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S1
Supporting Information for “Structural Analysis of Pyrolytic
Lignins Isolated from Switchgrass Fast Pyrolysis Oil”.
Michael Fortin1, Megan Mohadjer Beromi
1, Amy Lai
1, Paul C. Tarves
1, Charles A. Mullen
2,
Akwasi Boateng2, Nathan M. West
1*
1Department of Chemistry and Biochemistry, University of the Sciences, 600 South 43rd Street,
Philadelphia, Pennsylvania 19104, United States
2USDA-ARS, Eastern Regional Research Center, 600 E. Mermaid Lane, Wyndmoor, PA 19038,
United States
Table of Contents
Experimental Details ..................................................................................................................... S2
FTIR spectra of lignin samples ..................................................................................................... S4
Table S1. FTIR quantification of condensed structures................................................................ S4
Table S2. FTIR peak assignments ................................................................................................ S4
Table S3. Assignment of 13
C-1H correlation signals in the HSQC spectrum for polysaccharides
found in hemicellulose .................................................................................................................. S5
Table S4. Assignment of 13
C-1H correlation signals in the HSQC spectrum for lignin functional
groups ............................................................................................................................................ S6
DEPT 135 Spectra......................................................................................................................... S7
1H-
13C HMBC spectra................................................................................................................. S11
1H-
13C HSQC spectra .................................................................................................................. S16
GC-MS Chromatograms from [K][Mn(malonate)2(H2O)2] Oxidations ..................................... S19
Pyrolyzed Lignin Solvent Fractionation Diagram ...................................................................... S28
References ................................................................................................................................... S30
S2
Experimental Details
Production of switchgrass pyrolysis oil
The pyrolysis was conducted using the previously described reactor and methods.1-4
Carthage
switchgrass cultivar was the biomass feedstock for the pyrolysis. The biomass was ground in a
Wiley mill and sifted through minus 2-mm mesh before use. Fast-pyrolysis of switchgrass was
carried out in a bubbling fluidized bed of quartz sand at temperatures of ∼500 °C with a
residence time of <1.0 s. The system comprised a 7.5 cm (3 in.) diameter fluidized bed reactor
section, followed immediately by a cyclone to remove biochar. Pyrolysis vapors were condensed
by a series of four condensers cooled by cold water (∼4 °C); the remaining aerosols were
collected by electrostatic precipitators (ESP). The ESP fraction of the pyrolysis oil typically
contains most of the aerosols and pyrolytic lignins and hence was the fraction that was used for
isolation of the pyrolytic lignin described in this work.
Procedure for extracting lignin from biomass
The method is based on literature procedures.5-6
Ten grams of dried ball milled switchgrass was
placed in a 1 liter round bottom flask. To which was added 300 ml of dioxane: water 9:1 v/v
solution, containing 0.1 N hydrochloric acid. The flask was fixed with a reflux condenser and
refluxed under argon for 1 hour. The liquid was isolated by vacuum filtration, and neutralized
with 8 grams of sodium bicarbonate. The pH was check by litmus paper. The solution was
filtered, and concentrated to ¼ the original volume by rotary evaporation. The lignin was
precipitated from ice cold water, by adding drop-wise in 400 ml volume with rapid stirring. The
solids were filtered dried over phosphorous pentoxide, at 30 °C in a vacuum oven. Any lipids
present were extracted with by Soxhlet using hexanes as the solvent. Lignin extraction resulted
in 3.7 g, 37% efficiency.
Treatment of lignin under DFRC conditions
Based on the published procedure.7
(Step 1) Acetyl Bromide Derivatization. Acetyl bromide in acetic acid (1:9 v/v; 12.5 ml) was
added to 50 mg sample of lignin. The reaction was stirred at 50 oC for 3 h in a flask. The solvent
was then evaporated to dryness under reduced pressure.
(Step 2) Reductive Cleavage. The above residue was immediately dissolved in the acidic
reduction solvent (dioxane/acetic acid/water = 5:4:1 = v/v/v, 12.5 mL). Zinc dust (250 mg) was
added, and the mixture was stirred at room temperature for 30 min. Then reaction mixture was
then quantitatively transferred to a saturated ammonium chloride solution (50 mL) in a
separatory funnel using methylene chloride (20 mL). The aqueous layer was extracted with
methylene chloride (2 x 10 mL). The combined extracts were evaporated to dryness under
reduced pressure and placed into the desiccator, over P2O5, for 24 h. The final acetylation step of
S3
the standard acetylation step of the standard DFRC protocol was not carried out so that the
released phenols could be labeled with 31
P, and determine by NMR.
Oxidative cleavage using potassium permanganate
Based on the published procedure;8 40 mg of pyrolyzed lignin was suspended in 40 ml of tert-
butyl alcohol:water (3:1, v/v) in a 250 ml round bottom flask. Next 40 ml of 0.5 M sodium
hydroxide, 100 ml of 0.06 M sodium periodate, and 20 ml of 0.03 M potassium permanganate
were added in this order to start the reaction. The mixture was kept at a temperature of 82 oC for
6 h with vigorous stirring. The color of the reaction remained purple throughout the reaction so
no additional amounts of sodium periodate and potassium permanganate were required. The
reaction was quenched by the addition of 10 ml of ethanol added dropwise. The mixture was
allowed to stand for 20 minutes to allow the manganese dioxide, formed during oxidation, to
settle out. The solution was then filtered through a plug of silica gel to remove the manganese
dioxide, after which the plug was washed with 1% sodium bicarbonate to ensure all the lignin
oxidation products were filtered. The filtrate was extracted twice by 50 ml of diethyl ether,
which in turn was extracted with 15 ml of 1% sodium bicarbonate. The aqueous phases were
combined and adjusted to a pH of 6.5 with 9 M sulfuric acid. The solution was then evaporated
to 30 ml. The solution was then diluted with 20 ml of tert-butyl alcohol water (1:1, v/v), and 0.9
g sodium carbonate. To this solution was added 5 ml of 30% hydrogen peroxide. The solution
was then heated with stirring at 50 oC for 10 minutes. The reaction was quenched upon the
addition of 100 mg of manganese dioxide, after which the mixture was allowed to stand for 2
hours. Next the mixture was filtered through celite, and the filtrate was acidified to a pH of 2
with 9 M sulfuric acid. The solution was extracted with 50 ml of acetone:dichloromethane (1:1,
v/v) three times, and the organic layers were combined, and dried with anhydrous sodium
sulfate. The solvent was removed by rotary evaporation. The residue was suspended in
dichloromethane and derivatized with TMSCl.
Oxidative Cleavage using [K][(malonate)2(H2O)2]
A 10 ml Schlenk tube, equipped with stir-bar, was charged with 40 mg of pyrolyzed lignin and
3.53 mg (~5 mol %) [K][Mn(malonate)2(H2O)2] in 5 ml THF, or acetonitrile. The contents was
then exposed to one 1 atm of oxygen. The tube was sealed and was placed in an oil bath 80 °C
with vigorous stirring for 14h. After which the liquid was passed through a silica plug,
concentrated in vacuo. The residue was suspended in acetonitrile and injected into the GC.
S4
FTIR spectra of lignin samples
Table S1. FTIR quantification of condensed structures.
Wavenumbers F1 F2 F3 F4 Switchgrass
1510 cm-1
0.03060 0.03697 0.0136 0.345 0.4208
1595 cm-1
.03705 0.03727 0.0134 0.642 0.4238
Ratio 0.8256 0.99195 0.98529 1.00872 0.9929
Table S2. FTIR peak assignments.
Fraction 1 Fraction 2 Fraction 3 Fraction 4 Non pyrolyzed Assignments
3415 O-H stretch
3296 3898 3412 3316 3450 O-H stretch
1722 1715 1715 1713 1715 C=O stretch unconjugated ketones
1647 1612 1612 1634 1596 C=O stretch conjugated to aromatic
ring
1456 1516 1516 1456 1516 C-H deformations, asymmetric in –
CH3 and ..-CH2-
1319 1370 1370 1341 1382 Syringyl ring breathing with C-O
stretching
1228 1264 1261 1319 1261 Guaiacyl ring breathing with C-O
stretching
1120 1111 1111 1125 1099 C-H bomd deformation in syringyl
ring
1059 1067 C-O stretch sugar ring
1032 1049 1052 1041 1021 Aromatic C-H deformation plus C-O
deformation in primary alcohols
851 891 891 841 Out of plane C-H bend in aromatic
ring
A B C
S5
Table S3. Assignment of 13
C-1H correlation signals in the HSQC spectrum for polysaccharides
found in hemicellulose.
Chemical shift C/H (ppm) Assignment
58.9/3.6 -D-Xylp (C5/H5)
60.7/3.5 -D-Xylp (C4/H4)
62.6/3.4 -D-Xylp (C3/H3)
68.7/3.2 -D-Xylp (C2/H2)
76.4/3.2 -D-Xylp
79.6/4.1 -D-Xylp
99.2/5.2 4-O-MeGlcA anomeric
98.7/4.7 (1-4)--D-Glcp (C1H1)
102.7/4.3 (1-4)--D-Xylp anomeric
102.2/5.2 (1-4)--D-Araf anomeric
101.7/5.2 -D-Xylp Reducing end
114.6/5.0 -D-Xylp Reducing end
S6
Table S4. Assignment of 13
C-1H correlation signals in the HSQC spectrum for lignin functional
groups.
Chemical shift C/H (ppm) Assignment
20.7/2.1 Biaryl methylene
53.0/3.4 C-H Phenyl coumarin
53.5/3.07 C-H Resinol
55.6/3.7 OMe
62.5/3.7 (C-H) Phenyl coumarin
69.7/3.5 (C-H) Resinol
89.5/5.0 (C-H) Phenyl coumarin
104.1/6.5 (C2,6/H2,6) Syringyl
107.1/7.1 CStilbene C=O Syringyl
112.7/6.9 (C2,/H2) C=O Guaiacyl
115.5/5.8 (C-H) p- Coumaraylated ester
115/5.6 (C5/H5) in Guaiacyl
119.1/6.6 C=O C6/H6 in Guaiacyl
123.2/7.4 Phenolic ether linked ferulate ester
126.5/7.3 (CStilbene
129.4/7.3 (C2,/H2,) p-OH phenyl (cinnamyl alcohol)
129.4/6.8 (C6/H6)p-OH phenyl (cinnamyl alcohol)
129.4/5.2 (C2,6/H2,6) Coniferyl alcohol (allylic
alcohol)
132.1/7.7 (C2,6/H2,6) p-hydroxybenzoate (phenolic
OH free)
154.1/7.9 (C-H) Ferulate ester
S29
Extraction of pyrolyzed lignin, Part 2: Separation of fractions 1-4 from hexane insoluble material
S30
References
1) Boateng, A. A.; Daugaard, D. E.; Goldberg, N. M.; Hicks, K. B. Ind. Eng. Chem. Res. 2007,
46, 1891.
2) Boateng, A. A.; Mullen, C. A.; Goldberg, N.; Hicks, K. B.; Jung, H.-J. G.; Lamb, J. F. S. Ind.
Eng. Chem. Res. 2008, 47, 4115.
3) Nsimba, R. Y.; Mullen, C. A.; West, N. M.; Boateng, A. A. ACS Sustainable Chem. Eng.
2013, 1, 260.
4) Nsimba, R. Y.; West, N.; Boateng, A. A. J. Agric. Food. Chem. 2012, 60, 12525.
5) Bjorkman, A. Nature 1954, 174, 1057.
6) Guerra, A.; Filpponen, I.; Lucia, L. A.; Saquing, C.; Baumberger, S.; Argyropoulos, D. S. J.
Agric. Food. Chem. 2006, 54, 5939.
7) Lu, F.; Ralph, J. J. Agric. Food. Chem. 1997, 45, 2590.
8) Gellerstedt, G. In Methods in Lignin Chemistry; Lin, S. Y., Dence, C. W., Eds.; Springer:
1992, p 322.
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