ch1 fuels from crude oil
TRANSCRIPT
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Crude oil is extracted from the Earths crust. It is formed
over millions of years from plant and animal remains
buried under layers of rock.
Crude oil is not very useful as it is it is thick,
black, sticky and doesnt burn too well but
modern society is critically dependent onproducts which are obtained from crude oil:
e.g. petrol and other fuels
plastics and fabrics
medicines
crude oil
Oils and fuelsobtained from
crude oil
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Crude oil is a finite resource. This means there is a limited amount of it. Since it
takes millions of years to form we say it is non-renewable.
We can be sure that it will run out completely if we carry on using it at the rate we
have been doing. Some estimates put the remaining crude oil reserves at about40 years left.
What has to be done ?
1) Develop alternative fuels and energy sources which are renewable e.g. biofuels
2) Develop alternative routes to manufacture plastics, medicines etc.
3) Conserve existing crude oil reserves reduce wasted fuel use, recycle plastics
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Crude oil is not a single substance, but a mixture containing many different
chemical compounds
The majority of these are hydrocarbons which means that they are made only
from carbon and hydrogen atoms. The carbon atoms form a chain and thehydrogen atoms connect to the carbon atoms:
carbon atomshydrogen
atoms
Four different hydrocarbon molecules of the kind found in crude oil
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Note that each carbon atom has fourbonds and that each hydrogen has one bond.
This is always true in hydrocarbon molecules.
The family of substances with a carbon chain and hydrogen atoms connected to all
the other places where bonds can form is called the ALKANES.
The smallest alkane, with one carbon atom, is METHANE CH4The next smallest, with two carbon atoms is ETHANE C2H6Then comes a 3-carbon chain, called PROPANE C3H8 and a 4-carbon chain, called BUTANE C
4
H10
and a 5-carbon chain, called PENTANE C5H12
In general, for an alkane with n carbon atoms, the formula is:
We call this the GENERAL FORMULA for the alkanes
Natural gas
contains 90%
methane Petrol contains alkanes such asoctane, 8 carbons long
CnH2n+2
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Drawing such detailed pictures of the molecules is time-consuming and chemists
prefer to use a simpler notation:
The molecular formula tells you how many of each atom are present in the
molecule, but not how the atoms are connected
e.g. The molecular formula formethane is CH4The molecular formula forpropane is C3H8
The displayed formula uses the element symbols and shows
which atoms are connected to which other atoms in the molecule
e.g. The displayed formula formethane is
The displayed formula forpropane is
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One property of any mixture is that it can be separated
by physical means (i.e. without doing any chemical
reactions). Physical means could include filtering, or
using magnets, or evaporation, for example.
Different mixtures require different physical means. In
the case of crude oil, the mixture is separated using
boiling and condensing.
The process is called fractional distillation. It works
because each different hydrocarbon has a differentboiling point:
The longerthe chain the higherthe temperature
has to be in order to turn the hydrocarbon from
liquid to gas i.e. the higher the boiling point
The process starts by heating the crude oil up until all
of the hydrocarbon molecules are gases. They are
then passed into the bottom of a fractionating
column
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Hydrocarbons
enter here as
gases.
The fractionating
column gets
cooler the further
up the molecules
travel.
Each molecule
rises up the tower
until it gets to the
point where it
condenses backinto a liquid trays
collect the liquid at
different levels.
The liquid collected in each
tray contains hydrocarbons
with a specific range of chain
lengths these are called
fractions
Some very short chain hydrocarbons
come out of the top still as gases
they are collected too
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The different fractions obtained by fractional distillation of crude oil have different
properties and therefore different uses. Some are shown below:
Name Alkanes in this fraction Uses
Refinery gas CH4 to C4H10
Gasoline C4H10 to C12H26
Kerosine C11H24 to C15H32
Diesel C15H32 to C18H38
Residue C50H102 and longer(bitumen for
road repairs)
Note:you dont
have to learn
names of specific
fractions, or the
range of
hydrocarbons in
each, but you
should know theuses, and be able
to relate uses to
the typical size of
the hydrocarbon
molecules
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As the length of the
carbon chain in an
alkane increases
The boiling point
increases
It gets harder to turn
the hydrocarbon into
a gas
It gets less runny
and more thick and
sticky
It gets harder to
ignite, burning with a
more smoky flame
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Evaluating fuels
You may be asked to discuss how good or bad a fuel is, comparing it to other
fuels for example.
A good fuel needs to be: Easy to ignite, but not so flammable that it is dangerous to handle
Easy to transport and pump around (liquids are better than solids or gases)
Safe to handle and store
Cheap and readily available not expensive to produce
Clean - polluting as little as possible when it burns
(examine the products of combustion, including any trace substances which may
be present e.g. sulphur in fossil fuels)
vs.
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Burning pure hydrocarbons
Burning is a chemical reaction between a fuel and oxygen, in which energy is
released. With most fuels, each of the elements it is made of can react with oxygen to
make an oxide.
If there is enough oxygen available - The carbon reacts with oxygen to make carbon dioxide
(CO2)
The hydrogen reacts with oxygen to make hydrogen oxide
(H2O aka water!)
If there isnt enough oxygen available
Water will still be made, but The carbon may react to form carbon monoxide (CO) Pure carbon (soot) may be produced
(this is what makes a flame yellow and luminous)
hydrocarbon + oxygen carbon dioxide + water
(e.g. methane)
hydrocarbon + oxygen carbon monoxide + water
(e.g. methane)
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Inside a motor vehicle engine, the fuel is mixed with air before it is ignited. This is
so that there is oxygen available to react with the hydrocarbon molecules.
Unfortunately that isnt all the oxygen reacts with.
Fossil fuels also contain traces ofsulphur. When the sulphur in the fuel is burned itreacts with oxygen in the air to form sulphur dioxide, which can be emitted in the
exhaust of the vehicle.
At the temperatures inside engines, nitrogen in the air is also burned, reacting with
oxygen to form nitrogen oxides. These gases can also be emitted in the exhaust.
Both nitrogen oxides and sulphur
dioxide can dissolve in rain droplets,
reacting to form strongly acidic
solutions, and falling as acid rain
(see next section for the problems
this causes, and what can be done
to reduce them).
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Alternatives to fuels from crude oil 1) Hydrogen
Hydrogen can be obtained by electrolysis of water. It is a gas, lighter than air, and
extremely flammable. Technology is currently under development to use hydrogen
as a fuel, but there are lots of challenges remaining.
Evaluating hydrogen as a fuel:
Available ? Yes easy to produce
Clean ? Yes the only product when it burns is water
Storage ? Not easy its a gas so its bulky. New technology needed.
Perhaps hydrogen could be made by a reaction as it is needed
Safe to use ? Not as safe as petrol ignites much more easilyProblems for safe storage and safe refuelling
Ignition ? Very easy (too easy !) to ignite
A hydrogen-fuelled carHistorically, using hydrogenhas a bad reputation !
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Alternatives to fuels from crude oil 2) Ethanol
Ethanol can be made using products from crude oil, but it can also be made by
fermentation of plant matter this is called bioethanol. Biofuels such as this do not
deplete our crude oil reserves so they are called renewable fuels. They can be used
as alternatives to petrol/diesel.
Evaluating bioethanol as a fuel:
Available ? Yes easy to produce, but requires a lot of land to grow plants.
Clean ? Same main products, CO2 and H2O - but no sulphur dioxide.
Storage ? Much the same as petrol to store and transport. Its a liquid.
Safe to use ? Similar to petrol less damaging to environment if spilled
because it gets broken down more easily.
Ignition ? Easy to ignite more so than petrol.
An ethanol-fueled car
Ethanol can be
blended with
petrol to help
conserve crude oil
reserves and to
reduce the cost of
the fuel
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When fossil fuels burn, a variety of products may be formed which have impact on
health and the environment:
Carbon dioxide formed when the carbon in hydrocarbons reacts with a plentiful
supply of oxygen. Causes Global Warming.
Carbon monoxide formed when the carbon in hydrocarbons reacts with a limited
supply of oxygen. Toxic, colourless and odourless Dangerous to Health !.
Particulates particles of carbon formed when hydrocarbons burn in a limited
supply of oxygen. May also be coated with unburned fuel. Cause Global Dimming.
Sulphur dioxide formed when traces of sulphur in fossil fuels burn, reacting with
oxygen in the air. Causes acid rain.
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Global warming and the Greenhouse Effect
Carbon dioxide and other greenhouse gases form a
layer in the upper atmosphere which allows the suns
energy to pass through, warming the Earths surface.
Rather than escaping back into space, the radiated
heat from the Earths surface is trapped by this layer (in
the same way the glass in a greenhouse traps the heat
from the sun). This causes temperatures to get steadily
warmer the phenomenon is termed Global Warming.
NOTE: THIS HAS NOTHING TO DO WITH THE OZONE LAYER !
Effects of Global Warming:
include drought and flooding and melting of the polar ice caps
Then
Now
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Carbon monoxide poisoning
Carbon monoxide is deadly. This is because it is colourless, odourless and
poisonous, so you wont be able to tell if you are breathing it in. Its toxic effect
works by preventing respiration from happening properly. A headache is one of the
first symptoms.
Rather than haemoglobin in the blood transporting oxygen to where it is needed, as
it should, the haemoglobin bonds to carbon monoxide molecules instead, and
oxygen starvation to the tissues and organs occurs.
Badly-maintained gas fires or water heaters are a common source of carbonmonoxide poisoning. This happens when the air-holes get blocked and the gas
burns with less oxygen from the air than it should.
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Global Dimming
As the atmosphere becomes contaminated
with particulates (soot, particles of
unburned fuel) so the light from the sun
will be progressively blocked out. The
particles will scatter back into space sunlight
which would otherwise have reached Earth.
The effects of Global Dimming would be:
1) Decreased light levels affecting rates of crop growth and healthiness of plants
2) Lower temperatures as less of the Suns energy heats the Earths surface
Increased amounts of particulates in the air willalso have effects on health increased
respiratory problems such as asthma, so putting
more particulates into the atmosphere is not a
cure for Global Warming !
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Acid RainGases such as sulphur dioxide and nitrogen oxides,
formed when fossil fuels are burnt, cause acid rain.
These gases dissolve in droplets of waterin the
atmosphere (i.e. rain droplets) to form strongly acidic
solutions, which can damage trees and aquatic
ecosystems as well as slowly attacking building
materials such as limestone.
Carbon dioxide also forms an acidic solution when itdissolves in water droplets, but it is much more weakly
acidic.
Because the atmosphere is constantly moving, the place
where acid rain falls may be in an entirely different
country to the place where the polluting gases wereformed. Remote areas of great natural beauty can be
destroyed by acid rain from urban areas many hundreds
of miles upwind.
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Reducing the damage that acid rain causes
Two approaches are used:
1) Remove the sulphur from the fuelOil refineries can process fractions which are to be used as fuels in order to
remove the traces of sulphur from the fuel. This is called desulphurisation.
At petrol stations, look for pumps labelled as Ultra-low sulphur fuel
2) Remove the sulphur dioxide from the emissionsWhen fossil fuels are burnt in power stations, huge
quantities of fuel are consumed, so it is not cost effective
to buy desulphurised fuels. The fuels do contain traces of
sulphur, and the flue-gases do contain sulphur dioxide.
What is done here is to install a scrubber. This is a
system that the flue gases pass through which removesthe sulphur dioxide by reacting it with quicklime. The
process is called flue-gas desulphurisation.