JPH04362008A - Treatment of hydrogen sulfide containing gas - Google Patents

Abstract

PURPOSE:To develop a method for directly producing sulfuric acid together with sulfur and gaseous hydrogen when treating hydrogen sulfide. CONSTITUTION:Into a gaseous hydrogen sulfide absorption process 1, are introduced gaseous hydrogen sulfide (gas to be treated) and iron salt water solution which contains a trivalent iron ion and simultaneously restrains free acid concentration within 2mol/liter. Sulfur from sulfuric acid and sulfur thus produced is separated in a sulfur separation process 2. Water solution obtained by separating sulfur is introduced into an electrochemical regeneration process 3 to obtain hydrogen and then sulfuric acid is recovered through a sulfuric acid separation process 4.

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-containing gas, and more particularly to a method for efficiently producing and recovering sulfur, sulfuric acid, or even hydrogen from hydrogen sulfide-containing gas and water.

0002

[Prior art and problems to be solved by the invention] Conventionally,
Hydrogen sulfide emitted during oil refining was industrially treated using the Claus process. However, in this method, the sulfur component in hydrogen sulfide is recovered as sulfur, but the hydrogen component is not recovered as hydrogen gas but instead becomes water, making it impossible to utilize it industrially efficiently.

Currently, there are three methods for recovering sulfur and hydrogen gas from hydrogen sulfide by oxidation and electrochemical treatment.
A method using a solution containing valent iron ions is known. Such a method involves contacting and oxidizing hydrogen sulfide using a hydrochloric acid-based iron salt aqueous solution containing trivalent iron ions, separating the generated sulfur, and then electrochemically regenerating the hydrochloric acid-based iron salt aqueous solution. A method has been proposed in which hydrogen is generated through treatment and recovered (Japanese Patent Publication No. 1-53201).

However, according to this method, when hydrogen sulfide is brought into contact with a hydrochloric acid-based iron salt aqueous solution and oxidized to produce sulfur, sulfur oxides such as sulfur dioxide and sulfuric acid are produced as by-products and accumulated. In the end, it precipitated as iron salts, causing blockages in the piping system, making it impossible to continue operation. In addition, in the subsequent electrochemical regeneration process, iron ions migrate and accumulate in the cathode electrolyte through the ion exchange membrane of the electrolytic cell due to the electrical driving force, reducing electrolytic efficiency. At the same time, it may precipitate as iron salts in the electrolytic cell, causing clogging problems. For this reason, although it is easy to consider replacing a portion of the electrolyte with a new one, the cost of purchasing a new electrolyte and the cost of processing the used solution will be considerable.

[0005] The present inventors have found that by-products such as sulfur oxides are suppressed, the quality of the gas is improved, the corrosiveness to the metal materials constituting the reaction vessel is low, and the corrosion resistance is low in the electrochemical regeneration process. As a result of intensive research to develop an efficient hydrogen sulfide treatment method using electrolytic voltage, we found that by using a phosphoric acid-based iron chloride aqueous solution or a phosphoric acid-hydrochloric acid-based iron chloride aqueous solution to oxidize hydrogen sulfide, The above problems have been solved (Japanese Patent Application No. 3-100094, etc.).

However, the sulfur obtained in this way is
In fact, at present it is mainly used as a raw material for producing sulfuric acid. Therefore, if sulfuric acid can be directly produced together with hydrogen gas when treating hydrogen sulfide, there is an advantage that the process for producing sulfuric acid can be significantly shortened. The present inventors continued their research from this point of view and found that the above object could be achieved by suppressing the free acid concentration in the iron salt aqueous solution used. The present invention was completed based on this knowledge.

[0007]

[Means for Solving the Problems] That is, the present invention provides hydrogen sulfide-containing gas to an iron salt aqueous solution containing trivalent iron ions.
Sulfur and sulfuric acid are produced by contacting and absorbing hydrogen sulfide at 120 to 200°C while maintaining the free acid concentration in the aqueous solution within a range not exceeding 2 mol/liter. The present invention provides a method for treating hydrogen sulfide-containing gas. The present invention also provides a method for contacting a hydrogen sulfide-containing gas with an iron salt aqueous solution containing trivalent iron ions at 120 to 200°C while maintaining the free acid concentration in the aqueous solution within a range of not exceeding 2 mol/liter. By absorbing and oxidizing hydrogen sulfide, sulfur and sulfuric acid are generated from hydrogen sulfide, and after separating the generated sulfur or sulfur and sulfuric acid, this aqueous solution is introduced into the anode part of the electrolytic cell and electrolyzed. The present invention also provides a method for treating hydrogen sulfide-containing gas, which is characterized in that hydrogen is generated and recovered from the cathode portion of an electrolytic cell at the same time as the oxidation.

The treatment method of the present invention includes a step of bringing hydrogen sulfide-containing gas into contact with and absorbing an iron salt aqueous solution containing trivalent iron ions (gas-liquid contact step), and the iron salt used in this step The aqueous solution contains free acids such as hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, oxalic acid, etc. in a concentration range not exceeding 2 mol/liter. This gas-liquid contact step proceeds, for example, as follows.

[0009] In the gas-liquid contact step, that is, the method of the present invention, as described above, a gas containing hydrogen sulfide is first brought into contact with an aqueous iron salt solution containing trivalent iron ions. 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 contains hydrogen sulfide. There is no problem even if the gas is mixed in as long as it is inert to trivalent iron ions. For example, a mixed gas of hydrogen sulfide and hydrogen, carbon monoxide, carbon dioxide, hydrocarbons (methane, ethane, etc.), ammonia, nitrogen, etc. can also be used.

[0010] In the method of the present invention, it is necessary to use an aqueous iron salt solution as the absorption liquid that is brought into contact with the hydrogen sulfide-containing gas. Here, as the iron salt aqueous solution, a ferric salt aqueous solution containing trivalent iron ions (ferric ions) is used. Examples of the ferric salt constituting this ferric salt aqueous solution include ferric chloride, ferric sulfate, ferric phosphate, ferric nitrate, and ferric oxalate. The ferric salt aqueous solution used in the present invention is not limited to a single solution of the above-mentioned ferric salts, but may also be a mixed solution containing two or more types of ferric salts, and even a ferric salt aqueous solution as long as it does not impede the purpose of the present invention. It may also contain iron salts or other salts. The ion concentration in the iron salt aqueous solution used is not particularly limited, but ferric ions are usually in the range of 0.1 to 6.0 mol/liter, preferably 1.0 to 5.0 mol/liter. . If the ferric ion content is less than 0.1 mol/liter, the hydrogen sulfide absorption rate will decrease, and if it exceeds 6.0 mol/liter, there will be problems with solubility, which is not preferable. Further, although ferrous ion is not essential, it should normally be present in an amount of 5.0 mol/liter or less, preferably in a range of 0.5 to 4.0 mol/liter. The main purpose of adding ferrous ions is to improve efficiency in electrochemical processing, but if the amount exceeds 5.0 mol/liter, precipitation of iron salts occurs, which is not preferable.

Further, in the present invention, as mentioned above, it is important to maintain the free acid concentration in the iron salt aqueous solution within a range not exceeding 2 mol/liter. By using an aqueous iron salt solution with a low free acid concentration, it is possible to increase the production of sulfuric acid. The concentration of the free acid should normally be 2 mol/liter or less, preferably 1.5 to 0.1 mol/liter. Here, if the free acid concentration exceeds 2 mol/liter, the selectivity of sulfuric acid decreases, making it impossible to achieve the object of the present invention. In addition, in the above gas-liquid contact step, as the reaction progresses, free acid is generated in the iron salt aqueous solution and gradually increases, so the iron salt aqueous solution used initially does not contain free acid (that is, the free acid concentration is 0). (mol/liter) aqueous solution may be applied. Additionally, if the free acid concentration exceeds 2 mol/liter as the reaction process progresses, it is necessary to remove the free acid from the iron salt aqueous solution by appropriate means to maintain the concentration within a predetermined range. desirable.

[0012] There are no particular restrictions on the method of carrying out this gas-liquid contact step (hydrogen sulfide gas absorption step), but methods conventionally used for gas absorption using liquids, such as bubble columns, spray columns, wet wall columns, etc. A general-purpose absorption tower such as a stirred absorption tower, a packed bubble tower, or a packed tower may be used. The reaction formula of the gas-liquid contact step for producing sulfur and sulfuric acid from hydrogen sulfide in this step is shown below. H2 S+4H2 O+8Fe3+=H2 SO4
+8H+ +8Fe2+...(I) H2 S+
2Fe3+=S+2H+ +2Fe2+
(II) That is, hydrogen sulfide gas is oxidized by ferric ions to produce sulfuric acid and sulfur, and the ferric ions are reduced to ferrous ions. As a result, sulfuric acid and sulfur will be contained in the iron salt aqueous solution.

[0013] The temperature in the above gas-liquid contact step is usually 1
The temperature is 20-200°C, preferably 140-180°C. A low temperature below 120° C. is not preferred because the selectivity of sulfuric acid decreases. In addition, in order to perform the separation particularly quickly, the melting point of sulfur must be higher than the melting point of sulfur, and the melting point of sulfur is 120
It should be above ℃. At high temperatures exceeding 200° C., restrictions arise regarding the material of the device. By setting the temperature above the melting point of sulfur, sulfur is generated in a molten state, and the sulfur and the aqueous solution can be easily separated based on the difference in specific gravity. Below this temperature range, sulfur does not become molten and is difficult to separate and recover in high purity.

[0014] The pressure during the catalytic reaction is not particularly limited as long as it is sufficient to prevent moisture evaporation and maintain the liquid phase within a range that does not cause any operational problems, and is necessary to maintain the above-mentioned desired temperature. However, 1.5 atmospheres or more is usually preferred.

[0015] The sulfur, sulfuric acid and divalent iron ions produced in the above contact reaction may be treated by various physical or chemical methods, and are not particularly limited. For example, to treat sulfur, physical treatment methods include sedimentation separation, centrifugation, etc., and chemical treatment methods include methods of converting it into other sulfur compounds. Examples of methods for treating divalent iron ions include a method of regenerating divalent iron ions into trivalent iron ions or a method of converting them into metallic iron. To treat sulfuric acid, there are chemical treatment methods such as ion exchange membranes and ion exchange columns. Here, a sulfur separation process using sedimentation separation as a preferred method of treating sulfur;
A preferred method for treating divalent iron ions is an electrochemical regeneration treatment step in which electrochemical regeneration treatment is performed, and a preferred method for treating sulfuric acid is a sulfuric acid separation step using an ion exchange membrane.

Sulfur separation process There are various methods for this process, and the conditions and operating procedures may be selected as appropriate. Among these, preferable methods include liquid-liquid separation of the sulfur produced above as molten sulfur, followed by sedimentation separation based on the difference in specific gravity;
One method is to collect it. The sulfur separation device used in this sulfur separation step is not particularly limited, and devices of various structures can be used. For example, general thickener format,
An empty column drum format, a sedimentation pond format, etc. may be selected as appropriate depending on 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 separates sulfur through the aforementioned sulfur separation step.
The target is the aqueous solution after it has been collected. This step is not limited, as there are various methods as described above. Preferred methods include the following method. The aqueous solution (absorption liquid) after sulfur recovery obtained in the sulfur separation step includes:
Contains a lot of ferrous ions. In this regeneration step, ferrous ions are converted to ferric ions and hydrogen gas is generated, for example by electrolysis, etc.
Aqueous solution containing a large amount of valent iron ions (ferric ions) (
At the same time, the hydrogen gas is separated and recovered. The reaction that proceeds here is shown by the following reaction formula. 2Fe2++2H+ =2Fe3++H2 (
Gas) (III) 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 contacting step again. Note that as a device for performing this electrochemical regeneration step, an electrolytic cell or the like of a type commonly used for ordinary electrolysis or the like can be used.

[0018] In an electrolytic cell in which such a process is carried out, 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 permselective membrane as the diaphragm. For example, in electrolysis, an aqueous iron salt solution treated as described above is placed in the anode part of the electrolytic cell, while an aqueous solution containing hydrogen ions at a predetermined concentration is usually put in the cathode part, or an aqueous solution containing hydrogen ions at a predetermined concentration is usually put in the anode part of the electrolytic cell, or an aqueous solution containing hydrogen ions at a predetermined concentration is put in the anode part of the electrolytic cell. This is done by replenishing moisture to the extent that the diaphragm does not dry out and applying a voltage.

When a hydrogen ion permselective membrane is used as the diaphragm, if desired, a porous gas diffusive electrode, such as a graphite fiber cloth, preferably carrying a catalyst such as platinum, is used.
It may be brought into direct contact with the diaphragm. In addition, this electrolysis is normally performed at 25-100 degreeC.

In the present invention, in the electrochemical regeneration process, divalent iron ions are electrolytically oxidized to trivalent iron ions at the anode, and hydrogen is generated at the cathode.

By electrochemically treating the iron salt aqueous solution containing divalent iron ions from which the generated sulfur has been removed, hydrogen is generated and the divalent iron ions are converted into trivalent iron ions. Since it is regenerated into iron ions, the regenerated treatment liquid can be used repeatedly as a hydrogen sulfide absorption liquid.

Sulfuric Acid Separation Step Similar to the electrochemical regeneration treatment step, this step targets the aqueous solution after sulfur has been separated and recovered through the sulfur separation step described above. In this step, for example, sulfuric acid contained in the iron salt aqueous solution is subjected to diffusion dialysis using an ion exchange membrane modified with ordinary basic functional groups, and then concentrated sulfuric acid is further concentrated using a hydrophobic porous tube. can be obtained. The ion exchange membrane used here may be a strongly basic anion exchange membrane such as Neocepta AFN (manufactured by Tokuyama Soda Co., Ltd.) or Selemion DMV (manufactured by Asahi Glass Co., Ltd.). Examples of the hydrophobic porous tube include POREFLON (manufactured by Sumitomo Electric Industries, Ltd.). Regarding the order of the above three steps, that is, the sulfur separation step, the electrochemical regeneration treatment step, and the sulfuric acid separation step, the sulfur separation step is usually performed first, and then the electrochemical regeneration treatment step or the sulfuric acid separation step is performed. . Here, either the electrochemical regeneration process or the sulfuric acid separation process may be performed first. That is, the sulfur separation step, the electrochemical regeneration step, and the sulfuric acid separation step may be performed in this order, or the sulfur separation step, the sulfuric acid separation step, and the electrochemical regeneration step may be performed in this order.

Next, an example of a preferred embodiment of the present invention is shown in FIG.
Explain according to the following. The present invention is not limited to the following method. FIG. 1 is a schematic diagram showing an example of an apparatus for implementing the present invention as described above. As shown in Figure 1,
In the gas-liquid contact step 1 (for example, absorption tower), hydrogen sulfide (H2S) gas, which is the gas to be treated, and an iron salt aqueous solution containing trivalent iron ions, specifically, a ferric salt aqueous solution, etc. are introduced. do. In the initial state, a freshly prepared ferric salt aqueous solution may be introduced into the absorption tower. After starting the operation of the apparatus, it is efficient and preferable to supply the iron salt aqueous solution obtained in the sulfuric acid separation step 4 (for example, using an ion exchange membrane).

The inside of the absorption tower is heated by a heating device (not shown). When the gas to be treated and the aqueous iron salt solution are introduced into the absorption tower and brought into contact with each other, the reaction proceeds according to the reaction formulas (I) and (II), producing sulfuric acid and sulfur. At this time, it is preferable that the inside of the reaction system be at or above the melting point of sulfur, since sulfur will hardly adhere to the inner wall of the absorption tower.

Next, the iron salt aqueous solution containing sulfuric acid and sulfur is
Sent to sulfur separation step 2 (sulfur separation device). Note that, if desired, a step of coalescing the molten sulfur droplets may be provided before this step. In the sulfur separation device, molten sulfur is precipitated in an iron salt aqueous solution due to the difference in specific gravity. It is easily recovered from the bottom of the separator. Furthermore, if sulfur is separated in a molten state, the internal structure of the sulfur separation device can be simplified.

Furthermore, the liquid after sulfur recovery coming out of the sulfur separation device is supplied to an electrochemical regeneration step 3 (for example, an electrolytic cell). In this electrolytic cell, the reaction (III) described above proceeds. As the apparatus used in this electrochemical treatment, as already mentioned above, a conventional type of electrolytic cell can be used. This electrolytic cell is provided with a diaphragm between an anode and a cathode, and the electrode is made of an acid-resistant material such as graphite or carbon fiber. It is preferable to use a hydrogen ion permselective membrane as the diaphragm.

[0027] Note that if the concentration of precipitated sulfur in the iron salt aqueous solution supplied to the electrolytic cell is high, the electrolytic performance will decrease.
It is better to remove as much of the precipitated sulfur from the aqueous solution as possible to the electrolytic cell. Furthermore, if desired, a filter can be provided in front of the electrolytic cell.

Next, the iron salt aqueous solution containing sulfuric acid that has undergone the above treatment is supplied to a sulfuric acid separation step 4 (for example, a strong basic anion exchange membrane). Here, the sulfuric acid in the aqueous solution is selectively separated by diffusion dialysis. The separated sulfuric acid water can be further subjected to membrane distillation and collected as concentrated sulfuric acid.

[0029]

EXAMPLES Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Examples 1 to 6 and Comparative Examples 1 to 3 100 ml of a predetermined amount of hydrogen sulfide absorption liquid (iron salt aqueous solution) containing trivalent iron ions was put into a 150 ml semi-batch type reactor, and the hydrogen sulfide-containing gas (composition :H
2S: 10%, N2: 90%) was introduced over 3 hours at an amount of 24 to 26 mmol of H2S to carry out a contact and absorption reaction. Note that the reaction pressure was 5 kg/cm2. During the reaction, a total amount of about 5 liters of gas flowing out from the pressure control valve was collected with a gas holder (tetra bag). After the reaction was completed, the temperature was lowered, the pressure was removed and the atmosphere was replaced with nitrogen, and the sulfur produced from the reaction solution was filtered and removed. The recovered reaction gas was mixed well and analyzed for hydrogen sulfide and sulfur dioxide using a suction type gas detection tube. In addition, sulfur dioxide and sulfuric acid in the recovered reaction solution were analyzed. 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 obtained are shown in Table 1. Note that the conversion rate of hydrogen sulfide, the selectivity of sulfur dioxide, and the selectivity of sulfuric acid are each defined by the following formulas.

Conversion rate of hydrogen sulfide (%) = (1-residual hydrogen sulfide mol/charged hydrogen sulfide mo
l) x 100 Selectivity of sulfur dioxide (%) = (mol of sulfur dioxide in gas and liquid/mol of reacted hydrogen sulfide) x 100 Selectivity of sulfuric acid (%) = (mol of sulfuric acid in liquid/mol of reacted hydrogen sulfide) x 100

Example 7 In the anode chamber of a minicell device (electrode area: 10 cm2, anode chamber: carbon plate/carbon fiber cloth, diaphragm: commercially available cation exchange membrane, cathode chamber: carbon fiber cloth with platinum catalyst/carbon plate), The aqueous solution from which sulfur was removed (from Example 6) was placed in the cathode chamber with sulfuric acid (
1.5 mol/liter) at a rate of 5 ml/min, and the electrolytic voltage at a current density of 100 mA/cm2 was measured. Electrolysis was performed at 50°C. The electrolytic voltage was 850 mV, and hydrogen gas was generated from the cathode. Next, after repeating the absorption of hydrogen sulfide-containing gas similar to Example 6, the oxidation reaction, and the same treatment as the electrochemical treatment described above 10 times, 100 ml of the obtained aqueous solution was added to a dialysis minicell device (membrane area : 10 cm2, membrane: commercially available anion exchange membrane) in countercurrent flow with ion-exchanged water to perform diffusion dialysis. Here, the passage speed of the minicell device was 0.1 ml/min for both the aqueous solution and ion-exchanged water. The dialysis temperature is room temperature 25°C. The results obtained are shown in Table 2.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

[Table 3]

[0035]

[Table 4]

[0036]

As described above, according to the present invention, sulfur and sulfuric acid can be efficiently produced and recovered from hydrogen sulfide gas. Furthermore, by performing an electrochemical regeneration step, divalent iron ions can be regenerated into trivalent iron ions and hydrogen gas can be generated. As described above, the method of the present invention has industrial utility as a method that can extremely efficiently recover sulfuric acid, sulfur, and hydrogen from hydrogen sulfide-containing gas that is produced as a by-product during oil refining, natural gas production, or geothermal utilization. is high.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the entire process steps of the present invention.

[Explanation of symbols]

1: Gas-liquid contact process 2: Sulfur separation process 3: Electrochemical regeneration process 4: Sulfuric acid separation process

Claims (2)

[Claims] Claim 1: Contacting a hydrogen sulfide-containing gas with an iron salt aqueous solution containing trivalent iron ions at 120 to 200°C while maintaining the free acid concentration in the aqueous solution within a range of not exceeding 2 mol/liter; By absorbing and oxidizing hydrogen sulfide,
A method for treating hydrogen sulfide-containing gas, which is characterized by generating sulfur and sulfuric acid. 2. Contacting a hydrogen sulfide-containing gas with an iron salt aqueous solution containing trivalent iron ions at 120 to 200°C while maintaining the free acid concentration in the aqueous solution within a range of not exceeding 2 mol/liter; By absorbing and oxidizing hydrogen sulfide, sulfur and sulfuric acid are generated from hydrogen sulfide, and after separating the generated sulfur or sulfur and sulfuric acid, this aqueous solution is introduced into the anode part of the electrolytic cell and electrolyzed. A method for processing hydrogen sulfide-containing gas, which comprises oxidizing the gas and simultaneously generating and recovering hydrogen from the cathode section of an electrolytic cell.