Effective Hydrolysis of Cellulose into Glucose over Sulfonated Sugar

Article pubs.acs.org/IECR

Effective Hydrolysis of Cellulose into Glucose over Sulfonated SugarDerived Carbon in an Ionic Liquid Min Liu,*,† Songyan Jia,†,‡ Yanyan Gong,† Chunshan Song,†,§,∥ and Xinwen Guo*,† †

State Key Laboratory of Fine Chemicals, PSU−DUT Joint Center for Energy Research, School of Chemical Engineering, Dalian University of Technology, Dalian, Liaoning 116024, China ‡ Dalian National Lab for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China § EMS Energy Institute, PSU-DUT Joint Center for Energy Research and Department of Energy & Mineral Engineering, and ∥ Department of Chemical Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, United States S Supporting Information *

ABSTRACT: Sulfonated sucrose-derived carbon, glucose-derived carbon, and nut shell activated carbon (NSAC) catalysts were prepared and characterized by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). FT-IR and XPS spectra showed that −SO3H groups could be introduced into the carbon precursors after the sulfonation treatment. Higher concentration of −SO3H groups in the sulfonated sucrose-carbon and glucose-carbon most likely accounts for their higher activities compared to sulfonated NSAC. Hydrolysis of microcrystalline cellulose was examined in a common ionic liquid, 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), with the sulfonated carbon catalysts. Maximum yields of glucose (59%) and total products (80%, defined as the sum of glucose, cellobiose, and 5-hydroxymethylfurfural) could be obtained with sulfonated sucrose-carbon at 120 °C for 4 h. With a regeneration procedure, the catalyst could be reused.

1. INTRODUCTION The upcoming shortage of petroleum-based resources is attracting more and more attention. Exploring and developing alternative energies will be necessary to achieve sustainable development. Biomass, a renewable and CO2 neutral feedstock, has been proposed as an alternative to the petroleum-based resources.1 Effectively converting biomass into fuels and chemicals would relieve reliance on fossil fuels. Cellulose is the most abundant component of biomass, accounting for 35−50% of lignocellulosic biomass. Cellulose consists mainly of glucose units linked together by β-1,4glucosidic bonds.2,3 Effective hydrolysis of cellulose would yield glucose, which is a potential feedstock for the production of fuels and chemicals, such as 5-hydroxymethylfurfural (HMF) and alkylglycosides.4−8 However, with a large amount of intraand intermolecular hydrogen bonds, cellulose has a robust crystalline structure, so the effective depolymerization of cellulose remains a great challenge.9,10 Enzymatic hydrolysis is a common process for the production of glucose from cellulose. However, enzymes are expensive, and the process generally requires purification of feedstock, proper pH value, and proper temperature, which limits its use for economic production of glucose on a large scale.11 Mineral acids, such as H2SO4, are usually employed as catalysts on the industrial scale.12 Nevertheless, the corrosiveness and hazards of handling mineral acids and waste acids would limit the adoption of this process. Recently, many studies have been reported on acid-catalyzed hydrolysis of cellulose. All kinds of mineral, organic, and heteropoly acids could be used to hydrolyze the β-1,4glucosidic bonds.10,13−16 However, these homogeneous catalysts will lead to unacceptable amounts of waste. Heterogeneous catalysts, such as zeolite, metal-supported carbon, and © XXXX American Chemical Society

aluminum oxide, are easier to separate and have been explored for the degradation of cellulose,17,18 while the activities of those solid catalysts are relatively low. More recently, an encouraging sulfonated carbon catalyst has been reported by Onda et al.17,19 to be effective to saccharify cellulose into glucose with a notable 41% yield. Since then, many studies have been conducted on the hydrolysis of cellulose by using sulfonated carbon catalysts. It is worthwhile to note that these reports are devoted to hydrolyzing cellulose in aqueous systems.20−23 Water has a low dissolving capacity for cellulose, which would reduce the accessibility of β-1,4-glucosidic bonds, leading to lower reactivity of cellulose, so the above system takes a longer time and requires a higher temperature. Ionic liquids (ILs), consisting of anions and cations, are essentially salts with melting points around ambient temperature. Because ILs are nonflammable, nonvolatile, and recyclable and can dissolve many chemicals, they have been used in a variety of research fields.24−26 Swatloski and coworkers are the first to report that imidazolium-based ILs can dissolve cellulose.27 Then ILs have been shown to dissolve lignin, wood, and other biomass, which opens the door for the valorization of biomass.28−30 Recently, it was found that acidic IL systems are effective for the hydrolysis of cellulose to cellooligomers, glucose, and reducing sugars.31−35 Functionalized acidic ILs can be used as both solvent and catalyst for the saccharification of cellulose.36 Moreover, metal chlorides are also shown to accelerate the hydrolysis of cellulose in ILs.37−40 Received: February 21, 2013 Revised: May 14, 2013 Accepted: May 15, 2013

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dx.doi.org/10.1021/ie400571e | Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Industrial & Engineering Chemistry Research

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Figure 1. (a) FT-IR spectra of (1) NSAC, (2) glucose-carbon, and (3) sucrose-carbon. (b) FT-IR spectra of sulfonated (1) NSAC, (2) glucosecarbon, and (3) sucrose-carbon.

water until no sulfate anion was detected in the filtrate. Then the sulfonated carbon catalysts were dried at 100 °C for use. 2.3. Typical Reaction Procedure. [BMIM]Cl was dried under vacuum before use. Twenty-five milligrams of microcrystalline cellulose and 500 mg of [BMIM]Cl were added into a reaction vial with a magnetic stir bar. After the solution was stirred at 120 °C for 20 min, it appeared to be homogeneous. Then 12.5 mg of sulfonated carbon catalyst and 25 μL of H2O (molar ratio ∼ 10:1 to glucose units in cellulose) were added into the reaction vial. The sealed vial was stirred and heated at the reaction temperature in an oil bath for a predetermined period of time. The reaction was quenched by adding 3 mL of cold deionized H2O into the reaction vial. After the sample solution was filtered and diluted, it was analyzed by high performance liquid chromatography (HPLC). 2.4. Analysis Method. HPLC was performed on an Agilent 1200 Series chromatograph with a refractive index detector and a BioRad Amines HPX-87H column (300 mm × 7.8 mm). Aqueous solution of 0.005 M H2SO4 was used as the mobile phase at a flow rate of 0.55 mL/min. The column and detector temperatures were 65 and 50 °C, respectively. Authentic cellobiose, glucose, and HMF were used to identify the retention time. The product yields were quantified by an external standard method. Fourier transform infrared (FT-IR) spectra were recorded on a Bruker EQUINOX 55 spectrometer. KBr was used to prepare transparent sample disks. X-ray photoelectron spectroscopy (XPS) analysis was performed on a Thermo Scientific Escalab 250 instrument using an Al Kα source to excite the photoelectrons from the samples.

In this work, sulfonated sucrose-derived carbon, glucosederived carbon, and nut shell activated carbon were prepared and examined as catalysts for the hydrolysis of cellulose in an IL, 1-butyl-3-methylimidazolium chloride ([BMIM]Cl). The objective of this work is to explore an effective system for producing valuable products from cellulose by the combination of recycle IL and cheap sulfonated carbon catalysts. The water concentration, timing of water addition, reaction time, temperature, mass ratio of catalyst to cellulose, and reusability of catalyst were examined in detail.

2. EXPERIMENTAL SECTION 2.1. Materials. Glucose (99%) and sulfuric acid (H2SO4, 98%) were purchased from Tianjin Kermel Chemical Reagent Co., Ltd. (China). Sucrose (99%) was purchased from TianJin Bodi Chemical Holding Co., Ltd. (China). Microcrystalline cellulose was purchased from Sinopharm Chemical Reagent Co., Ltd. (China). Nut shell activated carbon (NSAC) was purchased from Beijing Guanghuajingke Activated Carbon Co., Ltd. (China). Hβ zeolite was provided by the Department of Catalysis Chemistry and Engineering, Dalian University of Technology (China). 1-Butyl-3-methylimidazolium chloride ([BMIM]Cl, 99%) was purchased from Henan Lihua Pharmaceutical Co., Ltd. (China). Cellobiose (98%) and 5hydroxymethylfurfural (HMF, 98%) were purchased from Acros Organics (Belgium). All of these chemicals were used as received, except for those specified. 2.2. Preparation of Carbon Catalysts. The sugar-derived carbon (sugar-carbon) was prepared according to the reported procedure.41,42 Aqueous solutions of sucrose and glucose with a carbon concentration of 12 mol/L were prepared at room temperature, respectively. Then the sugar solutions were transferred into Teflon-lined autoclaves and aged at 180 °C for 15 h. The suspension solutions were dried at 100 °C to obtain black carbon powders. The sulfonation of the carbon precursors was conducted according to the report.42,43 Two grams each of sucrose-carbon, glucose-carbon, and NSAC were added into a Teflon-lined autoclave. Then 30 mL of 98% H2SO4 (15 mL for per gram of carbon) was added, and the carbon precursors were sulfonated at 200 °C for 15 h. After the autoclaves cooled to room temperature, the sulfonated carbon catalysts were filtered and washed by hot (80 °C) deionized

3. RESULTS AND DISCUSSION 3.1. Characterization of Catalysts. Figure 1a presents the FT-IR spectra of three different carbon precursors. The absorbance peak around 3400−3500 cm−1 is associated with the −OH vibrational stretching mode. For NSAC, apart from the −OH peak, no more IR features are observed. For sucrosecarbon and glucose-carbon, the absorbance peak around 1750 cm−1 is the stretching mode of the CO bond, which is possibly formed during the carbonization of glucose and sucrose. The absorbance at about 1600 cm−1 is the stretching mode for the CC bond as reported.44 The absorbances around 1250 and 1050 cm−1 are the C−C and C−O stretching bands of sucrose-carbon and glucose-carbon.44 B



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Figure 2. XPS spectra of sulfonated sucrose-carbon catalyst. The gray line represents the original XPS data.

respectively.46 The S 2p spectrum is fitted into two separate peaks, of which the one at 168.2 eV implies that −SO3H groups are introduced into the sucrose-carbon as reported,20 while the other at about 164 eV implies some sulfur exists in other states, such as C−S−C.47 The C 1s and O 1s spectra of sulfonated NSAC (see the Supporting Information, Figure S1) show that there are fewer CO bonds in the sulfonated NSAC. The XPS spectra of sulfonated glucose-carbon are similar to those of sucrose (see the Supporting Information, Figure S2). Moreover, XPS spectra show that the surface sulfur contents of sulfonated sucrose-carbon, glucose-carbon, and NSAC are 0.72, 1.09, and 0.39%, respectively, which indicates that more −SO3H groups are introduced into sucrose-carbon and glucose-carbon. 3.2. Catalytic Hydrolysis of Cellulose. Figure 3 presents the results on the hydrolysis of microcrystalline cellulose in the presence of different catalysts and the blank test. The reaction conditions were as follows: microcrystalline cellulose (25 mg), [BMIM]Cl (500 mg), H2O (25 μL), solid catalyst (12.5 mg) or H2SO4 (9 mol % to glucose units in cellulose); time (60 min); and temperature (120 °C). When no catalyst was added, only less than 5% glucose was detected. The sulfonated carbon catalysts showed different activities for the hydrolysis reaction. For convenience, the sum of glucose, cellobiose, and HMF is defined as the total product in this paper. In the presence of sulfonated glucose-carbon, a 31% yield of glucose and a 49% total yield of product could be achieved, while in the presence of sulfonated sucrose-carbon the yields of glucose and total product were increased to 36 and 53%, respectively. The

Figure 1b shows the FT-IR spectra of three different carbon precursors after the sulfonation treatment. The absorbance peak around 3400−3500 cm−1 is assigned to the −OH vibrational stretching mode. The stronger −OH absorbances of sulfonated sucrose-carbon and glucose-carbon imply that more −OH groups exist in the two catalysts. During the sulfonation, concentrated H2SO4 may lead to the formation of CO and CC bonds via oxidation, esterification, and dehydration reactions, which account for the new absorbance peaks at about 1750 and 1600 cm−1 in the FT-IR spectrum of sulfonated NSAC. For sulfonated sucrose-carbon and glucosecarbon, the peaks around 1750 and 1600 cm−1 are significantly enhanced, which is possibly because the abundant −OH groups in sucrose-carbon and glucose-carbon precursors underwent oxidation, esterification, and dehydration reactions. OSO and −SO3H produce stretching absorbances around 1377, 1250, and 1040 cm−1, respectively.20,45 Herein the remarkable enhancements at these characteristic positions imply that −SO3H groups are introduced into the sucrose-carbon and glucose-carbon precursors. The relatively weak peaks around 1400 and 1250 cm−1 in the FT-IR spectrum of sulfonated NSAC indicate that fewer −SO3H groups are introduced. Figure 2 presents the XPS spectra of sulfonated sucrosecarbon. The C 1s spectrum is fitted into three separate peaks. The peak at 284.2 eV is assigned to the C−C or C−H bond, the peak at 286.1 eV is assigned to the C−OH or C−S bond, and the peak at 288 eV is associated with the CO bond.46 The O 1s spectrum is fitted into two separate peaks at 533.1 and 531.3 eV, which are associated with C−OH and CO, C



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dissolved cellulose could be recovered from ILs by adding water.27 Therefore, the large amount of water led to the precipitation of cellulose (Supporting Information, Table S1, entry 1), which decreased the accessibility of β-1,4-glucosidic bonds and lowered the product yields. On the basis of this point, we examined the effect of the initial amount of water addition. Four microcrystalline cellulose samples (25 mg) were dissolved in [BMIM]Cl (500 mg), and then 25, 50, 75, and 100 μL of H2O were added into each reaction vial, respectively. It was found that a trace amount of solid precipitated in the sample with 50 μL of H2O, while the one with 100 μL of H2O appeared suspended, which implies that the initial amount of water should not be over 50 μL of H2O in our system. It appears that increasing the amount of water for improving the hydrolysis of cellulose is not compatible with the dissolution of cellulose in ILs. Fortunately, Binder and Raines proposed an effective method to balance the solubility and hydrolysis of cellulose by gradually adding water during the hydrolysis.35 As can be seen in Table S1 in the Supporting Information, when four units of H2O was added within the first 30 min totaling 100 μL (Supporting Information, Table S1, entry 3), the yields of glucose and total product increased with prolonging reaction time and reached maxima of 50 and 66% after 5 h, respectively. The cellobiose could be further hydrolyzed into glucose with prolonged reaction time, and a side dehydration reaction would lead to the conversion of glucose into HMF.35 With increasing amount of water (Supporting Information, Table S1, entries 4 and 5), the yields of glucose and total product were improved and reached maxima of 57 and 80% after 4 h, respectively. The decreased product yields imply that decomposition reactions may occur after longer time. Compared with previous work,17,19−23 higher yields of glucose can be produced rapidly under milder conditions, which pronounces the advantage of using a system containing IL and sulfonated carbon catalyst. We then tested the stability of glucose with different amounts of water, because whether glucose is stable in the catalytic reaction system will affect the product yield. After heating 25 mg of glucose in 500 mg of [BMIM]Cl with 12.5 mg of sulfonated sucrose-carbon catalyst and different amounts of water at 120 °C for 1 h, the recovery of glucose reached 92% when 270 μL of H2O (molar ratio 108-fold to glucose units in cellulose) was added as illustrated in Figure 4. When 150 μL of

Figure 3. Product yields of a blank test and experiments for the hydrolysis of cellulose in the presence of different catalysts in [BMIM]Cl. A, no catalyst; B, sulfonated glucose-carbon; C, sulfonated sucrose-carbon; D, sulfonated NSAC; E, Hβ zeolite; F, 9 mol % H2SO4.

sulfonated NSAC essentially did not work for the hydrolysis reaction. As shown in the FT-IR and XPS spectra (Figures 1 and 2), fewer −SO3H groups of NSAC lead to lower acidity, which likely accounts for the inertness. Moreover, FT-IR spectra also show that the sulfonated NSAC contains fewer −OH groups, which could decrease its affinity with the hydrophilic reaction medium. Hβ zeolite exhibited a moderate activity for the hydrolysis of cellulose. When 9 mol % (molar ratio to glucose units in cellulose) H2SO4 was added as the catalyst, about 38% yield of glucose was produced, and the total product yield was slightly higher than those catalyzed by sulfonated glucose-carbon and sucrose-carbon catalysts. In all the experimental tests, the formation of cellobiose suggests that higher cellooligomers, such as cellotriose and cellotetrose, may be present. It is generally accepted that cellulose is first hydrolyzed into cellooligomers, which would subsequently undergo hydrolysis to produce monosaccharides.18,48 However, these cellooligomers were not analytically quantified because they could not be detected in our HPLC. In addition, previous work has shown that H2SO4 could catalyze the dehydration of glucose into HMF,49 which is consistent with HMF formation in this work. The −SO3H groups of sulfonated carbon catalysts may have a similar function as H2SO4, accounting for the formation of HMF in the presence of the sulfonated sucrosecarbon and glucose-carbon catalysts. Compared with H2SO4, the sulfonated sucrose-carbon and glucose-carbon have similar activities for the hydrolysis of microcrystalline cellulose, but they could avoid producing waste acids. Herein the sulfonated sucrose-carbon is selected as the catalyst for further study. As a coreactant, water is necessary for a hydrolysis reaction. In our previous work, the large addition of water significantly improved the acid-catalyzed hydrolysis of lignin model compounds.50,51 Since the β-O-4 bonds in lignin model compounds are also C−O−C bonds like glucosidic bonds in cellulose, we expected that the hydrolysis of cellulose can be improved in a fashion similar to that for lignin model compounds. First, a large excess amount of water was added (Supporting Information, Table S1, entry 1); however, only 16% yield of glucose and 27% yield of total product were obtained after 1 h. The results showed worse reactivity compared to the reaction with 10-fold water (molar ratio to glucose units in cellulose, Supporting Information, Table S1, entry 2). Swatloski and co-workers have indicated that the

Figure 4. Stability of glucose in [BMIM]Cl with sulfonated sucrosecarbon catalyst and different amounts of water. D



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Table 1. Results on the Hydrolysis of Cellulose with Higher Concentration of Watera added H2O (μL)

a

yield (%)

entry

0 min

10 min

20 min

30 min

50 min

70 min

90 min

time (h)

glucose

cellobiose

HMF

total

1

25

50

25

50

25

25

20

2

25

50

25

50

50

50

20

3 4 3 4

53 45 53 46

13 11 11 13

6 6 8 9

72 62 72 68

A 25 mg sample of microcrystalline cellulose was heated in 500 mg of [BMIM]Cl with 12.5 mg of sulfonated sucrose-carbon at 120 °C.

H2O (molar ratio 60-fold to glucose units in cellulose) was added, 78% glucose was recovered. As expected, the recovery of glucose sharply dropped to only 34% when no water was added. These results indicate that water has a positive effect for stabilizing glucose as reported.35 The decomposition products of glucose are HMF and other unidentified compounds, such as humins. In order to improve the yield of glucose by reducing its decomposition, the hydrolysis of cellulose was tested with a much larger amount of water. Herein the timing of adding water was prolonged to 90 min to avoid any precipitation of cellulose. As shown in Table 1, the much higher concentration of water did not improve the yields of glucose and total product. In contrast, their yields slightly decreased. It was speculated that the much larger amount of water had a negative effect by diluting the system, which led to the lower acidity. Moreover, the contact between cellulose and catalyst is also likely reduced in the diluted system. The above results imply that the yields of glucose and total product have an upper limit under the conditions employed. Table 2 shows the effect of the reaction temperature on the hydrolysis of microcrystalline cellulose. When the reaction was

Table 3. Effect of Mass Ratio of Catalyst to Cellulose on the Hydrolysis of Cellulosea .yield (%)

glucose

cellobiose

HMF

total

1 2 3

100 120 140

8 57 35

7 11 2

trace 12 17

15 80 54

glucose

cellobiose

HMF

total

1:1 1:2 1:3 1:4

59 57 53 52

12 11 12 7

9 12 9 10

80 80 74 69

A proper amount of microcrystalline cellulose was heated in 500 mg of [BMIM]Cl with 12.5 mg of sulfonated sucrose-carbon and total 150 μL of H2O at 120 °C for 4 h. The timing of water addition followed the procedures of , Table S1, entry 5, in the Supporting Information.

product (∼70%) could be achieved, which indicates that the catalyst is effective for the hydrolysis of concentrated cellulose in IL media. Finally, we examined the reusability of the sulfonated sucrose-carbon catalyst. After the first experimental run (Supporting Information, Table S1, entry 5, 4 h), the sulfonated sucrose-carbon was separated by filtration. The catalyst was dried at 100 °C and directly used for the second run for 4 h. However, compared with the fresh catalyst (Supporting Information, Table S1, entry 5), the yields of glucose, HMF, and total product dropped to 24, 4, and 41%, respectively, implying loss of activity. It was speculated that the acidity of the sulfonated sucrose-carbon catalyst decreased. According to the report by Lai et al.,53 the collected catalyst was regenerated in 40% H2SO4 solution at 100 °C, washed by deionized water, dried at 100 °C, and then used for the second run. Similar (or slightly lower) yields of glucose (50%), cellobiose (15%), HMF (7%), and total product (72%) could be achieved with the regenerated catalyst after the second run, which indicates that these cheap sulfonated carbon catalysts have the potential to be reused through proper post-treatment. For the reason why the catalyst is inactive during the second run, leaching of −SO3H groups and ion-exchange reaction are considered as primary factors. We tested the concentration of SO42− in the filtrate and found about 18.9% free SO42− groups existed in the solution, which indicates that some relatively instable −SO3H could leach from the catalyst. However, a large amount of −SO3H should still exist on the carbon. As illustrated in Figure S3 in the Supporting Information, the collected catalyst still showed strong OSO and −SO3− stretching absorbances around 1377, 1250, and 1040 cm−1. Ion exchange between −SO3H groups and [BMIM]Cl would cause the formation of −SO3[BMIM], so some of the original −SO3H of the catalyst became −SO3[BMIM], leading to the much decreased acidity of the catalyst.54 Further study on optimizing product yield and improving the reusability of catalyst is underway.

yield (%) T (°C)

catalyst/cellulose (mass)

1 2 3 4 a

Table 2. Effect of Reaction Temperature on the Hydrolysis of Cellulosea entry

entry

a

A 25 mg sample of microcrystalline cellulose was heated in 500 mg of [BMIM]Cl with 12.5 mg of sulfonated sucrose-carbon and total 150 μL of H2O for 4 h. The timing of water addition followed the procedures of Table S1, entry 5, in the Supporting Information.

carried out at 100 °C, it could occur but only very low yields of products were detected. The hydrolysis of the β-1,4-glucosidic bond is an endothermic reaction.52 With increasing temperature, the hydrolysis of cellulose proceeded more rapidly, and higher yields of products could be obtained. However, at a too high temperature (140 °C), the glucose yield dropped to 35%, possibly because of the instability of glucose under these conditions. The formation of HMF was significantly improved at elevated temperatures, which accounts for some loss of glucose. Table 3 shows the effect of mass ratio of catalyst to cellulose on the hydrolysis reaction. At the mass ratio of 1:1 catalyst and cellulose, the yields of glucose and total products reached the maxima of 59 and 80%, respectively. With a gradually decreasing mass ratio of catalyst to cellulose from 1:1 to 1:4, the yields of glucose and total product became slightly lower. However, reasonable yields of glucose (∼50%) and total E



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(8) Deng, W.; Liu, M.; Zhang, Q.; Tan, X.; Wang, Y. Acid-Catalysed Direct Transformation of Cellulose into Methyl Glucosides in Methanol at Moderate Temperatures. Chem. Commun. 2010, 46, 2668−2670. (9) O’Sullivan, A. C. Cellulose: The Structure Slowly Unravels. Cellulose 1997, 4, 173−207. (10) Tian, J.; Wang, J.; Zhao, S.; Jiang, C.; Zhang, X.; Wang, X. Hydrolysis of Cellulose by the Heteropoly Acid H3PW12O40. Cellulose 2010, 17, 587−594. (11) Moliner, M.; Román-Leshkov, Y.; Davis, M. E. Tin-Containing Zeolites Are Highly Active Catalysts for the Isomerization of Glucose in Water. Proc. Natl. Acad. Sci. U.S.A. 2010, 107, 6164−6168. (12) Saeman, J. F. Kinetics of Wood Saccharification Hydrolysis of Cellulose and Decomposition of Sugars in Dilute Acid at High Temperature. Ind. Eng. Chem. 1945, 37, 43−52. (13) Harmer, M. A.; Fan, A.; Liauw, A.; Kumar, R. K. A New Route to High Yield Sugars from Biomass: Phosphoric-Sulfuric Acid. Chem. Commun. 2009, 6610−6612. (14) Stein, T. V.; Grande, P.; Sibilla, F.; Commandeur, U.; Fischer, R.; Leitner, W.; María, P. D. Salt-Assisted Organic-Acid-Catalyzed Depolymerization of Cellulose. Green Chem. 2010, 12, 1844−1849. (15) Shimizu, K.; Furukawa, H.; Kobayashi, N.; Itaya, Y.; Satsuma, A. Effects of Brønsted and Lewis Acidities on Activity and Selectivity of Heteropolyacid-Based Catalysts for Hydrolysis of Cellobiose and Cellulose. Green Chem. 2009, 11, 1627−1632. (16) Ogasawara, Y.; Itagaki, S.; Yamaguchi, K.; Mizuno, N. Saccharification of Natural Lignocellulose Biomass and Polysaccharides by Highly Negatively Charged Heteropolyacids in Concentrated Aqueous Solution. ChemSusChem 2011, 4, 519−525. (17) Onda, A.; Ochi, T.; Yanagisawa, K. Selective Hydrolysis of Cellulose into Glucose over Solid Acid Catalysts. Green Chem. 2008, 10, 1033−1037. (18) Kobayashi, H.; Komanoya, T.; Hara, K.; Fukuoka, A. WaterTolerant Mesoporous-Carbon-Supported Ruthenium Catalysts for the Hydrolysis of Cellulose to Glucose. ChemSusChem 2010, 3, 440−443. (19) Onda, A.; Ochi, T.; Yanagisawa, K. Hydrolysis of Cellulose Selectively into Glucose Over Sulfonated Activated-Carbon Catalyst Under Hydrothermal Conditions. Top. Catal. 2009, 52, 801−807. (20) Suganuma, S.; Nakajima, K.; Kitano, M.; Yamaguchi, D.; Kato, H.; Hayashi, S.; Hara, M. Hydrolysis of Cellulose by Amorphous Carbon Bearing SO3H, COOH, and OH Groups. J. Am. Chem. Soc. 2008, 130, 12787−12793. (21) Pang, J.; Wang, A.; Zheng, M.; Zhang, T. Hydrolysis of Cellulose into Glucose over Carbons Sulfonated at Elevated Temperatures. Chem. Commun. 2010, 46, 6935−6937. (22) Vyver, S. V.; Peng, L.; Geboers, J.; Schepers, H.; Clippel, F.; Gommes, C. J.; Goderis, B.; Jacobs, P. A.; Sels, B. F. Sulfonated Silica/ Carbon Nanocomposites as Novel Catalysts for Hydrolysis of Cellulose to Glucose. Green Chem. 2010, 12, 1560−1563. (23) Lai, D.; Deng, L.; Li, J.; Liao, B.; Guo, Q.; Fu, Y. Hydrolysis of Cellulose into Glucose by Magnetic Solid Acid. ChemSusChem 2011, 4, 55−58. (24) Welton, T. Room-Temperature Ionic Liquids. Solvents for Synthesis and Catalysis. Chem. Rev. 1999, 99, 2071−2083. (25) Zhang, Z. C. Catalysis in Ionic Liquids. Adv. Catal. 2006, 49, 153−237. (26) Olivier-Bourbigou, H.; Magna, L.; Morvan, D. Ionic Liquids and Catalysis: Recent Progress from Knowledge to Applications. Appl. Catal., A 2010, 373, 1−56. (27) Swatloski, R. P.; Spear, S. K.; Holbrey, J. D.; Rogers, R. D. Dissolution of Cellose with Ionic Liquids. J. Am. Chem. Soc. 2002, 124, 4974−4975. (28) Pu, Y.; Jiang, N.; Ragauskas, A. J. Ionic Liquid as a Green Solvent for Lignin. J. Wood Chem. Technol. 2007, 27, 23−33. (29) Kilpeläinen, I.; Xie, H.; King, A.; Granstrom, M.; Heikkinen, S.; Argyropoulos, D. S. Dissolution of Wood in Ionic Liquids. J. Agric. Food Chem. 2007, 55, 9142−9148.

4. CONCLUSION Sulfonated sucrose-carbon, glucose-carbon, and NSAC were prepared and examined as catalysts for the hydrolysis of cellulose in an IL, [BMIM]Cl. Sulfonated sucrose-carbon and glucose-carbon catalysts exhibited catalytic activities comparable to H2SO4, while sulfonated NSAC failed in catalyzing the hydrolysis reaction. Higher −SO3H group concentration in sulfonated sucrose-carbon and glucose-carbon most likely accounts for their higher activities compared to sulfonated NSAC. The water concentration is important, because it affects both the hydrolysis and dissolution of cellulose in [BMIM]Cl. With four additions of water totaling 150 μL of H2O within the first 30 min, maximum yields of glucose (57%) and total product (80%) could be obtained at 120 °C for 4 h. After a simple regeneration procedure, the catalyst can be reused. The approach described herein should be useful for effective hydrolysis of cellulose into glucose as well as into other chemicals.

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ASSOCIATED CONTENT

S Supporting Information *

Table S1, effect of the concentration of water and reaction time; Figure S1, XPS spectra of sulfonated NSAC; Figure S2, XPS spectra of sulfonated glucose-carbon; Figure S3, FT-IR spectra of sulfonated sucrose-carbon before and after the hydrolysis of cellulose in [BMIM]Cl. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +86-411-84986134 (M.L.). E-mail: [email protected] (M.L.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The work was financially supported by the National Natural Science Foundation of China (No. 20803005).

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REFERENCES

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