Although the con-version of cellulose could be increased much by using ionic liquids as a solvent for the hydrolysis, the use of corrosive mineral acid and/or low glucose yields is the l
Trang 1Hydrolysis of ionic cellulose to glucose
Huyen Thanh Voa,b, Vania Tanda Widyayaa, Jungho Jaea,b, Hoon Sik Kimc, Hyunjoo Leea,b,⇑
a
Clean Energy Research Center, Korea Institute of Science and Technology, Seoul 136-791, South Korea
b
University of Science and Technology, Deajeon 305-355, South Korea
c
Department of Chemistry, Kyung Hee University, Seoul 130-701, South Korea
h i g h l i g h t s
Water-soluble ionic cellulose was
synthesized from cellulose and ionic
liquid
Hydrolysis of water-soluble cellulose
generated glucose in aqueous media
Sulfonated active carbon showed high
catalytic activity and good reusability
g r a p h i c a l a b s t r a c t
a r t i c l e i n f o
Article history:
Received 24 March 2014
Received in revised form 5 June 2014
Accepted 8 June 2014
Available online 24 June 2014
Keywords:
Cellulose
Water-soluble
Hydrolysis
Ionic liquid
Glucose
a b s t r a c t
Hydrolysis of ionic cellulose (IC), 1,3-dimethylimidazolium cellulose phosphite, which could be synthe-sized from cellulose and dimethylimidazolium methylphosphite ([Dmim][(OCH3)(H)PO2]) ionic liquid, was conducted for the synthesis of glucose The reaction without catalysts at 150 °C for 12 h produced glucose with 14.6% yield To increase the hydrolysis yield, various acid catalysts were used, in which the sulfonated active carbon (AC-SO3H) performed the best catalytic activity in the IC hydrolysis In the presence of AC-SO3H, the yields of glucose reached 42.4% and 53.9% at the reaction condition of
150 °C for 12 h and 180 °C for 1.5 h, respectively; however the yield decreased with longer reaction time due to the degradation of glucose Consecutive catalyst reuse experiments on the IC hydrolysis demon-strated the catalytic activity of AC-SO3H persisted at least through four successive uses
Ó 2014 Elsevier Ltd All rights reserved
1 Introduction
Cellulose, the most abundant biopolymer in nature, attracts
much interest as a resource for biofuels like bioethanol and
biobut-anol as well as for platform chemicals such as
5-hydroxymethyl-furfural (HMF) and levulinic acid (LA) In the conversion of
cellulose to fuels or chemicals, the first step is depolymerization
of cellulose to its monomeric compound, glucose, via hydrolysis
The major obstacles for the hydrolysis of cellulose in mild condi-tions are the high crystallinity of cellulose resulting from strong inter- and intra-molecular hydrogen bonds and the low solubility
of cellulose in water and common organic solvents
Homogeneous catalysts such as mineral acids (Camacho et al.,
1996) and enzymes (Katz and Reese, 1968) demonstrate superior hydrolysis activity to heterogeneous catalysts due to their easier accessibility to the reaction center However, homogeneous cata-lysts have many disadvantages such as reaction system corrosion, waste recycle expense for mineral acids and cause of the undesired glucose degradation products like HMF in enzymatic processes Heterogeneous catalysts have been widely studied for cellulose hydrolysis due to their advantages in separation and catalytic http://dx.doi.org/10.1016/j.biortech.2014.06.025
0960-8524/Ó 2014 Elsevier Ltd All rights reserved.
⇑Corresponding author at: Clean Energy Research Center, Korea Institute of
Science and Technology, Seoul 136-791, South Korea Tel.: +82 2958 5868; fax: +82
2958 5809.
E-mail address: hjlee@kist.re.kr (H Lee).
Contents lists available atScienceDirect Bioresource Technology
j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / b i o r t e c h
Trang 2activity These catalysts include sulfonated active carbon
(Suganuma et al., 2008; Toda et al., 2005), polymer based acids
(Rinaldi et al., 2010), and layer-transition metal oxides (Takagaki
et al., 2008; Zhang and Fang, 2012) Among these materials,
sulfo-nated active carbon showed superior catalytic activity for cellulose
hydrolysis In a recent report, the hydrolysis of microcrystalline
cellulose (MCC) with sulfonated activated carbon achieved 64% of
total reducing sugars (TRS) yield, with 4% of glucose yield at
100 °C for 6 h (Suganuma et al., 2008) Layer-transition metal
oxi-des have also been used as acid catalysts for the hydrolysis of
bio-polymers Proton-containing transition metal oxide, HNbMoO6,
exhibited a remarkable performance for the hydrolysis of
cellobi-ose and starch (Takagaki et al., 2008) This catalyst achieved 20%
glucose yield in the hydrolysis of starch at 100 °C for 15 h
How-ever, for the hydrolysis of cellulose, the catalytic activity of
HNb-MoO6was meager due to the low density of Bronsted acid site as
well as low surface area
In heterogeneous reaction, due to the water insoluble
charac-teristic of cellulose, only the exterior acid sites of the catalysts
can be accessible to cellulose and this leads to low hydrolysis
effi-ciency To enhance the accessibility of water molecules or catalyst
sites on the hydrolysis centers of cellulose chains, various kinds of
pretreatment have been employed, for example, ball milling (Onda
et al., 2008) and ionic liquid (Li and Zhao, 2007) treatment
Ionic liquids (IL) can be used either as a pretreatment reagent
that destroys the cellulose crystalline structure before hydrolysis
or as a reaction solvent in which dissolution and hydrolysis of
cel-lulose occur simultaneously For instance, by using ILs (chloride
([Bmim][Cl]))and acid catalyst, the conversion of cellulose to
sug-ars could be increased even under mild reaction conditions Li
et al obtained about 77% of TRS yield and maximum 43% glucose
yield by using [Bmim][Cl] and mineral acids (H2SO4and HCl) at
100 °C for 9 h (Li and Zhao, 2007) At the catalytic system of
[Bmim][Cl] and solid acid catalyst, about 28% of TRS yield was
achieved at 100 °C for 5 h with Amberlyst-15 DRY resin (Rinaldi
et al., 2008) and 69% of TRS yield was produced at 130 °C for 3 h
with sulfonated active carbon (Guo et al., 2012) Although the
con-version of cellulose could be increased much by using ionic liquids
as a solvent for the hydrolysis, the use of corrosive mineral acid
and/or low glucose yields is the limitation of these methods
Recently, we reported that the reaction of cellulose with
formed ionic cellulose, 1,3-dimethylimidazolium cellulose
phos-phite (Scheme S1, Supplementary data), which can be dissolved
in water due to the ionic structure (Vo et al., 2012) In this paper,
we studied the hydrolysis of this ionic cellulose dissolved in water
to obtain glucose using various kinds of acid catalyst (Scheme S2,
Supplementary data) We also used other water-soluble cellulose
derivatives for hydrolysis and compared the TRS yields with our
ionic cellulose
2 Experimental
2.1 Materials
Microcrystalline cellulose (MCC) and other cellulose
deriva-tives, such as cellulose acetate, ethyl cellulose, methyl cellulose,
sodiumcarboxymethyl cellulose (CMC-Na) and hydroxyethyl
cellulose, were purchased from Sigma–Aldrich Chemical Co
1,3-dimethylimidazolium methylphosphite ([Dmim][(OCH3)(H)PO2])
was prepared according to our recent report (Vo et al., 2012)
Solvents were purchased from J.T Baker and used as received
Decrystalized cellulose (DC) was synthesized by dissolving MCC
in [Bmim]Cl (10 wt%) at 130 °C for 2 h as described in literature
(Kim et al., 2010) Carboxymethylcellulose (CMC, H-form) was syn-thesized by the neutralization of CMC-Nawithphosphoric acid This process was described in Supplementary data (Fig S1, Supplemen-tary data) Catalysts for hydrolysis like phosphorous acid, sulfuric acid, dry Amberlyst-15 (4.8 mmol/g acidity) and Nafion-NR50 (0.9 mmol/g acidity) were obtained from the Sigma–Aldrich Chem-ical Co Activated carbon was received from Strem ChemChem-icals Inc 2.2 Preparation of ionic cellulose
Microcrystalline cellulose (0.5 g) and [Dmim][(OCH3)(H)PO2] (5 g) were loaded into 25 mL one-necked round bottom flask The mixture was then heated to 120 °C in an oil bath and allowed to react for 1 h After the reaction, the mixture was cooled to room temperature and diluted with 10 mL of water To this diluted solu-tion was dropped with 20 mL of acetonitrile to produce the precip-itates The resulting precipitates were filtered and washed with acetonitrile at least three times, and finally, vacuum dried at room temperature overnight to give the desired ionic cellulose The degree of substitution of phosphorous in ionic cellulose was calcu-lated based on the phosphorous content as described in previous literature (Vo et al., 2012) Ionic cellulose obtained has the degree
of substitution of phosphorous of 0.36 which corresponded to the molecular weight of ionic glucose unit of 219 g/mol
2.3 Hydrolysis of ionic cellulose Typically, 0.1 g of ionic cellulose dissolved in 5 mL of distilled water and catalyst were introduced into a sealed pressure glass tube (Ace, 15 mL, pressure limit is 20 bar) The glass tube was placed in an oil bath which was maintained at 150 °C for the desired reaction time After the reaction, sample was cooled to room temperature and centrifuged at a rate of 10,000 rpm for
10 min to separate the solid and liquid products
For the product analyses, solid product was washed with water and dried under vacuum for 12 h, and was then characterized by FT-IR Aqueous solution was analyzed using HPLC (Younglin 9100) equipped with RI detector (YL9170) and column (Shodex SUGAR-KS802, 8.0 300 (mm) ID) which was maintained at
80 °C The mobile phase was deionized water at a flow rate of 0.6 mL/min The total reducing sugar (TRS) in the liquor samples
Zhao, 2007; Miller, 1959).The concentration of cellobiose, glucose, fructose, levulinic acid and HMF were calculated based on the stan-dard curve obtained with known concentrations of the substances The yields of each component were calculated based on the total glucose unit in the ionic cellulose used as follows
Yield of glucose ð%Þ ¼ 100
½glucose produced ðmolÞ=IC used ðgÞ=219ðmol=gÞ
2.4 Preparation and characterization of sulfonated carbon material Sulfonated active carbon was prepared as described in the
(1 g) was stirred with concentrated sulfuric acid (96%, 20 mL) at
150 °C for 24 h under N2 gas with flow rate of 50 mL/min After cooling to the room temperature, the black solid was repeatedly washed with distilled-water (3 L) The solid was then hydrother-mally treated in a bomb-reactor at 150 °C for 3 h for the complete removal of H2SO4physically adsorbed on the carbon material The solid was washed again with water until pH of solution was about 6–7 Finally, the sulfonated active carbon was dried under the vac-uum at 70 °C for 12 h The FT-IR spectrum of synthesized carbon appeared the vibration bands at 1372 cm1(S=O stretching) and
Trang 31025 cm1(SO3-stretching) giving the evidence of the presence of
–SO3H groups in the resulting material (Fig S2, Supplementary
0.25 mmol of SO3H/g of carbon The BET surface area of catalyst
was 1175 m2/g
2.5 Instrument
The catalyst was characterized by FT-IR, elemental analysis, and
BET techniques Infrared spectra were obtained by using Nicolet
FT-IR spectrometer (iS10, USA) equipped with a SMART MIRACLE
accessory C, H, N, O, and S contents of the catalyst were
character-ized by CHNOS elemental analyzer (Model: Fisons EA 1108) The
Brunauer–Emmet–Teller (BET) surface area was determined by a
Belsorp-mini II instrument (BEL Inc., Japan) Products were
ana-lyzed by1H-NMR recorded using Bruke Avance 400
3 Results and discussions
3.1 Hydrolysis of ionic cellulose
The hydrolysis of ionic cellulose (IC) was conducted in the
pres-ence of various kinds of catalyst as shown inTable 1 In a typical
reaction, IC (100 mg, 0.45 mmol of glucose unit) dissolved in water
(5 ml) and the catalyst (0.025 mmol of H+) was added in a sealed
pressure glass tube and heated at 150 °C for 12 h After the
reac-tion, the product solution was analyzed by HPLC The results
revealed that not only glucose but also cellobiose, 5-HMF and small
amounts of levoglucosan and levulinic acid were formed together
3.1.1 Hydrolysis in the absence of catalyst
In the absence of catalyst, the hydrolysis of ionic cellulose
pro-duced cellobiose and glucose with yields of 8.4% and 14.6%,
respec-tively (Table 1, Entry 1), indicating that the hydrolysis of IC in
water happened substantially even without additional catalysts
The formation of glucose from the hydrolysis of IC without
[Dmim][(OH)(H)PO2] (pKa = 2.9), which was separated from the
IC, as shown inScheme 1 At 150 °C, hydrolysis of the C–O–P bond
in IC could also happen to generate [Dmim][(OH)(H)PO2].1H-NMR
spectrum of hydrolysis product in Fig S3(Supplementary data)
verified the existence of [Dmim][(OH)(H)PO2] along with the
pro-duced saccharides In fact, the addition of [Dmim][(OH)(H)PO2]
increased the yield of glucose up to 23.5% (Table 1, Entry 2),
how-ever, compared to other sulfonic acid-based catalysts, the catalytic
activity was not high due to its relatively weak acidity
precipitates after the reaction IR and XRD analyses revealed that
the precipitates were decrystallized cellulose (DC) (Figs S4 and
S5inSupplementary data) Furthermore, no glucose or cellobiose having phosphite groups were detected after the reaction These results suggest, in the absence of extra catalyst, the hydrolysis of C–O–P bond occurred faster than that of glucosidic bond in the hydrolysis of IC
3.1.2 Effect of acid catalysts Various homogeneous and solid acid catalysts were tested for the reaction The molar ratio of the H+in acid catalyst to the glu-cose unit (GU) in IC was set to 0.05 Polyprotic acids such as
H3PO3and H2SO4 were regarded as monoprotic acids due to the decreased acidity from the second proton As shown inTable 1, the H3PO3(pKa1= 2.0) and H2SO4 (pKa1= 3.0) produced glucose with yields of 28.9% and 30.4%, respectively, which, as expected, were two times higher than that produced from the reaction con-ducted in the absence of catalysts (Table 1, Entry 3 and 4) However, interestingly, in the case of heterogeneous AC-SO3 H-catalyzed reaction, the TRS and glucose yields reached 52.0% and 42.5% when the H+/GU ratio was 0.05 (Table 1, Entry 5), which were higher than those at H2SO4system The higher glucose and TRS yields of AC-SO3H catalyst could be ascribed to the slower C–O–P hydrolysis rate than that of homogeneous H2SO4
To verify this possibility, [Dmim][(OCH3)(H)PO2] was hydro-lyzed to [Dmim][(OH)(H)PO2] and methanol using AC-SO3H and
H2SO4at 100 °C (Scheme S3, Supplementary data).Fig S6(in Sup-plementary data) reveals the formation of methanol in H2SO4 cat-alyzed reaction was faster than that at AC-SO3H system Therefore,
it could be concluded that, in the IC hydrolysis catalyzed by H2SO4, dephosphorylation proceeded faster than glycosidic bond hydroly-sis to generate insoluble cellulose which could not be hydrolyzed anymore In fact, the hydrolysis of decrystallized cellulose (DC), which was obtained from the solution of cellulose dissolved in
2010), revealed that the catalytic activities of both H2SO4 and AC-SO3H for this reaction were very poor (Table 2, Entry 1)
Table 1also shows that other heterogeneous catalysts, Amber-lyst-15 and Nafion-NR50 obtained 31.8% and 27.8% of glucose yields which were comparable to those of homogeneous acid cat-alysts, but lower than that of AC-SO3H Although these three solid acid catalysts have SO3H functional group, they are different in their acid strength The Hammett’s acidity values (H0) of
Suganuma et al., 2008) However, the differences in AC-SO3H, Amberlyst-15, and Nafion-NR50 performances seem most likely
to come from the surface area not from the acidity The surface area of AC-SO3H is 1,177 m2/g while those of Amberlyst-15 and Nafion-NR50 are only 45 and <1 m2/g, respectively The large sur-face area could absorb IC more efficiently, thereby facilitating the hydrolysis of IC Furthermore, as Onda et al reported, the presence
promoted the accessibility of IC to the reaction sites, SO3H, resulting in enhanced IC hydrolysis activity (Onda et al., 2008) 3.1.3 Effect of reaction condition
The effects of reaction time and temperature on the yields of glucose and HMF were investigated at the various catalyst systems, and the results are shown inFig 1a As the reaction time increased
to 12 h at 150 °C, the yields of glucose increased linearly with all of the tested catalysts, whereas the yields of HMF remained constant However, after 12 h, the glucose started to degrade and the ten-dency was more noticeable at no catalyst (NC) and H2SO4catalyst systems with an increase in HMF formation After 24 h, HMF yield increased to 9.9% and 4.3% at NC and H2SO4systems, respectively HMF is known to be produced more favorably in lower glucose concentration and weak acid medium (McKibbins et al., 1962)
Table 1
Ionic cellulose hydrolysis using different catalysts a
Entry Catalyst Yield (%)
H +
/GU b TRS Cellobiose Glucose HMF
2 [Dmim][(OH) (H)PO 2 ] 4.0 30.6 5.6 23.5 5.4
5 AC-SO 3 H 0.05 52.0 5.6 42.5 0.5
6 Amberlyst-15 0.05 42.5 4.0 31.8 2.4
7 Nafion-NR50 0.05 30.3 0.3 27.8 1.6
a
Reaction condition: cellulose derivative (100 mg), water (5 mL) and acid
catalyst (0.025 mmol), 150 °C, 12 h.
Trang 4Interestingly, at the AC-SO3H-catalyzed reaction, the glucose also
degraded after 12 h, but the rate of degradation was slightly lower
than those of NC and H2SO4 Furthermore, the concentration of
HMF was constant after 24 h The different tendencies in the
glu-cose degradation and the HMF formation with different catalysts
results from the existence of homogeneous acidic proton in the
reaction
The hydrolysis of IC was also conducted at 180 °C and the
results are depicted inFig 1b In AC-SO3H catalyzed reaction, the
maximum glucose yield obtained was 53.8% for 1.5 h reaction,
which was 11% greater than that obtained at 150 °C for 12 h NC
yields of 31.4% and 41.6%, respectively, with 3 h reaction All these
glucose yields were higher than those obtained at 150 °C for 12 h
using the same catalyst systems However, along with the increase
in the hydrolysis rate, the glucose degradation rate was faster at
180 °C.Fig 2also shows that the catalyst with the highest activity,
AC-SO3H, decomposed the formed glucose more quickly than other
catalysts
A higher reaction temperature affects the yield of HMF At NC
system, HMF yield increased to 15% after a 12 h reaction at
180 °C, while in HSO -catalyzed reaction, the HMF yield reached
the maximum of 10% at 3 h and started to decrease after that At the same time, the formation of dark-brown precipitates was observed in H2SO4-catalyzed reaction at 180 °C, indicating the for-mation of humin from glucose and HMF at a high reaction temper-ature (Girisuta et al., 2006; Souza et al., 2012) Previous kinetic studies of glucose degradation done by Girisuta et al revealed that the activation energy for the humin formation from glucose is higher than that for the other degraded products.This conclusion suggests that glucose is favored to form humin at high temperature and in acidic medium (Girisuta et al., 2006) On the other hand, the rapid degradation of glucose did not accompany the increase of HMF yield in the AC-SO3H catalyzed reaction, thereby suggesting the decomposition of glucose to other materials However, we did not detect any evidence of the decomposed materials like dark-brown precipitates as well as other presumable peaks from HPLC analysis, due to the absorption of degraded materials by high surface area AC-SO3H
The effect of catalyst amount on the IC hydrolysis was also investigated and the results are shown inFig 2a As the weight ratio of catalyst to IC was increased from 0 to 1, the yield of glucose
Table 2
Hydrolyses of various water-soluble cellulose derivatives a
Solubility b
No catalyst H 2 SO 4 AC-SO 3 H
5 Carboxymethyl cellulose (CMC) 1 c
a
Reaction condition: cellulose derivative (0.45 mmol of glucose derivative unit), water (5 mL) and acid (0.025 mmol), 150 °C, 12 h.
b
Solubility in water: gram of cellulose derivative/100 g of water at 25 °C.
c
Solubility of CMC in water at 100 °C: carboxymethyl cellulose (H-form) is insoluble in cold water but soluble in hot water.
Fig 1 The yields of glucose and 5-HMF in ionic cellulose hydrolysis at 150 °C (a)
and 180 °C (b) without catalyst (NC) and with H 2 SO 4 and AC-SO 3 H.
Fig 2 The effect of AC-SO 3 H dosage (a) and the reusability of AC-SO 3 H (b) in ionic cellulose hydrolysis at 150 °C for 12 h.
Trang 5was linearly increased However, at the weight ratio higher than 1,
the glucose yield was decreased, indicating that the catalyst also
degrade the formed glucose On the other hands, the yields of
cel-lobiose and 5-HMF were decreased with increasing the catalyst
amount
3.1.4 Reusability of AC-SO3H catalyst
After IC hydrolysis at 150 °C for 12 h, AC-SO3H was separated
from the reaction solution by decantation and reused for the next
reactions.Fig 2b shows that the glucose yield gradually decreased
in subsequent reactions
The possibility of acid leaching from AC-SO3H was examined at
150 and 180 °C 0.1 g of solid acid in 5 mL of deionized water in a
sealed tube was heated at the reaction temperature for 12 h at
150 °C and for 3 h at 180 °C After that, the aqueous phase was
ana-lyzed by ion chromatography The results revealed, at the reaction
condition of 150 °C for 12 h and 180 °C for 3 h, the amounts of
sul-furic acid leached from 1 g of AC-SO3H were 0.026 and 0.024 mmol,
respectively, which correspond to about 10% of –SO3H
concentra-tion on fresh AC-SO3H It can be confirmed that the catalytic
activ-ity of AC-SO3H is ascribed to the heterogeneous part rather than
homogeneous part by the leached H2SO4
Although the glucose yields decreased at the consecutive runs,
the yields of cellobiose increased, and almost similar TRS yields
were obtained for all runs At the 4th run, the yield of glucose
restored to the maximum value of 41.3% when reaction time
pro-longed to 18 h These results infer AC-SO3H can maintain its
cata-lytic activity after several times reuse
3.2 Hydrolysis of water-soluble cellulose derivatives
Hydrolyses of some water-soluble cellulose derivatives which
acid catalysts In a typical reaction, cellulose derivative (0.45 mmol
based on the glucose unit) dissolved in water (5 ml) and catalyst
(0.025 mmol) were heated at 150 °C for 12 h To compare the
hydrolysis yields of cellulose derivatives with different structures,
TRS values were measured by DNS method Furthermore,
hydroly-sis of microcrystalline cellulose (MMC) and decrystallized cellulose
(DC) obtained from [Bmim][Cl]-pretreated MMC were also
con-ducted (Kim et al., 2010)
Table 2presents the yields of TRS obtained from the hydrolysis
of MMC and decrystallized MMC (DC), methyl cellulose (MC),
hydroxyethyl cellulose (HEC), carboxymethyl cellulose (CMC),
and ionic cellulose (IC) In the absence of catalysts, very small
amounts of water-soluble oligomers were obtained from MMC,
DC, and other water soluble cellulose, whereas ionic cellulose gave
a TRS yield of 24.6%
In the presence of acid catalysts H2SO4and AC-SO3H, the TRS
yields were enhanced with all the water-soluble cellulose
deriva-tives while MMC, DC gave a marginal increase in TRS value,
indicat-ing that water solubility of cellulose derivative is a decisive factor in
the acid-catalyzed hydrolysis TRS yields achieved from HEC
hydro-lyses were 34.8% and 27.0% with H2SO4and AC-SO3H, respectively,
while CMC produced 29.1% and 26.1% with H2SO4 and AC-SO3H,
respectively Both water-soluble cellulose substrates yielded
greater TRS values with H2SO4than those with AC-SO3H, because
of the low solubility of cellulose in water which reduced the
acces-sibility of cellulose chains to the acid sites on AC-SO3H Among the
tested water-soluble cellulose, MC produced the lowest yield of TRS
values of 15.3% and 10.9% with H2SO4and AC-SO3H, respectively,
which resulted from the solubility decrease of MC in water at high
temperature Overall, IC showed superior hydrolysis performance
to any other water soluble cellulose, using either H2SO4or AC-SO3H
Although the IC obtained high glucose yield, after the reaction,
the glucose and ionic material [Dmim][(OH)(H)PO] should be
sep-arated for the utilization of produced glucose We confirmed that the isolated [Dmim][(OH)(H)PO2] can be used again for the synthe-sis of IC by the reaction with cellulose The formed glucose and [Dmim][(OH)(H)PO2] mixture could be separated by several meth-ods which have recently been studied such as chromatography (Mai et al., 2012), adsorbents (Francisco et al., 2011) and mem-branes (Abels et al., 2013), or glucose can be transformed to vola-tile materials in the presence of [Dmim][(OH)(H)PO2]
4 Conclusions The hydrolysis of ionic cellulose (IC) at 150 °C produced glucose with 14.6% in the absence of catalysts because the released [Dmim][(OH)(H)PO2] species from IC acted as a homogeneous cat-alyst Among the tested catalysts in IC hydrolysis, sulfonated active carbon catalyst (AC-SO3H) exhibited a better performance in glu-cose yield than homogeneous catalysts due to the fast dephospho-rylation of IC at homogeneous catalyst systems A glucose yield of 53.9% was obtained at 180 °C for 1.5 h and AC-SO3H also demon-strated its good reusability IC also showed superior hydrolysis per-formance to any other water soluble cellulose with both H2SO4and AC-SO3H
Acknowledgements This research was supported by Creative Allied Project (CAP) of the Korea Research Council of Fundamental Science and Technol-ogy (KRCF)/Korea Institute of Science and TechnolTechnol-ogy (KIST) (Pro-ject No 2E24832)
Appendix A Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.biortech.2014 06.025
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