KR20220102391A - Highly porous carbon with controlled pore size via hydrothermal carbonization and the method for manufacturing thereof - Google Patents

Abstract

The present invention discloses porous carbon capable of easily controlling pore size using hydrothermal carbonization and a preparation method thereof. According to the present invention, the preparation method comprises the steps of: mixing a biomass precursor, an activator, and water to provide a mixture; applying one of rapid temperature raising and rapid cooling to hydrothermally carbonize the mixture for a preset time and cooling the same; drying the solid by the hydrothermal carbonization and cooling; and activating the solid, wherein the rapid temperature raising is to raise the temperature of a reactor to a preset temperature and then add the mixture into the reactor, and the rapid cooling is to add the hydrothermal carbonized solid into the cooling water.

Description

The porous carbon with controlled pore size via hydrothermal carbonization and the method for manufacturing thereof

The present invention relates to a porous carbon with easy pore size control using hydrothermal carbonization and a method for preparing the same, and more particularly, to a biomass-based porous carbon having a controlled pore size and a method for preparing the same.

Porous carbon or activated carbon can be manufactured from any material including carbon components, so it has the advantage of excellent material accessibility and very low production cost, so it is being actively applied to various fields.

In general, such porous carbon consists of a carbonization process that removes volatile substances contained in the carbon chain at a temperature of 500 °C or higher, and an activation process that further promotes the formation of internal pores.

Biomass is a raw material that can be used abundantly on Earth, and besides just wood and plants, urban waste such as coffee grounds can also be a raw material for porous carbon.

Biomass can be an eco-friendly and economical raw material because it uses materials that have already been used or are considered to have no utility. However, there is a disadvantage in that it is difficult to control the specific surface area or the degree of pore development when manufacturing porous carbon using this.

Republic of Korea Patent Publication No. 10-1565036

In order to solve the problems of the prior art, the present invention intends to propose a porous carbon capable of easily adjusting the optimal pore size in an environmentally friendly manner and a method for manufacturing the same.

In order to achieve the object as described above, according to an embodiment of the present invention, the steps of providing a mixture by mixing a biomass precursor, an activator and water; Cooling after hydrothermal carbonization of the mixture for a preset time by applying one of rapid heating and rapid cooling; drying the solid by the hydrothermal carbonization and cooling; and activating the solid, wherein the rapid temperature increase is to add the mixture to the reactor after raising the reactor to a preset temperature, and the rapid cooling is to inject the hydrothermal carbonized solid into cooling water A method for producing porous carbon.

The biomass precursor may be at least one of cellulose, lignin, chitosan, coal, coke, and plastic.

The activator may be at least one of zinc chloride, potassium hydroxide and potassium carbonate.

The biomass precursor may be mixed in water at a ratio of 0.15 g/L to 0.2 g/L.

The biomass precursor and the activator may be mixed in 1:1.5 to 1:2.5 weight percent.

According to another aspect of the present invention, there is provided a porous carbon prepared by the above method.

According to the present invention, there is an advantage in that the pore size can be easily adjusted by changing the temperature increase and cooling process of the hydrothermal carbonization reaction.

1 is a schematic diagram of a method for producing porous carbon using hydrothermal carbonization according to a preferred embodiment of the present invention.
2 is a schematic diagram of a subdivision method of a hydrothermal carbonization process.
3 shows the nitrogen adsorption/desorption isotherm of the synthesized porous carbon for comparison of physical properties.
4 shows a pore distribution diagram of porous carbon according to a hydrothermal carbonization process.
5 is a view showing spectra of IR analyzed to check whether functional groups are generated after final activation.
6 is a view showing the nitrogen adsorption/desorption isotherm of the material activated after adding zinc chloride in advance to the hydrothermal carbonization process and the material finally activated after separately adding zinc chloride after the hydrothermal carbonization process.
7 is a view showing the pore distribution of porous carbon according to the order of addition of zinc chloride.
8 is a view showing the results of experiments using lignin as a precursor and varying the mixing ratio with zinc chloride.

Since the present invention can have various changes and can have various embodiments, specific embodiments are illustrated in the drawings and described in detail.

However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.

Hydrothermal synthesis is relatively environmentally friendly because it uses water instead of using other organic solvents, and has the advantage of being easy to modify the surface of a carbon material when applied to a carbonization process. However, in the hydrothermal carbonization process, there has been no report of an effect on the temperature increase and cooling process, so only porous carbon having a uniform pore distribution has been manufactured, which makes it difficult to apply it to various fields.

The present invention proposes a manufacturing method for having a desired pore size for efficient application of porous carbon using hydrothermal carbonization.

1 is a schematic diagram of a method for producing porous carbon using hydrothermal carbonization according to a preferred embodiment of the present invention.

Referring to FIG. 1 , a biomass precursor, an activator and water are mixed to provide a mixture (step 100).

Here, the biomass precursor may be at least one of cellulose, lignin, chitosan, coal, coke, and plastic.

In addition, the activator may be at least one of zinc chloride, potassium hydroxide and potassium carbonate.

Preferably, the biomass precursor may be mixed with water at a ratio of 0.15 g/L to 0.2 g/L. More preferably, it may be mixed at a ratio of 0.16 g/L.

In order to promote the specific surface area and pore volume of the porous carbon, the biomass precursor and the activator may be mixed in a ratio of 1:1.5 to 1:2.5 by weight, more preferably, in a ratio of 1:2.

With respect to the mixture provided as in step 100, one of rapid heating and rapid cooling is applied to hydrothermally carbonize the mixture for a preset time and then cooling (step 102).

In step 102, the rapid temperature increase is to increase the temperature of the reactor to a preset temperature and then add the mixture to the reactor heated to the hydrothermal carbonization temperature.

Here, the preset temperature is a hydrothermal carbonization temperature, for example, may be 230 °C.

Rapid cooling is cooling by injecting the hydrothermal carbonized solid into cooling water.

Unlike the rapid temperature increase described above, the natural temperature increase is to gradually raise the hydrothermal carbonization temperature to the hydrothermal carbonization temperature after inputting the mixture into the reactor, for example, it may mean to raise the temperature from 60 °C to 230 °C for 120 minutes.

In addition, natural cooling can be defined as the process of cooling the solid obtained by hydrothermal carbonization to 60 °C naturally without putting it in cooling water.

According to this embodiment, after performing the hydrothermal carbonization and cooling process by applying one of rapid heating and rapid cooling, the obtained solid is dried (step 104), and the dried solid is subjected to an activation temperature (eg, 800 °C). Activate in C) (step 106). The activated solid is washed to prepare porous carbon with various pores (step 108).

According to this embodiment, by subdividing the temperature raising and cooling process in the hydrothermal carbonization process, when the mixture is suddenly exposed to high temperature and slowly exposed during the hydrothermal carbonization process, and when rapid cooling is performed in the cooling process, and naturally Determine the effect of the difference on the porous carbon as it cools.

Example: Preparation of porous carbon using cellulose and zinc chloride

Cellulose, one of biomass, was mixed with zinc chloride and water as a precursor to prepare porous carbon.

The mixing ratio of cellulose and zinc chloride was 1:2, and 1 L of water per 0.167 g of cellulose was mixed and put in a sealed reactor, followed by hydrothermal carbonization.

2 is a schematic diagram of a subdivision method of a hydrothermal carbonization process.

2 is a subdivision of the temperature increase and cooling rate into four, and below, a method for producing porous carbon according to the difference in temperature increase and cooling rate through nomenclature will be described in detail.

First, Figure 2a shows a hydrothermal carbonization process through natural temperature rise and natural cooling.

Referring to Figure 2a, in the process of hydrothermal carbonization through natural temperature increase and natural cooling, a material mixed with cellulose, zinc chloride and water is put into the reactor, and the temperature is gradually increased from room temperature to 230 °C, which is the hydrothermal carbonization temperature, and reaches 230 °C. After the hydrothermal carbonization reaction for 4 hours was completed, it was slowly cooled to room temperature.

After hydrothermal carbonization, the solid was recovered and dried at 110 °C.

After the dried solid was finely ground with a mortar, carbon dioxide gas was flowed from the furnace as an activation gas, and activation was carried out through heat treatment at 800 °C for 2 hours.

After activation, the material was washed with 1 M hydrochloric acid and filtered until the acidity was neutralized.

Finally, after drying at 110 °C, porous carbon was prepared.

As described above, the porous carbon synthesized through the hydrothermal carbonization process through natural temperature rise and natural cooling was named ZHTP.

Figure 2b shows the hydrothermal carbonization process through natural temperature rise and rapid cooling.

As shown in FIG. 2B, after the hydrothermal carbonization process, the porous carbon was synthesized by rapidly lowering the temperature using cooling water without gradually cooling to room temperature.

The porous carbon synthesized through natural temperature rise and rapid cooling was named ZHTP_c.

Here, drying, activation, and filtering of the solid obtained after hydrothermal carbonization are the same as in the preparation of ZHTP, and the same applies hereafter.

Figure 2c shows the hydrothermal carbonization process through rapid temperature increase and natural cooling.

As shown in FIG. 2c, after the reactor was heated to the hydrothermal carbonization temperature, the mixture was put into the reactor to perform the hydrothermal carbonization reaction, and then porous carbon was synthesized through natural cooling.

The synthesized porous carbon was named ZHTP_h.

Figure 2d shows the hydrothermal carbonization process through rapid temperature rise and rapid cooling.

As shown in Figure 2d, both the temperature raising process and the cooling process before hydrothermal carbonization were changed, and porous carbon was prepared through the rapid temperature increase and rapid cooling process.

The synthesized porous carbon was named ZHTP_h-c.

3 shows the nitrogen adsorption/desorption isotherm of the synthesized porous carbon for comparison of physical properties.

The specific surface area and pore volume of porous carbon were calculated from the experimental results on the nitrogen adsorption/desorption isotherm, and are shown in Table 1 below.

Sample S _BET
(m ² /g) V _total
(cm ³ /g) V _micro
(cm ³ /g) V _meso
(cm ³ /g) V _meso
/V _total (%) ZHTP 1926 0.932 0.716 0.216 23.2 ZHTP_c 2477 1.335 0.919 0.416 31.3 ZHTP_h 2780 2.067 1.057 1.01 48.9 ZHTP_h-c 682 0.407 0.249 0.158 38.8

Referring to Table 1, it can be seen that the activation process that promotes pore development is the same, and there is a difference in the formation of pores despite only changing the temperature increase and cooling rate in the hydrothermal carbonization prior to the activation process.

ZHTP carbonized through natural temperature rise and natural cooling has a high specific surface area close to 2000 m ² /g, and the development of pores centered on micropores can be confirmed through nitrogen adsorption and desorption reforming.

In the case of ZHTP_c material carbonized through natural temperature increase and rapid cooling, the adsorption/desorption type is similar to that of ZHTP, but it has a more developed specific surface area and pore volume.

The ZHTP_h material, which is carbonized through rapid heating and natural cooling, has a surface area of 2780 m ² /g, which is more improved than the previous two materials.

In particular, it can be seen that ZHTP_h has a hysteresis loop in the adsorption/desorption type, so that more medium pores are formed compared to other materials. In addition, it has a large pore volume of 2.067 cm ³ /g, so it is understood that the above synthesis method will be useful when a large pore volume is required depending on the field to be used.

Different from the existing natural heating and cooling processes, the porous carbon produced through either rapid heating or rapid cooling has improved specific surface area and pore volume than porous carbon (ZHTP) synthesized by the conventional method.

On the other hand, ZHTP_h-c, which was rapidly heated and cooled at the same time, showed the lowest specific surface area.

Since ZHTP_h-c undergoes a rapid cooling process after a rapid temperature rise, the reaction time in the reactor is relatively shorter than other materials. Therefore, it can be interpreted that the pores remain relatively undeveloped even after the final activation because more volatile substances remain compared to other materials.

In Table 1, when the total pore volume of porous carbon and the degree of formation of micropores and mesopores were confirmed, the temperature before hydrothermal carbonization was rapidly increased, such as ZHTP_h and ZHTP_h-c, regardless of the size of the specific surface area. You can see the ball is developing.

4 shows a pore distribution diagram of porous carbon according to a hydrothermal carbonization process.

As described above, it can be seen that the pore distribution is also different because the physical properties of the porous carbon prepared through different temperature raising and cooling processes are different.

In porous carbon (ZHTP) carbonized through natural temperature increase and natural cooling, it was confirmed that pores were developed at less than 2 nm, which is the range of micropores, and in particular, many pores were developed around 0.7 nm.

On the other hand, it was confirmed that porous carbon (ZHTP_c) carbonized through natural temperature increase and rapid cooling developed pores in the mesopore region of 2-3 nm.

In the porous carbon (ZHTP_h) carbonized through rapid temperature rise and natural cooling, many mesopores were formed in the nitrogen adsorption/desorption isotherm, which can also be confirmed in the pore distribution diagram.

Considering the 48.3% degree of mesopore formation confirmed in Table 1, it can be seen that the pores were developed in a wider range than other materials in the mesopore region.

Porous carbon (ZHTP_h-c) carbonized through rapid temperature rise and rapid cooling does not appear to have developed pores compared to other materials because the surface area of the material itself is not high. It can be seen that the development of qigong is subdivided.

5 is a view showing spectra of IR analyzed to check whether functional groups are generated after final activation.

In the case of general porous carbon, the functional group cannot be confirmed because the volatile material disappears during the carbonization and activation process and only carbon remains.

However, when the hydrothermal carbonization process is performed, a functional group with oxygen or hydrogen may be generated by reaction with water.

Even in the porous carbon according to this embodiment, it can be seen that a carbonyl group was formed through the fact that specific peaks were generated in the vicinity of 1700 cm ^-1 , 1370 cm ^-1 , and 1210 cm ^-1 .

However, the degree varies depending on the subdivision in the hydrothermal carbonization process. In the case of ZHTP_c with developed mesopores and a high specific surface area, it can be seen that these functional groups are very strongly attached.

In contrast, in the case of ZHTP, a carbonyl group was formed, but the extent was low.

It can be seen that in the case of ZHTP_h and ZHTP_h-c, which were rapidly heated, the carbonyl group was hardly formed.

That is, when the temperature of the mixed raw material composed of biomass, zinc chloride, and water is gradually increased to facilitate the carbonization reaction, and rapid cooling is performed to terminate the hydrothermal carbonization reaction, such a carbonyl group is clearly formed. However, it can be understood that in the process of rapid temperature increase, the reaction proceeds aggressively, making it difficult to form a carbonyl group.

FIG. 6 is a view showing nitrogen adsorption/desorption isotherms of a material activated by adding zinc chloride in advance to the hydrothermal carbonization process and a material finally activated after separately adding zinc chloride after the hydrothermal carbonization process.

The carbon that has undergone activation after mixing zinc chloride with the solid that has undergone hydrothermal carbonization is named HTZP_h.

In order to confirm the effect of zinc chloride and hydrothermal carbonization on each other, nitrogen adsorption and desorption isotherms of porous carbon activated by separately adding zinc chloride after hydrothermal carbonization were checked.

It can be seen that HTZP_h has a relatively low specific surface area and develops mainly in micropores.

Through the difference in the characteristics of the two porous carbons of ZHTP_h and HTZP_h, it can be understood that when zinc chloride is added before hydrothermal carbonization, pore development is further promoted during the final activation process.

In particular, this synthesis method can be viewed as an advantage of the manufacturing process because it is not necessary to introduce a separate activator addition method, such as an impregnation method, since the active agent such as zinc chloride is sufficiently mixed in the hydrothermal carbonization process.

7 is a view showing the pore distribution of porous carbon according to the order of addition of zinc chloride.

ZHTP_h, which was activated after adding zinc chloride to the hydrothermal carbonization process in advance, has pores distributed even in the region after 2 nm. The degree of stomatal development in the

Instead, it can be seen that the micropores in the vicinity of 0.7 nm are largely developed.

By simply changing the order of addition of zinc chloride, it is possible to obtain a material with differently developed micropores or mesopores.

8 is a view showing the results of experiments using lignin as a precursor at different mixing ratios with zinc chloride, and Table 2 shows the specific surface area and pore volume of porous carbon according to the mixing ratio of zinc chloride and the order of addition.

Sample S _BET
(m ² /g) V _total
(cm ³ /g) V _micro
(cm ³ /g) V _meso
(cm ³ /g) V _meso
/V _total (%) HTZP[2]_lig4h 1645 0.808 0.613 0.195 24.1 HTZP[3]_lig4h 1429 0.759 0.532 0.227 29.91 ZHTP[2]_lig4h 852 0.358 0.34 0.018 5.03 ZHTP[3]_lig4h 176 0.077 0.071 0.006 8.17

Referring to FIG. 8 and Table 2, when the amount of zinc chloride is increased from two to three times, it is understood that the surface area or pore volume is greatly reduced regardless of the mixing order before and after hydrothermal carbonization.

This phenomenon is judged to collapse due to excessive pore development during the final activation process due to excessive addition of zinc chloride, and it can be seen that the mixing ratio of the biomass precursor and the activator is preferably 1:2.

The above-described embodiments of the present invention have been disclosed for purposes of illustration, and various modifications, changes, and additions will be possible within the spirit and scope of the present invention by those skilled in the art having ordinary knowledge of the present invention, and such modifications, changes and additions should be regarded as belonging to the following claims.

Claims (6)

mixing the biomass precursor, the activator and water to provide a mixture;
Cooling after hydrothermal carbonization of the mixture for a preset time by applying one of rapid temperature rise and rapid cooling;
drying the solid by the hydrothermal carbonization and cooling; and
activating the solid;
The rapid temperature rise is to put the mixture into the reactor after raising the temperature to a preset temperature in the reactor,
The rapid cooling is a method for producing porous carbon by adding the hydrothermal carbonized solid to cooling water. According to claim 1,
The biomass precursor is at least one of cellulose, lignin, chitosan, coal, coke, and plastic. According to claim 1,
The method for producing porous carbon, wherein the activator is at least one of zinc chloride, potassium hydroxide and potassium carbonate. According to claim 1,
The biomass precursor is a porous carbon production method in which the water is mixed in a ratio of 0.15 g / L to 0.2 g / L. According to claim 1,
The method for producing porous carbon wherein the biomass precursor and the activator are mixed in 1:1.5 to 1:2.5 weight percent. A porous carbon produced by the method according to claim 1 .

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