Download Production of Materials by Jimmy Huang

Module 1 - Production of Materials
Chapter 1 - Fossil Fuels Provide Energy and Raw Materials
Ethylene From Cracking Crude Oil Fractions
Cracking is the name given to the chemical process of breaking large hydrocarbon molecules
into smaller ones e.g. dodecane (C12H26) into octane (C8H18). Ethylene, or ethene, is a colourless
gas with the structural formula C2H4.
Catalytic Cracking
Catalytic cracking is the process in which high molecular weight fractions from crude oil are
broken into lower molecular weight substances in order to increase the output of high-demand
products. Oil refineries often do this to increase the production of gasoline through converting
some of the lower demand fractions.
This process occurs in a cat cracker, where alkanes with 15 to 25 carbon atoms per molecule are
broken down into smaller molecules (one alkane and one alkene) e.g. C15H32  C10H22 + C5H10.
The alkene further splits into smaller alkenes until either ethylene or propene (or both) is formed
e.g. C5H10  C2H4 + C3H6. Therefore, the overall products of catalytic cracking are alkanes of
shorter chain lengths and small alkenes.
The catalysts used are inorganic compounds known as zeolites, which are compounds of
aluminium, silicon, oxygen and other metal ions. The reaction is carried out at 500°C in the
absence of air and with pressures above atmospheric levels. The ethylene and propene which are
by products of catalytic cracking are starting materials for making plastics.
Thermal Cracking
Thermal or steam cracking is a process in which a mixture of alkanes with steam is passed through
hot metal tubes (700 to 1000°C) and at just above atmospheric pressure to decompose alkanes
completely into small alkenes such as ethylene, propene and butene. E.g. C11H24  4C2H4 + C3H6 +
H2.
Steam is present as an inert diluent i.e. it allows the process to occur at just above atmospheric
pressure while keeping the concentrations of the reacting gases low enough to ensure that the
desired result occur. Sometimes, the feedstock for thermal cracking is a mixture of ethane and
propane obtained from natural gas.
Usefulness of Ethene
The presence of a double bond in alkenes makes them much more reactive than alkanes. The
reactive double bond means it can converted to useful products such as ethanol and the starting
materials for plastics.
Polymerisation of Ethylene
Polymerisation is a chemical reaction in which many identical small molecules combine together
to form one large molecule. The small molecule is called a monomer, while the larger product is
called a polymer. These polymers are essentially long alkane molecules, with each molecule
containing from a few hundred to a few thousand monomer units.
In addition polymerisation, monomers add together in a growing chain so that all molecules
present in the monomer are present in the polymer. Monomers containing the double C=C bond
join together when the double bond is broken and the monomers join together. The number of
monomers involved range from 100 to 100,000. Such a process requires a catalyst or initiator to
start the process.
Production of Polyethylene
When liquid ethylene is heated in the presence of a catalyst, the molecules will join together to
form a long chain or polymer called polyethylene. The number monomer units present will range
from 1,000 to 50,000 units.
In low-density polyethylene (LDPE), the degree of branching is much greater meaning dispersion
forces between molecules are weaker, resulting in soft and flexible plastics. In its production, the
reaction is initiated by a catalyst (e.g. organic peroxides) which will produce free radicals which
are electron deficient. The radical will then attack the double bond, breaking this bond and
instead creating a covalent bond between the radical and carbon. This still results in a radical,
which attacks another ethylene molecule and continues the process. It is most often used for
'Glad Wrap', plastic bags and containers for milk etc.
In high-density polyethylene (HDPE), the presence of fewer side branches allow the chains to
pack closely together, thus creating more dispersion forces. This gives the plastic strength and
toughness but makes it less flexible. Its production requires the Ziegler-Natta catalyst, to which
ethylene molecules are added when the polymer chain is growing. It's properties make it suitable
for containers, children's toys and playground equipment.
Vinyl Chloride (Chloroethene)
Vinyl chloride is the monomer used to produce the polymer PVC (polyvinyl chloride) through the
process of addition polymerisation. It has the structure CH2=CH-Cl. Apart from polyethylene, PVC is
the cheapest and most widely used polymer.
PVC is used in electrical wire coating for its toughness and flexibility and also its ability to insulate. It
is also found in water pipes as it doesn't corrode and is easy to form into long tubes. Pure PVC is
not particularly useful as it is hard and brittle, though the inclusion of various additives allows it to
obtain favourable properties.
Styrene (Phenylethene)
Styrene is the monomer used to produce the polymer polystyrene. This includes a phenyl group,
which places one of the hydrogen atoms in the ethylene molecule. Although it comes in many
forms, the most common is Styrofoam, which is produced by blowing gas throughout liquid
polystyrene.
Polystyrene is used in foam cups due to its ability to insulate heat, as well as for packaging as it
absorbs contact well and is strong in compression. It can also be produced as a hard, clear, brittle
plastic which is often used in the manufacture of CDs, tapes and drinking glasses.
Chapter 2 - Reducing Dependence on Fossil Fuels
Alternative Sources of Compounds
The raw materials for polymers come from crude oil, though there is concern that oil reserves are
going to be used up in the next few decades. Major uses include for cars, planes and trains, and
the petrochemical industry consumers only about 3% to 5% to the total oil used in the world today.
A possible alternative is ethanol, which can be obtained from agricultural crops.
Condensation Polymers
Condensation polymers are polymers that form by the elimination of a small molecule (e.g. water)
when pairs of monomer molecules join together. This usually involves a reaction between two
monomers containing a carboxylic acid group and either an alcohol or an amine group.
Cellulose is a naturally occurring condensation polymer, which forms from the monomer glucose.
Glucose has the molecular formula C6H12O6, which can be written as HO-C6H10O4-OH. When the
monomers are joined together, HOH join together to form H2O and the remaining O bonds with
the C. This happens to all of the glucose monomers to form a long cellulose chain.
Cellulose is the major component of plant material or of biomass. Biomass can be defined as the
material produced by living things.
Cellulose as a Raw Material
Each glucose unit of cellulose has six carbon atoms joined together so it could be regarded as a
basic structure for making starting molecules for petrochemicals e.g. ethylene with two carbon
atoms and propylene with three carbon atoms.
However for this to occur, cellulose needs to be broken down into glucose and then into ethanol,
and this would require energy. The source of this energy would probably be from oil, which
defeats the purpose.
Biopolymers
Biopolymers are long chained compounds made from biobased materials, produced by living
organisms. They can come in a total of seven classes which include: polynucleotides, polyamides,
polysaccharides, polyisoprenes, lignin, polyphosphate and polyhydroxyalkanoates. They are
useful as they are available on a sustainable basis as it is produced from living organisms. Further, it
can be broken down naturally into CO2 and H2O.
A useful biopolymer is BHP or Biopol which involves the microorganism alcaligenes eutrophus in its
production. In its development, the rights to the biopolymer was frequently sold and transferred as
it was expensive to produce. Rights currently lie with Metabolix, which is developing it on a large
scale under the name Mirel. As it is biodegradable, it is frequently used in plastic bags and
containers etc.
Chapter 3 - The Availability of Other Resources from Renewable Resources
Ethanol As A Source of Ethylene
Ethanol has the structural formula CH3-CH2-OH, meaning it is an alkane with one H atom replaced
by the OH functional group. It is the most widely used alcohol, which is a family of carbon
compounds containing the OH group. Ethylene can be made from ethanol through the process
of dehydration.
Dehydration is a chemical reaction in which water is removed from a compound. Ethanol is
dehydrated by heating it with concentrated sulfuric or phosphoric acid which acts as a catalyst.
This catalyst is needed as the double bond in ethylene is highly reactive and will not form easily.
Hydration is the reverse reaction and in this case, involves the addition of water to ethylene to
form ethanol. It also needs heat and a catalyst, which is usually a dilute aqueous sulfuric acid.
Ethanol As A Solvent
Ethanol is a good solvent for both polar and non-polar substances due to its structure. The nonpolar CH3 end can dissolve non-polar substances through dispersion forces, while the OH end can
dissolve polar substances due to the powerful hydrogen bonding. For these properties, ethanol is
widely used in cosmetics, food colouring, antiseptics and cleaning agents.
Ethanol As A Renewable Resource and a Fuel
Ethanol is a liquid and burns readily, and has therefore been proposed as an alternative fuel for
automobiles. It is already used as a petrol extender as ordinary petrol engines can handle fuel
with an ethanol content of between 10% and 20%. In Brazil in the 1980s, up to 94% of new vehicles
sold were run exclusively on ethanol.
It is said to be a renewable resource as it is made through CO2, water and sunlight (via glucose)
and when it is burnt, it returns to carbon dioxide and water. This makes it a carbon neutral fuel, as
the CO2 released is similar to the amount used up in its synthesis. Further, the oxygen present in
ethanol means that toxic additives no long have to be used. However, large areas of land would
be required to produce suitable crops to produce ethanol, and there would be requirements to
remove different forms of waste produced.
Fermentation of Sugars
Fermentation is the process through which glucose is broken down to ethanol and CO2 by the
action of enzymes present in yeast. Until 60 years ago, the fermentation of sugars and starches
from plant material was the major source of ethanol. It is an exothermic reaction.
For it to occur, it requires a suitable grain or fruit mashed up in water, yeast, warm temperatures
and the exclusion of oxygen. Enzymes first convert any starch or sucrose into glucose, and then
other enzymes convert this into ethanol and carbon dioxide. Under normal conditions,
fermentation can proceed until the ethanol concentration reaches about 15%.
C6H12O6 (aq)  2CH3-CH2-OH (aq) + 2CO2 (g)
Heat of Combustion of Ethanol
The molar heat of combustion is the heat liberated when one mole of a substance undergoes
complete combustion with oxygen at standard atmospheric pressure. For ethanol, this figure is
1360 kj mol, or about 29.7 kj per gram of ethanol.
Advantages and Disadvantages for the use of Ethanol
Advantages
 Renewable resource - obtainable

from fermentation of glucose
 Sugar cane farms will capture CO2

released when ethanol is burnt
 Ethanol will mix with water and

form a dilute mixture in the event

of a leakage
Straight Chained Alkanols
1) Methanol - CH3OH
2) Ethanol - C2H5OH
3) Propanol - C3H7OH
4) Butanol - C4H9OH
5) Pentanol - C5H11OH
6) Hexanol - C6H13OH
7) Heptanol - C7H15OH
8) Octanol - C8H17OH
Disadvantages
Large areas of land are required
to farm sugar cane
Ethanol will escape if it mixes of
water in the event of a leakage
It has a lower density level
Currently production of ethanol is
more expensive than extraction
from fossil fuels
Chapter 4 - Oxidation and Reduction Reactions As A Source of Energy
Displacement Reactions
A displacement reaction is an oxidation-reduction reaction in which a metal converts the ion of
another metal to the neutral atom. This will occur when a metal is dropped into solution
containing ions of a less active metal. As a result, the metal will dissolve and the ions of the other
metal are deposited out of solution. Oxidation is the loss of electrons while reduction is the gain of
electrons. Oxidation-reduction reactions are also called redox reactions and electron transfer
reactions.
Displacement Reactions and the Reactivity Series
The more reactive metal is the one that will displace the other metal from a solution of its ions. In
other words, the metal further left on the activity series will lose electrons more easily and is easily
oxidised. According to the above example, Zn is to the left of Cu on the activity series.
NOTE:
Oxidation Is Loss, Reduction Is Gain (Oil Rig)
Oxidation occurs at the anode, reduction occurs at the cathode (An ox, red cat)
Oxidation States
For monatomic atoms, the oxidation state of the element is the charge on the ion e.g. the
oxidation state of copper in Cu2O (2Cu+ O2-) is +1 and the oxidation state of iron in FeS (Fe2+ S2-) is
+2.
The oxidation state of an element present in its stable elemental state is zero, regardless of the
formula of the molecule of the element. An increase in oxidation state corresponds to a loss in
electrons (i.e. oxidation) while a decrease in oxidation state corresponds to a gain of electrons
(i.e. reduction).
Galvenic Cells
A galvanic cell is a device in which a chemical reaction occurs in such a way that it generates
electricity. A redox equation can generate electricity when the reduction and oxidation reactions
occur at different locations and there is a wire for the electrons to pass through.
A cell can be constructed by suspending a strip of copper metal in a beaker of copper sulfate
and suspending a strip of zinc metal in a beaker of zinc sulfate. The wire connecting the two
electrodes allows the transfer of electrons while the salt bridge allows the transfer of ions.
When it produces electricity:
1) One electrode liberates electrons which flow out into the external circuit
2) These electrons flow through the metallic conductor to the other electrode
3) The reaction at the other electrode consumes these electrons
4) Ions migrate through the solutions and the salt bridge to maintain electrical neutrality
The electrodes are the two pieces of metal that are connected through the external circuit. An
electrolyte is a substance which in a solution or molten conducts electricity i.e. the solutions in a
galvanic cells are electrolytes. The chemical reactions occurring at the electrodes are called
electrode processes/reactions. The anode is the electrode at which oxidation occurs and the
cathode is the electrode at which reduction occurs.
Dry Cell (Leclanché Cell)
A dry cell is the most common and cheapest form of battery, and is widely used in torches, radios
and cameras. It consists of a zinc outer casing, which is the anode or negative terminal, an
aqueous paste of ammonium chloride and a mixture of powdered carbon, manganese dioxide
and ammonium chloride around a carbon rod which is the positive terminal.
At the negative terminal, the oxidation half reaction is:
Zn(s)  Zn2+(aq) + 2eAt the carbon rod (positive terminal), the reduction half reaction is:
2MnO2(s) + 2H+(aq) + 2e-  Mn2O3(s) + H2O(l)
Initially, no zinc chloride is present but as the cell is used, zinc ions are formed and ammonium ions
are discharged. Manganese is reduced from an oxidation state of +4 to +3. This cell initially has a
voltage of 1.5 volts but this gradually decreases as the cell is used.
The cell is relatively cheap and as the first commercially available battery, it has had a profound
impact on society as it has allowed torches, portable radios and battery-operated clocks and
toys possible. Today, it is best used for items that only require small currents and also, it is relatively
easy to store and use. Another benefit is the minimal impact that it has upon the environment. The
manganese is readily oxidised to a stable insoluble manganese (IV) oxide and so becomes
immobilised. Small quantities of zinc are not an issue and ammonium salts and carbon are
harmless.
However for its size, the dry cell does not contain a lot of electricity (low energy density) and is
unable to provide a large current that might be required for many uses. Further, the ordinary dry
cell has to be discarded after one use as it is not rechargeable and this contributes to the waste
humans dump into landfill. Also, the battery may leak when it becomes flat with the zinc casing
being eaten away during operation.
Button (Silver Oxide) Cell
The silver oxide or button cell is a small cell that is widely used in miniature appliances such as
watches, hearing aids and calculators. Despite being small, they can provide considerable
amounts of electricity at a very constant voltage over long periods of time.
The oxidation reaction at the anode is:
Zn(s) + 2OH–(aq) → Zn(OH)2(s) + 2e–
The reduction reaction that occurs at the cathode is:
Ag2O(s) + H2O(l) + 2e-  2Ag(s) + 2OH-(aq)
The button cell is very practical due to its small size and tendency to be light weighted. However,
it may be relatively expensive compared to other dry cells for its size due to the presence of silver,
which is an expensive metal. However, it has still had a profound impact on society. Its small size
has allowed for the development of miniature products e.g. watches. Also, its non-toxic nature
has allowed its use inside the human body e.g. it is frequently used in pacemakers etc.
After one use, button cells have to discarded as they cannot be recharged, though they provide
a constant voltage throughout their usage. The potassium hydroxide used in the form of paste is
slightly caustic though it is only present in very small quantities. Otherwise, there are no highly toxic
materials present that are likely to harm the environment.
Standard Reduction Potentials
Any galvanic cell can be considered as two half cells, with each half-cell consisting of both a
reactant and its oxidised or reduced protect (i.e. a couple). An individual voltage known as a half
cell potential can be assigned to each half-cell couple to measure the relative tendency of the
more oxidised form of the couple to gain electrons.
Reduction potentials are usually measured under standard conditions and are therefore called
standard reduction potentials. A measure of the reduction potential for a half-cell can only be
obtained by joining it with a common or reference couple i.e. the H+ and H2 couple.
The cell potential or the electromotive force of a galvanic cell is the potential difference (in volts)
between electrodes. It can also be considered to be the maximum voltage the galvanic cell can
deliver. It can be calculated by finding the difference in reduction potentials of the couples
involved in the two half-cell reactions.
A redox reaction can only take place if the cell potential E° has a positive value. However, this
does not guarantee that a redox reaction will take place. If the E° is calculated to be negative for
a particular redox reaction, the reaction will not take place to any appreciable extent.
Chapter 5 - Nuclear Chemistry Provides Metals
Radioactivity
Radioactivity is the spontaneous emission of
radiation by certain elements. For some elements,
all isotopes are radioactive while for others, only
some isotopes are radioactive. For this reasons, we
use the term radioisotopes.
The radioactive emission comes from the nucleus
of the isotope. Therefore unstable nuclei are
radioactive and stable nuclei are not radioactive.
If the number of protons are plotted against the
number of neutrons, we can establish a band of
stability.
For lighter elements (Z < 20), stable isotopes have
a ratio of neutrons to protons of about 1.0. At Z =
50, the ratio is about 1.3 and at Z = 80, it is about
1.5. Points for unstable nuclei lie outside this zone.
Further, there are no stable isotopes with atomic
numbers greater than bismuth.
Types of Radioactive Decay
Alpha emission involves the emission of an alpha particle (helium nucleus) from the unstable
nucleus. When this occurs, the atomic mass decreases by 4 and the atomic number decreases by
2. All elements with an atomic number greater than 83 and some lighter elements undergo this
form of decay.
Beta emission involves the emission of a beta particle (electron) from the nucleus. This process
involves the conversion of a neutron into a proton and an electron. The electron is expelled
immediately from the nucleus.
Positron emission involves the release of a positron, or a particle that has the same mass of an
electron but with a positive charge. Positrons are produced when protons are converted to
neutrons and is the opposite of beta decay in that the atomic number decreases by one.
Electron capture occurs when one of the inner-orbital electrons is captured by the nucleus. This
has the effect of converting a proton to a neutron.
Gamma emission involves the emission of high-energy photons from the nucleus. In this way, the
nucleus can lose excess energy and this will usually accompany most other types of radioactive
decay.
Transuranic Elements
Transuranic elements are elements that come after element 92 (uranium) on the periodic table.
They are not found naturally and are produced in nuclear reactors when protons are shot into the
nucleus of atoms. All transuranic elements are radioactive isotopes.
Scientists have been able to produce elements with atomic numbers up to 118. The later ones
were made by bombarding high speed positive particles (e.g. helium) with heavy nuclei (e.g. U238).
Production of Commercial Radioisotopes
In a linear accelerator, positive particles are accelerated in a straight line along the axes of a
series of cylinders made alternatively positive and negative. This means particles are always
pushed behind by a positive cylinder and pulled forward by a negative one. This allows the
production of transuranic elements by bombarding heavy nuclei with high speed positive
particles.
Cyclotrons are similar in that they accelerate positive particles, though they do so in a spiral path
and therefore save space. It uses a strong magnetic field to force the particles into a spiral path
e.g. the National Medical Cyclotron at RPA produces radio-isotopes for medicine.
Nuclear fission reactors are a source of neutrons that are readily absorbed by the target nucleus
and do not need to be accelerated. As neutrons are uncharged, they do not experience the
strong electrostatic repulsive forces associated with bombardment by positively charged
particles.
Detecting Radiation
Photographic film indicates the presence of radioactivity when it darkens. This was the first way
radioactivity was detected. These are used on the radiation badges of laboratory workers, with
the degree to which the film has darkened being an indicator of their exposure.
A Geiger-Muller counter works when a beta ray enters through the thin end of the Geiger tube,
hits a gas molecule and ionises it by knocking an electron out. This electron is accelerated
towards the central electrode and as it gains energy, it ionises more argon atoms so there is a
cascade of electrons. This constitutes an electrical pulse which is amplified and measured through
clicks or a digital counter.
A scintillation counter uses the fact that when certain substances are exposed to radiation, they
emit a flash of light which can be collected and multiplied with a photomultiplier. The electrical
signal generated can then operate an electric counter.
Uses of Radioisotopes
Technetium-99 is a radioisotope used widely in medicine. It emits gamma radiation after it has
entered into someone's body, allowing imaging to be completed using a gamma camera.
Chemical properties allow it to be combined with other elements in order to examine specific
parts of the human body e.g. when combined with tin, it attaches to red blood cells, allowing the
examination of blood flow and the heart.
Technetium emits low energy gamma radiation, meaning damage to the human body is
minimised. Further, it has a short half life of approximately 6 hours, which is practical and minimises
the exposure of the patients to the radiation. Also, it is reasonably reactive, allowing it to be
combined with the different elements
Strontium-90 is used in industry as an emitter in thickness gauges as radiation loses energy as it
passes through matter, depending on thickness and density. If the material is too thick, less
radiation passes through to the detector. This can be combined with other processes e.g. in the
manufacture of paper.
As it has a half life of 28.8 years, it is practical as an emitter and does not have to be regularly
changed for operation. It is most often used in a chemically inert form, further reducing the
amount of maintenance required.
Recent Discoveries of Elements
Ununpentium (Uup) was formed from experienced carried out throughout 2003 in Russia in a joint
effort with the United States. Four nuclei were identified, though the claim has not yet been
ratified by IUPAC. It was formed through bombarding the Americium nuclei with calcium nuclei,
though it decayed in less than a second by alpha decay.
243Am
+ 48Ca  288Uup + 31n
Darmstadtium was discovered in 2001 by Hofmaan et al at GSI, Darmstadt in Germany. Such an
element is not present in the environment and only a few atoms have ever been made. It is
expected to have similar properties to platinum.
208PB
+ 62Ni  269Ds + 1n
Roentgenium was discovered on the 8th of December 1994 at GSI, Darmstadt in Germany after an
eighteen day experiment. Only a few atoms have ever been made, though it is expected to have
properties similar to gold. Generally, it has a half life of 1.5 milliseconds, though three isotopes are
known.
209Bi
+ 64Ni  272Rg + 1n