Operation simulation of a recycled electrochemical ozone generator using artificial neural network

The present work has focused on the modeling and simulation of a recycled ozone generator system via electrochemical oxidation of water. To produce ozone, a Pyrex glass electrochemical reactor, comprised of two separate half-cell by Nafion 117 membrane was applied. The applied anode and cathode electrodes were Ti/Sn-Sb-Ni and platinized titanium, respectively. The modeling and simulation of the reactor operation were done via artificial neural network (ANN) technique. In this regard, four important operational parameters (i.e. electrolyte concentration, applied voltage, flow rate and electrolysis time) and the generated ozone concentration were considered as the independent inputs and the network output, respectively. To find out the best model, six numbers of three-layered ANNs with different functions were constructed and optimized. Best simulation was related to a model, consist of Levenberg–Marquardt Back propagation learning algorithm (trainlm) and tangent sigmoid (tansig) as transfer function in the both hidden and output layers. Also, application of 10 hidden neurons and 80 iterations for the network calibration caused to satisfy the network training while overfitting was prevented. The K-fold cross-validation method, employed for the model evaluation, showed high correlation coefficient (0.9936) and low mean square error (3.58 × 10⁻⁴) for the testing data. Sensitivity analysis indicated order of relative importance the operational parameters on the ozone production as: time > [electrolyte] > voltage > flow rate.     

Polymer electrolyte-type electrochemical ozone generator with an oxygen cathode

A new electrochemical ozone generator which has a proton exchange polymer membrane as an electrolyte, pure water as a source material and an oxygen diffusion electrode as a cathode was proposed to eliminate hydrogen evolution on the cathode and also to reduce electrolytic power consumption. The device was evaluated under varied operating conditions changing current density, temperature and oxygen flow rate. The water permeable high performance gas electrode enabled current density operation over 1.0 A cm⁻² without generating hydrogen gas in the cathode side outlet gas. The power consumption was successfully reduced to two thirds of that of the hydrogen evolution type electrolyzer over a period of three months' operation.     

Sampling dynamics for pressurized electrochemical cells

A model describing the gas distribution within a constant pressure electrolysis system and how the distribution impacts electrochemical efficiencies is presented. The primary system of interest is the generation of syngas (CO and H₂) associated with the co-electrolysis of H₂O and CO₂. The model developed for this system takes into account the primary process variables of operation including total system pressure, applied current, and the in-flow of reactant gases. From these, and the chemical equilibria within the system, the impact on electrochemically generated gases is presented. Comparison of predicted and measured faradaic efficiency of an electrode's processes reveals significant disagreement under certain conditions. Methods to minimize and account for the discrepancy are presented with the goal of being able to discern, in a real-time manner, degradation of electrode performance. Comparison of the model to experimental data shows a strong correlation between the two with slight variation in experimental data, which is attributed to reversible system dynamics such as wetting of the gas diffusion electrode used as the cell cathode.     

电化学臭氧产生技术研究进展

臭氧是一种广泛应用的绿色氧化剂,介绍了电化学产生臭氧的优点和最新报道的臭氧产生机理,重点讨论了影响电化学产生臭氧电流效率的诸多因素.通过评述电化学产生臭氧系统的现状,展望了电化学产生臭氧技术的发展方向.     

Performance of a multipurpose research electrochemical reactor

This paper reports on a multipurpose research electrochemical reactor with an innovative design feature, which is based on a filter press arrangement with inclined segmented electrodes and under a modular assembly. Under bipolar connection, the fraction of leakage current is lower than 4%, depending on the bipolar Wagner number, and the current distribution is closely uniform. When a turbulence promoter is used, the local mass-transfer coefficient shows a variation of ±10% with respect to its mean value. The fluidodynamics of the reactor responds to the dispersion model with a Peclet number higher than 10. It is concluded that this reactor is convenient for laboratory research.     

Oxidation of maleic acid under control of the catalyst potential in a pressurized electrochemical reactor

Maleic acid was oxidized on a platinized-platinum catalyst in a pressurized electrochemical reactor, at temperatures higher than 343 K, in a potential range where an active adsorbed intermediate is formed. In the presence of O₂, when potential was either spontaneously established or imposed by a potentiostat, similar activities and similar evolution of activities versus potential values were obtained. These results could imply that the same mechanism occurs, involving gaseous oxygen as oxygen source. Lower activities were obtained in electrocatalytic oxidation, in the absence of gaseous oxygen, involving a different mechanism.     

Performance of a diesel generator fuelled with palm oil

Pure palm oil may be employed in diesel engines as an alternative fuel. Engine performance and emissions were influenced by basic differences between diesel fuel and palm oils such as mass based heating values, viscosity, density and molecular oxygen content. The high viscosity of palm oil resulted in poor atomisation, carbon deposits, clogging of fuel lines and starting difficulties in low temperatures. When heated at 100 °C palm oil presented lower viscosity, better combustion and less deposits. Tests were conducted in a naturally aspirated MWM 229 direct injection four-stroke 70 kW diesel-generator fueslled with 100% palm oil.     

基于增压吸收的吸收式蓄能装置的性能分析

吸收式蓄能技术具有蓄能密度高、热损失小等特点,是一种具有发展潜力的蓄能技术,但目前的技术尚存在吸收效果差、效率不高等问题。提出基于增压吸收的吸收式蓄能方法,并阐述其装置的工作原理和特点,通过数学模型研究在不同工况下增压对其热力学性能的影响规律。结果表明：当蒸发温度与发生温度越低、冷凝温度越高时,增压器改善吸收式蓄能循环的性能系数（COP）越明显;与无增压吸收式蓄能循环相比,蓄能密度（ESD）得到提高,当增压比为3时,其ESD可提高30%～295%。     

Energy conversion and temperature dependence in ozone generator fed by synthetic air

A homogenous chemical kinetic model consisting of 21 species and 118 reactions is applied to investigate energy conversion and its temperature dependence in ozone generator fed by synthetic air. The portion of electric energy converted into reaction heat, gas heating and heat loss to surroundings (by convection) in terms of the total electric energy input, the conversion ratios η_reaction, η_gas, and η_loss, are obtained. The detailed reaction pathway including the degree of transformation among species for ozone production is also obtained via simulation of the reaction kinetics. In addition, sensitivity analysis and rate-of-production analysis for the three foremost species O₃, O, and N₂(A) are performed to understand quantitatively the temperature dependence of sensitivity coefficient and production rate for each individual reaction. η_reaction shows a steep rise at low specific energy, but then suffers a gradual decrease at high specific energy. η_loss has a contrary behavior. And η_gas increases steadily with the increase of specific energy. The η_reaction peak of 35.1% is achieved at specific energy of 0.17 J/cm³ at the conditions under investigation. Additionally, inlet gas temperature only has a small effect on energy conversion. Moreover, high gas temperature in discharge gap is confirmed to be not favorable for ozone formation from the view of reaction heat. The sensitivity coefficients of reactions with electron participation are sensitive to gas temperature. O+O₂+O₂→O₂+O₃ and O+O₂+N₂→N₂+O₃ account for about 70% and 30% of generated ozone respectively at the given conditions. And e+O₂→e+O+O, N₂(A)+O₂→N₂O+O, and N₂(A)+O₂→O+O+N₂ are responsible for about 51.3%, 14.7%, and 32.0% of oxygen atom, respectively.     

Characterization of an electrochemical reactor for the ozone production in electrolyte-free water

The filter-press electrochemical ozonizer is characterized as a function of the applied electric current, temperature, and linear velocity of the electrolyte-free water. Lead dioxide electroformed on surface of a non-platinized fine mesh stainless steel support was used as anode. Electrolysis of the electrolyte-free water was carried out using the membrane electrode assembly (MEA) adequately compressed by means of a specially designed clamping system. Electrochemical characterization studies were carried out galvanostatically as a function of temperature and linear velocity of the circulating water. It was verified that the electrochemical ozone production (EOP) taking place at the reacting zones formed at the solid polymer electrolyte (SPE)/mesh electrode interface is not considerably affected by circulating water when the linear velocity inside the distribution channels is higher than 1.20 cm s⁻¹. A current efficiency for the EOP of 13% and a specific electric energy consumption of 70 Wh g⁻¹ were obtained when an electric current of 130 A was applied at 30 °C. The reactor service life test revealed that the MEA using the lead dioxide fine mesh electrode as anode and a fine mesh stainless steel electrode as cathode, pressed against the SPE, is stable for the ozone production.     

Tailoring crystal facet microenvironments for simultaneous electrochemical ozone and hydrogen peroxide production

Developing a bifunctional electrocatalyst that can effectively produce O₃ and H₂O₂ is significant for the electrochemical synthesis of O₃ and H₂O₂ for the synergistic oxidative degradation of organic pollutants. In this study, SnO with various exposed facets was synthesized by tailoring the crystal facet microenvironment for oxygen intermediates adsorption for electrochemical ozone production (EOP) and two-electron oxygen reduction reaction (2e⁻ ORR). The Faraday efficiency of SnO-1 with a high (110) facet ratio for O₃ was 22.0%, while SnO-4 with a high (002) facet ratio achieved a selectivity of 93.6% for H₂O₂. The theoretical calculation indicates that their excellent performances originated from the strong adsorption of the (110) facet on O* and O₂* and the suitable adsorption and desorption strength of the (002) facet on OOH*, respectively. This study provides an attractive strategy for the development of a bifunctional electrocatalyst for advanced electrochemical oxidation by tailoring the crystal facet microenvironment.     

Performance criteria and nomenclature in electrochemical engineering

This paper is a recommendation of the Working Party on Electrochemical Engineering of the European Federation of Chemical Engineering. It was prepared by a sub-committee composed of: G. Kreysa (Frankfurt am Main) Chairman F. Coeuret (Rennes) A. Storck (Nancy) H. Wendt (Darmstadt)The helpful discussions and comments of colleagues in the Working Party are gratefully acknowledged.Presented at the 34th ISE meeting, Erlangen, 18–23 September, 1983.Any comments and opinion on the performance criteria and nomenclature proposed in this paper should be communicated direct to the author (Editor).     

A mathemathical model for the calculation of the concentration at the outlet of an ozone generator

A mathematical model was generated to predict the composition of the outlet gas of ozone generators. In order to make the modelling possible it was important to predict the occurrence time and the exact location of each individual discharge zone. This was done by connecting a specially constructed ozone generator, which would locate the discharge zones, to a nanosecond pulse generator which would impose regular occurrence times for discharge columns. The experimental and theoretical outlet concentrations of this ozone generator were compared. The result was an excellent match which justified the assumptions made in the model. The mathematical model was also used to study the effect of different factors affecting the production of ozone.     

Performance degradation study of a direct methanol fuel cell by electrochemical impedance spectroscopy

A stability test of a direct methanol fuel cell (DMFC) was carried out by keeping at a constant current density of 150 mA cm⁻² for 435 h. After the stability test, maximum power density decreased from 68 mW cm⁻² of the fresh membrane-electrode-assembly (MEA) to 34 mW cm⁻² (50%). Quantitative analysis on the performance decay was carried out by electrochemical impedance spectroscopy (EIS). EIS measurement of the anode electrode showed that the increase in the anode reaction resistance was 0.003 Ω cm². From the EIS measurement results of the single cell, it was found that the increase in the total reaction resistance and IR resistance were 0.02 and 0.05 Ω cm², respectively. Summarizing the EIS measurement results, contribution of each component on the performance degradation was determined as follows: IR resistance (71%) > cathode reaction resistance (24%) > anode reaction resistance (5%). Transmission electron microscopy (TEM) results showed that the average particle size of the Pt catalysts increased by 30% after the stability test, while that of the PtRu catalysts increased by 10%.     

Optimization of a corona wire‐to‐cylinder ozone generator. Comparison with economical criteria. part i : Oxygen

The experimental results obtained with a wire‐to‐cylinder ozone generator (20 cm length, inner diameter ～ 12 mm), using a 4 to 60 L/h oxygen flow‐rate range, negative DC high voltage being applied to the wire, are analyzed. As for the “classical” industrial ozone generators, the chemical engineering method, based on the energy density concept (Becker parameter ß = P/Q) and the global coefficients of formation K_f and destruction K_d of ozone, was applied. Our results, comparable with those obtained by other authors, show that it is equally possible to optimize the ozone production in a wire‐to‐cylinder ozone generator by relying on the economical criterion γ = β/C² or its inverse C.η more directly measurable in the usual practice. In the same way, it appears that the residence time (or contact time) of the reactant gas with the electrical discharge inside the reactor is a fundamental parameter which seems to be of some seconds or tens of seconds.     

Performance improvement of Nafion based solid state electrochemical supercapacitor

An electrochemical supercapacitor in all solid configuration using perfluorosulfonate ionomer as polymer electrolyte has been successfully realized. Electrodes of supercapacitor have been prepared using activated carbon material and Nafion ionomer. This latter had the double function of binder and electrolyte. Nafion 115 membrane has been used as electrolyte separator in the preparation of small scale supercapacitors. The capacitance performance of these devices is comparable or better than traditional systems, which use sulfuric acid as electrolyte. The electrochemical evaluation of studied supercapacitor has been carried out by cyclic voltammetry, dc charge/discharge measurements and electrochemical impedance spectroscopy. A capacitance of 90 F/g (referred to the weight of active carbon material in the electrode) has been obtained with carbon having surface area (SA) of about 1000 m²/g and, a capacitance of 130 F/g with activated carbon having SA of 1500 m²/g. These interesting results have been tentatively explained with an optimal configuration of electrodes and with the concomitant beneficial effects on the carbon pores of adsorbed water and Nafion distribution, which produce low distribute resistance in the carbon composite electrodes.     

Performance of an anode-supported tubular solid oxide fuel cell (SOFC) under pressurized conditions

An anode-supported tubular solid oxide fuel cell (SOFC) with a 15-μm thick YSZ electrolyte and an active area of 100 cm² was successfully fabricated by co-firing process, and the cell performance was measured under both atmospheric and pressurized conditions. The experimental results showed that the cell performance was significantly improved under the pressurized condition. When the pressure was increased from 1 to 6 atm, the maximum power density increased from 135.0 to 159.0 mW cm⁻² at 650 °C, and from 266.7 to 306.0 mW cm⁻² at 800 °C. The maximum power density at 800 °C and 4 atm was decreased from 334.8 to 273.9 mW cm⁻² when increasing the fuel utilization from 10% to 90%. Under the test condition of 70% fuel utilization, 800 °C and 4 atm, the cell could run stably at 0.7 V and 350 mA cm⁻² for 50 h, almost without any performance loss.     

Capture of submicrometer particles in a pressurized electrostatic precipitator

This study investigated the influence of gas pressure on the submicrometer particle capture performance of an electrostatic precipitator (ESP). Current-voltage characteristics and particle capture performance of the ESP were studied in air and in simulated flue gas (SFG) under 1, 2, and 3 atm. Using negative corona and air as the feed gas, the penetration of most particles of 40–400 nm in diameter decreased from 8 × 10^?4 ? 2 × 10^?2 to 2 × 10^?4 ? 1 × 10^?2 as pressure increased from 1 atm to 3 atm at constant current; and increased from 3 × 10^?5 ? 1 × 10^?3 to 2 × 10^?4 ? 1 × 10^?2 as pressure was elevated when the voltage was held roughly constant. Similar type of disparity under different pressures was also observed for positive corona and for SFG. Experiments set up to capture fly ash in the ESP showed that with constant current, higher pressure resulted in a higher initial charge fraction of the particles from the furnace, which could facilitate the penetration of fly ash particles. A semiempirical model was developed based on the Deutsch–Anderson equation and experimental data under 1, 2, and 3 atm to calculate the particle penetrations under high pressure. The total charge number on a particle (n') is calculated by incorporating the effects of current (I) and pressure (P) on relative weights of the diffusion charging number (n_diff) and field charging number (n_field), that is, n' = B₁(I,P)n_diff + B₂(I,P)n_field, where B₁(I,P) and B₂(I,P) are both empirical coefficients dependent on current and pressure. Experimental penetrations under 1.5 and 2.5 atm validated this model over the particle diameter range in 100–400 nm.

Copyright © 2016 American Association for Aerosol Research     

Degradation of unsaturated triglycerides injected into a pressurized reactor

To evaluate the precombustion chemistry of vegetable oils under conditions that exist in a diesel engine, several pure unsaturated triglycerides (triolein, trilinolein, trilinolenin) were injected into a pressurized reactor where they were subjected to thermal and oxidative degradation under varying conditions of atmosphere (air or nitrogen), temperature and pressure. Vapor samples were collected and then analyzed by gas chromatography/mass spectrometry techniques. In general, the samples consisted of similar mixtures regardless of the reaction conditions or triglyceride used as starting material. The most prominent compounds identified in these samples were fatty acids of different chain lengths and a variety of aliphatic hydrocarbons. Smaller numbers of other classes of compounds, such as aldehydes, were also detected. Presented at the 81st AOCS Annual Meeting, Baltimore, MD, April 1990.