Bed Electrochemical Reactor Research Articles

Behavior analysis of a porous bed electrochemical reactor the treatment of petrochemical industry wastewater contaminated by hydrogen sulfide (H2S)

The concern for the removal of contaminants, such as hydrogen sulfide (H2S), during crude oil processing has been intensified. Sulfur compounds, such as dissociated H2S, are detected in the effluents of process gas condensation and streams of acid water. The objective of this study is to apply electrochemical oxidation to neutralize H2S in industrial effluents. Tests were performed in a porous bed electrochemical reactor, which was composed of reticulated vitreous carbon. The oxidation process is direct and potentiostatically controlled, and the dissociated sulfide was oxidized to sulfate and/or thiosulfate, main product of the reaction. Figures of merit were constructed to evaluate the performance of electrochemical reactor under different hydrodynamic conditions, by varying the flow rate, and overpotential, by varying the distance between the electrodes in the reactor. The figures of merit indicated that the best condition for the formation of thiosulfate occurred at the lowest flow rate used, 1.05Lh−1 and at a greater distance between the electrodes, 60mm.

A Trickle Bed Electrochemical Reactor for Generation of Hydrogen Peroxide and Degradation of an Azo Dye in Water

AbstractA trickle bed electrochemical reactor was used to generate hydrogen peroxide in dilute electrolyte and then degrade an azo dye, i.e. reactive brilliant red X-3B in water by electro-Fenton process. The trickle bed reactor was composed of carbon black-polytetrafluoroethylene coated graphite chips. During the preparation of coated graphite chips, coating times and surfactant dosage were optimized to improve electro-generation of H

Design and Development of Packed Bed Electrochemical Reactors (PBER’s) Using Scrap Lead Dioxide as Novel Electrodes

The present work focuses on the effective utilization of discarded Lead dioxide particles as particulate electrodes in a carefully designed packed bed electrolyser. It is known that particulate electrodes provide a large electrode area in proportion to conventional flat electrode configuration. Consequently, this packed bed electrolyser, will be exceptionally useful when dealing with slow reactions. This design entirely avoids the necessity of expensive valve metals as substrates and associated noble metal oxide undercoating. In the present study, an optimized design of a packed bed electrochemical reactor setup using peeled off electro deposited Lead dioxide particles was carried out. The above electrolyser was used for studying its effectiveness in the electrochemical oxidation of Sodium Chlorate to Sodium Perchlorate, which is the starting raw material for the manufacture of rocket propellant oxidizers. Effect of certain parameters like electrolyte flow rates, current density and thickness in the desired current efficiencies for the formation of perchlorates were estimated. Results indicate that this electrolyser proves to be a potential method for improving the reaction rates of slow reactions like perchlorate formation, utilizing cheaper discarded Lead dioxide particles.

Electrochemical capacitance behavior of a packed bed electrochemical reactor toward phenol electro-oxidation

The electrochemical capacitance behavior of a packed bed electrochemical reactor (PBER) toward phenol electro-oxidation in aqueous solution was studied. In the absence of phenol, a decrease in the response current (i) coupled with an increase of the specific capacitance (C s ) was obtained for PBER compared with a flat-bed electrochemical reactor. However, following intercalation of phenol, simultaneous improvement of i, and reduction of C s were observed. The reasons for the former were ascribed to an increased resistance, an abundant pore structure for charge, and electrolyte transportation owing to the packing of the fixed granular active carbon (GAC) filler, whereas anode extension and formation of the polyoxyphenylene film on the anode and the GAC surface were responsible for the latter. Although significant attenuation (42.06 % after 300 cycles at current density 1.90 mA cm−2) of C s was observed for PBER in the long cycle test, the non-negligible C s value (30.86 mF cm−2) holds great promise for pulsating power supplies. An equivalent circuit associated with electrochemical capacitance and resistance distribution was proposed, which gives an exhaustive explanation of the electrical characteristics during the phenol electro-oxidation process.

Numerical Simulation of the Primary, Secondary and Tertiary Potential Distribution on Porous Cathode in a Flow-through Packed Bed Reactor. Influence of Thickness, Concentration and Hydrodynamics in Porous Media

Packed bed electrodes can be used for electrochemical recovery of heavy metals from a variety of industrial and laboratory model solutions. The packed bed electrode forms a porous flow-through (Figure 1) configuration providing large surface area usually depleting the concentration of several metal ions below 0.1 ppm. For design porpoises of these electrodes, it is necessary to study the influence of geometry (cathode thickness), flow rate and concentration on potential distribution.Numerical simulations of primary, secondary and tertiary current distributions on the porous cathode of a packed bed electrochemical reactor (Figure 1) were calculated. For primary and secondary current distribution, Laplace equations with its respective boundary conditions (constant potential for primary current distribution and charge transfer kinetics described by a Tafel approximation in secondary current distribution) were evaluated using the finite element method. For tertiary current distribution, the influence of hydrodynamics was taken in account, considering Navier-Stokes model with Brinkman extension for porous media. Once Brinkman equations was solved and local velocity distributions were obtained, local mass transfer coefficients were evaluated by means of following relationship: Kma=cvb where Km is local mass transport coefficient, a is the specific area, v is local velocity, c and b are empirical constants taken from literature. The effects of flow rate, ion concentration, matrix conductivity and thicknes on the distribution of current on porous cathode are analyzed. Results of current distribution obtained by Nava et. al 2008 [1] enable comparisons with the simulations.

Wall-to-Bed Mass Transfer in a Three-Phase Fluidized Bed with Twisted Tape as Internal

Experimental data on limiting current are obtained at point electrodes fixed flush with the inner surface of the outer cylinder of a three-phase fluidized bed electrochemical reactor in the presence of coaxially placed twisted tape inserts. Wall-to-bed mass transfer coefficient data are computed from the measured limiting current data. Glass balls of different diameters are employed as solid phase, nitrogen as gas phase and an electrolyte belonging to ferri–ferro redox system as liquid phase. Twisted tapes of different pitch values and width values are used as turbulent promoters. It is found that the use of twisted tape turbulent promoters in the three-phase fluidized beds yielded an augmentation of 25 %. Further it is observed that the mass transfer coefficient values are relatively uninfluenced by the longitudinal distance, and the liquid and gas velocities within the range of values considered for these variables. Further, the mass transfer coefficient is found to decrease with increase in tape pitch, tape width and particle diameter. A correlation is provided for the estimation of mass transfer coefficient using least squares regression analysis.

Electrocoagulation in a packed bed reactor-complete treatment of color and cod from real textile wastewater

This paper deals with the efficiency of electrocoagulation (EC) for the abatement of COD and absorbance (i.e. color) from real textile wastewater using a packed bed electrochemical reactor in a unique design, not previously encountered in the literature for the treatment of textile wastewater by electrocoagulation. The cylindrical iron reactor was used as a cathode while the packed bed formed from wrapped iron wire netting was used as an anode. Various operating parameters, such as current density, initial pH, wastewater recirculation flow rate and continuous flow regime, were examined for intensifying the performance of the process. Also, calculation of electrical energy consumption and the characterization of sludge formed during electrocoagulation have been performed. The initial COD concentration of 1953 mg/L was reduced to 61 mg/L with a removal efficiency of 96.88%, while the color of the wastewater was almost completely removed. The experimental results, throughout the present study, have indicate that electrocoagulation of textile wastewater using a uniquely designed reactor was very effective and direct dischargeable effluent, complying with legal requirements, was obtained. The XRD analysis of the sludge produced during EC reveals that maghemite (Fe2O3) is the main by-product formed after EC.

Treatment of Petrochemical Wastewater Containing Phenolic Compounds by Electrocoagulation Using a Fixed Bed Electrochemical Reactor

Treatment of Petrochemical Wastewater Containing Phenolic Compounds by Electrocoagulation Using a Fixed Bed Electrochemical Reactor

Removal of toxic metals from aqueous effluents by electrodeposition in a spouted bed electrochemical reactor

This work investigates the removal of metal ions from synthetic aqueous effluents using a spouted bed electrochemical reactor whose cathode was composed of 1.0 mm copper particles. Using a Box–Behnken factorial design, the effects of current (I), electrode thickness (L), draught distance (d) and support electrolyte concentration (Cs) on current efficiency (CE), space–time yield (Y) and energy consumption (EC) were analysed. The results were statistically analysed and the effect of each variable was evaluated using the surface response methodology. The results showed that Cs is the most important variable to consider in the process optimization. A current of 8.0 A can be applied in order to obtain high Y and CE with an acceptable EC. Electrode thicknesses greater than 1.3 cm are not recommended because the irregular potential distribution leads to a Y drop owing to the low CE observed for this condition. The draught distance does not have statistical significance; therefore, the particle circulation rate is not important in this kind of electrochemical reactor.

Efficient degradation of Reactive Blue 4 in carbon bed electrochemical reactor

A fixed bed electrochemical reactor comprising stainless steel cathode/granular activated carbon (GAC) bed//Carbon anode//GAC bed//stainless steel cathode configuration was fabricated and tested for degradation of Reactive Blue 4 aqueous solutions (RB4). On the basis of measured concentrations of residual RB4 dye and total organic carbon (TOC), approximately 80–90% of RB4 dye was found to be degraded at 0.30–0.90A and 13.4±0.1V in 6h under recirculation batch mode of operation (flow rate, 1.8Lh−1). The dye removal due to adsorption on carbon was ∼9–10% under the same experimental conditions but excluding applied current. The apparent Faradic efficiency and electrical energy consumption were estimated to be 2.8% and 16.0kWhkg−1 RB4 at the optimum current and voltage (0.6A, 13.3V). Further, the adsorption of the dye on GAC bed, cyclic voltammetric response of RB4, SEM and FT-IR characterization of original and spent carbon and ion chromatographic analysis of inorganic intermediates were carried out to elucidate the mechanism of dye degradation. It appears that the dye degradation takes place by ready scission of SO3H groups, and oxidation of mainframe chromophore (anthraquinone group). The chlorotriazine group resists to the electrooxidation and remains as the final reaction product.

Study of the rate of diffusion controlled liquid–solid reactions accompanied with gas generation in batch fixed bed reactor in relation to wastewater treatment

Factors affecting the rate of liquid–solid diffusion controlled reactions at gas evolving fixed bed reactor were studied by measuring the mass transfer coefficient of cathodic copper deposition from acidified CuSO4 above the limiting current where simultaneous H2 evolution takes place in a reactor packed with either cylinders or Rasching rings with no net electrolyte flow. Variables studied were particle size, bed height and H2 discharge velocity. The rate of mass transfer was found to be proportional to the square root of H2 discharge rate. Bed height and particle size were found to have a negligible effect on the rate of mass transfer. For a given set of conditions the mass transfer coefficient at a fixed bed of cylinders is higher than that at a fixed bed of Raschig rings. A mathematical model based on bombardment of the mass transfer surface by high kinetic energy bubbles is presented to explain the results. Mass transfer data at the cylinder bed reactor were correlated by the equationJ=1.58(Re⋅Fr)−0.166While the data at a fixed bed of Raschig rings were correlated by the equationJ=1.4(Re⋅Fr)−0.162Practical applications of the results in the design and operation of fixed bed electrochemical and catalytic reactors used in wastewater treatment were highlighted.

Enhanced treatment of endocrine disrupting chemicals by a granular bed electrochemical reactor

Continuous treatments of trace endocrine disrupting chemicals (EDCs) such as 17β-estradiol (E2), bisphenol-A, nonylephenol, 4-t-octyl phenol and pentachlorophenol were carried out using a granular bed electrolytic reactor. Experimental results showed that the EDCs were removed by the reactor over 150 days and removal efficiencies were nearly the same in the presence and absence of humic substance. Energy consumption for the treatment was around several Wh/m(3). For longer operation or higher loading conditions, Fenton oxidation was effective to regenerate electrodes. Calculated results by a mathematical model developed assuming liquid film mass-transfer as a rate-limiting step were in good agreement with observed results. Based on the model, enhancement of reactor performance was discussed.

Kinetics of electrooxidation of landfill leachate in a three-dimensional carbon bed electrochemical reactor

The electrooxidation of high strength leachate from an industrial solid waste landfill site was carried out in a three-dimensional carbon bed electrode reactor (TDR). This paper discusses the kinetics and mechanism of electrooxidation on the basis of time course variation of COD, TOC and TKN (total Kjeldahl nitrogen) from the raw leachate. The batch experiments were run at different applied currents (1–3 A) for a period of 6 h. A two-stage pseudo-first order reaction kinetics model was developed based on the initial rapid removal of pollutants (Phase I) followed by slow oxidation kinetics (Phase II). About 60–64% COD was removed within 1 h with a rate constant 5.83 × 10 −3 min −1 in Phase I, which was near 5–7 times greater than that of Phase II (0.81–1.03 × 10 −3 min −1). The mineralization efficiency was found to be significant in the range 0.83–0.84. The apparent faradic efficiency and specific energy consumption for COD removal were also estimated. The mechanism of electrooxidation was discussed with the help of adsorption, kinetic and SEM results.

Modeling a perforated bipole trickle bed electrochemical reactor for the generation of alkaline peroxide

This paper describes the modeling of a novel perforated bipole electrochemical reactor with trickle-bed cathodes employed in the electrosynthesis of alkaline peroxide solutions. The model engages an electronic analogue of the 3D electrode/bipoles to solve the coupled material, energy and voltage (charge) balances that estimate the potential, current density, composition, pressure and temperature profiles through the reactor. The predictions of this model are compared to the performance of a bench scale experimental reactor operating at superficial current densities up to 5 kA m−2. With eddy diffusion through the diaphragm as the single adjustable parameter the model shows good agreement with peroxide current efficiency but underestimates the electrochemical specific energy consumption by about 2 kWh/kg H2O2 at 5 kAm−2.

Scale-up of a fixed bed electrochemical reactor consisting of parallel screen electrode used for p-aminophenol production

The behavior of a fixed bed consisting of amalgamated copper screens has been investigated for the electrolytic reduction of nitrobenzene to p-aminophenol under potentiostatic condition (controlled potential). The preparative electrolysis of nitrobenzene was carried out using supporting electrolytes consisting of 2 M H 2SO 4 in a solution of 50% 2-propanol/50% water (v/v). The criterion for scale-up ( ɛ n ) was determined through application of one-dimensional model. The polarization curves that describe the reduction of nitrobenzene to p-aminophenol were obtained experimentally by using a pilot scale for different nitrobenzene concentrations and flow rates of catholyte. It was found that the effectiveness factor ( ɛ n ) increases with increasing flow rate, and decreasing nitrobenzene concentration. An optimum thickness of bed equal to 0.6 cm was obtained, in which the effectiveness factor not less than 0.588, to ensure a well distribution of current and potential.

Mass transfer behaviour of a flow-by fixed bed electrochemical reactor under different hydrodynamic conditions

Mass transfer behaviour of a flow-by electrode made of a fixed bed of Raschig rings and cylinders supported by a vertical plate feeder electrode was studied. The rate of mass transfer of the bed–plate assembly was determined under single phase, gas sparging and two phase flow-by measuring the limiting current of the cathodic deposition of copper from acidified copper sulphate solutions. Variables studied were: particle diameter, height of bed–plate assembly, physical properties of the solution, superficial gas velocity, superficial solution velocity. The data under different conditions were correlated by dimensionless equations. Although the mass transfer coefficient of the bed electrode is less than that of the plate electrode, it was found that the volumetric mass transfer coefficient of the bed electrode and hence its productivity is higher than that of the plate electrode by a factor which ranges from 2.8 to 9.6 depending on the operating conditions. Power consumption calculation has shown that for a given set of conditions, bed electrodes consume less electrical energy in kWh/kg than the plate electrode under different flow conditions.

An approximate solution to the model of a sparged packed bed electrode reactor

An approximate analytical solution to the mathematical model of a sparged packed bed electrochemical reactor (SPBER) in which a gaseous reactant undergoes direct anodic oxidation is presented. The model is based on two strongly nonlinear partial differential equations and is solved by the inverse operator method (IOM). The solution is used to study the direct anodic oxidation of propylene. The approximate IOM solution is useful in that it enables the direct investigation of the effect of model parameters on the operation of the reactor. Current density against electrode potential, polarization data, for the anodic oxidation of propylene in the SPBER is presented. Nonlinear parameter estimate methods are used to fit the model to experimental data to obtain physically meaningful values of kinetic parameters.

Mass transfer behaviour of a flow-by fixed bed electrochemical reactor composed of a vertical stack of screens under single and upward two phase flow

Rates of mass transfer were studied at a vertical array of closely packed screens under single and two phase (gas–liquid) flow by measuring the limiting current for the cathodic reduction of ferricyanide ions. Variables studied were screen characteristics (mesh number and wire diameter), physical properties of the solution, solution flow rate, gas flow rate and the effect of surface active agents. The single phase data were correlated by the equation:J = 0.52 Re L -0.55 while the two phase data were correlated by the equations:Sh=0.87 Sc0.33 Re L 0.35 Reg 0.12for the conditions 10 < Re < 125 and 1.4 < Re g < 77; andSh=0.62 Sc0.33Re L 0.11 Reg 0.25for the conditions 1.1 < Re L < 22 and 1.4 < Re g < 77. The presence of surfactant was found to reduce the rate of mass transfer in both single phase and two phase flow, the percentage reduction being higher in the case of single phase flow.

Mass Transfer Model of Chromium Reduction in a Fluidized Bed Electrochemical Reactor

A batch recycling fluidized bed electrochemical reactor system was used to recover Cr(VI) from a very dilute solution containing 2.5 g Cr/L at pH 2. It was found that the electrowinning rate is controlled by mass transfer and that the reduction process of Cr(VI) is interrupted by the formation of Cr(H2O)3 3+. The Cr2O7 2− and Cr(H2O)6 3 concentration-time relationship can be predicted by a plug flow model. A finite difference method and a complex optimization technique were used to estimate the mass transfer coefficient. At Rep between 10 and 30, the Cr2O7 2− and Cr(H2O)6 3+ mass transfer coefficients lie between 1.52-3.20 × 10−6 and 1.17-2.50 × 10−6 cm/s, respectively, and increase with the Reynolds number based on the particulate cathode.

Mass transfer behaviour of a fixed bed electrochemical reactor with a gas evolving upstream counter electrode

AbstractMass transfer rates were determined at a horizontal screen cathode stirred by oxygen bubbles evolved at a horizontal anode placed below the screen by measuring the limiting current of the cathodic reduction of ferricyanide ion from alkaline solution. Variables studied were oxygen discharge rate, ferricyanide concentration and number of closely packed screens forming the cathode. For a single screen cathode the data were correlated by the equation:J = 0.249 (Re Fr)‐0.25The mass transfer coefficient was found to decrease with increasing the number of screens forming the cathode. Implications of the present work for improving the performance of the flow‐through packed bed electrochemical reactor were highlighted.