Fiderman Machuca-Martínez

Photocatalytic Mineralization of Commercial Herbicides in a Pilot-Scale Solar CPC Reactor: Photoreactor Modeling and Reaction Kinetics Constants Independent of Radiation Field

The six-flux absorption-scattering model (SFM) of the radiation field in the photoreactor, combined with reaction kinetics and fluid-dynamic models, has proved to be suitable to describe the degradation of water pollutants in heterogeneous photocatalytic reactors, combining simplicity and accuracy. In this study, the above approach was extended to model the photocatalytic mineralization of a commercial herbicides mixture (2,4-D, diuron, and ametryne used in Colombian sugar cane crops) in a solar, pilot-scale, compound parabolic collector (CPC) photoreactor using a slurry suspension of TiO(2). The ray-tracing technique was used jointly with the SFM to determine the direction of both the direct and diffuse solar photon fluxes and the spatial profile of the local volumetric rate of photon absorption (LVRPA) in the CPC reactor. Herbicides mineralization kinetics with explicit photon absorption effects were utilized to remove the dependence of the observed rate constants from the reactor geometry and radiation field in the photoreactor. The results showed that the overall model fitted the experimental data of herbicides mineralization in the solar CPC reactor satisfactorily for both cloudy and sunny days. Using the above approach kinetic parameters independent of the radiation field in the reactor can be estimated directly from the results of experiments carried out in a solar CPC reactor. The SFM combined with reaction kinetics and fluid-dynamic models proved to be a simple, but reliable model, for solar photocatalytic applications.

Boundary Layer of Photon Absorption Applied to Heterogeneous Photocatalytic Solar Flat Plate Reactor Design

This study provides information to design heterogeneous photocatalytic solar reactors with flat plate geometry used in treatment of effluents and conversion of biomass to hydrogen. The concept of boundary layer of photon absorption taking into account the efficient absorption of radiant energy was introduced; this concept can be understood as the reactor thickness measured from the irradiated surface where 99% of total energy is absorbed. Its thickness and the volumetric rate of photons absorption (VRPA) were used as design parameters to determine (i) reactor thickness, (ii) maximum absorbed radiant energy, and (iii) the optimal catalyst concentration. Six different commercial brands of titanium dioxide were studied: Evonik-Degussa P-25, Aldrich, Merck, Hombikat, Fluka, and Fisher. The local volumetric rate of photon absorption (LVRPA) inside the reactor was described using six-flux absorption-scattering model (SFM) applied to solar radiation. The radiation field and the boundary layer thickness of photon absorption were simulated with absorption and dispersion effects of catalysts in water at different catalyst loadings. The relationship between catalyst loading and reactor thickness that maximizes the absorption of radiant energy was obtained for each catalyst by apparent optical thickness. The optimum concentration of photocatalyst Degussa P-25 was 0.2 g/l in 0.86 cm of thickness, and for photocatalyst Aldrich it was 0.3 g/l in 0.80 cm of thickness.

Photocatalytic Treatment of A Dye Polluted Industrial Effluent With A Solar Pilot-Scale CPC Reactor

Abstract Printing and textile industries produce considerable amounts of dye polluted wastewater. Most of these residues are non-biodegradable and are persistent in the environment. The TiO2-based photocatalysis has been tested for degradation of several dyes and pigments used at industrial scale. In this study, an effluent sample from washing streams of printing-rollers was treated by heterogeneous photocatalysis. The system used for this test was a CPC pilot-scale reactor. The experimental design consisted in a Taguchi system with the initial concentration of pollutant mixture (dilution factor), and the catalyst load as main effects. The noise factor was the accumulated UV solar energy, and the dye degradation was the response variable. The best signal-to-noise ratios were achieved at larger dilution factors and catalyst loads. The kinetics of this heterogeneous photocatalytic degradation treatment was modeled by a modified Langmuir-Hinselwood expression with accumulated UV energy per unit of volume as independent variable. The kinetic and adsorption parameters were found with this mathematical model.

Modeling the Photocatalytic Mineralization in Water of Commercial Formulation of Estrogens 17-β Estradiol (E2) and Nomegestrol Acetate in Contraceptive Pills in a Solar Powered Compound Parabolic Collector

Endocrine disruptors in water are contaminants of emerging concern due to the potential risks they pose to the environment and to the aquatic ecosystems. In this study, a solar photocatalytic treatment process in a pilot-scale compound parabolic collector (CPC) was used to remove commercial estradiol formulations (17-β estradiol and nomegestrol acetate) from water. Photolysis alone degraded up to 50% of estradiol and removed 11% of the total organic carbon (TOC). In contrast, solar photocatalysis degraded up to 57% of estrogens and the TOC removal was 31%, with 0.6 g/L of catalyst load (TiO2 Aeroxide P-25) and 213.6 ppm of TOC as initial concentration of the commercial estradiols formulation. The adsorption of estrogens over the catalyst was insignificant and was modeled by the Langmuir isotherm. The TOC removal via photocatalysis in the photoreactor was modeled considering the reactor fluid-dynamics, the radiation field, the estrogens mass balance, and a modified Langmuir–Hinshelwood rate law, that was expressed in terms of the rate of photon adsorption. The optimum removal of the estrogens and TOC was achieved at a catalyst concentration of 0.4 g/L in 29 mm diameter tubular CPC reactors which approached the optimum catalyst concentration and optical thickness determined from the modeling of the absorption of solar radiation in the CPC, by the six-flux absorption-scattering model (SFM).

Mixing Rules Formulation for a Kinetic Model of the Langmuir-Hinshelwood Semipredictive Type Applied to the Heterogeneous Photocatalytic Degradation of Multicomponent Mixtures

Mixing rules coupled to a semipredictive kinetic model of the Langmuir-Hinshelwood type were proposed to determine the behavior of the heterogeneous solar photodegradation with TiO2-P25 of multicomponent mixtures at pilot scale. The kinetic expressions were expressed in terms of the effective concentration of total organic carbon . An expression was obtained in a generalized form which is a function of the mixing rules as a product of a global contribution of the reaction rate constant and a mixing function . Kinetic parameters of the model were obtained using the Nelder and Mead (N-M) algorithm. The kinetic model was validated with experimental data obtained from the degradation of binary mixtures of chlorinated compounds (DCA: dichloroacetic acid and 4-CP: 4-chlorophenol) at different initial global concentration, using a CPC reactor at pilot scale. A simplex-lattice design experiment was adopted to perform the runs.

Modelo Matemático para Estimación de Eficiencias Fotónicas No-Intrínsecas en Reacciones Fotocatalíticas Heterogéneas

A semi-empirical model was formulated to estimate the photonic efficiency of photocatalytic reactions in heterogeneous systems. This is a function of a pre-exponential factor called intrinsic photonic-efficiency and an exponential factor that quantified the effect of catalyst loading, geometry, and initial concentration of substrate. The assumptions and the model were validated on the photodegradation of dichloroacetic acid in three lab-scale heterogeneous photocatalytic reactors, using TiO2-P25 and low energy monochromatic radiation. It was found that the model is highly predictive for photonic efficiencies with relative errors below 1.8%.

Efecto de la Dispersión de Radiación sobre el Rendimiento Cuántico en la Degradación Fotocatalítica de Ácido Dicloroacético

Different models of radiation scattering used to valuate its effect on the amount of radiant energy absorbed by a photocatalyst in the determination of quantum yields were analyzed. The radiation field in a heterogeneous photodecomposition of dichloroacetic acid catalyzed by particles of titanium dioxide was simulated using a one-dimensional model to evaluate the absorption and scattering of radiation in the reaction space. The results obtained by the different models of nonisotropic phase function with the isotropic phase function were compared. It was found that the scattering of isotropic radiation is a reasonable approximation for scattering produced by suspended particles of titanium dioxide.

Distillery Wastewater Treated by Electrochemical Oxidation with Boron-Doped Diamond Electrodes

Abstract Electrochemical oxidation of pretreated distillery wastewater was performed using a boron doped diamond anode (BDD). The role of direct oxidation of organic matter was assessed with experiments of linear sweep voltammetry, noting that the deactivation of the electrode surface occurs in the region of potentials below oxygen evolution. Then, galvanostatic bulk electrolyses were conducted during 4 hours at current densities (20 mAcm-2, 30 mAcm-2 and 40 mAcm-2) corresponding to high anodic potentials, in a single compartment flow cell in a re-circulated batch process. Two different flow rates were evaluated, finding that the process was controlled by the mass transport of organics towards the anode. Initial pH variation did not significantly affect the oxidation process. Analyses of the treated samples were carried out by UV spectroscopy, Pt-Co color, COD and TOC. The degradation of organic compounds measured as TOC was up to 81%; 88% COD removal efficiencies and 98% color removal were also obtained.

Synthesis of Mg-Al layered double hydroxides by electrocoagulation

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CHAPTER 16:Photocatalytic Reactor Modeling

The fundamental aspects of photocatalytic reactor modeling are detailed in this chapter. The relevance of the radiation and scattering models applied to compound parabolic collectors (CPCs) and flat plate photoreactor (FPR) geometries with a kinetic model for different compounds is shown. The key factors of the modeling of a solar photoreactor and the optimization methods are explored from a new point of view. The mathematical structure of the model applied to the solar scale is described including its experimental validation.