Degradation regeneration method of waste reverse osmosis membrane treated by vacuum plasma

Abstract

The invention provides a degradation regeneration method of a waste reverse osmosis membrane treated by vacuum plasma, which comprises the following steps: cleaning the waste reverse osmosis membrane, fixing the waste reverse osmosis membrane in a flat state, and carrying out vacuum plasma treatment to obtain a degradation regeneration membrane. According to the regeneration method provided by the invention, the molecular structure of the polymer on the surface of the waste reverse osmosis membrane is regulated and controlled through physical, chemical or physicochemical synergy of plasma etching, the waste membrane is converted into a nanofiltration membrane or an ultrafiltration membrane, and the interception capability of ionic salt of the membrane is improved. In the treatment process, no chemical reagent is used, the process is simple, the treatment time is short, and the recycling efficiency of the waste membrane is greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane treatment, and in particular to a regeneration method for reverse osmosis membranes, and more particularly to a downgraded regeneration method for waste reverse osmosis membranes treated by vacuum plasma. Background Art

[0002] A reverse osmosis membrane (RO membrane) is a highly efficient separation material based on the principle of a semi-permeable membrane. Its core function is to overcome the osmotic pressure of the solution by applying an external pressure, forcing water molecules to selectively pass through the membrane layer, while pollutants such as dissolved salts, organic substances, and microorganisms are intercepted, thereby achieving water purification and solute concentration. As the core component of membrane separation technology, the reverse osmosis membrane has become a key technical means in the fields of seawater desalination, brackish water treatment, industrial wastewater reuse, and medical pure water preparation due to its excellent separation performance.

[0003] However, reverse osmosis membranes face severe pollution challenges during long-term operation: problems such as the deposition of colloidal particles, the growth of microorganisms, and the scaling of organic substances and inorganic salts will significantly reduce the membrane flux, and at the same time lead to a decrease in solute rejection rate or an increase in system operating pressure, ultimately resulting in the failure of the membrane element. With the expansion of the use scale of reverse osmosis membranes, the treatment of waste membrane modules has become a serious problem. At present, waste reverse osmosis membranes are mostly disposed of by incineration or landfill, which not only causes waste of resources but also environmental pollution.

[0004] Existing studies have achieved the recycling of waste membranes through regeneration technologies. For example, CN111495203A discloses a method for converting waste reverse osmosis membranes into nanofiltration or ultrafiltration membranes, including: cleaning the reverse osmosis membranes in a combined manner of circulation and immersion, and then performing oxidative degradation using an oxidant. CN113457456A discloses a modified reuse method for waste reverse osmosis membranes, including: circulating and heating the waste reverse osmosis membranes using acidic or alkaline agents and ultrasonic assistance for cleaning, then performing oxidative modification and high-pressure circulating heating treatment, and finally performing hydroxylation modification using a hydroxylation agent. CN117085511A discloses a conversion and reuse method for waste polyamide reverse osmosis membranes, including: circulating cleaning and soaking the waste membrane module, performing low-pressure circulating flow flushing using an oxidant to oxidize and degrade the polyamide layer, and finally forming a new modified layer through layer-by-layer self-assembly.

[0005] Existing regeneration technologies usually adopt oxidation soaking treatment, such as sodium hypochlorite and potassium permanganate, to remove pollutants on the membrane surface and partially restore the membrane pore structure, and then adjust the separation performance through membrane surface modification. However, on the one hand, it is difficult to achieve precise control with the oxidation soaking method, which may overly damage the polyamide active layer and it is difficult to determine the efficacy of the regenerated membrane; on the other hand, the oxidation soaking method will also affect the support layer and the service life of the downgraded regenerated membrane; in addition, the oxidation soaking method requires a large amount of oxidation reagents, which not only does not conform to the environmental protection concept of green and low-carbon, but usually requires soaking for several days, with poor environmental protection and economy.

[0006] Therefore, developing an efficient, stable and economical method for regenerating waste reverse osmosis membranes to precisely control the chemical properties of the membrane surface has become the key to solving the problem of resource utilization of waste membranes. Summary of the Invention

[0007] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a simple and precise downgrading and regeneration method for waste reverse osmosis membranes treated by vacuum plasma. The polyamide layer on the surface of the waste reverse osmosis membrane is etched to realize its downgrading and regeneration into a nanofiltration membrane or an ultrafiltration membrane.

[0008] To achieve this purpose, the present invention adopts the following technical solutions:

[0009] The present invention provides a simple and precise downgrading and regeneration method for waste reverse osmosis membranes treated by vacuum plasma, and the downgrading and regeneration method includes the following steps:

[0010] After cleaning the waste reverse osmosis membrane, fix the waste reverse osmosis membrane in a flat state and perform vacuum plasma treatment to obtain a downgraded regenerated membrane.

[0011] The regeneration method provided by the present invention etches the waste reverse osmosis membrane through plasma under vacuum conditions, and uses ions or free radicals in the plasma generated by low-pressure discharge to etch the polymer on the surface of the waste reverse osmosis membrane, such as the polyamide layer, simultaneously generating physical and / or chemical synergistic etching effects, regulating the molecular structure and surface morphology of the polymer, converting the waste reverse osmosis membrane into a nanofiltration membrane or an ultrafiltration membrane, and improving its ion salt rejection ability. Compared with chemical oxidation soaking, no chemical reagents are used during the process, there is no secondary pollution, and the treatment time is greatly reduced, improving the conversion and recycling efficiency of waste membranes.

[0012] Preferably, the pressure of the vacuum plasma treatment is 1-200 Pa, for example, it can be 1 Pa, 5 Pa, 10 Pa, 30 Pa, 50 Pa, 75 Pa, 100 Pa, 125 Pa, 150 Pa, 175 Pa or 200 Pa, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0013] Preferably, the power of the vacuum plasma treatment is 50 - 300 W, for example, it can be 50 W, 60 W, 70 W, 75 W, 80 W, 90 W, 95 W, 100 W, 105 W, 110 W, 120 W, 130 W, 140 W, 150 W, 200 W, 250 W or 300 W, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable, preferably 90 - 200 W.

[0014] Preferably, the time of the vacuum plasma treatment is 60 - 360 s, for example, it can be 60 s, 90 s, 120 s, 150 s, 180 s or 360 s, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0015] Preferably, the working gas for the vacuum plasma treatment includes reactive gas and / or inert gas, preferably inert gas, or a combination of reactive gas and inert gas.

[0016] Preferably, the reactive gas includes any one or at least two combinations of air, oxygen or nitrogen. Typical but non-limiting combinations include the combination of air and oxygen, the combination of oxygen and nitrogen, the combination of air and nitrogen, or the combination of air, oxygen and nitrogen.

[0017] Preferably, the inert gas includes argon and / or helium, preferably argon.

[0018] Preferably, the flow rate of the working gas for the vacuum plasma treatment is 20 - 70 sccm, for example, it can be 20 sccm, 25 sccm, 30 sccm, 35 sccm, 40 sccm, 45 sccm, 50 sccm, 52 sccm, 54 sccm, 55 sccm, 56 sccm, 58 sccm, 60 sccm, 62 sccm, 64 sccm, 65 sccm, 66 sccm, 68 sccm or 70 sccm, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0019] In the present invention, the unit "sccm" represents standard milliliters per minute.

[0020] Preferably, the cleaning method includes rinsing with water.

[0021] Preferably, the cleaning temperature is 10 - 50 °C, for example, it can be 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C or 50 °C, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0022] Preferably, the degradation and regeneration method further includes: soaking and storing the degraded and regenerated membrane in water.

[0023] As a preferred technical solution of the degradation and regeneration method provided by the present invention, the degradation and regeneration method includes the following steps:

[0024] (1) Cleaning the waste reverse osmosis membrane with water at a cleaning temperature of 10 - 50°C until the surface dirt is removed, obtaining a pretreated waste reverse osmosis membrane;

[0025] (2) Fixing the pretreated waste reverse osmosis membrane on a glass plate, keeping it in a flat state, and placing it in a vacuum chamber for vacuum plasma treatment. The pressure of the vacuum plasma treatment is 1 - 200 Pa, the power of the vacuum plasma treatment is 90 - 200 W. The vacuum plasma treatment uses a reactive gas and / or an inert gas as the working gas, the flow rate of the working gas is 20 - 70 sccm, and the time of the vacuum plasma treatment is 60 - 360 s. After the vacuum plasma treatment, a degraded and regenerated membrane is obtained, and the degraded and regenerated membrane is soaked and stored in water.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] The regeneration method provided by the present invention regulates the surface polymer morphology of the waste reverse osmosis membrane through the physical, chemical, or physicochemical synergistic etching effect of plasma, converts the waste membrane into a nanofiltration membrane or an ultrafiltration membrane, and at the same time improves the retention ability of ionic salts compared with nanofiltration membranes and ultrafiltration membranes. During the treatment process, no chemical reagents are used, the process is simple, the treatment time is short, and the regeneration efficiency of the waste membrane is greatly improved. Specific Embodiments

[0028] The technical solutions of the present invention will be further described below through specific embodiments.

[0029] To clearly illustrate the technical solutions of the present invention, in the specific embodiments, the treatment object used is the same waste reverse osmosis membrane module. The waste time of the waste reverse osmosis membrane is less than 6 months, and the storage state is intact. Under the conditions of a temperature of 25°C, a film pressing pressure of 1.2 MPa, and an operating pressure of 1 MPa, the flux of the NaCl solution (NaCl concentration is 2 g / L) of the waste reverse osmosis membrane is 6.67 L·m -2 ·h -1 .

[0030] Example 1

[0031] This example provides a method for degrading and regenerating a waste reverse osmosis membrane. The degradation and regeneration method includes the following steps:

[0032] (1) Separate the shell of the waste reverse osmosis membrane, unfold and lay flat the waste reverse osmosis membrane into waste reverse osmosis membrane sheets and cut them. Then, rinse with clean water at a rinsing temperature of 25°C until the surface dirt is removed;

[0033] (2) Fix the cut and rinsed waste reverse osmosis membrane sheets on the glass plate, keep them in a flat state, and place them in the vacuum chamber of the vacuum plasma instrument;

[0034] (3) Perform vacuum plasma treatment on the waste reverse osmosis membrane sheets. The process parameters of the vacuum plasma treatment include: the pressure is 50 Pa, the power is 100 W, the working gas is argon. The vacuum plasma treatment instrument has two gas channels. Pass argon into both gas channels, and the gas flow rate is 30 sccm for both, that is, the total flow rate of argon is 60 sccm, and the treatment time is 90 s. After the treatment, take out the waste reverse osmosis membrane sheets to obtain downgraded regenerated membranes, and soak the downgraded regenerated membranes in ultrapure water for storage.

[0035] Example 2

[0036] This example provides a method for downgrading and regenerating waste reverse osmosis membranes. The downgrading and regenerating method includes the following steps:

[0037] (1) Separate the shell of the waste reverse osmosis membrane, unfold and lay flat the waste reverse osmosis membrane into waste reverse osmosis membrane sheets and cut them. Then, rinse with clean water at a rinsing temperature of 25°C until the surface dirt is removed;

[0038] (2) Fix the cut and rinsed waste reverse osmosis membrane sheets on the glass plate, keep them in a flat state, and place them in the vacuum chamber of the vacuum plasma instrument;

[0039] (3) Perform vacuum plasma treatment on the waste reverse osmosis membrane sheets. The process parameters of the vacuum plasma treatment include: the pressure is 50 Pa, the power is 100 W, the working gas is argon. The vacuum plasma treatment instrument has two gas channels. Pass argon into both gas channels, and the gas flow rate is 30 sccm for both, that is, the total flow rate of argon is 60 sccm, and the treatment time is 180 s. After the treatment, take out the waste reverse osmosis membrane sheets to obtain downgraded regenerated membranes, and soak the downgraded regenerated membranes in ultrapure water for storage.

[0040] That is, compared with Example 1, the power of the vacuum plasma treatment is 100 W and the treatment time is 180 s.

[0041] Example 3

[0042] This example provides a method for downgrading and regenerating waste reverse osmosis membranes. The downgrading and regenerating method includes the following steps:

[0043] (1) Separate the discarded reverse osmosis membrane housing, unfold and lay flat the discarded reverse osmosis membrane into a membrane sheet and cut it, then rinse it with clean water at a rinsing temperature of 25°C until the surface dirt is removed;

[0044] (2) Fix the cut and rinsed discarded reverse osmosis membrane sheet on a glass plate, keep it in a flat state, and place it in the vacuum chamber of a vacuum plasma instrument;

[0045] (3) Perform vacuum plasma treatment on the discarded reverse osmosis membrane sheet. The process parameters of the vacuum plasma treatment include: the pressure is 50 Pa, the power is 100 W, the working gas is argon. The vacuum plasma treatment instrument has two gas channels. Pass argon into both gas channels, and the gas flow rate of each is 30 sccm, that is, the total flow rate of argon is 60 sccm, and the treatment time is 360 s. After the treatment is completed, take out the discarded reverse osmosis membrane sheet to obtain a degraded and regenerated membrane, and place the degraded and regenerated membrane in ultrapure water for soaking and preservation.

[0046] That is, compared with Example 1, the power of the vacuum plasma treatment is 100 W and the treatment time is 360 s.

[0047] Example 4

[0048] This example provides a method for degrading and regenerating discarded reverse osmosis membranes. Compared with Example 1, the power of the vacuum plasma treatment is 90 W and the treatment time is 90 s, and the rest are the same as in Example 1.

[0049] Example 5

[0050] This example provides a method for degrading and regenerating discarded reverse osmosis membranes. Compared with Example 1, the power of the vacuum plasma treatment is 90 W and the treatment time is 180 s, and the rest are the same as in Example 1.

[0051] Example 6

[0052] This example provides a method for degrading and regenerating discarded reverse osmosis membranes. Compared with Example 1, the power of the vacuum plasma treatment is 150 W and the treatment time is 90 s, and the rest are the same as in Example 1.

[0053] Example 7

[0054] This example provides a method for degrading and regenerating discarded reverse osmosis membranes. Compared with Example 1, the power of the vacuum plasma treatment is 150 W and the treatment time is 180 s, and the rest are the same as in Example 1.

[0055] Example 8

[0056] This embodiment provides a method for downgrading and regenerating waste reverse osmosis membranes. Compared with Embodiment 1, the power of the vacuum plasma treatment is 200 W, and the treatment time is 90 s. The rest are the same as those in Embodiment 1.

[0057] Embodiment 9

[0058] This embodiment provides a method for downgrading and regenerating waste reverse osmosis membranes. Compared with Embodiment 1, the power of the vacuum plasma treatment is 200 W, and the treatment time is 180 s. The rest are the same as those in Embodiment 1.

[0059] Embodiment 10

[0060] This embodiment provides a method for downgrading and regenerating waste reverse osmosis membranes. Compared with Embodiment 1, the total flow rate of argon is set to 20 sccm, and the treatment time is 360 s. The rest are the same as those in Embodiment 1.

[0061] Embodiment 11

[0062] This embodiment provides a method for downgrading and regenerating waste reverse osmosis membranes. Compared with Embodiment 1, the working gas is set as a mixture of argon and air, and the volume ratio of argon to air is 1:1. The rest are the same as those in Embodiment 1. That is, argon and air with a flow rate of 30 sccm are respectively introduced into the two gas channels of the vacuum plasma processor.

[0063] Embodiment 12

[0064] This embodiment provides a method for downgrading and regenerating waste reverse osmosis membranes. Compared with Embodiment 1, the working gas is set as nitrogen, and the flow rate of the working gas is the same, that is, the total flow rate of nitrogen is 60 sccm. The rest are the same as those in Embodiment 1.

[0065] Comparative Example 1

[0066] This comparative example provides a method for downgrading and regenerating waste reverse osmosis membranes. Compared with Embodiment 1, no vacuum plasma treatment is performed. That is, after the waste reverse osmosis membrane is cleaned, it is placed in ultrapure water for soaking and preservation.

[0067] Comparative Example 2

[0068] This comparative example provides a method for downgrading and regenerating waste reverse osmosis membranes. Compared with Embodiment 1, the vacuum plasma treatment is replaced with an oxidation treatment. The rest are the same as those in Embodiment 1.

[0069] The specific process of the oxidation treatment is as follows: Circulating immersion is performed for 24 h using a sodium hypochlorite solution with an active chlorine concentration of 1000 mg / L as the oxidant.

[0070] Comparative Example 3

[0071] This comparative example provides a nanofiltration membrane, which is the commercially available film DuPont NF 90-4040 purchased.

[0072] Comparative Example 4

[0073] This comparative example provides an ultrafiltration membrane, which is the purchased Ande PS polysulfone membrane.

[0074] The degraded and regenerated membranes obtained in the examples and comparative examples were evaluated for membrane performance, and the results are listed in Table 1.

[0075] The method for membrane performance evaluation is as follows: Weigh 4 g of ionic salt and dissolve it in 2 L of ultrapure water to prepare a 2 g / L salt solution. Use a reverse osmosis membrane test device to conduct a cross-flow permeation experiment. Set the temperature to 25 °C, the membrane pressing pressure to 1.2 MPa, and the operating pressure to 1 MPa to obtain membrane rejection and flux data.

[0076] Table 1

[0077]

[0078] As can be seen from Table 1, the method for downgrading and regenerating waste reverse osmosis membranes provided by the present invention, through vacuum plasma treatment of waste reverse osmosis membranes, etching the polyamide layer on the surface of waste reverse osmosis membranes, downgrading and regenerating waste reverse osmosis membranes into nanofiltration membranes or ultrafiltration membranes with excellent performance, realizing the recycling of waste reverse osmosis membranes, has a short processing time, high efficiency, and does not require the use of any additional chemical reagents, without secondary pollution.

[0079] In Example 1, under the conditions of a power of 100 W and a treatment time of 90 s, the flux of the regenerated membrane reached 18 L·m -2 ·h -1 or more, and at the same time had the retention ability for both monovalent salts and divalent salts. Compared with the commercial nanofiltration membrane in Comparative Example 3, while maintaining a comparable ionic salt retention ability, the flux was significantly improved; in Examples 2-3, when the treatment time was increased to 180 s or 360 s, the flux of the regenerated membrane was significantly improved, and at the same time, a certain ionic salt retention ability was maintained. Compared with the commercial ultrafiltration membrane in Comparative Example 4, both the flux and the retention ability were significantly improved, and the obtained regenerated membrane reached the performance index of the commercial ultrafiltration membrane and even exceeded its performance. Compared with Example 1 in Examples 4-9, when the plasma treatment power was changed, the flux and rejection rate of the regenerated membrane showed a trend of first increasing and then decreasing with the increase of power, and the overall rejection rate was better than that of the commercial ultrafiltration membrane; in Example 11, under the condition of using two different channel gases, argon and air, the membrane flux of the regenerated membrane was increased, and at the same time, it had the retention ability for both monovalent salts and divalent salts, but the effect was slightly lower than that in Example 1 where both channels were argon; in Example 12, both channels were nitrogen, and the membrane flux of the regenerated membrane was also increased, and its effect was slightly lower than that in Example 1.

[0080] Compared with Example 1, in Comparative Example 1, only the waste reverse osmosis membrane was cleaned. After the waste membrane was treated by plasma, the flux increased by about 3 times. The plasma treatment can realize the reuse of the membrane and extend the service life of the membrane. In Comparative Example 2, oxidation regeneration was carried out using an oxidant. Its ion salt retention effect was significantly weaker than that of plasma treatment, the treatment time was extremely long, the treatment efficiency was low, and strong oxidizing chemical reagents were required during the treatment, which was prone to secondary pollution.

[0081] The regeneration method provided by the present invention regulates the polymer morphology on the surface of the waste reverse osmosis membrane through the physical and chemical synergistic means of plasma etching, converts the waste membrane into a nanofiltration membrane or an ultrafiltration membrane, and at the same time improves the ion salt retention ability compared with the nanofiltration membrane and the ultrafiltration membrane. During the treatment process, no chemical reagents are used, the process is simple, the treatment time is short, and the regeneration efficiency of the waste membrane is greatly improved.

[0082] The specific embodiments described above have further elaborated the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for downgrading and regenerating waste reverse osmosis membranes treated by vacuum plasma, characterized in that, The degradation and regeneration method includes the following steps: After cleaning the waste reverse osmosis membrane, the waste reverse osmosis membrane is fixed in a flat state and subjected to vacuum plasma treatment to obtain a degraded and regenerated membrane.

2. The degradation regeneration method according to claim 1, wherein The pressure of the vacuum plasma treatment is 1 - 200 Pa.

3. The degradation regeneration method according to claim 1 or 2, characterized in that, The power of the vacuum plasma treatment is 50 - 300 W.

4. The degradation and regeneration method according to any one of claims 1-3, characterized in that The time of the vacuum plasma treatment is 60 - 360 s.

5. The degradation regeneration method according to any one of claims 1-4, characterized in that, The working gas of the vacuum plasma treatment includes reactive gas and / or inert gas.

6. The degenerate regeneration method as claimed in claim 5, wherein The reactive gas includes any one or a combination of at least two of air, oxygen, or nitrogen; Preferably, the inert gas includes argon and / or helium.

7. The degradation regeneration method according to any one of claims 1-6, characterized in that The flow rate of the working gas of the vacuum plasma treatment is 20 - 70 sccm.

8. The degradation regeneration method according to any one of claims 1-7, characterized in that, The cleaning method includes rinsing with water; Preferably, the cleaning temperature is 10 - 50 °C.

9. The degradation regeneration method according to any one of claims 1-8, characterized in that, The degradation and regeneration method further includes: soaking the degraded and regenerated membrane in water for storage.

10. The degradation regeneration method according to any one of claims 1-9, characterized in that, The degradation and regeneration method includes the following steps: (1) Clean the waste reverse osmosis membrane with water at a temperature of 10 - 50 °C until the surface dirt is removed to obtain a pretreated waste reverse osmosis membrane; (2) Fix the pretreated waste reverse osmosis membrane on a glass plate, keep it in a flat state, and place it in a vacuum chamber for vacuum plasma treatment. The pressure of the vacuum plasma treatment is 1 - 200 Pa, the power of the vacuum plasma treatment is 90 - 200 W, the vacuum plasma treatment uses reactive gas and / or inert gas as the working gas, the flow rate of the working gas is 20 - 70 sccm, the time of the vacuum plasma treatment is 60 - 360 s. After the vacuum plasma treatment, a degraded and regenerated membrane is obtained, and the degraded and regenerated membrane is soaked in water for storage.

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