JPH028963B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for decolorizing colored concentrated sulfuric acid, which makes it possible to decolorize colored concentrated sulfuric acid in a short time and maintain the required light transmittance without causing cloudiness.

Conventionally, when concentrated sulfuric acid, which is made from smelting exhaust gas, is colored by impurities in the ore, especially organic substances and oils mixed in during processing such as scrap in the converter, the following methods are available for decolorizing it: It is being done.

(1) H ₂ O ₂ method This method is a method for decolorizing colored concentrated sulfuric acid using H ₂ O ₂ liquid as an oxidizing agent at room temperature. As the H ₂ O ₂ liquid, a commercially available product with a H ₂ O ₂ concentration of 35% is used as is.
Since this H ₂ O ₂ solution has a slow reaction rate at room temperature, it has to be added in large excess relative to the chemical equivalent, and the reaction time for the decolorization process also takes 30 to 50 hours. Moreover, most of the H ₂ O ₂ remains even after decolorization, and the residual H ₂ O ₂
Fe ²⁺ is gradually oxidized and becomes insoluble Fe ³⁺ salt, resulting in significant cloudiness, which is a major cause of quality deterioration. This phenomenon is particularly noticeable when stored at an acid temperature of 35°C or higher. In any case, the transmittance of concentrated sulfuric acid decreases due to this cloudiness and often falls below 40 (commercial acids usually have a transmittance of
80 or higher is required). In addition, even if the Fe ³⁺ salt, which is a cloudy component, is temporarily removed to maintain transparency, as long as H ₂ O ₂ remains, Fe ²⁺ in the concentrated sulfuric acid will oxidize or the storage container will corrode. Therefore, the recurrence of the clouding phenomenon cannot be avoided.

(2) KMnO ₄ method This method is a method for decolorizing colored concentrated sulfuric acid using KMnO ₄ as an oxidizing agent. In the case of this method, because the reaction rate of KMnO ₄ is fast and the degree of excess addition is slight, unlike the case of the above H ₂ O ₂ method, the clouding phenomenon caused by insoluble Fe ³⁺ salt is not a particular problem. However, due to the use of heavy metal compounds, there are problems such as an increase in ignition residue, an increase in Mn ions, and large variations in transparency.
There is also a concern about secondary coloring.

The present invention solves the above drawbacks of _the traditional _H2O2 method,
To provide a method for decolorizing colored concentrated sulfuric acid, which makes it possible to decolorize colored concentrated sulfuric acid in a short time and maintain the required light transmittance without causing cloudiness.
The gist is that in a decolorizing method by adding hydrogen peroxide to colored concentrated sulfuric acid generated in the process of producing sulfuric acid using smelting exhaust gas as raw material, the colored concentrated sulfuric acid is Purity 2.5~
Add and mix less than 15% hydrogen peroxide in an amount equivalent to 1 to 2 times the KMnO ₄ titration value of the concentrated sulfuric acid at 25°C,
Furthermore, there is provided a method for decolorizing colored concentrated sulfuric acid, characterized in that deaeration is performed after residual H ₂ O ₂ is decomposed and disappeared.

As described above, the present invention provides H ₂ O ₂ containing no heavy metal elements and having a purity of 2.5 to less than 15% to 70 to 70% in a decolorizing tank.
It is added to and mixed with colored concentrated sulfuric acid maintained at a temperature range of 130°C to allow the decolorization reaction to proceed in a short time, and at the same time, the instability of H ₂ O ₂ in the above temperature range is used to decompose residual excess H ₂ O ₂ . The decolorization process is completed by vanishing and then degassing. Decolorization tank capacity remains
Decomposition of H ₂ O ₂ and degassing are determined by the residence time required for degassing, but when degassing, the capacity of the decolorization tank can be considerably reduced by performing acid air ration.

The decolorized concentrated sulfuric acid is then cooled to around room temperature and then stored.

The decolorization reaction conditions in the present invention will be described.

(1) Amount of H ₂ O ₂ added The quality of the decolorizing acid is such that the total amount of residual organic matter, Fe ²⁺ , residual H ₂ O _2, etc. is 20 g based on the KMnO ₄ titration value.
If KMnO ₄ /TH ₂ SO ₄ or less, it can be comparable to the reagent sulfuric acid in terms of coloring, but for that purpose
The concentration of sulfuric acid at 25℃ as the amount of H ₂ O ₂ added
It is in the range of 1 to 2 times the equivalent of the KMnO ₄ titration value.

(2) Purity of H ₂ O ₂ The purity of H ₂ O ₂ added in the present invention is 2.5~
In the range of less than 15%. If the purity is less than 2.5%, the decolorization time will be too long, making it unsuitable for industrial use. An example of the relationship between H ₂ O ₂ purity and decolorization rate is
KMnO ₄ titration value 90g/TH ₂ SO ₄ , H ₂ O ₂ equivalent 1.0
The case is shown in the drawing. As the figure shows, the decolorization rate is extremely high in the range of H ₂ O ₂ purity of 2.5-15%. In this way, the decolorization rate is higher when the purity of H ₂ O ₂ is dilute, so if a dilute aqueous H ₂ O ₂ solution is added, dilution of the colored concentrated sulfuric acid may become a problem, but in reality, the concentration of the concentrated sulfuric acid is Since the purity and addition amount of H ₂ O ₂ are adjusted so that it does not fall below 98%, this problem does not occur.

(3) Decolorization temperature The decolorization temperature in the present invention is in the range of 70 to 130°C. In the decolorization reaction of colored concentrated sulfuric acid, the reaction temperature is kept as high as possible in order to increase the decolorization reaction rate and to reduce the amount of residual H ₂ O ₂ that causes plant corrosion and re-clouding of the decolorizing acid after storage. It is preferable to increase the average residence time,
As an example, an average residence time of 15 minutes at a reaction temperature of 110 to 130°C is sufficient. If the reaction temperature is less than 70°C, the decolorization reaction rate will be slow, and if it exceeds 130°C, the decomposition of H ₂ O ₂ will be rapid.

The above configuration provides the following effects.

(1) Improved decolorization efficiency reduces H ₂ O ₂ consumption.

(2) Since there is no residual H ₂ O ₂ , cloudiness does not occur and the required light transmittance can be maintained.

[Brief explanation of drawings]

The drawing shows the raw acid KMnO ₄ titration value 90g/TH ₂ SO ₄ ,
FIG. ₂ is a graph showing the relationship between H ₂ O 2 purity and decolorization rate when H ₂ O ₂ equivalent is 1.0.

Claims (1)

[Claims] 1. In a method of decolorizing colored concentrated sulfuric acid generated from the process of producing sulfuric acid using smelting exhaust gas as a raw material by adding hydrogen peroxide, the colored concentrated sulfuric acid has a purity of 2.5 to less than 15% within a temperature range of 70°C or higher and lower than 130°C. of hydrogen peroxide to 1 of the KMnO ₄ titration value of the concentrated sulfuric acid at 25°C.
A method for decolorizing colored concentrated sulfuric acid, which comprises adding and mixing ~2 equivalents, further decomposing and eliminating residual H ₂ O ₂ , and then degassing.