1. 5th
International Scientific Conference May 20-22, 2014 Tatranské Matliare
Renewable Energy Sources 2014 High Tatras, Slovak Republic
CONVERSION OF LIGNIN TO LIQUID COMPOUNDS
Kalabová, M., Šutý, Š., Lauko, T., Jablonský, M., Ház, A., Sládková, A., Šurina, I.
Institute of Natural and Synthetic Polymers, Department of Wood, Pulp and Paper,
Slovak University of Technology, Radlinského 9, 812 37 Bratislava, Slovakia
e-mail: kalabova.magdalena@gmail.com
Abstract
This paper reports a process for converting lignin into value-added chemicals. The thermochemical process is
termed solvolysis (alcoholysis) of lignin. The reaction consists of heating the lignin at high temperatures (270 –
300°C) in the air atmosphere. Lignin reacts with hydrogen-donor in the presence of alcohol in a high-pressure
reactor. A liquid fraction and a significant amount of the char are the most important products of solvolytic
depolymerization reaction. The pressure and temperature behavior of observed process was described. A used
method employed in this report was described, and also some important results were noticed. Thermal treatment
in the air atmosphere can be a promising conversion of lignin into value-added chemicals.
Keywords
Lignin, solvolysis, acid, alcohol, value-added chemicals
1 INTRODUCTION
Lignin is a copolymer consisting of the
monolignols called p-coumaryl alcohol, coniferyl
alcohol and sinapyl alcohol. The lignin monomers
are linked by these cleavages: β-O-4-aryl ether, -
O-4-aryl ether, 4-O-5-diaryl ether, β-5-
phenylcoumaran, 5-5-biphenyl and ββ- (Resinol)
[1]. The most abundant linkages in a lignin
structure are β-O-4 aryl ether bonds.
Depolymerization of lignin is achieved by
thermochemical process. This process lead to
breaking the most important bonds such as β-O-4
aryl ether and 5-5-biphenyl bonds remain
untouched. Nowadays, lignin is not used only in
combustion process for the heat production. Its
structure gives new possibilities for its usage in the
future. Lignin appears the new source for chemicals
and fuels. Common challenge in the lignin
degradation to liquids, containing phenolic
compounds, includes the degree of
depolymerization and deoxygenation. Lignin
depolymerization has been explored within
solvolysis and also pyrolysis approach [2].
Solvolytic depolymerization treatment was
performed in the presence of hydrogen donors like
tetralin [3, 4]. Davoudzadeh et al. [5] used tetralin
with phenol as solvent for lignin hydrogenolysis.
Hydrogen donating solvents such as 9, 10-
dihydroanthracene (AnH2) and derivatives [6] were
used for lignin depolymerization because it is a
stronger hydrogen donor compared to tetralin [7].
Liquefaction of biomass for the production of
chemicals by solvolysis was performed in acetone,
ethanol or water [8]. Ethanol is appropriate solvent
for biomass because of its good properties and it
has a low critical temperature. The idea of lignin
degradation leads to usage of the cheap and simple
chemicals that can give value-added chemicals [7].
Formic acid and acetic acid can be used as
hydrogen donor chemicals. A solvolytic reaction in
the presence of some alcohols such as methanol,
ethanol and 2-propanol is interesting because of
their low cost and less harmful impact on the
environment. A molecular elimination of formic
acid is occurred by the solvolytic process at high
temperatures (Fig.1)
Fig. 1 Formic acid molecular elimination occurs
during solvolysis.
A main reaction is a solvolytic breaking the β-O-4-
aryl ether bonds. As a result of this process are
guaiacol and Hibbert’s ketones. Then guaiacol
reacts with ethanol at high temperatures during
deoxygenation process and decomposing formic
acid to hydrogen and carbon dioxide. The main
products of solvolytic reaction are phenol, 2-methyl
phenol, 3-methyl phenol and 2,3 – dimethyl phenol,
cresol, catechol and other phenolic derivates.
2 EXPERIMENTAL
Part of this paper describes the solvolytic one-step
lignin depolymerization. A closed system stirred

2. 5th
International Scientific Conference May 20-22, 2014 Tatranské Matliare
Renewable Energy Sources 2014 High Tatras, Slovak Republic
reactor from Parr Instruments was used for all
experiments. A reactor was filled with dry lignin
powder, acid (formic or acetic) and alcohol
(methanol, ethanol or isopropanol) in the different
volumes. The lignin was dried for 24 hours at 105
°C before using it in the reactor. The same volumes
of different kinds of acid and also different kinds of
alcohols were used in all experiments. Then the
reactor was closed and heated to 300°C for 5 hours.
The used lignin from Swedish company Innventia
AB was characterized. The elemental analysis made
by Vario Macro Cube was C (65 wt %); N (0.12 wt
%); H (5.44 wt %); (1.14 wt %) S and O (28.3 wt
%) was calculated by difference [9]. After 5-hour
reaction time in reactor was finished, a heater and
also the reactor stirring were turn off. A reactor was
cooled by the air stream to room temperature. It has
never been cooled by cold water because a char
amount can arise. An experimental process of
conversion lignin to liquid is described on the
following picture (Fig. 2).
Fig. 2 Lignin to liquid conversion
Elemental analysis: A solid product (char) was
analysed by elemental analysis by Vario Macro
Cube. The elemental composition of char in the
CHNS was performed and oxygen amount was
calculated by difference.
A heat of combustion: Higher heating value of char
was determined in a FTT calorimetric bomb used a
standard method.
GCMS analysis: A liquid samples were analysed by
GS/MS analyser. Firstly, samples were filtrated by
syringe filters. Before analysis, the filtrated samples
must be diluted with an appropriate solvent.
3 RESULTS AND DISCUSSIONS
In an experimental part were performed 6
combinations of lignin reaction with acid and
alcohol in one step (Tab.1).
Tab.1 Six combination of lignin reaction with acid
and alcohol.
The pressure and temperature behavior of reaction
was investigated for all experiments. In a closed
reactor was observed an autogenous pressure but
the highest value was changed according to the
used acid or alcohols. The highest pressure was
observed by the lignin reaction with formic acid
with all kinds of alcohols. A lignin reaction with
acetic acid and all kinds of alcohol wasn’t
performed in so high pressure. A formic acid was
converted to carbon dioxide and hydrogen during
the lignin depolymerisation in a large amount. A
temperature course in lignin reaction with formic
acid and three kinds of used alcohols is shown on
the following picture on the first three positions. On
the second three positions is shown a lignin reaction
with acetic acid and also three kinds of used
alcohols (Fig. 3).
Fig. 3 A temperature course in the same reaction
time (5h). Two kinds of acids and three kinds of
alcohols were used.
A temperature course didn’t depend on used
alcohol. It had almost the same temperature
progress. It was the same in a case of lignin
reaction with acetic acid and also three kinds of
used alcohols. A temperature 300 °C was achieved
between 75 – 90 minutes of reaction time in both
cases. A difference in a pressure course of the
Exp. SM
[g]
acid
[ml]
alcohol
[ml]
T
[°C]
t
[h]
1 13
Lignin
30
HCOOH
40
MeOH
300 5
2 13
Lignin
30
HCOOH
40
EtOH
300 5
3 13
Lignin
30
HCOOH
40
2-PrOH
300 5
4 13
Lignin
30
CH3COOH
40
MeOH
300 5
5 13
Lignin
30
CH3COOH
40
EtOH
300 5
6 13
Lignin
30
CH3COOH
40
2-PrOH
300 5

3. 5th
International Scientific Conference May 20-22, 2014 Tatranské Matliare
Renewable Energy Sources 2014 High Tatras, Slovak Republic
lignin reaction with acid and alcohols is visible.
The higher values of pressure were achieved in a
case lignin reaction with formic acid and alcohols.
A temperature stabilised at the constant values after
75 minutes. The pressure had to be regulated
because of limitation of reactor. The max pressure
in reactor is limited to 200 bar. If the pressure was
190 bar in a reactor, it was necessary to open a
valve and release the congested gas. On the
following picture is shown a pressure course in the
lignin treatment with acids and alcohols.
Fig. 4 A pressure course in the same reaction time
(5h). Two kinds of acids and three kinds of alcohols
were used.
GCMS analysis of the liquid products was carried
out by the same conditions. The samples were
diluted in a 1:1 ratio in acetone and were analysed.
On all of pie charts we can see a part belonging to
acetone and also chemicals used for the lignin
treatment. All chemicals were taken into account
and shown in a pie chart.
Fig. 5 A pie chart – GCMS analysis of liquid phase
for lignin treatment with formic acid and methanol.
300 °C, 5 h, formic acid : methanol 3:4 (70 ml
loading).
Fig. 6 A pie chart – GCMS analysis of liquid phase
for lignin treatment with formic acid and ethanol.
300 °C, 5 h, formic acid : ethanol 3:4 (70 ml
loading).
Fig. 7 A pie chart – GCMS analysis of liquid phase
for lignin treatment with formic acid and
isopropanol. 300 °C, 5 h, formic acid : isopropanol
3:4 (70 ml loading).
Fig. 8 A pie chart – GCMS analysis of liquid phase
for lignin treatment with acetic acid and methanol.
300 °C, 5 h, acetic acid : methanol 3:4 (70 ml
loading).
Alcohols
24%
Acetone
(solvent for
dilution)
37%
Esters 1%
Phenolic
compounds
22%
Furans 1%
Others 15%
Alcohols
35%
Acetone
(solvent for
dilution)
56%
Phenolic
compounds
5%
Others
4%
Alcohols
34%
Acetone
(solvent for
dilution)
25%
Phenolic
compouds
21%
Furans
1%
Others
19%
Acetone
(solvent for
dilution)
30%
Esters
26%
Acetic acid
17%
Phenolic
compounds
8%
Others
19%

4. 5th
International Scientific Conference May 20-22, 2014 Tatranské Matliare
Renewable Energy Sources 2014 High Tatras, Slovak Republic
Fig. 9 A pie chart – GCMS analysis of liquid phase
for lignin treatment with acetic acid and ethanol.
300 °C, 5 h, acetic acid : ethanol 3:4 (70 ml
loading).
Fig. 10 A pie chart – GCMS analysis of liquid
phase for lignin treatment with acetic acid and
isopropanol. 300 °C, 5 h, acetic acid : isopropanol
3:4 (70 ml loading).
The highest yields of phenolic compounds were
achieved during lignin treatment with the formic
acid. The treatment with the acetic acid wasn’t so
effective. When we don’t take into account solvents
and main chemicals used for lignin treatment, the
main products are phenolic compounds in a case of
formic acid and alcohols. In a case of usage the
acetic acid, the main products are esters, ethyl
acetate in reaction with ethanol and isopropyl
acetate in reaction with isopropanol.
4 CONCLUSIONS
This report investigated the solvolytic
depolymerization reaction of lignin. The different
amount of phenols and phenols derivates were
related to used acid and alcohol. A highest amount
of phenolic compounds were investigated in lignin
treatment with formic acid and methanol or iso-
propanol. A solvolytic depolymerisation reaction
can be used for lignin conversion to liquids.
5 ACKNOWLEDGEMENTS
This article was created with the support of the
Ministry of Education, Science, Research and Sport
of the Slovak Republic within the Research and
Development Operational Programme for the
project "University Science Park of STU
Bratislava", ITMS 26240220084, and
by the project of National Centre for Research and
Application of Renewable Energy Sources, ITMS:
26240120016, and by the project Finalization of
Infrastructure of the National Centre for Research
and Application of Renewable Energy Sources,
ITMS: 26240120028, and
by the project Competence centre for new
materials, advanced technologies and energetics
ITMS: 26240220073, co-funded by the European
Regional Development Fund.
This publication was supported by the Slovak
Research and Development Agency under the
contract No. APVV-0850-11, and by the project
VEGA 1/0775/13.
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Alcohols
14%
Esters
3%
Acetic acid
16%
Acetone
(solvent for
dilution)
22%
Phenolic
compounds
6%
Ethyl
acetate
36%
Others
3%
Acetone
(solvent for
dilution)
21%
Esters
7%
Isopropyl
acetate
66%
Others
6%