Simultaneous Upgrading of Furanics and Phenolics through Hydroxyalkylation/Aldol Condensation Reactions

Article abstract of DOI:10.1002/cssc.201601251

The simultaneous conversion of cyclopentanone and m-cresol has been investigated on a series of solid-acid catalysts. Both compounds are representative of biomass-derived streams. Cyclopentanone can be readily obtained from sugar-derived furfurals through Piancatelli rearrangement under reducing conditions. Cresol represents a family of phenolic compounds, typically obtained from the depolymerization of lignin. In the first biomass conversion strategy proposed here, furfural is converted in high yields and selectivity to cyclopentanone (CPO) over metal catalysts such as Pd-Fe/SiO₂ at 600 psi (～4.14 MPa) H₂ and 150 °C. Subsequently, CPO and cresol are further converted through acid-catalyzed hydroxyalkylation. This C?C coupling reaction may be used to generate products in the molecular weight range that is appropriate for transportation fuels. As molecules beyond this range may be undesirable for fuel production, a catalyst with a suitable porous structure may be advantageous for controlling the product distribution in the desirable range. If Amberlyst resins were used as a catalyst, C₁₂–C₂₄ products were obtained whereas when zeolites with smaller pore sizes were used, they selectively produced C₁₀ products. Alternatively, CPO can undergo the acid-catalyzed self-aldol condensation to form C₁₀ bicyclic adducts. As an illustration of the potential for practical implementation of this strategy for biofuel production, the long-chain oxygenates obtained from hydroxyalkylation/aldol condensation were successfully upgraded through hydrodeoxygenation to a mixture of linear alkanes and saturated cyclic hydrocarbons, which in practice would be direct drop-in components for transportation fuels. Aqueous acidic environments, which are typically encountered during the liquid-phase upgrading of bio-oils, would inhibit the efficiency of base-catalyzed processes. Therefore, the proposed acid-catalyzed upgrading strategy is advantageous for biomass conversion in terms of process simplicity.

Full text of DOI:10.1002/cssc.201601251

Accepted Article
Title: Simultaneous upgrading of furanics and phenolics via
hydroxyalkylation/aldol condensation reactions
Authors: TUONG V BUI, Tawan Sooknoi, and Daniel E. Resasco
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ChemSusChem
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Simultaneous upgrading of furanics and phenolics via
hydroxyalkylation/aldol condensation reactions
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Tuong V. Bui, Tawan Sooknoi, Daniel E. Resasco*
School of Chemical, Biological and Materials Engineering
University of Oklahoma
100 E. Boyd St., Norman, OK 73019, USA
Abstract:
The simultaneous conversion of cyclopentanone and m-cresol has been investigated on a series of solid acid catalysts. Both
compounds are representative of biomass-derived streams. Cyclopentanone can be readily obtained from sugar-derived furfurals via
Piancatelli rearrangement under reducing conditions. Cresol represents the family of phenolics, typically obtained from the
depolymerization of lignin. In the first biomass conversion strategy proposed here, furfural is converted in high yields and selectivity
o
to cyclopentanone (CPO) over metal catalysts such as Pd-Fe/SiO
2
catalyst at 600 psia H
2
and 150 C. Subsequently, CPO and cresol
are further converted via acid-catalyzed hydroxyalkylation. This C-C coupling reaction may be used to generate products in the
molecular weight range that is appropriate for transportation fuels. Since molecules beyond this range may be undesirable for fuel
production, a catalyst with suitable porous structure may be advantageous for controlling the product distribution in the desirable
range. In fact, when Amberlyst resins were used as a catalyst, C12-C24 products were obtained, whereas when zeolites with smaller
pore sizes were used, they selectively produced C10 products. Alternatively, CPO can undergo the acid-catalyzed self-aldol
condensation to form C10 bicyclic adducts. As an illustration of the potential of practical implementation of this strategy for biofuel
production, the long chain oxygenates obtained from hydroxyalkylation/aldol condensation were successfully upgraded via
hydrodeoxygenation to a mixture of linear alkanes and saturated cyclic hydrocarbons, which in practice would be direct drop-in
components for transportation fuels. Aqueous acidic environments, typically encountered during the liquid-phase upgrading of bio-oils
would inhibit the efficiency of base-catalyzed process. Therefore, the proposed acid-catalyzed upgrading strategy is advantageous in
terms of process simplicity for biomass conversion.
Introduction
upgrading practically impossible. Therefore, greater efforts are
needed to help in the development of more efficient biomass
upgrading technologies with a number of unit operations that
make the process economically feasible. Although several
strategies have been investigated to process vapors and liquids
derived from biomass pyrolysis, finding efficient processes that
can be techno-economically attractive has been challenging [1].
The direct catalytic hydrotreating of condensed bio-oil faces
major problems [2, 3], including low yields of liquids in the fuel
range and high hydrogen pressures, which complicates their
integration with a pyrolysis system [4]. Incorporation of pre-
hydrogenated bio-oils into conventional petroleum feedstocks in
refinery operations, such as the fluidized catalytic cracking
Fossil sources exhibit undoubted technological and economical
advantages for production of chemicals and transportation fuels.
2 4
However, emission of greenhouse gases (CO and CH ) is an
issue of critical concern regarding global warming and climate
change. This concern has led to increased research efforts with
the goal of commercializing fuels and chemicals from biomass
sources that would greatly reduce the carbon footprint.
However, techno-economic evaluations indicate that immediate
implementation is not possible. The great variety of oxygenated
compounds with incompatible chemistries makes a single-stage
Corresponding Author: Prof. Dr. D. E Resasco
E-mail: ouresasco@gmail.com
(
FCC) and hydrotreating units [5, 6] have also shown technical
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ChemSusChem
10.1002/cssc.201601251
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impediments that may obstruct their implementation in
commercial processes. Some important advances have been
made in the upgrading of pyrolysis vapors that leads to
enhanced stability of the condensed liquid by forming C-C bonds
before adjusting the oxygen content [7, 8].
strategies for upgrading biomass-derived furanics via C-C
coupling reaction have been analyzed in our recent review [28].
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Interestingly, Hronec et al. [29, 30] have shown that the
Piancatelli ring rearrangement in reducing condition is also a
promising route to stabilize furfural into cyclopentanone. This is
a remarkable pathway, because the O heteroatom is removed
from the ring, producing CPO a useful chemical and potential
building block for C-C coupling reactions [29]. Although the
Piancatelli ring rearrangement of furfuryl alcohol readily occurs
in hot liquid water without the need of an additional catalyst,
hydrogenation is required to first hydrogenate the CO group in
furfural, as well as the resulting C=C double bond after the ring
closure to obtain CPO. For this reaction, noble metal catalysts
such as Pt, Pd, Ru, Ir as well as inexpensive metals such as Ni,
Cu have been used in the conversion of furfural in aqueous
In the last few years, we have investigated possible
conversion paths for separated vapors and liquids obtained from
fractionation of bio-oil via step-wise condensation of pyrolysis
vapors [9, 10] as well as multistage pyrolysis process [11, 12].
The core of this approach is to carry out the sequence of thermal
treatments by heating the biomass at increasing temperatures
so that the bio-oil is fractionated into different streams, each one
enriched in either light oxygenates, or sugar-derived
compounds, or phenolics-derived compounds, respectively [11,
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12]. Accordingly, by segregating each specific group of
functional molecules in a separate fraction, a combined catalytic
upgrading strategy can be developed more selectively and
effectively, exploiting the different chemistries of each fraction
and optimizing the upgrading instead of a single hydrotreating
step for the full bio-oil [13-15].
2
phase under H pressure [31, 32]. For example, over 75% yield
of CPO has been reported over Pt/C or Ni-CNTs [22, 33]. High
selectivity toward cyclopentanone is a definite techno-economic
advantage of this approach compared to other upgrading
strategies. For the Piancatelli rearrangement, the presence of
liquid water plays a crucial role in the reaction [20, 22, 30].
Moreover, the presence of acetic acid in the reaction mixture
provides a positive effect on the yield of the desired products
[29]. That is, components that are naturally present in biomass-
derived streams, i.e., aqueous solutions with high acidity, favor
the occurrence of this reaction. Not only CPO is a very
convenient building block for carbon retention in the liquid fuel
range, but reaching high conversions of furanics to this single
molecule greatly reduces catalyst deactivation by avoiding the
typical resinification of furfurals to humins. From all of this, we
propose that the path of furanics to cyclopentanone is a very
effective strategy for upgrading of furfural-rich streams [28].
The fraction of light-oxygenates is rich in acetic acid, acetol,
and acetaldehyde. We have previously proposed [14] that they
could undergo ketonization to produce acetone, which in turn
could be coupled with furfural, an abundant component in the
8
sugar-derived stream, to produce C -C13 oxygenates over basic
catalysts [16, 17]. Alternatively, instead of directly condensing
with acetone, furfural can also be pre-stabilized into key
intermediates to diminish carbon losses and humins formation, a
major cause of catalyst deactivation. The intermediate products
are still functional, so they can be further upgraded (C-C bond-
chain enlarged) to a wide range of desirable products.
Hydrogenation-decarbonylation of furfural to furan
compounds (i.e., methyl furan, dimethyl furan) [18, 19], ring
rearrangement of furfural to cyclopentanone (CPO) via
Piancatelli reaction [20-22], or oxidation of furfural to carboxylic
acids [23, 24] are outstanding examples of furfural conversion
into more stable forms that have been recently reported in the
literature. In the so-called Sylvan process, methyl furan is
condensed with different types of carbonyl compounds, such as
acetone, butanal, or furfural [25, 26] to elongate the carbon
chain and bring the products to the fuel range. Dimethyl furan
can also be coupled with ethylene via Diels-Alder reaction to
produce valuable aromatics such as p-xylene [27]. Specific
The phenolics fraction can also be used to effectively
incorporate into the fuel range those oxygenates that are too
2 4
small to be directly hydrotreated. That is, converting C -C
oxygenates to alcohols greatly facilitates their incorporation via
alkylation. For example, iso-propanol, obtained from
hydrogenation of acetone, can produce hydrocarbons in a
molecular weight range suitable for the gasoline/diesel pool.
Corma et al. [25, 34, 35] have pointed out the feasibility of
forming C-C bonds between carbonyl compounds with other
organic molecules whenever their electron-density is high
enough to promote the electrophilic-attack of the oxonium ion
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ChemSusChem
10.1002/cssc.201601251
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generated by the protonation of the carbonyl group. Phenolics
compounds such as m-cresol and guaiacol, abundant species in
biomass pyrolysis vapors, are suitable candidates as
hydroxyalkylation aromatic substrates. In fact, several studies
have reported successful examples of hydroxyalkylation in
systems comprising acetaldehyde/p-cresol [36], acetaldehyde
with conversion increasing from 8 to 38% as the temperature
increases, keeping a good carbon balance. For instance, 13%
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CPO conversion was obtained at 100 C, with 40% selectivity to
AC products, 60% selectivity to HAA products and a carbon
balance of 98%. Higher temperatures favor the formation of
monomer and dimer coupling products (1, 3, 4, and 5). Above
o
/
[
phenol [37], formaldehyde/guaiacol [38], acetaldehyde/o-xylene
39], aldehyde/benzene derivatives [40, 41], acetone / phenol
120 C, the decomposition of the trimer (6) becomes evident and
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undesired reactions start to occur. For example, at 145 C, the
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[42], benzaldehyde/benzene derivatives [43], paraformaldehyde
carbon balance dropped from almost 100 to 83 %, most
probably due to polymerization as indicated by the change in
color of the solution. One problem associated with the use of a
resin catalyst like Amberlyst 15 is the decomposition of the
polymeric matrix that may become significant as temperature
increases.
/
[
anisole [44], formaldehyde/benzene [45], formaldehyde / phenol
46] over acid-functionalized solids, such as Amberlyst acidic
resin and acidic zeolites to produce crucial platforms for the
chemical industry. For example, Rode et al. [47] have reported
80-95% yields of coupling products from the reaction of
acetaldehyde/p-cresol over Hβ and bentonite clay catalysts
The acid-catalyzed formation of AC products is in itself an
interesting outcome of the study since the aldol condensation of
cyclopentanone has been typically reported over basic catalysts,
impregnated with dodecatungstophosphoric acid.
In this contribution, we propose a novel approach for the
simultaneous upgrading of furfural and m-cresol, two model
compounds that represent two streams of sequential biomass
thermal treatment at moderate and high temperatures. In this
strategy, furfural is first pre-stabilized as cyclopentanone via the
Piancatelli rearrangement/hydrogenation process [22, 48]. This
intermediate product is then used to hydroxyalkylate m-cresol
2 3 2
such as MgO, KF/Al O , CaO-CeO , CaO, magnesium–
aluminum hydrotalcites (MgAl-HT) and lithium–aluminum
hydrotalcites (LiAl-HT) [48], or even in NaOH solutions [30].
While it is widely known that the aldol condensation can be
catalyzed by both bases and acids, the latter has seldom been
reported for cyclopentanone. Zou et al. [49] reported the self-
aldol condensation of cyclopentanone and cyclohexanone in
glass reactor over MOF-encapsulating phosphotungstic,
Amberlyst 15 and HZSM-5 materials. The reaction was
and generate
C
10-C24 oxygenates,
a suitable range for
transportation fuel precursors.
Results and Discussion
o
conducted at 130 C in pure cyclic ketone for 48h and moderate
conversion of the ketones could be obtained. However, no
information related to carbon balance was reported.
1.
Hydroxyalkylation of m-cresol/cyclopentanone
a) Product distribution over solid acid Amberlyst 15:
In this work, the experiments were conducted in a Parr
reactor in more controlled and quantitative ways than previous
studies with shorter reaction times and direct measurement of
the carbon balance. The results summarized in Figure 2 confirm
that solid acids such as Amberlyst 15 are capable of producing
acceptable yields of AC products (1+2). The yield of the
monomer (1) increases over time, reaching 16% after 6 hrs of
reaction. The amount of dimer product (2) is very small, reaching
only about 1% yield. Excellent carbon balances of 94-97% were
observed in both cases. Although the reaction conditions and
catalyst formulations will need to be optimized to enhance the
yield to coupling compounds, these preliminary results are
promising enough to be considered an interesting approach for
biomass conversion, particularly since the acidic environment is
The hydroxyalkylation of m-cresol and CPO yields various
cyclopentyl-substituted cresol compounds including (3), (4), (5)
and (6) (HAA products) as shown in path B Scheme 1. Two
products from self-aldol condensation of cyclopentanone
including (1) and (2) (AC products) were also observed, as
shown in path A. In most cases, the formation of product (2) is
negligible compared to that of the other products; therefore, in
most runs, product (1) is the only representative of the self-aldol
condensation reaction.
Figure 1 shows the reaction data obtained after 2 h in a
batch reactor on Amberlyst 15 in the temperature range 65-
o
1
45 C at a 2:1 m-cresol/CPO molar feed ratio. The results
demonstrate that the acid resin displays an acceptable activity,
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ChemSusChem
10.1002/cssc.201601251
FULL PAPER
commonly found in bio-oil upgrading. The high content of water
in real pyrolysis mixtures would require to operate in biphasic
system [50]. Implementation of the concepts derived from model
compound studies in the separation and conversion of bio-oil to
fuel may demonstrate the advantage of using solid emulsifier
materials such as hydrophobized zeolites [51, 52] nanotubes,
and other amphiphilic catalysts that stabilize emulsions [53] to
achieve maximized adducts yields for the reaction.
2 2 3
and HAA, the zeolite Hβ and amorphous SiO -Al O yielded only
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AC products (at 250°C).
It is possible that the drop in HAA selectivity might be due
to different steric constrains in the catalysts. For instance,
Amberlyst resins have large cavities that may allow the
formation and desorption of the relatively large HAA products
(see example of products 3, 4, 5 and 6 in Scheme 1). By
contrast, the more constrained Zeolite Hβ may only allow the
smaller AC products (93% selectivity) leave the zeolite, while the
HAA, if formed will remain trapped inside the microporous
structure. It is suggestive that the homogenous p-TSA exhibits a
higher selectivity to large HAA products (3 + 4 + 5 + 6) (Figure
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b) Comparison of different solid acid catalysts:
Based on these observations, several solid catalysts with
different characteristics, including a resin with higher acid
density (Amberlyst 36), a microporous zeolite (Hβ), and a
3) in comparison to the behavior of solid catalysts. More
2 2 3
mesoporous acid catalyst (SiO -Al O ) were investigated and
specifically, at comparable CPO conversion (15-20%) the yields
of 3, 4, 5 and 6 were 2.4%, 1.7%, 0.16% and 0.4% on Amberlyst
compared to a homogeneous catalyst, para-toluene sulfuric acid
(p-TSA) to explore the effect of catalyst topology and acidity. To
make a proper comparison of selectivity, we adjusted the
reaction temperature to reach an overall CPO conversion of
about 15 %. Specifically, the activity comparison was made at
36 while they are much higher, reaching 5.2%, 1.3%, 1.8% and
12.4%, respectively with the homogeneous catalyst p-TSA.
To check the effect of reaction temperature to the product
distribution, reaction runs were conducted on zeolite Hβ at
different temperatures (100-250°C). As shown in the Table 1,
the selectivity on this zeolite did vary with temperature. Higher
selectivity toward HAA is favorable as the temperature
deceases. This observation agrees with those obtained from
homogeneous catalysts in which low temperature favors the
formation of HAA products rather than AC products.
o
o
1
00 C for Amberlyst and p-TSA, and at 250 C for H, SiO
2
-
Al . The results are summarized in Table 1 and Figure 3.
2
O
3
Amberlyst 36 shows an analogous behavior to Amberlyst 15,
reaching 15% CPO conversion with selectivities of 38% and
62% for AC and HAA products, respectively. Interestingly, while
(
at 100°C) Amberlyst resins catalyzed the generation of both AC
Table 1. Activity and Average pore size of sceened catalysts
o
Catalyst
T, C Conversion,
Selectivity, %
Yield, %
Acid
density,
mmol/gcat
Conversion
per site
Carbon
balance,
%
Average
pore
size, nm
%
AC
HAA
AC
HAA
(mol.L-
1.
mmolacid-1)
1.3
c
p-TSAa
Amberlyst 15
Amberlyst 36
100
100
100
20
12.8
15.3
9.3
39.6
38
90.7
60.4
62
2.9
3
27.5
3.5
5.8
97
94
94
-
29
24
a
a
c
c
4.7
0.6
c
4.9c
4.5
4.6
0.7
100
120
200
250
6.8
11
11.7
16.3
-
-
28.9
15
7
-
-
2.02
3.38
3.48
90
93
92
94
71.1
85
93
0.2
2.9
0.045
0.2
0.5
Zeolite Hβb
0.75d
0.6f
11
4.86
1
1
00
50
0.76
1.14
5.42
17
-
-
99
98
95
-
-
1
2
5
-
-
-
-
0.32
0.48
2.29
7.26
14.3
98
99
95
96
85
b
0.53e
4.8g
SiO
2
-Al
2
O
3
200
50
280
0.9
10.4
21.6
0.004
0.1
0.7
2
33.8
a
b
c
d
e
f
g
Glass reactor; Parr reactor; reported by manufacturer; measured by TPD-isopropyl amine ref [54] ref. [55], measured by BET-N
ads./des.
2
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However, at this point, it can be concluded that although the
temperature can change product distribution, the porous
characteristic of solid acid catalysts is the dominant factor that
and 36, which were able to achieve measureable yields (7-9%)
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at low temperatures (100-120 C), the Hβ catalyst only generated
small amounts of condensation products at these temperatures
o
makes AC products dominant (i.e., over 70% sel. at 120 C). At
(traces of AC and HAA products were detected).
It is
o
100 C, no adducts were observed. In the case of SiO
2
-Al
2
O
3
, the
conceivable that the diffusion of these large products out of the
micro-porous structure is greatly hindered at low temperatures in
this zeolite, leading to some disappearance of CPO, but without
the formation of any noticeable coupling products. Figure 5d
shows the distribution of HAA products from zeolite Hβ as a
function of reaction temperature. At low temperatures (100-
same analysis was conducted with temperature range from 100
o
to 280 C. Interestingly, high selectivity towards AC is observed
in all cases. With a large pore size, (average 4.8 nm) and rather
slow reactions, one would not expect internal mass transfer
limitations on this mesoporous material. As shown in Figure 4a,
the variation of overall CPO conversion as a function of
temperature indicates an apparent activation energy of about 50
kJ/mol, while on the Hβ zeolite, which is clearly affected by mass
transfer limitations, the apparent activation energy is only
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o
120 C), the major product is (5), which is necessarily produced
from product (3). By contrast, at higher temperatures, the
selectivity towards product (5) decreases while that to (3)
increases. Clearly, at high enough temperatures, product (5)
begins to decompose via C-C cleavage yielding back product
(3). The low selectivity towards product (4) might be due to the
higher abundance of m-cresol with respect to CPO (m-cresol/CP
feed ratio = 2:1).
4.5kJ/mol. Moreover, when the product yields are used for the
Arrhenius plot (Figure 4b), apparent activation energy values of
about 90 and 140 kJ/mol are obtained for AC and HAA
formation, respectively.
The low activity exhibited by the amorphous silica-alumina
catalyst towards formation of HAA products could be due to the
relatively weak acid strength of this material. Indeed, calorimetry
In fact, as shown in Table 1, the carbon balance is over
90% for all cases. That is, by using a less reactive intermediate
such as cyclopentanone, not only the carbon losses can be
minimized, but valuable condensation products can be obtained
with less humins formation.
2 2 3
measurements of ammonia adsorption on SiO -Al O give
evidence of much lower density of strong acid sites than
Amberlyst or any zeolite [56, 57]. Therefore, the acid strength of
the mesoporous silica-alumina might not be high enough for
catalyzing HAA reaction. That is, only materials with strong
acidity and large pore structure could be effective catalysts for
the HAA reaction.
c) Effect of temperature on the competition between self-aldol
condensation (AC) and hydroxyalkylation (HAA):
The investigated reaction, in fact, is complicated since two
possible parallel reactions are taking place at the same time.
The relative rate between two pathways depends on factors
such as feed ratio, temperature, etc. Moreover, the porous
characteristic of each solid catalyst places different influence in
the diffusion of formed products and so on the obtained product
distribution. A series of experiments was conducted with a
homogeneous catalyst (para-toluene sulfuric acid) to get an
insight into the nature of this reaction. In this case, there is no
possible role of porous cavities affecting the product distribution
as in solid acid catalysts. As shown in Figure 6a, at low
To gain a deeper understanding of the pathway for HAA
product formation on zeolite Hβ, several separate runs were
conducted at 250°C with varying amounts of catalyst. As seen in
Figure 5a, b the yields of HAA and AC products uniformly
increase with the amount of catalyst, as expected. At the same
time, it is observed that while the selectivity to product (3)
dominates at low yields (at the lowest catalyst mass) the
selectivity to products (4) and (5) increased with overall
conversion which demonstrates the expected series/parallel
sequence for this reaction, i.e., CPO → (3); followed by (3) →
(4) or (3) → (5). In this case, no traces of product (6) were
observed
o
temperatures (e.g., 60 C), hydroxyalkylation products (HAA)
dominate, with selectivity above 90%. As temperature increases,
the selectivity toward aldol condensation products (AC) slowly
o
increases (up to 150 C) but beyond this temperature, it jumps
o
o
Another series of independent runs was conducted,
keeping the catalyst mass constant while varying temperatures.
As shown in Figure 5c, contrary to the behavior of Amberlyst 15
dramatically from 20% at 200 C to 60% at 250 C. The change of
product distribution with increasing temperature in this case
might be due to the low stability of the HAA C-C coupling
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products (the alcohol) that makes it easily decomposed back to
increases from 3.7 to 5.4%. Interestingly, when the m-
cresol/CPO ratio increases to 7:1, only HAA products are
obtained with no traces of AC products.
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CPO and m-cresol at high temperature (250 C) before
dehydration. This results in more abundant AC products at
o
2
50 C.
2.
Hydrodeoxygenation of coupling products obtained in
the first step
At the lowest temperature, only the C-C coupling monomer
o
(
3) is observed in the products. However, at 100 C, the trimer
Hydrodeoxygenation is the final step after accomplishing
(6) is formed easily, becoming one of the most abundant
products and reaching 45% selectivity. As the temperature is
further increased, the selectivity to (6) greatly decreases with the
other products increasing, even when the reactant conversion
remained unchanged. It is clear that (6) starts decomposing
the desired molecular weight via C-C coupling. For practical
implementation as fuels, the coupling compounds generated
from hydroxyalkylation would need to be saturated and
deoxygenated to produce alkanes with properties similar to
those derived from petroleum energy sources. To demonstrate
the sequence, first, the C-C coupling step was carried via HAA
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back to monomer (3). Indeed, negligible amounts of the trimer
o
(
6) are detected at 250 C. Likewise, as shown previously
o
reaction on a 3g Amberlyst 36 sample in a Parr reactor (150 C,
(Figure 1), similar decomposition of the trimer (6) is observed
m-cresol/CPO=2:1, 12h). In this step, the goal is to obtain a
reasonable yield of coupling products, which can be used later
as feedstock for the HDO upgrading. In this case, 51% CPO
conversion with a wide range of long-chain oxygenates was
obtained, as shown in Figure 8, with (1) and (3) as major
products, accounting for 18% and 14% yield, respectively.
o
over the solid acid Amberlyst 15 at temperatures above 120 C.
Figure 6b also shows similar trends for the trimers (4) and (5),
which initially increase with temperature, but then decrease,
o
reaching a maximum selectivity at 200 C (~20%).
The possible reaction mechanism includes four primary
steps: (a) protonation of cyclopentanone on acid sites to form an
enolate, (b) C-C coupling of the activated CPO with another
CPO or m-cresol to form condensation products (ACol and
HAAol), (c) deprotonation, and (d) dehydration of the resulting
alcohols to generate the AC and HAA products. It is possible
that the rate limiting step for each reaction could be one of
those. However, in the presence of acid catalysts the
dehydration step is relatively fast. It should be noted that the
relative activation energy between each step could be shifted,
depending on catalysts with different acid strength. More
detailed kinetic and theoretical studies are required on each
To carry out the HDO upgrading step, 2 ml of the liquid
product of the previous step was diluted in 118 ml of undecane
2 3
solvent together with 500 mg of 2% Pd/Al O catalysts. The
o
catalyst was reduced at 150 C for 3 h under 400 psia of H
2
. The
o
HDO run was conducted at 250 C in the batch reactor for 12 h.
The most abundant products were cyclopentane and methyl
cyclohexane, which come from the hydrogenation/dehydration of
CPO and m-cresol. Long-chain hydrocarbon products include
fully saturated C10 alkanes, C12 cyclic and C12 alkane products
which are generated from the ring opening of the saturated
species (1) and hydrogenation of (3), followed by the ring
opening, respectively (Scheme 2 and Figure 9). Trace amount
of carbon chain longer than 12 was observed, which is probably
due to the decomposition of dimer/trimer at the high
temperatures and long reaction time used in this experiment.
The observed alkanes represent over 39% selectivity of the
upgraded liquid. In fact, hydrogenated products derived from m-
cresol, such as methylcyclohexane or methylcyclohexanol, also
individual reaction to obtain
understanding of the system.
a
more comprehensive
d) Effect of feed ratio:
Both AC and HAA can yield products with longer carbon
chains, which can subsequently be hydrodeoxygenated to
molecules that directly fall in the gasoline/diesel range. In some
applications, in may be desirable to produce a narrow molecular
weight distribution. In this case, our results show that a narrower
molecular weight distribution can indeed be obtained by
adjusting the m-cresol/CPO feed ratio. As illustrated in Figure 7,
as the m-cresol/CPO increases from 2:1 to 5:1, the yield of AC
products drops from 4.5% to 1.4% while that of HAA products
7
fall into gasoline range (C -C12). Therefore, the whole applicable
products in the fuel range would account for 90% of the
upgraded liquid. More interestingly, the carbon balance for the
HAA and HDO steps are 96% and 95%, respectively, resulting in
over 90% efficiency for the whole catalytic upgrading process,
which starts from CPO and results in with drop-in liquid fuel
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products. This promising result illustrates the great potential of
this strategy for biomass-derived liquid fuel production.
for 2 hrs in the presence of Amberlyst 15, Amberlyst 36, or p-
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TSA (Sigma Aldrich) catalysts. Alternatively, the reaction was
o
conducted in a Parr reactor at 100-250 C, under 300 psia N
2
for
2
hrs in the presence of Zeolite Hβ (Zeolyst) or SiO
(Sigma Aldrich). In all cases, the amount of catalyst used was
.15 g and the feed was either pure CPO or m-cresol/CPO
2 2 3
-Al O
Conclusions
0
The Piancatelli rearrangement of furanic compounds to
CPO represents a very attractive biomass upgrading strategy
that pre-stabilizes reactive molecules such as furfural into a
useful and less reactive ketone. Compared to conventional
mixtures. The effect of m-cresol/CPO ratio (2:1, 5:1, and 7:1) on
the product distribution was examined in the Parr reactor at
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o
120 C, 300 psia N
2
for 2 hrs in the presence of 1 g Amberlyst 15
in decalin solvent. The aldol condensation of cyclopentanone
hydrogenation/hydrogenolysis
strategies,
this
approach
o
was examined in Parr reactor at 100 C and 300 psia N
2
for 2
demands less energy and less H
2
consumption. In addition, the
and 6 hrs. 0.5M of CPO in decalin solvent over 1 g Amberlyst
5.
high water and acid content of bio-oil are in fact favorable for this
conversion, which makes the process more appealing in terms
of practical implementation. The production of this stable
intermediate can be followed by C-C bond formation reactions,
such as self-aldol condensation or hydroxyalkylation with
1
The product mixture was analyzed by Shimadzu QP2010S
gas chromatograph/mass spectrometer (GC-MS) and quantified
by GC-FID Agilent 6890 equipped with a flame ionization
detector for quantification. Both GC’s were equipped with a
Zebron ZB-1701 column with dimensions of 60m x 0.25 mm x
phenolics-derived fractions.
process is followed by a hydrodeoxygenation step a mixture of
10-C16 hydrocarbons, which are in the gasoline/diesel range can
When the C-C bond forming
C
0.25 μm.
be effectively obtained. For example, when the product stream
from the AC/HAA reaction of CPO and m-cresol was followed by
HDO on a bifunctional catalyst over 90% efficiency of the whole
catalytic upgrading process starting from CPO was
demonstrated, which highlights the potential of this strategy for
future biofuel applications.
The conversion (X), yield and selectivity were calculated as:
CCPOin CCPOout
C n
CCPOin ;
i
X 
Ci
Yi 
CCPOin
;
Si 
C
The major obstacle of this approach is that the large
organic molecules produced by the HAA reaction are trapped in
microporous catalysts, particularly at low temperatures.
Thermally stable zeolites that can be operated at higher
temperatures show a lower degree of trapping, but the problem
still subsists. Further research on acidic materials with
hierarchical structures with a proper mesoporous/microporous
balance that minimizes the diffusion path of large adducts out of
the catalyst cavities would be desirable.
i
The carbon balance for the HAA reaction was calculated
as:
CCPOproducts CCPOout
Carbonabalance 
CCPOin
The carbon balance for the HDO step was calculated as:
C n

i
Ci
product
feed
Carbonabalance 
C n

i
Ci
where CCPO(in, out): Concentration of cyclopentanone before
and after reaction;
C: Concentration of each product;
i
n: Number of cyclopentanone molecule in molecular
structure of products;
Experimental Section
The conversion of furfural to cyclopentanone was carried
o
out in a Parr reactor at 150 C, 14-40 bar for 6 hrs in water
solvent over 0.15 g 2% Pd-Fe/SiO
2
catalyst, at an initial
i
nC: Number of carbons in molecular structure
concentration of furfural of 200 mM. The hydroxyalkylation of m-
cresol with cyclopentanone was conducted at atmospheric
Acknowledgements
o
pressure in a glass reactor in the temperature range 65-140 C,
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The authors thank the Department of Energy for funding the
experimental part of this work under grant DE-SC0004600 and
the theoretical part under grant DE-EE0006287 of the Bioenergy
Technology Office CHASE program.
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Keywords: C-C coupling 1 • hydroxyalkylation 2 •phenolics 3 •
cyclopentanone 4 • biofuels 5
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Table of content
Tuong V. Bui, Dr. Tawan Snooknoi,
Prof. Daniel E. Resasco*
We are here proposing an attractive
strategy to effectively upgrade two
fractions
simultaneously via hydroxyalkylation/
adol condensation reactions. As the
results, after HDO processing,
saturated alkanes with carbon chain
ranging from
obtained, which could be used as
transportation fuel or refinery feed.
Page No. – Page No.
of
torrefraction
Simultaneous upgrading of furanics
and phenolics via hydroxyalkylation
/aldol condensation reactions
(
(Insert TOC Graphic here: max.
width: 5.5 cm; max. height: 5.0 cm))
C10-C16 could be
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Figures and Schemes
Click here to download Graphical Material Figure and Scheme
Final.docx
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Figures and Schemes
Scheme 1. Products from hydroxyalkylation of m-cresol and cyclopentanone
5
0
1
2
Yield of (1)
Yield of (3)
Yield of (4)
Yield of (5)
Yield of (6)
Conversion
Yield of AC
Yield of HAA
4
0
10
8
30
20
10
0
6
4
2
0
50
70
90
110
130
150
5
0
70
90
110
130
150
o
o
Temperature, C
Temperature, C
Figure 1. Catalytic performance of Amberlyst 15 at different temperatures. Product (1) – (6) are presented in Scheme 1
2
5
0
5
0
5
0
Conversion
Yield of (1)
Yield of (2)
2
1
1
2
h
6h
o
2
Figure 2. The acid-catalyzed aldol condensation of cyclopentanone over Amberlyst 15 (Parr reactor at 100 C and 300 psia N for 2 and 6 hrs in decalin solvent
over 1 g Amberlyst 15.)
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1
1
1
1
6
Yield of (1)
Yield of (2)
Yield of (3)
Yield of (4)
Yield of (5)
Yield of (6)
4
2
0
8
6
4
2
0
Figure 3. Yield of coupling products from different catalysts at comparable CPO conversion
4
.5
3
6
b)
a)
3
2
1
0
4
2
0
.5
2
-2
-4
.5
1
AC
Hβ
-6
HAA
SiO2-Al2O3
.5
-8
0
-10
0
.0015
0.002
0.0025
ln(1/T)
0.003
0.0017 0.0018 0.0019 0.002 0.0021 0.0022
ln(1/T)
Figure 4. Arrhenius plots for a) overall CPO conversion over Hβ and SiO
2
-Al
2
O
3 2 2 3
; and b) Yield of AC and HAA products over SiO -Al O .
8
0
2
5
Selectivity of (3)
Selectivity of (4)
Selectivity of (5)
b)
Yield of AC
Yield of HAA
70
a)
20
15
10
5
0
6
5
4
0
0
0
30
2
1
0
0
0
0
100 200 300 400 500 600 700
0
100 200 300 400 500 600 700
Mass of catalysts (mg)
Mass of catalysts (mg)
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80
70
60
50
40
30
20
10
0
1
1
2
0
8
6
4
2
0
c)
d)
Yield of AC
Yield of HAA
Selectivity of (3)
Selectivity of (4)
Selectivity of (5)
1
00 120 140 160 180 200 220 240 260
80 100 120 140 160 180 200 220 240 260
o
o
Temperature, C
Temperature, C
Figure 5. a) Yield of AC, HAA products and b) Distribution of HAA products at different mass of catalysts c) Yield of AC and HAA products and d) Distribution of
HAA products at different temperatures
1
00
Selectivity to (3)
Selectivity to (4)
Selectivity to (5)
Selectivity to (6)
b)
1
00
Selectivity of AC
Selectivity of HAA
a)
80
8
6
4
2
0
0
0
0
0
6
4
2
0
0
0
0
6
0oC
100 C 150 C 200 C 250 C
o
o
o
o
0
50
100
150
200
250
300
o
o
Temperature, C
Temperature, C
Figure 6. a) Selectivity of aldol condensation and hydroxylalklyation products (AC and HAA) at different temperatures (Reaction condition: m-
o
o
o
o
o
cresol/cyclopentanone=2/1, Parr reaction, reaction volume 120ml, the conversions at 60 C, 100 C, 150 C, 200 C, 250 C are 20%, 20%, 23%, 21%, 20%,
respectively) b) Selectivity of hydroxyalkylation products at different temperatures
16
14
12
10
8
6
4
2
0
Conversion
Yield of AC
Yield of HAA
2
:1
5:1
7:1
o
2
Figure 7. The distribution of AC and HAA products at different m-cresol/CPO ratios over Amberlyst 15 (Parr reactor at 120 C, 300 psia N for 2 hrs in the
presence of 1 g Amberlyst 15 in decalin solvent)
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Scheme 2. Biofuel production scheme starting from cyclopentanone
60
50
40
30
20
10
0
5
1
1
8
1
4
7
5
2
Figure 8. Conversion/Yield of HAA reaction between CPO and m-cresol (dash-black bar is the conversion of CPO, yellow bars are the yield of each product)
80
70
60
50
40
30
20
10
0
C10 alkane
8.8
C12 cyclic
4
C12 alkane
2
5.6
2
3
C16 alkane
.6
2
Figure 9. Selectivity of each saturated products in HDO upgraded liquid
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Graphical abstract
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