Browsing by Author "Casas, Jose A."
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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.
- Experimental and modelling study of CWPO over P-doped carbon black catalystsPublication . Díaz de Tuesta, Jose Luis; Quintanilla, Asunción; Casas, Jose A.; Rodriguez, Juan; Ribeiro, Rui; Silva, Adrián; Faria, Joaquim; Gomes, HelderThe catalytic wet peroxide oxidation (CWPO) of 4-nitrophenol (4-NP) with phosphorous doped carbon black catalysts (P-CB) was studied in the present work. The effect of reaction time (0-8 h), temperature (50-80 ºC) and initial pH (2-4) on 4-NP removal and hydrogen peroxide consumption was investigated. Results exhibited the presence of an induction period showing an inverse dependence with the operating temperature and initial pH (pH0). The power law model described well the reaction rates of 4-NP removal and hydrogen peroxide consumption. The slow initial rates were reproduced by taking into account the evolution of pH, expressed in terms of proton concentration in the model. Fitted kinetic equations and estimated parameter values are summarized in Table 1. As can be seen in Figure 1, the kinetic model properly describes the oxidation process.
- 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.
- N, B and P doped carbon blacks for the CWPO of 4-nitrophenol solutionsPublication . Díaz de Tuesta, Jose Luis; Quintanilla, Asunción; Casas, Jose A.; Rodriguez, Juan; Ribeiro, Rui; Silva, Adrián; Faria, Joaquim; Gomes, HelderA previous work has demonstrated that the Chemviron Carbon Black (CB, ref.:2156090) is a catalyst capable to combine a good activity with an adequate stability for long term use and high efficiency of H2O2 consumption in the CWPO of phenol [1]. In the current work, this catalyst was tested for the oxidation of 4-nitrophenol (4-NP). Furthermore, the catalyst was doped with nitrogen, boron and phosphorous in order to increase its activity.
- Reaction lag-phase in the CWPO of 4-nitrophenol solutions with P-doped carbon black catalystsPublication . Díaz de Tuesta, Jose Luis; Quintanilla, Asunción; Casas, Jose A.; Rodriguez, Juan; Ribeiro, Rui; Silva, Adrián; Faria, Joaquim; Gomes, HelderPrevious works have demonstrated that Chemviron Carbon Black (CB) is a catalyst capable to combine a good activity with an adequate stability for long term use and high efficiency of H2Ü2 consumption in the catalytic wet peroxide oxidation (CWPO) process [l]. Phosphorous doping was now used as a mean to increase the catalyst performance.
- Simulation and optimization of the CWPO process by combination of aspen plus and 6-factor doehlert matrix: Towards autothermal operationPublication . Díaz de Tuesta, Jose Luis; Quintanilla, Asunción; Moreno, Daniel; Ferro, Víctor R.; Casas, Jose A.This work aims to present an industrial perspective on CatalyticWet Peroxide Oxidation (CWPO) technology. Herein, process simulation and experimental design have been coupled to study the optimal process conditions to ensure high-performance oxidation, minimum H2O2 consumption and maximum energetic effciency in an industrial scale CWPO unit. The CWPO of phenol in the presence of carbon black catalysts was studied as a model process in the Aspen Plus® v11 simulator. The kinetic model implemented, based on 30 kinetic equations with 11 organic compounds and H2O2 involvement, was valid to describe the complex reaction network and to reproduce the experimental results. The computer experiments were designed on a six-factor Doehlert Matrix in order to describe the influence of the operating conditions (i.e., the different process temperatures, inlet chemical oxygen demands, doses of H2O2 and space time) on each selected output response (conversion, e ciency of H2O2 consumption and energetic effciency) by a quadratic model. The optimization of the WPO performance by a multi-criteria function highlighted the inlet chemical oxygen demand as the most influential operating condition. It needed to have values between 9.5 and 24 g L-1 for autothermal operation to be sustained under mild operating conditions (reaction temperature: 93–130 ºC and pressure: 1–4 atm) and with a stoichiometric dose of H2O2.
- The pH effect on the kinetics of 4-nitrophenol removal by CWPO with doped carbon black catalystsPublication . Díaz de Tuesta, Jose Luis; Quintanilla, Asunción; Casas, Jose A.; Morales-Torres, Sergio; Faria, Joaquim; Silva, Adrián; Gomes, HelderP, B and N-doped carbon blacks prepared with H3PO4, urea and H3BO3 were tested as catalysts in the wet peroxide oxidation of a concentrated 4-nitrophenol (4-NP) model solution (C4-NP=5 g·L−1). The highest catalytic activity was found for P-doped carbon black (complete removal of 4-NP after 4 h at 80 °C, Ccat=2.5 g·L−1, CH2O2 17.8 g·L = 1 and initial pH 3, whereas 44-19% removals were reached with the other catalysts). That was ascribed to the strongest acidity (pHPZC=3.5) and hydrophilic character of the catalyst. Initial pH affected the oxidation, allowing to increase strongly the conversion of 4-NP with the P-doped catalyst decreasing the initial pH from 4 to 2 (4-NP removal from 20% to 99% after 8 h of reaction time at 50 °C, Ccat=2.5 g·L−1 andCH2O2 17.8 g·L = 1). An autocatalytic-power-law kinetic model was developed to predict the observed induction period and the dependence on the pH of the 4-NP oxidation, H2O2 consumption and pH evolution (k4- NP=2.2·10−5M−2min−1, kH2O2 4.0·10 M ·min = 6 3 1 and k 5.1·10 M min H + = 3 0.23 1 at 80 °C).