular structure (the pitch of graphite layers is lower or higher than the value d of standard graphite)002Pitch 0.335nm) and potassium hydroxide is mainly suitable for carbon material raw materials with relatively regular microstructures.
In step 1, the mass ratio of the alkali metal hydroxide to the carbon material raw material is 1: 1-5: 1. the mass ratio of the alkali metal hydroxide to the carbon material raw material is controlled within the range of 1: 1-5: 1, so that the molten hydroxide can be effectively impregnated into the carbon material raw material, and the expected activating pore-forming effect is achieved. If the ratio is lower than 1:1, the impregnation of the hydroxide on the carbon material raw material is insufficient, and the pore-forming effect is affected; if the ratio is more than 5:1, a large excess of hydroxide will be caused, which increases the process treatment cost, and also causes a problem of recovering excess hydroxide.
In the step 2, a feeding rotary inlet and a supplementary feeding hole 2 are arranged at the front end of the reactive double-screw extrusion system, and the reactive double-screw extrusion system is provided with a heating part and a temperature detection part 3 in a propelling area 5, a kneading area 6 and a high-temperature distribution mixing area 7; the kneading area 6 and the high-temperature distribution mixing area 7 are correspondingly provided with gas volatile matter discharge ports 4 which are used for discharging volatile salt and flammable gaseous alkali metal generated in the kneading area 6 and the high-temperature distribution mixing area 7; the axial distance of the reactive double-screw extrusion system is 22-30 mm, the diameter of the screw shaft is 28-36 mm, and the total length of the screw shaft is 1100-1300 mm.
Specifically, the activated carbon material is extruded by a reactive double-screw extrusion system, the pretreated carbon material pretreated by alkali metal hydroxide enters the reactive double-screw extrusion system through a feeding screw inlet, the material advances along the axial direction of the double screws under the rotation of the double screws, when the pretreated carbon material advances to a pushing zone 5, the pretreated carbon material is heated to 400 ℃ and mixed to form a molten mass, when the molten mass advances to a kneading zone 6, the molten mass is mixed and sheared in the kneading zone 6 and heated to 600 ℃, and under the mixing shearing action of the double screws, the alkali metal hydroxide is fully contacted with the carbon material and fully permeates into each pore channel of the carbon material; when the material (melt) is pushed into the high-temperature distribution mixing zone 7, the melt is heated to 800 ℃ in the high-temperature distribution mixing zone 7, and under the mixing and shearing action of the twin-screw, the alkali metal hydroxide and the carbon material undergo pore-forming reaction, and sodium and/or potassium in the alkali metal hydroxide intercalates the layered structure in the carbon structure, so that internal voids are generated, and the activated carbon material with ultrahigh specific surface area is prepared.
It is emphasized that the activated carbon material is extruded by using the reactive twin-screw extrusion system, on one hand, the temperatures of the propelling zone 5, the kneading zone 6 and the high-temperature distribution mixing zone 7 can be accurately controlled by arranging the corresponding heating components and temperature detection components 3 in the propelling zone 5, the kneading zone 6 and the high-temperature distribution mixing zone 7, and the continuous production of the activated carbon material is ensured; on the other hand, by arranging the gas volatile matter discharge port 4 in the kneading zone 6 and the high-temperature distribution mixing zone 7, volatile salts and flammable gaseous alkali metals generated in the extrusion process can be discharged in a segmented manner, and the blockage of the flue when the volatile salts and the flammable gaseous alkali metals are discharged through the flue is avoided.
Because the high-temperature alkali metal hydroxide has strong corrosivity, the material of the reactive double-screw extrusion system adopts 316S austenitic stainless steel, and the 316S austenitic stainless steel has good alkali resistance and corrosion resistance at the high temperature of 1200 ℃, so that the reactive double-screw extrusion system can be prevented from being corroded by the high-temperature alkali metal hydroxide.
The continuous blending reaction process is not suitable for high-viscosity reactants, the mixing mode and the heating temperature can be accurately controlled in a segmented mode, and high-temperature volatile matters generated in the reaction process can be effectively controlled due to the fact that the whole system is closed.
The twin-screw extrusion system of the present invention exhibits high efficiency, which is not generally available in static processes, in the specific process of activating a carbon material with respect to a molten alkali metal hydroxide, and the high efficiency of the twin-screw extrusion system is mainly embodied in the following three aspects:
1) the double-screw extrusion system has excellent material conveying capacity, especially for some high viscosity or material with great performance parameter fluctuation, owing to the rotation of the screw and forced axial periodic vibration. The reactive twin-screw extrusion system can realize continuous treatment of the molten salt activated carbon material of hydroxide, and simultaneously obtain larger treatment flux.
2) The extrusion process of the twin screw extrusion system is a high shear process whereby deep mixing of high viscosity materials can be achieved, while devolatilization can also be achieved in the process. The two points are the key points to be solved for activating the carbon material by the hydroxide molten salt, and the deep mixing directly improves the impregnation effect of the hydroxide molten salt on the carbon material and the subsequent intercalation pore-forming process, so that the ideal pore-forming effect can be achieved under the condition of lower hydroxide consumption; the deep mixing process is favorable for devolatilization, and byproducts such as gas molecules, volatile metal salts and the like generated in the intercalation pore-forming process are timely removed from the system, so that negative effects caused by accumulation are avoided.
3) The twin-screw extrusion system has a core unit (including the advancing zone 5, the kneading zone 6 and the high-temperature distribution mixing zone 7) concentrated from the viewpoint of the equipment structure, which makes it possible to greatly simplify the temperature control and discharge system in a complicated manner. Therefore, compared with a push plate kiln system, the device occupies small space, the corresponding maintenance and auxiliary system is simple, and the bolt screw extrusion system has obvious advantages from the aspects of economy and environmental protection.
In the step 2 and the step 3, the axial distance of the reactive double-screw extrusion system is 22-30 mm, the diameter of the screw shaft is 28-36 mm, and the total length of the screw shaft is 1100-1300 mm; the reactive twin-screw extrusion system is provided with three functional zones along the axial direction: a propelling zone 5 with the temperature of 380-450 ℃, a kneading zone 6 with the temperature of 580-620 ℃ and a high-temperature distribution mixing zone 7 with the temperature of 780-850 ℃; the adopted twin-screw extrusion system is different from a common twin-screw extrusion system suitable for a lower temperature, the adopted twin-screw extrusion system is required to be suitable for a high-temperature reaction which is more difficult to control, and firstly, 316S alloy steel (the main components are carbon 0.0.35, silicon 1.000, manganese 2.0, phosphorus 0.045, sulfur 0.030 and chromium 16-18) with high temperature resistance and corrosion resistance is adopted; and secondly, the temperature of different areas needs to be controlled in a partitioning mode.
The mixture of the carbon material and the alkali metal hydroxide is solid powder and is conveyed into a double-screw cavity through a feeding rotary inlet; the hydroxide is melted in the propulsion zone 5 and mixed with the carbon material raw material particles to form a molten mass, the molten mass enters the kneading zone 6, the hydroxide deeply soaks the carbon material raw material particles and fully permeates the carbon material raw material particles to each pore system, and an activation pore-forming reaction occurs in the high-temperature distribution mixing zone 7.
As shown in figure 1, a propelling zone 5, a kneading zone 6 and a high-temperature distribution mixing zone 7 of the double-screw extrusion system are sequentially distributed along the axis of the double screws from a feeding rotary inlet 1 to a discharging outlet, the distribution length of the propelling zone 5 accounts for 30-35% of the total length of the screw shaft, the distribution length of the kneading zone 6 accounts for 8-12% of the total length of the screw shaft, the distribution length of the high-temperature distribution mixing zone 7 accounts for 40-45% of the total length of the screw shaft, and the balance is empty volume. The temperature settings of the three functional zones are respectively: the temperature of the propulsion zone 5 is 380 to 450 ℃, the temperature of the kneading zone 6 is 580 to 620 ℃ and the temperature of the high-temperature distribution mixing zone 7 is 780 to 850 ℃. The heating adopts an independent external heating unit, the temperature adopts an independent program control unit, and the external heating unit and the program control unit only adopt the external heating unit and the program control unit of the conventional double-screw extrusion system, so that the description is omitted.
In the process of activation treatment, various alkali metal salts can remain in the pore structure of the carbon particles in the conversion process of the alkali metal hydroxide and the carbon particles, and in order to remove the alkali metal salts, in step 4, the cooled solid is uniformly mixed with deionized water with the mass 2-20 times that of the cooled solid to form water-carbon slurry, and excessive alkali metal hydroxide is impregnated.
The chemical reaction equation of the activation pore-forming process of the alkali metal hydroxide on the carbon material is as follows:
hydroxide carbon reduction process:
intercalation of potassium atoms to carbon:
potassium atom release to construct pores: KC8+H2O→KOH+8C+1/2H2
And (3) separating excessive alkali metal hydroxide from the treated mixture through an impregnation process, concentrating the impregnation solution containing the hydroxide to the concentration of 45-50% by using the waste heat of the tail gas discharged by a double-screw extrusion system, continuously heating until the solvent is volatilized, recovering the hydroxide solid, and adding the recovered hydroxide into a new reaction batch for recycling.
And 4, carrying out ultrasonic treatment on the water-carbon slurry for 5-30 min. The water-carbon slurry is subjected to ultrasonic treatment for 5-30 min, so that the excessive alkali metal hydroxide can be completely impregnated.
In the step 1, the carbon material is one of petroleum coke, coal, multi-walled carbon nanotubes, nano carbon black and biomass-based carbonized material; the carbon material raw material needs to be preheated by a corundum tube furnace, the heat treatment container is made of aluminum oxide, the temperature range of the heat treatment process is 600-700 ℃, the heat treatment process is carried out in nitrogen gas flow, and the nitrogen gas flow rate is 80-300 ml/min.
The heat treatment of the carbon material can ensure that small molecules and volatile components in the carbon material are separated from the structure, and the carbon material is suitable for activating the alkali metal hydroxide only when the pure carbon element content of the material reaches more than 95 percent.
Example 1
100g of the carbon material raw material (the kind of the carbon material raw material is listed in Table 1) subjected to the pre-carbonization treatment and 300g of KOH powder were uniformly stirred and mixed, and the precession rate of a reactive twin-screw extrusion system was 20 r/min. The flow rate of the reactive twin-screw extrusion system was 0.4 kg/h. The axial distance of the reactive double-screw extrusion system is 26mm, the diameter of the screw shaft is 31mm, and the total length of the screw shaft is 12000 mm; the reactive twin-screw extrusion system is provided with three functional zones along the axial direction: a propelling zone 5 with the temperature of 400 ℃, a kneading zone 6 with the temperature of 600 ℃ and a high-temperature distribution mixing zone 7 with the temperature of 800 ℃; and mixing and eluting the cooled sample by using 2.0kg of deionized water for three times, wherein the treatment time in ultrasonic cleaning is 20min each time, and filtering and drying the solid sample. The pore characteristics of the sample were determined by nitrogen isothermal adsorption and desorption. The specific experimental results are shown in table 1.
Table 1 example 1 experimental results for the preparation of activated carbon materials
Example 2
100g of the carbon material raw material (the kind of the carbon material raw material is shown in Table 2) subjected to the pre-carbonization treatment and 300g of NaOH powder were uniformly stirred and mixed, and the precession rate of a reactive twin-screw extrusion system was 20 r/min. The flow rate of the reactive twin-screw extrusion system was 0.4 kg/h. The axial distance of the reactive double-screw extrusion system is 26mm, the diameter of the screw shaft is 31mm, and the total length of the screw shaft is 12000 mm; the reactive twin-screw extrusion system is provided with three functional zones along the axial direction: a propelling zone 5 with the temperature of 400 ℃, a kneading zone 6 with the temperature of 600 ℃ and a high-temperature distribution mixing zone 7 with the temperature of 800 ℃; and mixing and eluting the cooled sample by using 2.0kg of deionized water for three times, wherein the treatment time in ultrasonic cleaning is 20min each time, and filtering and drying the solid sample. The pore characteristics of the sample were determined by nitrogen isothermal adsorption and desorption. The specific experimental results are shown in table 2.
Table 2 example 2 experimental results for the preparation of activated carbon material
Example 3
100g of the carbon material raw material subjected to the pre-carbonization treatment (the types of the carbon material raw material are listed in Table 3) and 300g of NaOH/KOH (1:1) powder are stirred and mixed uniformly, and the precession rate of a reactive twin-screw extrusion system is 20 r/min. The flow rate of the reactive twin-screw extrusion system was 0.4 kg/h. The axial distance of the reactive double-screw extrusion system is 26mm, the diameter of the screw shaft is 31mm, and the total length of the screw shaft is 12000 mm; the reactive twin-screw extrusion system is provided with three functional zones along the axial direction: a propelling zone 5 with the temperature of 400 ℃, a kneading zone 6 with the temperature of 600 ℃ and a high-temperature distribution mixing zone 7 with the temperature of 800 ℃; and mixing and eluting the cooled sample by using 2.0kg of deionized water for three times, wherein the treatment time in ultrasonic cleaning is 20min each time, and filtering and drying the solid sample. The pore characteristics of the sample were determined by nitrogen isothermal adsorption and desorption. The specific experimental results are shown in table 3.
Table 3 example 3 experimental results for the preparation of activated carbon material
Example 4
A100 g sample of pre-carbonized petroleum coke was mixed with KOH as follows: physical mixing of direct particles (M1), impregnation of carbon material with aqueous hydroxide solution (M2), and blending of pre-molten hydroxide with carbon material raw material (M3). The precession rate of the reactive twin-screw extrusion system was 20 r/min. The flow rate of the reactive twin-screw extrusion system was 0.4 kg/h. The axial distance of the reactive double-screw extrusion system is 26mm, the diameter of the screw shaft is 31mm, and the total length of the screw shaft is 12000 mm; the reactive twin-screw extrusion system is provided with three functional zones along the axial direction: a propelling zone 5 with the temperature of 400 ℃, a kneading zone 6 with the temperature of 600 ℃ and a high-temperature distribution mixing zone 7 with the temperature of 800 ℃; and mixing and eluting the cooled sample by using 2.0kg of deionized water for three times, wherein the treatment time in ultrasonic cleaning is 20min each time, and filtering and drying the solid sample. The pore characteristics of the sample were determined by nitrogen isothermal adsorption and desorption. The specific experimental results are shown in table 4.
Table 4 example 4 experimental results for the preparation of activated carbon materials
Example 5
A 100g sample of the pre-carbonized petroleum coke was mixed with KOH using direct particle physical mixing (M1). The twin screw extrusion reaction was conducted under conditions such that the twin screw precession rate and flow rate are shown in Table 5. The axial distance of the reactive double-screw extrusion system is 26mm, the diameter of the screw shaft is 31mm, and the total length of the screw shaft is 12000 mm; the reactive twin-screw extrusion system is provided with three functional zones along the axial direction: a propelling zone 5 with the temperature of 400 ℃, a kneading zone 6 with the temperature of 600 ℃ and a high-temperature distribution mixing zone 7 with the temperature of 800 ℃;
and mixing and eluting the cooled sample by using 2.0kg of deionized water for three times, wherein the treatment time in ultrasonic cleaning is 20min each time, and filtering and drying the solid sample. The pore characteristics of the sample were determined by nitrogen isothermal adsorption and desorption. The specific experimental results are shown in table 5.
Table 5 example 5 experimental results for the preparation of activated carbon materials
Comparative example 1
The existing treatment process for activating a carbon material by using an alkali metal hydroxide is to directly heat a mixture of a carbon material raw material and a hydroxide, and generally, there are two ways to realize the program change of temperature along with time: 1) carrying out heat treatment on the raw material mixture by adopting a static heating unit, and carrying out temperature programmed control on the heating unit; 2) the push plate kiln is adopted, and containers filled with raw material mixtures move and advance at different temperature gradient units of the kiln according to a certain speed.
Another common mode used in industry is a rotary kiln, but using molten hydroxide as a reactant, the viscosity is too high in the operating state to allow efficient transfer of the material in the reactor. Due to the volatility of hydroxides at high temperatures, rotary kilns require external heating, which is difficult to achieve in rotary kilns. The possibility of a rotary kiln heat treatment regime is substantially eliminated. Whether a static heating unit or a pusher kiln system is used, the raw material mixture is in an undisturbed state throughout the heat treatment process. Gradually melting hydroxide in the raw material mixture into liquid in the temperature rising process, and then impregnating carbon raw material particles; as the treatment temperature is increased, the alkali metal hydroxide is reduced by carbon element to generate metal sodium or potassium atoms, and the sodium or potassium atoms are intercalated to cause the structure to expand to generate structural pores. The interaction process of the hydroxide and the carbon material is a strong mass and heat transfer process, but adverse factors such as high temperature and viscosity of reaction materials and strong corrosion and volatility limit the reactor form which can be adopted. The adoption of a static reaction process brings inevitable problems:
first, mass transfer is inadequate; the forward mass transfer is impregnation of the hydroxide to the carbon material particles, and in order to realize full impregnation of the liquid hydroxide to the carbon material particles in a static process, a larger hydroxide/carbon material mass ratio must be adopted, which directly leads to the multiplied increase of the raw material cost and also increases the problem of excessive hydroxide recovery; mass transfer reversal, which means that by-products or volatile products produced during the reaction must be removed from the reaction system as quickly as possible, if the process is impeded, resulting in a decrease in reaction efficiency and side reactions, is also a serious problem in static processes.
Secondly, the heat transfer efficiency is low, and the local temperature difference is large; in the process of sodium or potassium atom intercalation, high porosity can be formed in the rapid heating process, a very high hole making effect is generated, the performance of the material can be greatly fluctuated due to large temperature gradient difference between parts in the static heating process, and the difference between material preparation batches is large.
Thirdly, the static process is a single batch processing process, the continuity of the whole process cannot be realized, and the static process has no value of practical application in view of the economical efficiency of the processing process.
Compared with the comparative example described above, the twin-screw extrusion system of the present invention shows high efficiency which is not exhibited by the usual static process in the specific process of activating a carbon material with respect to a molten alkali metal hydroxide, and the high efficiency of the twin-screw extrusion system is mainly exhibited in the following four aspects:
(1) aiming at the fact that high-temperature alkali metal hydroxide has high corrosivity, the material of the reactive double-screw extrusion system adopted by the invention is 316S austenitic stainless steel (the main special components are 0.030 carbon, 1.000 silicon, 2.0 manganese, 0.045 phosphorus, 0.030 sulfur and 16-18 chromium), and the 316S austenitic stainless steel has good alkali resistance and corrosion resistance at the high temperature of 1200 ℃, so that the reactive double-screw extrusion system can be prevented from being corroded by the high-temperature alkali metal hydroxide.
(2) The double-screw extrusion system has excellent material conveying capacity, especially for some high viscosity or material with great performance parameter fluctuation, owing to the rotation of the screw and forced axial periodic vibration. The characteristic twin-screw extrusion system can realize continuous treatment of the molten salt activated carbon material of hydroxide, and simultaneously obtain larger treatment flux.
(3) The extrusion process of the twin screw extrusion system is a high shear process whereby deep mixing of high viscosity materials can be achieved, while devolatilization can also be achieved in the process. The two points are the key points to be solved for activating the carbon material by the hydroxide molten salt, and the deep mixing directly improves the impregnation effect of the hydroxide molten salt on the carbon material and the subsequent intercalation pore-forming process, so that the ideal pore-forming effect can be achieved under the condition of lower hydroxide consumption; the deep mixing process is favorable for devolatilization, and byproducts such as gas molecules, volatile metal salts and the like generated in the intercalation pore-forming process are timely removed from the system, so that negative effects caused by accumulation are avoided.
(4) The twin-screw extrusion system has a core unit (including the advancing zone 5, the kneading zone 6 and the high-temperature distribution mixing zone 7) concentrated from the viewpoint of the equipment structure, which makes it possible to greatly simplify the temperature control and discharge system in a complicated manner. Therefore, compared with a push plate kiln system, the device occupies small space, the corresponding maintenance and auxiliary system is simple, and the bolt screw extrusion system has obvious advantages from the aspects of economy and environmental protection.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (10)
1. A method of extruding an activated carbon material using a reactive twin screw extrusion system, comprising the steps of:
step 1, mixing a carbon material raw material with an alkali metal hydroxide to obtain a pretreated carbon material;
in the step 1, preheating the carbon material raw material at a preheating temperature of 600-700 ℃ in a nitrogen gas flow at a nitrogen flow rate of 80-300 ml/min, wherein the preheating process is used for enabling the content of pure carbon elements in the carbon material raw material to reach more than 95%;
step 2, injecting the pretreated carbon material into a reactive double-screw extrusion system; the pretreated carbon material sequentially passes through a propelling zone, a kneading zone and a high-temperature distribution mixing zone along the feeding direction of the reactive double-screw extrusion system; the distribution length of the propelling zone accounts for 30-35% of the total length of the screw shaft, the distribution length of the kneading zone accounts for 8-12% of the total length of the screw shaft, and the distribution length of the high-temperature distribution mixing zone accounts for 40-45% of the total length of the screw shaft;
the precession rate and the flow rate of the reactive double-screw extrusion system are respectively 5-50 r/min and 0.1-1 kg/h; the pretreated carbon material is heated to 380-450 ℃ in a propulsion zone and mixed to form a molten mass, the molten mass is heated to 580-620 ℃ in a kneading zone, and alkali metal hydroxide permeates into the carbon material; heating the molten mass to 780-850 ℃ in a high-temperature distribution mixing zone, and carrying out pore-forming reaction on the alkali metal hydroxide and the carbon material to obtain a solid material;
in the step 2, the reactive twin-screw extrusion system is a closed system;
volatile matter gas discharge ports are correspondingly arranged in the kneading area and the high-temperature distribution mixing area and used for discharging volatile salt and flammable gaseous alkali metal generated in the kneading area and the high-temperature distribution mixing area; the distance between shafts of the reactive double-screw extrusion system is 22-30 mm, the diameter of the screw shaft is 28-36 mm, and the total length of the screw shaft is 1100-1300 mm;
step 3, cooling the solid material obtained by the treatment in the step 2 in nitrogen, soaking excessive alkali metal hydroxide by using deionized water, filtering and drying to obtain an activated carbon material;
in the step 3, uniformly mixing the cooled solid material with deionized water to form water-carbon slurry, and carrying out ultrasonic treatment on the water-carbon slurry for 5-30 min; and then heating the water-carbon slurry by utilizing the waste heat of tail gas discharged by a double-screw extrusion system until the deionized water is volatilized, recovering to obtain alkali metal hydroxide, and adding the recovered alkali metal hydroxide into a new reaction batch for recycling.
2. The method for extruding an activated carbon material using a reactive twin-screw extrusion system according to claim 1, wherein in the step 2, a feed screw inlet and a supplementary feed port are provided at a front end of the reactive twin-screw extrusion system, and the reactive twin-screw extrusion system is provided with a heating means and a temperature detecting means in each of a feeding zone, a kneading zone and a high-temperature distribution mixing zone;
the distance between shafts of the reactive double-screw extrusion system is 26-30 mm, and the diameter of the screw shaft is 31-36 mm.
3. The method for extruding an activated carbon material using a reactive twin-screw extrusion system according to claim 1, wherein in the step 1, the mass ratio of the alkali metal hydroxide to the carbon material raw material is 1: 1-5: 1.
4. the method for extruding the activated carbon material by using the reactive twin-screw extrusion system according to claim 1, wherein in the step 3, the cooled solid material is uniformly mixed with deionized water 2-20 times by mass to form the water-carbon slurry.
5. The method for extruding the activated carbon material by using the reactive twin-screw extrusion system according to claim 4, wherein in the step 3, the aqueous carbon slurry is subjected to ultrasonic treatment for 20-30 min.
6. The method for extruding an activated carbon material using a reactive twin-screw extrusion system as described in claim 1, wherein in said step 1, the alkali metal hydroxide pellets are physically mixed with pellets of a carbon material raw material, and the alkali metal hydroxide is in a dry state during the mixing.
7. The method for extruding an activated carbon material using a reactive twin-screw extrusion system according to claim 1, wherein in the step 1, an aqueous alkali metal hydroxide solution is impregnated into a carbon material raw material.
8. The method of extruding an activated carbon material using a reactive twin screw extrusion system as claimed in claim 1, wherein in step 1, a pre-melted alkali metal hydroxide is blended with a carbon material raw material.
9. The method for extruding an activated carbon material using a reactive twin-screw extrusion system according to claim 1, wherein in the step 1, the alkali metal hydroxide is one of potassium hydroxide, sodium hydroxide or a mixture of both.
10. The method of extruding an activated carbon material using a reactive twin screw extrusion system as claimed in any one of claims 1 to 9, wherein in step 1, the carbon material feedstock is one of petroleum coke, coal, multi-walled carbon nanotubes, nano carbon black and biomass-based carbonitrides.
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| CN2041683U (en) * | 1988-12-14 | 1989-07-26 | 广州市工程咨询公司 | Multiple screw arbor charring furnace for chemistry making activated carbon |
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