C1 Iron

1. C1 Iron • Sources of Iron (Iron Ores) • Haematite (Fe2O3) • Magnetite (Fe3O4) • Pyrite (FeS2) • Scrap/recycled iron

2. Production of Iron: The blast furnace • Ingredients are added at the top of the blast furnace (through hopper): • Iron ore (usually small pellets, contain the iron), • coke (impure carbon made by heating coal) • limestone (calcium carbonate, removes high melting point impurities by forming ‘slag’) • Preheated air is blown in through nozzles at the bottom of the furnace. The air is enriched with oxygen and may also include hydrocarbons (such as oil, natural gas) that may replace up to 40% of the coke. • Liquid iron collected at end of process from the bottom of the furnace.

4. Blast Furnace Processes • Coke burns in preheated air to form carbon dioxide: C(s) + O2(g)  CO2(g) H = –298 kJ mol-1 • With increased temperatures, the limestone decomposes to calcium oxide: CaCO3(s)  CaO(s) + CO2(g) • The carbon dioxide produced in both reactions above react with more hot coke to produce carbon monoxide: C(s) + CO2(g)  CO(g)

5. Blast Furnace Processes • The reducing gases (i.e. CO) pass up the furnace where they reduce the iron oxides in a series of stages depending on the temperature and composition of the gas. Examples of overall reactions: Fe2O3(s) + 3 CO(g)  2 Fe(l) + 3 CO2(g) Fe3O4(s) + 4 H2(g)  3 Fe(l) + 4 H2O(g) FeO(s) + CO(g)  Fe(l) + CO2(g) • The iron produced is in the liquid state at a the temperature of the furnace (~700 oC)

6. Blast Furnace Processes • Calcium oxide from earlier reacts with oxide impurities from the ore forming a liquid called “slag” which contains calcium silicate and calcium aluminate: CaO(s) + SiO2(s)  CaSiO3(l) CaO(s) + Al2O3(s)  Ca(AlO2)2(l) • Molten iron and slag of impurities trickle to bottom of furnace. Less dense slag floats on molten iron for easy separation. • Liquid iron can be run out of the bottom into molds called “pigs” to produce what is called pig iron.

7. Environmental Considerations • Hot waste gases used to heat incoming air, reducing energy costs of process. • Waste gases are not released into atmosphere due to poisonous CO • Slag can be used for building roads, or treated to make by-products including cement and thermal insulation

8. Conversion of Iron into Steel • Why Steel? • Iron from blast furnace contains ~4% carbon. Causes: • Brittleness • Reduced melting point • Majority of iron is converted into Steel • steel is general name for a mixture of iron and carbon and other materials. • Varying composition causes varying properties

9. Alloys • Steel is an alloy. Alloy is: • Homogenous mixture • Contains at least one metal • Formed when liquid metals are mixed and solidified with uniform composition. • Presence of other elements in the metallic lattice changes regular array of metal atoms, changing properties of the alloy • Alloys generally stronger than pure metal. • See diagram 14.2, IB text

10. Basic Oxygen Process (BOP) • Oxygen blown through 7:3 mixture of molten and scrap iron and small quantities of alloying elements such as nickel and chromium are added. • Oxygen combines with unwanted carbon and sulfur to form oxides which escape as gases: C(s) + O2(g)  CO2(g) S(s) + O2(g)  SO2(g) • Oxides of silicon and phosphorus are also formed: 4 P(s) + 5 O2(g)  P4O10(s) Si(s) + O2(g)  SiO2(s)

11. Basic Oxygen Process (BOP) • These oxides combine with the lime (CaO) that is added to the converter to form a slag consisting of calcium phosphate and calcium silicate. • Practice: Write the balanced equations for the above processes

12. Basic Oxygen Process (BOP) • The redox reactions are very exothermic. Scrap iron is added to help control temperature. • Finally, oxygen dissolves in the steel during the process. This is removed by adding controlled amounts of aluminum or silicon before steel can be casted or rolled.

14. The percentage of carbon has a dramatic effect on properties:

15. Alloying Element Properties given to steel Uses Cobalt Easily magnetized Magnets Molybdenum Maintains strength at high temperature High speed drill bits Manganese Tough Safes Stainless steel (nickel, chromium) Resists corrosion Surgical instruments, cutlery Titanium Withstands high temperatures Aircraft, turbine blades Vanadium Strong, hard High speed tools The addition of small amounts of other transition metals changes the properties of the material even further:

16. Heat Treatment of Steel • Changing the composition of the steel is only one way to adjust its properties • Steel can also be subjected to heating and cooling, which can change the structure of the metal:

17. Heat Treatment of Steel • Tempering: steel is heated to a temperature of about 400-600 oC and allowed to cool slowly. Makes the steel less brittle / more tough as internal stresses in structure are removed. • Annealing: steel is heated to a higher temperature of about 1000 oC. Followed by slow cooling, the structure recrystallizes into many finer grains making the metal softer (more malleable and ductile). • Quenching: when the steel heated for annealing is immersed into cold water or oil for rapid cooling. Makes the metal very hard.

18. C1 Practice Exercise • The iron produced in a blast furnace contains about 5% impurities: • State the major impurity • This iron can be converted into steel. It is melted in a basic oxygen converter and two chemicals are added. State the two chemicals added. • Describe the essential chemical processes that take place during the conversion of iron into steel.

19. C2 The Oil Industry • Crude oil: very important raw material • Complex mixture of hydrocarbons (mostly alkanes) • Main use: source of fuel for world’s energy demands of transportation and electricity generation • Only about 10% of it is used, after refining, as a chemical feedstock. • Used for production of organic compounds such as plastics, pharmaceuticals, pesticides, food additives, detergents, cosmetics, dyes, and solvents.

20. C2 The Oil Industry • Oil is a limited resource!!! • Future generations may wonder why most of it is being burned with all the attendant problems of pollution and global warming rather than using oil to make useful products..

21. Oil Refining: Impurity removal • Crude oil is useless before it is refined. • Sulfur impurities (mainly H2S) block active sites in catalysts during later refining and must be removed: • Hydrogen sulfide removed by dissolving in a basic solution of potassium carbonate: H2S(g) + CO32-(aq)  HS–(aq) + HCO3– (aq) • Hydrogen sulfide recovered from solution by later reversing the reaction. Then it is burned in the air to form sulfur dioxide: 2H2S(g) + O2(g)  2SO2(g) + 2H2O(l)

22. Impurity removal • The sulfur dioxide can then react with more hydrogen sulfide to produce elemental sulfur: 2H2S(g) + SO2(g)  3S(s) + 2H2O(g) • Desulfurization helps reduce acid rain pollution that would result if the sulfur was burned with the oil.

23. Fractional distillation of Oil • Crude oil is separated into different fractions on the basis of their boiling points. • Crude oil is heated to a temperature of about 450 oC • All of the components are vaporized and allowed to pass up a distillation column. • As the components move up the column, the molecules condense depending on their size. • Smaller molecules containing 1-4 carbon atoms travel all the way to the top and condense as the refinery gas fraction. • Molecules of larger molecular mass condense and are collected at the lower levels corresponding to their higher boiling points.

24. Diagram of Fractional Distillation apparatus. • Also shows the composition and characteristics of crude oil fractions.

25. Oil Refining: Cracking • Cracking is the process conducted at high temperatures in order to break down large hydrocarbons into smaller, more useful molecules. • Products are generally alkanes and alkenes. • Examples: C16H34 C8H18 + C8H16 C10H22 C8H18 + C2H4 alkane alkene

26. Cracking • Alkanes produced are usually branched isomers (i.e. 2,2,4-trimethylpentane) and are added to gasoline to improve the octane rating. • Straight chain molecules have a greater tendency to auto-ignite in the internal combustion engine as the piston compresses the fuel-air mixture. This reduces the power and wastes fuel. • The higher the octane number, the less likely the fuel is to auto-ignite or knock. Cracking can produce gas with higher octane number.

27. Thermal Cracking • Feedstock: very long chain alkanes from very heavy fractions • Heated to temperatures of 800 – 850 oC at pressures of up to 70 atm and then cooled rapidly. • Produces shorter chain alkanes, alkenes, and coke (impure carbon) • Ethene is a favored product as it is a key starting material for synthesis of many other chemicals.

28. Steam Cracking • Feedstock: ethane, butane, and alkanes with 8 carbon atoms. • The feedstock is preheated, vaporized, and mixed with steam and then converted to low molecular mass alkenes at 1250–1400 oC. • Steam dilutes the feedstock and produces a higher yield of ethane and other low molecular mass alkenes

29. Catalytic Cracking • The use of a silica/alumina (from mineral zeolite) catalyst enables the cracking to take place at the relatively lower temperature of about 500 oC. • Requires less energy and reduces costs • Produces a mixture of alkanes, alkenes, and compounds which contain the benzene ring (aromatics).

30. Hydrocracking • Heavy hydrocarbon fractions are mixed with hydrogen at a pressure of about 80 atm and cracked over palladium on a zeolite surface. • High yield of branched chain alkanes and cycloalkanes with some aromatic compounds with a high octane number is produced for use in high quality gasoline. • Presence of hydrogen ensures that no unsaturated alkenes are produced.

31. Refinery / Cracking Towers

32. C2 Practice Exercise • Deduce an equation for the cracking of C11H24 in which an alkene and an alkane are formed in the ratio 3:1. • Explain why cracking is a useful process. • Although alkanes can be cracked with heat alone, it is more common for oil companies to use catalysts. Suggest two reasons for this. • State the name of a catalyst used in catalytic cracking.