阅读说明：本技术 反渗透膜和反渗透膜的制造方法 (Reverse osmosis membrane and method for producing reverse osmosis membrane ) 是由 北野宏树 山口晃生 远藤守信 奥提兹·梅迪纳·约苏埃 于 2019-01-24 设计创作，主要内容包括：本发明的反渗透膜具备：多孔性支承基材(2)；以及形成于多孔性支承基材(2)的表面,由含有组织化的碳的碳膜构成的分离活性层(3)。(The reverse osmosis membrane of the present invention comprises: a porous support base material (2); and a separation active layer (3) formed on the surface of the porous support base (2) and composed of a carbon film containing organized carbon.)

1. A reverse osmosis membrane comprising:

a porous support substrate; and

and a separation active layer formed on the surface of the porous support base and composed of a carbon film containing organized carbon.

2. A reverse osmosis membrane according to claim 1,

the salt rejection rate when desalting an NaCl aqueous solution having a concentration of 3.2 mass% under a filtration pressure of 5.5MPa or more is 99% or more.

3. A reverse osmosis membrane according to claim 1 or claim 2,

the porous support substrate comprises: a non-woven fabric-like backing layer; and a porous plastic layer formed on the backing layer.

4. A method of manufacturing a reverse osmosis membrane, comprising:

a coating film forming step of forming a coating film that is soluble in a predetermined solvent on a surface of a porous support base that is insoluble in the solvent;

a pre-carbon film forming step of forming a pre-carbon film on the coating film by a physical vapor deposition method using carbon as a target material;

a coating film removal step of removing the coating film by dissolving the coating film with the solvent after the carbon film is formed; and

and a texturizing step of compressing the pre-carbon film to form a separation active layer composed of a carbon film containing texturized carbon.

Technical Field

The present invention relates to a reverse osmosis membrane and a method for producing a reverse osmosis membrane.

Background

As a separation active layer in a Reverse Osmosis Membrane (RO Membrane), use of a carbon Membrane has been attempted. For example, patent document 1 describes a reverse osmosis membrane using a hard carbon film (diamond-like carbon film) as a separation active layer.

Patent document 2 describes a reverse osmosis membrane using a carbon membrane having an amorphous carbon structure containing nitrogen atoms as a separation active layer.

Disclosure of Invention

An object of the present invention is to provide a reverse osmosis membrane using a carbon membrane having excellent desalting performance (separation performance) as a separation active layer.

(means for solving the problems)

The technical scheme is as follows. That is to say that the first and second electrodes,

<1> a reverse osmosis membrane comprising: a porous support substrate; and a separation active layer formed on the surface of the porous support base and composed of a carbon film containing organized carbon.

<2> the reverse osmosis membrane according to <1>, wherein a salt rejection is 99% or more when an aqueous NaCl solution (concentration: 3.2 mass%) is desalted under a filtration pressure of 5.5MPa or more.

<3> the reverse osmosis membrane according to <1> or <2>, wherein the porous support base material comprises: a non-woven fabric-like backing layer; and a porous plastic layer formed on the backing layer.

<4> a method for producing a reverse osmosis membrane, comprising: a coating film forming step of forming a coating film that is soluble in a predetermined solvent on a surface of a porous support base that is insoluble in the solvent; a pre-carbon film forming step of forming a pre-carbon film on the coating film by a physical vapor deposition method using carbon as a target material; a coating film removal step of removing the coating film by dissolving the coating film with the solvent after the carbon film is formed; and a texturizing step of compressing the pre-carbon film to form a separation active layer composed of a carbon film containing texturized carbon.

(advantageous effects)

According to the invention of the present application, a reverse osmosis membrane using a carbon membrane having excellent desalting performance (separation performance) or the like as a separation active layer can be provided.

Drawings

Fig. 1 is an explanatory view schematically showing a cross-sectional structure of a reverse osmosis membrane.

Fig. 2 is a schematic view of a cross-flow filtration type filtration apparatus.

Fig. 3 is a graph showing the evaluation results of water permeation/desalination in each of the membranes of example 1 and comparative example 1.

Fig. 4 is a graph showing diffraction patterns of the films of samples 1 to 3 obtained by TEM.

FIG. 5 is a graph in which the relationship between the intensity and the distance of the diffraction pattern in each of the films of samples 1 to 3 shown in FIG. 4 is extracted from a line inclined at 45 DEG through the center.

Detailed Description

[ reverse osmosis membrane ]

Fig. 1 is an explanatory view schematically showing a cross-sectional structure of a reverse osmosis membrane 1. The reverse osmosis membrane 1 comprises: a porous base material 2; and a separation active layer 3 formed on the surface of the porous support base 2 and composed of a carbon film containing organized carbon.

The reverse osmosis membrane 1 filters a solution to be filtered, thereby separating a specific substance contained in the solution from the solution. For example, when the solution to be filtered is brine, the reverse osmosis membrane 1 filters the brine (sodium chloride aqueous solution) to remove pure water and salt (NaCl) from the brine. This is presumed to be that water molecules in the brine are introduced so as to be dissolved in the carbon film as the separation active layer 3, and move diffusively in the carbon film. It is also assumed that sodium ions and chloride ions in the brine are in a cluster state with at least a plurality of water molecules, and are prevented from entering the carbon film.

(porous support base)

The porous support substrate 2 is a member for supporting the porosity of the separation active layer 3, and is in the form of a sheet, and as the porous support substrate 2, a so-called nanofiltration membrane (NF membrane) or ultrafiltration membrane (UF membrane) may be used, and the pure water permeability L p of the porous support substrate 2 is not particularly limited as long as the object of the present invention is not impaired, and is, for example, 200L/(m membrane)²·h·MPa)～3500L/(m²·h·MPa)。

As the porous support base material 2, for example, a base material having a two-layer structure including a backing layer 2A in a nonwoven fabric form and a porous plastic layer 2B formed on the surface of the backing layer 2A can be used.

The backing layer 2A is formed of resin fibers in a nonwoven fabric shape, and is in a sheet shape (layer shape). As the resin used for the backing layer 2A, a resin insoluble in an impregnation liquid (solvent) described later is selected. Examples of the resin used for the backing layer 2A include polyester resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT); polyolefin resins such as ethylene and propylene. The backing layer 2A is made of nonwoven fabric and thus has liquid permeability.

The porous plastic layer 2B is composed of a porous plastic layer (sheet) laminated on the surface of the backing layer 2A. The porous plastic layer 2B has a plurality of pores of about 0.001 to 10 μm penetrating in the thickness direction.

As the plastic material (resin material) constituting the porous plastic layer 2B, a material that is insoluble in an impregnation liquid (solvent) described later and can maintain the shape in a state where pores are formed is selected. Examples of the plastic material (resin material) used for the porous plastic layer 2B include Polysulfone (PSF), Polyacrylonitrile (PAN), and the like. The method for forming the pores in the porous plastic layer 2B is not particularly limited, and the pores can be formed by a known method as appropriate.

The thickness of the porous support base material 2 is not particularly limited as long as the object of the present invention is not impaired, and may be appropriately set according to the object, and may be set in a range of, for example, 20 μm to 100 μm.

Examples of commercially available porous support substrates include UF membranes (trade name "GR 40 PP", manufactured by Alfa L aval Co., Ltd.), UF membranes (trade name "MW 2450F 30", manufactured by General Electric Co., Ltd.), and the like.

The porous support base material 2 may be laminated with other layers as long as the object of the present invention is not impaired. The porous support base material 2 may have a shape other than a sheet shape as long as the object of the present invention is not impaired.

(separation of active layer)

The separation active layer 3 is formed of a carbon film containing organized carbon, and has a function of separating a specific substance contained in a solution from the solution. In the separation active layer 3, pores having a size as seen in the porous plastic layer 2B of the porous support substrate 2 are not formed. It is presumed that the separation active layer 3 does not have a constant through-hole, and has a hole with a changing shape.

The separation active layer 3 is formed on at least the surface of the porous support substrate 2 that is in contact with the solution to be filtered. In the case of the present embodiment, in the sheet-like porous support substrate 2, the separation active layer 3 is formed on one substrate surface.

The separation active layer 3 is composed of a carbon film containing locally organized carbon. In the present specification, "organized carbon" refers to a film structure in which a specific and significant periodic distance is formed between carbon atoms in amorphous carbon (diamond-like carbon) having no specific structural periodicity. The carbon structure and the crystallization are different concepts, and the presence of the carbon structure is estimated from the analysis result of the carbon film by TEM described later. The separation active layer (carbon film) 3 is only required to have at least a part of carbon organized, and it is not necessary to have the entire carbon of the carbon film 3 organized.

In the separation active layer 3, carbon (other than carbon atoms) may contain other atoms such as nitrogen atoms.

For example, in the texturing step described later, the separation active layer 3 is formed by compressing the amorphous pre-carbon film under high pressure. The method for forming the separation active layer 3 (the carbon film containing organized carbon) is not particularly limited as long as the object of the present invention is not impaired, and for example, the separation active layer 3 (the carbon film containing organized carbon) may be formed through a step other than the organizing step described later. For example, the separation active layer according to another embodiment may be structured by heating the pre-carbon film, or may be formed by using a film formation pressure.

The thickness of the separation active layer 3 may be set to, for example, a range of 5nm to 100nm, as long as the object of the present invention is not impaired.

[ method for producing reverse osmosis membrane ]

The method for producing a reverse osmosis membrane according to the present embodiment includes: a coating film forming step, a pre-carbon film forming step, a coating film removing step, and a texturing step.

(coating film formation step)

The coating film forming step is a step of forming a coating film that is soluble in a predetermined solvent on the surface of the porous support base material 2 that is unnecessary in the solvent.

Before the separation active layer 3 is formed, a coating film is formed on the surface of the porous support base 2 in advance. The coating film is formed so as to cover the surface of the porous plastic layer 2B while blocking the pores of the porous plastic layer 2B of the porous support substrate 2.

The coating film is not particularly limited as long as it can be removed by a predetermined solvent in a coating film removal step described later, and may be appropriately selected from known resin materials and known solvents according to the purpose. Examples of such a coating film include a PVP solution obtained by dissolving polyvinylpyrrolidone (PVP) powder in a mixed solvent of water and ethanol.

The method of forming the coating film on the surface of the porous support base material 2 (the surface of the porous plastic layer 2B) is not particularly limited, and a known coating method can be applied. For example, a method of forming a coating film on the surface of a porous support base material by immersing the porous support base material in a predetermined container containing a coating solution for forming a coating film for a predetermined time and then pulling up the porous support base material from the coating solution may be mentioned. The coating film on the porous support base material 2 is dried appropriately.

The thickness of the coating film is not particularly limited as long as the object of the present invention is not impaired, and may be, for example, 1mg/cm per unit area of the surface of the porous support base material²～20mg/cm²The range of (solid component) is given to the coating solution for forming the coating film.

(Pre-carbon film formation Process)

The pre-carbon film forming step is a step of forming a pre-carbon film serving as a base of the separation active layer 3 on the coating film by a physical vapor deposition method using carbon as a target. The pre-carbon film is an amorphous carbon film that is not compressed (not structured) in a structuring step described later.

The pre-carbon film is formed as a coating film laminated on the porous support base 2 by a physical vapor deposition method using carbon as a target. As the physical vapor deposition method, for example, a High current pulse Magnetron Sputtering method (HiPIMS: High Power Impulse Magnetron Sputtering) and the like are mentioned as described later.

The carbon used as the target is not particularly limited as long as the object of the present invention is not impaired, and for example, high-purity graphite is preferable, and graphite having a purity of 5N or more (purity of 99.999% or more) is particularly preferable.

In the pre-carbon film forming step, a physical vapor deposition method such as HiPIMS for forming a pre-carbon film is performed in an atmosphere containing a rare gas. Further, the reaction may be carried out in an atmosphere containing a rare gas and nitrogen gas, as required.

Examples of the rare gas include argon (Ar), neon (Ne), krypton (Kr), and xenon (Xe).

The nitrogen gas may be used together with a rare gas such as argon when forming the pre-carbon film. In view of improving the high desalting performance and high water permeability of the finally obtained separation active layer 3, it is preferable to use nitrogen gas in combination.

The ratio of the rare gas to the nitrogen gas in the process gas during the formation of the pre-carbon film is set to 1: 0.1 to 1: 10, for example, where the ratio of the rare gas (Ar) to the nitrogen gas is 1: 0.1 to 1: 10.

The thickness of the pre-carbon film is adjusted by appropriately setting the film formation time.

The pre-carbon film has an amorphous carbon structure (D L C structure), and it is presumed that in the pre-carbon film, other than sp²Sp exists in addition to the carbon atom of the hybrid orbital (graphitic structure)³Carbon atoms of hybridized orbitals (diamond structure), sp³The proportion of carbon atoms of the hybrid orbital becomes high. When such an amorphous pre-carbon film is compressed by a high pressure in a texturing step described later, the density of the amorphous pre-carbon film is increased and the amorphous pre-carbon film is textured.

(coating film removing step)

The coating film removal step is a step of removing the coating film by dissolving it with a predetermined solvent after the formation of the pre-carbon film.

After the pre-carbon film is formed on the coating film, the porous support base material 2 on which the pre-carbon film is formed is dissolved and removed by a vibration method using a predetermined solvent.

For example, in the case where the coating film is made of PVP, as a solvent for dissolving and removing the coating film, an aqueous ethanol solution (in a volume ratio of ethanol to water of 8: 2) is used.

Depending on the type of the coating film, a known organic solvent such as ether, ethyl acetate, acetone, or methylene chloride may be used as the solvent for dissolving and removing the coating film, in addition to water or an alcohol such as ethanol. These may be used alone or in combination of two or more.

When the coating film contacts a predetermined solvent, the coating film is eluted in the solvent and removed from the porous support base material 2. As a result, the pre-carbon film is formed to be laminated on the porous plastic layer 2B of the porous support base 2.

(texturizing Process)

The texturizing step is a step of compressing the pre-carbon film on the porous support base 2 and forming a separation active layer composed of a carbon film containing texturized carbon on the porous support base 2. As a method of compressing the pre-carbon film, for example, a method of contacting a fluid with the pre-carbon film under high pressure, compressing the pre-carbon film, and organizing the same is used. The fluid to be used is not particularly limited as long as the object of the present invention is not impaired, and examples thereof include a gas and a liquid. In addition, the pre-carbon film may be structured by applying a high pressure to the pre-carbon film using a predetermined press or the like without using a fluid.

For example, the texturizing step is performed using a liquid (for example, pure water) capable of permeating the pre-carbon film as a fluid and using a filter device of a cross-flow filtration system described later. The pressure applied to the pre-carbon film is preferably 5.5MPa or more. The upper limit of the applied pressure is not particularly limited as long as the object of the present invention is not impaired, and is set to 7MPa or less for convenience of a filter device to be described later, for example.

The time for applying a high pressure to the pre-carbon film is not particularly limited as long as the object of the present invention is not impaired, and is, for example, 1 hour or more, preferably 10 hours or more, and more preferably 20 hours or more.

In another embodiment, a carbon film containing organized carbon (separation active layer 3) may be formed by physical vapor deposition or the like without forming a pre-carbon film on the porous support base 2.