Effective production of octane from biomass derivatives under mild conditions

Article abstract of DOI:10.1002/cssc.201100361

Cool cats dont feel pressure: Furfural is catalytically converted into octane in high yields at relatively low pressures and temperatures. In a three-step process, two bifunctional catalysts, Pt/Co₂AlO₄ and Pt/NbOPO₄, play crucial roles in achieving C₈-ols from 4-(2-furyl)-3-buten-2-one and transforming the C₈-ols into octane, respectively.

Full text of DOI:10.1002/cssc.201100361

DOI: 10.1002/cssc.201100361
Effective Production of Octane from Biomass Derivatives under Mild
Conditions
Wenjie Xu, Qineng Xia, Yu Zhang, Yong Guo, Yanqin Wang,* and Guanzhong Lu*[a]
The diminishing reserves of fossil fuels have rendered the pro-
duction of liquid fuels from renewable biomass resources par-
ticularly attractive, and worldwide many efforts have been de-
voted to the conversion of biomass into transportation
fuels.[1,2] The overall goals when converting lignocellulosic bio-
mass to hydrocarbon fuels are the removal of oxygen and the
formation of CÀC bonds; the latter to control the molecular
weight of the final hydrocarbons.[2h]
mentioned above. Herein, we show how furfural (a biomass
product, obtained from the dehydration of xylose) can be con-
verted to octane under mild conditions with high yield.
Scheme 1 shows the essential features of the reaction path-
ways for the production of octane from furfural and acetone,
comprising the aldol condensation of furfural with acetone,
So far, two integrated processes to produce liquid alkanes
from biomass-derived carbohydrates exist, both developed by
Dumesic’s group. In “aqueous-phase processing”,[2b,c] furfural or
5-hydroxymethylfurfural (HMF) first undergoes an aldol con-
densation with acetone in the presence of a basic catalyst, fol-
lowed by hydrogenation of the condensation products (4–
5.5 MPa). Then, long-chain alkanes are formed by dehydration/
hydrogenation (5.2–6 MPa, 250–2608C). The other process in-
volves the integrated catalytic conversion of g-valerolactone
(GVL), produced from levulinic acid by dehydration/hydrogena-
tion (4 MPa, 2008C),[2e] to liquid alkanes.[2d] In this process, the
decarboxylation of GVL first occurs at elevated temperature
and pressure (3.6 MPa, 3758C) to produce a gas stream com-
posed of butene and CO2. This stream is then fed directly into
an oligomerization reactor to form condensable alkanes. Both
strategies are creative, but must be operated at high pressure
or temperature.
Very recently, we developed a new Pt/Co2AlO4 catalyst to di-
rectly open furan rings and produce pentanediols from furfural
under mild conditions (1–1.5 MPa, 130–1508C).[3] 4-(2-Furyl)-3-
buten-2-one 1 has a molecular structure that is similar to furfu-
ral. It is a single aldol adduct of furfural with acetone and also
an important intermediate in aqueous phase processing for
converting lignocellulosic biomass to octane. However, it must
Scheme 1. Reaction pathways for the conversion of biomass-derived furfural
into octane.
[4b]
be hydrogenated over a Ru/C[4a] or Pd/MgoÀZrO2 catalyst at
4.5–5.5 MPa to prevent polymerization of C=C over a Pt/acid
catalyst in the next step. If it could be hydrogenated over a Pt/
Co2AlO4 catalyst similar to furfural, 1,7- and 2,5-octanediol
would be obtained in mild conditions. The dehydration/hydro-
genation of diols or polyols is known to be easier than for tet-
rahydrofuran derivatives. As a result, the reaction conditions of
the process would be much milder than for the two processes
further hydrogenation of the condensation products, and final-
ly dehydration/hydrogenation of C8-ols [including 4-(2-tetrahy-
drofuryl)-butan-2-ol 3, 2,5-octanediol 4, and 1,7-octanediol 5].
Two catalysts are needed in this process: one is a bifunctional
Pt/Co2AlO4 catalyst, which can catalyze CÀC bond formation to
get a longer carbon chain (Co2AlO4 itself is a solid base cata-
lyst) and the hydrogenolysis of furan ring to get polyols; and
the other is a solid-acid-supported noble metal catalyst, Pt/
NbOPO4, to catalyze the dehydration/hydrogenation to get
liquid alkanes.
[a] W. Xu, Q. Xia, Y. Zhang, Y. Guo, Prof. Y. Wang, Prof. G. Lu
Key Laboratory for Advanced Materials
Research Institute of Industrial Catalysis
East China University of Science and Technology
No. 130 Meilong Road, Shanghai (PR China)
Fax: (+86)21-64253824
We began our study from the aldol condensation of furfural
with acetone (Scheme 1, step 1). Co2AlO4 is a good solid base
catalyst that can catalyze the aldol condensation, even after
loading with Pd[5] or Pt. The reaction was carried out in a batch
reactor with Pt/Co2AlO4 or NaOH as catalyst. Under optimized
conditions, the conversion of furfural was 99.9% in all condi-
E-mail: wangyanqin@ecust.edu.cn
zhlu@ecust.edu.cn
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.201100361.
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ChemSusChem 2011, 4, 1758 – 1761

crease the side reactions in
step 3. So, the scale-up experi-
ment of the hydrogenation of 4-
(2-furyl)-3-buten-2-one 1 in THF
was carried out in 500 mL batch
reactor at 1308C and 1–1.5 MPa
to supply enough reactant for
the next step. We found that
the total yield of 1,7- and 2,5-oc-
tanediol (57%, Table 1, entry 7)
was a little bit higher than the
maximum value (53%) in etha-
nol, and almost no 2-methyl-1,6-
dioxaspiro[4.4]nonane 6 was de-
tected.
Table 1. Selective hydrogenation of 4-(2-furyl)-3-buten-2-one in ethanol over Pt/Co2AlO4 at different pressures
and temperatures.[a]
Entry
P
T
Yield 2
Yield 3
Yield 4
Yield 5
Yield 6
[MPa]
[8C]
[%]
[%]
[%]
[%]
[%]
1
2
3
4
5
6
7[b]
0.5
1
1.5
2
1
1
140
140
140
140
130
150
130
86.0
1.2
2.7
3.4
51.6
22.3
0
3.1
29.5
38.4
47.5
20.3
32.3
38.0
4.5
46.6
32.7
27.2
14.6
23.9
42.0
1.8
7.0
13.5
12.3
6.0
2.3
9.9
9.0
5.1
5.6
7.4
1.0
10.4
15.5
1
[a] Reaction time: 20 h; Pt content 1.8 wt%. [b] THF as solvent.
Table 2. Dehydration/hydrogenation of a 3 wt% C8-ols solution over Pt/NbOPO4 at various temperature and
space velocities in THF at 2.5 MPa.[a]
The dehydration/hydrogena-
tion of the C8-ols (Scheme 1,
step 3) was carried out in a
fixed-bed reactor over Pt-loaded
NbOPO4 as catalyst, because Pt/
Nb2O5 or Pt/NbOPO4 is an excel-
lent water-resistant bifunctional
catalyst and was used in the de-
hydration/hydrogenation reac-
tion of polyols.[2c] Also, the cata-
lytic properties of niobium oxide
are similar to ReOx and CoOx,
which can catalyze the hydroge-
nolysis of CÀO on the tetrahy-
Entry
WHSV
T
[8C]
Conv.
[%]
Selectivity[b]
to 7 [%]
Selectivity
to 8 [%]
Selectivity
to 9 [%]
Selectivity
to 10 [%]
[hÀ1
]
1
2
3
4
1.2
1.2
1.2
0.6
1.8
1.2
0.6
165
175
185
175
175
175
175
92.5
99.9
99.9
99.9
99.9
99.9
99.9
49.3
68.8
71.9
84.2
46.7
42.8
41.3
37.8
21.3
18.2
12.1
36.2
21.7
15.0
9.3
5.5
7.9
0.8
0
0
3.7
0
5
11.6
30.3
36.2
0.5
1.3
2.6
6[c]
7[c]
[a] Pt content is 5 wt%. [b] Including iso-octane and octane. [c] 95% 4-(2-tetrahydrofuryl)-butan-2-ol as reac-
tant.
tions, the yields of 4-(2-furyl)-3-buten-2-one 1 (F–A, single aldol
adduct) and difurfurylideneactone (F–A–F, double aldol adduct)
could be tuned by changing the molar ratio of acetone to fur-
fural (see Supporting Information).
drofurfural ring.[3,6] The catalyst was pelletized and sieved to
40–60 mesh size. Then, 2.0 g of catalyst was loaded in the
stainless steel tubular reactor with an inner diameter of 6 mm.
The reaction was operated at T=165–1858C and P=2.5 MPa.
Mesoporous NbOPO4 with a high surface area (254 m2gÀ1) and
strong acidic sites was prepared and characterized (see Sup-
porting Information). Table 2 summarizes the results (C8-ols
conversion and product selectivities) for the conversion of
3 wt% C8-ols in THF at various temperatures and space veloci-
ties over the bifunctional 5 wt% Pt/NbOPO4 catalyst. The selec-
tivity to octane is about 50% at T=1658C and WHSV=1.2 hÀ1
(entry 1), very close to the content of octanediols (57%) in the
reactant solution, indicating that octanediols are almost com-
pletely converted to octane. Surprisingly, a further increase of
the temperature, from 1658C to 1758C, gave a selectivity to
octane of 68.8% (entry 2); much higher than the octanediol
content of 57% in the reactant solution. This result indicates
that under these mild conditions, a part of 4-(2-tetrahydrofur-
yl)-butan-2-ol 3 is dehydrated, undergoes ring-opening, and is
hydrogenated into octane on Pt/NbOPO4 catalyst.
Then, the hydrogenation of a 5 wt% solution of 4-(2-furyl)-3-
buten-2-one 1 (+95%, purified by vacuum distillation) in etha-
nol under mild conditions was investigated in a 120 mL batch
reactor over Pt/Co2AlO4 (Scheme 1, step 2). The hydrogenation
gave four main products: 4-(2-tetrahydrofuryl)-butan-2-ol 3,
2,5-octanediol 4, 1,7-octanediol 5, and 2-methyl-1,6-dioxaspiro-
[4.4]nonane 6. The time course of the hydrogenation of 1 over
Pt/Co2AlO4 under 1 MPa and at 1408C is shown in Figure S4
(Supporting Information), the pathway is similar to furfural[3]
and drawn in Scheme S1. The influences of pressure and tem-
perature on the reaction over Pt/Co2AlO4 were investigated
and are summarized in Table 1. The conversions of 4-(2-furyl)-
3-buten-2-one(I) are 99.9% in all conditions and the optimized
conditions are 1408C and 1 MPa (entry 2). The lower optimal
pressure compared to that of the hydrogenolysis of furfural
(1.5 MPa, 1408C)[3] may be due to the different substituents.
The maximum yield of diols is 53.6%.
To confirm that mesoporous Pt/NbOPO4 can really convert
4-(2-tetrahydrofuryl)-butan-2-ol 3 to octane, control experi-
ments were carried out under the same conditions. Pure 4-(2-
tetrahydrofuryl)-butan-2-ol (3, +95%) was prepared by hydro-
genation of 4-(2-furyl)-3-buten-2-one 1 over a Pd/Co2AlO4 cata-
lyst[5a] at 4 MPa and 1208C, and was fed as the reactant. The
main products were octane (ca. 41%), 2-propyl-tetrahydropyr-
However, when ethanol was used as solvent in the next de-
hydration/hydrogenation of C8-ols (Scheme 1, step 3), several
competitive side reactions, for example, etherification of etha-
nol itself and etherification of ethanol with octanol into octyl
ethyl ether on the acid sites can occur. Unlike ethanol, tetrahy-
drofuran (THF) is a more inert solvent and used in the produc-
tion of jet and diesel fuel range alkanes,[4a] which would de-
an
7
(15–20%), and 2-butyl-tetrahydrofuran
9
(30-36%)
ChemSusChem 2011, 4, 1758 – 1761
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www.chemsuschem.org
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(Table 2, entries 6 and 7). These results confirm the ring-open-
ing of tetrahydrofuran and show that the selectivity to octane
is high, almost matching the previous data of hydrogenation
of C8-ols. We have not yet determined the mechanism of tetra-
hydrofuran ring-opening on Pt/NbOPO4. We expect that it may
be related to its Lewis-acidic sites, because ring-opening of tet-
rahydrofuran does not take place on Pt/ZSM-5 while on ReOx
or Mo-species modified Rh/SiO2 catalyst it requires a high H2
pressure (8 MPa).[6]
from dehydration of xylose) to octane with high yield under
mild conditions. A novel aspect of the strategy outlined here is
that through designing two new bifunctional Pt/Co2AlO4 and
Pt/NbOPO4 catalysts, octane can be produced at lowered oper-
ating pressures and temperatures throughout the whole pro-
cesses. The bifunctional Pt/Co2AlO4 catalyst converts 4-(2-furyl)-
3-buten-2-one 1 to octanediol, while mesoporous Pt/NbOPO4
not only converts diols to octane, but also partially opens the
tetrahydrofuran ring in 4-(2-tetrahydrofuryl)-butan-2-ol 3 (ca.
41%) and improves the final yield of octane even under such
mild conditions. In particular, at P=2.5 MPa, T=1758C, and
WHSV=0.6 hÀ1, the final octane yield reaches ca. 76%, which
is the highest value reported under such mild conditions so
far.
To increase the yield to octane, we carried out the experi-
ments at higher temperature and lower space velocity (Table 2,
entries 3 and 4). At WHSV=1.2 hÀ1, when the temperature in-
creased from 1758C to 1858C the selectivity to octane increas-
es by just 3.1%. In contrast, when the WHSV was decreased to
0.6 hÀ1, C8-ols were almost quantitatively converted to octane
(selectivity 84.2%, final yield 76%) with the formation of small
amounts of side products; 2-propyl-tetrahydropyran 8 and 2-
butyl-tetrahydrofuran 9. Significantly, Pt/NbOPO4 shows out-
standing stability in a 38 h activity test (Figure 1). A further in-
crease of the space velocity to 1.8 hÀ1 caused a decrease in se-
lectivity to octane, although the conversion of C8-ols was main-
tained at 99.9% (entry 5).
Experimental Section
The Pt/Co2AlO4 catalyst was prepared by co-precipitation.[5] The Pt/
NbOPO4 catalysts were prepared by incipient wetness impregna-
tion of mesoporous NbOPO4 (see Supporting Information for prep-
aration and characterization) with platinum nitrate, followed by
drying at 1008C and calcination at 5008C for 4 h.
The hydrogenolysis of 4-(2-furyl)-3-buten-2-one 1 was carried out
in a stainless autoclave containing 0.4 g of 1, 10 mL EtOH, and
0.2 g of catalyst at PH =0.5–2 MPa and T=130–1508C under mag-
2
netic stirring. Hydrogen was consumed during the reaction and
more was supplied from time to time to maintain the pressure.
The dehydration/hydrogenation of C8-diols was carried out in a
fixed-bed reactor system. The catalyst was pelletized and sieved to
40–60 mesh size. Then, 2.0 g of catalyst was loaded in the stainless
steel tubular reactor with an inner diameter of 6 mm. The reaction
was operated at 165–1858C and 2.5 MPa. More details of the pro-
cedures are supplied as Supporting Information.
Acknowledgements
This project was supported financially by the 973 Program of
China (2010CB732300), the National Natural Science Foundation
of China (20973058), the Commission of Science and Technology
of Shanghai Municipality (08JC1407900, 10XD1401400) and the
Fundamental Research Funds for the Central Universities, China.
We thank Prof. Xueqing Gong for useful discussions.
Figure 1. Products distribution in the dehydration/hydrogenation of a
3 wt% C8-diols solution over Pt/NbOPO4 at various temperatures and space
~
&
*
velocities in THF. : Conversion; : selectivity to octane 7; : selectivity to 2-
^
propyl-tetrahydropyran 8; : selectivity to 2-butyl-tetrahydrofuran 9.
Keywords: alkanes
·
biomass
·
dehydrogenation
·
heterogeneous catalysis · platinum
Furthermore, during the dehydration/hydrogenation of C8-
ols, we found that less CÀC cleavage occurred because only
small amounts of CH4, CO, and CO2 were detected in the gas
phase and there no C7 or C6 products were detected in liquid
phases. This is rather different from aqueous-phase proces-
sing,[2b,c] where CÀC cleavage always occurs and quantities of
CnÀ1 always co-exist with Cn alkanes because of the high tem-
peratures and pressures. Hence, the mild conditions in our pro-
cess not only decrease the cost of a biorefinery and improve
operational safety, but may also prevent CÀC cleavage and in-
crease the octane yield.
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of furfural (an important low-cost biomass product, obtained
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ChemSusChem 2011, 4, 1758 – 1761

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Published online on November 2, 2011
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www.chemsuschem.org
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