Electrolysis other applications

Lithium chloride is used in the production of lithium metal by electrolysis. It also is used in metallurgy as a eutectic melting composition with potassium chloride (LiCl 41 mol% KCl 59 mol%). Other applications are in low temperature dry-cell batteries as a dehumidifier in air conditioning in welding and soldering flux as a desiccant in fireworks and in mineral waters and soft drinks. 

When metals are produced by any method, the extent to which they must be purified depends on the applications intended. For many purposes, the crude metals containing appreciable quantities of impurities may be employed for other applications, extensive refining may be necessary. Since this problem involves so many variables, it seems sufficient merely to indicate the general character of the refining processes most commonly utilized. Purification by electrolysis has already been discussed, and this is unquestionably one of the most important and useful methods. Some metals, notably iron and lead, may be purified by oxidation of the impurities by gaseous oxygen (from air), followed by the removal of the oxidized impurities. Still other metals, such as mercury and zinc, are sufficiently volatile that they may be purified by distillation. 

One mol of water produces one mol of GH2 plus a half-mol of Oz gas, both in their normal diatomic forms. As illustrated in Figure 1.48c, the electricity needed to convert water into H2 and 02 can be obtained from any electricity source, including solar converters or wind turbines. In other applications, such as in nuclear submarines, electrolysis can also be used to generate 02 from water. 

After the 15-hour electrolysis process, unplug your power supply, and then open the cell. Carefully remove the clay pot, and then dump its contents into a clean beaker or similar glass container—the anode compartment will contain the bleach. The cathode compartment will contain some sodium hydroxide. You can discard the cathode liquid if desired, or you can use it for other applications. Your bleach should then be quickly fdtered, to remove any insoluble impurities, and then stored in any suitable containers. The bleach solution will be about 20 to 25% concentration. Note the cathode liquid will probably also contain some bleach admixed with the sodium hydroxide, and un-reacted salt. 

Industrial production of perfluorinated ionomers, Nafion membranes, and all perfluorinated membranes is costly due to several factors first, the monomers used are expensive to manufacture, since the synthesis requires a large number of steps and the monomers are dangerous to handle. The precautions for safe handling are considerable and costly. Secondly, the PSEPVE monomer is not used for other applications, which limits the volume of production. The most significant cost driver is the scale of production. Today, the volume of the Nafion market for chlor-aUcali electrolysis (150,000 m year ) and fuel cells (150,000 m year ) is about 300,000 m year resulting in a production capacity of 65,000 kg year. When compared to large-scale production of polymers like Nylon (1.2 x 10 m year ), the perfluorinated ionomer membrane is a specialty polymer produced in small volumes. 

Hydrogen is also formed in large quantities as a byproduct in petrochemical processes, refineries, coking plants (coke oven gas) and in chemical and electrochemical processes e.g. chloralkali-electrolysis. Other processes such as the photochemical production of hydrogen or thermal dissociation of water are only used in special applications and are currently industrially unimportant. 

Other applications of electrolysis that students could research include sodium production by electrowinning (the Downs process) (a useful website on this process is detailed in the Other resources section at the end of the chapter). 

The chlorine that is produced during the manufacture of liquid sodium is a valuable byproduct that is used to manufacture chlorinated solvents, pesticides, and in other applications. Far more chlorine is needed than sodium. More economical processes involving the electrolysis of sodium chloride solutions in water are used to manufacture chlorine along with sodium hydroxide. 

Electrolysis also has numerous other applications. For example, most metals are foimd in Earth s crust as metal oxides. Converting them to pure metals requires the reduction of the metal, a nonspontaneous process. Electrolysis can be used to produce these metals. Electrolysis can also be used to plate metals onto other metals. For example, silver can be plated onto another, less expensive metal using the electrolytic cell shown in A Figure 16.17. In this cell, a silver electrode is placed in a solution containing silver ions. An electrical current then causes the oxidation of silver at the anode (replenishing the silver ions in solution) and the reduction of silver ions at the cathode (coating the ordinary metal with solid silver). 

Many enzymes exhibit a pH optimum of their activity. Working in a solution outside that optimum, an electrolysis of solution components involving H+ or OH at the microelectrode can induce a local pH shift toward the pH optimum of the enzyme activity, thereby switching on enzyme activity locally. The product of the enzymatic reaction may be collected at the microelectrode tip after applying the detection potential to it. This event would mark the end of the electrolysis causing the local pH shift. The locally changed pH will dissipate rapidly and switch off the enzyme activity. This principle has been demonstrated with fluorescence spectroscopic observation of the enzyme activity [100] and may soon find other applications as microelectrode-induced localized pH shifts have also been utilized in SECM microfabrication techniques (see Chapter 15). It remains to be found whether interesting enzyme systems exist which can be manipulated by rather small pH... 

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. 

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