Membrane separation system and method for operating same

Abstract

The present invention provides a membrane separation system suitable for stable, continuous operation. A membrane separation system according to the present invention comprises a first membrane separation device having a reverse osmosis membrane, and a second membrane separation device having a pervaporation membrane. This membrane separation system executes a pressure-lowering operation for lowering the gauge pressure P1 of a first non-permeating fluid supplied to the second membrane separation device when at least one condition selected from the group consisting of the following conditions (1) and (2) is satisfied. (1) The gauge pressure P1 exceeds a first set value. (2) The difference (P1 - P2) between the gauge pressure P1 and the gauge pressure P2 of a second permeating fluid discharged from the second membrane separation device exceeds a second set value.

Description

Membrane separation system and operating method thereof

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

[0002] A membrane separation method has been developed as a method for separating volatile organic compounds from a solution containing the volatile organic compounds. As an example of membrane separation methods, a pervaporation method using a pervaporation membrane is known. The pervaporation method is suitable for separating volatile organic compounds from a solution containing the volatile organic compounds. Compared with distillation methods such as vacuum distillation, for example, the pervaporation method also tends to be able to suppress energy consumption and emission of gases such as carbon dioxide. As an example, Patent Document 1 discloses a system for separating and purifying ethanol from an ethanol fermentation broth using an ethanol-selective hydrophobic pervaporation membrane.

[0003] Japanese Patent No. 4048279

[0004] According to studies conducted by the present inventors, a membrane separation system combining a first membrane separation device having a reverse osmosis membrane and a second membrane separation device having a pervaporation membrane is suitable for performing efficient membrane separation treatment. However, the above membrane separation system has room for improvement from the viewpoint of stably performing continuous operation.

[0005] Accordingly, an object of the present invention is to provide a membrane separation system suitable for performing stable continuous operation.

[0006] The present invention provides a membrane separation system comprising: a first membrane separation device having a reverse osmosis membrane that separates a supply fluid into a first permeate fluid and a first non-permeate fluid; and a second membrane separation device having a pervaporation membrane that separates the first non-permeate fluid into a second permeate fluid and a second non-permeate fluid, wherein when at least one condition selected from the group consisting of the following conditions (1) and (2) is satisfied, a pressure reduction operation is performed to reduce the gauge pressure P1 of the first non-permeate fluid supplied to the second membrane separation device: (1) The gauge pressure P1 exceeds a first set value; (2) The difference (P1-P2) between the gauge pressure P1 and the gauge pressure P2 of the second permeate fluid discharged from the second membrane separation device exceeds a second set value.

[0007] Furthermore, the present invention provides a method for operating a membrane separation system comprising: a first membrane separation device having a reverse osmosis membrane for separating a supply fluid into a first permeable fluid and a first impermeable fluid; and a second membrane separation device having a permeation vaporization membrane for separating the first impermeable fluid into a second permeable fluid and a second impermeable fluid, wherein the operating method includes performing a depressurization operation to reduce the gauge pressure P1 of the first impermeable fluid supplied to the second membrane separation device when at least one condition selected from the group consisting of the following conditions (1) and (2) is met: (1) The gauge pressure P1 exceeds a first set value. (2) The difference (P1 - P2) between the gauge pressure P1 and the gauge pressure P2 of the second permeable fluid discharged from the second membrane separation device exceeds a second set value.

[0008] Furthermore, the present invention provides a membrane separation system comprising: a first membrane separation device having a reverse osmosis membrane for separating a supply fluid into a first permeable fluid and a first impermeable fluid; and a second membrane separation device having a permeation vaporization membrane for separating the first impermeable fluid into a second permeable fluid and a second impermeable fluid, wherein at least one selected from the group consisting of the following requirements (I) and (II) is satisfied: (I) During operation, the gauge pressure P1 of the first impermeable fluid supplied to the second membrane separation device is maintained at 1 MPa or less. (II) During operation, the difference (P1 - P2) between the gauge pressure P1 of the first impermeable fluid supplied to the second membrane separation device and the gauge pressure P2 of the second permeable fluid discharged from the second membrane separation device is maintained at 1.1 MPa or less.

[0009] According to the present invention, a membrane separation system suitable for stable continuous operation can be provided.

[0010] This is a schematic diagram of the membrane separation system of Embodiment 1. This is a schematic cross-sectional view showing an example of the first membrane separation device. This is a schematic cross-sectional view showing an example of the second membrane separation device. This is a schematic cross-sectional view showing an example of a permeation vaporization membrane. This is a schematic cross-sectional view showing another example of the second membrane separation device. This is a schematic diagram of the membrane separation system of Embodiment 2. This is a schematic cross-sectional view showing an example of the third membrane separation device. This is a schematic diagram of the membrane separation system of Embodiment 3. This is a schematic diagram of the membrane separation system of Embodiment 4.

[0011] A membrane separation system according to a first aspect of the present invention comprises: a first membrane separation device having a reverse osmosis membrane for separating a supply fluid into a first permeable fluid and a first impermeable fluid; and a second membrane separation device having a permeation vaporization membrane for separating the first impermeable fluid into a second permeable fluid and a second impermeable fluid, wherein a depressurization operation is performed to reduce the gauge pressure P1 of the first impermeable fluid supplied to the second membrane separation device when at least one condition selected from the group consisting of the following conditions (1) and (2) is met: (1) The gauge pressure P1 exceeds a first set value. (2) The difference (P1 - P2) between the gauge pressure P1 and the gauge pressure P2 of the second permeable fluid discharged from the second membrane separation device exceeds a second set value.

[0012] In a second embodiment of the present invention, for example, the membrane separation system according to the first embodiment further comprises a connection path connected to the first membrane separation device and the second membrane separation device, for sending the first impermeable fluid from the first membrane separation device to the second membrane separation device.

[0013] In a third embodiment of the present invention, for example, the membrane separation system according to the second embodiment further comprises a branch path branching off from the connection path, and the depressurization operation is performed by sending a portion of the first impermeable fluid from the connection path to the branch path.

[0014] In a fourth embodiment of the present invention, for example, the membrane separation system according to the third embodiment further comprises a storage unit for storing the supply fluid, and the branching path is connected to the storage unit.

[0015] In a fifth embodiment of the present invention, for example, a membrane separation system according to a third or fourth embodiment further comprises a supply path connected to the first membrane separation device for supplying the supply fluid to the first membrane separation device, wherein the branch path is connected to the supply path.

[0016] In a sixth embodiment of the present invention, for example, a membrane separation system according to any one of the third to fifth embodiments further comprises a third membrane separation device having a permeable vaporization membrane, wherein the branch path is connected to the third membrane separation device.

[0017] In a seventh embodiment of the present invention, for example, a membrane separation system according to any one of the third to sixth embodiments further comprises a recovery unit for recovering a portion of the first impermeable fluid, wherein the branching path is connected to the recovery unit.

[0018] In an eighth aspect of the present invention, for example, a membrane separation system according to any one of the third to seventh aspects further comprises a valve for adjusting the flow rate of the first impermeable fluid sent from the connection path to the branch path.

[0019] In a ninth aspect of the present invention, for example, the membrane separation system according to the eighth aspect controls the depressurization operation by at least one operation selected from the group consisting of (A) and (B) below: (A) Adjust the opening of the valve so that the gauge pressure P1 falls below the first set value. (B) Adjust the opening of the valve so that the difference (P1 - P2) falls below the second set value.

[0020] In a tenth aspect of the present invention, for example, a membrane separation system according to any one of the second to ninth aspects further comprises a pressure sensor arranged in the connection path for measuring the gauge pressure P1.

[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 pressure sensor for measuring the gauge pressure P2.

[0022] In a twelfth aspect of the present invention, for example, in a membrane separation system according to any one of the first to eleventh aspects, the permeation vaporization membrane has a separation functional layer containing a hydrophobic material.

[0023] In a thirteenth aspect of the present invention, for example, in the membrane separation system according to the twelfth aspect, the hydrophobic material includes a compound having a siloxane bond.

[0024] In a fourteenth aspect of the present invention, for example, in a membrane separation system according to any one of the first to thirteenth aspects, the second membrane separation device has a spiral membrane element including the permeation vaporization membrane.

[0025] In a 15th aspect of the present invention, for example, in a membrane separation system according to any one of the first to 14th aspects, the supply fluid is a solution containing a volatile organic compound.

[0026] In a sixteenth aspect of the present invention, for example, in the membrane separation system according to the fifteenth aspect, the solution comprises water and an alcohol as the organic compound.

[0027] A method for operating a membrane separation system according to a 17th aspect of the present invention is a method for operating a membrane separation system comprising: a first membrane separation device having a reverse osmosis membrane for separating a supply fluid into a first permeable fluid and a first impermeable fluid; and a second membrane separation device having a permeation vaporization membrane for separating the first impermeable fluid into a second permeable fluid and a second impermeable fluid, wherein the method for operating a membrane separation system includes performing a depressurization operation to reduce the gauge pressure P1 of the first impermeable fluid supplied to the second membrane separation device when at least one condition selected from the group consisting of the following conditions (1) and (2) is met: (1) The gauge pressure P1 exceeds a first set value. (2) The difference (P1 - P2) between the gauge pressure P1 and the gauge pressure P2 of the second permeable fluid discharged from the second membrane separation device exceeds a second set value.

[0028] A membrane separation system according to the 18th aspect of the present invention comprises: a first membrane separation device having a reverse osmosis membrane for separating a supply fluid into a first permeable fluid and a first impermeable fluid; and a second membrane separation device having a permeation vaporization membrane for separating the first impermeable fluid into a second permeable fluid and a second impermeable fluid, wherein at least one selected from the group consisting of the following requirements (I) and (II) is satisfied: (I) During operation, the gauge pressure P1 of the first impermeable fluid supplied to the second membrane separation device is maintained at 1 MPa or less. (II) During operation, the difference (P1 - P2) between the gauge pressure P1 of the first impermeable fluid supplied to the second membrane separation device and the gauge pressure P2 of the second permeable fluid discharged from the second membrane separation device is maintained at 1.1 MPa or less.

[0029] In a 19th embodiment of the present invention, for example, the membrane separation system according to the 18th embodiment further comprises a connection path connected to the first membrane separation device and the second membrane separation device, for sending the first impermeable fluid from the first membrane separation device to the second membrane separation device.

[0030] In a 20th embodiment of the present invention, for example, the membrane separation system according to the 19th embodiment further comprises a branch path branching off from the connection path, and a depressurization operation is performed to reduce the gauge pressure P1 of the first impermeable fluid by sending a portion of the first impermeable fluid from the connection path to the branch path.

[0031] In a 21st embodiment of the present invention, for example, the membrane separation system according to the 20th embodiment further comprises a storage unit for storing the supply fluid, and the branching path is connected to the storage unit.

[0032] In a 22nd embodiment of the present invention, for example, a membrane separation system according to a 20th or 21st embodiment further comprises a supply path connected to the first membrane separation device for supplying the supply fluid to the first membrane separation device, wherein the branch path is connected to the supply path.

[0033] In a 23rd embodiment of the present invention, for example, a membrane separation system according to any one of the 20th to 22nd embodiments further comprises a third membrane separation device having a permeable vaporization membrane, wherein the branch path is connected to the third membrane separation device.

[0034] In a 24th embodiment of the present invention, for example, a membrane separation system according to any one of the 20th to 23rd embodiments further comprises a recovery unit for recovering a portion of the first impermeable fluid, wherein the branching path is connected to the recovery unit.

[0035] In a 25th embodiment of the present invention, for example, a membrane separation system according to any one of the 20th to 24th embodiments further comprises a valve for adjusting the flow rate of the first impermeable fluid sent from the connection path to the branch path.

[0036] In a 26th aspect of the present invention, for example, the membrane separation system according to the 25th aspect controls the depressurization operation by at least one operation selected from the group consisting of (A) and (B) below: (A) Adjust the opening of the valve so that the gauge pressure P1 falls below a first set value. (B) Adjust the opening of the valve so that the difference (P1 - P2) falls below a second set value.

[0037] In a 27th aspect of the present invention, for example, a membrane separation system according to any one of the 19th to 26th aspects further comprises a pressure sensor arranged in the connection path for measuring the gauge pressure P1.

[0038] In the 28th aspect of the present invention, for example, a membrane separation system according to any one of the 18th to 27th aspects further comprises a pressure sensor for measuring the gauge pressure P2.

[0039] In a 29th aspect of the present invention, for example, in a membrane separation system according to any one of the 18th to 28th aspects, the permeation vaporization membrane has a separation functional layer containing a hydrophobic material.

[0040] In a 30th aspect of the present invention, for example, in the membrane separation system according to the 29th aspect, the hydrophobic material includes a compound having a siloxane bond.

[0041] In a 31st embodiment of the present invention, for example, in a membrane separation system according to any one of the 18th to 30th embodiments, the second membrane separation device has a spiral membrane element including the permeation vaporization membrane.

[0042] In a 32nd aspect of the present invention, for example, in a membrane separation system according to any one of the 18th to 31st aspects, the supply fluid is a solution containing a volatile organic compound.

[0043] In a 33rd aspect of the present invention, for example, in the membrane separation system according to the 32nd aspect, the solution comprises water and an alcohol as the organic compound.

[0044] A method of operating a membrane separation system according to a 34th aspect of the present invention is a method of operating a membrane separation system comprising: a first membrane separation device having a reverse osmosis membrane that separates a feed fluid into a first permeate fluid and a first non-permeate fluid; and a second membrane separation device having a pervaporation membrane that separates the first non-permeate fluid into a second permeate fluid and a second non-permeate fluid, wherein at least one selected from the group consisting of the following requirements (i) and (ii) is satisfied. (i) The operating method includes maintaining a gauge pressure P1 of the first non-permeate fluid supplied to the second membrane separation device at 1 MPa or less. (ii) The operating method includes maintaining a difference (P1-P2) between the gauge pressure P1 of the first non-permeate fluid supplied to the second membrane separation device and a gauge pressure P2 of the second permeate fluid discharged from the second membrane separation device at 1.1 MPa or less.

[0045] Hereinafter, details of the present invention will be described, but the following description is not intended to limit the present invention to specific embodiments.

[0046] <Embodiment of Membrane Separation System> The membrane separation system of the present embodiment includes a first membrane separation device and a second membrane separation device. The first membrane separation device has a reverse osmosis membrane (RO membrane) that separates a feed fluid into a first permeate fluid and a first non-permeate fluid. The second membrane separation device has a pervaporation membrane (PV membrane) that separates the above-mentioned first non-permeate fluid into a second permeate fluid and a second non-permeate fluid.

[0047] The membrane separation system of the present embodiment executes a pressure reduction operation to lower the gauge pressure P1 of the first non-permeate fluid supplied to the second membrane separation device when at least one condition selected from the group consisting of the following conditions (1) and (2) is satisfied. (1) The above-mentioned gauge pressure P1 exceeds a first set value. (2) A difference (P1-P2) between the above-mentioned gauge pressure P1 and a gauge pressure P2 of the second permeate fluid discharged from the second membrane separation device exceeds a second set value.

[0048] As described above, a membrane separation system combining a first membrane separation device having an RO membrane and a second membrane separation device having a PV membrane is suitable for efficient membrane separation processing. However, according to the inventors' studies, when this membrane separation system is operated continuously, the flow rate of the first impermeable fluid discharged from the first membrane separation device tends to increase, and the pressure of the fluid tends to increase. It is thought that the flow rate of the first impermeable fluid fluctuates depending on the state of the RO membrane during operation of the membrane separation system (for example, whether or not fouling occurs) and the temperature of the supply fluid.

[0049] When the pressure of the first impermeable fluid supplied to the second membrane separator increases, excessive pressure is applied to the PV membrane in the second membrane separator, which tends to deform the PV membrane. In particular, if the second membrane separator has a spiral-type membrane element, excessive pressure on the PV membrane can cause it to collapse into adjacent spacers within the element. When the PV membrane deforms or collapses, the separation performance of the PV membrane decreases, making it difficult to obtain the second permeable fluid or second impermeable fluid with the desired composition.

[0050] To prevent excessive pressure from being applied to the PV membrane, it is conceivable to disconnect the first membrane separation unit from the membrane separation system and avoid continuous processing. However, in this case, the first non-permeable fluid discharged from the first membrane separation unit would need to be temporarily stored in a tank, which would significantly increase the carbon footprint.

[0051] In the membrane separation system of this embodiment, as described above, when at least one condition selected from the group consisting of conditions (1) and (2) is met, a depressurization operation is performed to reduce the gauge pressure P1 of the first impermeable fluid supplied to the second membrane separation device. This prevents excessive pressure from being applied to the PV membrane of the second membrane separation device, and suppresses deformation and collapse of the PV membrane during operation of the membrane separation system. Thus, the membrane separation system of this embodiment is suitable for stable continuous operation.

[0052] In the membrane separation system of this embodiment, the above-mentioned depressurization operation is preferably performed by extracting a portion of the first impermeable fluid that is sent to the second membrane separation device. As an example, the membrane separation system is connected to the first membrane separation device and the second membrane separation device, and is provided with a connection path for sending the first impermeable fluid from the first membrane separation device to the second membrane separation device, and further includes a branch path that branches off from the connection path. With this configuration, the depressurization operation can be performed by sending a portion of the first impermeable fluid from the connection path to the branch path.

[0053] In this embodiment, the depressurization operation is not limited to the method described above. For example, the depressurization operation may be performed using a depressurization unit (e.g., a throttle valve) located in the above connection path. This depressurization unit is typically a component that depressurizes the first non-permeable fluid even during normal operation of the membrane separation system. In this specification, a depressurization operation using a depressurization unit means an operation in which the depressurization conditions by the depressurization unit are changed from those during normal operation to further depressurize the first non-permeable fluid.

[0054] Furthermore, according to the inventors' studies, performing a depressurization operation using the above-mentioned depressurization section can cause fluctuations in the pressure of the supply fluid within the first membrane separation device, which may result in the failure to obtain the first permeate fluid or the first impermeable fluid with the desired composition. In contrast, a depressurization operation that extracts a portion of the first impermeable fluid sent to the second membrane separation device has the advantage of minimizing fluctuations in the composition of the first permeate fluid and the first impermeable fluid.

[0055] In the membrane separation system of this embodiment, it is preferable that the gauge pressure P1 of the first impermeable fluid supplied to the second membrane separation device is maintained at 1 MPa or less (preferably 0.5 MPa or less, more preferably 0.1 MPa or less, and even more preferably 0.08 MPa or less) by combining a depressurization operation with normal operation.

[0056] Furthermore, in the membrane separation system of this embodiment, it is preferable that the difference (P1-P2) between the gauge pressure P1 of the first impermeable fluid supplied to the second membrane separation device and the gauge pressure P2 of the second permeable fluid discharged from the second membrane separation device is maintained at 1.1 MPa or less (preferably 0.5 MPa or less, more preferably 0.2 MPa or less) by combining a depressurization operation with normal operation.

[0057] Another aspect of the present invention provides a membrane separation system comprising: a first membrane separation device having a reverse osmosis membrane for separating a supply fluid into a first permeable fluid and a first impermeable fluid; and a second membrane separation device having a permeation vaporization membrane for separating the first impermeable fluid into a second permeable fluid and a second impermeable fluid, wherein at least one selected from the group consisting of the following requirements (I) and (II) is satisfied. (I) During operation, the gauge pressure P1 of the first impermeable fluid supplied to the second membrane separation device is maintained at 1 MPa or less. (II) During operation, the difference (P1 - P2) between the gauge pressure P1 of the first impermeable fluid supplied to the second membrane separation device and the gauge pressure P2 of the second permeable fluid discharged from the second membrane separation device is maintained at 1.1 MPa or less. In the above membrane separation system, it is preferable that both of the above requirements (I) and (II) are satisfied. However, in some cases, only one of the above requirements (I) and (II) may be satisfied.

[0058] Furthermore, from another aspect, the present invention provides a method for operating a membrane separation system comprising: a first membrane separation device having a reverse osmosis membrane for separating a supply fluid into a first permeable fluid and a first impermeable fluid; and a second membrane separation device having a permeation vaporization membrane for separating the first impermeable fluid into a second permeable fluid and a second impermeable fluid, wherein at least one selected from the group consisting of the following requirements (i) and (ii) is satisfied. (i) The above operating method includes maintaining the gauge pressure P1 of the first impermeable fluid supplied to the second membrane separation device at 1 MPa or less. (ii) The operating method includes maintaining the difference (P1 - P2) between the gauge pressure P1 of the first impermeable fluid supplied to the second membrane separation device and the gauge pressure P2 of the second permeable fluid discharged from the second membrane separation device at 1.1 MPa or less. It is preferable that both of the above requirements (i) and (ii) are satisfied in the above operating method for the membrane separation system. However, in some cases, only one of the above requirements (i) and (ii) may be met.

[0059] In this specification, "normal operation" typically means steady-state operation. When simply referred to as "operation," it means operation from the start of operation until the system switches to steady-state operation, excluding the initial period of operation before the system switches to steady-state operation (for example, the period from the start of operation until one hour has elapsed).

[0060] Hereinafter, preferred embodiments 1 to 4 of this embodiment will be described with reference to Figures 1 to 9. Elements common to embodiments 1 to 4 are denoted by the same reference numerals, and their descriptions may be omitted. The descriptions of embodiments 1 to 4 are mutually applicable, as long as they do not conflict technically. Furthermore, embodiments 1 to 4 may be combined with each other, as long as they do not conflict technically.

[0061] [Embodiment 1] Figure 1 is a schematic diagram of the membrane separation system 100 of Embodiment 1. As shown in Figure 1, the membrane separation system 100 comprises a first membrane separation device 10 and a second membrane separation device 20. The first membrane separation device 10 is a membrane separation device that performs membrane separation of a supply fluid using an RO membrane 11. The RO membrane 11 of the first membrane separation device 10 can separate the supply fluid into a first permeable fluid and a first impermeable fluid. The second membrane separation device 20 is a membrane separation device that performs membrane separation of the first impermeable fluid discharged from the first membrane separation device 10 using a PV membrane 21. The PV membrane 21 of the second membrane separation device 20 can separate the first impermeable fluid into a second permeable fluid and a second impermeable fluid.

[0062] In this embodiment, the supply fluid supplied to the first membrane separation device 10 is typically a liquid, and preferably a solution S containing a volatile organic compound C.

[0063] The membrane separation system 100 preferably further comprises a storage section 30 and a supply path 40. The storage section 30 is typically a storage tank for storing the supply fluid to be supplied to the first membrane separation device 10. The storage section 30 may also be a fermentation tank for producing organic compound C by fermentation of a carbon source by microorganisms, or it may be a waste liquid tank for storing waste liquid or wastewater discharged from a chemical plant or the like.

[0064] The supply path 40 is connected to the outlet 31 of the storage unit 30 and the supply fluid inlet (inlet 13a) of the first membrane separator 10, and is a path for supplying supply fluid from the storage unit 30 to the first membrane separator 10. Preferably, a pump 50 for controlling the flow rate and pressure of the supply fluid is provided in the supply path 40. The pump 50 can send pressurized supply fluid to the first membrane separator 10. A heat exchanger (not shown) for adjusting the temperature of the supply fluid may also be provided in the supply path 40. In addition, a pressure sensor (not shown) for measuring the gauge pressure PS of the supply fluid supplied to the first membrane separator 10 may also be provided in the supply path 40.

[0065] The membrane separation system 100 preferably further comprises a first discharge path 41 and a connection path 42. The first discharge path 41 is connected to the permeate fluid outlet (outlet 14a) of the first membrane separation device 10 and is a path for discharging the first permeate fluid from the first membrane separation device 10. The first discharge path 41 has an opening (outlet 41a) formed therein for discharging the first permeate fluid from the first discharge path 41.

[0066] The connection path 42 is connected to the impermeable fluid outlet (outlet 13b) of the first membrane separation device 10 and the impermeable fluid inlet (inlet 23a) of the second membrane separation device 20, respectively, and is a path for supplying the first impermeable fluid from the first membrane separation device 10 to the second membrane separation device 20.

[0067] Preferably, a pressure reduction section 51 and pressure sensors 52 and 53 are arranged in the connection path 42. The pressure reduction section 51 is a component for reducing the pressure of the first impermeable fluid discharged from the first membrane separator 10, and can be a throttle valve, a regulator (pressure regulating valve), etc. The pressure reduction section 51 is typically a throttle valve. The pressure sensors 52 and 53 are arranged, for example, between the pressure reduction section 51 and the second membrane separator 20, in this order along the direction of movement of the first impermeable fluid. Pressure sensor 52 is a sensor for measuring the gauge pressure P3 of the first impermeable fluid that has passed through the pressure reduction section 51. Pressure sensor 53 is a sensor for measuring the gauge pressure P1 of the first impermeable fluid supplied to the second membrane separator 20. In particular, it is preferable that the membrane separation system 100 includes a pressure sensor 53 for measuring the gauge pressure P1.

[0068] The membrane separation system 100 preferably further comprises a second discharge path 43 and a third discharge path 44. The second discharge path 43 is connected to the permeate fluid outlet (outlet 24a) of the second membrane separation device 20 and is a path for discharging the second permeate fluid from the second membrane separation device 20. The second discharge path 43 has an opening (discharge port 43a) for discharging the second permeate fluid from the second discharge path 43. It is preferable that a pressure sensor 54 for measuring the gauge pressure P2 of the second permeate fluid discharged from the second membrane separation device 20 is placed in the second discharge path 43. In other words, it is preferable that the membrane separation system 100 is equipped with a pressure sensor 54 for measuring the gauge pressure P2.

[0069] A pressure reducing device (not shown) for reducing the pressure within the permeate space of the second membrane separation device 20 may be provided in the second discharge path 43. The pressure reducing device is preferably 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 vacuum pump 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 within the permeate space of the second membrane separation device 20 can be appropriately adjusted.

[0070] The depressurization device may be a multi-stage Roots vacuum pump or a diaphragm vacuum pump. A multi-stage Roots vacuum pump, for example, can quickly raise the pressure in a space to a predetermined value and offer excellent durability. A diaphragm vacuum pump, for example, can perform depressurization operations efficiently and at low cost.

[0071] The third discharge path 44 is connected to the impermeable fluid outlet (outlet 23b) of the second membrane separator 20 and is a path for discharging the second impermeable fluid from the second membrane separator 20. The third discharge path 44 has an opening (outlet 44a) formed therein for discharging the second impermeable fluid from the third discharge path 44.

[0072] The membrane separation system 100 preferably further includes a branch path 45 that branches off from the connection path 42. Typically, the branch path 45 branches off from the connection path 42 at a branching position 60 located between the pressure sensors 52 and 53. In the example of Figure 1, the branch path 45 is connected to the inlet 32 ​​of the storage unit 30. In the example of Figure 1, the branch path 45 functions as a return line that can return a portion of the first impermeable fluid from the connection path 42 to the storage unit 30. The branch path 45 may be connected to the supply path 40 instead of the storage unit 30, or together with the storage unit 30. In this case, the branch path 45 may merge with the supply path 40 at a merging position (not shown) located between the storage unit 30 and the pump 50.

[0073] The membrane separation system 100 preferably further comprises a valve 55 that adjusts the flow rate of the first impermeable fluid sent from the connection path 42 to the branch path 45. The valve 55 is typically a flow control valve. The valve 55 may also be a simple on / off valve. In the example in Figure 1, the valve 55 is located in the branch path 45. However, the valve 55 may be located in the connection path 42. More specifically, the valve 55 may be a three-way valve located at the branch position 60 of the connection path 42.

[0074] The membrane separation system 100 may further include a controller 90 that controls each component of the membrane separation system 100. The controller 90 is, for example, a DSP (Digital Signal Processor) that includes an A / D conversion circuit, input / output circuits, arithmetic circuits, and a memory device. The controller 90 stores a program for properly operating the membrane separation system 100. For example, the controller 90 can receive pressure information from each pressure sensor and control the valve 55 based on this information. More specifically, the controller 90 can perform the above-described depressurization operation by adjusting the opening degree of the valve 55 when at least one condition selected from the group consisting of conditions (1) and (2) above is met. The opening degree of the valve 55 can be adjusted, for example, by electrically controlling the actuator of the valve 55.

[0075] The controller 90 may be configured to control the valve 55 based on a given command, or it may be configured to automatically control the valve 55 when the above-described conditions (1) or (2) are met. Alternatively, the controller 90 may not control the valve 55, and the worker may operate the valve 55.

[0076] In particular, the membrane separation system 100 of this embodiment is preferably controlled by at least one operation selected from the group consisting of (A) and (B) below. In (A) and (B) below, the opening degree of the valve 55 can be appropriately adjusted according to the degree of deviation between the gauge pressure P1 and the first set value, and the degree of deviation between the difference (P1-P2) and the second set value. (A) Adjust the opening degree of the valve 55 so that the gauge pressure P1 falls below the first set value. (B) Adjust the opening degree of the valve 55 so that the difference (P1-P2) falls below the second set value.

[0077] Each of the pathways in the membrane separation system 100 is composed of, for example, metal or resin piping, unless otherwise specified.

[0078] (First Membrane Separation Apparatus) As shown in Figure 2, the first membrane separation apparatus 10 comprises an RO membrane 11 and a tank 12. The tank 12 has a first chamber 13 and a second chamber 14. The first chamber 13 functions as a supply space to which a supply fluid S0 is supplied. The second chamber 14 functions as a permeation space to which a first permeate fluid S1 is supplied. The first permeate fluid S1 is obtained by the supply fluid S0 permeating through the RO membrane 11. The RO membrane 11 is located inside the tank 12. Inside the tank 12, the RO membrane 11 separates the first chamber 13 and the second chamber 14. The RO membrane 11 extends from one of a pair of walls of the tank 12 to the other.

[0079] The first chamber 13 has an inlet 13a and an outlet 13b. The second chamber 14 has an outlet 14a. The inlet 13a of the first chamber 13 is an opening for supplying the supply fluid S0 to the first membrane separation device 10. The outlet 14a of the second chamber 14 is an opening for discharging the first permeate fluid S1 from the first membrane separation device 10. The outlet 13b of the first chamber 13 is an opening for discharging the supply fluid S0 (first non-permeate fluid S2) that did not permeate the RO membrane 11 from the first membrane separation device 10. Each of the inlet 13a, outlet 13b, and outlet 14a is formed, for example, on the wall surface of the tank 12.

[0080] The first membrane separation apparatus 10 is suitable for a continuous flow membrane separation method. However, the first membrane separation apparatus 10 may also be used for a batch membrane separation method.

[0081] Known RO membranes can be used as RO membranes 11. In this specification, "RO membrane" means a membrane that removes 93% or more of sodium chloride when a test solution with a sodium chloride concentration of 2000 mg / L is filtered at an operating pressure of 1.5 MPa.

[0082] The RO film 11 typically includes a dense layer and a porous support that supports the dense layer. The thickness of the dense layer is not particularly limited, but is, for example, 0.001 to 2 μm, and preferably 0.005 to 1 μm. As the porous support, one described later for the PV film 21 can be used.

[0083] The material for the dense layer is not particularly limited, and polymer materials such as modified polyethersulfone, cellulose ester (e.g., cellulose acetate), polyamide (e.g., aromatic polyamide), polyester, polyimide, vinyl polymer, polyethersulfone, and ethylene-vinyl alcohol copolymer can be used.

[0084] The thickness of the RO film 11 is not particularly limited, but is preferably 10 to 200 μm, and more preferably 20 to 75 μm.

[0085] The molecular weight cutoff of the RO membrane 11 is, for example, 10,000 or less, preferably 5,000 or less, and more preferably 1,000 or less. The lower limit of the molecular weight cutoff of the RO membrane 11 is not particularly limited, and is, for example, 100. The molecular weight cutoff of the RO membrane 11 can be determined by the following method. First, prepare a plurality of polyethylene glycols having different average molecular weights and monodisperse molecular weight distributions. An aqueous solution containing one of the plurality of polyethylene glycols at a concentration of 5,000 ppm is prepared at a temperature of 25°C and a pressure of 4 kg / cm². 2 Under these conditions, the material is supplied to the surface of the RO membrane 11. This allows the exclusion rate of polyethylene glycol to be measured. The exclusion rate of other polyethylene glycols is measured in a similar manner. A fractionation curve is created showing the relationship between the obtained exclusion rates and the average molecular weight of polyethylene glycol. Based on the fractionation curve, the average molecular weight of polyethylene glycol at which the exclusion rate is 90% is identified. The identified average molecular weight can be considered as the fractionation molecular weight of the RO membrane 11.

[0086] (Second Membrane Separation Apparatus) As shown in Figure 3, the second membrane separation apparatus 20 comprises a PV membrane 21 and a tank 22. The tank 22 has a first chamber 23 and a second chamber 24. The first chamber 23 functions as a supply space to which a first impermeable fluid S2 is supplied. The second chamber 24 functions as a permeation space to which a second permeable fluid L1 is supplied. The second permeable fluid L1 is obtained by the first impermeable fluid S2 permeating through the PV membrane 21. The PV membrane 21 is located inside the tank 22. Inside the tank 22, the PV membrane 21 separates the first chamber 23 and the second chamber 24. The PV membrane 21 extends from one of a pair of walls of the tank 22 to the other.

[0087] The first chamber 23 has an inlet 23a and an outlet 23b. The second chamber 24 has an outlet 24a. The inlet 23a of the first chamber 23 is an opening for supplying the first impermeable fluid S2 to the second membrane separator 20. The outlet 24a of the second chamber 24 is an opening for discharging the second permeable fluid L1 from the second membrane separator 20. The outlet 23b of the first chamber 23 is an opening for discharging the first impermeable fluid S2 (second impermeable fluid L2) that did not permeate the PV membrane 21 from the second membrane separator 20. Each of the inlet 23a, outlet 23b, and outlet 24a is formed, for example, on the wall surface of the tank 22.

[0088] The second membrane separation apparatus 20 is suitable for a continuous flow membrane separation method. However, the second membrane separation apparatus 20 may also be used for a batch membrane separation method.

[0089] As shown in Figure 4, the PV film 21 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. Preferably, the PV film 21 is a film that preferentially allows organic compound C to permeate from a solution S containing a volatile organic compound C. The PV film 21 may further include a protective layer (not shown) that protects the separation functional layer 1.

[0090] The separation function layer 1 is, for example, a layer that can preferentially allow organic compound C to pass through from the above solution S. Typically, it is a dense layer (non-porous layer) in which no pores can be observed when viewed with a scanning electron microscope (SEM) at a magnification of 5000x.

[0091] The separation functional layer 1 preferably 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 the water exceeds 90°. The static contact angle of water can be measured using a commercially available contact angle meter.

[0092] 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. A compound having siloxane bonds is typically a silicone polymer. The silicone polymer 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). The hydrophobic material can be used alone or in combination of two or more. In this specification, a PV membrane 21 equipped with the separation functional layer 1 containing the above-mentioned polymers may be referred to as a "polymer-type separation membrane." Polymer-type separation membranes tend to deform or collapse when the gauge pressure P1 of the first non-permeable fluid increases.

[0093] 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.

[0094] 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.

[0095] 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 applications involving the separation of water-containing solutions S 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.

[0096] 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.

[0097] 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.

[0098] The filler content in the separation functional layer 1 is, for example, 5 wt% or more, and may be 10 wt% or more, 30 wt% or more, or even 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%.

[0099] 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, and even 30 μm or more.

[0100] Examples of the 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; and mesh screens. The porous support 2 may also be a combination of two or more of these materials.

[0101] 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.

[0102] The protective layer, for example, covers the surface of the separation functional layer 1. The material of the protective layer is not particularly limited, and 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.

[0103] 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.

[0104] (Method of operating the membrane separation system) -Normal operation The operating method of the membrane separation system 100 is carried out as follows, for example. First, a storage unit 30 for storing the supply fluid S0 is prepared. The supply fluid S0 is preferably a solution S containing a volatile organic compound C. The solution S is typically an aqueous solution containing the organic compound C. The 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 20°C to 260°C.

[0105] 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.

[0106] Examples of organic compound C include alcohols, ketones, and esters, and are typically alcohols. That is, solution S preferably contains water and an alcohol as organic compound C. 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] Solution S 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 solution S 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%.

[0111] 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, solution S may be a fermentation liquid containing organic compound C as a fermentation product. However, solution S is not limited to a fermentation liquid, and may also be waste liquid or wastewater discharged from a chemical plant or the like.

[0112] Solution S 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. Microorganisms that produce fermentation products are typically fungi. Examples of carbon sources include polysaccharides such as starch and monosaccharides such as glucose.

[0113] Next, the supply fluid S0 is supplied from the storage unit 30 to the first membrane separation device 10 through the supply path 40. The amount of supply fluid S0 is not particularly limited and is determined according to the processing capacity of the first membrane separation device 10. Preferably, the supply fluid S0 is pressurized by a pump 50 located in the supply path 40. The gauge pressure PS of the supply fluid S0 supplied to the first membrane separation device 10 is, for example, 1 MPa or more, and may be 3 MPa or more, or even 5 MPa or more. The upper limit of the gauge pressure PS of the supply fluid S0 is, for example, 20 MPa or less, and may be 10 MPa or less.

[0114] When the supply fluid S0 is supplied to the first membrane separation device 10, the supply fluid S0 comes into contact with one side of the RO membrane 11 of the first membrane separation device 10. As a result, the first permeate fluid S1 can be obtained on the other side of the RO membrane 11 (i.e., the second chamber 14). For example, if the supply fluid S0 is a solution S containing an organic compound C, the RO membrane 11 treatment can yield the first permeate fluid S1, which is a liquid with a lower organic compound C content than the supply fluid S0.

[0115] The first permeate fluid S1 is discharged to the outside of the first membrane separation device 10 through the outlet 14a. This first permeate fluid S1 is discharged to the outside of the membrane separation system 100, for example, through the outlet 41a of the first discharge path 41. The first permeate fluid S1 discharged to the outside of the membrane separation system 100 may be recovered using a recovery tank or the like, if necessary.

[0116] On the other hand, in the first chamber 13 of the first membrane separation apparatus 10, a first impermeable fluid S2 that did not permeate the RO membrane 11 is obtained. For example, if the supply fluid S0 is a solution S containing an organic compound C, the RO membrane 11 treatment can yield a first impermeable fluid S2 that has a higher content of organic compound C than the supply fluid S0. In this case, the ratio of the content of organic compound C in the first impermeable fluid S2 (wt%) to the content of organic compound C in the supply fluid S0 (wt%) is not particularly limited, and is, for example, 2 to 10.

[0117] The first impermeable fluid S2 is discharged to the outside of the first membrane separator 10 through the outlet 13b. This first impermeable fluid S2 is sent from the first membrane separator 10 to the second membrane separator 20 through the connection path 42. In normal operation of the membrane separator system 100, it is preferable that all of the first impermeable fluid S2 discharged from the first membrane separator 10 is sent to the second membrane separator 20. In other words, in normal operation, it is preferable that the valve 55 located in the branch path 45 is closed and the first impermeable fluid S2 does not pass through the branch path 45.

[0118] The first impermeable fluid S2 is preferably depressurized by a depressurization unit 51 located in the connection path 42. During normal operation, the gauge pressure P1 of the first impermeable fluid S2 supplied to the second membrane separator 20 is, for example, 1 MPa or less, and may be 0.5 MPa or less, 0.1 MPa or less, or even 0.08 MPa or less. The lower limit of the gauge pressure P1 of the first impermeable fluid S2 is, for example, 0.001 MPa or more, and may be 0.01 MPa or more.

[0119] When the first impermeable fluid S2 is supplied to the second membrane separator 20, the first impermeable fluid S2 comes into contact with one surface of the PV membrane 21 of the second membrane separator 20. In this state, the second permeable fluid L1 can be obtained in the second chamber 24 by reducing the pressure in the space adjacent to the other surface of the PV membrane 21 (i.e., the second chamber 24). The pressure reduction in the second chamber 24 can be performed by a pressure reducing device located in the second discharge path 43. The gauge pressure of the second chamber 24 when the pressure is reduced is, for example, -0.0513 MPa (absolute pressure 50 kPa) or less, and may also be -0.0813 MPa (absolute pressure 20 kPa) or less, -0.0913 MPa (absolute pressure 10 kPa) or less, -0.0963 MPa (absolute pressure 5 kPa) or less, -0.0983 MPa (absolute pressure 3 kPa) or less, and even -0.0993 MPa (absolute pressure 2 kPa) or less.

[0120] For example, if the supply fluid S0 is a solution S containing an organic compound C, treatment with the PV film 21 can yield a second permeable fluid L1 in which the content of organic compound C is higher than that of the first impermeable fluid S2. In this case, the ratio of the content of organic compound C in the second permeable fluid L1 to the content of organic compound C in the first impermeable fluid S2 (wt%) is not particularly limited, and is, for example, 2 to 10.

[0121] The second permeate fluid L1 is discharged to the outside of the second membrane separation device 20 through the outlet 24a. This second permeate fluid L1 is discharged to the outside of the membrane separation system 100, for example, through the outlet 43a of the second discharge path 43. The second permeate fluid L1 discharged to the outside of the membrane separation system 100 may be recovered using a recovery tank or the like, if necessary.

[0122] On the other hand, in the first chamber 23 of the second membrane separation apparatus 20, a second impermeable fluid L2 that did not permeate the PV membrane 21 is obtained. For example, if the supply fluid S0 is a solution S containing an organic compound C, the PV membrane 21 treatment can yield a second impermeable fluid L2 that has a lower organic compound C content than the first impermeable fluid S2.

[0123] The second impermeable fluid L2 is discharged to the outside of the second membrane separation device 20 through the outlet 23b. This second impermeable fluid L2 is discharged to the outside of the membrane separation system 100, for example, through the outlet 44a of the third discharge path 44. The second impermeable fluid L2 discharged to the outside of the membrane separation system 100 may be recovered using a recovery tank or the like, if necessary.

[0124] - Pressure reduction operation As described above, when the membrane separation system 100, which combines the first membrane separation device 10 and the second membrane separation device 20, is operated continuously, the flow rate of the first impermeable fluid S2 discharged from the first membrane separation device 10 tends to increase, and the pressure of the fluid S2 tends to increase. The membrane separation system 100 of this embodiment performs a pressure reduction operation to lower the gauge pressure P1 of the first impermeable fluid S2 supplied to the second membrane separation device 20 when at least one condition selected from the group consisting of the following conditions (1) and (2) is met. (1) The above gauge pressure P1 exceeds the first set value. (2) The difference (P1 - P2) between the above gauge pressure P1 and the gauge pressure P2 of the second permeable fluid L1 discharged from the second membrane separation device 20 exceeds the second set value.

[0125] In other words, in this embodiment, the method of operating the membrane separation system 100 includes performing the above-mentioned depressurization operation when at least one condition selected from the group consisting of conditions (1) and (2) above is met.

[0126] The membrane separation system 100 preferably performs a depressurization operation when condition (1) of the above conditions (1) and (2) is met. The setting values ​​for conditions (1) and (2) can be appropriately set according to the type of RO membrane 11 or PV membrane 21. For example, the first setting value is, for example, a value of 1 MPa or less, and may be 0.5 MPa or less, 0.1 MPa or less, or even 0.08 MPa or less. The first setting value may be set within the range of 0.05 MPa to 1 MPa.

[0127] The second setting value may be, for example, a value of 1.1 MPa or less, and may also be a value of 0.5 MPa or less, or even 0.2 MPa or less. The second setting value may also be set within the range of 0.15 MPa to 1.1 MPa.

[0128] The depressurization operation is preferably performed by sending a portion of the first impermeable fluid S2 from the connection path 42 to the branch path 45. This operation can be performed, for example, by opening a valve 55 located in the branch path 45. In the example shown in Figure 1, the first impermeable fluid S2 sent to the branch path 45 is returned to the storage unit 30. This allows the first impermeable fluid S2 to be reused without being discarded.

[0129] As described above, the pressure reduction operation is preferably controlled by at least one operation selected from the group consisting of (A) and (B) below: (A) Adjust the opening of valve 55 so that the gauge pressure P1 falls below a first set value. (B) Adjust the opening of valve 55 so that the difference (P1 - P2) falls below a second set value.

[0130] The depressurization operation is performed until conditions (1) and (2) are no longer met. Specifically, it is performed until the gauge pressure P1 falls below the first set value and the difference (P1 - P2) falls below the second set value. After the depressurization operation, the normal operation described above can be performed again. By combining the depressurization operation with the normal operation in the membrane separation system 100, stable continuous operation can be achieved.

[0131] [Modifications of the second membrane separation device] The second membrane separation device 20 may be a spiral-type membrane element, a hollow fiber membrane element, a disc-tube type membrane element in which multiple permeable vaporization membranes are laminated, a plate-and-frame type membrane element, etc. Figure 5 shows a spiral-type membrane element. The second membrane separation device 25 in Figure 5 comprises a central tube 26 and a laminate 27. The laminate 27 contains a PV membrane 21. In other words, the second membrane separation device 25 has a spiral-type membrane element containing a PV membrane 21.

[0132] The central tube 26 has a cylindrical shape. Multiple holes or slits are formed on the surface of the central tube 26 to allow the second permeable fluid L1 to flow into the interior of the central tube 26. Examples of materials for the central tube 26 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 26 is, for example, in the range of 20 to 100 mm.

[0133] The laminate 27 further includes a supply-side channel material 28 and a permeate-side channel material 29 in addition to the PV film 21. The laminate 27 is wound around the central tube 26. The second membrane separation device 25 may further include an outer covering material (not shown).

[0134] As the supply-side channel material 28 and the permeate-side channel material 29, for example, a net, woven fabric, or knitted fabric made of resin consisting of polyethylene, polypropylene, polyethylene terephthalate (PET), polyphenylene sulfide (PPS), or ethylene-chlorotrifluoroethylene copolymer (ECTFE) can be used.

[0135] The membrane separation in the second membrane separation device 25 is carried out, for example, as follows: First, the first impermeable fluid S2 is supplied to one end of the wound laminate 27. The space inside the central tube 26 is depressurized. As a result, the second permeable fluid L1 that has permeated through the PV membrane 21 of the laminate 27 moves into the central tube 26. The second permeable fluid L1 is discharged to the outside through the central tube 26. The first impermeable fluid S2 (second impermeable fluid L2) processed in the second membrane separation device 25 is discharged to the outside from the other end of the wound laminate 27.

[0136] In addition, in the membrane separation system 100, the first membrane separation device 10 may also be 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, etc. The first membrane separation device 10 may also be a spiral-type membrane element having the same configuration as the second membrane separation device 25.

[0137] [Embodiment 2] Figure 6 is a schematic diagram of the membrane separation system 110 of Embodiment 2. As shown in Figure 6, the membrane separation system 110 further comprises a third membrane separation device 70 having a PV membrane 71. In the example of Figure 6, a branch path 45 branching off from the connection path 42 is connected to the impermeable fluid inlet (inlet 73a) of the third membrane separation device 70. The membrane separation system 110 further comprises a fourth discharge path 46 and a fifth discharge path 47. Except as described above, the configuration of the membrane separation system 110 of Embodiment 2 is the same as the configuration of the membrane separation system 100 of Embodiment 1.

[0138] The third membrane separation device 70 is a membrane separation device that uses a PV membrane 71 to perform membrane separation on the first impermeable fluid S2 sent through the branch path 45. The PV membrane 71 of the third membrane separation device 70 can separate the first impermeable fluid S2 into a third permeable fluid and a third impermeable fluid. In the example of Figure 6, the second membrane separation device 20 and the third membrane separation device 70 can be considered to be connected in parallel.

[0139] The fourth discharge path 46 is connected to the permeate fluid outlet (outlet 74a) of the third membrane separator 70 and is a path for discharging the third permeate fluid from the third membrane separator 70. The fourth discharge path 46 has an opening (outlet 46a) formed therein for discharging the third permeate fluid from the fourth discharge path 46. A pressure sensor (not shown) for measuring the gauge pressure of the third permeate fluid discharged from the third membrane separator 70 may be placed in the fourth discharge path 46.

[0140] A vacuum pressure device (not shown) for reducing the pressure within the permeate space of the third membrane separation device 70 may be provided in the fourth discharge path 46. The vacuum pressure device is preferably 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 these vacuum pumps include those described above in Embodiment 1. The vacuum pressure device may be a multi-stage Roots type vacuum pump or a diaphragm type vacuum pump.

[0141] The fifth discharge path 47 is connected to the impermeable fluid outlet (outlet 73b) of the third membrane separator 70 and is a path for discharging the third impermeable fluid from the third membrane separator 70. The fifth discharge path 47 has an opening (outlet 47a) formed therein for discharging the third impermeable fluid from the fifth discharge path 47.

[0142] (Third Membrane Separation Apparatus) As shown in Figure 7, the third membrane separation apparatus 70 comprises a PV membrane 71 and a tank 72. The tank 72 has a first chamber 73 and a second chamber 74. The first chamber 73 functions as a supply space to which a first impermeable fluid S2 is supplied. The second chamber 74 functions as a permeation space to which a third permeable fluid L3 is supplied. The third permeable fluid L3 is obtained by the first impermeable fluid S2 permeating through the PV membrane 71. The PV membrane 71 is located inside the tank 72. Inside the tank 72, the PV membrane 71 separates the first chamber 73 and the second chamber 74. The PV membrane 71 extends from one of a pair of walls of the tank 72 to the other.

[0143] The first chamber 73 has an inlet 73a and an outlet 73b. The second chamber 74 has an outlet 74a. The inlet 73a of the first chamber 73 is an opening for supplying the first impermeable fluid S2 to the third membrane separator 70. The outlet 74a of the second chamber 74 is an opening for discharging the third permeable fluid L3 from the third membrane separator 70. The outlet 73b of the first chamber 73 is an opening for discharging the first impermeable fluid S2 (third impermeable fluid L4) that did not permeate the PV membrane 71 from the third membrane separator 70. Each of the inlet 73a, outlet 73b, and outlet 74a is formed, for example, on the wall surface of the tank 72.

[0144] The third membrane separation apparatus 70 is suitable for a continuous flow membrane separation method. However, the third membrane separation apparatus 70 may also be used for a batch membrane separation method.

[0145] In the membrane separation system 110, the third membrane separation device 70 may be 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, or the like. The third membrane separation device 70 may also be a spiral-type membrane element having the same configuration as the second membrane separation device 25 in Figure 5.

[0146] Examples of PV membrane 71 include those described above as the PV membrane 21 of the second membrane separation device 20. The composition and structure of PV membrane 71 may be the same as or different from PV membrane 21.

[0147] (Method of operating the membrane separation system) - Depressurization operation In the membrane separation system 110, it is preferable to perform the depressurization operation by sending a portion of the first impermeable fluid S2 from the connection path 42 to the branch path 45. In the example of Figure 6, the first impermeable fluid S2 sent to the branch path 45 is sent to the third membrane separation device 70.

[0148] When the first impermeable fluid S2 is supplied to the third membrane separator 70, the first impermeable fluid S2 comes into contact with one surface of the PV membrane 71 of the third membrane separator 70. In this state, the third permeable fluid L3 can be obtained in the second chamber 74 by reducing the pressure in the space adjacent to the other surface of the PV membrane 71 (i.e., the second chamber 74). The pressure reduction in the second chamber 74 can be performed by a pressure reducing device located in the fourth discharge path 46. The gauge pressure of the second chamber 74 when the pressure is reduced is, for example, -0.0513 MPa (absolute pressure 50 kPa) or less, and may also be -0.0813 MPa (absolute pressure 20 kPa) or less, -0.0913 MPa (absolute pressure 10 kPa) or less, -0.0963 MPa (absolute pressure 5 kPa) or less, -0.0983 MPa (absolute pressure 3 kPa) or less, and even -0.0993 MPa (absolute pressure 2 kPa) or less.

[0149] As an example, if the supply fluid S0 is a solution S containing an organic compound C, a third permeable fluid L3 containing a higher concentration of organic compound C than the first impermeable fluid S2 can be obtained by treatment with the PV film 71. In this case, the ratio of the content of organic compound C in the third permeable fluid L3 (wt%) to the content of organic compound C in the first impermeable fluid S2 (wt%) is not particularly limited, and is, for example, 2 to 10.

[0150] The third permeate fluid L3 is discharged to the outside of the third membrane separation device 70 through the outlet 74a. This third permeate fluid L3 is discharged to the outside of the membrane separation system 100, for example, through the outlet 46a of the fourth discharge path 46. The third permeate fluid L3 discharged to the outside of the membrane separation system 100 may be recovered using a recovery tank or the like, if necessary. The third permeate fluid L3 may also be mixed with the second permeate fluid L1.

[0151] On the other hand, in the first chamber 73 of the third membrane separation apparatus 70, a third impermeable fluid L4 that did not permeate the PV membrane 71 is obtained. For example, if the supply fluid S0 is a solution S containing an organic compound C, the PV membrane 71 treatment can yield a third impermeable fluid L4 that has a lower organic compound C content than the first impermeable fluid S2.

[0152] The third impermeable fluid L4 is discharged to the outside of the third membrane separation device 70 through the outlet 73b. This third impermeable fluid L4 is discharged to the outside of the membrane separation system 100, for example, through the outlet 47a of the fifth discharge path 47. The third impermeable fluid L4 discharged to the outside of the membrane separation system 100 may be recovered using a recovery tank or the like, if necessary. The third impermeable fluid L4 may also be mixed with the second impermeable fluid L2.

[0153] As described above, according to the membrane separation system 110 of Embodiment 2, when a depressurization operation is performed, the first impermeable fluid S2 can be efficiently separated by membrane in both the second membrane separation device 20 and the third membrane separation device 70.

[0154] [Embodiment 3] Figure 8 is a schematic diagram of the membrane separation system 120 of Embodiment 3. As shown in Figure 8, the membrane separation system 120 further includes a bypass path 48 that branches off from the third discharge path 44 and merges with the branch path 45. Except as described above, the configuration of the membrane separation system 120 of Embodiment 3 is the same as the configuration of the membrane separation system 110 of Embodiment 2.

[0155] More specifically, the bypass path 48 branches off from a branching point 61 in the third discharge path 44 and merges at a merging point 62 in the branch path 45. The merging point 62 is preferably located between the valve 55 and the third membrane separator 70. It is preferable that a three-way valve is provided at both the branching point 61 and the merging point 62. These three-way valves may be controlled by the controller 90.

[0156] (Method of operating the membrane separation system) - Normal operation During normal operation of the membrane separation system 120, it is preferable that the second impermeable fluid L2 discharged from the second membrane separation device 20 moves in the order of the third discharge path 44, the bypass path 48, and the branch path 45 and is sent to the third membrane separation device 70. It is preferable that the second impermeable fluid L2 sent to the third membrane separation device 70 is further membrane-separated in the third membrane separation device 70. The conditions for membrane separation in the third membrane separation device 70 are those described above in Embodiment 2. During normal operation of the membrane separation system 120, the second membrane separation device 20 and the third membrane separation device 70 can be considered to be connected in series.

[0157] - In the depressurization membrane separation system 120, it is preferable to perform the depressurization operation by sending a portion of the first impermeable fluid S2 from the connection path 42 to the branch path 45. Furthermore, when performing the depressurization operation, the three-way valves located in the third discharge path 44 and the branch path 45 are switched so that the second impermeable fluid L2 is discharged to the outside of the membrane separation system 100 through the outlet 44a of the third discharge path 44. In other words, the system is configured so that the second impermeable fluid L2 does not pass through the bypass path 48. This makes it possible to perform the depressurization operation described above in Embodiment 2.

[0158] As described above, according to the membrane separation system 120 of Embodiment 3, the third membrane separation device 70 can be used in both normal operation and reduced pressure operation.

[0159] [Embodiment 4] Figure 9 is a schematic diagram of the membrane separation system 130 of Embodiment 4. As shown in Figure 9, the membrane separation system 130 further includes a recovery unit 80 for recovering a portion of the first impermeable fluid S2. In the example of Figure 9, a branching path 45 branching off from the connection path 42 is connected to the inlet 81 of the recovery unit 80. The membrane separation system 130 further includes a return path 49. Except as described above, the configuration of the membrane separation system 130 of Embodiment 4 is the same as the configuration of the membrane separation system 100 of Embodiment 1.

[0160] The recovery unit 80 is preferably a buffer tank for temporarily storing the first impermeable fluid S2 sent through the branching path 45.

[0161] The return path 49 is connected to the outlet 82 of the recovery unit 80 and merges with the connection path 42. More specifically, the return path 49 merges with the connection path 42 at a merging point 65 located between the branching point 60 and the pressure sensor 53. The return path 49 is a path for returning the first impermeable fluid S2 stored in the recovery unit 80 to the connection path 42. Preferably, the return path 49 is equipped with a pump 56 that controls the flow rate and pressure of the first impermeable fluid S2 returned to the connection path 42.

[0162] (Operation method of the membrane separation system) - Depressurization operation In the membrane separation system 130, it is preferable to perform the depressurization operation by sending a portion of the first impermeable fluid S2 from the connection path 42 to the branch path 45. In the example of Figure 9, the first impermeable fluid S2 sent to the branch path 45 is sent to the recovery unit 80.

[0163] The first impermeable fluid S2 sent to the recovery unit 80 is temporarily stored in the recovery unit 80. Preferably, this first impermeable fluid S2 is returned from the recovery unit 80 to the connection path 42 via the return path 49 during normal operation after the depressurization operation. However, the first impermeable fluid S2 in the recovery unit 80 does not necessarily have to be returned to the connection path 42 in some cases.

[0164] The membrane separation system of this embodiment is suitable for separating organic compounds from solutions containing volatile organic compounds.

Claims

1. A membrane separation system comprising: a first membrane separation device having a reverse osmosis membrane for separating a supply fluid into a first permeable fluid and a first impermeable fluid; and a second membrane separation device having a permeation vaporization membrane for separating the first impermeable fluid into a second permeable fluid and a second impermeable fluid, wherein a depressurization operation is performed to reduce the gauge pressure P1 of the first impermeable fluid supplied to the second membrane separation device when at least one condition selected from the group consisting of the following conditions (1) and (2) is met: (1) The gauge pressure P1 exceeds a first set value. (2) The difference (P1 - P2) between the gauge pressure P1 and the gauge pressure P2 of the second permeable fluid discharged from the second membrane separation device exceeds a second set value.

2. The membrane separation system according to claim 1, further comprising a connection path connected to the first membrane separation device and the second membrane separation device, for sending the first impermeable fluid from the first membrane separation device to the second membrane separation device.

3. The membrane separation system according to claim 2, further comprising a branching path branching off from the connection path, wherein the depressurization operation is performed by sending a portion of the first impermeable fluid from the connection path to the branching path.

4. The membrane separation system according to claim 3, further comprising a storage section for storing the supply fluid, wherein the branching path is connected to the storage section.

5. The membrane separation system according to claim 3, further comprising a supply path connected to the first membrane separation device for supplying the supply fluid to the first membrane separation device, wherein the branch path is connected to the supply path.

6. The membrane separation system according to claim 3, further comprising a third membrane separation device having a permeable vaporization membrane, wherein the branching path is connected to the third membrane separation device.

7. The membrane separation system according to claim 3, further comprising a recovery unit for recovering a portion of the first non-permeable fluid, wherein the branching path is connected to the recovery unit.

8. The membrane separation system according to claim 3, further comprising a valve for adjusting the flow rate of the first impermeable fluid sent from the connection path to the branch path.

9. The membrane separation system according to claim 8, wherein the depressurization operation is controlled by at least one operation selected from the group consisting of (A) and (B) below: (A) Adjusting the opening of the valve so that the gauge pressure P1 is below the first set value. (B) Adjusting the opening of the valve so that the difference (P1 - P2) is below the second set value.

10. The membrane separation system according to claim 2, further comprising a pressure sensor disposed in the connection path for measuring the gauge pressure P1.

11. The membrane separation system according to claim 1, further comprising a pressure sensor for measuring the gauge pressure P2.

12. The membrane separation system according to claim 1, wherein the permeable vaporization membrane has a separation functional layer containing a hydrophobic material.

13. The membrane separation system according to claim 12, wherein the hydrophobic material comprises a compound having a siloxane bond.

14. The membrane separation system according to claim 1, wherein the second membrane separation device has a spiral membrane element including the permeable vaporization membrane.

15. The membrane separation system according to claim 1, wherein the supply fluid is a solution containing a volatile organic compound.

16. The membrane separation system according to claim 15, wherein the solution comprises water and an alcohol as the organic compound.

17. A method for operating a membrane separation system comprising: a first membrane separation device having a reverse osmosis membrane for separating a supply fluid into a first permeable fluid and a first impermeable fluid; and a second membrane separation device having a permeation vaporization membrane for separating the first impermeable fluid into a second permeable fluid and a second impermeable fluid, wherein the method for operating the membrane separation system includes performing a depressurization operation to reduce the gauge pressure P1 of the first impermeable fluid supplied to the second membrane separation device when at least one condition selected from the group consisting of the following conditions (1) and (2) is met: (1) The gauge pressure P1 exceeds a first set value. (2) The difference (P1 - P2) between the gauge pressure P1 and the gauge pressure P2 of the second permeable fluid discharged from the second membrane separation device exceeds a second set value.

18. A membrane separation system comprising: a first membrane separation device having a reverse osmosis membrane for separating a supply fluid into a first permeable fluid and a first impermeable fluid; and a second membrane separation device having a permeation vaporization membrane for separating the first impermeable fluid into a second permeable fluid and a second impermeable fluid, wherein at least one selected from the group consisting of the following requirements (I) and (II) is satisfied: (I) During operation, the gauge pressure P1 of the first impermeable fluid supplied to the second membrane separation device is maintained at 1 MPa or less. (II) During operation, the difference (P1 - P2) between the gauge pressure P1 of the first impermeable fluid supplied to the second membrane separation device and the gauge pressure P2 of the second permeable fluid discharged from the second membrane separation device is maintained at 1.1 MPa or less.

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