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Journal ArticleDOI

Two-dimensional heterogeneous model for a reticulated-foam photocatalytic reactor

01 Apr 2000-Aiche Journal (John Wiley & Sons, Ltd)-Vol. 46, Iss: 4, pp 829-842
TL;DR: In this paper, a 2D heterogeneous convection reaction model for a gas-solid lamp-in-tube annular photocatalytic reactor is presented, where the catalyst (TiO2) is supported on a reticulated-foam monolithic structure placed in the annular space between the UV lamp and the reactor wall.
Abstract: A 2-D heterogeneous convection reaction model for a gas–solid lamp-in-tube annular photocatalytic reactor is presented. The catalyst (TiO2) is supported on a reticulated-foam monolithic structure placed in the annular space between the UV lamp and the reactor wall. Mass balances for individual species are coupled through the reaction-rate expression that appears in the boundary condition at the fluid–solid interface in heterogeneous catalytic reactor models. The heterogeneous reaction rate is modeled using semiempirical Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetics with adsorption constants for various species. The local volumetric rate of energy absorption (LVREA) term in the rate expression was computed using a 3-D polychromatic radiation-field model. The overall system of nonlinear partial differential equations was solved using a combination of the Crank-Nicolson method and the globally convergent Newton-Raphson method. The apparent, average quantum yield in the LHHW kinetic rate form is the single adjustable parameter in the model. Isopropanol (IPA) was chosen as the test contaminant to conduct experimental performance measurements for model validation. Model-predicted radial and axial profiles for bulk and surface concentration reveal that the extent to which mass transport influences the operation of a photocatalytic reactor is determined largely by the local magnitude of the LVREA. Similitude in the scale-up of an annular lamp-in-tube heterogeneous photocatalytic reactor is achieved only when the dimensionless radial radiation profile, as well as corresponding magnitudes of a geometric number, the Peclet number, the Stanton number, and the photocatalytic analog of the Damkohler number, are identical.
Citations
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Journal ArticleDOI
20 Mar 2008-Nature
TL;DR: Some of the science and technology being developed to improve the disinfection and decontamination of water, as well as efforts to increase water supplies through the safe re-use of wastewater and efficient desalination of sea and brackish water are highlighted.
Abstract: One of the most pervasive problems afflicting people throughout the world is inadequate access to clean water and sanitation. Problems with water are expected to grow worse in the coming decades, with water scarcity occurring globally, even in regions currently considered water-rich. Addressing these problems calls out for a tremendous amount of research to be conducted to identify robust new methods of purifying water at lower cost and with less energy, while at the same time minimizing the use of chemicals and impact on the environment. Here we highlight some of the science and technology being developed to improve the disinfection and decontamination of water, as well as efforts to increase water supplies through the safe re-use of wastewater and efficient desalination of sea and brackish water.

6,967 citations

Journal ArticleDOI
TL;DR: In this paper, a review of the recent progress in the fabrication of inorganic nanomaterials for photocatalytic water disinfection is presented, as well as the antimicrobial mechanisms are discussed.
Abstract: Traditional water disinfection methods such as chlorination and ozonation inevitably form harmful disinfection by-products (DBPs). UV irradiation is a safe alternative but it is very energy intensive. It makes perfect sense to enhance the utilization of photons by integrating engineered photocatalytic nanostructures in the treatment system. UV-light active photocatalytic inorganic nanomaterials, such as titania, are capable of inactivating various bacteria and viruses. They work by generating powerful but short-lived oxygen-based radicals upon irradiation. Unlike conventional chemical disinfectants, the antimicrobial nanomaterials are not consumed in the process. Photocatalytic water disinfection is a green technology because the same materials can be used over and over again. This paper reviews the recent progress in the fabrication of inorganic nanomaterials for photocatalytic water disinfection. A variety of UV and even visible-light driven water disinfection systems are introduced. Their advantages and limitations as well as the antimicrobial mechanisms are discussed.

173 citations

Journal ArticleDOI
TL;DR: In this article, the degradation of trichloroethylene (TCE) in an air stream is studied using different values of the pollutant feed concentration, relative humidity and light intensity under operating conditions where kinetic control of the process is established.
Abstract: In a previous article, the modeling and experimental verification of the radiation field inside a reactor made of several TiO2 coated, parallel, flat glass fiber meshes, bilaterally UV irradiated was accomplished. The degradation of trichloroethylene (TCE) in an air stream is studied using different values of the pollutant feed concentration, relative humidity and light intensity under operating conditions where kinetic control of the process is established. A kinetic model based on a reaction scheme that involves atomic chlorine as an active reaction intermediate is developed for describing concentration dependencies. It includes, explicitly, the effect of the absorbed light intensity on the rate. The interaction of the existing radiation field with the solid semiconductor to generate electrons, and holes in the reaction catalyst activation step is also modeled. All kinetic parameters are estimated from experiments. The obtained kinetic expression gives a first-order dependence with respect to the TCE concentration and accounts for a competitive effect of water vapor and TCE for the catalyst active sites. An additional important feature of the derived expression is its ability to represent both limiting cases concerning the dependence of the reaction rate with the irradiation rate; that is, order 1 or order 0.5, as well as all possible intermediate values. In fact, the equivalent dependence obtained in this work was 0.6, a value closer to the second case. The results show good agreement between predictions derived from the proposed kinetic expression and TCE experimental concentration data at the reactor's exit. The proposed reactor design provides a practical device for the treatment of contaminated air; it permits a fairly uniform irradiation of the catalytic meshes and a good ratio of the irradiated surface area with respect to the volume of the gaseous reacting mixture. With these features, rather high TCE conversions can be obtained. © 2005 American Institute of Chemical Engineers AIChE J, 2005

130 citations

Journal ArticleDOI
TL;DR: In this paper, the authors provide a sound theoretical basis for quantifying the inherent light energy utilization capabilities and performance limitations of candidate commercial photocatalytic oxidation (OCO) reactor configurations.

80 citations

Journal ArticleDOI
TL;DR: Adsorption performance is closely related to the characteristics of substrates and therefore, the development of a substrate with high adsorption ability is a promising trend for improving the performance of the UV-PCO technology.

78 citations

References
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Journal ArticleDOI
TL;DR: The slow pace of hazardous waste remediation at military installations around the world is causing a serious delay in conversion of many of these facilities to civilian uses as discussed by the authors, which is a serious problem.
Abstract: The civilian, commercial, and defense sectors of most advanced industrialized nations are faced with a tremendous set of environmental problems related to the remediation of hazardous wastes, contaminated groundwaters, and the control of toxic air contaminants. For example, the slow pace of hazardous waste remediation at military installations around the world is causing a serious delay in conversion of many of these facilities to civilian uses. Over the last 10 years problems related to hazardous waste remediation have emerged as a high national and international priority.

17,188 citations

Book
01 Jan 1974

3,981 citations

Book
01 Jan 1966

2,966 citations

Journal ArticleDOI
TL;DR: An important finding was that competitive adsorption between water and trace (sub-ppmv) contaminants has a significant effect on the oxidation rates of formaldehyde, toluene, and 1,3-butadiene.
Abstract: Persistent indoor air contaminants, those originating from emissions by interior furnishings, occupants, and materials of construction, typically exist in concentrations below 100 parts per billion (ppb) on an individual basis. The total of distinct contaminants may number in the hundreds with an equivalent accumulated concentration of one part per million. This study investigated the effects of humidity and trace (sub-ppmv) contaminant levels on the oxidation rates of formaldehyde, toluene, and 1,3-butadiene. The evaluation also included variations in UV intensity and flow residence time. UV intensities from inexpensive mercury fluorescent lamps, those which are expected to be employed in a practical photocatalytic purifier, are in the mW/cm 2 range. For this reason, the study included UV intensities in that range. The reactor element used in the study was a low pressure drop alumina reticulate, wash-coated with Degussa P25 titania. The data indicated that the reaction was first-order for the three reactants at the subppmv level. An important finding was that competitive adsorption between water and trace (sub-ppmv) contaminants has a significant effect on the oxidation rate. The dependencies of humidity and contaminant concentrations on the oxidation rates are explained as being the results of competitive adsorption on available hydroxyl adsorption sites and of changes in hydroxyl radical population levels

587 citations