Microwave-assisted activation-free method for preparing asphalt-based porous carbon

Abstract

The invention aims to provide a microwave-assisted activation-free asphalt-based porous carbon preparation method, and belongs to the technical field of asphalt-based porous carbon preparation. Asphalt is dissolved in a deep eutectic solvent for the first time, and the mixture is treated through microwave heating. Due to the action of an extreme bond in the eutectic solvent, the asphalt can be rapidly heated by microwave heating, so that the volatilization of light components in the asphalt is promoted, and the formation of pores is further promoted. The process not only effectively avoids the problems in the traditional pore structure regulation, but also simplifies the complex activation step in the traditional method.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of asphalt-based porous carbon, and particularly relates to a method for preparing asphalt-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, with characteristics such as strong aromaticity, high carbon content, low ash content, and easy graphitization. It is an excellent raw material for preparing porous carbon and shows 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 generates pores by mixing a carbon precursor with an activator and activating it at high temperature. Commonly used activators include KOH, H3PO4, and ZnCl2, etc. Patent CN116730337A proposes a method for preparing coal tar pitch-based porous carbon by using double salt compounds (such as K2CO3 and Na2CO3) to assist potassium hydroxide. This method faces challenges such as high production cost, poor safety, and being unfavorable for large-scale industrial production. (2) Physical activation method. Patent CN117342554A discloses a coal tar pitch-based activated carbon and its preparation method. This method uses physical activation technology to introduce gases such as carbon dioxide, air, or water vapor at a temperature of 650-800 °C, and generates pores by their weak oxidation effect, thereby effectively preparing granular or powdered activated carbon. This method has lower requirements for equipment corrosion prevention, lower cost, and higher safety. However, this process has relatively strict temperature requirements and also results in higher energy consumption. (3) Hybrid activation method, that is, a 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, so it requires more complex process flow and equipment support, thereby increasing the operation difficulty and cost. Currently, there is no patent report on using activation-free technology to prepare asphalt-based porous carbon.

[0003] As a new heating method, microwave heating technology has received extensive attention due to its advantages such as fast heating speed, uniform temperature distribution, and high energy conversion efficiency. Under the action of a microwave electric field, polar molecules will continuously rotate, generate frictional force, and thus be converted into heat energy, resulting in an increase in the temperature of the substance. However, most asphalt molecules have weak polarity or are non-polar molecules and lack wave absorption characteristics, so they cannot be directly microwave-heated. Patent CN117965035A discloses a modified method for activating asphalt using microwave chemical effects, which is mainly applied to road asphalt. This method makes the asphaltene in asphalt evenly dispersed and its chemical properties become more active through the chemical effects induced by microwave heating, thereby reducing the viscosity, but this patent does not involve the field of porous carbon preparation.

[0004] Deep eutectic solvents are generally composed of hydrogen bond donors (such as urea, alcohol compounds, etc.) and hydrogen bond acceptors (such as choline chloride, salts, etc.). Their unique feature lies in their excellent solubility and relatively low melting point, enabling them to efficiently dissolve some substances that are usually difficult to dissolve. Patent CN112852471A introduces a method for extracting oil sand asphalt assisted by deep eutectic solvents, which can effectively achieve the clean separation of asphalt and significantly improve the extraction rate. Although there have been studies on using deep eutectic solvents to treat asphalt, there is currently no related technology to combine deep eutectic solvents with asphalt to prepare porous carbon. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing asphalt-based porous carbon by microwave-assisted activation-free, which has low cost and is environmentally friendly and pollution-free. The present invention first dissolves asphalt in a deep eutectic solvent, and the mixture is treated by microwave heating. Due to the presence of polar bonds in the deep eutectic solvent, it can cause the molecules therein to vibrate rapidly to generate heat, and the temperature is raised to 700°C - 1200°C within 1 - 10 minutes for high-temperature carbonization. At this time, the light components in the asphalt and the pyrolysis volatilization of DES generate gas to form pores. No activator is added throughout the process, and porous carbon can be prepared only by high-temperature carbonization.

[0006] The present invention adopts the following technical solutions: A method for preparing asphalt-based porous carbon by microwave-assisted activation-free, comprising the following steps: In the first step, asphalt and a deep eutectic solvent are mixed in a mass ratio of 1:5 - 60, and slag removal treatment is carried out to obtain a mixed solution; In the second step, the mixed solution is placed in an oxidation furnace, and under different atmosphere conditions, it is heated from room temperature to 180 - 350°C at an oxidation heating rate of 20 - 100°C / h, and then cooled to room temperature to discharge to obtain an oxidized material; In the third step, the oxidized material is placed in a microwave experimental furnace, maintaining an inert atmosphere, and rapidly heated for carbonization at a power of 500 - 1200W. The heating process takes 1 - 10 minutes, the carbonization temperature is controlled between 700 - 1200°C, 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.

[0007] Further, the asphalt in the first step includes any one of petroleum asphalt, coal asphalt, natural asphalt, oil residue asphalt, and biomass tar.

[0008] Further, 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).

[0009] Among them, the hydrogen bond acceptor is choline chloride, and the hydrogen bond donor includes any one of ethylene glycol, hydroquinone, urea, glycerol, phenol, glycerin, and urea.

[0010] Furthermore, the mass ratio of asphalt to the deep eutectic solvent is 1:10 - 40.

[0011] Furthermore, the atmosphere condition in the second step includes any one of air and oxygen.

[0012] Furthermore, the oxidation heating rate in the second step is 30 - 80 °C / h, and the heating temperature is 200 - 300 °C.

[0013] Furthermore, the inert atmosphere in the third step includes any one of nitrogen and argon.

[0014] Furthermore, the power in the third step is 600 - 1000 W.

[0015] Furthermore, the carbonization temperature in the third step is 800 - 1100 °C.

[0016] Furthermore, the carbonization constant temperature time in the third step is 5 - 20 min.

[0017] The beneficial effects of the present invention are as follows: 1. The deep eutectic solvent adopted in the present invention has the advantages of low melting point, good environmental protection performance, high solubility, adjustable property, excellent thermal stability, and recyclability.

[0018] 2. Due to the action of polar bonds in the deep eutectic solvent, microwave heating can rapidly raise the temperature of asphalt, thereby promoting the volatilization of light components in asphalt and further promoting the formation of pores. This process not only effectively avoids the problems in traditional pore structure regulation but also simplifies the complex activation steps in traditional methods.

[0019] 3. The microwave-assisted activation-free method adopted in the present invention effectively optimizes the pore structure and specific surface area of asphalt without an activator. Description of the Drawings

[0020] Figure 1 It is the SEM image of the asphalt-based porous carbon prepared in Example 1 of the present invention.

[0021] Figure 2 It is the SEM image of the asphalt-based porous carbon prepared in Comparative Example 1 of the present invention. Detailed Embodiments

[0022] To make the objectives, technical solutions and advantages of the present invention more clear and understandable, specific embodiments of the present invention are described in detail, but not limited thereto. Unless otherwise specified, the raw materials used in the embodiments are all ordinary commercially available products; the methods used are all common methods in the art unless otherwise specified.

[0023] Example 1 A method for microwave-assisted activation-free preparation of asphalt-based porous carbon, comprising the following steps: First step, mix biomass tar with a deep eutectic solvent (molar ratio of choline chloride to glycerol = 1:5) according to a mass ratio of 1:25, and perform slag removal treatment; second step, place the mixed solution in an oxidation furnace, under an air atmosphere condition, with an oxidation heating rate of 80 °C / h, heat from room temperature to 300 °C, and then cool to room temperature to obtain the oxidized material; third step, place the oxidized material in a microwave experimental furnace, maintain an inert atmosphere, and perform rapid heating carbonization at a power of 1000 W. The heating process takes 8 min, the temperature is controlled at 1100 °C, and the constant temperature time is set to 20 min, and then cool to room temperature to obtain microwave-assisted activation-free asphalt-based porous carbon.

[0024] Figure 1 SEM image of the asphalt-based porous carbon prepared in Example 1. It reveals its unique porous structure. The material has irregular pore shapes, rough pore walls, and uneven distribution of pores in the material. This structure significantly improves the specific surface area and porosity of the material.

[0025] Comparative Example 1 First step, mix biomass tar with a deep eutectic solvent (molar ratio of choline chloride to glycerol = 1:5) according to a mass ratio of 1:25, and perform slag removal treatment; second step, place the mixed solution in an oxidation furnace, under an air atmosphere condition, with an oxidation heating rate of 80 °C / h, heat from room temperature to 300 °C, and then cool to room temperature to obtain the oxidized material; third step, place the oxidized material in a tube furnace for steam activation, activate at 3 °C / min, the heating process takes 357 min, the temperature is controlled at 1100 °C, and the constant temperature time is set to 20 min, and then cool to room temperature to obtain steam-activated asphalt-based porous carbon.

[0026] Figure 2 SEM image of the asphalt-based porous carbon prepared in Comparative Example 1. It shows the microscopic structural characteristics of closely packed particles, flat surface and fewer pores.

[0027] Example 2 A method for microwave-assisted activation-free preparation of asphalt-based porous carbon, comprising the following steps: First step: Mix coal tar pitch with a deep eutectic solvent (molar ratio of choline chloride to ethylene glycol = 1:2) at a mass ratio of 1:40, and perform slag removal treatment; Second step: Place the mixed solution in an oxidation furnace, under an air atmosphere condition, with an oxidation heating rate of 30 °C / h, heat from room temperature to 300 °C, and then cool to room temperature and discharge to obtain the oxidized material; Third step: Place the oxidized material in a microwave experimental furnace, maintain an inert atmosphere, and rapidly heat and carbonize at a power of 950 W. The heating process takes 6 min, the temperature is controlled at 900 °C, the constant temperature time is set to 15 min, and then it is cooled to room temperature to obtain microwave-assisted activation-free asphalt-based porous carbon.

[0028] Example 3 A method for preparing asphalt-based porous carbon by microwave-assisted activation-free includes the following steps: First step: Mix petroleum asphalt with a deep eutectic solvent (molar ratio of choline chloride to ethylene glycol = 1:5) at a mass ratio of 1:20, and perform slag removal treatment; Second step: Place the mixed solution in an oxidation furnace, under an air atmosphere condition, with an oxidation heating rate of 30 °C / h, heat from room temperature to 300 °C, and then cool to room temperature and discharge to obtain the oxidized material; Third step: Place the oxidized material in a microwave experimental furnace, maintain an inert atmosphere, and rapidly heat and carbonize at a power of 600 W. The heating process takes 10 min, the temperature is controlled at 900 °C, the constant temperature time is set to 15 min, and then it is cooled to room temperature to obtain microwave-assisted activation-free asphalt-based porous carbon.

[0029] Example 4 A method for preparing asphalt-based porous carbon by microwave-assisted activation-free includes the following steps: First step: Mix oil residue asphalt with a deep eutectic solvent (molar ratio of choline chloride to hydroquinone = 1:3) at a mass ratio of 1:30, and perform slag removal treatment; Second step: Place the mixed solution in an oxidation furnace, under an air atmosphere condition, with an oxidation heating rate of 45 °C / h, heat from room temperature to 275 °C, and then cool to room temperature and discharge to obtain the oxidized material; Third step: Place the oxidized material in a microwave experimental furnace, maintain an inert atmosphere, and rapidly heat and carbonize at a power of 700 W. The heating process takes 4 min, the temperature is controlled at 900 °C, the constant temperature time is set to 5 min, and then it is cooled to room temperature to obtain microwave-assisted activation-free asphalt-based porous carbon.

[0030] Example 5 A method for preparing asphalt-based porous carbon by microwave-assisted activation-free includes the following steps: First step: Mix petroleum asphalt with a deep eutectic solvent (molar ratio of choline chloride to urea = 1:2) at a mass ratio of 1:15, and perform slag removal treatment; Second step: Place the mixed solution in an oxidation furnace, under an air atmosphere condition, with an oxidation heating rate of 50 °C / h, heat from room temperature to 220 °C, and then cool to room temperature to discharge the oxidized material; Third step: Place the oxidized material in a microwave experimental furnace, maintain an inert atmosphere, rapidly heat and carbonize at a power of 800 W. The heating process takes 8 min, the temperature is controlled at 1000 °C, the constant temperature time is set to 8 min, and then it is cooled to room temperature to obtain microwave-assisted activation-free asphalt-based porous carbon.

[0031] Example 6 A method for preparing asphalt-based porous carbon by microwave-assisted activation-free includes the following steps: First step: Mix natural asphalt with a deep eutectic solvent (molar ratio of choline chloride to glycerol = 1:8) at a mass ratio of 1:30, and perform slag removal treatment; Second step: Place the mixed solution in an oxidation furnace, under an air atmosphere condition, with an oxidation heating rate of 70 °C / h, heat from room temperature to 220 °C, and then cool to room temperature to discharge the oxidized material; Third step: Place the oxidized material in a microwave experimental furnace, maintain an inert atmosphere, rapidly heat and carbonize at a power of 750 W. The heating process takes 10 min, the temperature is controlled at 900 °C, the constant temperature time is set to 8 min, and then it is cooled to room temperature to obtain microwave-assisted activation-free asphalt-based porous carbon.

[0032] Example 7 A method for preparing asphalt-based porous carbon by microwave-assisted activation-free includes the following steps: First step: Mix coal tar pitch with a deep eutectic solvent (molar ratio of choline chloride to urea = 1:6) at a mass ratio of 1:10, and perform slag removal treatment; Second step: Place the mixed solution in an oxidation furnace, under an air atmosphere condition, with an oxidation heating rate of 50 °C / h, heat from room temperature to 300 °C, and then cool to room temperature to discharge the oxidized material; Third step: Place the oxidized material in a microwave experimental furnace, maintain an inert atmosphere, rapidly heat and carbonize at a power of 660 W. The heating process takes 4 min, the temperature is controlled at 850 °C, the constant temperature time is set to 6 min, and then it is cooled to room temperature to obtain microwave-assisted activation-free asphalt-based porous carbon.

[0033] Example 8 A method for preparing asphalt-based porous carbon by microwave-assisted activation-free includes the following steps: First step: Mix oil residue asphalt with a deep eutectic solvent (molar ratio of choline chloride to urea = 1:5) at a mass ratio of 1:30, and perform slag removal treatment; Second step: Place the mixed solution in an oxidation furnace, under air atmosphere conditions, with an oxidation heating rate of 60 °C / h, heat from room temperature to 280 °C, and then cool to room temperature to obtain the oxidized material; Third step: Place the oxidized material in a microwave experimental furnace, maintain an inert atmosphere, and rapidly heat and carbonize at a power of 700 W. The heating process takes 8 min, the temperature is controlled at 960 °C, and the constant temperature time is set to 25 min. Then cool to room temperature to obtain microwave-assisted activation-free asphalt-based porous carbon.

[0034] Example 9 A method for preparing asphalt-based porous carbon by microwave-assisted activation-free includes the following steps: First step: Mix biomass tar with a deep eutectic solvent (molar ratio of choline chloride to phenol = 1:2) at a mass ratio of 1:30, and perform slag removal treatment; Second step: Place the mixed solution in an oxidation furnace, under air atmosphere conditions, with an oxidation heating rate of 40 °C / h, heat from room temperature to 280 °C, and then cool to room temperature to obtain the oxidized material; Third step: Place the oxidized material in a microwave experimental furnace, maintain an inert atmosphere, and rapidly heat and carbonize at a power of 650 W. The heating process takes 6 min, the temperature is controlled at 750 °C, and the constant temperature time is set to 15 min. Then cool to room temperature to obtain microwave-assisted activation-free asphalt-based porous carbon.

[0035] Example 10 A method for preparing asphalt-based porous carbon by microwave-assisted activation-free includes the following steps: First step: Mix natural asphalt with a deep eutectic solvent (molar ratio of choline chloride to glycerol = 1:3) at a mass ratio of 1:25, and perform slag removal treatment; Second step: Place the mixed solution in an oxidation furnace, under air atmosphere conditions, with an oxidation heating rate of 40 °C / h, heat from room temperature to 260 °C, and then cool to room temperature to obtain the oxidized material; Third step: Place the oxidized material in a microwave experimental furnace, maintain an inert atmosphere, and rapidly heat and carbonize at a power of 1100 W. The heating process takes 10 min, the temperature is controlled at 1000 °C, and the constant temperature time is set to 10 min. Then cool to room temperature to obtain microwave-assisted activation-free asphalt-based porous carbon.

[0036] Table 1 Specific surface area and pore volume of asphalt porous carbon prepared in Examples 1 - 10 According to the data in Table 1, although the specific surface area of the asphalt-based porous carbon prepared in Example 1 is slightly lower than that of the similar material obtained by the steam activation method in Comparative Example 1, the pore volumes of the two are comparable. A significant advantage of this method is that no activator is required, making the operation process simpler and faster. In addition, this method not only successfully avoids the problems that may be encountered in the traditional pore structure regulation process, but also significantly simplifies the complex activation steps in the traditional process. At the same time, this method also performs excellently in energy conservation, emission reduction and energy consumption reduction, with significant environmental and economic benefits.

[0037] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, 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, it should be considered as the scope recorded in this specification. The above embodiments only represent several implementation manners of the present application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A method for preparing asphalt-based porous carbon by microwave-assisted activation-free, characterized in that: It includes the following steps: In the first step, asphalt and a deep eutectic solvent are mixed at a mass ratio of 1:5 - 60, and slag removal treatment is carried out to obtain a mixed solution; In the second step, the mixed solution is placed in an oxidation furnace. Under different atmosphere conditions, with an oxidation heating rate of 20 - 100 °C / h, it is heated from room temperature to 180 - 350 °C, and then cooled to room temperature to discharge, thus obtaining an oxidized material; In the third step, the oxidized material is placed in a microwave experimental furnace. Keeping an inert atmosphere, it is rapidly heated for carbonization at a power of 500 - 1200 W. The heating process takes 1 - 10 min, the carbonization temperature is controlled between 700 - 1200 °C, the carbonization constant temperature time is set to 1 - 30 min, and then it is cooled to room temperature, and microwave-assisted activation-free asphalt-based porous carbon can be obtained.

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

3. A method for microwave-assisted activation-free preparation of asphalt-based porous carbon according to claim 1, characterized in that: The deep eutectic solvent described 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); Among them, the hydrogen bond acceptor is choline chloride, and the hydrogen bond donor includes any one of ethylene glycol, hydroquinone, urea, glycerol, phenol, glycerin, and urea.

4. A method for microwave-assisted preparation of asphalt-based porous carbon without activation according to claim 1, characterized in that: The mass ratio of asphalt to the deep eutectic solvent is 1:10 - 40.

5. A method for preparing asphalt-based porous carbon by microwave-assisted activation-free, characterized in that: The atmosphere conditions described in the second step include any one of air and oxygen.

6. The method for preparing an asphalt-based porous carbon by microwave-assisted non-activation according to claim 1, wherein: The oxidation heating rate described in the second step is 30 - 80 °C / h, and the heating temperature is 200 - 300 °C.

7. A method for microwave-assisted preparation of asphalt-based porous carbon without activation according to claim 1, characterized in that: The inert atmosphere described in the third step includes any one of nitrogen and argon.

8. A method for preparing asphalt-based porous carbon by microwave-assisted non-activation according to claim 1, characterized in that: The power described in the third step is 600 - 1000 W.

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

10. A method for microwave-assisted activation-free preparation of asphalt-based porous carbon according to claim 1, characterized in that: The carbonization constant temperature time described in the third step is 5 - 20 min.

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