METHOD FOR PREPARING HYDROGEN SULFIDE FROM SULFUR DIOXIDE BY ELECTROCHEMICAL REDUCTION

Abstract

A method for preparing hydrogen sulfide from sulfur dioxide by electrochemical reduction includes electrochemically reducing sulfur dioxide absorbed in an aqueous solution into gaseous hydrogen sulfide with a membrane electrode, resulting in efficient and selective conversion of the sulfur dioxide absorbed in the aqueous solution into the hydrogen sulfide to avoid a deactivation of a cathode due to colloidal sulfur produced on the cathode and adhesion onto a surface of the cathode, wherein the method is carried out at ambient temperature and normal pressure without addition of a reducing agent, having no waste salts produced, and is simple in operation, and is convenient for large-scale application.

Claims

1. A method for preparing hydrogen sulfide from sulfur dioxide by an electrochemical reduction, comprising electrochemically reducing the sulfur dioxide absorbed in an aqueous solution into gaseous hydrogen sulfide with a membrane electrode, wherein the membrane electrode is a porous membrane with a catalytic function.

2. The method according to claim 1, wherein the porous membrane with the catalytic function is composed of a porous hydrophobic membrane substrate and at least one of elemental metal, metal sulfide, and metal selenide as catalytic materials supported on a surface of the porous hydrophobic membrane substrate, or the porous membrane with the catalytic function is composed of a material with the catalytic function and a surface hydrophobic function.

3. The method according to claim 2, wherein the porous hydrophobic membrane substrate is composed of a porous hydrophobic material, or is composed of a porous material with a surface hydrophobic treatment; the elemental metal is at least one selected from the group consisting of lead, copper, cobalt, iron, nickel, gold, silver, platinum, and palladium; the metal sulfide is at least one selected from the group consisting of lead sulfide, copper sulfide, cobalt sulfide, iron sulfide, nickel sulfide, gold sulfide, silver sulfide, platinum sulfide, and palladium sulfide; and the metal selenide is at least one selected from the group consisting of lead selenide, copper selenide, cobalt selenide, iron selenide, nickel selenide, gold selenide, silver selenide, platinum selenide, and palladium selenide.

4. The method according to claim 3, wherein the porous hydrophobic material is at least one selected from the group consisting of PTFE, PEEK, PP, PE, a carbon cloth, and a porous carbon paper; and the porous material with the surface hydrophobic treatment is a porous material with a surface modified by hydrophobic macromolecules or hydrophobic micromolecules, or is a porous material with a hydrophobic surface processed in a micro-nano scale.

5. The method according to claim 2, wherein the material with the catalytic function and the surface hydrophobic function is a carbon cloth, a porous carbon paper, or a porous metal material with a surface hydrophobic treatment.

6. The method according to claim 1, wherein the electrochemical reduction of the sulfur dioxide absorbed in the aqueous solution is carried out by using a three-electrode system with the aqueous solution absorbed with the sulfur dioxide as a cathode compartment electrolyte and the membrane electrode as a working electrode.

7. The method according to claim 1, wherein the aqueous solution absorbed with the sulfur dioxide is obtained by absorbing the sulfur dioxide into lye or water, or the aqueous solution absorbed with the sulfur dioxide is obtained by injecting sulfur dioxide microbubbles into an acid electrolyte.

8. The method according to claim 1, wherein a pH of the aqueous solution absorbed with the sulfur dioxide is adjusted to be less than 5 during the electrochemical reduction.

9. The method according to claim 6, wherein a potential of the working electrode is controlled to −0.1 V to −2.0 V versus a reference electrode during the electrochemical reduction.

10. The method according to claim 2, wherein the electrochemical reduction of the sulfur dioxide absorbed in the aqueous solution is carried out by using a three-electrode system with the aqueous solution absorbed with the sulfur dioxide as a cathode compartment electrolyte and the membrane electrode as a working electrode.

11. The method according to claim 3, wherein the electrochemical reduction of the sulfur dioxide absorbed in the aqueous solution is carried out by using a three-electrode system with the aqueous solution absorbed with the sulfur dioxide as a cathode compartment electrolyte and the membrane electrode as a working electrode.

12. The method according to claim 4, wherein the electrochemical reduction of the sulfur dioxide absorbed in the aqueous solution is carried out by using a three-electrode system with the aqueous solution absorbed with the sulfur dioxide as a cathode compartment electrolyte and the membrane electrode as a working electrode.

13. The method according to claim 5, wherein the electrochemical reduction of the sulfur dioxide absorbed in the aqueous solution is carried out by using a three-electrode system with the aqueous solution absorbed with the sulfur dioxide as a cathode compartment electrolyte and the membrane electrode as a working electrode.

14. The method according to claim 6, wherein the aqueous solution absorbed with the sulfur dioxide is obtained by absorbing the sulfur dioxide into lye or water, or the aqueous solution absorbed with the sulfur dioxide is obtained by injecting sulfur dioxide microbubbles into an acid electrolyte.

15. The method according to claim 6, wherein a pH of the aqueous solution absorbed with the sulfur dioxide is adjusted to be less than 5 during the electrochemical reduction.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] The following examples are used to further illustrate the present invention, but not to limit the protection scope of the claims of the present invention.

[0025] In the following examples, sulfur dioxide absorbed in an aqueous solution was electrochemically reduced by using a three-electrode system, the cathode and anode compartments of the three-electrode system were separated by the DuPont N117 proton exchange membrane, the electrolyte in the cathode compartment was a sodium hydroxide solution absorbing sulfur dioxide, the electrolyte in the anode compartment was a Na.sub.2SO.sub.4/H.sub.2SO.sub.4 mixed solution, a membrane electrode was used as a working electrode, Pt was used as a counter electrode, Hg/Hg.sub.2SO.sub.4 was used as a reference electrode, and a reduction potential may be −1.2 V to −1.8 V (vs SCE).

[0026] The preparation of Au/PTFE membrane electrode in the following examples was as follows. An Au catalyst was supported on a PTFE porous membrane (commodity raw material purchased directly) substrate by magnetron sputtering with specific parameters: vacuum level below 1.3×10.sup.−4 Pa, sputtering rate 10000 Å/min, substrate temperature 150° C., cathode voltage 420 V, electric current 13 A, sputtering vacuum 1 Pa, and sputtering time 6 min.

[0027] The preparation of CoS.sub.2/PTFE membrane electrode in the following examples was as follows. CoS.sub.2 and carbon black was directly dispersed in an ethanol solvent to form an ink with a concentration of 10% w/w, the ink was loaded on the surface of the PTFE porous membrane substrate by spraying in 1 mg/cm.sup.2 and then dried, to obtain the CoS.sub.2/PTFE membrane electrode.

[0028] The preparation of hydrophobic carbon paper in the following examples was as follows. Carbon paper was soaked in an ethyl acetate solution with 1% v/v octadecanethiol for 4 min and then air dried.

[0029] In the following examples, unless otherwise specified, the chemical reagents used are all conventional commercially available analytical reagents.

Comparative Example 1

[0030] 10 mL of aqueous solution absorbed with sulfur dioxide (with 0.1 mol/L of SO.sub.2) was taken into the cathode compartment as the cathode electrolyte, 10 mL of aqueous sodium sulfate (0.1 mol/L) was used as the anode electrolyte, and the pH of the cathode and anode electrolytes was adjusted to 0.5 with sulfuric acid. There was no hydrogen sulfide produced after electrolysis was carried out with the reduction potential of −0.8 V using the Au/PTFE membrane electrode as the working electrode. It indicates from the comparative example that there is no hydrogen sulfide produced with the reduction potential of −0.8 V.

Example 1

[0031] 10 mL of aqueous solution absorbed with sulfur dioxide (with 0.1 mol/L of SO.sub.2) was taken into the cathode compartment as the cathode electrolyte, 10 mL of aqueous sodium sulfate (0.1 mol/L) was used as the anode electrolyte, and the pH of the cathode and anode electrolytes was adjusted to 0.5 with sulfuric acid. There was hydrogen sulfide produced with a Faraday efficiency of 99.56% after electrolysis was carried out with the voltage of −1.2 V using the Au/PTFE membrane electrode as the working electrode.

Example 2

[0032] 10 mL of aqueous solution absorbed with sulfur dioxide (with 0.1 mol/L of SO.sub.2) was taken into the cathode compartment as the cathode electrolyte, 10 mL of aqueous sodium sulfate (0.1 mol/L) was used as the anode electrolyte, and the pH of the cathode and anode electrolytes was adjusted to 0.5 with sulfuric acid. There was hydrogen sulfide produced with a Faraday efficiency of 97.93% after electrolysis was carried out with the reduction potential of −1.4 V using the Au/PTFE membrane electrode as the working electrode.

Example 3

[0033] 10 mL of aqueous solution absorbed with sulfur dioxide (with 0.1 mol/L of SO.sub.2) was taken into the cathode compartment as the cathode electrolyte, 10 mL of aqueous sodium sulfate (0.1 mol/L) was used as the anode electrolyte, and the pH of the cathode and anode electrolytes was adjusted to 0.5 with sulfuric acid. There was hydrogen sulfide produced with a Faraday efficiency of 89.93% after electrolysis was carried out with the reduction potential of −1.6 V using the Au/PTFE membrane electrode as the working electrode.

Example 4

[0034] 10 mL of aqueous solution absorbed with sulfur dioxide (with 0.1 mol/L of SO.sub.2) was taken into the cathode compartment as the cathode electrolyte, 10 mL of aqueous sodium sulfate (0.1 mol/L) was used as the anode electrolyte, and the pH of the cathode and anode electrolytes was adjusted to 0.5 with sulfuric acid. There was hydrogen sulfide produced with a Faraday efficiency of 79.29% after electrolysis was carried out with the reduction potential of −1.8 V using the Au/PTFE membrane electrode as the working electrode.

Example 5

[0035] 10 mL of aqueous solution absorbed with sulfur dioxide (with 0.1 mol/L of SO.sub.2) was taken into the cathode compartment as the cathode electrolyte, 10 mL of aqueous sodium sulfate (0.1 mol/L) was used as the anode electrolyte, and the pH of the cathode and anode electrolytes was adjusted to 0.1 with sulfuric acid. There was hydrogen sulfide produced with a Faraday efficiency of 75.22% after electrolysis was carried out with the reduction potential of −1.4 V using the Au/PTFE membrane electrode as the working electrode.

Comparative Example 2

[0036] To show the advantages of hydrogen sulfide production with the Au/PTFE membrane electrode, the electrocatalytic performance of Au foil was tested under the same conditions.

[0037] 10 mL of aqueous solution absorbed with sulfur dioxide (with 0.1 mol/L of SO.sub.2) was taken into the cathode compartment as the cathode electrolyte, 10 mL of aqueous sodium sulfate (0.1 mol/L) was used as the anode electrolyte, and the pH of the cathode and anode electrolytes was adjusted to 0.1 with sulfuric acid. There were elemental sulfur produced with a Faraday efficiency of 80.11% and hydrogen sulfide produced with a Faraday efficiency of 4.85% after electrolysis was carried out with the reduction potential of −1.4 V using the Au foil as the working electrode.

Example 6

[0038] 10 mL of aqueous solution absorbed with sulfur dioxide (with 0.1 mol/L of SO.sub.2) was taken into the cathode compartment as the cathode electrolyte, 10 mL of aqueous sodium sulfate (0.1 mol/L) was used as the anode electrolyte, and the pH of the cathode and anode electrolytes was adjusted to 0.5 with sulfuric acid. There was hydrogen sulfide produced with a Faraday efficiency of 95.30% after electrolysis was carried out with the reduction potential of −1.4 V using the hydrophobic carbon paper as the working electrode.

Example 7

[0039] 10 mL of aqueous solution absorbed with sulfur dioxide (with 0.1 mol/L of SO.sub.2) was taken into the cathode compartment as the cathode electrolyte, 10 mL of aqueous sodium sulfate (0.1 mol/L) was used as the anode electrolyte, and the pH of the cathode and anode electrolytes was adjusted to 0.5 with sulfuric acid. There was hydrogen sulfide produced with a Faraday efficiency of 96.10% after electrolysis was carried out with the reduction potential of −1.4 V using the CoS.sub.2/PTFE membrane electrode as the working electrode.

Example 8

[0040] 10 mL of aqueous solution absorbed with sulfur dioxide (with 0.1 mol/L of SO.sub.2) was taken into the cathode compartment as the cathode electrolyte, 10 mL of aqueous sodium sulfate (0.1 mol/L) was used as the anode electrolyte, and the pH of the cathode and anode electrolytes was adjusted to 0.5 with sulfuric acid. There was hydrogen sulfide produced with a Faraday efficiency of 92.50% after electrolysis was carried out with the reduction potential of −1.3 V using the copper-plated titanium fiber mesh after hydrophobic treatment as the working electrode.

Comparative Example 3

[0041] 10 mL of aqueous solution absorbed with sulfur dioxide (with 0.1 mol/L of SO.sub.2) was taken into the cathode compartment as the cathode electrolyte, 10 mL of aqueous sodium sulfate (0.1 mol/L) was used as the anode electrolyte, and the pH of the cathode and anode electrolytes was adjusted to 0.5 with sulfuric acid. There were sulfur mainly produced and hydrogen sulfide produced with a Faraday efficiency of 21.36% after electrolysis was carried out with the reduction potential of −1.3 V directly using the copper-plated titanium fiber mesh as the working electrode, and there was liquid seepage on the surface of the electrode during the electrolysis.

Example 9

[0042] The aqueous solution absorbed with sulfur dioxide (0.1 mol/L of SO.sub.2) with pH=0.5 was used as the cathode electrolyte, and the aqueous sodium sulfate (0.1 mol/L) was used as the anode electrolyte. The Au/PTFE membrane electrode was used as the working electrode (7 cm×7 cm), and the Pt/C gas diffusion electrode was used as the counter electrode (7 cm×7 cm). SO.sub.2 electrolysis was carried out by using a (10 cm×10 cm) flow electrolytic cell. An experimental bipolar membrane in the flow electrolytic cell was used as a membrane for separating the cathode and anode compartments. The distance between the bipolar membrane and the counter electrode was 0 mm, and the distance between the bipolar membrane and the working electrode was 1 mm. The circulation flow rate of the electrolytes in the cathode and anode compartments was 5 mL/min. At the working voltage of −1.4 V (versus reference electrode), the Faraday efficiency of hydrogen sulfide produced by electrolysis was 95.86%, the current density was 38.1 mA/cm.sup.2, there was no attenuation after continuous electrolysis for 50 h, and the separation rate of hydrogen sulfide was 98.1%.