CHEM 2017 2008CHEM 2017 2008

lect 7 + 8lect 7 + 8

F chemicalsF chemicals

HYDROGEN FLUORIDEHYDROGEN FLUORIDE INORGANIC FLUORIDESINORGANIC FLUORIDES FLUORINEFLUORINE

CALCIUM FLUORIDECALCIUM FLUORIDE KNOWN TO LOWER THE MELTING KNOWN TO LOWER THE MELTING

POINT OF MINERALS (16th C)POINT OF MINERALS (16th C) Early chemists: HF – glass apparatus Early chemists: HF – glass apparatus

attackedattacked F realised to be similar to Cl (1813), but F realised to be similar to Cl (1813), but

not isolatednot isolated HF first clearly prepared only in 1850s HF first clearly prepared only in 1850s

HFHF

First made by slowly heating First made by slowly heating POTASSIUM HYDROGEN FLUORIDEPOTASSIUM HYDROGEN FLUORIDE

EARLY USE OF HF IN ETCHING EARLY USE OF HF IN ETCHING GLASSGLASS

1930S INTRODUCTION OF 1930S INTRODUCTION OF CHLOROFLUOROCARBONS AS CHLOROFLUOROCARBONS AS REFRIGERANTSREFRIGERANTS

MANHATTEN PROJECTMANHATTEN PROJECT

USE OF UFUSE OF UF66 FOR FOR 235235U ENRICHMENTU ENRICHMENT

235235U vs U vs 238238UU

GAS CENTRIFUGES – SLIGHTLY DIFFERENT GAS CENTRIFUGES – SLIGHTLY DIFFERENT DIFFUSION RATES DIFFUSION RATES

CONTAINMENT VESSELS – FOR CORROSIVE CONTAINMENT VESSELS – FOR CORROSIVE F-CONTAINING COMPOUNDS – PERFLUORO F-CONTAINING COMPOUNDS – PERFLUORO ORGANIC COMPOUNDS FOUND TO BE ORGANIC COMPOUNDS FOUND TO BE SUITABLE SUITABLE

CFCs - environmental CFCs - environmental problemsproblems

CFCs relatively stable CFCs relatively stable When released rise through earth’s When released rise through earth’s

atmosphere unchangedatmosphere unchanged In the stratosphere generate Cl radicals, In the stratosphere generate Cl radicals,

that destroy ozone in a catalytic actionthat destroy ozone in a catalytic action Montreal ProtocolMontreal Protocol Replace CFCs with HCFCsReplace CFCs with HCFCs Less stable in the atmosphere – Less stable in the atmosphere –

decompose at lower levels decompose at lower levels

FLUORSPARFLUORSPAR

CALCIUM FLUORIDE – VARIABLE CALCIUM FLUORIDE – VARIABLE PURITYPURITY

USED IN STEEL MAKING SINCE 1860sUSED IN STEEL MAKING SINCE 1860s Metallurgical grade: 60-80%Metallurgical grade: 60-80% Ceramic grade (glass) 85-95%Ceramic grade (glass) 85-95% Acid grade: 97+% (HF manufacture)Acid grade: 97+% (HF manufacture)

FLUORSPARFLUORSPAR

Helps separation of metal in steel Helps separation of metal in steel production from slag and impurities such production from slag and impurities such as P, S, Si removed as their oxidesas P, S, Si removed as their oxides

Also used in Cu, Sn, Zn refining Also used in Cu, Sn, Zn refining Used in glass (small crystals of calcium Used in glass (small crystals of calcium

fluoride render glass milky) - also fluoride render glass milky) - also fluorides can be added to adjust fluorides can be added to adjust coefficients of expansion of glasscoefficients of expansion of glass

PRODUCTION OF HFPRODUCTION OF HF

HF - ANHYDROUS OR AQUEOUS HF - ANHYDROUS OR AQUEOUS SOLUTIONSOLUTION

CaFCaF22 + H + H22SOSO44 CaSO CaSO44 + 2HF + 2HF

30m long reactor for 20kt yr30m long reactor for 20kt yr-1-1

Crude acid purified Crude acid purified Calcium sulphate: neutralise with lime – Calcium sulphate: neutralise with lime –

historically sent to landfill; now more uses historically sent to landfill; now more uses examined e.g. self-levelling floor coatingsexamined e.g. self-levelling floor coatings

HFHF

Very highly corrosiveVery highly corrosive Extreme precautions needed in handling Extreme precautions needed in handling

to avoid contact with skin – eats into to avoid contact with skin – eats into bones – very serious burns and bone bones – very serious burns and bone damagedamage

Fairly volatile b pt: 19CFairly volatile b pt: 19C

CFC / HCFCsCFC / HCFCs

Programme of replacing CFCs well Programme of replacing CFCs well organised depending on applicationorganised depending on application

Catalytic processes being developed to Catalytic processes being developed to convert old product to new productconvert old product to new product

Fluorinated chromiaFluorinated chromia

CFC conversionCFC conversion

Equilibrium limited by HCl formationEquilibrium limited by HCl formation

Separate desired product from HCl and Separate desired product from HCl and recyclerecycle

Conversion per pass 10-20% but Conversion per pass 10-20% but selectivity is high - very few by-productsselectivity is high - very few by-products

Other uses of HFOther uses of HF

Electrochemical fluorination:Electrochemical fluorination: Aliphatic hydrocarbon conversion to perfluoro-Aliphatic hydrocarbon conversion to perfluoro-

substituted systems by electrolysis using substituted systems by electrolysis using liquid anhydrous HFliquid anhydrous HF

e.g. Ce.g. C88HH1717SOSO22F F C C88FF1717SOSO22F as an F as an

intermediate for surfactants, textile treatments, intermediate for surfactants, textile treatments, surface coatingssurface coatings

e.g. Ce.g. C77FF1515COF used in teflon manufactureCOF used in teflon manufacture

TEFLONTEFLON

Poly(CPoly(C22HH44) = polyethylene) = polyethylene

Poly(CPoly(C22FF44) = teflon) = teflon

Perfluorohydrocarbon Perfluorohydrocarbon derivativesderivatives

More stable than hydrocarbon More stable than hydrocarbon equivalentsequivalents

Thermal shock resistance is higher Thermal shock resistance is higher (COMPUTER CHIP TESTING)(COMPUTER CHIP TESTING)

COOLING FOR SUPERCOMPUTERSCOOLING FOR SUPERCOMPUTERS SYNTHETIC OXYGEN CARRIERS SYNTHETIC OXYGEN CARRIERS

(Artificial blood in surgical procedures) (Artificial blood in surgical procedures)

HFHF

Aromatic fluorocarbonsAromatic fluorocarbons Balz-Schiemann diazotation reaction as a Balz-Schiemann diazotation reaction as a

procedure for introducing F onto an aromatic procedure for introducing F onto an aromatic ringring

Used in drug synthesisUsed in drug synthesis

HFHF

In aluminium production:In aluminium production: Synthetic cryolite, NaSynthetic cryolite, Na33(AlF(AlF66) as the fused salt ) as the fused salt

used to dissolve alumina in Al manufactureused to dissolve alumina in Al manufacture

As an acid catalyst in hydrocarbon As an acid catalyst in hydrocarbon conversions:conversions: Petroleum refining, CPetroleum refining, C44 branched C branched C8 8 alkanes alkanes

for high octane gasolinefor high octane gasoline

HF refining catalystsHF refining catalysts

HF more efficient catalyst than sulphuric HF more efficient catalyst than sulphuric acid, 0.068kg rather than 0.23kgacid, 0.068kg rather than 0.23kg

Fewer by-productsFewer by-products Easier separationEasier separation

[Solid acid catalysts even more desirable [Solid acid catalysts even more desirable – ease of handling, less dangerous]– ease of handling, less dangerous]

HF MISCELLANEOUS USESHF MISCELLANEOUS USES

Scale removal from stainless steelScale removal from stainless steel Oil-well acidification: improved flow rate Oil-well acidification: improved flow rate

of oil as wells become depletedof oil as wells become depleted Etching of electronic chipsEtching of electronic chips UFUF66 production (nuclear fuel) production (nuclear fuel)

Frosted light-bulbsFrosted light-bulbs Manufacture of various inorganic fluoridesManufacture of various inorganic fluorides

INORGANIC FLUORIDESINORGANIC FLUORIDES

F is highly reactiveF is highly reactive High electronegativity: high oxidation High electronegativity: high oxidation

state of metals reached easilystate of metals reached easily FF- - anion very small, so high coordination anion very small, so high coordination

number possiblenumber possible Wide range of M-F bond strengths Wide range of M-F bond strengths

possible so very diverse range of possible so very diverse range of compounds possiblecompounds possible

FLUORINE AND FLUORIDES FLUORINE AND FLUORIDES IN SOUTH AFRICAIN SOUTH AFRICA

NECSANECSA

Experience gained in U enrichmentExperience gained in U enrichment

Now more widely applied to manufacture Now more widely applied to manufacture of F-containing chemicals of F-containing chemicals