JPH0366932B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a pervaporative separation method for separating water-organic liquid mixtures or organic-organic liquid mixtures using membranes.

[Conventional technology]

Conventionally, a liquid mixture to be separated is supplied to the feed liquid side (primary side) of two chambers separated by a separation membrane,
Maintain low vapor pressure by reducing the pressure on the permeate side (secondary side) or flowing inert gas, and allow components with high affinity with the membrane to preferentially permeate into the secondary side as vapor. A method of separating a water-organic liquid mixture by a pervaporation method has been implemented, and various experimental examples have been reported in which a water-organic liquid mixture was separated by such a pervaporation method. For example, U.S. Patent No.
No. 2953502 includes an experimental example of separating azeotropic liquids using cellulose acetate membranes and polyvinyl alcohol membranes, J. Polymer SCI, Symposium No.
41145-153 (1973), an experimental example of separating water/methanol mixed liquid in the presence of sodium formate using a cellophane membrane, Journal of Applied
Polymer Science vol. 26 (1981), page 3223, contains an experimental example in which a water-methanol mixed liquid was separated using a grafted polyvinyl alcohol membrane.
Special Publication No. 54-10548, No. 54-10549 and Special Publication No. 59-
No. 49041 reports an experimental example in which a water-organic liquid mixture was separated using a synthetic polymer membrane into which ionic groups were introduced.

[Problem that the invention seeks to solve]

Unlike reverse osmosis, pervaporation does not have concentration limitations due to osmotic pressure, so it is not limited to separating liquid mixtures with low concentrations, but can separate liquid mixtures with a wide range of concentrations. It also has the characteristics of being able to separate azeotropic mixtures and isomers with close boiling points (for example, ortho and para isomers, cis and trans isomers) that are difficult to separate using distillation methods.

However, the separation membranes used in conventional pervaporation methods have the following problems and are not practical. In other words, the separation rate when a mixed liquid passes through a polymer membrane once [generally, the weight ratio of component A to component B after passing through the membrane is expressed as A before passing through the membrane.
The value divided by the weight ratio of the component to the B component is expressed as a separation coefficient α. That is, α ^A _B = (W _A /W _B ) in the permeate / (W A /W _B in the permeate)
W _B ) (in the formula, W _A and W _B indicate the weights of component A and component B, respectively)] are small, so in order to separate or concentrate to the desired concentration, it is necessary to pass through a large number of membranes. In particular, the permeation rate through a polymer membrane [generally, the permeation rate per unit membrane surface area and unit time, that is, Q (Kg/m ² hr)] ] becomes a high value that is practical, the separation coefficient α becomes extremely low.

The above-mentioned membranes all have a separation coefficient of about 10, and have low separation performance. Therefore, an object of the present invention is to provide a pervaporative separation method that can maintain a high separation coefficient and process at a high permeation rate when separating water-organic liquid mixtures or organic-organic liquid mixtures by pervaporative methods. It is about providing.

[Means for solving problems]

The present inventors have made extensive studies to achieve this objective, and have surprisingly found that when pervaporative separation is performed using a drying membrane composed of a polymer with an ionized glycoside skeleton as its main chain, extremely high It was discovered that a mixed liquid can be treated at a high permeation rate while maintaining a separation coefficient, leading to the present invention. That is, the present invention is composed of a polymer having a glycoside skeleton as a main chain having an anionic group forming an alkali metal salt with a counter cation, and has a water content of 25% by weight or less. This is a pervaporative separation method characterized by pervaporatively separating a water-organic liquid mixture or an organic-organic liquid mixture using a membrane dried as described above. (referred to as saccharide-based dry film).

In the present invention, if the membrane is made into an alkali metal salt membrane and then dried before pervaporation, a high separation coefficient can be obtained in the separation of a water-organic liquid mixture or an organic-organic liquid mixture. However, the term "dry membrane" as used in the present invention refers to a membrane whose moisture content is 25% by weight or less, preferably 15% by weight or less. There are no particular restrictions on the method of drying the membrane, but for example, the membrane may be left in dry air or vacuum dried. For convenience, attach the ionized polysaccharide membrane to a pervaporation device, and before starting pervaporation separation, dry the secondary side of the membrane by keeping it at a reduced pressure of, for example, 0.3 mmHg for about 10 minutes with a vacuum pump, or dry it. It may be dehydrated by immersing it in an organic liquid having a water content of 0 to 20% by weight. Note that heating may be freely performed to the extent that the film does not denature. The moisture content of the membrane can be easily measured using a moisture meter.

In the anionic polysaccharide dry membrane used in the method of the present invention, the anionic group includes all anionic groups that can form salts, but for practical purposes, sulfate ester residues, sulfonic acid residues, etc. groups, carboxylic acid residues, phosphoric acid ester residues and phosphonic acid residues are preferably used. The anionic polysaccharide dry membrane used in the present invention is a membrane obtained by drying a membrane having one or more groups selected from the group of ionic groups, for example, by the method described above.

Specific examples of the anionic polysaccharide dry membrane used in the present invention include salts of natural polysaccharides such as alginic acid, pectic acid, chondroitin sulfate, hyalonic acid, xanthan gum, etc. These derivatives, e.g.
Salts of partially methylesterified alginic acid, carbomethoxylated alginic acid, phosphorylated alginic acid, aminated alginic acid, etc., semi-synthetic polyesters such as CM cellulose, cellulose sulfate, cellulose phosphate, sulfoethyl cellulose, phosphoethyl cellulose, phosphorylated guar gum, phosphorylated chicken, etc. Examples include dry films made of sugar salts and the like. Among these, in the present invention, dry membranes made of alginates, alginic acid derivative salts, and cellulose derivative salts are preferably used in terms of membrane formability, mechanical strength, and membrane performance.

The anionic polysaccharide-based dry membrane used in the present invention is a dried film containing the above-mentioned anionic polysaccharide-based polymer as a main component, but is blended with a polymer that is compatible with the anionic polysaccharide. For example, membranes obtained by drying blend membranes with neutral polysaccharides such as PVA, pullulan, and starch, and graft membranes grafted with hydrophilic vinyl monomers such as acrylic acid are also included.

In the anionic polysaccharide dry membrane used in the present invention, the anionic group must form a salt with a counter cation to the group. When the anionic group is a sulfuric acid ester residue, a sulfonic acid residue, a phosphonic acid residue, etc., counter cations for the group include lithium, sodium, potassium,
Ions of alkali metals such as rubidium and cesium are effective and preferred in the present invention.
In addition, in the present invention, when the same polymer has a cation and an anion and is ionized within and/or between molecules, or when the counter ion is a polyion (for example, alginic acid and polyethyleneimine, alginic acid and Also includes ion complexes such as chitosan).

In order to more specifically explain the anionic polysaccharide-based dry membrane used in the present invention, the ionization method thereof will be explained using alginic acid-based polysaccharide membranes and cellulose derivative membranes as examples of the anionic polysaccharide-based dry membranes. will be described in detail, but the present invention is not limited in any way by this specific example.

First, an alginate polysaccharide membrane, which is an example of an anionic polysaccharide dry membrane, will be described. Alginic acid is a sticky polyuronic acid extracted from brown algae such as kelp.
This is a block copolymer consisting of three types of blocks: a GG block in which only L-guluronic acid (G) of the (1→4) bond is arranged, and an MG block in which M and G are arranged alternately. Alginic acid forms a salt with an alkali such as sodium hydroxide or potassium hydroxide and easily dissolves in water. Therefore, by casting a solution of this alginate on a glass plate and drying it naturally, it becomes transparent. A homogeneous alginate film is formed. Alternatively, the alginate solution may be dissolved in a water-soluble organic solvent (e.g. ethanol, isopropanol,
When brought into contact with acetone, etc.) or a concentrated salt solution, the salt has the property of coagulating and precipitating, so a wet coagulation film can also be made using this property. Alginic acid polysaccharide refers to alginic acid and its derivatives. Before pervaporation using such an alginate polysaccharide membrane, it is dried to a water content of 25% by weight or less, for example, according to the method described above. When ionizing the membrane, multiple types of countercations may be used simultaneously. As the ion source, salts or hydroxides are used in the case of metal ions, and salts or amines are used in the case of ammonium ions. Methods for preparing an anionic alginate polysaccharide membrane having these cations as countercations include immersing the alginate polysaccharide membrane or alginate polysaccharide salt membrane in a solution containing the cations and performing ion exchange; There is a method in which ions are exchanged sequentially by performing pervaporation treatment with a mixed liquid containing such cations.

In the present invention, the content of countercation in the membrane is
Since there are suitable contents depending on the type of countercation and the liquid mixture to be separated, it is selected appropriately depending on each system. For example, when the liquid mixture to be separated is a water/ethanol mixture, it is desirable to use a membrane with an ionized cation content of 2 mol % or more (based on the carboxyl groups of alginic acid).

Anionic polysaccharide dry membranes, including the alginate polysaccharide dry membrane, are hydrophilic, so when the liquid mixture to be separated is a water-organic liquid mixture,
Membrane performance is greatly affected by water concentration. The concentration of the organic liquid at which the anionic polysaccharide-based dry membrane exhibits high performance has a suitable concentration range depending on the type of membrane, the type of ion, and the type of organic liquid. It is selected accordingly. For example, when a water/ethanol mixture is separated using a dry membrane made of sodium alginate, the ethanol concentration is desirably 70% by weight or more, preferably 85% by weight or more.

In order to improve the water resistance and mechanical strength of the anionic polysaccharide film, it is desirable to further crosslink it.
There are methods such as forming ester bonds between polysaccharide molecules using polyhydric alcohols, and forming acetal bonds between molecules using aldehydes. The ionization method, crosslinking method, etc. described above can also be applied to other anionic polysaccharides.

Whether or not metal ions are coordinated in the film can be determined quantitatively using atomic absorption spectroscopy, but an alginate-metal salt film is formed because the film is colored in a color unique to the salt. You can confirm that.

Carboxymethylcellulose, which is a cellulose derivative salt, can be easily obtained by reacting chloroacetic acid with cellulose under alkaline conditions, and cellulose sulfate can be easily obtained by reacting a chlorosulfonic acid-pyridine mixture with cellulose. The anionic cellulose derivative thus obtained can be ionized in the same manner as the ionization of the alginic acid polysaccharide described above. Further, similar crosslinking methods and drying methods can be used.

The thickness of the separation membrane used in the method of the present invention is 1μ
-300μ, preferably 5-200μ. If the film thickness is thinner than this, the strength of the film will be insufficient or the durability will be insufficient. Furthermore, if the membrane thickness is thicker than this, the amount of liquid mixture permeating through the membrane will be small, making it impractical. Furthermore, when the ionized polysaccharide membrane is used by being attached to a support membrane, such as a microporous membrane, the ionized polysaccharide membrane can be sufficiently used even if the thickness of the ionized polysaccharide membrane is reduced. In this case, the thickness of the ionized polysaccharide membrane can be reduced to about 0.1 μm. The shape of the separation membrane is used as a flat membrane (flat membrane), but it can also be used in other shapes such as a cylindrical shape or a hollow fiber shape to increase the membrane surface area.

Water-organic liquid mixtures that can be separated by the pervaporation separation method of the present invention include water/methanol, water/ethanol, water/n-propanol,
water/isopropanol, water/n-butanol,
Water/isobutanol, water/n-amyl alcohol, water/n-hexanol, water/2-ethylhexanol, water/n-octanol, water/ethylene glycol, water/1,3-propanediol,
Water/alcohol mixtures such as water/1,4-butanediol, water/1,2-propylene glycol, water/glycerin; water/tetrahydrofuran,
Water/dioxane, water/methyl ethyl ketone, water/
Acetone, water/N,N-dimethylacetamide,
Examples include water/N,N-dimethylformamide. In addition, organic-organic liquid mixtures include methyl acetate/methyl alcohol, ethyl acetate/ethyl alcohol, benzene/cyclohexane, methanol/acetone, benzene/methanol, benzene/ethanol, acetone/chloroform, methanol/acetone, ethylbenzene/styrene,
Examples include parachloroethylbenzene/parachlorostyrene, toluene/methylcyclohexane, and the like.

In particular, the pervaporative separation method of the present invention can be applied to water-organic liquid mixtures and organic-organic liquid mixtures.
Polar organic liquids (e.g. alcohols, ketones, etc.)
It is particularly effective in separating mixtures containing

The pervaporation device used in the present invention is not particularly limited, and any conventionally known device can be used, and such a device can be operated under conventional conditions to separate the organic mixed liquid. In performing pervaporation, the larger the pressure difference between the feed liquid side and the permeate side, the more effective it is, but for industrial implementation it is preferable to provide a pressure difference of 0.5 to 1 atmosphere. The pressure on the feed liquid side is preferably at or near atmospheric pressure, and the pressure on the permeate side is preferably maintained at a reduced pressure below the vapor pressure of the permeate component. Methods for maintaining the permeate side at reduced pressure include drawing a vacuum to reduce the pressure, or flowing a gas that does not react with the components to maintain a low vapor pressure. Separation temperature is 40℃
The temperature above and below the azeotropic temperature of the organic liquid mixture to be separated is normal, but is not particularly limited. One ionized polysaccharide-based membrane is used to separate liquid mixtures.
If the desired concentration cannot be obtained by passing the sample multiple times, it is possible to concentrate and separate the sample to the desired concentration by installing a similar device in succession and passing the sample multiple times, or by combining it with distillation.

〔Effect of the invention〕

By using the method of the present invention, it is possible to efficiently treat a mixed liquid at a high permeation rate while maintaining a higher separation coefficient than in conventional separation methods using membranes. Therefore, the separation system can be made more compact, the processing capacity can be increased, and the cost can be reduced.The present invention is effective in shortening the separation and purification process in the chemical industry, etc., and in practical application of membrane separation methods to save energy. The above-mentioned usefulness is extremely large.

[Example] Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Sodium alginate (manufactured by Hanui Chemical Co., Ltd.)
1000CPS) was made into a 1% by weight aqueous solution, which was cast onto a glass plate and air-dried to obtain a homogeneous transparent sodium alginate film with a thickness of 10μ.

The membrane was attached to a pervaporation device (effective membrane area 7.0 cm ² ), and the secondary side of the membrane was first heated to 0.3 mmHg using a vacuum pump.
Hold for 10 minutes to dry the membrane. The water content of the film was measured using a Shimadzu electronic moisture meter (EB-280MOC model) and was found to be 12% by weight. Next, a 60°C ethanol/water (90/10 weight ratio) mixture was supplied,
Pervaporative separation was performed while maintaining the secondary side of the membrane at 0.3 mmHg. The separation coefficient and permeation rate 6 hours after starting pervaporative separation are 29880 and 202 g/
It was ^m2・hr.

Example 2 The same sodium alginate membrane as in Example 1 was immersed in an ethanol/water (50/50 weight ratio) mixture for 13 hours at 30°C, and then ethanol/water (90/10 weight ratio).
It was immersed in the mixed solution for 1 minute to dehydrate. The moisture content of the film was measured using the moisture meter used in Example 1.
It was 14.5% by weight.

The membrane was installed in the same pervaporation device as in Example 1,
An ethanol/water (90/10 weight ratio) mixture at 60° C. was supplied to one side of the membrane for 5 minutes. 0.3 on the secondary side of the membrane
When pervaporation separation was performed while maintaining the temperature at mmHg, the separation coefficient and permeation rate 6 hours after starting pervaporation were 12,900 and 250 g/m ² ·hr, respectively.

Comparative Examples 1-2 The same sodium alginate membrane as in Example 1 was soaked in an ethanol/water (50/50 weight ratio) mixture at 30°C for 13 minutes.
After soaking for an hour, the membrane was placed in the same pervaporation device as in Example 1 without drying, and a 60°C ethanol/water (90/10 weight ratio) mixed solution was supplied to one side of the membrane for 5 minutes. Reduce the pressure on the secondary side to 0.3mmHg,
Pervaporative separation was performed. The separation coefficient and permeation rate 6 hours after starting pervaporation are respectively
10.70, 510 g/m ² hr (Comparative Example 1).

In addition, the same sodium alginate membrane as in Example 1 was added to a mixed solution of ethanol/water (50/50 weight ratio) for 30 minutes.
Soaked for 13 hours at °C and air dried in air. The water content of the membrane was 30.5% by weight. When pervaporation separation was carried out in the same manner as in Comparative Example 1, the separation coefficient and permeation rate 6 hours after starting pervaporation were 432 and 314 g/m ² ·hr, respectively (Comparative Example 2).

Claims (1)

[Claims] 1. Consisting of a polymer having a glycoside skeleton as a main chain having an anionic group forming an alkali metal salt with a counter cation, and having a water content of 25% by weight or less 1. A pervaporative separation method characterized in that a water-organic liquid mixture or an organic-organic liquid mixture is pervaporatively separated using a membrane that is dried so as to have the following properties. 2 Claims in which the anionic group is one or more groups selected from the group consisting of sulfuric acid ester residues, sulfonic acid residues, carboxylic acid residues, phosphoric acid ester residues, and phosphonic acid residues. The pervaporative separation method described in item 1. 3. The pervaporative separation method according to claim 1 or 2, wherein the polymer is an alginate or an alginic acid derivative salt. 4. The permeation separation method according to claim 1 or 2, wherein the polymer is a cellulose derivative salt.