Chlorate Production Research Articles

Studying the Link between the Potential of a Metal-Oxide Anode, the Current Efficiency for Chlorate, and the Current Losses for the Oxygen and Chlorine Evolution in a Wide Range of the Chlorate Electrolysis Conditions

Dependences of the current efficiency for chlorate and current losses for the oxygen evolution on the anode potential are studied. The study is performed in a cell without directed electrolyte circulation during the electrolysis of chloride–chlorate solutions of various compositions at the ORTA and ORTA-I1 anodes, at different current densities, temperatures, and solution pH. At identical temperatures, the dependences have extremums. The anode potentials corresponding to extremums coincide with critical potentials (found in a polarization study) for anodes covered with coatings containing ruthenium dioxide. The current efficiency for chlorate at ORTA-I1 is higher than that at ORTA, while the extremum region is less pronounced. The problem of how to substantially decrease the specific power consumption in the chlorate production by simultaneously increasing the anodic current density and the electrolysis temperature is considered.

An experimental investigation of bubble-induced free convection in a small electrochemical cell

The sodium chlorate production process is run in large electrolysers where electrolyte flows between the electrodes due to the natural convection from hydrogen gas evolution. A brief review is given of electrolytic gas generation at electrode surfaces and of previous studies. A small, enclosed rectangular cell was used to electrolyse both a Na2SO4 and a NaCl/NaClO3 solution, in order to produce hydrogen and oxygen bubbles at one or both of the electrodes. The two-phase flow regimes, bubble sizes, gas fraction and fluid velocities between the electrodes were investigated using microscope enhanced visualisation, laser doppler velocimetry and particle image velocimetry. The practicality of each of the measuring methods is analysed and it is concluded that laser doppler velocimetry is the most robust method for measuring such systems. The experimental results are discussed and conclusions are drawn relating gas evolution to the hydrodynamics of electrolyte flowing through a narrow vertical channel. The major conclusions are that fluid flow in systems with bubble evolution can transform from a laminar to a turbulent behaviour, throughout the length of the cell, and that both turbulence and laminar behaviour can exist across the cell channel at the same horizontal plane.

Low Overpotential Nanocrystalline Ti-Fe-Ru-O Cathodes for the Production of Sodium Chlorate

Low Overpotential Nanocrystalline Ti-Fe-Ru-O Cathodes for the Production of Sodium Chlorate

Technical Applications of Nanocrystalune Materials

AbstractAfter discussing various applications of nanocrystalline solids which are presently under development, this paper describes in more detail the potential use of nanocrystalline materials for the production of sodium chlorate, a paper bleaching agent. The technology and advantages of using nanocrystalline solids as cathode material for this electrochemical process are discussed. The paper concludes by presenting the world market and potential savings associated with the use of this new technology.

Ruthenium Dioxide as Cathode Material for Hydrogen Evolution in Hydroxide and Chlorate Solutions

Ruthenium dioxide as electrocatalyst on an activated cathode for chlorate production was investigated with respect to its activity towards hydrogen evolution, hypochlorite reduction, and chlorate reduction, respectively. Investigations were made in the presence, as well as in the absence, of a chromium hydroxide film in 1M and in typical chlorate electrolyte. Low overvoltages for hydrogen evolution were found and, at technical current densities, an effect of catalyst coating thickness. Commercial DSA® electrodes with as the active compound were tested as cathodes and were less active but more stable than the coatings produced by us. Hypochlorite and chlorate were reduced in the absence of chromate, chlorate reduction being fast on ruthenium dioxide compared to the other electrode materials and by far the dominating cathodic reaction in chlorate electrolyte without chromate and hypochlorite at 70°C, 3 kA/m2.

Photodecomposition du bioxyde de chlore et des ions chlorite par irradiation u.v. en milieu aqueux-partie II. Etude cinetique

The decomposition of ClO 2 and ClO 2 − by u.v. radiation leads to the production of chlorate, chloride and oxygen as end-products via complex reactions which are initiated by the products generated by the primary reactions of photolysis (Buxton and Subhani, 1972a; Mialocq et al., 1973; Karpel Vel Leitner et al., 1992). As far as the rate of decomposition is concerned, Bowen and Cheung (1932) and Zika et al. (1985) have shown that the quantum yield of photodecomposition of chlorine dioxide (overall reaction) increases when the wavelength decreases [Zika et al. (1985): φ = 0.46 at 366 nm and 1.4 at 296.7 nm]. However, the values of the quantum yield of photodecomposition of ClO 2 and ClO 2 − at 253.7 nm as well as the quantum yields for the primary reactions of photolysis of ClO 2 and ClO 2 − at different wavelengths are not given in the literature. The aim of this work was to study the kinetics of photodecomposition of chlorine dioxide and of chlorite by u.v. irradiation.

Etude du mecanisme et de la cinetique de l'action du chlore sur le bioxyde de chlore en solution aqueuse diluee

Abstract The aim of this work was to study the mechanism and the rate of the reaction between chlorine and chlorine dioxide in dilute aqueous solution at pH values near neutrality. The results showed that chlorination of aqueous solutions of chlorine dioxide leads to the production of chlorate (as an end by‐product) and to chlorite (as an intermediate). Secondary reactions between chlorite and chlorine yield chlorate. The overall stoichiometry for the reaction of chlorine with chlorine dioxide corresponds to the production of one mole of chlorate/mole of chlorine dioxide and to the consumption of 0.5 mole of chlorine/mole of chlorine dioxide. The data obtained from experiments carried out at different pH values (6.5 < pH < 10.8) and with different initial concentrations of reactants (chlorine and chlorine dioxide) showed that the rate of disappearance of chlorine dioxide can be described by a second‐order kinetic equation (d[ClO2]/dt = k[Chlorine][ClO2]) and that the second‐order rate constants increase w...

Etude cinetique de l'action du chlore sur les ions chlorites en solution aqueuse diluee

Abstract The reaction between chlorine and chlorite ions in dilute aqueous solution and at pH values ranging from 6.2 to 8.5 was examined in this study. The results showed that chlorine‐chlorite reactions lead via parallel pathways to the production of chlorate (as an end by‐product) and to chlorine dioxide (as an intermediate). The yield of chlorine dioxide increased as the initial concentrations of reactants increased and decreased with reaction time in the presence of excess chlorine because of secondary reactions between chlorine and chlorine dioxide. The overall stoechiometry corresponded to the production of one mole of chlorate/mole of chlorite and to the consumption of one mole of chlorine/mole of chlorite. Experiments carried out with low concentrations of chlorite (< 40 μmol l‐1) and chlorine (< 80 μmol l‐1) (conditions which favor the production of chlorate as opposed to chlorine dioxide) showed that the rate of decrease in the concentration of chlorite is second‐order with respect to chlorite ...

Low-temperature ashing of organic materials for determination of chloride

The low-temperature plasma ashing technique was applied to organic materials containing sodium chloride and residual ash was analyzed for chloride using ion chromatography. Recovery of the chloride was approximately 50%, while 20–30% of the chloride had been converted to chlorate. The remaining fraction of the chloride could have been volatilized due to electron and ion bombardments onto the sample surface within the glow discharge region. Pretreatment of the sample by impregnating with potassium carbonate improved the recovery of the chloride to 90% with practically no production of chlorate.

A comment on the mechanism of anodic chlorate formation

An analysis of the mechanism of sodium chlorate production based on the electrolytic formation and simultaneous hydrolysis and diffusion and chlorine is presented which differs from previous analyses in that chlorine hydrolysis occurs in a reaction layer of thickness less than the hydrodynamic diffusion layer.

ChemInform Abstract: CHEMICAL, ELECTROCHEMICAL, AND TECHNOLOGICAL ASPECTS OF SODIUM CHLORATE MANUFACTURE

A critical review of the chemistry, electrochemistry, and engineering principles involved in the production of sodium chlorate is presented. Various chlorate manufacturing technologies were discussed, with emphasis on materials of construction, and trends towards developing cost and energy effective methods for producing sodium chlorate.

Chemical, Electrochemical, and Technological Aspects of Sodium Chlorate Manufacture

A critical review of the chemistry, electrochemistry, and engineering principles involved in the production of sodium chlorate is presented. Various chlorate manufacturing technologies were discussed, with emphasis on materials of construction, and trends towards developing cost and energy effective methods for producing sodium chlorate.

Electrochemical Deposition of Conducting Ruthenium Oxide Films from Solution

not Available.

Optimal Control of a Twin-Screw Extruder by Means of a Microprocessor

We have described, in previous works (Abdallah, Lafav, 1976), the design and the implementation of an on-line quality sensor for PVC products. This has made possible to carry out an Optimal pilot operation of an industrial extruder which is intended to the non-stop production of polyvinyl chlorate (PVC) tubesThe optimal closed-loop control is the solution of the constraint minimization of a cost functional, given by the quadratic error between the desired product quality and the measured oneTo do so, we first produce a linearized static model describing the extruder and its local regulators which gives rise to a well-posed minimization problem. This mathematical model is obtained by a piecewise linearization of a nonlinear model, previously off-line identified by means of a bank of input/ output signals taken on the process in the vicinity of a given nominal working pointThen, a non-linear programming method of conjugate-gradient type is used to calculate, when required, the new and unique set noints for the local regulatorsThe complexity of the solution computed in real-time, needs the use of an evolved microprocessor. The optimal piloting algorithm is implemented on this microprocessor fitted out with industrial inputs/outputs allowing a direct process connectionVarious tests undertaken on the extrusion site have shown that the following targets have been efficiently reached :-disturbance compensation about a given nominal steady state point,-high convergence rate of the designed minimization algorithm when compared with the process time constants,-robustness of the control with regard to model errors and nominal working points

The production of chlorate with a bipolar pump cell

AbstractChlorate has been produced in a system consisting of an electrochemical pump cell (space‐time ∼ 150 ms) and a holding volume. The overall current efficiency has been determined as a function of ratio of tank:cell volume, electrolyte concentration and applied voltage, and the interaction of the electrochemical and chemical reactions investigated. At low applied voltages the reduction of dispersed and dissolved oxygen provides an alternative counter reaction to the more normal evolution of hydrogen, although only at low current densities on graphite. Space‐time yields range from 0.52 to 8.76 mol h−1 dm−3 at energy yields of 2.65 to 7.59 kW h kg−1.

Entwicklung und Trend der Chlordioxid‐Bleiche mit integrierter Chlorat‐Elektrolyse für die Zellstoff‐Industrie

AbstractDevelopment and trends in chlorine dioxide bleaching with integrated chlorate electrolysis for the cellulose industry. Rising demand for cellulose and paper and the environmental measures necessary in this branch of industry compel the companies involved to invest large sums. In particular, waste water from bleaching operations causes difficulties in biological waste water purification owing to high chlorolignin content. The sequence of chlorination steps have been optimized for each quality of wood, and the increasing use of chlorine dioxide leads to an expansion of chlorate electrolysis and chlorine dioxide plant at the expense of chlorine. The consumption of chemicals for the various cellulose qualities is considered. During the past 30 years, the Münchner process for production of ClO2 has proved environmentally sound and is being continuously improved. Only hydrochloric acid and water are needed as raw materials. The chlorine formed in this process is converted into hydrochloric acid, hypochlorite, and chlorine water. All steps of the processes require only liquids and gases permitting a favourable, closed mode of operation without by‐products or waste salts. New chlorate cells built since 1969 are equipped exclusively with coated titanium anodes (load between 6 and 100 kA) with DC efficiencies of 92 to 95%. Annual world production of sodium chlorate exceeds 1 million tonnes. The rate of increase has long remained steady at 5%.

Calculation of local current densities and terminal voltage for a monopolar sandwich electrolyser: application to chlorate cells

Chemical engineering calculations are performed for a new type of monopolar electrolyser with power leads located on its sides, used for chlorate production. The calculation gives the value of the total cell voltage as well as of local current densities for given current load and given electrode dimensions, interelectrode gap etc. On this basis the optimization of the system is possible.

ChemInform Abstract: PREPARATION AND APPLICATIONS OF GRAPHITE SUBSTRATE LEAD DIOXIDE (GSLD) ANODE

AbstractÜbersicht.

Preparation and Applications of Graphite Substrate Lead Dioxide (GSLD) Anode

The GSLD anodes have been developed for obtaining suitable size anodes for use in high amperage cells in the production of chlorates and perchlorates. The performance characteristics of the anodes in the preparation of chlorates and perchlorates are described. The use of the GSLD anode in other inorganic preparations like bromates iodates, and periodates is also included.

The performance of a bi-polar thin film cell for chlorate production

The performance of a bi-polar thin film cell for chlorate production