Solvent-free γ-valerolactone hydrogenation to 2-methyltetrahydrofuran catalysed by Ru/C: A reaction network analysis

Article abstract of DOI:10.1039/c3gc41803k

2-Methyltetrahydrofuran (2-MTHF) is considered to be an attractive biomass based platform chemical with high potential as a biofuel compound and as a green solvent. 2-MTHF can be synthesised from bio-based levulinic acid (LA) and γ-valerolactone (GVL). Herein the optimum reaction conditions for the hydrogenation of GVL over Ru/C have been studied. A full conversion of GVL has been obtained under solvent free conditions with a maximum yield of 2-MTHF of 43%. The optimized conditions have been employed in a mechanistic study of the synthesis of 2-MTHF. Several side reactions have been investigated to explore the full reaction network of this heterogeneously catalysed system and to elucidate the factors influencing product selectivity. Additionally an efficient solvent-free hydrogenation reaction of LA into 2-MTHF could be achieved delivering 90% conversion of LA with a yield of 2-MTHF of 61% by removing water from the system in a two-step approach.

Full text of DOI:10.1039/c3gc41803k

Green Chemistry
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Solvent-free γ-valerolactone hydrogenation
to 2-methyltetrahydrofuran catalysed by Ru/C:
a reaction network analysis
Cite this: Green Chem., 2014, 16,
1358
Mohammad G. Al-Shaal, Adam Dzierbinski and Regina Palkovits*
2-Methyltetrahydrofuran (2-MTHF) is considered to be an attractive biomass based platform chemical
with high potential as a biofuel compound and as a green solvent. 2-MTHF can be synthesised from bio-
based levulinic acid (LA) and γ-valerolactone (GVL). Herein the optimum reaction conditions for the
hydrogenation of GVL over Ru/C have been studied. A full conversion of GVL has been obtained under
solvent free conditions with a maximum yield of 2-MTHF of 43%. The optimized conditions have been
employed in a mechanistic study of the synthesis of 2-MTHF. Several side reactions have been investi-
gated to explore the full reaction network of this heterogeneously catalysed system and to elucidate the
factors influencing product selectivity. Additionally an efficient solvent-free hydrogenation reaction of LA
into 2-MTHF could be achieved delivering 90% conversion of LA with a yield of 2-MTHF of 61% by remov-
ing water from the system in a two-step approach.
Received 31st August 2013,
Accepted 25th November 2013
DOI: 10.1039/c3gc41803k
www.rsc.org/greenchem
recent years.8,13–18 Particular attention has been paid to the
production of 2-methyltetrahydrofuran (2-MTHF), a compound
Introduction
While the global consumption of fossil fuels is dramatically that can be derived based on lignocellulose. 2-MTHF may find
increasing, the rapid depletion of fossil resources, coupled use as an alternative solvent for many reactions19,20 or as a fuel
with the associated problem of global warming, is causing component.21–23 The attractiveness of 2-MTHF as a green
increasing concern with regard to the stability of the global solvent and fuel is partially attributed to the wide number of
economy and environment.1 For these reasons, many research feedstocks it can be derived from. Substantially, 2-MTHF can
groups have focused on alternative carbon sources.2 Ligno- be obtained via the acid catalysed dehydration of cellulose,
cellulosic biomass, derived from wood, grass, and agricultural complex carbohydrates and simple C5 and C6 sugars to levuli-
waste, represents one of the most viable replacements of fossil nic acid (LA) and furfural.24–27 These intermediates can
fuels.3–7 Virtually, using biomass feedstocks in biofuel pro- undergo subsequent catalytic reduction steps to produce
duction offers many advantages in comparison to fossil fuel. 2-MTHF as the desired target product (Scheme 1).28–30
For example, biomass feedstocks could enable more sustain-
LA represents a platform chemical for many compounds
able production processes and facilitate product flexibility.8–10 and several studies have reported the conversion of LA to
Moreover lignocellulosic biomass could reduce CO2 emissions 2-MTHF. For example, Elliott et al. reported on the transform-
since natural renewable resources provide a closed carbon ation of LA into 2-MTHF via the reaction intermediates
cycle.11,12 In spite of the present broad research on biomass γ-valerolactone (GVL) and 1,4-pentanediol (1,4-PDO). They
utilisation, new processes must be developed to enable its tested several supported noble metals under different reaction
efficient conversion to fuels and chemicals.
conditions utilizing water and 1,4-dioxane as solvents.31 In an
Heterogeneous catalysis may provide an efficient methodo- attempt to produce novel biofuel compounds, several studies
logy for biomass conversion allowing for high reaction rates have demonstrated that tuning the acidity and the active metal
and high selectivity of the target products. For this reason, the of the catalyst alternates the product distribution in the hydro-
catalytic conversion of biomass to promising biomass-based genation of LA or GVL.9,32,33 For example, Lange et al.
chemicals over solid catalysts has received much attention in suggested an acid-catalysed ring-opening of GVL to pentenoic
acid followed by a subsequent hydrogenation to pentanoic
acid and stated that a careful adjustment of the acid/metal
ratio is essential to control the formation of pentenoic acid
Chair for Heterogeneous Catalysis and Chemical Technology, Institut für Technische
versus 2-MTHF.9,10 Further studies have focused on the conver-
und Makromolekulare Chemie, RWTH, Aachen University, Worringerweg 1, D-52074
sion of LA and GVL into 2-MTHF in the presence of
Aachen, Germany. E-mail: palkovits@itmc.rwth-aachen.de
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(200 °C, 18 h). While molecular ruthenium catalysts allowed
an efficient transformation of GVL into 2-MTHF, the opposite
case was observed for supported ruthenium nanoparticles. Fan
et al. reported that utilisation of 5% Ru/C enabled about 2%
conversion of GVL with undetectable amounts of the target
product applying 60 bar of H2 pressure at 200 °C and 6 h with
ethanol as a solvent.35
These findings together with our previous results on the
hydrogenation of LA to GVL motivated us to investigate the
heterogeneously catalysed hydrogenation reaction of GVL to
2-MTHF over Ru/C in more detail. For this reason, different
factors such as the reaction temperature, H2 pressure and reac-
tion time were tested applying Ru/C as a catalyst. The system
was studied in the absence of a solvent. The obtained results
confirm the efficient production of 2-MTHF based on GVL over
Ru/C in a solvent-free reaction system.
In a first set of experiments the influence of the reaction
temperature was investigated (Table 1, entries 1–3). Evidently
an increase of the reaction temperature leads to higher cataly-
tic activity. While no conversion was observed at 130 °C
(Table 1, entry 1), increasing the temperature to 190 °C
resulted in a moderate yield of 2-MTHF. However the hydro-
genation of GVL to 2-MTHF was coupled with the formation of
2-butanol, 1,4-PDO and traces of 2-pentanol (Table 1, entries 2
and 3). Varying the H2 pressure in a second set of experiments
showed a relation between GVL conversion and the applied H2
pressure (Table 1, entries 3–8). Obviously high hydrogen press-
ures are necessary to enable an efficient transformation of
GVL. This effect could be related to an increasing concen-
tration of H2 dissolved in the liquid with enhanced H2
pressure.38 However, future studies will focus on a full kinetic
investigation of the reaction network to gain deeper insights.
The highest conversion of GVL was observed after 4 h under
120 bar of H2 at 190 °C where comparable amounts of
2-MTHF, 1,4-PDO and 2-pentanol were present in the reaction
mixture (Table 1, entry 8). However due to pressure limitations
of the used autoclave systems a maximum pressure of 100 bar
was selected for subsequent experiments. Noteworthy, up to a
H2 pressure of 80 bar, only a minor increase in GVL conversion
and 2-MTHF formation could be observed, delivering a
maximum of 16% GVL conversion and 9% 2-MTHF yield.
Considering these points, a third set of experiments was
dedicated to the influence of reaction time on product for-
mation (Table 1, entries 9–12 and 3). As expected a prolonged
reaction time resulted in increasing conversion of GVL as well
as enhanced 2-MTHF formation. Almost full conversion of
Scheme 1 Example of 2-MTHF synthesis from lignocellulosic biomass.
homogeneous ruthenium catalysts.23,34 Recently, Fan et al.
reported a yield of 2-MTHF as high as 91% based on GVL as a
substrate dissolved in ethanol and Cu/ZrO2 as a catalyst.35
However, although several studies have addressed the hydro-
genation of GVL to 2-MTHF in recent years, little attention has
been paid to analysing the involved reaction pathways. The
present paper summarizes the influence of reaction conditions
on the conversion of GVL into 2-MTHF and reveals a mechan-
istic study of a heterogeneously catalysed hydrogenation reac-
tion of GVL into 2-MTHF under solvent-free conditions. Ru/C
was selected as the catalyst of choice since it has been success-
fully employed in previous studies focusing on the hydrogen-
ation of LA to GVL.36 Aiming at a comprehensive analysis of
GVL hydrogenation the reaction network has been explored
elucidating the origin of other products such as 1- and 2-pen-
tanol, 2-butanol, pentane, butene and butane, respectively.
Additionally, the stability of several reaction intermediates
under the applied conditions has been studied and the results
were used to develop a one-pot two step reaction protocol for
the direct hydrogenation of LA into 2-MTHF catalysed by Ru/C.
Results and discussion
Conversion of GVL into 2-MTHF
The production of 2-MTHF based on GVL as a substrate was GVL was obtained after 24 h, providing a mixture of 2-MTHF,
investigated by several groups.34,35,37 However, only a few 2-butanol and small amounts of 2-pentanol (Table 1, entry 12).
studies have focused on ruthenium catalysts in the hydrogen- Interestingly the selectivity of 2-MTHF remained almost con-
ation of GVL.23,34 Horváth et al. obtained a conversion of 72% stant for the first 8 h of the reaction with around 54% but
to 2-MTHF under 75 bar of hydrogen pressure (200 °C, 20 h) in decreased subsequently to 43% after 24 h of reaction.
the presence of a molecular ruthenium/phosphine system as a
The poor concentration of the reaction intermediate 1,4-
catalyst.34 The highest yield of 2-MTHF has been reported by PDO can be attributed to its rapid transformation into
Leitner et al. with a molecular ruthenium catalyst and a 2-MTHF.37,39 These findings support the fact that the for-
triphos ligand.23 LA-derived GVL served as a substrate and mation of 1,4-PDO is the rate determining step in the hydrogen-
92% yield of 2-MTHF could be reached applying 100 bar of H2 ation reaction of GVL. Further investigations of the reaction
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Table 1 GVL hydrogenation using Ru/C as a catalysta
GVL conversion
[%]
2-MTHF
yield [%]
2-Butanol
yield [%]
1,4-PDO
yield [%]
2-Pentanol
yield [%]
Entry
T [°C]
pH2 b [bar]
t [h]
1
2
3
4
5
6
7
8
130
160
190
190
190
190
190
190
190
190
190
190
100
100
100
30
40
60
4
4
4
4
4
4
4
4
6
<1
7
22
5
—
3
12
5
6
8
<1
1
4
3
3
3
3
28
6
8
1
4
5
—
—
—
1
—
5
<1
<1
<1
<1
<1
<1
<1
23
<1
<1
4
8
16
14
91
31
41
80
>99
80
9
120
100
100
100
100
31
17
22
33
43
9
10
11
12
8
16
24
6
1
—
30
36
7
a Conditions: GVL (3 g, 29.9 mmol); Ru (5%)/support (150 mg, 0.07 mmol of Ru); solvent free. b Pressure at room temperature.
system and the involved reaction pathways are discussed in the 4-hydroxypentanal leads to the formation of 2-butanol. In
following sections.
order to identify the main pathway leading to the formation
of 2-butanol GVL was treated for 24 hours at 190 °C under
100 bar of N2 using an equivalent amount of water and 5%
Ru/C. Analysis of the gaseous phase and the product mixture
Elucidation of the main reaction pathways
With the goal of producing 2-MTHF from GVL, different
studies have documented a wide variety of possible by-pro- shows no conversion of GVL to GHVA or 2-butanol confirming
ducts including methane, butane, isobutene, 2-butanol, that under the applied conditions the Ru/C catalyst is not able
pentane, isopentane, 1-pentanol and 2-pentanol.23,29,31,34
to facilitate the hydration reaction of GVL according to
Initially the hydrogenation of GVL over Ru/C leads to the pathway 1. This finding suggests that 2-butanol is not resulting
formation of 1,4-PDO as an intermediate which undergoes an from the first reaction pathway. To confirm the second
pathway as a source of 2-butanol, 1,4-PDO was used as a sub-
etherification reaction to 2-MTHF. Several by-products are
formed in the course of the reaction such as 1-pentanol, 2-pen- strate applying 100 bar of H2 at 190 °C. Besides the expected
tanol, and 2-butanol. Additionally gas phase analysis reveals hydration/hydrogenation products of 1,4-PDO such as 2-penta-
nol and 2-MTHF, 2-butanol was formed with a yield of 11%
the production of further by-products including methane and
butane. While the formation of 2-pentanol can be attributed to after 4 h and 40% after 24 h, respectively. These findings
a catalytic dehydration and hydrogenation of the intermediate emphasise that 2-butanol is predominantly formed via hydro-
genation/decarbonylation reactions of GVL according to
pathway 2 (Scheme 2).
1,4-PDO, the origin of 2-butanol, butane and methane requires
further investigations.
Two distinct pathways may demonstrate the source of
2-butanol in the product mixture (Scheme 2). The first pathway
Although the results indicate that 2-butanol originates from
GVL and 1,4-PDO via a decarbonylation reaction a further ana-
suggests a hydration reaction of GVL to γ-hydroxyvaleric acid lysis of the gaseous phase showed the presence of methane
(GHVA) in the presence of water occurring as a by-product of instead of CO. We suggest that the observed methane can be
attributed to a direct methanation of CO over Ru/C.41 Another
2-MTHF production. Similar to the decarboxylation reaction of
fatty acids on activated carbon,40 GHVA undergoes decarboxy- possibility is the heterogeneously catalysed hydrogenation of
lation to 2-butanol. In the second pathway GVL is hydrogen- carbon monoxide to methanol and a dehydration reaction of
methanol to methane. While methanol synthesis using a wide
ated to 1,4-PDO which is in an equilibrium with
4-hydroxypentanal. A catalysed decarbonylation reaction of variety of noble metal catalysts was studied extensively,42–44 we
have focused on the catalytic dehydration of methanol. Thus
we conducted an experiment starting from methanol and
heated it up under a H2 atmosphere (190 °C and 100 H2 bar)
over 5% Ru/C. After 4 h, methanol was fully converted into a
gaseous phase and GC analysis confirmed the presence of
methane with 100% yield.
To identify the source of butane in GVL hydrogenation two
pathways have been considered. The first route includes a de-
carboxylation reaction of GVL into 1-butene and CO2. This
pathway was discussed previously by Dumesic et al. utilising
Scheme 2 Proposed reaction pathways for the formation of 2-butanol.
amorphous and acidic Al2O3/SiO2 catalyst.45 The acidic catalyst
Pathway 1 includes a hydration of GVL and decarboxylation of GHVA to
assists the protonation and subsequent proton transfer steps
CO2 and 2-butanol. Pathway 2 includes a consequent hydrogenation
which results in decarboxylation to 1-butene and CO2. In the
reaction of GVL followed by decarbonylation to CO and 2-butanol.
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Scheme 3 Proposed mechanisms for the synthesis of butane. Pathway
1 includes a ring opening and direct decarboxylation of GVL to CO2 and
1-butene followed by hydrogenation of 1-butene to butane. Pathway
2 includes a dehydration of 2-butanol and hydrogenation of 1-butene
to butane.
second pathway of butane synthesis 1-butene can also be pro-
duced by a dehydration of 2-butanol. For both pathways,
butane is the final product produced by a simultaneous hydro-
genation of the obtained 1-butene. To identify the chemical
route leading to the formation of 1-butene and butane in our
reaction system, GVL was heated to 190 °C under 100 bar of N2
for 24 h over 5% Ru/C as a catalyst and in the absence of
water. Analysing the reaction mixture and the gaseous phase
indicated no conversion of GVL into butane and CO2. This
result suggests that the acidity of Ru/C is not sufficient to
enable a direct decarboxylation reaction of GVL, and thus the
first pathway is not likely to occur under the applied reaction
conditions. Further reference experiments showed that heating
of 2-butanol to 190 °C (100 bar of H2, 5% Ru/C, 4 h) results in
full conversion to butane. This finding supports the hypothesis
of a dehydration and hydrogenation sequence of 2-butanol
according to the second reaction pathway (Scheme 3).
Scheme 4 Analysis of reaction network includes the synthesis of
2-MTHF from GVL and other secondary reactions over Ru/C in a batch
reactor.
discussed side and reversible reactions for a solvent free direct
conversion of GVL into 2-MTHF over Ru/C.
Conversion of LA into 2-MTHF
A direct conversion of LA to 2-MTHF was reported for the first
time in 1947 where the formation of 2-MTHF was barely
observed by heating LA under a pressure of H2 (200 bar,
190 °C, 1 h) in the presence of Cu2Cr2O5.39 Similarly poor
yields of 2-MTHF were reported by Elliott et al. for different
heterogeneous catalysts in a batch system.37 For instance
employing 10% Ru/C enabled full conversion of LA into GVL
and 1,4-PDO while the yield of 2-MTHF was only 12% after 6 h
at 120 °C in 1,4-dioxane as a solvent.31
Stability of 2-MTHF
In addition to the determination of the origin of main by-pro-
In an attempt to improve the yield towards 2-MTHF, we
ducts, we have focused on the stability of the target product have focused on the direct hydrogenation of LA to 2-MTHF
2-MTHF since its stability under the applied conditions could under solvent free conditions. The use of 5% Ru/C allowed the
be a major challenge considering the maximum product full conversion of LA after 24 h delivering a biphasic product
selectivity. Therefore 2-MTHF was used as a substrate and mixture. However analysis of the liquid phase indicated the
heated to 190 °C under a H2 pressure of 100 bar for 24 h apply- presence of 2-butanol and 2-pentanol with a selectivity close to
ing Ru/C as a catalyst. Interestingly 2-MTHF was fully con- 40% and 60%, respectively, while only trace amounts of
verted into 2-pentanol together with traces of pentane, 1,4- 2-MTHF, GVL and 1-pentanol were formed. These results high-
PDO and 2-butanol. These findings indicate that 2-pentanol is light the difference between the hydrogenation of GVL and the
formed by a catalytic hydrogenation of 2-MTHF,46 as well as a hydrogenation of LA into 2-MTHF under the same reaction
hydrogenation reaction of 1,4-PDO. As discussed in the case of conditions. It is plausible to argue that the production of
2-butanol,
a dehydration/hydrogenation sequence starting 2-MTHF starting from GVL involves hydrogenation and dehy-
from 2-pentanol leads to the formation of pentane. Finally the dration of pure GVL while in a one-pot reaction the synthesis
presence of trace amounts of 1,4-PDO and 2-butanol verifies of 2-MTHF from LA comprises initially the production of water
the reversibility of the dehydration and dehydrogenation of and GVL as an intermediate. Thus water resulting from the
1,4-PDO to GVL and 4-hydroxypentanal, respectively. Further hydrogenation of LA may inhibit the later dehydration reaction
investigations concerning the stability of 2-MTHF emphasise of 1,4-PDO to 2-MTHF. To examine this hypothesis GVL was
its further transformation under the applied reaction con- hydrogenated in the presence of an equivalent amount of
ditions. A hydrogenation of GVL (100 bar of H2 pressure, water. Similarly to the one-pot hydrogenation of LA, 2-butanol,
190 °C, 5% Ru/C) for 48 h shows only traces of 2-MTHF and 2-pentanol and methane were the only products of this reac-
1,4-PDO while the main products are 2-pentanol, 2-butanol tion with yields of 38%, 37% and 25% respectively. Therefore
and methane, respectively. This test suggests that the extended the presence of water in the reaction mixture seems indeed to
contact of the Ru/C catalyst with 2-MTHF facilitates a sub- inhibit 2-MTHF formation. While GVL is hydrogenated to 1,4-
sequent hydrogenation of 2-MTHF to 2-pentanol. Scheme 4 PDO, the presence of water prohibits the acid-catalysed dehy-
summarises the overall reaction network including the dration of 1,4-PDO into 2-MTHF. Instead, 1,4-PDO undergoes a
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the system inhibits the dehydration step and shifts the main
reaction toward the formation of 2-pentanol instead of the
desired production of 2-MTHF. In line with this, a two-step
reaction including an intermediate removal of water enables a
full conversion of LA together with 61% yield of 2-MTHF.
Scheme 5 Catalytic hydrogenation of LA in a one pot-reaction for
Experimental procedures
24 h.
Chemicals
subsequent transformation into the more stable 2-butanol and
2-pentanol (Scheme 5).
2-Butanol (99.5%), GVL (99%), 1-hexanol (99.5%), LA (≥98%),
2-MTHF (99.5%), 1,4-PDO (99%), 1-pentanol (≥99%), 2-penta-
nol (≥98%) and ruthenium on carbon (5 wt%) were purchased
from Sigma-Aldrich. Methanol (99.8%) and ethanol (99.9%)
were purchased from Chemsolute. All chemicals were used
without further purification or drying.
Indeed removing water from the previous reaction mixture
shifts the reaction towards the desired 1,4-PDO etherification
reaction. For example, a high conversion of LA towards
2-MTHF was reported by Elliott et al. using a continuous
process applying different supported catalysts.31 In fact the use
of a continuous system provides a simultaneous removal of
released water from the catalyst enabling a higher selectivity
towards 2-MTHF. Inspired by this successful example of
2-MTHF production, we have focused on the removal of water
in our batch system. Therefore a two-step hydrogenation reac-
tion was conducted to enable an effective transformation of LA
into 2-MTHF. In the first hydrogenation step, LA was totally
converted to GVL under 12 bar of H2 pressure (190 °C,
45 min).36 At the end of this step the formed water was evapor-
ated from the reaction mixture, and the catalyst was collected,
washed, and dried. The second hydrogenation step was con-
ducted using the dried catalyst and the produced GVL applying
100 bar of H2 pressure (190 °C). Under these conditions neat
GVL transforms via a hydrogenation reaction into 1,4-PDO
which undergoes a subsequent etherification to 2-MTHF. After
four hours of reaction we have been able to obtain 90% conver-
sion of GVL and 61% yield of 2-MTHF confirming the possi-
bility of a direct transformation of LA into 2-MTHF over Ru/C
in a batch system.
General procedure
Each experiment was conducted in a Schlesinger B18rb250-01
autoclave reactor with a volume of 50 mL being charged with
the substrate and Ru/C. The agitation of these compounds was
provided by a magnetic bar. Prior to the reaction the auto-
claves were flushed four times with hydrogen before applying
100 bar of hydrogen pressure and heating to 190 °C.
After termination of the respective reaction periods, the
autoclave was cooled down and a sample of the gaseous phase
for gas chromatographic (GC) analysis was collected. The
depressurisation was followed by the collection and filtration
of the liquid phase. Analogously the liquid samples were ana-
lysed by GC and HPLC.
Time dependent screenings
In the time dependent screening experiments, GVL (3 g,
30.0 mmol) and Ru/C (150 mg, 0.07 mmol of Ru) were charged
into an autoclave, 100 bar of hydrogen pressure were applied
and the mixture was heated to 190 °C varying the reaction time
(4, 6, 8, 16, 24, and 48 h).
Mechanistic study
Conclusions
The mechanistic study focused on the investigation of further
substrates under the previously optimised reaction conditions.
Experiments involving GVL (3 g, 30.0 mmol), 1,4-PDO (3.12 g,
30.0 mmol) and methanol (0.96 g, 30.0 mmol) were conducted
for 4 hours, while experiments using LA (3.47 g, 30.0 mmol),
2-pentanol (2.64 g, 30.0 mmol), 2-MTHF (1.0 g, 11.6 mmol)
and 2-butanol (2.22 g, 30.0 mmol) lasted for 24 hours. All reac-
tions were performed at 190 °C under 100 bar of hydrogen
pressure.
We were able to demonstrate the conversion of γ-valerolactone
(GVL) into 2-methyltetrahydrofuran (2-MTHF) over Ru/C in a
batch reactor. The reaction conditions were optimised and full
conversion of GVL with a maximum yield of 2-MTHF of 43%
was obtained at 190 °C (100 bar, 24 h). Several side reactions
were identified resulting in by-products such as 2-butanol,
butane, 1,4-PDO, 2-pentanol, 1-pentanol, pentane and
methane. Investigating the origin of the main reaction pro-
ducts, we have been able to introduce a comprehensive over-
view of the reaction network. The stability of the target product
Sample analysis
2-MTHF was examined under the mentioned reaction con- Gaseous reaction products were analysed by GC using an
ditions emphasising that 2-MTHF undergoes a hydrogenation Agilent HP6890 chromatograph and a Restek Shincarbon ST
reaction to 2-pentanol for reaction times longer than 24 h.
column with dimensions of 2 m × 1 mm and a thermal con-
The study also focused on the conversion of levulinic acid ductivity detector (TCD). The carrier gas was helium with a
(LA) into 2-MTHF in a solvent free one-pot reaction. We could constant flow rate of 15 mL min−1 and an inlet temperature of
demonstrate that the addition and the formation of water in 100 °C. The following temperature program was used in the
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The aqueous phases for one-pot LA hydrogenation reactions
were analysed with a Shimadzu lc 2020 liquid chromatograph
using three Organic-Acid/CS columns with dimensions of
300 mm × 8 mm, 100 × 8 mm and 40 mm × 8 mm and a refrac-
tive index detector (RI). The eluent was a solution of 154 µL of
trifluoroacetic acid in 1 L water with a flow rate of 1 mL min−1
and a retention time of 40 min.
The organic liquid phases of all reactions were analysed
with an Agilent HP6890 gas chromatograph using a CP-Sil-
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Acknowledgements
We wish to thank the Higher Institute of Applied Science and
Technology of Syria for the studentship of Mohammad G. Al-
Shaal (grant number 32/2012). This work was supported by the 23 (a) F. M. A. Geilen, B. Engendahl, A. Harwardt,
Robert Bosch Foundation in the frame of the Robert Bosch
Junior Professorship for the efficient utilization of renewable
resources. This work was performed as part of the Cluster of
Excellence “Tailor-Made Fuels from Biomass” funded by the
W. Marquardt, J. Klankermayer and W. Leitner, Angew.
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Excellence Initiative by the German federal and state govern- 24 J. A. Dumesic, D. M. Aonso, E. I. Guerbuez and S. G. Wettstein,
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