JPH04326929A - Separation membrane - Google Patents

Abstract

PURPOSE:To prevent the expansion of a semipermeable membrane due to negative pressure action by embedding the thick parts on both sides of a fabric body excepting the intermediate part thereof in the sponge like layer parts of respective semipermeable membranes and leaving the gap for a transmitted fluid path to the intermediate part of the fabric body. CONSTITUTION:Semipermeable membranes 2,2 are provided to both surfaces of a fabric body 1 having a three-dimensional structure and have skin layers on the surfaces thereof and the respective thick parts 11, 11 on both sides of the fabric body 1 excepting the intermediate part 10 thereof are embedded in the sponge like layer parts of the semipermeable membranes 2,2. Therefore, a gap for a transmitted fluid flow path is left to the intermediate part 10 of the fabric body 1. In this separation membrane, the outsides of the semipermeable membranes 2,2 are used as raw liquid sides and the solvent in a raw liquid is transmitted through the skin layers of the semipermeable membranes 2,2 and this transmitted liquid flows to the gap for the transmitted fluid flow path of the intermediate part 10 of the fabric body 10. In this case, even when the pressure of the gap for the transmitted fluid flow path of the intermediate part of the fabric body becomes higher than the outside pressure of the semipermeable membranes, since the semipermeable membranes are strongly embedded in and bonded to the fabric body, the outward expansion of the semipermeable membranes can be prevented.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is used for the separation of a specific liquid from a solution, the separation of a specific gas from a mixed gas, the separation of solids from a liquid or gas, the separation of a gas from a gas-containing liquid, etc. It relates to separation membranes.

0002

[Prior Art] Semipermeable membranes used for separating specific liquids, separating specific gases from mixed gases, separating solids from liquids or gases, separating gases from gas-containing liquids, etc. Since its mechanical strength is low, a membrane formed on a support such as a non-woven fabric (a membrane formed by coating a membrane-forming solution on a non-woven fabric) is usually used.

In order to process a stock solution using a membrane module using this separation membrane, the surface side of the semipermeable membrane, ie, the skin layer side, is used as the stock solution side, and the back side of the semipermeable membrane, ie, the support side, is used as the permeate liquid side. It is necessary to apply transmembrane pressure with the stock solution side as the high pressure side. In this case, on the back side of the semipermeable membrane,
Although pressure is applied to the groove edge or hole edge of the permeate passage member,
Damage to the semipermeable membrane can be prevented due to the presence of the support layer.

0004

[Problems to be Solved by the Invention] However, when backwashing a membrane module, the backwash liquid acts on the semipermeable membrane as reverse pressure (negative pressure), and the permeate chamber side When discharging the stock solution from the stock solution chamber while the permeate has accumulated, the pressure difference between the heights of the permeate acts as negative pressure (
In particular, if the permeate tank is installed at a high place, the negative pressure will be extremely large).Furthermore, if the stock solution is withdrawn abruptly, a space will be created in the stock solution chamber and the permeate will pass through the membrane from the permeate side. A reduced pressure space may be formed without the supply air following, and negative pressure may act, and under such negative pressure, the skin layer side of the semipermeable membrane is compressed by the groove edge of the concentrate passage member, etc. There is a risk that the skin layer may be damaged.

An object of the present invention is to provide a separation membrane that can effectively prevent damage to the semipermeable membrane even when negative pressure is applied.

[0006]

[Means for Solving the Problems] In the separation membrane of the present invention, semipermeable membranes having skin layers on the surface are provided on both sides of a woven fabric body, and an intermediate portion of the woven fabric body is provided on the sponge-like layer portion of each semipermeable membrane. This structure is characterized in that each of the thickness portions on both sides except for the woven fabric body is buried, and a gap for a permeate fluid flow path remains in the intermediate portion of the woven fabric body.

[0007]

[Operation] Even if negative pressure is applied, that is, even if the pressure in the gap for the permeate fluid flow path in the middle part of the woven fabric becomes higher than the pressure outside the semipermeable membrane, the sponge layer of both semipermeable membranes is embedded and bonded to the woven fabric body, and this bonding strength is strong because the sponge layer bites into the fiber gaps of the woven fabric, preventing each semipermeable membrane from bulging outward. Even if the sponge layer on the surface of the semipermeable membrane contacts the edge of the groove of the liquid passage member, the pressure at the contact point can be effectively reduced, and damage to the semipermeable membrane can be avoided.

[0008]

Embodiment FIG. 1 is an explanatory diagram showing an embodiment of the present invention. In FIG. 1, numeral 1 is a woven fabric body having a three-dimensional structure. 2, 2 are semipermeable membranes provided on both sides of the woven fabric body 1;
It has a skin layer on its surface, and each thick portion 11, 11 on both sides of the woven fabric body 1 except for the middle portion 10 is embedded in the sponge-like layer portion of each semipermeable membrane 2, 2. Therefore, a gap for the permeate fluid flow path remains in the intermediate portion 10 of the woven fabric body.

In this separation membrane, the outside of each semipermeable membrane is used as the stock solution side, and the solvent in the stock solution permeates through the skin layer of each semipermeable membrane, and the permeate passes through the middle part of the woven fabric. It flows through the gap for the fluid flow path. In this case, even if a negative pressure acts, that is, even if the pressure in the gap for the permeate fluid flow path in the middle part of the woven fabric becomes higher than the pressure on the outside of the semipermeable membrane, each semipermeable membrane remains in the woven fabric. Since the semipermeable membrane is firmly embedded and bonded to the membrane, outward expansion of the semipermeable membrane is prevented, and even if the semipermeable membrane surface contacts an edge such as a groove edge of the concentrate passage member, the contact pressure is suppressed. Since the temperature can be kept sufficiently low, damage to the surface of the semipermeable membrane can be well prevented.

The separation membrane of the present invention can be used as a reverse osmosis membrane, an ultrafiltration membrane, or a precision filtration membrane depending on the polymer material used.Furthermore, by using the separation membrane of the present invention as a support membrane, mechanical It is also possible to produce reverse osmosis composite membranes, gas separation membranes, and pervaporation membranes with excellent mechanical strength.

[0011] The membrane material used in the present invention is not particularly limited as long as it is a polymer with film-forming properties;
For example, polysulfone-based polymers, hydrophilic polyolefin-based polymers, polyvinylidene fluoride, polyacrylonitrile-based polymers, cellulose acetate, polyimide, polyamic acid, etc., mixtures thereof, or charged sulfonic acid groups, carboxyl groups, amino groups, etc. Those into which groups have been introduced can be used.

[0012] The film-forming solution uses a material in which a high molecular weight polymer is dissolved in a solvent, and the polymer concentration varies depending on the molecular weight and type of the polymer, but is usually 5 to 4.
0%, preferably 10-30%.

[0013] The solvent used as the membrane forming solution must be one that can dissolve the high molecular weight polymer and be miscible with water, such as N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl Polar solvents such as -2-pyrrolidone, dimethyl sulfoxide, acetone, IPA, THF, dioxane, etc. can be used.

As additives to be added to the membrane forming solution, 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 this additive varies depending on the type of polymer and the type of additive, but it is usually
1 to 200 parts by weight, preferably 5 to 1 parts by weight
It is 50 parts by weight.

The woven fabric used in the present invention must be capable of being impregnated with a membrane-forming solution, have an appropriate thickness, and have a gap in the middle of the thickness that can serve as a permeate passage.
It must have a crushing strength that can maintain the gap for the permeate passage under the pressure of the raw solution, and it must be able to maintain the gap for the permeate passage even when the membrane shrinks when the impregnated membrane-forming solution coagulates in the coagulation liquid. Those that satisfy the following requirements are used.

The structure of the woven fabric includes a woven fabric whose entire surface is woven three-dimensionally uniformly, a woven fabric whose surface is densely woven and a coarsely woven fabric in the middle, and a woven fabric whose surface is woven uniformly in three dimensions; Woven fabrics with fibers woven into them can be used. If the thickness of the woven fabric is too thin, it will be difficult to impregnate only the surface of the woven fabric with the membrane-forming solution and ensure a gap for the permeate passage.On the other hand, if the woven fabric is too thick, the membrane module The membrane area per unit volume is small, and the non-impregnated part for the permeate passage becomes thicker than necessary, making it difficult to guarantee pressure resistance when pressurized, so the thickness of the woven fabric is usually 0. 1 mm to 10 mm, preferably
It is desirable to set it as 0.3 mm - 5 mm.

The material of the fiber 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, glass fiber, etc. can be used.

To produce the separation membrane of the present invention, only both surfaces of a woven fabric are impregnated with a membrane-forming solution, and the woven fabric is passed perpendicularly between two rolls with an adjusted gap. The thickness of the film-forming solution layer on both surfaces of the woven fabric is adjusted to be approximately equal, and a skin layer is formed by evaporation of the solvent from the surface of the film-forming solution layer.Then, it is immersed in a coagulation solution to remove the solvent-containing solution inside the film. A method can be used in which a portion of the state is solidified and undergoes a phase transition into a sponge layer. It is also possible to use a method of forming a skin layer and a sponge layer in a coagulating solution without evaporating the solvent.

The separation membrane of the present invention is used as a membrane for a spiral type membrane module or a plate and frame type membrane module. For those that use a membrane support plate, such as plate & frame type membrane modules and rotating disk type modules, the woven fabric should have sufficient porous properties. If a membrane support plate is used, the membrane support plate can be omitted by using a material hardened with resin or the like (resin or the like is used that does not elute into the permeate) to the extent that the membrane can be maintained.

In the separation membrane of the present invention, the semipermeable membranes on both sides are bonded to the woven fabric body, and even if the pressure between these semipermeable membranes becomes higher than the pressure outside the semipermeable membrane, the semipermeable membranes Can prevent bulges. In this case, as is clear from the following examples, it plays an extremely important role that the bonding strength between the woven fabric body and the semipermeable membrane is extremely high.

Example 18% by weight of polysulfone was dissolved in N-methyl-2-pyrrolidone to prepare a film forming solution. This membrane-forming solution is impregnated only on the surface of a 2.5 mm thick woven fabric with a gap in the center of the thickness that serves as a permeate flow path, and both surfaces are densely woven. It was passed between two rolls and immersed in water to form semipermeable membranes on both sides. This membrane exhibited performance as an ultrafiltration membrane, with a rejection rate of polyethylene glycol 20,000 of 62%.

[0022] Also, the same film forming solution was applied on the nonwoven fabric,
A pressure twice as high as the pressure at which the nonwoven fabric and the semipermeable membrane were separated by applying pressure from the permeate side of the separation membrane obtained by immersing it in water was applied to the permeate flow path of the example product, but no abnormality was observed. I couldn't watch it.

[0023]

[Effects of the Invention] The separation membrane of the present invention has the structure as described above, and semipermeable membranes are embedded on both sides of the woven fabric body, and a gap for the permeate passage is secured in the middle of the woven fabric body. Even if negative pressure is applied, the semipermeable membrane can be prevented from swelling, and the tension between the semipermeable membrane and the groove edge of the stock solution passage member can be well avoided under negative pressure.
Damage to the semipermeable membrane can be prevented.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

[Explanation of symbols]

1 Woven fabric 10　　　Thickness middle part of woven fabric body 2 Semi-permeable membrane

Claims (1)

[Claims] Claim 1: A semipermeable membrane having a skin layer on the surface is provided on both sides of a woven fabric body, and each thickness portion on both sides of the woven fabric body except for an intermediate portion is embedded in a sponge-like layer portion of each semipermeable membrane, A separation membrane characterized in that a gap for a permeate fluid flow path remains in the intermediate portion of the woven fabric body.