Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L2/00—Methods or apparatus for disinfecting or sterilising materials or objects other than foodstuffs or contact lenses; Accessories therefor
  • A61L2/02—Methods or apparatus for disinfecting or sterilising materials or objects other than foodstuffs or contact lenses; Accessories therefor using physical phenomena
  • A61L2/08—Radiation
  • A61L2/088—Radiation using a photocatalyst or photosensitiser
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J19/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
  • B01J19/12—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor employing electromagnetic waves
  • B01J19/122—Incoherent waves
  • B01J19/123—Ultraviolet light
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J19/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
  • B01J19/12—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor employing electromagnetic waves
  • B01J19/122—Incoherent waves
  • B01J19/127—Sunlight; Visible light
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/30—Treatment of water, waste water, or sewage by irradiation
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/30—Treatment of water, waste water, or sewage by irradiation
  • C02F1/32—Treatment of water, waste water, or sewage by irradiation with ultraviolet light
  • C02F1/325—Irradiation devices or lamp constructions
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/72—Treatment of water, waste water, or sewage by oxidation
  • C02F1/725—Treatment of water, waste water, or sewage by oxidation by catalytic oxidation
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L2202/00—Aspects relating to methods or apparatus for disinfecting or sterilising materials or objects
  • A61L2202/10—Apparatus features
  • A61L2202/16—Mobile applications, e.g. portable devices, trailers, devices mounted on vehicles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
  • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
  • B01J21/063—Titanium; Oxides or hydroxides thereof
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J2219/00761—Details of the reactor
  • B01J2219/00763—Baffles
  • B01J2219/00765—Baffles attached to the reactor wall
  • B01J2219/0077—Baffles attached to the reactor wall inclined
  • B01J2219/00772—Baffles attached to the reactor wall inclined in a helix
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J2219/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
  • B01J2219/0873—Materials to be treated
  • B01J2219/0881—Two or more materials
  • B01J2219/0884—Gas-liquid
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J2219/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
  • B01J2219/0873—Materials to be treated
  • B01J2219/0892—Materials to be treated involving catalytically active material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
  • B01J35/39—Photocatalytic properties
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
  • B01J35/56—Foraminous structures having flow-through passages or channels, e.g. grids or three-dimensional monoliths
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/0215—Coating
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/72—Treatment of water, waste water, or sewage by oxidation
  • C02F1/722—Oxidation by peroxides
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/72—Treatment of water, waste water, or sewage by oxidation
  • C02F1/727—Treatment of water, waste water, or sewage by oxidation using pure oxygen or oxygen rich gas
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/72—Treatment of water, waste water, or sewage by oxidation
  • C02F1/78—Treatment of water, waste water, or sewage by oxidation with ozone
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
  • C02F2103/02—Non-contaminated water, e.g. for industrial water supply
  • C02F2103/04—Non-contaminated water, e.g. for industrial water supply for obtaining ultra-pure water
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2201/00—Apparatus for treatment of water, waste water or sewage
  • C02F2201/32—Details relating to UV-irradiation devices
  • C02F2201/322—Lamp arrangement
  • C02F2201/3227—Units with two or more lamps
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2305/00—Use of specific compounds during water treatment
  • C02F2305/10—Photocatalysts

Definitions

• the present invention generally relates to a method and apparatus for the purification and disinfection of water. More specifically, the present invention relates to an apparatus and method of use of a semiconductor material for the photocatalytic degradation of organic and inorganic pollutants and microorganisms in water and ultrapure water 1 .
• the present invention is an apparatus and method incorporating a rigid, three-dimensionally open celled, fluid permeable, photocatalytic semiconductor unit.
• Heterogeneous photocatalysis is the general term that describes the technical approach, [Mills, A.; Le Hunte, S.; “An Overview of Semiconductor Photocatalysis,” J. PhotoChem. & PhotoBio. A: Chemistry 108 (1997) 1 - 35] and [Hoffman, M.R.; Martin, S.T.; Choi, W.; Bruemann, D.W.; “Environmental Applications of Semiconductor Photocatalysis,” Chem Rev 1995, 95, 69-96].
• the specific process is properly described as semiconductor-sensitized photomineralization of organics by oxygen. It may be summarized as:
• Ultrapure water refers to water pre-treated by methods known to those skilled in the art to remove suspended and dissolved inorganic and organic matter. interface, oxidation-reductionprocesses are initiated. These include:
• Uncertain reaction pathway resulting in the reduction of oxygen to various reactive species including:
• OH* the hydroxyl radical.
• the hydroxyl radical is an extremely potent oxidizing agent (redox potential of +2.8 V), capable of oxidizing almost all organic compounds.
• redox potentials for the more conventional oxidants chlorine and ozone are +1.36 and +2.07 V, respectively. Hydroxyl radicals also kill and breakdown microorganisms and endotoxins.
• TiO 2 is the most widely investigated because it is chemically stable, has a suitable bandgap structure for UV/Visible photoactivation, and is relatively inexpensive.
• TiO 2 exists in two principal crystalline forms: rutile and anatase.
• the rutile form of TiO 2 is widely used as a pigment and can be found in almost anything white — paint, paper, textiles, inks, plastics and cosmetics.
• Anatase the low temperature form (stable below ⁇ 600°C) is the most photoactive form.
• Nanoscale (5 — 50 nm) anatase particles with very high surface areas (50 - 5 ( 30 m 2 /gm) show high photoactivity when irradiated with UV light ( ⁇ 390nm) in the presence of water.
• a transition metal e.g., platinum, palladium, silver
• a variety of methods improve the quantum efficiency of TiO 2 by doping with various metals to extend the spectral response into the more efficient visible light wavelengths, [Borgarello, E. et al. "Visible Light Induced Water Cleavage in Colloidal Solutions of Chromium-Doped TiO 2 Particles," J. Am. Chem. Soc.1982, 104, 2996-3002] or to increase the minority carrier diffusion length, [Augustynski, J.; Hinden, J. Stalder, C; J. Electrochem. Soc.
• the reactor was illuminated with a 20 watt, black light UV fluorescent tube. He monitored the destruction of: salicylic acid, phenol, 2-chlorophenol, 4-chlorophenol, benzoic acid, 2- naphthol, naphthalene, and florescin in water, [J. Physical Chemistry 91 (1987) 3328-3333].
• U.S. Pat. No. 4,892,712 to Robertson et al. disclosed the attachment by the sol-gel process of anatase TiO 2 to a fiberglass mesh substrate.
• This mesh was wrapped around a light source contained within a quartz glass cylinder and emitting UV radiation in a wavelength range of 340 to 350 nanometers (nm).
• the entire structure was placed within a stainless steel cylinder containing fluid inlet and outlet ports thereby creating a reactor. Polluted water was passed through this reactor for purification.
• Robertson's mesh is not rigid, three- dimensionally open celled and lacks permanent bonding of the semiconductor to the mesh.
• Professor I. R. Bellobono prepared photocatalytic membranes immobilizing 23% of
• Titanium Dioxide (Degussa P-25). Controlled amounts of appropriate monomers and polymers, containing the semiconductor to be immobilized and photoinitiated by a proprietary photocatalytic system was photografted onto a non-woven polyester tissue. The final porosity of the photosynthesized membrane was regulated at 2.5-4.0 microns. He trade named this membrane "Photoperm”TM.
• a fluid containment structure surrounded the membrane creating a reactor. The reactor volume occupied by the fluid was 2.51iters (1) and the membrane surface area was 250 linear centimeters (cm 2 ). The reactor was illuminated with a cylindrical high-pressure mercury arc lamp at a power of 2 kilowatts (kW) and at a wavelength of 254nm.
• Cittenden, et al. discloses a method and apparatus for destroying organic compounds in fluids [The 1995 American Society of Mechanical Engineers (ASME) International Solar Energy Conference, Maui, Hawaii, USA].
• TiO 2 was attached by wash coating to a 35x60- mesh silica gel substrate. The substrate was placed within a plastic tube that allowed the penetration of UV light.
• Organic pollutants in a water stream passed axially through the tube. Natural light and/or artificial UV light oxidize the investigated organic pollutants.
• Cittenden' s invention is not three-dimensionally open celled, not durable, and has very limited fluid permeability.
• Anderson discloses a method to make ceramic titanium membranes by the sol-gel process. [J. Membrane Science 30 (1988) 243-258]. These membranes are porous and transparent to UV illumination. They are made from a titanium alkoxide and then fired to form the anatase crystalline structure. Unlike the present invention, Anderson's invention is not open celled, not three-dimensionally reticulated, not durable, and has very limited fluid permeability.
• the object of the present invention is to substantially improve upon the prior art to produce an effective, quantum efficient, durable, economic, commercial apparatus for the rapid photocatalytic purification and disinfection of water and ultrapure water.
• current technology struggles to achieve 2 parts-per-billion (ppb) in Total Organic Carbon (TOC). This represents a limit on the industry's ability to achieve further improvements in the chip density and speed.
• the present invention which achieves 500 parts-per-trillion (ppt) in TOC, or better, represents a breaktlirough for both the water purification and semiconductor industry.
• the invention also has profound implications for other water purification systems, including those related to environmental cleanup.
• the apparatus of the present invention involves a reactor apparatus and a method for its use for photo-promoted, catalyzed degradation of compounds in a fluid stream.
• the effectiveness of the process is determined in part by the mass transfer efficiency, which is the rate at which the contaminant is transported from the fluid stream to the photocatalytic surface where it can be destroyed. Mass transfer is greatly aided by proximity.
• the photocatalyst is widely and uniformly distributed in the volume of water to be treated, such that a contaminant is never far from a catalyst surface
• the present invention is the uniform illumination of the catalyst within the volume of water to be treated. Since the catalyst itself absorbs the light, its concentration in the volume is limited to allow sufficient penetration of the activating photons.
• the support structure does not block illumination of the volume of water to be treated. Thus, the volume fraction of support material is minimized and/or has high transparency to the activating photons.
• the substrate material is preferably made from glass or other materials transparent or semitransparent to the photoactivating wavelengths between 180nm and 700nm. This is possible using a rigid, three-dimensionally open celled photocatalytic semiconductor unit. In an embodiment which bonds or chemically integrates the substrate with the semiconductor, the unit is also preferably made from transparent or semitransparent materials.
• the water flow through the catalyst is turbulent to improve mixing and mass transfer rates between the organic contaminants and the oxidizing species generated at the catalyst surface. Laminar flow is largely avoided.
• the open celled structure utilized in a first preferred embodiment of the present invention substantially represents a breakthrough over the prior art and allows for the commercial use of photocatalytic technology in ultrapure water production because it optimizes mass transfer, surface area, illumination, water flow, durability, rigidity, and so forth.
• the photocatalytic semiconductor unit provides a high surface area, rigid structure on which the photocatalyst is deposited or into which it is incorporated.
• the interstitial struts forming the open celled structure of the photocatalytic semiconductor unit are relatively thin, so volume fraction of substrate support material is low and flow is not significantly restricted. The ramification and alignment of the struts with respect to the flow direction will generate tortuous flow paths and enhance mass transport.
• the rigidity of the support structure provides a stable base to permanently attach or incorporate a highly active TiO 2 surface.
• FIG. 1 is a partial cross-sectional side view in elevation showing a first preferred embodiment of a point-of-use reactor with LED's as the source of photoactivating light.
• FIG. 2A is a partial cross-sectional side view in elevation of a cylindrical tube reactor in which water flows in and passes radially through the open celled photocatalytic substrate and axially past the UV light source;
• FIG. 2B is a cross-sectional end view of the reactor of FIG. 2 A;
• FIG. 3 is a schematic drawing of a purification system that includes an air injection system for injecting gas into the water before it is introduced into the photocatalytic system;
• FIG. 4 is a view showing detail of the open celled photocatalytic semiconductor unit of the first preferred embodiment of the present invention.
• FIG. 5 is a partial cross-sectional perspective view of a reactor tube having an alternative semiconductor unit substrate structure
• FIG. 5 A is a partial cross-sectional side view in elevation showing detail of the surface topography of the substrate structure shown in FIG. 5;
• FIG. 6 is a schematic drawing of an experimental test system used to evaluate the performance of the present invention
• FIG. 7 shows the results of a flow rate optimization study
• FIG. 8 shows the comparison of the photocatalytic destruction of acetic acid over time for a fiberglass mat substrate and a three-dimensionally open celled photocatalytic semiconductor unit utilized in an embodiment of the present invention.
• FIG. 9 shows a comparison of the photocatalytic destruction of acetic acid over time for UV photolysing/mixed bed ion exchange system compared to the UV photolysing/mixed bed ion exchange plus an open celled semiconductor unit.
• the present invention is directed to the use of a photocatalytic semiconductor unit photo-actively charged with a semiconductor for use in a reactor apparatus and method for the purification and disinfection of water for the semiconductor industry, environmental cleanup, and for the home point-of-use market.
• the present invention discloses an apparatus and method for purifying water and ultrapure water that solves problems of the prior art by transporting water through a rigid, three dimensionally open-cell material characterized by an inert, porous, photoactivating light semitransparent, fluid permeable, high surface area substrate onto which a photocatalytic semiconductor layer is permanently bonded, into which it is incorporated, or of which it is fabricated.
• the material described in the present invention and the apparatus and method for its use in photocatalytic purification and disinfection of water and ultrapure water is further characterized by high contact efficiency turbulent fluid flow with relatively low pressure drop.
• the photocatalytic substrate is not open celled but nonetheless presents a large surface area over which the water flows and that also induces turbulent flow of the water through the system. It will be readily appreciated by those skilled in the art that the current invention can be used to purify water in manufacturing semiconductors and pharmaceuticals, in biotechnology, power plant water, bottled water, municipal water supplies, point-of-use, to name just a few examples.
• three dimensionally open-cell substrates made from a variety of materials are scientifically described and commercially available. Such materials, all of which may be suitable for use in the present invention, include alumina, titania, aluminum, gold, copper, metal alloys, carbon, silica, glass, quartz, organic polymers, silicon carbide, silicon nitride, boron nitride, zirconium, tungsten carbide, and many more.
• alumina titania
• aluminum gold, copper, metal alloys
• carbon silica, glass, quartz
• organic polymers silicon carbide, silicon nitride, boron nitride, zirconium, tungsten carbide, and many more.
• Custom substrates may also be made utilizing the stereolithograhic process or selective laser sintering or other methods familiar to those experienced in the art.
• the rigid, three-dimensionally open celled substrate utilized in a first preferred embodiment of the current invention possesses a highly variable surface, with an easily controlled surface roughness and a huge macro surface area, depending on the overall pore size from approximately 4 to 96 pores per linear centimeter (ppc), approximately 10 to 240 pores per linear inch (ppi).
• the concentrated yet compact surface area opens the possibility of using a great variety of attachment methods; such as, without being limited to, sol-gel process, ion assisted gun deposition ion beam sputtering, chemical vapor deposition, aerosol application, evaporation deposition, etc.
• Literature and the prior art explain the procedures necessary for the permanent bonding of TiO 2 to a substrate.
• sol-gel process refer to: U.S. Pat. No. 4,892,712 to Robertson; U.S. Pat. No. 6,013,372 to Hayakawa , et al., and U.S. Pat. No.
• the semiconductor layer may also be formed chemically in situ by oxidation of the underlying metal, either electrochemically or thermally or by chemical reaction. See for example Titanium Dioxide Film Electrodes Prepared by Thermal Oxidation, [J. Electrochem. Soc. 139, no. 7, (1992) 1803 by Choi Yong-kook et. al. and In Situ Raman Spectra of Anodically Formed Titanium Dioxide Layers in Solutions of H2SO4, KOH and HNO3, [J. Electrochem. Soc. 138 no. 10 (1991) 2964].
• the substrate is made of the same material as the semiconductor layer and the two materials are chemically integrated. This creates stable surface capable of withstanding tremendous turbulent flow. Photocatalytic activity of many semiconductor surfaces is enhanced by a process of doping or coating these surfaces with a variety of metals, including transition metals such as, but not limited to, platinum, palladium, ruthenium, iridium, rhodium, gold, silver, copper, tin, iron, cobalt, vanadium, niobium, and zinc. Combinations of these metals and their oxides, sulfides or other compounds are known to those experienced in these arts. By altering the doping of TiO 2 the band gap energy can be shifted to the visible spectrum (400nm-700nm).
• An enhancement of the preferred embodiment is a film made from the anatase form of TiO 2 in a usable grain size for particles from 1 to 30 nanometers in diameter.
• An active surface thickness can vary from 1 to 190 micrometers.
• Platinum was found to be effective dopant to increase activity when applied in the range of from 0.025 to 3% by weight of the titanium dioxide, though a range of 0.05 to 1% may be optimal.
• Platinum as specified above increased the TOC destruction activity by a factor of 2 to 3.
• a further enhancement of the dopant is a vanadium compound, such as vanadium pentoxide (0.1 to 15% by weight of the TiO 2 ) on a semiconductor such as TiO 2 , when used in combination with ozone. It increases the rate of destruction of TOC by a factor of 2-8 times. This enhancement applies in the dark as well as under illumination. This means that if light does not penetrate to the interior of the substrate, TOC will still be destroyed.
• a further enhancement of the first preferred embodiment of the apparatus and method of the present invention consists using a combination or set of open celled substrates, each with its own particular variety of parameters and enhancements and each designed to operate on a particular component of the TOC.
• one set may work on polar/non-polar components, while others work on hydrophobic/ hydrophilic components, aromatic/aliphatic components, alcoholic/acidic components and chemical/biological components.
• the members of the set are used in a series combination where water flows thru first one member and then another member.
• This enhancement enlarges the scope of the invention by bringing a complete collection of destruction capabilities to bear on combinations of contaminants, even though individual members of the set are alone incapable of achieving acceptable overall TOC destruction levels.
• Preferred light sources include, without being limited to low, medium and high- pressure mercury lamps, xenon lamps, and conventional and ultraviolet emitting LED's, or any other light source that activates the semiconductor by producing light at a wavelength of between 180 to 700 nm.
• Open celled photocatalytic semiconductor units Each cause turbulent water flow, and the open celled photocatalytic semiconductor unit, in particular, causes dramatically turbulent water flow, causing the water flowing through its pores to shear, thrashing from side to side within the pores, and to speed up and slow down according to the cross section of the pore openings. Further, it causes microturbulence within the pores themselves. Open celled photocatalytic semiconductor units provide many ways to control turbulence by adjusting pores sizes and pore distributions, pore wall formations and surface textures.
• known methods exist to grade the size of the pores so that they start large near the surface at approximately 4 ppc (-10 ppi), and then diminish in size towards the photocatalytic semiconductor unit interior at approximately 96 ppc (-240 ppi), thus providing tailored light guides.
• the water itself may be modified such as by adding microscopic gas bubbles (such as gaseous oxygen, ozone, or peroxides) to guide the light into the interior.
• the materials of construction of the photocatalytic semiconductor unit can be varied from reflective (metals) to opaque (TiO 2 , carbon, metals) to transparent (silica, alumina) to provide further control over the penetration of the photoactivating light.
• innovative designs can incorporate light guides including, but not limited to, light fibers, quartz blocks, voids, gaps and separations.
• FIG. 1 shows an example of a point-of-use reactor 10 with LED' s 12 as the photoactivating light.
• Contaminated source water flows into the reactor housing 14 through inlet 16. The water then flows through the open celled semiconductor unit 18 that is photoactivated by LED's 12.
• a support/wiring plate 20 holds the LED lights.
• a transparent plate 22 is provided to isolate the LED lights from the water flow. Purified water exits the reactor through outlet 24.
• the point-of-use reactor housingH can be constructed from a variety of thermoplastics (polyproplylene, etc), or metals (304 stainless steel, 316 stainless steel, etc), or other materials that are both inert to degradation by the LED light source and resistant to corrosion by water. Further, the enclosure may either be integral with the semiconductor unit or separable, the latter configuration preferable in cases where the removal and installation of a replaceable semiconductor unit is desired.
• the semiconductor unit defines a fluid passage 26 in fluid communication with inlet 16 and outlet 24.
• the point-of-use reactor can use an open celled semiconductor unit that is photoactivated by LED's that emit UV energy at 390 nm or lower.
• the point-of-use reactor can also use an open celled semiconductor unit that is doped to shift the band gap to visible wavelengths. In this reactor, an LED that emits visible wavelengths is utilized. This latter configuration enables a more efficient use of the LED energy.
• the point-of-use reactor is designed to be commercialized into markets defined by low and intermittent demand for purified water, such as potable water in the home.
• This reactor is superior to existing technologies because it uses only a small percentage of energy and it does not transmit heat to the product water while not in use (eliminating the need to rinse the system to ambient temperature prior to using product water).
• the reactor only requires low power electrical energy per LED, making it both safe for the user in an environment that includes water and electricity and enabling the reactor to be utilized in portable applications (e.g., battery or solar powered).
• FIG. 2A is a partial cross-sectional side view in elevation of a cylindrical tube reactor 30, suitable for commercial/industrial applications, having a generally elongate housing 32 into which water flows through inlet 34 and then passes radially through the open celled photocatalytic unit 36 and axially past a UV light source comprising tube type lamps 38 and 40 as the photoactivating light.
• FIG. 2B is an end view of the same commercial/industrial reactor 30.
• the open celled photocatalytic semiconductor unit 36 is a cylinder.
• Both the exterior photoactivating lights 38 and interior photoactivating lights 40 are tubes enclosed by cylindrical quartz sleeves 42. After contaminated source water flows into the reactor through inlet 34, it flows radially through the open celled semiconductor unit and passes by the exterior the photoactivating lights.
• the contaminated water flows axially through the reactor, through the substrate and over the photoactive surface, where the photoreactive surface is activated by both the exterior photoactivating lights and by the interior photoactivating lights.
• Purified water flows out through outlet 44.
• the commercial/industrial reactor is designed to be commercialized into markets defined by high and continuous demand for purified water.
• the configuration of the reactor is designed to be modular so that longer and/or parallel reactors can be employed for higher flows.
• Series reactors with different sets of open celled photocatalytic semiconductor unit specifications and/or different wavelengths for the exterior and interior photoactivating lights can be employed for custom purification of source water with different polar/non-polar components, hydrophobic/hydrophilic components, aromatic/aliphatic components, alcoholic/acidic components, and chemical/biological components.
• FIG. 3 is a schematic drawing of a water purification system 50 that includes a gas injection system 52 for injecting gaseous oxygen, ozone, or peroxides, and thereby modifying the water to facilitate the passage of light into the interior of the semiconductor unit.
• the gas injection system includes a gas supply, tank, or reservoir 54 in fluid communication with a mixing chamber 56 through a gas line 58.
• the mixing chamber is preferably a venturi.
• FIG.4 is a sectional view showing detail of an open celled photocatalytic semiconductor unit 70.
• the unit includes a plurality of differentially sized pores 72, with pore sizes ranging from 4 to 96 ppc (-10 to 240 ppi).
• FIG. 5 is a partial cross-sectional perspective view of a reactor tube having an alternative semiconductor unit substrate structure.
• the photocatalytic system 80 includes a reactor housing 82 having a water inlet end 84 and an outlet end 86.
• Running axially substantially the entire length of the housing are a plurality of tube-type lights 88 encased within quartz sleeves 90.
• the semiconductor unit of this embodiment promotes fluid flow over and around the photoactive surface area.
• the principle of action remains the same, as the substrate is coated or impregnated with a catalyst that promotes hydroxyl radical migration to the surface of the substrate when exposed to light of selected wavelengths. Contaminant molecules exposed to the surface are thus oxidized. It will be recognized that there are innumerable possible configurations of the semiconductor substrate.
• Such configurations may include, for example, a helical screw substrate 92 surrounding an axially disposed rod 96, as shown.
• a helical screw substrate 92 surrounding an axially disposed rod 96, as shown.
• surface contours or topography 98 including bumps, protrusions, corrugations, ridges, fins, flanges, mesh, three-dimensional matrices, as shown in Fig. 5 A.
• the thrust of the surface features is to enhance turbulent flow by creating counter-rotating vortices, cross-current mixing, division and recombination of water, and otherwise mixing and agitating the water stream.
• FIG. 6 is a schematic drawing of a laboratory water purification system 120 utilized in evaluating the present invention.
• the water system utilized for laboratory testing is configured to provide the flexibility required for a wide range of laboratory experiments.
• the exact volume of the water system is carefully measured.
• the feedwater for any experiment is added through a covered storage tank 122. Feedwater can range from typical point-of-use water to ultrapure water.
• An exact amount of organic impurities is also added through the storage tank. Since the water volume of the system is precisely known, the level of organics in an experiment can be mixed to a predetermined level and verified with the TOC analyzer 134.
• the system includes a pump 124, a rotometer 126, a throttling valve 128 to control system flow, an ultraviolet (UV) photolysing unit 130 with 185/254 nm UV lamps, a test chamber with a photocatalytic surface 132, a TOC analyzer 134, and a mixed bed ion exchange (MBIX) unit 136.
• Valves 138 are provided to isolate the UV photolysing unit 130; Valves 140 isolate the test cell and the test chamber 132; valves 142 isolate the MBLX unit; and shunt valves 143a-c allow the photolysing unitl30, the TOC analyzer 134, and the MBLX unit 136 to be selectively bypassed, either individually or in any combination.
• the TOC analyzer 134 measures TOC, temperature, and resistivity. The water from the TOC analyzer can be returned to the storage tank, or the same stream can be diverted to drain from the TOC analyzer if desired.
• the system enables testing of variables including, but not limited to feedwater water quality (including analysis, conductivity, temperature), feedwater TOC, system flow rate, choice of applying either 185/254 nm, 254 nm UV energy or no light energy at all, choice of applying the MBLX unit (including the choice of resins installed), a choice of the TOC analyzer utilized, the choice of the light source utilized to illuminate the photocatalytic surface (including wavelength, power, and the option to illuminate from multiple locations including 180 degrees), the choice to add microbubbles in the feedwater to the photocatalytic surface, and all of the possible choices and variations associated with the photocatalytic surface, including, but not limited to, material, surface preparation, surface coating, doping, size of pores, pore dispersion matrix, thickness of the ligaments, and the thickness of the photocatalytic surface.
• feedwater water quality including analysis, conductivity, temperature
• feedwater TOC system flow rate
• choice of applying either 185/254 nm, 254 nm UV energy or no light energy at all
• EXAMPLE 1 - Fig. 7 depicts TOC removal rate as a function of flow rate.
• the rigid 3- dimensional open celled semiconductor unit 99.5% alumina, 45 ppi, 1.5 inches in diameter by 0.50 inches thick
• a 2: 1 mixture of alumina sol and 35 nm particle TiO2 in the anatase form was placed in the photocatalytic reactor of the test loop of FIG. 6.
• Acetic acid was spiked through the tank 122 and the flow was adjusted with valve 128 and monitored with flow meter 126.
• the photocatalytic substrate was illuminated with 365 nm light at 3 milliwatts/cm 2 .
• the water was shunted past the ultraviolet (UV) photolysing unit 130 and MBIX unit 136 and passed through the photocatalytic reactor cell 132 which contains the photocatalytic semiconductor unit.
• the rate of oxidation of the acetic acid was monitored with a TOC analyzer 134 over time comparing two different flow rates.
• First order rates are compared among the different surfaces that have been tested to create a useful ranking of different surfaces and geometries.
• the first order rates are found to be significantly dependent on flow rates, which is related to the degree of turbulence and mixing that occurs. It is clear from FIG. 7. that peak effectiveness in this sample is found at a flow rate of 0.8 gpm with 14.3% TOC reduction in one hour compared to 9.2% TOC reduction at 0.5 gpm.
• EXAMPLE 2 - FIG. 8 compares the performance of a prior art substrate and the open celled semiconductor unit utilized in the present invention. It uses the same water loop configuration of FIG. 6. That is the water is shunted by the ultraviolet (UV) photolysing unit 130 and the MBIX unit 136.
• the photocatalytic surfaces compared are fused silica (20 ppi, 1.5 inches in diameter by 0.25 inches thick) and fiberglass mat. TiO 2 in the anatase form was deposited via sol gel techniques to the fused silica and the fiberglass mat. Both samples were platinum doped. Water was passed through the open celled fused silica and fiberglass mat at 1 gallon per minute (gpm) and illuminated at 3milliwatts/cm 2 at 365 nm wavelength.
• gpm gallon per minute
• FIG. 8 compares the fiberglass mat substrate to the fused silica open celled semiconductor unit.
• the open celled fused silica underwent 57% mineralization in 13 minutes while fiberglass mat had 11% mineralization in 13 minutes. Turbulent flow of water through the open celled semiconductor unit utilized in the present invention explains the better results. Even though the fiberglass mat is semitransparent to UV light and has more surface area than the open celled photocatalytic semiconductor unit, it does not induce or enhance turbulent mixing.
• EXAMPLE 3 In FIG. 9 water in laboratory water purification system 120 of FIG. 6 was spiked with acetic acid (10 ppb) through tank 122 and passed through an ultraviolet (UV) photolysing unit 130 and then a test chamber with a photocatalytic surface 132 utilized in the present invention and then through the MBLX unit 136 and monitored with a TOC analyzer 134.
• the test chamber with a photocatalytic surface 132 was illuminated with a 365nm (3 mW/cm2) light. The flow was 0.7 gpm.
• FIG. 9 shows the results. First the destruction of acetic acid was evaluated with the ultraviolet (UV) photolysing unit 130 and the MBLX unit 136 in operation. Next the destruction of acetic acid was evaluated with the same configuration plus a test chamber with a photocatalytic surface 132 contaimng the open celled semiconductor unit utilized in the present invention. With the ultraviolet (UV) photolysing unit 130 and the MBLX unit 136 in operation, the water reached a steady state barrier around 1.5 ppb TOC and then started to climb. While TOC in the water passing through the ultraviolet (UV) photolysing unit 130 and the MBIX unit 136 in operation plus the photocatalytic open celled reactor with good light penetration, turbulent flow, and high surface area was reduced to 0.50 ppb.
• UV ultraviolet
• the essential method of using the above-described apparatus for photocatalytic degradation of organic, inorganic, and microbiological contaminants in a fluid stream involves the following steps: (1) providing a reactor enclosure having a water inlet and a water outlet; providing at least one semiconductor unit, disposed within the reactor enclosure and interposed between, and in fluid communication with, the water inlet and the water outlet, and with which the fluid stream comes into contact, wherein the semiconductor unit includes a substrate having a photoreactive semiconductor surface fabricated of semiconductor material; (2) providing a light emitting means in optical proximity to the semiconductor surface for promoting electrons from the valance band to the conduction band of the semiconductor material; and (3) directing a fluid stream over the semiconductor surface while engaging the light emitting means to photactivate the semiconductor surface, whereby contaminants are removed from the fluid stream by photocatalytic reaction.

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