Download The Effect of Irradiatied Adsorbed Species on cellulose by ESR

The Effect of Free Radical
Precursors on the Radiolysis of
Cellulose
Matthew O’Reilly
Senior Comprehensive Exam
Catholic University Chemistry Dept.
Outline
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Cellulose and its degradation
Methods of pre-treatment
Experimental Approaches
Acknowledgements
Cellulosic Ethanol
• Cellulosic ethanol is the preferred biofuel
• Cellulose is one of the most widespread natural polymers and is a
key component of plant’s cell walls
• The production of cellulosic ethanol biofuel is based on fermentation
of glucose derived from plant cellulose.
• Producing cellulose (and subsequently ethanol) from cellulose is
difficult because of the complex and rigid structure of the
lignocellulosic materials of the cell walls in plant materials
• Pre-treatment with chemicals or radiation is necessary in order to
break down the lignocellulosic structure and produce cellulose
fragments
Process Flow Sheet of Plant
Material to Ethanol
Lignocellulosic Plant Material
↓
Pre-treatment (e.g. AFEX, other acids
or bases)
Cellulose and large fragments
↓
Hydrolysis (enzymatic or acidic)
Glucose ( and xylose etc.)
↓
Ethanol
Fermentation
Cellulose Structure
Mosier, N.; Wyman, C.; Dale,B.;
Elander,R.; Lee,Y.;
Holtzapple,M; Ladisch,M.
Features of promising
technologies for pretreatment
of lignocellulosic biomass.
BioResource Technology 2005,
96, 673-686.
Mosier, N.; Wyman, C.;
Dale,B.; Elander,R.;
Lee,Y.; Holtzapple,M;
Ladisch,M. Features of
promising technologies for
pretreatment of
lignocellulosic biomass.
BioResource Technology.
2005, 96, 673-686.
Mosier, N.; Wyman, C.; Dale,B.; Elander,R.;
Lee,Y.; Holtzapple,M; Ladisch,M. Features of
promising technologies for pretreatment of
lignocellulosic biomass. BioResource
Technology. 2005, 96, 673-686.
Pre-treatments on Cellulose
• Requirements for effective pre-treatment:
1) Avoids need for reducing the size of
biomass particles.
2)Limits formation of degradation
products that inhibit growth of fermentative
microorganisms
3) Minimizes energy demands and
limits cost.
Decomposing Cellulose to Glucose
The University of Edinburgh, Institute of Cell &
Molecular Biology: The Microbial World.
http://www.biology.ed.ac.uk/research/groups/jde
acon/microbes/armill.htm (accessed Jan 3,
2010).
Cellulose Strucuture
• The structure of cellulose is very rigid and strong, which is why
radiation or strong acids or enzymes must be used to facilitate its
break-down. The monomer units of cellulose consist of pyranose
rings in the chair conformation with axial hydrogen atoms. This
structure is characterized by high rigidity and restricts the
conformational transitions.
MIT. Chemistry- A Way
of Life.
web.mit.edu/clubchem/i
mages/benzophenone.p
ng. (accessed Jan. 5,
2010).
Breakdown of Cellulose using
Gamma Radiation
Ershov, B.G. Radiation-Chemical Degradation of
cellulose and other polysaccharides. Russian
Chemical Reviews. 1998, 67, 314-334.
• The propagation of the free radical with scission of the polymeric
chain.
• First, cellulose decomposes into large fragments and then to the
ulitimate radiolysis products which include RCHO, RCOOH, CO2,
CO, etc…
• The optimal yield obtained using this method was 50:1 radical
formation. This ratio is critical in determing the economic feasibility
of this process.
Radiation Pretreatment
• Radiation pre-treatment helps in accomplishing two purposes:
1) Break-up of the lignocellulosic cell wall structure to allow
access to the cellulose fibers during subsequent treatment
2) Degradation of cellulose into smaller polymeric fragments
• The economic feasibility of using radiation as a pretreatment
depends on the yield of free radicals formed upon radiolytic scission
of bonds.
• The focus of the research conducted dealt with the following
question: Is it possible to enhance the yield of radicals through the
use of free radical initiators?
Free Radical Initiators
•Adsorbing free radical initiators onto cellulose and exposing them to radiation
may enhance the number of free radicals that are formed upon irradiation and
thus enhance the degradation of cellulose. The different species used as
intiators in the present study have been hydrogen peroxide, benzoyl peroxide,
bromine water and benzophenone.
MIT. Chemistry- A Way of Life.
web.mit.edu/clubchem/images/b
enzophenone.png. (accessed
Jan. 5, 2010).
Determination of Glucose Yield
using Benedict’s Reagent
• Method: Soaking cotton balls with differing concentrations of 30%
hydrogen peroxide (a source of OH radicals upon irradiation)
• OH radicals are very powerful oxidizing agents and they produce
radicals capable of initiating chain reactions.
MIT. Chemistry- A Way of Life.
web.mit.edu/clubchem/images/ben
zophenone.png. (accessed Jan. 5,
2010).
Effect of H2O2 on Glucose
Production
• The degradation of cellulose was by measured by
glucose yields using Benedict’s reagent.
• Cotton balls were soaked in different concentrations of
hydrogen peroxide were exposed to gamma radiation.
• Samples of differing concentrations of H2O2 were made
and a cotton ball was placed in each respective solution.
The samples were then exposed to gamma radiation.
• The samples were analyzed using a GenTech UV/Vis
Spectrophotometer. The two wavelengths obtained for
each sample were at 700nm and 515nm which
corresponded to the Cu+ and Cu2+ respectively.
Determination of Glucose Yields by
the use of Benedict’s Reagent
• The Benedict’s Reagent test is used to analyze the
content of reducing sugars in solutions, which in this
case would be glucose. The reaction for the Benedict’s
reagent is shown below.
• If glucose is present the solution will turn from green
(representing the Cu2+ in the reagent) to a brick red
color (representing the Cu+ product).
-CHO+2Cu2++H2O → -COOH+2Cu++2H+
Problems
• Cannot use Benedict’s method in presence of H2O2
H2O2 + Cu+ → H2O + Cu2+
Thus it is not possible to observe reduction of Cu2+ by
glucose.
1st solution: Boil sample to decompose H2O2 before
adding Benedict’s solution
2nd solution: Add catalase enzyme before adding
Benedict’s solution.
Catalase Enzyme
• Since residual H2O2 interferes with the Benedict method
the analysis of the samples was done by decomposing
the excess H2O2 with catalase and then allowing the
glucose product to react with Benedict’s solution
• Catalase is a common enzyme that catalyzes the
breakdown of hydrogen peroxide into water and oxygen.
The decomposition of hydrogen peroxide with catalase is
as follows:
2H2O2 → 2H2O + O2
Sample with Catalase enzyme
UV Spectrophotometer Glucose
Determination
•
The data obtained from the first trials showed a consistent error that was
believed to be caused by the presence of the hydrogen peroxide. In order
to try and remove the residual H2O2 interferences the samples were boiled
first for 5 minutes and then for 20. The results were inconsistent.
-The sample with the catalase enzyme showed good results, with the
sample irradiated with the smallest concentration of H2O2 showing the
smallest amount of glucose production and the sample irradiated with the
largest concentration of H2O2 showing the highest glucose formation.
•
The method has low sensitivity to low concentrations of glucose
ESR
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ESR: Detects substances with unpaired electrons such as free radicals.
In the ESR technique, a magnetic field is applied allowing the unpaired
electron spins to form two distinct energy levels.
Microwaves are applied at a frequency of 9 GHz in the presence of a
magnetic field to allow resonance transition between the two levels.
New Mexico State University: Dept.
of Chemistry.
http://www.chemistry.nmsu.edu/stud
ntres/chem435/Lab7/. (accessed
Jan.5 2010).
Experiments with Additives
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1g of cellulose powder
10 mL of 1% solution of each additive
Stirring together for 1 day
Decantation and air-drying
Irradiation of part of the sample with 100 kGy Co-60 gamma source
ESR spectroscopy performed
Results
Pure irradiated benzophenone ESR
spectra of pure irradiated benzophenone
with a peak at 3350 gauss.
Pure unirradiated
benzophenone
ESR of Pure Irradiated Cellulose
Pure irradiated celluloseESR spectra
of pure irradiated cellulose with a
maximum peak around 3345G and
some splitting peaks at 3320G and
3335G.
Pure unirraditated cellulose
Cellulose with 0.2g benzophenone
Irradiated cellulose with 0.2g
benzophenone ESR shows a peak at
3345 with a larger magnitude than
that of cellulose and benzophenone
as well as a peak at 3320G.
Irradiated cellulose with 0.2g
benzophenone after 2 months
shows a splitting of the large peak
at 3347G with another smaller one
at 3320G.
Cellulose with 0.5g benzophenone
Irradiated cellulose with 0.5g
benzophenone ESR shows a split
peak at 3340G with smaller peak at
3320G.
Irradiated cellulose with 0.5g
benzophenone after 2 months ESR
shows a peak at 3345G and another
at 3320G.
Discussion
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The ESR technique showed free radicals that were present in the structure.
The samples that were not exposed to radiation showed no results on the
ESR spectra because no free radicals were present. The samples that
were exposed to radiation each showed unique spectra caused by the free
radicals present in that structure.
The spectra of the pure irradiated benzophenone and cellulose each had
distinctive features and when benzophenone was added, elements of each
ones spectra can be seen in the spectra of the mixture. This mixture also
showed unique elements of its own that were not present in either the
benzophenone or cellulose ESR. This supports the idea that perhaps the
benzophenone incorporated itself into the structure of cellulose.
The spectra after two months from when the original samples were
analyzed, the spectra of the 0.2g of benzophenone showed interesting
changes in the shape of the spectra. The 0.5g of benzophenone added did
not show distinct changes.
Reasons for Change in Spectra
• The spectrum of the irradiated benzophenone-treated cellulose is
different from that of the separate ingredients because the free
radical may have incorporated itself into the cellulose structure.
• The later change in the spectrum (of the 0.2g benzophenone-doped
sample) can be attributed to the reaction of the original radical with
atmospheric oxygen.
R•+O2→RO2•
• This hypothesis could have been tested by storing the sample under
an inert gas such as argon or nitrogen instead of air.
• Further experiments were planned but could not be carried out due
to the failure of the ESR system.
Acknowledgements
• Dr. Barkatt
• Dr. Al-Sheikhly of University of Maryland
• Ms. Marina Chumakov
Minimizing Undesirable HMF
Formation in Chemical Pretreatment
• HMF (Hydroxymethyl furfural) which leads
to the formation of levulinic acid and formic
acid
• Inhibitory to microbial fermentation
AFEX (Ammonia Fiber Explosion)
• Flow aqueous ammonia through a column
reactor packed with biomass at elevated
temperatures.
• Aqueous ammonia reacts with lignin and cause
depolymerization of lignin and cleavage of lignincarbohydrate linkages.
• Good method, but need to increase the extent of
delignification to achieve better fractionation of
biomass and hence higher yields of glucose.
Glucose→Ethanol
• Fermentation
C6H12O6 → 2 C2H5OH + 2 CO2
• Combustion
C2H5OH + 3 O2 → 2 CO2 + 3 H2O
Lignin
• Lignin structure made
up primarily of
methoxylated
polyphenol rings