CN117861451A - Cross-linked thermal rearranged polybenzoxazole hollow fiber gas separation membrane and preparation method and application thereof - Google Patents
Cross-linked thermal rearranged polybenzoxazole hollow fiber gas separation membrane and preparation method and application thereof Download PDFInfo
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Abstract
The invention provides a cross-linked thermal rearranged polybenzoxazole hollow fiber gas separation membrane and a preparation method and application thereof, and belongs to the technical field of polymer membrane separation. In the process of synthesizing the polymer, a phenolphthalein diamine monomer with a lactone ring is introduced to be polycondensed with dianhydride to generate polyimide, then the polyimide is prepared into a hollow fiber membrane precursor, then the hollow fiber membrane precursor is crosslinked at a lower temperature, and then the temperature is further increased to prepare the thermal rearranged hollow fiber membrane. At this time, the flowability is blocked because the polymer chains are crosslinked, the thickening degree of the skin layer is greatly reduced, and the plasticizing resistance is improved.
Description
Technical Field
The invention relates to the technical field of polymer membrane separation, in particular to a cross-linked thermal rearranged polybenzoxazole hollow fiber gas separation membrane, and a preparation method and application thereof.
Background
With the recent great development of industry in various countries in the world, the demand for human energy is increasing. Up to now, the energy sources for large-scale industrial applications are basically derived from traditional fossil fuels, which release a large amount of carbon dioxide after combustion, so that the global climate is gradually changed due to the greenhouse effect. Global warming continues to continue and reducing the level of carbon dioxide in the atmosphere is one of the important challenges facing humans today.
Natural gas, although also a fossil fuel, has a significantly lower carbon dioxide emission than coal and petroleum, and releases the same amount of heat after combustion, and therefore, the use of natural gas is one of the important means for effectively controlling carbon dioxide emissions at present. However, in the process of natural gas production, the original natural gas produced is often accompanied by a high concentration of carbon dioxide. This not only reduces the heating value of the natural gas, but also causes problems of pipeline corrosion and increased transportation costs during transportation. Thus, the original natural gas needs to be separated and purified.
Compared with the traditional separation technology such as chemical adsorption and pressure swing adsorption, the membrane separation technology has the characteristics of high efficiency, low energy consumption, low cost and strong environmental sustainability. Common membrane forms are flat-plate membranes, roll-type membranes, hollow fiber membranes, etc., wherein hollow fiber membranes have received a great deal of attention because of their advantages of high packing density and easy integration and scale-up. However, when used for natural gas separation, the membranes tend to plasticize due to the action of highly condensed gases such as carbon dioxide and heavy hydrocarbons. Plasticization refers to the swelling of the polymer matrix with an increase in upstream gas pressure, an increase in mobility of its molecular chains, and a rapid increase in flux of the gas separation membrane, with a rapid decrease in selectivity.
The thermal rearrangement polymer is a polymer with heterocyclic structure formed by mutual reaction of imine ring of polyimide and ortho-position functional group of polyimide, and common thermal rearrangement polymers include Polybenzimidazole (PBI), polybenzoxazole (PBO), polybenzothiazole (PBT) and the like. The molecular chains of the polymers are rigid structures, have good thermal stability, and are microporous materials with high free volume fractions. However, these polymers are difficult to synthesize directly, and the conversion of polyimide with ortho-functional groups by high temperature heat treatment is a simpler process. The membranes prepared by thermal rearrangement reactions have high permeability and appropriate selectivity, and can also form a network structure if interchain thermal rearrangement occurs, improving the swelling resistance of the membranes.
In the case of asymmetric membrane precursors, during the preparation of the asymmetric membrane precursor into a thermally rearranged membrane at high temperatures, the porous sub-layer collapses, causing thickening of the skin layer, which reduces the flux of the membrane. Therefore, how to suppress the skin thickening phenomenon during the heat treatment is a problem that needs to be solved at present.
Disclosure of Invention
In view of the above, the present invention aims to provide a cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane, and a preparation method and application thereof.
In order to inhibit the skin thickening degree in the heat treatment process as much as possible, the invention introduces a phenolphthalein diamine monomer with a lactone ring in the process of synthesizing a polymer, and polycondensates the phenolphthalein diamine monomer with dianhydride to generate polyimide. The existence of the lactone ring not only can improve the solubility of the polymer, but also can degrade to generate free radicals in the lower temperature heat treatment process, so that the polymer chains are combined by cross-linking reaction. By utilizing the characteristic of a lactone ring, the phenolphthalein polyimide is prepared into a hollow fiber membrane precursor, then is crosslinked at a lower temperature, and then the temperature is further increased to prepare the thermally rearranged hollow fiber membrane. At this time, the flowability is blocked because the polymer chains are crosslinked, the thickening degree of the skin layer is greatly reduced, and the plasticizing resistance is improved.
In order to achieve the above object, the present invention provides the following technical solutions: a cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane having the structure of formula i:
wherein m represents the mole fraction of the 6FDA-DAP repeating unit in one molecular chain, n represents the mole fraction of the 6FDA-DAM repeating unit in the same molecular chain, m 1 、m 2 Represents the mole fraction of 6FDA-DAP repeating units in different molecular chains, and satisfies 0.1.ltoreq.m.ltoreq.0.9, 0.1.ltoreq.n.ltoreq.0.9, 0.1.ltoreq.m 1 ≤0.9，0.1≤m 2 ≤0.9，m+n＝1。
Preferably, the pore structure of the crosslinked thermally rearranged polybenzoxazole hollow fiber gas separation membrane is composed of a dense skin layer and a porous sublayer; the thickness of the cortex is 1-50000nm, the inner diameter is 0.05-0.5 mm, and the outer diameter is 0.1-1 mm.
The invention also provides a preparation method of the cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane, which comprises the following steps:
step 1, preparing polyimide into precursor casting solution;
step 2, spinning the precursor film casting solution by a dry-jet wet spinning method to prepare a polyimide hollow fiber film precursor with an acetate group or a hydroxyl group at the ortho position;
and 3, performing heat treatment on the polyimide hollow fiber membrane precursor with the ortho-position containing the acetate group or the hydroxyl group to obtain the cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane.
Preferably, the polyimide is obtained by polymerization of dianhydride monomer and diamine monomer; the dianhydride monomer is 2,2' -bis (3, 4-dicarboxyphenyl) hexafluoropropane; the diamine monomer is 2,4, 6-trimethyl-1, 3-phenylenediamine and 3,3' -diaminophenolphthalein.
Further preferably, the diamine monomer and dianhydride monomer are in a molar ratio of 1:1; the proportion of 3,3 '-diaminophenolphthalein to the total mole of 2,4, 6-trimethyl-1, 3-phenylenediamine and 3,3' -diaminophenolphthalein diamine in the diamine monomer is 0-100 mole% and is not 0; the ratio of the 2,4, 6-trimethyl-1, 3-phenylenediamine to the total mole of 2,4, 6-trimethyl-1, 3-phenylenediamine and 3,3' -diaminophenolphthalein diamine is 100 to 0 mole% and not 100 mole%.
Preferably, the polyimide is prepared by chemical imidization or one-step method.
Preferably, the precursor film casting solution is obtained by uniformly mixing the polyimide, N-methylpyrrolidone, tetrahydrofuran and ethanol; the mass fraction of polyimide in the casting film liquid precursor is 15-40%.
Preferably, the spinning process parameters in the process of spinning the precursor film casting liquid by a dry-jet wet spinning method are as follows: the temperature of the casting solution is between room temperature and 50 ℃, the temperature of the spinneret is between room temperature and 100 ℃, and the air gap is between 5 and 30cm.
Preferably, the heat treatment is to heat crosslink the mixture for 0.1 to 3 hours at a temperature from room temperature to 250 to 400 ℃, and then to continue the heat rearrangement reaction at a temperature of 400 to 500 ℃ for 0.1 to 3 hours.
Preferably, the temperature rising rate during the temperature rising is 3-10 ℃/min.
The invention also provides application of the cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane in gas separation.
The beneficial technical effects are as follows:
1. the invention prepares the cross-linked thermal rearranged polybenzoxazole hollow fiber gas separation membrane by heat treatment of polyimide with excellent film forming property, solves the problems that polybenzoxazole is indissolvable in common solvents and difficult to prepare, and has simple and easy operation process.
2. The molecular structure of the cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane prepared by the invention is of a cross-linked network structure and has high CO 2 /CH 4 、CO 2 /N 2 、O 2 /N 2 Selectivity and excellent plasticizing resistance, and pure CO with pressure of 30 atm 2 Can be stably operated.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a partial skin enlarged view of the crosslinked thermally rearranged polybenzoxazole hollow fiber gas separation membranes obtained in examples 1 to 4, where (a) is a partial skin enlarged view of example 1, (b) is a partial skin enlarged view of example 2, (c) is a partial skin enlarged view of example 3, and (d) is a partial skin enlarged view of example 4;
FIG. 2 is an enlarged view of a partial skin layer of the crosslinked thermally rearranged polybenzoxazole hollow fiber gas separation membrane obtained in comparative example 2;
FIG. 3 is an enlarged view of the whole morphology image and the partial cortex of the hollow fiber gas separation membrane obtained in comparative example 1, wherein (a) is an enlarged view of the whole morphology image and (b) is an enlarged view of the partial cortex;
FIG. 4 is an infrared spectrum of a cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane obtained in example 1;
fig. 5 is a graph of the plasticization resistance of the hollow fiber gas separation membranes of example 3 and comparative examples 1 and 2, wherein (a) is a graph of the plasticization resistance of comparative example 1, (b) is a graph of the plasticization resistance of comparative example 2, and (c) is a graph of the plasticization resistance of example 3.
Detailed Description
Various exemplary embodiments of the invention will now be described in detail, which should not be considered as limiting the invention, but rather as more detailed descriptions of certain aspects, features and embodiments of the invention.
It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In addition, for numerical ranges in this disclosure, it is understood that each intermediate value between the upper and lower limits of the ranges is also specifically disclosed. Every smaller range between any stated value or stated range, and any other stated value or intermediate value within the stated range, is also encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.
It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the invention described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from consideration of the specification of the present invention. The specification and examples of the present invention are exemplary only.
As used herein, the terms "comprising," "including," "having," "containing," and the like are intended to be inclusive and mean an inclusion, but not limited to.
The invention provides a cross-linked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane, which has a structure shown in a formula I:
wherein m represents the mole fraction of the 6FDA-DAP repeating unit in one molecular chain, n represents the mole fraction of the 6FDA-DAM repeating unit in the same molecular chain, m 1 、m 2 Represents the mole fraction of 6FDA-DAP repeating units in different molecular chains, and satisfies 0.1.ltoreq.m.ltoreq.0.9, 0.1.ltoreq.n.ltoreq.0.9, 0.1.ltoreq.m 1 ≤0.9，0.1≤m 2 ≤0.9，m+n＝1。
In some embodiments, the pore structure of the crosslinked thermally rearranged polybenzoxazole hollow fiber gas separation membrane is comprised of a dense skin layer and a porous sublayer; the dense cortex thickness is preferably 1 to 50000nm, more preferably 1 to 500nm, the inner diameter is preferably 0.05mm to 0.5mm, more preferably 0.1 to 0.2mm, and the outer diameter is preferably 0.1mm to 1mm, more preferably 0.2 to 0.4mm.
The cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane provided by the invention has an asymmetric structure with a compact cortex and a porous sublayer; the polyimide polymer is synthesized by taking 2,2 '-bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6 FDA) as a dianhydride monomer, 2,4, 6-trimethyl-1, 3-phenylenediamine (DAM) and 3,3' -Diaminophenolphthalein (DAP) as diamine monomers through a chemical imidization method or a one-step method, the synthesized polyimide is prepared into a hollow fiber membrane precursor, and then the hollow fiber membrane precursor is subjected to heat treatment at high temperature.
The method specifically comprises the following steps:
step 1, preparing polyimide into precursor casting solution;
step 2, spinning the precursor film casting solution by a dry-jet wet spinning method to prepare a polyimide hollow fiber film precursor with an acetate group or a hydroxyl group at the ortho position;
and 3, performing heat treatment on the polyimide hollow fiber membrane precursor with the ortho-position containing the acetate group or the hydroxyl group to obtain the cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane.
Polyimide is firstly prepared into precursor film casting liquid.
In some embodiments, the polyimide is obtained from a dianhydride monomer and a diamine monomer by polymerization; the dianhydride monomer is 2,2' -bis (3, 4-dicarboxyphenyl) hexafluoropropane; the diamine monomer is 2,4, 6-trimethyl-1, 3-phenylenediamine and 3,3' -diaminophenolphthalein. In the invention, 2,4, 6-trimethyl-1, 3-phenylenediamine is introduced to increase the molecular weight of the obtained polyimide, so that the problem that spinning is difficult due to low viscosity of the casting solution in the subsequent preparation process of the hollow fiber membrane is avoided, and the flux of the hollow fiber membrane is improved.
In some embodiments, the diamine monomer and dianhydride monomer molar ratio is 1:1; the proportion of 3,3 '-diaminophenolphthalein to the total mole of 2,4, 6-trimethyl-1, 3-phenylenediamine and 3,3' -diaminophenolphthalein diamine in the diamine monomer is 0 to 100 mole% and is not 0, preferably 30 to 70 mole%, more preferably 50 to 70 mole%; the ratio of the 2,4, 6-trimethyl-1, 3-phenylenediamine to the total mole of 2,4, 6-trimethyl-1, 3-phenylenediamine and 3,3' -diaminophenolphthalein diamine is 100 to 0 mole% and not 100 mole%, preferably 70 to 30 mole%, more preferably 50 to 30 mole%.
In some embodiments, the polyimide preferably has a weight average molecular weight of 10000 ～ 2000000, more preferably 100000 ～ 1000000.
In some embodiments, the polyimide is prepared by a chemical imidization process or a one-step process.
In other embodiments, when the polyimide preparation process is a chemical imidization process, the process comprises the steps of:
(1) At 0 ℃, firstly, N is used 2 Purging for about 15 minutes, after which diamine monomer 2,4, 6-trimethyl-1, 3-phenylenediamine (DAM) and 3,3' -Diaminophenolphthalein (DAP) and dianhydride monomer hexafluoropropane dianhydride (6 FDA) were dissolved in N-methylpyrrolidone (NMP), the molar proportions of monomers being diamine monomers: dianhydride monomer=1:1, the solid content of the solution is 15-30wt%, and the solution is placed in an ice-water mixture to be stirred and dissolved for 2-24 h.
(2) Taking acetic anhydride as a dehydrating agent and pyridine as a catalyst to carry out chemical imidization, reacting for 2-24 hours, precipitating and filtering the obtained product in methanol, and drying the product at the temperature of 50-250 ℃ in vacuum to obtain a polyimide polymer; the molar ratio of the acetic anhydride to the diamine monomer is 5:1, and the molar ratio of the pyridine to the diamine monomer is 2.5:1.
In other embodiments, when the polyimide preparation method is a one-step method, the method comprises the steps of:
3,3 '-Diaminophenolphthalein (DAP) and 2,4, 6-trimethyl-1, 3-phenylenediamine (DAM) and 2,2' -bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6 FDA) are dissolved in m-cresol under nitrogen protection, isoquinoline is added as a catalyst, and stirred at 180-220 ℃ for 4-8 hours. The resulting polymer solution was precipitated in methanol, filtered and dried. The ratio of diamine and dianhydride is the same as in the chemical imidization method.
In some embodiments, the precursor film casting solution is obtained by uniformly mixing the polyimide with N-methylpyrrolidone, tetrahydrofuran and ethanol; the mass fraction of polyimide in the casting film liquid precursor is 15-40%.
In the invention, after the precursor film casting liquid is obtained, the precursor film casting liquid is spun by a dry-jet wet spinning method to prepare the polyimide hollow fiber film precursor with the ortho-position containing acetate group or hydroxyl group. The structural formula of the polyimide hollow fiber membrane precursor containing the acetate group or the hydroxyl group at the ortho position is as follows:
wherein m and n represent the molar fractions of the respective repeating units and satisfy 0.1.ltoreq.m.ltoreq.0.9, 0.1.ltoreq.n.ltoreq.0.9, and m+n=1;
r represents an acetate group (-OOCCH) 3 ) Or hydroxyl (-OH), R is-OOCCH if polyimide is synthesized by chemical imidization 3 If polyimide is synthesized by a one-step process, R is-OH.
In some embodiments, the spinning process parameters in the spinning of the precursor film casting solution by a dry-jet wet spinning method are as follows: the temperature of the casting solution is between room temperature and 50 ℃, the temperature of the spinneret is between room temperature and 100 ℃, the air gap is between 5 and 30cm, and a nascent fiber film is formed under the combined action of an external coagulation bath and a core solution; the external coagulation liquid and the core liquid can be one or a mixture of more than two of alcohol, water, N-dimethylformamide, N-dimethylacetamide and N-methylpyrrolidone.
After the nascent fiber membrane is obtained, the invention also comprises a solvent exchange and drying step; the solvent exchange is to soak the as-spun fiber membrane with running water, methanol, n-hexane to remove residual solvent. The drying mode is not particularly limited in the present invention, and methods well known to those skilled in the art can be adopted.
In the invention, after the polyimide hollow fiber membrane precursor is obtained, the polyimide hollow fiber membrane precursor containing acetate groups or hydroxyl groups at the ortho positions is subjected to heat treatment to obtain the cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane.
In some embodiments, the heat treatment is divided into heat crosslinking at a temperature from room temperature to 250-400 ℃ for 0.1-3 hours, and then continuing to raise the temperature to 400-500 ℃ and holding for 0.1-3 hours for a thermal rearrangement reaction; the atmosphere in the heat treatment is nitrogen, helium or argon. The invention firstly carries out crosslinking on the hollow fiber membrane at a lower temperature, improves the glass transition temperature of the polymer, reduces the mobility of molecular chains, and greatly reduces the collapse degree of the cortex in the thermal rearrangement reaction process at a higher temperature.
In some embodiments, the rate of temperature increase at the time of temperature increase is preferably 3-10 ℃/min.
The invention also provides application of the cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane in gas separation. The cross-linked thermal rearranged polybenzoxazole hollow fiber gas separation membrane provided by the invention has high CO 2 /CH 4 、CO 2 /N 2 、O 2 /N 2 The catalyst has the advantages of selectivity, high flux, excellent thermal stability and plasticizing resistance, and can be used in the fields of carbon dioxide removal, air separation and the like of natural gas and flue gas.
For a better understanding of the present invention, the following examples are further illustrated, but are not limited to the following examples.
Example 1
(1) At 0 ℃, at first at N 2 After purging under an atmosphere for about 15 minutes, 36.05g of 2,4, 6-trimethyl-1, 3-phenylenediamine (DAM) and 41.76g of 3,3' -Diaminophenolphthalein (DAP) (molar ratio of DAM to DAP 2:1) were dissolved in 713.22g N-methylpyrrolidone (NMP), and the mixture was stirred in an ice-water mixture, and after completion of the dissolution, 159.93g of hexafluoropropane dianhydride (6 FDA) was added thereto, followed by further stirring.
(2) Stirring the solution at room temperature for 24 hours to form a viscous polyamic acid solution; then 183.76g of acetic anhydride and 71.19g of pyridine were added for imidization, the polymer was allowed to settle in methanol after reacting at room temperature for 24 hours, washed with methanol for 24 hours, and then placed in a vacuum oven for drying at 100 to 250 ℃ for 48 hours.
(3) And uniformly mixing the dried polyimide with tetrahydrofuran, N-methylpyrrolidone and absolute ethyl alcohol at room temperature, stirring for 8 hours to obtain a precursor casting solution with polyimide content of 30wt.%, ultrasonically defoamating the precursor casting solution, and pouring the precursor casting solution into a feed solution tank for continuous defoamation for 12 hours.
(4) Spinning the precursor film casting liquid by a dry-jet wet spinning method, introducing nitrogen with the pressure of 0.3MPa into a liquid material tank, wherein the temperature of the liquid material is 50 ℃, the air gap is 7cm, the flow rate of core liquid is 1ml/min, the flow rate of the liquid material is 3ml/min, the core liquid is a mixture of water and N-methylpyrrolidone (15/85 wt.%), the external solidification is water with the temperature of 50 ℃, and the filament collecting speed is set to be 50m/min. Soaking the spun hollow fiber membrane in water for 24 hours, then transferring the hollow fiber membrane into methanol for soaking for 30 minutes, repeating the soaking for 3 times, transferring the hollow fiber membrane into normal hexane for soaking for 30 minutes, repeating the soaking for 3 times, and finally drying the hollow fiber membrane at the vacuum temperature of 120 ℃ to obtain the polyimide hollow fiber membrane precursor with the ortho-position containing the acetate group.
(5) And (3) placing the polyimide hollow fiber membrane precursor with the ortho-position containing the acetate group into a tubular furnace, introducing nitrogen, blowing for 15min to discharge air in the furnace, heating to 350 ℃ at a heating rate of 5 ℃/min under the atmosphere, keeping for 1h, continuously raising the temperature to 450 ℃ and keeping for 30min, and obtaining the crosslinked thermally rearranged polybenzoxazole hollow fiber gas separation membrane after the tubular furnace is naturally cooled.
The infrared spectrogram of the obtained polyimide hollow fiber membrane precursor and the cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane is shown in figure 4, 1558cm -1 、1484cm -1 The absorption peak at the site is the characteristic absorption peak of the polybenzoxazole structure, which proves the structure.
Example 2
(1) 36.05g of 2,4, 6-trimethyl-1, 3-phenylenediamine (DAM), 41.76g of 3,3' -Diaminophenolphthalein (DAP), 159.93g of hexafluoropropane dianhydride (6 FDA), 1343.58g of m-cresol, 12ml of isoquinoline were weighed into a three-necked flask, and the mixture was stirred in N 2 Stirring and reacting for 8 hours at 190 ℃ in the atmosphere to obtain a high-viscosity polyimide solution, pouring the solution into methanol to enable the polymer to be settled, washing the polymer for 24 hours by using the methanol, and then placing the polymer into a vacuum oven for drying for 48 hours at 100-250 ℃.
(2) And uniformly mixing the dried polyimide with tetrahydrofuran, N-methylpyrrolidone and absolute ethyl alcohol at room temperature, stirring for 8 hours to obtain a precursor casting solution with polyimide content of 30wt.%, ultrasonically defoamating the precursor casting solution, and pouring the precursor casting solution into a feed solution tank for continuous defoamation for 12 hours.
(3) Spinning the precursor film casting liquid by a dry-jet wet spinning method, introducing nitrogen with the pressure of 0.3MPa into a liquid material tank, wherein the temperature of the liquid material is 50 ℃, the air gap is 7cm, the flow rate of core liquid is 1ml/min, the flow rate of the liquid material is 3ml/min, the core liquid is a mixture of water and N-methylpyrrolidone (15/85 wt.%), the external solidification is water with the temperature of 50 ℃, and the filament collecting speed is set to be 50m/min. Soaking the spun hollow fiber membrane in water for 24 hours, then transferring the hollow fiber membrane into methanol for soaking for 30 minutes, repeating the steps for 3 times, transferring the hollow fiber membrane into normal hexane for soaking for 30 minutes, repeating the steps for 3 times, and finally drying the hollow fiber membrane at the vacuum temperature of 120 ℃ to obtain the polyimide hollow fiber membrane precursor with the ortho-position containing hydroxyl.
(4) And (3) placing the polyimide hollow fiber membrane precursor with the ortho-position hydroxyl into a tubular furnace, introducing nitrogen to purge for 15min to discharge air in the furnace, heating to 350 ℃ at a heating rate of 5 ℃/min under the atmosphere, keeping for 1h, continuously raising the temperature to 450 ℃ and keeping for 30min, and obtaining the cross-linked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane after the tubular furnace is naturally cooled.
Example 3
(1) Step (1) was performed as in example 1.
(2) Step (2) was performed as in example 1.
(3) Step (3) was performed as in example 1.
(4) Step (4) was performed as in example 1.
(5) After placing the polyimide hollow fiber membrane precursor with the acetate group at the ortho position into a tubular furnace, introducing nitrogen gas to purge for 15min to discharge air in the furnace, heating to 350 ℃ at a heating rate of 5 ℃/min under the atmosphere at a flow rate of 400ml/min, and keeping for 1h. And then continuously raising the temperature to 475 ℃ and keeping for 30min, and obtaining the cross-linked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane after the tube furnace is naturally cooled.
Example 4
(1) The procedure is as in example 1, step (1), except that the molar ratio of DAM to DAP is 1:1.
(2) Step (2) was performed as in example 1.
(3) Step (3) was performed as in example 1.
(4) Step (4) was performed as in example 1.
(5) Step (5) was performed as in example 1.
Comparative example 1
The difference from example 1 is that the heat treatment procedure of step (5) for the polyimide hollow fiber membrane precursor having an acetate group or a hydroxyl group in the ortho position is omitted.
Comparative example 2
(1) Step (1) was performed as in example 1.
(2) Step (2) was performed as in example 1.
(3) Step (3) was performed as in example 1.
(4) Step (4) was performed as in example 1.
(5) After the hollow fiber membrane was placed in a tube furnace, nitrogen was purged for 15 minutes to discharge air in the furnace at a flow rate of 400ml/min, and the temperature was directly heated to 475℃at a heating rate of 5℃per minute under this atmosphere and maintained for 30 minutes. And after the tube furnace is naturally cooled, obtaining the cross-linked thermal rearrangement polybenzoxazole hollow fiber gas separation membrane.
The inner and outer diameters of the hollow fiber gas separation membranes produced in examples 1 to 4 and comparative examples 1 to 2 were measured with an optical microscope. The specific data are shown in Table 1.
Table 1 comparison of inner and outer diameters (unit: μm) of hollow fiber gas separation membranes produced in examples and comparative examples
Electron micrographs of the precursor fibers and crosslinked thermally rearranged hollow fiber membranes obtained in the examples and comparative examples are shown in fig. 1-3. The section of the membrane is of a full sponge structure and has no finger-shaped hole structure. The thickness of the raw film skin layer in comparative example 1 was within 1. Mu.m. When the hollow fiber sections after the heat treatment were observed, the final skin thicknesses of the hollow fiber membranes of examples 1, 2, 3 and 4, which were subjected to low-temperature pre-crosslinking, were all between 1 and 2 μm, and there was no significant thickening compared with the original membrane (comparative example 1). The skin layer of comparative example 2, which was not crosslinked at low temperature, was significantly thickened as compared with the original film (comparative example 1), and its thickness was about 5. Mu.m.
The pure gas separation properties of the crosslinked thermally rearranged polybenzoxazole hollow fiber membrane and polyimide hollow fiber membrane precursor obtained in examples and comparative examples are shown in table 2. The test pressure was 0.5MPa and the test temperature was 35 ℃.
Table 2 comparison of pure gas separation performance of hollow fiber membranes of examples and comparative examples
From the data in the table, it can be seen that the membrane skins after low temperature pre-crosslinking are thinner (examples 1-4), so the flux is also higher. It can be seen from examples 1 and 4 that the flux decreases with decreasing DAM content in the molecular structure. As can be seen from examples 1 and 3, the flux gradually increases with increasing thermal rearrangement temperature.
The plasticization resistance of the crosslinked thermally rearranged polybenzoxazole hollow fiber membranes and polyimide hollow fiber membrane precursors obtained in example 3, comparative example 2 and comparative example 1 is shown in fig. 5. The fibrous film precursor is plasticized at a pressure of about 200 psi. The plasticization resistance of the heat-treated hollow fiber membrane was improved as compared to the precursor fiber, wherein the crosslinked thermally rearranged hollow fiber membrane of example 3 was not plasticized at a pressure of 450psi, and the hollow fiber membrane of comparative example 2, which was not pre-crosslinked at a low temperature, was CO-crosslinked after a pressure of 350psi 2 The permeability of (a) increases with increasing pressure, i.e. plasticization occurs.
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.
Claims (10)
1. A cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane characterized by having a structure represented by formula i:
wherein m represents the mole fraction of the 6FDA-DAP repeating unit in one molecular chain, n represents the mole fraction of the 6FDA-DAM repeating unit in the same molecular chain, m 1 、m 2 Represents the mole fraction of 6FDA-DAP repeating units in different molecular chains, and satisfies 0.1.ltoreq.m.ltoreq.0.9, 0.1.ltoreq.n.ltoreq.0.9, 0.1.ltoreq.m 1 ≤0.9，0.1≤m 2 ≤0.9，m+n＝1。
2. The crosslinked thermally rearranged polybenzoxazole hollow fiber gas separation membrane of claim 1, wherein the pore structure of the crosslinked thermally rearranged polybenzoxazole hollow fiber gas separation membrane is composed of a dense skin layer and a porous sublayer; the thickness of the cortex is 1-50000nm, the inner diameter is 0.05-0.5 mm, and the outer diameter is 0.1-1 mm.
3. The method for preparing the crosslinked thermally rearranged polybenzoxazole hollow fiber gas separation membrane according to claim 1 or 2, which is characterized by comprising the steps of:
step 1, preparing polyimide into precursor casting solution;
step 2, spinning the precursor film casting solution by a dry-jet wet spinning method to prepare a polyimide hollow fiber film precursor with an acetate group or a hydroxyl group at the ortho position;
and 3, performing heat treatment on the polyimide hollow fiber membrane precursor with the ortho-position containing the acetate group or the hydroxyl group to obtain the cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane.
4. The method according to claim 3, wherein the polyimide is obtained by polymerizing a dianhydride monomer and a diamine monomer; the dianhydride monomer is 2,2' -bis (3, 4-dicarboxyphenyl) hexafluoropropane; the diamine monomer is 2,4, 6-trimethyl-1, 3-phenylenediamine and 3,3' -diaminophenolphthalein.
5. The method of claim 4, wherein the diamine monomer and dianhydride monomer are in a molar ratio of 1:1; the proportion of 3,3 '-diaminophenolphthalein to the total mole of 2,4, 6-trimethyl-1, 3-phenylenediamine and 3,3' -diaminophenolphthalein diamine in the diamine monomer is 0-100 mole% and is not 0; the ratio of the 2,4, 6-trimethyl-1, 3-phenylenediamine to the total mole of 2,4, 6-trimethyl-1, 3-phenylenediamine and 3,3' -diaminophenolphthalein diamine is 100 to 0 mole% and not 100 mole%.
6. The method of claim 3, wherein the polyimide is prepared by chemical imidization or one-step method.
7. The preparation method according to claim 3, wherein the spinning process parameters in the spinning of the precursor casting solution by a dry-jet wet spinning method are as follows: the temperature of the casting solution is between room temperature and 50 ℃, the temperature of the spinneret is between room temperature and 100 ℃, and the air gap is between 5 and 30cm.
8. A method according to claim 3, wherein the heat treatment is to heat-crosslink the mixture at a temperature from room temperature to 250 to 400 ℃ for 0.1 to 3 hours, and then to continue the heat rearrangement reaction at a temperature from 400 to 500 ℃ for 0.1 to 3 hours.
9. The method according to claim 8, wherein the temperature rise rate at the time of the temperature rise is 3 to 10 ℃/min.
10. Use of a cross-linked thermally rearranged polybenzoxazole hollow fiber gas separation membrane according to claim 1 or 2 in gas separation.
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