JP2860833B2 - Separation membrane - Google Patents

Description

The present invention relates to the separation of certain liquids from solutions, the separation of certain gases from gas mixtures, the separation of solids from liquids or gases, the separation of gas-containing liquids. The present invention relates to a separation membrane used for separation of a gas.

(Prior Art) The separation membrane includes a composite membrane, an asymmetric membrane, and the like. In the latter, a dense skin layer is provided on the surface of a sponge layer. The thickness of the skin layer in this asymmetric membrane is
Usually, it is 0.1-1.5 μm, and solute rejection is performed in this part. On the other hand, the thickness of the sponge layer is usually 50 to 250 μm
It supports the skin layer and guarantees the mechanical strength of the separation membrane.

In recent years, the application field of separation membranes has been remarkably expanding, and the processing pressure has been increased to process high-concentration substances. The permeated liquid passage material spacer has a coarse net to reduce the pressure loss of permeated liquid and prevent liquid pooling. As a result, the strength of the separation membrane is required to be increased.

In a conventional asymmetric membrane, a base fabric is provided on the back surface of the sponge layer for mechanical reinforcement, but peeling easily occurs between the sponge layer and the woven fabric.

For this reason, it has been proposed to embed a woven fabric in the sponge layer in the asymmetric membrane described above (Japanese Patent Laid-Open No. 47957/1979).
JP-A-48-21750, JP-A-50-54578).

In the woven fabric, as long as the total cross-sectional area of the fibers is the same, reducing the fiber diameter and increasing the number of fibers can promote the uniform load of stress accordingly, which is effective in mechanical strength. Thus, fibers embedded in the sponge layer have a small wire diameter (50 μm or less) and a fine mesh (200 mesh or more). (Problems to be Solved) However, in a separation membrane, Often in contact with strong chemicals for cleaning, in those in which a woven fabric is buried in the sponge layer, this chemical comes into contact with the fibers of the woven fabric, and deterioration of the fiber surface due to the chemical is inevitable. If the fiber diameter is too small, the reduction in the strength of the woven fabric due to the chemical becomes significant, and the mechanical reinforcing effect of the woven fabric is lost relatively early. Also, if the mesh of the woven fabric is too fine, the film forming solution applied to the woven fabric during the production of the separation membrane cannot completely enter the eyes of the woven fabric due to its surface tension, and the air remains and the sponge It is difficult to sufficiently increase the bonding strength between the layer and the woven fabric, and as a result, the external force acting on the membrane cannot be sufficiently shared by the woven fabric, and the woven fabric may not be able to exert a sufficient reinforcing effect. .

In a conventional asymmetric membrane, a skin layer is provided only on the side in contact with a stock solution, and the same applies to a separation membrane in which a woven fabric is embedded in the sponge layer. However, when the operation of the membrane module is stopped in a case where the membrane module is installed at a high place, for example, when the operation of the membrane module is stopped, a back pressure is applied to the membrane due to the formation of a vacuum of trithierie in the stock solution chamber of the membrane module, In this case, the back pressure is transmitted to the skin layer via the sponge layer ⇒ woven fabric ⇒ sponge layer, but since the sponge layer and the woven fabric have almost no pressure receiving action, most of the back pressure is received by the skin layer, The sponge portion between the skin layer and the woven fabric and the woven fabric are easily separated.

An object of the present invention is to provide a separation membrane in which a woven fabric is embedded in a sponge layer of the asymmetric membrane, which can sufficiently maintain a reinforcing effect even under chemical contact with the woven fabric, and furthermore, bond the woven fabric and the sponge layer. It is an object of the present invention to provide a separation membrane having high strength and capable of avoiding separation of the binding interface even under the action of a counter pressure.

(Means for Solving the Problems) The separation membrane of the present invention has a skin layer on a sponge layer, and in a membrane in which a woven fabric is embedded in the sponge layer, the woven fabric has a fiber diameter of 50 to 250 μm and a mesh of 30. The structure is characterized in that ~ 200 woven fabrics are used, and the skin layers can be provided on both surfaces of the sponge layer with different coarse densities.

In the above, the fiber diameter (diameter) of the woven fabric is 50 to 250 μm
The reason is that, at 50 μm or less, the woven fabric strength is significantly reduced due to deterioration of the fiber surface under chemical contact, and it is difficult to satisfactorily exert the mechanical reinforcing action on the woven fabric, while at 250 μm or less, the sponge layer This is because the woven fabric is inevitably protruded from the sponge layer as it approaches the thickness.

The reason why the mesh of the woven fabric is set to 30 to 250 is that when the film forming liquid is applied to the woven fabric when the separation membrane is manufactured at 300 or more, air remains in the eyes of the woven fabric and the sponge layer is In the case of 30 mesh or less, the mesh of the woven fabric is too coarse, and under the action of the undiluted solution pressure, the membrane material is liable to be damaged due to the penetration of the membrane material into the mesh of the woven fabric. Because.

In the above, the reason why the skin layers are provided on both sides of the sponge layer is to cope with negative pressure in the membrane module stock solution chamber, and the reason for making the coarse densities of both skin layers different is that the skin layer in contact with the stock solution is Depending on the separation performance and permeation performance, a reverse osmosis membrane grade, an ultrafiltration membrane grade or a microfiltration membrane is good, and the side in contact with the filtrate is lower than this grade to ensure as much permeation flow as possible. .

The separation membrane of the present invention can be produced, for example, by the following method.

(1) The woven fabric and the film are simultaneously fed while being overlapped, a film-forming solution is applied on the woven fabric, and these are vertically passed between two rolls with a gap adjusted, and then vertically coagulated ( (2) a method of forming a skin layer and a sponge layer in water by coagulation, and (2) evaporating the solvent from the surface of the film forming liquid layer before leaving the roll and entering the coagulation liquid. A method of forming a layer, then vertically immersing in a coagulating liquid, coagulating a concentrated liquid state portion containing a solvent inside the membrane with water and transferring the layer to a sponge layer, (3) a method in which only the woven fabric is fed out The membrane liquid is impregnated, and the solvent is impregnated under different atmospheres, for example, at different temperatures, humidity, or in a state of an organic solvent vapor (for example, on one side, the vapor is difficult to escape). (4) woven cloth impregnated with the film forming solution When immersed in a liquid, the method of shifting the time to solidify in the front and back, creating a skin layer on both sides, the the single-side coating method or interfacial crosslinking methods may be used a method in which a dense skin layer with.

The membrane material used in the present invention is not particularly limited as long as it is a polymer having a film-forming property. Examples thereof include polysulfone-based polymers, hydrophilic polyolefin-based polymers, polyvinylidene fluoride, polyacrylonitrile-based polymers, cellulose acetate, and the like. Polyimide, polyamic acid, etc., a mixture thereof, or a sulfonic acid group,
Those into which a charged group such as a carboxyl group or an amino group is introduced can be used.

The above-mentioned film-forming solution is obtained by dissolving a high-molecular polymer as a material in a solvent, and the polymer concentration varies depending on the molecular weight and type of the polymer.
Preferably it is 10 to 30%. For the solvent, it is necessary to use a solvent that dissolves the high-molecular polymer and can be mixed with water, N, N-dimethylacetamide, N, N-dimethylformamide, N-methyl-2-pyrrolidone, dimethylsulfoxide, Polar solvents such as acetone, IPA, THF, dioxane can be used. As the additive, for example, inorganic salts such as lithium chloride and magnesium perchlorate, and organic substances such as ethylene glycol, polyethylene glycol, polyvinylpyrrolidone, acetone and formamide can be used. The concentration of the additive varies depending on the type of the polymer and the type of the additive, but is usually 1 to 200 parts by weight, preferably 5 to 150 parts by weight.

The material of the woven fabric is not particularly limited as long as it has mechanical strength and resistance to the solvent of the film forming solution. For example, polyester, polypropylene, polyethylene, polyamide and the like can be used.

(Description of Examples) Hereinafter, examples of the present invention will be described in comparison with comparative examples.

Example 1 A film-forming solution was prepared by dissolving 16 g of polysulfone in 84 g of N, N-dimethylformamide. Spread a polyester woven cloth with a fiber diameter of 71 μm and 110 mesh on a polyester film with a thickness of 50 μm, pour the film-forming solution, and then leave it for 3 minutes to confirm that air has escaped from the woven cloth. , And passed vertically between two rolls whose gap was adjusted to 0.2 mm. Next, the membrane was immersed in a water tank in a vertical state, and the membrane-forming solution was solidified to obtain a separation membrane having a thickness of 195 μm. This separation membrane exhibits the performance as an ultrafiltration membrane,
The rejection of polyethylene glycol 20,000 on the front side and the back side (side in contact with the polyester film) was 72% and 8%, respectively.

Example 2 As a film-forming solution, 16 g of polysulfone and 2 g of sulfonated polyethersulfone were dissolved in 84 g of N, N-dimethylformamide to prepare a film-forming solution. Example 1 using this film forming solution
In the same manner as in the above, a separation membrane having a thickness of 193 μm was obtained. The dextran (molecular weight 2 million) rejection of this separation membrane was 7
5% and substantially 0% on the back side.

Comparative Example 1 The same film-forming solution as used in the example was used, and the polyester woven fabric used had a fiber diameter of 40 μm and 25 mesh. Lay the above polyester woven cloth on a 50 μm thick polyester film, pour the film forming solution, and then leave it for 3 minutes. With the film attached, place vertically between the two rolls with the gap adjusted to 0.2 mm. Passed in state. Then
Immerse it in a water tank in a vertical state, and solidify the film forming solution to a thickness of 196
A μm separation membrane was obtained. In this separation membrane, the rejection of polyethylene glycol 20,000 was 30% and 5%, respectively.

Comparative Example 2 The same film-forming solution as in the example was used. 100μ thickness
Then, the film-forming solution was poured into a polyester non-woven fabric having a thickness of 0.2 m, and then allowed to stand for 3 minutes, and then passed vertically between two rolls having a gap adjusted to 0.2 mm. Next, the membrane was immersed in a water tank in a vertical state, and the membrane-forming solution was solidified to obtain a separation membrane having a thickness of 195 μm. This membrane had a polyethylene glycol 20,000 rejection of 74%.

For each of the above examples and comparative examples,
When the strength retention was measured by immersing in a 3% NaOH solution,
After 100 hours, in Examples 1 and 2, 90-92
%, Whereas it was only about 50% in Comparative Example 1 and about 17% in Comparative Example 2. After 600 hours, it was about 80% in Examples 1 and 2. On the other hand, it was about 35% in Comparative Example 1 and substantially 0 in Comparative Example 2.

Also, in any of Examples 1 and 2, no air residue was observed, and the peel strength of the woven fabric could be made ² kg / cm ^{2. In} Comparative Example 1, however, air residue was observed. In Example 2, only a peel strength of 0.8 kg / cm ² was obtained.

(Effect of the Invention) The separation membrane of the present invention has the same configuration as described above, and has a fiber diameter of the woven fabric of 50 μm to 25 μm as long as it can be embedded in the sponge layer.
Because it is thick as 0μm, even if the fiber surface deteriorates due to chemical cleaning, it is possible to sufficiently maintain the strength of the woven fabric,
In addition, since the mesh of the woven fabric is set to be as large as 30 mesh to 200 mesh within a range capable of maintaining the function of supporting the membrane against pressure, the mesh of the woven fabric when the film forming solution is poured is used. Can sufficiently eliminate the residual air and sufficiently increase the binding strength between the woven fabric and the sponge layer. Therefore, in the separation membrane of the present invention, the force acting on the membrane for excellent binding between the sponge layer and the woven fabric can be favorably shared with the woven fabric, and the strength of the woven fabric can be stably maintained, The asymmetric membrane can be effectively reinforced with a woven fabric. In addition, since the skin layers are provided on both sides of the sponge layer, the binding between the woven fabric and the sponge layer can be maintained well even under the action of the back pressure, and the woven fabric can be reinforced under the action of the back pressure. The effect can be fully guaranteed.

The separation membrane of the present invention can be used as a reverse osmosis membrane, an ultrafiltration membrane or a microfiltration membrane, depending on the polymer material used.
Further, by using the separation membrane of the present invention as a support membrane, a reverse osmosis composite membrane, a gas separation membrane, and a pervaporation membrane can also be manufactured.

Claims (2)

(57) [Claims] 1. A membrane having a skin layer on a sponge layer and a woven cloth embedded in the sponge layer, wherein the woven cloth has a fiber diameter
A separation membrane, wherein a woven fabric having a mesh of 50 to 250 μm and a mesh of 30 to 200 is used. 2. The separation membrane according to claim 1, wherein the skin layers are provided on both surfaces of the sponge layer at different coarse densities.