Energy 101 Series: Biofuels * more than just corn-based ethanol

Report
HHMI Teachers’ Workshop:
Biofuels – More Than Ethanol From Corn Starch
Aditya Kunjapur, Ph.D. Candidate, MIT
July 20, 2014
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Outline
• Context for biofuels and key facts
• Photosynthesis and carbon fixation
• Feedstocks
• Fuels
• Recap
2
Outline
• Context for biofuels and key facts
• Photosynthesis and carbon fixation
• Feedstocks
• Fuels
• Recap
3
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
Photosynthesis
- Plants
- Algae
- Cyanobacteria
Photons
Energy
Enzymatic
- Same organism
- Different organism
Fuels
or
Chemicals
Biomass
+ CO2
Inorganic
Molecules
Chemosynthesis
- Chemolithotrophs
(in deep oceans,
isolated caves, etc)
Energy Capture
Thermochemical
-
Ethanol
Biodiesel
Jet Fuel
Methane
- Pyrolysis
- Gasification
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
4%
13%
35%
5%
Hydropower
Biomass Wood
Biomass Biofuels
Biomass Waste
Wind
21%
Other
22%
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 emissions
SC Opinion on Greenhouse Gas Accounting in Relation to Bioenergy: http://www.eea.europa.eu/about-us/governance/scientificcommittee/sc-opinions/opinions-on-scientific-issues/
Image: http://www.extension.org/sites/default/files/w/2/22/BiofuelLifeCycle.jpg
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Outline
• Context for biofuels and key facts
• Photosynthesis and carbon fixation
• Feedstocks
• Fuels
• Recap
12
Photosynthesis: Overview
• Oxidation/reduction (Redox) reactions
– CO2 gets reduced to glucose
– H2O gets oxidized to O2
Image: http://www.phschool.com/science/biology_place/biocoach/images/photosynth/photo1.gif
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Photosynthesis: Inside a Chloroplast
Image: http://hyperphysics.phy-astr.gsu.edu/hbase/organic/imgorg/rubc3.gif
14
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
47% Non-Bioavailable
Photons
100%
Sunlight
40% Loss in Dark
and PhotoRespiration
~5%
Net Leaf
Efficiency
53% (in 400-700 nm range)
30% Not
Absorbed
68% Loss in Conversion of
ATP and NADPH to glucose
9%
(Collected
as sugar)
37%
(Absorbed
Photon
Energy)
24% Wavelength
Mismatch
28%
(Energy Captured
in Chlorophyll)
Figure based on statistics listed here: http://en.wikipedia.org/wiki/Photosynthetic_efficiency
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Outline
• Context for biofuels and key facts
• Photosynthesis and carbon fixation
• Feedstocks
• Fuels
• Recap
19
Feedstocks
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
Image: http://www1.eere.energy.gov/biomass/images/Feedstock1.jpg
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Estimated corn use for ethanol production (2011):
4.9 billion bushels or 279 billion pounds
Image: http://ericpetersautos.com/wp-content/uploads/2012/12/corn-1.gif
Source of facts: EIA – Biofuel Trends and Issues – Oct 2012
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Drawbacks of Corn as a Feedstock
• Used for food
• Grows slowly
• Grows only on arable land
• Provides low energy per acre
• Is an annual crop
Image: http://media.treehugger.com/assets/images/2011/10/bushcorn-jj-001.jpg
http://www.shirkebiofuels.com/images/biofuel-feedstock.gif
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Can grow up to 8
feet in 6 weeks
Image: http://newswire.uark.edu/images/miscanthus.JPG
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Energy yield per acre does not favor corn
?
Source: “Biodiesel from microalgae.” http://www.sciencedirect.com/science/article/pii/S0734975007000262#
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Bioreactors/ponds used to grow algae
Bioreactors required to cultivate high cell densities
Images: http://www.inventgeek.com/Projects/Photo-Bio-reactor-V2/main.jpg
http://assets.inhabitat.com/files/bioreactor1.jpg ;
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Bioreactors/ponds used to grow algae
- Algal cells make up very small fraction of pond
- Dewatering and processing is cost-prohibitive
Images: both from http://www.asulightworks.com/blog/asu-and-ua-team-arid-raceway-algae-test-bed
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Cellulose
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I Gelfand et al. Nature 000, 1-4 (2013) doi:10.1038/nature11811
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Cellulosic biofuel – a reality?
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Outline
• Context for biofuels and key facts
• Photosynthesis and carbon fixation
• Feedstocks
• Fuels
• Recap
33
Pathway to ethanol
Under anaerobic conditions (no O2):
Glycolysis
(~10 enzymatic reactions)
Pyruvate
decarboxylase
Alcohol dehydrogenase
Image: http://www.emc.maricopa.edu/faculty/farabee/biobk/alcferm.gif
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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
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Images: (Left) http://www2.raritanval.edu/departments/Science/fulltime/Weber/Microbiology%20Majors/Chpater5/chapter5sub/figure_05_30_labeled.jpg
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Outline
• Context for biofuels and key facts
• Photosynthesis and carbon fixation
• Feedstocks
• Fuels
• Recap
40
Overview of BioEnergy
Photosynthesis
- Plants
- Algae
- Cyanobacteria
Photons
Energy
Enzymatic
- Same organism
- Different organism
Fuels
or
Chemicals
Biomass
+ CO2
Inorganic
Molecules
Chemosynthesis
- Chemolithotrophs
(in deep oceans,
isolated caves, etc)
Energy Capture
Thermochemical
-
Ethanol
Biodiesel
Jet Fuel
Methane
- Pyrolysis
- Gasification
Chemical Conversion
41
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?
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