Biofuels and Bio-derived Chemicals Flashcards
Why have liquid hydrocarbons been a benefical fuels for vehicles in the past?
- They have a high energy content so can provide energy efficiently
- Liquids are easy to store in tanks and pump into engines
- Can be transported in bulk via pipelines
- Are pretty cheap
What are the predominant issues around liquid hydrogocarbon use?
- Oil reserves are depleted
- Oil mostly comes from politically-unstable or conflict zones
- Contribute to CO₂ emissions
- Also form other forms of air pollution (e.g. NOx gases)
What is the benefit of blending in biofuels with current fossil fuels?
Biofuels offers clear benefits both for security of energy supply and for mitigating climate change
What is the main idea around biofuels?
- Producers will form biomass through photosynthesis
- Biomass can then be converted into biofuel
- Burning the biomass recovers stored energy, releasing CO₂
Why are biofuels technically not zero carbon?
- Nitrate fertilisers used to grow these plants can release NO₂ which is a GHG
- Plants do not necessarily grow all year round
- Biomass contains large amount of water- therefore need to dry requring energy
- Energy use in harvesting + transport
Why did the Mexican ‘Tortialla Riots’ happen in 2007
Growing biomass for fuel can compete with food crops (“food vs fuel”) and can force up the price of food
In Mexico masize was being used for bioethanol and not food which caused riots
Why do biofuel strategies and chemistry have to be different for each engine type?
- Different types of engines (Diesel, Petrol + Jet) need different types of fuel
- Diesel engines fuel larger vessels (trains, lorries, ships) and are more tolerant of fuel quality
- However aircraft engines cannot affordto fail - water in the fuel could freeze in cold high altitudes
What is the most simple way to form biofuel?
- Break the biomass down into simple chemical units (i.e. gasification)
- (CH₂O)ₙ → ₙCO + ₙH₂ (Syngas)
- The use the Fischer Tropsch process to form more complex hydrocarbons (energy intensive)
- Syngas + Heterogeneous catalyst → Hydrocarbons (≥C₈)
How has shell utilised Gas-to-Liquid processes in Qatar?
- Using gas that would otherwise have been flared to make 4% of the world’s diesel via Fischer Tropsch
- Syngas from biomass can be fed directly into these pre-existing Fischer Tropsch plants (provided sulfur residues were removed first)
What is a slightly more complicated way of producing biofuel from biomass?
- Using fats and oils (from seeds) using a transesterification reaction to form Fatty Acid Methyl Esters (FAMEs)
- Form a biodiesel which engines can run on
What is the issues surrounding producing biodiesel from seeds
- Large amounts of waste biomass - because you are only using the oil from plants/seeds etc
- What do you do with the glycerol? - for every 3 molecules of FAME these is 1 molecule of glycerol produced (likely impure too)
The yield of biodiesel depends on the type of plant used
Which type of plant would produce a high yield vs a low yield
Why is it not as simple as that?
- Oil Palm seeds gives around 500 gallons per acre
- Hence incentive to use palm oil rather than something like soy bean (only around 60 gallons per acre)
- But the problem with Palm oil is it only grows in the tropics and hence palm oil is grown on land which has very often been obtained by cutting down rainforest
What are the implications of cutting down forest to plant Palm trees for biodiesel?
- Rainforests are occupied by all sorts of exotic animals, particularly in Indonesia and Malaysia with Orangutans - protecting may avoid customers from buying this type of fuel due to fear of its impacts
- Rainforets often have been there for thousands of years and peat has formed around them due to falling leaves and branches which have been compacted. When the forest is cut down to plant Palm trees, the peat starts emitting CO₂. This can be far more than the amoount of CO₂ that is being captured by growing palm trees
How is bioethanol formed
- From the fermentation of starch and cellulose to bioethanol to blend with petrol for petrol engines
- After fermentation, needs to be seperate EtOH from ester, usually via distillation
(in some cases more energy is inputed than is derived from ethanol + significant improvements needed)
What % of bioethanol can European cars run off?
- Limited to 5% in gasoline in Europe (E5), and newer cars tolerate 10% (E10)
- E85 is used in the USA and E100 in Brasil however
What is the difference between first and second generation bioethanol technologies?
- Mature technology for 1st generation from sugar + corn (maize)
- Developing technology for 2nd generation from ligno-cellulosics (parts of plants humans don’t eat)
- Hydrolysis is needed to release the C5 and C6 sugars and separate lignin
- Hence not using a potential food source
- They are also have a higher yield per acre
How can Biogas be made?
- Biogas can be made by fermenting many different things, including waste water (sewage works) resulting in mostly methane and hydrogen sulphide being formed
- Biomethane can then be used as fuel on the gas grid
- Have been sucessful for powering Notts buses as they only run for a short time, on a fixed timetable
New technology utilising waste food to create aircraft fuel would be benefical
Especially due to food waste being massive due to population size
How does it work?
- Wet waste = food + sewage waste
- Process which takes wet waste which is fermented, ketonized and hydrogenated
- Overall forming volatile fatty acids (between 3 to 8 Cs) which are then extended into C5-C15 ketones
- Then through either hydrodeoxygenation or Aldol condensation forms sustainable aircraft fuels
Why may biofuels be particuarly applicable for a continent like Africa?
- Africa has a big potential for growing biomass for fuel (big land area, warm climate)
- Africa has a rapidly increasing population and an increasing demand for fuel (with no indigenous oil sources)
- Adequate fuel supplies and clean energy are central to achieving the STGs
- Links also between European and African markets
