TWI543810B - Hollow cellulose acetate fiber film and a method for manufacturing the same - Google Patents

Description

Method for preparing cellulose acetate hollow fiber membrane and finished product thereof

The present invention relates to a hollow fiber membrane, in particular to a method for preparing a cellulose acetate hollow fiber membrane and a finished product thereof.

The industry is highly developed, and the pollution problem is becoming more and more serious, threatening the safety of people's drinking water. With the rise of quality of life and health awareness, water quality regulations are becoming stricter. Therefore, all kinds of water purification procedures are actively promoted at home and abroad to ensure the safety of drinking water.

In the case of ordinary film water purification, there is often a problem that microorganisms grow and block the film to cause a decrease in permeation flow. This problem increases the cost of reverse cleaning and chemical cleaning. In order to overcome the aforementioned problems, it is often treated by an inexpensive method of chlorine injection to inhibit the growth of microorganisms, but most of the films are susceptible to destruction by residual chlorine and need to be improved.

According to the classification of the geometry of the film, it can be divided into two categories: symmetric and asymmetric. Symmetrical film It means that the cross-section structure of the film is fairly uniform. An asymmetric film means that the film has a plurality of layers having different cross sections.

Hollow fiber membranes generally have four different preparation methods: melt spinning, dry spinning, wet spinning, and dry-wet spinning, with dry-wet spinning being most commonly used. In the dry-wet spinning method, a polymer is dissolved in a solvent to form a polymer dope, and then ejected through a spun nozzle having an outer tube and a center tube surrounded by the outer tube. During the spraying process, the central tube will eject a core liquid, and the outer tube will eject the polymer spinning solution. After the ejection, the core liquid and the polymer spinning solution pass through the atmosphere first, and the surface of the polymer spinning solution is partially solidified, and then enters into a coagulation tank containing a coagulant to solidify the polymer spinning solution. Become a hollow fiber membrane.

Cellulose acetate fiber is an acetylated cellulose polymer, which is often made into different types of films, including flat membranes, spiral membranes and hollow fiber membranes. The unique chlorine-resistance of cellulose acetate can be cleaned by inexpensive chlorine injection method, which reduces the cost of consumption. It is quite attractive because of its advantages of good chlorine resistance and pollution resistance, high hydrophilicity and low price. In addition, cellulose acetate is an environmentally friendly material that can be biodegraded into carbon dioxide and water after being disposed of. The fly in the ointment is that the cellulose acetate hollow fiber membrane made of cellulose acetate has a low percolation flow and needs further improvement.

US Pat. No. 6,163,536 and US Pat. No. 7,442,302 disclose a method for producing a hollow fiber membrane, mainly by adding an aqueous polymer polyvinylpyrrolidone (Polyvinylpyrrolidone, abbreviated as PVP) in a polymer spinning solution. When the polymer spinning solution is sprayed through the nozzle and contacted with water contained in the core liquid or the coagulation tank, the aqueous polymer PVP is eluted, and the obtained hollow fiber membrane is formed into a hole. Good osmotic flow rate, however, the aqueous polymer PVP causes an increase in the viscosity of the polymer dope, and an expansion effect occurs at the die when the spout is ejected, resulting in a problem of poor quality such as cracks in the produced hollow fiber membrane. .

The first object of the present invention is to provide a method for preparing a cellulose acetate hollow fiber membrane, which does not cause expansion at the die when the nozzle is ejected, and the cellulose acetate hollow fiber membrane obtained has better quality. And also has a good seepage flow.

The method for preparing the cellulose acetate hollow fiber membrane comprises the following steps: Step A: providing a portion of a cellulose acetate solution. The cellulose acetate solution includes 10% by weight to 30% by weight of a cellulose acetate material, 0.1% by weight to 1.5% by weight of a modified acid, and a total of 100% by weight of a solvent in combination with the aforementioned components. Step B: The cellulose acetate solution was formed into a cellulose acetate hollow fiber membrane by a dry-wet spinning method.

The cellulose acetate material is selected from the group consisting of cellulose triacetate, cellulose diacetate, cellulose acetate propionate, cellulose acetate butyrate, and any combination of the foregoing. Cellulose triacetate has advantages such as better mechanical strength and heat resistance. Therefore, preferably, the cellulosic material is cellulose triacetate.

The solvent is selected from the group consisting of dimethyl sulfoxide (DMSO), nitrogen, dimethylformamide (DMF), acetone, dichloromethane, chloroform, 1-methyl- 2-Pyrrolidone (1-Methyl-2-pyrrolidone, NMP), methyl acetate, and any combination of the foregoing.

Preferably, the cellulose acetate hollow fiber membrane is further prepared by a step C between the step A and the step B. In this step C, the cellulose acetate solution is heated to 85 ° C to 95 ° C and stirred for 2 to 3 hours. If the heating temperature is lower than 85 ° C, the dissolution of cellulose acetate is not good; if the heating temperature is higher than 95 ° C, the cellulose acetate solution will be burnt. If the stirring time is too short, the dissolution of the cellulose acetate material is not good; if the stirring time is too long, the solvent will be excessively volatilized.

Preferably, in the step B, the cellulose acetate solution and a core liquid are extruded from a spinning nozzle, passed through an atmosphere of 10 cm to 30 cm, and then immersed in a coagulant. The core liquid and the coagulant are respectively water or a combination of water and an organic solvent. The organic solvent is selected from the group consisting of dimethyl hydrazine, nitrogen, nitrogen-dimethylformamide, acetone, dichloromethane, chloroform, 1-methyl-2-pyrrolidone, methyl acetate, and the foregoing Any combination of materials. When the cellulose acetate solution passes through the atmosphere, for example, less than 10 cm, the outer layer may have a dense structure, and the mechanical strength of the obtained cellulose acetate hollow fiber membrane is not good. When the cellulose acetate solution passes through the atmosphere for a distance of more than 30 cm, the outer layer forms an excessively dense structure, so that the obtained cellulose acetate is obtained. The percolation flow rate of the hollow fiber membrane is not good. Therefore, in order to strike a balance between the mechanical strength and the seepage flow, the cellulose acetate solution is preferably in the range of 10 cm to 30 cm in the atmosphere.

The modified acid is selected from the group consisting of boric acid, sulfuric acid, acetic acid, and any combination of the foregoing. Preferably, the modified acid is from 0.5 wt% to 0.75 wt% acetic acid. More preferably, the modified acid is boric acid, sulfuric acid, and any combination of the foregoing. The modified acid, in addition to being able to be dissolved in the core liquid and the coagulant, has a certain affinity with cellulose acetate to be uniformly mixed with cellulose acetate to facilitate the formation of pores. Therefore, the modified acid is preferably a boric acid affinity, preferably boric acid, sulfuric acid and acetic acid.

The method for preparing the cellulose acetate hollow fiber membrane has the effect of replacing the hydrophilic polymer with a modified acid, and since the molecule of the modified acid is small, it does not have the viscoelastic property of the polymer, so when the nozzle is ejected, it does not There is a problem of expansion, so that the cellulose acetate hollow fiber membrane obtained can have better physical properties and indeed achieve the first object of the present invention. In addition, the modified acid has a smaller molecule and better mobility, and can form larger and more pores on the surface, and at the same time increase the permeation flow rate of the obtained cellulose acetate hollow fiber membrane.

The second object of the present invention is to provide a cellulose acetate hollow fiber membrane having a preferred permeate flow rate.

The cellulose acetate hollow fiber membrane is obtained by the method for preparing the cellulose acetate hollow fiber membrane described above, and comprises an outer surface, and an outer surface and an outer surface The inner surface of the space. The inner surface has a plurality of holes. The holes account for 15.4% to 62.9% of the area of the inner surface.

The effect of the cellulose acetate hollow fiber membrane is that the ratio of the area occupied by the pores is 15.4% to 62.9%, which can effectively increase the seepage flow and achieve the second object of the present invention.

11‧‧‧Preparation solution steps

12‧‧‧ Mixing and mixing steps

13‧‧‧Finished spinning steps

21‧‧‧ inner surface

22‧‧‧ outer surface

23‧‧‧ holes

Other features and effects of the present invention will be clearly shown in the embodiments with reference to the drawings, wherein: FIG. 1 is a flow chart of the preparation method of the cellulose acetate hollow fiber membrane of the present invention and a finished product thereof; FIG. 2 is the cellulose acetate of the present invention. A photograph taken by a scanning electron microscope of a method for producing a hollow fiber membrane and a finished product thereof, the cross section of the cellulose acetate hollow fiber membrane obtained in the fifth embodiment is shown in the drawing; A photograph taken by another scanning electron microscope of Example 5, which shows the inner surface of the cellulose acetate hollow fiber membrane obtained in the fifth embodiment; and FIG. 4 shows the preparation method of the cellulose acetate hollow fiber membrane of the present invention and the finished product thereof. A photograph taken by a scanning electron microscope of Comparative Example 1 showing a cross section of the cellulose acetate hollow fiber membrane obtained in Comparative Example 1; and FIG. 5 is another scanning electron of Comparative Example 1. Photo taken by microscope, picture The inner surface of the cellulose acetate hollow fiber membrane obtained in Comparative Example 1 is illustrated; and Fig. 6 is a photograph of a cellulose acetate hollow fiber membrane of the present invention and a photograph taken by a scanning electron microscope of an example 10 of the finished product. The cross section of the cellulose acetate hollow fiber membrane obtained in the tenth embodiment is shown in the drawing; Fig. 7 is a photograph taken by another scanning electron microscope of the tenth embodiment, which is illustrated in the tenth embodiment. The inner surface of the cellulose acetate hollow fiber membrane obtained; Fig. 8 is a photograph of a method for producing a cellulose acetate hollow fiber membrane of the present invention and a scanning electron microscope of an example 15 of the finished product, and the embodiment 15 is illustrated. a cross section of the obtained cellulose acetate hollow fiber membrane; and FIG. 9 is a photograph taken by another scanning electron microscope of Example 15, which shows the cellulose acetate hollow fiber obtained in Example 15. The inner surface of the membrane.

"Embodiment 1"

Referring to Table 1 and Figure 1, an embodiment 1 of the present invention for preparing a cellulose acetate hollow fiber membrane and a finished product thereof comprises a preparation solution step 11, a stirring mixing step 12, and a finished spinning step 13.

The preparation solution step 11 is to take 18 wt% of cellulose triacetate as a cellulose acetate material, 0.2 wt% of boric acid as a modified acid, and 81.8 wt% of 1-methyl-2-pyrrolidone as a solvent, and mix them into one. Cellulose acetate solution.

The stirring and mixing step 12 is to heat the cellulose acetate solution to 90 ° C and stir for 2.5 hours.

The finished spinning step 13 is a cellulose acetate hollow fiber membrane formed by a dry-wet spinning method. The method is to first provide a spinning nozzle, pure water for respectively as a core liquid and a coagulant, and a spinning groove spaced apart from the spinning nozzle for containing the coagulant. The spun has an inner tube and an outer tube spaced coaxially inside and outside. The inner tube defines a first passage for the flow of the core fluid and cooperates with the outer tube to define a sandwich passage for the cellulose acetate solution to flow outside of the first passage. Next, the cellulose acetate solution was extruded from the spinning nozzle together with the core liquid, and moved 15 cm in the atmosphere, and then entered into the coagulant of the spinning tank, and was taken up by a roller machine.

The resulting cellulose acetate hollow fiber membrane will comprise an outer surface 22 and an inner surface 21 which is coaxially inner and outer spaced apart from the outer surface 22. The inner surface 21 has a plurality of holes 23. The average pore diameter of the pores 23 and the ratio of the area occupied were measured, and the seepage flow of the cellulose acetate hollow fiber membrane and the tensile stress which can be withstood were measured and recorded in Table 1.

Embodiments 2 to 15

Examples 2 to 15 are similar to Example 1, except that the modified acids used in the respective examples are different or the proportions of the components are different. The modified acid used in each of the examples, and the proportion of each component, are shown in Table 1.

Comparative Example 1

Comparative Example 1 was similar to Example 1, except that the modified acid was not added in Comparative Example 1. The proportion of each component in Comparative Example 1 is shown in Table 1.

Referring to Table 1, FIG. 2, FIG. 3 and FIG. 5, comparing Examples 1 to 5 with Comparative Example 1, it was found that when the cellulose acetate solution included 0.2% by weight of boric acid, the tensile strength thereof was determined by Comparative Example 1. 3.53 MPa was upgraded to 5.41 MPa, and when the cellulose acetate solution included 1.0 wt% of boric acid, the bleed flow rate was increased from 320.13 LMH/Bar of Comparative Example 1 to 484.62 LMH/Bar, and the tensile strength was still 4.17 MPa. Therefore, the addition of an appropriate amount of boric acid to cellulose acetate can indeed achieve the purpose of producing a cellulose acetate hollow fiber membrane having better mechanical strength and permeation flow rate. Further, the average pore diameter of the pores 23 of Examples 1 to 5 and the area ratio of the pores 23 were both larger than that of Comparative Example 1, and increased with the use of boric acid. As can be seen from Fig. 3, the aperture and number of the holes 23 are significantly larger than those of the comparative example 1 of Fig. 5.

Referring to Table 1, Figure 5, Figure 6, and Figure 7, Examples 6 to 10 were observed. Although the permeate flow rate increased as the amount of acetic acid used increased, the tensile strength decreased to worse than the comparative example. Further observation revealed that when the amount of acetic acid used was from 0.5 wt% to 0.75 wt%, the tensile strength decreased slightly, but the permeate flow rate was increased. Therefore, when the amount of acetic acid is from 0.5% by weight to 0.75% by weight, an equilibrium can be obtained between the tensile strength and the seepage flow. As can be seen from Figure 7, the cellulose acetate containing acetic acid The cellulose acetate hollow fiber membrane made of the vitamin solution has a number of pores 23 which is much larger than that of Comparative Example 1, and the pores 23 are respectively slit-like.

Referring to Table 1, FIG. 5, FIG. 8 and FIG. 9, comparing Examples 11 to 15 with Comparative Example 1, it was found that when the cellulose acetate solution included 0.2% by weight of sulfuric acid, the tensile strength thereof was determined by Comparative Example 1. 3.53Mpa is raised to 4.6Mpa, and when the cellulose acetate solution includes 1.0wt% sulfuric acid, the seepage flow can be greatly increased from 320.13LMH/Bar of Comparative Example 1 to 551.11LMH/Bar, and the tensile strength is still 3.72Mpa. . Therefore, the addition of an appropriate amount of sulfuric acid to cellulose acetate can indeed achieve the purpose of producing a cellulose acetate hollow fiber membrane having good mechanical strength and good permeation flow. Further, the average pore diameter of the pores 23 of Examples 11 to 15 and the area ratio of the pores 23 were larger than those of Comparative Example 1, and increased as the amount of sulfuric acid used increased. As can be seen from Fig. 9, the aperture and number of the holes 23 are significantly larger than those of the comparative example 1 of Fig. 5, and are also larger and larger than the embodiment 5 of Fig. 3.

In summary, the effect of the method for preparing the cellulose acetate hollow fiber membrane in the present invention is that the hydrophilic polymer is replaced by the modified acid, and since the modified acid has a small molecule and does not have the viscoelastic property of the polymer, the spinning nozzle is used. When it is ejected, there is no problem of expansion, so that the cellulose acetate hollow fiber membrane obtained can have better physical properties and does achieve the object of the present invention. Further, the modified acid has a small molecule and a good mobility, and can form a large and large number of pores 23 on the surface, and at the same time, can improve the permeation flow rate of the obtained cellulose acetate hollow fiber membrane.

However, the above is only the preferred embodiment of the present case. When it is not possible to limit the scope of the implementation of this case, all the simple equivalent changes and modifications made in accordance with the scope of patent application and the content of the patent specification in this case are still in this case. Within the scope of the patent.

Chemicals and Equipment

Microstructure Analysis

The cellulose acetate hollow fiber membrane was placed in a freezer for 24 hours to form ice crystals on the surface of the cellulose acetate hollow fiber membrane, placed in a freeze dryer, and subjected to freeze-drying treatment at -40 ° C for 72 hours, followed by removal. The freeze-dried cellulose acetate hollow fiber membrane is immersed in liquid nitrogen and broken, and the cross section thereof is exposed, and is fixed on the machine table with a carbon tape, and then placed in a vacuum gold plating apparatus to evaporate 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.

Hole Area Rate Calculation

Five square blocks were randomly placed on the inner surface of the cellulose acetate hollow fiber membrane. The total area of the holes in the square blocks is calculated, and the total area of the holes is divided by the total area of the square blocks of the inner surfaces, that is, the area ratio of the holes is obtained.

"Average seepage test"

A cellulose acetate hollow fiber membrane having a length of 14 cm was cut out, and the average permeate flow was measured in such a manner that pure water permeated outward from the inner tube of the cellulose acetate hollow fiber membrane. The percolating solution passing through the cellulose acetate hollow fiber membrane was taken up in a beaker placed on an electronic scale. The electronic balance can display the weight of the percolate and transfer the data to a personal computer connected to the electronic balance, and continuously record the flow of the percolate using the software, and then calculate the specific flux of the membrane.

Flux ratio, also referred to as a film transfer coefficient Water _{(Water mass transfer coefficient, MTC w} ), the common unit LHM / bar, for the flux values (Flux) and net driving pressure (Net driving pressure, NDP) the ratio, by To study the degree of clogging of the film when operating at each pure water yield, the calculation is as follows: MTC _w = (Q _p × TCF) ÷ (A × NDP)

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 water temperature (deg.] C).

A is the effective area through the membrane (m ^2).

NDP is the net driving pressure (bar), NDP = [(P _f + P _c ) ÷ 2] - P _p - Δπ.

P _f represents the pressure at the inflow end of the film.

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 film.

Δπ is the net seepage pressure at the inflow end and the water producing end of the film.

Tensile Strength Test

The prepared cellulose acetate hollow fiber membrane was cut with a surgical scissors for a sample of 16 cm in length. Use the universal tensile tester clamp to clamp the opposite ends of the sample, each The end of each clip is 3 cm, so that the reserved part in the middle is 10 cm. After the clip is clamped, the universal tensile tester can be installed.

11‧‧‧Preparation solution steps

12‧‧‧ Mixing and mixing steps

13‧‧‧Finished spinning steps

Claims (9)

A method for preparing a cellulose acetate hollow fiber membrane, comprising: Step A: providing a portion of a cellulose acetate solution comprising 10% by weight to 30% by weight of a cellulose acetate material, and 0.1% to 1.5% by weight of a modified medium An acid, and a total of 100% by weight of the solvent together with the aforementioned components; and Step B: forming the cellulose acetate solution into a cellulose acetate hollow fiber membrane by a dry-wet spinning method; wherein the modified acid is selected from the group consisting of boric acid , sulfuric acid, acetic acid, and any combination of the foregoing. The method for producing a cellulose acetate hollow fiber membrane according to claim 1, wherein the cellulose acetate material is selected from the group consisting of cellulose triacetate, cellulose diacetate, cellulose acetate propionate, cellulose acetate butyrate, and Any combination of the foregoing materials. The cellulose acetate hollow fiber membrane according to claim 1, wherein in the step A, the cellulose acetate solution comprises 0.5% by weight to 0.75% by weight of acetic acid. The method for producing a cellulose acetate hollow fiber membrane according to claim 1, wherein the solvent is selected from the group consisting of dimethyl hydrazine, nitrogen, nitrogen-dimethylformamide, acetone, dichloromethane, and chloroform. , 1-methyl-2-pyrrolidone, methyl acetate, and any combination of the foregoing. The method for preparing a cellulose acetate hollow fiber membrane according to claim 1, further comprising a step C between the step A and the step B, in the step C, The cellulose acetate solution is heated to 85 ° C to 95 ° C and stirred for 2 to 3 hours. The method for preparing a cellulose acetate hollow fiber membrane according to claim 1, wherein in the step B, the cellulose acetate solution and a core liquid are extruded from a spinning nozzle, passed through an atmosphere of 10 cm to 30 cm, and then immersed in a kind. Coagulant. The method for producing a cellulose acetate hollow fiber membrane according to claim 6, wherein the core liquid and the coagulant are water, respectively, or a combination of water and an organic solvent, and the organic solvent is selected from the group consisting of dimethyl ketone. Niobium, nitrogen, nitrogen-dimethylformamide, acetone, dichloromethane, chloroform, 1-methyl-2-pyrrolidone, methyl acetate, and any combination of the foregoing. A cellulose acetate hollow fiber membrane obtained by the method for producing a cellulose acetate hollow fiber membrane according to any one of claims 1 to 7, comprising: an outer surface; an inner surface spaced apart from the outer surface The inner surface has a plurality of holes that account for 15.4% to 62.9% of the area of the inner surface. The cellulose acetate hollow fiber membrane according to claim 8, wherein the permeate flow rate is from 330 LMH/Bar to 560 LMH/Bar.