JPS596811B2 - How to oxidize sulfite ions - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in means for oxidizing sulfite ions in an aqueous solution containing sulfite ions more rapidly by contacting them with an oxygen-containing gas.

As an example of wet flue gas desulfurization, it is known to absorb S02 with an aqueous NaOH solution to convert it into sodium sulfite.

However, as the COD (chemical oxygen demand) remains low, it cannot be discharged as waste as it is; conventionally, it is oxidized with oxygen or air and discharged as an aqueous sodium sulfate solution.

In this type of oxidation using oxygen or air, if the oxidation rate is slow, the equipment becomes large and consumes a lot of power, so various ideas have been devised.

It is known that the simplest method is to add heavy metal ions as a catalyst, but on the other hand, harmful heavy metals are added to the waste liquid, which goes against the goal of preventing pollution.

The present invention was able to obtain an oxidation rate two to three times faster by using a porous material without using these harmful heavy metal ions.

Silica gel, activated clay, activated alumina, diatomite, etc.
Although it is well known that porous materials are used as catalysts or co-catalysts, it is unexpected that they exhibit significant catalytic effects when used in the oxidation of sodium sulfite.

In the case of oxidation of sulfite ions, it is generally known that in high concentration regions, the zero-order reaction, or reaction rate, is independent of concentration, but in the low-concentration region, first-order reaction, or reaction rate, is proportional to concentration. The point at which the transition occurs is said to be around 2% (by weight) in the case of sodium sulfite.

In the examples as well, in the case of no catalyst, the transition point of the reaction order clearly appears near the 1st to 2nd coefficient (weight).

(Figures 2 and 3) However, when using the catalyst of the present invention,
Almost no such tendency was observed, and only a slight decrease in the reaction rate was observed.

This shows that it is more effective when oxidizing sulfite ions almost completely in a continuous device.In the case of a continuous device, the concentration of the internal liquid and the extracted liquid are considered to be equal, so the The reaction is progressing at the reaction rate of the concentration of the liquid, and only the reaction rate at that concentration is required, and if the sulfite ions are almost completely oxidized and extracted, adding a catalyst 5
This is because the oxidation rate is ~10 times higher (FIGS. 2 and 3).

In other words, by using a catalyst, continuous equipment can reduce
It can be reduced by a factor of 10 to %K in a batch system.

As described above, by using the method of oxidizing sulfite ions by adding a porous substance according to the present invention, oxidation of sulfite ions is rapid and technically easy, and since the added substance is insoluble, separation after extraction is also easy. It is safe because it is not toxic even if it is discharged.

Example 1 As shown in Figure 1, the oxidizer main body has a circular diameter of approximately 40 m.
A container with a glass perforated plate 8 having a diameter of about 800 mm and a height of about 800 mm was used.

First, the valve 11 is opened, and the oxygen is supplied from the oxygen cylinder 10 to the oxidizer main body 7 through the rotameter set flow meter 3, humidifier 4, and mist separator 5, and then to the oxidizer main body 7.
Oxygen was sent into the liquid through the tube to cause gas-liquid contact.

The liquid temperature was about 60°C, and the container 7 was kept warm with a heater 9 to avoid heat radiation, and the temperature of the constant temperature bath 6 was kept at 60°C.

The liquid volume was 80011 liters and the oxygen supply rate was 1.511/min. Sampling was performed at regular time intervals, and the concentration of sodium sulfite was analyzed by the iodine titration method to track the oxidation reaction.

As a liquid, activated clay was added as a catalyst to a 10% (by weight) solution of sodium sulfite at a pH in the range of 6 to 10.5.
．． The test was carried out for the case where 1% (by weight) was added and the case where no catalyst was used.

The results are shown in FIG.

Embodiment 2 As shown in FIG. 1, the valve 12 is opened and atmospheric air is drawn through the oil mist separator 2 by the blower 1. It was fed into the oxidizer 7 at a rate of 1/min.

The liquid volume was 800ml as in Example 1, and ζ-pn was 6.
Using an aqueous solution of sodium sulfite in the range of ~105 io% (by weight), the range was further expanded as a catalyst, and porous silica gel, activated alumina, diatomaceous earth, and activated clay were each added individually in the amount of 01% (by weight). It was carried out under the same conditions as in the case.

The liquid temperature was 60° C., and the constant temperature bath temperature was kept at 60° C. The sampling method and analysis method were the same as in Example 1.

The results are shown in FIG.

[Brief explanation of drawings]

Figure 1 (experimental equipment flow sheet), 1...Blower, 2...Oil mist separator, 3...
・Flowmeter (rotameter), 4... humidifier (washing bottle), 5... water mist separator, 6...
... Constant temperature chamber, 7 ... Equipment main body, 8 ...
...Glass perforated plate, 9...Heater, 10...
...Oxygen cylinder, 11... Valve (oxygen side), 12... Valve (air side), Figure 2 (Sodium sulfite reduction value versus oxidation time with oxygen) Vertical axis: Sodium sulfite concentration (weight) Horizontal axis: Oxygen oxidation time (minutes) ○ No catalyst ● Activated clay o. Part i (weight) addition Figure 3 (Reduction value of sodium sulfite versus oxidation time with air) Vertical axis: Sodium sulfite concentration (weight%) Horizontal axis: Oxidation time with air (hours) ○ No catalyst △ Diatomaceous earth o. 1% (weight) addition● Activated clay 〃 Activated alumina 〃 × Silica gel.

Claims (1)

[Claims] 1. Aqueous solution containing sodium sulfite at pH 6-10
．． 5. A method in which sodium sulfite in the aqueous solution is oxidized by contacting with an oxygen-containing gas in the coexistence of porous silica gel activated clay, activated alumina, diatomite, or a mixture thereof.