JP6901725B2 - Zeolite separation membrane and its manufacturing method - Google Patents

Description

The present invention relates to a zeolite separation membrane and a method for producing the same.

Zeolites have pores peculiar to crystals and are substances that can be expected to have ideal molecular sieving properties. However, zeolite is generally obtained as powder crystals, and it is necessary to accumulate a lot of know-how to create a macrozeolite membrane without intercrystal cracks.
As a method for producing a macrozeolite film using zeolite microcrystals, a zeolite film is precipitated on a support of a porous body such as alumina by a hydrothermal synthesis method or a vapor phase method using silica and alumina as starting materials. There is a method of making it (Patent Document 1). Further, a method of forming a zeolite membrane on a support using zeolite microcrystals as seed crystals has also been reported (Patent Document 3).

Japanese Unexamined Patent Publication No. 2003-210950 Japanese Unexamined Patent Publication No. 2013-59714 Japanese Unexamined Patent Publication No. 2016-174996 Japanese Unexamined Patent Publication No. 2016-179417

The pore size of the zeolite crystal is about 1.0 nm, and it can be suitably used as a separation membrane for selectively separating a specific component from a mixture of a plurality of components. However, if there are defects such as cracks in the zeolite membrane, the separation action does not work in the defective part. Therefore, in order to fully exert the separation action by the zeolite membrane, a macro zeolite membrane completely free of defects is required. Must be prepared. Considerable know-how is required to produce such a zeolite membrane.
An object of the present invention is to provide a zeolite membrane capable of reliably utilizing the separating action of zeolite crystals by pores, and a suitable method for producing the zeolite membrane.

The zeolite separation membrane according to the present invention is a zeolite separation membrane in which zeolite microcrystals are bonded to each other, and the surface of each of the zeolite microcrystals is coated with graphene oxide, and zeolite is passed through the graphene oxide. It is characterized in that microcrystals are bonded without gaps.
Further, the zeolite separation membrane according to the present invention is a zeolite separation membrane in which zeolite microcrystals are bonded to each other, and the surface of each of the zeolite microcrystals is coated with graphene, and zeolite is interposed through the graphene. It is characterized in that microcrystals are bonded without gaps.
The meaning that the zeolite microcrystals are bonded without gaps means that the zeolite microcrystals are densely bonded via graphene oxide or graphene, and the separation function based on the pore structure of the zeolite crystals is maintained, that is, zeolite. It means that it is configured as a separation film in a state in which defects such as cracks that impair the separation function by crystals are completely eliminated.

Further, the method for producing a zeolite separation film according to the present invention includes a step of preparing a dispersion liquid in which a zeolite microcrystal and graphene oxide are dispersed in water, and a graphene oxide on the surface of the zeolite microcrystal in the dispersion liquid. To obtain a dispersion of zeolite microcrystals coated with graphene oxide, and a zeolite microcrystal coated with graphene oxide from a dispersion in which zeolite microcrystals coated with graphene oxide are dispersed. It is characterized by comprising a step of filtering to obtain a zeolite separation film in which zeolite microcrystals are bonded without gaps via graphene oxide that coats the surface of the zeolite microcrystals.
Further, in the step of preparing the dispersion liquid of the zeolite microcrystals coated with the graphene oxide, the graphene oxide and the zeolite microcrystals interact with each other in the dispersion liquid, and the graphene oxide is formed on the surface of the zeolite microcrystals. By adjusting the pH value to which the zeolite adheres, the surface of the zeolite microcrystal can be reliably and easily coated with graphene oxide.
Further, the method for producing a zeolite separation membrane according to the present invention is described as a subsequent step of obtaining a zeolite separation membrane in which zeolite microcrystals are bonded without gaps via graphene oxide that coats the surface of the zeolite microcrystals. A step of reducing the graphene oxide that coats the surface of the zeolite microcrystals to obtain a zeolite separation membrane in which the zeolite microcrystals are bonded without gaps via the graphene that coats the surface of the zeolite microcrystals is provided. It is a feature.

The zeolite separation membrane according to the present invention can be provided as a separation membrane that surely has a separation function by pores of zeolite crystals. Further, according to the method for producing a zeolite separation membrane according to the present invention, the zeolite separation membrane can be reliably and easily produced.

It is a schematic diagram which shows the structure of the zeolite separation membrane (a) which coated the zeolite microcrystal with graphene, and the zeolite separation membrane (b) which consists of a zeolite microcrystal. It is a structural drawing of MFI zeolite and BEA zeolite. AFM image (atomic force microscope image) and thickness measurement profile of graphene oxide. It is a graph which shows the result of having measured the pH change of the surface charge density of graphene oxide, and the structural model figure of graphene oxide. It is a graph which shows the result of having investigated the change by pH of the surface charge density of a zeolite microcrystal and graphene oxide. It is a graph which shows the result of having measured the change of the ionic strength when ammonium chloride was added to the dispersion liquid of a zeolite microcrystal and graphene oxide, and the pH was changed. It is a figure which shows the action when ammonium chloride is added to the dispersion liquid of a zeolite microcrystal and graphene oxide. It is a photograph which shows the result of having experimented the dispersion state of a zeolite microcrystal and graphene oxide by changing the addition amount of ammonium chloride added to the aqueous dispersion liquid of a zeolite microcrystal and graphene oxide. It is a photograph showing the state immediately after preparing a dispersion liquid by setting the addition amount of ammonium chloride to 0.05 M, and after 48 hours have passed. Regarding the aqueous dispersion of zeolite microcrystals, graphene oxide, and zeolite microcrystals coated with graphene oxide, it was measured whether or not the dispersion state changed in the state of being in equilibrium with the initial state in which the dispersion was prepared. It is a graph which shows the result. Photograph showing the results of experiments on the dispersibility of zeolite microcrystals coated with graphene oxide with and without addition of ammonium chloride to the aqueous dispersion of zeolite microcrystals and graphene oxide. Is. It is a figure which shows the example of the heat treatment process which prepares the zeolite microcrystal which is coated with graphene oxide, and is formed the zeolite microcrystal which is coated with graphene. Nitrogen adsorption isotherm graph (a), nitrogen adsorption isotherm graph under low pressure (b), graph showing pore distribution of graphene-zeolite separation membrane (c), zeolite separation membrane composed of graphene-coated zeolite microcrystals It is an SEM image of. Nitrogen adsorption isotherm graph (a), nitrogen adsorption isotherm graph under low pressure (b), graph showing pore distribution of graphene-zeolite separation membrane (c), zeolite separation membrane composed of graphene-coated zeolite microcrystals It is an SEM image of. Nitrogen adsorption isotherm graph (a), nitrogen adsorption isotherm graph under low pressure (b), graph showing pore distribution of graphene-zeolite separation membrane (c), zeolite separation membrane composed of graphene-coated zeolite microcrystals It is an SEM image of. Nitrogen adsorption isotherm graph (a), nitrogen adsorption isotherm graph under low pressure (b), graph showing pore distribution of graphene-zeolite separation membrane (c), zeolite separation membrane composed of graphene-coated zeolite microcrystals It is an SEM image of. It is a graph which shows the result of having measured the surface area of a zeolite microcrystal and the surface area of a zeolite microcrystal coated with graphene. It is a graph (a) which measured the relationship between the helium pressure and the flow velocity, and the graph which shows the result of having investigated the permeability of nitrogen and helium.

(Structure of Zeolite Separation Membrane)
The zeolite separation membrane according to the present invention has a function of separating a mixed gas or the like by utilizing the minute pore structure of the zeolite crystals, and has a sheet-like form in which zeolite microcrystals are bonded without gaps. It is formed. In the present invention, in order to bond the zeolite microcrystals without gaps, the surface of the zeolite microcrystals is coated with graphene or graphene oxide, and the zeolite microcrystals are bonded without gaps via graphene or graphene oxide. Constructed as a membrane.

FIG. 1 (a) schematically shows the structure of a zeolite separation membrane formed by coating the surface of the zeolite microcrystals 10 with graphene 12, and FIG. 1 (b) schematically shows a zeolite separation membrane composed of only the conventional zeolite microcrystals 10. It was shown to. FIGS. 1 (a) and 1 (b) show that when the mixed gas is passed through the zeolite separation membrane, only minute molecules pass through the zeolite separation membrane and are separated.

In FIG. 1A, graphene 12 is drawn so as to be continuously arranged (in the form of a sheet) between the adjacent zeolite crystallites 10, but graphene 12 is continuous between the zeolite crystallites. It is not distributed. Actually, the graphene 12 is smaller than the zeolite microcrystals 10, and the surface of the zeolite microcrystals 10 is coated with a plurality of graphenes 12.
The size of the zeolite microcrystal 10 is not particularly limited, but in order to cover it with a plurality of graphenes (a size of about 10 nm to several tens of nm), a small diameter one of 50 nm or more. Those with a diameter of 100 nm and those with a large diameter of about 10 μm to 20 μm can be used.

The pores of graphene or graphene oxide covering the zeolite microcrystals 10 are much larger than the pores of the zeolite microcrystals and do not affect the molecular separation action based on the pore structure of the zeolite microcrystals. Further, the zeolite separation membrane is used by supporting it on a support 14 having pores having a diameter larger than the pores of the zeolite separation membrane such as alumina.

As shown in FIGS. 1 (a) and 1 (b), in order for the separation action of the zeolite microcrystals due to the pore structure to function effectively, the zeolite microcrystals are mutually (both in the planar direction and in the stacking direction). It needs to be configured as a tightly bonded film without gaps. If a slight gap (pore) is present in the zeolite microcrystal film due to a defect or the like, the separation action due to the pore structure of zeolite is hindered. FIG. 1 (b) shows that the separation action is insufficient if the zeolite microcrystals are not bonded without gaps.
In the zeolite separation membrane according to the present invention, the surface of the zeolite microcrystals is coated with graphene or graphene oxide, and the zeolite microcrystals are bonded via graphene or graphene oxide to ensure that the zeolite microcrystals are formed. It is tightly bonded and a separating action based on the crystal structure of zeolite can be surely obtained.

The zeolite separation membrane does not originally have conductivity, but the zeolite separation membrane in which the zeolite microcrystals are coated with graphene according to the present invention has conductivity. Therefore, in this case, by applying a voltage to the zeolite separation membrane, charged molecules can be retained in the zeolite separation membrane, and uncharged molecules can be separated.

(Manufacturing method of zeolite separation membrane)
<Action of zeolite microcrystals and graphene oxide>
In the method for producing a zeolite separation membrane according to the present invention, the surface of the zeolite microcrystals is coated with graphene oxide, and the zeolite microcrystals coated with graphene oxide are bonded to each other to form a sheet-shaped zeolite separation membrane (compression molding). Membrane) is prepared.
The zeolite microcrystals used in the experiment for producing the zeolite separation membrane are MFI zeolite (manufactured by Waseda University, Mitsubishi Chemical), BEA zeolite (manufactured by Waseda University), and zeolite F9 (size 10 μm or more) manufactured by Toso.
Table 1 shows the sizes and pore diameters of MFI zeolite and BEA zeolite. In addition, FIG. 2 shows the structures of MFI zeolite and BEA zeolite.

The reason for using relatively small zeolite microcrystals as MFI zeolite and BEA zeolite is that when the zeolite microcrystals are coated (wrapped) with graphene oxide, the smaller zeolite microcrystals are coated with graphene oxide. I thought it would be easy. Of course, the size of the zeolite microcrystals used to prepare the zeolite separation membrane is not limited to the sizes shown in Table 1.

FIG. 3 shows an AFM image (atomic force microscope image) of graphene oxide used for coating zeolite microcrystals and a profile of measured thickness.
The part that looks dark in the AFM image is the substrate for measurement, and the part that looks slightly bright is graphene oxide. The height profile is an AFM image measured by scanning across the boundary between the substrate and graphene oxide.
From the measurement result of the height profile, the thickness of graphene oxide is about 2 nm, and it seems that 3-5 graphene oxides to be measured overlap.

The reason why the zeolite microcrystals are coated with graphene oxide in the method of the present invention is that the zeolite microcrystals are coated with graphene oxide so that the zeolite microcrystals do not bond (integrate) with each other through graphene oxide. This is because the zeolite microcrystals are easily bonded to each other.
In order to enable the surface of the zeolite microcrystals to be coated with graphene oxide, in the method of the present invention, a dispersion liquid in which the zeolite microcrystals and graphene oxide are dispersed in water is prepared (step of preparing the dispersion liquid), and between the particles. Zeolite microcrystals are coated with graphene oxide using the electrostatic interaction of.

To see the electrostatic interaction, the surface charge density of graphene oxide was investigated. FIG. 4 shows the results of investigating how the surface charge density of graphene oxide changes with pH. From FIG. 4, it can be seen that graphene oxide is negatively charged and that the surface charge density hardly changes in the pH range of about 2 to 10.
FIG. 4 shows a structural model diagram of graphene oxide.

FIG. 5 shows the results of measuring the change in charge density with pH for the MFI zeolite, BEA zeolite, and F9 zeolite shown in Table 1. FIG. 5 also shows the surface charge density of graphene oxide at each pH value.
In FIG. 5, since both the zeolite microcrystal and graphene oxide have a negative surface charge, simply dispersing them in water causes them to repel each other, and the zeolite microcrystal is coated with graphene oxide. Indicates that is difficult.

<Action by adjusting the pH of the dispersion>
In the present invention, as a method for interacting the zeolite microcrystals with graphene oxide, the surface charge density of graphene oxide hardly changes in the pH range of about 1 to 10, whereas the surface charge density of the zeolite microcrystals changes due to the pH change. Since the surface charge density changes, by changing the ionic strength using ammonium chloride, the Debye length, which indicates the thickness of the electric double layer that determines the electrostatic repulsion between particles, is controlled (thinned). The surface of the zeolite microcrystals was controlled to be easily covered with graphene oxide.

FIG. 6 shows the results of measuring the change in ionic strength when the pH was changed by adding ammonium chloride to the dispersion of zeolite microcrystals and graphene oxide. FIG. 7 shows that the addition of ammonium chloride protonates graphene oxide and increases the pH of the dispersion.
The measurement results shown in FIG. 6 show that the surface charges of zeolite microcrystals and graphene oxide change rapidly in a very narrow region where the pH is between 3-4.

FIG. 8 shows the dispersion of the zeolite microcrystals and graphene oxide when the pH of the dispersion was changed by changing the amount of ammonium chloride added to the aqueous dispersion (colloidal dispersion) of the zeolite microcrystals and graphene oxide. The result of experimenting how the state changes is shown.
FIG. 8 shows how the zeolite microcrystals and graphene oxide interact with each other depending on the amount of ammonium chloride added, and the volume of the colloidal dispersion system changes. The results of this experiment show that FIG. 11 shows the dispersed state of the zeolite microcrystals and graphene oxide depending on whether ammonium chloride is added to the dispersion liquid in which the zeolite microcrystals and graphene oxide are dispersed in water or not. The result of the experiment to see if it becomes like this is shown.
The surface of the zeolite microcrystals is coated with graphene oxide, and the zeolite microcrystals coated with graphene oxide are dispersed and not aggregated.

In FIG. 9, the amount of ammonium chloride added is set to 0.05 M, which is a condition under which the zeolite microcrystals and graphene oxide strongly interact with each other. It shows the state immediately after creation and after 48 hours have passed. The experimental results shown in FIG. 9 show that for all the zeolite microcrystals, the interaction between the zeolite microcrystals and graphene oxide is completed after 48 hours have passed, and the zeolite microcrystals are covered with graphene oxide. It shows that it has progressed (a step of preparing a dispersion of zeolite microcrystals coated with graphene oxide).

FIG. 10 shows a dispersion in which each of the zeolite microcrystals, graphene oxide, and zeolite microcrystals coated with graphene oxide is dispersed in water, and equilibrates with the initial state (start) in which the dispersion was prepared for about 20 hours. Whether or not the dispersed state changes in the state (equilibrium) is shown by the volume per weight of the system in the dispersed state.
From FIG. 10, it can be seen that the dispersed state of graphene oxide is maintained extremely well even in the initial state and the equilibrium state.
In addition, the zeolite microcrystals, which had good dispersibility in the initial state, settle over time, that is, the packing volume at equilibrium becomes extremely small.
Looking at the zeolite microcrystals coated with graphene oxide, a comparison between the initial state and the equilibrium state shows that the packing volume is only slightly reduced in the equilibrium state, and the dispersibility is maintained well. ing.

FIG. 11 shows an experiment on how the dispersion state of the zeolite microcrystals and graphene oxide differs depending on whether ammonium chloride is added to the aqueous dispersion of the zeolite microcrystals coated with graphene oxide or not. The result is shown.
FIG. 11 (a) shows a state in which a dispersion liquid of a zeolite microcrystal (Zeolite / GO) coated with graphene oxide to which ammonium chloride is added is viewed from above the container. It can be seen that Zeolite / GO is well dispersed in the dispersion liquid.

In FIG. 11 (b), ammonium chloride was added to prepare a Zeolite / GO dispersion, and in FIG. 11 (c), ammonium chloride was added to prepare a Zeolite / GO dispersion, and then dispersed at 60 ° C. Indicates a state in which the liquid is heated and dried. Zeolite / GO precipitates remain on the bottom of the container due to the drying process, but those without ammonium chloride are unevenly distributed in a part of the bottom of the container, while those with ammonium chloride added precipitate on the bottom of the container. Objects adhere evenly and remain. From this experiment, it can be seen that the addition of ammonium chloride to the dispersion improves the dispersibility of the zeolite microcrystals coated with graphene oxide.

<Preparation of Zeolite Separation Membrane by Graphene Oxide Coating>
As described above, the separation membrane composed of zeolite microcrystals coated with graphene oxide is prepared by adjusting the pH of the dispersion so that the zeolite microcrystals and graphene oxide strongly interact with each other. After preparing a dispersion of zeolite microcrystals coated with, it can be obtained by filtering the dispersion into a sheet with a filter. The zeolite separation membrane thus obtained is obtained as a separation membrane in which the surface of the zeolite microcrystals is coated with graphene oxide and the zeolite microcrystals are densely bonded to each other via graphene oxide. Since it can be obtained as a separation membrane in which zeolite microcrystals are closely bonded via graphene oxide, it can be suitably used for separation of a mixed gas or the like.
The operation of coating the zeolite microcrystals with graphene oxide only needs to set the conditions for controlling the pH of the dispersion liquid, and has an advantage that it is extremely easy as a method for producing a zeolite separation membrane.

<Preparation of zeolite separation membrane by graphene coating>
The zeolite separation membrane made of zeolite microcrystals coated with graphene can be obtained by a method of thermally reducing the separation membrane made of zeolite microcrystals coated with graphene oxide obtained by the above method.
FIG. 12 shows an example of a heat treatment step for producing a zeolite microcrystal coated with graphene from a zeolite microcrystal coated with graphene oxide. In this heat reduction treatment, the temperature is raised from room temperature to 573 K at a heating rate of 1 K / min in the inert machine body, held at 573 K for 30 minutes, and then lowered to room temperature at a temperature lowering rate of 1 K / min.

FIG. 13 shows the experimental results of confirming the pore structure of a zeolite separation membrane composed of graphene-coated zeolite microcrystals using 100 nm size MFI zeolite as the zeolite microcrystals.
FIG. 13 (a) is a nitrogen adsorption isotherm graph, FIG. 13 (b) is a nitrogen adsorption isotherm graph under low pressure, and FIG. 13 (c) is a graph showing the pore distribution of the graphene-zeolite separation membrane. In each case, the measurement results for the graphene-zeolite separation membrane and the measurement results for zeolite as a comparative example are shown. FIG. 13 (d) is an SEM image of a zeolite separation membrane composed of graphene-coated zeolite microcrystals.

From the measurement results shown in FIGS. 13 (a) and 13 (b), there is no significant change in the amount of nitrogen adsorbed near zero relative pressure between the zeolite separation membrane composed of zeolite microcrystals coated with graphene and ordinary zeolite. It can be seen that the pores derived from the zeolite crystals are retained even in the zeolite separation membrane made of zeolite microcrystals coated with graphene.
The graph of the pore distribution in FIG. 13 (c) shows that there is no significant change in the pores of 1 nm or less, and that there is a change in the interparticle structure between the zeolite microcrystals coated with graphene due to the graphene coating. , Indicates that wide mesopores are generated.
From the scanning electron microscope image of FIG. 13 (d), it is observed that the zeolite microcrystals are wrapped with graphene.

FIG. 14 shows the measurement results of the zeolite separation membrane composed of graphene-zeolite microcrystals using 200 nm size MFI zeolite as the zeolite microcrystals, and FIG. 15 shows the measurement result using 300 nm size MFI zeolite as the zeolite microcrystals. The results of measurement for a zeolite separation membrane composed of graphene-zeolite microcrystals are shown.
As for FIGS. 14 and 15, it can be seen that the zeolite separation membrane made of graphene-coated zeolite microcrystals has a pore structure similar to that of ordinary zeolite crystals, as in the measurement results shown in FIG. The pore structure varies depending on the size of the zeolite microcrystals used.

FIG. 16 shows the results of similar measurements on a zeolite separation membrane made of graphene-zeolite microcrystals using zeolite F9 as the zeolite microcrystals.
Zeolite F9 is a microcrystal with a size of about 10 μm, unlike MFI zeolite. In this case, it is possible that nitrogen adsorption at extremely low pressure is not sufficient and graphene blocks the pores of the zeolite crystallites. However, even in this case, the characteristics of the pore structure of the zeolite microcrystals can be seen.

FIG. 17 shows the results of measuring the surface area of ordinary zeolite microcrystals and the surface area of graphene-coated zeolite microcrystals. From FIG. 17, it can be seen that coating the zeolite microcrystals with graphene reduces the surface area by about 10-30%. However, even when the zeolite microcrystals are coated with graphene, the effectiveness of the pores of the zeolite microcrystals is clear from the above-mentioned experimental results of nitrogen adsorption.

<Example of separation experiment>
FIG. 18 shows the results of examining the characteristics of a zeolite separation membrane composed of graphene oxide / zeolite microcrystals prepared using 100 μm MFI zeolite microcrystals. The experiment was carried out by pasting the zeolite separation membrane on an alumina oxide filter having 200 nm pores.
FIG. 18A measures the relationship between the helium pressure and the flow velocity, and shows that the helium pressure and the flow velocity are linear and that the zeolite separation membrane has no cracks.
FIG. 18 (b) shows the permeability of nitrogen and helium by the change of the mixed gas supply side (Feed) and after the membrane permeation (Filtrate). According to this, after 16 hours, the helium pressure permeates the membrane, and then the pressure increases, but the nitrogen decreases. From this, it can be seen that helium is selectively transmitted. The selection coefficient is 1.9.
The results of this experiment show the separation characteristics of a zeolite separation membrane composed of graphene oxide / zeolite microcrystals.

10 Zeolite microcrystals 12 Graphene 14 Support

Claims (5)

A zeolite separation membrane formed by bonding zeolite microcrystals to each other.
A zeolite separation membrane characterized in that the surface of each of the zeolite microcrystals is coated with graphene oxide, and the zeolite microcrystals are bonded without gaps via the graphene oxide. A zeolite separation membrane formed by bonding zeolite microcrystals to each other.
A zeolite separation membrane characterized in that the surface of each of the zeolite microcrystals is coated with graphene, and the zeolite microcrystals are bonded without gaps via the graphene. A step of preparing a dispersion liquid in which zeolite microcrystals and graphene oxide are dispersed in water, and
A step of depositing graphene oxide on the surface of zeolite microcrystals in the dispersion to obtain a dispersion of zeolite microcrystals coated with graphene oxide.
The zeolite microcrystals coated with graphene oxide are filtered from the dispersion liquid in which the zeolite microcrystals coated with graphene oxide are dispersed, and the zeolite microcrystals are gapped through the graphene oxide covering the surface of the zeolite microcrystals. A method for producing a zeolite separation membrane, which comprises a step of obtaining a zeolite separation membrane which is formed without being bonded. In the step of preparing a dispersion liquid of zeolite microcrystals coated with graphene oxide.
The zeolite separation membrane according to claim 3, wherein the dispersion liquid is adjusted to a pH value at which graphene oxide and the zeolite microcrystals interact with each other to adhere graphene oxide to the surface of the zeolite microcrystals. Manufacturing method. As a post-process to obtain a zeolite separation membrane in which zeolite microcrystals are bonded without gaps via graphene oxide that coats the surface of zeolite microcrystals.
A step of reducing graphene oxide that coats the surface of the zeolite microcrystals to obtain a zeolite separation membrane in which the zeolite microcrystals are bonded without gaps via the graphene that coats the surface of the zeolite microcrystals. The method for producing a zeolite separation membrane according to claim 3 or 4, wherein the zeolite separation membrane is produced.

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