Reactive extraction of levulinate esters and conversion to γ-Valerolactone for production of liquid fuels

Article abstract of DOI:10.1002/cssc.201000396

Reactive extraction of cellulose-derived levulinic and formic acids with butene is utilized to obtain levulinate and formate esters, thereby allowing for recovery and recycle of H₂SO₄. The esters are converted over a dual-catalyst-bed system to GVL and 2-butanol, followed by production of butene to be recycled for reactive extraction and to be converted to liquid fuels by oligomerization.

Full text of DOI:10.1002/cssc.201000396

DOI: 10.1002/cssc.201000396
Reactive Extraction of Levulinate Esters and Conversion to g-Valerolactone
for Production of Liquid Fuels
Elif I. Gꢀrbꢀz, David Martin Alonso, Jesse Q. Bond, and James A. Dumesic*[a]
Biomass has been identified as a source of renewable carbon
for the production of energy, fuels, and chemicals, facilitating a
decreased dependence upon petroleum and a global reduc-
tion in greenhouse gas emissions. A promising approach for
the utilization of lignocellulosic biomass is the controlled re-
duction of the biomass feedstock’s oxygen content, to produce
platform chemicals that retain sufficient functionality for up-
grading to a variety of end products. In this respect, levulinic
acid (LA) has been identified as an attractive platform molecule
from which fine chemicals (e.g., d-aminolevulinic acid, diphe-
nolic acid) and fuel additives (e.g., levulinate esters, methylte-
trahydrofuran) can be produced.[1] A particularly promising de-
rivative of LA is g-valerolactone (GVL),[2] from which gasoline,
jet fuel, and diesel fuel components can be produced.[3–6] The
production of equimolar quantities of levulinic acid and formic
acids can be achieved, in good yield, from lignocellulosic bio-
mass[7,8] and cellulose[5] through hydrolysis with dilute sulfuric
acid. The hydrolysis of cellulose has been demonstrated
through several strategies. For example, treatments that use
dilute sulfuric acid,[5] concentrated hydrochloric acid,[9] solid
acids,[10] or ionic liquids[11] all yield levulinic and formic acids as
degradation products. To date, the preparation of levulinic acid
through hydrolysis with dilute sulfuric acid appears to offer the
most promising balance of cost, yield, and scalability, although
further developments are needed in product recovery and sul-
furic acid management. GVL can be obtained through the re-
duction of levulinic acid over a metal catalyst, preferably by
consuming hydrogen generated in situ via the decomposition
of formic acid.[12–14] However, the production of GVL by catalyt-
ic reduction of LA is complicated by the need to separate LA
from sulfuric acid, as residual sulfur leads to low catalytic activi-
ty and deactivation with time-on-stream.[5,15] Although promis-
ing strategies have been demonstrated for the production of
GVL from levulinic and formic acids,[16,17] these strategies are
carried out without sulfuric acid and its carryover must be ad-
dressed. Therefore, the motivation of the present work is to
demonstrate improved sulfuric acid management in levulinic
acid-centered biorefining. In the present state of the art, H2SO4
is recovered from LA in an energy-intensive process that in-
volves solvent extraction combined with distillation. Herein, we
report an improved, synergistic biorefining strategy that does
not require the use of external solvents or energy-intensive
distillation steps to separate the levulinic and formic acids
from H2SO4, and instead employs reactive extraction, using
butene, to produce hydrophobic esters of levulinic and formic
acids. Moreover, we show that these esters spontaneously sep-
arate from H2SO4 and can be converted to GVL over a dual-cat-
alyst-bed system. As we have shown previously, GVL can be
converted to butene and CO2 by catalytic decarboxylation over
an acid catalyst,[3] thereby providing the source of butene re-
quired for the reactive extraction step.
The process proposed herein relies on the extraction of levu-
linic and formic acids using alkenes (i.e., butene), in lieu of
using alcohols, for the production of levulinate and formate
esters, as first proposed by Manzer et al.[18] In particular, even
though Ayoub[19] has demonstrated the reactive extraction of
LA using alcohols, such as 1-pentanol, to form hydrophobic
levulinate esters, this extraction requires an external source of
alcohol and necessitates a distillation step for solvent recovery
from the ester product. In contrast, the use of butene as an ex-
tracting solvent is particularly advantageous, because butene
can be produced from GVL[3] and separates spontaneously
from the ester product upon decreasing the system pressure,
eliminating both the use of externally produced extracting sol-
vents and the need for distillative solvent recovery. The ester
products can be used directly as fuel additives[18,20] or to pro-
vide a platform for the production of specialty chemicals.[21]
Importantly, we show in the present manuscript that levulinate
esters can be converted to GVL in good yield using a dual-cat-
alyst-bed in a single reactor system, while utilizing formate
esters and unconverted formic acid (FA) as in situ sources of
hydrogen. This dual-catalyst-bed system achieves almost quan-
titative yields of H2 from FA and formate esters (over a Pd/C
catalyst) as well as high rates of GVL production from LA and
levulinate esters (over a Ru/C catalyst), whereas the simultane-
ous utilization of FA and formates to reduce LA and levulinates
cannot be achieved using either of these catalysts alone.
The strategy presented in this paper, summarized in
Figure 1, begins with the production of an aqueous solution
containing equimolar concentrations (2m) of LA and FA by hy-
drolysis of cellulose at 423 K using sulfuric acid (0.5m).[5] Some
of the water and the FA co-product are then removed by an
evaporation step to obtain a more concentrated solution of LA
and sulfuric acid, containing residual amounts of water and FA,
analogous to the initial stages of the Biofine Process.[7,8] The FA
product in water is retained for downstream hydrogen produc-
tion (in the dual-catalyst-bed system mentioned above), and
the concentrated LA product is contacted with butene, gener-
ating sec-butyl levulinate (BL) and sec-butyl formate (BF) esters
as major and minor products, respectively, using H2SO4 as a
catalyst. We have demonstrated that high yields, 85%, of the
levulinate ester can be attained at moderate temperatures
[a] E. I. Gꢀrbꢀz, Dr. D. M. Alonso, Dr. J. Q. Bond, Prof. J. A. Dumesic
Chemical and Biological Engineering Department
University of Wisconsin
Madison, WI 53706 (USA)
Fax: (+1)608-262-5434
E-mail: dumesic@engr.wisc.edu
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.201000396.
ChemSusChem 2011, 4, 357 – 361
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
357

Figure 1. Overall processing strategy, using first a single vessel for cellulose deconstruction and extraction of levulinic and formic acids, followed by a cascade
of flow reactors for production of GVL and butene. The red arrows represent streams that are recycled. Butene can be converted into liquid fuels by oligome-
rization reactions.
(<373 K) and short contact times (<120 min). Excess butene
can be recovered by vaporization, and the concentrated ester
product is then contacted with water, during which the hydro-
phobic ester separates spontaneously from the aqueous
phase, the latter of which retains 99% of the sulfuric acid to
be recycled for use in biomass deconstruction. The BL and BF
esters are subsequently processed in combination with the
aqueous FA product stream (obtained from the evaporation
step) using a dual-catalyst-bed in a single reactor to produce
GVL in nearly quantitative yields
extraction step, and the remainder of the butene (with inert
CO2) can be upgraded by oligomerization to obtain high-mo-
lecular weight alkenes suitable for jet-fuel applications.[3] The
details for the butene oligomerization step have been pub-
lished previously,[3] where an 87% yield was reported for C8+
alkenes from an equimolar mixture of butene and CO2. Table 1
shows results for reactive extraction of levulinic and formic
acids at various conditions. As shown in entry 1, esterification
of the aqueous solution obtained directly from the cellulose
with 2-butanol and CO2 as co-
products. The liquid effluent
from this reactor, consisting of
an aqueous solution of GVL and
2-butanol, can undergo decar-
boxylation and dehydration (of
GVL and butanol, respectively)
Table 1. Levulinic and formic acid conversions with sec-butyl levulinate and sec-butyl formate yields obtained
for butene extraction experiments with different aqueous phase concentrations, temperatures, and reaction
times. Butene:LA molar ratio is equal to 5:1.
Feed [M]
Entry T [K] t [h] LA FA H2SO4 H2O Conversion
Yield [%] LA
LA
H2O [ggÀ1 H2SO4
LA [%]
BL
org[a] [%] aq[a] [%] LA]
aq [M]
over
a SiO2/Al2O3 catalyst to
1
2
3
4
5
6
7
403 16
2
8
8
8
8
4
0
0
0
0
0
0
0.5
2
2
2
2
40
0
0
0
2
2
3
2
0
5
100
7
12
12
7
100
40
11(24)[c]
20(24)[c]
-
-
obtain butene and CO2.[3] Our ex-
periments for the simultaneous
conversion of GVL and a secon-
dary alcohol over SiO2/Al2O3 re-
sulted in almost quantitative
yields to the corresponding al-
kenes from both lactone and al-
cohol. A portion of the butene
can be recycled for the reactive
353
333
403
373
353
353
353
2
4
2
2
2
2
2
4.5 91
4.5 86
4.5 85
4.5 91
30
16.5 55
85
78
73
82
0
5
5
5
5
-
6
1
1
0.4
0.4
0.4
0.4
-
0.4
1.5
1.6
1
0
6.4 0 1.6
6.3 2.3 1.6
48
8
9[b]
11.3 84(48)[c]
11.3 60(49)[c]
78(43)[c] 5(28)[c]
59(47)[c] 20(27)[c]
353 12 6.3 2.3 1.6
[a] The percentages are calculated based on LA in the initial feed. Partition coefficient (Morg/Maq =1). [b] Bute-
ne:LA molar ratio is equal to 2:1. [c] Refer to FA/BF.
358
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ChemSusChem 2011, 4, 357 – 361

deconstruction step, described by Serrano-Ruiz et al. (2m LA
and FA in 0.5m H2SO4),[5] does not take place at our reaction
conditions, which are similar to conditions suggested by
Manzer et al.[18] Importantly, however, we have found that the
formation of butyl esters can be achieved with high yields by
employing a concentration step
aqueous phase with the remainder of the unconverted LA
(20%).
Table 2 shows that it is possible to convert BL to GVL and
butanol over a Ru/C catalyst (entry 1). While this conversion
has been proposed in a patent by the Shell Oil Company,[22]
(see Supporting Information) to
remove at least a portion of the
Table 2. Butyl levulinate and butyl formate conversions with GVL and CO2 yields and production rates for vari-
ous feed compositions over 10 wt% Pd/C, 5 wt% Ru/C or the dual-catalyst-bed system. P=35 bar, T=423 K for
entries 3 and 4 and T=443 K for the other entries.
water. Increasing the concentra-
tion of LA and H2SO4 results in
high yields of levulinates
(>85%) at short contact times
(2 h; entry 2) and allows for
quantitative recovery of the sul-
furic acid upon contact with
water. It is important to note
that the concentration step can
be accomplished with a single
evaporation, and it is the only
energy-demanding separation in
this process. Through the forma-
tion of hydrophobic butyl esters,
the need for solvent extraction
and distillation are eliminated,
reducing the energy demand of
levulinic acid recovery. Increasing
the temperature leads to a de-
crease in the yields (entries 2–5),
an increase in the production of
degradation products, and a re-
Entry Feed
Catalyst WHSV [hÀ1] Conversion [%]
BL/BF
Yield [%] Gas phase conver-
GVL/CO2 sion [%][f]
1[a]
2[a]
3[a]
4[a]
2m BL
Ru/C
Ru/C
Ru/C
Ru/C
5.5[b]
5.5[b]
0.9[b]
1.3[b]
21/-
78/-
91/-
24/45
19/-
76/-
89/-
22/22
0.5
0.9
1.5
0.7
2m BL & 6m H2O
1m BL & 6m H2O
1m BL & 1m BF & 6m
H2O
5[a]
6[a]
7
2m BF
Pd/C
Pd/C
Pd/C
Pd/C
+Ru/C
0.5[b]
0.5[b]
1.5[e]
0.9[e]
-/10
-/43
-/5
-/41
4/95
-
-
0
12
2m BF & 6m H2O
Simulated feed[c]
Extraction product[d]
(Table 1, entry 9)
51/98 (including FA)
96/98 (including LA & 95/92
FA)
8
[a] 1-butanol is the solvent. [b] WHSV is calculated using the weight of only the esters in the feed. [c] Organic
stream: 4.43m BL and 1.55m BF (no additional solvent), aqueous stream: 1.96m FA. [d] Organic stream: 3.40m
BL, 1.23m LA and 0.96m BF, 0.67m FA (no additional solvent), aqueous stream: 1.83m FA. [e] WHSV is calculat-
ed using total weight of feed and catalyst. (aq. stream volume/org. stream volume=1.5) For entry 8, the
weight ratio of Pd/C to Ru/C=1.3. [f] Light alkanes produced from the total butanol (solvent + obtained from
conversion of butyl esters) and butene present.
duction in the amount of H2SO4 recovered. The amount of FA
present in the LA solution is determined by the extent of evap-
orative concentration step (see Supporting Information). The
presence of FA decreases the concentration of water and in-
creases the yield of BL from 48% (entry 7) to 78% (entry 8),
with 43% yield of BF from FA. Upon contact with water after
the esterification step, the aqueous phase contains the H2SO4
and a portion of the unconverted LA and FA, and this aqueous
solution can be recycled to the cellulose deconstruction reac-
tor, in which the LA and FA species are essentially inert.[5] The
organic phase after the esterification step and contacting with
water contains the BF and BL esters and the rest of unconvert-
ed LA and FA (see Table 1 and Supporting Information for de-
tailed analysis). The final amounts of LA and FA in the organic
phase depend on the amount of water added to phase sepa-
rate the esters (see Supporting Information). For example, as
shown in entry 7, at 55% conversion of LA, when 6 g of water
per gram of LA is added, only 11% of the unconverted acid is
retained in the organic phase, whereas 89% remains in the
aqueous phase. At a similar LA conversion (60%), in entry 9,
when only 1 g of water per gram of LA is added, 50% of the
unconverted LA is partitioned into the organic phase and the
remainder (50%) remains in the aqueous phase. At these con-
ditions the organic stream contains 80% of the LA initially
present in the aqueous feed solution with sulfuric acid, 60%
being in the form of the ester product and 20% being the un-
converted LA, while 99% of the SA is recovered (1.6m) in the
we demonstrate here that the rate of GVL production can be
increased significantly by co-feeding water along with the
ester (entry 2). We suggest that the presence of water leads to
hydrolysis of the ester and thereby enables the reduction to
proceed through an LA intermediate, leading to a higher over-
all rate for GVL production. However, an important deficiency
of the Ru/C catalyst is that it does not achieve effective conver-
sion of LA and BL in the presence of FA and BF. For example, it
can be seen from entries 3 and 4 in Table 2 that BF inhibits the
production of GVL from BL over Ru/C. Moreover, the Ru/C cata-
lyst leads to the undesirable dehydration of FA to produce CO
and H2O, as well as the desirable dehydrogenation pathway to
yield CO2 and H2,[23] thereby decreasing the hydrogen produc-
tion rate from BF. In addition, the Ru/C catalyst leads to metha-
nation of CO[24] (formed by dehydration of formic acid), which
consumes additional H2 (required for LA reduction).
The limitations of the Ru/C catalyst for the combined con-
version of levulinic and formic esters can be alleviated by
using an upstream bed of Pd/C, which favors the desirable de-
hydrogenation of FA to H2 and CO2 compared to dehydration
reactions leading to H2O and CO. In particular, it has been re-
ported that nearly quantitative yields of CO2 and H2 can be ob-
tained from FA over Pd/C at temperatures from 360 to
470 K.[25] As seen in entries 5 and 6, we have observed that
water is necessary to achieve high rates of BF conversion over
Pd/C, suggesting that this conversion takes place through the
intermediate formation of FA. In the presence of water, CO2 is
ChemSusChem 2011, 4, 357 – 361
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www.chemsuschem.org
359

obtained with almost 100% selectivity, confirming a negligible
rate of dehydration compared to the dehydrogenation of FA.
The positive effect of water on the conversion of levulinic and
formic esters is particularly advantageous, since it allows co-
feeding over the dual-catalyst-bed system of the aqueous solu-
tion of FA, obtained from the evaporation step prior to reac-
tive extraction, along with the organic ester stream. Entry 7 of
Table 2 shows that a Pd/C catalyst alone is not effective to con-
vert a feed mixture that contains BL and BF in the organic
stream and FA in the aqueous stream. Specifically, while 50%
of BL is converted to LA over Pd/C, further reduction to GVL
takes place at a very slow rate (0.002 mmolminÀ1 gÀ1). In con-
trast, it has been demonstrated that nearly quantitative yields
of GVL can be obtained from the reduction of LA over Ru/
C[6,18,26,27] at higher activities compared to Pd/C, Pt/C, Rh/C, Re/
C, and Ni/C.[26] Thus, given the comparable reaction conditions
for decomposition of formate esters over Pd/C and for hydro-
genation of levulinate esters over Ru/C, along with the lack of
CO2 methanation over Ru/C,[24] synergy is achieved by combin-
ing the catalytic properties of Pd/C and Ru/C in a dual-catalyst-
bed reactor to achieve in situ hydrogen generation alongside
GVL production. To study this hypothesis, a dual-catalyst-bed
of Pd/C followed by Ru/C was used to convert the organic so-
lution of levulinate and formate products obtained by reactive
extraction with butene (see Table 1, entry 9), along with the
aqueous solution of FA obtained in the evaporation step prior
to reactive extraction. Entry 8 in Table 2 shows that BF and FA
are converted to CO2 and H2 over Pd/C (92% yield), and the
conversion of BL and LA to GVL over Ru/C is excellent (95%
yield). In the effluent from this dual-catalyst-bed reactor, a
small amount of sulfuric acid was detected (0.01m); however,
the catalytic process is stable versus time-on-stream with this
feed stream, as demonstrated in Figure 2, where the GVL pro-
duction rate remains constant at 0.05 mmolminÀ1 gÀ1 after
400 h on stream, corresponding to 94% conversion of LA and
BL. Finally, for proper evaluation of the proposed process, we
consider a detailed material balance (see Supporting Informa-
tion) for the results described in Table 2, Entry 8. If unconvert-
ed LA and FA are recycled to cellulose deconstruction, approxi-
mately 98% GVL and 88% butene yields can be obtained.
These estimates consider all the losses in the process, includ-
ing the generation of unidentified side products and butane
(deep hydrogenation product). On a mass basis, 18.3 kg of
butene can be obtained from 100 kg of cellulose, and this
number corresponds to 88% of the theoretical maximum
butene yield, with 60% yield of levulinic and formic acids from
cellulose considered as the basis. For the current experimental
conditions, the ratio of the butene recycle stream to the
butene product stream is equal to 1.5 and could be decreased
by increasing the amount of formic acid evaporated and opti-
mizing extraction conditions to minimize the formation of 2-
butanol.
In summary, we have described an integrated biorefining
strategy for the production of butyl esters and GVL starting
from cellulose and utilizing reactive extraction of levulinic and
formic acids with butene. This strategy simplifies the recovery
and recycle of sulfuric acid for cellulose deconstruction and en-
ables downstream catalytic processing in the absence of sulfur.
The mixture of levulinic and formic esters, along with residual
levulinic and formic acids, can be converted to an aqueous so-
lution of GVL and 2-butanol in a single step over a dual-cata-
lyst-bed consisting of Pd/C followed by Ru/C, in which H2 gen-
erated from FA and its ester over Pd/C is used for the reduc-
tion of LA and its ester to GVL over Ru/C. This dual-catalyst-
bed system operates over a wide range of organic acid and
ester concentrations, making it adaptable to various extraction
conditions. In addition, the biorefining strategy described here
eliminates the need for extraction/distillation to recover sulfu-
ric acid and purify levulinic acid, thus potentially advancing the
cost effective production of alkenes from renewable lignocellu-
losic resources. Finally, with minor alterations to this strategy,
levulinic acid, levulinates or GVL can be obtained as alternative
end-products. In the case of GVL
production, increased processing
cost due to product isolation
may be justified in value added
applications, such as the produc-
tion of a-methylene-g-valerolac-
tone,[26]
caprolactone,[28]
or
adipic acid.[28]
Experimental Section
Details for feed compositions prior
to the reactive extraction step, and
for compositions of aqueous and
organic solutions formed after re-
active extraction with butene in a
batch system are given in the Sup-
porting Information. Carbon-sup-
ported catalysts containing either
5 wt% Ru or 10wt% Pd were pur-
chased from Sigma–Aldrich. Both
catalysts were reduced in situ
Figure 2. Rates of production of GVL (squares) and CO2 (triangles) versus time-on-stream over the dual-catalyst-
bed reactor system (2 g 10 wt% Pd/C followed by 1.5 g 5 wt% Ru/C) co-feeding the organic stream prepared
from the butene extraction step and the aqueous stream obtained from the evaporation step prior to extraction.
T=443 K, P=35 bar.
360
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ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 2011, 4, 357 – 361

under H2 flow at 673 K (ramp rate of 0.5 KminÀ1) for 2 h. The cata-
lytic reaction kinetics studies were carried out in a fixed bed,
down-flow reactor consisting of a half-inch stainless steel tube fol-
lowed by a gas–liquid separator at room temperature to collect
the liquid effluent phase for off-line analysis. Gas chromatography
was used to analyze the organic liquid samples, whereas liquid
chromatography was used to analyze aqueous phase samples. Gas-
eous products were analyzed on-line by gas chromatography. De-
tails of the experimental set-up and procedures are given in the
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Acknowledgements
This work was supported in part by the U.S. Department of
Energy Office of Basic Energy Sciences, and by the DOE Great
Lakes Bioenergy Research Center (httꢀ://www.greatlakesbioener-
gy.org), which is supported by the U.S. Department of Energy,
Office of Science, Office of Biological and Environmental Re-
search, through Cooperative Agreement DE-FC02–07ER64494 be-
tween The Board of Regents of the University of Wisconsin
System and the U.S. Department of Energy. In addition, this work
was supported in part by the Defense Advanced Research Proj-
ects Agency (DARPA) and Army Research Lab (ARL) through the
Defense Science Office Cooperative Agreement W911NF-09–2–
0010/09–005334 B 01 (Surf-Cat: Catalysts for production of JP-8
range molecules from lignocellulosic biomass). The views, opin-
ions, and/or findings contained in this article are those of the au-
thors and should not be interpreted as representing the official
views or policies, either expressed or implied, of the Defense Ad-
vanced Research Projects Agency or the Department of Defense.
Keywords: biofuels
· heterogeneous catalysis · reactive
extraction · sustainable chemistry · valerolactone
[1] J. J. Bozell, L. Moens, D. C. Elliott, Y. Wang, G. G. Neuenschwander, S. W.
Received: November 16, 2010
Fitzpatrick, R. J. Bilski, J. L. Jarnefeld, Resour., Conserv. Recycl. 2000, 28,
227.
Published online on January 4, 2011
ChemSusChem 2011, 4, 357 – 361
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemsuschem.org
361