Chemistry: electrical and wave energy – Processes and products – Processes of treating materials by wave energy
Reexamination Certificate
2001-08-01
2003-07-01
Wong, Edna (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Processes of treating materials by wave energy
C204S158200, C210S748080
Reexamination Certificate
active
06585863
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the photocatalytic degradation of organic compounds by zeolite and/or mesoporous material hosted photocatalysts. The present invention further relates to a method of treating a contaminated aqueous liquid or gaseous fluid containing organics using a combination of visible or solar light energy in the presence of a photocatalyst to decompose the organic impurities in the liquid or gaseous fluid.
BACKGROUND OF THE INVENTION
Contaminated water is becoming a growing problem in many areas of the world. It is desirable to be able to efficiently and effectively remove such contamination (e.g. halogenated organic materials) from aqueous liquids such as water containing chlorinated hydrocarbons, e.g., chlorinated phenols. Prior art removal techniques have included the use of ultraviolet light radiation to decompose halogenated organic compounds. For example, Chou et al., U.S. Pat. No. 4,764,278, discloses a method for reducing the concentration of haloorganic compounds in water by first extracting the haloorganic compounds from the water using a water immiscible alkane hydrocarbon solvent. The solvent is then separated from the water and regenerated by exposing the solvent to ultraviolet light to degrade the haloorganic compounds.
Ultrasonic energy has also been used in the removal of halogenated organics from an aqueous liquid. For example, Sittenfield U.S. Pat. No. 4,477,357 describes a process for removal of contaminants such as halogenated organics from a liquid. Halogenated organic materials in oil or water are mixed with an equal amount of an alkaline agent, such as a hydroxide or a carbonate of an alkali metal or an alkaline earth metal, and then exposed to ultrasonic energy to decompose the halogenated organic contaminant. The presence of the alkaline agent is said to significantly accelerate the dehalogenation and decomposition of organic ring structures. U.S. Pat. No. 5,130,031 to Johnston also describes the treatment of aqueous liquids using light energy, ultrasonic energy and a photocatalyst. Sierka et al., in “Catalytic Effects Of Ultraviolet Light And/Or Ultrasound On The Ozone Oxidation Of Humic Acid and Trihalomethane Precursors”, describe the catalytic effects of the use of both UV irradiation and ultrasound, either singly or in combination, on the ozone oxidation of organic materials, such as humic acid, in aqueous solutions. It is believed that the most effective reactor conditions for both the destruction of nonvolatile total organic carbon and trihalomethane formation potential utilized both ultrasound and UV irradiation in combination with ozone.
Another known technique of removing contaminants from fluids comprises the use of illuminated photocatalysts such as titanium dioxide. The ability of ultraviolet illuminated titanium dioxide to destroy organic contaminants in water (Carey et al., Dull. Environ. Contam. Toxicol. 16, 697, (1976)) has been well known for many years. However, heretofore, none of the prior processes has emerged as a commercially viable process. There are several reasons why these prior processes have not been commercially successful.
First, current evidence supports the notion that destruction of organic contaminants occurs on the surface of the photocatalyst, and therefore an increase in surface area is required for high rates of reaction. To achieve this, slurries of colloidal titanium dioxide have typically been used in many processes; however, the recovery of the colloidal photocatalyst in the discharged effluent has not been cost efficient for high volume applications.
Second, immobilization of titanium dioxide on a support within the photoreactor has been suggested and has resolved the retention problem described in the previous paragraph. However, this solution has come at the expense of increasing mass transfer problems associated with movement of the contaminants in water to the immobilizing support which was more distantly spaced (for light penetration purposes) than the dispersed colloidal particles. Immobilization also creates a lack of uniformity in irradiation of photocatalytic particles, which are immobilized at different distances and with different orientations to the light source. Larger photoreactors would therefore be needed to cope with the inefficiencies introduced by immobilization. With colloidal slurries (i.e. previous paragraph), mixing provided all particles with equal probability of being in low and high light intensity regions of the photoreactor.
Third, when treating dilute solutions, the resulting mass transfer problems reduce significantly the rate of chemical destruction in both the slurried and immobilized titanium dioxide processes described above.
Unfortunately, these problems serve to restrict the fluid volumes treatable by a given amount of photocatalyst in any given time, and necessitate the use of large reactors to handle large fluid volumes. Since many applications, such as municipal drinking water purification, require treatment of large volumes with low concentrations of contaminants, prior art processes involving the use of photocatalysts in this manner have been severely limited for such applications.
In light of the foregoing, it is desirable to have a process capable of purifying aqueous solutions while minimizing or eliminating the above-mentioned deficiencies of the prior art. Ideally, such a process would be useful to remove chemical contaminants from aqueous solutions in a relatively simple and efficient manner, and would decompose or transform the removed contaminants to dischargeable and innocuous or otherwise desirable products which could, at the discretion of the user, be diluted with purified fluid or captured for further processing such as microbial treatment. Further, it would be advantageous if such a process could be easily adapted for purifying liquid and/or gas phase fluids.
In recent years, advanced oxidation processes have emerged as potentially powerful methods of transforming organic pollutants in water or air into harmless substances. These methods are called advanced oxidation processes because they promote free radical reactions, which lead to complete oxidation of the organic compounds to yield CO
2
, H
2
O and corresponding salts. In photocatalytic degradation the oxidizing species are generated from dissolved oxygen or from water, in situ, on the photocatalytic particles (i.e. TiO
2
), which absorb light.
While these methods have been shown to be successful in removing organic contaminants from aqueous liquids and decomposing such organic materials, the reaction times are slow leading to reduced economic attractiveness of such processes, especially for continuous or on line treatment systems.
Accordingly, it is an object of the present invention to provide an efficient and cost effective method for degradation of organic compounds in aqueous systems.
SUMMARY OF THE INVENTION
The present invention relates to method for treating a liquid contaminated with organic compounds which method will rapidly decompose the organic contaminants. The method provided eliminates the need to provide ultraviolet light energy. The present method comprises exposing a contaminated liquid to visible light while contacting the contaminated liquid with a semiconductor photocatalyst, wherein the semiconductor photocatalyst comprises a transition metal atom exchanged into the framework of a zeolite and/or mesoporous molecular sieve material, which are subsequently loaded with a photoactive material, such as titanium dioxide.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a novel process for efficiently removing organic compounds from contaminated aqueous liquids by contacting the contaminated liquid with a photocatalyst, while simultaneously exposing the contaminated liquid to visible light energy to decompose the organic compounds.
To be commercially feasible, photocatalytic degradation must be relatively inexpensive, safe, and use a nontoxic catalyst. The ideal method would produce no toxic by-products, utilize concent
Davydov Lev
France Paul Amaat
Smirniotis Panagiotis George
Cook C. Brant
Miller Steve W.
Procter & Gamble Company
Wong Edna
Zerby Kim W.
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