Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – With means applying electromagnetic wave energy or...
Reexamination Certificate
2000-03-22
2001-11-13
Mayekar, Kishor (Department: 1741)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
With means applying electromagnetic wave energy or...
C210S748080
Reexamination Certificate
active
06315963
ABSTRACT:
FIELD OF THE INVENTION
Ultraviolet (UV) reaction chambers are typically employed in the ultra-purification of water as well as in the conditioning of other fluids generally. Such “sanitization” or “disinfection” processes typically entail microbial destruction, total organic content (TOC) reduction, and ozone destruction. In the absence of a catalyst, these reactions are commonly referred to as photolytic reactions. Carried out in the presence of a catalyst, these reactions are known as photocatalytic reactions.
Photocatalytic reactions are heterogeneous or homogenous chemical reactions that take place on semiconductor surfaces in the presence of an energy source sufficient to overcome the Energy Gap of the semiconductor material to promote electron and hole mobility within the valence and conductance bands of the semiconductor material. Mobile electrons and holes react with chemical species in fluids to promote desirable alterations of those chemical species. Classical reactions take place in aqueous solutions where the semiconductor material produces hydroxyl and peroxide species to mineralize organic compounds to carbon dioxide, water, and inorganic acids. These “redox” reactions reduce metals from an oxidized state to a metallic form which are then absorbed onto a porous catalyst surface. In a much broader sense, such chemical processes are useful for the treatment or “conditioning” of fluids.
The subject invention relates generally to treatment of fluids via both photolytic and photocatalytic reactions, and to a method and apparatus for the enhancement of said fluid treatment, in particular. More specifically, the subject invention relates to a novel substrate capable of insertion into existing UV reaction chambers to enhance photolytic reactivity, and to the selection and application of photocatalytic materials onto said substrate to enhance photocatalytic reactivity.
BACKGROUND OF THE INVENTION
Photocatalysis belongs to the family of Advanced Oxidation Processes (AOP) that utilize an oxidant species to break carbon bonds with other carbon atoms, nitrogen, chlorine, sulfur, fluorine and other elements. The array of species that have been affected by photocatalysis in laboratory studies include, inter alia, simple organic compounds, chlorinated organic compounds, petroleum products, municipal wastewater, metal-containing photographic by-products, bacteria and viruses.
AOPs can either use an oxidant alone, or may be used in conjunction with a catalyst to promote its desired effect. Common stand-alone AOPs for the purpose of treating aqueous fluids are ozonation and combustion. Catalytic AOPs include hydrogen peroxide and a metal in the presence of ultraviolet (UV) light to promote hydroxyl radicals. This combination is commonly referred to as Fenton's Reagent. UV, at times, is considered an AOP. There are documented processes that utilize UV with ozone, or with hydrogen peroxide for the purpose of treating water and wastewater for organic destruction and disinfection.
Photocatalysis is an AOP based on a solid semiconductor material that is bombarded with UV radiation to excite the electrons and holes within the semiconductor material to produce oxidation-reduction (redox) reactions.
Two methods of photocatalysis have been suggested in literature. The first concerns the formation of free radicals. Electron-hole pairs migrate to the surface of the catalyst and react with hydroxyl ions (OH•) and dissolved oxygen (O
2
) to form hydroxyl radicals (OH.) in solution. Hydroxyl radicals then react with organic substrates in the fluid to oxidize them. Hydroxyl radicals have the highest oxidizing strength of common oxidizing species such as ozone, peroxide, and chlorine-based compounds.
The second method, a method most widely confirmed, is similar with electron, hole and hydroxyl reactions, but they take place on the catalyst surface with the absorbed organic species. As discussed, there are redox reactions taking place. At the anodic area (oxidizing) of the catalyst, holes are reacting with water to create hydroxyl radicals, and the organic species and their intermediate products. At the cathodic area (reducing) of the catalyst, the electrons are reacting with the oxygen to reduce it to the superoxide species, which in turn reacts with holes to assist in the organic matter oxidation. Precious metals that are metallized to the semiconductor (in areas not illuminated) aid in the reducing reactions at the cathodic area. It has also been shown in literature that precious metals act as oxidizers when in the illuminated area of the catalyst.
The art is often described in terms of either a suspended/slurried photocatalyst or a fixed photocatalyst. Suspended catalysts are those utilizing fine particles of a semiconductor material, generally to increase catalyst surface area. U.S. Pat. No. 5,589,678 (Butters, et al) provides a description of photocatalytic slurries. Suspended catalysts are limited to maximum concentrations in the fluid since they (1) increase turbidity, (2) absorb light, and (3) refract light, thus decreasing overall UV transmission in an illuminated reactor.
Fixed catalysts, to which the subject invention are directed, employ a singular or multi-pieced support or substrate to which the photocatalyst is applied. Fixed catalysts have been perceived as having less overall catalyst surface area then suspended catalysts, but do not require removal and recovery of the suspended catalyst particles. An example of a fixed catalyst support design is presented in U.S. Pat. No. 5,790,934 (Say et al). The Say invention utilizes multiple fins located in a radial or longitudinal arrangement and suffers from various shortcomings and limitations. First, the fixed substrate fins are situate at a certain distance away from the UV source. Reactivity is greatest in close proximity to the light source and decreases with distance. Also, the apparatus may not be inserted into existing UV chambers, nor allow for cleaning of the UV sources without removing the apparatus.
U.S. Pat. No. 5,126,111 (Al-Ekabi et al) provides a fiberglass mesh design, however, again it is located at a distance away from the UV source, cannot be inserted into commercial UV chambers, nor compress and expand to allow for UV source cleaning. Further, this invention requires the UV spectra to be in the range of 340-360 nm that is outside the capability of standard bulb designs, i.e. 185 nm and 254 nm. Other mesh designs are illustrated in U.S. Pat. No. 4,892,712 (Robertson et al) and U.S. Pat. No. 5,766,455 (Berman et al). Neither of these designs allow for close contact with the source or permit compression and expansion within a standard UV chamber.
Some fixed catalyst substrates have been proposed to increase overall catalyst surface area through catalyst absorption onto silica gel, zeolites, carbon black, and porous metals, however, the micropores of these fixed catalysts may not allow sufficient illumination to penetrate for efficient catalyst activation. Also, these materials are packed into a reactor where proper illumination of some surfaces of a majority of the catalysts may not be accomplished.
U.S. Pat. No. 5,501,801 (Zhang, et al) illustrates the use of silica gel and zeolite substrates as photocatalytic supports.
Another fixed substrate design is the use of titanium metal pieces (rods, spheres, beads, chunks, and the like) that are oxidized to form the desired titanium dioxide layer. As discussed in U.S. Pat. No. 5,868,924 (Nachtman, et al) and U.S. Pat. No. 5,395,552 (Melanson, et al), titanium metal, or its alloys, are inserted into a UV chamber along the length of the UV source, at a distance away from the UV source.
A replaceable coated cartridge is presented in U.S. Pat. No. 5,736,055 (Cooper) that provides a design for a replaceable piece in a photocatalytic reactor that combines a flexible photocatalytic surface with a rigid base. Again, the inner photocatalytic surfaces of the cartridge are at a distance away from the UV source(s) and are not readily adjustable to facilitate maintenance of the U
Massinger Law Office
Mayekar Kishor
Tran Thao
LandOfFree
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