LECTURE 8 CELLULOSIC BIOETHANOL Flashcards
Benefits of ethanol
- reduces tailpipe carbon monoxide emissions by as much as 30%, toxic content by 13% (mass) and 21% potency
- but may not overall be better for emissions considering how much is going into the process of making ethanol
Drivers for Cellulosics
- add value to rural economy
- government targets
- less competitive with food
- cellulosic crops usually perennials soil management low, less plowing and agrochemicals
- up to 85% GHG emission savings
- Potential 10 units energy per unit of fossil energy
Cellulosic feedstocks
- coppice (short rotation) forestry and wood products
- agricultural waste (the bit left after we harvested the food)
LIGNOCELLULOSE STRAW EDDITION
- bulky difficult to transport
- water repellent
- cellulose embedded n lignin
- hollow
- so light that you have to transport so much to get energy back
CELLULOSE
- B1-4 LINKED GLUCOSE CHAIN
- INDUSTRIAL APPLICATIONS:
- VISOCOSE CELLOPHANE RAYON
- NITROCELLULOSE in hand cream
- METHYLCELLULOSE
- BIO-ETHANOL
Hemicellulose
- branched and unbranched mixed sugar chains
- monomers of xylose with glucose, mannose, arabinose, galactose and rhamnose
any of a class of substances which occur as constituents of the cell walls of plants and are polysaccharides of simpler structure than cellulose.
emicelluloses have random, amorphous structure with little strength. They are easily hydrolyzed by dilute acid or base as well as a myriad of hemicellulase enzymes.
Challenges of working with lignocellulose
• Bulky & difficult to breakdown
• Accessing the sugars in cellulose & hemicellulose
requires large energy input
• Handling and storage of biomass an issue
why not burn it
- Simplest way of unlocking the energy potenBal of biomass
• 10 % Primary energy consumpBon
– inefficient & polluBng • EsBmated biomass resources – 250 EJ/yr, 1-5W/m2
Biomass
What energy services are required & their value Are there co-products or benefits?
• CollecBon, transport, storage & handling costly
• Demand for liquid fuel stocks compared with energy producBon when cheaper alternaBves available
Dispersed density – infrastructure for dispersed generaBon?
• Good for niche markets where biomass is concentrated,
e.g. forestry, food processing
• PotenBal in combined heat & power systems (CHP) for localised communiBes or industrial operaBons
• Possible use for co-firing in fossil fuel energy plants
How to Meet the Energy Demand?
Use fossil fuels to generate heat and energy Gas = 7.2 kg CO2 / gal
Coal = 10.2 kg CO2 / gal
• Burn lignin residues 0.05 kg CO2 / gal
• Combined heat and power systems (CPH) / energy recycling
Important Considerations for Agricultural Waste Use
Impacts on animal feed and bedding
• Impacts on soil quality - ~ 30% ploughed back in
Maintaining soil structure & biota
Controlling erosion
Replacing nutrients, reduce ferBlizaBon
But too much can cause more GHG release (Nox loss)
• Changes to agricultural practice? Growing, harvest & storage – competitive price
Bagasse
- residue from extraction from sugarcane
- 30% remaining after extraction
- 400m tonnes globally
- combusted to provide heat and electricity for ethanol distillation
- teated with cellulases to produce bioethanol (Brazil is looking at this)
Burning = no need for fossil fuel input
enzymic- helps meet bioethanol demand diversification
USA CELLULOSIC INDUSTRY
2030 TARGET OF 30% BIOFUELS = 60 BILL US GAL
- Expect 15-18 billion gal from corn starch
- estimates 1.3 bill dry tonnes agriculture and municipal waste by 2030
- prediction that cellulosic ethanol will overtake standard corn ethanol using the waste is gonna be the way forward
-
challenges of cellulosic ethanol
cost too big -2$ per gallon
- bc of feedstock cost, to breakdown, to transport, for the enzymes, for the fermentation ( but minor)
if instead it was 0.5$ it’s fine , but atm it’s 1.4$
GMO CROPS FOR LIGNIN
so it’s thought if lignin content is reduced cellulose content increses
however no lignin means it won’t stand up
