PHOTOCATALYTIC OXIDATION OF HYDROGEN CHLORIDE WITH OXYGEN

Abstract

The invention relates to a method for the production of chlorine by means of photocatalytic oxidation of gaseous hydrogen chloride with oxygen as an oxidizing agent, in which the reaction is started on the surface of a photocatalyst by the action of UV radiation in a selective energy range.

Claims

1.-12. (canceled)

13. A method for heterogeneously photocatalyzed oxidation of hydrogen chloride by means of UV radiation, wherein a gas mixture composed of at least hydrogen chloride, oxygen and optionally further minor constituents is produced and is passed over a solid photocatalyst and the reaction is started on the surface of the catalyst by exposure to UV radiation in a selective energy range.

14. The method as claimed in claim 13, wherein the photocatalyst comprises at least one photoactive material such as a transition metal or transition metal oxide or a semiconductor material.

15. The method as claimed in claim 14, wherein the photocatalyst comprises, as additional catalytic active component (co-catalyst), metals of transition groups 1, 7 or 8 of the Periodic Table of the Elements or oxides, oxychlorides or chlorides of the metals of transition groups 1, 3, 6, 7 or 8, or mixtures of these metals or metal compounds.

16. The method as claimed in claim 14, wherein the photocatalyst as photoactive material comprises one or more compounds selected from the series: AlCuO.sub.2, Al.sub.xGa.sub.yIn.sub.1-x-yN, Al.sub.xIn.sub.1-xN, AlN, B.sub.6O, BaTiO.sub.3, CdS, CeO.sub.2, Fe.sub.2O.sub.3, GaN, Hg.sub.2SO.sub.4, In.sub.xGa.sub.1-xN, In.sub.2O.sub.3, KTaO.sub.3, LiMgN, NaTaO.sub.3, Nb.sub.2O.sub.5, NiO, PbHfO.sub.3, PbTiO.sub.3, PbZrO.sub.3, Sb.sub.4Cl.sub.2O.sub.5, Sb.sub.2O.sub.3, SiC, SnO.sub.2, SrCu.sub.2O.sub.2, SrTiO.sub.3, TiO.sub.2, WO.sub.3, ZnO, ZnS, ZnSe.

17. The method as claimed in claim 13, wherein the photocatalytic HCl oxidation with UV radiation is conducted at elevated pressure, particularly at a pressure of up to 25 bar.

18. The method as claimed in claim 13, wherein the reaction temperature of the photocatalytic HCl oxidation with UV radiation is at most 250? C.

19. The method as claimed in claim 13, wherein the photocatalytic HCl oxidation is combined with one or more other types of HCl oxidation reactions selected from the series: catalytic gas phase oxidation, thermal gas phase oxidation and electrolysis of HCl gas, and is conducted downstream as a further stage to the one or more other HCl oxidation reactions.

20. The method as claimed in claim 19, wherein the other HCl oxidation reaction applied is the catalyzed oxidation reaction of hydrogen chloride with gases comprising oxygen.

21. The method as claimed in claim 19, wherein firstly the major portion of the HCl oxidation is conducted in the other catalyzed oxidation process, in particular up to an HCl conversion of at least 70%, which is upstream of the photocatalyzed HCl oxidation with UV radiation.

22. The method as claimed in claim 13, wherein the UV radiation for the photocatalyzed oxidation encompasses an energy range from 3.2 to 4 eV.

23. The method as claimed in claim 13, wherein the co-catalyst used for the photocatalyzed oxidation is one or more catalysts selected from the series: ruthenium oxide, ruthenium chloride and ruthenium oxychloride.

24. The method as claimed in claim 13, wherein a UV LED lamp is used as UV light source of the UV radiation.

Description

EXAMPLES

Example 1 (Inventive)

[0054] A catalyst consisting of ruthenium oxide supported on titanium dioxide was charged in a fixed bed in an annular gap quartz photoreactor (annular gap diameter 7 mm) and a gas mixture of 0.25 L/h (standard conditions STP) hydrogen chloride, 1 L/h (STP) oxygen and 10 L/h nitrogen (STP) were passed therethrough at room temperature. The quartz photoreactor was irradiated externally with a 5 m UV LED light band (12 W/meter) with UV light of the wavelength 365 nm. After 1 h, the product gas stream was passed into a 30% by weight potassium iodide solution for 15 min. The iodine formed was then back-titrated with 0.1N thiosulfate standard solution to determine the amount of chlorine introduced. A hydrogen chloride conversion of 90.1% was measured.

Example 2 (Comparative Example)

[0055] A catalyst consisting of ruthenium oxide supported on titanium dioxide was charged in a fixed bed in an annular gap quartz photoreactor (annular gap diameter 7 mm) and a gas mixture of 1 L/h (standard conditions STP) hydrogen chloride, 4 L/h (STP) oxygen and 5 L/h nitrogen (STP) were passed therethrough at room temperature. No UV light was irradiated into the reactor. After 2 h, the product gas stream was passed into a 30% by weight potassium iodide solution for 30 min. The iodine formed was then back-titrated with 0.1 N thiosulfate standard solution to determine the amount of chlorine introduced. A hydrogen chloride conversion of 0.0% was measured.

Example 2 (Comparative Example)

[0056] Titanium dioxide (DMS2005-0260) was charged in a fixed bed in an annular gap quartz photoreactor (annular gap diameter 7 mm) and a gas mixture of 1 L/h (standard conditions STP) hydrogen chloride, 4 L/h (STP) oxygen and 5 L/h nitrogen (STP) were passed therethrough at room temperature. The quartz photoreactor was irradiated externally with a 5 m UV LED light band (12 W/meter) with UV light of the wavelength 365 nm. After 2 h, the product gas stream was passed into a 30% by weight potassium iodide solution for 30 min. The iodine formed was then back-titrated with 0.1 N thiosulfate standard solution to determine the amount of chlorine introduced. A hydrogen chloride conversion of 0.2% was measured.