JP2002018226A - Method for adsorptive separation of carbon dioxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for adsorptive separation of carbon dioxide in a gas such as exhaust combustion gas exhausted from an electric power station. SOLUTION: A low silica X type zeolite molded body containing at least 95% low silica X type zeolite with a molar ratio of SiO2/Al2O3 of 1.9-2.1 is brought into contact with a mixed gas containing carbon dioxide with a molar fraction of at least 5% and a gas with a lower polarity than carbon dioxide to perform adsorptive separation of carbon dioxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adsorbing and separating carbon dioxide from a mixed gas comprising two or more components including carbon dioxide and a gas having a polarity lower than that of carbon dioxide.
More specifically, the present invention relates to a method for adsorbing and separating carbon dioxide from combustion exhaust gas discharged from a fixed source such as a thermal power plant.

[0002]

2. Description of the Related Art Carbon dioxide is contained not only in combustion exhaust gas but also in natural gas or in a small amount in air.
Also, carbon dioxide is by-produced when hydrogen is obtained by steam reforming of natural gas, naphtha, coke, methanol and the like. Industrially by-produced carbon dioxide, including combustion exhaust gas, is a greenhouse gas that causes global warming, and has attracted attention in recent years. In addition, in the air separation by the cryogenic separation method, a small amount of about 300 to 400 ppm of carbon dioxide in the air becomes solid by cooling, causing a trouble such as blocking a heat exchanger.

As a method for separating and removing carbon dioxide, there have been proposed and carried out a method of absorbing carbon dioxide in an alkaline solution or an amine solution as a chemical absorption method and a method of removing carbon dioxide by adsorbing it on an adsorbent as a physical adsorption method. Activated carbon or zeolite is used as the adsorbent. In the physical adsorption method using an adsorbent such as zeolite, a temperature / pressure swing method (PTSA method) in which temperature and pressure are varied, a pressure swing method in which only pressure is varied (PSA method),
Temperature swing method (TSA) to change the temperature at the time of desorption
Method), the carbon dioxide is adsorbed and separated. Generally, carbon dioxide is adsorbed on an adsorbent at a low temperature and a high pressure, and carbon dioxide is desorbed from the adsorbent at a temperature and a pressure higher than the adsorption temperature to regenerate the adsorbent. At this time, a gas that is less adsorbed than carbon dioxide and does not contain carbon dioxide may be heated and circulated for purging.

As is conventionally known, zeolite adsorbents adsorb molecules by the interaction between cations and molecules present in zeolite, and the larger the polarity of the adsorbed molecules, the greater the interaction and the larger the adsorption capacity. Become. Considering the typical molecules present in the combustion exhaust gas, the order of the magnitude of the interaction between the zeolite and the molecule is water> carbon dioxide>
It becomes nitrogen, and the adsorption capacity is also in this order. Since water is often difficult to desorb when adsorbed on zeolite, it is used after almost all of it has been removed by alumina or the like in advance.

[0005] For example, when adsorbing and removing carbon dioxide in exhaust gas such as combustion exhaust gas, a typical carbon dioxide concentration in the exhaust gas is about 5 to 40%, and most of the remaining is nitrogen. The adsorption pressure when adsorbing and separating carbon dioxide in the exhaust gas by bringing the exhaust gas into contact with the adsorbent is generally about 1 to 2 atm, though it depends on the process. In the composition of the exhaust gas, the content of nitrogen is larger than that of carbon dioxide, but the strength of interaction with zeolite is overwhelmingly greater in carbon dioxide, and the amount of carbon dioxide adsorbed by coexisting nitrogen is not significantly reduced.

A zeolite adsorbent which has been used as an adsorbent for removing carbon dioxide from a mixed gas such as an exhaust gas is A-type zeolite or SiO ₂ /
It was an X-type zeolite having an Al ₂ O ₃ molar ratio of 2.5 or more. However, when carbon dioxide in the exhaust gas discharged from a fixed source or the like is adsorbed and separated, the amount of the exhaust gas to be treated is very large, so that the amount of the zeolite adsorbent used also increases. For this reason, an adsorbent having high carbon dioxide adsorption performance has been demanded in order to reduce the size of the apparatus or reduce the power consumption.

In JP-A-61-68116, a faujasite-type zeolite having an Si / Al atomic ratio of 1.2 to 3 is used as a method for selectively adsorbing carbon dioxide. Japanese Patent No. 2660703 proposes a method of adsorbing, separating and recovering carbon dioxide gas using CaX zeolite. JP-A-3-21316, JP-A-5-228
326 JP or Hei 9-187622 discloses the method of recovering carbon dioxide SiO ₂ / Al ₂ O ₃ molar ratio was used NaX or CaX zeolite 2.5 is disclosed. JP-A-3-229611 discloses a P
As a method of recovering CO ₂ by the SA method, NaX zeolite is used. Japanese Patent Application Laid-Open No. 7-39752 proposes an A-type zeolite adsorbent exchanged with barium ions as a carbon dioxide adsorbent. JP 1
In Japanese Patent Publication No. 0-101318, NaX zeolite is used in a method for producing high-purity carbon dioxide. As described above, the zeolite used to adsorb and separate carbon dioxide is A-type zeolite or SiO ₂ / Al ₂ O
₃ molar ratio was X-type zeolite 2.5. Tokuhei 6
JP-A-88768 discloses a faujasite-type zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of 2 to 100, but preferably has a SiO ₂ / Al ₂ O ₃ molar ratio of more than 3. Has been mentioned. As described above, the zeolite used for adsorbing and separating carbon dioxide was A-type zeolite or X-type zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of 2.5 or more.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for adsorbing and separating carbon dioxide in a gas such as flue gas discharged from a power plant.

[0009]

Means for Solving the Problems The present inventors have made intensive studies on the above problems, and as a result, have reached the present invention. That is, the present invention provides a method for adsorbing and separating carbon dioxide by bringing a mixed gas comprising two or more components including carbon dioxide and a gas having a polarity lower than that of carbon dioxide into contact with a zeolite adsorbent. ₂ / Al ₂ O ₃ molar ratio of 95% a low silica X-type zeolite 1.9-2.1
A low silica X-type zeolite molded article containing the above, wherein the molar fraction of carbon dioxide in the mixed gas when contacting the zeolite adsorbent is 5% or more,
This is a method for adsorbing and separating carbon dioxide. Hereinafter, the present invention will be described in detail.

The adsorbent used in the present invention is SiO ₂ /
Al ₂ O ₃ molar ratio is low silica X-type zeolite shaped body containing more than 95% of the low silica X-type zeolite 1.9 to 2.1.

As described above, the adsorption of gas to zeolite is caused by the interaction between cations present in zeolite and gas molecules. Therefore, the larger the number of cations, the more gas can be adsorbed. The number of cations in the zeolite depends on the number of Al forming the crystal skeleton of the zeolite, and when the number of Al increases, that is, SiO ₂ / Al ₂ O ₃
As the molar ratio decreases, the number of cations increases. It is known from the Loewenstein rule that the SiO ₂ / Al ₂ O ₃ molar ratio of zeolite is a minimum of 2.0. Thus, the low silica X-type zeolite crystal SiO ₂ / Al ₂
Although the O ₃ molar ratio is theoretically 2.0 as the minimum value, in consideration of measurement errors in chemical composition analysis and the like, in the present invention, 1.
The case of 9 to 2.1 is defined as a low silica X-type zeolite,
It is characterized by using it.

The SiO ₂ / Al ₂ O ₃ molar ratio is theoretically 2.
Examples of the zeolite 0 include A-type zeolites in addition to low-silica X-type zeolites. However, type A zeolite has a small pore size of about 4 to 5 angstroms,
The low silica X zeolite is advantageous for gas separation because it is as large as about 7 to 8 Å. Various methods have been disclosed as methods for synthesizing low silica X-type zeolite crystals, for example, Japanese Patent Application Laid-Open No. H11-217212.
JP, JP-A-10-310422, JP-A-10-310422
What is necessary is just to manufacture by the method described in -343112 or the like.

The zeolite adsorbent used in the present invention is:
A high-purity compact containing 95% or more of the low-silica X-type zeolite as described above, and preferably a compact containing 98% or more. As a result, a high adsorptivity and separation ability for carbon dioxide can be obtained.

Since zeolite crystal powder has no self-binding property, when used as the adsorbent of the present invention, it is formed into beads, pellets and the like by adding various binders and the like. Usually, since the binder does not have the property of adsorbing gas, the adsorption performance of the adsorbent is lower than the adsorption performance of the zeolite crystal powder by the amount of the binder. Therefore, in order not to lower the adsorption performance of the zeolite adsorbent used in the present invention, it is preferable that the binder component is converted into a zeolite crystal (binderless) after molding.

A high-purity binderless low silica X-type zeolite can be obtained, for example, as follows. Examples of low silica X-type zeolite powder include, for example,
Those manufactured by the methods described in JP-A-217212, JP-A-10-310422, JP-A-11-343112 and the like can be used. With respect to 100 parts by weight of the zeolite powder, 10 to 50 parts by weight of kaolin clay is uniformly kneaded while controlling the water content. As the binder to be used, kaolin clay which can be converted into low silica X-type zeolite is used. If the amount of kaolin clay added is too small, sufficient strength of the molded body cannot be obtained, and if it is too large, crystallization to zeolite does not proceed sufficiently even with binderless conversion, and a low silica X-type zeolite binder is used. The purity of the low silica X-type zeolite in the molded article is reduced. The amount of water in the kneaded material varies depending on the number of added kaolin clay and the subsequent molding method. Further, in order to enhance the granulation property of the kneaded product, various organic or inorganic granulation auxiliaries may be added within a range that does not significantly affect subsequent baking and binderlessness. The obtained kneaded product is molded by various molding methods. For example, pellet granulation by an extrusion granulation method, or bead granulation by a stirring granulation method or a tumbling granulation method may be mentioned.

After drying the obtained molded body,
Calcination at preferably 600 to 650 ° C.
A shaped body containing zeolite is obtained. Calcination is necessary in order to facilitate the transformation of the added kaolinous clay into a low-silica X-type zeolite by binderless treatment. The calcination changes the kaolin clay into amorphous metakaolin, which facilitates the transformation to low silica X-type zeolite. Drying and baking can be performed by a usual method, for example, using a hot air dryer, a muffle furnace, a rotary kiln, a tubular furnace, or the like.

The high-purity low-silica X-type zeolite compact used in the present invention is a low-silica X-type zeolite obtained as described above.
It can be obtained by contacting a shaped zeolite-containing molded body with a caustic solution. The caustic solution at this time is a caustic solution in which the amount of Si dissolved from the molded body is larger than the amount of Al dissolved when the low-silica X-type zeolite-containing molded body is brought into contact, or a caustic solution containing an Al component. Is used. For example, the caustic solution used is preferably a mixed solution of sodium hydroxide and potassium hydroxide, and the mixing ratio of sodium hydroxide and potassium hydroxide is K / (Na + K) = 0.
1 to 0.4 is preferred. Even if it is less than 0.1 or more than 0.4, the binderless conversion is insufficient, impurities such as A-type zeolite, sodalite, F-type zeolite and E-type zeolite are easily generated, and low silica X-type zeolite binderless molding. It is not preferable because the content of the low silica X-type zeolite in the body may decrease.

The caustic solution in which the amount of Si dissolved from the low-silica X-type zeolite-containing compact is larger than the amount of Al dissolved is:
For example, it is a caustic solution in which the solubility of silicate is higher than that of aluminate. Since the solubility of the solution varies depending on the composition, concentration and temperature of the solution, the composition and concentration of the caustic solution to be used differ depending on the binderless temperature.

The binderless temperature can be increased to 40 ° C. or higher. The higher the temperature, the more advantageous the binderless speed. However, metakaolin is converted into a low-silica X-type zeolite by an exothermic reaction. Considering the temperature limit of the equipment material to be used and the suppression of the generation of impurities, 70-80
C is preferred.

Therefore, in this temperature range and in the above-mentioned mixing ratio of sodium hydroxide and potassium hydroxide, caustic solution in which the solubility of silicate is higher than that of aluminate is about 6 mol Per liter or more, and the higher the concentration of the caustic solution, the higher the degree. Preferably, the concentration is about 8 mol / l or more because the effect becomes remarkable and the binderless speed is advantageous. Even when the concentration of the caustic solution is around 6 mol / liter, if the treatment time for binderless treatment is short, the progress of binderless treatment may be insufficient,
It is preferable that the concentration of the caustic solution be higher, since the binderless process proceeds sufficiently in a short time. Therefore, when the concentration of the caustic solution is 6 mol / liter or more, the time required for binderless conversion is at least 10 hours or more.
In the case of 8 mol / liter or more, a contact time of at least 5 hours is required.

The caustic solution containing an Al component includes, for example, a caustic solution containing a water-soluble Al component such as sodium aluminate, a low silica X-type zeolite, a kaolin clay, and other solid Al components. It is a caustic solution and when metakaolin is transformed into low silica X-type zeolite,
There is no limitation on the form of solid or other Al components as long as the Al component is actively taken in. It is also preferable to reuse the caustic solution used once or more for the binderless process. When Al content is contained, the same effect is produced even when the concentration of the caustic solution is lower than when Al content is not contained, so that the progress of binderlessness is sufficient.

The amount of the alkali metal hydroxide in the caustic solution is required to be at least 5 times the amount that is sufficient for all the kaolinous clay in the low silica X-type zeolite-containing compact to be transformed into the low silica X-type zeolite. You. In particular, in order to increase the content of low-silica X-type zeolite in the low-silica X-type zeolite binderless molded article and to rapidly reduce the binder, it is necessary to use 10%.
More than twice is preferred.

However, if the ratio is more than 30 times, the amount of Al and Si dissolved in the caustic solution increases, so that the strength is lowered and the cost is increased due to the large amount of the caustic solution used.

The method of contacting the low-silica X-type zeolite-containing compact with the caustic solution is not particularly limited, but it is simple to pack the low-silica X-type zeolite-containing compact into a fixed-bed column and circulate the caustic solution. It is efficient.

The high-purity low-silica X-type zeolite molded product obtained by the above-described method has a remarkably improved pressure resistance compared to the low-silica X-type zeolite binderless molded product obtained by the prior art, and the particle size is small. With a particle size in the range of 1.4 to 1.7 mm, a pressure resistance of 1.0 kgf or more can be achieved, and it can be used sufficiently industrially.

Furthermore, in order to use the adsorbent of the present invention for adsorption separation of carbon dioxide, the high-purity low-silica X-type zeolite compact must be ion-exchanged with alkali metal and / or alkaline earth metal ions. Preferably, the exchange rate is 80% or more. More preferably, it is 90% or more. As the alkali metal, lithium, sodium and potassium are preferable, and as the alkaline earth metal, magnesium and calcium are preferable. Particularly, lithium, sodium and calcium are preferred. Since the type of cation affects the interaction of adsorption with carbon dioxide, a cation having a large carbon dioxide adsorption capacity is preferably used.

The ion exchange can be performed by a commonly known method such as a batch method and a column flow method. The temperature and the concentration of the solution at the time of ion exchange can be set under arbitrary conditions. The higher the temperature, the more advantageous in ion exchange equilibrium or speed. A temperature of 50 ° C. or higher is preferably used. The higher the concentration of the solution, the more advantageous for ion exchange. Usually, a solution having a concentration of 1 mol / liter or more is used. The compound used for ion exchange is not particularly limited as long as it can be easily provided as an aqueous solution, and for example, chloride, nitrate, sulfate, carbonate and the like can be used. Further, for example, since lithium is relatively expensive compared to other cations, a solution obtained by removing impurities from a solution once used for ion exchange can be used as an ion exchange solution.

The zeolite before ion exchange usually contains sodium and / or potassium as exchangeable cations. Therefore, when this zeolite is ion-exchanged with another cation, sodium, potassium, and the like existing from the beginning may remain. However, even if cations existing before ion exchange remain after ion exchange, they can be used as the adsorbent of the present invention. An adsorbent in which a transition metal ion such as zinc is exchanged as a cation other than the alkali metal and / or the alkaline earth metal can also be used.

After ion exchange, dry to some extent
By performing calcination activation at 0 to 550 ° C. under a flow of dehumidified air or nitrogen, it can be used as an adsorbent.

The adsorbent used in the present invention preferably has a high equilibrium adsorption amount of carbon dioxide and a high adsorption / desorption rate. If the adsorbent has a fast adsorption / desorption rate, PS
Since the cycle time can be shortened when used in the A method, the TSA method or the PTSA method, it is possible to increase the processing gas amount. The adsorption / desorption speed when adsorbing and removing carbon dioxide is generally affected by the macropore structure of the zeolite adsorbent. The macropores are pores formed between the zeolite crystal particles and affect the mass transfer rate in the particles. Therefore, it is preferable that the pore volume and the pore diameter are large. The high-purity binderless low silica X-type zeolite compact obtained by the above method has a macropore volume of 0.1.
At 25 cc / g or more, the average pore diameter of the macropores is 0.
35 μm or more can be achieved, and a mass transfer rate that does not decrease the original adsorption performance of the adsorbent can be obtained. If the pore volume and the average pore diameter are smaller than these, a sufficient mass transfer rate cannot be obtained, and the original performance of the adsorbent may not be obtained.

The molded article may be in the form of beads or pellets, and has an average particle diameter of preferably 0.5 to 3 mm, more preferably 0.5 to 2 mm. If the average particle size is larger than 3 mm, the surface area per unit volume of the packed bed becomes small, and there is a possibility that the mass transfer speed in the particles becomes small. If the average particle diameter is smaller than 0.5 mm, the pressure loss of the packed bed becomes too large, and the power consumption may deteriorate, which is not preferable. The average particle size can be measured by a general method, and a method by sieving, a method of obtaining from a pressure loss at the time of gas flow and an Elgan equation, and the like can be used.

The adsorbent used in the present invention includes a pressure swing method (PSA method) for separating by raising and lowering a pressure, a temperature swing method (TSA method) for separating by raising and lowering the temperature,
Alternatively, pressure-temperature swing method (PTSA) in which separation is performed by performing both pressure swing and temperature swing
Method 2) can be used effectively when carbon dioxide is adsorbed and separated by the method. In particular, when the carbon dioxide is adsorbed and separated using the high-purity binderless low silica X-type zeolite molded body, the carbon dioxide adsorption capacity is large,
It is possible to reduce the size of the separation device and reduce the power consumption.

The gas used in the present invention is a mixed gas comprising two or more components including carbon dioxide and a gas having a polarity lower than that of carbon dioxide, and examples thereof include combustion exhaust gas. The gases less polar than carbon dioxide include nitrogen,
Oxygen, rare gas and the like can be mentioned. The temperature at the time of adsorption / desorption of carbon dioxide is not particularly limited.
To 100 ° C., and the temperature for desorption is 20 to 30
0 ° C. is preferred. The mixed gas contains carbon dioxide in a molar fraction of 5% or more. According to the present invention, carbon dioxide can be surely adsorbed and separated.

[0034]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. In addition, each evaluation was implemented by the method shown below.

(1) Method of measuring chemical composition After completely dissolving a sample using nitric acid and hydrofluoric acid,
Emission spectrometer (PerkinElmer, model optim
a3000) to identify the concentrations of various metal ions,
When an ion equivalent ratio, for example, an equivalent ratio of Li ions in a zeolite containing Li ions, Na ions, and K ions, is calculated as Li / (Li + Na + K).

(2) Method of measuring crystal structure X-ray diffractometer (Model MXP-, manufactured by Mac Science)
It measured using 3).

(3) Measuring method of water equilibrium adsorption amount A sample dried at 60 ° C. or more was subjected to a temperature of 25 ° C.
% Desiccator at 900 ° C
It was heated for an hour and measured. That is, the weight after moisture adsorption is X
_1, the weight after heating this 900 ° C. 1 hour a little and X _2,
The water equilibrium adsorption amount (%) was determined from the following equation.

Water equilibrium adsorption (%) = ｛(X ₁ -X ₂ ) /
X ₂ ｝ / 100 (4) Adsorption capacity 25 ° C. with BELSORP 28SA manufactured by Nippon Bell Co.
Alternatively, the amount of carbon dioxide adsorbed at 40 ° C. was measured.
As a pretreatment, a vacuum activation of 350 ° C. for 2 hours (1 × 1
0 ^-3 mmHg or less). Dual adsorption isotherm
-Site Langmuir formula (Ind. Eng. C.)
hem. Res. 1996, 35, 2477-248
3) was approximated. 150 m using the obtained adsorption isotherm
The amount of carbon dioxide adsorbed at mHg was determined.

(5) Macropore Volume and Average Pore Diameter of Macropores Using a mercury intrusion porosimeter (manufactured by Micromeritics, Model: Pore Sizer 9310), the activated adsorbent was added at 1 to 30,000 psi. It was measured in the pressure range (pore diameter ranging from 60 Å to 200 μm).

Example 1 First, a low silica X-type zeolite powder was synthesized by the following procedure.

In a 20-liter stainless steel reaction vessel, 10770 g of an aqueous solution of sodium silicate (Na ₂ O = 3.8% by weight, SiO ₂ = 12.6% by weight), and water 13
30 g, sodium hydroxide (99% purity) 1310 g,
3630 g of industrial potassium hydroxide aqueous solution (purity 48%)
And kept at 45 ° C. using a water bath while stirring at 100 rpm. An aqueous solution of sodium aluminate (Na ₂ O = 20.0% by weight, Al ₂ O
(O ₃ = 22.5% by weight) was charged over 1 minute. Immediately after the addition, the mixture became cloudy and gelation started. Immediately before the end of the charging, the viscosity of the whole gel increased, and although the slurry partially stayed in the upper portion of the reaction vessel, the whole fluidized uniformly after about 3 minutes. When the entire slurry was fluidized, low silica X-type zeolite powder (ignition loss 22.5%) 4.22
g was dispersed in a small amount of water and added. The amount of the low silica X-type zeolite added at this time was 0.1% by weight based on the low silica X-type zeolite produced. After completion of the addition, the composition of the slurry was 3.39Na ₂ O · 1.31K ₂ O · 1.90
SiO ₂ · Al ₂ O ₃ · 74.1H ₂ O, and the concentration of low silica X-type zeolite theoretically produced is 14.7% by weight. The stirring is continued at 100 rpm as it is,
Aging was performed at 5 ° C. for 4 hours. After aging, the temperature was raised to 70 ° C. over 1 hour while continuing stirring. After the temperature was raised, stirring was stopped, and crystallization was performed at 70 ° C. for 8 hours. The obtained crystals were filtered, sufficiently washed with pure water, and dried at 70 ° C. overnight.

The obtained low silica X-type zeolite powder is
As a result of X-ray diffraction, it was a faujasite type zeolite single phase, and as a result of composition analysis, the chemical composition was found to be 0.7
2Na ₂ O · 0.28K ₂ O · Al ₂ O ₃ · 2SiO ₂ , S
The iO ₂ / Al ₂ O ₃ molar ratio is 2.0, and the water equilibrium adsorption amount is 3
It was 3.5%.

To 100 parts by weight of the low silica X-type zeolite powder, 20 parts by weight of kaolin clay having a SiO ₂ / Al ₂ O ₃ molar ratio of 2.0 (manufactured by Drive Lunch Kaolin Co., Ltd., product name: Hydrite PXN) were mixed. After mixing for 15 minutes with a maller mixer (manufactured by Shinto Kogyo Co., Ltd., model MSG-15S),
The required amount of water was added for 15 minutes, and then kneaded for 1.5 hours. The water content of the obtained kneaded product was about 38% by weight.

The kneaded material was converted into beads having an average particle size of 1.6 mm (particle size range: 1.2 to 2.0 mm) using a blade stirring type granulator Henschel mixer (Model: FM / I-750, manufactured by Mitsui Mining Co., Ltd.). The mixture was subjected to stirring granulation molding, sized using a marmerizer molding machine (Model Q-1000, manufactured by Fuji Paudal Co., Ltd.), and then dried at 60 ° C. overnight. Then, at 600 ° C. under a stream of air using a tubular furnace (manufactured by Advantech Co.)
After firing for a period of time, the kaolin in the granulated product was metakaolinized to obtain a low silica X-type zeolite-containing molded product.

The low-silica X-type zeolite-containing compact was charged to a 13 liter SUS304 column having a volume of 9.0 liters.
g, and washed with pure water at 40 ° C. After washing, 40 ° C
25.2 liters of a caustic solution (NaOH: 7.2 mol /
Liter, KOH: 2.8 mol / l) was circulated from the bottom of the column at 560 cc / min for 3 hours. Thereafter, the temperature was increased from 40 ° C. to 70 ° C. while circulating the caustic liquid.
, And crystallized as it was by circulation for 6 hours. At this time, the amount of the alkali metal hydroxide in the caustic solution is
The amount of kaolin in the low-silica X-type zeolite-containing molded article was 18 times the amount required to transform into low-silica X-type zeolite.

After recovering the caustic solution, the inside of the column was sufficiently washed with pure water to obtain a low silica X-type zeolite binderless compact. The water-equilibrium adsorption amount of the obtained low-silica X-type zeolite binderless molded product is 33.4%, and the low-silica X-type zeolite binder is calculated from the water-equilibrium adsorption amount of the low-silica X-type zeolite 33.5%. The content of the low silica X-type zeolite in the molded article was 99.7%. The result of X-ray diffraction was a single phase of faujasite-type zeolite, and no diffraction line derived from impurities was confirmed.

The low silica X-type zeolite binderless compact is brought into contact with a lithium chloride aqueous solution whose pH has been adjusted to about 11 with lithium hydroxide to perform ion exchange.
A low-silica X-type zeolite binderless molded article was obtained.
This Li-type low silica X-type zeolite binderless molded product was subjected to chemical analysis. As a result, the Li ion exchange rate was 98.3.
%, And the ion exchange rates of Na and K are 1.3% and 0.1%, respectively.
4%, SiO ₂ / Al ₂ O ₃ molar ratio was 2.0. The obtained Li-type low silica X-type zeolite binderless compact was fired and activated at 500 ° C. for 3 hours in a dehumidified air flow using a tubular furnace (manufactured by Advantech).

The amount of carbon dioxide adsorbed on the obtained Li-type low silica X-type zeolite binderless adsorbent was measured. 25
Table 1 shows the amounts of carbon dioxide adsorbed at 150 mmHg at 40 ° C and 40 ° C. Table 2 shows the results of measuring the macropore volume and the average pore diameter of the macropores by a mercury intrusion method.

Example 2 A low silica X-type zeolite binderless compact obtained in the same manner as in Example 1 was dissolved in lithium carbonate solution (pH 7) obtained by dissolving lithium carbonate with hydrochloric acid.
Was brought into contact with an aqueous solution adjusted to about 11, thereby performing ion exchange to obtain a Li-type low silica X-type zeolite binderless molded article. As a result of chemical analysis of this Li-type low silica X-type zeolite binderless compact, the Li ion exchange rate was 9%.
5.3%, Na ion exchange rate 2.3%, K ion exchange rate 1.7%, Mg ion exchange rate 0.3%, Ca ion exchange rate 0.4%, SiO ₂ / Al ₂ The O ₃ molar ratio is 2.
It was 0. The obtained Li-type low silica X-type zeolite binderless compact was fired and activated at 500 ° C. for 3 hours in a dehumidified air flow using a tubular furnace (manufactured by Advantech).

The amounts of carbon dioxide and nitrogen adsorbed on the obtained Li type low silica X type zeolite binderless adsorbent were measured. Table 1 shows the amounts of carbon dioxide adsorbed.

Example 3 A low silica X-type zeolite binderless compact obtained in the same manner as in Example 1 was brought into contact with an aqueous sodium chloride solution adjusted to a pH of about 11 with sodium hydroxide to carry out ion exchange to obtain a Na-type zeolite binder. A low silica X-type zeolite binderless molded product was obtained. This Na-type low silica X-type zeolite binderless molded product was subjected to chemical analysis. As a result, the Na ion exchange rate was 97.9%, the K ion exchange rate was 2.1%, and SiO ₂ /
The Al ₂ O ₃ molar ratio was 2.0. The obtained Na-type low-silica X-type zeolite binderless molded body was placed in a tubular furnace (manufactured by Advantech Co., Ltd.) under dehumidified air flow,
It was fired and activated at 500 ° C. for 3 hours.

The amount of carbon dioxide adsorbed on the obtained Na-type low silica X-type zeolite binderless adsorbent was measured. Table 1 shows the amounts of carbon dioxide adsorbed.

Example 4 A low silica X-type zeolite binderless compact obtained in the same manner as in Example 1 was brought into contact with a lithium chloride aqueous solution whose pH was adjusted to about 11 with lithium hydroxide to carry out ion exchange to obtain a Li-type. A low silica X-type zeolite binderless molded product was obtained. As a result of chemical analysis of this Li-type low silica X-type zeolite binderless molded product, the Li ion exchange rate was 8%.
6.0%, the ion exchange rates of Na and K were 10.7, respectively.
% And 3.3%, and the SiO ₂ / Al ₂ O ₃ molar ratio was 2.0. The obtained Li-type low silica X-type zeolite binderless compact was fired and activated in the same manner as in Example 1.

The amount of carbon dioxide adsorbed on the obtained Li type low silica X type zeolite binderless adsorbent was measured. Table 1 shows the amounts of carbon dioxide adsorbed under the above conditions.

Example 5 A low-silica X-type zeolite binderless compact obtained in the same manner as in Example 1 was brought into contact with an aqueous solution of calcium chloride whose pH was adjusted to about 11 with calcium hydroxide to carry out ion exchange. A low silica X-type zeolite binderless molded product was obtained. As a result of chemical analysis of the Ca-type low silica X-type zeolite binderless compact, the Ca ion exchange rate was 94.4% and the ion exchange rates of Na and K were 3.
5% and _{2.1%, SiO 2 / Al 2} O 3 molar ratio was 2.0. The obtained Ca-type low silica X-type zeolite binderless compact was fired and activated in the same manner as in Example 1.

The amount of carbon dioxide adsorbed on the obtained Ca type low silica X type zeolite binderless adsorbent was measured. Table 1 shows the amounts of carbon dioxide adsorbed under the above conditions.

Comparative Example 1 A low-silica X-type zeolite-containing compact was obtained in the same manner as in Example 1 except that kaolin was used in an amount of 30 parts by weight. The molded product was placed in a polypropylene column having an internal volume of 3.1 liters.
Filled to 2 kg. 8.1 liters of caustic solution (NaO
(H: 2.2 mol / L, KOH: 0.9 mol / L) and the binderless treatment was performed in the same manner as in Example 1. The amount of the alkali metal hydroxide in the caustic solution at this time was 7.5 times the amount that was sufficient for all the kaolin in the low silica X-type zeolite-containing compact to be transformed into the low silica X-type zeolite.

Thereafter, the inside of the column was sufficiently washed with pure water to obtain a low-silica X-type zeolite binderless molded article. The water-equilibrium adsorption amount of the obtained low-silica X-type zeolite binderless molded product is 30.5%, and the low-silica X-type zeolite binder is calculated from the water-equilibrium adsorption amount of the low-silica X-type zeolite 33.5%. Low silica X
It was confirmed that the content of the zeolite was 91%. As a result of X-ray diffraction, diffraction lines derived from A-type zeolite were confirmed in addition to diffraction lines derived from faujasite-type zeolite. This binderless low silica X-type zeolite was subjected to Li ion exchange in the same manner as in Example 1 and subjected to chemical analysis. As a result, the Li ion exchange rate was 97.9%, and
The ion exchange rates of a and K are 1.9% and 0.2%, respectively.
The SiO ₂ / Al ₂ O ₃ molar ratio was 2.0. The obtained Li-type low silica X-type zeolite binderless molded body is
The firing was activated in the same manner as in Example 1.

The amount of carbon dioxide adsorbed on the obtained Li-type low silica X-type zeolite binderless adsorbent was measured. Table 1 shows the amounts of carbon dioxide adsorbed under the above conditions. Table 2 shows the results of measuring the macropore volume and the average pore diameter of the macropores by a mercury intrusion method.

Comparative Example 2 Adsorption of binderless NaX zeolite (SiO ₂ / Al ₂ O ₃ molar ratio 2.5, Na ion exchange rate 100%, manufactured by Tosoh Corporation) conventionally used for carbon dioxide adsorption separation. The amounts were measured and the results are shown in Table 1. The binderless NaX was a faujasite-type zeolite single phase from the result of X-ray diffraction, and no diffraction line derived from impurities was confirmed.

Comparative Example 3 Binderless CaX zeolite (SiO ₂ / Al ₂ O ₃ molar ratio 2.5, Ca ion exchange rate 92%: manufactured by Tosoh Corporation) conventionally used for adsorption and separation of carbon dioxide
Was measured, and the results are shown in Table 1. The binderless CaX was a faujasite-type zeolite single phase from the result of X-ray diffraction, and no diffraction line derived from impurities was confirmed.

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[Table 1]

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[Table 2]

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According to the above results, when the adsorbent of the present invention is used to perform adsorption separation of carbon dioxide in exhaust gas such as combustion exhaust gas discharged from a fixed source, it has been conventionally used. Since the amount of adsorbed carbon dioxide is larger than that of the adsorbent used, carbon dioxide can be removed with high efficiency, and the size of the adsorption device can be reduced, and the power consumption required for adsorption separation can be reduced.

Claims (17)

[Claims] 1. A method for adsorbing and separating carbon dioxide by bringing a mixed gas comprising at least two components including carbon dioxide and a gas having a polarity lower than that of carbon dioxide into contact with a zeolite adsorbent, wherein the zeolite adsorbent comprises SiO 2 ₂ / Al ₂ O ₃ molar ratio of 95 to low silica X-type zeolite 1.9-2.1
% Of a low-silica X-type zeolite compact containing at least
A method for adsorbing and separating carbon dioxide, wherein the molar fraction of carbon dioxide in the mixed gas at the time of contact with the zeolite adsorbent is 5% or more. 2. The method for adsorbing and separating carbon dioxide according to claim 1, wherein the low silica X-type zeolite compact is ion-exchanged with alkali metal and / or alkaline earth metal ions. 3. The method for adsorbing and separating carbon dioxide according to claim 2, wherein the ion exchange rate of said alkali metal and / or alkaline earth metal ions is at least 80% or more. 4. The method for adsorbing and separating carbon dioxide according to claim 2, wherein the ion exchange rate of the alkali metal and / or alkaline earth metal ions is at least 90% or more. 5. The method according to claim 2, wherein said alkali metal comprises at least one of lithium, sodium and potassium, and said alkaline earth metal comprises at least one of magnesium and calcium. The method for adsorptive separation of carbon dioxide according to the above. 6. The method for adsorbing and separating carbon dioxide according to claim 1, wherein said low silica X-type zeolite compact contains 98% or more of low silica X-type zeolite. 7. The carbon dioxide according to claim 1, wherein said low-silica X-type zeolite compact is substantially composed of only low-silica X-type zeolite without a binder. Adsorption separation method. 8. The low-silica X-type zeolite molded body has a macropore volume of 0.25 cc / g or more and an average pore diameter of the macropores of 0.35 μm or more. Item 8. The method for adsorbing and separating carbon dioxide according to any one of Items 1 to 7. 9. The adsorption and separation of carbon dioxide according to claim 1, wherein the low silica X-type zeolite molded body has an average particle diameter in a range of 0.5 to 3 mm. Method. 10. The method for adsorbing and separating carbon dioxide according to claim 1, wherein the low silica X-type zeolite molded article has an average particle diameter in a range of 0.5 to 2 mm. . 11. The method according to claim 1, wherein the adsorption separation is carried out by a pressure swing method and / or a temperature swing method.
10. The method for adsorbing and separating carbon dioxide according to any one of 10. 12. The temperature at which carbon dioxide is adsorbed is 20.
The method for adsorbing and separating carbon dioxide according to any one of claims 1 to 11, wherein the temperature is from 100 to 100 ° C. 13. The temperature for desorbing carbon dioxide is 20.
The method for adsorbing and separating carbon dioxide according to any one of claims 1 to 12, wherein the temperature is -300C. 14. The low-silica X-type zeolite molded product,
Low silica X-type zeolite and SiO ₂ / Al ₂ O ₃ molar ratio of SiO ₂ / Al ₂ O ₃ molar ratio of 1.9 to 2.1 is 1.9
The low-silica X-type zeolite-containing molded article is obtained by molding and firing using the kaolinous clay of 2.1, and the amount of dissolved Si from the low-silica X-type zeolite-containing molded article is A
1 by contacting the low-silica X-type zeolite-containing compact with a caustic solution greater than the dissolution amount of 1 to convert the kaolinic clay in the low-silica X-type zeolite-containing compact into a low-silica X-type zeolite. The method for adsorbing and separating carbon dioxide according to any one of claims 1 to 13, which is manufactured. 15. The low-silica X-type zeolite molded product,
15. The method for adsorptive separation of carbon dioxide according to claim 14, wherein the method is produced by contacting with a caustic solution of 6 mol / l or more for 10 hours or more. 16. The low-silica X-type zeolite molded product,
15. The method for adsorptive separation of carbon dioxide according to claim 14, wherein the method is produced by contacting with a caustic solution of 8 mol / l or more for 5 hours or more. 17. The low-silica X-type zeolite molded product,
The method for adsorbing and separating carbon dioxide according to any one of claims 14 to 16, wherein the method is produced by contacting with a caustic solution containing an Al component.