Effects of Organosolv Fractionation Process on the Properties of

Switchgrass Lignin as a Precusor for Carbon Products Pyoungchung Kim,

1* Darren Baker1, Nicole Labbé

1

1Center for Renewable Carbon, University of Tennessee, Knoxville TN 37996

* Corresponding Author. Email: pkim1@utk.edu

Introduction

Feedstock : Switchgrass

Extractives Removal

Accelerated Solvent Extractor (ASE)

H2O extraction

• 100 oC, 7 min/cycle, 3 cycles

EtOH extraction

• 100 oC, 7 min/cycle, 3 cycles

Solvent Fractionation : Extractive-free

feedstock

Solvent mixture

H2O (50%), EtOH (36%), MIBK (14%),

Catalyst : H2SO4 (0.6 %, 0.05 M)

Study variables

Reaction time : 10, 20, 30, 40, 60, 80 min

10 min/cycle

Pressure : 1600 – 1700 psi

Temperature : 140, 160, 180 oC

Products

Cellulose : washed with DI water (2L)

Lignin : washed with DI water (2L)

Moisture content Extractives Ash Cellulose Hemicellulose Lignin

Average (%) 7.4 6.3 2.4 33.7 28.1 22.3

St dev (%) 0 0.0 0.3 0.7 0.9 0.6

Time (min)

0 20 40 60 80 100

Rem

ain

ed

bio

mass

(%

)

20

40

60

80140 oC

160 oC

180 oC

Time (min)

0 20 40 60 80 100

Hem

icellu

lose

(%

)

0

10

20

30

40

50

60

140 oC

160 oC

180 oC

Time (min)

0 20 40 60 80 100

Cellu

lose

(%

)

50

60

70

80

90

100

110

120

140 oC

160 oC

180 oC

Time (min)

0 20 40 60 80 100

Lig

nin

(%

)

0

10

20

30

40

50

60

140 oC

160 oC

180 oC

Biomass recovery Cellulose in solid fraction

Hemicellulose in

solid fraction

Lignin in solid fraction

Biomass loss in the reactor showed a gradual increase by reaction time under different temperature

and presented a loss up to 45 % at 140 oC, 55 % at 160 oC and 64 % at 180 oC for 60 min reaction

time.

Of the solid fraction, cellulose decreased less than 3 % under 140 oC, 7 % under 160 oC for 60 min,

and 30 % under 180 oC for 60 min.

Hemicellulose fraction significantly decreased for 60 min to 78 % under 140 oC, 88 % under 160 oC

and 95 % under 180 oC.

Simultaneously, lignin fraction also decreased to 72 % under 140 oC, 87 % under 160 oC and 87 %

for 30 min and did not decreased by time under 180 oC.

Principal component analysis (PCA) of FTIR spectra of lignin showed that lignins produced at 180 oC were apparently separated with other lignins produced 140 and 160 oC by the first principal

component (PC1, accounting for 75% of the total spectral variance) (Scores plot).

TGA showed that lignins produced at high temperature produced more residues (40.8±1.0%)

than lignins produced at low temperature (35.6±2.1% – 36±1.0%). This indicates that lignins at

high temperature may contain more condensed aromatic structures, which is more thermally

stable.

Derivative thermograms (DTG) showed that the first stage of maximum degradation (Tmax) at 280 oC is related to thermally weak side chains such as β-O-4 linkage in lignin. The second stage of

Tmax at 380 oC is related to lignin itself. The third stage of Tmax at higher than 650 oC is related to

functional groups present in lignins and their derivatives leading to complex crosslinked

structures that are thermally stable.

With increasing reaction time and temperature to isolate lignin from biomass, side chains were

broken and decreased.

Experimental set-up

Chemical composition (switchgrass)

Biomass recovery by Wet chemistry

Lignin by FT-IR

Introduction The desire to reduce fossil fuel derived products and mitigate greenhouse gas emissions with

increasing demand for natural products has led to the rapid expansion of the biomass-based

industry. The application of biomass fractionation provides clean product streams to produce a wide

range of value added products such as materials, chemicals, fuel, heat and power.

Clean fractionation is a type of organosolv pre-treatment that upgrades biomass feedstocks for a

biorefinery by separating the cellulose, hemicellulose, and lignin into pure streams for conversion

into value-added products.

Organosolv fractionation uses a mixture of an organic solvent and water to cleanly separate the

three major components of biomass. Through this solvent fractionation technique, the extraction

efficiency is improved, which reduces conversion times and increases yields, allowing the biomass

to be processed more economically. After fractionation, the solvent fraction is rich in lignin and

hemicellulose components and cellulose is present in the solid phase.

Objective The objective of this study was to optimize processing parameters of organosolv fractionation,

including time and temperature in terms of producing a derived lignin for carbon based materials

production

Switchgrass

ASE

(H2O, EtOH, MIBK, H2SO4)

Cellulose

Liquid fraction

extractivesASE

(H2O, EtOH)

Lignin

Hemicellulose

Solid fraction

Evaporation

Washing

Accelerated Solvent

Extractor (ASE)

Scores plot of PC2 (12%) showed that lignins

were also separated by longer reaction time with

higher temperature.

Loadings plot of PC2 indicate that lignins

produced at longer reaction time with higher

temperature were more oxidized.

Loadings plot by PC1 indicate that more

condensed aromatic structures are produced from

lignins produced at 180 oC

Lignin by Pyrolysis-GC/MS

Lignin by Thermogravimetric analysis

Gas chromatograms produced by pyrolysis at 450 oC for 12 s showed that lignins produced at

different temperature and time contained dominantly peaks of guaiacyl and syringyl subunits

and small peaks of carbohydrates (acetic acid, furfural) that were chemically bonded to lignin

even after washed by deionized water.

0 5 10 15 20 25 30 35 40

Inte

nsit

y (

a.u

.)

Time (min)

Furfural

MIBK

Acetic acid

Acetic acid Phenol

Methyl

Phenol

Guaiacol

Dimethyl

phenol

Methyl

guaiacol Mehtyl

benzalde

hyde

Ethylguai

acol

Vinyl

guaiacol

Propenyl

guaiacol

Syringol

Vanillin

Vanillic

acid

Acetosyringone

Methoxy

methylbenzo

furan

Methyl

eugenol

Vanillin Coniferyl

aldehyce

140-80

160-80

180-80

Temp (oC)

100 200 300 400 500 600 700 800 900

Wt

(%)

0

20

40

60

80

100

DT

G (

dw

t(%

)/dte

mp)

-0.06

-0.04

-0.02

0.00

180 oC-80min 180 oC-40min 160 oC-80min 160 oC-40min 140 oC-80min 140 oC-40min

Maximum yield of lignin was produced at 160 oC for 60 min and 180 oC for 30 min.

Increasing temperature and reaction time produced more condensed aromatic skeleton and less β-

O-4 linkage.

Lignins produced from switchgrass contained complex crosslinked structures with functional groups

and their derivatives.

Future work Structural features of lignin by Nuclear Magnetic Resonance.

Molecular weight distribution by Gel Permeation Chromatography.

References

Conclusion and Future work

Sing et al. “Lignin–carbohydrate complexes from sugarcane bagasse: Preparation, purification, and

characterization, Carbohydrate Polymers, 62, 57-66 (2005)

Bozell et al. “Biomass fractionation for the biorefinery: Heteronuclear mulitple quantum coherence-nuclear

magnetic resonance investigation of lignin isolated from solvent fractionation of switchgrass, Agriculture and

food chemistry, 59 9232-42 (2011)

SunGrant Initiative

Acknowledgement Wavenumber (cm-1

)

60080010001200140016001800

Loadin

g p

lot

(PC

1 7

5%

)

-0.10

-0.05

0.00

0.05

0.10 Loadings plot of PC1

Wavenumber (cm-1

)

60080010001200140016001800

Loadin

gs

plo

t (P

C2 1

2%

)-0.10

-0.05

0.00

0.05

0.10

0.15

1600 1504

G

1464

G

1408

1123

G

1030

1530

1719 1295

1220

G1157

830

Loadings plot of PC2

PC1 (76%)

-6 -4 -2 0 2 4 6

PC

2 (

12

%)

-2

-1

0

1

2

3

140-60

140-80

160-60

160-80

180-30

180-40

180-50

180-60

180-80

Scores plot