KR102019466B1

KR102019466B1 - Continuous Process of Preparing Hollow Fiber Membrane Wherein Uniform Bead Structures Are Evenly Formed Throughout the Membrane Using Extruder

Info

Publication number: KR102019466B1
Application number: KR1020130009427A
Authority: KR
Inventors: 이수민; 이준석
Original assignee: 주식회사 엘지화학
Priority date: 2013-01-28
Filing date: 2013-01-28
Publication date: 2019-09-06
Also published as: KR20140096628A

Abstract

The present invention relates to a method for producing a hollow fiber membrane in which a spherical structure of uniform size is evenly formed throughout the membrane by a continuous process using an extruder. The method of the present invention utilizes an extruder without using a conventional stirrer-type extrusion equipment, and forms spherical structures formed by spherulite as a result of heat-induced phase separation in the membrane cross-sectional structure due to mixing of poor solvents. By adjusting the range, it is possible to prepare a microfiltration hollow fiber separator having a high strength and uniform pore size.
The manufactured hollow fiber membrane is excellent in mechanical strength and water permeability, and is very suitable for water treatment such as purified water, reuse and process water, ultrapure water pretreatment, and can be used as a support for the hollow fiber ultrafiltration membrane.

Description

Continuous Process of Preparing Hollow Fiber Membrane Wherein Uniform Bead Structures Are Evenly Formed Throughout the Membrane Using Extruder}

The present invention relates to a method for producing a hollow fiber membrane in which a spherical structure of uniform size is evenly formed throughout the membrane by a continuous process using an extruder.

Membranes used to separate certain components, such as gases, liquids or solids, especially ionic materials, by appropriately combining a dense structure or a porous structure to selectively permeate and exclude certain components, thereby providing selectivity to the removal material while permeating The material is designed to pass through with low resistance.

Recently, many technologies using a membrane having such a structure have been applied to a process of treating purified water and wastewater. These membranes for water treatment are classified into polymer membranes, ceramic membranes, metal membranes, organic / inorganic composite membranes according to their materials, and according to their performance, precision filtration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO). Divided into acts.

On the other hand, in the method for producing a membrane made of a polymer resin, a polymer solution containing a good solvent and a pore-forming agent is cast and extruded at a low temperature where phase separation by heat does not occur, and thus the polymer resin is used in a non-solvent. A nonsolvent induced phase separation method in which a porous structure is formed by coagulating is generally used. The non-solvent-induced phase separation method has the advantage of freely controlling the size of the pores, but when the finger-like macropores are formed, the mechanical strength of the membrane is weak and the membrane breaks during operation. .

In another method, the thermally induced phase separation method is a method of mixing a polymer resin with a poor solvent and spinning the polymer resin at a temperature raised to a temperature higher than the temperature at which phase separation occurs due to heat to cool and solidify the membrane. It is common to have a spherical structure by spherulite. The thermally induced phase separation method has an advantage in that a membrane having strong mechanical strength is easily manufactured, but it is difficult to reduce the pore size.

In this regard, Korean Patent No. 10-1179161 discloses melting and mixing polyvinylidene fluoride-based (PVDF) resins, pore formers, good solvents and poor solvents in a reactor and inducing non-solvent induced phase transitions, thereby avoiding fingerless and overall spherical shape. It describes about the method of manufacturing the hollow fiber membrane of the shape which the cell of is connected. However, the above technique has a disadvantage in that the spherical size of the prepared membrane cross-sectional structure is larger than 5 to 10 μm, so that the porosity is large but the strength is weak. Also, as a discontinuous film forming method using a reactor, the polymer is dissolved in the reactor and bubbles are removed. Since the stabilization process takes a lot of time, not only the productivity is greatly reduced, but it is difficult to spin the high viscosity polymer solution and difficult to manage the process, such as having to adjust the temperature of the pipe connected to the nozzle when spinning the solution at a high temperature.

Therefore, while securing excellent productivity in a continuous process, at the same time, there is a need for a manufacturing technology of hollow fiber membranes that can appropriately control the shape, pore size and shape of the membrane by adjusting the type of polymer and diluent and the manufacturing parameters according to the phase separation process. exist.

Throughout this specification, many papers and patent documents are referenced and their citations are indicated. The disclosures of cited papers and patent documents are incorporated herein by reference in their entirety, and the level of the technical field to which the present invention belongs and the contents of the present invention are more clearly explained.

Republic of Korea Patent No. 10-1179161

The present inventors have tried to develop a method of securing high productivity and high permeability simultaneously by effectively controlling the structure of the separator while using a continuous process method without using a conventional agitator type extrusion equipment. As a result, by adopting a continuous process using a compressor and heat-induced phase separation using a poor solvent and effectively controlling the spherical structure by spherite, a hollow fiber membrane having a uniform spherical structure evenly formed throughout the film was produced. The invention was completed.

Accordingly, it is an object of the present invention to provide a method for producing a hollow fiber membrane in which a spherical structure of uniform size is evenly formed throughout the membrane by a continuous process using an extruder.

Another object of the present invention is to provide a high-permeability high-strength hollow fiber membrane having a uniform sized spherical structure prepared by the above method evenly formed throughout the membrane.

Other objects and advantages of the present invention will become apparent from the following detailed description, claims and drawings.

One aspect of the present invention is a continuous process using an extruder, a method for producing a hollow fiber membrane having a structure in which a spherical structure of uniform size in which the particle size is in the range of 0.5 to 3 ㎛ evenly formed throughout the membrane, (i) Supplying a raw material including a polyvinylidene fluoride (PVDF) resin and a poor solvent to an extruder; (ii) mixing and melting the fed materials by the cylinder temperature of the extruder and the rotation of the screw; And (iii) extruding and spinning the mixed solution.

The present invention complements the disadvantages of the conventional polyvinylidene fluoride-based separation membrane manufacturing process by the non-solvent induced phase separation method and the thermal induced phase separation method and the prepared membrane characteristics, while adopting a continuous process and heat induced phase separation using an extruder The spherical structure of the hollow fiber membrane was effectively controlled. As a result, a spherical structure having a constant size in the range of 0.5 to 3 µm was formed to form a uniformly distributed cross-sectional structure throughout the separation membrane, while reducing flow path resistance. At the same time, mechanical strength could be increased.

The formation of spherical structures by spherite does not always lead to excellent porosity and permeability, and in order to ensure high strength and high permeability at the same time, it is necessary to control the structures so that the spheres are not too tightly adhered and the membrane strength is not weakened. Most importantly, the method of the present invention allows the spherical structure to be evenly distributed throughout the separator at appropriate intervals without being too tightly coupled, while allowing the spherical size to be very uniformly distributed throughout the membrane. In addition, since the spherical diameter is formed to a small size of 3 ㎛ or less at the same time to ensure excellent strength at the same time. Hereinafter, each step of the method of the present invention will be described in detail.

(i) Polyvinylidene fluoride ( PVDF ) Resin and Poor solvent Supplying a raw material material to the extruder

Among the above components, polyvinylidene-based resin (PVDF), which is the first polymer, may have a weight average molecular weight of 250,000 to 400,000, and may be 20 to 50% by weight, more specifically, 30 to 40% by weight of the total composition. Can be used in quantities. Polyvinylidene fluoride (PVDF) may be dried in a dehumidifying dryer having a drying temperature of 40 ~ 90 ℃ prior to feeding to the extruder.

The poor solvent among the components is a solvent having a weak ability to dissolve the polymer, means that the interaction energy between the solvent and the polymer is smaller than the average of the interaction energy between the solvent molecules, and can be used without limitation as long as it satisfies these conditions. In one embodiment, the poor solvent is gamma butyl lactone (GBL), ethylene glycol (EG), propylene glycol, diethylene glycol (DEG), triethylene glycol (TEG), dipropylene glycol (DPG), glycerol, Maleic anhydride, propylene carbonate (PC) or combinations thereof may be used, but is not necessarily limited thereto.

Preferably, the raw material may further comprise a hydrophilic resin, which is mixed together to compensate for the low compatibility of the polyvinylidene-based resin with water and to perform a function as a pore forming agent. Hydrophilic resin is a polymer having a polar or charged functional group so as to have compatibility with water can be used without limitation as long as it satisfies these conditions. For example, polyvinylpyrrolidone (PVP), polypropylene glycol (PEG), acrylamide resin, other acrylic resins, allylamine, ethyleneimine, amine resins such as oxazoline may be used as the hydrophilic resin, It is not necessarily limited thereto.

In addition, in one embodiment, the raw material is characterized in that it does not contain an inorganic pore-forming agent. When a large amount of inorganic pore-forming agents such as silica, alumina, titanium oxide, etc. are used in the film formation, an additional process for removing the inorganic powder is required after the film formation, and as a result, it is necessary to obtain high economical efficiency and productivity in a continuous process. The object of the present invention cannot be achieved.

The method of the present invention in a continuous process using an extruder is a spherical structure of spherite without the use of the above inorganic pore-forming agent is not too dense, evenly distributed at appropriate intervals and high particle size throughout the membrane By having a uniformity there is an advantage that can form appropriate pores.

In a preferred embodiment, the content and weight percentage of each component included in the raw material may be as follows.

1st polymer (P1): 30-40 weight% of polyvinylidene-type resin (PVDF)

2nd polymer (P3): 5-20 weight% of polypropylene glycol (PEG)

First poor solvent (S1): 10-30 wt% of gamma -butyl lactone (GBL)

Second poor solvent (S2): 10-30% by weight of propylene carbonate (PC)

In addition to the above-mentioned components, additives for the purpose of imparting porosity, strength, and other functionalities may be supplied to the extruder, and the polymer component of these components may be mixed with a polypolyvinylidene fluoride resin and dried to extruder hopper. It may be supplied through, or a poor solvent and a hydrophilic polymer such as low molecular weight polyethylene glycol (PEG) may be supplied to the extruder through a liquid pump.

( ii ) The cylinder temperature of the extruder Screw Mixing and melting the supplied materials by rotation

Membrane Preparation As a mixing step of the polymer solution raw material, all mixing is performed in the screw in the cylinder of the extruder. Although a single screw extruder can also be used, it is preferable to use a twin screw extruder in order to improve mixing efficiency.

In one embodiment, the cylinder of the extruder may be temperature controlled for each cylinder, each temperature may be adjusted within 50 to 250 ℃ in consideration of the melting point of the polymer resin. Specifically, the portion containing the polymer solvent may be adjusted to about 50 ° C., the melting zone is about 150 to 200 ° C., and the portion to be discharged may be adjusted to about 110 to 140 ° C.

The configuration of the segment of the screw can be optimized to increase the mixing efficiency, for example the rotational speed of the screw can be adjusted to 150 to 300 rpm. In this case, the supplied materials are simultaneously melted by mixing with the temperature of the cylinder and the rotation of the screw.

( iii Extrude the mixed solution and Radiating step

This is the step of extruding and spinning the mixed solution. The mixed molten polymer solution is extruded by the temperature of the cylinder and the screw rotation to the gear pump, and then the polymer solution can be extruded and spun through the nozzle by the metering gear pump. Preferably, the mixed solution may be spun together with the internal coagulating solution.

The method of the present invention may further comprise the step of cooling and solidifying the spun solution through a coagulation bath in addition to the steps of (i) to (iii) above.

Another aspect of the present invention is to provide a high-permeability high-strength hollow fiber membrane, characterized in that the spherical structure of uniform size in the particle size range of 0.5 to 3 ㎛ evenly formed throughout the membrane.

The hollow fiber membrane of the present invention formed by forming a raw material including the polyvinylidene fluoride (PVDF) -based resin and a poor solvent by adopting a continuous process using an extruder and heat-induced phase separation is a result of heat-induced phase separation in its cross-sectional structure. The spherical structure formed by spherulite could be controlled in a range of 3 μm or less, that is, 0.5 to 3 μm.

In addition, the hollow fiber separation membrane of the present invention is characterized in that the spherical structure of uniform size is distributed evenly throughout the membrane, and the pore size is very uniform as a whole.

As such, the small spherical structure of 0.5 to 3 μm is not too dense and evenly distributed at appropriate intervals, and since the uniformity of the particles is very high throughout the membrane, there is an advantage of minimizing the resistance of the flowing water. Therefore, the hollow fiber membrane of the present invention can achieve excellent mechanical strength and water permeability at the same time, and as a result is very suitable for water treatment such as purified water, reuse and process water, ultrapure water pretreatment.

In addition, since the mechanical strength is very excellent and the resistance of flowing water can be minimized, it can be used as a supporter of the hollow fiber ultrafiltration membrane.

The method of the present invention uses an extruder to produce a separator in a continuous process without using a conventional stirrer-type extrusion equipment, spherulite which is a result of heat induced phase separation in the membrane cross-sectional structure by mixing the poor solvent By forming the spherical structure by 0.5 to 3 ㎛ range, it is possible to produce a high-filtration hollow fiber membrane having a uniform high pore size of high strength.

The manufactured hollow fiber separation membrane is excellent in mechanical strength and water permeability, and is very suitable for water treatment such as purified water, reuse and process water, ultrapure water pretreatment, and can be used as a support for the hollow fiber ultrafiltration membrane.

Figure 1 shows a scanning electron micrograph of the separator prepared in Example 1 (Fig. 1a: the membrane cross-section, Fig. 1b: enlarged membrane cross-section, Fig. 1c: enlarged membrane surface).
FIG. 2 is a scanning electron micrograph of the separator prepared in Example 2 (FIG. 2A: enlarged cross section of the separator; FIG. 2B: enlarged surface of the separator).
3 is a scanning electron micrograph of the separator prepared in Example 3 (Fig. 3a: enlarged cross section of the separator, Fig. 3b: enlarged surface of the separator).
FIG. 4 is a scanning electron micrograph of the separator prepared in Example 4 (FIG. 4A: enlarged cross section of the separator; FIG. 4B: enlarged surface of the separator).
FIG. 5 is a scanning electron micrograph of the separator prepared in Example 5 (FIG. 5A: enlarged cross section of the separator; FIG. 5B: enlarged surface of the separator).
FIG. 6 is a scanning electron micrograph of the separator prepared in Example 6 (FIG. 6A: enlarged cross section of the separator; FIG. 6B: enlarged surface of the separator).
7 is a scanning electron micrograph of the separator prepared in Example 7 (FIG. 7A: enlarged cross section of the separator; FIG. 7B: enlarged surface of the separator).
8 is a scanning electron micrograph of the separator prepared in Example 8 (FIG. 8A: enlarged cross section of the separator; FIG. 8B: enlarged surface of the separator).

Hereinafter, the present invention will be described in more detail with reference to Examples. These examples are only for illustrating the present invention in more detail, and the scope of the present invention is not limited by these examples in accordance with the gist of the present invention to those skilled in the art. Will be self explanatory.

Example

Example One

Polyvinylidene fluoride resin PVDF (solvay 6060 grade, molecular weight 322kDa) 40% by weight, 20% by weight of gamma butyrolactone (GBL), 20% by weight of propylene carbonate (PC), 20% by weight of polyethylene glycol (PEG 400) The mixing ratio was determined, polyvinylidene-based resin was supplied to the hopper of the extruder, and GBL, PC and PEG were supplied to the cylinder of the extruder through the liquid feed pump. The temperature of the extruder 0-9 zones (C0-C9) was set according to each composition and composition ratio. The screw rotation speed was 300 times / min and the material mixed in the extruder cylinder was melt extruded in the twin screw extruder and finally spun through the gear pump and nozzle to enter the coagulation bath. The outer and inner diameters of the nozzles were 2.0 mm and 1.2 mm, respectively, and the distance between the nozzle and the coagulation bath was set to 50 mm. A mixture of (GBL: EG (ethylene glycol) = 8: 2) was used as the internal coagulant. In addition, a mixture of (GBL: PC: D.I. = 4: 1: 1) was used as the external coagulation bath and the temperature of the coagulation solution was set to 20 ° C. The hollow fiber membrane subjected to the coagulation tank was manufactured in the hollow fiber membrane product of the present invention by extraction at least one day in a washing tank and dried at room temperature.

The PVDF hollow fiber separator prepared by the above method had an outer diameter of 1 to 1.2 mm and an inner diameter of 0.5 to 0.8 mm. Tensile strength 12.32Mpa, 20% elongation, mechanical strength is excellent, and the average pore size of the hollow fiber membrane measured by permporometer (PMI) equipment was 0.14 ㎛. In addition, it was confirmed that it is a fine filtration membrane having a pure water flux of 790 L / m 2 · hr and a porosity of 65% at 1 bar and 25 ° C.

The scanning electron micrograph of the prepared membrane is shown in Fig. 1 (Figs. 1A to 1C), which shows a shape in which a spherical structure by spherite is connected without a finger, and the diameter of the spherical particles is about 2 μm. Was measured. In addition, it was confirmed that the diameters of the beads particles distributed throughout the separation membrane were almost the same, so that the particle uniformity was very high.

Example 2

The same process as in Example 1 was carried out under the same conditions with a PEG concentration of 15%.

Example 3

The same process as in Example 1 was carried out under the same conditions with a PEG concentration of 10%.

Example 4

The same process as in Example 1 was carried out under the same conditions with a PEG concentration of 5%.

Example 5

The film solution was formed under the same conditions as in Example 1 with the polymer solution composition and composition ratio of PVDF 40% and GBL 60%.

Example 6

The polymer solution composition and composition ratio were PVDF 40%, GBL 42%, and DEG 18%.

Example 7

The same process as in Example 1 was carried out under the same conditions as the polymer solution temperature of 120 ℃.

Example 8

The same process as in Example 1 was carried out under the same conditions as the polymer solution temperature of 100 ℃.

The basic physical properties measured for the separators prepared in Examples 1 to 8 are summarized in Table 1 below, but the content of each component of the present invention is not limited to the numerical values shown in Table 1, and those skilled in the art can determine the numerical ranges in the tables. Reasonable summaries and inferences can be used as a basis. The parameters in Table 1 are just one of the embodiments of the present invention, which should not be construed as essential conditions of the present invention.

Example number One 2 3 4 5 6 7 8 Polymer solution composition and composition ratio PVDF (%) 40 40 40 40 40 40 40 40 PEG (%) 20 15 10 5 - - 20 20 GBL (%) 20 22.5 25 27.5 60 42 20 20 PC (%) 20 22.5 25 27.5 - - 20 20 DEG (%) - - - - - 18 - - Polymer solution temperature (℃) 110 110 110 110 110 110 120 100 Air gap (mm) 50 50 50 50 50 50 50 50 Composition of Coolant GBL (%) 66.6 66.6 66.6 66.6 66.6 66.6 66.6 66.6 PC (%) 16.7 16.7 16.7 16.7 16.7 16.7 16.7 16.7 D.I. (%) 16.7 16.7 16.7 16.7 16.7 16.7 16.7 16.7 Cooling temperature (℃) 20 20 20 20 20 20 20 20 Average pore size (㎛) 0.15 0.38 0.09 0.25 0.30 0.16 0.10 0.31 Pure penetration rate (L / m2h) 790 1250 196 352 425 845 542 957 Tensile Strength (MPa) 12.32 7.40 11.18 12.90 7.52 7.96 11.40 13.10 Spherical particle diameter (μm) 2.0 1.0 1.0 2.2 1.8 1.8 3.0 1.0

Claims

In a continuous process using an extruder, as a method for producing a hollow fiber membrane having a spherical structure of a spherite of uniform size in the particle size range of 0.5 to 3 ㎛ evenly formed throughout the film,
(i) feeding a raw material comprising polyvinylidene fluoride (PVDF) -based resin, a poor solvent and a hydrophilic resin to the extruder;
(ii) mixing and melting the fed materials by the cylinder temperature of the extruder and the rotation of the screw; And
(iii) extruding and spinning the mixed solution,
The temperature of the cylinder is adjusted to 50 to 250 ℃,
The rotational speed of the screw is adjusted to 150 to 300 rpm,
The hydrophilic resin may be polyvinylpyrrolidone (PVP), polypropylene glycol (PEG), acrylamide resin, acrylic resin, amine resin, polyetherimide (PEI), polyimide (PI), polyamide (PA) And cellulose acetate (CA).

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The method of claim 1 wherein the raw material does not comprise an inorganic pore former.

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The method of claim 1 wherein the mixed solution in (iii) is spun together with internal coagulating solution.

The method of claim 1 further comprising the step of cooling and solidifying the solution spun in (iii) through a coagulation bath.

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