Chapter 21 Petrol Crude oil Crude oil is

Chapter 21 Petrol

Crude oil • Crude oil is a fossil fuel. • It was formed from the bodies of tiny sea creatures which died millions of years ago. • Bacteria turned the bodies of these creatures into crude oil and natural gas.

Petrol is formed by the fractional distillation of crude oil. Some of the different fractions formed are: · Petroleum Gas - Metacarpans added for smell. · Petrol · Naphta - Petrochemical Industry · Kerosene - Aviation Fuel. · Diesel. · Lubricating Oil.

Octane Number Knocking - early explosion due to petrol-air mixture. The petrol explodes as it is compressed instead of being caused by a spark. (Auto-ignition). Octane Number - Measure of the tendency of fuels to resist knocking. The octane number of a fuel can be measured by comparing the performance of 2, 2 -4 tri-methyl pentane (iso-octane) which has an octane number of 100 and Heptane which is not efficient and has an octane number of 0. The shorter the alkane the higher the octane number. The more branched the chain the higher the octane number. Cyclic compounds have a higher octane number than straight chain compounds.

Octane Number

Making Petrol Tetra-ethyl lead -Reduces knocking. However it caused health problems and is poisonous. 4 ways to increase octane number. 1. Isomerisation. Branching caused by alkanes heated in the presence of a suitable catalyst. 2. Catalytic Cracking. Long chained hydrocarbons broken down into short chain molecules for which there is great demand. Large alkanes form alkanes and alkenes. 3. Reforming (De. Hydrocyclisation. ) Reforming involves the use of catalysts to form ring compounds. -Hydrogen given off. 4. Adding Oxygenates. Three oxygen containing molecules, methanol, and MTBE are added to petrol to increase its octane number. MTBE stands for methyl tertiary butyl ether. (2 -methoxy-2 methylpropane)