Mordenite zeolite membrane and method for producing the same

Abstract: A mordenite (MOR) zeolite membrane is formed on a porous substrate and dominantly oriented in a specific crystalline direction. A method for producing a mordenite (MOR) zeolite membrane includes the steps of: immersing a porous substrate in a gel of raw material which contains zeolite constitution elements and contains 40-400 of SiO 2 /Al 2 O 3 in molar ratio, 10-120 of H 2 O/Na 2 O in molar ratio, and 10 40 of H 2 O/SiO 2 in molar ratio, and subjecting the gel in the presence of the porous substrate to hydrothermal synthesis at 150°C or more to make zeolite crystallized to form a membrane thereof. The MOR zeolite membrane is oriented in a specific crystalline direction.

Description: Background of the Invention and Related Art Statement The present invention is directed to an MOR zeolite membrane which is dominantly oriented in a specific crystalline direction and a method for producing the membrane. Zeolite has a frame structure of crystalline aluminosilicate and a mesh-like structure composed of fine pores of a minute uniform diameter. Thus, zeolite is used as a molecule sieve or a catalyst. For example, JP-A-7-330326 discloses a zeolite membrane which is formed on a single crystal substrate of an oxide, a semiconductor or a metal and oriented in a specific crystalline direction, and zeolite membranes of A type, Y type and the like are given in the examples. In addition, WO92/13631 discloses zeolite membranes comprising an oriented single layer of ZSM-5 (MFI), an A type, a Y type, an X type and the like. WO97/25272 discloses an MFI zeolite membrane oriented along the b axis and a method for producing the membrane. Further, WO96/01683 discloses an MFI zeolite membrane oriented along the a axis and the c axis and the method for producing the membrane. US 5429743 describes an inorganic composite membrane having molecular sieve crystals (e.g. mordenite crystals) applied to a support surface. A gastight matrix is present between the crystals to make sure that material transport through the membrane is via the micropores in the crystals. WO97/33684 describes a method for preparing a molecular sieve (zeolite) film on the surface of a substrate. A zeolite membrane with the MFI structure is preferred in this document. However, a mordenite (MOR) zeolite membrane oriented in a specific crystalline direction is not known till now. An MOR zeolite membrane is superior in acid resistance in comparison with zeolite membranes of an A type, a Y type and the like, and it is extremely useful if such an MOR zeolite membrane can be obtained. Summary of the Invention The present invention aims to provide an MOR zeolite membrane dominantly oriented in a specific crystallization direction and a method for producing the membrane. According to the present invention, there is provided a mordenite (MOR) zeolite membrane as set out in claim 1. According to the present invention, there is further provided a method for producing a mordenite (MOR) zeolite membrane as set out in claim 2. In the invention, it is preferable that the porous substrate is disposed in a reaction vessel so that a surface on which a membrane is formed becomes perpendicular, and that the gel of the raw material contains SiO 2 /Al 2 O 3 of 100-400 in molar ratio, H 2 O/Na 2 O of 10-100 in molar ratio, and H 2 O/SiO 2 of 10-30 in molar ratio. Brief Description of the Drawings Fig. 1(a) is an SEM photograph showing a crystal structure of a surface of the membrane obtained in Example 1, and Fig. 1(b) is an SEM photograph showing a crystal structure of a section of the membrane obtained in Example 1. Fig. 2(a) is an SEM photograph showing a crystal structure of a surface of the membrane, and Fig. 2(b) is an SEM photograph showing a crystal structure of a section of the membrane obtained in Example 2. Fig. 3 is an SEM photograph showing a crystal structure of a section of the membrane obtained in Example 3. Fig. 4 is a graph showing an X-ray diffraction pattern of the membrane obtained in Example 3. Fig. 5 is an SEM photograph showing a crystal structure of a section of the membrane obtained in example 4. Detailed Description of the Invention The present invention is hereinbelow described in detail. The present invention is a mordenite (MOR) zeolite membrane dominantly oriented in a specific crystalline direction and formed on a porous substrate. Such an MOR zeolite membrane can be produced by immersing a porous substrate in a gel of raw material containing zeolite constitution elements having a specific composition and subjecting the gel in the presence of the porous substrate to hydrothermal synthesis at 150°C or more. In the above MOR zeolite membrane, the crystalline direction is not particularly limited and, it is oriented along any one of the a axis, b axis and c axis. This MOR zeolite membrane has a high ratio of silica and is superior in acid resistance in comparison with an A-type zeolite membrane and a Y-type zeolite membrane, and therefore can be applied for use requiring acid resistance in fields of molecule sieves and catalysts. Next, a method for producing the above MOR zeolite membrane is described. As a raw material, there is used a raw material solely constituted by a simple substance including silicon, aluminum, and an alkali metal, which are zeolite constitution elements, a compound thereof, and the like. It is important that the gel of raw material has a composition range of 40-400 of SiO 2 /Al 2 O 3 in molar ratio, 10-120 of H 2 O/Na 2 O in molar ratio, and 10-40 of H 2 O/SiO 2 in molar ratio. In the case that a raw material has a composition outside the above range, an MOR zeolite membrane dominantly oriented in a specific crystalline direction may not be obtained. As a composition range of the raw materials, it is more preferable that the molar ratio of SiO 2 /Al 2 O 3 is 100-400, the molar ratio of H 2 O/Na 2 O is 10-100, and the molar ratio of H 2 O/SiO 2 is 10-30. Next, a porous substrate is immersed in the raw-material gel having the above composition range. In the present invention, not a generally-used dense substrate but a porous substrate is employed. A material for a porous substrate is not limited, and various kinds of materials such as ceramics, metals and the like may be used. There is exemplified, as a non-limited example, a substrate made of a ceramic of general oxide such as alumina, zirconia, titania, silica, or the like; a compound oxide such as silicazirconia, silicatitania, or the like; and a substrate made of a metal such as iron, stainless steel, copper, tantalum, or the like. Membrane formation by crystallization is performed by subjecting a gel of raw material for zeolite to hydrothermal synthesis with putting a porous substrate having a seed crystal applied thereon in an autoclave. The important thing here is to perform hydrothermal synthesis at a temperature of 150°C or more. If a temperature of hydrothermal synthesis is below 150 °C, an MOR zeolite membrane dominantly oriented in a specific crystalline direction may not be produced. It is required that a temperature of hydrothermal synthesis is 150°C or more for securing an orientation property. It is more preferable that the hydrothermal synthesis is at 165 - 195°C, e.g. 165 - 175°C, and it is particularly preferable that the temperature is around 180°C. In addition, it is preferable in the present inventive process to dispose a porous substrate in a reaction vessel so that a surface of said substrate on which a membrane is formed becomes perpendicular. The expression "dispose the substrate perpendicularly" means that the substrate is disposed in a reaction vessel in such a manner that the substrate surface on which membrane is formed is placed perpendicularly to the ground. Thus, by performing hydrothermal synthesis with a porous substrate being disposed perpendicularly in a reaction vessel, a crystallized MOR zeolite membrane dominantly oriented along the b axis or the c axis may be produced. In the case that a porous substrate is disposed in a reaction vessel so that a surface of the substrate on which a membrane is formed becomes horizontal to the ground, one may obtain an MOR zeolite membrane having only a lower layer being oriented in a specific crystalline direction, with a not-oriented upper layer. Incidentally, a so-called seeding step, in which a seed crystal is applied beforehand upon crystallizing by using hydrothermal synthesis is not required in producing an MOR zeolite membrane of the present invention. However, it is preferable to perform a seeding step because a dense zeolite membrane may be obtained, and as a consequence a membrane having a good separation performance may be obtained. The present invention is hereinbelow described with reference to Examples and Comparative Examples in more detail. However, the present invention is not limited thereto. (Example 1: b-axis oriented MOR zeolite membrane) 0.425g of sodium aluminate was mixed with sodium hydroxide solution (7.26gNaOH+28.8gH 2 O) to give a mixture, and the mixture was sufficiently stirred at room temperature (20°C). 72g of colloidal silica (30wt% SiO 2 + 0.6wt% Na 2 O) was added to the resultant, and it was sufficiently mixed at 50°C till a transparent solution was obtained. The resultant raw material gel had a molar ratio of 10Na 2 O : 0.15Al 2 O 3 : 36SiO 2 : 440H 2 O. The surface of a porous alumina tube (10mm of outer diameter, 60mm long) having a fine pore diameter of 0.1 µ m was washed, and a commercial mordenite seed crystal (molar ratio: SiO 2 /Al 2 O 3 = 10.2) was applied on the surface of the substrate by a dip method. Then, they were dried by 100°C for 15 minutes. The prepared raw material gel solution was put in an autoclave, and the porous alumina tube was perpendicularly sunk in the gel by the use of a Teflon support stand. Then, the autoclave was closed. Subsequently, hydrothermal synthesis was performed at 180°C for 5 hours. After being cooled, the porous alumina tube was taken out, and a membrane formed on the surface thereof was sufficiently washed with distilled water. Then, the resultant product was dried at 100°C. The membrane formed on the substrate was subjected to X-ray diffraction and SEM observation of a section and a surface, and it was confirmed that the membrane was a mordenite (MOR) zeolite membrane dominantly oriented along the b axis. Fig. 1(a) is an SEM photograph showing a crystal structure of a surface of the membrane, and Fig. 1(b) is an SEM photograph showing a crystal structure of a section of the membrane. (Comparative Example 1) The same procedure as in Example 1 was repeated until the hydrothermal synthesis, which was performed at 100°C for 2 weeks. After being cooled, the porous alumina tube was taken out, and a membrane formed on the surface of the substrate was sufficiently washed with distilled water. Then, the resultant product was dried at 100°C. The membrane formed on the substrate was subjected to X-ray diffraction and SEM observation of a section and a surface, in which no X-rays diffraction peak was recognized, and the membrane was confirmed to be amorphous. (Example 2: c-axis oriented MOR zeolite membrane) 3.7045g of aluminum sulfuric anhydride was sufficiently mixed with sodium hydroxide solution (12.595g NaOH + 40g H 2 O) at room temperature to obtain a solution. A mixture of 80g of colloidal silica and 192g of water was sufficiently mixed with the above-obtained solution for 1 hour. The formed raw material gel had a molar ratio of 0.38Na 2 O : 0.025Al 2 O 3 : SiO 2 : 40H 2 O. The surface of a porous alumina tube (10mm of outer diameter, 60mm long) having a fine pore diameter of 0.1 µ m was washed, and a commercial mordenite seed crystal (molar ratio: SiO 2 /Al 2 O 3 = 10.2) was applied on the surface by a slurry coat method. Then, the tube was dried at 100°C for 15 minutes. The above gel was put in an autoclave, and the porous alumina tube was sunk in the gel by the use of a Teflon support stand. The autoclave was closed, and hydrothermal synthesis was performed at 180°C for 5 hours. After being cooled, the porous alumina tube was taken out, and a membrane formed on the surface was sufficiently washed with distilled water. Then, the resultant product was dried by 100°C. The membrane formed on the substrate tube was subjected to X-ray diffraction and SEM observation of a section and a surface, and it was confirmed that the membrane was a mordenite (MOR) zeolite membrane dominantly oriented along the c axis which was oriented in parallel with a substrate of the porous alumina tube. Fig. 2(a) is an SEM photograph showing a crystal structure of a surface of the membrane, and Fig. 2(b) is an SEM photograph showing a crystal structure of a section of the membrane. (Comparative Example 2) 2.277g of aluminum sulfuric anhydrite was sufficiently mixed with sodium hydroxide solution (0.23g NaOH + 6g H 2 O) at room temperature to a solution. 20g of colloidal silica was sufficiently mixed with the solution for 2 hours. The formed raw material gel had a molar ratio of 3Na 2 O : Al 2 O 3 : 20Si 2 O : 200H 2 O. The surface of a porous alumina tube (a diameter of 10mm, 60mm long) having a fine pore diameter of 0.1 µ m was washed, and a commercial mordenite seed crystal (molar ratio : SiO 2 /Al 2 O 3 = 10.2) was applied on the surface by a slurry coat method. Then, the tube was dried at 100°C for 15 minutes. The above gel solution was put in an autoclave, and the porous alumina tube was sunk perpendicularly by the use of a Teflon support stand. The autoclave was closed, and hydrothermal synthesis was performed at 180°C for 5 hours. After being cooled, the porous alumina tube was taken out, and a membrane formed on the surface was sufficiently washed with distilled water. Then, the resultant product was dried at 100°C. The membrane formed on the substrate was subjected to X-ray diffraction and SEM observation of a section and a surface, in which no X-ray diffraction peak was recognized, and the membrane was confirmed to be amorphous. (Comparative Example 3) 1.129g of aluminum sulfuric anhydride were sufficiently mixed with sodium hydroxide solution (3.84g NaOH + 78g H 2 O) at room temperature to obtain a solution. 20g of colloidal silica was sufficiently mixed with the resultant solution for 1 hour. The formed raw materials gel had a molar ratio of 0.48Na 2 O : 0.033Al 2 O 3 : SiO 2 : 50H 2 O. The surface of a porous alumina tube (10mm of outer diameter, 60mm long) having a fine pore diameter of 0.1 µ m was washed, and a commercial mordenite seed crystal (molar ratio: SiO 2 /Al 2 O 3 = 10.2) was applied on the surface by a slurry coat method. Then, the tube was dried at 100°C for 15 minutes. The above gel solution was put in an autoclave, and a porous alumina tube was sunk perpendicularly in the gel by the use of a Teflon support stand. The autoclave was closed, and hydrothermal synthesis was performed at 180°C for 5 hours. After being cooled, the porous alumina tube was taken out, and a membrane formed on the surface was sufficiently washed with distilled water. Then, the resultant product was dried at 100°C. The membrane formed on the substrate was subjected to X-ray diffraction and SEM observation of a section and a surface, in which no X ray diffraction peak was recognized, and the membrane was confirmed to be amorphous. (Example 3: c-axis oriented MOR zeolite membrane) A raw material was prepared and hydrothermal synthesis was performed in the same manner as in Example 2 except that a raw-material gel had a molar ratio of 0.28Na 2 O : 0.0042Al 2 O 3 : SiO 2 : 12.2H 2 O and that a hydrothermal synthesis was performed at 180°C for 2 days. The membrane formed on the substrate was subjected to X-ray diffraction and SEM observation of a section and a surface, and it was confirmed that the membrane was a mordenite (MOR) zeolite membrane dominantly oriented along the c axis which was oriented in parallel with a substrate of the porous alumina tube. Fig. 3 is an SEM photograph showing a crystal structure of a section of the membrane, and Fig. 4 is a graph showing an X-ray diffraction pattern. (Comparative Example 4) A raw material was prepared and hydrothermal synthesis was performed in the same manner as in Example 3 except that hydrothermal synthesis was performed at 100°C. The membrane formed on the substrate was subjected to X-ray diffraction and SEM observation of a section and a surface, and it was confirmed that the membrane was not oriented in a specific direction and had random orientation though crystallization was recognized. (Comparative Example 5) A raw material was prepared and hydrothermal synthesis was performed in the same manner as in Example 3 except that hydrothermal synthesis was performed at 140°C. The membrane formed on the substrate was subjected to X-ray diffraction and SEM observation of a section and a surface, and it was confirmed that the membrane was not oriented in a specific direction and had random orientation though crystallization was recognized. (Comparative Example 6) A raw material was prepared and hydrothermal synthesis was performed in the same manner as in Example 2 except that a raw material gel had a molar ratio of 0.15Na 2 O : 0.05Al 2 O 3 : SiO 2 : 10H 2 O. After being cooled, the porous alumina tube was taken out, and it was found to find out that no membrane was formed on the porous alumina tube. (Example 4) A raw material was prepared and hydrothermal synthesis was performed in the same manner as in Example 3 except that porous alumina tube was sunk horizontally in an autoclave and that hydrothermal synthesis was performed at 180°C for 24 hours. The membrane formed on the substrate was subjected to X-ray diffraction and SEM observation of a section and a surface, and it was confirmed that a membrane was not oriented in a layer on the upper side and dominantly oriented along c axis only in a layer on the lower side which was near the porous alumina tube substrate side though crystallization was recognized. Fig. 5 is an SEM photograph showing a crystal structure of a section of the membrane. As discussed above, according to the present invention, there can be provided an MOR zeolite membrane oriented in a specific crystalline direction and a preferable method for producing the membrane.

Claims: A mordenite (MOR) zeolite membrane consisting of a porous substrate and a crystalline mordenite (MOR) zeolite layer formed on a surface of said substrate, characterised in that said mordenite (MOR) zeolite layer is dominantly oriented to a specific direction. A method for producing a mordenite (MOR) zeolite membrane according to claim 1 comprising the steps of: immersing a porous substrate in a gel of raw material which contains zeolite constitution elements and contains SiO 2 /Al 2 O 3 in a molar ratio of 40-400, H 2 O/Na 2 O in a molar ratio of 10-120, and H 2 O/SiO 2 in a molar ratio of 10-40, and subjecting the gel in the presence of porous substrate to hydrothermal synthesis at 150°C or more to make zeolite crystallized to form a membrane thereof. A method as defined in claim 2, wherein the porous substrate is disposed in a reaction vessel so that a surface of the substrate on which a membrane is formed becomes perpendicular to the reaction vessel. A method as defined in claim 2 or 3, wherein as a composition range of the raw materials, the molar ratio of SiO 2 /Al 2 O 3 is 100-400, the molar ratio of H 2 O/Na 2 O is 10-100, and the molar ratio of H 2 O/SiO 2 is 10-30.

Inventors: MATSUKATA MASAHIKO, MATSUKATA, MASAHIKO
Applicants: MATSUKATA MASAHIKO, NGK INSULATORS LTD, MATSUKATA, MASAHIKO, NGK INSULATORS, LTD.
Application year: 2001
Main classification: B01D71
IPC codes: B01J35, B01D71, C01B39, B01J29