A method for the production of hydrogen sulfide from pulsed electrolysis of gaseous sulfur dioxide

Abstract

The application discloses a method for generating hydrogen sulfide by pulse electrolysis of gaseous sulfur dioxide, and belongs to the technical field of resource utilization of industrial sulfur dioxide flue gas. The method adopts a two-chamber flow electrolytic cell as an electrolysis system, passes electrolyte into an anode chamber and passes gaseous sulfur dioxide into a cathode chamber, applies pulse current or pulse potential between the anode and the cathode to perform electrolysis, and catalytically reduces and converts the gaseous sulfur dioxide into hydrogen sulfide. The method directly uses SO2 gas as a reactant, is not limited by the solubility of SO2 in liquid, improves the mass transfer of the reactant, significantly reduces the ohmic resistance of the electrolytic cell, reduces the reaction voltage, and adopts a pulse power supply mode to promote the periodic adsorption of SO2 and the consumption and accumulation of protons, promote the conversion of SO2 into H2S, improve the reduction efficiency of sulfur dioxide, and reduce energy consumption.

Description

Technical Field

[0001] This invention relates to a method for preparing hydrogen sulfide by electrolytic reduction of sulfur dioxide, and particularly to a method for efficiently converting sulfur dioxide into hydrogen sulfide by using sulfur dioxide gas as a direct reactant and improving mass transfer efficiency and reducing the voltage of the electrolytic cell. This method belongs to the field of industrial sulfur dioxide flue gas resource utilization technology. Background Technology

[0002] Sulfur dioxide (SO2) is a common air pollutant, and its emissions not only threaten human health but also cause significant harm to the environment. Converting SO2 into hydrogen sulfide (H2S), a high-value chemical product, through electrocatalysis can effectively reduce SO2 emissions and enable its resource utilization.

[0003] H2S, as an important chemical raw material, is widely used in the production of organic and inorganic sulfides, and plays a vital role in environmental protection fields such as wastewater purification, sludge treatment, and metal ion removal. Furthermore, H2S can be used in fuel cells and sulfur production, demonstrating its potential value in the energy sector. Therefore, developing an efficient, stable, and economical method for converting SO2 to H2S is of great significance.

[0004] In existing technologies, liquid-phase electrolysis is limited by the low solubility of SO2 and the high voltage of the electrolytic cell, which hinders its industrial application. For example, Chinese patent (publication number: CN115354353A) discloses a method for reducing SO2 to prepare H2S based on a dual-electrode flow electrolytic cell. Although it improves the current density and flux, it still faces the problems of low mass transfer efficiency and easy flooding of the electrodes.

[0005] Furthermore, Chinese patent (publication number CN112725816A) discloses a method for preparing hydrogen sulfide through electrocatalytic reduction of sulfur dioxide and synergistic membrane separation. This method adds an acidification separation chamber for H2S, enabling H2S separation. However, this method still faces the following problems: 1. Dilute sulfuric acid needs to be added to all three electrode chambers, posing a risk of waste acid leakage; 2. SO2 dissolves in the catholyte in the cathode chamber to produce SO3. 2- 3. The electrolytic cell described in this method has a three-chamber structure and uses anion exchange membrane and cation exchange membrane respectively, which increases the resistance of the electrolytic cell. Summary of the Invention

[0006] To address the problems of high cell pressure, limited reactant availability, and easy flooding of the gas diffusion electrode in the electrocatalytic reduction of SO2 to H2S using existing liquid-phase flow electrolytic cells, this invention aims to provide a method for producing hydrogen sulfide from gaseous sulfur dioxide via pulsed electrolysis. This method uses a two-chamber flow electrolytic cell as the electrolysis system and employs pulsed current or pulsed potential to directly and efficiently catalytically reduce gaseous SO2 into hydrogen sulfide gas. Furthermore, the periodicity of the pulsed current or potential enables the adsorption and reduction of sulfur dioxide, improving the conversion efficiency of SO2 to H2S, reducing energy consumption, overcoming the technical problem of limited mass transfer in liquid-phase electrolysis, reducing the generation of waste salts and acids, avoiding flooding of the gas diffusion electrode, and improving reaction stability. This method is simple to operate, low in cost, and conducive to large-scale production.

[0007] To achieve the above-mentioned technical objectives, the present invention provides a method for producing hydrogen sulfide by pulsed electrolysis of gaseous sulfur dioxide. The method employs a two-chamber flow electrolytic cell as the electrolysis system. The two-chamber flow electrolytic cell includes an anode chamber and a cathode chamber. The anode chamber uses an inert anode, and the cathode chamber uses a cathode loaded with a sulfur dioxide reduction catalytic material. The cathode chamber and the anode chamber are separated by a membrane. Electrolyte is introduced into the anode chamber and sulfur dioxide gas is introduced into the cathode chamber. A pulsed current or pulsed potential is applied between the anode and cathode to perform electrolysis, and the sulfur dioxide gas is catalytically reduced and converted into hydrogen sulfide.

[0008] like Figure 1 As shown: When a low potential or low current is applied, SO2 and protons are adsorbed on the electrode surface without reduction. When a high potential or high current is applied, the SO2 adsorbed on the electrode combines with protons and is reduced to H2S. The efficient generation of H2S can be achieved by periodically adjusting the reaction on the electrode surface using an electric field. Figure 2 As shown: According to the linear voltammetric curves of the electrode under different SO2 concentrations, the initial cell potential for SO2 reduction is ~1.5V under different SO2 concentrations. As the potential continues to increase, the increase in electrode current becomes larger, and SO2 reduction reaction tends to occur on the electrode surface. However, under low potential or lower current conditions, the electrode surface mainly adsorbs reactants.

[0009] The technical solution of this invention directly utilizes SO2 gas as a reactant. The diffusion coefficient of SO2 in the gas is 11.5 mm. 2 The diffusion coefficient ( / s) is much greater than that in the liquid phase (0.0015 mm). 2 The electrode, with a per-second ratio (%), overcomes the problem of limited mass transfer of reactants. Furthermore, because the electrode is in direct contact with the proton exchange membrane, the high proton concentration on the electrode surface provides the necessary proton-rich environment for SO2 reduction, thus achieving efficient H2S generation.

[0010] As a preferred embodiment, during the electrolysis process, the pulse period of the pulsed current is 5s to 5min, and the ratio of high current time to low current time in each cycle is 5% to 95%: 95% to 5%. As a more preferred embodiment, the high current is 0.2 to 10 A, and the low current is less than 0.2 A.

[0011] As a preferred embodiment, during the electrolysis process, the pulse period of the pulse potential is 5s to 5min, and the ratio of high potential time to low potential time in each cycle is 5% to 95%: 95% to 5%. As a more preferred embodiment, the high potential is 3 to 5V, and the low potential is less than 3V.

[0012] This invention employs pulsed current or voltage electrolysis of gaseous SO2. By applying a low potential (low current) to adsorb SO2 and applying a high potential (high current) to catalytically reduce SO2, this pulsed potential (current) control method achieves efficient H2S generation, improves the conversion efficiency of SO2 to H2S, and reduces energy consumption.

[0013] As a preferred embodiment, the membrane is a proton exchange membrane or a bipolar membrane. All membranes are conventional commercial products.

[0014] As a preferred embodiment, the cathode is composed of carbon felt, carbon paper, carbon cloth, titanium felt, proton exchange membrane or bipolar membrane loaded with sulfur dioxide reduction catalytic material.

[0015] As a preferred embodiment, the sulfur dioxide reduction catalyst comprises at least one of elemental copper, platinum, or palladium, a metal sulfide of copper, platinum, or palladium, or a metal selenide of copper, platinum, or palladium. Preferred sulfur dioxide reduction catalysts are those known in the art to possess high electrocatalytic activity for the reduction of sulfur dioxide.

[0016] As a preferred embodiment, the inert anode is one of the following: platinum sheet, platinum mesh, nickel foam, platinum carbon paper, iridium oxide carbon paper, titanium felt, titanium sheet, and titanium mesh.

[0017] As a preferred embodiment, the SO2 volume concentration in the sulfur dioxide gas is 0.1% to 100%, and the equilibrium gas is an inert gas, such as argon or helium.

[0018] The electrolyte in the anode chamber of this invention can be water or an aqueous solution, which may contain electrolytes to improve conductivity. The electrolyte primarily generates hydrogen protons through electrolysis, which combine with sulfur anions reduced at the cathode to produce hydrogen sulfide gas.

[0019] Compared with the prior art, the technical solution of the present invention brings the following beneficial technical effects:

[0020] 1) This invention directly uses gaseous SO2 as raw material to electrolytically reduce and convert it into H2S, breaking through the problem of limited mass transfer of SO2 in traditional liquid systems and solving the problem of difficulty in separating H2S caused by water flooding of the gas diffusion electrode.

[0021] 2) This invention achieves the conversion of SO2 to H2S through pulse power supply, which significantly reduces the voltage of the electrolytic cell, improves the H2S generation efficiency, and reduces energy consumption.

[0022] 3) The present invention supports various electrolyte and gas concentration conditions through pulse electrolysis of gaseous sulfur dioxide to generate hydrogen sulfide. By simplifying equipment design and operation process, it reduces production costs and is suitable for industrial-scale application.

[0023] 4) The method of generating hydrogen sulfide by pulse electrolysis of gaseous sulfur dioxide has high potential application value. For example, there is a low concentration of SO2 in the flue gas of non-ferrous smelting. If the flue gas is directly passed into the electrolytic cell, the H2S generated by reduction can be directly used to capture heavy metal ions in the flue gas or purify heavy metal ions in wastewater, which has great application prospects. Attached Figure Description

[0024] Figure 1 This is a schematic diagram illustrating the principle of pulsed electric field-controlled reaction.

[0025] Figure 2 Linear voltammetric curves of the electrode under different SO2 concentrations.

[0026] Figure 3 This is a schematic diagram of an electrolytic cell for producing hydrogen sulfide from gaseous sulfur dioxide via pulse electrolysis.

[0027] Figure 4 The H2S Faraday efficiency is given in Examples 1, 2, 3 and 4.

[0028] Figure 5 The H2S partial current density is shown in Examples 1, 2, 3 and 4. Detailed Implementation

[0029] The following embodiments are intended to further illustrate the present invention and are not intended to limit the invention. Any adjustments and improvements made without departing from the concept of the present invention are within the scope of protection of the present invention.

[0030] Unless otherwise specified, all chemical reagents used in the following examples are conventional commercially available products of analytical grade. The experiment on the production of hydrogen sulfide from gaseous sulfur dioxide by pulsed electrolysis includes pulsed potential and pulsed current.

[0031] In the following examples, the CoNiS / CF catalyst was obtained by a two-step hydrothermal method. The preparation process is based on existing literature (“Oriented intergrowth of the catalyst layer in membrane electrode assembly for alkaline water electrolysis”, Wan L, et al., Nature Communications, 2022, 13(1): 7956.) (denoted as CoNiS / CF).

[0032] In the following embodiments, the electrolysis system is a two-chamber flow electrolytic cell, such as... Figure 3 As shown, the two-chamber flow electrolyzer includes an anode chamber and a cathode chamber. The anode chamber uses an IrO2 / CP anode, and the cathode chamber uses a CoNiS / CF cathode. The cathode chamber and the anode chamber are separated by a commercially available proton exchange membrane. H2O is introduced into the anode chamber and sulfur dioxide gas is introduced into the cathode chamber. Electrolysis is performed by applying a pulsed current or pulsed potential between the anode and cathode, and the sulfur dioxide gas is catalytically reduced and converted into hydrogen sulfide.

[0033] Comparative Example 1

[0034] Experiment on the production of hydrogen sulfide from gaseous sulfur dioxide by DC potential electrolysis:

[0035] CoNiS / CF was used as the cathode, iridium oxide-loaded carbon paper as the anode (denoted as IrO2 / CP), and a proton exchange membrane was used as the diaphragm. The electrode area was 1 cm². 2 The SO2 concentration was 5%, and the electrolysis was performed under direct current for 20 min at an applied potential of 3V. The Faraday efficiency of H2S was 48.14%, and the partial current density was 129.72 mA / cm². 2 .

[0036] Example 1

[0037] Experiment on the production of hydrogen sulfide from gaseous sulfur dioxide by pulsed potential electrolysis:

[0038] CoNiS / CF was used as the cathode, iridium oxide-loaded carbon paper as the anode (denoted as IrO2 / CP), and a proton exchange membrane was used as the diaphragm. The electrode area was 1 cm². 2 The SO2 concentration (volume concentration) was 5%, and the gas flow rate was 10 mL / min. The pulse period was 4 min, with the high potential time accounting for 50%. A high potential of 3V was applied for 2 min, followed by a low potential of 2.5V for 2 min. The Faraday efficiency of H2S was 75.62%. Figure 4 The partial current density is 229.74 mA / cm². 2 ( Figure 5).

[0039] Example 2

[0040] CoNiS / CF was used as the cathode, iridium oxide-loaded carbon paper as the anode (denoted as IrO2 / CP), and a proton exchange membrane was used as the diaphragm. The electrode area was 1 cm². 2 The SO2 concentration was 5%, and the gas flow rate was 10 mL / min. The pulse period was 4 min, with the high potential time accounting for 50%. A high potential of 4V was applied for 2 min, followed by a low potential of 2.5V for 2 min. The Faraday efficiency of H2S was 66.11% ( Figure 4 The partial current density is 334.76 mA / cm². 2 ( Figure 5 ).

[0041] Example 3

[0042] CoNiS / CF was used as the cathode, iridium oxide-loaded carbon paper as the anode (denoted as IrO2 / CP), and a proton exchange membrane was used as the diaphragm. The electrode area was 1 cm². 2 The SO2 concentration was 5%, and the gas flow rate was 10 mL / min. The pulse period was 2 min, with the high potential time accounting for 50%. A high potential of 3V was applied for 1 min, and a low potential of 2.5V was applied for 1 min. The Faraday efficiency of H2S was 76.97%. Figure 4 The partial current density is 233.77 mA / cm². 2 ( Figure 5 ).

[0043] Example 4

[0044] CoNiS / CF was used as the cathode, carbon paper loaded with iridium oxide was used as the anode (denoted as IrO2 / CP), and a proton exchange membrane was used as the diaphragm. The electrode area was 1 cm². 2 The SO2 concentration was 5%, and the gas flow rate was 10 mL / min. The pulse period was 1 min, with the high potential time accounting for 50%. A high potential of 3V was applied for 30 s, and a low potential of 2.5V was applied for 30 s. The Faraday efficiency of H2S was 88.14% ( Figure 4 The partial current density is 266.94 mA / cm². 2 ( Figure 5 ).

[0045] Example 5

[0046] CoNiS / CF was used as the cathode, carbon paper loaded with iridium oxide was used as the anode (denoted as IrO2 / CP), and a proton exchange membrane was used as the diaphragm. The electrode area was 1 cm². 2The SO2 concentration was 5%, and the gas flow rate was 10 mL / min. The pulse period was 1 min, with the high potential time accounting for 50%. A high current of 200 mA was applied for 30 s, and a low potential of 10 mA was applied for 30 s. The Faraday efficiency of H2S was 90.22%, and the partial current density was 94.73 mA / cm². 2 .

[0047] Example 6

[0048] CoNiS / CF was used as the cathode, iridium oxide-loaded carbon paper as the anode (denoted as IrO2 / CP), and a proton exchange membrane was used as the diaphragm. The electrode area was 1 cm². 2 The SO2 concentration was 5%, and the gas flow rate was 10 mL / min. The pulse period was 1 min, with 75% of the time spent at high potential. A high current of 200 mA was applied for 45 s, and a low potential of 10 mA was applied for 15 s. The Faraday efficiency of H2S was 90.07%, and the partial current density was 137.36 mA / cm². 2 .

[0049] In summary, by optimizing the pulse electrolysis conditions, this invention achieves efficient and low-cost gas-phase SO2 to H2S conversion, and has broad prospects for industrial applications.

Claims

1. A method for producing hydrogen sulfide by pulsed electrolysis of gaseous sulfur dioxide, comprising a two-chamber flow electrolyzer as the electrolysis system, wherein the two-chamber flow electrolyzer includes an anode chamber and a cathode chamber, the anode chamber employs an inert anode, the cathode chamber employs a cathode loaded with a sulfur dioxide reduction catalyst, and the cathode chamber and the anode chamber are separated by a diaphragm, characterized in that: Electrolyte is introduced into the anode chamber and sulfur dioxide gas is introduced into the cathode chamber. Electrolysis is performed by applying a pulsed current or pulsed potential between the anode and cathode, and the sulfur dioxide gas is catalytically reduced and converted into hydrogen sulfide.

2. The method for generating hydrogen sulfide by pulse electrolysis of gaseous sulfur dioxide according to claim 1, characterized in that: During the electrolysis process, the pulse period of the pulsed current used is 5s to 5min, and the ratio of high current time to low current time in each cycle is 5% to 95%: 95% to 5%.

3. The method for generating hydrogen sulfide by pulse electrolysis of gaseous sulfur dioxide according to claim 2, characterized in that: The high current is 0.2~10 A, and the low current is less than 0.2 A.

4. The method for generating hydrogen sulfide by pulse electrolysis of gaseous sulfur dioxide according to claim 1, characterized in that: During the electrolysis process, the pulse period of the pulse potential used is 5s to 5min, and the ratio of high potential time to low potential time in each cycle is 5% to 95%: 95% to 5%.

5. The method for generating hydrogen sulfide by pulse electrolysis of gaseous sulfur dioxide according to claim 4, characterized in that: The high potential is 3~5V, and the low potential is less than 3V.

6. A method for generating hydrogen sulfide by pulse electrolysis of gaseous sulfur dioxide according to any one of claims 1 to 5, characterized in that: The diaphragm is a proton membrane or a bipolar membrane.

7. A method for generating hydrogen sulfide by pulse electrolysis of gaseous sulfur dioxide according to any one of claims 1 to 5, characterized in that: The cathode is composed of carbon felt, carbon paper, carbon cloth, titanium felt, proton exchange membrane or bipolar membrane loaded with sulfur dioxide reduction catalytic material.

8. The method for generating hydrogen sulfide by pulse electrolysis of gaseous sulfur dioxide according to claim 7, characterized in that: The sulfur dioxide reduction catalyst includes at least one of the following: elemental copper, platinum, or palladium; metal sulfides of copper, platinum, or palladium; and metal selenides of copper, platinum, or palladium.

9. The method for generating hydrogen sulfide by pulse electrolysis of gaseous sulfur dioxide according to claim 1, characterized in that: The inert anode is one of the following: platinum sheet, platinum mesh, nickel foam, platinum carbon paper, iridium oxide carbon paper, titanium felt, titanium sheet, and titanium mesh.

10. The method for generating hydrogen sulfide by pulse electrolysis of gaseous sulfur dioxide according to claim 1, characterized in that: The SO2 volume concentration in the sulfur dioxide gas is 0.1%~100%, and the equilibrium gas is an inert gas.

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