KR101269574B1 - Acetylated alkyl cellulose membrane using thermal induced phase separation and preparing method thereof - Google Patents

Abstract

The present invention relates to an acetylated alkyl cellulose separation membrane prepared using a thermally induced phase separation method using a polyethylene glycol poor solvent and a method for preparing the separation membrane. The separation membrane of the present invention has excellent mechanical properties and excellent flow rate. It has excellent hydrophilicity and excellent membrane fouling resistance, making it suitable for use as a membrane for water treatment.

Description

Acetylated alkyl cellulose membrane using thermal induced phase separation and preparing method

The present invention relates to an acetylated alkyl cellulose separation membrane prepared using a thermally induced phase separation method using a polyethylene glycol poor solvent and a method for preparing the separation membrane.

Recently, the interest in using a separation membrane due to the reliability and easy automation of water quality in the water treatment process has increased. Separation membrane used for water purification treatment is required to have a strong durability, etc., and also a membrane fouling resistance is greatly required. Polysulfone (PSF), polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride (PVDF) are known as general separator materials. However, these polymer materials have hydrophobic properties and thus have a weak point of membrane contamination. have. Therefore, there is a need to develop a membrane of a new hydrophilic polymer material that can satisfy the membrane fouling resistance required as a separator for water treatment.

 Cellulose acetate is well known as a hydrophilic polymer separator material. Membranes using these hydrophilic polymer materials are excellent in resistance to membrane contamination, but have a problem of poor mechanical strength. Accordingly, in order to apply a hydrophilic polymer having high membrane fouling resistance as a separator material, another improvement of mechanical strength is required.

As a method of manufacturing a porous membrane having excellent mechanical strength, there is a thermal induced phase separation (TIPS). Thermally induced phase separation is largely divided into solid-liquid phase separation and liquid-liquid phase separation. Korean Patent No. 805,977 discloses a method for preparing a high strength hollow fiber membrane using a polyvinylidene fluoride polymer using a solid-liquid phase separation method, and Korean Patent No. 966,718 uses a liquid-liquid phase separation method. A method of producing a high strength hollow fiber membrane using a polyvinylidene fluoride polymer is disclosed. However, as described above, when the membrane is manufactured by thermally induced phase separation (TIPS) using the existing hydrophobic polymer material, mechanical properties may be satisfied, but the membrane fouling resistance is weak due to the use of the hydrophobic polymer material. Still remains.

On the other hand, Fu et al. Prepared a hollow fiber membrane using a thermally induced phase separation method using cellulose acetate butyrate in Desalination 233, but did not obtain a separation membrane having high strength characteristics.

An object of the present invention is to provide a polymer solution for preparing an acetylated alkyl cellulose separation membrane having high permeate flow rate, excellent mechanical properties and membrane fouling resistance as characteristics required for the separation membrane for water treatment.

Another object of the present invention is to provide a method for preparing an acetylated alkyl cellulose separator using polyethylene glycol as a poor solvent by a TIPS process.

In order to solve the above problems, the present invention is characterized by the polymer solution for the production of acetylated alkyl cellulose separation membrane using a heat-induced phase separation method containing acetylated alkyl cellulose and polyethylene glycol as a poor solvent.

In addition, the present invention is to prepare a polymer solution by mixing 10 to 30% by weight of acetylated alkyl cellulose and 70 to 90% by weight of the poor solvent of polyethylene glycol; Heating the polymer solution to prepare a spinning solution; And spinning the spinning solution and the inner hole former from a nozzle to phase-transfer the spinning solution to produce a hollow fiber membrane. Characterized in that the manufacturing method of the acetylated alkyl cellulose separation membrane using a thermally induced phase separation method comprising a.

Acetylated alkyl cellulose separator of the present invention has an average pore size of 0.05 to 0.4 μm, a pure permeate flow rate of 500 to 2,000 L / m 2 · hr (1 kg / cm 2), tensile strength of 9 to 20 MPa, and distilled water Relative permeate flow rate (contamination degree) after 6 hours of operation relative to the initial permeate flow rate is 0.7 to 0.9, which is suitable as a separation membrane for water treatment.

The present invention relates to a polymer solution comprising an acetylated alkyl cellulose polymer material and a polyethylene glycol (PEG) poor solvent, and a method for preparing a separator by thermally induced phase separation (TIPS) using the polymer solution.

The present invention has a technical feature of using acetylated alkyl cellulose as a separator material. Separation membranes made of cellulose acetate, known as hydrophilic polymers, have poor mechanical strength and must increase the thickness of the membrane to some extent, and as the thickness of the membrane increases, the permeate flow rate decreases and the module area decreases, thereby reducing module efficiency. have. However, according to the present invention, the membrane is prepared by thermally induced phase separation (TIPS) using acetylated alkyl cellulose, thereby maintaining membrane fouling resistance due to the excellent hydrophilicity of the polymer material with excellent mechanical strength.

As in the present invention, in order to apply TIPS using a hydrophilic polymer material, a technique of selecting an optimal poor solvent is important. Accordingly, the present invention is characterized in that polyethylene glycol (PEG) is selected as a poor solvent in order to apply acetylated alkyl cellulose to thermally induced phase separation (TIPS). Polyethylene glycol (PEG) has been generally used as a pore-forming agent for the manufacture of porous separators, but has a disadvantage in that the polymer solution cannot be manufactured and its strength is low when a large amount of the polymer is inferior in solubility with the polymer. However, in the present invention, by using polyethylene glycol (PEG) as a poor solvent of acetylated alkyl cellulose, thermally induced phase separation (TIPS) can be applied, and thus, a membrane having excellent mechanical strength can be prepared.

The method for producing a membrane for water treatment of the present invention is characterized in that the acetylated alkyl cellulose is dissolved in a poor solvent of polyethylene glycol near the melting point and then prepared by phase shifting in a non-solvent. The production method is thermally induced phase separation (TIPS), and in particular, liquid-liquid phase separation.

The present invention will be described in more detail as follows.

First, a poor solution of acetylated alkyl cellulose and polyethylene glycol is mixed to prepare a polymer solution.

Acetylated alkyl cellulose used in the present invention has hydrophilic properties, so that membrane contamination by organic substances is less likely to occur, and exhibits high transmittance. As the acetylated alkyl cellulose, it is preferable to use a polymer having a relatively high molecular weight in a weight average molecular weight in the range of 50,000 to 2 million, preferably in the range of 200,000 to 1 million. If the weight average molecular weight of the acetylated alkyl cellulose is less than 50,000, the strength after spinning is very low, making it difficult to use as a separator. If the weight average molecular weight exceeds 2 million, the thermally induced phase separation method using a poor solvent is used. This is because the viscosity is so high that it is difficult to prepare a spinning solution. In addition, the acetylated alkyl cellulose used in the present invention refers to cellulose substituted with an alkyl group having 1 to 3 carbon atoms and an acetyl group. That is, cellulose in which three hydroxy groups are bonded in a cellulose unit structure and some of the three hydroxy groups are substituted with alkyl or acetyl is referred to as 'acetylated alkyl cellulose' in the present invention. As the acetylated alkyl cellulose, the substitution degree of the alkyl group and the acetyl group per unit structure of cellulose is used in the range of 1.0 to 2.0 molar ratio, respectively. In using acetylated alkyl cellulose as a membrane material, if the degree of acetylation is too low, the acetylation degree is 1.0 molar ratio because the polymer may be swelled and eluted during the washing process after preparing the membrane by applying the thermal induced phase separation method (TIPS). It is good to keep the above. The method for producing acetylated alkyl cellulose used in the present invention may be prepared by a general method, for example, by acetylating an alkyl cellulose using an acetylating agent such as acetic anhydride or acetyl chloride (AcCl). .

In the present invention, polyethylene glycol (PEG) is used as a poor solvent of acetylated alkyl cellulose. That is, polyethylene glycol (PEG) is not a good solvent that dissolves acetylated alkyl cellulose well, but is a poor solvent capable of melting the polymer when heated up to near the melting point of acetylated alkyl cellulose. The poor solvent used in the TIPS process serves to suppress the formation of macrovoids in the membrane, maximize the pore size and porosity of the membrane, and affect the temperature change, viscosity change, and ease of molding process of the polymer solution. Go crazy. Polyethylene glycol (PEG) used in the present invention as the poor solvent, it is preferable to use a weight average molecular weight of 200 to 1,000, preferably a weight average molecular weight of 200 to 600 range. The reason is that the melting point of the acetylated alkyl cellulose is about 170 ° C, and it is easy to prepare the polymer solution by heating up to the temperature around the melting point.If the average molecular weight exceeds the above range, the polymer solution cannot be prepared. May be generated.

In order to prepare the polymer solution of the present invention, 10 to 30% by weight of acetylated alkyl cellulose is mixed with 70 to 90% by weight of polyethylene glycol poor solvent. In this case, when the content of the acetylated alkyl cellulose is less than 10% by weight, the strength of the separator is lowered. When the content of the acetylated alkyl cellulose is less than 30% by weight, the viscosity of the polymer solution is too high to facilitate spinning, and thus, the concentration range may be maintained.

In order to purify the prepared polymer solution, the polymer solution may be warmed and then filtered to remove insoluble components. In more detail the purification process, the polymer solution is heated to a temperature of 60 to 200 ℃ completely dissolved acetylated alkyl cellulose, and then left at room temperature for 3 to 10 hours and then filtered to obtain a purified polymer solution Manufacture.

The membrane may be prepared by forming a membrane using the polymer solution prepared by the above method. In the present invention, to provide a method for producing a hollow fiber membrane as a representative membrane.

First, considering that the melting point of the acetylated alkyl cellulose is about 170 ° C, the spinning solution is prepared by heating the polymer solution within the range of 100 ° C to 200 ° C, which is the temperature around the melting point of the acetylated alkyl cellulose. If the heating temperature for the preparation of the polymer solution is less than 100 ℃ complete dissolution does not occur, there is a problem that the processability is degraded, if the polymer exceeds 200 ℃ is decomposed.

The prepared spinning solution is spun onto a nozzle forming a hollow fiber membrane to prepare a hollow fiber membrane by phase-transferring the spinning solution. When the spinning solution is spun from the spinning nozzle, an internal coagulation bath is injected into the nozzle for spinning the spinning solution using a metering pump to form an inner hole of the hollow fiber membrane.

As the internal coagulation bath, one or two or more kinds of mixed solvents selected from ethylene glycol systems such as triethylene glycol, diethylene glycol, and ethylene glycol may be used. In the internal coagulation bath, one or two or more selected from water, alcohols and ketones may be used as the nonsolvent, and preferably water may be used as the nonsolvent. When non-solvent is added, the use of the non-solvent / non-solvent ratio in a 1/0 to 1 / 0.5 weight ratio, more preferably in a 1/0 to 1 / 0.4 weight ratio, forms pores without damaging the internal holes. I can do it.

As the external coagulation bath in which the phase transition occurs, one or two or more kinds of mixed solvents selected from ethylene glycol systems such as triethylene glycol, diethylene glycol, and ethylene glycol, or a mixed solution of the ethylene glycol system and water may be used.

At this time, the internal coagulation bath is in the range of -10 ° C to 150 ° C, the phase transition bath maintains a temperature of -10 ° C to 150 ° C, more preferably in both cases is carried out under the conditions of maintaining 10 ° C to 120 ° C. If the temperature of the internal coagulation bath is too low, the cross-sectional structure of the hollow fiber membrane is densely formed, and the mechanical strength of the hollow fiber membrane is increased, but the porosity is lowered, causing a sudden drop in water permeability. If the temperature of the internal coagulation bath is too high, Although the porosity increases on the inner surface of the hollow fiber membrane, weak bonds are formed in the cross-sectional structure, so that the mechanical strength of the hollow fiber membrane is weakened. If the temperature of the phase transition bath is too low, the porosity of the surface of the hollow fiber membrane is reduced, leading to a decrease in permeability. If the temperature of the phase transition tank is too high, the porosity and the pore size of the surface of the hollow fiber membrane are increased, the permeation rate increases, but the mechanical strength is increased. Since the problem of weakening of the hollow fiber membranes occurs rapidly, it is preferable to maintain the above range.

The hollow fiber formed through the above process is immersed in the non-solvent to finally solidify. As the non-solvent, one or two or more selected from water, ethylene glycol, diethylene glycol, triethylene glycol, alcohols, and ketones can be used. You may use the mixed liquid which mixed the good solvent or the poor solvent with the said nonsolvent. The good solvent uses one or two or more selected from dimethylacetamide, dimethylformamide, N-methyl-2-pyrrolidone and dimethyl sulfoxide.

The hollow fiber membrane obtained as described above has a smell of the solvent at the surface of the hollow fiber membrane for 3 to 6 hours in a water bath which is raised to 70 ° C. to 100 ° C., more preferably below the boiling point of water, in order to remove the remaining solvent. Hydrothermal treatment is performed until the condition is reached. Hot water treatment has the advantage of increasing the water transmittance and strength.

 The final manufactured hollow fiber separator was induced by forming a flow path through which water flows from the outside to the inside, and the outer layer has an asymmetric structure with smaller pores than the inner layer. That is, the pore size of the outer layer is in the range of 0.05 to 0.2 μm, and the pore size of the inner layer is in the range of 0.1 to 1 μm. If the pore size of the outer layer is too small below the above range, the permeate flow rate is too small to decrease the efficiency. If the pore size of the inner layer is less than the above range, the resistance is large, and a high pressure is required for the permeation. If the pore size exceeds the above range, the strength of the separator is greatly reduced.

The separation membrane of the present invention prepared by the above method has an average pore size of 0.05 to 0.4 ㎛, pure permeate flow rate of 500 ~ 2000 L / ㎡ · hr (1 kg / ㎠), tensile strength of 9 to 20 MPa, distilled water Relative permeate flow rate after 6 hours of operation compared to initial permeate flow rate is 0.7 to 0.9, which is excellent in fouling resistance and excellent in mechanical properties such as tensile strength.

The present invention as described above will be described in more detail based on the following examples, but the scope of the present invention is not limited by the following examples.

[Example]

Example 1 Preparation of Acetylated Methyl Cellulose Membranes

After weighing to 10% by weight of methyl cellulose (PMA, Samsung Fine Chemicals, DS: 1.7) and 90% by weight of pyridine, the methyl cellulose was dissolved in the pyridine to prepare a solution. Next, acetic anhydride was weighed to have a molar ratio of 3 per unit of cellulose, and then, it was added to the solution and acetylated at 90 ° C. for 3 hours. Next, after the acetylation reaction was completed, it was solidified in water to prepare 100% acetylated methyl cellulose (AMC ₁₀₀ ). The prepared acetylated methyl cellulose (AMC ₁₀₀ ) has a methyl group substitution degree of 1.7 per cellulose unit (Unit), and an acetyl group substitution degree of 1.3.

The acetylated methyl cellulose (AMC ₁₀₀ ) 20% by weight and poor solvent were weighed so that the weight average molecular weight was 80% by weight of polyethylene glycol (PEG 200) 200. The AMC ₁₀₀ and PEG 200 were mixed and completely dissolved by heating at 170 ° C for 3 hours, and then 120 ° C. It was stabilized by standing for 2 hours in. Bubbles of the stabilized polymer solution were removed and filtered to prepare a purified polymer solution.

The purified polymer solution was heated at 120 ° C to prepare a spinning solution. Extrude the spinning solution into a 5 cm gap between the nozzle and the primary external coagulation bath in a double-tubular nozzle while using triethylene glycol as an external coagulation bath while adding triethylene glycol as an internal coagulation bath to the inner hole. To prepare a hollow fiber membrane. At the time of spinning, the temperature of the spinning solution was adjusted to 150 ° C, the temperature of the internal coagulation bath was 40 ° C, and the temperature of the external coagulation bath was 25 ° C.

Example 2 Preparation of Acetylated Methyl Cellulose Membranes

In the same manner as in Example 1, a hollow fiber-type separator was prepared in the TIPS process, but polyethylene glycol (PEG600) having a number average molecular weight of 600 was used instead of PEG200 as a poor solvent.

Example 3 Preparation of Acetylated Methyl Cellulose Membranes

In the same manner as in Example 1, a hollow fiber-type separator was manufactured by TIPS process, but diethylene glycol was used instead of ethylene glycol as an external coagulation bath.

Example 4 Preparation of Acetylated Methyl Cellulose Membranes

In the same manner as in Example 1, a hollow fiber-type separator was prepared by using a TIPS process, but a mixture of 50 wt% of ethylene glycol and 50 wt% of water was used instead of ethylene glycol alone as an external coagulation bath.

Comparative Example 1. Preparation of Acetylated Methyl Cellulose Separator

In the same manner as in Example 1, a hollow fiber-type separator was prepared in the TIPS process, but polyethylene glycol PEG2000 having an average molecular weight of 2000 was used instead of PEG200 as a poor solvent.

Comparative Example 2. Preparation of Cellulose Acetate Separator

In the same manner as in Example 1, a hollow fiber-type separator was prepared by TIPS process, but cellulose acetate was used instead of acetylated methyl cellulose as a polymer material.

Comparative Example 3. Preparation of PVDF Separator

In the same manner as in Example 1, a hollow fiber-type separator was manufactured by TIPS process, but polyvinylidene fluoride (PVDF, solvay) was used instead of acetylated methyl cellulose as a polymer material. That is, a polymer solution was prepared by mixing 40% by weight of polyvinyllidene flouride (PVDF, solvay) polymer and 60% by weight of gamma-butyrolactone, and using gamma-butyrolactone as an internal coagulation bath. A mixture of 50% by weight of ethylene glycol and 50% by weight of gamma-butyrolactone was used as the external coagulation bath.

[Experimental Example]

Experimental Example 1 Physical Property Measurement Experiment

The physical properties of the hollow fiber separators prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were measured by the following method, and the results are shown in Table 1 below.

In this experiment, the average pore size was measured using PMI. In addition, the net permeate flow rate was measured by pressing the pure water (20 ℃) in the water tank in the Out-In method by manufacturing a module having a constant length and the number of strands of the hollow fiber membrane. Tensile strength was measured by using a tensile strength meter to measure the force at the time of cutting and breaking, divided by the cross-sectional area of the hollow fiber.

division Average pore size
(Μm) Pure permeation amount
(L / ㎡ · hr, 1kg / ㎠) Tensile Strength (MPa) Example 1 0.2 1200 12 Example 2 0.4 1500 10 Example 3 0.3 1200 11 Example 4 0.09 700 13 Comparative Example 1 0.08 600 7 Comparative Example 2 0.06 200 6 Comparative Example 3 0.4 1200 7

Experimental Example 2: Measurement of membrane fouling resistance

The membrane fouling resistance of the separation membrane for water treatment prepared in Examples 1 to 4 and Comparative Examples 1 to 3 was measured. A 500 ppm aqueous solution of bovine serum albumin was used as a membrane fouling agent, and the membrane fouling degree was expressed as a relative flux by comparing the permeate after 6 hours of operation with the initial flux using distilled water. The relative flux was calculated by the following Equation 1, and the results are shown in Table 2 below.

division Relative Permeate Flow Rate Example 1 0.78 Example 2 0.81 Example 3 0.74 Example 4 0.83 Comparative Example 1 0.63 Comparative Example 2 0.61 Comparative Example 3 0.35

The separation membranes of Examples 1 to 3 according to the present invention can be confirmed that the relative permeate flow rate is high, and through this, it can be confirmed that the present invention has superior membrane fouling resistance than the conventional separator.

Claims (8)

Acetylated alkyl cellulose; And
Polyethylene glycol as a poor solvent;
Polymer solution for the production of acetylated alkyl cellulose separation membrane using a thermally induced phase separation method comprising a.
The method according to claim 1,
The acetylated alkyl cellulose has a weight average molecular weight in the range of 50,000 to 2 million, characterized in that the substitution degree of the alkyl group per unit structure (cellulose) of 1.0 to 2.0 molar ratio and the degree of substitution of the acetyl group of 1.0 to 2.0 molar ratio Polymer solution.
The method according to claim 1,
The polyethylene glycol is a polymer solution, characterized in that the weight average molecular weight ranges from 200 to 1,000.
Preparing a polymer solution by mixing 10-30 wt% of acetylated alkyl cellulose and 70-90 wt% of the poor solvent of polyethylene glycol;
Heating the polymer solution to prepare a spinning solution; And
Preparing a hollow fiber membrane by spinning the spinning solution and an inner hole forming agent through a nozzle to phase-transfer the spinning solution;
Method for producing an acetylated alkyl cellulose membrane using a thermally induced phase separation method comprising a.
The method of claim 4,
Method for producing an acetylated alkyl cellulose separation membrane using a thermally induced phase separation method characterized in that to prepare a spinning solution by heating the polymer solution in a temperature range of 100 ℃ to 200 ℃.
The method of claim 4,
The hollow fiber membrane has a pore size of 0.05 ~ 0.2 ㎛ range of the outer layer, the pore size of the inner layer range of 0.1 to 1 ㎛ characterized in that the method of producing an acetylated alkyl cellulose separation membrane using a thermally induced phase separation method.
The method of claim 4,
The internal coagulation bath used in the phase transition process is ethylene glycol-based, and the external coagulation bath is ethylene glycol-based alone or acetylated alkyl cellulose using a heat-induced phase separation method, characterized in that a mixed solution of ethylene glycol and water. Method for producing a separator.
The compound according to any one of claims 4 to 7, wherein
The average pore size of the membrane is 0.05 to 0.4 µm, the net permeate flow rate is 500 to 2000 L / m 2 · hr (1 kg / cm 2), the tensile strength is 9 to 20 MPa, and 6 hours compared to the initial permeate flow rate using distilled water. A method for producing an acetylated alkyl cellulose separation membrane using a thermally induced phase separation method, characterized in that the relative permeate flow rate after operation is 0.7 to 0.9.