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Chemical Industry

Chemical Industry. Chemical reactions and physical processes on a large scale to convert raw materials into useful products. Conditions of the reactions are controlled to produce the best yield of product possible at an economic rate. YIELD : Quantity of product formed

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Chemical Industry

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  1. Chemical Industry • Chemical reactions and physical processes on a large scale to convert raw materials into useful products. • Conditions of the reactions are controlled to produce the best yield of product possible at an economic rate. YIELD: Quantity of product formed • Theoretical: Predicted by equation • Actual: Quantity actually obtained

  2. Haber Process • Process to produce ammonia. • Developed by German Chemist Fritz Haber • N2(g) + 3H2(g) 2NH3(g)H = –46kJmol-1 CONDITIONS FOR HIGH YIELD • High pressure (less molecules on the product side) • Low temperature (forward reaction is exothermic)

  3. Haber Process ACTUAL CONDITIONS • High Pressure (200-250 atmospheres pressure). If pressure is too high, expensive structural requirements are needed for the plant. • Moderately high temperature (~ 400oC). If the temperature is low then the yield is high, but it takes a long time for the reaction to produce the product (Rate low)

  4. Haber Process • Iron catalyst increases rate of forward and back reaction. • Yield of ammonia is approximately 45% of the theoretical yield

  5. Haber Process

  6. Contact Process • Product of sulfur dioxide from sulfur or metal sulfides • S(s) + O2(g) SO2(g) • 2ZnS(s) + O2(g)  2ZnO(s) +SO2(g) • Conversion of sulfur dioxide to sulfur trioxide • 2SO2(g) + O2(g) 2SO3(g)H = –99kJmol-1

  7. Contact Process • Absorption of sulfur trioxide into concentrated sulfuric acid to form oleum • SO3(g) + H2SO4(l) H2S2O7(l) REACTION THAT CONTROLS YIELD • 2SO2(g) + O2(g) 2SO3(g)H = –99kJmol-1 CONDITIONS FOR HIGH YIELD • High pressure • Low temperature

  8. Contact Process ACTUAL CONDITIONS • Atmospheric pressure. Yield is about 85-90% at this pressure. Costs to increase pressure are not offset by much greater yield. • Temperature: 450oC. Compromise between yield and rate. • Vanadium pentoxide catalyst (V2O5) increases rate of reaction.

  9. Contact Process • Sulfur trioxide is dissolved in concentrated sulfuric acid as it forms to maximise yield. • Acid is transported as oleum (less corrosive) and diluted as required by buyer which reduces transport costs. H2S2O7(l) + H2O(l) 2H2SO4(aq) • 600kJ of energy is released for every mole of acid formed. Some of this energy is used to produce electricity for the plant.

  10. Flow Diagrams • Used to represent the movement of materials through various components of the plant. • May include diagrams of equipment or show the process through a series of boxes and arrows. May show quantities of material and energy.

  11. Haber Process

  12. Contact Process

  13. Flow Diagrams RAW MATERIALS • Converted by chemical/ physical means into useful products. Examples include coal, oil, natural gas, air, limestone, sand, metal ores, water WASTE PRODUCTS • No use or market for the product. Disposal can be a problem if they are toxic or produced in large amounts.

  14. Flow Diagrams BY PRODUCTS • Not the main product, but do have a use either within the plant or commercially. E.g. sulfur dioxide from metal smelters

  15. Metals • Most occur in the earth’s crust as minerals • The most common occurrences are • K, Ca, Na, Mg as salts(Cl–, SO42–, CO32–) • Al, Fe, Sn as oxides • Zn, Ni, Pb, Cu as sulfides • Au, Ag, Pt as the uncombined metal

  16. Metal Reactivity • When metals react they undergo oxidation (lose electrons) M  Mx+ + xe • More easily a metal is oxidised, the less easily its ions are reduced to the metal • When determining the reactivity of a metal its reactions with water, acid and metal displacement reactions are considered

  17. Metal Reactivity • Example: Reactions of Calcium • Water: Ca(s) +H2O(l)Ca(OH)2(s)+ H2(g) • Acid: Ca(s) + 2H+(aq)  Ca2+(aq) + H2(g) • Displacement: Ca(s) + Zn2+(aq) Ca2+(aq) + Zn(s)

  18. Metals from their Ores • Ore deposit is a region in the earth’s crust where the concentration of a metallic mineral is at a level where the extraction of the metal is commercially viable

  19. Metals from their Ores • Concentration of the mineral (removal of the gangue) • Conversion of the concentrate into a substance suitable for reduction. (Most common chemical process metal sulfide to metal oxide) • Reduction of the metal compound to metal via chemical means or electrolysis. • Refining the metal to remove trace impurities

  20. Production of Zinc • Zinc ore (zinc blende) is mined at Broken Hill (NSW) and Mt Isa (Qld). Contains approx 2-8% zinc • Crushed and ground into small particles at the mine ready for froth flotation

  21. Froth Flotation • Ore is added to tanks containing water, frothing agents and collector molecules (molecules with polar and non polar ends) • ZnS is attracted to the polar end of collector molecules and is carried to the surface of tanks on the froth when air is blown through the mixture. This is skimmed off. • Gangue remains on the bottom of the tank as a sludge

  22. Froth Flotation

  23. Production of Zinc • The zinc sulfide is roasted in air to form zinc oxide 2ZnS(s) + 3O2(g) 2ZnO(s) + 2SO2(g) • Sulfur dioxide is used to make sulfuric acid for next step (Contact process) • Oxide is leached with sulfuric acid ZnO(s) + H2SO4(aq)  ZnSO4(aq) + H2O(l)

  24. Production of Zinc • Zinc powder is added to displace less reactive metals (Ag+, Cd2+, Cu2+). These are collected and processed. Electrolysis of zinc sulfate • Anode (Lead or silver/lead) 2H2O(l) O2(g) + 4H+(aq) + 4e • Cathode (aluminium or zinc) Zn2+(aq) +2e  Zn(s)

  25. Production of Zinc • Overall 2Zn2+(aq) +2H2O(l)2Zn(s) +O2(g) + 4H+(aq) • The zinc produced is 99.95% pure and requires no further purification

  26. Reduction using Electrolysis • Metals more active than zinc can’t be produced by electrolysis of aqueous solutions. • If a solution of a more active metal is electrolysed then 2H2O(l) + 2e  H2(g) + 2OH–(aq) occurs at the cathode in preference to the reduction of the metal. • A molten electrolyte is required with metals above zinc

  27. Reduction of Aluminium • Molten alumina Al2O3 is mixed with cryolite Na3AlF6, CaF2 and AlF3 . • This mixture has a melting point of ~1000oC compared to alumina which melts at 2030oC • This means the electrolysis is carried out at a lower temperature saving money

  28. Reduction of Aluminium Anode (Carbon) • 2O2–(l) O2(g) +4e • C(s) + O2(g)  CO2(g) • The anode is eaten away and requires regular replacement. Cathode (Carbon lined steel tank) • Al3+(l) + 3e  Al(l) • The aluminium forms below the molten electrolyte and can be tapped off.

  29. Reduction of Aluminium Overall • 4Al3+(l) +6O2–(l) +3C(s) 4Al(l) + 3CO2(g)

  30. Chemical Reduction • Metals below aluminium can be produced by reduction with carbon • Iron: 3C(s) + Fe2O3(s) 2Fe(s) + 3CO(g) • Zinc: C(s) + ZnO(s)  Zn(s) + CO(g) • These metal are more easily reduced than metals higher in the reactivity series

  31. Energy • The Reduction stage consumes most energy and so is the most costly stage of any metal production. • Electrolysis of a molten (non aqueous) electrolyte requires the more energy than other methods of reduction. • Consequently it is preferable (cost wise) if a metal can be either chemically reduced or produced by electrolysis of an aqueous solution.

  32. Energy Least Energy required: Least expensive • Chemical Reduction • Electrolysis of aqueous solution • Electrolysis of molten liquid Most Energy required: Most expensive

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