JPH01234312A - Method for averting damage of chlorine - Google Patents

Abstract

PURPOSE:To absorb and remove Cl2 alone, by washing gas contg. Cl2 and CO3 with an aq. mixed soln. of alkali(earth) metal hydroxide and alkali(earth) metal sulfite while regulating the pH value of the aq. mixed soln. to a specified range. CONSTITUTION:The Cl2 alone in the gas contg. Cl2 and CO2 is removed, by using the aq. soln. or suspension contg. alkali(earth) metal sulfite (e.g., Na2SO3) and alkali(earth) metal hydroxide (e.g., NaOH) in <=2times molar ratio to the sulfite, as washing liq., as occasion demands, while supplying the liq. having the compsn. same to one of the aq. soln. or suspension initially charged, so as to regulate the pH value of the washing liq. to 1.9-6.3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for absorbing and removing chlorine gas contained in carbon dioxide gas generated during the production and use of chlorine.

[Conventional technology]

Chlorine is produced and used on a large scale industrially, but the chlorine gas diluted with other gases produced during this process cannot be released directly into the atmosphere due to its toxicity, and is usually It is removed by absorption with alkaline substances.

However, if the gas mixed with chlorine is acidic like carbon dioxide, not only chlorine but also carbon dioxide will be absorbed by the alkaline solution, so the amount of alkali required for absorption will be the total amount of carbon dioxide and chlorine gas. It is decided against. In particular, when the amount of chlorine contained is very small, a large amount of alkali is required to remove the small amount of chlorine, which is disadvantageous.

Therefore, a method for selectively absorbing and removing chlorine in carbon dioxide gas is desired.

In West German Patent No. 2413358, carbonic acid is removed by using a multi-stage countercurrent absorption equipment using an alkali metal hydroxide and/or alkaline earth metal hydroxide and operating the final stage on the liquid side at a pH of approximately 7.5. A method of absorbing only chlorine from a mixture of gas and chlorine as hypochlorite of alkali metals and alkaline earth metals is shown.

However, as shown in Figure 1, p117.5 is greater than the first dissociation constant (pKa) of carbonic acid, which is 6.35, and carbon dioxide gas reacts with alkali metal hydroxides and/or alkaline earth metal hydroxides. This is the area where hydrogen carbonate is produced.

Therefore, in order to absorb only chlorine from a mixture of carbon dioxide gas and chlorine in this region, it is necessary to use exactly the same mole of alkali as chlorine, and it is difficult to balance the alkali when the concentration of chlorine fluctuates. Become.

In addition, I) H7,5 is close to the dissociation constant of hypochlorous acid, so if the pH is lower than this, hypochlorous acid becomes free acid and easily decomposes, so the pH must be controlled strictly. It is necessary to do so. Furthermore, if the purpose is to remove chlorine, the generated hypochlorite solution cannot be disposed of as it is due to its strong oxidizing properties and odor, so it must be reduced separately.

[Problem to be solved by the invention]

The present invention provides a method for simply and efficiently removing only chlorine as a harmless chloride in a wide pH range from a mixed gas containing chlorine and carbon dioxide.

[Means to solve the problem]

As a result of intensive studies in order to realize the above method, the present inventors have discovered that chlorination is possible using a mixed aqueous solution of an alkali metal hydroxide/or alkaline earth metal hydroxide and a sulfite of an alkali metal or alkaline earth metal. The present inventors have discovered that when cleaning a mixed gas containing carbon dioxide and carbon dioxide, it is possible to absorb and reduce only chlorine by adjusting the pH of the cleaning solution to a specific range, and have completed the present invention.

That is, the present invention provides an alkali metal hydroxide and/or alkaline earth metal sulfite and an alkali metal hydroxide and/or alkaline earth metal sulfite in a molar ratio less than twice that of the alkali metal and/or alkaline earth metal sulfite. Supply an aqueous solution or suspension containing metal hydroxide to adjust the pH of the cleaning solution to 1.9.
This is a chlorine abatement method characterized by cleaning a mixed gas containing chlorine gas and carbon dioxide gas with this cleaning liquid while adjusting it to a range of 6.3 to remove only chlorine from the mixed gas.

The present invention will be explained in detail below.

As the alkali metal hydroxide used in the present invention, lithium,
These are hydroxides of alkali metals such as sodium and potassium, and examples of alkaline earth metal hydroxides include hydroxides of magnesium, calcium, barium, etc.

Further, the metal as the sulfite may be an alkaline earth metal salt such as magnesium, galcium, or barium, but
Alkali metals having high solubility in water are preferred.

The ratio of the alkali metal hydroxide and/or alkaline earth metal hydroxide to the alkali metal and/or alkaline earth metal sulfite used in the present invention is such that the hydroxide is twice the molar ratio of the sulfite. It is necessary to do the following.

In this method, it is necessary to add the alkali necessary to neutralize chlorine and at the same time add the sulfite necessary to reduce chlorine. An equivalent amount of the reducing sulfite is required.

If the alkali exceeds twice the mole of the sulfite, ρ1
Even if 1 is adjusted to 1.9 to 6.3, the reducing sulfite is insufficient and chlorine is not absorbed.

When the amount is less than 2 times the mole, the sulfite acts as a substitute for hydroxide, and the more sulfite there is, the more bisulfite ions in the absorption liquid, and its buffering effect lowers the pH. becomes easier. Therefore, no alkali is present, and it is also possible to absorb the sulfite alone.

In this method, an appropriate pH value of 91 (range is 1.9 to 6.3) for the reaction that absorbs chlorine, and at high pHl exceeding 6.3, carbon dioxide gas becomes bicarbonate ions as shown in Figure 1. , since alkali is consumed, the amount of alkali consumed increases and is uneconomical.

Furthermore, if the pH is less than 1.9, it is not preferable because free sulfurous acid is generated and decomposition tends to occur to generate sulfurous acid gas.

The pH of the aqueous solution is adjusted by adding an alkali metal sulfite and/or alkaline earth metal sulfite to an alkali metal hydroxide and/or alkaline earth metal hydroxide in a molar ratio less than twice that of the sulfite. While adjusting the amount added, the pH is 1.
All you have to do is keep it in the range of 9 to 6.3.

In this case, the hydroxide and the sulfite may be added as a solid or an aqueous solution, but an aqueous solution is preferable, and a mixed solution may be used, or of course they may be added separately as an aqueous solution. Good too.

In the case of alkali metal salts and alkaline earth metal salts, the concentration of the aqueous solution is preferably within a range in which the raw materials and the produced salt and sulfate are dissolved, but it is also possible to operate in a slurry state.

The reaction temperature is the saturation fil! of the salt! When operating in a nearly homogeneous system, consideration must be given to solubility, but usually alkali metal, alkaline earth metal sulfites,
Since the saturation concentration of all chlorides does not have a large dependence on temperature, the advantage of concentration amplifier by raising the temperature is not so great.

The reaction rate between chlorine and sulfite increases as the temperature rises, but due to the problems of corrosion and deterioration of the reactor material,
The temperature is preferably above 70°C.

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

The number of stages depends on the permissible amount of chlorine in the gas after treatment, but because the reaction and absorption speed is high, so many stages are not required.

[Action and effect]

Conventional chlorine abatement methods have been complicated, such as supplying an appropriate amount of alkali in response to changes in chlorine concentration, and strictly adjusting the pH of the absorption liquid.

In the method of the present invention, the pH range for absorption control is wide, and only chlorine can be efficiently absorbed and removed using a simple method of supplying alkali, sulfite, etc.

As described above, the present invention is of great practical value.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to Examples.

Example 1 A 10% by weight sodium sulfite aqueous solution (1N) was placed in a flask equipped with a bottomed overflow tube under stirring at 11 min.
n carbon dioxide gas and 100 #li! A mixture of chlorine gas of 1/1 inch was bubbled through the tube, and changes in ρ■ were monitored.

At first, the entire amount of gas blown was absorbed, but as the blown gas continued, the pH decreased, and when the pH reached 6 or less, some gas began to pass through. When the pH becomes 4 or less, add 15.7cc/wi of lOx sodium sulfite aqueous solution.
Feed was started at a rate of n to maintain pl+ at 4.

In this state, the gas that has passed through the solution without being absorbed is removed by N/
When a potassium diiodide solution and an N/2 caustic soda aqueous solution were passed through a trap and titrated with N/10 sodium thiosulfate using a starch aqueous solution as an indicator to detect the chlorine in the trap, the chlorine concentration in the waste gas was determined. It was less than lppm capacity.

In addition, the carbonic acid absorbed in the N/2 potassium iodide solution and the N/2 caustic soda solution was mixed with N/10 NaOH and N/IQIICf, respectively, using methyl orange as an indicator.
Titration was carried out using fi, and it was confirmed that all of the carbon dioxide gas that was blown into the reactor was not absorbed but passed through.

Example 2 A reactor similar to Example 1 was charged with an aqueous solution containing 8.6% by weight of sodium sulfite and 1.4% by weight of caustic soda.
Same < 1 (!/l1in of carbon dioxide and 100cc
/win chlorine gas was mixed and flowed, and when the pH reached 4, an aqueous solution with the same composition as the preparation solution was added to 12.1 m
Start feeding at l/min and maintain pH at 4. The gas that passed through this state was analyzed in the same manner as in Example 1, and chlorine was found to be 1 pρ-vol. % or less, and it was confirmed that the entire amount of carbon dioxide gas was passing through.

Example 3 30 volumes of carbon dioxide χ,
Nitrogen and oxygen 70 volume χ, chlorine gas 1,000 volume pp
A mixed gas (1) containing m is introduced at 50ONrrr/Hr, and an absorption liquid (
2). Inside the tower, there is water (5) 278 kg/
While adding Hr, the aqueous solution (3) containing 10 parts Ix of sodium sulfite is adjusted to pH 4.0 at about 94.5 kg/Hr, and at the same time the liquid volume is kept constant by overflow (4).

When the treated gas (6) that passed through the upper part of the column was sampled and subjected to absorption analysis using an N/10 aqueous potassium iodide solution, the amount of chlorine was 1 ppm or less.

[Brief explanation of the drawing]

FIG. 1 shows the aqueous solution used as an absorbent in the present invention.
It shows the state of each ion according to ρ11. FIG. 2 shows the flow of chlorine absorption in Example 3, and each symbol in the figure has the following meaning. 1. Mixed gas 2. Absorption liquid 3.10 weight 2 Sodium sulfite aqueous solution 4 Overflow pipe 5. Water 6, Gas after treatment 7. Absorption tower 8, circulation pump 9. Metering Pump 10, 10% by weight Sodium Sulfite Aqueous Solution Storage Tank Patent Applicant Mitsui Toatsu Chemical Co., Ltd. ρ-Procedure Amendment Report) February 1999 Commissioner of the Patent Office Yoshi 1) Takeshi Moon 1, Incident Display Showa 1963 Patent Application No. 59428 2 Name of the invention Method for eliminating chlorine 3 Relationship with the case of the person making the amendment Patent applicant address 3-2-5 Kasumigaseki, Chiyoda-ku, Tokyo Name (31
2) Mitsui Toatsu Chemical Co., Ltd. 4. Number of inventions increased by the amendment: 0 5. Detailed explanation column of the invention in the specification subject to the amendment and Figure 1 6 of the drawings, Contents of the amendment (2) As shown in the attached sheet . 7.53H

Claims (1)

[Claims] an alkali metal and/or alkaline earth metal sulfite;
2 of alkali metal and/or alkaline earth metal sulfites
Supply an aqueous solution or suspension containing an alkali metal hydroxide and/or alkaline earth metal hydroxide at a ratio of twice the molar ratio or less to adjust the pH of the cleaning solution to a range of 1.9 to 6.3. A chlorine abatement method characterized by cleaning a mixed gas containing chlorine gas and carbon dioxide gas with this cleaning liquid while adjusting it, and removing only chlorine from the mixed gas.