TWI410272B - Cellulose acetate hollow fiber membrane and the method of manufacturing the same - Google Patents

Abstract

The present invention relates to a method of manufacturing a cellulose acetate hollow fiber membrane, comprising: providing a cellulose acetate solution including 15 to 30 wt% cellulose acetate, 0.1 to 1.2 wt% alkaline compound, and the rest is solvent, forming the cellulose acetate hollow fiber membrane from the cellulose acetate solution by using the dry-wet spinning method. The present invention also provides a cellulose acetate hollow fiber membrane formed by using the method mentioned above, and the average flux of the cellulose acetate hollow fiber membrane is 22 to 160 LMH/bar.

Description

Cellulose acetate hollow fiber membrane and preparation method thereof

The present invention relates to a hollow fiber membrane, and more particularly to a cellulose acetate hollow fiber membrane.

In recent years, due to the increasing pollution of water sources, or with the advancement of science and technology, the requirements for water safety and purity of process water have been increasing. The removal of fine particle contaminants is accomplished by using various advanced water purification membranes. Among various separation films, cellulose acetate hollow fiber membranes are commonly included.

When the film is used for water treatment, it is often accompanied by microbial growth, which causes the film to clog, resulting in a decrease in the percolation flow rate, and an increase in the operating cost of backwashing and chemical cleaning. In order to overcome this problem, it is often cheap to chlorinate to reduce microbial growth. Only most of the film materials are easily damaged by residual chlorine reaction. Cellulose acetate has unique chlorine resistance, so cheap chlorine can be used. Ways to reduce operating costs.

Cellulose acetate hollow fiber membrane is an acetylated cellulose polymer, which is often made into different types of films, including flat membranes, spiral membranes and hollow fiber membranes. Because of its advantages of anti-chlorine, anti-pollution, high hydrophilicity, and low price, it is attracting attention. In addition, cellulose acetate is a green material, and its waste can be biodegraded into carbon dioxide and water by burying. However, the percolation flow rate of such a hollow fiber membrane is low and needs further improvement.

There are generally four methods for preparing hollow fiber membranes: dry-wet spinning, wet spinning, melt spinning, and dry spinning, among which dry-wet spinning is most commonly used. The dry-wet spinning method dissolves the polymer in a solvent to form a polymer solution, and then flows out through the spinning nozzle. After flowing out, the polymer solution is first dry-spun in the atmosphere at a distance to partially cure the outer surface of the film. Then, it is immersed in the coagulation tank and solidified to form the hollow fiber membrane by the exchange action between the solvent and the non-solvent. The invention has the advantages that a heterogeneous hollow fiber membrane structure can be formed, the membrane surface is a uniform dense layer, and the membrane layer has a selective filter layer, and the center of the membrane is a thick layer of pores, which can reduce the seepage resistance and provide membrane structural support.

US 6,163,536 discloses a hollow fiber membrane, and US 6,890,436 discloses a porous hollow fiber membrane which is prepared by adding an aqueous polymer to a polymer solution. The aqueous polymer is selected from the group consisting of polyvinylpyrrolidone, polyethylene glycol, and polyvinyl alcohol, and the water contained in the polymer solution and the internal coagulant or the external coagulant. Upon contact, the aqueous polymer will dissolve to form pores, so that the obtained hollow fiber membrane has a better permeate flow rate. However, the addition of a water-based polymer is still limited by the increase in the permeation flow rate, and a large improvement cannot be obtained.

From the above, it is known that when the cellulose acetate hollow fiber membrane is applied to the water purification process, the primary problem to be solved is insufficient permeation flow. Therefore, how to improve the seepage flow of the cellulose acetate hollow fiber membrane under the premise of maintaining a good clean water level is the focus of current development.

Accordingly, a first object of the present invention is to provide a method of preparing a cellulose acetate hollow fiber membrane having a good permeate flow rate.

Thus, the method of the present invention for preparing a cellulose acetate hollow fiber membrane comprises preparing a cellulose acetate solution comprising 15 to 30 wt% cellulose acetate, 0.1 to 1.2 wt% of a basic compound, and the balance being Solvent; the cellulose acetate solution is formed into a cellulose acetate hollow fiber membrane by a dry-wet spinning method.

A second object of the present invention is to provide a cellulose acetate hollow fiber membrane excellent in permeation flow rate.

Thus, the cellulose acetate hollow fiber membrane of the present invention is obtained by a method for producing a cellulose acetate hollow fiber membrane as described above; wherein the cellulose acetate hollow fiber membrane has an average permeate flow rate of 22 to 160 LMH/bar.

The method for preparing a cellulose acetate hollow fiber membrane of the present invention has a good average permeation flow rate by adding a basic compound to a cellulose acetate solution to obtain a cellulose acetate hollow fiber membrane.

The method for preparing a cellulose acetate hollow fiber membrane comprises: preparing a cellulose acetate solution comprising 15 to 30 wt% cellulose acetate, 0.1 to 1.2 wt% of a basic compound, and the rest being a solvent; The cellulose acetate solution is formed into a cellulose acetate hollow fiber membrane by a dry-wet spinning method.

The addition of the basic compound causes a change in the hydrophilicity and pH of the cellulose acetate solution, resulting in a change in the microstructure of the cellulose acetate hollow fiber membrane, thereby increasing the permeation flow rate of the hollow fiber membrane.

Preferably, the basic compound is selected from the group consisting of sodium hydroxide, ammonium hydroxide, or potassium hydroxide.

Preferably, the cellulose acetate is selected from the group consisting of cellulose triacetate, cellulose diacetate, cellulose acetate butyrate or cellulose acetate propionate. More preferably, the cellulose acetate is selected from the group consisting of cellulose diacetate.

Preferably, the solvent is a combination of water and an organic solvent selected from the group consisting of nitrogen, nitrogen, dimethylmethanamide (DMF), acetone, dichloromethane, trichlorobenzene. Methane, nitrogen-methyl-2-pyrrolidone, or methyl acetate. More preferably, the solvent is a combination of water and nitrogen, nitrogen-dimethylformamide.

Preferably, after the cellulose acetate solution is prepared, it is allowed to stand at room temperature for 8 to 24 hours, and the cellulose acetate is completely dissolved in the solvent, and then subjected to a dry-wet spinning method.

Preferably, the cellulose acetate hollow fiber membrane is prepared by flowing the cellulose acetate solution and an internal coagulant from a spinning port to the atmosphere, passing a distance of 10 to 30 cm, and then immersing in an external coagulant. Got it. The spout has an outer tube and a central tube surrounded by the outer tube for circulating the cellulose acetate solution; the central tube is for circulating the inner coagulant. The cellulose acetate solution precipitates into two phases during solidification, wherein one phase contains more polymer materials, and after solidification, the main structure of the surface dense thin layer is formed, and the other phase contains more solvent, and forms a center after solidification. A thick layer of holes.

Preferably, the internal coagulant is selected from water or a combination of water and an organic solvent selected from the group consisting of nitrogen, nitrogen-dimethylformamide, acetone, dichloromethane, chloroform, Nitro-methyl-2-pyrrolidone or methyl acetate. More preferably, the internal coagulant is water.

The external coagulant is selected from the group consisting of water or a combination of water and an organic solvent selected from the group consisting of nitrogen, nitrogen-dimethylformamide, acetone, dichloromethane, chloroform, and nitrogen-methyl. -2-pyrrolidone or methyl acetate. More preferably, the external coagulant is water.

Preferably, the cellulose acetate solution is discharged from the outer tube of the spun at a rate of from 1 to 10 g/min, and the rate at which the internal coagulant flows out from the central tube of the spun is from 5 to 15 g/min.

A cellulose acetate hollow fiber membrane obtained by a method for producing a cellulose acetate hollow fiber membrane as described above; wherein the cellulose acetate hollow fiber membrane has an average permeate flow rate of 22 to 160 LMH/bar.

Preferably, the cellulose acetate hollow fiber membrane has an inner surface void area ratio of 18 to 50%.

Preferably, the cellulose acetate hollow fiber membrane has an outer surface void area ratio of 27 to 58%.

The present invention will be further illustrated by the following examples, but it should be understood that this embodiment is intended to be illustrative only and not to be construed as limiting.

<Chemicals and equipment>

1. Cellulose acetate: purchased from Aldrich, having an acetamino group content of 39.7% and a molecular weight of 50,000.

2. Sodium hydroxide: purchased from Shimajiu Pharmaceutical Co., Ltd., with a purity of 99%.

3. Ammonium hydroxide: purchased from J.T. Baker, concentration 28%.

4. Potassium hydroxide: purchased from Aldrich, purity 99%.

5. Nitrogen, nitrogen-dimethylformamide: purchased from J.T. Baker.

6. Ethanol: purchased from Fulin Biochemical Technology Co., Ltd., with a purity of over 95%.

7. Freeze dryer: Model "EYELA FDU-1200".

8. Vacuum gold plating equipment: purchased from Hitachi, model "E1010".

9. Scanning Electron Microscope (SEM): purchased from Hitachi, model "S-3000N".

10. Universal stretching machine: purchased from SHIMADZU, model "AG-IS".

<Examples 1 to 6> [Example 1] Preparation of cellulose acetate hollow fiber membrane

First, a cellulose acetate solution containing 0.12 wt% sodium hydroxide, 25 wt% cellulose diacetate, 4.88 wt% water, and 70 wt% nitrogen, nitrogen-dimethylformamide, uniformly mixed. Thereafter, it was allowed to stand at room temperature for one day to completely dissolve the cellulose acetate in the solvent.

The cellulose acetate solution was subjected to a dry-wet spinning method. A spin port having an outer tube and a center tube surrounded by the outer tube having an outer diameter of 0.8 mm and an outer tube having an inner diameter of 1.5 mm. The cellulose acetate solution was pushed out from the outer tube at a rate of 2.5 g/min with nitrogen, while water was discharged from the center tube, and water was used as an internal coagulant. After passing a distance of 20 cm in the atmosphere, the mixture was immersed in a pure In the coagulation tank of water, after being solidified into a hollow fiber membrane, it is taken up by a roller machine.

[Examples 2 to 6 ]

The cellulose acetate hollow fiber membranes of Examples 2 to 6 were prepared in the same manner as in Example 1, except that the basic compounds and the proportions of the components used in the respective examples, and the chemicals used in Examples 2 to 6 were used. And the detailed usage is recorded in Table 1.

<Comparative Examples 1 to 2> [Comparative Example 1] Preparation of cellulose acetate hollow fiber membrane

The preparation method of the cellulose acetate hollow fiber membrane of Comparative Example 1 was substantially the same as that of Example 1, except that the basic compound was not added. The chemicals used in Comparative Example 1 and the detailed amounts are shown in Table 1.

[Comparative Example 2]

The preparation method of the cellulose acetate hollow fiber membrane of Comparative Example 2 was substantially the same as that of Example 1, except that the content of the basic compound was 0.06 wt%. The chemicals used in Comparative Example 2 and the detailed amounts of each component are reported in Table 1.

<Physical evaluation>

The cellulose acetate hollow fiber membranes of Examples 1 to 6 and Comparative Examples 1 to 2 were analyzed by the following items, and the analysis results are detailed in Table 2.

Microstructure analysis

The hollow fiber membrane was placed in a freezer for 24 hours to produce ice crystals on the surface of the cellulose acetate hollow fiber membrane, and then placed in a freeze dryer, and subjected to freeze-drying treatment at -40 ° C for 72 hours, followed by taking out the frozen Dry cellulose acetate hollow fiber membrane sample.

The freeze-dried cellulose acetate hollow fiber membrane sample is immersed in liquid nitrogen and broken, and the cross section is exposed, fixed on a stage with a carbon tape, and placed in a vacuum gold plating apparatus to be vapor-deposited on the cross section. A layer of Au/Pd metal was plated, and the cross-sectional structure of the cellulose acetate hollow fiber membrane was observed by a scanning electron microscope (SEM) (the cross section of Example 4 is shown in FIG. 1 and the cross section of Comparative Example 1 is shown in FIG. 4), and the structure of the inner and outer surfaces (the structure of the embodiment 4 is as shown in Figs. 2 and 3, the structure of the comparative example 1 is as shown in Figs. 5 and 6), and the inner surface average pore diameter and the outer surface are respectively calculated. Average pore diameter, and inner surface void area ratio, outer surface void area ratio.

2. Tensile strength test

The cellulose acetate hollow fiber membrane was cut into a sample having a length of 7 cm by a surgical scissors, and the ends of the hollow fiber membrane sample were clamped by a clamp of a universal stretching machine, and the ends were each clamped by 2 cm so that the middle portion was reserved. It was 3 cm and then subjected to a tensile test.

3. Hole area ratio

First, ten square blocks are randomly taken from the inner surface and the outer surface of the cellulose acetate hollow fiber membrane.

The total area of the holes in the ten square blocks of the inner surface is calculated, and the total area of the inner surface holes is divided by the total area of the square inner square blocks to obtain the inner hole area ratio.

Calculate the sum of the outer surface areas of the outer surface of the ten square blocks, and divide the total hole area by the total area of the ten outer surface square blocks, that is, the outer surface void area ratio.

4. Average seepage test

A cellulose acetate hollow fiber membrane having a length of 12 cm was cut out, and the average permeate flow rate was measured in such a manner that fresh water permeated outward from the inner tube of the hollow fiber membrane. The percolating liquid passing through the hollow fiber membrane is taken up in a beaker placed on an electronic scale, the electronic balance shows the weight of the percolating liquid and the data is transmitted to a personal computer connected to the electronic balance, and the flow of the percolate is continuously recorded by the software. The specific flux of the film is then calculated.

At the beginning of the introduction of clean water, the percolation rate of the cellulose acetate hollow fiber membrane is not stable, and the measurement is required after the percolation flow rate is stabilized. Wherein, when the alkaline electrolyte is added in an amount of 0.06 wt%, the permeate flow rate of 200 to 270 min is measured; and when the alkaline electrolyte is added in an amount of 0.12 wt%, the permeate flow rate of 400 to 900 min is measured; When the amount of alkaline electrolyte added is 0.24 wt%, the osmotic flow rate of 600 to 1000 min is measured by clear water; when the amount of alkaline electrolyte added is 0.49 wt%, the osmotic flow rate of 580 to 650 min is measured by clear water; The amount of electrolyte added was 0.98 wt%, and the permeate flow rate of 600 to 1000 min was measured by clear water.

Specific flux, also known as Water mass transfer coefficient (MTC _w ), common unit is LHM/bar, flux value (Flux, J) and net driving pressure (NDP) The ratio is used to determine the degree of blockage of the film film set when operating at each water yield. The calculation is as follows:

MTC _w = (Q _p × TCF) ÷ (A × NDP)

Where Q _p is the water production flux (L/hrs); TCF is the temperature correction factor (usually the state when the temperature is corrected to 25 ° C), TCF=1.03 ^(25-T) , T is the inlet water temperature (°C) A is the effective membrane area (m ² ); NDP is the net driving pressure (bar), NDP = [(P _f + P _c ) ÷ 2] - P _{p -} Δπ; where P _f represents the film inlet end The pressure, P _c represents the pressure at the end of the membrane concentrated wastewater, P _p represents the pressure at the water producing end of the membrane, and Δπ is the net osmotic pressure at the inflow end and the water producing end of the membrane.

The microstructure shown in Fig. 1 (the cross-sectional structure of Example 4) and Fig. 4 (the cross-sectional structure of Comparative Example 1) were observed. Comparative Example 1 did not add a basic compound to the cellulose acetate solution, and the pores of the obtained cellulose acetate hollow fiber membrane were flat, and Example 4 added 0.98 wt% of sodium hydroxide to the cellulose acetate solution. The pores of the cellulose acetate hollow fiber membrane obtained were in the form of water droplets, indicating that the addition of a basic compound changes the microstructure of the cellulose acetate hollow fiber membrane.

As can be seen from Table 2, Comparative Example 1 did not add a basic compound to the cellulose acetate solution, and the obtained cellulose acetate hollow fiber membrane had an average permeate flow rate of only 14.69 LMH/bar; Comparative Example 2 only added 0.06 wt% of the alkali. For compounds, the average seepage flow is still not ideal.

Examples 1 to 4 added 0.12 to 0.98 wt% of sodium hydroxide to the cellulose acetate solution, and the permeation flow rate was remarkably improved. Among them, when adding 0.98 wt% sodium hydroxide, the average seepage flow can reach 155.02 LMH/bar. Further, the average bleeding flow rate and tensile strength of the cellulose acetate hollow fiber membrane were superior to those of Comparative Example 1 in the range of 0.1 to 1.2 wt% of the addition of the basic compound. Example 5 and Example 6 were respectively added with 0.98 wt% of potassium hydroxide and ammonium hydroxide, and the average permeation flow rate (58.80 LMH/bar, 47.39 LMH/bar, respectively) and the tensile strength were also significantly higher than when no basic compound was added. Upgrade.

In summary, the method for preparing a cellulose acetate hollow fiber membrane of the present invention comprises the method of adding 0.1 to 1.2 wt% of a basic compound to obtain a microstructure, a surface average pore diameter and a surface pore area of the cellulose acetate hollow fiber membrane. The rate and the like are changed such that the cellulose acetate hollow fiber membrane has a better average permeation flow rate and mechanical strength.

The above is only the preferred embodiment of the present invention, and the scope of the invention is not limited thereto, that is, the simple equivalent changes and modifications made by the scope of the invention and the description of the invention are All remain within the scope of the invention patent.

Figure 1 is an SEM image illustrating the cross-sectional configuration of Embodiment 4;

Figure 2 is an SEM image illustrating the inner surface structure of the embodiment 4;

Figure 3 is an SEM image illustrating the outer surface structure of Embodiment 4;

Figure 4 is an SEM image illustrating the cross-sectional configuration of Comparative Example 1;

Figure 5 is an SEM image showing the inner surface structure of Comparative Example 1;

Fig. 6 is an SEM image showing the outer surface structure of Comparative Example 1.

Claims (10)

A method for preparing a cellulose acetate hollow fiber membrane, comprising: preparing a cellulose acetate solution comprising 15 to 30 wt% cellulose acetate, 0.1 to 1.2 wt% of a basic compound, and the rest being a solvent, Wherein, the cellulose acetate solution does not include inorganic fine particles; and the cellulose acetate solution is formed into a cellulose acetate hollow fiber membrane by a dry-wet spinning method. The method for producing a cellulose acetate hollow fiber membrane according to claim 1, wherein the basic compound is selected from sodium hydroxide, ammonium hydroxide, or potassium hydroxide. The method for producing a cellulose acetate hollow fiber membrane according to the first aspect of the invention, wherein the cellulose acetate is selected from the group consisting of cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, or propionic acid acetate. Cellulose. The method for producing a cellulose acetate hollow fiber membrane according to the first aspect of the invention, wherein the solvent is a combination of water and an organic solvent selected from the group consisting of nitrogen and nitrogen-dimethylformamide Acetone, dichloromethane, chloroform, nitrogen-methyl-2-pyrrolidone or methyl acetate. The method for producing a cellulose acetate hollow fiber membrane according to the first aspect of the invention, wherein the cellulose acetate hollow fiber membrane is discharged from the spinning port to the atmosphere through the cellulose acetate solution and an internal coagulant. , after a distance of 10 to 30 cm, and then immersed in an external coagulant Got it. The method for producing a cellulose acetate hollow fiber membrane according to the invention of claim 5, wherein the internal coagulant is selected from water or a combination of water and an organic solvent selected from the group consisting of nitrogen and nitrogen. - dimethylformamide, acetone, dichloromethane, chloroform, nitrogen-methyl-2-pyrrolidone or methyl acetate. The method for producing a cellulose acetate hollow fiber membrane according to claim 5, wherein the external coagulant is selected from the group consisting of water or a combination of water and an organic solvent selected from the group consisting of nitrogen and nitrogen. - dimethylformamide, acetone, dichloromethane, chloroform, nitrogen-methyl-2-pyrrolidone or methyl acetate. A cellulose acetate hollow fiber membrane obtained by a method for producing a cellulose acetate hollow fiber membrane according to any one of claims 1 to 7, wherein the average permeation flow rate of the cellulose acetate hollow fiber membrane It is 22 to 160 LMH/bar. The cellulose acetate hollow fiber membrane according to item 8 of the patent application, wherein the inner surface pore area ratio is 18 to 50%. According to the cellulose acetate hollow fiber membrane of the eighth aspect of the patent application, the outer surface void area ratio is from 27 to 58%.