阅读说明：本技术 改性纺丝原液、中空纤维碳膜及其制备方法和应用 (Modified spinning solution, hollow fiber carbon membrane and preparation method and application thereof ) 是由 吴历斌 李为 周亚新 于 2020-07-02 设计创作，主要内容包括：本发明涉及一种改性纺丝原液、中空纤维碳膜及其制备方法和应用。所述改性纺丝原液包括10～40份聚合物、0.1～15份交联剂和55～85份溶剂。所述中空纤维碳膜由改性纺丝原液经纺丝、氧化交联、碳化得到。本发明碳膜的均匀性好、缺陷少,具有较高抗压强度、较好韧性等机械性能,能可控调节孔径及分布,可用于物料分离领域,能显著提高渗透通量、明显改善选择性,获得兼具高通量和高选择性的分离用碳膜。(The invention relates to a modified spinning solution, a hollow fiber carbon membrane, and a preparation method and application thereof. The modified spinning solution comprises 10-40 parts of polymer, 0.1-15 parts of cross-linking agent and 55-85 parts of solvent. The hollow fiber carbon film is obtained by spinning, oxidizing, crosslinking and carbonizing modified spinning solution. The carbon film has good uniformity, few defects, high compressive strength, good toughness and other mechanical properties, can controllably adjust the aperture and the distribution, can be used in the field of material separation, can obviously improve the permeation flux and the selectivity, and can obtain the carbon film for separation with high flux and high selectivity.)

1. A modified spinning solution comprises, by weight, 10-40 parts of a polymer, 0.1-15 parts of a crosslinking agent and 55-85 parts of a solvent; preferably, the paint comprises 12-20 parts of polymer, 0.1-5 parts of cross-linking agent and 75-85 parts of solvent.

2. The modified dope of claim 1, wherein:

the polymer is selected from at least one of polyvinylidene fluoride, phenolic resin, polyacrylonitrile, polysulfone and polyether sulfone; and/or the presence of a gas in the gas,

the cross-linking agent is selected from at least one of ethyl orthosilicate, methyl orthosilicate, vinyltriethylsilane, vinyltrimethoxysilane, methyltriethoxysilane, p-xylylenediamine, p-phenylenediamine, m-phenylenediamine and m-xylylenediamine; and/or the presence of a gas in the gas,

the solvent is at least one selected from dimethylacetamide, dimethylformamide, dimethyl sulfoxide, methyl pyrrolidone and triethyl phosphate.

3. A method of preparing the modified dope according to claim 1 or 2, comprising mixing components comprising a polymer, a crosslinking agent and a solvent to obtain the modified dope.

4. The production method according to claim 3, characterized in that:

based on 100 parts by weight of the modified spinning solution, 10-40 parts of polymer, 0.1-15 parts of cross-linking agent and 55-85 parts of solvent.

5. A hollow fiber carbon membrane obtained by spinning, oxidatively crosslinking, and carbonizing the modified spinning dope of claim 1 or 2 at a high temperature.

6. A method of producing a hollow fiber carbon membrane according to claim 5, comprising the steps of:

(1) spinning the modified spinning solution to obtain a hollow fiber membrane;

(2) oxidizing and crosslinking the hollow fiber original membrane to obtain a hollow fiber crosslinked membrane;

(3) and (3) carbonizing the hollow fiber cross-linked membrane at high temperature.

7. The method for producing a hollow fiber carbon membrane according to claim 6, characterized in that:

in the step (1), the hollow fiber membrane is formed by spinning through any one of dry-wet spinning and wet spinning.

8. The method for producing a hollow fiber carbon membrane according to claim 6, characterized in that:

in the step (2), heating the hollow fiber membrane from room temperature to 200-400 ℃ in air or in vacuum or inert atmosphere, and staying for 30-90 min for oxidation and crosslinking reaction, wherein the heating rate is 1-20 ℃/min; preferably, the temperature is increased to 250-380 ℃, and the mixture stays for 40-90 min; the heating rate is 2-15 ℃/min.

9. The method for producing a hollow fiber carbon membrane according to claim 6, characterized in that:

in the step (3), in a vacuum or inert atmosphere, heating the hollow fiber cross-linked membrane to 450-700 ℃, and staying for 15-120 min for high-temperature carbonization; preferably, the temperature is increased to 450-600 ℃, and the mixture stays for 30-120 min.

10. Use of the hollow fiber carbon membrane according to claim 5 or the hollow fiber carbon membrane obtained by the method according to any one of claims 6 to 9 in gas separation such as air separation oxygen, refinery tail gas purification or concentration, liquid separation such as aromatic xylene separation, hydrophobic alcohol permeation, and oil-water separation.

Technical Field

The invention relates to the field of membranes, in particular to a modified spinning solution, a hollow fiber carbon membrane, and a preparation method and application thereof.

Background

The continuous expansion of the application field of the membrane separation technology puts higher requirements on the production of membrane materials. According to different membrane materials, the membranes can be divided into two categories, namely polymer membranes and inorganic membranes; the polymer membrane is most widely applied, for example, microfiltration membranes, ultrafiltration membranes and nanofiltration membranes are widely applied to the fields of seawater desalination, food and medicine and the like, but outstanding problems exist, for example, the use process is greatly limited by operation pressure and use temperature, the chemical stability is poor, the cleaning and sterilization are difficult, secondary pollution is caused, and the like.

The inorganic film mainly includes a ceramic film, a metal film, a carbon film, a molecular sieve film, and the like. In contrast, the ceramic membrane has been applied to the fields of microfiltration and ultrafiltration due to excellent chemical stability, high pressure resistance and easy cleaning, and even has been developed and applied in the field of nanofiltration, but the ceramic membrane is formed by sintering fine oxides with different particle sizes for multiple times at high temperature, the minimum pore diameter can reach nanometer, but the pore diameter is more difficult to control and the preparation process is complicated, the control factors are more, and the pore diameter membrane at the nanometer level and below is not applied in a large scale; compared with ceramic membranes, the porous metal membrane has the advantages of slightly poor chemical stability, relatively simple preparation and controllable pore size, and at least comprises two parts, wherein one part is a support body with high porosity and large pore size, the other part is a thin pore layer which is also called a pore size control layer, and a transition layer is sometimes needed between the two parts. The preparation process is generally as follows: mixing the fine metal powder with a proper medium to form a suspension, coating the suspension on a support body, drying, degreasing at a certain temperature, and finally sintering at a high temperature to obtain the composite material. The contact parts of the particles are sintered together during the sintering process, and the pores among the particles form a pore channel. Therefore, the porous metal film is still relatively complex to prepare, the fine pore size is difficult to control, and the seesaw is formed by high permeation flux and high selectivity, so that the seesaw is always out of balance and is difficult to balance. In addition, although the molecular sieve membrane utilizes the regular pore characteristics of zeolite molecular sieves, such as uniform pore size and rich pore structure, the high flux must be guided by seed crystals and template agents to carry out directional growth, the high selectivity must be subjected to secondary or multiple crystallization to eliminate defects (similar to a wooden barrel short plate), the high flux and the high selectivity are mutually restricted and hardly balanced, the separation performance of the molecular sieve membrane is sharply reduced along with the increase of the use pressure in the use process, so that the selectivity drops, and the permeation flux is too low if the molecular sieve membrane is repaired. Even if the problem of balance between high permeation flux and high selectivity is not considered, the difficulties of difficult large-scale crystallization, complex batch production, low pressure tolerance and the like of the molecular sieve membrane are the biggest bottlenecks limiting the industrial application of the molecular sieve membrane.

The carbon film is used as a novel inorganic film with excellent performance, is generally formed by carrying out high-temperature pyrolysis and carbonization treatment on a carbon-containing precursor in an inert or vacuum environment, has better capabilities of resisting high temperature, acid and alkali, resisting organic solvents and the like, and also has higher permselectivity on micromolecular gas or liquid with similar molecular size. Meanwhile, the Carbon membrane is easy to form a large-area membrane due to uniform pore size distribution and large adjustable range, and becomes a high-performance separation membrane with the most industrialized prospect (Carbon,2003,41:253 and 266). The carbon film may be classified into a supported carbon film (composite carbon film) and an unsupported carbon film (homogeneous carbon film) according to the structure of the film, wherein the supported carbon film is reported more, and a metal-supported composite carbon film, a ceramic-supported composite carbon film, a carbon-supported tubular composite carbon film, and a flat composite carbon film have been developed because of the use of a support. The unsupported carbon membrane can be further subdivided into a plate membrane, a hollow fiber membrane and a capillary carbon membrane, wherein the plate membrane is difficult to directly carry out industrial application and is mainly used for laboratory research or process development due to poor mechanical property and incapability of forming a large-area membrane; the capillary carbon film is still in the technical critical stage due to the reasons of multiple control factors, complicated steps, poor repeatability and the like in the forming process. The hollow fiber membrane has very high specific surface area/volume ratio, good dimensional stability and better mechanical property (compared with a capillary carbon membrane), is more important suitable for large-scale production, and is the best breakthrough for realizing the cross-over development of the carbon membrane, solving the technical problems at present and leading to the realization of industrial application. Unfortunately, to date, no hollow fiber type carbon membrane has been reported except Science, which reports reverse osmosis type carbon membranes after attempts for PX/OX separation (Science,1016,353: 804-; moreover, Ryan et al only in supplementary literature, with core and shell liquid compositions, vaguely mentions the carbon membrane as a hollow fiber, and no description is given of the carbon membrane configuration. Therefore, hollow fiber type carbon membranes and their preparation are still blank.

Disclosure of Invention

The invention aims to provide a hollow fiber carbon film (or called hollow fiber carbon film, also called hollow fiber carbon film and hollow carbon film) which is low in cost, convenient to operate, easy to repeat and suitable for large-scale production, aiming at the problems in the existing carbon film and the preparation method thereof.

One of the purposes of the invention is to provide a modified spinning solution which comprises, by weight, 10-40 parts of a polymer, 0.1-15 parts of a cross-linking agent and 55-85 parts of a solvent;

preferably, the modified spinning solution comprises 12-20 parts of polymer, 0.1-5 parts of cross-linking agent and 75-85 parts of solvent.

In the modified spinning solution, the polymer is preferably at least one of polyvinylidene fluoride, phenolic resin, polyacrylonitrile, polysulfone and polyethersulfone, and more preferably at least one of polyvinylidene fluoride or phenolic resin;

the cross-linking agent is preferably selected from at least one of ethyl orthosilicate, methyl orthosilicate, vinyltriethylsilane, vinyltrimethoxysilane, methyltriethoxysilane, p-xylylenediamine, p-phenylenediamine, m-phenylenediamine and m-xylylenediamine, and more preferably at least one of p-xylylenediamine and m-xylylenediamine;

the solvent is an organic solvent, preferably at least one of dimethylacetamide, dimethylformamide, dimethyl sulfoxide, methyl pyrrolidone and triethyl phosphate, and more preferably at least one of dimethylacetamide, methyl pyrrolidone or dimethylformamide.

The modified dope, most preferably the modified dope comprises polyvinylidene fluoride, p-phenylenediamine and/or p-xylylenediamine, dimethylacetamide and/or methylpyrrolidone.

Furthermore, the modified spinning solution may also contain additives, which are selectively added or directly omitted according to the requirements of the hollow fiber carbon membrane on the wall pore size, distribution characteristics and porosity.

The additive can be adjuvant commonly used in the art, such as polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), LiCl, LiNO₃Or K₂CO₃And the dosage is conventional dosage or adjusted according to the requirements of actual conditions.

According to a preferred embodiment of the present invention, the modified spinning solution may further include 1 to 10 parts of polyethylene glycol.

The invention also provides a preparation method of the modified spinning solution, which comprises the step of mixing components including a polymer, a cross-linking agent and a solvent to obtain the modified spinning solution.

In the preparation method of the modified spinning solution, based on 100 parts by weight of the modified spinning solution, 10-40 parts of polymer, 0.1-15 parts of cross-linking agent and 55-85 parts of solvent are used;

preferably, the polymer is 12-20 parts, the cross-linking agent is 0.1-5 parts, and the solvent is 75-85 parts.

The invention also aims to provide a hollow fiber carbon membrane which is obtained by spinning, oxidizing, crosslinking and carbonizing the modified spinning solution at high temperature.

The hollow fiber carbon membrane has a wall pore average pore diameter of

The fourth object of the present invention is to provide a method for preparing the hollow fiber carbon membrane, comprising the steps of:

(1) spinning the modified spinning solution to obtain a hollow fiber membrane;

(2) oxidizing and crosslinking the hollow fiber original membrane to obtain a hollow fiber crosslinked membrane;

(3) and (3) carbonizing the hollow fiber cross-linked membrane at high temperature.

The invention is realized by the following technical scheme: firstly, preparing modified spinning solution containing high molecular polymer, cross-linking agent, organic solvent and the like, carrying out method spinning on the spinning solution to prepare a hollow fiber membrane, carrying out low-temperature oxidation and cross-linking reaction on the hollow fiber membrane at a lower temperature independently or in a retention step to obtain a hollow fiber cross-linked membrane, and carrying out high-temperature carbonization on the hollow fiber cross-linked membrane under the protection of vacuum or inert atmosphere to obtain the hollow fiber carbon membrane.

In the above-described method for producing a hollow fiber carbon membrane,

in the step (1), the hollow fiber membrane is spun and formed by adopting any one of dry-wet spinning (also called dry-jet wet spinning) or wet spinning; the hollow fiber raw membrane is preferably prepared by dry-wet spinning.

In the step (2), heating the hollow fiber membrane from room temperature to 200-400 ℃ in air or in vacuum or inert atmosphere, and staying for 30-90 min for oxidation and crosslinking reaction, wherein the heating rate is 1-20 ℃/min; preferably, the temperature is increased to 250-380 ℃, and the mixture stays for 40-90 min; the heating rate is 2-15 ℃/min.

In the step (3), in a vacuum or inert atmosphere, heating the hollow fiber cross-linked membrane to 450-700 ℃, and staying for 15-120 min for high-temperature carbonization; preferably, the temperature is increased to 450-600 ℃, and the mixture stays for 30-120 min.

According to a preferred embodiment of the present invention, the method for preparing the hollow fiber carbon membrane comprises the steps of:

firstly, preparing modified spinning solution

1) Slowly adding weighed cross-linking agents, high-molecular polymers, optional pore-foaming agents and other auxiliaries into a spinning tank containing an organic solvent, and stirring for 24-48 hours under the protection of nitrogen and sealing conditions;

2) vacuumizing and standing the mixture or performing ultrasonic defoaming for 12-24 h;

3) adjusting the nitrogen pressure of the spinning tank to 0.1-1 MPa, and filtering impurities to obtain a membrane casting solution;

② spinning hollow fiber membrane

4) Injecting the casting solution into a spinning nozzle through a metering pump, simultaneously introducing the polyester yarns into the spinning nozzle through traction, and allowing the polyester yarns to flow out together with the casting solution, wherein the casting solution is uniformly coated on the outer surface of the polyester yarns of the support body; in the process of uniformly coating the casting solution on the outer surface of the support polyester yarn, adjusting the looseness of the film yarn at the front end of the film yarn by using a tension drafting machine;

5) preparing a hollow fiber precursor (namely a hollow fiber membrane) through a coagulating bath phase conversion process;

③ preparing hollow fiber cross-linked membrane by oxidation

6) Placing the hollow fiber raw membrane in a muffle furnace, raising the temperature from room temperature Tr To an oxidation temperature To, staying at t1, and performing I) single oxidation and crosslinking reaction on the hollow fiber raw membrane To obtain a hollow fiber crosslinked membrane;

7) or skipping step 6), placing the hollow fiber raw membrane in a furnace under vacuum or inert gas protection, raising the temperature from room temperature Tr To the oxidation temperature To and staying at t1, and carrying out the steps of II) process oxidation and crosslinking reaction To obtain the hollow fiber crosslinked membrane;

carbonizing to prepare hollow fiber carbon film

8) Transferring the hollow fiber cross-linked membrane obtained by the single oxidation and cross-linking reaction in the step 6) into a furnace protected by vacuum or inert gas, quickly heating the hollow fiber cross-linked membrane from the room temperature Tr To the temperature To, then slowly heating the hollow fiber cross-linked membrane To the carbonization temperature Tc, and staying at t2 To finish high-temperature carbonization treatment;

9) or skipping step 8), carrying out the process oxidation and crosslinking reaction steps in the step 7), and keeping the prepared hollow fiber crosslinked membrane in a vacuum or inert gas protection furnace, slowly heating from To the carbonization temperature Tc and staying at t2 To complete the high-temperature carbonization treatment;

in the preparation method of the hollow fiber carbon film, in the process of preparing the hollow fiber cross-linked membrane through oxidation, the temperature is programmed To rise To the oxidation temperature To of 200-400 ℃ at the speed of 1-20 ℃/min, and the temperature is kept for t1 of 30-90 min;

in the preparation method of the hollow fiber carbon film, in the process of preparing the hollow fiber carbon film by carbonization, the temperature programming is To be increased from To the carbonization temperature Tc of 450-700 ℃ at the rate of 0.25-10 ℃/min, and the time t2 is 15-120 min; preferably, the heating rate is 0.25-5 ℃/min.

In the preparation method of the hollow fiber carbon film, the step of preparing the hollow fiber cross-linked film by oxidation can select the lower temperature To, and independently carry out oxidation and cross-linking reaction before the step of high-temperature carbonization, and then carry out the step of high-temperature carbonization; alternatively, the hollow fiber carbon membrane may be prepared by performing oxidation and crosslinking at a temperature To for a residence time t1 during the high temperature carbonization step, and then performing high temperature carbonization at a temperature programmed To the carbonization temperature Tc for a time period t 2.

The fifth purpose of the invention is to provide the application of the hollow fiber carbon membrane or the hollow fiber carbon membrane obtained by the preparation method in gas separation such as air separation oxygen, refinery tail gas purification or concentration, liquid separation such as aromatic hydrocarbon xylene separation, hydrophobic alcohol permeation and oil-water separation.

The key point of the invention is to prepare modified spinning solution, especially the composition formula of the modified spinning solution and the combination of high molecular polymer/cross-linking agent, and then to spin, cross-link and carbonize the modified spinning solution. The prepared modified spinning solution is as follows: the specially selected cross-linking agent and the adapted high molecular polymer are dissolved in the organic solvent together according to the proportion to realize the uniform mixing at the molecular level, and any additive or auxiliary agent is not added in the subsequent step; the cross-linking agent plays a cross-linking role in subsequent low-temperature oxidation and cross-linking reaction and reacts with the high-molecular polymer to generate an insoluble infusible special structure.

Therefore, the hollow fiber type carbon film provided by the invention is prepared by taking a polymer as a carbon-containing precursor (raw material), adding an adaptive modifier and/or additive to prepare a modified spinning solution, then spinning and molding to directly obtain a hollow fiber original film, no chemical reagent is added after spinning, the hollow fiber original film is directly subjected to low-temperature oxidation and generates a cross-linking reaction to generate a hollow fiber cross-linking film, the hollow fiber cross-linking film generates an insoluble and infusible special heat-resistant structure in the low-temperature oxidation and cross-linking reaction process, and the characteristics of obvious deformation or collapse, gaps, pore diameters and the like of the abundant original pore structure of the hollow fiber cross-linking film are maintained and further developed even the hollow fiber cross-linking film is subjected to higher-temperature pyrolysis and high-temperature carbonization treatment, new gaps and pore structures are generated by thermal cracking, and a graphite structure is continuously generated in the carbonization process, the double-slit ultra-fine micropores and the ultra-fine micropores which jointly form the carbon film respectively guide material transportation and screening separation, and jointly complete high permeation flux and high selectivity, thereby realizing double high performance of the hollow fiber film.

The invention has the beneficial effects that:

the modified spinning solution different from the prior art is adopted for spinning to generate a hollow fiber membrane, the membrane is further subjected to crosslinking reaction to generate an insoluble and infusible heat-resistant structure, and the shape characteristics (such as hollowness, multiple pores, pore wall pores and the like) of the hollow fibers are maintained in the subsequent high-temperature carbonization process, so that the hollow fiber carbon membrane with high porosity and very fine pore diameter (including two categories of ultra-fine pores and ultra-fine pores) can be directly prepared. More importantly, the relative content of the superfine micropores and the superfine micropores can be flexibly adjusted by adjusting the proportion or matching combination of the cross-linking agent and the high molecular polymer; the porosity of the hollow fiber carbon membrane and the sizes of the two types of pores can be flexibly controlled by adjusting the carbonization temperature Tc and the heat preservation time.

Drawings

FIG. 1 is a cross-sectional view of a hollow fiber carbon membrane of example 1.

FIG. 2 is a pore size distribution diagram of the hollow fiber carbon membrane of example 1.

Detailed Description

While the present invention will be described in detail with reference to the following examples, it should be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the present invention.

The starting materials used in the embodiments of the present invention are commercially available.

Example 1:

preparing modified spinning solution

1) Weighing 1Kg of PVDF powder according to 12 wt% of modified spinning solution, adding the PVDF powder into a kettle-type container containing dimethylacetamide (DMAc), and then adding 0.5 wt% of p-xylylenediamine and 2 wt% of PEG400 to complete primary mixing;

2) filling nitrogen with the pressure of 0.3MPa into the container, then discharging to the normal pressure, repeating the steps for 3 times, finally keeping the pressure in the kettle to be 0.11MPa (gauge pressure of 0.01MPa), heating the reaction kettle to about 50 ℃, intensively and mechanically stirring for 24 hours, vacuumizing, standing and defoaming the mixture for 12 hours to obtain a casting film material liquid precursor;

3) adjusting the nitrogen pressure of the spinning tank to 0.3MPa, and filtering impurities to obtain a membrane casting solution;

② spinning hollow fiber membrane

4) Injecting the film casting solution into a spinning nozzle through a metering pump, leading the polyester yarns into the spinning nozzle through traction, and flowing out together with the film casting solution, wherein the film casting solution is uniformly coated on the outer surfaces of the polyester yarns; meanwhile, the tension drafting machine is used for adjusting the looseness of the film yarn at the front end of the film yarn;

5) preparing a hollow fiber precursor (namely a hollow fiber membrane) through a coagulating bath phase conversion process, and drying for 24 hours at room temperature for later use;

③ preparing hollow fiber cross-linked membrane by oxidation

6) Placing the hollow fiber raw membrane in a muffle furnace, heating the hollow fiber raw membrane from the room temperature Tr at the speed of 8 ℃/min To the temperature To of 260 ℃, staying for the time t1 of 60min, and carrying out oxidation and crosslinking reaction on the hollow fiber raw membrane To generate an insoluble and infusible heat-resistant structure, namely obtaining a hollow fiber crosslinked membrane;

carbonizing to prepare hollow fiber carbon film

7) Moving the hollow fiber crosslinked membrane obtained by independently carrying out oxidation and crosslinking reactions in the step 6) into a closed carbonization furnace protected by an N2 atmosphere, rapidly heating from room temperature Tr To To-260 ℃ at a speed of 16 ℃/min, then slowly heating To 535 ℃ at a speed of 3 ℃/min, then slowly heating To Tc-550 ℃ at a speed of 0.25 ℃/min, and staying for t 2-60 min To complete carbonization treatment, thereby obtaining the hollow fiber carbon membrane;

the test shows that the hollow fiber carbon membrane has intact shape (see figure 1), and average pore diameter of wall pores(see FIG. 2). Wherein, the aperture test adopts low temperature N₂And the adsorption method is calculated and characterized according to a DFT method.

Comparative example 1:

preparing spinning solution

1) Weighing 1Kg of PVDF powder according to 12 wt% of a spinning solution, adding the PVDF powder into a kettle-type container containing DMAc, and then adding 2 wt% of PEG400 to complete primary mixing;

2) mixing conditions, mechanical stirring and defoaming are the same as those of example 1, and an unmodified casting solution precursor is obtained;

3) removing impurities to obtain a casting solution which is the same as the casting solution obtained in the example 1;

the method and the process for spinning the hollow fiber membrane are the same as those of the embodiment 1;

the process and parameters for preparing the hollow fiber cross-linked membrane by oxidation are the same as those of the embodiment 1;

the process and conditions for preparing the hollow fiber carbon membrane by carbonization were the same as in example 1;

the test shows that the hollow fiber carbon film has serious deformation, part of gaps are closed, the pore channels are blocked, and the porosity is 15 percent lower than the corresponding value of the embodiment 1.

Example 2:

preparing modified spinning solution

1) Weighing 1Kg of PVDF powder according to 15 wt% of modified spinning solution, adding the PVDF powder into a kettle type container containing dimethyl pyrrolidone (NMP), and then adding 0.8 wt% of m-xylylenediamine and PEG4004 wt% to complete primary mixing;

2) filling nitrogen with the pressure of 0.5MPa into the kettle type container, then discharging to the normal pressure, repeating the steps for 3 times, finally keeping the pressure of 0.11MPa (gauge pressure of 0.01MPa) in the kettle, heating the reaction kettle to about 60 ℃, intensively and mechanically stirring for 36 hours, vacuumizing, standing and defoaming the mixture for 20 hours to obtain a casting solution precursor;

3) adjusting the nitrogen pressure of the spinning tank to 0.3MPa, and filtering impurities to obtain a membrane casting solution;

② spinning hollow fiber membrane

Preparing the hollow fiber membrane according to the embodiment 1, and drying at room temperature for 36h for standby;

③ preparing hollow fiber cross-linked membrane by oxidation

6) Placing the hollow fiber raw membrane in a muffle furnace, heating the hollow fiber raw membrane from room temperature Tr at a speed of 12 ℃/min To a temperature To of 280 ℃, staying for a time t1 of 60min, and carrying out oxidation and crosslinking reaction on the hollow fiber raw membrane To generate an insoluble and infusible heat-resistant structure, thus obtaining a hollow fiber crosslinked membrane;

carbonizing to prepare hollow fiber carbon film

7) Transferring the hollow fiber crosslinked membrane obtained by independently performing oxidation and crosslinking reactions in the step 6) into N₂In a closed carbonization furnace protected by atmosphere, quickly heating from room temperature Tr at 15 ℃/min To To-220 ℃, then slowly heating To 535 ℃ at 5 ℃/min, then slowly heating To Tc-550 ℃ at 0.35 ℃/min, and staying for t 2-60 min To finish carbonization treatment, thereby obtaining the hollow fiber carbon film;

the test shows that the hollow fiber carbon film has intact shape and average wall pore diameter

Comparative example 2:

preparing spinning solution

1) Weighing 1Kg of PVDF powder according to 15 wt% and adding the PVDF powder into a kettle type container containing NMP, and then adding 4 wt% of PEG400 to complete primary mixing;

2) mixing conditions, mechanical stirring and defoaming are the same as those of example 2, and an unmodified casting solution precursor is obtained;

3) removing impurities to obtain a casting solution which is the same as the casting solution obtained in the example 2;

the method and the process for spinning the hollow fiber membrane are the same as the example 2;

the process and parameters for preparing the hollow fiber cross-linked membrane by oxidation are the same as those of the embodiment 2;

the process and conditions for preparing the hollow fiber carbon membrane by carbonization were the same as in example 2;

the test shows that the hollow fiber carbon film has serious deformation, part of gaps are closed, the pore channels are blocked, and the porosity is 18 percent lower than the corresponding value of the embodiment 2.

Example 3:

preparing modified spinning solution

1) Weighing 1Kg of PVDF powder according to 18 wt% and adding the PVDF powder into a kettle-type container containing dimethylacetamide (DMAc) and Dimethylformamide (DMF) in a mass ratio of 2:1, and then adding 1 wt% of p-xylylenediamine and PEG 4003 wt% to complete primary mixing;

2) filling nitrogen with the pressure of 0.5MPa into the kettle type container, then discharging to the normal pressure, repeating the steps for 3 times, finally keeping the pressure of 0.11MPa (gauge pressure of 0.01MPa) in the kettle, heating the reaction kettle to about 60 ℃, intensively and mechanically stirring for 36 hours, vacuumizing, standing and defoaming the mixture for 20 hours to obtain a casting solution precursor;

3) adjusting the nitrogen pressure of the spinning tank to 0.3MPa, and filtering impurities to obtain a membrane casting solution;

② spinning hollow fiber membrane

Preparing a hollow fiber raw membrane as described in example 1, and drying at room temperature for 36h for later use;

③ preparing hollow fiber cross-linked membrane by oxidation

Carrying out cross-linking reaction on the hollow fiber raw membrane according to the process and parameters described in the embodiment 1 to obtain a hollow fiber cross-linked membrane;

carbonizing to prepare hollow fiber carbon film

The above-mentioned cross-linked hollow fiber membrane was carbonized under the same conditions and procedures as in example 1 to obtain a hollow fiber carbon membrane.

The test shows that the hollow fiber carbon film has intact shape and average wall pore diameter

Comparative example 3:

preparing modified spinning solution

1) Weighing 1Kg of PVDF powder according to 18 wt% and adding the PVDF powder into a kettle-type container containing dimethylacetamide (DMAc) and Dimethylformamide (DMF) in a mass ratio of 2:1, and then adding 3 wt% of PEG400 to complete primary mixing;

2) mixing conditions, stirring and defoaming are the same as in example 3, and an unmodified casting solution precursor is obtained;

3) removing impurities to obtain a casting solution which is the same as the casting solution in the example 3;

the method and the process for spinning the hollow fiber membrane are the same as those of the embodiment 3;

preparing a hollow fiber cross-linked membrane by oxidation;

4) preparing a methanol solution according to 5 wt% of NaOH and 2 wt% of p-xylylenediamine, immersing the spun hollow fiber membrane into the methanol solution for 36 hours, carrying out pre-crosslinking reaction to obtain a hollow fiber pre-modified membrane, and then drying for later use;

5) placing the hollow fiber pre-modified membrane in a muffle furnace, heating the hollow fiber pre-modified membrane from the room temperature Tr at 8 ℃/min To To ═ 260 ℃, staying for t1 ═ 60min, and carrying out oxidation and crosslinking reaction on the hollow fiber pre-modified membrane To generate an insoluble and infusible heat-resistant structure, namely obtaining a hollow fiber crosslinked membrane;

the process and conditions for preparing the hollow fiber carbon membrane by carbonization were the same as in example 3;

the test shows that the hollow fiber carbon film has partial deformation, closed pores and blocked pores, and the porosity is 11% lower than that of the carbon film in example 3.

Compared with the results obtained in example 3, the hollow fiber carbon membrane of the present comparative example still has a significant difference, mainly manifested by a lower porosity and a larger deformation. Shows that: after the (unmodified) spinning solution is prepared and the hollow fiber is spun, even if a chemical crosslinking modification procedure is added in the subsequent steps, although the deformation can be partially relieved or weakened and the pore channel blockage can be reduced, the effect is still not ideal, and the method is still inferior to the hollow fiber carbon membrane obtained by directly spinning, oxidizing crosslinking and carbonizing the modified spinning solution. Moreover, the subsequent steps are added with a chemical crosslinking modification procedure, which is more complex than the method of the invention, the preparation process is prolonged, the preparation time is increased, and the preparation cost is obviously increased.

Example 4:

preparing modified spinning solution

1) Weighing 1Kg of thermosetting phenolic resin alcohol solution with the solid content of 75 percent according to 20 weight percent, adding the thermosetting phenolic resin alcohol solution into a kettle type container with dimethyl pyrrolidone (NMP), then adding 5 weight percent of Vinyl Triethoxysilane (VTES) and PEG 4001 wt percent, and finishing primary mixing;

2) filling nitrogen with the pressure of 0.5MPa into the kettle type container, then discharging to normal pressure, repeating the steps for 3 times, finally keeping the pressure of 0.11MPa (gauge pressure of 0.01MPa) in the kettle, intensively and mechanically stirring at room temperature for 36 hours, vacuumizing, standing and defoaming the mixture for 20 hours to obtain a casting film feed liquid precursor;

3) adjusting the nitrogen pressure of the spinning tank to 0.3MPa, and filtering impurities to obtain a membrane casting solution;

② spinning hollow fiber membrane

Preparing a hollow fiber raw membrane as described in example 1, and drying at room temperature for 36h for later use;

③ preparing hollow fiber cross-linked membrane by oxidation

Carrying out cross-linking reaction on the hollow fiber raw membrane according to the process and parameters described in the embodiment 1 to obtain a hollow fiber cross-linked membrane;

carbonizing to prepare hollow fiber carbon film

The above-mentioned cross-linked hollow fiber membrane was carbonized under the same conditions and procedures as in example 1 to obtain a hollow fiber carbon membrane.

The test shows that the hollow fiber carbon film has intact shape and average wall pore diameter

The carbon membranes obtained in any of examples 1 to 4 were each well retained in shape (hollow shape) and had average pore diameters of wall poresAnd the porosity of the carbon film in any of examples 1-3 is improved by more than 10% compared with the corresponding value of the comparative example. At the same time, the porosity of any of the carbon films of examples 1-3 was about 5% higher than that of example 4, indicating that the carbon films prepared with the preferred polymer, crosslinker, performed better. When CO is carried out₂/CH₄The permeation flux of the hollow fiber carbon membrane of any of examples 1 to 3 was higher by 15% or more than that of the comparative example, and the selectivity was kept similar or substantially the same.

Therefore, the hollow fiber carbon film prepared by the modified spinning solution not only 1) has good porosity, but also is improved by more than 10% compared with the traditional method; 2) the permeability and the selectivity are excellent: not only maintains good selectivity, but also improves the permeation flux by more than 15 percent compared with the traditional method, and 3) the preparation process is simpler and more convenient than the traditional method, the process is reduced, and the cost is reduced.