The document summarizes research on the thermal decomposition of lignin in the presence of a hydrogen donor solvent (2-propanol). Key findings include: 1) The maximum bio-oil yield of 42 wt.% was achieved at a reaction time of 15 minutes. Further increasing the reaction time did not significantly increase yields. 2) Analysis showed the reaction produced short-chain alkylphenol compounds as the 2-propanol solvent donated hydrogen atoms, reducing unsaturated bonds on the aromatic rings. 3) Gas chromatography/mass spectrometry analysis identified 19 monomeric phenolic compounds in the bio-oil, and their percentages increased with longer reaction times.

1. Chemical and Biological Engineering
BioMaP REU
August 2nd, 2013
Alejandra Martínez Guajardo, Kwang Ho Kim, Xianglan Bai, Robert C. Brown
Acknowledgements: This material is based upon work supported by the National Science Foundation under Grant No. EEC 1156933
Hydrogen Donor Solvent Assisted Thermal Decomposition of Lignin
Introduction
Materials and Methods
Results & Discussions
Lignin
• Makes up ~30% of lignocellulosic biomass, one of the world’s most abundant renewable materials
• It is separated in wood pulping process while manufacturing paper
• Phenols and benzenes can be produced from lignin by cracking, making it the source of valuable chemicals
• 19 monomeric phenolic compounds were identified using GC/MS and percentages of peak
areas were compared
• The yield of short chain alkylphenols increased with reaction time and this was accompanied
by a decrease in phenols with unsaturated side chains
• It is likely that hydrogen originating from 2-propanol mainly reacted with C=C bonds on side
chains of aromatic rings
Sample: Corn stover organosolv lignin (100 mg)
• Solvent: 2-propanol (1 mL)
Analytical Methods:
• Molecular weight distribution using GPC
(Gel permeation chromatography)
• Compositional analysis by GC/MS
(Gas chromatography/Mass spectrometry)
Product Recovery Process:
• Slurry product was extracted with 5 mL of acetone
• Solution was then filtered to recover solids and liquid
• The mixture of liquid and acetone was dried at 50ºC to
obtain bio-oil
[1] Kleinert, M., & Barth, T. (2008). Phenols from Lignin. Chemical Engineering Technology, 31(5), 736-745.
WILEY-VCH Verlag. Retrieved from http://doi.wiley.com/10.1002/ceat.200800073
[2] Vasilakos, N. P. (1985). Hydrogen-donor solvents in biomass liquefaction. Department of Chemical Engineering,
University of Texas, Austin, TX, Retrieved from http://pubs.acs.org/doi/pdf/10.1021/i200029a015
Average Molecular Weight and Polydispersity (GPC)
Bio-oil Yield
Molecular Weight Distribution (GPC)
• The yield of bio-oil reached a maximum point of
42 wt.% at the reaction time of 15 minutes
• It then started to level off as reaction time further
increased
Hydrogen Donor Solvent Assisted Thermal Decomposition of Lignin
• Lignin decomposes into bio-oil, biochar and non-condensable gases, generating free radicals that lead to
secondary reactions and the formation of large molecular weight compounds
• Solvolysis is a chemical reaction in the presence of solvent at elevated temperature and pressure
• A hydrogen donor solvent represents a possible pathway to avoid reactive functional groups in bio-oil
Equipment:
• Stainless steel batch reactor (volume of 3 mL)
• Heating medium: Techne industrial fluidized bed
Conditions:
• Reaction temperature: 300°C
• Reaction time: 5, 15, 30 and 45 minutes
Time (min)
2
7
8
10
11
13
14
15
19
10
13
1
5
6
7
18
184
3
14 15
9
16
17
12
12
Compositional Analysis (GC/MS)
Conclusions
References
• Optimum reaction time for maximum bio-oil yield was 15 minutes in the present experimental condition.
Further increase in reaction time reduced the yield of bio-oil.
• During solvolysis, phenols with unsaturated C=C bonds on side chains react with hydrogen atoms from 2-
propanol, and convert into short chain alkylphenols.
• Thermal decomposition of lignin in a hydrogen donor solvent could produce bio-oil with substantial
amount of stable monomeric phenols.
Lignin
SolidsLiquidsGases
GPC GC/MS
•Lignin solvolysis was conducted in
sealed glass capsule reactor
• The capsule reactor was heated in a
small furnace. At the end of reaction, the
volatiles were directly sent to online
GC/MS for analysis
• Allowed investigation of primary
products of reaction
Results from Micro Reactor coupled with GC/MS
Yield (wt.%) 5 min 10 min 15 min
Total monomeric phenols 3.86±0.25 4.05±0.09 4.28±0.47
Short chain alkylphenols 1.59±0.06 1.86±0.02 2.42±0.27
•In the online micro reactor, the yield of total
phenols increased from 3.9 to 4.3 wt.% with
increasing reaction time from 5 to 15 min
• The yield of short chain alkylphenols also
increased with higher reaction times
R1= H, CH3, CH2CH3 or CH2CH2CH3
R2 and R3= H or OCH3
Short chain alkylphenols
0
10
20
30
40
50
60
0.5 1 1.5 2 2.5 3 3.5
Selectivity(%)
Reaction time (min)
Selectivity of short chain alkylhenols
5 10 15
• The molecular weight of bio-oil ranged 700 to 858 Da, which slightly decreased with increasing
reaction time to 45 minutes
• Along with molecular weight, polydispersity decreased from 2.26 to 1.65
0
2
4
6
8
10
12
14
20 200 2000
Percentage(%)
Molecular Weight [Da]
5 min
15 min
30 min
45 min
1
2
• Compounds with a molecular weight range of 300 to 850 Da increased with reaction time
• High molecular weight compounds (>1000 Da) decreased as the reaction was extended
• It is likely that both thermal depolymerization of lignin and recombination of small
depolymerization products occurred simultaneously at increased reaction time
Results from batch reactor
Lignin Solvolysis in Batch Reactor
Micro Solvolysis Reactor coupled with online GC/MS
0.E+00
5.E+07
1.E+08
2.E+08
2.E+08
3.E+08
3.E+08
RelativeAmount(MSPeakArea,normalized)
5min
15min
30min
45min
Hydrogen donor and free
radical form a lower
molecular weight product
2-propanol reaction as a hydrogen donor
C C CH H
H
H
H
H
H
OH
C C CH H
H
H
H
H
H
O
heat
+ H∙
H∙ + R∙ RH n(R∙) (R)n
When there is no hydrogen
source, radicals recombine
and turn into char
0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
50%
5 min 15 min 30 min 45 min
LiquidYield
Reaction Time
Selectivity of short alkylphenols
0
100
200
300
400
500
600
700
800
900
1000
MolecularWeight(Da)
Weight Average
5 min
15 min
30 min
45 min
0
0.5
1
1.5
2
2.5
Polydispersity
Polydispersity
5 min
15 min
30 min
45 min