1. 11.8 – NOTES Altering Fuels

2. B.9 Altering Fuels
The gasoline fraction only represents 18% of the total crude oil (5-12 carbons in a chain)
Using certain techniques can get up to 47% of crude oil

3. Cracking
Taking large chain hydrocarbons and breaking them into smaller chains, using catalysts and heat

4. Catalyst
Something that increases the speed of a reaction and lowers the temperature needed to start the reaction
They are not used in the reactions – they are not part of the product
Allows the burning of fuel to be cracked more efficiently because it takes place at a lower temperature (500 C rather than 700C), which needs less energy

6. A 16 carbon chain could be made into two 8 carbon chains
Can produce molecules of up to 14 carbons through cracking
C5-C12 are used in gasoline

7. Octane rating
Gas is made of mostly straight chain alkanes
Premature burning results in pinging/knocking
Branched chains don’t knock as much
Octane rating tests efficiency
Free running and under a load and then the average is taken
Higher octane numbers result in better anti-knock characteristics
Prior to the 70s, lead was added to increase octane rating
Tetraethyl lead ((C­2H4)4Pb)
Why was lead banned from fuels?
Bad for the environment, can cause many health problems

9. Oxygenated fuels
Fuels that have extra C, H and O to enhance octane
Less energy is delivered, but the octane increases and reduces pollutants

10. Types of addititives to make oxygenated fuels
Methanol
Formula: CH3OH
Made from: natural gas, coal, corn, wood
Structure:

11. Ethanol
Formula:C2H5OH
Gasohol % ethanol, 90% gasoline
Can usually run in cars without modifications
Structure:

12. MTBE- methyl tertiary-butyl ether
Has an octane rating of 116
Most common additive in the 1990s
Contaminates groundwater/drinking supplies
Results in unpleasant taste or odor in drinking water
Under consideration to reduce/ban

13. Other ways to boost octane rating
Alter the structure by turning straight chains to branched chains
Isomerization
Conversion of straight chain hydrocarbons into branched chains
Newly made branched chains are mixed with cracked hydrocarbons to produce high quality fuel
One of the largest problems with isomerization is the high cost
Isomerization Graphic: