Hydrogen separation or concentration method, hydrogen separation or concentration device

Abstract

To provide a method for separating or concentrating hydrogen from a mixed gas containing hydrogen having a high water content, and to provide a device for realizing the method.SOLUTION: Provided is a hydrogen separation or concentration method, which is a method in which, using a zeolite membrane, hydrogen is permeated and separated from a gas mixture containing at least hydrogen and water vapor, and in which the water vapor partial pressure of the gas mixture is set at 0.6 kPa or more and 12.4 kPa or less, and the temperature of the gas mixture when permeating through the zeolite membrane is set at 80°C or more and 200°C or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for separating or concentrating hydrogen and an apparatus for separating or concentrating hydrogen. [Background technology]

[0002] In recent years, membrane separation and concentration methods using membranes such as polymer membranes and zeolite membranes have been proposed as methods for separating gas mixtures. Polymer membranes, such as flat membranes and hollow fiber membranes, are easy to process but have the disadvantage of low heat resistance. Furthermore, polymer membranes have low chemical resistance and many of them swell upon contact with organic compounds, particularly organic solvents and organic acids, limiting the range of applications for separation and concentration. Zeolite membranes are typically used for separation and concentration as zeolite membrane composites, in which zeolite is formed in the form of a membrane on a support made of an inorganic material. Separation and concentration using inorganic membranes can be performed over a wider temperature range than polymer membranes and can also be applied to the separation of mixtures containing organic compounds.

[0003] As a method for separating gas mixtures (gases) using membranes, methods using polymer membranes have been proposed since the 1970s. However, while polymer membranes are characterized by their excellent processability, they have the problem of degrading due to heat, chemicals, and pressure, resulting in a decrease in performance. In recent years, various inorganic membranes with good chemical resistance, oxidation resistance, heat stability, and pressure resistance have been proposed to solve these problems. Among these, zeolites have regular sub-nanometer pores, which act as molecular sieves, allowing specific molecules to selectively pass through, and are expected to demonstrate high separation performance.

[0004] In Patent Document 1, the permeance of H2, CH4, and CO2 in dry gas is evaluated using a zeolite membrane composite containing a CHA-type aluminosilicate zeolite. Patent Document 2 describes a method of methanating COG gas and separating hydrogen using a zeolite membrane at 0 to 500° C. The optimum temperature for hydrogen separation is said to be 0 to 100° C. (Paragraph

[0053] ). Patent Document 3 describes a CHA zeolite separation membrane and describes the separation of CO2 / N2 and CO2 / CH4. Patent Document 4 describes a heterogeneous zeolite separation membrane that simultaneously has CHA and DDR zeolite crystal structures. The separation performance for CO2 / N2 or CO2 / CH4 mixed gases is evaluated under dry and wet conditions. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2017-64716 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-108256 [Patent Document 3] Japanese Patent Application Publication No. 2019-89058 [Patent Document 4] Japanese Patent Application Publication No. 2020-151709 Summary of the Invention [Problem to be solved by the invention]

[0006] One of the main methods for producing hydrogen is steam reforming of natural gas. In this case, the components contained in the outlet gas, other than hydrogen, are mainly methane, carbon dioxide, carbon monoxide, and water vapor. When using hydrogen, these components must be removed. From the standpoint of polarity, the separation of hydrogen and methane is the most important challenge, and this can be achieved using a zeolite membrane. Excess water vapor is first removed from the reformed gas, which is usually reduced to a water vapor pressure of about room temperature. Further dehydration requires cooling equipment, but since reforming equipment is a high-pressure gas facility, installing cooling equipment is not desirable. Therefore, when using a zeolite membrane for hydrogen separation, a mixed gas containing hydrogen with a high water content is supplied to the zeolite membrane.

[0007] It is also preferable to use coke oven exhaust gas (COG) as a hydrogen source, but COG contains methane, carbon monoxide, and C2 or higher hydrocarbon components in addition to hydrogen. Because the C2 or higher hydrocarbon components in COG can clog the zeolite membrane, it is preferable to perform a steam reforming process to decompose the C2 or higher hydrocarbon components before gas separation of the COG. When hydrogen is separated from this steam-reformed COG gas using a zeolite membrane, a mixed gas containing hydrogen with a high water content is supplied to the zeolite membrane, just like the steam-reformed natural gas gas mentioned above.

[0008] According to the investigations conducted by the present inventors, it was found that when a gas with a high water content is supplied to a zeolite membrane, the hydrogen permeance is hindered. The above-mentioned separation membranes (Patent Documents 1 to 4) could not address this problem. In view of the above, an object of the present invention is to provide a method for efficiently separating or concentrating hydrogen from a mixed gas containing hydrogen with a high water content, and an apparatus for implementing the method. [Means for solving the problem]

[0009] The present inventors have encountered the above-mentioned problem, which had not been recognized before, and have conducted extensive research to solve it, and have found the following.

[0010] When separating hydrogen from a mixed gas, if water is present in the mixed gas, the water will be adsorbed onto the zeolite membrane, reducing the amount of gas that can pass through. By setting the temperature of the mixed gas to a predetermined temperature, the effect of the water being adsorbed onto the zeolite membrane can be reduced.

[0011] Based on the above, the present inventors have completed the following invention. [1] A method for separating hydrogen from a gas mixture containing at least hydrogen and water vapor by permeation using a zeolite membrane, comprising: The method for separating or concentrating hydrogen, wherein the temperature of the gas mixture when passing through the zeolite membrane is 80°C or higher and 200°C or lower. [2] The method for separating or concentrating hydrogen according to [1], wherein the water vapor partial pressure of the gas mixture is 0.6 kPa or more and 12.4 kPa or less. [3] The method for separating or concentrating hydrogen according to [1] or [2], wherein the zeolite membrane contains a CHA-type aluminosilicate zeolite, and in an X-ray diffraction pattern obtained by irradiating the membrane surface with X-rays, the peak intensity around 2θ=17.9° has a value less than 0.5 times the peak intensity around 2θ=20.8°, and the peak intensity around 2θ=9.6° has a value between 2.0 times and 4.0 times the peak intensity around 2θ=20.8°.

[0012] [4] The method for separating or concentrating hydrogen according to any one of [1] to [3], wherein the zeolite has a SiO2 / Al2O3 ratio of 20 or more and 500 or less. [5] The method for separating or concentrating hydrogen according to any one of [1] to [4], wherein the zeolite membrane is subjected to a silylation treatment. [6] The method for separating or concentrating hydrogen according to any one of [1] to [5], wherein the gas mixture is obtained by steam reforming a gas containing a hydrocarbon component.

[0013] [7] The method for separating or concentrating hydrogen according to any one of [1] to [6], wherein the gas mixture is obtained by steam reforming a gas containing hydrogen, methane, and hydrocarbon components having two or more carbon atoms. [8] The method for separating or concentrating hydrogen according to [6] or [7], wherein the steam reforming is carried out at a temperature of 600°C or less. [9] The method for separating or concentrating hydrogen according to any one of [6] to [8], further comprising a step of dehydrating the gas mixture after the steam reforming.

[0014]

[10] A hydrogen separation or concentration device, comprising a membrane separator equipped with the zeolite membrane, and performing the hydrogen separation or concentration method according to any one of [1] to [9].

[11] The hydrogen separation or concentration device according to

[10] , further comprising a reformer.

[12] The hydrogen separation or concentration device according to

[10] or

[11] , further comprising a dehydrator. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a method for efficiently separating or concentrating hydrogen from a mixed gas containing hydrogen with a high water content, and an apparatus for implementing the method. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 shows a surface XRD image of the inorganic porous support-CHA type zeolite membrane composite prepared in Experimental Example 1. [Figure 2] Figure 2 shows the XRD of CHA-type zeolite powder. [Figure 3] FIG. 3 is a schematic diagram of one embodiment of an apparatus used for gas separation. [Figure 4] 4(a) is a graph showing the temperature dependence of the hydrogen permeance and ideal separation factor of the dry mixed gas in Experimental Example 1. FIG. 4(b) is a graph showing the temperature dependence of the methane permeance and ideal separation factor of the dry mixed gas in Experimental Example 1. [Figure 5] 5(a) is a graph showing the temperature dependence of the hydrogen permeance and ideal separation factor of the steam-containing mixed gas in Experimental Example 1. FIG. 5(b) is a graph showing the temperature dependence of the methane permeance and ideal separation factor of the steam-containing mixed gas in Experimental Example 1. [Figure 6] 6(a) is a graph showing the temperature dependence of the hydrogen permeance and ideal separation factor of the dry mixed gas in Experimental Example 2. FIG. 6(b) is a graph showing the temperature dependence of the methane permeance and ideal separation factor of the dry mixed gas in Experimental Example 2. [Figure 7] 7(a) is a graph showing the temperature dependence of the hydrogen permeance and ideal separation factor of the steam-containing mixed gas in Experimental Example 2. FIG. 7(b) is a graph showing the temperature dependence of the methane permeance and ideal separation factor of the steam-containing mixed gas in Experimental Example 2. [Figure 8] 8(a) is a graph showing the temperature dependence of the hydrogen permeance and ideal separation factor of the dry mixed gas in Experimental Example 3. FIG. 8(b) is a graph showing the temperature dependence of the methane permeance and ideal separation factor of the dry mixed gas in Experimental Example 3. [Figure 9] 9(a) is a graph showing the temperature dependence of the hydrogen permeance and ideal separation factor of the steam-containing mixed gas in Experimental Example 3. FIG. 9(b) is a graph showing the temperature dependence of the methane permeance and ideal separation factor of the steam-containing mixed gas in Experimental Example 3. [Figure 10] FIG. 10 is a schematic diagram of another embodiment of an apparatus for use in gas separation. DETAILED DESCRIPTION OF THE INVENTION

[0017] The following describes in more detail the embodiments of the present invention. However, the description of the constituent elements described below is an example of an embodiment of the present invention, and the present invention is not limited to these contents, and can be implemented in various modifications within the scope of its gist.

[0018] <Method for separating or concentrating hydrogen> The method for separating or concentrating hydrogen of the present invention is a method for separating hydrogen from a gas mixture containing at least hydrogen and water vapor by permeating the gas mixture using a zeolite membrane, in which the water vapor partial pressure of the gas mixture is set to 0.6 kPa or more and 12.4 kPa or less, and the temperature of the gas mixture when permeating the zeolite membrane is set to 80°C or more and 200°C or less.

[0019] In the present invention, the zeolite membrane may be a single zeolite membrane or a zeolite membrane composite in which a zeolite membrane is formed on a porous support, but from the viewpoint of strength, a zeolite membrane composite is preferred.

[0020] (Zeolite membrane) In the present invention, the zeolite membrane may contain, as components constituting the zeolite membrane, inorganic binders such as silica and alumina, organic substances such as polymers, or silylating agents for modifying the zeolite surface, in addition to zeolite, as necessary. The zeolite membrane may contain a portion of amorphous components, but is preferably a zeolite membrane that is substantially composed of zeolite alone.

[0021] The proportion of CHA-type aluminosilicate in the zeolite membrane is usually 10% by volume or more, preferably 30% by volume or more, more preferably 60% by volume or more, and even more preferably 80% by volume or more. A zeolite membrane composed solely of CHA-type aluminosilicate is most preferred because it has the best gas permeability and separation properties.

[0022] The thickness of the zeolite membrane is not particularly limited, but is usually 0.1 μm or more, preferably 0.6 μm or more, and more preferably 1.0 μm or more. It is usually 100 μm or less, preferably 60 μm or less, and more preferably 20 μm or less. If the membrane thickness is too large, the permeation rate tends to decrease, while if it is too small, the selectivity and membrane strength tend to decrease.

[0023] The particle size of the zeolite forming the zeolite membrane is not particularly limited, but if it is too small, the grain boundaries will become large, which tends to reduce permeability and other properties. Therefore, it is usually 30 nm or more, preferably 50 nm or more, and more preferably 100 nm or more, with the upper limit being equal to or less than the membrane thickness. Furthermore, it is more preferable if the zeolite particle size is the same as the membrane thickness. When the zeolite particle size is the same as the membrane thickness, the zeolite grain boundaries are smallest. Zeolite membranes obtained by hydrothermal synthesis, which will be described later, are preferred because the zeolite particle size and membrane thickness may be the same.

[0024] The shape of the zeolite membrane is not particularly limited, and any shape can be used, such as tubular, hollow fiber, monolith, honeycomb, etc. The size is also not particularly limited, and for example, in the case of a tubular membrane, a length of 2 cm to 200 cm, an inner diameter of 0.5 cm to 2 cm, and a thickness including the support of 0.5 mm to 4 mm are practical and preferred.

[0025] (Zeolite) In the present invention, the zeolite membrane contains a CHA-type aluminosilicate zeolite. Preferably, the zeolite constituting the zeolite membrane is a CHA-type aluminosilicate. The aluminosilicate is mainly composed of oxides of Si and Al, and may contain other elements as long as the effects of the present invention are not impaired.

[0026] In the present invention, the SiO2 / Al2O3 molar ratio of the aluminosilicate is not particularly limited, but is usually 6 or more, preferably 10 or more, more preferably 20 or more, more preferably 30 or more, even more preferably 32 or more, still more preferably 35 or more, and particularly preferably 40 or more. The upper limit is usually such that Al is present in an amount similar to that of an impurity, and the SiO2 / Al2O3 molar ratio is usually 500 or less, preferably 100 or less, more preferably 90 or less, even more preferably 80 or less, particularly preferably 70 or less, and most preferably 50 or less. If the SiO2 / Al2O3 molar ratio is less than the lower limit, the density of the zeolite membrane may decrease and durability tends to decrease. The SiO2 / Al2O3 molar ratio can be adjusted by the reaction conditions of the hydrothermal synthesis, which will be described later.

[0027] The SiO2 / Al2O3 molar ratio is a value obtained by scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX). To obtain information on a film only a few microns thick, measurements are usually taken at an X-ray acceleration voltage of 10 kV.

[0028] (CHA type zeolite) In the present invention, CHA-type zeolite refers to a zeolite with a CHA structure, a code for specifying the structure of zeolites established by the International Zeolite Association (IZA). It is a zeolite with a crystalline structure equivalent to that of naturally occurring chabazite. CHA-type zeolite has a structure characterized by three-dimensional pores consisting of eight-membered oxygen rings with a diameter of 0.38 × 0.38 nm, and its structure is characterized by X-ray diffraction data.

[0029] Framework density (T / nm) of CHA-type zeolite 3 ) is 14.5. The SiO2 / Al2O3 molar ratio is the same as above. Here, the framework density (T / nm 3 ) is the nm of zeolite 3 (1000Å 3 ) and this value is determined by the structure of the zeolite. The relationship between framework density and zeolite structure is shown in ATLAS OF ZEOLITE FRAMEWORK TYPES Fifth Revised Edition 2001 ELSEVIER.

[0030] (Inorganic porous support) The inorganic porous support may be any porous inorganic substance that is chemically stable enough to allow zeolite to be crystallized into a membrane on its surface, etc. Specific examples include sintered ceramics such as silica, α-alumina, γ-alumina, mullite, zirconia, titania, yttria, silicon nitride, and silicon carbide; sintered metals such as iron, bronze, and stainless steel; glass; and molded carbon materials.

[0031] Among inorganic porous supports, a ceramic sintered body has the effect of increasing the adhesion at the interface by partially converting into zeolite during the synthesis of the zeolite membrane. Furthermore, inorganic porous supports containing at least one of alumina, silica, and mullite are more preferred because they can be easily partially zeoliteized, which strengthens the bond between the support and the zeolite and makes it easier to form a dense membrane with high separation performance.

[0032] The shape of the support is not particularly limited as long as it can effectively separate gas mixtures and liquid mixtures. Specific examples include flat, tubular, cylindrical, honeycomb, and monolithic supports having a large number of cylindrical or prismatic holes. In the present invention, a zeolite membrane is formed on the surface of an inorganic porous support or the like, and preferably the zeolite is crystallized into a membrane.

[0033] The average pore size of the support is not particularly limited, but a controlled pore size is preferred. The pore size is usually 0.02 μm or more, preferably 0.05 μm or more, more preferably 0.1 μm or more, and usually 20 μm or less, preferably 10 μm or less, more preferably 5 μm or less. If the pore size is too small, the permeation rate tends to be low, while if the pore size is too large, the strength of the support itself tends to be insufficient or it tends to be difficult to form a dense zeolite membrane. The average pore size of the support can be measured by mercury intrusion porosimetry.

[0034] The surface of the support may be polished with a file or the like as needed. The surface of the support means the surface portion of the support on which the zeolite membrane is formed, and may be any surface of the support, or may be multiple surfaces. For example, in the case of a cylindrical support, it may be either the outer surface or the inner surface, or in some cases, both the outer and inner surfaces.

[0035] The porosity of the support is not particularly limited and does not need to be particularly controlled, but it is usually preferable that the porosity is 20% or more and 60% or less. The porosity affects the permeation flow rate when separating gas or liquid, and if the porosity is less than the lower limit, the diffusion of the permeate tends to be hindered, while if the porosity is more than the upper limit, the strength of the support tends to decrease. The porosity of the support can be measured by mercury intrusion porosimetry.

[0036] (Zeolite membrane composite) The zeolite membrane composite is a membrane of zeolite fixed to the surface of a support or the like, and in some cases, it is preferable that a portion of the zeolite is fixed to the inside of the support.

[0037] The zeolite membrane composite is preferably, for example, one in which zeolite is crystallized into a membrane on the surface of a support by hydrothermal synthesis.

[0038] The position of the zeolite membrane on the support is not particularly limited. When a tubular support is used, the zeolite membrane may be attached to the outer surface, the inner surface, or even both surfaces depending on the application system. The zeolite membrane may also be laminated on the surface of the support, or may be crystallized to fill the pores in the surface layer of the support. In this case, it is important that the crystallized membrane layer does not have cracks or continuous micropores, and forming a so-called dense membrane improves separation performance.

[0039] In the present invention, the zeolite membrane composite preferably has an X-ray diffraction pattern obtained by irradiating the membrane surface with X-rays, in which the intensity of the peak near 2θ=17.9° is less than 0.5 times the intensity of the peak near 2θ=20.8°.

[0040] Here, peak intensity refers to the measured value minus the background value. The peak intensity ratio (hereinafter sometimes referred to as "peak intensity ratio A"), expressed as (peak intensity around 2θ = 17.9°) / (peak intensity around 2θ = 20.8°), is usually less than 0.5, preferably 0.48 or less. There is no particular lower limit, but it is usually 0.001 or more.

[0041] In the zeolite membrane composite of the present invention, the intensity of the peak near 2θ=9.6° in the X-ray diffraction pattern is preferably 2.0 to less than 4.0 times the intensity of the peak near 2θ=20.8°.

[0042] The peak intensity ratio (hereinafter sometimes referred to as "peak intensity ratio B"), expressed as (peak intensity around 2θ=9.6°) / (peak intensity around 2θ=20.8°), is usually 2.0 or more, preferably 2.1 or more, more preferably 2.3 or more, and particularly preferably 2.5 or more. The upper limit is usually less than 4.0, preferably 3.9 or less, more preferably 3.7 or less, and particularly preferably 3.5 or less.

[0043] The X-ray diffraction pattern referred to here is obtained by irradiating the surface on which the zeolite is mainly attached with X-rays using a CuKα radiation source, with the scanning axis set to θ / 2θ. The shape of the sample to be measured may be any shape that allows X-rays to be irradiated onto the surface of the membrane composite on which the zeolite is mainly attached. In order to clearly represent the characteristics of the membrane composite, it is preferable to use the prepared membrane composite as is, or one cut to an appropriate size limited by the apparatus.

[0044] The X-ray diffraction pattern referred to here may be measured by fixing the irradiation width using an automatic variable slit when the surface of the zeolite membrane composite is curved. The X-ray diffraction pattern when an automatic variable slit is used refers to a pattern after variable-to-fixed slit correction.

[0045] Here, the peak near 2θ=17.9° refers to the maximum peak present in the range of 17.9°±0.6° among peaks not attributable to the substrate.

[0046] The peak near 2θ=20.8° refers to the largest peak present in the range of 20.8°±0.6° among peaks not attributable to the substrate.

[0047] The peak near 2θ=9.6° refers to the maximum peak present in the range of 9.6°±0.6° among peaks not attributable to the substrate.

[0048] According to the COLLECTION OF SIMULATED XRD POWDER PATTERNS FOR ZEOLITE Third Revised Edition 1996 ELSEVIER, the peak at 2θ=9.6° in the X-ray diffraction pattern is in the rhombohedral setting and has the space group

[0049]

number

[0050] When the peak is (No. 166), it is a peak derived from the plane with index (1,0,0) in the CHA structure.

[0051] In addition, the peak at 2θ=17.9° in the X-ray diffraction pattern is in the rhombohedral setting according to the COLLECTION OF SIMULATED XRD POWDER PATTERNS FOR ZEOLITE Third Revised Edition 1996 ELSEVIER.

[0052]

number

[0053] When the peak is (No. 166), it is a peak derived from the plane with index (1,1,1) in the CHA structure.

[0054] According to the COLLECTION OF SIMULATED XRD POWDER PATTERNS FOR ZEOLITE Third Revised Edition 1996 ELSEVIER, the peak at 2θ=20.8° in the X-ray diffraction pattern is in the rhombohedral setting and has the space group

[0055]

number

[0056] When the peak is taken as (No. 166), it is a peak derived from the plane with index (2,0,-1) in the CHA structure.

[0057] According to Halil Kalipcilar et al., “Synthesis and Separation Performance of SSZ-13 Zeolite Membranes on Tubular Supports”, Chem. Mater. 2002, 14, 3458-3464, the typical ratio (peak intensity ratio B) of the peak intensity derived from the (1,0,0) plane to the peak intensity derived from the (2,0,-1) plane in a CHA-type aluminosilicate zeolite membrane is less than 2.

[0058] Therefore, a ratio of 2.0 or more and less than 4.0 is considered to mean that the zeolite crystals grow with a moderate orientation, for example, such that the (1,0,0) plane of the CHA structure in the rhombohedral setting is nearly parallel to the surface of the membrane composite. The growth of zeolite crystals with an orientation in the zeolite membrane composite is advantageous in that it allows for the production of a dense membrane with high separation performance.

[0059] The term "moderate orientation" here means that there are a moderate proportion of crystallites with the (1,0,0) plane oriented nearly parallel to the surface of the membrane composite relative to the total crystallites. This proportion is higher than that of powdered CHA-type aluminosilicate, in which the crystallites are randomly oriented, and is lower than that of CHA-type aluminosilicate zeolite membranes in which the (1,0,0) planes of many crystallites are oriented nearly parallel to the surface, such as those with a peak intensity ratio B of 4 or more.

[0060] According to the above-mentioned literature (Halil Kalipcilar et al.), the typical ratio (peak intensity ratio A) of the peak intensity derived from the (1,1,1) plane to the peak intensity derived from the (2,0,-1) plane in a CHA-type aluminosilicate zeolite membrane is less than 0.5.

[0061] Therefore, a ratio of less than 0.5 is thought to mean that, for example, when the CHA structure is in a rhombohedral setting, the zeolite crystals are not oriented to a large extent in their growth so that the (1,1,1) plane is nearly parallel to the surface of the membrane composite.

[0062] Here, the low degree of orientation of the zeolite crystals means that the proportion of zeolite crystallites with their (1,1,1) planes oriented nearly parallel to the surface of the membrane composite is low relative to the total crystallites, and that the orientation of the (1,1,1) planes of the crystallites is almost random.

[0063] In this way, the peak intensity ratios A and B being within the above-mentioned specific ranges indicates that the zeolite crystals have grown with a moderate orientation, and a dense membrane with high separation performance has been formed.

[0064] A dense zeolite membrane in which CHA-type zeolite crystals grow with a moderate degree of orientation can be achieved, as will be described below, by, for example, particularly preferably using a specific organic template and allowing K ions to coexist in the aqueous reaction mixture when forming a zeolite membrane by hydrothermal synthesis.

[0065] In the present invention, the water adsorption amount of the zeolite membrane composite at a relative pressure of 0.8, determined from the water vapor adsorption isotherm of the zeolite membrane composite, is preferably from 2 to 10 times the water adsorption amount at a relative pressure of 0.2.

[0066] Here, an adsorption isotherm is a graph in which the change in pressure and adsorption amount is measured while the material is kept at a constant temperature. Generally, the horizontal axis represents the relative pressure (P / P0) obtained by dividing the equilibrium pressure by the saturated vapor pressure, and takes values ​​from 0 to 1. In the present invention, the water (water vapor) adsorption amount (g / g) to the zeolite membrane composite at a relative pressure of 0.8 and a relative pressure of 0.2 is used as an index.

[0067] As described above, the zeolite membrane composite of the present invention preferably has a ratio of the water adsorption amount at a relative pressure of 0.8 to the water adsorption amount at a relative pressure of 0.2 of 2 to 10, and this value is preferably 2.1 or more, more preferably 2.2 or more, and is preferably 8 or less, more preferably 5 or less.

[0068] This value generally correlates with the adsorption of water into mesopores in zeolite membranes; a larger value indicates a larger hydrophilic mesopore volume, while a smaller value indicates a smaller hydrophilic mesopore volume. If this value is too large, the membrane will have many mesopores and a low density, resulting in a high permeation rate but low separation performance. On the other hand, if this value is too small, the membrane will have almost no mesopores and a high density, resulting in a high separation performance but low permeation rate. By adjusting this value to between 2 and 10, it is possible to obtain a membrane with good separation performance and high permeation rate.

[0069] (Method of manufacturing zeolite membrane composite) In the present invention, the method for forming the zeolite membrane is not particularly limited as long as it is a method that can form the above-mentioned specific zeolite membrane on the support, and any of the following methods can be used: (1) a method of crystallizing zeolite into a membrane on the support, (2) a method of fixing zeolite to the support with an inorganic binder or an organic binder, (3) a method of fixing a polymer in which zeolite is dispersed, or (4) a method of impregnating the support with a zeolite slurry and, in some cases, suctioning it to fix the zeolite to the support. By these methods, an inorganic porous support-zeolite membrane composite can be obtained.

[0070] Among these, a method of crystallizing zeolite into a membrane on an inorganic porous support is particularly preferred. Although there are no particular limitations on the crystallization method, a method of placing the support in a reaction mixture for hydrothermal synthesis used to produce zeolite (hereinafter, this may be referred to as an "aqueous reaction mixture") and directly carrying out hydrothermal synthesis to crystallize zeolite on the surface of the support is preferred.

[0071] Specifically, for example, an aqueous reaction mixture whose composition has been adjusted to be homogenous may be placed in a heat-resistant and pressure-resistant container such as an autoclave, in which a support is loosely fixed, and then the container is sealed and heated for a certain period of time.

[0072] The aqueous reaction mixture preferably contains a Si element source, an Al element source, an alkali source, and water, and further contains an organic template as required.

[0073] Examples of the Si element source that can be used in the aqueous reaction mixture include amorphous silica, colloidal silica, silica gel, sodium silicate, amorphous aluminosilicate gel, tetraethoxysilane (TEOS), and trimethylethoxysilane.

[0074] Examples of Al element sources that can be used include sodium aluminate, aluminum hydroxide, aluminum sulfate, aluminum nitrate, aluminum oxide, amorphous aluminosilicate gel, etc. In addition to the Al element source, other element sources such as Ga, Fe, B, Ti, Zr, Sn, and Zn may also be contained.

[0075] The type of alkali used as the alkali source is not particularly limited, and alkali metal hydroxides and alkaline earth metal hydroxides can be used.

[0076] Examples of metal species in the metal hydroxide include Na, K, Li, Rb, Cs, Ca, Mg, Sr, and Ba, and are preferably Na and K, and more preferably K. Two or more types of metal species in the metal hydroxide may be used in combination, and specifically, it is preferable to use Na and K, or Li and K, in combination.

[0077] Specifically, examples of alkali sources that can be used include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide, and cesium hydroxide; and alkaline earth metal hydroxides such as calcium hydroxide, magnesium hydroxide, strontium hydroxide, and barium hydroxide.

[0078] The alkali source used in the aqueous reaction mixture can be hydroxide ions, which are counter anions of the organic template described below.

[0079] In the crystallization of zeolite, an organic template (structure-directing agent) can be used as needed, but zeolite 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 increases, improving crystallinity.

[0080] The organic template may be of any type as long as it can form the desired zeolite membrane, and one type of template may be used, or two or more types may be used in combination. As the organic template, amines and quaternary ammonium salts are usually used. For example, preferred examples of the organic templates include those described in U.S. Pat. No. 4,544,538 and U.S. Patent Publication No. 2008 / 0075656.

[0081] Specifically, examples include cations derived from alicyclic amines such as cations derived from 1-adamantanamine, cations derived from 3-quinacridinal, and cations derived from 3-exo-aminonorbornene. Among these, cations derived from 1-adamantanamine are more preferred. When cations derived from 1-adamantanamine are used as organic templates, CHA-type zeolites capable of forming dense membranes are crystallized.

[0082] Among the cations derived from 1-adamantanamine, N,N,N-trialkyl-1-adamantanammonium cations are more preferred. The three alkyl groups in the N,N,N-trialkyl-1-adamantanammonium cation are usually independent alkyl groups, preferably lower alkyl groups, more preferably methyl groups. The most preferred compound among them is N,N,N-trimethyl-1-adamantanammonium cation.

[0083] Such cations are accompanied by anions that do not adversely affect the formation of CHA-type zeolite. Representative examples of such anions include halogen ions such as Cl-, Br-, and I-, hydroxide ions, acetates, sulfates, and carboxylates. Among these, hydroxide ions are particularly preferred, and in the case of hydroxide ions, they function as an alkali source as described above.

[0084] Another organic template that can be used is the N,N,N-trialkylbenzylammonium cation. In this case, the alkyl groups are each independently selected, preferably lower alkyl groups, more preferably methyl groups. Among these, the most preferred compound is the N,N,N-trimethylbenzylammonium cation. The anion associated with this cation is the same as above.

[0085] The ratio of the elemental Si source to the elemental Al source in the aqueous reaction mixture is usually expressed as the molar ratio of the oxides of the respective elements, i.e., the SiO2 / Al2O3 molar ratio.

[0086] This SiO2 / Al2O3 ratio is not particularly limited as long as it is a ratio that allows the formation of a zeolite having the above-mentioned SiO2 / Al2O3 ratio, but is usually 5 or more, preferably 20 or more, more preferably 30 or more, even more preferably 40 or more, and particularly preferably 50 or more. The upper limit is usually 500 or less, preferably 200 or less, more preferably 150 or less, and even more preferably 140 or less. When the SiO2 / Al2O3 ratio is within this range, it is possible to crystallize a CHA-type aluminosilicate zeolite that can form a dense film.

[0087] The ratio of the silica source to the organic template in the aqueous reaction mixture, expressed as the molar ratio of the organic template to SiO (organic template / SiO ratio), is usually 0.005 or more, preferably 0.01 or more, more preferably 0.02 or more, and usually 1 or less, preferably 0.4 or less, more preferably 0.2 or less. Within this range, a dense zeolite membrane can be formed, and the formed zeolite is highly acid-resistant, with Al being less likely to be desorbed. Furthermore, under these conditions, a particularly dense and acid-resistant CHA-type aluminosilicate zeolite can be formed.

[0088] The ratio of Si element source to metal hydroxide is M (2 / n) The O / SiO (where M represents an alkali metal or alkaline earth metal, and n represents its valence of 1 or 2) molar ratio is usually 0.02 or more, preferably 0.04 or more, more preferably 0.05 or more, and usually 0.5 or less, preferably 0.4 or less, more preferably 0.3 or less.

[0089] When forming a zeolite membrane of CHA-type aluminosilicate, it is preferable to include potassium (K) among alkali metals in order to form a denser and more crystalline membrane. The molar ratio of K to the total of alkali metals and alkaline earth metals is usually 0.01 or more, preferably 0.1 or more, more preferably 0.3 or more, and the upper limit is usually 1 or less.

[0090] The addition of K to the aqueous reaction mixture formed within the preferred range of the present invention, as described above, changes the space group in the rhombohedral setting.

[0091]

number

[0092] When (No. 166) is used, there is a tendency to moderately increase the ratio of the peak intensity around 2θ = 9.6°, which is a peak derived from the plane with index (1,0,0) in the CHA structure, to the peak intensity around 2θ = 20.8°, which is a peak derived from the plane with index (2,0,-1).

[0093] The ratio of the Si element source to water, in terms of the molar ratio of water to SiO (H2O / SiO2 molar ratio), is usually 10 or more, preferably 30 or more, more preferably 40 or more, and particularly preferably 50 or more, and is usually 1000 or less, preferably 500 or less, more preferably 200 or less, and particularly preferably 150 or less.

[0094] When the molar ratio of the materials in the aqueous reaction mixture is within these ranges, dense zeolite membranes can be produced. The amount of water is particularly important in producing dense zeolite membranes, and dense membranes tend to be produced under conditions where the water content is higher relative to the silica content than under conditions typically used in powder synthesis.

[0095] Generally, the amount of water used when synthesizing powdered CHA-type aluminosilicate zeolite is an HO / SiO molar ratio of about 15 to 50. By using a high HO / SiO molar ratio (50 or more and 1000 or less), i.e., by using conditions with a high water content, it is possible to obtain a zeolite membrane composite with high separation performance, in which CHA-type aluminosilicate zeolite is crystallized in the form of a dense membrane on the surface of the support or the like.

[0096] Furthermore, during hydrothermal synthesis, it is not necessary to have seed crystals present in the reaction system, but adding seed crystals can promote the crystallization of zeolite on the support. The method for adding seed crystals is not particularly limited, and methods such as adding seed crystals to an aqueous reaction mixture, as in the synthesis of powdered zeolite, or attaching seed crystals to a support can be used. When producing a zeolite membrane composite, it is preferable to attach seed crystals to a support. Attaching seed crystals to a support in advance makes it easier to produce a dense zeolite membrane with good separation performance.

[0097] The seed crystals to be used may be of any type as long as they are zeolite that promotes crystallization, but for efficient crystallization, they preferably have the same crystal type as the zeolite membrane to be formed. When forming a zeolite membrane of CHA-type aluminosilicate, it is preferable to use CHA-type zeolite seed crystals.

[0098] The seed crystals preferably have a small particle size, and may be crushed before use as necessary. The particle size is usually 0.5 nm or more, preferably 1 nm or more, more preferably 2 nm or more, and usually 5 μm or less.

[0099] The method for attaching the seed crystals to the support is not particularly limited, and examples that can be used include a dipping method in which the seed crystals are dispersed in a solvent such as water and the support is immersed in the dispersion to attach the seed crystals to the surface, or a method in which the seed crystals are mixed with a solvent such as water to form a slurry, which is then applied to the support. The dipping method is desirable for controlling the amount of attached seed crystals and producing a membrane composite with good reproducibility.

[0100] The solvent in which the seed crystals are dispersed is not particularly limited, but water or an alkaline aqueous solution is particularly preferred. The type of alkaline aqueous solution is not particularly limited, but a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution is preferred. These alkaline species may also be mixed. The alkali concentration is not particularly limited, but is usually 0.0001 mol% or more, preferably 0.0002 mol% or more, more preferably 0.001 mol% or more, and even more preferably 0.002 mol% or more. The alkali concentration is also usually 1 mol% or less, preferably 0.8 mol% or less, more preferably 0.5 mol% or less, and even more preferably 0.2 mol% or less.

[0101] The amount of seed crystals to be dispersed is not particularly limited, and is usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 0.5% by mass or more, based on the total mass of the dispersion, and is usually 20% by mass or less, preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0102] If the amount of dispersed seed crystals is too small, the amount of seed crystals attached to the support will be small, which may result in areas on the support surface where zeolite is not produced during hydrothermal synthesis, resulting in a defective film.If the amount of seed crystals in the dispersion is too large, the amount of seed crystals attached to the support by the dipping method will be almost constant, which will result in a lot of wasted seed crystals and is disadvantageous in terms of cost.

[0103] It is desirable to attach seed crystals to a support by dipping or by applying a slurry, and then dry the support before forming a zeolite membrane.

[0104] The amount of seed crystals to be attached to the support in advance is not particularly limited. 2 The mass per unit area is usually 0.01 g or more, preferably 0.05 g or more, more preferably 0.1 g or more, and usually 100 g or less, preferably 50 g or less, more preferably 10 g or less.

[0105] If the amount of seed crystals is less than the lower limit, crystallization becomes difficult, and membrane growth tends to be insufficient or uneven. Furthermore, if the amount of seed crystals exceeds the upper limit, the seed crystals may increase the surface irregularities, or seed crystals that fall from the support surface may facilitate the growth of spontaneous nuclei, inhibiting membrane growth on the support. In either case, it tends to be difficult to produce a dense zeolite membrane.

[0106] When forming a zeolite membrane on a support by hydrothermal synthesis, there is no particular limitation on the method for immobilizing the support, and any form such as vertical placement, horizontal placement, etc. In this case, the zeolite membrane may be formed by a static method, or by stirring the aqueous reaction mixture.

[0107] The temperature for forming the zeolite membrane is not particularly limited, but is usually 100°C or higher, preferably 120°C or higher, and more preferably 150°C or higher, and usually 200°C or lower, preferably 190°C or lower, and more preferably 180°C or lower. If the reaction temperature is too low, the zeolite may be difficult to crystallize. If the reaction temperature is too high, a type of zeolite different from the zeolite of the present invention may be easily produced.

[0108] The heating (reaction) time is not particularly limited, but is usually 1 hour or more, preferably 5 hours or more, and more preferably 10 hours or more, and usually 10 days or less, preferably 5 days or less, more preferably 3 days or less, and even more preferably 2 days or less. If the reaction time is too short, the zeolite may be difficult to crystallize. If the reaction time is too long, a type of zeolite different from the zeolite of the present invention may be easily produced.

[0109] The pressure during zeolite membrane formation is not particularly limited, and the autogenous pressure generated when an aqueous reaction mixture placed in a sealed container is heated to this temperature range is sufficient. If necessary, an inert gas such as nitrogen may be added.

[0110] The zeolite membrane composite obtained by hydrothermal synthesis is washed with water, then heat-treated, and dried. Here, heat treatment means drying the zeolite membrane composite by applying heat, or calcining the template when a template is used.

[0111] The temperature of the heat treatment, when aimed at drying, is usually 50° C. or higher, preferably 80° C. or higher, more preferably 100° C. or higher, and usually 200° C. or lower, preferably 150° C. or lower. When aimed at calcining the template, the temperature is usually 350° C. or higher, preferably 400° C. or higher, more preferably 430° C. or higher, even more preferably 450° C. or higher, and usually 900° C. or lower, preferably 850° C. or lower, even more preferably 800° C. or lower, particularly preferably 750° C. or lower.

[0112] The heat treatment time is not particularly limited as long as it is sufficient to dry the zeolite membrane or calcinate the template, and is preferably 0.5 hours or more, more preferably 1 hour or more. The upper limit is not particularly limited, and is usually within 200 hours, preferably within 150 hours, more preferably within 100 hours, and particularly preferably within 24 hours.

[0113] When the hydrothermal synthesis is carried out in the presence of an organic template, it is appropriate to wash the obtained zeolite membrane composite with water and then remove the organic template by, for example, heat treatment or extraction, preferably heat treatment, i.e., calcination.

[0114] If the calcination temperature is too low, the proportion of the organic template remaining tends to be high, resulting in fewer pores in the zeolite, which may reduce the amount of gas permeation during separation and concentration. If the calcination temperature is too high, the difference in thermal expansion coefficient between the support and the zeolite will be large, which may cause the zeolite membrane to be prone to cracks, leading to a loss of density in the zeolite membrane and reduced separation performance.

[0115] The calcination time varies depending on the rate of temperature increase and decrease, but is not particularly limited as long as it is a time that allows the organic template to be sufficiently removed, and is preferably 1 hour or more, more preferably 5 hours or more. There is no particular upper limit, and for example, it is usually within 200 hours, preferably within 150 hours, more preferably within 100 hours, and particularly preferably within 24 hours. Calcination may be carried out in an air atmosphere, or in an atmosphere in which oxygen or an inert gas is added to air.

[0116] The rate of temperature rise during firing is desirably as slow as possible to prevent cracks in the zeolite membrane due to the difference in thermal expansion coefficient between the support and the zeolite. The rate of temperature rise 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. In consideration of workability, the rate is usually 0.1°C / min or more.

[0117] The rate of temperature drop after firing must also be controlled to avoid cracking of the zeolite membrane. As with the rate of temperature rise, the slower the rate, the better. The rate of temperature drop 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. In consideration of workability, the rate is usually 0.1°C / min or more.

[0118] The zeolite membrane may be subjected to ion exchange or silylation treatment as required. When synthesis is performed using a template, ion exchange is usually performed after removing the template. The ions to be exchanged include protons, Na + , K. + , Li + Alkali metal ions such as Ca 2+ , Mg 2+ , Sr 2+ , Ba 2+ and ions of transition metals such as Fe, Cu, Zn, Ag, Al, Ga, and La. Among these, protons, Na + , Mg 2+ , Ca 2+ and Fe, Al, Ga, La ions are preferred.

[0119] Ion exchange can be performed by treating the zeolite membrane after calcination (when a template is used, for example) with an aqueous solution containing an ammonium salt such as NH4NO3 or NaNO3 or the ions to be exchanged, or in some cases with an acid such as hydrochloric acid, usually at a temperature between room temperature and 100°C, followed by rinsing with water. If necessary, the membrane may be further calcined at 200°C to 500°C. The silylation treatment will be described later.

[0120] The air permeability of the zeolite membrane composite after heat treatment is usually 10 L / (m 2 ·h) or more, preferably 20 L / (m 2 ·h), more preferably 30L / (m 2 ·h) or more, more preferably 35 L / (m 2 ·h) or more, and particularly preferably 100 L / (m 2 The upper limit of the permeation rate is not particularly limited, but is preferably 1000 L / (m 2 ·h) or less, more preferably 800L / (m 2 ·h) or less, more preferably 700 L / (m 2 ·h) or less.

[0121] Here, the air permeability is the amount of air permeated [L / (m ] 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 will be described in detail in the Examples section. 2 ·h)].

[0122] The air permeability is a value that is linked to the gas permeability. A membrane with a high air permeability also has a high gas permeability, but an membrane with an excessively high air permeability tends to have poor separation performance. As described above, the zeolite membrane of the present invention has a moderately high air permeability, a high gas permeability, and good separation performance, and is particularly suitable for separating gas components.

[0123] The zeolite composite membrane thus produced has excellent properties and can be suitably used as a membrane separation means for gas mixtures in the present invention.

[0124] (Silylation treatment) It is also preferable to subsequently contact the zeolite membrane composite with a Si element source (hereinafter, this may be referred to as "silylation treatment"). As a result, the zeolite membrane surface is modified with the Si compound, and can be made to have specific physicochemical properties. For example, it is thought that forming a layer containing a large amount of Si-OH on the zeolite membrane surface can improve the hydrophilicity of the membrane surface and thereby improve separation performance. In addition, modifying the zeolite membrane surface with the Si compound can also have the secondary effect of sealing fine defects present on the membrane surface.

[0125] The silica source used in the silylation treatment can be contacted with the zeolite membrane composite in the form of a liquid or gas. When contacting as a liquid, the liquid used for the silylation treatment is not particularly limited as long as it is in a state in which the zeolite membrane composite can be immersed under the conditions of the silylation treatment. It may be a solution of a Si element source, for example, a Si compound, with a solvent, or a liquid without a solvent, such as a sol or gel. Here, the solvent may be water or an organic solvent. Furthermore, solvents that become liquid under pressure at temperatures above their boiling points are also included. In this case, the pressure may be either autogenous pressure or pressurized pressure. Furthermore, the liquid for the silylation treatment is sufficient as long as it contains at least a Si compound, and may also contain other element sources (compounds), such as an Al compound.

[0126] First, the case where water is used as the solvent will be described. When water is used as the solvent, the temperature of the solution is usually 20°C or higher, preferably 60°C or higher, more preferably 80°C or higher, and usually 200°C or lower, preferably 150°C or lower, more preferably 130°C or lower. If the temperature is above the lower limit, the dehydration condensation reaction and hydrolysis reaction that occur between the Si compound, the membrane surface, and the Si compound proceed sufficiently, resulting in sufficient modification by the Si compound and sufficient improvement in the hydrophilicity of the membrane surface. If the temperature is below the upper limit, there is little possibility that the zeolite will be partially dissolved in water, causing damage to the zeolite membrane.

[0127] The immersion time is usually 1 hour or more, preferably 4 hours or more, more preferably 8 hours or more, and usually 100 hours or less, preferably 50 hours or less, more preferably 24 hours or less. If the immersion time is equal to or greater than the lower limit, the membrane surface changes sufficiently, and a sufficient effect can be obtained. If the immersion time is equal to or less than the upper limit, the zeolite is less likely to be partially dissolved in water and break down. The pressure during the silylation treatment is not particularly limited, and atmospheric pressure or the autogenous pressure generated when the treatment solution placed in a sealed container is heated to the above-mentioned temperature range is sufficient. If necessary, an inert gas such as nitrogen may be added.

[0128] Examples of usable Si compounds include alkoxysilanes such as tetraethoxysilane, tetramethoxysilane, methyltriethoxysilane, and 3-aminopropyltriethoxysilane, amorphous silica, fumed silica, colloidal silica, silica gel, sodium silicate, silicate oligomers, and silica sol. Among these, alkoxysilanes are preferred in terms of reactivity, and tetraethoxysilane, 3-aminopropyltriethoxysilane, and silicate oligomers are particularly preferred, as they have fewer alkyl groups and are highly hydrophilic after hydrolysis. Examples of the Al compound that can be used include sodium aluminate, aluminum hydroxide, aluminum sulfate, aluminum nitrate, aluminum oxide, alumina sol, amorphous aluminosilicate gel, and aluminum alkoxides such as aluminum isopropoxide. Among these, aluminum alkoxides are preferred. These Si compounds may be used alone or in combination of two or more. When an Al compound is used in combination with a Si compound, it may be used alone or in combination of two or more.

[0129] The content of the Si compound or Al compound in the solution is, as the total concentration of Si element and Al element, usually 0.01% by mass or more, preferably 0.03% by mass or more, more preferably 0.1% by mass or more, and usually 20% by mass or less, preferably 10% by mass or less, more preferably 5% by mass or less. In the case of Si element, the concentration is usually 0.01% by mass or more, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and usually 10% by mass or less, preferably 5% by mass or less, more preferably 2% by mass or less. It is preferable to have an acid or base present in the solution as a catalyst for the dehydration condensation reaction between the OH groups on the zeolite surface and the Si compound, the dehydration condensation reaction between the Si compound, and the hydrolysis reaction of the alkoxy groups. Therefore, if the solution is acidic, the pH is usually 0 to 5, preferably 0.5 to 4, and more preferably 1 to 3, and if the solution is basic, the pH is usually 8 to 13, preferably 9 to 13, and more preferably 10 to 12.

[0130] By adding basic substances such as NaOH, KOH, and amines to water, trace amounts of OH -1 Ions may be actively present, in which case OH in the aqueous solution -1 The ion concentration is usually 0.01 mol / L or less, more preferably 0.005 mol / L or less, and usually 0.0001 mol / L or more, preferably 0.0005 mol / L or more, more preferably 0.001 mol / L or more. -1 The presence of OH ions makes it possible to achieve the same effect in a shorter time than without them. -1 When the ion concentration is equal to or lower than the upper limit, the zeolite membrane is less likely to be dissolved and destroyed, and strict control of the treatment time becomes unnecessary.

[0131] Examples of the acid to be present in the aqueous solution include organic acids such as carboxylic acids and sulfonic acids, and inorganic acids such as sulfuric acid and phosphoric acid. Of these, carboxylic acids and inorganic acids are particularly preferred. Preferred carboxylic acids include formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, maleic acid, phthalic acid, lactic acid, citric acid, and acrylic acid, with formic acid, acetic acid, and lactic acid being more preferred, and acetic acid being particularly preferred. Preferred inorganic acids include sulfuric acid, nitric acid, phosphoric acid, and hydrochloric acid, with sulfuric acid, nitric acid, and phosphoric acid being more preferred.

[0132] The concentration of the acidic substance in the aqueous solution is preferably 0.01 mol / l or more, more preferably 0.05 mol / l or more, and preferably 10 mol / l or less, more preferably 1 mol / l or less. Also, H + The concentration is usually 1 x 10 -10 mol / l or more, preferably 1×10 -8 mol / l or more, more preferably 1×10 -7 mol / l or more, particularly preferably 1×10 -5 mol / L or more, and is usually 10 mol / L or less, preferably 5 mol / L or less, and more preferably 1 mol / L or less. H + A basic substance may be present so that the concentration falls within the above range. Examples of the basic substance include NaOH, KOH, and amines.

[0133] Next, the immersion treatment using an organic solvent will be described. In this case, the temperature of the solution is usually 20°C or higher, preferably 60°C or higher, more preferably 80°C or higher, and usually 200°C or lower, preferably 150°C or lower, more preferably 110°C or lower. If the temperature is above the above lower limit, the dehydration condensation reaction and hydrolysis reaction that occur between the Si compound, the membrane surface, and the Si compound proceed sufficiently, resulting in sufficient modification by the Si compound and sufficient improvement in the hydrophilicity of the membrane surface. If the temperature is below the above upper limit, there is little possibility that the zeolite will be partially dissolved in water, causing damage to the zeolite membrane. The immersion time is usually 0.5 hours or more, preferably 1 hour or more, more preferably 3 hours or more, and usually 50 hours or less, preferably 24 hours or less, more preferably 10 hours or less. If the immersion time is equal to or greater than the lower limit, the membrane surface changes sufficiently, and a sufficient effect can be obtained. If the immersion time is equal to or less than the upper limit, the zeolite is less likely to be partially dissolved in water and break down.

[0134] The pressure during the silylation treatment is not particularly limited, and can be atmospheric pressure under reflux conditions as needed. Alternatively, the treatment can be carried out under the autogenous pressure that occurs when the treatment solution placed in a sealed container is heated to the temperature range described above. Furthermore, an inert gas such as nitrogen can be added as needed. Examples of organic solvents that can be used include nonpolar solvents such as toluene and hexane, alcohol solvents such as anisole and isopropyl alcohol, and polar solvents such as acetone. Among these, toluene and isopropyl alcohol are particularly preferred. These organic solvents may be used alone or in combination of two or more. Furthermore, when an organic solvent is used, water may be added to the system. The concentration of water that can be added is usually 0.001% by mass or more, preferably 0.05% by mass or more, more preferably 0.2% by mass or more, and usually 5% by mass or less, preferably 3% by mass or less, more preferably 2% by mass or less.

[0135] The types of Si compounds and Al compounds that can be used are the same as when water is used as the solvent, but the Si compounds are preferably alkoxysilanes, with tetraethoxysilane, 3-aminopropyltriethoxysilane, and silicate oligomers being particularly preferred, and the Al compounds are particularly preferably aluminum alkoxides. These Si compounds may be used alone or in combination of two or more. When an Al compound is used in combination with a Si compound, it may be used alone or in combination of two or more. The content of the Si compound in the solution is usually 0.01% by mass or more, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and usually 10% by mass or less, preferably 5% by mass or less, more preferably 2% by mass or less, in terms of the concentration of the Si element. The content of the Al compound is usually 0.01% by mass or more, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and usually 10% by mass or less, preferably 5% by mass or less, more preferably 1% by mass or less, in terms of the concentration of the Al element.

[0136] In the silylation treatment, when the substrate is immersed in a liquid containing at least a Si element source, for example, a Si compound, the treatment can be performed without adding a solvent. In particular, when a silicate oligomer is used as the Si compound, the solvent need not be added. Even when no solvent is added, the substrate may contain, for example, an Al compound as another element source (compound). When silylation treatment is performed without adding a solvent, the immersion temperature is usually 1°C or higher, preferably 5°C or higher, more preferably 10°C or higher, and particularly preferably 15°C or higher, and usually 200°C or lower, preferably 150°C or lower, more preferably 130°C or lower, particularly preferably 100°C or lower, and most preferably 80°C or lower. If the temperature is above the above lower limit, the fluidity of the Si compound increases, and the Si compound and Al compound adhere uniformly to the zeolite membrane composite surface, preventing partial modification. If the temperature is below the above upper limit, the reactions between Si compounds, between Al compounds, and between Si compounds and Al compounds proceed slowly, allowing the adhesion and reaction to the zeolite membrane composite surface to proceed sufficiently.

[0137] The immersion time is usually 0.5 seconds or more, preferably 1 second or more, more preferably 2 seconds or more, and particularly preferably 3 seconds or more, and usually 10 hours or less, preferably 7 hours or less, more preferably 5 hours or less, even more preferably 3 hours or less, and particularly preferably 1 hour or less. When no solvent is added to a liquid containing a Si compound, the concentration of the Si compound is higher than when a solvent is added, so the silylation process generally tends to be completed sufficiently at a lower temperature and in a shorter time than when a solvent is added.

[0138] The pressure during the silylation treatment is not particularly limited, and atmospheric pressure or the autogenous pressure generated when the treatment solution placed in a sealed container is heated to the above-mentioned temperature range is sufficient. Furthermore, an inert gas such as nitrogen may be added if necessary. When silylation treatment is performed without adding a solvent, when the zeolite membrane composite is immersed in a liquid containing Si compounds, in the case of a tubular zeolite membrane composite, it is desirable to prevent a large amount of Si compounds and Al compounds from permeating into the support by sealing only the bottom or both the top and bottom with a silicone rubber stopper or Teflon (registered trademark) tape. By contacting the Si compounds and Al compounds only with the surface of the zeolite membrane and preventing their permeation into the support, the surface of the zeolite membrane can be efficiently silylated while maintaining a high permeation rate.

[0139] When the silylation treatment is performed without adding a solvent, the zeolite composite membrane may be immersed in a liquid, sol, or gel containing at least the above-mentioned Si element source, e.g., a Si compound, and then heated. The heating temperature is usually 30°C or higher, preferably 50°C or higher, and more preferably 70°C or higher, and usually 300°C or lower, preferably 250°C or lower, more preferably 200°C or lower, and particularly preferably 150°C or lower. When the temperature is above the lower limit, the modification of the zeolite membrane surface with the Si compound or Al compound is sufficiently fixed. When the temperature is below the upper limit, the Si-OH formed by the modification does not condense to form Si-O-Si bonds, and the hydrophilicity of the membrane surface is sufficiently improved.

[0140] When heating after immersion, the heating time is usually 30 minutes or more, preferably 1 hour or more, more preferably 1.5 hours or more, and even more preferably 2 hours or more, and usually 30 hours or less, preferably 25 hours or less, more preferably 20 hours or less, and even more preferably 15 hours or less. When the time is equal to or greater than the above lower limit, the modification with the Si compound and Al compound on the zeolite membrane surface is sufficiently fixed. When the time is equal to or less than the above upper limit, heating is performed within a range in which the modification with the Si compound and Al compound is sufficiently fixed, which is advantageous in terms of energy. When heating after immersion, water may be present in the heating system, which facilitates the hydrolysis of alkoxysilanes contained in silicate oligomers and the like, facilitating sufficient modification of the zeolite membrane surface.

[0141] Heating after immersion can be carried out using a conventional dryer or the like, or the immersed membrane may be placed in a sealed container and heated. When the immersed membrane is placed in the sealed container, a small amount of water may be present so as not to come into contact with the membrane.

[0142] Next, we will explain the case where the silica source is contacted as a gas. There are no particular restrictions on the silica source used in the silylation treatment, as long as it has vapor pressure. A Si compound containing Si atoms is made into a gaseous state and, depending on the conditions, is supplied to the zeolite membrane portion of the zeolite membrane composite together with water vapor, and reacted. This results in the formation of a silica layer on the surface of the zeolite membrane. The effect is the same as when the silica source is contacted as a liquid, as described above. Examples of Si compounds containing Si atoms that can be used in this treatment include, as liquid raw materials before vaporization of gaseous raw materials, alkylalkoxysilanes such as methyltriethoxysilane, 3-aminopropyltriethoxysilane, and 1,1,3,3-tetramethoxy-1,3-dimethylpropanedisiloxane; organosilicon compounds containing siloxanes such as hexamethyldisiloxane; organosilicon compounds containing silazane such as hexamethyldisilazane; silicates such as tetramethoxysilane and tetraethoxysilane; and silicate oligomers such as methylsilicate oligomer and ethylsilicate oligomer.

[0143] Among these, silicate or silicate oligomer is preferred in terms of reactivity, tetraethoxysilane and methyl silicate oligomer are particularly preferred, methyl silicate oligomer is more preferred, and polymethoxysiloxane is most preferred. These Si compounds may be used singly or in combination of two or more.

[0144] The Si compound can be converted into a gas by vaporizing it from a liquid Si compound by heating, or by placing the liquid Si compound in a container and bubbling an inert gas for transportation such as nitrogen, helium, argon, xenon, or krypton into the liquid Si compound to generate a gas. The treatment method is not particularly limited as long as it allows the raw material gas to be supplied to the zeolite membrane composite and reacted. For example, a method is available in which the zeolite membrane composite, together with a Si compound liquid and water, is sealed in a sealed reactor and heated. The gas generated by vaporization of the Si compound in the sealed reactor and the water vapor generated from the water at high temperature are reacted on the zeolite membrane composite. The sealed reactor is not particularly limited, and any container can be used as long as it can accommodate the shape and dimensions of the zeolite membrane composite. For example, a stainless steel autoclave with a Teflon (registered trademark) inner cylindrical container can be used. By placing the stainless steel autoclave with the inner cylindrical container in a thermostatic bath at the desired temperature, the saturated vapor pressure of the water vapor and the gas generated from the Si raw material supply source at that temperature is achieved, and saturated vapor of the gas generated from the Si raw material and the water vapor is generated in the container. The shape of the water vapor and Si raw material supply source is not particularly limited as long as they are contained in a sealed reactor. Water and liquid Si raw material may be placed in small containers or impregnated into porous materials.

[0145] The treatment temperature is usually 20°C or higher, preferably 60°C or higher, more preferably 80°C or higher, and usually 200°C or lower, preferably 150°C or lower, more preferably 130°C or lower. When the temperature is above the lower limit, the dehydration condensation reaction and hydrolysis reaction between the Si compound, the zeolite membrane, and the Si compound proceed sufficiently, the modification treatment with the Si compound is carried out sufficiently, and the hydrophilicity of the zeolite membrane is sufficiently improved. On the other hand, when the temperature is below the upper limit, the reaction of the zeolite membrane does not proceed too far, the permeation resistance is reduced, and a membrane sample with high permeation performance is obtained. In the production method of the present invention, all steps are preferably carried out at 200° C. or lower.

[0146] The treatment time is usually 1 hour or more, preferably 2 hours or more, more preferably 3 hours or more, and usually 24 hours or less, preferably 8 hours or less, more preferably 5 hours or less. When the treatment time is equal to or greater than the lower limit, the reaction of the zeolite membrane proceeds sufficiently, and sufficient effects are obtained. On the other hand, when the treatment time is equal to or less than the upper limit, the reaction of the zeolite membrane does not proceed too much, and the permeation resistance is reduced, resulting in a membrane sample with high permeation performance. The zeolite composite membrane thus produced has excellent properties as described above and can be suitably used as a membrane separation means in the separation or concentration method of the present invention.

[0147] (gas mixture containing at least hydrogen and water vapor) In the method for separating or concentrating hydrogen of the present invention, the gas mixture to be separated or concentrated contains at least hydrogen and water vapor.

[0148] In the hydrogen separation or concentration method of the present invention, the water vapor partial pressure in the gas mixture is preferably 0.6 kPa or more and 12.4 kPa or less. The inventors' investigations revealed that when the water content in the gas mixture is this high, the water is adsorbed onto the zeolite separation membrane, inhibiting hydrogen permeance. The present invention solves this problem. The partial pressure of water vapor in the gas mixture is more preferably 1.2 kPa or more and 7.4 kPa or less.

[0149] The gas mixture is preferably one obtained by removing excess steam from gas obtained by steam reforming methane-containing gas. As mentioned above, it can be used when producing hydrogen from natural gas, but coke oven gas (COG gas) can also be used as a raw material.

[0150] (Modification process) Coke oven gas is a gas obtained when coal is carbonized in a coke oven, and its main components are hydrogen, methane, carbon monoxide, and hydrocarbons (including hydrocarbon components with two or more carbon atoms). Because coke oven gas contains a large amount of hydrogen, it is a desirable hydrogen source. However, when coke oven gas containing hydrocarbon components with two or more carbon atoms is allowed to pass through a zeolite separation membrane, the hydrocarbon components with two or more carbon atoms may clog the zeolite membrane.

[0151] For this reason, the hydrogen separation or concentration method of the present invention preferably includes, as a pretreatment step for the gas mixture, a steam reforming step at a temperature lower than that of steam reforming of natural gas, to the extent that hydrocarbon components having two or more carbon atoms are decomposed. In the steam reforming step, hydrocarbon components having two or more carbon atoms are decomposed, resulting in an equilibrium state of hydrogen, methane, carbon dioxide, and carbon monoxide. The higher the temperature in this equilibrium state, the more favorable it is for hydrogen production; however, hydrogen production in this equilibrium state is an endothermic reaction, and a large amount of heat is required. In this case, as described above, the gas mixture after reforming contains a large amount of water vapor.

[0152] The coke oven gas steam reforming process is preferably carried out at a temperature of 600°C or less. By setting the steam reforming process at 600°C or less, hydrocarbon components having two or more carbon atoms can be efficiently decomposed while reducing the amount of heat used. The lower limit of the temperature is preferably 400°C or more.

[0153] (Dehydration process) The hydrogen separation or concentration method of the present invention preferably further comprises a dehydration step of the gas mixture after the reforming step. After undergoing steam reforming in the reforming step, the gas mixture contains a large amount of moisture. In the dehydration step, moisture in the gas mixture is removed to a certain extent before the gas mixture is subjected to the membrane separation step.

[0154] For example, in high-pressure gas facilities, the installation of a cooler is limited. Therefore, the dehydration process must be performed at room temperature. In such cases, sufficient dehydration cannot be performed, and even after dehydration, water vapor at the above-mentioned predetermined water vapor partial pressure remains in the gas mixture. Even in such cases, the hydrogen separation or concentration method of the present invention makes it possible to separate or concentrate hydrogen without reducing the hydrogen permeance.

[0155] (Membrane separation process) In the hydrogen separation or concentration method of the present invention, a gas mixture consisting of a plurality of gas components is brought into contact with the above-described zeolite membrane, and hydrogen is separated and concentrated from the gas mixture by permeation. One of the separation functions of the zeolite membrane in the present invention is separation as a molecular sieve, and it can suitably separate gas molecules having a size equal to or larger than the effective pore size of the zeolite used from gas molecules having a size smaller than that.

[0156] Therefore, the highly permeable gas component in the present invention is a gas component consisting of gas molecules that easily pass through the pores of the zeolite crystalline phase of the CHA-type aluminosilicate, and is preferably a gas component consisting of gas molecules with a molecular diameter of approximately 0.38 nm or less. The effective pore size of zeolite can be controlled by the type of metal introduced, ion exchange, acid treatment, silylation treatment, etc. Controlling the effective pore size can also improve separation performance.

[0157] The pore size is slightly affected by the atomic size of the metal species introduced into the zeolite framework. When a metal with an atomic size smaller than that of silicon, such as boron (B), is introduced, the pore size becomes smaller. When a metal with an atomic size larger than that of silicon, such as tin (Sn), is introduced, the pore size becomes larger. In addition, the pore size may be affected by acid treatment, which removes the introduced metal from the framework.

[0158] When ion exchange is performed with monovalent ions with large ionic radii, the effective pore diameter tends to become smaller, while when exchange is performed with monovalent ions with small ionic radii, the effective pore diameter approaches the pore diameter of the CHA structure. Even in the case of divalent ions such as calcium, the effective pore diameter approaches the pore diameter of the CHA structure depending on the position of the exchange site.

[0159] The effective pore size of zeolite can also be reduced by silylation treatment. By silylating the terminal silanols on the outer surface and then stacking a silylated layer, the effective pore size of the pores facing the outer surface of the zeolite is reduced.

[0160] 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 physical 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.

[0161] By substituting Al for Si in the zeolite framework, it is possible to increase the polarity, which allows highly polar gas molecules to be actively adsorbed into and permeate the zeolite pores. Furthermore, decreasing the amount of Al substitution results in a zeolite membrane with low polarity, which is advantageous for the permeation of low polarity gas molecules. It is also possible to control polarity by adding Ga, Fe, B, Ti, Zr, Sn, or Zn to the element source other than the Al element source.

[0162] In addition, ion exchange can be used to control the molecular adsorption performance and the pore size of the zeolite, thereby controlling the permeability.

[0163] In the present invention, the temperature of the gas mixture to be subjected to the zeolite membrane must be 80° C. or higher and 200° C. or lower. The lower limit is preferably 100° C. or higher, more preferably 120° C. or higher, and the upper limit is preferably 180° C. or lower, more preferably 140° C. or lower. By setting the temperature of the gas mixture in this manner, a predetermined hydrogen permeance can be ensured even when the gas mixture contains water vapor at a predetermined water vapor partial pressure.

[0164] The pressure of the feed gas may be the same if the gas to be separated is at a high pressure, or may be adjusted to a desired pressure by reducing the pressure as appropriate. If the pressure of the gas to be separated is lower than the pressure used for separation, the pressure may be increased using a compressor or the like.

[0165] The pressure of the supply gas is not particularly limited, but is usually atmospheric pressure or higher, preferably 0.1 MPa or higher, more preferably 0.15 MPa or higher, and even more preferably 2 MPa or higher, and the upper limit is usually 20 MPa or lower, preferably 10 MPa or lower, and more preferably 6 MPa or lower.

[0166] The pressure difference between the hydrogen gas on the supply side and the hydrogen gas on the permeation side is not particularly limited, but is usually 20 MPa or less, preferably 10 MPa or less, more preferably 8 MPa or less, and even more preferably 6 MPa or less, and is usually 0.001 MPa or more, preferably 0.01 MPa or more, and more preferably 0.02 MPa or more.

[0167] Here, the differential pressure refers to the difference between the partial pressure on the supply side and the partial pressure on the permeation side of the gas. Furthermore, pressure [Pa] refers to absolute pressure unless otherwise specified.

[0168] The pressure on the permeation side is not particularly limited, but is usually 10 MPa or less, preferably 5 MPa or less, more preferably 1 MPa or less, and even more preferably 0.5 MPa or less. There is no particular limit to the lower limit, as long as it is 0 MPa or more. When the pressure is 0 MPa, separation can be performed until the concentration of the highly permeable gas in the less permeable gas is at its lowest. If there is an application in which the permeation side gas is used at a high pressure, the permeation side pressure can be set high.

[0169] The flow rate of the feed gas should be a rate that can compensate for the decrease in permeating gas and that can mix the gases so that the concentration of the less permeable gas in the feed gas in the immediate vicinity of the membrane matches the concentration in the entire gas.Depending on the pipe diameter of the separation unit and the separation performance of the membrane, the flow rate is usually 0.5 mm / sec or more, preferably 1 mm / sec or more, with no particular upper limit, and usually 2 m / sec or less, preferably 1 m / sec or less.

[0170] In the method for separating or concentrating a gas mixture of the present invention, a sweep gas may be used. In the method using a sweep gas, a gas different from the feed gas is passed through the permeation side of the membrane, 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, and is preferably 20 MPa or less, more preferably 10 MPa or less, and even more preferably 1 MPa or less, with the lower limit being preferably 0.09 MPa or more, more preferably 0.1 MPa or more. In some cases, the sweep gas may be used at reduced pressure.

[0171] The flow rate of the sweep gas is not particularly limited as long as it can sufficiently replace the permeating gas, and is usually 0.5 mm / sec or more, preferably 1 mm / sec or more, with no particular upper limit, and is usually 1 m / sec or less, preferably 0.5 m / sec or less.

[0172] The apparatus used for gas separation is not particularly limited, but is usually used as a module. The membrane module may be, for example, an apparatus as schematically shown in Figures 3 and 10, or a membrane module exemplified in "Gas Separation and Purification Technology" (Toray Research Center, Inc., 2007, p. 22).

[0173] When performing membrane separation of gases, membranes may be used in multiple stages. That is, the gas to be separated may be supplied to a membrane module, and the non-permeated gas that does not permeate the membrane may be supplied to another membrane module, or the permeated gas may be supplied to another membrane module. The former method can further increase the concentration of less permeable components in the non-permeated side, while the latter method can further increase the concentration of more permeable components in the permeated gas. When separation is performed using multiple membranes, the gas pressure may be adjusted by a pressure booster or the like as necessary when supplying gas to the membrane in the latter stage.

[0174] In addition, when using multiple stages, membranes with different performance may be installed in each stage. Generally, membranes with high permeability tend to have low separation performance, while membranes with high separation performance tend to have low permeability. Therefore, when processing gas components to be separated or concentrated to a desired concentration, membranes with high permeability require a smaller membrane area, but the low-permeability components to be concentrated on the non-permeate side tend to easily permeate to the permeate side. Membranes with high separation performance tend to require a larger membrane area, but the low-permeability components to be concentrated on the non-permeate side are less likely to permeate to the permeate side. When using a single type of membrane for separation, the relationship between the required membrane area and the permeation rate of the target gas to be concentrated is difficult to control. However, using membranes with different performance makes this easier. By installing membranes to achieve the optimal relationship between membrane area and permeation rate of the target gas to be concentrated, based on the membrane cost and the price of the gas to be separated and recovered, the overall benefits can be maximized.

[0175] The zeolite membrane composite of the present invention has excellent chemical resistance, oxidation resistance, heat stability, and pressure resistance, and also exhibits high permeability and separation performance, and has excellent durability.

[0176] The term "high permeability" as used herein refers to a sufficient throughput. However, in the hydrogen separation or concentration method of the present invention, even if the gas mixture to be separated contains water vapor at a predetermined water vapor partial pressure, the permeance [mol·(m 2 ·s·Pa) -1 ] means to indicate. For example, when hydrogen is passed through at a temperature of 100°C and a differential pressure of 0.098 MPa, the permeance is preferably 1 x 10 -8 More preferably, 3×10 -8 More preferably, 5 × 10 -8 More preferably, 7 × 10 -8 or more, most preferably 1 × 10 -7 The upper limit is not particularly limited, and is usually 3 × 10 -4 The following is the result.

[0177] For example, when methane is passed through under the same conditions, the permeance [mol (m 2 ·s·Pa) -1 ] is preferably 3 x 10 -7 Less than or equal to 3 x 10 -8 Less than or equal to 1×10 -8 Ideally, the permeance is 0, but in practice it is 10 -9 ~10 -14 There may be cases where the order is more than enough.

[0178] Here, permeance (also called "permeability") is the amount of permeating substance divided by the product of the membrane area, time, and the partial pressure difference between the supply side and the permeation side of the permeating substance, and its unit is [mol (m 2 ·s·Pa) -1 ], which is calculated by the method described in the Examples section.

[0179] The selectivity of a zeolite membrane is expressed by an ideal separation factor and a separation factor. The ideal separation factor and the separation factor are indicators of selectivity generally used in membrane separation, and the ideal separation factor is a value calculated by the method described in the Examples section, and the separation factor is a value calculated by the method described below.

[0180] In addition, when separating mixed gases, the separation factor is calculated using the following formula (2). Separation factor = (Q'1 / Q'2) / (P'1 / P'2) (2) [In equation (2), Q'1 and Q'2 are the permeation amounts [mol (m 2 ·s) -1 ], and P'1 and P'2 represent the partial pressures [Pa] of the high-permeability gas and the low-permeability gas in the supply gas, respectively.

[0181] The separation factor can also be calculated using the following formula (3): Separation factor = (C'1 / C'2) / (C1 / C2) (3) (In formula (3), C'1 and C'2 represent the concentrations [mol %] of the highly permeable gas and the less permeable gas in the permeating gas, respectively, and C1 and C2 represent the concentrations [mol %] of the highly permeable gas and the less permeable gas in the supply gas, respectively.)

[0182] For example, when carbon dioxide and methane are permeated at a temperature of 50°C and a differential pressure of 0.1 MPa, the ideal separation factor is usually 10 or more, preferably 20 or more, more preferably 30 or more, even more preferably 40 or more, and particularly preferably 50 or more. The upper limit of the ideal separation factor is when only carbon dioxide permeates, in which case the factor is infinite, but in practice the separation factor may be about 100,000 or less.

[0183] For example, when a mixed gas of carbon dioxide and methane in a volume ratio of 1:1 is permeated at a temperature of 100°C and a differential pressure of 0.098 MPa, the separation factor is usually 10 or more, preferably 20 or more, more preferably 30 or more, even more preferably 40 or more, and particularly preferably 50 or more. The upper limit of the separation factor is when only carbon dioxide permeates, in which case it is infinite, but in practice the separation factor may be about 100,000 or less.

[0184] As described above, the zeolite membrane composite of the present invention has excellent chemical resistance, oxidation resistance, heat stability, and pressure resistance, and also exhibits high permeability and separation performance and is highly durable. Therefore, it can be particularly suitably used, for example, in the following gas separation techniques.

[0185] Hydrogen separation technologies include hydrogen recovery in the oil refining industry, hydrogen recovery and purification (mixtures of hydrogen, carbon monoxide, carbon dioxide, hydrocarbons, etc.) in various reaction processes in the chemical industry, and the production of high-purity hydrogen for fuel cells. Hydrogen for fuel cells is produced by the steam reforming reaction of methane, and requires the separation of hydrogen from a gas mixture of H2, CO, CH4, and H2O.

[0186] In particular, the method of the present invention is particularly suitable for applications in which hydrogen is separated and concentrated from gas mixtures containing a predetermined amount of water vapor obtained by steam reforming natural gas or coke oven gas (COG), particularly in high-pressure gas facilities where a dehydrator using a cooler cannot be installed.

[0187] <Hydrogen separation or concentration equipment> (membrane separator) The hydrogen separation or concentration device of the present invention includes a membrane separator as an essential component. An example of the membrane separator is the device shown in FIG.

[0188] (reformer) The hydrogen separation or concentration device of the present invention preferably further includes a reformer. The reformer is a device that reacts the raw material gas with steam in a reforming furnace to produce hydrogen and also decomposes hydrocarbon components having two or more carbon atoms. For example, a Ni catalyst, a Ru catalyst, or the like is used as the reforming catalyst.

[0189] (dehydrator) The hydrogen separation or concentration device of the present invention preferably further includes a dehydrator. A known gas-liquid separator can be used as the dehydrator. As mentioned above, high-pressure gas facilities have the limitation that a cooler cannot be installed. For this reason, dehydration must be performed at room temperature, and a dehydrator without a cooling function is preferably used as the dehydrator. [Example]

[0190] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples as long as it does not depart from the gist of the invention. Note that the values ​​of various production conditions and evaluation results in the following examples represent preferred upper or lower limit values ​​in the embodiments of the present invention, and a preferred range may be defined by combining the above-mentioned upper or lower limit values ​​with the values ​​of the following examples or values ​​of the examples themselves.

[0191] In the following experimental examples, the physical properties and separation performance of the zeolite membrane were measured by the following methods. (1) X-ray diffraction (XRD) The XRD measurement was carried out under the following conditions. Device name: X'PertPro MPD manufactured by PANalytical, Netherlands Optical system specifications: Entrance side: sealed X-ray tube (CuKα) Soller Slit (0.04rad) Divergence Slit (Variable Slit) Sample stage: XYZ stage Light receiving side: Semiconductor array detector (X' Celerator) Ni-filter SollerSlit (0.04rad) Goniometer radius: 240 mm Measurement conditions: X-ray output (CuKα): 45 kV, 40 mA Scan axis: θ / 2θ Scanning range (2θ): 5.0-70.0° Measurement mode: Continuous Reading width: 0.05° Counting time: 99.7 seconds Automatic variable slit (Automatic-DS): 1 mm (irradiation width) Horizontal divergence mask: 10 mm (irradiation width)

[0192] The X-rays were irradiated perpendicular to the axial direction of the cylindrical tube. To minimize noise, the X-rays were aimed primarily at the other line above the surface of the sample stage, rather than the line tangent to the surface of the sample stage. In addition, the irradiation width was fixed at 1 mm using an automatic variable slit for measurement, and the XRD pattern was obtained by performing variable slit to fixed slit conversion using the XRD analysis software JADE 7.5.2 (Japanese version) from MaterialsData, Inc.

[0193] (2) SEM-EDX ·Equipment name: SEM:FE-SEM Hitachi:S-4800 EDX:EDAX Genesis Acceleration voltage: 10kV The entire field of view (25 μm×18 μm) was scanned at a magnification of 5000 times, and X-ray quantitative analysis was performed.

[0194] (3) SEM The SEM measurement was carried out under the following conditions. ·Equipment name: SEM:FE-SEM Hitachi:S-4100 Acceleration voltage: 10kV

[0195] (4) Air permeability Under atmospheric pressure, one end of the zeolite membrane composite was sealed, and the other end was connected to a 5 kPa vacuum line while maintaining airtightness. The flow rate of air passing through the zeolite membrane composite was measured with a mass flow meter installed between the vacuum line and the zeolite membrane composite, and the air permeation rate [L / (m 2 The mass flow meter used was a KOFLOC 8300 for N2 gas with a maximum flow rate of 500 ml / min (20°C, 1 atmosphere equivalent). When the mass flow meter reading on the KOFLOC 8300 was 10 ml / min (20°C, 1 atmosphere equivalent) or less, a Lintec MM-2100M for air gas with a maximum flow rate of 20 ml / min (0°C, 1 atmosphere equivalent) was used for measurements.

[0196] (5) Mixed gas permeation test The mixed gas permeation test was carried out as follows using the apparatus shown schematically in FIG.

[0197] In Fig. 3, a cylindrical zeolite membrane composite 1 is placed in a thermostatic bath (not shown) while being housed in a stainless steel pressure-resistant container 2. The thermostatic bath is equipped with a temperature control device so that the temperature of the sample gas can be adjusted. One end of the cylindrical zeolite membrane composite 1 is sealed with a columnar end pin 3. The other end is connected with a connector 4, and the other end of the connector 4 is connected to a pressure-resistant vessel 2. The inside of the cylindrical zeolite membrane composite 1 is connected to a pipe (permeate gas discharge pipe) 11 for discharging a permeate gas 8 via the connector 4, and the pipe 11 extends to the outside of the pressure-resistant vessel 2. A pressure gauge 5 for measuring the pressure on the supply side of the sample gas is connected to a point leading to the pressure-resistant vessel 2. Each connection is airtight.

[0198] When a mixed gas permeation test is performed in the apparatus shown in Figure 3, a sample gas (feed gas 7) is supplied at a constant pressure between the pressure vessel 2 and the zeolite membrane composite 1, and the permeated gas 8 that has permeated the zeolite membrane composite 1 is measured by a flow meter (not shown) connected to a pipe 11, and its composition is analyzed by gas chromatography or the like (not shown).

[0199] The apparatus shown in FIG. 7 can also be used to conduct a single-component gas permeation test as follows. In Fig. 7, a cylindrical zeolite membrane composite 1 is placed in a thermostatic bath (not shown) while being housed in a stainless steel pressure-resistant container 2. The thermostatic bath is equipped with a temperature control device so that the temperature of the sample gas can be adjusted. One end of the cylindrical zeolite membrane composite 1 is sealed with a circular end pin 3. The other end is connected by a connector 4, which is in turn connected to a pressure-resistant vessel 2. A pipe 11 for discharging a permeation gas 8 is connected to the inside of the cylindrical zeolite membrane composite 1 via the connector 4, and the pipe 11 extends to the outside of the pressure-resistant vessel 2. A pipe 12 (sweep gas introduction pipe) for supplying a sweep gas 9 is inserted into the zeolite membrane composite 1 via the pipe 11. Furthermore, a pressure gauge 5 for measuring the pressure on the supply side of the sample gas and a back-pressure valve 6 for adjusting the pressure on the supply side are connected to somewhere leading to the pressure-resistant vessel 2. Each connection is airtight.

[0200] 7, when a single-component gas permeation test is performed, a sample gas (supply gas 7) is supplied at a constant flow rate between the pressure vessel 2 and the zeolite membrane composite 1, and the pressure on the supply side is kept constant by the back pressure valve 6. The flow rate of the exhaust gas 10 discharged from the pipe 11 is measured.

[0201] More specifically, to remove components such as moisture and air, the sample is dried at a temperature higher than the measurement temperature, and then purged with exhaust or the supply gas to be used. After the sample temperature and the differential pressure between the supply gas 7 side and the permeation gas 8 side of the zeolite membrane composite 1 are kept constant, the flow rate of the sample gas (permeation gas 8) that has permeated the zeolite membrane composite 1 is measured, and the gas permeance [mol (m 2 ·s·Pa) -1 The pressure used to calculate permeance is the pressure difference (differential pressure) between the supply side and permeation side of the feed gas.

[0202] Based on the above measurement results, the ideal separation factor α is calculated using the following formula (1). α=(Q1 / Q2) / (P1 / P2) (1) [In equation (1), Q1 and Q2 represent the permeation amounts [mol (m 2 ·s) -1 ], and P1 and P2 indicate the pressure difference [Pa] between the supply side and the permeation side of the high-permeability gas and the low-permeability gas, respectively. This indicates the ratio of the permeance of each gas, and therefore the permeance of each gas can be calculated and determined from the ratio.

[0203] [Experimental Example 1 (Zeolite membrane (without silylation treatment))] Using the same procedure as in Example 1 of JP 2017-64716 A, an inorganic porous support-CHA type zeolite membrane composite was prepared by directly hydrothermally synthesizing a CHA type aluminosilicate zeolite on an inorganic porous support.

[0204] The XRD pattern of the produced zeolite membrane is shown in Figure 1. The "*" in the figure indicates a peak derived from the support. XRD measurement confirmed that CHA-type zeolite was produced. The ratios of (peak intensity near 2θ = 9.6°) / (peak intensity near 2θ = 20.8°) were 3.0 and (peak intensity near 2θ = 17.9°) / (peak intensity near 2θ = 20.8°) were 0.47.

[0205] The XRD pattern of powdered CHA-type zeolite (the zeolite commonly referred to as SSZ-13 in U.S. Pat. No. 4,544,538; hereinafter referred to as "SSZ-13") is shown in Figure 2. The peak intensity near 2θ = 9.6° / peak intensity near 2θ = 20.8° was 0.91, and the peak intensity near 2θ = 17.9° / peak intensity near 2θ = 20.8° was 0.32.

[0206] Compared to powdered CHA-type zeolite, the zeolite membrane obtained in Example 1 had a similar (peak intensity around 2θ=17.9°) / (peak intensity around 2θ=20.8°) ratio, but a higher (peak intensity around 2θ=9.6°) / (peak intensity around 2θ=20.8°) ratio, suggesting orientation to the (1,0,0) plane in the rhombohedral setting.

[0207] The SiO2 / Al2O3 molar ratio of the zeolite membrane was measured by SEM-EDX and was found to be 66.

[0208] A mixed gas permeation test was performed using the CHA-type zeolite membrane composite prepared above, using the apparatus shown in Figure 3. As a pretreatment, the zeolite membrane composite was dried for approximately 30 minutes at 120 °C with CO2 as the feed gas 7 introduced between the cylinder between the pressure vessel 2 and the zeolite membrane composite 1, maintaining a flow rate of 0.3 L / min and a pressure of approximately 0.15 MPa. The inside of the cylinder containing the zeolite membrane composite 1 was set to 0.10 MPa (atmospheric pressure). The gases evaluated were a hydrogen / methane mixed gas (without water vapor) and a hydrogen / methane mixed gas (with water vapor). The hydrogen and methane flow rates were both 0.5 L / min. Water vapor was supplied by bubbling the test gas through a pressure vessel filled with water at room temperature. The water vapor partial pressure in the 0.4 MPa feed gas was 3.3 kPa. The water vapor partial pressure was determined by measuring the dew point of the supply gas at atmospheric pressure using a dew point meter (VAISALA handheld dew point meter DM70), determining the saturated vapor pressure at that dew point, and converting it to a pressure at 0.4 MPa. The pressure on the supply side was then set to 0.4 MPa, the supply gas was changed to a hydrogen / methane mixed gas (without steam), and the flow rate of the permeated gas was measured and the composition was analyzed. At this time, the differential pressure between the supply gas 7 side and the permeated gas 8 side of the zeolite membrane composite 1 was 0.3 MPa. Next, the supply gas was changed to a hydrogen / methane mixed gas (with steam), and a similar evaluation was performed. The membrane was then dried again, and the temperature was set to 50°C. After the temperature stabilized, a similar evaluation was performed. After the evaluation at 50°C, the membrane was dried again, and the temperature was changed to 80°C, 100°C, 120°C, 140°C, and 180°C, and measurements were performed in the same manner.

[0209] The left column of Table 1 shows the permeance of hydrogen and methane at each temperature and the ideal separation factor (H2 / CH4) when a mixed gas without water vapor (dry) is used.

[0210] The right column of Table 1 shows the permeance of hydrogen, methane, and water vapor at each temperature, as well as the ideal separation factor (H2 / CH4) when a mixed gas containing water vapor (wet) is used.

[0211] [Table 1]

[0212] Graphs of hydrogen or methane permeance at each temperature are shown in Figures 4(a), (b) and 5(a) and (b). From these graphs, it can be seen that without water vapor (dry), hydrogen permeance tends to decrease as the temperature increases, but with water vapor (wet), hydrogen permeance tends to increase as the temperature increases, demonstrating that high permeance can be maintained between 80°C and 180°C.

[0213] [Experimental Example 2 (Zeolite membrane (with silylation treatment))] An inorganic porous support-CHA-type zeolite membrane composite was prepared under the same conditions as in Experimental Example 1. Air saturated with water vapor was supplied to the zeolite membrane composite at room temperature to adsorb water vapor into the zeolite membrane composite. The zeolite membrane composite was then placed upright in a 200 ml Teflon (registered trademark) inner cylindrical container. A porous tubular body, previously impregnated with 0.3 g of polymethoxysiloxane (MKC (registered trademark) silicate silicate, MS-56, manufactured by Mitsubishi Chemical Corporation), a methyl silicate oligomer serving as a silica raw material, was placed upright in the inner cylindrical container. The inner cylindrical container was then sealed in an autoclave and maintained at 90°C in a thermostatic chamber for 4 hours. After cooling, the zeolite membrane composite was removed and heat-treated in a thermostatic chamber at 130°C for 3 hours. Hereinafter, this treatment will be referred to as "silylation treatment 1." Using the inorganic porous support-CHA-type zeolite membrane composite subjected to silylation treatment 1, the permeance was measured at 50°C, 100°C, 120°C, and 140°C for a hydrogen / methane mixed gas (without water vapor) and a hydrogen / methane mixed gas (with water vapor) in the same manner as in Experimental Example 1. The water vapor partial pressure in the presence of water vapor was 3.0 kPa. The results are shown in Table 2, Figures 6(a), (b), and 7(a) and (b).

[0214] [Table 2]

[0215] This shows that without steam (dry), the effect of temperature on hydrogen permeance is relatively small, but with steam (wet), hydrogen permeance tends to increase as the temperature rises, and that high hydrogen permeance and high hydrogen / methane selectivity can be maintained between 100°C and 140°C.

[0216] In Experimental Example 2, the silylation treatment significantly improved the hydrogen permeance in the presence of water vapor by increasing the temperature. This shows that increasing the temperature is effective in improving hydrogen permeance.

[0217] [Experimental Example 3 (Zeolite membrane (with silylation treatment))] An inorganic porous support-CHA type zeolite membrane composite was prepared under the same conditions as in Experimental Example 1. This zeolite membrane composite was subjected to a silylation treatment in the same manner as in Experimental Example 2, except that polymethoxysiloxane (MKC (registered trademark) silicate, MS-51, manufactured by Mitsubishi Chemical Corporation), which is a methyl silicate oligomer, was used as the silica raw material. Hereinafter, this treatment will be referred to as "silylation treatment 2." Using the inorganic porous support-CHA-type zeolite membrane composite subjected to silylation treatment 2, the permeance was measured at 100°C, 120°C, 140°C, 160°C, and 180°C for a hydrogen / methane mixed gas (without water vapor) and a hydrogen / methane mixed gas (with water vapor) in the same manner as in Experimental Example 1. The water vapor partial pressure in the presence of water vapor was 3.0 kPa. The results are shown in Table 3, Figures 8(a), (b), and 9(a) and (b).

[0218] [Table 3]

[0219] This shows that without steam (dry), the effect of temperature on hydrogen permeance is relatively small, but with steam (wet), hydrogen permeance tends to increase as the temperature increases, and that high hydrogen permeance and high hydrogen / methane selectivity can be maintained between 100°C and 180°C.

Claims

1. A method for separating hydrogen from a gas mixture containing at least hydrogen and water vapor by permeation using a zeolite membrane, comprising: The temperature of the gas mixture when passing through the zeolite membrane is set to 100°C or more and 200°C or less. Methods for separating or concentrating hydrogen.

2. 2. The method for separating or concentrating hydrogen according to claim 1, wherein the partial pressure of water vapor in the gas mixture is 0.6 kPa or more and 12.4 kPa or less.

3. 3. The method for separating or concentrating hydrogen according to claim 1 or 2, wherein the zeolite membrane contains a CHA-type aluminosilicate zeolite, and in an X-ray diffraction pattern obtained by irradiating the membrane surface with X-rays, the peak intensity around 2θ = 17.9° has a value less than 0.5 times the peak intensity around 2θ = 20.8°, and the peak intensity around 2θ = 9.6° has a value 2.0 times or more but less than 4.0 times the peak intensity around 2θ = 20.8°.

4. The SiO of the zeolite ２ / Al ２ O ３ The method for separating or concentrating hydrogen according to any one of claims 1 to 3, wherein is 20 or more and 500 or less.

5. 5. The method for separating or concentrating hydrogen according to claim 1, wherein the zeolite membrane has been subjected to a silylation treatment.

6. 6. The method for separating or concentrating hydrogen according to claim 1, wherein the gas mixture is obtained by steam reforming a gas containing a hydrocarbon component.

7. 7. The method for separating or concentrating hydrogen according to claim 1, wherein the gas mixture is obtained by steam reforming a gas containing hydrogen, methane, and hydrocarbon components having two or more carbon atoms.

8. 8. The method for separating or concentrating hydrogen according to claim 6, wherein the steam reforming is carried out at a temperature of 600°C or less.

9. The method for separating or concentrating hydrogen according to any one of claims 6 to 8, further comprising a step of dehydrating the gas mixture after the steam reforming.

10. The method for separating or concentrating hydrogen according to any one of claims 1 to 9, wherein the temperature of the gas mixture when passing through the zeolite membrane is 100°C or higher and 200°C or lower (excluding 100°C).

11. A hydrogen separation or concentration device comprising a membrane separator equipped with the zeolite membrane, and performing the hydrogen separation or concentration method according to any one of claims 1 to 10.

12. The hydrogen separation or concentration apparatus according to claim 11, further comprising a reformer.

13. The hydrogen separation or concentration apparatus according to claim 11 or 12, further comprising a dehydrator.

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