GB2356858A - Combined photocatalytic and ultrasonic degradation of orgainc contaminants - Google Patents

Abstract

Treatment of aqueous liquid containing organic contaminants comprises contacting the liquid with a material comprising a semiconductor photocatalyst loaded on a molecular sieve material, irradiating the liquid to cause photocatalysis and simultaneous exposure to ultrasound energy. The semiconductor photocatalyst is preferably a titania, and the molecular sieve material may be mesoporous and/or a zeolite. Zinc oxide, cadmium sulfide, iron oxide, gallium phosphide, tin oxide and tungsten oxide may also be used a photocatalysts. Composite photocatalysts and processes for their preparation are also described.

Description

7676WJB 2356858 PHOTOCATALYTIC DEGRADATION OF ORGANIC COMPOUNDS

FIELD OF THE INVENTION

The present invention relates to the photocatalytic degradation of organic compounds by zeolite and mesoporous material hosted photocatalysts combined with ultrasound. The present invention further relates to a method of treating an aqueous liquid containing organics using a combination of light energy and ultrasonic energy in the presence of a photocatalyst to decompose the organic impurities in the liquid.

BACKGROUND OF THE INVENTION

It is desirable to remove 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, Siftenfield 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 frorn 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 2 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 3 methods are called advanced oxidation processes because they promote free radical reactions which lead to complete oxidation of the organic compounds to yield C02, H20 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. Ti02) which absorb light.

While these methods have been shown to be successful in removing organic contaminants from aqueous liquids and decomposing such organic materials, usually the reaction times are slow leading to reduced economic attractiveness of such processes, especially for continuous or on line treatment systems.

SUMMARY OF THE INVENTION

The. present invention relates to method for treating a liquid contaminated with organic comDounds which method will rapidly decompose the organic contaminants. The method comprises using a combination of exposure of the contaminated liquid to energy and ultrasonic energy in the presence of a photocatalyst, wherein the photocatalyst comprises a zeolite or other mesoporous molecular sieve material loaded with a semiconductor photocatalyst such as titanium dioxide.

DETAILED DESCRIPTION OF THE INVENTION

The 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 ultrasound energy and 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 concentrated solar energy to reduce light energy costs, exhibit high yields, and be applicable to a wide variety of organics. It has been discovered that when photocatalytic degradation using a zeolite or other microporous molecular sieve, is combined with ultrasound, in accordance with the present invention, the result is substantially higher degradation rates. The disclosed process has the potential to offer both improved rates and efficiencies (hence throughputs) under optimized conditions; the ability to use impure or cheaper forms of the photocatalyst; significant increases (as much as fivefold) in the degradation rate of aqueous organics without poisoning of the catalyst; improvements in conventional suspended catalyst separation methods such as ultrafiltration; and for applications involving treatment of waste water containing suspended solids, the use of sonication may also assist in the release of hydrophobic organics adsorbed on soil particles, for subsequent reaction at the photocatalyst surface.

The use of molecular sieves such as zeolites and mesoporous materials as support structures for Ti02 provides is beneficial for many reasons. First, the well-defined porous structures (large surface area) of zeolites offer a special environment for the formation of fine 4 titania particles, with unusual morphologies and thus altered photoactivity. Second, they allow pre-concentration of non-polar organic molecules and selective adsorption onto a zeolite. Third, zeolites enhance catalytic activity through properties ranging from surface acidity to reactive intermediate stabilization. Fourth, the pores of 12 membered ring zeolites and mesoporous materials, especially MCM41, are large enough to have titania species packed inside the pores.

Fifth, the local high electrostatic field in a zeolite cage causes a shift of the optimum operation from the UV range into the visible part of the spectrum and sixth, zeolites are believed to not scatter photons as strongly as TiO2 does.

Additionally, the materials with mesoporous character offer two other advantages when used in accordance with the present invention. First, the uniform one- dimensional mesopores such as those of MCM41 allow faster diffusion of oxygen, reactive species and organic substrates within the catalyst surface than the microporous; zeolites and second mesoporous materials allow the packing of Ti02 inside the catalyst pores.

Photocatalvst By use of the term "photocatalyst" is meant any compound in which irradiation of such compound with electromagnetic radiation of visible or ultraviolet wavelength will result in the generation of conduction band electrons (ecb) and valence band holes (h"Vb) that can then undergo oxidation reactions at the catalyst surface with species such as water or inorganic and organic compounds. The initiating step in this photocatalytic process requires illumination with light of energy higher than the band gap of the semiconductor photocatalyst (e.g., <380 nm. for anatase Ti02, the most effective and widely studied photocatalyst). Electromagnetic radiation within a wavelength range of from about 250 nanometers; (nm) to about 450 nm will usually have such an energy level.

The preferred photocatalyst is a Ti02 loaded zeolite or other mesoporous molecular sieve material. These may be provided in a wide distribution of average particle sizes ranging from an average particle size of as small as, for example, from about 0. 05 microns to as large as, for example, 1,000 microns in diameter. Since large surface areas are desired for the photocatalyst to provide a large amount of active sites, small particles will be desired. It will be appreciated, however, that larger size particles could be used, i.e., particles larger than 1,000 micron in size. The particulate photocatalyst, such as Ti02 loaded zeolite, may be added in dry form to the contaminated liquid and mixed together to form a suspension prior to exposure of the contaminated liquid to the ultraviolet light and ultrasound energy. Alternatively, the dry particulate catalyst may be premixed as a slurry or suspension with an aqueous liquid miscible with the contaminated liquid, and this premix may then be added to the contaminated liquid prior to exposure of the contaminated liquid to the ultraviolet light and ultrasound energy.

Typical zeolites and mesoporous materials include ZSM-4 (Omega), ZSM-5, ZSM-11, ZSM-12, ZSM-20, ZSM-22, ZSM-23, ZSM-35, ZSM-48, ZSM-50, MCM-22, PSH-3, MCM48, MCM49, Beta, X, Y, and L, as well as ferrierite, mordenite, dachiardite, clinoptilolite, offretite, erionite, gmelinite, chabazite, etc. Other molecular sieves contemplated include, for example, MCM-9, VPI-5, MCM-20, SAPO-11, SAPO-17, SAPO-34, SAPO-37, MCM-36, and MCM41.

Also included within the definition of the useful molecular sieves are crystalline porous silicoaluminophosphates such as those disclosed in U.S. Pat. No. 4,440, 871, the catalytic behavior of which is similar to that of the aluminosilicate zeolites. Zeolite Beta is described in U.S. Pat. No. Re. 28,341 (of original U.S. Pat. No. 3,308,069), to which reference is made for details of this catalyst. Zeolite X is described in U.S. Pat. No. 2,882, 244, to which reference is made for the details of this catalyst. Zeolite L is described in U.S. Pat. No. 3,216,789, to which reference is made for the details of this catalyst. Zeolite Y is described in U.S. Pat. No.

3,130,007, to which reference is made for details of this catalyst. Low sodium ultrastable zeolite Y (USY) is described in U.S. Pat. Nos.3,293,192; 3,354,077; 3,375,065; 3, 402,996; 3,449,070; and 3,595,611, to which reference is made for details of this catalyst. Dealuminized zeolite Y can be prepared by the method disclosed in U.S. Pat. No. 3,442,795, to which reference is made for details of this catalyst, Zeolite ZSM-3 is described in U.S. Pat. No. 3,415,736, to which reference is made for details of this catalyst. Zeolite ZSM-5. is described in U.S. Pat. No. Re.

29,948 (of original U.S. Pat. No. 3,702,886), to which reference is made for details of this catalyst. Zeolite ZSM-I 1 is described in U.S. Pat. No. 3,709,979, to which reference is made for the details of this catalyst. Zeolite ZSM-12 is described in U.S. Pat. No. 3,832,449, to which reference is made for the details of this catalyst. Zeolite ZSM-20 is described in U.S. Pat. No.

3,972,983, to which reference is made for the details of this catalyst. Zeolite ZSM-22 is described in U.S. Pat. No. 4,556,477, to which reference is made for the details of this catalyst.

Zeolite ZSM-23 is described in U.S. Pat. No. 4,076,842, to which reference is made for the details of this catalyst. Zeolite ZSM-35 is described in U.S. Pat. No. 4, 016,245, to which reference is made for the details of this catalyst. Zeolite ZSM-50 is described in U.S. Pat. No.

4,640,829, to which reference is made for details of this catalyst.

U.S. Pat. No. 4,962,239 to which reference is made above is incorporated herein by reference in its entirety. This patent teaches a process for preparing ethers over catalyst comprising a particular class of zeolites, e.g., MCM-22 and PSH-3. MCM-36 is described in U.S. Ser. No.

07/811,360, filed Dec. 20,1991, and is incorporated herein by reference in its entirety. MCM-41 is described in U.S. Pat. No. 5,098,684, to which reference is made for the details of this catalyst. MCM-49 is described in U.S. Pat. No. 5,236,575, and is incorporated herein by reference in its entirety.

6 Zeolite catalvsts The zeolite particles useful herein are particles of a crystalline aluminosilicate corresponding to the formula xM?j,OA1203 YSi02 zH2 0 in which M is a cation, generally an ammonium or metal cation, most commonly a mono- or divalent metal cation (e.g., a sodium, potassium, or other alkali metal cation, or another cation such as calcium or magnesium); n is the valence of the cation; x is the coefficient of the metal oxide; y is the coefficient of silica; and z is the number of molecules of water of hydration. They are preferably zeolites having a particle size of 0.1-20 im (e.g., 2-5p) and a Si02/AI2 03 molecular ratio less than or equal to 14, more preferably a zeolite A, zeolite C, zeolite X, or zeolite Y, most preferably a zeolite Y. It is known to use titanium dioxide and/or other pigments with a zeolite, as in U.S. Pat. Nos. 4,220,567 (Kindervater et al.), 4,752,341 (Rock), and 4,874,433 (Kiss et al.); and Domenech et al., "Cyanidephoto-oxidetion using a Ti02 -coated zeolite," Chem. Ind., Vol. 18, page 106, 1989, teach that titanium dioxide employed as a photocatalyst, can be supported with 3 ANG.

molecular sieves. In general, the products of the invention are titaniacoated zeolites having a particle size of 0.2-20Lrn, with a mean size preferably less than or equal to 1 Olam; a Ti02 content of 1-50%, preferably 2-30%, by weight; and a Ti02 coating thickness which is preferably 0.001 1 gm, more preferably 0.005-0.2 lam.

Mesoporous Material Catalysts:

As used herein, the term "large pore size mesoporous material catalysts" means any porous material having a mean pore size of greater than about 20 Angstroms and having oxidative catalytic properties resulting at least in part from the presence of metal bound to (under typical use conditions of the present invention compositions) the large pore size crystalline material. Preferred are oxidative catalysts.

The metal may therefore be present in the catalyst by physical interactions with the porous material, by ionic or covalent bonding, or by clusters of metals likewise bound or attached to the porous material.

The metal may be incorporated into the catalyst by adsorbing it as an aqueous cation, with or without simple ligands such as acetate. The metal may also be incorporated by adsorbing it as a volatile low-valent metal carbonyl, with or without post-treatment to decarbonylate the adsorbed metal carbonyl in-situ.

Methods for attaching metals to porous materials, and attaching functional groups to porous materials to which metals may thereto be attached, are known in the art, being described for example in U.S. Patent 5,145,816, issued September 8, 1992 to Beck et al., and in "A New Family of Mesoporous Molecular Sieves Prepared with Liquid Crystal Templates", by Beck et al, J. Am. Chem. Soc., Vol. 114, No. 27, pp. 10834-10843 (1992), incorporated by reference herein in their entirety.

7 Preferred large pore size mesoporous material catalysts useful herein have mean pore size of about 15 Angstroms or greater, more preferably of about 100- 1000 Angstroms, and most preferably about 500-600 Angstroms. Also, preferred mesoporous material catalysts herein have surface area of at least about 300 m2/g, more preferably at least about 400 m2/g and most preferred being at least about 500 m2/g.

Preferred large pore size mesoporous material catalysts are silicate or aluminosilicate catalyst materials. These include liquid crystal template synthesized silicate and aluminosilicate materials, such as those described in "A New Family of Mesoporous Molecular Sieves Prepared with Liquid Crystal Templates", by Beck et al, J. Am. Chem. Soc., Vol. 114, No. 27, pp. 10834 10843 (1992). These materials are additionally characterized by high crystallinity and low water solubility. Most preferred are such materials which are crystalline on the basis of X-ray powder pattern.

Methods for evaluating the physical characteristics of the catalysts useful herein are well known in the art, being described for example in Kirk-Othmer Encyclopedia of Chemical Technology, Fourth Edition, Vol. 5, pp. 383-418 (1993), the disclosures therein being incorporated herein by reference in their entirety.

Highly preferred are those catalysts described as "mesoporous molecular sieve" materials as taught, for example, in U.S. Patent 5,102,643, issued April 7, 1992 to Kresge et al., U.S. Patent 5,250,282, issued October 5, 1993 to Kresge et al., U.S. Patent 5,264,203, issued November 30, 1993 to Beck et al., U.S. Patent 5,145,816, issued September 8, 1992 to Beck et al., and U.S. Patent 5,098,684, issued March 24, 1992 to Kresge et al., the disclosures of all these patents being incorporated herein by reference in their entirety.

One particularly preferred mesoporous material is MGM-41. MCM-41 refers to a mesoporous, material with a hexagonal silicate phase MCM-41 can be successfully synthesized using the method described by A. Sayari et al. (Chemistry Materials, 9, 1997).

Loadinq with TiO7 Titania is loaded into the pores of zeolites or mesoporous molecular materials such as USY and MCM-41. This is also commonly referred to as doping of the materials with titania. A slurry of each zeolite or other mesoporous molecular material is formed and 0.5-50% of precursor is added to result in the desired titania loading. Typically the amount of titania loaded is less than 25% by weight of the catalyst to avoid blocking of the pores. Higher concentrations may be used but are not deemed to be necessary and would add expense to the process in terms of material costs. The precursor used to load the zeolites is ammonium-titanium oxalate and the precursor for the mesoporous molecular material is titanium- isopropoxide. Other titanium salts can be used for this as long as they do not result in the formation of a very acidic environment or the destruction of the zeolite or mesoporous molecular material itself. It will be 8 understood by one of skill in the art, that the size of the precursor used must be smaller than the pore openings of the zeolite or mesoporous molecular material.

In either instance, the concentration of the particulate photoGatalyst in the contaminated liquid should range from about 100 milligrams per liter of contaminated liquid to about 2 grams per liter of contaminated liquid. Higher concentrations may be used but are not deemed to be necessary and only would add expense to the process, both from the standpoint of additional material costs as well as additional processing costs, e.g., if the catalyst must be separated from the purified liquid after the organic compound has been decomposed. Typically, the concentration of the photocatalyst in the contaminated liquid will be about 1 gram per liter. Lower concentrations may be used, but this may result in a lowering of the decomposition rate. In this regard, it will be appreciated that the actual amount of catalyst used will depend upon the surface area of the catalyst which will, in turn, depend upon the porosity and/or particle size of the particulate catalyst. A typical surface area range will be from about 1 to about 1 OOOm2 /gram of photocatalyst such as Ti02 loaded zeolites.

Li-qht Source As stated above, the electromagnetic radiation source should be a light source which provides energy higher than the band gap of the semiconductor catalyst. To accomplish this, the electromagnetic radiation or light source will be within the wavelength range of from about 250 nm. to about 450 nm. For a photocatalyst such as Ti02, for example, the wavelength range will be from about 290 nm to about 400 nm, and preferably from about 300 nm. to about 360 nm., i.e., an ultraviolet light source. The intensity of the light source will be inversely proportional to the amount of time which it will takes to affect the desired decomposition of the organic compounds, i.e., the weaker the light source, the longer the decomposition time will be. This, in turn, will affect the overall efficiency of the process and will be of particular importance when the process is being run on a continuous basis rather than as a batch operation.

For a light source which is coupled directly to an optical cell containing the contaminated liquid, the intensity of the light source, at the selected wavelength should be at least about 1,000 microwatts per inch 2 of exposure area per liter of liquid to achieve complete decomposition within a reasonable exposure period. Such light sources are commercially available, e.g., a mercury lamp source, or sunlight may be used as the source of light radiation of ultraviolet wavelength. The distance that the light source is located from the liquid to be irradiated is important since much of the light energy may be absorbed within a few cm. of the liquid surface.

Therefore, depending upon the size and geometry of the reaction vessel, as well as the intensity of the light source, it may be appropriate to use a plurality of such light sources dispersed around the perimeter of the vessel, as well as above and below the respective top and bottom surfaces of the vessel.

9 In general, it may be stated that the relationship of the intensity of the light source (or sources) to the dimensions of the reaction vessel should be such that the light entering the reaction vessel will still have sufficient intensity or energy to initiate photocatalytic decomposition of the organic material in the liquid when it reaches the furthest extremity of the volume of the vessel. For a single light source, for example, this would mean the opposite wall of the vessel.

However, if a plurality of such light sources were to be spaced around the perimeter of the reaction vessel, this distance would mean the distance to the center of the vessel.

It should be noted in this regard that the decomposition rate will be dependent upon not only the intensity of the light source and the dimensions of the reaction vessel, but also on the type and concentration of catalyst, the intensity of the sonication source, and the type and concentration of the organic material being decomposed.

Ultrasound The ultrasound or acoustic energy is provided by one or more sonication apparatuses or ultrasound generators operating at between from about 1 KHz to about 1 MHz, preferably from about 10 KHz to about 100 KHz, and most preferably about 20 KHz, at a power level which may be within a range of from about 10 watts to about 2,500 wafts. It should be noted here that such a power range will be dependent upon the size of the vessel into which the ultrasound energy will be coupled. If the vessel is sufficiently large, it may be preferable to utilize more than one generator rather than increasing the power level of an individual generator to more than about 2,500 wafts. A single ultrasound generator having a power range of from about 10 to about 2,500 wafts will usually provide sufficient power for a reaction vessel up to about 2 liters in volume. Thus, the total power range of the ultrasound source may be expressed as a power range equivalent to from about 10 to about 2,500 wafts for a 2 liter vessel.

The sonication apparatus is coupled, through an appropriate transducer or sonication tip, directly into the optical cell or vessel which contains the contaminated liquid. That is, the transducer or sonication tip is immersed directly in the liquid to be decomposed within the cell.

Such an ultrasound generator may comprise any commercially available apparatus capable of operating within these ranges such as, for example, Ultrasonic Processor W-2500, available from the Heat Systems Company. It should be noted here that the intensity of the sonication, like the intensity of the light radiation, will be proportional to the distance of the liquid being acted upon from the transducer or sonication tip. Therefore, depending upon the size of the vessel, it may be preferable to utilize a plurality of transducers or sonication tips, with the power level of the sonication source adjusted accordingly, as well as using more than one ultrasound generator as discussed above.

As in the previously discussed relationship between the intensity of the light source (or sources) to the dimensions of the reaction vessel, the power level of the sonication source (or sources) should be such that the ultrasound energy imparted to the liquid in the reaction vessel will still have sufficient energy to accelerate photocatalytic degradation of the organic material in the liquid when it reaches the farthest extremity of the volume of the vessel. This, for a single transducer or sonication tip immersed in the liquid, would mean the farthest point in the vessel from the location of the transducer or tip, i.e., probably the opposite wall of the vessel.

However, if a plurality of such sonication tips were to be immersed in the liquid, for example, around the perimeter of the reaction vessel, this distance would mean the distance to the center of the vessel, as in thecase of the use of multiple light sources. While, as stated above, there is not the intention to be bound by theories of operation of the process of the invention, it is believed that by combining sonication and photocatalytic degradation, reaction enhancement is provided due to: cavitational effects which lead to dramatic increases in temperature and pressure at the localized microvoid implosion sites; cleaning or sweeping of the photocatalyst surface due to acoustic microstreaming which allows or provides more active sites; increased mass transport of reactants and products at the catalytic surface and in solution; increased photoGatalyst surface area due to fragmentation or pitting of the photocatalyst particles by the sonication', cavitational inducement of radical intermediates which become involved in the destruction of the organic compounds; and reaction of the organic substrate directly with the photogenerated surface holes and electrons.

Tvpes of or-qanic compounds deqraded All types of organic compounds can be cleaned from contaminated liquids by use of the present invention. The type and size of the compound to be removed from the liquid will determine the pore size of the catalyst that should be used. The organic compounds present in the contaminated liquid to be purified may comprise compounds such as, chlorinated phenols (e.g., 2,4-dichlorophenol, 4-chlorophenol, pentachlorophenol), chlorinated biphenyls (e.g., 3 chlorobiphenyl and 4,4'-dichlorophenyt), brominated biphenyls, and halogenated benzene derivatives (e.g., chlorobenzene, 4-chlorotoluene, chlorinated dioxin, and halogenated benzofurans). Examples of halogenated aliphatic organics include halogenated hydrocarbons such as fluoromethanes, ethanes, propanes, etc.; chloromethanes, ethanes, propanes, etc.; bromomethanes, ethanes, propanes, etc.; and mixtures of same; halogenated alkenes, such as trichloroethylene; halogenated alcohols, such as 1-chloro-2-propenol; halogenated ketones; halogenated aldehydes, such as aldrin aldehyde; halogenated carboxylic acids, such as trichloroacetic. acid; and halogenated ethers, such as bis(2- chloroisopropyf)ether. Other organic compounds which can effectively be removed from contaminated liquids include, but are not limited to, aromatics and polyaromatics, paraffins, olefins, ketones, aldehydes, organic acids and alcohols. A representative, but non-exhaustive listing of different kinds and types of organic materials able to be degraded is provided by Table I below.

TABLE 1

ALKANES AND THEIR DERIVATIVES Straight Chain AWanes (such as octane, decane, and hexadecane) Branched Chain Alkanes (such as isooctanes) Cycloalkanes (such as cyclohexane) ARENES AND THEIR DERIVATIVES Benzene Alkylbenzenes (such as toluene and xylenes) Phenol Oxygen Substituted and Carbon Substituted Alkylphenols Aniline Nitrogen Substituted and Carbon Substituted Alkylanilines Catechol Oxygen Substituted and Carbon Substituted Alkylcatechols Resorcinol Oxygen Substituted and Carbon Substituted Alkylresorcinols Cresols Oxygen Substituted and Carbon Substituted Alkyleresols Hydroquinone Oxygen Substituted and Carbon Substituted AlkyMydroquinones Benzyl Chloride Mkyllbenzyl Chlorides Chlorobenzenes Alkylchlorobenzenes Dichlorobenzenes Alkylclichlorobenzenes Polychlorobenzenes Polychloroalkylbenzenes Nitrobenzene AlkyInitrobenzenes Dinitrotoluenes Chlorophenols Oxygen Substituted and Carbon Substituted Mkylchlorophenols Polychlorophenols Oxygen Substituted and Carbon Substituted Alkylpolychloro- 12 phenols Diphenylethylene Stilbenes Naphthalene Chloronaphthalenes Alkylinaphthalenes Naphthols Oxygen Substituted and Carbon Substituted AlkyInaphthols Chloronaphthols Benzoic Acid Oxygen Substituted and Carbon Substituted Alkylbenzoic Acids Salicylic Acid Oxygen Substituted and Carbon Substituted Alkylsalicyclic Acids Chlorobiphenyls Dichlorobiphenyls Polychlorobiphenyls Ring-Chlorinated Phenylacetic Acids Dichlorodiphenyitrichloroethane (DDT) OLEFINS AND UNSATURATED HALIDES Simple Alkenes Alkadienes Vinyl Chloride Vinyl Bromide Dichloroethylenes Trichloroethylene Tetrachloroethylene ALKYLHALIDES Dichloroethanes and Dibromoethanes Trichloroethanes and Tribromoethanes Tetrachloroethanes and Tetrabromoethanes C FC:13, C F 2 C12, and Other Ch lorofluorocarbons Methyl Chloride and Methyl Bromide Methylene Dichloride and Methylene Dibromide Chloroform and Brornoform Carbon Tetrachloride and Carbon Tetrabromide EXAMPLES OF OTHER CLASSES 13 Chlorinated Dioxins Chlorinated Dibenzofurans Trichloroacetic Acid Alkyl and Aryl Thiocarbamates Alkyl and Aryl Amines Alkyl and Aryl Mercaptans Alkyl and Aryl Thioethers Polymeric Materials Related to Any or All of the Above Classes A cursory reading of Table I will reveal many classes of substances whose members have been classified as toxic, environmentally hazardous compositions by federal and state agencies such as the EPA, OSHA, and NIOSH. In addition, many of these substances are known or believed to be carcinogenic or carcinogen-promoters whose use is carefully controlled by various health and safety agencies. All of these comprise the membership of the general class of organic material able to be completely degraded into environmentally safe reaction products comprising at least carbon dioxide.

The concentration of such organic compounds in the aqueous liquid may range from as little as 2 ppm to as much as 2,000 ppm. After purification by the process of the invention, the concentration of such organic impurities in the previously contaminated liquid may be reduced to less than 1.0 ppm. Exposure of the contaminated aqueous liquid containing such organic compounds to both UV radiation and ultrasound energy, in the presence of the particulate catalyst, results in decomposition of the organic compounds into purified liquid, environmentally compatible reaction products comprising at least carbon dioxide which may then be subsequently removed from the liquid. A separate source of oxygen is usually not necessary for the formation of the C02 decomposition product, since there will normally be sufficient dissolved oxygen in the aqueous liquid. However, a separate source of oxygen (e.g. ozone, H202) may be optionally provided if desired, which could be introduced into the contaminated liquid through a sparger ri ng or the like.

Process A contaminated liquid source such as water containing organic contaminants, in a concentration which may range from about 2 ppm to about 2,000 ppm, is mixed with a source of particulate catalyst which may be in dry form or, preferably, in a previously formed suspension or slurry. The optical cell may comprise any reaction vessel having sidewalls (or one or more openings in the sidewalls) transparent to electromagnetic radiation, e.g., UV light radiation of from about 300 nm to about 360 nm for a photocatalyst, to permit the liquid in optical cell to be 14 irradiated by light energy from a light source which is preferably coupled directly to the sidewall of the cell to permit the most efficient coupling of the light energy to the cell from the source. While the light source has been described as a single source, it will be readily appreciated that the light energy may be passed through the transparent sidewalls or windows through a plurality of such light sources arranged around the periphery of the optical cell, as previously discussed, to uniformly illuminate the liquid therein with light of the proper wavelength during the decomposition of the organic compounds in the contaminated liquid in cell.

There is an ultrasound energy source which provides ultrasound energy to the contaminated liquid in the cell simultaneous with irradiation of the liquid with the light source through a transducer immersed in the contaminated liquid in the cell. The dimensions of the cell are selected, with respect to the location and energy levels of the light and acoustical energy sources, so that all of the liquid in the cell will be exposed to both light energy and acoustical energy at an energy level sufficient to cause decomposition of the organic molecules in the liquid.

The optical cell may be further provided with temperature controlling means to maintain the liquid being treated within the cell within a temperature range of from about 15.degree. C. to about 60.degree. C. Pressure control means may also be provided to increase the hydrostatic pressure within the cell from sub-atmospheric pressure up to a pressure of about 500 psi. The organic compounds in the aqueous liquid decompose in the optical cell upon exposure to both the light radiation and ultrasound energy in the presence of the particulate photocatalyst.

Because of the synergistic effect of exposing the organic compounds to both of said energy sources in the presence of the photocatalyst, the compounds quickly break down at a rate faster than when each energy source is used alone, although it will be appreciated that this rate will be dependent upon the cell volume of contaminated liquid being treated, the type of contaminated liquid, the intensity of the light and ultrasound energy sources and, when the process is being run on a continuous basis, the throughput or flow rate of the contaminated liquid through the cell.

EXPERIMENTAL DESIGN AND GENERAL PROTOCOL The experiments hereinafter employ the solid catalyst, either as an aqueous slurry which was fully coated onto a solid support material (such as the internal surface of the reaction cell wall); or as an aqueous slurry which was partly coated onto a solid support and partly dispersed in the fluid reaction medium; or as a suspension completely dispersed into the fluid reaction medium alone. There is no meaningful difference in the quality or quantity of reaction products obtained via the positioning of the solid catalyst.

All catalysts were characterized using Nicolet powder X-ray diffractometer equipped with a CuKa source to assess their crystallinity. MCM-41 powders were run from 2 to 7 degrees (20) to assess the crystallinity of the matrix and from 20 to 50 to assess the crystallinity of the Ti02 loading. USY-based samples were run from 8 to 50 degrees corresponding to both loading and support. Furthermore, the powders were characterized by UV-Vis Shimadzu 2501PC with an integrating sphere attachment ISR1200 for their diffuse reflectance in the range of wavelengths of 200 to 800 nm. BET and pore size distribution studies are being conducted (using Micromeritics Gemini apparatus) to characterize the synthesized MCM-41 and USY-2.6 samples.

The photocatalytic testing (photodegradation of phenol with an initial concentration of 2 mM) was performed in a batch quartz reactor (Ace Glass) using 450W UV- Visible mercury lamp. The suspended catalyst in aqueous system was mixed, oxygenated, and irradiated during each reaction run. Certain runs included ultrasonication of the reaction suspension, which was performed by the VWR ultrasonic processor at 20 kHz and at an amplitude of -50 % corresponding to the power input of 100-120W. The concentration of phenol in the reactor was controlled using HP 6890 gas chromatograph equipped with a flame ionization detector and thermal conductivity detector. Typical loading of the solid catalyst varied from 1-10 grams per liter of fluid reaction mixture.

The following examples will serve to further illustrate the practice of the process of the invention:

EXAMPLE1

Ti02 loaded USY was prepared using the following recipe: 0.31 g of bisammonium titanoxo oxalate (to achieve 25 wt % loading of USY) was combined with 80 ml of water in a beaker. The slurry is mixed at 200 RPM until it becomes transparent (all oxalate dissolves). 0.25 g of USY with Si/All ratio 2.8 supplied by PQ Corporation is added to the system and it is allowed to stir for 8 hours at room temperature. It is then stirred with simultaneous heating at 35-40 C until all water evaporates. The powder is scraped off the walls of the beaker and placed to dry overnight at 150 C. The catalyst is placed into a boat-like crucible and calcined at 450 C for 10 hours (heating rate -5 C/min).

About 850 ml of a contaminated aqueous solution containing 2mM of Phenol was placed in a 1000 ml cylindrical jacketed glass cell having about a 6 cm inner diameter. A sufficient amount of particulate TiO-Ioaded USY, having a particle size of about 1 micron and pore size of 7-8 Angstroms, was added to provide a concentration of about 0.1 wt % of catalyst, based on total weight of the solution, including the catalyst. The cell was irradiated for 120 minutes by a 450W UV-Visible mercury lamp source supplied by ACE Glass and having a nominal power of about microwattS/CM2 at 355 nm and which was positioned I inch from the outer jacket wall of the cell. The solution was sonicated for 60 min using a 1/2" titanium hom immersed 5 cm. into the solution in the cell and powered by a VWR ultrasonic processor at 20 kHz. The amplitude of the 16 ultrasonic vibration at the tip of the horn was set to amplitude of -50 % corresponding to the power input of 90W. During the sonication and photolysis, the cell was water cooled to maintain the solution temperature at 30 degree C. During sonication and photolysis, samples were withdrawn and analyzed for phenol concentration by means of a gas chromatograph equipped with a flame ionization detector. A second sample of the same contaminated liquid was also treated in the same manner except that no ultrasound was used. Table 2 shows the marked improvement in removal of phenol from the solution when both UV light irradiation and ultrasound are used in combination with the photocatalyst. In contrast to destruction of phenol when UV light radiation was used without ultrasound. When ultrasound was used without UV light, it had no effect on the degradation of phenol.

Table 2

Catalyst Titania Ultrasound Ultrasound content, off on Kpp, wt.% K.pp, 11(gTi02 Min) 1/(gTi02 Min) Ti02/USY 125 10.033 10.041 Kapp is determined by plotting In(C/CO) as a function of time, then the slope divided by the weight content of titanium dioxide in the vessel.

Example 2

This example describes the degradation of phenol as described in the previous example with the exception that a different photocatalyst is used. MCM41 samples were prepared in the presence of hexadecyltrimethylammonium bromide (HDTABr) used as a template. The following are the typical preparation procedure: 35 grams of Ludox (HS-40 colloidal silica 40 wt %) solution was added to 14.55 ml of water under stirring, and 18.2 ml of 40 % tetramethylammonium hydroxide added. Independently, 18.25 gm of HDTABr was dissolved in 33 ml of water, and subsequently 7 ml of 28 % NH40H was introduced. The mixtures containing Ludox and HDTABr were stirred together for 30 minutes, then transferred into polypropylene bottle and heated under autogenous pressure without stirring at 90 - 100 C for 3 days. The mixture was filtered, washed, dried, and calcined at 550 C for 10 hours under air flow. Ramp 2 degrees per minute up, 15 degrees per minute down. The resulting catalyst was dispersed in -100 ml of isopropanol, and titanium isopropoxide (TIPO) was added to achieve 10 % Ti02 loading. The system was dried while stirring at ambient temperature. It was then placed in the oven to dry at 100 C for 1 hour.

Water was added to hydrolyze the TIPO, and the system was stirred for I hour. The solids were then filtered off, washed, and dried for 1 hour at 100 C. They were then transferred into a boat-like 17 crucible and calcined at 450 C for 2 hours with a temperature ramp of 2 deg/min up, and 15 deg/min down.

Several contaminated water samples containing a 2 millimolar concentration of phenol was treated in the same manner as the samples treated in example 1. Particulate TiO2-loaded MCM41, having a particle size of about 1 micron and pore size of about 38 Angstroms, was added to provide a concentration of about 0.12 wt % of catalyst, based on total weight of the solution, including the catalyst. As shown in Table 3, when the sample was exposed to both UV light and ultrasound a rapid destruction of phenol was noted, whereas the use of UV light without ultrasound resulted in a 10% reduction of the apparent rate constant.

Table 3

Catalyst Titania Ultrasound off Ultrasound on content, Kapp, Kapp, wt.% 1/(gT!02 Min) 1/(gTi02 Min) Ti02/MCM-41 10 0.00341 0.0352 18

Claims (17)

WHAT IS CLAIMED IS:

1. A process for the treatment of an aqueous liquid containing organic contaminants said process characterized by the steps of.

a) contacting the aqueous liquid with a semiconductor photocatalyst loaded into a molecular sieve material while; b) irradiating the aqueous liquid with light of a wavelength higher than the band gap of the semiconductor photocatalyst; and C) simultaneously exposing the aqueous liquid to ultrasound energy.

2. The process of claim I wherein said photocatalyst is a titania which is loaded into a molecular sieve material, preferably a zeolite.

3. The process of any of claims 1-2 wherein said photocatalyst is a titania which is loaded into a molecular sieve material, preferably a mesoporous molecular sieve material.

4. The process of any of claims 1-3 wherein said liquid is irradiated with light of wavelengths ranging from 200 to 800 nm.

5. The process of any of claims 1-4 wherein said liquid is irradiated with UV light of wavelengths ranging from 290 to 380 rim, preferably from 300 to 360 mn.

6. The process of any of claims 1-5 wherein the average particle size of said photocatalyst loaded molecular sieve material ranges from 0.05 to 1,000 microns.

7. The process of any of claims 1-6 wherein the intensity level of said light irradiating said liquid is at least 1,000 microwatts/in 2 of exposure area per liter of liquid.

8. The process of any of claims 1-7 wherein the power level of said ultrasound energy is equivalent to a range of from 10 to 2,500 watts for a 2 liter vessel.

9. The process of any of claims 1-8 wherein said ultrasound energy ranges from I KHz to I MHz, preferably from 10 KHz to 100 KHz.

10. The process of any of claims 1-9 wherein said photocatalyst is selected from the group consisting of titanium dioxide, zinc oxide, cadmium sulfide, iron oxide, gallium phosphide, tin oxide, silicon carbide, and tungsten oxide.

19

11. A process according to any of claims 1-10 for purifying an aqueous liquid containing organic contaminants by decomposing said contaminants wherein said contacting step (a) comprises mixing said liquid with a semiconductor photocatalyst loaded into a molecular sieve material to form a suspension of said photocatalyst loaded molecular sieve material and said liquid having a concentration of from 100 milligrams to 2 grams of said photocatalyst loaded molecular sieve material per liter of liquid; said irradiating step (b) comprises exposing said suspension to light radiation of energy higher than the band gap of said photocatalyst; said exposing step (c) comprises simultaneously exposing said suspension to ultrasonic energy within a range of from I KHz to 1 MHz at a power level equivalent to a range of from 10 to 2,500 watts for a 2 liter vessel; and said process is further characterized by the step of separating said liquid from said photocatalyst loaded molecular sieve material after decomposition of said organic contaminants.

12. A process for the treatment of an aqueous liquid containing organic contaminants substantially as described herein with reference to the examples.

13. A process for the production of a composite photocatalyst comprising loading a semi conductor photocatalyst into a molecular sieve material.

14. The process of claim 13 wherein said semi-conductor photocatalyst is a titania and said molecular sieve material is a zeolite.

15. The process of claim 13 wherein said photocatalyst is a titania and said molecular sieve material is a mesoporous molecular sieve material.

16. A process for the production of a composite photocatalyst substantially as described herein with reference to the examples.

17. A composite photocatalyst obtainable by the process of claim 13 or or claim 16.