JP2001347123A - Adsorptive separation method for carbon dioxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for adsorptively separating carbon dioxide from a gaseous mixture containing the carbon dioxide by using low-silica X type zeolite of high purity which has the excellent performance to adsorptively separate that race carbon dioxide and is made binderless. SOLUTION: The absorptive separation method for the carbon dioxide is characterized in that when a zeolite adsorbent and the gaseous mixture composed of >=2 kinds of components containing the carbon dioxide and gases having the polarity lower than the polarity of the carbon dioxide are brought into contact with each other, the partial pressure of the carbon dioxide ranges from 0.1 to 59 mmHg and the zeolite adsorbent is a low-silica X type zeolite which is 1.9 to 2.0 in SiO2/Al2O3 molar ratio and in which the content of the low-silica X type zeolite is >=95% and more preferably the absorbent is subjected to ion exchange at >=90% with lithium and/or sodium.

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 removing carbon dioxide from a gas stream of a mixed gas comprising two or more components containing carbon dioxide and a gas having a polarity lower than that of carbon dioxide. In a cryogenic separation method in which gas components are separated into components such as nitrogen, oxygen, and argon after being compressed and cooled until they are oxidized, carbon dioxide to be removed as impurities or inconvenient components in the process as a pretreatment is used as a raw material. The present invention relates to a method for adsorbing and removing from a mixed gas such as air.

[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 a physical adsorption method using an adsorbent such as zeolite, carbon dioxide is adsorbed and removed by a temperature / pressure swing method (PTSA method) in which temperature and pressure are varied, or a pressure swing method (PSA method) in which only pressure is varied. It is. 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 molecules existing in the air, the size of the interaction between the zeolite and the molecules is water> carbon dioxide>nitrogen>oxygen> argon, and the adsorption capacity increases in this order.

When carbon dioxide in air is adsorbed and removed,
Carbon dioxide concentration is about 300ppm, nitrogen concentration is about 78%
When the adsorbent is contacted at a pressure of 5 to 10 atm, the partial pressure of carbon dioxide is about 2 mmHg, and the partial pressure of nitrogen is about 4 to 8 atm. Although carbon dioxide has a large polarity and is adsorbed in a large amount on zeolite even at a low partial pressure, adsorption of carbon dioxide is hindered by a large amount of coexisting nitrogen, and the adsorption amount is reduced. In addition, almost all of the water is removed in advance by an adsorbent such as alumina.

A zeolite adsorbent which has been used as an adsorbent for removing carbon dioxide from a mixed gas such as air is A-type zeolite or SiO ₂ / Al ₂
It was an X-type zeolite having an O ₃ molar ratio of 2.5 or more. However, when air separation is performed by the cryogenic separation method, the amount of air to be treated is very large, so that the amount of the zeolite adsorbent used to adsorb and remove carbon dioxide also increases. For this reason, from the downsizing of the equipment or the reduction of the power consumption unit,
Even when nitrogen coexists, an adsorbent having high carbon dioxide adsorption performance is required.

[0007] JP-A-8-252419 discloses a method for removing carbon dioxide from a gas stream.
-50 ° C. using a zeolite of type X having a silicon to aluminum atomic ratio of about 1.0 to about 1.15 which has been exchanged with the cations of the Group 3, 3A, 3B, lanthanide series and mixtures thereof. It has been proposed to adsorb in the range of about 80 ° C., but as shown in Table 1 on page 6, only the amount of carbon dioxide absorbed when the pressure of the carbon dioxide gas was changed was measured. It does not measure the adsorption selectivity between carbon dioxide and nitrogen gas.

Also, preferred ions as ions of each group are listed as exchange cations, sodium and lithium are preferred as Group 1A ions, and calcium is preferred as Group 2A ions, and Table 1 on page 6 thereof.
The comparison of the carbon dioxide absorption between NaLSX and Li, CaLSX (sample containing lithium-calcium exchange adsorbent, containing 95 equivalents of lithium ions and 5 equivalents of calcium ions) was performed. Although it is shown that the carbon dioxide absorption amount is larger, the adsorption selectivity between carbon dioxide and nitrogen gas is not measured.

Japanese Patent Application Laid-Open No. H11-179137 proposes a method for removing water vapor and carbon dioxide from a gas by using sodium LSX zeolite to remove carbon dioxide after removing water vapor.

However, there is no description of a method for separating carbon dioxide from a mixed gas containing carbon dioxide and nitrogen.

Japanese Patent Application Laid-Open No. 11-253736 proposes an X-type zeolite containing calcium, sodium and potassium and having an Si / Al ratio of 1 to 1.5 as a method for purifying air by adsorption before low-temperature distillation. .

Further, in WO 00/01478, a sodium type SiO ₂ / Al ₂ O ₃ ratio of 1.8-2.2 containing less than 8% of potassium ions is used as an adsorbent for gas purification.
Has been proposed. However, the adsorbent used here has an insufficient purity of the zeolite crystals used, or the content of the zeolite crystals is reduced because the adsorbent contains a binder, and the adsorbent originally has Adsorption performance was not fully demonstrated.

Generally, the zeolite adsorbent is mixed with a binder and formed into an arbitrary shape. However, since the binder has no adsorbing performance, the adsorbing performance is reduced by an amount corresponding thereto. Therefore, a method for converting the binder component into zeolite has been proposed. JP-A-5-163015 discloses an X-type zeolite powder having a SiO ₂ / Al ₂ O ₃ molar ratio lower than 2.5, a kaolin-type clay converted to metakaolin, a molded product containing sodium hydroxide and potassium hydroxide. A low-silica X-type zeolite binderless molded body which is aged and crystallized in an aqueous solution of sodium hydroxide and potassium hydroxide at a temperature of 40 to 100 ° C. for several hours to several days. . Japanese Patent Application Laid-Open No. 11-76810 describes a low silica X-type zeolite molded body having a SiO ₂ / Al ₂ O ₃ molar ratio of at least 95% of ₂ . However, the production method is such that low-silica X-type zeolite powder is agglomerated with a binder containing at least 80% of a clay capable of being converted into zeolite, and the resulting mixture is formed, dried, and dried to form a mixture of 500 to 7%.
The solid product obtained is calcined at a temperature of 00 ° C., and the obtained solid product is a solution of sodium hydroxide and potassium hydroxide, and the maximum content of potassium hydroxide is 30 mol% with respect to the sum of sodium hydroxide and potassium hydroxide. This is a method of contacting with a certain caustic aqueous solution of at least 0.5 molar concentration. The low silica X-type zeolite binderless molded product obtained by these methods is:
The compressive strength is very low, the A-type zeolite is mixed, and the overall SiO ₂ / Al ₂ O ₃ molar ratio by chemical analysis is higher than 2.0, which is the theoretical value of low-silica X-type zeolite. The problem was that the purity of the low-silica X-type zeolite in the inside was also insufficient.

In WO99 / 05063, at least 95
% Describes a method for producing a zeolite body composed of LSX. Japanese Patent Application Laid-Open No. H11-76
No. 810, a method of contacting with a caustic solution of at least 0.5 molar concentration, and the pressure strength of the LSX zeolite obtained by such a method of contacting with a caustic solution having a relatively low concentration is low. It was a problem. Further, the obtained LSX zeolite is not used for adsorption and separation of carbon dioxide, particularly for adsorption and separation of carbon dioxide in the air, and no study has been made on a cation species excellent in adsorption selectivity between carbon dioxide and nitrogen.

[0015]

SUMMARY OF THE INVENTION An object of the present invention is to provide a cryogenic separation method for separating air at a low temperature, for example, by using carbon dioxide to be removed as a disadvantageous component in the process as a raw material such as air or other mixed gas. It is to provide a method of adsorbing and removing from the water.

[0016]

Means for Solving the Problems As a result of intensive studies on the above-mentioned problems, the present inventors have found that a mixed gas composed of two or more components including carbon dioxide and a gas having a polarity lower than carbon dioxide is brought into contact with the zeolite adsorbent. In the method of adsorbing and separating carbon dioxide, the partial pressure of carbon dioxide when the mixed gas is brought into contact with the zeolite adsorbent is 0.1 to 50.
mmHg, wherein the zeolite adsorbent is Si
A low silica X-type zeolite having an O ₂ / Al ₂ O ₃ molar ratio of 1.9 to 2.1 and a low silica X-type zeolite content of 95
% Or less, and it is preferable to use, as the adsorbent, a zeolite which is ion-exchanged with 90% or more of lithium and / or sodium, and more preferably 95% or more of lithium and zeolite. And / or using zeolite ion-exchanged with sodium as the adsorbent, most preferably by ion-exchange with 90% or more of sodium, the highest carbon dioxide selectivity is selected. type zeolite shaped body, SiO ₂ / Al ₂ O ₃ low silica molar ratio of 1.9 to 2.1 X type zeolite and SiO ₂
A low-silica X-type zeolite-containing molded article is obtained by molding and firing using a kaolinous clay having a / Al ₂ O ₃ molar ratio of 1.9 to 2.1. By contacting the low-silica X-type zeolite-containing compact with a caustic solution in which the amount of Si dissolved is greater than the amount of Al-dissolved, the kaolinic clay in the low-silica X-type zeolite-containing compact is reduced to low-silica X-type zeolite. The performance of removing the carbon dioxide can be dramatically improved by being manufactured by denaturation, and the average of the low-silica X-type zeolite molded product whose particle diameter is adjusted to 1.4 to 1.7 mm by sieving. It has been found that a pressure resistance of 1.0 kgf or more can be achieved, and the present invention has been completed.

[0017]

As described above, for example, in the above-mentioned cryogenic separation method for separating air at a low temperature, carbon dioxide to be removed as an inconvenient component in the process is adsorbed and removed from a mixed gas such as air as a raw material. By increasing the adsorption capacity by making the zeolite molded body binderless, having a molded body strength capable of withstanding industrial use pressure, and preferably performing ion exchange with a specific cation such as sodium by 90% or more. As a result, the selectivity of carbon dioxide was improved, and it was possible to adsorb and remove more efficiently.

Hereinafter, the present invention will be described in detail.

The adsorbent used in the present invention is SiO ₂ /
It is a low silica X-type zeolite having an Al ₂ O ₃ molar ratio of 1.9 to 2.1, and the content of the low silica X-type zeolite is 95%.
The low-silica X-type zeolite compact described above is preferably ion-exchanged with 90% or more of lithium and / or sodium, and more preferably ion-exchanged with 95% or more of lithium and / or sodium, Most preferably, the adsorbent is ion-exchanged with 90% or more of sodium.

As described above, gas absorption into zeolite
Deposition is the interaction between cations present in zeolite and gas molecules
The higher the number of cations, the more
Gas can be adsorbed. Kachi in zeolite
ON number depends on the number of Al that forms the crystal skeleton of zeolite
However, if the number of Al increases, that is, SiO_Two/ Al_TwoO _Three
As the molar ratio decreases, the number of cations increases. Zeory
G SiO_Two/ Al_TwoO_ThreeThe molar ratio must be at least 2.0.
Are known by the Lawenstein rule. Low
Silica X-type zeolite crystal SiO_Two/ Al_TwoO_ThreeMolar ratio
Is 2.0 theoretically,
In consideration of errors, etc., low series
It is clear that zeolite X falls within the scope of the present invention.
is there. SiO_Two/ Al_TwoO_ThreeZeolite with a molar ratio of 2.0
A type zeolite besides low silica X type zeolite
There is. However, zeolite A has a pore size of about 4-5.
Å, while that of low silica X-type zeolite is
It is as large as about 7-8 °, which is advantageous for gas separation. Low silica
There are various methods for synthesizing X-type zeolite crystals.
Japanese Patent Application Laid-Open No. H11-217212 is disclosed.
, JP-A-10-310422, JP-A-11-3
No. 43112, etc.
I just need.

Since zeolite crystal powder has no self-bonding property, when it is used as an adsorbent industrially, it is formed into beads, pellets or the like by adding various binders. Usually, since the binder does not have the property of adsorbing gas, the adsorption performance of the adsorbent used industrially is lower than the adsorption performance of the zeolite crystal powder by the amount containing the binder. The binder component is converted into zeolite crystals (binderless) in order not to lower the adsorption performance even in the formed zeolite adsorbent.

A high-purity binderless low-silica type X zeolite can be obtained as follows. Low silica X
As the zeolite powder, Japanese Patent Application Laid-Open No. 11-21721
No. 2, JP-A-10-310422, JP-A-1
What was manufactured by the method described in 1-343112, etc. 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, kaolinous clay which can be converted into low silica X-type zeolite is used. If the added number of kaolin clay is too small, sufficient strength of the molded body cannot be obtained, and if it is too large, crystallization does not proceed sufficiently and low silica X
The low silica X type zeolite purity in the type zeolite binderless molded body is reduced. The amount of water to be adjusted in the kneaded material is
It depends on the number of kaolin clay added and the subsequent granulation 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 granulated by various granulation 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 granules,
Calcination at preferably 600 to 650 ° C.
A shaped body containing zeolite is obtained. Calcination is indispensable for facilitating 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 used in the present invention has a low-silica X-type zeolite-containing molded body obtained as described above and a low-silicon X-type zeolite-containing molded body having an amount of dissolved Si. It is characterized in that it is brought into contact with a caustic solution having a larger amount of Al dissolved therein, or is brought into contact with a caustic solution to which Al has been added in advance. For example, the caustic solution used is preferably a mixed solution of sodium hydroxide and potassium hydroxide. The mixing ratio of sodium hydroxide and potassium hydroxide is preferably K / (Na + K) = 0.1 to 0.4. When the content is less than 0.1 or more than 0.4, the binderless formation is insufficient, and impurities such as A-type zeolite, sodalite, F-type zeolite and E-type zeolite are easily generated. However, the content of the low silica X-type zeolite is undesirably reduced.

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 to 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 at 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 moles. 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 / l, if the treatment time for binderless treatment is short, the progress of binderless treatment becomes insufficient, and the higher the concentration of caustic solution, the shorter the binderless treatment. It is preferable because it proceeds sufficiently. Therefore, the time required for binderless conversion is at least 10 hours or more when the concentration of the caustic solution is 6 mol / l or more, and at least 5 hours or more when the concentration of the caustic solution is 8 mol / l or more. Needed.

The caustic solution to which Al is added in advance is
For example, a caustic solution to which a water-soluble Al content such as sodium aluminate is added, or a low-silica X-type zeolite or a caustic solution to which kaolin clay or other solid Al content is added, wherein metakaolin is transformed into a low-silica X-type zeolite. When doing, if it is a state that actively takes in the Al content,
The form of the solid and other Al components is not limited. Also,
It is also preferable to reuse the caustic solution that has been used once or more for the binderless process. Therefore, in the case where such an Al component is added in advance, the same effect is produced even when the concentration of the caustic solution is low as compared with the case where the Al component is not added in advance, 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, and the strength decreases, and the amount of the caustic solution used is large.

The method for 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.

Further, in order to use the adsorbent of the present invention for the adsorption and separation of carbon dioxide, the high-purity low-silica X-type zeolite compact obtained by the above-mentioned method preferably has a lithium and / or sodium content of 90% or more. And more preferably 95% or more of lithium and / or sodium. The highest carbon dioxide selectivity is chosen by ion exchange, most preferably with 90% or more sodium. Cations in zeolites are one of the important factors that determine adsorption selectivity in adsorptive separation. For example, in cryogenic separation in which air is cooled to cryogenic temperature and separated by adsorbing and removing carbon dioxide in air as a pretreatment, the pressure at which the low silica X-type zeolite adsorbent is brought into contact with the mixed gas is generally Is about 5 to 10 atmospheres. In this case, the concentration of carbon dioxide in the air is about 300
ppm, the partial pressure is about 1 to 2.5 mmHg, but the coexisting nitrogen has a concentration of about 78%, and the partial pressure is about 4 to 8 atm. Despite the fact that carbon dioxide has a much larger interaction than nitrogen, the amount of carbon dioxide adsorbed is reduced by the coexisting nitrogen. For this reason, for example, as an adsorbent for adsorbing and removing carbon dioxide in the air, an adsorbent that has a large amount of adsorbed carbon dioxide at a low partial pressure and a small rate of decrease in the amount of adsorbed carbon by coexisting nitrogen is preferably used. Can be

The method of ion-exchanging the binderless high-purity low-silica X-type zeolite molded product includes a batch method,
It can be carried out by a commonly known method such as 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 more expensive than sodium, a solution obtained by removing impurities from a solution once used for ion exchange can be used as an ion exchange solution.

It is to be noted that sodium and potassium are usually present as exchangeable cations in the binderless high-purity low-silica X-type zeolite compact before the ion exchange. For this reason, when this compact is ion-exchanged with lithium and / or sodium, these originally existing cations may remain. As described above, even if cations existing before ion exchange remain after ion exchange, they can be used as the adsorbent of the present invention. Adsorbents in which transition metal ions such as divalent ions of calcium and magnesium and zinc are exchanged as cations other than lithium and / or sodium 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 high-purity low-silica X-type zeolite molded product obtained by the above-described method has a remarkably improved pressure-resistant strength as compared with the low-silica X-type zeolite binderless molded product obtained by the prior art, and the particle size is small. An average compressive strength of 1.0 kgf or more can be achieved with particles in the range of 1.4 to 1.7 mm, and can be used industrially sufficiently.

In the case of the adsorbent used in the present invention, an adsorbent having a high adsorption and desorption rate in addition to a large equilibrium adsorption amount of carbon dioxide is preferable. For example, the rate of adsorption and desorption when adsorbing and removing carbon dioxide in air is generally affected by the macropore structure of the zeolite adsorbent. Macropores are pores formed between 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 pore volume of 0.25 cc / g or more and an average pore diameter of 0.3.
5 μm or more can be achieved, and a mass transfer rate can be obtained without lowering the original adsorption performance of the adsorbent. 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 cannot be obtained.

[0038] The molded article may be in the form of beads or pellets, and has an average particle diameter of 0.5.
３3 mm, more preferably 0.5-2 mm. If the average particle diameter is larger than 3 mm, the surface area per unit volume of the packed bed becomes small, and the mass transfer speed in the particles becomes small, which is not preferable. 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 decreases, 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 above-mentioned high-purity binderless low-silica X-type zeolite molded body can be obtained by a pressure swing method in which separation is performed by increasing or decreasing a pressure, a temperature swing method in which separation is performed by increasing or decreasing a temperature, or a pressure swing and a temperature swing. It can be used effectively when carbon dioxide is adsorbed and separated by a pressure-temperature swing method in which separation is performed by performing both. In particular, when the carbon dioxide is adsorbed and separated using the high-purity binderless low-silica X-type zeolite molded body, the selectivity of carbon dioxide is high, the size of the separation apparatus can be reduced, and the power source unit can be reduced. is there.

[0040]

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, ICP
Optical 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) Measurement method of crystal structure X-ray diffractometer (model MXP-, manufactured by Mac Science)
It measured using 3). (3) Measurement method of moisture equilibrium adsorption amount A sample dried at 60 ° C. or more was subjected to a temperature of 25 ° C. and a relative humidity of 80.
% 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 igniting this at 900 ° C. for 1 hour was defined as X2, and the moisture equilibrium adsorption amount (%) was determined from the following equation.

Water equilibrium adsorption (%) = ｛(X1-X2)
/ X2｝ / 100 (4) Adsorption capacity BELSORP 28SA and BEL manufactured by Nippon Bell Co.
The carbon dioxide adsorption amount and the nitrogen adsorption amount at 25 ° C. or 40 ° C. were measured by SORP HP. As a pretreatment, a vacuum activation (1 × 10 −3 m) was performed at 350 ° C. for 2 hours.
mHg or less). Du each adsorption isotherm
al-Site Langmuir formula (Ind. En.
g. Chem. Res. 1996, 35, 2477-2
483).

Using the obtained adsorption isotherm, the adsorption amount of carbon dioxide as a single component at 2 mmHg and the ideal solution theory (AIChEJJ 1965, 11, 121-1)
27), the two-component system of carbon dioxide-nitrogen
The carbon dioxide adsorption amount in mmHg and carbon dioxide selectivity were calculated. For carbon dioxide selectivity, P is the total pressure, Y1 is the molar fraction of carbon dioxide, X1 is the amount of carbon dioxide adsorbed on Y1,
2 was calculated as the nitrogen molar fraction, and X2 was calculated as the nitrogen adsorption amount at Y2 by the following formula. Note that, here, P was calculated as 6.239 atm, Y1 was calculated as 0.00042, and Y2 was calculated as 0.99958.

Carbon dioxide selectivity (-) = (X1 / PY)
1) / (X2 / PY2) (5) Macropore volume and average pore diameter Using a mercury intrusion porosimeter (Micromeritics, Model: Poisizer 9310), activated activated adsorbent was 1 to 30,000 psi. Pressure range (60 ° ~
(Pore diameter in the range of 200 μm). (6) Method for measuring average compressive strength Referring to the test method described in JIS-R-1608, a Kiya type digital hardness tester (Model KHT-20, manufactured by Fujiwara Seisakusho)
N), at normal temperature and normal pressure in an atmosphere, the activated molded body as a specimen is pressed at a constant speed (1 mm / sec) against a pressure plate (made of stainless steel, 5 mm in diameter) to apply a compressive load. Maximum load that the compact can withstand (unit: kg
f) was measured. The results are shown as a simple average of 25 measured values. Since the compressive strength depends on the particle diameter, the measurement sample was measured by sieving to adjust the particle diameter to 1.4 to 1.7 mm.

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

Stainless steel reaction volume with internal volume of 20 liters
Sodium silicate aqueous solution (Na _TwoO = 3.8 weight
%, SiO_Two= 12.6% by weight) 10770 g, water 13
30 g, sodium hydroxide (99% purity) 1310 g,
3630 g of industrial potassium hydroxide aqueous solution (purity 48%)
And use a water bath while stirring at 100 rpm.
At 45 ° C. Aluminium kept at 40 ° C in this solution
Sodium acid solution (Na _TwoO = 20.0% by weight, Al_Two
O_Three= 22.5% by weight)
Was. Immediately after the addition, the mixture became cloudy and gelation started. Immediately after loading
Before, the viscosity of the whole gel increased and the slurry
After about 3 minutes, the whole became uniform
Fluidized. Low silica when the entire slurry is fluidized
X-type zeolite powder (Ignition loss 22.5%) 4.22
g was dispersed in a small amount of water and added. The low silicide added at this time
The amount of the X-type zeolite depends on the amount of the low-silica X-type
It is 0.1% by weight based on the weight. Slurry after completion of addition
Has a composition of 3.39Na_TwoO1.31K_TwoO • 1.90
SiO_Two・ Al_TwoO_Three・ 74.1H_TwoO and theoretically raw
The low silica X-type zeolite concentration to be formed is 14.7 times.
%. The stirring is continued at 100 rpm as it is,
Aging was performed at 5 ° C. for 4 hours. After aging, do not continue stirring.
The temperature was raised to 70 ° C. over 1 hour. After heating, stop stirring
The crystallization was stopped at 70 ° C. for 8 hours. The resulting crystal
Is filtered and thoroughly washed with pure water, and then dried at 70 ° C. overnight.
did.

The low silica X-type zeolite powder obtained 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%.

With respect to 100 parts by weight of the LSX powder, Si
Kaolin clay having a molar ratio of O ₂ / Al ₂ O ₃ of 2.0 (manufactured by Drive Ran Kaolin Co., Ltd., product name Hydrite PXN) 2
After mixing 0 parts by weight for 15 minutes with a mix maller mixer (manufactured by Shinto Kogyo Co., Ltd., model MSG-15S), the required amount of water was added to 15 parts by weight.
And then kneaded for 1.5 hours. The water content of the obtained kneaded product was about 38% by weight.

The kneaded product was converted into beads having an average particle diameter 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.), 3
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 SUS304 column having an internal volume of 13 liters by 9.0 k.
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 molded product. 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
The molded body is prepared by adjusting the pH of the molded body to about 11 with lithium hydroxide.
Lithium chloride is brought into contact with an aqueous solution to perform ion exchange, and Li
A low-silica X-type zeolite binderless molded article was obtained.
This Li-type low silica X-type zeolite binderless molded body
Was subjected to chemical analysis, and 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_Two/ Al_TwoO _ThreeThe molar ratio was 2.0. Profit
The obtained low silica X-type zeolite binderless molded body,
Dehumidified air flow using a tubular furnace (Advantech)
Was fired at 500 ° C. for 3 hours.

The adsorbed amounts of carbon dioxide and nitrogen of the obtained low silica X-type zeolite binderless adsorbent were measured.
Table 1 shows the carbon dioxide adsorption amount and selectivity in the two-component system under the above conditions. Table 2 shows the results of measuring the pore volume and the average pore diameter by the mercury intrusion method. Particle size 1.4 ~
The average compressive strength at 1.7 mm was 1.7 kgf.

Example 2 A low-silica X-type zeolite binderless compact obtained in the same manner as in Example 1 was prepared by dissolving lithium carbonate in 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 low silica X-type zeolite binderless compact was fired and activated at 500 ° C. for 3 hours using a tubular furnace (manufactured by Advantech) under a flow of dehumidified air.

The amounts of carbon dioxide and nitrogen adsorbed on the obtained low silica X-type zeolite binderless adsorbent were measured.
Table 1 shows the carbon dioxide adsorption amount and selectivity in the two-component system under the above conditions. The average compressive strength at a particle diameter of 1.4 to 1.7 mm was 1.5 kgf.

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 solution of sodium chloride whose pH was adjusted to about 11 with sodium hydroxide to carry out ion exchange to obtain an Na-type zeolite. 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. Low silica X obtained
The zeolite binderless molded body was placed in a tubular furnace (manufactured by Advantech) under a flow of dehumidified air at 500
Activated by firing at 3 ° C. for 3 hours.

The adsorbed amounts of carbon dioxide and nitrogen of the obtained low silica X-type zeolite binderless adsorbent were measured.
Table 1 shows the carbon dioxide adsorption amount and selectivity in the two-component system under the above conditions. The average compressive strength at a particle diameter of 1.4 to 1.7 mm was 1.5 kgf.

Example 4 A low-silica X-type zeolite binderless compact obtained in the same manner as in Example 1 was contacted with an aqueous sodium carbonate solution to carry out ion exchange to obtain a Na-type low-silica X-type zeolite binderless compact. Was. As a result of chemical analysis of this Na-type low silica X-type zeolite binderless molded product, the Na ion exchange rate was 95.6%, the K ion exchange rate was 3.6%,
The Mg ion exchange rate is 0.3%, and the Ca ion exchange rate is 0.1%.
The molar ratio of SiO ₂ / Al ₂ O ₃ was 2.0%. The obtained low silica X-type zeolite binderless molded body is
Using a tubular furnace (manufactured by Advantech), firing activation was performed at 500 ° C. for 3 hours under a flow of dehumidified air.

The adsorbed amounts of carbon dioxide and nitrogen of the obtained low silica X-type zeolite binderless adsorbent were measured.
Table 1 shows the carbon dioxide adsorption amount and selectivity in the two-component system under the above conditions. The average compressive strength at a particle diameter of 1.4 to 1.7 mm was 1.4 kgf.

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 low silica X-type zeolite binderless compact was fired and activated in the same manner as in Example 1.

The adsorbed amounts of carbon dioxide and nitrogen of the obtained low silica X-type zeolite binderless adsorbent were measured.
Table 1 shows the carbon dioxide adsorption amount and selectivity in the two-component system under the above conditions. Table 2 shows the results of measuring the pore volume and the average pore diameter by the mercury intrusion method. Particle size 1.4 ~
The average compressive strength at 1.7 mm was 1.4 kgf.

Example 5 The 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. Note that Ca and Mg were not detected. The obtained low silica X-type zeolite binderless compact was fired and activated in the same manner as in Example 1.

The adsorbed amounts of carbon dioxide and nitrogen of the obtained low silica X-type zeolite binderless adsorbent were measured.
Table 1 shows the carbon dioxide adsorption amount and selectivity in the two-component system under the above conditions. The average compressive strength at a particle diameter of 1.4 to 1.7 mm was 1.5 kgf.

Example 6 A low-silica X-type zeolite binderless molded product (Na, K) was obtained without ion-exchanging the low-silica X-type zeolite binderless molded product obtained in the same manner as in Example 1. Chemical analysis of the (Na, K) type low silica X type zeolite binderless molded product showed that the Na ion exchange rate was 7%.
4.5%, K ion exchange rate 25.5%, SiO ₂ /
The Al ₂ O ₃ molar ratio was 2.0. Note that Ca and Mg were not detected. The obtained low silica X-type zeolite binderless compact was fired and activated in the same manner as in Example 1.

The adsorbed amounts of carbon dioxide and nitrogen of the obtained low silica X-type zeolite binderless adsorbent were measured.
Table 1 shows the carbon dioxide adsorption amount and selectivity in the two-component system under the above conditions. The average compressive strength at a particle diameter of 1.4 to 1.7 mm was 1.4 kgf. Comparative Example 2 The same low silica X-type zeolite-containing molded article as in Example 1 was obtained.
Caustic concentration 3.0 mol / L Caustic solution 16.2 L (NaOH: 2.2 mol / L, KOH: 0.8
(Mol / liter), and a binderless process was performed in the same manner as in Example 1. At this time, the amount of the alkali metal hydroxide in the caustic solution was 7.5 times the amount of all the kaolin in the low silica X-type zeolite-containing compact which was transformed into the 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 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%. The content of the low silica X-type zeolite in the molded article was 91.0%. 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.

The low silica X-type zeolite binderless compact was subjected to sodium ion exchange in the same manner as in Example 3. As a result of chemical analysis of this Na-type low silica X-type zeolite binderless molded product, the Na ion exchange rate was 9%.
6.5%, K ion exchange rate is 3.5%, SiO ₂ / Al ₂
The O ₃ molar ratio was 2.0. The obtained low silica X-type zeolite binderless compact was fired and activated at 500 ° C. for 3 hours using a tubular furnace (manufactured by Advantech) under a flow of dehumidified air.

The adsorbed amounts of carbon dioxide and nitrogen of the obtained low silica X-type zeolite binderless adsorbent were measured.
Table 1 shows the carbon dioxide adsorption amount and selectivity in the two-component system under the above conditions. The average compressive strength at a particle diameter of 1.4 to 1.7 mm was 0.6 kgf.

Example 7 A low silica X-type zeolite binderless compact obtained in the same manner as in Example 1 was brought into contact with a calcium chloride aqueous solution whose pH was adjusted to about 11 with calcium hydroxide, and ion exchange was carried out. 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. Note that Mg was not detected. The obtained low silica X-type zeolite binderless compact was fired and activated in the same manner as in Example 1.

The adsorbed amounts of carbon dioxide and nitrogen of the obtained low silica X-type zeolite binderless adsorbent were measured.
Table 1 shows the carbon dioxide adsorption amount and selectivity in the two-component system under the above conditions.

Comparative Example 3 The amount of adsorbed binderless NaX zeolite (SiO ₂ / Al ₂ O ₃ molar ratio 2.5: manufactured by Tosoh Corporation) conventionally used for carbon dioxide adsorption separation was measured. 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.

[0072]

[Table 1]

[Table 2]

Claims (18)

[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. The partial pressure of carbon dioxide when contacting the gas is in the range of 0.1 to 50 mmHg, and the zeolite adsorbent is SiO ₂ / Al ₂ O ₃
A low silica X-type zeolite having a molar ratio of 1.9 to 2.1,
A method for adsorbing and separating carbon dioxide, which is a low-silica X-type zeolite molded article having a low-silica X-type zeolite content of 95% or more. 2. The method for adsorbing and separating carbon dioxide according to claim 1, wherein the particle diameter is 1.4 for measurement by sieving.
A method for adsorbing and separating carbon dioxide, characterized in that the low silica X-type zeolite molded body has an average pressure resistance of 1.0 kgf or more when the molded body is made to have a size of about 1.7 mm. 3. The method for adsorbing and separating carbon dioxide according to claim 1, wherein the low silica X-type zeolite compact is ion-exchanged with lithium and / or sodium by 90% or more. 4. The method for adsorbing and separating carbon dioxide according to claim 3, wherein said low silica X-type zeolite compact is ion-exchanged with lithium and / or sodium by 95% or more. 5. The method for adsorbing and separating carbon dioxide according to claim 1, wherein the low silica X-type zeolite compact is ion-exchanged with sodium by 90% or more. 6. The method for adsorbing and separating carbon dioxide according to claim 5, wherein the low silica X-type zeolite compact is ion-exchanged with 95% or more of sodium. 7. The method for adsorbing and separating carbon dioxide according to claim 1, wherein the low silica X-type zeolite molded article has a low silica X-type zeolite content of 98% or more. 8. The adsorption of carbon dioxide according to claim 1, wherein said low silica X-type zeolite molded body is substantially free of a binder and consists only of low silica X-type zeolite. Separation method. 9. 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 0.35 μm or more.
9. The method for adsorbing and separating carbon dioxide according to any one of items 1 to 8. 10. The method for adsorbing and separating 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. . 11. The method for adsorbing and separating carbon dioxide according to claim 7, wherein the low silica X-type zeolite molded body has an average particle diameter in a range of 0.5 to 2 mm. 12. The method according to claim 1, wherein the adsorption and separation are performed by a pressure swing method and / or a temperature swing method. 13. The temperature at which carbon dioxide is adsorbed is 0 to 10.
The method of claim 1, wherein the temperature is 70 ° C. 14. The temperature for desorbing carbon dioxide is 40.
The method for adsorbing and separating carbon dioxide according to claim 1, wherein the temperature is from -200 ° C. 15. 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. The body is SiO
₂ / Al ₂ O ₃ low silica X-type zeolite and SiO ₂ / Al ₂ O ₃ molar ratio of the molar ratio of 1.9 to 2.1 is 1.9 to 2.1
The low silica X-type zeolite-containing molded body is obtained by molding and calcining using kaolin clay of
By contacting the low-silica X-type zeolite-containing molded body with a caustic solution in which the amount of Si dissolved from the shaped zeolite-containing molded body is greater than the amount of Al dissolved, the kaolin content in the low-silica X-type zeolite-containing molded body is reduced. Clay low silica X
2. The method for adsorbing and separating carbon dioxide according to claim 1, wherein the method is produced by transforming into a zeolite. 16. The low-silica X-type zeolite molded product,
The method for adsorptive separation of carbon dioxide according to claim 15, wherein the method is produced by contacting with a caustic solution of 6 mol / liter or more for 10 hours or more. 17. The low-silica X-type zeolite molded product,
2. The method according to claim 1, which is produced by contacting with a caustic solution of 8 mol / l or more for 5 hours or more.
6. The method for adsorbing and separating carbon dioxide according to 5. 18. The low-silica X-type zeolite molded product,
The method for adsorbing and separating carbon dioxide according to any one of claims 15 to 17, wherein the method is produced by being brought into contact with a caustic solution to which Al has been added in advance.