Method for preparing multichannel ceramic hollow fiber membrane

Abstract

The Invention relates to a method for preparing a multichannel hollow fiber membrane. According to a certain ratio, ceramic powder, a macromolecular polymer, an organic solvent, and a dispersant are mixed evenly to prepare a membrane casting solution; and after bubble removing processing is performed on the membrane casting solution, a membrane green body is formed with the cooperation of a multichannel hollow fiber die and phase inversion. After the membrane green body is roasted at a high temperature, a multichannel ceramic hollow fiber membrane is formed. The multichannel ceramic hollow fiber membrane has an asymmetric structure and a skeleton structure in an inner cavity and can meet the strength and flux requirements of a ceramic hollow fiber membrane.

Claims

1. A method for preparing a multichannel ceramic hollow fiber membrane, comprising the following steps: (1) preparing a uniform and stable membrane casting solution by mixing evenly a ceramic powder, a macromolecular polymer, an organic solvent, and a dispersant; wherein, the ceramic powder accounts for 55-65%, the macromolecular polymer 4-8%, the organic solvent 27-38%, and the dispersant 0.6-1.6% of the total mass of the membrane casting solution; (2) removing bubbles from the membrane casting solution via vacuum; (3) driving the membrane casting solution through a multichannel hollow fiber die via air pressure into an internal coagulation bath to form a preliminary green body, passing the preliminary green body through an air gap and then into an external coagulation bath to form a multichannel ceramic hollow fiber membrane green body, wherein a phase inversion occurs in the internal coagulation bath and the external coagulation bath; (4) drying the multichannel ceramic hollow fiber membrane green body at 40° C.-60° C.; and (5) sintering the multichannel ceramic hollow fiber membrane green body in a furnace and raising the temperature through a program to obtain a multichannel ceramic hollow fiber membrane.

2. The method according to claim 1, wherein said ceramic powder is one or two selected from the group consisting of yttria-stabilized zirconia, aluminum oxide and titanium oxide, with an average particle diameter between 0.05 μm and 4 μm; said macromolecular polymer is one or two selected from the group consisting of polyether sulfone, polysulfone and vinylidene fluoride homopolymers; said organic solvent is one or two selected from the group consisting of N-methylpyrrolidone, dimethylformamide, dimethylacetamide and trichloromethane; and said dispersant is one or two selected from the group consisting of polyvinylpyrrolidone, ethylcellulose and polyethylene glycol.

3. The method according to claim 1, wherein said external coagulation bath is one or two selected from water, ethanol and N-methylpyrrolidone; said internal coagulation bath is one or two selected from deionized water, dimethylformamide and N-methylpyrrolidone; said internal and external coagulation baths both have a temperature of 15-35° C.; and said internal coagulation bath flows at a rate at 40-60 mL/min.

4. The method according to claim 1, wherein the vacuum for removing the bubbles is 0.1-0.2 MPa and the time for removing the bubbles is 1-2 h.

5. The method according to claim 1, wherein the air gap is 10-40 cm; and the driving air pressure is 0.1-0.4 MPa.

6. The method according to claim 1, wherein the program raises the temperature to 500-600° C. at a rate of 1-20° C./min and then to 1400-1600° C. at a rate of 3-5° C./min, maintains that temperature for 4-8 h, then cools the temperature to 500-600° C. at a rate of 3-5° C./min and finally to room temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 Flow chart of dry/wet spinning;

(2) FIG. 2 SEM image of YSZ seven-channel ceramic hollow fiber membrane (Zone A—skeleton structure; Zone B—supporting trigonum; Zone C—area of finger-like pore; Zone D—area of sponge structure);

(3) FIG. 3 SEM image of Al.sub.2O.sub.3 seven-channel ceramic hollow fiber membrane (Zone A—skeleton structure; Zone B—sponge structure; Zone C—vesicular structure);

(4) FIG. 4 SEM image of YSZ four-channel ceramic hollow fiber membrane (Zone A—skeleton structure; Zone B—supporting trigonum; Zone—area of finger-like pore; Zone D—area of sponge structure);

(5) FIG. 5 SEM image of Al2O3 four-channel ceramic hollow fiber membrane (Zone A—skeleton structure; Zone B—supporting trigonum; Zone C—area of finger-like pore; Zone D—area of sponge structure).

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS OF THE INVENTION

(6) The detailed embodiments and drawings are given to illustrate the preparation technology of the multichannel ceramic hollow fiber membrane.

Embodiment 1 Preparation of YSZ Seven-Channel Hollow Fiber Membrane

(7) The N-Methylpyrrolidone, polyvinylpyrrolidone, polyether sulfone and YSZ are mixed evenly in a certain order according to a mass proportion of 0.3:0.01:0.04:0.65. The evenly mixed membrane casting solution is transferred into a spinning pot for removing the bubbles under the vacuum degree of 0.1 MPa for 2 h. Tap water is selected as the external coagulation bath with the temperature of 15° C., while deionized water as the internal coagulation bath with the temperature of 15° C.; the flow of the internal coagulation bath is 40 mL/min and air clearance 10 cm; driven by the pressure of 0.14 MPa, the membrane casting solution is squeezed out of the spinning nozzle for preliminary formation under the effect of internal coagulation bath and seven-channel spinning nozzle; through full phase inversion in the external coagulation bath, a green body of the YSZ seven-channel ceramic hollow fiber membrane with a certain microstructure is formed. The entire spinning process is shown in FIG. 1. The green body is placed in the furnace for sintering. The temperature is risen to 500° C. at a heating rate of 1° C./min in the first place, then it is risen to 1400° C. at a heating rate of 3° C./min and preserved with the heat for 5 h, and then cooled to 500° C. at a rate of 3° C./min and finally cooled naturally. The outer diameter of the prepared seven-channel ceramic hollow fiber membrane is 2.92 mm and the channel diameter 0.61 mm as shown in FIG. 2. The property of the YSZ seven-channel ceramic hollow fiber membrane is measured through four methods as pure water flux method, three-point bending strength method, Archimedes drainage method and gas bubble-pressure method. The pure water flux of the YSZ seven-channel ceramic hollow fiber membrane is 1.68 L.Math.Pa.sup.−1.Math.m.sup.−2 min.sup.−1, the breakage load 19 N, the porosity factor 65% and the average pore diameter 1.4-1.6 μm.

Embodiment 2 Preparation of Al.SUB.2.O.SUB.3 .Seven-Channel Hollow Fiber Membrane

(8) The dimethylacetamide, polyvinylpyrrolidone, polyether sulfone and Al.sub.2O.sub.3 are mixed evenly in a certain order according to a mass proportion of 0.372:0.008:0.07:0.55. The evenly mixed membrane casting solution is transferred into a spinning pot for removing the bubbles under the vacuum degree of 0.2 MPa for 1 h. Ethanol is selected as the external coagulation bath with the temperature of 25° C., while dimethylacetamide as the internal coagulation bath with the temperature of 20° C.; the flow of the internal coagulation bath is controlled at 60 mL/min and air clearance 40 cm; driven by the pressure of 0.2 MPa, the membrane casting solution is squeezed out of the spinning nozzle for preliminary formation under the effect of internal coagulation bath and seven-channel spinning nozzle. Through full phase inversion in the external coagulation bath, a green body of the Al.sub.2O.sub.3 seven-channel ceramic hollow fiber membrane with a certain microstructure is formed. The green body is placed in the furnace for sintering. The temperature is risen to 600° C. at a heating rate of 2° C./min in the first place, then it is risen to 1600° C. at a heating rate of 5° C./min and preserved with the heat for 8 h, and then cooled to 600° C. at a rate of 5° C./min and finally cooled naturally. The outer diameter of the prepared Al.sub.2O.sub.3 seven-channel ceramic hollow fiber membrane is 3.37 mm and the channel diameter 0.65 mm as shown in FIG. 3. The measurement method is the same as that in Embodiment 1. The pure water flux of the Al.sub.2O.sub.3 seven-channel ceramic hollow fiber membrane is 1.43 L.Math.Pa.sup.−1.Math.m.sup.−2 min.sup.−1, the breakage load 20 N, the porosity factor 56% and the average pore diameter 1.2-1.4 μm.

Embodiment 3 Preparation of YSZ Four-Channel Hollow Fiber Membrane

(9) The trichloromethane, polyethylene glycol, polyvinylidene fluoride and YSZ are mixed evenly in a certain order according to a mass proportion of 0.305:0.01:0.045:0.64. The evenly mixed membrane casting solution is transferred into a spinning pot for removing the bubbles under the vacuum degree of 0.1 MPa for 2 h. Tap water is selected as the external coagulation bath with the temperature of 25° C., while N-Methylpyrrolidone as the internal coagulation bath with the temperature of 25° C.; the flow of the internal coagulation bath is controlled at 50 mL/min and air clearance 20 cm; driven by the pressure of 0.32 MPa, the membrane casting solution is squeezed out of the spinning nozzle for preliminary formation under the effect of internal coagulation bath and four-channel spinning nozzle; through full phase inversion in the external coagulation bath, a green body of the YSZ four-channel ceramic hollow fiber membrane with a certain microstructure is formed. The green body is placed in the furnace for sintering. The temperature is risen to 600° C. at a heating rate of 2° C./min in the first place, then it is risen to 1500° C. at a heating rate of 4° C./min and preserved with the heat for 6 h, and then cooled to 600° C. at a rate of 4° C./min and finally cooled naturally. The outer diameter of the prepared YSZ four-channel ceramic hollow fiber membrane is 2.60 mm and the channel diameter 0.86 mm as shown in FIG. 4. The measurement method is the same as that in Embodiment 1. The pure water flux of the YSZ seven-channel ceramic hollow fiber membrane is 1.8 L.Math.Pa.sup.−1.Math.m.sup.−2 min.sup.−1, the breakage load 22 N, the porosity factor 56% and the average pore diameter 2.6-2.9 μm.

Embodiment 4 Preparation of Al.SUB.2.O.SUB.3 .Four-Channel Hollow Fiber Membrane

(10) The dimethylacetamide, polyvinylpyrrolidone, polyether sulfone and Al.sub.2O.sub.3 are mixed evenly in a certain order according to a mass proportion of 0.27:0.016:0.07:0.644. The evenly mixed membrane casting solution is transferred into a spinning pot for removing the bubbles under the vacuum degree of 0.2 MPa for 1 h. Ethanol is selected as the external coagulation bath with the temperature of 35° C., while dimethylacetamide as the internal coagulation bath with the temperature of 35° C.; the flow of the internal coagulation bath is controlled at 40 mL/min and air clearance 30 cm; driven by the pressure of 0.4 MPa, the membrane casting solution is squeezed out of the spinning nozzle for preliminary formation under the effect of internal coagulation bath and four-channel spinning nozzle. Through full phase inversion in the external coagulation bath, a green body of the Al.sub.2O.sub.3 four-channel ceramic hollow fiber membrane with a certain microstructure is formed. The green body is placed in the furnace for sintering. The temperature is risen to 600° C. at a heating rate of 2° C./min in the first place, then it is risen to 1550° C. at a heating rate of 4° C./min and preserved with the heat for 5 h, and then cooled to 500° C. at a rate of 4° C./min and finally cooled naturally. The outer diameter of the prepared Al.sub.2O.sub.3 four-channel ceramic hollow fiber membrane is 2.78 mm and the channel diameter 0.9 mm as shown in FIG. 5. The measurement method is the same as that in Embodiment 1. The pure water flux of the Al.sub.2O.sub.3 seven-channel ceramic hollow fiber membrane is 2.4 L.Math.Pa.sup.−1.Math.m.sup.−2 min.sup.−1, the breakage load 25 N, the porosity factor 53% and the average pore diameter 1.4-1.5 μm.