Production of Materials 1

Production of MaterialsPart 1: Fossil Fuel Products

Industrial Sources of EthyleneEthylene is a colourless, flammable gas with low solubility in water. It is a widely used raw material in the petrochemical industry, but very little ethylene occurs naturally in petroleum, so it is made by cracking.

Catalytic CrackingCatalytic cracking is the process where high molecular weight fractions from crude oil are broken into lower molecular weight substances to increase the output of products in higher demand. Oil refineries often do this to increase the production of gasoline by converting some of the fractions in lower demand.

The 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 ethylene or propene is formed (e.g. C5H10 C2H4 + C3H6). Thus, 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.

Thermal CrackingThermal or steam cracking is a process in which a mixture of alkanes with steam is passed through hot metal tubes (700 to 1000°C) 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, allowing 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.

The Double Bond of EthyleneEthylene is an alkene, so it has a very reactive double bond and is more reactive than its corresponding alkane. The double bond is the site of high electron density and molecules that are electron attracting readily combine with alkenes at this point (e.g. F, Cl). Alkenes often undergo addition, where molecular groups or atoms are added across the double bond. Ethylene can undergo several transformations, such as hydrogenation, halogenation, hydrohalogenation, and polymerisation and can be made into ethanol.

Polymerisation of EthylenePolymerisation is a chemical reaction in which many identical small molecules combine together to form one large molecule. For polymerisation to occur, the monomers must have a structure that can change to accommodate the additional bond between the two molecules. Ethylene serves as a monomer from which polymers are produced. The double bond of the ethylene monomer opens up to accommodate the additional bond needed to join the repeating subunits together.

Production of Materials 2

Addition polymerisation (chain growth polymerisation) is where the monomer adds to the growing polymer chain with the inclusion of all its atoms. The monomers are unsaturated and one bond in the double bond is broken, allowing the monomers to join together. The number of monomers range from 100 to 100000. This reaction requires a catalyst or initiator to start the process, but it proceeds quickly as it is a chain reaction.

Production of PolyethyleneWhen liquid ethylene is heated in the presence of a catalyst, the ethylene molecules join together to form a long chain called polyethylene. The number of monomer units present will range from 1000 to 50000 units.

The production of low density polyethylene (LDPE) occurs at temperatures of 100-300°C and at pressures of 1500-3000 atmospheres. The reaction is initiated by a catalyst (e.g. organic peroxides), which produces free radicals that are electron deficient. These attack and break the double bond of an ethylene monomer, so a covalent bond is formed between the radical and carbon. The resulting molecule is also a radical, which attacks another ethylene monomer and will propagate the process. A growing polymer chain terminates when two free radical polymers react to form a covalent bond.

The branching in LDPE means the polymer chains cannot pack as closely together, reducing the dispersion forces between the strands, resulting in soft, flexible, low density plastics with relatively low melting points. LDPE polymers are more transparent and are commonly used for cling wrap, plastic bags and containers for milk and juices.

The production of high density polyethylene (HDPE) requires temperatures of about 60°C and pressures of a few atmospheres and uses a Ziegler-Natta catalyst, on the surface of which ethylene molecules are added to the polymer chain, which reduces the degree of branching. HDPE is a linear polymer chain, allowing them to pack closely together and the dispersion forces between the chains hold them together tightly, resulting in durable and tough polymers. HDPE appears translucent or white and are used for containers, children’s toys and playground equipment.

Vinyl Chloride (Chloroethene)Vinyl chloride is the monomer used to produce the polymer polyvinyl chloride (PVC) through addition polymerisation. Pure PVC is not particularly useful as it is hard and brittle, tending to decompose when heated, but the inclusion of various additives have extended its range of uses. PVC that is softened is used for electrical insulation and garden hoses, while rigid forms of PVC are used for household items, drainage and sewage pipes, guttering and window frames.

Production of Materials 3

Styrene (Phenylethene) Styrene is the monomer used to produce the polymer polystyrene. It has a phenyl group that replaces a hydrogen atom in the ethylene molecule. Crystal polystyrene is a hard, brittle, clear plastic, which can be used in CD and audio cassette cases and clear plastic drinking glasses.

It is also produced as Styrofoam, which is produced by blowing gas through liquid polystyrene. It is used in foam cups and Eskies because of its insulating ability and in packaging as it can absorb the impact and remain strong when compressed.

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Part 2: Biomass Research

Alternative Sources of CompoundsThe raw materials for making polymers come from crude oil, but there is concern that oil reserves will be used up in the next few decades. Major uses of crude oil are for cars, planes and trains, while the petrochemical industry consumes only 3 to 5% of the total oil used in the world today. Thus, if energy and material needs are to be fulfilled in the future, alternative sources of these raw materials should be developed. A possible alternative is ethanol, which can be obtained from agricultural crops.

Condensation PolymersCondensation polymers are polymers that form by the elimination of a small molecule (e.g. water) when pairs of monomer molecules join together. It usually involves a reaction between 2 monomers with a functional group, such as a carboxylic acid, hydroxyl or amine group.

Polyesters are formed through the reaction of dicarboxylic acid and a diol with the dimers forming first and monomers adding to the dimer to increase chain length. (E.g. PET (polyethylene terephthalate) from 1,2 – ethandiol and terephthalic acid)

Polyamides are formed from the reaction of dicarboxylic acid and a diamine (NH2 functional groups). (E.g. Nylon 6 from 6-aminohexaonic acid)

Cellulose is a naturally occurring condensation polymer, which forms from the monomer β-glucose (C6H12O6), which can be written as HO-C6H10O4-OH. It is the single most abundant polymer in the biosphere, being a major component of plant material and hence, biomass, which is material produced by living things. The polymerisation occurs by the elimination of water molecules from between pairs of glucose molecules. This happens to up to 10000 glucose monomers to form a long cellulose chain.

The –CH2OH groups on C5 alternate on opposite sides of the chain, giving it a linear structure. The H-bonds between the chains result in long, strong cellulose fibres accounting for its strength and because of this and the linear structure, fewer –OH groups can interact with water, so cellulose is insoluble and resistant to chemical attack.

Production of Materials 5

Cellulose as a Raw MaterialEach glucose unit of cellulose has 6 carbon atoms joined together, so it can be regarded as a basic structure for making starting molecules for petrochemicals (incl. ethylene and propene). However, for this to occur, cellulose needs to be broken down into glucose, then ethanol and ethylene, but this is difficult as cellulose chains form H-bonds that result in compact fibres, making it difficult to break the glucose-glucose.

Cellulose can be broken down to glucose by digestion by cellulase enzymes or digestion with a strong acid. Thus, cellulose has the potential to be an alternative raw material, but the energy input required and the relatively higher cost than glucose from starch makes it currently unfeasible.

BiopolymersBiopolymers are polymers that are completely or mostly made by living organisms. They come in seven classes including polynucleotides, polyamides, polysaccharides, polyisoprenes, lignin, polyphosphate and polyhydroxyalkanoates. They are useful as they are available on a sustainable basis, renewable, non-toxic and usually biodegradable.

A useful polymer is PHB or Biopol, which involves the micro-organism alcaligenes eutrophus in its production. In its development, the rights to the biopolymer were frequently sold and transferred as it was too expensive to produce. Rights current lie with Metabolix, which is developing it on a large scale under the name Mirel.

The plastic producing bacteria are grown in fermentation vats and fed on molasses or methanol. The polymer is made by stressing the bacteria by removing nitrogen and oxygen from its environment. The plastic is extracted by using a hot solvent to break open the cell walls and separating the polymer from the cell debris. The amount of PHB the organism can produced is from 30 to 80% of its own dry weight. As it is biodegradable, it is commonly used in plastic bags, containers and packaging.

Production of Materials 6

Part 3: Renewable Ethanol

Ethanol as a Source of EthyleneEthanol has the structural formula CH3-CH2-OH, so it is an alkane with an H atom replaced with an OH functional group. Ethylene can be made from ethanol through the process of dehydration.

Dehydration is a chemical reaction where water is removed from a compound. Ethanol is dehydrated by heating it at 350°C with concentrated H2SO4 as a catalyst.

Hydration is the reverse reaction, involving the addition of water to ethylene to form ethanol. This occurs at 280°C using dilute H2SO4 as a catalyst.

Ethanol as a SolventEthanol is a good solvent for both polar and non-polar substances due to its structure. The polar OH end interacts with other polar molecules and forms dipole-dipole forces or H-bonds, favouring the solubility of polar solutes. The non-polar CH3-CH2- chain forms dispersion forces with non-polar solutes, favouring the solubility of non-polar solutes in ethanol. As such, ethanol is widely used in cosmetics, food colouring, antiseptics and cleaning agents.

Ethanol as a Renewable Resource and a FuelEthanol is a liquid that burns readily and is easily transportable and undergoes combustion to release carbon dioxide, water and heat, so it has 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 10 to 20%. As the ethanol molecule contains oxygen, the combustion is usually complete and toxic additives no longer have to be used.

Ethanol is considered a renewable resource as it is made from CO2, water and sunlight (through glucose present in cereal crops (e.g. sugar cane), which are renewable) and when burned, it produces CO2 and water, which are necessary for photosynthesis to produce glucose from which ethanol is derived.

Fermentation of SugarsFermentation is a process where glucose is broken down into ethanol and dioxide by the action of the enzymes present in the yeast. For it to occur, certain conditions are required including a suitable grain or fruit mashed up in water, yeast, warm temperatures and anaerobic conditions.

The starting material for the fermentation process is a carbohydrate (e.g. glucose, sucrose or starch). Enzymes first convert any starch or sucrose into glucose and other enzymes convert this into ethanol and carbon dioxide. Under normal conditions, fermentation can proceed until the ethanol concentration reaches about 15%.

C6H12O6 (aq) yeast→ 2CH3-CH2-OH (aq) + 2CO2 (g) + heat

Molar Heat of Combustion of EthanolThe molar heat of combustion of a substance is the heat liberated when one mole of a substance undergoes complete combustion at standard atmospheric pressure. For ethanol, this figure is 1367kJ mol-1

Production of Materials 7

Advantages and Disadvantages for the Use of Ethanol as a FuelAdvantages Disadvantages

No engine modifications needed for mixtures of less than 15% ethanol

Less greenhouse emissions and other pollutants than petrol

Toxic additives no longer required to promote the fuel’s even burning due to oxygen atom in ethanol

Renewable resource – obtained from fermentation of glucose

Non-toxic and breaks down into harmless substances when spilled

Large areas of land required to farm suitable crops to produce ethanol

Disposal of smelly waste from fermentation Lower energy content than petrol, so fuel

economy is reduced Expensive to produce due to high energy

input (not carbon neutral) Forms an azeotropic mixture with water, so

spills could contaminate waterways Possible damage to engine parts

Straight Chained Alkanols1) Methanol - CH3OH2) Ethanol - C2H5OH3) Propanol - C3H7OH4) Butanol - C4H9OH5) Pentanol - C5H11OH6) Hexanol - C6H13OH7) Heptanol - C7H15OH8) Octanol - C8H17OH

Production of Materials 8

Part 4: Electrochemical Methods

Displacement ReactionsA displacement reaction is an oxidation-reduction reaction where a metal converts the ion of another metal to the neutral atom. This occurs when a metal is placed into a solution containing ions of a less active metal. As a result, the metal will dissolve and the ions of the other metal will be reduced. Oxidation is the loss of electrons, while reduction is the gain of electrons.

The more reactive metal will displace the other metal from a solution of its ions. Therefore, a metal further to the left of the activity series oxidise more easily (e.g. Zn would displace Cu from a solution of its ions as it is more reactive)

Oxidation StatesOxidation states are a system of assigning numbers to atoms to keep track of the numbers of electrons transferred in redox reactions. An increase in the oxidation state indicates oxidation, while as decrease in the oxidation state corresponds to reduction.

Substances in its elemental form have an oxidation state of 0. Monatomic atoms are assigned the charge on the ion. The sum of the oxidation states of the atoms in a neutral molecule or ionic compound add up to 0. The sum of the oxidation states of atoms in a polyatomic ion is given the charge on the ion.

Galvanic CellsA galvanic cell is a device where a chemical reaction occurs in such a way that it generates electricity. A redox reaction can generate electricity when the oxidation and reduction half cells are separated 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 permits the transfer of ions to complete the flow of negative charge and to maintain electrical neutrality.

In its operation:1) The anode (site of oxidation) liberates electrons that flow through the external circuit to the

cathode (site of reduction) where the electrons are consumed2) Ions migrate through the salt bridge to maintain electrical neutrality

The electrodes are the 2 conductors connected through the external circuit. An electrolyte is a substance in solution or molten that conducts electricity.

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The Dry-Cell (Leclanche Cell)A dry cell consists of a zinc outer casing, which is the anode, an aqueous past of ammonium chloride and a mixture of carbon, manganese dioxide and ammonium chloride around a carbon rod, which is the cathode.

The oxidation half reaction is: Zn(s) Zn2+(aq) + 2e-

The reduction half reaction is: 2MnO2(s) + 2NH4+

(aq) + 2e- Mn2O3(s) + 2NH3(g) + H2O(l)

The overall reaction is: Zn(s) + 2MnO2(s) + 2NH4+

(aq) Zn2+(aq) + Mn2O3(s) + 2NH3(g) + 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. The cell initially has a voltage of 1.5 volts, but gradually decreases as the cell is used up.

The dry cell is relatively cheap and as the first commercially available battery, it has had a profound impact on society, allowing torches, portable radios, battery operated clocks, toys and portable electronic devices to be possible. It is best used for devices that only need small currents. The dry cell is robust, easy to store and use, making it practical to use. However, it has a low energy density for its size at 0.09kWh/kg, and is unable to deliver large currents required for some devices.

The dry cell has minimal impacts on the environment with manganese (III) readily oxidised to manganese (IV) oxide, which is stable and insoluble, so it become immobilised. Carbon and ammonium salts are harmless and small quantities of zinc are not an issue. Further, the dry cell is discarded after one use as it cannot be recharged and contributes to landfill. Also, the battery may develop leaks when it is used up as the zinc casing gets eaten away during operation.

Button Cell (Silver Oxide Cell) The button cell has an upper casing of Ag2O and Ag that acts as the cathode. The layer below this is an electrolyte solution of potassium hydroxide in a porous medium, which allows the cell to deliver a constant voltage over its lifetime as the concentration of this electrolyte solution doesn’t change during operation.

The oxidation half reaction is: Zn(s) + 2OH-(aq) Zn(OH)(s) + 2e-

The reduction half reaction is: Ag2O(s) + H2O(l) + 2e- 2Ag(s) + 2OH-(aq)

The overall reaction is: Zn(s) + Ag2O(s) + H2O(l) Zn(OH)(s) + 2Ag(s)

The button cell is very practical due to its small size and light weight. It also delivers a constant voltage over a long time and has a high energy density of 0.125kWh/kg. However, it is relatively expensive compared to other cells as it uses silver, which is an expensive metal. It has had a significant impact on society, allowing for the development of miniature products (e.g. watches, hearing aids), while its non-toxic nature allows for use inside the human body (e.g. pacemakers).

Production of Materials 10

However, as button cells cannot be recharged they are discarded after one use, contributing to landfill. The potassium hydroxide electrolyte is slightly caustic, but is only present in small quantities, so it is not a major issue. Otherwise, there are no highly toxic materials present that are likely to harm the environment.

Standard Reduction PotentialsOn the table of standard reduction potentials, anything on the right will react with anything on the left that is below it. The more positive the half-cell potential, the more likely it will be the reduction reaction.

Of the two half-cell equations, the one that is higher up in the table is reversed to become the oxidation half reaction and the sign of the Eo value is reversed. To add two half equations, electrons must balance, but voltages of half equations are not multiplied through. If the overall voltage is calculated to be positive, the reaction is spontaneous, but if it is negative, the reaction will not occur unless forced.

Production of Materials 11

Part 5: Nuclear Materials

RadioactivityRadioactivity is the spontaneous emission of radiation by certain elements from the disintegration of an unstable nucleus. For some elements, only some isotopes are radioactive, so they are termed as 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 protons in an atom are plotted against the number neutrons, a zone of stability can be established. For elements with Z < 20, stable nuclei tend to have a neutron to proton ratio of about 1, but as the atomic number increases, the neutron to proton ratio for a stable nucleus also increases. Points for unstable nuclei lie outside the zone of stability, with all nuclei with Z > 83 being unstable.

Types of Radioactive DecayAlpha emission involves the loss of 2 proton and 2 neutrons from the nucleus. When this occurs, the mass number decreases by 4 and the atomic number decreases by 2. All elements with an atomic number greater than 83 undergo this form of decay.

U92238 radioactive

decay→

Th90234 + He2

4

Beta emission involves a neutron that forms a proton and an electron, which is expelled from the nucleus. There is no change to the mass number, but the atomic number increases by 1. (High n:p)

C614 radioactive

decay→

N+ ¿714 e−1

0 ¿

Positron emission is the opposite of beta decay and occurs when a proton is converted into a neutron. There is no change to the mass number, but the atomic number decreases by 1. (Low n:p)

K1938 radioactive

decay→

Ar1838 + e1

0

Electron capture occurs when an inner orbital electron is captured by the nucleus, which converts a proton into a neutron. There is no change to the mass number, but the atomic number decreases by 1. (Low n:p)

Hg80201 + e−1

0 radioactivedecay

→

Au79201

Gamma emission involves the emission of high energy photons from the nucleus to lose excess energy from the nucleus and will usually accompany most other types of radioactive decay.

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Properties of RadiationAlpha particle (α ) Beta particle (β) Gamma rays (γ)Mass of 4amu Small mass of 5x10-4 amu No massLeast penetrating, travels about 5cm through air, easily stopped by a sheet of paper or skin

More penetrating, travel about 100cm through air, stopped by 5mm thick sheet of aluminium

Most penetrating, passes through several cm of lead or more than a metre of concrete

Strongest ionisation ability Medium ionisation ability Lowest ionisation abilityDeflected by both electric and magnetic fields

Deflected by both electric and magnetic fields

Unaffected by electric and magnetic fields

Move slowly at ~5% of c Move up to ~99% of c Travels at c

Transuranic ElementsTransuranic elements are those that come after Uranium on the Periodic Table and do not occur naturally on Earth. They are produced by bombarding heavy nuclei with high speed positive particles – usually nuclei of lighter elements.

Production of Commercial RadioisotopesIn a linear accelerator, positive particles are accelerated in a straight line along the axes of a series of cylinders made alternatively positive and negative (by alternating electric and magnetic fields) so the particles are always pushed from behind by a positive cylinder and pulled forward by a negative one.

Cyclotrons are similar to linear accelerators except that they use a strong magnetic field to constrain the particles in a spiral path to make the machine more compact (e.g. the National Medical Cyclotron at RPA produces radioisotopes 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 cannot be accelerated in a particle accelerator as it does not experience the electrostatic forces.

Detection of RadiationPhotographic 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 as the ionising radiation that it picks up causes the Argon gas molecules to ionise, with the gaseous cations and electrons produced being attracted to electrodes. The electron is accelerated towards the central electrode and as it gains energy, it ionises more argon atoms so there is a cascade of electrons reaching the electrode. 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 then operates an electric counter.

A cloud chamber is a container where the radiation interacts with a cold supersaturated alcohol vapour. The vapour condenses around ions that are formed during the ionisation of the air, so cloud like trails show the path of the radiation.

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Uses of RadioisotopesTechnetium-99m is a radioisotope used widely in medicine. It is a gamma emitter, used predominantly in medical tracer diagnosis, with a 6 hour half-life, meaning that exposure to radiation is minimised. It emits low energy gamma radiation, so damage to the human body is minimised and it can be detected using a gamma ray sensitive camera. It is often used in medical diagnosis of the heart, bone, lung, brain, thyroid and blood flow.

It can produce a number of oxidation states, enabling it to be readily combined with different chemicals to target specific parts of the body (e.g. when combined with tin, it attaches to red blood cells, allowing the examination of circulation and the heart).

Cobalt-60 is a radioisotope used widely in industry. It is a beta and gamma emitter with a 5.3 year half-life. It can be used to sterilise hospital supplies, irradiate food to kill micro-organisms, sterilisation of insect pests, detect of cracks and flaws in metal (e.g. castings and welds on aircraft and ships) and as the radioactive source in thickness gauges, by having a fixed level of radiation to be received by the detector as radiation loses energy as it passes through matter.

Its low energy emission and long half-life, ensures that the source does not need to be regularly replaced. It is usually used in a chemically inert form, reducing the amount of maintenance required.

Recent Discoveries of ElementsUnunpentium (Uup) was formed from experiments carried out throughout 2003 in Russia in a joint effort with the United States. Four nuclei were identified and was formed by bombarding the Americium nuclei with Calcium nuclei, though it decayed in less than a second by alpha decay.

Am+ Ca2048 → Uup115

28895243 +3( n0

1 )

Darmstadtium (Ds) was discovered in 2001 by Hofmann 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. It was made by bombarding the Lead nuclei with Nickel nuclei.

Pb+ ¿2862 → Ds110

26982208 + n0

1

Roentgenium (Rg) 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 and it is expected to have properties similar to gold. Generally, it has a half-life of 1.5 milliseconds, though three isotopes are known.

Bi+ ¿2864 → Rg111

27283209 + n0

1