Unit 1: Chapter 5 - Products from Oils Flashcards
Cracking Hydrocarbons
Large hydrocarbons are less useful to us as fuels as they do not burn easily. Yet, there is an increasing demand for more fuels.
This can be resolved by a process called CRACKING.
This can be cracked by vaporizing the large hydrocarbon and is passed over STEAM and a CATALYST, which is then heated to a very HIGH TEMP. These split to form smaller, useful molecules.
Example of cracking:
Decane is a medium-sized molecule with 10 carbon atoms. When we heat it to 500C with a catalyst, it breaks down. One of the molecules that is formed is pentane.
C10H22 -> C5H12 + C3H6 + C2H4
The ending, ‘ane’ means it is an alkane.
The ending ‘ene’ shows it is an alkene (unsaturated hydrocarbon’)
UNSATURATED CARBONS (ALKENES)
CnH2n (NOTE: ‘n’ is not a specific term.)
Within alkenes is a DOUBLE BOND.
TESTING FOR ALKANES AND ALKENES
POSITIVE TEST:
unsaturated hydrocarbon + bromine water -> colourless product
NEGATIVE TEST:
saturated hydrocarbon + bromine water -> no reaction
Making Polymers from Alkenes
POLYMERIZATION: The process of joining thousands of monomers to form a polymer.
Changing ethene into a polymer:
The smallest unsaturated hydrocarbon molecule can be turned into a polymer known as poly(ethene).
This prefix can be added to many other alkenes. For example, propene can be turned into poly(propene). This forms a very tough plastic and is used to make carpets, milk crates and ropes.
H H H H H H H H
\ / | | | | | |
C=C + 2 more ethenes -> –C–C–C–C–C–C–
/ \ | | | | | |
H H H H H H H H
Note that no atoms are gained or lost in polymerization. It must also be noted that the double bonds are not then, but there are still 2 spaces missing on the sides of the poly(ethene).
New and Useful Polymers
Polymers have different properties for different purposes. Medicine is an area where polymers show great benefits. Some developments include:
- Softer linings for dentures (False teeth)
- New packaging material
- Implants that can slowly release drugs in a patients
LIGHT-SENSITIVE PLASTERS
Traditional plasters are uncomfortable when taking them off. Now the stickiness of the plaster can be ‘switched’ off.
HYDROGELS
Hydrogels are able to trap water with a matrix-like chain in the polymer. This can be useful for treating wounds as it would allow it to heal in moist, sterile conditions. This can treat burns.
This can also be used for contact lenses too.
SHAPE-MEMORY POLYMERS
A shape-memory polymer uses temperature of the body to make the thread tighten and close the wound. This is an example of a ‘smart-polymer’.
NEW USES FOR OLD POLYMERS
Bottles that are made out of PET are good for drinking bottles. It is strong, light, transparent and tough. This means they carry less for transport and are easier to carry around.
Recycled bottles can be recycled for polyester fibers, for clothing, fleece jackets and filling for duvet covers, School uniforms and football shirts are also made out of recycled bottles.
Plastic Waste
The problem of plastics is how resistant it is to decay and lack of reactivity. It takes hundreds are years to break down and take up valuable space in the landfill site.
BIO-DEGRADABLE PLASTICS (ADVANTAGES)
These plastics rot away more easily than normal plastic.
There is natural cornstarch built into the plastic to allow microorganisms to feed on the plastic.
Another plastic called Poly(lactic acid) can be made from cornstarch and it is totally bio-degradable, however limits its use as it CANNOT be put in the microwave.
Although, PLA can be mixed with normal plastic to make it stronger and makes it a lot easier to biodegrade faster.
Using plastics such as PLA helps preserve our supplies of crude oil. Crude oil is the raw material for many traditional plastics, such as poly(ethene).
DISADVANTAGES
Raise same issues as bio-fuels; biodegradable plastics large amounts of land for agriculture and may cause higher food prices in poorer countries as a result. This could lead to starvation.
There is also the issue of destroying tropical habitats of wildlife for more agriculture.
Some degradable plastics break down in light, however will not decompose in landfills. The best solution would probably to reuse existing carrier bags.
RECYCLING PLASTICS
Plastic waste can be awkward as it takes up a lot of space to transport. The energy savings are also less than other recycled materials. It would help if plastics would already sorted.
Ethanol
FERMENTATION
Ethanol can be made by FERMENTATION of SUGAR. Enzymes in the yeast break down the sugar into ethanol and CO2.
C6 H12 O6 -> 2C2 H5 OH + 2CO2
It can be used as a solvent and is used to clean brushes after using oil-based paints. It is also used to make perfume. It is also used as a fuel and can be mixed with petrol.
Requires batch process which takes a lot of time. This is a lot longer than a continuous process.
HYDRATION from ethene
Ethene is the main by-product of cracking and is used in industry.
Ethene + Steam -> (catalyst) Ethanol
- HIGH ENERGY + PRESSURE
- Reversible reaction - unreacted ethene and steam is needed to be recycled. The process is continuous, but produces NO WASTE PRODUCTS.
- Relies of crude oil, which is a non-renewable source.
