A high permeability and selectivity reverse osmosis membrane and a method for preparing the same

Abstract

This invention relates to the field of seawater desalination technology, specifically to a high-permeability and selective reverse osmosis membrane and its preparation method. The high-permeability and selective reverse osmosis membrane is obtained by sequentially immersing a porous support layer in an aqueous solution and an oil solution for interfacial polymerization, thereby forming a desalination layer on the surface of the porous support layer. This invention increases the compatibility of the water / oil phases by adding N-methylpyrrolidone to the aqueous phase and methyl benzoate to the oil phase, thereby reducing the surface tension of the two phase solutions, promoting the diffusion of amine monomers into the organic phase, and altering the surface morphology and polymer chain aggregation state of the separation layer. This results in a higher roughness and cross-linking degree of the desalination layer, and improved permeability and selectivity.

Description

Technical Field

[0001] This invention relates to the field of seawater desalination technology, specifically to a highly permeable and selective reverse osmosis membrane and its preparation method. Background Technology

[0002] In the past, seawater desalination has proven to be a sustainable and feasible solution to the problem of water scarcity. Reverse osmosis (RO) systems, as the core component of seawater desalination, use RO membranes to separate salt from high-concentration brine. However, due to the high pressure involved in the desalination process, seawater desalination consumes a great deal of energy. Therefore, the preparation of highly permeable and selective RO membranes is urgently needed, as this can not only produce deionized water but also reduce the energy consumption and cost of the desalination process.

[0003] Currently, seawater desalination membrane technology typically involves sequentially immersing a porous support layer in m-phenylenediamine and trimesoyl chloride, followed by interfacial polymerization. The resulting reverse osmosis membrane retains all ions, achieving a NaCl rejection rate of over 98%, producing deionized water. However, conventional reverse osmosis membranes suffer from a limiting equilibrium problem: either high water flux results in a low rejection rate, or vice versa.

[0004] Patent CN108525532A discloses a high-flux reverse osmosis membrane and its preparation method and system. It uses coating or spraying to coat an organic amine solution onto a porous support membrane, then performs interfacial polymerization between the porous support membrane and an organic halide solution, then cleans the composite membrane with an oxidizing solution, and finally performs hydrophilic treatment on the composite membrane to form a high-flux and high-rejection-rate reverse osmosis membrane. However, this patented technology adds oxidation and hydrophilic treatment steps to the preparation of the reverse osmosis membrane, which increases the complexity of operation and material costs during industrialization, and the performance still needs to be improved.

[0005] Therefore, this invention aims to improve and upgrade the existing m-phenylenediamine-trimethylammonium chloride system process, optimize the chemical structure of the polyamide layer, and prepare an RO membrane with excellent membrane performance. This process combines the material characteristics of high water flux, high rejection rate, and low operating energy consumption with the process characteristics of low cost and low operability, thereby promoting the widespread application of RO membranes in the field of seawater desalination. Summary of the Invention

[0006] To achieve the above-mentioned technical objectives, the present invention provides a method for preparing a highly permeable and selective reverse osmosis membrane.

[0007] The technical solution of this invention:

[0008] A method for preparing a highly permeable and selective reverse osmosis membrane includes the following steps:

[0009] Step 1: Prepare a porous support layer.

[0010] Step 1.1 Dissolve the polymer and benzenesulfonic acid in dimethylformamide (DMF) or dimethylacetamide (DMAC) and stir. After complete dissolution, allow to stand to remove bubbles to obtain the casting solution; the polymer is polysulfone or polyethersulfone; the mass fraction of the polymer is 16-20 wt%.

[0011] Step 1.2 The casting solution is coated onto a nonwoven fabric, and a base film is formed by liquid-solid phase conversion. The conditions for liquid-solid phase conversion are: time 1-2 min, phase conversion water bath temperature 12-22℃, thermosetting water bath temperature 60-80℃, and film thickness 5.0-6.0 mil.

[0012] Step 1.3 Immerse the base membrane in deionized water for preservation to obtain the porous support layer;

[0013] Step 2: Prepare the desalination layer

[0014] Step 2.1 Immerse the porous support layer in an aqueous solution for interfacial reaction for 1-3 minutes, and drain the surface water droplets: by weight percentage, the aqueous solution consists of m-phenylenediamine 1.5%-3.0%, aniline 0.5%-1.5%, 4-aminobenzenesulfonic acid 0.5%-1.5%, N-methylpyrrolidone (NMP) 1%-6%, sodium hydroxide 0.01%-0.5%, with the remainder being water;

[0015] Step 2.2 Immerse the porous support layer treated in Step 2.1 in an oil phase solution for interfacial reaction for 1-2 minutes to obtain a desalination layer; the oil phase solution comprises, by weight percentage, 0.1%-0.3% trimesoyl chloride, 0.05%-0.15% oxaloyl chloride, 0.5%-0.8% methyl benzoate, with the balance being an organic solvent; the organic solvent is any one or more of n-hexane, cyclohexane, ethylcyclohexane, n-octane, and n-heptane;

[0016] Step 2.3 Place the membrane obtained in Step 2.2 in an oven at 70-80℃ for 1-5 minutes to obtain a high-permeability and selective reverse osmosis membrane; the high-permeability and selective reverse osmosis membrane is an RO membrane with a desalination layer as the outer layer and a porous support layer as the inner layer.

[0017] The beneficial effects of this invention are:

[0018] On the one hand, the reverse osmosis membrane prepared by the method of this invention has high permeability and high selectivity, which can achieve high and high yield of deionized water, specifically in the following ways:

[0019] 1) High water production. Under the same operating pressure, the reverse osmosis membrane of the present invention has a higher water production than the polyamide RO membrane.

[0020] 2) High desalination rate. The reverse osmosis membrane of this invention has a high rejection rate and can also efficiently remove metal ions, dissolved organic matter, colloids, bacteria and viruses.

[0021] 3) Low operating energy consumption. The RO membrane of this invention has a rough surface and a small contact angle, which increases the flux and reduces the energy consumption of the reverse osmosis membrane during operation.

[0022] On the other hand, the method of this invention is characterized by its simple and easy-to-implement steps and low material cost. This invention improves the efficiency and quality of the interfacial polymerization reaction by scientifically adjusting the components of the aqueous and oil phase solutions, achieving one-step synthesis of high-performance RO membranes and reducing the need for post-processing steps. Specifically, it is manifested in:

[0023] This invention adds N-methylpyrrolidone to the aqueous phase and methyl benzoate to the oil phase, thereby increasing the compatibility of the water / oil phases, reducing the surface tension of the two-phase solutions, promoting the diffusion of amine monomers into the organic phase, changing the surface morphology of the separation layer and the aggregation state of polymer chains, and effectively improving the roughness, crosslinking degree, permeability and selectivity of the desalination layer. Detailed Implementation

[0024] Example 1:

[0025] A method for preparing a highly permeable and selective reverse osmosis membrane includes the following steps:

[0026] Step 1: Prepare a porous support layer.

[0027] Step 1.1 Add 18wt% polysulfone (PS) and 2wt% benzenesulfonic acid to 80wt% N,N-dimethylformamide (DMF) or dimethylacetamide (DMAC) and stir at high speed at 180°C for 6 hours. After complete dissolution, allow to stand under vacuum to remove bubbles and obtain casting solution.

[0028] Step 1.2 The casting solution is coated onto the nonwoven fabric using a coating system, and a base film is formed by liquid-solid phase conversion. The conditions for liquid-solid phase conversion are: time 1 min, phase conversion water bath temperature 18℃, thermosetting water bath temperature 70℃, and film thickness 5.5 mil.

[0029] Step 1.3 Immerse the base membrane in deionized water for preservation to obtain the porous support layer;

[0030] Step 2: Prepare the desalination layer

[0031] Step 2.1 Immerse the porous support layer in an aqueous solution for interfacial reaction for 2 minutes, then drain the surface water droplets. The aqueous solution, by weight percentage, comprises 2% m-phenylenediamine, 1% aniline, 0.8% 4-aminobenzenesulfonic acid, 3% N-methylpyrrolidone (NMP), and 0.03% sodium hydroxide, with the remainder being ultrapure water. The aqueous solution is prepared by adding m-phenylenediamine, aniline, 4-aminobenzenesulfonic acid, N-methylpyrrolidone (NMP), and sodium hydroxide to ultrapure water and stirring until completely dissolved.

[0032] Step 2.2 Immerse the porous support layer treated in Step 2.1 in an oil phase solution for interfacial reaction for 1 min to obtain a desalination layer; the oil phase solution consists of 0.15% trimesoyl chloride, 0.1% oxaloyl chloride, and 0.5% methyl benzoate by weight percentage, with the balance being cyclohexane; the oil phase solution is prepared by adding trimesoyl chloride, oxaloyl chloride, and methyl benzoate to cyclohexane and stirring until completely dissolved;

[0033] Step 2.3 Place the membrane obtained in Step 2.2 in an oven at 75°C for 3 minutes to obtain a high-permeability and selective reverse osmosis membrane (abbreviated as RO-M1 membrane); the high-permeability and selective reverse osmosis membrane is an RO membrane with a desalination layer as the outer layer and a porous support layer as the inner layer.

[0034] Comparative Example 1

[0035] The difference from Example 1 is that N-methylpyrrolidone was not added to the aqueous solution in step 2.1, but everything else was the same, and the resulting membrane was an RO-M2 membrane.

[0036] Comparative Example 2

[0037] The difference from Example 1 is that 4-aminobenzenesulfonic acid was not added to the aqueous solution in step 2.1, but everything else was the same, and the resulting membrane was an RO-M3 membrane.

[0038] Comparative Example 3

[0039] The difference from Example 1 is that N-methylpyrrolidone and 4-aminobenzenesulfonic acid were not added to the aqueous solution in step 2.1, but the rest were the same, and the resulting membrane was RO-M4.

[0040] Comparative Example 4

[0041] The difference from Example 1 is that methyl benzoate was not added to the oil phase solution in step 2.2, but everything else was the same, and the resulting membrane was RO-M5.

[0042] Membrane performance removal test

[0043] Five RO membranes (denoted as RO-M1, RO-M2, RO-M3, RO-M4, and RO-M5) prepared in Example 1 and Comparative Examples 1-4, and commercial reverse osmosis membranes (denoted as RO-1 and RO-2) were cut and placed on a cross-flow membrane testing platform for membrane performance testing. Under the test conditions of an operating pressure of 800 psi, a sodium chloride original aqueous solution concentration of 35000 ppm, a solution temperature of 25°C, and a pH value of 6.5-7.5, the water flux and rejection rate after 30 minutes of membrane operation were measured. The results are shown in Table 1. It can be seen that the RO membranes prepared by the method described in this patent have higher flux and sodium chloride desalination rate than ordinary commercial nano-RO membranes. The addition of N-methylpyrrolidone can cause the initially formed polyamide chains to swell, forming a dense porous structure, thereby improving membrane flux and rejection rate; the addition of 4-aminobenzenesulfonic acid is conducive to the diffusion of amine, thereby forming a thinner separation layer and improving membrane flux; the above two have a certain synergistic effect. Methyl benzoate in the oil phase reduces intermolecular aggregation of polyamide, thereby providing more water channels and increasing membrane flux.

[0044] Table 1: NaCl Removal Test

[0045]

[0046] Diaphragm lifespan operation

[0047] Under test conditions of 800 psi operating pressure, 35000 ppm sodium chloride solution concentration, 25℃ solution temperature, and pH value of 6.5-7.5, the initial flux and initial desalination rate of the membrane were tested. After 24 hours of continuous operation, the flux and desalination rate of the membrane were measured again, and the flux decay rate of the membrane was calculated. The results are shown in Table 2. It can be seen that after 24 hours of lifetime operation, the RO membrane prepared by the method described in this patent has higher flux permeability and selectivity than ordinary commercial RO membranes, and the decay rate is not much different, indicating that the self-made membrane has better performance.

[0048] Table 2: Lifetime Operation Test

[0049]

Claims

1. A highly permeable and selective reverse osmosis membrane, characterized in that, The high-permeability and selective reverse osmosis membrane is obtained by sequentially immersing a porous support layer in an aqueous solution and an oil solution for interfacial polymerization, thereby forming a desalination layer on the surface of the porous support layer; the aqueous solution contains 4-aminobenzenesulfonic acid and N-methylpyrrolidone, and the oil solution contains methyl benzoate.

2. The method for preparing a high-permeability and selective reverse osmosis membrane as described in claim 1, characterized in that, Includes the following steps: Step 1: Prepare a porous support layer. Step 1.1 Dissolve the polymer and benzenesulfonic acid in dimethylformamide or dimethylacetamide and stir. After complete dissolution, allow to stand to remove bubbles and obtain the casting solution; the polymer is polysulfone or polyethersulfone. Step 1.2 The casting solution is coated onto a nonwoven fabric, and a base film is formed by liquid-solid phase conversion. The conditions for liquid-solid phase conversion are: time 1-2 min, phase conversion water bath temperature 12-22℃, thermosetting water bath temperature 60-80℃, and film thickness 5.0-6.0 mil. Step 1.3 Immerse the base membrane in deionized water for preservation to obtain the porous support layer; Step 2: Prepare the desalination layer Step 2.1 Immerse the porous support layer in an aqueous solution for interfacial reaction for 1-3 minutes, then drain the surface water droplets; the aqueous solution contains 0.5wt%-1.5wt% 4-aminobenzenesulfonic acid and 1wt%-6wt% N-methylpyrrolidone. Step 2.2 Immerse the porous support layer treated in Step 2.1 in an oil phase solution for interfacial reaction for 1-2 minutes to obtain a desalination layer; the oil phase solution contains 0.5wt%-0.8wt% methyl benzoate. Step 2.3 The membrane obtained in Step 2.2 is dried to obtain a high-permeability and selective reverse osmosis membrane; the high-permeability and selective reverse osmosis membrane is an RO membrane with a desalination layer as the outer layer and a porous support layer as the inner layer.

3. The method of claim 2, wherein the membrane has a high permeability and a high selectivity. The mass fraction of the polymer is 16-20 wt%.

4. The method for preparing a high-permeability and selective reverse osmosis membrane as described in claim 2, characterized in that, The aqueous solution comprises, by weight percentage, 1.5%-3.0% m-phenylenediamine, 0.5%-1.5% aniline, 0.5%-1.5% 4-aminobenzenesulfonic acid, 1%-6% N-methylpyrrolidone (NMP), 0.01%-0.5% sodium hydroxide, with the balance being water.

5. The method for preparing a high-permeability and selective reverse osmosis membrane as described in claim 2, characterized in that, The oil phase solution comprises, by weight percentage, 0.1%-0.3% trimesoyl chloride, 0.05%-0.15% oxaloyl chloride, 0.5%-0.8% methyl benzoate, with the balance being organic solvent.

6. The method for preparing a high-permeability and selective reverse osmosis membrane as described in claim 5, characterized in that, The organic solvent is any one or more of n-hexane, cyclohexane, ethylcyclohexane, n-octane, and n-heptane.

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