1. Fossil Fuels and Ethylene Flashcards
Describe the composition of Petroleum (Crude oil).
A mixture of hydrocarbons, consisting mainly of alkanes and cycloalkanes.
Define fractional distillation
Process to separate a mixture such as petroleum into its compounds according to their boiling points
Difference of boiling points in fractional distillation?
50 degrees celsius.
Why must crude oil be refined?
Crude oil must be refined by fractional distillation to obtain raw materials to make plastics, polymers and fuels.
What are light crudes?
High concentration of gasoline and kerosene
What are heavy crudes?
High proportions of higher BP compounds.
What is the sequence in fractional distillation? From top to bottom.
- Light gases
- Gasoline
- Naptha
- Kerosene
- Gas Oil
- Lubricating Oil
- Residue
IUPAC name for Ethylene
Ethene
Main sources of Ethene?
Australia and USA: Piped natural gas directly, and cracked into ethane, propane to obtain ethylene.
Define cracking.
Cracking is a process in which molecules of carbon compounds are broken down into smaller molecules with lots of heat/ catalyst.
Define catalytic cracking.
High molecular weight (BP) fractions converted into lower molecular weight (BP) using a catalyst
Why is catalytic cracking carried out?
To increase the output of high demand products.
Define cat cracker.
Column which catalytic cracking occurs.
What is an alkane broken into during cat cracking?
Alkanes are broken into two smaller molecules- alkAne and alkEne.
What is a catalyst used in catalytic cracking?
Zeolite
What is the composition of Zeolite?
Crystalline aluminosillicates (Al + Si +O2 + metal ions)
What is the structure of Zeolite which makes it such an effective catalyst?
It has tunnels and cavities through and in molecules. This gives it large surface area per unit mass.
What happens during Cat cracking?
Starts on the inner surface of molecule. Catalyst absorbs reactants in zeolite pores, weakening their bonds and reducing activation energy. High internal surface area.
At what conditions does Cat cracking occur?
- 500 degrees celsius
- Above atmospheric pressure
- No air.
Define steam cracking.
A non-catalytic process. A form of thermal cracking in which a mixture of alkanes is fed through:
- A hot metal pipe with steam to decompose.
Into small alkanes such as ethene, propene and butene.
Define Thermal cracking
- Heating the fraction to very high temperatures in the ABSENCE OF AIR
- Expensive: energy required to maintain high temperatures.
- Difficult to control and produce: bond breaking could occur anywhere.
Describe features of furnaces.
- Produces yields of C2H4
- 100 pyrolysis coils/ 80 m in length
- Feedstocks are heated (750- 900 degree celsius)
Describe Intitiation
Free radicals are produced when hyrdrocarbons are split into fragments. Reactive due to presence of unpaired electron.
Describe Propagation
Free radicals propagate to produce smaller free radicals and release small alkenes such as C2H4
Describe Termination
Hydrocarbon molecules can reform when free radicals react with each other.
Why are alkanes relatively unreactive?
- Saturated Compounds
What are the two important reactions of alkanes?
Combustion and Reactions with Halogens
What does combustion of alkanes produce?
Carbon dioxide and water
What is required for alkanes to react with halogens?
UV light
Describe alkane + halogen reactions?
This is a substitution reaction as hydrogen atom from an alkane is replaced by a halogen atom.
Excess halogen can replace remaining hydrogen atoms.
Why are alkEnes very reactive?
Presence of double bond.
How is alkene undergo addition reactions?
Double bond opens up to provide two single bonds where now new substances can add on.
What reacts with alkene?
- Halogens
- Hydrogen Halides
- Water
- Hydrogen
How many products are formed in addition reaction?
One
Ethene + Bromine
1,2- dibromoethane
What is HOBR
HOBR is hydrobromine acid which forms when bromine reacts with water molecules.
Br (aq) is when Br is dilluted with water.
C3H6 +HBr
2- bromo propane
Describe the test you would use to distinguish alkane and alkene.
- Bromine water added (red-brown colour, and see if it reacts)
- Alkene: Undergo addition reaction, and bromine will change from red-brown to colourless very quickly.
- Alkane: Undergo substitution reaction very slowly in the presence of UV light.
Safety precaution when handling bromine
Bromine is corrosive.
- Use fume cupboard
- Use very small quantities of chemicals
- Wearing labcoats
- Warft the smell using hands instead of inhaling directly.
During hydration reaction with Alkenes (Alkene + Water), what is the catalyst?
SO4
