Modification method for prolonging service life of pervaporation membrane in seawater

Abstract

The invention belongs to the field of membrane pollution control, and particularly relates to a modification method for prolonging the service life and performance of a pervaporation membrane in seawater. According to the method, the pervaporation membrane is soaked in deionized water for treatment, so that anticorrosive substances on the surface of the membrane are stripped, the soaked pervaporation membrane is pasted in a membrane assembly, then the membrane assembly is soaked in a tannic acid solution for 60 s, and after soaking is finished, the membrane assembly is taken out. The membrane assembly is taken out, the surface of the membrane is washed with deionized water and then moved into a ferric chloride solution to be soaked for 60 s, finally, the surface of the membrane is washed with deionized water, so that the polyphenol coating is successfully attached to the surface of the membrane, and the unique property of the polyphenol coating becomes the key for prolonging the service life of the membrane; when the PH is lower than 3, most-OH groups in the tannic acid are protonated, so that the polyphenol coating is disintegrated and separated from the pervaporation membrane, and pollutants accumulated on the surface of the membrane are removed at the same time. And subsequently. The surface of the pervaporation membrane is coated with a new polyphenol coating again, so that the service life of the pervaporation membrane is prolonged, and the method also has important significance in reducing the treatment cost of desalinated seawater.

Description

Technical Field

[0001] The invention belongs to the field of membrane pollution control, and in particular relates to a modification method for extending the life of a pervaporation membrane in seawater. Technical Background

[0002] Seawater desalination is the best choice to solve the lack of desalination resources in coastal areas, and it has great commercial value. Pervaporation process is one of the processes with the highest interception rate among the current seawater desalination methods. It can use low-grade thermal energy to save more energy consumption, and the pervaporation process has low requirements for the working environment. The application prospect of pervaporation process for seawater desalination technology is very broad.

[0003] Pervaporation is a new type of heat-driven membrane concentration process. Different from the pure pressure-driven membrane process, the driving force of the pervaporation process comes from the vapor pressure difference formed by the temperature of the feed side and the vacuum degree of the permeate side. It only needs to provide the latent heat of vaporization for the phase change from liquid to vapor. Most of the membrane processes used in the pervaporation process are hydrophilic dense membranes. Inorganic salt ions and organic matter in seawater cannot pass through the membrane surface, ensuring the quality of the fresh water produced; therefore, the life of the pervaporation membrane directly affects the efficiency of seawater desalination.

[0004] In order to extend the membrane life of the pervaporation process in seawater desalination, it was found through research that the polyphenol coating formed by mixing tannic acid solution and ferric chloride solution can be easily and stably coated on the surface of the pervaporation membrane, providing a protective layer for the pervaporation base membrane. Although the membrane surface thickness is increased, the polyphenol coating greatly improves the hydrophilicity of the membrane surface and improves the rapid transfer of water molecules, which in turn increases the water flux. And because most of the -OH groups in tannic acid are protonated when the pH is less than 3, the polyphenol coating disintegrates and detaches from the pervaporation membrane, while removing pollutants accumulated on the membrane surface, thereby extending the life of the pervaporation membrane and reducing the treatment cost of desalinated seawater. Summary of the invention

[0005] The purpose of the present invention is to solve the membrane pollution problem of the pervaporation process in desalination of seawater, combine the characteristics of polyphenol coating in membrane modification, and propose a modification method for extending the life of the pervaporation membrane in seawater.

[0006] like Figure 1 As shown, a flow chart of a modification method for extending the life of a pervaporation membrane in seawater specifically comprises the following steps:

[0007] Step 1: Soak the pervaporation membrane in deionized water for 12 h;

[0008] Step 2: prepare 0.24mmol / L tannic acid solution, 1.44mmol / L ferric chloride solution and hydrochloric acid solution with pH=2 respectively;

[0009] Step 3: Fixing the pervaporation membrane soaked in step 1 on the membrane assembly;

[0010] Step 4: Soak the membrane assembly with the pervaporation membrane in step 3 in the tannic acid solution prepared in step 2 for 60 seconds;

[0011] Step 5: Take out the membrane assembly in step 4, rinse the membrane surface with deionized water, and then transfer it to the ferric chloride solution prepared in step 2 for 60 seconds;

[0012] Step 6: Take out the membrane assembly in step 5 and rinse the membrane surface with deionized water, so as to conduct the desalination seawater membrane concentration experiment;

[0013] Step 7: Soak the desalinated seawater membrane assembly obtained in step 6 in the hydrochloric acid solution with a pH of 2 prepared in step 2 for 2 hours, rinse the membrane surface with deionized water, and then transfer it to a deionized water solution for soaking and storage;

[0014] Step 8: Repeat the steps 4 to 7 for the membrane assembly in step 7 to complete the multi-cycle desalination seawater membrane concentration experiment with high pollution resistance.

[0015] The membrane assembly in step three is a plate-type flat plate with a built-in hollow grid, which is used to fix the pervaporation membrane so that the front side of the pervaporation membrane contacts the solution and the back side remains dry.

[0015] The beneficial effects of the present invention are:

[0016] When the pH is lower than 3, most of the -OH groups in tannic acid are protonated, causing the polyphenol coating to disintegrate on the pervaporation membrane. The modified polyphenol coating is completely detached from the pervaporation membrane, and the pollutants accumulated on the membrane surface are also removed. The process can be repeated many times, thereby greatly reducing the contamination of the pervaporation membrane by inorganic salt ions and other substances in seawater, extending the life of the pervaporation membrane, and greatly reducing the cost of desalinating seawater.

[0017] The modification reagents used in the present invention only include ferric chloride, tannic acid and hydrochloric acid, and the dosage of the reagents is extremely small, and the time consumption is short and the operation is simple, which can greatly reduce the modification cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a process flow chart of the present invention.

[0019] Figure 2 It is a comparison chart of the concentration experiments of the modified membrane and the original membrane in three consecutive cycles in the present invention.

[0020] Figure 3 It is a contact angle (hydrophilicity) diagram of the modified membrane and the original membrane in the present invention.

[0021] Figure 4 It is the chemical structural formula diagram of tannic acid in the present invention. DETAILED DESCRIPTION

[0022] The present invention is further described below in conjunction with the accompanying drawings and specific implementation examples, but the protection scope of the present invention is not limited thereby.

[0023] The present invention utilizes tannic acid solution and ferric chloride solution to complex on the membrane surface to form a polyphenol coating, and the polyphenol coating can be removed by hydrochloric acid, and pollutants accumulated on the membrane surface can be removed at the same time, and the process can be repeated for many times, which can effectively prolong the life of the pervaporation membrane in seawater.

[0024] The pervaporation membrane was soaked in deionized water for 12 hours, and 0.24mmol / L tannic acid solution, 1.44mmol / L ferric chloride solution and PH=2 hydrochloric acid solution were prepared respectively. The soaked pervaporation membrane was fixed in the membrane assembly to ensure that the front side of the membrane could contact the solution during the soaking process, while the back side would not contact the solution.

[0025] Furthermore, the membrane assembly with the pervaporation membrane was immersed in the prepared tannic acid solution for 60 seconds, and then the membrane assembly was taken out and the membrane surface was cleaned with deionized water, and then it was moved into the prepared ferric chloride solution for 60 seconds, and then the membrane surface was cleaned with deionized water, and then the desalination seawater membrane concentration experiment could be carried out.

[0026] Furthermore, the pervaporation membrane that has completed the desalination seawater membrane concentration experiment is immersed in a prepared hydrochloric acid solution with a pH of 2 for 2 hours, and then the membrane surface is rinsed with deionized water, and then moved into a deionized water solution for storage. By repeating the above steps, a high-pollution-resistant multi-cycle desalination seawater membrane concentration experiment can be completed.

[0027] Furthermore, the polyphenol-coated membrane and the original membrane were subjected to desalination seawater concentration experiments. To enhance the contrast, both membranes were immersed in a hydrochloric acid solution for cleaning after each cycle. By observing the changes in membrane flux, the effect of the polyphenol coating on extending the life of the desalination seawater pervaporation membrane was determined. The difference between the two can be seen. Figure 2 , Throughout the three consecutive cycles of the experiment, the flux of the polyphenol coated membrane was always much higher than that of the original membrane at the same stage, which shows that the polyphenol coating has a good effect in extending the life of the desalination seawater pervaporation membrane.

[0028] It can be seen from the experimental results that the present invention prolongs the life of the desalinated seawater pervaporation membrane by attaching a polyphenol coating on the membrane surface, and the coating can be easily removed by a hydrochloric acid solution.

[0029] The above description is only an implementation scheme of the present invention. It should be pointed out that for ordinary technicians in this field, appropriate improvements and modifications can be made without departing from the design principles of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A modification method for extending the life of a pervaporation membrane in seawater, characterized in that The specific steps are as follows: Step 1: Soak the pervaporation membrane in deionized water for 12 h; Step 2: prepare 0.24mmol / L tannic acid solution, 1.44mmol / L ferric chloride solution and hydrochloric acid solution with pH=2 respectively; Step 3: Fixing the pervaporation membrane soaked in step 1 on the membrane assembly; Step 4: Soak the membrane assembly with the pervaporation membrane in step 3 in the tannic acid solution prepared in step 2 for 60 seconds; Step 5: Take out the membrane assembly in step 4, rinse the membrane surface with deionized water, and then transfer it to the ferric chloride solution prepared in step 2 for 60 seconds; Step 6: Take out the membrane assembly in step 5 and rinse the membrane surface with deionized water, so as to conduct the desalination seawater membrane concentration experiment; Step 7: Soak the desalinated seawater membrane assembly obtained in step 6 in the hydrochloric acid solution with a pH of 2 prepared in step 2 for 2 hours, rinse the membrane surface with deionized water, and then transfer it to a deionized water solution for soaking and storage; Step 8: Repeat the steps 4 to 7 for the membrane assembly in step 7 to complete the multi-cycle desalination seawater membrane concentration experiment with high pollution resistance.

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