KR102562397B1 - 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 with easy pore size control using hydrothermal carbonization and a method for preparing the same. According to the present invention, mixing a biomass precursor, an activator and water to provide a mixture; hydrothermal carbonizing the mixture for a preset time by applying one of rapid heating and rapid cooling, followed by cooling; drying the solid by the hydrothermal carbonization and cooling; And a step of activating the solid, wherein the rapid temperature raising is to inject the mixture into the reactor after raising the temperature of 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 is provided.

Description

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

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

Porous carbon or activated carbon is actively applied in various fields because it can be manufactured from all materials including carbon components, has excellent material accessibility, and has the advantage of very low production cost.

Such porous carbon is generally composed 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 in abundance on Earth. In addition to simple 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 useless. However, when porous carbon is produced using this, it is difficult to control the specific surface area or the degree of pore development.

Korean Registered Patent Publication 10-1565036

In order to solve the above-mentioned problems of the prior art, the present invention proposes an environmentally friendly porous carbon and a method for manufacturing the same, which can easily control the optimal pore size.

In order to achieve the above object, according to an embodiment of the present invention, providing a mixture by mixing a biomass precursor, an activator and water; hydrothermal carbonizing the mixture for a preset time by applying one of rapid heating and rapid cooling, followed by cooling; drying the solid by the hydrothermal carbonization and cooling; And a step of activating the solid, wherein the rapid temperature raising is to inject the mixture into the reactor after raising the temperature of 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 with water at a ratio of 0.15 g/L to 0.2 g/L.

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

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

According to the present invention, there is an advantage in that the pore size can be easily controlled by changing the temperature raising and cooling processes 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 in a hydrothermal carbonization process.
3 shows nitrogen adsorption and desorption isotherms of porous carbon synthesized for comparison of physical properties.
Figure 4 shows the pore distribution of porous carbon according to the hydrothermal carbonization process.
5 is a diagram showing spectra of IR analyzed to determine whether a functional group has been generated after final activation.
6 is a view showing nitrogen adsorption and desorption isotherms of a material activated after adding zinc chloride in advance in a hydrothermal carbonization process and a material finally activated after separately adding zinc chloride after the hydrothermal carbonization process.
7 is a diagram showing the pore distribution of porous carbon according to the order of addition of zinc chloride.
8 is a view showing the results of an experiment using lignin as a precursor and varying the mixing ratio of zinc chloride.

Since the present invention can make various changes and 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 other organic solvents, and has the advantage of being easy to modify the surface of carbon materials when applied to the carbonization process. However, only porous carbon having a uniform pore distribution has been produced so far because no effect on the temperature raising and cooling process has been reported in the hydrothermal carbonization process, which makes it difficult to apply 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 mixture material is provided by mixing a biomass precursor, an activator, and water (step 100).

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

Also, 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, they 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 at a weight percent of 1:1.5 to 1:2.5, more preferably at a ratio of 1:2.

For the mixture provided in step 100, one of rapid heating and rapid cooling is applied to hydrothermal carbonize the mixture for a preset time, and then it is cooled (step 102).

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

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

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

Unlike the rapid temperature increase described above, the natural temperature increase may mean that the mixture is introduced into the reactor and then gradually raised to the hydrothermal carbonization temperature, for example, from 60 °C to 230 °C for 120 minutes.

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

According to this embodiment, after carrying out 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). C) is activated (step 106). The activated solid is washed to prepare porous carbon in which various pores are formed (step 108).

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

Example: Preparation of Porous Carbon Using Cellulose and Zinc Chloride

Porous carbon was prepared by mixing cellulose, one of biomass, with zinc chloride and water as a precursor.

The mixing ratio of cellulose and zinc chloride was set to 1:2, and 0.167 g of cellulose was mixed with 1 L of water, put into a sealed reactor, and hydrothermal carbonization was performed.

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

FIG. 2 subdivides the temperature raising and cooling rates into four types. Hereinafter, a method for producing porous carbon according to a difference in temperature raising and cooling rates will be described in detail through nomenclature.

First, FIG. 2a shows a hydrothermal carbonization process through natural temperature increase and natural cooling.

Referring to Figure 2a, in the process of hydrothermal carbonization through natural temperature increase and natural cooling, a mixture of cellulose, zinc chloride, and water was put into the reactor and gradually heated from room temperature to 230 ° C, which is the temperature of hydrothermal carbonization, and reached 230 ° C After completion of the hydrothermal carbonization reaction for 4 hours, it was gradually cooled to room temperature.

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

After finely grinding the dried solid in a mortar, activation was carried out through heat treatment at 800 °C for 2 hours while flowing carbon dioxide gas as an activation gas in a furnace.

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

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

The porous carbon synthesized through the hydrothermal carbonization process through natural temperature increase and natural cooling was named ZHTP.

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

As shown in FIG. 2B, porous carbon was synthesized by rapidly lowering the temperature using cooling water instead of slowly cooling to room temperature after the hydrothermal carbonization process.

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

Here, the drying, activation and filtering of the solid obtained after hydrothermal carbonization are the same as for the production 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 raising the temperature of the reactor to the hydrothermal carbonization temperature, the mixture was introduced into the reactor to undergo a hydrothermal carbonization reaction, followed by natural cooling to synthesize porous carbon.

The porous carbon thus synthesized was named ZHTP_h.

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

As shown in FIG. 2d, porous carbon was prepared through a rapid heating and cooling process by changing both the heating process and the cooling process before hydrothermal carbonization.

The porous carbon thus synthesized was named ZHTP_h-c.

3 shows nitrogen adsorption and desorption isotherms of porous carbon synthesized for comparison of physical properties.

The specific surface area and pore volume of the porous carbon were calculated through the experimental results in the nitrogen adsorption and desorption isotherms, which 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 for promoting pore development is the same, and there is a difference in the formation of pores even though only the temperature raising and cooling rates are changed in the hydrothermal carbonization before the activation process.

ZHTP carbonized through natural temperature increase and natural cooling has a high specific surface area close to 2000 m ² /g, and it can be confirmed through nitrogen adsorption and desorption opening that pores in the center of micropores are developed.

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

ZHTP_h material carbonized through rapid temperature increase 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 confirmed that ZHTP_h has a hysteresis loop in the adsorption-and-desorption open form, and more mesopores are formed than other materials. In addition, since it has a large pore volume of 2.067 cm ³ /g, it is understood that the above synthesis method will be useful when a large pore volume is required depending on the field of use.

Unlike conventional natural temperature raising and natural cooling processes, porous carbon produced through either rapid heating or rapid cooling has a higher specific surface area and pore volume than porous carbon (ZHTP) synthesized by conventional methods.

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

Since ZHTP_h-c goes through a rapid cooling process after a rapid temperature increase, the reaction time in the reactor is relatively shorter than other materials. Therefore, since more volatile substances remain than other materials, it can be interpreted that pores are not developed relatively much after final activation.

When the total pore volume of porous carbon and the degree of formation of micropores and mesopores were confirmed in Table 1, regardless of the size of the specific surface area, when the temperature before hydrothermal carbonization was rapidly raised, such as ZHTP_h and ZHTP_h-c, it was relatively intermediate You can see that the ball develops.

Figure 4 shows the pore distribution of porous carbon according to the hydrothermal carbonization process.

As described above, it can be confirmed that the pore distribution is also different because the porous carbon produced through different heating and cooling processes has different physical properties.

Porous carbon (ZHTP) carbonized through natural temperature increase and natural cooling was confirmed to have developed pores in the micropore area range of less than 2 nm, especially around 0.7 nm.

In contrast, porous carbon (ZHTP_c) carbonized through natural temperature increase and rapid cooling was confirmed to have developed pores in the mesopore range of 2-3 nm.

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

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

Porous carbon (ZHTP_h-c) carbonized through rapid temperature increase 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 stomatal development is segmented.

5 is a diagram showing spectra of IR analyzed to determine whether a functional group has been generated after final activation.

In the case of general porous carbon, volatile substances disappear during carbonization and activation and only carbon remains, so functional groups cannot be identified.

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

It can be seen that a carbonyl group was formed through the fact that specific peaks occurred around 1700 cm ^-1 , 1370 cm ^-1 , and 1210 cm ^-1 in the porous carbon according to the present embodiment.

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 confirmed that these functional groups are very strongly attached.

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

In the case of ZHTP_h and ZHTP_h-c subjected to rapid temperature increase, it can be seen that carbonyl groups were hardly formed.

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

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

After mixing zinc chloride with the hydrothermal carbonization solid, the activated carbon 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 adding zinc chloride separately after hydrothermal carbonization were confirmed.

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, ZHTP_h and HTZP_h, it can be seen that when zinc chloride is added before hydrothermal carbonization, pore development is further promoted during the final activation process.

In particular, in this synthesis method, since the activator of zinc chloride is sufficiently mixed in the hydrothermal carbonization process, there is no need to introduce a separate activator addition method such as an impregnation method later, which can be seen as an advantage in the manufacturing process.

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

ZHTP_h, which was activated by adding zinc chloride in advance to the hydrothermal carbonization process, can confirm that pores are distributed even in the area beyond 2 nm, but HTZP_h, which is a material that is separately impregnated and finally activated after zinc chloride is hydrothermal carbonized, has medium pores. The degree of stomatal development could not be ascertained.

Instead, it can be confirmed that micropores around 0.7 nm are greatly developed.

A material with differently developed micropores or mesopores can be obtained by simply changing the order of addition of zinc chloride.

8 is a view showing the results of experiments using lignin as a precursor and different mixing ratios of 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 2 to 3 times, it is understood that the surface area or pore volume greatly collapses regardless of the mixing order before and after hydrothermal carbonization.

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

The embodiments of the present invention described above have been disclosed for illustrative purposes, and those skilled in the art having ordinary knowledge of the present invention will be able to make various modifications, changes, and additions within the spirit and scope of the present invention, and such modifications, changes, and additions will be considered to fall within the scope of the following claims.

Claims (6)

(a) mixing a biomass precursor, an activator and water to provide a mixture;
(b) hydrothermal carbonizing the mixture for a preset time by applying one of rapid heating and rapid cooling, followed by cooling;
(c) drying the solid obtained by step (b); and
(d) activating the solid;
In the step (b), in order to generate mesopores, the temperature of the reactor is raised to the hydrothermal carbonization temperature, and the mixture is introduced into the reactor heated to the hydrothermal carbonization temperature to perform a rapid hydrothermal carbonization reaction for a predetermined time. After the hydrothermal carbonization reaction by raising the temperature, naturally cooling the solid obtained by the hydrothermal carbonization reaction by the rapid temperature increase for a preset time, and introducing the mixture into the reactor to heat the solid at the first temperature for a preset time. After the hydrothermal carbonization reaction by the natural temperature increase in which the temperature is raised to the carbonization temperature and the hydrothermal carbonization reaction is carried out for a predetermined time, the solid obtained by the hydrothermal carbonization reaction by the natural temperature increase is put into cooling water to rapidly cool,
The method for producing porous carbon wherein the biomass precursor and the activator are mixed in a weight percent of 1:1.5 to 1:2.5. According to claim 1,
The biomass precursor is at least one of cellulose, lignin, chitosan, coal, coke, and plastic. According to claim 1,
Wherein the activator is at least one of zinc chloride, potassium hydroxide and potassium carbonate. According to claim 1,
The method for producing porous carbon wherein the biomass precursor is mixed with water at a ratio of 0.15 g / L to 0.2 g / L.


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