Browsing by Author "Munoz, Macarena"
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- Aplicación del proceso Fenton al tratamiento de aguas oleosasPublication . Munoz, Macarena; Domínguez, Carmen M.; Díaz de Tuesta, Jose Luis; Gomes, Helder; Casas, Jose A.En este trabajo se explora la viabilidad de procesos tipo Fenton, homogéneo y heterogéneo, para el tratamiento de contaminantes lipofílicos contenidos en aguas oleosas. Se ha seleccionado el colorante Sudán IV como contaminante modelo y el ciclohexano como fase oleosa. Atendiendo al distinto coeficiente de reparto en el sistema bifásico agua-ciclohexano, se han seleccionado cuatro catalizadores basados en hierro; dos compuestos de hierro homogéneos: una sal soluble en la fase acuosa y un complejo soluble en la fase orgánica, y dos catalizadores heterogéneos: hierro soportado en carbón activo (localizado preferentemente en la fase orgánica) y magnetita natural (con afinidad por ambas fases y principalmente concentrado en la interfase). El estudio preliminar de los cuatro catalizadores en la descomposición de H2O2 (en ausencia de contaminante) reveló que los catalizadores homogéneos son más activos y, por tanto, presentan mayor potencial para ser utilizados en sistemas bifásicos. En presencia de estos materiales (10 mg L-1) se consiguen conversiones de contaminante superiores al 50% a las 24 h de reacción, trabajando con la cantidad estequiométrica de oxidante. Los resultados obtenidos son prometedores y abren la puerta a la síntesis y aplicación de nuevos catalizadores homogéneos adecuados para este tipo de sistemas.
- Condensation by-products in wet peroxide oxidation: Fouling or catalytic promotion? Part I: Evidences of an autocatalytic processPublication . Quintanilla, Asunción; Díaz de Tuesta, Jose Luis; Figueruelo, Cristina; Munoz, Macarena; Casas, Jose A.The deposition of condensation by-products onto the catalyst surface upon wet peroxide and wet air oxidation processes has usually been associated with catalyst deactivation. However, in Part I of this paper, it was demonstrated that these carbonaceous deposits actually act as catalytic promoters in the oxygen-assisted wet peroxide oxidation (WPO-O2) of phenol. Herein, the intrinsic activity, nature and stability of these species have been investigated. To achieve this goal, an up-flow fixed bed reactor packed with porous Al2O3 spheres was used to facilitate the deposition of the condensation by-products formed in the liquid phase. It was demonstrated that the condensation by-products catalyzed the decomposition of H2O2 and a higher amount of these species leads to a higher degree of oxidation degree The reaction rates, conversion values and intermediates’ distribution were analyzed. The characterization of the carbonaceous deposits on the Al2O3 spheres showed a significant amount of condensation by-products (~6 wt.%) after 650 h of time on stream. They are of aromatic nature and present oxygen functional groups consisting of quinones, phenols, aldehydes, carboxylics and ketones. The initial phenol concentration and H2O2 dose were found to be crucial variables for the generation and consumption of such species, respectively
- Condensation by-products in wet peroxide oxidation: Fouling or catalytic promotion? Part II: Activity, nature and stabilityPublication . Quintanilla, Asunción; Díaz de Tuesta, Jose Luis; Figueruelo, Cristina; Munoz, Macarena; Casas, Jose A.The deposition of condensation by-products onto the catalyst surface upon wet peroxide and wet air oxidation processes has usually been associated with catalyst deactivation. However, in Part I of this paper, it was demonstrated that these carbonaceous deposits actually act as catalytic promoters in the oxygen-assisted wet peroxide oxidation (WPO-O2) of phenol. Herein, the intrinsic activity, nature and stability of these species have been investigated. To achieve this goal, an up-flow fixed bed reactor packed with porous Al2O3 spheres was used to facilitate the deposition of the condensation by-products formed in the liquid phase. It was demonstrated that the condensation by-products catalyzed the decomposition of H2O2 and a higher amount of these species leads to a higher degree of oxidation degree The reaction rates, conversion values and intermediates’ distribution were analyzed. The characterization of the carbonaceous deposits on the Al2O3 spheres showed a significant amount of condensation by-products (~6 wt.%) after 650 h of time on stream. They are of aromatic nature and present oxygen functional groups consisting of quinones, phenols, aldehydes, carboxylics and ketones. The initial phenol concentration and H2O2 dose were found to be crucial variables for the generation and consumption of such species, respectively.
- Modified carbide-derived carbons used in the catalytic wet peroxide oxidation of oily wastewatersPublication . Díaz de Tuesta, Jose Luis; Munoz, Macarena; Domínguez, Carmen M.; Casas, Jose A.; Gläsel, Jan; Etzold, Bernard; Silva, Adrián; Faria, Joaquim; Gomes, HelderModified carbide-derived carbon (CDC) materials, prepared from TiC, were tested as catalysts in the decomposition of H2O2 and in the catalytic wet peroxide oxidation (CWPO) of 4-nitrophenol (4-NP), either in aqueous phase or in biphasic medium. The reactive extraction of Ti from the metal carbide (2 μm) was carried out to prepare the CDC materials, as described elsewhere [1]. Briefly, 0.03 m s−1 Cl2 gas was used (1.5 mol m−3 in He) as extraction agent during 5 h at 800, 1000 and 1200 ºC. Afterwards, H2 was used for 0.5 h at the extraction temperature to remove residual chlorine, resulting in CDC-800, CDC-1000 and CDC-1200 materials, respectively. Additionally, CDC-800 was treated with a mixture of 98% H2SO4 and 30% w/v H2O2 (3:1) at room temperature for 3 h by two methods: (1) wetting the material in the oxidative solution and (2) oxidizing the material partially encapsulated with WAX paraffin, resulting in CDC-800-Ox and CDC-800-Wax, respectively. Firstly, the materials were tested in the decomposition of H2O2 and, then, in the adsorption and CWPO of 4-NP, adapting the experimental procedure described in previous works [2-3] at the following operating conditions: 25-50 ºC, pH0 = 3.0, and concentrations of solid material, 4-NP and H2O2 of 2.5 g/L, 5.0 g/L and 17.8 g/L, respectively. Cyclohexane, c-C6 (O/W volume ratio = 1:5) was used to simulate oily wastewater and study the influence of the oil phase presence in the medium.