Parametrical analysis of the degradation of gas phase trichloroetylene in a photocatalytic reactor with titanium dioxide coated glass fiber meshes

El estudio de la degradación de Tricloroetileno (TCE) en aire en un reactor fotocatalítico con dióxido de titanio depositado sobre un lecho fijo ha permitido obtener en un trabajo previo, una expresión cinética que contempla la influencia de la concentración del contaminante, la Radiación Incidente y el efecto competitivo del agua y el TCE por los sitios activos del catalizador(1). En este trabajo se resuelve numéricamente la ecuación diferencial en derivadas parciales de transferencia de materia en un reactor fotocatalítico constituido por mallas de vidrio con dióxido de titanio depositado e irradiadas mediante radiación UV. Esta solución numérica evita la introducción de un coeficiente de transferencia de materia sobre la superficie catalítica, obtenido a partir de correlaciones típicas para interfaces gas-sólido bajo el régimen de flujo correspondiente(2,3). Modificando los parámetros relevantes del sistema resulta posible simular el comportamiento del reactor bajo distintas condiciones de operación.The analysis of Trichloroethylene (TCE) degradation in air in a photocatalytic reactor with titanium dioxide coated on a fixed bed has provided in a previous work, a Kinetic expression which takes into account the pollutant concentration, the Incident Radiation and the competition between water and TCE for the photocatalytic active sites(1). In this work, the numerical solution of the mass transfer partial differential equation in a photocatalytic reactor with glass fiber meshes coated with titanium dioxide and UV irradiated is accomplished. This numerical solution avoids the use of a mass transfer coefficient over the catalytic surface, obtained by means of typical correlations for gas-solid interfaces under the correspondent flow regime(2,3). Changing the relevant system parameters, it is possible to simulate the reactor behaviour under different operation conditions.Fil: Esterkin, C. R.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Negro, Antonio Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Cassano, Alberto Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Alfano, Orlando Mario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin

Photoreactor Modeling: Applications to Advanced Oxidation Processes

A general methodology for photoreactor analysis and design based on the fundamentals of chemical reaction engineering and radiative transfer in participating media is presented. Three applications in the field of advanced oxidation processes are considered to illustrate the proposed approach: (i) a photocatalytic reactor for air purification, (ii) a homogeneous photo-Fenton solar reactor, and (iii) a heterogeneous photocatalytic slurry reactor. In the first case, the procedure is exemplified with the modeling of a multiannular photocatalytic reactor for perchloroethylene removal from contaminated air streams. A rigorous physical and mathematical model of the multiannular concentric photoreactor was developed and experimentally verified. The second approach is illustrated with the degradation of a model pollutant by the Fenton and photo-Fenton reactions in a nonconcentrating, flat-plate solar reactor. Formic acid was chosen as the model substrate. The effect of the reaction temperature on the pollutant degradation rate is analyzed. In the case of the slurry photoreactor, the intrinsic kinetics of the photocatalytic decomposition of a toxic organic compound in aqueous solution, using suspended titanium dioxide catalytic particles and ultraviolet polychromatic radiation, is studied. The kinetic parameters are evaluated for different catalyst loadings, irradiation levels and pollutant initial concentrations. By means of these illustrative examples, the need of a systematic and rigorous approach to the analysis and design of photoreactors is emphasized.Fil: Alfano, Orlando Mario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Cassano, Alberto Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin

Scaling-Up of Photoreactors: Applications to Advanced Oxidation Processes

A general procedure to perform the scaling-up of photochemical reactors from first principles is presented, working with three applications to Advanced Oxidation Technologies. This work is not a review paper on the subject; it is an abridged description of the analysis and design methods developed with our coworkers during the last fifteen years. The objective of our commitment was to scaling-up photoreactors of any type, starting from small-scale laboratory reactors results, with the additional imposed restraint of never making use of empirically adjusted parameters. All our proposals are based on the principles of chemical reactor engineering science and the rigorous application of radiation field theory. The description is made starting from one process where the design makes use of a radiation model that only requires two optical properties: the radiation absorption and reflection coefficients of the employed catalyst (TiO2). The procedure is illustrated with catalytic wall reactors in the gas phase. The kinetics was obtained in a small flat plate laboratory reactor (Total reacting surface area=81 cm2) and extrapolated to a much larger reactor made of three concentric annular cylindrical tubes with all their walls coated with the catalyst (Total reacting surface area=5,209 cm2). Both the laboratory and the pilot size reactor had to be modeled. The pollutant degraded was perchloroethylene (PCE) in air. A complete reaction sequence was employed. In both cases, Philips lamps of different sizes but of the same type TL/08-F4T5/BLB were used. Results were quite satisfactory. The next case concerns a simple homogeneous reaction studying the degradation of formic acid employing H2O2 and UVC radiation (Germicidal). The kinetic model and the reaction sequence were obtained in a small laboratory batch reactor (V=70 cm3) and extrapolated to a continuous tubular reactor of annular cross section (A=65 cm2) having L=2m of reaction length. In this case, the required optical property is the absorption coefficient of hydrogen peroxide to apply the radiative transfer equation (RTE) without scattering. Similarly as in previous case, both the laboratory reactor and the larger continuous reactor had to be mathematically described. In both cases, the same type of lamp was employed: Philips TUV lamp. Predictions of the reactor performance were quite acceptable. The third illustration, considers a TiO2, slurry photocatalytic reactor for degrading 4- chlorophenol. In this case, the complete RTE is required. Thus, all the optical properties are needed: the absorption and scattering coefficients as well as the phase function for scattering. The kinetic model and the reaction sequence were obtained in a small laboratory, batch reactor (of variable size from 29 to 290.4 cm3) and extrapolated to a larger reactor (V=734.4 cm3) having completely different irradiation conditions and configuration. Once more, it was necessary to model both the laboratory reactor and the larger scale one. In both cases, lamps with very similar spectral output power distribution were employed (Actinic type: Philips TL/08 and TLK/09N). Very satisfactory results were obtained. There are several key points to note in a procedure that permits to move from laboratory reactors to significant scale-ups without experimentally adjustable parameters. The approach is based on four necessary conditions: (i) to have a validated kinetic scheme (a detailed mechanism or a precise empirical representation), (ii) to have a validated, intrinsic reaction kinetic expression as a function of position and time [R(x,t)], (iii) to use in both reactors the same spectral radiation output power distribution [l for monochromatic radiation and f(l) for the polychromatic cases], and (iv) to apply and correctly solve a rigorous mathematical model to both the laboratory and the large-scale reactor.Fil: Alfano, Orlando Mario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Cassano, Alberto Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin

Design and Analysis of Homogeneous and Heterogeneous Photochemical Reactors

A short chapter to make a complete discussion of photoreactoreactor analysis and design is an impossible task unless we decide that the readers of this work have a previous background on the subject and chemical engineering fundamentals. Moreover, we can increase its feasibility if coverage is restricted to only a fraction, albeit significant, of some homogeneous and heterogeneous photoreactions. On these premises, it is possible to concentrate our effort in those aspects that are distinctive of homogeneous photochemical and heterogeneous photocatalytic processes. For the missing details, the reader is referred to the original publications. The distinct aspect of these reactions is the unavoidable existence of a radiation field inside the reactor, which only in very special and unusual cases can be considered uniform in space and frequently is not even constant in time. This is so because inside the reaction space, besides geometrical effects produced by the characteristics of the reactor geometry, there must be absorption of radiation to produce the reaction activation. This absorption means attenuation of the incoming intensities; i.e. without attenuation, there is no photochemical reaction. In some heterogeneous systems, scattering is another source of variation in the incoming rays. Hence, spatial variations are unavoidable. These intrinsic non-uniformities, unfortunately often neglected or not properly accounted for, are responsible for the majority of the difficulties associated with photoreactor analysis and design. Many different shapes and configurations are possible for either single-phase or multiphase reactors (Braun et al., 1993; Cassano et al., 1995; Puma and Yue, 1998; Ray, 1998; Cassano and Alfano, 2000; Alfano et al., 2000). Again, we will restrict ourselves to describe in more details only a few of them. A systematic approach to the design of a reactor should start by discussing the field of velocity distributions. Much progress has been achieved in this area and the hydrodynamic characterization of a great variety of reactors is already known. For the sake of brevity in our work we will concentrate on two types of systems: a perfectly mixed reaction space and a fully developed unidirectional flow in a tubular reactor. In practical terms this is not a serious limitation; computational fluid mechanics commercially available calculating codes can be used to solve almost any other form of reactor configuration.Fil: Cassano, Alberto Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Alfano, Orlando Mario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin

A Reaction Kinetic Model for Ozone Decomposition in Aqueous Media valid for Neutral and Acidic pH

A kinetic scheme for ozone decomposition in aqueous media has been developed. It can be applied for an extended range of pHs from acidic to neutral operating conditions. All experiments were made in a homogeneous medium under an assured kinetic controlling regime. Under no circumstances, a headspace existed in the reactor volume. The starting point of the reaction was always under the prerequisite of a true state of initial equilibrium conditions for the mixture water?ozone?oxygen. The model, that is not intended to be a true reaction mechanism,was derived fromthe 18 reaction steps mechanism proposed by Bühler et al. [R.E. Bühler, J. Staehelin, J. Hoigné, Ozone decomposition inwater studied by pulse radiolysis. 1. HO2/O2− and HO3/O3− as intermediates, J. Phys. Chem. 88 (1984) 2560?2564] and Staehelin et al. [J. Staehelin, R.E. Bühler, J. Hoigné, Ozone decomposition inwater studied by pulse radiolysis. 2. OH and HO4 as chain intermediates, J. Phys. Chem. 88 (1984) 5999?6004]. Most of the kinetic constants are known, but unfortunately they have not been obtained at the same pH (variations from 0.9 to almost 13 exist) and in one particular case was the result of a parametric estimation resorting to assumptions about the value of four other unknown constants in the proposed reaction sequence. With an accurate phenomenological modification represented by an analytical expression, a function of pH was introduced in what was found to be the most critical constant of the previously mentioned mechanism. The resulting set of reactions steps reproduces with very good agreement experiments made at pH 3, 4.8 and 6.3. These results should be useful to be applied as background information to analyze the use of ozone to degrading chlorinated organic compounds that render reaction by products (HCl), which reduce the pH of the reacting medium along the reaction evolution. Thus, the ultimate objective of this work is to derive a working and practical reaction sequence valid under these variable operating conditions.Fil: Lovato, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Martin, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Cassano, Alberto Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin

Decolorization of Water for Domestic Supply Employing UV Radiation and Hydrogen Peroxide

A kinetic study concerning water decolorization using a combination of low wavelength UV radiation (253.7 nm) and hydrogen peroxide has been performed. Kinetic studies were carried out in a specially designed flat plate reactor, made in such a way that almost “isoactinic” conditions are achieved. Results were analyzed in terms of a very simple kinetics expression. Absorbed radiation effects were duly quantified by means of a one-dimensional radiation field model. With experimental degradation rates, a kinetics expression relating the initial color (expressed in terms of initial total organic carbon) with the most important process variables was proposed and the decolorization kinetics parameters were obtained. The initial decolorization rates at 25°C can be properly represented with an equation of the following form: RTOC0=-kCTOC0ea(z).Fil: Martin, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Alfano, Orlando Mario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Cassano, Alberto Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin

Degradation of dichloroacetic acid in homogeneous aqueous media employing ozone and UVC radiation

A tentative workable mechanism for dichloroacetic acid decomposition (DCA) in aqueous media employing ozone and UVC radiation has been developed. All experiments were made in a homogeneous medium under assured kinetic control regime. Under no circumstances did a headspace exist in the reactor volume. The starting point of the reaction with UVC radiation was always under the prerequisite of a confirmed state of initial equilibrium conditions for the mixture water-ozone-oxygen at 20 ?C. The explored variables were: (i) DCA initial concentration, (ii) ozone concentration and (iii) fluence rate at the reactor window. The model comprises three parallel reactions: (1) direct photolysis, (2) direct ozonation and (3) ozone + UVC degradation. Complete DCA removal was achieved, and the mass balance, considering DCA disappearance and chloride ion formation, closed within very small error. The combination of ozone and UVC radiation produces a significant amount of hydrogen peroxide as an important reaction by-product. The direct photolysis can be well represented with a six step reaction sequence. The direct ozonation mechanism comprises 22 steps and, with the entire set of kinetic constants completed in this work, it is independent of the reaction pH in the range from 3 to 6.3. Lastly, the associated use of ozone and UVC radiation becomes necessary to consider the existence of radiation absorption by three species, namely DCA, ozone and hydrogen peroxide. The developed system, including the three parallel reactions, led to the proposal of a 37 step reaction mechanism. Finally the reaction kinetics, the mass balances and the radiation field corresponding to this complex system were rigorously modeled and the most significant features of the mathematical representation are briefly described. The simulation results rendered from this model agree very well with the measured experimental data. This outcome will be essential for deriving a complete reactor model that must be appropriate to describe, in the future, the more practical two-phase operating system.Fil: Lovato, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); Argentina. Universidad Nacional del Litoral; ArgentinaFil: Martin, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); Argentina. Universidad Nacional del Litoral; ArgentinaFil: Cassano, Alberto Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); Argentina. Universidad Nacional del Litoral; Argentin

Water Decolorization Using UV Radiation and Hydrogen Peroxide: A Kinetic Study

Sometimes, provision of water for domiciliary consumption faces the problem of natural contamination originated by the presence of organic substances such as humic or fulvic acids. Very often, after conventional sanitary treatments this water exhibits a persistent yellowish coloration that affects its use. Moreover, these substances may act as precursors of tri-halomethanes formation during pre-desinfection with chlorine. This paper presents, with a simplified mechanistic approach, the intrinsic reaction kinetics of natural water decolorization employing UV radiation and hydrogen peroxide. The main variables for the model are: contaminant concentration expressed as TOC, hydrogen peroxide concentration and the photon absorption rate.Fil: Martin, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Alfano, Orlando Mario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Cassano, Alberto Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin

Kinetics of Bacteria Disinfection with UV Radiation in an Absorbing and Nutritious Medium

A kinetic model for water disinfection employing UV-C radiation   was developed that is valid for clear waters as well as for a concentrated and nutritious medium. Escherichia coli was used as a test bacteria. The kinetic model is a modification of the series event inactivation mathematical description that takes into account the radiation absorption rate corresponding to the existing, viable bacteria and the radiation attenuation produced by the quasi transparent or the translucent environment. It also explains two additional observed phenomena: (i) the effect of bacteria growth in the nutritious medium during disinfection and (ii) a further reduction in the inactivation rate that was attributed to some form of bacteria protection produced by a not well understood association of the bacteria with of the components of the concentrated culture. Comparing theoretical predictions from the model with experimental concentration vs. time data, the model parameters were obtained. Predictions show good agreement with collected experimental data within the range of the explored variables.Fil: Labas, Marisol Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Martin, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Cassano, Alberto Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin

The local and observed photochemical reaction rates revisited

In a broad sense, photochemical reactions proceed through pathways involving several reaction steps. The initiation step is the absorption of energy both by the reactant or sensitizer molecules and in some cases, by the catalyst, leading to intermediate products that ultimately give rise to stable end products. Preferably, the reaction rate expression is derived from a proposed mechanism together with sound simplifying assumptions; otherwise, it may be adopted on an empirical basis. Under a kinetic control regime, the rate expression thus obtained depends on the local rate of photon absorption according to a power law whose exponent very often ranges from one half to unity. The kinetic expression should be valid at every point of the reactor volume. However, due to radiation attenuation in an absorbing and/or scattering medium, the value of the photon absorption rate is always a function of the spatial position. Therefore, the overall photochemical reaction rate will not be uniform throughout the entire reaction zone, and the distinction between local and volume average photochemical reaction rates becomes mandatory. Experimental values of reaction rates obtained from concentration measurements performed in well-mixed reaction cells are, necessarily, average values. Consequently, for validation purposes, experimental results from these cells must be compared with volume averages of the mechanistically or empirically derived local reaction rate expressions. In this work it is shown that unless the rate is first order with respect to the photon absorption rate or the attenuation in the absorbing and/or scattering medium is kept very low, when the averaging operation is not performed, significant errors may be expected.Fil: Alfano, Orlando Mario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Irazoqui, Horacio Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Cassano, Alberto Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin