hhmi teachers’ workshop: biofuels – more than ethanol from corn starch aditya kunjapur, ph.d....
TRANSCRIPT
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HHMI Teachers’ Workshop:Biofuels – More Than Ethanol From Corn Starch
Aditya Kunjapur, Ph.D. Candidate, MITJuly 20, 2014
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Outline
• Context for biofuels and key facts
• Photosynthesis and carbon fixation
• Feedstocks
• Fuels
• Recap
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• Context for biofuels and key facts
• Photosynthesis and carbon fixation
• Feedstocks
• Fuels
• Recap
Outline
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What is “BioEnergy”
According to the International Energy Agency (IEA):
“Material which is directly or indirectly produced by
photosynthesis and which is utilized as a feedstock in the
manufacture of fuels and substitutes for petrochemical and
other energy intensive products.”
IEA Bioenergy: http://www.ieabioenergy.com/IEABioenergy.aspx
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Overview of BioEnergy
Energy
Photosynthesis
Chemosynthesis
Photons
Inorganic Molecules
- Plants- Algae- Cyanobacteria
- Chemolithotrophs (in deep oceans, isolated caves, etc)
Fuelsor
Chemicals
Biomass+ CO2
Enzymatic - Same organism- Different organism
Thermochemical - Pyrolysis- Gasification
- Ethanol- Biodiesel- Jet Fuel- Methane
Energy Capture Chemical Conversion
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Some advantages of bioenergy compared to other renewables
• The only renewable source that can replace fossil fuels in
all energy markets – in the production of heat, electricity,
and fuels for transport (IEA)
• The source of a variety of drop-in liquid fuels
• The source of petroleum in the first place
• The primary way by which atmospheric CO2 is consumed
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Breakdown of US renewables in 2011
35%
22%
21%
5%
13%
4%
HydropowerBiomass WoodBiomass BiofuelsBiomass WasteWindOther
http://www.eia.gov/totalenergy/data/monthly/pdf/sec10_3.pdf
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Percentage of the world’s energy• Biomass-based energy accounted for ~10% of world
total primary energy supply in 2009
– Includes cooking/heating in developing countries
• Global production of biofuels:
– 2000: 16 billion liters
– 2011: 100+ billion liters
• Total road transport fuel globally: 3%
– Brazil: 23%Source: IEA
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Life cycle of traditional biofuels
Important consideration: life cycle greenhouse gas emissionsSC Opinion on Greenhouse Gas Accounting in Relation to Bioenergy: http://www.eea.europa.eu/about-us/governance/scientific-committee/sc-opinions/opinions-on-scientific-issues/Image: http://www.extension.org/sites/default/files/w/2/22/BiofuelLifeCycle.jpg
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• Context for biofuels and key facts
• Photosynthesis and carbon fixation
• Feedstocks
• Fuels
• Recap
Outline
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Photosynthesis: Overview
Image: http://www.phschool.com/science/biology_place/biocoach/images/photosynth/photo1.gif
• Oxidation/reduction (Redox) reactions– CO2 gets reduced to glucose
– H2O gets oxidized to O2
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Photosynthesis: Inside a Chloroplast
Image: http://hyperphysics.phy-astr.gsu.edu/hbase/organic/imgorg/rubc3.gif
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Photosystems convert light energy into reducing equivalents
Image: http://www.biologycorner.com/resources/photosystem.jpg
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The Calvin Cycle uses those reducing equivalents to turn CO2 into sugar
Image: https://benchprep.com/blog/wp-content/uploads/2012/08/Calvin_cycle.jpg
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Typical efficiency of photosynthesis
18Figure based on statistics listed here: http://en.wikipedia.org/wiki/Photosynthetic_efficiency
100% Sunlight
47% Non-Bioavailable Photons
53% (in 400-700 nm range)
30% Not Absorbed
37% (Absorbed
Photon Energy)
24% Wavelength Mismatch
28%(Energy Captured
in Chlorophyll)
68% Loss in Conversion of ATP and NADPH to glucose
9%(Collected as sugar)
40% Loss in Dark and Photo-Respiration
~5%Net Leaf Efficiency
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• Context for biofuels and key facts
• Photosynthesis and carbon fixation
• Feedstocks
• Fuels
• Recap
Outline
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Feedstocks
Image: http://www1.eere.energy.gov/biomass/images/Feedstock1.jpg
Two categories of photosynthetic organisms:
1) Those that capture light energy into
non-fuel biomass
- Chemical conversion still required
2) Those that capture light energy and
produce a fuel
- Only physical separation required
21Image: http://ericpetersautos.com/wp-content/uploads/2012/12/corn-1.gifSource of facts: EIA – Biofuel Trends and Issues – Oct 2012
Estimated corn use for ethanol production (2011):4.9 billion bushels or 279 billion pounds
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Drawbacks of Corn as a Feedstock
Image: http://media.treehugger.com/assets/images/2011/10/bushcorn-jj-001.jpghttp://www.shirkebiofuels.com/images/biofuel-feedstock.gif
• Used for food
• Grows slowly
• Grows only on arable land
• Provides low energy per acre
• Is an annual crop
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Can grow up to 8 feet in 6 weeks
Image: http://newswire.uark.edu/images/miscanthus.JPG
25Source: “Biodiesel from microalgae.” http://www.sciencedirect.com/science/article/pii/S0734975007000262#
Energy yield per acre does not favor corn
?
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Bioreactors/ponds used to grow algae
Images: http://www.inventgeek.com/Projects/Photo-Bio-reactor-V2/main.jpghttp://assets.inhabitat.com/files/bioreactor1.jpg ;
Bioreactors required to cultivate high cell densities
27Images: both from http://www.asulightworks.com/blog/asu-and-ua-team-arid-raceway-algae-test-bed
- Algal cells make up very small fraction of pond- Dewatering and processing is cost-prohibitive
Bioreactors/ponds used to grow algae
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Cellulose
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31I Gelfand et al. Nature 000, 1-4 (2013) doi:10.1038/nature11811
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Cellulosic biofuel – a reality?
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• Context for biofuels and key facts
• Photosynthesis and carbon fixation
• Feedstocks
• Fuels
• Recap
Outline
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Pathway to ethanol
Glycolysis(~10 enzymatic reactions)
Image: http://www.emc.maricopa.edu/faculty/farabee/biobk/alcferm.gif
Pyruvate decarboxylase
Alcohol dehydrogenase
Under anaerobic conditions (no O2):
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Drawbacks of ethanol• Hygroscopic
• Miscible with water
• Low energy density
• Requires different
distribution system
than gasoline
• Limit to how much can
be added to
conventional engines
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The E10 “Blend Wall”
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Alternative fuel options
• Longer, branched alcohols
• Biodiesel
• Methane
– Methanogens
– CO2 + 4H2 CH4 + 2H2O
– Important for waste-to-energy
Image: http://canola.ab.ca/image.axd/images/uploads/news/bio_pump_200x250.jpg?m=Crop&w=200
39Images: (Left) http://www2.raritanval.edu/departments/Science/full-time/Weber/Microbiology%20Majors/Chpater5/chapter5sub/figure_05_30_labeled.jpg
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• Context for biofuels and key facts
• Photosynthesis and carbon fixation
• Feedstocks
• Fuels
• Recap
Outline
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Overview of BioEnergy
Energy
Photosynthesis
Chemosynthesis
Photons
Inorganic Molecules
- Plants- Algae- Cyanobacteria
- Chemolithotrophs (in deep oceans, isolated caves, etc)
Fuelsor
Chemicals
Biomass+ CO2
Enzymatic - Same organism- Different organism
Thermochemical - Pyrolysis- Gasification
- Ethanol- Biodiesel- Jet Fuel- Methane
Energy Capture Chemical Conversion
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Recap and take home points• Traditional biofuels have several drawbacks
• When evaluating a biofuel process, consider:– Carbon lifecycle
– Food versus fuel
– Land (or water) required
– Feedstock transportation
– Desired end fuel
• Research efforts directed toward production of advanced and cellulosic biofuels make most sense (just my opinion!)
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Thank you for listening!
Questions?