JPH0461802B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an improved method for treating hydrogen sulfide. More specifically, the present invention
By combining treatment with an aqueous iron salt solution containing trivalent iron ions and electrochemical treatment, hydrogen sulfide or hydrogen sulfide-containing gas is treated in a closed system, and sulfur and hydrogen can be economically removed, especially the generated sulfur. This relates to a method that allows for easy and highly pure recovery of nearly 100%. [Prior Art] Conventionally, hydrogen sulfide contained in acid gas, natural gas, etc. discharged during oil refining has been industrially treated by the Claus process, which involves partial combustion with air. However, this Claus method has the disadvantage that although the sulfur content in hydrogen sulfide is recovered as sulfur, the hydrogen content is not recovered as hydrogen gas but becomes water. In recent years, with the depletion of petroleum resources, energy conservation measures have been actively taken in various fields, and it is desirable to recover the hydrogen content in hydrogen sulfide as hydrogen gas from the standpoint of energy conservation. Hydrogen is recovered from hydrogen sulfide contained in acid gas and natural gas released during oil refining, considering that hydrogen is currently produced by the steam reforming method that consumes natural gas. is extremely desirable. However, it is known that when hydrogen sulfide comes into contact with an aqueous solution containing trivalent iron ions, it is easily oxidized to produce sulfur. When using, for example, a ferric chloride aqueous solution as the aqueous solution containing trivalent iron ions, sulfur is produced from hydrogen sulfide according to the reaction formula shown below. 2FeCl ₃ +H ₂ S→2FeCl+2HCl+S... (I) That is, hydrogen sulfide is oxidized by ferric chloride to produce sulfur, while ferric chloride is reduced to become ferrous chloride. As a method for treating hydrogen sulfide using such a reaction between trivalent iron ions and hydrogen sulfide, for example, a method using an aqueous solution containing copper sulfate and ferric sulfate as an absorption liquid (Japanese Patent Publication No. 56-23650) is proposed. In this method, hydrogen sulfide is absorbed using the aqueous solution, and then this solution is heated under oxygen pressure.
Pressure treatment is performed at a temperature of 120℃ or higher to generate molten sulfur, copper sulfate, and ferric sulfate. The molten sulfur is collected and removed, and the treatment solution containing copper sulfate and ferric sulfate is repeatedly used as an absorbent. The method is to do so. However, in this method, since the oxidation treatment is performed in the presence of sulfur, impurities are generated, and the sulfur separation and recovery performance is not sufficient, and the absorption rate of hydrogen sulfide is not always satisfactory. Furthermore, there is a drawback that the hydrogen content in hydrogen sulfide is not recovered as hydrogen gas and oxygen is consumed. In addition, hydrogen sulfide and trivalent iron ions are reacted to produce a solution containing sulfur and divalent iron ions, and the divalent iron ions are electrochemically converted into trivalent iron ions.
A method has been proposed (Japanese Unexamined Patent Publication No. 181706/1983) in which hydrogen is generated while returning the hydrogen to a valent state. However, although this method has the advantage of being able to absorb hydrogen sulfide at a relatively high rate and recovering hydrogen, the sulfur produced is fine particles that are difficult to separate and recover. has the disadvantage that it is not recovered. In such a situation, the present inventors established a closed system including a sulfur melt separation method and filed an application (Japanese Patent Application No. 58060/1982).
There is. In this method, a liquid in which hydrogen sulfide has been absorbed is heated under pressure in an absorption tower, and the generated sulfur is separated in a molten state. [Problems to be Solved by the Invention] Incidentally, the sulfur precipitated in the absorption tower contains colloidal sulfur. Colloidal sulfur is sticky and has poor separability, so it is necessary to aggregate the sulfur in a stirring tank prior to separation, and to also provide a concentrator to reduce the load on the separator. It has been difficult to reduce costs due to such ancillary equipment. [Means for solving the problem] Considering the above-mentioned problems that need to be solved, we focused on the fact that colloidal sulfur discharged from the absorption tower has a high adsorption property to hydrophobic materials. As a result of the investigation, it was found that the hydrogen sulfide-containing gas was brought into contact with an iron salt solution containing trivalent iron ions to absorb hydrogen sulfide, and after separating the generated sulfur, this aqueous solution was electrochemically treated. Contains colloidal sulfur and aggregated sulfur that precipitate in the gas-liquid contact device when regenerating divalent iron ions therein to trivalent iron ions and generating hydrogen to recover sulfur and hydrogen. The liquid containing colloidal sulfur is separated into a liquid containing substantially colloidal sulfur and a liquid containing substantially aggregated sulfur, and the liquid containing colloidal sulfur is treated with an adsorption device filled with an adsorbent to form a colloid. Separates into sulfur and liquid,
A method for treating hydrogen sulfide has been achieved, which comprises electrochemically treating a mixture of the liquid obtained by treatment with an adsorption device and a liquid separated from a liquid containing aggregated sulfur. It is. The gas to be treated used in the method of the present invention may be hydrogen sulfide alone or a mixed gas of hydrogen sulfide and other gases such as hydrogen, carbon dioxide, hydrocarbons, ammonia, etc. In the method of the present invention, examples of the iron salt aqueous solution containing trivalent iron ions used as the absorption liquid include a ferric chloride aqueous solution, a ferric sulfate aqueous solution, and a ferric phosphate aqueous solution. These ferric salt aqueous solutions preferably contain free hydrochloric acid, sulfuric acid, phosphoric acid, etc., in order to facilitate electrochemical treatment in subsequent steps. Further, ferrous salt may or may not be contained. In the present invention, among these ferric salt aqueous solutions, a ferric chloride aqueous solution containing hydrochloric acid in a free state is particularly suitable.
The content of ferric salt is usually selected in the range of 0.1 to 5 moles per kg of water, and the content of free acid is preferably in the range of 0.5 to 15 moles per kg of water. As a method for bringing the hydrogen sulfide or hydrogen sulfide-containing gas into contact with the iron salt aqueous solution containing trivalent iron ions, a method commonly used in gas absorption using a liquid, such as a method using a general-purpose absorption tower, can be adopted. can. The temperature at this time is
Usually, temperatures from room temperature to 100°C are used.
In this way, when hydrogen sulfide is absorbed into the iron salt aqueous solution containing trivalent iron ions, the hydrogen sulfide is oxidized to produce sulfur as shown in the reaction formula (I) above, On the other hand, trivalent iron ions are reduced to divalent iron ions. In the method of the present invention, the generated sulfur is composed of colloidal sulfur and sulfur aggregate particles in which colloidal sulfur is aggregated, suspended in the apparatus,
The sulfur aggregate particles can be recovered using a general filtration device or a melt separation system previously proposed by the present inventors (Japanese Patent Application No. 58060/1982).
The slurry concentration of sulfur agglomerated particles is 1 to 30% even when colloidal sulfur is included in the slurry.
It may be % by weight, and it is particularly desirable to adjust it to a range of 5 to 20 % by weight. To adjust the slurry concentration, for example, a centrifugal separation method or a gravity sedimentation method can be used. In this adjustment process, there is no need to concentrate even the cotoid sulfur content.
The colloidal sulfur content can be separately recovered by an adsorption method. A conceptual diagram of this is shown in FIG. In the figure, 1 is an absorption tower and 2 is a concentration tank. It is also possible to adjust the desired slurry concentration by extracting the flocs that have settled at the bottom of the absorption tower together with the liquid, and in this case, the concentration tank 2 shown in Figure 1 can be omitted. . Sulfur in a slurry state thus prepared can be easily filtered and recovered using a general filtration device. On the other hand, it is also possible to recover sulfur in a molten state by the operation previously described by the present inventors in Japanese Patent Application No. 61-58060. When using this recovery method, the heating temperature is 120℃ or higher, preferably 120 to 150℃.
Selected in the range of °C. If this temperature is less than 120℃, sulfur will not be in a molten state, making it difficult to separate and obtaining high purity, and if it exceeds 150℃, the viscosity of the molten sulfur will increase, making it inconvenient to handle. . There are no particular restrictions on the pressure as long as it is sufficient to maintain the desired temperature. This treatment may be performed in an air atmosphere or, if desired, in an inert gas atmosphere such as nitrogen. Note that, after separating sulfur in a molten state, the resulting iron salt aqueous solution is preferably cooled to filter out precipitates such as ammonium salts, if desired. In the present invention, apart from the treatment of the slurry thus prepared, the colloidal sulfur produced in the absorption tower is introduced into an adsorption tower filled with adsorbent and removed by adsorption. The adsorbed liquid and the filtrate from which sulfur was filtered out as described above or the aqueous solution obtained by melting and separating sulfur are combined and subjected to electrochemical treatment. As can be understood from the above explanation, the function of an adsorption tower is to adsorb and remove sulfur from a colloidal sulfur suspension.
The material is selected from among hydrophobic materials such as fiber, polyethylene, polypropylene, and polytetrafluoroethylene. There are no particular restrictions on the form of the adsorbent; for example, fibrous,
Various forms such as pellet-like and ring-like forms can be adopted. However, among various forms, fibrous forms are preferable, and in the case of pellet or ring-shaped adsorbents, the adsorption tower may be large. The operating conditions for the adsorption tower are preferably from room temperature to approximately 80°C, and the sulfur concentration at the tower outlet is preferably designed to be 10 ppm or less. Any type of adsorption tower may be used as long as it can achieve the above-mentioned purpose. Fig. 2 shows a conceptual diagram of the simplest form for carrying out the present invention, but in addition to this, for example, the 120 to 150 °C It is also possible to melt and wash out the sulfur adhering to the adsorbent with a part of the absorbing liquid whose temperature has been raised to 100 mL, and to reflux this liquid to the entrance of the melting separation tank 3. In this case, by preparing two or more adsorption towers 5 and performing adsorption treatment in one while recovering sulfur in the other, the entire system can be operated without interruption. Furthermore, it is also possible to simplify the system, to continuously extract the adsorbent to which sulfur is attached, and to refill the original adsorption tower 5 after completion of sulfur recovery. Furthermore, it is also possible to form a multi-tubular heat exchanger type adsorption tower 5 using a tube made of this adsorbent, and to adsorb sulfur on the outside of the tube by passing a colloidal sulfur suspension through the shell side. The sulfur thus deposited may be melted and removed by passing a heated fluid of 120° C. or higher through the tube after a suitable period of time has elapsed. It goes without saying that the load on the adsorption tower 5 can be reduced by refluxing part of the adsorption liquid introduced into the adsorption tower 5 to the adsorption tower 1. In addition, in the electrolytic cell 4, the reaction 2FeC ₂ +2HCle -→ 2FeCl ₃ +H ₂ ↑ ...() takes place, but the electrolytic cell used in this electrochemical treatment is of a conventionally used type. can be used. This electrolytic cell is provided with a diaphragm 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 electrolysis, an iron salt aqueous solution containing divalent iron ions treated as described above is placed in the anode chamber of the electrolytic cell, and an aqueous solution containing hydrogen ions at a predetermined concentration is usually placed in the cathode chamber, or Alternatively, this can be done by replenishing moisture to the extent that the diaphragm between the anode and cathode does not dry out and applying voltage. In the anode chamber, divalent iron ions are electrolytically oxidized to trivalent iron ions, and at the cathode, divalent iron ions are electrolytically oxidized to trivalent iron ions. Hydrogen is generated. When a hydrogen ion permselective membrane is used as the diaphragm, a porous gas diffusive electrode, such as a graphite fiber cloth, preferably carrying a catalyst such as platinum, may be brought into direct contact with the diaphragm, if desired. . This electrolysis is usually carried out at room temperature or above, preferably at 30 to 80°C. The iron salt aqueous solution containing divalent iron ions to be introduced into the anode chamber preferably contains free acid in a range of 0.5 to 15 moles per kg of water in order to lower the cell voltage during electrolysis. The free acid herein means an acid that does not participate in the redox reaction of iron ions. 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 to trivalent iron ions. Since it is regenerated, this treatment liquid can be used repeatedly to absorb hydrogen sulfide. [Effects of the Invention] According to the method of this invention, the following effects can be enjoyed. (1) Stirred tank for colloidal sulfur suspension;
Even when a concentrating device is not used or is required, the concentrating device is very compact, so the entire device is compact. (2) Hydrogen and sulfur can be economically recovered from hydrogen sulfide, and in particular, the generated sulfur can be recovered easily and with high purity to nearly 100%. (3) Iron salt aqueous solutions containing iron ions can be recycled. In addition, if the concentration of sulfur in the electrolytic cell supply solution is high, the current density per unit electrode area in the electrolytic cell will decrease, and in other words, the electrolytic capacity will decrease, so sulfur in the iron salt aqueous solution entering the electrolytic cell is It is better to remove it. Further, if desired, a filter or a preliminary electrolytic cell may be provided in front of the electrolytic cell. [Examples] Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples in any way. Example 1 The colloidal sulfur suspension drained from the adsorption tower was collected in an adsorption tower (inner diameter 80 mm) filled with Teflon pellets.
mm, tower height 2500mm, pellet particle size 5mm)
When continuously supplied at 4000 ppm, the following outlet concentration was achieved by changing the inflow rate.

[Table] After continuous feeding for 5 hours at a liquid inflow rate of 6 per hour, the Teflon pellets were taken out in a wet state, placed in a sealed container, and heated to 130°C. The sulfur adhering to the pellets was eluted;
We were able to recover an amount equivalent to 99.7% by weight. Example 2 The adsorption tower used in Example 1 was filled with carbon fibers and a colloidal sulfur suspension was continuously supplied at an inlet concentration of 1000 ppm, and the outlet concentration was as follows.

[Table] After continuous supply for 2 hours at a liquid inflow rate of 6 per hour, the carbon fibers were taken out in a wet state and supplied to a sealed container, and the temperature was raised to 130°C. The sulfur attached to the carbon fibers was eluted, but 91.1 of attached sulfur
% by weight could be recovered. Example 3 An adsorption tower with an inner diameter of 40 mm and a tower height of 1500 mm was filled with polyethylene Raschig rings of 3 mm diameter, and the inlet concentration was
When a 1600 ppm colloidal sulfur suspension was continuously supplied, the outlet concentration was as follows.

[Table] Example 4 In Example 3, when a cotoid ion suspension with an inlet concentration of 1600 ppm was continuously supplied to the adsorption tower while air was fed at a flow rate of 200 ml per minute,
I got the following results.

[Table] From these examples, it can be seen that fibrous materials are more effective as adsorbents, and even with pellets and Raschig ring, if the contact time is increased, the outlet concentration can be increased to 10 ppm.
It was confirmed that the following can be done.

[Brief explanation of the drawing]

FIG. 1 is a schematic flow diagram showing an example of the slurry concentration adjustment step in the present invention, and FIG. 2 is a schematic flow diagram showing an example of carrying out the method for treating hydrogen sulfide of the present invention. 1: absorption tower, 2: concentration tank, 3: melting separation tank,
4: Electrolytic cell, 5: Adsorption tower.

Claims (1)

[Claims] 1. Hydrogen sulfide-containing gas is brought into contact with an iron salt solution containing trivalent iron ions to absorb hydrogen sulfide, and after separating the generated ions, this aqueous solution is electrochemically treated to remove two of them. 3 valent iron ions
In recovering sulfur and hydrogen by regenerating into valent iron ions and generating hydrogen, substantially colloidal sulfur is removed from a liquid containing colloidal sulfur and aggregated sulfur precipitated in a gas-liquid contact device. The liquid containing colloidal sulfur is separated into a liquid containing substantially aggregated sulfur, and the liquid containing colloidal sulfur is treated with an adsorption device filled with an adsorbent to separate the colloidal sulfur and the liquid, and the liquid is adsorbed. A method for treating hydrogen sulfide, comprising electrochemically treating a mixture of the liquid obtained by the treatment in the apparatus and the liquid separated from the liquid containing aggregated sulfur.