Energy-efficient production of 1-octanol from biomass-derived furfural-acetone in water

Article abstract of DOI:10.1039/c5gc01119a

An energy-efficient catalytic system for the one-pot production of 1-octanol from biomass-derived furfural-acetone (FFA) under mild conditions in water was developed, by sequential hydrogenation/hydrogenolysis over a hydrophilic Pd/NbOPO₄ catalyst. A strategy of creating an intentional "phase problem" has been employed to prevent the over-hydrogenolysis of 1-octanol into n-octane and therefore increased the selectivity to 1-octanol. The effects of reaction conditions as well as a variety of noble-metal loaded bifunctional catalysts have been systematically investigated to maximize the yield of 1-octanol. Moreover, the addition of liquid acids to the catalytic system further enhanced the selectivity towards the formation of 1-octanol. There is a strong correlation between the acid strength of an acidic additive and the sum yield of 1-octanol and octane. With the addition of TfOH, the highest yield of 1-octanol (62.7%) was obtained from one-pot conversion of biomass-derived FFA over Pd/NbOPO₄.

Full text of DOI:10.1039/c5gc01119a

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Energy-efficient production of 1-octanol from
biomass-derived furfural-acetone in water†
Cite this: DOI: 10.1039/c5gc01119a
Qineng Xia, Yinjiang Xia, Jinxu Xi, Xiaohui Liu and Yanqin Wang*
An energy-efficient catalytic system for the one-pot production of 1-octanol from biomass-derived fur-
fural-acetone (FFA) under mild conditions in water was developed, by sequential hydrogenation/hydro-
genolysis over a hydrophilic Pd/NbOPO4 catalyst. A strategy of creating an intentional “phase problem” has
been employed to prevent the over-hydrogenolysis of 1-octanol into n-octane and therefore increased
the selectivity to 1-octanol. The effects of reaction conditions as well as a variety of noble-metal loaded
bifunctional catalysts have been systematically investigated to maximize the yield of 1-octanol. Moreover,
the addition of liquid acids to the catalytic system further enhanced the selectivity towards the formation
of 1-octanol. There is a strong correlation between the acid strength of an acidic additive and the sum
yield of 1-octanol and octane. With the addition of TfOH, the highest yield of 1-octanol (62.7%) was
obtained from one-pot conversion of biomass-derived FFA over Pd/NbOPO4.
Received 25th May 2015,
Accepted 1st July 2015
DOI: 10.1039/c5gc01119a
www.rsc.org/greenchem
an important solvent in biomass conversion.29 Currently,
1-octanol is mainly produced from the petroleum-based
Introduction
Biomass has been considered as a promising alternative to pet- process.28 Recently, Julis and Leitner30 reported for the first
roleum resources and extensive efforts have been made world- time that 1-octanol could be synthesized from furfural and
wide to convert renewable biomass into fuels and value-added acetone. They first converted furfural to FFA by aldol conden-
chemicals.1–4 Lignocellulose is the most abundant biomass sation in the presence of excess acetone. After evaporation of
resource on earth which consists of cellulose, hemicellulose acetone, neat FFA was then hydrogenated into 4-(2-tetrahydro-
and lignin.5 In lignocellulose conversion, 5-hydroxymethyl- furyl)-2-butanol (THFA) over Ru/C at 120 °C and 120 bar H2
furfural (HMF) and furfural are two extremely important pressure. Finally, 1-octanol and dioctyl ether were obtained by
biomass platform chemicals, which are typically produced by selective deoxygenation and ring opening over Ru/C in [EMIM]-
acid-catalyzed dehydration of fructose and xylose respectively.6–10 [NTf2] with acidic additive [BSO3BIM][NTf2] at 150 °C and 120
So far, a great number of strategies and approaches have been bar H2 pressure.30 The strategy for the synthesis of 1-octanol
put forward to convert furfural compounds into the down- from biomass-derived platforms with a retrosynthetic analysis
stream value-added products, such as methylfurans,11–14 long- concept was creative. However, the process could be further
chain alkanes,15–17 diols18–20 and acids.21,22 In recent studies, improved if a more eco-friendly solvent and a more efficient
furfural-acetone (FFA, C8) was produced by the aldol conden- catalytic system was employed.
sation of furfural with acetone and was used as a platform
More recently, we reported that n-octane can be produced
molecule for gasoline-fuel synthesis.15,16,23–25 It is noted that directly from FFA with yields higher than 90% under mild con-
acetone is also available from renewable biomass through ditions in cyclohexane over multifunctional niobium phos-
acetone–butanol fermentation and can be regarded as a phate supported Pd catalysts.31 The proposed reaction pathway
biomass-derived chemical.26,27
showed that 1-octanol had been produced before it was finally
1-Octanol is a particularly attractive industrial product converted into n-octane. From this point of view, if the catalyst
widely used in detergents, surfactants and fragrance pro- or the reaction condition was appropriately modified to
duction as well as chemical synthesis.28 It also serves as prevent 1-octanol from finally converting to n-octane, the one-
pot efficient production of 1-octanol from FFA could be envi-
saged. In the literature, NbOPO4 has been extensively studied
Key Lab for Advanced Materials, Research Institute of Industrial Catalysis,
as a water-tolerant solid acid and has been applied in
East China University of Science and Technology, # 130, Meilong Road, Shanghai,
dehydration,32–34 hydrolysis35,36 and esterification.37 It also
200237, P. R. China. E-mail: wangyanqin@ecust.edu.cn
possesses a strong hydrophilic character due to its large
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
c5gc01119a
metal size.38 Therefore, if water was used as a solvent for the
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M/NbOPO4 (M = Pt, Pd, and Ru) catalysts were prepared by
incipient wetness impregnation of NbOPO4 with aqueous
solution of Pt(NO3)2, Pd(NO3)2, and RuCl3, respectively. After
impregnation, the catalysts were dried at 100 °C for 12 h, fol-
lowed by calcination in air at 500 °C for 3 h with a rate of
2 °C min−1. Pd/H-Beta was also prepared by the same pro-
cedure. Metal loading was 5 wt% in all cases. Pd and Pt cata-
lysts were used without pre-reduction and reduced in situ
during the reaction. Ru/NbOPO4 was reduced at 300 °C under
the flow of 10% H2/Ar gas mixture before use.
Scheme 1 One-pot production of 1-octanol from biomass-derived FFA
over Pd/NbOPO4 in water.
Catalyst characterization
The N2 adsorption/desorption isotherm of NbOPO4, the X-ray
diffraction (XRD) pattern, the X-ray photoelectron spectroscopy
(XPS) pattern and the transmission electron microscopy (TEM)
image of Pd/NbOPO4 are provided in the ESI.†
production of 1-octanol from FFA using hydrophilic Pd/NbOPO4
as a catalyst, it would actually cause a man-made “phase
problem” to prevent the over-hydrogenolysis of 1-octanol,
because 1-octanol would separate spontaneously from the
water phase once it was generated owing to its immiscibility,
while hydrophilic Pd/NbOPO4 would stay in the aqueous phase
throughout the reaction, which will separate with 1-octanol.
Herein, we describe an energy-efficient catalytic system for
the one-pot production of 1-octanol from biomass-derived
FFA, using hydrophilic Pd/NbOPO4 as a catalyst and water as a
solvent, as shown in Scheme 1. The over-hydrogenolysis of
1-octanol to n-octane can be largely avoided and 1-octanol can
be easily separated from water after being produced, which
makes this catalytic system much more energy-efficient for the
industrial production. Moreover, strong acidity is found to be
in favor of the cleavage of the secondary C–O bond compare to
the primary C–O bond, which can be attributed to the greater
stability of secondary carbenium ion structures than primary
carbenium ion structures in water.39 Therefore, liquid acids
were added to further increase the system acidity, which
enhance the selectivity of secondary C–O bond cleavage,
leading to the primary alcohol formation. With the addition of
TfOH, the highest yield of 1-octanol (62.7%) was obtained
from one-pot conversion of biomass-derived FFA over a hydro-
philic Pd/NbOPO4 catalyst.
The NH3-TPD was carried out in an apparatus (PX200,
Tianjin Golden Eagle Technology Co. Ltd) equipped with a
thermal conductivity detector (TCD). The samples (100 mg)
were loaded into a U-shaped quartz tube. Prior to TPD
measurements, the samples were pretreated in flowing N2
(45 ml min−1) for 1 h at 500 °C, and then cooled to 50 °C. NH3
was adsorbed onto the samples by exposure to flowing 10%
NH3 in a N2 gas mixture (50 ml min−1) for 45 min at 50 °C.
Residual and physical adsorbed NH3 was removed by purging
the samples with flowing N2 (45 ml min−1) at 90 °C for 1 h.
Desorption of NH3 was performed by heating the samples at a
rate of 10 °C min−1 under flowing N2 (45 ml min−1) from 90 °C
to 550 °C.
Catalytic reaction and product analysis
The one-pot production of 1-octanol from FFA was carried out
in a 50 mL Teflon-lined stainless-steel autoclave. Typically,
0.2 g of FFA, 0.1 g of Pd/NbOPO4 and 4 g of water were put
into the autoclave. The reaction was hydrogenated at room
temperature and 2.5 MPa H2 pressure for 3 h first to saturate
FFA and then reacted at elevated temperature (e.g., 190 °C) for
another 18 h. After the reaction, the reactor was quenched in
an ice/water bath. The products in the liquid phase were
extracted by 4 mL of cyclohexane and both organic and
aqueous phases were analyzed by GC (Agilent 7890) equipped
with a HP-5 column and an FID detector using the internal
standard method. The yields of products were calculated by
using the equation: yield [%] = (mol of carbon in product)/
(mol of carbon in reactant) × 100%.
Experimental section
Chemicals
Pt(NO3)2·xH2O and Pd(NO3)2·xH2O were purchased from
Heraeus Materials Technology Shanghai Ltd (Shanghai,
China). RuCl3·3H2O was purchased from Aladdin Reagent Co.,
Ltd (Shanghai, China). γ-Al2O3 and H-Beta were purchased
from Nankai University Catalyst Co., Ltd (Tianjin, China). All
other chemicals were purchased from Sinopharm Chemical
Reagent Co., Ltd (Shanghai, China). All purchased chemicals
were of analytical grade and used without further purification.
Results and discussion
Reaction pathway and practicability study
We have investigated the reaction pathway of one-pot conver-
sion of FFA to n-octane in cyclohexane over multifunctional
Pd/NbOPO4 catalysts, and found that 1-octanol had been gen-
erated before it was finally converted into n-octane.31 So first
Catalyst preparation
Hydrophilic NbOPO4 used here was prepared by a hydro- of all, we studied the reaction profile of one-pot FFA conver-
thermal method at pH = 2 according to our previous reports.33 sion in the aqueous phase over Pd/NbOPO4 to investigate the
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practicability of 1-octanol production. The catalytic reaction and held for 6 h, the amount of THFA was drastically
was carried out at room temperature and 2.5 MPa for 3 h first decreased, giving a medium yield of 1-octanol (22.6%), with
to saturate FFA before being heated up to 170 °C. FFA is just 15.6% yield of 2-methyl-5-propyltetrahydrofuran (MPTHF),
slightly soluble in water, so directly heating up to a high temp- 18.7% yield of 2-butyltetrahydrofuran (BTHF) and 4.2% yield
erature without pre-hydrogenation of the highly unsaturated of octane. Small amounts of other products such as 1,4-octyl-
FFA would cause severe cokes. The product distribution of ene glycol (1,4-OG), 1,7-OG, 2,5-OG, 2-octanol, and 4-octanol
one-pot conversion of FFA with different reaction times is were also detected. Further reaction for another 6 h at 170 °C
shown in Fig. 1, and the main reaction pathway according to showed a mild increase in the yield of 1-octanol to 30.9%, and
the reaction time plot is proposed in Scheme 2. For the first this yield was further slightly increased to 33.1% when the
3 h being hydrogenated at room temperature, FFA was comple- reaction continued for 18 h, with very little amounts of THFA
tely converted to saturated intermediates with 87.1% yield of remaining. As expected, extension of the reaction time to 24 h
tetrahydrofurfural alcohol (THFA, 4-(2-tetra-hydrofuryl)-2- did not make much difference to that of 18 h, revealing that
butanol and its isomer 3-(5-methyl-2-tetra-hydrofuryl)-1-propa- 1-octanol, BTHF, and MPTHF were relatively stable in aqueous
nol), indicating that the hydrogenation of FFA is relatively medium under these conditions. It was because 1-octanol,
easy, thus makes it possible for coupling the THFA hydrode- BTHF and MPTHF all separated spontaneously from water,
oxygenation step with the FFA hydrogenation step into a one-pot while the hydrophilic catalyst Pd/NbOPO4 remained in the
reaction. Then the reaction temperature was raised to 170 °C aqueous phase throughout the reaction, which caused an
intentional “phase problem” to prevent further conversion of
water-insoluble compounds. This was remarkably different
from our previous work,31 in which all the oxygen-containing
compounds were ultimately converted to octane under the
same conditions except that cyclohexane was used as a solvent,
revealing that the solvent could impose a significant influence
on the product distribution.
Effects of reaction conditions
The effects of reaction temperature and initial H2 pressure
were systematically investigated to optimize the reaction con-
ditions and improve the selectivity of 1-octanol. Table 1 shows
the product distribution achieved over Pd/NbOPO4 under
different reaction conditions. FFA was hydrogenated at room
temperature for 3 h first and its final conversion was 100% in
all cases. Entries 1–5 show that it is possible to increase the
yield of 1-octanol by optimizing the reaction temperature,
which has a significant effect on the final product distribution.
Fig. 1 The product distribution of one-pot conversion of FFA at
In particular, when the reaction temperature was raised from
160 to 200 °C, the yields of THFA, MPTHF and other by-
products (mainly 2-octanol and 4-octanol) decreased mono-
tonously whereas the yield of octane increased monotonously,
leading to the yield of 1-octanol peaking at 190 °C, first rising
from 29.8% to 39.9% and then falling to 36.6%. This is prob-
ably because high temperature would promote the mass trans-
fer of the reactants and H2, leading to a faster hydrogenolysis
rate.40 Compared to reaction temperature, the H2 pressure has
minor effects on the final product distributions (entries 4, 6,
and 7). However, an increase in the initial H2 pressure from
2.5 to 6 MPa leads to a slight increase in the yield of octane,
indicating that high H2 pressure favors hydrodeoxygenation.
different reaction times. The reaction was hydrogenated at room temp-
erature and 2.5 MPa for 3 h first and then reacted at 170 °C for a certain
period of time.
Catalytic performance of various catalysts
Under the optimized reaction conditions, we investigated
a series of Pd catalysts with different hydrophilic oxygen-
containing supports, namely Pd/NbOPO4, Pd/γ-Al2O3, Pd/H-Beta
and Pd/Nb2O5, as their catalytic performance and NH3-TPD
profile of the supports are summarized in Table 2 and Fig. 2
respectively. The yields of 1-octanol were strongly related to the
Scheme 2 Proposed reaction pathway of the one-pot FFA conversion
over Pd/NbOPO4 in water. The reaction was hydrogenated at room
temperature and 2.5 MPa for 3 h first and then reacted at 170 °C for a
certain period of time.
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Table 1 Reaction results of the one-pot conversion of FFA at different temperatures and pressuresa
Yieldb [%]
Entry
T (°C)
P (MPa)
1-Octanol
MPTHF
BTHF
THFAc
Octane
Othersd
1
2
3
4
5
6
7
160
170
180
190
200
190
190
2.5
2.5
2.5
2.5
2.5
4
29.8
33.1
36.7
39.9
36.6
36.4
38.5
19.1
17.4
16.2
16.8
15.6
18.9
18.2
21.9
22.5
26.1
23.6
27.1
24.6
23.0
6.4
3.1
0
0
0
0
0
3.1
6.6
7.8
10.8
13.8
13.5
13.5
19.7
17.3
13.2
8.9
6.9
6.6
6
6.8
a The reaction was hydrogenated at room temperature for 3 h first and then reacted at elevated temperature for another 18 h. b >99% conversion
was observed in all cases. MPTHF, BTHF, and THFA are abbreviations for 2-methyl-5-propyltetrahydrofuran, 2-butyltetrahydrofuran, and
4-(2-tetrahydrofuryl)-2-butanol. c “THFA” includes 4-(2-tetrahydrofuryl)-2-butanol and its isomer (5-methyl-2-tetrahydrofuranpropanol). d Unless
otherwise specified, “others” include 2-octanol, 4-octanol, dioctyl ether, 2,5-octylene glycol, 1,7-octylene glycol and other un-defined products.
Table 2 Reaction results of the one-pot conversion of FFA over different catalystsa
Yield [%]
Entry
Catalystb
Octane
1-Octanol
MPTHF
BTHF
THFA
Others
1
2
3
4
5
6
Pd/NbOPO4
Pd/γ-Al2O3
Pd/H-Beta
Pd/Nb2O5
Pt/NbOPO4
Ru/NbOPO4
10.8
0
35.5
2.0
11.4
8.0
39.9
0
33.4
26.8
23.8
2.5
16.8
0
0.9
10.9
31.6
13.3
23.6
0
2.4
57.6
23.8
40.7
0
97.0
0
0
0
8.9
3.0
21.8
2.7
9.4
0
35.5c
a The reaction was hydrogenated at room temperature and 2.5 MPa for 3 h first and then reacted at 190 °C for another 18 h. b All metal loading
was 5 wt%. c The by-products were mainly heptane and 2-methyl-5-ethyltetrahydrofuran.
(entry 3), slightly lower than the yield over Pd/NbOPO4, this is
in good accordance with their relative quantity of acidic sites
(see Fig. 2). However, the over-hydrogenolysis over Pd/H-Beta
was much more significant with a much higher octane yield
obtained (entry 3), probably because the zeolite was not hydro-
philic enough to avoid the over-hydrogenolysis of 1-octanol. In
our recent work,31 Pd/Nb2O5 had an outstanding performance
for hydrodeoxygenation of FFA in cyclohexane medium,
thanks to the significant promotional effect of NbOx on the
cleavage of the C–O bond. However, in this catalytic system,
only 26.8% yield of 1-octanol was produced with BTHF being
the dominant product, though the intermediates (THFA) were
quantitatively converted and there was no significant over-
hydrogenolysis (entry 4), indicating that the C–O cleavage was
constantly active but the selectivity towards 1-octanol for-
mation was inferior. This is also consistent with the strength
and quantity of the acidic sites of these two niobium-based
catalysts (Fig. 2).
Fig. 2 NH3-TPD profiles of different supports. (a) NbOPO4, (b) H-Beta,
(c) γ-Al2O3, and (d) Nb2O5.
acidic properties of the supports. In contrast to the reaction
Other noble-metal (Pt, Ru) loaded NbOPO4 was also investi-
results over Pd/NbOPO4 (entry 1), FFA only underwent hydro- gated under the optimized reaction conditions (entries 5
genation reaction over Pd/γ-Al2O3, giving rise to 97% yield of and 6). Only 23.8% yield of 1-octanol was produced over the
hydrogenated intermediates (THFA), without any C–O bond Pt/NbOPO4 catalyst, with MPTHF being the primary product
cleavage products (entry 2), owing to the weak acidity of (31.6%). This was probably due to the very high activity of
γ-Al2O3 support. Over catalysts with the more acidic H-Beta as hydrogenolysis over Pt/NbOPO4 and thus the hydrogenolysis
support, 33.4% yield of 1-octanol was obtained respectively rate of the primary hydroxyl group of THFA was relatively fast,
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leading to the formation of MPTHF. Surprisingly, only a very
little amount of 1-octanol (2.5%) was obtained over Ru/
NbOPO4, although the intermediates (THFA) had been comple-
tely converted. These completely different results indicate that
the metals do not just play a role as hydrogenation catalysts,
but also surely have the synergistic effect with the support to
influence the selectivity of the final products.
Catalytic performance of Pd/NbOPO4 with different acidic
additives
In view of the strong correlation between the 1-octanol yield
and the acidity of the catalysts, liquid acids were added into
the reaction solution along with the Pd/NbOPO4 catalyst in
order to further increase the system acidity. As the products
would spontaneously separate from the aqueous solution,
adding homogeneous acids to the aqueous solution will not
cause any separation problems and the aqueous phase along
with the homogeneous acids can be recycled after the reaction.
As expected, the yields of 1-octanol and octane were highly
related to the acid strength of the liquid acids added (Table 3
and Fig. 3). Indeed, the addition of a superacid, trifluoro-
methanesulfonic acid (TfOH) gave the highest yield (62.7%) of
Fig. 3 Correlation between the acid strength of an acidic additive and
the sum yield of 1-octanol and octane.
water. However, stronger acidity would also lead to the increase
of over-hydrogenolysis, though not so significant.
The recyclability of the catalytic system
1-octanol from one-pot conversion of FFA, although the over- The recyclability of the catalytic system comprised of the
hydrogenolysis of 1-octanol to octane also increased. With hydrophilic Pd/NbOPO4 catalyst and the acidic additive TfOH
strong mineral acids such as H2SO4 and HCl as additives, was then investigated under the optimal reaction conditions.
about 55% yield of 1-octanol was obtained, along with about After each reaction cycle, the products were extracted by cyclo-
19% yield of octane. These results indicate that the strong hexane and the aqueous phase together with the Pd/NbOPO4
acids could promote the over-hydrogenolysis of 1-octanol at catalyst and the acidic additive was directly used for the next
the same time. Interestingly, in the presence of p-toluenesulfo- run. TfOH aqueous solution with the same concentration was
nic acid (p-TSA), 29.8% yield of octane was produced, although added to compensate the loss of aqueous solution in the prior
p-TSA was not the strongest acid. This is probably owing to the run. The product distributions obtained from each cycle are
molecular structure of p-TSA, which has a large organic phen- shown in Fig. 4. The conversion of FFA remained 100% and
methyl group and an inorganic sulfonic acid group, that could there was no significant change in the product distribution,
actually play a role as a biphasic catalyst. The lowest yield with only a slight decline in the yield of 1-octanol (from 62.7%
(37.7%) of 1-octanol was obtained with a weak acetic acid to 49.1%) after four successive runs, indicating that the cata-
(HAc) as an additive. These results show that stronger acidity lytic system was relatively stable and recyclable under the reac-
can increase the selectivity to secondary C–O bond cleavage tion conditions in this work. The ICP analysis of the reaction
leading to the formation of primary alcohol, which can be solution showed that the concentration of Pd was below the
attributed to the higher stability of the secondary carbenium detection limit, further confirming the high stability of the
ion structure than the primary carbenium ion structure in catalyst.
Table 3 Reaction results of the one-pot conversion of FFA over Pd/NbOPO4 in the presence of various acidic additivesa
Yield [%]
Entry
Additive
pKa
2.12
−3
−7
4.76
Octane
1−Octanol
MPTHF
BTHF
Others
1
2
3
4
5
6
H3PO4
H2SO4
HCl
HAc
p-TSA
TfOH
8.9
18.4
19.5
7.7
29.8
23.7
50.5
55.8
54.8
37.7
42.9
62.7
9.1
7.7
5.5
15.1
2.0
2.6
27.2
13.9
15.2
34.3
17.9
5.5
4.3
4.2
5.0
5.2
7.4
5.5
−2.8
−15
a Reaction conditions: 0.2 g of FFA, 0.1 g of Pd/NbOPO4, a certain amount of liquid acid (2 mmol of [H] in all cases), and 4 g of water were put
into a 50 mL Teflon-lined autoclave. The reaction was hydrogenated at room temperature and 2.5 MPa for 3 h first and then reacted at 190 °C for
another 18 h.
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Conclusions
In summary, we have demonstrated an energy-efficient cata-
lytic system for the one-pot production of 1-octanol from
biomass-derived FFA in water, by sequential hydrogenation/
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hydrogenolysis using
a hydrophilic Pd/NbOPO4 catalyst
together with an acidic additive. Up to 62.7% yield of 1-octanol
was obtained under the optimal conditions over Pd/NbOPO4
together with TfOH as an acidic additive. The approach of
creating an intentional “phase problem” by using a hydro-
philic catalyst in water is proved to be able to prevent the over-
hydrogenolysis of 1-octanol, as 1-octanol would separate spon-
taneously from water once generated during the reaction due
to their immiscibility, which makes this catalytic system much
more energy-efficient for the industrial production. This
approach provides a new strategy to enhance the selectivity of
the target products by phase separation, for reactions whose
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This project was supported financially by the NSFC of China
(no. 21273071, 21403065), the Science and Technology Com-
mission of Shanghai Municipality (13520711400, 13JC1401902,
10dz2220500), the China Postdoctoral Science Foundation and
the Fundamental Research Funds for the Central Universities,
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