JPS6114082B2 - - Google Patents

Description

[Detailed description of the invention]

It is well known that sodium A-type zeolite has an effective adsorption pore type of 4 Å and has molecular adsorption properties. This is generally synthesized by the method described in Japanese Patent Application Publication No. 32-6713. Sodium A synthesized by this method
Zeolite type zeolite has ion exchange properties, and it is clear from Japanese Patent Application Publication No. 1983-619 etc. that the adsorption properties of zeolite can be changed by exchanging some of the sodium ions in zeolite with other ions. be. When part of the sodium ion in sodium A-type zeolite is exchanged with calcium ions, the effective adsorption pore size becomes 5 Å (5A-type zeolite), which is useful for industrial purposes such as natural gas purification and separation of n- and i-paraffins. used for a purpose. However, after synthesis, ion-exchanged type A zeolite is usually obtained as very fine powdered crystals, and in many cases cannot be used industrially in this form. Therefore, this powdered crystal is molded into a shape and size suitable for each use, for example, columnar or spherical, using a certain inorganic or organic binder. Thereafter, these molded bodies are fired at a high temperature higher than a predetermined temperature in order to impart the desired performance to the molded bodies and to impart mechanical strength that can withstand industrial use. However, during such high-temperature firing or when heating and regenerating zeolite after use, the water coexisting in zeolite becomes high temperature and high pressure and acts on the zeolite due to the so-called hydrothermal action, which causes the crystal structure of the zeolite to deteriorate. Part of it is often destroyed.
Zeolite whose crystal structure has been destroyed is
The adsorption rate of molecules to be adsorbed is slowed down, and the adsorption capacity is significantly reduced. An object of the present invention is to provide a method for producing type 5A zeolite whose crystal structure is less likely to change due to hydrothermal action as described above, and whose adsorption properties are less likely to deteriorate. That is, the present invention exchanges some of the sodium ions in sodium A-type zeolite with calcium ions to produce 5A-type zeolite. It is characterized by being maintained within the range of 11.3 to 11.9. In the present invention, the sodium A-type zeolite used for ion exchange can be obtained by the known method described above, that is, by mixing an alumina source, a silica source, and an alkali source in a predetermined ratio and crystallizing the mixture. The sodium A-type zeolite thus obtained is in the form of fine particles, and the alkaline component coexisting in the reaction system remains attached, and this alkaline component is usually removed by repeated washing with water. The sodium A-type zeolite from which most of the attached alkali content has been removed is then brought into contact with a solution containing calcium ions, usually an aqueous solution of a water-soluble calcium salt such as calcium chloride, to convert the sodium ions in the zeolite into calcium ions. Exchange. In the present invention, during this ion exchange, sodium A
The pH of the aqueous solution in contact with type zeolite is 11.3~
It is essential to keep it within the range of 11.9. Said
When the pH is lower than 11.3, the thermal stability of the resulting 5A zeolite deteriorates, and therefore, repeated adsorption and thermal regeneration deteriorate the adsorption properties. Moreover, if it is higher than 11.9, impurities will increase in the product, which is not preferable. More specific methods of the present invention include, for example,
There is a method in which the pH of an aqueous solution containing zeolite is adjusted within a predetermined range during ion exchange. At this time, the pH of the aqueous solution is preferably adjusted using calcium hydroxide. Another method is to separate partially ion-exchanged zeolite from the ion exchange solution and, when washing it, use washing water containing calcium ions to maintain the pH of the aqueous solution in which the zeolite was washed within the above range. The present inventors have confirmed that even by such a washing operation, the sodium ions in the sodium A-type zeolite are ion-exchanged with calcium ions, and a 5A-type zeolite with improved thermal stability can be obtained. In any case, in the present invention, when all or part of the sodium ions in the sodium A-type zeolite are ion-exchanged with calcium ions, the pH of the aqueous solution in contact with the zeolite at the time of ion exchange is 11.3 to 11.9. It is characterized by keeping it within the range of . The conditions for ion exchange are not particularly limited, other than the above-mentioned pH range, but the ion exchange is usually carried out at a temperature of room temperature or higher and for a sufficient time to achieve the desired exchange rate. The ion-exchanged calcium A type zeolite is obtained as a product after normal washing and drying. Furthermore, those that are kneaded with a binder such as clay, molded, and then fired have high adsorption performance, especially for molecules with weak polarity. The calcium type A zeolite obtained in the present invention has little thermal deterioration during calcination or thermal regeneration as described above, and has high adsorption performance even after these operations. The preparation and properties of thermally stabilized zeolites according to the invention are illustrated by the following examples. Example 1 and Comparative Example 1 Using water glass, sodium aluminate, and water as raw materials, SiO ₂ /Al ₂ O ₃ = 2, Na ₂ O/SiO ₂ = 1.2,
The mixture was mixed so that H ₂ O/Na ₂ O=32, and the reaction composition was maintained at 80° C. for 27 hours. After that, a part of the reaction product was taken out, filtered,
After washing with water and drying, the reaction product was analyzed by X-ray diffraction, and it was confirmed that the reaction product was sodium A-type zeolite containing no impurities. This sodium A-type zeolite was divided into four parts in slurry form so that the weight of hydrated crystals was 20 g per sample. After washing each sample with water until the pH of the washing water reached the value shown in Table 1, each sample was placed in 590 c.c. of a 1N calcium chloride aqueous solution and stirred at room temperature for 18 hours to perform ion exchange. Ta. After separating the samples, each sample was washed with a certain amount of distilled water, dried at 100°C, and placed in a vacuum desiccator at a relative humidity of 80% to absorb a saturated amount of water. Chemical analysis was performed to determine the ion content. The exchange rate was calculated.
Table 1 shows the ion exchange solution pH, washing water pH, and ion exchange rate during ion exchange of each sample. (Sample number 4 is shown as Comparative Example 1. The same applies hereinafter.)

[Table] Samples Nos. 1 to 4 were heated and dried at 100°C, and then left to stand in a vacuum desiccator at 20% relative humidity for a sufficient period of time to adsorb a saturated amount of water in this state. Thereafter, these samples were placed in an electric furnace at 600° C. and kept there for 2 hours to activate them, and then left to stand again in a vacuum desiccator at 20% relative humidity for 18 hours to adsorb moisture. By measuring the weight in the activated state and the weight after water adsorption, the effective water adsorption capacity was determined based on the sample in the activated state. This operation
The experiment was repeated 12 times and the change in effective water adsorption capacity was monitored. The results are shown in Table 2. However, the value at cycle number 0 represents the amount of dehydration from the initial hydration state at 20% relative humidity to the activated state at 600°C. All units are weight percentages.

[Table] Some samples were collected after 5 cycles of the above heat regeneration-hydration cycle test, and the equilibrium adsorption capacity of carbon dioxide was measured, including unused samples and samples after 12 cycles. . The measurement was carried out using a quartz spring balance, and the adsorption isotherm of each sample at 25°C was determined. Table 3 shows the equilibrium adsorption capacity of each sample at a partial pressure of 100 mmHg. All units are weight percentages.

[Table] In addition, as a result of measuring the amount of n-butane and i-butane adsorbed on unused samples 1 to 4 using the quartz spring balance method, all samples were found to be so-called 5A type due to the difference in adsorption amount. This was confirmed. The untreated product and the samples after 5 and 12 cycles of the above heat regeneration-hydration cycle test were placed in a vacuum desiccator at 80% relative humidity to adsorb a saturated amount of water, and then 2θ = 5 An X-ray (Cu-Kα) diffraction pattern up to ~40° (θ is the black reflection angle) was photographed, and the crystallinity of each sample was calculated. The method for calculating crystallinity is as follows. A = sum of peak intensities of all peaks of type A zeolite at 2θ = 5 to 40° of untreated product. B = sum of peak intensities of all peaks of type A zeolite with 2θ = 5 to 40° in the sample after 5 cycles or the sample after 12 cycles Crystallinity = B / A The calculation results of crystallinity are shown in Table 4 .

[Table] Example 2 After synthesizing sodium A-type zeolite under the same conditions as Example 1, the pH of the washing water for the generated crystals was
I washed it with water until it reached 10.7. After drying at 100°C, it was placed in a vacuum desiccator at a relative humidity of 80% to adsorb a saturated amount of water. 20g of this hydrated sodium A-type zeolite
was placed in 590 c.c. of a 1N aqueous calcium chloride solution whose pH was adjusted to 12.0 by adding calcium hydroxide, and the mixture was stirred at room temperature for 18 hours to perform ion exchange. After ion exchange, the crystals were separated and the pH of the ion exchange solution was measured and found to be 11.8. Furthermore, when the separated crystals were washed with a certain amount of distilled water, the pH of the washing water was 11.7. After drying the A-type zeolite crystals produced at 100℃, the relative humidity is 80%.
After complete hydration in a vacuum desiccator, a compositional analysis was performed and the calcium ion exchange rate was found to be
It was 89.6%. (This is referred to as Sample 5.) Repeat the heating regeneration-hydration cycle for the obtained Sample 5 in the same manner as in Example 1, and determine the effective moisture adsorption capacity at a relative humidity of 20% for each cycle. Ta. The results are shown in Table 5. The unit is weight percentage.

[Table] In addition, the untreated product obtained using the same method as Example 1 and
Table 6 shows the value of the carbon dioxide adsorption capacity of the sample after 10 cycles at 25°C and 100 mmHg, and the crystallinity of the sample after 10 cycles determined by the same method as in Example 1.

[Table] Comparative Example 2 After synthesizing sodium A-type zeolite under the same conditions as in Example 1, the pH of the washing water for the generated crystals was
I washed it with water until it reached 10.7. After drying at 100°C, it was placed in a vacuum desiccator at a relative humidity of 80% to adsorb a saturated amount of water. 20 g of this hydrated sodium A-type zeolite was placed in 590 c.c. of a 1N aqueous solution of pH 7.8 in which only calcium chloride was dissolved in distilled water, and ion exchange was performed by stirring at room temperature for 18 hours. After the ion exchange, the crystals were separated and the pH of the ion exchange solution was measured and found to be 8.0. Furthermore, when the separated crystals were washed with a certain amount of distilled water, the pH of the washing water was 10.3. After drying the A-type zeolite crystals produced at 100℃, the relative humidity is 80%.
After complete hydration in a vacuum desiccator, compositional analysis was performed, and the calcium ion exchange rate was found to be
It was 84.7%. (This is referred to as Sample 6) The heating regeneration-hydration cycle was repeated in the same manner as in Example 1 for the obtained Sample 6. The effective water adsorption amount after 10 cycles was 20.2. In addition, the untreated product obtained using the same method as in Example 1 and
Table 7 shows the value of the carbon dioxide adsorption capacity of the sample after 10 cycles at 25°C and 100 mmHg, and the crystallinity of the sample after 10 cycles determined by the same method as in Example 1.

[Table] In addition, as a result of measuring the adsorption amount of n-butane and i-butane using the quartz balance method for untreated samples 5 and 6, it was found that both samples were so-called 5A type due to the difference in adsorption amount. was confirmed. Example 3 After synthesizing sodium A-type zeolite under the same conditions as Example 1, the pH of the washing water for the generated crystals was
I washed it with water until it reached 10.7. After drying at 100°C, it was placed in a vacuum desiccator at a relative humidity of 80% to adsorb a saturated amount of water. 20 g of this hydrated sodium A-type zeolite was placed in 590 c.c. of a 1N aqueous solution of pH 7.8 containing only calcium chloride in distilled water, and the mixture was heated at room temperature.
Ion exchange was performed by stirring for 18 hours. The pH of the exchange solution at the end of ion exchange was 8.7. The separated crystals were dissolved in a saturated aqueous solution of calcium hydroxide with a pH of 12.5.
Washed three times with 200 c.c. The pH of the washing water after the third washing was 11.7. Thereafter, it was further washed once with 200 c.c. of distilled water. The pH of the washing water was 11.2. The resulting A-type zeolite crystals were dried at 100° C. and completely hydrated in a vacuum desiccator at a relative humidity of 80%, followed by compositional analysis, and the calcium ion exchange rate was found to be 87.7%. (This is referred to as Sample 7) The heat regeneration-hydration cycle was repeated on the obtained Sample 7 in exactly the same manner as in Example 1.
The effective moisture adsorption capacity was determined at a relative humidity of 20% for each cycle. The results are shown in Table 8. The unit is weight percentage.

[Table] Example 4 and Comparative Example 3 Sodium A-type zeolite was synthesized under exactly the same conditions as in Example 1. In some cases, the pH when performing calcium ion exchange using 1N calcium chloride aqueous solution was adjusted to 11.8 by adjusting the amount of washing water, and at room temperature.
The mixture was stirred for 18 hours to perform ion exchange. The calcium exchange rate of the type A zeolite obtained was 83%. 100 parts by weight of the above type A zeolite in an activated state and clay
After thoroughly kneading 20 parts by weight while adding an appropriate amount of water, the mixture was molded into a cylindrical shape with a diameter of 1.5 mm and a length of about 5 mm. Sample 8 was obtained by firing this molded body at 650°C. After thoroughly washing the remainder of the synthesized sodium A-type zeolite with water, perform calcium ion exchange using a 1N calcium chloride aqueous solution to adjust the pH to 8.9.
The mixture was stirred at room temperature for 18 hours for ion exchange. The calcium exchange rate of the obtained type A zeolite is
It was 82%. 100 parts by weight of this type A zeolite in an activated state and 20 parts by weight of clay were sufficiently kneaded while adding an appropriate amount of water, and then formed into a cylinder having a diameter of 1.5 mm and a length of about 5 mm. This molded body is 650
Sample 9 (referred to as Comparative Example 3) was obtained by firing at ℃. For Samples 8 and 9, adsorption isotherms of nitrogen and ethane were measured using the apparatus shown in Table 9, and the adsorption capacities at the partial pressures shown in Table 9 were compared.

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Claims (1)

[Scope of Claims] 1. When sodium A-type zeolite is brought into contact with an aqueous solution containing calcium ions to exchange the sodium ions in the zeolite with calcium ions, the zeolite is in contact with the zeolite during the ion exchange. A method for producing heat-stabilized type A zeolite, which comprises maintaining the pH of an aqueous solution in the range of 11.3 to 11.9. 2 During ion exchange using calcium hydroxide
A method according to claim 1 for adjusting pH.