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CHEM 2017 2008 lect 7 + 8 F chemicals

CHEM 2017 2008 lect 7 + 8 F chemicals. HYDROGEN FLUORIDE INORGANIC FLUORIDES FLUORINE. CALCIUM FLUORIDE KNOWN TO LOWER THE MELTING POINT OF MINERALS (16th C) Early chemists: HF – glass apparatus attacked F realised to be similar to Cl (1813), but not isolated

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CHEM 2017 2008 lect 7 + 8 F chemicals

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  1. CHEM 2017 2008lect 7 + 8F chemicals

  2. HYDROGEN FLUORIDE • INORGANIC FLUORIDES • FLUORINE

  3. CALCIUM FLUORIDE • KNOWN TO LOWER THE MELTING POINT OF MINERALS (16th C) • Early chemists: HF – glass apparatus attacked • F realised to be similar to Cl (1813), but not isolated • HF first clearly prepared only in 1850s

  4. HF • First made by slowly heating POTASSIUM HYDROGEN FLUORIDE • EARLY USE OF HF IN ETCHING GLASS • 1930S INTRODUCTION OF CHLOROFLUOROCARBONS AS REFRIGERANTS

  5. MANHATTEN PROJECT • USE OF UF6 FOR 235U ENRICHMENT • 235U vs 238U • GAS CENTRIFUGES – SLIGHTLY DIFFERENT DIFFUSION RATES • CONTAINMENT VESSELS – FOR CORROSIVE F-CONTAINING COMPOUNDS – PERFLUORO ORGANIC COMPOUNDS FOUND TO BE SUITABLE

  6. CFCs - environmental problems • CFCs relatively stable • When released rise through earth’s atmosphere unchanged • In the stratosphere generate Cl radicals, that destroy ozone in a catalytic action • Montreal Protocol • Replace CFCs with HCFCs • Less stable in the atmosphere – decompose at lower levels

  7. FLUORSPAR • CALCIUM FLUORIDE – VARIABLE PURITY • USED IN STEEL MAKING SINCE 1860s • Metallurgical grade: 60-80% • Ceramic grade (glass) 85-95% • Acid grade: 97+% (HF manufacture)

  8. FLUORSPAR • Helps separation of metal in steel production from slag and impurities such as P, S, Si removed as their oxides • Also used in Cu, Sn, Zn refining • Used in glass (small crystals of calcium fluoride render glass milky) - also fluorides can be added to adjust coefficients of expansion of glass

  9. PRODUCTION OF HF • HF - ANHYDROUS OR AQUEOUS SOLUTION • CaF2 + H2SO4 CaSO4 + 2HF • 30m long reactor for 20kt yr-1 • Crude acid purified • Calcium sulphate: neutralise with lime – historically sent to landfill; now more uses examined e.g. self-levelling floor coatings

  10. HF • Very highly corrosive • Extreme precautions needed in handling to avoid contact with skin – eats into bones – very serious burns and bone damage • Fairly volatile b pt: 19C

  11. CFC / HCFCs • Programme of replacing CFCs well organised depending on application • Catalytic processes being developed to convert old product to new product • Fluorinated chromia

  12. CFC conversion • Equilibrium limited by HCl formation • Separate desired product from HCl and recycle • Conversion per pass 10-20% but selectivity is high - very few by-products

  13. Other uses of HF • Electrochemical fluorination: • Aliphatic hydrocarbon conversion to perfluoro-substituted systems by electrolysis using liquid anhydrous HF • e.g. C8H17SO2F  C8F17SO2F as an intermediate for surfactants, textile treatments, surface coatings • e.g. C7F15COF used in teflon manufacture

  14. TEFLON • Poly(C2H4) = polyethylene • Poly(C2F4) = teflon

  15. Perfluorohydrocarbon derivatives • More stable than hydrocarbon equivalents • Thermal shock resistance is higher (COMPUTER CHIP TESTING) • COOLING FOR SUPERCOMPUTERS • SYNTHETIC OXYGEN CARRIERS (Artificial blood in surgical procedures)

  16. HF • Aromatic fluorocarbons • Balz-Schiemann diazotation reaction as a procedure for introducing F onto an aromatic ring • Used in drug synthesis

  17. HF • In aluminium production: • Synthetic cryolite, Na3(AlF6) as the fused salt used to dissolve alumina in Al manufacture • As an acid catalyst in hydrocarbon conversions: • Petroleum refining, C4 branched C8 alkanes for high octane gasoline

  18. HF refining catalysts • HF more efficient catalyst than sulphuric acid, 0.068kg rather than 0.23kg • Fewer by-products • Easier separation • [Solid acid catalysts even more desirable – ease of handling, less dangerous]

  19. HF MISCELLANEOUS USES • Scale removal from stainless steel • Oil-well acidification: improved flow rate of oil as wells become depleted • Etching of electronic chips • UF6 production (nuclear fuel) • Frosted light-bulbs • Manufacture of various inorganic fluorides

  20. INORGANIC FLUORIDES • F is highly reactive • High electronegativity: high oxidation state of metals reached easily • F- anion very small, so high coordination number possible • Wide range of M-F bond strengths possible so very diverse range of compounds possible

  21. FLUORINE AND FLUORIDES IN SOUTH AFRICA • NECSA • Experience gained in U enrichment • Now more widely applied to manufacture of F-containing chemicals

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