RESUMEN
A methodology for photocatalytic reactor modeling applied to advanced oxidation processes for chemical pollution abatement is presented herein. Three distinct reactor configurations typically employed in the field of air and water purification-wall reactors, slurry reactors, and fixed-bed reactors-are considered to illustrate the suggested approach. Initially, different mechanistically derived kinetic expressions to represent the photocatalytic rate of pollutant degradation are reviewed, indicating the main assumptions made by the authors in the published contributions. These kinetic expressions are needed to solve the mass balances of the reactant species in the photocatalytic reactors. As is well known, at least one of the steps of the reaction mechanism requires evaluation of the rate of electron-hole generation, which depends on the photon absorption rate: a volumetric property for reactions with the catalyst particles in aqueous suspension or a surface property for systems with a fixed catalyst deposited on an inert support. Subsequently, the different techniques for evaluating the optical properties of slurry and immobilized systems, and the numerical methods applied to calculate the photon absorption rate, are described. The experimental and theoretical results of pollutant degradation in each reactor type are then presented and analyzed. Finally, the definition, calculation, and relevance of different efficiency parameters are briefly reviewed. Using these illustrative examples, we emphasize the need for a systematic and rigorous approach for photocatalytic reactor modeling in order to overcome the inherent drawbacks of photocatalysis and to improve the overall efficiency of the process.
Asunto(s)
Luz , Modelos Teóricos , Contaminantes Químicos del Agua/química , Catálisis , Ácido Clofíbrico/química , Cinética , Oxidación-Reducción , Fotones , Titanio/químicaRESUMEN
This work presents the photocatalytic degradation of the pharmaceutical drug clofibric acid in a fixed-bed reactor filled with TiO2-coated glass rings. Experiments were carried out under UV radiation. A kinetic model that takes into account radiation absorption by means of the local surface rate of photon absorption (LSRPA) has been developed. The LSRPA was obtained from the results of a radiation model. The Monte Carlo method was employed to solve the radiation model, where the interaction between photons and TiO2-coated rings was considered. Data from experiments carried out with rings with different numbers of catalyst coatings and different irradiation levels were used to estimate the parameters of the kinetic model. A satisfactory agreement was obtained between model simulations and experimental results.
Asunto(s)
Ácido Clofíbrico , Vidrio/química , Modelos Teóricos , Titanio/química , Contaminantes Químicos del Agua , Ácido Clofíbrico/análisis , Ácido Clofíbrico/química , Ácido Clofíbrico/efectos de la radiación , Cinética , Fotólisis , Contaminantes Químicos del Agua/análisis , Contaminantes Químicos del Agua/química , Contaminantes Químicos del Agua/efectos de la radiaciónRESUMEN
The removal of two blood lipid regulators, clofibric acid (CLA) and gemfibrozil (GFZ), was evaluated using two identical aerobic membrane bioreactors with 6.5 L effective volume each. Polysulfone ultrafiltration hollow fiber membranes were submerged in the reactors. Different operating conditions were tested varying the organic load (F/M), hydraulic residence time (HRT), biomass concentration measured as total suspended solids in the mixed liquor (MLTSS) and the sludge retention time (SRT). Complete GFZ removal was obtained with F/M of 0.21-0.48 kg COD kgTSS⻹ d⻹, HRT of 4-10 hours, SRT of 10-32 d and MLTSS of 6-10 g L⻹. The GFZ removal can be attributed to biodegradation and there was no accumulation of the compound in the biomass. The CLA removals improved with the SRT and HRT increase and F/M decrease. Average removals of 78-79% were obtained with SRT 16-32 d, F/M of 0.21-0.34 kgCOD kgTSS⻹ d⻹, HRT of 7-10 hours and MLTSS of 6-10 g L⻹. Biodegradation was found to be the main removal pathway.
Asunto(s)
Reactores Biológicos , Ácido Clofíbrico/química , Gemfibrozilo/química , Membranas Artificiales , Eliminación de Residuos Líquidos/métodos , Contaminantes Químicos del Agua/química , Biomasa , Ácido Clofíbrico/metabolismo , Gemfibrozilo/metabolismo , Hipolipemiantes/química , Hipolipemiantes/metabolismo , Aguas del Alcantarillado , Ultrafiltración/instrumentación , Ultrafiltración/métodosRESUMEN
A kinetic study of the photocatalytic degradation of the pharmaceutical clofibric acid is presented. Experiments were carried out under UV radiation employing titanium dioxide in water suspension. The main reaction intermediates were identified and quantified. Intrinsic expressions to represent the kinetics of clofibric acid and the main intermediates were derived. The modeling of the radiation field in the reactor was carried out by Monte Carlo simulation. Experimental runs were performed by varying the catalyst concentration and the incident radiation. Kinetic parameters were estimated from the experiments by applying a non-linear regression procedure. Good agreement was obtained between model predictions and experimental data, with an error of 5.9 % in the estimations of the primary pollutant concentration.
Asunto(s)
Ácido Clofíbrico/química , Ácido Clofíbrico/efectos de la radiación , Modelos Químicos , Contaminantes Químicos del Agua/química , Cinética , Procesos Fotoquímicos , Titanio/química , Rayos Ultravioleta , Purificación del AguaRESUMEN
A tetrazole isosteric analogue of clofibric acid (1) was prepared using a short synthetic route and was characterized by elemental analysis, NMR ((1)H, (13)C) spectroscopy, and single-crystal X-ray diffraction. The in vitro inhibitory activity of 1 against 11ß-hydroxysteroid dehydrogenase type 1 (11ß-HSD1) was evaluated, showing a moderate inhibitory enzyme activity (51.17% of inhibition at 10 µM), being more active than clofibrate and clofibric acid. The antidiabetic activity of compound 1 was determined at 50 mg/Kg single dose using a non insulin dependent diabetes mellitus rat model. The results indicated a significant decrease of plasma glucose levels, during the 7h post-administration. Additionally, we performed a molecular docking of 1 into the ligand binding pocket of one subunit of human 11ß-HSD1. In this model, compound 1 binds into the catalytic site of 11ß-HSD1 in two different orientations. Both of them, show important short contacts with the catalytic residues Ser 170, Tyr 183, Asp 259 and also with the nicotinamide ring of NADP(+).
Asunto(s)
Ácido Clofíbrico/química , Hipoglucemiantes/síntesis química , Tetrazoles/química , 11-beta-Hidroxiesteroide Deshidrogenasa de Tipo 1/antagonistas & inhibidores , 11-beta-Hidroxiesteroide Deshidrogenasa de Tipo 1/metabolismo , Animales , Sitios de Unión , Glucemia/análisis , Dominio Catalítico , Cristalografía por Rayos X , Diabetes Mellitus Experimental/tratamiento farmacológico , Evaluación Preclínica de Medicamentos , Humanos , Enlace de Hidrógeno , Hipoglucemiantes/química , Hipoglucemiantes/uso terapéutico , Ratones , Simulación del Acoplamiento Molecular , Ratas , Relación Estructura-Actividad , Tetrazoles/síntesis química , Tetrazoles/uso terapéuticoRESUMEN
Pharmaceutical and Personal Care Products (PPCPs) are considered emerging contaminants, and their efficient removal from water is going to be a challenging endeavor. Microporous adsorbent materials, including pillared clays, could offer a potential solution if tailored properly. Although pillared clays have been employed previously for the removal of organics, the effective removal of PPCPs will only be possible if their surface and textural properties are manipulated from the bottom-up. This work presents the use of modified inorganic-organic pillared clays (IOCs) for the adsorption of salicylic acid, clofibric acid, carbamazepine, and caffeine. The IOCs have been modified with Co(2+), Cu(2+), or Ni(2+) to induce complexation-like adsorbate-adsorbent interactions at ambient conditions, in an attempt to provide an efficient and yet reversible driving force in the sub-ppm concentration range. Furthermore, the IOCs were partially calcined to increase effective surface area by an order of magnitude while preserving some hydrophobicity. In general, the Ni(2+) IOCs exhibited the greatest interaction with salicylic and clofibric acids, respectively, while the Co(2+) adsorbents excelled at adsorbing caffeine at low concentrations. All of the metal-modified IOCs showed comparable adsorption capacities for the case of carbamazepine, probably due to the lack of availability of particular functional groups in this adsorbate.