Hydrodeoxygenation of the angelica lactone dimer, a cellulose-based feedstock: Simple, high-yield synthesis of branched C7-C10 gasoline-like hydrocarbons

Article abstract of DOI:10.1002/anie.201308143

Dehydration of biomass-derived levulinic acid under solid acid catalysis and treatment of the resulting angelica lactone with catalytic K ₂CO₃ produces the angelica lactone dimer in excellent yield. This dimer serves as a novel feedstock for hydrodeoxygenation, which proceeds under relatively mild conditions with a combination of oxophilic metal and noble metal catalysts to yield branched C₇-C₁₀ hydrocarbons in the gasoline volatility range. Considering that levulinic acid is available in >80 % conversion from raw biomass, a field-to-tank yield of drop-in, cellulosic gasoline of >60 % is possible. Fuel for thought: Biomass-derived levulinic acid can be converted in three simple steps via the angelica lactone dimer into branched, gasoline-range hydrocarbons in high yield by using a combination of oxophilic metal and noble metal catalysts (see scheme). Copyright

Full text of DOI:10.1002/anie.201308143

.
Angewandte
Communications
DOI: 10.1002/anie.201308143
Renewable Chemicals
Hydrodeoxygenation of the Angelica Lactone Dimer, a Cellulose-
Based Feedstock: Simple, High-Yield Synthesis of Branched C –C
7
10
Gasoline-like Hydrocarbons**
Mark Mascal,* Saikat Dutta, and Inaki Gandarias
Abstract: Dehydration of biomass-derived levulinic acid
under solid acid catalysis and treatment of the resulting
angelica lactone with catalytic K CO produces the angelica
Motor gasoline is a mixture of C to C n-alkanes and
4 12
isoalkanes along with varying proportions of cycloalkanes,
arenes, and oxygenates. An important characteristic of
gasoline is its antiknock index, which is estimated by
measuring the octane rating of the fuel. Straight-chain alkanes
generally have octane numbers inferior to branched alkanes.
For example, the Research Octane Numbers (RONs) of
hexane and its isomer 3-methylpentane are 25 and 75,
2
3
lactone dimer in excellent yield. This dimer serves as a novel
feedstock for hydrodeoxygenation, which proceeds under
relatively mild conditions with a combination of oxophilic
metal and noble metal catalysts to yield branched C –C
7
10
hydrocarbons in the gasoline volatility range. Considering
that levulinic acid is available in > 80% conversion from raw
biomass, a field-to-tank yield of drop-in, cellulosic gasoline of
[
20]
respectively. Further branching gives even higher RONs.
Regular unleaded gasoline is generally 87 octane in the US,
with premium grades up to 93. A higher octane rating allows
for a higher compression ratio, which translates to more
power and better performance of the engine. In this study, we
demonstrate a high-yielding, three-step preparation of gaso-
line-like, branched C –C hydrocarbons using biomass-
>
60% is possible.
I
n the race to produce biomass-derived, hydrocarbon-based,
drop-in automotive fuels, most effort has focused on the
condensation chemistry of carbohydrate derivatives, which
7
10
can provide molecules with extended carbon chains (> C ) for
derived levulinic acid as the sole organic starting material.
Levulinic acid (LA, 1) is one of the most recognizable
products in the modern concept of the biorefinery. LA is on
the U.S. National Renewable Energy Laboratory top-twelve
6
deoxygenation to alkanes with hydrogen and a catalyst.
Examples abound. One of the earliest efforts in this area was
[
1]
the aqueous phase reforming (APR) process, in which
sugars and hydrogen reacted to give hydrocarbons, based on
work originally described by Huber, Cortright, and Dumesic
[
21]
list of value-added chemicals from biomass,
as well as
Bozellꢀs newer top-ten list of chemical opportunities from
[
2,3]
[22]
in 2004–2005.
reported by the research groups of Dumesic,
Since then, related approaches have been
biorefinery carbohydrates. While a number of routes have
[
4,5]
[6–8]
Corma,
which have been summarized in recent
In many cases, the electrophile is a furfural,
been described over the years for the production of LA from
biomass, the most efficient to date are the “Biofine Process,”
a two-stage, high-pressure, high-temperature procedure for
[
9–13]
and others,
[
14–17]
reviews.
either 5-(hydroxymethyl)furfural (HMF) or furfural itself.
These processes have inherent drawbacks in the poor avail-
[18]
[23]
which yields of 1 between 70 and 80% have been reported,
and the hydrolysis of biomass-derived 5-(chloromethyl)fur-
[19]
[24]
ability of HMF on an industrial scale, and the lower relative
abundance of C sugars in biomass compared to C , respec-
fural, which gives 1 in > 80% overall yield.
It is well known that 1 can undergo intramolecular
5
6
[25]
tively. In other instances, polyols, biogenic ketones, g-valer-
olactone, or related molecules are used as feedstocks. In all
cases, however, the products are linear alkanes or long-chain
alkanes with single branches, and are generally described by
the authors as renewable substitutes or additives for diesel or
jet fuel. In no study that we are aware of have branched
alkanes suitable for drop-in use as gasoline been produced by
any of these methods.
dehydration to give a-angelica lactone (AL, 2; Scheme 1),
although the reaction has attracted relatively little interest in
the renewables field, being largely eclipsed by the reduction
[
26]
and subsequent cyclization of 1 to g-valerolactone.
The
reaction, as described, has generally involved the slow
distillation of 2 from a mixture of 1 and a strong acid catalyst.
The reaction gives AL in good yields, but also results in
a polymeric residue in the distillation pot, which would
present problems for recycling the acid on scale up. We
proposed that the use of a heterogeneous acid catalyst in this
reaction would facilitate product separation and catalyst
recycling. This was ultimately accomplished by using mont-
morillonite clay (K10), which gave > 90% yields of isolated 2
without the formation of polymeric materials or noticeable
deactivation of the catalyst over three consecutive cycles. In
a typical preparation, a mixture of LA and K10 (10 wt%) was
distilled using a fractionating column under controlled
vacuum (50 mmHg), resulting in a two-phase mixture of
water and product, which could simply be separated.
[*] Prof. M. Mascal, Dr. S. Dutta, Dr. I. Gandarias
Department of Chemistry, University of California Davis
1
Shields Avenue, Davis, CA 95616 (USA)
E-mail: mjmascal@ucdavis.edu
[
**] Financial support to I.G. by the Department of Education of the
Basque Government (“Programa Postdoctoral de Perfecciona-
miento de Doctores”) is gratefully acknowledged. Paul Hrvatin is
acknowledged for his technical support in product analysis.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201308143.
1
854
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we have found that Ir-ReO /SiO is also
x
2
highly active in the HDO of lactones.
The Ir-ReO /SiO catalyst was pre-
x
2
[
38]
pared and reactions were carried out in
batch mode as described above for the
Scheme 1.
Cu-ZnO/Al O3 system, except that
2
a range of temperatures between 200
It is also known that 2 can dimerize, although again, the
reaction is largely obscure. The angelica lactone dimer (ALD,
Table 1: Conversion of the angelica lactone dimer (3) and hydrocarbon
yield with different catalyst systems.
[
27]
3
) was first described in 1914, but not structurally charac-
[a]
Catalyst
T
t
Conv. Hydrocarbon yield [%]
[
28]
terized until 1954.
The dimerization reaction is a base-
[8C] [h] [%]
catalyzed conjugate addition between the double bond
isomers of 2, which exist in equilibrium under the reaction
conditions. Catalysts have included hydroxide or alkoxide
C
7
C
8
C
9
C
10 total
Cu-ZnO/Al O + g-Al O 300
3
3
100
100
3
4
12
5
21 41
2
3
2
3
Cu-ZnO/Al O +
HPW/MCM-41
300
15 35 14 68
2
3
[
29]
[29]
[30]
[b]
salts, active metals, tertiary amines, and organometal-
[
31]
lic compounds, and we also tried these methods, but with
mixed results. The most attractive procedure from an applied
standpoint made use of anhydrous K CO as the base in
Ir-ReO
x
/SiO
2
2
2
2
300
240
220
200
240
220
240
3
6
7
7
6
7
6
100
100
100
100
100
100
100
4
1
1
0
2
2
1
16 19 33 72
13 10 60 84
11
6
8
4
Ir-ReO /SiO
x
Ir-ReO /SiO
6
1
70 88
3 10
x
2
3
Ir-ReO /SiO
x
a solid-state reaction, but the reported yield was only
Pt-ReO /C
Pt-ReO /C
Pt-WO /Al O
3
18 60 88
7
1
x
[28]
1
0.8%.
In our hands, optimization of this reaction by
13 26
10 19
x
conducting it in a melt eventually resulted in a 94% yield of 3.
We saw 3 as a potentially valuable renewable feedstock
7
x
2
[
a] Molar %C yields as determined by GC-MS integration against
n-alkane standards. [b] 20 wt% 12-phosphotungstic acid (HPW) loaded
[
32]
for hydrodeoxygenation (HDO),
due to its C10 carbon
count and branched character which, as described above,
would make it an ideal precursor to cellulosic gasoline.
Traditional hydrotreating catalysts such as sulfided NiMo and
CoMo are commonly used for the reduction of esters to
hydrocarbons, but we were deterred by the gradual deactiva-
on mesoporous silica (MCM-41).
and 3008C were studied. The results for the deoxygenation
of 3 are shown in Table 1. Starting at the same temperature as
used for Cu-ZnO/Al O , an improved yield of 72% hydro-
[33]
tion of these catalysts by sulfur leaching. We were attracted
to a copper-zinc mixed oxide catalyst on alumina (Cu-ZnO/
Al O ) that has been used to hydrogenate esters to the
2
3
carbons was observed on using the Ir-ReO /SiO catalyst. A
x
2
considerable degree of CꢀC bond cleavage was seen, as was
2
3
corresponding alcohols in nearly quantitative yield under
the case with the copper-zinc catalyst, which prompted us to
attempt the hydrogenation at lower temperatures. As shown
in Table 1, reduction of the reaction temperature first to 240
and then to 2208C increased the selectivity for the C10
product, that is, the product which would result if no CꢀC
[
34]
relatively mild conditions (2308C). Since g-Al O is known
2
3
[
35]
to dehydrate alcohols under similar conditions, we specu-
lated that a combination of these two catalysts could achieve
a one-pot conversion of 3 into hydrocarbons. In a typical
reaction, 3 and the catalysts (10 wt% Cu-ZnO/Al O3
+
bond cleavage occurred, while increasing the overall hydro-
carbon yield up to 88%. Decreasing the reaction time (not
shown) or the reaction temperature (2008C) was found to
lower the yield of hydrocarbons.
2
2
0 wt% g-Al O ) were loaded into a pressure vessel and the
2 3
system was pressurized with hydrogen to about 50 bar and
heated with stirring at 3008C for three hours. Analysis of the
reaction mixture showed a 41% yield of C –C hydrocarbons
In light of the strong performance of the Ir-ReO /SiO
2
7
10
x
alongside a considerable quantity of alcohol and ether
products. Since the dehydration of the intermediate alcohols
catalyst, we elected to try two other catalysts consisting of an
oxophilic metal–noble metal combination, namely Pt-ReO /
x
[
39]
[40]
was apparently not efficient enough, we replaced the g-Al O3
C
and Pt-WO /Al O . Pt-ReO /C also gave a high yield
x 2 3 x
2
with phosphotungstic acid (H W O P) loaded on mesopo-
of hydrocarbons at 2408C, although the yield decreased
significantly at 2208C. With the Pt-WO /Al O catalyst,
however, the hydrocarbon yield was notably lower at the
3
12 40
rous silica (MCM-41), which is known to dehydrate aliphatic
x
2
3
[
36]
alcohols under even milder conditions than g-Al O . When
2
3
a combination of Cu-ZnO/Al O3 and HPW/MCM-41 was
same temperature at which the M-ReO catalysts performed
2
x
employed, the total yield of hydrocarbons improved to 68%.
The hydrogenation of carbohydrate derivatives in general
tends to favor noble metal catalysts, and recently it was
reported that such catalysts modified with an oxophilic metal
such as Re show higher catalytic activity in CꢀO bond
well (2408C).
As shown in Table 1, a degree of control over the
hydrocarbon distribution can be exercised through choice of
the reaction temperature and catalyst. A narrow range of
products in the given carbon range results under milder
conditions, as shown in Scheme 2 for the reaction carried out
with the Ir-ReO /SiO2 catalyst at 2208C. The Pt-ReO /C
[
37]
hydrogenolysis.
In particular, an Ir-ReO /SiO catalyst
x 2
described by Tomishige and co-workers has demonstrated
great promise in the reduction of glycitols to alkanes under
x
x
catalyst shows a somewhat lower selectivity towards the C10
product in favor of the C9 isoalkanes. The carbon mass
[
38]
mild conditions, along with good reusability. Interestingly,
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1855

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Angewandte
Communications
Central to market considerations is the concept of the
drop-in” product, which is only formally satisfied by a literal
“
equivalent of the commercial product that seamlessly inte-
grates into the prevailing transportation infrastructure. The
C –C isoalkanes described here could be blended with C –C
7
10
4
6
n-alkanes that are available through other processes, such as
[2,38]
the hydrogenation of simple sugars,
to serve as drop-ins
for the paraffinic fraction of gasoline. The aromatic fraction
could, in turn, be derived from other renewables, such as 2,5-
[
42]
dimethylfuran, which has a high RON (119), or its C H
2
4
[43]
cycloaddition-dehydration product para-xylene. Other bio-
refinery products, such as g-valerolactone and its deriva-
[44]
[45]
tives,
methyl tetrahydrofurans,
sugar hydrogenoloysis
[46]
[47]
products, and valeric esters could serve as useful oxy-
genate additives. Thus, in principle, a basic combination of
chemical-catalytic processes has the potential to supply
essentially the full component spectrum of motor gasoline
entirely from renewable resources.
In summary, we describe here a method whereby a fully
practical feedstock (levulinic acid, 1) is efficiently converted
in three steps into the main component fraction of gasoline.
We introduce the angelica lactone dimer (3) as a novel
feedstock for the HDO process, rendered practical here by
both the development of a scalable approach to angelica
lactone (2) itself and the production of 3 in nearly quantitative
Scheme 2. Reaction conditions: 2.0 g 3, 0.30 g Ir-ReO /SiO , 54 bar H ,
x
2
2
2
208C, 7 h; total yield 88%. The hydrocarbons were identified by
matching MS fragmentation patterns to NIST database spectra.
Table 2: Reusability of Ir-ReO /SiO catalyst.
x
2
[
a]
Recycle
Conv. [%]
Hydrocarbon yield [%]
yield. Finally, we have adapted Cu-ZnO, Pt-ReO , and Ir-
x
ReO catalysts to the HDO of cyclic esters, with branched
x
C7
C8
C9
C10
total
alkane distribution governed by temperature. This work not
only opens up an unprecedented route between raw biomass
and branched alkanes, but may also encourage fresh efforts
towards the identification of new renewable platform chem-
icals beyond sugars and simple furans.
1
2
3
100
100
100
1
1
1
12
10
9
5
5
6
67
68
69
85
84
85
[
2
a] Reaction conditions: 2.0 g ALD (3), 0.30 g Ir-ReO /SiO , 54 bar H ,
208C, and 7 h. Recovered catalyst was recalcined between experiments.
x 2 2
Received: September 17, 2013
Keywords: biofuels · biomass conversion · isoalkanes ·
.
balances can be satisfied by taking decarbonylation (C !C
levulinic acid · sustainable chemistry
1
0
9
7
products) and/or ethyl group cleavage (C !C and C !C
1
0
8
9
products) into account.
The stability of the Ir-based catalyst was also tested and
the results are shown in Table 2. Recovered catalyst was
recycled three times to confirm its robust nature (see the
Supporting Information for experimental details). The selec-
tivity was also essentially unchanged.
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[
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Angew. Chem. Int. Ed. 2014, 53, 1854 –1857
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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