A porous fiber-reinforced polyamide hollow fiber membrane

Abstract

The present invention relates to a hollow fiber membrane, and in particular to a porous fiber reinforced polyamide hollow fiber membrane. The present invention uses porous fibers as reinforcing fibers, and its porous structure can form channels during water mass transfer, thereby improving the problem that the fibers become water transfer resistance; and by wrapping the polyamide that is the same as the membrane-forming polymer outside the fiber, the strength of the porous fiber can be compensated to a certain extent, and on the other hand, the fusion problem between the reinforcing fiber and the membrane-forming polymer is achieved, and the dissolution of the internal fiber can be avoided.

Description

Technical Field

[0001] The invention relates to a hollow fiber membrane, in particular to a porous fiber-reinforced polyamide hollow fiber membrane. Background Art

[0002] Hollow fiber membrane is a common type of membrane, which has been widely used in the field of water treatment due to its high filling area. However, hollow fiber membrane has the problem of low strength during application, so researchers have gone to great lengths to increase the strength of hollow fiber membrane.

[0003] In the prior art, reinforcing fibers are added to hollow fiber membranes to improve their strength, which has achieved good results. The greater the number of fibers added, the better the strength improvement effect. However, more reinforcing fibers will inevitably bring resistance to water transmission, thereby reducing the flux of the membrane.

[0004] On the other hand, there is a fusion problem between the reinforcing fiber and the film-forming polymer. One solution is to use the material of the film-forming polymer to prepare the reinforcing fiber, but it requires the separate preparation of reinforcing fibers of specific materials, and the reinforcing fiber will partially dissolve during contact with the casting liquid, thereby reducing the fiber strength. Therefore, how to perfectly solve the above problems is an urgent problem to be solved for reinforced hollow fiber membranes. Summary of the invention

[0005] In view of the above problems, the present invention uses porous fibers as reinforcing fibers, whose porous structure can form channels during water mass transfer, thereby improving the problem of fibers becoming water transfer resistance; and by wrapping the fiber with the same polyamide as the film-forming polymer, the strength of the porous fiber can be compensated to a certain extent. On the other hand, the fusion problem between the reinforcing fiber and the film-forming polymer is achieved, and the dissolution of the internal fiber can be avoided.

[0006] The present invention provides a porous fiber-reinforced polyamide hollow fiber membrane, wherein the hollow fiber membrane is made of polyamide, and its side wall comprises two or more porous fibers, the outer surface of the porous fiber is wrapped by interfacially polymerized polyamide, and the outer diameter of the porous fiber is 0.1-10 μm.

[0007] Another method, the present invention provides a method for preparing a porous fiber-reinforced polyamide hollow fiber membrane, comprising the following steps:

[0008] The first step: mixing a fiber-forming polymer, sodium bicarbonate and a fiber-forming solvent to form a spinning solution, and forming fibers by electrospinning;

[0009] Step 2: immersing the fiber in an acidic solution to eliminate sodium bicarbonate in the fiber to form a porous fiber;

[0010] Step 2: immersing the porous fiber in an aqueous solution containing an amine monomer and an oil solution containing an acyl chloride monomer, taking it out and drying it to form a porous fiber wrapped with polyamide;

[0011] Step 3: Mixing polyamide resin, hydrophilic agent, porogen and organic solvent to form a casting solution;

[0012] Step 4: The polyamide-wrapped porous fibers and the casting solution are simultaneously extruded through a spinneret, and after passing through an air gap, enter a coagulation bath for coagulation and forming, and after rinsing and drying, a porous fiber-reinforced polyamide hollow fiber membrane is formed.

[0013] The fiber-forming polymer in the spinning solution is one of polyvinylidene fluoride, polyester or nylon, and its content is 15-30wt%.

[0014] The content of sodium bicarbonate in the spinning solution is 3-10wt%, more preferably, the content of sodium bicarbonate in the spinning solution is 6-9wt%.

[0015] The acidic solution is one of hydrochloric acid, sulfuric acid and nitric acid with a pH of 0-3.

[0016] In the third step, the amino monomer is selected from one of ethylenediamine, m-phenylenediamine and piperazine, and the concentration of the amino monomer in the aqueous phase monomer is 0.01-1 wt %.

[0017] In the third step, the acyl chloride monomer is selected from one of trimesoyl chloride, terephthaloyl chloride, phthaloyl chloride and isophthaloyl chloride, and the concentration of the acyl chloride monomer in the oil phase solution is 0.005-0.5wt%.

[0018] In the fourth step, the weight average molecular weight of the polyamide resin is 10000-50000, and the content of the polyamide resin in the casting solution is 20-40wt%; the hydrophilic agent is selected from one of ethylene glycol, glycerol, isopropanol or n-butanol, and the content is 1-10wt%; the porogen is selected from one of polyvinyl pyrrolidone, polyethylene glycol, polyvinyl alcohol, zinc chloride, lithium chloride, and lithium bromide, and the content is 0.5-10wt%.

[0019] In the fifth step, the spinneret core liquid flow rate is 5-50ml / min, and the spinning speed is 1-20m / min; the distance of the air gap is 5-40cm, the temperature in the coagulation bath is 15-50°C, and the coagulation bath is selected from water or a mixture of an organic solvent and water.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] First, the present invention realizes the porous structure of the fiber by preparing the fiber by blending the polymer with the porous nanomaterial, solves the problem that the fiber becomes the resistance of water transmission, and significantly improves the flux of the membrane; secondly, the present invention can improve the strength reduction problem caused by the porous structure of the fiber by wrapping the same polyamide as the film-forming polymer on the outside of the fiber, on the one hand, and solves the fusion problem between the reinforcing fiber and the film-forming polymer, and the outer wrapped polyamide can avoid the dissolution of the internal fiber. Moreover, the outer wrapped polyamide is formed by interfacial polymerization, and its porous structure can avoid the porous structure of the fiber from being blocked. DETAILED DESCRIPTION Example 1

[0022] The hollow fiber membrane prepared in this embodiment includes the following steps:

[0023] Step 1: 18 wt% PVDF, 8 wt% sodium bicarbonate and N,N-dimethylacetamide were mixed to form a spinning solution, and a fiber with an outer diameter of 5 μm was formed by electrospinning;

[0024] Step 2: Immersing the above fibers in a hydrochloric acid solution with a pH of 2.0 for 16 hours to form porous fibers;

[0025] Step 3: immersing the porous fiber in an aqueous solution containing 0.02 wt% of piperazine and in a n-hexane solution containing 0.01 wt% of terephthaloyl chloride, and then drying the porous fiber in an oven at 60° C. to form a polyamide-wrapped porous fiber;

[0026] Step 4: 25 wt% polyamide resin with a weight average molecular weight of 20,000, 2 wt% ethylene glycol, 1 wt% lithium chloride and N,N-dimethylacetamide are mixed to form a casting solution;

[0027] Step 5: extrude the five polyamide-wrapped porous fibers and the casting liquid through a spinneret at the same time, and after passing through an air gap, enter a coagulation bath for coagulation and forming, and after rinsing and drying, form a porous fiber-reinforced polyamide hollow fiber membrane, the spinneret core liquid flow rate is 20 ml / min, the spinning speed is 10 m / min; the air gap distance is 20 cm, the temperature in the coagulation bath is 20°C, and the coagulation bath is a mixture of N,N-dimethylacetamide and water.

[0028] Step 6: The strength of the hollow fiber membrane was characterized. The results showed that the breaking strength was 21.1 MPa, the breaking elongation was 165%, and the pure water flux at 25°C under 0.1 MPa was 811 L / m 2 h. Example 2

[0029] The hollow fiber membrane prepared in this embodiment includes the following steps:

[0030] Step 1: 18 wt% PVDF, 2 wt% sodium bicarbonate and N,N-dimethylacetamide were mixed to form a spinning solution, and a fiber with an outer diameter of 5 μm was formed by electrospinning;

[0031] Step 2: Immersing the above fibers in a hydrochloric acid solution with a pH of 2.0 for 16 hours to form porous fibers;

[0032] Step 3: immersing the porous fiber in an aqueous solution containing 0.02 wt% of piperazine and in a n-hexane solution containing 0.01 wt% of terephthaloyl chloride, and then drying the porous fiber in an oven at 60° C. to form a polyamide-wrapped porous fiber;

[0033] Step 4: 25 wt% polyamide resin with a weight average molecular weight of 20,000, 2 wt% ethylene glycol, 1 wt% lithium chloride and N,N-dimethylacetamide are mixed to form a casting solution;

[0034] Step 5: extrude the five polyamide-wrapped porous fibers and the casting liquid through a spinneret at the same time, and after passing through an air gap, enter a coagulation bath for coagulation and forming, and after rinsing and drying, form a porous fiber-reinforced polyamide hollow fiber membrane, the spinneret core liquid flow rate is 20 ml / min, the spinning speed is 10 m / min; the air gap distance is 20 cm, the temperature in the coagulation bath is 20°C, and the coagulation bath is a mixture of N,N-dimethylacetamide and water.

[0035] Step 6: The strength of the hollow fiber membrane was characterized. The results showed that the breaking strength was 25.1 MPa, the breaking elongation was 171%, and the pure water flux at 25°C under 0.1 MPa was 602 L / m 2 h.

[0036] Comparative Example 1

[0037] The hollow fiber membrane prepared in this comparative example comprises the following steps:

[0038] Step 1: 18 wt% PVDF and N,N-dimethylacetamide were mixed to form a spinning solution, and a fiber with an outer diameter of 5 μm was formed by electrospinning;

[0039] Step 2: 25 wt% polyamide resin with a weight average molecular weight of 20,000, 2 wt% ethylene glycol, 1 wt% lithium chloride and N,N-dimethylacetamide are mixed to form a casting solution;

[0040] Step 3: 5 fibers and the casting liquid are extruded through the spinneret at the same time. After passing through a period of air gap, they enter the coagulation bath for coagulation and forming. After rinsing and drying, a polyamide hollow fiber membrane is formed. The spinneret core liquid flow rate is 20 ml / min, and the spinning speed is 10 m / min. The air gap distance is 20 cm, the temperature in the coagulation bath is 20°C, and the coagulation bath is a mixture of N, N-dimethylacetamide and water.

[0041] Step 4: The strength of the hollow fiber membrane was characterized. The results showed that the breaking strength was 27.0 MPa, the breaking elongation was 189%, and the pure water flux at 25°C under 0.1 MPa was 438 L / m 2 h.

[0042] Comparative Example 2

[0043] The hollow fiber membrane prepared in this comparative example comprises the following steps:

[0044] Step 1: 18 wt% PVDF, 8 wt% sodium bicarbonate and N,N-dimethylacetamide were mixed to form a spinning solution, and a fiber with an outer diameter of 5 μm was formed by electrospinning;

[0045] Step 2: Immersing the above fibers in a hydrochloric acid solution with a pH of 2.0 for 16 hours to form porous fibers;

[0046] Step 3: 25 wt% polyamide resin with a weight average molecular weight of 20,000, 2 wt% ethylene glycol, 1 wt% lithium chloride and N,N-dimethylacetamide are mixed to form a casting solution;

[0047] Step 4: extrude the five polyamide-wrapped porous fibers and the casting liquid through a spinneret at the same time, and after passing through an air gap, enter a coagulation bath for coagulation and forming, and after rinsing and drying, form a porous fiber-reinforced polyamide hollow fiber membrane, the spinneret core liquid flow rate is 20 ml / min, the spinning speed is 10 m / min; the air gap distance is 20 cm, the temperature in the coagulation bath is 20°C, and the coagulation bath is a mixture of N,N-dimethylacetamide and water.

[0048] Step 5: The strength of the hollow fiber membrane was characterized. The results showed that the breaking strength was 18.9 MPa, the breaking elongation was 136%, and the pure water flux at 25°C under 0.1 MPa was 832 L / m 2 h.

[0049] The preferred embodiments of the present invention have been described in detail above, but it should be understood that after reading the above teachings of the present invention, those skilled in the art may make various changes or modifications to the present invention. These equivalent forms also fall within the scope defined by the appended claims of the present invention.

Claims

1. A porous fiber-reinforced polyamide hollow fiber membrane, characterized in that The hollow fiber membrane is made of polyamide, and its side wall contains more than or equal to two porous fibers. The outer surface of the porous fiber is wrapped with polyamide by interfacial polymerization, and the outer diameter of the porous fiber is 0.1~10μm; the preparation method of the porous fiber includes: the first step: mixing a fiber-forming polymer, sodium bicarbonate and a fiber-forming solvent to form a spinning solution, and forming fibers by electrospinning; the second step: immersing the fiber in an acidic solution to eliminate the sodium bicarbonate in the fiber to form a porous fiber; the third step: immersing the porous fiber in an aqueous solution containing an amino monomer and an oily solution containing an acyl chloride monomer in turn, taking it out and drying it to form a porous fiber wrapped with polyamide; the fiber-forming polymer in the spinning solution is one of polyvinylidene fluoride, polyester or nylon.

2. A method for preparing a porous fiber-reinforced polyamide hollow fiber membrane according to claim 1, characterized in that The method comprises the following steps: the first step: mixing a fiber-forming polymer, sodium bicarbonate and a fiber-forming solvent to form a spinning solution, and forming fibers by electrostatic spinning; Step 2: immersing the fiber in an acidic solution to eliminate sodium bicarbonate in the fiber to form a porous fiber; Step 3: immersing the porous fiber in an aqueous solution containing an amine monomer and an oil solution containing an acyl chloride monomer, taking it out and drying it to form a porous fiber wrapped with polyamide; Step 4: Mixing polyamide resin, hydrophilic agent, porogen and organic solvent to form a casting solution; Step 5: The polyamide-wrapped porous fibers and the casting solution are extruded through a spinneret simultaneously, and after passing through an air gap, they enter a coagulation bath for coagulation and forming, and after rinsing and drying, a porous fiber-reinforced polyamide hollow fiber membrane is formed.

3. The preparation method according to claim 2, characterized in that The content of fiber-forming polymer in the spinning solution is 15-30wt%.

4. The preparation method according to claim 2, characterized in that The content of sodium bicarbonate in the spinning solution is 3-10wt%.

5. The preparation method according to claim 4, characterized in that The content of sodium bicarbonate in the spinning solution is 6-9wt%.

6. The preparation method according to claim 2, characterized in that The acidic solution has a pH of 0-3 and is selected from one of hydrochloric acid, sulfuric acid and nitric acid.

7. The preparation method according to claim 2, characterized in that In the third step, the amino monomer is selected from one of ethylenediamine, m-phenylenediamine and piperazine, and the concentration of the amino monomer in the aqueous phase monomer is 0.01-1 wt %.

8. The preparation method according to claim 4, characterized in that In the third step, the acyl chloride monomer is selected from one of trimesoyl chloride, terephthaloyl chloride, phthaloyl chloride and isophthaloyl chloride, and the concentration of the acyl chloride monomer in the oil phase solution is 0.005-0.5wt%.

9. The preparation method according to claim 4, characterized in that In the fourth step, the weight average molecular weight of the polyamide resin is 10000-50000, and the content of the polyamide resin in the casting solution is 20-40wt%; the hydrophilic agent is selected from one of ethylene glycol, glycerol, isopropanol or n-butanol, and the content is 1-10wt%; the porogen is selected from one of polyvinyl pyrrolidone, polyethylene glycol, polyvinyl alcohol, zinc chloride, lithium chloride, and lithium bromide, and the content is 0.5-10wt%.

10. The preparation method according to claim 4, characterized in that In the fifth step, the spinneret core liquid flow rate is 5-50ml / min, and the spinning speed is 1-20m / min; the distance of the air gap is 5-40cm, the temperature in the coagulation bath is 15-50°C, and the coagulation bath is selected from water or a mixture of an organic solvent and water.