Method of manufacturing membrane element

Abstract

To provide a membrane element manufacturing method that enables a membrane element with a predetermined blocking rate to be manufactured in a short period of time by controlling chemical damage caused to a membrane by a chemical solution.SOLUTION: A method of manufacturing a membrane element includes a blocking rate adjustment step of adjusting a blocking rate by passing a chemical solution through a primary-side channel of a membrane element. When the chemical solution is passed in the blocking rate adjustment step, a difference between pressures applied to both membrane surfaces of the membrane element is set lower than an osmotic pressure of the chemical solution.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a membrane element. [Background technology]

[0002] Industrial wastewater discharged from factories contains a mixture of various organic matter, but traditionally it has been incinerated as is. Because incineration consumes a large amount of energy, improvements are needed from the perspective of reducing the environmental impact (environmental protection) and building a recycling-oriented society (sustainable society). Therefore, methods have been proposed to reduce energy consumption by subjecting industrial wastewater to various membrane processes to concentrate and reduce its volume before incinerating it.

[0003] One advantageous example of such membrane treatment is the reverse osmosis (RO) method, which has been widely used in the desalination of seawater, etc. Reverse osmosis is a technology that applies pressure to the concentrated solution side separated by a semipermeable membrane such as a reverse osmosis membrane (RO membrane) or a nanofiltration membrane (NF membrane), and makes the operating pressure difference between the treated liquid side (primary side) and the permeation side (secondary side) higher than the osmotic pressure difference between the concentrated solution side and the dilute solution side, thereby selectively allowing the solvent to permeate through the semipermeable membrane. Membrane treatment using reverse osmosis typically uses a membrane element containing a semipermeable membrane. However, due to the high rejection rate of the membrane (membrane element), the conditions for using the membrane element are somewhat limited, narrowing the scope of application. For example, the membrane element has an upper limit on the operating pressure difference that can be used, limiting the concentration of solutions to which reverse osmosis can be applied. In addition, as the treatment progresses, the water to be treated becomes more concentrated, and if the gradually increasing osmotic pressure exceeds the maximum operating pressure of the membrane element, membrane treatment becomes impossible. Furthermore, as the water to be treated becomes more concentrated, membrane clogging becomes more likely. Therefore, improvements to the semipermeable membrane and membrane element are required to apply reverse osmosis to the treatment of concentrating industrial wastewater containing a high concentration of a mixture or the treatment of industrial wastewater containing a low concentration of a mixture to a high concentration.

[0004] The above-mentioned operating conditions and application range can be alleviated or broadened by using semipermeable membranes or membrane elements with a low rejection ratio. For example, by setting the semipermeable membrane rejection ratio low and using a membrane element equipped with a semipermeable membrane that preferentially permeates water and slightly permeates solutes such as mixtures, the pressure difference between the primary and secondary pressures (transmembrane pressure difference) is reduced, thereby easing operating conditions and broadening the application range. Furthermore, clogging of the semipermeable membrane can be suppressed. Using such a membrane element, even highly concentrated treated water can be concentrated by single-stage or multi-stage membrane treatment, and even low-concentration treated water can be concentrated to a high concentration. It is important that the semipermeable membranes and membrane elements used in such methods have a low rejection ratio to keep the gradually increasing osmotic pressure of the treated liquid within the maximum operating pressure range of the membrane element. Several methods for reducing the rejection ratio of semipermeable membranes have been proposed. For example, Patent Document 1 describes a method in which an aqueous solution of chlorine-based inorganic compounds is passed through an RO membrane to chemically damage the membrane. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5037175 Summary of the Invention [Problem to be solved by the invention]

[0006] Here, adjusting and controlling the rejection of a semipermeable membrane to a predetermined value is relatively easy for semipermeable membranes or flat membranes before being incorporated into a membrane element. However, because semipermeable membranes incorporated into a membrane element are tightly packed within a casing (housing), it is difficult to uniformly chemically damage the semipermeable membrane in the thickness and plane directions, making it difficult to adjust and control the rejection to the desired value. For example, one method for adjusting the rejection of a membrane element is to pass an aqueous solution containing a very low concentration of chlorine-based compounds through the membrane element, thereby causing chemical damage to the semipermeable membrane. However, this method requires a long period of time for passing the aqueous solution containing chlorine-based compounds (contact time with the membrane), resulting in poor operational efficiency. Furthermore, there is no correlation between the time the aqueous solution containing chlorine-based compounds is passed through and the amount of decrease in rejection. As described below, once a certain period of time has passed, the rejection rapidly and significantly decreases, making it impossible to adjust the rejection to the desired value. This problem also exists in the method described in Patent Document 1. Specifically, in this method, "0.167 mg / L sodium hypochlorite solution is added to 2.4 m 3 This requires a long time of 90 days to pass the solution through the filter at a flow rate of 1 / 2000 / h. Furthermore, there is no correlation between the time of passing the solution and the amount of decrease in permeability, so it is not possible to control the decrease in rejection and adjust it to the desired rejection.

[0007] An object of the present invention is to provide a membrane element method capable of producing a membrane element having a predetermined rejection rate in a short period of time by controlling chemical damage to the membrane caused by a chemical solution. [Means for solving the problem]

[0008] The present inventors investigated and examined the progress and extent of chemical damage to semipermeable membranes caused by chemical solutions, based on the premise that the use of chemical solutions containing relatively high concentrations of damaging components can cause chemical damage to semipermeable membranes in a short period of time. As a result, they found that the time during which the chemical solution passes through the semipermeable membrane (contact time) drops sharply after a certain point, and as a result, they were unable to find a specific relationship between the time of passage and the rejection rate (degree of chemical damage) that holds throughout the entire time of passage. Therefore, rather than the commonly used method of permeating a chemical solution through a semipermeable membrane (passing the chemical solution through a primary flow path and allowing the water in the chemical solution to pass through and circulate in a secondary flow path), which is a commonly used treatment method for membrane modules, they came up with the idea of ​​passing the chemical solution through the primary flow path, but not allowing water to pass through or circulate in the secondary flow path, leaving an air layer. Further investigations based on this idea revealed that by setting the pressure difference applied to both membrane surfaces of the membrane module to be smaller than the osmotic pressure of the chemical solution to be used, it is possible to uniformly chemically damage the semipermeable membrane incorporated in the housing in both the thickness and planar directions, even when using a membrane module. Furthermore, it was discovered that a linear relationship exists between the product of the concentration of the damaging component in the chemical solution and the time the chemical solution passes through (contact time with the chemical solution) (the exposure intensity of the damaging component to the semipermeable membrane) and the amount of chemical damage to the semipermeable membrane (rejection rate) over the entire range of variation in the exposure intensity. Furthermore, it was discovered that by determining the exposure intensity based on this linear relationship, a predetermined rejection rate can be achieved and set in a short period of time. The present invention was completed based on these findings.

[0009] That is, the object of the present invention has been achieved by the following means. <1> A method for manufacturing a membrane element, comprising a rejection adjustment step of passing a chemical solution through a primary flow path of the membrane element to adjust the rejection, A method for manufacturing a membrane element, wherein when the chemical solution is passed through the membrane element in the rejection adjusting step, the pressure difference applied to both membrane surfaces of the membrane element is set to be smaller than the osmotic pressure of the chemical solution. <2> The membrane element is a reverse osmosis membrane element or a nanofiltration membrane element. <1> A method for producing the membrane element according to claim 1. <3> The chemical solution is an aqueous solution containing hypochlorite. <1> or <2> A method for producing the membrane element according to claim 1. <4> The available chlorine concentration of the hypochlorite is 2 to 10 mass%. <3> A method for producing the membrane element according to claim 1. [Effects of the Invention]

[0010] The present invention can provide a membrane element method that can control chemical damage to a membrane caused by a chemical solution, and as a result, can produce a membrane element having a predetermined rejection rate in a short period of time. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram illustrating one embodiment of a system capable of carrying out the membrane element manufacturing method of the present invention. [Figure 2] FIG. 2 is a graph showing the relationship between the rejection rate and the product of the concentration of the damage-inflicting component in the chemical solution and the contact time of the chemical solution in Examples, Comparative Examples, and Reference Examples. DETAILED DESCRIPTION OF THE INVENTION

[0012] In the present invention and this specification, a semipermeable membrane that has a reduced rejection (performance) and allows water to pass preferentially while allowing solutes to pass through is referred to as a "loose membrane" or "deteriorated membrane." Its rejection is not particularly limited and can be, for example, 90% or less, preferably 20 to 80%. On the other hand, a semipermeable membrane with a high rejection (a membrane whose rejection has not been reduced) is sometimes referred to as a "high-performance membrane." Its rejection is not particularly limited, but is typically 95% or more. The rejection of a semipermeable membrane also includes the rejection of a membrane element unless otherwise specified. In the present invention and this specification, the reverse osmosis method includes the RO method and the NF (nanofiltration) method. Therefore, unless otherwise specified, the terms RO membrane, RO membrane element, and RO membrane module include RO membrane and NF membrane, RO membrane element and NF membrane element, and RO membrane module and NF membrane module, respectively. In addition, in the present invention and this specification, the term "membrane element" refers to a component equipped with a semipermeable membrane, such as a component constructed by integrating a semipermeable membrane, a support, and a flow path material, and the term "membrane module" refers to an assembly in which one or more membrane elements are housed and integrated in a pressure vessel, which serves as a basic unit constituting a plant. Here, a membrane element or a membrane module having a loose membrane is referred to as a "loose membrane element" and a "loose membrane module," respectively. In the present invention and this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0013] [[Membrane element manufacturing method]] The method for producing a membrane element of the present invention (hereinafter sometimes referred to as the "production method of the present invention") includes the following rejection adjustment step. <Rejection rate adjustment process> A process in which the rejection rate of a membrane element is adjusted by making the pressure difference applied to both membrane surfaces of the membrane element smaller than the osmotic pressure of the chemical solution and passing the chemical solution through the primary flow path of the membrane element. As described above, the manufacturing method of the present invention is a method for adjusting and reducing the rejection rate of the semipermeable membrane (membrane element) by chemically damaging the semipermeable membrane through a chemical solution containing a damaging component that causes chemical damage (e.g., oxidation) to the semipermeable membrane upon contact with the semipermeable membrane, by setting the pressure difference applied across both membrane surfaces of the membrane element to be less than the osmotic pressure of the chemical solution, thereby suppressing water permeation into the secondary flow path and circulating the chemical solution (evenly) within the primary flow path.

[0014] Generally, as described in Patent Document 1, membrane or membrane module treatment is performed by passing a chemical solution through a semipermeable membrane, i.e., by setting the pressure difference (transmembrane pressure) applied to both membrane surfaces to be equal to or greater than the osmotic pressure of the chemical solution. In contrast, in the production method of the present invention, when passing a chemical solution through the primary flow path of a membrane element, the transmembrane pressure is set to be smaller than the osmotic pressure of the chemical solution. This prevents water in the chemical solution from passing through the semipermeable membrane and into the secondary flow path (the secondary flow path forms an air layer at this time). This makes it possible to highly and uniformly control chemical damage (oxidation) of the semipermeable membrane by the chemical solution in both the thickness and planar directions, even when the semipermeable membrane is tightly integrated within the casing. As a result, the rejection of the semipermeable membrane can be set to a predetermined value in a short period of time. Although the reasons for this are not clear in detail, in conventional treatment methods, the permeation rate of damaging components in the chemical solution is slower than that of water, and a concentration distribution (concentration gradient) occurs at least in the thickness direction of the semipermeable membrane for the damaging components that permeate with water, making the degree of concentration distribution and the rate of progression more likely to change. As a result, it is thought that it is difficult to control chemical damage at least in the thickness direction of the semipermeable membrane and that this can change rapidly. In contrast, in the rejection adjustment process of the present invention, water is not allowed to flow (permeate) through the semipermeable membrane, so the permeation rate of the damaging components is constant in the thickness direction of the semipermeable membrane due to diffusion control, and the occurrence of a concentration distribution of the damaging components at least in the thickness direction of the semipermeable membrane can be suppressed. As a result, chemical damage can be uniformly progressed in the thickness direction and planar direction of the semipermeable membrane (highly controlled rejection), and a linear relationship is established between the exposure intensity of the damaging components to the semipermeable membrane and the rejection rate over the entire range of fluctuations in the exposure intensity. It is thought that this linear relationship makes it possible to achieve and set a desired rejection rate in a short period of time.

[0015] In membrane modules, there are generally two types of rejection (removal rate): apparent rejection and true rejection. In the present invention, "rejection" refers to the apparent rejection Robs[-] defined by the following formula (1): Formula (1): Robs=1-(Cp / Cb) In equation (1), Cb is the concentration of the treated liquid [mol / m 3 ], and Cp is the permeate concentration [mol / m 3 ] is shown. In the present invention, the rejection of the membrane element or membrane (membrane incorporated in the membrane element) to be treated is not particularly limited, but typically exhibits a high rejection, preferably 95% or more. On the other hand, the rejection of the membrane element or membrane produced by the production method of the present invention is not particularly limited and can be set to an appropriate rejection. For example, the rejection of the loose membrane described above can be mentioned. In this way, the method for producing a membrane element of the present invention can convert a semipermeable membrane into a loose membrane by lowering the rejection, and therefore can also be called a method for producing a loose membrane element.

[0016] [Membrane element] The membrane element used in the present invention is not particularly limited as long as it is a component that integrates a membrane, a support, and a flow path material, and a general membrane element can be used. Examples of the membrane element include a membrane element equipped with an RO membrane or an NF membrane, such as a reverse osmosis membrane element and a nanofiltration membrane element. In the rejection adjustment step of the present invention, the rejection of the semipermeable membrane incorporated in the membrane element can be highly controlled, and therefore the structure of the membrane element to be used is not particularly limited, and examples thereof include spiral membrane elements and hollow fiber membrane elements. In particular, spiral membrane elements, in which the membrane is stored in a spirally wound state within a casing and therefore adjustment of the rejection is more difficult, are preferably used.

[0017] The semipermeable membrane incorporated in the membrane element may be a semipermeable membrane used in reverse osmosis, such as an RO membrane or an NF membrane. The material constituting these semipermeable membranes is not particularly limited, and examples thereof include cellulose acetate, aromatic polyamide, polyvinyl alcohol, polysulfone, etc., with aromatic polyamide being preferred. The above materials may be either non-crosslinked or crosslinked. The degree of crosslinking in the crosslinked material is not particularly limited, and may be fully crosslinked or partially crosslinked.

[0018] The membrane element may be manufactured as appropriate, or a commercially available product may be used.

[0019] [Chemical solution] The chemical solution used in the production method of the present invention is usually a mixture of a damaging component and water, and is preferably an aqueous solution containing the damaging component. The damaging agent can be appropriately determined depending on the material of the semipermeable membrane to be treated, the desired rejection, etc., and examples thereof include inorganic halogen-based oxidizing agents, oxygen-based oxidizing agents, and organic compound oxidizing agents. Preferred inorganic halogen-based oxidizing agents are inorganic oxidizing agents containing chlorine atoms, such as chlorate, hypochlorite, chlorite, chlorine dioxide, chloramine, and N-chloroisocyanurate. The cations constituting the various salts are not particularly limited, and examples thereof include cations of elements belonging to Group 1 or Group 2 of the periodic table, ammonium cations, and organic cations. An example of an organic compound oxidizing agent is dimethyl sulfoxide. Specific examples of the chemical solution include an aqueous solution containing hypochlorite, an aqueous dimethylformamide solution, and an aqueous dimethyl sulfoxide solution.

[0020] The concentration of the damaging component in the chemical solution is not particularly limited and can be appropriately determined, for example, taking into consideration the time difference depending on the location of the membrane, productivity, etc., as described below. The concentration of the damaging component in the chemical solution can be determined by conducting a preliminary experiment described below, similarly to the chemical solution flow time, preferably within the range described below. For example, when an aqueous sodium hypochlorite solution is used as the chemical solution, the sodium hypochlorite concentration can be 2 to 10 mass% in terms of effective chlorine concentration. Generally, the time from the start of passing the chemical solution until it comes into contact with the membrane, and the time from the end of treatment until the chemical solution is discharged and cleaning is completed, vary depending on the location on the membrane, resulting in actual treatment times varying depending on the location on the membrane. When the concentration of damaging components in the chemical solution is high, the treatment time is shorter, resulting in relatively large time differences depending on the location on the membrane. This causes uneven exposure intensity within the membrane, making it difficult to control the level of chemical damage. Furthermore, when the concentration of damaging components in the chemical solution is low, it takes a long time to perform the rejection adjustment step (to reduce the rejection to the target value), resulting in low productivity. Taking these points into consideration, the treatment time in the manufacturing method of the present invention is preferably 30 minutes or more but less than 300 minutes, and more preferably 90 minutes or more but less than 180 minutes.

[0021] The temperature and pH of the chemical solution are not particularly limited and can be determined appropriately. For example, the temperature can be set to 0 to 45°C, but is preferably set to 20 to 30°C in consideration of the degree of chemical damage, workability, etc.

[0022] [Break rate adjustment process] The production method of the present invention (rejection adjustment step) can be carried out by appropriately selecting an apparatus configuration (system) that can pass a chemical solution through the primary flow path (concentration flow path) of a membrane element by the method and conditions described below. One embodiment of a system for carrying out the production method of the present invention is, for example, system 1 shown in Figure 1. This system 1 includes a membrane element 2 to be treated, a chemical tank 3 that stores a chemical solution, and a cleaning water tank 4 that stores cleaning water. The chemical tank 3 has a transfer path 5 that connects the chemical tank 3 to the inlet of the primary flow path of the membrane element 2, and a transfer path 6 that connects the outlet of the primary flow path of the membrane element 2 to the chemical tank 3. The transfer path 5 has, in order from the upstream side (chemical tank 3 side), a pump 3A and a pump P1, and the transfer path 6 has, in order from the upstream side (membrane element 2 side), a pump P2 and a valve. The transfer path 5 and the transfer path 6 form a circulation path that includes the chemical tank 3 and the membrane element 2, and the chemical solution stored in the chemical tank 3 is transferred to the membrane element 2 via the transfer path 5, flows through the primary flow path, and is then discharged from the membrane element 2 and returned to the chemical tank 3 via the transfer path 6. On the other hand, the wash water tank 4 has a transfer path 7 connecting the wash water tank 4 and the transfer path 5, and a transfer path 8 connecting the transfer path 6 and the wash water tank 4. The transfer path 7 has a pump 4A. The transfer path 7 (including the transfer path 5) and the transfer path 8 (including the transfer path 6) form a circulation path including the wash water tank 4 and the membrane element 2, and the wash water stored in the wash water tank 4 is transferred to the membrane element 2 via the transfer path 7 and the transfer path 5, circulates through the primary side flow path, and is then discharged from the membrane element 2 and returns to the wash water tank 4 via the transfer path 6 and the transfer path 8. A transfer path 9 equipped with a valve is connected to the outlet of the secondary side flow path of the membrane element 2, and this transfer path 9 is connected to the transfer path 6. Using such a system 1, the production method of the present invention (rejection adjustment step) can be carried out.

[0023] As described above, the rejection adjustment step is a step in which a chemical solution is passed through the primary flow path of the membrane element to adjust the rejection, and the condition for this step is to set the pressure difference (transmembrane pressure difference) applied to both membrane surfaces of the membrane element to be smaller than the osmotic pressure of the chemical solution. In this way, by causing the chemical solution to flow only through the primary flow path without allowing the water in the chemical solution to permeate the semipermeable membrane, excessive or uneven chemical damage (deterioration) of the semipermeable membrane can be suppressed, and chemical damage can be controlled to a high or uniform level.

[0024] The rejection adjustment step can be performed by any method, as long as the chemical solution is passed through the membrane element under pressure lower than the osmotic pressure. Typically, a pump is used to pass the chemical solution through the membrane element. Unlike separation and concentration, the rejection adjustment step does not require a pressure higher than the osmotic pressure. Therefore, the pump used to pass the chemical solution is not particularly limited, and a general-purpose pump can be used. For example, a centrifugal pump or a diaphragm pump can be used. However, since the chemical solution near the semipermeable membrane needs to be renewed during contact with the semipermeable membrane (liquid contact), for example, a pump capable of passing the chemical solution at a flow rate of 10 to 50 L / min for a 4-inch diameter membrane element is preferred, and a pump capable of passing the chemical solution at a flow rate of 15 to 25 L / min is more preferred. When the diameter of the membrane element is other than 4 inches, the flow rate for the pump can also be determined by converting the flow rate for the 4-inch diameter in proportion to the cross-sectional area.

[0025] The conditions for the rejection adjustment step are not particularly limited as long as the pressure difference (transmembrane pressure difference) applied to both membrane surfaces of the membrane element is set to be smaller than the osmotic pressure of the chemical solution. The primary pressure (the pressure applied to the chemical solution), secondary pressure, and pressure difference (synonymous with the pressure difference between the primary and secondary pressures) are all appropriately determined taking into consideration the osmotic pressure of the chemical solution, the maximum operating pressure, and the like. For example, the primary pressure can be 0.02 to 0.50 MPa, and the secondary pressure can be 0.01 to 0.49 MPa. In the present invention, the pressure difference can be 0.01 to 0.20 MPa, preferably 0.01 to 0.10 MPa, in order to allow the chemical solution to flow evenly through the primary side of the membrane while preventing it from penetrating to the secondary side. There are no particular limitations on the pressure difference between the pressure difference and the osmotic pressure of the chemical solution, but the lower limit of the pressure difference can be, for example, 0.005 MPa or more, preferably 0.01 MPa or more, in terms of high-level or uniform control of chemical damage and pressure controllability.

[0026] The flow rate of the chemical liquid is not particularly limited and can be determined as appropriate, and for example, for a membrane element with a diameter of 4 inches, it can be 10 to 50 L / min, and preferably 15 to 25 L / min. When the diameter of the membrane element is other than 4 inches, the flow rate for the above-mentioned 4-inch diameter can also be determined by converting it in proportion to the cross-sectional area.

[0027] In the rejection adjustment step, the rejection of the semipermeable membrane can be reduced by increasing the concentration of the damaging component in the chemical solution and by increasing the contact time (flow time) of the chemical solution with the semipermeable membrane. Furthermore, the rejection can be reduced linearly (straight-line) with respect to the product of the concentration of the damaging component and the contact time (exposure intensity of the damaging component to the semipermeable membrane). Therefore, the contact time between the chemical solution and the semipermeable membrane can be appropriately determined taking into account the concentration of the damaging component in the chemical solution, the rejection, and the like, and is set to the contact time required to achieve the desired rejection. The contact time required to achieve the desired rejection can be determined, for example, by the following method 1 and / or method 2. The contact time thus determined is used as the contact time in the rejection adjustment step using the membrane element. Method 1: Disassemble the membrane element in advance, remove the flat membrane to be treated, and then apply a chemical solution of a specified concentration. A preliminary experiment was conducted in which a flat membrane was immersed in water to determine the time required for contact with the liquid until the desired rejection rate was reached. Directly determine the interval. Method 2: The above preliminary experiment was carried out in the same manner as Method 1, and the product of the concentration of the damaging component and the contact time was calculated. The linear relationship of the rejection rate to the concentration is determined, and the contact time is determined from this linear relationship. In Method 2, instead of or in addition to the contact time, the damaging component of the chemical solution is measured. The concentration of the moiety can also be determined.

[0028] In the present invention, the product of the concentration (mass%) of the damaging component and the contact time (min) is not particularly limited. For example, for a sodium hypochlorite aqueous solution, it can be 10 to 1000 (mass% min), preferably 30 to 500 (mass% min), and more preferably 100 to 300 (mass% min). Furthermore, the contact time in the rejection adjustment process using a membrane element is determined as described above and can be significantly shorter than the conventional rejection reduction conditions, such as the 90 days described in Patent Document 1, and is specifically the treatment time described above. The contact time is measured from the point (0 seconds) when the chemical solution begins to pass through the membrane element. The above linear relationship cannot be uniquely determined due to variations in the concentration of the damaging component, the size of the membrane, the flow rate of the chemical solution, etc., and is therefore usually determined in advance by a preliminary experiment as described above.

[0029] The secondary flow path of the membrane element is normally filled with air and does not allow water to pass through. However, in the present invention, the secondary flow path may be filled in advance with a liquid that does not contain damaging components, such as water or an inert gas. By carrying out the rejection adjusting step in this manner, the rejection of the membrane can be set (reduced) to a predetermined value, preferably within the above range, in a short period of time.

[0030] In the manufacturing method of the present invention, in order to set the rejection rate of the semipermeable membrane to a predetermined value, for example, the above-mentioned rejection rate adjustment step can be carried out after determining the liquid flow time that will result in the predetermined rejection rate and the appropriate concentration of the damaging component using the above-mentioned methods 1 and 2.However, the predetermined rejection rate can be easily adjusted by carrying out a manufacturing method (a preferred embodiment of the manufacturing method of the present invention) that applies method 2, which determines in advance the relationship between the rejection rate and the product of the concentration of the damaging component and the liquid flow time. That is, a preferred embodiment of the manufacturing method of the present invention is a manufacturing method for a membrane element including a rejection adjustment step of adjusting the rejection of the membrane element by making the pressure difference applied to both membrane surfaces of the membrane element smaller than the osmotic pressure of the chemical solution and passing the chemical solution through the primary flow path of the membrane element, wherein the rejection adjustment step includes the following sub-steps 1 to 3. Sub-step 1: The pressure difference applied to both membrane surfaces of the membrane element is made smaller than the osmotic pressure of the chemical solution. When chemicals are passed through the primary flow path of the membrane element, damage caused by the chemicals contained in the chemicals At least one of the concentration of the component to be added and the time for passing the liquid is changed to obtain the desired results. Sub-process to determine the relationship between the product of liquid time and rejection rate (linear relationship) Sub-step 2: From the relationship obtained in sub-step 1, the concentration and the amount of the substance to be rejected are calculated. Sub-step to determine the liquid time product Sub-step 3: Set the concentration and / or the liquid flow time to satisfy the product obtained in the above sub-step 2. The pressure difference applied to both membrane surfaces of the membrane element is made smaller than the osmotic pressure of the chemical solution. Sub-process 3 of passing the chemical solution through the primary flow path of the membrane element

[0031] In the above-mentioned sub-step 1, it is preferable to carry out multiple types, preferably three or more types, of rejection adjustment steps in which at least one of the concentration of the damage-inflicting component and the liquid-passing time is changed, in order to determine the above relationship more accurately. In this case, the condition to be changed may be only the concentration, only the liquid-passing time, or both the concentration and the liquid-passing time. The conditions other than the concentration and the liquid-passing time in the rejection adjustment step in sub-step 1 are the same as the conditions in the rejection adjustment step in the production method of the present invention.

[0032] In the above-mentioned sub-step 2, after carrying out a plurality of types of rejection adjustment steps in the sub-step 1, for example, as shown in FIG. 2, for each rejection adjustment step, (concentration × liquid-flow time, rejection) is plotted as (X, Y) on a Cartesian coordinate system to obtain an approximation line showing the relationship between the product of the concentration and the liquid-flow time and the rejection.

[0033] In the above sub-step 3, the product of the concentration and the liquid-flow time that results in a predetermined rejection is determined from the approximation line obtained in sub-step 2, and the concentration and / or the liquid-flow time in the rejection adjustment step of sub-step 3 is determined. Thereafter, the determined concentration and / or flow time are set, and sub-step 3 is carried out in the same manner as in the rejection adjustment step in the production method of the present invention. The conditions in the rejection adjustment step in sub-step 3 other than the concentration and flow time are the same as the conditions in the rejection adjustment step in the production method of the present invention.

[0034] [Cleaning process] In the present invention, as described above, after the rejection adjusting step or sub-step 3 in the production method of the present invention is performed (after a predetermined liquid passing time has elapsed), it is preferable to discharge the chemical solution from the membrane element and then perform a cleaning step in which a cleaning solution is passed through. In this way, the chemical solution is quickly discharged to stop further progress of chemical damage, thereby making it possible to set the rejection to a predetermined value. The method for discharging the chemical solution from the membrane element is not particularly limited. For example, a gas may be passed through the membrane element, but passing cleaning water through it is preferred. The cleaning solution used in the cleaning step may be any solution that does not chemically damage the membrane, and is usually water, such as tap water, ion-exchanged water, purified water, or (ultra)pure water. The method and conditions for carrying out the cleaning step are not particularly limited as long as they allow the cleaning solution to be passed through at least the primary side of the membrane element. For example, the method for carrying out the cleaning step can be the same as the method for carrying out the rejection adjustment step, and the conditions for carrying out the cleaning step can be determined appropriately. The cleaning step can be carried out continuously in one go, but it is preferable to carry out the cleaning step in multiple steps with different cleaning solutions, as this can reliably stop the progression of chemical damage.

[0035] [Other processes] In the production method of the present invention (including preferred embodiments of the production method of the present invention), steps other than the rejection adjusting step (including substeps 1 to 3) and the washing step can also be carried out. For example, a step of determining the contact time required to reach the desired rejection (preliminary experiment) can be included.

[0036] The production method of the present invention performs a simple rejection adjustment step in which the pressure difference applied to both membrane surfaces of the membrane element is set to be smaller than the osmotic pressure of the chemical solution and the chemical solution is passed through the primary flow path, thereby enabling the rejection of the membrane (membrane element) to be highly controlled and the target rejection to be set in a short period of time. Furthermore, commercially available membrane elements can be used, and membrane elements exhibiting the target rejection can be produced simply, quickly, and with good workability.

[0037] The manufacturing method of the present invention is a method for manufacturing a membrane element for treating a membrane element, but it can also be used for treating a membrane module in which a plurality of membrane elements are housed in a pressure vessel as an integrated unit, and the rejection of the plurality of membrane elements is adjusted at once to produce a membrane module in which a plurality of membrane elements set to a predetermined rejection are housed in a pressure vessel. That is, the manufacturing method of the membrane element of the present invention can also be applied to a membrane module, and in this case it can also be said to be a method for manufacturing a membrane module exhibiting a predetermined rejection.

[0038] In the production method of the present invention, the membrane element is the object of treatment, and therefore the membrane element itself before being incorporated into a plant can be the object of treatment alone, or the membrane element incorporated into a plant can be the object of treatment.

[0039] The membrane module produced by the production method of the present invention can be used as it is or together with other membrane elements, preferably housed in a pressure-resistant vessel as a membrane module, for treating various liquids to be treated. The liquid to be treated is not particularly limited, and examples thereof include various industrial wastewaters containing organic solvents and other organic compounds, seawater, and recycled liquids in which valuable materials are dissolved. [Example]

[0040] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0041] [Example 1] <Manufacturing membrane elements with reduced rejection> A rejection adjustment step was carried out by passing a sodium hypochlorite aqueous solution (assumed osmotic pressure 1.2 MPa) with an effective chlorine concentration of 2.0 mass% as the chemical solution through a TM810V membrane element (product name, built-in cross-linked fully aromatic polyamide RO membrane, diameter 4 inches, rejection (salt rejection) 99.8%, manufactured by Toray Industries, Inc.) at a pressure difference of 0.06 MPa (primary side pressure 0.07 MPa, secondary side pressure 0.01 MPa) applied to both membrane surfaces (hereinafter referred to as membrane surface differential pressure) and a flow rate of 18 L / min for 19 minutes. After the liquid was passed through (19 minutes after the start of the liquid passing), the aqueous sodium hypochlorite solution was promptly drained from the membrane element, and then the membrane element was washed three times with different amounts of water (washing volume: 20 L of water each time) to carry out a washing step. The rejection of the membrane element thus produced was measured by the following method, and the results are shown in Table 1.

[0042] <Method for measuring the rejection rate> The apparent rejection rate of the element was calculated using the following formula, which takes into account the increase in concentration within the element.

number

[0043] In equation (2), the initial feed flow rate is Qf [m 3 / s], initial salt concentration is Wf [wt%], final feed flow rate is Qr [m 3 / s], and the final salt concentration is Wr [wt%]. The initial salt concentration is not the concentration of the feed liquid, but the concentration after circulation including hold-up water. The final feed flow rate and final salt concentration were calculated by measuring the permeate flow rate and permeate salt concentration and calculating from the material balance on the feed side and permeate side.

[0044] [Example 2] A sodium hypochlorite aqueous solution with an effective chlorine concentration of 5.0 mass% (assumed osmotic pressure 1.2 MPa) was passed through a membrane element, TM810V (product name, built-in cross-linked fully aromatic polyamide RO membrane, 4-inch diameter, rejection (salt rejection) 99.8%, manufactured by Toray Industries, Inc.), for 19 minutes at a membrane surface differential pressure of 0.06 MPa (primary side pressure 0.07 MPa, secondary side pressure 0.01 MPa) and a flow rate of 18 L / min, to carry out the rejection adjustment process. After the liquid had passed through, the aqueous sodium hypochlorite solution was promptly drained from the membrane element, and then washing was carried out three times with different amounts of water (washing amount: 20 L of water each time) to carry out a washing step. The rejection of the membrane element thus produced was measured in the same manner as in Example 1. The results are shown in Table 1.

[0045] [Example 3] A sodium hypochlorite aqueous solution with an effective chlorine concentration of 2.3% by mass (assumed osmotic pressure 1.2 MPa) was passed through a membrane element, TM810V (product name, built-in cross-linked fully aromatic polyamide RO membrane, 4-inch diameter, rejection (salt rejection) 99.8%, manufactured by Toray Industries, Inc.), for 62 minutes at a membrane surface differential pressure of 0.06 MPa (primary side pressure 0.07 MPa, secondary side pressure 0.01 MPa) and a flow rate of 18 L / min, to carry out the rejection adjustment process. After the liquid had passed through, the aqueous sodium hypochlorite solution was promptly drained from the membrane element, and then washing was carried out three times with different amounts of water (washing amount: 20 L of water each time) to carry out a washing step. The rejection of the membrane element thus produced was measured in the same manner as in Example 1. The results are shown in Table 1.

[0046] [Comparative Example 1] A sodium hypochlorite aqueous solution with an effective chlorine concentration of 1.9% by mass (assumed osmotic pressure 1.2 MPa) was passed through a membrane element, TM810V (product name, built-in cross-linked fully aromatic polyamide RO membrane, 4-inch diameter, rejection (salt rejection) 99.8%, manufactured by Toray Industries, Inc.), for 20 minutes at a membrane surface differential pressure of 1.99 MPa (primary side pressure 2.00 MPa, secondary side pressure 0.01 MPa) and a flow rate of 10 L / min, to carry out the rejection adjustment process. After the liquid had passed through, the aqueous sodium hypochlorite solution was promptly drained from the membrane element, and then washing was carried out three times with different amounts of water (washing amount: 20 L of water each time) to carry out a washing step. The rejection of the membrane element thus produced was measured in the same manner as in Example 1. The results are shown in Table 1.

[0047] Comparative Example 2 A sodium hypochlorite aqueous solution with an effective chlorine concentration of 1.9% by mass (assumed osmotic pressure 1.2 MPa) was passed through a membrane element, TM810V (trade name, built-in cross-linked fully aromatic polyamide RO membrane, diameter 4 inches, rejection (salt rejection) 99.8%, manufactured by Toray Industries, Inc.), at a membrane surface differential pressure of 1.99 MPa (primary side pressure 2.00 MPa, secondary side pressure 0.01 MPa) and a flow rate of 10 L / min, for 50 minutes to perform the rejection adjustment process. After the liquid had passed through, the aqueous sodium hypochlorite solution was promptly drained from the membrane element, and then washing was carried out three times with different amounts of water (washing amount: 20 L of water each time) to carry out a washing step. The rejection of the membrane element thus produced was measured in the same manner as in Example 1. The results are shown in Table 1.

[0048] Comparative Example 3 A sodium hypochlorite aqueous solution with an effective chlorine concentration of 1.9% by mass (assumed osmotic pressure 1.2 MPa) was passed through a membrane element, TM810V (trade name, built-in cross-linked fully aromatic polyamide RO membrane, diameter 4 inches, rejection (salt rejection) 99.8%, manufactured by Toray Industries, Inc.), for 73 minutes at a membrane surface differential pressure of 1.99 MPa (primary side pressure 2.00 MPa, secondary side pressure 0.01 MPa) and a flow rate of 10 L / min, to carry out the rejection adjustment process. After the liquid had passed through, the aqueous sodium hypochlorite solution was promptly drained from the membrane element, and then washing was carried out three times with different amounts of water (washing amount: 20 L of water each time) to carry out a washing step. The rejection of the membrane element thus produced was measured in the same manner as in Example 1. The results are shown in Table 1.

[0049] [Reference examples 1~6] In Examples 1 to 3 and Comparative Examples 1 to 3, the rejection adjustment step was carried out in the same manner as in each Example and Comparative Example, except that in place of the membrane element, a flat membrane removed from this membrane element was used, and the flat membrane was immersed in the chemical solution for the same time as the liquid passing time. Furthermore, the flat membrane was treated by carrying out the washing step in the same manner as in Examples 1 to 3 and Comparative Examples 1 to 3, except that the flat membrane removed from the chemical solution after the rejection adjustment step was immersed and washed three times in 1 L of water. The rejection of the obtained flat membrane was measured in the same manner as in Example 1. The results of each Reference Example are shown as "Flat membrane rejection" in the column for Examples or Comparative Examples in which the conditions for the rejection adjustment step were the same.

[0050] Table 1 shows the measured rejection rates and the conditions of the rejection rate adjustment step in each Example and Comparative Example. In Table 1, "concentration" indicates the concentration of the sodium hypochlorite aqueous solution (effective chlorine concentration), and "liquid contact time" indicates the time during which the sodium hypochlorite aqueous solution was passed through (Examples and Comparative Examples) or the time of immersion in the sodium hypochlorite aqueous solution (Reference Example). [Table 1]

[0051] Figure 2 is a graph showing the relationship between concentration × contact time and rejection rate, plotting (concentration × contact time, rejection rate) on a Cartesian coordinate system (X, Y) where "concentration × contact time" and "rejection rate" in Table 1 are used. The approximate dashed line in FIG. 2 indicates the relationship between the rejection rate and the product of the concentration and the contact time in the reference example. The rejection adjustment steps in Examples 1 to 3 and the preparation of FIG. 2 correspond to the above-mentioned method 2 for determining the contact time required to achieve the target rejection, i.e., sub-step 1 in a preferred embodiment of the production method of the present invention. The approximation line showing the relationship between the rejection and the product of the concentration and contact time in Examples 1 to 3 is Y ≈ -0.004X + 0.9(R 2 =0.9998).

[0052] The results in Table 1 and Figure 2 reveal the following: First, when a flat membrane is used, in Reference Examples 1 to 3 corresponding to Examples 1 to 3, and Reference Examples 4 to 6 corresponding to Comparative Examples 1 to 3, a linear relationship is established between the concentration of the chemical solution (sodium hypochlorite aqueous solution) x contact time (immersion time) and the rejection rate. In contrast, Comparative Examples 1 to 3, in which the differential pressure was set to a pressure equal to or greater than the (assumed) osmotic pressure of the chemical solution (sodium hypochlorite aqueous solution) when passing it through the membrane element, were able to reduce the rejection of the RO membrane. However, in Comparative Example 3, in which the contact time was lengthened, the rejection dropped sharply and significantly compared to Comparative Example 2, and a linear relationship did not hold between the concentration x contact time and the rejection. Therefore, when a chemical solution is passed through a membrane element at a differential pressure equal to or greater than the osmotic pressure, particularly when the concentration x contact time exceeds 95 (mass% min), it is clear that the rejection of the membrane element cannot be adjusted to a predetermined value based on the concentration x contact time. In other words, it is impossible to manufacture a membrane element that exhibits a predetermined rejection based on the concentration x contact time. On the other hand, in Examples 1 to 3, in which the differential pressure when passing the chemical through the membrane element was set to a pressure lower than the (assumed) osmotic pressure of the chemical, the rejection of the RO membrane could be reduced. Moreover, even with membrane elements that are less likely to treat uniformly than flat membranes, the linear relationship shown by the approximation line above holds between the concentration x contact time and rejection. Therefore, it can be seen that by performing the rejection adjustment step with a concentration and / or contact time set based on the concentration x contact time, the rejection of the membrane element can be adjusted to a predetermined value, i.e., a membrane element exhibiting a predetermined rejection can be manufactured. [Explanation of symbols]

[0053] 1 System 2. Membrane element 3 Chemical tank 3A pump 4 Cleaning water tank 4A Pump 5~9 Transport route P1 and P2 pumps

Claims

1. A method for manufacturing a membrane element, comprising a rejection adjustment step of passing a chemical solution through a primary flow path of the membrane element to adjust the rejection, A method for manufacturing a membrane element, wherein when the chemical solution is passed through the membrane element in the rejection adjusting step, the pressure difference applied to both membrane surfaces of the membrane element is set to be smaller than the osmotic pressure of the chemical solution.

2. The method for producing a membrane element according to claim 1, wherein the membrane element is a reverse osmosis membrane element or a nanofiltration membrane element.

3. The method for producing a membrane element according to claim 1 or 2, wherein the chemical solution is an aqueous solution containing hypochlorite.

4. The method for producing a membrane element according to claim 3, wherein the hypochlorite has an available chlorine concentration of 2 to 10 mass %.

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