KR102512058B1 - Manufacturing method of porous carbon having ultra-high strength and macro pore size - Google Patents

Abstract

The present invention relates to a method for producing porous carbon having high-strength macropores, and more particularly, to preparing a mixture using a binder including a spherical phenol resin, furpril alcohol, and a catalyst; Preparing a molded body using the mixture; Curing the molded body; and carbonizing the cured molded body.

Description

Manufacturing method of porous carbon having ultra-high strength and macro pore size}

The present invention relates to a method for producing porous carbon having macro pores of high strength, and more particularly, to a method for producing high strength and high strength porous carbon by a simple powder process using spherical phenolic resin particles as a skeleton without using a template or a foaming agent. Provided is porous carbon having macropores and at the same time having a pore size easily controllable.

Porous carbon such as carbon foam is lightweight, has high heat resistance, chemical stability, and can control thermal and electrical properties, so it is used in various fields such as catalyst supports, filters, refractory materials, electrodes, and energy storage devices. The outstanding properties of porous carbon are based on its characteristic porosity characteristics of up to 95% and a wide range of pore sizes from micropores (diameter < 2 nm) to macropores (diameter > 50 nm). Therefore, it is important to develop a manufacturing method that can easily control the pore structure using simple and appropriate raw materials and processes for the utilization of carpon foam.

The raw material used in the manufacture of carbon foam has been developed by Ford in 1964 by carbonizing phenol-formaldehyde, followed by phenolic resin, polyurethane, and petroleum pitch. Various carbon precursors such as pitch and biomass have been studied. In general, these carbon precursors can be classified into two groups: hydrocarbons and polymer derivatives.

Polymers generally have a lower residual carbon ratio than aromatic hydrocarbons because they contain elements such as chlorine, oxygen, or nitrogen in addition to hydrogen and carbon. However, polymers have the advantage of being easy to process because they do not require pretreatment before use. The carbon yield of various carbon foam raw materials reported by Rietz et al. was high in the order of coal tar pitch (52.5%), phenol-formaldehyde (52.1%), liquid furpril polymer (49.1%), and epoxy resin (10.1%). %), and urethane resin (8.2%) had relatively low residual carbon. Polymers such as phenol-formaldehyde are preferred as raw materials for porous carbon because they are economical due to their high residual carbon ratio.

The most important factor in adjusting the pore structure of porous carbon is the manufacturing method. Representative methods for producing porous carbon include carbonization of a porous polymer through heat treatment, a method using a mold such as silica, or a method including a chemical reaction. However, normal carbonization of polymers results in large deformation of the pore structure, and the template method requires an additional step to remove the template. In addition, the method through chemical reaction is very difficult to control the pore structure.

The method of using the foaming agent is a method of forming a porous body by blowing a gas of several tens of atmospheres while heating the carbon raw material such as pitch to a softening temperature or higher in an airtight container such as an autoclave. There are limitations limited to carbon sources with In addition, there are disadvantages in that manufacturing processes such as airtight containers and high-pressure gas injection are complicated and compressive strength is inevitably weak. In addition, the method using a template such as polyurethane foam has the advantage of being able to control the open pore structure, but complicated processes and manufacturing costs such as impregnating a template such as polyurethane foam with phenol or furpril resin to cure and carbonize There is a problem with increasing

On the other hand, porous carbon such as carbon foam is inferior in mechanical properties such as compressive strength due to its sponge-like pore structure, which limits its use. Therefore, extensive research has been conducted on improving the mechanical properties of porous carbon by reinforcing it with fibers or powder. Wang et al. produced a carbon foam with a compressive strength of 12.8 MPa at an apparent density of 0.71 g/cm ³ , and Li et al. produced a carbon foam with a mixture of mesophase pitch and mesocarbon microbeads to achieve an apparent density of 0.78 g/cm ³ . and reported that a compressive strength of 23.7 MPa was obtained. In the case of carbon foam without mesocarbon microbeads, an apparent density of 0.82 g/cm ³ and a compressive strength of 11.0 MPa were reported, and it was reported that crack suppression and deformation by the microbeads increased the compressive strength.

As such, various studies have been conducted to control the pore structure and improve the strength.

[8] X. Wang, J. Zhong, Y. Wang, M. Yu, A study of the properties of carbon foam reinforced by clay, Carbon 44(8) (2006) 1560-1564. [14] C.H. Riesz, S. Susman, Synthetic binders for carbon and graphite, Carbon, Pergamon, 1960, pp. 609-623. [23] S. Li, Y. Song, Y. Song, J. Shi, L. Liu, X. Wei et al., Carbon foams with high compressive strength derived from mixtures of mesocarbon microbeads and mesophase pitch, Carbon 45(10 ) (2007) 2092-2097. [24] X. Wang, R. Luo, Y. Ni, R. Zhang, S. Wang, Properties of chopped carbon fiber reinforced carbon foam composites, Mater. Lett. 63(1) (2009) 25-27. [35] S. Zhang, M. Liu, L. Gan, F. Wu, Z. Xu, Z. Hao et al., Synthesis of carbon foams with a high compressive strength from arylacetylene, New Carbon Mater. 25(1) (2010) 9-14. [36] D. Baran, M.F. Yardim, H. Atakul, E. Ekinci, Synthesis of carbon foam with high compressive strength from an asphaltene pitch, Carbon 60 (2013) 564. [37] H. Liu, T. Li, X. Wang, W. Zhang, T. Zhao, Preparation and characterization of carbon foams with high mechanical strength using modified coal tar pitches, J. Anal. Appl. Pyrolysis 110 (2014) 442-447. [38] C. Banerjee, V.K. Chandaliya, P.S. Dash, B.C. Meikap, Effect of different parameters on porosity and compressive strength of coal tar pitch derived carbon foam, Diam. Relat. Mater. 95 (2019) 83-90.

The present invention has been made to solve the problems of the prior art, and an object of the present invention is to mix-mould-harden-carbonize a porous carbon body using spherical phenolic resin particles of various sizes without a conventional foaming agent or template. It is an object of the present invention to provide a method for producing porous carbon having macro pores and easily controlling the pore size by a simple powder process.

Another object of the present invention is to provide a method for producing porous carbon having high-strength macropores while manufacturing the porous carbon body without a foaming agent or template.

Another object of the present invention is to provide a method for producing porous carbon having a continuously connected open cell structure by using spherical phenolic resin particles of various sizes as a skeleton without a conventional foaming agent or template. is to do

In order to achieve the above object, the present invention comprises the steps of preparing a mixture using a binder containing a spherical phenolic resin and furpril alcohol and a catalyst; Preparing a molded body using the mixture; Curing the molded body; and carbonizing the cured molded body.

Preferably, the catalyst is oxalic acid.

The oxalic acid is preferably included in at least 10 parts by weight based on the total weight of the binder. When the amount of the oxalic acid added is less than 10 parts by weight, the curing rate of furfryl alcohol is significantly reduced, resulting in excessively long curing time.

The binder is preferably included in an amount of 5 to 25 parts by weight based on the total weight of the spherical phenolic resin and the binder. If the amount of the binder added is less than 5 parts by weight, the bonding force between the spherical phenolic resin particles is lowered, making it difficult to maintain the shape of the molded body after molding, and if it is more than 25 parts by weight, an excessive amount of the liquid binder is released to the outside of the molded body during molding. It flows out, causing a problem that molding becomes difficult.

The curing is carried out in an air atmosphere, and preferably at least 5 hours at a temperature of 70 ~ 80 ℃, at least 5 hours at a temperature of 170 ~ 190 ℃, respectively.

If the primary curing temperature is 80° C. or higher, rapid evaporation of the water component produced by curing furfryl alcohol causes swelling or cracking of the molded body. That is, the curing is performed in two separate steps because immediately raising the temperature to 170 ~ 190 ° C causes the defect problem of the molded body as described above.

The step of carbonizing the cured molded body; is carried out in a nitrogen atmosphere, and is preferably carbonized by maintaining at least 1000 °C. When carbonization is performed at less than 1000° C., there is a problem in that undecomposed components such as hydrogen (H) or oxygen (O) remain.

In the carbonization step, the temperature is raised to 1000 °C at 1 °C per minute or less, and preferably maintained for at least 1 hour. The problem of cracking is caused.

The pore structure of the porous carbon is formed by adjusting the size of the fine spherical powder of the spherical phenolic resin, and the smaller the size of the fine spherical powder, the lower the shrinkage rate and porosity, and the higher the density and compressive strength.

In addition, the present invention is manufactured by the above-described manufacturing method, porous carbon having high strength macropores characterized in that it has an open pore structure in which a neck is formed between the backbones composed of spherical phenolic resin particles of various sizes. to provide.

According to the present invention as described above, the effect of easily controlling the pore size and obtaining high strength is expected by a simple powder process of mixing-molding-curing-carbonization using spherical phenolic resin particles of various sizes.

In addition, the present invention is expected to produce a porous carbon body without a foaming agent or a template.

In addition, the present invention is expected to produce porous carbon having a continuously connected open cell structure by using spherical phenolic resin particles of different sizes as a skeleton without a conventional foaming agent or template.

1 is a schematic diagram showing a method for producing porous carbon having macro pores of high strength according to an embodiment of the present invention.
2 is an electron microscope and an optical microscope photograph of porous carbon having an average particle diameter of 8 μm (P8), 25 μm (P25), and 100 μm (P100) of the skeleton particles used in the present invention.
3 is a graph showing the cured resin state of porous carbon having an average particle diameter of 8 μm (P8), 25 μm (P25), and 100 μm (P100) of the skeleton particles used in the present invention and nitrogen atmosphere at 1000 ° C. for 1 hour. The graph shows the result of particle size analysis after carbonization.
Figure 4 is a cured body of porous carbon prepared using skeletal particles of different sizes according to a preparation example of the present invention (left of each photo, indicated as P8H, P25H, P100H), carbonized body (right of each photo, This is a comparison picture showing each half of the specimens (marked P8C, P25C, and P100C, respectively).
5 is a photograph showing a cross section observed with an optical microscope after impregnating and polishing P8H, P25H, P100H and P8C, P25C, and P100C specimens with a polymer for analyzing the pore structure of porous carbon prepared according to an embodiment of the present invention. am.
6 is a measurement of the pore distribution of a hardened body and a carbonized body prepared using skeletal particles of 8 μm (P8), 25 μm (P25), and 100 μm (P100) according to an embodiment of the present invention using MIP This is the graph showing the result.
7 is a stress-strain relationship obtained by performing a compression test on porous carbon according to an embodiment of the present invention and a SEM micrograph of a fracture surface after a compression test.
8 is a graph showing a log-log plot of the Gibson-Ashby model (solid line) and a comparison between the present invention and the prior art.

Hereinafter, the present invention will be described in more detail based on preferred embodiments and accompanying drawings.

According to the definition of the International Union of Pure and Applied Chemistry (IUPAC), micropores defined in the present invention are pores with a diameter of 2 nm or less, mesopores are pores with a diameter of 2 to 50 nm, and macropores. (macropore) means a pore having a diameter of 50 nm or more.

In the present invention, individual particles of spherical phenolic resin may be expressed as "fine spherical powder".

In the present invention, 8 (referred to as P8), 25 (referred to as P25) and 100 (referred to as P100) spherical phenolic resins and furyl alcohol were used as binders, and oxalic acid, an environmentally friendly organic acid, was added as a catalyst to cure. The density, carbon yield, shrinkage, porosity, pore size distribution, and mechanical strength of the prepared porous carbon were measured, and the controllability of the pore structure and the possibility of low-cost mass production were evaluated.

<Ingredients>

Spherical phenolic resin (HF type, Gun Ei Chem., Japan) powder in a fully cured state was used as the backbone of the porous carbon foam. To control the pore size, different diameters of 8, 25, and 100 μm backbone particles (labeled P8, P25, and P100, respectively) were used. As a binder, 98% pure furpril alcohol (C ₅ H ₆ O ₂ , Daejeong Chemical) with a high residual carbon content was used, and 98.5% pure oxalic acid (C ₂ H ₂ O ₄ , Daejeong Chemical Gold) was used.

<Manufacturing process>

Step 1: A binder was prepared by completely dissolving oxalic acid in an amount of 10 wt% with respect to liquid furpril alcohol.

Step 2: 25 wt% of the prepared binder was added to the spherical phenolic resin powder, mixed, and uniaxially pressed at a pressure of 5 MPa to prepare a molded body having a diameter of 36 mm.

Step 3: The molded body was cured twice at 80 ° C for 5 hours and at 170 ° C for 5 hours to prevent explosion in an atmospheric atmosphere using an oven.

Step 4: After curing, the temperature was raised to 1000 °C at 1 °C per minute in a nitrogen atmosphere (0.8 L/min), maintained for 1 hour, and completely carbonized to prepare a porous carbon body.

A schematic diagram of such a manufacturing process is shown in FIG.

<evaluation>

The size and shape of the skeletal particles were analyzed using a scanning electron microscope (SEM, JSM-6390, JEOL, Japan), an optical microscope (Axiolab 5, Karl Zeiss, Germany), and a particle size analyzer (LA-950V2, HORIBA, Japan). . To observe the fine spherical powder structure of the prepared carbon foam, the carbon foam was impregnated with a polymer resin, polished, and observed with an optical microscope. In particular, the fracture surface was observed with an SEM. The porosity and density of the carbon foam were measured using the Archimedes principle, and the pore size distribution was measured using a mercury impregnation method (MIP, AutoPore IV, Micromeritics, USA), respectively. To measure the compressive strength, a total of three measurements were taken at 0.5 mm/min using a standard tester (Inspekt table 250 kN, Hewlett Packard, Germany) and the average value was taken.

The results of observing the P8, P25, and P100 skeletal particles used in the present invention using an electron microscope and an optical microscope are shown in FIG. 2. From the electron micrographs of FIGS. 2a to 2c, it can be seen that each particle is a nearly perfect spherical powder and has a diameter similar to the particle size suggested by the manufacturer. The optical micrographs of FIGS. 2d to 2f also showed the same size and shape as the electron micrographs, but a large number of internal pores presumed to have occurred in the manufacturing process were observed in some of the P100 powder and P25 powder having large particle sizes. Regarding the internal pores of the powder, as a result of density measurement using a pycnometer, density values of 1.287, 1.264, and 1.257 g/cm ³ were shown for P8, P25, and P100, and there were many defects (pores) inside the skeletal particles. The larger the particle size contained, the lower the value.

Figure 3 shows the results of particle size analysis of P8, P25, and P100 used as skeleton particles in the resin state before carbonization and after carbonization in a nitrogen atmosphere at 1000 ° C. for 1 hour. All three skeleton particles showed a normal distribution, and mean particle diameters in the resin state were 10.9, 24.7, and 107.8 μm, respectively, showing small errors from the particle sizes suggested by the manufacturer. The average particle diameters after carbonization were 8.6, 23.6, and 106.0 ㎛, which decreased slightly during the carbonization process. The reason for the decrease in particle size can be attributed to the thermal decomposition of the phenolic resin and the oxidation reaction by the oxygen adsorbed to the sample or the nitrogen circulated. The reason for the larger decrease in the size of the small particles is that these decomposition and oxidation reactions were more active because the surface area was larger than the volume.

4 shows carbon foam prepared according to the experimental method of this experiment using skeletal particles of different sizes after primary curing (left side of each photo, indicated as P8H, P25H, P100H) and after carbonization (right side of each photo). , Marked as P8C, P25C, and P100C, respectively) are comparative photographs of halves collected. As shown, it can be confirmed that only carbon remains completely after carbonization, and the color is changed to black. Although there was a dimensional change due to shrinkage during curing and carbonization after molding, it can be confirmed that there is almost no deformation such as bending or cracking. This can be seen as a huge advantage.

Table 1 shows the residual carbon ratio, shrinkage, true density, apparent density and porosity of the carbonized material (P8C, P25C, P100C) compared to the cured material (P8H, P25H, P100H). It was reported that the residual carbon ratio of the phenolic resin was about 52% and that of the liquid furpril alcohol polymer was about 49%. In the preliminary experiment of the present invention, only the spherical phenol resin was carbonized, and as a result, the residual carbon ratio was about 51%, whereas when the substantially porous carbon was produced, the residual carbon ratio was as low as about 44%. This is presumably because furryl alcohol, which has a boiling point of about 170° C., evaporates and is lost before polymerization during the curing process.

As shown in FIG. 3, the shrinkage rate of the spherical phenol skeleton particles increased as the particle size decreased during the carbonization process. It seems to be because it was used more often.

The true density of the porous carbon measured by the Archimedes principle was about 1.48 g/cm ³ for all three specimens, similar to that of typical amorphous carbon. The reason why the real density of porous carbon having large skeleton particles is slightly low is presumed to be that defects inside the particles remain as closed pores, as observed in the optical micrograph of the skeleton particles as shown in FIG. 2 . For P8C, P25C, and P100C, the apparent density of the carbon foam measured by the Archimedes principle was 1.01, 1.00, and 0.94, which decreased as the particle size increased, and the porosity was 31.9, 32.6, and 35.8, which increased as the particle size of the skeleton decreased. Packing density has nothing to do with the size of the constituent particles and is related to the particle size distribution. In the present invention, since skeleton particles having a similar particle size distribution were used, the difference in apparent density and porosity is due to the fact that the smaller the particle size in the carbonization process, the greater the shrinkage rate. It can be inferred that

Characteristics of carbon foam P8C, P25C, P100C Sample name Carbon Yield (%) Shrinkage rate (%) True density (g/cm ³ ) Bulk density (g/cm ³ ) Porosity (%) P8C 42.3 25.2 1.49 1.01 31.9 P25C 44.3 22.0 1.48 1.00 32.6 P100C 44.8 18.5 1.46 0.94 35.8

For the analysis of the pore structure, P8H, P25H, P100H, P8C, P25C, and P100C specimens were impregnated with a polymer and polished, and the cross section was observed with an optical microscope and is shown in FIG. 5. Both the molded body and the carbonized body specimen exhibited a porous structure, and it could be confirmed that the size of the pores was proportional to the size of the spherical phenolic resin skeleton particle size used as the skeleton. Even though the porous body was prepared by applying pressure to the spherical phenolic resin, there were gaps between particles and open pores were formed as a whole. It is believed that this is because the water released during the condensation polymerization of furpril alcohol was vaporized and loosened the structure of the compacted body during the curing process.

6 is a result of measuring the pore distribution of a cured product and a molded product prepared using P8, P25, and P100 skeletal particles using MIP. First, in the cured foam of FIG. 6a, the distribution of pores was relatively uniform in all three specimens, and the average pore size for the used skeleton particles P8, P25, and P100 was 1.89, 7.01, and 38.99 ㎛, which increased in proportion to the particle size used. did Since spherical particles were used and gaps between particles were used as pores, the size of the pores can be seen as proportional to the size of the skeleton particles. The pore size formed by the spherical particles of P8, P25, and P100 can be theoretically calculated to be 1.7, 5.2, and 20.7 μm when the coordination number is 6. The difference between the measured and calculated values is presumed to be due to the loosened structure as a result of evaporation of water released during polymerization of furfuryl alcohol upon curing at 80 °C.

Due to shrinkage of the samples during carbonization, the pore sizes of P8C, P25C and P100C decreased after carbonization, as shown in Fig. 6(b). In addition, the formation of pores with a size larger than 100 μm was observed in P100C after carbonization, which is presumed to be formed by removing furpril alcohol clusters formed between coarse particles during carbonization.

7 is a SEM micrograph of a stress-strain relationship obtained by performing a compression test on porous carbon and a fracture surface after the compression test. As shown in Fig. 7(a), P8C and P25C composed of fine particles brittle at a critical load, whereas P100C showed a sawtooth curve plastic behavior at a much lower load and then fractured. Specimens with large grains also have larger pores between grains, which acts as a defect where fracture occurs, so the fracture strength decreases as the grain size increases. On the other hand, the plastic behavior of P100C can be understood by analyzing the structure of the fracture surface (Fig. 7 (b) and (c)). In the case of P8C, most of the fracture occurred at the grain boundary, resulting in cracks in the specimen (FIG. 7 (b)). However, P100C showed an intragranular fracture pattern in which cracks propagated as the particles were destroyed (FIG. 7 (c)). In the magnified micrograph of the P100C fracture surface shown in Fig. 7(c), it is clearly visible the Wallner line (white arrow), which is a faint curve indicating that the crack propagated in the contact area of the particles. Backtracing the line, we can clearly observe the fracture origin where several hackle lines (black arrows) emerge from the particle contact.

In compression tests, tensile stresses can develop around defects such as pores in a direction nearly perpendicular to the loading axis due to the elastic mismatch between the particles and pores. These tensile stresses generate wing cracks in the direction parallel to the load axis, which is the case for the P8C and P25C specimens. On the other hand, when the particle size is large, such as the P100C specimen, the contact force applied to each particle for a given compressive load increases in proportion to the square of the particle radius because the number of contacts between particles is greatly reduced. On the other hand, the critical load to initiate cracks in the contact area increases proportionally with the particle radius according to Auerbach's law. For this reason, in the case of the P100C specimen, the intragranular fracture pattern is larger than the intergranular fracture in the neck area. Since the intragranular fracture of P100C can reduce the total modulus of elasticity, it can be assumed that the sawtooth-shaped stress-strain curve is observed after the critical load, as shown in FIG. 7 (a).

The maximum theoretical mechanical strength achievable for open-cell vitreous carbon with a specific relative density can be calculated from Equation 1 (Gibson-Ashby model).

....................... (1)

....................... (One)

where σ ^* is the fracture strength of the porous body, σ _f is the fracture strength of the solid material (= 580 MPa), and ρ ^* /ρ _s is the relative density. Figure 8 is a log-log plot of the Gibson-Ashby model (solid line), the compressive strength of the porous carbon related to the present invention and literature (documents disclosed in non-patent literature among prior literature. 8, 23, 24, 35-38 ) shows the comparison. From the above results, it can be seen that the macroporous carbon sample with small matrix spherical particles has higher compressive strength. The highest value of 106.8 MPa, which is higher than the Gibson-Ashby model, is observed for P8C, and as shown in Fig. 8, this value is confirmed to be significantly higher than that of materials with similar densities.

As a result, the pore structure of the porous carbon of the present invention is made by adjusting the size of the fine spherical powder of the spherical phenolic resin, and the smaller the size of the fine spherical powder, the lower the shrinkage rate and porosity, and the higher the density and compressive strength. showed

In addition, it can be seen that the porous carbon of the present invention has an open pore structure with a neck between the phenol resin fine spherical powders.

Claims (9)

Preparing a mixture using a binder containing a spherical phenolic resin and furpril alcohol and a catalyst;
Preparing a molded body using the mixture;
curing the molded body; and
carbonizing the cured molded body;
Method for producing porous carbon having high-strength macropores, characterized in that comprises a. According to claim 1,
The catalyst is a method for producing porous carbon having high-strength macropores, characterized in that oxalic acid. According to claim 2,
The oxalic acid is a method for producing porous carbon having high-strength macropores, characterized in that contained at least 10 parts by weight based on the total weight of the binder. According to claim 1,
The binder is a method for producing porous carbon having high-strength macropores, characterized in that contained 5 to 25 parts by weight relative to the total weight of the spherical phenolic resin and the binder. According to claim 1,
The curing is carried out in an air atmosphere, characterized in that at least 5 hours at a temperature of 70 ~ 80 ℃, at least 5 hours at a temperature of 170 ~ 190 ℃, characterized in that the process for producing porous carbon having macro pores of high strength. According to claim 1,
The step of carbonizing the cured molded body; is carried out in a nitrogen atmosphere, a method for producing porous carbon having high-strength macropores, characterized in that carbonized by maintaining at least 1000 ℃. According to claim 6,
The carbonization step is a method for producing porous carbon having high-strength macropores, characterized in that the temperature is raised at 1 ° C. or less per minute to 1000 ° C., and maintained for at least 1 hour. According to claim 1,
The pore structure of the porous carbon is made by adjusting the size of the fine spherical powder of the spherical phenolic resin, and the smaller the size of the fine spherical powder, the lower the shrinkage rate and the porosity, and the higher the density and compressive strength. Method for producing porous carbon having macro pores. It is prepared by the manufacturing method of claim 1,
Porous carbon with high-strength macropores, characterized in that it has an open pore structure in which a neck is formed between fine spherical powders of spherical phenolic resins of different sizes.

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