Desalination method

Abstract

A desalination method comprises introducing a solution to be treated including salt and water into a capacitive deionization device including an electrode unit, and applying a voltage to the capacitive deionization device so as to allow the salt to be separated from the solution to be treated by the electrode unit, so that the solution to be treated is converted into a purified liquid.. The electrode unit includes a porous positive electrode body and a porous negative electrode body spaced apart from the porous positive electrode body. Each of the porous positive electrode body and the porous negative electrode body has a hydrophilic side and a hydrophobic side disposed opposite to the hydrophilic side. The hydrophilic side of the porous positive electrode body and the hydrophilic side of the porous negative electrode body set face to face. The solution to be treated flows from the hydrophobic side of one of the porous positive electrode body and the porous negative electrode body toward the hydrophilic sides, and flows out from the hydrophobic side of the other one of the porous positive electrode body and the porous negative electrode body.

Description

Technical Field

[0001] This invention relates to a method for treating aqueous solutions, and more particularly to a desalination method. Prior Technology

[0002] In recent years, the world has been increasingly affected by climate change, with frequent droughts and other disasters. This has led to measures such as reduced water supply, water rationing, farmland closures, and business shutdowns to maintain daily life. Currently, due to water scarcity, seawater desalination is considered a solution that is unaffected by natural rainfall, provides a stable water supply, and has a relatively low environmental impact. Most current seawater desalination methods use membrane filtration or distillation, but these methods are not only costly but also energy-intensive. Therefore, effectively removing salts (such as sodium chloride) from the water is a pressing issue that needs to be addressed.

[0003] Chinese mainland patent publication CN113149143 discloses a method for simultaneous desalination and degradation of organic matter based on hierarchical hydrophobic / hydrophilic electrodes. This method includes using a capacitive deionization device to treat a system containing oxidants and saline organic wastewater, obtaining purified fresh water. The capacitive deionization device includes a device body, a cathode disposed on the device body, and an anode disposed on the device body and spaced apart from the cathode. Each of the anode and cathode includes a hydrophilic porous carbon layer formed of hydrophilic porous carbon and a hydrophobic layer formed on the surface of the hydrophilic porous carbon layer. The hydrophobic layer includes at least one of a hydrophobic conductive polymer layer formed of a hydrophobic conductive polymer and a hydrophobically modified metal compound layer.

[0004] Although the method in this Chinese mainland patent application can simultaneously remove salt from wastewater and degrade organic matter in wastewater, the method still has a poor salt removal rate. Summary of the Invention

[0005] Therefore, the object of the present invention is to provide a desalination treatment method.

[0006] Therefore, the desalination method of the present invention includes introducing a liquid to be treated, comprising salts and water, into a capacitive deionization device including an electrode unit, and applying a voltage to the capacitive deionization device to cause the salts in the liquid to be treated to be removed from the liquid by means of the electrode unit, thereby transforming the liquid to be treated into a purified liquid. The electrode unit includes a porous positive electrode and a porous negative electrode spaced apart from the porous positive electrode. Each of the porous positive electrode and the porous negative electrode has a hydrophilic side and a hydrophobic side disposed opposite to the hydrophilic side. The hydrophilic side of the porous positive electrode and the hydrophilic side of the porous negative electrode are arranged face-to-face. The liquid to be treated flows from the hydrophobic side of one of the porous positive electrode and the porous negative electrode towards the hydrophilic side, and flows out from the hydrophobic side of the other of the porous positive electrode and the porous negative electrode.

[0007] The advantages of this invention are as follows: Through the positional design of the hydrophobic and hydrophilic sides, and utilizing the principle of unidirectional moisture conduction, the flow direction of the liquid to be treated is effectively guided and controlled unidirectionally from the hydrophobic side towards the hydrophilic side. Simultaneously, the liquid to be treated is confined and retained between the hydrophilic sides and diffuses between them, which helps to effectively adsorb salts in the liquid to be treated into the electrode unit, thereby removing the salts from the liquid to be treated, increasing the desalination rate, and thus improving the purification efficiency of the liquid to be treated. It is worth noting that the porous positive and negative electrodes of this invention have dual wetting characteristics, allowing the liquid to be treated to diffuse from the hydrophobic side to the hydrophilic side and diffuse on the surface of the hydrophilic side, thereby improving the desalination rate. Simple Explanation of the Diagram

[0008] Other features and effects of the present invention will be clearly presented in the embodiments with reference to the drawings, wherein: Figure 1 is a schematic diagram illustrating the capacitor deionization device of the desalination treatment method of the present invention. Implementation

[0009] Referring to Figure 1, the desalination method of the present invention includes introducing a liquid to be treated, comprising salts and water, into a capacitor deionization device including an electrode unit, and applying a voltage to the capacitor deionization device so that the salts in the liquid to be treated are removed from the liquid to be treated through the electrode unit, thereby transforming the liquid to be treated into a purified liquid.

[0010] The desalination method of the present invention will be described in detail below.

[0011] [[] [Liquid to be treated] []]

[0012] The liquid to be treated may be, for example, but is not limited to, seawater, tap water, or wastewater. The wastewater may be, for example, but is not limited to, domestic wastewater, industrial wastewater, or agricultural wastewater. In some embodiments of the present invention, the concentration of the salt in the liquid to be treated is 60 ppm to 150 ppm. The salt in the liquid to be treated may be, for example, but is not limited to, sodium chloride. In some embodiments of the present invention, the salt is sodium chloride.

[0013] [[] [Capacitor Deionization Device] []]

[0014] The capacitive deionization device of the present invention is a flow-through type capacitive deionization device. Referring to Figure 1, the capacitive deionization device includes an electrode unit 1, an isolation unit 2, and a current collection unit 3.

[0015] The electrode unit 1 includes a porous positive electrode 11 and a porous negative electrode 12 spaced apart from the porous positive electrode 11. The porous positive electrode 11 has a hydrophobic side 111 and a hydrophilic side 112 opposite to the hydrophobic side 111. The porous negative electrode 12 has a hydrophilic side 121 and a hydrophobic side 122 opposite to the hydrophilic side 121. The hydrophilic side 112 of the porous positive electrode 11 and the hydrophilic side 121 of the porous negative electrode 12 are arranged face to face.

[0016] In some embodiments of the present invention, the water contact angle of the hydrophilic side 112 of the porous positive electrode 11 is 0 to 20 degrees. In some embodiments of the present invention, the water contact angle of the hydrophobic side 111 of the porous positive electrode 11 is 130 to 140 degrees.

[0017] In some embodiments of the present invention, the porous positive electrode 11 is formed by treating one hydrophobic side of a hydrophobic porous conductor with a modifier, thereby transforming the hydrophobic side of the hydrophobic porous conductor into the hydrophilic side. The hydrophobic porous conductor includes a porous conductive element and a hydrophobic material dispersed within the porous conductive element. The porous conductive element is, for example, but not limited to, a porous carbon conductive sheet or a porous conductive polymer film. The porous carbon conductive sheet is, for example, but not limited to, porous carbon felt or porous activated carbon cloth. The porous conductive polymer film is, for example, but not limited to, a porous poly(3,4-ethylenedioxythiophene) film. The hydrophobic material can be used alone or in combination, and the hydrophobic material is, for example, but not limited to, metal oxides, reduced graphene oxide, or polydimethylsiloxane (PDMS). The metal oxide is, for example, but not limited to, zinc oxide, aluminum oxide, or zirconium dioxide (ZrO₂). Such modifiers include, but are not limited to, atmospheric plasma, butylene, cellulose, or pectin.

[0018] The porous negative electrode 12 may be the same as or different from the porous positive electrode 11.

[0019] In some embodiments of the present invention, the water contact angle of the hydrophilic side 121 of the porous negative electrode 12 is 0 to 10 degrees. In some embodiments of the present invention, the water contact angle of the hydrophobic side 122 of the porous negative electrode 12 is 130 to 140 degrees.

[0020] In some embodiments of the present invention, the porous negative electrode 12 is made by treating one side of a hydrophobic porous conductor with a modifier, thereby making that side of the hydrophobic porous conductor hydrophilic. The hydrophobic porous conductor includes a porous conductive element and a hydrophobic material dispersed in the porous conductive element. The porous conductive element is, for example, but not limited to, a porous carbon conductive sheet or a porous conductive polymer film. The porous carbon conductive sheet is, for example, but not limited to, porous carbon felt or porous activated carbon cloth. The porous conductive polymer film is, for example, but not limited to, a porous poly(3,4-ethylenedioxythiophene) film. The hydrophobic material can be used alone or in combination, and the hydrophobic material is, for example, but not limited to, metal oxides, reduced graphene oxide, or polydimethylsiloxane (PDMS). The metal oxide is, for example, but not limited to, zinc oxide, aluminum oxide, or zirconium dioxide (ZrO₂). Such modifiers include, but are not limited to, atmospheric plasma, butylene, cellulose, or pectin.

[0021] The isolation unit 2 includes a separator for separating the porous positive electrode 11 from the porous negative electrode 12. Such separators are, for example, separators conventionally used in the battery field, such as cellulose membranes or ion exchange membranes, and will not be described further.

[0022] The current collector unit 3 includes a first current collector 31 disposed on the hydrophobic side 111 of the porous positive electrode 11 and a second current collector 32 disposed on the hydrophobic side 122 of the porous negative electrode 12. The first current collector 31 and the second current collector 32 are, for example, current collectors conventionally used in the field of batteries, and will not be described in detail here.

[0023] The liquid to be treated enters through the first current collector 31 and contacts the hydrophobic side 111 of the porous positive electrode 11. Then, it flows toward the hydrophilic side 112 of the porous positive electrode 11, and then sequentially passes through the hydrophilic side 121 and the hydrophobic side 122 of the porous negative electrode 12, thereby flowing out through the second current collector 32. It is worth noting that the liquid to be treated can also enter through the second current collector 32.

[0024] In some embodiments of the present invention, the voltage is 1.4 Volt to 1 Volt.

[0025] The present invention will be further described with reference to the following embodiments, but it should be understood that the embodiments are for illustrative purposes only and should not be construed as limiting the implementation of the present invention.

[0026] Preparation Example 1

[0027] Using an ultrasonic oscillator, a first mixture containing 150 mg of graphene oxide (prepared using the Hummers method) and 30 mL of sulfuric acid was agitated for 30 minutes to uniformly disperse the graphene oxide in the sulfuric acid, forming a second mixture. Then, 60 mg of zinc oxide (prepared using a hydrothermal method) was mixed with the second mixture to form a third mixture. Next, the third mixture was placed in an electrochemical system comprising a graphite electrode (as the counter electrode), a porous carbon felt (as the working electrode; brand: Shanghai Carbon; model: SHTS; dimensions: 25 mm long, 25 mm wide, and 2 mm thick; water contact angle: 120 degrees), and a silver chloride electrode (as the reference electrode). Then, using cyclic voltammetry, a first cyclic potential is applied to the third mixture, starting from a starting potential of 1 Volt and increasing at a rate of 0.05 V to an ending potential of -0.1 Volt. Then, the voltage is returned from the ending potential to the starting potential at a rate of 0.05 V, for a total of 200 cycles. This allows the zinc oxide and graphene oxide to adhere to the interior and surface of the porous carbon felt. Next, a second cyclic potential is applied, starting from 0 Volt... The initial potential of lt is applied at a rate of 0.05V to the final potential of -1.6Volt, and then returned from the final potential to the initial potential at a rate of 0.05V, for a total of 10 cycles. This reduces the graphene oxide attached to the interior and surface of the porous carbon felt to reduced graphene oxide, making the surface of the porous carbon felt hydrophobic, thus forming a hydrophobic porous carbon felt with two oppositely arranged hydrophobic sides. The hydrophobic porous carbon felt comprises porous carbon felt, zinc oxide, and reduced graphene oxide. The water contact angle of the hydrophobic sides of the hydrophobic porous carbon felt is 135 degrees.

[0028] Next, the hydrophobic porous carbon felt was placed in a plasma treatment device, and in an environment containing argon gas at a flow rate of 5 slm and helium gas at a flow rate of 5 sccm, one of the hydrophobic sides of the hydrophobic porous carbon felt was subjected to two surface treatments using atmospheric plasma at a voltage of 8000 volts, so as to transform the hydrophobic side into the hydrophilic side, thus obtaining the treated carbon felt. The water contact angle of the hydrophilic side of the treated carbon felt is 0 degrees.

[0029] Comparative Preparation Example 1

[0030] Porous carbon felt (brand: Shanghai Carbon; model: SHTS; dimensions: 25 mm long, 25 mm wide, and 2 mm thick). Both opposite sides of this porous carbon felt are hydrophobic, with a water contact angle of 120 degrees.

[0031] Comparative Preparation Example 2

[0032] An ultrasonic oscillator was used to agitate a first mixture containing 150 mg of graphene oxide (prepared using the Hummers method) and 30 mL of sulfuric acid for 30 minutes to uniformly disperse the graphene oxide in the sulfuric acid, forming a second mixture. Then, 60 mg of zinc oxide (prepared using a hydrothermal method) was mixed with the second mixture to form a third mixture. Next, the third mixture was placed in an electrochemical system comprising a platinum electrode (as the counter electrode), a porous carbon felt (as the working electrode; brand: Shanghai Carbon; model: SHTS; dimensions: 25 mm long, 25 mm wide, and 2 mm thick; water contact angle: 120 degrees), and a silver chloride electrode (as the reference electrode). Then, using cyclic voltammetry, a first cyclic potential was applied to the third mixture, starting from a potential of 1 volt and increasing at a rate of 0.05 V to an end potential of -0.1 volt, then returning to the starting potential at a rate of 0.05 V, for a total of 200 cycles. This allowed the zinc oxide and graphene oxide to adhere to the interior and surface of the porous carbon felt. Next, a second cyclic potential was applied, starting from a potential of 0 volt and increasing at a rate of 0.05 V to an end potential of -1.6 volt, then returning to the starting potential at a rate of 0.05 V, for a total of 10 cycles. This reduced the graphene oxide adhered to the interior and surface of the porous carbon felt to reduced graphene oxide. The porous carbon felt is hydrophobic due to the presence of zinc oxide, forming a hydrophobic porous carbon felt with two oppositely arranged hydrophobic sides. The hydrophobic porous carbon felt comprises porous carbon felt, zinc oxide, and reduced graphene oxide. The water contact angle of the hydrophobic sides of the hydrophobic porous carbon felt is 135 degrees.

[0033] Example 1

[0034] A 150-liter solution containing sodium chloride and water was continuously introduced into a flow-through capacitive deionization device at a flow rate of 4 mL / min. The sodium chloride concentration in the solution was 60 ppm. The flow-through capacitive deionization device, as shown in Figure 1, included two spaced-apart treated carbon felt pieces from Preparation Example 1 (serving as a porous positive electrode and a porous negative electrode, respectively; dimensions: length 25 mm, width 25 mm, thickness 2 mm) and a spacer (material: silicone pad; brand: MISUMI; model: GELS3-100; dimensions: length 100 mm, width 100 mm, thickness 3 mm) between the treated carbon felt pieces. The hydrophilic sides of the treated carbon felt pieces were arranged face-to-face.

[0035] The liquid to be treated enters through the hydrophobic side of one of the treated carbon felt pieces and diffuses towards the hydrophilic side of the treated carbon felt pieces. At the same time, a voltage of 1.2 Volt is applied to the flow-through capacitor deionizer. Then, the liquid to be treated is continuously allowed to flow and exit through the hydrophobic side of the other of the treated carbon felt pieces, so that sodium chloride is adsorbed by the treated carbon felt pieces and removed from the liquid to be treated, thereby transforming the liquid to be treated into a purified liquid.

[0036] Examples 2 to 3

[0037] The desalination methods in Examples 2 and 3 are generally similar to those in Example 1, except that the sodium chloride concentration is changed, as shown in Table 1.

[0038] Comparative Example 1

[0039] The desalination treatment method of Comparative Example 1 is generally similar to that of Example 1, except that in Comparative Example 1, the treated carbon felt pieces of Example 1 are replaced with the porous carbon felt of Comparative Preparation Example 1.

[0040] Comparative Example 2

[0041] The desalination treatment method of Comparative Example 2 is generally similar to that of Example 1, except that in Comparative Example 2, the hydrophilic side of one of the treated carbon felt pieces is arranged face to face with the hydrophobic side of the other of the treated carbon felt pieces.

[0042] Comparative Example 3

[0043] The desalination treatment method of Comparative Example 3 is generally similar to that of Example 1, except that in Comparative Example 3, the hydrophobic sides of the treated carbon felt are arranged face to face.

[0044] Evaluation Project

[0045] Sodium chloride adsorption capacity (unit: mg / g, or unit: mg / cm²) and adsorption rate (unit: %) measurement: Several standards with known sodium chloride concentrations were prepared. Then, the conductivity of these standards was measured using a benchtop water quality analyzer (brand: Yellow Springs Instrument; model: Multilab IDS 4010-3w). A coordinate graph showing the relationship between the sodium chloride concentration and conductivity was then plotted, yielding a standard curve formula. Next, the conductivity of the purified solutions from Examples 1 to 3 and Comparative Examples 1 to 3 was measured using the same benchtop water quality analyzer. The conductivity was then substituted into the aforementioned standard curve formula to calculate the sodium chloride concentration in these purified solutions. Finally, based on the sodium chloride concentration in these purified solutions and the sodium chloride concentration in the solution awaiting treatment, the sodium chloride adsorption capacity and adsorption rate were calculated. The sodium chloride adsorption capacity (mg / g) is calculated as [sodium chloride concentration in the purified solution (ppm) x volume of the purified solution (L) - sodium chloride concentration in the solution to be treated (ppm) x volume of the solution to be treated (L)] / [weight of the porous positive electrode (g) + weight of the porous negative electrode (g)]. The sodium chloride adsorption capacity (mg / cm²) is calculated as [sodium chloride concentration in the purified solution (ppm) x volume of the purified solution (L) - sodium chloride concentration in the solution to be treated (ppm) x volume of the solution to be treated (L)] / opening area of ​​the isolation unit (cm²). The adsorption rate (%) is calculated as {[sodium chloride concentration in the purified solution (ppm) x volume of the purified solution (L) - sodium chloride concentration in the solution to be treated (ppm) x volume of the solution to be treated (L)] / [sodium chloride concentration in the solution to be treated (ppm) x volume of the solution to be treated (L)]} x 100%.

[0046] Table 1 Porous positive electrode Porous negative electrode body set up Sodium chloride concentration (ppm) in the solution to be treated Sodium chloride adsorption capacity (mg / g) Sodium chloride adsorption capacity (mg / cm²) Adsorption rate (%) Example 1 Preparation Example 1 Preparation Example 1 These hydrophilic sides face to face 60 32.82 0.72 32 2 Preparation Example 1 Preparation Example 1 100 79.32 1.73 46.2 3 Preparation Example 1 Preparation Example 1 150 133.74 2.92 51.1 Comparative example 1 Comparative Preparation Example 1 Comparative Preparation Example 1 -- 60 6.21 0.12 0.5 2 Preparation Example 1 Preparation Example 1 Hydrophilic side and hydrophobic side face to face 60 28.02 0.57 25 3 Preparation Example 1 Preparation Example 1 These hydrophobic sides face 60 31.315 0.68 30

[0047] In summary, through the design of the positions of the hydrophobic and hydrophilic sides, and utilizing the principle of unidirectional moisture conduction, the flow direction of the liquid to be treated is effectively guided and controlled unidirectionally from the hydrophobic side towards the hydrophilic side. Simultaneously, the liquid to be treated is confined and retained between the hydrophilic sides and diffuses between them, which facilitates the effective adsorption of salts in the liquid to be treated into the electrode unit, thereby removing the salts from the liquid and increasing the desalination rate, thus improving the purification efficiency of the liquid to be treated. It is worth noting that the porous positive and negative electrodes of this invention possess dual wetting characteristics, allowing the liquid to diffuse from the hydrophobic side to the hydrophilic side and diffuse on the surface of the hydrophilic side, thereby increasing the desalination rate and effectively achieving the objectives of this invention.

[0048] However, the above description is merely an embodiment of the present invention and should not be construed as limiting the scope of the present invention. Any simple equivalent changes and modifications made in accordance with the scope of the patent application and the contents of the patent specification of the present invention shall still fall within the scope of the patent of the present invention.

[0049] 1: Electrode Unit 11: Porous positive electrode body 111: Hydrophobic side 112: Hydrophilic side 12: Porous negative electrode body 121: Hydrophilic side 122: Drainage side 2: Isolation Unit 3: Current collector unit 31: First collector 32: Second collector

Claims

1. A desalination method comprising: introducing a solution to be treated, comprising salts and water, into a capacitive deionization device including an electrode unit, and applying a voltage to the capacitive deionization device to cause the salts in the solution to be treated to be removed from the solution by means of the electrode unit, thereby transforming the solution to be treated into a purified solution, wherein... The electrode unit includes a porous positive electrode and a porous negative electrode spaced apart from the porous positive electrode. Each of the porous positive electrode and the porous negative electrode has a hydrophilic side and a hydrophobic side disposed opposite to the hydrophilic side. The hydrophilic side of the porous positive electrode and the hydrophilic side of the porous negative electrode are arranged face to face. The liquid to be treated flows from the hydrophobic side of one of the porous positive electrode and the porous negative electrode toward the hydrophilic side, and flows out from the hydrophobic side of the other of the porous positive electrode and the porous negative electrode.

2. The desalination treatment method as described in claim 1, wherein, The water contact angle on the hydrophilic side of this porous positive electrode is 0 to 10 degrees.

3. The desalination treatment method as described in claim 2, wherein, The water contact angle on the hydrophobic side of the porous positive electrode is 130 to 140 degrees.

4. The desalination treatment method as described in claim 1, wherein, The water contact angle on the hydrophilic side of this porous negative electrode is 0 to 10 degrees.

5. The desalination treatment method as described in claim 4, wherein, The water contact angle on the hydrophobic side of the porous negative electrode is 130 to 140 degrees.

6. The desalination method as described in claim 1, wherein, The voltage ranges from 1.4 Volt to 1 Volt.

7. The desalination treatment method as described in claim 1, wherein, The salt is sodium chloride.

8. The desalination method as described in claim 1, wherein, The concentration of the salt in the solution to be treated is between 60 ppm and 150 ppm.

9. The desalination method as described in claim 1, wherein, The porous positive electrode and the porous negative electrode may be the same or different, and each is formed by treating a hydrophobic side of a hydrophobic porous conductor with a modifier to transform it into a hydrophilic side.

10. The desalination method as described in claim 9, wherein, The hydrophobic porous conductor includes a porous conductive element and a hydrophobic material dispersed in the porous conductive element.

11. The desalination method as described in claim 10, wherein, The hydrophobic material is selected from metal oxides, reduced graphene oxide, polydimethylsiloxane, or any combination thereof.

12. The desalination method as described in claim 1, wherein, The capacitive deionization device includes an isolation unit disposed between the porous positive electrode and the porous negative electrode.

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