A composite film and a preparation method thereof

Abstract

The present invention provides a composite membrane and a preparation method thereof. In the preparation method provided by the present invention, a core liquid, a spinning solution 1, a spinning solution 2, and an outer protection solution are respectively provided first, and then the four solutions are simultaneously extruded through 4 channels in a spinneret. By controlling the content of dopamine hydrochloride and the solvent concentration in the outer protection solution and regulating the pH of the core liquid, etc., a microfiltration membrane with a loose outer layer and controllable pore size is prepared, improving the water flux of the double-layer composite hollow fiber membrane; then, by utilizing the mutual penetration and reaction of the components in the outer protection solution and the core liquid to generate hydrophilic and adhesive polydopamine, which penetrates between and on the inner and outer surfaces of two different types of membrane materials, namely the microfiltration membrane and the ultrafiltration membrane, the hydrophilic property and anti-pollution property of the double-layer composite hollow fiber membrane are improved. In addition, polydopamine is formed as a hydrophilic binder inside and outside the double-layer composite membrane during the film-forming process, and there is no need to perform a hydrophilization treatment on the hollow fiber membrane after its successful preparation. The preparation method is simple and the process is simplified.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane separation, and more particularly to a composite membrane and a preparation method thereof. Background Art

[0002] Membrane separation technology refers to the use of the screening effect of biological membranes to separate, purify, and concentrate a feed liquid to achieve the purpose of purification. Membrane separation technology has been widely used in the fields of food, fermentation, water treatment, and biopharmaceuticals due to its advantages of high separation efficiency, low energy consumption, being able to operate at room temperature, and easy recovery of separated products.

[0003] According to the membrane filtration method, it is divided into external pressure type and internal pressure type. Compared with the internal pressure membrane filtration method, external pressure filtration, as Figure 1 shown, is that a feed liquid with complex components enters from side A, passes through the outer surface of the hollow fiber membrane, and under the action of transmembrane pressure, the filtrate flows out from side C, and the concentrated liquid after the pollutants are intercepted flows out from side B. In this way, it will not cause blockage inside the membrane filaments, enabling it to operate stably for a long time. This is also one of the reasons why external pressure filtration has become the mainstream membrane filtration form.

[0004] The key to membrane separation technology lies in the membrane material. According to different membrane pore sizes, it can be divided into reverse osmosis membranes, nanofiltration membranes, ultrafiltration membranes, and microfiltration membranes. Microfiltration membranes, with pore sizes of 0.1 - 1 μm, are mainly used to intercept substances such as suspended solids, bacteria, and large molecular weight colloids; ultrafiltration membranes, with pore sizes of 3 - 100 nm, are mainly used to intercept relatively small-sized substances such as organic substances, proteins, and polypeptides. The conventional membrane filtration process flow is that the feed liquid is pretreated through a microfiltration membrane and then enters the ultrafiltration membrane module for further purification. In this process, two or more membrane filters are used in combination to enhance the impurity removal effect and improve the product recovery rate, but the cost is greatly increased. With the development of technology, people have gradually turned their attention to composite membranes.

[0005] Chinese Patent CN101642683B discloses a double-layer composite hollow fiber nanofiltration membrane, its preparation method and special tool. It uses the non-solvent induced phase inversion method to prepare the double-layer composite nanofiltration membrane, and the core liquid and two spinning solutions are co-extruded through a special tool - a three-channel spinneret. Although this method can produce the hollow fiber composite nanofiltration membrane in one step and control the pore size of the inner surface of the composite nanofiltration membrane by the core liquid concentration, it cannot regulate the pore size of the outer surface of the composite nanofiltration membrane. Since the outer surface of the membrane plays a separation and filtration role in external pressure filtration, the size of the pore size on the outer surface directly affects the filtration accuracy and filtration efficiency. Chinese Patent CN115672057A discloses a ultrafiltration-nanofiltration integrated composite separation membrane and its preparation method. This method mainly coats an amine and acyl chloride solution on the surface of the ultrafiltration membrane, and forms a polyamide nanofiltration functional layer through interfacial polymerization. However, the prepared composite membrane actually only has a single nanofiltration performance and is not a truly ultrafiltration-nanofiltration composite membrane. Chinese Patent CN212356645U discloses a separation membrane for groundwater pollution remediation. This membrane needs to first prepare a polyvinylidene fluoride membrane, and then coat an adhesive polydopamine solution added with zwitterionic polypeptide on the surface of the prepared polyvinylidene fluoride membrane to improve the hydrophilicity of the surface. Furthermore, it is ensured that one side of the membrane has hydrophilicity and the other side has hydrophobicity, so that in the separation process of groundwater non-aqueous phase liquid emulsion, water can only permeate from the hydrophilic layer side to the hydrophobic layer side, while the emulsion micro-droplets are retained on the hydrophilic layer side, thereby realizing the efficient separation of the emulsion. This method has cumbersome steps and complex processes, which is not conducive to large-scale commercialization. To sum up, for the existing double-layer composite membranes, either the pore size of their outer surface cannot be regulated and the expected effect of external pressure composite membrane separation cannot be fully achieved; or their functions are single and the ultrafiltration-nanofiltration composite function cannot be truly realized; or their preparation steps are very cumbersome and the processes are complex, which is not conducive to large-scale commercialization. Summary of the Invention

[0006] In view of this, the present invention provides a composite membrane and its preparation method. The composite membrane prepared by the present invention can simultaneously realize the microfiltration and ultrafiltration functions, can effectively improve the flux and anti-pollution ability, and its preparation process is simple.

[0007] The present invention provides a preparation method of a composite membrane, comprising the following steps:

[0008] A) Provide spinning solution 1, spinning solution 2, core liquid and outer protection solution;

[0009] Wherein,

[0010] The preparation raw materials of the spinning solution 1 include:

[0011] Polymer 15% - 20%;

[0012] Hydrophilic additive 10% - 20%;

[0013] Solvent: 60% - 75%;

[0014] The raw materials for preparing the spinning solution 2 include:

[0015] Polyvinylidene fluoride: 15% - 18%;

[0016] Hydrophilic additive: 10% - 15%;

[0017] Solvent: 67% - 75%;

[0018] The core liquid includes a base liquid and a pH regulator:

[0019] The raw materials for preparing the base liquid include:

[0020] Tris(hydroxymethyl)aminomethane: 0.5% - 2%;

[0021] Water: 63% - 69.5%;

[0022] Organic solvent: 30% - 35%;

[0023] The raw materials for preparing the outer protective liquid include:

[0024] Dopamine hydrochloride: 0.2% - 1%;

[0025] Water: 24% - 34.5%;

[0026] Organic solvent: 55% - 80%;

[0027] B) Co - extrude the spinning solution 1, spinning solution 2, core liquid, and outer protective solution together from 4 adjacent channels in the multi - spinneret, wherein the core liquid, spinning solution 1, spinning solution 2, and outer protective solution are extruded in the order from the inner channel to the outer channel;

[0028] Among them, the number of channels of the multi - spinneret ≥ 4;

[0029] C) After extrusion in step B), enter the air gap to complete the primary phase inversion to obtain the nascent membrane filaments; then enter the gel bath to complete the secondary phase inversion; then enter the water washing bath for water washing and stretching to complete the complete phase inversion; finally, dry to obtain the composite membrane.

[0030] Preferably, in the raw materials for preparing the spinning solution 1:

[0031] The polymer is at least one of cellulose acetate, polyacrylonitrile, polyethersulfone, polysulfone, and polyamide;

[0032] The hydrophilic additive is at least one of polyvinylpyrrolidone, polyvinyl alcohol, and polyethylene glycol;

[0033] The solvent is at least one of N-methylpyrrolidone, N,N-dimethylacetamide and N,N-dimethylformamide.

[0034] Preferably, in the raw materials for preparing the spinning solution 2:

[0035] The hydrophilic additive is at least one of polyvinylpyrrolidone, polyvinyl alcohol and polyethylene glycol;

[0036] The solvent is at least one of N-methylpyrrolidone, N,N-dimethylacetamide and N,N-dimethylformamide.

[0037] Preferably, the spinning solution 1 is prepared by the following preparation method:

[0038] S1. Mix and dissolve the hydrophilic additive and the solvent to obtain a mixed solution 1;

[0039] S2. Mix and heat the mixed solution 1 with the polymer to obtain the spinning solution 1.

[0040] Preferably, in step S1, the temperature of the mixing and dissolving is 35-40°C;

[0041] In step S2, the temperature of the heating is 75-90°C.

[0042] Preferably, the spinning solution 2 is prepared by the following preparation method:

[0043] K1. Mix and dissolve the hydrophilic additive and the solvent to obtain a solution 1;

[0044] K2. Mix and heat the solution 1 with the polymer to obtain the spinning solution 2.

[0045] Preferably, in step K1, the temperature of the mixing and dissolving is 35-40°C;

[0046] In step K2, the temperature of the heating is 75-90°C.

[0047] Preferably, in step B):

[0048] The flow rate of the core liquid is 10-15 mL / min;

[0049] The flow rate of the spinning solution 1 is 5-8 mL / min;

[0050] The flow rate of the spinning solution 2 is 7-11 mL / min;

[0051] The flow rate of the outer protective liquid is 7-9 mL / min.

[0052] Preferably, in step C):

[0053] The height of the air gap is 100 - 500 mm, and the temperature of the air gap is 50 - 70 °C;

[0054] The gel tank contains water; the temperature of the water is 50 - 70 °C;

[0055] The water temperature in the water washing tank is 60 - 80 °C, and the stretching speed is 20 - 30 m / min;

[0056] The drying temperature is 60 - 80 °C.

[0057] The present invention also provides a composite membrane prepared by the preparation method described in the above technical solution.

[0058] In the preparation method provided by the present invention, the core liquid, spinning solution 1, spinning solution 2 and outer protective solution are respectively provided first, and then the four solutions are simultaneously extruded through 4 channels in the spinneret. By controlling the content of hydrochloric acid dopamine and the solvent concentration in the outer protective liquid, and regulating the pH of the core liquid, etc., a microfiltration membrane with a loose outer layer and controllable pore size is prepared, which improves the water flux of the double-layer composite hollow fiber membrane; then, by using the mutual penetration and reaction of the components in the outer protective liquid and the core liquid to generate hydrophilic and adhesive polydopamine, which penetrates through two different types of membrane materials, namely the microfiltration membrane and the ultrafiltration membrane, and their inner and outer surfaces, the hydrophilic property and anti-pollution property of the double-layer composite hollow fiber membrane are improved. In addition, polydopamine is formed as a hydrophilic binder inside and outside the double-layer composite membrane during the film-forming process, and there is no need to perform hydrophilization treatment on the hollow fiber membrane after it is successfully prepared. Therefore, this preparation method is simple and the process is simplified.

[0059] The experimental results show that in the double-layer composite membrane prepared by the present invention, the outer layer is a loose microfiltration membrane with a controllable pore size of 0.1 - 0.22 μm, and the inner layer is an ultrafiltration membrane with a pore size of 15 - 20 nm, which can simultaneously realize the microfiltration and ultrafiltration functions. The obtained composite membrane has a low water contact angle, a pure water flux of more than 3080 LMH / bar, and a membrane flux recovery rate of more than 90%, significantly improving the water flux, hydrophilic property and anti-pollution property of the double-layer composite hollow fiber membrane. Description of the Drawings

[0060] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0061] Figure 1 It is a schematic diagram of the external pressure filtration use of the water treatment membrane;

[0062] Figure 2Schematic diagram of spinning extrusion when taking a quadruple spinneret as an example in the present invention;

[0063] Figure 3 Schematic diagram of the film formation mechanism of the double-layer film of the present invention;

[0064] Figure 4 SEM test result diagram in the product test of the present invention. Detailed implementation manners

[0065] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the description of this application herein are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0066] In this article, among the technical features described in an open-ended manner, a closed technical solution composed of the listed features is included, and an open technical solution including the listed features is also included.

[0067] The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0068] In this article, regarding numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to integers, each integer between the minimum and maximum values of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0069] In this article, regarding the units of data ranges, if only the unit is attached after the right endpoint, it means that the units of the left endpoint and the right endpoint are the same. For example, 90,000 to 300,000 means that the units of the left endpoint "9" and the right endpoint "30" are both 10,000.

[0070] Only some numerical ranges are specifically disclosed in this article. However, any lower limit can be combined with any upper limit to form a range not explicitly recorded; and any lower limit can be combined with other lower limits to form a range not explicitly recorded. Similarly, any upper limit can be combined with any other upper limit to form a range not explicitly recorded. In addition, each individually disclosed point or single numerical value itself can be used as a lower limit or an upper limit and combined with any other point or single numerical value or combined with other lower limits or upper limits to form a range not explicitly recorded.

[0071] The present invention provides a method for preparing a composite film, comprising the following steps:

[0072] A) Provide spinning solution 1, spinning solution 2, core solution and outer protective solution;

[0073] Among them,

[0074] The raw materials for preparing the spinning solution 1 include:

[0075] Polymer 15% - 20%;

[0076] Hydrophilic additive 10% - 20%;

[0077] Solvent 60% - 75%;

[0078] The raw materials for preparing the spinning solution 2 include:

[0079] Polyvinylidene fluoride 15% - 18%;

[0080] Hydrophilic additive 10% - 15%;

[0081] Solvent 67% - 75%;

[0082] The core solution includes a base solution and a pH regulator:

[0083] The raw materials for preparing the base solution include:

[0084] Tris(hydroxymethyl)aminomethane 0.5% - 2%;

[0085] Water 63% - 69.5%;

[0086] Organic solvent 30% - 35%;

[0087] The raw materials for preparing the outer protective solution include:

[0088] Dopamine hydrochloride 0.2% - 1%;

[0089] Water 24% - 34.5%;

[0090] Organic solvent 55% - 80%;

[0091] B) Co-extrude the spinning solution 1, spinning solution 2, core solution and outer protective solution together from 4 adjacent channels in the multi-orifice spinneret. Among them, the core solution, spinning solution 1, spinning solution 2 and outer protective solution are extruded in the order from the inner channel to the outer channel;

[0092] Among them, the number of channels of the multi-orifice spinneret ≥ 4;

[0093] C) After extrusion in step B), enter the air gap to complete the preliminary phase inversion to obtain the nascent membrane filaments; then enter the gel bath to complete the secondary phase inversion; then, enter the water washing bath for water washing and stretching to complete the complete phase inversion; finally, dry to obtain the composite membrane.

[0094] The preparation method of the present invention can prepare a double-layer composite hollow fiber membrane integrating microfiltration and ultrafiltration. The membrane preparation process is simple, the pore size of the outer surface can be precisely controlled, the microfiltration and ultrafiltration functions can be achieved simultaneously, and the excellent hydrophilicity of the membrane endows it with high flux and anti-pollution ability.

[0095] Regarding step A) :

[0096] A) Provide spinning solution 1, spinning solution 2, core liquid and outer protection solution.

[0097] [Regarding spinning solution 1]:

[0098] In the present invention, the preparation raw materials of the spinning solution 1 include:

[0099] 15% - 20% of polymer;

[0100] 10% - 20% of hydrophilic additive;

[0101] 60% - 75% of solvent.

[0102] Among them:

[0103] The polymer is preferably at least one of cellulose acetate, polyacrylonitrile, polyethersulfone, polysulfone and polyamide, more preferably cellulose acetate and / or polyacrylonitrile, and most preferably polyacrylonitrile. In the present invention, the weight average molecular weight of the polymer is preferably 90,000 - 300,000, more preferably 150,000 - 300,000. In the present invention, the mass percentage of the polymer in the preparation raw materials of the spinning solution 1 is 15% - 20%, specifically 15%, 16%, 17%, 18%, 19%, 20%.

[0104] The hydrophilic additive is preferably at least one of polyvinylpyrrolidone, polyvinyl alcohol and polyethylene glycol, more preferably polyvinylpyrrolidone and / or polyvinyl alcohol, and most preferably polyvinyl alcohol. In the present invention, the weight average molecular weight of the hydrophilic additive is preferably 150,000 - 300,000, more preferably 200,000 - 300,000. In the present invention, the mass percentage of the hydrophilic additive in the preparation raw materials of the spinning solution 1 is 10% - 20%, specifically 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%.

[0105] The solvent is preferably at least one of N-methylpyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide, more preferably N,N-dimethylformamide. In the present invention, the mass percentage of the solvent in the raw materials for preparing the spinning solution 1 is 60% to 75%, specifically 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%.

[0106] In the present invention, the total amount of the above polymer, hydrophilic additive, and solvent is preferably 100%.

[0107] In the present invention, the spinning solution 1 is preferably prepared by the following method: S1. Mix and dissolve the hydrophilic additive and the solvent to obtain a mixed solution 1; S2. Mix and heat the mixed solution 1 with the polymer to obtain the spinning solution 1.

[0108] In step S1, the temperature of the mixing and dissolving is preferably 35 to 40°C, specifically 35°C, 36°C, 37°C, 38°C, 39°C, 40°C, more preferably 40°C. The mixing and dissolving method is preferably stirring and mixing and dissolving. The stirring time is preferably 1 to 3 h, specifically 1 h, 2 h, 3 h, more preferably 2 h, until completely dissolved.

[0109] In step S2, the heating temperature is preferably 75 to 90°C, specifically 75°C, 76°C, 77°C, 78°C, 79°C, 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C, 90°C. The mixing and heating are carried out under stirring. The stirring time is preferably 8 to 12 h, specifically 8 h, 9 h, 10 h, 11 h, 12 h, more preferably 10 h. After the above treatment, the spinning solution 1 is obtained.

[0110] [Regarding the spinning solution 2]:

[0111] In the present invention, the raw materials for preparing the spinning solution 2 include:

[0112] Polyvinylidene fluoride 15% - 18%;

[0113] Hydrophilic additive 10% - 15%;

[0114] Solvent 67% - 75%.

[0115] Wherein:

[0116] The polymer is different from the polymer used in Spinning Solution 1 and is polyvinylidene fluoride. In the present invention, the weight-average molecular weight of the polymer is preferably 300,000 to 600,000, more preferably 450,000 to 600,000, and most preferably 600,000. In the present invention, the mass percentage of the polymer in the raw materials for preparing Spinning Solution 2 is 15% to 18%, specifically 15%, 16%, 17%, or 18%.

[0117] The hydrophilic additive is preferably at least one of polyvinylpyrrolidone, polyvinyl alcohol, and polyethylene glycol, more preferably polyvinylpyrrolidone. In the present invention, the weight-average molecular weight of the hydrophilic additive is preferably 800,000 to 1,100,000, more preferably 1,000,000 to 1,100,000, and most preferably 1,100,000. In the present invention, the mass percentage of the hydrophilic additive in the raw materials for preparing Spinning Solution 2 is 10% to 15%, specifically 10%, 11%, 12%, 13%, 14%, or 15%.

[0118] The solvent is preferably at least one of N-methylpyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide, more preferably N-methylpyrrolidone and / or N,N-dimethylacetamide, and most preferably N-methylpyrrolidone. In the present invention, the mass percentage of the solvent in the raw materials for preparing Spinning Solution 2 is 55% to 80%, specifically 55%, 60%, 65%, 70%, 75%, or 80%.

[0119] In the present invention, the total amount of the above polymer, hydrophilic additive, and solvent is preferably 100%.

[0120] In the present invention, Spinning Solution 2 is preferably prepared by the following method: K1. Mix and dissolve the hydrophilic additive and the solvent to obtain Solution 1; K2. Mix and heat the Solution 1 with the polymer to obtain Spinning Solution 2.

[0121] In step K1, the temperature of the mixing and dissolving is preferably 35 to 40 °C, specifically 35 °C, 36 °C, 37 °C, 38 °C, 39 °C, or 40 °C, and more preferably 40 °C. The method of the mixing and dissolving is preferably stirring and mixing for dissolution. The stirring time is preferably 1 to 3 h, specifically 1 h, 2 h, or 3 h, and more preferably 2 h until completely dissolved.

[0122] In step K2, the heating temperature is preferably 75 to 90 °C, specifically 75 °C, 76 °C, 77 °C, 78 °C, 79 °C, 80 °C, 81 °C, 82 °C, 83 °C, 84 °C, 85 °C, 86 °C, 87 °C, 88 °C, 89 °C, or 90 °C. The mixing and heating are carried out under stirring. The stirring time is preferably 8 to 12 h, specifically 8 h, 9 h, 10 h, 11 h, or 12 h, and more preferably 10 h. After the above treatment, Spinning Solution 2 is obtained.

[0123] [Regarding the core liquid]:

[0124] In the present invention, the core liquid comprises a base liquid and a pH regulator.

[0125] In the present invention, the raw materials for preparing the base liquid include:

[0126] Tris 0.5% - 2%;

[0127] Water 63% - 69.5%;

[0128] Organic solvent 30% - 35%.

[0129] Wherein:

[0130] The source of the Tris has no special limitation and can be a commercially available product. The mass percentage of the Tris in the raw materials for preparing the base liquid is 0.5% - 2%, specifically it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%.

[0131] The water is preferably pure water. The mass percentage of the water in the raw materials for preparing the base liquid is 63% - 69.5%, specifically it can be 63%, 64%, 65%, 66%, 67%, 68%, 69%, 69.5%.

[0132] The organic solvent is preferably at least one of N - methylpyrrolidone, N,N - dimethylacetamide and N,N - dimethylformamide, more preferably the same as the solvent in the spinning solution 1. In the present invention, the mass percentage of the organic solvent in the raw materials for preparing the base liquid is 30% - 35%, specifically it can be 30%, 31%, 32%, 33%, 34%, 35%.

[0133] In the present invention, the total amount of the above - mentioned Tris, water and organic solvent is preferably 100%.

[0134] In the present invention, in addition to the base liquid, it further comprises a pH regulator. In the present invention, the pH regulator is preferably at least one of a sodium carbonate solution, a potassium bicarbonate solution, a sodium hydroxide solution and a potassium hydroxide solution, more preferably a sodium hydroxide solution and / or a potassium hydroxide solution, and most preferably a sodium hydroxide solution. In the present invention, the concentration of the pH regulator is preferably 1 - 3 mol / L, more preferably 1 - 2 mol / L. In the present invention, the amount of the pH regulator is preferably such that the pH value of the obtained core liquid reaches 9 - 11, specifically it can be 9, 10, 11, and more preferably 9.

[0135] In the present invention, the core liquid is preferably prepared by the following method: mix tris(hydroxymethyl)aminomethane and water uniformly, and then add an organic solvent and mix uniformly; then add a pH regulator to adjust the pH value to obtain the core liquid. Among them, the above operation process is preferably carried out at room temperature, specifically 20-30°C.

[0136] [Regarding the outer protective liquid]:

[0137] In the present invention, the raw materials for preparing the outer protective liquid include:

[0138] Dopamine hydrochloride 0.2% - 1%;

[0139] Water 24% - 34.5%;

[0140] Organic solvent 55% - 80%.

[0141] Among them:

[0142] The source of the dopamine hydrochloride is not particularly limited and can be a commercially available product. The mass percentage of the dopamine hydrochloride in the raw materials for preparing the outer protective liquid is 0.2% - 1%, specifically 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%.

[0143] The water is preferably pure water. The mass percentage of the water in the raw materials for preparing the outer protective liquid is 24% - 34.5%, specifically 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 34.5%.

[0144] The organic solvent is preferably at least one of N-methylpyrrolidone, N,N-dimethylacetamide and N,N-dimethylformamide, and more preferably the same as the solvent in the spinning solution 2. The mass percentage of the solvent in the raw materials for preparing the outer protective liquid is 55% - 80%, specifically 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%.

[0145] In the present invention, the total amount of the above dopamine hydrochloride, water and organic solvent is preferably 100%.

[0146] In the present invention, the outer protective liquid is preferably prepared by the following method: mix dopamine hydrochloride and water uniformly, and then add an organic solvent and mix uniformly to obtain the outer protective liquid. Among them, the above operation process is preferably carried out at room temperature, specifically 20-30°C.

[0147] Regarding step B) :

[0148] B) Co-extrude the spinning solution 1, spinning solution 2, core solution, and outer protective solution together from 4 adjacent channels in the multi-orifice spinneret. Among them, the core solution, spinning solution 1, spinning solution 2, and outer protective solution are extruded in the order from the inner channel to the outer channel.

[0149] In the present invention, the number of channels in the multi-orifice spinneret ≥ 4, more preferably 4, that is, a quadruple orifice spinneret.

[0150] In the present invention, the spinning solution 1, spinning solution 2, core solution, and outer protective solution are co-extruded together from 4 adjacent channels in the multi-orifice spinneret. Moreover, the core solution, spinning solution 1, spinning solution 2, and outer protective solution are extruded in the order from the inner channel to the outer channel. Taking the quadruple orifice spinneret as an example, see Figure 2 , which are the first channel, the second channel, the third channel, and the fourth channel from the inside to the outside. The core solution flows in from the first channel, the spinning solution 1 flows in from the second channel, the spinning solution 2 flows in from the third channel, and the outer protective solution flows in from the fourth channel, and they are co-extruded. When the number of channels in the multi-orifice spinneret > 4, by analogy, any 4 adjacent channels can be selected and used in the above order.

[0151] In the present invention, the flow rate of the core solution is preferably 10 - 15 mL / min, specifically it can be 10 mL / min, 11 mL / min, 12 mL / min, 13 mL / min, 14 mL / min, 15 mL / min, and more preferably 12 - 15 mL / min. The flow rate of the spinning solution 1 is preferably 5 - 8 mL / min, specifically it can be 5 mL / min, 6 mL / min, 7 mL / min, 8 mL / min, and more preferably 6 - 8 mL / min. The flow rate of the spinning solution 2 is preferably 7 - 11 mL / min, specifically it can be 7 mL / min, 8 mL / min, 9 mL / min, 10 mL / min, 11 mL / min, and more preferably 9 - 11 mL / min. The flow rate of the outer protective solution is preferably 7 - 9 mL / min, specifically it can be 7 mL / min, 8 mL / min, 9 mL / min, and more preferably 8 - 9 mL / min.

[0152] The composite membrane of the present invention is prepared by the non-solvent induced phase inversion method. In the present invention, the core liquid, spinning solution 1, spinning solution 2, and outer protective solution are co-extruded from 4 adjacent channels in a multi-orifice spinneret. When spinning solution 1 contacts the core liquid, the presence of the non-solvent causes it to undergo phase inversion and solidify into a membrane. The phase inversion rate is related to the non-solvent concentration in the core liquid. The higher the non-solvent content in the core liquid, the faster the phase inversion rate when contacting the spinning solution, and the smaller the pore size of the formed membrane. Similarly, when spinning solution 2 contacts the outer protective liquid, the presence of the non-solvent causes it to undergo phase inversion and solidify into a membrane. By increasing the solvent concentration in the outer protective liquid, the phase inversion rate becomes slower, and the pore size of the formed membrane becomes larger. Therefore, by controlling the solvent and non-solvent content in the outer protective liquid, the pore size of the outer surface of the double-layer composite membrane can be controlled.

[0153] The film-forming mechanism of the double-layer composite membrane of the present invention is as follows:

[0154] See Figure 3 , the four media of the core liquid, spinning solution 1, spinning solution 2, and outer protective solution are co-extruded from the spinneret at different rates. Tris in the core liquid penetrates through membrane 1 (the membrane formed by spinning solution 1) to the region of membrane 2 (the membrane formed by spinning solution 2), while dopamine hydrochloride diffuses from membrane 2 to the region of membrane 1. Dopamine hydrochloride can react and self-polymerize with the Tris solution in the presence of alkalinity and oxygen to form a polydopamine network structure. Polydopamine has strong adhesiveness and can adhere to the surface of most organic or inorganic substances. Therefore, it can strengthen the binding between membrane 1 and membrane 2. In addition, the polydopamine structure contains a large number of active groups such as amino and phenolic hydroxyl groups, which can significantly enhance the hydrophilicity of the entire double-layer membrane, greatly improve the permeation flux of the double-layer membrane, and significantly improve the filtration efficiency and anti-protein fouling performance.

[0155] In the double-layer composite membrane obtained in the present invention, the first separation layer (outer layer) is a microfiltration membrane, and the pore size of the outer surface of the microfiltration membrane is 0.1 - 0.22 μm. The second separation layer (inner layer) is an ultrafiltration membrane, and the pore size of the ultrafiltration membrane is 15 - 20 nm. The pore size of the outer surface membrane of the first separation layer is controlled by the solvent concentration of the outer protective liquid, and the pore size of the inner surface membrane of the second separation layer is controlled by the non-solvent concentration of the core liquid. Dopamine hydrochloride in the outer protective liquid and the Tris buffer solution in the core liquid combine to form polydopamine with hydrophilicity and adhesiveness during the film-forming process. Polydopamine not only strengthens the binding of the double-layer composite membrane but also further improves the performance of the double-layer composite membrane such as flux and anti-protein fouling.

[0156] Regarding step C) :

[0157] C) After extrusion in step B), it enters the air gap to complete the preliminary phase inversion and obtain the nascent membrane filaments; then it enters the gel bath to complete the secondary phase inversion; after that, it enters the water washing bath for water washing and stretching to complete the complete phase inversion; finally, it is dried to obtain the composite membrane.

[0158] In the present invention, in step B), after each spinning solution is extruded from the multi-orifice spinneret, it enters the air gap (i.e., air bath), and the preliminary phase inversion from the spinning solution to the nascent membrane filaments is completed in the air gap. Among them, the height of the air gap (i.e., the distance of the air section between the spinneret and the gel bath) is preferably 100 - 500 mm, more preferably 300 - 500 mm. In the present invention, the temperature of the air gap is preferably 50 - 70 °C, more preferably 60 - 70 °C.

[0159] In the present invention, after the nascent membrane filaments are obtained through preliminary phase inversion, they enter the gel bath, and solvents, hydrophilic additives, etc. in the nascent membrane filaments are largely eluted in the gel bath, and the secondary phase inversion is completed in the gel bath. In the present invention, the gel bath is preferably composed of water; the water is preferably pure water. The temperature of the water is preferably 50 - 70 °C, more preferably 60 - 70 °C.

[0160] In the present invention, the membrane filaments after the secondary phase inversion in the gel bath enter the water washing bath, and after being washed and stretched in the water washing bath, the membrane filaments are completely phase-inverted. In the present invention, the water temperature of the water washing bath is preferably 60 - 80 °C, more preferably 70 - 80 °C. The stretching speed of the water washing bath is preferably 20 - 30 m / min, more preferably 25 - 30 m / min.

[0161] In the present invention, after the above treatment, the completely phase-inverted membrane filaments are dried. In the present invention, the drying temperature is preferably 60 - 80 °C, more preferably 70 - 80 °C. After the above treatment, it enters the wire winding device to obtain a double-layer composite hollow fiber membrane.

[0162] The present invention also provides a double-layer composite membrane prepared by the preparation method described in the above technical solution.

[0163] In the preparation method provided by the present invention, the core liquid, spinning solution 1, spinning solution 2, and outer protective solution are respectively provided first, and then the four solutions are simultaneously extruded through 4 channels in the spinneret. By controlling the content of hydrochloric acid dopamine and the solvent concentration in the outer protective liquid, and regulating the pH of the core liquid, etc., a microfiltration membrane with a loose outer layer and controllable pore size is prepared, improving the water flux of the double-layer composite hollow fiber membrane; then, by using the mutual penetration and reaction of the components in the outer protective liquid and the core liquid to generate hydrophilic and adhesive polydopamine, which penetrates through two different types of membrane materials, namely the microfiltration membrane and the ultrafiltration membrane, and their inner and outer surfaces, the hydrophilic property and anti-pollution property of the double-layer composite hollow fiber membrane are improved. In addition, polydopamine is formed as a hydrophilic binder inside and outside the double-layer composite membrane during the film-forming process, and there is no need to perform a hydrophilization treatment on the hollow fiber membrane after it is successfully prepared. Therefore, this preparation method is simple and the process is simplified.

[0164] The experimental results show that in the double-layer composite membrane prepared by the present invention, the outer layer is a loose microfiltration membrane with a controllable pore size of 0.1 - 0.22 μm, and the inner layer is an ultrafiltration membrane with a pore size of 15 - 20 nm. It can simultaneously achieve the functions of microfiltration and ultrafiltration. The water contact angle of the obtained composite membrane is relatively low, the pure water flux is above 3080 LMH / bar, and the membrane flux recovery rate is above 90%. It significantly improves the water flux, hydrophilic property and anti-pollution property of the double-layer composite hollow fiber membrane.

[0165] To further understand the present invention, the preferred embodiments of the present invention will be described below in conjunction with examples. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0166] Example 1

[0167] A) Provide spinning solution 1, spinning solution 2, core solution and outer protection solution;

[0168] Among them,

[0169] The raw materials for preparing spinning solution 1 are:

[0170] 15% polyacrylonitrile;

[0171] 10% polyvinyl alcohol;

[0172] 75% N,N-dimethylformamide.

[0173] Preparation: Add 100 g of polyvinyl alcohol (molecular weight 300,000) to 750 g of N,N-dimethylformamide, stir at 40 °C for 2 h until completely dissolved. Then add 150 g of polyacrylonitrile (molecular weight 200,000) to it and stir at 80 °C for 10 h to obtain spinning solution 1.

[0174] The raw materials for preparing spinning solution 2 include:

[0175] 18% polyvinylidene fluoride;

[0176] 15% polyvinylpyrrolidone;

[0177] 67% N-methylpyrrolidone.

[0178] Preparation: Add 150 g of polyvinylpyrrolidone (molecular weight 1,100,000) to 670 g of N-methylpyrrolidone, stir at 40 °C for 2 h until completely dissolved. Then add 180 g of polyvinylidene fluoride (molecular weight 600,000) to it and stir at 80 °C for 10 h to obtain spinning solution 2.

[0179] Preparation of the core liquid: Dissolve 6 g of Tris in 600 g of water, stir evenly at room temperature, then add 300 g of N,N-dimethylformamide and stir evenly at room temperature. Then, adjust the pH to 11 with a sodium hydroxide solution (concentration 2 mol / L), and the amount of the sodium hydroxide solution used is about 94 g to obtain the core liquid.

[0180] Preparation of the outer protective liquid: Add 5 g of dopamine hydrochloride to 345 g of pure water, stir evenly at room temperature, then add 650 g of N-methylpyrrolidone and stir evenly at room temperature to obtain the outer protective liquid.

[0181] B) Extrude the core liquid, spinning solution 1, spinning solution 2, and outer protective solution together from a quadruple spinneret. Among them, the core liquid is extruded from the first flow channel of the spinneret at a flow rate of 12 mL / min. Spinning solution 1 enters the second flow channel of the spinneret, contacts the core liquid, and its flow rate is 6.8 mL / min. Spinning solution 2 enters the third flow channel of the spinneret, and its flow rate is 8.5 mL / min. The outer protective liquid enters the fourth flow channel of the spinneret and contacts the spinning solution 2 in the third flow channel, and its flow rate is 9 mL / min.

[0182] C) After being extruded in step B), the spinning solution enters the air gap, and the preliminary phase inversion from the spinning solution to the nascent membrane filament is completed in the air gap. Among them, the height of the air gap is 300 mm, and the temperature of the air gap is 60 °C.

[0183] The nascent membrane filament enters the gel bath from the air gap, so that solvents, hydrophilic additives, etc. in the nascent membrane filament are largely eluted in the gel bath, and the secondary phase inversion is completed in the gel bath. Among them, the gel bath contains pure water, and the water temperature is 60 °C.

[0184] After the membrane filament undergoes the secondary phase inversion in the gel bath, it enters the water washing bath. After being washed and stretched in the water washing bath, the membrane filament is completely phase-inverted. Among them, the water temperature in the water washing bath is 70 °C, and the stretching speed is 20 m / min.

[0185] The membrane filament that has been completely phase-inverted in the water washing bath enters the oven for drying treatment (temperature 60 °C) to obtain the composite membrane.

[0186] Example 2

[0187] A) Provide spinning solution 1, spinning solution 2, core liquid, and outer protective solution;

[0188] Among them,

[0189] The raw materials for preparing spinning solution 1 are:

[0190] Polysulfone 17%;

[0191] Polyethylene glycol 16%;

[0192] N-methylpyrrolidone 67%.

[0193] Preparation: Add 160 g of polyethylene glycol (molecular weight 2 million) to 670 g of N-methylpyrrolidone, and stir at 40 °C for 2 h until completely dissolved. Then add 170 g of polysulfone (molecular weight 1.5 million) thereto, and stir at 80 °C for 10 h to obtain spinning solution 1.

[0194] The raw materials for preparing spinning solution 2 include:

[0195] Polyvinylidene fluoride 20%;

[0196] Polyvinyl alcohol 17%;

[0197] N,N-dimethylacetamide 63%.

[0198] Preparation: Add 170 g of polyvinyl alcohol (molecular weight 9 million) to 630 g of N,N-dimethylacetamide, and stir at 40 °C for 2 h until completely dissolved. Then add 200 g of polyvinylidene fluoride (molecular weight 4.5 million) thereto, and stir at 80 °C for 10 h to obtain spinning solution 2.

[0199] Preparation of the core liquid: Dissolve 15 g of Tris in 580 g of water, stir evenly at room temperature, add 350 g of N-methylpyrrolidone, and stir evenly at room temperature. Then, adjust the pH to 9 with potassium hydroxide solution (concentration 2 mol / L), and the amount of potassium hydroxide solution used is about 55 g to obtain the core liquid.

[0200] Preparation of the outer protective liquid: Add 10 g of dopamine hydrochloride to 240 g of pure water, stir evenly at room temperature, then add 750 g of N,N-dimethylacetamide and stir evenly at room temperature to obtain the outer protective liquid.

[0201] B) Co-extrude the core liquid, spinning solution 1, spinning solution 2 and the outer protective solution together from a quadruple spinneret. Among them, the core liquid is extruded from the first flow channel of the spinneret at a flow rate of 13.5 mL / min. Spinning solution 1 enters the second flow channel of the spinneret, contacts with the core liquid, and its flow rate is 7.5 mL / min. Spinning solution 2 enters the third flow channel of the spinneret, and its flow rate is 9 mL / min. The outer protective liquid enters the fourth flow channel of the spinneret and contacts with the spinning solution 2 in the third flow channel, and its flow rate is 8 mL / min.

[0202] C) After extrusion in step B), the spinning solution enters the air gap, and a preliminary phase inversion from the spinning solution to the nascent film fiber is completed in the air gap. Among them, the height of the air gap is 400 mm, and the temperature of the air gap is 70 °C.

[0203] The nascent membrane filaments enter the gel bath from the air gap, causing a large amount of solvents, hydrophilic additives, etc. in the nascent membrane filaments to be eluted in the gel bath, and completing the secondary phase inversion in the gel bath. Among them, the gel bath contains pure water with a water temperature of 70 °C.

[0204] After the membrane filaments undergo secondary phase inversion in the gel bath, they enter the water washing bath. Through the water washing and stretching in the water washing bath, the membrane filaments are completely phase-inverted. Among them, the water temperature in the water washing bath is 80 °C, and the stretching speed is 25 m / min.

[0205] After the membrane filaments are completely phase-inverted in the water washing bath, they enter the oven for drying treatment (temperature 80 °C), thereby obtaining the composite membrane.

[0206] Comparative Example 1

[0207] It is carried out according to Example 1, except that the outer protection solution is not prepared, and a triple spinneret is used for extrusion during the extrusion from the spinneret. Specifically as follows:

[0208] A) Provide spinning solution 1, spinning solution 2, and core solution (without outer protection solution):

[0209] The compositions and preparations of spinning solution 1, spinning solution 2, and core solution are the same as those in Example 1.

[0210] B) The core solution, spinning solution 1, and spinning solution 2 are co-extruded from the triple spinneret together. Among them, the core solution is extruded from the first flow channel of the spinneret at a flow rate of 12 mL / min. Spinning solution 1 enters the second flow channel of the spinneret and contacts the core solution, with a flow rate of 6.8 mL / min. Spinning solution 2 enters the third flow channel of the spinneret, with a flow rate of 8.5 mL / min.

[0211] C) After the spinning solution is extruded in step B), it enters the air gap, and the preliminary phase inversion from the spinning solution to the nascent membrane filaments is completed in the air gap. Among them, the height of the air gap is 300 mm, and the air gap temperature is 60 °C.

[0212] The nascent membrane filaments enter the gel bath from the air gap, causing a large amount of solvents, hydrophilic additives, etc. in the nascent membrane filaments to be eluted in the gel bath, and completing the secondary phase inversion in the gel bath. Among them, the gel bath contains pure water with a water temperature of 60 °C.

[0213] After the membrane filaments undergo secondary phase inversion in the gel bath, they enter the water washing bath. Through the water washing and stretching in the water washing bath, the membrane filaments are completely phase-inverted. Among them, the water temperature in the water washing bath is 70 °C, and the stretching speed is 20 m / min.

[0214] After the membrane filaments are completely phase-inverted in the water washing bath, they enter the oven for drying treatment (temperature 60 °C), thereby obtaining the composite membrane.

[0215] Comparative Example 2

[0216] Implemented according to Example 2, except that the outer protective solution is not prepared, and a triple spinneret is used for extrusion during spinneret extrusion. Specifically as follows:

[0217] A) Provide spinning solution 1, spinning solution 2, and core solution (without outer protective solution):

[0218] The compositions and preparations of spinning solution 1, spinning solution 2, and core solution are the same as those in Example 2.

[0219] B) Co-extrude the core solution, spinning solution 1, and spinning solution 2 together from the triple spinneret. Among them, the core solution is extruded from the first flow channel of the spinneret at a flow rate of 13.5 mL / min. Spinning solution 1 enters the second flow channel of the spinneret and contacts the core solution, with a flow rate of 7.5 mL / min. Spinning solution 2 enters the third flow channel of the spinneret, with a flow rate of 9 mL / min.

[0220] C) The spun solution after extrusion in step B) enters the air gap, and the preliminary phase inversion from the spun solution to the nascent membrane filament is completed in the air gap. Among them, the height of the air gap is 400 mm, and the temperature of the air gap is 70 °C.

[0221] The nascent membrane filament enters the gel bath from the air gap, so that solvents, hydrophilic additives, etc. in the nascent membrane filament are largely eluted in the gel bath, and the secondary phase inversion is completed in the gel bath. Among them, the gel bath contains pure water, and the water temperature is 70 °C.

[0222] The membrane filament after the secondary phase inversion in the gel bath enters the water washing bath, and after being washed and stretched in the water washing bath, the membrane filament is completely phase-inverted. Among them, the water temperature in the water washing bath is 80 °C, and the stretching speed is 25 m / min.

[0223] The membrane filament that has been completely phase-inverted in the water washing bath enters the oven for drying treatment (temperature 80 °C), thereby obtaining a composite membrane.

[0224] Product testing :

[0225] 1. SEM test

[0226] The Hitachi TM4000 desktop scanning electron microscope is selected for the determination of the membrane surface morphology. Through the scanning electron microscope, not only the membrane surface morphology can be determined, but also the pore size on the membrane surface can be characterized. The test results are shown in Figure 4 . It can be seen that for the double-layer composite membranes obtained in Examples 1-2, the outer surface is loose and macroporous, with a pore size of about 0.1 - 0.22 μm. The outer surfaces of the double-layer composite membranes obtained from Comparative Examples 1-2 are all dense and microporous, with an outer surface pore size of about 15 - 20 nm. This double-layer composite membrane has a single function and can only achieve the ultrafiltration function, and cannot achieve the dual ultrafiltration-microfiltration effect.

[0227] 2. Contact angle test

[0228] The hydrophilic property of the membrane is usually described by the static water contact angle, and the contact angle is measured using a German dataphysics OCA25 video optical contact angle measuring instrument. The smaller the contact angle value, the better the hydrophilicity of the membrane surface. See Table 1 for the test results.

[0229] Table 1: Contact angles of the inner and outer surfaces of the double-layer composite membranes obtained in each example and comparative example

[0230] Outer surface (°) Inner surface (°) Example 1 56.3±2.1 42.7±0.8 Example 2 43.6±0.9 35.4±1.2 Comparative example 1 97.8±0.6 63.4±1.1 Comparative example 2 95.6±1.2 62.6±0.8

[0231] It can be seen that in Examples 1-2, the membrane preparation method of the present invention is adopted, and the hydrophilic and adhesive polydopamine is generated by the mutual penetration and reaction of the components in the outer protective liquid and the core liquid, which penetrates through two different types of membrane materials, namely the microfiltration membrane and the ultrafiltration membrane, significantly improving the hydrophilicity of the inner and outer surfaces of the double-layer composite membrane.

[0232] 3. Pure water flux test

[0233] The membrane module is tested by the external pressure filtration method. The test water temperature is adjusted to be stable at 25 ± 0.5 °C, and the flux on the permeate side is measured under the condition of 1 bar. The larger the pure water flux result, the better the permeation performance of the membrane and the higher the filtration efficiency.

[0234] Calculation of pure water flux:

[0235]

[0236] In the formula:

[0237] P: Pure water permeability, L / (m 2 ﹒h) / bar (LMH / bar);

[0238] V: Pure water throughput, L;

[0239] S: Effective membrane area, m 2 ;

[0240] T: Time taken for pure water with a volume of V to permeate, h.

[0241] See Table 2 for the test results:

[0242] Table 2: Pure water flux results of the double-layer composite membranes obtained in each example and comparative example

[0243] Pure water flux (LMH / bar) Example 1 3080.9 Example 2 3578.6 Comparative example 1 750.8 Comparative example 2 890.4

[0244] It can be seen that in Examples 1-2, the membrane preparation method of the present invention is adopted, and the pure water flux of the composite membrane is significantly improved, mainly because the outer protective liquid can regulate the pore size of the outer surface of the double-layer composite membrane.

[0245] 4. Evaluation of membrane anti-fouling performance

[0246] To evaluate the anti-fouling performance of the double-layer composite membrane, the Flux Recovery Rate (FRR) was used for evaluation. The higher the FRR value, the better the anti-fouling performance of the membrane.

[0247] Under the condition of 1 bar, the double-layer composite membrane was used to filter a bovine serum albumin (BSA) solution with a concentration of 1 g / L. After filtering for 2 h, the membrane was backwashed with purified water at a pressure of 1 bar for 10 min. After the backwashing was completed, the pure water flux of the membrane was measured again. According to the pure water fluxes P1 and P2 of the membrane before and after filtering the BSA solution, the FRR can be calculated by the following formula:

[0248]

[0249] The test results are shown in Table 3:

[0250] Table 3: Membrane flux recovery rate results of the double-layer composite membranes obtained in each example and comparative example

[0251] FRR Example 1 90.6％ Example 2 92.7％ Comparative example 1 53.2％ Comparative example 2 56.7％

[0252] It can be seen that the double-layer composite membranes prepared by the preparation method of the present invention in Examples 1-2 have a higher flux recovery rate, indicating that the double-layer composite membranes prepared in Examples 1-2 have more excellent anti-fouling performance.

[0253] In summary, in Examples 1-2, a double-layer composite hollow fiber membrane was prepared by using a quadruple spinneret. By controlling the content of the outer protective liquid hydrochloric acid dopamine and the solvent concentration in the fourth flow channel, and regulating the pH of the core liquid in the first flow channel, etc., a microfiltration membrane with a loose outer layer and a controllable pore size of 0.1-0.22 μm was prepared; then, by using the mutual penetration and reaction of the components in the outer protective liquid and the core liquid to generate hydrophilic and adhesive polydopamine, which penetrated between two different types of membrane materials, namely the microfiltration membrane and the ultrafiltration membrane, the water flux, hydrophilic property and anti-fouling performance of the double-layer composite hollow fiber membrane were significantly improved.

[0254] The composite membrane prepared by the present invention can be applied to the filtration of domestic water, the food industry (clarification of gelatin, glucose, fruit juice, etc.), the concentration, purification and separation of macromolecular substances in the pharmaceutical industry, and the sterilization filtration of biological solutions.

[0255] In this article, specific examples are used to illustrate the principles and implementation modes of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention, including the best mode, and also enables any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that for those of ordinary skill in the art in the technical field, without departing from the principles of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention. The protection scope of the present invention patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to the literal description of the claims, or if they include equivalent structural elements that have no substantial difference from the literal description of the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A method for preparing a composite membrane, characterized in that, It includes the following steps: A) Provide spinning solution 1, spinning solution 2, core liquid and outer protective liquid; Among them, The raw materials for preparing the spinning solution 1 include: Polymer 15% - 20%; Hydrophilic additive 10% - 20%; Solvent 60% - 75%; The raw materials for preparing the spinning solution 2 include: Polyvinylidene fluoride 15% - 18%; Hydrophilic additive 10% - 15%; Solvent 67% - 75%; In the spinning solution 2, the total amount of the above polyvinylidene fluoride, hydrophilic additive and solvent is 100%; The core liquid includes a base liquid and a pH regulator: The raw materials for preparing the base liquid include: Tris (hydroxymethyl) aminomethane 0.5% - 2%; Water 63% - 69.5%; Organic solvent 30% - 35%; The raw materials for preparing the outer protective liquid include: Dopamine hydrochloride 0.2% - 1%; Water 24% - 34.5%; Organic solvent 55% - 80%; The organic solvent in the outer protective liquid is the same as the solvent in the spinning solution 2; B) Co - extrude the spinning solution 1, spinning solution 2, core liquid and outer protective liquid together from 4 adjacent channels in a multi - spinneret, where the core liquid, spinning solution 1, spinning solution 2 and outer protective liquid are extruded in the order from the inside to the outside of the channels; Among them, the number of channels of the multi - spinneret ≥ 4; The flow rate of the outer protective liquid is 7 - 9 mL / min; The flow rate of the spinning solution 2 is 7 - 11 mL / min; The flow rate of the core liquid is 10 - 15 mL / min; The flow rate of the spinning solution 1 is 5 - 8 mL / min; C) After extrusion in step B), enter the air gap to complete the primary phase inversion to obtain the nascent membrane filaments; then enter the gel bath to complete the secondary phase inversion; then enter the water washing bath for water washing and stretching to complete the complete phase inversion; finally, dry to obtain the composite membrane.

2. The preparation method according to claim 1, wherein, In the raw materials for preparing the spinning solution 1: The polymer is at least one of cellulose acetate, polyacrylonitrile, polyethersulfone, polysulfone and polyamide; The hydrophilic additive is at least one of polyvinylpyrrolidone, polyvinyl alcohol and polyethylene glycol; The solvent is at least one of N - methylpyrrolidone, N,N - dimethylacetamide and N,N - dimethylformamide.

3. The preparation method according to claim 1, characterized in that, In the raw materials for preparing the spinning solution 2: The hydrophilic additive is at least one of polyvinylpyrrolidone, polyvinyl alcohol and polyethylene glycol; The solvent is at least one of N - methylpyrrolidone, N,N - dimethylacetamide and N,N - dimethylformamide.

4. The preparation method according to claim 1, wherein The spinning solution 1 is prepared by the following preparation method: S1. Mix and dissolve the hydrophilic additive and the solvent to obtain a mixed solution 1; S2. Mix and heat the mixed solution 1 with the polymer to obtain the spinning solution 1.

5. The preparation method according to claim 4, wherein In step S1, the temperature of the mixing and dissolving is 35 - 40 °C; In step S2, the temperature of the heating is 75 - 90 °C.

6. The preparation method according to claim 1, characterized in that, The spinning solution 2 is prepared by the following preparation method: K1. Mix and dissolve the hydrophilic additive and the solvent to obtain a solution 1; K2. Mix and heat the solution 1 with polyvinylidene fluoride to obtain the spinning solution 2.

7. The preparation method according to claim 6, wherein In step K1, the temperature of the mixing and dissolving is 35 - 40 °C; In step K2, the heating temperature is 75 to 90 °C.

8. The preparation method according to claim 1, wherein, In step C): The height of the air gap is 100 to 500 mm, and the temperature of the air gap is 50 to 70 °C; The gel tank contains water; the temperature of the water is 50 to 70 °C; The water temperature in the water washing tank is 60 to 80 °C, and the stretching speed is 20 to 30 m / min; The drying temperature is 60 to 80 °C.

9. A composite film prepared by the preparation method according to any one of claims 1 to 8.

Images