Carbon material with ultrahigh specific surface area as well as preparation method and application thereof

Abstract

The invention relates to the technical field of preparation of porous carbon materials, in particular to a carbon material with an ultrahigh specific surface area and a preparation method and application thereof, and the preparation method comprises the following steps: ball-milling and mixing a carbon precursor and a chemical activator to obtain a homogeneous mixture; synchronously carbonizing and activating the homogeneous mixture to obtain a carbonized compound; washing and drying the carbonized compound to obtain a carbon material with an ultrahigh specific surface area; the carbon precursor is waste phenolic resin. The waste phenolic resin is efficiently converted into the high-specific-surface-area porous carbon material (super activated carbon) through ball-milling-assisted homogenization and a synchronous carbonization / activation process, and the method has remarkable advantages in the aspects of environmental protection, process efficiency, material performance, application value and the like, not only solves the problem of thermosetting resin recovery, but also improves the recovery efficiency of the thermosetting resin. And the waste resin is converted into a high-added-value carbon material, so that the development of circular economy is promoted, and the dual-carbon strategic target is met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of porous carbon material preparation, and in particular to a carbon material with super-high specific surface area and a preparation method and application thereof. BACKGROUND

[0002] Porous carbon materials have a wide range of applications in catalysis, gas adsorption and separation, energy storage and environmental management due to their high specific surface area, tunable pore structure and excellent chemical stability. In particular, super activated carbon with a specific surface area of >2000 m 2 / g can not only be used as an electrode material for supercapacitors to provide high power density and fast charging and discharging capabilities, but also as a hydrogen storage medium to exhibit low cost and high capacity in fuel cells, and can be used for VOCs adsorption, heavy metal removal and CO2 capture, with high efficiency and renewable characteristics.

[0003] Currently, the preparation of porous carbon materials mainly relies on physical activation (such as CO2, steam activation) or chemical activation (such as KOH, ZnCl2 activation). However, traditional methods have problems such as high raw material cost, complex process and high energy consumption, which limit their large-scale application. Therefore, developing a low-cost, high-efficiency and sustainable preparation process has become a research hotspot.

[0004] Phenolic resin (PF) is a thermosetting polymer widely used in composite materials, adhesives, coatings, electronic packaging and refractory materials, etc. Its cross-linked structure can be converted into a high-carbon-content porous carbon material at high temperatures, which has the following advantages: high carbon yield (>50%), suitable for preparing high specific surface area carbon materials; tunable molecular structure, which can affect the pore distribution of the final carbon material through the curing process; wide sources, including industrial waste (such as waste circuit boards, automobile parts, electronic components, etc.).

[0005] However, the recovery of waste phenolic resin faces severe challenges: for example, thermosetting resins cannot be reprocessed by melting or dissolution, and traditional disposal methods (landfilling, incineration) result in resource waste and environmental pollution; existing carbonization and activation processes are mostly aimed at pure resins or soluble oligomers (such as US8492307B2), which cannot directly process solid waste phenolic resin, and the process is complex (requires dissolution, polymerization, drying, etc.). Conventional solid-state mixing methods (such as CN1646423) are difficult to achieve high uniformity activation, resulting in uneven pore distribution and affecting hydrogen storage or capacitance performance.

[0006] Therefore, it is urgent to develop an efficient, low-cost and green sustainable waste phenolic resin upgrading and reconstruction technology. SUMMARY

[0007] The application aims to provide a preparation method of carbon material with super high specific surface area, which can efficiently convert waste phenolic resin into high specific surface area porous carbon material through ball milling assisted homogenization and synchronous carbonization / activation process.

[0008] In a first aspect, the application provides a preparation method of carbon material with super high specific surface area, comprising the following steps:

[0009] S1, mixing a carbon precursor with a chemical activator by ball milling to obtain a homogeneous mixture;

[0010] S2, synchronously performing carbonization and activation treatment on the homogeneous mixture to obtain a carbonized composite;

[0011] S2, washing and drying the carbonized composite to obtain carbon material with super high specific surface area;

[0012] The carbon precursor is waste phenolic resin.

[0013] The application can efficiently convert waste phenolic resin into high specific surface area porous carbon material (super active carbon) through ball milling assisted homogenization and synchronous carbonization / activation process. Research shows that the specific surface area of the carbon material prepared by the application can reach 3400 m 2 / g, which is significantly higher than that of commercial active carbon (800-1500 m 2 / g), the mesopore ratio can be adjusted to 40%-60%, which is much better than that of physical activation method, and by optimizing the process parameters, super active carbon suitable for different applications can be obtained.

[0014] As preferred in the technical solution, the waste phenolic resin includes any one of monohydroxy phenolic resin, polyhydroxy phenolic resin, substituted base modified phenolic resin and heteroatom doped phenolic resin.

[0015] Among them, the polyhydroxy phenolic resin includes resorcinol-formaldehyde resin and m-benzotriol-formaldehyde resin, the resorcinol-formaldehyde resin has higher reactivity and crosslinking density than phenol-formaldehyde resin, so that higher carbon yield can be obtained, and more abundant microporous structure can be formed after activation. The substituted base modified phenolic resin includes cardanol-formaldehyde resin and bisphenol A-formaldehyde resin, the pyrolysis of the fatty chain in the cardanol-formaldehyde resin can produce additional pores, which is suitable for preparing mesoporous rich active carbon. The heteroatom doped phenolic resin includes nitrogen-containing phenolic resin and boron-containing phenolic resin, wherein in-situ nitrogen doping can enhance the electrochemical performance of the carbon material, and then be applied to the field of supercapacitors.

[0016] For the different structures of waste phenolic resin, high-efficiency conversion can be realized by ball milling and adjustment of carbonization activation parameters. For example, for high-crosslinking resins (such as m-benzene triol resin), low-temperature ball milling + grinding aid (liquid nitrogen or ethanol) can be used to enhance the crushing effect; for resins containing fatty chains (cashew phenol), the amount of KOH can be reduced to avoid excessive corrosion; for heteroatom resins (such as nitrogen / boron), gradient pyrolysis can be designed to retain the doping elements.

[0017] As a preferred embodiment of the present application, the chemical activator includes any one of potassium hydroxide, sodium hydroxide, potassium carbonate and sodium carbonate, and is preferably potassium hydroxide.

[0018] As a preferred embodiment of the present application, the homogeneous mixing of waste phenolic resin and chemical activator helps to form a porous carbon material with uniform pore size distribution and high specific surface area. The waste phenolic resin polymer and the chemical activator can be fully mixed through the ball milling process. Specifically, the ball milling time is controlled to be 15-120 min.

[0019] To further realize the nanoscale uniform mixing of waste phenolic resin and chemical activator, the present application adopts a two-step ball milling method, i.e., first coarsely grinding the waste resin to 100-500 μm, then adding the chemical activator to finely grind it to a particle size of <50 μm, while introducing ethanol as a grinding aid to improve the mixing efficiency and avoid local overheating.

[0020] As a preferred embodiment of the present application, the mass ratio of the chemical activator to the waste phenolic resin is (0.5-6):1, which ensures that the material has both microporous (<2 nm) and mesoporous (2-50 nm) structures, and the volume fraction of macropores (>50 nm) approaches 0%. In addition, studies have shown that when the mass ratio of carbon precursor to activator is low, a microporous structure with uniform pore size distribution will be formed in the carbonized composite; as the content of activator increases, mesoporous structures gradually form in the material, and the final porous carbon will change from microporous dominant to mesoporous dominant.

[0021] As a preferred embodiment of the present application, the homogeneous mixture is heated to 500-900℃ and kept for 0.5-8h during carbonization and activation treatment, which simultaneously realizes polymer carbonization and chemical pore formation.

[0022] To further balance the pore structure and yield, the present application uses a gradient temperature program to regulate the carbonization and activation process. First, slowly heat to 300-500℃ at a heating rate of 2-5℃ to fully crosslink the resin and avoid pore collapse, and then quickly heat to 700-900℃ at a heating rate of 10-20℃ to generate microporous and mesoporous hierarchical pores through the cooperation of nitrogen and chemical activator vapor.

[0023] As the technical scheme is preferably, in the carbonization and activation treatment, the present application does not make strict limitation to the atmosphere for carbonization and activation, nitrogen / argon protection can be selected, or it can be carried out under air atmosphere.

[0024] As the technical scheme is preferably, in the washing, after multiple times of washing with dilute hydrochloric acid, water washing is adopted to completely remove the residual activator and impurities.

[0025] As the technical scheme is preferably, in the drying, the carbonized compound is placed in an oven at 120-150 DEG C for drying overnight.

[0026] Therefore, by adjusting the ball milling time, the proportion of activator, the carbonization temperature and time and other parameters, the target product with specific surface area of 1600-3400 m 2 / g (determined by BET method) can be obtained.

[0027] In the second aspect, the present application also discloses the carbon material with ultra-high specific surface area prepared by the preparation method, the specific surface area of the carbon material is 1500-3400 m 2 / g, the carbon material simultaneously has microporous and mesoporous structures, and the proportion of macropore volume tends to be close to 0%, and should also belong to the protection scope of the present application.

[0028] In the third aspect, the present application also discloses the application of the carbon material with ultra-high specific surface area in supercapacitor electrode material, hydrogen storage medium and environmental adsorption material, and is particularly suitable for hydrogen energy storage medium, catalyst carrier, adsorbent or electrode material, and should also belong to the protection scope of the present application.

[0029] The preparation method of the carbon material with ultra-high specific surface area has at least the following beneficial effects:

[0030] 1. The traditional waste phenolic resin (such as circuit board, brake pad, electronic packaging waste) cannot be recycled by melting or dissolution, and incineration or landfill will cause dioxin emission and soil pollution. The present application directly processes solid waste without dissolution or complex pretreatment, and provides a green upgrading and reconstruction way, which not only solves the problem of recycling of thermosetting resin, but also converts waste phenolic resin into high value-added carbon material, and reduces resource waste.

[0031] 2. Compared with the solution method which needs multiple steps of dissolution, polymerization and drying, the present application simplifies the process and reduces energy consumption through ball milling solid-state mixing and synchronous carbonization / activation process.

[0032] 3. The carbon material prepared by the present application has a specific surface area of 3400 m 2 / g, which is significantly higher than that of commercial activated carbon (800-1500 m 2The mesoporous proportion of the super activated carbon can be adjusted to 40-60%, which is much better than the physical activation method, and by optimizing the process parameters, the super activated carbon suitable for different applications can be obtained.

[0033] Therefore, the application converts the waste phenolic resin into high specific surface area porous carbon material (super activated carbon) by ball milling assisted homogenization and synchronous carbonization / activation process, which has significant advantages in environmental protection, process efficiency, material performance and application value. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed in the specific embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0035] Figure 1 Nitrogen adsorption isotherm of the porous activated carbon carbon material prepared by the application at 77K (ball milling for 1 hour, activation temperature 700℃);

[0036] Figure 2 Effect of the mass ratio of the chemical activator (KOH) to the carbon precursor (phenolic resin) on the BET specific surface area of the obtained porous carbon;

[0037] Figure 3 Effect of the mass ratio of the chemical activator (KOH) to the carbon precursor (phenolic resin) on the average pore size;

[0038] Figure 4 Effect of the mass ratio of the chemical activator (KOH) to the carbon precursor (phenolic resin) on the pore volume;

[0039] Figure 5 Effect of the activation time on the specific surface area of the obtained porous carbon material;

[0040] Figure 6 Effect of the activation temperature on the specific surface area of the obtained porous carbon material;

[0041] Figure 7 Effect of the ball milling time on the specific surface area of the obtained porous carbon material;

[0042] Figure 8 Hydrogen storage capacity of the porous carbon material at 77K temperature;

[0043] Figure 9 Relationship between the hydrogen excess adsorption amount and the specific surface area. DETAILED DESCRIPTION

[0044] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0045] It is also important to note that the terms used herein are not intended to limit the particular embodiments of the present application to the preferred embodiments described. Rather, the terms are used only to describe specific embodiments of the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0046] The technical solutions of the present application will be described clearly and completely below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0047] Embodiment 1

[0048] S1, a proper amount of potassium hydroxide was mixed with waste phenolic resin particles and ball milled, the ball milling time was 15-120 min, and a homogeneous mixture was prepared;

[0049] As shown in Table 1, a series of samples (sample numbers C-BM-1 to C-BM-25) were prepared using different experimental conditions.

[0050] S2, the mixture of potassium hydroxide and waste phenolic resin obtained after ball milling was carbonized / activated at high temperature (500-900°C) under an inert atmosphere, the activation time was 0.5-8 hours, and a carbonized composite was obtained;

[0051] S3, the carbonized composite was washed with dilute hydrochloric acid and deionized water for several times, and then dried in an oven at 150°C overnight, and a carbon material with super-high specific surface area was obtained.

[0052] Embodiment 2

[0053] S1, the waste phenolic resin was first coarsely ground to 100-500 μm, then the chemical activator was added according to the mass ratio of potassium hydroxide to waste phenolic resin particles of 4:1, and finely ground to a particle size of <50 μm, and a homogeneous mixture was prepared;

[0054] S2, the mixture of KOH and waste phenolic resin after ball milling was first slowly heated to 300°C at a heating rate of 2-5°C / min under inert atmosphere and kept for 1 h to remove water, then quickly heated to 700°C at a heating rate of 10-20°C / min and kept for 2 h to obtain carbonized composite;

[0055] S3, the carbonized composite was washed by dilute hydrochloric acid and deionized water for several times, and then dried in an oven at 150°C overnight to obtain carbon material with ultrahigh specific surface area (sample No. C-BM-26).

[0056] Test Example

[0057] The specific surface area was measured by 77K low temperature nitrogen adsorption instrument (Micromeritics ASAP 2010), and the low temperature hydrogen adsorption test was carried out at 77K by using high pressure adsorption instrument (PCTPro 2000, Hy-Energy Scientific Instruments).

[0058] Figure 1 The nitrogen adsorption isotherms of the porous carbons prepared by different chemical activator / waste phenolic resin ratios are shown, and the synthesis conditions and the specific surface area and pore volume data of the obtained porous carbons are listed in detail in Table 1.

[0059] Table 1 BET specific surface area and pore volume parameters of porous carbon materials under different preparation conditions

[0060]

[0061] From Table 1 and Figure 1 It can be seen that the porous carbon material prepared by the ball milling assisted chemical activation method has an extremely high specific surface area (for example, the highest can reach 3388m 2 / g). Studies have shown that this high specific surface area and uniform pore size distribution characteristics are due to the highly homogeneous mixing of the carbon precursor and the activator. And the optimal activation process parameter combination can be determined: when the mass ratio of KOH / waste phenolic resin is 4:1, the ball milling time is 60 minutes, and the activation temperature is 700°C for 4 hours, the porous super activated carbon material with a specific surface area close to 3400m 2 / g and a pore volume exceeding 2.0cm 3 / g can be obtained.

[0062] Figure 2 The effect of the mass ratio of chemical activator (KOH) to carbon precursor (waste phenolic resin) on the BET specific surface area of the obtained porous carbon is shown.

[0063] From Figure 2It can be seen that under activation conditions at 700℃, when the amount of KOH added increases from 0.5g to 4g: the specific surface area increases from 1600m² to... 2 / g continued to increase to 3400m 2 / g, when KOH is in excess (>4g), the specific surface area decreases slightly (see Figure 2 The reason may be that excessive etching caused the carbon skeleton to become thinner, and some of the pore structure collapsed.

[0064] Figure 3 and Figure 4 The effects of the mass ratio of chemical activator (KOH) to carbon precursor (waste phenolic resin) on average pore size and pore volume are shown.

[0065] Depend on Figures 3-4 It can be seen that under the conditions of ball milling time of 1 hour, activation temperature of 700℃, and activation time of 4 hours, as the ratio of KOH / waste phenolic resin increases, the average pore size of the obtained porous carbon material increases from 1.6 nm to 2.7 nm, and the volume ratio of mesopores (2-50 nm) increases from less than 10% to more than 70%, and the material changes from micropore-dominated to mesopore-dominated.

[0066] Figure 5 and Figure 6 The effects of activation time and activation temperature on the specific surface area of ​​the obtained porous carbon materials are shown respectively.

[0067] like Figures 5-6 As shown, to obtain the highest possible specific surface area, the optimal conditions are a carbonization temperature of 700℃ and an activation time of 4 hours (peak specific surface area 3388m²). 2 / g). Too low a carbonization temperature or too short an activation time will result in insufficient formation of the carbon skeleton and insufficient etching of the carbon skeleton by the chemical activator; while too high a temperature or too long an activation time may lead to excessive etching of the carbon skeleton by the chemical activator, causing partial collapse or sintering of the pores, thereby reducing the specific surface area and pore volume of the obtained porous carbon material.

[0068] Figure 7 The effect of ball milling time on the specific surface area of ​​the obtained porous carbon material.

[0069] Depend on Figure 7 It can be seen that when the ball milling time increases from 15 minutes to 60 minutes, the specific surface area of ​​the resulting product increases significantly (from 2200 m² / g). 2 / g increased to 2700m 2 When the ball milling time exceeds 60 minutes, the specific surface area decreases slightly. This indicates that 60 minutes of ball milling is sufficient to ensure a uniform mixture of potassium hydroxide and waste phenolic resin.

[0070] Experimental Example 2

[0071] The present invention further tested the adsorption capacity of the porous carbon material obtained in Example 1 for hydrogen at liquid nitrogen temperature, and the results are as follows: Figures 8-9 As shown.

[0072] Depend on Figures 8-9 It can be seen that the excess hydrogen adsorption capacity is closely related to the specific surface area. The carbon material obtained under the conditions of a potassium hydroxide to waste phenolic resin mass ratio of 4, a ball milling time of 1 h, a carbonization temperature of 700℃, and an activation time of 4 h (peak specific surface area 3388 m²) 2 The / g) has the highest hydrogen storage capacity, with a hydrogen storage capacity of up to 6.1wt% under conditions of 77K and 30 atm.

[0073] Furthermore, after testing the hydrogen storage capacity of some samples in Table 1, it was found that the specific surface area of ​​the obtained carbon material is linearly positively correlated with the hydrogen storage capacity.

[0074] Compare with Example 1

[0075] Referring to the method disclosed in US8492307 B2:

[0076] Oligomeric phenol-formaldehyde was synthesized by reacting 13 mmol phenol, 26 mmol formaldehyde and 1.3 mmol potassium hydroxide at 70 °C for about 1 hour.

[0077] While stirring, gradually add an appropriate amount of potassium hydroxide solution (5M) to the phenol-formaldehyde oligomer solution;

[0078] The oligomer-KOH solution was heated overnight in an oven at 160°C. During this heating process, the phenol-formaldehyde oligomer continued to crosslink and polymerize under the catalysis of potassium hydroxide, forming a thermosetting carbonizable polymer.

[0079] The polymer is carbonized / activated at high temperatures (approximately 500°C to 900°C) in an inert gas atmosphere;

[0080] The final carbon material was rinsed several times with dilute hydrochloric acid and deionized water, and then dried overnight in an oven at 150°C.

[0081] Although this method can prepare materials with a specific surface area of ​​1400 m² 2 / g and 3000m 2 The method yields carbon material per gram, but it requires solution mixing, polymerization, drying to form a solid, and then carbonization activation, making the process complex and costly. Furthermore, it cannot use solid phenolic resin, meaning it cannot treat waste phenolic resin. Most importantly, the large amount of chemical activator KOH introduced during mixing negatively impacts the polymerization process, preventing the formation of high-quality phenolic resin. Therefore, the specific surface area of ​​the final carbon material cannot reach the 3388 m² of this invention. 2 / g ultra-high specific surface area category.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not limited thereto; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for producing a carbon material having an ultrahigh specific surface area, characterized by, The method comprises the following steps: S1, mixing a carbon precursor with a chemical activator by ball milling to obtain a homogeneous mixture; S2, simultaneously performing carbonization and activation treatment on the homogeneous mixture to obtain a carbonized composite; S2, washing and drying the carbonized composite to obtain a carbon material with ultrahigh specific surface area; The carbon precursor is waste phenolic resin.

2. The production method according to claim 1, characterized by, The waste phenolic resin includes any one of monohydroxy phenolic resin, polyhydroxy phenolic resin, substituted phenolic resin and heteroatom doped phenolic resin.

3. The preparation method according to claim 1, characterized in that, The chemical activator includes any one of potassium hydroxide, sodium hydroxide, potassium carbonate and sodium carbonate.

4. The method of claim 1, wherein, The ball milling time is 15-120 min.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the chemical activator to the waste phenolic resin is (0.5-6):

1.

6. The method of claim 1, wherein, The carbonization and activation treatment is performed by heating the homogeneous mixture to 500-900 ℃ and keeping for 0.5-8 h.

7. The preparation method according to claim 1, characterized in that, The washing is performed by multiple washing with dilute hydrochloric acid and then water washing.

8. The method of claim 1, wherein, The drying is performed by placing the carbonized composite in an oven at 120-150 ℃ and drying overnight.

9. A carbon material having an ultrahigh specific surface area, characterized by, The carbon material prepared according to the preparation method of any one of claims 1-8 has a specific surface area of 1500-3400 m 2 / g, and simultaneously has micropore and mesopore structures and a macropore volume ratio close to 0%.

10. The carbon material with ultrahigh specific surface area according to claim 9 is applied in catalysis, gas purification, fuel cell / battery electrode and gas storage.

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