4(b) Crude oil Flashcards
crude oil?
as a mixture, it isn’t a very useful substance
fractions?
different hydrocarbons: each consists of groups of hydrocarbons of similar length
fractional distillation?
molecules in each fraction have similar properties and boiling points so they can be separated in a fractional column.
what does the boiling and melting point of each fraction depend on?
the number of carbon atoms in the chain
size + length determines which fraction it will be separated into
most fractions contain many alkanes –> compounds C with a single bond
fractional column temperature gradient?
very hot (bottom) and cool (top)
how does a fractioning column work?
crude oil enters the column
- crude oil heated so it will rise
what happens to the hydrocarbons that have a low boiling point, in a fractional column?
- vapors of hydrocarbons with very high boiling points will immediately condense into liquid at the higher temps lower down tapped off at the bottom of the column
what happens to the hydrocarbons that have a high boiling point, in a fractional column?
vapours of hydrocarbons with low boiling points will rise
where are smaller and bigger hydrocarbons collected?
- smaller is at the top (some as gases)
- bigger at the lower sections
main properties of the main fractions of crude oil? (how to know the difference)
- viscosity
- colour
- melting/ boiling point
- volatility
viscosity?
ease of liquid flow (large viscosity - thick and flows less easily)
factors that affect the viscosity of crude oil?
- if no of carbon atoms is high, the attraction between the hydrocarbon molecules also increases
- results in the liquid becoming more viscous with increasing length of chain (flow less easy)
factors that affect the colour of crude oil?
as C chain length increases the color of the liquid gets darker as it gets thicker and more viscous
factors that affect the melting/boling point of crude oil?
as molecules get larger, intermolecular attractions become greater:
- more heat needed to separate the molecules
- increase molecular size. greater boiling point.
volatility?
tendency of a substance to vaporise
factors affecting volatility?
increase molecular size, hydrocarbon liquids become less volatile, due to the attraction between the molecules increasing with increasing molecular size
what are the different fractions?
refinery gases (1-4), gasoline (4-12), kerosene (12-16), diesel (14-18), fuel oil (19-25) and bitumen (more than 70)
uses of refinery gases?
domestic heating and cooking
uses of gasoline?
fuel for cars
uses of kerosene?
jet fuel
diesel uses?
diesel engines
heavy fuel oil uses?
ship and power stations
bitumen uses?
surfacing roads and roofs
how to remember to order of the fractions?
Red Grandmas plant Kangaroos Dung Happily Farting On Bugs
what composes fossil fuels?
coal, oil, natural gas, oil shales and tar sands
what does combustion of fossil fuels contribute too?
source of atmospheric polution
How are fossil fuels obtained?
non-renewable fossil fuels are obtained from crude oil by fractional distilation
what do all these fuels contain?
carbon, hydrogen and a small amount of sulfur
products of combustion?
- releases:
- CO2
- CO
- oxides of Nitrogen and sulfur
products of incomplete combustion?
in addition incomplete combustion of fuels gives rise to unburned hydrocarbon and carbon particles
what is a fuel?
it is a substance which releases energy in an exothermic reaction
products of combustion of fossil fuels
water and carbon dioxide
when does incomplete combustion occur?
when there is insufficient O2 to burn
products of incomplete combustion?
unburnt fuel (soot), CO and water
what is CO?
- toxic and odorless gas which can cause dizziness, loss of onerousness and eventually death
what does CO do to the body?
it binds well to hemoglobin which therefore cannot bind oxygen and carbon dioxide for gas exchange
how are nitrogen oxides (NO and NO2) formed?
when nitrogen and oxygen react in the high pressure and temperature conditions of internal combustion engines (car engines) and blast furnaces.
How are nitrogen oxides dangerous?
In the atmosphere, nitrogen oxides can combine with water to
produce nitric acid (HNO3)
effects of nitric acid?
acid rain with similar effects as SO2 as well as producing photochemical smog and breathing difficulties in particular for people suffering from asthma
catalyst converters use?
designed to reduce the polluting gases produced in car exhausts
sources of sulfur dioxide?
combustion of fossil fuels - especially coal.
fossil fuels are often contaminated with small amounts of sulfur impurities so when combusted the fuels get oxidized to sulfur dioxide.
effects of sulfur dioxide?
- acid rain (dissolves in rainwater droplets to from sulfuric acid)
affects of acid rain?
- causes corrosion to metal buildings and statues made of carbonate rock
- damage to aquatic animals
- pollute crops and water supplies
- irritates lungs, throats and eyes
saturated molecules?
Contain single bonds only
unsaturated molecules?
contain double bonds between carbon atoms (alkenes)
cracking?
the process of converting long chain alkane molecules (further processing) into short chain molecules (more useful)
2 methods of cracking?
- catalyst cracking
- steam cracking
process of catalyst cracking?
- heat the hydrocarbon molecules to around 600-700 degrees to vaporize them
- the vapor passes over a hot powered catalyst of aluminum oxide
- process break covalent bonds in the molecules as they come into contact with the surface of the catalyst (causing thermal decomposition reactions)
in what way are hydrocarbons broken down using catalyst cracking?
in a random way which produces a mixture of smaller alkanes and alkenes
supply?
how much of a particular fraction can be produced from refining the crude oil
demand?
how much customers want to buy
why is cracking necessary?
because generally the demand outstrips the supply and cracking converts surplus unwanted fractions into more useful ones
is cracking endo or exo?
endothermic reaction
