Raw material liquid concentration system and method

Abstract

To provide a hollow fiber membrane, membrane module, raw material liquid concentration system and raw material liquid concentration method, capable of concentrating the objective component in a raw material liquid to high concentration level with few alteration even if the liquid is highly viscous.SOLUTION: Provided is a porous hollow fiber membrane for concentrating a raw material liquid having a viscosity of 3 cP or more but 600 cP or less by a membrane distillation. The air permeability of the membrane is 500 L / h.m2.kPa or more, and the percolation speed of ethanol aqueous solution having 20 mass% concentration at application of pressure of 200 kPa is 100 mL / h.m2 or less. Besides, the inner diameter of the hollow fiber membrane is 0.3 mm or more but 2.0 mm or less.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a hollow fiber membrane, a membrane module, a raw material liquid concentration system, and a raw material liquid concentration method useful for concentrating a highly viscous raw material liquid in a food manufacturing process and an industrial process. More specifically, the present invention relates to a raw material liquid concentration system and a raw material liquid concentration method for concentrating a raw material liquid by separating a part of a solvent from the highly viscous raw material liquid used in a food manufacturing process and an industrial process by membrane distillation.

Background Art

[0002] In recent years, due to consumers' health consciousness, consumers have shown interest in food products harvested, extracted, or concentrated from natural sources. For example, a concentrated liquid obtained by putting a raw material liquid derived from natural products into an evaporator and heating and evaporating the water is added as a sweetener to various dishes, confectioneries, and the like. However, when the raw material liquid is heated at a high temperature, many components contained in the raw material liquid are deteriorated or lost, so there is a problem that the flavor components are deteriorated and discolored in the obtained concentrated liquid.

[0003] On the other hand, also in an industrial process, there are cases where concentration of a raw material liquid containing valuable substances that are easily decomposed by heating is required. Such a raw material liquid needs to be concentrated by a method that suppresses heating, similar to the above food products.

[0004] Therefore, generally, the reverse osmosis membrane method and the forward osmosis membrane method have been used as methods for concentrating a raw material liquid without requiring heating. For example, Patent Documents 1 and 2 describe a method for concentrating maple syrup by the reverse osmosis membrane method, and Patent Document 3 describes a method for concentrating a liquid food by the forward osmosis membrane method. Further, Patent Document 4 describes a method for concentrating a liquid food by a combination of the reverse osmosis membrane method and the membrane distillation method.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] However, in the reverse osmosis membrane method, since it is necessary to apply a pressure higher than the osmotic pressure of the concentrated solution to the raw material solution, there is a limit to the concentration. Further, in the reverse osmosis membrane method, since a high pressure is applied to the membrane, the components contained in the raw material solution are likely to be adsorbed on the membrane, and there is a problem that the membrane performance deteriorates when repeated operation is performed.

[0007] On the other hand, in the membrane distillation method, since heating is required, there is a problem that deterioration of the concentrated solution, decomposition of valuable substances, discoloration, etc. occur depending on the heating method or temperature. Further, for example, in the production of liquid food products such as sugar solutions such as maple syrup and honey, coffee extracts, tea extracts, juices, flavor emulsions, food oil emulsions, etc., the raw material solution is inherently highly viscous. Therefore, when a linear velocity above a certain level is maintained to increase the membrane distillation efficiency, there is also a problem that the pressure loss increases, leading to wetting of the membrane and thus a decrease in the concentration performance due to clogging of the porous structure of the membrane.

[0008] An object of the present invention is to solve the above problems and provide a hollow fiber membrane, a membrane module, a raw material solution concentration system, and a raw material solution concentration method capable of concentrating a target component in a raw material solution with little alteration to a high concentration even when the raw material solution is highly viscous. [Means for Solving the Problems]

[0009] The present invention includes the following aspects. [1] A porous hollow fiber membrane for concentrating a raw material solution having a viscosity of 3 cP or more and 600 cP or less by membrane distillation, The air permeability is 500 L / h·m 2 ·kPa or more, the water permeation rate of an ethanol aqueous solution with a concentration of 20% by mass at a pressure of 200 kPa is 100 mL / h·m 2 or less, and a hollow fiber membrane having a hollow fiber inner diameter of 0.3 mm or more and 2.0 mm or less. [2] The air permeability is 1000 L / h·m 2 ·kPa or more and 5000 L / h·m 2 ·kPa or less, the water permeation rate is 50 mL / h·m 2 or less, and the hollow fiber membrane according to the above aspect 1, wherein the hollow fiber inner diameter is 0.5 mm or more and 1.5 mm or less. [3] The hollow fiber membrane according to the above aspect 1 or 2, which is composed of at least one resin selected from the group consisting of polysulfone, polyethersulfone, polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, and polychlorotrifluoroethylene. [4] The hollow fiber membrane according to any one of the above aspects 1 to 3, wherein the raw material liquid is Japanese maple sap having a Brix value of 2 or more and 70 or less. [5] A membrane module for concentrating a raw material liquid having a viscosity of 3 cP or more and 600 cP or less by membrane distillation, the membrane module having a porous hollow fiber membrane and a substantially cylindrical or substantially polygonal module case for housing the hollow fiber membrane, the membrane module having a membrane fixing portion at both axial ends of the module case, wherein the hollow fiber membrane is fixed with an open end by a fixing resin, and a raw material liquid flow-through opening for flowing the raw material liquid from the open end into the inside of the hollow fiber membrane, and having a vapor outlet on a side surface for communicating with the gas phase portion of the membrane module and taking out the vapor in the gas phase portion to the outside of the membrane module, the opening area of the vapor outlet is 1 / 1500 or more of the membrane area of the hollow fiber membrane, the effective length of the hollow fiber membrane is 100 times or more and 1000 times or less of the hollow fiber inner diameter, The membrane module, wherein an opening area of the raw material liquid flow-through opening is 0.2 times or more and 8.0 times or less of a total opening cross-sectional area of the hollow fibers. [6] The opening area of the vapor outlet is 1 / 1000 or more and 1 / 250 or less of a membrane area of the hollow fiber membrane, wherein an effective length of the hollow fiber membrane is 100 times or more and 800 times or less of an inner diameter of the hollow fiber, The membrane module according to the above aspect 5, wherein the opening area of the raw material liquid flow-through opening is 0.2 times or more and 5.0 times or less of the total opening cross-sectional area of the hollow fibers. [7] The module case is composed of at least one resin selected from the group consisting of polypropylene, polysulfone, polyethersulfone, polyvinylidene fluoride, polyphenylene ether, ABS resin, fiber reinforced plastic, and vinyl chloride resin, and / or at least one metal selected from the group consisting of stainless steel, brass, brass, and titanium. The membrane module according to the above aspect 5 or 6. [8] The membrane module according to any one of the above aspects 5 to 7, wherein the raw material liquid is Japanese alder tree sap having a Brix value of 2 or more and 70 or less. [9] The membrane module according to any one of the above aspects 5 to 8, wherein the hollow fiber membrane is the hollow fiber membrane according to any one of the above aspects 1 to 4.

[10] A raw material liquid concentration system for concentrating a raw material liquid having a viscosity of 3 cP or more and 600 cP or less by membrane distillation, The raw material liquid concentration system includes a raw material liquid tank for storing the raw material liquid, a heating unit for heating the raw material liquid, a membrane distillation unit having a porous hollow fiber membrane for concentrating the raw material liquid heated by the heating unit, and a circulation pump for circulating the raw material liquid from the raw material liquid tank to the heating unit and the membrane distillation unit in this order and returning it to the raw material liquid tank. The hollow fiber membrane is arranged to receive the raw material liquid in the hollow part and discharge vapor to the outside of the hollow fiber membrane. At a raw material liquid inflow site of the hollow fiber membrane, the raw material liquid temperature is 30°C or more and 80°C or less, the raw material liquid pressure is 10 kPa or more and 300 kPa or less, and the pressure outside the hollow fiber membrane is reduced to -80 kPa or less. The differential pressure between the raw material liquid pressure and the outside pressure of the hollow fiber membrane is 395 kPa or less, and the linear velocity of the raw material liquid inside the hollow fiber membrane is 0.05 m / s or more and 1.0 m / s or less, such that a raw material liquid concentration system is configured.

[11] A method for producing a raw material liquid concentrate by concentrating a raw material liquid having a viscosity of 3 cP or more and 600 cP or less by membrane distillation, the method comprising: a heating step of heating the raw material liquid; a concentration step of flowing the heated raw material liquid through the hollow portion of a porous hollow fiber membrane and concentrating it by membrane distillation, circulating the raw material liquid concentrated in the concentration step and merging it with the raw material liquid before concentration, at the raw material liquid inflow site of the hollow fiber membrane, the temperature of the raw material liquid is 30°C or more and 80°C or less, the pressure of the raw material liquid is 10 kPa or more and 300 kPa or less, the outside pressure of the hollow fiber membrane is reduced to -80 kPa or less, the differential pressure between the raw material liquid pressure and the outside pressure of the hollow fiber membrane is 395 kPa or less, and the linear velocity of the raw material liquid inside the hollow fiber membrane is 0.05 m / s or more and 1.0 m / s or less.

[12] The method according to aspect 11 above, wherein the temperature of the raw material liquid is 40°C or more and 70°C or less.

[13] The method according to aspect 11 or 12 above, wherein the outside pressure of the hollow fiber membrane is -90 kPa or less.

[14] The pressure of the raw material liquid is 30 kPa or more and 210 kPa or less, and the differential pressure between the raw material liquid pressure and the outside pressure of the hollow fiber membrane is 300 kPa or less. The method according to any one of aspects 11 to 13 above.

[15] The method according to any one of aspects 11 to 14 above, wherein the linear velocity of the raw material liquid inside the hollow fiber membrane is 0.05 m / s or more and 0.5 m / s or less.

[16] The method according to any one of aspects 11 to 15 above, wherein in the heating step, the raw material liquid is heated by bringing it into contact with a heating section at 90°C or less.

[17] The method according to aspect 16 above, wherein the heating section is a heat exchanger that circulates a heat medium which is steam at 50°C or higher or hot water at 50°C or higher.

[18] The method according to aspect 16 or 17 above, wherein the heating section utilizes waste heat.

[19] Further comprising an additional concentration step of flowing the concentrated raw material liquid through an evaporator after the concentration step, and the temperature of the raw material liquid in the additional concentration step is equal to or higher than the temperature of the raw material liquid in the concentration step, the method according to any one of aspects 11 to 18 above.

[20] Further comprising a preliminary concentration step of preliminarily concentrating the raw material liquid with a reverse osmosis membrane, and supplying the preliminarily concentrated raw material liquid to the concentration step, the method according to any one of aspects 11 to 19 above.

[21] The method according to aspect 20 above, wherein the raw material liquid is a sugar solution, the Brix value of the raw material liquid preliminarily concentrated in the preliminary concentration step is 40 or less, and the Brix value of the raw material liquid concentrated in the concentration step is 70 or less.

[22] The method according to aspect 21 above, wherein the raw material liquid is a sugar solution, the Brix value of the raw material liquid preliminarily concentrated in the preliminary concentration step is 35 or less, and the Brix value of the raw material liquid concentrated in the concentration step is 62 or less.

[23] Further comprising a filtration step of filtering the raw material liquid with a filtration membrane to remove impurities, and supplying the filtered raw material liquid to the concentration step, the method according to any one of aspects 11 to 22 above.

[24] The method according to aspect 23 above, wherein the pore diameter of the filtration membrane is 20 μm or less.

[25] The method according to aspect 24 above, wherein the pore diameter of the filtration membrane is 1.0 μm or less.

[26] The method according to any one of aspects 23 to 25 above, wherein the filtration membrane is arranged in a cross-flow configuration.

[27] The method according to any one of aspects 23 to 26 above, further comprising a backwashing step of backwashing the filtration membrane.

[28] The method according to any one of aspects 23 to 27 above, wherein the concentration step and the filtration step are performed in independent raw material liquid flow paths.

[29] The method according to any one of aspects 11 to 28 above, wherein the raw material liquid is sap of Acer palmatum Thunb. with a Brix value of 2 or more and 70 or less.

[30] The method according to any one of the above aspects 11 to 29, wherein the step of removing the raw material liquid adhering to the hollow fiber membrane by passing water through the hollow portion of the hollow fiber membrane is performed one or more times per day.

[31] The method according to any one of the above aspects 11 to 30, wherein the step of removing the membrane contaminants adhering to the hollow fiber membrane by passing a chemical solution having a pH of 5 or less or a pH of 9 or more through the hollow portion of the hollow fiber membrane is performed one or more times per week.

[32] The method according to any one of the above aspects 11 to 31, wherein the concentration step is performed using the hollow fiber membrane according to any one of the above aspects 1 to 4 or the membrane module according to any one of the above aspects 5 to 9.

[33] The method according to any one of the above aspects 11 to 32, which uses the raw material liquid concentration system according to the above aspect 10.

[34] A method for producing maple syrup, comprising concentrating a raw material liquid that is Caedae sap using the hollow fiber membrane according to any one of the above aspects 1 to 4, the membrane module according to any one of the above aspects 5 to 9, the raw material liquid concentration system according to the above aspect 10, or the method for producing a concentrated raw material liquid according to any one of the above aspects 11 to 33. [Effect of the Invention]

[0010] According to one aspect of the present invention, there can be provided a hollow fiber membrane, a membrane module, a raw material liquid concentration system, and a raw material liquid concentration method capable of concentrating the target component in the raw material liquid to a high concentration with little alteration even when the raw material liquid has a high viscosity. [Brief Description of the Drawings]

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention (hereinafter also referred to as the present embodiments) will be specifically and detailedly described with non-limiting examples. In the drawings of the present disclosure, elements with the same reference numerals are intended to have the same configuration or function as each other.

[0013] The present inventor has found a membrane and a membrane module that have good vapor extraction efficiency (i.e., concentration efficiency) in the concentration of a raw material liquid by membrane distillation at low temperature operation and can also cope with the pressure increase accompanying the increase in the viscosity of the raw material liquid. Concentration at low temperature is advantageous in avoiding alteration, decomposition, discoloration, etc. of the target component in the raw material liquid. The present inventor has also found that by devising the pressure, linear velocity, pretreatment method, etc. in membrane distillation, the solvent can be separated from the raw material liquid with high efficiency and stably for a long period of time.

[0014] <Hollow fiber membrane> One aspect of the present invention is a porous hollow fiber membrane for concentrating a raw material liquid having a viscosity of 3 cP or more and 600 cP or less by membrane distillation, having an air permeability of 500 L / h·m 2 ·kPa or more, the water permeation rate of a 20 mass% ethanol aqueous solution at 200 kPa pressurization being 100 mL / h·m 2 or less, and having a hollow fiber inner diameter of 0.3 mm or more and 2.0 mm or less, provides a hollow fiber membrane.

[0015] The porous membrane according to the present embodiment needs to have pores (communication holes) that communicate from one surface of the membrane to the other surface. These communication holes may be included in the network of the membrane material such as a polymer, and may be branched holes or straight holes. These pores need to allow vapor to pass through but not the water to be treated (liquid).

[0016] The hollow fiber membrane preferably has hydrophobicity to prevent wetting. The water contact angle is an index representing hydrophobicity. In this embodiment, it is preferable that the water contact angle of any part of the hollow fiber membrane is 90° or more, more preferably 110° or more, and still more preferably 120° or more. There is no particular upper limit for the water contact angle, but in reality, it is preferably about 150° or less. The water contact angle is a value measured at 25 °C by the droplet method. The droplet method is a method of dropping, for example, 2 μL of pure water onto the surface of the object to be measured and quantifying the angle formed by the object to be measured and the droplet by analysis from a projected image.

[0017] The pore size and pore size distribution of the hollow fiber membrane are also strongly causally related to wetting suppression. The average pore size of the hollow fiber membrane in this embodiment is preferably in the range of 0.01 μm or more and 1.0 μm or less, and more preferably in the range of 0.03 μm or more and 0.6 μm or less. When the average pore size is 0.01 μm or more, the permeation resistance of the vapor does not become too large, and the production rate of the raw material liquid concentrate does not decrease. When the average pore size is 1.0 μm or less, the wetting suppression effect by improving the hydrophobicity of the membrane is greatly preferable. From the viewpoint of achieving both the production rate of the raw material liquid concentrate and wetting suppression, a narrower pore size distribution of the hollow fiber membrane is preferable. Specifically, it preferably has a pore size distribution in which the ratio of the maximum pore size to the average pore size is in the range of 1.2 to 2.5. The pore size of the hollow fiber membrane is a value measured by the method for measuring the average pore size described in ASTM:F316-86 (also known as the half-dry method).

[0018] From the perspective of the production rate of the raw material liquid concentrate, the porosity of the hollow fiber membrane is preferably 50% by volume or more and 85% by volume or less. When this value is 50% by volume or more, the production rate of the raw material liquid concentrate is good. When it is 85% by volume or less, the strength of the membrane itself is good, and problems such as breakage are less likely to occur during long-term use.

[0019] The hollow fiber membrane according to this embodiment allows a heated raw material liquid to flow inside the hollow fiber membrane and keeps the outside under reduced pressure, so that only volatile components mainly composed of water can be taken out from the raw material liquid while retaining non-volatile valuable substances. At this time, vapor moves using the vapor pressure difference, which is the difference between the vapor pressure of the raw material liquid and the absolute pressure on the reduced-pressure side, as the driving force. For membrane distillation at low temperatures, it is preferable that the membrane can efficiently pass vapor even with a slight vapor pressure difference. Also, in the low-temperature concentration of a high-viscosity raw material liquid, the differential pressure between membranes tends to increase and membrane wetting is likely to occur, so it is preferable that the membrane has a high liquid entry pressure (LEP).

[0020] In the process of concentrating the raw material liquid, as the degree of concentration (concentration ratio) increases, the viscosity of the solution gradually increases. In the case of the conventional membrane distillation method, when the viscosity of the solution reaches 3 cP or more, the pressure loss associated with passing the raw material liquid through the flow path of the raw material liquid increases, so efficient concentration is not possible. Also, when operating for a long time in such a state, membrane wetting occurs and the concentration performance deteriorates over time. Furthermore, when the viscosity of the solution exceeds 600 cP, it becomes difficult to pump the liquid using a liquid delivery pump. Examples of raw material liquids having a viscosity of 3 cP or more and 600 cP or less include various sugar solutions, such as maple sap (i.e., the raw material for maple syrup) and birch sap (i.e., the raw material for birch syrup) with a Brix value (i.e., the sugar content value measured by a Brix meter) of 2 or more and 70 or less, coconut liquid endosperm, honey, and other sugar solutions, as well as liquid food products such as coffee extract, tea extract, broth, flavor emulsions, and food oil emulsions. Also, industrial process liquids such as wastewater concentrated by a reverse osmosis membrane and aqueous solutions containing inorganic ions such as the inducing solution used in a forward osmosis membrane concentration system can be mentioned.

[0021] The hollow fiber membrane according to this embodiment is particularly suitable for concentrating a raw material liquid having a viscosity of 3 cP or more and 600 cP or less. Specifically, the air permeability of the hollow fiber membrane is, in one aspect, 500 L / h·m 2 ·kPa or more, preferably 1000 L / h·m 2 ·kPa or more, or 2000 L / h·m 2 ·kPa or more, or 2500 L / h·m 2·kPa or more. The air permeability is preferably 5000 L / h·m 2 ·kPa or less. When the air permeability is 500 L / h·m 2 ·kPa or more, the membrane resistance to vapor transfer does not become too large, and the concentration operation under a slight vapor pressure difference under low-temperature conditions is easy. Further, when the air permeability is 5000 L / h·m 2 ·kPa or less, the air permeability does not become too large and the pressure resistance of the membrane is good.

[0022] The hollow fiber membrane is filled with an ethanol (EtOH) aqueous solution having a concentration of 20% by mass at 25°C inside the hollow fiber (i.e., the hollow part). When pressurized to 200 kPa, the water permeation rate of the EtOH aqueous solution permeating to the outside of the hollow fiber is, in one aspect, 100 mL / h·m 2 or less, preferably 50 mL / h·m 2 or less. When the water permeation rate is within the above range, since the membrane is difficult to wet, the inconvenience that the membrane is wetted due to the increase in the differential pressure between the membranes accompanying the increase in the concentration of the raw material liquid and the concentration performance deteriorates is preferably avoided. From the viewpoint of suppressing membrane wetting, the lower the water permeation rate is, the better. However, from the viewpoint of obtaining good membrane distillation performance, in one aspect, 0.1 mL / h·m 2 or more, or 1.0 mL / h·m 2 or more may be sufficient.

[0023] The inner diameter of the hollow fiber membrane is, in one aspect, 0.3 mm or more and 2.0 mm or less, and preferably 0.5 mm or more and 1.5 mm or less. When the inner diameter is 0.3 mm or more, even if the pressure loss increases with the increase in the concentration of the raw material liquid, the liquid feeding does not become difficult. When the inner diameter is 2.0 mm or less, the internal volume of the hollow fiber per unit membrane area does not become too large and the dead volume of the concentration system does not become too large.

[0024] The hollow fiber membrane according to this embodiment preferably contains a hydrophobic polymer as a main constituent component. A hydrophobic polymer is a polymer having a low affinity for water. From this viewpoint, the hollow fiber membrane is preferably composed of at least one resin selected from the group consisting of polysulfone, polyethersulfone, polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, and polychlorotrifluoroethylene. From the viewpoints of hydrophobicity, film-forming property, mechanical durability, and thermal durability, polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, and polychlorotrifluoroethylene are more preferable. It is more preferable that impurities such as plasticizers are removed by refining after polymerization of these polymers or after forming a film from these polymers.

[0025] As a method for producing the hollow fiber membrane, a thermal-induced phase separation method in which a molten resin film is cooled to cause phase separation to form a porous layer, or a dry-wet method (non-solvent phase separation method) in which a resin film in a solution state is brought into contact with a non-solvent to cause phase separation to form a porous layer can be preferably used.

[0026] From the viewpoints of pressure resistance for flowing a high-viscosity raw material liquid and efficient vapor transfer, it is preferable to apply a coating of a hydrophobic polymer to the porous membrane obtained by the thermal-induced phase separation method or the non-solvent phase separation method. The hydrophobic polymer may be used to form a hydrophobic film on all or part of the surface of the raw material liquid side (liquid phase part side), the vapor permeation side (gas phase part side), and the inside of the membrane (wall surface in the pores) of the porous membrane to impart water repellency to the membrane or improve the water repellency of the membrane.

[0027] Examples of the hydrophobic polymer coated on the hollow fiber membrane include the following: (a) A silicone-based polymer and a polymer gel that form a crosslinked structure by reacting with a silane coupling agent; (A) Resins having siloxane bonds, such as dimethyl silicone gel, methylphenyl silicone gel, reactive modified silicone gel into which organic functional groups such as amino groups are introduced, and silicone gel subjected to fluoroalkyl modification; (B) A solution obtained by dissolving a polymer having a (per)fluoroalkyl group, a (per)fluoropolyether group, an alkylsilyl group, a fluorosilyl group, etc. in a side chain in a solvent; (C) A hydrophobic polymer thin film having a fluoroalkyl group, an alkylsilyl group, a fluorosilyl group, etc. in a side chain; (D) A water repellent having a fluoroalkyl group, an alkylsilyl group, a fluorosilyl group, etc. in a side chain, etc. As the hydrophobic polymer, in particular, one or more polymers selected from (meth)acrylate monomers having a (per)fluoroalkyl group or a (per)fluoropolyether group having 1 to 12 carbon atoms, and vinyl monomers are preferable.

[0028] <Membrane module> One aspect of the present invention provides a membrane module for concentrating a raw material liquid having a viscosity of 3 cP or more and 600 cP or less by membrane distillation.

[0029] Figs. 1 and 2 are schematic views showing an example of the membrane module of the present embodiment. Referring to Figs. 1 and 2, in one aspect, the membrane module 10 has a porous hollow fiber membrane 1 and a module case 2 having a substantially cylindrical or substantially polygonal column shape that houses the hollow fiber membrane 1. The hollow fiber membrane 1 may be the hollow fiber membrane according to the present embodiment described above in one aspect. Here, the "substantially cylindrical shape" includes, for example, a cylindrical shape, an elliptical column shape, etc., and shapes similar thereto. The "substantially polygonal column shape" includes, for example, a polygonal column shape having a polygon with 3 to 100 vertices as a base, and shapes similar thereto. The "shapes similar thereto" is a concept including shapes in which corners of a cylinder, a polygonal column, etc. are cut, shapes in which corners are rounded, shapes in which the axis is bent or curved, and combinations thereof. As the shape of the membrane module, a cylindrical shape, an elliptical column shape, a polygonal column shape having a polygon with 4 to 12 vertices as a base, and shapes similar thereto are preferable, and a cylindrical shape, an elliptical column shape, a quadrangular column shape, and shapes similar thereto are more preferable.

[0030] The module case 2 may have, at both axial ends, a membrane fixing portion 21 in which the hollow fiber membrane 1 is fixed with an opening end by a fixing resin, and a raw material liquid flow opening 22 for allowing the raw material liquid to flow from the opening end into the hollow fiber membrane 1. The module case 2 may have, on its side surface, a vapor outlet 23 that communicates with the gas phase portion of the membrane module 10 and takes out the vapor in the gas phase portion to the outside of the membrane module 10.

[0031] The membrane module may be composed of a cartridge and a housing. In that case, by setting a cartridge in which the hollow fiber membrane is fixed with a fixing resin with respect to a housing having a vapor outlet, it can be used as a membrane module. The hollow fiber membrane bundle fixed in the membrane module may optionally have one or more members selected from a net, a nonwoven fabric, a cartridge case, etc.

[0032] 〈Membrane fixing portion〉 In the membrane fixing part 21, the fixing resin for adhering and fixing the hollow fiber membrane desirably has good mechanical strength and heat resistance up to about 100°C, for example. Examples of resins that can be used as the fixing resin include thermosetting epoxy resins and thermosetting urethane resins. From the viewpoint of heat resistance, epoxy resins are preferred, but from the viewpoint of handleability, urethane resins are preferred.

[0033] The filling rate of the hollow fiber membrane based on the cross-sectional area obtained by cutting the membrane fixing part in a plane perpendicular to the axial direction of the membrane module is preferably 15% or more, more preferably 20% or more, from the viewpoint of miniaturization of the membrane module. Also, in order to uniformly fix the hollow fibers with the fixing resin, this filling rate is preferably 74% or less, more preferably 70% or less. The filling rate (%) of the hollow fiber membrane is calculated by (total cross-sectional area of the hollow fiber membrane) ÷ (cross-sectional area of the membrane fixing part) × 100. Note that the cross-sectional area of the hollow fiber membrane refers to the area of the portion surrounded by the outer periphery of the hollow fiber and is a concept including the area of the hollow part.

[0034] 〈Effective membrane length〉 The effective length of the hollow fiber membrane 1 in the membrane module 10 is defined as the shortest distance between two membrane fixing parts respectively arranged at both axial ends of the membrane module.

[0035] When flowing a high-viscosity raw material liquid inside the hollow fiber membrane, the pressure loss in the laminar flow region is proportional to the effective length and inversely proportional to the square of the inner diameter. From the viewpoint of increasing the effective length ratio per total length of the hollow fiber membrane (that is, using the membrane more effectively), the effective length of the hollow fiber membrane is preferably 100 times or more, or 250 times or more, or 500 times or more of the inner diameter of the hollow fiber membrane. In order to reduce the pressure loss, it is preferably 1000 times or less, or 800 times or less of the inner diameter of the hollow fiber membrane.

[0036] 〈Vapor outlet〉 The vapor outlet 23 in the membrane module 10 communicates with the gas phase part of the membrane module and can take out the vapor in the gas phase part to the outside of the membrane module. The vapor taken out to the outside of the membrane module can be condensed and recovered, for example, by a vapor condensation part described later.

[0037] In order to prevent pressure loss associated with an increase in vapor flow rate under reduced pressure, the vapor outlet preferably has an area sufficient to keep the vapor flow rate below a desired value. From this perspective, the opening area of the vapor outlet 23 of the module is preferably 1 / 1500 or more, and more preferably 1 / 1000 or more, of the membrane area of the hollow fiber membrane 1. When the module case 2 main body has a plurality of vapor outlets 23, the opening area of the vapor outlet is evaluated as the total area of all the openings. Although there is no limitation on the size of the vapor outlet, as described above, since the membrane module has a substantially cylindrical or substantially polygonal columnar shape, it is more preferable that the vapor outlet is within a range that does not impair the mechanical strength of the membrane module. From this perspective, the opening area of the vapor outlet 23 of the membrane module 10 is more preferably 1 / 250 or less of the membrane area of the hollow fiber membrane 1.

[0038] 〈Raw material liquid flow-through opening〉 The raw material liquid flow-through opening 22 in the membrane module 10 is installed outside the membrane fixing portions 21 arranged at both axial ends of the membrane module 10. The membrane module 10 is connected to the raw material liquid flow path of the raw material liquid concentration system through the raw material liquid flow-through opening 22, and the raw material liquid can flow inside the hollow fiber membrane.

[0039] In order to prevent an increase in pressure loss when flowing a highly viscous raw material liquid to be concentrated, the opening area of the raw material liquid flow-through opening 22 is preferably 0.2 times or more of the total opening cross-sectional area of the hollow fibers. Also, in order to reduce the dead space in the raw material liquid flow path piping, it is preferably 8.0 times or less, and more preferably 5.0 times or less, of the total opening cross-sectional area of the hollow fibers.

[0040] 〈Module case〉 As described above, since the membrane distillation in the present embodiment is operated with the gas phase portion of the hollow fiber membrane in a reduced pressure state, a compressive stress is applied to the module case 2 in its axial direction. In order to suppress dimensional changes of the membrane module due to this compressive stress, the portion of the membrane module other than both axial ends may be covered with the module case. The module case may be composed of a single or a plurality of members, and may have an arbitrary member configuration according to desire, such as a configuration having a main body portion and a cap portion attached to the main body portion and having an opening for raw liquid flow, for example. The module case has a vapor outlet 23 having a sufficient area so as not to obstruct the flow of vapor generated from the raw liquid. The module case may be composed of, for example, a resin and / or a metal. From the viewpoints of workability at the time of attaching the vapor outlet 23 and durability against compressive stress, the module case is preferably composed of, for example, at least one resin selected from the group consisting of polypropylene, polysulfone, polyethersulfone, polyvinylidene fluoride, polyphenylene ether, ABS resin, fiber reinforced plastic, and vinyl chloride resin, and / or at least one metal selected from the group consisting of stainless steel, brass, brass, and titanium.

[0041] 〈Raw Liquid Concentration System and Raw Liquid Concentration Method〉 One aspect of the present invention provides a raw liquid concentration system and a raw liquid concentration method (i.e., a method for producing a raw liquid concentrate) for concentrating a raw liquid having a viscosity of 3 cP or more and 600 cP or less by membrane distillation. The raw liquid concentration method of the present embodiment can be implemented using the raw liquid concentration system of the present embodiment in one aspect, and the concentration step of the method can be implemented using the hollow fiber membrane or the membrane module of the present embodiment in one aspect.

[0042] Figs. 3 and 4 are conceptual diagrams for explaining the raw material liquid concentration system and the raw material liquid concentration method of the present embodiment. Referring to Figs. 3 and 4, the raw material liquid concentration system 100 according to the present embodiment includes a raw material liquid tank 101 for storing the raw material liquid, a heating unit 103 for heating the raw material liquid, a membrane distillation unit 104 having a porous hollow fiber membrane for concentrating the raw material liquid heated by the heating unit 103, and a circulation pump 102 (for example, a gear pump) for circulating the raw material liquid from the raw material liquid tank 101 to the heating unit 103 and the membrane distillation unit 104 in this order and then to the raw material liquid pump 101. The above hollow fiber membrane is arranged to receive the raw material liquid in the hollow part and discharge the vapor to the outside of the hollow fiber membrane. The membrane distillation unit 104 has a structure that separates a liquid phase part through which the raw material liquid flows from a gas phase part for taking out the vapor, and can reduce the pressure of the gas phase part. In one aspect, the membrane distillation unit 104 may have the membrane module 10 of the present embodiment. In another aspect, the hollow fiber membrane included in the membrane distillation unit 104 may be the hollow fiber membrane according to the above-described present embodiment.

[0043] The raw material liquid concentration system 100 is configured such that, in one aspect, the raw material liquid temperature is 30°C or higher and 80°C or lower at the raw material liquid inflow site of the hollow fiber membrane, in one aspect, the raw material liquid pressure is 10 kPa or higher and 300 kPa or lower, in one aspect, the pressure outside the hollow fiber membrane is reduced to -80 kPa or lower, the differential pressure between the raw material liquid pressure and the pressure outside the hollow fiber membrane is 395 kPa or lower, and in one aspect, the raw material liquid linear velocity inside the hollow fiber membrane is 0.05 m / s or higher and 1.0 m / s or lower.

[0044] Referring to Figs. 3 and 4, the method for manufacturing the concentrated raw material liquid according to the present embodiment includes, for example, a step of heating the raw material liquid in the heating unit 103, and a concentration step of flowing the heated raw material liquid through the hollow part of a porous hollow fiber membrane in, for example, the membrane distillation unit 104 and concentrating it by membrane distillation. In this method, the raw material liquid concentrated in the concentration step is circulated and merged into the raw material liquid before concentration, for example, the raw material liquid in the raw material liquid tank 101.

[0045] In the method for producing the raw material liquid concentrate of the present embodiment, at the raw material liquid inflow site of the hollow fiber membrane, in one aspect, the temperature of the raw material liquid is 30°C or higher and 80°C or lower, in one aspect, the pressure of the raw material liquid is 10 kPa or higher and 300 kPa or lower, in one aspect, the pressure outside the hollow fiber membrane is reduced to -80 kPa or lower, in one aspect, the differential pressure between the pressure of the raw material liquid and the pressure outside the hollow fiber membrane is 395 kPa or lower, and in one aspect, the linear velocity of the raw material liquid inside the hollow fiber membrane is 0.05 m / s or higher and 1.0 m / s or lower.

[0046] The raw material liquid concentration system 100 may have a vapor condensation unit 105 that condenses the vapor generated in the membrane distillation unit 104. In one aspect, the vapor condensation unit 105 is connected to the vapor outlet 23 of the membrane module 10 via a vapor pipe. A demister may be installed in the vapor pipe to prevent the raw material liquid from mixing into the condensed water.

[0047] In addition to the above, the raw material liquid concentration system 100 may further include, for example, a condensate tank 106, a withdrawal pump 107, a decompression device 108, a flow regulator (not shown), a pressure regulator (not shown), etc. Further, in addition to the heating unit 103, the raw material liquid concentration system 100 may further have a structure capable of keeping warm the raw material liquid flow path including the raw material liquid tank 101 and the vapor condensation unit.

[0048] The vapor condensation unit 105 may have a gas phase part communicating with the membrane distillation unit 104 (for example, the vapor outlet 23 of the membrane module 10) and a cooling body for aggregating the vapor diffused from the membrane distillation unit 104 (for example, the vapor outlet 23 of the membrane module 10). The cooling body maintains a low temperature by allowing a cooling medium (for example, cooling water) to flow inside. The structure of the cooling body may be, for example, a structure in which tubes are gathered or a structure in which plates are overlapped. When the cooling body part comes into contact with the vapor diffused into the gas phase part of the vapor condensation unit 105, the vapor is cooled and condensed into distilled water (permeate water). By storing this in the condensate tank 106 and recovering it, distilled water can be obtained.

[0049] In the membrane distillation unit 104, by reducing the pressure on one side of the hollow fiber membrane, vapor can be extracted from the raw material liquid using the vapor pressure difference, which is the difference between the vapor pressure of the raw material liquid and the absolute pressure in the depressurized section, as the driving force. When the raw material liquid is at a high temperature, the vapor pressure difference becomes larger and the concentration efficiency improves. On the other hand, from the perspective of suppressing deterioration of the concentrated liquid, decomposition or discoloration of valuable substances, it is advantageous to keep the raw material liquid below a predetermined temperature. That is, in order to improve the concentration efficiency while maintaining the quality of the concentrated liquid, at the raw material liquid inflow site of the hollow fiber membrane in the membrane distillation unit 104, the raw material liquid temperature is preferably 30°C or higher and 80°C or lower, and more preferably 40°C or higher and 70°C or lower. If it is below the above upper limit temperature, it is easy to maintain the quality, and if it is above the above lower limit temperature, the vapor pressure of the raw material liquid does not become too small and the concentration proceeds well.

[0050] When the pressure in the gas phase part of the membrane distillation unit 104 is reduced, the vapor pressure difference between the raw material liquid and the gas phase part becomes larger, so the concentration efficiency improves. When performing membrane distillation at a low temperature, it is advantageous to set the pressure in the gas phase part below a predetermined value. Specifically, when the atmospheric pressure is set to 0 kPa, the pressure in the gas phase part (i.e., the pressure outside the hollow fiber membrane) is preferably -80 kPa or lower, and more preferably -90 kPa or lower. Although the lower the above pressure is, the better, from the perspective of facilitating process control, in one aspect, it may be -99 kPa or higher, or -97 kPa or higher.

[0051] When circulating the raw material liquid through the membrane distillation unit 104, in order to uniformly circulate the raw material liquid throughout the hollow fiber membrane, a raw material liquid pressure equal to or higher than a predetermined value is advantageous. Specifically, the raw material liquid pressure is preferably 10 kPa or higher, and more preferably 30 kPa or higher. Considering the pressure resistance of the hollow fiber membrane and the module case, it is advantageous to keep the raw material liquid pressure below a predetermined value. Specifically, it is preferably 300 kPa or lower, or 210 kPa or lower.

[0052] In membrane distillation using a hollow fiber membrane, when the transmembrane differential pressure, which is the pressure difference between the liquid phase part and the gas phase part, exceeds the liquid intrusion pressure, the raw material liquid moves from the liquid phase part to the gas phase part, leading to loss of the raw material liquid. Therefore, in the membrane distillation unit 104, it is advantageous to keep the transmembrane differential pressure below the liquid intrusion pressure. Specifically, the pressure difference between the liquid phase part and the gas phase part (i.e., the differential pressure between the raw material liquid pressure and the pressure outside the hollow fiber membrane) is preferably 395 kPa or less, or 380 kPa or less, or 300 kPa or less. From the viewpoint of obtaining good concentration efficiency, the above differential pressure is preferably 50 kPa or more, or 80 kPa or more, or 90 kPa or more.

[0053] In membrane distillation, it is difficult to directly heat the membrane surface where the water in the raw material liquid evaporates. Therefore, in order to supply the latent heat required for evaporation, it is advantageous to keep the linear velocity of the raw material liquid above a predetermined value. Specifically, the linear velocity of the raw material liquid inside the hollow fiber membrane is preferably 0.05 m / s or more. On the other hand, since the pressure of the liquid phase part also increases as the linear velocity of the raw material liquid increases, it is advantageous to keep the linear velocity below a predetermined value. Specifically, the linear velocity of the raw material liquid inside the hollow fiber membrane is preferably 1.0 m / s or less, and more preferably 0.5 m / s or less.

[0054] 〈Heating of the raw material liquid〉 In the heating step, from the viewpoint of suppressing decomposition or denaturation of the raw material liquid due to heating, it is preferable to heat the raw material liquid by bringing it into contact with a heating section at 90°C or lower. The heating section 103 for heating the raw material liquid, which is useful in the heating step, may have a structure in which the raw material liquid is heated by heating a part of the raw material liquid flow path. As a method for heating the raw material liquid, a method of supplying heat from a heat medium to the raw material liquid by a heat exchanger, or a method of heating a piping portion with an electric heating wire, a flame, etc. can be used. Since the piping surface of the heating section becomes the hottest inside the raw material liquid flow path, from the viewpoint of suppressing decomposition or denaturation of the raw material liquid due to heating, the surface temperature of the heating section 103 (i.e., the temperature of the part in contact with the raw material liquid) is preferably 90°C or lower.

[0055] In order to minimize the surface temperature of the heating section 103, it is more preferable to heat the raw material liquid by supplying heat from the heat medium to the raw material liquid using a heat exchanger. It is more preferable to use warm water or steam (for example, steam depressurized below atmospheric pressure) as the heat medium. From the perspective of heat utilization efficiency, the temperature of the warm water or steam is preferably 50°C or higher. From the perspective of avoiding deterioration, decomposition, discoloration, etc. of the target component in the raw material liquid, the temperature of the warm water or steam is preferably 100°C or lower. Further, from the perspective of reducing the concentration energy cost, the waste heat generated in processes other than the concentration process may be used to heat the raw material liquid.

[0056] In membrane distillation, the vapor pressure drop due to the solute in the raw material liquid also affects the efficiency of membrane distillation. As the concentration increases, the concentration of the solute rises, and the vapor pressure of the raw material liquid significantly decreases due to the vapor pressure drop. As a result, the vapor pressure difference between the liquid phase part and the gas phase part becomes smaller, and the efficiency of membrane distillation decreases. From the perspective of suppressing the heating of the raw material liquid, it is preferable to keep the concentration of the raw material liquid below a certain level. Taking a sugar solution as an example, the Brix value after concentration by membrane distillation is preferably 70 or lower, more preferably 67 or lower, or 62 or lower.

[0057] 〈Pretreatment〉 In the raw material liquid concentration method of this embodiment, in order to improve the energy efficiency of the entire concentration method, pretreatment may be performed before the concentration process for the purposes of pre-concentration, removal of impurities (for example, fiber components in sap), etc. Referring to FIG. 4, in one aspect, the raw material liquid is first supplied to a preliminary tank 109 upstream of the raw material liquid tank 101, introduced into a pretreatment unit 111 via a liquid feed pump 110 for pretreatment, and then supplied to the raw material liquid pump 101. The pretreatment unit 111 may be a filtration membrane for impurity removal, a reverse osmosis membrane for pre-concentration, a combination thereof, etc. In one aspect, the concentration process and the filtration process and / or pre-concentration process as the pretreatment process are performed in independent raw material liquid flow paths.

[0058] More specifically, in one aspect, as shown in FIG. 4, the raw material liquid concentrated in the membrane distillation unit 104 may be circulated to the raw material liquid tank 101 without passing through the pretreatment unit 111. That is, in one aspect, the raw material liquid concentrated in the concentration step may be circulated and merged with the raw material liquid before concentration after the pretreatment step (that is, the pretreatment unit may be arranged in series with the membrane distillation unit).

[0059] On the other hand, in another aspect, separately from the raw material liquid circulation path that returns from the raw material liquid tank 101 through the membrane distillation unit 104 to the raw material tank 101, a pretreatment path for circulating the raw material liquid from the raw material liquid tank 101 through the pretreatment unit 111 to the raw material liquid tank 101 may be provided (that is, the pretreatment unit may be arranged in parallel with the membrane distillation unit). Such a pretreatment mode is advantageous in that it can remove impurities newly generated due to the increase in concentration accompanying the concentration of the raw material liquid over time while maintaining the raw material liquid circulation flow rate in the raw material liquid circulation flow path.

[0060] 〈Filter membrane〉 In one aspect, the pretreatment unit may have a filter membrane. In the raw material liquid, there is a high possibility of the presence of insoluble components such as dietary fiber. If membrane distillation is performed as it is, it may cause problems such as excessive pressure increase in the liquid phase part, damage to the membrane due to rubbing, and membrane clogging due to deposition of insoluble components on the membrane surface. Therefore, in order to perform membrane distillation more efficiently, it is preferable to remove insoluble components. The membrane filtration method is suitable for removing insoluble components. In one aspect, from the viewpoint of efficiently removing insoluble components in the raw material liquid, a filter membrane with a pore diameter of 20 μm or less is preferable. The pore diameter of the filter membrane is more preferably 1.0 μm or less. The pore diameter of the filter membrane may be, for example, 0.1 μm or more, or 0.3 μm or more from the viewpoint of filtration efficiency.

[0061] (Cross-flow filtration) Performing the removal of insoluble components by the above-described membrane filtration in a crossflow filtration mode is preferable from the viewpoint of preventing clogging of the filtration membrane. In crossflow filtration, a crossflow filtration membrane module having a flat membrane or a hollow fiber membrane can be used. In one aspect, the filtration membrane module has two or more inlets and outlets combined on the flow path side of the liquid to be filtered, and one or more outlets on the flow path side of the permeate. By applying pressure while circulating the liquid to be filtered through such a filtration membrane module, it is possible to obtain a permeate while preventing the deposition of insoluble components on the membrane surface. There are no particular restrictions on the circulation flow rate of the liquid to be filtered and the flow rate of the permeate, but from the viewpoint of performing efficient filtration, the circulation flow rate of the liquid to be filtered is preferably 3 times or more, more preferably 10 times or more, the flow rate of the permeate.

[0062] 〈Backwashing of the filtration membrane〉 In the removal of insoluble components by the filtration membrane, backwashing may be periodically performed for the purpose of removing the insoluble components deposited on the surface of the filtration membrane and maintaining the membrane performance. Examples of the fluid used for backwashing include water, the permeate in the membrane filtration step, the condensate obtained by membrane distillation, and the like. Also, an air backwash method, the air backwash method, may be used. The timing of performing the backwashing can be determined from an increase in the intermembrane differential pressure of the filtration membrane, a decrease in the permeate flow rate, and the like. Further, the backwashing may be performed at a preset cycle (for example, once per hour).

[0063] (Reverse osmosis membrane) The reverse osmosis membrane is not particularly limited, but preferred examples are hollow fiber membranes made of cellulose acetate and composite membranes having a separation layer containing polyamide. The reverse osmosis membrane is used for pre-concentrating the raw material liquid. By arranging the raw material liquid on the separation layer side of the reverse osmosis membrane and applying pressure, only the water in the raw material liquid can be permeated and removed. In this case, as the raw material liquid is concentrated, the solute concentration in the raw material liquid may exceed the saturation concentration and precipitate as insoluble components. Further, as the pretreatment section, a reverse osmosis membrane and the above-described filtration membrane may be used in combination. In this case, it is more preferable from the viewpoint of improving the removal efficiency of insoluble components to flow the raw material liquid, for example, in the order of the reverse osmosis membrane and the filtration membrane (that is, to arrange the reverse osmosis membrane upstream of the filtration membrane).

[0064] Generally, a reverse osmosis membrane can selectively allow only water to permeate through the membrane by pressurizing the feed solution above its osmotic pressure. In the pre-concentration process using a reverse osmosis membrane, as the feed solution is concentrated, the osmotic pressure of the feed solution increases. Therefore, when concentrating the feed solution to a high concentration, it is necessary to apply a higher pressure. Taking the concentration of a sucrose aqueous solution by a reverse osmosis membrane as an example, according to the reference (Journal of Food Engineering 155 (2015) 10-15), the osmotic pressure of a sucrose aqueous solution of 2 mol / kg-H2O (i.e., Brix value of 40.6) is approximately 67 atmospheres, and the osmotic pressure of a sucrose aqueous solution of 3 mol / kg-H2O (i.e., Brix value of 50.7) is approximately 100 atmospheres.

[0065] Also, when the feed solution has a high viscosity, the influence of concentration polarization on the membrane surface becomes significant, so a pressure higher than the above osmotic pressure is required. From the above, it is expected to be difficult to concentrate the sugar solution to a Brix value of 40 or higher when using a reverse osmosis membrane. In the pre-concentration process, from the perspective of efficiency, the concentration of the feed solution after pre-concentration is preferably a Brix value of 40 or less, or a Brix value of 35 or less, or a Brix value of 30 or less.

[0066] 〈Cleaning of Hollow Fiber Membrane〉 In the raw material liquid concentration method of the present embodiment, for the purpose of removing insoluble components precipitated with the concentration of the raw material liquid, preventing the mixing of the raw material liquid during the raw material liquid switching, etc., particularly for removing the raw material liquid adhering to the hollow fiber membrane, the liquid phase part of the membrane module can be washed regularly. Specifically, it is preferable to wash by passing water through the hollow part of the hollow fiber membrane once or more a day. Further, for the purpose of removing components that are hardly soluble in water, sterilizing the inside of the system, etc., particularly for removing membrane contaminants adhering to the hollow fiber membrane, it is also preferable to perform washing using a chemical solution once or more a week. As the water used for washing, potable water, permeated water of a reverse osmosis membrane, condensed water obtained in the raw material liquid concentration system of the present embodiment, etc. may be used. As the chemical solution used for washing, a chemical solution with a pH of 5 or less (for example, an acidic aqueous solution such as hydrochloric acid, aqueous citric acid solution, etc.) or a chemical solution with a pH of 9 or more (for example, an alkaline aqueous solution such as aqueous sodium hydroxide solution, aqueous sodium hypochlorite solution, etc.) can be used. Further, by using the acidic aqueous solution and the alkaline aqueous solution in order, both inorganic components and organic components can be efficiently removed.

[0067] 〈Additional Concentration by Evaporation〉 In the raw material liquid concentration method of the present embodiment, for the purpose of sterilizing the concentrated raw material liquid, flavoring by heating, etc., in order to improve the energy efficiency of the entire concentration method, an additional concentration step by an evaporator (not shown) can be included after the concentration step. In order to obtain the intended sterilization or flavoring effect, in the additional concentration step, it is preferable to heat the concentrated raw material liquid to a temperature equal to or higher than the raw material liquid temperature in the concentration step by membrane distillation. In one aspect, the evaporator may be arranged downstream of the aforementioned filtration membrane.

[0068] 〈Method for Producing Maple Syrup〉 One aspect of the present invention provides a method for producing maple syrup, which includes concentrating a raw material liquid that is sap from Acer mono using the hollow fiber membrane of the present embodiment described above, the membrane module of the present embodiment described above, the raw material liquid concentration system of the present embodiment described above, or the method for producing a concentrated product of the raw material liquid of the present embodiment described above. According to one aspect of the present invention, by using this method, maple syrup excellent in color tone and flavor can be produced.

Examples

[0069] Hereinafter, exemplary embodiments of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples in any way.

[0070] 《Measurement of Various Physical Properties of Hollow Fiber Membranes》 [Outer Diameter, Inner Diameter, and Membrane Thickness] Regarding the outer diameter and inner diameter of the hollow fiber membrane, the hollow fiber membrane was thinly cut with scissors in a direction perpendicular to its longitudinal direction, and the outer diameter and inner diameter of the cross-section were measured using a microscope, respectively. The membrane thickness was calculated by the following formula (1). Membrane thickness (mm) = [Outer diameter (mm) - Inner diameter (mm)] / 2 (1)

[0071] [Average Pore Diameter] The average pore diameter of the hollow fiber membrane was measured by the method for measuring the average pore diameter described in ASTM:F316 - 86 (also known as the half - dry method). The measurement was carried out under standard measurement conditions of 25°C and a pressure increase rate of 0.01 atm / second using ethanol as the liquid for a hollow fiber membrane approximately 10 cm long. The average pore diameter was determined by the following formula (2). Average pore diameter [μm] = 2,860 × (Surface tension of the liquid used [dyne / cm]) / (Half - dry air pressure [Pa]) (2) Here, as the surface tension of ethanol at 25°C, a value of 21.97 dyne / cm was used.

[0072] [Maximum Pore Diameter] The maximum pore size of the hollow fiber membrane was measured using the bubble point method. One end of a hollow fiber membrane with a length of 8 cm was blocked, and a nitrogen gas supply line was connected to the other end via a pressure gauge. In this state, nitrogen gas was supplied to replace the inside of the line with nitrogen, and then the hollow fiber membrane was immersed in ethanol. At this time, the hollow fiber membrane was immersed in ethanol while applying a very slight pressure of nitrogen to the line so that ethanol would not flow back into the line. With the hollow fiber membrane immersed, the pressure of the nitrogen gas was slowly increased, and the pressure P at which nitrogen gas bubbles began to stably emerge from the outer wall of the hollow fiber membrane was recorded. From this value, the maximum pore size d [μm] of the hollow fiber membrane was calculated using the following formula (3): d = C1γ / P (3) {In the formula, C1 is a constant, γ is the surface tension [dyne / cm], and P is the pressure [Pa].} It was calculated by. When ethanol was used as the immersion liquid, the value of the product of the constant C1 and the surface tension γ was set to C1γ = 0.0879 [N / m].

[0073] [Porosity] The porosity of the hollow fiber membrane was determined by the method described below. The hollow fiber membrane was cut to a certain length, its weight was measured, and the porosity was calculated using the following formula (4): Porosity (%) = 100 - [mass of hollow fiber membrane (g) × 100] / [polymer density (g / cm 3 ) × {(outer diameter (cm) / 2) 2 - (inner diameter (cm) / 2) 2} × 3.14 × length (cm)] (4) It was determined by.

[0074] [Air permeability] It was measured in accordance with ISO 9237. Dry air was allowed to flow into the membrane module, and the pressure (kPa) at the inlet and outlet of the membrane module and the dry air flow rate (L / h) at the outlet of the membrane module were measured. The dry air flow rate (L / h) was divided by the differential pressure (kPa) between the above inlet and the above outlet and the membrane area to calculate the air permeability (L / m 2 ·h·kPa).

[0075] [Viscosity of the raw material liquid] The viscosity of the raw material liquid was measured as the solution viscosity using a viscometer manufactured by Thermo Scientific (model name "HAAKE ViscoTester iQ").

[0076] [Brix value] It was measured using a refractometer (Atago PAL-1). The refractometer was calibrated to 0% with distilled water before measurement.

[0077] [Visible light transmittance] The concentrated liquid was filtered using an ultrafiltration filter (Amicon Ultra-0.5, PLGC UltraCel-10 membrane, 10 kDa, UFC501008). After that, a sufficient amount of the filtrate was placed in a double-sided transparent quartz cell with a screw cap for a spectrophotometer (GL Science Inc. S15-UV-10, optical path length 10 mm, optical path width 10 mm), and the visible light transmittance was determined by measuring the UV / vis spectrum. Glycerin was used as the blank. The UV / vis analysis conditions are as follows. -UV / vis conditions- UV / vis apparatus: JASCO V-770 manufactured by JASCO Corporation Measurement mode: Abs Measurement wavelength: 800 - 200 nm Data acquisition interval: 0.5 nm Light source: D2, WI Light source switching: 340 nm Correction: Baseline

[0078] 《Implementation of membrane distillation》 The membrane distillation in Examples 1 - 21 and Comparative Examples 2 - 6 was carried out using a raw material liquid concentration system having a configuration according to FIG. 3 or 4, in which a membrane module having a configuration according to FIGS. 1 and 2 was provided as the membrane distillation section.

[0079] The membrane module as the membrane distillation section had the configuration as described in each example and comparative example, and the outlet of the vapor condensation section was connected to the condensate tank by piping. Then, the pressure in the system was adjusted by connecting the gas phase part of the condensate tank to a decompression device via a pressure regulator.

[0080] A heating section using a heat exchanger was provided in the raw material liquid flow path, and warm water was used as the heat medium. A gear pump was used as the circulation pump to circulate the raw material liquid in the raw material liquid flow path, and the back pressure valve provided at the outlet of the membrane module was used to adjust the pressure of the raw material liquid. Cooling water (CW) at 10 °C was circulated through the steam condensation section at a flow rate of 10 L / min.

[0081] [Measurement of Flux] Membrane distillation was performed, and a weighing scale or an integrated flow meter was used to measure the weight of the distilled water flowing into the condensate tank. The following mathematical formula (5): Flux = weight of distilled water obtained by membrane distillation for 1 hour of operation ÷ membrane area ÷ operation time (1 hour) (5) was used to calculate Flux. Evaluation was carried out according to the following criteria. A: 10.0 kg / m 2 ·h or more B: 5.0 kg / m 2 ·h or more and less than 10.0 kg / m 2 ·h C: 1.0 kg / m 2 ·h or more and less than 5.0 kg / m 2 ·h D: less than 1.0 kg / m 2 ·h

[0082] [Measurement of raw material liquid pressure during operation] During operation, the raw material liquid pressure was measured at the raw material liquid inlet of the membrane module.

[0083] [Measurement of the maximum transmembrane differential pressure during operation] During operation, the maximum transmembrane differential pressure was measured as the maximum value of the differential pressure between the raw material liquid pressure and the pressure outside the hollow fiber membrane in the concentration test.

[0084] [Repeated operability] Evaluation was carried out according to the following criteria. A: The air permeability after operation is 90% or more of that before operation B: The air permeability after operation is 75% or more and less than 90% of that before operation C: The air permeability after operation is 60% or more and less than 75% of that before operation D: Air permeability after operation is less than 60% of that before operation

[0085] [Coloring] It was evaluated according to the following criteria. A: Visible light transmittance at 560 nm is 85% or more B: Visible light transmittance at 560 nm is 80% or more and less than 85% C: Visible light transmittance at 560 nm is 75% or more and less than 80% D: Visible light transmittance at 560 nm is less than 75%

[0086] [Flavor] The obtained raw material liquid concentrate was provided to 5 panelists for tasting, and the flavor was evaluated according to the following two criteria. A: All 5 panelists judged that the original flavor of the raw material was strong. B: The number of panelists who judged that the original flavor of the raw material was strong was 1 or more and 4 or less. C: None of the panelists judged that the original flavor of the raw material was strong.

[0087] 《Example 1》 [Hydrophobization of hollow fiber membrane] Regarding 3700 hollow fiber membranes made of PVDF (polyvinylidene fluoride) with an inner diameter of 0.35 mm, an outer diameter of 0.64 mm, an average pore diameter of 0.21 μm determined from ASTM-F316-86, a maximum pore diameter of 0.29 μm, and a porosity of 72%, after completely immersing them once in a fluororesin-based water repellent FS-392B (0.5% by mass) manufactured by Fluoro Technology Co., Ltd., they were pulled up and dried to apply a hydrophobic polymer to the inner and outer surfaces of the hollow fiber membranes.

[0088] [Fabrication of hollow fiber membrane module] In the production of the membrane module, a thermosetting epoxy resin was used as the fixing resin, and the hollow fiber membrane was adhesively fixed in the module case by centrifugal adhesion to form membrane fixing parts at both axial ends. The membrane fixing parts were configured such that the shortest distance between the two membrane fixing parts (i.e., the effective length of the hollow fiber membrane) was about 300 mm. As the module case, a cylindrical case made of polysulfone with an inner diameter of 55 mm and an outer diameter of 60 mm was used. On the outer peripheral side surface of this case, there was provided one vapor outlet with an area of 0.0010 m 2 by a 1.5S pipe. Also, at both axial ends of this case, caps for connecting the membrane module to the raw material liquid flow path of the raw material liquid concentration system were attached. The cap was provided with an opening of 2.5S and 0.0028 m 2 as an opening for raw material liquid flow. The air permeability of the obtained membrane module was 600 L / h·m 2 ·kPa, and the water permeation rate of a 20 mass% EtOH aqueous solution at 200 kPa pressure was 80 mL / h·m 2 .

[0089] Using the membrane module obtained in the above [Production of membrane module], a raw material liquid concentration system with a configuration according to FIG. 3 was assembled, and 140 kg of maple water was concentrated by membrane distillation according to the conditions in Tables 1 to 3. The time taken to concentrate unfiltered maple water (Brix 2.0, viscosity 3.2 cP, the same below) to Brix 70 (viscosity 370 cP) was 76.4 hours, the maximum membrane differential pressure during concentration was 108.2 kPa, the total Flux in all concentration tests was 1.5 kg / m 2 ·h, and the air permeability of the membrane module after the concentration test was 70% of the initial value. The visible light transmittance of the obtained raw material liquid concentrate was 79%, and the unique aroma of maple water was relatively maintained.

[0090] From the above results, it was verified that the membrane and membrane module of Example 1 could concentrate maple water, which is the raw material liquid, to a high viscosity of Brix 70 without excessive coloring or flavor deterioration, and the membrane performance after concentration was also good.

[0091] 《Example 2》 The air permeability after water repellent treatment is 1200 L / h·m 2 ·kPa. A concentration test was conducted under the same conditions as in Example 1 except for this. The time taken to concentrate maple water to Brix 70 was 38.2 hours, the maximum transmembrane differential pressure during concentration was 108.2 kPa, the total calculated Flux for the entire concentration test was 3.0 kg / m 2 ·h, and the air permeability of the membrane module after the concentration test was 72% of the initial value. The visible light transmittance of the obtained raw material liquid concentrate was 81%, and the unique aroma of maple water was relatively maintained. From the above results, it was verified that the membrane and membrane module of Example 2 can concentrate maple water, which is the raw material liquid, to a high viscosity of Brix 70 without excessive coloring or flavor deterioration, and the membrane performance after concentration is also good.

[0092] 《Example 3》 The air permeability after water repellent treatment is 4800 L / h·m 2 ·kPa. A concentration test was conducted under the same conditions as in Example 1 except for this. The time taken to concentrate maple water to Brix 70 was 13.0 hours, the maximum transmembrane differential pressure during concentration was 108.2 kPa, the total calculated Flux for the entire concentration test was 8.8 kg / m 2 ·h, and the air permeability of the membrane module after the concentration test was 71% of the initial value. The visible light transmittance of the obtained raw material liquid concentrate was 83%, and the unique aroma of maple water was relatively maintained. From the above results, it was verified that the membrane and membrane module of Example 3 can concentrate maple water, which is the raw material liquid, to a high viscosity of Brix 70 without excessive coloring or flavor deterioration, and the membrane performance after concentration is also good.

[0093] 《Example 4》 The water permeation rate of a 20 mass% aqueous EtOH solution at 200 kPa pressure was 40 mL / h·m 2 . A concentration test was conducted under the same conditions as in Example 3 except for this. The time taken to concentrate maple water to Brix 70 was 12.6 hours, the maximum transmembrane differential pressure during concentration was 108.2 kPa, the total calculated Flux for the entire concentration test was 9.1 kg / m 2·h, and the air permeability of the membrane module after the concentration test was 85% of the initial value. The visible light transmittance of the obtained raw material liquid concentrate was 81%, and the unique aroma of maple water was relatively maintained. From the above results, it was verified that the membrane and membrane module of Example 4 could concentrate maple water, which was the raw material liquid, to a high viscosity of Brix 70 without excessive coloring or flavor deterioration, and the membrane performance after concentration was also very good.

[0094] 《Example 5》 1000 hollow fiber membranes made of PVDF (polyvinylidene fluoride) with an inner diameter of 0.68 mm and an outer diameter of 1.25 mm were used, and a membrane module was fabricated by fixing them so that the shortest distance between the membrane fixing parts was about 500 mm. The concentration test was carried out under the same conditions as in Example 4 except that the linear velocity of the raw material liquid flowing through the hollow fiber membrane during the concentration test was 0.1 m / s, and the heat medium in the heating part was vacuum steam at 88 °C. The time taken to concentrate maple water to Brix 70 was 13.8 hours, the maximum membrane differential pressure during concentration was 139.0 kPa, and the total calculated Flux of the entire concentration test was 9.5 kg / m 2 ·h, and the air permeability of the membrane module after the concentration test was 87% of the initial value. The visible light transmittance of the obtained raw material liquid concentrate was 83%, and the unique aroma of maple water was relatively maintained. From the above results, it was verified that the membrane and membrane module of Example 5 could concentrate maple water, which was the raw material liquid, to a high viscosity of Brix 70 without excessive coloring or flavor deterioration, and the membrane performance after concentration was also very good.

[0095] 《Example 6》 A module was fabricated using 200 hollow fiber membranes made of PVDF (polyvinylidene fluoride) with an inner diameter of 1.40 mm and an outer diameter of 2.57 mm. The concentration test was carried out under the same conditions as in Example 5 except that the heat medium in the heating part was warm water at 88 °C and the raw material liquid flow-through opening in the cap part had a size of 2.0S, 0.0018 m 2 The time taken to concentrate maple water to Brix 70 was 27.0 hours, the maximum membrane differential pressure during concentration was 110.2 kPa, and the total calculated Flux of the entire concentration test was 11.8 kg / m 2·h, and the air permeability of the membrane module after the concentration test was 86% of the initial value. The visible light transmittance of the obtained raw material liquid concentrate was 80%, and the unique aroma of maple water was relatively maintained. From the above results, it was verified that the membrane and membrane module of Example 6 could concentrate maple water, which is the raw material liquid, up to a high viscosity of Brix 70 without excessive coloring or flavor deterioration, and the membrane performance after concentration was also very good.

[0096] 《Example 7》 A module was fabricated using 100 hollow fiber membranes made of PVDF (polyvinylidene fluoride) with an inner diameter of 1.85 mm and an outer diameter of 3.40 mm, and under the same conditions as in Example 6 except that the cap part had an opening of 1.5S, 0.0010 m 2 A concentration test was conducted. The time taken to concentrate maple water to Brix 70 was 43.1 hours, the maximum transmembrane differential pressure during concentration was 103.6 kPa, and the total calculated Flux for the entire concentration test was 11.2 kg / m 2 ·h, and the air permeability of the membrane module after the concentration test was 89% of the initial value. The visible light transmittance of the obtained raw material liquid concentrate was 84%, and the unique aroma of maple water was relatively maintained. From the above results, it was verified that the membrane and membrane module of Example 7 could concentrate maple water, which is the raw material liquid, up to a high viscosity of Brix 70 without excessive coloring or flavor deterioration, and the membrane performance after concentration was also very good.

[0097] 《Example 8》 There were 3 vapor outlets on the side of the membrane module with a size of 2.5S, 0.0030 m 2 A concentration test was conducted under the same conditions as in Example 5 except that the temperature of the raw material liquid at the inlet was 55 °C, the vacuum part was -95 kPa, the surface temperature of the heating part was 65 °C, and the heat medium flowing through the heating part was 70 °C warm water. The time taken to concentrate maple water to Brix 70 was 14.3 hours, the maximum transmembrane differential pressure during concentration was 151.0 kPa, and the total calculated Flux for the entire concentration test was 9.2 kg / m 2·h, and the air permeability of the membrane module after the concentration test was 85% of the initial value. The visible light transmittance of the obtained raw material liquid concentrate was 86%, and the unique maple water flavor was maintained. From the above results, under the membranes, membrane modules, and operating conditions of Example 8, for maple water as the raw material liquid, while greatly reducing excessive coloring and flavor deterioration due to heating, it can be concentrated to a high viscosity of Brix 70, and the membrane performance after concentration was also verified to be very good.

[0098] 《Example 9》 A concentration test was conducted under the same conditions as in Example 8 except that the raw material liquid temperature at the raw material liquid inlet of the membrane module was 45°C, the surface temperature of the heating section was 55°C, and the heat medium flowing through the heating section was 60°C warm water. The time taken to concentrate the maple water to Brix 70 was 21.5 hours, the maximum transmembrane differential pressure during concentration was 151.0 kPa, and the cumulative Flux for the entire concentration test was 6.1 kg / m 2 ·h, and the air permeability of the membrane module after the concentration test was 84% of the initial value. The visible light transmittance of the obtained raw material liquid concentrate was 91%, and the unique maple water flavor was maintained. From the above results, under the membranes, membrane modules, and operating conditions of Example 9, for maple water as the raw material liquid, it can be concentrated to a high viscosity of Brix 70 with little effect on excessive coloring and flavor deterioration due to heating, and the membrane performance after concentration was also verified to be very good.

[0099] 《Example 10》 A concentration test was conducted under the same conditions as in Example 8 except that the raw material liquid temperature at the raw material liquid inlet of the membrane module was 35°C, the surface temperature of the heating section was 45°C, and the heat medium flowing through the heating section was 50°C warm water. The time taken to concentrate the maple water to Brix 70 was 30.5 hours, the maximum transmembrane differential pressure during concentration was 151.0 kPa, and the cumulative Flux for the entire concentration test was 4.3 kg / m 2·h, and the air permeability of the membrane module after the concentration test was 88% of the initial value. The visible light transmittance of the obtained raw material liquid concentrate was 90%, and the unique aroma of maple water was maintained. From the above results, under the membranes, membrane modules, and operating conditions of Example 10, for maple water as the raw material liquid, it can be concentrated to a high viscosity of Brix70 with little influence of excessive coloring or flavor deterioration due to heating, and the membrane performance after concentration is also very good.

[0100] 《Example 11》 100 hollow fiber membranes made of PVDF (polyvinylidene fluoride) with an inner diameter of 1.85 mm and an outer diameter of 3.40 mm were used and fixed so that the shortest distance of the membrane fixing part ring was about 278 mm, and on the side, 1.0S, 0.0004 m 2 with a steam outlet was fabricated. Further, a concentration test was conducted under the same conditions as in Example 8 except that the linear velocity of the raw material liquid inside the hollow fiber membrane was 0.45 m / s. The time taken to concentrate maple water to Brix70 was 85.9 hours, the maximum transmembrane differential pressure during concentration was 366.2 kPa, and the total calculated Flux for the entire concentration test was 10.1 kg / m 2 ·h, and the air permeability of the membrane module after the concentration test was 60% of the initial value. The visible light transmittance of the obtained raw material liquid concentrate was 87%, and the unique aroma of maple water was relatively maintained. From the above results, under the membranes, membrane modules, and operating conditions of Example 11, for maple water as the raw material liquid, it can be concentrated to a high viscosity of Brix70 without excessive coloring or flavor deterioration due to heating, and the membrane performance after concentration is also good.

[0101] 《Example 12》 100 hollow fiber membranes made of PVDF (polyvinylidene fluoride) with an inner diameter of 1.85 mm and an outer diameter of 3.40 mm were used and fixed so that the shortest distance of the membrane fixing part ring was about 93 mm, and on the side, an inner diameter of 6 mm, 0.000028 m 2A membrane module having three steam outlets was fabricated. Further, a concentration test was conducted under the same conditions as in Example 11 except that 35 kg of maple water was used and the linear velocity of the feed liquid inside the hollow fiber membrane was 0.80 m / s. The time taken to concentrate the maple water to Brix 70 was 60.8 hours, the maximum transmembrane differential pressure during concentration was 379.6 kPa, the cumulative Flux for the entire concentration test was 10.7 kg / m 2 ·h, and the air permeability of the membrane module after the concentration test was 63% of the initial value. The visible light transmittance of the obtained feed liquid concentrate was light yellow with 86%, and the unique aroma of maple water was relatively maintained. From the above results, it was verified that under the membranes, membrane modules, and operating conditions of Example 12, for maple water as the feed liquid, it could be concentrated to a high viscosity of Brix 70 without excessive coloring or flavor deterioration due to heating, and the membrane performance after concentration was also good.

[0102] 《Example 13》 A concentration test was conducted under the same conditions as in Example 8 except that a valve was provided at the outlet of the feed liquid flow path of the membrane module to apply back pressure to the module, and the pressure at the inlet of the feed liquid flow path of the membrane module at the start of the test was set to 30 kPa. The time taken to concentrate the maple water to Brix 70 was 13.5 hours, the maximum transmembrane differential pressure during concentration was 191.0 kPa, the cumulative Flux for the entire concentration test was 9.7 kg / m 2 ·h, and the air permeability of the membrane module after the concentration test was 87% of the initial value. The visible light transmittance of the obtained feed liquid concentrate was 85%, and the unique aroma of maple water was maintained. From the above results, it was verified that under the membranes, membrane modules, and operating conditions of Example 13, for maple water as the feed liquid, while greatly reducing excessive coloring and flavor deterioration due to heating, it could be concentrated to a high viscosity of Brix 70, and the membrane performance after concentration was also very good.

[0103] 《Example 14》(Series total filtration) A concentration test was conducted under the same conditions as in Example 8, except that the raw material liquid was introduced into the raw material liquid tank after subjecting it to vacuum filtration (total filtration) using filter paper with a pore size of 20 μm as the filtration membrane. The time taken to concentrate the maple water to Brix 70 (280 cP) was 12.9 hours, the maximum transmembrane differential pressure during concentration was 163.0 kPa, the cumulative Flux for the entire concentration test was 10.2 kg / m 2 ·h, and the air permeability of the membrane module after the concentration test was 85% of the initial value. The visible light transmittance of the obtained raw material liquid was 86%, and the unique aroma of maple water was maintained. From the above results, it was verified that under the membrane and membrane module of Example 14 and the operating conditions, for the maple water as the raw material liquid, while greatly reducing excessive coloring and flavor deterioration due to heating, it could be concentrated to a high viscosity of Brix 70, and the membrane performance after concentration was also very good.

[0104] 《Example 15》(Series Cross-Flow Filtration) A concentration test was conducted under the same conditions as in Example 8, except that the raw material liquid was cross-flow filtered using a PVDF hollow fiber membrane with a pore size of 0.8 μm as the filtration membrane, and the filtered raw material liquid was introduced into the raw material liquid tank. The filtration membrane was backwashed regularly with distilled water. The time taken to concentrate the maple water to Brix 70 (215 cP) was 10.9 hours, the maximum transmembrane differential pressure during concentration was 149.0 kPa, the cumulative Flux for the entire concentration test was 12.0 kg / m 2 ·h, and the air permeability of the membrane module after the concentration test was 91% of the initial value. The visible light transmittance of the obtained raw material liquid concentrate was 87%, and the unique aroma of maple water was maintained. From the above results, it was verified that under the membrane and membrane module of Example 15 and the operating conditions, for the maple water as the raw material liquid, while greatly reducing excessive coloring and flavor deterioration due to heating, it could be concentrated to a high viscosity of Brix 70, and the membrane performance after concentration was also very good.

[0105] 《Example 16》(Parallel Cross-Flow Filtration) A PVDF hollow fiber membrane with a pore size of 0.8 μm was used as the filtration membrane. A filtration circulation path was provided that returned from the raw material liquid tank through the filtration membrane back to the raw material liquid tank, separate from the membrane distillation circulation path that returned from the raw material liquid tank through the membrane distillation section back to the raw material tank. A concentration test was conducted under the same conditions as in Example 8 except that cross-flow filtration was performed using the filtration membrane. The filtration membrane was periodically backwashed with distilled water. The time taken to concentrate maple water to Brix 70 was 10.7 hours, the maximum transmembrane pressure difference during concentration was 149.0 kPa, and the total calculated Flux for the entire concentration test was 12.2 kg / m 2 ·h. Also, the air permeability measured after passing water through the inside of the hollow fibers of the membrane module for 30 minutes for washing after the concentration test was 95% of the initial value. The visible light transmittance of the obtained raw material liquid concentrate was 87%, and the unique aroma of maple water was maintained. From the above results, under the membranes and membrane modules of Example 16 and the operating conditions, for maple water as the raw material liquid, while greatly reducing excessive coloring and flavor deterioration due to heating, it can be concentrated to a high viscosity of Brix 70, and it was verified that the decline in membrane performance was significantly suppressed by performing water washing after concentration.

[0106] 《Example 17》(Waste heat utilization) A concentration test was conducted under the same conditions as in Example 15 except that 70°C industrial wastewater was used as the heat medium in the heating section to utilize waste heat. The time taken to concentrate maple water to Brix 70 was 10.5 hours, the maximum transmembrane pressure difference during concentration was 149.0 kPa, and the total calculated Flux for the entire concentration test was 12.5 kg / m 2 ·h. Also, the air permeability measured after passing an aqueous citric acid solution and an aqueous sodium hydroxide solution through the inside of the hollow fibers of the membrane module for 30 minutes each in sequence for washing after the concentration test was 97% of the initial value. The visible light transmittance of the obtained raw material liquid concentrate was 88%, and the unique aroma of maple water was maintained. From the above results, under the membranes and membrane modules of Example 17 and the operating conditions, for maple water as the raw material liquid, while greatly reducing excessive coloring and flavor deterioration due to heating, it can be concentrated to a high viscosity of Brix 70, and it was verified that the decline in membrane performance was significantly suppressed by performing chemical solution washing after concentration.

[0107] Example 18 (Filter Membrane + Reverse Osmosis Membrane) A raw material liquid preliminary concentrate obtained by concentrating with a reverse osmosis membrane up to Brix 35 was filtered with a filter membrane, and then a concentration test was conducted under the same conditions as in Example 15 except that the raw material liquid preliminary concentrate after permeation was introduced into the raw material liquid tank. The time taken to concentrate maple water to Brix 70 (150 cP) was 1.2 hours, the maximum transmembrane differential pressure during concentration was 149.0 kPa, and the total calculated Flux for the entire concentration test was 6.0 kg / m 2 ·h. Also, the air permeability measured after sequentially passing an aqueous citric acid solution and an aqueous sodium hydroxide solution through the inside of the hollow fibers of the membrane module for 30 minutes each for washing with water after the concentration test was 98% of the initial value. The visible light transmittance of the obtained raw material liquid concentrate was 92%, and the unique aroma of maple water was maintained. From the above results, under the membranes, membrane modules, and operating conditions of Example 18, for maple water as the raw material liquid, while greatly reducing excessive coloring and flavor deterioration due to heating, it was verified that it could be concentrated to a high viscosity of Brix 70, and by performing chemical cleaning after concentration, a significant decrease in membrane performance was suppressed.

[0108] Example 19 (Filter Membrane + Reverse Osmosis Membrane) A raw material liquid preliminary concentrate obtained by concentrating with a reverse osmosis membrane up to Brix 30 was filtered with a filter membrane, and then a concentration test was conducted under the same conditions as in Example 15 except that the raw material liquid preliminary concentrate after permeation was introduced into the raw material liquid tank. The time taken to concentrate maple water to Brix 62 (102 cP) was 1.1 hours, the maximum transmembrane differential pressure during concentration was 149.0 kPa, and the total calculated Flux for the entire concentration test was 8.1 kg / m 2·h, and the air permeability measured after sequentially passing an aqueous citric acid solution and an aqueous sodium hydroxide solution through the inside of the hollow fibers of the membrane module for 30 minutes each and then performing a water wash was 99% of the initial value. The visible light transmittance of the obtained raw material liquid concentrate was 94%, and the unique maple water aroma was maintained. From the above results, under the membranes, membrane modules, and operating conditions of Example 19, for maple water as the raw material liquid, while greatly reducing excessive coloring and flavor deterioration due to heating, it was verified that it could be concentrated to a high viscosity of Brix 62, and by performing chemical cleaning after concentration, a significant reduction in membrane performance was suppressed.

[0109] 《Example 20》(Additional Concentration by Evaporation) A concentration test was performed under the same conditions as in Example 15, except that after concentrating the raw material liquid to Brix 50 by membrane distillation, it was further heated and concentrated to Brix 70 at a temperature of 100 °C or higher using an atmospheric distillation apparatus as an evaporator. The time taken to concentrate maple water to Brix 50 (51 cP) by membrane distillation was 6.2 hours, the maximum transmembrane differential pressure during concentration was 139.7 kPa, and the cumulative flux of membrane distillation in the entire concentration test was 15.0 kg / m 2 ·h. Also, the air permeability measured after sequentially passing an aqueous citric acid solution and an aqueous sodium hydroxide solution through the inside of the hollow fibers of the membrane module for 30 minutes each and then performing a water wash was 99% of the initial value. The visible light transmittance of the raw material liquid concentrate obtained after concentration in the atmospheric distillation apparatus was 81%, and it had a strong unique maple syrup aroma. From the above results, under the membranes, membrane modules, and operating conditions of Example 20, for maple water as the raw material liquid, while greatly reducing excessive coloring and flavor deterioration due to heating, it was verified that it could be concentrated to a high viscosity of Brix 70, and by performing chemical cleaning after concentration, a significant reduction in membrane performance was suppressed.

[0110] 《Example 21》(Concentration of Aqueous Magnesium Chloride Solution) A concentration test was conducted under the same conditions as in Example 8 except that a 20% by mass aqueous magnesium chloride solution was used as the raw material solution. The time taken to concentrate the aqueous magnesium chloride solution to 30% by mass was 1.1 hours, the maximum transmembrane differential pressure during concentration was 134.7 kPa, and the cumulative Flux for the entire concentration test was 12.0 kg / m 2 ·h. Also, the air permeability measured after the concentration test was 97% of the initial value. From the above results, it was verified that in the case of using an aqueous magnesium chloride solution as the raw material solution under the membranes, membrane modules, and operating conditions of Example 21, it was possible to concentrate up to a high viscosity of 30% by mass, and the membrane performance after concentration was also very good.

[0111] 《Comparative Example 1》(Reverse Osmosis Membrane) Maple water was concentrated using a reverse osmosis membrane in the same manner as in Example 18. When the Brix value of the raw material solution exceeded 40, the water permeation performance of the reverse osmosis membrane significantly decreased, and it became difficult to concentrate further. 《Comparative Example 2》(Flat Membrane, Low Air Permeability) A flat membrane module was produced in the same manner as in Example 1 except that a porous flat membrane with a water repellency treatment air permeability of 300 L / h·m 2 ·kPa and a membrane thickness of 20 μm was folded into a pleated shape and housed in a cylindrical case. A concentration test was conducted under the same conditions as in Example 8 except for using the said flat membrane module. The time taken to concentrate the maple water to Brix 70 was 174.8 hours, the maximum transmembrane differential pressure during concentration was 191.0 kPa, and the cumulative Flux for the entire concentration test was 0.75 kg / m 2 ·h. The visible light transmittance of the obtained raw material solution concentrate was 83%, and the unique aroma of maple water was lost. From the above results, it was verified that under the membranes, membrane modules, and operating conditions of Comparative Example 2, it was not possible to efficiently circulate a high-viscosity raw material solution throughout the membrane, and it was also not possible to efficiently extract the vapor in the raw material solution, resulting in a time-consuming concentration process and the loss of aroma components.

[0112] 《Comparative Example 3》(Flat Membrane, High Air Permeability) The air permeability after the water repellency treatment was 6000 L / h·m2 is kPa, and the water permeation rate of a 20 mass% ethanol aqueous solution at 200 kPa is 140 mL / h·m 2 A concentration test was conducted under the same conditions as in Comparative Example 1 except for the above. The time taken to concentrate maple water to Brix 70 was 9.0 hours, the maximum transmembrane differential pressure during concentration was 191.0 kPa, and the total calculated Flux for the entire concentration test was 14.5 kg / m 2 ·h. The visible light transmittance of the obtained raw material liquid concentrate was 82%, and the unique aroma of maple water was maintained. A partially wet portion could be observed in the membrane module after the concentration test, and the air permeability was 50% of the initial value. From the above results, it was verified that under the membrane and membrane module of Comparative Example 2 and the operating conditions, the LEP of the membrane was insufficient, so the membrane was easily wetted by the raw material liquid, making repeated operation difficult.

[0113] 《Comparative Example 4》(Small inner diameter, low air permeability) The air permeability after the water repellent treatment is 4800 L / h·m 2 A pleated flat membrane module similar to that in Comparative Example 1 was used except that the air permeability was kPa, and a concentration test was conducted under the same conditions as in Comparative Example 1 except that the linear velocity of the raw material liquid inside the pleats of the flat membrane module was 0.18 m / s. The time taken to concentrate maple water to Brix 70 was 10.2 hours, the maximum transmembrane differential pressure during concentration was 418.0 kPa, and the total calculated Flux for the entire concentration test was 8.0 kg / m 2 ·h. The visible light transmittance of the obtained raw material liquid concentrate was 82%, and the unique aroma of maple water was maintained. A partially wet portion could be observed in the membrane module after the concentration test, and the air permeability was 40% of the initial value. From the above results, it was verified that under the membrane and membrane module of Comparative Example 4 and the operating conditions, the pressure easily increased, and the membrane was wetted as the transmembrane differential pressure increased, making repeated operation difficult.

[0114] 《Comparative Example 5》(Flat membrane, high raw material liquid temperature) A pipe wound with a ribbon heater was used as the heating section, and the raw material liquid was heated at a surface temperature of 110 °C. A concentration test was conducted under the same conditions as in Example 8, except that the temperature of the raw material liquid at the raw material liquid inlet of the membrane module was 90 °C. The time required to concentrate maple water to Brix 70 was 7.3 hours. The maximum transmembrane differential pressure during concentration was 176.0 kPa, and the cumulative Flux for the entire concentration test was 18.0 kg / m 2 ·h. The visible light transmittance of the obtained raw material liquid concentrate was 73%, and the unique aroma of maple water was lost. After the concentration test, there were many blockages due to aggregates in the raw material liquid at the membrane adhesion part of the membrane module. Furthermore, a wet part was observed on a part of the membrane, and the air permeability was 40% of the initial value. From the above results, it was verified that under the membrane, membrane module, and operating conditions of Comparative Example 5, the raw material liquid was likely to be denatured and deteriorated at high temperatures, and the quality could not be maintained.

[0115] 《Comparative Example 6》(Flat membrane, reduced pressure) A concentration test was conducted under the same conditions as in Example 8, except that the temperature of the raw material liquid at the raw material liquid inlet of the membrane module was 80 °C and the pressure in the reduced pressure section was -20 kPa. The cumulative Flux for the entire concentration test was as low as 0.50 kg / m 2 ·h, and the test was terminated during concentration. From the above results, it was verified that under the membrane, membrane module, and operating conditions of Comparative Example 6, a sufficient vapor pressure difference could not be obtained on the raw material liquid side and in the reduced pressure section, and concentration could not be achieved.

[0116]

Table 1

[0117]

Table 2

[0118]

Table 3

Industrial Applicability

[0119] The membrane for membrane distillation, membrane module, and operation method according to the present invention can be suitably applied to a high-concentration raw liquid concentration process.

Explanation of symbols

[0120] 10 Membrane module 1 Hollow fiber membrane 2 Module case 21 Membrane fixing part 22 Raw liquid flow-through opening 23 Steam outlet 100, 200 Raw liquid concentration system 101 Raw liquid tank 102 Circulation pump 103 Heating part 104 Membrane distillation part 105 Steam condensation part 106 Condensate tank 107 Extraction pump 108 Vacuum device 109 Reserve tank 110 Liquid feeding pump 111 Pretreatment part

Claims

1. A porous hollow fiber membrane for concentrating a raw material liquid having a viscosity of 3 cP or more and 600 cP or less by membrane distillation, The air permeability is 500 L / h·m 2 ·kPa or more, and The water permeation rate of an aqueous ethanol solution with a concentration of 20% by mass at a pressure of 200 kPa is 100 mL / h·m 2 or less, and wherein the inner diameter of the hollow fiber is 0.3 mm or more and 2.0 mm or less, a hollow fiber membrane.

2. The air permeability is 1000 L / h·m 2 ·kPa or more and 5000 L / h·m 2 ·kPa or less, and The water permeability is 50 mL / h·m 2 or less, and The hollow fiber membrane according to claim 1, wherein the inner diameter of the hollow fiber is 0.5 mm or more and 1.5 mm or less.

3. The hollow fiber membrane according to claim 1 or 2, which is composed of at least one resin selected from the group consisting of polysulfone, polyethersulfone, polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, ethylene tetrafluoroethylene copolymer, and polychlorotrifluoroethylene.

4. The hollow fiber membrane according to any one of claims 1 to 3, wherein the raw material liquid is cedar sap having a Brix value of 2 or more and 70 or less.

5. A membrane module for concentrating a raw material liquid having a viscosity of 3 cP or more and 600 cP or less by membrane distillation, wherein the membrane module has a porous hollow fiber membrane and a substantially cylindrical or substantially polygonal module case for housing the hollow fiber membrane, the membrane module has, at both axial ends of the module case, a membrane fixing portion in which the hollow fiber membrane is fixed with an opening end by a fixing resin, and an opening for raw material liquid flow for allowing the raw material liquid to flow from the opening end into the hollow fiber membrane, and has, on a side surface, a vapor outlet for communicating with a gas phase portion of the membrane module and taking out vapor in the gas phase portion to the outside of the membrane module, the opening area of the vapor outlet is 1 / 1500 or more of the membrane area of the hollow fiber membrane, the effective length of the hollow fiber membrane is 100 times or more and 1000 times or less the inner diameter of the hollow fiber, and the opening area of the opening for raw material liquid flow is 0.2 times or more and 8.0 times or less the total opening cross-sectional area of the hollow fiber, a membrane module.

6. The opening area of the vapor outlet is 1 / 1000 or more and 1 / 250 or less of the membrane area of the hollow fiber membrane, the effective length of the hollow fiber membrane is 100 times or more and 800 times or less the inner diameter of the hollow fiber, and the opening area of the opening for raw material liquid flow is 0.2 times or more and 5.0 times or less the total opening cross-sectional area of the hollow fiber, the membrane module according to claim 5.

7. The membrane module according to claim 5 or 6, wherein the module case is made of at least one resin selected from the group consisting of polypropylene, polysulfone, polyethersulfone, polyvinylidene fluoride, polyphenylene ether, ABS resin, fiber-reinforced plastic, and vinyl chloride resin, and / or at least one metal selected from the group consisting of stainless steel, brass, copper, and titanium.

8. The membrane module according to any one of claims 5 to 7, wherein the raw material liquid is Japanese maple sap having a Brix value of 2 or more and 70 or less.

9. The membrane module according to any one of claims 5 to 8, wherein the hollow fiber membrane is the hollow fiber membrane according to any one of claims 1 to 4.

10. A raw material liquid concentration system for concentrating a raw material liquid having a viscosity of 3 cP or more and 600 cP or less by membrane distillation, wherein the raw material liquid concentration system includes a raw material liquid tank for storing the raw material liquid, a heating unit for heating the raw material liquid, a membrane distillation unit having a porous hollow fiber membrane for concentrating the raw material liquid heated by the heating unit, and a circulation pump for circulating the raw material liquid from the raw material liquid tank through the heating unit and the membrane distillation unit in this order and returning it to the raw material liquid tank. The hollow fiber membrane is arranged to receive the raw material liquid in the hollow portion and discharge the vapor to the outside of the hollow fiber membrane. At the raw material liquid inflow site of the hollow fiber membrane, the temperature of the raw material liquid is 30°C or more and 80°C or less, the pressure of the raw material liquid is 10 kPa or more and 300 kPa or less, the pressure outside the hollow fiber membrane is reduced to -80 kPa or less, the differential pressure between the pressure of the raw material liquid and the pressure outside the hollow fiber membrane is 395 kPa or less, and the linear velocity of the raw material liquid inside the hollow fiber membrane is 0.05 m / s or more and 1.0 m / s or less. The raw material liquid concentration system is configured as described above.

11. A method for producing a raw material liquid concentrate by concentrating a raw material liquid having a viscosity of 3 cP or more and 600 cP or less by membrane distillation, the method including: a heating step of heating the raw material liquid; a concentration step of flowing the heated raw material liquid through the hollow portion of a porous hollow fiber membrane and concentrating it by membrane distillation; circulating the raw material liquid concentrated in the concentration step and merging it with the raw material liquid before concentration; at the raw material liquid inflow site of the hollow fiber membrane, the temperature of the raw material liquid is 30°C or more and 80°C or less, the pressure of the raw material liquid is 10 kPa or more and 300 kPa or less, the pressure outside the hollow fiber membrane is reduced to -80 kPa or less, The differential pressure between the raw material liquid pressure and the outside pressure of the hollow fiber membrane is 395 kPa or less, and the linear velocity of the raw material liquid inside the hollow fiber membrane is 0.05 m / s or more and 1.0 m / s or less. A method.

12. The method according to claim 11, wherein the raw material liquid temperature is 40°C or more and 70°C or less.

13. The method according to claim 11 or 12, wherein the outside pressure of the hollow fiber membrane is -90 kPa or less.

14. The raw material liquid pressure is 30 kPa or more and 210 kPa or less, and the differential pressure between the raw material liquid pressure and the outside pressure of the hollow fiber membrane is 300 kPa or less. The method according to any one of claims 11 to 13.

15. The method according to any one of claims 11 to 14, wherein the linear velocity of the raw material liquid inside the hollow fiber membrane is 0.05 m / s or more and 0.5 m / s or less.

16. The method according to any one of claims 11 to 15, wherein in the heating step, the raw material liquid is heated by bringing it into contact with a heating section at 90°C or less.

17. The method according to claim 16, wherein the heating section is a heat exchanger that circulates a heat medium that is steam at 50°C or more or hot water at 50°C or more.

18. The method according to claim 16 or 17, wherein the heating section utilizes waste heat.

19. After the concentration step, the method further includes an additional concentration step of flowing the concentrated raw material liquid through an evaporator, and the raw material liquid temperature in the additional concentration step is equal to or higher than the raw material liquid temperature in the concentration step. The method according to any one of claims 11 to 18.

20. The method according to any one of claims 11 to 19, further including a preliminary concentration step of preliminarily concentrating the raw material liquid with a reverse osmosis membrane, and supplying the preliminarily concentrated raw material liquid to the concentration step.

21. The raw material liquid is a sugar solution, the Brix value of the raw material liquid preliminarily concentrated in the preliminary concentration step is 40 or less, and the Brix value of the raw material liquid concentrated in the concentration step is 70 or less. The method according to claim 20.

22. The raw material liquid is a sugar solution, the Brix value of the raw material liquid preliminarily concentrated in the preliminary concentration step is 35 or less, and the Brix value of the raw material liquid concentrated in the concentration step is 62 or less. The method according to claim 21.

23. The method according to any one of claims 11 to 22, further including a filtration step of filtering the raw material liquid with a filtration membrane to remove impurities, and supplying the filtered raw material liquid to the concentration step.

24. The method according to claim 23, wherein the pore diameter of the filtration membrane is 20 μm or less.

25. The method according to claim 24, wherein the pore size of the filtration membrane is 1.0 μm or less.

26. The method according to any one of claims 23 to 25, wherein the filtration membrane is arranged in a crossflow configuration.

27. The method according to any one of claims 23 to 26, further comprising a backwashing step of backwashing the filtration membrane.

28. The method according to any one of claims 23 to 27, wherein the concentration step and the filtration step are performed in raw material liquid flow paths independent of each other.

29. The method according to any one of claims 11 to 28, wherein the raw material liquid is Japanese maple sap having a Brix value of 2 or more and 70 or less.

30. The method according to any one of claims 11 to 29, wherein a step of removing the raw material liquid adhering to the hollow fiber membrane by passing water through the hollow portion of the hollow fiber membrane is performed one or more times per day.

31. The method according to any one of claims 11 to 30, wherein a step of removing membrane contaminants adhering to the hollow fiber membrane by passing a chemical solution having a pH of 5 or less or a pH of 9 or more through the hollow portion of the hollow fiber membrane is performed one or more times per week.

32. The method according to any one of claims 11 to 31, wherein the concentration step is performed using the hollow fiber membrane according to any one of claims 1 to 4 or the membrane module according to any one of claims 5 to 9.

33. The method according to any one of claims 11 to 32, using the raw material liquid concentration system according to claim 10.

34. A method for producing maple syrup, comprising concentrating a raw material liquid that is Japanese maple sap using the hollow fiber membrane according to any one of claims 1 to 4, the membrane module according to any one of claims 5 to 9, the raw material liquid concentration system according to claim 10, or the method for producing a raw material liquid concentrate according to any one of claims 11 to 33.

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