Transcript Biofuels

An Ecological Perspective
(BIOL 346)
Talk Eight:
Biofuels
Introduction
Biofuel is a type of fuel whose energy is derived from
biological carbon fixation.
Biofuels include fuels derived from biomass conversion,
as
well
as
solid
biomass,
liquid
fuels
and
various biogases.
Although fossil fuels have their origin in ancient carbon
fixation, they are not considered biofuels by the
generally accepted definition because they contain
carbon that has been "out" of the carbon cycle for a
very long time.
What is a Biofuel?
• Layman’s Definition:
– “A fuel that gains its’ energy through the use
of already existing carbon in the atmosphere.”
• Unlike other renewable energy sources,
biomass can be converted directly into liquid
fuels, called "biofuels," to help meet
transportation fuel needs.
• The two most common types of biofuels in
use today are ethanol and biodiesel.
Bio-alcohol
• Bio alcohol is only obtained from biomass or biodegradable parts of waste and is usually intended
for the use as biofuel. But Bio alcohol can not only
be made of waste but also wood, straw or whole
plants. If Bio alcohol is used as fuel, there are also
different mixture ratios.
• Bio alcohol is also used to activate fireplaces like
ethanol fireplaces. It is also used as a disinfectant
in a mixture with water and then it is also used as
solvent. It is also a part of medical treats and in
the industry it is used as solvent. It is also used as
fuel or denatured alcohol - therefore other
ingredients are mixed with ethanol.
Bioalcohol
• Bioethanol is ethanol fuel (ethyl alcohol, the same stuff we
drink) made from plant matter (as with most ethanol).
• Currently most of it is made from corn, but in the future
more and more of it will be made from cheaper organic
material such as grass and various plant waste.
• It can be used as a fuel similar to gasoline, but is
commonly used as a gasoline additive to minimize
emissions.
• It can also be used as a total gasoline replacement to
power our cars with only minor modifications to a standard
gasoline engine.
Biogas
•Biogas production using anaerobic
(oxygen free) digestion is a
biological treatment process to
reduce odor, produce energy and
improve the storage and handling
characteristics of manure.
•A biogas production system must
be specially designed and requires
regular attention by someone
familiar with the needs and
operation of the digester.
Bio-diesel
• Bio-diesel is a form of diesel fuel
manufactured from vegetable oils, animal fats,
or recycled restaurant greases. It is safe,
biodegradable, and produces less air pollutants
than petroleum-based diesel.
• Bio-diesel is meant to be used in standard
diesel engines and is thus distinct from the
vegetable and waste oils used to
fuel converted diesel engines. Bio-diesel can
be used alone, or blended with petro diesel.
• Bio-diesel can also be used as a low carbon
alternative to heating oil.
The Plant Cell wall
• The cell wall is the organelle
that ultimately controls the
shape of plant cells and
consequently of organs and
whole organisms.
• It is sometimes naturally
strengthened and made
considerably more resistant
to such abuses as pathogen
infection by the release of
specific oligosaccharides and
enzymes and by overlaying or
impregnation with cutin,
suberin, waxes or silica
Plant pathogens
• In order to infect and enter a plant cell, a pathogen
must get through the plant cell wall.
• How complex this cell wall?
• Cellulose
• Cross-linking Glucans:
•
Xyloglucan (XG).
•
Glucuronoarabinoxylan (GAX).
•
Mannans, Glucomannans, Starch, Callose
Galactomannans.
• Pectin :
•
Homogalacturonan (HGA).
•
Rhamnogalacturonan-I (RG-I).
•
Rhamnogalacturonan-II (RG-II).
• Proteins and lignin?
How does the pathogen do this?
• Substrate induction:
• Pathogen always produces very low levels of cell wall
degrading enzymes (CWDE).
– Mainly pectinases
• Upon initial contact with plant, a small number of pectin
related monomers are released
• These induce gene expression in the pathogen to make
more CWDE
• The additional enzymes release more monomers which also
act as inducers of gene expression
How does the pathogen do this?
• Catabolite Repression:
• At high enough concentrations, the monomers released from
the continued breakdown of the Plant Cell Wall repress the
synthesis of CWDE.
• This reduces the production of the enzymes by the
pathogen
• Mostly, when this occurs, the pathogen has successfully
degraded the plant cell wall.
• Just think about all the
different enzymes!
• With just pectin:
• Pectin Lyase (PL)
• Break the chain and release molecules
with an unsaturated double bond
• Pectin methylesterase (PME)
• Remove methyl groups – this alters
solubility and thus the rate at which
other pectinases work
• endoPolygalacturonan (PG)
• Break
the
links
between
two
galacturonan molecules in the chain
• ectoPolygalacturonan
• Break off terminal
molecules only
galacturonan
Just for pectin – there are more enzymes!
Just how many enzymes?
• sdc
• Induction:
• Extracellular enzymes expressed
at low levels generate metabolites
that
signal
pathogen
to
dramatically
increase
the
expression level of genes encoding
plant cell wall degrading enzymes.
• Utilization:
• Extracellular
enzymes
and
transporters
specific
for
translocation
of
cell
wall
degradation
products
enable
pathogen to use plant cell material
for growth.
• Some extracellular proteins may
generate
metabolites
that
modulate gene expression of
cellulases and hemicellulases during
the utilization phase.
The trouble with Lignin…
Lignin is:
• Complex aromatic polymer that’s an important component of plant secondary
cell walls provides rigidity and mechanical support to plant tissues
However…
• The highly phenolic polymers in lignin are very degradation resistant.
• The complexity of the bonds formed among lignin monomers are less
reactive
• Chemical diversity of lignin compared to simple polymers precludes the
ability of any single enzyme to degrade it
Therefore: Lignin is hard to get rid of..
The trouble with Lignin…
Pre-treatment:
Phenol monomers produced by the degradation of Lignin are
fermentation inhibitors of growth and ethanol production in S. cerevisiae.
pentose-utilizing strains Escherichia coli, Pichia stipititis, and
Zymomonas mobilis produce ethanol in concentrated hemicellulose liquors but
require detoxification.
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How to get rid of Lignin
1.Breed it out!
Irx4 is a mutant of Arabidopsis Thaliana:
• Down-regulation of cinnamoyl-CoA reductase (CCR) gene
• CCR is involved in the latter stages of lignin biosynthesis
• Irx4 = irregular xylem 4: named for phenotype.
Irx4 Arabidopsis mutant
Has significantly reduced
lignin content
Low to No significant
reduction in cellulose and
hemicellulose content.
Irx4 Arabidopsis mutant (b):
• Has a dwarfed phenotype
compared to WT (a)
• Also, because Lignin is an
important constituent of the
secondary cell wall of the xylem
the mutant (d) experiences
collapse of vessel elements in
the xylem compared to the WT
(c)
•Lignin deficient mutants are weaker and harder to rear –overall
weakness makes them more susceptible to fungal pathogens
•CCR is also part of Defense Response Pathway that leads to
reactive
Oxygen species
How to get rid of Lignin
2. Chew it up!
Synergy between fungal pathogen
enzymes diverse enough for the
complexity of Lignin rich sources like
Sugarcane Bagasse
SUGARCANE
Sugarcane stalks are crushed to extract their juices. There is a biomass
remaining called bagasse.
Bagasse
• Is considered to be lignocellulose (combination of both cellulose and
hemicellulose)
• Dry weight of sugarcane bagasse composition:
42% cellulose, 22% lignin, and 28% hemicellulose
• Can be utilized as a fuel source: produce steam or substrate for production
of bioethanol
Clostridium celluovorans
This is a microorganism that:
• Is an anaerobic bacterium
• Is mesophilic (meaning moderate temperature)
• Is Cellulytic
• Has the ability to utilize carbon sources: cellulose, xylan, and pectin
This bacterium contains a cellusome in which specific enzymes were isolated:
• Xylanase A (XynA)
• Mannanase A (ManA)
• Endoglucancase E (EngE): has ability for some xylanase activity
Study was conducted:
• Looked at the enzymes in different ratios
• Effectiveness in degrading sugarcane bagasse
Recap
Fungal pathogens are involved in the production of
Biofuels with particular respect to the cell wall in
that:
• Enzymatic Hydrolysis is a necessary pretreatment
before fermentation of the simple sugars can yield
biofuels
• Pathogens are also involved in the production of the
ideal biofuel source: low-lignin mutants are difficult to
rear due to increased susceptibility to fungal pathogens
• Synergy between the right mixture of enzymes is used
to optimize the degradation of the fermentation
inhibiting Lignin
So what?
• Many if not all of these enzymes can be isolated
and used to digest isolated biomass – PCWM
• Breaking down each of the many components of the
cell wall will allow us to find ways to use them all.
• So many enzymes, so many pathogens, so many
combinations.
– Is it even possible?
What is a biofuel?
• A biofuel is a renewable
energy source, unlike other
natural resources such as
petroleum, coal, and nuclear
fuels.
• One legal definition of
biofuel is "any fuel with an
80% minimum content by
volume of materials
derived from living
organisms harvested within
the ten years preceding
its manufacture".
What is a biofuel?
Like coal and petroleum,
biomass is a form of stored
solar energy. The energy of
the sun is "captured"
through the process of
photosynthesis in growing
plants.
One of the major advantages
of biofuel over most other
fuel types is that it is
biodegradable, and so
relatively harmless to the
environment if spilled.
Predicted increase in global mean
temperature due to CO2 accumulation
The carbon in biofuels was
recently extracted from
atmospheric carbon dioxide
by growing plants, so burning
it does not result in a net
increase of carbon dioxide in
the Earth's atmosphere.
Therefore, many people
believe that a way to reduce
the amount of carbon dioxide
released into the atmosphere
is to use biofuels to replace
non-renewable sources of
energy.
www.metoffice.com/research/hadleycent
Ethanol from Cornstarch
Courtesy of Bruce Ferguson, Edenspace
Switchgrass
• A warm season grass and
is one of the dominant
species of the central
North American tallgrass
prairie.
• Switchgrass can be found
in remnant prairies, along
roadsides, pastures and
as an ornamental plant in
gardens.
Switchgrass
• ethanol fuel — production
due to its hardiness
against poor soil and
climate conditions, rapid
growth and low
fertilization and
herbicide requirements.
• Switchgrass is also
perennial, unlike corn and
sugarcane, and has a huge
biomass output, the raw
plant material used to
make biofuel, of 6-10
tons per acre
The challenge is efficient conversion
• Burning switchgrass (10
t/ha) yields 14.6-fold
more energy than input
to produce*
• But, converting
switchgrass to ethanol
calculated to consume
45% more energy than
produced
Other
Steam
Transport
Biomass
Grinding
Electricity
Energy consumption
*Pimentel & Patzek, Nat Res Res 14,65 (2005)
Sugar beet
• Sugar beet is a hardy
biennial plant that can
be grown commercially
in a wide variety of
temperate climates.
• During its first growing
season, it produces a
large (1–2 kg) storage
root whose dry mass is
15–20% sucrose by
weight.
Sugar beet
• If not harvested,
during its second
growing season, the
plant uses the nutrients
in this root to produce
flowers and seeds.
• In commercial beet
production, the root is
harvested after the
first growing season,
when the root is at its
maximum size.
Biochemical Composition in Sugar
Beet Pulp vs. ‘Typical’ Dicot
Sugar Beet
• 30% cellulose and
hemicellulose
• 19% pectin
– 70% RGA-I
– 0.8% ferulic acid
• 50% sugar (arabinose,
galactose, rhamnose,
etc)
• Increased pectin
concentration
important
• Feruloyl esters
‘Typical’ Dicot
• 20-30% cellulose
• 20% hemicellulose
• 11-15% pectin
What can be done
• Pyrolysis heats the biomass to temperatures
of 300oC – 500oC. in the absence of air.
• The biomass “melts” and vaporizes, producing
petroleum-like oil called bio-crude.
• This bio-crude can be converted to gasoline or
other chemicals or materials.
Pyrolysis
• The chemical decomposition of a condensed
substance by heating and is a special case of
thermolysis.
• Geologists view crude oil and natural gas as the
product of compression and heating of ancient
organic materials over geological time.
• Formation of petroleum occurs from hydrocarbon
pyrolysis, in a variety of mostly endothermic
reactions at high temperature and/or pressure
crude oil composition
• Mostly alkanes, cycloalkanes and various aromatic
hydrocarbons while the other organic compounds
contain nitrogen, oxygen and sulfur, and trace
amounts of metals such as iron, nickel, and copper.
• As crude oil is made from plant material, it is
reasonable to suggest that pyrolysis of sugar beet
would result in the formation of the same
components.
Fuel from crude
• Crude oil is separated into
fractions by fractional
distillation. The fractions at
the top of the fractionating
column have lower boiling
points than the fractions at
the bottom.
• The heavy bottom fractions
are often cracked into
lighter, more useful
products. All of the fractions
are processed further in
other refining units.
Conclusions
• Up to 2005 biofuels were more costly than fossil
fuels.
• 2012 estimates:
– Estimated ethanol production cost in 2012 was
$0.46 per gasoline energy equivalent L.
– Wholesale gasoline prices averaged $0.44/L in 2012
– Estimated soybean biodiesel production cost in 2012
was $0.55 per diesel EEL,
– Diesel wholesale prices averaged $0.46/L in 2012
• Recently:
– Decrease in fossil-fuel prices
– Increase in corn prices
Conclusions
• Biofuels can not replace fossil fuels without
having impact on food supplies.
• Even if all corn grown in U.S.A were
dedicated to produce biofuels it would be
far from meeting the energy demand of U.S
alone.
• Because it would meet only 12% of gasoline
demand and 6% of diesel demand.
The End!
Any Questions?