An additive for membrane, a seawater desalination membrane, and a preparation method and application thereof

Abstract

The present invention provides a preparation method of an additive for a membrane, comprising the steps of: S1, mixing ore materials and polymers into a polar small molecule solvent together to obtain a liquid to be treated; the ore materials include kaolinite or montmorillonite; the polymers include one or more of polyacrylic acid, polyvinyl alcohol, gallic acid and tannic acid; the mass ratio of the ore materials to the polymers is 1:0.2 - 2, and the mass-volume ratio of the ore materials to the polar small molecule solvent is 60 - 150 mg: 30 ml; S2, performing ultrasonic liquid-phase exfoliation treatment on the liquid to be treated to obtain a treated liquid; S3, performing solid-liquid separation on the treated liquid, and taking the upper-layer liquid as the additive for the membrane. The present invention uses the additive for the membrane in a seawater desalination membrane, which can enable the seawater desalination membrane to have a high water flux and rejection rate during forward osmosis.

Description

Technical Field

[0001] The present invention relates to the field of seawater desalination, and particularly to an additive for membranes, a seawater desalination membrane, and their preparation methods and applications. Background Art

[0002] Water shortage is a worldwide common phenomenon. According to statistics, there are more than 100 countries in the world suffering from varying degrees of water shortage, and 28 countries in the world are listed as water-deficient or severely water-deficient countries. In another 30 years, the number of water-deficient countries will reach 40 - 52, and the water-deficient population will increase by more than 8 times, reaching 2.8 billion to 3.3 billion. In countries and regions with severe freshwater shortage, it even affects people's basic survival.

[0003] Among the existing total water volume in the world, seawater accounts for about 97%. Using seawater desalination technology to obtain fresh water from the sea is the current main development trend. At present, seawater desalination experiments are usually carried out by forward osmosis or reverse osmosis methods. However, limited by the performance of seawater desalination membranes such as water flux and rejection rate, the current seawater desalination experiment results are not good, and the reverse osmosis process is prone to generate large energy consumption.

[0004] In view of this, it is necessary to provide an additive for membranes, a seawater desalination membrane, and their preparation methods and applications to solve or at least alleviate the technical defect that the water flux and rejection rate of the seawater desalination membrane are relatively low. Summary of the Invention

[0005] The main purpose of the present invention is to provide an additive for membranes, a seawater desalination membrane, and their preparation methods and applications, aiming to solve the technical problem that the water flux and rejection rate of the seawater desalination membrane are relatively low.

[0006] To achieve the above purpose, the present invention provides a preparation method of an additive for membranes, including the steps of:

[0007] S1, mixing ore materials and polymers into a polar small molecule solvent together to obtain a liquid to be treated;

[0008] The ore materials include kaolinite or montmorillonite;

[0009] The polymers include one or more of polyacrylic acid, polyvinyl alcohol, gallic acid, and tannic acid;

[0010] The mass ratio of the ore materials to the polymers is 1:0.2 - 2, and the mass-volume ratio of the ore materials to the polar small molecule solvent is 60 - 150 mg:30 ml;

[0011] S2, performing ultrasonic liquid-phase exfoliation treatment on the liquid to be treated to obtain a treated liquid;

[0012] S3, performing solid-liquid separation on the treated liquid, and taking the upper-layer liquid as the additive for membranes.

[0013] Furthermore, the ultrasonic liquid-phase exfoliation treatment includes: exfoliating the liquid to be treated at an ultrasonic power of 300 - 500 W for 12 - 24 h.

[0014] Furthermore, the polar small molecule solvent includes one or more of water, methanol, and isopropanol.

[0015] The present invention also provides a membrane additive, which is prepared by using the preparation method of the membrane additive described in any one of the above.

[0016] The present invention also provides a preparation method of a seawater desalination membrane, including: passing the membrane additive described in any one of the above through a microfiltration membrane, so that the active components in the membrane additive are loaded onto the microfiltration membrane to obtain the seawater desalination membrane.

[0017] Furthermore, the loading method includes vacuum loading.

[0018] Furthermore, the volume of the membrane additive: the cross-sectional area of the microfiltration membrane is 1 - 2 mL:1 cm 2 .

[0019] The present invention also provides a seawater desalination membrane, which is prepared by using the preparation method of the seawater desalination membrane described in any one of the above.

[0020] The present invention also provides an application of the membrane additive described in any one of the above and / or the seawater desalination membrane described in any one of the above in desalinated water.

[0021] Furthermore, the desalination of the brine is carried out by the forward osmosis method.

[0022] Compared with the prior art, the present invention has at least the following advantages:

[0023] By alternatively adding kaolinite and montmorillonite to a polymer into a polar small molecule solvent and performing ultrasonic exfoliation, the present invention can obtain an additive capable of improving the membrane flux and rejection rate, thereby obtaining an efficient seawater desalination membrane, which has strong applicability in the field of seawater desalination.

[0024] Moreover, the polymers in the present invention are selected from polyacrylic acid, polyvinyl alcohol, gallic acid, and tannic acid, which have hydrophilic groups such as carboxyl and hydroxyl groups. When combined with kaolinite or montmorillonite, they can greatly improve the flux and selective separation performance of the membrane.

[0025] The polar small molecule solvent in the present invention is selected from one of water, methanol, and isopropanol, which can make the morphology of the obtained kaolinite / montmorillonite nanosheets more regular without affecting the structural properties of the kaolinite and montmorillonite nanosheets.

[0026] In addition, both the kaolinite and montmorillonite required by the present invention can be obtained from coal gangue and coal slime. They have a wide range of sources and low prices, and can be used to dispose of solid wastes such as coal gangue and coal slime. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0028] Figure 1 It is the SEM diagram of the ground kaolinite in Embodiments 1-4 of the present invention and the ground montmorillonite in Embodiments 5-8; wherein, (a) is the SEM diagram of the ground kaolinite in Embodiments 1-4, and (b) is the SEM diagram of the ground montmorillonite in Embodiments 5-8;

[0029] Figure 2 It is the infrared diagram of the seawater desalination membrane in Embodiments 1-8 of the present invention.

[0030] The realization, functional characteristics and advantages of the objectives of the present invention will be further described in conjunction with the embodiments with reference to the drawings. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0032] Moreover, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that those of ordinary skill in the art can implement them. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0033] The present invention provides a preparation method of a membrane additive, including the steps of:

[0034] S1, mixing the ore material and the polymer into a polar small molecule solvent together to obtain a liquid to be treated;

[0035] The ore material is kaolinite or montmorillonite, and both the kaolinite and montmorillonite can be obtained from coal gangue or coal slime.

[0036] The polymer is one or more of polyacrylic acid, polyvinyl alcohol, gallic acid, and tannic acid.

[0037] The mass ratio of the mineral material to the polymer is 1:0.2 - 2; for example, the mass ratio of the mineral material to the polymer can be 1:0.2, 1:1, or 1:2, as well as 1:0.2 - 1, or 1:1 - 2.

[0038] The mass - volume ratio of the mineral material to the polar small - molecule solvent is 60 - 150 mg:30 ml; for example, it can be 60 mg:30 ml.

[0039] The polar small - molecule solvent can include or be one or more of water, methanol, and isopropanol.

[0040] S2. Perform ultrasonic liquid - phase exfoliation treatment on the liquid to be treated to obtain a treated liquid.

[0041] The ultrasonic liquid - phase exfoliation treatment includes: exfoliating the liquid to be treated for 12 - 24 h at an ultrasonic power of 300 - 500 W; the ultrasonic liquid - phase exfoliation treatment can be carried out in an ultrasonic cleaner.

[0042] S3. Perform solid - liquid separation on the treated liquid, and take the upper - layer liquid (supernatant) as the membrane additive. The method of solid - liquid separation can be to let it stand for 10 - 40 minutes or centrifuge it at 3000 - 5000 rpm for 3 minutes.

[0043] It should be understood that in the present invention, the mineral material is specifically defined as kaolinite or montmorillonite. In some known mechanisms of the present invention, since kaolinite / montmorillonite powder is a crystal with a significant layered structure, the bubbles and cavities generated by ultrasound in the solution, when they burst, produce high - energy impacts that cause the three - dimensional layered crystal to undergo interlayer dissociation, and thus monolayer or few - layer nanosheet materials can be produced.

[0044] However, it should be noted that the present invention has made further improvements on the basis of traditional ultrasonic liquid - phase exfoliation. With the help of the added specific polymer and polar small - molecule solvent, the interlayer force of the crystal is weakened and its interlayer spacing is increased, effectively assisting the process of liquid - phase ultrasonic exfoliation.

[0045] The present invention also provides a membrane additive, which is prepared by using the preparation method of the membrane additive described in any of the above embodiments.

[0046] Based on the membrane additive, the present invention provides a method for preparing a seawater desalination membrane, comprising: passing the membrane additive as described in any of the above embodiments through a microporous filtration membrane, so that the active ingredient in the membrane additive is loaded onto the microporous filtration membrane to obtain the seawater desalination membrane; the active ingredient is a substance that can be loaded onto the microporous filtration membrane after ultrasonic exfoliation.

[0047] The loading method includes vacuum loading. Specifically, the microporous filtration membrane can be placed at the bottom of the membrane additive, and then a vacuum pump is used to evacuate from the lower part of the microporous filtration membrane (under closed conditions), so that the membrane additive passes through the microporous filtration membrane from top to bottom, and the active ingredient in the membrane additive is loaded into the microporous filtration membrane.

[0048] The microporous filtration membrane involved in the present invention is a mixed cellulose (MCE) membrane (Mixed Cellulose Ester (MCE) Membrane), which is sourced from Tianjin Jinteng Experimental Equipment Co., Ltd.; those skilled in the art should know that the mixed cellulose (MCE) membrane is a commonly used aqueous membrane, which is composed of a mixture of cellulose nitrate ester and cellulose acetate ester.

[0049] When performing the loading, the volume of the membrane additive: the cross-sectional area of the microporous filtration membrane can be 1-2 mL: 1 cm 2 . It should be noted that the cross-sectional area of the microporous filtration membrane is the water-permeable area of the microporous filtration membrane. Exemplarily, the cross-section of the microporous filtration membrane can be a circular surface, the diameter of the circular surface can be 50 mm; the pore diameter of the microporous filtration membrane can be 0.2 um.

[0050] The present invention also provides a seawater desalination membrane, which is prepared by using the method for preparing a seawater desalination membrane as described in any of the above embodiments.

[0051] Based on the efficacy of the membrane additive and the performance of the seawater desalination membrane, the present invention provides an application of the membrane additive as described in any of the above embodiments and / or the seawater desalination membrane as described in any of the embodiments in desalinating brine, and the brine can be seawater.

[0052] In the specific application process, the reverse osmosis method or the forward osmosis method can be adopted.

[0053] Among them, the reverse osmosis method has developed most rapidly in the desalination of brine (seawater). In the reverse osmosis method, the hydrostatic pressure forces the brine to pass through the semipermeable membrane, and the salt dissolved in the water is blocked on one side of the membrane, while the fresh water finally flows to the other side of the membrane.

[0054] However, the reverse osmosis method is restricted by the low freshwater recovery rate and the high cost caused by energy consumption. Commercially, approximately 40% of seawater and 80% of saline groundwater can be recovered as fresh water, with the by-product being concentrated salt. The factory requires 3 to 10 kilowatt-hours of electricity to produce 1,000 liters of fresh water, which is equivalent to the energy consumed by an electric clothes dryer several times, and most of this energy is used to pass the brine through the membrane.

[0055] Considering the energy consumption of the reverse osmosis method and the relatively low rejection rate of substances such as sodium chloride by the reverse osmosis method. And in view of the excellent forward osmosis performance of the seawater desalination membrane provided by the invention, therefore, it is preferred to use the seawater desalination membrane in the present invention for the forward osmosis method, that is, to desalinate the brine by the forward osmosis method.

[0056] Exemplarily, in the actual application process, the forward osmosis method can be: bringing the feed liquid (brine) into contact with one side of the seawater desalination membrane, and during the contact process, bringing the other side of the seawater desalination membrane into contact with the driving liquid; the osmotic pressure of the feed liquid (brine) is lower than the osmotic pressure of the driving liquid, so that the water in the feed liquid flows into the driving liquid, realizing the separation of water and substances such as sodium chloride in the feed liquid, providing a basis for the desalination of the feed liquid (brine).

[0057] For example, inject the feed liquid into one end of a U-shaped tube, inject the driving liquid into the other end, and separate the feed liquid and the driving liquid with the seawater desalination membrane, and the seawater desalination membrane is located in the middle of the U-shaped tube.

[0058] To facilitate a further understanding of the invention, the following is an example for illustration:

[0059] Example 1

[0060] 1. Mix 60 mg of kaolinite and a set amount of polyacrylic acid into 30 mL of water to obtain the liquid to be treated; among them, the SEM image of kaolinite is as shown in Figure 1 part (a) of the figure, and the kaolinite is ground with a grinder before use and sieved through a 60-mesh sieve.

[0061] After subjecting the liquid to be treated to ultrasonic liquid-phase exfoliation for 16 h under the condition of an ultrasonic power of 400 W, and then performing solid-liquid separation by standing for 20 minutes, the supernatant is taken as the membrane additive.

[0062] Among them, the set amounts are 12 mg, 60 mg, and 120 mg respectively (corresponding to the concentrations of polyacrylic acid being 0.4 mg / mL, 2 mg / mL, and 4 mg / mL in sequence), and all the experiments in this example are carried out with different set amounts (each set amount corresponds to one experiment).

[0063] 2. Through vacuum filtration with a vacuum pump, all membranes are filtered through a microporous filtration membrane with an additive during each experiment, so that the active ingredients in the membrane additive are loaded into the microporous filtration membrane, obtaining a seawater desalination membrane.

[0064] Among them, the microporous filtration membrane is a mixed cellulose (MCE) membrane (Mixed Cellulose Ester (MCE) Membrane), with a pore size of 0.2 μm, a diameter of 50 mm, circular, and is sourced from Tianjin Jinteng Experimental Equipment Co., Ltd.

[0065] 3. Conduct a forward osmosis experiment on the seawater desalination membrane in a U-shaped tube for 4 hours, and measure its water flux and rejection rate of sodium chloride; among them, one side of the seawater desalination membrane is 50 mL of 3.5 wt% sodium chloride solution, and the other side is 50 mL of deionized water.

[0066] 4. Take the seawater desalination membranes of the same batch, and make 100 mL of deionized water pass through the seawater desalination membrane from top to bottom under the condition of vacuum filtration, and measure the filtration flux of the seawater desalination membrane for water.

[0067] The test results corresponding to different concentrations of polyacrylic acid in this example are shown in the following table:

[0068] Kaolinite + Polyacrylic Acid with Different Concentrations Rejection Rate % <![CDATA[Water flux L / m 2 ·h]]> <![CDATA[Filtration flux L / m 2 ·h·bar]]> 0.4 mg / ml 93.91 1.39 2536.50 2 mg / ml 94.02 1.74 3049.19 4 mg / ml 95.02 2.08 3980.89

[0069] Example 2

[0070] Compared with Example 1, in this example, only polyacrylic acid is replaced by polyvinyl alcohol, and other conditions remain unchanged.

[0071] The test results corresponding to different concentrations of polyvinyl alcohol in this example are shown in the following table:

[0072] Kaolinite + Polyvinyl Alcohol with Different Concentrations Rejection Rate % <![CDATA[Water flux L / m 2 ·h]]> <![CDATA[Filtration flux L / m 2 ·h·bar]]> 0.4 mg / ml 94.91 0.35 203.28 2 mg / ml 94.83 0.35 15.92 4 mg / ml 94.81 0.35 6.63

[0073] Example 3

[0074] Compared with Example 1, in this example, only polyacrylic acid is replaced by gallic acid, and other conditions remain unchanged.

[0075] The test results corresponding to different concentrations of gallic acid in this example are shown in the following table:

[0076] Kaolinite + Gallic Acid with Different Concentrations Rejection Rate % <![CDATA[Water flux L / m 2 ·h]]> <![CDATA[Filtration flux L / m 2 ·h·bar]]> 0.4 mg / ml 94.63 1.39 4941.80 2 mg / ml 95.84 0.69 5211.35 4 mg / ml 95.34 1.39 6514.19

[0077] Example 4

[0078] Compared with Example 1, in this example, only polyacrylic acid is replaced by tannic acid, and other conditions remain unchanged.

[0079] The test results corresponding to different concentrations of tannic acid in this example are shown in the following table:

[0080] Kaolinite + Tannic Acid with Different Concentrations Rejection Rate % <![CDATA[Water flux L / m 2 ·h]]> <![CDATA[Filtration flux L / m 2 ·h·bar]]> 0.4 mg / ml 94.76 2.08 641.22 2 mg / ml 94.94 1.39 1174.69 4 mg / ml 93.98 1.39 1706.10

[0081] Example 5

[0082] In this example, compared with Example 1, only kaolinite is replaced by montmorillonite, and other conditions remain unchanged; among them, the SEM image of montmorillonite is as shown in Figure 1 part (b) of

[0083] The test results corresponding to different concentrations of polyacrylic acid in this example are shown in the following table:

[0084] Montmorillonite + Polyacrylic Acid with Different Concentrations Rejection Rate % <![CDATA[Water flux L / m 2 ·h]]> <![CDATA[Filtration flux L / m 2 ·h·bar]]> 0.4 mg / ml 94.87 1.39 50.80 2 mg / ml 93.75 1.04 67.05 4 mg / ml 94.29 1.39 81.73

[0085] Example 6

[0086] In this example, compared with Example 5, only polyacrylic acid is replaced by polyvinyl alcohol, and other conditions remain unchanged.

[0087] The test results corresponding to different concentrations of polyvinyl alcohol in this example are shown in the following table:

[0088] Montmorillonite + Polyvinyl Alcohol with Different Concentrations Rejection Rate % <![CDATA[Water flux L / m 2 ·h]]> <![CDATA[Filtration flux L / m 2 ·h·bar]]> 0.4 mg / ml 95.82 0.35 6.53 2 mg / ml 96.50 0.69 3.78 4 mg / ml 95.24 0.35 1.84

[0089] Example 7

[0090] In this example, compared with Example 5, only polyacrylic acid is replaced by gallic acid, and other conditions remain unchanged.

[0091] The test results corresponding to different concentrations of gallic acid in this example are shown in the following table:

[0092] Montmorillonite + Gallic Acid with Different Concentrations Rejection Rate % <![CDATA[Water flux L / m 2 ·h]]> <![CDATA[Filtration flux L / m 2 ·h·bar]]> 0.4 mg / ml 95.61 0.69 56.20 2 mg / ml 95.46 0.35 71.66 4 mg / ml 94.85 0.35 82.60

[0093] Example 8

[0094] In this example, compared with Example 5, only polyacrylic acid is replaced by tannic acid, and other conditions remain unchanged.

[0095] The test results corresponding to different concentrations of tannic acid in this example are shown in the following table:

[0096] Montmorillonite + Tannic Acid with Different Concentrations Rejection Rate % <![CDATA[Water flux L / m 2 ·h]]> <![CDATA[Filtration flux L / m 2 ·h·bar]]> 0.4 mg / ml 95.17 1.04 49.26 2 mg / ml 95.00 0.35 54.08 4 mg / ml 95.12 0.69 58.39

[0097] Comparative Example 1

[0098] In this comparative example, compared with Example 1, a seawater desalination membrane was not prepared (Steps 1 and 2 were deleted), and the seawater desalination membranes in Steps 3 and 4 were replaced by microfiltration membranes (the same as in Example 1), and other conditions remained unchanged.

[0099] The test results corresponding to the microfiltration membrane in this comparative example are shown in the following table:

[0100] / Rejection Rate % <![CDATA[Water flux L / m 2 ·h]]> <![CDATA[Filtration flux L / m 2 ·h·bar]]> Microfiltration Membrane 84％ 1.04 20543

[0101] Analysis Example 1

[0102] Through Figure 1 It can be known that: before ultrasonic treatment, both kaolinite and montmorillonite are large lamellar blocks.

[0103] Through Figure 2 It can be known that: after adding different polymers, additional peaks appear in the infrared spectrum, indicating that carboxyl groups, hydroxyl groups, etc. have been successfully grafted onto the membrane, and the seawater desalination membrane has been successfully modified.

[0104] From the test data in Examples 1 - 8, it can be known that:

[0105] After adding different polymers, there are differences in the water flux and rejection rate of kaolinite and montmorillonite. Among them, the rejection rate of all seawater desalination membranes is greater than 93%, and the highest rejection rate can reach about 96%, meeting the requirements of the current seawater desalination membranes on the market for the rejection rate, but the water fluxes have their own advantages and disadvantages.

[0106] In terms of the suction filtration flux, after adding different polymers, there are very significant changes in the suction filtration fluxes of kaolinite and montmorillonite. Among them, the suction filtration flux of gallic acid is the largest, and the others are polyacrylic acid, tannic acid, and polyvinyl alcohol in turn. At the same time, when the concentration of the added polymer decreases, the suction filtration fluxes of gallic acid, polyacrylic acid, and tannic acid decrease in turn; while for polyvinyl alcohol, as the added concentration decreases, the suction filtration flux increases instead.

[0107] From the test data in Comparative Example 1, it can be known that:

[0108] The suction filtration flux of the microfiltration membrane without using additives is 20543L / m 2 ·h·bar, but its rejection rate during forward osmosis is only 84%, which cannot reach the rejection rate of the seawater desalination membranes required on the market.

[0109] In the above technical solutions of the present invention, the above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural transformation made under the technical concept of the present invention by using the content of the specification and drawings of the present invention, or directly / indirectly applied in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A preparation method of an additive for a membrane, characterized in that, Including the steps: S1. Mix the ore material and the polymer together into a polar small molecule solvent to obtain a liquid to be processed; The ore material includes kaolinite; The polymer includes one or more of polyacrylic acid, gallic acid, and tannic acid; The mass ratio of the ore material to the polymer is 1:0.2 - 2, and the mass - volume ratio of the ore material to the polar small molecule solvent is 60 - 150 mg:30 mL; S2. Perform ultrasonic liquid - phase exfoliation treatment on the liquid to be processed to obtain a processed liquid; S3. Perform solid - liquid separation on the processed liquid, and take the upper - layer liquid as the membrane additive.

2. The preparation method of the film additive according to claim 1, characterized in that The ultrasonic liquid - phase exfoliation treatment includes: exfoliating the liquid to be processed for 12 - 24 h at an ultrasonic power of 300 - 500 W.

3. The preparation method of the film additive according to claim 1, characterized in that, The polar small molecule solvent includes one or more of water, methanol, and isopropanol.

4. A membrane additive, characterized in that, Prepared by using the preparation method of the membrane additive according to any one of claims 1 - 3.

5. A method for preparing a seawater desalination membrane, characterized in that, Including: Pass the membrane additive according to claim 4 through a microporous filtration membrane to load the active components in the membrane additive onto the microporous filtration membrane to obtain the seawater desalination membrane.

6. The preparation method of the seawater desalination membrane according to claim 5, characterized in that, The loading method includes vacuum loading.

7. The method for preparing a seawater desalination membrane according to claim 5 or 6, characterized in that, Volume of the additive for the membrane: The cross-sectional area of the microfiltration membrane is 1-2 mL:1 cm 2 .

8. A seawater desalination membrane, characterized in that, Prepared by using the preparation method of the seawater desalination membrane according to any one of claims 5 - 7.

9. Application of a seawater desalination membrane according to claim 8 in desalinating brine.

10. The application according to claim 9, characterized in that, Desalinate the brine by the way of forward osmosis.

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