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C1.5 - Other Substances from Crude Oil
Transcript of C1.5 - Other Substances from Crude Oil
A world of plastic
How many different uses of plastic can you spot?
The word ‘polymer’ comes from the Greek words poly (meaning ‘many’) and meros (meaning ‘parts’).
Polymers are very large molecules made when hundreds of monomers join together to form long chains.
Plastics are synthetic polymers that can be shaped by heat or pressure.
What are polymers?
The monomers in a polymer are joined together by covalent bonds between atoms.
In a covalent bond, each atom shares one or more electron with another atom. The bonds are sometimes shown as sticks.
What keeps the chain together?
Many polymers are formed from alkenes, which are a family of hydrocarbon molecules with the general formula CnH2n.
Alkenes contain at least one double covalent bond between carbon atoms. The double bond makes them very reactive.
What are polymers made from?
The simplest alkene is ethene (C2H4).
The second simplest alkene is propene (C3H6).
double covalent bond
How are monomers turned into polymers?
Natural and synthetic polymers
Polyethene (sometimes called polythene) is a polymer made from ethene.
The process by which polyethene and other polymers is made is called addition polymerization. This is because many monomers (ethene molecules) are added together.
How is polyethene made?
Drawing polymers – shorthand formulae
Polymers contain thousands of molecules, so how can their structures be easily drawn?
Part of the polymer molecule can be drawn:
A better way is to show a shorthand formula:
The ‘n’ means that the polymer contains a very large number of the repeating unit shown in the brackets.
What’s the polymer?
What is the shorthand formula for polypropene?
The monomer is propene (C3H6):
which can be drawn as:
1.Draw two C atoms that were in the double bond with a single covalent bond.
2.Draw the brackets and the ‘n’.
4.Add the atoms that were attached to each C atom of the double bond.
3.Add the links outside the brackets.
What’s the monomer?
What is the monomer of polyvinylchloride (PVC)?
1.Draw two C atoms joined with a double covalent bond.
2.Add the atoms attached to each C atom.
3.Draw the brackets and ‘n’.
The equation for the reaction can be drawn as:
What are the properties of plastics?
Plastics are all different, but they show a few general properties:
they do not conduct electricity and are poor conductors of heat
they are unreactive – most are not affected by water or air, and many are not affected by chemicals.
Why is the unreactivity of plastics both useful and problematic?
Their unreactivity makes plastics durable and able to safely contain and protect many substances. However, it also means that they persist in the environment for a long time.
lined-up chains make plastics dense, rigid and harder to melt (e.g. high-density polyethene).
The properties of plastics depend greatly on how the polymer chains are arranged:
branching chains make plastics light, soft and easy to melt (e.g. low-density polyethene)
What makes plastics different?
What factors might determine the properties of a plastic?
Temperature, pressure and catalysts affect the length and branching of the polymer chain.
The type of monomer used affects the type of forces between polymer chains.
Additives can ‘lubricate’ polymer chains, join them together with cross-links, or preserve them from decay.
Changing the properties of plastics
Cooked spaghetti is solid when cold, but soft when warm. The strands can slide past each other. It is the same with many polymers.
weak intermolecular forces – these let the chains slide past each other
What do polymer chains and spaghetti have in common?
What are thermosoftening plastics?
Plastics made of these polymers are stretchy and have a low melting point. They are called thermosoftening plastics.
Thermosoftening plastics (also called ‘thermoplastics’) do not contain cross-links.
Uses of thermosoftening plastics
This means they are flexible, stretchy and have a low melting point. It also means they can be moulded and shaped after they have been made, many times.
What are some examples of thermoplastics?
Plastics made of these polymers cannot be stretched, are rigid and have a high melting point. They are called thermosetting plastics (or ‘thermosets’).
strong intermolecular forces (cross-links) – these hold the chains firmly in place
Some polymer chains cannot slide past each other.
What are thermosetting plastics?
Thermosetting plastics contain cross-links. This means that they:
Uses of thermosetting plastics
What type of objects might you make from thermosetting plastics?
will break when bent
have a high melting point (they char rather than melt)
must be moulded into shape when they are being made,
uPVC is perfect for window frames as it is strong, light and durable.
chains packed tightly together
The ‘u’ stands for unplasticized, and means the polymer is rigid.
Adding a plasticizer lets the chains slide.
Oiling the chains?
How will the plasticizer change the polymer’s properties?
The polymer will be flexible, not rigid.
Matching polymers to their uses
In the UK, 3.5 million tonnes of plastic packaging is thrown away each year!
There are three ways to dispose of waste plastics:
Each method of disposal has its own advantages and disadvantages.
Why has the issue of dealing with waste plastic in a cheap and environmentally-friendly way become more important?
How much waste plastic?
Plastic bags are a major source of waste at landfill. British shoppers use over 8 billion of them a year!
Landfill is a convenient method of waste disposal but it is only designed to bury rubbish, not to break it down.
Most plastics are made up of tightly bonded molecules that cannot be decomposed by micro-organisms. These will remain buried at landfill sites for thousands of years without rotting.
The UK has 4,000 landfill sites and it is predicted that the largest of these will become full in less than 5 years.
What happens to plastics in landfill sites?
Landfill – pros and cons
Most plastic products carry a symbol that shows which type of polymer they are made from.
Many plastic items look and/or feel similar to each other but they are actually made from different materials, e.g. margarine tubs (polystyrene) and plant pots (polypropene).
Usually, the only types of plastic to be recycled are PET, PVC and HDPE.
If different polymers are mixed together during recycling, it can reduce the quality and value of the final recycled plastic.
How are plastics identified for recycling?
Recycling symbols for plastics
Recycling plastic uses less water and energy resources than in producing new plastics, and produces fewer greenhouse gases.
This is because the polymer chains become damaged or contaminated with food or other types of plastic.
What is the effect of recycling plastics?
One problem with recycling, however, is that is reduces the strength and versatility of the plastic over time.
Recycling – pros and cons
Biodegradable plastics are increasingly being used in carrier bags, bin bags and food packaging.
One of the problems with traditional plastics is that they do not break down when thrown away.
Biodegradable plastics are plastics that can be broken down. They are converted into carbon dioxide, water and minerals by micro-organisms.
Biodegradable plastics, such as polylactide, are plant-based polymers. They are often made from starch that has been
modified to become more stable.
What are biodegradable plastics?
what can businesses and individuals do to reduce the amount of waste they produce?
Dealing with waste is important, but there are many issues involved:
if more products are made of biodegradable plastics, how will the management of landfill sites change?
Dealing with waste
how many products could be made from biodegradable plastic?
what will happen to closed landfill sites in future?
– A substance that can be naturally broken down by micro-organisms.
– A chemical bond that joins one polymer chain to another.
– A molecule that is the building block of a polymer.
– A long chain molecule formed from many monomers joined together.
– The reaction used to convert monomers into a polymer.
– A type of plastic that is hard, rigid and has a high melting point.
– A type of plastic that is flexible, stretchy and has a low melting point.
The large hydrocarbon molecules in the heavier fractions can be broken down into smaller, more useful, molecules to meet demand for raw materials for fuels and plastics.
Crude oil often contains more heavier fractions than lighter fractions. Lighter fractions are more useful and therefore more desirable.
The amount of each type of fraction obtained by fractional distillation does not usually match the amount of each fraction that is needed.
Supply and demand
Alkenes are reactive molecules that are used to make plastics and other chemicals.
The hydrocarbon molecules are heated until they turn into vapour, and then mixed with a catalyst. The molecules break apart, forming smaller alkanes and alkenes.
Large hydrocarbon molecules can be broken down into smaller molecules using a catalyst. This is called catalytic cracking, and is an example of a thermal decomposition reaction.
The second simplest alkene is propene. It has the formula C3H6.
The simplest alkene is ethene. It has the formula C2H4.
Alkenes are very similar to alkanes, but they have one important difference: they contain at least one double covalent bond between carbon atoms.
Alkenes are a family of hydrocarbon compounds with the general formula CnH2n.
What are alkenes?
A test to distinguish between saturated and unsaturated compounds is to add red bromine water. In the presence of unsaturated compounds, the red colour disappears.
An unsaturated compound contains
at least one double covalent bond
between carbon atoms.
A saturated compound
only contains single covalent bonds
between carbon atoms.
Alkenes are examples of
Alkanes are examples of
Saturated vs. unsaturated
aluminium oxide catalyst
mineral wool soaked in oil
What might this gas be?
Catalytic cracking can be done in the laboratory by heating mineral wool soaked in oil with a catalyst, producing a gas.
Catalytic cracking in the lab
Other impurities that need to be removed include nitrogen, oxygen, water and dissolved metals.
One of the most important impurities to remove is sulfur. When burnt, this forms the gas sulfur dioxide, which causes acid rain.
An important step in refining is removing impurities from fractions. These can damage equipment that uses the fraction, and cause pollution.
True or false?
discuss the values of using products from crude oil as fuels or as raw materials for plastics and other chemicals
evaluate the social, economic and environmental impacts of the uses, disposal and recycling of polymers
identify the advantages and disadvantages of making ethanol from renewable and non-renewable sources.
Hydrocarbons can be cracked to produce smaller, more useful molecules. This process involves heating the hydrocarbons to vaporise them. The vapours are either
passed over a hot catalyst or mixed with steam and heated to a very high temperature so that thermal decomposition reactions then occur.
b) The products of cracking include alkanes and unsaturated hydrocarbons called alkenes. Alkenes have the general formula CnH2n.
c) Unsaturated hydrocarbon molecules can be represented in molecular and displayed fromulae
d) Alkenes react with bromine water, turning it from orange to colourless.
e) Some of the products of cracking are useful as fuels.
C1.5.1 Obtaining useful substances from crude oil - Topic Outcomes
What do the markings on plastic materials mean?