c8 fuels and atmospheric science
Crude oil is a finite source made of a mixture of hydrocarbons. It contains molecules in which carbon atoms are in chains or rings and is an important source of useful substances such as fuels and feedstock
Hydrocarbons are compounds which contain hydrogen and carbon only
The many hydrocarbons in crude oil can be split into fractions, which contain molecules with a similar number of carbon atoms by fractional distillation.
some properties of hydrocarbons depend on the size of their molecules
Boiling point, viscosity and flammability.
as we go up fractional distillation column, boiling point and and viscosity decreases while flammability increases.
the fractions produced in fractional distillation can be processed to produce fuels,
examples of fractions and their uses are
Gases - used in domestic heating and cooking, good because they are easy to ignite
Petrol - used as fuel in cars
Kerosene - used as fuel for aircraft
diesel - fuel for some large vehicles
fuel oil - large ships and power stations
Bitumen - used to surface roads and roofs
Most of the hydrocarbons in crude oil are hydrocarbons called alkanes
alkanes form part of the homologues series with the same general formula cn h2n+2
have similar chemical properties
The complete combustion of hydrocarbons as fuels releases energy and produces carbon dioxide and water
Ch4+O2 = H2O +cO2
incomplete combustion occurs when there is a lack of oxygen, consequently producing carbon monoxide and soot rather than carbon dioxide
The gas released into the atmosphere when a fuel is burnt may include carbon dioxide, water vapour, carbon monoxide, sulfur dioxide and oxides of nitrogen
Carbon monoxide is a toxic gas - its colourless and odourless so cant easily be detected
Sulfur dioxide form impurities in some hydrocarbon fuels. When sulfur dioxide dissolves in water it causes acid rain lead to weathering and destruction
When fuels are burnt in engines oxygen and nitrogen can react together at high temperatures to produce oxides of nitrogen also polluants.
Hydrogen versus petrol
Hydrogen produces water, no harmful co2 produced
hydrogen fuels are very efficient
Most hydrogen is produced by reacting stem with non renewable coal
doesnt work at very low temperatures
petrol
Products are water co2 a natural gas
produces oxides of nitrogen
Easily stored and transported
works at low temperatures
Cracking and alkanes
Larger saturated carbons can be broken down to produce smaller and more useful molecules some of which are unsaturated alkanes
cracking necassary to produce useful short chain molecules such as petrol
requires high temperature and a catalyst
Products of cracking include Alkanes and alkenes
Alkenes are more reactive than alkanes. There is demand for fuels with samller molecules
Alkanes - saturated hydrocarbons - no double bonds
Alkenes are unsaturated hydrocarbons - theres one or more double bond between carbons
The early atmosphere
Evidence for the early atmosphere is limited because of the timescale of 4.6 billion years
mainly carbon dioxide
water vapour condensed to form the oceans
Volcanoes produced nitrogen which gradually built up in the atmosphere may have been small portions of methane
Organisms evolved that changed the atmosphere in a significant way
Primitive plants produced the oxygen which is now in the atmosphere by photosynthesis
Algae first produced oxygen over 2.7 billion years ago and now this oxygen is in the atmosphere, over the next billion years plants evolved and the percentage of oxygen increases
Test for oxygen
Glowing splint inserted into test tube -splint relights in oxygen
Greenhouse gases in the atmosphere maintain temps high enough to support life
visible ligth is absorbed by the earth
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