CN111663148A - Method for preventing elemental sulfur from adhering to electrode surface in process of electrocatalytic reduction of sulfur dioxide - Google Patents

Abstract

The invention discloses a method for preventing elemental sulfur from adhering to the surface of an electrode during electrocatalytic reduction of sulfur dioxide. The electrocatalytic reduction process adopts a three-electrode system. The cathode and anode chambers of the three-electrode system are separated by a proton membrane. The electrolyte in the cathode chamber is a sulfur dioxide absorption solution with surfactant added, and the electrolyte in the anode chamber is Na ₂ SO ₄ /H. _{2 SO4} mixed solution, with lead and other metal electrodes as the working electrode, Pt as the counter electrode, and saturated calomel electrode as the reference electrode, after electrocatalytic reduction, elemental sulfur particles are precipitated from the electrolyte in the cathode chamber. The problem of the adhesion of elemental sulfur precipitated on the electrode surface during the electrocatalytic reduction of sulfur dioxide is solved by adding a surfactant. The method can not only electrocatalytically reduce sulfur dioxide to generate elemental sulfur, but also can effectively prevent the poisoning of the electrode surface by elemental sulfur. The process is short and simple to operate, and there is no secondary pollution, which is beneficial to industrial application.

Description

A method to prevent elemental sulfur from adhering to the electrode surface during electrocatalytic reduction of sulfur dioxide Methods

technical field

The invention relates to a method for synthesizing elemental sulfur by electrocatalytic reduction of sulfur dioxide, in particular to a method for using a surfactant to prevent the elemental sulfur generated in the process of electrocatalytic reduction of sulfur dioxide from adhering to the surface of an electrode, and belongs to non-ferrous smelting flue gas recovery useful resources technical field.

Background technique

Based on the concept of environmental protection and resource recycling, the current research on air pollution has gradually focused on the direction of how to recycle pollutants. For the resource utilization of sulfur dioxide polluted gas, it is mainly to produce sulfuric acid by oxidation or to produce sulfur by reduction. With the increasing demand for sulfur in my country, the technology of how to convert sulfur dioxide into elemental sulfur simply and effectively has received continuous attention and development. Electrocatalytic reduction of sulfur dioxide to form elemental sulfur is a promising method due to mild reaction conditions, low energy consumption and simple operation. However, the electroreduction catalysts involved in the prior art generally have the problem of low catalytic reduction efficiency, and the In the process of reducing sulfur dioxide to form elemental sulfur at the cathode, the effective area of the electrode is reduced because sulfur itself is easy to adhere to the electrode material, and the electrolysis efficiency will be greatly reduced after long-term continuous electrolysis. _2. Technical problems that need to be solved urgently in the electrocatalytic reduction process.

SUMMARY OF THE INVENTION

Aiming at the defects of the existing method for electrocatalytic conversion of sulfur dioxide into elemental sulfur, the catalytic efficiency is low, and the elemental sulfur adheres to the electrode surface to poison the electrode. The method can effectively prevent the elemental sulfur generated by reduction from adhering and poisoning the electroreduction catalyst, and the method can be implemented at normal temperature and pressure, the operation is simple, the energy consumption can be greatly reduced, and it is favorable for popularization and application.

In order to achieve the above-mentioned technical purpose, the present invention provides a method for preventing elemental sulfur from adhering to the surface of the electrode in the process of electrocatalytic reduction of sulfur dioxide, the electrocatalytic reduction process adopts a three-electrode system, and the cathode chamber and the anode chamber of the three-electrode system adopt a proton membrane ( DuPont N117), the electrolyte in the cathode chamber is a sulfur dioxide absorbing solution with surfactant added, and the electrolyte in the anode chamber is a mixed solution of Na ₂ SO ₄ /H ₂ SO ₄ , with metal electrodes (lead, copper, titanium, etc.) ) as the working electrode, Pt as the counter electrode, and saturated calomel electrode (SCE) as the reference electrode. After electrocatalytic reduction, elemental sulfur particles are precipitated from the electrolyte in the cathode chamber. The reduction voltage is controlled at -0.6V to -1.2V.

In a preferred solution, the surfactant is at least one of isopropanol, sodium dodecylbenzenesulfonate, and polyvinylpyrrolidone. By using the preferred surfactant, the adhesion of elemental sulfur generated by the electrocatalytic reduction of sulfur dioxide on the surface of the electrocatalytic reduction electrode can be reduced, thereby significantly reducing the poisoning effect of elemental sulfur on the electrode.

In a preferred solution, the surfactant is added at a concentration of 0.1 to 5 g/L in the sulfur dioxide absorption solution.

In a preferred solution, the sulfur dioxide absorption liquid is a sulfur dioxide water absorption liquid or a sulfur dioxide alkaline absorption liquid. The water absorbing liquid of sulfur dioxide is mainly H ₂ SO ₃ solution, and the alkaline absorbing liquid of sulfur dioxide is ammonium sulfite solution, potassium sulfite solution, sodium sulfite solution, etc. These absorbing liquids are all suitable for the technical scheme of the present invention.

In a preferred solution, the metal electrode is a lead electrode, a copper electrode or a titanium electrode. The electrocatalytic reduction efficiency of sulfur dioxide can be significantly improved by selecting a suitable metal electrode as the electrocatalytic reduction catalyst. Especially when the lead electrode is used as the electrocatalytic reduction catalyst, the electrocatalytic reduction efficiency of sulfur dioxide is much better than that of copper electrode and titanium electrode.

In a preferred solution, the pH of the sulfur dioxide absorption solution is controlled to be less than 2 during the electrocatalytic reduction process. Controlling the acidic environment with pH less than 2 is beneficial to the electrocatalytic reduction of sulfur dioxide. If the pH is higher than 2, the electrocatalytic reduction of sulfur dioxide is difficult to carry out. The pH can be adjusted to less than 2 with the help of inorganic acids.

In a preferred solution, the temperature is controlled above room temperature during the electrocatalytic reduction process. The electrocatalytic reduction of sulfur dioxide can proceed smoothly at room temperature.

In a preferred solution, the reduction potential is controlled to be -0.6V to -1.2V (relative to the saturated calomel electrode) during the electrocatalytic reduction process. It is difficult to obtain elemental sulfur in the electrolysis process at the reduction potential of -0.6V to 0V, while when the reduction potential exceeds -1.2V, the hydrogen evolution reaction during the electrolysis process is serious, which greatly reduces the Faradaic efficiency of reducing elemental sulfur.

The present invention generates elemental sulfur through electrocatalytic reduction of sulfur dioxide: first, sulfur dioxide generates thiosulfate (S ₂ O ₃ ^2- ) in the reaction process, and S ₄ O ₆ ^2- is SO ₂ and thiosulfate (eq .1), and secondly, S ₄ O ₆ ^2- can be generated by the redox reaction of S ₂ O ₃ ^2- (eq.3). Combining the above two reaction paths, it can be speculated that S ₂ O ₃ ^2- is The precursor of S ₄ O ₆ ^2- ; since thiosulfate and tetrasulfate are easily converted to elemental sulfur at low pH, the reaction pathway in this system can be speculated as shown in Eq. 4 and Eq. 5. S ₂ O ₃ ^2- and S ₄ O ₆ ^2- are the intermediate products of the reaction, and the lead (copper, titanium, etc.) electrode mainly acts on the formation process of the intermediate products and accelerates the transfer of electrons.

4SO ₂ +3H ₂ O→2SO ₄ ^2- +S ₂ O ₃ ^2- +6H ⁺ (1)

2SO ₂ +S ₂ O ₃ ^2- +2H ⁺ +2e→S ₄ O ₆ ^2- +H ₂ O (2)

2S ₂ O ₃ ^2- →S ₄ O ₆ ^2- +2e (3)

S ₄ O ₆ ^2- +H ⁺ →S+SO ₂ +H ₂ O+SO ₄ ^2- (4)

S ₂ O ₃ ^2- +H ⁺ →S+SO ₂ +H ₂ O+SO ₄ ^2- (5)

Relative to the prior art, the beneficial effects brought by the technical solution of the present invention:

1) The technical scheme of the present invention has higher activity for electrocatalytic reduction of sulfur dioxide or sulfite ions to generate elemental sulfur by using metal electrodes (lead, copper, titanium, etc.), and can effectively recover the high-concentration sulfur dioxide gas in the non-ferrous smelting flue gas. Sulfur resources can be converted into elemental sulfur with higher value, which not only solves the problem of environmental pollution, but also produces economic value;

2) The technical solution of the present invention uses a surfactant to reduce the adhesion of elemental sulfur generated by electrocatalytic reduction of sulfur dioxide on the electrode surface, so as to solve the technical problem of poisoning the electrode due to the adhesion of elemental sulfur on the electrode surface.

3) The technical scheme of the present invention can realize the conversion of the sulfur dioxide absorption liquid at room temperature and normal pressure, the reaction conditions are mild, the energy consumption is low, and the industrial application is favorable.

4) The technical solution of the present invention adopts the method of electrocatalytic reduction, which has the characteristics of high reaction efficiency.

Description of drawings

[Figure 1] is a comparison of the influence of the addition of different surfactants on the i-t curve.

[Figure 2] is the SEM image of the electrode surface before and after adding surfactant.

[Figure 3] is a comparison of the effect of adding different concentrations of surfactant on the i-t curve.

[Figure 4] shows the current density and hydrogen evolution potential of different electrodes at lower overpotentials.

Detailed ways

The following examples are intended to further illustrate the content of the present invention, rather than limit the scope of protection of the claims of the present invention.

The sulfur dioxide absorbing solution in the following examples adopts a three-electrode system for electrocatalytic reduction. The cathode chamber and anode chamber of the three-electrode system are separated by DuPont N117 proton membrane. The electrolyte in the cathode chamber is sulfur dioxide absorption solution, and the electrolyte in the anode chamber is a mixed solution of Na ₂ SO ₄ /H ₂ SO ₄ . The metal sheet is used as the working electrode, and the Pt is used as the Counter electrode, SCE was used as reference electrode.

In the following examples, there is no special description, and the chemical reagents used are all conventional commercially available products, which are analytically pure reagents.

Example 1

Analytical pure sodium sulfite, no surfactants.

50mL of water and sodium sulfite (0.08mol/L) in a certain proportion were mixed uniformly and taken into the cathode chamber as catholyte, 50mL of anhydrous sodium sulfate solution was used as anolyte, lead sheet was used as working electrode, and Pt was used as counter electrode. electrode, SCE was used as reference electrode. Conduct electrochemical performance tests. In the process, select -0.8V electrolysis potential, control the same electrolysis power (400C), sulfite concentration is 0.08mol/L, use sulfuric acid to adjust the pH of cathode and anode electrolysis chamber to 0.5, stirring speed 1000rmp, test current density-time curve (i-t curve). The slope of the i-t curve is 0.09.

Example 2

Mix 50mL of water, sodium sulfite (0.08mol/L), and 5% isopropanol solution (0.01mol/L) in a certain proportion and take it into the cathode chamber as catholyte, and 50mL of anhydrous sodium sulfate solution as the anode Electrolyte, lead sheet as the working electrode, Pt as the counter electrode, SCE as the reference electrode, the electrochemical performance test. In the process, select -0.8V electrolysis potential, control the same electrolysis power (400C), sulfite concentration is 0.08mol/L, use sulfuric acid to adjust the pH of cathode and anode electrolysis chamber to 0.5, stirring speed 1000rmp, test current density-time curve (i-t curve). The slope of the i-t curve can be reduced from 0.09 to 0.06.

Example 3

Mix 50mL of water, sodium sulfite (0.08mol/L), and 0.3g/L polyvinylpyrrolidone (PVP) in a certain proportion and take it into the cathode chamber as the catholyte solution, and 50mL of anhydrous sodium sulfate solution as the anolyte solution. , lead sheet as the working electrode, Pt as the counter electrode, SCE as the reference electrode, the electrochemical performance test. In the process, select -0.8V electrolysis potential, control the same electrolysis power (400C), sulfite concentration is 0.08mol/L, use sulfuric acid to adjust the pH of cathode and anode electrolysis chamber to 0.5, stirring speed 1000rmp, test current density-time curve (i-t curve). The slope of the i-t curve can be reduced from 0.09 to 0.05.

Example 4

Analytical pure sodium sulfite, and 0.01mol/L sodium dodecylbenzenesulfonate (SDBS) as the surfactant.

Mix 50mL of water, sodium sulfite (0.08mol/L), and 0.01mol/L sodium dodecylbenzenesulfonate (SDBS) in a certain proportion and take it into the cathode chamber as the catholyte, and 50mL of anhydrous sodium sulfate. The aqueous solution was used as the anolyte, the lead sheet was used as the working electrode, the Pt was used as the counter electrode, and the SCE was used as the reference electrode, and the electrochemical performance was tested. In the process, select -0.8V electrolysis potential, control the same electrolysis power (400C), sulfite concentration is 0.08mol/L, use sulfuric acid to adjust the pH of cathode and anode electrolysis chamber to 0.5, stirring speed 1000rmp, test current density-time curve (i-t curve). The slope of the i-t curve can be reduced from 0.09 to 0.03.

Example 5

Analytical pure sodium sulfite, four different concentrations of sodium dodecyl benzene sulfonate (SDBS) were selected as the surfactant.

Mix 50mL of water, sodium sulfite (0.08mol/L), sodium dodecylbenzenesulfonate (SDBS) (0.01mol/L, 0.0075mol/L, 0.005mol/L, 0.0025mol/L) in a certain ratio Then take it into the cathode chamber as catholyte, 50 mL of anhydrous sodium sulfate aqueous solution as anolyte, lead sheet as working electrode, Pt as counter electrode, SCE as reference electrode, and conduct electrochemical performance test. In the process, select -0.8V electrolysis potential, control the same electrolysis power (400C), sulfite concentration is 0.08mol/L, use sulfuric acid to adjust the pH of cathode and anode electrolysis chamber to 0.5, stirring speed 1000rmp, test current density-time curve (i-t curve). After linear fitting, the slopes are 0.0056, 0.0053, 0.0055, and 0.0056, respectively. The difference between these slopes is small, indicating that the SDBS concentration has little effect on the current attenuation in a certain period of time, that is, it is small. The concentration of SDBS also has a good inhibitory effect on the adhesion of sulfur on the electrode surface, so in the subsequent experiments, the amount of SDBS added was controlled at 0.0025mol/L.

Example 6

Analytical pure sodium sulfite, reduction voltage -0.8V, pH=0.25, and 0.01mol/L sodium dodecylbenzenesulfonate (SDBS) as the surfactant.

Mix 50mL of water, sodium sulfite (0.08mol/L), and surfactant (0.01mol/L sodium dodecylbenzenesulfonate) in a certain proportion and take it into the cathode chamber as the catholyte, and 50mL of anhydrous sulfuric acid. The aqueous solution of sodium was used as the anolyte, the lead sheet was used as the working electrode, the Pt was used as the counter electrode, and the SCE was used as the reference electrode. The reduction voltage is -0.8V, the water is circulated and cooled at room temperature, and the electrolysis is stopped after 30 minutes, and elemental sulfur is generated. Electrolysis obtains a milky white or milky yellow suspension. The suspension was transferred to a beaker and kept in a constant temperature water bath at 70-80°C. After a period of time, the small solid particles in the solution agglomerated, and the solution became clear. Then, the solution was suction filtered to obtain a solid product, which was dried at 60° C. to constant weight, and the Faradaic efficiency was 83.5%.

Example 7

Electrocatalytic performance of different electrodes and comparison of electrocatalytic selectivity. The current density and hydrogen evolution potential of different electrodes at lower overpotentials were mainly compared. In the electrolysis experiment, lead, titanium and copper were used as cathodes respectively. The electrolyte in the cathode chamber was a mixed solution of 0.08mol/L Na ₂ SO ₃ and 0.5mol/L H ₂ SO ₄ , and the electrolyte in the anode chamber was 0.08 mol/L Na ₂ SO 4 . ₄ and 0.5mol/LH ₂ SO ₄ mixed solution, adjust the pH of the two electrolysis chambers to 0.5, and perform a linear voltammetry test on the solution. The results are shown in Figure 4. There is no obvious difference in the initial potential of lead and titanium electrolysis, which is about -0.4V (relative to SCE). At a more negative potential, the reduction peak current in the Pb electrode system is significantly enhanced compared with that of the titanium and glassy carbon electrodes. It shows that Pb has good catalytic performance. Cu shows a smaller onset reduction potential, but the hydrogen evolution reaction of Cu is also vigorous at low potential, and the potential window of SO ₂ catalytic reduction reaction on the surface of copper electrode is narrow (-0.5～-0.75V vs. SCE), while The hydrogen evolution potential of the Pb electrode is significantly higher than that of Ti, Cu, etc., and the potential window for SO ₂ reduction is wider, which is beneficial to suppress the hydrogen evolution reaction and improve the SO ₂ reduction efficiency by controlling the potential. It is a better SO ₂ electroreduction. Catalytic cathode material.

Claims (8)

1. A method for preventing elemental sulfur from adhering to the surface of an electrode in the process of electrocatalytic reduction of sulfur dioxide is characterized by comprising the following steps: the electrocatalytic reduction process adopts a three-electrode system, a cathode chamber and an anode chamber of the three-electrode system are separated by adopting a proton membrane, the electrolyte in the cathode chamber is sulfur dioxide absorption liquid added with a surfactant, and the electrolyte in the anode chamber is Na₂SO₄/H₂SO₄Mixing the solution, using a metal electrode as a working electrode,pt is used as a counter electrode, a saturated calomel electrode is used as a reference electrode, and elemental sulfur particles are separated out from electrolyte in a cathode chamber after electrocatalytic reduction.

2. The method of claim 1, wherein the step of preventing elemental sulfur from adhering to the surface of the electrode during the electrocatalytic reduction of sulfur dioxide comprises: the surfactant is at least one of isopropanol, sodium dodecyl benzene sulfonate and polyvinylpyrrolidone.

3. A method for preventing elemental sulphur from adhering to an electrode surface during electrocatalytic reduction of sulphur dioxide as claimed in claim 1 or 2, wherein: the addition concentration of the surfactant in the sulfur dioxide absorption liquid is 0.1-5 g/L.

4. The method of claim 1, wherein the step of preventing elemental sulfur from adhering to the surface of the electrode during the electrocatalytic reduction of sulfur dioxide comprises: the sulfur dioxide absorption liquid is sulfur dioxide water absorption liquid or sulfur dioxide alkaline absorption liquid.

5. The method of claim 1, wherein the step of preventing elemental sulfur from adhering to the surface of the electrode during the electrocatalytic reduction of sulfur dioxide comprises: the metal electrode is a lead electrode, a copper electrode or a titanium electrode.

6. The method of claim 1, wherein the step of preventing elemental sulfur from adhering to the surface of the electrode during the electrocatalytic reduction of sulfur dioxide comprises: and controlling the pH value of the sulfur dioxide absorption liquid to be less than 2 in the electrocatalytic reduction process.

7. The method of claim 1, wherein the step of preventing elemental sulfur from adhering to the surface of the electrode during the electrocatalytic reduction of sulfur dioxide comprises: the temperature is controlled to be above room temperature in the electrocatalytic reduction process.

8. The method of claim 1, wherein the step of preventing elemental sulfur from adhering to the surface of the electrode during the electrocatalytic reduction of sulfur dioxide comprises: the reduction potential is controlled to be-0.6V to-1.2V in the electrocatalytic reduction process, relative to a saturated calomel electrode.

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