Carbon electrolytic processes

Inorganic Methods. Before the development of electrolytic processes, hydrogen peroxide was manufactured solely from metal peroxides. Eady methods based on barium peroxide, obtained by air-roasting barium oxide, used dilute sulfuric or phosphoric acid to form hydrogen peroxide in 3—8% concentration and the corresponding insoluble barium salt. Mote recent patents propose acidification with carbon dioxide and calcination of the by-product barium carbonate to the oxide for recycle. 

Oxidative surface treatment processes can be gaseous, ie, air, carbon dioxide, and ozone Hquid, ie, sodium hypochlorite, and nitric acid or electrolytic with the fiber serving as the anode within an electrolytic bath containing sodium carbonate, nitric acid, ammonium nitrate, ammonium sulfate, or other electrolyte. Examples of electrolytic processes are described in the patent Hterature (39,40)... 

Purification. The metal obtained from both electrolytic processes contains considerable oxygen, which is beheved to cause brittieness at room temperature. For most purposes the metal as plated is satisfactory. However, if ductile metal is desired, the oxygen can be removed by hydrogen reduction, the iodide process, calcium refining, or melting ia a vacuum ia the presence of a small amount of carbon. 

Many metals are extracted from their compounds, as found in ores, by electrolytic processes. By far the most important is the Hall-Heroult process, invented in 1886, for producing aluminium from alumina, itself refined from bauxite ore. Alumina is dissolved in molten cryolite, Na3Alp6, and electrolysed, using carbon anodes and the aluminium itself as cathode. While various details are being steadily improved, the basic process is still the same today. 

The development of electrical power made possible the electrochemical industry. Electrolysis of sodium chloride produces chlorine and either sodium hydroxide (from NaCl in solution) or metallic sodium (from NaCl fused). Sodium hydroxide has applications similar to sodium carbonate. The ad vantage of the electrolytic process is the production of chlorine which has many uses such as production of polyvinyl chloride. PVC, for plumbing, is produced in the largest quantity of any plastic. 

The electrolytic processing of concentrated ore to form the metal depends on the specific chemical properties of the metallic compound. To produce aluminum about 2 to 6 percent of purified aluminum oxide is dissolved in ciyolite (sodium alumi-no-fliioride, Na AlF ) at about 960°C. The reduction of the alumina occurs at a carbon (graphite) anode ... 

Deville (2) An early process for making sodium by reducing sodium carbonate with carbon at or above 1,100°C. Developed in 1886 and used until it was superseded by electrolytic processes. See Downs and Castner (4). 

Wunsche An electrolytic process for liberating bromine from a bromide solution. It uses carbon electrodes and a porous clay separator. Developed in Germany in 1902. See also Kossuth. 

Preparation. High purity nickel can be produced through electrolytic process or by the carbonyl process. In the latter case carbon monoxide reacts at 50°C with impure Ni (or nickel-copper matte) to give the volatile tetracarbonyl from which the metal (99.9-99.99% purity) is obtained by decomposition at 200-230°C through the reaction ... 

Preparation. Sulphides are readily converted to oxide by roasting in air, that remove all sulphur as S02 this pre-treatment is followed by pyrometallurgical process by heating with carbon, or electrolytic process to obtain zinc. It is also possible by controlled oxidation to convert ZnS to the water soluble ZnS04, which can be extracted and electrolyzed to produce zinc. Crude zinc obtained by pyrometallurgical process can be refined by distillation taking into account the comparatively low boiling temperature of zinc. 

The above mentioned unique properties of carbon have transformed it into an attractive material that is widely used in various electrolytic processes in the chemical industry. Several applications of carbon are reviewed below. 

Electrolyte management, that is, the control over the optimum distribution of molten carbonate electrolyte in the different cell components, is critical for achieving high performance and endurance with MCFCs. Various processes (i.e., consumption by corrosion reactions, potential driven migration, creepage of salt and salt vaporization) occur, all of which contribute to the redistribution of molten carbonate in MCFCs these aspects are discussed by Maru et al. (4) and Kunz (5). 

Fig. 9.10 shows a typical CV of a (CH), film in a LiClO -propylene carbonate electrolyte. The voltammogram presents well-defined peaks both in the anodic (doping) and in the following cathodic (undoping) scans this confirms that the doping process of polyacetylene, as suggested by (9.10), can indeed be driven electrochemically and in a reversible way. 

These studies have been mainly carried out using cyclic voltammetry and frequency response analysis as experimental tools. As a typical example. Fig. 9.12 illustrates the voltammogram related to the p-doping process of a polypyrrole film electrode in the LiClQ -propylene carbonate electrolyte, i.e. the reaction already indicated by (9.16). 

The zinc that is produced today starts as the zinc sulfide (ZnS) minerals zinc blende or sphalerite or from zinc carbonate (ZnCO ) known as smithsonite or calamine. In the electrolytic process, these minerals are dissolved in water to form the electrolyte in the cell where the zinc cations are attracted and collected at the cathode and deposited as a dull, brittle type of zinc. 

Chromium may be produced from high-carbon ferrochrome by electrolytic process. Alternatively, the metal may be obtained by electrolysis of chromic... 

Manganese may be produced by electrolytic processes. Aqueous solutions of manganese(ll) sulfate are used as the electrolyte. Mn ore is roasted and reduced with carbon or sihcon to convert the higher oxides of manganese into MnO. The products are then leached with dilute sulfuric acid at pH 3. MnO dissolves in the acid forming manganese(ll) sulfate. The solution is filtered and separated from insoluble residues. It then is neturahzed with ammonia to pH 6-7. 

Manganese(II) carbonate occurs in nature as the mineral rhodochrosite [14476-12-1] (manganese spar). This ore also is used to produce manganese dioxide (by electrolytic process). The pure compound is used as gemstones and as a pigment (manganese white). 

In the electrolytic process, a fused mixture of anhydrous rare earth chlorides (obtained above) and sodium or potassium chloride is electrolyzed in an electrolytic cell at 800 to 900°C using graphite rods as the anode. The cell is constructed of iron, carbon or refractory hnings. Molten metal settles to the bottom and is removed periodically. 

The general methods for the production of the alkali metals are (1) Electrolytic processes involving the electrolysis of (a) the fused hydroxide, or (b) a fused salt— chloride, nitrate, cyanide, etc. (2) Chemical processes involving the reduction of hydroxide, or carbonate, or other salt with carbon, metal carbide, iron, calcium, magnesium, aluminium, etc. W. Spring 5 claims to have reduced a little potassium chloride by passing hydrogen over the salt at a red heat. 

The production of caustic soda has largely replaced that of carbonate by the Leblanc process, although the electrolytic process is a serious competitor in this field. 

In (1) the electrolytic process, a nickel of 99.9% purity is produced, along with slimes which may contain gold, silver, platinum, palladium, rhodium, iridium, ruthenium, and cobalt, which are subject to further refining and recovery. In (2) the Mond process, the nickel oxide is combined with carbon monoxide to form nickel carbonyl gas, Ni(CO)4. The impurities, including cobalt, are left as a solid residue. Upon fuitlier heating of the gas to about 180°C, the nickel carbonyl is decomposed, the freed nickel condensing on nickel shot and the carbon monoxide recycled. The Mond process also makes a nickel of 99.9% purity. 

SPERRY PROCESS. An electrolytic process for the manufacture of lead carbonate, basic (white lead) from desilivenzed lead containing, some bismuth, The impure lead forms the anode. A diaphragm separates anode and cathode compartments, and carbon dioxide is passed into the solution. Impurities, including bismuth, remain on the anode as a slime blanket,... 

The older method for the production of sodium (or potassium hydroxide) is sometimes called the chemical process to distinguish it from electrolytic processes. The chemical process involves the treatment of sodium carbonate with calcium hydroxide ... 

---