KR20010039398A - Polyamide Nanofiltration Composite Membranes Having PVA Protecting Layers - Google Patents

Abstract

PURPOSE: A polyamide nano separation membrane obtained by adding a polyvinyl alcohol layer as a protecting layer to a polyamide active layer having low chemical stability such as chlorine resistance is provided, which has excellent chemical stability in wide ranges of pH as well as high water permeability. CONSTITUTION: The nano separation membrane is characterized in that it comprises a cross linked polyvinyl alcohol as a protecting layer on a polyamide composite comprising a porous supporting body and a polyamide active layer, wherein the cross linked polyvinyl alcohol has a thickness of 0.01 to 0.1 micrometer. The membrane is prepared by adding a mixture solution of one or two or more ionomers selected from the group consisting of sodium alginate, chitosan and sulfonated polystyrene with polyvinyl alcohols to a polyamide active layer.

Description

Polyamide Nanofiltration Composite Membranes Having PVA Protecting Layers

The present invention relates to the production of a nanocomposite membrane having a novel composite membrane structure having excellent chemical stability by adding a polyvinyl alcohol layer on a polyamide active layer in a composite membrane structure using polyamide as an active layer.

Nano-membrane is a membrane having an intermediate property between ultrafiltration membrane and reverse osmosis membrane, and has a property of easily passing monovalent ions and effectively filtering multivalent ions. In particular, these separators are very effective for removing low molecular weight organic matter. Nano-membrane having such characteristics has a wide range of applications. Typical examples include the manufacture of cheese whey, seafood processing, removal of minerals from water, purification of contaminated groundwater, ultrapure water, removal of heavy metals in wash water, yeast manufacturing process, textile industry, electroless plating Industry, the manufacture of low molecular weight organic substance, etc. are mentioned.

Nano-membrane membranes are currently manufactured and sold mainly in the US, Japan, and Israel, and representative products include the following: ASP35 (Advanced Membrane Technology), MPF21; MPF32 (Kriyat Weizmann), CTA-LP; Fluid Systems (TFCS), BQ01; MX07; HG01; SX01; SX10 (Osmonics), 8040-LSY-PVDI (Hydranautics), NF CA30; NF PES10 (Hoechst), WFN0505 (Stork Frosland).

These are mostly composite membranes prepared by coating an active layer of a thin film on the surface of a porous support. The composite membrane structure is generally recognized as the most suitable membrane structure having high permeability and high rejection rate. These membranes are mainly surface-polymerized using piperazine, isophthaloyl chloride, tetraphthaloyl chloride, and trimesoyl chloride as monomers. These are prepared by coating the active layer of the thin film on the surface of the porous support.

The chemical stability of the nano separator of the composite membrane structure is greatly affected by the chemical stability of the active layer itself. The active layer is an important part of determining the separation performance in the composite membrane, and is located in the outermost part of the separation membrane, so that the active layer is in direct contact with the material to be separated. Therefore, the chemical properties of the substance to be separated directly affect the active layer, and when the substance to be separated is a substance such as a strong acid or a strong base, the active layer may be severely damaged. Once the active layer is damaged, the separator can no longer perform well. In view of this, the chemical stability of the active layer itself is the most important property that the chemically stable nano-membrane should have.

Among the many products currently on sale, the most representative is the NS300 manufactured by Cadottte, and the membrane is a polysulfone support using piperazine and trimesoyl chloride as monomers. It was prepared by forming a polyamide network crosslinked by interfacial polymerization on the surface.

Nano-membranes formed of cross-linked polyamide layers generally have high permeability and high molecular weight removal ability, while having relatively low chlorine resistance and chemical stability. In particular, these membranes have a looser crosslinked structure than the polyamide membranes for reverse osmosis, and thus exhibit lower chlorine resistance and chemical stability than reverse osmosis membranes. It is well known that they are chemically unstable because of the amide bonds of their coating layers, polyamide, and the amide bonds are easily hydrolyzed under strong acid strong bases. Therefore, it is an urgent problem to reinforce the chemical stability of the nano separator made of polyamide.

Therefore, an object of the present invention is to solve the problems of the prior art at once.

In other words, the present invention aims to produce a composite membrane structure prepared by adding a complementary protective layer on the active layer in order to solve the physical limitation of the polyamide, which has a low chlorine resistance and chemical stability, despite excellent water permeability and foreign matter removal rate. .

Accordingly, the present invention aims to produce nanoseparation membranes that are stable even in extremely poor conditions such as high acidity as well as low acidity based on the composite membrane structure.

The present invention adds a chemically stable material PVA (Polyvinyl alcohol) as a protective layer to the polyamide active layer on the porous support to produce a chemically stable polyamide nano separator.

PVA satisfies three requirements that can be used as active layer materials of chemically stable nano-membrane: excellent chemical stability, good mechanical strength and ease of thin film formation, and easy control of crosslinking and crosslinking degree.

PVA is a water-soluble polymer in which the scanning chamber is formed of -C-C- covalent bond, which is one of the chemically stable structures, and has -OH group as a side group. Since PVA is formed in a chemically stable main chain structure, PVA is a very stable substance with little possibility of being affected chemically by the substance to be separated.

Since PVA is water soluble, it is easy to form a film by dipping or casting to an organic polymer support, and the mechanical strength of the formed film is excellent, so it is less likely to be damaged during operation of the membrane.

In addition, since PVA has a -OH group on the main chain, it is easy to crosslink using an aldehyde compound. In general, the reaction rate of the -OH group and the aldehyde group under an acid catalyst is very fast. Due to this rapid reaction rate, the degree of crosslinking of the PVA active layer can be easily controlled and the desired degree of crosslinking can be made within a short time. PVA having such characteristics is used in the present invention for forming a protective film of the polyamide active layer. Nano-membrane membrane having such a structure not only shows high permeability and foreign matter removal rate, but also is very stable in the range of pH 1-pH 13.

The present invention also relates to a method for producing a nano separator having a PVA layer as a protective layer on a polyamide composite.

As an example of a method for producing a nano-separation membrane having a PVA layer as a protective layer on a polyamide composite, for example, an active layer is coated on a porous support to prepare a polyamide composite membrane and maximize chemical stability while minimizing a decrease in the permeability of the composite membrane. A PVA layer with a thickness of as much as possible is coated on the surface of the polyamide active layer. Suitable thicknesses of the PVA layer are on the order of 0.01-0.1 μm. If the thickness of the PVA layer is smaller than 0.01 mu m, the function of protecting the polyamide active layer is inferior, while if the thickness of the PVA layer is larger than 0.1 mu m, the water permeability is poor.

In some cases, a PVA / ionomer mixed solution in which an ionomer is mixed in addition to the above PVA may be added to the polyamide active layer. As the ionomer, one or two or more substances selected from the group consisting of sodium alginate, chitosan, and sulfonated polystyrene may be used, and sodium alginate is particularly preferable. The PVA / ionomer mixing ratio is preferably 99/1 to 90/10 on a volume basis. If the mixing ratio is greater than 99/1, it is difficult to show the effect of ions, and if it is less than 90/10, there may be a problem in the crosslinking reaction.

The concentration of the PVA solution or PVA / ionomer mixed solution used for coating is preferably 0.01 to 1.0% by weight. The PVA solution or the PVA / ionomer mixed solution may use one or two or more substances selected from the group consisting of water and a weakly acidic aqueous solution as a solvent.

In some cases, it is necessary to crosslink the PVA solution layer and the PVA / ionomer solution layer in order to have better mechanical properties. For example, glutaraldehyde, formaldehyde, or a mixed aldehyde thereof is added under an acidic catalyst such as HCl, and crosslinked by treatment for 1 second to 10 minutes. In some cases, in order to prevent an excessive crosslinking reaction, isopropanol (IPA), ethanol (Ethanol: EtOH), methanol (Methanol: MeOH), acetone, or the like may be mixed. It is preferable that the mixing ratio of the mixed solution of the aldehyde compound and the organic solvent (for example, the mixed solution of Acetone / Glutaraldehyde) is 99/1 to 60/40. As the solvent, one or more substances selected from the group consisting of isopropanol, ethanol, methanol, acetone, and the like are used.

Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited by an Example.

The composite membranes prepared in the following examples were all tested under the following transmission test conditions.

Permeation test condition

In order to determine the permeation performance of the prepared composite membranes, a permeation experiment was conducted using a general reverse osmosis permeation test apparatus. The feed solution used was a 1000 ppm aqueous PEG 600 solution and the pressure used was 200 psi. In order to measure the amount of permeate, permeate was collected for a certain time, and the weight was measured and expressed in units of ㎥ / ㎡ day. Rejection percentage was calculated using the following equation, and the concentrations of feed solution and permeate were measured using HPLC.

% Clearance = [(C _f -C _p ) / C _f ] x 100

In the above formula, C _f represents the concentration of feed liquid and C _p represents the concentration of permeate.

In addition, in order to examine the chemical stability of the prepared composite membranes, these composite membranes were examined for stability in the range of pH 1 to pH 13, and the details are shown in the Examples.

EXAMPLE

Example 1 (composite membrane I)

A polysulfone ultrafiltration membrane (hereinafter referred to as a support) having a fractional molecular weight of 30,000 was immersed in an aqueous 1% piperazine solution for 1 minute. The piperazine aqueous solution used at this time was mixed with 1% triethylamine (Triethylamine). Remove the support from the piperazine aqueous solution, remove the excess solution remaining on the surface, and then use it for about 10 seconds in a hexane solution containing 0.5% by weight of trimesoyl chloride to interfacially polymerize the amine coated on the support. Soaked. In this way, a polyamide (PA) composite membrane having a polysulfone ultrafiltration membrane as a support was prepared.

In order to form the PVA active layer again on the surface of the prepared polyamide composite membrane, the prepared polyamide composite membrane was immersed in a 0.3 wt% PVA / Sodium alginate (SA) (95/5, volume%) solution prepared in advance for 1 minute and then taken out. It was hung and dried at room temperature in air. In order to crosslink the formed PVA active layer, the dried composite membrane was immersed in an isopropanol / glutaaldehyde (90/10; volume ratio) mixed solution as a crosslinking solution and immersed at room temperature for 1 minute. The PVA composite membrane I thus prepared was stored in distilled water for permeation experiment. The results of the permeation experiment are shown in Table 1.

Example 2 (Composite Membrane II)

Composite Membrane II was prepared by the method of Example 1, wherein the concentration of the PVA / SA aqueous solution used was 0.2% by weight. The permeation test results are shown in Table 1.

Example 3 (Composite Membrane III)

Composite membrane III was prepared by the method of Example 1, wherein the concentration of the PVA / SA aqueous solution used was 0.1% by weight. The results of the permeation experiment are shown in Table 1.

Example 4 Composite Membrane IV

Composite membrane IV was prepared by the method of Example 3, wherein the polymer solution used was 0.1 wt% aqueous PVA solution. The results of the permeation experiment are shown in Table 1.

Comparative Example 1 (Composite Film V)

A general polyamide composite membrane (composite membrane IV) was prepared in order to compare the chemical stability of the composite layers I, II, and III coated with the protective layer with the composite membrane without the protective layer. The manufacturing conditions of the composite film IV were the same as in Example 1, but at this time, PVA / SA was not coated. The results of the permeation experiment are shown in Table 1.

Example 4 (Chemical Treatment of Prepared Composite Membranes)

In order to confirm the chemical stability of the composite membranes I, II, III, IV, and V prepared above, an aqueous solution having pH 1, pH 12, and pH 13 was prepared using HCl, K ₂ CO ₃ , and NaOH. . The prepared composite membranes I, II, and III were immersed in each of the prepared solutions, and subjected to chemical treatment at room temperature for 17 hours. Thereafter, all of the composite membranes were taken out, rinsed with excess distilled water, and stored in distilled water for a predetermined time to remove all residual compounds remaining in the composite membrane, followed by permeation experiment. The results are shown in Table 2.

Table 1: Permeability of Composite Membranes I, II, III, IV and V

Separator Before treatment Permeability (㎥ / ㎡day) % Removal Membrane Ⅰ 1.06 98.9 Membrane Ⅱ 1.32 98.0 Membrane Ⅲ 2.04 98.0 Membrane Ⅳ 1.68 97.5 Separator Ⅴ 2.52 97.5

(Operating pressure: 200 psi, Feed solution: 1000 ppm PEG 600 aqueous solution)

Table 2: Permeability of Composite Membranes I, II, III, and IV after Chemical Treatment

Separator After treatment (at pH 1) After treatment (at pH 12) After treatment (at pH 13) Permeability (㎥ / ㎡day) % Removal Permeability (㎥ / ㎡day) % Removal Permeability (㎥ / ㎡day) % Removal Membrane Ⅰ 1.27 98.5 1.12 98.5 1.20 97.6 Membrane Ⅱ 1.42 98.0 1.50 98.4 1.55 97.5 Membrane Ⅲ 1.90 98.0 2.01 98.5 2.10 97.0 Membrane Ⅳ 1.70 97.6 1.69 98.0 1.70 97.2 Separator Ⅴ 2.50 97.5 2.72 94.4 4.32 0

(Operating pressure: 200 psi, Feed solution: 1000 ppm PEG 600 aqueous solution)

Example 5 Composite Membrane VI, VI, VI

A composite membrane was prepared by the method of Example 1, but the concentration of PVA / SA solution was 0.1% by weight, and the immersion time in the isopropanol / glutaaldehyde (90/10; volume ratio) mixed solution, which is a crosslinking solution, was respectively 2 minutes (composite membrane). VI), 3 minutes (composite membrane VII) and 5 minutes (composite membrane VII). In order to confirm the chemical stability of the composite membranes thus prepared, a chemical treatment and a permeation experiment were performed using the NaOH solution (pH 13) by the method described in Example 4. The results are shown in Table 3 below.

Table 3: Permeability of Composite Membranes Ⅴ, Ⅵ, Ⅶ

Separator Before treatment After treatment (at pH 13) Permeability (㎥ / ㎡day) % Removal Permeability (㎥ / ㎡day) % Removal Separation membrane Ⅵ 1.82 98.5 1.85 98.0 Membrane Ⅶ 1.60 98.7 1.63 98.1 Membrane Ⅷ 1.24 98.7 1.25 98.5

When a polyamide composite having a PVA layer as a protective layer is used as a nano separation membrane, not only does it exhibit high water permeability and foreign matter removal rate, but also has excellent chemical stability, such as being usable at a wide range of pH, for example.

Claims (8)

A polyamide nanoseparation membrane comprising a crosslinked polyvinyl alcohol layer as a protective layer on a polyamide composite composed of a porous support and a polyamide active layer. The polyamide nano separator of claim 1, wherein the crosslinked polyvinyl alcohol layer has a thickness of 0.01 μm to 0.1 μm. A method for producing a polyamide nanoseparation membrane, comprising adding a polyvinyl alcohol (PVA) solution onto a polyamide composite composed of a porous support and a polyamide active layer. The polyvinyl alcohol solution of claim 3, wherein the PVA solution is mixed with one or two or more ionomers selected from the group consisting of sodium alginate, chitosan, and sulfonated polystyrene. Method for producing a polyamide nano separation membrane, characterized in that added to the amide active layer. The method of claim 4, wherein the mixing ratio of PVA / ionomer is 99/1 to 90/10 based on the volume, and the concentration of the mixed solution is 0.01 to 1.0% by weight. The crosslinking according to any one of claims 3 to 5, wherein glutaraldehyde, formaldehyde, or a mixed aldehyde thereof is added to the coated PVA protective layer under an acidic catalyst and treated for 1 second to 10 minutes. Method for producing a polyamide nano separation membrane, characterized in that. The method of claim 6, wherein the aldehyde compound solution is mixed with one or two or more organic solvents selected from the group consisting of organic solvents mixed with water such as isopropanol, ethanol, methanol, acetone, and the like. The method of claim 7, wherein the mixing ratio (alcohol / aldehyde compound: volume ratio) of the mixed solution of the alcohol and the aldehyde compound is 99/1 to 60/40.