Photocatalytic oxidation of organics using a porous titanium dioxide membrane and an efficient oxidant

• US 5,779,912 A
• Filed: 01/31/1997
• Issued: 07/14/1998
• Est. Priority Date: 01/31/1997
• Status: Expired due to Term

• Current Assignee: Lynntech Power Systems Limited
• Original Assignee: Lynntech Incorporated
• Inventors: Hodko, Dalibor, Murphy, Oliver J., Gonzalez-Martin, Anuncia
• Primary Examiner(s): McCarthy, Neil
• Application Number:
  US08/791,599
• Time in Patent Office: 529 Days
• Field of Search: 210/748, 210/763, 422/186.3
• US Class Current: 210/748.14
• CPC Class Codes: B01D 2251/104 Ozone
• CPC Class Codes: B01D 2251/106 Peroxides
• CPC Class Codes: B01D 2255/20707 Titanium
• CPC Class Codes: B01D 53/864 Removing carbon monoxide or hydrocarbons
• CPC Class Codes: B01D 53/8668 Removing organic compounds not provided for in B01D53/8603 - B01D53/8665
• CPC Class Codes: B01J 19/123 Ultraviolet light
• CPC Class Codes: B01J 19/127 Sunlight; Visible light
• CPC Class Codes: B01J 19/2415 Tubular reactors
• CPC Class Codes: B01J 19/2475 Membrane reactors
• CPC Class Codes: B01J 2219/00067 Liquid level measurement
• CPC Class Codes: B01J 2219/00144 Sunlight; Visible light
• CPC Class Codes: B01J 2219/00162 controlling the pressure
• CPC Class Codes: B01J 2219/00164 controlling the flow
• CPC Class Codes: B01J 2219/0883 Gas-gas
• CPC Class Codes: B01J 35/30 characterised by their physical properties
• CPC Class Codes: B01J 35/39 Photocatalytic properties
• CPC Class Codes: B01J 8/009 Membranes, e.g. feeding or removing reactants or products to or from the catalyst bed through a membrane
• CPC Class Codes: C01B 3/38 using catalysts
• CPC Class Codes: C02F 1/325 Irradiation devices or lamp constructions
• CPC Class Codes: C02F 1/4672 by electrooxydation
• CPC Class Codes: C02F 1/722 : Oxidation by peroxides
• CPC Class Codes: C02F 1/725 : by catalytic oxidation
• CPC Class Codes: C02F 1/78 : with ozone C02F1/4672 takes precedence
• CPC Class Codes: C02F 2101/303 : Complexing agents
• CPC Class Codes: C02F 2101/322 : Volatile compounds, e.g. benzene
• CPC Class Codes: C02F 2101/363 : PCB's; PCP's
• CPC Class Codes: C02F 2201/009 : Apparatus with independent power supply, e.g. solar cells, windpower, fuel cells for electrolysis apparatus C02F2201/46165
• CPC Class Codes: C02F 2201/3223 : Single elongated lamp located on the central axis of a turbular reactor
• CPC Class Codes: C02F 2201/328 : Having flow diverters (baffles)
• CPC Class Codes: C02F 2305/10 : Photocatalysts
• CPC Class Codes: Y02A 20/212 : Solar-powered wastewater sewage treatment, e.g. spray evaporation
• CPC Class Codes: Y02P 20/52 : using catalysts, e.g. selective catalysts
• CPC Class Codes: Y02W 10/37 : using solar energy

Abstract

A method and apparatus for mineralizing organic contaminants in water or air provides photochemical oxidation in a unique two-phase or three-phase boundary system formed in each pore of a TiO₂ membrane in a photocatalytic reactor. In the three-phase system, gaseous oxidant, liquid contaminant, and solid semiconductor photocatalyst meet and engage in an efficient oxidation reaction. The porous membrane has pores which have a region wherein the meniscus of the liquid varies from the molecular diameter of water to that o f a capillary tube resulting in a diffusion layer that is several orders of magnitude smaller than the closest known reactors. The photocatalytic reactor operates effectively at ambient temperature and low pressures.

Claims

1. A process for oxidizing organic contaminants, comprising the steps of:

providing a fluid containing the organic contaminants over a photocatalyst disposed on a first surface of a porous substrate having pores therethrough to a second surface;

providing an oxidant to the second surface and through the pores of the porous substrate into contact with the photocatalyst on the first surface; and

exposing the photocatalyst to ultraviolet light.

2. The process of claim 1, wherein the photocatalyst comprises titanium dioxide.

3. The process of claim 1, wherein the photocatalyst comprises a titanium dioxide based binary oxide.

4. The process of claim 3, wherein the titanium dioxide based binary oxide is selected from TiO₂ /SiO₂, TiO₂ /ZrO₂, TiO₂ /SnO₂, TiO₂ /WO₃, TiO₂ /MoO₃, and mixtures thereof.

5. The process of claim 1, wherein the oxidant is selected from the group consisting of, oxygen, ozone, hydrogen peroxide and combinations thereof.

6. The process of claim 5, wherein:

the fluid flows through a fluid cell adjacent the first surface, the fluid cell comprising a UV transmission surface positioned to expose the photocatalyst, a fluid inlet, and a fluid outlet; and

the oxidant flows through an oxidant cell adjacent the second surface, the oxidant cell comprising an oxidant inlet.

7. The process of claim 6, wherein the ultraviolet light is provided by an ultraviolet source.

8. The process of claim 7, wherein the oxidant comprises between about 10% to about 18% by weight of electrochemically generated ozone.

9. The process of claim 8, wherein the ultraviolet source is solar light and the ultraviolet transmission surface of the fluid cell is a ultraviolet transmission surface of a solar photoreactor.

10. The process of claim 8, wherein the ultraviolet source is an ultraviolet lamp and the ultraviolet transmission surface of the fluid cell is an ultraviolet transmission surface of the ultraviolet lamp.

11. The process of claim 8, wherein the ultraviolet source is an ultraviolet lamp which includes the ultraviolet wavelength range of 220-280 nm and the ultraviolet transmission surface of the fluid cell is a ultraviolet transmission surface of the ultraviolet lamp.

12. The process of claim 1, further comprising, the step of:

providing a two-phase or three-phase interface between the solid photocatalyst the contaminant and the oxidant; and

oxidizing organic contaminants at the interface.

43. The process of claim 7, wherein the oxidant comprises hydrogen peroxide.

44. The process of claim 7, wherein the oxidant comprises a source of oxygen.

13. An apparatus for oxidizing organic contaminants, comprising:

a porous substrate comprising a first photocatalytic surface, a second surface and pores extending therethrough;

means for flowing a fluid containing organic contaminants over the first photocatalytic surface;

means for flowing an oxidant through the pores of the porous substrate into the flowing fluid; and

means for exposing the photocatalytic surface to ultraviolet light.

14. The apparatus of claim 13, wherein the photocatalytic surface comprises porous titanium dioxide.

15. The apparatus of claim 13, wherein the photocatalytic surface comprises a porous titanium dioxide based binary oxide.

16. The apparatus of claim 15, wherein the titanium dioxide based binary oxide is selected from TiO₂ /SiO₂, TiO₂ /ZrO₂, TiO₂ /SnO₂, TiO₂ /WO₃, TiO₂ /MoO₃, and mixtures thereof.

17. The apparatus of claim 13, wherein the oxidant is oxygen, ozone, hydrogen peroxide, or combinations thereof.

18. The apparatus of claim 14, wherein:

the means for flowing a fluid comprises a fluid cell adjacent the porous first photocatalytic surface, the fluid cell comprising a ultraviolet transmission surface positioned to expose the first photocatalytic surface to ultraviolet light, a fluid inlet, and a fluid outlet; and

the means for flowing the oxidant comprises an oxidant cell adjacent the second surface, the oxidant cell comprising an oxidant inlet.

19. The apparatus of claim 18, further comprising an oxidant source connected to the oxidant inlet, and an organic contaminant source connected to the fluid inlet.

20. The apparatus of claim 19, further comprising a ultraviolet source which exposes the first photocatalytic surface to ultraviolet light.

21. The apparatus of claim 20, wherein the oxidant source comprises an electrolytic cell which generates an oxygen stream comprising from about 10% to about 18% by weight of ozone.

22. The apparatus of claim 21, wherein the ultraviolet source is solar light and the ultraviolet transmission surface of the fluid cell is a ultraviolet transmission surface of a solar photoreactor.

23. The apparatus of claim 21, wherein the ultraviolet source is an ultraviolet lamp and the ultraviolet transmission surface is part of the ultraviolet lamp.

24. The apparatus of claim 21, wherein the ultraviolet source is an ultraviolet lamp which includes the ultraviolet wavelength range of 220-280 nm and the ultraviolet transmission surface of the fluid cell is a ultraviolet transmission surface of the ultraviolet lamp.

25. An apparatus for oxidizing organic contaminants, comprising:

a porous substrate having a photocatalyst disposed on one surface and pores extending therethrough;

a fluid cell adjacent the photocatalyst surface, the fluid cell comprising a fluid inlet, a fluid outlet, and a ultraviolet transmission surface positioned to expose the porous photocatalyst surface; and

an oxidant cell adjacent a second, opposed surface of the porous substrate, the oxidant cell comprising an oxidant inlet.

26. The apparatus of claim 25, wherein the photocatalyst surface comprises titanium dioxide.

27. The apparatus of claim 26, wherein the photocatalyst surface comprises a porous titanium dioxide based binary oxide.

28. The apparatus of claim 27, wherein the titanium dioxide based binary oxide is selected from TiO₂ /SiO₂, TiO₂ /ZrO₂, TiO₂ /SnO₂, TiO₂ /WO₃, TiO₂ /MoO₃, and mixtures thereof.

29. The process of claim 25, wherein the oxidant is oxygen, ozone, hydrogen peroxide, or combinations thereof.

30. The apparatus of claim 29, further comprising an oxidant source connected to the oxidant inlet, and an organic contaminant source connected to the fluid inlet.

31. The apparatus of claim 30, further comprising an ultraviolet source which exposes the photocatalyst surface to ultraviolet light.

32. The apparatus of claim 31, wherein the oxidant source comprises an electrolytic cell which generates an oxygen stream comprising from about 10% to about 18% by weight of ozone.

33. The apparatus of claim 32, wherein the ultraviolet source is solar light and the ultraviolet transmission surface of the fluid cell is an ultraviolet transmission surface of a solar photoreactor.

34. The apparatus of claim 32, wherein the ultraviolet source is an ultraviolet lamp and the ultraviolet transmission surface of the fluid cell is a ultraviolet transmission surface of the ultraviolet lamp.

35. The apparatus of claim 32, wherein the ultraviolet source is an ultraviolet lamp which includes the ultraviolet wavelength range of 220-280 nm.

36. The apparatus of claim 25, wherein the fluid inlet directs the oganic contaminant toward the porous photocatalyst surface.

37. A process for oxidizing organic contaminants, comprising the steps of:

introducing the organic contaminants over a first surface of a porous photocatalyst;

introducing an oxidant over an opposing surface of the porous photocatalyst; and

contacting the organic contaminants with the oxidant adjacent the first surface.

38. The process of claim 37, farther comprising the step of:

exposing the photocatalyst surface to ultraviolet light.

39. A photocatalytic reactor for oxidizing organic contaminants, comprising:

a substrate having first and second opposed faces and pores communicating between the faces, wherein at least the first face is photocatalytic;

a fluid cell communicating with the first face and allowing transmission of ultraviolet light onto the first face; and

an oxidant cell communicating with the second face.

40. The photocatalytic reactor of claim 39, wherein the substrate has sufficient porosity for passage of the oxidant.

41. The photocatalytic reactor of claim 39, wherein the substrate has a porosity between about 40 and about 70 percent.

42. The photocatalytic reactor of claim 39, further comprising a flow controller for controlling the amount of oxidant passing through the pores.