Membrane separation system and method for operating membrane separation system

Abstract

A membrane separation system according to the present invention comprises a membrane separation unit, a pressure-reducing unit, a first condensation unit, and a second condensation unit. The membrane separation unit has: a pervaporation membrane that separates a feed fluid containing a volatile organic compound into a permeate fluid and a non-permeate fluid; and a feed space and a permeate space separated by the pervaporation membrane. The pressure-reducing unit reduces the pressure in the permeate space of the membrane separation unit. The first condensation unit and the second condensation unit are disposed in said order between the membrane separation unit and the pressure-reducing unit. In the membrane separation system, for example, the first condensation unit condenses permeate fluid discharged from the membrane separation unit to produce a first condensed fluid, the second condensation unit condenses permeate fluid discharged from the first condensation unit to produce a second condensed fluid, and the organic compound content in the second condensed fluid is higher than the organic compound content in the first condensed fluid.

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 aqueous solutions containing various substances. For example, Patent Document 1 discloses a system that separates and recovers ethanol from a fermentation product obtained by ethanol fermentation, using a silicalite membrane as an ethanol-selective hydrophobic pervaporation membrane.

[0003] Japanese Patent No. 4048279

[0004] The pervaporation method can be performed using a membrane separation unit including a pervaporation membrane, and a supply space and a permeate space separated by the pervaporation membrane. By depressurizing the permeate 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. Thereby, a gaseous permeate fluid in which the volatile organic compound is concentrated is obtained. The gaseous permeate fluid is liquefied in a condensing unit. Thereby, a liquid permeate fluid is obtained. In a membrane separation system using the pervaporation method, depressurization of the permeate space of the membrane separation unit is performed by a decompression unit provided downstream of the membrane separation unit.

[0005] It is known that the concentration of the permeate fluid obtained by a membrane separation system using the pervaporation method, that is, the content of the volatile organic compound in the permeate fluid, depends on membrane performance such as the separation coefficient and permeation flux of the pervaporation membrane. Therefore, in order to increase the content of the volatile organic compound in the permeate fluid, for example, it is necessary to treat the permeate fluid that has permeated through the pervaporation membrane using another pervaporation membrane, which increases the required energy.

[0006] Accordingly, an object of the present invention is to provide a membrane separation system that can increase the concentration of the obtained permeate fluid with a simple configuration.

[0007] The present invention provides a membrane separation system comprising a membrane separation unit, a depressurization unit, a first condensation unit, and a second condensation unit, wherein the membrane separation unit 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 depressurization unit depressurizes the permeable space of the membrane separation unit, and the first condensation unit and the second condensation unit are arranged in this order between the membrane separation unit and the depressurization unit.

[0008] In another aspect, the present invention provides a method for operating a membrane separation system comprising a membrane separation unit, a depressurization unit, a first condensation unit, and a second condensation unit, wherein the first condensation unit and the second condensation unit are arranged in this order between the membrane separation unit and the depressurization unit, the membrane separation unit has a permeable vaporization membrane and a supply space and a permeation space separated by the permeable vaporization membrane, the method for operating a membrane separation system comprising: depressurizing the permeation space of the membrane separation unit with the depressurization unit; separating a supply fluid containing volatile organic compounds into a permeable fluid and an impermeable fluid with the permeable vaporization membrane of the membrane separation unit; condensing the permeable fluid discharged from the membrane separation unit with the first condensation unit to produce a first condensed fluid; and condensing the permeable fluid discharged from the first condensation unit with the second condensation unit to produce a second condensed fluid, the method for operating a membrane separation system comprising controlling the cooling temperature of the first condensation unit to a value higher than the cooling temperature of the second condensation unit.

[0009] According to the present invention, a membrane separation system can be provided that can increase the concentration of the resulting permeate fluid 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 diagram showing an example of the first condensation section and the second condensation section of the membrane separation system. 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 the membrane separation system used in calculation example 4.

[0011] A membrane separation system according to a first aspect of the present invention comprises a membrane separation unit, a depressurization unit, a first condensation unit, and a second condensation unit, wherein the membrane separation unit 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 depressurization unit depressurizes the permeable space of the membrane separation unit, and the first condensation unit and the second condensation unit are arranged in this order between the membrane separation unit and the depressurization unit.

[0012] In a second aspect of the present invention, for example, in the membrane separation system according to the first aspect, the first condensation unit condenses the permeate fluid discharged from the membrane separation unit to produce a first condensed fluid, the second condensation unit condenses the permeate fluid discharged from the first condensation unit to produce a second condensed fluid, and the content of the organic compound in the second condensed fluid is higher than the content of the organic compound in the first condensed fluid.

[0013] In a third embodiment of the present invention, for example, in a membrane separation system according to the first or second embodiment, during operation, the cooling temperature of the first condensation unit is controlled to be higher than the cooling temperature of the second condensation unit.

[0014] In a fourth aspect of the present invention, for example, the membrane separation system according to the second aspect further comprises: a discharge path for guiding the permeate fluid discharged from the first condensation section to the second condensation section; a first condensation fluid path for discharging the first condensation fluid from the first condensation section; and a second condensation fluid path for discharging the second condensation fluid from the second condensation section.

[0015] In a fifth aspect of the present invention, for example, the membrane separation system according to the fourth aspect further comprises a bypass path that guides the first condensed fluid discharged from the first condensation section to the second condensed fluid path.

[0016] In a sixth aspect of the present invention, for example, in the membrane separation system according to the fifth aspect, the bypass path merges with the second condensing fluid path at a confluence point, and further comprises a concentration sensor provided downstream of the confluence point of the second condensing fluid path, and a flow control valve provided in the bypass path.

[0017] In a seventh aspect of the present invention, for example, in the membrane separation system according to the sixth aspect, the opening of the flow control valve is adjusted based on the monitoring results from the concentration sensor so that the concentration of the mixed fluid flowing through the second condensed fluid path downstream of the confluence point satisfies a predetermined range.

[0018] In the eighth aspect of the present invention, for example, a membrane separation system according to any one of the second to seventh aspects further comprises: a supply fluid path for guiding the supply fluid into the supply space of the membrane separation unit; a permeable fluid path for discharging the permeable fluid from the permeable space of the membrane separation unit; a non-permeable fluid path for discharging the non-permeable fluid from the supply space of the membrane separation unit; and a return path for returning the first condensed fluid discharged from the first condensation unit to at least one selected from the group consisting of the supply fluid path and the non-permeable fluid path.

[0019] In a ninth embodiment of the present invention, for example, a membrane separation system according to any one of the second to eighth embodiments has a plurality of membrane separation units, each having a membrane separation unit, a depressurization unit, a first condensation unit, and a second condensation unit, wherein the plurality of membrane separation units of 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.

[0020] In a tenth embodiment of the present invention, for example, the membrane separation system according to the ninth embodiment is configured such that the first condensed fluid discharged from the first condenser connected to the membrane separation unit located upstream merges with the supply fluid supplied to the membrane separation unit located downstream.

[0021] In an eleventh aspect of the present invention, for example, a membrane separation system according to any one of the first to tenth aspects further comprises a third condensation unit that condenses the exhaust gas discharged from the depressurization unit to generate a third condensation fluid.

[0022] In a twelfth aspect of the present invention, for example, a membrane separation system according to any one of the second to eleventh aspects further comprises a first recovery unit for recovering the first condensed fluid and a second recovery unit for recovering the second condensed fluid.

[0023] In a thirteenth aspect of the present invention, for example, the membrane separation system according to the twelfth aspect further comprises a mixing unit for mixing the first condensed fluid recovered in the first recovery unit and the second condensed fluid recovered in the second recovery unit to obtain a mixed fluid.

[0024] A method for operating a membrane separation system according to a fourteenth aspect of the present invention is a method for operating a membrane separation system comprising a membrane separation unit, a depressurization unit, a first condensation unit, and a second condensation unit, wherein the first condensation unit and the second condensation unit are arranged in this order between the membrane separation unit and the depressurization unit, the membrane separation unit has a permeable vaporization membrane and a supply space and a permeation space separated by the permeable vaporization membrane, the method for operating a membrane separation system comprising: depressurizing the permeation space of the membrane separation unit with the depressurization unit; separating a supply fluid containing volatile organic compounds into a permeable fluid and an impermeable fluid with the permeable vaporization membrane of the membrane separation unit; condensing the permeable fluid discharged from the membrane separation unit with the first condensation unit to produce a first condensed fluid; and condensing the permeable fluid discharged from the first condensation unit with the second condensation unit to produce a second condensed fluid, the method for operating a membrane separation system comprising: controlling the cooling temperature of the first condensation unit to a value higher than the cooling temperature of the second condensation unit.

[0025] 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.

[0026] <Embodiment of Membrane Separation System> The membrane separation system of this embodiment comprises a membrane separation unit having a permeable vaporization membrane, a depressurization unit, a first condensation unit, and a second condensation unit. The membrane separation unit has a supply space and a permeation space separated by the permeable vaporization membrane. The permeable vaporization membrane separates the supply fluid containing volatile organic compounds into a permeable fluid and an impermeable fluid. The depressurization unit reduces the pressure in the permeation space of the membrane separation unit. The first condensation unit and the second condensation unit are arranged in this order between the membrane separation unit and the depressurization unit.

[0027] According to the membrane separation system of this embodiment, the concentration of the resulting permeate fluid, that is, the content of volatile organic compounds in the permeate fluid, can be increased with a simple configuration.

[0028] The following describes a specific example of the membrane separation system of this embodiment with reference to the drawings.

[0029] Figure 1 is a schematic diagram showing an example of the membrane separation system of this embodiment. The membrane separation system 100A in Figure 1 comprises a membrane separation unit 10 having a permeable vaporization membrane 11, a depressurization unit 30, a first condensation unit 41, and a second condensation unit 42. The first condensation unit 41 and the second condensation unit 42 are arranged in this order between the membrane separation unit 10 and the depressurization unit 30.

[0030] The membrane separation unit 10 has a supply space 13 and a permeate space 14 separated by a permeate vaporization membrane 11. The permeate vaporization membrane 11 separates the supply fluid F0 containing a volatile organic compound C into a permeate fluid F1 and an impermeable fluid F2. The depressurization unit 30 depressurizes the permeate space 14 of the membrane separation unit 10.

[0031] The first condensation unit 41 condenses the permeate fluid F1 discharged from the membrane separation unit 10 to produce a first condensed fluid C1. In the first condensation unit 41, a portion of the gaseous permeate fluid F1 is liquefied, and a liquid first condensed fluid C1 is obtained. The second condensation unit 42 condenses the permeate fluid F1 that was not condensed in the first condensation unit 41 to produce a second condensed fluid C2. In the second condensation unit 42, the gaseous permeate fluid F1 that was not condensed in the first condensation unit 41 is liquefied, and a liquid second condensed fluid C2 is obtained. The content of organic compound C in the second condensed fluid C2 is higher than the content of organic compound C in the first condensed fluid C1.

[0032] In this embodiment, the supply fluid F0 contains a volatile organic compound C and water. According to the membrane separation system 100A, during operation, the cooling temperature t1 of the first condensation section 41 can be controlled to a higher value than the cooling temperature t2 of the second condensation section 42. According to the inventors' studies, when the cooling temperature t1 of the first condensation section 41 is controlled to a higher value than the cooling temperature t2 of the second condensation section 42, the water contained in the permeate fluid F1 is more easily condensed in the first condensation section 41, which is located upstream. On the other hand, the organic compound C contained in the permeate fluid F1 is more easily condensed in the second condensation section 42, which is located downstream. As a result, the content of organic compound C in the second condensate fluid C2 discharged from the second condensation section 42 can be increased to a higher level than the content of organic compound C in the permeate fluid F1 discharged from the membrane separation section 10. According to the membrane separation system 100A, with a simple configuration, the content of volatile organic compound C in the obtained permeate fluid can be increased beyond the membrane performance of the permeation vaporization membrane 11.

[0033] In the membrane separation system 100A, during operation, the cooling temperature t1 of the first condensation section 41 is controlled to be higher than the cooling temperature t2 of the second condensation section 42. By controlling the system to satisfy t1 > t2 during operation, as described above, the content of organic compound C in the second condensed fluid C2 discharged from the second condensation section 42 can be increased compared to the content of organic compound C in the permeate fluid F1 discharged from the membrane separation section 10.

[0034] During operation, the cooling temperature t1 of the first condensing unit 41 may be controlled to a range greater than 0°C and less than or equal to 20°C. The cooling temperature t1 may also be controlled to a range greater than 5°C and less than or equal to 20°C.

[0035] During operation, the cooling temperature t2 of the second condensing unit 42 may be controlled to a range of -80°C or higher and 0°C or lower. The cooling temperature t2 may be controlled to a range of -50°C or higher and 0°C or lower, or to a range of -20°C or higher and 0°C or lower.

[0036] 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.

[0037] 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.

[0038] The pressure p1 in the first condensation section 41 and the pressure p2 in the second condensation section 42 can be controlled by controlling the operation of the depressurization section 30.

[0039] The pressure reducing unit 30 may be a vacuum device such as a vacuum pump. The vacuum pump is typically a gas transport type vacuum pump, 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 pump as the pressure reducing unit 30 may be equipped with a variable speed mechanism for changing the rotation speed, etc. An example of a variable speed mechanism is an inverter that drives the pump motor. By controlling the rotation speed of the pump with the variable speed mechanism, the pressure p1 in the first condensing unit 41 and the pressure p2 in the second condensing unit 42 can be appropriately adjusted.

[0040] For example, a water-cooled heat exchanger can be used as the first condensing section 41 and the second condensing section 42. 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, water, etc. can be used as the refrigerant.

[0041] FIG. 2 is a schematic configuration diagram showing an example of a first condensing section 41 and a second condensing section 42. In FIG. 2, the membrane separation section 10 is omitted. The membrane separation system 100A may include a first refrigerant path 99a and a second refrigerant path 99b. The first refrigerant path 99a connects, for example, a refrigerant outlet 41e of the first condensing section 41 and a refrigerant inlet 41d of the first condensing section 41. The second refrigerant path 99b connects, for example, a refrigerant outlet 42e of the second condensing section 42 and a refrigerant inlet 42d of the second condensing section 42.

[0042] The membrane separation system 100A may further include a first cooling section 49a and a second cooling section 49b for cooling the refrigerant. The first cooling section 49a and the second cooling section 49b are typically chillers. The first cooling section 49a may be provided in the first refrigerant path 99a. The refrigerant passed through the inside of the first condensing section 41 can be cooled by the first cooling section 49a. The second cooling section 49b may be provided in the second refrigerant path 99b. The refrigerant passed through the inside of the second condensing section 42 can be cooled by the second cooling section 49b.

[0043] Each of the first refrigerant path 99a and the second refrigerant path 99b may be provided with, for example, a temperature sensor that measures the temperature of the refrigerant. During operation, based on the measurement results of each temperature sensor, the temperature of the refrigerant passed through the inside of the first condensing section 41 and the inside of the second condensing section 42 may be controlled by controlling the operations of the first cooling section 49a and the second cooling section 49b such that a cooling temperature t1 of the first condensing section 41 becomes a value higher than a cooling temperature t2 of the second condensing section 42.

[0044] Each of the first refrigerant path 99a and the second refrigerant path 99b may be provided with, for example, a pump that controls the flow rate of the refrigerant.

[0045] The membrane separation system 100A may include one cooling path instead of the first refrigerant path 99a and the second refrigerant path 99b. The cooling path may be provided with a cooling section for cooling the refrigerant. In this case, it is desirable that the second condensing section 42 is arranged on an upstream side of the cooling path, and the first condensing section 41 is arranged on a downstream side thereof such that the cooling temperature t1 of the first condensing section 41 becomes a value higher than the cooling temperature t2 of the second condensing section 42.

[0046] The membrane separation system 100A may further include pressure sensors that respectively measure the pressure p1 in the first condensing section 41 and the pressure p2 in the second condensing section 42. The pressure p1 in the first condensing section 41 and the pressure p2 in the second condensing section 42 may be controlled by controlling the operation of the pressure reducing section 30 based on the measurement results of the pressure sensors.

[0047] The membrane separation system 100A may further include a supply section 71 that stores the feed fluid F0. The supply section 71 stores the feed fluid F0 to be supplied to the membrane separation section 10. The supply section 71 is, for example, a tank that stores the feed fluid F0. The supply section 71 may also be a culture tank for producing the organic compound C through fermentation of a carbon source by microorganisms.

[0048] The membrane separation system 100A may further include a filtration separation section 61 that filters and separates the feed fluid F0 to be supplied to the membrane separation section 10. The filtration separation section 61 filters and separates the feed fluid F0 to be supplied to the membrane separation section 10. According to the filtration separation section 61, impurities contained in the feed fluid F0 can be separated and removed. In addition, according to the filtration separation section 61, the content of the organic compound C contained in the feed fluid F0 can be increased, so a more concentrated feed fluid F0 can be supplied to the membrane separation section 10. The filtration separation section 61 has, for example, a filtration membrane. As the filtration membrane, for example, a reverse osmosis membrane, an ultrafiltration membrane, or the like can be used.

[0049] The membrane separation system 100A may further include a filtration separation unit 62 for filtering and separating the impermeable fluid F2. The filtration separation unit 62 filters and separates the impermeable fluid F2 sent from the membrane separation unit 10. The filtration separation unit 62 can separate and remove impurities contained in the impermeable fluid F2. 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. Also, 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.

[0050] The membrane separation system 100A further includes a discharge path 91 for guiding the permeate fluid F1 discharged from the first condensation section 41 to the second condensation section 42, a first condensation fluid path 92 for discharging the first condensation fluid C1 from the first condensation section 41, and a second condensation fluid path 93 for discharging the second condensation fluid C2 from the second condensation section 42.

[0051] The membrane separation system 100A further includes a bypass path 94 that guides the first condensed fluid C1 discharged from the first condensation section 41 to the second condensed fluid path 93. With this configuration, for example, during operation, by controlling the flow of a portion of the first condensed fluid C1 to the bypass path 94, a portion of the first condensed fluid C1 can be mixed with the second condensed fluid C2 flowing through the second condensed fluid path 93 to obtain a mixed fluid C3. By controlling the flow rate of the first condensed fluid C1 flowing through the bypass path 94, the content of organic compound C in the obtained mixed fluid C3 can be adjusted.

[0052] In the membrane separation system 100A, the bypass path 94 is connected to the downstream end 92q of the first condensing fluid path 92 and merges with the second condensing fluid path 93 at the confluence point 93p. With this configuration, the first condensing fluid C1 can be guided from the first condensing section 41 to the second condensing fluid path 93.

[0053] The second condensing fluid path 93 has a first portion 93a and a second portion 93b. The first portion 93a is the portion that connects the second condensing section 42 and the confluence point 93p. The second portion 93b is the portion that connects to the confluence point 93p and is the portion downstream of the confluence point 93p.

[0054] The membrane separation system 100A may further include a concentration sensor 53 provided in the second portion 93b of the second condensing fluid path 93, and a flow control valve 55 provided in the bypass path 94. The concentration sensor 53 is a concentration sensor for measuring the content of organic compound C in the mixed fluid C3 flowing through the second portion 93b of the second condensing fluid path 93. The flow control valve 55 is a flow control valve for adjusting the flow rate of the first condensing fluid C1 flowing through the bypass path 94. The flow control valve 55 makes it possible to adjust the flow rate of the first condensing fluid C1 mixed with the second condensing fluid C2.

[0055] In the membrane separation system 100A, the opening of the flow control valve 55 may be adjusted based on the monitoring results from the concentration sensor 53 so that the concentration of the mixed fluid C3 flowing through the second condensed fluid path 93 downstream of the confluence point 93p satisfies a predetermined range. With this configuration, the content of organic compound C in the mixed fluid C3 can be controlled to the above predetermined range.

[0056] The first condensed fluid path 92 may be equipped with a concentration sensor 51 for measuring the content of organic compound C in the first condensed fluid C1 flowing through the first condensed fluid path 92. With this configuration, the concentration sensor 51 can monitor the content of organic compound C in the first condensed fluid C1 flowing through the first condensed fluid path 92. Therefore, for example, the flow rate of the first condensed fluid C1 leading to the bypass path 94 can be adjusted based on the monitoring results. Although not shown in the figures, the bypass path 94 may be equipped with a flow meter for measuring the flow rate of the first condensed fluid C1 flowing through the bypass path 94.

[0057] A concentration sensor 52 may be provided in the first portion 93a of the second condensed fluid path 93 for measuring the content of organic compound C in the second condensed fluid C2 flowing through the first portion 93a. With this configuration, the concentration sensor 52 can monitor the content of organic compound C in the second condensed fluid C2 flowing through the first portion 93a. Therefore, for example, the content of organic compound C in the mixed fluid C3 can be controlled to a desired range based on the monitoring results. Although not shown in the figures, a flow meter may be provided in the first portion 93a of the second condensed fluid path 93 for measuring the flow rate of the second condensed fluid C2 flowing through the first portion 93a.

[0058] A recovery unit 75 for recovering the mixed fluid C3 may be connected to the second condensing fluid path 93. The recovery unit 75 is, for example, a tank for storing the liquid mixed fluid C3.

[0059] The membrane separation system 100A further includes a supply fluid path 81, a permeable fluid path 82, and a non-permeable fluid path 83 as fluid pathways.

[0060] The supply fluid path 81 connects the supply fluid outlet 71b of the supply unit 71 and the supply fluid inlet 10a of the membrane separation unit 10, and is a path that guides the supply fluid F0 from the supply unit 71 to the supply space 13 of the membrane separation unit 10. A pump for controlling the flow rate of the supply fluid F0 may be placed in the supply fluid path 81. A concentration sensor for measuring the content of organic compound C in the supply fluid F0 may also be placed in the supply fluid path 81.

[0061] In the example shown in Figure 1, the supply 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 supply 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 membrane separation section 10.

[0062] The permeate fluid path 82 connects the permeate fluid outlet 10b of the membrane separation unit 10 and the permeate fluid inlet of the first condensation unit 41, and is a path that guides the permeate fluid F1 from the permeate space 14 of the membrane separation unit 10 to the first condensation unit 41. A concentration sensor for measuring the content of organic compound C in the permeate fluid F1 may be placed in the permeate fluid path 82.

[0063] The impermeable fluid path 83 is connected to the impermeable fluid outlet 10c of the membrane separation unit 10 and is a path for discharging the impermeable fluid F2 from the supply space 13 of the membrane separation unit 10. A concentration sensor for measuring the content of organic compound C in the impermeable fluid F2 may be placed in the impermeable fluid path 83.

[0064] In the example shown in Figure 1, the impermeable fluid path 83 connects the impermeable fluid outlet 10c of the membrane separation unit 10 to the fluid inlet of the filtration separation unit 62.

[0065] The membrane separation system 100A may further include a return path 95 that returns the first condensed fluid C1 discharged from the first condensation section 41 to at least one selected from the group consisting of a supply fluid path 81 and a non-permeable fluid path 83. With such a configuration, for example, during operation, the flow rate of the first condensed fluid C1 flowing through the bypass path 94 can be controlled by controlling the flow of a portion of the first condensed fluid C1 through the return path 95. Therefore, it is easy to adjust the content of organic compound C in the resulting mixed fluid C3.

[0066] In the membrane separation system 100A, the return path 95 is connected to the downstream end 92q of the first condensed fluid path 92 and merges with the supply fluid path 81 at the merging point 81p. In the example shown in Figure 1, the merging point 81p is located in the second portion 81b of the supply fluid path 81. That is, the first condensed fluid C1 returned to the supply fluid path 81 is supplied to the membrane separation unit 10. However, the merging point 81p may also be located in the first portion 81a of the supply fluid path 81. That is, the first condensed fluid C1 returned to the supply fluid path 81 may be supplied to the filtration separation unit 61.

[0067] The membrane separation system 100A may further include a heating device 45 for heating the supply fluid F0 to be supplied to the membrane separation unit 10. With such a configuration, for example, if the temperature of the supply fluid F0 is low, the temperature of the supply fluid F0 to be supplied to the membrane separation unit 10 can be increased by using the heating device 45. In the example of Figure 1, the heating device 45 is located downstream of the confluence point 81p in the second portion 81b of the supply fluid path 81. However, the heating device 45 may be located upstream of the confluence point 81p in the second portion 81b of the supply fluid path 81.

[0068] 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 the first condensation unit 41, the second condensation unit 42, the first cooling unit 49a, the second cooling unit 49b, etc.

[0069] Each of the pathways in the membrane separation system of this embodiment consists of, for example, metal or resin piping, unless otherwise specified.

[0070] [Supply Fluid] The supply fluid F0 contains a volatile organic compound C, such as an alcohol. The supply fluid F0 is typically a fermentation liquid. The fermentation liquid is obtained by using microorganisms to ferment a carbon source such as glucose or synthesis gas in an aqueous solution. Therefore, when the supply fluid F0 is a fermentation liquid, the supply fluid F0 contains the volatile organic compound C along with the microorganisms that produce the organic compound C. The microorganisms that produce the organic compound C are typically fungi. The supply fluid F0 contains, for example, the organic compound C, water, and microorganisms. The supply fluid F0 is typically an aqueous solution containing the organic compound C, water, and microorganisms.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] The supply 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 supply 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%.

[0078] 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 supply fluid F0 may be a fermented liquid containing organic compound C as a fermented product. However, the supply fluid F0 is not limited to a fermented liquid, but may also be wastewater or effluent discharged from a chemical plant or the like.

[0079] The supply 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 fungi. Examples of carbon sources include polysaccharides such as starch and monosaccharides such as glucose.

[0080] [Membrane Separation Unit] Figure 3 is a schematic cross-sectional view showing an example of a membrane separation unit 10. The membrane separation unit 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 supply fluid F0 is supplied. The second chamber 14 functions as a permeation space to which the permeate fluid F1 is supplied. The permeate fluid F1 is obtained by the supply fluid F0 permeating through the permeation vaporization membrane 11.

[0081] 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.

[0082] 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 supply fluid F0 to the supply space (first chamber 13). The permeable fluid outlet 10b is an opening for discharging the permeable fluid F1 from the permeable space (second chamber 14). The impermeable fluid outlet 10c is an opening for discharging the supply fluid F0 (impermeable fluid F2) that did not permeate the permeation vaporization membrane 11 from the supply space (first chamber 13). The supply fluid inlet 10a, the permeable fluid outlet 10b, and the impermeable fluid outlet 10c are each formed, for example, on the wall surface of the container 12.

[0083] The membrane separation unit 10 is suitable for a continuous flow membrane separation method. However, the membrane separation unit 10 may also be used in a batch membrane separation method.

[0084] [Permeation vaporization membrane] As described above, the permeation vaporization membrane 11 separates the supply fluid F0 into a permeable fluid F1 and an impermeable fluid F2.

[0085] Figure 4 is a schematic cross-sectional view showing an example of a permeation vaporization membrane 11 in the 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, for example, in direct contact with 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.

[0086] The permeation vaporization membrane 11 may further include a protective layer (not shown) that protects the separation functional layer 1.

[0087] (Separation Functional Layer) The separation functional layer 1 is a layer that can preferentially permeate specific components contained in the supply fluid F0. For example, the separation functional layer 1 is a layer that can preferentially permeate organic compound C contained in the supply fluid F0.

[0088] If the separation functional layer 1 is a layer that can preferentially allow organic compound C contained in the supply fluid F0 to pass through, it is preferable that the separation functional layer 1 contains 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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%.

[0096] If the separation functional layer 1 is a layer that can preferentially permeate organic compound C contained in the supply fluid F0, 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.

[0097] If the separation functional layer 1 is a layer that can preferentially permeate organic compound C contained in the supply fluid F0, 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.

[0098] (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.

[0099] 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.

[0100] (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.

[0101] 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.

[0102] (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.

[0103] <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 the membrane separation unit 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 the membrane separation unit; condensing the permeate fluid discharged from the membrane separation unit to produce a first condensed fluid by a first condensation unit; and condensing the permeate fluid discharged from the first condensation unit to produce a second condensed fluid by a second condensation unit. The operating method includes controlling the cooling temperature of the first condensation unit to a value higher than the cooling temperature of the second condensation unit. According to this operating method, the content of volatile organic compounds in the permeate fluid can be increased by a simple process.

[0104] Next, an example of an operating method for the membrane separation system 100A described above will be explained with reference to Figure 1. The operating method for the membrane separation system 100A includes, for example, reducing the pressure of the permeate space 14 of the membrane separation unit 10 by the depressurization unit 30 (step 1), separating the supply fluid F0 containing a volatile organic compound C into a permeate fluid F1 and an impermeable fluid F2 by the permeation vaporization membrane 11 of the membrane separation unit 10 (step 2), condensing the permeate fluid F1 discharged from the membrane separation unit 10 to produce a first condensed fluid C1 by the first condensation unit 41 (step 3), and condensing the permeate fluid F1 discharged from the first condensation unit 41 to produce a second condensed fluid C2 by the second condensation unit 42 (step 4). The operating method for the membrane separation system 100A also includes controlling the cooling temperature t1 of the first condensation unit 41 to a value higher than the cooling temperature t2 of the second condensation unit 42.

[0105] According to the operating method of the membrane separation system 100A, the cooling temperature t1 of the first condensation section 41 is controlled to a higher value than the cooling temperature t2 of the second condensation section 42. As a result, water contained in the permeate fluid F1 is more easily condensed in the first condensation section 41, which is located upstream. On the other hand, organic compound C contained in the permeate fluid F1 is more easily condensed in the second condensation section 42, which is located downstream. As a result, the content of organic compound C in the second condensed fluid C2 discharged from the second condensation section 42 can be increased compared to the content of organic compound C in the permeate fluid F1 discharged from the membrane separation section 10. According to the operating method of the membrane separation system 100A, the content of volatile organic compound C in the obtained permeate fluid can be increased beyond the membrane performance of the permeation vaporization membrane 11 through a simple process.

[0106] <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 membrane separation unit 10, a reduced pressure unit 30, a first condensation unit 41, and a second condensation unit 42. The first condensation unit 41 and the second condensation unit 42 are arranged in this order between the membrane separation unit 10 and the reduced pressure unit 30. The production method includes reducing the pressure of the permeate space 14 of the membrane separation unit 10 using the reduced pressure unit 30, separating the supply fluid F0 containing a volatile organic compound C into a permeate fluid F1 and an impermeable fluid F2 using the permeate vaporization membrane 11 of the membrane separation unit 10, condensing the permeate fluid F1 discharged from the membrane separation unit 10 to produce a first condensed fluid C1 using the first condensation unit 41, condensing the permeate fluid F1 discharged from the first condensation unit 41 to produce a second condensed fluid C2 using the second condensation unit 42, and recovering the organic compound C. The manufacturing method includes controlling the cooling temperature t1 of the first condensing section 41 to a value higher than the cooling temperature t2 of the second condensing section 42.

[0107] In the method for producing organic compounds according to this embodiment, the organic compound C may be an alcohol. According to this production method, the alcohol can be separated from the supply fluid F0 containing the volatile alcohol at a high concentration.

[0108] [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 5 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 5.

[0109] In the following section, we will further explain the case where the membrane separation unit 10 of the membrane separation system 100A described above includes a spiral-shaped membrane element, using Figure 5 as an example.

[0110] The spiral-shaped membrane element 15 shown in Figure 5 comprises a central tube 16 and membrane leaves 19 that are wrapped around the central tube 16 and have a permeable vaporization membrane 11.

[0111] The central tube 16 has a cylindrical shape. Through holes 16h are formed on the surface of the central tube 16 to allow the supply 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.

[0112] The membrane element 15 has a plurality of membrane leaves 19. Each membrane leaf 19 includes a permeable vaporization membrane 11 and a permeable flow channel material 17. For example, a membrane leaf 19 has two permeable vaporization membranes 11. The two permeable vaporization membranes 11 are overlapped and sealed on three sides to form a bag-like structure. The permeable flow channel material 17 is positioned between the two permeable vaporization membranes 11 so as to be located inside the bag-like structure. The permeable flow channel material 17 secures a space (permeable space) between the two permeable vaporization membranes 11 as a flow channel for the permeable fluid F1. In this way, the permeable flow channel material 17 is used in combination with the permeable vaporization membrane 11. The number of membrane leaves 19 is not particularly limited and can be, for example, 2 to 50.

[0113] 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 supply fluid F0.

[0114] 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.

[0115] 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).

[0116] The membrane separation unit 10, which includes the membrane element 15 shown in Figure 5, can be operated, for example, in the following way. First, a supply 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 depressurization unit 30. As a result, the permeate fluid F1 that has permeated through the permeation vaporization membrane 11 of the membrane leaf 19 moves into the inside of the central tube 16. The permeate fluid F1 is discharged to the outside through the central tube 16. The supply fluid F0 (non-permeable fluid F2) processed in the membrane separation unit 10 is discharged to the outside from the other end of the wound membrane leaf 19.

[0117] <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 5 of the membrane separation system of this embodiment will be described with reference to Figures 6 to 10. 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.

[0118] [Modification 1 of the Membrane Separation System] Figure 6 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 6 has a plurality of membrane separation units 200, each of which is equipped with a membrane separation unit 10, a reduced pressure unit 30, a first condensation unit 41, and a second condensation unit 42. The plurality of membrane separation units 10 of the plurality of membrane separation units 200 are connected in series. Except for this, the membrane separation system 100B has basically the same configuration as the membrane separation system 100A (Figure 1) described above. With the membrane separation system 100B, for each of the plurality of membrane separation units 200, it is possible to increase the content of volatile organic compounds C in the obtained permeate fluid beyond the membrane performance of the permeation vaporization membrane 11.

[0119] In the membrane separation system 100B, multiple membrane separation units 10 are connected in series so that the impermeable fluid F2 discharged from the membrane separation unit 10 located upstream is supplied to the membrane separation unit 10 located downstream. In the example shown in Figure 6, the membrane separation system 100B comprises three membrane separation units 200. In Figure 6, the membrane separation unit 200 with the second membrane separation unit 10 and the membrane separation unit 200 with the third membrane separation unit 10 are not shown.

[0120] In the membrane separation system 100B, the return path 95 merges with the supply fluid path 81 at the merging position 81p. In the example shown in Figure 6, the merging position 81p is located in the supply fluid path 81 connected to the supply space 13 of the first-stage membrane separation unit 10. That is, the first condensed fluid C1 returned to the supply fluid path 81 is supplied to the first-stage membrane separation unit 10. However, the merging position 81p may also be located in the supply fluid path connected to the supply space 13 of the second-stage membrane separation unit 10 (corresponding to the impermeable fluid path 83 connected to the supply space 13 of the first-stage membrane separation unit 10). That is, the first condensed fluid C1 returned to the supply fluid path 81 may be supplied to the second-stage membrane separation unit 10. Alternatively, the merging position 81p may also be located in the supply fluid path connected to the supply space 13 of the third-stage membrane separation unit 10 (corresponding to the impermeable fluid path 83 connected to the supply space 13 of the third-stage membrane separation unit 10). In other words, the first condensed fluid C1 returned to the supply fluid path 81 may be supplied to the third membrane separation unit 10.

[0121] [Modified Membrane Separation System 2] Figure 7 is a schematic diagram showing modified membrane separation system 2 of this embodiment. In the modified membrane separation system 100C shown in Figure 7, the return path 95 returns the first condensed fluid C1 discharged from the first condensation unit 41 to the impermeable fluid path 83. In other words, the first condensed fluid C1 discharged from the first condensation unit 41 connected to the membrane separation unit 10 located upstream is configured to merge with the supply fluid supplied to the membrane separation unit 10 located downstream. Except for this, the membrane separation system 100C has basically the same configuration as the membrane separation system 100B (Figure 6) described above. With the membrane separation system 100C, for each of the multiple membrane separation units 200, the content of volatile organic compounds C in the obtained permeable fluid can be increased beyond the membrane performance of the permeation vaporization membrane 11. In addition, for example, by controlling the flow of a portion of the first condensed fluid C1 to flow in the return path 95 during operation, the flow rate of the first condensed fluid C1 flowing in the bypass path 94 can be controlled. Therefore, it is easy to adjust the content of organic compound C in the resulting mixed fluid C3.

[0122] In the membrane separation system 100C, the return path 95 merges with the impermeable fluid path 83 at the merging position 83p. In the example shown in Figure 7, the merging position 83p is located in the impermeable fluid path 83 connected to the supply space 13 of the first-stage membrane separation unit 10. That is, the first condensed fluid C1 returned to the impermeable fluid path 83 is supplied to the second-stage membrane separation unit 10. However, the merging position 83p may also be located in the impermeable fluid path 83 connected to the supply space 13 of the second-stage membrane separation unit 10. That is, the first condensed fluid C1 returned to the impermeable fluid path 83 may be supplied to the third-stage membrane separation unit 10.

[0123] [Modification 3 of the Membrane Separation System] Figure 8 is a schematic diagram showing modification 3 of the membrane separation system of this embodiment. The membrane separation system 100D of modification 3 shown in Figure 8 includes a third condensation unit 43 that condenses the exhaust gas discharged from the depressurization unit 30 to produce a third condensed fluid C4. Except for this, the membrane separation system 100D has basically the same configuration as the membrane separation system 100A (Figure 1) described above. According to the membrane separation system 100D, the permeate fluid contained in the exhaust gas discharged from the depressurization unit 30 can be further condensed and recovered as the third condensed fluid C4.

[0124] Similar to the first condensation section 41 and the second condensation section 42, a water-cooled heat exchanger can be used as the third condensation section 43.

[0125] The membrane separation system 100D further includes a third condensing fluid path 96 for discharging the third condensing fluid C4 from the third condensing section 43. A recovery section 76 for recovering the third condensing fluid C4 may be connected to the third condensing fluid path 96. The recovery section 76 is, for example, a tank for storing the liquid third condensing fluid C4.

[0126] In the example shown in Figure 8, the third condensed fluid path 96 is connected to the recovery unit 76. However, the third condensed fluid path 96 may be configured to return the third condensed fluid C4 discharged from the third condensing unit 43 to at least one selected from the group consisting of the supply fluid path 81 and the impermeable fluid path 83. The third condensed fluid path 96 may also merge with the second condensed fluid path 93, or it may be connected to the recovery unit 75.

[0127] [Modification 4 of the Membrane Separation System] Figure 9 is a schematic diagram showing modification 4 of the membrane separation system of this embodiment. The membrane separation system 100E of modification 4 shown in Figure 9 does not have a bypass path 94 and a return path 95. Except for these, the membrane separation system 100E has basically the same configuration as the membrane separation system 100A (Figure 1) described above. With the membrane separation system 100E, the first condensed fluid C1 and the second condensed fluid C2, which have different organic compound C contents, can be recovered separately.

[0128] The membrane separation system 100E includes, instead of the recovery unit 75, a first recovery unit 74a for recovering the first condensed fluid C1 and a second recovery unit 74b for recovering the second condensed fluid C2. The first recovery unit 74a may be connected to the first condensed fluid path 92. The second recovery unit 74b may be connected to the second condensed fluid path 93. The first recovery unit 74a and the second recovery unit 74b are, for example, tanks for storing liquid condensed fluids.

[0129] The content of organic compound C in the mixed fluid may be controlled to a desired range by mixing the first condensed fluid C1 recovered in the first recovery unit 74a with the second condensed fluid C2 recovered in the second recovery unit 74b.

[0130] [Modification 5 of the Membrane Separation System] Figure 10 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 10 includes a mixing unit 77 for mixing the first condensed fluid C1 recovered in the first recovery unit 74a and the second condensed fluid C2 recovered in the second recovery unit 74b to obtain a mixed fluid C5. Except for this, the membrane separation system 100F has basically the same configuration as the membrane separation system 100E (Figure 9) described above. With the membrane separation system 100F, the content of organic compound C in the mixed fluid C5 can be controlled to a desired range.

[0131] The membrane separation system 100F includes a first mixing path 97 that guides the first condensed fluid C1 discharged from the recovery section 74 to the mixing section 77, and a second mixing path 98 that guides the second condensed fluid C2 discharged from the recovery section 75 to the mixing section 77. The first mixing path 97 merges with the second mixing path 98 at the confluence position 98p. With this configuration, the first condensed fluid C1 can be guided from the first recovery section 74a to the second mixing path 98.

[0132] The second mixing path 98 has a first portion 98a and a second portion 98b. The first portion 98a is the portion that connects the second recovery section 74b and the confluence position 98p. The second portion 98b is the portion that connects the confluence position 98p and the mixing section 77.

[0133] The membrane separation system 100F may further include a concentration sensor 54 provided in the second portion 98b of the second mixing path 98, and a flow rate control valve 56 provided in the first mixing path 97. The concentration sensor 54 is a concentration sensor for measuring the content of organic compound C in the mixed fluid C5 flowing through the second portion 98b of the second mixing path 98. The flow rate control valve 56 is a flow rate control valve for adjusting the flow rate of the first condensed fluid C1 flowing through the first mixing path 97. With this configuration, for example, the flow rate of the first condensed fluid C1 mixed with the second condensed fluid C2 can be controlled by adjusting the opening of the flow rate control valve 56 while monitoring the content of organic compound C in the mixed fluid C5 flowing through the second portion 98b of the second mixing path 98 using the concentration sensor 54. As a result, the content of organic compound C in the mixed fluid C5 can be controlled to a desired range.

[0134] The above-described embodiments are mutually applicable, insofar as they do not conflict with technical standards. The above embodiments and their variations may be combined with each other, insofar as they do not conflict with technical standards.

[0135] For example, in the membrane separation system 100A of this embodiment (Figure 1), the return path 95 may be configured to return the first condensed fluid C1 discharged from the first condensation section 41 to the impermeable fluid path 83.

[0136] The present invention will be described in more detail below with reference to calculation examples, but the present invention is not limited thereto.

[0137] [Preparation of Permeable Vapor-Related Film] First, a permeable vapor-related film was prepared by the following method. A silicone resin composition (coating solution) was prepared by adding 2 parts by weight of a curing agent containing polyorganosiloxane P1 (SRX212 containing a platinum catalyst, manufactured by Dow-Toray) and 10 parts by weight of silica filler (AEROSIL RX50, manufactured by Nippon Aerosil Co., Ltd.) to 100 parts by weight of a silicone main component (BY24-489, manufactured by Dow-Toray), which is a polyorganosiloxane mixture. A coating film (thickness 10 μm) was obtained by applying the coating solution onto a porous support. As the porous support, CF-30S (a laminate of a polysulfone microporous layer and a PET nonwoven fabric) manufactured by Nitto Denko Corporation was used. The coating film was formed on the polysulfone microporous layer of CF-30S. The weight-average molecular weight M of the silicone main component was 25200. Next, the coated film was heated at 150°C for 10 minutes to cure it, thereby creating a separation functional layer with a thickness of 4 μm. In this way, a permeable vaporization film was obtained.

[0138] (Calculation Examples 1-3) Simulations were performed when the membrane separation system 100A shown in Figure 1 was operated using the fabricated permeation vaporization membrane. Specifically, it was assumed that the permeation vaporization membrane 11 provided in the membrane separation unit 100A was the permeation vaporization membrane described above. It was assumed that the spiral-type membrane element shown in Figure 5 was used as the membrane separation unit 10. However, it was assumed that a filtration separation unit 61 was not provided between the supply unit 71 and the membrane separation unit 10, and that the supply fluid F0 was sent from the supply unit 71 to the membrane separation unit 10. In Calculation Examples 1-3, it was assumed that the first condensed fluid C1 was sent to the return path 95 and the bypass path 94.

[0139] In the operation of the membrane separation unit 10 in calculation examples 1 to 3, it was assumed that the supply fluid F0 sent from the supply unit 71 to the membrane separation unit 10 contains isopropanol (IPA) as the volatile organic compound C; that the permeate space 14 of the membrane separation unit 10 is depressurized by the depressurization unit 30 to obtain a gaseous permeate fluid F1; that the obtained permeate fluid F1 is condensed in the first condensation unit 41 to obtain a first condensed fluid C1; and that the permeate fluid F1 that was not condensed in the first condensation unit is condensed in the second condensation unit 42 to obtain a second condensed fluid C2. It was also assumed that the temperature of the supply fluid F0 supplied to the membrane separation unit 10 is raised to 40°C using the heating device 45.

[0140] (Calculation Example 4) A simulation was performed on the membrane separation system 500 shown in Figure 11 when it was operated using the fabricated permeation vaporization membrane. The membrane separation system 500 included a membrane separation section 510, a depressurization section 530 that depressurizes the permeation space of the membrane separation section 510, and a first condensation section 541 that condenses the permeate fluid F51 discharged from the membrane separation section 510 to produce a first condensed fluid C51. The first condensation section 541 was located between the membrane separation section 510 and the depressurization section 530. The membrane separation section 510 had a permeation vaporization membrane 511 that separates a supply fluid F50 containing a volatile organic compound C into a permeate fluid F51 and an impermeable fluid F52, and a supply space and a permeation space separated by the permeation vaporization membrane 511. In the membrane separation system 500, it was assumed that the above-described permeation vaporization membrane was used as the permeation vaporization membrane 511 provided in the membrane separation section 510. As the membrane separation section 510, it was assumed that a spiral-shaped membrane element as shown in Figure 5 would be used.

[0141] In the operation of the membrane separation unit 10 in calculation example 4, it was assumed that the supply fluid F50 sent from the supply unit 571 to the membrane separation unit 10 contains IPA as a volatile organic compound, that the permeable space of the membrane separation unit 510 is depressurized by the depressurization unit 530 to obtain a gaseous permeable fluid F51, and that the obtained permeable fluid F51 is condensed in the first condensation unit 541 to obtain a first condensed fluid C51. It was also assumed that the temperature of the supply fluid F50 supplied to the membrane separation unit 10 is raised to 40°C using the heating device 545.

[0142] In calculation examples 1 to 3, the IPA content in the first condensate C1 and the IPA content in the second condensate C2 were calculated assuming the conditions shown in Table 1 are met. In calculation example 4, the IPA content in the first condensate C51 was calculated assuming the conditions shown in Table 1 are met. The calculations were performed using Symmetry, a process modeling software from Schlumberger.

[0143]

[0144] Table 2 shows the simulation results for calculation examples 1 to 4.

[0145]

[0146] From the simulation results of Calculation Example 4, it can be seen that the IPA content in the permeate fluid (first condensed fluid C51) obtained from the permeate vaporization membrane 11, that is, the concentration of the permeate fluid which depends on the membrane performance of the permeate vaporization membrane 11, is 42 wt%. In contrast, in the simulation results of Calculation Examples 1 to 3, it was possible to increase the IPA content in the obtained permeate fluid (second condensed fluid C2) beyond the membrane performance of the permeate vaporization membrane 11. From these results, it can be seen that, with the membrane separation system of this embodiment, it is possible to increase the content of volatile organic compound C in the obtained permeate fluid beyond the membrane performance of the permeate vaporization membrane 11 with a simple configuration.

[0147] (Calculation Examples 5-7) A simulation was performed when the membrane separation system 100A shown in Figure 1 was operated using the fabricated permeation vaporization membrane. Specifically, it was assumed that the permeation vaporization membrane 11 provided in the membrane separation unit 100A was the permeation vaporization membrane described above. It was assumed that the membrane separation unit 10 was a spiral-type membrane element as shown in Figure 5. However, it was assumed that there was no filtration separation unit 61 between the supply unit 71 and the membrane separation unit 10, and that the supply fluid F0 was sent from the supply unit 71 to the membrane separation unit 10.

[0148] In the operation of the membrane separation unit 10 in calculation examples 5 to 7, it was assumed that the supply fluid F0 sent from the supply unit 71 to the membrane separation unit 10 contains isopropanol (IPA) as the volatile organic compound C; that the permeate space 14 of the membrane separation unit 10 is depressurized by the depressurization unit 30 to obtain a gaseous permeate fluid F1; that the obtained permeate fluid F1 is condensed in the first condensation unit 41 to obtain a first condensed fluid C1; and that the permeate fluid F1 that was not condensed in the first condensation unit 41 is condensed in the second condensation unit 42 to obtain a second condensed fluid C2. It was also assumed that the temperature of the supply fluid F0 supplied to the membrane separation unit 10 is raised to 40°C using the heating device 45.

[0149] In calculation examples 5 and 6, it was assumed that the first condensed fluid C1 was sent to the return path 95 and the bypass path 94, as described in the operating conditions below. <Operating conditions> ・Before the start of the mixing operation, the flow control valve 55 was closed and the first condensed fluid C1 was sent to the return path 95 and the bypass path 94. ・At the start of the mixing operation, the flow control valve 55 was slightly opened and the mixing operation was considered to have started when the IPA content in the mixed fluid C3 reached 46 wt%. ・Mixing operation (Calculation example 5) When the IPA content in the mixed fluid C3 exceeded 46 wt%, the opening of the flow control valve 55 was increased to increase the flow rate of the first condensed fluid C1 that merged into the second condensed fluid path 93. (Calculation example 6) When the IPA content in the mixed fluid C3 fell below 46 wt%, the opening of the flow control valve 55 was decreased to reduce the flow rate of the first condensed fluid C1 that merged into the second condensed fluid path 93.

[0150] In calculation example 7, it was assumed that the first condensed fluid C1 would not merge with the second condensed fluid path 93 via the bypass path 94, and that all (100%) of the first condensed fluid C1 would be sent to the return path 95.

[0151] In calculation examples 5 to 7, the IPA content in the first condensed fluid C1 and the IPA content in the second condensed fluid C2 were calculated for the case where the assumption conditions shown in Table 3 are met, both at the start of operation and after the mixing operation. The calculations were performed using Symmetry, a process modeling software from Schlumberger.

[0152]

[0153] Table 4 shows the simulation results for calculation examples 5 to 7.

[0154]

[0155] As can be seen from the comparison of the simulation results with calculation examples 5 to 7, the content of organic compound C in the resulting mixed fluid C3 could be adjusted by controlling the flow rate of the first condensed fluid C1 that merges into the second condensed fluid path 93 during operation.

[0156] 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 membrane separation unit, a pressure reduction unit, a first condensation unit, and a second condensation unit, wherein the membrane separation unit 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 pressure reduction unit reduces the pressure of the permeable space of the membrane separation unit, and the first condensation unit and the second condensation unit are arranged in this order between the membrane separation unit and the pressure reduction unit.

2. The membrane separation system according to claim 1, wherein the first condensation unit condenses the permeate fluid discharged from the membrane separation unit to produce a first condensed fluid, the second condensation unit condenses the permeate fluid discharged from the first condensation unit to produce a second condensed fluid, and the content of the organic compound in the second condensed fluid is higher than the content of the organic compound in the first condensed fluid.

3. The membrane separation system according to claim 1, wherein during operation, the cooling temperature of the first condensation section is controlled to be higher than the cooling temperature of the second condensation section.

4. The membrane separation system according to claim 2, further comprising: a discharge path for guiding the permeate fluid discharged from the first condensation section to the second condensation section; a first condensation fluid path for discharging the first condensation fluid from the first condensation section; and a second condensation fluid path for discharging the second condensation fluid from the second condensation section.

5. The membrane separation system according to claim 4, further comprising a bypass path for guiding the first condensed fluid discharged from the first condensation section to the second condensed fluid path.

6. The membrane separation system according to claim 5, further comprising: a bypass path that merges with the second condensing fluid path at a confluence point; a concentration sensor provided downstream of the confluence point of the second condensing fluid path; and a flow control valve provided in the bypass path.

7. The membrane separation system according to claim 6, wherein, based on the monitoring results from the concentration sensor, the opening of the flow control valve is adjusted so that the concentration of the mixed fluid flowing through the second condensed fluid path downstream of the confluence point satisfies a predetermined range.

8. The membrane separation system according to claim 2, further comprising: a supply fluid path for guiding the supply fluid into the supply space of the membrane separation unit; a permeable fluid path for discharging the permeable fluid from the permeable space of the membrane separation unit; a non-permeable fluid path for discharging the non-permeable fluid from the supply space of the membrane separation unit; and a return path for returning the first condensed fluid discharged from the first condensation unit to at least one selected from the group consisting of the supply fluid path and the non-permeable fluid path.

9. The membrane separation system according to claim 2, comprising a plurality of membrane separation units each having a membrane separation unit, a depressurization unit, a first condensation unit, and a second condensation unit, wherein the plurality of membrane separation units of 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.

10. The membrane separation system according to claim 9, wherein the first condensed fluid discharged from the first condenser connected to the membrane separation unit located upstream is configured to merge with the supply fluid supplied to the membrane separation unit located downstream.

11. The membrane separation system according to claim 1, further comprising a third condensation unit that condenses the exhaust gas discharged from the pressure reduction unit to generate a third condensed fluid.

12. The membrane separation system according to claim 2, further comprising a first recovery unit for recovering the first condensed fluid and a second recovery unit for recovering the second condensed fluid.

13. The membrane separation system according to claim 12, further comprising a mixing unit for mixing the first condensed fluid recovered in the first recovery unit and the second condensed fluid recovered in the second recovery unit to obtain a mixed fluid.

14. A method for operating a membrane separation system comprising a membrane separation unit, a depressurization unit, a first condensation unit, and a second condensation unit, wherein the first condensation unit and the second condensation unit are arranged in this order between the membrane separation unit and the depressurization unit, the membrane separation unit has a permeable vaporization membrane and a supply space and a permeation space separated by the permeable vaporization membrane, the method for operating a membrane separation system comprising: depressurizing the permeation space of the membrane separation unit with the depressurization unit; separating a supply fluid containing volatile organic compounds into a permeable fluid and an impermeable fluid with the permeable vaporization membrane of the membrane separation unit; condensing the permeable fluid discharged from the membrane separation unit with the first condensation unit to produce a first condensed fluid; and condensing the permeable fluid discharged from the first condensation unit with the second condensation unit to produce a second condensed fluid, the method for operating a membrane separation system comprising controlling the cooling temperature of the first condensation unit to a value higher than the cooling temperature of the second condensation unit.

Images