阅读说明：本技术 聚（苯并恶唑-共-酰胺）中空纤维气体分离膜及其应用 (Poly (benzoxazole-co-amide) hollow fiber gas separation membrane and application thereof ) 是由 曹义鸣 叶璐 王丽娜 介兴明 康国栋 于 2020-06-04 设计创作，主要内容包括：一种热致重排聚(苯并恶唑-共-酰胺)中空纤维气体分离膜及应用,该膜为具有致密皮层的非对称结构；其是通过对邻位含羟基的聚酰胺前驱体中空纤维膜高温热处理得到的。本发明的热致重排聚(苯并恶唑-共-酰胺)中空纤维膜柔韧性较好,耐有机溶剂和耐酸碱能力好,且具有很好的热稳定性和抗压性能,尤其适于CO-(2)、SO-(2)等酸性气体的分离回收。(A thermotropic rearrangement poly (benzoxazole-co-amide) hollow fiber gas separation membrane and application, the membrane is an asymmetric structure with compact skin layer; the polyamide hollow fiber membrane is obtained by carrying out high-temperature heat treatment on a polyamide precursor hollow fiber membrane containing hydroxyl at the ortho-position. The thermotropic rearrangement poly (benzoxazole-CO-amide) hollow fiber membrane has good flexibility, good organic solvent resistance, acid and alkali resistance, good thermal stability and compressive property, and is especially suitable for CO 2 、SO 2 And separating and recovering the acid gas.)

1. A poly (benzoxazole-co-amide) hollow fiber gas separation membrane characterized by: the membrane is an asymmetric structure with a compact skin layer and a porous supporting layer, and is obtained by preparing a polyamide precursor hollow fiber membrane containing hydroxyl at the ortho position by an immersion phase inversion method and then carrying out high-temperature heat treatment on the precursor hollow fiber membrane.

2. The hollow fiber gas separation membrane according to claim 1, which has a dense outer skin layer and a porous support inner layer structure, the fiber membrane having an inner diameter of 0.01 to 10.0mm (preferably 0.1 to 1mm), a wall thickness of 0.01 to 10.0mm (preferably 0.1 to 1mm), a skin thickness of 1 to 10000nm (preferably 1 to 100nm), a porosity of 10% to 90% (preferably 50% to 90%), a pore size distribution of the dense outer skin layer of 0.01 to 10nm (preferably 0.3 to 1nm), and a pore size distribution of the porous support layer of 0.1 to 100000nm (preferably 1 to 1000 nm).

3. The hollow fiber gas separation membrane of claim 1, wherein the poly (benzoxazole-co-amide) copolymer has the formula of repeating units:

m and n represent the mole fraction of the corresponding repeating unit, and satisfy 0.1. ltoreq. m.ltoreq.0.9, 0.1. ltoreq. n.ltoreq.0.9, and m + n 1;

the ortho hydroxyl-containing polyamide precursor has the following structural formula of a repeating unit:

m and n represent the mole fraction of the corresponding repeating unit, and satisfy 0.1. ltoreq. m.ltoreq.0.9, 0.1. ltoreq. n.ltoreq.0.9, and m + n.ltoreq.1.

4. The hollow fiber gas separation membrane according to claim 1 or 3, wherein the weight average molecular weight of the polyamide raw material containing a hydroxyl group at the ortho position is 10000 to 2000000 (preferably 100000-1000000).

5. The hollow fiber gas separation membrane of claim 1,

the high-temperature heat treatment process is carried out in an inert atmosphere and/or an air atmosphere, wherein the inert atmosphere is one or more than two of nitrogen or inert gas (argon or helium);

the temperature is increased from room temperature to 200-.

6. The hollow fiber gas separation membrane of claim 1, wherein: the polyamide precursor hollow fiber membrane containing hydroxyl at the ortho position is of an asymmetric structure with a non-compact surface, and the inner layer of the fiber is looser relative to the outer layer; the preparation method is prepared by an immersion phase conversion method, and comprises the following specific operation steps:

(1) preparing a precursor spinning solution by an in-situ synthesis method: under the temperature of-10 to 150 ℃ and an inert atmosphere, synthesizing a polyamide precursor solution containing hydroxyl at the ortho position with the concentration of 15 to 30 wt% by using 2, 2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane (APAF) and 4, 4' -diaminodiphenyl ether (ODA) as diamine monomers, terephthaloyl chloride (TPC) as a diacyl chloride monomer and N-methylpyrrolidone (NMP) as a solvent through a solution polycondensation method, and defoaming for later use;

wherein, the molar equivalent of APAF accounts for 10 to 90 percent of the molar fraction of the mixed diamine monomer of APAF and ODA, and the molar equivalent of TPC diacid chloride is 1.0 to 1.1 (preferably 1.01 to 1.05);

(2) the polyamide hollow fiber membrane containing hydroxyl at the ortho-position is prepared by adopting an immersion phase inversion method wet spinning or dry wet spinning, and the spinning process parameters are as follows: the spinning temperature is 20-150 ℃, the dry spinning distance is 0-50 cm, and a hollow nascent fiber membrane is formed under the action of an external gel bath and an internal core liquid;

(3) washing residual solvent of the nascent fiber membrane by using flowing water;

(4) and drying to obtain the polyamide precursor asymmetric hollow fiber membrane with a porous structure and containing hydroxyl at the ortho position.

7. The hollow fiber gas separation membrane of claim 6, wherein: the core liquid in the step (2) can be one of alcohol, ketone, deionized water and N-methyl pyrrolidone aqueous solution or a mixture of more than two of the alcohol, the ketone, the deionized water and the N-methyl pyrrolidone aqueous solution.

8. The hollow fiber gas separation membrane of claim 6, wherein: in the step (2), the gel bath is water, or one or more than two of alcohol (such as methanol and/or ethanol) solution with volume concentration of 1-20%, ketone (such as acetone) solution, N-methylpyrrolidone aqueous solution, etc.

9. The production of a hollow fiber gas separation membrane according to claim 6, characterized in that: the step (3) of washing away residual solvent refers to washing the prepared polyamide precursor hollow membrane containing hydroxyl at the ortho position in flowing deionized water for 8-72 hours.

10. Use of a hollow fibre gas separation membrane according to any of claims 1 to 9 in gas separation.

Technical Field

The invention relates to a high polymer separation membrane technology, in particular to a thermally-rearranged poly (benzoxazole-co-amide) hollow fiber gas separation membrane and a preparation method thereof.

Background

The thermotropic rearrangement polymer is a microporous polymer with high free volume and rigid skeleton structure, and can be used as a gas separation membrane material, the high free volume of the thermotropic rearrangement polymer can realize the rapid transmission of gas, the rigid skeleton structure can improve the diffusion selectivity, and a molecular window with adjustable size is formed. 2007, Park [ reference [1 ]]H.B.Park,C.H.Jung,Y.M.Lee,A.J.Hill,S.J.Pas,S.T.Mudie,E.Van Wagner,B.D.Freeman,D.J.Cookson,Polymers with cavities tuned for fast selective transport of small molecules and ions[J],Science,318(2007)254-258.]In Science, the in-situ heat treatment of a soluble polyimide precursor film containing functional groups at the ortho positions is firstly reported, and in the high-temperature heat treatment process, the polymer precursor is subjected to intramolecular rearrangement reaction in a solid state, so that polymer films with rigid aromatic heterocyclic structures, such as Polybenzimidazole (PBI), Polybenzoxazole (PBO), Polybenzothiazole (PBT) and the like, are formed. Although the thermally rearranged polymer membrane has excellent gas permeation separation performance, chemical stability, thermal stability and the like, the membrane has poor flexibility due to excessively high temperature of the molecular rearrangement reaction, and the scale-up and application of the membrane are also limited. For gas separation, the hollow fiber membrane has the advantages of large specific surface area, high filling density, low relative price and the like, and is more suitable for industrial application. In recent years, some scientific research has been devoted to the preparation of hollow fiber membranes of thermally rearranged polymers, and some efforts have been made, generally, a polyimide precursor hollow fiber membrane having a dense skin layer is prepared by an immersion gel method, and then a high-flux gas separation membrane of thermally rearranged polymer hollow fibers is obtained by a high-temperature treatment [ reference [2 ]]S.Kim,S.H.Han,Y.M.Lee,Thermally rearranged(TR)polybenzoxazole hollow fiber membranes for CO₂ capture[J],Journal of Membrane Science,403-404(2012)169-178.[3]K.T.Woo,J.Lee,G.Dong,J.S.Kim,Y.S.Do,W.-S.Hung,K.-R.Lee,G.Barbieri,E.Drioli,Y.M.Lee,Fabrication of thermally rearranged(TR)polybenzoxazole hollow fiber membranes with superior CO₂/N₂ separation performance[J],Journal of Membrane Science,490(2015)129-138.[4]K.T.Woo,J.Lee,G.Dong,J.S.Kim,Y.S.Do,H.J.Jo,Y.M.Lee,Thermally rearranged poly(benzoxazole-co-imide)hollow fiber membranes for CO₂ capture[J],Journal of Membrane Science,498(2016)125-134.]Compared with polyimide, the Polyamide (PHA) containing hydroxyl at the ortho-position is used as a precursor, the molecular rearrangement reaction can be carried out at a lower temperature, and the molecules are prevented from thermal degradation at a higher temperature, so that the obtained polybenzoxazole film has better mechanical properties, the reaction has less strict requirements on heat treatment atmosphere, and an effective thermotropic rearrangement polymer film can be formed in an air atmosphere. However, the traditional aromatic polyamide has the characteristics of difficult dissolution and difficult dissolution, the processability is poor, the rigid aromatic ring structure and intermolecular hydrogen bonds enable the aromatic polyamide to have higher cohesive energy density, the polymer chains are tightly stacked, the free volume is smaller, and the gas permeability of the membrane is limited. To date, few documents have produced aromatic polyamide hollow fiber gas separation membranes by a one-step process, and aromatic polyamides produced by a submerged gel process are mostly used as nanofiltration, reverse osmosis or forward osmosis techniques. Tianjin film Tech Co Ltd [ reference 5]Fanning, Huxiayu, Gaoshi, Lishuliangli, aromatic polyamide hollow fiber membrane and preparation method and application thereof [ P]China, 106693729B]The invention discloses a method for preparing an aromatic polyamide hollow fiber membrane by a melt spinning method, which comprises the steps of adding an aromatic polyamide polymer, a compound solvent, an additive and the like into a double-screw extruder, carrying out melt extrusion at about 250 ℃ through a spinneret plate, allowing the melt extrusion to enter a water tank for solidification and molding, and carrying out post-treatment on a hollow fiber membrane by a winding and drafting thermal method to prepare a high-temperature-resistant polyamide hollow fiber membrane which can be used for nanofiltration or reverse osmosis technology. Although this invention can produce an aromatic polyamide hollow fiber membrane having higher requirements for performance, the process has high requirements for equipment. Considering the phenomenon that a skin layer is thickened due to the collapse of a membrane hole in the heat treatment process of a precursor hollow fiber membrane, the invention firstly adopts spinning solution with lower concentration to prepare the polyamide precursor porous membrane, and then utilizes the thermal densification principle to obtain the thermal rearrangement polymer hollow fiber gas separation with a thinner dense skin layer through high-temperature heat treatmentAnd (3) a membrane. When preparing the polyamide precursor spinning solution, in order to ensure that the concentration of the solution meets the requirement, an in-situ synthesis method is adopted to directly prepare the spinning solution.

Disclosure of Invention

The invention aims to provide a preparation method of a poly (benzoxazole-co-amide) hollow fiber gas separation membrane.

In order to achieve the purpose, the invention adopts the technical scheme that:

a thermotropic rearrangement poly (benzoxazole-co-amide) hollow fiber gas separation membrane and its preparation, the membrane is an asymmetric structure with compact skin layer; the polyamide hollow fiber membrane is obtained by preparing a polyamide precursor hollow fiber membrane containing hydroxyl at the ortho-position by an immersion phase inversion method and then carrying out in-situ heat treatment on the precursor hollow fiber membrane. The process flow comprises the following steps: under the temperature of minus 10 to 150 ℃ and an inert atmosphere, synthesizing a polyamide precursor solution containing hydroxyl at the ortho position with the concentration of 15 to 30 weight percent by a solution polycondensation method by taking 2, 2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane (APAF) and 4, 4' -diaminodiphenyl ether (ODA) as diamine monomers, terephthaloyl chloride (TPC) as a diacid chloride monomer and N-methylpyrrolidone (NMP) as a solvent, and defoaming for later use; the spinning solution is pressed out of the spinning liquid tank by compressed nitrogen, is metered by a metering pump and then enters a filter, then enters a cavity between an inner pipe and an outer pipe of the intubation type spinning nozzle, and enters a gel bath after being pressed out and passing through an air layer dry spinning stage with a certain height. The core liquid is pressed into an inner pipe of a nozzle from a storage container by an advection pump, and is extruded out of the nozzle together with the spinning solution, so that the spinning solution enters a gel bath to be solidified into nascent fiber after a dry spinning stage, and then the nascent fiber is properly stretched, washed and dried to obtain a polyamide precursor hollow fiber membrane containing hydroxyl at the ortho-position, and then the precursor hollow fiber membrane undergoes molecular rearrangement and skin layer densification at a certain high temperature to obtain the thermotropic rearrangement poly (benzoxazole-co-amide) hollow fiber gas separation membrane.

The preparation method of the poly (benzoxazole-co-amide) hollow fiber gas separation membrane comprises the following steps:

(1) preparing a precursor spinning solution by an in-situ synthesis method: under the temperature of minus 10 to 150 ℃ and an inert atmosphere, synthesizing a polyamide precursor solution containing hydroxyl at the ortho position with the concentration of 15 to 30 weight percent by a solution polycondensation method by taking 2, 2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane (APAF) and 4, 4' -diaminodiphenyl ether (ODA) as diamine monomers, terephthaloyl chloride (TPC) as a diacid chloride monomer and N-methylpyrrolidone (NMP) as a solvent, and defoaming for later use;

(2) the polyamide hollow fiber membrane containing hydroxyl at the ortho-position is prepared by adopting an immersion phase inversion method wet spinning or dry wet spinning, and the spinning process parameters are as follows: spinning at 20-150 ℃ and at a dry spinning distance of 0-50 cm, and forming a hollow fiber primary membrane under the action of an external gel bath and an internal core solution;

(3) washing off residual solvent of the polyamide hollow fiber membrane by using flowing water;

(4) and drying to obtain the polyamide precursor asymmetric hollow fiber membrane with a porous structure and containing hydroxyl at the ortho position.

(5) Then carrying out in-situ heat treatment on the polyamide precursor hollow fiber membrane containing hydroxyl at the ortho position to obtain the poly (benzoxazole-co-amide) hollow fiber membrane.

The weight average molecular weight of the polyamide raw material containing hydroxyl at the ortho-position in the step (1) is 10000-2000000.

The core liquid in the step (2) can be one of alcohol, ketone, deionized water, N-methyl pyrrolidone aqueous solution or a mixture of alcohol, ketone, deionized water and N-methyl pyrrolidone aqueous solution.

In the step (2), the gel bath is water, or alcohol solution, ketone solution, N-methylpyrrolidone aqueous solution and the like with certain concentration, and the temperature range is 20-80 ℃.

The step (3) of washing away residual solvent refers to washing the prepared polyamide precursor hollow membrane containing hydroxyl at the ortho position in flowing deionized water for 8-72 hours.

The high-temperature heat treatment in step (5) may be carried out under an inert atmosphere (one or more of nitrogen or inert gas) or an air atmosphere, and the temperature is raised from room temperature to 200-400 ℃ at a rate of 1-20 ℃/min and maintained at this temperature for 1-3 hours.

The thermotropic rearrangement poly (benzoxazole-co-amide) hollow fiber membrane can be used for gas separation and has excellent thermal stability, chemical stability, compression resistance and better mechanical property.

The invention has the following advantages:

1. the poly (benzoxazole-co-amide) hollow fiber membrane is prepared by carrying out in-situ heat treatment on the polyamide precursor hollow fiber membrane with good solubility and containing hydroxyl at the ortho position, so that the problems that polybenzoxazole is difficult to dissolve in a common organic solvent and is difficult to form are solved;

2. the invention firstly prepares the porous asymmetric membrane structure on the surface of the polyamide precursor containing hydroxyl at the ortho position, and then densifies the skin layer through the heat treatment process to obtain the poly (benzoxazole-co-amide) hollow fiber membrane with the compact skin layer, thereby solving the problems that the aromatic polyamide is difficult to dissolve and infusible and is difficult to prepare into the hollow fiber gas separation membrane;

3. according to the invention, the flexibility of the poly (benzoxazole-co-amide) hollow fiber membrane can be improved by adopting the ether bond-containing polyamide precursor with hydroxyl at the ortho position.

Drawings

FIG. 1(a) is an electron micrograph of a cross section of a hollow fiber membrane obtained in comparative example, (b) example 1, (c) example 2 and (d) example 3.

FIG. 2 thermogravimetric curves of the hollow fiber membranes obtained in comparative example, example 1, example 2 and example 3.

Detailed Description

The present invention will be described in detail with reference to examples.

Example 1

In a 1000ml three-necked flask with mechanical stirring, 54g of 2, 2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane (APAF) and 29g of 4, 4' -dihydroxydiphenyl ether (ODA) were dissolved in 410g of anhydrous NMP under a nitrogen atmosphere. After cooling to 0 ℃, 60g of terephthaloyl chloride was added thereto in portions. And (3) reacting the solution at 0 ℃ for 12h, and performing vacuum defoaming to obtain a precursor spinning solution with the polyamide concentration of 25.8 wt%. And then putting the mixture into a spinning material tank for dry-wet spinning, wherein the spinning temperature is 80 ℃, the dry spinning distance is 2.5cm, the core liquid is a deionized water/N-methyl pyrrolidone mixture (20/80 wt.%), the core liquid flow is 1.5ml/min, the gel bath is water, and the water bath temperature is 40 ℃. The spun polyamide precursor nascent hollow fiber membrane is subjected to drying treatment after being washed in flowing deionized water for 24 hours. The weight average molecular weight of the polyamide precursor was 500000-800000. The infrared spectrogram verifies that the polyamide precursor has the following repeated structural unit:

the resulting polyamide precursor hollow fiber membrane was placed in a muffle furnace, heated to 300 ℃ at a rate of 5 ℃/min under nitrogen, and maintained at that temperature for 1 hour. After the heat treatment, the muffle furnace is slowly cooled to room temperature at the speed of less than 10 ℃/min to obtain the thermotropic rearranged poly (benzoxazole-co-amide) hollow fiber membrane. The infrared spectrum proves that the obtained poly (benzoxazole-co-amide) has the following repeating structural unit:

example 2

The heat treatment temperature for the precursor film was adjusted to 350 ℃, and other conditions and processes were the same as in example 1.

Example 3

The heat treatment temperature for the precursor film was adjusted to 370 ℃, and other conditions and processes were the same as in example 1

Comparative example

The polyamide precursors of the examples were not heat treated at high temperature to compare the effect of heat treatment on film properties.

The inner and outer diameters of the precursor films and the thermo-rearrangement polymer hollow fiber films obtained in comparative example and example were measured by a graduated optical microscope, and as a result, as shown in table 1, the pore diameter of the film decreased with the increase in the heat treatment temperature.

TABLE 1 comparison of pore sizes of fibrous membranes in examples and comparative examples

The electron microscope photos of the cross sections of the precursor membrane and the thermotropic rearranged polymer hollow fiber membrane obtained in the comparative example and the example are shown in figure 1, the cross section of the membrane presents a fine spongy pore structure, and only a small amount of finger-shaped pore structures exist, so that the obtained membrane has better compression resistance. The pore size distribution and porosity are shown in Table 2

TABLE 2 comparison of skin thickness, porosity and pore size distribution of fibrous membranes in examples and comparative examples

Thermogravimetric analysis is carried out on the precursor membrane and the thermotropic rearrangement polymer hollow fiber membrane obtained in the comparison and the example, the heating rate is 10 ℃/min, the temperature range is 40-900 ℃, the result is shown in figure 2, the thermal stability of the example 1-3 is superior to that of the comparison, and the obtained thermotropic rearrangement polymer hollow fiber membrane has excellent heat resistance and can be used in high-temperature environment.

The pure gas permeation separation performance of the precursor film and the thermally rearranged polymer film obtained in the comparative example and example is shown in table 3, the gas purity is 99.99%, the test pressure is 0.5MPa, and the test temperature is 20 ℃. As can be seen from Table 3, the hollow fiber membrane of the precursor is almost non-selective for oxygen and nitrogen, and O is generated after the molecular thermal rearrangement₂/N₂The selectivity is improved by 1.5-3 times.

TABLE 3 comparison of pure gas permeation selection Performance of fibrous membranes of the examples and comparative examples

1GPU＝10^-6cm³(STP)(cm²·s·cmHg)

The thermotropic rearrangement poly (benzoxazole-CO-amide) hollow fiber membrane has good flexibility, good organic solvent resistance, acid and alkali resistance, good thermal stability and compressive property, and is especially suitable for CO₂、SO₂And separating and recovering one or more than two kinds of acid gases.