KR100424880B1 - Method for ion exchanging of zeolite - Google Patents

Abstract

The present invention relates to a method for ion exchange of zeolite, comprising: (a) a polar non-aqueous solvent containing a zeolite containing a monovalent cation and a source of the transition metal cation to be ion-exchanged, whose molecular size is smaller than the pore size of the zeolite; Mixing in the ion exchange reaction; And (b) calcining the zeolite exchanged with the transition metal cation at a temperature of 200 to 450 ° C. According to the present invention, the zeolite can be prepared in a good crystal state by being ion-exchanged with a cation of the transition metal without further purification, thereby improving the adsorption and catalytic properties.

Description

Ion exchange method of zeolite {Method for ion exchanging of zeolite}

FIELD OF THE INVENTION The present invention relates to ion exchange methods of zeolites, and more particularly to methods of preparing partially or totally dehydrated zeolites comprising cations of transition metals such as cobalt, nickel or zinc, in particular high polarity or polarizable ratios. The present invention relates to a process for producing a faujasite type zeolite exchanged with cobalt, nickel and zinc ions from an aqueous solvent without further purification.

Zeolites are crystalline inorganic solids with nano-sized pores (ie, windows of zeolites having nanometer size) and are widely used as ion exchangers, adsorbents and catalysts in industrial processes.

Zeolites are generally synthesized in a form containing monovalent cations such as sodium, potassium or sodium-potassium mixed cations. These zeolites have useful properties in the form as they are synthesized, but are often preferred to be ion exchanged to improve their adsorptive and / or catalytic properties.

The electric field gradient of monovalent cations is weaker than positive cations, so these cations generally have a limited ability to attract, polarize, and adsorb guest molecules, and Efficiency may be lowered. However, exceptionally, lithium ions (Li ⁺ ) are small in spite of monovalent cations and thus have large electric field gradients on their surfaces.

In addition, sometimes transition metal cations are introduced into zeolites by ion exchange for various applications; They can selectively coordinate guest molecules over filled-shell cations, and because they are easily accessible to other oxidation states, they can be introduced into zeolites to provide new mechanisms for the function of zeolites as adsorbents and catalysts. have.

Zeolites containing transition metals are generally known to catalyze in the following reactions.

(1) hydroformylation of olefins;

(2) hydrosulfuration of alcohols;

(3) oxidation of alkenes;

(4) conversion of olefins to thiols;

(5) decomposition of nitromethane; And

(6) Fisher-Tropsch catalysis.

Various methods have been attempted to prepare a zeolite including a transition metal, and specifically, there are methods as follows.

(1) ion exchange from an aqueous solution or a solid phase reaction;

(2) hydrothermal synthesis methods; And

(3) Adsorption and decomposition reactions of volatile organometallic compounds.

In general, the ion exchange reaction is by direct exchange of monovalent cations in zeolite and other cations (eg, divalent ions) in aqueous solution. Unfortunately, however, the results are not always simple. In some cases, only a portion of the original cation (usually sodium ions) can be replaced, and attempts to solve this clearly show the limitation of possible ion exchange rates.

If the cation to be ion exchanged can be hydrolyzed, the concentration of H ⁺ ions in the solution can be increased by a power of 10 to promote H ⁺ exchange. The temperature and acidity of the chemical treatments applied to the zeolites have been shown to reduce or eliminate the orderly and repeatedly arranged silicon / aluminum (Si / Al) sequence in three-dimensional space. This effect appears to be stronger when ion exchange is carried out at high temperatures and especially when vacuum dehydration is carried out at high temperatures. This is undesirable because it causes alteration, damage, destruction or dissolution of the zeolite skeleton, especially the aluminosilicate zeolite skeleton with a low silicon content.

For example, it has been observed that hydrolysis of the zeolite backbone results in the formation of 5-coordinating Al ³⁺ in type A zeolites partially exchanged with Co ²⁺ ions and Ni ²⁺ ions. In addition, the zeolite framework itself is changed and reconstituted upon vacuum dehydration at high temperature, and the Si / Al array (X-type zeolite exchanged with Zn ²⁺ ions) or crystalline (Co) is regularly and repeatedly arranged in three-dimensional space. X-type zeolites exchanged with ²⁺ and Ni ²⁺ ions) (Donghan Bae et al., Structure of cobalt (II) -exchanged zeolite X , Microporous and Mesoporous Materials 33 (1999) 265-280; Donghan Bae et al., Crystal Structure of zeolite X nickel (II) -exchanged at pH 4.3 and partially dehydrated, Ni ₂ (NiOH) ₃₅ (Ni ₄ AlO ₄ ) ₂ (H ₃ O) ₄₆ Si ₁₀₁ Al ₉₁ O _{384 ,} Microporous and Mesoporous Materials 40 (2000) 219-232; Donghan Bae et al., Extensive intrazeolitic hydrolysis of Zn (II): partial structure of partially and fully hydrated Zn (II) -exchanged zeolite X , Microporous and Mesoporous Materials 40 (2000) 233- 245).

Ion exchange by solid phase reaction is carried out by grinding the zeolite with an oxide or salt containing the cation to be exchanged and then draining off the water molecules together with volatile products such as hydrogen halide compounds and ammonia at high temperatures. The advantage of this method over the direct ion exchange from aqueous solution is that it avoids hydrolysis and large hydrated shells (shells) of small, acidic cations in aqueous solution. However, due to severe grinding, the crystallinity of the zeolite may be lost, and in some cases, there is a disadvantage that precipitation may occur.

New zeolites containing transition metal cations in the backbone can also be prepared by hydrothermal synthesis, but it is very difficult to explore the local structure of these cations. As a result, information on the chemical environment of charge balancing cations before and after ion exchange is not readily available. There is a limit to their application as a catalyst or adsorbent or to a wide range of applications without detailed information on the structure and chemical composition of the new zeolites. In addition, thermodynamic and kinetic stability and porosity of the new constituent backbone are also questionable.

Adsorption and decomposition of volatile organometallic compounds is another method of preparing zeolites containing transition metals. The disadvantage of this method is that after decomposition, excess metal may form microcrystals on the zeolite outer surface, and the position of the metal cations is uneven or poorly analyzed.

Accordingly, the present invention provides a method for efficiently preparing a zeolite containing a cation of a transition metal without the above-mentioned difficulty or additional purification.

1 is an X-ray diffraction analysis of hydrated zeolite X,

2 is an X-ray diffraction analysis of the Co ion-exchanged zeolite according to Example 2 of the present invention,

FIG. 3 is an X-ray diffraction analysis result of zeolite exchanged by Co ion according to Example 3 of the present invention.

The present invention to achieve the object as described above,

(a) mixing a zeolite containing a monovalent cation with a source of a transition metal cation to be ion exchanged in a polar non-aqueous solvent whose molecular size is smaller than the pore size of the zeolite; And

(b) calcining the zeolite exchanged with the transition metal cation at a temperature of 200 to 450 ℃ provides an ion exchange method of the zeolite.

According to an embodiment of the present invention, the polar non-aqueous solvent is preferably methanol, formamide or acetonitrile.

In a preferred embodiment of the present invention, the cation of the transition metal is preferably a divalent cation of cobalt, nickel or zinc.

In an embodiment of the present invention, the ion exchange reaction is preferably carried out in the range of 50 ℃ to within the boiling point of the solvent.

In an embodiment of the present invention, the ion exchange reaction is preferably carried out under the condition of pH 5-8.

In an embodiment of the present invention, it is preferable to further include a filtration and drying step after the ion exchange reaction.

In an embodiment of the present invention, the zeolite before the ion exchange reaction preferably contains sodium ions, potassium ions or a mixture thereof.

In the embodiment of the present invention, the zeolite preferably has a skeleton in which the atomic ratio of silicon to aluminum is 1: 1 to 1.5.

Hereinafter, the present invention will be described in more detail.

The present inventors have diligently researched to solve the problems of the conventional method of ion-exchanging transition metal cations (divalent or higher) in zeolite, and found that the conventional method has the following problems.

That is, in the case of ion exchange reaction using an aqueous solution, since the H ₃ O ⁺ ions generated when the metal ions are hydrolyzed attack the zeolite skeleton to remove aluminum (Al) contained in the zeolite skeleton, the zeolite skeleton is eventually destroyed. May be caused.

In addition, even when using a polar organic solvent, there was no consideration of the size of the solvent molecules surrounded by transition metal ions. That is, the transition metal ions surrounded by the solvent molecules can more easily penetrate into the pores of the zeolite only when the size of the solvent molecules is smaller than the pores (windows) of the zeolite.

In addition, in the past, when the temperature of the solution in which the ion exchange reaction proceeds is too high, it is determined that the skeleton destruction of the zeolite will occur more easily. However, the study of the present inventors confirmed that the result is excellent when the reaction temperature rises to near the boiling point of the solvent. Therefore, in the present invention, the ion exchange reaction is carried out at a temperature in the range of 50 ° C to the boiling point of the solvent, more preferably 50 to 180 ° C.

Accordingly, the present invention provides a zeolite exchanged with a transition metal cation in a polar organic solvent of a size suitable for passage of zeolite pores within the range of 50 ° C. to the boiling point of the solvent, and then The process of firing a zeolite at high temperature to activate it to have properties as a catalyst and / or adsorbent is described.

The zeolite used in the examples of the present invention is a synthetic zeolite having a skeleton having a silicon: aluminum atomic ratio of about 1: 1 to 1.5. Although a zeolite having a silicon content higher than this may be used, a zeolite having a low silicon content may be used as described above in order to clearly contrast the effects of the present invention in view of the fact that skeletal fracture is prominent during transition metal cation exchange. Zeolites having the same proportions were used.

Synthetic zeolites suitable for use in the present invention include type A, type X and type Y zeolites.

Particularly preferred zeolites in the practice of the present invention include X-type zeolites and Y-type zeolites having a skeleton having a silicon: aluminum atomic ratio of about 1: 1.08 to 1.45.

The ion exchange process of the transition metal can be carried out by conventional zeolite ion exchange methods well known in the art, which can be followed by an insignificant subsequent procedure. For example, the ion exchange step can be carried out as a single non-aqueous exchange step using excess transition metal ions as a solution of soluble salts in a suitable organic solvent, in a stirred tank containing zeolite powder or in a column using zeolite pellets. have.

According to a preferred embodiment of the present invention, the initial zeolite in powder form is suspended in an organic solvent, for example methanol, and the desired transition metal ion while maintaining the mixture suspended in the temperature range of 18 ° C. to the boiling point of the organic solvent. A solution of an organic solvent containing a source (eg in the form of a salt) is added. This procedure can be repeated until the desired level of cation exchange is obtained.

Next, the zeolite exchanged with transition metal ions is recovered from the suspension to obtain a zeolite exchanged with the desired transition metal, preferably by filtration and washing the filter cake with the organic solvent used.

Water is a good solvent for many salts because the water molecules are strongly coordinated with the cations, and the resulting solvated cations interact strongly with large amounts of solvent by hydrogen bonding. These solvated cations can likewise be hydrogen bonded to the zeolite backbone. Thus, the inventors have found that a good ion exchange solvent satisfies the following conditions.

1) It should be a good solvent for the salt of the ions to be exchanged into the zeolite. In this respect, highly polarizable or polarizable solvents are most preferred.

2) Solvent molecules should be small enough to pass through the window of zeolite. And,

3) The cation complexed by this solvent must be able to hydrogen bond with the zeolite backbone and hydrogen bond with other solvent molecules inside the zeolite.

Among the more than 100 important organic solvents, methanol and formamide were selected as good ion exchange solvents because they were determined to best meet the above conditions. In addition, acetonitrile was chosen because it has a size similar to formamide but is aprotic and has a larger dipole moment. All solvents were used as received from the manufacturer without further drying. In each case hydrated zeolite and hydrated water from CoCl ₂ .6H ₂ O provide additional water to the system. Of course, water in the zeolite is the most important. Water molecules present in hydrated zeolites and wet methanol participate in the coordination sphere of Co ²⁺ ions. This small amount of water can act as a catalyst to accelerate the ion exchange process by reducing the size of solvated cations by substituting one or two methanol molecules in the coordination sphere, and this effect can be maximized at high temperatures.

In organic solvent solutions, the transition metal ion exchange reaction can be carried out at any temperature, but the reaction rate increases considerably as the reaction temperature rises, preferably near the boiling point of the solvent.

The amount of transition metal ions required in the final ion exchange step is generally three to five times the stoichiometric amount required to obtain the desired ion exchange degree of the transition metal ions, in order to obtain complete ion exchange degree.

The pH of the reaction solution is preferably 5 to 8. If the pH is less than 5, the crystallinity of the zeolite may be damaged or completely destroyed. If the pH is above 8, the metal ion is M ^{n +} (OH). _It is undesirable because it can penetrate into the zeolite in the form of _n and overexchange can occur.

The form of the ion exchanged product may vary and may be in powder form, aggregate or molded into particles such as extruded pellets.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments of the present invention. The following examples are merely illustrative of the present invention, and the scope of the present invention is not limited thereto.

<Example 1>

The exchange of the sodium ion type X zeolite (Na ₇₉ Al ₇₉ Si ₁₁₃ O _384), a methanol solution of a powder of 0.05M CoCl ₂ · 6H ₂ O (4 times the stoichiometric amount needed for complete exchange of Co ²⁺ ion) Mixed with. The temperature of the mixture was heated to 60 ° C. and the pH was kept at 8. After reacting for 48 hours, the slurry was filtered and washed with methanol. Drying at a high temperature of 400 ℃ to obtain a Co ^{2 +} ion-exchanged zeolite.

<Example 2>

Co ²⁺ ion-exchanged zeolite was obtained in the same manner as in Example 1 except that formamide was used instead of methanol as the nonpolar organic solvent and the reaction temperature was 120 ° C.

<Example 3>

Co ²⁺ ion-exchanged zeolite was obtained in the same manner as in Example 1 except that acetonitrile was used instead of methanol as the nonpolar organic solvent and the reaction temperature was 70 ° C.

<Example 4>

A divalent cation of a transition metal Co ²⁺ ions instead of Ni ²⁺ ions in order to exchange, except that the NiCl ₂ with the salt is carried out in the same manner as in Example 1 to obtain a Ni ²⁺ ion exchanged zeolite.

For the ion exchange zeolites prepared in Examples 1-4 above, the position, ion exchange degree and crystallinity of the ion exchanged divalent cations in the zeolite backbone were analyzed using the method described below.

1) Location Analysis of Divalent Cations

The location of Co ²⁺ ions was analyzed using X-ray diffraction analysis and electron spectroscopy. The analysis results are as follows.

In Table 1, a is a positional and thermal variable given by × 10 ⁴ , where the number in parentheses is the standard deviation estimated in units of the least significant number given for the corresponding variable. Anisotropic temperature variable = exp [-2π ² a ^-2 ( h ² U ₁₁ + k ² U ₂₂ + l ² U ₃₃ +2 hk U ₁₂ +2 hl U ₁₃ +2 kl U ₂₃ )]. b is an occupancy variable, given as the number of atoms or ions per unit cell. c is fixed by symmetry. d is a thermal variable of Na (II ′), which is fixed at the least-squares extreme.

According to the results shown in Table 1, about 31 cobalt ions per unit cell were found at three crystallographic positions; 14 at site I, 15 at site II, and the other two at site I '. In addition, only four sodium ions per unit cell were found at site I '. Considering the electrostatic repulsion between the ions, the cation sites in the D6Rs are almost completely filled with cobalt ions, so that in the sodalite cavities the cation sites in S6R remain unoccupied. have. About 17 hydronium ions per unit cell were found in only one location, near the four-rings present in the super cage. Since dehydration took place at very high temperatures (eg 400 ° C.) and the sodalite cavities were empty, no oxides were found in the sodalite.

2) Ion Exchange Degree Analysis

Diffraction data were obtained with an automated x-ray diffractometer (Simens four-circle computer controlled P3 x-ray diffractometer). As the radiation source, molybdenum (K _α1 , λ = 0.70930 μs; K _α2 , λ = 0.71359 μs; K _{α (avg)} , λ = 0.71030 μs) was used. Since the zeolite X crystals substituted with transition metals gave very weak reflections, the tubes were set at 45 kV and 30 mA to get as much reflection as possible.

Solvent H ₂ O H ₂ O H ₂ O ^a CH ₃ OH Exchange temperature (° C) Dehydration temperature (° C) Unit cell Constant collected number of reflections Number of units Reflection reflection (Fo> 4σ (Fo)) Mercury R (strength) R ₁ (Fo> 4σ (Fo)) wR ₂ (strength) Good Good Space Group Ion Exchange Degree (%) 232324.920 (7) 367311545490.19040.08340.25931.068 Fd3 74 2325024.782 (9) 357411383640.320.0780.1470.896 Fd3 80 23400 ---------- 6040024.641 (8) 27795902640.23760.0690.1150.913 Fd3m 96

a means that the decision has completely lost its crystallinity.

From Table 2, it can be seen that Co-zeolite X obtained in a methanol solution retains crystallinity even after dehydration at high temperature (for example, 400 ° C.). This is supported by a relatively large diffraction data set and a low merging R index. On the other hand, Co-X crystals obtained in an aqueous solution dehydrated at the same temperature (400 ° C.) are in good contrast to the complete loss of their crystallinity. The results of X-ray diffraction analysis on the four crystals obtained under the different conditions summarized in Table 2 reveal the effects of water detoxification and dehydration temperature on the crystallinity of zeolites by hydrolysis of hydrated M ²⁺ ions in zeolites. Shows.

3) Crystallinity Analysis

Cobalt (Co, K _α , λ = 1.79026 kPa) was used as a source for obtaining a diffractogram, and the packing density was about 0.8 g / cm ³ . The integration time was 4 seconds / step and the step size was 0.025 ° 2θ / step.

1 is an X-ray diffraction analysis of the hydrated zeolite X, Figure 2 is an analysis result of the cobalt ion exchanged zeolite prepared in Example 1, Figure 3 is a cobalt ion exchanged zeolite prepared in Example 2 The result of the analysis. 2 and 3, a = 24.905 and * represents a new peak.

It can be seen from the results of FIGS. 1 to 3 that the crystallinity of the Co-zeolite Xs obtained as a result of ion exchange performed at a high temperature near the boiling point of the used organic solvents is no different than before ion exchange. In particular, it is more firmly supported that there is no characteristic change before and after ion exchange in the high temperature 2θ region.

From the above results, it can be confirmed that even after high temperature dehydration, the zeolite exchanged with the transition metal which maintains the characteristic chemical structure, physicochemical properties and crystallinity is produced.

Since the ion exchange zeolite prepared according to the present invention improves not only adsorption and catalytic properties but also crystallinity, gas separation, purification, separation of olefins from paraffins having the same carbon number in the skeleton, separation of carbon dioxide from air, nitrogen It is useful as a catalyst and / or adsorbent in a wide range of industrial processes, including the separation of nitrogen from a mixture of air and other atmospheric gases.

Claims (8)

(a) a zeolite containing a monovalent cation and a source of a transition metal cation to be ion-exchanged in a polar non-aqueous solvent having a solvent molecule smaller than the pore size of the zeolite, and the boiling point of the solvent Performing an ion exchange reaction within a range; And (b) calcining the zeolite exchanged with the transition metal cation at a temperature of 200 to 450 ° C. The method of claim 1 wherein the polar non-aqueous solvent is methanol, formamide or acetonitrile. The method of claim 1, wherein the cation of the transition metal is a divalent cation of cobalt, nickel or zinc. delete The method of claim 1 wherein the ion exchange reaction is carried out at a pH of 5 to 8. The method of claim 1, further comprising a filtration and drying step after the ion exchange reaction step and before the firing step. The method according to claim 1, wherein the monovalent cation contained in the zeolite before the ion exchange reaction is sodium ion, potassium ion or a mixture thereof. The method according to claim 1, wherein the zeolite has a skeleton in which the atomic ratio of silicon to aluminum is 1: 1 to 1.5.