KR101935974B1 - Method for simultaneously removing NOx and SOx - Google Patents

Abstract

The present invention relates to a method for simultaneously removing nitrogen oxides and sulfur oxides, and more particularly, to a method for removing nitrogen oxides and sulfur oxides which are main pollutants generated in a combustion process by using iron oxide reduction pairs without using a complicated high- And the iron oxide reduction pair is oxidized by the nitrogen oxide during the removal process and can be reused as an oxidizing agent to the fuel cell cathode electrode to produce electricity.

Description

Method for simultaneous removal of NOx and SOx [

The present invention relates to a method for simultaneous removal of nitrogen oxides (NO _x ) and sulfur oxides (SO _x ), which are pollutants, by simultaneous removal of nitrogen oxides and sulfur oxides using iron oxide reduction pairs.

Conventionally, as a method of removing nitrogen oxides (NO _x ) and sulfur oxides (SO _x ) in the exhaust gas, most of them have been used in combination with a denitration technique and a desulfurization technique.

Method most commonly it used as a typical x removal technologies inde selective catalytic reduction (Selective Catalytic Reduction, SCR) with a catalyst, wherein the nitrogen oxide (NO _x) by the ammonia and the reaction injected as a reducing agent is converted with water, nitrogen, literature [Chemical Engineering Progress, pp. 39-45, January 1994, it is disclosed that the catalyst used is a V ₂ O ₅ -WO ₃ -TiO ₂ catalyst and can remove nitrogen oxides up to 90% or more depending on the reaction conditions, It is used at high temperature conditions such as 250 to 400 ° C.

It is known that carbon oxides such as activated carbon, carbon fiber or activated coke can remove nitrogen oxides (NO _x ) even at low temperatures of 100 to 250 ° C [K. Kusakabe, H. Kawamura, HJ Kim and S. Morooka, Fuel, 69, 917, 1990; J. Muniz, G. Marban and AB Fuertes, Appl. Catal. B: Environmental, 23, 25, 1999]. However, carbon-based catalysts are capable of removing NO _x at low temperatures, but have a disadvantage in that the denitration performance is somewhat low.

As a representative desulfurization technique, a wet desulfurization technique using an alkaline solution such as slaked slurry is well known, but there is a disadvantage that the equipment cost is high, and a technique of spraying slaked lime or the like into the exhaust gas by dry or semi- But it has a disadvantage that the SO _x removal efficiency is somewhat low.

Therefore, in most combustion processes in which NO _x is generated, sulfur components in the fuel are oxidized and SO _x is generated. Since these two pollutants need to be removed strictly, it is necessary to remove NO _x and SO _x at the same time The development of a system that can be used is urgent.

Accordingly, the present inventors have found that NO _x , which is a main pollutant generated in the combustion process, can be absorbed through a solution such as FeSO ₄ and absorbed to SO _x , and the absorbed NO _x is oxidized And SO _x is oxidized to form SO ₃ , thereby completing the present invention.

An object of the present invention is to develop a new process capable of effectively removing nitrogen oxides and sulfur oxides which are main pollutants generated in a combustion process without using a complicated high-temperature catalyst process or expensive facilities.

In order to accomplish the above object, the present invention provides a method for simultaneous removal of nitrogen oxides and sulfur oxides, which comprises the step of absorbing nitrogen oxides and sulfur oxides into a iron divalent ion solution of an iron redox pair.

More particularly, the present invention relates to a process for absorbing nitrogen oxide and sulfur oxide in an iron divalent ion solution of an iron redox pair (first step); (Step 2) of oxidizing the iron oxide redeposited pair with excess nitrogen oxide not absorbed; And a step of supplying electricity to the cathode electrode of the fuel cell by oxidizing the iron oxide reduction pair (the third step), so that the nitrogen oxides and the sulfur oxides can be removed at the same time, Fuel cells can produce electricity.

As the iron divalent ion solution of the iron-redox pair, either FeSO ₄ solution or FeCl ₂ solution can be used.

The present invention also relates to a fuel cell comprising an anode electrode, a cathode electrode and an electrolyte or ion exchange membrane between the anode electrode and the cathode electrode, wherein the cathode electrode comprises an iron oxide reduction pair as an oxidizing agent, The solution absorbs nitrogen oxides and sulfur oxides, and the iron oxide reduction pair oxidized by the nitrogen oxides is supplied to the fuel cell cathode electrode, thereby providing a method for simultaneously removing nitrogen oxides and sulfur oxides using the fuel cell.

According to the present invention, nitrogen oxides and sulfur oxides, which are main pollutants generated in a combustion process, can be effectively removed at the same time by using only iron oxidation-reduction pairs without using a complicated high temperature catalyst process or expensive facilities. In addition, during the removal process, the iron oxide reduction pair is oxidized by the nitrogen oxide and is reused as an oxidizing agent to the fuel cell cathode electrode to produce electricity.

1 is a schematic view illustrating a configuration of a fuel cell system according to an embodiment of the present invention.
2 is an experimental result showing the performance of the fuel cell according to an embodiment of the present invention.

Hereinafter, a method for simultaneously removing nitrogen oxides and sulfur oxides using a fuel cell will be described in detail as an embodiment of the present invention.

A fuel cell comprising an anode electrode utilizing an oxidation reaction of a fuel and a cathode electrode utilizing a reduction reaction of an oxidant and an electrolyte or an ion exchange membrane disposed between the anode electrode and the cathode, And a reaction in which divalent iron ions are produced by reduction reaction of trivalent iron ions at the cathode electrode using an oxidation-reduction pair.

The fuel cell using the existing iron oxide reduction pair used a regeneration process in which the ferric ion and the trivalent iron ion were oxidized by oxygen, but the regeneration speed was slow at a low pH and the microbial process had to be used.

Accordingly, in the present invention, the use of nitrogen oxide (NO _x ) having oxidizing property in addition to oxygen is used to regenerate bivalent iron ions as trivalent iron ions. In particular, by using an appropriate ligand, an adsorbent capable of absorbing low- Performing together can compensate for slower playback speeds.

NO _x can be decomposed and removed by the following reaction.

[Reaction Scheme 1]

4Fe ²⁺ + 2NO + 4H ^+? 4Fe ³⁺ + N ₂ + 2H ₂ O

8Fe ²⁺ + 2NO ₂ + 8H ^+? 8Fe ³⁺ + N ₂ + 4H ₂ O

In addition, NO _x can oxidize SO _x to SO ₃ as a strong oxidizing agent. At this time, SO ₃ is absorbed very well in water and can be absorbed and removed by a solution containing an iron oxide reduction pair according to the following reaction.

[Reaction Scheme 2]

_{2Fe (NO) SO 4 + 2SO} 2 + 2H 2 O ↔ 2FeSO ₄ + N ₂ + 2H ₂ SO ₄

A reduction reaction of the oxidant occurs at the cathode electrode.

As the oxidizing agent according to the present invention, a different kind of oxidizing agent is used. Most conventional fuel cells use a platinum catalyst for the cathode electrode and the anode electrode. In particular, since the rate of hydrogen oxidation reaction of the anode electrode is relatively faster than the rate of oxygen reduction reaction of the cathode electrode, a large amount of platinum catalyst is usually used for the cathode electrode. However, in the present invention, in order to provide a fuel cell having high efficiency without using a platinum catalyst, an iron oxidation-reduction pair having a high reaction rate as an oxidant is supplied instead of oxygen having a low reaction rate.

According to the present invention, the redox pair of the stabilized iron ion used for the reduction reaction of the cathode has a standard potential of 0.77 V, and the activation energy is very low and the reaction speed is very high.

At this time, the reactant generated through the reduction reaction in the cathode electrode can be oxidized upon contact with the contaminant having the standard reduction potential of 0.77 V or more, and thus supplied to the cathode electrode again.

1 is a schematic view illustrating a configuration of a fuel cell system according to an embodiment of the present invention. The reactant discharged from the cathode electrode is preferably provided with a transfer line for transferring the reactant into contact with the NO _x and SO _x pollutants of the exhaust gas and then oxidizing the reactant to the oxidant supply port. At this time, contact with contaminants may be performed by connecting a separate contaminant supply line in the transfer line.

According to one embodiment of the present invention, the iron oxide redirection pair, which is the oxidizing agent, can be regenerated by NO _x , and preferably the iron redox pair is FeSO ₄ . FeSO ₄ can adsorb a large amount of NO gas by forming Fe (NO) SO ₄ as an absorbent that absorbs NO gas well. The absorbed NO gas is used in a regeneration process for oxidizing iron ions as shown in Reaction Scheme 3 below and oxidizes SO ₂ to SO ₃ to be absorbed in the solution as shown in Reaction Scheme 4 below.

[Reaction Scheme 3]

2Fe ²⁺ + 2NO + 4H ⁺ -> Fe ³⁺ + N ₂ + 2H ₂ O

[Reaction Scheme 4]

2NO + 2SO ₂ + 2H ₂ O -> N ₂ + 2SO ₃ + 2H ₂ O-> N ₂ + 2H ₂ SO ₄

That is, when the iron trivalent ions are reduced by the oxidizing agent, a potential of 0.77 V can be obtained, and the reaction can be rapidly performed without using a noble metal catalyst. This reaction can be used to operate the fuel cell. After the reaction, the reduced bivalent iron ions are transferred to the cathode electrode of the fuel cell to decompose and recover the contaminants. These reactions can convert hydrogen energy into electrical energy.

Hereinafter, the present invention will be described with reference to the following examples. However, the following examples are given to aid understanding of the present invention, but the scope of the present invention is not limited to the following examples.

≪ Example 1 >

A 5% Nafion ™ (manufactured by Du Pont) was added to a carbon black (Basf-Pt / Vulcan XC72R) catalyst carrying platinum at 20% in such a manner that the weight ratio of the catalyst and the Nafion solution was 80:20, 30 parts by weight of ultrapure water and isopropyl alcohol were added to parts by weight to prepare a catalyst slurry. This catalyst slurry was coated on carbon paper (manufactured by Toray Industries, Inc.) so as to have a platinum content of 0.5 mg / cm ² to prepare an anode electrode.

The cathode electrode was prepared in the same manner as in the production of the anode electrode using carbon black not carrying platinum as a catalyst. This catalyst slurry was coated on a carbon paper (manufactured by Toray Industries, Inc.) so as to have a carbon black catalyst of 1 mg / cm ² to prepare a cathode electrode.

A cation exchange membrane Nafion 212 (manufactured by DuPont) was placed between the cathode electrode and the anode electrode, followed by heating and pressing at a temperature of 120 ° C. for about 3 minutes while applying a pressure of 100 kg / cm ² . Respectively.

≪ Example 2 >

A 0.5 M FeSO ₄ + 2M H ₂ SO ₄ solution was prepared to produce an oxidant (iron redox pair) to feed the fuel cell cathode. The iron redox couple solution turned blue when it absorbed NO _x as sky blue. At this time, when SO _x is supplied, SO _x is absorbed in water and reacted with NO _x to be oxidized. At this time, the excess NO _x oxidizes the iron redox pair to generate Fe ³⁺ ions, and the solution turned yellow in color. The yellow solution was fed to the fuel cell reduction electrode as a trivalent iron ion and produced electricity without the precious metal catalyst.

<Experimental Example 1>

Hydrogen was supplied to the anode electrode of the fuel cell of the above example at a rate of 27 ml / min, and the yellow solution of Example 2 was supplied at a rate of 2 ml / min to the cathode electrode. At this time, the active area of the unit cell was 5 cm ² , and the current density was measured at an atmospheric pressure of 50 ° C. The results are shown in FIG.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It will be understood that various modifications and changes may be made without departing from the scope of the appended claims.

Claims (4)

delete A step of absorbing and removing nitrogen oxides and sulfur oxides from the iron divalent iron ions in the iron redox pair (first step); Oxidizing the excess iron oxide redox couple from the bivalent iron ion to the trivalent iron ion (step 2); And a step (third step) of supplying an oxidized iron oxidation-reduction pair to the cathode electrode of the fuel cell to produce electricity,
Wherein the nitrogen oxides in the first step are oxidized and absorbed into a solution containing an iron oxide reduction pair to remove the nitrogen oxide and sulfur oxide simultaneously. 3. The method of claim 2, wherein the iron divalent iron ion solution of the iron redox pair is any one of FeSO ₄ solution and FeCl ₂ solution.

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