Fuels From Crude Oil Flashcards

1
Q

Explain process of fractional distillation

A

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.

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2
Q

Which fraction is used for petrol

A

C5 to C10 (gasoline fraction)

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3
Q

What is crude oil

A

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

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4
Q

Does crude oil contain more short or long chain hydrocarbons and what does this result in

A

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

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5
Q

What is cracking

A

Process of breaking up larger hydrocarbon chains into smaller and more useful ones

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6
Q

Conditions for thermal cracking

A

High temperature and pressure and steam

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7
Q

What does thermal cracking produce more of and what is the use of this

A

Produces more alkenes which are important feedstock for chemicals(used to make other products)

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8
Q

Conditions for catalytic cracking

A

Zeolite catalyst and 450 degrees Celsius

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9
Q

What does catalytic cracking produce more of

A

Makes more branched alkanes

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10
Q

Three advantages of catalytic cracking over thermal

A

-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

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11
Q

What impurities are removed from fuels

A

Refined to remove sulfur compounds which when burnt can cause acid rain

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12
Q

What is octane number

A

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

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13
Q

Three ways to increase the octane number of fuels

A

-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

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14
Q

What is the zeolite catalyst used in catalytic cracking called

A

Sodium aluminium silicate

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15
Q

What are zeolites

A

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

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16
Q

What is reformation

A

Converting straight-chain alkanes into branched-chain or cyclic alkanes or arenes eg benzene and turns cyclic alkanes into arenes

17
Q

Conditions required for reforming

A

Platinum catalyst, 500 degrees Celsius and high pressure

18
Q

What is an arene

A

Molecule with a cyclic structure containing a benzene ring

19
Q

Why is reformation done

A

As cyclic/branched compounds burn more smoothly as fuels and give more efficient combustion