JPH07207499A - Method for regenerating water incorporated deteriorated low temperature type fused salt liquid - Google Patents

Abstract

PURPOSE:To easily regenerate a water incorporated, deteriorated, low temp. type fused salt liquid by heating the water incorporated, deteriorated liquid of a specific low temp. type fused salt liquid to a specific temp., and maintaining it at the temp. before cooling it to a specific temp. and maintaining it at the temp. to remove the formed deposit. CONSTITUTION:A low temp. type fused salt liquid mainly consisting of aluminum halogenide and organic nitrogen contg. onium halogenide is strong hydroscopicity, and when water is incorporated, the liquid is deteriorated to particularly lower Al electrodepositing limit current density. When the water incorporated, deteriorated liquid is regenerated, the fused salt liquid is heated to 50-100 deg.C and maintained at that temp. In this way, the hydroxide group contg. aluminum complex ion seeds formed by the water is dehydrated. Then, the fused salt liquid is cooled to <=30 deg.C and maintained at that temp. to crystallize oxide contg. aluminum complex ion seeds formed by the heating and maintaining. The deposit formed by this is removed by filtration, etc., to regenerate the water incorporated, deteriorated liquid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for regenerating a conductive low-temperature molten salt solution obtained by mixing an aluminum halide and an organic nitrogen-containing onium halide, which is deteriorated due to mixing of water.

[0002]

2. Description of the Related Art Aluminum halide 20-80 mol
% And organic nitrogen-containing onium halide 20 to 80 mo
The molten salt solution mixed with 1% has a high conductivity at room temperature, and thus can be used as a plating solution for electrolytic aluminum or an electrolytic solution for secondary batteries. In this molten salt solution, aluminum chloride is mainly used as an aluminum halide, and as the organic nitrogen-containing onium halide, (di) alkylimidazolium chloride and alkylpyridinium chloride are mainly used.

Since this molten salt solution has a strong hygroscopic property, its handling, use and storage have conventionally been carried out in a dry inert gas such as dry nitrogen gas or argon gas. However, it is difficult to completely prevent the mixing of water because there is a limit in removing water in the inert gas and shutting off water by the inert gas. Generally, when water is mixed in a molten salt solution, physical characteristics and chemical characteristics are changed, and particularly, Al electrodeposition limit current density is lowered. In the case of an electroplating solution, a plating rate is increased, and a secondary battery electrolyte solution is also added. In this case, the charging speed will be reduced.

For example, FIG. 4 shows aluminum chloride 64mo.
l% -Ethylmethyl imidazolium chloride 36 mol%
New molten salt solution (Al electrodeposition current limit: 4.7 kA /
m ² ), H ₂ O was added to investigate the relationship between the H ₂ O addition amount and the Al electrodeposition limit current density. The Al electrodeposition limit current density decreased with the H ₂ O addition amount. Will end up.

As a method of regenerating the molten salt solution which has deteriorated in this way, only one component, the organic nitrogen-containing onium halide, is added to the deterioration solution, and the concentration thereof is increased to a predetermined range to form a precipitate. A method has been proposed in which after the precipitate is formed and the precipitate is removed, the other component, an aluminum halide, is added to adjust both components to concentrations suitable for use (JP-A-4-254600). But,
In this method, each component must be added alternately and the concentration adjustment operation must be performed each time the addition is performed, so the operation is complicated. In addition, since the liquid amount increases after the regeneration, an excessive amount of molten salt liquid will be prepared. further,
This method can remove the hydroxyl group-containing aluminum complex ion species, but cannot remove the oxygen-containing aluminum complex ion species.

[0006]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention regenerates a low temperature molten salt solution containing an aluminum halide and an organic nitrogen-containing onium halide which are deteriorated by mixing water as the main components. It provides a method.

[0007]

According to the present invention, a molten salt solution is used.
After heating and holding at 0 to 150 ° C., cooling and holding at 30 ° C. or lower are performed to remove the generated precipitate.

The decrease in the limit current density of Al electrodeposition is due to the fact that the aluminum complex ion species contributing to the Al electrodeposition reaction are hydrolyzed and the soluble impurities are accumulated in the liquid as follows. That is, in a molten salt solution in which an organic nitrogen-containing onium halide and an aluminum halide are mixed, aluminum complex ions of AlX ₄ ⁻ and Al ₂ X ₇ ⁻ (X is a halogen element) are present. Equation (1) is maintained in equilibrium, and on the anode side during electrolysis, equation (2),
On the cathode side, the reaction of formula (3) occurs. 2AlX ₄ ⁻ ⇔ Al ₂ X ₇ ⁻ + X ⁻ (1) 7AlX ₄ ⁻ + Al (anode) → 4Al ₂ X ₇ ⁻ + 3e ⁻ (2) 4Al ₂ X ₇ ⁻ + 3e ⁻ → Al (electrodeposition) + 7AlX ₄ ⁻ … (3)

However, if water is mixed in the molten salt solution,
AlX ₄ ⁻ and Al ₂ X ₇ ⁻ are hydrolyzed into a hydroxyl group-containing aluminum complex ion species as shown in the following formulas (4) and (5), which are further expressed by the formulas (6) and (7). It decomposes into oxygen-containing aluminum complex ion species and accumulates as soluble impurities. AlX ₄ ⁻ + H ₂ O → Al (OH) X ₃ ⁻ + H ⁺ + X ⁻ (4) Al ₂ X ₇ ⁻ + H ₂ O → Al ₂ (OH) X ₆ ⁻ + H ⁺ + X ⁻ (5) Al (OH ^{_{) X 3 - → AlOX 2 -}} + H + + X - ... (6) Al 2 (OH) X 6 - → Al 2 OX 5 - + H + + X - ... (7)

[0010]

In order to develop a method for regenerating a mixed molten salt solution of an aluminum halide deteriorated by moisture and an organic nitrogen-containing onium halide, the present inventors have studied the chemical change of the deteriorated solution, and as a result, (4) ), The hydroxyl group-containing aluminum complex ion species generated by the formula (5) is converted to the oxygen-containing aluminum complex ion species as shown in the formulas (6) and (7) when heated, and the oxygen-containing aluminum complex ion species It has been found that the aluminum complex ion species precipitate as a crystalline precipitate when the molten salt solution is cooled and kept at a low temperature.

FIG. 1 shows aluminum chloride (hereinafter referred to as AlCl
₃ ) 64 mol% -ethylmethylimidazolium chloride (hereinafter referred to as EMIC) 36 mol% molten salt solution (-OH) bond of a hydroxyl group-containing aluminum complex ion species generated when H ₂ O is added up to 3 vol% The change in the IR absorption peak intensity at 3400 cm ^-1 due to the above is shown. The IR absorption peak intensity on the vertical axis is the peak intensity when H ₂ O is added at 3 vol% and is 1.0. The relative peak intensity is displayed. According to this, it can be confirmed that the peak strength increases with the amount of H ₂ O added, and the hydroxyl group-containing aluminum complex ion species in the molten salt solution increase.

FIG. 2 shows that H ₂ O is added to a new molten salt solution having the above composition.
3% by volume was heated from room temperature to 100 ° C, and the relationship between the time of holding at that temperature and the IR absorption peak intensity at 3400 cm ^-1 was shown. It gradually became smaller and finally reached the same level as the new solution. This means that the concentration of the hydroxyl group-containing aluminum complex ion species can be reduced to the same concentration as that of the new solution by lengthening the heating and holding time to some extent. The IR absorption peak intensity display on the vertical axis is the same as in the case of FIG.

The fact that the hydroxyl group-containing aluminum complex ion species in the molten salt solution is reduced by heating is due to the above formula (6),
Although the hydroxyl group-containing aluminum complex ion species are changed to the oxygen-containing aluminum complex ion species by the formula (7), the heating temperature is set to 50 to 150 ° C. at which the molten salt solution is not decomposed. If it is lower than 50 ° C, the rate of decrease of hydroxyl group-containing aluminum complex ion species is slow, and if it exceeds 150 ° C, the evaporation of AlCl ₃ from the molten salt solution becomes remarkable. The heating and holding time is such that the IR absorption peak strength is 10 times the absorption peak strength before heating.
% Or less, preferably the time until the absorption peak strength becomes zero.

FIG. 3 shows that H ₂ O is added to a new molten salt solution having the above composition.
Was added at 3 vol% and heated to 100 ° C and held at 340
Cooling temperature that causes precipitation when cooling the solution with IR absorption peak intensity of 0 cm ^{-1 set} to 0, and necessary for recovering Al electrodeposition limiting current density to the same level as the new solution after removing the precipitate It shows the relationship between the cooling retention time and
It shows that a precipitate is formed when cooled to 0 ° C or lower, and solidifies at -80 ° C or lower. Further, it is shown that the cooling holding time can be shortened by lowering the cooling temperature in order to recover the Al electrodeposition limit current density to the same level as the new solution after removing the precipitate. Therefore, in order to remove the oxygen-containing aluminum complex ion species as a precipitate, the molten salt solution should be kept at 30 ° C.
Below, preferably from 0 ℃ or less 2 from the freezing point of the molten salt solution
It is suitable to cool to ~ 3 ° C higher range. The cooling time is 2 hours or longer, preferably 10 hours or longer. The precipitate may be removed by a known method such as a centrifugation method or a filtration method.

[0015]

【Example】

Example 1 AlCl ₃ and EMIC were mixed to give an AlCl ₃ concentration of 5
5mol%, 64mol% molten salt liquid (freezing point about -1 respectively
5 ° C., about −85 ° C.) was prepared and the Al electrodeposition limit current density of each liquid was determined. Next, add 3 vol% H ₂ O to each solution.
Was added to deteriorate the liquid, and then the limiting current density of Al electrodeposition and the hydroxyl group-containing aluminum complex ion species (-OH)
The IR absorption peak intensity at 3400 cm ^-1 due to binding was measured. After that, heat treatment is not applied to the deteriorated liquid, the deteriorated liquid is heated to 80 ° C., and the temperature is maintained until the IR absorption peak strength reaches 50% (comparative example) before heating and the new liquid level. And the prepared liquids were -100
By cooling and holding in the range of -40 ° C for 30 hours, the generated precipitate was removed by centrifugation, and after the removal, the Al electrodeposition limit current density was measured. Sample No. 1 shown in the comparative example
The numbers 1 and 12 show the effects of the temperature of the heat treatment. No. 11 was performed at a heat treatment temperature of 45 ° C., and No. 12 was performed at 200 ° C.

The Al electrodeposition limit current densities of the respective solutions were determined by Ni strike plating (film thickness: 0.3 μm) on cold rolled steel plate (AK steel, plate thickness: 0.5 mm) electrolytically degreased and pickled by a conventional method.
m), the solution temperature is 90 ° C, and the plating solution flow rate is 1.0 m / se.
c, electric Al plating was performed at an energization amount of 15 kC / m ² to obtain the maximum current density at which white Al plating was obtained. All of these operations were performed in an N ₂ atmosphere. Table 1 shows the Al electrodeposition limit current density at each stage.

[0017]

[Table 1]

[0018] In Example 2 Example 1, AlCl ₃ AlCl instead of -EMIC molten salts solution ₃ - butyl pyridinium di chloride (BPC) molten salts solution, AlCl ₃ concentration 64 mol% of the liquid (freezing point around -70 C.) was used to regenerate the deteriorated liquid mixed with water by the same operation. The results are shown in Table 2.

[0019]

[Table 2]

[0020]

As described above, according to the present invention, the molten salt liquid deteriorated due to the inclusion of water can be regenerated into a new liquid state and repeatedly used. Further, in the present invention, since the molten salt solution is regenerated by the temperature operation, the operation is simple and the liquid amount does not increase after the regenerating.

[Brief description of drawings]

FIG. 1 is a (—OH) bond of a hydroxyl group-containing aluminum complex ion species generated when H ₂ O is added up to 3 vol% to a new solution of a molten salt solution of aluminum chloride 64 mol% -ethylmethylimidazolium chloride 36 mol%. 3 is a graph showing changes in IR absorption peak intensity at 3400 cm ⁻¹ due to the above.

[Fig. 2] shows a new molten salt liquid containing 64 mol% of aluminum chloride and 36 mol% of ethylmethylimidazolium chloride added with 3 vol% of H ₂ O, heated from room temperature to 100 ° C, and kept at that temperature. 3 is a graph showing the relationship between IR absorption peak intensity at 3400 cm ^-1 and.

FIG. 3 shows an IR absorption peak at 3400 cm ⁻¹ by adding 3 vol% of H ₂ O to a new molten solution of aluminum chloride 64 mol% -ethylmethylimidazolium chloride 36 mol% system and heating at 100 ° C. The relationship between the cooling temperature at which precipitates are formed when the solution with zero strength is cooled and the cooling holding time required to recover the Al electrodeposition limit current density after removing the precipitates to the same level as the new solution It is a graph shown.

FIG. 4 shows the relationship between the amount of added H ₂ O and the limiting current density of Al when H ₂ O was added to a new liquid of a molten salt solution of aluminum chloride 64 mol% -ethylmethylimidazolium chloride 36 mol%. It is a graph shown.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukio Uchida 5 Ishizu Nishimachi, Sakai City, Osaka Prefecture Nisshin Steel Co., Ltd. Surface Treatment Research Department, Steel Research Laboratories, Inc. 3-1, Mitsubishi Petrochemical Co., Ltd. Tsukuba Research Institute (72) Inventor Asahi Kominato 8-3-1 Chuo, Ami-cho, Inashiki-gun, Ibaraki Mitsubishi Petrochemical Co., Ltd. Tsukuba Research Institute

Claims (1)

[Claims] 1. When regenerating a water-mixed deterioration liquid of a low temperature molten salt liquid containing aluminum halide and an organic nitrogen-containing onium halide as main components, the molten salt liquid is used in an amount of 50 to 50%.
A method for regenerating a water-mixed deteriorated low-temperature molten salt solution, which comprises heating and holding at 150 ° C., and then cooling and holding at 30 ° C. or lower to remove a generated precipitate.