Electrochemical Flow Reactor Research Articles

Design and application of a modular and scalable electrochemical flow microreactor

Electrochemistry constitutes a mild, green and versatile activation method of organic molecules. Despite these innate advantages, its widespread use in organic chemistry has been hampered due to technical limitations, such as mass and heat transfer limitations which restraints the scalability of electrochemical methods. Herein, we describe an undivided-cell electrochemical flow reactor with a flexible reactor volume. This enables its use in two different modes, which are highly relevant for flow chemistry applications, including a serial (volume ranging from 88 μL/channel up to 704 μL) or a parallel mode (numbering-up). The electrochemical flow reactor was subsequently assessed in two synthetic transformations, which confirms its versatility and scale-up potential.

Parametric Mathematical Modelling of Cristal Violet Dye Electrochemical Oxidation Using a Flow Electrochemical Reactor with BDD and DSA Anodes in Sulfate Media

AbstractAn important issue in electrochemical oxidations of pollutant compounds, like organic dyes, is identifying a suitable correlation between operational conditions and electrochemical process performance. In such sense, this work deals with the parametric modelling of direct electrochemical incineration of crystal violet (CV) dye in a FM01-LC flow electrochemical reactor with a plastic spacer configuration using boron doped diamond (BDD) and dimensionally stable (IrO2and IrO2-SnO2-Sb2O5) anode plates. Mathematical model takes into account the fluid dynamics effects by the use of FM01-LC reactor considering mass transport rate of organic compound (R) from bulk solution to electrode surface, characterized by a dispersion coefficient and Pe number. The effect of strong oxidants produced in the electrode surface can be neglected since the characteristic time constant reaction of pollutants with such oxidants is lower than those describing the diffusion of organic compound to the electrode surface. Model parameters were estimated throughout a fitting method of the experimental data. The model proposed here predicted a 99.7 removal percentage of CV with boron doped diamond and IrO2-SnO2-Sb2O5anodes obtained experimentally, meanwhile a 79 % removal with the IrO2anode was reached at Re = 2204 during an electrolysis time of 7200 s for both cases. In the case of IrO2anodes, complex interactions between hydroxyl-radical and electrode surface provokes an intermediate kinetic process, with an effectiveness factor of 0.59. When BDD and IrO2-SnO2-Sb2O5anodes were used, the removal process mediated by hydroxyl-radicals absorbed in electrode surface was fully limited by mass transport.

Phenomenological behavior coupling hydrodynamics and electrode kinetics in a flow electrochemical reactor. Numerical analysis and experimental validation

Parallel plate electrochemical reactors are frequently used in industry because its high range of applications in several electrochemical processes related with electrosynthesis, environment electrochemistry and energy storage systems. In such sense, the aim of this work is deal with the reaction environment characterization of a parallel plate flow reactor having a net-like spacer, by the employment of original experimental and theoretical techniques in order to evaluate the influence of transport phenomena on overall reactor performance. Flow distribution is analyzed by the use of automatic measurement of flow paths using image processing techniques, based on mathematical morphology theory. On the other hand, a theoretical model of current-potential distribution under intermediate kinetics control (tertiary current-potential distribution) based on numerical solution of turbulent diffusion-convection and binary electrolyte theory is proposed. In this case, concentration at electrode surface was determined in terms of dimensionless Damkhöler number, obtained from a mass balance at electrode-electrolyte interface in steady state. RTD curves obtained by image processing techniques describes correctly the fluid dynamics behavior in electrochemical reactor. Meanwhile, correspondence between calculated and experimental polarization curves using the oxidation of chloride ions to chlorine as model electrochemical reaction was made with an error values lesser than 7%, indicating a good agreement between theoretical model and experimental tests. Results founded in the parallel plate flow electrochemical reactor used here, evidenced that the methodology proposed to analyze the hydrodynamic and electrochemical behavior are adequate to its use in other electrochemical devices, particularly, when they work under intermediate kinetic and limiting current conditions.

Modeling of the Electro-Peroxone Process for the Degradation of Orange Reactive 16 Dye

Synthetic dyes are used extensively in many industries, such as textile, printing among others. Some of the dyes, however, are discharged in industrial wastewaters and can cause serious aesthetic and environmental damage to receiving water bodies. Decolorization and pollutant degradation are two major tasks in dye wastewater treatment. Because of the strong decolorization ability of ozone, it has been widely used in dye wastewater treatment. However, ozone usually has limited oxidation ability to mineralize refractory synthetic dyes effectively to CO2 and H2O. To improve pollutant mineralization efficiency, ozone is often used in particularly with O3 and H2O2 together (i.e., the so-called peroxone process) has a significant synergistic effect on organic mineralization [1]. The electro-peroxone (E-peroxone) process is a novel electrochemical advanced oxidation process (EAOP) that is enabled by in situ generation of hydrogen peroxide (H2O2) from cathodic oxygen (O2) reduction during conventional ozonation. The electro-generated H2O2 can considerably enhance ozone (O3) transformation to hydroxyl radicals (•OH), thus greatly enhancing pollutant degradation by the E-peroxone process than by conventional ozonation [2]. In this context, the experimental characterization and modeling of the reaction environment in electrochemical flow reactors is mandatory to control homogeneous fluid flow, mass transport to and from electrode surface and current and potential distribution, aiming to prevent parasitic reactions that impact negatively on the current efficiency and energy consumption. Furthermore, the modeling of EAOPs is also needed to enhance the reaction kinetics. The numerical simulation can also be a powerful tool to devise new reactors for EAOPs, thus contributing to a smarter scale-up [3]. So, in this work, the E-peroxone process for the degradation of the orange reactive 16 dye, using Ir-Sn-Sb oxides as anode, an unmodified graphite felt on top of carbon cloth as air-diffusion in the cathode fitted into an undivided filter-press cell, operating in recirculation mode, was simulated using a parametric model. The experiments were performed in a laboratory reactor with recirculation of 2 dm3 of 0.05M Na2SO4 solutions at pH 3.0 upon continuous air feeding (5 psi) to the cathode and continuous ozone feeding (0.5 dm3 min-1) at the exit of the reactor. The potential to produce H2O2 is 0.695 V|SHE, reported by Perez et. al. (2018) [4], which was used in this case. In the degradation of the dye, different flows (1.9, 1.5, 1.1 and 0.75 dm3 min-1) and then current densities (0.004-0.00625 A cm-2) were tested to determine the optimal conditions of the degradation. The discoloration of the dye was measurement at 498 nm by a spectrophotometer uv/vis, and the degradation of the organic matter was followed by TOC. The results of the decolorization of reactive orange 16 dye show that the optimal flow is 1.9 dm3 min-1, achieving a discoloration of 98.4% against 77.4% to 0.75 dm3 min-1 in a time of one hour of process. Good agreement between simulations and experimental TOC decays was obtained. [1] Bakheet, B. et al. Electro-peroxone treatment of Orange II dye wastewater, Water Research, 47 (2013) 6234-6243. [2] Zhou, M., Oturan, M., Sirés I., Electro-fenton process, New trend and scale-up, Springer, Singapore, 2018. [3] Perez, T., Sirés, I., Brillas, E., Nava, J.L., Solar photoelectro-fenton plant modeling for the degradation of the antibiotic erythtomycin in sulfate medium, Electrochimica Acta, 228 (2017) 45-56. [4] Perez, T., Coria, G., Sirés, I., Nava, J.L., Uribe, A., Electrosynthesis of hydrogen peroxide in a filter-press flow cell using graphite felt as air-diffusion cathode, Journal of Electroanalytical Chemistry, 812 (2018) 54-58.

Local mass-transfer study in a decaying swirling flow electrochemical reactor under single-phase and two-phase (gas-liquid) flow

Mass transfer was studied at the external electrode of a cylindrical electrochemical reactor with decaying swirling flow using a single phase electrolyte and also a dispersion of a gas phase in the solution. The local mass-transfer coefficients were measured with a segmented cathode using the reduction of ferricyanide as test reaction. Two strategies were used to introduce the gas phase. In the first case the gas was fed by three holes symmetrically drilled at the bottom of the central anode tube and in the second one by means of a tee fitting at the reactor inlet. The best performance was obtained with the single phase electrolyte giving 0.78 as the exponent of the Reynolds number and the mass-transfer distribution along the reactor length is more uniform than that reported for a parallel plate electrochemical reactor under laminar flow conditions. The mass-transfer enhancement factor related to an annular duct with axial developing flow ranges from 8 to 11. This high value is the consequence of two factors: (i) the intensive forced convection produced by the swirling flow at the outer electrode and (ii) the sudden expansion of the flow at the entrance due to the small tangential inlet. The fed of a gas phase in the reactor has scarce influence on the mass-transfer performance. A comparison of mass-transfer results with previous studies is made.

Electrochemical technology for the treatment of real washing machine effluent at pre-pilot plant scale by using active and non-active anodes

Real effluent of washing machine is one of the major sources of microplastics and fabrics in municipal and surface water. The effluents constitute large volume of wastewater with different surfactants since every household and industries nowadays use washing machine rather than traditional hand washing.In this work, a real effluent of washing machine was treated by electrooxidation (EO) in a pre-pilot plant scale electrochemical flow reactor using active (Ti/Pt) or non-active (boron doped diamond (BDD)) anodes and Ti cathode. The effect of anode material (Ti/Pt or BDD) and the applied current density (16.6, 33.3 and 66.6 mA cm−2) on the decay of the organic matter, in terms of chemical oxygen demand (COD) during the electrochemical treatment was examined using the as-received effluent or by adding Na2SO4 as supporting electrolyte (as auxiliary in the conductivity). A decreased in organic matter (COD) was always observed when an increase on the applied current density was achieved at both anodes; however, BDD anode showed a well-defined trend as well as higher removal efficiency at all current densities studied when compared to Ti/Pt. Besides, faster and higher COD decay was attained by adding Na2SO4 to the real effluent compared to as-received effluent regardless of anode material used. Active chlorine species were also electrochemically produced at both anodes from the Cl− ions in the real effluent, contributing to the elimination of the pollutants. The mineralization of organic matter in the effluent was also determined, obtaining >90% of total organic carbon (TOC) reduction after 360 min with BDD anode at 33.3 and 66.6 mA cm−2. Based on the achieved results, EO is an efficient and effective treatment approach for the remediation of organic micropollutants in washing machine effluent especially with BDD anode.

Design of an Electrocatalytic Flow Reactor for the Electrosynthetic Aldol Reaction of Acetone

Organic electrosynthesis is a field within electrochemistry that concerns the synthesis of organic products using the electron as a redox agent instead of chemical reductants or oxidants. It offers several important advantages to conventional synthetic methods, such as less aggressive process conditions (reactions can be carried out at ambient temperature and pressure), higher selectivity (precise control of reaction by control of electrode potential), ability to produce unstable or hazardous reagents in situ and less generation of pollutants and waste streams. It is a versatile and inherently environmental-friendly technique, considered a “clean” and “green” process. Its advantages make it an interesting alternative for industrial applications. However, despite its potential, its implementation is limited. A major drawback is the lack of the necessary combined knowledge on organic synthesis, electrochemistry and engineering aspects. This work aims to bridge the gap between the engineering aspects and the fundamental electrochemical mechanistic insights of a reaction. One reaction that exhibits drawbacks to which electrosynthesis offers an answer, is the aldol condensation: an important reaction for the formation of carbon-carbon bonds. The often several possible reaction pathways between the various reactants and products of the aldol condensation make it difficult to promote the desired reaction. The homogeneous catalysts which are often used in industry require an intensive purification afterwards which often destroys the catalyst. Additionally the purification causes large waste streams. In this work, the potential-controlled electrochemical aldol reaction of acetone to diacetone alcohol is studied in a standard batch electrolysis set-up as well as in an electrochemical continuous flow microfluidic reactor. In the batch set-up the influence of a number of parameters such as electrolyte composition, electrode material and electrolysis potential is described. Starting with pure acetone and a quaternary ammonium salt as support electrolyte, a maximum concentration of 15 m% diacetone alcohol is obtained after 2 h electrolysis in a divided set-up with a platinum electrode at -2.5 V [1, 2]. These results are taken into account in the optimisation towards maximum space-time yield and diacetone alcohol selectivity in the electrochemical micro flow reactor. Employing a flow cell system has important benefits which allows for a more efficient reaction such as a high surface-to-volume ratio of the electrode area to the reaction volume and close proximity of the electrodes. In addition optimization of the flow rate and cell height allows high yields of product in continuous operation. Incorporating a membrane in the reactor prevents cross-over of products which is detrimental for the yield. [1] D. Pauwels, B. Geboes, J. Hereijgers, D. Choukroun, K. De Wael, T. Breugelmans, The application of an electrochemical microflow reactor for the electrosynthetic aldol reaction of acetone to diacetone alcohol, Chemical Engineering Research and Design, 128 (2017) 205-2013. [2] D. Pauwels, J. Hereijgers, K. Verhulst, K. De Wael, T. Breugelmans, Investigation of the electrosynthetic pathway of the aldol condensation of acetone, Chemical Engineering Journal, 289 (2016) 554-561. Figure 1: Exploded view of the electrochemical microreactor. 1: Electrode material 2: PEEK housing with hole for the electrode (2a: WE, 2b: CE), 3: POM spacer with serpentine reaction channel. 4: Aluminium parts with holes for the in- and outlet tubing, hole for the reference electrode (4a only) and holes for the electrode connections. Figure 1

Ni-Catalyzed Electrochemical Decarboxylative C-C Couplings in Batch and Continuous Flow.

An electrochemically driven, nickel-catalyzed reductive coupling of N-hydroxyphthalimide esters with aryl halides is reported. The reaction proceeds under mild conditions in a divided electrochemical cell and employs a tertiary amine as the reductant. This decarboxylative C(sp3)–C(sp2) bond-forming transformation exhibits excellent substrate generality and functional group compatibility. An operationally simple continuous-flow version of this transformation using a commercial electrochemical flow reactor represents a robust and scalable synthesis of value added coupling process.

Study of Hydrodynamics at AsahiTM prototype electrochemical flow reactor, using computational fluid dynamics and experimental characterization techniques

Fluid pattern inside of flow electrochemical reactors is strongly affected by geometric inlets design and the use of net-like spacers (or turbulence promoters). In this report a comparison of the hydrodynamic behavior between empty and net-like spacer-filled channel of a parallel plate reactor based in CH-0 electrolyzer of Asahi Glass Co. is presented. RANS equations were solved by means of a Computational Fluid Dynamics (CFD) package (COMSOL 4.4a™). Simulations were validated through experimental flow characterization techniques such as flow visualizations and residence time distribution (RTD) tests. CFD studies evidenced that net-like spacer homogenizes flow distribution for all flow rates studied in this report (0.15–0.63ms−1), causing an increase in local Reynolds numbers in this configuration in comparison with typical empty channel. The flow behavior generated by these spacers could improve mass transport performance, nevertheless, an additional cost for electrolyte pumping must be considered. Comparisons of theoretical and experimental RTD curves and flow visualizations showed that the formulation of the numerical simulation proposed here is appropriate to reproduce the flow pattern inside the net-like spacer-filled channel of a filter press type electrolyzer and can be used for further scaling-up studies.

Electrochemical Deprotection of para-Methoxybenzyl Ethers in a Flow Electrolysis Cell.

Electrochemical deprotection of p-methoxybenzyl (PMB) ethers was performed in an undivided electrochemical flow reactor in MeOH solution, leading to the unmasked alcohol and p-methoxybenzaldehyde dimethyl acetal as a byproduct. The electrochemical method removes the need for chemical oxidants, and added electrolyte (BF4NEt4) can be recovered and reused. The method was applied to 17 substrates with high conversions in a single pass, yields up to 92%, and up to 7.5 g h-1 productivity. The PMB protecting group was also selectively removed in the presence of some other common alcohol protecting groups.

Indium Recovery in an Electrochemical Flow Reactor. Simulation and Experiment

Indium Recovery in an Electrochemical Flow Reactor. Simulation and Experiment

3D-printed porous electrodes for advanced electrochemical flow reactors: A Ni/stainless steel electrode and its mass transport characteristics

Porous electrodes have shown high performance in industrial electrochemical processes and redox flow batteries for energy storage. These materials offer great advantages over planar electrodes in terms of larger surface area, superior space time yield and enhanced mass transport. In this work, a highly ordered porous stainless steel structure was manufactured by 3D-printing and coated with nickel from an acidic bath by electrodeposition in a divided rectangular channel flow cell. Following the electrodeposition, the volumetric mass transport coefficient of this electrode was determined by the electrochemical reduction of 1.0×10−3moldm−3 of ferricyanide ions by linear sweep voltammetry and chronoamperometry. The convection diffusion characteristics are compared with other geometries to demonstrate the novelty and the advantages of 3D-printed porous electrodes in electrochemical flow reactors. Robust porous electrodes with tailored surface area, composition, volumetric porosity and flow properties are possible.

Performance analysis of a continuous serpentine flow reactor for electrochemical oxidation of synthetic and real textile wastewater: Energy consumption, mass transfer coefficient and economic analysis

A continuous flow electrochemical reactor was developed, and its application was tested for the treatment of textile wastewater. A parallel plate configuration with serpentine flow was chosen for the continuous flow reactor. Uniparameter optimization was carried out for electrochemical oxidation of synthetic and real textile wastewater (collected from the inlet of the effluent treatment plant). Chemical Oxygen Demand (COD) removal efficiency of 90% was achieved for synthetic textile wastewater (initial COD - 780 mg L−1) at a flow rate of 500 mL h−1 (retention time of 6 h) and a current density of 1.15 mA cm−2 and the energy consumption for the degradation was 9.2 kWh (kg COD)−1. The complete degradation of real textile wastewater (initial COD of 368 mg L−1) was obtained at a current density of 1.15 mA cm−2, NaCl concentration of 1 g L−1 and retention time of 6 h. Energy consumption and mass transfer coefficient of the reactions were calculated. The continuous flow reactor performed better than batch reactor with reference to energy consumption and economy. The overall treatment cost for complete COD removal of real textile wastewater was 5.83 USD m−3.

Boron doped micro/nanocrystalline diamond electrodes used on the electrochemical flow reactor to degrade brilliant green dye

ABSTRACTA systematic study was performed concerning the production, characterization, and application of BDD and BDND films grown on Ti substrate to degrade brilliant green dye using an electrochemical flow reactor. Films were grown in a hot filament chemical vapour deposition (HFCVD) reactor using H2/CH4 (BDD) and H2/CH4/Ar (BDND) gas mixtures. Boron doping was performed by dissolution of B2O3 in methanol in the appropriate B/C ratio to obtain good conductive electrodes. The electrolysis was carried out using BDD/Ti and BDND/Ti as anode material analyzing the influence of different current densities and flow rates. During the electrolysis, aliquots of the treated solution were analyzed by UV-Vis and Total Organic Carbon (TOC) measurements. The electrode efficiencies were compared considering the color removal as well as the TOC mineralization in the end of each electrolysis. The absorption bands intensity from UV/Vis spectra clearly decreased up to their completely vanishing at current density of 100 mA/cm2 for both electrodes. These results were corroborated by TOC measurements where 50% of the organic material was removed.

Electrochemical Oxidation of Lignin for Production of Value Added Chemicals

Electrochemical oxidation of lignin for production of value added chemicals Raziyeh Ghahremani and John A. Staser (Center for Electrochemical Engineering Research, Department of Chemical and Biomolecular Engineering, Ohio University) The polyphenolic structure of lignin makes it the ideal raw material to produce commercial aromatic compounds[1]. However, due to the difficulty of the conversion process of lignin, it is usually burned to produce heat and energy[2]. Electrochemical oxidation is an environmentally friendly, inexpensive, and efficient depolymerization process which can take place at relatively low pressure and temperature, and the reaction can be controlled by potential or current[1]. However, high cost of materials for preparing electrodes, also deactivation of the electrode during the reaction due to impurities makes electrochemical oxidation processes more elaborate and expensive, prohibiting its broad application[3]. Therefore, it is critical to develop a low cost and efficient electrode for the electrochemical oxidation of lignin. In this work, the inexpensive Ni-Co electrocatalysts were developed for use in the electrochemical oxidation of lignin to produce other value added chemicals. We have developed nanoparticle electrocatalysts that are suitable for a continuous flow electrochemical reactor to be integrated into existing biorefineries. Gas chromatography and mass spectroscopy (GC-MS) was applied to analyze the products and the results showed that valuable chemicals like vanillin, apocynin and other aromatic compounds are produced by the electrochemical oxidation of lignin, the concentration of chemicals also were increased during the time of oxidation. We will also present techno-economic analyses that can be used as a benchmark for integrating the electrochemical reactor into the biorefinery. [1] O. Movil, M. Garlock, and J. A. Staser, “Non-precious metal nanoparticle electrocatalysts for electrochemical modification of lignin for low-energy and cost-effective production of hydrogen,” Int. J. Hydrog. Energy, vol. 40, no. 13, pp. 4519 – 4530, 2015. [2] D. Klein-Marcuschamer, P. Oleskowicz-Popiel, B. A. Simmons, and H. W. Blanch, “Technoeconomic analysis of biofuels: A wiki-based platform for lignocellulosic biorefineries,” Biomass Bioenergy, vol. 34, no. 12, pp. 1914 – 1921, 2010. [3] Y. Zhang, Y. Peng, X. Yin, Z. Liu, and G. Li, “Degradation of lignin to BHT by electrochemical catalysis on Pb/PbO2 anode in alkaline solution,” J. Chem. Technol. Biotechnol., vol. 89, no. 12, pp. 1954–1960, 2014.

Silver recovery from simulated photographic baths by electrochemical deposition avoiding Ag2S formation

Aiming at recovering silver from a simulated photographic wastewater, a study on electrochemical deposition with modulated current was developed. In cathodic potentials where hydrogen formation occurs, Ag2S formation was noticed over the electrode due to parasitic reactions. Therefore, in a galvanostatic process, the electrodeposition would only be feasible if conducted under current control to avoid Ag2S formation. An electrochemical flow reactor was used for silver electrodeposition under current control using a stainless steel plate. The modulated current values for the electrodeposition were calculated according to the limiting current kinetic control, applying the mass transfer coefficient calculated from experimental values of diffusion coefficient of silver ions and diffusion layer thickness. Silver electrodeposition was achieved at high efficiency rates, low energy consumption and without the presence of parasitic reactions. The highly negative potentials were avoided when the limiting current was applied and, consequently, sulfur sulfide was not formed over silver deposit. The modulated current electrodeposition of silver revealed to be a feasible process to recover silver from spent photographic baths.

The Origin of Life in Alkaline Hydrothermal Vents.

Over the last 70 years, prebiotic chemists have been very successful in synthesizing the molecules of life, from amino acids to nucleotides. Yet there is strikingly little resemblance between much of this chemistry and the metabolic pathways of cells, in terms of substrates, catalysts, and synthetic pathways. In contrast, alkaline hydrothermal vents offer conditions similar to those harnessed by modern autotrophs, but there has been limited experimental evidence that such conditions could drive prebiotic chemistry. In the Hadean, in the absence of oxygen, alkaline vents are proposed to have acted as electrochemical flow reactors, in which alkaline fluids saturated in H2 mixed with relatively acidic ocean waters rich in CO2, through a labyrinth of interconnected micropores with thin inorganic walls containing catalytic Fe(Ni)S minerals. The difference in pH across these thin barriers produced natural proton gradients with equivalent magnitude and polarity to the proton-motive force required for carbon fixation in extant bacteria and archaea. How such gradients could have powered carbon reduction or energy flux before the advent of organic protocells with genes and proteins is unknown. Work over the last decade suggests several possible hypotheses that are currently being tested in laboratory experiments, field observations, and phylogenetic reconstructions of ancestral metabolism. We analyze the perplexing differences in carbon and energy metabolism in methanogenic archaea and acetogenic bacteria to propose a possible ancestral mechanism of CO2 reduction in alkaline hydrothermal vents. Based on this mechanism, we show that the evolution of active ion pumping could have driven the deep divergence of bacteria and archaea.

Development of Three-Dimensional Electrodes of PbO2Electrodeposited on Reticulated Vitreous Carbon for Organic Eletrooxidation

The application of electrochemical technology for the degradation of organic pollutants often faces two main problems, related to the anode material and mass transport limitations. Although PbO2 electrode is inexpensive and provides satisfactory electrooxidation kinetics, in the form of plane electrodes it is unable to resolve the mass transfer problem that arises at low concentrations of organics. In this work, an electrochemical flow reactor was developed for the preparation of three-dimensional electrodes consisting of PbO2 films electrodeposited onto reticulated vitreous carbon. The electrodes were characterized in terms of the substrate coating, morphology, structure, and electrocatalytic activity in the decoloration reaction of Reactive Blue 19 dye. The results showed that it was possible to deposit a uniform film of PbO2 on the surface of the substrate after optimization of the current density and deposition time (0.7 mA cm-2 for 30 min). Comparison of the plane and three-dimensional electrodes revealed that the turbulence generated by the porous matrix significantly accelerated the dye decoloration kinetics, increasing 3.3-fold the first order kinetic constant (from 0.010 min-1 for VC/PbO2 to 0.033 min-1 for RVC/PbO2).

Recent R&D towards Aqueous Reprocessing of FBR Fuels

The mixed Pu-rich carbide spent fuel with a burn up of 155 GWd/t from the Fast Breeder Test Reactor is being reprocessed in a hot-cell facility by PUREX process. Based on the input from the operation of this facility, R&D activities were carried out to improve the recovery, decontamination factors, economy and to reduce the waste volumes. Reduction of uranyl ions in a continuous flow electrochemical reactor and electrolytic as well as chemical reduction of 4M HNO3 from liquid waste could be accomplished in continuous mode. Using the optimized parameters, suitable electrolytic cells/experimental setups were designed for the plant capacity of 6 L/h. Studies on the extraction kinetics of Ru with 30% TBP in NPH revealed that better decontamination factor with respect to Ru can be achieved using fast contactors like centrifugal extractors (CEs). Towards developing a spent solvent recovery system to reduce organic waste volumes, a pilot plant was set up, which could recover diluent as top product of distillation column and 40% TBP as bottom product from inactive degraded solvent. A solvent recovery system using short path distillation was also developed for installation in hot cells.

Electrodeposition of PbO2 on Reticulated Vitreous Carbon for Organic Electrooxidation

The problems caused by the growing of the environmental contamination by organics have been calling the attention of researches, authorities, and population in general since their effects have been more present in our lives. Environmental contamination can be avoided by using, in most cases, biological treatments; however, some classes of compounds are refractory to this kind of treatment and require different technologies to oxidize the organic compound. In this context, the electrochemical technology emerged as an alternative environmentally, technically, and economically viable. Advantages of electrochemical technology are elimination of transport and storage of hazardous chemicals, reduction of the workmanship, and ease to automatization. Despite these advantages, for the effective use of the electrochemical technology for effluent treatment some drawbacks must be overcome, mainly mass transfer limitations resulting of the low concentrations in industrial effluents, which affect the current efficiency and the energy consumption. As an attempt to improve mass transfer, in this work we address the electrochemical oxidation using three-dimensional electrodes of reticulated vitreous carbon (RVC) covered by PbO2film as the electroactive material. The RVC/PbO2 electrode was prepared in a flow electrochemical reactor. The PbO2 film was electrodeposited on RVC applying different charges by varying the current density and electrolysis time. The porosities (in pores per inch) of the RVC substrates were 45, 60, and 80 ppi. The electrode was characterized by electrochemical techniques and scanning electronic microscopy. The decolorization reaction of the reactive blue 19 dye was used to evaluate the electrocatalytic power of the RVC/PbO2and compared to the flat plate electrode. The results for the 45 ppi RVC showed that the PbO2electrodeposition was not uniform within RVC due to non-uniform current penetration (Fig. 1 and 2). The best electrodeposit morphology and uniformity was obtained applying low current densities for longer electrolysis time (Fig 1c). Contrary, fast decolorization rate was obtained using the films deposited applying high current density (Fig. 2). A comparison between the flat plate and RVC/PbO2electrodes in Fig. 3 shows that the three-dimensional electrode was very effect to remove color. In order to increase the electrode specific surface area, PbO2 films were electrodeposited on RVC with 60 ppi and 80 ppi. After current density optimization, the PbO2 film was successfully deposited on the 60 ppi RVC. On the other hand, an optimum current density cannot be found in order to obtain a uniform deposit on the 80 ppi RVC. Moreover, the low porosity of this electrode and the high hydrophobic nature of RVC led to low surface wettability, thus contributing for the uneven PbO2 film. Figure 1