JPS61291407A - Recovery of sulfuric acid - Google Patents

Abstract

PURPOSE:To recover high-purity sulfuric acid suitable for use in electronic industry, by adding SO2 gas to waste sulfuric acid having high concentration and generated from an integrated circuit production step, diluting the mixture with pure water, cooling the diluted solution and diffusing and dialyzing sulfuric acid ion to the pure-water side by a diffusion and dialysis membrane. CONSTITUTION:Concentrated water sulfuric acid containing impurities and discharged from the resist-peeling step in an integrated circuit producing factory is added with more than equivalent amount of SO2 gas based on H2O2 existing in the waste sulfuric acid. The residual H2O2 is reduced and removed by this procedure to prevent the deterioration of the dialysis membrane used in the following process. The treated sulfuric acid is diluted with pure water to a sulfuric acid concentration of <=40wt% and cooled to suppress the generation of heat of dilution in dialysis and prevent the deformation and degradation of the membrane with heat. The diluted waste sulfuric acid is treated with a diffusion and dialysis membrane to diffuse and dialyze sulfuric acid ion to the pure water side. The regenerated sulfuric acid recovered by the above process has extremely high purity corresponding to that of the guaranteed reagent or usable in electronic industry.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for recovering high-purity sulfuric acid from high-concentration waste sulfuric acid discharged from the process of manufacturing integrated circuits. The present invention relates to a method for recovering sulfuric acid of special reagent grade or quality that can be used in the electronic industry from waste sulfuric acid.

[Prior Art] Various methods have been used to recover sulfuric acid from waste sulfuric acid. That is, (1) Vacuum concentration method A method of heating and concentrating waste sulfuric acid under reduced pressure, crystallizing and separating dissolved salts, and recovering sulfuric acid.

(2) Cooling concentration method A method of cooling waste sulfuric acid and recovering sulfuric acid by precipitating salts due to the difference in solubility.

(3) Vacuum concentration cooling method Combination of (1) and (2) above.

(4) Submerged Combustion Concentration Method A method that uses a submerged combustion burner to increase the thermal efficiency of concentration.

(5) Pyrolysis waste sulfuric acid is heated to SO2 in a furnace. A method of recovering sulfuric acid by adding and absorbing it after decomposition.

(6) Diffusion dialysis method A method in which waste sulfuric acid and water are flowed countercurrently through the membrane using an anion exchange membrane, and the sulfuric acid is recovered and purified by transferring the sulfuric acid to the water side using the selective permeability of the ion exchange membrane to compensate for the concentration difference in sulfuric acid. .

(7) A recovery method that utilizes the difference in solvent extraction solubility to extract and remove salts and organic substances from waste sulfuric acid.

[Problems to be Solved by the Invention] When considering the quality and recovery cost of recovered sulfuric acid with respect to these methods, problems arise when using high-purity sulfuric acid.

Methods (1) to (4) are recovery methods that are applied to waste acids that are discharged in large quantities on an industrial scale, such as Bickling waste acid, petroleum refinery waste acid, cellophane/rayon waste acid, and synthetic fiber waste acid.
This recovered sulfuric acid is mostly reduced to the process where the waste acid was generated.
Also, purity is not very important. That is, since the removal of salts is not complete, it is difficult to use it in the same way as new sulfuric acid.

Method (5) yields highly pure sulfuric acid, but at 360℃
Corrosion of equipment, halogens, and NO due to decomposition at higher temperatures
Currently, the cost is higher than that of new sulphur due to problems such as pretreatment.

Regarding (6), it is used for recovering sulfuric acid from alumite electrolytic baths, stabilizing metal pickling baths, adjusting the acidity of various plating baths, refining industrial sulfuric acid, etc., and produces high-purity sulfuric acid without the need for electrical energy. This is a method for recovering with high yield.

However, this diffusion dialysis method requires a sulfuric acid concentration of 40 Wt$.
It has been found that in the above case, a large amount of heat of dilution of the sulfuric acid is generated which diffuses into the water through the dialysis membrane, resulting in deterioration of the structure and function of the membrane. In addition, due to leakage of salts such as Fe, heavy metals, and alkali metals, high-purity sulfuric acid for electronic industry (
It is difficult to obtain the quality of ELi acid).

Japanese Patent Application Laid-open No. 58-58112 discloses a method for recovering high-purity sulfuric acid by diffusion dialysis, in which dialysis is performed in multiple stages, and the salt concentration is successively lowered to achieve the desired quality. However, it is not necessarily economically advantageous.

Integrated circuits (Int.
It is difficult to apply these conventional diffusion dialysis methods to the regeneration of a large amount of waste sulfuric acid generated from the resist stripping process in the production of erated C1rcuts (abbreviated as IC) due to the following points.

B. H2SO4 concentration is 80 to 85 wH: The film softens and deteriorates due to the heat of dilution.

Existence of H2O in the waste sulfuric acid; H2O2 blended into the raw material remains and deteriorates the membrane by oxidation.

C. Leakage of salts in waste acid, resist stripping process Fe, old, Ha, dissolved in sulfuric acid,
Ions such as K and Mn migrate to the water side in proportion to their concentration in the stock solution during diffusion dialysis. Therefore, the metal ion content in the recovered sulfuric acid may exceed the level for the electronic industry.

The requirements for purity of sulfuric acid (EL sulfuric acid) used in the electronics industry are becoming stricter as the degree of integration of ICs increases, but as a rough guide, for example, SEMI (Se
miconductor equipments an
d Mater-ials In5titudinal 5t
EL sulfuric acid (andard) requires a standard of 1 ppm or less for all metals contained in 95 to 97 wt% sulfuric acid, but most of the EL sulfuric acid actually supplied to the market has a level of 1/10 or less of that level. Most of them are standard.

[Means for Solving the Problems] The present invention solves the above-mentioned problems in order to recover sulfuric acid of the electronic industry level that requires extremely high purity. The present invention is a method for treating and recovering highly concentrated waste sulfuric acid containing impurities, which is characterized by including the following steps (a) to (c).

(b) A step of adding sulfur dioxide gas to the waste sulfuric acid in an amount equivalent to or more than the hydrogen peroxide contained in the waste sulfuric acid, (b) A step of diluting the waste sulfuric acid to 40wt1 or less with pure water and cooling it, and (c) a step of diluting the waste sulfuric acid. A process to obtain regenerated sulfuric acid by diffusion dialysis of sulfuric acid ions into pure water using a diffusion dialysis membrane.

The recovered sulfuric acid obtained by the present invention can be reduced to a required concentration by a method such as vacuum evaporation and used again in the resist stripping process.

Hereinafter, the recovery method of the present invention will be explained in detail for each step based on the block diagram of FIG.

(+) Raw material waste sulfuric acid The waste sulfuric acid that is the object of the present invention is a sulfuric acid waste liquid used in the resist stripping process in IC manufacturing in the electronics industry. This waste sulfuric acid has a sulfuric acid concentration of 80wt or more, and the impurities it contains vary depending on the IC processed, but in general, in addition to particles such as peeling resist, PB, Fe, Ni, Ha,
It contains several ppm of K, etc., and several quantities of hydrogen peroxide, which was added to promote resist peeling, remains.

(2) SO2 addition step Hydrogen peroxide remaining in the raw material waste sulfuric acid deteriorates the dialysis membrane by oxidation in the subsequent diffusion dialysis process, so it must be sufficiently removed in advance. Therefore, raw material waste sulfuric acid is treated with sulfur dioxide gas.

The treatment is carried out simply by blowing sulfur dioxide gas into the raw material waste sulfuric acid. The amount of sulfur dioxide gas to be added may be at least equivalent to the amount of hydrogen peroxide remaining in the raw material waste sulfuric acid. The purity of the titanite gas used may be commercially available, but it is preferably as pure as possible.

(3) Dilution and cooling step The SO2-treated sulfuric acid solution is diluted with pure water to less than 40 wt$. The degree of dilution is such that the amount of dilution heat generated by the sulfuric acid that diffuses through the dialysis membrane during diffusion dialysis in the next step does not cause softening of the membrane, deformation due to expansion, or deterioration of the dialysis function, and the heat resistance of the membrane. Varies depending on gender, but generally 40wt$
or less, and if the heat resistance of the film is improved, it will be 40wt$
Dilutions in excess of 20% may also be employed.

When diluting the sulfuric acid solution, a large amount of heat of dilution is generated, so the diluting group is sufficiently cooled. Indirect cooling using cooling water is employed, and it is advantageous to use low-concentration regenerated sulfuric acid obtained in the subsequent diffusion dialysis step as the cooling water for heat exchange. That is, in order to use the high-purity regenerated sulfuric acid obtained by the present invention for resist stripping again as EL sulfuric acid, it is necessary to increase the sulfuric acid concentration by means such as vacuum concentration, and for this purpose, the thermal efficiency is improved as preheating. This is because it is possible.

It is preferable that the pure water used for dilution be as pure as possible.
Usually, pure or distilled water purified by ion exchange treatment is used.

(4) Diffusion dialysis process The sulfuric acid solution diluted to a concentration that does not cause temperature rise due to dilution heat is brought into contact with ultrapure water through the diffusion dialysis membrane, and sulfate ions in the sulfuric acid solution are selectively transferred to the ultrapure water side. The purified regenerated sulfuric acid, which is substantially free of metal ions, is obtained by diffusion dialysis.

Suspended particles present in the raw material waste sulfuric acid do not pass through the dialysis membrane, so they can be left as is, but they adhere to the dialysis membrane and affect the membrane's diffusion permeation efficiency, and large amounts of sedimentation may shorten the time for membrane replacement. Therefore, it is preferable to remove the suspended particles in advance. Any method can be used to remove these suspended particles, but ultrafiltration using microporous ceramics or the like is usually used. It should be noted that commercially available dialysis machines usually come with a filter for removing sludge and oil from the stock solution.

The ultrapure water used is of high purity used in the electronics industry. The standards are becoming stricter year by year as ICs become more sophisticated, and it is preferable that the ultrapure water used in the present invention conforms to them.The ultrapure water currently used has an electrical resistivity value of 1.
7.5-18 MΩ-cm or more, 0.27
The number of particles of 1111 or higher is 20, the number of viable bacteria is 1 or less.
2/rooml.

The acid recovery rate can be changed depending on the dialysis operating conditions, and the acid recovery rate can be controlled by the metal ion content of the stock solution, as the leakage of metal ions from salts also increases when the recovery rate is whisked. desirable.

Generally, when comparing the permeation rate of acids and salts through an anion exchange membrane, the permeation rate of salts is 1/100 to 1/1000 of that of acids;
As the acid recovery rate is increased and the acid concentration on both sides of the membrane approaches equilibrium, the acid permeation rate decreases and the amount of cations transferred increases, resulting in a decrease in the removal rate of various ions.

In the present invention, by limiting the recovery rate of sulfuric acid in diffusion dialysis, leakage of various ions into the recovered sulfuric acid can be prevented, and highly purified recovered sulfuric acid can be obtained. The preferred recovery rate in diffusion dialysis is about 80% or less, and this recovery rate can vary depending on the content of various ions in the stock solution. Making the flow rate of ultrapure water smaller than the flow rate of the stock solution has the effect of increasing the concentration of recovered sulfuric acid and suppressing the recovery rate of sulfuric acid.

Note that the concentration of recovered sulfuric acid obtained in the present invention is usually 30 to 4.
0wtX, and 8 to reuse as ELi acid.
It is concentrated to 0wt1 or more. Although any method can be used for concentration, a vacuum multi-stage evaporation method is generally used. In this case, for preheating the recovered sulfuric acid, a large amount of dilution heat generated in the sulfuric acid solution dilution and cooling step (3) is effectively utilized by heat exchange.

[Operation] The method of the present invention first treats high-concentration waste sulfuric acid generated from the IC manufacturing process in the electronics industry with SO2 to reduce and remove residual hydrogen peroxide, thereby preventing deterioration of the dialysis membrane. . In addition, the sulfuric acid concentration was adjusted to 40% prior to diffusion dialysis.
Dilute to below wt% and cool to suppress generation of dilution heat during dialysis and prevent membrane deformation and deterioration due to heat. Furthermore, by controlling the recovery rate of sulfuric acid in diffusion dialysis, leakage of various ions to the recovered sulfuric acid can be minimized, and highly purified sulfuric acid can be recovered.

[Effects] According to the present invention, EL sulfuric acid can be effectively recovered again from waste sulfuric acid discharged from a resist stripping process using expensive EL sulfuric acid that requires ultra-high purity in the electronics industry.

When sulfuric acid was recovered by diffusion dialysis using an anion exchange membrane for the waste sulfuric acid that was not subjected to any pretreatment such as reduction or dilution according to the present invention, it became impossible to recover the sulfuric acid after 5 hours due to deterioration of the membrane. On the other hand, in an embodiment according to the present invention, 100
No change was observed in the membrane function even after continuous operation for hours.

From this, it is estimated from the life of general anion exchange membranes that by regularly cleaning the membrane,
Can be used continuously for 3 to 5 years.

The price of EL sulfuric acid at the time of origin was more than 10 times that of industrial sulfuric acid, and even if new sulfuric acid recovery including concentration equipment is installed, 80% acid recovery can be achieved in a short period of time.

[Example] Examples according to the present invention will be shown below, but the present invention is not limited thereto.

Various analyzes and measurements adopted in Examples etc. are based on the following test methods.

Sulfuric acid content: JIS-K 1322 Sulfuric acid test method KMnO4 reducing substance (as S02): JIS-K
8951 Sulfuric acid (reagent) ゛Heavy metals (as PB) 2
Same as above Fe, Ni: In the ICP emission spectrometry method, N
a: Flame spectroscopic analysis method Number of particles: Number of particles larger than 0.5 lum/+00+wl, HI
AC/ROYOC4100-3413CL Laser Sensor Example I Waste sulfuric acid discharged from the resist stripping process of an IC manufacturing factory was used as raw material waste sulfuric acid. Its composition is shown in Table 1.

After adding 4z of 802 to this raw material waste sulfuric acid, it was mixed with an equal weight of ion-exchanged water, diluted, and cooled.
Dialysis was performed using ultrapure water (specific resistance: 18 MΩ·am) using 8 pieces (approximately 0.15 mm thick and 2.09 dmz area). Continuous treatment was carried out at a supply rate of diluted sulfuric acid at 150 ml/hr and a supply rate of ultrapure water at 125+1/hr.

3B, 5wtX recovered sulfuric acid was obtained, and the recovery rate determined from the sulfuric acid concentration of the dialysis residual solution was 78%. The component analysis values of the 0 recovered sulfuric acid are shown in Table 1.

This recovered sulfuric acid was concentrated by distillation under reduced pressure at 180"0 on a BOTorr to obtain 88.3 wt$ of concentrated magnetic acid. As shown in Table 1, the component analysis values were sufficient to be used as EL sulfuric acid. Met.

For reference, the corresponding SEMI standard values are shown in Table 1.

Comparative Example 1 The dialysis conditions in the dialysis treatment of Example 1 were as follows: diluted sulfuric acid supply rate: 105 m1/hr, ultrapure water supply rate: 120 m1/hr.
When continuous treatment was carried out at a sulfuric acid recovery rate of 92%, the amount of leakage of each metal component increased as shown in Table 1. Although this recovered sulfuric acid has been considerably purified, when concentrated, there is a risk that the content of Pb, Na, and K may be slightly higher than that of EL sulfuric acid.

Comparative Example 2 When the raw material waste sulfuric acid of Example 1 was directly subjected to diffusion dialysis treatment, the ion exchange membrane was softened and deformed due to the generation of heat, making dialysis impossible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an apparatus illustrating an embodiment of the invention.

Claims (3)

[Claims] (1) In a method for treating and recovering highly concentrated waste sulfuric acid containing impurities generated from the integrated circuit manufacturing process, the following (
A method for recovering sulfuric acid, comprising the steps of (a) to (c). (b) A step of adding sulfur dioxide gas to the waste sulfuric acid in an amount equivalent to or more than the hydrogen peroxide contained in the waste sulfuric acid, (b) A step of diluting the waste sulfuric acid to 40 wt% or less with pure water and cooling it, and (c) dilution. A process to obtain regenerated sulfuric acid by diffusing sulfuric acid ions into pure water using a diffusion dialysis membrane. (2) The method according to claim 1, wherein the cooling in step (b) is by heat exchange with the regenerated sulfuric acid from step (c). (3) The method according to claim 1 or 2, wherein the recovery rate of sulfate ions into regenerated sulfuric acid in step (c) is controlled to 80% or less.