JPH05171482A - Method for removing gaseous hydrogen sulfide - Google Patents

Abstract

PURPOSE:To easily and efficiently regenerate and recycle an alkaline absorbent and to recover H2S as sulfur without oxidizing the H2S to sulfuric acid in the method in which a raw gas contg. H2S is brought into contact with the absorbent to remove H2S. CONSTITUTION:An alkaline absorbent having absorbed hydrogen sulfide is electrolyzed and regenerated, and the regenerated absorbent is circulated and used to remove hydrogen sulfide. H2S is fixed as S<2-> in the absorbent of Na0H, etc., according to 2NaOH+H2S Na2S+2H2O. The S<2-> is electrolyzed into S at a positive electrode 8A according to S<2-> S+2e<->. The generated S is dissolved in the absorbent as alkali polysulfides. H2 is generated at a negative electrode 8B according to 2H<+>+2e<-> H. The overall chemical equation is expressed by Na2S+2H2O NaOH+S+H2, alkalinity is restored, and alkali need not be supplied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing hydrogen sulfide gas, and more particularly, to a method for removing H ₂ S from a gas containing hydrogen sulfide gas (hereinafter referred to as "H ₂ S") generated during anaerobic biological treatment. ₂
The present invention relates to a method of efficiently removing S at low cost and recovering H ₂ S as sulfur (S).

[0002]

Conventionally, as a method for removing H ₂ S from the H ₂ S-containing gas, the following ~ methods. Wet method: Using caustic soda (NaOH) as an absorbent,
Clean the raw gas with alkali. Dry method: H ₂ S is immobilized in the form of an iron sulfide compound using an iron material. Bio-oxidation method: Resorbed in water, biologically oxidized to sulfuric acid, and discharged out of the system.

[0003]

The conventional methods of removing H ₂ S described above have the following drawbacks, respectively, and cannot be said to be suitable processing methods. That is, in the wet method, since H ₂ S, which is an acidic gas, is absorbed by NaOH, it is necessary that the absorbing solution is always alkaline. As a result, the neutralization cost is high and the drainage solution is Since some of the strong alkali is discarded, residual NaOH is wasted. In the dry method, the iron material must be replaced while the iron material always retains its reserve capacity (H ₂ S absorption capacity), and at the time of this replacement, sulfuric acid is generated and heat is generated due to air oxidation, which is a work risk. Is afraid. In addition, in the biological oxidation method of H
When biologically oxidizing ₂ S, the reaction proceeds to sulfuric acid, which is the final oxidation state, and therefore an alkali is necessary for neutralizing this sulfuric acid. Moreover, when water is used as the absorbing liquid, its H ₂ S absorption efficiency is inferior to that of the alkaline liquid,
The absorption tower becomes larger.

[0004] For this reason, conventionally, performs H ₂ S absorption by using H ₂ S absorption efficient alkaline absorbing solution,
There has been a demand for application of a technique for recovering excess alkali or a technique for recovering H ₂ S without oxidizing it to sulfuric acid.

Incidentally, it has been conventionally known that a gas containing nitrogen oxides and sulfur oxides is purified with an iron-based absorbing solution and electrolytic regeneration of the absorbing solution used is carried out (Japanese Patent Laid-Open No. 53-2625).
7). However, this method is a technique in the case where the oxide-based gas is absorbed by the iron-based absorbing liquid, and the target gas component and the absorbing liquid are different from the technique of absorbing H ₂ S by the alkaline absorbing liquid. Hitherto, no proposal has been made on an efficient regeneration technique for an alkali absorbing liquid that has absorbed H ₂ S gas.

The present invention was made in view of the above conventional circumstances, in the method of the raw gas containing H ₂ S is contacted with an alkaline absorbing solution for removing H ₂ S, and facilitates the alkaline absorbing solution An object of the present invention is to provide a method for removing H ₂ S that can be efficiently regenerated and recycled for reuse, and that can be efficiently recovered as S without oxidizing H ₂ S to sulfuric acid.

[0007]

The method of removing H ₂ S of the present invention is a method of removing hydrogen sulfide gas by bringing a raw gas containing hydrogen sulfide gas into contact with an alkali absorbing liquid to remove hydrogen sulfide gas. It is characterized in that the alkali absorbing liquid is electrolyzed and regenerated, and the regenerated liquid is circulated and used in the hydrogen sulfide gas removal treatment step of the raw gas.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a cross-sectional view showing one embodiment of the H ₂ S removing method of the present invention.

In the figure, 1 is a gas cleaning tower and 2 is an electrolytic cell. A raw gas introduction pipe 3 and an absorption liquid discharge pipe 4 are connected to the bottom of the gas cleaning tower 1, and a processing gas discharge pipe 5 is connected to the upper portion. In addition, in the upper part of the gas cleaning tower 1,
A sprinkler plate 6 for absorbing liquid is provided, and a circulation pipe 7 including a pump 7A is connected to the sprinkler plate 6.
The liquid in the electrolytic bath 2 is supplied.

The gas cleaning tower 1 is connected to the electrolytic cell 2 through the discharge pipe 4.
Of the anode (positive electrode) 8 so as to be immersed in the liquid in the electrolytic cell 2.
A and a cathode (negative electrode) 8B are provided. Reference numeral 9 is a DC power source, and 10 is an absorbing liquid drawing tube.

In order to carry out the present invention with such an apparatus, first, a raw gas containing H ₂ S is introduced into the gas washing tower 1 through the introduction pipe 3, and an alkali absorbing liquid is sprinkled through the water spray plate 6. Then, the raw gas is brought into countercurrent contact with the alkali absorbing solution to absorb H ₂ S in the alkali absorbing solution. The processing gas from which H ₂ S has been absorbed and removed is discharged from the system through the exhaust pipe 5. On the other hand, the alkali absorbing solution that has absorbed H ₂ S is sent to the electrolytic cell 2 through the discharge pipe 4, and the current of the DC power supply 9 is passed inside the electrolytic cell 2 to be electrolyzed. That is, in the alkali absorbing liquid, H ₂
Since S is fixed in the form of sulfur ion S ^2-
Anode (positive electrode) 8 by electrolyzing a solution containing ^2-
In A, S ²⁻ is oxidized to produce S, and this S becomes alkali polysulfide in the liquid and dissolves. On the other hand, in the cathode (negative electrode) 8B, hydrogen ions H ⁺ in the liquid are reduced to generate hydrogen gas H ₂ .

The liquid in which the alkali is regenerated and the S ²⁻ is removed by such electrolysis is fed to the gas cleaning tower 1 through the circulation pipe 7 and is circulated and reused as the alkali absorbing liquid. When recycled and reused, polysulphurization proceeds and the viscosity of the alkali absorption liquid increases, so a part of it is withdrawn, neutralized with acid, and the precipitate of elemental sulfur that forms is collected (not shown). ).

In the present invention, the alkali absorbing solution may be an aqueous solution containing alkalinity such as NaOH, Na ₂ CO ₃ or the like, and its pH is 9 or more from the viewpoint of H ₂ S absorption efficiency. Is desirable.

The standard redox potential (2
It is important that the ionic strength 0) at 5 ° C. be lower than 1.23V. That is, electrolysis of water (2H ₂ O → O ₂ +
4H ⁺ + 4e ⁻ ) requires a potential of + 1.23V,
Since the potential required to generate S from S ²⁻ (S ² → → S + 2e ⁻ ) is −0.48 V, the reaction on the positive electrode side is S ^{2 −.}
The potential is 1.23V in order to keep the generation of S by the oxidation of
Less than If the potential is higher than this, electrolysis of water occurs and the input energy is wasted, which is not preferable. However, when SO ₃ ions and S ₂ O ₄ ions are contained in the liquid, alkali and electricity consumption due to these oxidations are required unless they are +0.17 V and −0.08 V or less, respectively, which is not preferable.

[0016]

The H ₂ S gas is fixed in the form of S ^2-in the next reaction by an alkali absorbing solution such as NaOH. H ₂ S + 2NaOH → Na ₂ S + 2H ₂ O (gas absorption) When this alkaline absorbent that has absorbed H ₂ S is electrolyzed, S ²⁻ is oxidized to S and H ⁺ is reduced to H ₂ by the following reaction. As a result, the alkali is regenerated. Further, the generated S is alkali polysulfide (Na
₂ S _X ) and dissolves.

Positive electrode side: S ^2- → S + 2e ⁻ (recovery of S) Negative electrode side: 2H ⁺ + 2e ⁻ → H ₂ (gas release) Electrolysis reaction of positive and negative electrodes Na ₂ S + 2H ₂ O → S + H ₂ + 2NaOH (of alkali) Playback)

[0018]

EXAMPLES The present invention will be described in more detail with reference to the following examples.

Example 1 By the method shown in FIG. 1, H ₂ S was removed, the alkali absorbing solution was regenerated, and S was recovered.

That is, 500 μl / l of H ₂
The S-containing raw gas was bubbled through a 5 liter gas scrubber at 10 liters / minute. On the other hand, a 0.5 N NaOH aqueous solution was passed from the top of the gas washing tower at 0.01 liter / min,
The liquid having absorbed H ₂ S was continuously extracted from the bottom and fed to the electrolytic cell.

At this time, the removal efficiency of H ₂ S was 99%. H in gas cleaning with water performed for comparison
The removal efficiency of ₂ S was 50%, and it was confirmed that the alkali absorbing solution can efficiently absorb and remove the alkali.

The H ₂ S-absorbed alkaline absorbing solution from the gas cleaning tower is continuously electrolyzed by applying a DC voltage of 5 V in a 0.5 liter electrolytic cell equipped with a 5 mmφ carbon electrode. I did.

As a result, almost no O ₂ gas was generated from the anode (positive electrode), and 5 ml of H ₂ gas was generated from the cathode (negative electrode) per minute.

Although the liquid in the electrolytic cell turned yellow with time and the viscosity gradually increased, it was circulated and reused as an alkali absorbing liquid in the washing tower and continuously operated for 30 days.

During this continuous operation, the removal rate of H ₂ S was maintained at the initial value (99%), and the pH of the alkali absorption liquid circulated in the gas cleaning tower was always 12 or more. A part of this absorption liquid was drawn out and neutralized with hydrochloric acid to collect a precipitate of elemental sulfur.

On the other hand, for comparison, when the continuous operation was performed without electrolysis, H ₂ S
The removal rate decreased, and an H ₂ S odor was also observed in the alkali absorbing solution. Therefore, the H ₂ S removal rate could be maintained by periodically replacing half of the alkali absorption liquid in the system with a new NaOH aqueous solution and repeating the operation.

[0027]

As described above in detail, according to the method H ₂ S removal of the present invention, in an absorption method for removing H ₂ S by removing efficient alkaline absorption liquid H ₂ S, alkalinity of the absorbent To easily and efficiently reproduce H ₂ S and
Can be generated as. Since the generated S dissolves as alkali polysulfide, the electrodes are not contaminated.

Therefore, it is not necessary to replenish the alkali absorbing solution, and the processing cost can be reduced. Further, it is possible to collect H ₂ S as solid S, which facilitates the recovery work, and is also industrially extremely advantageous because S can be recycled.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an implementation method of the H ₂ S removal method of the present invention.

[Explanation of symbols]

 1 Gas Washing Tower 2 Electrolysis Tank 6 Sprinkler Plate 8A Anode 8B Cathode

Claims (1)

[Claims] 1. A method for removing hydrogen sulfide gas by contacting a raw gas containing hydrogen sulfide gas with an alkali absorbing liquid, wherein the alkali absorbing liquid absorbing hydrogen sulfide gas is electrolyzed and regenerated, and the regenerated liquid is A method for removing hydrogen sulfide gas, characterized by being recycled for use in a process for removing hydrogen sulfide gas from a raw gas.