Fossil + Biofuels Flashcards
Fuel definition
- a substance that burns in oxygen to release a usable amount of energy
- a substance with stored energy that can be released for use as heat or power
Carbon neutral
doesn’t result in any net production of carbon dioxide from sourcing or consumption
Renewable
can be replenished at a rate equal to or faster than consumption
*a fuel is considered non-renewable if it cannot be replenished at the rate at which it is consumed
Renewable Energy Sources
Solar
Hydropower
Tidal + wave power
Wind turbines
Geothermal
Biofuels
Photosynthesis
- the process that converts light energy into chemical energy and as a source of glucose and oxygen for respiration in living things
6CO2(g) + 6H2O(l) → C6H12O6(aq)+ 6O2(g)
carbon dioxide + water gives glucose and oxygen
Cellular Respiration
- oxidation of glucose as the primary carbohydrate energy source
C6H12O6(aq) + 6O2(g) → 6CO2(g) + 6H2O(l)
glucose + oxygen gives carbon dioxide + water
*opposite to photosynthesis
Flashpoint
-Lowest temperature at which a particular organic compound gives off sufficient vapours to ignite
-Low flashpoint means it can ignite at a fairly low temperature
-Low flashpoint also means it gives off vapours (turns into a gas) at a fairly low temperature → corresponds with low melting & boiling points
Fossil Fuels
- Formed in the earth’s crust from plant / animal remains
- decomposition of buried dead organisms- plant and animal matter
-Takes millions of years
-Needs intense heat & pressure
- Eg crude oil, coal seam gas, petrodiesel
-Non renewable → finite
- contain carbon + hydrogen
Petrodiesel
- fossil fuel
- Mixture of straight chain + branced alkanes & aromatics (containing benzene rings)
- High energy density
Biofuels
-Sourced directly from organic matter
-More carbon neutral than fossil fuels because the organic matter they’re made from (plants) consumes carbon dioxide for photosynthesis while growing, so when converted into biofuel, this partially offsets the carbon dioxide released in combustion. Hence, the NET amount of carbon dioxide released into the atmosphere is less than fossil fuels.
- plant materials used to generate these fuels are produced via photosynthesis, removing carbon dioxide from the atmosphere
- renewable
- predicted to have less impact on the environment than fossil fuels
-Not completely carbon neutral b/c transporting, harvesting, etc can produce carbon dioxide too
-Renewable because they can be replenished at a rate greater than or equal to consumption
Biogas
- Formed from the breakdown of organic matter (algae, crops, wood, compostable garbage) in absence of oxygen
- By anaerobic bacteria e.g compost bin
- Mostly methane (approx 60%), but also some carbon dioxide
- rubbish tips, sewage, piggeries, food processing plants
Bioethanol
-Fermentation of glucose from plant matter (usually agricultural waste eg wheat, corn, sugarcane pulp) using yeast which is produced by an enzyme
-Glucose → ethanol + carbon dioxide
C6H12O6 (aq) gives 2CH3CH2OH (aq) + 2CO2 (g) (EXOTHERMIC)
-This ethanol is then distilled to produce bioethanol
Why are biofuels carbon neutral?
the organic matter they’re made from (plants) consumes carbon dioxide while growing, so when converted into biofuel, this partially offsets the carbon dioxide released in combustion. Hence, the NET amount of carbon dioxide released into the atmosphere is less than fossil fuels.
What is the composition of biogas?
Mostly methane (60%), some carbon dioxide
What happens after fermentation of glucose to produce bioethanol?
The ethanol produced is distilled to isolate bioethanol
Why are fossil fuels non-renewable?
- Take millions of years to form
- So cannot be replenished at a rate greater than or equal to consumption
What is the chemical equation for cellular respiration?
C6H12O6(aq) + 6O2(g) → 6CO2(g) + 6H2O(l)
Biodiesel
- a renewable fuel made from animal fats or oils from crops (eg leftover oil after deep frying)
- The reaction between fat + a small alcohol molecule such as methanol is known as transesterfication
- Fatty acid methyl esters
- The fatty acids are reacted with methanol, using a catalyst like KOH
Transesterfication
exchanging the organic functional group of an ester with the organic group of an alcohol
What are the differences in properties between biodiesel and petrodiesel?
BIODIESEL:
- polar ester linkage and longer chain length, so can form both dispersion and dipole dipole forces.
- stronger intermolecular forces, so more tightly packed molecules, so more viscous
- renewable
- less energy dense
- hygroscopic because ester link can form hydrogen bonds with water molecules
PETRODIESEL:
- straight chain + branched alkanes and aromatics, so can only form disperson forces
- less viscous so flows better through fuel lines, and in colder conditions
- non renewable
- more energy dense
- less hygroscopic, so can be stored longer without absorbing water and deterioriating
Biodiesel advantages + disadvantages
ADVANTAGES
- Can be more carbon neutral
- Does not contain sulfur → not released into the atmosphere during combustion (can cause acid rain)
- Burns more completely (the C=O makes it easier to oxidise/combust)
DISADVANTAGES:
- Hygroscopic → absorbs water → can freeze and form chunks of ice in the fuel, can corrode engines
-gels/crystallizes at a higher temp → more viscous sooner than petrodiesel → unsuitable for cold climates
-Lower energy content
Cloudpoint
- Temperature below which the waxy components in diesel start to separate and precipitate out, giving the diesel a cloudy appearance.
- Biodiesel has a higher cloudpoint than petrodiesel, meaning it starts to form wax at a higher temperature
- Let’s say this temperature for biodiesel in 0 degrees. This means that once the temperature gets into the minuses, tiny tiny particles of wax form in the fuel, which can impact its use and performance, as well as damage engines
Biodiesel vs petrodiesel boiling points
Biodiesel is composed of fatty acid methyl esters → has a polar ester linkage
Petrodiesel is composed of straight chain alkanes and aromatics → non - polar
Biodiesel can therefore form dipole dipole forces between molecules whereas petrodiesel molecules can only form dispersion forces
Biodiesel molecules also tend to be longer than petrodiesel molecules, so stronger dispersion forces form between biodiesel molecules
The stronger intermolecular forces of attraction between biodiesel molecules require more energy to overcome, so it has a higher boiling point than petrodiesel
Why is biodiesel more viscous than petrodiesel at lower temperatures?
Explain the structure and bonding of each one
Stronger intermolecular forces between biodiesel molecules means they pack more tightly together
As temperature decreases, viscosity of both fuels increases because they have less kinetic energy
biodiesel is more viscous because the molecules are still more tightly bound to each other so cannot flow as freely as petrodiesel
THIS MEANS THAT PETRODIESEL IS A MORE SUITABLE FUEL TO USE AT LOW TEMPERATURES AS IT WON’T CLOG AND RUIN ENGINES
Drawbacks of biofuel
The animal / plant matter they’re made from needs lots of land & water to grow → resource + space intensive
Biogas & biodiesel have a lower energy content than their fossil fuel equivalents (this means you need more of them to release the same amount of energy)
Biogas vs methane, coal seam gas, natural gas
Biodiesel vs petrodiesel
Biodiesel cannot be used in cold temperatures (when you go to the mountains, if you have a diesel engine you’re meant to put antifreeze in it to stop the engine clogging up)
Safety
Fuels often have a low boiling point, flashpoint & high flammability → easy to combust
Proper storage: away from sources of ignition
Use: in well ventilated areas
Complications: fuel specific fire extinguishers
Chemical Structure of biodiesel and petrodiesel
Biodiesel: fatty acid methyl esters
Petrodiesel: straight chain alkanes & aromatics (hydrocarbons)
Biodiesel vs petrodiesel: what’s different?
What are the downsides of biodiesel in terms of using it as a fuel?
Lower energy content
Higher viscosity at the same temperature
biodiesel (due to its ester group) will have greater viscosity compared to petrodiesel and hence this may reduce its suitability due to flow rates.
biodiesel (due to its ester group) will have a lower flashpoint compared to petrodiesel and hence make starting engines more difficult
petrodiesel is a hydrocarbon whereas biofuels are esters
