JPH1095612A - Silver-containing zeolite, separation of gas using the same and production of zeolite - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a zeolite better in separation coefficient than that of a conventional adsorbent when used for gas separation. SOLUTION: This silver-containing zeolite is produced by exchanging 10-100% of ion exchangeable cations in an X type zeolite with silver ions. The silver- containing zeolite is used to separate a component gas from a mixed gas. The method for producing the silver-containing zeolite is to carry out the ion exchange of an NaX type zeolite or a CaX type zeolite in a silver salt solution and provide the silver-containing zeolite in which 10-100% of the ion exchangeable cations in the zeolite are exchanged with the silver ions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silver-containing zeolite which is preferably used for gas adsorption separation, particularly for separation of oxygen and nitrogen in air, a gas separation method using the same, and a method for producing zeolite. .

[0002]

[Prior art]

(Gas separation adsorbent) As an adsorbent for industrial gas separation, synthetic zeolite, natural zeolite, silica gel, alumina gel, activated carbon, molecular sieve carbon and the like are used. For the purpose of separating oxygen and nitrogen in the air,
Zeolite and molecular sieve carbon are used. Zeolites generally have a greater equilibrium adsorption of nitrogen than oxygen.
By utilizing this property, oxygen or nitrogen gas is separated from air. Data on the equilibrium of oxygen and nitrogen adsorption by zeolites are shown in the following documents, for example. 1) DM
Ruthven, AIChE Journal, Vol.22, No.4, p.753 (1976)
Describes A-type zeolites. 2) Adsorption technology handbook (published by NTS, 199
(3 years), p. 15 (Takaaki Tamura) describes a natural zeolite. 3) Same as above, p. 699 (Wataru Ito) describes natural zeolites. 4) Same as above, page 723 (Matsunaga Matsunaga) contains data on commercially available synthetic zeolites.

(Separation method) As a gas separation method, PSA
Method (Pressure Swing Adsorption method, pressure fluctuation adsorption method)
The method called is well known. This method comprises the steps of components A and B
When the amount of adsorption to the adsorbent is greater than that of component B in the mixed gas consisting of, the mixed gas is flowed at a high pressure in the adsorbent bed for a certain period of time, and while component A is adsorbed on the bed, component B is removed. The component A is removed from the bed by removing (adsorbing step) and then reducing the pressure to a certain low pressure (desorption step or regeneration step), and the mixed gas is separated into the components A and B by repeating these steps sequentially.

[0004]

The air contains about 21% oxygen and about 78% nitrogen by volume. A zeolite adsorbent used for separating oxygen and nitrogen from air is required to have a large nitrogen / oxygen adsorption ratio (separation coefficient). Conventionally used zeolites generally satisfy the requirements, but are not sufficiently satisfactory. In particular, in order to improve the separation efficiency, the improvement of the separation coefficient is constantly required.

The present invention has been made in view of the above circumstances, and has as its object to provide a zeolite having a higher separation coefficient than conventional adsorbents when used for gas separation.

[0006]

The invention according to claim 1 of the present invention is a silver-containing zeolite obtained by exchanging 10 to 100% of ion-exchangeable cations in an X-type zeolite with silver ions. The invention according to claim 2 is a gas separation method, comprising separating a component gas from a mixed gas using the silver-containing zeolite according to claim 1. The invention according to claim 3 is the gas separation method according to claim 2, wherein the mixed gas is a mixed gas containing oxygen and nitrogen, and oxygen and nitrogen are separated from the mixed gas. According to a fourth aspect of the present invention, there is provided a silver-containing zeolite in which NaX-type zeolite or CaX-type zeolite is ion-exchanged in a silver salt solution, and 10 to 100% of ion-exchangeable cations in the zeolite are exchanged with silver ions. And a method for producing a zeolite.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Zeolite is a structure of a condensed acid of silicate, and its basic unit is a SiO ₄ tetrahedron in which four oxygens (O) formed around silicon (Si) are located at the top. Is an AlO ₄ tetrahedron in which aluminum (Al) is substituted for this Si, and this and other various basic structural units are three-dimensionally combined to form a channel (passage) and a cage (cavity). doing. Various channels and cages exhibit various properties such as adsorption and ion exchange. According to the present invention, a silver-containing zeolite suitable for oxygen / nitrogen adsorption separation is obtained by changing the pore size or electrostatic field of zeolite crystals by exchanging ion-exchangeable cations constituting zeolite with silver ions. In the zeolite, when monovalent and divalent cations are represented by M ¹ and M ² , respectively, the composition is represented by the following formula. _{^{(M 1, M 2 1/2)}} m (AlmSinO2 (m + n)) · xH2O, (n ≧ m) M1 = Li +, Na +, K +, Pb +, Me 4 N + (TMA), Et ₄ N ⁺ (TEA), Pr ₄ N ⁺ (TPA), C ₈ H ₁₆ N ⁺ M 2 = Ca ²⁺ , Mg ²⁺ , Ba ²⁺ , Sr ²⁺ , C ₈ H ₁₈ N ₂ ²⁺ synthetic zeolite , The SiO ₂ / Al ₂ O ₃ ratio is approximately 1.8
A type of ~ 1.9, X type of 2-3,
Those having 3 to 6 are called Y type. Some or all of the monovalent and divalent cations can be reversibly exchanged with other cations.

An X-type zeolite in which the ion-exchangeable cation is Ca alone or mainly Ca in consideration of valence is called CaX type. The ion-exchangeable cation is Na
Is referred to as NaX type. There are various kinds of cations coexisting with Ca or Na as described above. CaX
By immersing the type zeolite or the NaX type zeolite in a silver salt solution, calcium or sodium can be exchanged for silver (Ag). The exchange amount can be adjusted by selecting the concentration of the silver salt, the ion exchange reaction temperature, and the reaction time. As the silver salt, for example, silver nitrate, silver chlorate, silver perchlorate, silver acetate, silver hexafluorophosphate, silver tetrafluoroborate, and the like can be used, and among them, silver nitrate can be preferably used.

Since Ag ⁺ has a larger ionic radius than Ca ²⁺ or Na ⁺ , the channels and cages of the zeolite (silver-containing zeolite) ion-exchanged with Ag ⁺ are narrowed, so that the pore diameter is reduced and the pore volume is reduced. It is also estimated that the specific surface area will be small. However, the pore diameter does not become so small that it does not allow nitrogen or oxygen to pass through, and the electrostatic field of the pores exchanged with Ag ⁺ ions acts on the quadrupole moment of the nitrogen molecule to affect the adsorption of the nitrogen molecule. It is presumed that the silver-containing zeolite in which some or all of the ion-exchangeable cations were exchanged with Ag ions because of their contribution to increase the separation coefficient.

A silver-containing zeolite obtained by exchanging 10 to 100% of ion-exchangeable cations of NaX-type zeolite or CaX-type zeolite with silver has a higher oxygen / nitrogen separation coefficient at the same temperature and the same pressure as the raw material zeolite. There is a feature. And the separation factor are the same temperature, the amount of adsorption of nitrogen at the same pressure (qN ₂₎ and the adsorption amount of the oxygen ratio _{(qO 2) (qN 2 /} qO 2). Further, the silver-containing zeolite of the present invention can be used for gas separation other than nitrogen / oxygen separation, for example, separation of nitrogen from a mixed gas of nitrogen and methane,
It can be used as an adsorbent in gas separation such as separation of nitrogen from a mixed gas of nitrogen and argon, removal of carbon dioxide from air, and separation of hydrogen and carbon monoxide from gases containing hydrogen and carbon monoxide. In addition, the silver-containing zeolite of the present invention has an antibacterial function, for example, if it is used as an adsorbent for a water purifier, it can prevent the growth of bacteria in the vessel after use, due to the bacteriostatic and antibacterial effects of the Ag ions possessed. It can also be used as a dexterous adsorbent.

[0011]

【Example】

(Raw material) As the X-type zeolite, a commercially available CaX-type zeolite (beads (small spheres) having a diameter of 1.4 to 2.4 mm) was used. This adds 10.
It contained 2% by weight. The composition of this raw material was analyzed as follows. 0.5 g of a sample heated and dehydrated at 400 ° C. is precisely weighed and placed in a Teflon container, and hydrofluoric acid and perchloric acid are added and heated at 250 to 280 ° C. to volatilize silicon fluoride. The reduction was defined as the amount of SiO ₂ . Next, perchloric acid and water are added to the sample and dissolved by heating. After cooling, nitric acid is added. This solution was added to an atomic absorption spectrometer and I
Quantitative analysis of elements (Na, Ca, Al) other than silicic acid was performed using a CP (high frequency inductively coupled plasma emission) analyzer. The content of water of crystallization was determined by thermogravimetric analysis. As a result, the raw material zeolite SiO ₂ / Al ₂ O ₃ = 3.1
0, Na ₂ O / Al ₂ O ₃ = 0.02, CaO / Al ₂ O ₃
= 1.03. From the above analysis results, the composition of this raw material zeolite was Ca44.3Na1.72Al86.0Si133.3O448.195H2O. The total ion-exchangeable capacity (theoretical ion-exchange capacity) of this raw material zeolite is 4.40 meq /
g.

(Exchange of Silver Ions) In the treatment for exchanging cations in the raw material zeolite for silver (Ag) ions, the raw material zeolite (0.1 g) is converted to silver nitrate (AgN
O ₃ ) was carried out by a batch method of dipping in an aqueous solution (100 mL) for a certain period of time. The sample is subjected to solid-liquid separation and the Ag contained in the solution
⁺ , Na ⁺ and Ca ²⁺ were quantitatively analyzed by high frequency inductively coupled plasma emission spectrometry and atomic absorption spectrometry. The exchange amount of silver ions was determined as the decrease amount of silver ions in the solution. Ag
The uptake amount of ^{+ and} the amount of released (Na ⁺ + Ca ²⁺ ) were 1: 1, indicating that ideal ion exchange was performed.

[0013] Five kinds of silver-containing zeolites (samples) having different ion exchange amounts were prepared. Sample: The concentration of the aqueous silver nitrate solution was 6.05 meq / L, the temperature was 25 ° C., and the reaction time was 2 hours. The uptake of Ag ⁺ was 0.57 meq / g, which was 1 of the theoretical exchange capacity.
2.9%. Sample: The concentration of the aqueous silver nitrate solution was 6.05 meq / L, the temperature was 25 ° C., and the reaction time was 4 hours. The uptake of Ag ⁺ was 0.93 meq / g, which was 2 times the theoretical exchange capacity.
1.1%. Sample: The concentration of the aqueous silver nitrate solution was 6.05 meq / L, the temperature was 25 ° C., and the reaction time was 48 hours. The uptake of Ag ⁺ was 2.11 meq / g, which was 4 times the theoretical exchange capacity.
8.0%. Sample: The concentration of the aqueous silver nitrate solution was 15.4 meq / L, the temperature was 25 ° C., and the reaction time was 48 hours. The uptake of Ag ⁺ was 3.57 meq / g, which was 8 times the theoretical exchange capacity.
1.1%. Sample: The concentration of the aqueous silver nitrate solution was 15.4 meq / L, the temperature was 50 ° C., and the reaction time was 48 hours. The uptake of Ag ⁺ was 4.39 meq / g, which was 9 times the theoretical exchange capacity.
9.8%. Hereinafter, five types of samples were sequentially analyzed for 13-AgX and 21-AgX.
AgX, 48-AgX, 81-AgX, 100-
Abbreviated as AgX. The raw material zeolite is abbreviated as CaX.

(Structural characteristics of silver-containing zeolite) Raw material zeolite
Fig. 7 shows powder X-ray diffraction diagrams of light CaX and 100-AgX.
It is shown in FIG. The X-ray source is CuKα. Raw material zeolite C
aX and three types of silver-containing zeolites, a total of four types of Fouries
FIG. 2 shows the results of the conversion infrared spectroscopy. This
For example, in CaX, 760 cm^-1Absorption peaks
Of tetrahedral chains that are sensitive to the type of exchange cation
669cm corresponding to symmetric vibration^-1Absorption peak of Si
567cm, corresponding to the symmetric expansion and contraction of (Al) .O^-1Absorption of
The peak corresponds to the expansion and contraction of the double six-membered ring, 461 cm ^-1Sucking
The yield peak corresponds to the vibration of the Si (Al) .O bond.
You. Sensitive to the type of exchange cation of silver ion exchanger
The absorption peak corresponding to the symmetrical vibration of the chain
-AgX is 752cm^-1Nearby, 81-AgX is 738c
m^-1Near, 100-AgX is 733cm^-1Near to near
Were present. From these data, the silver-containing zeolite according to the present invention was
Olite does not destroy the structure of the raw zeolite.
Some or all of the cations in the starting zeolite are silver
It can be seen that the ions have been exchanged. In addition, the four types
According to the thermogravimetric analysis of samples of the type
It was observed that crystallization water had been eliminated. Heat to 400 ° C
The specific surface area of the above four types of samples was determined as the raw material zeolite C.
aX is 650m^Two/ G, 635 m for 48-AgX^Two/ G,
81-AgX is 410m^Two/ G, 100-AgX is 36
2m^Two/ G. Thus, the silver-containing zeolite is
The specific surface area is smaller than that of the raw material zeolite CaX, and the amount of silver exchanged
The smaller the value, the smaller the value. Ca in CaX zeolite
Ca as thione²⁺And Na⁺Is Ag with a large ion radius⁺
It is assumed that the specific surface area in the pores decreased as a result of
Measured. The specific surface area was measured at a temperature of -196 ° C.
BET (Br
unauer, Emett, Teller)
You. From the data of nitrogen adsorption and desorption at -196 ° C,
DH, a model that assumes a cylindrical shape with open ends
(Dollimore, Heal) method to calculate pore distribution
As a result, CaX corresponds to the maximum diameter of the channel.
0.80 nm and 1.60 n corresponding to the maximum diameter of the cage
m was confirmed. The pore volume is determined by the silver ion exchange.
It decreased with an increase in the exchange rate.

(Adsorption of Nitrogen and Oxygen) Raw material zeolite Ca
X and a total of six samples of the above five types of silver-containing zeolites, a fully automatic gas adsorber (Nippon Bell Co., Ltd., BELSO
RP28SA) was used to measure the adsorption isotherms of oxygen and nitrogen. The temperature was 25 ° C. Each sample is 400
Heated to ° C to remove moisture. FIG. 3 shows the results of the adsorption measurement. Table 1 shows nitrogen and oxygen adsorption amounts and separation coefficients at 200 Torr and 760 Torr.

[Table 1] As shown in FIG. 3 and Table 1, the silver-containing zeolite, but the nitrogen adsorption amount as compared with the raw material zeolite and oxygen adsorption amount is reduced, nitrogen and oxygen separation factor (qN ₂ / qO ₂₎ increased. The maximum separation factor is 10.0 (81-AgX, 200
Torr) and the separation factor of the raw material zeolite CaX is 1.
Reached 72 times.

Further, a commercially available NaX type zeolite was used as a raw material zeolite instead of CaX type, and a silver-containing zeolite was synthesized in the same manner. In this silver-containing zeolite, as the amount of ion-exchanged silver increased, the specific surface area decreased and the pore volume decreased as compared with the raw material zeolite (NaX). Further, the nitrogen / oxygen separation coefficient was larger than that of the raw material zeolite, and the same result as in the above example was obtained.

[0017]

As described above, according to the present invention,
The following effects can be obtained. The silver-containing zeolite according to claim 1 is obtained by exchanging 10 to 100% of the ion-exchangeable cations in the X-type zeolite with silver ions, and has a higher nitrogen / oxygen separation coefficient at the same temperature and the same pressure as the raw material zeolite. And has excellent gas separation characteristics. According to the gas separation method of the second aspect, the gas separation efficiency can be improved by separating the component gas from the mixed gas using the silver-containing zeolite of the first aspect,
It is possible to reduce processing costs such as production of a component gas from the mixed gas or removal of impurities from the mixed gas.
According to a third aspect of the present invention, there is provided a gas separation method according to the second aspect, wherein the mixed gas is a mixed gas containing oxygen and nitrogen, and oxygen and nitrogen are separated from the mixed gas, whereby air separation by the PSA method is performed. The system can be simplified and the cost can be reduced, and oxygen and nitrogen can be produced at low cost. The method for producing a zeolite according to claim 4 is characterized in that:
aX-type zeolite or CaX zeolite is ion-exchanged in a silver salt solution to obtain a silver-containing zeolite in which 10 to 100% of ion-exchangeable cations in the zeolite are exchanged with silver ions to obtain the same temperature and the same pressure. Thus, it is possible to produce a silver-containing zeolite having an excellent gas separation characteristic in which the nitrogen / oxygen separation coefficient is higher than that of the raw material zeolite. In particular, a silver-containing zeolite having a nitrogen / oxygen separation coefficient exceeding 10 can be obtained by exchanging cations of CaX-type zeolite with Ag ions.

[Brief description of the drawings]

FIG. 1 is a powder X-ray diffraction diagram of a zeolite according to an example of the present invention.

FIG. 2 is an infrared spectrum diagram of a zeolite according to an example of the present invention.

FIG. 3 is a nitrogen and oxygen adsorption isotherm of a zeolite according to an example of the present invention.

Claims (4)

[Claims] 1. A silver-containing zeolite obtained by exchanging 10 to 100% of ion-exchangeable cations in an X-type zeolite with silver ions. 2. A gas separation method comprising using the silver-containing zeolite according to claim 1 to separate a component gas from a mixed gas. 3. The gas separation method according to claim 2, wherein the mixed gas is a mixed gas containing oxygen and nitrogen, and oxygen and nitrogen are separated from the mixed gas. 4. A method for obtaining a silver-containing zeolite in which NaX-type zeolite or CaX-type zeolite is ion-exchanged in a silver salt solution and 10 to 100% of ion-exchangeable cations in the zeolite are exchanged with silver ions. Characteristic method for producing zeolite.