Chemistry C9: Crude oil and fuels

Is crude oil a finite resource or infinite?

Finite

• Will eventually run out

Where is crude oil found?

In rocks

How is crude oil formed?

• Over millions of years from the remains of plankton buried in mud

• Layer upon layer of rock was laid down on top creating conditions to make crude oil

Conditions needed to make crude oil

• High pressure

• High temperature

• Absence of oxygen

What is crude oil?

• Mixture of hydrocarbons

• Remains of an ancient biomass consisting mainly of plankton that was buried in mud

Hydrocarbons

Molecules made up of hydrogen + carbon atoms only

Alkanes

• General formula: C_nH_2n+2

• Saturated molecules

• Hydrocarbons

Why are alkanes saturated molecules?

• Only single covalent bond between C atoms

  • So contain as many H atoms as possible

• C atoms are fully bonded to H atoms

First 4 alkanes

1. Methane- CH4

2. Ethane- C2H6

3. Propane- C3H8

4. Butane- C4H10

Viscosity

Thickness of a fluid

• High: flow slowly

Flammability

How easily a hydrocarbon combusts

• Short chain: Very flammable

Boiling point

Temperature at with a liquid changes to a gas

Volatility

Tendency to turn into a gas

Saturated

Single covalent bond between C atoms

What happens to … as the size of a hydrocarbon molecule increases and why?

1. Viscosity

2. Flammability

3. Boiling point

1. Increases

2. Decreases

3. Increases

What does the properties of hydrocarbons depend on?

Size of molecule

• ie chain length of their molecules

Why are short-chain hydrocarbon molecules more useful than longer-chain ones?

Lighter fractions = make better fuels

• Ignite easily

• Burn well

• Less smokey flames (cleaner)

How do you make hydrocarbons in crude oil useful?

Separate them

• Use fractional distillation

Fractions

Contain hydrocarbons with a similar number of C atoms

• In FD, crude oil separated into fractions

Fractional distillation of crude oil

1. Crude oil heated to v high temp

2. It boils- all hydrocarbons evaporate + turn into a gas

3. Crude oil vapours enter the FD column (hotter at bottom, cooler at top)

4. HC vapours rise up the column

5. HC condense when they reach their BP

6. Liquid fractions are then removed

Temperatures in the fractional distillation column

• Hotter at bottom

• Cooler at top

What happens to very long chain hydrocarbons in fractional distillation?

Have very high BP

• So are removed at the bottom of the column

What happens to very short chain hydrocarbons in fractional distillation?

Very low BP

• Don’t condense

• So are removed from the top of the column as gases

What fractions are used as fuels?

1. Petrol + diesel: to fuel cars

2. Kerosene: jet fuel

3. Heavy fuel oil: to power ships

4. Liquified petroleum gas: camping stoves

What are some chemicals used as for the petrochemical industry?

Feedstock

• Solvents, lubricants, detergents, polymers

Feedstock

A chemical used to make other chemicals

What does the combustion of hydrocarbon fuels do?

Release energy

What happens to the carbon and hydrogen atoms during combustion?

• React with oxygen

• Oxidised

Products of complete combustion of a hydrocarbon (unlimited O2)

• CO2

• H2O

How to test for products of complete combustion of a hydrocarbon

1. CO2, limewater, turns cloudy

2. Water, blue cobalt chloride paper, turns pink

3. Water, white anhydrous copper sulfate, turns blue

Products of incomplete combustion

carbon monoxide, carbon, water

Why is carbon monoxide dangerous?

• Toxic gas

• Colorless + odourless

• CO binds to RBC instead of O2

Compare complete with incomplete combustion

1. Products

2. How much O2 is available

3. Bunsen flame used

4. How much energy is released

CC:

1. CO2 + H2O

2. Excess O2

3. Blue flame

4. Max amount

IC:

1. CO + H2O

2. Limited O2

3. Orange

4. Limited

Why are larger, less useful hydrocarbon molecules cracked?

To produce smaller, more useful molecules

• LC HC = poor fuels (difficult to vaporise)

Cracking

Long chain alkane is broken down (cracked) to produce smaller chain, more useful ones by thermal decomposition

Main demand for crude oil

• Fuels

• Feedstock (starting materials) in chemical industry

Products of cracking

• Alkane

• Alkene

2 methods to carry out cracking

1. Catalytic cracking

2. Steam cracking

Conditions catalytic cracking

1. High temperature

2. Catalyst (speed up reaction)

Conditions for steam cracking

1. High temperature

2. Steam

Process of cracking

1. A heavy fraction distilled from crude oil is heated to vaporise the hydrocarbons

2. The vapour is then either:

   • Passed over a hot catalyst

   • Mixed with steam + heated to a v high temp

Where does cracking occur in?

Crackers

• At an oil refinery in steel vessels

What type of reaction is cracking?

Thermal decomposition

Alkene

• CnH2n

• Unsaturated HC

  • Double CB betw 2 C atoms

What are alkenes used for?

1. To make polymers

2. As starting materials for other useful chemicals (feedstock)

Which is more reactive: alkanes or alkenes

Alkenes more reactive than alkanes

How can you test for alkenes (unsaturated hydrocarbon)

1. Use bromine water (orange)

2. Shake alkene with bromine water

3. Turns colourless

How to distinguish between alkanes and alkenes using bromine water

1. Alkane + BW = no color change (orange)

2. Alkene + BW = becomes colorless

Which hydrocarbons are saturated and unsaturated?

• Alkanes = saturated

• Alkenes = unsaturated

Why do alkenes and alkanes react differently?

Presence of a double covalent bond between 2 C atoms

What are the fractions produced from the FD of crude oil processed to produce?

1. Fuels

2. Feedstock for the petrochemical industry

What do the vast array of natural + synthetic carbon compounds occur due to?

The ability of C atoms to form families of similar compounds

Complete combustion of a hydrocarbon fuel

• Releases energy

• C + H2 in the fuels are oxidised.

• Produces CO2 + H2O

What are hydrocarbons cracked (broken down) to produce?

Smaller, more useful molecules

What are some of the products of cracking used for + why?

Fuels

• High demand for fuels w small molecules

What does the FD of crude oil do?

Separates the hydrocarbons from crude oil into fractions