Zeolite, zeolite membrane composite, method for producing zeolite, and method for separating liquid or gas using zeolite membrane composite

Abstract

To provide a zeolite capable of yielding a zeolite membrane with high permeability, a method for producing the zeolite, and further a zeolite membrane composite in which a membrane made of the zeolite is formed.SOLUTION: The zeolite contains fluorine atoms of 0.02 at% or more and 0.3 at% or less at a depth of 50 nm from its surface.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a zeolite, a zeolite composite membrane, a method for producing a zeolite, and a method for separating a liquid or gas using the zeolite composite membrane. [Background technology]

[0002] When it comes to producing zeolites, it is not easy to reproducibly synthesize zeolites with the desired structure, as there are a huge number of structures (over 255 types) despite the fact that zeolites have only two main constituent elements, aluminum and silicon. That is, with general inorganic substances, it is possible to synthesize a desired substance by preparing constituent elements according to the desired composition and synthesizing them. However, it has been difficult to obtain a zeolite with a desired structure even when an alumina source and a silica source are charged in the same ratio as that of a zeolite with a desired structure.

[0003] To solve this problem, research has been conducted into methods for determining the structure of zeolite during the initial stage of synthesis, the so-called nucleation stage. Specifically, structure-directing agents (SDAs) and seed crystals are effective, and these structures are used to initiate crystal growth during the nucleation stage, making it possible to synthesize zeolites with the desired structure. The above method made it possible to reproducibly produce zeolites with the desired structure, and so zeolites were industrialized as adsorbents and synthetic catalysts, taking advantage of their characteristics. Furthermore, by synthesizing zeolites into membranes by utilizing the pores inherent in their structure, they began to be used as separation membranes.

[0004] Zeolite membranes are inorganic membranes with pores derived from their crystalline structure. These pores are very small, measuring only a few angstroms, but are characterized by uniform diameters. This allows zeolite membranes to separate relatively small substances such as gases. Polymer membranes are commonly used for separation. Zeolite membranes, on the other hand, have the advantage of being more heat-resistant, acid-resistant, and chemical-resistant than polymer membranes, allowing them to be used under harsh conditions. Therefore, attempts have been made to improve the apparent conversion rate by using zeolite membranes for separation in high-temperature, high-pressure reaction fields, such as ammonia synthesis and MeOH synthesis. As these applications expand, there is a demand for improved properties of zeolite membranes, particularly their important permeability.

[0005] For example, Patent Documents 1 and 2 disclose a method for producing a ZSM-5 zeolite membrane, which comprises aging a raw material mixture for hydrothermal synthesis containing an alumina source, a silica source, and a fluorine compound but not containing a structure-directing agent, and then inserting a support having seed crystals into the raw material mixture for hydrothermal synthesis to perform hydrothermal synthesis, wherein the raw material mixture for hydrothermal synthesis has a feed composition in which the Si / Al molar ratio is 5 or more and 30 or less, and the F / Si molar ratio is 0.5 or more and 2.0 or less. According to the inventions disclosed in Patent Documents 1 and 2, a high-quality ZSM-5 zeolite membrane that has hydrophilicity and water-selective permeability while maintaining the high acid resistance of ZSM-5 zeolite can be produced without using a structure-directing agent or performing a calcination treatment. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-247599 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-131600 Summary of the Invention [Problem to be solved by the invention]

[0007] The objective of the present invention is to improve the properties of zeolite, particularly the permeability of zeolite membranes. Permeation through zeolite membranes occurs when gas passes through the pores in the zeolite structure. To improve this, it is necessary to precisely control the zeolite structure, and by this control, it is possible to make gas pass through more easily. Therefore, an object of the present invention is to provide a zeolite that can form a highly permeable zeolite membrane, a method for producing the zeolite, and a zeolite composite membrane in which a membrane made of the zeolite is formed. [Means for solving the problem]

[0008] To achieve the above objectives, we focused on the crystal growth process from the middle to late stages of zeolite synthesis, which has not received much attention in zeolite research. Research on zeolite membranes has mainly focused on the factors that determine their structure and the methods for forming them into membranes. As the factors that determine their structure have been discussed above, zeolite research has focused on the early stages of synthesis, particularly nucleation. However, even if the initial structure of the synthesis is determined by using SDA or seed crystals, there is a good chance that the structure will be disrupted during the crystal growth process in the middle to late stages of the synthesis, resulting in the introduction of hydroxyl groups that should not be there, or the formation of dangling bonds or defects. Furthermore, as mentioned above, there are more than 255 types of zeolite structures, so the structure may change to a different one, or the structure may become disrupted and become amorphous (non-crystalline).

[0009] As mentioned above, a conventional technique has been reported in which a highly hydrophilic ZSM-5 zeolite membrane is synthesized by adding a halogen compound such as fluorine atoms to a raw material mixture for hydrothermal synthesis. According to this technique, a large amount of halogen element is required, approximately equal to the amount of silica element. This amount is considered to be necessary to have an effect on the entire raw material mixture for hydrothermal synthesis. On the other hand, in the present invention, it has been found that halogen compounds such as F atoms only need to act on the terminals of crystal growth, and that a very small amount is sufficient to achieve a sufficient effect. Furthermore, it has been confirmed that if the amount of halogen compounds such as F atoms is in excess of the appropriate amount used in the present invention, even if the amount is less than approximately equivalent to the amount of silica element, it can have a negative effect on crystallinity. Therefore, it is believed that the zeolite of the present invention is obtained based on a principle completely different from that of conventional technology.

[0010] That is, the present invention has the following configuration. [1] Zeolite containing 0.02 at% to 0.3 at% of fluorine atoms at a depth of 50 nm from the surface. [2] A zeolite in which the ratio of silicon atoms to aluminum atoms (Si / Al2), when expressed as SA1 at a depth of 200 nm from the surface and as SA2 at a depth of 2000 nm from the surface, has a change rate represented by the following formula (a) of 1.0% or more and 80.0% or less. ((SA1-SA2) / SA1) × 100 (a) [3] Zeolite in which the sum of the normalized area intensities of Si-O-AlOH and bridging Si(OH)Al is less than 24.2 when measured by Fourier transform infrared spectroscopy. [4] A zeolite composite membrane comprising an inorganic porous support and a membrane made of the zeolite according to any one of [1] to [3] above. [5] A method for producing a zeolite by adding a fluorine compound to a raw material mixture for hydrothermal synthesis containing an alumina source and a silica source, characterized in that the molar ratio of fluorine atoms to silicon atoms (F / Si) in the raw material mixture for hydrothermal synthesis is 0.001 or more and less than 0.06. [6] The method for producing a zeolite according to the above [5], wherein the fluorine compound is sodium fluoride. [7] A zeolite composite membrane having a membrane formed thereon, the membrane being made of a zeolite obtained by the production method according to [5] or [6] above. [8] A method for separating a liquid or a gas, which uses the zeolite membrane composite according to [4] or [7] above. [9] A method for separating nitrogen and ammonia using the zeolite membrane composite according to [4] or [7] above.

[10] A method for separating hydrogen and methanol, using the zeolite membrane composite according to [4] or [7] above. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a zeolite from which a highly permeable zeolite membrane can be obtained, a method for producing the zeolite, and a zeolite composite membrane in which a membrane made of the zeolite is formed. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a conceptual diagram showing a module for evaluating methanol separation. [Figure 2] FIG. 1 shows the permeance of methanol. [Figure 3] FIG. 10 is a diagram showing a depth profile of Comparative Example 1. [Figure 4] FIG. 10 is a diagram showing a depth profile of Example 2. [Figure 5] FIG. 1 is a diagram showing the results of FT-IR measurement. DETAILED DESCRIPTION OF THE INVENTION

[0013] Representative embodiments for carrying out the present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be carried out in various modified forms as long as they do not depart from the gist of the present invention.

[0014] [Zeolite] The zeolite of the present invention is characterized by having a fluorine atom concentration of 0.02 at% or more and 0.3 at% or less at a depth of 50 nm from the surface. The fluorine atom concentration is extremely small compared to the aluminum and silicon, which are the main elements constituting zeolites. A fluorine atom concentration in the above range has the effect of controlling crystal growth suitable for permeability when formed into a zeolite membrane. More specifically, when the concentration is below the upper limit, fluorine does not inhibit the affinity of the target component, induces suitable crystal growth, and ensures permeability when formed into a zeolite membrane. From the above perspective, the fluorine atom concentration at a depth of 50 nm from the surface is preferably 0.1 at% or more and 0.3 at% or less. Here, at% means atomic %, and refers to the ratio (%) of the number of fluorine atoms to the total number of atoms at a depth of 50 nm from the surface.

[0015] The zeolite of the present invention is characterized in that the ratio of silicon atoms to aluminum atoms (the so-called silica-alumina ratio of 2, which is expressed as Si / Al2 to match this) is expressed as SA1 at a depth of 200 nm from the surface and as SA2 at a depth of 2000 nm from the surface, and the rate of change represented by the following formula (a) is 1.0% or more and 80.0% or less. ((SA1-SA2) / SA1) × 100 (a)

[0016] When the conversion rate is 1.0% or more, the zeolite membrane composite described below has a structure in which the target gas or the like to be separated can easily enter the zeolite membrane, and the zeolite membrane composite as a whole has a structure in which specific components can easily enter and exit. This structure is thought to be linked to improved permeability. Furthermore, when the conversion rate is 1.0% or more, the number of adsorption points for gas or the like increases from the zeolite surface in the depth direction, so that gas or the like that has entered the zeolite membrane is less likely to return to the surface, and gas is thought to easily permeate from the surface in the depth direction. On the other hand, if the rate of change is 80% or less, the desired structure of the zeolite can be maintained. From the above viewpoint, the rate of change is preferably 3% or more and 70% or less, and more preferably 5% or more and 60% or less. The rate of change was calculated from Si / Al2 determined by the method described in the examples.

[0017] Furthermore, in the zeolite of the present invention, when measured by Fourier transform infrared spectroscopy (hereinafter referred to as "FT-IR"), the sum of the normalized area intensity of Si-O-AlOH and bridging Si(OH)Al (hereinafter simply referred to as "area intensity") is less than 24.2. The Si-O-AlOH and bridging Si(OH)Al peaks are due to defects in the zeolite, and a smaller area intensity is preferable. Specifically, the area intensity is preferably less than 24.2, more preferably 24 or less, even more preferably 20 or less, and particularly preferably 19.6 or less. When the area intensity is less than 24.2, there are fewer defects in the zeolite, and when a zeolite membrane is formed, there is less resistance in the zeolite pores through which the target gas, liquid, etc. to be separated moves, resulting in improved permeability.

[0018] The zeolite in this specification is a zeolite as defined by the International Zeolite Association (IZA, hereinafter referred to as "IZA"), whose structure is characterized by X-ray diffraction data. In the present invention, the zeolite constituting the zeolite membrane is preferably an aluminosilicate. The aluminosilicate is composed mainly of oxides of Si and Al, and may contain other elements as long as the effects of the present invention are not impaired. The cationic species contained in the zeolite of the present invention are preferably cationic species that are easily coordinated to the ion exchange sites of the zeolite, such as cationic species selected from the group consisting of elements of Groups 1, 2, 8, 9, 10, 11, and 12 of the periodic table, NH4 + and two or more of these cationic species, more preferably cationic species selected from the group of elements of Groups 1 and 2 of the periodic table, NH4 + and two or more cationic species thereof.

[0019] The SiO2 / Al2O3 molar ratio of the aluminosilicate is not particularly limited, but is usually 6 or more, preferably 7 or more, and more preferably 8 or more, and is usually 500 or less, preferably 100 or less, more preferably 80 or less, even more preferably 50 or less, particularly preferably 45 or less, even more preferably 30 or less, and most preferably 25 or less. By using a zeolite with an SiO2 / Al2O3 molar ratio in such a specific range, it is possible to improve the density of the zeolite membrane, as well as its durability, such as chemical reactivity resistance and heat resistance, which will be described later. From the viewpoint of separation performance for permeating specific components from a mixed gas composed of multiple components, it is preferable to use a zeolite exhibiting the above SiO2 / Al2O3 molar ratio, because acid sites due to Al element, etc., become adsorption sites for specific components. Furthermore, by using a zeolite exhibiting a more preferable SiO2 / Al2O3 molar ratio in accordance with a specific component, such as water, methanol, or ammonia, high permeability and high selectivity can be achieved in separation. The SiO2 / Al2O3 molar ratio of the zeolite can be adjusted by the reaction conditions of the hydrothermal synthesis, which will be described later.

[0020] The structure of the zeolite used in the present invention, when expressed in terms of the codes specified by the IZA, includes, for example, ABW, ACO, AEI, AEN, AFI, AFT, AFX, ANA, ATN, ATT, ATV, AWO, AWW, BIK, CHA, DDR, DFT, EAB, EPI, ERI, ESV, FAU, GIS, GOO, ITE, JBW, KFI, LEV, LTA, MER, MON, MTF, OWE, PAU, PHI, RHO, RTE, RWR, SAS, SAT, SAV, SIV, TSC, UFI, VNI, YUG, AEL, AFO, AHT, DAC, FER, HEU, IMF, ITH, MEL, MFS, MWW, OBW, RRO, SFG, STI, SZR, TER, TON, TUN, WEI, MFI, MON, PAU, PHI, and MOR.

[0021] Among the zeolites with the above structure, the framework density is 18.0T / nm 3The following zeolites are preferred, more preferably CHA, FAU, MFI, LTA, and RHO, and even more preferably MFI. When permeating components other than the specific component are present in the mixed gas, the use of a zeolite with a low framework density can reduce the resistance to permeation of these permeating components, while making it easier to increase the permeation amount of the specific component of interest. Here, the framework density (unit: T / nm 3 ) is the unit volume of zeolite (1 nm 3 It means the number of T atoms (atoms other than oxygen that make up the zeolite framework) present per 1000 sq m (1000 sq m), and this value is determined by the structure of the zeolite. The relationship between framework density and zeolite structure is shown in ATLAS OF ZEOLITE FRAMEWORK TYPES Fifth Revised Edition 2007 ELSEVIER.

[0022] Zeolites with suitable structures are described in detail below. (CHA type zeolite) The CHA-type zeolite used in the present invention is a zeolite with a CHA structure, which is a code defined by IZA to define the structure of zeolites. CHA-type zeolite has a structure characterized by three-dimensional pores consisting of eight-membered oxygen rings with a diameter of 3.8 × 3.8 Å, and this structure is characterized by X-ray diffraction data. The framework density of the CHA-type zeolite used in the present invention is 14.5 (unit: T / nm 3 )

[0023] (FAU type zeolite) The FAU zeolite used in the present invention refers to a zeolite with the FAU structure, a code for specifying the structure of zeolites established by the IZA. FAU zeolite has a structure characterized by three-dimensional pores consisting of six-membered oxygen rings with a diameter of 7.4 × 7.4 Å, and this structure is characterized by X-ray diffraction data. The framework density of the FAU zeolite used in the present invention is 12.7 (unit: T / nm3 )

[0024] (MFI type zeolite) The MFI zeolite used in the present invention refers to a zeolite with an MFI structure, a code for specifying the structure of zeolites as defined by the IZA. MFI zeolite has a structure characterized by three-dimensional pores consisting of 10-membered oxygen rings with diameters of 5.1 × 5.5 Å or 5.3 × 5.6 Å, and this structure is characterized by X-ray diffraction data. The framework density of the MFI zeolite used in the present invention is 17.9 (unit: T / nm 3 )

[0025] (LTA type zeolite) The LTA zeolite used in the present invention is an LTA structure, a code that specifies the structure of zeolites as defined by IZA. LTA zeolite has a structure characterized by three-dimensional pores consisting of eight-membered oxygen rings with a diameter of 4.1 × 4.1 Å, and this structure is characterized by X-ray diffraction data. The framework density of the LTA zeolite used in the present invention is 12.9 (unit: T / nm 3 )

[0026] (RHO type zeolite) The RHO-type zeolite used in the present invention refers to a zeolite with an RHO structure, a code that specifies the structure of zeolites as defined by the IZA. RHO-type zeolite has a structure characterized by three-dimensional pores consisting of eight-membered oxygen rings with a diameter of 3.6 × 3.6 Å, and this structure is characterized by X-ray diffraction data. The framework density of the RHO-type zeolite used in the present invention is 14.1 (unit: T / nm 3 )

[0027] [Zeolite manufacturing method] The method for producing a zeolite of the present invention is characterized in that a fluorine compound is added to a raw material mixture for hydrothermal synthesis containing an alumina source and a silica source, and the molar ratio of fluorine atoms to silicon atoms (F / Si) is 0.001 or more and less than 0.06. Specifically, the hydrothermal synthesis raw material mixture, which has been adjusted in composition and made uniform, is placed in a heat-resistant and pressure-resistant container such as an autoclave, which is then sealed and heated for a certain period of time, whereby the hydrothermal synthesis can be produced. The raw material mixture for hydrothermal synthesis contains a Si atom source, an Al atom source, an alkali source, and water, and further contains an organic template (structure-directing agent) and seed crystals as needed.

[0028] In the zeolite production method of the present invention, the molar ratio of fluorine to silicon in the raw material mixture for hydrothermal synthesis is crucial. When no fluorine is added, i.e., when the molar ratio of fluorine to silicon is 0, the zeolite has a uniform Si / Al2 molar ratio from the surface to the interior. In contrast, adding a certain amount of fluorine can control the Si / Al2 molar ratio from the surface to the interior of the zeolite and suppress unintended crystal defects such as Si-O-AlOH and bridging Si(OH)Al. On the other hand, excessive addition of fluorine can cause undesirable effects such as excessive changes in the Si / Al2 molar ratio, an increase in unintended crystal defects such as Si-O-AlOH and bridging Si(OH)Al, and even strong suppression of crystal growth itself. Specific examples include variations in zeolite crystal growth. In the present invention, the molar ratio of fluorine atoms to silicon atoms (F / Si) in the raw material mixture for hydrothermal synthesis is preferably 0.001 or more and less than 0.06. This range allows the crystal growth of zeolite to be controlled within a preferred range. More preferably, the molar ratio of fluorine atoms to silicon atoms (F / Si) is 0.002 or more and 0.02 or less. Fluorine affects the crystal growth of zeolite, and the extent of this effect varies depending on various conditions, such as the composition of the raw material mixture for hydrothermal synthesis and the hydrothermal synthesis temperature. Therefore, it is preferable to adjust the amount of fluorine added in accordance with the synthesis conditions, for example, CHA, FAU, MFI, LTA, RHO, etc.

[0029] The raw material mixture for hydrothermal synthesis will be described in detail below. (silicon atom source) The silicon (Si) atom source used in the raw material mixture for hydrothermal synthesis is not particularly limited, and examples thereof include aluminosilicate zeolite, fumed silica, colloidal silica, amorphous silica, sodium silicate, methyl silicate, ethyl silicate, silicon alkoxides such as trimethylethoxysilane, tetraethyl orthosilicate, aluminosilicate gel, etc., and examples thereof include fumed silica, colloidal silica, amorphous silica, sodium silicate, methyl silicate, ethyl silicate, silicon alkoxides, and aluminosilicate gel. These may be used alone or in combination of two or more. The Si atom source is used so that the amounts of the other raw materials used relative to the Si atom source fall within the preferred ranges described above or below.

[0030] (Aluminum atom source) The aluminum (Al) atom source is not particularly limited, and examples thereof include aluminosilicate zeolite, amorphous aluminum hydroxide, aluminum hydroxide having a gibbsite structure, aluminum hydroxide having a bayerite structure, aluminum nitrate, aluminum sulfate, aluminum oxide, sodium aluminate, boehmite, pseudo-boehmite, aluminum alkoxide, and aluminosilicate gel. Of these, amorphous aluminum hydroxide, sodium aluminate, boehmite, pseudo-boehmite, aluminum alkoxide, and aluminosilicate gel are preferred, and amorphous aluminum hydroxide, sodium aluminate, and aluminosilicate gel are particularly preferred. These may be used alone or in combination of two or more.

[0031] The aluminosilicate zeolite may be used alone or in combination of two or more. When an aluminosilicate zeolite is used as the Al atom source, it is preferable that the aluminosilicate zeolite accounts for 50 mass% or more, particularly 70 to 100 mass%, and especially 90 to 100 mass% of the total Al atom source. When an aluminosilicate zeolite is used as the Si atom source, it is preferable that the aluminosilicate zeolite accounts for 50 mass% or more, particularly 70 to 100 mass%, and especially 90 to 100 mass% of the total Si atom source.

[0032] (Al atom / Si atomic ratio) The preferred range of the amount of aluminum atom source (including the above-mentioned aluminosilicate zeolite and other aluminum atom sources) used relative to the silicon (Si atoms) contained in the raw material mixture other than the seed crystals (Al atom / Si atom ratio) is, in terms of molar ratio, usually 0.001 or more, preferably 0.002 or more, more preferably 0.003 or more, and even more preferably 0.004 or more, and usually 1.0 or less, preferably 0.5 or less, more preferably 0.2 or less, and even more preferably 0.1 or less. Controlling the amount used within this range makes it easier to control the contents of nitrogen atoms and alkali metal elements in the zeolite within the preferred ranges of the present invention. In order to increase the Al atom / Si atom ratio, the amount of silicon atom source used relative to the aluminum atom source can be reduced, while in order to decrease this ratio, the amount of silicon atom source used relative to the aluminum atom source can be increased. The raw material mixture for hydrothermal synthesis may contain, in addition to the Si atom source and the Al atom source, other atom sources such as Ga, Fe, B, Ti, Zr, Sn, and Zn.

[0033] (Alkaline source) The type of alkali used as the alkali source is not particularly limited, and alkali metal hydroxides and alkaline earth metal hydroxides can be used. The metal species of these metal hydroxides are usually sodium (Na), potassium (K), lithium (Li), rubidium (Rb), cesium (Cs), calcium (Ca), magnesium (Mg), strontium (Sr), and barium (Ba), preferably Na, K, and Cs, and more preferably Na and Cs. Two or more types of metal species of the metal oxides may be used in combination, and specifically, it is preferable to use Na and Cs in combination. Specific examples of metal hydroxides that can be used include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide, and cesium hydroxide; and alkaline earth metal hydroxides such as calcium hydroxide, magnesium hydroxide, strontium hydroxide, and barium hydroxide. Furthermore, hydroxide ions, which are counter anions of the organic template described below, can be used as the alkali source used in the raw material mixture for hydrothermal synthesis. In the crystallization of the zeolite according to the present invention, an organic template is not necessarily required. However, by using a type of organic template (structure-directing agent) corresponding to each structure, the ratio of silicon atoms to aluminum atoms in the crystallized zeolite increases, thereby improving the crystallinity, and therefore it is preferable to use an organic template.

[0034] (organic template) The organic template may be of any type as long as it can form the desired zeolite. One type of template may be used, or two or more types may be used in combination. The type of organic template suitable for the reaction varies depending on the zeolite structure to be synthesized, and an organic template that can obtain the desired zeolite structure should be used. Specifically, for example, tetrapropylammonium hydroxide is preferably used for the MFI structure. When the organic template is a cation, it is accompanied by an anion that is not detrimental to the formation of the zeolite. Representative of such anions are Cl. - , Br - , I -These include halogen ions, hydroxide ions, acetates, sulfates, and carboxylates, etc. Among these, hydroxide ions are particularly preferred, and in the case of hydroxide ions, they function as an alkali source as described above.

[0035] The molar ratio of the Si atom source to the organic template in the hydrothermal synthesis raw material mixture (organic template / SiO ratio) is typically 0.005 or greater, preferably 0.01 or greater, more preferably 0.02 or greater, particularly preferably 0.05 or greater, and particularly preferably 0.1 or greater, and typically 1 or less, preferably 0.5 or less, more preferably 0.3 or less, particularly preferably 0.25 or less, and particularly preferably 0.2 or less. When the organic template / SiO ratio of the hydrothermal synthesis raw material mixture is within this range, a dense zeolite membrane can be formed, and a zeolite with excellent acid resistance and low Al desorption can be obtained. Furthermore, under these conditions, a particularly dense and acid-resistant MFI-type aluminosilicate zeolite can be formed.

[0036] The use of an appropriate amount of alkali metal atom source facilitates the coordination of the organic structure-directing agent (described below) with aluminum in a suitable state, thereby facilitating the formation of a crystal structure. The molar ratio R / Si of the alkali metal atom source (R) to the silicon (Si) contained in the mixture of raw materials for hydrothermal synthesis other than the seed crystals is usually 0.01 or more, preferably 0.02 or more, more preferably 0.03 or more, even more preferably 0.04 or more, and particularly preferably 0.05 or more, and is usually 1.0 or less, preferably 0.6 or less, more preferably 0.4 or less, even more preferably 0.2 or less, and particularly preferably 0.1 or less. When the molar ratio of the alkali metal atom source to silicon (R / Si) is smaller than the above upper limit, the produced zeolite is easily dissolved, and the zeolite can be obtained in a sufficient yield without failing to be obtained. When R / Si is larger than the above lower limit, the raw material Al atom source and Si atom source are sufficiently dissolved, resulting in a homogeneous raw material mixture for hydrothermal synthesis, and the zeolite yield can be ensured.

[0037] (amount of water) The amount of water in the raw material mixture for hydrothermal synthesis in the present invention is preferably larger than that in ordinary hydrothermal synthesis. A large amount of water makes it possible to make the Si / Al (molar ratio) uniform and to easily set it to 0.2 or less. Specifically, the molar ratio of water to silicon (Si atoms) contained in the raw material mixture other than the seed crystals is preferably 45 or more, more preferably 60 or more, and even more preferably 70 or more. The upper limit of the amount of water, expressed as a molar ratio to silicon (Si atoms) contained in the raw material mixture other than the seed crystals, is preferably 300 or less, more preferably 200 or less, and even more preferably 150 or less. If the amount is less than the upper limit, the reaction mixture will not be too dilute, and zeolite can be obtained in a sufficient yield.

[0038] (fluoride source) The fluorine source used in producing the zeolite of the present invention is preferably water-soluble and is not particularly limited, but preferably includes hydrogen fluoride, sodium fluoride, sodium bifluoride, sodium silicofluoride, ammonium fluoride, cryolite, aluminum fluoride, etc., more preferably fluorine compounds such as sodium fluoride and aluminum fluoride, and particularly preferably sodium fluoride. The presence of fluorine compounds in the raw material mixture for hydrothermal synthesis affects zeolite crystal growth, although the exact mechanism is unclear. While fluorine atoms may be dispersed throughout the zeolite, their uneven distribution within a few hundred nanometers of the zeolite surface suggests that they are present at the growth edge and catalytically participate in crystal growth. Furthermore, the fact that fluorine atoms are present only on the surface of the zeolite when used in small amounts suggests that relatively small amounts are effective. The effects of fluorine atoms on crystal growth vary widely, including the Si / Al molar ratio from the surface to the interior of the zeolite, the crystallinity (e.g., crystallite size), and the Si-O or Al-O structure. Therefore, favorable effects can be achieved by adjusting the amount of fluorine added to suit the desired structure, synthesis conditions, and application. Although this patent focuses on fluorine atoms, it is not limited to this, and it is believed that halogen atoms of the same group that can form a bonding state similar to that of fluorine with silicon or aluminum, specifically chlorine, bromine, iodine, anstatine, and tennessine in addition to fluorine, also have a similar effect on crystal growth. However, from the viewpoints of corrosiveness and productivity, it is preferable to use fluorine atoms.

[0039] (seed crystal) In the present invention, seed crystals may be used as one component of the raw material (raw material compound) for producing “zeolite.” When forming an MFI-type aluminosilicate zeolite, it is preferable to use MFI-type zeolite as the seed crystals. The seed crystals may be crushed before use as necessary. The particle size is usually 1 nm or more, preferably 10 nm or more, more preferably 50 nm or more, even more preferably 0.1 μm or more, particularly preferably 0.5 μm or more, especially preferably 0.7 μm or more, and most preferably 1 μm or more, and is usually 5 μm or less, preferably 3 μm or less, more preferably 2 μm or less, most preferably 1.5 μm or less, and particularly preferably 1.2 μm or less.

[0040] (hydrothermal synthesis) The reaction temperature when forming a zeolite by hydrothermal synthesis is not particularly limited, and may be any temperature suitable for obtaining the desired zeolite structure. It is usually 100°C or higher, preferably 120°C or higher, more preferably 130°C or higher, particularly preferably 140°C or higher, particularly preferably 150°C or higher, and most preferably 160°C or higher, and usually 210°C or lower, preferably 200°C or lower, more preferably 190°C or lower, and particularly preferably 180°C or lower. If the reaction temperature is too low, the zeolite may be difficult to crystallize. If the reaction temperature is too high, a different type of zeolite from the desired zeolite may be easily produced. The heating (reaction) time when forming a zeolite by hydrothermal synthesis is not particularly limited, and may be any time suitable for obtaining the target zeolite structure, but is usually 1 hour or more, preferably 5 hours or more, and more preferably 10 hours or more, and usually 10 days or less, preferably 5 days or less, more preferably 3 days or less, even more preferably 2 days or less, and particularly preferably 1 day or less. If the reaction time is too short, the zeolite may be difficult to crystallize. If the reaction time is too long, a type of zeolite different from the target zeolite may be easily produced. The pressure during hydrothermal synthesis is not particularly limited, and the autogenous pressure that occurs when the mixture of raw materials for hydrothermal synthesis placed in a sealed vessel is heated to the above-mentioned temperature range is sufficient. Furthermore, an inert gas such as nitrogen may be added as necessary.

[0041] (Washing, heat treatment, drying) The zeolite obtained by hydrothermal synthesis is washed with water, then heat-treated and dried. Here, heat treatment means drying the zeolite by applying heat, and also means removing an organic template, if used, by calcining the organic template. When the purpose of the heat treatment is drying, the temperature is usually 50° C. or higher, preferably 80° C. or higher, more preferably 100° C. or higher, and usually 200° C. or lower, preferably 150° C. or lower. When the purpose is to remove the organic template by calcination, the temperature is usually 350° C. or higher, preferably 400° C. or higher, more preferably 450° C. or higher, even more preferably 500° C. or higher, and usually 900° C. or lower, preferably 800° C. or lower, even more preferably 700° C. or lower, particularly preferably 600° C. or lower.

[0042] When the purpose is to remove the organic template by calcination, too low a temperature for the heat treatment tends to result in a large proportion of the organic template remaining, whereas too high a temperature for the heat treatment may destroy the crystalline structure of the zeolite. The heat treatment time is not particularly limited as long as it is sufficient to sufficiently dry the zeolite and remove the organic template by calcination, and is preferably 0.5 hours or more, more preferably 1 hour or more, for the purpose of drying, and is preferably 1 hour or more, more preferably 5 hours or more, for the purpose of removing the organic template by calcination, although this varies depending on the rate of temperature increase and decrease. The upper limit of the heating time is not particularly limited, and is usually 200 hours or less, preferably 150 hours or less, more preferably 100 hours or less. The heat treatment for calcining the organic template may be carried out in an air atmosphere, but may also be carried out in an atmosphere containing an inert gas such as nitrogen or oxygen.

[0043] When the hydrothermal synthesis is carried out in the presence of an organic template, it is appropriate to wash the obtained zeolite with water and then remove the organic template by, for example, heat treatment or extraction, preferably by the above-mentioned heat treatment, i.e., calcination. During the heat treatment for calcining and removing the organic template, it is desirable to raise the temperature at a slow rate. The rate is usually 5°C / min or less, preferably 2°C / min or less, more preferably 1°C / min or less, even more preferably 0.5°C / min or less, and particularly preferably 0.3°C / min or less. The lower limit of the rate is usually 0.1°C / min or more, taking into account workability. In addition, in a heat treatment for the purpose of calcining and removing an organic template, it is desirable to slow down the temperature drop rate after the heat treatment, similar to the temperature rise rate. The temperature drop rate is usually 5°C / min or less, preferably 2°C / min or less, more preferably 1°C / min or less, even more preferably 0.5°C / min or less, and particularly preferably 0.3°C / min or less. The lower limit of the temperature drop rate is usually 0.1°C / min or more, taking workability into consideration.

[0044] [Zeolite membrane composite] In the present invention, the above-mentioned zeolite is made into a zeolite membrane composite for use in separating liquids and gases, but the form and use are not limited thereto. Zeolites have the property of adsorbing and permeating liquids and gases not only on their surface but also inside, and one of the applications utilizing this property is the separation of liquids and gases. Therefore, the high-quality zeolite obtained by the crystal growth control technique of the present invention may be used for other purposes in a form other than a zeolite membrane composite. For example, zeolite may be formed into a powder or pellets of an easily manageable shape and size and used as an adsorbent for specific gas species or as a synthesis catalyst. By forming a zeolite membrane composite, high permeability can be achieved as a separation membrane, and desirable improvements can be achieved, such as an improved adsorption rate as an adsorbent and an improved reaction rate as a synthesis catalyst.

[0045] The zeolite membrane composite of the present invention has zeolite on a porous support. The shape of the zeolite is not limited to a thin film, and may be spherical, cubic, rectangular, or a combination of these, or may even be an amorphous shape without a clear shape. The zeolite membrane composite is one in which zeolite is attached to and integrated with a support described below, preferably crystallized and fixed, and includes one in which part of the zeolite is fixed to the inside of the support. As the zeolite membrane composite, for example, one in which zeolite is crystallized into a membrane on the surface of a porous support by hydrothermal synthesis is preferred. The zeolite membrane in the zeolite membrane composite of the present invention is preferably formed from the above-mentioned zeolite. The position of the zeolite membrane on the porous support is not particularly limited, and the zeolite membrane may be formed on the outer surface of a tubular support, on the inner surface, or even on both surfaces depending on the application system. The zeolite membrane may be formed by laminating it on the surface of the support, or may be crystallized so as to fill the pores in the surface layer of the support. In this case, it is important that the crystallized membrane layer does not have cracks or continuous micropores, and forming a so-called dense membrane is preferable in terms of improving separation performance.

[0046] <Porous support> The porous support used in the present invention preferably has chemical stability that allows zeolite to be crystallized into a membrane on its surface. Suitable porous supports include porous polymers such as polysulfone, cellulose acetate, aromatic polyamide, vinylidene fluoride, polyethersulfone, polyacrylonitrile, polyethylene, polypropylene, polytetrafluoroethylene, and polyimide; ceramic sinters such as silica, α-alumina, γ-alumina, mullite, zirconia, titania, yttria, silicon nitride, and silicon carbide; sintered metals and mesh-like molded bodies such as iron, bronze, and stainless steel; and inorganic porous bodies such as glass and carbon molded bodies. Among these, inorganic porous supports such as ceramic sinters, metal sinters, glass, and carbon molded bodies are preferred as porous supports used in high-temperature regions because of their excellent mechanical strength, deformation resistance, thermal stability, and reactivity resistance at high temperatures.

[0047] The inorganic porous support is preferably a sintered ceramic, which is a solid material whose principal or majority components are inorganic non-metallic substances. As described above, preferred ceramic sintered bodies include ceramic sintered bodies containing α-alumina, γ-alumina, silica, mullite, zirconia, titania, yttria, silicon nitride, silicon carbide, etc., but these may be sintered bodies of a single material or a mixture of two or more materials sintered together. A part of the surface of these ceramic sintered bodies may be converted into zeolite during zeolite membrane synthesis, which increases the adhesion between the porous support and the zeolite membrane, thereby improving the durability of the zeolite membrane composite. In particular, inorganic porous supports containing at least one of alumina, silica, and mullite are more preferred because they can be easily partially zeoliteized, resulting in a stronger bond between the inorganic porous support and the zeolite, making it easier to form a dense zeolite membrane with high separation performance. The porous support used in the present invention preferably has, on its surface (hereinafter also referred to as "porous support surface"), the action of crystallizing the zeolite formed on the porous support.

[0048] The pore size of the porous support used in the present invention is not limited, and the porosity is usually 20% or more, more preferably 30% or more, and usually 60% or less, preferably 50% or less. The porosity of the portion other than the vicinity of the surface of the porous support affects the permeation flow rate when separating gas or liquid, and when the porosity is above the lower limit, the permeate tends to diffuse easily, while when it is below the upper limit, it tends to be easier to prevent a decrease in the strength of the porous support. In addition, as a method for controlling the permeation flow rate, a porous support formed by combining layers of porous bodies with different porosities may be used.

[0049] <Zeolite> The zeolite in the zeolite membrane composite of the present invention is the above-mentioned zeolite. The membrane separation of the present invention utilizes the adsorption of specific components onto zeolite, and is characterized by separation based on a hopping mechanism within the zeolite pores. Therefore, although not particularly limited, zeolites with pore sizes close to the molecular diameters of the specific components are often preferred because they tend to improve separation selectivity. From this perspective, for example, when the specific components are water, ammonia, or methanol, the zeolite structure preferably has 8-membered oxygen ring pores.

[0050] On the other hand, pores larger than the 8-membered oxygen ring are preferable because they increase permeability, but may result in reduced nitrogen separation performance. However, even when using a zeolite with pores larger than the 8-membered oxygen ring, if a zeolite with a reduced SiO2 / Al2O3 molar ratio is used, the pore size of the zeolite membrane is controlled by specific components adsorbed on the Al site, allowing for high permeability and highly selective separation of ammonia. Therefore, the effective pore size of the zeolite used in membrane separation is an important design factor, as it significantly affects the pore size of the zeolite membrane to which a specific component is adsorbed. The effective pore size of the zeolite can also be controlled by the type of metal introduced into the zeolite, ion exchange, acid treatment, silylation treatment, etc. It is also possible to improve separation performance by controlling the effective pore size using other methods. For example, the pore size of a zeolite is slightly affected by the atomic size of the metal species introduced into the zeolite framework. When a metal with an atomic size smaller than that of silicon, such as boron (B), is introduced, the pore size becomes smaller, while when a metal with an atomic size larger than that of silicon, such as tin (Sn), is introduced, the pore size becomes larger. In addition, the pore size may be affected by desorbing the metal introduced into the zeolite framework through acid treatment.

[0051] Furthermore, when the ions in zeolite are exchanged with monovalent ions having a large ionic radius, the effective pore size becomes smaller. On the other hand, when the ions are exchanged with monovalent ions having a small ionic radius, the effective pore size becomes close to the pore size inherent in the zeolite structure.

[0052] Furthermore, the effective pore size of zeolite can also be reduced by silylation treatment. For example, by silylating the terminal silanols on the outer surface of a zeolite membrane and then laminating a silylated layer, the effective pore size of the pores facing the outer surface of the zeolite can be reduced.

[0053] In the present invention, as described in detail below, zeolite is formed into a membrane and used for gas separation, but the shape and use are not limited to this. For example, zeolite is synthesized into a powder and used as a synthetic catalyst, or an active metal species is supported on the zeolite and used as a synthetic catalyst. This invention is based on technology for precisely controlling the structure of zeolite, and by adjusting this to suit the application, the properties can be improved in other applications as well. The separation function of the zeolite membrane composite used in the present invention is not particularly limited, but is manifested by controlling the surface properties of the zeolite to control the affinity and adsorption of gas molecules to the zeolite membrane. That is, by controlling the polarity of the zeolite, the adsorption of specific components to the zeolite can be controlled, making it easier to permeate. For example, by controlling the polarity of the zeolite by adding nitrogen atoms, the affinity of ammonia to the zeolite can be controlled, making it easier to permeate.

[0054] In addition, the polarity of zeolite can be increased by substituting Al atoms for Si atoms in the zeolite framework, which allows highly polar gas molecules to be actively adsorbed and permeated into the zeolite pores. It is also possible to control the polarity of the resulting zeolite by adding other atom sources besides Al atoms, such as Ga, Fe, B, Ti, Zr, Sn, and Zn, to the raw material mixture for hydrothermal synthesis. In addition, ion exchange can be used to control not only the pore size of the zeolite but also its molecular adsorption performance, thereby controlling the permeation rate.

[0055] <Zeolite membrane> The zeolite membrane in the present invention refers to a membranous material made of zeolite, preferably formed by crystallizing zeolite on the surface of a porous support. The membrane may contain, as necessary, inorganic binders such as silica and alumina, organic substances such as polymers, or silylating agents for modifying the zeolite surface, in addition to zeolite.

[0056] The preferred zeolite contained in the zeolite membrane used in the present invention is as described above, but the zeolite contained in the zeolite membrane may be one type or multiple types. Furthermore, the zeolite membrane may contain zeolites that tend to form in a mixed phase, such as ANA, GIS, and MER, or amorphous components other than crystals.

[0057] There are no particular restrictions on the zeolite and porous support that constitute the zeolite membrane composite, and it is preferable to use any combination of the above-mentioned zeolites and porous supports. Among these, particularly preferred combinations of zeolite and porous support include an MFI zeolite-porous alumina support, an RHO zeolite-porous alumina support, a DDR zeolite-porous alumina support, an AFI zeolite-porous alumina support, a CHA zeolite-porous alumina support, and an AEI zeolite-porous alumina support, and preferably a CHA zeolite-porous alumina support, an MFI zeolite-porous alumina support, and an RHO zeolite-porous alumina support, and more preferably an MFI zeolite-porous alumina support and an RHO zeolite-porous alumina support.

[0058] (Zeolite membrane thickness) The thickness of the zeolite membrane used in the present invention is not particularly limited, but is usually 0.1 μm or more, preferably 0.3 μm or more, more preferably 0.5 μm or more, even more preferably 0.7 μm or more, even more preferably 1.0 μm or more, and particularly preferably 1.5 μm or more. It is also usually 100 μm or less, preferably 60 μm or less, more preferably 20 μm or less, even more preferably 15 μm or less, even more preferably 10 μm or less, and particularly preferably 5 μm or less. When the thickness of the zeolite membrane is equal to or greater than the above lower limit, defects tend to be less likely to occur and separation performance tends to be improved. When the thickness of the zeolite membrane is equal to or less than the above upper limit, permeation performance tends to be improved. Furthermore, in the high-temperature region, cracks are less likely to occur in the zeolite membrane due to temperature rise, which tends to suppress a decrease in permeation selectivity at high temperatures.

[0059] <Method of manufacturing zeolite membrane composite> In the present invention, the method for producing the zeolite membrane composite is not particularly limited as long as it is a method capable of forming the above-mentioned zeolite membrane on a porous support, and the zeolite membrane composite can be produced by any known method. For example, any of the following methods can be used: (1) a method of crystallizing zeolite into a membrane on a support, (2) a method of fixing zeolite to a support with an inorganic binder or an organic binder, (3) a method of fixing a polymer in which zeolite is dispersed to a support, and (4) a method of fixing zeolite to a support by impregnating the support with a zeolite slurry. Among these, a method of crystallizing zeolite in a membrane form on a porous support is particularly preferred. Although there are no particular limitations on the crystallization method, a method of placing the porous support in a reaction mixture for hydrothermal synthesis (a mixture of raw materials for hydrothermal synthesis) used to produce zeolite and directly carrying out hydrothermal synthesis to crystallize zeolite on the surface of the porous support is preferred. In this case, the zeolite membrane composite can be produced, for example, by placing a mixture of raw materials for hydrothermal synthesis, which has been homogenized by adjusting the composition, in a heat-resistant and pressure-resistant container such as an autoclave containing a porous support therein, sealing the container, and heating the mixture for a certain period of time.

[0060] The raw material mixture for hydrothermal synthesis contains a Si atom source, an Al atom source, an alkali source, and water, and further contains an organic template (structure-directing agent) and seed crystals as needed. A method for producing an MFI zeolite membrane composite, which is a particularly suitable example of a method for producing a zeolite membrane composite, will be described in detail below, although the zeolite membrane and the method for producing the same of the present invention are not limited thereto.

[0061] In the method for producing a zeolite membrane composite of the present invention, the molar ratio of fluorine to silicon in the raw material mixture for hydrothermal synthesis is crucial. Generally, when no fluorine is added, i.e., when the molar ratio of fluorine to silicon is 0, the zeolite membrane has a uniform Si / Al2 molar ratio from the surface to the back. In contrast, adding a certain amount of fluorine can control the Si / Al2 molar ratio from the surface to the back of the zeolite membrane. However, adding excessive fluorine can cause excessive changes in the Si / Al2 molar ratio and, further, can have undesirable effects on crystal growth. Specifically, this can cause variations in zeolite crystal growth, resulting in a membrane with a thin or missing membrane in some places, or, in more extreme cases, a membrane that no longer functions as a membrane at all. From the above viewpoints, in an MFI zeolite membrane, when the molar ratio of fluorine to silicon is in the range of 0.001 or more and less than 0.06, the Si / Al2 molar ratio in the zeolite membrane can be controlled within a preferred range. Note that fluorine affects the crystal growth of zeolite, and the degree of this effect varies depending on various conditions such as the composition of the raw material mixture for hydrothermal synthesis and the hydrothermal synthesis temperature. Therefore, in the case of other zeolite structures such as CHA, FAU, MFI, LTA, and RHO, or even in the case of an MFI zeolite, it is preferable to adjust the amount of fluorine added according to the synthesis conditions.

[0062] The raw materials for the zeolite that constitutes the zeolite membrane in the zeolite membrane composite can be the silicon atom source, aluminum atom source, alkali source, organic template, and water described above, and the Al atom / Si atom ratio and the amount of water are also the same as those described above. The particle size of the seed crystals is desirably close to the pore size of the support, and they may be crushed before use as necessary. The particle size is usually 1 nm or more, preferably 10 nm or more, more preferably 50 nm or more, even more preferably 0.1 μm or more, particularly preferably 0.5 μm or more, especially preferably 0.7 μm or more, and most preferably 1 μm or more, and is usually 5 μm or less, preferably 3 μm or less, more preferably 2 μm or less, most preferably 1.5 μm or less, and particularly preferably 1.2 μm or less. Depending on the pore size of the support, a smaller particle size of the seed crystal may be desirable, and the seed crystal may be crushed as necessary. The particle size of the seed crystal is usually 0.5 nm or more, preferably 1 nm or more, and more preferably 2 nm or more, and usually 5 μm or less, preferably 3 μm or less, and more preferably 2 μm or less.

[0063] The method for attaching seed crystals to a porous support is not particularly limited, and examples thereof include a dipping method in which seed crystals are dispersed in a solvent such as water and the porous support is immersed in the dispersion to attach the seed crystals to the surface, and a method in which seed crystals are mixed with a solvent such as water to form a slurry and then applied to the support. The dipping method is desirable for controlling the amount of attached seed crystals and producing zeolite membranes with good reproducibility, while the application of seed crystals in a slurry form is desirable in terms of closely adhering the seed crystals to the porous support. Furthermore, following the dipping method, it is also suitable to rub and press the support to which the seed crystals are attached with fingers wearing latex gloves, for example, in order to closely adhering the seed crystals to the porous support and / or to remove excess seed crystals.

[0064] The solvent in which the seed crystals are dispersed is not particularly limited, but water or an alkaline aqueous solution is particularly preferred. The type of alkaline aqueous solution is not particularly limited, but a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution is preferred. These alkaline species may also be mixed. The alkali concentration of the alkaline aqueous solution is not particularly limited, but is usually 0.0001 mol% or more, preferably 0.0002 mol% or more, more preferably 0.001 mol% or more, and even more preferably 0.002 mol% or more. The alkali concentration is also usually 1 mol% or less, preferably 0.8 mol% or less, more preferably 0.5 mol% or less, and even more preferably 0.2 mol% or less.

[0065] The amount of seed crystals to be dispersed is not particularly limited, and is usually 0.05% by mass or more, preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, particularly preferably 2% by mass or more, and most preferably 3% by mass or more, based on the total weight of the dispersion. Also, it is usually 20% by mass or less, preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 4% by mass or less. If the amount of dispersed seed crystals is too small, the amount of seed crystals attached to the porous support will be small, and therefore, there will be areas on the porous support where zeolite is not produced during hydrothermal synthesis, which may result in a defective membrane. On the other hand, for example, the amount of seed crystals attached to the porous support by the dipping method will be almost constant once the amount of seed crystals in the dispersion exceeds a certain level, so if the amount of seed crystals in the dispersion is too large, a lot of seed crystals will be wasted, which is disadvantageous in terms of cost.

[0066] It is desirable to attach seed crystals to a porous support by dipping or by applying a slurry, then dry the porous support, and then form a zeolite membrane. The drying temperature is usually 50°C or higher, preferably 80°C or higher, and more preferably 100°C or higher, and usually 200°C or lower, preferably 180°C or lower, and more preferably 150°C or lower. The drying time is not limited as long as the porous support is sufficiently dry, but is usually 10 minutes or longer, preferably 30 minutes or longer. On the other hand, there is no particular upper limit, but from an economical viewpoint, it is usually 5 hours or shorter.

[0067] The amount of seed crystals to be attached to the porous support in advance is not particularly limited, and the amount is determined by the number of crystals per 1 m of the membrane-forming surface of the porous support. 2 The mass per unit area is usually 0.1 g or more, preferably 0.3 g or more, more preferably 0.5 g or more, even more preferably 0.8 g or more, and most preferably 1.0 g or more, and is usually 100 g or less, preferably 50 g or less, more preferably 10 g or less, even more preferably 8 g or less, and most preferably 5 g or less. When the amount of seed crystals attached is equal to or greater than the lower limit, crystals tend to be easily formed, the film tends to grow sufficiently, and the film tends to grow uniformly. Furthermore, when the amount of seed crystals is equal to or less than the upper limit, the seed crystals do not increase the surface irregularities, and seed crystals that fall from the support do not easily grow spontaneous nuclei, thereby preventing the film growth on the support. Therefore, within the above range, a dense zeolite membrane tends to be produced.

[0068] As described above, after the seed crystals of the porous support are attached, hydrothermal synthesis, water washing, heat treatment, and drying are carried out under the same conditions as those described above for the production of zeolite. It is desirable to keep the temperature increase rate as slow as possible during the heat treatment for calcining and removing the organic template to prevent cracks from forming in the zeolite membrane due to the difference in thermal expansion coefficient between the porous support and the zeolite. The temperature increase rate is usually 5°C / min or less, preferably 2°C / min or less, more preferably 1°C / min or less, even more preferably 0.5°C / min or less, and particularly preferably 0.3°C / min or less. The lower limit of the temperature increase rate is usually 0.1°C / min or more, taking workability into consideration. In addition, in the heat treatment for calcining and removing the organic template, the temperature drop rate after the heat treatment must also be controlled to avoid cracking of the zeolite membrane. As with the temperature increase rate, the slower the temperature drop rate, the more desirable it is. The temperature drop rate is usually 5°C / min or less, preferably 2°C / min or less, more preferably 1°C / min or less, even more preferably 0.5°C / min or less, and particularly preferably 0.3°C / min or less. The lower limit of the temperature drop rate is usually 0.1°C / min or more, taking workability into consideration.

[0069] <<Ion exchange>> The synthesized zeolite membrane may be ion-exchanged if necessary. When a zeolite membrane is synthesized using an organic template, ion exchange is usually performed after removing the organic template. In the present invention, the ions to be exchanged are NH4 + or any of the cationic species obtained by protonating an organic amine having 1 to 20 carbon atoms, such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, dimethylethylenediamine, tetramethylethylenediamine, diethylenetriamine, triethylenetetraamine, aniline, methylaniline, benzylamine, methylbenzylamine, hexamethylenediamine, N,N-diisopropylethylamine, N,N,N-trimethyl-1-adamantanamine, pyridine, and piperidine, and other cationic species are also preferred. + , K. + , Li + , Rb + , Cs + Alkali metal ions such as Ca 2+ , Mg 2+ , Sr 2+ , Ba 2+ and ions of alkaline earth metals such as Fe, Cu, Zn, Ga, La, etc. may also be present. Among these, proton, NH4 + , Na + , Li + , Cs + Among these ions, Fe ions, Ga ions, and La ions are preferred. A mixture of these ions may be present in the zeolite.

[0070] By controlling the cation species and their amounts to be ion-exchanged in this way, it is possible to control the affinity of the zeolite with a specific component and the effective pore size within the zeolite pores, thereby increasing the permeation selectivity and improving the permeation rate. In addition, the zeolite of the present invention contains Na +When Na ions are contained, the content thereof is, in terms of molar ratio relative to the Al atoms in the zeolite, usually 0.01 or more, preferably 0.02 or more, more preferably 0.03 or more, even more preferably 0.04 or more, and particularly preferably 0.05 or more. On the other hand, the upper limit is not particularly limited, but is usually 0.10 or less, preferably 0.070 or less, more preferably 0.065 or less, even more preferably 0.060 or less, and particularly preferably 0.055 or less. Na ions in such a specific range + By using a zeolite with a high atomic ratio of SiO2 / Al, it is possible to separate specific components from a mixed gas with high permeability.

[0071] Ion exchange can be performed by treating the zeolite membrane after calcination (e.g., when an organic template is used) with nitrates, sulfates, phosphates, organic acid salts, hydroxides of the cations to be ion-exchanged, halogen salts of Cl or Br, or, in some cases, acids such as hydrochloric acid, typically at temperatures between room temperature and 100°C, followed by water washing or hot water washing at 40°C to 100°C. The solvent used for the ion exchange treatment can be water or an organic solvent as long as it dissolves the salt to be ion-exchanged. The concentration of the salt to be treated is typically 10 mol / L or less, with a lower limit of 0.1 mol / L or more, preferably 0.5 mol / L or more, and more preferably 1 mol / L or more. These treatment conditions can be set appropriately depending on the salt and solvent used. When using an acid such as hydrochloric acid, the acid destroys the crystalline structure of the zeolite, so the concentration of the acid used for the treatment is usually set to 5 mol / L or less, and the temperature and time are set appropriately. Furthermore, since the ion exchange rate increases when the ion exchange treatment is repeated, the number of ion exchange treatments is not particularly limited, and the treatment may be repeated until the desired effect is achieved. Furthermore, since the presence of residues from the ion exchange treatment raw materials in the zeolite pores after the ion exchange treatment hinders gas permeability, the ion-exchanged zeolite membrane may be calcined at 200 to 500°C as needed to remove the residues after the ion exchange treatment.

[0072] <<Nitrate treatment>> In the present invention, the synthesized zeolite membrane may be subjected to a nitrate treatment, if necessary. The nitrate treatment may be performed while the zeolite membrane contains the organic template, or after the organic template has been removed by calcination. The nitrate treatment may be performed, for example, by immersing the zeolite membrane composite in a solution containing nitrate. This may be preferable because the nitrate has the effect of sealing fine defects present on the membrane surface. Furthermore, when nitrate is present in the zeolite pores, it has the effect of improving the affinity of the zeolite membrane with ammonia, and is therefore preferably used as a method for improving ammonia permeability. The solvent used for the nitrate treatment may be water or an organic solvent as long as the salt dissolves therein, and the nitrate to be used is not limited, but examples thereof include magnesium nitrate, calcium nitrate, barium nitrate, aluminum nitrate, gallium nitrate, indium nitrate, iron nitrate, cobalt nitrate, nickel nitrate, copper nitrate, and zinc nitrate. These may be used alone or in combination of two or more. Among these, magnesium nitrate, calcium nitrate, barium nitrate, aluminum nitrate, gallium nitrate, and indium nitrate are preferred, with magnesium nitrate, calcium nitrate, barium nitrate, and aluminum nitrate being more preferred, and aluminum nitrate being particularly preferred because it has a significant effect of sealing fine defects present on the surface of the zeolite membrane, thereby improving ammonia separation performance.

[0073] The nitrate concentration is usually 10 mol / L or less, with a lower limit of 0.1 mol / L or more, preferably 0.5 mol / L or more, and more preferably 1 mol / L or more. The treatment temperature is usually from room temperature to 150°C or less, and the treatment may be carried out for approximately 10 minutes to 48 hours. These treatment conditions may be appropriately set depending on the type of nitrate and solvent used. The zeolite membrane after the nitrate treatment may be washed with water, and by repeating the water washing, the nitrogen atom content of the zeolite membrane can be adjusted to a preferred range.

[0074] <<Aluminum salt treatment>> The zeolite membrane composite of the present invention may be subjected to an aluminum salt treatment, if necessary. The aluminum salt treatment may be performed while the zeolite membrane composite contains the organic template, or after the organic template has been removed by calcination. The aluminum salt treatment may be performed, for example, by immersing the zeolite membrane composite in a solution containing an aluminum salt. This may have the effect of causing the aluminum salt to seal fine defects present on the membrane surface. Furthermore, when aluminum salt is present in zeolite pores, it has the effect of attracting ammonia gas, and is therefore preferably employed as a method for improving ammonia gas permeability.

[0075] The solvent used in the aluminum salt treatment may be water or an organic solvent as long as the salt dissolves therein, and there is no limitation on the aluminum salt used, but examples include aluminum nitrate, aluminum sulfate, aluminum chloride, aluminum phosphate, aluminum acetate, aluminum carbonate, aluminum hydroxide, etc. These may be used alone or in combination of two or more. The concentration of the aluminum salt is usually 10 mol / L or less, with a lower limit of 0.1 mol / L or more, preferably 0.5 mol / L or more, and more preferably 1 mol / L or more. The treatment temperature is usually from room temperature to 150°C or less, and the treatment may be carried out for about 10 minutes to 48 hours. These treatment conditions may be appropriately set depending on the aluminum salt and the type of solvent used. The zeolite membrane after the aluminum salt treatment may be washed with water, and the Al atom content of the zeolite membrane can be adjusted by repeating the water washing. In order to increase the Si atom / Al atom ratio of the present invention, it is preferable to reduce the concentration or amount of aluminum salt used for treatment or to increase the number of water washings after the aluminum salt treatment. On the other hand, in order to decrease the ratio, it is preferable to increase the concentration or amount of aluminum salt used for treatment or to decrease the number of water washings after the aluminum salt treatment.

[0076] (Silylation treatment) The zeolite composite membrane of the present invention may be subjected to a silylation treatment, if necessary. The silylation treatment is carried out by immersing the zeolite composite membrane in a solution containing, for example, a Si compound. This modifies the zeolite membrane surface with the Si compound, thereby imparting specific physicochemical properties. For example, by reliably forming a layer containing a large amount of Si—OH on the zeolite membrane surface, the polarity of the membrane surface is improved, thereby improving the separation performance of polar molecules. In addition, modifying the zeolite membrane surface with a Si compound can sometimes have the effect of sealing fine defects present on the membrane surface. Furthermore, the pore size of zeolite can be controlled by silylation treatment, and this treatment can also be suitably used as a method for improving the ammonia permeation selectivity.

[0077] The solvent used for the silylation treatment may be water or an organic solvent. The solution may also be acidic or basic, in which case the silylation reaction is catalyzed by the acid or base. There are no limitations on the silylating agent used, but alkoxysilanes are preferred. The treatment temperature is usually from room temperature to 150°C or less, and the treatment may be carried out for approximately 10 minutes to 30 hours. These treatment conditions may be appropriately set depending on the silylating agent and solvent used.

[0078] <<Nitrogen atom content on the zeolite membrane surface>> In the present invention, the content of nitrogen atoms contained in the surface of the zeolite membrane of the present invention can be controlled by, as described above, adjusting the Al atom / Si atom ratio of the zeolite by selecting a cation species containing nitrogen atoms in the zeolite contained in the zeolite membrane, adjusting the content of nitrogen atoms by adjusting the amount of ion exchange by ion exchange, using an organic template (structure-directing agent) containing nitrogen atoms when producing the zeolite membrane as needed and adjusting the amount of the organic template added or the heating temperature and heating time when the organic template is removed by baking, treating the zeolite membrane with nitrate, adjusting the number of times of water washing when washing the nitric acid-treated zeolite membrane with water, or by an appropriate combination of these methods.

[0079] <<Aluminum atom content on the surface of zeolite membrane composite>> As described above, the content of Al atoms contained in the surface of the zeolite membrane composite of the present invention can be controlled by adjusting the Al atom / Si atom ratio in the zeolite contained in the zeolite membrane, treating the zeolite membrane with an aluminum salt, adjusting the number of times the aluminum salt-treated zeolite membrane is washed with water, or by appropriately combining these methods.

[0080] <<Content of alkali metal elements contained on the surface of zeolite membrane composite>> As described above, the content of alkali metal elements contained in the surface of the zeolite membrane composite of the present invention can be controlled by adjusting the Al atom / Si atom ratio in the zeolite contained in the zeolite membrane, adjusting the content of alkali metal elements by adjusting the amount of ion exchange by ion exchange, adjusting the number of times the zeolite membrane is washed with water, or by appropriately combining these methods. The zeolite composite membrane produced in this manner has excellent properties and can be suitably used as the membrane separation means for mixed gases in the present invention.

[0081] <Uses of zeolite membrane composites> The zeolite membrane composite of the present invention can selectively permeate and separate a specific component from a mixed gas containing at least the specific component. For example, it can selectively permeate and separate methanol from a mixed gas containing methanol as the specific component and hydrogen as the other component, or it can selectively permeate and separate ammonia from a mixed gas containing ammonia as the specific component and nitrogen as the other component. Although a mixed gas containing two components is described here, it is also possible to selectively permeate and separate a specific component from a mixed gas containing three or more components. Therefore, it is even more effective when used in combination with a production method that uses such a mixed gas. In particular, since methanol and ammonia are catalytic reactions, the reaction rate slows down when equilibrium is reached or approached, making it difficult to obtain large amounts of methanol or ammonia. By placing a zeolite membrane composite in this reaction field, the produced methanol or ammonia can be selectively removed from the reaction field, allowing for efficient production of methanol or ammonia. By using the more permeable zeolite membrane composite obtained by the present invention, the target products can be obtained even more efficiently. [Example]

[0082] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples as long as it does not deviate from the gist of the invention. Note that the values ​​of various production conditions and evaluation results in the following examples represent preferred upper or lower limit values ​​in the embodiments of the present invention, and a preferred range may be defined by combining the above upper or lower limit values ​​with the values ​​of the following examples or values ​​of the examples themselves.

[0083] (1) Fluorine atom concentration In the zeolite membrane composites of each Example and Comparative Example, the fluorine atom concentration at a depth of 50 nm from the surface of the zeolite was measured by X-ray photoelectron spectroscopy (hereinafter referred to as "XPS"). After measuring the F concentration at the zeolite surface, the zeolite was etched in the depth direction using an Ar ion gun, and the F concentration at a depth of 50 nm was measured. The XPS device used was "KRATOS ULTRA2" manufactured by Shimadzu Corporation, and measurements were performed under the following measurement conditions. X-ray source: Monochromatic Al-Kα (1486.6eV) Output: 15kV-375W Charge neutralization: Filament current = 0.43 V, Filament bias = 1 V, Charge balance = 4 V Ion gun: Ar ions, acceleration voltage 5 kV (10.8 nm / min in SiO2)

[0084] (2) Ratio of silicon atoms to aluminum atoms (Si / Al2) In the zeolite membrane composites of each Example and Comparative Example, Si / Al2 (SA1) at a depth of 200 nm and Si / Al2 (SA2) at a depth of 2000 nm from the surface of the zeolite membrane were measured by XPS. The rate of change was calculated using the following formula (a). ((SA1-SA2) / SA1) × 100 (a) The measurement conditions are the same as those for (1) fluorine atom concentration.

[0085] (3) FT-IR measurement The normalized area intensity of Si-O-AlOH and bridging Si(OH)Al was determined by FT-IR, and the sum of these was used for evaluation. The equipment used was VERTEX 70V (manufactured by Bruker Optics), and the measurement conditions were as follows: Method: Vacuum heating diffuse reflectance method Measurement resolution: 4cm -1 Measurement wavelength range: 7500~600cm -1 Measurement detector: MCT (mercury-cadmium-tellurium) Total measurements: 32 Reference: Diamond powder Temperature program: Degas at room temperature for 15 minutes, heat to 300°C at 10°C / min, hold for 30 minutes, cool to 50°C at 10°C / min.

[0086] Single spectra were extracted before degassing, room temperature degassing (1 minute, 15 minutes), heated degassing (50°C to 300°C in 50°C intervals), 300°C degassing for 30 minutes, and cooled degassing (250°C to 50°C in 50°C intervals). The absorbance spectrum was derived using a single spectrum of the diamond powder (after 15 minutes of degassing at room temperature). The obtained absorbance spectrum was measured at 4000 cm -1After linear baseline subtraction, the KM (Kubelka-Munk) transformation was performed. The KM transformed spectrum was 4000-3050 cm -1 was fitted with six Voigt functions, and the -1 (Si-O-AlOH), 3590 cm -1 The area intensity around the bridging Si(OH)Al was calculated. -1 The intensity was normalized by the peak area around (the overtone of the skeletal vibration). The area intensity was obtained by fitting a peak created with a Viogt function to the shape of the spectrum. Usually, peak area values ​​can be obtained by peak fitting with a Viogt function using the spectrometer analysis software, so this can be used.

[0087] Comparative Example 1 [Production of zeolite membrane composite] (Raw material mixture for hydrothermal synthesis) 0.11 g of sodium aluminate (Kishida Chemical Co., Ltd., containing 62.2% Al2O3 by mass) was added to a mixture of 12.6 g of 50% by mass sodium hydroxide aqueous solution (Wako Co., Ltd.) and 118.4 g of demineralized water, and the mixture was stirred. After confirming that the mixture was dissolved, 30.0 g of colloidal silica (Nissan Chemical Co., Ltd., Snowtex 40) was added, and the mixture was stirred at 50°C for 4 hours to prepare a raw material mixture for hydrothermal synthesis. The composition (molar ratio) of this raw material mixture for hydrothermal synthesis was SiO2 / Al2O3 / NaOH / H2O = 1 / 0.035 / 0.27 / 40.

[0088] (Porous support) The porous support was prepared by cutting an alumina tube (outer diameter 12 mm, inner diameter 9 mm) manufactured by Noritake Co., Ltd. into an 8 cm piece, washing it with demineralized water through a flow path, and then drying it.

[0089] (Seed crystal dispersion) MFI type zeolite was ground in a mortar and prepared, and seed crystals were dispersed in the ground zeolite so that the seed crystal concentration was 0.4 mass %, to prepare a seed crystal dispersion.

[0090] (Production of Zeolite Membrane Composite) The porous support was immersed in the above-mentioned seed crystal dispersion for 30 seconds, and then dried at 70° C. for 1 hour to attach the seed crystals to the porous support. The mass of the attached seed crystals was 0.04 g. The porous support with the attached seed crystals was immersed vertically in a Teflon (registered trademark) inner tube containing the above-mentioned mixture of raw materials for hydrothermal synthesis. The autoclave was then sealed and heated to 180°C in a thermostatic chamber over two hours, after which it was left to stand for 12 hours while heated under autogenous pressure. After the specified time had elapsed, the porous support-zeolite membrane composite was removed from the reaction mixture and allowed to cool. After washing, the porous support-zeolite membrane composite was immersed in 90°C demineralized water for one hour three times. The porous support-zeolite membrane composite was then removed from the demineralized water and dried at 120°C for four hours to obtain a zeolite membrane composite. The results of the evaluation using the above method are shown in Table 1.

[0091] Examples 1 and 2 and Comparative Examples 2 and 3 [Production of zeolite membrane composite] A porous support-zeolite membrane composite was obtained in the same manner as in Comparative Example 1, except that a predetermined amount of sodium fluoride manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. was added to the mixture of raw materials for hydrothermal synthesis. The amount of sodium fluoride (NaF / SiO2 molar ratio) was 0.002 in Example 1, 0.02 in Example 2, 0.2 in Comparative Example 2, and 1 in Comparative Example 3. The results of evaluation in the same manner as in Comparative Example 1 are shown in Table 1.

[0092] [Evaluation of methanol permeability of zeolite membrane composites] Methanol separation evaluation was performed using the module shown schematically in Figure 1. Figure 1 shows a module in which the methanol separation membrane is tubular and the zeolite membrane is on the surface of the tube. The feed gas used for the methanol permeability evaluation was a mixed gas of methanol and hydrogen, and the methanol used was Fujifilm Wako Pure Chemical Industries, Ltd. (99.8%).

[0093] As shown in Fig. 1, a cylindrical zeolite membrane composite 1 is housed in a stainless steel (SUS304) pressure vessel 2, which is temperature-controllable (not shown). One end of the zeolite membrane composite 1 is connected to a pipe 4 via a connection 3, and the other end of the pipe 4 is connected to the stainless steel pressure vessel 2, which is then connected to a pipe (not shown) for supplying a sweep gas S outside the pressure vessel 2. The other end of the zeolite membrane composite 1 is connected to a pipe 4' via a connection 3', and the other end of the pipe 4' is connected to the stainless steel pressure vessel 2, which is then connected to an exhaust gas pipe (not shown) outside the pressure vessel 2. The pressure inside the zeolite membrane composite 1 can be measured by a pressure gauge (not shown) installed in a pipe that supplies a sweep gas.

[0094] The pressure vessel 2 is equipped with a pipe 5 for introducing a mixed gas as a supply gas G and a pipe 6 for discharging a gas that does not permeate the zeolite membrane composite 1 (hereinafter referred to as "non-permeating gas H"). A back pressure valve 7 for adjusting the pressure of the mixed gas between the surface of the zeolite membrane composite 1 and the pressure vessel is connected to the pipe 6, and the back pressure valve 7 is connected to an exhaust gas pipe. Each connection is airtight. In the evaluation of methanol separation using the module shown in Figure 1, methanol is vaporized in advance in a preheater, and then mixed with hydrogen gas. The methanol is supplied at a constant flow rate and composition between the pressure vessel and the surface of the zeolite membrane composite 1, and the pressure of the supply gas is kept constant by the back-pressure valve 7. The gas that does not permeate the zeolite membrane composite 1 is discharged through the pipe 6 as non-permeated gas H.

[0095] A sweep gas S is passed through the inside of the zeolite membrane composite 1, and the sweep gas discharged from the pipe 4 and the gas that has permeated the zeolite membrane composite 1 (hereinafter referred to as "permeated gas T") are discharged from the module through the pipe 4'. Quantitative analysis of each gas component was performed using an online gas chromatograph equipped with a thermal conductivity detector (TCD) using N2 as the internal standard for both the non-permeable gas H and the permeable gas T. After the temperature and gas flow rate had stabilized, the values ​​obtained after the analytical results had stabilized were used. The partial pressure of each component in the module varies from upstream to downstream of the reactor, but the average partial pressures at the inlet and outlet sides are used. The partial pressure of each component at the outlet side was calculated using the ratio of each component determined by gas chromatography. The differential pressure of each component was calculated from the partial pressure difference between the non-permeable gas H and the permeable gas T.

[0096] Based on the measurement results, the permeance [mol / (m 2 The permeance (s·s·Pa) was calculated. For each gas component, the difference between the partial pressure of the gas on the supply side and the partial pressure of the gas on the permeation side is taken as the pressure difference, and the permeation amount per unit time per unit membrane area that the supplied mixed gas comes into contact with is calculated by dividing this pressure difference. Specifically, it can be calculated using the following formula (A). Permeance = Q / (P(supply) - P(transmission)) (A) [In formula (A), Q is the permeation rate [mol / (m 2 s), and P (supply) and P (permeation) represent the partial pressure [Pa] of the gas to be calculated in the supply gas G and the partial pressure [Pa] of the gas to be calculated in the permeation gas T, respectively.

[0097] The evaluations of Examples 1 and 2 and Comparative Examples 1 to 3 were specifically measured under the following conditions. The length of the zeolite membrane composite 1 connected to the module in contact with the mixed gas G was set to 55 mm. Furthermore, a mixed gas of methanol and hydrogen in a volume ratio of 86:150 was supplied as supply gas G from a supply port upstream of the module at a rate of 236 ml / min (0° C., 1 atm equivalent). The pressure between the module and the membrane was controlled by a back pressure valve installed downstream of the module, and the pressure of the mixed gas was set to 0.25 MPaG. N2 was passed through the zeolite membrane composite as a sweep gas at 65 ml / min (0°C, 1 atm equivalent), and the gas that permeated the zeolite membrane composite was carried along with it and discharged from the module.

[0098] Figure 2 shows the amount of sodium fluoride (NaF / SiO2 molar ratio) added to the hydrothermal synthesis raw materials in Examples 1 and 2 and Comparative Examples 1 to 3, and the methanol permeance at a module temperature of 250°C. These results demonstrate that a zeolite membrane composite with high methanol permeability can be obtained by adding a fluorine amount (F / Si molar ratio) greater than 0, preferably 0.001 or greater, or by adding a fluorine amount (F / Si molar ratio) less than 0.2, preferably less than 0.06. A zeolite membrane composite with high methanol permeability can be obtained by adding a fluorine amount (F / Si molar ratio) of 0.002 or greater but less than 0.02. Although the amount of sodium fluoride added is extremely small compared with the other major alumina, silica, and alkali sources, a surprising effect was achieved. It is believed that sodium fluoride does not directly interact with these elements, but rather exerts some kind of repeated influence locally or catalytically.

[0099] The depth profiles of Comparative Example 1 and Example 2 are shown in Figures 3 and 4, respectively. First, in Comparative Example 1, fluorine was detected only on the outermost surface and not in any deeper portion. Although sodium fluoride was not added, it is believed that a small amount of fluorine was detected eluting from the components used during hydrothermal synthesis, specifically the inner tube of the autoclave (made of Teflon). On the other hand, in Example 2, fluorine was detected not only on the outermost surface but also in a portion up to approximately 100 nm, but not in a portion deeper than 100 nm. While fluorine was detected at 400 nm, this is thought to be due to measurement noise, taking into account the detection values ​​before and after. The fact that fluorine was detected not only on the outermost surface but also in a portion up to 100 nm is interpreted as indicating that fluorine was intentionally added. Therefore, it can be seen that the effect can be achieved by containing fluorine at least in a portion 50 nm from the outermost surface, more preferably 0.02 at% or more, even more preferably 0.1 at% or more, but less than 0.44 at%, more preferably 0.40 at% or less, and even more preferably 0.30 at% or less.

[0100] Next, in Comparative Example 1, the Si / Al2 molar ratio is nearly uniform from the surface to the depth. Specifically, the Si / Al2 molar ratio at 2000 nm changes only 0.9% from the Si / Al2 molar ratio at 200 nm. On the other hand, in Comparative Example 2, the Si / Al2 molar ratio changes significantly from the surface to the depth. Specifically, the Si / Al2 molar ratio at 2000 nm changes by 80.5% from the Si / Al2 molar ratio at 2000 nm. Therefore, it can be seen that the effect can be obtained, for example, when the rate of change in the Si / Al2 molar ratio at 2000 nm from the outermost surface to the Si / Al2 molar ratio at 2000 nm is at least 0.9%, more preferably 1.0% or more, and even more preferably 5.0% or more, but less than 80.5%, more preferably 80.0% or less, and even more preferably 60.0% or less. While this is one possibility, it suggests that the surface of the zeolite (i.e., the gas inlet side) has fewer adsorption sites or lower affinity, while the deeper portions (i.e., the gas outlet side) have more adsorption sites or higher affinity, resulting in a structure that allows gas to pass through the zeolite more easily. A small conversion rate allows gas to enter the zeolite but return, resulting in clogging. However, a large conversion rate allows gas to roll downhill toward the outlet, resulting in high permeability. However, adding too much fluorine (F / Si molar ratio) can cause the Si / Al2 molar ratio to change too much, resulting in an unexpected structure, such as a change from an MFI type to a different type in extreme cases. In Example 2, the Si / Al2 molar ratio was approximately 2.0 at a thickness of 2000 nm, raising concerns that the MFI type may not even be formed in portions deeper than 2000 nm. Therefore, appropriately adjusting this conversion rate is the key to creating a desirable zeolite. Furthermore, the Si / Al2 molar ratios at 200 nm from the surface of Comparative Example 1 and Example 2 are characterized by large variations in Comparative Example 1 and small variations in Example 2. This indicates that there is a lot of disorder in the composition near the surface, as well as in the structure. It is suspected that there is a lot of disorder in the entrance structure of the pores through which gas passes, which is causing a large resistance to gas permeation.In other words, it is suggested that the structure of Comparative Example 1 makes it difficult for gas to enter the zeolite, while the structure of Example 2 makes it relatively easy for gas to enter the zeolite. These structures are thought to make it easier for specific components to enter and exit the zeolite membrane composite as a whole, which is linked to the improvement in permeability.

[0101] The FT-IR measurement results for Comparative Example 1 and Examples 1, 2, and 3 are shown in Figure 5. The normalized area intensities of Si-O-AlOH and bridging Si(OH)Al are lower in Examples 1 and 2 than in Comparative Example 1. Si-O-AlOH and bridging Si(OH)Al are bonds that do not exist in an ideal MFI zeolite structure, and it is preferable to have fewer of these. These unintended bonds are thought to cause resistance to the permeation of specific components. Therefore, the sum of the normalized area intensities of Si-O-AlOH and bridging Si(OH)Al is preferably less than 24.2, and more preferably 19.6 or less.

[0102] Table 1 summarizes the amount of sodium fluoride used during the production of the zeolite membrane composite, the fluorine atom concentration at a depth of 50 nm from the surface, the rate of change expressed by formula (a) of the silicon atom to aluminum atom ratio (SA1) at a depth of 200 nm from the surface and the silicon atom to aluminum atom ratio (SA2) at a depth of 2000 nm from the surface, the sum of the normalized area intensities of Si-O-AlOH and bridging Si(OH)Al in FT-IR measurements, and the permeance of MeOH in Comparative Example 1, Examples 1 and 2, and Comparative Examples 2 and 3. The F concentration at a depth of 50 nm in Comparative Example 1 was below the detection limit and is therefore indicated as ND. The F concentration at a depth of 50 nm and the rate of change in SA in Comparative Example 3 were not measured because the amount used was five times that of Comparative Example 2, and the F concentration was clearly high.

[0103] [Table 1] [Industrial Applicability]

[0104] By using the zeolite membrane composite of the present invention, methanol or ammonia can be synthesized more efficiently than conventional methods. Therefore, the zeolite, zeolite membrane composite, zeolite production method, and liquid or gas separation method using the zeolite membrane composite of the present invention are technologies of great industrial value. [Explanation of symbols]

[0105] 1 Zeolite membrane composite 2. Pressure vessel 3, 3' Connection between membrane complex and piping 4, 4' piping 5. Piping for introducing mixed gas 6 Piping 7 Back pressure valve S sweep gas G Supply gas T permeable gas H Non-permeable gas

Claims

1. A zeolite containing 0.02 at % or more and 0.3 at % or less of fluorine atoms at a depth of 50 nm from the surface.

2. The ratio of silicon atoms to aluminum atoms (Si / Al ２ ) is expressed as SA1 at a depth of 200 nm from the surface and as SA2 at a depth of 2000 nm from the surface, the rate of change represented by the following formula (a) is 1.0% or more and 80.0% or less. ((SA1-SA2) / SA1)×100...(a)

3. A zeolite in which the sum of the normalized area intensities of Si--O--AlOH and bridging Si(OH)Al is less than 24.2 when measured by Fourier transform infrared spectroscopy.

4. A zeolite composite membrane comprising a membrane comprising the zeolite according to any one of claims 1 to 3 formed on an inorganic porous support.

5. A method for producing a zeolite by adding a fluorine compound to a raw material mixture for hydrothermal synthesis containing an alumina source and a silica source, wherein the molar ratio of fluorine atoms to silicon atoms (F / Si) in the raw material mixture for hydrothermal synthesis is 0.001 or more and less than 0.

06.

6. The method for producing a zeolite according to claim 5, wherein the fluorine compound is sodium fluoride.

7. A method for separating liquids or gases, which uses the zeolite membrane composite according to claim 4.

8. A method for separating nitrogen and ammonia, which uses the zeolite membrane composite according to claim 4.

9. A method for separating hydrogen and methanol, which uses the zeolite membrane composite according to claim 4.

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