JPH0813682B2 - How to treat hydrogen sulfide - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating hydrogen sulfide, and more specifically, in a method for recovering sulfur and hydrogen gas from a hydrogen sulfide-containing gas, by using a specific iron salt aqueous solution, impurities are by-produced. The present invention relates to a method for treating hydrogen sulfide, which can suppress sulfur and efficiently recover sulfur and hydrogen.

[0002]

2. Description of the Related Art Conventionally, the problems to be solved by the invention
Hydrogen sulfide discharged during oil refining was industrially processed by the Claus method. However, according to this method, although the sulfur component in hydrogen sulfide is recovered as sulfur, the hydrogen component is not recovered as hydrogen gas but becomes water, which cannot be efficiently utilized industrially. Currently, as a method for recovering sulfur and hydrogen gas from hydrogen sulfide by oxidation and electrochemical treatment, a method using a solution containing trivalent iron ions is known. As a method like this,
Hydrogen sulfide is contacted and oxidized using a hydrochloric acid iron salt aqueous solution containing trivalent iron ions to separate generated sulfur, and then the hydrochloric acid iron salt aqueous solution is subjected to electrochemical regeneration treatment to generate hydrogen. Then, a method of collecting this is proposed (Japanese Patent Publication No. 1-53201).

According to this method, however, when hydrogen sulfide is brought into contact with an aqueous solution of a hydrochloric acid-based iron salt and oxidized to produce sulfur, a relatively large amount of sulfur oxides such as sulfur dioxide and sulfuric acid are by-produced. . Therefore, the quality of the gas after processing was quite low. Further, this method is unsuitable as an industrial method because it is highly corrosive to the metal material of the reaction vessel in the above-mentioned oxidation or the electrochemical treatment to be carried out when a hydrochloric acid-based iron salt aqueous solution is used. there were.
Furthermore, in the electrochemical regeneration treatment, the efficiency is low,
It required a high electrolysis voltage. As described above, at present, a treatment method for efficiently recovering sulfur and hydrogen from hydrogen sulfide has not been developed.

[0004]

Therefore, the present inventors have solved the above-mentioned problems, suppressed by-products such as sulfur oxides, improved the quality of gas, and added to the metal material constituting the reaction vessel. Therefore, we have conducted intensive studies to develop a method for treating hydrogen sulfide that is less corrosive and that is more efficient in the electrochemical regeneration treatment process at low electrolysis voltage. As a result, they have found that the objective can be achieved by using a phosphoric acid-based iron chloride aqueous solution or a phosphoric acid-hydrochloric acid-based iron chloride aqueous solution in oxidizing hydrogen sulfide. The present invention has been completed based on such findings.

That is, according to the present invention, the gas containing hydrogen sulfide is 3
When an iron salt solution containing divalent iron ions is brought into contact with and absorbed to cause an oxidation reaction to generate a solution containing divalent iron ions and sulfur, and hydrogen sulfide is treated, a phosphoric acid-based solution is used as the iron salt solution. Provided is a method for treating hydrogen sulfide, which comprises using an aqueous solution of iron chloride or an aqueous solution of phosphoric acid-hydrochloric acid-based iron chloride, and further to remove sulfur in a solution containing divalent iron ions and sulfur produced by the above-mentioned treatment method. After the separation, the solution is subjected to an electrochemical regeneration treatment to regenerate divalent iron ions into trivalent iron ions to recover hydrogen, thereby providing a method for treating hydrogen sulfide.

As described above, the method for treating hydrogen sulfide of the present invention includes the step of contacting and absorbing the hydrogen sulfide-containing gas with the iron salt solution containing trivalent iron ions (gas-liquid contact step). As the iron salt solution used in the step, a phosphoric acid-based iron chloride aqueous solution or a phosphoric acid-hydrochloric acid-based iron chloride aqueous solution is applied. This gas-liquid contact step proceeds as follows. Gas-Liquid Contact Step That is, in the method of the present invention, as described above, the contact treatment between the hydrogen sulfide-containing gas and the phosphoric acid-based iron chloride aqueous solution or the phosphoric acid-hydrochloric acid-based iron chloride aqueous solution containing the trivalent iron ions is performed. The gas that can be treated in this gas-liquid contact step is a hydrogen sulfide-containing gas, and is not limited to pure hydrogen sulfide gas as long as it is a gas containing hydrogen sulfide. As long as the gas is inert to the trivalent iron ion, it may be mixed in. For example, a mixed gas of hydrogen sulfide and hydrogen, carbon monoxide, carbon dioxide, hydrocarbon (methane, ethane, etc.), ammonia, nitrogen, etc. can be used.

In the present invention, a phosphoric acid-type iron chloride aqueous solution or phosphoric acid-
It is necessary to use a hydrochloric acid-based iron chloride aqueous solution. Here, the phosphoric acid-based iron chloride aqueous solution or the phosphoric acid-hydrochloric acid-based iron chloride aqueous solution contains a trivalent iron ion (ferric ion) for oxidation, that is, a phosphoric acid aqueous solution containing ferric chloride. Alternatively, it is a phosphoric acid-hydrochloric acid aqueous solution. Further, the absorbing solution may contain a ferrous salt, other salts, etc., as long as the object of the present invention is not impaired. The ion concentration in the aqueous iron salt solution used is not particularly limited, but ferric ion is 0.1 to 5.0.
It is in the range of mol / l, preferably 0.5-1.5 mol / l. When the content of ferric ion is less than 0.1 mol / l, the absorption rate of hydrogen sulfide decreases, and when it exceeds 5.0 mol / l, there is a problem in solubility, which is not preferable.
The ferrous ion is not essential, but ferrous chloride is used, and is usually present in the range of 0.1 to 5.0 mol / liter, preferably 0.5 to 1.5 mol / liter. . The addition of ferrous ion is mainly for improving the efficiency in the electrochemical treatment, but if it is less than 0.1 mol / liter, the effect cannot be obtained, and if it exceeds 5.0 mol / liter, iron salt is added. Precipitation of (particularly ferrous chloride) occurs, which is not preferable.

Further, in the present invention, as described above, a phosphoric acid-based aqueous solution or a phosphoric acid-hydrochloric acid-based aqueous solution containing the above ions is used as the absorbing liquid. By using a phosphoric acid-based or phosphoric acid-hydrochloric acid-based aqueous solution, sulfur oxide by-products can be suppressed to a low level. The concentration of phosphoric acid is not particularly limited,
Usually 0.5 to 7.0 mol / liter, preferably 0.5 to 3.0
Mol / l, more preferably 0.7 to 1.5 mol / l. Here, if the phosphoric acid concentration is less than 0.5 mol / liter, the effect of using phosphoric acid is insufficient, and the by-products of sulfur oxides, especially sulfuric acid, increase. Also, 7.
When it exceeds 0 mol / liter, precipitation of iron salt occurs, which is not preferable. The concentration of phosphoric acid in the case of using an aqueous solution of phosphoric acid-hydrochloric acid may be selected in the same range as the concentration of phosphoric acid, and the concentration of hydrochloric acid used together is not particularly limited, but is usually 0.5 to 5. 3.0 mol / liter, preferably 0.7-
It is 1.5 mol / liter. Further, when the phosphoric acid-hydrochloric acid-based aqueous solution is used more effectively, it is preferable to set the phosphoric acid concentration and the hydrochloric acid concentration to around 1 mol / liter. Here, if the concentration of hydrochloric acid is less than 0.5 mol / liter, the effect of using hydrochloric acid is insufficient, and in particular, the by-product of sulfuric acid increases. Further, if it exceeds 3.0 mol / liter, sulfur oxides are by-produced, which is not preferable.

The gas-liquid contacting step (hydrogen sulfide gas absorption step 1) is not particularly limited, but is a method conventionally used in gas absorption by a liquid, such as a bubble column, a spray column or a wet wall column. A general-purpose absorption tower such as a stirring absorption tower, a packed bubble tower, or a packed tower may be adopted.

The reaction formula of the gas-liquid contact step for producing sulfur from hydrogen sulfide in this step is shown below. 2Fe ³⁺ + H ₂ S = 2Fe ²⁺ + 2H ⁺ + S (precipitation) (I) That is, hydrogen sulfide is oxidized by ferric ion to produce sulfur, and ferric ion becomes ferrous ion. Be reduced. As a result, sulfur is contained in the phosphoric acid-based aqueous solution or the phosphoric acid-hydrochloric acid-based aqueous solution.

The temperature in the gas-liquid contact step (contact reaction) is usually 50 to 150 ° C., preferably 120 to 140.
° C. If the temperature is lower than 50 ° C., the absorption rate of hydrogen sulfide decreases, which is not preferable. Further, in order to carry out the separation particularly quickly, the melting point of sulfur should be 120 ° C. or higher, although the melting point of sulfur differs depending on the allotrope. By thus setting the melting point of sulfur or higher, sulfur is produced in a molten state, and the sulfur and the aqueous solution can be easily separated by the difference in specific gravity. Below this temperature range, sulfur will not be in a molten state,
Separation is difficult and high-purity recovery is difficult. On the other hand, if the temperature is higher than 150 ° C., the viscosity of molten sulfur increases, which may make handling inconvenient.

The pressure for the catalytic reaction is not particularly limited as long as it is a pressure required to prevent evaporation of water and maintain the desired temperature within a range that does not hinder the operation.
It is preferably at least 1.5 atm.

Treatment of divalent iron ions and sulfur generated in the above-mentioned catalytic reaction may be carried out by various physical or chemical methods, and is not particularly limited. For example, in treating sulfur, physical treatment methods include a precipitation separation method and a centrifugal separation method, and as chemical treatment methods, a method of further converting to another sulfur compound can be mentioned. Moreover, as a method of treating divalent iron ions, a method of regenerating divalent iron ions into trivalent iron ions or a method of using metallic iron can be mentioned. here,
A preferred method for treating sulfur is a sulfur separation step, and a preferred method for treating divalent iron ions is an electrochemical regeneration treatment step.

Sulfur Separation Step There are various methods for this step, and the conditions and operating procedures may be appropriately selected. Among them, a preferable method is a method in which the sulfur generated above is used as molten sulfur, liquid-liquid separation is performed, and this is separated by settling due to the difference in specific gravity and then recovered. The sulfur separator used in this sulfur separation step is not particularly limited, and various structures can be used.
For example, a general thickener type, a superficial drum type, a settling basin type, etc. may be appropriately selected according to the size of the molten sulfur droplets to be separated and recovered and the designed recovery rate.

Electrochemical Regeneration Treatment Step This electrochemical regeneration treatment step targets the aqueous solution after the sulfur has been separated and recovered through the sulfur separation step described above. There are various methods for this step as well, and the method is not limited. The following methods are preferred. The aqueous solution (absorption liquid) after the sulfur recovery obtained in the sulfur separation step contains a large amount of ferrous ions.
In this regeneration step, for example, by electrolysis, ferrous ions are converted to ferric ions, hydrogen gas is generated, and an aqueous solution containing a large amount of trivalent iron ions (ferric ions) (absorption Liquid) is regenerated and hydrogen gas is separated and recovered. The reaction that proceeds here is represented by the following reaction formula. 2Fe ²⁺ + 2H ⁺ = 2Fe ³⁺ + H ₂ (gas) (II) That is, ferrous ions are oxidized and regenerated into ferric ions and hydrogen gas is generated. The regenerated solution can be subjected to the gas-liquid contact step again. As an apparatus for carrying out this electrochemical regeneration step, an electrolytic cell of the type commonly used for ordinary electrolysis or the like is used.

A diaphragm is provided between an anode and a cathode in the electrolytic cell for carrying out such steps, and an acid resistant material such as graphite or carbon fiber is used for the electrode.
It is preferable to use a hydrogen ion selective permeable membrane as the diaphragm. For example, in the electrolysis, an iron phosphate aqueous solution containing divalent iron ions treated as described above is put in the anode part of the electrolytic cell, while an aqueous solution containing hydrogen ions of a predetermined concentration is usually put in the cathode part. It is carried out by putting in or supplying water to such an extent that the diaphragm between the anode and the cathode is not dried and applying a voltage.

When a hydrogen ion-selective permeable membrane is used as the diaphragm, a porous gas diffusion electrode, for example, a graphite fiber cloth, preferably one carrying a catalyst such as platinum, is used, if desired.
It may be brought into direct contact with the diaphragm. The electrolysis is usually performed at 25 to 100 ° C.

In the present invention, since the by-products in the above-mentioned catalytic reaction are extremely small, the gas quality after the treatment can be considerably improved. Further, since the electrolytic solution in the electrochemical regeneration treatment step is a phosphoric acid aqueous solution or a phosphoric acid-hydrochloric acid aqueous solution, electrolysis can be performed at a relatively low electrolysis voltage. Here, it is preferable to use hydrochloric acid as the electrolytic solution of the cathode part because the electrolytic voltage can be lowered. When hydrochloric acid is used, it is usually 0.5 to 6.0 mol / liter, preferably 0.5 to
Electrolysis can be performed at a concentration of about 5.0 mol / liter. Here, if it is less than 0.5 mol / liter, a high electrolysis voltage is required, and if it exceeds 6.0 mol / liter, a high electrolysis voltage is required, and further, the partial pressure of hydrogen chloride increases. Greater corrosiveness. In the anode part, the divalent iron ions are electrolytically oxidized into trivalent iron ions, and hydrogen is generated in the cathode part.

In this way, hydrogen is generated by electrochemically treating the phosphoric acid-based iron chloride aqueous solution or the phosphoric acid-hydrochloric acid-based iron chloride aqueous solution containing the divalent iron ions from which the generated sulfur has been removed. At the same time, the divalent iron ions are regenerated into trivalent iron ions, and thus the regenerated treatment liquid can be repeatedly used as a hydrogen sulfide absorbing liquid.

Next, an example of the preferred embodiment of the present invention is shown in FIG.
Follow the instructions below. FIG. 1 is a schematic diagram showing an example of an apparatus for carrying out the present invention as described above. As shown in FIG. 1, in the hydrogen sulfide gas absorption step 1 (for example, an absorption tower), a hydrogen sulfide (H ₂ S) gas, which is a gas to be treated, and a phosphoric acid-based iron chloride aqueous solution containing trivalent iron ions or A phosphoric acid-hydrochloric acid-based iron chloride aqueous solution, specifically, a phosphoric acid aqueous solution or a phosphoric acid-hydrochloric acid aqueous solution containing ferric chloride is introduced. In the initial state, the ferric chloride aqueous solution may be prepared by introducing a newly prepared solution into the absorption tower. It is efficient and preferable to supply the ferric chloride aqueous solution obtained in the electrochemical regeneration step 3 (for example, an electrolytic cell) after the operation of the apparatus is started.

The inside of the absorption tower is heated by a heating device (not shown). When the gas to be treated and the ferric chloride aqueous solution are introduced into the absorption tower and brought into contact with each other, the reaction proceeds according to the reaction formula (I) to generate sulfur.
At this time, if the inside of the reaction system is at least the melting point of sulfur, sulfur hardly adheres to the inner wall of the absorption tower, which is preferable.

Next, the phosphoric acid-based iron chloride aqueous solution or phosphoric acid-hydrochloric acid-based iron chloride aqueous solution containing sulfur is subjected to the sulfur separation step 2.
(Sulfur separator). If desired, a step of coalescing the molten sulfur droplets may be provided before this step.
In the sulfur separator, sulfur is melted and precipitated in a phosphoric acid-based iron chloride aqueous solution or a phosphoric acid-hydrochloric acid-based iron chloride aqueous solution due to a difference in specific gravity. It is easily recovered from the bottom of the separator. Further, if sulfur is separated in a molten state, the internal structure of the sulfur separator can be simplified.

Further, the liquid recovered from the sulfur separating device after recovery of sulfur is supplied to the electrochemical regeneration step 3 (for example, an electrolytic cell). In this electrolytic cell, the reaction (II) proceeds. As an apparatus used in this electrochemical treatment, an electrolytic cell of a conventionally used type can be used as already described above. In this electrolytic cell, a diaphragm is provided between an anode and a cathode, and an acid resistant material such as graphite or carbon fiber is used for the electrode.
It is preferable to use a hydrogen ion selective permeable membrane as the diaphragm.

If the concentration of sulfur in the phosphoric acid-based iron chloride aqueous solution or the phosphoric acid-hydrochloric acid-based iron chloride aqueous solution supplied to the electrolytic cell is large, the electrolytic performance is deteriorated. Therefore, the sulfur in the aqueous solution sent to the electrolytic cell is reduced. Should be removed as much as possible. If desired, a filter may be provided in front of the electrolytic cell.

[0025]

EXAMPLES Next, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Example 1 Hydrogen sulfide absorbing solution containing trivalent iron ions (composition: FeCl
₃ 0.7 mol / l, taking into FeCl ₂ 1.0 mol / l and H ₃ PO ₄ 4.5 mol / liter) reactor of 100 ml 150ml semibatch method, a hydrogen-containing gas sulfide (composition: H ₂ S: 10%,
N _2: 90%, blowing amount of H ₂ S 25-30 mmol) 3
It was introduced over time and the reaction was carried out. Reaction temperature is 130
The reaction pressure was 4 ° C. and the reaction pressure was 4 kg / cm ² . During the reaction, about 5 liters of the total amount of gas flowing out from the pressure control valve was collected by the gas holder (tetra bag). After the completion of the reaction, the temperature was lowered, the pressure was released, and the atmosphere was replaced with nitrogen to remove the sulfur produced from the reaction solution by filtration. The recovered reaction gases were mixed well and hydrogen sulfide and sulfur dioxide were analyzed using a suction type gas detector tube. In addition, the sulfur dioxide and sulfuric acid in the recovered reaction solution are converted into SO ₂
Was analyzed by ion chromatography, and H ₂ SO ₄ was analyzed by ICP (inductively coupled plasma) emission spectroscopy. From the obtained results, the conversion rate of hydrogen sulfide, the selectivity of sulfur dioxide and the selectivity of sulfuric acid were determined. The results are shown in Table 1. The hydrogen sulfide conversion rate, sulfur dioxide selectivity and sulfuric acid selectivity are defined by the following equations.

Hydrogen sulfide conversion rate (%) = (1-remaining hydrogen sulfide mol / charged hydrogen sulfide mol) x 100 Sulfur dioxide selectivity (%) = (Sulfur dioxide in gas and liquid mol / reacted hydrogen sulfide mol) ) × 100 Sulfuric acid selectivity (%) = (sulfuric acid in liquid mol / reacted hydrogen sulfide mol) × 100

Next, a minicell device (electrode area: 10c
m ² , anode chamber: carbon plate / carbon fiber cloth, diaphragm: commercially available cation exchange membrane, cathode chamber: carbon fiber cloth with platinum catalyst / carbon plate)
The reaction liquid from which sulfur was removed by filtration was passed through the anode chamber of the above, and water was passed through the cathode chamber at a rate of 5 ml / min, and the electrolytic voltage at a current density of 100 mA / cm ² was measured. The reaction was carried out at 50 ° C. The electrolysis voltage was 649 mV.

Example 2 The reaction was performed in the same manner as in Example 1 except that the composition of the solution shown in Table 1 was used.
The results are shown in Table 1.

Examples 3 to 14 The same procedure as in Example 1 was carried out except that the liquid in the cathode chamber shown in Table 1 was used. The results are shown in Table 1.

Examples 15 and 16 The reaction was carried out in the same manner as in Example 1 except that the composition of the solution shown in Table 1 was used.
The results are shown in Table 1.

Comparative Examples 1 to 4 Similar to Example 1 except that the composition of the oxidation reaction solution is shown in Table 1 and the liquid in the cathode chamber is shown in Table 1 in Example 1. went. The results are shown in Table 1.

Comparative Example 5 The procedure of Example 1 was repeated, except that the composition of the oxidation reaction solution was changed to that shown in Table 1. The results are shown in Table 1.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

[Table 3]

[0037]

[Table 4]

[0038]

[Table 5]

[0039]

[Table 6]

[0040]

[Table 7]

[0041]

As described above, according to the present invention, sulfur and hydrogen are removed by utilizing the oxidation of trivalent iron ions from a hydrogen sulfide-containing gas which has been conventionally performed using a hydrochloric acid-based aqueous solution. By using a phosphoric acid-based or phosphoric acid-hydrochloric acid-based aqueous solution for recovery, it is possible to reduce the by-product of sulfur oxides generated in the steps of hydrogen sulfide absorption and oxidation reaction. Further, due to such reduction of impurities, the electrolysis voltage can be lowered in the electrochemical regeneration step, the treatment efficiency is improved, and the obtained treated gas is of high quality.
Furthermore, the phosphoric acid-based aqueous solution or the phosphoric acid-hydrochloric acid-based aqueous solution has much less corrosiveness to the metal material of the container in the absorption, oxidation reaction, electrochemical regeneration step, etc. than in the conventional method, and thus is used in industrial processes. Is extremely advantageous in. As described above, the method of the present invention is industrially effectively utilized as an extremely efficient method for removing hydrogen sulfide from a hydrogen sulfide-containing gas and a method for recovering sulfur and hydrogen.

[Brief description of drawings]

FIG. 1 is a schematic diagram of all processing steps of the present invention.

[Explanation of symbols]

 1: Gas-liquid contact step 2: Sulfur separation step 3: Electrochemical regeneration step

Claims (8)

[Claims] 1. A hydrogen sulfide-containing gas is contacted with and absorbed by an iron salt solution containing trivalent iron ions to cause an oxidation reaction, and a solution containing divalent iron ions and sulfur is produced to treat hydrogen sulfide. In this regard, a method for treating hydrogen sulfide, characterized in that a phosphoric acid-based iron chloride aqueous solution is used as the iron salt solution. 2. A hydrogen sulfide-containing gas is brought into contact with and absorbed by an iron salt solution containing trivalent iron ions to cause an oxidation reaction to generate a solution containing divalent iron ions and sulfur to treat hydrogen sulfide. In this regard, a method for treating hydrogen sulfide, characterized in that a phosphoric acid-hydrochloric acid-based iron chloride aqueous solution is used as the iron salt solution. 3. A hydrogen sulfide-containing gas is brought into contact with and absorbed by an iron salt solution containing trivalent iron ions to cause an oxidation reaction to produce a solution containing divalent iron ions and sulfur, and then the produced sulfur is separated. After that, this solution is subjected to electrochemical regeneration treatment.
A method for treating hydrogen sulfide, which comprises using a phosphoric acid-based iron chloride aqueous solution as the iron salt solution when regenerating trivalent iron ions to trivalent iron ions to recover hydrogen. 4. A hydrogen sulfide-containing gas is brought into contact with and absorbed by an iron salt solution containing trivalent iron ions to cause an oxidation reaction to produce a solution containing divalent iron ions and sulfur, and then the produced sulfur is separated. After that, this solution is subjected to electrochemical regeneration treatment.
A method for treating hydrogen sulfide, which comprises using a phosphoric acid-hydrochloric acid-based iron chloride aqueous solution as the iron salt solution in regenerating trivalent iron ions to trivalent iron ions to recover hydrogen. 5. The phosphoric acid concentration of the phosphoric acid-based iron chloride aqueous solution is 0.5.
The treatment method according to claim 1 or 3, wherein the treatment amount is about 7.0 mol / liter. 6. The treatment method according to claim 2, wherein the phosphoric acid concentration of the phosphoric acid-hydrochloric acid type iron chloride aqueous solution is 0.5 to 7.0 mol / liter. 7. The treatment method according to claim 3, wherein a hydrochloric acid-containing liquid is used as an electrolytic solution for the cathode portion in the electrochemical regeneration treatment. 8. A hydrochloric acid-containing liquid having a hydrochloric acid concentration of 0.5 to 6.0 mol / mol.
The processing method according to claim 7, which is liter.