Alkanes Flashcards
What is an alkane
Saturated hydrocarbon found in crude oil
Steps for fractional distillation
The vaporised oil enters the column and rises through the trays
The column has a temperature gradient where it is cooler at the top
As vapour rises the longest hydrocarbons run down the the bottom and don’t vaporise
The shortest hydrocarbons come off as a gas at the top of the column
Fractions are removed and collected at different levels
5 fractions of crude oil and their uses
Gas - used in stove gas
Kerosine - used as jet fuel and heating
Diesel oil - used as diesel fuel
Fuel oil - used in ships and power stations
Petrol - used in petrol cars
Gas fraction of crude oil?
Naptha
Why is cracking necessary
Heavier fractions are in lower demand than lighter fractions which are more valuable
2 types of cracking
Thermal
Catalytic
Thermal cracking conditions and products
1000°C
70atm pressure
Mainly alkenes
Catalytic cracking conditions and products
450°C and slight pressure with zeolite catalyst
Mainly aromatic hydrocarbons
Why is zeolite useful in catalytic cracking
Lowers temperature and pressure needed for cracking to occur, lowering costs and speeding up the process
Why are alkanes good fuels
Most burn readily to release large amounts of energy
Alkane complete combustion products
CO2 and water
Alkane incomplete combustion products
Carbon monoxide and carbon and water (sometimes CO2 aswell)
Problems with soot and carbon monoxide (+ how to remove CO2)
Soot can cause breathing problems and clog up engines
CO is poisonous and bonds to haemoglobin preventing oxygen binding - can be removed using a catalytic converter
What is the greenhouse effect
CO2 bonds absorb infrared radiation from the sun but emit some of it back into the earth
What is the ozone layer
Lowest level of atmosphere made of sunlight, hydrocarbons and nitrogen dioxide
How is photochemical smog made?
Solid carbon particulates mixed with ozone
What do photochemical smog and ozone do to humans?
Photochemical smog harms the respiratory system in animals and damaged plants
Ozone is also toxic to humans too
How is nitrogen oxide made
When nitrogen and oxygen from the air combine under high temps and pressure in car engines
How do catalytic converters help the environment
Reduce the amount of unburnt hydrocarbons and nitrogen oxides going into the atmosphere
Acid rain problems
Damages plants, kills fish and causes erosion of buildings
How does burning fossil fuels cause acid rain
Some fossil fuels contain sulfur based impurities
When burned the sulfur reacts with oxygen to produce sulfur dioxide
Sulfur dioxide is an acidic gas which reacts with water in the atmosphere to form sulfuric acid in acid rain (nitrogen oxides do this too)
How to remove SO2 from flue gases
Wet scrubbing
Calcium carbonate or oxide is dissolved in water and acidic sulfur dioxide gas is sprayed on
Free radical substitution (alkanes to halogenoalkanes) CH4 + Cl2 -> CH3Cl + HCL
UV light condition
Initiation: sunlight breaks the Cl-Cl bond in a process called photodissociation Cl-Cl -> 2Cl•
Propagation: Cl• + CH4 -> HCL + •CH3
•CH3 + Cl2 -> CH3Cl + •Cl
Termination: •CH3 + •Cl -> CH3Cl
(2•Cl -> Cl2 and 2•CH3 -> CH3CH3)
