KR101488237B1 - Preparation Process of Dry Adsorbent for Selective Capture of Gaseous Carbon Dioxide - Google Patents

Abstract

The present invention relates to a method for manufacturing a carbon nanotube, comprising: impregnating an activated carbon with an aqueous solution of potassium hydroxide and then performing heat treatment; And a step of aminating the activated carbon treated with potassium hydroxide. The method of claim 1, wherein the selective adsorption of carbon dioxide to carbon dioxide in the exhaust gas of the industry or the indoor air is carried out.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a process for preparing a selective dry adsorbent for gaseous carbon dioxide,

The present invention relates to a process for the production of selective dry collectors for gaseous carbon dioxide which is highly selective for the carbon dioxide present in industrial exhaust gases or indoor air.

Techniques for capturing carbon dioxide in the exhaust gas, one of the greenhouse gases, and carbon dioxide in the indoor space of the multipurpose facility, are divided into dry and wet. The wet process is a typical technique using an amine, but there are problems in the hazard of the amine, the necessity of additional facilities for wastewater treatment, and the number of recovered carbon dioxide. In addition, since the limit of the wet process is too clear to be applied in an indoor environment, various dry-collecting processes have been variously researched and developed.

The adsorbent collector for dry cleaning must be selected and economical to be applied in the field. Various adsorbents such as zeolite, metal oxide, ceramic materials such as alumina, activated carbon and the like have been developed and produced. However, the selective removal of the carbon dioxide contained in the exhaust gas still does not reach the performance of the amine absorbent on the aqueous solution. This is an efficient, low-cost, renewable and long-life universal adsorbent capable of collecting carbon dioxide (0.04-0.3%) present in the air at high concentration (7-15% Has been urgently required.

In the case of the carbon dioxide adsorption reactor, it is known that the pressure inside the vessel is required to be 1 atm or more, and this adsorption reaction condition lowers the active applicability of the dry adsorption process. Therefore, it is necessary to develop an adsorbent capable of sufficiently exhibiting its performance at room temperature and atmospheric pressure while sufficiently utilizing the microporous structure of activated carbon. It is especially necessary to develop a technology that selectively captures only specific substances by maximizing chemical attraction between molecules rather than a general physical capture process.

Korean Patent Laid-Open Publication No. 1993-0012576 discloses a technique for producing activated carbon having excellent adsorbability without increasing the reduction rate by continuous treatment of activated carbon carbonized from palm-based or coal-based raw material at high temperature with steam and ammonia, No. 2012-0074078 discloses a high-temperature heat treatment step in which a woody raw material is flowed at a temperature of 800 ° C to 900 ° C for a certain period of time to form a surface activation favorable to adsorption of siloxane, Temperature raw material is flowed at a temperature of 400 ° C to 500 ° C for a certain period of time to provide an oxygen-containing functional group favorable to adsorption of hydrogen sulfide, thereby improving the adsorption capability of activated carbon

However, conventional dry collectors still have a very low ability to collect and select for capturing carbon dioxide present in industrial exhaust gases or indoor air.

The inventors of the present invention have conducted intensive research to develop a dry collector having excellent adsorbability to carbon dioxide present in industrial exhaust gas or indoor air. As a result, they have found that the surface of activated carbon can be treated with potassium and amine, And the present invention has been completed.

Accordingly, it is an object of the present invention to provide a method for producing an optional dry collector for gaseous carbon dioxide, which is excellent in selective adsorption ability on carbon dioxide present in industrial exhaust gas or indoor air.

It is another object of the present invention to provide an optional dry collector for gaseous carbon dioxide which is excellent in selective adsorption ability against carbon dioxide present in industrial exhaust gas or indoor air.

The present invention relates to a process for the production of selective dry collectors for gaseous carbon dioxide,

(i) a step of impregnating an activated carbon with an aqueous solution of potassium hydroxide, followed by heat treatment; And

(ii) aminating the activated carbon treated with potassium hydroxide.

In the step (i), the activated carbon preferably has fine pores and has a large specific surface area for adsorbing carbon dioxide. The active carbon may be pellet-type or granular-type coal origin or palm kernel-derived activated carbon, but is not limited thereto.

In one embodiment, the activated carbon is a granular activated carbon having a specific surface area of coal origin of 1000 to 1500 m ² / g and a particle size of 1 to 2 mm.

In the step (i), it is preferable to use an aqueous potassium hydroxide solution having a concentration of 1 to 5 mol per 1 mol of potassium hydroxide. If the concentration of the potassium hydroxide aqueous solution is less than 1 mole, the amount of potassium fixed on the activated carbon surface is low and the selectivity to carbon dioxide is low. If the concentration is more than 5 moles, the amount of potassium impregnated on the activated carbon surface is not uniformly distributed But the specific surface area can be reduced.

The aqueous potassium hydroxide solution is preferably used in a volume ratio of 1 to 10 times that of activated carbon. When the amount of the aqueous solution of potassium hydroxide is less than 1 time, the activated carbon can not be sufficiently impregnated.

In the step (i), the activated carbon is impregnated with an aqueous solution of potassium hydroxide to uniformly coat the surface of the activated carbon with potassium hydroxide, followed by filtration, drying and heat treatment at 400 to 600 ° C. The heat treatment is preferably performed in a nitrogen atmosphere.

Potassium hydroxide is highly effective in attaching metal ions to the surface of activated carbon with high basicity of potassium, and is basically an effective material for increasing the basicity of the activated carbon surface. In addition, potassium hydroxide has a high solubility in water at room temperature. At over 405 ℃, potassium hydroxide is completely dissolved by the following reaction and decomposed into potassium oxide (K ₂ O).

[Reaction Scheme 1]

2 KOH _{(s) -} > K ₂ O _(s) + H ₂ O _(l)

And potassium oxide forms potassium carbonate through chemical reaction with carbon dioxide.

[Reaction Scheme 2]

K ₂ O + CO _{2 -} > K ₂ CO ₃

The potassium oxide is a highly reactive oxide, but carbonaceous activated carbon helps to stabilize the potassium oxide.

On the other hand, when the concentration of potassium hydroxide is increased, the surface of the activated carbon becomes unstable, and when it is dried in the air, a phenomenon of ignition occurs, but the surface of the activated carbon can be stabilized by the amination step described later.

In the step (ii), activated carbon treated with potassium hydroxide is aminated using ammonia or the like to form a nitrogen functional group on the surface of activated carbon. In the amination step, various kinds of radicals are formed on the activated carbon surface by flowing ammonia gas at 600 to 800 ° C.

When activated carbon is supported in a high concentration aqueous solution of potassium hydroxide, potassium and hydroxide in the ionic state are adhered to the activated carbon surface to form molecular sieve of potassium hydroxide, and when water is evaporated through the heat treatment, it is transformed into highly reactive potassium oxide form Which is a condition that can explosively react with oxygen in the air. However, by introducing an amination process, such unstable surface active sites can be stabilized by NH, NH radicals, hydrogen ions, etc., which are decomposed in ammonia. Therefore, a higher concentration aqueous solution of potassium hydroxide can be used.

The amination process serves to stabilize the surface of the activated carbon exposed to the high concentration potassium hydroxide, and can further provide a basic adsorption point necessary for adsorption of carbon dioxide.

Since the carbon dioxide is a weak Lewis acidic gaseous substance, the inner and outer surfaces of the activated carbon are made basic so that the selectivity to carbon dioxide from various mixed gases can be improved. Such adsorption selectivity can be very usefully applied to trap carbon dioxide in exhaust gas at a high concentration or room air at a low concentration.

Accordingly, the present invention provides an optional dry collector for gaseous carbon dioxide produced by the above process.

The present invention relates to a method for preparing selective dry collectors for gaseous carbon dioxide by fixing potassium and amine on the surface of activated carbon in a two-step process so that selective adsorption and capture of weakly acidic carbon dioxide gas molecules at room temperature and atmospheric pressure According to the production method of the present invention, the ignition of the activated carbon adsorbent under abnormal conditions including temperature increase can be suppressed, and a stable basic surface structure can be formed.

The selective dry collector for gaseous carbon dioxide produced according to the present invention has excellent adsorptivity and selectivity to carbon dioxide present in industrial exhaust gas or indoor air.

FIG. 1 is a configuration diagram of a reaction apparatus for a heat treatment and an amination process according to the production method of the present invention.

Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these embodiments are for illustrative purpose only and that the scope of the present invention is not limited to these embodiments.

Production Example 1-4:

Activated carbon used for surface modification was activated carbon (WSC-470) made from coconut shell and activated carbon (WSC-490) made from coal. The activated carbon had a cylindrical pellet shape with an average length of 9 mm and a diameter of 4 mm. The raw activated carbon was pulverized, sieved to 1-2 mm, granulated into granular particles, and homogenized to a size of 1 mm to 2 mm.

The specific surface area and porosity of each activated carbon particle were measured and are shown in Table 1.

division Activated carbon S _BET (m ² / g) V _T (cm ³ / g) dp (nm) V _micro (cm < ³ > / g) V _meso (cm ³ / g) % a _ext Production Example 1
Production Example 2
Production Example 3
Production Example 4 P-CS
P-CL
G-CS
G-CL 1070.8
1205.1
1143.2
1324.4 0.463
0.513
0.505
0.601 1.728
1.702
1.768
1.812 0.467
0.453
0.432
0.490 0.050
0.060
0.074
0.102 0.76
0.69
0.90
0.98

* Palm tree peel Origin: P-CS: Pellet type, G-CS: Granular type

* Coal-derived activated carbon: P-CL: Pellet type, G-CL: Granular

In Table 1, S _BET means the specific surface area of particles that can be obtained from nitrogen gas adsorption at room temperature, V _T denotes the volume of pores formed on the inside and the outside of the activated carbon, and dp denotes the average diameter of the pores. In addition, V _micro and V _meso mean the volume of micro-pores and mesopores, respectively, and% a _ext is the ratio of the external surface area to the total area of activated carbon, Area.

The pH of the surface of activated carbon particles was 9.5 and the average density was 0.4 g / cm ³ .

Examples 1-4:

The activated carbon of Production Example 1-4 was immersed in a 1: 5 aqueous solution of potassium hydroxide at a ratio of 1: 5, followed by stirring at a speed of 100 rpm for 3 hours. The mixed solution was filtered, and then dried at 120 ° C. The dried activated carbon was stored in a desiccator.

Each sample was heat-treated at 600 DEG C for 2 hours in a nitrogen-atmosphere firing furnace using the reactor shown in Fig. After the heat treatment, the cooling was also performed in a nitrogen atmosphere. Table 2 shows the physical properties of activated carbon treated with potassium hydroxide.

Potassium hydroxide
Activated carbon S _BET (m ² / g) V _T (cm ³ / g) dp (nm) V _micro (cm ³ / g) V _meso (cm ³ / g) V _micro / V _T % a _ext KP-CS
KP-CL
KG-CS
KG-CL 1067.5
1019.3
1126.3
915.9 0.481
0.451
0.505
0.524 1.803
1.770
1.793
2.289 0.403
0.388
0.428
0.422 0.078
0.063
0.077
0.102 0.838
0.860
0.848
0.805 0.908
0.881
0.930
1.032

The activated carbon treated with potassium hydroxide was allowed to flow at a flow rate of 100 ccm (cm ³ / min) at 600 ° C. for 2 hours using the reactor shown in FIG. At this time, in order to prevent the oxidation reaction or the combustion of the activated carbon, the inflow of oxygen or air was blocked. After the amination process was completed, the activated carbon sample was allowed to stand in a vacuum oven at 105 ° C for about 2 hours to remove ammonia or nitrogen which might remain in the sample.

The amounts of activated carbon obtained in Production Examples 1 to 4 and the dry collectors (Examples 1 to 4) obtained by treating them with potassium hydroxide and aminating as described above (Examples 1 to 4) were measured for carbon dioxide adsorption amounts of 100%, 10% and 0.3% And the air flow rate including carbon dioxide was set at 100 ccm under ordinary conditions. The results are shown in Table 3 below.

sample CO ₂ adsorption amount (mmol / g) 100% 10% 0.3% Production Example 1
Production Example 2
Production Example 3
Production Example 4 2.197
2.136
2.176
2.091 0.646
0.550
0.489
0.451 0.030
0.029
0.029
0.026 Example 1
Example 2
Example 3
Example 4 2.330
2.530
2.320
2.333 1.375
0.756
0.806
0.896 0.300
0.380
0.340
0.730

It can be seen from Table 3 that the carbon dioxide adsorbing ability of the modified activated carbon composite obtained through the potassium hydroxide treatment and the amination process obtained in Examples 1 to 4 as compared with the raw activated carbon obtained in Production Examples 1 to 4 I could.

Example 5:

A dry collector was manufactured in the same manner as in Example 1 except that ammonia was flown at 800 ° C using the activated carbon of Production Example 1, and the amount of carbon dioxide adsorbed was measured. The results are shown in Table 4 below.

sample CO ₂ adsorption amount (mmol / g) 100% 10% 0.3% Example 5 2.342 1.052 0.440

From Table 4, it can be seen that the carbon dioxide adsorbing ability is similar to the case where the temperature of the amination step is set to 600 ° C even at 800 ° C.

Examples 6-7:

Except that the activated carbon of Production Example 1 and Production Example 4 was used instead of the aqueous solution of 1 molar potassium hydroxide in 2 molar potassium hydroxide aqueous solution and the time for heat treatment in ammonia atmosphere and ammonia flow for 1 hour, , A dry collecting body was produced in the same manner as in Example 1, and the amount of carbon dioxide adsorbed was measured. The results are shown in Table 5 below.

sample CO ₂ adsorption amount (mmol / g) 100% 10% 0.3% Example 6
Example 7 2.219
2.260 1.291
1.700 1.070
1.010

From Table 5, it can be seen that when using a 2 molar potassium hydroxide aqueous solution, the amount of adsorption to 100% carbon dioxide, which means the physical adsorption capacity, is slightly reduced, but the amount of adsorbed 10% And the adsorption amount (selectivity) for 0.3% carbon dioxide were equal or increased.

Examples 8-9:

Except that the activated carbon of Production Example 2 and Production Example 4 was used instead of 1 mole potassium hydroxide aqueous solution and 4 mole potassium hydroxide aqueous solution and the time for heat treatment in ammonia atmosphere and ammonia flow time for 1 hour respectively , A dry collector was prepared in the same manner as in Example 1, and the amount of adsorbed carbon dioxide was measured. The results are shown in Table 6 below.

sample CO ₂ adsorption amount (mmol / g) 100% 10% 0.3% Example 8
Example 9 2.035
1.950 1.370
2.151 1.620
1.505

From Table 6, it can be seen that when using a 4 molar potassium hydroxide aqueous solution, the adsorption capacity for 100% carbon dioxide, which means the physical adsorption capacity, is decreased compared with the case of using 1 molar potassium hydroxide aqueous solution, but the 10% And 0.3%, respectively. It was found that the selectivity to carbon dioxide was improved.

Examples 10-11:

The activated carbon of Production Example 4 was used instead of the aqueous solution of 1 mole of potassium hydroxide to prepare a 4-molar potassium hydroxide aqueous solution. The time for the heat treatment in the nitrogen atmosphere and the time for flowing the ammonia were 2 hours In the case of Example 11, a dry mass was produced in the same manner as in Example 1 except that the time was 0.5 hour and 1.5 hour, and the amount of carbon dioxide adsorption was measured. The results are shown in Table 7 below.

sample CO ₂ adsorption amount (mmol / g) 100% 10% 0.3% Example 10
Example 11 1.953
1.996 2.230
2.450 1.967
2.026

From Table 7, it can be confirmed that the adsorbent of Example 11 is superior in the selective adsorption amount to the low concentration carbon dioxide flow.

Examples 12-13:

Using the activated carbon of Production Example 4, in the case of Example 12, a 2-molar potassium hydroxide aqueous solution was used at a volume ratio of 10 times that of the activated carbon in place of the 1-molar potassium hydroxide aqueous solution. In the case of Example 13, A dry collector was manufactured in the same manner as in Example 1 except that the activated carbon was used at a volume ratio of 5 times, and the amount of carbon dioxide adsorbed was measured at an air flow rate of 150 ccm including carbon dioxide, Table 8 shows the results.

sample CO ₂ adsorption amount (mmol / g) 100% 10% 0.3% Example 12
Example 13 2.216
1.909 1.980
2.162 1.056
1.726

It can be seen from Table 8 that it is better to increase the molarity of the aqueous solution of potassium hydroxide in terms of increasing the selectivity to carbon dioxide. However, when it is impregnated with an excessively high concentration of potassium hydroxide aqueous solution, it may result in covering the pores of the activated carbon surface or decreasing the micropore size, so that the trapping performance for pure carbon dioxide may be rather reduced.

Claims (10)

(i) impregnating activated carbon with an aqueous solution of potassium hydroxide, and then heat-treating at 400 to 600 ° C; And
(ii) aminating the activated carbon treated with potassium hydroxide. < RTI ID = 0.0 > 21. < / RTI > The method according to claim 1, wherein the activated carbon in step (i) is a pellet or granular coal origin or a palm kernel derived activated carbon. The method according to claim 1, wherein the activated carbon in step (i) is a granular activated carbon having a specific surface area of from 1000 to 1500 m ² / g and a particle size of from 1 to 2 mm. The process according to claim 1, wherein in step (i), the aqueous potassium hydroxide solution is an aqueous potassium hydroxide solution having a concentration of 1 to 5 moles. The process according to claim 1, wherein the potassium hydroxide aqueous solution in step (i) is used in a volume ratio of 1 to 10 times that of activated carbon. delete The method according to claim 1, wherein the heat treatment in step (i) is performed in a nitrogen atmosphere. The method according to claim 1, wherein the activated carbon treated with potassium hydroxide in step (ii) is aminated using ammonia. The process according to claim 1, wherein the amination temperature in step (ii) is 600 to 800 占 폚. An optional dry collector for gaseous carbon dioxide produced by the process according to any one of claims 1 to 5 and 7 to 9.

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