Preparation method and system of reverse osmosis membrane element

Abstract

The invention discloses a reverse osmosis membrane element preparation method and system, and the method comprises the following steps: 1) washing a membrane element in a membrane shell, and removing a chemical agent or a residual solvent on the surface of the membrane element; (2) enabling the grafting solution to be in full contact with the membrane element so as to graft the flushed membrane element; wherein the grafting solution comprises an activating agent and a carboxyl source, the temperature of the grafting solution is 10-40 DEG C, and the grafting time is 0.7-6.0 h; (3) flushing the membrane element with a protective solution after grafting is completed; and (4) carrying out alkali washing, acid washing or acid-alkali alternate washing on the membrane element washed in the step (3). Through the grafting step, the carboxyl content on the surface of the reverse osmosis membrane element is increased, the combining capacity of pollutants and the membrane surface is reduced, and the grafted reverse osmosis membrane has the anti-pollution performance; in addition, by adding an acid washing or alkali washing process, the flux and the rejection rate of the membrane element are basically consistent with those of an ungrafted membrane.

Description

Technical Field

[0001] The present invention relates to the field of membrane separation technology, and in particular to a method and system for preparing a reverse osmosis membrane element. Background Art

[0002] Among the many industrial wastewater treatment technologies, membrane separation technology has received widespread attention and developed rapidly.

[0003] Reverse osmosis membrane separation technology, with its low energy consumption, small footprint, and environmental friendliness, is widely used in seawater desalination, pure water production, and industrial wastewater treatment. However, during use, reverse osmosis membranes are susceptible to membrane fouling, which reduces their flux and retention rate, further shortens their service life, and increases replacement costs. Currently, measures to combat membrane fouling in industrial wastewater treatment typically include pretreatment, adjusting operating parameters, using scale inhibitors, and membrane cleaning. While these methods have some effectiveness in preventing membrane fouling, in most cases, membrane fouling is unavoidable, and membrane elements still require frequent chemical cleaning. Modifying reverse osmosis membranes to enhance their anti-fouling properties is an effective approach to preventing membrane surface contamination. However, much existing research on anti-fouling reverse osmosis membranes remains limited to the membrane sheet stage. Certain modified or grafted formulations are not commercially viable, and processes and systems for producing anti-fouling reverse osmosis membrane elements are lacking.

[0004] CN 112827368 A discloses an anti-pollution reverse osmosis membrane and its preparation method. The membrane comprises a polyamide desalination layer surface modified with a fluorine-containing amine and a guanidine-containing compound. The polyamide desalination layer is first heat-treated, and then the desalination layer of the membrane is modified with the fluorine-containing amine and guanidine-containing compound. Because the modified membrane surface contains guanidine and fluorine, it can kill microorganisms deposited on the membrane surface, reducing the adhesion of pollutants and the subsequent deposition of pollutants. However, the fluorine on the membrane surface easily detaches from the reverse osmosis membrane surface, resulting in a short service life and a shorter duration of anti-pollution.

[0005] CN 114452845 A discloses an anti-pollution reverse osmosis membrane and its preparation method and application, comprising the following steps: first, preparing a polymer aqueous phase solution comprising polyvinyl alcohol, a dialdehyde cross-linking agent, and an inorganic acid; second, preparing an oil phase solution comprising polyacyl chloride, wherein the molar concentration of secondary hydroxyl groups in the polymer aqueous phase solution is greater than the molar concentration of acyl chloride groups in the oil phase solution; and finally, sequentially forming the polymer aqueous phase solution and the oil phase solution on the surface of the reverse osmosis membrane, and subjecting the membrane to heat treatment to form an anti-pollution layer, thereby obtaining the anti-pollution reverse osmosis membrane.

[0006] The above patent requires heat treatment of the reverse osmosis membrane, which increases the complexity and cost of membrane production. Although the reverse osmosis membrane can kill microorganisms to a certain extent, it cannot prevent the formation of pollutants on the membrane surface during the deep desalination process of reverse osmosis; and the research on the above anti-pollution reverse osmosis membrane is only at the membrane stage and cannot be used in industry. Summary of the Invention

[0007] In order to reduce the impact of membrane pollution on the life of reverse osmosis membranes and reduce the operating costs increased by control measures such as pretreatment and membrane cleaning, the present invention provides a reverse osmosis membrane element preparation method and system to accelerate the industrial application of reverse osmosis membrane elements.

[0008] To achieve the above-mentioned object of the invention, the first aspect of the present invention provides a method for preparing a reverse osmosis membrane element, comprising:

[0009] 1) Rinse the membrane elements in the membrane shell to remove chemicals or residual solvents on the surface of the membrane elements;

[0010] 2) fully contacting the grafting solution with the membrane element to graft the flushed membrane element; wherein the grafting solution includes an activator and a carboxyl source, the grafting solution temperature is 10-40° C., and the grafting time is 0.7 h-6.0 h;

[0011] 3) After grafting is completed, rinse the membrane element with protective liquid;

[0012] 4) The membrane element flushed in step 3) is subjected to alkali washing, acid washing or alternating acid and alkali washing.

[0013] Furthermore, the activator is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and the carboxyl source is polyacrylic acid.

[0014] Furthermore, the mass concentration of the 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) is 0.2-3.0%, and the mass concentration of the polyacrylic acid (PAA) is 0.1-3.0%.

[0015] Furthermore, in step 2), making the grafting solution and the membrane element fully contact each other includes: placing the membrane element in the circulating grafting solution.

[0016] Furthermore, the water flow rate of each membrane shell is adjusted to 0.05-1.30m 3 / h.

[0017] Furthermore, the number of membrane elements installed in each membrane shell is ≤6, and the membrane shells are arranged in parallel.

[0018] Furthermore, the protective solution in step 3) includes an organic solvent and a reducing agent; preferably, the organic solvent includes alcohol with a mass concentration of 0.1-1%, and the reducing agent includes sodium sulfite with a mass concentration of 0.05-1.5%.

[0019] Furthermore, the pH value of the alkaline washing is 9-13, the flux of the membrane element is adjusted to 20-48 lmh during the alkaline washing process, and the cleaning time is 0.5-6.5h.

[0020] Furthermore, the pH value of the acid washing is 1-4, the flux of the membrane element is adjusted to 20-50 lmh during the acid washing process, and the cleaning time is 0.5-6.5h.

[0021] Furthermore, the grafting solution temperature is 24-33°C, the grafting time is 1.5h-3.0h, the mass concentration of EDC is 0.3-2.0%, the mass concentration of PAA is 0.4-1.5%, and the water flow rate of each membrane shell is 0.1-1.0m 3 / h, the number of membrane elements is 4-16.

[0022] A second aspect of the present invention provides a reverse osmosis membrane element preparation system, comprising:

[0023] The membrane shell assembly comprises at least one membrane shell, wherein the membrane shell contains at least one membrane element.

[0024] Flushing liquid tank, used to provide flushing liquid to the inside of the membrane housing,

[0025] Grafting solution tank, used to provide grafting solution to the inside of the membrane shell,

[0026] Protective liquid tank, used to provide protective liquid to the inside of the membrane shell;

[0027] Cleaning liquid tank, used to provide acid or alkali solution to the inside of the membrane shell;

[0028] The liquid conveying device is connected between the flushing liquid tank and the membrane shell to convey the flushing liquid into the membrane shell; or connected between the grafting solution tank and the membrane shell to convey the grafting solution into the membrane shell; or connected between the protective liquid tank and the membrane shell to convey the protective liquid into the membrane shell; or connected between the cleaning liquid tank and the membrane shell to convey the acid or alkali solution into the membrane shell.

[0029] Furthermore, it also includes a filter, which is connected between the flushing liquid tank and the liquid conveying device to filter the flushing liquid; or connected between the grafting solution tank and the liquid conveying device to filter the grafting solution; or connected between the protective liquid tank and the membrane shell to filter the protective liquid; or connected between the cleaning liquid tank and the liquid conveying device to filter the acid or alkali solution.

[0030] Furthermore, it also includes a high-pressure pump connected between the cleaning liquid tank and the membrane shell, which is used to transport alkaline solution or acid solution into the interior of the membrane shell at high pressure.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] The present invention grafts reverse osmosis membrane elements to increase the carboxyl content on the membrane element surface and reduce the binding ability of pollutants to the membrane surface, so that the grafted reverse osmosis membrane element has strong anti-pollution performance and can be directly used in industry.

[0033] Since grafting carboxyl groups will reduce the flux of the base membrane element, the present invention adds alkaline washing and acid washing processes to make the flux and retention rate of the membrane element consistent with those of the ungrafted base membrane. In addition, the water used in the acid washing and alkaline washing in the present invention can be recycled, saving the preparation cost of the anti-pollution membrane element.

[0034] The process of the present invention is simple, occupies a small area, has low energy consumption, and the minimum preparation cost of the reverse osmosis membrane element is 44.6 yuan per element.

[0035] Other features and advantages of the present invention will be described in detail through the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0037] Figure 1 This is a process flow chart of a reverse osmosis membrane element preparation system.

[0038] The markings are as follows: flushing liquid tank 1, grafting solution tank 2, protection liquid tank 3, cleaning liquid tank 4, membrane shell group 5, liquid conveying device 6, filter 7, high-pressure pump 8. DETAILED DESCRIPTION

[0039] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0040] In the description of the present invention, it should be noted that the terms "center," "up," "down," "left," "right," "vertical," "horizontal," "inside," and "outside" and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of the present invention and simplify the description. They are not intended to indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The terms "first position" and "second position" refer to two different positions.

[0041] Unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," and "fixed" should be interpreted broadly. For example, they may refer to fixed or removable connections; mechanical or electrical connections; direct or indirect connections through an intermediary; and internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of these terms in the present invention based on specific circumstances.

[0042] Most pollutants have low solubility in water. During reverse osmosis system operation, concentration polarization causes a significant concentration of pollutants on the membrane surface on the concentrate side. When saturation is reached, they deposit on the membrane surface. Some pollutants are difficult to effectively prevent or control through chemical cleaning, significantly reducing the service life of the reverse osmosis membrane.

[0043] In order to reduce the impact of membrane fouling on the life of reverse osmosis membranes, reduce the operating costs increased by control measures such as pretreatment and membrane cleaning, and accelerate the industrial application of anti-fouling reverse osmosis membrane elements, the present invention provides a method for preparing reverse osmosis membrane elements, comprising:

[0044] 1) Rinse the membrane elements in the membrane shell to remove chemicals or residual solvents on the surface of the membrane elements;

[0045] 2) fully contacting the grafting solution with the membrane element to graft the flushed membrane element; wherein the grafting solution includes an activator and a carboxyl source, the grafting solution temperature is 10-40° C., and the grafting time is 0.7 h-6.0 h;

[0046] 3) After grafting is completed, rinse the membrane element with protective liquid;

[0047] 4) The membrane element flushed in step 3) is subjected to alkali washing, acid washing or alternating acid and alkali washing.

[0048] In some examples, the grafting solution temperature is 15°C, 20°C, 25°C, 30°C, 35°C, etc., and the grafting time is 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, etc.;

[0049] In some examples, the activator is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC), which is suitable for use in industrial-grade membrane elements; and the carboxyl source is polyacrylic acid (PAA).

[0050] In some examples, the mass concentration of the 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) is 0.2-3.0%, exemplified by 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, 2.8%, etc.; the mass concentration of the polyacrylic acid (PAA) is 0.1-3.0%, exemplified by 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, 2.8%, etc.; within the above mass concentration range, sufficient carboxyl groups can be grafted onto the surface of the reverse osmosis membrane without increasing the grafting cost due to waste of reagents.

[0051] In some examples, in step 2), allowing the grafting solution to fully contact the membrane element includes placing the membrane element in a circulating grafting solution.

[0052] In some examples, the number of membrane elements installed in each membrane shell is ≤ 6, and the membrane shells are arranged in parallel.

[0053] In some examples, when the number of membrane elements in the membrane shell is ≤3, the arrangement order of the membrane elements does not change during the grafting process; when the number of membrane elements in the membrane shell is >3, the arrangement order of the membrane elements is changed during the grafting process; the present invention can realize the grafting of multiple membrane elements at the same time, and improve the uniformity of the performance of the membrane elements after grafting by adjusting the grafting order of the membrane elements in the membrane shell and controlling the grafting number of membrane elements in a single membrane shell.

[0054] In some examples, changing the arrangement order of the membrane elements includes: swapping the first membrane with the last membrane, swapping the second membrane with the second-to-last membrane, and so on, according to the water inlet direction.

[0055] Preferably, the arrangement order of the membrane elements is changed when the grafting time reaches 1 / 3-2 / 3 of the total grafting time, for example, the order of the membrane elements is changed when the grafting time reaches half of the time.

[0056] Preferably, the water flow rate of each membrane shell is adjusted to 0.01-1.30m 3 / h to increase the grafting amount of carboxyl groups on the reverse osmosis membrane surface. 3 / h, 0.05m 3 / h, 0.08m 3 / h, 0.1m 3 / h, 0.2m 3 / h, 0.3m 3 / h, 0.4m 3 / h, 0.5m 3 / h, 0.6m 3 / h, 0.7m 3 / h, 0.8m 3 / h, 0.9m 3 / h, 1.0m 3 / h, 1.2m 3 / h, etc., to increase the grafting concentration of carboxyl groups on the surface of the reverse osmosis membrane.

[0057] In some examples, the protective solution in step 3) includes 0.1-1% alcohol and 0.05-1.5% sodium sulfite. After the grafting is completed, the protective solution is used to rinse the membrane element to remove the residual grafting solution and protect the grafted carboxyl groups.

[0058] As a preferred example, the grafting solution temperature is 24-33°C, the grafting time is 1.5h-3.0h, the mass concentration of EDC is 0.3-2.0%, the mass concentration of PAA is 0.4-1.5%, and the water flow rate of each membrane shell is 0.1-1.0m 3 / h, and the number of membrane elements is 4-16. The optimization and coordination of the above parameters can maximize the grafting of carboxyl groups on the membrane surface, thus achieving stronger anti-fouling performance.

[0059] In some examples, the pH value of the alkaline washing is 9-13, the flux of the membrane element is adjusted to 20-48 lmh during the alkaline washing process, and the cleaning time is 0.5-6.5 h.

[0060] In some examples, the pH value of the acid wash is 1-4, the flux of the membrane element is adjusted to 20-50 lmh during the acid wash, and the cleaning time is 0.5-6.5 h.

[0061] In the present invention, the flux range of the membrane element can be controlled by adjusting the operating pressure.

[0062] In some examples, the acid-base alternating cleaning time is kept the same as the time of the single alkaline cleaning or the single acid cleaning, that is, the total acid-base alternating cleaning time is 0.5-6.5 hours.

[0063] refer to Figure 1On the other hand, the present invention provides a reverse osmosis membrane element preparation system, comprising:

[0064] The membrane shell group 5 comprises at least one membrane shell, wherein the membrane shell contains at least one membrane element.

[0065] Flushing liquid tank 1, used to provide flushing liquid to the inside of the membrane shell,

[0066] Grafting solution tank 2, used to provide grafting solution to the inside of the membrane shell,

[0067] The protective liquid tank 3 is used to provide protective liquid to the inside of the membrane shell;

[0068] Cleaning liquid tank 4, used to provide acid or alkali solution to the inside of the membrane shell;

[0069] The liquid conveying device 6 is connected between the flushing liquid tank and the membrane shell to convey the flushing liquid into the interior of the membrane shell; or connected between the grafting solution tank and the membrane shell to convey the grafting solution into the interior of the membrane shell; or connected between the protective liquid tank and the membrane shell to convey the protective liquid into the interior of the membrane shell; or connected between the cleaning liquid tank and the membrane shell to convey the acid or alkaline solution into the interior of the membrane shell.

[0070] It is understandable that, in the present invention, before delivering the grafting solution into the interior of the membrane shell, the flushing liquid inside the membrane shell can be drained to avoid affecting the grafting effect.

[0071] Furthermore, it also includes a filter 7, which is connected between the flushing liquid tank and the liquid conveying device to filter the flushing liquid; or connected between the grafting solution tank and the liquid conveying device to filter the grafting solution; or connected between the protective liquid tank and the membrane shell to filter the protective liquid; or connected between the cleaning liquid tank and the liquid conveying device to filter the acid or alkali solution.

[0072] Furthermore, the liquid delivery device circulates the grafting solution into the membrane shell, so that the membrane elements are fully in contact with the circulated grafting solution.

[0073] Furthermore, a high-pressure pump 8 is included, which is connected between the cleaning liquid tank and the membrane shell and is used to transport alkaline solution or acid solution into the interior of the membrane shell at high pressure.

[0074] The following describes in detail the working process of a reverse osmosis membrane element preparation method and system of the present invention through examples.

[0075] Example 1: This example is to graft a single membrane element

[0076] 1. Use flushing liquid tank 1 to flush the membrane shell;

[0077] 2. The flushed membrane elements were tested before grafting. The test conditions were: 2000ppm NaCl, test pressure 1.55MPa, test temperature 25°C, test pH 7.1, and a single membrane element recovery rate of approximately 14%. The test results were: membrane element flux 45.50lmh, test rejection rate 99.77%;

[0078] 3. Drain the flushing water in the membrane shell and prepare 131L of grafting solution with the following mass concentrations: EDC 0.46% and PAA 0.18%);

[0079] 4. The grafting solution is circulated in the membrane shell through the water pump, and the circulation flow rate is 11.3m 3 / h, graft the flushed membrane elements, and adjust the operating parameters of the system: grafting solution temperature 20.5℃, water production 0.09m 3 / h, the grafting time is 3.6h;

[0080] 5. After grafting is completed, rinse the membrane element with a protective solution (0.1% alcohol and 0.3% sodium sulfite) to remove the residual grafting solution and protect the grafted carboxyl groups;

[0081] 6. Prepare sodium hydroxide solution with a pH value of 12 for alkaline washing, start the high-pressure pump, adjust the alkaline washing pressure to make the flux 46 lmh and the alkaline washing time 1.0 h;

[0082] 7. The reverse osmosis membrane elements after alkali washing were tested after grafting. The test conditions were: 2000ppm NaCl, test pressure 1.55MPa, test temperature 25°C, test pH 7.0, and the recovery rate of a single membrane element was approximately 14%. The test results showed that the membrane element flux was 45.21lmh and the test rejection rate was 99.80%.

[0083] 8. A test solution containing silicon pollutants was prepared, and the grafted membrane and the ungrafted membrane were tested under the same operating conditions. The flux decrease rate of the grafted membrane was 16.3%, and the flux decrease rate of the ungrafted membrane was 30.4%. In comparison, the flux decrease rate of the grafted membrane was reduced by 46.4%, and the anti-pollution performance was significantly enhanced.

[0084] The data show that in the embodiment of the present invention, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) is used as an activator and polyacrylic acid (PAA) is used as two chemical reagents to graft the reverse osmosis membrane element and then alkaline wash it. The anti-fouling performance of the grafted membrane is significantly enhanced, while the flux and retention rate are basically the same as before grafting.

[0085] Example 2: This example is to graft four membrane elements

[0086] 1. Use flushing liquid tank 1 to flush the membrane shell;

[0087] 2. The flushed membrane elements were tested before grafting. The test conditions were: 2000ppm NaCl, test pressure 1.55MPa, test temperature 25°C, test pH 7, and the recovery rate of a single membrane element was approximately 15%. The test results are shown in Table 1 below.

[0088] Table 1

[0089] Membrane properties before grafting 1# 2# 3# 4# Retention rate (%) 99.81 99.75 99.79 99.33 Flux (lmh) 45.97 42.61 43.86 47.39

[0090] 3. Drain the flushing water in the membrane shell and prepare 143 L of grafting solution with the following mass concentrations: EDC 0.15% and PAA 1.39%);

[0091] 4. The grafting solution is circulated in the membrane shell through the water pump, and the circulation flow rate is 13.5m 3 / h, graft the flushed membrane elements, and adjust the operating parameters of the system: grafting solution temperature 25℃, water production 0.43m 3 / h, grafting time is 2.5h;

[0092] 5. After grafting is completed, rinse the membrane element with a protective solution (0.2% alcohol and 0.8% sodium sulfite) to remove the residual grafting solution and protect the grafted carboxyl groups;

[0093] 6. Prepare hydrochloric acid solution with a pH value of 2 for pickling, start the high-pressure pump, adjust the pickling pressure to make the flux 45.0 lmh and the pickling time 1.0 h;

[0094] 7. The acid-washed reverse osmosis membrane elements were tested under the following conditions: 2000 ppm NaCl, test pressure 1.55 MPa, test temperature 25°C, test pH 7.0, and a single membrane element recovery rate of approximately 15%. The test results are shown in Table 2 below. As can be seen from Table 2, the flux of the membrane elements after acid washing remained consistent with that before grafting.

[0095] Table 2

[0096] Membrane properties after grafting 1# 2# 3# 4# Retention rate (%) 99.81 99.80 99.79 99.57 Flux (lmh) 45.26 42.33 43.59 47.01

[0097] 8. A test solution containing organic matter was prepared and four grafted membranes and one ungrafted membrane were tested under the same operating conditions. As shown in Table 3 below, the flux reduction rate of the grafted membrane was 15.0-17.0%, and the flux reduction rate of the ungrafted membrane was 34.0%. In comparison, the flux reduction rate of the grafted membrane was reduced by 50.0-55.9%, and the anti-fouling performance was significantly enhanced.

[0098] Table 3

[0099] Anti-pollution performance test after grafting 1# 2# 3# 4# Flux decrease rate (%) 15.0 16.5 15.3 17.0

[0100] Example 3

[0101] Similar to Example 2, except that: after 1.2 hours of grafting, the first membrane element and the fourth membrane element in the water inlet direction of the membrane shell were swapped, and the second membrane element and the third membrane element were swapped, and then grafting was carried out again for 1.2 hours under the same operating conditions.

[0102] A test solution containing organic matter was prepared, and four grafted membranes and one ungrafted membrane were tested under the same operating conditions. As shown in Table 4 below, the flux decrease rate of the grafted membrane was 15.1-15.5%, and the flux decrease rate of the ungrafted membrane was 34%. In comparison, the flux decrease rate of the grafted membrane was reduced by 54.4-55.6%, and the anti-fouling performance was significantly enhanced. In addition, the flux decrease rate of the grafted membrane was less volatile than that of Example 2.

[0103] Table 4

[0104] Anti-pollution performance test after grafting 1# 2# 3# 4# Flux decrease rate (%) 15.2 15.5 15.1 15.3

[0105] From the above data, it can be seen that when the order of grafting membranes is changed, the performance of the grafted membranes is more uniform.

[0106] Comparative Example 1: In this comparative example, four membrane modules were grafted without alkali washing.

[0107] 1. Use flushing liquid tank 1 to flush the membrane shell;

[0108] 2. The flushed membrane elements were tested before grafting. The test conditions were: 2000ppm NaCl, test pressure 1.55MPa, test temperature 25°C, test pH 7, and a single membrane element recovery rate of approximately 15%. The test results are shown in Table 5 below.

[0109] Table 5

[0110] Membrane properties before grafting 1# 2# 3# 4# Retention rate (%) 99.63 99.78 99.87 99.81 Flux (lmh) 44.28 47.93 42.26 45.55

[0111] 3. Drain the flushing water in the membrane shell and prepare 143 L of grafting solution with the following mass concentrations: EDC 0.15% and PAA 0.67%);

[0112] 4. The grafting solution is circulated in the membrane shell through the water pump, and the circulation flow rate is 12.9m 3 / h, graft the flushed membrane elements, and adjust the operating parameters of the system: grafting solution temperature 25℃, water production 0.40m 3 / h, grafting time is 3.0h;

[0113] 5. After grafting is completed, rinse the membrane element with a protective solution (0.5% alcohol and 0.1% sodium sulfite) to remove the residual grafting solution and protect the grafted carboxyl groups;

[0114] 6. The grafted reverse osmosis membrane elements were tested after grafting. The test conditions were: 2000ppm NaCl, test pressure 1.55MPa, test temperature 25°C, test pH 7.0, and a single membrane element recovery rate of approximately 14%. The test results are shown in Table 6 below. As can be seen from Table 6, the flux of the grafted membrane elements decreased significantly.

[0115] Table 6

[0116] Membrane properties after grafting 1# 2# 3# 4# Retention rate (%) 99.71 99.79 99.87 99.82 Flux (lmh) 40.76 43.35 38.61 40.13

[0117] 9. A test solution containing silicon pollutants was prepared and four grafted membranes and one ungrafted membrane were tested under the same operating conditions. As shown in Table 7 below, the average flux reduction rate of the grafted membrane was 16.0%, and the flux reduction rate of the ungrafted membrane was 34.1%. In comparison, the flux reduction rate of the grafted membrane was reduced by 53.1%, and the anti-pollution performance was significantly enhanced.

[0118] Table 7

[0119]

[0120]

[0121] From the above data, it can be seen that the flux of the grafted membrane is reduced by about 10% without acid washing or alkali washing. Under the same working conditions, the number of membrane components used will increase, which will increase the investment cost of the system.

[0122] Comparative Example 2

[0123] Similar to Example 2, except that the grafting temperature is 5°C.

[0124] A test solution containing organic matter was prepared, and four grafted membranes and one ungrafted membrane were tested under the same operating conditions. As shown in Table 8 below, the flux decrease rate of the grafted membrane was 26.2-31.2%, and the flux decrease rate of the ungrafted membrane was 34%. In comparison, the flux decrease rate of the grafted membrane was reduced by 8.2-22.9%, and the anti-fouling performance was relatively poor.

[0125] Table 8

[0126] Post-grafting pollution performance test 1# 2# 3# 4# Flux decrease rate (%) 26.2 26.9 31.2 27.3

[0127] From the above data, it can be seen that when the membrane element is grafted at a temperature of 5°C, the anti-silicon scale performance of the grafted membrane is relatively poor.

[0128] Obviously, the above embodiments of the present invention are merely examples for the purpose of illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not possible to enumerate all embodiments here. Any obvious variations or modifications arising from the technical solutions of the present invention are intended to fall within the spirit and scope of the present invention.

Claims

1. A method for preparing a reverse osmosis membrane element, characterized in that: include: 1) Rinse the membrane elements in the membrane shell to remove chemicals or residual solvents on the surface of the membrane elements; 2) fully contacting the grafting solution with the membrane element to graft the flushed membrane element; wherein the grafting solution includes an activator and a carboxyl source, the grafting solution temperature is 10-40° C., and the grafting time is 0.7 h-6.0 h; 3) After grafting is completed, rinse the membrane element with protective liquid; 4) The membrane element flushed in step 3) is subjected to alkali washing, acid washing or alternating acid and alkali washing.

2. The method for preparing a reverse osmosis membrane element according to claim 1, wherein: The activator is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and the carboxyl source is polyacrylic acid. Preferably, the mass concentration of the 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride is 0.2-3.0%, and the mass concentration of the polyacrylic acid is 0.1-3.0%.

3. The method for preparing a reverse osmosis membrane element according to claim 1, wherein: In step 2), the step of making the grafting solution and the membrane element fully contact each other includes: placing the membrane element in the circulating grafting solution.

4. The method for preparing a reverse osmosis membrane element according to claim 1, wherein: Adjust the water flow rate of each membrane shell to 0.05-1.30m 3 / h.

5. The method for preparing a reverse osmosis membrane element according to claim 1, wherein: The protective solution in step 3) includes an organic solvent and a reducing agent. Preferably, the organic solvent includes 0.1-1% alcohol, and the reducing agent includes 0.05-1.5% sodium sulfite.

6. The method for preparing a reverse osmosis membrane element according to claim 1, wherein: In the step 4), the pH value of the alkaline washing is 9-13, the flux of the membrane element is adjusted to 20-48 lmh during the alkaline washing process, and the cleaning time is 0.5-6.5h.

7. The method for preparing a reverse osmosis membrane element according to claim 1, wherein: In the step 4), the pH value of the pickling is 1-4, the flux of the membrane element is adjusted to 20-50 lmh during the pickling process, and the cleaning time is 0.5-6.5h.

8. A reverse osmosis membrane element preparation system, characterized in that: include: The membrane shell assembly comprises at least one membrane shell, wherein the membrane shell contains at least one membrane element. Flushing liquid tank, used to provide flushing liquid to the inside of the membrane housing, Grafting solution tank, used to provide grafting solution to the inside of the membrane shell, Protective liquid tank, used to provide protective liquid to the inside of the membrane shell; Cleaning liquid tank, used to provide acid or alkali solution to the inside of the membrane shell; The liquid conveying device is connected between the flushing liquid tank and the membrane shell to convey the flushing liquid into the membrane shell; or connected between the grafting solution tank and the membrane shell to convey the grafting solution into the membrane shell; or connected between the protective liquid tank and the membrane shell to convey the protective liquid into the membrane shell; or connected between the cleaning liquid tank and the membrane shell to convey the acid or alkali solution into the membrane shell.

9. The reverse osmosis membrane element preparation system according to claim 1, characterized in that: It also includes a filter connected between the flushing liquid tank and the liquid delivery device for filtering the flushing liquid; or connected between the grafting solution tank and the liquid delivery device for filtering the grafting solution; Or it is connected between the protective liquid tank and the membrane shell to filter the protective liquid; or it is connected between the cleaning liquid tank and the liquid conveying device to filter the acid or alkali solution.

10. The reverse osmosis membrane element preparation system according to claim 8 or 9, characterized in that: It also includes a high-pressure pump connected between the cleaning liquid tank and the membrane shell, which is used to transport alkaline solution or acid solution into the membrane shell at high pressure.

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