KR101509137B1 - Method of Removing Hydrogen Sulfide Using Heteropoly Acid - Google Patents

Abstract

The present invention relates to a hydrogen sulphide removal method, and more specifically, to a method used to remove hydrogen sulphide using heteropoly acid or the salt thereof as a medium. The method includes the steps of absorbing the hydrogen sulphide into the heteropoly acid or an aqueous solution of the salt thereof and oxidizing the absorbed hydrogen sulphide. Also included is a fuel cell used in the absorption and oxidization steps to electrochemically reproduce the heteropoly acid and the salt thereof. Accordingly, the present invention can resolve the issues regarding the decomposition occurring in a conventional iron-EDTA hydrogen sulphide process and generate electricity as well.

Description

[0001] The present invention relates to a method of removing hydrogen sulfide mediated by heteropoly acid,

The present invention relates to a method for removing hydrogen sulfide, and more particularly, to a method for removing hydrogen sulfide via heteropoly acid and producing electric energy using a fuel cell.

Hydrogen sulfide is a toxic and corrosive gas that occurs naturally or by industrial activity. Hydrogen sulfide is produced in large quantities during the processes necessary for human survival, such as petroleum refining for energy production and anaerobic digestion for sewage treatment. At present, annual hydrogen sulfide production is estimated to be 2.5 million tons worldwide and it is expected to increase continuously, so it is important to secure technology to effectively remove hydrogen sulfide.

One of the most widely known methods for removing hydrogen sulfide is the oxidation / reduction method of divalent iron / trivalent iron combined with EDTA, which can be performed at room temperature and atmospheric pressure, and sulfur can be obtained as a by-product. In general, the process using EDTA-bound iron is divided into two sub-processes: (1) absorption and oxidation, and (2) regeneration. First, in the absorption and oxidation process, hydrogen sulfide in the gaseous state is absorbed in the trivalent iron solution combined with EDTA, and then oxidized by sulfur trioxide to become sulfur. At the same time, trivalent iron receives electrons from hydrogen sulfide and is reduced to diatomaceous iron.

In the second step, the regeneration step, the reduced bivalent iron is oxidized by aeration and regenerated with trivalent iron. Since the recovered trivalent iron is put into the absorption / oxidation process again, the EDTA-bound iron can theoretically be used continuously without being lost. However, the most serious problem of existing processes using iron-EDTA compounds is the decomposition of EDTA. During the regeneration process, the oxygen released by the aeration oxidizes the bivalent iron to form a hydroxyl radical, and the hydroxyl radical decomposes the EDTA. The degraded EDTA is ultimately converted to glycine or the like. Since the EDTA is decomposed, the remaining iron particles react with the hydrogen sulfide to form a precipitate of FeS or the like, which causes deterioration of the entire process. A method of preserving the amount of EDTA by adding a radical scavenger such as sodium thiosulfate has been used in order to remove hydroxyl radicals generated during aeration, but the process essentially solving the decomposition of EDTA has not yet been found in the world to be. Therefore, it is necessary to study other mediators for removal of hydrogen sulfide besides iron-EDTA compounds.

As a result, the present inventors have made intensive efforts to solve the above problems. As a result, they have found that when molybdophosphate, which is one kind of heteropoly acid, is used in the hydrogen sulfide removal process, hydrogen sulfide is removed when a fuel cell system is introduced, And it is confirmed that the regeneration of molybdophosphate can be performed at the same time, and the present invention has been completed.

Y. Zhao, Q. ZHU, G. Gu, COMBINED REMOVAL OF SO2, H2S AND NOX FROM GAS STREAMS BY CHEMICAL ABSORPTION WITH AQUEOUS SOLUTION OF 12MOLYBDOPHOSPHORIC ACID AND ITS REDUCED SPECIES, Water, Air, and Soil Pollution 102: 157-176, 1998. R. Wang, Investigation on a new liquid redox method for H2S removal and sulfur recovery with heteropoly compounds, Separation and purification technology 31: 111-121, 2003.

An object of the present invention is to provide a method for simultaneously producing electricity production and heteropoly acid or salt thereof by introducing a fuel cell system into a hydrogen sulfide removing process using heteropoly acid or a salt thereof.

In order to accomplish the above object, the present invention provides a method for producing hydrogen sulfide, comprising: (a) an absorption oxidation step of absorbing hydrogen sulfide into an aqueous solution of an oxidized heteropoly acid or a salt thereof to oxidize hydrogen sulfide to sulfur; And (b) electrochemically oxidizing the reduced type heteropoly acid or an aqueous solution thereof reduced in step (a) to regenerate the oxidized heteropoly acid or a salt thereof.

The method of removing hydrogen sulfide according to the present invention does not need to consider the decomposition of EDTA, which is considered to be a serious problem in the process of removing hydrogen sulfide using EDTA-bonded iron, which is widely used in the past. Heteropoly acids such as molybdophosphate, Low operating cost can be expected. In addition to eliminating harmful gases and producing electrical energy, energy sufficiency in the entire process can be realized.

1 is an overall schematic diagram of the present invention.
FIG. 2 is a graph showing the rate at which sulfide ions of absorbed hydrogen sulfide are removed through oxidation-reduction reaction with molybdophosphate in the first step of absorption and oxidation of hydrogen sulfide according to the present invention, Phosphate aqueous solution according to the present invention.
FIG. 3 is a graph showing the absorption rate depending on the pH (A) and molybdophosphate concentration (B) of the molybdophosphate aqueous solution during the first step of the hydrogen sulfide absorption oxidation process according to the present invention.
4 is a cyclic voltage-current graph of a 1 mM molybdophosphate aqueous solution according to pH in the method of removing hydrogen sulfide according to the invention.
5 is a graph showing a polarization curve according to pH when a 5 mM molybdophosphate aqueous solution reduced by hydrogen sulfide is used as a positive electrode fuel of a fuel cell.
FIG. 6A is a graph showing a voltage generated during reduction of a molybdophosphate solution with hydrogen sulfide and oxidation of a reduced molybdophosphate aqueous solution by a fuel cell in the method of removing hydrogen sulfide according to the present invention, for 4 hours.
FIG. 6B is a graph showing the results of the reduction of the molybdophosphate solution to hydrogen sulfide and the reduction of the molybdophosphate color during the oxidation of the reduced molybdophosphate aqueous solution by the fuel cell for 4 hours in the method of removing hydrogen sulfide according to the present invention. Absorbance curve at 730 nm.
7 is a graph showing the open circuit voltage and the maximum power density produced according to the driving temperature when the molybdophosphate solution is reduced to hydrogen sulfide and used as the anode fuel of the fuel cell in the method of removing hydrogen sulfide according to the present invention.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In general, the nomenclature used herein and the experimental methods described below are well known and commonly used in the art.

In the present invention, a method of removing hydrogen sulfide by using heteropoly acid such as molybdophosphate (HPMo) or a salt thereof is carried out by using a chemically stable molybdophosphate and introducing a fuel cell system to regenerate electricity and molybdophosphate Can be done at the same time.

In the hydrogen sulfide removing method according to the present invention, molybdophosphate, which is one type of heteropoly acid, is used. It was confirmed that the decomposition of EDTA, which is considered to be a serious problem of the hydrogen sulfide removal process using the EDTA-bonded iron which is widely used in the process of removing hydrogen sulfide, is not considered.

In addition, the hydrogen sulfide removing method according to the present invention can produce electricity using a fuel cell, so that it is possible to realize not only the removal of noxious gas but also the production of electric energy and the energy sufficiency in the whole process.

Accordingly, in one aspect, the present invention provides a method for producing hydrogen sulfide, comprising: (a) an absorption oxidation step of absorbing hydrogen sulfide into an aqueous solution of an oxidized heteropoly acid or a salt thereof to oxidize hydrogen sulfide to sulfur; And (b) electrochemically oxidizing the reduced type heteropoly acid or an aqueous solution thereof reduced in step (a) to regenerate the oxidized heteropoly acid or a salt thereof.

The method for removing hydrogen sulfide according to the present invention comprises two steps: (a) an absorption oxidation process in which hydrogen sulfide is absorbed in an aqueous solution of heteropoly acid or an aqueous solution thereof and then oxidized to sulfur; And (b) electrochemically oxidizing the reduced heteropoly acid or its aqueous salt solution through the fuel cell during the absorption oxidation process.

The heteropoly acid or a salt thereof is one in which at least one element selected from the group consisting of molybdenum (Mo), tungsten (W), and vanadium (V) is a coordination element and an element of phosphorus (P) (PM ₁₂ O ₄₀ ^{3 -} ), tungstophosphate (PW ₁₂ O ₄₀ ^{3 -} ), molybdosilicate (SiMo ₁₂ ( ^- )), and the like are preferable examples of the heteropoly acid or its salt. O ₄₀ ^{4 -} ) and tungsten silicate (SiW ₁₂ O ₄₀ ^4- ). Preferably, molybdophosphate is used but not limited thereto. It is also possible to use a mode in which a part of molybdenum (Mo) or tungsten (W) is substituted with vanadium (V) in the above basic form.

The molecular weight of heteropoly acid differs depending on the basic skeletal form, but is very large, about 1,000 g or more per heteropoly anion. In addition, heteropolyacids are very small in surface area (less than 10 m ² / g) and are soluble in polar organic solvents such as water, alcohols and amines.

In the step (a), the pH of the aqueous solution of heteropoly acid or its salt is kept as low as possible so that the adsorbed sulfide ions are rapidly converted to sulfur. That is, it is preferable that the aqueous solution of the oxidized heteropoly acid or its salt has a pH of 1.5 or less.

Also, considering the fact that hydrogen sulfide is difficult to dissolve in an aqueous solution having a low pH, the concentration of the heteropoly acid or its salt aqueous solution is kept high to maximize the absorption efficiency. That is, the concentration of the aqueous solution of heteropoly acid or its salt may be 1 mM to 30 mM, preferably 5 mM to 25 mM, more preferably 5 mM to 10 mM. At the same time as this process, the heteropoly acid or its salt is reduced and becomes unable to absorb hydrogen sulfide. The temperature of the aqueous solution of the oxidized heteropoly acid or its salt may be between 20 ° C and 60 ° C.

The molar ratio of the sulfide ion (S ^2- ) of the hydrogen sulfide to the heteropoly acid or its salt may be 1: 1 to 1: 3, preferably 1: 1 to 1: 2. In the above range, the absorbed sulfide ion can be effectively converted to sulfur.

In the step (b), the reduced form of the reduced type heteropoly acid or its salt is electrochemically oxidized through the fuel cell to regenerate it as an oxidized form of heteropoly acid or a salt thereof. The step of electrochemically oxidizing is characterized in that it is used as a positive electrode electrolyte of a fuel cell, and the regenerated heteropoly acid or a salt thereof can be reused to absorb hydrogen sulfide again.

The pH of the positive electrode electrolyte solution of the fuel cell (b) is kept as low as possible so that the heteropoly acid or its salt has the best electrochemical activity. That is, the pH of the electrolytic solution may be 1.5 or less, preferably 1.0 or less, and more preferably 0.4 to 1. Further, the temperature of the electrolytic solution may be 20 to 60 캜.

Characterized in that the decomposition of the heteropoly acid or its salt does not occur in the previous step of the hydrogen sulfide removing method according to the present invention.

In another aspect, the present invention relates to an absorber for oxidizing hydrogen sulfide using an oxidized heteropoly acid or a salt thereof; And a fuel cell unit for oxidizing the reduced heteropoly acid or a salt thereof obtained in the absorption unit, and a system for regenerating hydrogen sulfide and a heteropoly acid or a salt thereof.

According to another aspect of the present invention, there is provided a method for producing a sulfide-based sulfide phosphor comprising the steps of: (a) an absorption oxidation step of absorbing hydrogen sulfide into an oxidized molybdophosphate aqueous solution to reduce molybdophosphate and oxidize hydrogen sulfide to sulfur; And (b) electrochemically oxidizing the reduced molybdophosphate aqueous solution reduced in the step (a) to regenerate the oxidized molybdophosphate.

In the absorption part, an absorption oxidation reaction in which the hydrogen sulfide which is the step (a) of the hydrogen sulfide removal method is absorbed into the aqueous solution of molybdophosphate which is in an oxidized state and is then oxidized to sulfur, takes place.

H ₂ S + HPMo (oxidation type) ---> S ⁰ + Mo-blue (reduction type)

Also, in the fuel cell, a step of electrochemically oxidizing the reduced molybdophosphate aqueous solution through the fuel cell in the absorption oxidation step (b) of the hydrogen sulfide removal method occurs, and the anode and the anode of the fuel cell The changes that occur in

Mo-blue (reduced form) + e ^- ---> HPMo (oxidized form) + H ⁺ (anode)

2H ⁺ + 2e ^- + 1/2 O ₂ ---> H ₂ O (cathode)

1 is a view showing an example of an apparatus for removing hydrogen sulfide using molybdophosphate. The hydrogen sulfide removal process proposed in the present invention is largely composed of two parts, an absorption part and a fuel cell part. The absorption part is a step in which gaseous hydrogen sulfide is injected into a liquid molybdophosphate aqueous solution and then absorbed so that the entire amount of the hydrogen sulfide introduced is absorbed in the liquid so that hydrogen sulfide is not present in the exhaust gas. The reactor used in the absorption process should maximize the contact time between the inlet gas and the liquid absorbent to enable active material transport. The absorption tower depicted in FIG. 1 is for illustrating the present invention, Is not limited by Fig. The reaction inside the absorber is as follows.

H ₂ S (g) ---> H ₂ S (1)

H ₂ S + HPMo (oxidation type) ---> S ⁰ + Mo-blue (reduction type)

The oxidized form of molybdophosphate oxidizes hydrogen sulfide to sulfur at a rapid rate of reaction, and itself is reduced to molybdenum blue. Molybdenum blue in a reduced form can no longer react with hydrogen sulfide. When hydrogen sulfide is introduced, molybdenum blue is filled with molybdenum blue, which can not absorb hydrogen sulfide, And this is done in the fuel cell section. The fuel cell unit is composed of a cathode, an anode electrode, and a proton ion membrane therebetween. In the cathode portion of the fuel cell, a reduced form of molybdenum blue is electrochemically oxidized on the electrode to lose electrons and convert to molybdophosphate oxidizing type (see below).

Mo-blue (reduced form) + e ^- ---> HPMo (oxidized form) + H ⁺ (anode)

On the other hand, in the anode, hydrogen ions supplied from the cathode, electrons carried in the external circuit, and oxygen supplied to the cathode are combined and reduced to water (see below).

2H ⁺ + 2e ^- + 1/2 O ₂ ---> H ₂ O (cathode)

The cathode and anode half reactions are fuel cell reactions that enable the production of electrical energy from the oxidation of molybdenum blue. Since the molybdophosphate regenerated through the fuel cell is in a form capable of absorbing hydrogen sulfide, the molybdophosphate can be injected again into the absorber and reused.

In another aspect, the present invention relates to a method for producing electricity using the aforementioned hydrogen sulfide removal and heteropoly acid or salt salt regeneration system. It is possible to produce electricity using a fuel cell, thereby not only removing harmful gas such as hydrogen sulfide but also producing electric energy at the same time, thereby realizing energy sufficiency.

Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these embodiments are only for illustrating the present invention and that the scope of the present invention is not construed as being limited by these embodiments.

[Example]

Example  One

The apparatus for removing hydrogen sulfide using the molybdenum phosphate of FIG. 1 is roughly divided into two parts, an absorber and a fuel cell. First, an experiment was conducted to investigate the oxidation rate of sulfide ions by molybdophosphate. The concentrations of molybdophosphate were 1.79 mM and 2.42 mM, respectively, and the concentration ratio was 1: 1 and 1: 1.35, respectively. The pH of the aqueous solution of molybdophosphate was adjusted to 0.8, 3.0, and 5.0, respectively, and the effect of the pH on the oxidation rate was tested for each concentration ratio. The results are shown in FIG. The sulfide removal rate (%) was measured using a UV-VIS spectrophotometer (DR 5000, Hach).

The relationship between the rate at which the sulfide ion of the absorbed hydrogen sulfide is removed through oxidation-reduction reaction with the molybdophosphate and the pH and concentration of the aqueous solution of molybdophosphate in FIG. 2 indicates that the molecular ratio of the sulfide ion and the molybdophosphate The lower the pH, the faster the sulphide ion is removed, and the lower the pH, the more favorable the sulphide ion removal is. In addition, it was confirmed that the sulfide ion removal effect was faster than that without injecting a larger amount of molybdophosphate molecule per sulfide ion molecule.

Example  2

To investigate the function of molybdophosphate as an absorbing solution, a hydrogen sulfide gas (remainder: nitrogen) at a concentration of 1000 ppm was injected into the molybdophosphate solution at a rate of 500 ml / min. The molybdophosphate concentration in the solution was fixed at 5 mM and the pH was changed to 0.8, 3.0 and 5.0. The effect of the pH on the water uptake was also examined. The molybdophosphate concentration was adjusted to 5 mM, 15mM, and 25mM, respectively, to investigate the effect of molybdophosphate concentration on the absorption rate. The results are shown in Fig. Absorption rate (%) was measured using Kitagawa H ₂ S detection tube (Komyo Rikagaku Kyo KK).

The concentration of HPMo (mM) PH of HPMo 5 0.8 5 3.0 5 5.0 15 0.8 25 0.8

As shown in the graph of the absorption rate according to the pH (A) and molybdophosphate concentration (B) of the molybdophosphate aqueous solution during the absorption oxidation process of the hydrogen sulfide of FIG. 3, the higher the pH, the higher the absorption rate of hydrogen sulfide , Which is due to its better melting property in aqueous solutions of higher pH due to the acidity of the hydrogen sulfide. However, even if the pH is low and the hydrogen sulfide is poorly soluble (pH = 0.8), it can be seen that increasing the molybdophosphate concentration can overcome the lower pH limit and achieve a water absorption of over 90%.

Example  3

Cyclic current - voltage analysis was performed to confirm the oxidation - reduction activity of molybdophosphate according to pH. The solution used for the analysis was analyzed with a concentration of 1 mM of molybdophosphate and 200 mM of sodium chloride in the range of 0.1 V to +0.8 V based on the silver / silver chloride electrode. This result is shown in Fig. The voltage was measured using a multimeter (Keithley 2700) during the reduction of the molybdophosphate solution to hydrogen sulfide and the oxidation of the reduced molybdophosphate aqueous solution to the fuel cell for 4 hours.

4, it can be seen that molybdophosphate has a significant redox activity at pHs of 0.8 and 1.5, and thus it is possible to know the performance of a fuel cell that electrochemically oxidizes molybdenum blue solution in this pH range The current-voltage curve and the power density curve were obtained for the sake of illustration.

4.5 mM of molybdophosphate was sufficiently reacted with 4.5 mM sodium sulfide to reduce the molybdophosphate to molybdenum blue, and the pH of the solution was adjusted to 0.8 and 1.4. The green current-voltage curve and the power density curve using the solution of this state as the fuel of the fuel cell are shown in FIG. From the results of FIG. 5, it can be seen that a large amount of electric power is generated under the condition of pH 0.8.

Example 4

A molybdophosphate solution was prepared by reacting 5 mM of molybdophosphate with 4.5 mM of sodium sulfide. The molybdophosphate was regenerated by adding a reduced molybdenum blue solution to an external resistance of 10 ohms to produce a current. The changes in the amount of current produced during 4 hours and the change in absorbance at 730 nm as blue molybdenum blue oxidized to yellow molybdophosphate are shown in FIG. The absorbance was measured by absorbance at 730 nm to the extent that the color of the reduced molybdophosphate changed to the color of the oxidized form while the molybdophosphate solution was reduced to hydrogen sulfide and then the reduced molybdophosphate aqueous solution was oxidized by the fuel cell for 4 hours. Were measured by UV-VIS spectrophotometer (DR 5000, Hach).

6A is a graph showing the amount of current produced during regeneration by connecting a reduced molybdenum blue solution prepared by sufficiently reacting 5 mM of molybdophosphate with 4.5 mM sodium sulfide to an external resistance of 10 ohms. At the beginning of the reaction, a relatively high amount of instantaneous current flows, which decreases sharply as the reaction progresses, then decreases linearly thereafter. The linear reduction is due to the fact that the amount of fuel in the fuel cell is decreasing as the reduced molybdenum blue is oxidized over time. 6A shows that a current can be produced when a molybdenum blue solution is connected to an external resistor.

The change in absorbance of the molybdenum blue solution during the same period of time is shown in FIG. 6B. Molybdenum blue, which has the strongest absorption spectrum at 730 nm, is gradually lost in its electrochemical oxidation, and after 4 hours it loses all of its original blue color and turns into its original molybdophosphate yellow color .

Example  5

The effect on the power density when the temperature of the fuel cell was changed to 20 ° C or 60 ° C at pH 0.8 was examined (Fig. 7). The open circuit voltage and the maximum power density are obtained by reducing the molybdophosphate solution to hydrogen sulfide and then using the open circuit voltage and the maximum power Density was measured using a potentiostat (CHI 604C).

FIG. 7 shows the results of how the open circuit voltage and power density change when the temperature of the fuel cell is changed to 20 ° C or 60 ° C at pH 0.8. Even when the temperature changes, the open circuit voltage does not change much, Was 36% higher than that at 20 ° C at 60 ° C.

Claims (11)

(a) an absorption oxidation step of absorbing hydrogen sulfide in an aqueous solution of oxidized heteropoly acid or an aqueous solution thereof to reduce heteropoly acid and oxidize hydrogen sulfide to sulfur; And
(b) electrochemically oxidizing the reduced type heteropoly acid or an aqueous solution thereof reduced in step (a) to recover the oxidized heteropoly acid or a salt thereof;
≪ / RTI >
The method according to claim 1, wherein the heteropoly acid or a salt thereof is at least one element selected from the group consisting of molybdenum (Mo), tungsten (W), and vanadium (V) Wherein the phosphorus element is a structure of an inorganic sum of axes which is a central element.
The method according to claim 1, wherein the heteropoly acid or a salt thereof is at least one selected from the group consisting of molybdophosphate (PMo ₁₂ O ₄₀ ^{3 -} ), tungsten phosphate (PW ₁₂ O ₄₀ ^{3 -} ), molybdosilicate (SiMo ₁₂ O ₄₀ ^{4 -} silicate (SiW ₁₂ O ₄₀ ^4-) method for removing hydrogen sulfide characterized in that one or more selected from the group consisting of.
The method according to claim 1, wherein the step of electrochemically oxidizing is used as a positive electrode electrolyte of a fuel cell.
The method according to claim 1, wherein the step of electrochemically oxidizing is used as a positive electrode electrolyte of a fuel cell.
The method for removing hydrogen sulfide according to claim 1, wherein the aqueous solution of the oxidized heteropoly acid or its salt has a pH of 1.5 or less.
The method according to claim 1, wherein the temperature of the aqueous solution of the oxidized heteropoly acid or its salt is 20 ° C to 60 ° C.
The method according to claim 1, wherein the concentration of the heteropoly acid or an aqueous solution thereof is 1 mM to 30 mM.
The hydrogen sulfide removal method according to claim 1, wherein the decomposition of the heteropoly acid or its salt does not occur in the previous step of the hydrogen sulfide removal method.
(a) an absorption oxidation step of absorbing hydrogen sulfide into an oxidized molybdophosphate aqueous solution to reduce molybdophosphate and oxidize hydrogen sulfide to sulfur; And
(b) electrochemically oxidizing the reduced molybdophosphate aqueous solution reduced in the step (a) to recover the oxidized molybdophosphate;
≪ / RTI >
An absorption part for oxidizing hydrogen sulfide using oxidized heteropoly acid or a salt thereof; And
And a fuel cell unit for oxidizing the reduced heteropoly acid or a salt thereof obtained in the absorber, wherein the hydrogen sulfide removal and heteropoly acid or a salt thereof is regenerated.

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