JPH0729034B2 - Hollow fiber composite membrane for organic matter separation - Google Patents

Description

TECHNICAL FIELD The present invention relates to a hollow fiber water / organic separation membrane. More specifically, it relates to a hollow fiber composite membrane for pervaporation and vapor permeation that preferentially permeates water or water vapor.

(Prior Art and Problems) With regard to concentration and separation of an organic aqueous solution using a membrane, a reverse osmosis method has been put into practical use for the concentration of some low-concentration organic aqueous solutions. However, the reverse osmosis method cannot be applied to a high-concentration aqueous solution having a high osmotic pressure because it is necessary to apply a pressure higher than the osmotic pressure of the separated solution to the liquid to be separated. There is a limit.

On the other hand, permeation vaporization method and vapor permeation method, which are separation methods that are not affected by osmotic pressure, are in the spotlight as new separation methods.

The pervaporation method is a method in which a separation liquid is supplied to the primary side of a membrane and the secondary side (permeation side) of the membrane is depressurized or a carrier gas is aerated so that the separated substance is permeated in a gaseous state. Is the way. The vapor permeation method is different from the pervaporation method in that the supply to the primary side of the membrane is mixed vapor. The membrane-permeable substance can be taken out by cooling and condensing.

As a separation method by pervaporation, a composite flat membrane and a module obtained by crosslinking polyvinyl alcohol with maleic anhydride or the like described in JP-A-59-109204 are known, but the separation coefficient is high, but sufficient. It is not possible to say that it has a permeation rate, a large-area membrane is required, and it is expected that the cost of the device or the operating cost will increase in combination with the plate-and-frame type module.

On the other hand, there are few examples of application to pervaporation of hollow fiber membranes that are widely used in fields such as ultrafiltration and reverse osmosis.

Journal of Membrane Science (Journal
of Membrane Science), 24, 101-119 (1985), separation of isopropanol and ethanol using a hollow fiber membrane of Nafion (registered trademark) 811 is reported.
Also, Journal of Membrane Science, No. 33
Vol., Pp. 71-81 (1987), a separation method called a membrane column in which a water preferential permeation type hollow fiber membrane (cellulose acetate) and an alcohol preferential permeation type hollow fiber membrane (silicon rubber) are combined is reported. .

An object of the present invention is to develop a more efficient separation membrane for separating an aqueous solution of an organic substance or a mixed vapor of an organic substance and water by a pervaporation method and a vapor permeation method.

(Means for Solving the Problems) As a result of intensive studies on the above points, the present invention has been achieved.

That is, when water / organic mixture and / or mixed vapor is supplied to the inside of the hollow fiber and then the outside of the hollow fiber is kept at a reduced pressure, when the water is selectively permeated, polyion complex activity is exerted on the inner surface of the hollow fiber. It was found that high separation performance can be obtained by using a hollow fiber composite membrane having a layer.

As a water-selective permeable membrane, it is necessary to enhance the affinity with water, and it is effective to use a polymer having an anionic group or a cationic group as a raw material. However, if the amount of these ionic groups is increased, the hydrophilicity of the membrane is increased, but the function as a separation membrane is generally significantly reduced.

The polyion complex membrane of the present invention has high separation performance and is resistant to water and other solvents. further,
By uniformly supplying the mixed liquid and vapor to the inside of the hollow fiber composite membrane having the polyion complex layer on the inner surface, permeation vaporization and vapor permeation separation with a compact module and energy saving became possible. The present invention will be described in more detail below.

The present invention is characterized by having a polyion complex layer on the inner surface of the hollow fiber, and the production method thereof is not particularly limited, but the polyion complex layer is formed from a wide range of polyanions and polycations having a quaternary ammonium group in the main chain. It can be easily obtained by dissolving them in a solvent (for example, a ternary solvent such as water-acetone-sodium bromide) which is dissolved from the selected combination and then coating the inside of the hollow fiber.

As another method, a polyanion such as polyacrylic acid, polymethacrylic acid, or polystyrenesulfonic acid is first thinly coated on the inner surface of the hollow fiber, and then contacted with an aqueous solution of a polycation having a quaternary ammonium group in the main chain. A polyion complex active layer may be formed on the inner surface. If necessary, this operation can be further repeated to form a defect-free polyion complex layer or to repair it.

On the contrary, the polyion complex layer can be formed on the inner surface of the hollow fiber only by first coating the inner surface of the hollow fiber with a polycation having a quaternary ammonium group in the main chain and contacting it with an aqueous solution of polyanion.

As a hollow fiber support, polysulfone (PSF), polyether sulfone (PES), polyphenylene oxide (PP
When O), polyimide, aromatic polyamide, etc. are used, the inner surface of the hollow fiber can be treated with a sulfonating agent such as chlorosulfonic acid to impart a sulfonic acid group to the inner surface, or sulfonated By appropriately controlling the conditions, it is possible to form a polyion complex on the inner surface with a polycation having a quaternary ammonium group in various main chains.

When a polyvinyl alcohol-based or cellulose-based hollow fiber membrane is used as a support, its reactivity is utilized to
A wide range of polyion complex membranes can be formed. For example, after introducing a sulfonic acid group using a sulfonating agent such as sulfuric acid or chlorosulfonic acid, or by reacting with sodium monochloroacetate in the presence of an alkali to carboxymethylate and introduce a carboxyl group, various Examples of the method include forming a polyion complex with a polycation having a quaternary ammonium group in its main chain.

As another inner surface treatment method, the inner surface of an asymmetric hollow fiber membrane such as polyacrylonitrile (PAN) or polymethylmethacrylate (PMMA) is hydrolyzed with an alkali to generate a carboxyl group, and then a quaternary chain is formed on the main chain. Forming a polyion complex by contacting with a polycation having an ammonium group is included. In this case, it is not always necessary to hydrolyze only the inner surface, and if the membrane strength can be maintained, the entire hollow fiber may be hydrolyzed.

Polyimide-based separation membranes are known to have excellent heat resistance and solvent resistance, but when using this polyimide-based material as a hollow fiber base membrane, the precursor polyamic acid is made hollow and cyclized. , In the process of imidization, it is not completely imidized but is left as a part of amic acid to form a complex with a polycation having a quaternary ammonium group in the main chain on its inner surface, or cyclize By contacting the inner surface with a polycation having a quaternary ammonium group in the main chain and then performing heat treatment or chemical treatment, a composite membrane having a polyion complex active layer substantially only on the inner surface can be obtained. Further, after producing a polyimide-based hollow fiber, by hydrolyzing only the imide group on the surface with an alkali or the like, it is possible to change to an amic acid structure and obtain a composite membrane in the same manner. .

In addition to this, as a method for forming a polyion complex on the inner surface of the hollow fiber, a monomer having an anionic group such as acrylic acid or vinyl sulfonic acid is grafted onto the inner wall of the hollow fiber such as polyvinyl alcohol or cellulose to form a polyion complex. You can list things to do. Alternatively, polyacrylic acid may be obtained by surface-grafting acrylonitrile and then hydrolyzing it.

The surface grafting method is preferably carried out because a three-dimensional structure can be produced by copolymerizing a small amount of a polyfunctional monomer.

As described above, there are various methods for producing the membrane having the polyion complex layer on the inner surface of the hollow fiber, and the method is selected according to the object to be separated.

For example, in a water / alcohol system, a combination of a polycarboxylic acid and a polycation having a quaternary ammonium group in its main chain is preferable, and the production method is also selected according to these active layers. The thickness of the polyion complex layer in these hollow fiber composite membranes is not particularly limited, but is preferably 2 μm or less in order to increase the permeation rate.

The present invention is characterized in that the supply liquid and / or steam is supplied to the inside of the hollow fiber to depressurize the outside, but this makes the flow path of the supply liquid and / or vapor uniform and reduces the degree of depressurization on the permeate side. Is particularly important for keeping constant.

The hollow fiber composite membrane for separating organic matter according to the present invention is applicable to a wide range of organic liquids and vapors. For example, organic acids such as formic acid, acetic acid, propionic acid and butyric acid, alcohols such as methanol, ethanol, 1-propanol, isopropanol and n-butanol, ketones such as acetone and methyl ethyl ketone, ethers such as tetrahydrofuran and dioxane, and aldehydes. An aqueous solution containing one or more compounds consisting of aldehydes such as propionaldehyde, amines such as pyridine and picoline,
Or a steam mixture with water.

(Example) Hereinafter, the present invention will be described more specifically with reference to Examples.

Example 1 As a hollow fiber support, a polyether sulfone ultrafiltration membrane manufactured by Daicel Chemical Industries, Ltd. (FUS-3081, inner / outer diameter = 800)
Ten modules (1300 μm, fraction 30,000) were bundled to prepare a module. After passing a 0.5 wt% polyacrylic acid (Aldrich, molecular weight 4 million) aqueous solution through the hollow fiber, dry by blowing hot air at 50 ° C for 30 minutes at 3 liters / min. An acid coat layer was formed. Then, a 2 wt% aqueous solution of a polycation (PCA 107) having a quaternary ammonium group in the main chain having the following structure was passed for 30 minutes to form a polyion complex, which was then air-dried as described above. By repeating this coating and polyion complexation treatment a total of two times to form a more complete polyion complex composite film, the permeation rate was evaluated by the pervaporation method (feeding solution 95% ethanol, 60 ° C). The separation factor was 1,260 at 0.24 kg / m ² · hr.

(Effects of the Invention) In the hollow fiber composite membrane for organic matter separation according to the present invention, not only is the polyion complex itself of the separation active layer suitable for pervaporation and separation of water / organic matter by a vapor permeation method, The following effects can be expected by forming on the inner surface of the hollow fiber.

i) It is possible to prevent damage to the surface of the composite membrane active layer during modularization.

ii) By supplying the separated liquid and / or vapor into the hollow fiber, the flow becomes more uniform than in the case of flowing to the outer surface, and the module efficiency is improved.

iii) The pressure loss can be minimized by using a decompression system outside the hollow fiber.

In addition, it can be expected that the hollow fiber composite membrane can be made into a compact module to be an efficient separation method as compared with a flat membrane type module.

Claims (3)

[Claims] 1. A membrane in which a water / organic mixture and / or a mixed vapor is supplied to the inside of a hollow fiber to selectively permeate water by keeping the outside of the hollow fiber at a reduced pressure. A hollow fiber composite membrane for separating organic substances, which has a polyion complex active layer composed only of a polycation having a quaternary ammonium group in the chain. 2. The hollow fiber composite membrane for separating organic substances according to claim 1, wherein the mixed liquid and / or mixed vapor of water / organic substance is water / ethanol. 3. The hollow fiber composite membrane for separating organic matter according to claim 1, wherein the polyanion forming the polyion complex active layer is a polycarboxylic acid.