Part 5: Biofuels Flashcards
Def: Biofuel
Fuel generated from biological material
Define and evaluate 1st Gen biofuels
Produced directly from the field, directly related to edible biomass
Advantages: Renewable, cleaner emissions, no pre-treatment required
Disadvantages: Low energy yield, Food or fuel debate, may raise food prices
Define and evaluate 2nd Gen biofuels
Derived from dedicated energy crops and other lignocellulosic plants and residue
Advantages: Renewable, reduces organic land fill, eliminates food price problem
Disadvantages: High energy cost, food or fuel debate, still lower energy yield
What is bioethanol
A biofuel produced through the fermentation of glucose
Describe the process of producing bioethanol
1) Milling to release starch
2) Saccharification to produce glucose
3) Fermentation to form ethanol
4) Distillation and rectification
5) Drying
Def: Saccharification
The heating and addition of water and enzymes to milled grain to produce glucose:
⍺-amylase converts starch to oligosaccharides and dextrin
Glucoamylase converts oligosaccharides and dextrin to glucose
What must be done to lignocellulose before fermentation
Pretreatment: Solubilises hemicellulose ad increases hydrolysability of cellulose.
This is done mechanically, chemically and/or biologically
Why is lignocellulose difficult toproduce energy from
The structure consists of cellulose, lignin and hemicellulose arranged to give it a very strong and stable structure, making it hard to break down into glucose for fermentation.
Def: Isobutanol
Next generation biofuel with characteristics:
Good blending with petrol
Good volatility
Less phase separation
~82% energy content of petrol
Lower moisture absorption
Briefly describe the process of isobutanol production
1) Glycolysis: produces pyruvate
2) Valine biosynthesis: Metabolises pyruvate into KIV
3) Ehrlich Pathway: Degradation of KIV to isobutanol via the KDC enzyme
How can isobutanol yield be improved
Metabolic engineering:
1) Overexpression of KDC enzyme
2) Overexpression of limiting factor enzymes
3) Improve enzyme specificity to pyruvate
4) Remove competing metabolic pathways
