CA1235684A

CA1235684A - Membraneous synthetic zeolite and process for producing the same

Info

Publication number: CA1235684A
Application number: CA000465117A
Authority: CA
Inventors: Satoshi Sakurada; Nobuaki Tagaya; Tsugio Maeshima; Takeshi Isoda
Original assignee: Toa Nenryo Kogyyo KK
Current assignee: Tonen General Sekiyu KK
Priority date: 1984-10-10
Filing date: 1984-10-10
Publication date: 1988-04-26

Abstract

18 This invention discloses a membraneous zeolite having a thickness of 1 .mu. m to 500 .mu. m and the production conditions to form the same. Since the membraneous zeolite of this invention consists almost of crystalline synthetic zeolite, it is expected to have excellent abilities for material separation. The thickness of this membrane can be controlled easily by adjusting pH of aqueous reaction mixture. At least one organic nitrogen containing cation have to be contained in the aqueous reaction mixture to form membraneous zeolite of present invention. The preferred composition of starting materials are also disclosed.

Description

68~

MEMBRANEOUS SYNT~1~TIC ZEOLITE AN~ PQOCESS
FOR PRODUCING THE SAME

BAC~GROUND OF T~1E INV~NTION

1. ~ield of the Invention This invention relates to a separation membrane for use in separating materials. More particularly, th;s invention relates to a membraneous æeolite for use as a separation memebrane and to a process for producing the same.

2. Description of the Prior Art Heretofore, material separation by a separation membrane has attracted notice and has actually found wide acceptance because of its good efficiency. However, separation membranes put into actual use are mostly organic materials typified by polymers, SG that there have been drawbacks that they are not satisfactory in respect of thermal stability and durability, that the selectivity in material separation and energy loss during operation are not satisfactory, and that the condition of its use must be limited.
Therefore, when the heat resistance and durability are taken into consideration, inor~anic separation membranes such as porous membranes and metallic membranes are advantageous. However, these inorganic separation membranes have a drawback that they generally have a low separation ef~iciency, and especially when metallic membranes are used, these are subject to corrosion and have markedly limited use.
Therefore, no inorganic separation membranes have been actually put into widespread use.
On the other hand, it is known that crystalline aluminosilicates, generally called æeolites, consist of a three-dimensional structure formed in such a way that regular tetrahedra of, chiefly, SiO4 are bonded to common oxygen atoms, and according to the manner of this ~ ~ ~ S~ 8 ~

bonding, these SiO4 tetrahedra constitute basic un;ts by forming 4-, 5-, 6-, $-, 10- or 12-membered ring formed hy interconnecting 4, 5, 6, 8, 10. or 12 regular tetrahe~ra chiefly consisting of ~i~4, and double rings formed by superposing each of these 4-, 5-, 6-, 8-, 10- or 12-membered rings, and these basic units are interconnected to determine the framework of a crystalline aluminosilicate.
Special cavities are present in this framework determined by the manner of bonding, and the entrance of the cavity structure forms an opening consisting of 6-, 8-, 10-or 12-membered rings. The cavities thus formed have uniform diameters, and lie in a state in which the molecules of a special sizes or below can be adsorbed but the molecules of larger si~es can not get into the cavities. Thus, the crystalline aluminosilicates are known as molecular sieves for the sake of their action, and by virtue of the above-mentioned properties, they are used in industry as adsorbents in a variety of chemical processes.
~urther, in the crystalline aluminosilicates, the 2~ aluminum atom in the framework constitutes a tetrahedral structure and produces a charge (A ~ 0 4 ~~ . In this case, in order to counterbalance this charge, a variety of ca tions, such as sodium ions, are introduced.
Because these cations have ion exchange ability, it is possible to produce solid acid points in the vicinity of the aluminum atoms and to impart catalytic ability to the crystalline aluminosilicate by exchanging the cations with a variety of cations such as metal cations or ammonium ions.
Namely, the molecular sieve adsorptive action is thought to arise from the two mechanisms :
(~) special substances are adsorbed by cavities determined by the framework according to their molecular shapes and si~es, and (2) substances having dipoles, quadrupoles, or unsaturated bonds and those having high polarity are adsorbed by the action of the cations present in the crystal ~3~i6~

structure, but it is generally believed that the cations are present where no molecular sieve action is exhibited.
Therefore scarcely any discussion of adsorptive separation have dealt with cationic species, their e%change ratio or the like except in such special cases where the radii of cations differ greatly as in the case of a combination of potassium and sodium, and where there is a difference in quantity due to the difference in the number of charges of cations as in the case of a combination of sodium and calcium. However, when a species to be adsorbed, which interacts with cationic species, is present, for example, when water is present, interruption of adsorption due to strong adsorption becomes a very serious problem. For adsorptive separation of such a water-containing system~ a silica-based membrane having hydrophobicity is thought to be suited and, in fact, it is effective in separating alcohols from water.
~ rom these conventional knowledges it is expected that if zeolite can be formed into membrane, the conventional ?0 drawbacks can be solved and a novel good inorganic membrane for material separation can be obtained.
As a result of extensive studies made under these circumstances, the inventors of this invention have found that it is possible to obtain membraneous zeolite having a ~5 molecular sieve adsorptive action.

SUMMARY OF THE IN~ENTION

Therefore, it is a primary object of this invention to provide an inorganic membrane excellent in selectivity in material separation, durability, and thermal stability.
It is a secondary object of this invention to provide a synthetic zeolite membrane which, in itself, has an excellent function of adsorptive separation.
Furtherl it is a third object of this invention to 35~8~
~ 4 --provide a process for producing a synthetic zeoli-te membrane which retains a crystal s-tructure which is capable of showing a molecular sieve adsorptive action.
In meeting these and other objeets, this invention provides a filter for substance separation, comprising a substrate made of a porous glass and a zeolite-based film formed direetly on the porous glass, the zeolite-based film having a thiekness of 1 ~Im to 500 ~m.
The invention also provides a process for produeing a filter for substanee separation eomprising:
(a) using as a starting material a glass compound having the following composition:
X230.3 ~ 30% by weight YO250 ~ 99% by weight 2~ 20~ by weight ignition loss0 ~ 10% by weight at 900 C, 1 hour wherein X is a member selected from the group consisting of aluminum, gallium and boron, or a mixture of at least two of them, and Y is a member selected from the group consisting of silicon and germanium, or a mixture thereof;
(b) adding an alkali and water to the glass eompound to form a mixture having the following composition in molar ratio:
Na2O/H2O ~ 0.01 ~R~ /H2O 0.0002 ~ 0.02 H2O ~YO2 1 ~ 200 wherein, CR~ is at least one organie nitrogen-eontaining eation and/or at least one organie nitrogen-containing eation souree whieh can be arbitrarily selected, and Y is a member seleeted from the group eonsisting of silicon and germanium, or a mixture thereof; and (e) heating and maintaining this reaction mixture at a crystallization temperature in a reaction vessel until ~23~6~4 - 4a -a zeolite crystal layer is formed on a glass surface.
Since the material separation membrane obtained in this invention comprises a zeolite as an inorganic material, it has high thermal resistance and can be used for material ~ ~ 3 ~

separation under temperature conditions which can not be adopted up to this time. This not only widens the scope of application of material separation but also can reduce energy loss in the process for material separation, and therefore the significance of this invention is great. ~he durability as a separation membrane is also improved in connection with the above.

Crystalline aluminosilicates can be generally produced by using SiOz as a source of silicon and AQ 2 O 3 as a source of aluminum in a ratio falling within a definite range, forming an aqueous reaction mixture by adding a suitable source of an alkali and water into above sources in a ratio falling within a definite range, and heating and maintaining the aqueous reaction mixture at a crystallization temperature until crystals are fo~med. This production condition can be reali~ed, for example, by maintaining the mixture at about 12~ to about 230C and an autogeneous pressure for about l0 hours to about l0 days.
Examples of the silicon sources for this case include sodium silicate, silica gel, silicic acid, aqueous colloidal silica gel, fused silica, powdery silica, and amorphous silica, among which sodium silicate, water glass, and colloidal silica are particularly preferred.
Examples of the aluminum sources include active alumina, r -alumina, alumina trihydrate, and aluminum salts such as nitrates and sulfates, among which sodium aluminate and aluminum sulfate are particularly preferred.
In this invention, although it is possible to mix separately prepared respective starting materials, with each other, it is preferred to use a glass compound containing an oxide of a Group m b element of the Periodic Table, represented by the general formula X2 O 3 , SiOz , and/or ~3S68~

Ge O 2 and, if necessary, Naz 0, more particularly the above-mentioned glass compound having an ignition loss (at 900c, 1 hour) of 0 to 10 % by weight.
Although the glass compound ~ A ) being used in this S invention is amorphous, it contains silicon and/or germanium atoms in the form of Y02 , and takes the form of an oxide in which the tetrahedra are connected to each other by bonding to common oxygen atoms. Preferable X's which may be contained in this glass compound are boron, aluminum, and gsllium. ~s these elements can take the form of the tetrahedral structure like the above silicon or germanium, these can form ~eolite.
Therefore, when a hydrothermal reaction is effected by using the aboYe glass compound ( A ) as a starting material, and an alkali is added during this hydrothermal reaction, the solid phase in the reaction mixture is first dissolved and forms zeolite nuclei, which grow into crystals and form a zeolite membrane.
In this case, when a gel is present in the reaction mixture, it forms a solid-phase amorphous phase which directly ~0 transforms into a crystalline phase and forms zeolite, and therefore it is impossible to obtain membraneous zeolite though it is possible to obtain lump- or powder-form zeolite.
Therefore, it is necessary to exclude any gel from the reaction mixture.
~5 In order to facilitate the deposition of ~eolite crystals in the hydrothermal reaction of this invention, it is necessary that the composition of the material glass compound falls within a definite range. Namely, the total content of X 2 O 3 in the glass compound ( A ~ used in this invention is 0 to 50 % by weight, preferably 0.5 to 30 % by weight, the total content of Y02 is ~0 ~ 99 % by weight, preferably 50 to 99 % by weight. ~urther, the preferable amount of Na2 0 is Q to 20 % by weight. ~xamples of these glass compound materials include borosilicate glass, soda lime glass, aluminosilicate glass and silica glass, 1~3568~

The alka]is which are added during the hydrothermal reaction in this invention may be those which are usually used, but because it is important to control the alkali concentration in order to form a zeolite membrane by growing crystals from the liquid phase, it is preferred to use a mixture ~A ) having the composition (in terms of a molar ratio) :
N a ~ O / H ~ O 0~ 0.01 ~R ) / H 2 O 0.0002 ~ 0.02 l~ H 2 O / Y O 2 1 ~ 200 wherein ~R ~ is at least one organic nitrogen-containing cation and~or at least one organic nitrogen-containing cation source which may be arbitrarilY selected, and N a 2 includes free Na2 0 and Na2 0 contained in the glass compound ~ A) , which can be controlled by adding sulfuric acid, hydrochloric acid, or nitric acid.
The organic nitrogen-containing cation source to be used in this invention may increase the pH value under a condition of the hydrothermal reaction, and thereby increases oligomers such as dimer and trimer, of silicate ions, and provides an environment faborable for the deposition of crystals from the solution. The organic nitrogen-containing cation source, which may be used for this purpose, may be one kind alone or an arbitrary combination of at least two of them.
~5 Examples of these organic nitrogen-containing cation sources include quaternary ammonium salts such as tetra-methylammonium, tetraethlammonlum, tetrabutylammonium, diethylammonium, triethylammonium, dibenzylammonium, dibenzyldimethylammonium, dibenzyldiethylammonium, benzyl-triethylammonium, and choline salts; alkylamines such as trimethylamine, triethylamine, tripropylamine, ethylenediamine, propanediamine, butanediamine, pentanediamine, hexanediamine, methylamine, ethylamine~ propylamine, butylamine, dimethylamine, diethylamine, and dipropylamine; aromatic amines such as benzylamine and aniline; and cyclic amines such as pyridine, ~L~3S~84 piperidine and Pyrrolidine, among which tetrapropylammonium salts, propylamine, and derivatives thereof are particularly preferable.
Since the alkali concentration thus greatly influences the growth of zeolite crystals in this invention, the thick-ness of a zeolite membrane formed can easily be controlled by adjusting the alkali concentration.
In this invention, it is necessary to use a base on which 2eolite crystals can be deposited in the form of a membrane.
1~ Examples of these bases include glass, mullite and cordierite ceramics, alumina, silica, and a base (e.g., metal~ coated with an inorganic substance, among which glass, especially silicate glass, is preferred, because it facilitates the deposition of zeolite crystals and can form excellent membrane.
Examples of the silicate glass include quartz glass based on Si O 2 , alkali silicate glass based on Na2 O-siO2 , soda lime 81ass based on Na2 O-CaO-Si O 2 , potash lime glass based on K2 O-CaO-Si O 2 , lead ~alkali) glass based on K2 O-PbO-Si O 2 , barium glass based on BaO-Si O 2 -B2 O 3 , and borosilicate ~0 glass based on Na2 O-B2 O 3 -SiO2 . Among these, the one which is substantially the same as the glass compound ~ A ~
is preferable. The glass layer having the surface thus coated with membraneous zeolite in this invention (referred to as an intermediate layer~ is prone to increase the Na2 O content as compared with the initial composition ratio, but still remains amorphous and can perform well as a support for the zeolite membrane.
In the hydrothermal reaction according to this invention, it is possible to add a mineralizer in performing crystal-lization. This mineralizer is one which can accelerate theformation of zeolite and includes, for example, neutral sal~s of an alkali metal or alkaline earth metal such as NaC e, Na2 CO3 , Na2 SO4, Na2 Se O 4, KC e, KBr, KF, eac e 2 , an~
BaBr2 . Among these mineralizers, Nac e is particularly perferred. The zeolite formed on the glass surface in the ?~Z356B4 g synthetic process of a zeolite membrane is removed from the reaction vessel, then washed with pure water, and dried at room temperature to 120 C for 1 to 16 hours. When this membrane is observed by means of a secondary electron microscope (SEM), large crystal grains having a particle size of several ~um to several hundreds um appear to be united with each other according to some bonding form.
Therefore, the X-ray diffraction pattern of the membraneous zeolite is similar to that of a single crystal, and many peaks appear additionally among the six main peaks which appear also in a single crystal, as shown in Table 1.

Interplanar spacings d(~) Relative intensity (I/Io) 11.2 + 0.2 Strong 10.1 + 0.2 Strong

3.86 + 0.05 Very Strong 3.76 + 0.05 Strong 3.72 + 0.05 Strong 3.64 + O.OS Strong Further, at least two diffraction peaks are observed between, 3.76 R and at least one diffraction peak is observed between 3.72 ~ and 3.64 ~.
These values were determined by standard techniques with an X-ray diffractometer (Geigerflex* RAD, model rA, manufactured by Rigaku Denki Co., Ltd.).
The radiation was K-~ doublet of copper, and a scintillation counter with a strip chart pen recorder was used. The peak heights and the positionsas a function of 2 O (where ~ is the Bragg angle) were read from the char-t.

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- 9a -From these data, the relative intensities and the interplanar spacings (d) R, in terms of Angstroms, corresponding to the recorded lines were determined.

;~356~

The composition ~in terms of a molar ratio of oxides) of thus-prepared zeolite of this invention was as fol]ows:
0 ~ l.0 Na2 0 0.1 ~l.0 ~ RR'0 X ~ O 3 l0~ l0.000 Y0z 0 ~~0 H2 wherein R and R'in the RR'0 represent an organic nitrogen-containing cation which may be different from each other, and ~ RR'0 for a case where at least two organic nitrogen-containing cations are mixed and used in the hydrothermal reaction of this invention means the sum of all RR'0 forrned by combining R and R' present in the reaction system.
Since the membraneous synthetic zeolite obtained in this invention is, in its essence, a zeolite having a function of separating molecules by selective adsorption, its performance of material separation is expected to be extremely high.
Further, as mentioned earlier, the electronic balance in the tetrahedron containing the aluminum of the crystalline sodium aluminosilicate according to this invention is maintained by holding cations such as sodium ions within the crystal. These cations are replaced by ion exchange by a variety of methods to form a hydrogen-form or metal ion-exchanged type zeolite, which can function as a solid acid catalyst.
The metal cations originally present at the time of the ~eolite synthesis can be replaced, at least in part, by ion exchange, etc. This ion exchange can be performed with a Group Il throu~h ~III metal of the Periodic Table, with ammonium ions, or with hydronium ions. This can be applied also to the membraneous synthetic zeolite of this invention, and permits material separation by using the membrane in various forms.

EXAMPLES
The following examples are provided to illustrate present invention, but are not to be construed as limiting present invention in any way.

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~xample 1 A 2Q0-cc autoclave was charged with ~.5 ~ of l.U5 mm-thick boronsilicate ~lass (95.3 ~ by weight of SiO2 , 2.87 ~ by weight of B2 O 3 , 0.26 % by weight of Al2 O 3 , and 0.02 %
by weight of Na2 O) together with a solution prepared by dissolving 0.6 ~ of NaOH and l.9 g of tetrapropylammonium bromide in 131 g of pure water, and then sealed. The reaction mixture was heated to 190C under agitation, and maintained at this temperature for 64 hours. After the completion of the reaction, the borosilicate glass was withdrawn from the autoclave, washed with pure water, and dried at 100C for about 16 hours.
A translucent zeolite layer was formed on the surface of the transparent glass, The powder X-ray diffraction analysis of the formed zeolite revealed that this zeolite was one having the X-ray diffraction pattern shown in Table ~, and had a ]ayer thickness of about 5 ~ m. The reaction conditions and the experimental results are as shown in Table 2.
Example 2 This experiment was carried out in the same way as in Example 1 except that the amount of NaOH added was varied as shown in Table 2.
A translucent layer was formed on the transparent surface of glass, and the thickness of the translucent layer was about 113 ~ m. An analysis of the product by powder X-ray diffractometry revealed that it was zeolite showing an X-ray diffraction pattern which was substantially the same as that in Example 1.

Example 3 This experiment was carried out by the same way as in Example 1, except that the amount of NaOH was varied as shown in Table 2.

~Z~35684 .

A translucent layer was formed on the transparent surface layer of glass, and the thickness of the translucent layer was about 170 ~m. An analysis of the product by powder X-ray diffractometry revealed that it was a zeolite showing sub-stantially the same X-ray diffract;on pattern as that in Example 1.

Example ~
A 200-cc autoclave was charged with 2.5 g of 1~15 mm-thick porous borosilicate glass Isurface area of 165.1 ~/g,88.7 % by weight of Si O 2 , 2.67 % by weight of B 2 3 ~
0.24 % by wei~ht of A12 O 3 , and 0.02 % by weight of Na2 ) together with a solution formed by dissolving 0.5 g of NaOH, 1.06 g of tetrapropylammonium bromide and 5.1 g of NaC~ in 73.4 g of pure water, and then selaed. The reaction mixture was heated to 1~3 C under agitation and maintained at this temperature for 63 hours. After the completion of the reaction, the reaction product was discharged from the autoclave, washed with pure water, and dried at 10~ C
~0 for about 16 hours.
The surface layer of the product was covered with a trans-lucent layer, and the thickness of this layer was about 325 ~ m, An analysis of the product by powder X-ray diffractometry reveled that it was a ~eolite having an X-ray diffraction pattern which was essentially the same as that in Example 1.
The experimental results are shown in Table 2.

Comparative Example This experiment was carried out in the same way as in Example ~, except that, as shown in table 2, no tetrapropy1-ammonium bromide was used, No translucent layer was formed on the surface layer of the product. An analysis of the product by powder X-ray dif~ractometry revealed that it was amorphous.

~5~:i89 Examples S to 9 The experiments were carried out in the same way as in Example 4, except that the Na2 O/Si O 2 molar ratio was different. As the experimental results in table 3 show, membraneous synthetic zeolites could be obtained in all cases.
These results illustrate that reaction conditions of present invention are suitable to form membraneous zeolite provided by this invention.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A filter for substance separation, comprising a substrate made of a porous glass and a zeolite-based film formed directly on the porous glass, the zeolite-based film having a thickness of 1 µm to 500 µm.

2. A filter according to claim 1, wherein said porous glass is a silicate glass.

3. A filter according to claim 2, wherein said porous glass is a borosilicate glass.

4. A filter according to claim 1, wherein at least 90% by weight of the zeolite is a crystalline synthetic zeolite.

5. A filter according to claim 4, wherein the crystalline portion of the zeolite has the following X-ray powder diffraction pattern characteristics:

and at least two diffraction peaks are present between 3.76 .ANG. and 3.72 .ANG., and at least one diffraction peak is present between 3.72 .ANG. and 3.64 .ANG..

6. A filter according to claim 5, wherein the synthetic zeolite has a composition, in terms of molar ratio of oxides, as follows:
0 - 1.0 Na2O ? 0.1 - 1.0 .SIGMA.RR'O ?X2O3 ? 10 - 10,000YO2 ?

wherein R and R' are each an organic nitrogen-containing cation which may be different from each other, .SIGMA.RR'O means the sum of all RR'O formed by arbitrary combination of R and R' present in the synthetic reaction system, X is a member selected from the group consisting of aluminum, gallium, and boron, or a mixture of at least two of them, Y is either silicon or germanium, or a mixture thereof.

7. A process for producing a filter for substance separation comprising:
(a) using as a starting material a glass compound having the following composition:
X2O3 0.3 ? 30% by weight YO2 50 ? 99% by weight Na2O 0 ? 20% by weight ignition loss 0 ? 10% by weight at 900° C, 1 hour wherein X is a member selected from the group consisting of aluminum, gallium and boron, or a mixture of at least two of them, and Y is a member selected from the group consisting of silicon and germanium, or a mixture thereof;
(b) adding an alkali and water to the glass compound to form a mixture having the following composition in molar ratio:
Na2O/H2O 0 ? 0.01 [R] /H2O 0.0002 ? 0.02 H2O /YO2 1 ? 200 wherein, [R] is at least one organic nitrogen-containing cation and/or at least one organic nitrogen-containing cation source which can be arbitrarily selected, and Y is a member selected from the group consisting of silicon and germanium, or a mixture thereof; and (c) heating and maintaining this reaction mixture at a crystallization temperature in a reaction vessel until a zeolite crystal layer is formed on a glass surface.