JP2788477B2 - Method for eliminating fluorine, bromine and iodine - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method of absorbing and harming fluorine, bromine or iodine contained in carbon dioxide gas produced in the production and use of fluorine, bromine or iodine. is there.

PRIOR ART Fluorine, bromine or iodine is produced and utilized on a large industrial scale, but fluorine, bromine or iodine gas diluted with other gases generated at that time has a low toxicity. Therefore, it cannot be released to the atmosphere as it is, and is usually absorbed and removed by an alkaline substance. But fluorine,
When the gas mixed with bromine or iodine is acidic like carbon dioxide, not only fluorine, bromine or iodine but also carbon dioxide is absorbed by the alkaline solution. It depends on the total amount of bromine or iodine gas. In particular, when the amount of fluorine, bromine or iodine contained is very small, there is a disadvantage that a large amount of alkali is required to remove a small amount of fluorine, bromine or iodine. Therefore, a method of selectively absorbing and removing fluorine, bromine or iodine in carbon dioxide gas is desired.

In German Patent 2413358, a multi-stage countercurrent absorption system using an alkali metal hydroxide and / or an alkaline earth metal hydroxide is used. Discloses a method of absorbing only chlorine from a mixture of chlorine as a hypochlorite of an alkali metal or an alkaline earth metal.

However, as shown in FIG. 1, pH 7.5 is a first dissociation constant (pKa) of carbonic acid of 6.35 or more, and carbon dioxide gas reacts with alkali metal hydroxide and / or alkaline earth metal hydroxide. This is the area where bicarbonate is generated.

Therefore, in order to absorb only chlorine from a mixture of carbon dioxide and chlorine in this region, it is necessary to use an alkali in an exactly equimolar amount with chlorine, and it is difficult to balance the alkali when the chlorine concentration fluctuates. Become.

For chlorine, pH 7.5 is around the dissociation constant of hypochlorous acid, so if the pH is lower than this, hypochlorous acid is easily decomposed in the form of a free acid, so pH control must be controlled. It needs to be done strictly. Further, if the purpose is to remove chlorine, the resulting hypochlorite solution cannot be discarded as it is because of its strong oxidizing property and odor, so it must be separately reduced.

When this method is applied to the case of bromine, the dissociation constant of hypobromous acid is 8.5, so that hypobromous acid becomes a free acid and bromine cannot be completely eliminated.

In the case of iodine, the dissociation constant is 9.7, which is the same as in the case of bromine.

[Problems to be solved by the invention]

The present invention provides a method for simply and efficiently removing fluorine, bromine or iodine as a harmless halide over a wide pH range from a mixed gas containing halogen gas, particularly fluorine, bromine or iodine and carbon dioxide gas.

[Means for solving the problem]

The present inventors have conducted intensive studies to realize the above method, and found that an alkali metal hydroxide and / or an alkaline earth metal hydroxide, an alkali metal sulfite and / or an alkaline earth metal sulfite When cleaning a mixed gas containing halogen and carbon dioxide gas with a mixed aqueous solution of salts, it was found that only the halogen can be absorbed and reduced if the pH of the cleaning solution was adjusted to a specific range and the cleaning was performed, and the present invention was completed. I let it.

That is, the present invention relates to an aqueous solution containing an alkali metal sulfite and / or an alkaline earth metal sulfite and an alkali metal hydroxide and / or an alkaline earth metal hydroxide in a molar ratio of not more than twice the sulfite. Or supply the suspension,
Cleaning the mixed gas containing fluorine, bromine or iodine and carbon dioxide gas with this cleaning solution while adjusting the pH of the cleaning solution to the range of 1.9 to 6.3, and removing fluorine, bromine or iodine in the mixed gas. , Bromine and iodine.

 Hereinafter, the present invention will be described in detail.

The mixed gas to be treated in the present invention contains carbon dioxide gas and halogen. The types of halogen gas include fluorine, chlorine, bromine and iodine, and any of these gases can be harmed.

The alkali metal hydroxide used in the present invention is, for example, a hydroxide of an alkali metal such as lithium, sodium, and potassium.As the alkaline earth metal hydroxide,
It is a hydroxide of magnesium, calcium, barium and the like.

Further, the metal as the sulfite is an alkali metal such as lithium, sodium and potassium and / or an alkaline earth metal such as magnesium, calcium and barium. An alkali metal is preferable because of its high solubility in water.

The amount of the alkali metal hydroxide and / or alkaline earth metal hydroxide used in the present invention must be not more than twice the molar ratio with respect to the alkali metal sulfite and / or the alkaline earth metal sulfite. It is.

In this method, it is necessary to add an alkali necessary for neutralizing fluorine, bromine or iodine, and at the same time, add a sulfite necessary for reducing fluorine, bromine or iodine.
For 2 equivalents of alkali required for neutralization, at least 1 equivalent of the reducing sulfite is required.

If the alkali exceeds twice the mol of the sulfite,
Is adjusted to 1.9 to 6.3, the reducing sulfite is insufficient and fluorine, bromine or iodine cannot be absorbed.

In the case of less than 2 moles, the sulfite acts as a substitute for the hydroxide, and the more the sulfite, the more bisulfite ion in the absorbing solution and the pH adjustment due to its buffering action. Becomes easier. Therefore, it is also possible to absorb only the sulfite without the presence of an alkali.

In this method, a suitable pH range for the reaction of absorbing fluorine, bromine or iodine is 1.9 to 6.3. At a high pH exceeding 6.3, as shown in FIG. Because it is consumed, the amount of alkali consumed is uneconomical.

If the pH is less than 1.9, free sulfurous acid is generated and decomposed to easily generate sulfurous acid gas, which is not preferable.

The pH of the aqueous solution is adjusted by mixing an alkali metal sulfite and / or an alkaline earth metal sulfite with an alkali metal hydroxide and / or an alkaline earth metal hydroxide having a molar ratio of 2 times or less the sulfite. PH is 1.9 ~ while adjusting the addition amount
What should be done is to be in the range of 6.3.

In this case, the hydroxide and the sulfite may be added in the form of a solid or an aqueous solution, but an aqueous solution is preferable, and the mixture may be supplied as a mixed solution or, of course, separately added as an aqueous solution. Is also good. In the case of an alkali metal salt or an alkaline earth metal salt, the concentration of the aqueous solution is preferably in a range in which the raw materials and the generated halides and sulfates are dissolved, but it is also possible to operate in a slurry state.

The reaction temperature, when operating in a homogeneous system near the saturated concentration of the salt, it is necessary to consider in consideration of the solubility, usually alkali metal, alkaline earth metal sulfite,
Since the dependence of the saturation concentration on the temperature is not so large in any of the halides, the merit of increasing the concentration by increasing the temperature is not so large.

The reaction rate of fluorine, bromine or iodine with a sulfite increases as the temperature rises, but is preferably 0 ° C. or more and 70 ° C. or less in view of corrosion and deterioration of the reactor material.

The reaction type may be absorption by bubbling of gas into the stirring tank or absorption in a washing tower type.

Although the number of stages depends on the permissible amount of fluorine, bromine or iodine in the gas after the treatment, the number of stages is not so large because the rate of reaction absorption is high.

[Action and effect]

The conventional method of removing fluorine, bromine or iodine is a complicated method such as a method of supplying an appropriate amount of an alkali corresponding to a change in the concentration of fluorine, bromine or iodine, or a method of strictly adjusting the pH of an absorbing solution.

In the method of the present invention, the pH range to be controlled during absorption is wide, and only fluorine, bromine and iodine can be efficiently absorbed and detoxified by a simple supply method of alkali or sulfite.

As described above, the present invention is extremely valuable in practical use.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to examples.

Example 1 A mixture of 1 / min carbon dioxide gas and 100 ml / min bromine gas was bubbled under stirring into a flask equipped with a bottomed overflow tube charged with a 10% by weight aqueous sodium sulfite solution 1, and the change in pH was tracked. did. At the beginning, the whole amount of gas blown is absorbed.
When the pH fell below pH 6, some gas began to pass. When the pH became 4 or less, a 10% aqueous solution of sodium sulfite was supplied at a rate of 15.7 cc / min to maintain the pH at 4.

In this state, the gas that passed through the solution without being absorbed
After passing through a trap of potassium iodide solution and an aqueous solution of N / 2 caustic soda and titrating with an aqueous starch solution as an indicator with N / 10 sodium thiosulfate, bromine in the trap was determined.The bromine concentration in the waste gas was determined. Was less than 1 ppm volume.

Further, the N / 2 potassium iodide solution and the carbonic acid absorbed in the N / 2 caustic soda solution were titrated with N / 10NaOH and N / 10HCl, respectively, using methyl orange as an indicator, and the entire amount of the injected carbon dioxide gas was absorbed. I confirmed that it was passing.

Example 2 An aqueous solution containing 8.6% by weight of sodium sulfite and 1.4% by weight of caustic soda was put into the same reactor as in Example 1, and 1 / min of carbon dioxide gas and 100 cc / min of bromine gas were mixed and flown. When the pH reached 4, an aqueous solution having the same composition as the charged solution was started to be supplied at 12.1 ml / min, and the pH was maintained at 4. The gas passed in this state was analyzed in the same manner as in Example 1, and it was confirmed that bromine was 1 ppm by volume or less and that the entire amount of carbon dioxide passed.

Example 3 A flask equipped with a bottomed overflow tube charged with a 0.5% by weight aqueous sodium sulfite solution 1 was stirred at 1 / min.
A mixture of carbon dioxide gas and nitrogen gas containing 0.5% by volume of iodine at 100 ml / min was bubbled to monitor a change in pH. At first, the whole amount of the gas blown was absorbed, but as the blowing continued, the pH dropped, and when the pH became 6 or less, some gas started to pass. When the pH drops to 4 or less, 0.5
% Aqueous sodium sulfite solution at 1.1 cc / min
H was kept at 4.

In this state, the gas that passed through the solution without being absorbed
After passing through a trap of potassium iodide solution and an aqueous solution of N / 2 caustic soda, titration was performed with N / 10 sodium thiosulfate using an aqueous starch solution as an indicator, and the iodine in the trap was determined. Was less than 1 ppm volume.

Further, the N / 2 potassium iodide solution and the carbonic acid absorbed in the N / 2 caustic soda solution were titrated with N / 10NaOH and N / 10HCl, respectively, using methyl orange as an indicator, and the entire amount of the injected carbon dioxide gas was absorbed. I confirmed that it was passing.

[Brief description of the drawings]

FIG. 1 shows that the aqueous solution used as an absorbent in the present invention comprises:
It shows the state of each ion depending on the pH.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-233122 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B01D 53/14-53/18 B01D 53 / 34-53/96

Claims (1)

(57) [Claims] An aqueous solution containing an alkali metal sulfite and / or an alkaline earth metal sulfite and an alkali metal hydroxide and / or an alkaline earth metal hydroxide in a ratio of not more than twice the molar ratio of the sulfite. Or by supplying a suspension and adjusting the pH of the washing solution to a range of 1.9 to 6.3, washing the mixed gas containing fluorine, bromine or iodine and carbon dioxide gas with this washing solution, and removing fluorine, bromine in the mixed gas. Or a method for removing fluorine, bromine and iodine, which comprises removing iodine.