JP2022132360A - Method for producing rho type zeolite - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous support-zeolite composite body which separates, for example, a nitrogen molecule that is a molecule smaller than CH₄ with sufficient treatment capacity and separation performance, a method for producing a zeolite film, and a separation method using the porous support-zeolite composite body.

SOLUTION: A porous support-zeolite film composite body has a porous support and a zeolite film formed on the porous support, contains an RHO type zeolite as the zeolite, and has a peak intensity in vicinity of 2θ=18.7° that is 1.0 time or more of a peak intensity in vicinity of 2θ=8.3°, in an X-ray diffraction pattern obtained by irradiating the surface of the zeolite film with X rays.

SELECTED DRAWING: Figure 2

COPYRIGHT: (C)2022,JPO&INPIT

Description

The present invention uses a zeolite membrane composite containing RHO-type zeolite that is suitable for separating and concentrating a gaseous or liquid mixture consisting of a plurality of components, a method for producing zeolite, and a zeolite membrane composite containing this RHO-type zeolite. The present invention relates to a method for separating fluid that has been trapped.

Carbon dioxide and nitrogen, carbon dioxide and methane, hydrogen and hydrocarbons, hydrogen and oxygen, hydrogen and carbon dioxide, nitrogen and oxygen, paraffins and olefins, for example, in the separation of gases discharged from thermal power plants and petrochemical industries. Zeolite membranes such as A-type membrane, FAU-type membrane, MFI-type membrane, SAPO-34 membrane, DDR-type membrane, CHA-type membrane, etc. are known as zeolite membranes for gas separation used for gas separation.

The A-type membrane is easily affected by moisture, it is difficult to obtain a membrane without crystal gaps, and the separation performance is not high. The pore diameter of the MFI membrane is 0.55 nm, and the pores are rather large for separating gas molecules, and the separation performance is not high.

DDR (Patent Document 1), SAPO-34 (non-patent Document 1) and SSZ-13 (Non-Patent Document 2) are known.

In the separation of carbon dioxide and methane, a CHA-type aluminosilicate zeolite membrane having a SiO ₂ /Al ₂ O ₃ molar ratio of 5 or more described in Patent Document 2 has high permeation performance and high separation performance.

Zeolite membranes have not been reported to separate molecules smaller than _CH4 , such as nitrogen molecules, from gases such as air and flue gas with sufficient throughput and separation performance.

The DDR type (Patent Document 1) has a low carbon dioxide permeance due to the two-dimensional zeolite structure. In addition, although the three-dimensional structure and CHA type SSZ-13 membrane (Patent Document 2) has a sufficiently large amount of CO ₂ permeation, the pore diameter is 3.8 Å, compared to the Kinetic Diameter (3.64 Å) of N ₂ molecules. Due to its large size, the separation performance of _N2 is low.

Patent Document 3 introduces a method of separating ammonia from a mixed gas of ammonia and nitrogen using a specific zeolite having eight-membered oxygen rings. However, the CHA-type zeolite membrane described in Patent Literature 3 cannot obtain a sufficient separation effect.

JP-A-2004-105942 Patent No. 5957828 JP 2014-58433

Shiguang Li et al., "Improved SAPO-34 Membranes for CO2/CH4 Separation", Adv. Mater. 2006, 18, 2601-2603 Halil Kalipcilar et al., "Synthesis and Separation Performance of SSZ-13 Zeolite Membranes on Tubular Supports", Chem. Mater. 2002, 14, 3458-3464

The present invention provides a porous support _- zeolite membrane composite that separates molecules smaller than CH4, such as nitrogen molecules, with sufficient throughput and separation performance, a method for producing the zeolite membrane, and the porous support- An object of the present invention is to provide a separation method using a zeolite membrane composite.

The gist of the present invention is as follows.

[1] A porous support-zeolite membrane composite comprising a porous support and a zeolite membrane formed on the porous support, wherein the zeolite membrane contains RHO-type zeolite, and the zeolite membrane In the X-ray diffraction pattern obtained by irradiating the surface with X-rays, the peak intensity near 2θ = 18.7° is 1.0 times or more the peak intensity near 2θ = 8.3°. porous support-zeolite membrane composite.

[2] A porous support-zeolite membrane composite comprising a porous support and a zeolite membrane formed on the porous support, wherein the zeolite membrane contains RHO-type zeolite, and the zeolite membrane In the X-ray diffraction pattern obtained by irradiating the surface with X-rays, the peak intensity near 2θ = 14.4° is 0.5 times or more the peak intensity near 2θ = 8.3°. porous support-zeolite membrane composite.

[3] In the X-ray diffraction pattern obtained by irradiating the zeolite membrane surface with X-rays, the peak intensity near 2θ = 14.4° is 0.5 times or more the peak intensity near 2θ = 8.3°. The porous support-zeolite membrane composite according to [1], characterized in that:

[4] At 50°C, the CO ₂ permeance is 1.0 × 10 ^-7 (mol/m ² · sec · Pa) or more, and the N ₂ permeance is 3.0 × 10 ^-8 (mol/m ² ·sec·Pa) or less, the porous support-zeolite membrane composite according to any one of [1] to [3].

[5] The porous support-zeolite membrane composite according to any one of [1] to [4], wherein the RHO-type zeolite has a SiO ₂ /Al ₂ O ₃ molar ratio of 4 or more.

[6] The porous support-zeolite membrane composite according to any one of [1] to [5], wherein the Cs content in the zeolite membrane is 1.5 or less in terms of Cs/Al ₂ O ₃ molar ratio. body.

[7] The porous support-zeolite membrane composite according to any one of [1] to [6] is brought into contact with a gas mixture or a liquid mixture comprising a plurality of components to allow components with high permeability to permeate. A method for separating a gaseous or liquid mixture, characterized in that the separation is carried out.

[8] A method for producing RHO-type zeolite, which comprises producing RHO-type zeolite using an aluminosilicate zeolite having a framework density of 15 T/1000 Å or less.

[9] The method for producing an RHO-type zeolite according to [8], wherein the aluminosilicate zeolite contains d6r or lta defined as a composite building unit by the International Zeolite Association (IZA) in its skeleton.

[10] The method for producing RHO-type zeolite according to [8] or [9], wherein the aluminosilicate zeolite is FAU-type zeolite or LTA-type zeolite.

According to the present invention, a porous support-zeolite membrane composite that separates molecules smaller than CH ₄ , such as nitrogen molecules, with sufficient throughput and separation performance, a method for producing the zeolite membrane, and the porous support - Separation methods using zeolite membrane composites are provided.

It is an X-ray chart of a zeolite membrane. It is an X-ray chart of a zeolite membrane. It is an X-ray chart of a zeolite membrane. It is a schematic diagram of the apparatus used for the mixed gas permeation test. It is a schematic diagram of the apparatus used for the permeation test of single-component gas.

Embodiments of the present invention will be described in more detail below. Various modifications can be made within the scope.

The porous support-zeolite membrane composite of the present invention (hereinafter sometimes simply referred to as "zeolite membrane composite") comprises a porous support and a zeolite membrane formed on the surface of the porous support. have. The zeolite membrane is preferably formed by crystallizing zeolite into a membrane.

[Porous support]
The porous support used in the present invention preferably has chemical stability such that zeolite can be crystallized into a film on its surface. Suitable porous supports include gas-permeable porous polymers such as polysulfone, cellulose acetate, aromatic polyamide, vinylidene fluoride, polyethersulfone, polyacrylonitrile, polyethylene, polypropylene, polytetrafluoroethylene, and polyimide. Ceramic sintered bodies such as silica, α-alumina, γ-alumina, mullite, zirconia, titania, yttria, silicon nitride, silicon carbide, metal sintered bodies such as iron, bronze and stainless steel, and mesh-shaped compacts, Examples include inorganic porous materials such as glass and carbon moldings. Among these, inorganic porous supports such as ceramic sintered bodies, metal sintered bodies, glass, and carbon molded bodies are preferred.

The inorganic porous support is preferably a sintered ceramic, which is a solid material whose basic component or most of which is composed of an inorganic non-metallic substance.

Preferred ceramic sintered bodies include ceramic sintered bodies containing alumina such as α-alumina and γ-alumina, silica, mullite, zirconia, titania, yttria, silicon nitride and silicon carbide. These may be a single sintered body, or may be a mixture of a plurality of materials and sintered. A part of the surface of these ceramic sintered bodies may be zeolitized during the synthesis of the zeolite membrane. This increases the adhesion between the porous support and the zeolite membrane.

An inorganic porous support containing at least one of alumina, silica, and mullite (particularly containing at least one of alumina or mullite) is easy to partially zeolize the inorganic porous support. This is more preferable because the bonding between the porous support and the zeolite becomes stronger, and a dense zeolite membrane with high separation performance is easily formed.

The porous support used in the present invention preferably has an action of crystallizing zeolite formed on the porous support on its surface (hereinafter also referred to as "porous support surface").

It is preferable that the pore size of the surface of the porous support is controlled. The average pore diameter of the porous support near the surface of the porous support is usually 0.02 μm or more, preferably 0.05 μm or more, more preferably 0.1 μm or more, more preferably 0.15 μm or more, and particularly preferably 0 .5 μm or more, particularly preferably 1 μm or more, and usually 20 μm or less, preferably 10 μm or less, more preferably 5 μm or less, particularly preferably 2 μm or less.

The surface of the porous support is preferably smooth, and if necessary, the surface may be polished with a file or the like.

The pore size of the portion of the porous support used in the present invention other than the vicinity of the surface of the porous support is not limited and need not be particularly controlled, but the porosity of the other portion is usually 20%. % or more, more preferably 30% or more, 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 and liquid. Body strength tends to decrease.

The shape of the porous support used in the present invention is not limited as long as it can effectively separate gas mixtures and liquid mixtures. and a honeycomb-shaped one having a monolith.

The tubular porous support generally has a length of 2 cm or more, preferably 4 cm or more, more preferably 8 cm or more, particularly preferably 10 cm or more, particularly preferably 20 cm or more, and usually 200 cm or more, preferably 150 cm or less, more preferably 2 cm or more. 100 cm or less. If the length of the porous support is shorter than this range, the amount of fluid to be separated and treated per tube may be small, and if it is longer than this range, the production may be troublesome.

The inner diameter of the tubular porous support is usually 0.2 cm or more, preferably 0.3 cm or more, more preferably 0.4 cm or more, still more preferably 0.5 cm or more, particularly preferably 0.6 cm or more, and most preferably It is 0.7 cm or more, more preferably 0.9 cm or more, and usually 2 cm or less, preferably 1.5 cm or less, and more preferably 1.2 cm or less.

The outer diameter is usually 0.3 cm or more, preferably 0.5 cm or more, more preferably 0.6 cm or more, still more preferably 0.8 cm or more, particularly preferably 1.0 cm or more, and usually 2.5 cm or less, preferably It is 1.7 cm or less, more preferably 1.3 cm or less.

The thickness is usually 0.1 mm or more, preferably 0.3 mm or more, more preferably 0.5 mm or more, still more preferably 0.7 mm or more, particularly preferably 1.0 mm or more, most preferably 1.2 mm or more, It is usually 4 mm or less, preferably 3 mm or less, more preferably 2 mm or less.

If the inner diameter, outer diameter and wall thickness are smaller than these ranges, the strength of the support may be lowered and the support may be easily broken. If the inner diameter and outer diameter are larger than this range, the number of porous supports per unit volume may become small. If the wall thickness is larger than this range, the transmission performance tends to decrease.

[RHO-type zeolite]
The RHO-type zeolite used in the present invention is a code that defines the structure of zeolite defined by the International Zeolite Association (IZA) and indicates the RHO structure. RHO-type zeolites have a structure characterized by having three-dimensional pores consisting of eight-membered oxygen rings with diameters of 3.6×3.6 Å, and the structure is characterized by X-ray diffraction data.

The framework density of the RHO-type zeolite used in the present invention is 14.1 T/1000 Å. Framework density means the number of elements constituting the skeleton other than oxygen per 1000 Å ³ of zeolite, and this value is determined by the structure of zeolite. The relationship between framework density and zeolite structure is shown in ATLAS OF ZEOLITE FRAMEWORK TYPES Fifth Revised Edition 2007 ELSEVIER.

[Zeolite membrane]
The zeolite membrane in the present invention is a membrane-like material composed of zeolite, preferably formed by crystallizing zeolite on the surface of the porous support. In addition to zeolite, the membrane may contain inorganic binders such as silica and alumina, organic substances such as polymers, and silylating agents for modifying the surface of zeolite, if necessary.

The zeolite membrane used in the present invention is characterized by containing RHO-type zeolite (hereinafter sometimes referred to as RHO-type zeolite membrane) as zeolite contained in the zeolite membrane, and preferably containing RHO-type zeolite as a main component. It is something to do. The zeolite membrane may partially contain zeolites of other structures such as mordenite type, MFI type, ANA type, and GIS type, and may contain amorphous components and the like. The zeolite membrane is usually composed of RHO-type zeolite in an amount of 70 wt % or more, preferably 80 wt % or more, more preferably 90 wt % or more.

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, and still more preferably 0.5 μm or more. 7 μm or more, particularly preferably 1.0 μm or more, most preferably 1.2 μm or more. Also, it is usually 100 μm or less, preferably 60 μm or less, more preferably 20 μm or less, still more preferably 10 μm or less, particularly preferably 5 μm or less, and most preferably 3 μm or less. When the thickness of the zeolite membrane is smaller than the above range, defects tend to occur and the membrane tends to have poor separation performance. When the thickness of the zeolite membrane is larger than the above range, the permeability tends to be low.

The particle size of the zeolite in the zeolite membrane is not particularly limited. It is more preferably 100 nm or more, still more preferably 200 nm or more, and particularly preferably 500 nm or more, and the upper limit is equal to or less than the thickness of the film. More preferably, the zeolite particle size is the same as the membrane thickness. This is because the zeolite grain boundary is the smallest when the zeolite particle size is the same as the film thickness. A zeolite membrane obtained by hydrothermal synthesis is preferable because the zeolite particle diameter and the membrane thickness may be the same.

The SiO ₂ /Al ₂ O ₃ molar ratio of the RHO-type zeolite contained in the zeolite membrane is not particularly limited, but is usually 4 or more, preferably 6 or more, more preferably 8 or more, and still more preferably 10 or more, particularly preferably 12 or more. The upper limit of the molar ratio is usually 100 or less, preferably 70 or less, more preferably 50 or less, still more preferably 30 or less, particularly preferably 25 or less, and most preferably 20 or less. If the SiO ₂ /Al ₂ O ₃ molar ratio is less than the lower limit, the durability tends to be lowered, and if it exceeds the upper limit, the gas adsorption capacity tends to be low and the gas permeation amount tends to be small.

The Cs/Al ₂ O ₃ molar ratio of the RHO-type zeolite contained in the zeolite membrane is not particularly limited, but is usually 1.5 or less, preferably 1.2 or less, more preferably 1.0 or less, It is more preferably 0.8 or less, still more preferably 0.6 or less, even more preferably 0.4 or less, particularly preferably 0.2 or less, and most preferably 0.1 or less. When the Cs/Al ₂ O ₃ molar ratio is higher than the upper limit, the pores of the RHO-type zeolite may be clogged with Cs ions, which tends to significantly reduce the amount of gas permeation, which is undesirable. The lower limit of the Cs/Al ₂ O ₃ molar ratio is not particularly limited, and is desirable because the smaller the value, the greater the amount of gas permeation, but it is usually 0.01 or more.

In the RHO-type zeolite membrane, the RHO-type zeolite preferably contains substantially no F element. Such an RHO-type zeolite membrane is formed without using fluorine compounds such as hydrofluoric acid and sodium fluoride as raw materials. The F/Al ₂ O ₃ molar ratio is usually 0.1 or less, preferably 0.05 or less, more preferably 0.01 or less, even more preferably 0.005 or less, even more preferably 0.001 or less, most preferably 0.0007 or less. If the F/Al ₂ O ₃ molar ratio is higher than the upper limit, there is a risk that F will mix into the liquid or gas to be separated during use of the zeolite membrane composite. There is no particular lower limit to the F/Al ₂ O ₃ molar ratio, and although it is desirable that the F element is substantially absent, it is usually at least 1.0×10 ⁻¹⁰ .

The SiO ₂ /Al ₂ O ₃ molar ratio, Cs/Al ₂ O ₃ molar ratio, and F/Al ₂ O ₃ molar ratio of the zeolite constituting the zeolite membrane were determined by scanning electron microscope-energy dispersive X-ray spectroscopy (SEM -EDX). In the case of the zeolite membrane composite, it is the value measured by SEM-EDX for the zeolite membrane of the zeolite membrane composite. The X-ray acceleration voltage is usually measured at 10 kV in order to obtain information only on films of a few microns.

As the zeolite membrane used in the present invention, a membrane-like material composed of zeolite can be used as it is, but it is usually used as a zeolite membrane composite in which zeolite is fixed in the form of a membrane on various supports, preferably It is used as a porous support-zeolite membrane composite described in detail below.

[Method for Forming Zeolite Membrane on Porous Support]
In the porous support-zeolite membrane composite of the present invention, the zeolite is preferably adhered to the surface of the porous support in the form of a membrane, and in some cases, a part of the zeolite membrane is attached to the surface of the porous support. It may also enter and adhere to the inside of the pores near the surface.

Such a zeolite membrane on a porous support can be produced by a method of crystallizing zeolite into a membrane on the surface of the porous support, a method of fixing zeolite to the porous support with an inorganic or organic binder, or a method of attaching zeolite to the porous support. It is formed by a method of fixing a dispersed polymer, a method of impregnating a slurry of zeolite into a porous support, and depending on the case, a method of fixing zeolite to a porous support by suction.

Among these methods, the method of crystallizing the zeolite into a film on the surface of the porous support is preferable. Specifically, the RHO-type zeolite is crystallized into a film by hydrothermal synthesis or the like on the surface of the porous support. A method is preferred.
In the present invention, the crystallized zeolite membrane is preferably dense and preferably free of cracks and continuous micropores inside the membrane.

A zeolite membrane is provided at an arbitrary position on the surface of the porous support. When the tubular porous support is provided with a zeolite membrane, the zeolite membrane may be attached to the outer surface, the inner surface, or both sides depending on the application system. Depending on the configuration of the apparatus, it is desirable to apply a zeolite membrane to the surface that comes into contact with the gas mixture or liquid mixture to be separated, as this will increase the fluid throughput.

In general, since the curvature of the outer surface is smaller than that of the inner surface, the zeolite formed on the surface of the support tends to grow in the same direction. is preferred.

The porous support-zeolite membrane composite of the present invention is a porous support-zeolite membrane composite comprising a porous support and a zeolite membrane formed on the porous support, wherein the zeolite In the X-ray diffraction pattern obtained by irradiating the zeolite membrane surface with X-rays, the peak intensity near 2θ = 18.7° is less than the peak intensity near 2θ = 8.3°. It is characterized by being 1.0 times or more. That is, the zeolite membrane formed on the porous support contains RHO-type zeolite, and in the X-ray diffraction pattern of the zeolite membrane surface, the intensity of the peak near 2θ = 18.7 ° and the intensity of the peak near 2θ = 8.3 ° The peak intensity ratio expressed by the ratio of the intensity of the peak ([intensity of the peak near 2θ = 18.7 °] / [intensity of the peak near 2θ = 8.3 °) (hereinafter referred to as the “peak intensity ratio A”)) is 1.0 or more, preferably 1.2 or more, more preferably 1.5 or more, and still more preferably 1.8 or more. The higher the peak intensity ratio A is, the better.

Further, the porous support-zeolite membrane composite of the present invention is a porous support-zeolite membrane composite comprising a porous support and a zeolite membrane formed on the porous support, The zeolite membrane contains RHO-type zeolite, and in the X-ray diffraction pattern obtained by irradiating the surface of the zeolite membrane with X-rays, the peak intensity near 2θ = 14.4 ° is the peak near 2θ = 8.3 ° It is characterized by being at least 0.5 times the strength. That is, the zeolite membrane formed on the porous support contains RHO-type zeolite, and in the X-ray diffraction pattern of the zeolite membrane surface, the intensity of the peak near 2θ = 14.4 ° and the intensity of the peak near 2θ = 8.3 ° The intensity ratio represented by the ratio of the peak intensity of ([intensity of the peak near 2θ = 14.4 °] / [intensity of the peak near 2θ = 8.3 °) (hereinafter referred to as “peak intensity ratio B” )) is 0.5 or more, preferably 0.7 or more, more preferably 1.0 or more, more preferably 1.5 or more, still more preferably 2.0 or more, particularly preferably 5 or more be. The higher the peak intensity ratio B is, the better.

In particular, the ratio of the peak intensity near 2θ = 18.7° to the peak intensity near 2θ = 8.3° is 1.0 or more, and the peak intensity near 2θ = 14.4° and 2θ It is preferable that the ratio to the peak intensity near =8.3° is 0.5 or more.

The X-ray diffraction pattern is obtained by irradiating the surface on which the zeolite is mainly adhered with X-rays from CuKα as a radiation source, with the scanning axis set to θ/2θ. The shape of the sample to be measured can be anything as long as the surface of the membrane composite on which the zeolite is mainly attached can be irradiated with X-rays. Whole bodies or cut to appropriate sizes as constrained by equipment are preferred.

When the surface of the zeolite membrane composite is curved, the X-ray diffraction pattern may be measured by fixing the irradiation width using an automatically variable slit. The X-ray diffraction pattern in the case of using an automatically variable slit refers to a pattern subjected to variable→fixed slit correction.

In the present invention, the peak intensity refers to the measured value minus the background value.

The peak near 2θ=18.7° refers to the largest peak present in the range of 18.7°±0.6° among the peaks not derived from the substrate.

The peak near 2θ=14.4° refers to the largest peak present in the range of 14.4°±0.6° among the peaks not derived from the substrate.

The peak around 2θ=8.3° refers to the largest peak present in the range of 8.3°±0.6° among the peaks not derived from the substrate.

According to COLLECTION OF SIMULATED XRD POWDER PATTERNS FOR ZEOLITES Fifth Revised Edition 2007 ELSEVIER, the peak near 2θ = 18.7° in the X-ray diffraction pattern is the space group

(No. 229), this is a peak derived from a plane with indices (3, 1, 0) in the RHO structure. The above space group is hereinafter referred to as "Im-3m".

According to COLLECTION OF SIMULATED XRD POWDER PATTERNS FOR ZEOLITES Fifth Revised Edition 2007 ELSEVIER, the peak near 2θ = 14.4° in the X-ray diffraction pattern is the index in the RHO structure when the space group is Im-3m (No. 229). is the peak derived from the (2,1,1) plane.

In addition, according to COLLECTION OF SIMULATED XRD POWDER PATTERNS FOR ZEOLITES Fifth Revised Edition 2007 ELSEVIER, the peak near 2θ = 8.3 ° in the X-ray diffraction pattern has an RHO structure when the space group is Im-3m (No. 229). is a peak derived from a plane with an index of (1, 1, 0) in .

A typical ratio of the peak intensity derived from the (3,1,0) plane to the peak intensity derived from the (1,1,0) plane is according to COLLECTION OF SIMULATED XRD POWDER PATTERNS FOR ZEOLITES Fifth Revised Edition 2007 ELSEVIER is 0.70.

Therefore, if this ratio is 1.0 or more, for example, the (3,1,0) plane when the RHO structure is Im-3m (No. 229) is nearly parallel to the surface of the membrane composite. It is thought that this means that the zeolite crystals are oriented and grown in the same direction. A dense membrane with high separation performance is formed by the orientation and growth of zeolite crystals.

A typical ratio of the intensity of the peak derived from the (2,1,1) plane and the peak intensity derived from the (1,1,0) plane is according to COLLECTION OF SIMULATED XRD POWDER PATTERNS FOR ZEOLITES Fifth Revised Edition 2007 ELSEVIER is 0.07.

Therefore, when this ratio is 0.5 or more, for example, when the RHO structure is Im-3m (No. 229), the (2,1,1) plane is nearly parallel to the surface of the membrane composite. It is thought that this means that the zeolite crystals are oriented and grown in the same direction. The orientation and growth of zeolite crystals form a dense membrane with high separation performance.

Thus, the fact that one of the peak intensity ratios A and B is a value within the above-described specific range means that the zeolite crystals are oriented and grow, and a dense membrane with high separation performance is formed. is shown.

A dense zeolite membrane in which RHO-type zeolite crystals are oriented and grown is obtained by using, for example, a specific aluminosilicate zeolite as an aluminum element source when the zeolite membrane is formed by a hydrothermal synthesis method, as described below. and/or using a specific organic template and/or using a specific alkaline element source.

[Method for producing RHO-type zeolite]
Specifically, the RHO-type zeolite in the present invention is produced by mixing an aluminum element source, a silicon element source, an alkali metal element source, an organic structure directing agent (template), and water, and hydrothermally synthesizing the resulting raw material mixture. It can be manufactured by
The method for producing an RHO-type zeolite according to the present invention is characterized by using an aluminosilicate zeolite having a framework density of 15 T/1000 Å or less as an aluminum element source.

The framework density of the aluminosilicate zeolite used is usually 15 T/1000 Å or less, preferably 14.8 T/1000 Å or less, more preferably 14.6 T/1000 Å ³ or less, still more preferably 14.5 T/1000 Å ³ or less, particularly preferably 14.3 T/1000 Å ³ or less, usually 10 T/1000 Å ³ or more, more preferably 10.5 T/1000 Å ³ or more, still more preferably 10.6 T/1000 Å ³ or more, particularly preferably 10.8 T/1000 Å ³ or more be.

Framework density is determined by Ch. It is a value described in ATLAS OF ZEOLITE FRAME WORK TYPES (Sixth Revised Edition, 2007, ELSEVIER) by Baerlocher et al., and represents skeletal density.

That is, the framework density means the number of T atoms (atoms other than oxygen atoms constituting the framework structure of the zeolite) existing per unit volume of 1000 Å ³ of the zeolite, and this value is determined by the composition of the zeolite. .

A high SAR RHO-type zeolite can be produced by forming a crystal structure again so that the zeolite-derived nanoparts constituting the framework surround the organic structure-directing agent. A zeolite with a framework density of 15 T/1000 Å or less is highly soluble and easily decomposed into nanoparts that constitute the framework, and is thus suitable for the production of RHO-type zeolite. If the framework density is less than 10 T/1000 Å, the zeolites may dissolve too much to serve as nanoparts.

As the aluminosilicate zeolite used as the source of aluminum element, those containing d6r or lta in the skeleton, which are defined as composite building units by the International Zeolite Association (IZA), are easily reconstituted into RHO-type zeolites, and are therefore preferred.

Aluminosilicate zeolites containing d6r or lta in the framework are AEI, AFT, AFX, CHA, EAB, ERI, FAU, GME, KFI, LEV, LTL, LTN, MOZ, MSO, MWW, OFF, SAS, SAT, SAV , SBS, SBT, SZR, TSC, WEN, LTA, CLO, KFI, LTN, PAU, TSC, UFI, more preferably AEI, AFT, AFX, CHA, ERI, FAU, KFI, LEV, LTL, MWW , SAV, LTA, KFI, LTN, PAU, and TSC, more preferably AEI, AFX, CHA, FAU, and LTA, particularly preferably FAU-type zeolite or LTA-type zeolite, and most preferably FAU-type zeolite ( Y-type zeolite).

The silica (SiO ₂ )/alumina (Al ₂ O ₃ ) molar ratio of the aluminosilicate zeolite used as an aluminum element source is usually 3 or more, preferably 5 or more, more preferably 7 or more, still more preferably 10 or more, and still more preferably 15. Above, it is particularly preferably 20 or more, most preferably 25 or more, and usually 100 or less, preferably 85 or less, more preferably 50 or less, and particularly preferably 35 or less. If the silica/alumina molar ratio is greater than the above upper limit, it may be difficult to dissolve in a basic solution. Silica/alumina molar ratios below the lower limit may result in very high solubility in basic solutions. An aluminosilicate zeolite having a silica/alumina molar ratio of 30 or less, particularly 25 or less, particularly 10 or less, is inexpensive and readily available, and is preferable for production.

The aluminosilicate zeolite may be used singly or in combination of two or more.

In the method for synthesizing the RHO-type zeolite of the present invention, an aluminum element source and/or a silicon element source other than the aluminosilicate zeolite is optionally used depending on the Al and Si contents of the target RHO-type zeolite. The amount of the aluminosilicate zeolite and the aluminum element source and/or silicon element source is the total amount of the aluminum element source and/or silicon element source other than the aluminosilicate zeolite, and the amount of the aluminum element source and the silicon element source used as described later. Used.

In the present invention, in order to effectively obtain the effects of the present invention by using the above-mentioned aluminosilicate zeolite, the above-mentioned Aluminosilicate zeolite (zeolite with a framework density of 15 T/1000 Å or less) is preferred. In addition, it is preferable that 50% by weight or more, particularly 70 to 100% by weight, particularly 90 to 100% by weight of the total silicon element source is the above-mentioned aluminosilicate zeolite (zeolite having a framework density of 15 T/1000 Å or less).

<Aluminum element source>
In the present invention, the composition of the raw material mixture may be prepared using an aluminum element source other than the aforementioned aluminosilicate zeolite (zeolite having a framework density of 15 T/1000 Å or less). The aluminum element source other than this aluminosilicate zeolite is not particularly limited, and various known substances can be used. aluminum, aluminum nitrate, aluminum sulfate, aluminum oxide, sodium aluminate, boehmite, pseudo-boehmite, aluminum alkoxide and the like. In addition, the aluminosilicate gel mentioned below as a silicon element source also serves as an aluminum element source. These may be used individually by 1 type, and may be used in mixture of 2 or more types.

From the viewpoint of ease of preparation of the raw material mixture and production efficiency, the molar ratio of aluminum (Al) in the aluminum element source (including aluminosilicate zeolite) to silicon (Si) contained in the raw material mixture other than the seed crystal Al/ Si is usually 0.01 or more, preferably 0.02 or more, more preferably 0.04 or more, more preferably 0.06 or more, usually 1.0 or less, preferably 0.5 or less, more It is preferably 0.2 or less, more preferably 0.1 or less. If the Al/Si ratio is greater than the above upper limit, the SiO ₂ /Al ₂ O ₃ molar ratio of the obtained RHO-type zeolite tends to be low, and the obtained RHO-type zeolite is easily soluble in an alkaline solution, It may be unsuitable for use as seed crystals in synthesizing zeolite membranes. If the Al/Si ratio is less than the above lower limit, it may be difficult to obtain the RHO-type zeolite.

<Silicon element source>
In the present invention, the composition of the raw material mixture may be adjusted by adding a silicon source other than the aluminosilicate zeolite (zeolite with a framework density of 15 T/1000 Å or less). Silicon element sources other than this aluminosilicate zeolite are not particularly limited, and various known substances can be used, for example, fumed silica, colloidal silica, amorphous silica, sodium silicate, methyl silicate, ethyl silicate, Silicon alkoxide such as trimethylethoxysilane, tetraethylorthosilicate, aluminosilicate gel, and the like can be used. Fumed silica, colloidal silica, amorphous silica, sodium silicate, methyl silicate, ethyl silicate, silicon alkoxide, and aluminosilicate gel are preferred. These may be used individually by 1 type, and may be used in mixture of 2 or more types.

The elemental silicon source is used so that the amount of the other raw materials to be used relative to the elemental silicon source is within the preferred range described above or below.

<Alkali metal element source>
Alkali metal atoms contained in the alkali metal element source used in the present invention are not particularly limited, and known ones used for synthesis of zeolite can be used. Crystallization is preferably carried out in the presence of at least one selected alkali metal ion. The alkali metal ion is preferably at least one of sodium, potassium and cesium, particularly preferably sodium and cesium. Including at least one of these alkali metal atoms facilitates the progress of crystallization and makes it difficult for by-products (impurity crystals) to form.

Alkali metal element sources include inorganic acid salts such as hydroxides, oxides, sulfates, nitrates, phosphates, chlorides and bromides of the above alkali metal atoms, acetates, oxalates, citrates, and the like. can be used. These may be used individually by 1 type, and may be used in mixture of 2 or more types.

When an appropriate amount of the alkali metal element source is used, the organic structure-directing agent described later can be easily coordinated to aluminum in a suitable state, thereby facilitating formation of a crystal structure. The molar ratio R/Si between the alkali metal element source (R) and the silicon (Si) contained in the raw material mixture for hydrothermal synthesis other than the seed crystal is usually 0.1 or more, preferably 0.2 or more, and more preferably is 0.25 or more, more preferably 0.3 or more, particularly preferably 0.35 or more, and usually 2.0 or less, preferably 1.5 or less, more preferably 1.0 or less, further preferably 0.35 or more. 8 or less, particularly preferably 0.6 or less, most preferably 0.4 or less.

If the molar ratio (R/Si) of the alkali metal element source to silicon is larger than the above upper limit, the zeolite produced tends to dissolve, and the zeolite may not be obtained or the yield may be extremely low. If R/Si is smaller than the above lower limit, the aluminum element source and the silicon element source as raw materials are not sufficiently dissolved, a homogeneous raw material mixture for hydrothermal synthesis cannot be obtained, and RHO-type zeolite is difficult to form. There is

As mentioned above, it is preferable to use Na and Cs as alkali metal element sources. The molar ratio Na/Cs of Na and Cs is usually 1 or more, preferably 2 or more, more preferably 3 or more, particularly preferably 5 or more, and usually 15 or less, preferably 10 or less, more preferably 8 or less. . If Na/Cs is larger than the above upper limit, the cost of Cs is high, which tends to be disadvantageous in terms of cost. If Na/Cs is less than the above lower limit, the effect of Cs may be too weak, making it difficult to form RHO-type zeolite.

<Organic Structure Directing Agent>
In crystallization of RHO-type zeolite, it is preferable to use an organic template (organic structure-directing agent). Synthesis using an organic template increases the ratio of silicon atoms to aluminum atoms in the crystallized zeolite, improving crystallinity.

Any organic template may be used as long as it can form RHO-type zeolite. Also, one type of template may be used, or two or more types may be used in combination.

In the production of RHO-type zeolites, macrocyclic compounds such as crown ethers, water-soluble cationic polymers, and amines are preferably used as organic templates. Although the macrocyclic compound is not particularly limited, macrocyclic compounds having heteroatoms such as oxygen, nitrogen, and sulfur as electron-donating (donor) atoms are preferred, and are easy to form zeolite crystals. from, especially 12-crown-4-ether, 15-crown-5-ether, 18-crown-6-ether, 24-crown-8-ether, dibenzo-18-crown-6-ether, cryptand [2.2 ], cryptand [2.2.2], and 18-crown-6-ether is particularly preferred.

The molecular weight of the water-soluble cationic polymer is usually 10,000 or more, preferably 100,000 or more, more preferably 150,000 or more, particularly preferably 200,000 or more, and usually 1,000,000 or less, preferably 1,000,000 or less, more preferably 500,000 or less, and still more preferably 400,000. Below, it is 350000 or less especially preferably. If the molecular weight is out of this range, the zeolite will be difficult to crystallize, and RHO-type zeolite may not be obtained, zeolites with other structures may be produced, and the yield may decrease. The water-soluble cationic polymer is not particularly limited, but is preferably a polymer quaternary amine compound such as polydiallyldialkylammonium salt, polydiaminodimethylammonium salt, polyvinylpyridine quaternary salt, polyethyleneimine, polyacrylamide, or the like. , more preferably polydiallyldialkylammonium salts and polydiaminodimethylammonium salts, and particularly preferably polydiallyldimethylammonium chloride.

When a material other than a water-soluble cationic polymer is used as the organic template, the amount of the organic template used is usually the molar ratio to silicon (Si) contained in the raw material mixture other than the seed crystal, from the viewpoint of the ease of crystal formation. 0.01 or more, preferably 0.05 or more, more preferably 0.1 or more, still more preferably 0.15 or more, usually 1 or less, preferably 0.5 or less, more preferably 0.3 or less . If it is less than the above lower limit, the RHO-type zeolite may not be produced sufficiently. On the other hand, if it is larger than the above upper limit, it may be disadvantageous because the cost is high.

When a water-soluble cationic polymer is used as an organic template, the amount of the organic template used is usually 1 in terms of molar ratio relative to silicon (Si) contained in the raw material mixture other than the seed crystal, from the viewpoint of ease of crystal formation. .0×10 ⁻⁶ or more, preferably 1.0×10 ⁻⁵ or more, preferably 2.0×10 ⁻⁵ or more, more preferably 2.5×10 ⁻⁵ or more, usually 1.0×10 ⁻³ or less, preferably 5.0×10 ⁻⁴ or less, more preferably 3.0×10 ⁻⁴ or less, still more preferably 1.3×10 ⁻⁴ or less, still more preferably 8.0×10 ⁻⁵ or less is. Outside the above range, the RHO-type zeolite may not be produced sufficiently.

<Amount of water>
In the method for producing the RHO-type zeolite of the present invention, the amount of water in the raw material mixture for hydrothermal synthesis is, from the viewpoint of the ease of forming crystals, the molar ratio to silicon (Si) contained in the raw material mixture other than seed crystals. It is usually 3 or more, preferably 5 or more, more preferably 8 or more, still more preferably 10 or more. From the viewpoint of cost reduction for waste liquid treatment, it is usually 100 mol or less, preferably 50 or less, more preferably 40 or less, still more preferably 30 or less, and particularly preferably 25 or less.

<Seed crystal>
In the present invention, seed crystals may or may not be added to the raw material mixture for hydrothermal synthesis, but adding seed crystals is desirable in that the synthesis time can be shortened. Zeolites used as seed crystals include LTA-type zeolite and RHO-type zeolite, preferably RHO-type zeolite. By using RHO-type zeolite, RHO-type zeolite can be obtained in a short time.

RHO-type zeolite containing a structure-directing agent is difficult to dissolve and is considered not to dissolve completely during zeolite membrane synthesis. Therefore, the RHO-type zeolite used for seed crystals is preferably an RHO-type zeolite containing a structure-directing agent. . However, RHO-type zeolite synthesized without using a structure-directing agent or from which the structure-directing agent is removed by calcination or the like may be used.

The average particle diameter of the RHO-type zeolite used as seed crystals is usually 0.05 μm or more, preferably 0.1 μm or more, more preferably 0.15 μm or more, particularly preferably 0.3 μm or more, and particularly preferably 0 0.5 μm or more, and usually 5.0 μm or less, preferably 3.0 μm or less, more preferably 2.0 μm or less. If the average particle size is smaller than the above lower limit, it tends to dissolve completely in the initial stage of synthesis, and may not play a role as a seed crystal. If the average particle size is larger than the above upper limit, it may be difficult to act as a seed crystal because it is difficult to dissolve.

The ratio (W ₁ /W ₂ × 100%) of the amount of seed crystals used (weight W ₁ ) to the amount of SiO ₂ (weight W ₂ ) in the raw material mixture for hydrothermal synthesis is 0.1% by weight or more. Also, in order to proceed the reaction more smoothly, it is preferably 0.5% by weight or more, more preferably 1% by weight or more, and particularly preferably 5% by weight or more. In addition, the upper limit of the amount used (W ₁ /W ₂ × 100%) is not particularly limited, but from the viewpoint of suppressing manufacturing costs, it is usually 30% by weight or less, preferably 25% by weight or less, more preferably 22% by weight or less, and further It is preferably 20% by weight or less, particularly preferably 15% by weight or less.

<Preparation of raw material mixture for hydrothermal synthesis>
In the method for producing the RHO-type zeolite of the present invention, before preparing the raw material mixture for hydrothermal synthesis, the above-mentioned structure-directing agent (preferably 18-crown-6-ether) and an alkali metal element source (preferably Na It is preferable to prepare a crown ether-alkaline aqueous solution in advance by mixing a part or all of water and heating to form a complex between the crown ether and Cs.

The temperature during mixing and heating is usually 50° C. or higher, preferably 60° C. or higher, more preferably 75° C. or higher, and usually 110° C. or lower, preferably 100° C. or lower, more preferably 90° C. or lower. If the heating temperature is lower than the above lower limit temperature, the crown ether and Cs may not sufficiently form a complex, making it difficult to form the RHO-type zeolite. Moreover, if the heating temperature is higher than the upper limit temperature, the heating energy is wasted, which may be disadvantageous in terms of cost.

The heating time is usually 1 hour or more, preferably 2 hours or more, more preferably 3 hours or more, and usually 10 hours or less, preferably 7 hours or less, more preferably 5 hours or less. If the heating time is shorter than the above lower limit time, the crown ether and Cs may not sufficiently form a complex, making it difficult to form the RHO-type zeolite. Further, if the heating time is longer than the upper limit time, the heating energy is wasted, which may be disadvantageous in terms of cost.

The resulting crown ether-alkali aqueous solution is added dropwise to the aluminosilicate zeolite as the source of aluminum element, and if necessary, other raw materials are added and mixed to obtain a raw material mixture for hydrothermal synthesis.

<Aging>
The raw material mixture for hydrothermal synthesis prepared as described above may be subjected to hydrothermal synthesis immediately after preparation. is preferred. Particularly in the case of scale-up, the agitation becomes poor and the mixing state of the raw materials becomes insufficient. Therefore, by aging the raw material while stirring it for a predetermined period, it is possible to improve the raw material to a more uniform state.

The aging temperature is usually 100° C. or lower, preferably 80° C. or lower, more preferably 60° C. or lower, and particularly preferably 40° C. or lower. . The aging temperature may be constant during aging, or may be changed stepwise or continuously. The aging time is not particularly limited, but is usually 2 hours or longer, preferably 3 hours or longer, more preferably 5 hours or longer, still more preferably 8 hours or longer, particularly preferably 12 hours or longer, and usually 30 days or shorter, preferably 30 days or longer. It is 10 days or less, more preferably 4 days or less, still more preferably 2 days or less.

<Hydrothermal synthesis>
In the hydrothermal synthesis, the raw material mixture for hydrothermal synthesis prepared as described above or the aged one is placed in a pressure vessel, and under self-generating pressure (autogenous pressure) or under gas heating to the extent that crystallization is not hindered. It is carried out by maintaining a predetermined temperature under pressure, under stirring, while rotating or rocking the container, or in a still state.

The reaction temperature during hydrothermal synthesis is usually 110°C or higher, preferably 120°C or higher, more preferably 130°C or higher, particularly preferably 140°C or higher, and usually 200°C or lower, preferably 180°C or lower, more preferably 180°C or lower. is 170° C. or less, more preferably 160° C. or less. Although the reaction time is not particularly limited, it is usually 10 hours or longer, preferably 20 hours or longer, more preferably 40 hours or longer, still more preferably 60 hours or longer, particularly preferably 70 hours or longer, and usually 30 days or shorter, preferably 10 hours or longer. days or less, more preferably 7 days or less, and even more preferably 5 days or less. The reaction temperature may be constant during the reaction, or may be changed stepwise or continuously.

By carrying out the reaction under the above conditions, zeolite of a type different from RHO-type zeolite is less likely to be produced, and RHO-type zeolite can be obtained in good yield.

<Recovery of RHO-type zeolite>
After the above hydrothermal synthesis, the product RHO-type zeolite is separated from the hydrothermal synthesis reaction solution. The resulting zeolite (hereinafter referred to as "SDA-containing zeolite") usually contains an organic structure-directing agent and/or an alkali metal in pores. The method for separating the zeolite containing SDA and the like from the hydrothermal synthesis reaction solution is not particularly limited, but usually includes a method such as filtration, decantation, or direct drying.

The zeolite containing SDA, etc. separated and recovered from the hydrothermal synthesis reaction solution is washed with water, dried, and then calcined as necessary to remove the organic structure directing agent, etc., used during production, to remove the organic structure directing agent, etc. Free zeolites can be obtained. The organic structure-directing agent can also be removed by the treatment method described below.

Treatment for removing both or one of the organic structure directing agent and alkali metal includes liquid phase treatment using an acidic solution or a chemical solution containing organic structure directing agent decomposition components, ion exchange treatment using resin, etc., and thermal decomposition treatment. can be employed, and these treatments may be used in combination. Generally, the contained organic matter is removed by a method such as firing at a temperature of 300° C. to 1000° C. in an atmosphere of air or an oxygen-containing inert gas, or an inert gas atmosphere, or extraction with an organic solvent such as an aqueous ethanol solution. A structure-directing agent or the like can be removed. Removal of the organic structure-directing agent and the like by calcination is preferable from the standpoint of manufacturability. In this case, the firing temperature is preferably 300° C. or higher, more preferably 400° C. or higher, still more preferably 450° C. or higher, particularly preferably 500° C. or higher, preferably 900° C. or lower, more preferably 850° C. or lower. More preferably, it is 800° C. or less. Nitrogen or the like can be used as the inert gas.

In the method for producing RHO-type zeolite of the present invention, by using an aluminosilicate zeolite as an aluminum element source, it is possible to produce RHO-type zeolite with a wide range of SiO ₂ /Al ₂ O ₃ molar ratios that could not be produced conventionally. can. Therefore, although the SiO ₂ /Al ₂ O ₃ molar ratio of the obtained RHO-type zeolite is not particularly limited, it is usually 100 or less, preferably 70 or less, more preferably 50 or less, still more preferably 40 or less, and more preferably 40 or less. preferably 30 or less, particularly preferably 25 or less, most preferably 20 or less, usually 4 or more, preferably 6 or more, more preferably 8 or more, still more preferably 10 or more, particularly preferably 12 or more . When it is in this range, for example, it has many active sites as a catalyst and is suitably used for uses such as catalysts. It is also desirable as a seed crystal for synthesizing a zeolite membrane because it has an appropriate solubility.

In addition, the SiO ₂ /Al ₂ O ₃ molar ratio referred to here is obtained by completely dissolving a zeolite sample by acid decomposition or alkali fusion, and then by inductively coupled plasma (ICP) emission spectrometry and / or ICP mass spectrometry to determine silicon atoms and aluminum Elemental analysis for determining the atomic content (% by weight), or using a standard sample for determining the content of silicon atoms and aluminum atoms by ICP emission spectrometry and/or ICP mass spectrometry, and the fluorescent X-ray intensity of the analyzed element and A value calculated by creating a calibration curve with the atomic concentration of the analysis element, and using this calibration curve to determine the silicon atom and aluminum atom content (% by weight) in the zeolite sample by X-ray fluorescence spectrometry (XRF). Say.

The average particle size of the RHO-type zeolite obtained by the RHO-type zeolite production method of the present invention is not particularly limited, but is usually 0.1 μm or more, preferably 0.2 μm or more, more preferably 0.5 μm or more, and still more preferably. is 0.8 μm or more, particularly preferably 1 μm or more, and usually 10 μm or less, preferably 8 μm or less, preferably 5 μm or less, more preferably 3 μm or less. If the average particle size is smaller than 0.1 μm, the RHO-type zeolite is likely to dissolve when used as seed crystals for zeolite membrane synthesis, so that the RHO-type zeolite dissolves completely in the initial stage of hydrothermal synthesis and does not act as seed crystals. tend to be unfavorable. In addition, when it is more than the upper limit, when the RHO-type zeolite is used as a seed crystal for zeolite membrane synthesis, the pore size is larger than the pore diameter of the support, so it cannot be well supported on the support, and it tends to be difficult to form a dense membrane. is not desirable. In addition, the above range is preferable from the viewpoint that gas diffusion is enhanced when used as a catalyst or the like, which is useful.

The specific surface area of the produced RHO-type zeolite is usually 300 m ² /g or more, preferably 400 m ² /g or more, more preferably 500 m ² /g or more, as a value measured by N ₂ adsorption after conversion to proton type. , usually 1000 m ² /g or less, preferably 800 m ² /g or less, more preferably 750 m ² /g or less. This range is preferable in that the number of active sites present on the inner surface of the pores increases when used as a catalyst or the like.

[Method for producing porous support-zeolite membrane composite]
The porous support-zeolite membrane composite of the present invention can be produced by, for example, (1) a method of crystallizing zeolite on a support into a membrane, and (2) 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; (4) a method of impregnating a support with a slurry of zeolite and, in some cases, sucking the zeolite onto the support, and the like. can be manufactured by

Among these, the method of crystallizing zeolite in the form of a film on a ceramic support is particularly preferred. The method of crystallization is not particularly limited, but a preferred method is to put the support in a raw material mixture for hydrothermal synthesis used for zeolite production and directly hydrothermally synthesize the zeolite on the surface of the support. .

That is, in the same manner as in the above-described RHO-type zeolite production method, an aluminum element source, a silicon element source, an alkali metal element source, an organic structure directing agent, and water are mixed, and the resulting raw material mixture for hydrothermal synthesis is added with a porous A zeolite membrane composite containing RHO-type zeolite as a main component can be obtained by hydrothermally synthesizing a support (preferably a support having seed crystals attached thereto) immersed therein.

As the raw material mixture for hydrothermal synthesis used in the production of the zeolite membrane composite containing RHO-type zeolite as the main component, the same raw material mixture for hydrothermal synthesis used in the production of RHO-type zeolite described above may be used. In order to produce a defect-free, dense film on a porous support, it is preferable to use a raw material mixture for hydrothermal synthesis containing an aluminum element source, an alkali metal element source, an organic structure-directing agent, and water, which will be described below. .

<Aluminum element source>
The aluminum element source used in the production of the porous support-zeolite membrane composite is not particularly limited, but includes aluminosilicate zeolite, amorphous aluminum hydroxide, aluminum hydroxide having a gibbsite structure, and aluminum hydroxide having a bayerite structure. , aluminum nitrate, aluminum sulfate, aluminum oxide, sodium aluminate, boehmite, pseudoboehmite, aluminum alkoxide, aluminosilicate gel, etc., aluminosilicate zeolite, amorphous aluminum hydroxide, sodium aluminate, boehmite, pseudoboehmite, aluminum Alkoxides and aluminosilicate gels are preferred, and aluminosilicate zeolite, amorphous aluminum hydroxide, sodium aluminate and aluminosilicate gels are particularly preferred. These may be used individually by 1 type, and may be used in mixture of 2 or more types.

As the aluminosilicate zeolite used as the aluminum element source, the same aluminosilicates as those used in the production of the RHO-type zeolite described above are preferred.

The aluminosilicate zeolite may be used singly or in combination of two or more. When an aluminosilicate zeolite is used as the aluminum element source, the aluminosilicate zeolite preferably accounts for 50% by weight or more, particularly 70 to 100% by weight, particularly 90 to 100% by weight, of the total aluminum element source. In addition, it is preferable that 50% by weight or more, particularly 70 to 100% by weight, particularly 90 to 100% by weight of the total silicon element source is the above-mentioned aluminosilicate zeolite. When the ratio of the aluminosilicate zeolite is within this range, the SAR of the RHO-type zeolite membrane is high, and the zeolite membrane is excellent in acid resistance and water resistance and has a wide range of applications.

The preferred range of the amount of the aluminum element source (including the above-mentioned aluminosilicate zeolite and other aluminum element sources) (the above-mentioned Al/Si ratio) relative to the silicon (Si) contained in the raw material mixture other than the seed crystal is It is the same as the production of the RHO-type zeolite described above. That is, it is usually 0.01 or more, preferably 0.02 or more, more preferably 0.04 or more, still more preferably 0.06 or more, and usually 1.0 or less, preferably 0.5 or less, more preferably is 0.2 or less, more preferably 0.1 or less.

If the Si/Al ratio is larger than the above upper limit, the SiO ₂ /Al ₂ O ₃ molar ratio of the obtained RHO-type zeolite membrane tends to be low, and the obtained RHO-type zeolite membrane has water resistance and acid resistance. is low, and its use as a zeolite membrane may be limited. If the Si/Al ratio is less than the above lower limit, it may be difficult to obtain an RHO-type zeolite membrane.

<Silicon element source>
In the present invention, the silicon element source of the raw material mixture for hydrothermal synthesis used in the production of the porous support-zeolite membrane composite is not particularly limited, but usually the silicon element source used in the above-described RHO-type zeolite production method is used. fumed silica other than aluminosilicate zeolite, colloidal silica, amorphous silica, sodium silicate, methyl silicate, ethyl silicate, silicon alkoxide such as trimethylethoxysilane, tetraethyl orthosilicate, aluminosilicate gel, etc. preferably aluminosilicate zeolite, fumed silica, colloidal silica, sodium silicate, methyl silicate, silicon alkoxide and aluminosilicate gel, more preferably aluminosilicate zeolite, colloidal silica and sodium silicate. These may be used individually by 1 type, and may be used in mixture of 2 or more types.

The elemental silicon source is used so that the amount of the other raw materials to be used relative to the elemental silicon source is within the preferred range described above or below.

<Alkali metal element source>
The porous support-zeolite membrane composite of the present invention (hereinafter sometimes referred to as "porous support-RHO type zeolite membrane composite" or simply "RHO type zeolite membrane composite" or "zeolite membrane composite") The alkali metal atoms contained in the alkali metal element source of the raw material mixture for hydrothermal synthesis used in the production of can be the same as those used in the above-described method for producing the RHO-type zeolite membrane.
The appropriate amount of the alkali metal element source in the raw material mixture for hydrothermal synthesis used in the production of the porous support-RHO type zeolite membrane composite is mol relative to silicon (Si) contained in the raw material mixture for hydrothermal synthesis other than seed crystals. ratio is usually 0.1 or more, preferably 0.2 or more, more preferably 0.25 or more, still more preferably 0.3 or more, particularly preferably 0.5 or more, and usually 2.0 or more, preferably It is 1.5 or less, more preferably 1.0 or less, still more preferably 0.8 or less, and particularly preferably 0.6 or less.
If the molar ratio of the alkali metal element source to silicon is at least this upper limit, the resulting zeolite is likely to dissolve, and the zeolite membrane is likely to have defects, resulting in a zeolite membrane with low separation performance, which may be unsuitable. If it is less than this lower limit, the aluminum element source and the silicon element source as raw materials may not be sufficiently dissolved, and it may be difficult to form RHO-type zeolite, making it difficult to obtain a dense RHO-type zeolite membrane.
In the present invention, it is preferable to use an alkali metal element source containing Na and Cs, and the molar ratio of Na and Cs is usually 1 or more, preferably 1.5 or more, more preferably 2 or more as Na/Cs, It is usually 10 or less, preferably 8 or less, more preferably 5 or less, still more preferably 3 or less. If the content is below the above lower limit, the cost of Cs is high, which tends to be disadvantageous in terms of cost. If the content is above the above upper limit, the effect of Cs may be too weak, making it difficult to form RHO-type zeolite, making it difficult to obtain a dense RHO-type zeolite membrane.

<Organic Structure Directing Agent>
An organic template (organic structure-directing agent) can be used in the production of the porous support-RHO type zeolite membrane composite, and one synthesized using an organic template is preferred. By synthesizing using an organic template, the ratio of silicon atoms to aluminum atoms in the crystallized zeolite is increased, the crystallinity is improved, and a zeolite membrane excellent in acid resistance and water resistance is suitable.

As the organic template, the same template as described in the RHO-type zeolite production method can be used in the same amount.

<Amount of water>
The amount of water in the raw material mixture for hydrothermal synthesis is usually 10 or more, preferably 20 or more, more preferably 30 or more, and still more preferably 40 or more in terms of molar ratio to silicon (Si) contained in the raw material mixture other than seed crystals. , particularly preferably 50 or more, usually 200 mol or less, preferably 150 or less, more preferably 100 or less, still more preferably 80 or less, particularly preferably 60 or less. If it is larger than the above upper limit, the reaction mixture may be too dilute, making it difficult to form a dense film without defects. If it is less than 10, the reaction mixture is so dense that spontaneous nucleation is likely to occur, inhibiting the growth of the RHO-type zeolite from the support and making it difficult to form a dense membrane.

<Preparation of raw material mixture for hydrothermal synthesis>
Before preparing the raw material mixture for hydrothermal synthesis, the structure-directing agent 18-crown-6-ether and the alkali metal element source (Na source and Cs source) and some or all of the water are mixed and heated. It is desirable to prepare a crown ether-alkaline aqueous solution in advance and form a complex between the crown ether and Cs.

The preferred temperature and time ranges for mixing and heating are the same as in the above-described method for producing RHO-type zeolite.

The resulting crown ether-alkali aqueous solution is added dropwise to the aluminosilicate zeolite as the source of aluminum element, and if necessary, other raw materials are added and mixed to obtain a raw material mixture for hydrothermal synthesis.

<Aging>
The raw material mixture for hydrothermal synthesis prepared as described above may be aged in the same manner as in the above-described method for producing RHO-type zeolite.

<Seed crystal>
In the hydrothermal synthesis, it is not always necessary to have seed crystals present in the reaction system, but the addition of the seed crystals promotes the crystallization of the zeolite on the support. The method of adding seed crystals is not particularly limited, and may be a method of adding seed crystals to an aqueous reaction mixture as in the synthesis of powdered zeolite, a method of depositing seed crystals on a support, or both. can be used.

When producing a zeolite membrane composite, it is preferable to attach seed crystals to the support. By adhering seed crystals to the support in advance, a dense zeolite membrane with good separation performance can be easily formed.

As for the seed crystals to be used, any type of zeolite can be used as long as it promotes crystallization. It is preferable to use, as seed crystals, RHO-type crystals of the same crystal type, or zeolite containing d6r or lta defined as a composite building unit by IZA in the skeleton, as the seed crystals are easily reconstituted into RHO-type zeolite. Specific examples of zeolites suitable as seed crystals include RHO-type zeolite, LTA-type zeolite, and FAU-type zeolite. RHO-type zeolite and LTA-type zeolite are more preferable, and RHO-type zeolite is particularly preferable. One type of these seed crystals may be used, or two or more types may be used in combination. When these zeolites are used as seed crystals, a dense RHO-type zeolite membrane composite can be obtained in a short time.

The RHO-type zeolite used for the seed crystal may be an RHO-type zeolite containing a structure-directing agent, or an RHO-type zeolite that does not contain a structure-directing agent by being synthesized or calcined without using a structure-directing agent. Either of these may be used, but RHO-type zeolite containing a structure-directing agent is particularly desirable because it is difficult to dissolve, and it is thought that RHO-type zeolite does not dissolve completely during synthesis and tends to become a nucleus when RHO-type zeolite grows.

If seed crystals with a large average particle size are used, the seed crystals may detach from the support during hydrothermal synthesis and may not play their role. Desirably, it may be pulverized and used as needed. The particle size is usually 1 nm or more, preferably 10 nm or more, more preferably 50 nm or more, still more preferably 0.1 μm or more, particularly preferably 0.5 μm or more, most preferably 1 μm or more, and usually 5 μm or less, preferably It is 3 µm or less, more preferably 2 µm or less, and particularly preferably 1.5 µm or less.
If the average particle size is smaller than the above lower limit, it tends to dissolve completely in the initial stage of synthesis, and may not play a role as a seed crystal. If the average particle size is larger than the above upper limit, it may be difficult to act as a seed crystal because it is difficult to dissolve.

The method for depositing seed crystals on the support is not particularly limited. A suction method in which crystals are dispersed in a solvent such as water, a support sealed at one end is immersed in the dispersion, and then the support is sucked from the other end to firmly adhere seed crystals to the surface of the support. A method of mixing seed crystals with a solvent such as water to form a slurry and applying the slurry onto a support can be used. The dipping method and the suction method are desirable for controlling the amount of seed crystals adhered and producing a membrane composite with good reproducibility. is desirable. In addition, for the purpose of bringing the seed crystals into close contact with the support and/or removing excess seed crystals, following the dipping method or the suction method, the support with the seed crystals adhered to it may be rubbed with a finger or the like wearing a latex glove. is also preferably performed.

Although the solvent for dispersing the seed crystals is not particularly limited, water is particularly preferred. The amount of seed crystals to be dispersed is not particularly limited, and is usually 0.05% by weight or more, preferably 0.1% by weight or more, more preferably 0.5% by weight or more, and still more preferably 0.5% by weight or more, based on the total weight of the dispersion. is at least 1% by weight, particularly preferably at least 2% by weight. Also, it is usually 20% by weight or less, preferably 10% by weight or less, more preferably 5% by weight or less, and still more preferably 3% by weight or less.

If the amount of seed crystals to be dispersed is too small, the amount of seed crystals adhering to the support is small, resulting in areas where zeolite is not formed partially on the surface of the support during hydrothermal synthesis, resulting in defective membranes. there is a possibility. If the amount of seed crystals in the dispersion is too large, the amount of seed crystals adhering to the support becomes almost constant in the dipping method or the coating method. be.

It is desirable to form a zeolite membrane after attaching seed crystals to a support by a dipping method, a suction method, or applying a slurry, followed by drying. The drying temperature is generally 50°C or higher, preferably 80°C or higher, more preferably 100°C or higher, and generally 200°C or lower, preferably 180°C or lower, more preferably 150°C or lower. The drying time is not a problem as long as it is sufficiently dried, but it is usually 10 minutes or more, preferably 30 minutes or more, and although the upper limit is not specified, it is usually 5 hours or less from an economical point of view.

For the purpose of bringing the seed crystals into close contact with the support after drying and/or removing excess seed crystals, the support with the seed crystals attached is rubbed with a finger wearing a latex glove. Pushing is also preferably performed.

The amount of seed crystals deposited in advance on the support is not particularly limited, and is usually 0.1 g or more, preferably 0.5 g or more, more preferably 1 g or more, more preferably 1 g or more, in terms of weight per ^square meter of substrate surface. is 3 g or more, and usually 100 g or less, preferably 50 g or less, more preferably 10 g or less, still more preferably 8 g or less.

If the amount of seed crystals is less than the lower limit, it becomes difficult to form crystals, which tends to result in insufficient film growth or non-uniform film growth. In addition, if the amount of seed crystals exceeds the upper limit, the seed crystals increase the unevenness of the surface, and the seed crystals that have fallen from the surface of the support facilitate the growth of spontaneous nuclei, hindering film growth on the support. It may be done. In either case, it tends to be difficult to form a dense zeolite membrane.

<Hydrothermal synthesis>
When a zeolite membrane is formed on a support by hydrothermal synthesis, there is no particular limitation on the method of immobilizing the support, and any configuration such as vertical placement or horizontal placement can be employed.

In the hydrothermal synthesis, the support supporting seed crystals as described above and the raw material mixture for hydrothermal synthesis prepared as described above or the aqueous gel obtained by aging the same are placed in a pressure vessel, and under self-generating pressure, or crystals are produced. This is carried out by maintaining a predetermined temperature under a gas pressurization that does not hinder the curing, under stirring, while rotating or rocking the container, or in a stationary state. Hydrothermal synthesis under static conditions is desirable for obtaining a dense RHO-type zeolite membrane composite in that it does not inhibit crystal growth from seed crystals on the support.

The temperature of hydrothermal synthesis when forming the zeolite membrane is not particularly limited, but is usually 110° C. or higher, preferably 120° C. or higher, more preferably 130° C. or higher, particularly preferably 140° C. or higher, and usually 200° C. or lower. It is preferably 180° C. or lower, more preferably 170° C. or lower, and still more preferably 160° C. or lower. If the reaction temperature is too low, it may become difficult to crystallize the zeolite. Also, if the reaction temperature is too high, zeolite of a type different from the zeolite of the present invention may be likely to be produced.

Although the reaction time is not particularly limited, it is usually 10 hours or longer, preferably 20 hours or longer, more preferably 40 hours or longer, still more preferably 60 hours or longer, particularly preferably 70 hours or longer, and usually 30 days or shorter, preferably 10 days. 7 days or less, more preferably 5 days or less. A type of zeolite different from the zeolite in the present invention may be likely to form.

The reaction temperature may be constant during the reaction, or may be changed stepwise or continuously.

The pressure during the formation of the zeolite membrane is not particularly limited, and the autogenous pressure generated when the aqueous reaction mixture placed in the closed container is heated to this temperature range is sufficient. Furthermore, if necessary, an inert gas such as nitrogen may be added.

The zeolite membrane composite obtained by hydrothermal synthesis is washed with water and then dried. The drying temperature is generally 50° C. or higher, preferably 80° C. or higher, more preferably 100° C. or higher, and generally 200° C. or lower, preferably 150° C. or lower.

The drying time is not particularly limited as long as the zeolite membrane is sufficiently dried, and is preferably 0.5 hours or longer, more preferably 1 hour or longer. The upper limit is not particularly limited, and is usually within 200 hours, preferably within 150 hours, more preferably within 100 hours.

It is also possible to improve the density of the zeolite membrane by repeating the hydrothermal synthesis several times. When the hydrothermal synthesis is repeated multiple times, the zeolite membrane composite obtained in the first hydrothermal synthesis is washed with water, dried by heating, and then immersed again in a newly prepared aqueous reaction mixture to perform the hydrothermal synthesis. Do it. The zeolite membrane composite obtained after the first hydrothermal synthesis does not necessarily need to be washed with water or dried, but by washing with water and drying, the composition of the aqueous reaction mixture can be maintained at the intended composition. When synthesized multiple times, the number of times of synthesis is usually 1 or more, preferably 2 or more, and usually 10 or less, preferably 5 or less, more preferably 3 or less.

When hydrothermal synthesis is carried out in the presence of an organic template, the organic template can be removed by, for example, heat treatment or extraction, preferably heat treatment, that is, calcination, after washing the obtained zeolite membrane composite with water. Appropriate.

The firing temperature is usually 250°C or higher, preferably 300°C or higher, more preferably 350°C or higher, still more preferably 400°C or higher, and usually 800°C or lower, preferably 700°C or lower, further preferably 600°C or lower, particularly preferably 600°C or lower. is below 500°C.

If the calcination temperature is too low, the proportion of the organic template remaining tends to increase, and the zeolite has fewer pores, which may reduce the amount of permeation during separation and concentration. If the calcination temperature is too high, the difference in coefficient of thermal expansion between the support and the zeolite will increase, which may make the zeolite membrane more susceptible to cracking, resulting in loss of compactness and lower separation performance.

The firing time varies depending on the rate of temperature increase and the rate of temperature decrease, but is not particularly limited as long as the organic template is sufficiently removed, and is preferably 1 hour or longer, more preferably 5 hours or longer. The upper limit is not particularly limited, and is usually within 200 hours, preferably within 150 hours, more preferably within 100 hours, particularly preferably within 24 hours. Firing may be performed in an air atmosphere, but may be performed in an oxygen-added atmosphere.

It is desirable that the rate of temperature rise during firing be as slow as possible in order to reduce cracking of the zeolite membrane due to the difference in thermal expansion coefficient between the support and the zeolite. The heating rate is usually 5°C/min or less, preferably 2°C/min or less, more preferably 1°C/min or less, and particularly preferably 0.5°C/min or less. Usually, it is 0.1° C./min or more in consideration of workability.

Also, the cooling rate after firing must be controlled to avoid cracks in the zeolite membrane. As with the heating rate, the slower the better. The temperature drop rate is usually 5°C/min or less, preferably 2°C/min or less, more preferably 1°C/min or less, and particularly preferably 0.5°C/min or less. Usually, it is 0.1° C./min or more in consideration of workability.

The zeolite membrane may be ion-exchanged if necessary. When Cs is used in synthesizing the RHO-type zeolite membrane composite of the present invention, ion exchange is desirable because Cs ions clog the pores and reduce the gas permeability coefficient. Ion exchange is usually performed after removal of the template when synthesized using a template. Ions to be exchanged include protons, alkali metal ions such as Na ⁺ , K ⁺ , and Li ⁺ , alkaline earth metal ions such as Ca ²⁺ , Mg ²⁺ , Sr ²⁺ , Ba ²⁺ , Fe ²⁺ , Fe ³⁺ , and Cu ²⁺ . , Zn ²⁺ , Ag ⁺ and other transition metal ions and Al ³⁺ . Among these, proton, Na ⁺ , K ⁺ , and Li ⁺ are preferred, and Na ⁺ is particularly preferred, in that they do not clog pores due to their small size and can increase the gas permeability coefficient.

Ion exchange is performed by immersing the zeolite membrane composite after calcination (when using a template, etc.) in an aqueous solution containing ions to be exchanged and heating. The ion concentration of the aqueous solution containing ions to be exchanged is usually 0.01 mol/L or more, preferably 0.1 mol/L or more, more preferably 0.5 mol/L or more, still more preferably 1 mol/L or more, and usually 5 mol/L or more. L or less, preferably 2 mol/L or less. If the ion concentration is lower than the lower limit, ion exchange may not be sufficiently performed. If the ion concentration is higher than the upper limit, the zeolite may dissolve and the zeolite membrane may lose its compactness, resulting in lower separation performance.

Types of counter ions generally include NO ₃ ⁻ and Cl ⁻ , and NO ₃ ⁻ is particularly preferred because it decomposes into gas upon firing. Also, NH ₄ NO ₃ is preferably used when ion-exchanging protons.

The temperature for ion exchange is usually room temperature or higher, preferably 40° C. or higher, particularly preferably 70° C. or higher, and usually 150° C. or lower, preferably 130° C. or lower, particularly preferably 100° C. or lower. If the temperature is lower than the lower limit, the rate of ion exchange may be slow and insufficient exchange may occur. If the temperature is higher than the upper limit, the zeolite may be dissolved and the zeolite membrane may lose its compactness, resulting in lower separation performance. The container used for heating is not particularly limited, but a closed container such as an autoclave is preferably used.

The heating time is not particularly limited, but is usually 30 minutes or longer, preferably 45 minutes or longer, more preferably 1 hour or longer, and usually 2 hours or shorter, preferably 1.5 hours or shorter. If the heating time is shorter than the lower limit, ion exchange may not be sufficient. If the heating time is longer than the upper limit, the zeolite may be dissolved, the denseness of the zeolite membrane may be lost, and the separation performance may be lowered.

After the ion exchange, it is desirable to sufficiently remove the aqueous solution used for the ion exchange by washing with water or the like. Furthermore, it may be fired at 200° C. to 500° C. if necessary.

In ion exchange, the ratio of exchanged ions can be increased by exchanging the solution and repeating the above-described treatment. When the ion exchange is repeated, it may be carried out after washing with water, after washing with water and drying, or after calcination. Further, depending on the purpose, it may be exchanged with NH ₄ NO ₃ to exchange with protons and then exchanged with metal ions such as Na + .

The number of repeated ion exchanges is usually 10 times or less, preferably 5 times or less. If the number of times of ion exchange is more than the upper limit, the zeolite is dissolved, the density of the zeolite membrane is lost, and the separation performance is lowered, which is not preferable.

The weight of the zeolite membrane obtained by subtracting the weight of the support before synthesis in the zeolite membrane composite after drying when synthesized without using an organic template or after calcination when synthesizing with an organic template is Usually 10 g/m ² or more, preferably 50 g/m ² or more, more preferably 100 g/m ² or more, and usually 1 kg/m ² or less, preferably 500 g/m ² or less, more preferably 300 g/m ² or less . When the weight of the zeolite membrane is less than the above lower limit, defects are likely to occur and the separation performance may be insufficient. When the weight is above the above upper limit, the amount of permeation tends to decrease, and the throughput tends to be insufficient.

The air permeation amount of the zeolite membrane composite after ion exchange is usually 300 L for zeolite membranes that have been ion-exchanged after drying if synthesized without using an organic template, or after calcination if synthesized using an organic template. /(m ² ·h) or less, preferably 200 L/(m ² ·h) or less, more preferably 180 L/(m ² ·h) or less. Although the lower limit of the permeation amount is not particularly limited, it is usually 0.01 ml/(m ² ·h) or more.

Here, the amount of air permeation is the amount of air permeation when the zeolite membrane composite is placed under atmospheric pressure and the inside of the zeolite membrane composite is connected to a vacuum line of 5 kPa, as described in detail in the section of Examples. [L/(m ² ·h)].

The CO ₂ permeance of the zeolite membrane composite after ion exchange is usually 1.0% for zeolite membranes that have undergone ion exchange after drying when synthesized without using an organic template, after calcination when synthesized using an organic template. 0×10 ⁻⁷ (mol/(m ² ·sec·Pa)) or more, preferably 1.2×10 ⁻⁷ (mol/(m ² ·sec·Pa)) or more, more preferably 1.4×10 ⁻⁷ (mol/(m ² ·sec·Pa)) or more, usually 1.0×10 ⁻⁴ (mol/(m ² ·sec·Pa)) or less, preferably 1.0×10 ⁻⁵ ( mol/(m ² ·sec·Pa)) or less, more preferably 5.0×10 ⁻⁶ (mol/(m ² ·sec·Pa)) or less.

In addition, the permeance of N ₂ is usually 1.0×10 ⁻¹⁰ (mol/(m ² ·sec·Pa)) or more, preferably 5.0×10 ⁻¹⁰ (mol/(m ² ·sec·Pa)). above, more preferably 1.0×10 ⁻⁹ (mol/(m ² ·sec·Pa)) or more, usually 3.0×10 ⁻⁸ (mol/(m ² ·sec·Pa)) or less, Preferably 2.7×10 ⁻⁸ (mol/(m ² ·sec·Pa)) or less, more preferably 2.5×10 ⁻⁸ (mol/(m ² ·sec·Pa)) or less, still more preferably It is 2.3×10 ⁻⁸ (mol/(m ² ·sec·Pa)) or less.

In addition, the permeance of CH ₄ is usually 1.0×10 ⁻¹¹ (mol/(m ² ·sec·Pa)) or more, preferably 1.0×10 ⁻¹⁰ (mol/(m ² ·sec·Pa)). above, more preferably 1.0×10 ⁻⁹ (mol/(m ² ·sec·Pa)) or more, usually 3.0×10 ⁻⁸ (mol/(m ² ·sec·Pa)) or less, It is preferably 1.0×10 ⁻⁸ (mol/(m ² ·sec·Pa)) or less, more preferably 5.0×10 ⁻⁹ (mol/(m ² ·sec·Pa)) or less.

Here, the permeance of each gas means that after the zeolite membrane composite is sufficiently dried, the pressure on the feed side is set to 0.4 MPa (absolute pressure) and the pressure on the permeate side is increased. It is the value at 50° C. when the pressure difference is 0.3 MPa.

The drying conditions of the zeolite membrane composite when measuring the permeance of various gases are not particularly limited as long as they are sufficiently dry conditions, but it is desirable to dry by heating, and the heating temperature is usually 100 ° C. or higher, preferably 140 ° C. or higher. , more preferably 170°C or higher, usually 300°C or lower, preferably 250°C or lower. Moreover, it is desirable to dry while permeating easily permeable gas, and it is desirable to dry while permeating He or H ₂ . At that time, the pressure difference between the feed side and the permeation side is usually 0.1 MPa or more, preferably 0.2 MPa or more, more preferably 0.3 MPa or more, and usually 1 MPa or less, preferably 0.8 MPa or less, more preferably It is 0.5 MPa or less. The drying time is usually 1 hour or more, preferably 1.5 hours or more, and usually 5 hours or less, preferably 3 hours or less, more preferably 2 hours or less. Drying can be most efficiently performed within the above range.

The zeolite membrane composite containing the RHO-type zeolite obtained in this manner has excellent properties, and can be suitably used as a membrane separation means for a mixture of gases or liquids in the present invention, particularly as a membrane separation means for N ₂ separation. can.

[Separation of gas mixture]
The zeolite membrane composite of the present invention can be applied to a method for separating a gas mixture or a liquid mixture, in which a gas mixture or liquid mixture composed of multiple components is brought into contact with each other and the highly permeable component is permeated and separated.

The gas mixture separation method is characterized by contacting the zeolite membrane composite with a gas mixture composed of a plurality of gas components, and permeating and separating the highly permeable gas components from the gas mixture. be. In particular, the zeolite membrane composite of the present invention can be suitably used for separating _N2 .

One of the separation functions of the zeolite membrane in the present invention is separation as a molecular sieve, and can suitably separate gas molecules having a size greater than or equal to the effective pore size of the zeolite used and gas molecules smaller than that. .

Therefore, the highly permeable gas component in the present invention is a gas component composed of gas molecules that easily pass through the pores of the RHO-type zeolite (preferably aluminosilicate) crystal phase, and has a molecular diameter of approximately 3.6 Å. A gas component consisting of lesser gas molecules is preferred.

The effective pore size of zeolite can be controlled by the metal species to be introduced, ion exchange, acid treatment, silylation, oxygen concentration during firing of the organic template, and the like. Separation performance can also be improved by controlling the effective pore size.

When ion exchange is performed with monovalent ions having a large ionic radius, the effective pore size tends to decrease, while when the ion exchange is performed with monovalent ions having a small ionic radius, the effective pore size is reduced to the RHO structure. The value is close to the pore diameter of Also in the case of divalent ions such as calcium, the effective pore diameter is close to the pore diameter of the RHO structure depending on the position of the exchange site.

Silylation can also reduce the effective pore size of zeolites. By silylating the terminal silanols on the outer surface and laminating a silylated layer, the effective pore diameter of the pores facing the outer surface of the zeolite becomes smaller.

Another separation function of the zeolite membrane composite of the present invention is to control the adsorption of gas molecules to the zeolite membrane by controlling the surface properties of the zeolite. That is, by controlling the polarity of the zeolite, it is possible to facilitate the permeation of molecules that are highly adsorbable to the zeolite.

By substituting Al for Si in the zeolite skeleton, the polarity can be increased, whereby highly polar gas molecules can be positively adsorbed and permeated into the zeolite pores. In addition, when the substitution amount of Al decreases, the zeolite membrane becomes a less polar zeolite membrane, which is advantageous for permeation of gas molecules with less polarity.

In addition, ion exchange can be used to control the adsorption performance of molecules and control the zeolite pore size, thereby controlling the permeation performance.

Preferred gas mixtures in the present invention include carbon dioxide, hydrogen, oxygen, nitrogen, methane, ethane, ethylene, propane, propylene, normal butane, isobutane, 1-butene, 2-butene, isobutene, sulfur hexafluoride, helium. , carbon monoxide, nitrogen monoxide, and water. Among the components of the gas mixture containing the gas, gas components with high permeance permeate the zeolite membrane composite and are separated, and gas components with low permeance are concentrated on the feed gas side.

Furthermore, the gas mixture more preferably contains at least two of the above components. In this case, the two components are preferably a combination of a high permeance component and a low permeance component.

The gas separation conditions vary depending on the target gas species, composition, and membrane performance, but the temperature is usually 0 to 300°C, preferably room temperature to 200°C, more preferably room temperature to 150°C.

The pressure of the supply gas may be the same as long as the gas to be separated is at a high pressure, or the pressure may be adjusted to a desired pressure by appropriately reducing the pressure. When the pressure of the gas to be separated is lower than the pressure used for separation, it can be used after increasing the pressure with a compressor or the like.

Although the pressure of the supplied gas is not particularly limited, it is usually atmospheric pressure or higher than atmospheric pressure, preferably 0.1 MPa or higher, more preferably 0.11 MPa or higher. Also, the upper limit is usually 20 MPa or less, preferably 10 MPa or less, more preferably 1 MPa or less.

Although the differential pressure between the gas on the supply side and the gas on the permeation side is not particularly limited, it is usually 20 MPa or less, preferably 10 MPa or less, more preferably 5 MPa or less, and still more preferably 1 MPa or less. Moreover, it is usually 0.001 MPa or more, preferably 0.01 MPa or more, and more preferably 0.02 MPa or more.

Here, the differential pressure means the difference between the partial pressure of the gas on the supply side and the partial pressure on the permeate side.
The pressure [Pa] in the present invention refers to absolute pressure unless otherwise specified.

The flow rate of the feed gas is such that it is possible to compensate for the reduction in permeation gas and that the concentration of the less permeable gas in the feed gas in the immediate vicinity of the membrane matches the concentration in the gas as a whole. It is sufficient if the flow rate is sufficient for mixing, and it is usually 0.5 mm/sec or more, preferably 1 mm/sec or more, although it depends on the pipe diameter of the separation unit and the separation performance of the membrane, and the upper limit is not particularly limited, usually 1 m /sec or less, preferably 0.5 m/sec or less.

A sweep gas may be used in the separation method of the present invention. The method using a sweep gas is a method in which a different kind of gas from the supply gas is flowed to the permeation side, and the gas that has permeated the membrane is recovered.

The pressure of the sweep gas is usually atmospheric pressure, but is not particularly limited. It is 0.1 MPa or more. Depending on the case, it may be used under reduced pressure.

The flow rate of the sweep gas is not particularly limited, but is usually 1×10 ⁻⁷ mol/(m ² ·s) or more and 1×10 ⁴ mol/(m ² ·s) or less.

The device used for separating the gas mixture is not particularly limited, but it is usually used as a module. The membrane module may be, for example, an apparatus as shown in FIGS. 4 and 5, or a membrane module exemplified in "Gas Separation and Purification Technology" Toray Research Center, 2007, page 22. .

[Separation performance]
The porous support-zeolite membrane composite of the present invention has excellent chemical resistance, oxidation resistance, heat stability, and pressure resistance, exhibits high permeation performance and separation performance, and has excellent durability. . In particular, it exhibits excellent separation performance for separation of inorganic gases and lower hydrocarbons.

The ^{high permeation} performance referred to here indicates a sufficient throughput. When permeated at a temperature of 50 ° C. and a differential pressure of 0.098 MPa, it is usually 1 × 10 ^-9 or more, preferably 5 × 10 ^-8 or more, more preferably 1 × 10 ^-7 or more, and the upper limit is not particularly limited. , usually less than 1×10 ⁻⁴ .

Here, the permeance is the amount of permeating substance divided by the product of the membrane area, the time, and the partial pressure difference between the feed side and the permeate side of the permeating substance, and the unit is [mol ·(m ² ·s·Pa) ⁻¹ ], which is a value calculated by the method described in the Examples section.

As described above, the zeolite membrane composite of the present invention has excellent chemical resistance, oxidation resistance, heat stability, and pressure resistance, exhibits high permeation performance and separation performance, and has excellent durability. It can be particularly suitably used for production of oxygen-enriched gas from air (medical use, oxygen-enriched air for combustion, etc.), _CO2 recovery by _N2 separation in combustion exhaust gas, and the like.

[Separation of liquid mixture]
In the method for separating or concentrating a liquid mixture of the present invention, a liquid mixture comprising a plurality of components is brought into contact with the porous support-zeolite membrane composite, and a highly permeable substance is permeated from the mixture. It is characterized by separating or concentrating the less permeable substance by permeating the highly permeable substance from the mixture. In the present invention, the same porous support-zeolite membrane composite as described above is used. Moreover, preferable ones are also the same as above.

In the separation or concentration method of the present invention, a liquid mixture composed of a plurality of components is brought into contact with one of the support side or the zeolite membrane side through a porous support provided with a zeolite membrane, and the mixture is placed on the other side. By applying a lower pressure than the contacting side, the mixture is selectively permeated with a substance that is highly permeable to the zeolite membrane (a substance in the mixture with a relatively high permeability), that is, as the main component of the permeable substance. Let This allows the highly permeable substance to be separated from the mixture. As a result, by increasing the concentration of specific components in the mixture (substances in the mixture with relatively low permeability), the specific components can be separated and recovered or concentrated.

The mixture to be separated or concentrated is not particularly limited as long as it is a liquid mixture composed of multiple components that can be separated or concentrated by the porous support-zeolite membrane composite of the present invention, and any mixture can be used. There may be.

When the mixture to be separated or concentrated is, for example, a mixture of an organic compound and water (hereinafter sometimes abbreviated as a "hydrous organic compound"), water usually has a high permeability to the zeolite membrane. So the water is separated from the mixture and the organic compounds are concentrated in the original mixture. A separation or concentration method called pervaporation method (pervaporation method) or vapor permeation method (vapor permeation method) is one embodiment of the method of the present invention. Since the pervaporation method is a separation or concentration method in which a liquid mixture is directly introduced into a separation membrane, the process including separation or concentration can be simplified.

Since the vapor permeation method is a separation/concentration method in which a liquid mixture is vaporized and then introduced into a separation membrane, it can be used in combination with a distillation apparatus or for separation at higher temperatures and pressures. In addition, the vapor permeation method reduces the influence of impurities contained in the feed liquid and substances that form aggregates and oligomers in the liquid state on the membrane because the liquid mixture is vaporized before being introduced into the separation membrane. can do. The porous support-zeolite membrane composite obtained by the present invention can be suitably used for any method.

In addition, when separation is performed at a high temperature by the vapor permeation method, the higher the temperature and the higher the concentration of the component with low permeability in the mixture, for example, the higher the concentration of the organic compound and water. The higher the concentration of the compound, the lower the separation performance, but the porous support-zeolite membrane composite obtained by the present invention exhibits high separation performance even at high temperatures and even when the concentration of the low-permeability component in the mixture is high. can be expressed. In general, the vapor permeation method separates a liquid mixture after it is vaporized, and thus the separation is usually performed under harsher conditions than in the pervaporation method. Therefore, durability of the membrane composite is also required. The porous support-zeolite membrane composite obtained by the present invention is suitable for the vapor permeation method because it has durability that enables separation even under high temperature conditions.

The porous support-zeolite membrane composite has specific physicochemical properties, so that not only when the concentration of the low-permeability component in the mixture is high, but also when the concentration of the low-permeability component is low However, it exhibits high permeation performance and selectivity, and has performance as a separation membrane with excellent durability. For example, in the case of a mixture of an organic compound and water, high selectivity is exhibited regardless of the concentration of water. That is, the zeolite membrane composite having specific physicochemical properties of the present invention is suitable for separating and concentrating mixtures over a wide range of concentrations.

Selectivity is expressed by the separation factor. The separation factor is the following index representing selectivity generally used in membrane separation.

Separation factor = ( _Pα / _Pβ )/( _Fα / _Fβ )
[Here, P _α is the mass percent concentration of the main component in the permeated liquid, P _β is the mass percent concentration of the secondary component in the permeated liquid, and F _α is the mass of the main component in the permeated liquid in the mixture to be separated. The percent concentration, _Fβ , is the weight percent concentration in the mixture to be separated of the component that becomes the minor component in the permeate. ]

The water-containing organic compound may be one whose water content has been adjusted in advance by a suitable water-adjusting method. Moisture control methods also include methods known per se, such as distillation, pressure swing adsorption (PSA), temperature swing adsorption (TSA), desiccant systems, and the like.

Furthermore, water may be further separated from the hydrous organic compound from which water has been separated by the zeolite membrane composite. Thereby, water can be separated to a higher degree, and the hydrous organic compound can be further concentrated.

Examples of organic compounds include carboxylic acids such as acetic acid, acrylic acid, propionic acid, formic acid, lactic acid, oxalic acid, tartaric acid, and benzoic acid, sulfonic acid, sulfinic acid, habituric acid, uric acid, phenol, enol, and diketone type compounds. , thiophenols, imides, oximes, aromatic sulfonamides, primary and secondary nitro compounds; alcohols such as methanol, ethanol, isopropanol (2-propanol); ketones such as acetone and methyl isobutyl ketone. aldehydes such as acetaldehyde; ethers such as dioxane and tetrahydrofuran; organic compounds containing nitrogen (N-containing organic compounds) such as amides such as dimethylformamide and N-methylpyrrolidone; esters such as acetates and acrylates etc.

Among these, the separation of hydrous organic compounds that can make use of both the molecular sieve and the hydrophilicity of RHO-type zeolite includes the separation of organic acids from mixtures of organic acids and water, and the separation of lower alcohols from water. Specific examples include separation of acetic acid and water, separation of ethanol and water, separation of methanol and water, and the like.

The organic compound may also be a polymer compound capable of forming a mixture (mixed solution) with water. Examples of such polymer compounds include those having a polar group in the molecule, for example, polyols such as polyethylene glycol and polyvinyl alcohol; polyamines; polysulfonic acids; polycarboxylic acids such as polyacrylic acid; Carboxylic acid esters; modified polymer compounds obtained by modifying polymers by graft polymerization, etc.; copolymer polymer compounds obtained by copolymerizing non-polar monomers such as olefins with polar monomers having polar groups such as carboxyl groups and the like.

The hydrous organic compound may be a mixture that forms an azeotrope, such as a mixture of water and phenol, and in the separation of the mixture that forms an azeotrope, water is selective and more efficient than separation by distillation. It is preferable because it can be easily separated. Specifically, mixtures of alcohols such as ethanol, 1-propanol, 2-propanol, 1-butanol, and 2-butanol and water; ethyl acetate, ethyl acrylate, methyl methacrylate, etc.; mixtures of esters and water , mixtures of carboxylic acids such as , formic acid, isobutyric acid and valeric acid with water; mixtures of aromatic organic substances such as phenol and aniline with water; mixtures of nitrogen-containing compounds such as acetonitrile and acrylonitrile with water.

Furthermore, the hydrous organic compound may be a mixture of water and a polymer emulsion. Here, the polymer emulsion is a mixture of a surfactant and a polymer that is commonly used in adhesives, paints, and the like. Polymers used in polymer emulsions include, for example, polyvinyl acetate, polyvinyl alcohol, acrylic resins, polyolefins, olefin-polar monomer copolymers such as ethylene-vinyl alcohol copolymers, polystyrene, polyvinyl ether, polyamide, polyester, and cellulose. thermoplastic resins such as derivatives; thermosetting resins such as urea resins, phenol resins, epoxy resins and polyurethanes; rubbers such as butadiene copolymers such as natural rubber, polyisoprene, polychloroprene and styrene-butadiene copolymers; mentioned. Further, as the surfactant, one known per se may be used.

EXAMPLES The present invention will be described in more detail with reference to Examples, but the present invention is not limited to the description of the Examples below as long as it does not exceed the gist of the invention.

(1) X-ray diffraction (XRD) measurement method XRD measurement was performed under the following conditions.
Apparatus name: New D8 ADVANCE manufactured by Bruker
Optical system: Concentrated optical system Optical system specifications Incident side: Sealed X-ray tube (CuKα)
Soller Slit (2.5°)
Divergence Slit (Variable Slit)
Sample stand: XYZ stage
Light receiving side: Semiconductor array detector (Lynx Eye 1D mode)
Ni-filter
Soller Slit (2.5°)
Goniometer radius: 280mm
Measurement conditions X-ray output (CuKα): 40 kV, 40 mA
Scan axis: θ/2θ
Scanning range (2θ): 5.0-70.0°
Measurement mode: Continuous
Read width: 0.01°
Counting time: 57.0 sec (0.3 sec x 190 ch)
Automatic variable slit (Automatic-DS): 1 mm (irradiation width)
Variable → fixed slit correction was performed on the measurement data.

The X-rays were applied in a direction perpendicular to the axial direction of the cylindrical tube (zeolite membrane composite). In addition, in order to avoid noise etc. as much as possible, X-rays are emitted from the sample stage surface, not the sample stage surface, of the two lines where the zeolite membrane composite placed on the sample stage and the plane parallel to the sample stage surface are in contact. I made it hit mainly on the other line at the top.

Also, the irradiation width was fixed at 1 mm by an automatic variable slit and measured. The XRD pattern was obtained by performing variable slit to fixed slit conversion using XRD analysis software JADE+9.4 (English version).
When calculating the peak intensity ratio, the intensity obtained by subtracting the baseline intensity from the measured value of the intensity of each peak was used.

(2) Air permeation amount One end of the zeolite membrane composite was sealed, the other end was connected to a vacuum line of 5 kPa in a sealed state, and a mass flow meter installed between the vacuum line and the zeolite membrane composite was used to remove air. The flow rate was measured and taken as the air permeation amount [L/(m ² ·h)]. As a mass flow meter, KOFLOC 8300, for N ₂ gas, maximum flow rate 500 ml/min (at 20° C., converted to 1 atm) was used. KOFLOC 8300, when the mass flow meter display is 10 ml/min (20°C, 1 atmosphere conversion) or less, Lintec MM-2100M for Air gas, maximum flow rate 20 ml/min (0°C, 1 atmosphere conversion) was measured using

(3) SEM measurement SEM measurement was performed under the following conditions.
Apparatus name: ULTRA55 (manufactured by Zeiss)
Accelerating voltage: 10 kV

(4) SEM-EDX measurement SEM observation: model name ULTRA55 (manufactured by Zeiss)
Accelerating voltage 10 kV
Observation magnification 2000 times WD 7 mm
Detector Chamber SE detector EDX analysis: Model name: Quantax200 (manufactured by Bruker)
Detector XFlash 4010
Accelerating voltage 10 kV
Collection time 60 s
A fixed range was scanned at a magnification of 2000 times, and X-ray quantitative analysis was performed.

At this time, a calibration curve obtained from a powder sample whose elemental content was determined by ICP analysis was used.

(5) Single-component gas permeation test A single-component gas permeation test was performed using an apparatus schematically shown in Fig. 5 as follows. The sample gas used was carbon dioxide (purity 99.9%, manufactured by Koatsu Gas Kogyo Co., Ltd.), methane (purity 99.999%, manufactured by Japan Fine Products), or helium (purity 99.995%, Japan Helium Center Co., Ltd.). manufactured by Toho Sanso Kogyo Co., Ltd.) or nitrogen (purity 99.99% manufactured by Toho Sanso Kogyo Co., Ltd.).

In FIG. 5, the zeolite membrane composite 1 is installed in a constant temperature bath (not shown) while being housed in a stainless steel pressure vessel 2 . The constant temperature bath is equipped with a temperature controller so that the temperature of the sample gas can be adjusted.

One end of the zeolite membrane composite 1 is sealed with a cylindrical endpin 3 . The other end is connected to the connecting portion 4 , and the other end of the connecting portion 4 is connected to the pressure vessel 2 . The inside of the cylindrical zeolite membrane composite and a pipe 11 for discharging the permeating gas 8 are connected via the connecting part 4 , and the pipe 11 extends to the outside of the pressure vessel 2 . A pressure gauge 5 for measuring the pressure on the supply side of the sample gas is connected to the pressure vessel 2 . Each connection is airtightly connected.

In the apparatus of FIG. 5, a sample gas (supply gas 7) is supplied between the pressure vessel 2 and the zeolite membrane composite 1 at a constant pressure, and the permeated gas 8 that has permeated the zeolite membrane composite is connected to a pipe 11. It is measured with a flow meter (not shown) provided.

More specifically, in order to remove components such as moisture and air, after drying at a measurement temperature or higher and purging with exhaust or the supply gas used, the sample temperature and the supply gas of the zeolite membrane composite 1 After the differential pressure between the 7 side and the permeating gas 8 side is constant and the permeating gas flow rate is stabilized, the flow rate of the sample gas (permeating gas 8) that has permeated the zeolite membrane composite 1 is measured, and the gas permeance [mol · (m ² ·s·Pa) ⁻¹ ]. The pressure difference (differential pressure) between the supply side and the permeate side of the supply gas is used as the pressure for calculating the permeance.

Based on the above measurement results, the ideal separation factor α is calculated by the following formula (1).

α=(QCO ₂ /Q _CH4 )/(PCO ₂ /P _CH4 ) (1)
[In formula (1), QCO ₂ and Q _CH4 represent the permeation amounts of carbon dioxide and methane [mol·(m ² ·s) ⁻¹ ], respectively, and PCO ₂ and P _CH4 represent the feed gas It shows the pressure [Pa] of certain carbon dioxide and methane. ]
Although the method for calculating the ideal separation factors for carbon dioxide and methane is shown here, the ideal separation factors for other gases are similarly calculated.

[Example 1] (Production of RHO-type zeolite)
An RHO-type zeolite was synthesized as follows.

84.1 g of 22.8 g of 18-crown-6-ether (manufactured by Tokyo Kasei Co., Ltd.), 5.8 g of NaOH (manufactured by Kishida Kagaku Co., Ltd.) and 4.7 g of CsOH.H ₂ O (manufactured by Mitsuwa Kagaku Co., Ltd.) of water, and the resulting solution was stirred at 80° C. for 3 hours to obtain a crown ether-alkali aqueous solution.

The crown ether-alkali aqueous solution was added dropwise to 29.8 g of FAU-type zeolite (SiO ₂ /Al ₂ O ₃ molar ratio (hereinafter sometimes referred to as “SAR”) = 30, CBV720 manufactured by Zeolyst), and further seed crystals were added. 0.6 g of RHO-type zeolite synthesized according to International Publication WO2015/020014 was added and stirred at room temperature for 2 hours to prepare a raw material mixture for hydrothermal synthesis. The composition (molar ratio) of this mixture is as follows.
SiO ₂ /Al ₂ O ₃ /NaOH/CsOH/H ₂ O/18-crown-6-ether=1/0.033/0.30/0.06/10/0.18

After the raw material mixture for hydrothermal synthesis was aged at room temperature for 24 hours, it was placed in a pressure vessel and allowed to stand still in an oven at 150° C. for hydrothermal synthesis for 72 hours. After this hydrothermal synthesis reaction, the reaction solution was cooled and the crystals produced were collected by filtration. After drying the collected crystals at 100°C for 12 hours, XRD of the obtained zeolite powder was measured. It was confirmed. Also, the XRD pattern is shown in FIG.

[Example 2] (Production of porous support-RHO type zeolite membrane composite)
A porous support-RHO type zeolite membrane composite was produced by direct hydrothermal synthesis of zeolite on a porous support. As the porous support, a mullite tube (Mullite Tube PM (outer diameter: 12 mm, inner diameter: 9 mm) manufactured by Nikkato Co., Ltd.) was cut to a length of 40 mm, washed with water, and dried.

The RHO-type zeolite obtained in Example 1 was pulverized with a ball mill and used as seed crystals. 10 g of the RHO-type zeolite obtained in Example 1, 300 g of 3φmm HD alumina balls (manufactured by Nikkato Co., Ltd.), and 90 g of water were placed in a 500-mL polyethylene bottle, and ground in a ball mill for 6 hours to obtain a 10% by weight RHO-type zeolite dispersion. did. Water was added to this zeolite dispersion so that the RHO-type zeolite was 3% by weight to obtain a seed crystal dispersion.

This seed crystal dispersion was dropped onto the support and rubbed with a finger wearing a latex glove (hereinafter sometimes referred to as a rubbing method) to attach seed crystals. The support with the seed crystal attached was dried at 100° C. for 5 hours or more. The weight of attached seed crystals was about 4.6 g/m ² .

The following was prepared as a raw material mixture for hydrothermal synthesis.

125.9 g of 6.8 g of 18-crown-6-ether (manufactured by Tokyo Kasei Co., Ltd.), 2.1 g of NaOH (manufactured by Kishida Kagaku Co., Ltd.) and 4.2 g of CsOH.H ₂ O (manufactured by Mitsuwa Kagaku Co., Ltd.) of water and stirred at 80° C. for 3 hours to obtain a crown ether-alkali aqueous solution.

The crown ether-alkali aqueous solution was added dropwise to 8.9 g of Y-type (FAU) zeolite (SAR=30, CBV720 manufactured by Zeolyst) to prepare a raw material mixture for hydrothermal synthesis.

The gel composition (molar ratio) of the obtained raw material mixture for hydrothermal synthesis was SiO ₂ /Al ₂ O ₃ /NaOH/CsOH/H ₂ O/18-crown-6-ether=1/0.033/0.36. /0.18/50/0.18.

The support to which the seed crystals are adhered is vertically immersed in a Teflon (registered trademark) inner cylinder containing the raw material mixture for hydrothermal synthesis, and the autoclave is sealed and heated at 150° C. for 72 hours under autogenous pressure. did.

After a predetermined period of time, the support-zeolite membrane composite was allowed to cool, removed from the autoclave, washed, and dried at 100° C. for 5 hours or longer. After drying, the air permeation amount in the state of zeolite (hereinafter sometimes referred to as "as-made") before template firing was 3.8 L/(m ² ·min). This porous support-zeolite membrane composite was used as a first RHO-type zeolite membrane composite.

<Repeated Synthesis>
The first RHO-type zeolite membrane composite was immersed in the raw material mixture for hydrothermal synthesis and hydrothermally synthesized to further synthesize RHO-type zeolite on the first RHO-type zeolite membrane composite. As the raw material mixture for hydrothermal synthesis, the same one as used in synthesizing the first RHO-type zeolite membrane composite was used, and the raw material mixture for hydrothermal synthesis was placed in a Teflon (registered trademark) inner cylinder. The first RHO-type zeolite membrane composite was immersed vertically and the autoclave was sealed and heated at 150° C. for 72 hours under autogenous pressure.

After a predetermined period of time, the support-zeolite membrane composite (RHO-type zeolite membrane composite) was allowed to cool, then removed from the autoclave, washed, and dried at 100° C. for 5 hours or longer. The air permeation amount of the RHO-type zeolite membrane composite before template firing (as-made) was 0.0 L/(m ² ·min). In order to remove the template from the obtained RHO-type zeolite membrane composite, it was baked in an electric furnace at 400° C. for 5 hours (template baking step) to obtain a second RHO-type zeolite membrane composite. At this time, the temperature rising rate and the temperature decreasing rate to 150° C. were both 2.5° C./min, and the temperature increasing rate and the temperature decreasing rate from 150° C. to 400° C. were 0.5° C./min. Based on the difference between the weight of the second RHO-type zeolite membrane composite after firing and the weight of the support, the weight of the RHO-type zeolite crystallized on the support was 215 g/m ² . The air permeation amount of the second RHO-type zeolite membrane composite after calcination was 0.21 L/(m ² ·min).

XRD measurement of the produced second RHO-type zeolite membrane composite revealed that RHO-type zeolite was produced. The XRD pattern is shown in FIG. * in FIG. 2 indicates the peak derived from the support. XRD measurement was performed under the conditions described above.

(Intensity of peak near 2θ=18.7°)/(Intensity of peak near 2θ=8.3°)=1.9, (Intensity of peak near 2θ=14.4°)/(2θ = intensity of peak near 8.3°) = 1.1.

The intensity of the peaks derived from the (3,1,0) and (2,1,1) planes in Im-3m (No. 229) is remarkably strong, suggesting that these planes are parallel to the surface of the membrane composite. It is considered that the zeolite crystals are oriented and grown in a direction close to

[Example 3] (Production of porous support-RHO type zeolite membrane composite)
As the porous support, a mullite tube (Mullite Tube PM (outer diameter: 12 mm, inner diameter: 9 mm) manufactured by Nikkato Co., Ltd.) was cut into a length of 40 mm, washed with water, and dried.

Prior to hydrothermal synthesis, seed crystals of RHO-type zeolite synthesized by the method shown below were attached to the support by rubbing.

<Creation of seed crystal>
7.9 g of 18-crown-6-ether (manufactured by Tokyo Chemical Industry Co., Ltd.) and 14 g of NaAlO ₂ (purity: 70% by weight or more, manufactured by Kishida Chemical Co., Ltd.), 3.8 g of NaOH (manufactured by Kishida Chemical Co., Ltd.) and 6 g of CsOH.H ₂ O (manufactured by Mitsuwa Kagaku Co., Ltd.) was dissolved in 54 g of water, and the resulting solution was stirred at 80° C. for 3 hours to obtain an aqueous crown ether-alkali solution.

The crown ether-alkali aqueous solution was added dropwise to 90 g of colloidal silica (silica concentration: 40% by weight, Snowtex 40, manufactured by Nissan Chemical Industries, Ltd.) to obtain a raw material mixture for hydrothermal synthesis.

The gel composition (molar ratio) of the raw material mixture for hydrothermal synthesis is shown below.

SiO ₂ /Al ₂ O ₃ /NaOH/CsOH/H ₂ O/18-crown-6-ether=1/0.1/0.36/0.06/10/0.05
After the raw material mixture for hydrothermal synthesis was aged at room temperature for 24 hours, it was placed in a pressure-resistant container and allowed to stand still in an oven at 110° C. for hydrothermal synthesis for 96 hours. After this hydrothermal synthesis reaction, the reaction solution was cooled and the crystals produced were collected by filtration. After the collected crystals were dried at 100° C. for 12 hours, XRD of the obtained zeolite powder was measured to confirm that it was RHO-type zeolite.

In the same manner as in Example 2, 10 g of the obtained RHO-type zeolite powder, 300 g of HD alumina balls (manufactured by Nikkato Co., Ltd.) of 3 mm diameter, and 90 g of water were placed in a 500 mL polyethylene bottle, and ball mill pulverization was performed for 6 hours. Water was added to a 10% by weight RHO-type zeolite dispersion obtained by ball milling so that the RHO-type zeolite was 3% by weight to obtain a seed crystal dispersion.

This seed crystal dispersion is added dropwise to the support, the seed crystals are adhered to the support by a rubbing method, dried in the same manner as in Example 2, and then a raw material mixture for hydrothermal synthesis prepared in the same manner as in Example 2. The autoclave was then immersed vertically in a Teflon (registered trademark) inner cylinder containing the gas, and the autoclave was sealed and heated at 150° C. for 72 hours under autogenous pressure.

After a predetermined period of time, the porous support-zeolite membrane composite was allowed to cool, then removed from the autoclave, washed, and dried at 100° C. for 5 hours or longer. After drying, one end of the cylindrical tubular membrane composite is sealed in a state before template firing (hereinafter sometimes referred to as "as-made"), and the other end is connected to a vacuum line to reduce the pressure in the tube and reduce the pressure in the vacuum line. When the air permeation amount was measured with the installed flow meter, the permeation amount was 0.2 L/(m ² ·min).

This porous support-zeolite membrane composite was calcined under the same conditions as in Example 2 to remove the template to obtain a porous support-RHO type zeolite membrane composite. Based on the difference between the weight of the porous support-RHO zeolite membrane composite and the weight of the support, the weight of the RHO zeolite crystallized on the support was 108 g/m ² . The air permeation amount after firing was 0.2 L/(m ² ·min).

XRD measurement of the produced RHO-type zeolite membrane composite revealed that RHO-type zeolite was produced. The XRD pattern is shown in FIG. * in FIG. 3 indicates a peak derived from the support. (Intensity of peak near 2θ = 14.4°)/(Intensity of peak near 2θ = 8.3°) = 2.5, (2, 1, 1) in Im-3m (No. 229) A plane orientation was assumed.

As a result of observing the surface of the obtained RHO-type zeolite membrane composite by SEM, crystals were densely formed on the surface. Further, as a result of observing the cross section with an SEM, the film thickness was about 0.5 to 7 μm, and the average was about 3 μm.

[Example 4] (Production of porous support-RHO type zeolite membrane composite)
An alumina tube (outer diameter 6 mm, average pore diameter 0.15 μm, manufactured by Noritake Co., Ltd.) was cut into 40 mm lengths as a porous support, washed with water, and then dried. A porous support-RHO zeolite membrane composite was synthesized in the same manner as the first RHO zeolite membrane composite of Example 2.

The as-made air permeation amount was 1.9 L/(m ² ·min). In order to remove the template in the same manner as in Examples 2 and 3, the obtained RHO-type zeolite membrane composite was calcined to obtain a porous support-RHO-type zeolite membrane composite. The weight of this RHO-type zeolite membrane composite was 55 g/m ² . As a result of observing this RHO-type zeolite membrane composite with an SEM, it was confirmed that crystals were densely formed on the surface.

<Ion exchange>
The template-removed RHO-type zeolite membrane composite thus obtained was placed in a Teflon container (registered trademark) inner cylinder (65 ml) containing a 1 M ammonium nitrate aqueous solution in which 3.2 g of ammonium nitrate was dissolved in 36.8 g of water. I put it in The autoclave was capped and heated to 100° C. for 1 hour under static autogenous pressure.

After a predetermined time had passed, the RHO-type zeolite membrane composite was taken out from the aqueous solution after being allowed to cool. The RHO-type zeolite membrane composite removed from the aqueous solution was subjected to the same ion exchange treatment again using a 1 M ammonium nitrate aqueous solution. After washing with water, it was dried at 100° C. for 4 hours or more to obtain an NH ₄ ⁺ -type RHO-type zeolite membrane composite.

In order to convert the NH ₄ ⁺ -type RHO-type zeolite membrane composite into the H ⁺ -type, the RHO-type zeolite membrane composite was calcined in an electric furnace at 400° C. for 2 hours. At this time, both the rate of temperature increase and the rate of temperature decrease to 150°C were set to 2.5°C/min, and the rate of temperature increase and temperature decrease from 150°C to 400°C were set to ^0.5 °C/min. A membrane composite was obtained.

In the X-ray diffraction pattern obtained by irradiating the membrane surface of the obtained RHO-type zeolite membrane composite with X-rays, (intensity of peak near 2θ = 14.4°)/(near 2θ = 8.3° The intensity of the peak) was 1.1, and the orientation to the (2,1,1) plane in Im-3m (No. 229) was presumed. The SiO ₂ /Al ₂ O ₃ molar ratio of the RHO-type zeolite membrane composite was 11 as measured by SEM-EDX. Also, the Cs/Al ₂ O ₃ molar ratio was 0.17.

The RHO-type zeolite membrane composite was subjected to the above-described single-component gas permeation test using the apparatus shown in FIG. 5, and the single-gas component permeation performance was measured. Prior to the measurement, the RHO-type zeolite membrane composite was pre-dried in the apparatus. At that time, the temperature of the constant temperature bath was set to 180 ° C., He was introduced as the supply gas 7 between the pressure vessel 2 and the zeolite membrane composite, the pressure was maintained at about 0.3 MPa, and the cylinder of the zeolite membrane composite was was dried for about 120 minutes at 0.098 MPa (atmospheric pressure) inside.

After that, the supplied gas was changed to each evaluation gas. At this time, the pressure on the supply side was set to 0.4 MPa, and the differential pressure between the supply gas 7 side and the permeated gas 8 side was set to 0.3 MPa. Moreover, the temperature of the constant temperature bath was set to 50°C. After the permeation gas flow rate stabilized, the flow rate of the sample gas (permeation gas 8) that permeated the zeolite membrane composite was measured, and the gas permeance [mol·(m ² ·s·Pa) ^-1 ] was calculated. The pressure difference (differential pressure) between the supply side and the permeate side of the supply gas was used as the pressure for calculating the permeance.

The permeance of each evaluation gas thus obtained is shown below.
CO ₂ : 1.5×10 ⁻⁷ mol·(m ² ·s·Pa) ⁻¹
N ₂ : 2.2×10 ⁻⁸ mol·(m ² ·s·Pa) ⁻¹
CH ₄ : 9.8×10 ⁻⁹ mol·(m ² ·s·Pa) ⁻¹

[Example 5] (Production of porous support-RHO type zeolite membrane composite)
As the porous support, an alumina tube (outer diameter 6 mm, average pore diameter 0.15 μm, manufactured by Noritake Co., Ltd.) was cut into a length of 40 mm, washed with water, and dried.

On the support, prior to hydrothermal synthesis, seed crystals of RHO-type zeolite synthesized by the method described in "Microporous and Mesoporous Materials 132 (2010) 352-356)" were ball-milled in the same manner as in Example 2 to obtain 3 weights. % seed crystal dispersion was prepared, and this dispersion was applied to the support by the rubbing method in the same manner as in Example 2, followed by drying.

The support to which the seed crystals were attached was vertically immersed in a Teflon (registered trademark) inner cylinder containing a raw material mixture for hydrothermal synthesis prepared in the same manner as in Example 2, and the autoclave was sealed and heated at 160°C. Heated under autogenous pressure for 18 hours.

After a predetermined period of time, the support-zeolite membrane composite was allowed to cool, removed from the autoclave, washed, and dried at 100° C. for 5 hours or longer. After drying, the air permeability in the as-made state was 1.5 L/(m ² ·min). In order to remove the template in the same manner as in Examples 2 to 4, the obtained RHO-type zeolite membrane composite was calcined to obtain an RHO-type zeolite membrane composite. Based on the difference between the weight of the zeolite membrane composite after firing and the weight of the support, the weight of the RHO-type zeolite crystallized on the support was 50 g/m ² .

<Ion exchange>
The RHO-type zeolite membrane composite was subjected to ion exchange in the same manner as in Example 4 to obtain an NH ₄ ⁺ -type RHO-type zeolite membrane composite.

In order to convert the NH ₄ ⁺ -type RHO-type zeolite membrane composite into the H ⁺ -type, the RHO-type zeolite membrane composite was fired in an electric furnace under the same conditions as in Example 4 to obtain an H ⁺ -type RHO-zeolite membrane composite. Obtained.

<Evaluation of membrane separation performance>
The RHO-type zeolite membrane composite was subjected to a single-component gas permeation test in the same manner as in Example 4 to evaluate the single-gas component permeation performance.
CO ₂ : 2.5×10 ⁻⁷ mol·(m ² ·s·Pa) ⁻¹
CH ₄ : 6.0×10 ⁻⁹ mol·(m ² ·s·Pa) ⁻¹
Also, the permeance ratio of CO ₂ and CH ₄ was 41.

[Example 6] (Production of porous support-RHO type zeolite membrane composite)
As the porous support, an alumina tube (outer diameter 6 mm, average pore diameter 0.15 μm, manufactured by Noritake Co., Ltd.) was cut into a length of 40 mm, washed with water, and dried.

A porous support-RHO type zeolite membrane composite was synthesized on the support in the same manner as in Example 2 prior to hydrothermal synthesis.

After a predetermined period of time, the support-zeolite membrane composite was allowed to cool, removed from the autoclave, washed, and dried at 100° C. for 3 hours or longer. After drying, the air permeability in the as-made state was 0.0 L/(m ² ·min). In order to remove the template from the obtained RHO-type zeolite membrane composite, it was baked in an electric furnace at 300° C. for 5 hours (template baking step) to obtain a second RHO-type zeolite membrane composite. At this time, the temperature was raised and lowered from room temperature to 100° C. for 2 hours, and the temperature elevation rate and temperature decrease rate from 100° C. to 300° C. were 0.5° C./min. The obtained RHO-type zeolite membrane composite was calcined to obtain an RHO-type zeolite membrane composite. Based on the difference between the weight of the zeolite membrane composite after firing and the weight of the support, the weight of the RHO-type zeolite crystallized on the support was 52 g/m ² .

<Evaluation of membrane separation performance>
Using the RHO-type zeolite membrane composite, an ammonia separation test from an ammonia/nitrogen mixed gas was conducted using the apparatus shown in FIG.
As a pretreatment, at 200 ° C., a mixed gas of ammonia and nitrogen as the supply gas 7 was introduced between the pressure vessel 2 and the RHO-type zeolite membrane composite, the pressure was maintained at about 0.3 MPa, and the RHO-type zeolite The inside of the cylinder of the membrane composite was dried at 0.098 MPa (atmospheric pressure) for about 120 minutes.

After that, a mixed gas of 10% ammonia/90% nitrogen (250° C.) was flowed at 100 SCCM, and the back pressure was set to 0.3 MPa. At this time, the differential pressure between the feed gas 7 side and the permeate gas 8 side of the RHO-type zeolite membrane composite was 0.2 MPa. As the gas that permeated the film, 5.4 sccm of argon gas was supplied from the line 9 in FIG. 4 as a sweep gas.

The concentration of ammonia in the obtained permeate gas was 66%. Further, when the permeance is calculated, the permeence of ammonia is 5.5×10 ⁻⁹ [mol/(m ² ·s·Pa)], and that of nitrogen is 2.7×10 ⁻¹⁰ [mol/(m ² ·s·Pa)]. Pa)] and the permeance ratio of ammonia to nitrogen was 21. Therefore, it was confirmed that the RHO-type zeolite membrane composite of the present invention separates nitrogen from a mixed gas containing nitrogen.

REFERENCE SIGNS LIST 1 zeolite membrane composite 2 pressure vessel 3 end pin 4 connection 5 pressure gauge 6 back pressure valve 7 supply gas 8 sweep gas 10 exhaust gas 11 pipe for discharging permeated gas 12 pipe for introducing sweep gas

Claims (9)

A method for producing RHO-type zeolite, which comprises producing RHO-type zeolite using an aluminosilicate zeolite having a framework density of 15 T/1000 Å or less. 2. The method for producing RHO-type zeolite according to claim 1, wherein said aluminosilicate zeolite contains d6r or lta in its framework, which is defined as a composite building unit by the International Zeolite Association (IZA). 3. The method for producing RHO-type zeolite according to claim 1, wherein said aluminosilicate zeolite is FAU-type zeolite or LTA-type zeolite. The method for producing an RHO-type zeolite according to any one of claims 1 to 3, wherein the silica/alumina molar ratio of the aluminosilicate zeolite is 5 or more and 85 or less. The method for producing RHO-type zeolite according to any one of claims 1 to 4, characterized in that the aluminosilicate zeolite accounts for 50-100% by weight of the total aluminum element source. The method for producing an RHO-type zeolite according to any one of claims 1 to 5, characterized in that the aluminosilicate zeolite has a framework density of 10 T/1000 Å or more. A method for producing the RHO-type zeolite from a raw material mixture for hydrothermal synthesis containing the aluminosilicate zeolite, characterized by adding RHO-type zeolite as a seed crystal to the raw material mixture for hydrothermal synthesis. 7. A method for producing an RHO-type zeolite according to any one of 1 to 6. The RHO according to claim 7, wherein the ratio of the RHO-type zeolite of the seed crystals to the amount of SiO ₂ in the raw material mixture for hydrothermal synthesis is 0.1% by weight or more and 15% by weight or less. A method for producing type zeolites. The method for producing RHO-type zeolite according to any one of claims 1 to 8, characterized in that the RHO-type zeolite has a SiO ₂ /Al ₂ O ₃ molar ratio of 10 or more.

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