JP2017100087A - Separation membrane structure and p-xylene concentration method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separation membrane structure and a p-xylene concentration method that can improve the selectivity, permeation rate and separability of p-xylene.SOLUTION: A separation membrane structure 10 comprises a porous support 20, and a zeolite membrane 30 formed on the porous support 20 and having a pore composed of a 12-membered oxygen ring. The zeolite membrane 30 comprises barium.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a separation membrane structure and a method for concentrating paraxylene.

  Conventionally, a method has been proposed in which paraxylene is separated from a fluid mixture of C8 aromatic compounds containing three types of isomers of xylene (paraxylene, metaxylene, orthoxylene) and ethylbenzene by a separation membrane. The method of separating using a separation membrane has the advantage of being easy to handle and capable of continuous operation compared to the method of separating using an adsorbent.

  As a method for separating para-xylene with a separation membrane, a method using a polymer membrane (see Patent Document 1) and a method using an MFI type zeolite membrane as a molecular sieve (see Patent Document 2 and Non-Patent Document 1) have been proposed. .

Special table 2007-519719 gazette JP 2002-69012 A

Separation and Purification Technology, Vol. s5 (1-3) (2001) p297-306

  However, in the method of Patent Document 1, when the fluid mixture of the C8 aromatic compound comes into contact, the polymer membrane swells, so that paraxylene selectivity is lowered.

  In the method of Patent Document 2, paraxylene is separated by utilizing the difference in molecular size, so that the pore diameter of the MFI type zeolite membrane cannot be increased, and the paraxylene permeation rate is reduced. In the method of Patent Document 2, when the concentration of components other than paraxylene in the fluid mixture of C8 aromatic compounds is high, components other than paraxylene penetrate into the pores of the MFI type zeolite membrane and Since the permeation is inhibited, the paraxylene separation performance is reduced.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a separation membrane structure and a paraxylene concentration method capable of improving paraxylene selectivity, permeation rate, and separation performance.

  The separation membrane structure according to the present invention includes a porous support and a zeolite membrane having pores formed on the porous support and constituted by oxygen 12-membered rings. The zeolite membrane contains barium.

  According to the present invention, it is possible to provide a separation membrane structure and a paraxylene concentration method capable of improving the selectivity, permeation rate and separation performance of paraxylene.

Cross section of separation membrane structure

(Configuration of separation membrane structure 10)
The separation membrane structure 10 according to the present embodiment selectively transmits paraxylene from a fluid mixture containing a C8 aromatic compound as a main component. C8 aromatic compounds exist as three isomers of xylene (paraxylene, metaxylene, orthoxylene) and ethylbenzene. The phrase “containing a C8 aromatic compound as a main component” means that the concentration of the C8 aromatic compound in the fluid mixture is 90% by weight or more.

  FIG. 1 is a cross-sectional view showing the configuration of the separation membrane structure 10. The separation membrane structure 10 includes a porous support 20 and a zeolite membrane 30.

(1) Porous support 20
The porous support 20 supports the zeolite membrane 30. The porous support 20 has chemical stability such that the zeolite membrane 30 can be formed into a film shape (crystallization, coating, or deposition) on the surface.

  The porous support 20 may have any shape that can supply a mixed gas containing at least methane and nitrogen to the zeolite membrane 30. Examples of the shape of the porous support 20 include a honeycomb shape, a monolith shape, a flat plate shape, a tubular shape, a cylindrical shape, a columnar shape, and a prismatic shape.

  The porous support 20 according to this embodiment includes a base 21, an intermediate layer 22, and a surface layer 23.

  The base 21 is made of a porous material. As the porous material, for example, ceramic, metal, organic polymer, glass, carbon, or the like can be used. Examples of the ceramic include alumina, silica, mullite, zirconia, titania, yttria, silicon nitride, and silicon carbide. Examples of the metal include aluminum, iron, bronze, and stainless steel. Examples of the organic polymer include polyethylene, polypropylene, polytetrafluoroethylene, polysulfone, and polyimide. From the viewpoint of chemical stability, it is preferable to use at least one of ceramic, metal, and glass as the porous material.

  The base 21 may contain an inorganic binder. As the inorganic binder, at least one of titania, mullite, easily sinterable alumina, silica, glass frit, clay mineral, and easily sinterable cordierite can be used.

  The average pore diameter of the substrate 21 can be set to, for example, 0.5 μm to 25 μm. The average pore diameter of the substrate 21 can be measured with a mercury porosimeter. The porosity of the substrate 21 can be set to, for example, 25% to 50%. The average particle diameter of the porous material constituting the substrate 21 can be set to 5 μm to 100 μm, for example. In the present embodiment, the “average particle diameter” is a value obtained by arithmetically averaging the maximum diameters of 30 measurement target particles measured by cross-sectional microstructure observation using SEM (Scanning Electron Microscope).

  The intermediate layer 22 is formed on the base 21. The intermediate layer 22 can be made of the porous material that can be used for the substrate 21. The average pore diameter of the intermediate layer 22 may be smaller than the average pore diameter of the substrate 21, and may be, for example, 0.005 μm to 2 μm. The average pore diameter of the intermediate layer 22 can be measured by a palm porometer or a nano palm porometer according to the size of the pore diameter. The porosity of the intermediate layer 22 can be set to, for example, 20% to 60%. The thickness of the intermediate layer 22 can be set to 30 μm to 300 μm, for example.

  The surface layer 23 is formed on the intermediate layer 22. The surface layer 23 can be composed of the porous material that can be used for the base 21. The average pore diameter of the surface layer 23 may be smaller than the average pore diameter of the intermediate layer 22, and may be, for example, 0.001 μm to 1 μm. The average pore diameter of the surface layer 23 can be measured by a palm porometer or a nano palm porometer according to the size of the pore diameter. The porosity of the surface layer 23 can be set to, for example, 20% to 60%. The thickness of the surface layer 23 can be set to 1 μm to 50 μm, for example.

(2) Zeolite membrane 30
The zeolite membrane 30 is formed on the porous support 20 (specifically, the surface layer 23). The thickness of the zeolite membrane 30 is not particularly limited, but can be, for example, 0.1 μm to 10 μm. When the zeolite membrane 30 is thickened, the paraxylene separation performance tends to improve, and when the zeolite membrane 30 is thinned, the paraxylene permeation rate tends to increase.

The zeolite membrane 30 has a structure in which the SiO ₄ tetrahedron and the AlO ₄ tetrahedron are three-dimensionally connected while sharing oxygen at the apex. The zeolite membrane 30 is composed of zeolite having pores composed of oxygen 12-membered rings (hereinafter referred to as “oxygen 12-membered ring pores”). Examples of such a framework structure (type) of zeolite include AFI, BEA, CAN, FAU, GME, LTL, MOR, MSE, MTW, and OFF.

  The diameter of the oxygen 12-membered ring pore is larger than the diameter of a pore constituted by a member ring of oxygen 10 or less (hereinafter referred to as “oxygen 10-membered ring pore”). For example, the pore diameter (0.74 nm) of a FAU type zeolite having oxygen 12-membered ring pores and the pore diameter (0.67 nm) of a BEA type zeolite are the pore diameters of MFI zeolite having oxygen 10-membered ring pores ( 0.55 nm) and larger than the molecular diameter (0.59 nm) of para-xylene to be separated. Therefore, by using zeolite having oxygen 12-membered ring pores, the paraxylene permeation rate of the zeolite membrane 30 can be improved as compared with the case of using zeolite having oxygen 10-membered ring pores.

  The pore diameter for each skeletal structure can be obtained from The International Zeolite Association (IZA) “Database of Zeolite Structures” [online], [November 11, 2015 search], Internet <URL: http: //www.iza- It is disclosed in structure.org/databases/>.

  The zeolite membrane 30 contains at least Si and Al. The molar ratio of Si atoms to Al atoms (Si / Al atomic ratio) in the zeolite membrane 30 is not particularly limited, but is preferably 2 or more and 50 or less. By setting the Si / Al atomic ratio to 2 or more, the denseness of the zeolite membrane 30 can be ensured. By setting the Si / Al atomic ratio to 50 or less, an amount of barium sufficient to selectively permeate paraxylene can be introduced into the zeolite membrane 30.

  The zeolite membrane 30 further contains barium. By including barium in the zeolite membrane 30, the selective permeation of paraxylene can be promoted in the zeolite membrane 30, so that the paraxylene selectivity of the zeolite membrane 30 can be improved. The molar ratio of barium atoms to aluminum atoms (Ba / Al atomic ratio) in the zeolite membrane 30 is not particularly limited, but is preferably 0.1 or more and 0.5 or less. By making (Ba / Al atomic ratio) 0.1 or more, the selectivity of para-xylene can be further improved. By setting the (Ba / Al atomic ratio) to 0.5 or less, pore blocking due to excessive barium can be suppressed.

  The zeolite membrane 30 may further contain at least one of an alkali metal and an alkaline earth metal. In particular, the paraxylene selectivity of the zeolite membrane 30 can be further improved by including an alkali metal in the zeolite membrane 30. Examples of the alkali metal include lithium, sodium, potassium, rubidium, cesium and francium, and potassium is particularly preferable.

  The molar ratio of alkali metal atoms to barium atoms in the zeolite membrane 30 (alkali metal / Ba atomic ratio) is not particularly limited, but is preferably 0.01 or more and 0.9 or less. By setting the (alkali metal / Ba atomic ratio) to 0.01 or more, the selectivity of paraxylene can be further improved. By setting the (alkali metal / Ba atomic ratio) to 0.9 or less, it is possible to suppress a reduction in paraxylene selectivity.

  Moreover, the zeolite membrane 30 may have a structure of two or more layers. When it has a structure of two or more layers, at least one layer may be made of zeolite having oxygen 12-membered ring pores and include barium. In that case, it is preferable that a layer made of zeolite having oxygen 12-membered ring pores and containing barium is exposed on the surface of the zeolite membrane 30 opposite to the porous support 20. Further, the entire zeolite membrane 30 is made of zeolite having oxygen 12-membered ring pores, the Si / Al atomic ratio is 2 or more and 50 or less, and the layer containing barium is above the layer having a larger Si / Al atomic ratio. More preferably, it is formed.

(Manufacturing method of the separation membrane structure 10)
A method for manufacturing the separation membrane structure 10 will be described.

(1) Formation of porous support 20 First, the molded body of the base 21 is formed by molding the raw material of the base 21 into a desired shape using an extrusion molding method, a press molding method, a cast molding method, or the like. Next, the molded body of the base body 21 is fired (for example, 900 ° C. to 1450 ° C.) to form the base body 21.

  Next, an intermediate layer slurry is prepared using a ceramic material having a desired particle diameter, and the intermediate layer 22 is formed on the surface of the substrate 21 to form a formed body of the intermediate layer 22. Next, the intermediate layer 22 is formed by firing the molded body of the intermediate layer 22 (for example, 900 ° C. to 1450 ° C.).

  Next, a surface layer slurry is prepared using a ceramic raw material having a desired particle diameter, and a surface layer slurry is formed on the surface of the intermediate layer 22 to form a surface layer 23 compact. Next, the molded body of the surface layer 23 is fired (for example, 900 ° C. to 1450 ° C.) to form the surface layer 23.

  Thus, the porous support 20 is formed.

(2) Formation of Zeolite Membrane 30 Next, the zeolite membrane 30 is formed on the surface of the porous support 20. The zeolite membrane 30 can be formed by a conventionally known method according to the framework structure.

  First, a seeding slurry obtained by diluting various zeolite seed crystals with ethanol or water is poured into the surface layer 23, and then the seeding slurry is dried by ventilation under predetermined conditions.

  Next, the porous support 20 is immersed in a pressure resistant container containing a raw material solution containing a silica source, an alumina source, an organic template, an alkali source, water, and the like.

  Next, a pressure-resistant container is put into a dryer, and a zeolite membrane is formed by performing heat treatment (hydrothermal synthesis) at 100 to 200 ° C. for about 1 to 240 hours. Next, the porous support 20 on which the zeolite membrane is formed is washed and dried at 80 to 100 ° C.

  Next, when the organic template is contained in the raw material solution, the porous support 20 on which the zeolite membrane is formed is put into an electric furnace and heated at 400 to 800 ° C. for about 1 to 200 hours in the atmosphere. The organic template is removed by burning.

  Next, when an alkali metal or alkaline earth metal is included in the zeolite membrane, by holding the ion exchange solution containing the alkali metal or alkaline earth metal in contact with the zeolite membrane for a predetermined time, Alkali metals and alkaline earth metals can be introduced into the zeolite membrane. Thereafter, the zeolite membrane introduced with alkali metal or alkaline earth metal is rinsed with water and dried. When a predetermined alkali metal or alkaline earth metal has already been introduced into the zeolite membrane at the time of forming the zeolite membrane, the introduction operation using the ion exchange liquid may not be performed.

  Next, in order to include barium in the zeolite membrane, the ion exchange solution containing barium is held for a predetermined time in contact with the zeolite membrane, thereby forming the zeolite membrane 30 into which barium has been introduced. Thereafter, the zeolite membrane 30 introduced with barium is rinsed with water and dried. In addition, in order to suppress generation | occurrence | production of the film | membrane defect accompanying the introduction | transduction of barium to the zeolite membrane 30, it is preferable to introduce | transduce barium at the temperature below room temperature using a dilute solution.

(Concentration method of para-xylene by the separation membrane structure 10)
A method for concentrating paraxylene by the separation membrane structure 10 will be described.

  First, a fluid mixture containing C8 aromatic compounds (para-xylene, meta-xylene, ortho-xylene, and ethylbenzene) as main components is heated to obtain supply steam. The supply steam may be pressurized or may not be pressurized. The temperature of the supply steam is not particularly limited, but is preferably 100 ° C. or higher and 300 ° C. or lower. By setting the supply steam to 100 ° C. or higher, it is possible to suppress an excessive increase in the amount of paraxylene adsorbed on the zeolite membrane 30. By setting the supply steam to 300 ° C. or lower, a sufficient amount of paraxylene adsorbed on the zeolite membrane 30 can be secured.

  Next, the outer surface side of the porous support 20 is set to a predetermined pressure lower than that of the supply steam while supplying the supply steam to the zeolite membrane 30. Then, permeate vapor containing para-xylene is collected from the outer surface of the porous support 20. Thereby, paraxylene contained in the C8 aromatic compound is concentrated.

(Other embodiments)
As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the summary of invention.

  For example, the porous support 20 includes the base body 21, the intermediate layer 22, and the surface layer 23, but may not include any one or both of the intermediate layer 22 and the surface layer 23.

  Further, the separation membrane structure 10 may further include a functional membrane or a protective membrane formed on the zeolite membrane 30. Such a functional film or a protective film is not limited to a zeolite film, but may be an inorganic film such as a carbon film or a silica film, or an organic film such as a polyimide film or a silicone film.

  Hereinafter, examples of the separation membrane structure will be described. However, the present invention is not limited to the examples described below.

(Preparation of separation membrane structure)
(1) Sample No. 1
Sample No. The separation membrane structure according to 1 includes a FAU type zeolite membrane that does not contain barium.

  First, a porous material was prepared by adding 20 parts by mass of an inorganic binder to 100 parts by mass of alumina particles having an average particle size of 30 μm, and further adding water, a dispersant and a thickener and kneading.

  Next, the prepared porous material was extruded to form a monolith type alumina molded body. Subsequently, the alumina substrate was formed by firing (1250 ° C., 1 hour).

  Next, PVA (organic binder) was added to alumina to prepare a slurry, and a surface layer molded body was formed on the inner surface of the through hole of the alumina substrate by a filtration method using the slurry. Subsequently, the surface layer was formed by firing (1250 ° C., 1 hour).

  Next, both end faces of the alumina substrate were sealed with glass. Thus, a monolithic alumina support was completed.

  Next, a FAU type zeolite membrane was formed on the inner surface of the alumina support. Specifically, first, the seeding slurry diluted with ethanol so that the concentration of the FAU-type zeolite seed crystal (Si / Al atomic ratio = 2.8) is 0.1% by mass is formed inside the surface layer of the alumina support. Poured into. Next, the seeding slurry was dried by ventilation under predetermined conditions (room temperature, wind speed 5 m / s, 10 minutes).

  Next, 16.0 g of sodium hydroxide (manufactured by Sigma Aldrich), 1.6 g of sodium aluminate (manufactured by Wako Pure Chemical Industries) and 137.0 g of distilled water were mixed, and about 30% by mass silica sol (trade name: Snowtex S) 45.5 g) (manufactured by Nissan Chemical Co., Ltd.) was added and stirred with a magnetic stirrer (room temperature, 30 minutes) to prepare a sol for film formation.

  Next, the film-forming sol was placed in a fluororesin inner cylinder (300 ml in internal volume) of a stainless steel pressure-resistant container, and an alumina support to which a FAU-type zeolite seed crystal was adhered was immersed. Then, the FAU type | mold zeolite membrane was formed by making it react for 24 hours in a 160 degreeC hot air dryer. Next, the alumina support was washed and dried at 100 ° C. for 12 hours or more.

(2) Sample No. 2
Sample No. The separation membrane structure according to 2 includes a FAU type zeolite membrane containing barium and alkaline earth metal (calcium).

  First, sample no. As in Example 1, an alumina support and a FAU type zeolite membrane were prepared. At this time, by adjusting the composition ratio of the film-forming sol, the sample no. The Si / Al atomic ratio was made smaller than 1.

  Next, an ion exchange solution adjusted to 0.1 mol / L by adding calcium chloride (manufactured by Kishida Chemical) to water was prepared. Then, by keeping the 60 ° C. ion exchange solution in contact with the FAU type zeolite membrane for 24 hours, almost all of the sodium in the FAU type zeolite membrane was ion exchanged with calcium. Thereafter, the FAU type zeolite membrane introduced with calcium was rinsed with water and dried (100 ° C., 12 hours).

  Next, a liquid for ion exchange prepared by adding barium chloride (manufactured by Kishida Chemical Co., Ltd.) to water to be 0.1 mol / L was prepared. Then, a part of calcium of the FAU type zeolite membrane was ion exchanged with barium by holding the ion exchange solution at 10 ° C. for 3 hours in contact with the FAU type zeolite membrane. Thereafter, the FAU type zeolite membrane into which barium was introduced was rinsed with water and dried (100 ° C., 12 hours).

(3) Sample No. 3-5
Sample No. The separation membrane structure according to 3 to 5 includes a FAU type zeolite membrane containing barium and an alkaline earth metal (calcium).

  First, sample no. As in Example 1, an alumina support and a FAU type zeolite membrane were prepared.

  Next, sample no. As in 2, almost all of the sodium in the FAU-type zeolite membrane was ion-exchanged with calcium.

  Next, sample no. As in 2, a part of calcium of the FAU type zeolite membrane was ion exchanged with barium. At this time, the introduction amount (atomic ratio) of barium was adjusted as shown in Table 1 by changing the temperature and time of ion exchange for each sample.

(4) Sample No. 6
Sample No. The separation membrane structure according to 6 includes a FAU type zeolite membrane containing barium and alkali metal (sodium).

  First, sample no. As in Example 1, an alumina support and a FAU type zeolite membrane were prepared.

  Next, a liquid for ion exchange prepared by adding barium chloride (manufactured by Kishida Chemical Co., Ltd.) to water to be 0.1 mol / L was prepared. Then, a part of sodium of the FAU type zeolite membrane was ion exchanged to barium by holding the ion exchange solution at 10 ° C. for 3 hours in a state of being in contact with the FAU type zeolite membrane. Thereafter, the FAU type zeolite membrane into which barium was introduced was rinsed with water and dried (100 ° C., 12 hours).

(5) Sample No. 7
Sample No. 7 is provided with a FAU type zeolite membrane containing barium and alkali metal (potassium).

  First, sample no. As in Example 1, an alumina support and a FAU type zeolite membrane were prepared.

  Next, an ion exchange solution adjusted to 0.1 mol / L by adding potassium chloride (manufactured by Kishida Chemical) to water was prepared. Then, the ion exchange solution at 60 ° C. was kept in contact with the FAU-type zeolite membrane for 24 hours to ion-exchange almost all of the sodium in the FAU-type zeolite membrane with potassium. Thereafter, the FAU type zeolite membrane introduced with potassium was rinsed with water and dried (100 ° C., 12 hours).

  Next, a liquid for ion exchange prepared by adding barium chloride (manufactured by Kishida Chemical Co., Ltd.) to water to be 0.1 mol / L was prepared. Then, a part of potassium of the FAU type zeolite membrane was ion exchanged to barium by holding the ion exchange solution at 10 ° C. for 3 hours in a state of being in contact with the FAU type zeolite membrane. Thereafter, the FAU type zeolite membrane into which barium was introduced was rinsed with water and dried (100 ° C., 12 hours).

(6) Sample No. 8
Sample No. The separation membrane structure according to No. 8 includes a FAU type zeolite membrane containing barium and alkali metal (potassium).

  First, sample no. In the same manner as in Example 7, after preparing an alumina support and a FAU type zeolite membrane, potassium was introduced into the FAU type zeolite membrane.

  Next, sample no. In the same manner as in Example 7, a part of potassium in the FAU type zeolite membrane was ion-exchanged to barium. At this time, the introduction amount (atomic ratio) of barium was adjusted as shown in Table 1 by changing the temperature and time of ion exchange.

(7) Sample No. 9
Sample No. The separation membrane structure according to No. 9 includes a BEA type zeolite membrane containing barium and an alkali metal (sodium).

  First, sample no. As in Example 1, an alumina support was prepared.

  Next, a BEA type zeolite membrane was formed on the inner surface of the alumina support. Specifically, first, the seeding slurry diluted with ethanol so that the concentration of the BEA type zeolite seed crystal (Si / Al atomic ratio = 5.0) is 0.1% by mass is formed inside the surface layer of the alumina support. Poured into. Next, the seeding slurry was dried by ventilation under predetermined conditions (room temperature, wind speed 5 m / s, 10 minutes).

  Next, after mixing 24.3 g of 35 mass% tetraethylammonium hydroxide (manufactured by Sigma Aldrich), 1.6 g of sodium aluminate (manufactured by Wako Pure Chemical Industries) and 143.1 g of distilled water, about 30 mass% silica sol (commodity) Name: Snowtex S, manufactured by Nissan Chemical Co., Ltd. (31.0 g) was added and stirred with a magnetic stirrer (room temperature, 90 minutes) to prepare a sol for film formation.

  Next, the film-forming sol was placed in a fluororesin inner cylinder (internal volume 300 ml) of a stainless steel pressure vessel, and the alumina support to which the BEA type zeolite seed crystals were adhered was immersed. Then, the BEA type | mold zeolite membrane was formed by making it react for 24 hours in a 140 degreeC hot air dryer. Next, the alumina support was washed and dried at 100 ° C. for 12 hours or more.

  Next, the temperature of the alumina support was raised to 500 ° C. in an electric furnace and maintained for 4 hours, thereby removing tetraethylammonium from the BEA type zeolite membrane.

  Next, a liquid for ion exchange prepared by adding barium chloride (manufactured by Kishida Chemical Co., Ltd.) to water to be 0.1 mol / L was prepared. Then, a part of sodium of the BEA zeolite membrane was ion-exchanged to barium by holding the ion exchange solution at 10 ° C. for 3 hours in contact with the BEA zeolite membrane. Then, the BEA type zeolite membrane into which barium was introduced was rinsed with water and dried (100 ° C., 12 hours).

(8) Sample No. 10-12
Sample No. The separation membrane structure according to 10 to 12 includes a BEA type zeolite membrane containing barium and alkali metal (potassium).

  First, sample no. As in 9, an alumina support and a BEA zeolite membrane were produced. At this time, sample no. In Nos. 11 and 12, sample nos. The Si / Al atomic ratio was made larger than 9.

  Next, sample no. In the same manner as in Example 7, potassium was introduced into the BEA zeolite membrane.

  Next, sample no. Similar to 9, a part of potassium of the BEA zeolite membrane was ion-exchanged to barium. At this time, the introduction amount (atomic ratio) of barium was adjusted as shown in Table 1 by changing the temperature and time of ion exchange for each sample.

(9) Sample No. 13
Sample No. The separation membrane structure according to 13 comprises a BEA zeolite membrane containing barium and alkali metal (sodium).

  First, sample no. As in 9, an alumina support and a BEA zeolite membrane were produced. At this time, sample no. In Nos. 11 and 12, sample nos. The Si / Al atomic ratio was made larger than 9.

  Next, sample no. As in 9, a part of sodium in the BEA type zeolite membrane was ion-exchanged to barium. At this time, the introduction amount (atomic ratio) of barium was adjusted as shown in Table 1 by changing the temperature and time of ion exchange for each sample.

(10) Sample No. 14
Sample No. The separation membrane structure according to No. 13 includes a BEA zeolite membrane that does not contain barium and alkali metals.

  First, sample no. As in 9, an alumina support and a BEA zeolite membrane were produced. At this time, the sample no. Was adjusted by adjusting the composition ratio of the film forming sol without adding sodium aluminate to the film forming sol. The Si / Al atomic ratio was made larger than 9. Sample No. Since no ion exchange site exists in the 14 BEA type zeolite membrane, barium or the like cannot be introduced.

(14) Sample No. 15
Sample No. The separation membrane structure according to 15 comprises an MFI type zeolite membrane that does not contain barium and alkali metals.

  First, sample no. As in Example 1, an alumina support was prepared.

  Next, an MFI type zeolite membrane was formed on the inner surface of the alumina support. Specifically, first, a seeding slurry diluted with ethanol so that the concentration of MFI-type zeolite seed crystals (Si / Al atomic ratio ≧ 200) is 0.1% by mass is poured into the surface layer of the alumina support. It is. Next, the seeding slurry was dried by ventilation under predetermined conditions (room temperature, wind speed 5 m / s, 10 minutes).

  Next, after mixing 1.4 g of 40 mass% tetrapropylammonium hydroxide solution (manufactured by SACHEM) and 0.7 g of tetrapropylammonium bromide (manufactured by Wako Pure Chemical Industries, Ltd.), 187.0 g of distilled water and about 30 mass% are mixed. A film-forming sol was prepared by adding 10.9 g of silica sol (trade name: Snowtex S, manufactured by Nissan Chemical Co., Ltd.) and stirring with a magnetic stirrer (room temperature, 30 minutes).

  Next, the film-forming sol was placed in a fluororesin inner cylinder (300 ml internal volume) of a stainless steel pressure-resistant container, and the alumina support to which the MFI-type zeolite seed crystals were adhered was immersed. Then, the MFI type | mold zeolite membrane was formed by making it react for 20 hours in a 160 degreeC hot air dryer. Next, the alumina support was washed and dried at 100 ° C. for 12 hours or more. Next, the alumina support was heated to 500 ° C. in an electric furnace and held for 4 hours to remove tetrapropylammonium from the MFI type zeolite membrane. Sample No. Since no ion exchange site exists in the 15 MFI type zeolite membrane, it is not possible to introduce barium or the like.

(Composition analysis of zeolite membrane)
Sample No. The molar concentration of Si contained in 1 to 15 zeolite membranes was quantitatively measured by a gravimetric method (JIS M 8853). Sample No. Molar concentrations of other components contained in 1 to 15 zeolite membranes were quantitatively measured by ICP emission analysis (ULTIMA2 manufactured by Horiba Seisakusho). The measurement results are summarized in Table 1.

(Evaluation of separation performance of zeolite membrane)
Sample No. A separation test for separating paraxylene from a mixed liquid of paraxylene and orthoxylene was performed using 1 to 15 separation membrane structures.

  First, a mixed liquid of para-xylene and ortho-xylene (p-xylene: o-xylene = 50: 50 (molar concentration ratio)) was heated to 110 ° C. to obtain supply steam. Next, the side surface of the alumina support was depressurized at a degree of vacuum of about 10 Torr while supplying steam to the cell of the separation membrane structure (inside the zeolite membrane). The permeated vapor collected from the side surface of the alumina support was collected in a trap cooled with liquid nitrogen.

  The total permeation flux was calculated from the mass of collected liquefied permeate vapor. The liquefied product of the permeated vapor was analyzed by gas chromatography to measure the molar concentration of the permeated vapor. Then, ((paraxylene concentration of permeated steam / orthoxylene concentration of permeated steam) / (paraxylene concentration of supplied steam / orthoxylene concentration of supplied steam)) was calculated as a separation factor of paraxylene. The calculation results are summarized in Table 1. In Table 1, sample no. A value normalized based on a separation factor of 1 is shown.

  Sample No. The paraxylene permeation amount in Sample No. It was 1/10 or less of the paraxylene permeation amount in 1-13.

  As shown in Table 1, sample no. From the comparison of 1 to 15, it was found that the paraxylene separation performance can be improved by including barium in the zeolite membrane having oxygen 12-membered ring pores.

  Sample No. 2 and Sample No. 3 to 12 and Sample No. 3-12 and sample no. From comparison with 13, it was found that the paraxylene separation performance can be further improved by setting the molar ratio of silicon atoms to aluminum atoms in the zeolite membrane to 2 or more and 50 or less.

  Sample No. 2 and 3 and sample no. 4 to 12 and sample No. 4-12 and sample no. From comparison with 13, it was found that the paraxylene separation performance can be further improved by setting the molar ratio of barium atoms to aluminum atoms in the zeolite membrane to be 0.1 or more and 0.5 or less.

  Sample No. 5 and sample no. From comparison with 6-8, it was found that the paraxylene separation performance can be improved by adding alkali metal (Na, K) compared to the case where the alkaline earth metal (Ca) is included in the zeolite membrane. .

  Sample No. 6-12 and sample no. Comparison with 13 indicates that the paraxylene separation performance can be further improved by setting the molar ratio of alkali metal atoms to barium atoms in the zeolite membrane to 0.9 or less.

  Sample No. 6 and sample no. 7 and sample no. 9 and sample no. From the comparison with 10, 11, it was found that the paraxylene separation performance can be further improved by including potassium in the zeolite membrane.

  Sample No. 6 and no. 9 comparison and sample no. 7 and no. From the comparison of 10, it was found that the FAU type can improve the paraxylene separation performance more than the BEA type.

  Sample No. In contrast, it was experimentally confirmed that when barium was introduced excessively and the Ba / Al atomic ratio was made larger than 0.5, the amount of paraxylene permeation decreased.

  Sample No. 15 showed almost no paraxylene separation performance. This is presumably because ortho-xylene penetrated into the pores of the MFI-type zeolite membrane and inhibited the permeation of para-xylene.

DESCRIPTION OF SYMBOLS 10 Separation membrane structure 20 Porous support body 21 Base body 22 Intermediate | middle layer 23 Surface layer 30 Zeolite membrane

Claims (13)

A separation membrane structure that selectively permeates para-xylene in a fluid mixture,
A porous support;
A zeolite membrane formed on the porous support and having pores constituted by oxygen 12-membered rings;
With
The zeolite membrane contains barium,
Separation membrane structure. The molar ratio of silicon atoms to aluminum atoms in the zeolite membrane is 2 or more and 50 or less.
The separation membrane structure according to claim 1. The molar ratio of barium atoms to aluminum atoms in the zeolite membrane is 0.1 or more.
The separation membrane structure according to claim 1 or 2. The molar ratio of barium atoms to aluminum atoms in the zeolite membrane is 0.5 or less.
The separation membrane structure according to any one of claims 1 to 3. The zeolite membrane contains an alkali metal,
The separation membrane structure according to any one of claims 1 to 4. The molar ratio of alkali metal atoms to barium atoms in the zeolite membrane is 0.9 or less.
The separation membrane structure according to claim 5. The molar ratio of alkali metal atoms to barium atoms in the zeolite membrane is 0.01 or more.
The separation membrane structure according to claim 5 or 6. The zeolite membrane contains potassium,
The separation membrane structure according to any one of claims 5 to 7. The zeolite membrane is composed of FAU type zeolite,
The separation membrane structure according to any one of claims 1 to 8. A method for concentrating paraxylene comprising a step of separating paraxylene in a fluid mixture by the separation membrane structure according to any one of claims 1 to 9. The fluid mixture is a mixture containing a C8 aromatic compound as a main component.
The method for concentrating paraxylene according to claim 10. The temperature of the fluid mixture is 100 ° C. or higher.
The method for concentrating paraxylene according to claim 10 or 11. The temperature of the fluid mixture is 300 ° C. or less.
The method for concentrating paraxylene according to any one of claims 10 to 12.

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