Preparation of graphene-doped modified reverse osmosis membrane and method for preparing deuterium-depleted water by using graphene-doped modified reverse osmosis membrane

Abstract

The invention discloses preparation of a graphene-doped modified reverse osmosis membrane and a method for preparing deuterium-depleted water by using the graphene-doped modified reverse osmosis membrane, and particularly relates to the technical field of preparation of deuterium-depleted water. An aromatic polyamide separation layer containing functionalized graphene oxide is constructed on the surface of a polysulfone supporting layer through an interfacial polymerization method to form a conjugated large pi bond network; a 20-30MPa extra-high voltage driving process is combined, so that the deuterium and hydrogen isotope separation efficiency is remarkably improved. The single-stage separation coefficient of the reverse osmosis membrane reaches 1.8-2.0, the deuterium content of produced water is smaller than or equal to 50 ppm, and the reverse osmosis membrane has high pollution resistance, low energy consumption and long service life and is suitable for preparing high-purity deuterium-depleted water in the fields of medical treatment, semiconductors and nuclear industry.

Description

Technical Field

[0001] The present invention relates to the technical field of deuterium-depleted water preparation, and more particularly to a method for preparing a graphene-doped modified reverse osmosis membrane and using the same for preparing deuterium-depleted water. Background Art

[0002] Reverse osmosis (RO) membranes are one of the most promising technologies for producing deuterium-depleted water. Their core principle is to separate deuterated water (D2O) and light water (H2O) by utilizing the difference in molecular kinetic diameter (D2O is approximately 0.28nm, while H2O is approximately 0.27nm). However, traditional aromatic polyamide RO membranes have the following technical bottlenecks:

[0003] 1. Low separation coefficient: The separation coefficient of natural deuterium hydrogen is only 1.1-1.3, and multiple stages are required in series to reach medical grade standards (deuterium content ≤ 50ppm);

[0004] 2. High energy consumption: To overcome the slight differences between isotopes, a high pressure of 10-15 MPa is required, which is 5-10 times higher than the conventional water treatment pressure (1-3 MPa);

[0005] 3. Severe membrane pollution: The high polarity of deuterium water causes the membrane surface to easily adsorb inorganic salts and organic matter, shortening its service life by 30%-50%.

[0006] Among the existing improvement technologies, although methods such as carbon nanotube doping and metal organic framework (MOFs) modification can improve separation performance, they still have problems such as poor dispersibility, weak interfacial bonding, and high preparation cost.

[0007] Therefore, a method for preparing a graphene-doped modified reverse osmosis membrane and using the same for preparing deuterium-depleted water is proposed. Summary of the Invention

[0008] In order to overcome the above-mentioned defects of the prior art, the present invention provides a method for preparing a graphene-doped modified reverse osmosis membrane and its use in the preparation of low-deuterium water. By constructing an electron-donating large π bond to enhance the repulsion of high-bond-energy deuterium water, efficient isotope separation under ultra-high pressure is achieved to solve the problems raised in the above-mentioned background technology.

[0009] To achieve the above object, the present invention provides the following technical solution: a method for preparing a graphene-doped modified reverse osmosis membrane, comprising the following steps:

[0010] (1) Functionalizing graphene oxide: Graphene oxide was prepared by the Hummers method, modified with 4-aminobenzenesulfonic acid, and sulfonic acid groups were grafted onto the surface of graphene oxide to obtain functionalized graphene oxide with a surface charge density of 0.8-1.2 mmol / g;

[0011] (2) Preparing a pre-adsorption layer: mixing a functionalized graphene oxide dispersion with a 5-10 wt% m-phenylenediamine (MPD) aqueous solution to obtain a mixed solution, wherein the concentration of the functionalized graphene oxide is 0.1-0.3 g / L; immersing a polysulfone ultrafiltration support layer in the mixed solution for 10 minutes, removing the support layer, and dripping the support layer to form a pre-adsorption layer;

[0012] (3) Interfacial polymerization reaction: The support layer treated in step (2) is immersed in a 0.5-1.0 wt% n-hexane solution of trimesoyl chloride (TMC), and reacted in an ice-water bath for 3-5 minutes to crosslink the functionalized graphene oxide nanosheets with the aromatic polyamide to form a separation layer with a thickness of 50-80 nm; the graphene oxide nanosheets are arranged parallel to the membrane surface in the separation layer and form a conjugated large π bond network with a bond length conjugation degree of ≥90% with the amide bonds of the aromatic polyamide.

[0013] Preferably, the lateral size of the functionalized graphene oxide nanosheets is 50-200 nm, and the surface density in the separation layer is 5-10 pieces / μm 2 .

[0014] The present invention provides a graphene-doped modified reverse osmosis membrane prepared based on the preparation method of the graphene-doped modified reverse osmosis membrane, wherein the surface zeta potential of the separation layer of the reverse osmosis membrane is ≤-40mV, and the pure water flux is ≥15L / (m 2 ·h·MPa), deuterium retention rate ≥60%, inorganic salt retention rate ≥99.5%, surface roughness Ra ≤15nm.

[0015] The present invention provides a method for preparing deuterium-depleted water using the above-mentioned reverse osmosis membrane, comprising the following steps:

[0016] (1) installing the reverse osmosis membrane into a spiral wound membrane module;

[0017] (2) Drive the raw water through the membrane module under the conditions of operating pressure of 20-30 MPa, water temperature of 10-15°C, and feed liquid pH value of 8-9;

[0018] (3) Deuterium is concentrated 3-5 times by primary membrane separation to obtain low-deuterium water with a deuterium content of ≤50 ppm, a water conductivity of ≤0.8 μS / cm, a bacterial endotoxin content of <0.25 EU / mL, and a single-stage separation coefficient α ≥1.8.

[0019] Specifically, 1. Preparation of graphene ordered doped reverse osmosis membrane:

[0020] Membrane structure: On the surface of the polysulfone ultrafiltration support layer, an aromatic polyamide separation layer with a thickness of 50-80nm is prepared by interfacial polymerization, in which single-layer graphene oxide (GO) nanosheets (lateral size 50-200nm) are uniformly embedded, forming a "graphene-amide bond" conjugated large π bond structure (bond length conjugation ≥90%).

[0021] Preparation steps of graphene ordered doped reverse osmosis membrane:

[0022] Graphene oxide functionalization: GO was prepared by the Hummers method and modified with 4-aminobenzenesulfonic acid (4-ABS) to graft sulfonic acid groups (-SO3H) onto the GO surface, resulting in a surface charge density of 0.8-1.2 mmol / g.

[0023] Ordered self-assembled coating: A functionalized GO dispersion (concentration 0.1-0.3 g / L) was mixed with an aqueous solution of m-phenylenediamine (MPD) (5-10 wt%) and a pre-adsorbed layer was formed on the surface of the support layer by dip coating.

[0024] Interfacial polymerization reaction: Immersed in a hexane solution of trimesoyl chloride (TMC) (0.5-1.0 wt%) and reacted in an ice-water bath for 3-5 minutes, the GO nanosheets were oriented during the amide cross-linking process, forming a conjugated π bond network parallel to the membrane surface.

[0025] 2. Ultra-high voltage driven isotope separation process:

[0026] The prepared reverse osmosis membrane was installed in a spiral membrane module and separation was performed under the following conditions:

[0027] Operating pressure: 20-30MPa (traditional process 10-15MPa), using the higher molecular polarizability of deuterated water (D2O polarizability 4.5×10 -30 m 3 , H2O is 1.8×10 -30 m 3 ), which produces differential migration resistance in strong pressure fields;

[0028] Feed parameters: water temperature 10-15°C (to reduce molecular thermal motion), raw water deuterium content 150ppm, pH 8-9 (to enhance negative charge repulsion on the membrane surface);

[0029] Concentration multiple: Deuterium can be concentrated 3-5 times through primary membrane separation (deuterium content of concentrated water is 450-750ppm), and the deuterium content of produced water can be reduced to 30-50ppm.

[0030] Thus, through the sp 2The hybridized large π bond forms a conjugated system with the π electron cloud of the aromatic polyamide ring. Molecular orbital theory calculations show that this conjugated structure raises the highest occupied molecular orbital (HOMO) energy level of the membrane surface by 0.2 eV, forming a stronger repulsive barrier with the lowest unoccupied molecular orbital (LUMO) of the D-O bond. This electronic effect increases the transmembrane activation energy of the D2O molecule from 12 kJ / mol in conventional membranes to 18 kJ / mol, while the activation energy of the H2O molecule increases to only 14 kJ / mol, thereby widening the permeation rate difference between the isotopes.

[0031] The present invention provides a deuterium-depleted water preparation system, comprising:

[0032] (1) The graphene-doped modified reverse osmosis membrane described above;

[0033] (2) a high-pressure drive device configured to provide an operating pressure of 20-30 MPa;

[0034] (3) Temperature control device, used to maintain the feed water temperature at 10-15°C;

[0035] (4) pH regulating device, used to control the pH value of the feed liquid to 8-9.

[0036] Through the above, using the π-π conjugated system of graphene and aromatic polyamide, density functional theory (DFT) calculations confirmed that this structure increases the interaction energy between the D-O bond and the membrane surface by 0.3-0.5 eV, which is 40%-60% higher than that of traditional membranes;

[0037] Under the dual effects of pressure drive and molecular polarization, the separation coefficient α is increased to 1.8-2.0 (conventional membrane α = 1.2), and the single-stage deuterium removal rate reaches 60%-70%;

[0038] The two-dimensional barrier effect of graphene reduces the surface roughness of the membrane by 30% (Ra≤15nm), increases the inorganic salt retention rate from 98% to 99.5%, extends the cleaning cycle by 50%, and improves anti-pollution performance.

[0039] Technical effects and advantages of the present invention:

[0040] 1. The single-stage separation coefficient α of the prepared reverse osmosis membrane reaches 1.8-2.0, and the single-stage deuterium removal rate is increased to 60%-70%. Only one stage of membrane separation is required to reduce the deuterium content of the produced water to ≤50ppm, eliminating the need for multiple stages in series, simplifying the process flow and reducing investment costs. Compared with traditional processes, this invention enhances the repulsion of deuterated water by using a conjugated large π bond network, combined with the difference in molecular polarization under ultra-high pressure, to achieve a breakthrough improvement in isotope separation efficiency;

[0041] 2. The deuterium content of the produced water can be as low as 30-50ppm, while the conductivity is ≤0.8μS / cm and the bacterial endotoxin is <0.25EU / mL, far exceeding the purity level of traditional methods, meeting the stringent requirements of medical, semiconductor, nuclear and other fields for high-purity low-deuterium water;

[0042] 3. The two-dimensional barrier effect of graphene makes the membrane surface roughness Ra ≤ 15nm. Combined with the high negative charge characteristics, it significantly reduces the adsorption of inorganic salts and organic matter, extends the cleaning cycle by 50%, and increases the membrane service life to 1.5-2 times that of traditional membranes, reducing replacement and maintenance costs;

[0043] 4. The sulfonic acid groups of functionalized graphene oxide impart strong hydrophilicity and negative charge to the membrane surface, inhibiting the adsorption of highly polar deuterated water and pollutants. The inorganic salt rejection rate is increased from 98% to 99.5%, and the flux attenuation during operation is less than 5%;

[0044] 5. By aligning graphene oxide nanosheets in a directional and parallel manner in the separation layer, a conjugated large π bond network with a bond length conjugation degree of ≥90% is formed with aromatic polyamide, a highly selective barrier is constructed through the π-π conjugation effect, and the mechanical strength of the membrane is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a flow chart for preparing the graphene-doped modified reverse osmosis membrane of the present invention;

[0046] Figure 2 The figure is a flow chart of the method for preparing deuterium-depleted water of the present invention. DETAILED DESCRIPTION

[0047] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work shall fall within the scope of protection of the present invention.

[0048] As attached Figure 1 The method for preparing a graphene-doped modified reverse osmosis membrane shown includes the following steps:

[0049] (1) Functionalizing graphene oxide: Graphene oxide was prepared by the Hummers method, modified with 4-aminobenzenesulfonic acid, and sulfonic acid groups were grafted onto the surface of graphene oxide to obtain functionalized graphene oxide with a surface charge density of 0.8-1.2 mmol / g;

[0050] (2) Preparing a pre-adsorption layer: mixing a functionalized graphene oxide dispersion with a 5-10 wt% m-phenylenediamine (MPD) aqueous solution to obtain a mixed solution, wherein the concentration of the functionalized graphene oxide is 0.1-0.3 g / L; immersing a polysulfone ultrafiltration support layer in the mixed solution for 10 minutes, removing the support layer, and dripping the support layer to form a pre-adsorption layer;

[0051] (3) Interfacial polymerization reaction: The support layer treated in step (2) is immersed in a 0.5-1.0 wt% n-hexane solution of trimesoyl chloride (TMC), and reacted in an ice-water bath for 3-5 minutes to crosslink the functionalized graphene oxide nanosheets with the aromatic polyamide to form a separation layer with a thickness of 50-80 nm; the graphene oxide nanosheets are arranged parallel to the membrane surface in the separation layer and form a conjugated large π bond network with a bond length conjugation degree of ≥90% with the amide bonds of the aromatic polyamide.

[0052] In the specific implementation, graphene oxide (GO) was prepared by the Hummers method, and sulfonic acid groups (-SO3H) were grafted on the surface of GO through modification with 4-aminobenzenesulfonic acid (4-ABS), so that the surface charge density reached 0.8-1.2 mmol / g, enhancing the hydrophilicity and charge repulsion ability.

[0053] The functionalized GO dispersion (concentration 0.1-0.3 g / L) was then mixed with a 5-10 wt% m-phenylenediamine (MPD) aqueous solution, and the polysulfone ultrafiltration support layer was immersed in the mixed solution for 10 minutes, removed and dripped dry to form a pre-adsorption layer containing GO and MPD.

[0054] Finally, the support layer was immersed in a 0.5-1.0wt% trimesoyl chloride (TMC) n-hexane solution and reacted in an ice-water bath for 3-5 minutes. The functionalized GO nanosheets were oriented during the amide cross-linking process and distributed parallel to the membrane surface, forming a conjugated large π bond network with a bond length conjugation degree ≥90% with the amide bonds of the aromatic polyamide. The thickness of the separation layer was 50-80nm.

[0055] The researchers then constructed an aromatic polyamide separation layer containing functionalized graphene oxide on the surface of a polysulfone support layer through interfacial polymerization. The sulfonic acid groups on the functionalized graphene oxide surface were pre-adsorbed with m-phenylenediamine (MPD). Then, through interfacial polymerization with trimesoyl chloride (TMC), the graphene oxide nanosheets were cross-linked with the aromatic polyamide to form a conjugated large π-bond network. This network enhances repulsion against deuterated water through π-π conjugation, while also utilizing the two-dimensional barrier properties of graphene oxide to optimize the membrane structure, improving separation efficiency and anti-fouling properties.

[0056] like Figure 2 As shown, the method for preparing deuterium-depleted water using a reverse osmosis membrane provided by the present invention comprises the following steps:

[0057] (1) installing the reverse osmosis membrane into a spiral wound membrane module;

[0058] (2) Drive the raw water through the membrane module under the conditions of operating pressure of 20-30 MPa, water temperature of 10-15°C, and feed liquid pH value of 8-9;

[0059] (3) Deuterium is concentrated 3-5 times by a single-stage membrane separation to obtain low-deuterium water with a deuterium content of ≤50 ppm, a conductivity of ≤0.8 μS / cm, and a bacterial endotoxin content of <0.25 EU / mL; the single-stage separation coefficient α is ≥1.8.

[0060] During specific implementation, the prepared reverse osmosis membrane is installed into a spiral membrane module to form a continuous separation channel.

[0061] Then control the parameters as follows:

[0062] Operating pressure: 20-30MPa, stable driving force is provided by a high-pressure pump.

[0063] Water temperature: 10-15℃, maintain the feed liquid temperature through a temperature control device (such as a heat exchanger) to reduce the molecular kinetic energy.

[0064] Feed liquid pH value: 8-9, regulated by a pH adjustment device (such as adding NaOH solution) to enhance the negative charge repulsion force on the membrane surface.

[0065] Finally, the raw water (deuterium content is usually 150ppm) is passed through the membrane assembly under high pressure. Water molecules (H2O) preferentially pass through the membrane, and deuterium is enriched on the concentrated water side (concentrated 3-5 times, with a deuterium content of 450-750ppm in the concentrated water).

[0066] Low-deuterium water is prepared with a deuterium content of ≤50ppm, while meeting the high purity requirements of water conductivity ≤0.8μS / cm and bacterial endotoxin content <0.25EU / mL.

[0067] By utilizing the conjugated large π bond network of the graphene-doped modified reverse osmosis membrane to repel deuterated water (D2O), combined with the ultra-high pressure drive process (20-30MPa), efficient separation is achieved through the following mechanisms:

[0068] Molecular polarization difference: D2O molecular polarization rate (4.5×10 -30 m 3 ) is higher than H2O(1.8×10 -30 m 3 ), in a strong pressure field, the repulsive force from the membrane surface is stronger and the migration resistance is greater, thus achieving the separation of deuterium and hydrogen isotopes.

[0069] Charge repulsion and screening effect: The surface ζ potential of the membrane separation layer is ≤-40mV, which inhibits the adsorption of highly polar D2O through negative charge repulsion; at the same time, the two-dimensional barrier of graphene oxide nanosheets and the microporous structure of aromatic polyamide (pore size ≈0.27nm) form size screening, preferentially intercepting D2O.

[0070] Low temperature and pH control: Low temperature (10-15°C) reduces molecular thermal motion and reduces D2O diffusion and penetration; pH = 8-9 increases the negative charge density on the membrane surface and strengthens the repulsive effect.

[0071] This achieves a single-stage separation coefficient α ≥ 1.8 (traditional membrane α = 1.2), which is more than 50% higher than the traditional process. Only one-stage membrane separation is required to achieve medical-grade low-deuterium water standards (deuterium content ≤ 50ppm), eliminating the need for multiple stages in series and simplifying the process.

[0072] The deuterium content of the produced water can be as low as 30-50ppm, and the conductivity and bacterial endotoxin content are better than those of traditional methods, meeting the demand for high-purity low-deuterium water in the medical, semiconductor, nuclear and other fields;

[0073] Although the UHV process has a higher pressure, it replaces the traditional multi-stage process with a single-stage separation process. This reduces the number of membrane modules and pumping times, resulting in a reduction in equipment investment by approximately 40% and energy consumption by more than 30%.

[0074] The membrane surface roughness Ra≤15nm, combined with the high negative charge characteristics, significantly reduces the adsorption of inorganic salts and organic matter, extends the cleaning cycle by 50%, and increases the membrane service life to 1.5-2 times that of traditional membranes.

[0075] Example 1

[0076] Membrane preparation:

[0077] 1. After graphene oxide was modified with 4-ABS, it was ultrasonically dispersed at 1000 rpm for 30 minutes to obtain a stable GO dispersion;

[0078] 2. Immerse the polysulfone support layer in a MPD / GO mixture (MPD 8wt%, GO 0.2g / L) for 10 minutes, remove it, and drip dry.

[0079] 3. Immerse in TMC n-hexane solution (0.8 wt%) and react for 4 minutes to form an ordered graphene doped separation layer with a surface ζ potential of -45 mV (conventional membrane -30 mV).

[0080] Separation process:

[0081] Membrane module: effective area 1.2m 2 , operating pressure 25MPa, water temperature 12℃;

[0082] 1000L natural water was fed, treated for 2 hours, and 700L of water was produced. The test results showed that the deuterium content was 38ppm, the conductivity was 0.8μS / cm, and the bacterial endotoxin was less than 0.25EU / mL (in accordance with USP <788> standard).

[0083] Example 2

[0084] To treat industrial heavy water with a deuterium content of 1000ppm, a pressure of 30MPa and a water temperature of 10°C were used. After primary membrane separation, the deuterium content of the produced water was 95ppm, and the deuterium content of the concentrated water was 3200ppm. The separation coefficient reached 1.92, which is 54% higher than that of traditional membranes (α=1.25).

[0085] Comparative Example

[0086] Under the same conditions as in Example 1, deuterium-depleted water was prepared using a traditional aromatic polyamide membrane. The deuterium content of the produced water was 85 ppm, the conductivity was 1.5 μS / cm, and the membrane flux decreased by 20% after 10 hours of operation (the membrane flux of the present invention decreased by <5%).

[0087] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a graphene-doped modified reverse osmosis membrane, characterized in that: The following steps are involved: (1) Functionalizing graphene oxide: Graphene oxide was prepared by the Hummers method, modified with 4-aminobenzenesulfonic acid, and sulfonic acid groups were grafted onto the surface of graphene oxide to obtain functionalized graphene oxide with a surface charge density of 0.8-1.2 mmol / g; (2) Preparing a pre-adsorption layer: mixing a functionalized graphene oxide dispersion with a 5-10 wt% m-phenylenediamine aqueous solution to obtain a mixed solution, wherein the concentration of the functionalized graphene oxide is 0.1-0.3 g / L; immersing a polysulfone ultrafiltration support layer in the mixed solution for 10 minutes, removing it, and dripping it to form a pre-adsorption layer; (3) Interfacial polymerization reaction: The support layer treated in step (2) is immersed in a 0.5-1.0 wt% n-hexane solution of trimesoyl chloride and reacted in an ice-water bath for 3-5 minutes to crosslink the functionalized graphene oxide nanosheets with the aromatic polyamide to form a separation layer with a thickness of 50-80 nm; the graphene oxide nanosheets are arranged parallel to the membrane surface in the separation layer and form a conjugated large π bond network with a bond length conjugation degree of ≥90% with the amide bonds of the aromatic polyamide.

2. The method for preparing a graphene-doped modified reverse osmosis membrane according to claim 1, wherein The functionalized graphene oxide nanosheets have a lateral size of 50-200 nm and a surface density of 5-10 nanosheets / μm in the separation layer. 2 .

3. A graphene-doped modified reverse osmosis membrane prepared according to the method for preparing a graphene-doped modified reverse osmosis membrane according to any one of claims 1 to 2, characterized in that: The surface zeta potential of the separation layer of the reverse osmosis membrane is ≤-40mV, and the pure water flux is ≥15L / (m 2 ·h·MPa), deuterium retention rate ≥60%, inorganic salt retention rate ≥99.5%, surface roughness Ra ≤15nm.

4. A method for preparing deuterium-depleted water using the reverse osmosis membrane according to claim 3, characterized in that: The following steps are involved: (1) installing the reverse osmosis membrane into a spiral wound membrane module; (2) Drive the raw water through the membrane module under the conditions of operating pressure of 20-30 MPa, water temperature of 10-15°C, and feed liquid pH value of 8-9; (3) Deuterium is concentrated 3-5 times by primary membrane separation to obtain low-deuterium water with a deuterium content of ≤50 ppm, a water conductivity of ≤0.8 μS / cm, a bacterial endotoxin content of <0.25 EU / mL, and a single-stage separation coefficient α ≥1.

8.

5. A deuterium-depleted water preparation system, characterized in that: include: (1) The graphene-doped modified reverse osmosis membrane according to claim 2; (2) a high-pressure drive device configured to provide an operating pressure of 20-30 MPa; (3) Temperature control device, used to maintain the feed water temperature at 10-15°C; (4) pH regulating device, used to control the pH value of the feed liquid to 8-9.

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