Transcript Plant Cell Walls February

Plant Cell Walls to Alcohols
This lesson looks at the break down of
plant material to demonstrate the
production of biofuels.
VOCABULARY:
Biofuel- A fuel derived, directly or
indirectly, from organic material
Biomass- Biological material derived from
living, or recently living organisms
Cellulose- An insoluble substance that is the
main constituent of plant cell walls; it is a
polysaccharide, or complex sugar,
consisting of chains of glucose monomers
Distillation- The action of purifying a liquid
by the process of heating and cooling;
distillation can be used to purify
substances or to remove one component
from a complex mixture
Hemicellulose- A polysaccharide
constituent of plant cell walls
Hydrolysis- The chemical breakdown of a
compound due to reaction with water
Lignin- A
complex
organic
polymer
found in plant
cell walls,
making them
rigid and
woody
Lignocellulosic recalcitrance- The natural
resistance of woody plant cell walls to
chemical and biological degradation
Pretreatment- The process to overcome
lignocellulosic recalcitrance and expose the
cellulose and hemicellulose so that individual
sugars can be released
Background: After wood residues have been
packaged and transported from logging sites to
conversion facilities, the next step of the biofuel
production process, CONVERSION, can begin.
The conversion process involves three distinct
steps: Pretreatment, Enzymatic Hydrolysis, and
Fermentation.
The process to overcome lignocellulosic
recalcitrance and expose the cellulose and
hemicellulose so that individual sugars can be
released is called PRETREATMENT.
Over the last four years, the NARA conversion
team evaluated and streamlined four different
pretreatment methods, in order to determine
the process that would be the most sustainable
and economically viable to incorporate into the
biojet fuel production pipeline.
1. SPORL (sulfite
pretreatment to overcome
recalcitrance of
lignocellulose): This
pretreatment method was
developed at the USDA Forest
Service, Forest Products
Laboratory, a NARA affiliate.
The process relies on heat,
chemicals (sodium bisulfite)
and mechanical grinding.
2. Mild bisulfite (MBS): This
process was developed at
Catchlight Energy and USDA
Forest Service, Forest Products
Laboratory. The process is
similar to SPORL.
3. Wet Oxidation (WO): Developed at
Washington State University’s Bioproducts,
Sciences and Engineering Laboratory (WSUBSEL), this process relies on pressure and
oxygen.
4. Dilute Acid (DA): This method uses sulfuric
acid and heat and has been widely studied and
used to pretreat crop residues like wheat straw
and corn stover.
Over the last two years, researchers at the USDA Forest Service
Forest Products Laboratory and Catchlight Energy made
modifications to the SPORL protocol to create a hybrid protocol
termed the mild bisulfite (MBS) pretreatment. MBS differs from
SPORL by employing calcium bisulfite instead of sodium bisulfite
and a lower cook temperature, which were instrumental to
improved conditions for downstream isobutanol production and for
adoption into existing biorefinery infrastructure.
In September 2014, the NARA team decided to select a
single pretreatment method to use in the conversion
process, in order to streamline the production pipeline. The
mild bisulfite protocol was unanimously chosen as the
preferred pretreatment method and work to scale the
process and produce 1000 gallons of bio-jet fuel is
currently underway.
Why is fermentation important?
A substantial element of the NARA project is to ensure that the wood residue to
biojet fuel conversion process is sustainable environmentally, socially, and
economically. The process engineering team at Gevo has been instrumental in
providing unit operation costs for the isobutanol to biojet fuel conversion steps
and capital cost estimates for infrastructure development. All of these inputs
help establish a basis for a developing techno-economic model used to gage the
complete cost of producing biojet fuel from wood residues and insure that the
process is economically sustainable.
Alcohols, like isobutanol, are not the only commercially
valuable products generated from the fermentation
process. Volatile fatty acids (VFAs) like acetic acid,
propionic acid and butyric acid are produced from
fermentation in specific bacteria. NARA member Birgitte
Ahring and her team at Washington State University’s
Bioproducts, Sciences and Engineering Laboratory (BSEL)
are optimizing a process called BioChemCat that uses
bacteria to convert cellulosic feedstock into volatile fatty
acids.
Creating the optimal conditions for yeast and
bacteria fermentation is one challenge taken up
by Gevo and Dr. Ahring’s group; removing the
valuable products from the fermentation broth
is another challenge. In a recent paper
published in the Journal of Supercritical Fluids
and funded by NARA, researchers at BSEL
describe a novel method used to extract volatile
fatty acids from the fermentation broth.
Their work expands opportunities to generate
valuable bio-based products from wood
residuals, which will provide support to the
NARA team’s goal to create an economically
viable wood-to-biojet fuel industry.
Fermentation methods
Gevo makes use of their proprietary technology GIFT®, Gevo’s
Integrated Fermentation Technology®, to convert those simple
sugars into isobutanol and simultaneously separate the isobutanol
from the fermentation broth. The GIFT® platform relies on
specialized yeast to serve as a biological catalyst. The yeast import
the glucose and other simple sugars from the wood residue solution
into their cell, generate isobutanol from the simple sugars, and then
secrete the isobutanol out of their cell and into the solution. As
isobutanol accumulates in the solution, it is separated and collected.
As simple as this process description sounds, there are
significant challenges. The wood residue solution is a
complex mixture of many chemicals including the simple
sugars. The isobutanol being produced, plus some of the
chemicals, called fermentation inhibitors, are toxic to yeast
and can significantly reduce growth and isobutanol output.
Gevo researchers are using multiple approaches to address
this challenge.
One approach takes advantage of yeast’s ability to reproduce rapidly
and modify its genetic makeup to adapt to varied environments. As
yeast reproduce in the wood residue solution, individual yeast
strains are isolated. These individual strains are evaluated for their
growth and isobutanol output and their ability to withstand the
toxic conditions. Over the course of testing many stains, individual
strains emerge as superior to other strains. These superior strains
are then selected and the cycle of strain selection and testing
continues. Ultimately strains are isolated that can resist the toxic
elements and produce isobutanol at a high level.
Another approach to improving isobutanol
yields was to evaluate yeast performance on
wood residue solution generated from different
upstream processes. Gevo tested yeast
performance on pretreated hydrolysate
samples, or wood residue solutions, derived
from multiple pretreatment protocols
developed within the NARA project.
Optimizations in upstream processes of
conversion pipeline, specifically the NARA
team’s decision to utilize mild bisulfite as the
preferred pretreatment method, has effectively
increased the efficiency of the fermentation
process by decreasing the number of
fermentation inhibitors and significantly
enhancing the efficiency of enzymatic
hydrolysis.
Gevo has optimized the fermentation process,
and performance has reached a level that can
enable further scale-up to support the
production of 1,000 gallon of biojet fuel. Gevo
will continue to provide input to refine the
process model in order to support the 1,000
gallon biojet fuel demonstration task.
Goals:
 What are the steps in the process of converting lignocellulosic biomass
to biofuel?
 What is the source of energy in plants and where is it stored?
 How can we harness the energy stored in plants to produce fuel?
 What are some of the challenges and complexities associated with the
conversion process?
Objectives:
Students will understand:
 where the energy in plants comes from
 the three basic steps of the conversion process
 the various methods used in each step of the conversion process
 that pretreatment is the most difficult step in biomass conversion to fuel
representing up to 20% of the cost of fuel production
 that there is an ongoing ethical debate about the techno-economic feasibility
of a biojet fuel industry
 that optimizing the conversion process is a very important step in creating an
economically sound and environmentally responsible biojet fuel industry
QUESTIONS
• What are the steps in the process of
converting lignocellulosic biomass to biofuel?
• What is the source of energy in plants and
where is it stored?
• How can we harness the energy stored in
plants to produce fuel?
• What are some of the challenges and
complexities associated with the conversion
process?
PLEASE note that pretreatment is the
most difficult step in biomass conversion
to fuel representing up to 20% of the cost
of fuel production
PLEASE note that there is an ongoing
ethical debate about the techno-economic
feasibility of a biojet fuel industry
PLEASE note: that optimizing the
conversion process is a very important step
in creating an economically sound and
environmentally responsible biojet fuel
industry
ACTIVITY 1- Materials:
• visual of a plant tissue that shows cell walls
• visual of plant cell wall cross-section showing lignin binding cellulos
• and hemicellulose
• scrap of paper for each student
• approximately 10 sugar cubes for each student or each group of students
• mud (or eggless cookie dough or peanut butter)
• hot water
• small (about 32 oz.) container
• cocoa krispies or other cereal that changes the milk color
• another piece of scrap paper for each student
ACTIVITY 2:
Step 1: 1/3 the students will be considered hemicellulous, 1/3 cellulose
and the rest lignins. Have them wear name cards of “H, C, or L”
Step 2: Have the celluloses form lines of 4-6 students and link arms.
Have the hemicelluloses do the same, but in lines separate from the
cellulose
lines. the hemicellulose and cellulose lines stand parallel to
Step 3: Have
each other.
Step 4: Have the lignins surround the hemicellulose and
cellulose lines. Then have the lignin students hold hands over
and through the cellulose/hemicellulose lines, so that the
lignins' arms are reaching through and across the lines.
The visual should be of lines of cellulose and
hemicellulose surrounded by a lignin web.
Question: Why it is necessary to pretreat
lignocellulosic biomass?
Ways in which biomass can be pretreated.
Compare at least two forms of pretreatment in
terms of their advantages and disadvantages.
Question: Explain how the first step of
the activity was similar to and different
from the actual removal of lignin.
PLEASE note : That hydrolysis is the breaking
up of polysaccharides (starches – in this case
cellulose and hemicellulose) into
monosaccharides.
PLEASE note that hydrolysis can use enzymes
or chemicals that break the bonds between
individual sugar molecules.
Question: How was hydrolysis represented
in the activity, and how this representation
was accurate or inaccurate.
PLEASE note that fermentation is the process
by which an organism such as a yeast takes in
sugars, uses the energy contained within them,
and changes them into alcohols.
PLEASE consider why it might be necessary to
have individual sugar monomers for the next
step in the process, fermentation by a yeast.
PLEASE note that different yeasts can have
different alcohol outputs (i.e. ethanol or
isobutanol)