Impurity carbon, oxidation

The story of steel begins when iron ore is fed into a blast furnace (Fig. 16.45). The furnace, which is approximately 40 m in height, is continuously filled at the top with a mixture of ore, coke (impure carbon obtained by heating coal in the absence of air), and limestone. Each kilogram of iron produced requires about 1.75 kg of ore, 0.75 kg of coke, and 0.25 kg of limestone. The limestone, which is primarily calcium carbonate, undergoes thermal decomposition to calcium oxide (lime) and carbon dioxide. The calcium oxide, which contains the Lewis base 02, helps to remove the acidic (nonmetal oxide) and amphoteric impurities from the ore ... 

The majority of metals are too reactive to exist on their own in the Earth s crust, and they occur naturally in rocks as compounds in ores (Figure 10.10). These ores are usually carbonates, oxides or sulfides of the metal, mixed with impurities. 

Raw stock for the direct synthesis of methylchlorosilanes, methylchlo-ride, has such impurities as moisture, methyl alcohol, oxygen, sulfur dioxide, methylenechloride, dimethyl ether, carbon oxide and dioxide, etc. Most of them negatively affect the synthesis of methylchlorosilanes harmful impurities are chemisorbed on the active centres of contact mass and foul the copper catalyst, which naturally inhibits the reaction of methyl-chloride with contact mass. A similar situation is observed in the direct synthesis of ethylchlorosilanes. 

The elements can be obtained by reduction of oxides or halides. Highly divide carbon black is used as a catalyst and black pigment, and impure carbon (coke) for reducing some metal oxides (e.g., in the manufacture of iron). Pure silicon prepared by reduction of SiCl4 with Mg is used in electronics (silicon chips) although much larger quantities of impure Si are used in steels. 

The catalytic purification process requires the use of many catalysts to convert impurities into compounds. Hydrogen, chlorides, oxygen, and carbon oxides are passed through several catalytic reactors. In the first reactor, the chlorides are absorbed. In the second reactor, oxygen and hydrogen react to obtain water/steam, which is easily removed. In the third reactor, the carbon oxides react with hydrogen to yield methane, which would be considered an acceptable impurity in this particular hydrogen product stream. 

The Ores of Iron. The chief ores of iron are its oxides hematite. Fe- Og, and magnetite, Fe O, and its carbonate side rite, FeCO.,. The hydrated ferric oxides such as limonite are also important. The sulfide pyrite, FeSo, is used as a source of sulfur dioxide, but the impure iron oxide left from its roasting is not satisfactory for smelting iron, because the remaining sulfur is a troublesome impurity. 

---