JPS6366563B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for separating a liquid mixture containing at least an organic liquid as one of its components by pervaporation.

This separation method is used to separate and purify chemical liquids (mainly organic solvents, hydrocarbons, etc.) that cannot be separated using normal distillation methods, such as azeotropic mixtures, solvents with similar boiling points, and isomers (ortho and para, cis and trans). For fractional separation, such as concentration and purification of mixed liquids and fruit juices containing thermally decomposable components, removal of trace impurities,
Furthermore, it is used to remove water generated during the esterification reaction.

(Prior technology) A mixed liquid is placed on one side of the separation membrane, and the other side is evacuated to reduce the pressure, or an inert gas is flowed to keep the vapor pressure low and the liquid permeates. The so-called pervaporation method, which separates a liquid mixture by evaporation, has been studied since the mid-1950s.

Many examples have been reported in which organic mixed liquids, especially water-alcohol mixed liquids, are separated by such pervaporation methods. For example, U.S. Patent No. 2953502 describes an experimental example of separating water-methanol mixed liquid using a cellulose acetate membrane (separation coefficient 5.1, permeation rate 3.1 Kg/m ² hr), No. 33 of Functional Materials December issue (1981). The page shows an experimental example of separating water and ethanol mixed liquid using a cellulose acetate membrane (separation coefficient 8.5, permeation rate 1.95Kg/
^m2・hr) and an experimental example in which a mixed liquid of water and isopropanol was separated using a cellophane membrane (separation coefficient
15.6, permeation rate 0.7Kg/ ^m2・hr), Journal of
Applied Polymer Science vol 26 (1981)
On page 3223, there is an experimental example in which a mixed liquid of water and methanol was separated using a grafted polyvinyl alcohol membrane (separation coefficient 22.6, permeation rate 0.2 Kg/m ² hr)
etc. have been reported.

(Problems to be Solved by the Invention) The methods for separating water-alcohol mixed liquid using these membranes cannot be implemented on a laboratory scale, but there are the following problems when implemented on an industrial scale.
It was far from being practical. In other words, (1) the separation rate when a water-alcohol mixed liquid passes through a polymer membrane once [generally, the weight ratio of the water component to the alcohol component after passing through the membrane is calculated as the weight ratio of the water component to the alcohol component before passing through the membrane] The value divided by the ratio is displayed as the separation coefficient α. In other words, α = (W/A in the permeate liquid/(W/A) in the permeate liquid (in the formula, W and A indicate the weight of the water component and the alcohol component, respectively)] is small, so the objective In order to separate or concentrate to the desired concentration, it must be passed through a very large number of membranes.

(2) Amount of permeation through a polymer membrane [Generally, the amount of permeation per unit membrane surface area and unit time, that is, Q
(expressed in Kg/m ² hr)] is small, so there are problems such as the need to increase the membrane surface area.

(Means for Solving the Problems) The present inventors solved the problems of the conventional pervaporation method and separated an organic mixed liquid by pervaporation with a high separation coefficient and high permeation rate. In order to provide this method, we conducted experiments using various membrane materials and found that at least 10 of the free amino groups in chitosan, which had not previously been used as a separation membrane for pervaporation, We have discovered that an N-modified chitosan membrane in which substituents with hydrophilic groups have been introduced in mol% actually achieves a higher separation coefficient and higher permeation rate than previously reported experimental values, and have thus arrived at the present invention. This is what I did. That is, the present invention provides an N-modified chitosan membrane (hereinafter referred to as N-
This is a method for separating a liquid mixture, which is characterized by separating a liquid mixture by pervaporation using a modified chitosan membrane (referred to as a modified chitosan membrane) in which at least an organic liquid is one of its components.

In the present invention, N-modified chitosan refers to free NH ₂ groups of chitosan as NHCOR(X) _o or NHOR(X).
_o group [R is a hydrocarbon group having 2 to 50 carbon atoms, X is OH,
represents a polar group such as COOH or SO ₃ H, which has a strong affinity for water, and n is an integer of 1 to 2]. Such an N-modified chitosan film is a chitosan film with a degree of deacetylation of 70 mol% or more, which will be described later, containing succinic anhydride, phthalic anhydride, sulfophthalic anhydride, trimellitic acid, β-propiolactone, a terpene compound, and a polyfunctional It can be obtained by reacting fatty acids etc. under heterogeneous reaction conditions. The degree of modification of the N-modified chitosan used in the present invention is 10 mol% or more (preferably 30 mol% or more) of the free amino groups of chitosan. In the method of the present invention, it is essential to use an N-modified chitosan membrane into which hydrophilic groups have been introduced through such modification, and it is more preferable to use an N-modified chitosan membrane that has hydrophilic groups such as acetic acid, propionic acid, and benzoic acid than unmodified chitosan membranes. The separation performance in pervaporation is superior to that of acylated chitosan membranes.

The chitosan used to obtain the N-modified chitosan film of the present invention is chitin, which is a component of the outer skin of crustaceans such as shrimp and crabs, and has an alkaline concentration of 30 to 50.
A substance obtained by deacetylation by heating with a wt% alkaline solution (e.g. sodium hydroxide aqueous solution) to a temperature of 60℃ or higher, and its chemical structure is D.
- β whose basic unit is glucosamine - (1 → 4)
It is a bonded polysaccharide that easily dissolves in dilute aqueous solutions such as acetic acid, hydrochloric acid, and phosphoric acid, forming a salt, but when it comes into contact with an alkaline aqueous solution, it solidifies and precipitates again. . Therefore, a chitosan film can be obtained by dissolving chitosan in the above-mentioned solvent, filtrating the resulting solution, and bringing it into contact with an aqueous alkaline solution, and this film is subjected to N-modification as described above. Furthermore, what is chitosan?
It is a general term for deacetylated products obtained by treating chitin with concentrated alkali, and the chitosan used for N-modification in the present invention has a degree of deacetylation of 70.
% or more is preferable.

The N-modified chitosan film may be a blend film obtained from a blend film of chitosan and polyvinyl alcohol (PVA). used for blending
PVA has a degree of saponification of 80% or more, preferably 98% or more. The N-modified chitosan membrane is a membrane containing the above-mentioned N-modified chitosan as at least one component, and also includes blend membranes, filler-added membranes, graft membranes, crosslinked membranes, and the like. These chitosan membranes have various structures such as homogeneous membranes, composite membranes, and asymmetric membranes.

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 N-modified chitosan membrane is used by being attached to a porous membrane (such as a microporous membrane), the N-modified chitosan membrane can be used sufficiently even if the thickness of the N-modified chitosan membrane is reduced. In this case N-
The thickness of the modified chitosan membrane can be reduced to about 0.1μ. The shape of the separation membrane is usually a flat membrane (flat membrane), but other shapes such as a cylindrical shape or a hollow fiber shape can also be used to increase the membrane surface area.

In the present invention, the "mixed liquid" which is the liquid to be separated
is an azeotropic mixture, a close boiling point mixture, etc.
The method of the present invention is particularly effective in separating organic mixed liquids. Among organic liquid mixtures, azeotropic liquid mixtures include:
Water/alcohol such as water/ethanol, water/isopropanol, methyl acetate/methyl alcohol, ethyl acetate/ethyl alcohol, benzene/
Examples include cyclohexane, methanol/acetone, benzene/methanol, benzene/ethanol, acetone/chloroform, and methanol/acetone. Further, examples of liquid mixtures with close boiling points include ethylbenzene/styrene, parachloroethylbenzene/parachlorostyrene, toluene/methylcyclohexane, butadiene/butenes, butadiene/butanes, and the like. water/acetone,
Water/ethylene glycol, water/glycerin, water/
The above mixture also includes liquid mixtures such as methanol that can be separated by ordinary distillation.

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. When 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. be. In addition, the pressure on the supply liquid side is preferably atmospheric pressure or a pressure close to it.
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. The separation temperature is usually 40°C or higher and lower than the azeotropic temperature of the organic liquid mixture to be separated, but is not particularly limited. When separating a liquid mixture, if the desired concentration cannot be obtained by passing it through a chitosan membrane once, the desired concentration can be achieved by installing a similar device in succession and passing it through multiple times, or by combining it with distillation. can be concentrated and separated.

(Effects of the Invention) According to the method of the present invention, a higher separation coefficient and higher permeation rate can be achieved than in conventional membrane separation methods. Therefore, according to the method of the present invention, the separation system can be made more compact, the processing capacity can be increased, and the cost can be reduced. It is effective in the production of chemical substances, and has extremely great industrial utility.

(Example) Next, the method of the present invention will be explained in more detail with reference to Examples.

Example 1 Three water-swollen chitosan membranes (8.5 x 8.5 cm ² ) with a degree of deacetylation of 99% were placed in a shear dish, and 50 ml of methanol was added. A solution of 3 g of succinic anhydride dissolved in 50 ml of methanol was added to the mixture, and the mixture was allowed to stand at room temperature for 18 hours.

After the reaction was completed, it was washed with methanol, immersed in methanol, and then dried on a glass plate. The degree of N-acylation determined from elemental analysis of the N-β-carboxypropionyl chitosan thus obtained was 68%, and the film thickness was 21 μm.

Set the membrane in a pervaporation device with an effective area of ^23.5cm2 , and mix ethanol to water (50/5
0wt/wt) mixture was supplied, and the exhaust chamber was depressurized to 7mmHg using a vacuum pump at 60°C to perform separation. At this time, the separation coefficient α ^H2O _EtOH of water (H ₂ O) with respect to ethanol (EtOH) was 58.1, and the permeation amount was 1.48 Kg/m ² ·h.

Example 2 Chitosan membrane with a degree of deacetylation of 99% (8.6×8.6
cm ² ) were placed in a shear dish, 50 ml of an acetonitrile-water mixture (4:1) was added, and the mixture was left for about 10 minutes. A mixture of acetonitrile and β-propiolactone (30 ml/20 ml) was added to this, followed by acetonitrile and water (10 ml/10 ml), and the mixture was reacted at room temperature for 2 hours. After the reaction, wash with 80% ethanol aqueous solution, immerse the membrane in 70 ml of 80% ethanol aqueous solution containing 0.5% NaOH for 4 hours, wash with 50% ethanol aqueous solution, and then wash twice with 50% ethanol aqueous solution. did. The obtained membrane was washed with a 70% ethanol aqueous solution and then dried on a glass plate. The N-reaction rate determined from the elemental analysis values of the β-propiolactone-reacted chitosan film obtained in this way is 64
%, and the film thickness was 20μ.

Membrane performance was measured under the same conditions as in Example 1 and found that α ^H2O _EtOH = 21.0 and Q = 4.42 Kg/m ² ·h.

Example 3 Three water-swollen chitosan membranes (8.5 x 8.5 cm ² ) with a degree of deacetylation of 99% were placed in a shear dish, and 20 ml of methanol was added. Next, a solution of 3 g of phthalic anhydride in 80 ml of methanol was added and left at room temperature for 18 hours. After the reaction was completed, it was treated in the same manner as in Example 2 to obtain a dry film. N- obtained in this way
The degree of acylation obtained from elemental analysis of O-carboxybenzoyl chitosan was 37%, and the film thickness was 22μ.

Membrane performance was measured under the same conditions as in Example 1 and found that α ^H2O _EtOH = 37.2 and Q = 1.88 Kg/m ² ·h.

Comparative Example 1 The membrane performance of a chitosan membrane with a degree of deacetylation of 99% and a thickness of 21 μm was measured under the same conditions as in Example 1, and it was found that α ^H2O _EtOH = 9.1 Q = 2.10 Kg/m ² ·h.

Comparative Example 2 Four water-swollen chitosan membranes (8.5 x 8.5 cm ² ) with a degree of deacetylation of 99% were placed in a shear dish, and 50 ml of methanol was added. A solution of 3 ml of acetic anhydride dissolved in 50 ml of methanol was added to this, and the mixture was allowed to stand at room temperature for 17 hours. After the reaction was completed, it was washed with methanol and water and dried on a glass plate.

The degree of N-acetylation determined from the elemental analysis value of the N-acetylated chitosan obtained in this way is 70.
%, and the film thickness was 21μ.

Membrane performance was measured under the same conditions as in Example 1 and found that α ^H2O _EtOH = 4.7 and Q = 9.98 Kg/m ² ·h.

Comparative Example 3 Using propionic anhydride as a reaction reagent, a N- film with an acylation degree of 70% and a film thickness of 20μ was prepared in the same manner as in Comparative Example.
Propionyl chitosan was obtained.

Membrane performance was measured under the same conditions as in Example 1 and found that α ^H2O _EtOH = 3.6 Q = 8.64 Kg/m ² ·h.

In addition, Examples 1, 2, 3 and Comparative Examples 1, 2, 3
The chitosan used was prepared as follows. Chitin flakes obtained from snow crab are placed in a 50% sodium hydroxide aqueous solution while blowing nitrogen gas.
Deacetylation is achieved by heating at 110°C for 1 hour, and the reactant is taken out and thoroughly washed with water. The same operation was repeated three times for this reaction product to obtain chitosan.
% acetic acid aqueous solution to prepare an approximately 2% chitosan solution. Pour this solution into a large amount of 1N aqueous sodium hydroxide solution and solidify it into a string. When this string-like chitosan is treated again under the same conditions as before, chitosan with a degree of deacetylation of 99% is obtained.

Next, chitosan film formation was performed as follows.
After immersing 0.5 g of chitosan in 35 to 70 ml of distilled water for about 30 minutes, 0.75 ml of glacial acetic acid was added and dissolved with stirring. Next, after suctioning this solution, a glass plate (mirror finish,
20 x 20 cm) and air-dried at room temperature. The obtained membrane was immersed in a 1N aqueous sodium hydroxide solution,
After insolubilization, it was thoroughly washed with distilled water to obtain a chitosan membrane with a degree of deacetylation of 99%.

Claims (1)

[Claims] 1 At least 10 mol% of free amino groups of chitosan
A liquid mixture containing at least an organic liquid as one of its components is separated by pervaporation using an N-modified chitosan membrane into which a substituent having a hydrophilic group is introduced. Separation method for liquid mixtures.