Alkanes from Crude Oil
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where does most of the energy we use globally come from
burning fossil fuels
what are the typical fossil fuels
• coal • natural gas • oil
what are most crude oils and natural gases
alkanes
what are the three main processes used to convert crude oil into fuels
• fractional distillation • cracking • reforming
what is crude oil
a complex mixture of compounds, mainly hydrocarbons
why is fractional distillation sometimes called fractionation
because it involves converting the crude oil into a small number of fractions
where is fractional distillation done
in a distillation column
what is firstly done to the crude oil before it enters the distillation column
• it is heated in a furnace • for most of it to be turned into vapour • which is then passed into the column near the bottom
what is special about the fractionating column which allows the different hydrocarbons to separate
• it has a temperature gradient - it is hot at the bottom and gets cooler as you go up
what happens when the vapor passes up the column through a series of bubble caps
• different fractions condense at different heights of the column • depending on the boiling temperature range of molecules in that fraction
what kind of molecules would you see near the bottom of the column
• the molecules would be larger • have longer chains • and therefore have higher boiling points
what kind of molecules would you see near the top of the column
• the molecules would be smaller • which shorter chains • and therefore have lower boiling points
does all of the vapor condense and why
• all of it doesnt condense • as some of the hydrocarbons are dissolved gases • so it reaches the very top
why is the demand for shorter hydrocarbons larger than longer hydrocarbons
• the world has fewer uses for longer hydrocarbons - and shorter ones make for good fuel and are able to be used when making polymers and other substances
due to there being a surplus of longer hydrocarbons and deficit of shorter ones, what has been the solution to balancing out the demand to supply ratio
• converting the longer chains into shorter ones - which is what cracking is
how is cracking done
• you pass the heavier hydrocarbons through a heated catalyst • this causes the larger molecules to break up into smaller ones • so from one large molecule, at least two smaller ones are formed
what is a common catalyst used for cracking
• zeolite - which is a compound of aluminium, silicon and oxygen
what could decane, C10H22, be cracked into and what are they used for
• octane C8H18 used for petrol - and ethene C2H4 used for making polymers
what is an advantageous point about cracking, specifically about the different types of hydrocarbons used and produced
• only alkanes are used for cracking as they require the least energy • but from it you can get alkanes and alkenes
what is a disadvantage or uncertainty that comes with using alkanes as fuels in cars (other than pollution…)
• during the combustion that takes place in car engines - not all hydrocarbons of the right size burn the same way
what kind of hydrocarbons burn more and less efficiently
• straight chain hydrocarbons burn less efficiently - those with branched chains and rings (cyclic compounds) burn more efficiently
what does the process of reforming do
• it converts straight chain alkanes into branched chains and cyclic hydrocarbons • by heating them with a catalyst
what would the catalyst be for reforming
platinum
what is the advantage that comes with reforming
it allows the fuel to burn more smoothly (efficiently) with oxygen in the engine