A microwave-assisted activation-free method for preparing pitch-based porous carbon

Abstract

The present invention aims to provide a microwave-assisted activation-free method for preparing pitch-based porous carbon. This method, which belongs to the technical field of pitch-based porous carbon preparation, dissolves pitch in a deep eutectic solvent and then heats the mixture using microwaves. Due to the polar bonds in the deep eutectic solvent, microwave heating rapidly heats the pitch, promoting the volatilization of light components in the pitch and further facilitating the formation of pores. This process not only effectively avoids the problems associated with traditional pore structure control but also simplifies the complex activation steps in traditional methods.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of pitch-based porous carbon, and in particular relates to a method for preparing pitch-based porous carbon by microwave-assisted activation-free method. Background Art

[0002] Asphalt is a complex organic matter composed of polycyclic aromatic hydrocarbons and their derivatives. It has the characteristics of strong aromaticity, high carbon content, low ash content and easy graphitization. It is an excellent raw material for preparing porous carbon and has shown broad application prospects in many fields such as environmental protection, energy storage, catalysis, adsorption and electronic devices. The preparation methods of asphalt-based porous carbon mainly include the following: (1) Chemical activation method. This method mixes the carbon precursor with an activator and activates it under high temperature conditions to generate pores. Commonly used activators include KOH, H3PO4 and ZnCl2. Patent CN116730337A proposes a method for preparing coal pitch-based porous carbon using double salt compounds (such as K2CO3 and Na2CO3) assisted by potassium hydroxide. This method faces challenges such as high production cost, poor safety and unfavorable large-scale industrial production. (2) Physical activation method. Patent CN117342554A discloses a coal pitch-based activated carbon and its preparation method. This method uses physical activation technology to effectively prepare granular or powdered activated carbon by introducing gases such as carbon dioxide, air or water vapor at a temperature of 650~800℃ and using their weak oxidation to generate pores. This method has low requirements for equipment corrosion protection, low cost and high safety. However, this process has strict temperature requirements and also leads to high energy consumption. (3) Mixed activation method, that is, physical and chemical coupling activation technology, can prepare activated carbon with a large specific surface area, developed pore structure and excellent adsorption performance. However, this method requires precise control of the conditions of chemical pretreatment and physical activation, and therefore requires more complex process flow and equipment support, which increases the difficulty and cost of operation. At present, there are no patent reports on the use of activation-free technology to prepare pitch-based porous carbon.

[0003] As an emerging heating method, microwave heating technology has attracted widespread attention due to its advantages such as fast heating speed, uniform temperature distribution and high energy conversion efficiency. Under the action of the microwave electric field, polar molecules will continue to rotate, generating friction, which is converted into heat energy, causing the temperature of the material to rise. However, most asphalt molecules are weakly polar or non-polar molecules and lack wave-absorbing properties, so they cannot be directly heated by microwaves. Patent CN117965035A discloses a modification method for activating asphalt using microwave chemical effects, which is mainly used for road asphalt. This method uses the chemical effect triggered by microwave heating to make the asphaltene in the asphalt evenly dispersed and the chemical properties more active, thereby reducing the viscosity, but the patent does not involve the field of porous carbon preparation.

[0004] Deep eutectic solvents are generally composed of hydrogen bond donors (such as urea and alcohols) and hydrogen bond acceptors (such as choline chloride and salts). Their unique characteristics lie in their excellent solubility and low melting point, enabling them to efficiently dissolve substances that are typically difficult to dissolve. Patent CN112852471A describes a method for extracting oil sands bitumen using a deep eutectic solvent, which effectively achieves clean bitumen separation and significantly improves extraction yield. While research has examined the use of deep eutectic solvents to treat bitumen, currently no technology exists that combines deep eutectic solvents with bitumen to produce porous carbon. Summary of the Invention

[0005] The present invention aims to provide a microwave-assisted, activation-free method for preparing asphalt-based porous carbon, which is low-cost, environmentally friendly, and pollution-free. For the first time, the present invention dissolves asphalt in a deep eutectic solvent and then heats the mixture with microwaves. The presence of polar bonds in the deep eutectic solvent causes the molecules therein to vibrate rapidly, generating heat. The temperature rises to 700°C to 1200°C within 1 to 10 minutes, leading to high-temperature carbonization. At this point, the light components and DES in the asphalt decompose and volatilize, generating gases that form pores. This entire process requires no activating agent; only high-temperature carbonization is required to produce porous carbon.

[0006] The present invention adopts the following technical solutions:

[0007] A method for preparing pitch-based porous carbon by microwave-assisted activation-free method comprises the following steps:

[0008] In the first step, asphalt and a deep eutectic solvent are mixed at a mass ratio of 1:5 to 60, and slag is removed to obtain a mixed solution;

[0009] The second step is to place the mixed solution in an oxidation furnace and heat it from room temperature to 180-350°C at an oxidation heating rate of 20-100°C / h under different atmosphere conditions, and then cool it to room temperature to obtain the oxidized material.

[0010] In the third step, the oxidized material is placed in a microwave experimental furnace, maintained in an inert atmosphere, and rapidly heated and carbonized at a power of 500~1200W. The heating process takes 1~10 minutes, and the carbonization temperature is controlled between 700~1200℃. The carbonization constant temperature time is set to 1~30 minutes, and then cooled to room temperature to obtain microwave-assisted activation-free asphalt-based porous carbon.

[0011] Furthermore, the asphalt in the first step includes any one of petroleum asphalt, coal asphalt, natural asphalt, oil residue asphalt, and biomass tar.

[0012] Furthermore, the deep eutectic solvent in the first step includes a hydrogen bond acceptor and a hydrogen bond donor; the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:(1~10).

[0013] The hydrogen bond acceptor is choline chloride, and the hydrogen bond donor includes any one of ethylene glycol, hydroquinone, urea, glycerol, phenol, glycerol and urea.

[0014] Furthermore, the mass ratio of asphalt to deep eutectic solvent is 1:10~40.

[0015] Furthermore, the atmosphere conditions in the second step include any one of air and oxygen.

[0016] Furthermore, in the second step, the oxidation heating rate is 30-80°C / h, and the heating temperature is 200-300°C.

[0017] Furthermore, the inert atmosphere in the third step includes any one of nitrogen and argon.

[0018] Furthermore, the power in the third step is 600~1000W.

[0019] Furthermore, the carbonization temperature in the third step is 800-1100°C.

[0020] Furthermore, the carbonization constant temperature time in the third step is 5 to 20 minutes.

[0021] The beneficial effects of the present invention are as follows:

[0022] 1. The deep eutectic solvent used in the present invention has the advantages of low melting point, good environmental performance, high solubility, adjustability, excellent thermal stability and recyclability.

[0023] 2. Due to the polar bonds in the deep eutectic solvent, microwave heating rapidly heats the asphalt, promoting the volatilization of light components and further promoting the formation of pores. This process not only effectively avoids the problems associated with traditional pore structure control but also simplifies the complex activation steps required in traditional methods.

[0024] 3. The microwave-assisted activation-free method adopted in the present invention effectively optimizes the pore structure and specific surface area of ​​asphalt without the use of an activator. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is an SEM image of the pitch-based porous carbon prepared in Example 1 of the present invention.

[0026] Figure 2 This is an SEM image of the pitch-based porous carbon prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, specific embodiments of the present invention are described in detail, but are not limited thereto. Unless otherwise specified, the raw materials used in the examples are all common commercial products; unless otherwise specified, the methods used are all commonly used methods in the art.

[0028] Example 1

[0029] A method for preparing pitch-based porous carbon by microwave-assisted activation-free method comprises the following steps:

[0030] In the first step, biomass tar and a low eutectic solvent (molar ratio of choline chloride to glycerol = 1:5) are mixed in a mass ratio of 1:25 and the residue is removed; in the second step, the mixed solution is placed in an oxidation furnace, and under air atmosphere conditions, the oxidation heating rate is 80°C / h, from room temperature to 300°C, and then the material is discharged when it is cooled to room temperature to obtain the oxidized material; in the third step, the oxidized material is placed in a microwave experimental furnace, maintaining an inert atmosphere, and rapidly heated at a power of 1000W for carbonization. The heating process takes 8 minutes, the temperature is controlled at 1100°C, the constant temperature time is set to 20 minutes, and then it is cooled to room temperature to obtain microwave-assisted activation-free asphalt-based porous carbon.

[0031] Figure 1 This SEM image shows the pitch-based porous carbon prepared in Example 1. It reveals its unique porous structure. The material exhibits irregular pore shapes, rough pore walls, and uneven pore distribution. This structure significantly increases the material's specific surface area and porosity.

[0032] Comparative Example 1

[0033] In the first step, biomass tar and a low eutectic solvent (the molar ratio of choline chloride to glycerol = 1:5) are mixed in a mass ratio of 1:25 and the residue is removed; in the second step, the mixed solution is placed in an oxidation furnace, and in an air atmosphere, the oxidation heating rate is 80°C / h, and the mixture is heated from room temperature to 300°C, and then the mixture is cooled to room temperature and discharged to obtain the oxidized material; in the third step, the oxidized material is placed in a tubular furnace for steam activation at a rate of 3°C / min. The heating process takes 357 minutes, the temperature is controlled at 1100°C, the constant temperature time is set to 20 minutes, and then the mixture is cooled to room temperature to obtain steam-activated asphalt-based porous carbon.

[0034] Figure 2 This is an SEM image of the pitch-based porous carbon prepared in Comparative Example 1. It shows the microstructural characteristics of dense particle distribution, smooth surface and few holes.

[0035] Example 2

[0036] A method for preparing pitch-based porous carbon by microwave-assisted activation-free method comprises the following steps:

[0037] In the first step, coal tar and a low eutectic solvent (the molar ratio of choline chloride to ethylene glycol = 1:2) are mixed in a mass ratio of 1:40 for slag removal; in the second step, the mixed solution is placed in an oxidation furnace, and under air atmosphere conditions, the oxidation heating rate is 30°C / h, from room temperature to 300°C, and then the material is discharged when it is cooled to room temperature to obtain the oxidized material; in the third step, the oxidized material is placed in a microwave experimental furnace, maintaining an inert atmosphere, and rapidly heated at a power of 950W for carbonization. The heating process takes 6 minutes, the temperature is controlled at 900°C, the constant temperature time is set to 15 minutes, and then it is cooled to room temperature to obtain microwave-assisted activation-free asphalt-based porous carbon.

[0038] Example 3

[0039] A method for preparing pitch-based porous carbon by microwave-assisted activation-free method comprises the following steps:

[0040] In the first step, petroleum asphalt and a low eutectic solvent (the molar ratio of choline chloride to ethylene glycol = 1:5) are mixed in a mass ratio of 1:20 and the residue is removed; in the second step, the mixed solution is placed in an oxidation furnace, and under air atmosphere conditions, the oxidation heating rate is 30°C / h, and the material is discharged when it is cooled to room temperature to obtain the oxidized material; in the third step, the oxidized material is placed in a microwave experimental furnace, maintaining an inert atmosphere, and rapidly heated at a power of 600W for carbonization. The heating process takes 10 minutes, the temperature is controlled at 900°C, the constant temperature time is set to 15 minutes, and then it is cooled to room temperature to obtain microwave-assisted activation-free asphalt-based porous carbon.

[0041] Example 4

[0042] A method for preparing pitch-based porous carbon by microwave-assisted activation-free method comprises the following steps:

[0043] In the first step, the oil residue asphalt and the low eutectic solvent (the molar ratio of choline chloride to hydroquinone = 1:3) are mixed in a mass ratio of 1:30 to remove the residue; in the second step, the mixed solution is placed in an oxidation furnace, and under air atmosphere conditions, the oxidation heating rate is 45°C / h, and the material is discharged from room temperature to obtain the oxidized material; in the third step, the oxidized material is placed in a microwave experimental furnace, maintaining an inert atmosphere, and rapidly heated at a power of 700W for carbonization. The heating process takes 4 minutes, the temperature is controlled at 900°C, the constant temperature time is set to 5 minutes, and then it is cooled to room temperature to obtain microwave-assisted activation-free asphalt-based porous carbon.

[0044] Example 5

[0045] A method for preparing pitch-based porous carbon by microwave-assisted activation-free method comprises the following steps:

[0046] In the first step, petroleum asphalt and a low eutectic solvent (the molar ratio of choline chloride to urea = 1:2) are mixed in a mass ratio of 1:15 and the residue is removed; in the second step, the mixed solution is placed in an oxidation furnace, and under air atmosphere conditions, the oxidation heating rate is 50°C / h, and the material is discharged from room temperature to obtain the oxidized material; in the third step, the oxidized material is placed in a microwave experimental furnace, maintaining an inert atmosphere, and rapidly heated at a power of 800W for carbonization. The heating process takes 8 minutes, the temperature is controlled at 1000°C, the constant temperature time is set to 8 minutes, and then it is cooled to room temperature to obtain microwave-assisted activation-free asphalt-based porous carbon.

[0047] Example 6

[0048] A method for preparing pitch-based porous carbon by microwave-assisted activation-free method comprises the following steps:

[0049] In the first step, natural asphalt and a low eutectic solvent (the molar ratio of choline chloride to glycerol = 1:8) are mixed in a mass ratio of 1:30 and the residue is removed; in the second step, the mixed solution is placed in an oxidation furnace, and under air atmosphere conditions, the oxidation heating rate is 70°C / h, from room temperature to 220°C, and then the material is discharged to room temperature to obtain the oxidized material; in the third step, the oxidized material is placed in a microwave experimental furnace, maintaining an inert atmosphere, and rapidly heated at a power of 750W for carbonization. The heating process takes 10 minutes, the temperature is controlled at 900°C, the constant temperature time is set to 8 minutes, and then it is cooled to room temperature to obtain microwave-assisted activation-free asphalt-based porous carbon.

[0050] Example 7

[0051] A method for preparing pitch-based porous carbon by microwave-assisted activation-free method comprises the following steps:

[0052] In the first step, coal tar and a low eutectic solvent (the molar ratio of choline chloride to urea = 1:6) are mixed in a mass ratio of 1:10 and the slag is removed; in the second step, the mixed solution is placed in an oxidation furnace, and under air atmosphere conditions, the oxidation heating rate is 50°C / h, and the material is discharged from room temperature to obtain the oxidized material; in the third step, the oxidized material is placed in a microwave experimental furnace, maintaining an inert atmosphere, and rapidly heated at a power of 660W for carbonization. The heating process takes 4 minutes, the temperature is controlled at 850°C, the constant temperature time is set to 6 minutes, and then it is cooled to room temperature to obtain microwave-assisted activation-free asphalt-based porous carbon.

[0053] Example 8

[0054] A method for preparing pitch-based porous carbon by microwave-assisted activation-free method comprises the following steps:

[0055] In the first step, the oil residue asphalt and the low eutectic solvent (the molar ratio of choline chloride to urea = 1:5) are mixed in a mass ratio of 1:30 for deslagging treatment; in the second step, the mixed solution is placed in an oxidation furnace, and under air atmosphere conditions, the oxidation heating rate is 60°C / h, and the material is discharged from room temperature to obtain the oxidized material; in the third step, the oxidized material is placed in a microwave experimental furnace, maintaining an inert atmosphere, and rapidly heated at a power of 700W for carbonization. The heating process takes 8 minutes, the temperature is controlled at 960°C, the constant temperature time is set to 25 minutes, and then it is cooled to room temperature to obtain microwave-assisted activation-free asphalt-based porous carbon.

[0056] Example 9

[0057] A method for preparing pitch-based porous carbon by microwave-assisted activation-free method comprises the following steps:

[0058] In the first step, biomass tar and a low eutectic solvent (the molar ratio of choline chloride to phenol = 1:2) are mixed in a mass ratio of 1:30 and the residue is removed; in the second step, the mixed solution is placed in an oxidation furnace, and under air atmosphere conditions, the oxidation heating rate is 40°C / h, from room temperature to 280°C, and then the material is discharged to obtain the oxidized material; in the third step, the oxidized material is placed in a microwave experimental furnace, maintaining an inert atmosphere, and rapidly heated at a power of 650W for carbonization. The heating process takes 6 minutes, the temperature is controlled at 750°C, the constant temperature time is set to 15 minutes, and then it is cooled to room temperature to obtain microwave-assisted activation-free asphalt-based porous carbon.

[0059] Example 10

[0060] A method for preparing pitch-based porous carbon by microwave-assisted activation-free method comprises the following steps:

[0061] In the first step, natural asphalt and a low eutectic solvent (the molar ratio of choline chloride to glycerol = 1:3) are mixed in a mass ratio of 1:25 for slag removal; in the second step, the mixed solution is placed in an oxidation furnace, and under air atmosphere conditions, the oxidation heating rate is 40°C / h, from room temperature to 260°C, and then the material is discharged when it is cooled to room temperature to obtain the oxidized material; in the third step, the oxidized material is placed in a microwave experimental furnace, maintaining an inert atmosphere, and rapidly heated at a power of 1100W for carbonization. The heating process takes 10 minutes, the temperature is controlled at 1000°C, the constant temperature time is set to 10 minutes, and then it is cooled to room temperature to obtain microwave-assisted activation-free asphalt-based porous carbon.

[0062] Table 1 Specific surface area and pore volume of pitch porous carbon prepared in Examples 1-10

[0063]

[0064] According to the data in Table 1, although the pitch-based porous carbon prepared in Example 1 has a slightly lower specific surface area than the similar material obtained by steam activation in Comparative Example 1, the pore volumes of the two are comparable. A significant advantage of this method is that it does not require the use of an activator, making the operation process simpler and faster. In addition, this method not only successfully avoids the problems that may be encountered in traditional pore structure regulation processes, but also significantly simplifies the complex activation steps in traditional processes. At the same time, this method also performs well in terms of energy conservation, emission reduction, and energy consumption reduction, with significant environmental and economic benefits.

[0065] The technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. The above embodiments only express several implementation methods of the present application. The description is relatively specific and detailed, but it cannot be understood as a limitation on the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several variations and improvements can be made, which all fall within the scope of protection of the present application. Therefore, the scope of protection of the patent in this application shall be based on the attached claims.

Claims

1. A method for preparing pitch-based porous carbon by microwave-assisted activation-free method, characterized in that: The steps include: In the first step, asphalt and a deep eutectic solvent are mixed at a mass ratio of 1:5 to 60, and slag is removed to obtain a mixed solution; The deep eutectic solvent comprises a hydrogen bond acceptor and a hydrogen bond donor; the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:(1-10); The hydrogen bond acceptor is choline chloride, and the hydrogen bond donor includes any one of ethylene glycol, hydroquinone, glycerol, phenol, glycerol and urea; The second step is to place the mixed solution in an oxidation furnace and heat it from room temperature to 180-350°C at an oxidation heating rate of 20-100°C / h under different atmosphere conditions, and then cool it to room temperature to obtain the oxidized material. In the third step, the oxidized material is placed in a microwave experimental furnace, maintained in an inert atmosphere, and rapidly heated and carbonized at a power of 500~1200W. The heating process takes 1~10 minutes, and the carbonization temperature is controlled between 700~1200℃. The carbonization constant temperature time is set to 1~30 minutes, and then cooled to room temperature to obtain microwave-assisted activation-free asphalt-based porous carbon.

2. The method for preparing pitch-based porous carbon by microwave-assisted activation-free method according to claim 1, characterized in that: The asphalt in the first step includes any one of petroleum asphalt, coal asphalt, natural asphalt, oil residue asphalt, and biomass tar.

3. The method for preparing pitch-based porous carbon by microwave-assisted activation-free method according to claim 1, characterized in that: The mass ratio of asphalt to deep eutectic solvent is 1:10~40.

4. The method for preparing pitch-based porous carbon by microwave-assisted activation-free method according to claim 1, characterized in that: The atmosphere conditions in the second step include any one of air and oxygen.

5. The method for preparing pitch-based porous carbon by microwave-assisted activation-free method according to claim 1, characterized in that: The oxidation heating rate in the second step is 30-80°C / h, and the heating temperature is 200-300°C.

6. The method for preparing pitch-based porous carbon by microwave-assisted activation-free method according to claim 1, characterized in that: The inert atmosphere in the third step includes any one of nitrogen and argon.

7. The method for preparing pitch-based porous carbon by microwave-assisted activation-free method according to claim 1, characterized in that: The power described in the third step is 600~1000W.

8. The method for preparing pitch-based porous carbon by microwave-assisted activation-free method according to claim 1, characterized in that: The carbonization temperature in the third step is 800-1100°C.

9. The method for preparing pitch-based porous carbon by microwave-assisted activation-free method according to claim 1, characterized in that: The carbonization constant temperature time in the third step is 5 to 20 minutes.

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