Crude Oil Flashcards
What is crude oil?
Crude oil is a mixture of hydrocarbons - compounds containing carbon and hydrogen only. Hydrocarbons are organic molecules.
Describe and explain how the industrial process of fractional distillation separates crude oil into fractions
Crude oil is heated and passed into a fractionating column, which is cooler at the top and hotter at the bottom. The crude oil is split into various fractions. At the top of the column, the temperature is lower so hydrocarbons with lower boiling points condense and are tapped off. As you go down the temperature increases so hydrocarbons with higher boiling points start condensing so they can be tapped off.
The hydrocarbons in refinery gases are so low that the temperature of the column never falls low enough for them to condense to liquids.
The temperature of the column isn’t hot enough to heat some of the large hydrocarbons around in crude oil and they remain as a liquid and are removed as residue form the bottom.
Recall the names and uses of the main fractions obtained from crude oil
Refinery Gases - LPG, domestic cooking & heating
Petrol - fuel for cars
Kerosine - fuel for jet aircraft, paraffin for small heaters & lamps, domestic heating oil
Diesel oil - fuel for buses, lorries, some cars, railway engines for lines that haven’t been electrified.
Fuel oil - ships boilers and industrial heating
Bitumen - melted and mixed with rock clippings to make surface of roads
Describe the trend in boiling point and viscosity of the main fractions
As the molecule gets bigger:
Boiling point increases - large molecules are attracted to each other more strongly than smaller ones so more heat is needed to break these stronger forces of attractions to produce the widely spread molecules in a gas.
Viscosity - Liquids become more viscous. Liquids containing smaller hydrocarbons are runnier and those containing larger molecules are much stickier due to the stronger forces of attractions between their molecules.
What happens if there is incomplete combustion?
If there isn’t enough air, you get carbon monoxide instead of carbon dioxide or soot and water
How do car engines produce pollutant gases?
In car engines, the temperature reached is high enough to allow nitrogen and oxygen from air to react, forming nitrogen oxides
What are the dangers of nitrous oxides and sulfur dioxide/
Nitrogen oxides and sulfur dioxide are pollutant gases, which contribute to acid rain
Some industrial processes give off NO and SO2 into the atmosphere
When they’re in the atmosphere, they react with rainwater to create H+ ions
Problems caused by acid rain:
Has a higher level of acidity; damages buildings and statues
Especially things made of limestone
Can reduce growth of/kill trees and crops
Lowers pH of water in lakes, killing fish
What is cracking?
Cracking is a useful process in which large hydrocarbon molecules are broken into smaller ones we need cracking because fractional distillation of crude oil produces more long chain hydrocarbons, than short chain hydrocarbons and there is not enough demand for longer chain molecules where as smaller chains are used to make petrol/diesel/fuel for vehicles and used to produce alkenes
which are used to make plastics.
Describe how long-chain alkanes are converted to alkenes and shorter-chain alkanes by catalytic cracking
The gas oil fraction is heated to give a gas and then passed over a catalyst of mine silicon dioxide and aluminium oxide at about 600-700 degrees. Cracking can also be carried out at a higher temperature without a catalyst. This process causes them to break into smaller molecules and as some atoms are lost from molecules, they become unsaturated (alkenes); they can form double bonds to produces alkenes and shorter chain alkanes
