JPH07802A - Method for producing silicic acid sol or alumina sol - Google Patents

Abstract

(57) [Summary] [Purpose] To stably produce silica sol or alumina sol using an electrodialyzer. [Structure] An aqueous solution of alkali silicate or alkali aluminate is introduced into the desalting chamber of an electrodialysis tank having alternating alkali-resistant anion exchange membranes and cation exchange membranes, and a caustic alkali aqueous solution is introduced into the concentrating chamber. Dialysis is performed to obtain silicic acid sol or alumina sol and caustic.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing silicic acid sol or alumina sol by an electrodialysis method using an alkali-resistant anion exchange membrane.

[0002]

2. Description of the Related Art Conventionally, as a method for producing silica sol, a method of treating an aqueous solution of sodium silicate with an acid or a method of treating the aqueous solution with a granular cation exchange resin to adsorb sodium ions is well known. Has been. However, these methods have significant drawbacks.

That is, in the former, not only the sodium salt of the acid used is produced and coexists with the sol, but the sol becomes unstable and gels, and the sodium salt is separated for a long time. It is not efficient and cannot produce good salt. In the latter case, the amount of sodium ions adsorbed by the ion exchange resin is limited, and when the aqueous sodium silicate solution is treated, the adsorbing ability is lost in a short time, so it is necessary to regenerate the ion exchange resin with an acid.
At this time, acid is required for each of the adsorption and regeneration steps, and sodium silicate is lost.

Furthermore, since silica sol tends to gel in the presence of a strong electrolyte, it causes gelation at the contact surface with the ion exchange resin and covers the ion exchange points on the ion exchange resin. The adsorption capacity for sodium ions decreases, and it is almost impossible to remove the gel that has entered the ion exchange resin.

As a method for removing sodium ions from an aqueous solution of a metal salt such as sodium silicate or sodium aluminate,
Diffusion dialysis and displacement dialysis can be considered. However, the diffusion dialysis method in which the former cation exchange membrane is used and the aqueous solution of the metal salt and water are countercurrently flowed through the membrane is not practical because the migration rate of sodium ions is poor.

In the latter case, a cation exchange membrane is used, through which the aqueous solution of metal salt and dilute sulfuric acid are caused to flow countercurrently to replace sodium in the aqueous solution of metal salt with hydrogen ion in dilute sulfuric acid. In the displacement dialysis method, the gelled substance is deposited on the surface of the cation exchange membrane, which makes continuous dialysis difficult.

For example, sodium silicate is decomposed by contact with an acid and liberates silicic acid. This silicic acid initially exists in a monomolecular state, but gradually polymerizes into a polymer and gels. It has been known. In order to prevent this, cation exchange is performed by increasing the linear velocity of the liquid by circulating it between the dialysis tank and a separately installed tank with a pump instead of slowly flowing the liquid as in the normal displacement dialysis method. It is possible to suppress the formation of the gelled product generated on the film to some extent.

However, even in this case, if the concentration of sodium ions in the solution facing the aqueous metal salt solution increases, the efficiency of substitution between sodium in the aqueous metal salt solution and hydrogen ions in the facing solution decreases. If the concentration of sodium ions in the counter liquid is kept low so that the efficiency does not decrease, the amount of liquid as drainage increases. To reduce this amount of drainage, a new electrodialysis facility will be required,
This method is also not a practical solution.

The present inventors have conducted various studies on these methods for producing a metal oxide sol and effectively recovering an alkali while preventing gelation from an aqueous solution of a metal salt. As a result, the present invention has been achieved. It was

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to obtain a stable silicic acid sol or an aqueous solution containing alkali silicate or alkali aluminate. A method for efficiently producing an alumina sol and an alkali is provided.

[0011]

The present invention uses an electrodialyzer constructed by alternately arranging cation exchange membranes and anion exchange membranes between an anode and a cathode, and uses the anion exchange membrane and the cation exchange membrane. An aqueous solution of alkali silicate or aluminum / alkali acid is supplied to the chamber composed of the membrane (desalting chamber), and an aqueous solution of caustic alkali is supplied to the chamber composed of the cation exchange membrane and the anion exchange membrane (concentration chamber). The method for producing a silicic acid sol or an alumina sol is characterized by using an alkali-resistant anion exchange membrane as the anion exchange membrane in performing an electrodialysis to obtain a caustic aqueous solution and a silicic acid sol or an alumina sol. .

The present invention will be described in more detail below. For example, in the case of sodium silicate, hydrolysis, which is an equilibrium reaction as shown in Chemical formula 1, occurs in an aqueous solution.

[0013]

Embedded image Na ₂ SiO ₃ + H ₂ O = NaOH + Na
HSiO ₃ NaHSiO ₃ + H ₂ O = NaOH + SiO ₂ + H
₂ O

When the aqueous solution is supplied to the desalting chamber of the electrodialysis device and electrodialysis is performed, NaO existing in the equilibrium reaction is obtained.
H moves to the concentration chamber and the equilibrium reaction moves to the right,
A silicic acid sol can be produced.

In the present invention, an anion exchange membrane that can withstand alkalinity is used in order to enable stable operation in practical use.

As the base material of such anion exchange membrane, an olefin polymer or a fluorinated olefin polymer is used. As the olefin polymer,
For example, ethylene, propylene, butene, homopolymers of olefins such as methylpentene, intercopolymers of these olefins, further, copolymers of olefins and other monomers are exemplified, specifically, high-density polyethylene, Examples thereof include low density polyethylene and polypropylene.

Examples of the fluorinated olefin polymer include various polymers or copolymers of ethylene tetrafluoride, ethylene trifluoride chloride, vinylidene fluoride, propylene hexafluoride and the like. Ethylene tetrafluoride, polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, ethylene-trifluoroethylene chloride copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, propylene-tetrafluoroethylene Ethylene oxide copolymers and the like.

The thickness of these substrates is usually 5 to 500 μm,
It is preferably about 20 to 300 μm.

The base material carries a polymerizable monomer. Examples of such a polymerizable monomer include vinyl pyridine and
Styrene or chloromethylstyrene and divinylbenzene are used.

If the amount of styrene, chloromethylstyrene or vinyl pyridine is too large, the flexibility of the resin layer is lowered and cracks are likely to occur. On the contrary, if the amount is too small, the electric resistance increases, which is not preferable. If the amount of divinylbenzene is too large, the electric resistance will be high, and if it is too small, the mechanical strength will be low, which is not preferable.

Therefore, the amount of the polymerizable monomer used is 10 to 80% styrene, 10 to 80% chloromethylstyrene, and 1 to 1% divinylbenzene based on the total weight of these.
30%, particularly preferably 15-70% styrene, 20-70% chloromethylstyrene, 5-2 divinylbenzene
It is appropriate to adopt 5%.

The polymerizable monomer thus impregnated into the substrate is partially polymerized by irradiation with ionizing radiation in the former stage, and is heated (without irradiation with the ionizing radiation) in the latter stage in the presence of a polymerization initiator. The rest is polymerized.

When the polymerizable monomer mixture is partially polymerized by irradiation with ionizing radiation such as gamma rays or electron beams, the conversion rate of the polymerization reaction is 80% or less, preferably 5 to 5.
It is desirable to select 50%, especially about 10-40%. If irradiation conditions that make the conversion rate of the polymerization reaction at this stage too large are adopted, deterioration of the substrate itself due to ionizing radiation occurs, and as a result it is difficult to obtain an anion exchange membrane having sufficient mechanical strength. Become.

Then, the remaining polymerization is carried out by heating in the presence of a polymerization initiator such as benzoyl peroxide without irradiation of ionizing radiation. In a usual polymerization operation, a method is employed in which a base material is impregnated with a polymerizable monomer mixture to which a polymerization initiator is added, a first stage ionizing radiation polymerization is carried out, and then a second stage heat polymerization is carried out.

As the ionizing radiation, Co ⁶⁰ or Cs ^{127 is used.}
A gamma ray from a radiation source or an electron beam from an electron beam accelerator is preferable, and the dose rate is 0.1 to 50 kilogray / hour,
Irradiation is preferably performed at 0.1 to 10 kilogray / hour. The irradiation dose is selected so as to obtain the above conversion rate of the polymerization reaction, and the irradiation temperature and time are also selected in the same manner.

Usually, the temperature is 60 ° C. or lower, preferably 10-40.
0.5 to 100 hours at a temperature of about ℃, preferably 1 to 5
By irradiation for about 0 hours, the desired conversion rate of the polymerization reaction can be achieved with an irradiation dose of 0.1 to 100 kilogray, preferably 1 to 50 kilogray.

The conditions of the latter-stage thermal polymerization are not particularly limited, but usually heating is carried out at a temperature not lower than the temperature at which the activity of the added polymerization initiator can be affected, and the remaining polymerization is carried out by heating. For example, when a polymerization initiator such as benzoyl peroxide is adopted, heat polymerization is carried out at 60 to 150 ° C., preferably 80 to 120 ° C. for 0.5 to 20 hours.

When the base material is impregnated with the polymerizable monomer mixture and polymerized, it is inert to the polymerization reaction,
In addition, a method is preferred in which the monomer-impregnated base material is sandwiched between a polyester film, a glass plate, an aluminum foil, and the like, which can be peeled off after the completion of the polymerization reaction.

In the present invention, the monomer mixture polymerized by impregnating the substrate is subjected to anion exchange group introduction reaction in the case of a suitable three-component mixture to form an anion exchange membrane. Usually, after the completion of the above-mentioned pre-stage and post-stage polymerization reactions, a method of aminating a chloromethyl group with a tertiary amine and introducing a quaternary ammonium-type anion exchange group by a conventionally known or well-known means. It is illustrated.

As the cation exchange membrane, a styrene-divinylbenzene cation exchange membrane generally used in industry can be used, but a fluorine-containing cation exchange membrane can also be used. Examples of such a fluorine-containing cation exchange membrane include a fluorovinyl polyether compound represented by Chemical formula ₂ and a general formula CF ₂ ═CZZ ′ (where Z and Z ′ are —H, —Cl, —F or CF _3). And a fluorinated olefin compound having an exchange capacity of 0.5 to 2.0 meq / g.
Those that are dry resins are preferred.

[0031]

## STR2 ## _{CF 2 = CFOCF 2 - (CFXOCF} 2) m - (CF
X ') _n- (CF ₂ OCFX ") _p -A

(Here, m is 0 to 3, n is 0 to 6, and p is 0.
~ 4. X, X ', X "are -F or 1 to 5 carbon atoms
Is a perfluoroalkyl group of and A is --COOH,-
It is a group that is converted to these groups by SO ₃ H or hydrolysis. )

An electrodialysis device is assembled by alternately arranging such cation exchange membranes and anion exchange membranes. As the anode used in the electrodialysis device, for example, a valve metal such as titanium or tantalum coated with a platinum group metal is used, and as the cathode, for example, nickel, iron or the like can be appropriately used.

The alkali salt of the metal oxide used in the present invention is, for example, sodium silicate or sodium aluminate. The alkali salts of these metal oxides are subjected to electrodialysis as an aqueous solution. Its concentration is generally SiO ₂
Alternatively, 1 to 20% by weight as Al ₂ O ₃ , preferably S
About 5 to 15% by weight is suitable as iO ₂ or Al ₂ O ₃ . If the concentration exceeds the above range, gelation is likely to occur, and conversely, if the concentration is less than the above range, the equipment for electrodialysis becomes excessive, which is not preferable.

The caustic alkali is caustic soda, caustic potash, etc., and its concentration is 10 to 300 g / l, preferably 50 to 200 g / l. If the concentration exceeds the upper limit, the efficiency of alkali recovery decreases,
On the other hand, if the amount is less than the lower limit, it is difficult to reuse the recovered alkali, which is not preferable.

The metal oxide salt and caustic alkali are electrodialyzed by introducing the former into the desalting chamber of the electrodialysis tank and the latter into the concentrating chamber, respectively. The current density at this time is 0.
5-5 A / dm ² is suitable.

[0037]

According to the present invention, when a metal oxide sol is produced from an aqueous solution containing a salt of a metal oxide, electrodialysis is carried out using an alkali-resistant anion exchange membrane to stabilize the metal oxide sol. And a caustic alkali is obtained, and the caustic alkali can be reused.

[0038]

【Example】

Example 1 The cation exchange membrane was composed of a styrene-divinylbenzene copolymer and was reinforced with a vinyl chloride woven cloth, a sulfonic acid type strong acid cation exchange membrane (ion exchange capacity 3.0 meq / g dry resin). , Film thickness 120 μm) was used.

The following were used as the alkali-resistant anion exchange membrane. That is, polypropylene cloth (thickness 1
80 μm) as a base material, and 25% by weight of divinylbenzene,
Styrene 20% by weight, chloromethylstyrene 55% by weight
A syrup having the composition of 2% by weight of benzoyl peroxide was dipped, sandwiched between two polyester films, and the outside was sandwiched between two glass plates and fixed. Then, gamma rays of Co ⁶⁰ were irradiated at room temperature for 15 kilogray to perform radiation polymerization, and further heat polymerization was performed in warm water at 90 ° C. for 14 hours to produce a polymer film. This polymerized membrane was subjected to amination treatment with 1N trimethylamine at 60 ° C. for 16 hours to obtain an anion exchange membrane, which was used.

Using these, an electrodialysis device was assembled. That is, 10 pairs of the above cation exchange membranes and anion exchange membranes were used, and they were alternately arranged between a platinum-plated titanium anode and a nickel cathode to form an electrodialysis cell.

In the desalting chamber of this electrodialysis tank, 5 liters of a sodium silicate aqueous solution (SiO ₂ 5% by weight, SiO ₂ / Na) was added.
₂ O 3.3) was electrodialyzed for 5 hours at an average current density of 1.0 A / dm ² while introducing 0.14 liter of a 10 wt% caustic soda aqueous solution into the concentration chamber.
6.15 wt% silicic acid sol was continuously obtained from the desalting chamber, and 10.4 wt% caustic soda was continuously obtained from the concentrating chamber. This solution was stable without gelation even after 1 week.

Example 2 Using the same electrodialysis tank as used in Example 1, 3 L of a 4.25 wt% sodium aluminate aqueous solution was placed in the desalting chamber and 10 wt% caustic soda aqueous solution was placed in the concentrating chamber. 0.1
Introduced 4 liters each, average current density 1.0A / dm
^When electrodialysis was carried out at ² for 10 hours, 5.6 wt% of alumina sol was obtained from the desalting chamber and 12 wt% of caustic soda was obtained from the concentrating chamber at a ratio of 0.8 liter.

[0043]

INDUSTRIAL APPLICABILITY The present invention makes it possible to stably and efficiently produce a metal oxide sol from an aqueous solution containing an alkali salt of a metal oxide, and further, a caustic aqueous solution can be recovered, which is industrially effective. It becomes possible to produce a sol.

Front page continuation (72) Inventor Hiroo Mori 2-1-2 Marunouchi, Chiyoda-ku, Tokyo Asahi Glass Co., Ltd. (72) Inventor Seiko Tanaka 2-1-2 Marunouchi, Chiyoda-ku, Tokyo Asahi Glass Co., Ltd.

Claims (2)

[Claims] 1. An electrodialysis device comprising a cation exchange membrane and an anion exchange membrane alternately arranged between an anode and a cathode, and a chamber (desorption chamber) comprising the anion exchange membrane and the cation exchange membrane. An aqueous solution of alkali silicate or alkali aluminate is supplied to the salt chamber, and a caustic aqueous solution is supplied to the chamber (concentration chamber) composed of the cation exchange membrane and the anion exchange membrane. A method for producing a silicic acid sol or an alumina sol, which comprises using an alkali-resistant anion exchange membrane as the anion exchange membrane in obtaining an aqueous solution and a silicic acid sol or an alumina sol. 2. An alkali-resistant anion exchange membrane has an olefin polymer or a fluorinated olefin polymer as a base material, on which a polymerizable monomer comprising styrene, chloromethylstyrene or vinylpyridine, divinylbenzene is added. The silicic acid sol according to claim 1, which is supported, partially polymerized by irradiation with ionizing radiation in the former stage, heated in the presence of a polymerization initiator in the latter stage to polymerize the rest, and then introduced an anion-exchange group. Method for producing alumina sol.