Transport fuels Flashcards
What are some drivers for using trasnport biofuels
GHG, energy supply security, legislation.
Transport make up 1/5th of total GHG
What is the RTFO
Renewable transport fuel obligation
required suppliers to ensure a proportion comes from renewables
Where do GHG emisisons come from, which generation is most intensive
exhaust, land use change, harvesting, processing, distribution
1st
How is biodiesel produced?
Bioethanol?
transesterifications
Fermentation
What are 2nd gen biofuels
non edibles including waste and lignocellulosics
fermentation and syngas derived fuel
What is 3rd generation biomass
harvesting and advanced processing of ultra high yield biomass (algae)
What does biodiesel consist of
triglycerides
Used to store energy, foods and soaps
What affects the quality of biodiesel
% saturates
Chain length of fats
Amount of free fatty acids (hygroscopic and can form soaps)
How does saturate % affect quality
Increases cetane number, cloud point, and stability
How does the transesterification process work
Add methanol and a catalyst at 50C to form FAME and glycerol
What are the properties of FAME
What does bio-ethanol produce
Suitable viscosity, good col temp and cetane number
Ethyl esters
Process of oil recovery
Crushing of seeds
Separation of oil from the meal (mechanic above 20, solvent below
De-gumming
Further purification
What is the max Biodiesel blend
Benefits of blend above 5%
20%
Reduce CO, HC, small PAH and particulates
Possibly increases NO and particulates
Disadvantages of bioethanol
Only glucose is readily fermented, enzymes stop operating if ethanol conc too high
Energy intensive distillation required
Advantages of blending ethanol
Can be used directly with engine adaptation or up to 22% in conventional engines
How are 1st generation crops fermented
sugars - disaccharides hydrolyse in water to glu/fru which ferment
Starchs are hydrolysed (using enzymes and chemicals) and then fermented.
How is ethanol seperated
Distillation (main energy) 95% and dehydration (molecular sieve)
How are 2nd generation fuels produced ethanol
Sugar platform: Holocellulose converted to fermentable sugars. Lignin is wasted and often used as boiler fuel.
Syngas platform: Converted to CO and H2 using gasification. Can be converted to a range of chemicals and HC fuels.
process of sugar platform concept
Milling > pre-treat > hydrolysis > fermentation
Pre-treatment used to break down cell wall
Hemicellulose readily hydrolysis to 5-carbon sugars (xylose), but hard to ferment.
Cellulose harder to hydrolysed to 6 carbon sugars (glu/fru) but easier to ferment.
What should pre-treatment do in sugar platform
High rate of hydrolysis
Minimal degredation
Inexpensive and mild conditions
Uses steam explosion or sulphuric acid
Process of syngas platform
Milling> gasification > fermentation and catalytic conversion > ethanol and fuels/chemicals
