Fractional distillation

  • Created by: Hindleyc
  • Created on: 12-05-18 15:30
What is petroleum?
Mixture consisting mainly of alkane hydrocarbons- can be separated
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Crude oil- composed of mainly? What does is contain a lesser amount of?
Mixture of straight and branched chain alkanes. Cycloalkanes and arenes (hydrocarbons containing a ring of carbon atoms and sulphur compounds- impurities)
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What does the exact composition depend on?
Conditions under which it was formed eg different location
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What does an increase of chain length do?
Increases boiling point of straight chain alkane- increased van Der Waals forces- increased contact SA so stronger Van Der Waals
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Why do branched chain alkanes lower boiling point?
Chains cant pack as closely together- fewer points of contact so weaker v.d.w
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Physical properties of alkanes- polarity?
Almost all Non-polar as electronegativities of C and H similar so only weak v.d.w exist between molecules- forces stronger in large molecules
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Boiling point?
Inc as chain length increases due to inc I.M forces.
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Solubility?
Insoluble in water as water held together by h bonds which are stronger than v d w forces
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Reactivity?
Fairly unreactive- strong c-c and c-h bonds so do not react with acids bases oxidising and reducing agents
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What are you burning?
Fumes
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Temperature graduation in fractional distillation column?
Low at top, high at bottom.
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How does it work?
Enters column and heated- vaporised . Rises and condenses- condensed liquid piped off if low bp then doesn't condense so taped off as gas
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What do bubble caps do?
Encourage mixing of liquid and vaporised fractions
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What is cracking?
Breaking of c-c bond in alkanes
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why?
Longer chains not as useful- in low demand, crude oil contains more longer chains than shorter chains so undergo cracking
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What are the 2 useful products?
Shorter more useful chains produced eg petrol. Some products are alkenes- more reactive than alkanes
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What else does it do?
Inc amount of gasoline and other economic fractions. increases branching in chains which is important factor for petrol. Produces alkenes- feedstock chemical
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What is thermal cracking?
Temp:700-1200k (high) Pressure: up to 7000 kPa (high). C-C bond breaks with 1 electron from pair going to each c atom, one H atom moves from one fragment to the other creating a shorter alkane and alkene. Lower proportion of branched chain alkanes
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What is catalytic cracking?
Zeolite catalyst- large pores where alkanes chain fits. Temp:700k (high). Pressure:slight pressure (low). Long chain alkane fits into pores, held in place and splits into alkene and branched alkane. Larger proportion of branched alkanes and arenes.
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What is there a lower proportion of?
Alkene molecules
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What are arenes?
Motor fuels and aromatic hc's
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adv and dis of catalytic?
Cheap but doesn't work on all fractions
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Compare Temp? pressure? extras needed? products in both?
Same- both high. Higher in thermal. catalyst in catalytic. Thermal- alkenes (&shorter alkanes). Catalytic- Alkanes and arenes
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What can alkanes undergo in excess oxygen? What type of reaction? Why is this good?
Complete combustion. Alkane+oxygen=carbon dioxide+ water. Highly Exothermic- makes good fuels as release large amounts of energy per gram of fuel.
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What can alkane undergo in limited oxygen?
Incomplete combustion- Alkane + oxygen= carbon monoxide and water/ Alkane+ oxygen= carbon and water
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What are alkanes with chain lengths 5-10 C's used for? Problem with modern combustion engines (more efficient now than in the past)
Fuels releasing CO2 into atmosphere. Incomplete combustion still occurs- also produce carbon and unburned HC's
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Problem with internal combustion engines and nitrogen?
Temp in engine can reach over 2000c so N and O can combine
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Eqn for N and O in internal combustion engine
N2+O2=2NO.
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What does nitrogen monoxide react further to form? What does Nitrogen dioxide gas react further with
Nitrogen dioxide- 2NO+O2=2NO2
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What does nitrogen dioxide gas react further with rain water and more oxygen to form?
Nitric acid- contributes to acid rain. 4NO2+2H2O+O2=4HNO3(aq)
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What is found as an impurity in crude oil and other fossil fuels?
Sulfur
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What does it burn in oxygen to form? what does this cause?
Sulfur dioxide causing air pollution- S(s)+O2(g)=SO2(g)
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What may sulphur dioxide by oxidised to form?
Sulfur trioxide 2SO2+O2=2SO3
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What do they both dissolve in water to form?
Acidic solutions. SO2+H20=H2SO3(aq). SO3+H2O=H2SO4(aq)
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What is acid rain? W hat does it do?
Sulphur and nitrogen oxides- more acidic solutions. Damage trees, aquatics lakes and rivers
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How was SO2 emissions removed from petrol and diesel before? why not now?
By removing all Sulphur impurities before being burnt- not practical
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What is used instead?
CaO as it is a base so undergo acid base neutralisation
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Method 1 - desulfurisation. What is sprayed into flue gas (SO2) forming calcium sulphite?
Calcium oxide and water
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What is calcium sulphite oxidised to form? What can this be used for?
Calcium sulphate. Gypsum- plasterboards
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Equation?
CaO+2H2O+SO2+0.5O2=CaSO4+2H2O
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What is method 2?
Calcium carbonate neutralisation
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Equation?
CaCO3+0.5O2+SO2=CaSO4+CO2
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What does a catalytic converter do?
Remove gases of pollutants.
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What does a catalytic converter contain?
Ceramic/metal in honeycomb structure for large SA
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What is it coated in?
Thin layer of catalytic metal- Platinum, Palladium or Rhodium
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What are the main waste gases?
CO,NOx,unburnt HC's
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What do they do in the converter?
Pass through structure and come into contact with catalyst
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What happens in a 3 way catalytic converter?
CO is oxidised to CO2, NOx is reduced to N2, HC's oxidised to CO2 and H2O
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What can it remove?
90% harmful gases from car exhausts
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What metal used in reduction?
Platinum and Rhodium- 2NOx=xO2+N2
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What metal is used in Oxidation?
Platinum and Palladium- 2CO+O2=2CO2. CxHy+(x+0.25y)O2=xCO2+0.5yH2O
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What does burning fossil fuels do?
Increase CO2 leading to climate change
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What are the 3 main green house gases and what do they do?
Water vapour, CO2, CH4. Absorb infrared radiation increasing temperature of atmosphere
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What does an inc in gg do?
Traps more heat from sun raising temp- energy trapped in bonds and vibrate
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Other cards in this set

Card 2

Front

Crude oil- composed of mainly? What does is contain a lesser amount of?

Back

Mixture of straight and branched chain alkanes. Cycloalkanes and arenes (hydrocarbons containing a ring of carbon atoms and sulphur compounds- impurities)

Card 3

Front

What does the exact composition depend on?

Back

Preview of the front of card 3

Card 4

Front

What does an increase of chain length do?

Back

Preview of the front of card 4

Card 5

Front

Why do branched chain alkanes lower boiling point?

Back

Preview of the front of card 5
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