Sodium chloride solution electrolysis

Performance of NEOSEPTA-F in Sodium Chloride Solution Electrolysis. Figure 5 shows the relationship of the cell voltage and the current efficiency respectively with the concentration of sodium hydroxide in catholyte when electrolysis of sodium chloride solution was carried out at the current density of 30 A/cm. From the economical viewpoint, i.e, the electrolysis power cost, depreciation of equipment cost, membrane cost and so on, the optimum concentration of sodium hydroxide for NEOSEPTA-F C-1000 is about 20 % and that for NEOSEPTA-F C-2000 is about 27 %. 

By the electrolysis of concentrated sodium chloride solution this process was initially used primarily for the production of sodium hydroxide but the demand for chlorine is now so great that the chlorine is a primary and not a by-product. 

Manufacture. Most chlorate is manufactured by the electrolysis of sodium chloride solution in electrochemical cells without diaphragms. Potassium chloride can be electroly2ed for the direct production of potassium chlorate (35,36), but because sodium chlorate is so much more soluble (see Fig. 2), the production of the sodium salt is generally preferred. Potassium chlorate may be obtained from the sodium chlorate by a metathesis reaction with potassium chloride (37). 

Brine Preparation. Rock salt and solar salt (see Chemicals frombrine) can be used for preparing sodium chloride solution for electrolysis. These salts contain Ca, Mg, and other impurities that must be removed prior to electrolysis. Otherwise these impurities are deposited on electrodes and increase the energy requirements. The raw brine can be treated by addition of sodium carbonate and hydroxide to reduce calcium and magnesium levels to below 10 ppm. If further reduction in hardness is required, an ion-exchange resin can be used. A typical brine specification for the Huron chlorate ceU design is given in Table 6. 

Other industrial applications of electrolysis include extraction/purification of metals from ores, electroplating, and the manufacture of certain chemicals such as sodium hydroxide. In the latter, sodium chloride solution when electrolysed is converted to sodium hydroxide to produce chlorine at the anode and hydrogen at the cathode. Both of these gaseous by-products are collected for industrial use chlorine is used in the production of bleach and PVC hydrogen is used as a fuel, to saturate fats, and to make ammonia. 

Sodium hypochlorite is produced by the electrolysis of cold sodium chloride solution. How long must a cell operate to produce 1.500 X 103 L of 5.00% NaCIO by mass if the cell current is 2.00 X 103 A Assume that the density of the solution is 1.00 g/cm3. 

Among electrolytic processes used to produce materials, we customarily distinguish those in which electrodes are reacting that is, where the metal or other electrode material is involved in the reaction (Chapter 16) from those with nonconsumable electrodes (Chapter 15). A very important industrial process with nonconsumable electrodes is the electrolysis of sodium chloride solution (brine) producing chlorine at the anode and sodium hydroxide NaOH (caustic soda) in the catholyte via the overall reaction... 

A mixture of hydrogen and chlorine gas, eventually in combination with air, can be very explosive if one of the components exceeds certain limits. In chlorine production plants, based on the electrolysis of sodium chloride solutions, there is always a production of hydrogen. It is, therefore, essential to be aware of the actual hydrogen content of chlorine gas process streams at any time. There are several places in the chlorine production process where the hydrogen content in the chlorine gas can accumulate above the explosion limits. Within the chloralkali industry, mainly two types of processes are used for the production of chlorine—the mercury- and the membrane-based electrolysis of sodium chloride solutions (brine). 

Sodium hydroxide is manufactured together with chlorine by electrolysis of sodium chloride solution. Various types of electrolytic cells are used commercially. They include the mercury cell, the diaphragm cell, and the membrane cell. 

The experiment is prepared by one student and demonstrated to the class. Assemble a device for electrolysis (see Fig. 52). Include rheostat 1 for 10-20 Q and ammeter 2 for 2-3 A in the circuit. Pour a saturated sodium chloride solution coloured with a neutral litmus solution into U-tube 3. Immerse carbon electrodes 4 (by one-third) into the solution. Connect the ends of the conductors to a direct-current source (an accumulator) and pass a current of about 2 A through the solution. What is observed Explain the change in the colour of the indicator solution. Write the equations of the reactions proceeding at the electrodes. 

Chlorate. Sodium chlorate, chlorate of soda, [CAS 7775-09-9], NaC103. white solid, soluble, mp 260 C, powerful oxidizing agent and consequently a fire hazard with dry organic materials, such as clothes, and with sulfur upon heating oxygen is liberated and the residue is sodium chloride formed by electrolysis of sodium chloride solution under proper conditions. Used (1) as a weedkiller (above hazard), (2) in matches, and explosives, (3) in the textile and leather indusUies. 

Hypochlorite. Sodium hypochlorite, [CAS 7681-52-9], NaOCl, commonly in solution by (1) electrolysis of sodium chloride solution under proper conditions. (2) reaction of calcium hypochlorite suspension in water and sodium carbonate solution, and then filtering. Used (1) as a bleaching agent fa textiles and paper pulp. (2) as a disinfectant, especially fa water. (3) as an oxidizing reagent. 

Sodium ion acts as a spectator ion and is not involved in the electrode reactions. Thus, the sodium chloride solution is converted to a sodium hydroxide solution as the electrolysis proceeds. The minimum potential required to force this nonspontaneous reaction to occur under standard-state conditions is 2.19 V plus the overvoltage. 

The electrolysis of saturated sodium chloride solution (brine) is the basis of a major industry. In countries where rock salt (sodium chloride) is found underground it is mined. In other countries it can be obtained by evaporation of sea water in large shallow lakes. Three very important substances are produced... 

Another somewhat more complicated cell for the production of chlorine and sodium hydroxide by the electrolysis of sodium chloride solution is the Castner-Kellner cell, which employs a liquid mercury cathode. 

Sodium hypochlorite. If, in the electrolysis of sodium chloride solution, provision is made for the intimate mixing of the chlorine and sodium hydroxide at low temperatures, the following reaction occurs ... 

Sodium carbonate. When sodium hydroxide is produced by the electrolysis of sodium chloride solution saturated with carbon dioxide, sodium carbonate is produced as follows ... 

Most processes are based on the electrolysis of a sodium chloride solution, but some plants operate with the molten salt. Three different cell types are used in electrolysis in water mercury cells, diaphragm cells, and membrane cells. Membrane cells are replacing the other two types in modern units, but it may not be economically feasible to convert older plants. 

Another widely used commercial method for the production of sodium hydroxide lies in the electrolysis of sodium chloride solution — a method which is economical when the chlorine simultaneously produced can also be utilized. 

A clear picture of the course of electrolysis of sodium chloride solution with a concentration of 5.1 moles of NaCl per litre at 12 °C and a current density of 6.7 A/sq. em can be seen in the graphical representation in Fig. 125. 

Sodium chlorate is produced by the electrolysis of a sodium chloride solution in an electrolyzer without a diaphragm, having an iron cathode and a magnetite or graphite anode. For the manufacture of potassium chlorate either the sodium chloride solution is used, or a mixed solution of both sodium and potassium chloride. The chlorate solution obtained will finally be converted with potassium chloride into potassium chlorate, which is separated by crystallisation while the mother liquor is returned to the electrolytic process. The potassium chloride solution will not be electrolyzed directly as potassium chlorate is sparingly soluble and the potassium chloride entrained in the chlorate crystals is not easy to remove. 

Electrolysis in this case only differs slightly from the sodium chlorate process. A sodium chloride solution or a mixed solution of sodium and potassium chloride is used as the electrolyte. The sodium chlorate in the electrolytically treated brine is converted to potassium salt by double decomposition with potassium... 

Summary Sodium hydroxide can be prepared by electrolyzing a sodium chloride solution in a two-compartment cell separated by a porous membrane. Chlorine gas is liberated at the positive anode and hydrogen and sodium hydroxide are liberated at the cathode. Use proper ventilation when running the electrolysis cell because of chlorine and hydrogen gas evolution. Run the cell in an area that is away from direct sunlight. 

Sodium hypochlorite is also manufactured by the electrolysis of sodium-chloride solution without a diaphragm (p. 97), the solution being less concentrated than that prepared by the chlorine process from sodium hydroxide, but free from the excess of alkali characteristic of that prepared by the older method.2 The process is carried out either in the apparatus designed by Kellner,3 or in that of Haas-Oettel,4 sodium chlorate being a by-product (v. infra). It is noteworthy that electrolysis of sodium-chloride solution with an alternating current also produces sodium hypochlorite.5... 

Electrolytic Process.—The production of sodium carbonate by the electrolysis of sodium-chloride solution is gradually supplanting the older methods. In the.operation a diaphragm is employed, and the details are described on pp. 97 and 98. The solution of sodium hydroxide formed is converted into carbonate by the action of carbon dioxide, the sodium hydrogen carbonate formed being decomposed by heat. 

Electrolysis of concentrated aqueous sodium chloride solution (called brine) yields aqueous sodium hydroxide, hydrogen gas, and chlorine gas— three important industrial chemicals. Calculate the mass of chlorine that can be produced by electrolysis of 50.0 kg of sodium chloride in concentrated aqueous solution ... 

In the electrolysis of an alkaline sodium chloride solution at 52°, Muller [Z, nnorg. Chem., 22, 33 (1900)] obtained the following results ... 

What difference is there in the electrolysis of a dilute sodium chloride solution with platinum electrodes and with mercury electrodes ... 

Fig. 5.—E. Miiller a Curves showing the Electrolysis of Sodium Chloride Solutions.

Electrolysis of strong aqueous sodium chloride solution (brine) yields hydrogen gas and hydroxide ions at the cathode while producing chlorine gas at the anode. 

Since ca. 97% of the chlorine is produced from the electrolysis of aqueous sodium chloride solution, the linked products sodium hydroxide and hydrogen are produced as byproducts ... 

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