Assessment of carbon monoxide formation in Fenton oxidation process: The critical role of pollutant nature and operating conditions

This work assesses the carbon monoxide formation upon Fenton process, the most popular method for Advanced Oxidation Processes (AOPs). CO concentrations in the order of 11,000 mg/Nm3 were measured in the Fenton oxidation of phenol after 180 min reaction at 90 °C and 3 bar. The Fenton oxidation performed on phenol and its oxidized intermediates such as hydroquinone, catechol and short-chain acids allows concluding that CO is produced through the oxidative cleavage of aromatic rings; the hydroquinone route being more selective to CO than catechol. In all cases, the carbon mass balance was satisfactorily closed to 100%. The study of the influence of the operational conditions shows that CO production is clearly favoured at H2O2 dosage above the stoichiometric value and low temperatures (T< 90º). The H2O2 dosage was the most influence variable. The results of this work evidence for the first time the production of noxious amounts of CO along with CO2 in Fenton processes. This finding highlights the importance of evaluating not only liquid phase intermediates due to their recalcitrant and/or toxic behavior, but also gas phase because of CO emissions.Financial support from the project CTM2016-76454-R (Ministerio de Economia y Competitividad-MINECO, Spain) is gratefully acknowledge

Kinetics of wet peroxide oxidation of phenol with a gold/activated carbon catalyst

Gold nanoparticles supported on activated carbon (Au/AC) have been tested in catalytic wet peroxide oxidation using phenol as target pollutant. In the current work, the effect of several operating conditions, including initial pH (3.5–10.5), catalyst load (0–6 g/L), initial phenol concentration (0.1–5 g/L), hydrogen peroxide dose (4–100% of the theoretical stoichiometric amount) and reaction temperature (50–80 °C) has been investigated. The results show that the Au/AC catalyst would be useful at relatively high pollutant to catalyst ratios (at least 0.4 w/w) and it can work efficiently within a wide range of pH (3.5–7.5). The catalyst suffers rapid deactivation but its activity can be completely restored by an oxidative thermal treatment at low temperature (200 °C). A kinetic model is presented, capable of describing the experimental results. This model is based on a rate equation of order one for hydrogen peroxide consumption and two for phenol oxidation and includes the catalyst deactivation and its temperature dependenceThe authors wish to thank the Spanish MICINN for the financial support through the projects CTQ2008-03988/PPQ and CTQ2010-14807. The Comunidad Autónoma de Madrid is also gratefully acknowledged for the financial support through the project S2009/AMB-158

Structured reactors based on 3D Fe/SiC Catalysts: understanding the effects of mixing

The application of structured reactors provides a number of advantages in chemical processes. In this paper, two different three-dimensional (3D) Fe/SiC catalysts with a square cell geometry have been manufactured by Robocasting: monoliths (D = 14 and H = 15 mm) and meshes (D = 24 and H = 2 mm) and studied in the catalytic phenol oxidation by hydrogen peroxide (H2O2) for the sustainable production of dihydroxybenzenes (DHBZ). The fluid dynamics, catalytic performance, reaction rates, external mass transport limitation, and catalyst stability have been compared in three different reactors, monolithic fixed-bed reactor, multimesh fixed-bed reactor, and monolithic stirrer reactor, at selected operating conditions. The results show that the mechanical stirring of the 3D Fe/SiC monoliths avoids the external mass transfer limitation caused by the presence of oxygen bubbles in the channels (produced from the HOx· species in autoscavenging radical reactions). In addition, the backmixing has a positive effect on the efficient consumption of H2O2 but an adverse effect on the phenol selectivity to DHBZ since they are overoxidized to tar products at longer contact times. On the other hand, the wall porosity, and not the backmixing, affects the susceptibility of the 3D Fe/SiC catalyst to the Fe leaching, as occurs in the mesh structures. In conclusion, the monoliths operating under plug-flow and external mass transfer limitation in the monolithic fixed-bed reactor (MFB) provide an outstanding phenol selectivity to DHBZ and catalyst stabilityThis work is supported by the following agencies and grants: the Spanish Government under projects RTI2018-095052-BI00 (MICINN/AEI/FEDER, UE) and EIN2020-112153 (MCINN/AEI/10.13039/501100011033), the latter was also supported by the European Union through “NextGenerationEU/PRTR”, Community of Madrid under project S2018/ EMT-4341, and CSIC project I-COOP+ 2019 (ref COOPB20405). P.L. acknowledges the Community of Madrid and the European Social Fund for the financial support received through the contract PEJ-2019-AI/IND-14385. The authors thank Juliana Mejía for her technical assistanc

Direct Hydroxylation of Phenol to Dihydroxybenzenes by H2O2 and Fe-based Metal-Organic Framework Catalyst at Room Temperature

A semi-crystalline iron-based metal-organic framework (MOF), in particular Fe-BTC, that contained 20 wt.% Fe, was sustainably synthesized at room temperature and extensively characterized. Fe-BTC nanopowders could be used as an efficient heterogeneous catalyst for the synthesis of dihydroxybenzenes (DHBZ), from phenol with hydrogen peroxide (H2O2), as oxidant under organic solvent-free conditions. The influence of the reaction temperature, H2O2 concentration and catalyst dose were studied in the hydroxylation performance of phenol and MOF stability. Fe-BTC was active and stable (with negligible Fe leaching) at room conditions. By using intermittent dosing of H2O2, the catalytic performance resulted in a high DHBZ selectivity (65%) and yield (35%), higher than those obtained for other Fe-based MOFs that typically require reaction temperatures above 70◦C. The long-term experiments in a fixed-bed flow reactor demonstrated good Fe-BTC durability at the above conditionsThe authors thank the financial support by Consejo Nacional de Ciencia y Tecnología (CONACYT) for the grant number 764635 and the project 256296; and to TNM for the supporting project 5627.19.P. Also, to the Spanish Ministerio de Ciencia, Innovación y Universidades (MICINN) and FEDER program (EU) through the projects: CTM2016-76454-R (MICINN) and RTI2018-095052-B-I00 ((MCIU/AEI/FEDER, UE

Ionic liquids breakdown by Fenton oxidation

Fenton oxidation has proved to be an efficient treatment for the degradation of ionic liquids (ILs) of different families viz. imidazolium, pyridinium, ammonium and phosphonium, in water. The intensification of the process, defined as the improvement on the efficiency of H2O2 consumption, by increasing the temperature is necessary to avoid high reaction times and the need of large excess of H2O2. In this work, temperatures within the range of 70-90°C have been used, which allowed an effective breakdown of the ILs tested (1 g L-1 initial concentration) with the stoichiometric amount of H2O2 and a relatively low Fe3+dose (50 mg L-1). Under these conditions conversion of the ILs was achieved in less than 10 min, with TOC reductions higher than 60% upon 4 h reaction time, except for the phosphonium IL. The remaining TOC corresponded mainly to short-chain organic acids. The treatment reduced substantially the ecotoxicity up to final values below 0.01 TU in most cases and a significant improvement of the biodegradability was achieved. Upon Fenton oxidation of the four ILs tested hydroxylated compounds of higher molecular weight than the starting ILs, fragments of ILs partially oxidized and short-chain organic acids were identified as reaction by-products. Reaction pathways are proposedThis research has been supported by the Spanish MICINN through the projects CTQ2008-03988 and CTQ2010-14807 and by the CM through the project S-2009/AMB-158

Condensation by-products in wet peroxide oxidation: Fouling or catalytic promotion? Part II: Activity, nature and stability

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.This research was supported by the Spanish MINECO through the project CTM-2016-76454-R and by the CM through the project P2018/EMT-4341. M. Munoz thanks the Spanish MINECO for the Ramón y Cajal postdoctoral contract (RYC-2016-20648).info:eu-repo/semantics/publishedVersio

Condensation by-products in wet peroxide oxidation: Fouling or catalytic promotion? Part I: Evidences of an autocatalytic process

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, respectivelyThis research was supported by the Spanish MINECO through the project CTM-2016-76454-R and by the CM through the project P2018/EMT-4341. M. Munoz thanks the Spanish MINECO for the Ramón y Cajal postdoctoral contract (RYC-2016-20648).info:eu-repo/semantics/publishedVersio

Degradation of imidazolium-based ionic liquids by catalytic wet peroxide oxidation with carbon and magnetic iron catalysts

BACKCGROUND: The ‘green’ image of ionic liquids (ILs) has changed in the last few years since numerous works have evidenced their non-biodegradability, persistence and high ecotoxicity, particularly for the most common imidazolium-based ILs. In this work, the feasibility of catalytic wet peroxide oxidation for the degradation of imidazolium-based ILs of different alkyl chain lengths has been studied under selected operating conditions (1000 mg L−1 IL, stoichiometric H2O2 dose, 2 g L−1 catalyst, pH 3 and 90 °C temperature) using different catalysts such as magnetic iron (Fe3O4) supported on γ-Al2O3 and activated carbon (AC) as well as bare carbon materials (graphite, AC). The catalytic activity and stability and the efficiency of H2O2 consumption have been evaluated. RESULTS: Although both AC-based catalysts led to the conversion of the IL, they yielded a low H2O2 consumption efficiency (24% and 45% with AC and Fe3O4/AC, respectively) due to the fast decomposition of H2O2 and the recombination of radical species into H2O and O2, non-reactive species under the operating conditions. In contrast, graphite and Fe3O4/γ-Al2O3 showed high activity allowing complete conversion and relatively high mineralization degrees of all the ILs tested in 1 h reaction time. Among those catalysts, Fe3O4/γ-Al2O3 exhibited a considerably greater stability upon four successive uses where iron leaching was negligible and the magnetic properties were maintained. CONCLUSIONS: Catalytic wet peroxide oxidation has proved to be an interesting alternative for the treatment of imidazolium-based ILs in water. The application of Fe3O4/γ-Al2O3 is particularly promising due to its high activity, remarkable stability and easy magnetic recoveryThis research has been supported by the Spanish MINECO through the project CTQ2013-4196-R and by the CM through the project S2013/MAE-271

Simulation and optimization of the CWPO process by combination of aspen plus and 6-factor doehlert matrix: Towards autothermal operation

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 authors thank the financial support by the Spanish Government and Comunidad de Madrid through the projects CTM2016-76454-R and S2018/EMT-4341, respectively. Also, the authors acknowledge financial support to the Portugal Government through the project UIDB/00690/2020.info:eu-repo/semantics/publishedVersio

Aplicación de metodologías de aprendizaje activo para promover la adquisición de competencias en la asignatura Minimización y Valorización de Residuos

[EN] The subject of Waste Minimization and Valorization of the Master in Chemical Engineering from the Rey Juan Carlos University and Autonomous University of Madrid (elective with reduced number of students), was designed and taught using a methodology based on active learning that has been evaluated after four years of experience. In order to achieve the acquisition of all the competences associated with the subject, and therefore better learning outcomes, a great diversity of training activities were selected, aimed at enhancing each of the basic, general, transversal and specific competences assigned. These include cooperative, collaborative, problem-based learning methodologies, case studies, flipping and networked teaching. The activities that give more prominence to the student, Case Studies and Presentation, allow to evaluate more competences, they lead to very good learning results, with high grades in the frequent evaluation (8-9,3) and favor the acquisition and integration of the knowledge thus obtaining good final grades. In addition, the methodology applied encouraged the students' commitment and motivation, with the assessment of the subjects being high and superior to the average of the master's degree and the other elective subjects.[ES] La asignatura de Minimización y Valorización de Residuos del Máster en Ingeniería Química por la Universidad Rey Juan Carlos y Universidad Autonoma de Madrid (optativa con número de alumnos reducido), se diseñó e impartió aplicando una metodología basada en el aprendizaje activo y participativo que ha sido evaluada tras cuatro años de experiencia. Con el objeto de conseguir la adquisición de todas las competencias asociadas a la asignatura, y por ende unos mejores resultados de aprendizaje, se seleccionaron una gran diversidad de actividades formativas enfocadas a potenciar cada una de las competencias básicas, generales, transversales y específicas asignadas. Éstas incluyen metodologías de aprendizaje colaborativo, cooperativo, basado en problemas, en casos de estudio, aulaAplicación de metodologías de aprendizaje activo para promover la adquisición de competencias enla asignatura Minimización y Valorización de Residuos2018, Universitat Politècnica de ValènciaCongreso IN-RED (2018)inversa y docencia en red. Las actividades que dan más protagonismo al estudiante, Casos de Estudio y Presentación, permiten evaluar más competencias, conducen a muy buenos resultados de aprendizaje, con altas calificaciones en la evaluación frecuente (8-9,3) y favorecen la adquisición e integración de los conocimientos lo que se traduce en buenas calificaciones finales. Además la metodología aplicada fomentó el compromiso y motivación de los estudiantes siendo la valoración de la asignatura por parte de los mismos alta y superior a la media del máster y de las otras asignaturas optativas.Gómez Sainero, L.; Díaz Nieto, E.; Quintanilla Gómez, A. (2018). Aplicación de metodologías de aprendizaje activo para promover la adquisición de competencias en la asignatura Minimización y Valorización de Residuos. En IN-RED 2018. IV Congreso Nacional de Innovación Educativa y Docencia en Red. Editorial Universitat Politècnica de València. 1212-1224. https://doi.org/10.4995/INRED2018.2018.8628OCS1212122