Catalytic upgrading of levulinic acid to 5-nonanone

Article abstract of DOI:10.1039/b923907c

Aqueous solutions of levulinic acid can be catalytically processed, through the intermediate formation of γ-valerolactone (GVL), to an organic liquid stream that spontaneously separates from water, and is enriched in pentanoic acid and 5-nonanone. This organic layer can serve as a source of chemicals or can be upgraded to hydrocarbon fuels.

Full text of DOI:10.1039/b923907c

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www.rsc.org/greenchem | Green Chemistry
Catalytic upgrading of levulinic acid to 5-nonanone†
Juan Carlos Serrano-Ruiz, Dong Wang and James A. Dumesic*
Received 13th November 2009, Accepted 6th January 2010
First published as an Advance Article on the web 27th January 2010
DOI: 10.1039/b923907c
Aqueous solutions of levulinic acid can be catalyti-
cally processed, through the intermediate formation of
c-valerolactone (GVL), to an organic liquid stream that
spontaneously separates from water, and is enriched in
pentanoic acid and 5-nonanone. This organic layer can
serve as a source of chemicals or can be upgraded to
hydrocarbon fuels.
(2-hydroxypropanoic acid), a prototypical over-functionalized
biomass-derived molecule, using a water-stable bifunctional
15
Pt(0.1%)/Nb
2
5
O catalyst. In this case, by combining dehy-
dration/hydrogenation (to reduce the oxygen content) and
C–C coupling reactions (to upgrade reactive intermediates),
it is possible to transform, in a single reactor, concentrated
aqueous solutions of lactic acid into an organic phase, that
spontaneously separates from water and is rich in ketones in the
16
Petroleum, currently the main raw material for the production of
fuels and chemicals, is a non-renewable resource in diminishing
C
4
–C range. Following the same approach, we detail herein
7
a catalytic strategy (including dehydration/hydrogenation and
C–C coupling reactions, Fig. 1) to upgrade concentrated aque-
ous solutions of levulinic acid into a set of valuable chemicals
and fuels using a limited number of reaction and separation
steps.
1
supply, the consumption of which leads to accumulation of
atmospheric CO , a greenhouse gas. These issues have stimulated
2
the search for alternative fuels and chemical feedstocks. In this
respect, biomass, being renewable, has been proposed to be
an important source of energy and organic carbon for our
It is known in the literature that levulinic acid, in the presence
of strong mineral or solid acids, dehydrates at moderate temper-
atures (573–623 K) yielding the corresponding cyclic product,
2
industrial society, and significant efforts are being made to
develop processes that allow the conversion of biomass and
3–7
17
biomass-derived products into liquid fuels and chemicals.
a-angelica lactone (AL, Fig. 1). This substance polymerizes
14
In the same manner that the petrochemical industry can be
over acidic surfaces, and we observed that upgrading routes
involving this intermediate over acidic catalysts typically lead to
deactivation of the catalyst and/or loss of carbon. Consequently,
we have employed an alternative path, depicted in Fig. 1, to
initiate catalytic conversion through the formation of the satu-
rated lactone, g-valerolactone (GVL), which is water-soluble and
8
essentially constructed from a few building blocks, a recent
study has identified (by screening of around 300 substances) 12
promising biomass derivatives based on, among other aspects,
their production costs and the potential of these molecules to
serve as building blocks for the development of bio-refinery
9
18
processes. Levulinic acid (LA, 4-oxopentanoic acid) occupies
more stable than the unsaturated lactone. Thus, by operating
a prominent place in this list because it can be obtained
inexpensively and in high yields via acid hydrolysis of waste
cellulosic materials (e.g., paper mill sludge, urban waste paper,
at lower temperatures (423 K) over a metal catalyst without the
presence of acidic sites (Ru/C), concentrated aqueous solutions
of levulinic acid were almost quantitatively converted to GVL
(Table 1, entry 1) through the intermediate 4-hydroxypentanoic
acid (Fig. 1), the presence of which was confirmed by GC-MS
analysis. The catalytic reduction of levulinic acid to GVL has
10
agricultural residues). Additionally, levulinic acid has the
potential to serve as a platform chemical for the production of a
11
wide range of value-added compounds such as fuel additives,
12,13
14
monomers for plastics and textiles,
and chemicals.
been previously carried out with high yields at high H pressures
2
19
Levulinic acid, as is common for all the biomass derivatives,
suffers from an excess of functionality that makes it difficult
to control its reactivity and direct the conversion to targeted
compounds. Consequently, one efficient strategy to catalytically
convert these resources is based on an initial reduction of the
oxygen content in the molecule, leading to the production of
less-reactive intermediates that can be subsequently upgraded
(100bar) andlow levulinic acid concentrations (7wt%) or using
13
solvents other than water. We note that, in our case, nearly
quantitative GVL yields can also be achieved for concentrated
aqueous solutions of LA (50 wt%) at milder conditions (35 bar).
The Ru/C catalyst showed high activity for the processing of
concentrated solutions of LA, making it necessary to operate at
-
1
high space velocities (WHSV = 32 h ) to decrease the conversion
below 100% to check for catalyst stability. At these conditions,
the catalyst showed slow deactivation with time on stream (from
5
to the desired products. This approach, which leads to better
control of reactivity, has been recently applied to lactic acid
9
0 to 68% conversion after 106 h), and treatment of the catalyst
under flowing H at 673 K for 2 h allowed for partial recovery
2
of the initial catalytic activity (83% conversion).
Department of Chemical and Biological Engineering, University of
Wisconsin-Madison, 1415 Engineering Drive, Madison, WI, 53706,
USA. E-mail: dumesic@engr.wisc.edu; Fax: +1 608 262 5434;
Tel: +1 608 262 1095
Aqueous solutions of GVL can be converted to pentanoic
acid (PA, Fig. 1), by means of combined ring-opening (on acid
sites) and hydrogenation reactions (on metal sites), over a water-
†
Electronic supplementary information (ESI) available: Catalyst
preparation, reaction kinetics studies, acknowledgements. See DOI:
0.1039/b923907c
stable bifunctional Pd/Nb
2
5
O catalyst at moderate temperatures
1
and pressures (Table 1, entries 2–6). This transformation has
5
74 | Green Chem., 2010, 12, 574–577
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Table 1 Carbon distributions and carbon selectivities for levulinic acid and GVL conversion over different catalysts
a
b
C distribution (%)
C selectivity (%)
T/K, P/bar,
WHSV/h-
1
Aq.
Org.
Gas GVL PA
C
C
+C
alkanes
Entry Catalyst
Feed
9
=O CO
x
4
5
6 7
C –C ketones
c
d
1
2
3
4
5
6
7
8
Ru(5%)/C
Pd(1%)/Nb
Pd(1%)/Nb
Pd(0.1%)/Nb
Pd(0.1%)/Nb
Pd(0.1%)/Nb
50 wt% LA
423, 35, 4.8e
100
—
—
—
—
—
—
—
—
37
72
79
95
81
86
91
—
63
28
21
5
19
14
9
96
—
—
—
—
—
—
—
—
—
54
65
92
6
—
—
2
—
13
6
6
1
12
11
8
—
83
35
22
5
6
3
—
—
—
—
—
7
c
f
2
2
O
O
2
2
2
5
50 wt% GVLc 598, 35, 1.2
g
h
5
50 wt% GVLc 598, 35, 1.2e
50 wt% GVLc 598, 35, 1.2
O
O
O
5
5
5
3
g
50 wt% GVLc 598, 35, 1.2
—i
57
82
84
g
50 wt% GVL 623, 35, 0.1
Ce0.5Zr0.5
Ce0.5Zr0.5
O
O
2
Pure PA
698, 20, 1.1
1
—
3
6
2
Organic layer 698, 20, 1.1
from entry 5
1
a
Percentage C distribution for a phase i is calculated as (moles of carbon detected in phase i divided by the sum of moles of carbon detected in the
b
three phases) ¥ 100. Percentage C selectivity for a product i is expressed as (moles of carbon as product i divided by the sum of moles of carbon for
all the detected products) ¥ 100. C
9
=O: 5-nonanone; CO
x 2 4 5 6 7
: CO and CO ; C : n-butane; C : n-pentane; C –C ketones: 2-hexanone and 3-heptanone.
c
d
e
f
Aqueous solutions. 4-Hydroxypentanoic acid (3%) and 1,4-pentanediol (1%) accounted for the rest of carbon. H
2
co-feed at 100 sccm. Methane
2
4%) accounted for rest of carbon. H at 25 sccm and He at 25 sccm co-feed. Nonane (1%) and 1-pentyl pentanoate (2%) accounted for rest of
i
g
h
(
carbon. Nonane (7%) and unidentified products (5%) accounted for rest of carbon.
Fig. 1 Catalytic approach used to upgrade levulinic acid by dehydration/hydrogenation and C–C coupling reactions.
1
4
previously been described by Ayoub and Lange over a variety
of bifunctional metal–acid catalysts. However, as depicted in
Fig. 1, production of the desired pentanoic acid is accompanied
by the formation of n-butane (produced by decarboxylation of
pentanoic acid yield (from 0 to 65%) at the same conditions of
temperature and pressure (Table 1, entry 4). Importantly, owing
21
to its low solubility in water, pentanoic acid was obtained in the
separator at the effluent of the reactor, as an organic layer that
spontaneously separated from water and accounted for almost
80% of the reacted carbon (see Table 1, entry 4). This liquid
organic oil was enriched in pentanoic acid, with minor amounts
butane and pentane dissolved in the liquid at the high system
pressure. A decrease in the hydrogen partial pressure in the re-
actor also favored the formation of pentanoic acid versus hydro-
genation and decarboxylation products (Table 1, entries 3 and
5). Therefore, proper choice of metal catalyst and reaction con-
ditions leads to a yield of pentanoic acid equal to 92%, with 95%
of the carbon being stored in the organic layer (Table 1, entry 5).
20
pentanoic acid over metal sites, with the release of stoicho-
metric amounts of CO ), along with n-pentane (as a result of
successive hydrogenations and dehydrations of pentanoic acid
over metal and acid sites, respectively). The formation of these
unwanted products and the yield to pentanoic acid were found to
be controlled by varying the metal loading of the catalyst. Thus,
catalyst converted concentrated aqueous
–C alkanes, CO and CO
at 598 K and 35 bar (Table 1, entry 2), a decrease in the metal
content by a factor of 10 caused a significant increase in the
x
while a Pd(1%)/Nb
2
O
5
solutions of GVL into a mixture of C
4
5
2
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Fig. 2 Applications for the catalytic upgrading of levulinic acid to fuels and chemicals.
The formation of pentanoic acid achieves reduction of the
oxygen content of levulinic acid, leading to a less-reactive,
hydrophobic intermediate that is appropriate for new upgrading
strategies to control reactivity (Table 1, entries 6–8). For exam-
ple, pentanoic acid can be converted to 5-nonanone by means
Fig. 2 outlines several important applications that can be
derived from the catalytic strategy described in this commu-
nication. For example, the route to upgrade aqueous solutions
of levulinic acid to fuels and chemicals involves the formation
of intermediate GVL, which has been proposed to be an
22
12
of ketonization reactions with the release of stoichiometric
amounts of CO and water (Fig. 1). We found that, by increasing
temperature and decreasing space velocity, this transformation
can be carried out over the same Pd/Nb catalyst used to
important precursor for the polymer industry and to be a
18
2
potential gasoline blending agent. Alternatively, GVL can be
converted in a single reactor to pentanoic acid, a hydropho-
bic product that spontaneously separates from water, whose
2
O
5
23
produce pentanoic acid, allowing the direct production of an
organic stream enriched in 5-nonanone from aqueous GVL
esters find applications in the perfume and food industries.
Additionally, pentanoic acid can be converted, by means of
24
in a single catalytic bed (Table 1, entry 6). The C
9
ketone
decarboxylation reactions, to 1-butene, a valuable chemical
for the production of plastics. We have also shown that
pentanoic acid can be upgraded with high yields to 5-nonanone,
which has applications as an industrial solvent in paints and
was produced with an optimized carbon yield of almost 60%,
with unreacted pentanoic acid, C4–5 alkanes and lower ketones
(
produced by scission of 5-nonanone) accounting for the rest of
25
the carbon stored in the effluent organic layer that spontaneously
separates from water. Although this strategy is beneficial in
that it minimizes the number of reactors involved (leading to
reduction of capital and operating costs for the process), the
number of reactions taking place in a single reactor is high,
and control over the individual steps (from GVL to PA to
resins. The organic stream of 5-nonanone can also serve as
a precursor for hydrocarbon fuels of different classes (diesel
and gasoline). In particular, 5-nonanone can be converted, by
means of hydrogenation/dehydration cycles over bifunctional
26
Pt/Nb
lubricity to be used as a diesel fuel blender. Additionally,
branched C hydrocarbons for use as gasoline components
2
O
5
,
to linear nonane, with good cetane number and
5
-nonanone) is difficult, thus limiting the ultimate yield to
the C ketone. This limitation can be overcome by utilizing
an additional bed of ceria–zirconia in a cascade approach.
In this case, the reaction conditions in the first Pd/Nb
reactor are adjusted to maximize the yield of pentanoic acid
Table 1, entry 5), which is then converted downstream to
-nonanone over ceria-zirconia at higher temperatures (Table 1,
9
9
could be obtained by dehydration/isomerization of 5-nonanol
(hydrogenation product of 5-nonanone) over a zeolite such as
USY.
5
,16
2
O
5
(
5
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obtained in a spontaneously-separating, high purity organic
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