JP7243356B2 - Zeolite separation membrane and separation method using the same - Google Patents

Description

The present invention relates to zeolite separation membranes. More specifically, it relates to the zeolite separation membrane and a method for separating hydrogen sulfide using the same.

In a natural gas refining plant, it is necessary to separate hydrogen sulfide contained in natural gas in order to avoid clogging of pipes in the liquefaction process. Until now, chemical absorption methods using bases such as amines have been used, but the energy required to desorb the absorbed hydrogen sulfide is large, and an enormous amount of energy was required to separate the hydrogen sulfide. Therefore, establishment of a hydrogen sulfide separation method using a separation membrane that can save energy and be simplified has been desired.

In recent years, a method for separating hydrogen sulfide using a zeolite membrane formed on the surface of an inorganic porous substrate has been reported. Zeolite membranes are widely used as molecular sieves because they have the property of selectively allowing molecules to pass through due to differences in molecular size and shape. For example, Patent Document 1 proposes FAU-type, DDR-type, LTA-type, LTL-type, MOR-type, MFI-type, SOD-type, and BEA-type zeolite membranes as hydrogen sulfide separation membranes. There is no description, and it was unclear whether the zeolite membrane can be applied as a hydrogen sulfide separation membrane. Although Patent Document 2 reports the hydrogen sulfide permeability of the CHA-type zeolite membrane, it only shows the permeation performance of a single component of hydrogen sulfide, and from a mixture containing hydrogen sulfide such as natural gas and a plurality of hydrocarbons. It was unclear whether hydrogen sulfide could be selectively separated. Furthermore, a hydrogen sulfide separation membrane that can stably separate hydrogen sulfide over a long period of time is desirable, but a zeolite separation membrane that is highly resistant to hydrogen sulfide has not been reported.

JP 2012-236142 A JP 2014-46267 A

The present invention provides a zeolite separation membrane that can be used for highly selective separation of hydrogen sulfide from hydrogen sulfide-accompanied gas by a method different from the chemical absorption method, the thermal swing adsorption method, etc. An object of the present invention is to provide a zeolite separation membrane whose hydrogen separation performance does not deteriorate.

As a result of extensive studies, the present inventors have found that hydrogen sulfide can be separated highly selectively from gases containing hydrogen sulfide and hydrocarbons by using a specific zeolite separation membrane, and have completed the present invention. rice field.

That is, the present invention provides a zeolite separation membrane in which a zeolite membrane is formed on the surface of a porous substrate, wherein the zeolite membrane has a Si/Al molar ratio of greater than 1.5 to 3.0 and an FAU type A zeolite separation membrane having a crystalline phase of , having a thickness of 1.0 μm or more and 5.0 μm or less, and containing silver ions as counter ions.

The present invention will be described in detail below.

The present invention relates to a zeolite separation membrane comprising a zeolite membrane formed on the surface of a porous substrate, wherein the zeolite membrane has a Si/Al molar ratio of greater than 1.5 to 3.0 and FAU type crystals. A zeolite separation membrane having phases, a thickness of 1.0 μm or more and 5.0 μm or less, and containing silver ions as counter ions. As a result, the zeolite separation membrane of the present invention has high heat resistance and allows hydrogen sulfide to permeate selectively over a long period of time when brought into contact with a gas containing hydrogen sulfide.

The zeolite membrane in the zeolite separation membrane of the present invention has a Si/Al molar ratio of greater than 1.5 and no greater than 3.0, preferably greater than 1.5 and no greater than 2.5. . Thereby, the zeolite separation membrane of the present invention has high heat resistance and can permeate hydrogen sulfide for a long period of time.

The zeolite membrane in the zeolite separation membrane of the present invention is FAU-type zeolite, preferably Y-type zeolite. This allows hydrogen sulfide to be separated more efficiently at higher temperatures.

The zeolite membrane in the zeolite separation membrane of the present invention contains silver ions as counterions. As a result, silver in the zeolite membrane reacts with hydrogen sulfide to form silver sulfide, so that hydrogen sulfide can be separated selectively over a long period of time even under exposure to hydrogen sulfide. At this time, when the film thickness is less than 1.0 μm, the separation performance of hydrogen sulfide is remarkably lowered due to deterioration of the film. On the other hand, when the film thickness is thicker than 5.0 μm, the permeation resistance of hydrogen sulfide increases and the permeation amount of hydrogen sulfide decreases. Therefore, the thickness of the zeolite membrane in the zeolite separation membrane of the present invention is 1.0 μm or more and 5.0 μm or less. The thickness of the zeolite membrane is preferably 1.5 μm or more and 4.5 μm or less.

The zeolite membrane in the zeolite separation membrane of the present invention is formed on the surface of a porous substrate. Thereby, hydrogen sulfide can be selectively separated by bringing the gas containing hydrogen sulfide into contact with the surface on which the zeolite membrane is formed.

The porous substrate is not particularly limited as long as it has strength to withstand pressure difference, heat resistance, and corrosion resistance to hydrogen sulfide. For example, an inorganic porous substrate, or an inorganic-organic hybrid A porous base material etc. are mentioned.

The inorganic porous substrate is not particularly limited as long as it is porous. Examples include sintered ceramics such as silica, alumina, mullite, zirconia, titania, silicon nitride, or silicon carbide, or stainless steel. sintered metal, glass, carbon molded body, etc. can be used.

The inorganic-organic hybrid porous substrate is not particularly limited, and examples thereof include those obtained by mixing or laminating the inorganic porous substrate and an organic substrate such as cellulose acetate.

From the viewpoint of strength, heat resistance, and corrosion resistance, inorganic porous substrates are preferred, and alumina porous substrates are more preferred.

The pore size of the surface layer of the porous substrate is preferably in the range of 0.05 µm to 3.0 µm, more preferably 0.08 µm to 2.0 µm, and further preferably 0.10 µm to 1.5 µm. The pore diameter of the substrate can be evaluated by a bubble point method, a mercury intrusion method, or the like. In addition, the porous substrate surface layer refers to the substrate surface portion forming the zeolite membrane. The pore diameter of the portion other than the base material surface layer forming the zeolite membrane is not particularly limited, but may be 0.05 μm or more and 3.0 μm or less, and further 0.30 μm or more and 1.5 μm or less.

In addition, since the porosity of the porous substrate influences the strength and permeation flow rate when hydrogen sulfide is separated, the porous substrate preferably has a porosity of 20% or more and 60% or less.

The crystal phase of the zeolite membrane formed on the surface of the porous substrate can be confirmed by XRD.

The shape of the porous substrate is not limited as long as it can effectively separate the gas mixture. A prismatic shape, a prismatic shape, a pyramidal shape, a truncated pyramidal shape, a cylindrical shape, or a honeycomb shape having a large number of prismatic holes can be used. Corrugated, tubular, cylindrical, conical, truncated conical, cylindrical, prismatic, prismatic, pyramidal, truncated pyramidal, or cylindrical porous substrates are hollowed out at the center A tube having a shape of a tube is preferable, and the tube may be a tube that penetrates through the tube, or a test tube that does not penetrate the tube.

The zeolite membrane in the zeolite separation membrane of the present invention contains silver ions as counterions. As a result, the zeolite membrane has high hydrogen sulfide permeability and excellent durability.

The Ag/Al molar ratio of the zeolite membrane in the zeolite separation membrane of the present invention is preferably 0.010 or more, more preferably 0.10 or more. Thereby, hydrogen sulfide can be separated over a long period of time and with high selectivity. Furthermore, the Ag/Al molar ratio is preferably 1.0 or less.

The Ag content of the zeolite membrane in the zeolite separation membrane of the present invention is preferably 0.4% by weight or more and 42% by weight or less. This makes the zeolite membrane more durable.

The Ag ion exchange rate (Ag/(Na+Ag) molar ratio) of the zeolite membrane in the zeolite separation membrane of the present invention is preferably 0.010 or more and 1.0 or less. Thereby, hydrogen sulfide can be separated over a long period of time and with high selectivity.

The zeolite membrane of the present invention may have its membrane surface modified with a silylating agent or the like.

The hydrogen sulfide permeability to the zeolite membrane is preferably 1×10 ⁻⁸ mol/m ² /s/Pa or more, more preferably 2×10 ⁻⁸ mol/m ² /s/Pa or more. As a result, the zeolite membrane area required for separating hydrogen sulfide can be reduced, which is economically advantageous and allows simplification of the apparatus.

The methane permeability to the zeolite membrane is preferably 1×10 ⁻⁸ mol/m ² /s/Pa or less, more preferably 0.8×10 ⁻⁸ mol/m ² /s/Pa or less. Thereby, hydrocarbons such as methane can be recovered more efficiently.

Next, the method for separating hydrogen sulfide according to the present invention will be described.

The hydrogen sulfide separation method of the present invention is a separation method using the zeolite separation membrane of the present invention.

In the method for separating hydrogen sulfide of the present invention, a gas containing hydrogen sulfide and hydrocarbons is brought into contact with a zeolite separation membrane after a dehydration step for removing moisture previously adsorbed on the zeolite membrane. Separation of hydrogen sulfide. It is preferable to have a step.

The dehydration method in the dehydration step is not particularly limited, and for example, a method of heat treatment at 550° C. or less under reduced pressure can be mentioned. The temperature is preferably 500° C. or lower, more preferably 400° C. or lower, in terms of high separation performance and high permeability of hydrogen sulfide. The temperature is preferably 50° C. or higher, more preferably 60° C. or higher, in terms of low energy consumption in the step before separation. From the viewpoint of separation performance and energy consumption, the temperature is preferably 50° C. or higher and 400° C. or lower. The pressure during dehydration may be under reduced pressure or under atmospheric pressure. Moreover, the atmosphere during dehydration may be an oxygen atmosphere or a non-oxygen atmosphere.

In the separation step, the zeolite membrane is contacted with a gas containing hydrocarbons and hydrogen sulfide. More specifically, it is carried out by bringing a hydrogen sulfide/hydrocarbon mixed gas into contact with one of two surfaces of a separation membrane consisting of a porous substrate having at least one surface coated with an FAU-type zeolite membrane. . More specifically, a gas is brought into contact with the membrane and hydrogen sulfide is selectively separated by permeation through the zeolite membrane and substrate. At this time, hydrocarbons and the like accompanying hydrogen sulfide are blocked by the zeolite membrane, and the amount of the hydrocarbons permeating the membrane is extremely small. When the separation factor is expressed as (permeability of hydrogen sulfide) / (permeability of methane), the separation in the present invention is a zeolite membrane having a separation factor of 3 or more, more preferably 4 or more, and still more preferably 5 or more. is done using

In the separation step, by maintaining the temperature of the zeolite membrane at −60° C. or higher and 110° C. or lower, hydrogen sulfide can be separated with higher selectivity. The membrane temperature in the separation step is preferably −60° C. or higher, more preferably −40° C. or higher, further preferably −20° C. or higher. As a result, condensation of hydrogen sulfide is suppressed in the pores of the zeolite membrane-substrate, and separation can be performed with higher selectivity. The film temperature is preferably 80° C. or lower, more preferably 50° C. or lower. Thereby, hydrogen sulfide can be permeated more selectively.

The pressure of the hydrogen sulfide/hydrocarbon mixed gas in the separation step is not particularly limited. As a result, the permeation amount of hydrogen sulfide per unit area of the membrane increases, that is, the separation performance is high, so the pressure is preferably 0.10 MPa or more, more preferably 0.20 MPa or more.

The hydrogen sulfide permeability in the separation step is preferably 1×10 ⁻⁸ mol/m ² /s/Pa or more, more preferably 2×10 ⁻⁸ mol/m ² /s/Pa or more. As a result, the zeolite membrane area required for separating hydrogen sulfide can be reduced, which is economically advantageous and allows simplification of the apparatus.

The methane permeability in the separation step is preferably 1×10 ⁻⁸ mol/m ² /s/Pa or less, more preferably 0.8×10 ⁻⁸ mol/m ² /s/Pa or less. Thereby, hydrocarbons such as methane can be recovered more efficiently.

The hydrocarbons in the hydrogen sulfide/hydrocarbon mixed gas preferably contain at least methane. Since methane is the main component of natural gas and the like, the separation method of the present invention can be industrially implemented. Hydrocarbons are not particularly limited, and include, for example, at least one of the group consisting of methane, ethane, propane, butane, pentane, ethylene, acetylene, propylene, propadiene, butene, and butadiene, including two or more. You can The hydrogen sulfide/hydrocarbon mixed gas may contain, in addition to the above gases, a third component such as carbon dioxide, water, nitrogen, oxygen, rare gas, and the like.

By using the zeolite separation membrane of the present invention, hydrogen sulfide can be separated stably over a long period of time with high selectivity without deterioration of the membrane.

Since the zeolite separation membrane of the present invention is excellent in durability, it can be used for a long time without applying a large amount of heat energy from outside the system, with high selectivity to hydrogen sulfide from hydrogen sulfide / hydrocarbon mixed gas, and without deterioration of the membrane. It is possible to permeate and separate in a relatively stable manner, and it is extremely energy efficient compared to the conventional chemical absorption method using a base such as amine, so it is possible to provide an energy-saving production process.

1 is a schematic diagram of a hydrogen sulfide separation performance evaluation apparatus using a zeolite separation membrane. FIG.

EXAMPLES The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples.

(X-ray diffraction measurement)
Using a general XRD device (device name: RINT Ultima III, manufactured by Rigaku Denki Co., Ltd.), the sample was subjected to XRD measurement. The measurement conditions were as follows.

Radiation source: CuKα rays (λ = 1.54 Å)
Measurement mode: step scan
Scanning conditions: 4° per minute
Divergence slit: 2/3deg
Scattering slit: 2/3deg
Receiving slit: 0.3mm
Step width: 0.02°
Measurement range: 2θ = 5 to 40°
(composition analysis)
The Si/Al molar ratio of the zeolite membrane was evaluated by calculating the lattice constant by the XRD method and referring to the non-patent document (T. Takaishi, The Journal of Physical Chemistry 99 (1995) 10982-10987). The silver content of the zeolite membrane was measured by energy dispersive X-ray spectroscopy (EDS). A general SEM-EDS device (device name: JSM-IT100 InTouchScope, manufactured by JEOL Ltd.) was used for the measurement.

(Film thickness evaluation)
The film thickness of the zeolite membrane was evaluated by cross-sectional observation of the membrane with a scanning electron microscope (SEM). A general SEM device (device name: JSM-IT100 InTouchScope, manufactured by JEOL Ltd.) was used for observation.

(Separation evaluation of hydrogen sulfide)
The separation performance of the zeolite membrane was evaluated using the separation performance evaluation apparatus shown in FIG. A hydrogen sulfide/methane mixed gas was supplied to the zeolite membrane surface using a mass flow controller. The supply pressure was regulated using a back pressure valve. The gas that permeated the membrane was recovered with a sweep gas (He 50 mL/min) and quantitatively analyzed by gas chromatography. A general gas chromatograph (device name: Agilent 7890B, manufactured by Agilent Technologies, Inc., TCD detector) was used for the measurement. A separation factor indicating hydrogen sulfide separation performance was calculated by the following equation.

Separation factor = (hydrogen sulfide concentration in permeate gas/methane concentration in permeate gas)
/ (concentration of hydrogen sulfide in supplied gas/concentration of methane in supplied gas)
Example 1
A Y-type zeolite membrane was prepared with reference to a non-patent document (H. Kita, K. Fuchida, T. Horita, H. Asamura, and K. Okamoto, Separation and Purification Technology 25 (2001) 261-268).

<Preparation of seed crystal-attached porous substrate>
As seed crystals, 12.5 g of HSZ-360HUA manufactured by Tosoh Corporation was dispersed in 50 ml of pure water and pulverized in a ball mill for 24 hours. Cylindrical porous substrate (material: α alumina, average pore diameter: 0.7 μm (surface side: 0.15 μm), porosity: 35 to 45%, length: 3 cm, outer diameter: 1 cm , inner diameter: 0.7 cm) was immersed and dried to support seed crystals on the outer surface of the substrate.

<Preparation of zeolite separation membrane>
2.6 g of sodium hydroxide (manufactured by Kanto Kagaku special grade), 26 g of distilled water, and 0.13 g of sodium aluminate (manufactured by Wako Pure Chemical Industries, Ltd.) were stirred and mixed at room temperature for 5 minutes (solution 1). Further, 14 g of sodium silicate solution (No. 3) (manufactured by Kishida Chemical Co., Ltd.) and 26 g of distilled water were stirred and mixed at room temperature for 5 minutes (solution 2). Solution 1 and solution 2 were mixed and stirred at 80° C. for 4 hours. A seed crystal-attached porous substrate was immersed in the resulting mixed solution, and hydrothermally synthesized at 85° C. for 24 hours. Next, the substrate taken out from the mixed solution was washed with distilled water and dried to obtain a zeolite separation membrane. The constituent phases of the zeolite membrane portion of the obtained porous substrate are identified by XRD, and the Si/Al ratio of the zeolite membrane portion is 1.7, and the crystal phase is NaY-type zeolite. It was confirmed.

The resulting NaY-type zeolite separation membrane was immersed in a 0.01 mol % AgNO ₃ aqueous solution for 3 hours and then washed with distilled water several times to obtain an AgY-type zeolite separation membrane. As a result of composition analysis, the Ag content of the obtained zeolite membrane was 42% by weight. The ion exchange rate (Ag/(Na+Ag) molar ratio) was 0.99 and the Ag/Al molar ratio was 0.99. The thickness of the zeolite membrane was 3.5 μm.

The obtained AgY-type zeolite separation membrane was installed in the constant temperature bath of the evaluation apparatus shown in FIG. 1, and dehydration treatment (150° C., 30 min, He 50 mL/min) was performed. After the dehydration treatment, 20 mL/min of hydrogen sulfide and 80 mL of methane were applied to the surface of the zeolite membrane so that a mixed gas with a hydrogen sulfide/methane molar ratio of 20/80 was obtained while the temperature of the constant temperature bath was maintained at 30°C. /min, and the supply pressure was 0.1 MPa. After the gas containing hydrogen sulfide was supplied for 1 hour, 6 hours, 12 hours and 14 hours, the hydrogen sulfide separation performance was evaluated. Table 1 shows the hydrogen sulfide permeability, methane permeability, and separation factor.

Comparative example 1
A NaY-type zeolite separation membrane was produced in the same manner as in Example 1, except that the immersion treatment with the AgNO ₃ aqueous solution was not performed. After dehydrating the separation membrane by the same method as in Example 1, hydrogen sulfide separation performance was evaluated after supplying hydrogen sulfide for 14 hours. Table 1 shows the hydrogen sulfide permeability, methane permeability, and separation factor. The constituent phases of the zeolite membrane were identified by XRD and confirmed to be FAU zeolite. The film thickness was 3.5 μm.

From the above examples, the zeolite separation membrane of the present invention has a separation factor of greater than 1 by contacting a gas containing hydrogen sulfide and using it in a hydrogen sulfide separation method. It can be seen that hydrogen sulfide can be selectively separated. Furthermore, it can be seen that the hydrogen sulfide permeability does not decrease, and the separation can be stably performed over a long period of time without deterioration of the membrane. Therefore, by applying the hydrogen sulfide separation method of the present invention to a hydrogen sulfide separation process for natural gas or the like, it is economically advantageous without inputting a huge amount of energy.

Example 2
An AgY-type zeolite separation membrane was prepared in the same manner as in Example 1, mounted in the constant temperature bath of the evaluation apparatus shown in FIG. 1, and dehydrated (70° C., 30 min, He 50 mL/min). After the dehydration treatment, the temperature of the constant temperature bath was kept at 30° C., and the gas containing hydrogen sulfide was supplied for 1 hour, and then the hydrogen sulfide separation performance was evaluated. The hydrogen sulfide permeability was 2.2×10 ⁻⁸ mol/m ² /s/Pa, the methane permeability was 3.5×10 ⁻¹⁰ mol/m ² /s/Pa, and the separation factor was 63.

Example 3
An AgY-type zeolite separation membrane was prepared in the same manner as in Example 1, mounted in the constant temperature bath of the evaluation apparatus shown in FIG. 1, and dehydrated (70° C., 120 min). Here, the dehydration treatment was carried out by supplying _N2 to the substrate surface side on which the zeolite membrane is formed (50 mL/min) and setting the other surface side to 100 Pa by a vacuum pump. After the dehydration treatment, the temperature of the constant temperature bath was kept at 30° C., and the gas containing hydrogen sulfide was supplied for 1 hour, and then the hydrogen sulfide separation performance was evaluated. The hydrogen sulfide permeability was 4.5×10 ⁻⁸ mol/m ² /s/Pa, the methane permeability was 8.5×10 ⁻¹⁰ mol/m ² /s/Pa, and the separation factor was 53.

By using the zeolite separation membrane of the present invention, it is possible to separate and remove hydrogen sulfide contained in hydrogen sulfide-containing hydrocarbon gas such as natural gas. In addition to natural gas, it is possible to remove hydrogen sulfide contained in biogas generated by anaerobic fermentation such as agricultural waste and food waste.

1 Hydrogen sulfide gas 2 Hydrocarbon gas 3 Helium 4 Mass flow controller 5 Mass flow controller 6 Mass flow controller 7 Constant temperature bath 8 Module 9 Porous substrate with zeolite membrane 10 Exhaust 11 Gas chromatograph 12 Exhaust 13 Pressure gauge 14 Vacuum pump 15 Exhaust 16 Back pressure valve 17 pressure gauge

Claims (6)

A zeolite separation membrane comprising a zeolite membrane formed on the surface of a porous substrate, the zeolite membrane having a Si/Al molar ratio of greater than 1.5 and 3.0 or less and an FAU type crystal phase. , the membrane has a film thickness of 1.0 μm or more and 5.0 μm or less, contains silver ions as counter ions, and has a hydrogen sulfide permeability to the zeolite membrane of 1×10 ⁻⁸ mol/m ² /s/Pa or more. A zeolite separation membrane characterized by: 2. The zeolite separation membrane according to claim 1, wherein the porous substrate is an alumina porous substrate. 3. The zeolite separation membrane according to claim 1, wherein the Ag/Al molar ratio of the zeolite membrane is 0.010 or more and 1.0 or less. A method for separating hydrogen sulfide, comprising using the zeolite separation membrane according to any one of claims 1 to 3. 5. The hydrogen sulfide according to claim 4, further comprising a separation step of contacting a gas containing hydrogen sulfide and hydrocarbons with a zeolite separation membrane after the dehydration step of removing moisture adsorbed on the zeolite membrane. separation method. 6. The method for separating hydrogen sulfide according to claim 5, wherein the hydrogen sulfide permeability is 2×10 ⁻⁸ mol/m ² /s/Pa or more and the hydrogen sulfide/methane separation factor is 5 or more. .

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