Hydrolysis-of-ionic-cellulose-to-glucose

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Bioresource Technology 167 (2014) 484–489 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech Hydrolysis of ionic cellulose to glucose Huyen Thanh Vo a,b, Vania Tanda Widyaya a, Jungho Jae a,b, Hoon Sik Kim c, Hyunjoo Lee a,b,⇑ a Clean Energy Research Center, Korea Institute of Science and Technology, Seoul 136-791, South Korea University of Science and Technology, Deajeon 305-355, South Korea c Department of Chemistry, Kyung Hee University, Seoul 130-701, South Korea b h i g h l i g h t s g r a p h i c a l a b s t r a c t  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. 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 synthesized 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 demonstrated 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 biobutanol as well as for platform chemicals such as 5-hydroxymethylfurfural (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. ⇑ 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). http://dx.doi.org/10.1016/j.biortech.2014.06.025 0960-8524/Ó 2014 Elsevier Ltd. All rights reserved. The major obstacles for the hydrolysis of cellulose in mild conditions 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 catalysts 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 H.T. Vo et al. / Bioresource Technology 167 (2014) 484–489 activity. 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, sulfonated 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 oxides have also been used as acid catalysts for the hydrolysis of biopolymers. Proton-containing transition metal oxide, HNbMoO6, exhibited a remarkable performance for the hydrolysis of cellobiose and starch (Takagaki et al., 2008). This catalyst achieved 20% glucose yield in the hydrolysis of starch at 100 °C for 15 h. However, for the hydrolysis of cellulose, the catalytic activity of HNbMoO6 was meager due to the low density of Bronsted acid site as well as low surface area. In heterogeneous reaction, due to the water insoluble characteristic of cellulose, only the exterior acid sites of the catalysts can be accessible to cellulose and this leads to low hydrolysis efficiency. 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 cellulose occur simultaneously. For instance, by using ILs (chloride anionic ILs such as 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]))and acid catalyst, the conversion of cellulose to sugars 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 (H2SO4 and 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 conversion 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 dimethylimidazolium methylphosphite ([Dmim][(OCH3)(H)PO2]) formed ionic cellulose, 1,3-dimethylimidazolium cellulose phosphite (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. 485 (Kim et al., 2010). Carboxymethylcellulose (CMC, H-form) was synthesized by the neutralization of CMC-Nawithphosphoric acid. This process was described in Supplementary data (Fig. S1, Supplementary 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 Chemical Co. Activated carbon was received from Strem Chemicals 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 solution was dropped with 20 mL of acetonitrile to produce the precipitates. 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 calculated 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 were analyzed by DNS method (Supplementary data) (Li and Zhao, 2007; Miller, 1959).The concentration of cellobiose, glucose, fructose, levulinic acid and HMF were calculated based on the standard 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 2. Experimental 2.1. Materials Microcrystalline cellulose (MCC) and other cellulose derivatives, such as cellulose acetate, ethyl cellulose, methyl cellulose, sodiumcarboxymethyl cellulose (CMC-Na) and hydroxyethyl cellulose, were purchased from Sigma–Aldrich Chemical Co. 1,3dimethylimidazolium 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 Sulfonated active carbon was prepared as described in the reference (Suganuma et al., 2008). The activated carbon powder (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 hydrothermally treated in a bomb-reactor at 150 °C for 3 h for the complete removal of H2SO4 physically 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 vacuum at 70 °C for 12 h. The FT-IR spectrum of synthesized carbon appeared the vibration bands at 1372 cm1 (S=O stretching) and 486 H.T. Vo et al. / Bioresource Technology 167 (2014) 484–489 1025 cm1 (SO3-stretching) giving the evidence of the presence of –SO3H groups in the resulting material (Fig. S2, Supplementary data). Sulfur content of the catalyst was determined to be 0.80 wt% by CHNOS elemental analysis, corresponding to 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 characterized 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 analyzed by 1H-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 presence of various kinds of catalyst as shown in Table 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 reaction, 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 produced cellobiose and glucose with yields of 8.4% and 14.6%, respectively (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 catalysts could be ascribed to the acidic ionic compound [Dmim][(OH)(H)PO2] (pKa = 2.9), which was separated from the IC, as shown in Scheme 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 produced saccharides. In fact, the addition of [Dmim][(OH)(H)PO2] increased the yield of glucose up to 23.5% (Table 1, Entry 2), however, compared to other sulfonic acid-based catalysts, the catalytic activity was not high due to its relatively weak acidity. Besides [Dmim][(OH)(H)PO2], we also observed some white precipitates after the reaction. IR and XRD analyses revealed that the precipitates were decrystallized cellulose (DC) (Figs. S4 and Table 1 Ionic cellulose hydrolysis using different catalysts.a Entry 1 2 3 4 5 6 7 Catalyst – [Dmim][(OH) (H)PO2] H3PO3 H2SO4 AC-SO3H Amberlyst-15 Nafion-NR50 Yield (%) H+/GUb TRS Cellobiose Glucose HMF 0 4.0 0.05 0.05 0.05 0.05 0.05 24.6 30.6 32.0 36.8 52.0 42.5 30.3 8.4 5.6 1.5 1.6 5.6 4.0 0.3 14.6 23.5 28.9 30.4 42.5 31.8 27.8 1.7 5.4 2.6 1.8 0.5 2.4 1.6 a Reaction condition: cellulose derivative (100 mg), water (5 mL) and acid catalyst (0.025 mmol), 150 °C, 12 h. b H+/GU is the molar ratio of H+ (acid catalyst) to glucose unit in IC. S5 in Supplementary 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 glucose unit (GU) in IC was set to 0.05. Polyprotic acids such as H3PO3 and H2SO4 were regarded as monoprotic acids due to the decreased acidity from the second proton. As shown in Table 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 conducted in the absence of catalysts (Table 1, Entry 3 and 4). However, interestingly, in the case of heterogeneous AC-SO3Hcatalyzed 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 H2SO4 system. 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 hydrolyzed to [Dmim][(OH)(H)PO2] and methanol using AC-SO3H and H2SO4 at 100 °C (Scheme S3, Supplementary data). Fig. S6 (in Supplementary data) reveals the formation of methanol in H2SO4 catalyzed 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 hydrolysis 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 1butyl-3-methylimidazolium chloride ([Bmim]Cl) (Kim et al., 2010), revealed that the catalytic activities of both H2SO4 and AC-SO3H for this reaction were very poor (Table 2, Entry 1). Table 1 also shows that other heterogeneous catalysts, Amberlyst-15 and Nafion-NR50 obtained 31.8% and 27.8% of glucose yields which were comparable to those of homogeneous acid catalysts, 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 ACSO3H, Amberlyst-15, and Nafion-NR50 are 11, 2.2, and 13, respectively (Rys and Steinegger, 1979; Moa et al., 2008; 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 surface area could absorb IC more efficiently, thereby facilitating the hydrolysis of IC. Furthermore, as Onda et al. reported, the presence of hydrophilic functional groups, COOH and OH, on AC-SO3H 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 in Fig. 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 tendency was more noticeable at no catalyst (NC) and H2SO4 catalyst systems with an increase in HMF formation. After 24 h, HMF yield increased to 9.9% and 4.3% at NC and H2SO4 systems, respectively. HMF is known to be produced more favorably in lower glucose concentration and weak acid medium (McKibbins et al., 1962). 487 H.T. Vo et al. / Bioresource Technology 167 (2014) 484–489 Table 2 Hydrolyses of various water-soluble cellulose derivatives.a Entry 1 2 3 4 5 6 a b c Cellulose type Microcrystalline cellulose (MCC) Decrystallized cellulose (DC) Methyl cellulose (MC) Hydroxyethyl cellulose (HEC) Carboxymethyl cellulose (CMC) Ionic cellulose (IC) YieldTRS (%) Solubilityb No catalyst H2SO4 AC-SO3H – – 2 1 1c 18 2.0 2.7 2.3 5.4 6.4 24.6 2.5 4.5 15.3 34.8 29.1 36.8 2.4 4.9 10.9 27.0 26.1 52.0 Reaction condition: cellulose derivative (0.45 mmol of glucose derivative unit), water (5 mL) and acid (0.025 mmol), 150 °C, 12 h. Solubility in water: gram of cellulose derivative/100 g of water at 25 °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 H2SO4 and AC-SO3H. Interestingly, 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 glucose 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 in Fig. 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 and H2SO4-catalyzed reactions also showed maximum glucose 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. 2 also 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 H2SO4-catalyzed reaction, the HMF yield reached Fig. 2. The effect of AC-SO3H dosage (a) and the reusability of AC-SO3H (b) in ionic cellulose hydrolysis at 150 °C for 12 h. 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 formation of humin from glucose and HMF at a high reaction temperature (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 in Fig. 2a. As the weight ratio of catalyst to IC was increased from 0 to 1, the yield of glucose 488 H.T. Vo et al. / Bioresource Technology 167 (2014) 484–489 was 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 cellobiose 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 analyzed 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 sulfuric acid leached from 1 g of AC-SO3H were 0.026 and 0.024 mmol, respectively, which correspond to about 10% of –SO3H concentration on fresh AC-SO3H. It can be confirmed that the catalytic activity 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 prolonged to 18 h. These results infer AC-SO3H can maintain its catalytic activity after several times reuse. 3.2. Hydrolysis of water-soluble cellulose derivatives Hydrolyses of some water-soluble cellulose derivatives which chemical structures are shown in Fig. S7 were conducted w/wo 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, hydrolysis of microcrystalline cellulose (MMC) and decrystallized cellulose (DC) obtained from [Bmim][Cl]-pretreated MMC were also conducted (Kim et al., 2010). Table 2 presents 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 H2SO4 and AC-SO3H, the TRS yields were enhanced with all the water-soluble cellulose derivatives while MMC, DC gave a marginal increase in TRS value, indicating that water solubility of cellulose derivative is a decisive factor in the acid-catalyzed hydrolysis. TRS yields achieved from HEC hydrolyses were 34.8% and 27.0% with H2SO4 and 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 H2SO4 than those with AC-SO3H, because of the low solubility of cellulose in water which reduced the accessibility 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 H2SO4 and 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 H2SO4 or AC-SO3H. Although the IC obtained high glucose yield, after the reaction, the glucose and ionic material [Dmim][(OH)(H)PO2] 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 synthesis of IC by the reaction with cellulose. The formed glucose and [Dmim][(OH)(H)PO2] mixture could be separated by several methods which have recently been studied such as chromatography (Mai et al., 2012), adsorbents (Francisco et al., 2011) and membranes (Abels et al., 2013), or glucose can be transformed to volatile 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 catalyst. Among the tested catalysts in IC hydrolysis, sulfonated active carbon catalyst (AC-SO3H) exhibited a better performance in glucose yield than homogeneous catalysts due to the fast dephosphorylation 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 demonstrated its good reusability. IC also showed superior hydrolysis performance to any other water soluble cellulose with both H2SO4 and AC-SO3H. Acknowledgements This research was supported by Creative Allied Project (CAP) of the Korea Research Council of Fundamental Science and Technology (KRCF)/Korea Institute of Science and Technology (KIST) (Project No. 2E24832). Appendix A. 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