Alkanes from Crude Oil

Question 1

where does most of the energy we use globally come from

Answer 1

burning fossil fuels

Question 2

what are the typical fossil fuels

Answer 2

• coal
• natural gas
• oil

Question 3

what are most crude oils and natural gases

Answer 3

alkanes

Question 4

what are the three main processes used to convert crude oil into fuels

Answer 4

• fractional distillation
• cracking
• reforming

Question 5

what is crude oil

Answer 5

a complex mixture of compounds, mainly hydrocarbons

Question 6

why is fractional distillation sometimes called fractionation

Answer 6

because it involves converting the crude oil into a small number of fractions

Question 7

where is fractional distillation done

Answer 7

in a distillation column

Question 8

what is firstly done to the crude oil before it enters the distillation column

Answer 8

• 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

Question 9

what is special about the fractionating column which allows the different hydrocarbons to separate

Answer 9

• it has a temperature gradient

- it is hot at the bottom and gets cooler as you go up

Question 10

what happens when the vapor passes up the column through a series of bubble caps

Answer 10

• different fractions condense at different heights of the column
• depending on the boiling temperature range of molecules in that fraction

Question 11

what kind of molecules would you see near the bottom of the column

Answer 11

• the molecules would be larger
• have longer chains
• and therefore have higher boiling points

Question 12

what kind of molecules would you see near the top of the column

Answer 12

• the molecules would be smaller
• which shorter chains
• and therefore have lower boiling points

Question 13

does all of the vapor condense and why

Answer 13

• all of it doesnt condense
• as some of the hydrocarbons are dissolved gases
• so it reaches the very top

Question 14

why is the demand for shorter hydrocarbons larger than longer hydrocarbons

Answer 14

• 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

Question 15

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

Answer 15

• converting the longer chains into shorter ones

- which is what cracking is

Question 16

how is cracking done

Answer 16

• 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

Question 17

what is a common catalyst used for cracking

Answer 17

• zeolite

- which is a compound of aluminium, silicon and oxygen

Question 18

what could decane, C10H22, be cracked into and what are they used for

Answer 18

• octane C8H18 used for petrol

- and ethene C2H4 used for making polymers

Question 19

what is an advantageous point about cracking, specifically about the different types of hydrocarbons used and produced

Answer 19

• only alkanes are used for cracking as they require the least energy
• but from it you can get alkanes and alkenes

Question 20

what is a disadvantage or uncertainty that comes with using alkanes as fuels in cars (other than pollution…)

Answer 20

• during the combustion that takes place in car engines

- not all hydrocarbons of the right size burn the same way

Question 21

what kind of hydrocarbons burn more and less efficiently

Answer 21

• straight chain hydrocarbons burn less efficiently

- those with branched chains and rings (cyclic compounds) burn more efficiently

Question 22

what does the process of reforming do

Answer 22

• it converts straight chain alkanes into branched chains and cyclic hydrocarbons
• by heating them with a catalyst

Question 23

what would the catalyst be for reforming

Answer 23

platinum

Question 24

what is the advantage that comes with reforming

Answer 24

it allows the fuel to burn more smoothly (efficiently) with oxygen in the engine

Question 25

what would pentane turn into if it was reformed

Answer 25

• it has the formula C5H12
• it would be turned into cyclopentane with a formula of C5H10
• meaning the byproduct s hydrogen, H2

Question 26

what would heptane, 7H16 convert into if it was reformed

Answer 26

• methylbenzene
• with hydrogen as the byproduct, 4H2
• it is a cyclic hydrocarbon with a circle in the middle but not an alkene

Question 27

what is another positive that comes with reforming of this nature

Answer 27

• the byproduct is hydrogen

- which is as very useful product