KR20120009820A - Method of producing forward osmosis membranes based on acetylated alkyl cellulose - Google Patents

Abstract

PURPOSE: A forward osmosis membrane based on acetylated alkyl cellulose and a method for manufacturing the same are provided to reduce energy consumption by implementing permeation based on osmotic pressure-based diffusion. CONSTITUTION: A forward osmosis membrane includes an acetylated alkyl cellulose porous support and a polyamide layer. The substitution degree of alkyl group in acetylated alkyl cellulose is between 0.1 and 2.9. The alkyl group in the acetylated alkyl cellulose is methyl group, ethyl group, propyl group, hydroxyethyl group, or hydroxypropyl group. The pore size of the porous support is between 1 and 1000nm. The thickness of the porous support is between 5 and 300um. The polyamide layer is formed by the reaction of multi-functional amine compound and amine reactive compound. The multi-functional amine compound is the compound of one or two selected from m-phenylene diamine, p-phenylene diamine, piperazine, and the derivative thereof.

Description

Separation membrane for forward osmosis using acetylated alkyl cellulose and its preparation method {Method of producing forward osmosis membranes based on acetylated alkyl cellulose}

The present invention relates to a polyamide composite membrane for forward osmosis, wherein a porous support is prepared on the basis of acetylated alkyl cellulose, and the surface of the support is coated with polyamide, and a method of manufacturing the same.

Forward osmosis is a membrane placed between a concentrated solution (draw solution) and a dilute solution that can cause osmotic pressure, and water moves from the dilute solution to the concentrated solution, and the solute is concentrated in the thick solution. It is the phenomenon of moving to a dilute solution. At this time, the membrane is hydrophilic and should have affinity with respect to water and the material that can limit the movement of the solute is most preferred. Due to this particularity, the membrane for forward osmosis is difficult to meet the performance when using a commercially available polymer.

Cellulose-based polymers have been shown to be more hydrophilic than other commercially available polymers, and thus are preferred as a membrane material for forward osmosis. However, in the case of commercialized cellulose-based polymer membranes, there is a problem that the physical properties are low due to the low molecular weight, and the problem that the solute is permeated from the induction solution occurs, which requires more research.

The forward osmosis membrane has a fundamentally different structure from the reverse osmosis membrane. Since the reverse osmosis membrane is composed of a structure that removes the solute by pressurizing more than the osmotic pressure of the solute contained in the feed, the active layer does not have much relation to the structure and properties of the support layer, and the active layer determines the overall characteristics. For this reason, in the reverse osmosis membrane, the polyamide thin film layer by interfacial polymerization is used as the active layer, because the active layer has a thinner and dense structure than the separator prepared by the phase inversion method.

On the other hand, in the case of the forward osmosis membrane, the two layers are in contact with water basically around the separation membrane, so the support layer as well as the active layer greatly influence the performance. For this reason, a polymer material having good affinity with water should be used as the support layer. The active layer of the forward osmosis membrane may be determined according to the type of solute to be removed, and the better the effective diffusion of the induced solution into the feed side, the more effective the separation membrane.

US Patent Publication No. 2006-0226067 prepared a membrane for forward osmosis using cellulose polymers (cellulose acetate, cellulose triacetate, cellulose acetyl propionate, cellulose acetyl butyrate, etc.) and examines the characteristics of forward osmosis. In this patent, in particular, an attempt was made to reduce the membrane thickness in order to increase the permeate flow rate. For this purpose, the permeation rate was maximized by impregnating a polyester mesh between the membrane cross-sections, but there was a problem in that the removal rate (desort diffusion of the solute) was lowered.

The type of commercialized cellulose polymer is limited, and has been attempted to improve the performance by the manufacturing method rather than the characteristics of the polymer material for improving the performance. Recently, as interest in forward osmosis membranes increases, announcements related to forward osmosis membranes have also increased. Professor M. Elimelech of Yale University in the United States has published a study to express the performance of forward osmosis membranes in a paper related to the osmosis membrane. Since then, a number of papers related to the manufacture of forward osmosis membranes have been published.

However, most of the papers published until now are basically trying to improve the performance by using commercially available polymers, which shows a lot of limitations to significantly improve the performance of the forward osmosis membrane.

Therefore, the present inventors have studied and tried to solve the problems of the prior art to produce a forward osmosis membrane support by synthesizing a novel cellulose-based polymer material with excellent hydrophilicity and to support the polyamide layer by interfacial polymerization to reduce the back diffusion of the solute The present invention has been completed by discovering that the performance of the forward osmosis membrane can be maximized by coating on it.

Accordingly, an object of the present invention is to provide a polyamide composite membrane for forward osmosis comprising an acetylated alkyl cellulose porous support and a polyamide layer, and a method for preparing the same.

The present invention provides an acetylated alkyl cellulose porous support; And a polyamide composite membrane for forward osmosis comprising a polyamide layer.

In addition, the present invention (a) after immersing the acetylated alkyl cellulose porous support in the polyfunctional amine aqueous solution to remove the excess amine aqueous solution; (b) contacting the porous support with an organic solution in which an amine reactive compound is dissolved to perform an interfacial polymerization reaction; And (c) immersing the product by interfacial polymerization in a basic aqueous solution and then washing with water.

The polyamide composite membrane for forward osmosis of the present invention prepared by the above method is coated with polyamide on an acetylated alkyl cellulose porous support, and the permeation flow rate is much better than that of polyamide coated on other types of polymeric porous separators. The advantage is that less despreading occurs.

In addition, the forward osmosis membrane according to the present invention can be effectively used for seawater desalination, sewage and wastewater treatment, and bio-compound concentration, because less energy is consumed and no change in feed occurs because it is permeated by diffusion by osmotic pressure.

The present invention relates to a polyamide composite membrane for forward osmosis comprising an acetylated alkyl cellulose porous support and a polyamide coating layer, the method for producing a polyamide composite membrane for forward osmosis (a) an acetylated alkyl cellulose porous support Removing the excess amine aqueous solution after immersion in the polyfunctional amine aqueous solution; (b) contacting the porous support with an organic solution in which an amine reactive compound is dissolved to perform an interfacial polymerization reaction; And (c) rinsing the product by the interfacial polymerization in a basic aqueous solution and then washing with water.

In the case of cellulose-based polymers, which are commercially available hydrophilic polymers, hydrolysis proceeds a lot in the process of acetylation, thereby decreasing molecular weight. Also, the types of cellulose-based polymers are limited. There was this. The present invention solves the above problems by acetylating alkyl cellulose, which is a water-soluble cellulose polymer, and preparing a forward osmosis membrane using the polymer, and has a higher permeation flow rate than other cellulose-based polymers and inversely through polyamide interfacial polymerization. It is characterized by providing a polyamide composite membrane for forward osmosis that can effectively prevent diffusion.

Hereinafter, the method of preparing a polyamide composite membrane for forward osmosis using the acetylated alkyl cellulose of the present invention will be described in more detail by dividing each step.

First, an acetylated alkyl cellulose porous support is prepared.

The acetylated alkyl cellulose refers to alkylation of a part of the hydroxy group of cellulose, and the alkylation means substitution of C ₁ to C ₆ alkyl or C ₁ to C ₆ hydroxyalkyl, and the like. , Methyl, ethyl, propyl, hydroxyethyl or hydroxypropyl and the like. It means that at least one or more of the hydroxy group of the cellulose is substituted with an alkyl group before acetylation, that is, a part of the hydroxy group of the cellulose means an alkyl group, a part is acetylated. Substitution degree of an alkyl group (when substituted by the maximum, substitution degree becomes 3) It is preferable to use what became 0.1-2.9. The degree of substitution means the degree to which the hydroxy group contained in the cellulose unit structure is substituted with another compound, and when one of the three hydroxy groups is substituted, one and two are substituted, and the degree of substitution is three when all three are substituted. . Acetylation means that 5-100% of the remaining unsubstituted hydroxy groups are acetylated.

Porous support using acetylated alkyl cellulose according to the present invention is dissolved in the acetylated alkyl cellulose in one or two or more solvents selected from the group consisting of a good solvent, poor solvent and non-solvent by a phase inversion method It can be prepared by going through a phase inversion process. As the phase inversion method, a known method such as a non-solvent induction phase separation method or a thermal induction phase separation method may be used. For example, the phase change may be performed by dissolving the polymer in a solvent system including a good solvent and precipitating the non-solvent to form pores.

As the good solvent, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, N-methyl-2-pyrrolidone or dimethyl sulfoxide may be used. The poor solvents include aliphatic and cyclic ketones such as acetone, methyl ethyl ketone, and gamma-butylyrolactone, dichloromethane, dichloroethane. Alkylated halides such as these, or cyclic ethers such as 1,4-dioxane, 1,3-dioxolane, and 1,3-dioxolane may be used. The non-solvent may be methanol. ), Alcohols such as ethanol, lactic acid, benzoic acid, aliphatic carboxylic acid such as toluene sulfonic acid, aromatic carboxylic acid, aliphatic sulfonic acid or aromatic sulfonic acid group can be used. By dissolving in various solvents as described above, the pore size of the porous support can be controlled, which greatly affects the permeation performance of the forward osmosis membrane.

The acetylated alkyl cellulose porous support has a pore size of 1 to 1000 nm, and when the pore size is less than 1 nm, the pores are too small so that the interfacial polymerization layer can not penetrate into the pores and maintain strength, 1000 nm. If it exceeds, there is a problem that the interfacial polymerization is not easily made due to the amine solution exits into the pores. The thickness of the acetylated alkyl cellulose porous support is preferably adjusted to 5 ~ 300 ㎛.

Thereafter, the prepared acetylated alkyl cellulose porous support is immersed in the polyfunctional amine aqueous solution, and then the excess amine aqueous solution is removed.

As for the polyfunctional amine compound used for the said polyfunctional amine aqueous solution, the monomolecular amine which has at least 2 or more amine functional group, More preferably, 2 to 3 amine functional group is preferable. In the present invention, the polyfunctional amine compound is not particularly limited, but preferably meta-phenylene diamine, para-phenylene diamine, p-phenylene diamine, piperazine and the substance. One or two or more compounds selected from the group consisting of derivatives thereof may be used. The polyfunctional amine compound is preferably used in an aqueous solution of 0.05 to 10% by weight, preferably 0.1 to 5% by weight. The immersion process is preferably performed for 5 seconds to 5 minutes in an aqueous polyfunctional amine solution, more preferably 10 seconds to 3 minutes.

Preferably, an organic sulfonic acid such as camphor sulfonic acid, a polar solvent such as dimethylsulfoxide, a diol such as triethyleneglycol, or sodium dodecyl sulfate as an additive to the polyfunctional amine aqueous solution. Surfactants such as sodium dodecyl sulfate may be used by adding 0.1 to 5% by weight in aqueous solution. By adding the additive, there is an advantage that the permeation flow rate can be greatly improved by increasing the roughness of the surface.

After removing the excess amine aqueous solution, the obtained porous support is brought into contact with the organic solution in which the amine-reactive compound is dissolved to perform an interfacial polymerization reaction. This process forms a polyamide layer on the porous support.

The amine-reactive compound may be used one or two or more compounds selected from the group consisting of polyfunctional acyl halides, polyfunctional sulfonyl halides, polyfunctional isocyanates and derivatives of the above substances, and the amine reactive compound may be used in 0.01% It is preferable to use it at -2 weight%, More preferably, it is used at 0.02-1 weight%. The interfacial polymerization reaction is preferably in the range of 5 seconds to 5 minutes, more preferably 10 seconds to 3 minutes. As the organic solvent used in the organic solution, it is preferable to use an alkane mixture (isoparaffin) such as alkanes having 6 to 14 carbon atoms or ISOL-C.

Hydrogen chloride (HCl) generated during interfacial polymerization can be removed using a basic reagent that can neutralize it. For example, amines such as triethylamine or caustic soda may be used.

The product is then dried at −10 to 90 ° C., preferably at 40 to 70 ° C. for 0.5 to 10 minutes, immersed in a basic aqueous solution and washed with water. As the basic aqueous solution, for example, an aqueous sodium carbonate solution of 0.05 to 3% by weight, preferably 0.1 to 1% by weight may be used. The non-reacted material may be removed through the dipping process, followed by washing with distilled water.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by the following Examples.

Manufacturing example

As alkyl cellulose, 10% by weight of methyl cellulose (PMA, Samsung Fine Chemicals, DS: 1.7), ethyl cellulose, hydroxyethyl cellulose, propyl cellulose, and hydroxypropyl cellulose were added to 90% by weight of pyridine, followed by acetylation degree. In order to adjust the molar ratio of acetic anhydride to 3 per unit alkyl cellulose unit was reacted for 3 hours at 90 ℃, and then solidified in water to prepare a polymer having a degree of acetylation of about 100% (AMC ₁₀₀ ).

Example  One : Acetylated methyl  cellulose( AMC Porous support using

A solution of 7% by weight of acetylated methyl cellulose, 30% by weight of acetone, 59% by weight of 1,4-dioxane, 2% by weight of methanol, and 2% by weight of maleic acid Cast into a 50 micron thick knife and solidify in water. The solvent was then removed. The pore size was fraction 100,000 when PEG was tested with polyethylene glycol (PEG).

Comparative example  1 to 7: porous support using conventional cellulose

Cellulose triacetate (CTA), cellulose acetate (CA), cellulose acetate butyrate (CAB), cellulose acetate propionate (CAP), polysulfone (PSf), polyether sulfone (CET) instead of the acetylated methyl cellulose of Example 1 A forward osmosis membrane was prepared in the same manner as in Example 1 except that PES) and polyacrylonitrile (PAN) were used as polymers. For comparison under the same conditions as in Example 1, in order to control the pore size, an additive was added to the polymer solution to adjust the fraction molecular weight to PEG 100,000.

Experimental Example  1: Permeation Experiment of Porous Support by Different Polymer Materials

This experiment was conducted to compare the permeation performance of the novel AMC and the existing cellulose of the present invention. The permeation experiment was carried out after the two membranes were filled on both sides with a separator interposed therebetween, one side of distilled water and the other side using a 20 wt% NaCl aqueous solution. Water moved from the distilled water to the induction solution, and the permeate flow rate was calculated by measuring the mass of the permeated solution. NaCl moves to the distilled water in the induction solution, and the salt transferred to the distilled water is expressed as conductivity (μS / cm). Conductivity was measured using a conductivity meter (Lamotte).

Table 1 shows the results of the polymer difference.

Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Polymer AMC CTA CA CAB CAP PSf PES PAN Permeate flow rate
(L / m ² hr) 90 42 34 41 29 2.1 6.1 1.3 Despread conductivity
(uS / cm) 12,000 9,500 8,400 11,000 88,000 5,000 7,500 4,000

As shown in Table 1, in Example 1 of the present invention, the permeate flow rate was 90 L / m ² hr, and the conductivity of the despread salt was 12,000 μS / cm, and the permeation rate was higher than that of the conventional cellulose polymer. It was confirmed that the flow rate was remarkably high.

Experimental Example  2 : Acetylated methyl  cellulose( AMC Permeation experiment according to the thickness of the porous support using

The forward osmosis membrane was prepared in the same manner as in Example 1, and the experiment was performed while changing the casting thickness as shown in Table 2 below.

The results are shown in Table 2 below.

50um 100um 150um 200um 250um Permeate flow rate
(L / m ² hr) 90 81 54 25 18 Despread conductivity
(μS / cm) 12,000 9,200 5,800 2,800 2,200

As shown in Table 2, the AMC of the present invention has excellent overall permeate flow rate, and is characterized by a rapid increase in permeate flow rate by reducing the thickness.

Example  2 : Acetylated methyl  Cellulose Forward osmosis  Polyamide Composite membrane

Polyamide interfacial polymerization was carried out on the acetylated methyl cellulose (AMC) porous support prepared in Example 1. First, the AMC porous support was immersed in an aqueous solution of 2% by weight of meta-phenylene diamine (MPD) and 1% by weight of triethylamine (TEA) for 1 minute. After the excess amine solution was removed, it was immersed in an organic solution in which 0.1% by weight of trimezoyl chloride (TMC) was dissolved in an ISOL-C solvent for 1 minute, and then dried at 60 ° C for 1 minute. After washing for 1 hour at room temperature in Na ₂ CO ₃ 0.1 wt% aqueous solution to prepare a polyamide composite membrane for forward osmosis using acetylated methyl cellulose.

Experimental Example  3: depending on the polyamide concentration used Forward osmosis  Polyamide Of composite membrane  Permeation Experiment

When the concentration of MPD, TEA and TMC was changed, the permeation experiment was carried out by preparing a composite membrane in the same manner as in Example 2 with the concentration of TEA and TMC at the rate of decreasing MPD. For example, when reducing MDP by 50% from 2% to 1%, TEA decreased from 1% to 0.5% by weight and TMC from 0.1% to 0.05% by weight.

The results are shown in Table 3 below.

MPD / TEA / TMC concentration (% by weight) 2/1 / 0.1 1 / 0.5 / 0.05 0.5 / 0.25 / 0.025 0 Permeate flow rate
(L / m ² hr) 11.3 13.1 18.9 90 Despread conductivity
(μS / cm) 220 410 1,000 12,000

As shown in Table 3, as the concentration of the monomer is increased during the polyamide production, the permeate flow rate decreases, and it can be seen that the conductivity of the reverse diffusion acid decreases.

Experimental Example  4: due to polymer material difference Forward osmosis  Polyamide Of composite membrane  Permeation Experiment

Interfacial polymerization was carried out in the same manner as in Example 2, except that the support before interfacial polymerization was changed as shown in Table 4 below. However, MPD concentration was carried out by interfacial polymerization at 0.5% by weight, and the support was prepared by fixing the casting thickness to 50 μm.

The results are shown in Table 4 below.

AMC CTA CA CAB CAP PSf PES PAN Permeate flow rate
(L / m ² hr) 23.1 13.1 9.1 10.2 11.1 0.23 3.8 0.56 Despread conductivity
(μS / cm) 520 450 350 370 530 81.1 150 210

As can be seen in Table 4, the polyamide composite membrane for forward osmosis according to the present invention has an excellent permeation flow rate of 23.1 L / m ² hr compared to the composite membrane using other cellulose, it was able to effectively prevent the back diffusion.

Taken together, the polyamide composite membrane for forward osmosis according to the present invention exhibits a higher permeation flow rate than other commercially available polymers using acetylated methyl cellulose as a support, and inversely, polyamide interfacial polymerization is performed on it. While maintaining the concentration of the salt to be diffused significantly lower than other polymers can still maintain a good permeate flow rate, it can be used as a good forward osmosis membrane.

Claims (13)

Acetylated alkyl cellulose porous support; And
Polyamide layer
Polyamide composite membrane for forward osmosis comprising a.
According to claim 1, wherein the acetylated alkyl cellulose polyamide composite membrane for forward osmosis, characterized in that the substitution degree of the alkyl group is 0.1 ~ 2.9.
The polyamide composite membrane for forward osmosis according to claim 1, wherein the alkyl group in the acetylated alkyl cellulose is methyl, ethyl, propyl, hydroxyethyl or hydroxypropyl.
The polyamide composite membrane according to claim 1, wherein the acetylated alkyl cellulose porous support has a pore size in the range of 1 to 1000 nm and a thickness in the range of 5 to 300 μm.
The method of claim 1, wherein the acetylated alkyl cellulose porous support is a phase inversion of the acetylated alkyl cellulose in one or two or more solvents selected from the group consisting of a good solvent, poor solvent and non-solvent Polyamide composite membrane for forward osmosis, characterized in that formed through.
The polyamide composite membrane according to claim 1, wherein the polyamide layer is formed by reacting a polyfunctional amine compound with an amine reactive compound.
The method of claim 6, wherein the multifunctional amine compound is in the group consisting of meta-phenylene diamine (m-phenylene diamine), para-phenylene diamine (p-phenylene diamine), piperazine (piperazine) and derivatives of the above substances A polyamide composite membrane for forward osmosis, characterized in that the selected one or two or more compounds.
7. The method of claim 6, wherein the amine reactive compound is one or two or more compounds selected from the group consisting of polyfunctional acyl halides, polyfunctional sulfonyl halides, polyfunctional isocyanates and derivatives of the above substances. Polyamide composite membrane.
(a) immersing the acetylated alkyl cellulose porous support in the polyfunctional amine aqueous solution and then removing the excess amine aqueous solution;
(b) contacting the porous support with an organic solution in which an amine reactive compound is dissolved to perform an interfacial polymerization reaction; And
(c) washing the product by the interfacial polymerization in a basic aqueous solution and then washing with water
Method for producing a polyamide composite membrane for forward osmosis comprising a.
10. The method of claim 9, wherein the acetylated alkyl cellulose porous support of step (a) is prepared by dissolving the acetylated alkyl cellulose in one or two or more solvents selected from the group consisting of good solvents, poor solvents and nonsolvents. Method for producing a polyamide composite membrane for forward osmosis, characterized in that it was prepared through a phase inversion process.
The method of claim 10, wherein the good solvent is dimethylformamide (dimethylformamide), dimethylacetamide (dimethylacetamide), N-methyl-2-pyrrolidone (N-methyl-2-pyrrolidone) or dimethyl sulfoxide (dimethylsulfoxide) Method for producing a polyamide composite membrane for forward osmosis characterized in that.
The method of claim 10, wherein the poor solvent is acetone (acetone), methyl ethyl ketone (methyl ethyl ketone), gamma- butyrolactone (r-butyrolactone), dichloromethane (dichloromethane), dichloroethane (1, A method for producing a polyamide composite membrane for forward osmosis, characterized in that it is 4-dioxane (1,4-dioxane) or 1,3-dioxolane (1,3-dioxolane).
The non-solvent according to claim 10, wherein the non-solvent is methanol, ethanol, lactic acid, benzoic acid, toluene sulfonic acid, aromatic carboxylic acid, aliphatic sulfonic acid or aromatic sulfonic acid. Method for producing a polyamide composite membrane for forward osmosis characterized in that.