KR100635715B1 - Method of producing carbon aerogel for water purifier using capacitive deionization - Google Patents

Abstract

The present invention relates to a method for producing a carbon airgel, wherein the method mixes resorcinol and formaldehyde in a predetermined ratio, adds distilled water in a solid fraction of 9% by weight, and adds a basic catalyst at a catalyst ratio of 100 or less. Forming a resorcinol-formaldehyde sol solution, impregnating the resorcinol-formaldehyde sol solution into a carbon paper, and then placing the carbon paper in a high pressure vessel under a atmospheric pressure and a temperature of 75 to 85 ° C. Gelling the resorcinol-formaldehyde sol in a solution; And pyrolyzing in a temperature range of 700 to 1000 ° C. under a nitrogen atmosphere.

Carbon aerogels, resorcinol, formaldehyde,

Description

Method of producing carbon aerogel for charged deionized water purifier {Method of producing carbon aerogel for water purifier using capacitive deionization}

1 is a graph showing the effect of the catalyst ratio and gelation temperature on the BET specific surface area.

2 is a graph showing the effect of the density of carbon paper on the BET specific surface area.

Figure 3 is a graph measuring the capacitance of the carbon airgel prepared by varying the manufacturing conditions.

The present invention relates to a method for producing a carbon airgel, and more particularly, to a method for producing a carbon airgel which can improve the capacitance of a carbon airgel electrode used in a charged deionized water purifier.

Capacitive deionization water purification technology first began to be studied in the 1960s and has recently been in the spotlight with the development of new porous carbon electrodes. The principle is so simple that when a voltage containing two porous electrodes is flowed, water containing ions flows between the electrodes, whereby cations are collected at the cathode and negative ions at the surface of the anode, thereby removing ions in the water. In other words, it uses a principle of adsorption of ions using electrical force. Once the electrode is saturated with ions, the ions easily come off when the opposite charge is applied, so there is no need to use an acid wash such as H ₂ SO ₄ or H ₂ NO ₃ and a base or salt solution such as NaOH for electrode regeneration. This does not happen. Charged deionized water purification technology does not have the risk of corrosion and contamination of the membrane and does not use a high-pressure pump, so compared with reverse osmosis, it requires less energy and is easier to maintain.

The first findings of charged deionized water purification technology were published at the University of Oklahoma in the early 1960s and related to the desalination process in brine [B. B. Arnold and G. W. Murphy, J. Phys. Chem. 65, 1961, 135-8]. Reports such as "Caudil" describe in detail a flow-through capacitor with pore activated carbon electrodes [D. D. Caudle, J. H. Tucker, J. L. Cooper, B. B. Arnold and A. Papastamataki, "Electrochemical Demineralization of Water with Carbon Electrodes", Research and Development Progress Report 188, US Department of the Interior, May, 1996]. U.S. Patent No. 3,515,664 describes a similar study conducted with activated carbon, and Johnson et al.'S experimental process demonstrates the rationale for the process, studies on the effects of changing parameters, and studies on various electrode candidates. Evaluation is included.

"Newman" developed a comprehensive theoretical model for the storage of pore carbon electrodes under Johnson's influence [A. M. Johnson and J. Newman, J. Electrochem. Soc. 118, 1971, 510-7. The analysis of "Newman" can be applied to all charged deionized water purification systems of general structure. Johnson stopped charging deionized water because of a number of problems, such as electrodes without deterioration, but previous price studies have shown that an efficient, low-cost desalination process based on this technology can be achieved if only proper electrode durability is achieved. Can be. Such work was not included in the study because this work was done before the invention of the carbon airgel electrode.

A few years later a study of charged deionized water was performed in Israel [Idem, J. Appl. Electrochem. 13, 1983, 473-87. The column was made of two separate vertical activated carbon layers, one acting as an anode and one as a cathode, with a concentration ratio of 1/100 at the inlet and outlet of the column.

U.S. Patents 5,415,768 and 5,360,540 propose charged deionized water purification techniques using activated carbon electrodes. Lawrence Livermor National Laboratory (L. L. N. L) of the United States discloses charged deionized water using carbon aerogels in US Pat. No. 5,425,858.

The core of water purification technology is affected by the physical properties of the carbon electrode. However, these technical results do not quantitatively indicate the correlation between the physical properties of the carbon electrode and the capacitance of the electrode.

Carbon aerogel electrode is prepared using a carbon aerogel composite, pyrolysis of the organic aerogel obtained through the sol-gel process and drying process using the organic material as a starting material to obtain a carbonized porous carbon aerogel. Representative organic aerogels are generally used by the methods proposed by L. L. N. L, “Pecalar” and the like [R. W. Pekala, ST Mayer, JF Poco, and JL Kaschmitter, "Novel forms of carbon II", (edited by C. Renschler, DM Cox, JJ Pouch and Y. Achiba), MRS Symp, Proc., 349, 79, 1994]. Resorcinol and formaldehyde are used as raw materials for the carbon electrode for water purification.

The method for producing a carbon airgel electrode is first impregnated with a sol solution obtained from condensation of resorcinol and formaldehyde on carbon paper (eg, Technical Papers, manufactured by Lyndall, USA). In order to prevent the evaporation of the synol-formaldehyde / carbon paper, it is placed between glass plates and subjected to gelation. Subsequently, water in the gel is substituted with acetone to obtain an aerogel complex impregnated with carbon paper. A thin film (about 150 μm) with a density of about 0.8 g / cm 3 can be obtained, which is connected to a titanium current integrator and pressurized to produce a carbon aerogel electrode, which is a foamed carbon aerogel electrode with high porosity and specific surface area. And it has the characteristics of ultra-mini-century structure.

However, the method of drying a carbon paper impregnated with a resorcinol-formaldehyde sol solution between glass plates and drying it has a problem that the density of the gel becomes high and the specific surface area is reduced.

Accordingly, an object of the present invention is to provide a method for manufacturing a carbon airgel having a specific surface area and an average pore size that can solve the above problems and improve the capacitance of the carbon airgel electrode.

In order to achieve the above object, the method for producing a carbon airgel according to the present invention,

Mixing resorcinol and formaldehyde in a predetermined ratio, adding distilled water at a solid fraction of 9% by weight and adding a basic catalyst at a catalyst ratio of 100 or less to form a resorcinol-formaldehyde sol solution,

Impregnating the resorcinol-formaldehyde sol solution into a carbon paper, and then placing the carbon paper in a high pressure vessel and gelling the resorcinol-formaldehyde sol under a nitrogen atmosphere at a pressure above atmospheric pressure and a temperature of 75 to 85 ° C .; And

Pyrolysis in a temperature range of 700 to 1000 ° C. under a nitrogen atmosphere.

Resorcinol-formaldehyde gel is formed by mixing a predetermined ratio of resorcinol and formaldehyde in an aqueous solution in the presence of a basic catalyst such as sodium carbonate and raising the temperature to react for a sufficient time. Resorcinol and formaldehyde generally react at a molar ratio of 1: 2 to form a gel, which is resorcinol which is trifunctional with 2,4,6 ring positions activated, and formaldehyde is difunctional ( bifunctional).

In the present invention, each of the resorcinol-formaldehyde sol solutions was prepared by changing the parameters of the resorcinol-formaldehyde sol-gel process and dried by impregnation with carbon paper having different densities. At this time, unlike the conventional method of putting between the glass plate and dried, the gelation was performed using a container that can be sealed. That is, the carbon paper impregnated with the resorcinol-formaldehyde sol solution is placed in a rectangular metal container, and nitrogen gas is injected to maintain the pressure in the container above atmospheric pressure, for example, 1.5 atm, and then maintain a constant temperature in a thermostat. Gelation was induced. When the gelation reaction is carried out in this way, the structure of the gel becomes dense when it is dried using a conventional glass plate, thereby increasing the density, thereby preventing the phenomenon of decreasing the specific surface area.

In order to obtain an electrode with a large capacitance, it is preferable to use a material having good electrical conductivity and a large specific surface area as the electrode material. Therefore, carbon aerogels are preferable as their specific surface area is larger. Since the specific surface area, average pore size and gelation rate of the carbon aerogels vary greatly depending on the catalyst ratio, the solid fraction and the gelation temperature, it is necessary to optimize these conditions.

Here, the "catalyst ratio" is the weight of resorcinol divided by the weight of the catalyst, and the "solid fraction" is the weight of resorcinol divided by the weight of the total solution.

In general, the gelation time of the resorcinol-formaldehyde sol solution is faster the greater the amount of catalyst, that is, the smaller the value of the catalyst ratio, the faster the greater the amount of diluent, that is, the lower the solid fraction.

In an embodiment of the present invention, the solid fraction is 9% by weight, and the specific surface area of the resorcinol-formaldehyde gel obtained by varying the catalyst ratio and the gelation temperature is measured. As a result, the catalyst ratio is 100 or less and the gelation temperature is 75. When it was -85 degreeC, especially 80 degreeC, the specific surface area showed high.

The carbon paper used in the present invention is a kind of support for supporting an airgel. Since airgel is a very low density material, the strength is somewhat weak, so it may be easily broken when manufactured in the form of a thin film. Therefore, a support is used to increase the strength of the electrode, but the physical properties of the manufactured carbon airgel electrode vary according to the type of support. . Considering the specific surface area of the carbon airgel, the preferred carbon paper density is 0.1 to 0.4 g / cm 2, and more preferably, the carbon airgel having the largest specific surface area can be obtained when the carbon paper density is 034 g / cm 2.

Gelled resorcinol-formaldehyde carbon paper is carbonized by thermal decomposition under a nitrogen atmosphere. At this time, when the reaction proceeds at a solid fraction of 9% by weight, a final pyrolysis temperature of 700 to 1000 ° C., and a temperature increase rate of 5 to 20 ° C./min, the specific surface area is 600 to 700 m 2 / g with an improved capacitance, and the average porosity thereof. Carbon aerogels of 4-6 nm in size can be obtained.

The present invention will be described in more detail with reference to the following Examples. However, it is apparent to those skilled in the art that the present invention is not limited to these examples.

Example 1

Resorcinol and formaldehyde were mixed in a molar ratio of 1: 2, and then distilled water was added to adjust the solid fraction to 9% by weight, and the catalyst ratio was changed to 50, 100, 200, 300, and 500, respectively. Added. The resorcinol-formaldehyde sol solution was uniformly mixed and the carbon paper was added to the solution and sufficiently impregnated. The carbon paper impregnated with the resorcinol-formaldehyde sol solution was placed in a high pressure container and sealed by maintaining 1.5 atm by injecting nitrogen gas. The vessel was subjected to gelation by varying the gelation temperature at 25, 50, and 80 ° C. in a thermostat. At this time, the gelation time was about 18 hours when the gelation temperature is less than 50 ℃, it was about 8 hours at 80 ℃. Thus, the BET specific surface area of the resorcinol-formaldehyde aerogel obtained by varying the catalyst ratio and the gelling temperature was measured, and the results are shown in FIG. 1.

1 is a graph showing the effect of the gelation temperature and the catalyst ratio on the BET specific surface area of the aerogel at 9% by weight of the solid fraction, it can be seen that the BET specific surface area is largely influenced by the catalyst ratio, the smaller the specific catalyst ratio increases there was. In order to enlarge a specific surface area, it is preferable to make gelation temperature 80 degreeC and catalyst ratio 100 or less.

Example 2

According to the method of Example 1, a resorcinol-formaldehyde sol solution was prepared at a solid fraction of 9% by weight and a catalyst ratio of 100, and impregnated with different carbon papers having density of 0.17, 0.34, and 0.68 g / cm 2 at 80 ° C. After gelation, pyrolysis was carried out at a temperature increase rate of 20 ° C / min at a final pyrolysis temperature of 700 to 1000 ° C. Thus, the BET specific surface area of the carbon aerogel obtained by changing the density of carbon paper was measured, and the result is shown in FIG.

2 is a graph showing the relationship between the density of carbon paper and the BET specific surface area of carbon aerogels at a catalyst ratio of 100 and a heating rate of 20 ° C./min. As shown in the graph of FIG. 2, as the final pyrolysis temperature increases, the specific surface area increases, and the specific surface area is highest when the density of the carbon paper is 0.34 g / cm 2.

Example 3

In the same manner as in Example 1 and Example 2, a resorcinol-formaldehyde sol solution was prepared under the conditions shown in Table 1, and then impregnated in 0.34 g / cm 2 carbon paper and gelled at 80 ° C. Capacitance of carbon aerogels prepared by pyrolysis at different speeds was measured, and the results are shown in FIG. 3.

Figure 3 is a graph measuring the capacitance of the carbon airgel prepared by changing the manufacturing conditions according to the frequency change. As can be seen in the graph of FIG. 3, the capacitance of Samples 1 to 3 having a specific surface area of 600 to 700 m 2 / g and an average pore size of 4 to 6 nm was relatively high.

Sample Specific surface area (㎡ / g) Average pore size (nm) Final pyrolysis temperature (℃) Temperature rise rate (℃ / min) Solid fraction (% by weight) Sample 1 653.7 5.1381 700 10 9 Sample 2 695.4 5.5143 800 20 9 Sample 3 708.8 4.8952 1000 5 9 Sample 4 294.2 6.3473 1000 20 6 Sample 5 332.1 6.4122 1000 20 9 Sample 6 564.7 5.8953 1000 20 12 Sample 7 328.5 7.1197 1000 20 15

As such, the process according to the invention can provide a carbon aerogel having a high specific surface area suitable for use as a carbon electrode by synthesizing, gelling and pyrolysing an organic sol under certain conditions, in particular improving the capacitance of the carbon electrode. It is possible to provide a carbon aerogel having a specific surface area and pore size.

Claims (6)

Mixing resorcinol and formaldehyde in a 1: 2 molar ratio, to which distilled water is added at a solid fraction of 9% by weight, and a basic catalyst is added at a catalyst ratio of 100 or less to form a resorcinol-formaldehyde sol solution. Wow, The resorcinol-formaldehyde sol solution was impregnated in a carbon paper having a density of 0.1 to 0.4 g / cm 2, and then the carbon paper was placed in a high pressure vessel, and the resorcinol-at a pressure of atmospheric pressure or higher and a temperature of 75 to 85 ° C. under a nitrogen atmosphere. Gelling the formaldehyde sol; And Method of producing a carbon airgel comprising the step of pyrolysis in a temperature range of 700 ~ 1000 ℃ under a nitrogen atmosphere. The method of claim 1, wherein the basic catalyst is sodium carbonate. The method of claim 1, wherein the temperature increase rate of the pyrolysis temperature is 5 ~ 20 ℃ / min. The method of claim 1, wherein the carbon airgel has a specific surface area of 600 to 700 m 2 / g and an average pore size of 4 to 6 nm. delete delete

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