Crude Oils as fuels
Branched and cyclic alkanes are the best fuels.They promote efficient combustion.
However hydrocarbons can lead to an increase in:
- Carbon Dioxide- a greenhouse gas
- Carbon Monoxide- a toxic gas that stops haemoglobin from picking up oxygen.
- Sulphur Dioxide- a contributor to acid rain
- Nitrogen Oxides- acid rain and the destruction of forests.
Global warming could cause climate change, with heavier rain, more frequent storms. Polar ice caps melting raising sea levels.
A fuel derived from recently living material such as plants or animal waste.
Key crops for biofuels are sugar cane and **** seed.
Ethanol can be made from fermenting sugar and other carbohydrates, using yeast producing zymase catalyst. It can be used in car engines without any modifications, and reduces harmful exhaust gases.
Advantages over alkenes to ethanol
- sustainable reactants- alkenes come from crude oil.
- Completed at lower temperatures and pressures. 37 degrees celcius, and 1atm v 300 degree celcius and 70 atm.
- These higher temperatures and pressures are expensive to maintain, and also can be dangerous.
- yeast dies at alcohol concentration of 13% so has to be replaced- not continuous process.
- Produces less pure ethanol than hydration.
fossil fuel combustion and global warming
Fossil fuels relase a lot of carbon dioxide in the air. Greenhouse gases absorb radiation by vibrating and then passing on the radiation to another nearby molecule. This keeps heat close to the surface of the Earth.
Carbon Capture and Storage CCS
- Underground porous rock
- Deep beneath the sea
- In old oil and natural gas field- this can also help extract the last 30% of oil.
- Reacted with metal oxides to make metal carbonates -- however very slow and energy intensive.
Pollutants from car engines
Combustion engines produce:
- Carbon Monoxide- produced by incomplete combustion. It can bind to hameoglobin and can be fatal. Also cause symptoms like decreased manual dexterity, disturbed vision and tiredness.
- Nitrogen Oxides- produced by nitrogen in the becoming oxidised under high temperatures. It can cause low-level ozone, and also becomes nitric acid, contributing to acid rain. They are also respiratory irritants.
- Unburnt Hydrocarbons- some are human carcinogens.
- Low level ozone- causies breathing difficulties and a susceptibility to infections.
1-Oxidation catalysts- reduce diesel engines production of carbon monoxide and unburnt hydrocarbons, by adding oxygen.
2CO + O2 > 2CO2
C12H26 + 18.5O2 > 13H20 + 12CO2
Three-way catalytic converters
Fitted to petrol engines
2CO +2NO > N2 and 2CO2
How it works:
- Hot gases are passed over the metal catalyst (e.g. rhodium, palladium and platinum) and are absorbed onto the surface.
- Temporary bonds form between the metal and the gases, weakening old bonds, and new covalent bonds are made (e.g. the gases react.)
- The products are the desorbed from the surface.
crude oil processing
Short chain alkanes and alkenes are more useful as fuels and for polymers than long chain alkanes. Therefore long chained hydrocarbons are broken down by cracking.
First they used metal oxide catalysts (e.g. Al2O3) but now a zeolite catalyst and temperatures of 450 centigrade is used.
Straight chained alkanes into branched alkanes. No change in formula.
Making cyclic hydrocarbons. Prodcues alot of H2, and has the same empirical formula as alkenes.
Both branched and cyclic hydrocarbons promote efficient combustion. The hydrodgen made from reforming is used in ammonia production and margarine production.
Actual yield of product x100 Theoretical yield of product
Why isnt it the theoretical amount?
- Not fully reacted - incomplete combustion
- By products formed/ product impure
- Reaction reached equilbrium
- Some product left in equipment
Molecular mass of desired product x100 Molecular mass of all products
By products can be wasteful, and exensive to get rid off, or useful and can be sold.
Addition reactions have atom economy of 100%, subsitution/elimination has less than 100%.
CFC's and ozone depletion
First used in refrigerators CFC's have now become a key problem in ozone depletion. This leads to increased UV and short wave radiation reaching Earth, and increasing skin cancer.
alternatives to CFCs
HFCs/ HCFC's/hydroflourocarbons are now used, but still play a role in ozone depletion.
Other halogen containing substances
Carbon-flourine bonds are very strong making PVCs and PTFEs very strong and resistant to chemical attack. It also has non-stick properties and heat resistance, and so is often used to coat pans.
The ozone layer filters different levels of UV radiation. It filters 5% of UV-a, which isnt damaging, 95% of UV-b which can cause skin cancer, and 100% of UV-c.
Formation of ozone:
O2 is split by homolytic fission to form two oxygen radicals.
O2 >>> 2O*
One of these oxygen radicals joins onto O2 molecule to make O3 and heat energy.
O2 + O >>> O3 and heat
How ozone works:
Basically the opposite of the above happens continously. This works by converting all UV radiation into heat energy.
O3 + UV >>> O2 +O
CFC's and Ozone
CFC molecule splits into a chlorine radical and a halogenoalkane radical.
The Cl radical catalyses the reaction converting O3 into O2.
O3 + Cl* >>> O2 + ClO*
ClO* + O >>> Cl* and O2
Overall equation is O3 +O >>> 2O2
Nitrogen Oxides (NO*) from lightning or aircraft engines also break down ozone:
NO* + O3 >>> NO2* +O2
NO2* +O >>> NO + O2 THE CATALYST IS STILL A RADICAL AFTER STEALING FIRST O.
Uses for different polymers
- Poly(phenylethene)-used for foam packaging, insulation and in the food trade.
- Poly(propene)- food packaging, carpet fibres and is very resistant to chemcial attack.
- poly(ethene) - widely used for shampoo bottles to plastic bags.
Polymers are very unbiodegradable, making them difficult tlo get rid off. However, any also contain colourants, and chemicals that contain harmful ions.
Sorting- Polymers must be sorted before recycling, because a slight combination of polymers can make a final products unusable.
Reclamation- Plastics are cut into small flakes, which are washed, then melted down to make new products.
More Polymers and waste
Polymers as fuel source:
Burning them under controlled conditions can release heat energy, which can be harnessed to make electricity.
Converting polymers into synthesis gas, a mixture of hydrogen and carbon monoxide. This is used as chemical feedstock to make products, or for fuel at oil refineries.
High chlorine conent makes it problematic. We dissolve chlorine in organic solvents, to separte it from other fumes, then make it into a precipitate and use it for coatings of electrical wiring.
Derived from sustainable raw materials, they can be broken down by bacteria to make CO2 and H2O.
Sustainability and Green Chemistry
By 2006,197 nations had signed up to this agreement, where CFC's were almost entirely banned.
Philosophies of green chemistry are below:
- Using renewable resources
- Saving money
- Preventing waste
- Maximising Atom economy
- Recycling and biodegradability- all products should be easily disposed of.
CO2 and its uses
CO2 isnt just a bad greenhouse gas; it has many good uses too, which is good because a lot of it is made as a byproduct of fermentation.
CO2 replaced CFC's in making foam, and there is not net increase of CO2 as the byprodyct is used.
CO2, under specific conditions, becomes a supercritical fluid, and a solvent. This works at 31 centigrade, and helped replace toxic or volatile organic solvents.
CO2 is also used to extract caffeine from coffee. This also uses supercritical CO2, and removes 97% of caffiene, but no flavouring, and there is no problems with toxicity. It is also used to extract the characteristic beer flavour from hops.
Supercritical CO2 is aslo used in dry cleaning instead of chlorinated hydrocarbons, removing toxic materials from waste and chemical synthesis.