Membrane separation system

Abstract

This membrane separation system comprises: at least one membrane separation unit that separates a supply fluid into a permeating fluid and a non-permeating fluid; a decompression unit that decompresses the interior of a permeation space of the at least one membrane separation unit; and a heat exchange unit that uses a discharge fluid discharged from the decompression unit to heat the supply fluid supplied to the at least one membrane separation unit. The membrane separation system furthermore comprises, e.g., a supply path that guides the discharge fluid to the heat exchange unit, a flow rate adjustment valve provided in the supply path, and a temperature sensor that measures the temperature of the supply fluid.

Description

Membrane Separation System

[0001] The present invention relates to a membrane separation system.

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

[0003] Japanese Patent No. 4048279

[0004] In a separation method using a separation membrane, when the temperature of the feed fluid supplied to the membrane separation device decreases, the permeation performance of the separation membrane decreases. As a result, the flow rate, concentration and the like of the obtained permeated fluid become unstable. In order to address this problem, conventionally, a temperature regulator is provided in the feed fluid path of the membrane separation device to heat the feed fluid. However, heating the fluid using only a temperature regulator leads to an increase in the cost of the entire system.

[0005] An object of the present invention is to provide a membrane separation system suitable for stably maintaining the temperature of a feed fluid supplied to a membrane separation unit at low cost.

[0006] The present invention provides a membrane separation system comprising: at least one membrane separation unit that separates a feed fluid into a permeate fluid and a non-permeate fluid; a pressure reduction unit that reduces pressure in a permeation space of the at least one membrane separation unit; and a heat exchange unit that heats the feed fluid supplied to the at least one membrane separation unit using discharged fluid discharged from the pressure reduction unit.

[0007] According to the present invention, the temperature of the feed fluid supplied to the membrane separation unit can be stably maintained at low cost.

[0008] This is a schematic diagram showing an example of the membrane separation system of this embodiment. This is a schematic cross-sectional view showing an example of the membrane separation section of the membrane separation system. This is a schematic cross-sectional view showing an example of the separation membrane provided in the membrane separation section. This is a schematic exploded perspective view showing another example of the membrane separation section. 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.

[0009] A membrane separation system according to a first aspect of the present invention comprises: at least one membrane separation unit that separates a supply fluid into a permeable fluid and an impermeable fluid; a depressurization unit that reduces the pressure within the permeable space of the at least one membrane separation unit; and a heat exchange unit that heats the supply fluid supplied to the at least one membrane separation unit using the discharged fluid discharged from the depressurization unit.

[0010] In a second embodiment of the present invention, for example, the membrane separation system according to the first embodiment further comprises a supply path for guiding the discharge fluid to the heat exchange section, a flow control valve provided in the supply path, and a temperature sensor for measuring the temperature of the supply fluid.

[0011] In a third embodiment of the present invention, for example, in the membrane separation system according to the second embodiment, the opening degree of the flow control valve is adjusted so that the temperature of the supply fluid is within a predetermined range, based on the result of monitoring the temperature of the supply fluid by the temperature sensor.

[0012] In a fourth embodiment of the present invention, for example, in a membrane separation system according to any one of the first to third embodiments, the at least one membrane separation unit has a separation membrane, and the separation membrane includes a permeable vaporization membrane.

[0013] In a fifth aspect of the present invention, for example, in the membrane separation system according to the fourth aspect, the supply fluid includes a raw fluid, and the raw fluid includes a solution containing a volatile organic compound.

[0014] In a sixth embodiment of the present invention, for example, the membrane separation system according to the fifth embodiment further comprises a supply unit for storing the raw fluid.

[0015] In a seventh aspect of the present invention, for example, in a membrane separation system according to any one of the first to sixth aspects, the depressurization section includes a vacuum pump.

[0016] In the eighth aspect of the present invention, for example, a membrane separation system according to any one of the first to seventh aspects further comprises a condensation unit that cools and condenses the permeate fluid.

[0017] In a ninth embodiment of the present invention, for example, a membrane separation system according to any one of the first to eighth embodiments further comprises a temperature controller for heating the supply fluid.

[0018] In a tenth embodiment of the present invention, for example, in a membrane separation system according to any one of the first to ninth embodiments, the at least one membrane separation unit includes a plurality of membrane separation units, and 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.

[0019] In an eleventh aspect of the present invention, for example, in a membrane separation system according to the tenth aspect, the heat exchange unit includes a heat exchange unit that heats the supply fluid supplied to the membrane separation unit located furthest downstream of the plurality of membrane separation units.

[0020] In a twelfth aspect of the present invention, for example, in a membrane separation system according to the eleventh aspect, the heat exchange section includes a plurality of heat exchange sections that heat the supply fluid supplied to each of the plurality of membrane separation sections.

[0021] In a thirteenth aspect of the present invention, for example, in the membrane separation system according to the twelfth aspect, the plurality of heat exchange units are connected in parallel.

[0022] In a fourteenth aspect of the present invention, for example, in the membrane separation system according to the twelfth aspect, the plurality of heat exchange units are connected in series such that the discharge fluid is supplied sequentially from the downstream side to the upstream side.

[0023] In a 15th embodiment of the present invention, for example, in the membrane separation system according to the 14th embodiment, the plurality of membrane separation units are arranged such that their vertical position decreases from the downstream side to the upstream side.

[0024] 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.

[0025] <Embodiment of the Membrane Separation System> The membrane separation system of this embodiment comprises at least one membrane separation unit, a depressurization unit, and a heat exchange unit. At least one membrane separation unit separates the supply fluid into a permeable fluid and an impermeable fluid. The depressurization unit reduces the pressure within the permeable space of at least one membrane separation unit. The heat exchange unit heats the supply fluid supplied to at least one membrane separation unit using the discharged fluid discharged from the depressurization unit.

[0026] In the membrane separation system of this embodiment, the high-temperature discharged fluid from the reduced-pressure section can be used as a heat transfer medium for the heat exchange section that heats the supply fluid supplied to at least one membrane separation section. Therefore, compared to conventional membrane separation systems, it is possible to heat the supply fluid at a lower cost. As a result, the temperature of the supply fluid supplied to the membrane separation section can be maintained stably at a low cost.

[0027] The following describes a specific example of the membrane separation system of this embodiment with reference to the drawings.

[0028] Figure 1 is a schematic diagram showing an example of a membrane separation system according to this embodiment. The membrane separation system 100A in Figure 1 includes a first membrane separation unit 10 as at least one membrane separation unit. The first membrane separation unit 10 separates the raw fluid F0, which is the supply fluid, into a first permeate fluid F1 and a first impermeable fluid F2. The membrane separation system 100A includes a depressurization unit 40 as a depressurization unit. The depressurization unit 40 depressurizes the permeate space of the first membrane separation unit 10 and discharges the high-temperature discharge fluid S1. The membrane separation system 100A includes a first heat exchange unit 51 as a heat exchange unit.

[0029] In the membrane separation system 100A, the first heat exchange unit 51 heats the raw fluid F0 supplied to the first membrane separation unit 10 using the high-temperature discharge fluid S1 discharged from the depressurization unit 40. More specifically, the first heat exchange unit 51 heats the raw fluid F0 by performing heat exchange between the discharge fluid S1, which is used as a heat transfer medium for heating, and the raw fluid F0, which is used as a heat transfer medium for cooling.

[0030] For example, the first heat exchange unit 51 heats the raw fluid F0 to a temperature range of 25°C to 60°C. The first heat exchange unit 51 may heat the raw fluid F0 to a temperature range of 30°C to 45°C, or to a temperature range of 35°C to 40°C.

[0031] As described above, in separation methods using separation membranes, the permeability of the separation membrane decreases when the temperature of the supply fluid supplied to the membrane separation device decreases. As a result, the flow rate and concentration of the obtained permeate fluid become unstable. In the membrane separation system 100A, the high-temperature discharge fluid S1 discharged from the depressurization section 40 can be used as a heat transfer medium for heating the first heat exchange section 51. Therefore, compared to conventional membrane separation systems, it is possible to heat the raw fluid F0 supplied to the first membrane separation section 10 at a lower cost. As a result, the temperature of the raw fluid F0 supplied to the first membrane separation section 10 can be maintained stably at a low cost.

[0032] In this embodiment, the raw fluid F0 supplied to the first membrane separation unit 10 may be a liquid or a gas. An example of a liquid raw fluid F0 is a solution containing a volatile organic compound. An example of a gaseous raw fluid F0 is a mixed gas containing an acidic gas, particularly a mixed gas containing carbon dioxide and nitrogen.

[0033] In this embodiment, the discharge fluid S1 is exhaust gas discharged from the pressure reduction unit 40. When the source fluid F0 is a liquid, the discharge fluid S1 mainly consists of, for example, water (water vapor) or volatile organic compounds. When the source fluid F0 is a gas, the discharge fluid S1 mainly consists of, for example, a mixed gas containing acidic gases, particularly a mixed gas containing carbon dioxide and nitrogen. "Main component" means the component that is present in the largest amount by weight in the discharge fluid S1.

[0034] In this embodiment, the temperature of the discharged fluid S1 from the pressure reduction section 40 is, for example, in the range of 50°C to 90°C. The temperature of the discharged fluid S1 may also be in the range of 40°C to 80°C.

[0035] The heat exchange section of the membrane separation system 100A is not limited to the first heat exchange section 51. For example, the membrane separation system 100A may further include a second heat exchange section 52 that heats the first impermeable fluid F2 discharged from the first membrane separation section 10. For example, the second heat exchange section 52 heats the temperature of the first impermeable fluid F2 discharged from the first membrane separation section 10 to a range of 25°C to 60°C. The second heat exchange section 52 may heat the temperature of the first impermeable fluid F2 to a range of 30°C to 45°C, or to a range of 35°C to 40°C.

[0036] In the membrane separation system 100A, the first membrane separation unit 10 has a separation membrane. The first membrane separation unit 10 has a first separation membrane 11 that separates the raw fluid F0 into a first permeable fluid F1 and a first impermeable fluid F2. A membrane separation system 100A having such a configuration is suitable, for example, for separating organic compounds from a solution containing volatile organic compounds.

[0037] In the membrane separation system of this embodiment, the depressurization section includes a vacuum device such as a vacuum pump. The depressurization section may also be 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 depressurization section 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 in the permeable space of the membrane separation section can be appropriately adjusted.

[0038] In the membrane separation system 100A, the depressurization unit 40 may be a multi-stage Roots type vacuum pump or a diaphragm type vacuum pump. A multi-stage Roots type vacuum pump can, for example, raise the pressure in the space to a predetermined value in a short time and provide excellent durability. A diaphragm type vacuum pump can, for example, perform depressurization operations efficiently and at low cost.

[0039] The membrane separation system of this embodiment may further include a condensing unit that cools and condenses the permeate fluid discharged from multiple membrane separation units.

[0040] The membrane separation system 100A includes a condensation unit 41. The condensation unit 41 cools and condenses the first permeate fluid F1 sent from the first membrane separation unit 10. The condensation unit 41 liquefies the gaseous first permeate fluid F1 to obtain a liquid first permeate fluid F1. The condensation unit 41 is a gas-liquid heat exchanger that generates heat exchange between a cooling medium, such as antifreeze, and the gaseous permeate fluid.

[0041] For example, the condensing unit 41 cools the temperature of the first permeate fluid F1 to a range of -80°C to 30°C. The condensing unit 41 may also cool the temperature of the first permeate fluid F1 to a range of -20°C to 20°C, or to a range of -10°C to 10°C.

[0042] As shown in Figure 1, the condensation section 41 may be provided upstream of the pressure reduction section 40. For example, if the raw fluid F0 is a solution containing a volatile organic compound, the first permeate fluid F1 may contain alcohol. If the first permeate fluid F1 containing alcohol gas flows directly into the pressure reduction section 40, the gas may condense within the pressure reduction section 40, generating liquid. The liquid generated within the pressure reduction section 40 may impair the function of the pressure reduction section 40. By providing the condensation section 41 upstream of the pressure reduction section 40, such problems can be avoided.

[0043] As shown in FIG. 1, the condensing section 41 may be connected to a recovery section 61 for recovering a liquid permeated fluid obtained by condensation. The recovery section 61 is, for example, a tank that stores the liquid first permeated fluid F1. When the raw fluid F0 is a solution containing a volatile organic compound, a concentration sensor 58 for measuring the content of the organic compound in the condensed first permeated fluid F1 may be disposed on a path connecting the condensing section 41 and the recovery section 61.

[0044] The membrane separation system of the present embodiment may further include a supply section that stores the raw fluid.

[0045] The membrane separation system 100A includes a supply section 60 as a supply section. The supply section 60 stores the raw fluid F0 to be supplied to the first membrane separation section 10. The supply section 60 is, for example, a tank that stores the raw fluid F0. The supply section 60 may be a culture tank for producing an organic compound by fermentation of a carbon source by microorganisms.

[0046] The membrane separation system of the present embodiment may further include an exhaust path that guides exhaust gas discharged from the condensing section to the pressure reducing section.

[0047] The membrane separation system 100A includes an exhaust path 81 as an exhaust path. The exhaust path 81 connects an exhaust outlet of the condensing section 41 and an exhaust inlet of the pressure reducing section 40, and is a path that guides the exhaust gas discharged from the condensing section 41 to the pressure reducing section 40.

[0048] The membrane separation system of the present embodiment may further include a supply path that guides the discharged fluid discharged from the pressure reducing section to the heat exchange section.

[0049] The membrane separation system 100A includes a first supply path 83 as a supply path. The first supply path 83 is a path that guides the high-temperature discharged fluid S1 discharged from the pressure reducing section 40 to the first heat exchange section 51. In the example of FIG. 1, the first supply path 83 connects a discharged fluid outlet of the pressure reducing section 40 and a discharged fluid inlet of the first heat exchange section 51.

[0050] As shown in Figure 1, the first supply path 83 may be provided with a temperature sensor 54a for measuring the temperature of the discharge fluid S1. For example, the temperature of the discharge fluid S1 may be monitored by the temperature sensor 54a, and the amount of discharge fluid S1 supplied to the first heat exchange unit 51 may be controlled based on the monitoring results.

[0051] The membrane separation system of this embodiment may further include a temperature sensor for measuring the temperature of the supply fluid supplied to at least one membrane separation unit.

[0052] The membrane separation system 100A includes a first temperature sensor 55 as the temperature sensor. The first temperature sensor 55 measures the temperature of the raw fluid F0 supplied to the first membrane separation unit 10. For example, the temperature of the raw fluid F0 may be monitored by the first temperature sensor 55, and the amount of discharge fluid S1 supplied to the first heat exchange unit 51 may be controlled based on the monitoring result.

[0053] The membrane separation system of this embodiment may further include a flow control valve provided in the supply path.

[0054] The membrane separation system 100A includes a first flow control valve 45 provided in the first supply path 83 as a flow control valve. For example, based on the result of monitoring the temperature of the raw fluid F0 by the first temperature sensor 55, the opening degree of the first flow control valve 45 may be adjusted so that the temperature of the raw fluid F0 is within a predetermined range. In this way, the flow rate of the discharge fluid S1 supplied to the first heat exchange unit 51 can be controlled. As a result, the temperature of the raw fluid F0 supplied to the first membrane separation unit 10 can be stably maintained. For example, if the temperature of the raw fluid F0 falls below a predetermined range as a result of monitoring the temperature of the raw fluid F0, the flow rate of the discharge fluid S1 supplied to the first heat exchange unit 51 may be increased by increasing the opening degree of the first flow control valve 45. For example, if the temperature of the raw fluid F0 exceeds a predetermined range as a result of monitoring the temperature of the raw fluid F0, the flow rate of the discharge fluid S1 supplied to the first heat exchange unit 51 may be decreased by decreasing the opening degree of the first flow control valve 45.

[0055] The membrane separation system of this embodiment may further include a discharge path for discharging the discharged fluid after heat exchange from the heat exchange section.

[0056] The membrane separation system 100A is equipped with a first discharge path 87 as a discharge path. The first discharge path 87 is a path for discharging the discharge fluid S1 after heat exchange from the first heat exchange section 51.

[0057] As shown in Figure 1, the membrane separation system 100A may further include a condenser 42 connected to the first discharge path 87. The condenser 42 cools and condenses the heat-exchanged discharge fluid S1 sent from the first heat exchange unit 51. The heat-exchanged discharge fluid S1 is more easily condensed than the high-temperature discharge fluid S1 discharged from the reduced pressure unit 40. When the membrane separation system 100A includes a condenser 42, the first discharge path 87 connects the discharge fluid outlet of the first heat exchange unit 51 to the discharge fluid inlet of the condenser 42.

[0058] As shown in Figure 1, the condensing unit 42 may be connected to a recovery unit 62 for recovering the liquid obtained by condensing the discharged fluid S1 after heat exchange. The recovery unit 62 is, for example, a tank for storing the liquid. If the raw fluid F0 is a solution containing volatile organic compounds, a concentration sensor for measuring the content of the organic compounds in the liquid may be placed in the path connecting the condensing unit 42 and the recovery unit 62.

[0059] The membrane separation system of this embodiment may further include a temperature controller for heating the supply fluid.

[0060] The membrane separation system 100A includes a temperature controller 71 that heats the raw fluid F0. The temperature controller 71 may be used auxiliaryly when the temperature of the discharged fluid S1 discharged from the depressurization section 40 is insufficient for the temperature of the raw fluid F0 to meet a predetermined range. For example, the operation of the temperature controller 71 may be controlled based on the result of monitoring the temperature of the raw fluid F0 by the first temperature sensor 55 so that the temperature of the raw fluid F0 meets a predetermined range. As shown in Figure 1, the temperature controller 71 may be connected to the first heat exchange section 51. For example, a heater can be used as the temperature controller 71.

[0061] The temperature controller in the membrane separation system 100A is not limited to the temperature controller 71. For example, the membrane separation system 100A may further include a temperature controller for heating the first impermeable fluid F2 discharged from the first membrane separation unit 10. The temperature controller may be connected to the second heat exchange unit 52.

[0062] The membrane separation system 100A further includes a source fluid path 91, a first permeable fluid path 92, and a first impermeable fluid path 93 as fluid pathways.

[0063] The raw fluid path 91 connects the raw fluid outlet 60b of the supply unit 60 and the raw fluid inlet 10a of the first membrane separation unit 10, and is a path that guides the raw fluid F0 from the supply unit 60 to the first membrane separation unit 10. A pump for controlling the flow rate of the raw fluid F0 may be placed in the raw fluid path 91. If the raw fluid F0 is a solution containing volatile organic compounds, a concentration sensor for measuring the content of organic compounds in the raw fluid F0 may be placed in the raw fluid path 91.

[0064] As shown in Figure 1, in the membrane separation system 100A, the first temperature sensor 55 is located on the raw fluid path 91.

[0065] The first permeable fluid path 92 connects the first permeable fluid outlet 10b of the first membrane separation unit 10 and the first permeable fluid inlet of the condensation unit 41, and is a path that guides the first permeable fluid F1 from the first membrane separation unit 10 to the condensation unit 41. If the raw fluid F0 is a solution containing a volatile organic compound, a concentration sensor for measuring the content of the organic compound in the first permeable fluid F1 may be placed in the first permeable fluid path 92.

[0066] The first impermeable fluid path 93 is connected to the first impermeable fluid outlet 10c of the first membrane separation unit 10 and is a path for discharging the first impermeable fluid F2 from the first membrane separation unit 10. If the raw fluid F0 is a solution containing a volatile organic compound, a concentration sensor for measuring the content of the organic compound in the first impermeable fluid F2 may be placed in the first impermeable fluid path 93.

[0067] As shown in Figure 1, in the membrane separation system 100A, the second heat exchange section 52 is provided on the first impermeable fluid path 93.

[0068] As shown in Figure 1, the first impermeable fluid path 93 may be connected to the impermeable fluid inlet 60a of the supply unit 60. In other words, in the membrane separation system 100A, the first impermeable fluid F2 may be mixed with the raw fluid F0 in the supply unit 60 and circulate through the raw fluid path 91 and the first impermeable fluid path 93. With this configuration, the first impermeable fluid F2 can be introduced from the first impermeable fluid path 93 to the supply unit 60. Furthermore, for example, if the raw fluid F0 is a fermentation liquid containing volatile organic compounds, when the first impermeable fluid F2 is returned to the supply unit 60, the fermentation liquid and the first impermeable fluid F2 are mixed within the supply unit 60. This reduces the content of organic compounds in the fermentation liquid. If the supply unit 60 is a culture tank, the reduction in the content of organic compounds in the fermentation liquid can suppress the cessation of fermentation by microorganisms. Therefore, the production of fermented products can be carried out continuously.

[0069] The membrane separation system of this embodiment may further include a control unit that controls each component of the membrane separation system. The control unit 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 control unit stores a program for properly operating the membrane separation system.

[0070] The membrane separation system 100A includes a control unit 70 as a control unit, which controls each component of the membrane separation system 100A. For example, the control unit 70 controls the temperature of the raw fluid F0 supplied to the first membrane separation unit 10 by controlling the operation of the pressure reducing unit 40, the first flow rate control valve 45, the temperature controller 71, etc. For example, based on the result of monitoring the temperature of the raw fluid F0 by the first temperature sensor 55, the control unit 70 controls the opening degree of the first flow rate control valve 45 so that the temperature of the raw fluid F0 satisfies a predetermined range.

[0071] Each of the pathways in the membrane separation system of this embodiment consists of, for example, metal or resin piping, unless otherwise specified.

[0072] As described above, the raw fluid F0 supplied to the first membrane separation unit 10 may be a liquid or a gas. An example of a liquid raw fluid F0 is a solution containing a volatile organic compound. An example of a gaseous raw fluid F0 is a mixed gas containing an acidic gas, particularly a mixed gas containing carbon dioxide and nitrogen.

[0073] The raw fluid F0 is typically a solution containing a volatile organic compound (hereinafter sometimes referred to as organic compound C). 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] The raw fluid F0 may contain one type of organic compound C, or it may contain two or more types of organic compound C. The content of organic compound C in the raw fluid F0 is, for example, 0.5 wt% or more, and may be 1 wt% or more, 2 wt% or more, or even 5 wt% or more. The upper limit of the content of organic compound C is not particularly limited, but is, for example, 50 wt%.

[0080] Organic compound C may be a fermented product produced by microorganisms fermenting a carbon source, or it may be alcohol produced by microorganisms (bio-alcohol). In other words, the raw fluid F0 may be a fermentation liquid containing organic compound C as a fermentation product. However, the raw fluid F0 is not limited to a fermentation liquid, but may also be waste liquid or wastewater discharged from a chemical plant or the like.

[0081] The raw fluid F0 may further contain other components besides water and organic compound C, such as microorganisms that produce fermentation products, a carbon source, a nitrogen source, and inorganic ions. The microorganisms that produce fermentation products are typically bacteria. Examples of carbon sources include polysaccharides such as starch and monosaccharides such as glucose.

[0082] Next, the first membrane separation unit 10 of the membrane separation system 100 will be described further.

[0083] [Membrane Separation Section] Figure 2 is a schematic cross-sectional view showing an example of the first membrane separation section 10. The first membrane separation section 10 comprises a first separation membrane 11 and a container 12. The container 12 has a first chamber 13 and a second chamber 14. The first chamber 13 functions as a supply space to which the raw fluid F0 is supplied. The second chamber 14 functions as a permeation space to which the first permeate fluid F1 is supplied. The first permeate fluid F1 is obtained by the raw fluid F0 permeating through the first separation membrane 11.

[0084] The first separation membrane 11 is located inside the container 12. Inside the container 12, the first separation membrane 11 separates the first chamber 13 and the second chamber 14. The first separation membrane 11 extends from one of a pair of walls of the container 12 to the other.

[0085] The first chamber 13 has a raw fluid inlet 10a and a first impermeable fluid outlet 10c. The second chamber 14 has a first permeable fluid outlet 10b. The raw fluid inlet 10a is an opening for supplying the raw fluid F0 to the supply space (first chamber 13). The first permeable fluid outlet 10b is an opening for discharging the first permeable fluid F1 from the permeation space (second chamber 14). The first impermeable fluid outlet 10c is an opening for discharging the raw fluid F0 (first impermeable fluid F2) that did not permeate the first separation membrane 11 from the supply space (first chamber 13). The raw fluid inlet 10a, the first permeable fluid outlet 10b, and the first impermeable fluid outlet 10c are each formed, for example, on the wall surface of the container 12.

[0086] The first membrane separation unit 10 is suitable for a continuous flow membrane separation method. However, the first membrane separation unit 10 may also be used in a batch membrane separation method.

[0087] [Separation Membrane] The first separation membrane 11 in the first membrane separation unit 10 and the second separation membrane 21 in the second membrane separation unit 20 are not particularly limited as long as they can separate the supply fluid into a permeable fluid and an impermeable fluid. For example, a permeation vaporization membrane, a reverse osmosis membrane, an ultrafiltration membrane, etc., can be used as the first separation membrane 11 and the second separation membrane 21.

[0088] The first separation membrane 11 may be a permeable vaporization membrane that separates the raw fluid F0 into a first permeable fluid F1 and a first impermeable fluid F2.

[0089] When the raw fluid F0 is a solution containing a volatile organic compound, the first separation membrane 11 is preferably a permeable vaporization membrane.

[0090] Figure 3 is a schematic cross-sectional view showing an example of a first separation membrane 11 in the first membrane separation unit 10. The first separation 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 first separation membrane 11 has, for example, a main surface 11a on the separation functional layer 1 side exposed to the supply space and a main surface 11b on the porous support 2 side exposed to the permeation space.

[0091] If the first separation membrane 11 is a permeation vaporization membrane, the first separation membrane 11 may further include a protective layer (not shown) that protects the separation functional layer 1.

[0092] (Separation Functional Layer) The separation functional layer 1 is a layer that can preferentially permeate specific components contained in the raw fluid F0. If the raw fluid F0 is a solution containing organic compound C, the separation functional layer 1 is, for example, a layer that can preferentially permeate organic compound C contained in the solution.

[0093] If the separation functional layer 1 is a layer that can preferentially allow organic compound C contained in a solution containing organic compound C 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] The filler content in the separation functional layer 1 is, for example, 10 wt% or more, preferably 30 wt% or more, and more preferably 40 wt% or more. The upper limit of the 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%.

[0101] If the separation functional layer 1 is a layer that can preferentially permeate organic compound C contained in a solution containing organic compound C, the thickness of the separation functional layer 1 is, for example, 200 μm or less, preferably 100 μm or less, and more preferably 80 μm or less. The thickness of the separation functional layer 1 may be 1.0 μm or more, 10 μm or more, or 30 μm or more.

[0102] If the separation functional layer 1 is a layer that can preferentially permeate organic compound C contained in a solution containing organic compound C, the separation functional layer 1 may have a microporous structure with an average pore size of less than 0.01 μm, but it may also be a dense layer without pores on its surface.

[0103] (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.

[0104] 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.

[0105] (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.

[0106] 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.

[0107] (Method for preparing a permeable vaporization membrane) A permeable vaporization membrane can be prepared, 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 applying the coating solution onto the porous support 2. The separation functional layer 1 is formed by drying the coating film.

[0108] From another perspective, the membrane separation system of this embodiment can be described as a separation system comprising: at least one separation unit that separates a supply fluid into a first fluid and a second fluid; a depressurization unit that reduces the internal space of the at least one separation unit; and a heat exchange unit that heats the supply fluid supplied to the at least one separation unit using the discharged fluid discharged from the depressurization unit.

[0109] In the separation system, the at least one separation unit may include a plurality of separation units. The plurality of separation units may be connected in series such that the first fluid discharged from the downstream separation unit is supplied as the supply fluid to the upstream separation unit.

[0110] This separation system can be applied to a membrane separation method using a separation membrane. That is, the separation unit may be a membrane separation unit. In this case, the first fluid may be a permeable fluid, and the second fluid may be an impermeable fluid.

[0111] This separation system is not limited to membrane separation methods using separation membranes, but can also be applied to distillation methods such as vacuum distillation. That is, the separation section may be a distillation column. In this case, the first fluid may be an unconcentrated liquid, and the second fluid may be a concentrated liquid.

[0112] <Embodiment of Operating Method for Membrane Separation System> The operating method for the membrane separation system of this embodiment includes, for example, separating the supply fluid into a permeable fluid and an impermeable fluid in at least one membrane separation unit, reducing the pressure in the permeable space of at least one membrane separation unit by a depressurization unit, and heating the supply fluid supplied to at least one membrane separation unit using the discharged fluid discharged from the depressurization unit by a heat exchange unit. According to this operating method, the temperature of the supply fluid supplied to the membrane separation unit can be maintained stably at low cost.

[0113] 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 in the permeate space of the first membrane separation unit 10 using a depressurization unit 40 (step 1), and separating the raw fluid F0 into a first permeate fluid F1 and a first impermeable fluid F2 in the first membrane separation unit 10 (step 2). Furthermore, the operating method includes heating the raw fluid F0 supplied to the first membrane separation unit 10 using the high-temperature discharge fluid S1 discharged from the depressurization unit 40 by the first heat exchange unit 51 (step 3).

[0114] According to the operating method of the membrane separation system 100A, the high-temperature discharged fluid S1 discharged from the depressurization section 40 is used as a heat transfer medium for heating the first heat exchange section 51, thereby heating the raw fluid F0 supplied to the first membrane separation section 10. As a result, compared to the operating method of conventional membrane separation systems, it is possible to heat the raw fluid F0 supplied to the first membrane separation section 10 at a lower cost. Consequently, the temperature of the raw fluid F0 supplied to the first membrane separation section 10 can be maintained stably at a low cost.

[0115] [Modifications of the Membrane Separation Section] The membrane separation section of the membrane separation system of this embodiment 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, etc. Figure 4 is a schematic unfolded perspective view showing another example of the membrane separation section. The membrane separation section may be a spiral-type membrane element as shown in Figure 4.

[0116] In the following section, we will further explain the case where the first membrane separation unit 10 of the membrane separation system 100A described above is a spiral-type membrane element, using Figure 4 as an example.

[0117] The first membrane separation unit 10 (membrane element) shown in Figure 4 comprises a central tube 16 and a membrane leaf 19 having a first separation membrane 11 and wrapped around the central tube 16.

[0118] The central tube 16 has a cylindrical shape. Through holes 16h are formed on the surface of the central tube 16 to allow the raw fluid F0 to flow into the interior of the central tube 16. The number of through holes 16h is not particularly limited and may be one or two or more. Examples of materials for the central tube 16 include resins such as acrylonitrile butadiene styrene copolymer resin (ABS resin), polyphenylene ether resin (PPE resin), and polysulfone resin (PSF resin); and metals such as stainless steel and titanium. The inner diameter of the central tube 16 is, for example, in the range of 20 to 100 mm.

[0119] The first membrane separation unit 10 has a plurality of membrane leaves 19. Each membrane leaf 19 includes a first separation membrane 11 and a permeate-side flow channel material 17. For example, a membrane leaf 19 has two first separation membranes 11. The two first separation membranes 11 are overlapped and sealed on three sides to form a bag-like structure. The permeate-side flow channel material 17 is positioned between the two first separation membranes 11 so as to be located inside the bag-like structure. The permeate-side flow channel material 17 secures a space (permeate space) between the two first separation membranes 11 as a flow channel for the first permeable fluid F1. In this way, the permeate-side flow channel material 17 is used in combination with the first separation membrane 11. The number of membrane leaves 19 is not particularly limited and can be, for example, 2 to 30.

[0120] The first membrane separation unit 10 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 leaves 19. More specifically, multiple supply-side flow channel materials 18 and multiple membrane leaves 19 are stacked alternately. The supply-side flow channel material 18 secures a space (supply space) between the membrane leaves 19 that serves as a flow channel for the raw fluid F0.

[0121] 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.

[0122] The outer surface of the membrane element is composed of a shell (not shown) made of a material that prevents fluid from passing through. The shell may be made of fiber-reinforced plastic (FRP). The membrane element may be housed in a casing (not shown).

[0123] The first membrane separation unit 10 (membrane element) shown in Figure 4 can be operated, for example, in the following way. First, the raw fluid F0 is supplied to one end of the wound membrane leaf 19. The space inside the central tube 16 is depressurized. Depressurization can be performed by the depressurization unit 40. As a result, the first permeate fluid F1 that has permeated through the first separation membrane 11 of the membrane leaf 19 moves into the central tube 16. The first permeate fluid F1 is discharged to the outside through the central tube 16. The raw fluid F0 (first non-permeable fluid F2) processed in the first membrane separation unit 10 is discharged to the outside from the other end of the wound membrane leaf 19.

[0124] In this embodiment, at least one membrane separation unit may include multiple membrane separation units. Multiple membrane separation units may be connected in series so that the impermeable fluid discharged from the membrane separation unit located upstream is supplied as a supply fluid to the membrane separation unit located downstream.

[0125] <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 4 of the membrane separation system of this embodiment will be described with reference to Figures 5 to 8. 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.

[0126] [Modification 1 of the Membrane Separation System] Figure 5 is a schematic diagram showing modification 1 of the membrane separation system of this embodiment. The membrane separation system 100B of modification 1 shown in Figure 5 includes a first membrane separation unit 10 and a second membrane separation unit 20 connected in series with each other, as at least one membrane separation unit. In this specification, "connected in series with each other" means a configuration in which multiple membrane separation units are connected to each other so that an impermeable fluid discharged from an upstream membrane separation unit is supplied to a downstream membrane separation unit. The second membrane separation unit 20 has a second separation membrane 21 that separates a first impermeable fluid F2, which is the supply fluid, into a second permeable fluid F3 and a second impermeable fluid F4. In the membrane separation system 100B, the depressurization unit 40 depressurizes the permeable space of the first membrane separation unit 10 and the permeable space of the second membrane separation unit 20 to discharge the high-temperature discharge fluid S1. The membrane separation system 100B includes a second heat exchange unit 52 as a heat exchange unit.

[0127] In the membrane separation system 100B, the second heat exchange unit 52 heats the first impermeable fluid F2 supplied to the second membrane separation unit 20, which is located furthest downstream, using the high-temperature discharge fluid S1 discharged from the depressurization unit 40. More specifically, the second heat exchange unit 52 heats the first impermeable fluid F2 by performing heat exchange between the discharge fluid S1, which is used as a heat transfer medium for heating, and the first impermeable fluid F2, which is used as a heat transfer medium for cooling.

[0128] For example, the second heat exchange unit 52 heats the temperature of the first impermeable fluid F2 to a range of 25°C to 60°C. The second heat exchange unit 52 may heat the temperature of the first impermeable fluid F2 to a range of 30°C to 45°C, or to a range of 35°C to 40°C.

[0129] In systems with multiple membrane separation devices, the temperature of the supply fluid supplied to the membrane separation devices tends to decrease from the upstream to the downstream side. This tendency is particularly pronounced when the separation membrane is a permeable vaporization membrane. In membrane separation system 100B, the high-temperature discharge fluid S1 discharged from the depressurization section 40 can be used as a heat transfer medium for heating the second heat exchange section 52. Therefore, compared to conventional membrane separation systems with multiple membrane separation devices, it becomes possible to heat the first impermeable fluid F2 supplied to the second membrane separation section 20 at a lower cost. As a result, the temperature of the first impermeable fluid F2 supplied to the second membrane separation section 20, which is located downstream of the first membrane separation section 10, can be maintained stably and at a low cost.

[0130] The heat exchange section of the membrane separation system 100B is not limited to the second heat exchange section 52. For example, the membrane separation system 100B may further include a first heat exchange section that heats the raw fluid F0 supplied to the first membrane separation section 10. In this case, for example, the first heat exchange section heats the temperature of the raw fluid F0 supplied to the first membrane separation section 10 to a range of 25°C to 60°C. The first heat exchange section may heat the temperature of the raw fluid F0 to a range of 30°C to 45°C, or to a range of 35°C to 40°C.

[0131] In the example shown in Figure 5, one depressurization unit 40 is connected to both the first membrane separation unit 10 and the second membrane separation unit 20. However, the number of depressurization units is not limited to one. A depressurization unit may be connected to both the first membrane separation unit 10 and the second membrane separation unit 20.

[0132] In the membrane separation system 100B, the condensation unit 41 cools and condenses the first permeate fluid F1 sent from the first membrane separation unit 10 and the second permeate fluid F3 sent from the second membrane separation unit 20. As shown in Figure 5, the condensation unit 41 may also cool and condense a mixed fluid of the first permeate fluid F1 and the second permeate fluid F3.

[0133] For example, the condensing unit 41 cools the temperature of the mixed fluid of the first permeate fluid F1 and the second permeate fluid F3 to a range of -80°C to 30°C. The condensing unit 41 may also cool the temperature of the mixed fluid to a range of -20°C to 20°C, or to a range of -10°C to 10°C.

[0134] The membrane separation system 100B includes a second supply path 84 as a supply path. The second supply path 84 is a path that guides the high-temperature discharge fluid S1 discharged from the depressurization section 40 to the second heat exchange section 52. In the example shown in Figure 5, the second supply path 84 connects the discharge fluid outlet of the depressurization section 40 to the discharge fluid inlet of the second heat exchange section 52.

[0135] As shown in Figure 5, the second supply path 84 may be provided with a temperature sensor 54b for measuring the temperature of the discharge fluid S1. For example, the temperature of the discharge fluid S1 may be monitored by the temperature sensor 54b, and the amount of discharge fluid S1 supplied to the second heat exchange unit 52 may be controlled based on the monitoring results.

[0136] The membrane separation system 100B includes a first temperature sensor 55 and a second temperature sensor 56 as temperature sensors for measuring the temperature of the supply fluid. The second temperature sensor 56 measures the temperature of the first impermeable fluid F2 supplied to the second membrane separation unit 20. For example, the temperature of the first impermeable fluid F2 may be monitored by the second temperature sensor 56, and the amount of discharge fluid S1 supplied to the second heat exchange unit 52 may be controlled based on the monitoring results.

[0137] The membrane separation system 100B includes a second flow control valve 46 provided in the second supply path 84 as a flow control valve in the supply path. For example, based on the result of monitoring the temperature of the first impermeable fluid F2 by the second temperature sensor 56, the opening degree of the second flow control valve 46 may be adjusted so that the temperature of the first impermeable fluid F2 is within a predetermined range. In this way, the flow rate of the discharge fluid S1 supplied to the second heat exchange unit 52 can be controlled. As a result, the temperature of the first impermeable fluid F2 supplied to the second membrane separation unit 20 can be stably maintained. For example, if the temperature of the first impermeable fluid F2 falls below a predetermined range as a result of monitoring the temperature of the first impermeable fluid F2, the flow rate of the discharge fluid S1 supplied to the second heat exchange unit 52 may be increased by increasing the opening degree of the second flow control valve 46. For example, if the temperature of the first impermeable fluid F2 is monitored and it exceeds a predetermined range, the flow rate of the discharge fluid S1 supplied to the second heat exchange unit 52 may be reduced by decreasing the opening of the second flow rate control valve 46.

[0138] The membrane separation system 100B is equipped with a second discharge path 88 as a discharge path. The second discharge path 88 is a path for discharging the discharge fluid S1 after heat exchange from the second heat exchange section 52.

[0139] As shown in Figure 5, in the membrane separation system 100B, the condensing section 42 is connected to the second discharge path 88. The condensing section 42 cools and condenses the heat-exchanged discharge fluid S1 sent from the second heat exchange section 52. The heat-exchanged discharge fluid S1 is more easily condensed than the high-temperature discharge fluid S1 discharged from the reduced pressure section 40. When the membrane separation system 100B is equipped with a condensing section 42, the second discharge path 88 connects the discharge fluid outlet of the second heat exchange section 52 to the discharge fluid inlet of the condensing section 42.

[0140] The membrane separation system 100B includes a temperature controller 72 for heating the first impermeable fluid F2. The temperature controller 72 may be used auxiliaryly when the temperature of the discharge fluid S1 discharged from the depressurization section 40 is insufficient for the temperature of the first impermeable fluid F2 to meet a predetermined range. For example, the operation of the temperature controller 72 may be controlled based on the result of monitoring the temperature of the first impermeable fluid F2 by the second temperature sensor 56 so that the temperature of the first impermeable fluid F2 meets a predetermined range. As shown in Figure 5, the temperature controller 72 may be connected to the second heat exchange section 52. A heater or the like can be used as the temperature controller 72.

[0141] The temperature controller in the membrane separation system 100B is not limited to the temperature controller 72. For example, if the membrane separation system 100B includes a first heat exchange unit that heats the raw fluid F0 supplied to the first membrane separation unit 10, the membrane separation system 100B may further include a temperature controller that heats the raw fluid F0. The temperature controller may be connected to the first heat exchange unit.

[0142] In the membrane separation system 100B, the first impermeable fluid path 93 connects the first impermeable fluid outlet 10c of the first membrane separation unit 10 to the first impermeable fluid inlet 20a of the second membrane separation unit 20, and is a path that guides the first impermeable fluid F2 from the first membrane separation unit 10 to the second membrane separation unit 20. If the raw fluid F0 is a solution containing a volatile organic compound, a concentration sensor for measuring the content of the organic compound in the first impermeable fluid F2 may be placed in the first impermeable fluid path 93.

[0143] As shown in Figure 5, in the membrane separation system 100B, the second heat exchange unit 52 and the second temperature sensor 56 are located on the first impermeable fluid path 93.

[0144] The membrane separation system 100B further includes a second permeable fluid path 94 and a second impermeable fluid path 95 as fluid pathways.

[0145] The second permeable fluid path 94 is connected to the second permeable fluid outlet 20b of the second membrane separation unit 20 and is a path for discharging the second permeable fluid F3 from the second membrane separation unit 20. If the raw fluid F0 is a solution containing a volatile organic compound, a concentration sensor for measuring the content of the organic compound in the second permeable fluid F3 may be placed in the second permeable fluid path 94.

[0146] In the membrane separation system 100B, the second permeable fluid path 94 merges with the first permeable fluid path 92 at the confluence position 92p. This configuration allows the second permeable fluid F3 to be guided from the second membrane separation section 20 to the condensation section 41.

[0147] The second impermeable fluid path 95 is connected to the second impermeable fluid outlet 20c of the second membrane separation unit 20 and is a path for discharging the second impermeable fluid F4 from the second membrane separation unit 20. If the raw fluid F0 is a solution containing volatile organic compounds, a concentration sensor for measuring the content of organic compounds in the second impermeable fluid F4 may be placed in the second impermeable fluid path 95.

[0148] As shown in Figure 5, the second impermeable fluid path 95 may be connected to the impermeable fluid inlet 60a of the supply unit 60. In other words, in the membrane separation system 100B, the second impermeable fluid F4 may be mixed with the raw fluid F0 in the supply unit 60 and circulate through the raw fluid path 91, the first impermeable fluid path 93, and the second impermeable fluid path 95. With this configuration, the second impermeable fluid F4 can be guided from the second impermeable fluid path 95 to the supply unit 60.

[0149] In the membrane separation system 100B, for example, the control unit 70 controls the temperature of the first impermeable fluid F2 supplied to the second membrane separation unit 20 by controlling the operation of the pressure reducing unit 40, the second flow rate control valve 46, the temperature controller 72, etc. For example, based on the results of monitoring the temperature of the first impermeable fluid F2 by the second temperature sensor 56, the control unit 70 controls the opening degree of the second flow rate control valve 46 so that the temperature of the first impermeable fluid F2 satisfies a predetermined range.

[0150] Since the configuration of the first membrane separation unit 10 and the configuration of the second membrane separation unit 20 are basically the same, the configuration of the second membrane separation unit 20 will not be explained.

[0151] Next, an example of an operating method for the membrane separation system 100B described above will be explained with reference to Figure 5. The operating method for the membrane separation system 100B includes, for example, reducing the pressure in the permeable space of the first membrane separation unit 10 and the permeable space of the second membrane separation unit 20 by the depressurization unit 40 (step 1), separating the raw fluid F0 into a first permeable fluid F1 and a first impermeable fluid F2 in the first membrane separation unit 10 (step 2-1), and separating the first impermeable fluid F2 into a second permeable fluid F3 and a second impermeable fluid F4 in the second membrane separation unit 20 (step 2-2). Furthermore, the operating method includes heating the first impermeable fluid F2 supplied to the second membrane separation unit 20 using the high-temperature discharge fluid S1 discharged from the depressurization unit 40 by the second heat exchange unit 52 (step 3).

[0152] According to the operating method of the membrane separation system 100B, the high-temperature discharge fluid S1 discharged from the depressurization section 40 is used as a heat transfer medium for heating the second heat exchange section 52, thereby heating the first impermeable fluid F2 supplied to the second membrane separation section 20. As a result, compared to the operating method of conventional membrane separation systems, it is possible to heat the first impermeable fluid F2 supplied to the second membrane separation section 20 at a lower cost. Consequently, the temperature of the first impermeable fluid F2 supplied to the second membrane separation section 20, which is located downstream of the first membrane separation section 10, can be maintained stably and at a low cost.

[0153] [Modified Membrane Separation System 2] Figure 6 is a schematic diagram showing modified membrane separation system 2 of this embodiment. The membrane separation system 100C of modified membrane separation system 2 shown in Figure 6 includes a third membrane separation unit 30 in addition to the first membrane separation unit 10 and the second membrane separation unit 20 as at least one membrane separation unit. The first membrane separation unit 10, the second membrane separation unit 20, and the third membrane separation unit 30 are connected in series with respect to each other. The third membrane separation unit 30 has a third separation membrane 31 that separates a second impermeable fluid F4, which is the supply fluid, into a third permeable fluid F5 and a third impermeable fluid F6. The membrane separation system 100C includes a first heat exchange unit 51, a second heat exchange unit 52, and a third heat exchange unit 53 as heat exchange units that heat the supply fluid supplied to the first membrane separation unit 10, the second membrane separation unit 20, and the third membrane separation unit 30, respectively.

[0154] In the membrane separation system 100C, the first heat exchange unit 51 heats the raw fluid F0 supplied to the first membrane separation unit 10 using the discharge fluid S1. The second heat exchange unit 52 heats the first impermeable fluid F2 supplied to the second membrane separation unit 20 using the discharge fluid S1. The third heat exchange unit 53 heats the second impermeable fluid F4 supplied to the third membrane separation unit 30 using the discharge fluid S1.

[0155] In the membrane separation system 100C, the high-temperature discharge fluid S1 discharged from the reduced pressure section 40 can be used as a heating medium selected from the group consisting of the first heat exchange section 51, the second heat exchange section 52, and the third heat exchange section 53.

[0156] The membrane separation system 100C includes a second supply path 84, a first supply path 83, and a third supply path 85 as supply paths. The first supply path 83 is a path that leads the discharge fluid S1 to the first heat exchange section 51. The third supply path 85 is a path that leads the discharge fluid S1 to the third heat exchange section 53. In the example shown in Figure 6, the path connected to the discharge fluid outlet of the pressure reduction section 40 branches into the first supply path 83, the second supply path 84, and the third supply path 85 at the branching position 84p. The first supply path 83 connects the branching position 84p to the discharge fluid inlet of the first heat exchange section 51. The second supply path 84 connects the branching position 84p to the discharge fluid inlet of the second heat exchange section 52. The third supply path 85 connects the branching position 84p to the discharge fluid inlet of the third heat exchange section 53.

[0157] In the membrane separation system 100C, the first heat exchange section 51, the second heat exchange section 52, and the third heat exchange section 53 are connected in parallel by the first supply path 83, the second supply path 84, and the third supply path 85. With this configuration, for example, the same flow rate of discharge fluid S1 can be supplied to each of the first heat exchange section 51, the second heat exchange section 52, and the third heat exchange section 53. Alternatively, for example, different flow rates of discharge fluid S1 can be supplied to each of the first heat exchange section 51, the second heat exchange section 52, and the third heat exchange section 53, so that the supply fluid supplied to a specific membrane separation section can be controlled to be preferentially heated. If the temperature of the supply fluid decreases from the upstream side to the downstream side, the amount of discharge fluid S1 supplied to the first heat exchange section 51, the second heat exchange section 52, and the third heat exchange section 53 may be increased in that order. If the temperature of the raw fluid F0 is low, the flow rate of the discharge fluid S1 supplied to the first heat exchange unit 51 may be increased compared to the amount of discharge fluid S1 supplied to the second heat exchange unit 52 and the third heat exchange unit 53.

[0158] In the example shown in Figure 6, the temperature sensor 54b is located in the path connecting the discharge fluid outlet of the pressure reduction unit 40 to the branching point 84p. For example, the temperature of the discharge fluid S1 may be monitored by the temperature sensor 54b, and the flow rate of the discharge fluid S1 supplied to the first heat exchange unit 51, the second heat exchange unit 52, and the third heat exchange unit 53 may be controlled based on the monitoring results.

[0159] The membrane separation system 100C includes a first temperature sensor 55, a second temperature sensor 56, and a third temperature sensor 57 as temperature sensors for measuring the temperature of the supply fluid. The third temperature sensor 57 measures the temperature of the second impermeable fluid F4 supplied to the third membrane separation unit 30. For example, the temperature of the raw fluid F0, the temperature of the first impermeable fluid F2, and the temperature of the second impermeable fluid F4 may be monitored by the first temperature sensor 55, the second temperature sensor 56, and the third temperature sensor 57, and the flow rate of the discharge fluid S1 supplied to the first heat exchange unit 51, the second heat exchange unit 52, and the third heat exchange unit 53 may be controlled based on the monitoring results.

[0160] The membrane separation system 100C includes, as flow rate control valves in the supply path, a second flow rate control valve 46 provided in the second supply path 84, a first flow rate control valve 45 provided in the first supply path 83, and a third flow rate control valve 47 provided in the third supply path 85. For example, based on the results of monitoring the temperature of the raw fluid F0, the temperature of the first impermeable fluid F2, and the temperature of the second impermeable fluid F4 by the first temperature sensor 55, the second temperature sensor 56, and the third temperature sensor 57, the opening degrees of the first flow rate control valve 45, the second flow rate control valve 46, and the third flow rate control valve 47 may be adjusted so that the temperatures of the raw fluid F0, the first impermeable fluid F2, and the second impermeable fluid F4 each meet a predetermined range. In this way, the flow rate of the discharge fluid S1 supplied to the first heat exchange section 51, the second heat exchange section 52, and the third heat exchange section 53 can be controlled. As a result, the temperature of the supply fluid supplied to each membrane separation section can be stably maintained. For example, if monitoring reveals that the temperature of the raw fluid F0 supplied to the first membrane separation unit 10 falls below a predetermined range, the first flow control valve 45 may be opened and the second and third flow control valves 46 and 47 may be closed to supply the discharge fluid S1 only to the first heat exchange unit 51, thereby preferentially heating the raw fluid F0. If monitoring reveals that the temperature of the supplied fluid is decreasing from the upstream to the downstream side, the amount of discharge fluid S1 supplied to the first heat exchange unit 51, the second heat exchange unit 52, and the third heat exchange unit 53 may be increased in the order of the first heat exchange unit 51, the second heat exchange unit 52, and the third heat exchange unit 53 by increasing the opening of the first flow control valve 45, the second flow control valve 46, and the third flow control valve 47.

[0161] The membrane separation system 100C includes a second discharge path 88, a first discharge path 87, and a third discharge path 89 as discharge paths. The first discharge path 87 is a path for discharging the discharge fluid S1 after heat exchange from the first heat exchange unit 51. The third discharge path 89 is a path for discharging the discharge fluid S1 after heat exchange from the third heat exchange unit 53. In the example shown in Figure 6, the first discharge path 87 merges with the second discharge path 88 at a merging position 88p. The third discharge path 89 merges with the second discharge path 88 at a merging position 89p.

[0162] The membrane separation system 100C includes a temperature controller 73 for heating the second impermeable fluid F4. The temperature controller 73 may be used auxiliaryly when the temperature of the discharge fluid S1 discharged from the depressurization section 40 is insufficient for the temperature of the second impermeable fluid F4 to meet a predetermined range. For example, the operation of the temperature controller 73 may be controlled based on the result of monitoring the temperature of the second impermeable fluid F4 by the third temperature sensor 57 so that the temperature of the second impermeable fluid F4 meets a predetermined range. As shown in Figure 6, the temperature controller 73 may be connected to the third heat exchange section 53. A heater or the like can be used as the temperature controller 73.

[0163] The temperature controllers in the membrane separation system 100C are not limited to the temperature controller 73 for heating the second impermeable fluid F4. For example, the membrane separation system 100C may further include a temperature controller for heating the raw fluid F0 and a temperature controller for heating the first impermeable fluid F2. The temperature controller for heating the raw fluid F0 may be connected to the first heat exchange unit 51. The temperature controller for heating the first impermeable fluid F2 may be connected to the second heat exchange unit 52.

[0164] As shown in Figure 6, in the membrane separation system 100C, the second impermeable fluid path 95 connects the second impermeable fluid outlet 20c of the second membrane separation unit 20 and the second impermeable fluid inlet 30a of the third membrane separation unit 30, and is a path that guides the second impermeable fluid F4 from the second membrane separation unit 20 to the third membrane separation unit 30.

[0165] As shown in Figure 6, in the membrane separation system 100C, the third heat exchange unit 53 and the third temperature sensor 57 are located on the second impermeable fluid path 95.

[0166] The membrane separation system 100C further includes a third permeable fluid path 96 and a third impermeable fluid path 97 as fluid pathways.

[0167] The third permeable fluid path 96 is connected to the third permeable fluid outlet 30b of the third membrane separation unit 30 and is a path for discharging the third permeable fluid F5 from the third membrane separation unit 30. If the raw fluid F0 is a solution containing a volatile organic compound, a concentration sensor for measuring the content of the organic compound in the third permeable fluid F5 may be placed in the third permeable fluid path 96.

[0168] In the membrane separation system 100C, the third permeable fluid path 96 merges with the second permeable fluid path 94 at the merging position 94p. This configuration allows the third permeable fluid F5 to be guided from the third membrane separation section 30 to the condensation section 41.

[0169] The third impermeable fluid path 97 is connected to the third impermeable fluid outlet 30c of the third membrane separation unit 30 and is a path for discharging the third impermeable fluid F6 from the third membrane separation unit 30. If the raw fluid F0 is a solution containing volatile organic compounds, a concentration sensor for measuring the content of organic compounds in the third impermeable fluid F6 may be placed in the third impermeable fluid path 97.

[0170] As shown in Figure 6, the third impermeable fluid path 97 may be connected to the impermeable fluid inlet 60a of the supply unit 60. In other words, in the membrane separation system 100C, the third impermeable fluid F6 may be mixed with the raw fluid F0 in the supply unit 60 and circulate through the raw fluid path 91, the first impermeable fluid path 93, the second impermeable fluid path 95, and the third impermeable fluid path 97.

[0171] The membrane separation system 100C includes a condensing unit 41 and, in addition, a condensing unit 43 connected in series downstream of the condensing unit 41. The condensing unit 43 further cools and condenses the permeate fluid after condensation sent from the condensing unit 41, for example. With this configuration, the concentration of the permeate fluid obtained in the downstream condensing unit 43 can be increased. The condensation temperature of the condensing unit 43 may be the same as or different from that of the condensing unit 41.

[0172] In the example shown in Figure 6, two condensing units (condensing unit 41 and condensing unit 43) are connected in series. However, three or more condensing units may be connected in series.

[0173] As shown in Figure 6, the condensing unit 43 may be connected to a recovery unit 63 for recovering the permeate fluid of the liquid obtained by condensation. The recovery unit 63 is, for example, a tank for storing the permeate fluid of the liquid. If the raw fluid F0 is a solution containing volatile organic compounds, a concentration sensor 59 for measuring the content of organic compounds in the condensed permeate fluid may be placed in the path connecting the condensing unit 43 and the recovery unit 63.

[0174] In the membrane separation system 100C, for example, the control unit 70 controls the temperature of the supply fluid supplied to each membrane separation unit by controlling the operation of the pressure reducing unit 40, the first flow rate control valve 45, the second flow rate control valve 46, the third flow rate control valve 47, the temperature controller 73, and so on. For example, the control unit 70 may control the opening degrees of the first flow rate control valve 45, the second flow rate control valve 46, and the third flow rate control valve 47, respectively, based on the results of monitoring the temperature of the raw fluid F0, the first impermeable fluid F2, and the second impermeable fluid F4 by the first temperature sensor 55, the second temperature sensor 56, and the third temperature sensor 57, so that the temperatures of the raw fluid F0, the first impermeable fluid F2, and the second impermeable fluid F4 each meet predetermined ranges.

[0175] Next, an example of how to operate the membrane separation system 100C will be described with reference to Figure 6. The operation method of the membrane separation system 100C includes, for example, reducing the pressure in the permeation spaces of the first membrane separation unit 10, the second membrane separation unit 20, and the third membrane separation unit 30 using a depressurization unit 40 (step 1), separating the raw fluid F0 into a first permeation fluid F1 and a first impermeable fluid F2 in the first membrane separation unit 10 (step 2-1), separating the first impermeable fluid F2 into a second permeation fluid F3 and a second impermeable fluid F4 in the second membrane separation unit 20 (step 2-2), and separating the second impermeable fluid F4 into a third permeation fluid F5 and a third impermeable fluid F6 using a third separation membrane 31 in the third membrane separation unit 30 (step 2-3). Furthermore, the operating method includes at least one selected from the group consisting of: heating the raw fluid F0 supplied to the first membrane separation unit 10 using the discharge fluid S1 by the first heat exchange unit 51 (step 3-1); heating the first impermeable fluid F2 supplied to the second membrane separation unit 20 using the discharge fluid S1 by the second heat exchange unit 52 (step 3-2); and heating the second impermeable fluid F4 supplied to the third membrane separation unit 30 using the discharge fluid S1 by the third heat exchange unit 53 (step 3-3).

[0176] According to the operating method of the membrane separation system 100C, the high-temperature discharge fluid S1 discharged from the reduced pressure section 40 can be used as at least one heating medium selected from the group consisting of the first heat exchange section 51, the second heat exchange section 52, and the third heat exchange section 53.

[0177] [Modification 3 of the Membrane Separation System] Figure 7 is a schematic diagram showing modification 3 of the membrane separation system of this embodiment. In the membrane separation system 100D of modification 3 shown in Figure 7, the third heat exchange section 53, the second heat exchange section 52, and the first heat exchange section 51 are connected in series by a third supply path 85, a second supply path 84, and a first supply path 83, so that the discharge fluid S1 is supplied from the downstream side to the upstream side, that is, in the order of the third heat exchange section 53, the second heat exchange section 52, and the first heat exchange section 51. Aside from this, the membrane separation system 100D has basically the same configuration as the membrane separation system 100C of modification 2 described above.

[0178] As shown in Figure 7, in the membrane separation system 100D, the third discharge path for discharging the heat-exchanged discharge fluid S1 from the third heat exchange section 53 corresponds to the second supply path 84. The second discharge path for discharging the heat-exchanged discharge fluid S1 from the second heat exchange section 52 corresponds to the first supply path 83. In the membrane separation system 102, the high-temperature discharge fluid S1 discharged from the depressurization section 40 can be used as a heat transfer medium for heating the heat exchange sections in the order of the third heat exchange section 53, the second heat exchange section 52, and the first heat exchange section 51, from downstream to upstream. The temperature of the discharge fluid S1 decreases in the order of the third heat exchange section 53, the second heat exchange section 52, and the first heat exchange section 51. Therefore, for example, if the temperature of the supply fluid decreases from upstream to downstream, it becomes possible to efficiently heat the supply fluid supplied to each membrane separation section.

[0179] The membrane separation system 100D includes a third flow control valve 47 provided in the third supply path 85 as a flow control valve provided in the supply path. For example, the opening degree of the third flow control valve 47 may be adjusted so that the temperature of the second impermeable fluid F4 is within a predetermined range, based on the result of monitoring the temperature of the second impermeable fluid F4 by the third temperature sensor 57. In this way, the flow rate of the discharge fluid S1 supplied to the third heat exchange section 53 can be controlled. Since the temperature of the discharge fluid S1 decreases in the order of the first heat exchange section 51, the second heat exchange section 52, and the third heat exchange section 53, if the temperature of the supply fluid decreases from the upstream side to the downstream side, it becomes possible to efficiently heat the supply fluid supplied to each membrane separation section.

[0180] The membrane separation system 100D may further include a second flow control valve provided in the second supply path 84 and a first flow control valve provided in the first supply path 83. For example, the opening degrees of the first flow control valve and the second flow control valve may be adjusted so that the temperature of the raw fluid F0 and the temperature of the first impermeable fluid F2 each meet predetermined ranges based on monitoring results from the first temperature sensor 55, the second temperature sensor 56, and the third temperature sensor 57.

[0181] The membrane separation system 100D may further include a third bypass path that directly leads the heat-exchanged discharge fluid S1 discharged from the third heat exchange unit 53 to the condensing unit 42, a second bypass path that directly leads the heat-exchanged discharge fluid S1 discharged from the second heat exchange unit 52 to the condensing unit 42, and a first bypass path that directly leads the heat-exchanged discharge fluid S1 discharged from the first heat exchange unit 51 to the condensing unit 42. The third discharge path 89, the second discharge path 88, the first discharge path 87, the third bypass path, the second bypass path, and the first bypass path may each be configured to be switchable. For example, if monitoring by the first temperature sensor 55, the second temperature sensor 56, and the third temperature sensor 57 indicates that it is not necessary to supply the discharge fluid S1 to the first heat exchange unit 51, the heat-exchanged discharge fluid S1 discharged from the second heat exchange unit 52 may be led to the second bypass path.

[0182] In the membrane separation system 100D, for example, the control unit 70 controls the temperature of the supply fluid supplied to each membrane separation unit by controlling the operation of the pressure reducing unit 40, the third flow control valve 47, the temperature controller 73, and so on. For example, based on the results of monitoring the temperature of the second impermeable fluid F4 by the third temperature sensor 57, the control unit 70 controls the opening degree of the third flow control valve 47 so that the temperature of the second impermeable fluid F4 meets a predetermined range.

[0183] Next, an example of how to operate the membrane separation system 100D will be described with reference to Figure 7. The operation method of the membrane separation system 100D includes, for example, reducing the pressure in the permeable spaces of the first membrane separation unit 10, the second membrane separation unit 20, and the third membrane separation unit 30 using a depressurization unit 40 (step 1), separating the raw fluid F0 into a first permeable fluid F1 and a first impermeable fluid F2 in the first membrane separation unit 10 (step 2-1), separating the first impermeable fluid F2 into a second permeable fluid F3 and a second impermeable fluid F4 in the second membrane separation unit 20 (step 2-2), and separating the second impermeable fluid F4 into a third permeable fluid F5 and a third impermeable fluid F6 using a third separation membrane 31 in the third membrane separation unit 30 (step 2-3). Furthermore, the operation method includes heating the second impermeable fluid F4 supplied to the third membrane separation unit 30 using the discharge fluid S1 by the third heat exchange unit 53, heating the first impermeable fluid F2 supplied to the second membrane separation unit 20 using the discharge fluid S1 by the second heat exchange unit 52, and heating the raw fluid F0 supplied to the first membrane separation unit 10 using the discharge fluid S1 by the first heat exchange unit 51 (step 3).

[0184] According to the operating method of the membrane separation system 100D, by using the hotter discharge fluid S1 as a heat transfer medium for heating the heat exchange section located downstream, the supply fluid supplied to each membrane separation section can be efficiently heated.

[0185] [Modification 4 of the Membrane Separation System] Figure 8 is a schematic diagram showing modification 4 of the membrane separation system of this embodiment. In the membrane separation system 100E of modification 4 shown in Figure 8, the third membrane separation unit 30, the second membrane separation unit 20, and the first membrane separation unit 10 are arranged such that their vertical positions become lower from the downstream side to the upstream side. Except for this, the membrane separation system 100E has basically the same configuration as the membrane separation system 100D of modification 3 described above.

[0186] In the membrane separation system 100E, the third supply path 85, the second supply path 84, and the first supply path 83 are arranged at an incline from downstream to upstream. This allows the high-temperature discharge fluid S1 discharged from the depressurization section 40 to flow easily from downstream to upstream in the order of the third supply path 85, the second supply path 84, and the first supply path 83. Therefore, even if condensation of the discharge fluid S1 occurs within the supply path, the supply path is less likely to become blocked. As a result, it becomes possible to efficiently heat the supply fluid supplied to each membrane separation section.

[0187] As shown in Figure 8, the membrane separation system 100E may further include a recovery unit 64 in addition to the recovery unit 62. The recovery unit 64 is provided branching off from the discharge path connecting the discharge fluid outlet of the first heat exchange unit 51 and the discharge fluid inlet of the condensation unit 42. With this configuration, for example, even if condensation of the discharge fluid S1 occurs in the supply path, the condensed liquid can be recovered by the recovery unit 64.

[0188] The operating method of the membrane separation system 100E is the same as that of the membrane separation system 100D in the modified example 3 described above, so the explanation is omitted.

[0189] 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.

[0190] The membrane separation system of this embodiment is particularly suitable for efficiently recovering volatile organic compounds from solutions containing such compounds.

Claims

1. A membrane separation system comprising: at least one membrane separation unit for separating a supply fluid into a permeable fluid and an impermeable fluid; a depressurization unit for reducing the pressure within the permeable space of the at least one membrane separation unit; and a heat exchange unit for heating the supply fluid supplied to the at least one membrane separation unit using the discharged fluid discharged from the depressurization unit.

2. The membrane separation system according to claim 1, further comprising: a supply path for guiding the discharged fluid to the heat exchange section; a flow control valve provided in the supply path; and a temperature sensor for measuring the temperature of the supply fluid.

3. The membrane separation system according to claim 2, wherein the opening of the flow control valve is adjusted so that the temperature of the supply fluid is within a predetermined range, based on the results of monitoring the temperature of the supply fluid by the temperature sensor.

4. The membrane separation system according to claim 1, wherein the at least one membrane separation unit has a separation membrane, and the separation membrane includes a permeable vaporization membrane.

5. The membrane separation system according to claim 4, wherein the supply fluid includes a raw fluid, and the raw fluid includes a solution containing a volatile organic compound.

6. The membrane separation system according to claim 5, further comprising a supply unit for storing the raw fluid.

7. The membrane separation system according to claim 1, wherein the pressure reduction section includes a vacuum pump.

8. The membrane separation system according to claim 1, further comprising a condensation unit for cooling and condensing the permeate fluid.

9. The membrane separation system according to claim 1, further comprising a temperature controller for heating the supply fluid.

10. The membrane separation system according to claim 1, wherein the at least one membrane separation unit includes a plurality of membrane separation units, and 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.

11. The membrane separation system according to claim 10, wherein the heat exchange section includes a heat exchange section that heats the supply fluid supplied to the membrane separation section located furthest downstream of the plurality of membrane separation sections.

12. The membrane separation system according to claim 11, wherein the heat exchange section includes a plurality of heat exchange sections that heat the supply fluid supplied to each of the plurality of membrane separation sections.

13. The membrane separation system according to claim 12, wherein the plurality of heat exchange units are connected in parallel.

14. The membrane separation system according to claim 12, wherein the plurality of heat exchange units are connected in series such that the discharge fluid is supplied sequentially from the downstream side to the upstream side.

15. The membrane separation system according to claim 14, wherein the plurality of membrane separation units are arranged such that their vertical position decreases from the downstream side to the upstream side.

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