Agent for recovering salt rejection performance of polyamide membrane, method for recovering salt rejection performance of polyamide membrane, and method for improving salt rejection performance of polyamide membrane

Abstract

To provide a desalination performance recovery agent for a polyamide membrane for recovering desalination performance of the polyamide membrane, a desalination performance recovery method of the polyamide membrane, and a desalination performance improvement method of the polyamide membrane.SOLUTION: The desalination performance-recovering agent for a polyamide membrane contains a solvent and any one of polyvinylpyrrolidone, pyrogallol, and polyvinyl alcohol mixed in the solvent, wherein the desalination performance-recovering agent in which polyvinylpyrrolidone is mixed in the solvent has a pH of 10 or less, the desalination performance-recovering agent in which pyrogallol is mixed in the solvent has a pH of 6 or less, and the desalination performance-recovering agent in which polyvinyl alcohol is mixed in the solvent has a pH of 9 or less.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present 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. [Background technology]

[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 desalination performance of reverse osmosis membranes inevitably declines 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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7177452 Summary of the Invention [Problem to be solved by the invention]

[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. [Means for solving the problem]

[0006] In order to achieve the above object, the desalination performance recovery agent for a polyamide membrane according to the present disclosure 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. [Effects of the Invention]

[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. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram illustrating the configuration of a recovery device that performs the method for recovering the desalination performance of a polyamide membrane according to the present disclosure. [Figure 2] 1 is a flowchart showing the procedure of an experiment for verifying the effect of a polyamide membrane desalination performance recovery agent according to the present disclosure. [Figure 3] FIG. 1 is a schematic diagram illustrating the configuration of an experimental device for conducting an experiment to verify the effect of a polyamide membrane desalination performance recovery agent according to the present disclosure. [Figure 4] 1 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 of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[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 membrane according to the present disclosure> Reverse osmosis membranes used in desalination plants, such as those used for seawater desalination, deteriorate over time, i.e., their desalination performance declines over time. Therefore, they are used to restore the desalination performance of deteriorated reverse osmosis membranes. This restoration is carried out by contacting the reverse osmosis membrane with a desalination performance restoration agent. The inventors of the present disclosure developed a desalination performance restoration agent for use in the restoration 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 the 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. Thus, the method for restoring the 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 water production plants equipped with polyamide membranes (e.g., seawater desalination plants), after removing solids and other impurities 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 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, and manganese, or organic substances, such as scale containing microorganisms and their metabolic products present in the water. The restoration of desalination performance described above is more effectively achieved by performing a cleaning operation to remove such adhered substances from the membrane surface, rather than performing the operation 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, membrane manufacturers recommend a two-step cleaning method, in which alkaline cleaning is followed by acid cleaning, and this is also commonly used.

[0016] As described above, the preferred pH range of the desalination performance recovery agent for polyamide membranes 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 desalination performance recovery agent for polyamide membranes 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 work of restoring desalination performance to be carried out using the acid washing solution as is or simultaneously with acid washing.

[0017] <Method for improving desalination performance of polyamide membrane according to the present disclosure> The desalination performance recovery agent of the present disclosure is intended for polyamide membranes with reduced desalination performance, but if it is applied to polyamide membranes with unreduced desalination performance (for example, new, unused membranes), it is possible to improve desalination performance. For example, by manufacturing a polyamide membrane with higher water production and lower desalination performance than conventional membranes and treating it with the desalination performance recovery agent of the present disclosure, it is possible to achieve higher water production than conventional membranes and desalination performance equivalent to conventional membranes. [Example]

[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 equipment used to conduct this experiment is shown in Figure 3. The experimental equipment 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 sodium chloride aqueous solution was injected into the tank 23, and then the pump 25 was started. The sodium chloride aqueous 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 sodium chloride aqueous solution flowing out from 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 using the following formula (1).

[0021]

number

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

[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. Figure 4 shows the relationship between pH and the salt permeation reduction rate (SPR) for each desalination performance recovery agent. Based on customer satisfaction with desalination performance recovery agents for polyamide membranes, a salt permeation reduction rate (SPR) of 40% or higher is preferred, with 60% or higher being even more preferred. 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 of the present invention comprises: A solvent; Any of polyvinylpyrrolidone, pyrogallol, and polyvinyl alcohol mixed in the solvent A desalination performance recovery agent for a polyamide membrane, comprising: The pH of the desalination performance recovery agent in which polyvinylpyrrolidone is mixed with the solvent is 10 or less, the pH of the desalination performance recovery agent in which pyrogallol is mixed with the solvent is 6 or less, and the pH of the desalination performance recovery agent in which polyvinyl alcohol is mixed with 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], The pH of the desalination performance recovery agent in which polyvinylpyrrolidone is mixed with the solvent is 3 or less, the pH of the desalination performance recovery agent in which pyrogallol is mixed with the solvent is 3 or less, and the pH of the desalination performance recovery agent in which polyvinyl alcohol is mixed with 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 recovering the desalination performance of a polyamide membrane according to one embodiment includes: The method includes a step of contacting the polyamide membrane with the desalination performance recovery agent 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 restoring the desalination performance of a polyamide membrane according to another embodiment is the method for restoring the desalination performance of a polyamide membrane according to [3], The step is carried out after the supply of seawater to the polyamide membrane is stopped.

[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 agent into contact with the polyamide membrane within an appropriate pH range. However, the amount of the agent supplied can be reduced by bringing the 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 method includes a step of contacting the desalination performance recovery agent for polyamide membranes according to [1] or [2] with a unused polyamide membrane.

[0035] According to the method for improving the desalination performance of a polyamide membrane of the present disclosure, 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. [Explanation of symbols]

[0036] 1 Recovery Device 4 Tank 6. Pump 8 Filters 10 Circulation Line 12 Polyamide membrane 20 Experimental Equipment 21 Polyamide membrane 22 cells 23 Tank 24 Piping 25 Pump 26 Piping 27 Piping

Claims

1. A solvent; Any of polyvinylpyrrolidone, pyrogallol, and polyvinyl alcohol mixed in the solvent A desalination performance recovery agent for a polyamide membrane, comprising: The desalination performance recovery agent for a polyamide membrane, 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. 2. The desalination performance recovery agent for a polyamide membrane according to 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 the 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 bringing the agent for recovering desalination performance for a polyamide membrane according to claim 1 or 2 into contact with an unused polyamide membrane.

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