Simultaneous electrosynthesis of alkaline hydrogen peroxide and sodium chlorate

Simultaneous electrosynthesis of alkaline hydrogen peroxide and sodium chlorate in the same cell was investigated. The alkaline hydrogen peroxide was obtained by the electroreduction of oxygen in NaOH on a fixed carbon bed while the chlorate was obtained by the reaction of anodic electrogenerated hypochlorite and hypochlorous acid in an external reactor. An anion membrane, protected on the anode side with an asbestos diaphragm, was used as the separator between the two chambers of the cell. The trickle bed electrode of dimensions 0.23 m high ×0.0362 m wide × 0.003 m thick was used on the cathode side. The anolyte chamber of the cell, 0.23 m high × 0.0362 m, wide × 0.003 m thick was operated at a fixed anolyte flow of 2.0 × 10^–6 m³ s^–1 while the oxygen loadings in the trickle bed was kept constant at 0.102 kg m^–2 s^–1. Other operating conditions include inlet and outlet temperatures of 27–33°C (anode side), 20–29°C (cathode side), cell voltages of 3.0–4.2 V (at current density of 1.2–2.4 kAm^–2) and a fixed temperature of 70°C in the anolyte tank.The effects of superficial current density, NaOH concentration (0.5–2.0 M) and catholyte liquid loadings (0.92–4.6 kg m^–2 s^–1) on the chlorate and peroxide current efficiencies were measured. The effect of peroxy to hydroxyl mole ratio on the chlorate current efficiency was also determined.Depending on the conditions, alkaline peroxide solution and sodium chlorate were cogenerated at peroxide current efficiency between 20.0 and 86.0%; chlorate current efficiency between 51.0 and 80.6% and peroxide concentration ranging from 0.069 to 0.80 M. The cogeneration of the two chemicals was carried out at both concentrated (2.4–2.8 M) and dilute (0–0.5 M) chlorate solutions. A relative improvement on the current efficiencies at concentrated chlorate was observed. A chloride balance indicated a less than 0.4% chloride loss to the catholyte. The results are interpreted in terms of the electrochemistry, chemical kinetics and the hydrodynamics of the cell.Nomenclature C _i concentration of speciesi (mol m^–3) - F Faraday constant (96 500 C mol^–1) - I current (A) - Q catholyte flow rate (m³s^–1) - total time of cell operation (s) - _i current efficiency of speciesi (%)     

Optimization of caustic current efficiency in a zero-gap advanced chlor-alkali cell with application of genetic algorithm assisted by artificial neural networks

The effects of various process parameters on caustic current efficiency (CCE) in a zero-gap oxygen-depolarized chlor-alkali cell employing a state-of-the-art silver plated nickel screen electrode (ESNS^®) were studied. For doing a thorough research, we selected the process parameters from both cathodic and anodic compartments. Seven process parameters were studied including anolyte pH, temperature, flow rate and brine concentration from the anode side, oxygen temperature and flow rate from the cathode side and the applied current density. The effect of these parameters on CCE was determined quantitatively. A feed forward neural network model with the Levenberg–Marquardt (LM) back propagation training method was developed to predict CCE. Then genetic algorithm (GA) was implemented to neural network model. The highest CCE (98.53%) was found after 20 times running GA at the following conditions: brine concentration (287 g/L), anolyte temperature (80 °C), anolyte pH (2.7), anolyte flow rate (408 cm³/min), oxygen flow rate (841 cm³/min), oxygen temperature (79 °C), and current density (0.33 A/cm²).     

影响离子膜电解槽槽电压的因素

阐述了离子膜电解槽操作温度、电流密度、电解液流量、阴极液质量分数、阳极液质量分数、阳极液ｐＨ值、阳极液中金属离子以及阴极材料等九方面对电解槽电压的影响。     

离子膜电解槽加酸探讨

采用向离子膜电解槽阳极液中加盐酸的方法可以提高阳极电流效率,同时可以降低氯中含氧和阳极液氯酸盐含量。以蓝星北化机厂家NBH-2.7型自然循环离子膜电解槽为例,阐述了阳极液加酸的作用、加酸点、加酸量控制和应注意的问题。     

操作条件对离子膜性能的影响

由西安西化热电化工有限责任公司离子膜电解装置10年来的运行状况,总结出影响离子膜性能的8个主要因素有：盐水质量、阴极液浓度、阳极液浓度、电解液温度、电流密度、阳极液酸度、电解液流量和开停车时的洗槽。     

Chlorate and oxygen formation in alkali chloride membrane electrolysis

During the operation of an industrial-scale membrane electrolysis plant over a number of years, a record was kept of the formation of the byproduct oxygen in the anode gas and chlorate in the anolyte parallel to the decline of the current efficiencies of the main products. It was found that the current efficiencies of the byproducts increase linearly with the declining current efficiencies of the main products, chlorine and caustic soda. Of the two types of anode used, one exhibited considerably more oxygen formation than the other. The high-oxygen anode was associated with distinctly lower chlorate formation than the low-oxygen anode. The increasing oxygen contents and chlorate formation rates associated with falling caustic current efficiency are reported for both types of anode. If hydrochloric acid is used to destroy the chlorate, the amount of acid must be increased as the caustic current efficiency falls. The amounts of hydrochloric acid required for the two types of anode are calculated as examples for 96% and 93% caustic current efficiency.     

Kinetics of the dissolution behaviour of anodic oxide films on niobium in NaOH solutions

The dissolution behaviour of the anodized niobium electrode in NaOH solutions was investigated as a function of alkali concentration, formation voltage, formation current density and temperature using potential and impedance measurements. The rate of dissolution is dependent on the alkali concentration. In dilute NaOH solutions (1 N) the anodic oxide film formed in 0.5 M H₂SO₄ is reasonably stable. On the other hand, at higher concentrations of NaOH (2 M), the anodized electrode is subject to continuous dissolution depending on the alkali concentration. Also, the dissolution process is considerably affected by temperature; at temperatures greater than 320 K the oxide film is destroyed in less than 30 min. The results show that the current density used during the formation of the oxide film has no effect on its dissolution rate.     

Sealing effects of anodic oxide films formed on Mg-Al alloys

Mg alloys were anodized in alkaline NaOH solutions with various additives as a non-chromate method. Specimen AZ91 was anodized at a potential that produced a strong surface dissolution reaction and generated a large amount of Mg(OH)₂. The effect of sealing after anodizing was investigated, focusing on the effects of sealing time, temperature and solution conditions. The current density decreased with increasing A1(OH)₃ concentration in 1 M NaOH solution during anodizing; sparking occurred at potentials above 80 V. The best corrosion resistance with anodizing in 1 M NaOH solution occurred at a potential of 4 V, which caused the strongest active dissolution reaction. The sealing effect improved with increasing time and temperature, and corrosion resistance was proportional to the relative ratio of Mg(OH)₂. If the oxygen thickness observed by EDX equaled the film thickness, the film formed at 4 V in 1 M NaOH was 10–15 Μm thickness. The optimum corrosion resistance in sealing at various solutions after anodizing was 1M-NaOH solution.     

Electrical and other properties of mutual radiation-induced methacrylic acid grafted polyethylene films

The radiation-induced grafting of methacrylic acid on to polyethylene films was applied to the synthesis of ion-exchange membranes. The grafting yield increased at first then decreased with the increase in the irradiation dose. The surface area, thickness, volume, and the water uptake of the grafted film increased linearly with the increase in grafting yield. The distribution pattern of carboxyl groups of graft chains in the direction of film thickness followed by EPMA line profiles of potassium which combined with carboxyl groups showed that a homogeneous distribution was not obtained until the grafting yield was more than 10%. When DC current was supplied to the membrane in NaOH solution, the reciprocal of the electric resistance increased with the increase in NaOH concentration. The specific electric resistance decreased exponentially with the increase in the content of ionic functional groups in the membrane. The steady state concentration of Na⁺ in catholyte and the current efficiency were ca. 15 and 20%, respectively.     

电解电渗析法制备硅溶胶

以RuO_x／Ti为阳极、铁镀镍为阴极与Nafion901阳离子交换膜组装成两室的电解电渗析槽,探讨了电解电渗析法制备硅溶胶过程中槽电压和pH值变化的基本规律,证实了增大电流密度和阳极液的进料液流速率可减少二氧化硅在阳极上的吸附沉积,增大二氧化硅的收率．在滴加操作中,通过实验找到了制备浓硅溶胶的较佳的初始组成和操作条件,基本上解决了二氧化硅在阳极上的沉积问题,最高槽电压不超过10V,最高电流密度可达150mA·cm~(-2),膜的平均电流效率在93％左右．     

Recovery of metals from complexed solutions by electrodeposition

Electrolytic recovery of metals from aqueous solutions containing complexing chelating agents such as EDTA, NTA, and citrate was studied in a two-chamber cell separating with a commercial cation-exchange membrane (CEM). Equimolar solutions of metal and a chelating agent as a catholyte and NaNO₃ as an anolyte were used; the effect of current densities, initial catholyte and anolyte pH, metal concentration and the type of the CEM, chelating agent and metal on the recovery of metals was determined. The recovery of metal increased with higher initial anolyte pH, concentration and current density, whereas it decreased with lower initial catholyte pH. The results show that electrodeposition seems to be an applicable method for the recovery of metals under appropriate conditions.     

The rapid electrochemical preparation of dissolved ferrate(VI): Effects of various operating parameters

The preparation of ferrate(VI) by the anodic dissolution of an iron wire gauze in concentrated NaOH solution is described. An anolyte of 0.35-0.48 M Na₂FeO₄ can be produced during 3-6 h electrolysis in initial 16 M NaOH solution at 35 °C. The experimental results indicate that the Fe(VI) concentration variation rate during electrolysis is close related to the factors such as current density, alkaline concentration, the ratio of effective surface area to anolyte volume, the passivation of iron anode and the decomposition of ferrate(VI), etc., and the relevant empirical equation is given. The alkalinity of anolyte has large effect on the electrogeneration of ferrate(VI), especially during an interval electrolysis.     

ELECTROCHEMICAL RECOVERY OF CHLORINE AND HYDROGEN FROM HYDROGEN CHLORIDE BY-PRODUCT PRODUCED IN THE PETROCHEMICAL INDUSTRY

Simultaneous production of hydrogen as an energy carrier and chlorine as a valuable chemical from recycled hydrogen chloride was investigated employing a lab-scale membrane electrolysis setup. The effects of various process parameters including current density (1–4 kA m^?2), cell temperature (45°–75°C), flow rate of hydrochloric acid feed (200–500 mL min^?1), and concentration of acid (18–21 wt.%) on the cell voltage and chlorine current efficiency (ChCE) were studied. The Taguchi design of experiments (L₁₆ array) was employed to design the minimum number of experiments necessary to fully study the process. A filter press type cell of 10 cm² surface area comprising a DSA anode, an alloy of predominantly nickel cathode and Nafion 115 membrane, was used. It was observed that increasing anolyte flow rate, anolyte concentration, or cell temperature caused a decrease in cell voltage and an increase in ChCE, while increasing current density linearly increased cell voltage and decreased ChCE.     

Boron removal by electrodialysis with anion-exchange membranes

The removal of boron from an aqueous solution was studied in a two-chamber cell separated with a commercial anion- exchange membrane as a function of current density, pH, type of the membrane, concentration and different type of salt solutions. At the end of these studies, the maximum value of boron removal was obtained under the conditions where the maximum current was applied; 0.1 M H₃BO₃ (pH = 9) and 0.001 M NaCl solutions were used as a catholyte and an anolyte solution, respectively. The AHA membrane was used for separating the two cells used in the electrodialysis experiments. All experiments were carried out at room temperature, and the concentration of boron at the anode cell was determined by ICP–AES. It was concluded that electrodialysis is an appropriate method for boron removal from aqueous solutions under suitable conditions.     

Dual solution-type HCHO fuel cell systems using an anion exchange resin membrane with electroless-plated Cu or Pd anode

Loading characteristics of a prototype HCHO fuel cell systems with an anion exchange membrane which separates the anolyte from the catholyte were investigated. Electrodes of Cu or Pd, deposited by an electroless-plating technique onto the membrane, showed high electrocatalytic activity to the anodic oxidation of HCHO in 1 M NaOH solution. The system with Cu anode and 1 M NaOH for both anolyte and catholyte showed high loading characteristics but poor durability, whereas that with 1 M K₂CO₃ showed low characteristics because of lowered pH of the anolyte. It was shown that a dual solution-type cell with 1 M K₂CO₃ anolyte and 1 M NaOH catholyte yielded improved characteristics as compared with the simple K₂CO₃ system. The output level was, however, at an unsatisfactory level owing to poor membrane conductance. The temperature dependence of the output performance was studied in the range 7–55°C.     

Preparation of ursodeoxycholic acid by direct electro-reduction of 7-ketolithocholic acid

A novel method of producing ursodeoxycholic acid was developed through direct electro-reduction of 7-ketolithocholic acid in a divided electrolytic cell. Titanium ruthenium mesh electrode was used as the anode, while high purity lead plate was used as the cathode. The process was optimized with regards to the electrolyte, temperature, concentration of methanol, current density and concentration of anolyte. When potassium bromide was used as the electrolyte, the saturated solution of 7-ketolithocholic acid in 85–93% (v/v) methanol, current density 9.52–28.6 A/m² and concentration of anolyte at 4–6% (w/w), the maximum percentage yield of ursodeoxycholic acid could be 47%. The method will provide a potential approach for large-scale production of ursodeoxycholic acid.     

Application of the Maxwell–Stefan theory to the membrane electrolysis process: Model development and simulations

A model is developed which describes the mass transfer in ion-selective membranes as used in the chloralkali electrolysis process. The mass transfer model is based on the Maxwell–Stefan theory, in which the membrane charged groups are considered as one of the components in the aqueous mixture. The Maxwell–Stefan equations are re-written in such a way that the current density can be used as an input parameter in the model, which circumvents an extensive numerical iterative process in the numerical solution of the equations. Because the Maxwell–Stefan theory is in fact a force balance, and the clamping force needed to keep the membrane charged groups in its place is not taken into account, the model is basically over-dimensioned: the mole fraction of the membrane can be calculated by using the equivalent weight (EW) of the membrane or by using the equations of continuity. In this work, the latter method has been chosen. The results of the computer model were verified in several ways, which show that the computer model gives reliable results. Several exploratory simulations have been carried out for a sulfonic layer membrane and the conditions as encountered in the chloralkali electrolysis process. As there are no (reliable) Maxwell–Stefan diffusivities available for a Nafion membrane, in this trend study the diffusivities were all chosen equal at a more or less arbitrary value of 1.10⁻¹⁰ m² s⁻¹. Due to this, the absolute values of several performance parameters are incorrect as compared with industrial chloralkali operation (e.g. an unrealistically high current efficiency of 95.7% was found), but the model can still be used to obtain trends. For example, it is shown that the thickness of the membrane hardly increases the current efficiency (CE), however, the required potential drop proportionally increases with thickness. The pH rapidly increases to values greater than 12 just inside the membrane at the anolyte side. Moreover, for different values of the pH in the anolyte, the pH profiles inside the membrane nearly coincide with each other. A change in the anolyte strength does not have a significant effect on the performance of the membrane. At low values of the current density, a high value of the current efficiency is found. However, this is not due to a low OH⁻ counter flux, but to the simultaneous transport of OH⁻ and Cl⁻ towards the catholyte.     

Analysis of molar flux and current density in the electrodialytic separation of sulfuric acid from spent liquor using an anion exchange membrane

Separation of sulfuric acid from a dilute solution involved a plate and frame type electrodialysis unit using a commercial anion exchange membrane. Experiments were conducted in batch with catholyte concentrations ranging from 1 to 5 wt%. Effect of applied current density, initial catholyte concentration and initial concentration difference of catholyte and anolyte on the molar flux was studied extensively. The maximum molar flux was estimated to be 10.52×10^-8 mol cm^-2s^-1 at 4.45 wt% catholyte concentration and applied current density of 30 mA cm^-2. Current efficiencies were observed to be 75 to 85% at lower current density, which rose to more than 100% at 20 and 30mA cm^-2, at equal initial concentration of catholyte and anolyte. Diffusive flux and flux due to membrane potential contributed very less compared to total flux in presence of applied electric current. An equation was developed to predict the practical molar fluxes, which fitted satisfactorily with minor standard deviation. Pristine and used membrane specimens were characterized using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM).     

电解法制备高纯ClO_2技术

为了开发经济实用的高纯ClO2制备工艺,对电解氯酸盐溶液制备ClO2的技术进行了研究。通过电解氯酸盐自动催化循环制备高纯ClO2的实验,讨论了氯酸盐的浓度、电解液的氢离子浓度、电解液温度、电流密度以及电解液中ClO2剩余浓度对产品气体中ClO2质量分数的影响。研究结果表明,实验产生的产品气体,ClO2的质量分数均在90%以上,当在最佳条件下,即氯酸盐浓度约为1.0 mol/L,电解液的氢离子浓度约为4.90 mol/L,电解液温度约为28℃,电流密度约为975 A/m2的条件下,产生ClO的质量分数可达98%左右。     

Valve metal behaviour of bismuth in NaOH

Galvanostatic anodization of bismuth in different media indicates that the formation of the oxide film depends simultaneously on both pH and the anions present in the anodization medium. Dissolution of these films in NaOH supports this observation. The film is formed of two layers. Open circuit impedance and potential measurements in NaOH indicate film growth. The anodic film formed in NaOH dissolves, however, in NaOH solutions following a zero order mechanism. A number of factors including formation voltage, NaOH concentration, current density and temperature are investigated. The activation energy of the oxide film dissolution is calculated. It may be concluded that the outer layer, in addition to being of a more defective structure, is probably of a higher oxidation state than the inner layer.