Ultra-low pressure reverse osmosis membrane and production process

Abstract

The application discloses a production process of an ultra-low pressure reverse osmosis membrane, which comprises the following steps: preparing a support layer casting solution; uniformly coating the support layer casting solution on a polyester non-woven fabric, and then performing air drying and water washing; preparing a water phase casting solution and an oil phase casting solution, and adding an acidic substance in the water phase casting solution and the oil phase casting solution; the acidic substance is insoluble in water and only reacts with alkali, the reaction product is soluble in water, and the particle diameter of the acidic substance is 1-5 um; coating the water phase casting solution and the oil phase casting solution on the non-woven fabric with the support layer respectively, and then sequentially performing drying, acid washing, water washing, alkali washing, water washing and drying to obtain the ultra-low pressure reverse osmosis membrane. The application can provide a reverse osmosis membrane which has a stable structure, a relatively high desalination rate and a relatively large water flux.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of reverse osmosis membrane purification, in particular to an ultra-low pressure reverse osmosis membrane and a production process. BACKGROUND

[0002] Reverse osmosis is a highly efficient water purification method, which has the advantages of high efficiency, low cost, no phase change, easy integration, modularization and automation, etc., and is widely used in many fields such as preparation of high-purity water in the electronic industry, preparation of medical water, seawater desalination, brackish water desalination, sewage recycling, etc. With the shortage of global freshwater resources and the increasing severity of water pollution, reverse osmosis technology plays an increasingly important role in water purification.

[0003] When treating high-salinity sewage with reverse osmosis membranes, high pressure is required for desalination treatment. The pollution level of domestic water purification sources is extremely low, and the salt content in the water is also low. Therefore, low-pressure or ultra-low-pressure reverse osmosis membranes suitable for this environment are born.

[0004] Low-pressure and ultra-low-pressure reverse osmosis membranes use a loose desalination layer structure to achieve high water flux while meeting the desalination purpose.

[0005] Currently, the methods for controlling the formation of a loose desalination layer include controlling the hydrolysis degree of acyl chloride to control the looseness of the desalination layer, or adding small-molecule alcohols or ethers to the water phase to participate in the reaction with the acyl chloride monomers in the oil phase to reduce the density of the desalination layer. However, the performance improvement effect brought by these methods is not significant. If the amount added is too small, the influence on the membrane performance is also very small. If the amount added is too large, it will cause the solubility of the water phase and oil phase to deteriorate, resulting in uneven and stable water phase and oil phase solution, and secondly, it will cause the membrane performance, especially the desalination rate, to decrease sharply.

[0006] In order to ensure high permeation flux, the reverse osmosis membrane is treated with an oxidizing agent, such as chlorine, to decompose the amide bond, but this will also significantly reduce the desalination rate. In addition, the decomposition of the amide bond will cause the desalination layer structure to be unstable, and the desalination rate will decrease significantly with use. SUMMARY

[0007] In view of the above-mentioned defects of the prior art, the purpose of the present application is to provide an ultra-low pressure reverse osmosis membrane and a production process, which can provide a reverse osmosis membrane with a stable structure, high desalination rate and large water flux.

[0008] The purpose of the present application is achieved by the following technical scheme:

[0009] The production process of the ultra-low pressure reverse osmosis membrane comprises the following steps:

[0010] The support layer casting solution is prepared.

[0011] The support layer casting solution is uniformly coated on the polyester non-woven fabric, and then air-dried and washed with water;

[0012] The water phase and oil phase casting solutions are prepared, and an acidic substance is added to the water phase and oil phase casting solutions; the acidic substance is insoluble in water and only reacts with alkali, and the reaction product is soluble in water; the particle diameter of the acidic substance is 1-5 um;

[0013] The water phase casting solution and the oil phase casting solution are respectively coated on the non-woven fabric with a support layer, and then sequentially dried, pickled, washed with water, washed with alkali, washed with water, and baked to obtain an ultra-low pressure reverse osmosis membrane.

[0014] Further, the support layer casting solution comprises 100-110 parts by weight of an aprotic polar solvent, and 15-20 parts by weight of a void material; the aprotic polar solvent is one or more of dimethylacetamide, acetonitrile, dimethylformamide, dimethyl sulfoxide, and hexamethylphosphoramide; and the void material is one or more of polysulfone, polypropylene, polyacrylonitrile, and aromatic polyamide fibers.

[0015] Further, the water phase casting solution comprises 100-120 parts by weight of pure water, 5-8 parts by weight of a polyamine, 1-2 parts by weight of a polyol, and 1-2 parts by weight of an acidic substance.

[0016] Further, the polyamine is one or more of o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, piperazine, triethylamine, ethylenediamine, diphenylmethane diamine, and hexamethylenetetramine.

[0017] Further, the polyol is one or more of dipropylene glycol, neopentyl glycol, diethylene glycol, dipropylene glycol, trimethylolpropane, and 1,4-butanediol.

[0018] Further, the oil phase casting solution comprises 4-8 parts by weight of an acyl halide oxide, 100-120 parts by weight of triethanolamine, and 1-2 parts by weight of an acidic substance.

[0019] Further, the acyl halide oxide is one or more of tetrafluoro xenon monoxide, sulfuryl chloride, sulfurous chloride, trimesyl chloride, terephthalyl chloride, isophthalyl chloride, and phthalyl chloride.

[0020] Further, the acidic substance is one or more of silicic acid, stannic acid, and germanic acid.

[0021] Further, the washing solution during the alkali washing is an alkaline aqueous solution containing sodium hydroxide with a pH value of 11-13; the alkali washing is performed by high-pressure permeation immersion washing, and after the washing is completed, the content of the acidic substance is not more than 5% of the original content.

[0022] An ultra-low pressure reverse osmosis membrane is prepared by the ultra-low pressure reverse osmosis membrane production process in any one of claims 1-9.

[0023] Due to the adoption of the above technical solutions, the present application has the following advantages:

[0024] 1. Acidic substances are added to the initial aqueous phase and oil phase of the polyamide desalination layer, so that the acidic substances enter the interfacial polymerization process as non-reactive substances, and finally form an acidic substance, a polyamide and a mixed desalination layer. After the interfacial polymerization is completed, the acidic substances are reacted by alkali washing, the space occupied by the original acidic substances forms a void, so that the desalination layer forms a loose structure, and the formation of the loose structure does not destroy the polyamide, so the structure of the polyamide layer is relatively stable, and a good desalination rate can be ensured.

[0025] 2. The content of the acidic substances and the particle diameter of the acidic substances can be directly and accurately controlled to control the loose structure form of the polyamide desalination layer, so as to ensure that the desalination rate and the water flux balance of different salt-containing water quality are met.

[0026] Other advantages, objects and features of the present application will be set forth in part in the specification which follows, and in part will become apparent to those skilled in the art upon examination of the following specification, or can be learned by practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0027] The drawings of the present application are as follows:

[0028] Figure 1 The cross-sectional electron microscope photograph of the ultra-low pressure reverse osmosis membrane prepared for experimental example 6 in the present embodiment.

[0029] Figure 2 The desalination layer electron microscope photograph of the ultra-low pressure reverse osmosis membrane prepared for experimental example 6 in the present embodiment.

[0030] Figure 3 The desalination layer electron microscope photograph of the ultra-low pressure reverse osmosis membrane prepared for experimental example 6 in the present embodiment. DETAILED DESCRIPTION

[0031] The present application will be further described below in combination with the drawings and examples.

[0032] Embodiment:

[0033] The ultra-low pressure reverse osmosis membrane is prepared according to the following steps:

[0034] The support layer casting solution is prepared by mixing 100-110 parts of aprotic polar solvent and 15-20 parts of voiding agent according to weight ratio; the aprotic polar solvent is one or more of dimethylacetamide, acetonitrile, dimethylformamide, dimethyl sulfoxide, and hexamethylphosphoramide; and the voiding agent is one or more of polysulfone, polypropylene, polyacrylonitrile, and aromatic polyamide fiber.

[0035] The support layer casting solution is uniformly coated on the polyester non-woven fabric with a coating thickness of 100-500 um, and then air-dried and washed with water.

[0036] The aqueous phase casting solution is prepared by mixing 100-120 parts of pure water, 5-8 parts of polyamine, 1-2 parts of polyol, and 1-2 parts of acidic substance according to weight ratio; the polyamine is one or more of o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, piperazine, triethylamine, ethylenediamine, diphenylmethane diamine, and hexamethylenetetramine; the polyol is one or more of dipropylene glycol, neopentyl glycol, diethylene glycol, monopropylene glycol, and 1,4-butanediol; and the acidic substance is one or more of silicic acid, stannic acid, and germanic acid; the particle diameter of the acidic substance is 1-5 um.

[0037] The oil phase casting solution is prepared by mixing 4-8 parts of acyl halide oxide, 100-120 parts of triethanolamine, and 1-2 parts of acidic substance according to weight ratio; the acyl halide oxide is one or more of tetrafluoro xenon monoxide, sulfuryl chloride, chlorosulfoxide, trimesyl chloride, terephthalyl chloride, isophthalyl chloride, and phthalyl chloride; and the acidic substance is one or more of silicic acid, stannic acid, and germanic acid; the particle diameter of the acidic substance is 1-5 um.

[0038] The aqueous phase casting solution is coated on the non-woven fabric with a coating thickness of 100-200 um, and then the oil phase casting solution is coated thereon with a coating thickness of 100-200 um; after the coating is completed, the coated non-woven fabric is dried in an oven at 50-60℃ for 20 minutes, and then washed with water to remove the acid.

[0039] After the water washing, the membrane is immersed in an alkaline solution containing sodium hydroxide with a pH value of 11-13, and then immersed and washed by high-pressure penetration of the membrane; specifically, high pressure is applied to one side of a water tank in which the membrane is isolated, so that the alkaline solution containing sodium hydroxide penetrates through the membrane, the acidic substance in the desalination layer reacts with OH- ions, and the acidic substance is reacted and dissolved in the alkaline aqueous solution, so that the acidic substance is removed, and a polyamide desalination layer with loose structure is formed.

[0040] After the alkaline washing is completed, the water washing and drying are performed to obtain the ultra-low pressure reverse osmosis membrane.

[0041] The present embodiment is subjected to experiment, all experimental examples are selected with dimethylacetamide, polyamine is first used with m-phenylenediamine, polyol is selected with 1, 4-butanediol, acyl halide oxide is selected with trimesoyl chloride, specific experimental examples are as follows:

[0042] In experimental example 1, the acidic substance is selected with silicic acid, the particle diameter of silicic acid is 1um, and the void material is selected with polysulfone.

[0043] In experimental example 2, the acidic substance is selected with silicic acid, the particle diameter of silicic acid is 2.5um, and the void material is selected with polysulfone.

[0044] In experimental example 3, the acidic substance is selected with silicic acid, the particle diameter of silicic acid is 5um, and the void material is selected with polysulfone.

[0045] In experimental example 4, the acidic substance is selected with silicic acid, the particle diameter of silicic acid is 1um, and the void material is selected with a mixture of aromatic polyamide fiber and polysulfone, and the amount of the two materials is 50% respectively.

[0046] In experimental example 5, the acidic substance is selected with silicic acid, the particle diameter of silicic acid is 2.5um, and the void material is selected with aromatic polyamide fiber, and the amount of the two materials is 50% respectively.

[0047] In experimental example 6, the acidic substance is selected with silicic acid, the particle diameter of silicic acid is 5um, and the void material is selected with aromatic polyamide fiber, and the amount of the two materials is 50% respectively.

[0048] In experimental example 7, the acidic substance is selected with silicic acid, the particle diameter of silicic acid is 1um, and the void material is selected with aromatic polyamide fiber.

[0049] In experimental example 8, the acidic substance is selected with silicic acid, the particle diameter of silicic acid is 2.5um, and the void material is selected with aromatic polyamide fiber.

[0050] In experimental example 9, the acidic substance is selected with silicic acid, the particle diameter of silicic acid is 5um, and the void material is selected with aromatic polyamide fiber.

[0051] The above 9 experimental examples are respectively made into ultra-low pressure reverse osmosis membranes marked as 1-9, and the type of SES20-400 ultra-low pressure large flux reverse osmosis membrane of Delanmeier is marked as 10, and the above 10 groups of membranes are subjected to reverse osmosis treatment on the city tap water with TDS value of 800 under the water pressure of 0.49 MPa, and the desalination rate and water flux are recorded when the continuous operation is 10 hours and 600 hours, and the specific structure is as follows:

[0052]

[0053] Water flux refers to the volume of water passing through a unit membrane area per unit time under a unit pressure, abbreviated as PWP, the unit is: liters / meter / pressure / hour, that is, the flow of water passing through the membrane under a unit pressure per unit membrane area; PWP = water flow per unit time * temperature correction factor / TMP / membrane area; wherein the membrane penetration pressure TMP = (Pin + Pout) / 2-Pp, that is, the average of the inlet pressure and the outlet pressure minus the filtrate pressure.

[0054] The rate of desalination refers to the percentage of the amount removed in the process of removing anions and cations in water by chemical or ion exchange method. In practical application, it generally refers to the desalination rate of the reverse osmosis system, and the calculation formula is: desalination rate = (total feed water salt content-total product water salt content) / total feed water salt content*100%.

[0055] According to the experimental results, it can be seen that the larger the particle diameter of the silicic acid used, the greater the water flux at the initial stage, and the lower the desalination rate, which is related to the size of the void formed after the reaction of the acidic substance; the larger the void, the more easily the relatively loose desalination layer is damaged in the later stage, and the greater the decrease in desalination rate with the increase of particle diameter, and the largest increase in water flux;

[0056] At the same time, the more the amount of aromatic polyamide fibers used in the void material, the lower the initial water flux compared to the amount of aromatic polyamide fibers used, because the polyamide desalination layer formed by the interfacial polymerization of polyamide fibers has a more compact structure, and the desalination layer is thickened, which increases the desalination rate but reduces the water flux, but the amplitude is small. With the use of the membrane, the structure connection between the desalination layer and the support layer can better protect the desalination layer, so that the desalination rate decreases at a smaller rate, and the water flux changes less.

[0057] In summary, the performance of experimental example 6 is more balanced, and the manufacturing cost is more controllable, the cross-sectional view and the top view of the desalination layer are shown in Figure 1 and Figure 2 The scheme of experimental example 6 is the best ultra-low pressure reverse osmosis membrane scheme.

[0058] The 9 groups of membranes in this embodiment are better than the existing No. 10 membrane on the market in terms of overall desalination rate, water flux and use performance.

[0059] Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solutions of the present application and are not limiting, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the present application, which should be covered by the claims of the present application.

Claims

1. A process for producing ultra-low pressure reverse osmosis membranes, characterized in that, Includes the following steps: Prepare the casting solution for the support layer; The support layer casting solution is evenly coated onto the polyester nonwoven fabric, and then air-dried and washed. Prepare aqueous and oil-phase casting solutions, and add acidic substances to both aqueous and oil-phase casting solutions; the acidic substances are insoluble in water and only react with alkali, the reaction products are soluble in water, and the particle diameter of the acidic substances is 1~5 μm; The aqueous phase casting solution and the oil phase casting solution are respectively coated onto a nonwoven fabric with a support layer, and then dried, acid-washed, water-washed, alkali-washed, water-washed and dried in sequence to obtain an ultra-low pressure reverse osmosis membrane. The aqueous casting solution comprises, by weight, 100-120 parts of pure water, 5-8 parts of polyamine, 1-2 parts of polyol, and 1-2 parts of acidic substance; the polyamine is one or a mixture of o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, piperazine, triethylamine, ethylenediamine, diphenylmethanediamine, and hexamethylenetetramine; the polyol is one or a mixture of dipropylene glycol, neopentyl glycol, diethylene glycol, dipropylene glycol, trimethylolpropane, and 1,4-butanediol. The oil phase casting solution comprises 4-8 parts by weight of acyl halide oxide, 100-120 parts by weight of triethanolamine, and 1-2 parts by weight of acidic substance; the acyl halide oxide is one or more of pyromellitic trioxide, terephthaloyl chloride, isophthaloyl chloride, and orthophthaloyl chloride. The acidic substance is one or more of silicic acid, stannic acid, and germanic acid; The washing solution used in the alkaline washing process is an alkaline aqueous solution containing sodium hydroxide with a pH value of 11-13; the alkaline washing is performed by high-pressure osmosis immersion washing, and the content of acidic substances after washing does not exceed 5% of the original content.

2. The ultra-low pressure reverse osmosis membrane production process according to claim 1, characterized in that, The casting solution for the support layer comprises 100-110 parts by weight of an aprotic polar solvent and 15-20 parts by weight of a void material; the aprotic polar solvent is one or a mixture of dimethylacetamide, acetonitrile, dimethylformamide, dimethyl sulfoxide, and hexamethylphosphoric triamine; the void material is one or a mixture of polysulfone, polypropylene, polyacrylonitrile, and aromatic polyamide fibers.

3. An ultra-low pressure reverse osmosis membrane, characterized in that, Prepared using the ultra-low pressure reverse osmosis membrane production process described in any one of claims 1 to 2.

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