JP2020121300A - Gas separation system and gas separation method - Google Patents

Abstract

To provide a gas separation system which suppresses defect formation of a carbon film and can stably operate for a long term.SOLUTION: A gas separation system has a pre-processing part with a filter, and a gas separation part system with a carbon film.SELECTED DRAWING: Figure 1

Description

The present invention relates to a gas separation system and a gas separation method.

A membrane separation method is known as a separation method for selectively separating and purifying a specific component from various mixed gases or mixed liquids. Since the membrane separation method utilizes a pressure difference and a concentration difference, it draws attention because it uses less heat energy and saves energy as compared with other separation methods.

In recent years, the membrane separation method has been particularly attracting attention as a powerful means in a carbon dioxide separation/storage system (CCS) that separates, collects, and stores a large amount of carbon dioxide emitted from a power plant, a steel plant, and the like. In particular, carbon membranes have attracted attention because they are excellent in durability against organic solvents and gas separation performance. However, the carbon film is generally fragile as carbonization progresses, and there is a problem in handleability. Therefore, as a carbon film having excellent flexibility, for example, a hollow fiber carbon film having a breaking elongation of 1 to 4%, which is obtained by carbonizing a hollow fiber carbon film precursor using polyphenylene oxide, has been proposed. (For example, see Patent Document 1). Further, as a carbon film excellent in pressure resistance, which suppresses damage in separation/purification under high-pressure conditions, for example, a core layer having a bicontinuous porous structure and a substantially bicontinuous formed around the core layer are used. A carbon membrane for fluid separation having a skin layer having no porous structure has been proposed (see, for example, Patent Document 2).

JP, 2013-71073, A International Publication No. 2016/13676

Although these technologies improve the flexibility and pressure resistance of the carbon film, when applied to a gas separation system that separates carbon dioxide, methane, etc. from natural gas, particles contained in natural gas cause defects on the carbon film surface. It was found that there are issues that are easily formed. Defects on the surface of the carbon film cause gas leakage during long-term operation, and therefore it is required to suppress such defects.

Therefore, it is an object of the present invention to provide a gas separation system that suppresses the formation of defects in a carbon film and can be stably operated for a long period of time.

The present invention which solves the above problems is a gas separation system having a pretreatment section having a filter and a gas separation section having a carbon membrane.

The gas separation system of the present invention can suppress the formation of defects in the carbon membrane and can operate stably for a long period of time.

It is the schematic which showed typically the gas separation system of this invention.

<Gas separation system>
The gas separation system of the present invention has a pretreatment unit having a filter and a gas separation unit having a carbon membrane, and has a pretreatment unit and a gas separation unit in this order from the upstream side of the gas to be separated. The pretreatment unit having a filter has a function of removing particulate matter existing in the gas stream supplied to the gas separation system, and the gas separation unit removes the particulate matter supplied from the pretreatment unit. It has the effect of separating the required gas from the generated gas stream. By removing the particulate matter by the pretreatment section, defects on the surface of the carbon film due to collision of the particulate matter with the carbon film in the gas separation section are suppressed, and gas leakage from the carbon film is suppressed and stable for a long period of time. Can operate the gas separation system. Further, it may have a pipe, a joint, a valve or the like for connecting the pretreatment section and the gas separation section. Further, it may have a measuring device for monitoring the pressure, temperature, gas composition and the like. In the present invention, the gas flowing through the entire gas separation system is a gas flow, the gas flow supplied to the pretreatment unit is a source gas, and the gas flow after passing through the pretreatment unit is a treated gas, a gas separation unit. The gas flow passing through the carbon film and passing through the carbon film is called a permeating gas, and the gas flow discharged without passing through the carbon film is called a purified gas.

FIG. 1 shows a schematic diagram of the gas separation system of the present invention. FIG. 1A shows a configuration having one pretreatment section and one gas separation section, in which the raw material gas 1 becomes the post-treatment gas 3 in the pretreatment section 2, and then the permeated gas 5 and the purification gas in the gas separation section 4. It is taken out as gas 6. FIG. 1B shows a configuration having two pretreatment units in series, and the raw material gas 1 becomes the post-treatment gas 3 by the two pretreatment units 2 connected in series, and the permeated gas in the gas separation unit 4 5 and purified gas 6 are taken out. FIG. 1C shows a configuration having two pretreatment units in parallel, and the raw material gas 1 is taken out as a post-treatment gas 3 by the two pretreatment units 2 connected in parallel, or by either of them. In the gas separation part 4, the permeated gas 5 and the purified gas 6 are taken out.

The gas separation system is mainly used by being installed in a plant. In this case, other equipment and facilities may be installed in the gas separation system as needed. For example, on the upstream side of the pretreatment unit, a metering unit (metering) that measures the flow rate of the raw material gas, a pressure gauge, a measuring instrument for composition analysis, etc. Then, it is possible to install and introduce necessary equipment as needed. On the other hand, for example, a thermometer, a flow meter, a measuring instrument such as a composition analyzer, a tank, a dryer, a heater, a cooler, a heat exchanger, a humidifier, and an absorption tower are provided on the downstream side of the pretreatment unit or the gas separation unit. From the viewpoint of what is required to send the obtained post-treatment gas to the next step, it is possible to appropriately install and introduce necessary equipment. By installing a measuring instrument between the pretreatment unit and the gas separation unit, it is possible to monitor what composition of gas is processed and to safely monitor the operation status of the gas separation system. The plant can be operated efficiently.

The gas separation system of the present invention can be suitably used as a gas separation system for separating carbon dioxide and methane from natural gas.

<Pre-processing unit>
The pretreatment unit has a filter. Furthermore, it is preferable to have a filter housing that holds the filter and forms the flow path of the source gas.

The pretreatment unit preferably has a plurality of filters. The arrangement of the plurality of filters is not particularly limited, and may be arranged in series or in parallel, or may be arranged in combination with series and parallel. When a plurality of filters are arranged in series, even if particles are not collected by the upstream filter, the speed of the particles is reduced by the filter, so that the particles are easily collected by the downstream filter. Further, it is possible to collect coarse particles first by the upstream filter and suppress clogging of the downstream filter. Therefore, the overall particle collection rate can be improved. On the other hand, when a plurality of filters are arranged in parallel, the cross-sectional area with respect to the volumetric flow rate of the raw material gas flow increases, so that the flow velocity of the raw material gas flow can be temporarily reduced, and the particles can be easily collected by the filter. be able to. When combining series and parallel, they may be arranged in parallel on the upstream side and in series on the downstream side, or may be arranged in series on the upstream side and parallel on the downstream side. Further, a plurality of filters can be arbitrarily arranged and designed by providing a middle stream between the upstream side and the downstream side and arranging them in series on the upstream side and the downstream side and in parallel on the middle stream side. From the viewpoint of temporarily stopping the raw material gas during filter replacement, the filter arrangement in the pre-treatment section is provided with a parallel part in part, and even during filter replacement, use lines other than the line that was temporarily stopped for filter replacement. Therefore, it is preferable to have a mechanism for continuing the operation of the gas separation system.

It is also preferable to further provide a filter for rough purification in the pretreatment section. If very large particles are collected by the filter of the pretreatment section, the pressure loss may spread at an early stage. By collecting such large particles first with the filter for rough purification, stable operation can be performed for a longer period.

Details of the filter of the preprocessing unit will be described later.

The material of the filter housing is preferably selected appropriately according to the operating conditions of the gas separation system such as pressure, temperature and gas composition. Further, particularly when the gas separation system is operated at a high pressure of 1 MPa or more, from the viewpoint of pressure resistance, the filter housing preferably has at least a part having a circular, elliptical, and/or arc-shaped portion. Preferably has a shape based on a pipe-shaped structure. As for the thickness of the filter housing, it is preferable that a necessary thickness that does not cause a safety problem is secured depending on the operating conditions of the gas separation system, and it is preferable to use the one whose strength has been calculated.

<Filter>
Examples of the shape of the filter include those having a rectangular, circular, or polygonal shape when viewed from the upstream side of the gas flow. From the viewpoint of ease of manufacturing the filter, the shape is preferably rectangular or polygonal. On the other hand, the shape is preferably circular from the viewpoint of suppressing uneven flow of the raw material gas and facilitating uniform flow. The shape of the filter is preferably selected as appropriate according to the efficiency of the gas separation system and the operating cost.

The material of the filter preferably has voids or pores, and particles can be collected by the voids or pores. For example, a fiber aggregate or a porous body in which particles are connected may be used. The fiber aggregate refers to an aggregate of two or more fibers, and particles can be collected by collision of particles with the fibers, capture of particles in voids between the fibers, and the like. The porous body in which the particles are connected has a portion in which the particles are connected and voids between the particles, and the voids between the particles form porosity. The material of the filter is preferably selected as appropriate according to conditions such as the type of raw material gas processed by the gas separation system and the shape and particle size of the particles contained in the raw material gas.

When the filter is formed of a fiber assembly, the fibers forming the fiber assembly may be long fibers or short fibers, and the diameter and cross-sectional shape thereof are not particularly limited. Examples of fibers include polymer fibers and inorganic fibers. Among these, polymer fibers, which are excellent in moldability and flexibility, are preferable. Further, since the polymer fiber is softer than the inorganic fiber, even when the polymer fiber is dropped from the filter, defects such as breakage of the gas separation portion can be further suppressed. That is, the filter of the pretreatment section in the gas separation system of the present invention is preferably composed of polymer fibers. On the other hand, inorganic fibers such as glass fibers and carbon fibers are preferable in that the heat resistance and chemical resistance of the filter can be improved. Examples of the form of the fiber assembly include woven fabric, knitted fabric, and non-woven fabric. A nonwoven fabric is preferable from the viewpoint of easy formation of the fiber aggregate. The method for forming these fiber aggregates is not particularly limited, and a conventionally known method can be used.

Among polymer fibers, general-purpose polymer fibers can reduce operating costs, and heat-resistant polymer fibers made from engineering plastics and super-engineering plastics can improve heat resistance and chemical resistance of filters. You can When the temperature of the gas processed by the gas separation system is less than 100°C, general-purpose polymer fibers are preferable, and when the gas temperature is 100°C or higher, heat-resistant polymer fibers are preferable. On the other hand, when treating natural gas, a material having resistance to impurities contained in the natural gas ejected from the ground is preferable, and crystalline or semi-crystalline polymer fiber is preferable.

When the polymer fiber has crystallinity, it has a function of preventing the crystal part from dissolving and swelling with respect to impurities, and can maintain the morphology of the fiber. It is preferable that the molecular fiber is composed of a polymer having crystallinity (hereinafter referred to as a crystalline polymer). Here, “having crystallinity” means having an endothermic peak upon melting when the polymer is subjected to differential scanning calorimetry at a temperature rising rate of 10° C./min.

The crystalline polymer that constitutes the polymer fiber is not particularly limited as long as it has the above characteristics. The crystalline polymer preferably has a glass transition temperature of less than 200°C. If the glass transition temperature is lower than 200°C, the amorphous part constituting the crystalline polymer has high mobility, and heat loss occurs when particles, which are a kind of impurities contained in the raw material gas, collide with the fiber. As a result, the kinetic energy of particles can be efficiently dispersed. From this viewpoint, the glass transition temperature of the crystalline polymer is preferably less than 150°C, more preferably less than 120°C. Although the lower limit of the glass transition temperature is not particularly limited, it is preferably 50° C. or higher because it is preferably high for the purpose of maintaining the fiber form at the operating temperature. The glass transition temperature is the temperature analyzed from the change in the baseline corresponding to the secondary phase transition observed during the differential scanning calorimetry described above.

Further, the melting point of the crystalline polymer constituting the polymer fiber is preferably 150° C. or higher because it is possible to achieve a high level of heat resistance and chemical resistance which are functions of the crystal part. The higher the melting point, the better the heat resistance and chemical resistance can be raised, but on the other hand, from the viewpoint of lowering the temperature during molding processing such as melt spinning and keeping the cost low, the lower melting point is preferable. Is preferred. From these viewpoints, the melting point is preferably 150° C. or higher and lower than 350° C., and more preferably 180° C. or higher and lower than 300° C. The melting point of the crystalline polymer means the temperature at which the peak top of the endothermic peak observed when the differential scanning calorimetry is performed is shown.

When the filter is formed of a porous body, examples of the porous body include a polymer porous body and an inorganic porous body. Examples of the polymer that constitutes the polymer porous body include general-purpose polymers and particles of heat-resistant polymers such as engineering plastics and super engineering plastics. As in the case of the fiber assembly, it is preferable to appropriately select the material depending on the temperature of the gas processed by the gas separation system. On the other hand, examples of the inorganic material forming the inorganic porous body include particles of alumina, zirconia, silica, carbon and the like. You may use 2 or more types of these.

Among these, since the inorganic porous material is excellent in heat resistance and chemical resistance, the shape change of the filter is small and the particles can be stably removed for a long period of time. Therefore, defects in the carbon membrane can be further suppressed, and the gas separation system can be stably operated for a longer period of time. In particular, when the source gas contains water, alumina and zirconia are more preferable from the viewpoint of suppressing deterioration of the filter.

The size, shape, etc. of the particles forming the porous body are not particularly limited. The average diameter of the particles forming the porous body is preferably 0.05 μm or more, and more preferably 0.1 μm or more, because the larger the diameter is, the larger the pores can be and the pressure loss can be reduced. On the other hand, the average diameter of the particles constituting the porous body is preferably 1,000 μm or less, more preferably 300 μm or less, because the smaller the diameter, the smaller the pores and the more easily the particles can be collected. The average diameter of the particles is measured as the diameter of the corresponding circle by forming a fractured surface of the particle, observing the fractured surface magnified using an electron microscope, and measuring the cross-sectional area of 20 randomly selected particles. However, it can be measured by calculating the arithmetic mean value thereof.

Further, the larger the pore size of the porous body, the more the pressure loss can be reduced, so that the pore size is preferably 0.1 μm or more. On the other hand, the pore size of the porous body is preferably 1,000 μm or less, more preferably 300 μm or less, because the smaller the diameter, the easier the particles can be collected. The pore diameter of the porous body can be measured by a nitrogen adsorption method when it is 0.2 μm or less, and by a mercury intrusion method specified in JIS R1655:2003 when it is 0.2 μm or more. The nitrogen adsorption method uses the BJH method for analyzing the distribution of pore volume with respect to the diameter of pores assumed to be cylindrical according to the Barrett-Joyner-Halenda standard model (for details, see J. Amer. Chem. Soc., 73, 373, 1951 etc.).

When the filter is formed of a porous material, it may further contain additives such as a binder, as long as the characteristics are not impaired.

The 0.4 μm initial particle collection rate defined in the test method type 2 of JIS B9908:2011 of the filter is preferably 70% or more. According to the studies made by the present inventors, since large particles having a diameter of 0.4 μm or more have a large mass, the impact force when they collide with the surface of the carbon film becomes relatively large, which tends to cause defects in the carbon film. I found out that Therefore, in the present invention, attention was paid to the 0.4 μm initial particle collection rate. The higher the 0.4 μm initial particle collection rate, the more particles will be collected, and the frequency of particle collisions with the carbon film can be reduced, so that the formation of defects in the carbon film can be further suppressed and the gas separation system can be used. It can be operated stably for a longer period of time. The 0.4 μm initial particle collection rate of the filter is more preferably 80% or more. On the other hand, as the 0.4 μm initial particle collection rate is lower, the pressure loss of the filter is reduced, and the operation efficiency of the gas separation system can be improved. The 0.4 μm initial particle collection rate of the filter is more preferably 95% or less, further preferably 90% or less. When a plurality of filters are provided, the 0.4 μm initial particle collection rate of at least one filter is preferably within the above range.

The 0.4 μm initial particle collection rate of the filter is, for example, in the case of a fiber assembly, by decreasing the fiber diameter, increasing the basis weight, and facilitating the adhesion of particles by surface treatment to the fiber, Can be increased. As the fiber diameter is smaller, the pressure loss as a filter can be reduced, and the 0.4 μm initial particle collection rate can be improved. The fiber diameter is preferably 300 μm or less, more preferably 100 μm or less. On the other hand, the thicker the fiber diameter, the higher the strength, and the breakage of the fiber during operation can be suppressed. The fiber diameter is preferably 0.1 μm or more. Further, the higher the basis weight of the filter, the higher the 0.4 μm initial particle collection rate can be. The basis weight of the filter is preferably 50 g/m ² or more, more preferably 70 g/m ² or more. On the other hand, the lower the basis weight of the filter, the more the pressure loss before and after the filter can be reduced, and the efficiency of the entire gas separation system can be increased. Basis weight of the filter is preferably from 1,000 g / ^{m 2} or less, 700 g / ^{m 2} or less is more preferable.

When the pretreatment unit has a plurality of filters, it is preferable that the 0.4 μm initial particle collection rate of the most downstream filter is higher than the 0.4 μm initial particle collection rate of the most upstream filter. .. By setting the filter configuration so that particles with a large particle size are captured by a coarse filter and particles with a small particle size are captured by a fine filter, the expansion of pressure loss due to blockage of the filter is suppressed. Therefore, the gas separation system can be stably operated for a longer period of time. From these points of view, the 0.4μ initial particle collection rate of the filter in the case of having a plurality of filters is preferably 70 to 80% on the upstream side and 80% or more on the downstream side.

Further, when the above-mentioned filter for rough purification is included, the 100 μm initial particle collection rate of the filter for rough purification is preferably 50% or more, more preferably 70% or more.

Further, the filter is preferably one in which the number of particles of 5 μm or more remaining in 1 m ³ of the gas after passing through the filter is 300,000 or less. Particles of 5 μm or more have a large mass and a high impact force when they collide with the carbon film while riding on a gas flow, and therefore particles of 5 μm or more are preferably removed in the pretreatment section. From this, the number of particles of 5 μm or more after passing through the filter is preferably 30,000 or less, more preferably 10,000 or less, and further preferably 3,000 or less. The number of particles of 5 μm or more can be measured using a conventionally known particle counter or the like. Examples of means for reducing the number of particles having a particle size of 5 μm or more include a method using the above-described preferable filter and a method of providing a plurality of filters.

<Gas separation part>
The gas separation system of the present invention has a gas separation unit having a carbon membrane that is a separation membrane. It is preferable that the gas separation unit further has an element having an end fixed with a potting agent that restricts a gas flow path, and a vessel that is a container for housing the element.

<Carbon film>
The carbon film in the present invention refers to a film in which 50% or more of its constituent elements are made of carbon, and examples thereof include a film obtained by heating and carbonizing raw material fibers. The carbon film may be formed on the surface of the support. As the amount of carbon increases, the film performance, chemical resistance, and heat resistance become better, while as the amount of carbon decreases, the film becomes softer and more resistant to breakage. From the viewpoint of balancing these characteristics, the amount of carbon is preferably 50 to 99%, more preferably 70 to 90%.

The carbon film may contain an element other than carbon. Examples of constituent elements other than carbon include hydrogen, oxygen, nitrogen, boron, sulfur, silicon, alkali metals, and alkaline earth metals. In the case of selectively separating carbon dioxide, it is preferable to contain nitrogen in an amount of 0.1 to 10%, and the affinity between the carbon film and carbon dioxide can be improved. The higher the amount of nitrogen, the higher the affinity with carbon dioxide, while the lower the amount, the more improved the heat resistance and chemical resistance of the carbon film. From these balances, the amount of nitrogen is more preferably 0.1 to 5%, further preferably 0.3 to 3%. Further, by containing silicon in an amount of 0.1 to 5%, it is possible to reduce the change in film performance over time. The larger the amount of silicon, the smaller the change in film performance, while the lower the amount, the higher the film performance itself tends to be. From these viewpoints, the amount of silicon is more preferably 0.1 to 3%, further preferably 0.2 to 1%.

The amount of the above element in the present invention can be determined by X-ray photoelectron spectroscopy analysis. Note that the above element amount is basically a value on the surface of the carbon film, but it may be measured after cleaning the surface of the carbon film by about 10 nm using an argon ion beam or the like from the viewpoint of preventing contamination from the environment. preferable.

<Element>
The element has at least one end fixed with a carbon film and a potting agent for restricting the gas flow while fixing the carbon film. Further, from the viewpoint of further suppressing the damage of the carbon film, a member for mechanically protecting the carbon film such as a tension member, an outer cylinder, an inner cylinder, or a sealing member for restricting a gas flow may be provided. ..

Examples of the potting agent include polymers such as thermoplastic resins and thermosetting resins. Since the thermoplastic resin is generally excellent in chemical resistance, it is suitable for the case where the gas separation system processes a raw material gas containing impurities that can become an organic solvent. On the other hand, the thermosetting resin often has high fluidity before curing, and is easily penetrated between the carbon film and the carbon film or between the carbon film and other members, thereby further suppressing gas flow leakage. be able to. Examples of the thermoplastic resin include polyolefin such as polyethylene and polypropylene, polyether, polyester, polyamide, polyimide, polyetherimide, polyamideimide, polysulfone, polyethersulfone, and polycarbonate. You may combine 2 or more types of these. Examples of the thermosetting resin include epoxy resin, urethane resin, melamine resin, unsaturated polyester resin and the like. You may combine 2 or more types of these.

When fixing the carbon film with a potting agent, the tension member has an action of suppressing the carbon film from the fixed end to the other fixed end from being broken by tension when the element has two or more fixed ends. .. For example, a wire, a gut, a rod, a pipe, a flat plate, or the like can be selected. Wire and Tegus are preferable because they are easily available and can increase the amount of carbon film in the element. Examples of the material of the wire include copper, iron and stainless steel, and stainless steel is preferable from the viewpoint of chemical resistance and strength. Examples of the material of Tegus include polyester and polyamide.

The outer cylinder and the inner cylinder have a function of protecting the carbon film. By using the outer cylinder, breakage of the carbon film due to external force can be further suppressed. Examples of the material of the outer cylinder include metals, polymers and wood, and metals and polymers are preferable. Examples of the metal include copper, iron, aluminum, and stainless steel, and aluminum is preferable from the viewpoint of workability and availability. Examples of the polymer include polyethylene, polypropylene, polyvinyl chloride, polymethylmethacrylate, polyetheretherketone, polyamideimide, polyimide, polyetherimide and the like. It can be appropriately selected from the viewpoints of chemical resistance and heat resistance.

The sealing material is preferably selected appropriately according to the type of gas stream processed by the gas separation system of the present invention. When the gas stream contains a component that becomes an organic solvent as an impurity, it is preferable to use a fluororesin in consideration of chemical resistance.

<Vessel>
Examples of the shape of the vessel include a cylinder, a double cylinder, a rectangular parallelepiped, and a polyhedron including a prism. A cylinder or a prism is preferable because it is easy to limit the gas flow path and it is easy to secure the sealing property between the parts forming the vessel. In particular, a cylindrical shape and a flange-sealed shape are preferable, and construction and operation can be facilitated.

<Gas separation method>
The gas separation method of the present invention is a method of removing particles from a raw material gas in a pretreatment unit and then separating a specific gas in the gas separation unit by using the above-described gas separation system. Since the raw material gas to be separated can remove particles in the pretreatment section, natural gas that easily contains particles as impurities is preferable, and it can be preferably used in a separation method for separating carbon dioxide and methane from natural gas. ..

The evaluation methods in Examples and Comparative Examples are shown below.
<Unit weight>
With respect to the filters used in each example and comparative example, the basis weight was measured according to JIS Z8908 (1998).
<Thickness>
The thickness of the filters used in each of the examples and comparative examples was measured according to JIS Z8908 (1998).
<Fiber diameter>
For the filters used in each of the Examples and Comparative Examples, 20 filter fibers were randomly selected, and the fibers whose diameters were to be measured by using a microscope showed 50% to 60% of the longitudinal or lateral length of the visual field. The diameter of each fiber was measured while the field of view was changed according to the fiber to be measured, and the number average value of the obtained diameters was taken as the fiber diameter.

<0.4 μm initial particle collection rate>
Regarding the filters used in each Example and Comparative Example,
The 0.4 μm initial particle collection rate was measured according to the test method type 2 of JIS B9908:2011.

<Defects of carbon film>
While supplying JIS-7 type test powder to the gas separation system in each Example and Comparative Example for 5 hours so that the concentration in air was 70±30 mg/m ³ and the wind speed was 2.5 m/s, The gas concentration passing through the carbon membrane of the separation part was measured. The presence or absence of carbon film defects was evaluated from the initial gas concentration and the amount of change in gas concentration after 5 hours had elapsed.

<Example 1>
A filter having a fiber diameter of 2.1 μm, a basis weight of 300 g/m ² , a thickness of 100 μm and an initial particle collection rate of 75% made of a polyester nonwoven fabric having a melting point of 258° C. and a glass transition temperature of 68° C. is fixed to a filter housing, It was installed in the pretreatment section. A gas separation system was constructed by providing a gas separation unit having a carbon fiber in the form of hollow fiber carbonized after spinning by a phase conversion method using polyimide as a raw material, downstream of the pretreatment unit. When the defects of the carbon film were evaluated by the above method, the concentration of the gas passing through the carbon film did not change even after 5 hours, and stable operation was possible.

<Example 2>
Downstream of the filter of Example 1, a fiber diameter of 2.1 μm made of a polyester nonwoven fabric having a melting point of 259° C. and a glass transition temperature of 67° C., a basis weight of 350 g/m ² , a thickness of 100 μm, and a 0.4 μm initial particle collection rate of 80%. A gas separation system was constructed in the same manner as in Example 1 except that the filter of 1 was further installed. When the defects of the carbon film were evaluated by the above method, the concentration of the gas passing through the carbon film did not change even after 5 hours, and stable operation was possible.

<Example 3>
A gas separation system was constructed in the same manner as in Example 1 except that a filter made of an alumina porous body and having a 0.4 μm initial particle collection rate of 80% was used instead of the filter made of a non-woven fabric. When the defects of the carbon film were evaluated by the above method, the concentration of the gas passing through the carbon film did not change even after 5 hours, and stable operation was possible.

<Comparative Example 1>
A gas separation system was constructed and evaluated in the same manner as in Example 1 except that no filter was installed in the pretreatment section. After 5 hours, the concentration of gas passing through the carbon film was changed, and damage to the carbon film was observed.

<Example 4>
A gas separation system was constructed in the same manner as in Example 1 except that polyester having a melting point of 226°C and a glass transition temperature of 43°C was used. When the defects of the carbon film were evaluated by the above method, the concentration of the gas passing through the carbon film did not change even after 5 hours, and stable operation was possible.

<Example 5>
A gas separation system was constructed in the same manner as in Example 1 except that polyphenylene sulfide having a melting point of 284° C. and a glass transition temperature of 89° C. was used. When the defects of the carbon film were evaluated by the above method, the concentration of the gas passing through the carbon film did not change even after 5 hours, and stable operation was possible.

<Example 6>
A gas separation system was constructed in the same manner as in Example 1 except that polypropylene having a melting point of 167°C and a glass transition temperature of -11°C was used. When the defects of the carbon film were evaluated by the above method, the gas concentration passing through the carbon film slightly changed after 5 hours, but relatively stable operation was possible.

<Comparative example 2>
A gas separation system was constructed in the same manner as in Example 1 except that high density polyethylene having a melting point of 127°C and a glass transition temperature of -68°C was used. When the defects of the carbon film were evaluated by the above method, the concentration of the gas passing through the carbon film was changed after 5 hours, and the damage of the carbon film was recognized.

1: Raw material gas 2: Pretreatment part 3: Posttreatment gas 4: Gas separation part 5: Permeation gas 6: Purified gas

Claims (9)

A gas separation system having a pretreatment section having a filter and a gas separation section having a carbon membrane. The gas separation system according to claim 1, wherein the filter has a 0.4 μm initial particle collection rate of 70% or more specified in the test method type 2 of JIS B9908:2011 of the filter. The gas separation system according to claim 1 or 2, wherein the filter is composed of polymer fibers. The gas separation system according to claim 3, wherein the polymer fiber is composed of a polymer having crystallinity (hereinafter, referred to as a crystalline polymer). The gas separation system according to claim 4, wherein the glass transition temperature of the crystalline polymer is lower than 200°C. The gas separation system according to claim 4 or 5, wherein the melting point of the crystalline polymer is 150°C or higher. The gas separation system according to claim 1, wherein the filter is made of an inorganic porous material. The pretreatment section has a plurality of filters, and the 0.4 μm initial particle collection rate of the most downstream filter is higher than the 0.4 μm initial particle collection rate of the most upstream filter. The gas separation system according to any one of 1. A gas separation method using the gas separation system according to claim 1, wherein particles are removed from the raw material gas in the pretreatment unit, and then a specific gas is separated in the gas separation unit.

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