JPH062575B2 - Clinoptilolite-type zeolite and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a zeolite useful as an adsorption separation agent mainly used for separation and purification of mixed gas,
In particular, the present invention provides a novel zeolite suitable for separating gas molecules having similar molecular diameters.

(Prior Art) The field of gas usage extends to every place from general households to industry, and the types of gas used also vary widely. Especially with the remarkable development of industry,
A large amount of high-purity gas or concentrated gas has been required. Along with that, there is an urgent need to develop a method for removing a trace amount of impurity gas components in the main component gas, that is, a purification technique or a concentration technique. Further, even in the field where the emphasis is placed on the separation represented by the concentration of oxygen or nitrogen in the air, there is a demand for an economical system with a high separation efficiency. In any case, since the performance of the adsorbent plays an extremely important role, the development of an adsorbent suitable for the target system is an important key.
In particular, zeolite having a constant pore size of the angstrom order is effective as these adsorbents, and has already begun to separate oxygen and nitrogen in the air, removal of carbon dioxide in the air, desulfurization of natural gas, etc. The process has been put to practical use. In most cases, the zeolite used for these has a larger pore size than the molecular size of the target gas. For example, CaA, X, and mordenite, which are used to separate oxygen and nitrogen in air, correspond to this. The molecular diameters of oxygen and nitrogen are 3.46Å and 3.64Å, respectively, and the pore sizes of CaA, X, and mordenite are 5Å and 8 respectively.
Å, 7Å. Therefore, this separation method is not a molecular sieve based on the pore size of the zeolite, but a separation method utilizing the adsorption capacity or difference in adsorption rate of gas molecules to the zeolite.

One of the practical examples of the separation method utilizing the molecular sieving action of zeolite is KA zeolite for removing water in ethylene of naphtha decomposition gas, and CaA zeolite for separating isoparaffin and n-paraffin. is there. In these cases, there is a considerable difference between the molecular diameters of the gas molecules to be separated and the main component gas molecules, so that the separation is relatively easy.

By the way, since the effective pore size of zeolite is determined by the crystal structure and the contained cation species, it is difficult to produce zeolite having an effective pore size of an arbitrary size. Therefore,
Zeolites cannot be used to separate molecules of any size that are similar in molecular size.

(Problems to be solved by the present invention) A zeolite capable of separating a gas molecule having a molecular diameter of less than 3.7Å and a gas molecule having a molecular diameter of 3.7Å or more has a conventional effective pore size of 3. No zeolite with an effective pore size of 7Å was present.

The inventors of the present invention have conducted extensive studies to produce an adsorbent having an effective pore size of 3.7Å that can be industrially used, and as a result, based on clinoptilolite-type zeolite as a base material, 0.4 as CaO / Al ₂ O ₃
It was previously found that the object can be achieved by adjusting the amount in the range of 0.75 to 0.75 (Japanese Patent Application No. 59-20984).
3).

It can be said that the adsorbent has epoch-making characteristics, considering that there is no zeolite with an effective pore size of 3.7 Å in the past, but under various conditions in order to use it as an industrial adsorbent. Then, the result of evaluating the adsorption property was 3.7.
Å It became clear that its function is not sufficient to efficiently separate neighboring molecules.

That is, the effective pore size of the adsorbent was judged to be 3.7Å in appearance, but even gas molecules having a molecular size of 3.7Å or more were gradually adsorbed when they were in contact for a long time, and adsorbed 3.7Å or more. A large amount of energy is required to desorb the molecule. This fact indicates that the true effective pore size of the adsorbent is greater than 3.7Å. Therefore, in order to obtain an adsorption separator that can be industrially used, it is necessary to control the effective pore diameter more precisely.

The inventors of the present invention have made extensive studies on the method, and as a result, found an effective method and conditions therefor, and arrived at the present invention.

(Means for Solving Problems) The zeolite of the present invention is a clinoptilolite-type zeolite. Clinoptilolite type zeolite is also naturally occurring, but it is also possible to synthesize, its typical composition of the general formula _{(Na 2, K 2) O} · Al 2 O 3 · 10SiO 2 · 8H
It is represented by ₂ O.

The zeolite of the present invention has a CaO / Al ₂ O ₃ molar ratio of 0.3 to 0.
It is a clinoptilolite-type zeolite having an adsorption index ratio of 75 or more and a normal butane of 3 or more, and after exchanging a part of the cations in the clinoptilolite-type zeolite with a predetermined amount of calcium ions, an aqueous solution containing an alkali component is prepared. It can be obtained by contacting (hereinafter abbreviated as “alkaline treatment”). The present invention may be a clinoptilolite-type zeolite alone, or may be used as a composition containing it as one of its components or a molded product thereof.

Hereinafter, the present invention will be described in more detail. The clinoptilolite-type zeolite that can be used as a starting material for the production of the clinoptilolite-type zeolite of the present invention may be either naturally occurring or synthetic, and after exchanging a part of its cations with calcium ions. It can be obtained by contacting with an aqueous solution containing an alkaline component, and the resulting product has a calcium ion content as a cation.
CaO / Al ₂ O ₃ molar ratio is 0.3 to 0.75,
A normal butane adsorption index ratio according to a normal butane adsorption test described later is 3 or more.

The shape when contacting with calcium ion exchange and an aqueous solution containing an alkaline component may be powder, lump, crushed or powder mixed with a binder, granulated and fired molded article, but calcium ion exchange After going
Alkaline treatment is an essential condition.

That is, the powder may be ion-exchanged and contacted with an alkaline component-containing aqueous solution and then molded and fired, or clinoptilolite-type zeolite powder is mixed with a binder, molded, and ion-exchanged after being fired. A method of performing an alical treatment can also be adopted. Alternatively, the crushed natural clinoptilolite may be subjected to ion exchange as it is, and then subjected to alkali treatment. Therefore, if the order of ion exchange and alkali treatment is correct, the morphology of the zeolite when performing those operations is not limited to the description and examples in this specification.

However, the CaO / Al ₂ O ₃ amount of calcium ions represented by the molar ratio excludes the CaO / Al ₂ O ₃ component contained in the binder and the like, and the CaO / Al ₂ O ₃ amount of the clinoptilolite-type zeolite. It is calculated from

The calcium ion exchange is usually carried out by adding clinoptilolite-type zeolite to an aqueous solution of highly soluble inorganic salts such as calcium chloride and calcium nitrate. The concentration and amount are selected so that the amount of calcium ions after exchange falls within the above range. In carrying out the method, any method such as a batch method, a flow method and a circulation method may be used, and an optimum method is adopted depending on the form of the zeolite. Usually, in that case, conditions may be set such that the amount of calcium ions is approximately within the above range in the ion exchange equilibrium state. This is because the amount of calcium ions reduced by the next alkali treatment is small. If the ion exchange equilibrium is not reached, variations in pore size will occur, so it is advantageous to raise the temperature of the exchange liquid to accelerate the equilibrium arrival time as much as possible, and exchange at a temperature of 50 ° C or higher. preferable. After completion of ion exchange, wash thoroughly with water or warm water until no coexisting anions are detected.

Next, the washed zeolite is usually dried and then subjected to an alkali treatment, but the drying after the alkali treatment is not an essential condition. The alkali treatment is performed by contacting the zeolite with an aqueous solution containing an alkali component. What is used as the alkali component is generally used a hydroxide of an alkali metal or an alkaline earth metal such as sodium hydroxide, potassium hydroxide, barium hydroxide, sodium silicate, sodium aluminate, etc., and a mixture of these. May be used as. The concentration of these aqueous solutions is in the range of 0.1 to 5 wt%, preferably 0.2 to 2 wt%. The amount of the aqueous solution containing these alkali components is such that the ratio to the zeolite to be treated (amount of aqueous solution / zeolite) is in the range of 2 to 10 ml / g. In general, when the concentration of the alkali component is high, the calcium ion exchanged earlier is re-exchanged with the metal ion in the aqueous solution, and the amount of calcium ion decreases, but the normal butane adsorption index ratio increases. Therefore, the normal butane adsorption index ratio can be changed by changing the concentration of the alkaline component. Further, when the amount of the alkaline aqueous solution is large, the amount of calcium ions decreases, but the CaO / Al ₂ O ₃ molar ratio described above is 0.3 to 0.
Must be in the range of 75.

As in the case of ion exchange, the method of alkali treatment may be any of batch method, flow method, circulation method and the like, and it is preferably carried out under humidification so that the aqueous solution sufficiently contacts with zeolite. The treatment time is usually 0.5 to 6 hours.

The alkali-treated zeolite is separated from the alkali component-containing aqueous solution and then dried without washing. The zeolite that has undergone the above steps may be mixed with a binder, if necessary, after being molded, or as it is, in a form of 300 to 70.
It can be used as a treatment separating agent by performing activation or calcination at a temperature of 0 ° C.

(Action and effect) The reason why the effective pore size of the clinoptilolite-type zeolite can be precisely reduced by contacting it with an aqueous solution containing an alkaline component after calcium ion exchange is not clear yet, but It is considered that the alkaline component existing in the pores or near the pore inlet acts to reduce the pore diameter. The effect is quantitatively measured by the normal butane adsorption index ratio by the normal butane adsorption test, and the value of this ratio serves as an index when separating a mixture of molecules in the vicinity of 3.7Å.

That is, zeolite having a normal butane adsorption index ratio of 3 or more exhibits a remarkable molecular sieving effect in adsorbing molecules having a molecular diameter of 3.7Å.

An example of methane (3.8Å), nitrogen (3.6Å), carbon dioxide (3.3Å) will be described as an example. Clinoptilolite-type zeolite that has undergone only calcium ion exchange and is not subjected to alkali treatment adsorbs carbon dioxide gas with a molecular diameter of 3.3 Å and nitrogen molecules with a molecular diameter of 3.6 Å, and has a molecular diameter of 3.8 Å
It also adsorbs some of the methane molecules. The normal butane adsorption index ratio 3 of such a zeolite is smaller than that.

On the other hand, the zeolite having a normal butane adsorption index ratio of 3 or more after the calcium ion exchange and alkali treatment does not adsorb methane at all, but adsorbs only nitrogen and carbon dioxide gas. As described above, the effective pore size of the zeolite of the present invention represented by the normal butane adsorption index ratio is evaluated by measuring the static adsorption capacity described later.

As an application of the characteristics of the zeolite according to the present invention, inorganic gases in coke oven gas containing a large amount of hydrocarbon gases, for example, removal of nitrogen, carbon monoxide, carbon dioxide gas, removal of inorganic gas in natural gas, Alternatively, it can be effectively used for separation of an inert gas mixture.

The zeolite according to the present invention can be applied to the separation, purification and concentration of the active ingredient in a mixed gas, which has been difficult in the past as shown in the above example.

The present invention will be described below with reference to examples. The static adsorption capacity method and the normal butane adsorption index ratio calculation method measured in the examples are as follows.

<Static adsorption capacity measuring method> Approximately 2 g of the sample was measured at 500 ° C with a constant capacity adsorption capacity measuring device
Then, after activating the vacuum for 2 hours, cooling to 30 ° C and introducing methane, nitrogen or carbon dioxide gas into the apparatus and then performing 760
The amount of adsorption is measured 30 minutes after the pressure is set to mmHg. After the measurement, the sample weight is precisely weighed to measure the static adsorption capacity.

<Normal Butane Adsorption Index Ratio Calculation Method> The sample is crushed and sized using a 40-80 mesh sieve, and then packed in a stainless steel column having an inner diameter of 3 mm and a length of 1 m and set on a gas chromatograph. Heat treatment is carried out for 16 hours under a column temperature of 300 ° C. and a helium pressure of 2 kg / cm ² G. After cooling the column temperature to 50 ° C, normal butane 0.
1 ml is collected with a gas tight microsyringe and injected into a gas chromatograph to start analysis. The normal butane adsorption index is determined from the retention time (T) from the time of this injection until the peak of normal butane is detected, the peak area (S), and the weight of the filled sample (W). The normal butane adsorption index of the crushed clinoptilolite-type zeolite that had been subjected only to calcium ion exchange and not subjected to alkali treatment was set to 1.0, and each of the samples subjected to molding or alkali treatment after calcium ion exchange had normal butane. After the adsorption index was determined, the ratio with the crushed product was calculated and used as the normal butane adsorption index ratio.

Examples 1 to 5 Natural clinoptilolite type zeolite crushed product was crushed to 200 mesh or less, and this powder was slurried at a concentration of 15 wt%.
To a 2 wt% calcium chloride solution,
The mixture was stirred at 0 ° C for 3 hours. Then, wash until chlorine ions are no longer detected, dry at 110 ° C and dry with CaO / Al ₂ O _3.
A dry powder with a molar ratio of -0.49 was obtained. To 100 parts by weight of this powder, 10 parts of kaolin clay and water were added and thoroughly kneaded,
It was formed into a spherical shape having a diameter of 1.5 to 3.0 mm. The molded body was dried at 105 ° C and then baked at 550 ° C for 2 hours.

Next, 50 g of a calcium-exchanged clinoptilolite-type zeolite molded product is added to an aqueous solution 200 containing an alkali component.
The mixture was placed in ml and treated with alkali at 60 ° C. for 3 hours with stirring. The zeolite was separated from the aqueous solution containing an alkali component and then dried at 130 ° C. without washing. Alkaline component and its concentration in the aqueous alkaline solution used in each example, CaO / Al ₂ O ₃ molar ratio in the zeolite after alkali treatment and normal butane adsorption index ratio and methane, nitrogen, carbon dioxide gas measured according to the above method Table 1 shows the static adsorption capacities of the above.

Comparative Example 1 A crushed product of natural clinoptilolite-type zeolite used as a raw material in Example 1 was subjected to calcium ion exchange in the same manner as in Example 1 to obtain a CaO / Al ₂ O ₃ molar ratio of 0.48. Obtained. This zeolite was tested for normal butane adsorption without alkali treatment, and its index was set to 1.
Table 1 shows the static adsorption capacities of methane, nitrogen and carbon dioxide gas of this zeolite.

Comparative Example 2 Normal butane adsorption index ratio of zeolite without alkali treatment of spherical molded article of CaO / Al ₂ O ₃ molar ratio −0.49 obtained in Example 1 and subjected to calcium ion exchange and methane, nitrogen, carbon dioxide gas The static adsorption capacity of is shown in Table 1.

Example 6 50 g of crushed clinoptilolite-type zeolite having a CaO / Al ₂ O ₃ molar ratio of −0.48 obtained in Comparative Example 1 was treated in the same manner as in Example 1 to prepare a 0.81 wt% sodium aluminate aqueous solution. After performing alkali treatment in 13
Dried at 0 ° C.

Normal butane adsorption index ratio of this zeolite and methane,
The static adsorption capacities of nitrogen and carbon dioxide are shown in Table 1.

Claims (3)

[Claims] 1. A CaO / Al ₂ O ₃ molar ratio of 0.3 to 0.7.
Clinoptilolite-type zeolite having a normal butane adsorption index ratio of 3 or more. 2. A clinoptilolite-type zeolite in which a part of cations are exchanged with calcium ions is maintained in a CaO / Al ₂ O ₃ molar ratio of the zeolite within a range of 0.3 to 0.75. As described above, an aqueous solution containing an alkali component having a concentration of 0.1 to 5 wt% and the aqueous solution / the zeolite weight ratio of 2 to
A method for producing a clinoptilolite-type zeolite by contacting at a ratio of 10. 3. The method according to claim 2, wherein the alkali component is an alkali metal hydroxide, an alkaline earth metal hydroxide, an alkali silicate compound, an alkali aluminate compound or a mixture of two or more of these compounds. The manufacturing method described in the item.