Method for manufacturing a membrane element

Abstract

Provided is a method for manufacturing a membrane element, including a rejection rate adjustment process of adjusting a rejection rate by passing a chemical reagent solution through a once-through channel of the membrane element, wherein a pressure difference applied to both membrane surfaces of the membrane element is set to be less than an osmotic pressure of the chemical reagent solution when the chemical reagent solution is passed in the rejection rate adjustment process.

Description

Technical Field

[0001] This invention relates to a method for manufacturing membrane elements. Background Technology

[0002] Factory wastewater, containing a mixture of various organic substances, has traditionally been directly incinerated. Incineration consumes a significant amount of energy, and improvements are needed from the perspectives of reducing environmental impact (environmental protection) and building a circular society (sustainable society). Therefore, a method has been proposed to concentrate and reduce the volume of factory wastewater through various membrane treatment processes before incineration, thereby reducing energy consumption.

[0003] As a membrane treatment method, reverse osmosis (RO), which has been widely used in seawater desalination and other processes, is an advantageous approach. Reverse osmosis is a technique that applies pressure to the concentrated solution side separated by a semi-permeable membrane such as a reverse osmosis membrane (RO membrane) or a nanofiltration membrane (NF membrane), making the operating pressure difference between the treated solution side (primary side) and the permeate side (secondary side) higher than the osmotic pressure difference between the concentrated solution side and the dilute solution side. This allows the solvent to selectively permeate through the semi-permeable membrane.

[0004] Reverse osmosis membrane treatment typically uses membrane elements containing semi-permeable membranes. However, due to the high rejection rate of the membrane (membrane element), the operating conditions of the membrane element are somewhat limited, resulting in a narrow application range. For example, there is an upper limit to the operating pressure differential that the membrane element can handle, thus limiting the concentration of the solution that can be used for reverse osmosis. Furthermore, as treatment progresses, the treated water becomes concentrated, and when the gradually increasing osmotic pressure exceeds the maximum operating pressure of the membrane element, membrane treatment can no longer proceed. Moreover, membrane fouling is prone to occur when the treated water is concentrated. Therefore, to apply reverse osmosis to the treatment of high-concentration industrial wastewater containing mixtures, or to the treatment of low-concentration industrial wastewater containing mixtures to a high concentration, improvements to the semi-permeable membrane and membrane element are necessary.

[0005] By using a semipermeable membrane or membrane element with a low rejection rate, the aforementioned operating conditions and application range can be relaxed or expanded. For example, when using a membrane element equipped with a semipermeable membrane, the pressure difference between the primary and secondary sides (intermembrane differential pressure) becomes lower, the operating conditions are relaxed, and the application range is expanded. The semipermeable membrane has a low rejection rate, allowing water to pass through preferentially and solutes such as mixtures to pass through slightly. Furthermore, membrane clogging can be suppressed. If such a membrane element is used, even high-concentration treated water can be concentrated by performing membrane treatment in one or more stages, and even low-concentration treated water can be concentrated to a high concentration. In order to suppress the gradually increasing osmotic pressure of the treated liquid within the maximum operating pressure range of the membrane element, it is important to adjust and control the rejection rate to a low value. Several methods for reducing the rejection rate of semipermeable membranes have been proposed; for example, Patent Document 1 describes a method that chemically damages the RO membrane by allowing an aqueous solution containing chlorine inorganic compounds to pass through it.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent No. 5037175 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] Here, adjusting and controlling the rejection rate of a semipermeable membrane to a specified value is relatively easy for semipermeable membranes or flat sheet membranes before they are assembled into a membrane element. However, semipermeable membranes assembled into a membrane element are tightly assembled within a housing (outer shell), making it difficult to uniformly chemically damage them in both the thickness and planar directions, thus hindering adjustment and control to the target rejection rate. For example, one method for adjusting the rejection rate of a membrane element is to chemically damage the semipermeable membrane by allowing an aqueous solution containing a very low concentration of chlorine compounds to pass through the membrane element. However, this method requires setting the time for the aqueous solution containing chlorine compounds to pass through (the contact time with the membrane) to a long duration, resulting in poor operational efficiency. Furthermore, there is no correlation between the liquid flow time of the aqueous solution containing chlorine compounds and the amount of reduction in rejection rate; as described later, when a certain flow time is exceeded, the rejection rate drops sharply and significantly, sometimes making it impossible to adjust to the specified rejection rate. Such problems also exist in the method described in Patent Document 1. Specifically, in this method, a 0.167 mg / L sodium hypochlorite aqueous solution is used at a concentration of 2.4 mg / L. 3At a flow rate of / h, the circulation time would require a long period of 90 days. Moreover, there is no correlation between the liquid circulation time and the amount of reduction in permeability, making it impossible to control the amount of reduction in retention rate and adjust it to the target retention rate.

[0011] The objective of this invention is to provide a method for manufacturing a membrane element that can produce a membrane element with a specified rejection rate in a short time by controlling the chemical damage to the membrane caused by a chemical reagent solution.

[0012] means for solving problems

[0013] The inventors, assuming that a chemical reagent solution containing a relatively high concentration of damage-inducing components can induce chemical damage to a semipermeable membrane in a short time, investigated and studied the progress and characteristics of chemical damage to the semipermeable membrane caused by the chemical reagent solution. The results showed that the liquid flow time (liquid contact time) between the semipermeable membrane and the chemical reagent solution decreased sharply at a certain point in time. Consequently, no specific relationship was found between the liquid flow time and the retention rate (degree of chemical damage) throughout the entire liquid flow time. Therefore, a method was conceived that allows the chemical reagent solution to flow through the primary side flow path, but does not require water to permeate into the secondary side flow path and form an air layer, instead of the method commonly used in membrane module processing where the chemical reagent solution permeates through the semipermeable membrane (allowing the chemical reagent solution to pass through the primary side flow path and water in the chemical reagent solution to permeate into the secondary side flow path and flow within the secondary side flow path). Further research based on this concept revealed that by setting the pressure difference applied to the two membrane surfaces of the membrane module to be less than the osmotic pressure of the chemical reagent solution used, even with a membrane module, the semipermeable membrane assembled within the housing can be chemically damaged uniformly in both the thickness and planar directions. Furthermore, it was found that a linear relationship exists between the product of the damage-contributing component concentration and the liquid flow time (liquid contact time) of the chemical reagent solution (the exposure intensity of the damage-contributing component to the semipermeable membrane) and the amount of chemical damage to the semipermeable membrane (retention rate). This linear relationship holds true across the entire range of variations in the exposure intensity. Moreover, by determining the exposure intensity based on this linear relationship, a predetermined retention rate can be achieved and set within a short time. This invention was accomplished through these findings.

[0014] That is, the objective of this invention is achieved through the following means.

[0015] <1> A method for manufacturing a membrane element includes a rejection rate adjustment step of passing a chemical reagent solution through a primary side flow path of the membrane element to adjust the rejection rate, wherein... In the retention rate adjustment process, when the chemical reagent solution is passed through, the pressure difference applied to the two membrane surfaces of the membrane element is set to be less than the osmotic pressure of the chemical reagent solution.

[0016] <2> according to <1> The method for manufacturing the membrane element, wherein the membrane element is a reverse osmosis membrane element or a nanofiltration membrane element.

[0017] <3> according to <1> or <2> The method for manufacturing the membrane element, wherein the chemical reagent solution is an aqueous solution containing hypochlorite.

[0018] <4> according to <3> In the method for manufacturing the membrane element, the effective chlorine concentration of hypochlorite is 2% to 10% by mass.

[0019] Invention Effects

[0020] The present invention provides a method for manufacturing membrane elements that can control chemical damage to the membrane caused by chemical reagent solutions, thereby enabling the manufacture of membrane elements with a specified rejection rate in a short time.

[0021] The above and other features and advantages of the present invention will become more apparent from the following description. Attached Figure Description

[0022] Figure 1 This is a schematic diagram illustrating one embodiment of a system capable of carrying out a method for manufacturing a membrane element according to the present invention.

[0023] Figure 2 This is a graph showing the relationship between the concentration of the damage-contributing component in the chemical reagent solution in the examples, comparative examples, and reference examples, the product of the liquid contact time of the chemical reagent solution, and the retention rate. Detailed Implementation

[0024] In this invention and specification, a semipermeable membrane that allows water to preferentially permeate and solutes to permeate by reducing its rejection rate (performance) is referred to as a "loose membrane" or "degraded membrane." Its rejection rate is not particularly limited; for example, it can be 90% or less, preferably 20% to 80%. On the other hand, a semipermeable membrane with a high rejection rate (a membrane whose rejection rate has not been reduced) is sometimes referred to as a "high-performance membrane." Its rejection rate is not particularly limited, and is typically 95% or higher. It should be noted that, unless otherwise stated, the rejection rate of a semipermeable membrane also includes the rejection rate of the membrane element.

[0025] In this invention and specification, reverse osmosis includes both RO (reverse osmosis) and NF (nanofiltration) methods. Therefore, unless otherwise stated, the terms RO membrane, RO membrane element, and RO membrane module respectively refer to RO membrane and NF membrane, RO membrane element and NF membrane element, and RO membrane module and NF membrane module.

[0026] Furthermore, in this invention and this specification, "membrane element" refers to a component that integrates a semi-permeable membrane, a support, and a flow path material, and other components that possess a semi-permeable membrane. "Membrane module" refers to an assembly that integrates one or more membrane elements within a pressure vessel, becoming a basic unit constituting a complete set of equipment. Here, membrane elements or membrane modules with porous membranes are referred to as "porous membrane elements" and "porous membrane modules," respectively.

[0027] In this invention and this specification, the numerical range indicated by “~” refers to the range that includes the values ​​recorded before and after “~” as the lower limit and upper limit.

[0028] [Membranes for manufacturing membrane elements]

[0029] The method for manufacturing the membrane element of the present invention (hereinafter, sometimes referred to as "the manufacturing method of the present invention") includes the following retention rate adjustment step.

[0030] <Retention Rate Adjustment Process>

[0031] The process of allowing a chemical reagent solution to pass through the primary flow path of a membrane element in a manner that makes the pressure difference applied to the two membrane surfaces less than the osmotic pressure of the chemical reagent solution, thereby adjusting the rejection rate of the membrane element.

[0032] As described above, the manufacturing method of the present invention is as follows: for a chemical reagent solution containing a damage-inducing component that imparts chemical damage (e.g., oxidation) to the semipermeable membrane through contact with the semipermeable membrane, the pressure difference applied to the two membrane surfaces of the membrane element is set to be less than the osmotic pressure of the chemical reagent solution. thereby suppressing water permeation into the secondary flow path while allowing the chemical reagent solution to flow (uniformly) in the primary flow path, thereby imparting chemical damage to the semipermeable membrane and adjusting and reducing the rejection rate of the semipermeable membrane (membrane element).

[0033] Generally, the processing of membranes or membrane modules, as described in Patent Document 1, is performed by permeating a chemical reagent solution through a semipermeable membrane, i.e., by setting the pressure difference applied to the two membrane surfaces (intermembrane differential pressure) to be greater than or equal to the osmotic pressure of the chemical reagent solution. In contrast, in the manufacturing method of the present invention, when the chemical reagent solution is passed through the primary flow path of the membrane element, the intermembrane differential pressure is set to be less than the osmotic pressure of the chemical reagent solution. Therefore, water in the chemical reagent solution is prevented from passing through the secondary flow path (in which case the secondary flow path becomes an air layer) without permeating the semipermeable membrane. Thus, even with a semipermeable membrane tightly assembled within a housing, chemical damage (oxidation) caused by the chemical reagent solution can be controlled highly and uniformly in both the thickness and planar directions, resulting in the semipermeable membrane's rejection rate being set to a predetermined value within a short time.

[0034] The detailed reasons are not yet clear, but in conventional processing methods, the permeation rate of the damage-inducing component in the chemical reagent solution is slower than that of water. For the damage-inducing component that permeates along with water, a concentration distribution (concentration gradient) is generated at least in the thickness direction of the semipermeable membrane, and the degree and rate of concentration distribution are easily variable. As a result, it is considered difficult to control the chemical damage in at least the thickness direction of the semipermeable membrane, and the damage changes drastically. In contrast, in the retention rate adjustment step of the present invention, since water is not allowed to flow (permeate) within the semipermeable membrane, the permeation rate of the damage-inducing component is kept constant in the thickness direction of the semipermeable membrane due to diffusion control, and the generation of the concentration distribution of the damage-inducing component can be suppressed at least in the thickness direction of the semipermeable membrane. As a result, chemical damage can be carried out uniformly in both the thickness and planar directions of the semipermeable membrane (highly controlled retention rate), and a linear relationship exists between the exposure intensity of the damage-inducing component to the semipermeable membrane and the retention rate throughout the entire range of the aforementioned exposure intensity variation. It is believed that based on this linear relationship, a predetermined retention rate can be achieved and set in a short time.

[0035] In membrane modules, there are usually two types of retention rates (removal rates): apparent retention rate and true retention rate. However, in this invention, "retention rate" refers to the apparent retention rate Robs[-] defined by the following formula (1).

[0036] Equation (1): Robs = 1 - (Cp / Cb)

[0037] In equation (1), Cb represents the concentration of the liquid being treated [mol / m]. 3 Cp represents the permeate concentration [mol / m³]. 3 ].

[0038] In this invention, the retention rate of the membrane element or membrane (the membrane assembled in the membrane element) being processed is not particularly limited, and generally exhibits a high retention rate, for example, preferably 95% or more. On the other hand, the retention rate of the membrane element or membrane manufactured by the manufacturing method of this invention is not particularly limited, and can be adjusted to an appropriate retention rate. For example, the retention rate of the porous membrane described above can be cited.

[0039] Thus, the method for manufacturing membrane elements of the present invention can reduce the rejection rate and convert a semipermeable membrane into a porous membrane, and therefore can also be called a method for manufacturing porous membrane elements.

[0040] [Membrane element]

[0041] There are no particular restrictions on the membrane element used in this invention, as long as it is a component that integrates the membrane, support, and flow agent. Ordinary membrane elements can be used.

[0042] As membrane elements, examples include membrane elements with RO membranes and NF membranes, such as reverse osmosis membrane elements and nanofiltration membrane elements.

[0043] In the retention rate adjustment process of the present invention, the retention rate of the semipermeable membrane assembled in the membrane element can be highly controlled. Therefore, there are no particular limitations on the structure of the membrane element used. For example, spiral membrane elements and hollow fiber membrane elements can be used. In particular, spiral membrane elements, which are more difficult to adjust, can be used to store the membrane in a spiral shape in the housing.

[0044] As a semipermeable membrane assembled in a membrane element, examples of semipermeable membranes used in reverse osmosis include RO membranes and NF membranes.

[0045] There are no particular limitations on the materials constituting these semipermeable membranes; examples include cellulose acetate, aromatic polyamides, polyvinyl alcohol, and polysulfone, with aromatic polyamides being preferred. It should be noted that the above materials can be non-crosslinked or crosslinked. Furthermore, there are no particular limitations on the degree of crosslinking in crosslinked materials; they can be fully crosslinked or partially crosslinked.

[0046] As membrane elements, they can be manufactured appropriately or commercially available products can be used.

[0047] [Chemical reagent solution]

[0048] The chemical reagent solution used in the manufacturing method of the present invention is typically a mixture of a damage-inducing component and water, preferably an aqueous solution containing the damage-inducing component. The damage-inducing agent can be appropriately determined based on the material of the semi-permeable membrane being treated and the desired rejection rate, and examples include inorganic halogenated oxidants, oxygen-containing oxidants, and organic compound oxidants. As an inorganic halogenated oxidant, inorganic oxidants containing chlorine atoms are preferred, such as chlorates, hypochlorites, chlorites, chlorine dioxide, chloramines, and N-chloroisocyanurates. There are no particular limitations on the cations constituting the various salts; examples include cations of elements belonging to Group I or Group II of the periodic table, ammonium cations, and organic cations. As an organic compound oxidant, dimethyl sulfoxide is an example. Specifically, as a chemical reagent solution, examples include aqueous solutions containing hypochlorite, aqueous solutions of dimethylformamide, and aqueous solutions of dimethyl sulfoxide.

[0049] There are no particular limitations on the concentration of the damage-inducing component in the chemical reagent solution; for example, it can be appropriately determined based on factors such as the time difference in membrane position and productivity, as described below. The concentration of the damage-inducing component in the chemical reagent solution can be determined through preliminary experiments as described later, and similarly to the liquid flow time of the chemical reagent solution, it is preferably within the range described later. For example, when using an aqueous sodium hypochlorite solution as the chemical reagent solution, the sodium hypochlorite concentration, expressed as available chlorine, can be set to 2% to 10% by mass.

[0050] Typically, the time from the start of circulating the chemical reagent solution to the point of liquid contact, and the time from the end of treatment to the discharge of the chemical reagent solution and completion of rinsing, vary depending on the membrane's location, resulting in a time difference in actual treatment time based on membrane location. When the concentration of the damage-inducing component in the chemical reagent solution is high, the treatment time is shorter, thus the time difference based on membrane location is relatively larger. This leads to uneven exposure intensity within the membrane, making it difficult to control chemical damage. Furthermore, when the concentration of the damage-inducing component in the chemical reagent solution is low, the retention rate adjustment process (reducing the retention rate to a target value) is time-consuming, reducing productivity. In view of these aspects, the treatment time in the manufacturing method of the present invention is preferably 30 minutes or more and less than 300 minutes, more preferably 90 minutes or more and less than 180 minutes.

[0051] There are no particular restrictions on the temperature and pH of the chemical reagent solution, and they can be appropriately determined. For example, the temperature can be set to 0℃~45℃, but considering the progress of chemical damage, workability, etc., it is preferable to set it to 20℃~30℃.

[0052] [Retention Rate Adjustment Process]

[0053] The manufacturing method (retention rate adjustment step) of the present invention can be implemented by appropriately selecting an apparatus structure (system) capable of allowing the chemical reagent solution to pass through the primary side flow path (concentration side flow path) of the membrane element, depending on the methods and conditions described later. As an embodiment of the system for implementing the manufacturing method of the present invention, examples can be listed as follows: Figure 1 System 1 is shown.

[0054] The system 1 includes a membrane element 2 for processing, a chemical reagent solution tank 3 for containing a chemical reagent solution, and a cleaning water tank 4 for containing cleaning water. The chemical reagent solution tank 3 has a conveying path 5 connecting the inlet of the primary flow path of the chemical reagent solution tank 3 and the membrane element 2, and a conveying path 6 connecting the outlet of the primary flow path of the membrane element 2 and the chemical reagent solution tank 3. The conveying path 5 has a pump 3A and a pump P1 sequentially from the upstream side (chemical reagent solution tank 3 side), and the conveying path 6 has a pump P2 and a valve sequentially from the upstream side (membrane element 2 side). A circulation path including the chemical reagent solution tank 3 and the membrane element 2 is formed through the conveying paths 5 and 6. The chemical reagent solution stored in the chemical reagent solution tank 3 is conveyed to the membrane element 2 via the conveying path 5, flows through the primary flow path, is discharged from the membrane element 2, and returns to the chemical reagent solution tank 3 via the conveying path 6. On the other hand, the cleaning water tank 4 has a conveying path 7 connecting the cleaning water tank 4 and the aforementioned conveying path 5, and a conveying path 8 connecting the conveying path 6 and the cleaning water tank 4. The conveying path 7 includes a pump 4A. A circulation path including a cleaning water tank 4 and a membrane element 2 is formed through conveying path 7 (including conveying path 5) and conveying path 8 (including conveying path 6). Cleaning water stored in the cleaning water tank 4 is conveyed to the membrane element 2 via conveying path 7 and conveying path 5, flows through this primary flow path, is discharged from the membrane element 2, and returns to the cleaning water tank 4 via conveying path 6 and conveying path 8. It should be noted that a conveying path 9 equipped with a valve is connected to the outlet of the secondary flow path of the membrane element 2; this conveying path 9 is connected to conveying path 6.

[0055] The manufacturing method (retention rate adjustment process) of the present invention can be implemented using such a system 1.

[0056] As described above, the rejection rate adjustment process is a process of adjusting the rejection rate by allowing the chemical reagent solution to pass through the primary flow path of the membrane element. As a condition, the pressure difference (inter-membrane differential pressure) applied to the two membrane surfaces of the membrane element is set to be less than the osmotic pressure of the chemical reagent solution. In this way, the chemical reagent solution flows only in the primary flow path without allowing water in the semipermeable membrane to permeate, thereby suppressing excessive or uneven chemical damage (deterioration) to the semipermeable membrane, and thus highly or uniformly controlling chemical damage.

[0057] The method for adjusting the rejection ratio is not particularly limited as long as the chemical reagent solution can be forced through the membrane element at a pressure lower than the aforementioned osmotic pressure. Typically, a pump is used to circulate the chemical reagent solution through the membrane element. In the rejection ratio adjustment process, unlike the separation and concentration process, a pressure higher than the osmotic pressure is not required. Therefore, there are no particular limitations on the pump used to circulate the chemical reagent solution, and general-purpose pumps can be used. For example, centrifugal pumps, diaphragm pumps, etc., can be used. However, during contact with the semi-permeable membrane (liquid contact), the chemical reagent solution near the semi-permeable membrane needs to be replenished. Therefore, for example, for a 4-inch diameter membrane element, a pump capable of circulating the chemical reagent solution at a flow rate of 10 L / min to 50 L / min is preferred, and a pump capable of circulating the chemical reagent solution at a flow rate of 15 L / min to 25 L / min is more preferred. It should be noted that when the diameter of the membrane element is greater than 4 inches, the pump flow rate can also be determined by converting the above-mentioned flow rate for a 4-inch diameter to a cross-sectional area ratio.

[0058] As a condition in the rejection rate adjustment process, there are no special restrictions as long as the pressure difference (inter-membrane differential pressure) applied to the two membrane surfaces of the membrane element is set to be less than the osmotic pressure of the chemical reagent solution.

[0059] The primary side pressure (the pressure applied to the chemical reagent solution), secondary side pressure, and pressure difference (which have the same meaning as the pressure difference between the primary and secondary side pressures) are all appropriately determined considering the osmotic pressure of the chemical reagent solution, the maximum operating pressure, etc. For example, the primary side pressure can be set to 0.02 MPa to 0.50 MPa, and the secondary side pressure can be set to 0.01 MPa to 0.49 MPa. In this invention, considering the goal of ensuring uniform flow of the chemical reagent solution on the primary side of the membrane without permeation to the secondary side, the pressure difference can be set to 0.01 MPa to 0.20 MPa, preferably 0.01 MPa to 0.10 MPa. Furthermore, there is no particular limitation on the pressure difference between the pressure difference and the osmotic pressure of the chemical reagent solution. Regarding the lower limit of the pressure difference, considering factors such as the control of the degree or uniformity of chemical damage and pressure controllability, it can be set to 0.005 MPa or more, preferably 0.01 MPa or more.

[0060] There are no particular restrictions on the flow rate of the chemical reagent solution, and it can be appropriately determined. For example, for a membrane element with a diameter of 4 inches, it can be set to 10 L / min to 50 L / min, preferably 15 L / min to 25 L / min. It should be noted that when the diameter of the membrane element is other than 4 inches, the above-mentioned flow rate for a diameter of 4 inches can also be determined by converting it to a cross-sectional area ratio.

[0061] In the retention rate adjustment process, increasing the concentration of the damaging component in the chemical reagent solution and extending the liquid contact time (liquid flow time) between the chemical reagent solution and the semipermeable membrane further reduces the retention rate of the semipermeable membrane. Furthermore, the retention rate decreases linearly relative to the product of the damaging component concentration and the liquid contact time (the exposure intensity of the damaging component to the semipermeable membrane). Therefore, the liquid contact time between the chemical reagent solution and the semipermeable membrane can be appropriately determined considering the concentration of the damaging component in the chemical reagent solution, the retention rate, etc., and set as the liquid contact time to achieve the target retention rate. The liquid contact time to achieve the target retention rate can be determined, for example, by method 1 and / or method 2 described below. The liquid contact time determined in this way is used as the liquid contact time in the retention rate adjustment process using the membrane element.

[0062] Method 1: Disassemble the membrane element beforehand, take out the flat sheet membrane to be treated, and conduct a preliminary experiment by immersing the flat sheet membrane in a chemical reagent solution of a specified concentration, thereby directly determining the liquid contact time until the desired rejection rate is achieved.

[0063] Method 2: Perform the above preliminary experiment in the same manner as Method 1, and determine the linear relationship between the retention rate and the product of the concentration of the damage-contributing component and the liquid contact time. Determine the liquid contact time based on this linear relationship.

[0064] It should be noted that in Method 2, the concentration of the damage-contributing component of the chemical reagent solution can be determined in addition to the liquid contact time or other factors.

[0065] In this invention, the product of the concentration (mass %) of the damage-inducing component and the liquid contact time (minutes) is not particularly limited. For example, for an aqueous solution of sodium hypochlorite, it can be set to 10 to 1000 (mass %·minute), preferably 30 to 500 (mass %·minute), and more preferably 100 to 300 (mass %·minute). Furthermore, the liquid contact time in the retention rate adjustment process using a membrane element, as determined above, can be significantly shortened compared to conventional retention rate reduction conditions, such as the 90 days in Patent Document 1, specifically as described in the processing time section above. It should be noted that the liquid contact time is measured from the moment the chemical reagent solution begins to pass through the membrane element (0 seconds).

[0066] It should be noted that the above linear relationship cannot be uniquely determined due to variations in the concentration of the damage-contributing component, the size of the membrane, the flow rate of the chemical reagent solution, etc. Therefore, it is usually determined through preliminary experiments as described above.

[0067] In the secondary flow path of the membrane element, water does not permeate and it is usually filled with air. However, in this invention, it can also be pre-filled with a liquid that does not contain damaging components, such as water or inactive gas.

[0068] When the retention rate adjustment process is performed in this way, the membrane retention rate can be set (reduced) to the preferred range and set (reduced) to a specified value in a short time.

[0069] In the manufacturing method of the present invention, in order to set the retention rate of the semipermeable membrane to a predetermined value, for example, it is sufficient to perform the above-described retention rate adjustment step based on determining the liquid flow time to achieve the predetermined retention rate through methods 1 and 2, and appropriately determining the concentration of the damage-inducing component. However, by implementing the manufacturing method of method 2 (a preferred embodiment of the manufacturing method of the present invention) which pre-determines the relationship between the product of the concentration of the damage-inducing component and the liquid flow time and the retention rate, the retention rate can be easily adjusted to the predetermined retention rate.

[0070] That is, the preferred embodiment of the manufacturing method of the present invention is a manufacturing method of a membrane element including a rejection rate adjustment step, wherein the rejection rate of the membrane element is adjusted by passing a chemical reagent solution through the primary side flow path of the membrane element in such a way that the pressure difference between the two membrane surfaces applied to the membrane element is set to be less than the osmotic pressure of the chemical reagent solution. The rejection rate adjustment step includes the following sub-steps 1 to 3.

[0071] Sub-process 1: When the chemical reagent solution is passed through the primary flow path of the membrane element with the pressure difference applied to the two membrane surfaces set to be less than the osmotic pressure of the chemical reagent solution, at least one of the concentration of the damage-contributing component in the chemical reagent solution and the liquid flow time is changed, and the relationship (linear relationship) between the product of concentration and liquid flow time and the rejection rate is calculated.

[0072] Sub-process 2: Based on the relationship obtained in sub-process 1 above, determine the product of concentration and liquid flow time relative to the specified retention rate.

[0073] Sub-process 3: This sub-process 3 involves passing the chemical reagent solution through the primary flow path of the membrane element in a manner that satisfies the concentration and / or liquid flow time of the product obtained in sub-process 2 above, and sets the pressure difference applied to the two membrane surfaces of the membrane element to be less than the osmotic pressure of the chemical reagent solution.

[0074] In sub-step 1 described above, from the viewpoint of being able to more accurately determine the aforementioned relationship, it is preferable to perform a type of retention rate adjustment step that modifies at least one of the concentration of the damage-inducing component and the liquid flow time in multiple, preferably three or more, variations. In this case, the modification condition can be only concentration, only liquid flow time, or both concentration and liquid flow time. The conditions in the retention rate adjustment step in sub-step 1, except for concentration and liquid flow time, are the same as the conditions in the retention rate adjustment step of the manufacturing method of the present invention.

[0075] In sub-process 2 above, after various retention rate adjustment processes were implemented in sub-process 1, for example, Figure 2 As shown, for each retention rate adjustment process, (concentration × liquid flow time, retention rate) is plotted as (X, Y) in an orthogonal coordinate system to obtain an approximate line representing the relationship between the product of concentration and liquid flow time and the retention rate.

[0076] In the above sub-process 3, based on the approximate line obtained in sub-process 2, the product of the concentration and liquid flow time required to achieve the specified retention rate is determined, and the concentration and / or liquid flow time in the retention rate adjustment process of sub-process 3 are determined.

[0077] Then, sub-step 3 is performed in the same manner as the retention rate adjustment step in the manufacturing method of the present invention, with the concentration and / or liquid flow time set to the determined values. The conditions in the retention rate adjustment step of sub-step 3, except for the concentration and liquid flow time, are the same as the conditions in the retention rate adjustment step in the manufacturing method of the present invention.

[0078] [Cleaning Process]

[0079] In this invention, as described above, it is preferable to perform a cleaning step after the retention rate adjustment step or sub-step 3 in the manufacturing method of this invention (after reaching the predetermined liquid flow time), in which the chemical reagent solution in the membrane element is discharged and then the cleaning liquid is circulated. By rapidly discharging the chemical reagent solution in this way and stopping further chemical damage, the retention rate can be set to a predetermined value.

[0080] There are no particular restrictions on the method for discharging the chemical reagent solution from the membrane element; for example, gas can flow through the membrane element, but it is preferable to flow cleaning water. The cleaning solution used in the cleaning process can be any liquid that will not chemically damage the membrane, typically water, such as tap water, ion-exchanged water, purified water, and (ultra)pure water. There are no particular restrictions on the method and conditions for carrying out the cleaning process, as long as they allow the cleaning solution to flow through at least one side of the membrane element. For example, the method for carrying out the cleaning process can be the same as the method for carrying out the rejection rate adjustment process, and the conditions for carrying out the cleaning process can be appropriately determined. The cleaning process can be carried out continuously in one go; however, from the perspective of reliably stopping chemical damage, it is preferable to carry it out in multiple stages while changing the cleaning solution.

[0081] [Other processes]

[0082] In the manufacturing method of the present invention (including the preferred embodiment of the manufacturing method of the present invention), steps other than the retention rate adjustment step (including sub-steps 1 to 3) and the cleaning step described above may also be performed. For example, steps such as determining the liquid contact time until the desired retention rate is achieved (the aforementioned preliminary experiment) can be included.

[0083] The manufacturing method of the present invention, through a simple retention rate adjustment step of passing the chemical reagent solution through a primary side flow path by setting the pressure difference applied to the two membrane surfaces of the membrane element to be less than the osmotic pressure of the chemical reagent solution, can highly control the retention rate of the membrane (membrane element) and can set the target retention rate in a short time. Furthermore, commercially available membrane elements can be used, and membrane elements exhibiting the target retention rate can be easily and quickly manufactured with good workability.

[0084] The manufacturing method of the present invention is a method for manufacturing membrane elements as the object of processing. However, it can also be used as a method for processing membrane modules in which multiple membrane elements are housed in a pressure vessel. First, the rejection rates of the multiple membrane elements are adjusted, and then a membrane module is manufactured in which multiple membrane elements with predetermined rejection rates are housed in a pressure vessel. That is, the manufacturing method of the membrane elements of the present invention can also be applied to membrane modules, and in this case, it can also be called a method for manufacturing membrane modules exhibiting predetermined rejection rates.

[0085] The manufacturing method of the present invention treats membrane elements as processing objects, so the membrane elements themselves before being assembled into the complete set of equipment can be treated as processing objects separately, or the membrane elements assembled into the complete set of equipment can be treated as processing objects.

[0086] The membrane module manufactured by the method of the present invention can be directly or together with other membrane elements, preferably housed in a pressure-resistant container to form a membrane module for the treatment of various liquids. There are no particular limitations on the liquid to be treated; examples include various factory wastewaters containing organic solvents or other organic compounds, seawater, and reclaimed liquids containing dissolved valuable substances.

[0087] Example

[0088] The present invention will be described in more detail below with reference to specific embodiments, but the present invention is not limited to these embodiments.

[0089] [Example 1]

[0090] <Manufacturing of Membrane Elements with Reduced Retention Rate>

[0091] Under conditions of a pressure difference (hereinafter referred to as the differential pressure between the two membrane surfaces) of 0.06 MPa (0.07 MPa on the primary side and 0.01 MPa on the secondary side) and a flow rate of 18 L / min, a sodium hypochlorite aqueous solution with an effective chlorine concentration of 2.0% by mass (with an assumed osmotic pressure of 1.2 MPa) was passed through a TM810V membrane element (trade name, built-in cross-linked fully aromatic polyamide RO membrane, 4 inches in diameter, 99.8% salt rejection rate, manufactured by Toray Industries, Inc.) for 19 minutes to perform a rejection rate adjustment process.

[0092] After the liquid flow begins (19 minutes after the start of liquid flow), the sodium hypochlorite aqueous solution is quickly drained from the membrane element, and then water is replaced while rinsing is performed 3 times (rinsing volume: 20L / time), thus completing the rinsing process.

[0093] The retention rate of the membrane element manufactured in this way was determined by the following method. The results are shown in Table 1.

[0094] <Methods for determining retention rate>

[0095] In Example 1, the apparent retention rate of the element was calculated using the following formula, which takes into account the concentration increase within the element.

[0096]

[0097] In equation (2), Qf[m 3 / s] represents the initial feed flow rate, Wf[weight%] represents the initial salt concentration, and Qr[m 3 / s] represents the final feed flow rate, and Wr[weight%] represents the final salt concentration.

[0098] The initial salt concentration is not the concentration of the added liquid, but the concentration after circulation, including the retained water.

[0099] Regarding the final feed flow rate and final salt concentration, the permeate flow rate and permeate salt concentration are measured and calculated based on the material balance on the feed side and the permeate side.

[0100] [Example 2]

[0101] Under conditions of a differential pressure of 0.06 MPa between the two membrane surfaces (0.07 MPa on the primary side and 0.01 MPa on the secondary side) and a flow rate of 18 L / min, a sodium hypochlorite aqueous solution with an effective chlorine concentration of 5.0% by mass (with an assumed osmotic pressure of 1.2 MPa) was passed through a TM810V membrane element (trade name, built-in cross-linked fully aromatic polyamide RO membrane, 4 inches in diameter, 99.8% salt rejection rate, manufactured by Toray Industries, Inc.) for 19 minutes to perform a rejection rate adjustment process.

[0102] After the liquid flows through, the sodium hypochlorite aqueous solution is quickly discharged from the membrane element, and then the membrane is cleaned three times while being converted to water (cleaning volume: 20L / time), thus completing the cleaning process.

[0103] For the membrane elements thus manufactured, the retention rate was determined in the same manner as in Example 1. The results are shown in Table 1.

[0104] [Example 3]

[0105] Under conditions of a differential pressure of 0.06 MPa between the two membrane surfaces (0.07 MPa on the primary side and 0.01 MPa on the secondary side) and a flow rate of 18 L / min, a sodium hypochlorite aqueous solution with an effective chlorine concentration of 2.3% by mass (with an assumed osmotic pressure of 1.2 MPa) was passed through a TM810V membrane element (trade name, built-in cross-linked fully aromatic polyamide RO membrane, 4 inches in diameter, 99.8% salt rejection rate, manufactured by Toray Industries, Inc.) for 62 minutes to perform a rejection rate adjustment process.

[0106] After the liquid flows through, the sodium hypochlorite aqueous solution is quickly discharged from the membrane element, and then the membrane is cleaned three times while being converted to water (cleaning volume: 20L / time), thus completing the cleaning process.

[0107] For the membrane elements thus manufactured, the retention rate was determined in the same manner as in Example 1. The results are shown in Table 1.

[0108] [Comparative Example 1]

[0109] Under conditions of a differential pressure of 1.99 MPa between the two membrane surfaces (primary side pressure of 2.00 MPa and secondary side pressure of 0.01 MPa) and a flow rate of 10 L / min, a sodium hypochlorite aqueous solution with an effective chlorine concentration of 1.9% by mass (with an assumed osmotic pressure of 1.2 MPa) was passed through a TM810V membrane element (trade name, built-in cross-linked fully aromatic polyamide RO membrane, 4 inches in diameter, 99.8% salt rejection rate, manufactured by Toray Industries, Inc.) for 20 minutes to perform a rejection rate adjustment process.

[0110] After the liquid flows through, the sodium hypochlorite aqueous solution is quickly discharged from the membrane element, and then the membrane is cleaned three times while being converted to water (cleaning volume: 20L / time), thus completing the cleaning process.

[0111] For the membrane elements thus manufactured, the retention rate was determined in the same manner as in Example 1. The results are shown in Table 1.

[0112] [Comparative Example 2]

[0113] Under conditions of a differential pressure of 1.99 MPa between the two membrane surfaces (primary side pressure of 2.00 MPa and secondary side pressure of 0.01 MPa) and a flow rate of 10 L / min, a sodium hypochlorite aqueous solution with an effective chlorine concentration of 1.9% by mass (with an assumed osmotic pressure of 1.2 MPa) was passed through a TM810V membrane element (trade name, built-in cross-linked fully aromatic polyamide RO membrane, 4 inches in diameter, 99.8% salt rejection rate, manufactured by Toray Industries, Inc.) for 50 minutes to perform a rejection rate adjustment process.

[0114] After the liquid flows through, the sodium hypochlorite aqueous solution is quickly discharged from the membrane element, and then the membrane is cleaned three times while being converted to water (cleaning volume: 20L / time), thus completing the cleaning process.

[0115] For the membrane elements thus manufactured, the retention rate was determined in the same manner as in Example 1. The results are shown in Table 1.

[0116] [Comparative Example 3]

[0117] Under conditions of a differential pressure of 1.99 MPa between the two membrane surfaces (primary side pressure of 2.00 MPa and secondary side pressure of 0.01 MPa) and a flow rate of 10 L / min, a sodium hypochlorite aqueous solution with an effective chlorine concentration of 1.9% by mass (with an assumed osmotic pressure of 1.2 MPa) was passed through a TM810V membrane element (trade name, built-in cross-linked fully aromatic polyamide RO membrane, 4 inches in diameter, 99.8% salt rejection rate, manufactured by Toray Industries, Inc.) for 73 minutes to perform a rejection rate adjustment process.

[0118] After the liquid flows through, the sodium hypochlorite aqueous solution is quickly discharged from the membrane element, and then the membrane is cleaned three times while being converted to water (cleaning volume: 20L / time), thus completing the cleaning process.

[0119] For the membrane elements thus manufactured, the retention rate was determined in the same manner as in Example 1. The results are shown in Table 1.

[0120] [Refer to Examples 1-6]

[0121] In Examples 1-3 and Comparative Examples 1-3, a flat sheet membrane removed from the membrane element was used instead of the membrane element, and the flat sheet membrane was immersed in the chemical reagent solution for the same time as the liquid flow time. Otherwise, the rejection rate adjustment process was performed in the same manner as in the Examples and Comparative Examples. After the rejection rate adjustment process, the flat sheet membrane removed from the chemical reagent solution was immersed in 1L of water for washing, and this process was repeated three times. Otherwise, the washing process was performed in the same manner as in Examples 1-3 and Comparative Examples 1-3, thereby treating the flat sheet membrane. The rejection rate of the obtained flat sheet membrane was measured in the same manner as in Example 1.

[0122] The results of each reference example are expressed as "sheet membrane rejection rate" in the column of the embodiment or comparative example where the conditions of the rejection rate adjustment process are the same.

[0123] Table 1 shows the conditions of the retention rate adjustment process in each embodiment and comparative example, along with the measured retention rates. It should be noted that "concentration" in Table 1 refers to the concentration of the sodium hypochlorite aqueous solution (available chlorine concentration), and "liquid contact time" refers to the liquid flow time of the sodium hypochlorite aqueous solution (embodiments and comparative examples) or the immersion time in the sodium hypochlorite aqueous solution (reference example).

[0124] [Table 1]

[0125] Figure 2 To plot (concentration × liquid contact time, retention rate) as (X, Y) in an orthogonal coordinate system for "concentration × liquid contact time" and "retention rate" in Table 1, a graph showing the relationship between concentration × liquid contact time and retention rate is generated.

[0126] It should be noted that, Figure 2 The approximate line shown by the dashed line represents the relationship between the concentration, the product of the liquid contact time, and the retention rate in the reference example.

[0127] Each retention rate adjustment process in Examples 1 to 3 and Figure 2The preparation is equivalent to sub-step 1 in the preferred embodiment of the manufacturing method of the present invention, which is the method for determining the liquid contact time to achieve the target retention rate as described above. The approximate line representing the relationship between the product of concentration and liquid contact time and the retention rate in Examples 1 to 3 is Y≈-0.004X+0.9(R). 2 =0.9998).

[0128] According to Table 1 and Figure 2 The results show the following.

[0129] First, when using a flat membrane, 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 exists between the concentration of the chemical reagent solution (sodium hypochlorite aqueous solution) × liquid contact time (immersion time) and the rejection rate.

[0130] In contrast, in Comparative Examples 1 to 3, where the differential pressure was set to a pressure above the (ideal) osmotic pressure of the chemical reagent solution (sodium hypochlorite aqueous solution) when the chemical reagent solution (sodium hypochlorite aqueous solution) was passed through the membrane element, the rejection rate of the RO membrane could be reduced. However, in Comparative Example 3, where the liquid contact time was extended, the rejection rate decreased sharply and significantly compared to Comparative Example 2, and the linear relationship between concentration × liquid contact time and rejection rate did not hold. Therefore, it can be seen that when the chemical reagent solution is passed through the membrane element as the object of treatment at a pressure difference above the osmotic pressure, for example, when the concentration × liquid contact time is greater than 95 (mass %·min), it is particularly impossible to adjust the rejection rate of the membrane element to a specified value based on the concentration × liquid contact time, that is, it is impossible to manufacture a membrane element exhibiting a specified rejection rate based on the concentration × liquid contact time.

[0131] On the other hand, in Examples 1 to 3, where the differential pressure is set to be less than the (conceived) osmotic pressure of the chemical reagent solution when it flows through the membrane element, the rejection rate of the RO membrane can be reduced. Furthermore, even for membrane elements that are difficult to process uniformly compared to flat sheet membranes, the linear relationship shown by the aforementioned approximate line between concentration × liquid contact time and rejection rate holds true. Therefore, it can be seen that by performing a rejection rate adjustment process using a concentration and / or liquid contact time set based on concentration × liquid contact time, the rejection rate of the membrane element can be adjusted to a predetermined value, i.e., a membrane element exhibiting a predetermined rejection rate can be manufactured.

[0132] The invention has been described together with its embodiments, but we believe that, unless otherwise stated, any details described are not intended to limit the invention and should be interpreted broadly without departing from the spirit and scope of the invention as shown in the appended claims.

[0133] This application claims priority based on Japanese Patent Application No. 2024-054170 filed on March 28, 2024, the contents of which are incorporated herein by reference as part of the description herein.

[0134] Label Explanation

[0135] 1 System

[0136] 2. Membrane element

[0137] 3 Chemical reagent solution container

[0138] 3A Pump

[0139] 4. Clean the water tank

[0140] 4A pump

[0141] 5-9 Conveying Path

[0142] Pumps P1 and P2

Claims

1. A method for manufacturing a membrane element, comprising a rejection rate adjustment step of passing a chemical reagent solution through a primary side flow path of the membrane element to adjust the rejection rate, wherein, In the retention rate adjustment process, when the chemical reagent solution is passed through, the pressure difference applied to the two membrane surfaces of the membrane element is set to be less than the osmotic pressure of the chemical reagent solution.

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

4. The method for manufacturing a membrane element according to claim 3, wherein, The effective chlorine concentration of hypochlorite is 2% to 10% by mass.

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