Method for improving performance of reverse osmosis membrane by using hydroxyethyl urea

Abstract

The invention relates to a method for improving the performance of a reverse osmosis membrane by using hydroxyethyl urea, which comprises the following steps of: pretreating the membrane, preparing a hydroxyethyl urea solution, and performing modification treatment (solution impregnation and ultrasonic assistance) to post-treatment. By accurately controlling the solution concentration, the dipping time, the temperature, ultrasonic auxiliary parameters and the like in the hydroxyethylurea modification process, the comprehensive improvement of the hydrophilicity, the anti-pollution performance and the stability of the reverse osmosis membrane is realized, and the method is suitable for industrial production and has very high practicability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of membrane materials, and particularly relates to a method for improving the performance of reverse osmosis membranes by using hydroxyethyl urea. BACKGROUND

[0002] Reverse osmosis membranes are the core components in the field of water treatment today, and are widely used in seawater desalination, industrial pure water preparation, wastewater treatment and many other important fields. With the increasing demand for efficient use of water resources and water quality in various industries, the expectation for the performance of reverse osmosis membranes is also growing. However, existing reverse osmosis membranes still face some problems that need to be solved in practical applications.

[0003] Firstly, in terms of hydrophilicity, many traditional reverse osmosis membranes lack sufficient hydrophilicity. The contact angle of water on the membrane surface is large, and water molecules are difficult to quickly adhere and pass through the membrane pores, which increases the resistance to water transmission and results in low water flux of the membrane. For example, in large-scale seawater desalination projects, low water flux means that more membrane components and higher energy consumption are needed to meet the water production demand, greatly increasing the operating cost.

[0004] Secondly, the anti-pollution performance is also a key problem. In complex water quality environments, organic matter, microorganisms, colloids and other pollutants in the water can easily adsorb on the membrane surface, forming a fouling layer that hinders the passage of water molecules and reduces the separation efficiency of the membrane. Moreover, the accumulation of pollutants can also cause the growth of microorganisms, further corroding the membrane material and shortening the service life of the membrane. For example, when treating industrial wastewater containing high concentrations of organic matter, reverse osmosis membranes often suffer from severe pollution in a short period of time, requiring frequent cleaning and maintenance, or even replacing the membrane elements, which not only affects production efficiency but also increases processing costs.

[0005] Furthermore, the stability of the membrane needs to be improved. Under different environmental conditions such as pH value and temperature, the structure and performance of some reverse osmosis membranes can change. For example, in solutions with high temperature or extreme pH value, the chemical structure of the membrane can be damaged, resulting in a decrease in desalination rate and inability to ensure stable water quality separation effect.

[0006] Currently, to improve the performance of reverse osmosis membranes, common methods include surface coating, blending modification, etc. However, the surface coating method may have the problem of poor adhesion of the coating to the membrane matrix, which can easily fall off during long-term use, affecting the durability of the modification effect. Although blending modification can improve some properties of the membrane to some extent, it may greatly change the original structure of the membrane, leading to a decrease in the selectivity of the membrane, and also may introduce some new impurities, affecting the stability of the membrane.

[0007] In summary, developing a modification method that can effectively improve the hydrophilicity, anti-fouling performance and stability of reverse osmosis membranes without negatively affecting the original structure and performance of the membranes has become a research hotspot and an urgent need in the field of reverse osmosis membrane technology. SUMMARY

[0008] The technical problem to be solved by the present application is to address the problems of insufficient hydrophilicity, poor anti-fouling performance and poor stability of existing reverse osmosis membranes. In order to improve these deficiencies, the present application provides a method for improving the performance of reverse osmosis membranes using hydroxyethyl urea.

[0009] To achieve the above-mentioned purpose, the present application is realized by the following technical scheme: A method for improving the performance of reverse osmosis membranes using hydroxyethyl urea, comprising the following steps: S1: selection and pretreatment of reverse osmosis membranes, selecting reverse osmosis membranes, cutting them, soaking the cut membranes in deionized water to remove impurities on the surface of the membranes, and then removing the drained water; S2: preparation of hydroxyethyl urea solution, accurately weighing a certain amount of hydroxyethyl urea solid, dissolving it in deionized water, and thoroughly stirring to prepare a hydroxyethyl urea solution with a concentration of 1.5%-2.5%; S3: modification treatment, completely immersing the pretreated reverse osmosis membranes in the prepared hydroxyethyl urea solution, placing the container in a constant temperature water bath device during the immersion process, keeping the temperature at 35℃-40℃, controlling the immersion time at 1.5-2.5H, and gently shaking the container every 0.5H to make the solution concentration more uniform; S4: post-treatment, including cleaning and drying, taking out the modified membrane from the hydroxyethyl urea solution, rinsing the membrane surface with deionized water to remove unreacted hydroxyethyl urea and possible by-products, gently rubbing the membrane surface during the rinsing process to ensure thorough cleaning, and naturally air-drying the cleaned membrane in a well-ventilated environment.

[0010] As a preferred scheme, the S3 step further includes ultrasonic assisted treatment. After 0.5 hours of immersion, the ultrasonic generator is turned on, the frequency is set to 25kHz-35kHz, and the ultrasonic treatment time is 15-30 minutes, and the state of the membrane is observed in real time during the ultrasonic process.

[0011] As a preferred scheme, the drying process in the S4 step can place the membrane in a vacuum drying oven at a temperature of 40℃ for 10-15 minutes to make the membrane reach a constant weight, obtaining the modified reverse osmosis membrane.

[0012] As a preferred scheme, the soaking time of the cut membrane in deionized water in the S1 step is controlled at 1-2.5H.

[0013] As a preferred solution, the heating is performed during the preparation of the solution in the S2 step, and the temperature of the heating is controlled below 50°C.

[0014] Compared with the prior art, the application has the beneficial effects that: the hydroxyethyl urea is innovatively selected as the modifier of the reverse osmosis membrane, and through the accurate control of the solution concentration, the immersion time, the temperature, and the ultrasonic auxiliary parameters in the modification process of the hydroxyethyl urea, the comprehensive improvement of the hydrophilicity, the anti-pollution performance and the stability of the reverse osmosis membrane is realized, which is suitable for industrial production and has strong practicability. DETAILED DESCRIPTION

[0015] The technical solutions of the application are further described and illustrated below through examples.

[0016] A method for improving the performance of a reverse osmosis membrane by using hydroxyethyl urea, comprising the following steps: S1: selection and pretreatment of the reverse osmosis membrane, selecting the reverse osmosis membrane, cutting it, and soaking the cut membrane in deionized water for 1-2.5 h to remove impurities on the surface of the membrane, and then removing the drained water; S2: preparation of a hydroxyethyl urea solution, accurately weighing a certain amount of hydroxyethyl urea solid, dissolving it in deionized water, and fully stirring to prepare a hydroxyethyl urea solution with a concentration of 1.5%-2.5%, and heating during the preparation of the solution, with the temperature of the heating controlled below 50°C; S3: modification treatment, completely immersing the pretreated reverse osmosis membrane in the prepared hydroxyethyl urea solution, placing the container in a constant temperature water bath device during the immersion process to maintain the temperature at 35°C-40°C, controlling the immersion time at 1.5-2.5 h, and gently shaking the container every 0.5 h during the immersion process to make the solution concentration more uniform; ultrasonic auxiliary treatment, starting the ultrasonic generator after 0.5 h of immersion, setting the frequency to 25kHz-35kHz, and setting the ultrasonic treatment time to 15 minutes-30 minutes, and observing the state of the membrane in real time during the ultrasonic process.

[0017] S4: post-treatment, including cleaning and drying, taking out the modified membrane from the hydroxyethyl urea solution, rinsing the surface of the membrane with deionized water to remove unreacted hydroxyethyl urea and possible by-products, gently rubbing the surface of the membrane during the rinsing process to ensure thorough cleaning, and placing the cleaned membrane in a well-ventilated environment for natural air drying, or placing the membrane in a vacuum drying oven for drying at a temperature of 40°C for 10-15 minutes to make the membrane reach a constant weight, and obtaining the modified reverse osmosis membrane.

[0018] Based on some core parameter data in the above steps, the following parameter adjustable range is proposed as the basis for the design of the examples: • Hydroxyethyl urea solution concentration: 1.5% - 2.5% • Immersion temperature: 35°C - 40°C • Immersion time: 1.5h - 2.5h • Ultrasonic frequency: 25kHz - 35kHz • Ultrasonic time: 15min - 30min • Pretreatment soaking time: 1h - 2.5h (fixed at 1.5h to eliminate interference variables) • Post-treatment method: uniformly use 40°C vacuum drying for 12min (fixed process to ensure comparability of results) Example

[0019] S1: Selection and pretreatment of reverse osmosis membrane, immerse the membrane in deionized water for 1.5h; S2: Preparation of hydroxyethyl urea solution, control the concentration of hydroxyethyl urea solution at 0%, which is deionized water; S3: Modification, immerse the pretreated reverse osmosis membrane in the prepared hydroxyethyl urea solution, keep the immersion temperature at 37°C during the immersion process, and control the immersion time at 2H (take the middle value); ultrasonic assisted treatment, start the ultrasonic generator after 0.5 hours of immersion, set the frequency to 0kHz (i.e. no ultrasonic), and the ultrasonic treatment time is 0 minute; S4: Post-treatment, cleaning and drying, place the cleaned membrane in a vacuum drying oven, dry at a temperature of 40°C for 12 minutes, and make the membrane reach a constant weight to obtain the modified reverse osmosis membrane.

[0020] Conclusion: The water flux improvement rate of the reverse osmosis membrane produced by the above steps is 0%, the 24h flux decay rate is 45%, and the desalination rate fluctuation is >10%. Based on this group of data as the control group, the influence of the concentration of hydroxyethyl urea solution, immersion time, temperature, ultrasonic frequency and time on the water flux improvement rate, 24h flux decay rate and desalination rate is verified. Example

[0021] S1: Selection and pretreatment of reverse osmosis membrane, immerse the membrane in deionized water for 1.5h; S2: Preparation of hydroxyethyl urea solution, control the concentration of hydroxyethyl urea solution at 1.5%; S3: Modification, immerse the pretreated reverse osmosis membrane in the prepared hydroxyethyl urea solution, keep the immersion temperature at 35°C during the immersion process, and control the immersion time at 1.5H; ultrasonic assisted treatment, start the ultrasonic generator after 0.5 hours of immersion, set the frequency to 25kHz, and the ultrasonic treatment time is 15 minutes; S4: Post-treatment, cleaning and drying, the cleaned membrane is placed in a vacuum drying oven, dried at a temperature of 40°C for 12 minutes, and the membrane is made to reach a constant weight to obtain the modified reverse osmosis membrane.

[0022] Conclusion: The reverse osmosis membrane produced by the above steps has a water flux improvement rate of 1.2%, a 24h flux decay rate of 38%, and a desalination rate fluctuation of 8.5%. Example

[0023] S1: Selection and pretreatment of reverse osmosis membrane, the membrane is soaked in deionized water for 1.5h; S2: Preparation of hydroxyethyl urea solution, control the concentration of hydroxyethyl urea solution to be 1.5%; S3: Modification treatment, the pretreated reverse osmosis membrane is completely immersed in the prepared hydroxyethyl urea solution, the immersion temperature is kept at 40°C during the immersion process, and the immersion time is controlled to be 2.5H; ultrasonic assisted treatment, after 0.5 hours of immersion, the ultrasonic generator is turned on, the frequency is set to 35kHz, and the ultrasonic treatment time is 30 minutes; S4: Post-treatment, cleaning and drying, the cleaned membrane is placed in a vacuum drying oven, dried at a temperature of 40°C for 12 minutes, and the membrane is made to reach a constant weight to obtain the modified reverse osmosis membrane.

[0024] Conclusion: The reverse osmosis membrane produced by the above steps has a water flux improvement rate of 1.8%, a 24h flux decay rate of 25%, and a desalination rate fluctuation of 5.2%. Example

[0025] S1: Selection and pretreatment of reverse osmosis membrane, the membrane is soaked in deionized water for 1.5h; S2: Preparation of hydroxyethyl urea solution, control the concentration of hydroxyethyl urea solution to be 2.0%; S3: Modification treatment, the pretreated reverse osmosis membrane is completely immersed in the prepared hydroxyethyl urea solution, the immersion temperature is kept at 35°C during the immersion process, and the immersion time is controlled to be 2.5H; ultrasonic assisted treatment, after 0.5 hours of immersion, the ultrasonic generator is turned on, the frequency is set to 25kHz, and the ultrasonic treatment time is 30 minutes; S4: Post-treatment, cleaning and drying, the cleaned membrane is placed in a vacuum drying oven, dried at a temperature of 40°C for 12 minutes, and the membrane is made to reach a constant weight to obtain the modified reverse osmosis membrane.

[0026] Conclusion: The reverse osmosis membrane produced by the above steps has a water flux improvement rate of 1.6%, a 24h flux decay rate of 28%, and a desalination rate fluctuation of 6.1%. Example

[0027] S1: selection and pretreatment of reverse osmosis membrane, immerse the membrane in deionized water for 1.5h; S2: preparation of hydroxyethyl urea solution, control the concentration of hydroxyethyl urea solution at 2.0%; S3: modification treatment, immerse the pretreated reverse osmosis membrane in the prepared hydroxyethyl urea solution completely, keep the immersion temperature at 38℃ during the immersion process, and control the immersion time at 2.0h; ultrasonic assisted treatment, start the ultrasonic generator after 0.5h of immersion, set the frequency at 30kHz, and the ultrasonic treatment time is 22min; S4: post-treatment, cleaning and drying, place the cleaned membrane into a vacuum drying oven, dry at a temperature of 40℃ for 12min, so that the membrane reaches a constant weight, and obtain the modified reverse osmosis membrane.

[0028] Conclusion: the reverse osmosis membrane produced by the above steps has a water flux improvement rate of 2.1%, a 24h flux decay rate of 18%, and a desalination rate fluctuation of 3.5%. Example

[0029] S1: selection and pretreatment of reverse osmosis membrane, immerse the membrane in deionized water for 1.5h; S2: preparation of hydroxyethyl urea solution, control the concentration of hydroxyethyl urea solution at 2.0%; S3: modification treatment, immerse the pretreated reverse osmosis membrane in the prepared hydroxyethyl urea solution completely, keep the immersion temperature at 40℃ during the immersion process, and control the immersion time at 1.5h; ultrasonic assisted treatment, start the ultrasonic generator after 0.5h of immersion, set the frequency at 35kHz, and the ultrasonic treatment time is 15min; S4: post-treatment, cleaning and drying, place the cleaned membrane into a vacuum drying oven, dry at a temperature of 40℃ for 12min, so that the membrane reaches a constant weight, and obtain the modified reverse osmosis membrane.

[0030] Conclusion: the reverse osmosis membrane produced by the above steps has a water flux improvement rate of 1.9%, a 24h flux decay rate of 22%, and a desalination rate fluctuation of 4.8%. Example

[0031] S1: selection and pretreatment of reverse osmosis membrane, immerse the membrane in deionized water for 1.5h; S2: preparation of hydroxyethyl urea solution, control the concentration of hydroxyethyl urea solution at 2.5%; S3: modification treatment, the pretreated reverse osmosis membrane is completely immersed in the prepared hydroxyethyl urea solution, the immersion temperature is kept at 35℃ during the immersion process, and the immersion time is controlled at 2.0H; ultrasonic auxiliary treatment, after the immersion process is performed for 0.5 hours, the ultrasonic generator is started, the frequency is set to 35kHz, and the ultrasonic treatment time is 30 minutes; S4: post-treatment, cleaning and drying, the cleaned membrane is placed into a vacuum drying box, dried at a temperature of 40℃ for 12 minutes, the membrane is made to reach a constant weight, and a modified reverse osmosis membrane is obtained.

[0032] Conclusion: The water flux improvement rate of the reverse osmosis membrane produced through the above steps is 2.3%, the 24h flux attenuation rate is 16%, and the desalination rate fluctuation is 3.2%. Example

[0033] S1: selection and pretreatment of the reverse osmosis membrane, the membrane is soaked in deionized water for 1.5h; S2: preparation of the hydroxyethyl urea solution, the concentration of the hydroxyethyl urea solution is controlled to be 2.5%; S3: modification treatment, the pretreated reverse osmosis membrane is completely immersed in the prepared hydroxyethyl urea solution, the immersion temperature is kept at 40℃ during the immersion process, and the immersion time is controlled at 2.5H; ultrasonic auxiliary treatment, after the immersion process is performed for 0.5 hours, the ultrasonic generator is started, the frequency is set to 30kHz, and the ultrasonic treatment time is 22 minutes; S4: post-treatment, cleaning and drying, the cleaned membrane is placed into a vacuum drying box, dried at a temperature of 40℃ for 12 minutes, the membrane is made to reach a constant weight, and a modified reverse osmosis membrane is obtained.

[0034] Conclusion: The water flux improvement rate of the reverse osmosis membrane produced through the above steps is 2.5%, the 24h flux attenuation rate is 15%, and the desalination rate fluctuation is 2.8%.

[0035] The above 8 groups of examples are arranged into a table as follows: From the above data, the following conclusions can be drawn: 1. The concentration of the hydroxyethyl urea solution is positively correlated with the water flux, which increases from 1.5% to 2.5%, and the water flux improvement rate increases from 1.2%-1.8% to 2.3%-2.5%, and is positively correlated with the anti-pollution property: when the concentration is 2.5%, the 24h flux attenuation rate is as low as 15%-16%, which is much lower than 25%-38% of the concentration of 1.5%, and when the concentration exceeds 2.5%, the membrane pores may be blocked, therefore, 2.5% is the optimal upper limit; 2. The impregnation temperature is positively correlated with the water flux and the desalination rate fluctuation. Under the same concentration of hydroxyethyl urea solution, the water flux at 40℃ is 0.2%-0.5% higher than that at 35℃ (as can be obtained by comparing Examples 2 and 3), and the desalination rate fluctuation range is smaller at 40℃ (as can be obtained by comparing Examples 7 and 8). Higher temperature can promote the chemical bonding reaction of hydroxyethyl urea molecules with the membrane surface and improve the modification uniformity; 3. The impregnation time is positively correlated with the water flux and the desalination rate fluctuation. Under the same concentration of hydroxyethyl urea solution, the water flux of 2.5h impregnation is 0.3%-0.5% higher than that of 1.5h, and the flux decay rate is reduced by 3%-5% (as can be obtained by comparing Examples 6 and 8). Longer impregnation time ensures that hydroxyethyl urea penetrates and reacts with the membrane surface sufficiently, avoiding insufficient local modification; 4. The effect of ultrasonic frequency is as follows: 30kHz-35kHz is better than 25kHz. Under the same conditions, the desalination rate fluctuation range at 30kHz is 1.5%-2% smaller than that at 25kHz (as can be obtained by comparing Examples 4 and 5). Medium-high frequency ultrasonic can promote convection of the solution, making hydroxyethyl urea more uniformly contact the membrane surface and reducing local concentration difference; 5. The effect of ultrasonic time is as follows: 22min-30min is better than 15min. The flux decay rate of 30min ultrasonic is 4%-6% lower than that of 15min (as can be obtained by comparing Examples 2 and 3). Sufficient ultrasonic time can break the bubbles on the membrane surface and enhance the adsorption of the modifier, but more than 30min may damage the membrane structure.

[0036] Based on the above-mentioned 8 groups of examples, the optimal choice should be Example 5, and the reasons are as follows: The performance is close to the maximum value: the water flux is increased by 2.1% (only lower than 2.5% of Example 8), the flux decay rate is 18% (only higher than 15%-16% of Examples 7-8), and the desalination rate fluctuation is 3.5% (satisfying the stability requirement); The cost is more optimal: the 2.0% concentration reduces the raw material cost by 20% compared with 2.5%, and the 2.0h impregnation time improves the production efficiency by 20% compared with 2.5h; The operation stability: the temperature of 38℃ and the ultrasonic time of 22min do not need precise control, reducing the operation difficulty in industrial production.

[0037] Therefore, the present application has the following effects: Significant improvement of hydrophilicity: After modification by hydroxyethyl urea, the hydrophilicity of the reverse osmosis membrane is greatly improved. Due to the strong hydrogen bond interaction between the hydroxyl groups in the hydroxyethyl urea molecule and water molecules, the contact angle of water on the membrane surface is significantly reduced. For example, the contact angle is reduced from 75° before modification to less than 45°, enabling water molecules to adhere to the membrane surface more quickly and pass through the membrane pores, thereby effectively increasing the water flux of the membrane. According to experimental tests, compared with the unmodified reverse osmosis membrane, the water flux is increased by 1.5%-2.5%, and more water can be treated in the same time, greatly improving the water treatment efficiency.

[0038] Enhanced anti-pollution performance: The presence of urea groups endows the modified reverse osmosis membrane with good anti-pollution performance. Urea groups can interact with common pollutants in water, such as organic matter and microorganisms, preventing their adsorption and deposition on the membrane surface. When treating simulated wastewater containing high concentrations of organic matter, the flux decay of the reverse osmosis membrane modified by hydroxyethyl urea is only 15% after 24 hours of continuous operation, while the flux decay of the unmodified membrane reaches 45%. This indicates that the modified membrane can effectively resist the erosion of pollutants, prolong the service life of the membrane, and reduce the cost caused by frequent cleaning and replacement of membrane components.

[0039] Improved stability: The stable chemical bonding between hydroxyethyl urea and the membrane material enhances the structural stability of the membrane. Under different pH values and temperature conditions, the modified reverse osmosis membrane can maintain more stable performance. For example, within a pH range of 5.0-7.5 and a temperature range of 25℃-40℃, the desalination rate of the modified membrane fluctuates by less than 3%, while the desalination rate of the unmodified membrane fluctuates by more than 10%. This enables the modified reverse osmosis membrane to operate stably under a wider range of water quality and environmental conditions, expanding its application range.

[0040] Environmentally friendly and simple process: Hydroxyethyl urea is a relatively environmentally friendly compound itself and does not introduce harmful impurities during the modification process, making it environmentally friendly. At the same time, the modification method used in the present invention is simple to operate and does not require complex equipment and high costs, making it easy to apply in actual production and having good economic and social benefits.

[0041] The present invention is not limited to the above embodiments, and based on the technical solutions disclosed in the present invention, those skilled in the art can make some substitutions and modifications to some technical features without creative labor, and these substitutions and modifications are within the protection scope of the present invention.

Claims

1. A method for improving the performance of reverse osmosis membranes using hydroxyethyl urea, characterized in that, The steps include the following: S1: Selection and pretreatment of reverse osmosis membrane. Select a reverse osmosis membrane, cut it, soak the cut membrane in deionized water to remove impurities from the membrane surface, and then drain the water. S2: Preparation of hydroxyethyl urea solution: Accurately weigh a certain amount of solid hydroxyethyl urea, dissolve it in deionized water, stir thoroughly, and prepare a hydroxyethyl urea solution with a concentration of 1.5%-2.5%. S3: Modification treatment. The pretreated reverse osmosis membrane is completely immersed in the prepared hydroxyethyl urea solution. During the immersion process, the container is placed in a constant temperature water bath to maintain the temperature at 35℃-40℃. The immersion time is controlled at 1.5-2.5 hours. During this period, the container is gently shaken every 0.5 hours to make the solution concentration distribution more uniform. S4: Post-treatment, including cleaning and drying, involves removing the modified membrane from the hydroxyethyl urea solution and rinsing the membrane surface with deionized water to remove unreacted hydroxyethyl urea and any possible byproducts. During rinsing, gently rub the membrane surface to ensure thorough cleaning. Place the cleaned membrane in a well-ventilated environment to air dry naturally.

2. The method for improving the performance of a reverse osmosis membrane using hydroxyethyl urea according to claim 1, characterized in that: The S3 step also includes ultrasonic-assisted treatment. After 0.5 hours of impregnation, the ultrasonic generator is turned on, the frequency is set to 25kHz-35kHz, and the ultrasonic treatment time is 15 minutes-30 minutes. During the ultrasonic process, the condition of the membrane should be observed in real time.

3. The method for improving the performance of a reverse osmosis membrane using hydroxyethyl urea according to claim 1, characterized in that: The drying process in step S4 involves placing the membrane in a vacuum drying oven and drying it at 40°C for 10-15 minutes to achieve a constant weight, thus obtaining the modified reverse osmosis membrane.

4. The method for improving the performance of a reverse osmosis membrane using hydroxyethyl urea according to claim 1, characterized in that: In step S1, the soaking time of the cut membrane in deionized water is controlled to be 1-2.5 hours.

5. The method for improving the performance of a reverse osmosis membrane using hydroxyethyl urea according to claim 1, characterized in that: In step S2, heating is performed during the preparation of the solution, and the heating temperature is controlled below 50°C.