Membrane separation system and method for operating membrane separation system

Abstract

A membrane separation system according to the present invention comprises: a plurality of membrane separation units each having a membrane separation part and a condensation part; a pressure reduction part; and a recovery part. In each of the plurality of membrane separation units, the membrane separation part has: a pervaporation membrane that separates a supply fluid containing a volatile organic compound into a permeate fluid and a retentate fluid; and a supply space and a permeation space that are separated by the pervaporation membrane. The condensation part condenses the permeate fluid discharged from the membrane separation part to generate a condensed fluid. The plurality of membrane separation parts are connected in series such that the retentate fluid discharged from a membrane separation part positioned at the upstream side is supplied as the supply fluid to a membrane separation part positioned at the downstream side. The pressure reduction part reduces the pressure of the permeation space in each of the plurality of membrane separation parts. The recovery part recovers a mixed fluid obtained by mixing the condensed fluids respectively discharged from the plurality of condensation parts.

Description

Membrane Separation System and Method of Operating Membrane Separation System

[0001] The present invention relates to a membrane separation system and a method of operating a membrane separation system.

[0002] As an example of a method for separating a volatile organic compound from an aqueous solution containing the volatile organic compound, a pervaporation method using a pervaporation membrane is known. The pervaporation method is suitable for separating volatile organic compounds from an aqueous solution containing various substances. For example, Patent Document 1 discloses a membrane separation system including a plurality of membrane modules connected in series. The membrane module has a raw fluid chamber and a permeate fluid chamber separated by a zeolite separation membrane. Patent Document 2 discloses a system for separating liquid organic matter and water including a plurality of pervaporation membrane modules connected in series, the plurality of pervaporation membrane modules including a first pervaporation membrane module located at the most upstream side and a second pervaporation membrane module located at the most downstream side.

[0003] Japanese Unexamined Patent Application Publication No. 2020-175333 Japanese Patent No. 6289852

[0004] The pervaporation method can be performed using a membrane separation section that has a pervaporation membrane, and a supply space and a permeation space separated by the pervaporation membrane. By depressurizing the permeation space while a supply fluid containing a volatile organic compound is in contact with the pervaporation membrane, the supply fluid that permeates through the pervaporation membrane vaporizes. Thus, a gaseous permeate fluid in which the volatile organic compound is concentrated can be obtained. The gaseous permeate fluid is liquefied in a condensation section, whereby a liquid permeate fluid is obtained. In a membrane separation system using the pervaporation method, depressurization of the permeation space of the membrane separation section is performed by a depressurization section provided downstream of the membrane separation section.

[0005] It is known that the concentration of a permeate fluid obtained by a membrane separation system using the pervaporation method, that is, the content of a volatile organic compound in the permeate fluid, depends on membrane performance such as the separation coefficient and permeation flux of the pervaporation membrane. Therefore, when the concentration of the supply fluid introduced into the membrane separation section fluctuates, the content of the volatile organic compound in the obtained permeate fluid becomes non-uniform.

[0006] Therefore, the present invention aims to provide a membrane separation system that can control the concentration of the permeate fluid with a simple configuration.

[0007] The present invention provides a membrane separation system comprising: a plurality of membrane separation units having a membrane separation unit and a condensation unit; a depressurization unit; and a recovery unit, wherein each of the plurality of membrane separation units has: a membrane separation unit having a permeation vaporization membrane that separates a supply fluid containing volatile organic compounds into a permeable fluid and an impermeable fluid, and a supply space and a permeable space separated by the permeation vaporization membrane; a condensation unit that condenses the permeable fluid discharged from the membrane separation unit to produce a condensed fluid; the plurality of membrane separation units are connected in series such that the impermeable fluid discharged from the membrane separation unit located on the upstream side is supplied as the supply fluid to the membrane separation unit located on the downstream side; a depressurization unit depressurizes the permeable space of each of the plurality of membrane separation units; and a recovery unit that recovers a mixed fluid obtained by mixing the condensed fluids discharged from each of the plurality of condensation units.

[0008] In another aspect, the present invention relates to a method for operating a membrane separation system comprising a plurality of membrane separation units having a membrane separation unit and a condensation unit, a depressurization unit, and a recovery unit, wherein each of the plurality of membrane separation units has a permeable vaporization membrane that separates a supply fluid containing a volatile organic compound into a permeable fluid and an impermeable fluid, and a supply space and a permeable space separated by the permeable vaporization membrane, the plurality of membrane separation units are connected in series such that the impermeable fluid discharged from the membrane separation unit located on the upstream side is supplied as the supply fluid to the membrane separation unit located on the downstream side, the operating method comprising: depressurizing the permeable space of each of the plurality of membrane separation units by the depressurization unit; separating the supply fluid into a permeable fluid and an impermeable fluid by the permeable vaporization membrane of each of the plurality of membrane separation units; condensing the permeable fluid discharged from the membrane separation unit by the condensation unit in each of the plurality of membrane separation units to produce a condensed fluid; and recovering a mixed fluid obtained by mixing the condensed fluids discharged from each of the plurality of condensation units by the recovery unit. The present invention provides a method for operating a membrane separation system, including the operation of the membrane separation system.

[0009] According to the present invention, a membrane separation system capable of controlling the concentration of the permeate fluid can be provided with a simple configuration.

[0010] This is a schematic diagram showing an example of the membrane separation system of this embodiment. This is a schematic cross-sectional view showing an example of the membrane separation section of the membrane separation system. This is a schematic cross-sectional view showing an example of the permeation vaporization membrane of the membrane separation section. This is a schematic unfolded perspective view showing a spiral-shaped membrane element. This is a schematic diagram showing a modified example 1 of the membrane separation system. This is a schematic diagram showing a modified example 2 of the membrane separation system. This is a schematic diagram showing a modified example 3 of the membrane separation system. This is a schematic diagram showing a modified example 4 of the membrane separation system. This is a schematic diagram showing a modified example 5 of the membrane separation system. This is a schematic diagram showing a modified example 6 of the membrane separation system. This is a schematic diagram showing a modified example 7 of the membrane separation system.

[0011] A membrane separation system according to a first aspect of the present invention comprises a plurality of membrane separation units having a membrane separation section and a condensation section, a depressurization section, and a recovery section, wherein each of the plurality of membrane separation units has a permeation vaporization membrane that separates a supply fluid containing volatile organic compounds into a permeable fluid and an impermeable fluid, and a supply space and a permeable space separated by the permeation vaporization membrane, the condensation section condenses the permeable fluid discharged from the membrane separation section to produce a condensed fluid, the plurality of membrane separation units are connected in series such that the impermeable fluid discharged from the membrane separation unit located on the upstream side is supplied as the supply fluid to the membrane separation unit located on the downstream side, the depressurization section depressurizes the permeable space of each of the plurality of membrane separation units, and the recovery section recovers a mixed fluid obtained by mixing the condensed fluids discharged from each of the plurality of condensation sections.

[0012] In a second embodiment of the present invention, for example, in the membrane separation system according to the first embodiment, each of the plurality of membrane separation units further has a discharge path that guides the condensed fluid discharged from the condensation section to the recovery section.

[0013] In a third embodiment of the present invention, for example, in the membrane separation system according to the second embodiment, each of the plurality of membrane separation units further comprises a concentration sensor and a flow rate control valve provided in the discharge path.

[0014] In a fourth aspect of the present invention, for example, in the membrane separation system according to the third aspect, the content of the organic compound in the mixed fluid obtained in the recovery unit is controlled by adjusting the opening degree of the flow control valve of each of the plurality of membrane separation units while monitoring the measured values ​​of the concentration sensors of each of the plurality of membrane separation units during operation.

[0015] In a fifth embodiment of the present invention, for example, a membrane separation system according to any one of the first to fourth embodiments further comprises a supply unit for storing a raw fluid, wherein the raw fluid is the supply fluid to be supplied to the membrane separation unit located furthest upstream among a plurality of membrane separation units.

[0016] In a sixth aspect of the present invention, for example, in a membrane separation system according to the fifth aspect, each of the plurality of membrane separation units further has a return path that returns the condensed fluid to at least one selected from the group consisting of a supply unit and a raw fluid path, and the raw fluid path guides the raw fluid from the supply unit to the supply space of the membrane separation unit located furthest upstream of the plurality of membrane separation units.

[0017] In a seventh embodiment of the present invention, for example, in the membrane separation system according to the sixth embodiment, the membrane separation unit located furthest upstream among the plurality of membrane separation units further has a circulation path that leads the impermeable fluid to at least one selected from the group consisting of the supply unit and the raw fluid path.

[0018] An operating method for a membrane separation system according to an eighth aspect of the present invention is an operating method for a membrane separation system comprising a plurality of membrane separation units having a membrane separation section and a condensation section, a depressurization section, and a recovery section, wherein each of the plurality of membrane separation sections has a permeation vaporization membrane that separates a supply fluid containing a volatile organic compound into a permeable fluid and an impermeable fluid, and a supply space and a permeable space separated by the permeation vaporization membrane, the plurality of membrane separation sections are connected in series such that the impermeable fluid discharged from the membrane separation section located upstream is supplied as the supply fluid to the membrane separation section located downstream, the operating method is to depressurize the permeable space of each of the plurality of membrane separation sections by the depressurization section, separate the supply fluid into a permeable fluid and an impermeable fluid by the permeation vaporization membrane of each of the plurality of membrane separation units, and condense the permeable fluid discharged from the membrane separation section by the condensation section in each of the plurality of membrane separation units to produce a condensed fluid. The recovery unit includes recovering a mixed fluid obtained by mixing the condensed fluids discharged from each of the plurality of condensing units.

[0019] The details of the present invention will be described below, but the following description is not intended to limit the present invention to any particular embodiment.

[0020] <Embodiment of Membrane Separation System> The membrane separation system of this embodiment comprises a plurality of membrane separation units, including a membrane separation unit and a condensation unit, and a recovery unit. In each of the plurality of membrane separation units, the membrane separation unit has a permeation vaporization membrane that separates a supply fluid containing volatile organic compounds into a permeable fluid and an impermeable fluid, and a supply space and a permeable space separated by the permeation vaporization membrane. The condensation unit condenses the permeable fluid discharged from the membrane separation unit to produce a condensed fluid. The plurality of membrane separation units are connected in series such that the impermeable fluid discharged from the membrane separation unit located upstream is supplied as a supply fluid to the membrane separation unit located downstream. The depressurization unit depressurizes the permeable space of each of the plurality of membrane separation units. The recovery unit recovers a mixed fluid obtained by mixing the condensed fluids discharged from each of the plurality of condensation units.

[0021] According to the membrane separation system of this embodiment, the concentration of the permeate fluid, that is, the content of volatile organic compounds in the permeate fluid, can be controlled with a simple configuration.

[0022] The following describes a specific example of the membrane separation system of this embodiment with reference to the drawings.

[0023] Figure 1 is a schematic diagram showing an example of a membrane separation system according to this embodiment. The membrane separation system 100A in Figure 1 comprises a first membrane separation unit 201, a second membrane separation unit 202, a first depressurization section 31, a second depressurization section 32, and a recovery section 75. That is, the membrane separation system 100A in Figure 1 comprises two membrane separation units as a plurality of membrane separation units: the first membrane separation unit 201 and the second membrane separation unit 202. The first membrane separation unit 201 includes a first membrane separation section 10 and a first condensation section 41 having a permeation vaporization membrane 11. The second membrane separation unit 202 includes a second membrane separation section 20 and a second condensation section 42 having a permeation vaporization membrane 21. The first membrane separation section 10 and the second membrane separation section 20 are connected in series so that a first impermeable fluid N1 discharged from the first membrane separation section 10 located upstream is supplied as a supply fluid to the second membrane separation section 20 located downstream.

[0024] The first membrane separation unit 10 has a supply space 13 and a permeable space 14 separated by a permeation vaporization membrane 11. The second membrane separation unit 20 has a supply space 23 and a permeable space 24 separated by a permeation vaporization membrane 21. The permeation vaporization membrane 11 separates the raw fluid F0 containing a volatile organic compound C as the supply fluid into a first permeable fluid T1 and a first impermeable fluid N1. The permeation vaporization membrane 21 separates the first impermeable fluid N1 as the supply fluid into a second permeable fluid T2 and a second impermeable fluid N2.

[0025] The membrane separation system 100A in Figure 1 includes a first depressurization section 31 and a second depressurization section 32 as depressurization sections. The first depressurization section 31 reduces the pressure of the permeate space 14 of the first membrane separation section 10. The second depressurization section 32 reduces the pressure of the permeate space 24 of the second membrane separation section 20. Although not shown in the figure, the membrane separation system 100A may also include a single depressurization section instead of the first depressurization section 31 and the second depressurization section 32. The permeate space 14 of the first membrane separation section 10 and the permeate space 24 of the second membrane separation section 20 may be reduced by a single common depressurization section.

[0026] The first condensation unit 41 condenses the volatile organic compound C contained in the first permeate fluid T1 discharged from the first membrane separation unit 10 to produce a first condensed fluid C1. According to the first condensation unit 41, the gaseous first permeate fluid T1 is liquefied, and a liquid first condensed fluid C1 is obtained. The second condensation unit 42 condenses the volatile organic compound C contained in the second permeate fluid T2 discharged from the second membrane separation unit 20 to produce a second condensed fluid C2. According to the second condensation unit 42, the gaseous second permeate fluid T2 is liquefied, and a liquid second condensed fluid C2 is obtained. Since the second membrane separation unit 20 uses the first non-permeate fluid N1 discharged from the first membrane separation unit 10 as its supply fluid, the content of organic compound C in the second condensed fluid C2 is lower than the content of organic compound C in the first condensed fluid C1.

[0027] In this embodiment, the recovery unit 75 recovers a mixed fluid C3 obtained by mixing the first condensed fluid C1 discharged from the first condensing unit 41 and the second condensed fluid C2 discharged from the second condensing unit 42. According to the membrane separation system 100A, the content of organic compound C in the resulting mixed fluid C3 can be controlled by adjusting the ratio of the first condensed fluid C1 and the second condensed fluid C2 to be mixed.

[0028] The content of organic compound C in the first condensed fluid C1 is, for example, 10 wt% or more. The content of organic compound C in the first condensed fluid C1 may be 20 wt% or more, and even 35 wt% or more. The upper limit of the content of organic compound C in the first condensed fluid C1 is not particularly limited, but is, for example, 50 wt%.

[0029] The content of organic compound C in the second condensed fluid C2 is, for example, less than 45 wt%. The content of organic compound C in the second condensed fluid C2 may be 30 wt% or less, and even 20 wt% or less. The lower limit of the content of organic compound C in the second condensed fluid C2 is not particularly limited, but is, for example, 8 wt%.

[0030] In the membrane separation system 100A, the pressure p1 in the first condensation section 41 may be controlled during operation to be approximately the same as the pressure p2 in the second condensation section 42.

[0031] During operation, the pressure p1 in the first condenser 41 and the pressure p2 in the second condenser 42 may be controlled to a range of 0.1 kPa or more and 20.0 kPa or less. Pressures p1 and p2 may be controlled to a range of 0.1 kPa or more and 10.0 kPa or less, or to a range of 0.1 kPa or more and 5.0 kPa or less. In this specification, unless otherwise specified, "pressure" means absolute pressure.

[0032] The pressure p1 in the first condensation section 41 can be controlled by controlling the operation of the first pressure reduction section 31. The pressure p2 in the second condensation section 42 can be controlled by controlling the operation of the second pressure reduction section 32.

[0033] The first pressure reducing section 31 and the second pressure reducing section 32 may be vacuum devices such as vacuum pumps. Vacuum pumps are typically gas transport type vacuum pumps, and examples include reciprocating vacuum pumps and rotary vacuum pumps. Examples of reciprocating vacuum pumps include diaphragm type and oscillating piston type vacuum pumps. Examples of rotary vacuum pumps include liquid-sealed pumps, oil rotary pumps (rotary pumps), mechanical booster pumps, and various dry pumps such as Roots type, claw type, screw type, turbo type, and scroll type. The pumps as the first pressure reducing section 31 and the second pressure reducing section 32 may be equipped with a variable speed mechanism for changing the rotational speed, etc. An example of a variable speed mechanism is an inverter that drives the motor of the pump. By controlling the rotational speed of the pump with the variable speed mechanism, the pressure p1 in the first condensing section 41 and the pressure p2 in the second condensing section 42 can be appropriately adjusted.

[0034] For the first condensing section 41 and the second condensing section 42, for example, a water-cooled heat exchanger can be used. A water-cooled heat exchanger generates heat exchange between a cooling medium (refrigerant) such as antifreeze and a permeate fluid. For example, ethylene glycol, propylene glycol, ethanol, and water can be used as the refrigerant. A refrigerant common to both the first condensing section 41 and the second condensing section 42 may be used.

[0035] The membrane separation system 100A may further include a refrigerant path (not shown) for circulating refrigerant to the first condensation section 41 and the second condensation section 42. The refrigerant path is configured, for example, so that the refrigerant passed through the first condensation section 41 is passed through the second condensation section 42.

[0036] The membrane separation system 100A may further include a cooling unit (not shown) for cooling the refrigerant. The cooling unit is typically a chiller. The cooling unit may be located in the refrigerant path. The cooling unit can cool the refrigerant as it passes through the first condenser 41 and the second condenser 42.

[0037] In the membrane separation system 100A, the cooling temperature t1 of the first condensation unit 41 may be controlled during operation to be approximately the same as the cooling temperature t2 of the second condensation unit 42.

[0038] During operation, the cooling temperature t1 of the first condensing section 41 and the cooling temperature t2 of the second condensing section 42 may be controlled to a range of -80°C or higher and 20°C or lower. The cooling temperatures t1 and t2 may be controlled to a range of -50°C or higher and 5°C or lower, or to a range of -20°C or higher and 0°C or lower.

[0039] The membrane separation system 100A may further include a supply unit 71 for storing the raw fluid F0, which is to be supplied to the first membrane separation unit 10. The supply unit 71 is, for example, a tank for storing the raw fluid F0. The supply unit 71 may also be a culture tank for producing organic compounds C by fermentation of a carbon source by microorganisms.

[0040] The first membrane separation unit 201 may further have a first discharge path 91 that guides the first condensed fluid C1 discharged from the first condensation section 41 to the recovery section 75. The second membrane separation unit 202 may further have a second discharge path 92 that guides the second condensed fluid C2 discharged from the second condensation section 42 to the recovery section 75. With such a configuration, for example, during operation, the content of organic compound C in the mixed fluid C3 obtained in the recovery section 75 can be easily controlled by adjusting the flow rate of the first condensed fluid C1 flowing through the first discharge path 91 and the flow rate of the second condensed fluid C2 flowing through the second discharge path 92.

[0041] As shown in Figure 1, the second discharge path 92 may merge with the first discharge path 91 at the merging position 91p. However, the first discharge path 91 and the second discharge path 92 may each be connected to the recovery unit 75.

[0042] In the example shown in Figure 1, the first discharge path 91 has a first section 91a, a second section 91b, and a third section 91c. The first section 91a and the second section 91b are sections that connect the first condensation section 41 to the confluence point 91p. The third section 91c is a section that connects the confluence point 91p to the recovery section 75.

[0043] The first membrane separation unit 201 may further include a concentration sensor 51 and a flow rate adjustment valve 55 provided in the first discharge path 91. The concentration sensor 51 is a concentration sensor for measuring the content rate of the organic compound C in the first condensed fluid C1 flowing through the first discharge path 91. The flow rate adjustment valve 55 is a flow rate adjustment valve for adjusting the flow rate of the first condensed fluid C1 flowing through the first discharge path 91. The second membrane separation unit 202 may further include a concentration sensor 52 and a flow rate adjustment valve 56 provided in the second discharge path 92. The concentration sensor 52 is a concentration sensor for measuring the content rate of the organic compound C in the second condensed fluid C2 flowing through the second discharge path 92. The flow rate adjustment valve 56 is a flow rate adjustment valve for adjusting the flow rate of the second condensed fluid C2 flowing through the second discharge path 92. According to this configuration, for example, by adjusting the opening degree of the flow rate adjustment valve 55 and the opening degree of the flow rate adjustment valve 56 while monitoring the content rate of the organic compound C in each of the first condensed fluid C1 and the second condensed fluid C2 by means of the concentration sensor 51 and the concentration sensor 52, the content rate of the organic compound C in the mixed fluid C3 obtained in the recovery unit 75 can be controlled within a desired range.

[0044] As shown in Figure 1, in the first discharge path 91, the flow rate adjustment valve 55 may be arranged downstream of the concentration sensor 51. In the second discharge path 92, the flow rate adjustment valve 56 may be arranged downstream of the concentration sensor 52.

[0045] In the example of Figure 1, the concentration sensor 51 is provided in the first portion 91a of the first discharge path 91. The flow rate adjustment valve 55 is provided in the second portion 91b of the first discharge path 91. The concentration sensor 52 is provided in the first portion 92a of the second discharge path 92. The flow rate adjustment valve 56 is provided in the second portion 92b of the second discharge path 92.

[0046] As shown in FIG. 1, the membrane separation system 100A may further include a concentration sensor 53 provided in the third portion 91c of the first discharge path 91. The concentration sensor 53 is a sensor for measuring the content of the organic compound C in the mixed fluid C3 recovered in the recovery unit 75. According to this configuration, for example, by adjusting the opening degree of the flow rate adjustment valve 55 and the opening degree of the flow rate adjustment valve 56 while monitoring the content of the organic compound C in the mixed fluid C3 with the concentration sensor 53, the content of the organic compound C in the mixed fluid C3 obtained by the recovery unit 75 can be controlled within a desired range.

[0047] The membrane separation system 100A further includes, as fluid paths, a raw fluid path 81, a first permeated fluid path 82, a first non-permeated fluid path 83, a second permeated fluid path 84, and a second non-permeated fluid path 85.

[0048] The raw fluid path 81 connects a raw fluid outlet 71b of a supply unit 71 and a supply fluid inlet 10a of a first membrane separation unit 10, and is a path for guiding a raw fluid F0 from the supply unit 71 to a supply space 13 of the first membrane separation unit 10. That is, the raw fluid path 81 corresponds to a supply fluid path in the first membrane separation unit 201. A pump (not shown) that controls the flow rate of the raw fluid F0 may be disposed in the raw fluid path 81. A concentration sensor (not shown) for measuring the content of the organic compound C in the raw fluid F0 may be disposed in the raw fluid path 81.

[0049] The first permeated fluid path 82 connects a permeated fluid outlet 10b of the first membrane separation unit 10 and a permeated fluid inlet of the first condensing unit 41, and is a path for guiding a first permeated fluid T1 from a permeation space 14 of the first membrane separation unit 10 to the first condensing unit 41. A concentration sensor (not shown) for measuring the content of the organic compound C in the first permeated fluid T1 may be disposed in the first permeated fluid path 82.

[0050] The first impermeable fluid path 83 connects the impermeable fluid outlet 10c of the first membrane separation unit 10 to the supply fluid inlet 20a of the second membrane separation unit 20, and is a path that guides the first impermeable fluid N1 from the supply space 13 of the first membrane separation unit 10 to the supply space 23 of the second membrane separation unit 20. In other words, the first impermeable fluid path 83 corresponds to the supply fluid path in the second membrane separation unit 202. A concentration sensor for measuring the content of organic compound C in the first impermeable fluid N1 may be placed in the first impermeable fluid path 83.

[0051] The second permeable fluid path 84 connects the permeable fluid outlet 20b of the second membrane separation unit 20 to the permeable fluid inlet of the second condensation unit 42, and is a path that guides the second permeable fluid T2 from the permeable space 24 of the second membrane separation unit 20 to the second condensation unit 42. A concentration sensor for measuring the content of organic compound C in the second permeable fluid T2 may be placed in the second permeable fluid path 84.

[0052] The second impermeable fluid path 85 is connected to the impermeable fluid outlet 20c of the second membrane separation unit 20 and is a path for discharging the second impermeable fluid N2 from the supply space 23 of the second membrane separation unit 20. A concentration sensor for measuring the content of organic compound C in the second impermeable fluid N2 may be placed in the second impermeable fluid path 85.

[0053] The first membrane separation unit 201 may further have a first return path 93 for returning the first condensed fluid C1 to at least one selected from the group consisting of a supply unit 71 and a raw fluid path 81. The second membrane separation unit 202 may further have a second return path 94 for returning the second condensed fluid C2 to at least one selected from the group consisting of a supply unit 71 and a raw fluid path 81. With such a configuration, for example, during operation, the flow rate of the first condensed fluid C1 and the flow rate of the second condensed fluid C2 to the recovery unit 75 can be adjusted by controlling the flow of a portion of the first condensed fluid C1 to the first return path 93 or a portion of the second condensed fluid C2 to the second return path 94. Therefore, it is easy to control the content of organic compound C in the mixed fluid C3 obtained in the recovery unit 75 to a desired range.

[0054] As shown in Figure 1, the first return path 93 and the second return path 94 may merge with the original fluid path 81 at the merging position 81p. In the example of Figure 1, the merging position 81p is located in the original fluid path 81. That is, the first condensed fluid C1 and the second condensed fluid C2 returned to the original fluid path 81 may be supplied directly to the first membrane separation unit 10.

[0055] In the example shown in Figure 1, the first return path 93 is configured to return the first condensed fluid C1 to the source fluid path 81. Although not shown, the first return path 93 may also be configured to return the first condensed fluid C1 to the supply unit 71. That is, the returned first condensed fluid C1 and second condensed fluid C2 may be supplied to the supply unit 71. In the example shown in Figure 1, the second return path 94 returns the second condensed fluid C2 to the source fluid path 81. Although not shown, the second return path 94 may also be configured to return the second condensed fluid C2 to the supply unit 71.

[0056] As shown in Figure 1, the first return route 93 may be a route that branches off from the first discharge route 91 at branching position 91q. The second return route 94 may be a route that branches off from the second discharge route 92 at branching position 92q.

[0057] As described above, in the example of Figure 1, the first discharge path 91 has a first portion 91a, a second portion 91b, and a third portion 91c. The first portion 91a is the portion connecting the first condensation section 41 and the branching position 91q. The second portion 91b is the portion connecting the branching position 91q and the merging position 91p.

[0058] In the example shown in Figure 1, the second discharge path 92 has a first portion 92a and a second portion 92b. The first portion 92a is the portion connecting the second condensation section 42 and the branching position 92q. The second portion 92b is the portion connecting the branching position 92q and the merging position 91p of the first discharge path 91.

[0059] The first membrane separation unit 201 may further include a flow control valve 57 provided in the first return path 93. The flow control valve 57 is a flow control valve for adjusting the flow rate of the first condensed fluid C1 flowing through the first return path 93. The second membrane separation unit 202 may further include a flow control valve 58 provided in the second return path 94. The flow control valve 58 is a flow control valve for adjusting the flow rate of the second condensed fluid C2 flowing through the second return path 94. With this configuration, the flow rate of the first condensed fluid C1 flowing through the first return path 93 can be adjusted by adjusting the opening degree of the flow control valve 57. The flow rate of the second condensed fluid C2 flowing through the second return path 94 can be controlled by adjusting the opening degree of the flow control valve 58.

[0060] The first membrane separation unit 201 may further include a heating device 45 for heating the raw fluid F0, which is to be supplied to the first membrane separation unit 10. With this configuration, for example, if the temperature of the raw fluid F0 is low, the temperature of the raw fluid F0 to be supplied to the first membrane separation unit 10 can be increased by using the heating device 45. The second membrane separation unit 202 may further include a heating device 46 for heating the first impermeable fluid N1, which is to be supplied to the second membrane separation unit 20. With this configuration, for example, if the temperature of the first impermeable fluid N1 is low, the temperature of the first impermeable fluid N1 to be supplied to the second membrane separation unit 20 can be increased by using the heating device 46.

[0061] In the example shown in Figure 1, the heating device 45 is located downstream of the confluence point 81p in the original fluid path 81. However, the heating device 45 may also be located upstream of the confluence point 81p in the original fluid path 81. In the example shown in Figure 1, the heating device 46 is located in the first impermeable fluid path 83.

[0062] The membrane separation system 100A may further include a control unit 70 that controls each component of the membrane separation system 100A. The control unit 70 may implement PID control such as feedback control, feedforward control, or a combination of these. The control unit 70 may be a DSP (Digital Signal Processor) including an A / D conversion circuit, input / output circuits, arithmetic circuits, and a memory device. The control unit 70 may store a program for properly operating the membrane separation system 100A. For example, the control unit 70 controls the operation of flow control valves 55, 57, 56, and 58.

[0063] The control unit 70 may control the content of organic compounds in the mixed fluid C3 obtained in the recovery unit 75 by controlling the operation of the flow control valves 55, 57, 56, and 58 based on the content of organic compounds in the first condensed fluid C1 measured by the concentration sensor 51 and the content of organic compounds in the second condensed fluid C2 discharged from the second condensation unit 42 measured by the concentration sensor 52.

[0064] Each of the pathways in the membrane separation system of this embodiment consists of, for example, metal or resin piping, unless otherwise specified.

[0065] [Raw Fluid] The raw fluid F0 contains a volatile organic compound C, such as an alcohol. The raw fluid F0 is typically a fermentation liquid. Fermentation liquids are obtained by fermenting a carbon source such as glucose or synthesis gas in an aqueous solution using microorganisms. Therefore, when the raw fluid F0 is a fermentation liquid, it contains the volatile organic compound C along with microorganisms that produce the organic compound C. The microorganisms that produce the organic compound C are typically fungi. The raw fluid F0 includes, for example, the organic compound C, water, and microorganisms. The raw fluid F0 is typically an aqueous solution containing the organic compound C, water, and microorganisms.

[0066] Organic compound C is not particularly limited as long as it is volatile. In this specification, "volatile organic compound" means, for example, an organic compound whose boiling point at atmospheric pressure (101.325 kPa) is between 20°C and 260°C.

[0067] The number of carbon atoms in organic compound C is not particularly limited and may be, for example, 10 or less, 8 or less, 6 or less, or even 4 or less. The lower limit of the number of carbon atoms in organic compound C may be 1 or 2. Organic compound C has functional groups containing oxygen atoms, such as hydroxyl groups, carbonyl groups, ether groups, and ester groups. In organic compound C, the number of functional groups containing oxygen atoms is typically one.

[0068] Examples of organic compound C include alcohols, ketones, and esters, and are typically alcohols. The alcohol may be an alkyl alcohol composed only of an alkyl group and a hydroxyl group, or an aryl alcohol containing an aryl group and a hydroxyl group. The alkyl alcohol may be linear, branched, or cyclic. Examples of alkyl alcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, 2-butanol, isobutanol, t-butanol, and n-pentanol. Examples of aryl alcohols include phenol.

[0069] The ketone may be a dialkylketone composed only of an alkyl group and a carbonyl group. Examples of dialkylketones include methyl ethyl ketone (MEK) and acetone.

[0070] The ester may be a fatty acid alkyl ester composed solely of an alkyl group and an ester group. Examples of fatty acid alkyl esters include ethyl acetate.

[0071] Note that organic compound C is not limited to those described above. Organic compound C may also be an aromatic hydrocarbon such as benzene, toluene, or xylene.

[0072] The raw fluid F0 may contain one type of organic compound C, or it may contain two or more types of organic compound C. The content of organic compound C in the raw fluid F0 is, for example, 0.5 wt% or more, and may be 1 wt% or more, 2 wt% or more, or even 5 wt% or more. The upper limit of the content of organic compound C is not particularly limited, but is, for example, 50 wt%.

[0073] Organic compound C may be a fermented product produced by microorganisms fermenting a carbon source, or it may be alcohol produced by microorganisms (bio-alcohol). In other words, the raw fluid F0 may be a fermentation liquid containing organic compound C as a fermentation product. However, the raw fluid F0 is not limited to a fermentation liquid, but may also be waste liquid or wastewater discharged from a chemical plant or the like.

[0074] The raw fluid F0 may further contain other components besides water and organic compound C, such as microorganisms that produce fermentation products, a carbon source, a nitrogen source, and inorganic ions. The microorganisms that produce fermentation products are typically bacteria. Examples of carbon sources include polysaccharides such as starch and monosaccharides such as glucose.

[0075] [Membrane Separation Section] Figure 2 is a schematic cross-sectional view showing an example of the first membrane separation section 10. The first membrane separation section 10 comprises a permeation vaporization membrane 11 and a container 12. The container 12 has a first chamber 13 and a second chamber 14. The first chamber 13 functions as a supply space to which the raw fluid F0 is supplied. The second chamber 14 functions as a permeation space to which the first permeation fluid T1 is supplied. The first permeation fluid T1 is obtained by the raw fluid F0 permeating through the permeation vaporization membrane 11. The configuration of the second membrane separation section 20 is basically the same as that of the first membrane separation section 10, so its description is omitted.

[0076] The permeable vaporization membrane 11 is located inside the container 12. Inside the container 12, the permeable vaporization membrane 11 separates the first chamber 13 and the second chamber 14. The permeable vaporization membrane 11 extends from one of a pair of walls of the container 12 to the other.

[0077] The first chamber 13 has a supply fluid inlet 10a and an impermeable fluid outlet 10c. The second chamber 14 has a permeable fluid outlet 10b. The supply fluid inlet 10a is an opening for supplying the raw fluid F0 to the supply space (first chamber 13). The permeable fluid outlet 10b is an opening for discharging the first permeable fluid T1 from the permeable space (second chamber 14). The impermeable fluid outlet 10c is an opening for discharging the raw fluid F0 (first impermeable fluid N1) that did not permeate the permeation vaporization membrane 11 from the supply space (first chamber 13). Each of the supply fluid inlet 10a, permeable fluid outlet 10b, and impermeable fluid outlet 10c is formed, for example, on the wall surface of the container 12.

[0078] The first membrane separation unit 10 is suitable for a continuous flow membrane separation method. However, the first membrane separation unit 10 may also be used in a batch membrane separation method.

[0079] [Permeation Vaporization Membrane] As described above, the permeation vaporization membrane 11 separates the raw fluid F0, which is the supply fluid, into a first permeable fluid T1 and a first impermeable fluid N1. The permeation vaporization membrane 21 separates the first impermeable fluid N1, which is the supply fluid, into a second permeable fluid T2 and a second impermeable fluid N2. The configuration of the permeation vaporization membrane 21 is basically the same as that of the permeation vaporization membrane 11, so its explanation is omitted.

[0080] Figure 3 is a schematic cross-sectional view showing an example of a permeation vaporization membrane 11 in the first membrane separation unit 10. The permeation vaporization membrane 11 comprises, for example, a separation functional layer 1 and a porous support 2 that supports the separation functional layer 1. The separation functional layer 1 is in direct contact with, for example, the porous support 2. The permeation vaporization membrane 11 has, for example, a main surface 11a on the separation functional layer 1 side exposed to the supply space 13, and a main surface 11b on the porous support 2 side exposed to the permeation space 14.

[0081] The permeation vaporization membrane 11 may further include a protective layer (not shown) that protects the separation functional layer 1.

[0082] (Separation Functional Layer) The separation functional layer 1 is a layer that can preferentially permeate specific components contained in the supply fluid. For example, the separation functional layer 1 is a layer that can preferentially permeate organic compound C contained in the supply fluid.

[0083] If the separation functional layer 1 is a layer that can preferentially allow organic compound C contained in the supply fluid to pass through, it is preferable that the separation functional layer 1 includes a hydrophobic material. In this specification, "hydrophobic material" means, for example, a material in which, when a 10 μL drop of water (at a temperature of 25°C) is dropped onto the surface of a test piece made of the material, the static contact angle of water exceeds 90°. The static contact angle of water can be measured using a commercially available contact angle meter.

[0084] Examples of hydrophobic materials include compounds having siloxane bonds (Si-O-Si bonds), olefin polymers, oils, and fluorinated compounds. The separation functional layer 1 preferably contains a compound having siloxane bonds as a hydrophobic material. Compounds having siloxane bonds are typically silicone polymers. Silicone polymers may be solid or liquid at 25°C. Specific examples of silicone polymers include polydimethylsiloxane (PDMS). Specific examples of olefin polymers include polyethylene and polypropylene. Examples of oils include hydrocarbon oils such as liquid paraffin. Examples of fluorinated compounds include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA). Hydrophobic materials can be used individually or in combination of two or more.

[0085] The separation functional layer 1 may contain a hydrophobic material as its main component, or may be composed substantially only of a hydrophobic material. "Main component" means the component that is present in the largest amount by weight in the separation functional layer 1.

[0086] The separation functional layer 1 may include a matrix containing a hydrophobic material and fillers dispersed in the matrix. The fillers are embedded within the matrix. Within the matrix, all fillers may be spaced apart from each other or partially aggregated.

[0087] The filler includes, for example, inorganic materials such as zeolite, silica, and bentonite. The zeolite included in the filler is preferably high-silica zeolite, which has a high silica-to-alumina ratio. High-silica zeolite is suitable for separating solutions containing organic compound C due to its excellent hydrolysis resistance. Examples of high-silica zeolite include HSZ (registered trademark) from Tosoh Corporation, HiSiv (registered trademark) from Union Showa Co., Ltd., USKY from Union Showa Co., Ltd., and Zeoal (registered trademark) from Nakamura Choko Co., Ltd.

[0088] The filler may contain 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 contains, for example, a metal ion and an organic ligand. Examples of metal ions include Zn ions. Examples of organic ligands include aromatic rings. Examples of aromatic rings included in the organic ligand include imidazole rings. Examples of organic ligands include 2-methylimidazole. A specific example of a metal-organic framework is ZIF-8.

[0089] The shape of the filler is, for example, particulate. In this specification, "particulate" includes spherical, ellipsoidal, flaky, and fibrous. The average particle size of the filler is not particularly limited, but is, for example, 50 μm or less, preferably 20 μm or less, and more preferably 10 μm or less. 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, a cross-section of the separation functional layer 1 is observed 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 considered to be the particle size (diameter of the particle) of that specific filler. The particle sizes of any number (at least 50) of fillers are calculated, and the average of the calculated values ​​is considered to be the average particle size of the filler.

[0090] The filler content in the separation functional layer 1 is, for example, 5 wt% or more, preferably 30 wt% or more, and more preferably 40 wt% or more. The upper limit of the filler content in the separation functional layer 1 is not particularly limited, but is, for example, 70 wt%. The matrix content in the separation functional layer 1 is not particularly limited, but is, for example, 30 wt% to 90 wt%.

[0091] If the separation functional layer 1 is a layer that can preferentially permeate organic compound C contained in the supply fluid, 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 0.1 μm or more, 1.0 μm or more, 10 μm or more, or 30 μm or more.

[0092] If the separation functional layer 1 is a layer that can preferentially permeate organic compound C contained in the supply fluid, the separation functional layer 1 may have a microporous structure with an average pore diameter of less than 0.01 μm, but it may also be a dense layer without pores on its surface.

[0093] (Porous support) Examples of porous support 2 include nonwoven fabrics; porous polytetrafluoroethylenes; aromatic polyamide fibers; porous metals; sintered metals; porous ceramics; porous polyesters; porous nylons; activated carbon fibers; latex; silicones; silicone rubbers; permeable (porous) polymers containing at least one selected from the group consisting of polyvinyl fluoride, polyvinylidene fluoride, polyurethane, polypropylene, polyethylene, polystyrene, polycarbonate, polysulfone, polyetheretherketone, polyacrylonitrile, polyimide, and polyphenylene oxide; metal foams having open or closed cells; polymer foams having open or closed cells; silica; porous glass; mesh screens, etc. The porous support 2 may be a combination of two or more of these.

[0094] The porous support 2 has an average pore diameter of, for example, 0.01 to 0.4 μm. The thickness of the porous support 2 is not particularly limited, but 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.

[0095] (Protective layer) The protective layer covers the surface of the separation functional layer 1, for example. The material of the protective layer is not particularly limited, and examples include silicone resin. The material of the protective layer may be the same as or different from the material of the matrix of the separation functional layer 1.

[0096] The thickness of the protective layer is not particularly limited, but is, for example, 0.5 μm or more, preferably 1 μm or more, more preferably 5 μm or more, and even more 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.

[0097] (Method for producing a permeable vaporization membrane) The permeable vaporization membrane 11 can be produced, for example, by forming a separation functional layer 1 on a porous support 2. Specifically, first, a coating solution containing the material for the separation functional layer 1 is prepared. The coating solution may contain a filler along with a dispersant for dispersing the filler in the coating solution. If the coating solution contains a compound having a siloxane bond, the coating solution may further contain a catalyst for curing the compound. Next, a coating film is obtained by coating the coating solution onto the porous support 2. The separation functional layer 1 is formed by drying the coating film. This gives rise to the permeable vaporization membrane 11.

[0098] <Embodiment of Operating Method for Membrane Separation System> The operating method for the membrane separation system of this embodiment includes, for example, reducing the pressure of the permeate space of each of the multiple membrane separation units by a depressurization unit; separating the supply fluid containing volatile organic compounds into a permeate fluid and an impermeable fluid by the permeation vaporization membrane of each of the multiple membrane separation units; condensing the permeate fluid discharged from the membrane separation unit by a condensation unit in each of the multiple membrane separation units to produce a condensed fluid; and recovering a mixed fluid obtained by mixing the condensed fluids discharged from each of the multiple condensation units in a recovery unit. According to this operating method, the content of volatile organic compounds in the permeate fluid can be controlled with a simple configuration.

[0099] Next, an example of the operation method of the membrane separation system 100A described above will be explained with reference to Figure 1. The operation method of the membrane separation system 100A is, for example, to reduce the pressure of the permeate space 14 of the first membrane separation unit 10 by the first pressure reduction unit 31 (step 1-1), to reduce the pressure of the permeate space 24 of the second membrane separation unit 20 by the second pressure reduction unit 32 (step 1-2), to separate the raw fluid F0 into a first permeate fluid T1 and a first impermeable fluid N1 by the permeate vaporization membrane 11 of the first membrane separation unit 10 (step 2-1), and to separate the first impermeable fluid N1 into a second permeate fluid T2 and a second impermeable fluid N2 by the permeate vaporization membrane 21 of the second membrane separation unit 20. The process includes: (step 2-2) condensing the first permeate fluid T1 discharged from the first membrane separation unit 10 by the first condensation unit 41 to produce a first condensed fluid C1 (step 3-1); condensing the second permeate fluid T2 discharged from the second membrane separation unit 20 by the second condensation unit 42 to produce a second condensed fluid C2 (step 3-2); and recovering a mixed fluid C3 in the recovery unit 75, which is a mixture of the first condensed fluid C1 discharged from the first condensation unit 41 and the second condensed fluid C2 discharged from the second condensation unit 42 (step 4).

[0100] According to the operating method of the membrane separation system 100A, the content of organic compound C in the resulting mixed fluid C3 can be controlled by adjusting the ratio of the first condensing fluid C1 and the second condensing fluid C2 to be mixed.

[0101] In addition to the steps described above, the operating method of the membrane separation system 100A may include returning the first condensed fluid C1 to at least one selected from the group consisting of the supply unit 71 and the raw fluid path 81, and returning the second condensed fluid C2 to at least one selected from the group consisting of the supply unit 71 and the raw fluid path 81.

[0102] For example, the content of organic compound C in the resulting mixed fluid C3 may be controlled to a desired range by operating the membrane separation system 100A as follows. First, flow control valves 55 and 56 are opened, and flow control valves 57 and 58 are closed. This sends all (100%) of the first condensed fluid C1 and all (100%) of the second condensed fluid C2 to the recovery unit 75. Next, it is determined whether the content of organic compound C in the mixed fluid C3 obtained in the recovery unit 75 meets the desired range. If the content of organic compound C in the mixed fluid C3 obtained in the recovery unit 75 exceeds the desired range, the flow control valve 57 is slightly opened to allow a portion of the first condensed fluid C1 to flow into the first return path 93. This allows the content of organic compound C in the mixed fluid C3 to be controlled to a desired range. If the content of organic compound C in the mixed fluid C3 obtained in the recovery unit 75 falls below a desired range, the flow control valve 58 is slightly opened to allow a portion of the second condensed fluid C2 to flow into the second return path 94. This allows the content of organic compound C in the mixed fluid C3 to be controlled to a desired range.

[0103] <Embodiment of Method for Producing Organic Compounds> The method for producing organic compounds according to this embodiment is a method for producing organic compounds using a plurality of membrane separation units having a membrane separation unit and a condensation unit, a depressurization unit, and a recovery unit. The plurality of membrane separation units are connected in series such that the impermeable fluid discharged from the membrane separation unit located on the upstream side is supplied as a supply fluid to the membrane separation unit located on the downstream side. Each of the plurality of membrane separation units has a permeation vaporization membrane that separates a supply fluid containing a volatile organic compound into a permeable fluid and an impermeable fluid, and a supply space and a permeation space separated by the permeation vaporization membrane. The production method includes depressurizing the permeation space of each of the plurality of membrane separation units using the depressurization unit, separating the supply fluid containing a volatile organic compound into a permeable fluid and an impermeable fluid using the permeation vaporization membrane of each of the plurality of membrane separation units, condensing the permeable fluid discharged from the membrane separation unit using the condensation unit to produce a condensed fluid, and recovering a mixed fluid obtained by mixing the condensed fluids discharged from each of the plurality of condensation units in the recovery unit.

[0104] In the method for producing organic compounds according to this embodiment, the volatile organic compound may be an alcohol. According to this production method, the alcohol can be separated from a supply fluid containing the volatile alcohol at a high concentration.

[0105] [Modifications of the Membrane Separation Section] The membrane separation section of the membrane separation system of this embodiment may include a spiral-type membrane element, a hollow fiber membrane element, a disc-tube type membrane element in which multiple permeation vaporization membranes are stacked, a plate-and-frame type membrane element, and the like. Figure 4 is a schematic unfolded perspective view showing a spiral-type membrane element. The membrane separation section may include a spiral-type membrane element as shown in Figure 4.

[0106] In the following, the case in which the first membrane separation unit 10 and the second membrane separation unit 20 of the membrane separation system 100A described above each include a spiral-type membrane element will be further explained with reference to Figure 4. Since the configuration of the first membrane separation unit 10 and the configuration of the second membrane separation unit 20 are basically the same, in the following, only the case in which the first membrane separation unit 10 includes a spiral-type membrane element will be explained, and the case in which the second membrane separation unit 20 includes a spiral-type membrane element will be omitted.

[0107] The spiral-shaped membrane element 15 shown in Figure 4 comprises a central tube 16 and membrane leaves 19 that are wrapped around the central tube 16 and have a permeable vaporization membrane 11.

[0108] The central tube 16 has a cylindrical shape. Through holes 16h are formed on the surface of the central tube 16 to allow the raw fluid F0 to flow into the interior of the central tube 16. The number of through holes 16h is not particularly limited and may be one or two or more. Examples of materials for 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.

[0109] The membrane element 15 has a plurality of membrane leaves 19. Each membrane leaf 19 includes a permeation vaporization membrane 11 and a permeation-side flow channel material 17. For example, a membrane leaf 19 has two permeation vaporization membranes 11. The two permeation vaporization membranes 11 are overlapped and sealed on three sides to form a bag-like structure. The permeation-side flow channel material 17 is positioned between the two permeation vaporization membranes 11 so as to be located inside the bag-like structure. The permeation-side flow channel material 17 secures a space (permeation space) between the two permeation vaporization membranes 11 as a flow channel for the first permeating fluid T1. In this way, the permeation-side flow channel material 17 is used in combination with the permeation vaporization membranes 11. The number of membrane leaves 19 is not particularly limited and can be, for example, 2 to 50.

[0110] The membrane element 15 further includes a supply-side flow channel material 18. The supply-side flow channel material 18 is located outside the bag-like structure described above and is stacked on the membrane leaf 19. More specifically, multiple supply-side flow channel materials 18 and multiple membrane leaf 19 are stacked alternately. The supply-side flow channel material 18 secures a space (supply space) between the membrane leaf 19 that serves as a flow channel for the raw fluid F0.

[0111] For the supply-side channel material 18 and the permeate-side channel material 17, for example, a net, woven fabric, or knitted fabric made of a resin such as polyethylene, polypropylene, polyethylene terephthalate (PET), polyphenylene sulfide (PPS), or ethylene-chlorotrifluoroethylene copolymer (ECTFE) can be used.

[0112] The outer surface of the membrane element 15 is composed of a shell (not shown) made of a material that prevents fluid from passing through. The shell may be made of FRP (fiber-reinforced plastic). The membrane element may be housed in a casing (not shown).

[0113] The first membrane separation unit 10, which includes the membrane element 15 shown in Figure 4, can be operated, for example, in the following way. First, the raw fluid F0 is supplied to one end of the wound membrane leaf 19. The space inside the central tube 16 is depressurized. Depressurization can be performed by the first depressurization unit 31. As a result, the first permeate fluid T1 that has permeated through the permeation vaporization membrane 11 of the membrane leaf 19 moves into the inside of the central tube 16. The first permeate fluid T1 is discharged to the outside through the central tube 16. The raw fluid F0 (first non-permeable fluid N1) processed in the first membrane separation unit 10 is discharged to the outside from the other end of the wound membrane leaf 19.

[0114] <Modifications of the Membrane Separation System> The membrane separation system of this embodiment is not limited to the membrane separation system 100A shown in Figure 1. Hereinafter, modifications 1 to 7 of the membrane separation system of this embodiment will be described with reference to Figures 5 to 11. In the following, elements common to the membrane separation system 100A described above will be given the same reference numerals, and detailed explanations will be omitted.

[0115] [Modification 1 of the Membrane Separation System] Figure 5 is a schematic diagram showing modification 1 of the membrane separation system of this embodiment. The membrane separation system 100B of modification 1 shown in Figure 5 further includes a filtration separation unit 61 that filters and separates the raw fluid F0, which is to be supplied as a supply fluid to the first membrane separation unit 10. Except for this, the membrane separation system 100B has basically the same configuration as the membrane separation system 100A (Figure 1) described above. The membrane separation system 100B makes it possible to increase the content of organic compound C in the raw fluid F0 supplied to the first membrane separation unit 10.

[0116] The filtration separation unit 61 separates and removes impurities contained in the raw fluid F0. Furthermore, the filtration separation unit 61 can increase the content of organic compound C in the raw fluid F0, so that a more concentrated raw fluid F0 can be supplied to the first membrane separation unit 10. The filtration separation unit 61 has, for example, a filtration membrane. As the filtration membrane, for example, a reverse osmosis membrane or an ultrafiltration membrane can be used.

[0117] In the example shown in Figure 5, the raw fluid path 81 has a first portion 81a and a second portion 81b. A filtration and separation section 61 is provided between the first portion 81a and the second portion 81b. The first portion 81a is the part that connects the raw fluid outlet 71b of the supply section 71 to the fluid inlet of the filtration and separation section 61. The second portion 81b is the part that connects the fluid outlet of the filtration and separation section 61 to the supply fluid inlet 10a of the first membrane separation section 10.

[0118] In the example shown in Figure 5, the confluence point 81p of the first return path 93 and the second return path 94 is located in the second portion 81b of the raw fluid path 81. That is, the first condensed fluid C1 and the second condensed fluid C2 returned to the raw fluid path 81 are supplied directly to the first membrane separation unit 10. However, the confluence point 81p may also be located in the first portion 81a of the raw fluid path 81. That is, the first condensed fluid C1 and the second condensed fluid C2 returned to the raw fluid path 81 may be supplied to the filtration separation unit 61.

[0119] In the example shown in Figure 5, the heating device 45 is located downstream of the confluence point 81p in the second portion 81b of the raw fluid path 81. However, the heating device 45 may also be located upstream of the confluence point 81p in the second portion 81b of the raw fluid path 81.

[0120] The membrane separation system 100B may further include a filtration separation unit 62 that filters and separates the second impermeable fluid N2 discharged from the second membrane separation unit 20. The filtration separation unit 62 can separate and remove impurities contained in the second impermeable fluid N2. Furthermore, since the content of organic compound C is increased in the fluid obtained on the non-filtering side of the filtration separation unit 62, the content of organic compound C in the obtained fluid can be further increased by, for example, supplying it to the filtration separation unit and the membrane separation unit. In addition, since the fluid obtained on the filtering side of the filtration separation unit 62 is highly purified water, wastewater incineration treatment is unnecessary, or it can be treated using microorganisms. The filtration separation unit 62 can be the same as that described for the filtration separation unit 61. The configuration of the filtration separation unit 61 and the configuration of the filtration separation unit 62 may be the same or different.

[0121] The operation method of membrane separation system 100B is basically the same as that of membrane separation system 100A described above, so the explanation will be omitted.

[0122] [Modification 2 of the Membrane Separation System] Figure 6 is a schematic diagram showing modification 2 of the membrane separation system of this embodiment. In the membrane separation system 100C of modification 1 shown in Figure 6, each of the multiple membrane separation units has a buffer tank provided in the discharge path. In the example of Figure 6, the first membrane separation unit 201 has a first buffer tank 77 provided in the first discharge path 91. The second membrane separation unit 202 has a second buffer tank 78 provided in the second discharge path 92. Except for this, the membrane separation system 100C has basically the same configuration as the membrane separation system 100A (Figure 1) described above. According to the membrane separation system 100C, the first condensed fluid C1 can be temporarily stored in the first buffer tank 77. The second condensed fluid C2 can be temporarily stored in the second buffer tank 78. Therefore, it is easy to control the content of organic compound C in the mixed fluid C3 obtained in the recovery unit 75 to a desired range.

[0123] The operating method of the membrane separation system 100C includes, in place of step 4 in the operating method of the membrane separation system 100A described above, temporarily storing the first condensed fluid C1 discharged from the first condensation unit 41 in the first buffer tank 77, temporarily storing the second condensed fluid C2 discharged from the second condensation unit 42 in the second buffer tank 78, and recovering a mixed fluid C3 in the recovery unit 75, which is a mixture of the first condensed fluid C1 discharged from the first buffer tank 77 and the second condensed fluid C2 discharged from the second buffer tank 78.

[0124] [Modified Membrane Separation System 3] Figure 7 is a schematic diagram showing modified membrane separation system 3 of this embodiment. In the membrane separation system 100D of modified membrane separation system 3 shown in Figure 7, the supply unit 71 has a first supply unit 711 and a second supply unit 712 connected in parallel to each other. The first supply unit 711 and the second supply unit 712 are configured to be switchable. Except for this, the membrane separation system 100D has basically the same configuration as the membrane separation system 100A (Figure 1) described above. With the membrane separation system 100D, for example, when the remaining amount of raw fluid F0 stored in the first supply unit 711 becomes low, the supply unit 71 to be used can be switched to the second supply unit 712. Therefore, it is not necessary to stop the operation of the membrane separation system 100D in order to replenish the raw fluid F0 in the supply unit 71.

[0125] In the membrane separation system 100D, the raw fluid path 81 includes a first raw fluid path 811 connected to the raw fluid outlet 71b of the first supply unit 711, and a second raw fluid path 812 connected to the raw fluid outlet 71b of the second supply unit 712. As shown in Figure 7, the second raw fluid path 812 may merge with the first raw fluid path 811 at the merging position 71p.

[0126] A flow control valve (not shown) may be provided in each of the first raw fluid path 811 and the second raw fluid path 812.

[0127] A main supply path (not shown) for supplying the raw fluid F0 may be connected to each of the first supply unit 711 and the second supply unit 712.

[0128] The operating method of the membrane separation system 100D may include, in addition to the steps in the operating method of the membrane separation system 100A described above, the following steps: introducing the raw fluid F0 from the first supply unit 711 to the supply space 13 of the first membrane separation unit 10; switching the supply unit 71 to be used from the first supply unit 711 to the second supply unit 712; and introducing the raw fluid F0 from the second supply unit 712 to the supply space 13 of the first membrane separation unit 10.

[0129] [Modification 4 of the Membrane Separation System] Figure 8 is a schematic diagram showing modification 4 of the membrane separation system of this embodiment. In the membrane separation system 100E of modification 4 shown in Figure 8, the first membrane separation unit 201 has a first circulation path 95 that guides the first impermeable fluid N1 to at least one selected from the group consisting of a supply unit 71 and a raw fluid path 81. Except for this, the membrane separation system 100E has basically the same configuration as the membrane separation system 100C of modification 2 (Figure 6) described above. In the membrane separation system 100E, by flowing a portion of the first impermeable fluid N1 into the first circulation path 95, the content of organic compound C in the second permeable fluid T2 discharged from the second membrane separation unit 20 can be reduced. This makes it possible to reduce the content of organic compound C in the second condensed fluid C2 discharged from the second condensation unit 42. According to the membrane separation system 100E, the content of organic compound C in the mixed fluid C3 obtained in the recovery unit 75 can be controlled using the first circulation path 95.

[0130] As shown in Figure 8, the first circulation path 95 may be a path that branches off from the first impermeable fluid path 83 at the branching position 83q and merges with the second return path 94 at the merging position 94p.

[0131] A flow control valve 59a may be provided downstream of the branching point 83q of the first impermeable fluid path 83. The flow control valve 59a is a flow control valve for adjusting the flow rate of the first impermeable fluid N1 flowing downstream of the branching point 83q of the first impermeable fluid path 83. A flow control valve 59b may be provided in the first circulation path 95. The flow control valve 59b is a flow control valve for adjusting the flow rate of the first impermeable fluid N1 flowing through the first circulation path 95. By adjusting the opening degree of the flow control valve 59a and the flow control valve 59b, the flow rate of the first impermeable fluid N1 flowing downstream of the branching point 83q of the first impermeable fluid path 83 and into the first circulation path 95 can be controlled.

[0132] In the example shown in Figure 8, the first return path 93 is configured to return the first condensed fluid C1 to the supply unit 71. In the example shown in Figure 8, the second return path 94 is configured to return the second condensed fluid C2 to the supply unit 71. That is, the returned first condensed fluid C1 and second condensed fluid C2 are supplied to the supply unit 71.

[0133] Although not shown in the diagram, in the membrane separation system 100E, the second membrane separation unit 202 may have a second circulation path that guides the second impermeable fluid N2 downstream of the branching position 83q of the first impermeable fluid path 83. A buffer tank may be provided in the second circulation path.

[0134] The operating method of the membrane separation system 100E may include, in addition to each step in the operating method of the membrane separation system 100C described above, introducing the first impermeable fluid N1 to at least one selected from the group consisting of the supply unit 71 and the raw fluid path 81.

[0135] For example, the content of organic compound C in the resulting mixed fluid C3 may be controlled to a desired range by operating the membrane separation system 100E as follows. First, only the flow control valve 59b is opened, and the flow control valves 55, 56, 57, 58, and 59a are closed. This returns all (100%) of the first impermeable fluid N1 to the supply unit 71. This reduces the content of organic compound C in the raw fluid F0. Also, all (100%) of the first condensed fluid C1 is stored in the first buffer tank 77. Once the content of organic compound C in the raw fluid F0 has decreased to the desired range, the flow control valve 59a is opened, and the flow control valve 59b is closed. This stores all (100%) of the second condensed fluid C2 in the second buffer tank 78. Next, the flow control valves 55 and 56 are opened. This allows the first condensed fluid C1 to be guided from the first buffer tank 77 to the recovery unit 75. The second condensed fluid C2 is introduced from the second buffer tank 78 to the recovery unit 75. By adjusting the opening of the flow control valves 55 and 56, the content of organic compound C in the mixed fluid C3 obtained in the recovery unit 75 can be controlled to a desired range.

[0136] [Modification 5 of the Membrane Separation System] Figure 9 is a schematic diagram showing modification 5 of the membrane separation system of this embodiment. The membrane separation system 100F of modification 5 shown in Figure 9 includes a filtration separation unit 61 that filters and separates the raw fluid F0, which is to be supplied to the first membrane separation unit 10, and a filtration separation unit 62 that filters and separates the second impermeable fluid N2 discharged from the second membrane separation unit 20. Except for this, the membrane separation system 100F has basically the same configuration as the membrane separation system 100E of modification 4 (Figure 8) described above. In other words, the membrane separation system 100F has a configuration that combines the membrane separation system 100B of modification 1 (Figure 5) and the membrane separation system 100E of modification 4 (Figure 8). The membrane separation system 100F can also control the content of organic compound C in the mixed fluid C3 obtained in the recovery unit 75.

[0137] The operating method of the membrane separation system 100F is basically the same as the operating method of the membrane separation system 100E in the modified example 4 described above, so the explanation will be omitted.

[0138] [Modification 6 of the Membrane Separation System] Figure 10 is a schematic diagram showing modification 6 of the membrane separation system of this embodiment. The membrane separation system 100G of modification 6 shown in Figure 10 does not include a first buffer tank 77 and a second buffer tank 78. Except for this, the membrane separation system 100G has basically the same configuration as the membrane separation system 100E of modification 4 (Figure 8) described above. The membrane separation system 100G can also control the content of organic compound C in the mixed fluid C3 obtained in the recovery unit 75.

[0139] The operating method of the membrane separation system 100G is basically the same as the operating method of the membrane separation system 100E in the modified example 4 described above, so the explanation will be omitted.

[0140] [Modification 7 of the Membrane Separation System] Figure 11 is a schematic diagram showing modification 7 of the membrane separation system of this embodiment. In the membrane separation system 100H of modification 7 shown in Figure 11, the supply unit 71 has a first supply unit 711 and a second supply unit 712 connected in parallel to each other, and the first supply unit 711 and the second supply unit 712 are configured to be switchable. Except for this, the membrane separation system 100H has basically the same configuration as the membrane separation system 100E of modification 4 (Figure 8) described above. The membrane separation system 100H can also control the content of organic compound C in the mixed fluid C3 obtained in the recovery unit 75.

[0141] In the membrane separation system 100H, a main supply path 80 for supplying the raw fluid F0 is connected to each of the first supply unit 711 and the second supply unit 712. As shown in Figure 11, the first return path 93 and the second return path 94 may merge with the main supply path 80 at the merging position 80p.

[0142] The operating method of the membrane separation system 100H is basically the same as the operating method of the membrane separation system 100E in the modified example 4 described above, so the explanation will be omitted.

[0143] [Other Modifications] The membrane separation system of the above embodiment and each of its modifications comprises two membrane separation units as a plurality of membrane separation units: a first membrane separation unit 201 and a second membrane separation unit 202. However, the membrane separation system may comprise three or more membrane separation units as a plurality of membrane separation units. For example, in addition to the first membrane separation unit 201 and the second membrane separation unit 202, it may further comprise a third membrane separation unit having a third membrane separation section, a third depressurization section, and a third condensation section. Also, in the above embodiment and each of its modifications, each membrane separation unit has one membrane separation section as a membrane separation section. However, each membrane separation unit may have two or more membrane separation sections connected in series as membrane separation sections. In this case, the impermeable fluid discharged from the membrane separation section located upstream is supplied as a supply fluid to the membrane separation section located downstream.

[0144] The above-described embodiments are mutually applicable, insofar as they do not conflict with technical standards. Each of the above embodiments and each of its modifications may be combined with each other, insofar as they do not conflict with technical standards.

[0145] The membrane separation system of this embodiment is suitable, for example, for efficiently recovering organic compounds from a supply fluid containing volatile organic compounds.

Claims

1. A membrane separation system comprising: a plurality of membrane separation units having a membrane separation section and a condensation section; a depressurization section; and a recovery section, wherein each of the plurality of membrane separation units has: the membrane separation section has a permeable vaporization membrane that separates a supply fluid containing volatile organic compounds into a permeable fluid and an impermeable fluid, and a supply space and a permeable space separated by the permeable vaporization membrane; the condensation section condenses the permeable fluid discharged from the membrane separation section to produce a condensed fluid; the plurality of membrane separation units are connected in series such that the impermeable fluid discharged from the membrane separation unit located upstream is supplied as the supply fluid to the membrane separation unit located downstream; the depressurization section depressurizes the permeable space of each of the plurality of membrane separation units; and the recovery section recovers a mixed fluid obtained by mixing the condensed fluids discharged from each of the plurality of condensation sections.

2. The membrane separation system according to claim 1, wherein each of the plurality of membrane separation units further has a discharge path that guides the condensed fluid discharged from the condensation section to the recovery section.

3. The membrane separation system according to claim 2, wherein each of the plurality of membrane separation units further comprises a concentration sensor and a flow control valve provided in the discharge path.

4. The membrane separation system according to claim 3, wherein, during operation, the content of the organic compound in the mixed fluid obtained in the recovery unit is controlled by adjusting the opening degree of the flow control valve of each of the plurality of membrane separation units while monitoring the measured values ​​of the concentration sensors of each of the plurality of membrane separation units.

5. The membrane separation system according to claim 1, further comprising a supply unit for storing a raw fluid, wherein the raw fluid is a supply fluid to be supplied to the membrane separation unit located furthest upstream among a plurality of membrane separation units.

6. The membrane separation system according to claim 5, wherein each of the plurality of membrane separation units further has a return path for returning the condensed fluid to at least one selected from the group consisting of the supply unit and the raw fluid path, and the raw fluid path guides the raw fluid from the supply unit to the supply space of the membrane separation unit located furthest upstream of the plurality of membrane separation units.

7. The membrane separation system according to claim 6, wherein the membrane separation unit located furthest upstream among the plurality of membrane separation units further has a circulation path that leads the impermeable fluid to at least one selected from the group consisting of the supply unit and the raw fluid path.

8. A method for operating a membrane separation system comprising a plurality of membrane separation units having membrane separation units and condensation units, a depressurization unit, and a recovery unit, wherein each of the plurality of membrane separation units has a permeable vaporization membrane that separates a supply fluid containing volatile organic compounds into a permeable fluid and an impermeable fluid, and a supply space and a permeable space separated by the permeable vaporization membrane, the plurality of membrane separation units are connected in series such that the impermeable fluid discharged from the membrane separation unit located upstream is supplied as the supply fluid to the membrane separation unit located downstream, the operating method comprising: depressurizing the permeable space of each of the plurality of membrane separation units with the depressurization unit; separating the supply fluid into a permeable fluid and an impermeable fluid with the permeable vaporization membrane of each of the plurality of membrane separation units; condensing the permeable fluid discharged from the membrane separation unit with the condensation unit in each of the plurality of membrane separation units to produce a condensed fluid; and recovering a mixed fluid obtained by mixing the condensed fluids discharged from each of the plurality of condensation units with the recovery unit. A method for operating a membrane separation system, including the operation of the membrane separation system.

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