Catalytic conversion of biomass using solvents derived from lignin

Article abstract of DOI:10.1039/c2gc35203f

We report an approach by which the hemicellulose and cellulose fractions of biomass are converted through catalytic processes in a solvent prepared from lignin into high value platform chemicals and transportation fuels, namely furfural, 5-hydroxymethylfurfural, levulinic acid and γ-valerolactone. The Royal Society of Chemistry.

Full text of DOI:10.1039/c2gc35203f

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COMMUNICATION
Catalytic conversion of biomass using solvents derived from lignin†
a,b
a
a
a
b
Pooya Azadi, Ronald Carrasquillo-Flores, Yomaira J. Pagán-Torres, Elif I. Gürbüz, Ramin Farnood
a
and James A. Dumesic*
Received 10th February 2012, Accepted 16th March 2012
DOI: 10.1039/c2gc35203f
We report an approach by which the hemicellulose and cellu-
lose fractions of biomass are converted through catalytic pro-
cesses in a solvent prepared from lignin into high value
platform chemicals and transportation fuels, namely fur-
fural, 5-hydroxymethylfurfural, levulinic acid and
γ-valerolactone.
aqueous phase. In addition, the organic solvent enables extrac-
tion of LA from acidic aqueous solutions (e.g., as produced in
10
the Biofine process ), which can then be utilized as a chemical
intermediate or can be selectively hydrogenated in the solvent to
GVL, the latter serving as a chemical intermediate for polymers
and solvents, as well as a blending agent for transportation fuels.
The energy density of GVL for use as a transportation fuel can
be increased by decarboxylation to form butene, followed by
The production of second-generation biofuels from lignocellulo-
sic biomass can be achieved through the intermediate production
butene oligomerization to gasoline (branched C species) or jet
8
1
11
of oxygenated platform molecules, such as furan intermediates
fuel (branched C –C species).
8
16
(
furfural (FuAl), furfuryl alcohol (FuOH) and 5-hydroxymethyl-
An underlying strategy to implement the roadmap outlined in
Scheme 1 is to identify organic solvents that can be used to
extract biomass-derived products and intermediates (such as
FuAl, FuOH, LA, GVL) from acidic aqueous solutions. In our
previous work, we have utilized 2-sec-butylphenol (SBP) as an
furfural (HMF)), levulinic acid (LA), and γ-valerolactone
2
(GVL). We report herein an approach by which the hemicellu-
lose and cellulose fractions of biomass can be converted to these
platform chemicals using an organic solvent obtained by depoly-
merization of lignin.
3,12
effective solvent.
In the present report, we show that the cata-
Scheme 1 shows our proposed roadmap for the conversion of
lignocellulosic biomass to fuels and chemicals. Solid biomass is
first subjected to mild pre-treatment in an aqueous solution con-
taining dilute acid to solubilize the hemicellulose as xylose, fol-
lowed by heating of this aqueous stream to achieve dehydration
of xylose to furfural. The use of a biphasic reactor is employed
in this step to continuously extract the reactive FuAl from the
lytic depolymerization of lignin can be used to produce a lignin-
derived solvent (LDS), containing alkyl-substituted phenolics
such as propyl guaiacol (PG) and propyl syringol (PS), that is
effective for selective biomass conversion processes, thereby
eliminating the need to purchase large amounts of a petroleum-
derived solvent and transport it to the biorefinery site. Lignin-
derived solvents based on PG and PS have the following attri-
butes to facilitate conversion of the cellulose and hemicellulose
fractions of biomass into fuels and chemicals: (i) they have high
partition coefficients for extraction of FuAl, FuOH, LA, and
GVL from aqueous solutions containing mineral acids, while not
extracting significant amounts of mineral acids, and (ii) they
have higher boiling points compared to that of the final product
(Table S.1†), such that the product is removed at the top of the
distillation column used to achieve the final product separation.
We prepared our lignin-derived solvent (LDS) from poplar
wood using hot-compressed water under moderate hydrogen
pressure (e.g., 4 MPa) utilizing a metal catalyst (i.e., Pd/C, Rh/C
and Pt black) to achieve selective hydrogenolysis of C–O–C
bonds in a one-pot reactor, followed by extraction from the
aqueous phase using diethyl ether (DEE) to obtain a mixture of
PG, PS, guaiacyl propanol and syringyl propanol. The final LDS
mixture was obtained by evaporating the DEE solvent, followed
by the removal of guaiacyl propanol and syringyl propanol from
the mixture by extraction with water, leaving a hydrophobic
organic phase composed of PS and PG in a 4 : 1 mass ratio. The
total yield of monomers (all four species) obtained from this
method is typically 30 wt%, which corresponds to 60% of the
3
aqueous phase. The remaining biomass is then subjected to
further treatment to solubilize cellulose as glucose, and a bipha-
sic reactor is employed in the subsequent step to dehydrate
glucose to HMF by enabling the continuous extraction of the
4
–7
reactive HMF product from the acidic aqueous phase.
HMF
can then undergo acid hydrolysis to LA and equimolar amounts
of formic acid (FA). Similarly, FuAl can be converted to LA by
8,9
first undergoing reduction to FuOH over a metal catalyst, fol-
lowed by conversion to LA over an acid catalyst. The selective
hydrolysis of FuOH and HMF to LA is favored at low concen-
trations of the reactant, and a biphasic reactor can be employed
for these conversions, where the function of the organic solvent
is to release the reactive reactant continuously into the acidic
a
University of Wisconsin-Madison, Department of Chemical and
Biological Engineering, Madison, WI 53706, USA. E-mail: dumesic@-
engr.wisc.edu; Fax: +608-262-5434; Tel: +608-262-1095
b
University of Toronto, Department of Chemical Engineering and
Applied Chemistry, Toronto, ON M5S 3E5, Canada
†
Electronic supplementary information (ESI) available: Lignin depoly-
merization, liquid–liquid extractions, biphasic reactions, selective hydro-
genation of LA to GVL. See DOI: 10.1039/c2gc35203f
13
theoretical maximum. Therefore, with catalytic aqueous phase
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Scheme 1 Roadmap for conversion of lignocellulosic biomass (rectangles) to chemicals (ovals) and fuels (pentagons), passing through the inter-
mediate formation of C and C sugars (hexagons). Dashed arrows indicate processes that can be carried out using a lignin-derived organic solvent for
5 6
the production of furfural, 5-hydroxymethylfurfural (HMF), levulinic acid, and/or γ-valerolactone (GVL).
Table 1 Liquid–liquid extractions of high value platform chemicals using alkylphenol solvents in a 1 : 1 mass ratio with aqueous solutions at 298 K
a
Entry
Solvent
Compound
Concentration (M)
% Mole in organic phase
Partition coefficient (Morg/Maq
)
1
2
3
4
5
6
7
8
9
PG
PG
PG
PG
PG
PG
PG
PG
LDS
LDS
LDS
LDS
LDS
LDS
LDS
LDS
FuAl
FuAl
0.2
1.0
0.2
1.0
0.2
1.0
0.7
2.0
0.2
1.0
0.2
1.0
0.2
1.0
0.7
2.0
70 ± 1
77 ± 1
77 ± 2
82 ± 1
75 ± 2
74 ± 3
40 ± 1
41 ± 2
68 ± 3
75 ± 2
78 ± 3
80 ± 2
73 ± 1
75 ± 2
39 ± 2
38 ± 1
2.8 ± 0.2
FuOH
FuOHb
HMFb
HMF
4.0 ± 0.4
2.9 ± 0.4
c
LA
0.68 ± 0.04
2.6 ± 0.4
c
LA
FuAl
FuAl
1
0
1
1
FuOH
FuOHb
HMFb
HMF
3.8 ± 0.6
1
1
1
1
1
2
3
4
5
6
2.9 ± 0.3
c
LA
LA
0.63 ± 0.04
c
a
c
b
Value reported is the average of entries. The initial aqueous solution was saturated with NaCl to increase the partitioning to the organic phase.
Aqueous solution also contained 0.5 M sulfuric acid.
treatment of 1 kg of dry wood under hydrogen, we can produce
0 g of phenolic monomers. The chemical structures of the
major phenolic monomers obtained from the depolymerization
of hardwood lignin are depicted in Fig. S.1,† and the selectivity
with respect to each monomer over different metal catalysts is
given in Table S.2 (see ESI†).
Table 1 shows results for liquid–liquid extractions of FuAl,
FuOH, HMF and LA using PG and LDS in contact with an
aqueous phase. For all entries, the extracted amounts in the
organic phase are comparable at the two concentrations evalu-
ated. Moreover, the LDS extracts all species with similar effec-
tiveness compared to pure PG. Even though the mass ratio of
PG : PS is 1 : 4 in the LDS, the structural similarity between PG
and PS is high, differing only by one methoxy group, thus result-
ing in similar behavior. The aqueous phase was saturated with
NaCl for entries 5, 6, 13 and 14 to increase the partitioning of
the target compound into the organic phase. Even though the
partitioning of LA is low (40%) (entries 7, 8, 15 and 16), the
extent of extraction can be improved by using an organic to
aqueous mass ratio higher than 1.
Table 2 shows results for the biphasic dehydration of glucose
and xylose to HMF and FuAl, the biphasic hydrolysis of FuOH
to LA, and the biphasic hydrolysis of HMF to LA. We have
reported elsewhere that SBP in contact with an acidic aqueous
7
14
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Table 2 Conversion of glucose, xylose, furfuryl alcohol and HMF in biphasic reactors to produce HMF, furfural and levulinic acid, respectively,
a
using PG, LDS and SBP as organic solvents
Product
b
Entry
1
Reactant
Glucose
wt%
5
Solvent
O : A
2
T (K)
Conversion (%)
Compound
HMF
Selectivity (%)
% in organic solvent
PG
443
85 ± 1
82 ± 2
91 ± 2
96 ± 2
97 ± 2
75 ± 2
75 ± 1
98 ± 2
99 ± 1
99 ± 1
100
58 ± 2
59 ± 2
67 ± 2
71 ± 2
73 ± 1
85 ± 2
82 ± 2
80 ± 2
63 ± 2
65 ± 2
66 ± 4
82 ± 3
88 ± 1
97 ± 1
75 ± 3
74 ± 2
75 ± 2
84 ± 2
90 ± 2
73 ± 2
76 ± 2
81 ± 5
LDS
SBP
PG
LDS
PG
LDSc
SBP
PG
2
3
HMF
1
3
423
443
Levulinic acid
Furfural
Xylose
1.5
0.15
4
Furfuryl alcohol
1
3
2
398
Levulinic acid
LDSc
SBP
a
b
c
Additional details of the experiments are given in Table S.4 of ESI.† Organic to aqueous solvent ratio by mass. Data taken from ref. 3.
7
,20
phase is an effective biphasic system for reactions of furan com-
pounds. The results in Table 2 now show that high selectivities
are achieved when PG is used as the extracting solvent. Impor-
tantly, high selectivities are also achieved when using LDS pre-
pared from poplar wood.
systems.
These systems utilized organic solvents (e.g., methyl
3
isobutyl ketone, 2-butanol and tetrahydrofuran), which suffer
from low partitioning of FuAl into the organic phase. Using
alkylphenol solvents (e.g., SBP) that have high partition coeffi-
cients for FuAl, it is possible to concentrate the FuAl to several
times the initial concentration of xylose in the aqueous phase by
using small amounts of the extractive solvent relative to the
The biphasic dehydration of glucose to HMF (Table 2, entry
1
0
) was carried out starting from 5 wt% glucose in an aqueous
3
.1 M HCl solution saturated with NaCl. A Lewis acid (AlCl in
aqueous layer. We demonstrate here that both PG and the LDS
3
this case), is utilized to catalyze the isomerization of glucose to
perform in a manner that is similar to the SBP solvent (Table 2,
entry 3), resulting in 85% and 82% selectivities to FuAl, respect-
ively, at 75% xylose conversion, using an organic to aqueous
mass ratio equal to 0.15. The partitioning of FuAl into the
organic layer leads to 75% and 84% of the FuAl being retained
in PG and LDS, respectively.
5,15,16
fructose,
from which HMF is produced in the presence of
the mineral acid catalyst. Using PG in a 2 : 1 mass ratio to the
aqueous phase, 58% selectivity towards HMF was obtained at
8
5% conversion, and 82% of the total HMF is retained in the
organic phase. Importantly, the LDS is able to extract up to 88%
of HMF, while exhibiting a similar behavior in the selectivity.
These results compare well to glucose conversion (91%) and
HMF selectivity (67%) obtained using SBP as the extractive
organic phase. The partitioning of the majority of the HMF into
the organic phase allows for its efficient separation and for the
recycling of the mineral acid present in the aqueous phase.
Several studies have also demonstrated the effectiveness of
The FuAl in the organic phase can be distilled out at this point
to serve as an end product or it can undergo subsequent hydro-
8,9
genation in the gas phase over a metal catalyst to form FuOH,
which can be converted in another biphasic reactor to LA. The
yield of LA by hydrolysis of FuOH is limited by polymerization
reactions, even at low concentrations. Thus, we implemented a
biphasic reactor system where the FuOH is slowly partitioned
into the aqueous phase from the organic phase. Due to the high
partitioning of FuOH into PG and the LDS, it is possible to
minimize the concentration of FuOH in the aqueous phase. The
LA yields obtained at complete conversion using PG (63% yield,
with 73% of LA being in PG) and the LDS (65% yield, with
76% of LA being in LDS) compare well with experiments using
SBP as a solvent, where 81% of the LA was partitioned into the
4,5,17,18
biphasic systems in the dehydration of glucose to HMF
utilizing high boiling organics (for example, dimethyl sulfoxide)
with the intention of suppressing side reactions; however, the use
of organic extractive solvents containing only C, H, and O
1
7
atoms, such as the LDS, is advantageous.
The hydrolysis of HMF to LA has previously been studied in
a single-phase system where HCl and H SO have been ident-
2
4
3
ified as the best catalysts for the system resulting in high yields
organic medium with comparable yields (∼65%). As shown
19
21
3
(
i.e., 94%). However, purification of LA and recovery of the
previously by Lange et al. and Gürbüz et al., a semi-batch
operation mode can be adopted to process higher concentrations
(∼10–20 wt%) of furfuryl alcohol.
mineral acid is an energy intensive process involving solvent
extraction combined with distillation steps. The application of
our biphasic processing strategy using PG and LDS, for an
organic : aqueous mass ratio of 3 : 1 (Table 2, entry 2), results in
high selectivities (72%) for production of LA at almost complete
conversion, allowing the processing of HMF in the extracting
solvent without the need of a purification step. Additionally, the
majority of the produced LA (75%) is recovered in the organic
phase, enabling the separation of LA from the mineral acid in
the aqueous phase.
Scheme 1 shows the hydrogenation of LA to GVL as a step
where both the C and C pathways can be combined and pro-
5
6
cessed into transportation fuels. Several publications have
12,22,23
addressed this reaction with a variety of methods.
In the
present study, we studied the conversion of LA to GVL, using
an organic stream containing LA and FA in PG that was prepared
by contacting PG with an aqueous stream of LA and FA pre-
pared to match the effluent composition from the acid-catalyzed
hydrolysis of cellulose. Table 3 shows the effects of temperature
and weight hourly space velocity (WHSV) on the hydrogenation
Analogous to the dehydration of glucose, conversion of
xylose to FuAl has been previously studied in biphasic
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Table 3 Hydrogenation of LA to GVL over 5 wt% Ru/C in the
presence of FA using PG as the solvent at different reaction conditions
Ru/C catalyst is effective for the conversion of LA to GVL in
the lignin-derived solvent, it is possible to use bimetallic cata-
lysts, such as RuSn, to further minimize the rates at which the
solvent is hydrogenated during the conversion of LA to GVL
and to ensure stable activity.
a
Conversion (%) GVL
selectivity
(%)
GVL rate
b
T
WHSV
(mmol/
−
1
−1
Entry (K) (h
)
LA
PG
cat
g h )
1
2
3
453 2.2
473 2.1
453 1.2
62
82
100
0.5
3.6
6.0
96
94
93
13.6
17.2
13.2
Acknowledgements
a
This material is based upon work supported as part of the Insti-
tute for Atom-efficient Chemical Transformations (IACT), an
Energy Frontier Research Center funded by the U.S. Department
of Energy, Office of Science, Office of Basic Energy Sciences,
and work supported by the DOE Great Lakes Bioenergy
Research Center (www.greatlakesbioenergy.org), which is sup-
ported by the U.S. Department of Energy, Office of Science,
Office of Biological and Environmental Research, through Coop-
erative Agreement DE-FC02-07ER64494 between The Board of
Regents of the University of Wisconsin System and the U.S.
Department of Energy. We also received funding from the
National Science Foundation under Award No. EEC-0813570
Feed composition corresponds to entry 2 in Table S.3:† LA/FA = 42%/
%. H pressure in the reactor was fixed at 13.8 bars. WHSV is defined
2
b
9
as mass of LA fed per mass of catalyst per hour.
(
i.e., the Center for Biorenewable Chemicals, CBiRC, at Iowa
State University). The authors thank Zuleika Oquendo for her assist-
ance in the performed investigations. Also, P. A. acknowledges
financial support from the NSERC Michael Smith scholarship.
Notes and references
1
2
D. Alonso, J. Bond and J. Dumesic, Green Chem., 2010, 12, 1493–1513.
I. Horvath, H. Mehdi, V. Fabos, L. Boda and L. Mika, Green Chem.,
2
008, 10, 238–242.
E. I. Gürbüz, S. G. Wettstein and J. A. Dumesic, ChemSusChem, 2012, 5,
83–387.
Y. Roman-Leshkov, J. Chheda and J. Dumesic, Science, 2006, 312,
1933–1937.
3
4
5
3
Fig. 1 Levulinic acid conversion versus time on stream over RuSn
4
/C
at 453 K, 34.5 bar H
2
pressure and WHSV= 0.4 h− . Feed is obtained
1
E. Nikolla, Y. Roman-Leshkov, M. Moliner and M. Davis, ACS Catal.,
2
011, 1, 408–410.
using PG to extract LA and FA from aqueous solution, according to
entry 2 in Table S.3.†
6
7
J. Chheda and J. Dumesic, Catal. Today, 2007, 123, 59–70.
J. Chheda, Y. Roman-Leshkov and J. Dumesic, Green Chem., 2007, 9,
3
42–350.
B. Nagaraja, A. Padmasri, B. Raju and K. Rao, J. Mol. Catal. A: Chem.,
007, 265, 90–97.
R. Rao, R. Baker and M. Vannice, Catal. Lett., 1999, 60, 51–57.
8
9
2
of LA to GVL in PG solvent using a Ru/C catalyst in a packed
bed flow reactor. Increasing the temperature from 453 to 473 K
increased the conversion of LA as well as the conversion of PG,
from 62% to 82% and from 0.5% to 3.6%, respectively. In a
similar manner, lowering the WHSV of the feed from 2.2 to
1
0 S. W. Fitzpatrick, US Pat., 5608105, 1997.
11 J. Q. Bond, D. Martin-Alonso, D. Wang, R. M. West and J. A. Dumesic,
Science, 2010, 327, 1110–1114.
2 D. Alonso, S. Wettstein, J. Bond, T. Root and J. Dumesic, Chem-
SusChem, 2011, 4, 1078–1081.
3 N. Yan, C. Zhao, P. J. Dyson, C. Wang, L. T. Liu and Y. Kou, Chem-
SusChem, 2008, 1, 626–629.
4 Y. Roman-Leshkov and J. Dumesic, Top. Catal., 2009, 52, 297–303.
5 H. Zhao, J. Holladay, H. Brown and Z. Zhang, Science, 2007, 316, 1597–
1
−1
1
.2 h affected the extent of hydrogenation for both LA and
1
PG, with an increase from 62% to 100% and from 0.5% to 6.0%,
respectively. Hydrogenation of PG solvent could be completely
suppressed with the addition of Sn to 5 wt% Ru/C in a 1 : 4
1
1
1600.
1
2,24
Ru : Sn molar ratio as demonstrated previously for SBP.
Even
16 M. Chidambaram and A. Bell, Green Chem., 2010, 12, 1253–1262.
7 Y. Roman-Leshkov, C. Barrett, Z. Liu and J. Dumesic, Nature, 2007, 447,
1
though the addition of Sn decreased the GVL production rate
3.4 mmol g−1 h ), RuSn /C exhibited good stability for 80 h of
−1
982–985.
(
4
1
1
8 J. B. Binder and R. T. Raines, J. Am. Chem. Soc., 2009, 131, 1979–1985.
9 B. Girisuta, L. Janssen and H. Heeres, Green Chem., 2006, 8, 701–709.
20 R. Xing, A. Subrahmanyam, H. Olcay, W. Qi, G. van Walsum, H. Pendse
and G. Huber, Green Chem., 2010, 12, 1933–1946.
1 J. Lange, W. van de Graaf and R. Haan, ChemSusChem, 2009, 2, 437–
operation at around 96% LA conversion, as shown in Fig. 1.
In summary, the use of lignin-derived alkylphenols as solvents
in biphasic reactors enables in situ separation of products and/or
reactants, thereby minimizing undesirable side reactions in the
aqueous phase and enabling the recycling of the mineral acid
catalysts in biomass processing. The overall processing strategy
presented here could benefit from further optimization of lignin
depolymerization processes to increase the yields obtained in the
production of alkylphenol compounds. In addition, while the
2
441.
22 J. Serrano-Ruiz, D. Wang and J. Dumesic, Green Chem., 2010, 12, 574–
577.
2
3 J. Serrano-Ruiz, D. Braden, R. West and J. Dumesic, Appl. Catal., B,
010, 100, 184–189.
2
2
4 S. G. Wettstein, J. Q. Bond, D. M. Alonso, H. N. Pham, A. K. Datye and
J. A. Dumesic, Appl. Catal., B, 2012, 117, 321–329.
1576 | Green Chem., 2012, 14, 1573–1576
This journal is © The Royal Society of Chemistry 2012