Production of renewable long-chained cycloalkanes from biomass-derived furfurals and cyclic ketones

Article abstract of DOI:10.1039/c8ra01723a

Developing renewable long-chain cycloalkanes from lignocellulosic biomass is of significance because it offers huge resource storage, wide applications in aviation/diesel fuels and mitigation of CO₂ emissions. In this paper, cycloalkanes with carbon chain lengths of 13-18 were produced from biomass-derived furfural species (furfural and 5-hydroxymethylfurfural) and cyclic ketones (cyclopentanone and cyclohexanone) via aldol condensation, followed by hydrogenation to saturate the CC and CO bonds, and hydrodeoxygenation to remove oxygen atoms. The aldol condensation of the furfural species with cyclic ketones was catalyzed by NaOH and the target condensation intermediates were obtained in yields of more than 90% at room temperature (30 °C) with a short reaction time (40 min). By using amorphous zirconium phosphate combined with Pd/C as the catalyst, liquid cycloalkanes were produced at the optimal conditions with a yield of 76%. When the combined solid catalyst was reused, the target products reduced after the second run but the initial yield could be largely recovered by recalcination of the spent zirconium phosphate. Considering that cyclopentanone and cyclohexanone can be easily produced from furfural (originating from hemicellulose) and phenol (originating from lignin), respectively, this condensation has the potential to achieve the integrated conversion of biomass-derived cellulose, hemicellulose and lignin to jet fuel and/or diesel additives.

Full text of DOI:10.1039/c8ra01723a

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PAPER
Production of renewable long-chained
cycloalkanes from biomass-derived furfurals and
Cite this: RSC Adv., 2018, 8, 13686
cyclic ketones†
a Caihong Zhang,ab Ning Shi,ab Xinghua Zhang,
a Chenguang Wanga
*
*
Qiying Liu,
and Longlong Maa
Developing renewable long-chain cycloalkanes from lignocellulosic biomass is of significance because it
offers huge resource storage, wide applications in aviation/diesel fuels and mitigation of CO2 emissions.
In this paper, cycloalkanes with carbon chain lengths of 13–18 were produced from biomass-derived
furfural species (furfural and 5-hydroxymethylfurfural) and cyclic ketones (cyclopentanone and
cyclohexanone) via aldol condensation, followed by hydrogenation to saturate the C]C and C]O
bonds, and hydrodeoxygenation to remove oxygen atoms. The aldol condensation of the furfural species
with cyclic ketones was catalyzed by NaOH and the target condensation intermediates were obtained in
yields of more than 90% at room temperature (30 ꢀC) with a short reaction time (40 min). By using
amorphous zirconium phosphate combined with Pd/C as the catalyst, liquid cycloalkanes were
produced at the optimal conditions with a yield of 76%. When the combined solid catalyst was reused,
the target products reduced after the second run but the initial yield could be largely recovered by
recalcination of the spent zirconium phosphate. Considering that cyclopentanone and cyclohexanone
can be easily produced from furfural (originating from hemicellulose) and phenol (originating from
lignin), respectively, this condensation has the potential to achieve the integrated conversion of biomass-
derived cellulose, hemicellulose and lignin to jet fuel and/or diesel additives.
Received 27th February 2018
Accepted 29th March 2018
DOI: 10.1039/c8ra01723a
rsc.li/rsc-advances
in the fuels from direct hydrodeoxygenation of these platforms
having short carbon chains.5,6 To synthesize long-chained
1. Introduction
alkanes with carbon numbers of more than 10, for jet fuel
and diesel use, condensations between suitable biomass-
derived platforms with special groups are necessary to extend
the carbon chains.6–9 Typically, the production of long-chained
alkanes involves three steps: depolymerization of the lignocel-
lulosic biomass into oxygenated platforms (FF, HMF, levulinic
acid, g-valerolactone and 2-methylfuran et al.); fuel precursor
formation by condensation; and hydrodeoxygenation of the fuel
precursors.9,10 Herein, the second step of platform condensa-
tion is the key to obtain structurally diversied fuel precursors;
the desired platforms and condensation methods must be
chosen in order to produce versatile hydrocarbon fuels by
hydrodeoxygenation.11 Aldol condensations of FF/HMF and/or
their derivatives with carbonyl groups like acetone,12–16 hydrox-
yacetone,17 butaldehyde,18 2-butanone,19 methyl isobutyl
ketone,20 levulinic acid11,21,22 and angelica lactone23 have
commonly been conducted to obtain the C9–C16 fuel precursors,
but these carbonyl compounds originate from fossil resources
or are produced from biomass by multi-step reactions, leading
to low efficiency and high cost for the entire synthesis. As an
alternative, hydroxyalkylation-alkylation of FF and 2-methyl-
furan obtained by hydrodeoxygenation of FF was reported to
Lignocellulosic biomass is a renewable resource with huge
storage, wide distribution and fast carbon cycles during
biomass growth and utilization. Biomass-derived fuels and
chemicals are regarded as an alternative to fossil energy, and
their development has obvious signicance for environmental
protection and reduced dependence on fossil energy. Therefore,
converting lignocellulosic biomass into fuels has attracted
worldwide attention during recent decades.1–4
Cellulose, hemicellulose and lignin are the three main
components of a typical lignocellulosic biomass, however, the
monosaccharide units (typically, glucose and xylose) and
derivatives (5-hydroxymethylfurfural (HMF) and furfural (FF))
are limited to carbon chains of length 6, while the phenolic
units (typically, phenol-, guaiacol- and syringyl-based primary
structures) are limited to carbon chains of length 9. This results
aCAS Key Laboratory of Renewable Energy, Guangzhou Institute of Energy
Conversion, Chinese Academy of Sciences, Guangzhou, 510650, P. R. China.
E-mail: liuqy@ms.giec.ac.cn; zhangxh@ms.giec.ac.cn; Fax: +86-20-87057737; Tel:
+86-20-87057751; +86-20-87057790
bUniversity of Chinese Academy of Sciences, Beijing, 100049, P. R. China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c8ra01723a
produce C15 fuel precursors with
a branched carbon
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framework.24–27 Despite the fact that the precursor could be were screened and the pathway for long-chained cycloalkane
converted into branched long-chain hydrocarbons, the main formation is discussed.
drawback was that only hemicellulose (the least abundant
component in a typical lignocellulosic biomass) could be
utilized. Interestingly, alternative routes including direct C–C
bond formation by condensation of monosaccharides/furfu-
2. Experimental section
2.1. Materials
rals,28 a-alkylation of ketones with 1-butanol,29 self-coupling by
two HMF molecules30 and oligomerization of angelica
lactone31,32 were used to produce C10–C15 precursors with high
yields, and hydrodeoxygenation to the relative long-chained
hydrocarbons was then conducted over supported metal cata-
lysts. Instead of the common furfurals, these routes extended
the platform molecules for target hydrocarbons by using
diversied structures.
FF (99%), HMF (98%), CP (99%), CH (99%), ZrOCl2$8H2O, Pt/C
(5 wt%), Pd/C (5 wt%) and Ru/C (5 wt%) were purchased from
Shanghai Crystal Pure Reagent Co., Ltd., China. Analytical grade
NaOH, KOH, Ba(OH)2, LiOH, K2CO3, Na2CO3, Mg(OH)2, H3PO4
and NH4H2PO4 were purchased from Tianjin Fuchen Chemical
Reagent Factory, China. Nb2O5$H2O was purchased from the
Conghua Tantalum Niobium Factory (Guangzhou, China). All
these chemicals and reagents were used without further
purication.
Compared to branched and normal hydrocarbons with long
chains, cyclic counterparts show particular advantages in view
of their low freezing points and high energy densities, which are 2.2. Catalyst preparation
preferential for drop-in jet and/or diesel fuels.33 Carbonyl-
Preparation of niobium phosphate (NbP). 6 g Nb2O5$H2O
containing HMF and FF are the two main platforms which
can be easily produced from biomass through a hydrolysis–
dehydration process. On the other hand, cyclopentanone (CP)
and cyclohexanone (CH) are two important cyclic ketones that
have special carbons with a-Hs. In particular, CP could be
selectively produced by hydrogenation-rearrangement of
hemicellulose-derived FF,34,35 and CH could be prepared with
very high yield from lignin-derived phenol.36,37 Thus, production
of cyclic hydrocarbons with long chains from these furfural
species and cyclic ketones are attractive for the integrated
utilization of biomass.38–40
Here, we developed a new route for the production of
cycloalkanes with carbon chain lengths of 13–18 from FF/HMF
and CP/CH (Scheme 1). Aldol condensations of these furfural
species with cyclic ketones (CP and CH) were rst conducted
over a base catalyst to produce the oxygenated precursors with
cyclic structures. Then these precursors were hydrogenated to
thermally stable intermediates by saturating the C]C and
C]O bonds over a metal catalyst. Finally they were transformed
to the long-chained cycloalkanes by using a catalyst of metal
combined with solid acid. The reaction parameters of each step
was added into 100 mL 5.0 mol Lꢁ1 H3PO4 aqueous solution and
vigorously stirred for 48 h at room temperature. Then the solid
residue was collected by ltration and fully washed with
deionized water until pH ¼ 5. This was followed by drying at
120 ꢀC and calcination at 400 ꢀC for 3 h (heating ramp of
5 C minꢁ1) in static air before use.
ꢀ
Preparation of zirconium phosphate (ZrP). 10 g ZrOCl2-
$8H2O and 7.14 g NH4H2PO4 were each dissolved in 100 mL
deionized H2O to obtain two transparent solutions. The two
solutions were mixed at the calculated molar ratio of P/Zr ¼ 2
and reacted for 8 h at room temperature under agitation. The
white precipitate was ltered, fully washed with deionized
water, dried at 100 ꢀC overnight, and calcined at a temperature
of 400 ꢀC for 4 h (heating ramp of 5 ꢀC minꢁ1) in static air before
use.
2.3. Catalyst characterization
X-ray powder diffraction (XRD) patterns of catalysts were ob-
tained using an X-ray diffractometer (X'Pert Pro MPD, Philip)
with Cu Ka radiation (l ¼ 0.154 nm) operated at 40 kV and
100 mA.
Scheme 1 Routes for long-chained cycloalkane production from furfural species and cyclic ketones.
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The Brunauer–Emmett–Teller (BET) specic surface areas condensations of FF and CH, HMF and CP and HMF and CH
were obtained from N2 isothermal adsorption–desorption were carried out by the procedure mentioned above, and the
measurements at 77 K using a QUADRASORB SI-MP-10/ solid intermediates were labeled as FF-CH-FF, HMF-CP-HMF
PoreMaster analyzer equipped with QuadraWin soware. The and HMF-CH-HMF, respectively.
mesoporous volumes and pore size distributions were calcu-
The structures of the aldol condensation intermediates were
lated by the desorption branch using the Barrett–Joyner– identied using 13C NMR analysis (Bruker BioSpin GmbH)
Halenda (BJH) method.
using CDCl3 or DMSO as the solvent.
Ammonia-temperature programmed desorption (NH3-TPD)
The yield of each condensation intermediate was calculated
was conducted in a U-tube quartz reactor (inner diameter 0.6 by the following equation:
cm) using an ASIQACIV200-2 automatic physical/chemical
ni ꢂ Ci
nf ꢂ Cf þ nk ꢂ Ck
Yi ¼
ꢂ 100%
(1)
adsorption analyzer (Quantachrome, US). Catalyst (0.15 g) was
ꢀ
loaded into the U-tube quartz reactor and heated to 400 C for
0.5 h (heating ramp of 10 ꢀC minꢁ1) under 30 mL minꢁ1 of He
where, Yi is the yield of condensation intermediate collected; ni,
nf and nk represent the moles of solid intermediate i, furan and
ketone introduced, respectively; and Ci, Cf and Ck indicate the
carbon numbers of solid intermediate i, introduced furan and
ketone, respectively.
ꢀ
ow. The system was cooled to 50 C, NH3 was adsorbed onto
the catalyst for 0.5 h until the saturation state was obtained and
then the catalyst was ushed with a He ow of 30 mL minꢁ1 to
remove the physically adsorbed NH3. The adsorption and
removal processes were monitored by the TCD signals. Then the
system was heated to 825 ꢀC with a heating ramp of 10 ꢀC minꢁ1
under the same He ow. The online MS (AMETEK DYCOR LC-
D200, US) was used to determine the effluent NH3 desorbed
2.5. Hydrodeoxygenation of condensation intermediates to
cycloalkanes
from the catalyst. The quantitative analysis of acidic sites was The hydrodeoxygenation of the condensation intermediates was
performed using a calibration loop of 250 mL in which 5% NH3- carried out in a 50 mL stainless steel reactor with a mechanical
95% Ar mixed gas was used for the single point calibration.
stirrer. The condensation intermediate (1 mmol), 15 mL H2O
Transmission electron microscopy (TEM) images were and a certain amount of catalyst (solid acid and metal) were
gained on a Gatan Ultra scan camera using a JEOL JEM-2100F added to the reactor. Aer purging ve times with H2, the
instrument operated at 200 kV. The samples were ultrasoni- reaction system was pressured to 4 MPa with H2 (room
cally dispersed in ethanol, and drops of each suspension were temperature). Then the reactor was heated to the target
placed on carbon-coated copper grids and then dried in air.
temperature and maintained at that temperature for the set
Scanning electron microscopy (SEM) images were recorded time under vigorous stirring (800 rpm). Aer the reaction, the
using an S-4800 instrument operated at 2 kV. The samples were reactor was cooled to room temperature, and 15 mL ethyl
placed on a conductive carbon tape adhered to an aluminium acetate was used to extract the organic products three times.
sample holder.
The organic layer was analyzed by gas chromatography (GC, GC-
Fourier transform infrared (FT-IR) spectra were recorded on 2014C, Shimadzu, Japan) and gas chromatography-mass spec-
a Bruker TENSOR27 spectrometer with a resolution of 4 cmꢁ1
The samples were pelleted with KBr before measurement.
.
trometry (GC-MS, Agilent 7890, US). For calculating the
conversion percentage, the solid residue was collected by
The Pd dispersion in Pd/C was tested by H2-chemisorption ltration, further rinsed with deionized water, collected by
using a Quantachrome-ASIQACIV200-2 automated gas sorption ltration again and dried in a freeze dryer for 48 h.
analyzer. The catalyst (0.2 g) was treated at 300 ꢀC with a heating
For reuse, the combined catalyst (ZrP and Pd/C) was recov-
ramp of
5 a hydrogen atmosphere ered by centrifugation from the reaction mixture, thoroughly
ꢀC minꢁ1 under
(30 mL minꢁ1). To clean the catalyst surface, the catalyst was rinsed with deionized water and directly used for the next cycle.
further heated to 350 ꢀC for 0.5 h under nitrogen (30 mL minꢁ1), Considering that the components of the combined catalyst were
ꢀ
and then cooled to 50 C for the H2-chemisorption test.
hard to separate from each other, to ascertain which catalyst led
to deactivation, comparative experiments were conducted by
hydrothermal treatment of ZrP and Pd/C at 300 ꢀC, followed by
either recalcination at 400 ꢀC in static air (for ZrP) or 300 ꢀC in
30 mL minꢁ1 of H2 ow (for Pd/C); heating ramps of
2.4. Aldol condensation of furfural species with cyclic
ketones
Aldol condensation of furfural species and cyclic ketones was 10 ꢀC minꢁ1 were used for both. For monitoring the saturation
conducted in a 250 mL conical ask under atmospheric pres- of C]C and C]O bonds by hydrogenation in the solid inter-
sure. Using FF and CP as example, 2 mmol FF and 1 mmol CP mediates, the sole Pd/C catalyst was used at relatively low
were introduced into the ask, followed by the addition of temperatures according to the hydrodeoxygenation process.
15 mL H2O and a certain amount of basic catalyst. The The structures of these hydrogenation intermediates were
condensation was conducted at 30 ꢀC for 40–120 min in a water identied using 13C NMR analysis (Bruker BioSpin GmbH)
bath with vigorous stirring (800 rpm). Aer the reaction, the using CDCl3 or DMSO as the solvent.
solid product was ltrated, fully washed with a 5% aqueous
The quantitative analysis of the extracted liquid products
ethanol solution and dried in a freeze dryer for 48 h. A yellowish was determined by GC (SHIMADZU 2014C) with a ame ioni-
solid was nally obtained and was labeled as FF-CP-FF. The zation detector (FID) and a HP-INNOWAX column (30 m ꢂ
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Fig. 1 XRD patterns of fresh ZrP and NbP (a), and fresh Pd/C (b).
0.25 mm ꢂ 0.25 mm). The oven temperature was programmed quantication of gas products was conducted using a typical
ꢀ
ꢀ
initially at 60 C for 2 min,ꢁa1nd then ramped up to 260 C at external standard.
ꢀ
a heating rate of 10 C min and held at this temperature for
another 10 min. The injector was kept at 280 ꢀC and used in was calculated by the following equations:
The conversion of intermediates and yield of liquid product
splitting mode (5 : 1) with helium as the carrier gas. Tridecane
Conversion (%) ¼ mintermediate residue
/
was used as the internal standard. The qualitative analysis of
liquid products was carried out by GC-MS (Agilent 7890, US)
used with the same capillary column and analytical conditions
to those of the GC analysis. The gas products (CH4, C2H6 and
C3H8, etc.) were collected with a sampling bag and analyzed by
a GC 9800 chromatography tester equipped with a FID and
a packed column (Porapak-Q column, 3 m ꢂ 3 mm). The
mintermediate loaded ꢂ 100%
(2)
(3)
mintermediate residue ¼ msolid residue ꢁ mcatalyst
npi ꢂ Cpi
Ypi
¼
ꢂ 100%
(4)
ni ꢂ Ci
and mintermediate
where, mintermediate
mean the
loaded
residue
intermediate le aer the reaction and the intermediate loaded
Fig. 2 SEM images of fresh NbP (a) and ZrP (b). TEM images of Pd/C (c) and ZrP (d). N2 adsorption–desorption curve of ZrP (e). The inset in (c)
shows the HRTEM image of Pd/C.
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Table 1 Textural properties, acidic densities and metal dispersion of solid acids and Pd/C
Average pore
Acidic densityc
Entry
Catalyst
Surface areaa (m2 gꢁ1
)
Pore volumeb (cm3 gꢁ1
)
diameterb (nm)
(mmol gꢁ1
)
Dd
1
2
3
4
5
ZrP
112.7
93.9
78.1
1025.9
932.5
0.25
0.27
0.20
0.28
0.25
6.8
5.6
7.9
3.8
4.3
1.55
1.31
0.58
—
—
—
—
0.49
0.36
Spent ZrPe
NbP
Pd/C
Spent Pd/Ce
—
a
The surface areas were estimated by the BET method using N2 at ꢁ196 ꢀC. b The pore volume and average pore diameter were determined by using
the desorption branch and BJH method. c The acidic densities were calculated by NH3-TPD measurements and a calibration loop of 250 mL. d The
dispersion of Pd was determined by H2-chemisorption. e The spent ZrP was treated at 300 ꢀC for 3 h, dried and recalcinated at 400 ꢀC for 4 h. The
spent Pd/C was treated at 300 ꢀC for 3 h, dried and recalcinated at 300 ꢀC for 3 h under H2 ow.
ꢀ
into the reactor by weight, respectively; msolid residue and mcatalyst higher than 450 C) were simultaneously presented on the two
represent the weight of solid collected aer the reaction and the catalysts' surfaces (Fig. 3). As compared with NbP
weight of catalyst introduced, respectively; Ypi is the yield of (0.58 mmol gꢁ1), ZrP presented a much higher acid density of
product i by hydrodeoxygenation; npi and Cpi represent the 1.55 mmol gꢁ1 (Table 1). The Pd/C showed a large surface area
moles of products i and carbon numbers of product i, respec- of more than 1000 m2 gꢁ1 with signicant numbers of meso-
tively; and ni and Ci indicate the moles of condensation inter- pores. Meanwhile, the Pd dispersion was as high as 0.49
mediate loaded and carbon number of condensation according to the H2-chemisorption analysis. Aer hydrothermal
intermediate, respectively.
treatment and recalcination, the surface area and acidic sites of
The turnover frequency (TOF) of the Pd/C based catalysts was the used ZrP were reduced, but more than 80% of the original
determined by using the following equation:
values were still retained while the pore volume and diameter
changed a little. The surface area of the used Pd/C was 90% of
that of the fresh catalyst. The Pd dispersion decreased to 0.36,
although high dispersion still remained during the hydro-
thermal treatment.
TOF (sꢁ1) ¼ converted FF-CP-FF in mmol/
((exposed Pd atom) ꢂ (acid in mmol) ꢂ second) (5)
Fig. 4 presents the FT-IR spectra of fresh, hydrothermally
treated, and regenerated ZrP. The three samples presented the
stretching vibrations of P–OH (the Bronsted acidic centers,
2354 cmꢁ1), and tetrahedral P–O (1082 cmꢁ1), and the bending
vibration of P–O–P (752 cmꢁ1), similar to the previous
reports.42–45 Aer hydrothermal treatment, the peak intensity
corresponding to P–O–P signicantly reduced while that corre-
sponding to P–OH increased, indicating that ZrP hydrolysis
occurred during the treatment process. Aer recalcination, the
P–O–P was regenerated at the expense of P–OH, based on the
corresponding intensity changes. This means that the hydro-
lyzed P–OH could be re-condensed to recover the original
3. Results and discussion
3.1. Catalyst characterization
Fig. 1 shows the XRD patterns of freshly prepared NbP, ZrP and
Pd/C catalysts. The obvious diffractions at 2q ¼ 19.8ꢀ, 28.0ꢀ,
40.2ꢀ, 44.9ꢀ, 57.8ꢀ and 65.1ꢀ indicate the crystalline nature of
NbP, consistent with the previous report.41 On the other hand,
the very weak and broadened diffractions observed in the range
of 15–70ꢀ for ZrP, show that ZrP presents an amorphous nature.
For Pd/C, peaks at 2q ¼ 40.1ꢀ, 43.9ꢀ and 68.3ꢀ were obtained but
the intensities were weak, implying that the Pd particles are tiny
and highly dispersed on the activated carbon surface.
The SEM images of NbP and ZrP, the TEM images of Pd/C
and ZrP, and the N2 adsorption–desorption curve of ZrP are
shown in Fig. 2. Based on the SEM analysis, the particle size of
the NbP was in the range of 10–20 nm, and that of ZrP was about
20 nm. The particle size of ZrP was consistent with the results
obtained from TEM measurement. For Pd/C, the Pd particles
were observed and their size was in the range of 2–3 nm, which
is consistent with the result of XRD. As shown in Fig. 2e and
Table 1, the surface area, pore capacity and diameter of ZrP were
112 m2 gꢁ1, 0.25 mL and 6.8 nm, respectively, which are larger
than those of NbP aside from the pore diameter. Both NbP and
ZrP showed similar acidity, and both weak acidic sites (observed
from NH3 desorption at temperatures below 350 ꢀC) and strong
acidic sites (observed from NH3 desorption at temperatures Fig. 3 NH3-TPD profiles of fresh ZrP and NbP.
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without any catalyst. However, when only a 5% molar equivalent
of NaOH (relative to CP) was added into the mixture of FF and
CP (at a FF : CP mole ratio of 2 : 1), the reaction took place
quickly, producing a 68% yield of solid product in 40 min. Aer
increasing the NaOH dosage to 10%, the conversion of FF and
CP reached 100% (based on GC measurements; data not
shown), and was accompanied by a high FF-CP-FF yield of 94%.
Further increasing the NaOH to 20% slightly increased the yield
of isolated condensation product FF-CP-FF to 96%. Other strong
bases such as LiOH, KOH and Ba(OH)2 also showed excellent
performance resulting in target product yields of 90% and
above. However, no condensation product was observed when
using the weak alkalis Mg(OH)2, Na2CO3 and K2CO3 as the
catalysts even aer 2 h, showing that such condensation pref-
erentially takes place over a strong base. Because the strong
base NaOH showed an excellent performance in the aldol
condensation of FF with CP, we further employed NaOH for
aldol condensations of FF with CH, and HMF with CP/CH. No
obvious difference was observed when CH was used to replace
CP as the starting material, which is in accordance with results
from a previous study.46 Condensation products (FF-CP-FF and
FF-CH-FF) were obtained in yields of over 90% from the
condensation of FF with both CH and CP. When HMF was used
as the starting material instead of FF, isolated condensation
products (HMF-CP-HMF and HMF-CH-HMF) were obtained in
over 95% yield. The condensation intermediates were yellowish
for FF-CP-FF, FF-CH-FF and HMF-CH-HMF, and red for HMF-
CP-HMF, as seen in the photographs of the isolated solid
intermediates (Fig. S1†). The molecular structures of these
intermediates were determined by 13C NMR measurement,
which conrmed the synthesis of the desired products by aldol
condensation without any impurities (Fig. S2–S4 and S6(a)†).
Fig. 4 FT-IR spectra of fresh, hydrothermally treated, and regenerated
ZrP.
structure. It was noted that the peak associated with the Zr–O–P
framework was largely unchanged for the three samples,
showing the hydrothermal stability of the prepared ZrP.
3.2. Condensation of furfural species with cyclic ketones
Aldol condensations of biomass-derived aldehydes (FF and
HMF) with cyclic ketones (CP and CH) with mole ratios of 2 : 1
were used to synthesize C10–C18 precursors for downstream
long-chained cycloalkane production. The condensation
mechanism using FF and CP as an example is shown in
Scheme S1.† The production of FF-CP-FF originates from
consecutive C–C bond formation via a classical carbanion
mechanism followed by dehydration over a base catalyst.
We began our study by choosing the aldol condensation of
FF and CP as the model reaction to investigate. Various alkali
3.3. Long-chain cycloalkanes by hydrodeoxygenation of
condensation intermediates
catalysts (LiOH, NaOH, KOH, Ba(OH)2, Mg(OH)2, Na2CO3,
ꢀ
Na2CO3) were used to catalyze this reaction at 30 C (Table 2). Aer obtaining the intermediates from the condensation of
The aldol condensation of FF with CP could not take place furfural species with cyclic ketones, we explored the
Table 2 Condensation of furfural species and cycle ketones over base catalystsa
Entry
Furfural species
Cyclic ketones
Catalyst dosageb (mol%)
Time (min)
Product
Isolated yieldc (C-mol%)
1
2
3
4
5
6
7
8
FF
FF
FF
FF
FF
FF
FF
FF
FF
FF
FF
HMF
HMF
CP
CP
CP
CP
CP
CP
CP
CP
CP
CP
CH
CP
CH
—
40
40
40
40
40
40
40
120
120
120
40
40
40
FF-CP-FF
FF-CP-FF
FF-CP-FF
FF-CP-FF
FF-CP-FF
FF-CP-FF
FF-CP-FF
FF-CP-FF
FF-CP-FF
FF-CP-FF
FF-CH-FF
HMF-CP-HMF
HMF-CH-HMF
0
NaOH, 5
NaOH, 10
NaOH, 20
KOH, 10
LiOH, 10
Ba(OH)2, 10
Mg(OH)2, 10
Na2CO3, 10
K2CO3, 10
NaOH, 10
NaOH, 10
NaOH, 10
68
94
96
93
87
92
0
0
0
92
96
98
9
10
11
12
13
a
b
All the reactions were conducted at 30 ꢀC and the mole ratio of furfural compounds to cyclic ketone was 2 : 1. Relative to cyclic ketone. c The
isolated yield was calculated for the target product based on the cyclic ketone.
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hydrodeoxygenation of the condensation intermediates to the conversion and the cycloalkane yield. We calculated the
cycloalkanes in an autoclave equipped with a mechanical average TOF of Pd/C combined with ZrP and NbP catalysts from
stirrer.
the Pd dispersion, respective acidic sites and FF-CP-FF conver-
Solvent is necessary for the hydrodeoxygenation process sion at 3 h. The values of 0.47 sꢁ1 and 0.87 sꢁ1 were obtained for
because the condensation products are all solid. The common Pd/C plus ZrP, and Pd/C plus NbP, respectively; NbP has a much
oxy-organic solvents (methanol, ethanol and tetrahydrofuran) lower value for acidic density. Fixing Pd/C as the hydrogenation
are not suitable because they could be digested under the catalyst, 38.7% and 70.0% of cycloalkanes were obtained with
hydrodeoxygenation conditions. Water is comparatively stable the addition of NbP and ZrP, respectively, evidencing their
during intermediate hydrodeoxygenation, and is suitable as obvious promotion effect in this process. The yield of cyclo-
a green and economical solvent. Supported metal combined alkanes obtained with ZrP was much higher than that with NbP,
with solid acid is typically used as an effective catalyst for this because the superior acidic properties of ZrP could enhance
process. For example, Huang et al. reported that carbon- dehydration and produce more cycloalkanes. As shown in
supported noble metals (Pd/C and Pt/C) combined with solid Fig. S7,† the cycloalkanes with 13–15 carbon atoms were the
acids (NbOPO4 and TaOPO4) are efficient in dehydration/ main products apart from some minor oxygenated compounds
hydrogenation of fuel precursors into liquid alkanes with at retention times of more than 15 min. Because the carbon
water as the reaction medium.47
chain of the FF-CP-FF intermediate contains 15 carbon atoms,
Using water as the solvent, we employed a one-pot hydro- the formation of C13 and C14 was ascribed to hydrocracking
deoxygenation of the FF-CP-FF intermediate into long-chained during the hydrodeoxygenation process. Among these products,
cycloalkanes. A low intermediate conversion of less than 10% the C13 and C14 cycloalkanes presented as the major products.
as well as negligible cycloalkane production (with a summed 54% of C13–C15 cycloalkanes were produced when using Pt/C
yield below 5%) were obtained when using Pd/C, Pt/C or Ru/C combined with ZrP as the catalyst. This indicates that Pd/C
alone as catalysts (Fig. 5a), suggesting that oxygen removal is and ZrP are preferable for this hydrodeoxygenation. Addition-
a main barrier for alkane formation in the current reaction ally, gas products including C1–C5 light alkanes were observed;
conditions. The addition of solid acid signicantly increased
Fig. 5 Hydrodeoxygenation of the FF-CP-FF intermediate to hydrocarbons over different solid acids and metals supported on activated carbon
catalysts (a), with different ZrP loadings (b), and with different Pd/C loadings (c). Reaction conditions: 1.0 mmol FF-CP-FF, 15 mL H2O, 0.05 g
metal supported on carbon, 0.10 g solid acid, 4 MPa H2 pressure, 300 ꢀC, 3 h.
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Fig. 6 The influence of reaction temperature (a) and time (b) on the hydrodeoxygenation of the FF-CP-FF intermediate over ZrP and Pd/C.
Reaction conditions: 1.0 mmol FF-CP-FF, 15 mL H2O, 0.05 g Pd/C, 0.10 g ZrP, 4 MPa H2 pressure.
the existence of solid acid promotes the formation of such increasing temperature, reaching the highest value of 29% at
ꢀ
products.
320 C due to the enhanced hydrocracking at higher tempera-
ZrP and Pd/C loadings were further investigated and the tures. Among these light alkanes, CH4 was selectively produced
results are shown in Fig. 5b–c. With increasing ZrP from 0.025 g (>85% of the gaseous products) no matter what temperature
to 0.1 g (xing the Pd/C dosage at 0.05 g), the intermediate was used (Fig. 7). The impact of reaction time was also inves-
ꢀ
conversion and cycloalkane yield signicantly increased from tigated at 300 C. At the short time of 1 h, the yield of C13–C15
53% to 96% and 47–76%, respectively, suggesting that the acid cycloalkanes was 34%. The cycloalkane yield increased to 56%
catalyst ZrP plays the critical role in oxygen removal. However, and 70% when prolonging the reaction time to 2 h and 3 h,
further increasing ZrP to 0.15 g led to a signicant decrease in respectively. However, further increasing the time led to
the cycloalkane yield, to 43%, as well as reduced conversion, a decreased cycloalkane yield. Similar to the effect of tempera-
which is perhaps caused by the intermediate coking and/or the ture, the lengthened time induced hydrocracking during the
produced cycloalkane hydrocracking to short-chain alkanes. In hydrodeoxygenation process and produced more light alkanes,
addition to the target products, the light alkanes (mostly CH4, resulting in reduced target products.
C2H6, C3H8 and trace butane, pentane) increased with
Hydrodeoxygenation of FF-CP-FF to produce cycloalkanes
increasing ZrP and reached the highest proportion of 19% at involves saturation of C]O/C]C bonds followed by oxygen
0.15 g ZrP. When the ZrP amount was xed at 0.1 g, the cyclo- removal. To ascertain this process, FF-CP-FF was hydrogenated
alkane yield increased with increasing amounts of Pd/C and the into water-soluble oxygenated chemicals at the low temperature
highest yield of 74% was obtained at 0.075 g Pd/C. When Pd/C of 150 ꢀC when using the single Pd/C catalyst (Fig. S5†) and the
was further increased to 0.1 g, the target products decreased but structures of the products were analyzed by the 13C NMR
to a lesser degree than occurred with excess ZrP. This result
shows that hydrocracking more likely occurred over solid acid.
Based on the conversion efficiency and detected products by GC
analysis, more than 90% of the carbon balance was obtained
under the optimized conditions, showing that coking was
suppressed during the process. At the same time, a decreased
carbon balance of about 80% was observed in the case of excess
ZrP or at a lower ratio of Pd/C to ZrP indicating that coking takes
places with excessive solid acid. It is noted that the highest yield
of 76% of cycloalkanes is comparable to that obtained in
previous reports.18–20
By using the combined catalyst (0.05 g Pd/C and 0.1 g ZrP),
we studied the inuences of reaction temperature and time on
cycloalkane production from the FF-CP-FF intermediate (Fig. 6).
At a low temperature of 260 ꢀC, a total cycloalkane yield of only
13% was obtained, but this greatly increased to 36% and 70%
when increasing the temperature to 280 ꢀC and 300 ꢀC,
respectively. However, further increasing the reaction temper-
ature to 320 C, decreased the cycloalkane yield to 49%. Addi-
tionally, the proportion of light alkanes increased with
Fig. 7 The influence of reaction temperature on gas product distri-
bution in FF-CP-FF hydrodeoxygenation. The reaction conditions are
as stated for Fig. 6(a).
ꢀ
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Table 3 Functional groups in FF-CP-FF and in samples hydrogenated
over Pd/C at different temperatures, as determined by 13C NMR
analysis
C]O (%) C]C (%) C–O (%) C–C (%)
FF-CP-FF
6.8
1.9
0
80.1
0.8
0
0
13.1
72.2
82.6
96.6
Hydrogenation at 150 ꢀ
C
26.3
17.2
3.5
Hydrogenation at 250 ꢀC
Hydrogenation at 300 ꢀ
C
0
0
technique (Fig. S6†). The peaks at around 200 ppm, corre-
sponding to C]O bonds, had not disappeared, suggesting that
the C]O bonds in the FF-CP-FF were not efficiently hydroge-
nated into C–O bonds. The peaks in the range of 100 ppm to
170 ppm, which are associated with C]C bonds, were greatly
decreased, indicating the hydrogenation of C]C bonds to C–C
bonds. For the products obtained at the higher temperature of
250 ꢀC, the peaks higher than 100 ppm all disappeared, con-
rming the saturation of these C]C and C]O bonds into C–O
and C–C bonds, respectively. The quantied analysis shown in
Table 3 further demonstrated the sequential C]C and C]O
bond hydrogenation. At the reaction temperature of 300 ꢀC,
most of the oxygen was removed by cracking the C–O bonds,
with only 3.5% of C–O bonds remaining in the nal products.
Introduction of solid acid promotes the dehydration of
hydrogenation-derived C–OH, to produce the target products
with high yields.
Fig. 8 shows the catalytic stability and regeneration perfor-
mance of Pd/C combined with ZrP. The cyclic alkanes decreased
from the initial 70% to a stable yield of 57% while simulta-
neously the light alkanes reduced from the initial 19% to below
10% during cycling. This decrease is due to a reduction in the
acidic sites caused by P leaching in this hydrothermal hydro-
deoxygenation according to our previous report.48 Considering
that mixed Pd/C and ZrP are hardly separable from each other,
Fig. 9 XRD patterns of hydrothermally treated ZrP and Pd/C followed
by recalcination.
we simulated the catalyst regeneration by hydrothermal treat-
ment of the individual Pd/C and ZrP followed by recalcination
according to the optimum reaction conditions. Interestingly, no
matter which catalyst was regenerated, the activity of the
combined catalyst could be recovered to the original level,
demonstrating the excellent regeneration performance. Aer
regeneration, the ZrP showed a similar amorphous nature to the
fresh catalyst (Fig. 9). The weak and broad diffractions of the
regenerated Pd/C show that Pd particles were still highly
dispersed on the carbon surface although their intensities were
slightly higher than those in the fresh catalyst. The good
retention of the physicochemical properties for both regen-
erated catalysts is the main reason for their excellent
performance.
Hydrodeoxygenation of other aldol condensation interme-
diates (FF-CH-FF, HMF-CP-HMF, HMF-CH-HMF) were also
investigated under the optimized reaction conditions by using
Fig. 8 Catalytic stability of ZrP and Pd/C in the hydrodeoxygenation of
FF-CP-FF to cyclic alkanes. Reaction conditions: 1.0 mmol FF-CP-FF,
15 mL H2O, 0.05 g Pd/C, 0.10 g ZrP, 4 MPa H2 pressure, 300 ꢀC, 3 h. Fig. 10
C13–C18 cycloalkane production from various condensation
Bars 1–3 show successive cycles, bar 4 represents the regenerated ZrP intermediates. Reaction conditions: 1.0 mmol condensation inter-
combined with fresh Pd/C and bar 5 represents the regenerated Pd/C mediates, 15 mL H2O, 0.05 g Pd/C, 0.1 g ZrP, 4 MPa H2 pressure,
combined with fresh ZrP.
300 ꢀC, 3 h.
13694 | RSC Adv., 2018, 8, 13686–13696
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Pd/C combined with ZrP as the catalyst. Cycloalkanes with
carbon chain lengths of between 13 and 18 were obtained. In
the cases of FF-CH-FF and HMF-CP-HMF, 55% and 72% yields,
respectively, of cycloalkanes were obtained. When using HMF-
CH-HMF as the feedstock, a 43% yield of cycloalkanes was ob-
8 P. Y. Bi, J. C. Wang, Y. J. Zhang, P. W. Jiang, X. P. Wu,
J. X. Liu, H. Xue, T. J. Wang and Q. X. Li, Bioresour.
Technol., 2015, 183, 10.
9 J. P. Lange, E. van der Heide, J. van Buijtenen and R. Price,
ChemSusChem, 2012, 5, 150.
tained. This indicates that the developed catalyst of Pd/C 10 J. Q. Bond, A. A. Upadhye, H. Olcay, G. A. Tompsett, J. Jae,
combined with ZrP is generally efficient for the production of
jet fuel and/or diesel hydrocarbons by hydrodeoxygenation of
these condensation intermediates (Fig. 10).
R. Xing, D. M. Alonso, D. Wang, T. Y. Zhang, R. Kumar,
A. Foster, S. M. Sen, C. T. Maravelias, R. Malina,
S. R. H. Barrett, R. Lobo, C. E. Wyman, J. A. Dumesic and
G. W. Huber, Energy Environ. Sci., 2014, 7, 1500.
11 C. R. Li, D. Q. Ding, Q. N. Xia, X. H. Liu and Y. Q. Wang,
ChemSusChem, 2016, 9, 1712.
4. Conclusions
12 Y. P. Li, X. M. Huang, Q. Zhang, L. G. Chen, X. H. Zhang,
T. J. Wang and L. L. Ma, Appl. Energy, 2015, 160, 990.
13 A. Bohre, B. Saha and M. M. Abu-Omar, ChemSusChem, 2015,
8, 4022.
14 G. W. Huber, J. N. Chheda, C. J. Barrett and J. A. Dumesic,
Science, 2005, 308, 1446.
Long-chained cycloalkanes with carbon chain lengths of 13–18
were obtained from furfural species (FF and HMF) and cyclic
ketones (CP and CH), all of which could be obtained from the
renewable lignocellulosic biomass. The aldol condensation ꢀof
the furfural species and cyclic ketones was conducted at 30 C
with a strong basic catalyst, to obtain over 90% yields of the
desired condensation intermediates. The long-chained cyclo-
alkanes with carbon chain lengths of 13–18 were produced via
hydrodeoxygenation of the condensation intermediates at
temperatures of 280–320 ꢀC and times of 1–4 h by using
a catalyst of Pd/C combined with the solid acid ZrP. Under the
optimized conditions, the highest yield of 76% of target prod-
ucts could be obtained. The combined catalyst showed reduced
yields of cycloalkanes aer the second and third cycles, but its
performance could be largely recovered to its original level by
hydrothermal treatment followed by recalcination of Pd/C
and ZrP.
´
´˜
15 L. Faba, E. Dıaz and S. Ordonez, ChemSusChem, 2014, 7,
2816.
16 M. X. Su, W. Z. Li, T. W. Zhang, H. S. Xin, S. Li, W. Fan and
L. L. Ma, Catal. Sci. Technol., 2017, 7, 3555.
17 G. Y. Li, N. Li, S. S. Li, A. Q. Wang, Y. Cong, X. D. Wang and
T. Zhang, Chem. Commun., 2013, 49, 5727.
18 G. Y. Li, N. Li, J. F. Yang, A. Q. Wang, X. D. Wang, Y. Cong
and T. Zhang, Bioresour. Technol., 2013, 134, 66.
´
19 M. H. Chavez-Sifontes, M. E. Domine and S. Valencia, Catal.
Today, 2015, 257, 305.
20 J. F. Yang, N. Li, G. Y. Li, W. T. Wang, A. Q. Wang,
X. D. Wang, Y. Cong and T. Zhang, ChemSusChem, 2013, 6,
1149.
Conflicts of interest
21 C. L. Cai, Q. Y. Liu, J. Tan, T. J. Wang, Q. Zhang and L. L. Ma,
Korean Chem. Eng. Res., 2016, 54, 519.
There are no conicts to declare.
22 J. Tan, Q. Y. Liu, C. L. Cai, S. B. Qiu, T. J. Wang, Q. Zhang,
L. L. Ma and G. Y. Chen, RSC Adv., 2015, 5, 58784.
23 J. L. Xu, N. Li, X. F. Yang, G. Y. Li, A. Q. Wang, Y. Cong,
X. D. Wang and T. Zhang, ACS Catal., 2017, 7, 5880.
24 A. Corma, O. de la Torre, M. Renz and N. Villandier, Angew.
Chem., Int. Ed., 2011, 50, 2375.
Acknowledgements
The authors are grateful for the nancial support from the
Natural Science Foundation of China (51576199, 51536009 and
51376185) and the Natural Science Foundation of Guangdong
Province (2017A030308010).
25 A. Corma, O. de la Torre and M. Renz, ChemSusChem, 2011,
4, 1574.
26 G. Y. Li, N. Li, Z. Q. Wang, C. Z. Li, A. Q. Wang, X. D. Wang,
Y. Cong and T. Zhang, ChemSusChem, 2012, 5, 1958.
27 M. Balakrishnan, E. R. Sacia and A. T. Bell, ChemSusChem,
2014, 7, 1078.
References
1 R. A. Sheldon, Green Chem., 2014, 16, 950.
2 M. J. Climent, A. Corma and S. Iborra, Green Chem., 2014, 16, 28 A. K. Misra and G. Agnihotri, Carbohydr. Res., 2004, 339,
516. 1381.
3 N. Shi, Q. Y. Liu, Q. Zhang, T. J. Wang and L. L. Ma, Green 29 G. Q. Xu, Q. Li, J. G. Feng, Q. Liu, Z. J. Zhang, X. C. Wang,
Chem., 2013, 15, 1967. X. Y. Zhang and X. D. Mu, ChemSusChem, 2014, 7, 105.
4 Y. H. Liao, Q. Y. Liu, T. J. Wang, J. X. Long, L. L. Ma and 30 D. J. Liu and Y. X. E. Chen, ACS Catal., 2014, 4, 1302.
Q. Zhang, Green Chem., 2014, 16, 3305.
5 Z. R. Zhang, J. L. Song and B. X. Han, Chem. Rev., 2017, 117,
6834.
6 F. Cheng and C. E. Brewer, Renewable Sustainable Energy
Rev., 2017, 72, 673.
31 M. Mascal, S. Dutta and I. Gandarias, Angew. Chem., Int. Ed.,
2014, 53, 1854.
32 J. Y. Xin, S. J. Zhang, D. X. Yan, O. Ayodele, X. M. Lu and
J. J. Wang, Green Chem., 2014, 16, 3589.
33 G. Y. Li, N. Li, X. K. Wang, X. R. Sheng, S. S. Li, A. Q. Wang,
Y. Cong, X. D. Wang and T. Zhang, Energy Fuels, 2014, 28,
5112.
7 A. Bohre, S. Dutta, B. Saha and M. M. Abu-Omar, ACS
Sustainable Chem. Eng., 2015, 3, 1263.
This journal is © The Royal Society of Chemistry 2018
RSC Adv., 2018, 8, 13686–13696 | 13695

View Article Online
RSC Advances
Paper
34 M. Hronec and K. Fulajtarova, Catal. Commun., 2012, 24, 42 A. Sinhamahapatra, N. Sutradhar, B. Roy, P. Pal, H. C. Bajaj
100. and A. B. Panda, Appl. Catal., B, 2011, 103, 378.
35 M. Hronec, K. Fulajtarova and T. Liptaj, Appl. Catal., A, 2012, 43 H. N. Kim, S. W. Keller, T. E. Mallouk, J. Schmitt and
437, 104. G. Decher, Chem. Mater., 1997, 9, 1414.
36 H. Z. Liu, T. Jiang, B. X. Han, S. G. Liang and Y. X. Zhou, 44 H. M. Gan, X. G. Zhao, B. N. Song, L. Guo, R. Zhang, C. Chen,
Science, 2009, 326, 1250.
37 G. Y. Xu, J. H. Guo, Y. Zhang, Y. Fu, J. Z. Chen, L. L. Ma and
Q. X. Guo, ChemCatChem, 2015, 7, 2485.
J. Z. Chen, W. W. Zhu and Z. S. Hou, Chin. J. Catal., 2014, 35,
1148.
45 A. Sinhamahapatra, N. Sutradhar, B. Roy, A. Tarafdar,
H. C. Bajaj and A. B. Panda, Appl. Catal., A, 2010, 385, 22.
38 M. Hronec, K. Fulajtarova, T. Liptaj, M. Stolcova,
N. Pronayova and T. Sotak, Biomass Bioenergy, 2014, 63, 291. 46 J. T. Li, G. F. Chen, J. X. Wang and T. S. Li, Synth. Commun.,
39 J. F. Yang, N. Li, G. Y. Li, W. T. Wang, A. Q. Wang, 1999, 29, 965.
X. D. Wang, Y. Cong and T. Zhang, Chem. Commun., 2014, 47 Y. B. Huang, Z. Yang, J. J. Dai, Q. X. Guo and Y. Fu, RSC Adv.,
50, 2572. 2012, 2, 11211.
40 T. V. Bui, T. Sooknoi and D. E. Resasco, ChemSusChem, 2017, 48 Q. Y. Liu, T. Zhang, Y. H. Liao, C. L. Cai, J. Tan, T. J. Wang,
10, 1631.
S. B. Qiu, M. H. He and L. L. Ma, ACS Sustainable Chem. Eng.,
2017, 5, 5940.
41 J. C. G. Da Silva, S. Folgueras-Dominguez and A. C. B. Dos
Santos, J. Mater. Sci. Lett., 1999, 18, 197.
13696 | RSC Adv., 2018, 8, 13686–13696
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