Fuels From Crude Oil Flashcards
Explain process of fractional distillation
Crude oil heated and most fractions(hydrocarbons with similar carbon chain lengths) vaporise, enter fractionating column which is hotter at bottom than top, vapours condense in trays depending on their boiling point. Some fractions do not vaporise and lower pressure is used to separate them.
Which fraction is used for petrol
C5 to C10 (gasoline fraction)
What is crude oil
A mixture composed mainly of straight and branched chain alkanes and also cycloalkanes and arenes(hydrocarbons containing a benzene ring) and impurities such as sulfur compounds
Does crude oil contain more short or long chain hydrocarbons and what does this result in
More long chain hydrocarbons while there is a greater demand for lower bp fractions as they make better fuels due to vaporising more easily, means shortage of shorter chain fractions and surplus of longer chain ones
What is cracking
Process of breaking up larger hydrocarbon chains into smaller and more useful ones
Conditions for thermal cracking
High temperature and steam
What does thermal cracking produce more of and what is the use of this
Produces more alkenes which are important feedstock for chemicals(used to make other products)
Conditions for catalytic cracking
Zeolite catalyst and 450 degrees Celsius
What does catalytic cracking produce more of
Makes more branched alkanes
Three advantages of catalytic cracking over thermal
-produces higher proportion of branched alkanes which burn more easily
-uses lower temperature and pressure so is cheaper and uses less energy
-produces higher proportion of arenes which are valuable feedstock chemicals
What impurities are removed from fuels
Refined to remove sulfur compounds which when burnt can cause acid rain
What is octane number
A measure of the performance of a fuel by its ability to resist knocking when ignited in a mixture with air in the cylinder of an internal-combustion engine
Three ways to increase the octane number of fuels
-cracking (makes smaller molecules and converts straight-chain hydrocarbons to branched and cyclic hydrocarbons)
-reforming (turns straight-chain alkanes into branched-chain or cyclic alkanes/arenes eg benzene and turns cyclic alkanes into arenes
-adding ethanol and ethers
What is the zeolite catalyst used in catalytic cracking called
Sodium aluminium silicate
What are zeolites
Have a 3D structure in which silicon, aluminium and oxygen atoms form tunnels and cavities into which small molecules can fit and reactions can be catalysed
