PRODUCTION OF FURFURAL: OVERVIEW AND CHALLENGES

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ABSTRACT
J-FOR Journal of Science & Technology for Forest Products and Processes: VOL.2, NO.4, 2012
44
The renewability and abundance of lignocellulosic biomass make it a viable resource for the production of platform chemicals such as fur-
fural. Currently, furfural is industrially produced through the acid hydrolysis of agro-based biomass. Alternatively, it can be produced from
woody biomass in an integrated forest biorenery. In this study, various processes developed for producing furfural at industrial and labora-
tory scales will be reviewed. Generally, furfural production yield was higher in bi-phasic systems than in aqueous systems. However, furfural
production in bi-phasic systems encounters certain technical challenges, including solvent recovery, process complexity, and environmental
issues, which prevent its practical implementation at industrial scales. This study also reviews the advantages and disadvantages of various
furfural production processes proposed in the literature.
MEHDI DASHTBAN, ALLAN GILBERT, PEDRAM FATEHI*
PRODUCTION OF FURFURAL:
OVERVIEW AND CHALLENGES
The majority of synthetic products are
currently produced from oil-based ma-
terials. Emerging biorenery technolo-
gies could help produce these products
from biomass. Plant biomass is com-
posed of three major components: cel-
lulose, hemicelluloses, and lignin. As the
consumption of lignocellulosic biomass
increases globally, the production of lig-
nocellulosic residues (wastes) will also
increase. Recently, the accommodation
of lignocellulosic residues from differ-
ent pulping processes in the production
of various value-added products was dis-
cussed [1–5]. The biorenery will also as-
sist the Canadian pulp and paper industry
to produce various value-added chemi-
cals (in addition to traditional pulp prod-
ucts) from its renewable feedstock, which
will increase its overall revenues [6–8].
Canada has enormous forest and
agro-based resources. According to the
BIOCAP Canada Foundation, 42% of to-
tal land area in Canada was covered with
forest in 2003, and approximately 6.8% of
land was used as farms for agriculture [9].
Moreover, a part of the harvested forest
and agro-based biomass has not yet been
used (i.e., it is wasted) [9]. Table 1 lists
some of the wastes produced in Canada
from 2001 to 2008. It was reported that
mill residues accounted for approximately
2.7 million metric tonnes (million MT) in
2005, while agro-based residues were ap-
proximately 17.8 million MT in 2001 [9–
11]. Highly abundant municipal solid and
animal wastes could also be considered as
potential biomass resources [11–13]. This
INTRODUCTION
biomass could be used in the production
of various value-added chemicals in dif-
ferent biorenery scenarios.
Generally, altered value-added chem-
icals such as dissolving pulp [2,3], nano-
crystalline cellulose (NCC), [14], and bio-
fuels such as ethanol [15] can be produced
from the cellulose in lignocellulosic mate-
rials . Lignin can also be used in the pro-
duction of value-added chemicals, includ-
ing phenols and adhesives [16]. Although
hemicelluloses can be used in the produc-
tion of ethanol or xylitol, their industrial
application through bioconversion routes
is challenging. On the other hand, hemi-
celluloses can be chemically converted to
furfural. This conversion is signicantly
faster and more industrially attractive than
the bioconversion of cellulose or hemicel-
luloses to ethanol [7].
Attempts at chemical conversion
of mono-sugars derived from biomass
hemicelluloses to fuels and chemicals have
been extensively reported in the literature.
For example, 5-hydroxymethylfurfural
(HMF) can be produced from glucose and
be further converted to 2,5-dimethylfuran
(DMF). DMF has 40% higher energy den-
sity than ethanol [17]. Levulinic acid (LA)
and furfural can also be produced from
5- and 6-carbon mono-sugars in catalytic
reactions [7]. LA can be further converted
to levulinate (EL), which is considered as
*Contact: pfatehi@lakeheadu.ca
PEDRAM FATEHI
Chemical Engineering
Department,
Lakehead University
Thunder Bay, On
Canada
MEHDI DASHTBAN
Chemical Engineering
Department,
Lakehead University
Thunder Bay, On
Canada
ALLAN GILBERT
Chemical Engineering
Department,
Lakehead University
Thunder Bay, On
Canada

J-FOR Journal of Science & Technology for Forest Products and Processes: VOL.2, NO.4, 2012 45
SPECIAL BIOREFINERY ISSUE
fuel [18], or to succinic acid by oxidation.
Formic acid, which is a value-added chem-
ical, is also formed as a by-product in the
LA production process [7].
This review focuses on various pro-
cesses which have been developed for
producing furfural from woody biomass,
agricultural residues, and commercially
available sugars. It also addresses the chal-
lenges and technical problems associated
with laboratory- and commercial-scale
furfural production processes.
FURFURAL
Furfural, an organic compound (hetero-
cyclic aldehyde) with a boiling point of
161.7°C (at 1 atm) and a density of 1160
kg/m3, was rst isolated as a by-product
of formic acid production in 1821 and
later produced through hydrolysis and de-
hydration of various crops. A large-scale
furfural production plant was started by
the Quaker Oats Company in 1922 using
agricultural by-products such as sugarcane
bagasse and corn cobs. The main reason
for furfural production was the fact that
massive quantities of oat hulls remained
unused after production of rolled oats
[19]. Traditionally, furfural was produced
using a two-step process: 1) hydrolysis of
lignocellulosic biomass using heat and acid
(mainly sulphuric acid) to release pentoses
(mostly xylose) from biomass and 2) cy-
clodehydration of the pentoses using acid
and steam to produce furfural [19,20].
Furfural was traditionally used for
resin production (in foundry technologies)
and as a solvent for lubricant production
[21]. Recently, it was proposed as a plat-
form chemical for the production of oth-
er furan-based chemicals such as furfuryl
alcohol (FFA), tetrahydrofurfuryl alcohol
(THFA), methyltetrahydrofuran (MTHF),
furoic acid, furfurylamine, and methylfu-
ran [22]. These furfural derivatives have
high potential for industrial applications.
For example, furfuryl alcohol produced
by hydrogenation of furfural can replace
oil-based binders in the foundry industry
[7]. Tetrahydrofuran (THF) can be pro-
duced from furfural (by decarbonylation
and then catalytic hydrogenation) and be
used as a monomer or a solvent in the
pharmaceutical and chemical industries
[7]. LA, which is produced from furfural
via furfuryl alcohol routes, can function
as a platform chemical with applications
in the pharmaceutical, agricultural, and
petroleum industries as a fuel or fuel ad-
ditive [22].
CURRENT FURFURAL PRODUC-
ERS
Currently, China, South Africa, and the
Dominican Republic are the major pro-
ducers of furfural and its derivatives
[6,21]. All these major furfural produc-
ers use agricultural residues as feedstock:
corncobs in China and bagasse in South
Africa and the Dominican Republic. Cur-
rent furfural production is estimated to
be 300,000 tons/year globally, with the
largest furfural production plant in the
Dominican Republic having a capacity of
35,000 tons/year [21,23].
INDUSTRIAL- AND PILOT-SCALE
FURFURAL PRODUCTION
In principle, any lignocellulosic residues
containing pentosans can be used as a
feedstock for furfural production. The
rst furfural production plant was a batch
process originally developed by Quaker
Oats Technology in the 1920s in the
United States. In this process, biomass
was treated with acid (2.2 wt.% (OD of
biomass) aqueous sulphuric or phosphoric
acid) and steam at 153°C in a hydrolysis
step which could convert the pentosans
in the biomass to pentoses. The generated
pentoses were then converted (i.e., cyclo-
dehydrated) into furfural in a subsequent
stage, and then furfural was recovered by
steam stripping from solution. The draw-
backs of this process were low yield (less
than 50% based on mono-sugars), sub-
stantial steam requirement, high efuent
production, (i.e., very acidic wastes), and
high operating cost, which led to the clo-
sure of plants in developed countries in
the 1990s [21,23]. The rather low yield
of this process was attributed to the fact
that the rst step (hydrolysis) was 50 times
faster than the second step (dehydration).
Consequently, a signicant number of side
reactions occurred because of the high
availability of mono-sugars in the process,
which ultimately reduced the quantity of
mono-sugars available for furfural pro-
duction [21,24].
Recently, Westpro has modied the
Quaker Oats Technology process in China
(Huaxia Furfural Technology) into a con-
tinuous process. This method uses xed-
bed reactors and a continuous dynamic
azeotropic distillation rening process,
which led to 4%–12% production yield
with respect to the initial weight of dry
biomass used (i.e., corn cobs, rice hulls,
ax dregs, cotton hulls, sugarcane bagasse,
and wood) [21,23]. However, no detailed
information is available with regard to this
technology.
SupraYield is another modication
of the Quaker Oats Technology process
introduced in the late 1990s [19,21]. In
this technology, lignocelluloses (sugarcane
bagasse) are hydrolysed in one stage, and
then pentoses are converted into furfural
in aqueous solution at its boiling point
TABLE 1 Lignocellulosic wastes from different sources.
Forest-based residues
Forest fl oor residues (roadside, annually)
Mill residues (2005)
12.8
Lignocellulosic Wastes Annual production
(million MT) References
2.7
17.79
180
25.8
[10,11]
[11]
[9]
[13]
[11-13]
Agricultural-based residues
Across Canada (2001)
Municipal solid waste (MSW)
Across Canada (2008)
Animal wastes
Across Canada (2006)

23 J-FOR Journal of Science & Technology for Forest Products and Processes: VOL.2, NO.4, 2012
46
(with or without phosphoric acid). The so-
lution containing furfural is then adiabati-
cally ash-distilled, which facilitates the
transfer of the furfural formed from the
aqueous phase to the vapour phase. This
process has a production yield of 50%–
70% and is less expensive than the tradi-
tional process described above. The high
temperature of this process (240°C) pro-
motes the conversion of mono-sugars to
furfural. This process was initially investi-
gated at a pilot scale in South Africa and
then commercialized by the Proserpine
Cooperative Sugar Mill in Queensland,
Australia in 2009 [21].
Alternatively, a single-step furfural
production process based on simultane-
ous hydrolysis and dehydration of lig-
nocellulosic biomass to furfural in dilute
sulphuric acid solution was developed by
Vedernikov. Because the pentoses pro-
duced would spontaneously be converted
to furfural, the presence of surplus pen-
toses in the solution would be limited,
and therefore the occurrence of side re-
actions and hence by-products would
be marginal. As a result, more pentoses
would be converted to furfural (furfural
yield was 75% in this case). In addition,
biomass cellulose appears to be preserved
in this process, which promotes the down-
stream application of cellulose in the pro-
duction of other value-added chemicals,
such as ethanol. This technology was as-
sessed in the former Soviet Union, Slove-
nia, Hungary, and Finland [24]. Although
this process had a higher furfural yield, the
signicant quantity of acidic wastes pro-
duced was an environmental concern.
In 2008, CIMV (Compagnie Indus-
trielle de la Matière Végétale) launched its
rst pilot-scale lignocellulosic biorenery
facility in Pomacle (Marne, France). This
process is based on a continuous fraction-
ation of biomass (wheat straw) under acid-
ic conditions (e.g., acetic acid and formic
acid at 185°C–210°C). The fractionated
components (lignin, cellulose, and hemi-
celluloses) would follow different routes:
hemicelluloses would be converted to xy-
litol, furfural, and furfuryl alcohol [25],
cellulose to bleached pulp (with properties
similar to those of hardwood pulps), and
lignin to resins and adhesives [19,26].
In another process, furfural was pro-
duced using a novel reactor known as the
multi-turbine column (MTC) developed at
TU Delft (Delft University of Technol-
ogy) in The Netherlands. In this process,
both acid hydrolysis of hemicellulosic
pentosans (obtained from pre-hydrolysis
of straw) to xylose and conversion to fur-
fural occur in one continuous reactor (i.e.,
it is a one-step process). In this technol-
ogy, 5% (wt.) aqueous solution contain-
ing pentosans was used as the feedstock,
which was directly added to the column
[25]. Furfural was produced in water in
the reactor and simultaneously transferred
into the vapour phase. Various acids and
salts were used to improve furfural pro-
duction, and the results showed that the
concentration of acid (HCl or H2SO4) and
NaCl affected furfural production selectiv-
ity, yields, and separation. Furfural yields
of over 83% with a purity of over 99%
were obtained under optimal conditions
(0.18 wt.% HCl, 1.7 M NaCl at 200°C)
[27]. One advantage of this method was
the minimal formation of by-products
such as HMF, acetic acid, and formic acid
[25]. Because this process is a continuous
reactor and distillation tower, it also fea-
tures low energy consumption, and there-
fore this technology seems to be a more
appropriate alternative to the traditional
batch process. However, the optimal yield
is achieved only when dilute solutions (5
wt.%) of pentosans are used. Therefore,
lignocellulosic biomass cannot be directly
used in this process. In other words, bio-
mass hemicelluloses must be initially sepa-
rated from the biomass and then diluted.
This technology is at the early stage of its
development, implying that more in-depth
analyses are required for commercializa-
tion of this process [28].
LABORATORY-SCALE FURFURAL
PRDUCTION
Because current furfural production plants
are still practicing original or modied
versions of the Quaker Oats Technology
process at industrial scales, the production
TABLE 2 Current industrial furfural production processes and their specifi cations.
Method Year of operation Raw materials Furfural yields ScaleProcess conditions References
Quaker Oats
Technology
SupraYield
Single-step
continuous
process
CIMV
MTC
1922
2009
2000
2008
2012
Sugarcane
bagasse/corncobs
Sugarcane
bagasse
Sugarcane
bagasse/corncobs
Wheat straw
Straw
Acid catalysts,
steam (153 °C)
Acid catalysts,
high temperatures
(180-240 °C)
Concentrated
sulphuric acid,
steam
High temperature
(230 °C) and
pressure
Acid hydrolysis,
high temperature
(200 °C)
50%
50-70%
75%
N/A
83%
Industrial
Industrial
Industrial
Pilot plant
Pilot plant
[21,23]
[19,21]
[24]
[25]
[25,28]

J-FOR Journal of Science & Technology for Forest Products and Processes: VOL.2, NO.4, 2012 47
SPECIAL BIOREFINERY ISSUE
yield and cost are not satisfactory, and en-
vironmental concerns with acidic process
wastes still exist. Many studies have been
carried out to improve furfural produc-
tion technology so that the process has
a higher yield and lower cost and is more
environmentally friendly. In this regard,
different catalytic systems using mono- or
bi-phasic processes have been developed,
as discussed in the following sections.
Furfural production in autocatalytic
systems
Table 3 lists various autocatalytic systems
for furfural production that have been de-
scribed in the literature. Furfural can be
produced by treating biomass at high tem-
perature (200°C or higher) and pressure
in batch systems. In this process, acetic
acid is liberated from hydrolysis of acetyl
groups associated with biomass hemicel-
luloses and acts as a catalyst for the re-
action. Furthermore, hemicelluloses are
isolated from biomass, depolymerized to
pentoses and hexoses, and simultaneously
the pentoses and hexoses are converted to
furfural and HMF respectively [29]. The
absence of mineral acid implies that the
aqueous solutions (and therefore aqueous
wastes) of this system are not very corro-
sive or toxic (i.e., environmental concerns
are reduced).
In one study, furfural production
was practiced from commercial xylose in a
batch reactor at high temperature (180°C
to 220°C) and 10 MPa pressure in water
[30]. As a result, a maximum of 50% fur-
fural (based on xylose) and formic acid (an
undisclosed concentration) were formed
as the main product and by-products of
this process respectively, while xylose con-
version was 95.8% at 220°C after 50 min
of reaction [30].
In another study (Table 3), the con-
version of commercial xylose to furfural
was assessed under aqueous subcritical
conditions using hot compressed water
(HCW) at a temperature range of 200°C–
300°C and 200 bar (Table 3) [31]. In this
process, formic and lactic acids (i.e., by-
products) were formed, which reduced the
pH of the solution from 6.5 to 3.2. The
high pressure, temperature, and formed
acids promoted xylose conversion into
furfural, which would ultimately provide
a more environmentally friendly process.
In addition, the xylose conversion rate was
increased from 70% to 100% by increas-
ing reaction temperature from 260°C to
300°C at 200 bar [31]. A similar result was
obtained in another study using commer-
cially available pentoses (arabinose, xylose,
galacturonic acid, and glucuronic acid) at
240°C and 10 MPa under aqueous sub-
critical water conditions. The pH of the
solution was also reported to decrease to
approximately 3.0 in this study [32].
Although these processes can be
practically implemented in industry, fur-
fural production yield is still low, and a
considerable quantity of by-products (e.g.,
formic acid) is formed. Furthermore, op-
erating a very highly pressurized furfural
production reactor may be technically
challenging.
Furfural production in aqueous-acid
catalytic systems
In these systems, various acids such as hy-
drochloric, phosphoric, acetic, or formic
acids are added to the reactor, in which
biomass is converted to furfural (as ap-
plied at industrial scales) in aqueous solu-
tions. Therefore, the difference between
aqueous-acid catalytic and autocatalytic
systems is that acid is added to the aque-
ous-acid catalytic systems. Moreover, the
production of by-products is usually high-
er in acid-catalytic than in autocatalytic
systems, which is due to the more exten-
sive occurrence of side reactions in acidic
systems. Therefore, the process condi-
tions, including temperature, time, acid
and pentose concentrations, should be
carefully monitored in furfural production
processes using this technique. In this re-
gard, furfural formation was studied using
commercial xylose solutions (0.067–0.20
mol/l) as a feedstock and formic acid as
the catalyst in a batch process under dif-
ferent experimental conditions [29]. The
results showed that the xylose conversion
rate was increased from 6.2% to 98.2%
by increasing temperature from 120°C to
200°C. The furfural yield was increased
(from 3.0% to 65.4%) by increasing tem-
perature (from 140°C to 200°C), whereas
it decreased with increasing time (from 20
min to 40 min). The selectivity of furfural
production varied from 42.3% to 72.7%
under different conditions [29]. The high-
est furfural yield of 65.4% was obtained
using 0.067 mol/l xylose concentration
and 30 wt.% formic acid concentration at
200°C after 20 min of reaction. These re-
sults demonstrate that the process condi-
tions should be monitored to reduce the
occurrence of side reactions. Note that
formic acid is formed during the decom-
position reactions of hemicelluloses and
furfural. Therefore, the concentration of
formic acid as a catalyst will increase in a
process using this technique.
Overall, it can be inferred that fur-
fural production yield is generally higher
in homogeneous catalytic systems than
TABLE 3 Laboratory-scale furfural production processes using autocatalytic systems.
Method Raw materials Furfural yields By-productsProcess conditions References
High temperature liquid water
(HTLW)
Hot compressed water
(HCW)
Subcritical water
Xylose
Xylose
Pentose
High temperature
(180-220 °C)
High temperature
(200-300 °C), 200 bar
High temperature
(240 °C), 10 MPa
50%
0.3 molar
yield1
0.3 molar
yield1
Formic acid
Formic acid
Formic acid
[30]
[31]
[32]
1The yield was determined based on the molar conversion of biomass to furfural.

23 J-FOR Journal of Science & Technology for Forest Products and Processes: VOL.2, NO.4, 2012
48
in autocatalytic systems. The application
of strong mineral-acid catalysts, such as
H2SO4 or HCl, produced a higher furfu-
ral yield than organic acids such as formic
acid in the homogeneous systems. The
main drawback of these systems is the
environmental concerns of dealing with
acidic process wastes. The separation, pu-
rication, and recovery of acids are costly
and technically challenging.
Furfural production in bi-phasic
systems
Table 4 lists some laboratory-scale bi-pha-
sic systems for furfural production. Furfu-
ral can be produced in a batch process in
a bi-phasic system. In this system, furfural
is produced from pentose (mainly xylose)
in an aqueous phase, and the formed fur-
fural will simultaneously be transferred
from the aqueous phase to an organic
phase in which the furfural is extracted. In
this system, the reaction medium (aque-
ous phase) containing acid catalysts has a
limited concentration of furfural because
the furfural is spontaneously transferred
as it is formed, which improves the over-
all furfural product yield. The interest of a
bi-phasic reaction is to minimize side reac-
tions and to avoid the azeotropic point of
the furfural-water mixture, which makes
separation difcult [33]. The aqueous
phase usually consists of water or a wa-
ter-dimethyl sulphoxide (DMSO) mixture
and an acid (HCl or H2SO4). The organic
phase, however, consists of different or-
ganic solvents such as methylisobutylk-
etone (MIBK), MIBK-2-butanol mixture,
tetrahydrofuran (THF), or dichlorometh-
ane (DCM), which have great afnity for
absorbing furfural [34].
In one study, the possibility of a
biorenery producing furfural from a
model spent liquor from FORMACELL
pulping (i.e., formic acid in solution) was
investigated [35]. The reaction was per-
formed using two different solvent sys-
tems including a mixture of acetic acid
and water (ACETOSOLV) with or with-
out adding 0.1% HCl as a catalyst. Furfu-
ral production was analyzed using these
acid solutions containing 20 mmol of xy-
lose, glucose, mannose, or xylan at 165°C.
Maximum furfural production of 55%
was obtained using FORMACELL liquor
at 165°C after 240 min. In the case of
ACETOCELL, 40.8% furfural yield was
obtained in the absence of HCl and 46.4%
in the presence of 0.1% HCl. Moreover,
HMF and acetoxymethylfurfural (AMF)
were produced from the hexoses in the
mixtures, with maximum yields of 18%
and 22% respectively in ACETOSOLV
(without HCl) [35].
In another attempt (Table 4), pro-
duction of furfural from mixed northern
hardwoods was investigated (Table 4). In
this work, wood chips consisting of ma-
ple, beech, birch, poplar, and aspen were
initially hydrolyzed in a pilot-scale reactor
(160°C with H-factor of 360 h) with hot
water or green liquor (a mixture of so-
dium carbonate, sodium sulphide, and so-
dium hydroxide) to extract hemicelluloses
[36]. The extracted hemicelluloses (10.7%
wt. concentration, which contained 2%
hemicelluloses in wood chips) were then
used as a feedstock for furfural produc-
tion in a continuous bi-phasic reactor [36].
The aqueous phase was a dilute mineral-
acid solution (0.44 M HCl or H2SO4) and
NaCl (5–20 g/100 g hemicelluloses). Xy-
lan from the extracted hemicelluloses was
converted into monomers in a separate
hydrolysis stage at 130°C for 30 min us-
ing sulphuric acid at pH 1, and then the
monomers were converted to furfural in
the second stage at 200°C. The furfural
produced in the second stage was ab-
sorbed by an organic phase containing
tetrahydrofuran (THF), which resulted in
90% furfural yield (based on the xylose in
the aqueous phase) [36].
In another study, various raw materi-
als (e.g., sucrose, inulin, starch, cellobiose,
xylan, fructose, and xylose) were used as a
feedstock at 10–30 (wt.%) concentrations
at 413°K–443°K. The feedstocks were
converted into HMF and furfural in an
aqueous phase (water and DMSO at ratios
of 5:5, 4:6, and 3:7), and then the HMF
and furfural were transferred to an or-
ganic phase containing MIBK-2-butanol
mixture (7:3 ratio) or DCM [37]. Furfural
selectivity was 91% and 76% for the de-
hydration of xylose and xylan respectively,
implying that furfural production is de-
pendent on the molecular weight of hemi-
celluloses, in that the larger the molecule,
the lower the furfural selectivity will be.
Generally, the presence of acid, salt,
and two phases in one process is opera-
tionally challenging. Moreover, the sol-
vent, acid, and salt should be recovered
to obtain an economically viable process.
The recovery process might be operable
at laboratory scales, but would be complex
and expensive at industrial scales. Conse-
quently, the commercialization of these
bi-phasic systems is challenging and may
not be technically possible or economical
with available technology.
Furfural production in solid catalyt-
ic/aqueous systems
In industry, 80%–85% of catalytic pro-
TABLE 4 Laboratory-scale furfural production processes using bi-phasic systems.
Method Raw materials Furfural yields By-productsProcess conditions References
ACETOCELL
Continuous two zone
biphasic reactor
Biphasic reactor
FORMACELL pulping
Waste aqueous
hemicellulose solutions
Biomass-derived mono-,
di- and polysaccharides
Acetic acid/formic
acid, 165°C
Sulphuric acid,
110-200°C
Sulfuric acid,
413-443 K
46.4%
90%
91%1
HMF and
AMF
Humins
HMF
[35]
[36]
[37]
1xylan yield

J-FOR Journal of Science & Technology for Forest Products and Processes: VOL.2, NO.4, 2012 49
SPECIAL BIOREFINERY ISSUE
esses use solid catalysts instead of liquid
ones [34]. Similarly, a furfural production
process can be implemented using solid
catalysts in aqueous solutions. If used in
the furfural production process, the solid
catalysts can be readily ltered from the
product suspension, which implies that
the separation (and hence the recovery) of
solid catalysts is easily feasible at industrial
scales. This fairly simple recovery system
signicantly reduces the operational cost
of furfural production at industrial scales
[34]. For this reason, over the past few
years, several studies have been carried
out to discover stable and recyclable solid
catalysts for the conversion of saccharides
into furfural.
Similarly to other catalytic systems
for furfural production, lignocellulosic
biomass can be used as the feedstock for
furfural production in solid catalytic sys-
tems in one- or two-stage processes. A
one-stage process enables simultaneous
depolymerization of pentosans to xylose
and conversion of pentose to furfural. A
two-stage process, however, controls the
depolymerization and conversion reac-
tions in two separate stages, meaning that
each can be optimized separately, which
may improve overall furfural production,
but at the expense of a more complex
process [38].
In one study, one- and two-stage
processes were used to produce furfural
using rice hulls as feedstock [38]. The re-
sults showed that furfural production was
very limited (0.7%–3.34% on a dry basis)
when the liquid/solid range was 13–50
ml/g and the sulphuric acid concentration
was 3 to 35 wt.% in a one-stage process at
125°C. However, furfural production was
enhanced in the presence of metallic ox-
ides (i.e., AIC13, ZnC12, ZnO, and TiO2)
as the solid catalysts in the reaction sys-
tem. Among the solid catalysts used, TiO2
demonstrated the most efcient catalytic
afnity for furfural production (4.3% fur-
fural based on dry mass of rice hulls). Al-
ternatively, a two-stage process was inves-
tigated using 3% H2SO4 in the rst stage at
125°C and 15% H2SO4 in the second stage
at 125°C in the presence of TiO2 as the
catalyst [38]. This process yielded 14.9%
furfural based on dry mass of rice hulls.
Furfural production in solid catalyt-
ic/bi-phasic systems
Recently, the use of solid catalysts in bi-
phasic systems has attracted attention.
Table 5 lists some laboratory-scale furfu-
ral production processes in solid catalytic/
bi-phasic systems. This interest can be
ascribed mainly to the signicantly higher
furfural yield of these processes compared
to other catalytic processes. In this respect,
a combination of water and MIBK or tol-
uene as a two-phase system (1:3 v:v) was
studied for converting xylose (commer-
cial xylose) to furfural at 170°C [39]. The
use of H-mordenite (0.5%) in the system
resulted in furfural selectivity and xylose
conversion rate of 95% and 66% respec-
tively (with a furfural yield of approximate-
ly 63%) [39]. This furfural selectivity was
higher than the selectivity (approximately
TABLE 5 Laboratory-scale furfural production in solid catalytic/aqueous systems.
Method Raw materials Furfural yields By-productsProcess conditions References
One- and two-stage
processes
Batch mode two-
phase process
HPAs-catalytic
process
Rice hulls
Xylose
Xylose
Sulphuric acid, metallic oxide
(AIC13, ZnC12, ZnO and TiO2)
catalysts, 125 °C
H-mordenite catalyst, water-
MIBK/toluene solvent, 170 °C
Bi-phasic process, DMSO, water,
water/toluene or water/MIBK
solvents, 140-200 °C
14.9%
63%
N/A
N/A
N/A
[38]
[39]
[40]
Micro-mesoporous
niobium (Nb) silicate-
catalytic process
Microporous SAPO-
catalytic process
Mesoporous TUD-1-
catalytic process
Micro-mesoporous
silica-sulphonic acid
group catalytic process
Sulphated zirconia
(SZ) catalytic
Mesoporous SBA-15
catalytic process
Xylose
Xylose
Mono-, di- and
polysaccharides
Xylose
Xylose
Xylose
[41]
[42]
[43]
[44]
[45]
[46]
N/A
N/A
HMF
N/A
N/A
N/A
58-67%
50%
38%
60%
75%
46%
70%
Microporous and mesoporous
niobium silicates (Na,H-AM-11
and Nb-MCM-41), water-toluene
solvent, 140-180 °C
SAPO-5, 11 and 40 catalysts,
water-toluene solvent, 170 °C
AL-TUD-1 catalyst, water-toluene
solvent, 170 °C
Micro-mesoporous silicas with
sulphonic acid groups, water-
toluene solvent, 140 °C
Mesoporous SZ-MCM-41, water-
toluene solvent, 160 °C
SBA-15-SH(C), SBA-15-SO3H(C)
and SBA-15-SO3H(G), water-
toluene solvent, 130-180 °C

23 J-FOR Journal of Science & Technology for Forest Products and Processes: VOL.2, NO.4, 2012
50
70%) of a process using a mineral-acid
(HCl or H2SO4) solution under otherwise
similar conditions [39]. However, this
method suffers from a lower xylose con-
version rate and from high solvent usage,
causing safety and environmental issues
for large-scale applications.
Heteropolyacids (HPA) have low
volatility, low corrosivity, and high ex-
ibility. Literature results show that the use
of HPA as a catalyst produced a smaller
quantity of by-products compared to min-
eral acids (in furfural production) [40]. In
one study, H3PW12O40 (PW), H4SiW12O40
(SiW), and H3PMo12O40 (PMo) were used
for furfural production from commercial
xylose (3 wt.% solution) in a homoge-
neous liquid phase in water. The results
showed a low xylose conversion rate (34%)
and furfural selectivity (2%) in the absence
of a catalyst. Adding 2% PW catalyst in
DMSO (as the solvent) at 140°C improved
the xylose conversion rate and furfural se-
lectivity to 100% and 67% respectively.
Alternatively, the solid catalysts were used
in water/toluene or water/MIBK (3:7 ra-
tio) in a bi-phasic system [40]. The furfural
yield (58%–67%) obtained in this system
was comparable to the furfural yield of
the H2SO4 catalytic system under other-
wise the same conditions [40]. Although
the HPAs used in the study are promis-
ing candidates for furfural production, the
possibility of recycling catalysts remains
to be assessed.
Niobium-containing materials such
as hydrated niobium oxide and niobium
phosphate could also be considered as
catalysts for furfural production. In one
study, microporous and mesoporous nio-
bium (Nb) silicates (H-AM-11 and Nb-
MCM-41) were used as solid catalysts in
a water-toluene mixture (3:7 ratio) in a
bi-phasic system. The reaction was con-
ducted using commercial xylose (3 wt.%)
with micro- and mesoporous catalysts
(3%) at 160°C [41]. The results showed
xylose conversions of 85% and 90% and
furfural yields of 46% and 50% for mi-
cro- and mesoporous catalysts respectively
[41]. The longer the retention of furfural
in the pores of the catalyst, the greater is
the possibility of conversion of furfural to
other by-products. In this case, the larger
pores of the mesoporous catalyst facilitat-
ed the diffusion of formed furfural from
the pores to the reaction medium and
eventually to the organic phase.
Alternatively, microporous silicoalu-
minophosphates (SAPO) have been used
as microporous solid zeolite SAPOs
(SAPO-5, -11, and -40) in bi-phasic sys-
tems at 170°C for furfural production [42].
In this study, the batch system was oper-
ated using 3% initial xylose concentration
and a water-toluene mixture (3:7). In the
absence of a solid catalyst, a small furfural
yield (5%) was obtained. The maximum
furfural yield (38%) and selectivity (55%)
were obtained using SAPO-11 (2%) under
the same conditions. The SAPO-5 cata-
lysts retained their catalytic activity after
three consecutive recyclings, suggesting
that these materials can be reused in the
reaction [42].
Although the analyses described
above have demonstrated various char-
acteristics of furfural production in solid
catalytic/ bi-phasic systems, the main raw
material for these analyses was commer-
cially available xylose (in solution). How-
ever, the hydrolysis of wood and agro-
based biomass results in hemicelluloses
with different molecular weights, implying
that the earlier investigations may not be
truly representative of furfural produc-
tion in a biorenery. Interestingly, in one
study, furfural production was performed
using mono- and polysaccharide (1%) so-
lutions at 170°C in the presence of 2%
aluminum-containing mesoporous TUD-
1 (AL-TUD1) [43]. In the case of mono-
saccharides, approximately 60% furfural
and 17%–20% HMF yields were obtained
using xylose and hexose respectively. In
the case of polysaccharides, simultaneous
hydrolysis and dehydration occurred un-
der these conditions. The conversion of
xylan or inulin to furfural or HMF yielded
approximately 18% and 20% respectively.
These results demonstrate that furfural
production is dependent on the proper-
ties of hemicelluloses and the content of
available pentosans in hemicelluloses. The
AL-TUD-1 catalyst used in this process
seems to be stable after recirculating in the
system for four consecutive runs, with no
signicant furfural yield loss.
As is well known, the surface prop-
erties of solid catalysts play an important
role in their performance. In this regard,
the inuence of surface modication of
solid catalysts in increasing furfural pro-
duction yield was investigated. In one
study, surface-modied silica (0.7 meq/g
sulphonic acid groups grafted onto the
surface) was used as a solid catalyst (2%)
in a one-phase DMSO system at 110°C–
170°C. In this system, the furfural selec-
tivity and yield were 82% and 75% re-
spectively. Adding unmodied catalyst
(MCM-41) resulted in 30% xylose conver-
sion and 4% furfural selectivity under the
same reaction conditions. Alternatively,
the silica was used in a bi-phasic system
of DMSO or water and toluene under the
same experimental conditions. In this case,
the maximum yield of 75% was obtained
using a mesoporous catalyst (MCM-41-
SO3Hs) and a water-toluene solvent after
24 h at 140°C [44]. The modied meso-
porous catalyst (i.e., MCM-41-SO3Hs)
used in the study showed a higher furfu-
ral selectivity and yield as well as a higher
conversion rate compared to unmodied
mesoporous catalyst (i.e., MCM-41) in bi-
phasic systems. Note that solid catalysts
may lose their surface activity after being
used in the reaction process. Therefore,
it is essential to investigate whether solid
catalysts are reusable. In the current study
using surface-modied silica, the stability
of the catalyst was tested through regen-
erating (washing) with methanol and treat-
ment with H2SO4. The use of the recov-
ered solid catalyst in furfural production
resulted in 37% lower xylose conversion
and 34% furfural selectivity under optimal
reaction conditions [44].
In another bi-phasic system with a
water-toluene mixture (7:1 ratio), sulphat-
ed zirconia materials (SZ), including sul-
phated zirconia (MSZ), alumina-modied
MSZ (MSAZ), and sulphated and persul-
phated zirconia supported on MCM-41
mesoporous silica (SZ-MCM-41, SAZ-
MCM-41, and PSZ-MCM-41 or PSZA-
MCM-41 respectively) were used as the
solid catalysts in a batch system [45]. In

J-FOR Journal of Science & Technology for Forest Products and Processes: VOL.2, NO.4, 2012 51
SPECIAL BIOREFINERY ISSUE
the absence of any catalyst, the bi-phasic
system yielded only 12% xylose conver-
sion and less than 1% furfural production
at 160°C after 4 h. Adding the unmodied
catalyst (SZ, 2%) to the system increased
the furfural yield to 9% and the xylose
conversion rate to 48%. However, apply-
ing different modied zirconia catalysts
(2%) enhanced the catalytic reaction and
increased the furfural yield (22%–46%)
and the xylose conversion rate (50%–96%)
under the same reaction conditions. The
maximum furfural yield of 46% with over
90% xylose conversion was obtained using
mesoporous modied (PSZA-MCM-41
and SAZ-MCM-41) zirconia catalysts
(2%) [45]. Among the catalysts used in the
study, SAZ-MCM-41 showed the highest
stability, with almost no signicant loss of
selectivity for furfural production even af-
ter three recycling runs [45].
In another study using surface-
functionalized (with sulphonated group)
mesoporous silica (SBA-15) [46], a batch
catalytic reaction was carried out using
3% commercial xylose concentration and
toluene-water (3:1 ratios) as a bi-phasic
system at different temperatures (130°C–
180°C). In the absence of catalyst, a low
xylose conversion rate and furfural selec-
tivity of 37.2% and 12.9% respectively
were obtained at 160°C using toluene-
water (3:1 ratio) as the solvent. Adding un-
modied mesoporous catalyst (SBA-15)
under the same reaction conditions slight-
ly increased the furfural selectivity and
yield to 13.5% and 5% respectively. The
maximum furfural selectivity and yield of
74% and 70% respectively were obtained
using SBA-15-SO3H(C) as the catalyst at
160°C. The furfural yields (70%) obtained
in this study using the solid acid catalyst
SBA-15-SO3H(C) were comparable to the
yield (approximately 70%) of the conven-
tional method using liquid H2SO4 acid un-
der otherwise the same conditions [46].
Regardless of the reaction media
used for furfural production, the main
advantage of using solid catalysts is their
technically viable separation from the re-
action media (and from products). This
will decrease the recovery cost of solid
catalysts at industrial scales. In addition,
this will address a part of the environmen-
tal concerns associated with the use of
mineral acids in conventional furfural pro-
cesses. Mesoporous solid catalysts such as
SBA-15-SO3H(C) or AL-TUD-1 showed
a higher furfural yield than microporous
solid catalysts such as SAPOs or AM-11.
The main disadvantages of these sol-
id-catalyst processes are that they do not
have a sufciently high xylose conversion
and furfural yield compared to conven-
tional mineral-acid processes; that solid
catalysts might be expensive or difcult to
produce at industrial scales; that lignocel-
lulosic biomass has seldom been used as a
feedstock to a furfural production process
in these systems (i.e., commercial xylose
has mainly been used as a feedstock), im-
plying that the results of the present stud-
ies may not be representative of furfural
production from lignocellulosic feedstock
in solid catalytic systems; and that large
quantities of solvents and solid catalysts in
bi-phasic systems make their commercial-
ization extremely challenging due to the
complexity of the process and the need to
recycle the materials. Moreover, some of
the solid catalysts seem to become deacti-
vated after a few runs, which makes their
recyclability unfavourable.
Production of wood chips is exten-
sive in Canada. However, the Canadian
pulp and paper sector has been faced with
a signicant decline in production in re-
cent years, which implies that the availabil-
ity of wood chips for the production of
other value-added chemicals (such as fur-
fural) is high [46]. As stated above, bi-pha-
sic systems have shown promising results
in terms of furfural production, but need
technical breakthroughs to facilitate their
commercialization. Moreover, advance-
ments in the treatment and recovery of
acidic wastes would help promote furfural
production in aqueous systems.
CONCLUSIONS
Furfural has been industrially produced in
mineral-acid solutions (aqueous-acid cata-
lytic solutions). Environmental concerns,
low yield, and poor furfural selectivity
(from hemicelluloses) are the main draw-
backs of these processes, which have led
to the closure of many furfural produc-
tion plants. Due to its wide range of ap-
plications, furfural has been considered as
one of the most promising value-added
chemicals that can be produced from lig-
nocellulosic biomass. As the need for fur-
fural increases globally, various processes
and raw materials are being considered for
furfural production. Large quantities of
lignocellulosic residues (wastes) from dif-
ferent agro- and forestry-based industries
are available globally. These materials have
been considered as feedstocks for furfural
production. The results for autocatalytic
processes are not convincing in terms of
yield and selectivity. The use of bi-phasic
systems has shown more promising results
in terms of furfural yields and selectivity.
However, these systems may not be com-
mercialized soon because the recovery of
solvents is not an easy task. Moreover, lit-
tle in-depth analysis has been carried out
on producing furfural from lignocellulosic
biomass. Therefore, research on solvent
recovery design and on the use of ligno-
cellulosic feedstock as raw material for
these systems is urgently needed. Solid-
catalytic systems have fewer environmen-
tal impacts and are technically feasible.
However, furfural yield and selectivity are
not as high as in mineral-acid processes.
In addition, little progress has been made
in using lignocellulosic biomass as raw
material for solid-catalyst systems. Exten-
sive research is ongoing to discover a solid
catalyst with high reaction performance
and recyclability. In this context, surface
modication of catalysts has also been
attempted. Although the results may be
promising, the effect of recycling on sur-
face modication is still unknown, which
presents a challenge for this approach. The
use of solid catalysts in bi-phasic systems
is unlikely to be industrially implemented
in the near future due to the complexity
of these systems.
ACKNOWLEDGEMENTS
The authors would like to acknowledge
NSERC for supporting this research
through an NSERC Discovery Grant.

23 J-FOR Journal of Science & Technology for Forest Products and Processes: VOL.2, NO.4, 2012
52
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