A method for preparing a high-permeability selective polyketone hollow fiber membrane

Abstract

The application relates to a preparation method of a high-permeability selective polyketone hollow fiber membrane and belongs to the membrane technology field. The method comprises the following steps: 1) dissolving polyketone in mixed diluents composed of a good solvent and a poor solvent, defoaming after uniform dissolution to obtain a casting solution; 2) extruding the casting solution and a core liquid into a hollow fiber membrane embryo through a spinneret, first entering a multistage bath to occur phase separation and be solidified and formed, first being a low-temperature cooling bath, then entering a medium-temperature surface cleaning bath, and finally performing high-temperature heat treatment, to obtain a hollow fiber membrane filament; and 3) cleaning the hollow fiber membrane filament with water, then cleaning the diluents away with an extracting agent, and obtaining the polyketone hollow fiber membrane after airing. The preparation method of the high-permeability selective polyketone hollow fiber membrane adopts mixed diluents to control and form a highly continuous three-dimensional network through structure in the membrane body, so that the membrane has permeability; the gradient temperature difference of the multistage cooling bath is controlled, the membrane has good separation precision, and the membrane can be applied to high-efficiency separation in an organic solvent system.

Description

Technical Field

[0001] This invention belongs to the field of membrane technology, specifically a method for preparing a high-permeability selective polyketone hollow fiber membrane. Background Technology

[0002] The petrochemical and pharmaceutical industries are among the pillar industries of the national economy. In these industries, processes such as material separation and purification, drug purification and refining, and solvent recovery mainly employ traditional methods like distillation, rectification, and crystallization, which are energy-intensive and costly, typically accounting for 40-70% of total investment and energy costs. Membrane separation technology is a novel technology that does not involve phase change and can achieve high-precision separation of substances using simple physical sieving. It has already made significant contributions to water resource recycling and seawater desalination. Applying membrane separation technology to material separation and purification in organic solvent systems to reduce energy consumption and achieve sustainable development is an inevitable trend. However, unlike applications in water systems, membrane materials used in organic solvents require not only high permeation separation characteristics but also robust solvent resistance. Polyketone (PK) is a new, environmentally friendly polymer polymerized from carbon monoxide and olefins (ethylene, propylene), and is a high-performance engineering plastic. PK membranes are characterized by low cost, good hydrophilicity, good chemical resistance, high temperature resistance, and good mechanical properties. However, due to the high heat and solvent resistance of these polymers, solution molding for film formation presents certain difficulties. Currently, most polyketone membranes are prepared by melt injection molding. However, membranes stretched after melt extrusion have problems with structural control and low permeation selectivity, making them unsuitable for the efficient separation of materials required in the current petroleum, chemical, and pharmaceutical industries. Summary of the Invention

[0003] To address the aforementioned problems in the existing technology, the present invention aims to provide a technical solution for preparing a high-permeability selective polyketone hollow fiber membrane. This method utilizes a mixed diluent to regulate the solubility of polyketone at high temperatures, enabling high-precision liquid-liquid phase separation. This results in a highly continuous three-dimensional network structure within the membrane body, thus providing permeability. By controlling the gradient temperature difference of the multi-stage bath, the phase transition rate on the membrane's outer surface is precisely controlled to obtain a separation skin with high separation accuracy. This allows the membrane to achieve excellent separation precision, enabling efficient separation applications in organic solvent systems.

[0004] The method for preparing a high-permeability selective polyketone hollow fiber membrane is characterized by comprising the following steps:

[0005] 1) At 180-240℃, dissolve 20-40 parts of polyketone in 60-80 parts of a mixed diluent consisting of a good solvent and a poor solvent. After the solution is dissolved evenly, degas it to obtain a casting solution.

[0006] 2) The casting solution and core solution are extruded through a spinneret to form a hollow fiber membrane preform, which is then directly introduced into a multi-stage bath to undergo phase separation and solidify. The multi-stage bath consists of three series solvent baths with different temperature gradients: first a low-temperature cooling bath, then a medium-temperature surface cleaning bath, and finally a high-temperature heat treatment bath to obtain hollow fiber membrane fibers.

[0007] 3) Place the hollow fiber membrane fibers in water for washing, then use an extractant to wash away the diluent. After washing and drying, the polyketone hollow fiber membrane is obtained.

[0008] The method for preparing a high-permeability selective polyketone hollow fiber membrane is characterized in that, in step 1), the dissolution temperature is 200-230℃, preferably 210-220℃; 25-35 parts of polyketone and 65-75 parts of diluent are used.

[0009] The method for preparing a high-permeability selective polyketone hollow fiber membrane is characterized in that, in step 1), the polyketone is a polyketone homopolymer and a polyketone copolymer with a molecular weight of 15,000-30,000, preferably 20,000-25,000.

[0010] The method for preparing a high-permeability selective polyketone hollow fiber membrane is characterized in that, in step 1), the good solvent is one of polyethylene glycol 200, propylene carbonate, dimethyl phthalate, diethyl phthalate, diethylene glycol, diphenyl carbonate, and dimethyl sulfoxide, and the poor solvent is one of triacetin, polyethylene glycol 600, dibutyl citrate, triethyl citrate, and diphenylmethane.

[0011] The method for preparing a high-permeability selective polyketone hollow fiber membrane is characterized in that, in step 1), the diluent is composed of 60-90 parts of good solvent and 10-40 parts of poor solvent, preferably 70-80 parts of good solvent and 20-30 parts of poor solvent.

[0012] The method for preparing a high-permeability selective polyketone hollow fiber membrane is characterized in that, in step 2), the inner diameter of the spinneret is 0.4-0.7 mm, the extrusion diameter of the polyketone liquid is 1.0-1.3 mm, and the slit size is controlled to be no less than 0.3 mm; the extrusion core liquid is at least one of polyethylene glycol 400, diethylene glycol, propylene carbonate, and dimethyl sulfone.

[0013] The method for preparing a high-permeability selective polyketone hollow fiber membrane is characterized in that, in step 2), the extruded hollow fiber membrane preform first passes through an air section and then enters a low-temperature cooling bath, wherein the length of the air bath section is 0-10 cm, preferably 2-5 cm.

[0014] The method for preparing a high-permeability selective polyketone hollow fiber membrane is characterized in that, in step 2), the multi-stage bath consists of three series solvent baths with different temperature gradients. The first solvent bath is at least one of the following: a mixture of 90 parts glycerol and 10 parts water at -10 to 10°C, polyethylene glycol 200, glycerol, and polyglycerol; the second solvent bath is at least one of ethanol, methanol, and ethyl acetate at 40 to 50°C; and the third solvent bath is at least one of dimethyl silicone oil, diethyl silicone oil, benzyl silicone oil, and methyl vinyl silicone oil at 100 to 150°C.

[0015] The method for preparing a high-permeability selective polyketone hollow fiber membrane is characterized in that, in step 3), the extractant is industrial alcohol at 55℃~65℃, and the temperature is preferably 60℃~62℃.

[0016] The method for preparing a high-permeability selective polyketone hollow fiber membrane is characterized in that: the temperature of the first-stage solvent bath is -5 to 8°C, preferably 0 to 4°C; the temperature of the second-stage solvent bath is 43 to 46°C; and the temperature of the third-stage solvent bath is 120 to 130°C.

[0017] The above-described method for preparing a high-permeability selective polyketone hollow fiber membrane solves the dissolution problem of polyketone by selecting a suitable diluent and dissolving it at high temperature to obtain a casting solution with film-forming properties. The polymers, additives, solvents, and diluents used in this invention are all optimized based on Hansen interaction theory, with a focus on the compatibility of these materials to prevent defects. Furthermore, the parameters such as the amount, molecular weight, concentration, and type of each component specified in this invention are based on the thermodynamic stability of the polyketone solution. Thermodynamic stability is a prerequisite for preparing high-performance hollow fiber membranes.

[0018] This invention utilizes a high-temperature dissolution method of thermally induced phase to first dissolve polyketone uniformly, thereby achieving extrusion molding. This invention employs a mixed diluent composed of a good solvent and a poor solvent to regulate the degree and speed of liquid-liquid phase separation of polyketone, giving the bulk a three-dimensional, highly permeable structure, thus achieving high permeability and solving the problem of low efficiency in current membrane separation processes. As is well known, in thermally induced phase separation membrane fabrication, the choice of diluent is particularly important, directly affecting the membrane's bulk structure and causing significant differences in permeability and mechanical properties, thus impacting the membrane material's performance in practical applications. Current diluent systems for polyketone are all single-system systems, mainly based on liquid-solid separation mechanisms. That is, during cooling, polyketone directly dilutes from the polyketone solution, making it difficult to form an interpenetrating network structure with the diluent system; instead, it forms a separate aggregated network structure with low permeability and strength, resulting in poor performance. This invention employs a combination of a good solvent and a poor solvent to form a mixed diluent. The good solvent solves the solubility problem of polyketone at high temperatures, thereby obtaining a uniform and transparent solution and ensuring the extrusion performance of the solution. The poor solvent can regulate the phase separation behavior of polyketone, enabling it to undergo better liquid-liquid phase separation under high-temperature conditions. That is, while the polyketone is still in a molten state, phase separation is induced by the poor solvent, allowing the polyketone and the diluent to form an interpenetrating structure in the liquid state. This structure solidifies during further cooling, resulting in a bicontinuous and highly interconnected three-dimensional network structure, thus endowing the membrane with high permeability. Furthermore, the degree and rate of phase separation of the polyketone solution can be controlled according to the type and concentration of the poor solvent used, thereby controlling the interpenetration degree of the three-dimensional network and obtaining a polyketone membrane with high porosity, achieving its high permeability in the solvent system.

[0019] This invention further enhances membrane separation precision by controlling the pore size of the membrane surface through a multi-stage bath with a temperature gradient. In the thermally induced phase separation process for preparing hollow fiber membranes, the control of the skin pore structure is crucial for achieving precise membrane separation, and this pore structure is closely related to the polymer concentration on the surface. Normally, the first-stage external cooling bath uses a solution or solvent that interacts weakly with the diluent but strongly with the polymer. During the molding process, this induces polymer chains to accumulate on the surface, increasing the polymer concentration and resulting in a dense pore structure within the polymer hollow fiber membrane, achieving fine-level separation characteristics. Simultaneously, a lower-temperature external coagulation bath increases the phase separation rate, further reducing membrane porosity. This invention further refines this by using alcohols with weak interactions with polyketide as a cooling bath, simultaneously lowering their temperature to accelerate the phase separation rate of the polyketide membrane, resulting in a denser pore structure on the surface. The surface of the membrane is further cleaned with alcohols or esters, which have good dissolving properties, using a primary alcohol cooling bath and diluent to impart effective separation pores. Finally, a high-temperature heat treatment bath is used to further repair and heal surface defects, achieving further densification and improving separation accuracy. Through three-stage control of the bath, a polyketone hollow fiber membrane with high separation accuracy in the skin layer is prepared, thereby achieving high-precision separation of materials in organic solvent systems. All parts mentioned in this application are parts by weight. Attached Figure Description

[0020] Figure 1 This is a three-dimensional through-structure diagram of the polyketone membrane body in Example 2;

[0021] Figure 2 This is an enlarged view of the polyketone film structure in Example 3. Detailed Implementation

[0022] The present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1:

[0024] 1) At 180°C, 20 parts of 15,000 molecular weight polyketide homopolymer were dissolved in 80 parts of a mixed diluent, which consisted of 60 parts of polyethylene glycol 200 and 40 parts of triacetin. After the mixture was dissolved evenly, the bubbles were removed to obtain the casting solution.

[0025] 2) Select a spinneret with an inner diameter of 0.4 mm and an extrusion diameter of 1.0 mm. Use polyethylene glycol 400 as the core liquid. Extrude the casting liquid and core liquid prepared in step 1) through the spinneret to form a hollow fiber membrane preform. Directly enter the -10℃ polyethylene glycol 200 to undergo phase separation and solidify. Then, enter the 40℃ methanol to wash away the surface diluent and the first-stage coagulation bath suspended on the surface to obtain clean effective pores. Then, perform a 100℃ dimethyl silicone oil heat treatment to thermally repair the effective pores and finally obtain hollow fiber membrane fibers.

[0026] 3) The prepared hollow fiber membrane fibers are placed in water for washing, and then placed in industrial alcohol at 55°C. After washing and drying, polyketone hollow fiber membrane products are obtained.

[0027] Example 2:

[0028] 1) At 240°C, 40 parts of 30,000 molecular weight polyketide homopolymer were dissolved in 60 parts of mixed diluent, which consisted of 70 parts of dimethyl phthalate and 30 parts of dibutyl citrate. After the mixture was dissolved evenly, the bubbles were removed to obtain the casting solution.

[0029] 2) Select a spinneret with an inner diameter of 0.7 mm and an extrusion diameter of 1.3 mm. Use polyglycerol as the core liquid. Extrude the casting solution and core liquid prepared in step 1) through the spinneret to form a hollow fiber membrane preform. Directly enter a mixture of 90 parts glycerol and 10 parts water at 10℃ to undergo phase separation and solidify. Then, enter 40℃ ethanol to wash away the surface diluent and the first-stage coagulation bath suspended on the surface to obtain clean effective pores. Then, perform heat treatment with benzyl silicone oil at 150℃ to heat repair the effective pores and finally obtain hollow fiber membrane fibers.

[0030] 3) The prepared hollow fiber membrane fibers are placed in water for washing, and then placed in industrial alcohol at 65°C. After washing and drying, polyketone hollow fiber membrane products are obtained.

[0031] Example 3:

[0032] 1) At 200℃, 30 parts of polyketide homopolymer with a molecular weight of 20,000 were dissolved in 70 parts of mixed diluent, which consisted of 75 parts of diethyl phthalate and 25 parts of diethyl phthalate. After the solution was dissolved evenly, the bubbles were removed to obtain the casting solution.

[0033] 2) Select a spinneret with an inner diameter of 0.5 mm and an extrusion diameter of 1.1 mm. Use propylene carbonate as the core liquid. Extrude the casting liquid and core liquid prepared in step 1) through the spinneret to form a hollow fiber membrane preform. Directly enter the 0℃ polyglycerol to undergo phase separation and solidify. Then, enter the 45℃ ethyl acetate to wash away the surface diluent and the first-stage coagulation bath suspended on the surface to obtain clean effective pores. Then, perform heat treatment with 130℃ benzyl silicone oil to heat repair the effective pores. Finally, obtain hollow fiber membrane fibers.

[0034] 3) The prepared hollow fiber membrane fibers are placed in water for washing, and then placed in industrial alcohol at 560°C. After washing and drying, polyketone hollow fiber membrane products are obtained.

[0035] Example 4:

[0036] 1) At 220℃, 36 parts of polyketide homopolymer with a molecular weight of 25,000 were dissolved in 64 parts of a mixed diluent, which consisted of 80 parts of diphenyl carbonate and 20 parts of diethyl phthalate. After the mixture was dissolved evenly, the bubbles were removed to obtain the casting solution.

[0037] 2) Select a spinneret with an inner diameter of 0.7 mm and an extrusion diameter of 1.3 mm. Use polyethylene glycol 400 as the core liquid. Extrude the casting liquid and core liquid prepared in step 1) through the spinneret to form a hollow fiber membrane preform. After passing through a 2 cm air section, enter glycerol at -5℃ to undergo phase separation and solidify. Then, enter ethanol at 45℃ to wash away the surface diluent and the first-stage coagulation bath suspended on the surface to obtain clean effective pores. Then, perform heat treatment with dimethyl silicone oil at 150℃ to heat repair the effective pores and finally obtain hollow fiber membrane fibers.

[0038] 3) The prepared hollow fiber membrane fibers are placed in water for washing, and then placed in industrial alcohol at 65°C. After washing and drying, polyketone hollow fiber membrane products are obtained.

[0039] Example 5:

[0040] 1) At 190°C, 25 parts of a 15,000 molecular weight polyketone copolymer were dissolved in 75 parts of a mixed diluent, which consisted of 85 parts of diethylene glycol and 15 parts of polyethylene glycol 600. After the solution was dissolved evenly, the bubbles were removed to obtain the casting solution.

[0041] 2) Select a spinneret with an inner diameter of 0.7 mm and an extrusion diameter of 1.3 mm. Use polyethylene glycol 400 as the core liquid. Extrude the casting liquid and core liquid prepared in step 1) through the spinneret to form a hollow fiber membrane preform. Directly enter glycerol at 5℃ to undergo phase separation and solidify. Then, enter ethanol at 50℃ to wash away the surface diluent and the first-stage coagulation bath suspended on the surface to obtain clean effective pores. Then, perform heat treatment with dimethyl silicone oil at 150℃ to heat repair the effective pores. Finally, obtain hollow fiber membrane fibers.

[0042] 3) The prepared hollow fiber membrane fibers are placed in water for washing, and then placed in industrial alcohol at 65°C. After washing and drying, polyketone hollow fiber membrane products are obtained.

[0043] Example 6:

[0044] 1) At 200℃, 30 parts of a 30,000 molecular weight polyketide copolymer were dissolved in 70 parts of a mixed diluent, which consisted of 90 parts of diethylene glycol and 10 parts of triacetin. After the solution was dissolved evenly, the bubbles were removed to obtain the casting solution.

[0045] 2) Select a spinneret with an inner diameter of 0.7 mm and an extrusion diameter of 1.3 mm. Using diethylene glycol as the core liquid, extrude the casting solution and core liquid prepared in step 1) through the spinneret to form a hollow fiber membrane preform. Directly enter the -10℃ glycerol to undergo phase separation and solidify. Then, enter 50℃ ethanol to wash away the surface diluent and the first-stage coagulation bath suspended on the surface to obtain clean effective pores. Then, perform a 150℃ dimethyl silicone oil heat treatment to thermally repair the effective pores and finally obtain hollow fiber membrane fibers.

[0046] 3) The prepared hollow fiber membrane fibers are placed in water for washing, and then placed in industrial alcohol at 65°C. After washing and drying, polyketone hollow fiber membrane products are obtained.

[0047] The following experimental data further demonstrates the beneficial effects of the present invention. Tables 1-6 show the performance test results of the polyketone hollow fiber membranes prepared in Examples 1-6 of the present invention.

[0048] Table 1. Performance of polyketone hollow fiber membranes prepared in Example 1

[0049] Polyketone hollow fiber membrane index Cut-off aperture 10-20 nanometers Ethanol flux 100LMH@bar Organic solvent resistance Ethanol, dimethylformamide, N-methylpyrrolidone, methanol, acetone, acetonitrile, alkanes, etc.

[0050] Table 2. Performance of polyketone hollow fiber membranes prepared in Example 2

[0051] Polyketone hollow fiber membrane index Cut-off aperture 1-5 nanometers Acetone flux 40LMH@bar Organic solvent resistance Ethanol, dimethyl sulfoxide, acetone, acetonitrile, alkanes, etc.

[0052] Table 3. Performance of the polyketone hollow fiber membrane prepared in Example 3

[0053] Polyketone hollow fiber membrane index Cut-off aperture 5-10 nanometers N-methylpyrrolidone flux 70 LMH@bar Organic solvent resistance Ethanol, 1-methyl-2-pyrrolidone, isopropanol, tetrahydrofuran, acetone, acetonitrile, alkanes, etc.

[0054] Table 4. Performance of the polyketone hollow fiber membrane prepared in Example 4

[0055] Polyketone hollow fiber membrane index Average aperture 3-8 nanometers 1-Methyl-2-pyrrolidone flux 60LMH@bar Organic solvent resistance Ethanol, 1-methyl-2-pyrrolidone, dimethylformamide, acetone, acetonitrile, alkanes, etc.

[0056] Table 5. Performance of the polyketone hollow fiber membrane prepared in Example 5

[0057] Polyketone hollow fiber membrane index Average aperture 10-15 nanometers Acetonitrile flux 80LMH@bar Organic solvent resistance Ethanol, dimethyl sulfoxide, dimethylformamide, ethyl acetate, acetone, acetonitrile, alkanes, etc.

[0058] Table 6. Performance of the polyketone hollow fiber membrane prepared in Example 6

[0059] Polyketone hollow fiber membrane index Cut-off aperture 7-13 nanometers Ethyl acetate flux 75LMH@bar Organic solvent resistance Ethanol, dimethyl sulfoxide, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, acetonitrile, alkanes, etc.

[0060] By measuring the solvent permeation flux, selectivity, and tensile strength of the polyketone hollow fiber membranes, it can be seen that the polyketone hollow fiber membranes prepared in Examples 1, 2, and 5 of this invention have excellent overall performance. Among them, the solvent permeation flux of Example 1 is the best, reaching 100 LMH@bar; the retention performance of Example 2 is the best, with a pore size of 1-5 nanometers; and the overall performance of the polyketone hollow fiber membranes prepared in Examples 3, 4, and 6 also achieves the effects described in this invention.

[0061] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-permeability selective polyketone hollow fiber membrane, characterized in that... Includes the following steps: 1) At 210-220℃, 25-35 parts of polyketide homopolymer with a molecular weight of 20,000-25,000 are dissolved in 65-75 parts of a mixed diluent composed of a good solvent and a poor solvent. The good solvent is one of dimethyl phthalate, diethyl phthalate, and propylene carbonate, and the poor solvent is one of triacetin and dibutyl citrate. The mixed diluent is composed of 70-80 parts of good solvent and 20-30 parts of poor solvent. After uniform dissolution, degassing is performed to obtain the casting solution. 2) Select a spinneret with an inner diameter of 0.4-0.7 mm, an extrusion diameter of 1.0-1.3 mm for the polyketide solution, and a slit size of not less than 0.3 mm. Use at least one of polyethylene glycol 400, diethylene glycol, propylene carbonate, and dimethyl sulfone as the core liquid. Extrude the casting solution and core liquid prepared in step 1) through the spinneret to form a hollow fiber membrane preform. After passing through an air section of 0-10 cm, directly enter a multi-stage bath to undergo phase separation and solidify. The multi-stage bath consists of three series solvent baths with different temperature gradients: the first solvent bath is a mixture of 90 parts glycerol and 10 parts water at -5 to 8°C, at least one of polyethylene glycol 200, glycerol, and polyglycerol; the second solvent bath is at least one of ethanol, methanol, and ethyl acetate at 43 to 46°C; and the third solvent bath is at 120 to 130°C, at least one of dimethyl silicone oil, diethyl silicone oil, benzyl silicone oil, and methyl vinyl silicone oil. Hollow fiber membrane filaments are obtained. 3) Place the hollow fiber membrane fibers in water for washing, then use an extractant at 60℃~62℃ to wash away the diluent. After washing and drying, the polyketone hollow fiber membrane is obtained.

2. The method for preparing a high-permeability selective polyketide hollow fiber membrane as described in claim 1, characterized in that... In step 1): 30 parts polyketone and 70 parts diluent.

3. The method for preparing a high-permeability selective polyketone hollow fiber membrane as described in claim 1, characterized in that... In step 1): the good solvent is dimethyl phthalate; the bad solvent is dibutyl citrate.

4. The method for preparing a high-permeability selective polyketone hollow fiber membrane as described in claim 1, characterized in that... In step 1): the mixed diluent consists of 75 parts of good solvent and 25 parts of bad solvent.

5. The method for preparing a high-permeability selective polyketone hollow fiber membrane as described in claim 1, characterized in that... In step 2): the length of the air segment is 2-5 cm.

6. The method for preparing a high-permeability selective polyketide hollow fiber membrane as described in claim 1, characterized in that... In step 2): the core fluid is polyethylene glycol 400.

7. The method for preparing a high-permeability selective polyketide hollow fiber membrane as described in claim 1, characterized in that... In step 2), the temperature of the first solvent bath is 0 to 4°C.

8. The method for preparing a high-permeability selective polyketone hollow fiber membrane as described in claim 1, characterized in that... In step 2): the first solvent bath is a mixture of 90 parts glycerol and 10 parts water; the second solvent bath is ethanol; and the third solvent bath is dimethyl silicone oil.

Images