Desalination performance recovery agent for polyamide film, method for recovering desalination performance of polyamide film, and method for improving desalination performance of polyamide film

Abstract

This desalination performance recovery agent for a polyamide film contains a solvent and any one of polyvinylpyrrolidone, pyrogallol, or polyvinyl alcohol mixed in a solvent. A desalination performance recovery agent in which polyvinylpyrrolidone is mixed in the solvent has a pH of 10 or less. A desalination performance recovery agent in which pyrogallol is mixed in the solvent has a pH of 6 or less. A desalination performance recovery agent in which polyvinyl alcohol is mixed in the solvent has a pH of 9 or less.

Description

Agent for restoring desalination performance of polyamide membrane, method for restoring desalination performance of polyamide membrane, and method for improving desalination performance of polyamide membrane

[0001] This disclosure relates to a desalination performance recovery agent for a polyamide membrane, a method for recovering the desalination performance of a polyamide membrane, and a method for improving the desalination performance of a polyamide membrane.This application claims priority based on Japanese Patent Application No. 2024-133300, filed with the Japan Patent Office on August 8, 2024, the contents of which are incorporated herein by reference.

[0002] Reverse osmosis membranes used for producing fresh water, such as by desalination of seawater, include those made of polyamide membranes and those made of cellulose acetate membranes. The degradation of desalination performance of reverse osmosis membranes inevitably occurs over time, resulting in the cost of periodic membrane replacement and disposal. To reduce these costs, desalination performance recovery agents have been developed that are brought into contact with reverse osmosis membranes to restore their desalination performance. The present applicant has disclosed an invention relating to a desalination performance recovery agent for cellulose acetate membranes in Patent Document 1.

[0003] Patent No. 7177452

[0004] Although there are already some desalination performance recovery agents for polyamide membranes that have been developed, there is a need for a desalination performance recovery agent that can further improve the recovery effect of polyamide membranes with simpler operations.

[0005] In view of the above circumstances, at least one embodiment of the present disclosure aims to provide a desalination performance recovery agent for a polyamide membrane, which has an improved effect of recovering the desalination performance of a polyamide membrane, a method for recovering the desalination performance of a polyamide membrane, and a method for improving the desalination performance of a polyamide membrane.

[0006] In order to achieve the above object, the desalination performance recovery agent for a polyamide membrane according to the present disclosure is a desalination performance recovery agent for a polyamide membrane comprising a solvent and any one of polyvinylpyrrolidone, pyrogallol, or polyvinyl alcohol mixed in the solvent, wherein the pH of the desalination performance recovery agent in which polyvinylpyrrolidone is mixed in the solvent is 10 or less, the pH of the desalination performance recovery agent in which pyrogallol is mixed in the solvent is 6 or less, and the pH of the desalination performance recovery agent in which polyvinyl alcohol is mixed in the solvent is 9 or less.

[0007] According to the desalination performance recovery agent for a polyamide membrane of the present disclosure, when the desalination performance recovery agent is brought into contact with a polyamide membrane, the desalination performance of the polyamide membrane can be recovered.

[0008] Fig. 1 is a schematic diagram of a recovery device for performing a method for recovering the desalination performance of a polyamide membrane according to the present disclosure. Fig. 2 is a flowchart showing the procedure of an experiment for verifying the effect of a desalination performance recovery agent for a polyamide membrane according to the present disclosure. Fig. 3 is a schematic diagram of an experimental device for performing an experiment for verifying the effect of a desalination performance recovery agent for a polyamide membrane according to the present disclosure. Fig. 4 is a graph showing the relationship between pH and salt permeation reduction rate SPR obtained from an experiment for verifying the effect of a desalination performance recovery agent for a polyamide membrane according to the present disclosure.

[0009] Hereinafter, desalination performance recovery agents for polyamide membranes according to embodiments of the present disclosure will be described with reference to the drawings. The embodiments described below represent one aspect of the present disclosure, but are not intended to limit the present disclosure and can be modified as desired within the scope of the technical concept of the present disclosure.

[0010] <Desalination Performance Recovery Agent for Polyamide Membranes of the Present Disclosure> Reverse osmosis membranes used in desalination plants, such as those used in seawater desalination plants, deteriorate over time, i.e., their desalination performance declines over time. Therefore, a desalination performance recovery agent is used to restore the degraded reverse osmosis membrane's desalination performance. This recovery is carried out by contacting the reverse osmosis membrane with a desalination performance recovery agent. The inventors of the present disclosure developed a desalination performance recovery agent to be used in the recovery of the desalination performance of polyamide membranes used as reverse osmosis membranes, and confirmed its effectiveness in restoring the desalination performance of polyamide membranes in the examples described below.

[0011] The desalination performance recovery agent for polyamide membranes of the present disclosure contains a solvent and either polyvinylpyrrolidone, pyrogallol, or polyvinyl alcohol mixed in the solvent. Examples of solvents that can be used include water, alcohol-based solvents, ketone-based solvents such as acetone, and water-soluble glycol-based solvents such as propylene glycol and glycerin. The pH of the desalination performance recovery agent containing polyvinylpyrrolidone mixed in the solvent is 10 or less, and in this case, the pH is preferably 3 or less. The pH of the desalination performance recovery agent containing pyrogallol mixed in the solvent is 6 or less, and in this case, the pH is preferably 3 or less. The pH of the desalination performance recovery agent containing polyvinyl alcohol mixed in the solvent is 9 or less, and in this case, the pH is preferably 2 or less.

[0012] <Method for restoring desalination performance of polyamide membrane according to the present disclosure> The method for restoring desalination performance of a polyamide membrane according to the present disclosure is carried out using, for example, a cleaning apparatus 1 for a reverse osmosis membrane shown in FIG. 1 . The cleaning apparatus 1 includes a tank 4, a pump 6, a filter 8, and a circulation line 10. The desalination performance recovery agent stored in the tank 4 is pressurized by the pump 6 to circulate through the circulation line 10, and after solid matter is removed by the filter 8, is supplied to the polyamide membrane 12. The desalination performance recovery agent passes through the polyamide membrane 12 while contacting the entire polyamide membrane 12. After passing through the polyamide membrane 12, the desalination performance recovery agent is returned to the tank 4. The desalination performance recovery agent returned to the tank 4 is pressurized again by the pump 6 and supplied to the polyamide membrane 12. In this way, the method for restoring desalination performance of a polyamide membrane according to the present disclosure includes a step of contacting the desalination performance recovery agent with the polyamide membrane 12.

[0013] The above-described operation is performed, for example, by stopping the supply of seawater to a polyamide membrane 12 used for desalination (water production) of seawater (water to be treated), and then installing the polyamide membrane 12 in the cleaning device 1, or by permanently or temporarily connecting the cleaning device 1 to the polyamide membrane 12. This configuration is not limited to this, and the desalination performance recovery agent may be added to seawater while desalination is being performed in a seawater desalination device (not shown) to bring the desalination performance recovery agent into contact with the polyamide membrane 12. However, when performing the operation of restoring desalination performance while desalination is being performed, a large amount of the desalination performance recovery agent must be supplied to bring the desalination performance recovery agent into contact with the polyamide membrane 12 at an appropriate pH range. However, the latter configuration is preferred because the amount of desalination performance recovery agent supplied can be reduced by using the above-described cleaning device 1 to bring the desalination performance recovery agent into contact with the polyamide membrane 12 after stopping the supply of seawater to the polyamide membrane 12.

[0014] In a water production plant equipped with a polyamide membrane (e.g., a seawater desalination plant), after removing impurities such as solids from the water to be treated using a pretreatment device, the water is pressurized using a high-pressure pump and brought into contact with the polyamide membrane, separating it into water that permeates the polyamide membrane and concentrated water that does not. During this process, clogging can occur due to the adhesion of inorganic substances such as compounds of sodium, calcium, magnesium, iron, manganese, etc., or organic substances such as scale containing microorganisms and their metabolic products contained in the water. The above-mentioned restoration of desalination performance is more effectively restored if it is performed after a cleaning operation to remove such adhered substances from the membrane surface, rather than if it is performed while such adhered substances remain on the membrane surface.

[0015] For example, if the deposits are inorganic, acid cleaning (e.g., citric acid cleaning) is performed, and if the deposits are organic, alkaline cleaning (e.g., sodium hydroxide cleaning) is performed. For cleaning polyamide membranes, two-step cleaning, which involves alkaline cleaning followed by acid cleaning, is recommended by membrane manufacturers and is commonly used.

[0016] As described above, the preferred pH range of the polyamide membrane desalination performance recovery agent of the present disclosure is 3 or less or 2 or less, and therefore the pH conditions are equivalent to those of acid washing in the cleaning operation of polyamide membranes. Therefore, by adjusting the pH of the polyamide membrane desalination performance recovery agent of the present disclosure to, for example, the preferred pH range described above, it can be used in combination with acid washing in the cleaning operation of polyamide membranes. That is, after alkaline cleaning of a polyamide membrane, the desalination performance recovery agent can be mixed with the cleaning solution before or after acid washing and brought into contact with the polyamide membrane, thereby allowing the acid washing solution to be used as is or simultaneously with the acid washing to restore desalination performance.

[0017] <Method for Improving the Desalination Performance of a Polyamide Membrane According to the Present Disclosure> The desalination performance recovery agent according to the present disclosure is intended for polyamide membranes with reduced desalination performance, but if it is applied to polyamide membranes whose desalination performance has not been reduced (for example, new, unused membranes), it is possible to improve the desalination performance. For example, by producing a polyamide membrane with higher water production and lower desalination performance than conventional membranes and treating it with the desalination performance recovery agent according to the present disclosure, it is possible to achieve higher water production than conventional membranes and desalination performance equivalent to conventional membranes.

[0018] The inventors of the present disclosure confirmed the effects of the above-mentioned desalination performance recovery agent for polyamide membranes through the experiment described below. The procedure of this experiment will be explained with reference to the flowchart in Figure 2. The polyamide membrane to be tested was evaluated for membrane performance (Step S1), and then the polyamide membrane was subjected to a degradation treatment (Step S2). Next, the performance of the degraded polyamide membrane was evaluated (Step S3), and then the desalination performance recovery treatment of the degraded polyamide membrane was performed (Step S4). Finally, the performance of the polyamide membrane that had been subjected to the desalination performance recovery treatment was evaluated (Step S5).

[0019] The configuration of the experimental apparatus used to conduct this experiment is shown in Figure 3. The experimental apparatus 20 includes a cell 22 in which a polyamide membrane 21 is installed, a tank 23 for storing a solution to be supplied to the cell 22, a pipe 24 connecting the cell 22 and the tank 23, a pump 25 attached to the pipe 24, a pipe 26 through which the liquid that has permeated the polyamide membrane 21 flows out of the cell 22, and a pipe 27 through which the solution that has not permeated the polyamide membrane 21 flows out of the cell 22. A reverse osmosis membrane element TMG20-400 available from Toray Industries, Inc. was used as the polyamide membrane 21.

[0020] In steps S1, S3, and S5 of the experimental procedure, a 2000 ppm aqueous sodium chloride solution was injected into the tank 23, and then the pump 25 was started. The aqueous sodium chloride solution was supplied to the cell 22 under conditions of a supply pressure of 1 MPa, a supply flow rate of 3.2 L / min, and a supply temperature of 30°C. The flow rate and sodium chloride concentration of the aqueous sodium chloride solution flowing out of the pipe 26 were measured. From the results of the membrane performance evaluation (steps S3 and S5) performed before and after the desalination performance recovery treatment (step S4), the salt permeation reduction rate SPR due to the desalination performance recovery treatment was calculated. The flow rate and concentration obtained in step S3 were used as Q ｐ，ｂ and C ｐ，ｂ and the flow rate and the concentration obtained in step S5 are Q ｐ，ａ and C ｐ，ａ The salt permeation reduction rate SPR was calculated by the following formula (1).

[0021]

[0022] In step S2 of the experimental procedure, 18 kg of a 1000 ppm aqueous sodium hypochlorite solution (pH 10) was poured into tank 23, and then pump 25 was started. The aqueous sodium hypochlorite solution was supplied to cell 22 over 30 hours at a supply temperature of 30°C, and the aqueous sodium hypochlorite solution was brought into contact with polyamide membrane 21, thereby deteriorating polyamide membrane 21.

[0023] In step S4 of the experimental procedure, 18 kg of 12 aqueous solutions (deionization performance recovery agents) were prepared by mixing polyvinylpyrrolidone, pyrogallol, and polyvinyl alcohol in water at a concentration of 100 ppm each, and adjusting the pH to 2, 4, 9, or 12 by adding hydrochloric acid or sodium hydroxide as needed. The degree of polymerization of the polyvinylpyrrolidone used was 50 to 27,000 (molecular weight: 5,000 to 3,000,000), and the degree of polymerization of the polyvinyl alcohol used was 100 to 4,000 and the degree of acetylation was 1 to 35%. After each deionization performance recovery agent was injected into tank 23, pump 25 was started and the deionization performance recovery agent was supplied to cell 22 over 6 hours at a supply temperature of 30°C. The deionization performance recovery agent was then brought into contact with polyamide membrane 21, thereby performing a deionization performance recovery treatment of polyamide membrane 21.

[0024] Twelve experiments, including step S4, were conducted using each of the 12 desalination performance recovery agents, and the salt permeation reduction rate (SPR) due to the desalination performance recovery treatment was calculated from each experiment. The relationship between pH and the salt permeation reduction rate (SPR) for each desalination performance recovery agent is shown in Figure 4. From the perspective of customer satisfaction with desalination performance recovery agents for polyamide membranes, the salt permeation reduction rate (SPR) is preferably 40% or higher, and more preferably 60% or higher. Based on this standard, it can be said that the pH of a desalination performance recovery agent containing polyvinylpyrrolidone as a solvent is preferably 10 or lower, the pH of a desalination performance recovery agent containing pyrogallol as a solvent is preferably 6 or lower, and the pH of a desalination performance recovery agent containing polyvinyl alcohol as a solvent is preferably 9 or lower. It can be said that the pH of a desalination performance recovery agent in which polyvinylpyrrolidone is mixed in the solvent is more preferably 3 or less, the pH of a desalination performance recovery agent in which pyrogallol is mixed in the solvent is more preferably 3 or less, and the pH of a desalination performance recovery agent in which polyvinyl alcohol is mixed in the solvent is more preferably 2 or less.

[0025] The contents described in each of the above embodiments can be understood, for example, as follows.

[0026] [1] A desalination performance recovery agent for a polyamide membrane according to one embodiment comprises a solvent and any one of polyvinylpyrrolidone, pyrogallol, or polyvinyl alcohol mixed in the solvent, wherein the pH of the desalination performance recovery agent in which polyvinylpyrrolidone is mixed in the solvent is 10 or less, the pH of the desalination performance recovery agent in which pyrogallol is mixed in the solvent is 6 or less, and the pH of the desalination performance recovery agent in which polyvinyl alcohol is mixed in the solvent is 9 or less.

[0027] According to the desalination performance recovery agent for a polyamide membrane of the present disclosure, when the desalination performance recovery agent is brought into contact with a polyamide membrane, the desalination performance of the polyamide membrane can be recovered.

[0028] [2] A desalination performance recovery agent for a polyamide membrane according to another embodiment is the desalination performance recovery agent for a polyamide membrane according to [1], wherein the pH of the desalination performance recovery agent in which polyvinylpyrrolidone is mixed in the solvent is 3 or less, the pH of the desalination performance recovery agent in which pyrogallol is mixed in the solvent is 3 or less, and the pH of the desalination performance recovery agent in which polyvinyl alcohol is mixed in the solvent is 2 or less.

[0029] According to this configuration, when the desalination performance recovery agent is brought into contact with the polyamide membrane, the desalination performance of the polyamide membrane can be recovered.

[0030] [3] A method for restoring the desalination performance of a polyamide membrane according to one embodiment includes a step of contacting the polyamide membrane with the agent for restoring desalination performance for polyamide membranes according to [1] or [2].

[0031] According to the method for restoring the desalination performance of a polyamide membrane of the present disclosure, the desalination performance of a polyamide membrane can be restored.

[0032] [4] A method for recovering the desalination performance of a polyamide membrane according to another embodiment is the method for recovering the desalination performance of a polyamide membrane according to [3], in which the step is carried out after stopping the supply of seawater to the polyamide membrane.

[0033] When the desalination performance recovery agent is brought into contact with the polyamide membrane during desalination, a large amount of the agent must be supplied to bring the desalination performance recovery agent into contact with the polyamide membrane within an appropriate pH range. However, the amount of the agent to be supplied can be reduced by bringing the desalination performance recovery agent into contact with the polyamide membrane using a cleaning device or the like after stopping the supply of seawater to the polyamide membrane.

[0034] [5] A method for improving the desalination performance of a polyamide membrane according to one embodiment includes the step of contacting a unused polyamide membrane with the desalination performance recovery agent for polyamide membranes according to [1] or [2].

[0035] According to the method for improving the desalination performance of a polyamide membrane disclosed herein, by applying the method to a polyamide membrane whose desalination performance has not deteriorated (for example, a new, unused membrane), it is possible to improve the desalination performance.

[0036] REFERENCE SIGNS LIST 1 recovery device 4 tank 6 pump 8 filter 10 circulation line 12 polyamide membrane 20 experimental device 21 polyamide membrane 22 cell 23 tank 24 piping 25 pump 26 piping 27 piping

Claims

1. A desalination performance recovery agent for a polyamide membrane, comprising a solvent and any one of polyvinylpyrrolidone, pyrogallol, or polyvinyl alcohol mixed in the solvent, wherein the pH of the desalination performance recovery agent in which polyvinylpyrrolidone is mixed in the solvent is 10 or less, the pH of the desalination performance recovery agent in which pyrogallol is mixed in the solvent is 6 or less, and the pH of the desalination performance recovery agent in which polyvinyl alcohol is mixed in the solvent is 9 or less.

2. The desalination performance recovery agent for polyamide membranes described in claim 1, wherein the pH of the desalination performance recovery agent in which polyvinylpyrrolidone is mixed in the solvent is 3 or less, the pH of the desalination performance recovery agent in which pyrogallol is mixed in the solvent is 3 or less, and the pH of the desalination performance recovery agent in which polyvinyl alcohol is mixed in the solvent is 2 or less.

3. A method for restoring the desalination performance of a polyamide membrane, comprising the step of contacting the polyamide membrane with the agent for restoring desalination performance for a polyamide membrane according to claim 1 or 2.

4. The method for recovering the desalination performance of a polyamide membrane according to claim 3, wherein the step is carried out after the supply of water to be treated to the polyamide membrane is stopped.

5. A method for improving the desalination performance of a polyamide membrane, comprising the step of contacting the desalination performance recovery agent for a polyamide membrane according to claim 1 or 2 with an unused polyamide membrane.

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