Method for producing hydrogen sulfide by pulse electrolysis of gas-phase sulfur dioxide

Abstract

The invention discloses a method for producing hydrogen sulfide from gas-phase sulfur dioxide through pulse electrolysis, and belongs to the technical field of industrial sulfur dioxide flue gas resource utilization. According to the method, a two-chamber flow electrolytic tank is adopted as an electrolysis system, electrolyte is introduced into an anode chamber, sulfur dioxide gas is introduced into a cathode chamber, pulse current or pulse potential is applied between an anode and a cathode for electrolysis, and the sulfur dioxide gas is converted into hydrogen sulfide through catalytic reduction. The method has the advantages that the method is not limited by solubility of SO2 in liquid, reactant mass transfer is improved, ohmic resistance of an electrolytic tank is remarkably reduced, reaction voltage is reduced, periodic adsorption of SO2 and consumption and accumulation of protons are promoted by adopting a pulse power supply mode, conversion of SO2 to H2S is promoted, the reduction efficiency of sulfur dioxide is improved, and energy consumption is reduced.

Description

Technical Field

[0001] The present invention relates to a method for preparing hydrogen sulfide by electrolytic reduction of sulfur dioxide, and in particular to a method for utilizing sulfur dioxide gas as a direct reactant to realize efficient conversion of sulfur dioxide into hydrogen sulfide by improving mass transfer efficiency and reducing electrolytic cell voltage, belonging to the technical field of resource utilization of industrial sulfur dioxide flue gas. Background Art

[0002] Sulfur dioxide (SO2) is a common air pollutant, and its emission not only threatens human health, but also causes serious harm to the environment. Converting SO2 into high-value-added chemical product hydrogen sulfide (H2S) through electrocatalytic technology can effectively reduce SO2 emissions and realize its resource utilization.

[0003] As an important chemical raw material, H2S is widely used in the production of organic and inorganic sulfides. It also plays an important role in environmental protection fields such as wastewater purification, sludge treatment and metal ion removal. In addition, H2S can also be used in fuel cells and sulfur preparation, reflecting its potential value in the energy field. Therefore, it is of great significance to develop an efficient, stable and economical method for converting SO2 to H2S.

[0004] In the prior art, 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, a Chinese patent (publication number: CN115354353A) discloses a method for preparing H2S by reducing SO2 based on a dual-electrode flow electrolytic cell. Although the current density and flux are improved, it still faces the problems of low mass transfer efficiency and easy flooding of electrodes.

[0005] In addition, a Chinese patent (publication number CN112725816A) discloses a method for preparing hydrogen sulfide by electrocatalytic reduction of sulfur dioxide and membrane separation. This method adds an acidification separation chamber for H2S to achieve H2S separation. However, this method still faces the following problems: 1. Dilute sulfuric acid needs to be added to the three cathode chambers described in this method, which faces the risk of waste acid leakage; 2. SO2 dissolves in the cathode liquid in the cathode chamber to produce SO3 2- , may enter the acidification chamber through the anion exchange membrane under the action of the electric field; 3. The electrolytic cell described in this method has a three-chamber structure, and uses anion exchange membranes and cation exchange membranes respectively, which increases the resistance of the electrolytic cell. Summary of the invention

[0006] In view of the problems of high cell pressure, limited reactants and easy flooding of gas diffusion electrodes in the process of electrocatalytic reduction of SO2 to prepare H2S in a liquid phase flow electrolytic cell in the prior art, the purpose of the present invention is to provide a method for pulse electrolysis of gaseous sulfur dioxide to produce hydrogen sulfide. This method uses a two-chamber flow electrolytic cell as an electrolysis system and adopts pulse current or pulse potential, so that gaseous SO2 can be directly used as a reactant for efficient catalytic reduction and conversion into hydrogen sulfide gas, and the adsorption and reduction process of sulfur dioxide is realized by the periodicity of pulse current or potential, thereby improving the conversion efficiency of SO2 to H2S and reducing energy consumption. At the same time, it breaks through the technical problem of limited mass transfer in liquid phase electrolysis, reduces the generation of waste salt and waste acid, avoids flooding of gas diffusion electrodes, and improves reaction stability. The method is simple to operate, low in cost, and is conducive to large-scale production.

[0007] In order to achieve the above technical objectives, the present invention provides a method for producing hydrogen sulfide by pulse electrolysis of gaseous sulfur dioxide, using a two-chamber flow electrolysis cell as an electrolysis system, the two-chamber flow electrolysis cell comprising an anode chamber and a cathode chamber, the anode chamber using an inert anode, the cathode chamber using a cathode loaded with a sulfur dioxide reduction catalytic material, the cathode chamber and the anode chamber being separated by a diaphragm, an electrolyte is introduced into the anode chamber and sulfur dioxide gas is introduced into the cathode chamber, a pulse current or a pulse potential is applied between the anode and the cathode for electrolysis, and the sulfur dioxide gas is catalytically reduced and converted into hydrogen sulfide.

[0008] like Figure 1 As shown in the figure: when low potential or low current is applied, SO2 and protons are adsorbed on the electrode surface and no reduction reaction occurs. When high potential or high current is applied, SO2 adsorbed by the electrode combines with protons and is reduced to H2S. The reaction on the electrode surface is regulated by periodic electric field intensity to achieve efficient generation of H2S. Figure 2 As shown: According to the linear voltammetric curves of the electrode under different SO2 concentrations, it can be seen that the starting trough potential of SO2 reduction under different SO2 concentrations is ~1.5V. As the potential continues to increase, the electrode current increases, and the SO2 reduction reaction tends to occur on the electrode surface; while at low potential or lower current, the electrode surface mainly adsorbs reactants.

[0009] The technical solution of the present invention directly uses SO2 gas as a reactant. The diffusion coefficient of SO2 in the gas (11.5 mm 2 / s) is much larger than the diffusion coefficient in the liquid phase (0.0015mm 2 / s), breaking the problem of limited reactant mass transfer. In addition, since the electrode is in direct contact with the proton membrane, the proton concentration on the electrode surface is high, providing the necessary proton-rich environment for the reduction of SO2 to achieve efficient generation of H2S.

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

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

[0012] The present invention adopts pulse current or voltage to electrolyze gaseous SO2, adsorbs SO2 by applying low potential (low current), and catalytically reduces SO2 by applying high potential (high current). Through this method of pulse controlled potential (current), efficient generation of H2S is achieved, the conversion efficiency of SO2 to H2S is improved, and energy consumption is reduced.

[0013] As a preferred solution, the diaphragm is a proton membrane or a bipolar membrane. The diaphragms are conventional commercial products.

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

[0015] As a preferred solution, the sulfur dioxide reduction catalytic material includes at least one of a metal element of copper, platinum or palladium, a metal sulfide of copper, platinum or palladium, and a metal selenide of copper, platinum or palladium. The preferred sulfur dioxide reduction catalytic materials are all catalytic materials known in the prior art that have high activity in electrocatalytic reduction of sulfur dioxide.

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

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

[0018] The electrolyte in the anode chamber of the present invention can be water or an aqueous solution, and the aqueous solution can contain an electrolyte that improves conductivity. The electrolyte mainly generates hydrogen protons through electrolysis to combine with sulfur anions reduced by the cathode to generate hydrogen sulfide gas.

[0019] Compared with the prior art, the technical solution of the present invention brings the following beneficial technical effects: 1) The present invention directly uses gaseous SO2 as a raw material for electrolytic reduction and conversion into H2S, which breaks through the problem of limited SO2 mass transfer in traditional liquid phase systems and solves the problem of difficulty in separating H2S due to flooding of the gas diffusion electrode.

[0020] 2) The present invention realizes the conversion of SO2 into H2S through pulse power supply, significantly reduces the voltage of the electrolytic cell, improves the H2S generation efficiency, and reduces energy consumption.

[0021] 3) The method of producing hydrogen sulfide by pulse electrolysis of gaseous sulfur dioxide in the present invention supports a variety of electrolyte and gas concentration conditions, reduces production costs by simplifying equipment design and operating process, and is suitable for industrial-scale application.

[0022] 4) The method of producing hydrogen sulfide by pulse electrolysis of gaseous sulfur dioxide of the present invention has a high potential application value. For example, there is low concentration of SO2 in the flue gas of non-ferrous smelting. If the flue gas is directly introduced into the electrolytic cell, the H2S produced 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the schematic diagram of the pulse electric field regulation reaction.

[0024] Figure 2 The linear voltammetric curves of the electrode under different SO2 concentrations.

[0025] Figure 3 Schematic diagram of an electrolytic cell for pulse electrolysis of gaseous sulfur dioxide to produce hydrogen sulfide.

[0026] Figure 4 is the Faraday efficiency of H2S in Examples 1, 2, 3 and 4.

[0027] Figure 5 is the H2S current density in Examples 1, 2, 3 and 4. DETAILED DESCRIPTION

[0028] The following examples are intended to further illustrate the present invention, but are not intended to limit the present invention. Corresponding adjustments and improvements made without departing from the concept of the present invention all fall within the scope of protection of the present invention.

[0029] Unless otherwise specified in the following examples, the chemical reagents used are conventional commercial products and are analytically pure. The experiment of pulse electrolysis of gaseous sulfur dioxide to produce hydrogen sulfide includes pulse potential and pulse current.

[0030] In the following examples, the CoNiS / CF catalyst was obtained by a two-step hydrothermal method. The preparation process was referred to the 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).

[0031] In the following examples, the electrolysis system is a two-chamber flow electrolysis cell, such as Figure 3 The two-chamber flow electrolysis cell comprises an anode chamber and a cathode chamber, wherein the anode chamber adopts an IrO2 / CP anode, and the cathode chamber adopts a CoNiS / CF cathode, wherein the cathode chamber and the anode chamber are separated by a commercial proton exchange membrane, H2O is introduced into the anode chamber and sulfur dioxide gas is introduced into the cathode chamber, and a pulse current or a pulse potential is applied between the anode and the cathode for electrolysis, and the sulfur dioxide gas is catalytically reduced and converted into hydrogen sulfide.

[0032] Comparative Example 1 Experiment on the production of hydrogen sulfide by direct current potential electrolysis of gaseous sulfur dioxide: CoNiS / CF was used as cathode, carbon paper loaded with iridium oxide was used as anode (denoted as IrO2 / CP), proton exchange membrane was used as diaphragm, and the electrode area was 1 cm 2 The SO2 concentration was 5%, the DC electrolysis was performed for 20 min, and the applied potential was 3 V. The Faraday efficiency of H2S was 48.14%, and the partial current density was 129.72 mA / cm 2 .

[0033] Example 1 Experiment on the production of hydrogen sulfide by pulse potential electrolysis of gaseous sulfur dioxide: CoNiS / CF was used as cathode, carbon paper loaded with iridium oxide was used as anode (denoted as IrO2 / CP), proton exchange membrane was used as diaphragm, and the electrode area was 1 cm 2 , SO2 concentration (volume concentration) is 5%, gas flow rate is 10 mL / min. Pulse period is 4 min, high potential time accounts for 50%. High potential 3V is applied for 2 min, low potential 2.5V is applied for 2 min. Faraday efficiency of H2S is 75.62% ( Figure 4 ), the current density is 229.74 mA / cm 2 ( Figure 5 ).

[0034] Example 2 CoNiS / CF was used as cathode, carbon paper loaded with iridium oxide was used as anode (denoted as IrO2 / CP), proton exchange membrane was used as diaphragm, and the electrode area was 1 cm 2 , SO2 concentration is 5%, gas flow rate is 10 mL / min. Pulse period is 4 min, high potential time accounts for 50%. High potential 4V is applied for 2 min, low potential 2.5V is applied for 2 min. Faraday efficiency of H2S is 66.11% ( Figure 4 ), the current density is 334.76 mA / cm 2 ( Figure 5 ).

[0035] Example 3 CoNiS / CF was used as cathode, carbon paper loaded with iridium oxide was used as anode (denoted as IrO2 / CP), proton exchange membrane was used as diaphragm, and the electrode area was 1 cm 2 , SO2 concentration is 5%, gas flow rate is 10 mL / min. Pulse period is 2 min, high potential time accounts for 50%. High potential 3V is applied for 1 min, low potential 2.5V is applied for 1 min. The Faraday efficiency of H2S is 76.97% ( Figure 4 ), the current density is 233.77 mA / cm 2 ( Figure 5 ).

[0036] Example 4 CoNiS / CF was used as cathode, carbon paper loaded with iridium oxide was used as anode (denoted as IrO2 / CP), proton exchange membrane was used as diaphragm, and the electrode area was 1 cm 2 , SO2 concentration is 5%, gas flow rate is 10 mL / min. Pulse period is 1 min, high potential time accounts for 50%. High potential 3V is applied for 30 s, low potential 2.5V is applied for 30 s. The Faraday efficiency of H2S is 88.14% ( Figure 4 ), the current density is 266.94 mA / cm 2 ( Figure 5 ).

[0037] Example 5 CoNiS / CF was used as cathode, carbon paper loaded with iridium oxide was used as anode (denoted as IrO2 / CP), proton exchange membrane was used as diaphragm, and the electrode area was 1 cm 2 , SO2 concentration is 5%, gas flow rate is 10 mL / min. Pulse period is 1 min, high potential time accounts for 50%. High current 200 mA is applied for 30 s, low potential 10 mA is applied for 30 s. The Faraday efficiency of H2S is 90.22%, and the partial current density is 94.73 mA / cm2 .

[0038] Example 6 CoNiS / CF was used as cathode, carbon paper loaded with iridium oxide was used as anode (denoted as IrO2 / CP), proton exchange membrane was used as diaphragm, and the electrode area was 1 cm 2 , SO2 concentration is 5%, gas flow rate is 10 mL / min. Pulse period is 1 min, high potential time accounts for 75%. High current 200 mA is applied for 45 s, low potential 10 mA is applied for 15 s. The Faraday efficiency of H2S is 90.07%, and the partial current density is 137.36 mA / cm 2 .

[0039] In summary, by optimizing the pulse electrolysis conditions, the present invention achieves efficient and low-cost gas-phase SO2 conversion to H2S, and has broad industrial application prospects.

Claims

1. A method for pulse electrolysis of gaseous sulfur dioxide to produce hydrogen sulfide, using a two-chamber flow electrolysis cell as an electrolysis system, the two-chamber flow electrolysis cell comprising an anode chamber and a cathode chamber, the anode chamber using an inert anode, the cathode chamber using a cathode loaded with a sulfur dioxide reduction catalytic material, the cathode chamber and the anode chamber being separated by a diaphragm, characterized in that: Electrolyte is introduced into the anode chamber and sulfur dioxide gas is introduced into the cathode chamber, and a pulse current or pulse potential is applied between the anode and the cathode for electrolysis, whereby the sulfur dioxide gas is catalytically reduced and converted into hydrogen sulfide.

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

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

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

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

7. A method for producing 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 membrane or bipolar membrane loaded with sulfur dioxide reduction catalytic material.

8. The method for producing hydrogen sulfide by pulse electrolysis of gaseous sulfur dioxide according to claim 7, characterized in that: The sulfur dioxide reduction catalytic material includes at least one of a metal element of copper, platinum or palladium, a metal sulfide of copper, platinum or palladium, and a metal selenide of copper, platinum or palladium.

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

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

Images