alkanes Flashcards
(30 cards)
what is petroleum
a mixture consisting mainly
alkane hydrocarbons
what are the steps of fractional distillation of petroleum
1-oil is preheated
2-then passed into the column with a temperature gradient hot at the bottom and decreases upwards
3-the hydrocarbons separate depending on their boiling points with depends on the size of the molecule this because the larger the molecule the larger the Vander walls
what happens to the heavier residues at he bottom of the fractionating column
they get distalated again but under a vacuum as by lowering the pressure the liquids boiling point decreases
what is cracking
conversion of large hydrocarbons to smaller hydrocarbons molecules by breaking the C-C bond
why do we crack hydrocarbons
the shorter chain hydrocarbons are in smaller demand and higher supply so we can crack the bigger ones which are of a lot lower demand into smaller ones
what are the two main types of cracking
thermal and catalytic
what are the conditions for thermal cracking
high pressure
high temperature
what does thermal cracking produce
mostly alkenes some alkanes
what is each fraction
each fraction is a group consisting of a group of compounds that have a similar boiling point and are removed at the same level
what happens in thermal cracking
the c-c bonds break a different point to give a mixture
what are the products of thermal cracking used for
they are used to make polymers
what are the conditions for catalytic cracking
higher temperature
moderate pressure
and the presence of a zeolite catalyst
what does catalytic cracking produce
cycloalkanes and branched alkanes as well as aromatic hydrocarbons such as benzene
what are the products of catalytic cracking used for and why
they are used as fules as they burn more cleanly
which is cheaper thermal or catalytic cracking
catalytic as it saves energy as lower temperature and pressure is needed
what is a fuel
releases energy when burnt
what is complete combustion
energy is obtained from the alkanes when they are combusted. the produces formed during the reaction are CO2 and H2O and depend of a abundant supply of oxygen
what is incomplete combustion
if there is limited supply of oxygen then incomplete combustion occurs producing CO and/or C (soot)
where does the pollutant sulphur come from and what are its effect
sulphur comes from impurities in the petroleum which reacts with oxygen from the air due to the high temperatures of the engine to form SO2
SO2 will dissolve into atmospheric water and from acid rain
how can SO2 be prevented from entering the atmosphere
through a process called fuel gas desulphurisation where chimneys of scrubbers are coated in calcium oxide or carbonate which reacts with the acid in a neutralisation reaction forming calcium sulphite which can be used in plaster board
where does the pollutant nitrogen oxide come from and what are its effects
nitrogen and oxygen react in the engine at the high temperatures to form nitrogen oxides which is toxic and can form acid rain
where does the pollutant unburned hydrocarbons come from and what are their effects
unburnt hydrocarbons react with nitrogen oxides to form low level ozone which contributed to formation of smog and causes raspatory problems
where does the pollutant carbon dioxide come from and what are their effects
carbon dioxide comes from the combustion of fuels and contributes towards global warming
where does the pollutant carbon monoxide come from and what are their effects
incomplete combustion of fuels forming a toxic gas
