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Production of Materials- 1
Production of Materials
1.
2.
Fossil fuel products
Fossil fuels provide both energy and raw materials such as ethylene,
for the production of other substances
Background: Fossil fuels are formed from the remains of organisms that lived on
Earth millions of years ago. Fossil fuels are rich in hydrocarbons that can be burnt to
release energy or used to make raw materials such as ethylene.
Ethylene is the same substance as ethene. Ethene is the IUPAC name for C2H4 while
ethylene is the name that is more commonly used in industry.
Ethylene (C2H4) can be used to produce useful substances such as polyethylene and
ethanol.
Polyethylene is the cheapest plastic. The weight of polyethylene produced each year
is greater than the total weight of all other plastics. Most plastic food bags, juice and
milk containers are made of, or lined with, polyethylene.

Construct word and balanced formulae equations of chemical reactions as they
are encountered.

An important part of the Preliminary course, that you must continue with
throughout the HSC course, is learning how to:
- construct word equations, e.g: methane + oxygen -----> carbon dioxide + water
and
- balance formulae equations, e.g: CH4 + 2O2 -----> CO2 + 2H2O
You must be able to do this for the reactions you encounter in
every module that you study, core and option.
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Production of Materials- 1
There are three important steps involved:
1. Show all reactants and all products in the word equation.
2. Write the correct formula for each reactant and each product.
3. Balance the formula equation by placing coefficients (numbers) in front of
formulas so that you have the same total number of each kind of atom on both
the reactant side and the product side. Remember that in chemical reactions
atoms are just rearranged, not created or destroyed.

Identify the industrial source of ethylene from the cracking of some of the
fractions from the refining of petroleum.
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Production of Materials- 1


Revise fractiontal distilation from Preliminary course.
Petroleum is a mixture of hydrocarbons. When petroleum undergoes fractional
distillation, some fractions, particularly petrol, are in demand and of high
economic value. Other fractions, called the ‘feed stock’, consisting of larger
molecules than in petrol and of low value, can be passed over a heated catalyst
that cracks the larger molecules into smaller molecules. A major by-product of
this catalytic cracking is ethylene, also known as ethene.

The products of cracking include short chain alkanes that can be used as
petrol, branched chain alkanes that improve the perofrmance of petrol, alkenes
(ethylene and propylene) and hydrogen.
For example decane is cracked to octane and ethene:
C10H22(g)  C8H18(g) + C2H4(g)

Steam Thermal Cracking
A process called steam thermal cracking is the main source of ethylene throughout
the world. In this process ethane (C2H6) gas from natural gas, or larger hydrocarbons
in low value petroleum fractions, are mixed with steam and passed through hot metal
coils. The steam removes carbon deposits from the metal coils. The heat from the
coils breaks bonds to change the ethane, or the larger hydrocarbons, to ethylene.
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Initial cracking required high temperatures.
A process called steam thermal cracking is the main source of ethylene
throughout the world.
Initial cracking required high temperatures.
Temperatures from 450°C to 700°C
Catalytic Cracking
 Initial cracking required high temperatures. The use of catalysts in ‘catalytic
cracking’ allows for much lower temperatures.
 Many gas reactions are catalysed using solid inorganic catalysts onto which
the gaseaous reactants are adsorbed. This weakens their bonds and reduces the
activation energy for the reaction.
 The main catalysts for catalytic cracking are a group of silicate minerals called
‘zeolites’. Zeolites are crystalline substances composed of aluminium, silicon
and oxygen. Zeolite crystals have a three-dimensional network structure
containing tiny pores. The reactant molecules are adsorbed in these pores
where the reactions are catalysed.
 Catalysts are added to the feed stock as a fine powder that is circulated in the
catalytic cracker.
 Identify that ethylene, because of the high reactivity of its double bond, is
readily transformed into many useful products.
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Production of Materials- 1

Ethylene can be transformed into many useful products because of the high
reactivity of its double bond.
An explanation
Alkenes are more chemically reactive than their corresponding alkanes. The yellow
colour of bromine water, which is due to the presence of bromine, is lost when the
bromine water comes in contact with an alkene, but not when in contact with an
alkane. This demonstrates the high reactivity of a C=C in an alkene compared with
the C-C in an alkane.


The chemistry of ethene is determined by its reactive double bond.
Reactions of Ethene
Ethene may undergo a large number of addition reactions to produce many
useful products:
1. Addition of hydrogen (hydrogenation)
Ethene is converted to ethane by heating it with hydrogen in the presence of a
metal catalyst such as nickel, platinum or palladium.
Ni
CH2=CH2(g) + H2(g)  CH3-CH3(g)
2. Addition of halogens (halogenation)
When halogens are added to ethene the double bond opens out and the
addition reaction takes place.
These halogenation reactions are used to distinguish between alkanes and
alkenes as alkanes do not readily react with halogens whereas alkenes do.
When a solution of bromine in a non-polar solvent (it has a red-brown colour),
the solution discolours as the bromine adds across the double bond.
CH2=CH2 + Br2  CH2Br-CH2Br (1,2-dibromoethane)
An aqueous solution of bromine, known as bromine water is also used to
distinguish between alkanes and alkenes. Bromine water is a yellow-brown
solution which discolours in the presence of alkenes.
CH2=CH2 + Br2(aq)  CH2OH-CH2Br + HBr(aq)
2-bromoethan-1-ol
hydrogen bromide
The addition of halogens to ethene produces some important products such as:
1,2-dichloroethane which is used to manufacture chloroethene which is used
to produce the plastic polyvinyl chloride, PVC.
3. Addition of hydrogen halides (hydrohalogenation)
Hydrogen halides such as HCl react with alkanes:
CH2=CH2(g) + HCl(g)  CH3-CH2Cl(g)
4. Addition of water (hydration)
Ethene is used in the production of ethanol by adding water in the presence of
a sulfuric or phosphoric acid catalyst:
H2SO4
CH2=CH2(g) + H2O(l) 
CH3-CH2OH(l)
Ethanol can then be oxidised to form ethanoic acid.
5. Oxidation of ethene
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Production of Materials- 1
The mild oxidation of ethene produces 1,2-ethanediol, (ethylene glycol) which
is used as antifreeze in cooling systems. Ethylene glycol lowers the freezing
point and raises the boiling point of water. It is also used in the manufacture of
magnetic tapes, photographic film and for making syntheic fibres.
The oxidation of ethene can be achieved by reacting ethene with cold, dilute
acidified potassium permanganate (KMnO4) or with oxygen/water:
CH2=CH2(g) +
Cold, dilute
H+ KMnO
/
4

CH2OH-CH2OH(l)
CH2=CH2(g) +
O2/H2O

CH2OH-CH2OH(l)
6. Reaction with benzene.
Ethene reacts with benzene to produce styrene which can then be used to make
polystyrene.
7. Production of polyethylene
The main use of ethene is to manufacture the polymer, polyethylene.

Some of the useful products made from ethylene are:
Product
Formula
Use
polyethylene
(CH2)n
plastic
ethylene oxide
(CH2)2O
steriliser
ethanol
C2H5OH
disinfectant
ethanoic acid
CH3COOH
food
preservative
Ethylene oxide
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Production of Materials- 1


Identify that ethylene serves as a monomer from which polymers are made.
Identify polyethylene as an addition polymer and explain the meaning of this
term.

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A monomer is a repeating unit which reacts to form a long polymer chain.
The reaction by which monomers become linked to form polymers is known
as polymerisation.
Addition polymerisation:
In addition polymerisation, the monomers simply add to the growing polymer
chain in such a way that all the atoms present in the monomer are also present
in the polymer.

Polyethylene is called an addition polymer.

Ethylene is polymerised to polyethylene


High pressures produce soft, low density polyethylene (LDPE) consisting of
tangled chains (with molecular masses < 100 000); used in flexible plastic
bags such as those used to store food.

Low pressures produce harder, high density polyethylene (HDPE) consisting
of aligned chains (with molecular masses > 100 000); used in crinkly plastic
bags as used for heavy duty garbage bags.

Outline the steps in the production of polyethylene as an example of a
commercially and industrially important polymer.

Two different forms of polyethylene can be manufactured, depending on the
reaction conditions.

To produce low density polyethylene (LDPE), a peroxide containing an O-O
bond that breaks easily forming free radicals is used to initiate the joining of
ethylene monomers. The process must occur under high gas pressure to
produce LDPE. These production conditions result in molecules with the short
branches that characterise LDPE.

To produce high density polyethylene (HDPE), low gas pressures and a
catalysts made of transition metals and organometallic compounds enables
more ordered orientation of ethylene to form the long unbranched and aligned
molecules in HDPE.

The difference in properties of the two forms are dependent on the degree of
branching of the polymer chains.
In LDPE the degree of branching is much greater and this reduces the
dispersion forces between strands. This results in soft, flexible, low density
plastics with relatively low melting points.

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Production of Materials- 1
This branching means that the polymer chains cannot pack as tightly together.
Consequently the density of the product is reduced.
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In HDPE the polymer chains can pack more closely together as a result
extensive dispersion forces exist between molecules. This gives HDPE
strength, toughness but makes it less flexible than LDPE.
The degree of branching and hence the density of the polymer is determined
by the conditions and catalysts used in the manufacturing process.
Production and Uses of LDPE
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Temperatures range from 100 - 300°C
Pressures range from 1500 – 3000 atmospheres
Initiators such as diethyl ether or benzoyl peroxide.
The polymerisation process consists of three stages: initiation, propagation and
termination.
1. Initiation
 The reaction is usually initiated with a catalyst, usually and organic peroxide.
These peroxides produce free radicals, a molecule with at least one unpaired
electron.
2. Propagation
The free radical is electron deficient and attacks the double bond in the ethene
molecule. This then produces an ethyl group with a free radical which can then
attack the double bond of another ethene molecule.
R-O + CH2=CH2  R-O-CH2-CH2
R-O-CH2-CH2 + CH2=CH2  R-O-CH2-CH2- CH2-CH2
A branch occurs when a chain curls back on itself and the free radical removes
a hydrogen froming a free radical in the chain.
3. Termination
Termination occurs when two free radical polymers react to form a covalent
bond. This is called a chain terminating reaction.
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Production of Materials- 1
Branching
• A branch occurs when a chain curls back on itself and the free radical removes
a hydrogen forming a free radical in the chain.

LDPE has a variety of uses. One of its main uses is for manufacturing of tough,
flexible, transparent film (cling wrap). It can also be moulded into soft, squeezable
plastic containers. LDPE is also used for insulation of wires and cables.
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Production of Materials- 1
Production and Use of HDPE

The polymerisation of HDPE uses an ionic catalyst called the Ziegler-Natta
catalyst. This consists of mixtures of compounds such as TiCl4 and Al(C2H5)3.
In this process ethene molecules are added to the growing polymer molecule on
the surface of the catalyst which reduces the amount of branching.
HDPE is used in the manufacture of gas pipes.
Due to its chemical resistance it can be moulded into containers for chemicals,
oils, detergents, petrol and solvents.
HDPE is used in toys, plastic buckets and playground equipment. It can also be
made into tough films such as freezer bags.
HDPE and LDPE are thermoplastic. They soften on heating.

Identify the following as commercially significant monomers:
-
vinyl chloride
styrene
by both their systematic and common names

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
Vinyl Chloride
Vinyl chloride is the preferred IUPAC name
Chloroethene is the systematic name
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Production of Materials- 1
Styrene
•
•

Styrene is the preferred IUPAC name.
Ethenylbenzene is the systematic name.
Describe the uses of the polymers made from the above monomers in terms of
their properties.

The table below provides the systematic and common names for some
commercially significant monomers. The table describes the properties that
account for the uses of some polymers produced from the selected monomers.
MONOMERS
Common
name
ethylene
vinyl
chloride
POLYMERS
Systematic
name
ethene
chloroethene
Name
Properties
Used for
LD polyethylene
low density,
soft
flexible
food bags
HD polyethylene
high density,
hard
crinkly
garbage
bags
polyvinylchloride
made rigid
and flame
resistant with
additives,
water
resistant
rigid pipes
and
gutters,
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flexible
raincoats
and
shower
curtains
garden
hoses,
kitchen
utensils,
furniture
Production of Materials- 1
covering.
styrene
ethenylbenzene
polystyrene
transparent,
due to few
crystals,
when gas
added forms
foam

compact
disc cases,
heat
insulation,
floats,
Styrofoam
cups etc,
drinking
glasses
Expanded polystyrene is made by producing gas bubbles inside polystyrene.
The low density of expanded polystyrene is used in flotation devices. The
trapped gas spaces make it an excellent insulator.
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Production of Materials- 1


Gather and present information from first-hand or secondary sources to write
equations to represent all chemical reactions encountered in the HSC course.

It is recommended that you write equations to represent the chemical reactions
as you gather information about them throughout this section of the module.
The information needed to write the equations might be gathered from firsthand investigations. You should check these against equations published in
secondary sources. For other reactions studied, write equations as a summary
of the chemistry involved.

When presenting equations in carbon chemistry, the emphasis is on showing
the structures of reactants and products, not on making sure that they are
balanced. The emphasis for this section of the syllabus is in showing structure
rather than in balancing equations.

The following are the equations that represent the processes presented in this
section of the syllabus:
Identify data, plan and perform a first-hand investigation to compare the
reactivities of appropriate alkenes with the corresponding alkanes in bromine
water .
Obtain Prac sheet and write up prac.
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Production of Materials- 1

Analyse information from secondary sources such as computer simulations,
molecular model kits or multimedia resources to model the polymerisation
process

You can simulate and then analyse the polymerisation process by using a
molecular model kit to construct a model of a long chain polymer from a
number of monomers, such as ethylene.
Begin with at least five separate models of the monomer. Initiate the
production of the polymer by changing the C=C double bonds of two
monomer models to C-C single bonds. Join the two reactive molecules with
one of the single bonds (electron pairs) released when a double bond changed
to a single bond. Continue this process to join the remaining monomers.
You will end up with a long chain like the following.
Remember that this simulation is a micro-view of a process that is repeated over and
over in the macro-production of a polymer. The many long chains produced are held
together by intermolecular forces or tangling of chains.
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