P1 4b crude oil Flashcards
what is crude oil?
mixture of different hydrocarbons
what are fractions?
groups of hydrocarbons in crude oil that are of similar chain lengths
how do you separate the fractions in crude oil?
fractional distillation
- in each fraction the hydrocarbons have similar boiling points and properties
what do the fractions mainly contain?
alkanes
how is fractional distillation carried out?
by a fractionating column
- very hot at the bottom, cool at the top
- crude oil enters and is heated so the vapours rise
- vapours with high boiling points will condense into liquid at the higher temperatures lower down the column
- and vise versa
where are the fractions containing smaller hydrocarbons collected?
at the top of the fractionating column as gases
where are the fractions containing bigger hydrocarbons collected?
at the lower parts as liquids
where does the temp decrease in the fractionating column?
as you move up the temperature decreases
what are the properties of crude oil?
viscosity
- ease of flow of a liquid
- higher viscosity liquids are thick and don’t flow easily
colour
- as the chain length increases the colour gets darker
melting/boiling points
- as the molecules get larger the intermolecular attractions becomes greater, so more heat is needed to separate the molecules
volatility
- the tendency to vaporise
- with increasing molecular size hydrocarbons they become less volatile
what are the main fractions in crude oil?
refinery gases petrol kerosene diesel fuel oil bitumen
what are refinery gases used for?
domestic heating and cooking
what is petrol used for?
fuel for cars
what is kerosene used for?
jet fuel
what is diesel used for?
diesel engines
what is heavy fuel oil used for?
ships and power stations?
what is bitumen used for?
surfacing roads and roofs
what are the products from combusting fuels?
burning of fossil fuels produces carbon dioxide, carbon monoxide, oxides of nitrogen, oxides of sulphur
what are the difference in products produced in incomplete and complete combustion?
complete - water - carbon dioxide incomplete - unburnt fuel (soot) - carbon monoxide - water
what are the dangers of carbon monoxide?
causes dizziness, loss of consciousness and can be fatal
- CO binds to haemoglobin
- prevents it from binding to O2 and CO2
how are nitrogen oxides formed?
when N and O react in high pressure and temperature conditions of internal combustion engines and blast furnaces
what are catalytic converters?
in cars exhaust systems
contain a series of transition metal catalysts
- catalysts are in a honeycomb to increase surface area
how do catalytic converters work?
redox reactions occur which neutralises the pollutant gases
- carbon monoxide is oxidised to carbon dioxide
what are the transition metals used in catalytic converters?
platinium and rhodium
how does sulphur dioxide form?
combustion of fossil fuels
- fossil fuel often contain sulphur impurities
when sulphur in the fuels get oxidised it creates sulphur dioxide
what are the effects of sulphur dioxide?
acid rain
- causes corrosion to metal structures, buildings, carbonate rocks and aquatic organisms
pollutes crop and water supply
irritates lungs, throats, and eyes
what contributes to acid rain?
sulphur and
nitrogen oxides
how is acid rain formed?
- sulphuric acid from sulphur in hydrocarbons
- nitrogen dioxide from car engines
what is a saturated molecule?
when it contains single bonds only
what is a unsaturated molecule?
when it contains double bonds between carbon atoms
what is cracking?
a process used to convert long chain molecules into short chain molecules that are more useful
what are the two ways to crack?
catalytic and steam cracking
what is the process of catalytic cracking?
- heating hydrocarbons to 470-550C to vaporise them
- the vapours then pass over a hot powdered catalyst of aluminium oxide
- it breaks covalent bonds causing thermal decomposition
what is the outcome of catalytic cracking?
produces a mixture of smaller alkanes and alkenes
why is cracking useful?
it increases the supply of particular fractions
- which supplies the demand
smaller hydrocarbons have a higher demand than supply, this is the opposite for fuel oil and bitumen
what type of reaction is cracking?
endothermic reaction
