JP2002306966A - Method for manufacturing highly activated photocatalyst and method for treating hydrogen sulfide using highly activated photocatalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a highly activated photocatalyst interacting with hydrogen sulfide to generate sulfur and hydrogen. SOLUTION: The highly activated photocatalyst is obtained by oxidizing a metallic sulfide such as zinc sulfide under an oxidizing atmosphere or with a prescribed oxidizing agent. The method for treating hydrogen sulfide using the highly activated photocatalyst is constituted of a hydrogen sulfide dissolving process for dissolving hydrogen sulfide gas, for example in a sodium hydroxide aqueous solution in a hydrogen sulfide dissolving tank 1 to prepare a sodium sulfide solution, a hydrogen recovering process for adding the highly activated photocatalyst in the sodium sulfide solution into a photocatalytic reactor 3, irradiating with ultraviolet ray to produce gaseous hydrogen and polysulfide ion and recovering hydrogen, and a sulfur recovering process for recovering sulfur from the polysulfide ion in a sulfur recovering tank 5 and recirculating the solution after the sulfur recovery to the hydrogen sulfide dissolving tank 1 to recycle in the hydrogen sulfide dissolving process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chemical industry for producing chemical substances such as hydrogen and sulfur, a chemical industry for treating hydrogen sulfide and the like generated in a desulfurization step, and a method for removing malodorous substances and air pollutants. The present invention relates to a technology for producing a highly active photocatalyst that can be used in the field of environmental protection and the like, and its utilization technology.

[0002]

2. Description of the Related Art The application of photocatalyst technology has begun to be put to practical use utilizing characteristics that promote various chemical reactions such as decomposition of environmental pollutants, odorous components and various germs. Examples include antibacterial tiles used in hospital operating rooms, filters for air purifiers and air conditioners, and glass for lighting on highways and the like. While these photocatalysts have been put to practical use using their oxidation promoting ability, research has also been conducted with the aim of obtaining hydrogen by applying a photocatalyst to water or the like, or reducing carbon by acting on carbon dioxide gas. I have. Further, the application of the photocatalyst is not limited to this, and it is also possible to obtain a useful chemical substance by making the harmful substance act on the photocatalyst. For example, it is conceivable to apply it to a desulfurization step of petroleum refining or metal refining.

[0003] Fig. 4 shows a crude oil desulfurization process which is generally performed at present. When distilling crude oil, heavy naphtha is hydrorefined to completely sulfide sulfur contained in the crude oil. It is recovered as hydrogen. Further, as shown in FIG. 5, the hydrogen sulfide generated here is oxidized to recover sulfur through a process called the Claus method. The Claus method is a process in which one-third of hydrogen sulfide is oxidized into sulfur dioxide gas, and this is reacted with the remaining hydrogen sulfide to form sulfur. That is, in the chemical formula, it is represented as follows.

[0004]

Embedded image 2H ₂ S + 3O ₂ → 2H ₂ O + 2SO ₂ 4H ₂ S + 2SO ₂ → 4H ₂ O + 6S

[0005] In this sulfur recovery step, not only the catalytic reaction of sulfur dioxide and hydrogen sulfide, but also heating and coagulation are repeated,
It requires a huge amount of energy. In addition, there is a problem that management of sulfurous acid gas is costly.

On the other hand, hydrogen gas is used in the hydrorefining of heavy naphtha in the crude oil desulfurization step shown in FIG. 4, and hydrogen gas is generally produced by a method as shown in FIGS.
FIG. 6 shows a hydrogen gas production method called a hydrocarbon gas decomposition method. In this hydrogen gas production method, using paraffin, ethylene, and propylene as raw materials, first remove sulfur compounds, and then react with steam at 400 ° C. or more on a nickel catalyst to generate hydrogen, carbon dioxide, and carbon monoxide. After adding water vapor and cooling to about 200 ° C., passing carbon dioxide and hydrogen over the catalyst of iron monoxide to generate carbon dioxide and hydrogen, the produced gas is cooled, and carbon dioxide is removed by the Garbotol method to remove hydrogen. Have gained.

[0007] The hydrogen gas production method shown in FIG. 7 is called a cryogenic hydrogen purification method or a nitrogen cleaning method, and generates hydrogen from a hydrogen-rich gas. Applicable to crude gas. In this manufacturing method, a raw material gas is compressed and washed with sodium hydroxide to first remove carbon dioxide gas, hydrogen sulfide, and the like. Next, it is cooled by a low-temperature purified hydrogen gas in a heat exchanger, and methane and C
Liquefied and removed four or more hydrocarbon gases. Then, in the nitrogen washing tower, carbon monoxide and nitrogen are discharged from the tower bottom in a liquid state by being raised from the bottom of the tower to the top and washed with liquefied nitrogen descending from the top, and purified and separated hydrogen is collected at the top of the tower. Taken out of

[0008] These hydrogen production methods require a purification step for avoiding poisoning of the catalyst mainly by sulfur compounds such as hydrogen sulfide, and require enormous energy to repeat heating and coagulation.

[0009]

As described above, the conventional hydrogen sulfide treatment method and the conventional hydrogen production method require enormous energy to repeat heating and coagulation. Therefore, if sulfur and hydrogen can be easily extracted from hydrogen sulfide, the treatment of hydrogen sulfide and the production of hydrogen can be performed simultaneously, and the problems of the conventional hydrogen sulfide treatment method and hydrogen production method can be solved. By using the extracted hydrogen in the desulfurization step, useful chemical recycling can be realized.

The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to provide a method for producing a highly active photocatalyst capable of producing sulfur and hydrogen from hydrogen sulfide.

It is another object of the present invention to provide a method for treating hydrogen sulfide, which can efficiently recover sulfur and hydrogen useful for industry in general from hydrogen sulfide in an economical process using a highly active photocatalyst. I do.

[0012]

As a result of investigations to achieve the above object, the present inventors have found that it is effective to modify metal sulfide known as a photocatalyst by oxidation treatment. . Examples of the metal sulfide include sulfides such as zinc, cadmium, and mercury. Among them, zinc sulfide is preferable.

As a method for oxidizing metal sulfide, a method of firing in an oxidizing atmosphere is possible and simple. Further, the metal sulfide may be oxidized in a liquid using an oxidizing agent. As the oxidizing agent, permanganic acid or a salt thereof (HMnO ₄ , MMnO ₄ ), chromic acid or a derivative thereof (CrO ₃ , M ₂ Cr ₂ O ₇ , M ₂ CrO ₄ , R ₂ CrO)
₄ , MCrO ₃ Cl, CrO ₂ Cl ₂ ), nitric acid or a derivative thereof (HNO ₃ , N ₂ O ₄ , N ₂ O ₃ , N ₂ O, Cu (N
O ₃ ) ₂ , Pb (NO ₃ ) ₂ , AgNO ₃ , KNO ₃ , NH ₄
NO ₃ ), peroxoic acid or a salt thereof (M ₂ S ₂ O ₈ , M ₂
SO ₅ , HCO ₃ H, CH ₃ CO ₃ H, C ₆ H ₅ CO ₃ H, C
₆ H ₄ (COOH) CO ₃ H, CF ₃ CO ₃ H) and sulfuric acid (H ₂ SO ₄ ) can be used alone or in combination of two or more. In the chemical formulas listed above, M represents an alkali metal, and R represents a hydrocarbon group.

The highly active photocatalyst obtained by oxidizing the metal sulfide in this manner can be used for promoting various reactions. In particular, by adding a highly active photocatalyst to a solution containing hydrogen sulfide, sulfur and hydrogen can be recovered from hydrogen sulfide by the redox action of the highly active photocatalyst.

This method for treating hydrogen sulfide with a highly active photocatalyst preferably comprises the following steps (1) to (3). That is, (1) a step of dissolving hydrogen sulfide in a neutral or alkaline solution, (2) a step of adding a highly active photocatalyst to a solution of hydrogen sulfide and irradiating light such as ultraviolet rays to collect hydrogen gas, 3) recovering sulfur from the solution after recovering the hydrogen gas, and recirculating the solution after recovering the sulfur as a solution for dissolving hydrogen sulfide to the step (1). The reaction formula of each step is represented by the following formula.

[0016]

## STR2 ## _{(1) H 2 S → H} + + HS - (2) 2HS - → H 2 + S 2 2- (3) S 2 2- → S 2- + S

The metal sulfide particles serving as the photocatalyst have a concentration gradient such as a sulfur atom, an oxygen atom, a metal atom, or an oxidation state between the vicinity of the surface of the metal sulfide and the inside of the particle due to the oxidation treatment. Conceivable. For this reason, free electrons and free holes generated by light irradiation move away from each other, and recombination of free electrons and free holes decreases,
Further, since the site of the oxidation reaction and the site of the reduction reaction are completely separated, recombination of the oxidation reaction product and the reduction reaction product can be prevented. As a result, the free electrons and free holes generated by light irradiation are effectively used for the intended redox reaction, and thus the metal sulfide particles oxidized by the method of the present invention have high photocatalytic activity.

When metal sulfide particles such as zinc sulfide and cadmium sulfide are used in a solution, the metal atoms in the metal sulfide dissolve as metal oxide ions due to their strong oxidizing power. There is. Therefore, sulfide ions are allowed to coexist in the reaction system using the highly active photocatalyst according to the present invention. As a result, the sulfide ions in the solution are oxidized to polysulfide ions, so that the metal atoms in the metal sulfide can be prevented from becoming metal oxide ions and eluted into the aqueous solution, and the photocatalytic properties do not deteriorate. As a method of coexisting sulfide ions, a method of dissolving hydrogen sulfide in a neutral or alkaline solution, or a method of using sulfide ions such as sodium hydrogen sulfide (NaHS) and sodium sulfide (Na ₂ S) is used. And a method of dissolving the salt.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of a method for producing a highly active photocatalyst and a method for treating hydrogen sulfide using the highly active photocatalyst according to the present invention will be described. The first embodiment of the method for producing a highly active photocatalyst according to the present invention is a method in which a metal sulfide among compound semiconductors, for example, a sulfide of zinc, cadmium, or mercury is used as a raw material and fired in an oxidizing atmosphere. It is.

In a second embodiment of the method for producing a highly active photocatalyst according to the present invention, the above-mentioned metal sulfide is dissolved in a solution of permanganic acid or a salt thereof, chromic acid or a derivative thereof, nitric acid or a derivative thereof. Oxidation treatment is performed with an oxidizing agent such as a derivative, peroxoacid or a salt thereof, and sulfuric acid.

In the case of producing zinc sulfide as a raw material, a chemical reaction process of a solution containing zinc ions and hydrogen sulfide is generally used, but zinc sulfide generated by this process has poor activity as a photocatalyst. By performing any of the above-described oxidation treatments on this, the activity as a photocatalyst can be significantly increased.

FIG. 1 schematically shows a processing system for explaining an embodiment of a method for processing hydrogen sulfide according to the present invention. This processing system is a hydrogen sulfide dissolving tank for dissolving hydrogen sulfide. 1, a photocatalytic reaction tank 3 for recovering hydrogen gas from a solution in which hydrogen sulfide is dissolved, and a sulfur recovery tank for recovering sulfur from the solution after hydrogen gas recovery and recycling the solution after sulfur recovery to the hydrogen sulfide dissolution tank 1 5 is comprised.

In the above configuration, the hydrogen sulfide dissolving tank 1 contains a neutral or alkaline solution, into which hydrogen sulfide gas is introduced and dissolved. The neutral or alkaline solution merely dissolves and dissociates hydrogen sulfide and provides a reaction site, and does not change itself. Here, a description will be given by taking an aqueous sodium hydroxide solution as an example, but the liquid is not limited to an aqueous solution as long as it is a liquid that dissolves and dissociates hydrogen sulfide. That is, methanol, ethanol, and the like can also be used.

When hydrogen sulfide gas is mixed into the aqueous sodium hydroxide solution in the hydrogen sulfide dissolving tank 1, a neutralization reaction as shown in the following equation occurs, and the hydrogen sulfide gas is dissolved in the aqueous sodium hydroxide solution and It becomes a sodium solution.

[0025]

Embedded image 2NaOH + H ₂ S → Na ₂ S + 2H ₂ O

The sodium sulfide solution is sent to the photocatalyst reactor 3, where the highly active photocatalyst according to the present invention is added,
When ultraviolet light is irradiated from the ultraviolet light source 7, hydrogen gas and polysulfide ions are generated and hydrogen gas is recovered as shown in the following equation.

[0027]

[Of 4] _{^{2S 2- → S 2 2- + 2e}} - 2H + + 2e - → H 2 ↑

If the dissolution of hydrogen sulfide and the generation of hydrogen are continued in this solution system, the polysulfide ions exceed their solubility, and eventually cause a disproportionation reaction (self-oxidation-reduction reaction). As shown, it changes to sulfur and sulfide ions.

[0029]

## STR5 ## S ₂ ^2- → S ^2- + S

In the sulfur recovery tank 5, polysulfide ions are recovered as sulfur using the above disproportionation reaction. The solution from which the sulfur has been recovered is returned to sodium hydroxide, and is reused as a solution for dissolving hydrogen sulfide.

As is clear from the above description, in this embodiment, sulfur can be recovered in the same manner as in the Claus method by decomposing hydrogen sulfide with a highly active photocatalyst, and furthermore, the sulfur is consumed in the desulfurization step. Can be supplied. In addition, this hydrogen sulfide treatment method can eliminate operations requiring a lot of energy such as heating and coagulation as in the Claus method, and is very extremely low in that sulfur dioxide gas, which is more dangerous than hydrogen sulfide, is not involved. Are better.

[0032]

The present invention will be described below in more detail with reference to examples. First, three types of samples as photocatalysts were produced as follows.

Example 1 Zinc sulfide (purity 99.999% or more) manufactured by Kojundo Chemical Co., Ltd.
0.0 g was fired in an electric furnace at a set temperature of 1000 ° C. for 1 hour. At this time, an oxygen gas was flowed at a flow rate of 10 ml / min to obtain an oxidizing atmosphere. This was rubbed with a mortar to obtain fine particles.

Example 2 Zinc sulfide (purity of 99.999% or more) manufactured by Kojundo Chemical Co., Ltd.
0.0 g of a 0.1 N potassium permanganate solution 10
0 ml and placed in an ultrasonic cleaner for 5 minutes. After that, the zinc sulfide is filtered, washed with pure water, and used in a general environment (about 2).
(5 ° C., 60 RH%). This was rubbed with a mortar to form fine particles.

Comparative Example Zinc sulfide (purity 99.999% or more) manufactured by Kojundo Chemical Co., Ltd.
0.0 g was rubbed with a mortar to obtain fine particles.

Next, in order to examine the activity of the above sample as a photocatalyst, an experiment of hydrogen generation by the photocatalyst was performed using an apparatus as shown in FIG. As shown in FIG. 2, this device has a photoreactive portion 11 made of quartz glass, a hydrogen quantifying portion 13 for quantifying generated hydrogen gas, and a device for preventing the pressure in the device from increasing due to hydrogen gas generation. , A 500 W mercury lamp for irradiating ultraviolet rays (not shown), and a condenser lens 19 for condensing ultraviolet rays 17.
And a reflecting mirror 21 for irradiating the ultraviolet rays 17 to the photocatalyst. The operation is as follows. First, the entire system is filled with an aqueous solution of sodium sulfide, and a certain amount of the photocatalyst is added to the photoreaction portion 11.
After the gas vent plug 23 is closed,
The mercury lamp is turned on, and the amount of generated hydrogen is measured at a constant irradiation time in the hydrogen determination section 13. In this experiment, the amount of the photocatalyst was 50 mg for each sample, and the aqueous sodium sulfide solution was 0.1 mol / l, 140 ml. Note that, as a reference example, the amount of hydrogen generated only by irradiation with ultraviolet light without introducing a photocatalyst was also measured.

Table 1 and FIG. 3 show the results of the above-described experiments using the samples of Example 1, Example 2, and Comparative Example as photocatalysts. In FIG. 3, the solid line a indicates the amount of hydrogen generated when Example 1 is added, the solid line b indicates the amount of hydrogen generated when the comparative example is added, and the broken line c indicates the amount of hydrogen generated in the reference example.

[0038]

[Table 1]

As is clear from Table 1 and FIG. 3, the photocatalysts of Examples 1 and 2 have significantly higher catalytic activities than the photocatalysts of Comparative Examples. Further, the reference example without the photocatalyst showed almost no change in the amount of generated hydrogen as compared with the comparative example. From this, the original zinc sulfide has poor photocatalytic activity, but the properties of zinc sulfide are changed by performing the above-mentioned oxidation treatment, and H ⁺ and SH ^- are converted into hydrogen and polysulfide ions by a redox reaction. It can be seen that the activity as has increased.

The reason why high oxidation activity can be obtained by such oxidation treatment is that a part of sulfur atoms of zinc sulfide is replaced by oxygen atoms, and the ratio thereof becomes higher on the particle surface, and the composition changes continuously. It is considered that space charges are generated and an electric field is generated in the depth direction of the particles. This electric field causes the free electrons and free holes to move away from each other, reducing recombination between free electrons and free holes. It is considered that the recombination between the product and the reduction reaction product is suppressed, and the catalytic activity is increased.

As is clear from the above description, a highly active photocatalyst can be obtained by subjecting a metal sulfide such as zinc sulfide to the above-mentioned oxidation treatment. By using this highly active photocatalyst for the treatment of hydrogen sulfide, harmful substances such as sulfurous acid gas are generated using hydrogen sulfide, which is an environmentally harmful substance, as a raw material without requiring energy other than the energy required for the light source. Without producing useful sulfur and hydrogen. If sunlight is used as the light source, the processing cost can be further reduced. Furthermore, if this method for treating hydrogen sulfide using a highly active photocatalyst is applied to the desulfurization step of crude oil, etc., hydrogen is generated from the hydrogen sulfide generated in the desulfurization step, and the generated hydrogen is reused in the desulfurization step. And a very economical desulfurization process can be realized.

[0042]

As described above, according to the first to third aspects of the present invention, an inexpensive and long-life photocatalyst can be obtained by oxidizing a metal sulfide in a gas phase or a liquid phase. This highly active photocatalyst makes it possible to efficiently recover sulfur and hydrogen from hydrogen sulfide.

According to the fourth and fifth aspects of the present invention, by treating hydrogen sulfide with a highly active photocatalyst, hydrogen sulfide, which is an environmentally harmful substance, can be used as a raw material in a simple process such as sulfurous acid gas. Without producing any harmful substances
It is possible to efficiently and inexpensively produce sulfur and hydrogen useful for industry in general. Furthermore, if the method for treating hydrogen sulfide using this highly active photocatalyst is applied to the desulfurization step of crude oil and the like, the hydrogen generated by the treatment of hydrogen sulfide can be reused in the desulfurization step, making it extremely useful for chemical recycling. Becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a hydrogen sulfide treatment system according to an embodiment of the present invention.

FIG. 2 is a view showing an experimental device for examining the activity of a highly active photocatalyst according to the present invention.

FIG. 3 is a diagram showing the activity of a highly active photocatalyst according to the present invention.

FIG. 4 is a view schematically showing a general crude oil desulfurization step.

FIG. 5: Conventional technology for treating hydrogen sulfide (Klaus method)
FIG.

FIG. 6 is a diagram illustrating a conventional technique (hydrocarbon gas decomposition method) of a hydrogen production method.

FIG. 7 is a diagram exemplifying a conventional technology of a hydrogen production method (a cryogenic hydrogen purification method or a nitrogen cleaning method).

[Explanation of symbols]

1 ... Hydrogen sulfide dissolving tank, 3 ... Photocatalytic reaction tank, 5 ... Sulfur recovery tank, 7 ... Ultraviolet light source, 11 ... Photoreaction part, 1
3 ... Hydrogen determination part, 15 ... Solution reservoir, 17 ... Ultraviolet light, 19 ... Condenser lens, 21 ... Reflection mirror, 23 ... Gas vent plug

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C01B 17/04 C01B 17/04 RF term (Reference) 4G069 AA02 AA08 BA48A BB04A BB04B BB09A BB09B BC35A BC35B BC36A BC37A CB81 FA01 FB40 FB41

Claims (5)

[Claims] 1. A method for producing a highly active photocatalyst, comprising firing a metal sulfide in an oxidizing atmosphere. 2. A method comprising oxidizing a metal sulfide with one or more selected from permanganic acid or a salt thereof, chromic acid or a derivative thereof, nitric acid or a derivative thereof, peroxoacid or a salt thereof, and sulfuric acid. A method for producing a highly active photocatalyst, comprising: 3. The method according to claim 1, wherein the metal sulfide is a sulfide of zinc, cadmium or mercury.
A method for producing the highly active photocatalyst according to the above. 4. Sulfidation using a highly active photocatalyst characterized by adding a highly active photocatalyst obtained by calcining a metal sulfide in an oxidizing atmosphere to a solution containing hydrogen sulfide to recover hydrogen and sulfur. How to treat hydrogen. 5. A first step of dissolving hydrogen sulfide in a neutral or alkaline solution, and adding a highly active photocatalyst obtained by calcining a metal sulfide in an oxidizing atmosphere to the solution after dissolving the hydrogen sulfide, A second step of recovering hydrogen gas by irradiating
A third step of recovering sulfur from the solution after hydrogen gas recovery, wherein the solution after sulfur recovery in the third step is reused as the solution in the first step. Processing method.