JP5481075B2 - Method for producing zeolite membrane - Google Patents

Description

  The present invention relates to a method for producing a zeolite membrane.

  Conventionally, zeolite membranes, carbon membranes, titania membranes and the like are disposed on the surface of a porous substrate and used as separation membranes. For example, a separation membrane arrangement in which a zeolite membrane is arranged as a separation membrane at a predetermined position of a porous substrate is disclosed.

Zeolite is a kind of silicate having a network-like crystal structure in which fine pores having a uniform diameter are formed. General formula: WmZnO ₂ n · sH ₂ O (W: sodium, potassium, calcium) Z: silicon, aluminum, etc., s takes various values), and there are many types (types) of crystal structures with different pore shapes. It has been. These zeolites have inherent adsorption capacity, catalyst performance, solid acid characteristics, ion exchange capacity, etc. based on their chemical composition and crystal structure, and adsorbents, catalysts, catalyst carriers, gas separation membranes, or It is used in various applications such as ion exchangers.

For example, MFI-type zeolite is a zeolite in which pores of about 0.5 nm are formed by a 10-membered oxygen ring in a crystal. Generally, nitrogen oxide (NO _x ), hydrocarbon (HC) in automobile exhaust gas is used. It is used in applications such as an adsorbent for adsorbing harmful substances such as, or a catalyst for decomposition.

  Normally, zeolite is powdery or granular, but a method for forming it into a membrane for use as a separation membrane is being developed. For example, a zeolite membrane can be obtained by reacting a zeolite raw material by hydrothermal synthesis and depositing zeolite crystals in the form of a membrane on the surface of the support. Here, hydrothermal synthesis refers to a method of synthesizing zeolite by heating a zeolite raw material in the presence of water (water vapor) under predetermined conditions.

  In the production of such a zeolite membrane, the zeolite membrane is simply formed by hydrothermal synthesis in the presence of the support, so that the surface of the support is exposed or the film thickness becomes too thick. There is a problem that it is difficult to form a thin film. On the other hand, the method of trying to eliminate such a problem by apply | coating a seed crystal to the support body surface is disclosed (for example, refer patent documents 1-3).

  Further, as a method for attaching a seed crystal to the support surface, a method is disclosed in which the support is immersed in an aqueous solution containing a zeolite raw material and the seed crystal is precipitated on the support surface (for example, Patent Document 4, 5).

  And the zeolite membrane for isolate | separating ethanol from the mixed solution of water and ethanol is disclosed (patent documents 6-7).

  On the other hand, a method for producing a defect-free silicalite MFI membrane for separating xylene isomers is disclosed (Patent Document 8). This MFI membrane can selectively permeate the xylene isomer para-xylene (5.85 kg) and block ortho-xylene (6.8 kg) and meta-xylene (6.8 kg) (for molecular size, Non-patent document 1).

  Further, it is disclosed that xylene isomers can be separated by a zeolite membrane obtained by impregnating a porous material with a template or impregnating a skeleton agent and then crystallizing (Patent Document 9). Furthermore, an MFI type zeolite membrane capable of separating para-xylene / ortho-xylene is disclosed (Patent Document 10).

JP-A-10-36114 JP 2002-201020 A Japanese Patent Laid-Open No. 2004-82008 JP 2004-307296 A JP 2000-26115 A International Publication No. 2007/058387 Pamphlet International Publication No. 2007/058388 Pamphlet JP 2002-537990 A Japanese Patent No. 3899418 J. et al. Memb. Sci. 320 (2008) 505-513

R. Szostak, “Handbook of Molecular sieves”, Van Northland Reinhold, New York, (1992).

  In recent years, it has been required to separate molecules having similar molecular sizes. Although the membranes of Patent Documents 6 to 7 are suitable for separation of water and ethanol, it was not possible to separate xylene isomers having a closer molecular size.

  In the manufacturing method of Patent Document 8, the support is masked using an impregnating material, and the hydrothermal synthesis is performed with the seed attachment surface facing downward, so the process is complicated and the manufacturing cost is likely to increase. . Furthermore, it cannot be applied to a support having a complicated shape (for example, a monolith shape) and is not suitable for scale-up. Also, from the test conditions, the xylene isomer separation condition is considered to be gas separation and is not suitable for liquid separation.

  In Patent Document 9, there is no membrane position selectivity due to the steps of impregnating and drying the templating agent and impregnating and drying the skeleton agent. In addition, it is highly possible that the inside of the porous body is filled with zeolite, making it difficult to form a thin film and inferior permeation performance. Furthermore, synthesis into a complex-shaped porous body is considered difficult. In addition, when this method is used, it may be necessary to use a hydrolyzable Si source.

  In Patent Document 10, it is unclear whether a sample shape is a pellet (plate shape) and good film performance can be exhibited even in other shapes. Since a raw material called TEOS (tetraethoxysilane) is used for the Si source, and it is expensive, it is not suitable for enlargement or industrialization.

  An object of the present invention is to provide a method for producing a zeolite membrane capable of separating xylene isomers.

  The inventors of the present application have found that a zeolite membrane for separating xylene isomers can be obtained by lowering the removal (firing) temperature of the structure-directing agent. That is, according to the present invention, the following method for producing a zeolite membrane is provided.

[1] A membrane forming step of forming a zeolite membrane containing a structure-directing agent capable of generating tetrapropylammonium ions (TPA) on the surface of the porous support, and the membrane forming step is formed after the membrane forming step. And a structure-directing agent removing step of removing the structure-directing agent by firing the zeolite membrane at 250 to 300 ° C.

[2] The method for producing a zeolite membrane according to [1], wherein the zeolite membrane is MFI type.

[3] The method for producing a zeolite membrane according to [1] or [2], wherein the support is made of alumina.

  A zeolite membrane that separates xylene isomers can be obtained by lowering the calcination temperature for removing the structure-directing agent (250 to 350 ° C.). Generation of defects can be suppressed by relaxing the thermal expansion difference in the structure-directing agent removal step of the support and the zeolite membrane.

It is a perspective view which shows one embodiment (monolith shape) of the support body used in the manufacturing method of the zeolite membrane of this invention. It is sectional drawing which shows one embodiment (monolith shape) of the support body used in the manufacturing method of the zeolite membrane of this invention. In Example 1, it is sectional drawing which shows roughly the state which put the support body and the silica sol in the pressure-resistant container. It is a schematic diagram which shows the whole testing apparatus which performs a pervaporation test.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments, and changes, modifications, and improvements can be added without departing from the scope of the invention.

(I) Separation membrane:
The separation membrane obtained by the production method of the present invention is a zeolite membrane formed on a porous support, and an MFI type zeolite membrane can be given as an example. In order to use the skeleton pore size of MFI-type zeolite as it is for separation of xylene isomers, silicalite is preferable (because ions are present in the pores and the pore size is reduced when low silica is used). .

(I-1) Pore:
The separation membrane of the present invention can be used to separate fluids of two or more different components. Paraxylene can be separated from ortho-xylene and meta-xylene having molecular sizes close to each other by the pores inherent to the zeolite crystal (5 to 6 mm in the MFI type). The paraxylene / orthoxylene separation factor is 1.3 to 330.3. Further, the permeation amount of paraxylene is 0.001 to 0.002 kg / m ² · h.

  The separation membrane of the present invention can separate molecules larger and smaller than the pores inherent to zeolite crystals. In particular, it can be applied to the separation of xylene isomers. Specifically, para-xylene can be separated from ortho-xylene and meta-xylene.

(I-2) Film thickness:
The zeolite membrane of the present invention has a thickness of 1 to 30 μm, preferably 1 to 20 μm, and particularly preferably 1 to 15 μm. When it is thinner than 1 μm, the separation efficiency of xylene isomers is lowered. If it is thicker than 30 μm, the permeation rate becomes slow and it takes time for membrane separation. Here, the film thickness of the zeolite film is a value obtained by observing the cross section of the zeolite film with a scanning electron microscope (SEM). When the film thickness is 1 to 30 μm, the minimum film thickness is 1 μm or more and is the maximum. It means that the film thickness is 30 μm or less.

(I-3) Support:
The zeolite membrane-arranged body of the present invention is one in which the zeolite membrane is disposed on the surface of the support. However, the zeolite membrane is disposed on the surface of the support so that the zeolite membrane can be a thin film. Therefore, it is possible to maintain the shape and prevent damage and the like. The support is not particularly limited as long as it can form a zeolite seed crystal on the surface and form a zeolite membrane, and the material, shape, and size thereof can be appropriately determined according to the application. Examples of the material constituting the support include alumina (α-alumina, γ-alumina, anodized alumina, etc.), ceramics such as zirconia, metals such as stainless steel, and the like. From the viewpoint, alumina is preferable. Alumina is preferably formed and sintered using alumina particles having an average particle diameter of 0.001 to 30 μm as raw materials. The support is preferably a porous body. The shape of the support may be any of a plate shape, a cylindrical shape, a tubular shape with a polygonal cross section, a monolith shape, a spiral shape, etc., but a monolith shape is preferable. Here, the monolith shape refers to a columnar shape in which a plurality of flow passages (channels) 52 are formed in parallel with the axial direction 53, such as the support 51 shown in FIGS. 1A and 1B. 1A and 1B show one embodiment (monolith shape) of a support used in the method for producing a zeolite membrane of the present invention, FIG. 1A is a perspective view, and FIG. 1B is a plan view. The support 51 is particularly preferably a monolithic porous body 54. Such a support made of a monolithic porous body can be formed by a known production method, for example, extrusion molding or the like.

(II) Manufacturing method:
An example of MFI type zeolite will be described in detail. However, since the method for producing a zeolite membrane of the present invention is characterized in that the zeolite seed crystals are appropriately attached to the support, zeolites other than MFI type zeolite, such as LTA, MOR, AFI, Naturally, it can also be applied to conventionally known zeolites such as BEA, FER, FAU, and DDR.

  The method for producing a zeolite membrane of the present invention comprises a membrane forming step of forming a zeolite membrane containing a structure-directing agent on the surface of a porous support, and the zeolite membrane formed in the membrane forming step after the membrane forming step is 250 to And a structure-directing agent removing step of removing the structure-directing agent by firing at 350 ° C. In addition, as long as the step before the structure-directing agent removal step is a synthesis method capable of forming a zeolite membrane containing a structure-directing agent on the surface of the porous support, a synthesis method (seed crystal generation step, membrane described later) will be described. It is not limited to a formation process.

(II-1) Seed crystal production step:
(II-1-1) seeding sol;
The seeding sol used in the method for producing a zeolite membrane of the present invention is a silica sol in which silica fine particles are dispersed in water, and contains at least a structure-directing agent therein. This seeding sol can be obtained by mixing a predetermined amount of silica sol having a predetermined concentration, water for adjusting the concentration, and a structure directing agent aqueous solution having a predetermined concentration. This seeding sol is crystallized into zeolite by hydrothermal treatment, which will be described later, to form a structure in which silica atoms derived from the silica sol are surrounded around the molecules of the structure directing agent. Then, the structure-directing agent is removed from the structure by heat treatment described later, and a zeolite crystal having a pore shape specific to the structure-directing agent can be formed.

  As the silica sol, a commercially available silica sol (for example, trade name: Snowtex S, manufactured by Nissan Chemical Industries, Ltd., solid content concentration: 30% by mass) can be suitably used. Here, the solid content means silica. However, what was prepared by dissolving silica fine powder in water, or what was prepared by hydrolyzing alkoxysilane may be used.

  In the seeding sol, the molar ratio of water to silica (fine particles) (water / silica molar ratio: a value obtained by dividing the number of moles of water by the number of moles of silica) is water / silica = 10-50. Is preferable, and it is still more preferable that it is 20-40. Thus, by increasing the silica concentration of the seeding sol, the zeolite seed crystal can be made into fine particles and adhered to the support surface. If the water / silica molar ratio is less than 10, the zeolite seed crystals may be precipitated inhomogeneously and excessively on the support surface, and if it is more than 50, the zeolite seed crystals may not be precipitated on the support surface. Here, the state in which the zeolite seed crystals are attached to the support surface, for example, in a scanning electron microscope (SEM) photograph, is quantitatively shown as the ratio of covering the support surface (area ratio on the photograph). It is preferable that it is 5 to 100%.

  As a structure-directing agent for MFI-type zeolite, tetrapropylammonium hydroxide (TPAOH) or tetrapropylammonium bromide (TPABr) that can generate tetrapropylammonium ion (TPA) is used. Accordingly, an aqueous solution containing TPAOH and / or TPABr can be suitably used as the structure directing agent aqueous solution.

  As the silica sol, it is also preferable to use a silica sol containing an alkali metal or alkaline earth metal hydroxide in addition to silica fine particles. TPAOH used as a structure-directing agent for MFI-type zeolite is a relatively expensive reagent. According to this method, a TPA source and an alkali source are obtained from a relatively inexpensive TPABr and an alkali metal hydroxide. Can do. That is, since this method can reduce the amount of expensive TPAOH used, the raw material cost can be reduced and zeolite can be produced at low cost.

  When mixing the silica sol and the structure directing agent aqueous solution, it is preferable to mix the two so that the molar ratio of TPA to silica (TPA / silica ratio) is in the range of 0.05 to 0.5. More preferably, it is in the range of 1 to 0.3. If the TPA / silica ratio is less than 0.051, seed crystals may not be precipitated, and if it exceeds 0.5, it may be excessively deposited on the support surface.

  Since the substance used as the structure directing agent varies depending on the type of zeolite, a structure directing agent corresponding to the desired type of zeolite is appropriately selected and used. For example, tetraethylammonium hydroxide (TEAOH) or tetraethylammonium bromide (TEABr) is used in the case of BEA type zeolite (also called “β-zeolite”), and 1-adamantanamine is used in the case of DDR type zeolite. use. The molar ratio of the structure-directing agent to silica (structure-directing agent / silica ratio) may be determined in accordance with a conventionally known synthesis method for each type of zeolite.

  Moreover, it is preferable that the water added at the time of preparation of the seeding sol does not contain impurity ions, specifically, distilled water or ion-exchanged water is preferable.

(II-1-2) support;
The support is not particularly limited as long as it can form a zeolite seed crystal on the surface and form a zeolite membrane, and the material, shape, and size thereof can be appropriately determined according to the application. As a material constituting the support, alumina is preferable from the viewpoint of support production and availability. Alumina is preferably formed and sintered using alumina particles having an average particle diameter of 0.001 to 30 μm as raw materials. The support is preferably a porous body. The shape of the support is preferably a monolith shape.

(II-1-3) Formation of zeolite seed crystals;
In order to produce a zeolite seed crystal, first, the support and the seeding sol are placed in a pressure vessel. At this time, it arrange | positions so that a support body may be immersed in the seeding sol. Thereafter, the pressure vessel is heated and a zeolite seed crystal is generated on the surface of the support by hydrothermal synthesis.

  Although it does not specifically limit as a pressure vessel, The stainless steel pressure vessel with a fluororesin inner cylinder, a nickel metal pressure vessel, etc. can be used. When the support is immersed in the seeding sol, it is preferable that at least a portion where the zeolite seed crystals are precipitated is submerged in the seeding sol, and the entire support may be submerged in the seeding sol. The temperature for hydrothermal synthesis is 90 to 130 ° C, and more preferably 100 to 120 ° C. If the temperature is lower than 90 ° C, hydrothermal synthesis is difficult to proceed, and if the temperature is higher than 130 ° C, the resulting zeolite seed crystals cannot be atomized. In particular, when the support is a porous body obtained by sintering alumina particles, each surface of the alumina particles located on the support surface is set by setting the temperature of hydrothermal synthesis to the above range (90 to 130 ° C.). Can be covered with zeolite seed crystals. The synthesis time for hydrothermal synthesis is preferably 3 to 18 hours, and more preferably 6 to 12 hours. If it is shorter than 3 hours, hydrothermal synthesis may not proceed sufficiently, and if it is longer than 18 hours, the zeolite seed crystals may become too large. Thus, if zeolite seed crystals are directly deposited on the surface of the support by hydrothermal synthesis, the zeolite seed crystals are difficult to peel off from the support. Problems such as uniformity can be prevented.

  Moreover, as a method of heating, the method of putting a pressure vessel into a hot-air dryer and heating, or attaching a heater directly to a pressure vessel and heating is mentioned.

  The particle diameter of the obtained zeolite seed crystal is preferably 1 μm or less, more preferably 0.5 μm or less, and particularly preferably 0.01 to 0.5 μm. If it is larger than 1 μm, a dense zeolite membrane may not be formed with a uniform film thickness with few defects in the membrane formation step. Here, the particle diameter of the zeolite seed crystal is a value obtained by observation with a scanning electron microscope (SEM), and when it is 1 μm or less, the maximum particle diameter is 1 μm or less.

  After the zeolite seed crystals are deposited on the surface of the support, it is preferable to boil and wash the support using water. Thereby, the production | generation of an excess zeolite can be prevented. The washing time is not particularly limited as long as the seeding sol is washed away, but it is preferable to repeat the washing for 0.5 to 3 hours 1 to 5 times. After washing, drying at 60 to 120 ° C. for 4 to 48 hours is preferable.

  Further, when a monolithic porous body 54 as shown in FIGS. 1A and 1B is used as a support, it is preferable to generate a zeolite seed crystal on the surface of the channel 52 of the support 51. In this case, when the support 51 is immersed in the seeding sol, it is preferable to immerse the support 51 in a state where the outer peripheral surface is covered with a tape such as a fluororesin.

(II-2) Film forming step:
(II-2-1) sol for film formation;
The film-forming sol uses the same silica sol, structure-directing agent and water contained in the seeding sol as described above, and uses more water than the seeding sol. It is preferable to use one having a reduced concentration.

  The molar ratio of water and silica (fine particles) contained in the sol for film formation (water / silica molar ratio) is preferably water / silica = 100 to 700, and more preferably 200 to 500. When the water / silica molar ratio is 100 to 700, a dense zeolite membrane with uniform thickness and few defects can be formed. If the water / silica molar ratio is less than 100, the silica concentration increases, so zeolite crystals are deposited in the film-forming sol and deposited on the surface of the zeolite film, so that cracks and the like are likely to occur during activation treatment such as firing. May be. If the water / silica molar ratio is greater than 700, the zeolite membrane may be difficult to be dense.

  When mixing the silica sol and the structure directing agent aqueous solution in the film-forming sol, the two are mixed so that the molar ratio of TPA to silica (TPA / silica ratio) is in the range of 0.05 to 0.5. It is preferable that it is in the range of 0.1 to 0.3. If the TPA / silica ratio is less than 0.05, the film is difficult to be dense, and if it exceeds 0.5, zeolite crystals may be deposited on the film surface.

(II-2-2) film formation;
Zeolite seed crystals deposited on the surface of the support are grown by hydrothermal synthesis to form a zeolite membrane made of zeolite crystals grown in the form of a film on the surface of the support. In order to form a zeolite membrane on the surface of the support, first, the support on which the zeolite seed crystals are deposited and the membrane-forming sol are first placed in a pressure vessel. Put in. At this time, it arrange | positions so that a support body may be immersed in the sol for film formation. Thereafter, the inside of the pressure vessel is heated and a zeolite membrane is formed on the surface of the support by hydrothermal synthesis. In addition, since the zeolite membrane obtained by hydrothermal synthesis contains tetrapropylammonium, it is preferable to perform a heat treatment after that in order to finally obtain a zeolite membrane.

  As the pressure vessel, it is preferable to use the pressure vessel used for producing the zeolite seed crystal. When the support is immersed in the film-forming sol, it is preferable that at least a portion where the zeolite film is formed is submerged in the film-forming sol, and the entire support may be submerged in the film-forming sol. 100-200 degreeC is preferable and the temperature in the case of performing hydrothermal synthesis has more preferable 120-180 degreeC. By setting it as such a temperature range, it becomes possible to obtain a dense zeolite membrane with uniform thickness and few defects. In the method for producing a zeolite membrane of the present invention, such a high quality membrane can be produced with good reproducibility, and the production efficiency is high. If the temperature is lower than 100 ° C, hydrothermal synthesis may not proceed easily, and if the temperature is higher than 200 ° C, the resulting zeolite membrane may be difficult to be made dense with few defects of uniform thickness.

  The synthesis time of hydrothermal synthesis is preferably 3 to 120 hours, more preferably 6 to 90 hours, and particularly preferably 10 to 72 hours. If it is shorter than 3 hours, hydrothermal synthesis may not proceed sufficiently, and if it is longer than 120 hours, the zeolite membrane may be too thick with a non-uniform thickness. Here, when the zeolite membrane is dense, it means that the surface of the support is not exposed when observed with a scanning electron microscope (SEM). Further, the defect of the zeolite membrane is, for example, when the coloring remaining like the rhodamine B solution is applied to the surface of the support and then washed quickly with water so that the remaining coloring can be visually observed, and there are few defects. Means that almost no coloring remains.

  The thickness of the obtained zeolite membrane is preferably 30 μm or less, more preferably 1 to 30 μm, further preferably 1 to 20 μm, particularly preferably 1 to 15 μm, and 1 to 10 μm. Most preferably. If it is thicker than 30 μm, the separation efficiency may decrease when used as a separation membrane. Here, the thickness of the zeolite membrane is a value obtained by observation with a scanning electron microscope (SEM). Since such a thin film can be formed, it is possible to obtain a separation film with high separation performance in combination with the above-described characteristics that the film thickness is uniform and dense with few defects.

  After forming a zeolite membrane on the support surface by hydrothermal synthesis, it is preferable to boil and wash the support using water. Thereby, it is possible to prevent extra zeolite crystals from adhering to the zeolite membrane. Although washing | cleaning time is not specifically limited, It is preferable to repeat washing | cleaning for 0.5 to 3 hours 1 to 5 times. After washing, drying at 60 to 120 ° C. for 4 to 48 hours is preferable.

(II-3) Structure-directing agent removal step:
Next, the structure-directing agent tetrapropylammonium is obtained by heat treatment (activation treatment) of the zeolite membrane formed on the surface of the support obtained by the above method (not limited to the above method). A structure-directing agent removing step is performed. As a result, a zeolite membrane is finally formed. The heating temperature is preferably 250 to 350 ° C., and the heating time is preferably 5 to 200 hours. The temperature raising / lowering speed is desirably 1 ° C./min or less. More preferably, it is 0.5 degrees C / min or less, More preferably, it is 0.1 degrees C / min or less. Moreover, an electric furnace etc. can be mentioned as an apparatus used for a heating.

(II-4) Film growth process:
The method for producing a zeolite membrane of the present embodiment preferably includes at least one membrane growth step of further growing the zeolite membrane formed on the surface of the support after the “(2) membrane formation step”. In particular, when the support is formed in a monolith shape and a zeolite film is formed on the surface in the channel, the silica component contained in the film-forming sol is insufficient in the channel, and only “(2) film forming step” The film formation may not be sufficient. In such a case, a zeolite membrane having a desired thickness can be formed by further growing the zeolite membrane by a membrane growth step. This film growth step may be performed not only once but also twice or more.

  In the operation of the film growth step, in the above “(II-2) film formation step”, instead of using “(1) the support obtained by precipitating zeolite seed crystals on the surface” obtained in the seed crystal generation step, Using “(2) the support having a zeolite membrane formed on the surface obtained in the membrane forming step”, the other operations may be the same as the above “(II-2) membrane forming step”. preferable.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these Examples.

Example 1
(Preparation of seeding sol)
95% of 40% tetrapropylammonium hydroxide solution (manufactured by SACHEM) and 18.88 g of tetrapropylammonium bromide (manufactured by Wako Pure Chemical Industries, Ltd.) are mixed, and further 82.54 g of distilled water and about 30 wt% silica sol (Snowtex) S, manufactured by Nissan Chemical Co., Ltd.) was added and stirred with a magnetic stirrer at room temperature for 30 minutes to prepare a seeding sol.

(Formation of zeolite seed crystals)
As shown in FIG. 2, the obtained seeding sol 66 is placed in a stainless steel 300 ml pressure vessel 61 in which a Teflon inner cylinder 62 is disposed inside a stainless vessel 63, and has a diameter of 12 mmφ and a thickness of 1 to 1. A porous alumina support 65 having a length of 2 mm and a length of 160 mm was immersed, fixed to the stainless steel container 63 by a fixing jig 64, and reacted in a hot air dryer at 110 ° C. for 10 hours. The support 66 after the reaction was sufficiently dried at 80 ° C. after 3 to 5 boiling washings.

(Preparation of film-forming sol)
After the above step, 0.66 g of 40% tetrapropylammonium hydroxide solution (manufactured by SACHEM) and 0.34 g of tetrapropylammonium bromide (manufactured by Wako Pure Chemical Industries, Ltd.) were mixed, and 229.6 g of distilled water was further added. About 30 wt% silica sol (Snowtex S, manufactured by Nissan Chemical Co., Ltd.) (5.2 g) was added, and the mixture was stirred with a magnetic stirrer at room temperature for 30 minutes to prepare a sol for film formation.

(Formation of zeolite membrane)
The obtained sol for film formation is placed in a stainless steel 300 ml pressure vessel with a Teflon (registered trademark) inner cylinder, immersed in the seeded porous alumina support, and heated in a hot air dryer at 180 ° C. for 60 hours. Reacted.

(Structure directing agent removal)
The support after the reaction was sufficiently dried at 80 ° C. after 3 to 5 boiling washings. The MFI membrane on the porous alumina support obtained as described above was heated to 300 ° C. in an electric furnace and held for 100 hours to remove tetrapropylammonium.

(Par-xylene / ortho-xylene pervaporation (PV) test)
FIG. 3 is a schematic diagram showing an entire test apparatus for performing a pervaporation test. As shown in FIG. 3, the supply liquid (paraxylene / orthoxylene = 10/90 (wt ratio)) placed in the supply liquid tank 31 is heated to about 50 ° C. (or 70 ° C.). The supply liquid is supplied from the supply liquid introduction port 33 to the supply liquid side space 36 of the SUS (stainless steel) module 35 by the supply pump 32, and the supply liquid discharged from the supply liquid discharge port 34 is supplied to the supply liquid tank 31. By returning, the supply liquid is circulated. The flow rate of the supply liquid is confirmed by a flow meter 39. By reducing the pressure on the support side (permeation side space 37) of the zeolite membrane 38 with the vacuum pump 43, the permeate vapor that permeates the zeolite membrane 38 and is discharged from the permeate vapor recovery port 40 is recovered by the liquid N ₂ trap 41. To do. The degree of vacuum in the transmission side space 37 is controlled by the pressure controller 42. The SUS module 35 has an internal space partitioned by a zeolite membrane 38 into a supply liquid side space 36 and a permeation side space 37, and a supply liquid introduction port 33 and a supply liquid discharge port 34 so as to communicate with the supply liquid side space 36. And a permeate vapor recovery port 40 for discharging permeate vapor to the outside is formed at the upper end portion of the permeate side space 37. In FIG. 3, the SUS module 35 is mounted with a cylindrical zeolite membrane disposed on the outer surface of a cylindrical support (not shown) in a cylindrical outer container made of SUS. It is a structure. The test was performed at 50 ° C. and 70 ° C., a transmission side vacuum degree of 0.2 torr, and a measurement time of 30 minutes. The initial performance shown in Table 1 was shown.

(Example 2)
The temperature was raised to 320 ° C. in an electric furnace and maintained for 100 hours to remove tetrapropylammonium.

(Example 3)
The temperature was raised to 280 ° C. in an electric furnace and maintained for 100 hours to remove tetrapropylammonium.

(Comparative Example 1)
Preparation of the seeding sol, formation of zeolite seed crystals, preparation of the film-forming sol, and formation of the zeolite film were performed in the same manner as in the examples.

(Structure directing agent removal)
The MFI film on the porous alumina support obtained as described above was heated to 500 ° C. in an electric furnace and held for 4 hours to remove tetrapropylammonium. When this was used in a para-xylene / ortho-xylene pervaporation (PV) test (feed solution: para-xylene / ortho-xylene = 10/90 (wt ratio)), the initial performance shown in Table 1 was shown.

(Comparative Example 2)
The temperature was raised to 400 ° C. in an electric furnace and maintained for 24 hours to remove tetrapropylammonium.

  In Examples 1 to 3, a zeolite membrane that separates xylene isomers is obtained by setting the firing temperature in the structure-directing agent removing step to remove the structure-directing agent to a lower temperature (280 to 320 ° C.) than in the past. I was able to.

  The method for producing a zeolite membrane of the present invention can be used as a method for producing a zeolite membrane capable of separating xylene isomers.

31: Supply liquid tank, 32: Supply pump, 33: Supply liquid introduction port, 34: Supply liquid discharge port, 35: SUS module, 36: Supply side space, 37: Permeation side space, 38: Zeolite membrane, 39: 40: Permeate vapor recovery port, 41: Liquid nitrogen trap, 42: Pressure controller, 43: Vacuum pump, 51: Support, 52: Flow passage (channel), 53: Axial direction, 54: Porous body 61: pressure vessel, 62: Teflon inner cylinder, 63: stainless steel container, 64: fixing jig, 65: porous alumina support, 66: seeding sol.

Claims (3)

Forming a zeolite membrane containing a structure-directing agent capable of generating tetrapropylammonium ions (TPA) on the surface of the porous support;
A method for producing a zeolite membrane comprising, after the membrane forming step, a structure directing agent removing step of removing the structure directing agent by baking the zeolite membrane formed in the membrane forming step at 250 to 300 ° C.   The method for producing a zeolite membrane according to claim 1, wherein the zeolite membrane is MFI type.   The method for producing a zeolite membrane according to claim 1, wherein the support is made of alumina.

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