Modifier for modifying waste reverse osmosis membrane into high-pressure concentration membrane and modification method thereof

Abstract

The present invention belongs to the technical field of reverse osmosis membrane modification, specifically relating to a modifier for converting waste reverse osmosis membranes into high-pressure concentrating membranes and a modification method thereof. The modifier comprises an alkaline cleaning solution, an acidic cleaning solution, an oxidizing modifying solution, a modifying aid solution, and a cleaning solution. The modification method comprises the following steps: first, cleaning the waste reverse osmosis membrane assembly with clean water; then, sequentially cleaning the waste reverse osmosis membrane with an alkaline cleaning solution and an acidic cleaning solution; then, synergistically modifying the reverse osmosis membrane with an oxidizing modifying solution and a modifying aid solution; and finally, rinsing the modifying solution from the membrane with a cleaning solution to obtain a high-pressure concentrating membrane. The present invention can reduce the salt rejection rate of waste reverse osmosis membranes to 80% to 92%, producing a high-pressure concentrating membrane suitable for multiple applications. This method addresses the gap in the modification of waste reverse osmosis membranes into high-pressure concentrating membranes.

Description

Technical Field

[0001] The invention belongs to the technical field of reverse osmosis membrane modification, and particularly relates to a modifier for modifying waste reverse osmosis membranes into high-pressure concentration membranes and a modification method thereof. Background Art

[0002] Reverse osmosis (RO) membranes are semipermeable membranes that remove salt and impurities from seawater or high-salinity waters through reverse osmosis (RO) membrane separation technology. The core principle is to use high pressure to drive water molecules through the membrane, while soluble salts, organic matter, and particulate matter are retained, thus separating freshwater from salt. They are commonly used in seawater desalination and pretreatment of industrial high-salinity wastewater. RO membranes typically have a salt rejection rate of 95-99% and operate at pressures of 5.5-8.5 MPa. When the salt rejection rate drops to approximately 95%, chemical or physical cleaning is required to restore the membrane's salt rejection rate.

[0003] High-pressure concentration membranes are membrane materials specifically designed for concentrating high-salinity or high-concentration solutions. They achieve solute-solvent separation through ultra-high pressure. They are suitable for treating liquids with extreme salinity or complex compositions. Operating pressures reach 7-10 MPa, and salt rejection rates typically range from 80% to 92% depending on application requirements. They are used in Zero Discharge (ZLD) industrial wastewater systems (such as those in the chemical and pharmaceutical industries), for the concentration of high-salinity brines (such as lithium extraction from salt lakes and salt production from seawater), and for the concentration of liquids in the food industry (such as juice and whey protein).

[0004] After repeated cleanings, reverse osmosis membranes eventually fail to meet their intended use. When the retention rate reaches 95% or lower and cannot be restored, they must be scrapped. According to statistics, approximately 800,000 4-inch and 8-inch RO membrane modules are sold annually, with spiral RO membranes accounting for approximately three-quarters of these. With the increasing application of seawater desalination, more RO membranes will be eliminated, resulting in significant waste and, if improperly handled, serious environmental pollution. Summary of the Invention

[0005] The purpose of the present invention is to provide a modifier for modifying waste reverse osmosis membranes into high-pressure concentration membranes and a modification method thereof.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a modifier for modifying a waste reverse osmosis membrane into a high-pressure concentration membrane, comprising the following components:

[0008] (a) an alkaline cleaning solution comprising an alkaline cleaning agent, an alkaline cleaning aid, and water; the alkaline cleaning agent being at least one of sodium hydroxide, potassium hydroxide, or sodium carbonate; the alkaline cleaning aid comprising at least one of sodium tripolyphosphate and tetrasodium ethylenediaminetetraacetic acid; the alkaline cleaning solution comprising 0.2 wt% to 3 wt% of the alkaline cleaning agent, 0.01 wt% to 0.5 wt% of the alkaline cleaning aid, and the balance being water;

[0009] (b) an acidic cleaning solution, comprising an acidic cleaning agent, an acidic cleaning aid, and water; the acidic cleaning agent comprises at least one of citric acid, oxalic acid, tartaric acid, nitric acid, or hydrochloric acid; the acidic cleaning aid comprises at least one of sodium metabisulfite and sodium dithionite; the acidic cleaning solution comprises 0.5 wt% to 3 wt% of the acidic cleaning agent, 0.05 wt% to 1 wt% of the acidic cleaning aid, and the balance is water;

[0010] (c) an oxidizing and modifying liquid comprising an oxidant and water; the oxidant comprising at least one of sodium hypochlorite, potassium permanganate, hydrogen peroxide, or peracetic acid; the oxidizing and modifying liquid comprising the oxidant in an amount of 0.2 wt % to 5 wt %, with the remainder being water;

[0011] (d) a modification auxiliary agent liquid, comprising a surfactant and water; the surfactant is at least one of sodium dodecylbenzenesulfonate, hexadecyldimethylallyl ammonium chloride, polyvinylpyrrolidone, or polyethylene glycol; the modification auxiliary agent liquid contains 0.1 wt% to 0.5 wt% of the surfactant; the balance is water;

[0012] (e) a cleaning solution consisting of a cleaning agent and water; the cleaning agent is sodium bisulfite or sodium thiosulfate; the cleaning agent content in the cleaning solution is 0.1 wt% to 0.2 wt%, and the balance is water.

[0013] The alkaline cleaning solution of the present invention can effectively decompose organic pollutants on the membrane surface, such as protein, grease, polysaccharide, colloid, etc.

[0014] The acidic cleaning solution of the present invention can dissolve inorganic salt deposits such as calcium carbonate, calcium sulfate, silicate, etc. The acid reacts with the scale layer to form soluble salts (such as Ca 2+ Mg 2+ ), which is then discharged with the cleaning fluid. It can also remove metal oxides, preventing metal ion deposition on the membrane surface, which can cause blockage or catalytic oxidation damage.

[0015] The oxidative modification liquid of the present invention attacks the amide bonds of the polyamide molecules through the oxidant, resulting in chain breakage, which reduces the cross-linking degree of the reverse osmosis membrane, makes the polymer chains looser, forms larger pore sizes or micro-defects, reduces the salt rejection rate of the membrane, increases the flux, and ultimately reduces the salt rejection rate of the membrane to 80-92%, realizing the function of a high-pressure concentration membrane.

[0016] The inventors found that it is more appropriate to control the concentration range of the oxidant in the range of 0.2wt%~5wt% of the mass of the oxidation modification liquid. If the concentration is too low, the oxidation effect is poor. If the concentration is too high, the oxidation effect is difficult to control and the oxidant excessively damages the membrane structure, resulting in a decrease in the mechanical strength of the membrane and a shortened service life of the membrane.

[0017] As the oxidant attacks the amide bonds of the polyamide molecules, it generates highly hydrophobic short-chain hydrocarbons, such as benzene ring fragments and alkanes, on the membrane surface. Hypochlorous acid also undergoes substitution reactions with aromatic rings, generating hydrophobic chlorinated compounds, such as chlorobenzene derivatives, on the membrane surface. The modification additive solution uses surfactants to wash away the hydrophobic small organic molecules adhering to the membrane surface, ensuring full contact between the oxidant and the membrane surface and enhancing the oxidation modification effect.

[0018] The cleaning solution of the present invention mainly washes away the oxidant remaining in the membrane to prevent the residual oxidant from causing excessive damage to the membrane, causing a significant reduction in the membrane desalination rate and the mechanical strength of the membrane, and affecting the service life of the membrane.

[0019] In a second aspect, the present invention provides a method for preparing a high-pressure concentration membrane by modifying a waste reverse osmosis membrane using the above-mentioned modifier, comprising the following steps:

[0020] (1) Clean the used reverse osmosis membrane assembly with clean water for 0.5 to 2 hours;

[0021] (2) soaking the waste reverse osmosis membrane assembly after cleaning in step (1) in the alkaline cleaning solution of component (a) for 1 to 2 hours, then circulating the cleaning solution at the rated operating flow rate for 1 to 2 hours, and then washing away the alkaline cleaning solution with clean water;

[0022] (3) soaking the waste reverse osmosis membrane assembly after alkaline cleaning in step (2) in the acidic cleaning solution of component (b) for 1 to 2 hours, then circulating the cleaning solution at the rated operating flow rate for 1 to 2 hours, and then washing away the acidic cleaning solution with clean water;

[0023] (4) The waste reverse osmosis membrane assembly after the acid cleaning in step (3) is circulated and cleaned with (c) oxidation modification liquid at the rated operating flow rate for 0.5 to 6 hours, and then (d) modification auxiliary liquid is mixed into (c) oxidation modification liquid and mixed, and the circulated cleaning is continued at the rated operating flow rate for 0.5 to 6 hours, and then the oxidation modification liquid and modification auxiliary liquid are washed away with clean water;

[0024] (5) The waste reverse osmosis membrane assembly modified by the adjustment in step (4) is circulated and cleaned with the cleaning solution (e) at the rated operating flow rate for 0.5 to 3 hours, and then the cleaning solution is washed away with clean water; thus, a high-pressure concentrating membrane is obtained.

[0025] The steps (1) to (5) are performed on a reverse osmosis membrane cleaning and modification test device;

[0026] In the step (1), the cleaning flow rate is 6m 3 / h~12m 3 / h; cleaning pressure is 0.1~0.5Mpa;

[0027] In the steps (2), (3) and (5), the rated operating flow is 6m 3 / h~12m 3 / h; the circulating cleaning pressure is 0.1~0.5Mpa;

[0028] In step (4), the circulating cleaning pressure is 0.1~2Mpa, and the rated operating flow is 8m 3 / h~16m 3 / h; when the pressure or flow rate is too low, the modification effect is poor and the cycle modification time is too long; when the pressure or flow rate is too high, the oxidant permeation is serious and it is difficult to control the desalination rate of the membrane, and the desalination rate of the membrane under the same parameters varies too much.

[0029] In step (4), the temperature of the oxidizing modification liquid and the modification aid liquid is 25-45°C. During the modification process, the cyclic modification temperature is 25-45°C to improve the activity of the oxidant. If the temperature is too low, the modification is slow and the modification time is long. If the temperature is too high, the polyamide membrane will soften and reduce its service life.

[0030] In the step (4), the waste reverse osmosis membrane assembly is first circulated and cleaned with (c) oxidation modification liquid at the rated operating flow rate, and then (d) modification auxiliary liquid is mixed into (c) oxidation modification liquid and mixed, and the cleaning is continued at the rated operating flow rate. This cleaning method first allows the oxidant to fully contact with the reverse osmosis membrane, and the oxidant attacks the amide bonds of the membrane polyamide molecules, so that the membrane desalination rate decreases and the flux increases; when the membrane surface is covered with hydrophobic small molecules, which hinder the oxidant from contacting the membrane, the modification auxiliary liquid is mixed with the oxidation modification liquid and then circulated and cleaned. The surfactant in the modification auxiliary liquid washes away the hydrophobic small molecular organic matter attached to the membrane surface, ensuring that the oxidant can fully contact with the membrane surface and improving the oxidation modification effect.

[0031] In the step (4), the (c) oxidation modification liquid and the (d) modification auxiliary liquid may be mixed before being circulated for cleaning. Compared with the cleaning method in which the waste reverse osmosis membrane assembly is first circulated for cleaning with the (c) oxidation modification liquid at the rated operating flow rate, and then the (d) modification auxiliary liquid is mixed into the (c) oxidation modification liquid, and the mixture is then circulated for cleaning at the rated operating flow rate, this cleaning method mixes the oxidation modification liquid with the modification auxiliary liquid before oxidative cleaning of the reverse osmosis membrane, resulting in a large change in the oxidant concentration, which not only prolongs the modification time but also causes a large change in the desalination rate after modification, making it difficult to achieve the modification target.

[0032] In step (4), the membrane may be first cleaned and modified with the oxidation modification liquid (c), then rinsed with water, then rinsed with the modification aid liquid (d), then rinsed with water, and the cleaning cycle may be repeated multiple times. Compared with the cleaning method in which the waste reverse osmosis membrane assembly is first cleaned and circulated with the oxidation modification liquid (c) at the rated operating flow rate, and then the modification aid liquid (d) is mixed with the oxidation modification liquid (c), and the cleaning cycle is continued at the rated operating flow rate, this cleaning method is complicated to operate, has a long cleaning cycle, and causes serious waste of reagents due to the repeated alternation of solutions.

[0033] With respect to these three modification and cleaning methods, the scheme of first cleaning with (c) oxidizing modification liquid and then mixing (d) modification auxiliary liquid into (c) oxidizing modification liquid for cleaning as described in step (4) is selected as the better scheme after comprehensive consideration.

[0034] In the step (4), the mixing ratio of the modification aid liquid to the oxidation modification liquid is 1-1.5:1.

[0035] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0036] The present invention provides a modifier and modification method for converting waste reverse osmosis membranes into high-pressure concentrating membranes. The method involves first using an alkaline cleaning solution to remove organic matter and other contaminants from the surface of the waste reverse osmosis membrane. Next, an acidic cleaning solution is used to remove inorganic salt precipitates and any metal oxides present on the membrane. An oxidizing modifying solution and a modification aid solution are then used to synergistically modify the membrane, moderately disrupting its chemical structure, increasing its pore size, reducing its rejection rate, and increasing its flux. Finally, a cleaning solution is used to remove residual oxidizing agent, preventing it from excessively damaging the membrane, which could significantly reduce its rejection rate and mechanical strength, and shorten its service life. This method can reduce the rejection rate of waste reverse osmosis membranes to 80% to 92%, producing a high-pressure concentrating membrane suitable for a variety of applications. This method addresses the gap in the field of converting waste reverse osmosis membranes into high-pressure concentrating membranes, providing significant economic and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1This is a diagram of the reverse osmosis membrane cleaning and modification device of the present invention.

[0038] In the figure: 1. Cleaning water tank, 2. Alkaline cleaning liquid tank, 3. Acidic cleaning liquid tank, 4. Oxidation modification liquid tank, 5. Modification auxiliary liquid tank, 6. Cleaning liquid tank, 7. Heating system, 8. Safety filter, 9. Reverse osmosis membrane assembly. DETAILED DESCRIPTION

[0039] The present invention is further described below through examples, but the scope of protection of the present invention is not limited thereto. In the following examples, unless otherwise specified, all raw materials used are commercially available. The membranes used were 8040 desalination membranes from brands such as Times Wharton, LG, and Toray, which were retired from desalination plants. The membrane flux was selected to achieve a rejection rate between 94% and 95%, with a flux range of 50 to 58 LMH.

[0040] The reverse osmosis membrane cleaning and modification device diagram is as follows: Figure 1 :

[0041] The equipment is mainly composed of a cleaning water tank 1, an alkaline cleaning liquid tank 2, an acid cleaning liquid tank 3, an oxidation modification liquid tank 4, a modification auxiliary liquid tank 5, a cleaning liquid tank 6, a heating system 7, a safety filter 8, a reverse osmosis membrane assembly 9, and supporting pipelines, valves, water pumps, and instruments.

[0042] The cleaning water tank 1, alkaline cleaning liquid tank 2, acidic cleaning liquid tank 3, oxidation modification liquid tank 4, and cleaning liquid tank 6 are connected in parallel, and are respectively connected in series with the security filter 8, booster pump, and reverse osmosis membrane assembly 9 through a water pump. The modification auxiliary agent liquid tank 5 is connected to the oxidation modification liquid tank 4, and the reverse osmosis membrane assembly 9 is provided with a concentrated water discharge pipe and a produced water discharge pipe, and a series pipe is provided between the concentrated water discharge pipe and the produced water discharge pipe; a return pipe is provided on the produced water discharge pipe, and the return pipe is respectively connected to the cleaning water tank 1, alkaline cleaning liquid tank 2, acidic cleaning liquid tank 3, oxidation modification liquid tank 4, and cleaning liquid tank 6; a pressure gauge, a thermometer and a flow meter are provided on the pipeline between the water pump and the security filter 8; a pressure gauge is provided on the pipeline between the booster pump and the reverse osmosis membrane assembly 9; a flow meter is provided on the concentrated water discharge pipe and the produced water discharge pipe; a thermometer and a flow meter are provided on the return pipe; and a heating system 7 is provided on the oxidation modification liquid tank 4. Example 1

[0043] A modifier for modifying a waste reverse osmosis membrane into a high-pressure concentration membrane comprises the following components:

[0044] (a) Alkaline cleaning solution

[0045] Add 4 kg of sodium hydroxide (0.2 wt%) and 0.2 kg of sodium tripolyphosphate (0.01 wt%) to 1995.8 kg of water and stir evenly to prepare 2000 kg of alkaline cleaning solution.

[0046] (b) Acidic cleaning fluid

[0047] 4 kg of citric acid (0.2 wt%), 2 kg of oxalic acid (0.1 wt%), 4 kg of hydrochloric acid (0.2 wt%, 31% concentration of hydrochloric acid), and 1 kg of sodium metabisulfite (0.05 wt%) were added to 1989 kg of water and stirred evenly to prepare 2000 kg of acidic cleaning solution.

[0048] (c) Oxidation modification liquid

[0049] 2 kg of sodium hypochlorite (0.2 wt%) was added to 996 kg of water and stirred evenly to prepare 1000 kg of oxidation modification liquid.

[0050] (d) Modified additive liquid

[0051] Add 1 kg of sodium dodecylbenzenesulfonate (0.1 wt%) to 999 kg of water and stir evenly to prepare 1000 kg of modification additive liquid.

[0052] (e) Cleaning fluid

[0053] Add 1 kg of sodium bisulfite (0.1 wt%) to 999 kg of water and stir evenly to make 1000 kg of cleaning solution.

[0054] A method for modifying a waste reverse osmosis membrane into a high-pressure concentration membrane, using the above-mentioned modifier, comprises the following steps:

[0055] (1) First, clean the waste reverse osmosis membrane with clean water for 0.5h, the cleaning pressure is 0.1Mpa, and the cleaning flow rate is 6m 3 / h.

[0056] (2) Add alkaline cleaning solution to the waste reverse osmosis membrane assembly after cleaning in step (1), soak for 1 hour, and then recycle the membrane assembly under the cleaning pressure of 0.1 MPa and the rated operating flow rate of 6 m 3 / h under the condition of circulated cleaning for 1h, and then rinsed off the alkaline cleaning solution with clean water;

[0057] (3) After alkaline cleaning in step (2), the waste reverse osmosis membrane assembly is passed through an acidic cleaning solution and soaked for 1 hour. Then, the circulating cleaning pressure is 0.1 MPa and the rated operating flow rate is 6 m 3 Circulate and clean for 1 hour at a rate of 1 / h, then rinse off the acidic cleaning solution with clean water;

[0058] (4) The oxidation modification liquid is introduced into the waste reverse osmosis membrane assembly after the acid cleaning in step (3), and the circulating cleaning pressure is 0.1 MPa, the oxidation modification liquid temperature is 25 ° C, and the rated operating flow rate is 8m 3 / h under the conditions of circulation cleaning for 0.5h; after cleaning, the modification agent liquid is added to the oxidation modification liquid tank 4 in a ratio of 1:1 and mixed with the oxidation modification liquid, and the circulation cleaning is continued for 6h under the same pressure, flow and temperature conditions, and then the oxidation modification liquid and modification agent liquid are washed off with clean water;

[0059] (5) A cleaning solution is introduced into the waste reverse osmosis membrane assembly that has been conditioned and modified in step (4), and the circulating cleaning pressure is 0.5 MPa and the rated operating flow rate is 6 m 3 The cleaning was circulated for 0.5 h under the condition of 1000 nm / h, and then the cleaning liquid was washed away with clean water to obtain a high-pressure concentration membrane.

[0060] Test the desalination rate of the high-pressure concentration membrane under the following conditions: pressure 5.5 MPa, test flow rate 6 m 3 / h~12m 3 / h, 32g / L sodium chloride solution; the test results are: single membrane desalination rate is 90~92%, and the flux is 52~71LMH. Example 2

[0061] A modifier for modifying a waste reverse osmosis membrane into a high-pressure concentration membrane comprises the following components:

[0062] (a) Alkaline cleaning solution

[0063] Add 30 kg of sodium hydroxide (1.5 wt%) and 10 kg of sodium tripolyphosphate (0.5 wt%) to 1960 kg of water and stir evenly to prepare 2000 kg of alkaline cleaning solution.

[0064] (b) Acidic cleaning fluid

[0065] 4 kg of citric acid (0.2 wt%), 2 kg of oxalic acid (0.1 wt%), 4 kg of hydrochloric acid (0.2 wt%, 31% concentration of hydrochloric acid), and 1 kg of sodium metabisulfite (0.05 wt%) were added to 1989 kg of water and stirred evenly to prepare 2000 kg of acidic cleaning solution.

[0066] (c) Oxidation modification liquid

[0067] Add 10 kg of sodium hypochlorite (1 wt%) to 990 kg of water and stir evenly to prepare 1000 kg of oxidation modification liquid.

[0068] (d) Modified additive liquid

[0069] 3.6 kg of sodium dodecylbenzenesulfonate (0.3 wt%) was added to 1196.4 kg of water and stirred evenly to prepare 1200 kg of modification additive liquid.

[0070] (e) Cleaning fluid

[0071] Stir 1.5 kg of sodium bisulfite (0.15 wt%) into 998.5 kg of water to make 1000 kg of cleaning solution.

[0072] A method for modifying a waste reverse osmosis membrane into a high-pressure concentration membrane, using the above-mentioned modifier, comprises the following steps:

[0073] (1) First, clean the waste reverse osmosis membrane with clean water for 2 hours, the cleaning pressure is 0.5Mpa, and the cleaning flow rate is 12m 3 / h.

[0074] (2) Add alkaline cleaning solution to the waste reverse osmosis membrane assembly after cleaning in step (1), soak for 2 hours, and then recycle the membrane assembly under the cleaning pressure of 0.5 MPa and the rated operating flow rate of 12 m 3 / h under the condition of circulated cleaning for 1.5h, and then rinsed off the alkaline cleaning solution with clean water;

[0075] (3) After alkaline cleaning in step (2), the waste reverse osmosis membrane assembly is passed through an acidic cleaning solution and soaked for 2 hours. Then, the membrane assembly is washed under a circulating cleaning pressure of 0.5 MPa and a rated operating flow rate of 12 m 3 / h under the condition of circulated cleaning for 1.5h, and then rinse off the acid cleaning solution with clean water;

[0076] (4) The oxidation modification liquid is introduced into the waste reverse osmosis membrane assembly after the acid cleaning in step (3), and the circulating cleaning pressure is 0.5 MPa, the oxidation modification liquid temperature is 45 ° C, and the rated operating flow rate is 16m 3 / h under the conditions of circulation cleaning for 3h; after cleaning, the modification agent liquid is added to the oxidation modification liquid tank 4 in a ratio of 1.2:1 and mixed with the oxidation modification liquid, and the circulation cleaning is continued for 6h under the same pressure, flow and temperature conditions, and then the oxidation modification liquid and modification agent liquid are washed off with clean water;

[0077] (5) A cleaning solution is introduced into the waste reverse osmosis membrane assembly that has been conditioned and modified in step (4), and the circulating cleaning pressure is 0.5 MPa and the rated operating flow rate is 12 m 3 The cleaning was circulated for 0.5 h under the condition of 1000 nm / h, and then the cleaning liquid was washed away with clean water to obtain a high-pressure concentration membrane.

[0078] Test the desalination rate of the high-pressure concentration membrane under the following conditions: pressure 5.5 MPa, test flow rate 6 m 3 / h~12m 3 / h, 32g / L sodium chloride solution; the test results are: single membrane desalination rate is 84~86%, and the flux is 73~87LMH. Example 3

[0079] A modifier for modifying a waste reverse osmosis membrane into a high-pressure concentration membrane comprises the following components:

[0080] (a) Alkaline cleaning solution

[0081] Add 30 kg of sodium hydroxide (3 wt%) and 5 kg of sodium tripolyphosphate (0.5 wt%) to 965 kg of water and stir evenly to prepare 1000 kg of alkaline cleaning solution.

[0082] (b) Acidic cleaning fluid

[0083] 5 kg of citric acid (0.5 wt%), 5 kg of oxalic acid (0.5 wt%), 20 kg of hydrochloric acid (2 wt%, 31% concentration of hydrochloric acid), and 5 kg of sodium metabisulfite (0.5 wt%) were added to 965 kg of water and stirred evenly to prepare 1000 kg of acidic cleaning solution.

[0084] (c) Oxidation modification liquid

[0085] Add 20 kg of sodium hypochlorite (2 wt%) to 980 kg of water and stir evenly to make 1000 kg of oxidation modification liquid.

[0086] (d) Modified additive liquid

[0087] Add 7.5 kg of hexadecyldimethylallylammonium chloride (0.5 wt%) to 1492.5 kg of water and stir evenly to prepare 1500 kg of modification additive liquid.

[0088] (e) Cleaning fluid

[0089] Add 2 kg of sodium bisulfite (0.2 wt%) to 998 kg of water and stir evenly to make 1000 kg of cleaning solution.

[0090] A method for modifying a waste reverse osmosis membrane into a high-pressure concentration membrane, using the above-mentioned modifier, comprises the following steps:

[0091] (1) First, clean the waste reverse osmosis membrane with clean water for 1.5 hours, the cleaning pressure is 0.3Mpa, and the cleaning flow rate is 10m 3 / h.

[0092] (2) Add alkaline cleaning solution to the waste reverse osmosis membrane assembly after cleaning in step (1), soak for 1 hour, and then recycle the membrane assembly under the cleaning pressure of 0.3 MPa and the rated operating flow rate of 10 m 3 / h under the condition of circulated cleaning for 2h, and then rinsed off the alkaline cleaning solution with clean water;

[0093] (3) After alkaline cleaning in step (2), the waste reverse osmosis membrane assembly is passed through an acidic cleaning solution and soaked for 1 hour. Then, the circulating cleaning pressure is 0.3 MPa and the rated operating flow rate is 10 m 3 / h under the condition of circulated cleaning for 2h, and then rinse off the acid cleaning solution with clean water;

[0094] (4) The oxidation modification liquid is introduced into the waste reverse osmosis membrane assembly after the acid cleaning in step (3), and the circulating cleaning pressure is 2 MPa, the oxidation modification liquid temperature is 30 ° C, and the rated operating flow rate is 12m 3 / h under the conditions of circulation cleaning for 6h; after cleaning, the modification agent liquid is added to the oxidation modification liquid tank 4 in a ratio of 1.5:1 and mixed with the oxidation modification liquid, and the circulation cleaning is continued for 3h under the same pressure, flow and temperature conditions, and then the oxidation modification liquid and modification agent liquid are washed off with clean water;

[0095] (5) A cleaning solution is introduced into the waste reverse osmosis membrane assembly that has been conditioned and modified in step (4), and the cleaning pressure is 0.3 MPa and the rated operating flow rate is 10 m 3 The cleaning was circulated for 3 hours under the condition of 1 / h, and then the cleaning liquid was washed away with clean water to obtain a high-pressure concentration membrane.

[0096] Test the desalination rate of the high-pressure concentration membrane under the following conditions: pressure 5.5 MPa, test flow rate 6 m 3 / h~12m 3 / h, 32g / L sodium chloride solution; the test results are: single membrane desalination rate is 82~84%, and the flux is 70~83LMH. Example 4

[0097] This embodiment is basically the same as embodiment 3, except that the composition of the modifier for modifying the waste reverse osmosis membrane into the high-pressure concentration membrane is changed as follows:

[0098] (b) Acidic cleaning fluid

[0099] 5 kg of citric acid (0.5 wt%), 5 kg of tartaric acid (0.5 wt%), 10 kg of nitric acid (1 wt%, 42% concentration of nitric acid), and 10 kg of sodium dithionite (1 wt%) were added to 970 kg of water and stirred evenly to prepare 1000 kg of acidic cleaning solution.

[0100] (c) Oxidation modification liquid

[0101] It is 1000kg of 5% concentration hydrogen peroxide.

[0102] (d) Modified additive liquid

[0103] Add 4.5 kg of sodium dodecylbenzenesulfonate (0.3 wt%) to 1495.5 kg of water and stir evenly to prepare 1500 kg of modification additive liquid.

[0104] The desalination rate of the high-pressure concentration membrane was tested under the following conditions: pressure 5.5 MPa, test flow rate 6 m3 / h~12 m3 / h, and 32 g / L sodium chloride solution; the test results showed that the single membrane desalination rate was 80~82%, and the flux was 89~97 LMH. Example 5

[0105] This embodiment is basically the same as embodiment 3, except that in step (4), the oxidation modification liquid is circulated for cleaning and modification for 6 hours, and then the modification auxiliary liquid is added and the modification is continued for 0.5 hours.

[0106] Test the desalination rate of the high-pressure concentration membrane under the following conditions: pressure 5.5 MPa, test flow rate 6 m 3 / h~12m 3 / h, 32g / L sodium chloride solution; the test results are: single membrane desalination rate is 81~83%, and the flux is 85~98LMH. Example 6

[0107] A modifier for modifying a waste reverse osmosis membrane into a high-pressure concentration membrane comprises the following components:

[0108] (a) Alkaline cleaning solution

[0109] Add 25 kg of potassium hydroxide (2.5 wt%), 5 kg of sodium carbonate (0.5 wt%), and 5 kg of tetrasodium ethylenediaminetetraacetate (0.5 wt%) to 965 kg of water and stir evenly to prepare 1000 kg of alkaline cleaning solution.

[0110] (b) Acidic cleaning fluid

[0111] 5 kg of citric acid (0.5 wt%), 5 kg of oxalic acid (0.5 wt%), 20 kg of nitric acid (2 wt%, 42% concentration of nitric acid), and 10 kg of sodium metabisulfite (0.5 wt%) were added to 960 kg of water and stirred evenly to prepare 1000 kg of acidic cleaning solution.

[0112] (c) Oxidation modification liquid

[0113] It is 1000kg of 3% concentration hydrogen peroxide.

[0114] (d) Modified additive liquid

[0115] Add 5 kg of hexadecyldimethylallylammonium chloride (0.5 wt%) to 997 kg of water and stir evenly to prepare 1000 kg of modification additive liquid.

[0116] (e) Cleaning fluid

[0117] Add 2 kg of sodium thiosulfate (0.2 wt%) to 998 kg of water and stir evenly to make 1000 kg of cleaning solution.

[0118] A method for modifying a waste reverse osmosis membrane into a high-pressure concentration membrane, using the above-mentioned modifier, comprises the following steps:

[0119] (1) First, clean the waste reverse osmosis membrane with clean water for 2 hours, the cleaning pressure is 0.5Mpa, and the cleaning flow rate is 12m 3 / h.

[0120] (2) Add alkaline cleaning solution to the waste reverse osmosis membrane assembly after cleaning in step (1), soak for 1 hour, and then recycle the membrane assembly under the cleaning pressure of 0.3 MPa and the rated operating flow rate of 12 m 3 / h under the condition of circulated cleaning for 2h, and then rinsed off the alkaline cleaning solution with clean water;

[0121] (3) After alkaline cleaning in step (2), the waste reverse osmosis membrane assembly is passed through an acidic cleaning solution and soaked for 1 hour. Then, the cleaning pressure is 0.3 MPa and the rated operating flow rate is 12 m 3 / h under the condition of circulated cleaning for 2h, and then rinse off the acid cleaning solution with clean water;

[0122] (4) The oxidation modification liquid is introduced into the waste reverse osmosis membrane assembly after the acid cleaning in step (3), and the circulating cleaning pressure is 1.5 MPa, the oxidation modification liquid temperature is 35 ° C, and the rated operating flow rate is 16m 3 / h under the conditions of circulation cleaning for 3h; after cleaning, the modification agent liquid is added to the oxidation modification liquid tank 4 in a ratio of 1.5:1 and mixed with the oxidation modification liquid, and the circulation cleaning is continued for 6h under the same pressure, flow and temperature conditions, and then the oxidation modification liquid and modification agent liquid are washed off with clean water;

[0123] (5) A cleaning solution is introduced into the waste reverse osmosis membrane assembly that has been conditioned and modified in step (4), and the circulating cleaning pressure is 0.3 MPa and the rated operating flow rate is 12 m 3 The cleaning was circulated for 3 hours under the condition of 1 / h, and then the cleaning liquid was washed away with clean water to obtain a high-pressure concentration membrane.

[0124] Test the desalination rate of the high-pressure concentration membrane under the following conditions: pressure 5.5 MPa, test flow rate 6 m 3 / h~12m 3 / h, 32g / L sodium chloride solution; the test results are: single membrane desalination rate is 86~88%, and the flux is 72~85LMH. Comparative Example 1

[0125] The difference between Comparative Example 1 and Example 1 is that the treatment method only includes steps (4) and (5), and the waste reverse osmosis membrane is not cleaned. The specific operations are as follows:

[0126] (1) The oxidation modification liquid is introduced into the waste reverse osmosis membrane assembly, and the circulating cleaning pressure is 0.1Mpa, the oxidation modification liquid temperature is 25℃, and the rated operating flow rate is 8m 3 / h under the conditions of circulation cleaning for 0.5h; after cleaning, the modification agent liquid is added to the oxidation modification liquid tank 4 and mixed with the oxidation modification liquid, and the circulation cleaning is continued for 6h under the same pressure, flow and temperature conditions, and then the oxidation modification liquid and modification agent liquid are washed off with clean water;

[0127] (2) The cleaning liquid is introduced into the waste reverse osmosis membrane assembly after adjustment and modification, and the circulating cleaning pressure is 0.5 MPa and the rated operating flow rate is 6 m 3 The cleaning was circulated for 0.5 h under the condition of 1000 nm / h, and then the cleaning liquid was washed away with clean water to obtain a high-pressure concentration membrane. Comparative Example 2

[0128] The difference between Comparative Example 2 and Example 3 is that the oxidative modification liquid in the modifier component (c) is prepared by uniformly stirring 60 kg of sodium hypochlorite (6 wt %) into 940 kg of water to prepare 1000 kg of oxidative modification liquid. Comparative Example 3

[0129] The difference between Comparative Example 3 and Example 3 is that in step (4) of the treatment method, only the (c) oxidizing and modifying liquid is used to clean the waste reverse osmosis membrane. Comparative Example 4

[0130] The difference between Comparative Example 4 and Example 3 is that in step (4) of the treatment method, (c) oxidation modification liquid is first used for circulation modification. After the modification, (c) oxidation modification liquid is flushed out with clean water and then treated with (d) oxidation modification liquid. The specific operation of step (4) is as follows:

[0131] The oxidation modification liquid is introduced into the waste reverse osmosis membrane assembly after the acid cleaning in step (3), and the circulating cleaning pressure is 2 MPa, the oxidation modification liquid temperature is 30 ° C, and the rated operating flow rate is 12m 3 / h for 6 hours; after cleaning, flush out the oxidized modified liquid in the system with clean water, add the modified auxiliary liquid, continue to circulate and clean for 3 hours under the same pressure, flow and temperature conditions, and then wash away the modified auxiliary liquid with clean water. Comparative Example 5

[0132] The difference between Comparative Example 5 and Example 3 is that the circulating cleaning pressure in step (4) of the treatment method is 3 MPa. Comparative Example 6

[0133] The difference between Comparative Example 6 and Example 3 is that the rated operating flow rate in step (4) of the treatment method is 18m 3 / h. Comparative Example 7

[0134] The difference between Comparative Example 7 and Example 3 is that the rated operating flow rate in step (4) of the treatment method is 6m 3 / h. Comparative Example 8

[0135] The difference between Comparative Example 8 and Example 3 is that the cyclic modification temperature in step (4) of the treatment method is 15°C. Comparative Example 9

[0136] The difference between Comparative Example 9 and Example 3 is that the cyclic modification temperature in step (4) of the treatment method is 50°C. Comparative Example 10

[0137] The difference between Comparative Example 10 and Example 3 is that the treatment method does not include step (5), but only includes steps (1) to (4).

[0138] The comparison of the modification results of the embodiment and the comparative example is shown in Table 1.

[0139]

[0140] As shown in Table 1, by comparing Example 1 and Comparative Example 1, if the membrane is not soaked and cleaned first with (a) an alkaline cleaning solution and (b) an acidic cleaning solution, the impurities attached to the membrane surface will hinder the oxidative modification of the polyamide membrane by the oxidant, resulting in poor modification effect and insignificant flux change.

[0141] From the comparison between Example 3 and Comparative Example 2, it can be seen that an excessively high concentration of oxidant will cause the oxidation reaction rate to be too fast due to the strong oxidizing effect, thereby causing the desalination rate to drop too quickly and be difficult to control, and the modification purpose cannot be achieved; especially when multiple waste reverse osmosis membranes are simultaneously modified into high-pressure concentration membranes with different desalination rates, since the desalination rate modification targets of different waste reverse osmosis membranes are different, an excessively high concentration of oxidant will cause the oxidation reaction rate to be too fast, and the desalination rate will be even more difficult to control.

[0142] From the comparison between Example 3 and Comparative Example 3, it can be seen that since no modification auxiliary liquid is added in Comparative Example 3, the hydrophobic small molecules generated during the oxidation modification process cannot be effectively removed, affecting the contact between the oxidant and the membrane surface, thereby slowing down the oxidation process and affecting the modification efficiency.

[0143] From the comparison between Example 3 and Comparative Example 4, it can be seen that although the modification auxiliary liquid is added in Comparative Example 4 to wash away the hydrophobic small molecules, the oxidation modification liquid has been discharged in advance and cannot continue to oxidatively modify the membrane surface, so the modification effect is worse than that of Example 3.

[0144] From the comparison between Example 3 and Comparative Example 5, it can be seen that when the modification pressure is too high, the oxidant permeates seriously and the oxidation modification process of the polyamide membrane is difficult to control, resulting in the difficulty in controlling the desalination rate and large changes in the flux.

[0145] From the comparison between Example 3 and Comparative Examples 6 and 7, it can be seen that the flow rate during the modification process using (c) the oxidizing modification liquid and (d) the modification auxiliary liquid in step (4) has a significant impact on the modification effect. When the flow rate is too high, the oxidant penetrates into the interior of the polyamide membrane, making the oxidation modification process difficult to control and causing a significant decrease in the desalination rate. Low flow rate will result in the oxidant not being able to evenly cover the membrane surface, which may form a cleaning "dead corner" and the local area is not fully contacted, affecting the overall modification effect and thus slowing the modification.

[0146] From the comparison between Example 3 and Comparative Examples 8 and 9, it can be seen that temperature is an important factor affecting the activity of the oxidant in the (c) oxidation modification liquid. When the temperature is too low, the oxidant activity is poor, the reaction with the polyamide membrane is slow, and the modification process is slow. When the temperature is too high, the oxidant activity is strong, and the reaction with the polyamide membrane is violent, aggravating the oxidation damage of the membrane. This membrane damage is irreversible and difficult to control, resulting in large differences in the modified desalination rate. In addition, too high a temperature will soften the membrane structure and reduce the service life.

[0147] Comparing Example 3 with Comparative Example 10, if the cleaning solution (e) is omitted and only water is used for cleaning, although the retention rate and flux of the modified membrane are not significantly different, as the membrane is used, the residual oxidant will continue to oxidize and damage the membrane structure, causing the retention rate to further decrease. The membrane's service life will also be shortened due to severe oxidation.

[0148] New commercially available high-pressure concentrating membranes with a rejection rate of 80-92% typically operate at pressures of 7-10 MPa and fluxes of 55-85 LMH. The used reverse osmosis membranes modified using this method have a rejection rate of 80-92%, an operating pressure of 6-10 MPa, and a flux of 52-97 LMH, meeting the requirements for high-pressure concentrating membranes.

Claims

1. A method for modifying waste reverse osmosis membranes into high-pressure concentration membranes using a modifier, characterized in that: The modifier includes the following components: (a) an alkaline cleaning solution comprising an alkaline cleaning agent, an alkaline cleaning aid, and water; the alkaline cleaning agent being at least one of sodium hydroxide, potassium hydroxide, or sodium carbonate; the alkaline cleaning aid comprising at least one of sodium tripolyphosphate and tetrasodium ethylenediaminetetraacetic acid; the alkaline cleaning solution comprising 0.2 wt% to 3 wt% of the alkaline cleaning agent, 0.01 wt% to 0.5 wt% of the alkaline cleaning aid, and the balance being water; (b) an acidic cleaning solution, comprising an acidic cleaning agent, an acidic cleaning aid, and water; the acidic cleaning agent comprises at least one of citric acid, oxalic acid, tartaric acid, nitric acid, or hydrochloric acid; the acidic cleaning aid comprises at least one of sodium metabisulfite and sodium dithionite; the acidic cleaning solution comprises 0.5 wt% to 3 wt% of the acidic cleaning agent, 0.05 wt% to 1 wt% of the acidic cleaning aid, and the balance is water; (c) an oxidizing and modifying liquid comprising an oxidant and water; the oxidant comprising at least one of sodium hypochlorite, potassium permanganate, hydrogen peroxide, or peracetic acid; the oxidizing and modifying liquid comprising the oxidant in an amount of 0.2 wt % to 5 wt %, with the remainder being water; (d) a modification auxiliary agent liquid, comprising a surfactant and water; the surfactant is at least one of sodium dodecylbenzenesulfonate, hexadecyldimethylallyl ammonium chloride, polyvinylpyrrolidone, or polyethylene glycol; the modification auxiliary agent liquid contains 0.1 wt% to 0.5 wt% of the surfactant; the balance is water; (e) a cleaning solution comprising a cleaning agent and water; the cleaning agent is sodium bisulfite or sodium thiosulfate; the cleaning agent content in the cleaning solution is 0.1 wt % to 0.2 wt %, and the balance is water; The method for preparing a high-pressure concentration membrane by modifying waste reverse osmosis membrane using the above-mentioned modifier comprises the following steps: (1) Clean the used reverse osmosis membrane assembly with clean water for 0.5 to 2 hours; (2) soaking the waste reverse osmosis membrane assembly after cleaning in step (1) in the alkaline cleaning solution of component (a) for 1 to 2 hours, then circulating the cleaning solution at the rated operating flow rate for 1 to 2 hours, and then washing away the alkaline cleaning solution with clean water; (3) soaking the waste reverse osmosis membrane assembly after alkaline cleaning in step (2) in the acidic cleaning solution of component (b) for 1 to 2 hours, then circulating the cleaning solution at the rated operating flow rate for 1 to 2 hours, and then washing away the acidic cleaning solution with clean water; (4) The waste reverse osmosis membrane assembly after the acid cleaning in step (3) is circulated and cleaned with (c) oxidation modification liquid at the rated operating flow rate for 0.5 to 6 hours, and then (d) modification auxiliary liquid is mixed into (c) oxidation modification liquid and mixed, and the circulated cleaning is continued for 0.5 to 6 hours at the rated operating flow rate, and then the oxidation modification liquid and modification auxiliary liquid are washed away with clean water; the circulation cleaning pressure is 0.1 to 2 MPa, and the flow rate is 8m 3 / h~16m 3 / h; the temperature of the oxidation modification liquid and the modification auxiliary liquid is 25~45℃; the mixing ratio of the modification auxiliary liquid and the oxidation modification liquid is 1~1.5:1; (5) The waste reverse osmosis membrane assembly modified by the adjustment in step (4) is circulated and cleaned with the cleaning solution (e) at the rated operating flow rate for 0.5 to 3 hours, and then the cleaning solution is washed away with clean water to obtain a high-pressure concentrating membrane; The steps (1) to (5) are carried out on a reverse osmosis membrane cleaning and modification test device.

2. The method for modifying waste reverse osmosis membrane into high-pressure concentration membrane using a modifying agent according to claim 1, characterized in that: In the step (1), the cleaning flow rate is 6m 3 / h~12m 3 / h; the cleaning pressure is 0.1~0.5Mpa; in the steps (2), (3) and (5), the rated operating flow rate is 6m 3 / h~12m 3 / h; the circulating cleaning pressure is 0.1~0.5Mpa.

Images