Membrane separation system and method for cleaning membrane separation device

Abstract

Provided is a membrane separation system suitable for suppressing the proliferation of unwanted microorganisms inside a membrane separation device. This membrane separation system (100) is provided with a membrane separation device (10). The membrane separation device (10) has a pervaporation membrane (11), and a supply space and a permeation space separated by the pervaporation membrane (11). The membrane separation system (100) performs: a membrane separation operation in which a solution (S) containing a volatile organic compound (C) is separated into a permeated fluid and a non-permeated fluid by decompressing the permeated space in a state in which the solution (S) is supplied to the supply space; and a cleaning operation in which the solution S is supplied to the supply space while the membrane separation operation is stopped, and the pervaporation membrane 11 is cleaned with the solution S.

Description

Technical Field

[0001] The invention relates to a membrane separation system and a cleaning method for a membrane separation device. Background Art

[0002] A method for producing volatile organic compounds (fermented products) such as alcohols by fermenting carbon sources such as glucose using microorganisms has been developed. The fermentation of the carbon source is carried out, for example, in a solution, typically in an aqueous solution. In this method, if the content of the fermented product in the aqueous solution increases, the fermentation based on the microorganism sometimes stops. In order to continuously produce a fermented product based on a microorganism, it is necessary to separate the fermented product from the aqueous solution.

[0003] As an example of a method for separating volatile organic compounds from an aqueous solution containing the organic compounds, a pervaporation method (pervaporation method) using a pervaporation membrane can be cited. The pervaporation method is suitable for separating volatile organic compounds from aqueous solutions containing various substances. Compared with the distillation method, the pervaporation method also tends to suppress energy consumption and carbon dioxide emissions. By combining a membrane separation device for performing the pervaporation method with a fermentation tank for producing fermented products, fermented products can be continuously produced. For example, Patent Document 1 discloses a membrane separation system that combines a membrane separation device and a fermentation tank.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2010-161987 Summary of the invention

[0007] Problems to be solved by the invention

[0008] According to the research of the inventors of the present application, when a solution containing volatile organic compounds is introduced into the supply space of a membrane separation device and the pervaporation method is performed, there is a tendency for unwanted microorganisms to proliferate at a position where the content of the organic compound in the solution is low (typically a position close to the outlet of the supply space). If the unwanted microorganisms proliferate, fouling (biofouling) occurs on the pervaporation membrane, and there is a tendency for the separation performance of the pervaporation membrane to decrease.

[0009] Therefore, an object of the present invention is to provide a membrane separation system suitable for suppressing the proliferation of unnecessary microorganisms inside a membrane separation device.

[0010] Means for solving problems

[0011] The present invention provides a membrane separation system, which is a membrane separation system comprising a membrane separation device.

[0012] The membrane separation device comprises a pervaporation membrane, and a supply space and a permeation space separated by the pervaporation membrane.

[0013] The membrane separation system performs:

[0014] membrane separation operation, in which a solution containing a volatile organic compound is supplied to the supply space, and the permeation space is depressurized to thereby separate the solution into a permeated fluid and a non-permeated fluid; and

[0015] In the cleaning operation, the solution is supplied to the supply space while the membrane separation operation is stopped, thereby cleaning the pervaporation membrane with the solution.

[0016] Furthermore, the present invention provides a method for cleaning a membrane separation device, which is a method for cleaning a membrane separation device having a pervaporation membrane, and a supply space and a permeation space separated by the pervaporation membrane.

[0017] The membrane separation device is capable of performing a membrane separation operation in which the solution containing a volatile organic compound is supplied to the supply space, and the pressure in the permeation space is reduced, thereby separating the solution into a permeated fluid and a non-permeated fluid.

[0018] The cleaning method includes supplying the solution to the supply space in a state where the membrane separation operation is stopped, thereby cleaning the pervaporation membrane with the solution.

[0019] Effects of the Invention

[0020] According to the present invention, it is possible to provide a membrane separation system suitable for suppressing the proliferation of unnecessary microorganisms inside a membrane separation device. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] [ Figure 1 ] is a schematic diagram showing an example of a membrane separation system.

[0022] [ Figure 2 ] is a schematic cross-sectional view showing an example of a membrane separation device.

[0023] [ Figure 3 ] is a schematic cross-sectional view of a pervaporation membrane included in a membrane separation device.

[0024] [ Figure 4A ] is a diagram for illustrating the cleaning operation of the membrane separation system.

[0025] [ Figure 4B ] is a diagram for illustrating the cleaning operation of the membrane separation system.

[0026] [ Figure 5] is a developed stereoscopic view schematically showing another example of a membrane separation device.

[0027] [ Fig. 6A ] is a schematic diagram showing a modified example of the membrane separation system.

[0028] [ Figure 6B ] is a schematic diagram showing a modified example of the membrane separation system. DETAILED DESCRIPTION

[0029] A membrane separation system according to a first aspect of the present invention is a membrane separation system comprising a membrane separation device.

[0030] The membrane separation device comprises a pervaporation membrane, and a supply space and a permeation space separated by the pervaporation membrane.

[0031] The above membrane separation system performs:

[0032] membrane separation operation, in which a solution containing a volatile organic compound is supplied to the supply space, and the permeation space is depressurized to separate the solution into a permeated fluid and a non-permeated fluid; and

[0033] In the cleaning operation, the solution is supplied to the supply space while the membrane separation operation is stopped, thereby cleaning the pervaporation membrane with the solution.

[0034] In the second aspect of the present invention, for example, in the membrane separation system of the first aspect, during the cleaning operation, the pressure of the permeation space is adjusted to a value higher than the pressure of the permeation space during the membrane separation operation.

[0035] In the third aspect of the present invention, for example, the membrane separation system of the first or second aspect alternately and repeatedly performs the membrane separation operation and the cleaning operation.

[0036] In a fourth aspect of the present invention, for example, in the membrane separation system of any one of the first to third aspects, the membrane separation device further comprises a supply space inlet for supplying the solution to the supply space during the membrane separation operation.

[0037] In the cleaning operation, the membrane separation system supplies the solution from the supply space inlet.

[0038] In a fifth aspect of the present invention, for example, in the membrane separation system of any one of the first to third aspects, the membrane separation device further comprises a supply space outlet for discharging the non-permeated fluid from the supply space during the membrane separation operation.

[0039] In the cleaning operation, the membrane separation system supplies the solution from the outlet of the supply space.

[0040] In a sixth aspect of the present invention, for example, in the membrane separation system of any one of the first to fifth aspects, a content rate of the organic compound in the permeated fluid is higher than a content rate of the organic compound in the solution.

[0041] In a seventh aspect of the present invention, for example, in the membrane separation system of any one of the first to sixth aspects, the organic compound is a fermentation product produced by a microorganism, and the solution is a fermentation liquid.

[0042] In an eighth aspect of the present invention, for example, in the membrane separation system according to any one of the first to seventh aspects, the organic compound is an alcohol.

[0043] In a ninth aspect of the present invention, for example, in the membrane separation system according to any one of the first to eighth aspects, the content of the organic compound in the solution is 1 wt % or more.

[0044] In a tenth aspect of the present invention, for example, the membrane separation system according to any one of the first to ninth aspects further includes a tank for storing the solution supplied to the membrane separation device.

[0045] In an eleventh aspect of the present invention, for example, the membrane separation system according to any one of the first to tenth aspects includes a plurality of the above-mentioned membrane separation devices, and the plurality of the above-mentioned membrane separation devices are connected in series or in parallel to each other.

[0046] In the twelfth aspect of the present invention, for example, the membrane separation system of the eleventh aspect performs the cleaning operation using at least one of the plurality of membrane separation devices while performing the membrane separation operation using the other membrane separation devices that are not performing the membrane separation operation.

[0047] A thirteenth aspect of the present invention is a method for cleaning a membrane separation device comprising a pervaporation membrane, and a supply space and a permeation space separated by the pervaporation membrane.

[0048] The membrane separation device is capable of performing a membrane separation operation in which the solution containing the volatile organic compound is supplied to the supply space, and the pressure in the permeation space is reduced, thereby separating the solution into a permeated fluid and a non-permeated fluid.

[0049] The cleaning method includes supplying the solution to the supply space while the membrane separation operation is stopped, thereby cleaning the pervaporation membrane with the solution.

[0050] Hereinafter, the present invention will be described in detail, but the following description is not intended to limit the present invention to specific embodiments.

[0051] <Membrane separation system>

[0052] like Figure 1 As shown, the membrane separation system 100 of this embodiment includes a membrane separation device 10. The membrane separation device 10 has a pervaporation membrane and a supply space and a permeation space separated by the pervaporation membrane. The membrane separation system 100 can perform a membrane separation operation using the membrane separation device 10 and a cleaning operation of the membrane separation device 10.

[0053] In the membrane separation operation, the membrane separation system 100 depressurizes the permeation space while supplying a solution S containing a volatile organic compound C to the supply space of the membrane separation device 10, thereby separating the solution S into a permeated fluid and a non-permeated fluid. In the cleaning operation, the membrane separation system 100 supplies the solution S to the supply space of the membrane separation device 10 while the membrane separation operation is stopped, thereby cleaning the pervaporation membrane with the solution S. The membrane separation operation and the cleaning operation will be described in detail later.

[0054] As described above, the membrane separation device 10 is a device that performs membrane separation on the solution S using a pervaporation membrane during membrane separation operation. The pervaporation membrane is typically a membrane that preferentially permeates the organic compound C contained in the solution S. Therefore, the content of the organic compound C in the permeated fluid separated by the pervaporation membrane is higher than that in the solution S. On the other hand, the content of the organic compound C in the non-permeated fluid is lower than that in the solution S. The solution S is typically an aqueous solution containing the organic compound C. However, the solution S may also be a non-aqueous solution that does not contain water.

[0055] The membrane separation system 100 is provided with a tank 20 in addition to the membrane separation device 10. The tank 20 stores a solution S to be supplied to the membrane separation device 10. It should be noted that, as described later, the organic compound C may be a fermentation product generated by microorganisms fermenting a carbon source. That is, the solution S may be a fermentation liquid containing the organic compound C as a fermentation product. The tank 20 may also be a fermentation tank for generating the organic compound C by fermenting a carbon source based on microorganisms.

[0056] The membrane separation system 100 further includes a first path 60, a second path 61, and a third path 62. The first path 60 is a path (solution supply path) for supplying the solution S from the tank 20 to the membrane separation device 10 during the membrane separation operation, and is connected to the outlet 21 of the tank 20 and the supply space inlet 13a of the membrane separation device 10. For example, a pump 40 for controlling the flow rate of the solution S is arranged on the first path 60.

[0057] The second path 61 is a path (non-permeable fluid discharge path) for discharging the non-permeable fluid from the membrane separation device 10 during the membrane separation operation, and is connected to the supply space outlet 13b of the membrane separation device 10. For example, a pump 41 for controlling the flow rate of the non-permeable fluid is arranged on the second path 61. It should be noted that the pump 41 may not be arranged on the second path 61. The second path 61 may be configured to be connected to the inlet 22 of the tank 20 and to deliver the non-permeable fluid to the tank 20 during the membrane separation operation. That is, during the membrane separation operation, the non-permeable fluid may be mixed with the solution S in the tank 20 and circulated in the first path 60 and the second path 61. When the non-permeable fluid is delivered to the tank 20, the solution S and the non-permeable fluid are mixed in the tank 20, and the content of the organic compound C in the solution S is reduced. When the tank 20 is a fermentation tank, the reduction in the content of the organic compound C in the solution S can suppress the stop of fermentation by microorganisms, thereby enabling continuous production of fermented products.

[0058] The third path 62 is a path (permeate fluid discharge path) for discharging the permeate fluid from the membrane separation device 10 during the membrane separation operation, and is connected to the permeate space outlet 14a of the membrane separation device 10. For example, a decompression device 42 is arranged on the third path 62. The decompression device 42 can decompress the permeate space of the membrane separation device 10. The decompression device 42 is preferably a vacuum device such as a vacuum pump. The vacuum pump is typically a gas-transporting vacuum pump, and a reciprocating vacuum pump, a rotary vacuum pump, etc. can be cited. As a reciprocating vacuum pump, a diaphragm type and a swing piston type vacuum pump can be cited. As a rotary vacuum pump, a liquid seal pump; an oil rotary pump (rotary pump); a mechanical booster pump; various dry pumps such as Roots type, claw type, screw type, turbine type, and vortex type can be cited. The pump as the decompression device 42 can also be provided with a variable speed mechanism for changing the rotation speed, etc. An example of a variable speed mechanism is an inverter that drives the motor of the pump. By controlling the rotation speed of the pump using a variable speed mechanism, etc., the pressure of the permeation space of the membrane separation device 10 can be appropriately adjusted.

[0059] A heat exchanger for cooling the permeated fluid may also be arranged on the third path 62. The permeated fluid of the gas can be condensed by the heat exchanger. The heat exchanger is, for example, a gas-liquid heat exchanger that generates heat exchange between a cooling medium such as an antifreeze liquid and the permeated fluid of the gas. The heat exchanger may be located between the membrane separation device 10 and the pressure reducing device 42 (on the upstream side of the pressure reducing device 42), or between the pressure reducing device 42 and the recovery unit 30 described later (on the downstream side of the pressure reducing device 42).

[0060] The membrane separation system 100 further includes a recovery unit 30. The recovery unit 30 recovers the permeated fluid sent from the membrane separation device 10 and can, for example, store the permeated fluid. The recovery unit 30 is, for example, a tank for storing the permeated fluid. The inlet 31 of the recovery unit 30 is connected to the third path 62.

[0061] The membrane separation system 100 may further include a controller 50 for controlling the various components of the membrane separation system 100. The controller 50 is, for example, a DSP (Digital Signal Processor) including an A / D conversion circuit, an input / output circuit, an operation circuit, a storage device, etc. A program for properly operating the membrane separation system 100 is stored in the controller 50. For example, the controller 50 can control the operation of the pumps 40 and 41, the pressure reducing device 42, etc., to switch between the membrane separation operation and the cleaning operation.

[0062] Unless otherwise specified, each path of the membrane separation system 100 is constituted by, for example, a pipe made of metal or resin.

[0063] [Membrane separation device]

[0064] like Figure 2 As shown, the membrane separation device 10 includes a pervaporation membrane 11 and a tank 12. The tank 12 has a first chamber 13 and a second chamber 14. The first chamber 13 functions as a supply space for supplying a solution S. The second chamber 14 functions as a permeation space for supplying a permeated fluid 80. The permeated fluid 80 is obtained by the solution S passing through the pervaporation membrane 11. It should be noted that Figure 2 The state of the membrane separation device 10 during the membrane separation operation is shown.

[0065] Pervaporation membrane 11 is disposed inside tank 12. Pervaporation membrane 11 partitions first chamber 13 and second chamber 14 inside tank 12. Pervaporation membrane 11 extends from one of a pair of wall surfaces of tank 12 to the other.

[0066] The first chamber 13 has a supply space inlet 13a and a supply space outlet 13b. The second chamber 14 has a permeation space outlet 14a. The supply space inlet 13a is an opening for supplying a solution S to the supply space (first chamber 13) during membrane separation operation. The permeation space outlet 14a is an opening for discharging a permeated fluid 80 from the permeation space (second chamber 14) during membrane separation operation. The supply space outlet 13b is an opening for discharging a solution S (non-permeated fluid 81) that has not permeated the pervaporation membrane 11 from the supply space (first chamber 13) during membrane separation operation. The supply space inlet 13a, the supply space outlet 13b, and the permeation space outlet 14a are formed, for example, on the wall surface of the tank 12, respectively.

[0067] The membrane separation device 10 is suitable for a flow-through (continuous) membrane separation method. However, the membrane separation device 10 can also be used for a batch-type membrane separation method.

[0068] (Pervaporation membrane)

[0069] As described above, pervaporation membrane 11 is typically a membrane (separation membrane) that preferentially permeates organic compound C contained in solution S. Pervaporation membrane 11 generates permeated fluid 80 of gas containing organic compound C by, for example, pervaporation.

[0070] like Figure 3 As shown, the pervaporation membrane 11 includes, for example, a separation functional layer 1 and a porous support 2 supporting the separation functional layer 1. The pervaporation membrane 11 may further include a protective layer (not shown) for protecting the separation functional layer 1. The separation functional layer 1 is, for example, directly in contact with the porous support 2. For example, the main surface 11a of the pervaporation membrane 11 on the separation functional layer side is exposed to the first chamber 13, and the main surface 11b of the porous support side is exposed to the second chamber 14.

[0071] (Separation Functional Layer)

[0072] Typically, the separation functional layer 1 is a layer that allows the organic compound C contained in the solution S to preferentially pass through. The separation functional layer 1, for example, includes a hydrophobic material. In this specification, "hydrophobic material" refers to, for example, a material whose static contact angle of water exceeds 90° when a 10 μL drop of water (temperature 25° C.) is dropped on the surface of a test piece composed of the material. It should be noted that the static contact angle of water can be measured using a commercially available contact angle meter.

[0073] As a hydrophobic material, for example, compounds having a siloxane bond (Si-O-Si bond), olefin polymers, oils, fluorine compounds, etc. can be cited. The separation functional layer 1 preferably contains a compound having a siloxane bond as a hydrophobic material. The compound having a siloxane bond is typically an organosilicon polymer. The organosilicon polymer can be solid or liquid at 25°C. As a specific example of an organosilicon polymer, polydimethylsiloxane (PDMS) and the like can be cited. As a specific example of an olefin polymer, polyethylene, polypropylene, etc. can be cited. As an oil, for example, hydrocarbon oils such as liquid paraffin can be cited. As a fluorine compound, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), etc. can be cited. The hydrophobic material can be used alone or in combination of two or more.

[0074] The separation functional layer 1 may contain a hydrophobic material as a main component, or may be substantially composed of only a hydrophobic material. The "main component" refers to the component that is contained in the largest amount by weight in the separation functional layer 1 .

[0075] The separation function layer 1 may include: a matrix including a hydrophobic material, and fillers dispersed in the matrix. The fillers are embedded in the matrix. In the matrix, all fillers may be spaced apart from each other or partially aggregated.

[0076] The filler includes, for example, inorganic materials such as zeolite, silica, and bentonite. The zeolite contained in the filler is preferably a high-silicon zeolite having a high ratio of silica to alumina. High-silicon zeolite is suitable for separating a solution S containing water due to its excellent hydrolysis resistance. As high-silicon zeolite, HSZ (registered trademark) manufactured by Tosoh Corporation, HiSiv (registered trademark) manufactured by United Showa Corporation, USKY manufactured by United Showa Corporation, and Zeoal (registered trademark) manufactured by Nakamura Superhard Co., Ltd. can be used.

[0077] The filler may include a metal-organic framework (MOF). The metal-organic framework is also called a porous coordination polymer (PCP). The metal-organic framework is preferably hydrophobic. The metal-organic framework includes, for example, metal ions and organic ligands. Examples of metal ions include Zn ions. Organic ligands include, for example, aromatic rings. Examples of aromatic rings contained in organic ligands include imidazole rings. Examples of organic ligands include 2-methylimidazole. Specific examples of metal-organic frameworks include ZIF-8.

[0078] The shape of the filler is, for example, particulate. In this specification, "particulate" includes spherical, ellipsoidal, scaly and fibrous. The average particle size of the filler is not particularly limited, for example, it is less than 50 μm, preferably less than 20 μm, and more preferably less than 10 μm. The lower limit of the average particle size of the filler is, for example, 0.01 μm. The average particle size of the filler can be determined, for example, by the following method. First, observe the cross section of the separation functional layer 1 with a transmission electron microscope. In the obtained electron microscope image, the area of ​​a specific filler is calculated by image processing. The diameter of a circle having the same area as the calculated area is regarded as the particle size (diameter of the particle) of the specific filler. The particle sizes of any number (at least 50) of fillers are calculated separately, and the average value of the calculated values ​​is regarded as the average particle size of the filler.

[0079] The content of the filler in the separation functional layer 1 is, for example, 10 wt% or more, preferably 30 wt% or more, and more preferably 40 wt% or more. The upper limit of the content of the filler in the separation functional layer 1 is not particularly limited, and is, for example, 70 wt%. The content of the matrix in the separation functional layer 1 is not particularly limited, and is, for example, 30 wt% to 90 wt%.

[0080] The thickness of the separation functional layer 1 is, for example, 200 μm or less, preferably 100 μm or less, and more preferably 80 μm or less. The thickness of the separation functional layer 1 may be 1.0 μm or more, 10 μm or more, or 30 μm or more.

[0081] The separation functional layer 1 may have a microporous structure with an average pore diameter of less than 0.01 μm, or may be a dense layer with no pores on the surface.

[0082] (Porous Support)

[0083] Examples of the porous support 2 include: nonwoven fabrics; porous polytetrafluoroethylene; aromatic polyamide fibers; porous metals; sintered metals; porous ceramics; porous polyesters; porous nylons; activated carbon fibers; latex; silicone; silicone rubber; a permeable (porous) polymer comprising at least one selected from polyvinyl fluoride, polyvinylidene fluoride, polyurethane, polypropylene, polyethylene, polystyrene, polycarbonate, polysulfone, polyetheretherketone, polyacrylonitrile, polyimide, and polyphenylene ether; a metal foam having open or closed cells; a polymer foam having open or closed cells; silicon dioxide; porous glass; a mesh, and the like. The porous support 2 may be a combination of two or more of these.

[0084] The porous support 2 has an average pore size of, for example, 0.01 to 0.4 μm. The thickness of the porous support 2 is not particularly limited, and is, for example, 10 μm or more, preferably 50 μm or more, and more preferably 100 μm or more. The thickness of the porous support 2 is, for example, 300 μm or less, and preferably 200 μm or less.

[0085] (Protective layer)

[0086] The protective layer, for example, covers the surface of the separation functional layer 1. The material of the protective layer is not particularly limited, and for example, a silicone resin can be cited. The material of the protective layer can also be the same as the material of the matrix of the separation functional layer 1. The thickness of the protective layer is not particularly limited, and for example, it is 0.5 μm or more, preferably 1 μm or more, more preferably 5 μm or more, and further preferably 10 μm or more. The thickness of the protective layer is, for example, 100 μm or less, preferably 50 μm or less, and more preferably 30 μm or less.

[0087] (Method for manufacturing pervaporation membrane)

[0088] The permeation vaporization membrane 11 can be made, for example, by forming a separation functional layer 1 on a porous support 2. In detail, first, a coating liquid containing a material for the separation functional layer 1 is prepared. The coating liquid may contain a filler and a dispersant for dispersing the filler in the coating liquid. In the case where the coating liquid contains a compound having a siloxane bond, the coating liquid may further contain a catalyst for curing the compound. Next, a coating film is obtained by applying the coating liquid on the porous support 2. The separation functional layer 1 is formed by drying the coating film.

[0089] [Operation of membrane separation system]

[0090] (Membrane separation operation)

[0091] The membrane separation operation of the membrane separation system 100 is carried out, for example, as follows. Figure 2 As shown, the solution S is supplied to the first chamber 13 of the membrane separation device 10 through the supply space inlet 13a. Thus, the solution S can be brought into contact with one surface (for example, the main surface 11a) of the pervaporation membrane 11.

[0092] The organic compound C contained in the solution S is not particularly limited as long as it is volatile. In this specification, the "volatile organic compound" refers to an organic compound having a boiling point of 20°C to 260°C, preferably 50°C to 260°C under atmospheric pressure (101.325 kPa). It should be noted that, when the concentration of the organic compound C in the aqueous solution is high, for example, an aqueous phase containing water as the main component and an organic phase having a higher content of the organic compound C than the aqueous phase are generated.

[0093] The number of carbon atoms in the organic compound C is not particularly limited, and may be, for example, 10 or less, 8 or less, 6 or less, or 4 or less. The lower limit of the number of carbon atoms in the organic compound C may be 1 or 2. The organic compound C may have a functional group containing an oxygen atom, such as a hydroxyl group, a carbonyl group, an ether group, or an ester group. In the organic compound C, the number of functional groups containing an oxygen atom is typically 1.

[0094] As the organic compound C, for example, alcohol, ketone, ester, etc. can be cited, preferably alcohol. In the case where the organic compound C is an alcohol, the organic compound C is easily miscible with water, and the environment in the system is not easy to deviate. The alcohol can be an alkyl alcohol consisting only of an alkyl group and a hydroxyl group, or an aryl alcohol containing an aryl group and a hydroxyl group. The alkyl alcohol can be any of a straight chain, a branched chain, and a ring. As the alkyl alcohol, for example, methanol, ethanol, n-propanol, isopropanol, n-butanol, 2-butanol, isobutanol, tert-butanol, n-pentanol, etc. can be cited, preferably n-butanol. n-Butanol is a compound that generates two phases (aqueous phase and organic phase) in an aqueous solution when the content rate in the aqueous solution is about 8wt% or more. Therefore, in the case where the organic compound C is n-butanol, for example, by adjusting the content rate of the organic compound C in the permeated fluid containing water to about 8wt% or more, an aqueous phase and an organic phase can be generated in the permeated fluid after liquefaction. In this case, by separating the aqueous phase and the organic phase, the permeated fluid can be easily purified. As the aryl alcohol, for example, phenol can be cited.

[0095] The ketone may be a dialkyl ketone consisting only of an alkyl group and a carbonyl group. Examples of the dialkyl ketone include methyl ethyl ketone (MEK) and acetone.

[0096] The ester may be a fatty acid alkyl ester consisting only of an alkyl group and an ester group. Examples of the fatty acid alkyl ester include ethyl acetate and the like.

[0097] It should be noted that the organic compound C is not limited to the above compounds and may be an aromatic hydrocarbon such as benzene, toluene, or xylene.

[0098] The organic compound C is preferably toxic to unwanted microorganisms (eg, viruses, bacteria, fungi, etc.) In the present specification, unwanted microorganisms are microorganisms that are different from microorganisms that produce fermentation products described below and that can cause fouling in the pervaporation membrane 11 .

[0099] The solution S may contain one organic compound C, or may contain two or more organic compounds C. The content of the organic compound C in the solution S may be, for example, 0.5 wt% or more, 1 wt% or more, 2 wt% or more, or 5 wt% or more. The upper limit of the content of the organic compound C is not particularly limited, and may be, for example, 50 wt%.

[0100] The organic compound C may be a fermentation product produced by microorganisms fermenting carbon sources, or may be alcohol (bioalcohol) produced by microorganisms. That is, the solution S may be a fermentation liquid containing the organic compound C as a fermentation product. However, the solution S is not limited to the fermentation liquid, and may also be waste liquid or wastewater discharged from chemical equipment, etc.

[0101] As described above, the solution S is typically an aqueous solution containing an organic compound C. The solution S may also contain other components such as microorganisms that generate fermentation products, carbon sources, nitrogen sources, and inorganic ions in addition to water and the organic compound C. The microorganisms that generate fermentation products are typically bacteria. As carbon sources, polysaccharides such as starch and monosaccharides such as glucose can be cited.

[0102] The amount of solution S supplied to the membrane separation device 10 is not particularly limited and is determined according to the processing capacity of the membrane separation device 10. The solution S supplied to the first chamber 13 may be preheated. As an example, the temperature of the solution S supplied to the first chamber 13 is 15°C to 75°C.

[0103] Next, while the solution S is in contact with one surface of the pervaporation membrane 11, the space adjacent to the other surface (for example, the main surface 11b) of the pervaporation membrane 11 is depressurized. Specifically, the second chamber 14 is depressurized through the space outlet 14a. The depressurization in the second chamber 14 can be performed, for example, by the decompression device 42. The pressure of the second chamber 14 is, for example, 50 kPa or less, and may also be 20 kPa or less, 10 kPa or less, 5 kPa or less, 3 kPa or less, and further may be 2 kPa or less. In addition, in this specification, "pressure" refers to absolute pressure unless otherwise specified.

[0104] By reducing the pressure in the second chamber 14, a permeate fluid 80 having a high content of organic compound C can be obtained on the other side of the pervaporation membrane 11. In other words, the permeate fluid 80 is supplied to the second chamber 14. In the second chamber 14, the permeate fluid 80 is typically a gas. The permeate fluid 80 is discharged to the outside of the membrane separation device 10 through the permeation space outlet 14a.

[0105] On the other hand, the content of the organic compound C in the solution S gradually decreases from the supply space inlet 13a toward the supply space outlet 13b of the first chamber 13. The solution S (non-permeable fluid 81) treated in the first chamber 13 is discharged to the outside of the membrane separation device 10 through the supply space outlet 13b. The non-permeable fluid 81 is typically a liquid.

[0106] The pervaporation membrane 11 of the membrane separation device 10 can preferentially permeate the organic compound C contained in the solution S. Therefore, the content of the organic compound C in the permeated fluid 80 obtained by the operation of the membrane separation device 10 is higher than that of the solution S supplied to the membrane separation device 10. The ratio of the content (wt%) of the organic compound C in the permeated fluid 80 to the content (wt%) of the organic compound C in the solution S is not particularly limited. The content of the organic compound C in the non-permeated fluid 81 discharged from the supply space outlet 13b is, for example, less than 0.5 wt%, and may be 0.4 wt% or less.

[0107] (Cleaning operation)

[0108] The cleaning operation of the membrane separation system 100 is implemented, for example, as follows. First, for the membrane separation device 10 that performs the membrane separation operation, the pressure of the permeation space (the second chamber 14) is increased, and the membrane separation operation is stopped. At this time, the pressure in the second chamber 14 is adjusted to a value at which the permeation fluid 80 is substantially not supplied to the second chamber 14. The pressure in the second chamber 14 may also be increased to the atmospheric pressure in the surrounding environment. In this way, the membrane separation system 100 adjusts the pressure of the permeation space to a value higher than the pressure of the permeation space in the membrane separation operation during the cleaning operation.

[0109] Next, while the membrane separation operation is stopped, solution S is supplied to the supply space (first chamber 13 ). Thus, solution S contacts one surface (eg, main surface 11 a ) of pervaporation membrane 11 , and pervaporation membrane 11 can be cleaned with solution S.

[0110] In detail, if the membrane separation system 100 performs membrane separation operation, there is a tendency that unwanted microorganisms proliferate at a position where the content of organic compound C in solution S is low (typically, a position close to the supply space outlet 13b). This tendency is particularly significant when the temperature of solution S is around 30°C to 40°C. During the cleaning operation, solution S with a relatively high content of organic compound C can be transported to the above-mentioned position. Thus, the proliferation of unwanted microorganisms can be suppressed. In particular, when organic compound C is toxic to unwanted microorganisms, the cleaning operation can reduce unwanted microorganisms, and the microorganisms can be killed depending on the situation. In the membrane separation system 100 of the present embodiment, solution S, which is the separation object in the membrane separation operation, is used during the cleaning operation, so there is no need to use a cleaning liquid different from solution S separately.

[0111] From another aspect of the present invention, the present invention provides a method for cleaning a membrane separation device 10, which is a method for cleaning a membrane separation device 10 having a pervaporation membrane 11, and a supply space and a permeation space separated by the pervaporation membrane 11, wherein:

[0112] The membrane separation device 10 can perform a membrane separation operation in which a solution S containing a volatile organic compound C is supplied to a supply space, and the solution S is depressurized in the permeation space, thereby separating the solution S into a permeated fluid 80 and a non-permeated fluid 81.

[0113] This cleaning method includes supplying a solution S to a supply space in a state where a membrane separation operation is stopped, thereby cleaning the pervaporation membrane 11 with the solution S.

[0114] In a preferred embodiment of the present invention, during the cleaning operation, the solution S is supplied from the supply space inlet 13a ( Figure 4A). In detail, the solution S is transported from the tank 20 to the supply space inlet 13a of the membrane separation device 10 through the first path 60. The solution S moves from the supply space inlet 13a to the supply space outlet 13b, and is discharged to the outside of the membrane separation device 10 through the supply space outlet 13b. The solution S discharged to the outside of the membrane separation device 10 returns to the tank 20, for example, through the second path 61. However, the cleaned solution S can also be discharged to the outside of the membrane separation system 100 through a discharge path (not shown) branched from the second path 61. In this cleaning operation mode, for example, by increasing the pressure in the second chamber 14 while the pump 40 is operating, the membrane separation operation can be easily switched to the cleaning operation.

[0115] In another preferred embodiment of the present invention, during the cleaning operation, the solution S is supplied from the supply space outlet 13b ( Figure 4B ). In detail, the solution S is transported from the tank 20 to the supply space outlet 13b of the membrane separation device 10 through the second path 61. The solution S moves from the supply space outlet 13b to the supply space inlet 13a, and is discharged to the outside of the membrane separation device 10 through the supply space inlet 13a. The solution S discharged to the outside of the membrane separation device 10 returns to the tank 20, for example, through the first path 60. However, the cleaned solution S can also be discharged to the outside of the membrane separation system 100 through a discharge path (not shown) branched from the first path 60. In this cleaning operation mode, the solution S moves in a direction opposite to the moving direction of the solution S in the membrane separation operation. According to this mode, the solution S with a relatively high content of organic compounds C can be quickly delivered to a position where unnecessary microorganisms are likely to proliferate during the membrane separation operation (typically a position close to the supply space outlet 13b). Thereby, the proliferation of unnecessary microorganisms can be more effectively suppressed.

[0116] In the membrane separation system 100, the time for performing the cleaning operation and the supply amount of the solution S during the cleaning operation are determined according to the membrane area of ​​the pervaporation membrane 11, the capacity of the membrane separation device 10, etc. As an example, the time for performing the cleaning operation is 0.5 hours to 1 hour. The supply amount of the solution S during the cleaning operation may be the same as or different from the supply amount of the solution S during the membrane separation operation.

[0117] The membrane separation system 100 preferably performs membrane separation operation and cleaning operation alternately and repeatedly. In the membrane separation system 100, the membrane separation operation and the cleaning operation can be switched regularly or at any timing. The cleaning operation is preferably performed before the unnecessary microorganisms fully proliferate during the membrane separation operation, for example.

[0118] [Modification of membrane separation device]

[0119] The membrane separation device 10 may be a spiral membrane element, a hollow fiber membrane element, a coil-type membrane element in which a plurality of pervaporation membranes are stacked, a plate-and-frame membrane element, or the like. Figure 5 A spiral type membrane element is shown. Figure 5 The membrane separation device 15 includes a central tube 16 and a stack 17 . The stack 17 includes a pervaporation membrane 11 .

[0120] The central tube 16 has a cylindrical shape. A plurality of holes or slits are formed on the surface of the central tube 16 for allowing the permeating fluid 80 to flow into the interior of the central tube 16. Examples of the material of the central tube 16 include resins such as acrylonitrile-butadiene-styrene copolymer resin (ABS resin), polyphenylene ether resin (PPE resin), and polysulfone resin (PSF resin); and metals such as stainless steel and titanium. The inner diameter of the central tube 16 is, for example, in the range of 20 to 100 mm.

[0121] The stack 17 includes a feed-side flow path material 18 and a permeate-side flow path material 19 in addition to the pervaporation membrane 11. The stack 17 is wound around the central tube 16. The membrane separation device 15 may further include an exterior material (not shown).

[0122] As the supply side flow path material 18 and the permeate side flow path material 19, for example, a net, woven fabric or knitted fabric made of a resin formed of polyethylene, polypropylene, polyethylene terephthalate (PET), polyphenylene sulfide (PPS) or ethylene-chlorotrifluoroethylene copolymer (ECTFE) can be used.

[0123] In the membrane separation device 15, for example, the membrane separation operation can be performed by the following method. First, a solution S is supplied to one end of the wound stack 17. The internal space of the central tube 16 is depressurized. As a result, the permeated fluid 80 that permeates the pervaporation membrane 11 of the stack 17 moves to the inside of the central tube 16. The permeated fluid 80 passes through the central tube 16 and is discharged to the outside. The solution S (non-permeated fluid 81) treated in the membrane separation device 15 is discharged to the outside from the other end of the wound stack 17.

[0124] <Modification of membrane separation system>

[0125] The membrane separation system 100 may include a plurality of membrane separation devices 10, and the plurality of membrane separation devices 10 may be connected in series or in parallel. In the present specification, the term "a plurality of membrane separation devices 10 are connected in series" means a configuration in which the plurality of membrane separation devices 10 are connected in series in such a manner that the solution S (a non-permeable fluid during membrane separation operation) discharged from the supply space of the front-stage membrane separation device 10 is supplied to the supply space of the rear-stage membrane separation device 10. The term "a plurality of membrane separation devices 10 are connected in parallel" means a configuration in which the plurality of membrane separation devices 10 are connected in parallel in such a manner that the solution S sent from the tank 20 is supplied to the respective supply spaces of the plurality of membrane separation devices 10. The number of membrane separation devices 10 in the membrane separation system 100 is not particularly limited, and is, for example, 2 to 5.

[0126] When the membrane separation system 100 includes a plurality of membrane separation devices 10, the membrane separation system 100 may perform a cleaning operation by other membrane separation devices 10 that are not performing a membrane separation operation while performing a membrane separation operation by at least one of the plurality of membrane separation devices 10. For details of this operation, refer to Fig. 6A and 6B Described later.

[0127] Fig. 6A It is a schematic diagram of a membrane separation system 110 having two membrane separation devices 10A and 10B connected in series. The membrane separation system 110 has the same structure as the membrane separation system 100 except for the case where the membrane separation system 110 has two membrane separation devices 10A and 10B. Therefore, the same reference numerals are used for the common elements in the above-mentioned membrane separation system 100 and the membrane separation system 110 of the modified example, and their description is sometimes omitted. That is, the description of each embodiment can be applied to each other as long as it is not technically contradictory. Moreover, the various embodiments can also be combined with each other as long as it is not technically contradictory.

[0128] As described above, in the membrane separation system 110, the membrane separation devices 10A and 10B are connected in series. In detail, the membrane separation system 110 further includes a connection path 63 that connects the membrane separation devices 10A and 10B to each other. The connection path 63 is connected to the supply space outlet 13b of the membrane separation device 10A and the supply space inlet 13c of the membrane separation device 10B. It should be noted that the first path 60 is connected to the supply space inlet 13a of the membrane separation device 10A, and the second path 61 is connected to the supply space outlet 13d of the membrane separation device 10B.

[0129] The third path 62 includes a first portion 62a and a second portion 62b. The first portion 62a of the third path 62 is connected to the permeation space outlet 14a of the membrane separation device 10A, and the second portion 62b is connected to the permeation space outlet 14b of the membrane separation device 10B. The second portion 62b merges with the first portion 62a at a merging position 70.

[0130] For example, two pressure reducing devices 42A and 42B are arranged on the third path 62. The pressure reducing device 42A is located between the membrane separation device 10A and the confluence position 70, and can reduce pressure in the permeation space of the membrane separation device 10A. The pressure reducing device 42B is located between the membrane separation device 10B and the confluence position 70, and can reduce pressure in the permeation space of the membrane separation device 10B. However, one pressure reducing device may be arranged on the third path 62, and the pressure reducing device may be located between the confluence position 70 and the recovery unit 30. That is, one pressure reducing device may be shared by the membrane separation devices 10A and 10B.

[0131] It should be noted that in the membrane separation system 110, the pervaporation membrane 11A of the membrane separation device 10A may be the same as or different from the pervaporation membrane 11B of the membrane separation device 10B except for the membrane area. The membrane area (m 2 ) relative to the total value of the membrane area of ​​the pervaporation membrane 11A and the membrane area of ​​the pervaporation membrane 11B (m 2 ) is not particularly limited.

[0132] The membrane separation system 110 can perform membrane separation operation and cleaning operation independently of each other for the membrane separation devices 10A and 10B. As an example, the membrane separation system 110 can be operated by the following method. First, the pump 40 is operated to supply the solution S from the tank 20 to the membrane separation device 10A, and then the solution S is supplied from the membrane separation device 10A to the membrane separation device 10B. In this way, the solution S can be brought into contact with each of the pervaporation membrane 11A of the membrane separation device 10A and the pervaporation membrane 11B of the membrane separation device 10B.

[0133] Next, the permeation space of the membrane separation device 10A is depressurized through the permeation space outlet 14a, and the permeation space of the membrane separation device 10B is depressurized through the permeation space outlet 14b. Thus, the membrane separation operation can be performed in both the membrane separation devices 10A and 10B, and permeated fluids can be obtained from the membrane separation devices 10A and 10B, respectively. It should be noted that the solution S (non-permeated fluid) treated in the membrane separation device 10A is sent to the membrane separation device 10B through the connection path 63, and is further treated in the membrane separation device 10B.

[0134] Next, in the state where the pump 40 is operated, the pressure of the permeation space of either the membrane separation device 10A or 10B is increased, and the membrane separation operation is stopped. Thus, in the membrane separation device that has stopped the membrane separation operation, the solution S is supplied to the supply space to perform the cleaning operation. In the other membrane separation device of the membrane separation devices 10A and 10B, the membrane separation operation is continued. For the membrane separation device that is performing the cleaning operation, the cleaning operation can be easily switched to the membrane separation operation by depressurizing the permeation space.

[0135] According to the above method, while the membrane separation operation is being performed by one of the membrane separation devices 10A and 10B, the cleaning operation can be performed by the other membrane separation device that is not performing the membrane separation operation. As a result, a certain amount or more of permeated fluid can be obtained at all times in the membrane separation system 110. In the membrane separation system 110, it is not necessary to stop the membrane separation operation in all the membrane separation devices in order to perform the cleaning operation.

[0136] It should be noted that the operation method of the membrane separation system 110 is not limited to the above method. For example, the cleaning operation may be performed on both the membrane separation devices 10A and 10B at the same time. When performing the cleaning operation, the solution S may be moved in a direction opposite to the moving direction of the above solution S. In particular, when the membrane separation operation is performed in the membrane separation device 10A and the cleaning operation is performed in the membrane separation device 10B, the solution S is moved from the tank 20 to the membrane separation device 10B by operating the pump 41, thereby effectively suppressing the proliferation of unnecessary microorganisms in the membrane separation device 10B.

[0137] Figure 6B 1 is a schematic diagram of a membrane separation system 120 including two membrane separation apparatuses 10A and 10B connected in parallel to each other. The membrane separation system 120 has the same configuration as the membrane separation system 100 except that the membrane separation system 120 includes two membrane separation apparatuses 10A and 10B.

[0138] As described above, in the membrane separation system 120, the membrane separation devices 10A and 10B are connected in parallel with each other. Specifically, the first path 60 includes a first portion 60a and a second portion 60b. The first portion 60a of the first path 60 is connected to the supply space inlet 13a of the membrane separation device 10A, and the second portion 60b is connected to the supply space inlet 13c of the membrane separation device 10B. The second portion 60b branches from the first portion 60a at the branch position 71. The branch position 71 is located, for example, between the pump 40 and the membrane separation device 10A.

[0139] In addition, the second path 61 has a first portion 61a and a second portion 61b. The first portion 61a of the second path 61 is connected to the supply space outlet 13b of the membrane separation device 10A, and the second portion 61b is connected to the supply space outlet 13d of the membrane separation device 10B. The second portion 61b merges with the first portion 61a at a merging position 72. The merging position 72 is located, for example, between the pump 41 and the membrane separation device 10A.

[0140] Similar to the above-mentioned membrane separation system 110, the third path 62 has a first portion 62a and a second portion 62b. The first portion 62a of the third path 62 is connected to the permeation space outlet 14a of the membrane separation device 10A, and the second portion 62b is connected to the permeation space outlet 14b of the membrane separation device 10B. The second portion 62b merges with the first portion 62a at the merging position 70.

[0141] For example, two pressure reducing devices 42A and 42B are arranged on the third path 62. The pressure reducing device 42A is located between the membrane separation device 10A and the confluence position 70, and can reduce pressure in the permeation space of the membrane separation device 10A. The pressure reducing device 42B is located between the membrane separation device 10B and the confluence position 70, and can reduce pressure in the permeation space of the membrane separation device 10B. However, one pressure reducing device may be arranged on the third path 62, and the pressure reducing device may be located between the confluence position 70 and the recovery unit 30. That is, one pressure reducing device may be shared by the membrane separation devices 10A and 10B.

[0142] It should be noted that in the membrane separation system 120, the pervaporation membrane 11A of the membrane separation device 10A may be the same as or different from the pervaporation membrane 11B of the membrane separation device 10B. The membrane area (m 2 ) relative to the total value of the membrane area of ​​the pervaporation membrane 11A and the membrane area of ​​the pervaporation membrane 11B (m 2 ) is not particularly limited.

[0143] The membrane separation system 120 can perform membrane separation operation and cleaning operation independently of the membrane separation devices 10A and 10B, similarly to the membrane separation system 110. As an example, the membrane separation system 120 can be operated by the following method. First, the pump 40 is operated to supply the solution S from the tank 20 to the membrane separation devices 10A and 10B, respectively. Thus, the solution S can be brought into contact with the pervaporation membrane 11A of the membrane separation device 10A and the pervaporation membrane 11B of the membrane separation device 10B, respectively.

[0144] Next, the permeation space of the membrane separation device 10A is depressurized through the permeation space outlet 14a, and the permeation space of the membrane separation device 10B is depressurized through the permeation space outlet 14b. Thus, membrane separation operation can be performed in both the membrane separation devices 10A and 10B, and permeated fluids can be obtained from each of the membrane separation devices 10A and 10B.

[0145] Next, while the pump 40 is operated, the pressure of the permeation space of one of the membrane separation devices 10A and 10B is increased, and the membrane separation operation is stopped. Thus, in the membrane separation device in which the membrane separation operation is stopped, the solution S is supplied to the supply space, and the cleaning operation is performed. In the other membrane separation device of the membrane separation devices 10A and 10B, the membrane separation operation is continued. For the membrane separation device in which the cleaning operation is performed, by depressurizing the permeation space, the cleaning operation can be easily switched to the membrane separation operation.

[0146] According to the above method, while the membrane separation operation is being performed by one of the membrane separation devices 10A and 10B, the cleaning operation can be performed by the other membrane separation device that is not performing the membrane separation operation. As a result, a certain amount or more of permeated fluid can be obtained at all times in the membrane separation system 120. In the membrane separation system 120, it is not necessary to stop the membrane separation operation in all the membrane separation devices in order to perform the cleaning operation.

[0147] It should be noted that the operation method of the membrane separation system 120 is not limited to the above method. For example, the membrane separation device 10A and the membrane separation device 10B may be cleaned at the same time. When the cleaning operation is performed, the solution S may be moved in the direction opposite to the moving direction of the solution S.

[0148] In the above Fig. 6A and 6B , the membrane separation system 110 and 120 having two membrane separation devices 10A and 10B are described. However, the number of membrane separation devices 10 provided in the membrane separation system may be 3 or more. As an example, in a membrane separation system having N1 (N1 is an odd number greater than 3) membrane separation devices 10, the system can be divided into a group of (N1-1) / 2 membrane separation devices 10 and a group of the remaining (N1-1) / 2+1 membrane separation devices 10, and a cleaning operation is alternately performed. Furthermore, in a membrane separation system having N2 (N2 is an even number greater than 4) membrane separation devices 10, the system can be divided into a group of N2 / 2 membrane separation devices 10 and a group of the remaining N2 / 2 membrane separation devices 10, and a cleaning operation is alternately performed.

[0149] Industrial Applicability

[0150] The membrane separation system of the present embodiment is suitable for suppressing the proliferation of unnecessary microorganisms inside the membrane separation device.

Claims

1. A membrane separation system, comprising a membrane separation device, The membrane separation device comprises a pervaporation membrane, and a supply space and a permeation space separated by the pervaporation membrane. The membrane separation system performs: membrane separation operation, in which a solution containing a volatile organic compound is supplied to the supply space, and the permeation space is depressurized to thereby separate the solution into a permeated fluid and a non-permeated fluid; and In the cleaning operation, the solution is supplied to the supply space while the membrane separation operation is stopped, thereby cleaning the pervaporation membrane with the solution.

2. The membrane separation system according to claim 1, wherein: In the cleaning operation, the pressure of the permeation space is adjusted to a value higher than the pressure of the permeation space in the membrane separation operation.

3. The membrane separation system according to claim 1, wherein: The membrane separation operation and the cleaning operation are performed alternately and repeatedly.

4. The membrane separation system according to claim 1, wherein: The membrane separation device further comprises a supply space inlet for supplying the solution to the supply space during the membrane separation operation. During the cleaning operation, the solution is supplied from the supply space inlet.

5. The membrane separation system according to claim 1, wherein: The membrane separation device further comprises a supply space outlet for discharging the non-permeated fluid from the supply space during the membrane separation operation. During the cleaning operation, the solution is supplied from the supply space outlet.

6. The membrane separation system according to claim 1, wherein: The content rate of the organic compound in the permeated fluid is higher than the content rate of the organic compound in the solution.

7. The membrane separation system according to claim 1, wherein: The organic compound is a fermentation product produced by microorganisms, The solution is a fermentation broth.

8. The membrane separation system according to claim 1, wherein: The organic compound is an alcohol.

9. The membrane separation system according to claim 1, wherein: The content of the organic compound in the solution is 1 wt % or more. 10 . The membrane separation system according to claim 1 , further comprising a tank for storing the solution supplied to the membrane separation device.

11. The membrane separation system according to claim 1, comprising a plurality of the membrane separation devices, A plurality of the membrane separation devices are connected in series or in parallel.

12. The membrane separation system according to claim 11, wherein: The membrane separation system performs the cleaning operation using at least one of the plurality of membrane separation devices while performing the membrane separation operation using the other membrane separation devices that are not performing the membrane separation operation.

13. A method for cleaning a membrane separation device, comprising: a membrane separation device having a pervaporation membrane, and a supply space and a permeation space separated by the pervaporation membrane; The membrane separation device is capable of performing a membrane separation operation in which the solution containing a volatile organic compound is supplied to the supply space, and the pressure in the permeation space is reduced, thereby separating the solution into a permeated fluid and a non-permeated fluid. The cleaning method includes supplying the solution to the supply space in a state where the membrane separation operation is stopped, thereby cleaning the pervaporation membrane with the solution.

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