JPH02211226A - Recovery of base - Google Patents

Abstract

PURPOSE:To efficiently remove base from a high viscosity base solution by using a fluorine-containing cation exchange membrane having specific ion exchange capacity and water content. CONSTITUTION:A base-containing solution is brought into contact with the single surface of a fluorine-containing cation exchange membrane composed of a repeating unit represented by formula I (wherein X is F or CF3, m is 0 or 1, n is 1-5, p and q are a positive number and p/q is l-7 and M is a cation such as an alkali metal, amine or the like), having ion exchange capacity of 0.6-2.5 milliequivalent/gram resin and containing 20-250wt.% of water and water or a dilute base solution is brought into contact with the other single surface thereof. By this method, the base is selectively diffused and dialyzed from the base-containing solution to be recovered and removed. By forming this cation exchange membrane into a hollow system or a hollow tube, the base can be efficiently recovered and removed from a high viscosity solution.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a new method for efficiently and selectively recovering or removing a base from a base-containing solution by diffusion dialysis using an ion exchange membrane.

Bases in the paper, pulp and regenerated cellulose industries, such as pulp processing waste containing caustic soda, alkali-containing solutions from metal processing processes, alkali-containing solutions from ion exchange resin regeneration processes, and even alkali-containing solutions obtained by diaphragm electrolysis. Selective recovery of the base in the solution containing it and debasing from the solution may be carried out in some cases for the purpose of effective resource utilization, and in some cases as a process in the manufacturing process. This is an absolutely necessary measure from a pollution standpoint.

(Prior art) As a means of recovering or removing a base from a base-containing solution, the base-containing solution is placed opposite to water via a cation exchange membrane, and the base is selected by diffusion dialysis using a base concentration gradient. A method has been proposed to collect the waste.

(Special Publication No. 36-19463) Such diffusion dialysis is
Since bases can be selectively recovered using a simple device without special reagents or means such as heating, it is expected to be widely used in many industrial fields.

However, conventional cation exchange membranes generally have a low base permeation rate, and therefore have the disadvantage of requiring large recovery equipment.

In order to improve these drawbacks, the applicant proposed the use of a cation exchange membrane made of a copolymer of ethylene and unsaturated carboxylic acid with specific physical properties as a diaphragm for diffusion dialysis in Japanese Patent Application No. 52-6786. It was proposed as a publication.

Although this method significantly improved the base permeation rate, it had drawbacks such as the base permeation rate decreasing over time if the membrane dried during use or if the concentration of the base-containing solution was high. .

(rJIH point to be solved by the invention) The purpose of the present invention is to solve the above-mentioned drawbacks of the prior art, and furthermore, it is an object of the present invention to solve the above-mentioned drawbacks of the prior art. An object of the present invention is to provide a diffusion dialysis method that can efficiently remove a base from a highly viscous base solution such as a viscose solution containing caustic soda obtained in the process of manufacturing viscose rayon.

(Means for Solving the Problems) The present invention has been made to solve the above-mentioned problems by contacting one side of a cation exchange membrane with a solution containing a base, and contacting the other side with a solution containing a base. In the recovery of a base by contacting with water or a dilute base solution and selectively diffusing and dialyzing the base from a solution containing the base, the ion exchange capacity of the cation exchange membrane is 0.6 to 2.5 meq/g resin, The present invention provides a method for recovering a base characterized by comprising a fluorine-containing cation exchange membrane having a water content of 20 to 250% by weight.

As the polymer of the fluorine-containing cation exchange membrane used in the present invention, a fluorine-containing cation exchange membrane having basically the above-mentioned specific physical properties is used. This is known to be used in cation exchange 1 for salt electrolysis, as will be explained later, but it is required that the cation exchange membrane for salt electrolysis does not allow base (OH) to permeate. On the other hand, the cation exchange membrane for base diffusion dialysis of the present invention is fundamentally different in that it is required to have high base permeability. It is quite surprising that a membrane of the same type as that used for salt electrolysis is used, albeit with a high water content.

Furthermore, as mentioned earlier, it is already known that a cation exchange membrane made of a copolymer of ethylene and unsaturated carboxylic acid having a specific moisture content is used for diffusion dialysis of bases. Ion exchange membranes have had drawbacks such as a decrease in base permeability during use and a significant decrease in base permeability upon drying. As a result of intensive research into ways to improve these drawbacks, the present inventor found that such drawbacks can be improved by using a fluorine-containing cation exchange membrane known as a cation exchange membrane for salt electrolysis. They discovered this and completed the present invention.

Here, it is not clear why the use of a fluorine-containing cation exchange membrane having a specific water content prevents a decrease in base permeability, but it is probably due to the following reasons.

An alkali ion ionomer consisting of tetrafluoroethylene and perfluorovinyl ether containing an acidic group has a high glass transition temperature, exhibits no thermoplasticity, and has a stable polymer structure. Ionomers, which are made of copolymers of Even when using a base ionomer as a membrane for base diffusion dialysis, the permeability of bases decreases during use, as the water content decreases or the structure of the polymer changes due to drying. It is explained that a diffusion dialysis membrane made of a fluoroethylene-based fluorine-containing ionomer has a stable polymer structure, so the water content does not change and the base permeability does not change.

However, such explanation is provided for the purpose of understanding the present invention, and does not limit the present invention in any way.

To explain the present invention in more detail below, the cation exchange membrane used in the present invention has a water content of 20 to 250% by weight and an ion exchange capacity of 0.6 to 265 milliequivalents/gram resin. A membrane is used.

When the water content is 20% by weight or less, the base permeation rate is low;
Particularly preferred is 25% by weight or more. Also, the moisture content is 250
If the content exceeds 150% by weight, the separation between the base and other impurities such as neutral salts and non-electrolytes will decrease, resulting in a decrease in strength, so 150% by weight or less is particularly preferred. This moisture content is
Even if it has the above range, if the ion exchange capacity is small, the selective permselectivity of the base will decrease, so it is preferably 0.6 or more, especially 1.0! equivalent weight per gram of resin or more is used.

A fluorine-containing cation exchange membrane having such physical properties has the general formula -(CF2CF2) e -(CF2CF)q -0(
CF2CF2)-(CF2), lA (1) MuA: C00M, SO3M or Po2(OM
hX is F or CFs, m is 0 or 1. n is 1 to 5,
p and q are positive numbers and the ratio p/q is 1-16. Examples include fluorine-containing cation exchange membranes in which M is hydrogen, an alkali metal, an alkaline earth metal, a metal, ammonium, or an amine cation.

Among them, fluorine-containing cation exchange membranes in which A is C00M and p/q is 1 to 7 have a large ion exchange capacity and a copolymer with high mechanical strength, and have low permeability of neutral salts and non-electrolytes. It is particularly preferably used because it has low permselectivity and excellent permselectivity for bases. If necessary, it can contain other third components.

The fluorine-containing cation exchange membrane comprises precursor polymers thereof,
For example, A is COOR (R is an alkyl group), CN, CO
Heat compression molding of thermoplastic resin such as P or 502F,
It can be processed into a film by means such as melt extrusion molding, or by coating and drying a suspension, emulsion, or solution of a precursor polymer or ion exchange resin. In addition, such cation exchange membranes are made by processing a copolymer having the above-mentioned specific physical properties alone into a membrane, and also by forming a porous membrane in order to provide practical strength such as dimensional stability and ease of handling. Reinforcement can be achieved using a flexible base material. Such a porous substrate can be used as a reinforced composite cation exchange membrane by being embedded in an ion exchanger layer, or can be used as a composite cation exchange membrane with a thin layer of ion exchanger and a porous substrate layer for the purpose of increasing base permeability. It can be a multi-layer cation exchange membrane.

The shape of the membrane is not limited to the general planar shape (bag-like, hollow fiber, hollow tube, etc.).Especially, in the case of a high viscosity solution containing a base with a viscosity of 10 poise or higher, In flat membrane filter press type dialysis tanks, it is difficult to balance the pressure between the raw solution side and the recovered liquid side, which can lead to damage to the membrane and difficulty in uniformly flowing a high viscosity solution into each chamber divided by the membrane. Therefore, the cation exchange membrane of the present invention has an inner diameter of 50μ to 10mm.
By using a hollow fiber type module, preferably 200μ to 4mmq, with a membrane thickness of 1μ to 1mm, preferably 10μ to 400μ, in the form of hollow fibers or hollow tubes, bases can be efficiently recovered from high viscosity solutions. Such a high viscosity solution is preferably used for recovering alkali from an alkaline aqueous solution of sodium xanthate or an alkaline solution containing various polymers in the production of viscose rayon or cellophane.

(If the membrane obtained is not converted into an ion exchange group, it is hydrolyzed. In the present invention, in order to maintain the water content of the ion exchange resin within a certain range, the hydrolysis conditions of the membrane or Subsequent processing conditions may be important.

For example, for membranes with low ion exchange capacity whose water content is lower than the range of the present invention, swelling treatment with water or a water-soluble organic solvent may be performed after hydrolysis, or hydration may be performed in the presence of a water-soluble organic solvent during hydrolysis. Decomposition is preferred. In any case, a high-performance alkali diffusion dialysis membrane can be obtained by appropriately selecting treatment conditions so as to obtain the water content of the present invention.

Thus, by contacting one side of the cation exchange membrane of the present invention with a solution containing a base and the other side with water or a dilute solution, the base can be selectively permeated by the known method of diffusion dialysis. be able to.

Next, the present invention will be explained with reference to examples, but first a measurement method will be described.

*Measurement of water content The weight of the membrane used for diffusion dialysis or the ion exchanger layer prepared under the same conditions in pure water at 25°C is wl.

The weight of the film after vacuum drying at 130°C is determined as W2,
It was calculated according to the following formula.

Water content - (w + -W2/W2) X 100 Note that the present invention is not limited to these examples.

Example (Example 1) Tetrafluoroethylene and CF2CF2 (CF2)
Ion exchange capacity with 3COOCH3 is 1.25! Equivalent /
Copolymer A of Gram resin was melt-extruded to a film thickness of 5.
A 0 micron copolymer A film was obtained. The film A was hydrolyzed with an aqueous caustic soda solution and then boiled in pure water for 1 hour.

On one side of the thus obtained membrane (effective area A m2), 2.6 mol/L of caustic soda and 1.3 mol/L of sodium aluminate were added.
Place a solution containing water on the other side, and set the temperature of the liquid in the painting chamber to 2.
Dialysis was carried out at 5°C for 2 hours (dialysis time t), and the diffusion dialysis coefficient U was calculated from the concentration difference ΔC (mol/L) in the m1 compartment, which was the number of moles of caustic soda and sodium aluminate that moved to the water side, using the following formula. Ta.

lJ=m/(AXΔcXt) As a result, UNaO[+=4, UAl=0.036U
AI/UNaOB=110. Moreover, the water content of the protective film was 25% by weight.

(Comparative Example 1) Measurements were made in exactly the same manner as in Example 1, except that the boiling treatment with pure water was not performed, and the water content of the protective film was 1.
At 2% by weight, UNaOH = 0, 8, UAI = 0.0
3, UAI/UNaOH = 150.

(Example 2) Tetrafluoroethylene and CF2-CFO (CF2)
Copolymer B with an ion exchange capacity of 1.8 meq/g resin with 3cOOcH3 was melt-extruded to a film thickness of 50
A micron copolymer B film was obtained. The film B is
After hydrolysis with a caustic soda aqueous solution, the membrane was divided into two parts and one of the membranes was boiled in pure water for 1 hour.

The diffusion dialysis coefficient and water content of the two membranes obtained were determined in the same manner as in Example 1. The results are shown in Table 1.

(Example 3) Tetrafluoroethylene and CF2-rich CFOCF2CF (
A copolymer C having an ion exchange capacity of 1.1 meq/g resin with CFRI0-(CF2)2S02F was melt-extruded to obtain a film C having a thickness of 50 microns. The film C was hydrolyzed with a dimethyl sulfoxide aqueous solution of caustic potash, and then boiled in pure water.

The diffusion dialysis coefficient and water content of the obtained membrane were determined in the same manner as in Example 1. The results are shown in Table 1.

(Example 4) Tetrefluoroethylene and CFzlICFO (CF2)
Ion exchange capacity with 3COOCH3 is 1.44! Equivalent /
A copolymer of gram resin is melt-extruded and molded to an inner diameter of 4.
A hollow fiber having an outer diameter of 50μ and an outer diameter of 550μ (film thickness of 50μ) was obtained. After hydrolyzing the hollow fiber with a caustic soda aqueous solution,
It was boiled in pure water for 1 hour.

The 120 hollow fibers obtained in this manner were bundled to create a module as shown in Figure 1.The effective length of the hollow fibers was approximately 60 mm.
It was cm. A solution containing 27 g/L of hemicellulose and 206 g/L of caustic soda was flowed inside the hollow fibers of the module at 90 mL/hr, and 150 mL/L was flowed in the outer cylinder on the outside of the hollow fibers in the countercurrent direction. When pure water was supplied at a rate of 120 mL/hr, a solution containing 2 g/L of hemicellulose and 135 g/L of caustic soda was recovered.

(Example 5) Copolymer B having an ion exchange capacity of 1.8 meq/g resin used in Example 2 was melt-extruded and then hydrolyzed with caustic soda to give an inner diameter of 1.9 mm.

A hollow tube with an outer diameter of 2.1 mm was obtained. The hollow tube thus obtained,
A module as shown in Fig. 1 was created by bundling 40 pieces with an effective length of 60 cm. Polyvinyl alcohol 180g/L1 caustic sorter 40g/L inside the hollow tube of the outer module
A solution with a viscosity of 260 poise was injected at 1 kg/cm2.
When pure water was supplied at 100 mL/hr in the countercurrent direction into the outer cylinder outside the hollow tube, a solution of 30 g/L of caustic soda was recovered at 110 mL/hr. did it.

[Brief explanation of the drawing]

FIG. 1 is a conceptual longitudinal cross-sectional view of an example of a base recovery device used in the present invention. ! , Hollow fiber cation exchange membrane 2, Processing liquid population 3, Processing liquid (dialysate) outlet 4, Recovery liquid population 5, Recovery liquid (diffusion liquid) outlet 6, Dialysis device 7, Partition wall

Claims (4)

[Claims] (1) Recovery of base by selectively diffusing and dialyzing the base from the base-containing solution by contacting one side of the cation exchange membrane with a solution containing a base and contacting the other side with water or a dilute base solution. A method for recovering a base, characterized in that the cation exchange membrane has an ion exchange capacity of 0.6 to 2.5 milliequivalents/gram resin and a fluorine-containing cation exchange membrane having a water content of 20 to 250% by weight. (2) The fluorine-containing cation exchange membrane has the general formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (1) X is F or CF_3, m is 0 or 1, n is 1 to 5,
p and q are positive numbers and the ratio p/q is 1-7. The base recovery method according to claim (1), wherein M is a repeating unit represented by an alkali metal, alkaline earth metal, metal, ammonium or amine cation. (3) The recovery method according to claim (1) or (2), wherein the fluorine-containing cation exchange membrane is a hollow fiber or a hollow tube. (4) The recovery method according to claim (3), wherein the base-containing solution is a high viscosity solution with a viscosity of 10 poise or more.