Selective Decomposition of Cellulose into Glucose and Levulinic Acid

Mar 24, 2014 - ABSTRACT: The selective decomposition of microcrystalline cellulose (MCC) by Fe-resin (a modified Dowex 50 by cation- exchange) solid ...
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Selective Decomposition of Cellulose into Glucose and Levulinic Acid over Fe-Resin Catalyst in NaCl Solution under Hydrothermal Conditions Hui Yang, Liqing Wang, Lishan Jia,* Chenchao Qiu, Qi Pang, and Xinwei Pan Department of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, Fujian, People’s Republic of China ABSTRACT: The selective decomposition of microcrystalline cellulose (MCC) by Fe-resin (a modified Dowex 50 by cationexchange) solid catalyst in 5 wt % NaCl solution under hydrothermal conditions has been investigated. The conversion of MCC increases from 24.4% (without catalyst) to 90.9%, and the yield of glucose and levulinic acid (LA) increases from 0.6% and 1.1% (without catalyst) to 38.7% and 33.3%, respectively, under 200 °C for 5 h. The role that Fe-resin/NaCl played in the system is discussed in detail: NaCl could disrupt the hydrogen-bond matrix among cellulose fibers to change highly crystalline cellulose into an amorphous form; Lewis acids on the Fe-resin further boost the depolymerization of amorphous cellulose into watersoluble sugars (WSSs); Fe ions on Fe-resin progressively released into NaCl solution are beneficial to the conversion of WSSs to glucose and LA. A three-step degradation scheme reflecting the main pathways of MCC degradation in the reaction is proposed.

1. INTRODUCTION One of the most attractive routes for reactions of cellulose is its depolymerization and conversion into useful organic compounds, such as glucose and levulinic acid (LA), for the replacement of current petroleum-based fuels. Thus far, mineral acids,1−3 enzymes,4 and supercritical water5 were used for the hydrolysis of cellulose, which results in many problems, such as corrosion hazards, difficulties in separation, control of enzymes, and harsh reaction conditions. Thus, it boosts the use of solid acid catalyst. Polymer based acid ion-exchange resin with Brønsted acid has catalytic activities for cellulose decomposition,6−8 but the yield of glucose or LA was limited due to the detrimental contact. To increase the contact sites between cellulose and solid acid, some researchers employed a resin with Brønsted acid to decompose the cellulose, assisted by ionic liquids (ILs)9−11 to enhance yield of the total reducing sugar or glucose. Taking the expensive cost and high viscosity of ILs into account, NaCl is a good substitute.12 Recently, some reports showed that metal chlorides13−16 displayed superior performance on the hydrolysis of cellulose due to the Lewis acidity of the cation, but they cannot be separated and recycled. In order to immobilize the cation with Lewis acidity, some heterogeneous Lewis acid catalysts, such as Cs2SnPW12O4017 and Sn0.75PW12O40,18 were employed to hydrolyze cellulose to promote the conversion of cellulose and/or yield the sugars (soluble oligosaccharides or total reducing sugars). However, very few studies have focused on the effects of resin with Lewis acids on the decomposition of cellulose. Herein, we report a kind of Fe-resin combined with Lewis acid properties and the advantages of solid phase through a straightforward preparation method to decompose cellulose in NaCl solution to obtain glucose and LA by a simple hydrothermal-catalytic system. We explore the complicated cascade reaction process of the transformation of cellulose in detail. In comparison with previous studies, this method © 2014 American Chemical Society

depending on Fe-resin/NaCl will shed light on the utilization of cellulose.

2. MATERIAL AND METHODS 2.1. Materials. The reactant microcrystalline cellulose (MCC, M101QD, powder: 1−250 μm, DP: 200−250) was purchased from Mingtai Chemical Co., Ltd. (Taiwan, China). Cation-exchange resin Dowex 50, containing highly crosslinked styrene−divinyl benzene copolymer beads functionalized with sulfonic groups, was purchased from Xilong Chemical Industries Co., Ltd. (GuangXi, China). D-(+)-glucose and levulinic acid with mass fraction purity of 0.99 and 0.98 were purchased from Sigma-Aldrich Co. (St Louis. MO, U.S.A.). HCl, FeCl3·6H2O and NaCl with mass fraction purity of 0.36− 0.38, 0.99, and 0.995, respectively, were provided by Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). All reagents and solvents above were of analytical grade and were used without further purification. 2.2. Catalyst Preparation. Dowex 50 was washed by deionized water several times to remove impurities and then dried to get the sample noted as Na-resin. A certain quality of Na-resin was soaked in 2 mol/L HCl with a solid/liquid ratio of 1:10 (g/mL) and stirred by magneton under 40 °C for 5 h. It was adjusted to neutral by deionized water after an overnight rest. After being dried under 100 °C for 5 h, the catalyst was noted as H-resin. For Fe-resin, a certain quality of H-resin was soaked in 10 wt % FeCl3 solution with a solid/liquid ratio of 1: 20 (g/mL). The rest of the steps are the same as those above. The mass exchange was 5%, which was determined by the mass difference of H-resin before and after soaking. Received: Revised: Accepted: Published: 6562

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Figure 1. Influence of (A) temperature and (B) time on the distribution of products. Reaction conditions: MCC 0.5 g, Fe-resin 0.3 g, 5 wt % NaCl solution 40 mL, (A) reaction time 5 h, and (B) reaction temperature 200 °C.

2.3. Decomposition of MCC. In a typical reaction procedure, 0.5 g MCC (dried under vacuum under 105 °C for 24 h before use), catalysts based on the preset dosages and/ or 2 g NaCl were introduced in a Teflon-lined stainless autoclave (80 mL) after being stirred, followed by the addition of 40 mL water. The autoclave was placed into a stainless steel heating jacket and then put in a drying oven under the desired temperature and time. After the appointed reaction time was reached, the autoclave was removed from the drying oven. After cooling to room temperature, the reaction mixture was separated by filtration. Liquid samples were further filtered through 0.45 μm membranes and stored under 4 °C for subsequent analysis. MCC conversion was determined by the change of its weight before and after the reaction. Monosaccharides were not detected, except glucose in hydrolysate. The yield of products and conversion were calculated according to eqs 1−6: glucose yield(%) = yield of glucose(g)/ MC(g) × 100

(1)

LA yield(%) = yield of LA(g)/ MC(g) × 100

(2)

TS yield(%) = yield of TS(g)/ MC(g) × 100

(3)

WSSs yield(%) = TS yield(%) − glucose yield(%)

(4)

conversion(%) = (1 − MRS(g)/MC(g)) × 100

(5)

rate was 1.0 mL/min. The column temperature was kept at 30 °C. The LA concentration was determined by GC-9560 equipped with a flame ionization detector (FID) and OV-17 capillary column (30 m × 0.25 m × 0.25 μm). Detector, column, and injector temperatures were 250 °C, 170 °C, and 230 °C, respectively. The total sugars (TS) concentration was measured by the phenol−sulfuric method.19 WSOCs were analyzed by GCMS-QP2010 Plus (Agilent 7820 and Agilent 5975C MSD). The GC column was Rtx-5MS Cap. Column (30 m × 0.25 mm × 0.25 μm), and the analysis was carried out with a suitable temperature programming procedure: 50 °C (hold 2 min) → 170 °C (15 °C/min, hold 2 min) → 250 °C (20 °C/min, hold 2 min), inlet temperature 200 °C. 2.4.2. Characterization of Residues of MCC and Solid Catalysts. The powder X-ray diffraction (XRD) patterns of MCC and the residues of MCC were recorded on a Panalytical X’Pert Pro X-ray diffractometer using Cu Ka radiation at 40 kV and 30 mA, over a 2θ range of 10°−45°in the step mode (0.0167°, 10 s). The crystallinity index (CrI) was determined by the Segal method, from eq 7:20 CrI = (I002 − Iam)/I002 × 100

where I002 is the maximum intensity of the (002) reflection, at 2θ of 22°−23°, and Iam is the intensity of diffraction at 2θ of 18°−19° for cellulose I. An X-ray photoelectron spectroscopy (XPS) analysis was performed on a PHI Quantum 2000 Scanning ESCA microprobe with a monochromatized microfocused Al X-ray source. The binding energy was calibrated by C1s as reference energy (C1s 284.8 eV). The atomic concentrations were calculated from the photoelectron peak areas, using Shirley background subtraction.21 A Micromeritics Tristar 3000 automated physisorption instrument was used to measure the N2-adsorption isotherms of the solid catalyst at liquid N2 temperature (−196 °C). The specific surface area was determined from the linear portion of the BET plot. Prior to the surface area measurement, the

WSOCs yield(%) = conversion(%) − TS yield(%) − LA yield(%)

(7)

(6)

where MC is the weight of MCC; MRS is the weight of solid residue; TS, WSSs, and WSOCs are denoted as total sugars, water-soluble sugars except glucose, and water-soluble organic compounds (e.g., formic acid, acetic acid, furfural, hydroxymethylfurfural, acetol), respectively. 2.4. Analytical Methods. 2.4.1. Liquid Products Analysis. The glucose concentration was determined by a highperformance liquid chromatograph Agilent Series 1100 equipped with a Hypersil ODS column and refractive index detector. The mobile phase was ultrapure water, and the flow 6563

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Table 1. Yield of Products and Conversion of MCC with Different Catalysts and Solvent under Hydrothermal Conditionsa,b,c,d yield (wt %) catalyst

solvent

sample

T (°C)

t (h)

conversion (wt %)

glucose

LA

ref

Fe-resin Fe-resin Amberlyst 15DRY Nafion NR50 Nafion SAC-13

water 5 wt % NaCl water [Bmim]Cl 25 wt % NaCl

MCC MCC Avicel PH-101 MCC cellulose

200 200 170 160 190

5 5 3 4 120

50.5 90.9 49.8

12.2 38.7

5.5 33.3 13.1

this work this work 8 10 32

a

34.5 25.1 b

The reaction container was an autoclave, equipped with a thermocouple and a magnetic stirrer. The hydrolysis of MCC was conducted after the pretreatment process by ([bmim]Cl) and 160 °C was the hydrolysis temperature. cThe reaction was carried out in a bomb flask. dEmpty cells indicate no data.

samples were degassed in vacuum under 150 °C for 4 h to remove physically adsorbed components. The surface acid amount of solid acid catalyst was quantitatively measured by UV spectrometry (Shimadzu UV1800, Kyoto, Japan) with pyridine (Py) and 2,6-dimethyl pyridine (DMPy) as adsorbates in cyclohexanen solvent. The specific process is as follows: (a) Py and DMPy was dissolved in cyclohexanen to reach a concentration of 0.632 mmol/L (C0), respectively; (b) solid acid catalyst was put into Py and DMPy solution in a appropriate solid liquid proportion (g/mL) and then was put into an ultrasonic oscillator under room temperature for 1 h; (c) the solution was measured in a UV−vis spectrophotometer at 251 and 265 nm, respectively. The concentration of Py and DMPy (C) was calculated based on a standard curve obtained with Py and DMPy. The total acid amount of solid acid or Brønsted acid amount was calculated as follows: Q i = (C0 − C) × V /(m × 1000)

water-soluble byproducts in the hydrolysis process.24 Hence, the optimum reaction time was 5 h in this study. Compared those data shown in Table 1, it is obvious that the performance of Fe-resin to decompose MCC for glucose and LA in 5 wt % NaCl solution was more efficient than that of resin with SO3H group in water, IL or high concentration NaCl solution. It indicated that Fe-resin in NaCl solution had a specific function for the degradation of MCC. 3.2. Reaction Procedure of MCC Converted into Glucose and LA. 3.2.1. Crystallinity of the Residues of MCC after Hydrolysis. As shown in Figure 2, MCC has typical

(8)

where C0 and C are the concentration of Py and DMPy before and after the adsorption, V (mL) is the volume of Py and DMPy cyclohexanen solution into which solid acid was put, and m (g) is the mass of solid acid. Lewis acid amount is the subtraction of Brønsted acid amount from total acid amount.

3. RESULTS AND DISCUSSION 3.1. Performance of Fe-Resin in NaCl Solution on the Decomposition of MCC. Figure 1A showed the effect of Feresin in 5 wt % NaCl solution (noted as Fe-resin/NaCl) on the decomposition of MCC under different temperatures for 5 h. It can be observed that the conversion of MCC increased from 26.3% to 91.4% with the temperature increased from 155 to 215 °C. The decomposition of MCC was relatively insensitive to temperature below 185 °C.22 When the temperature reached 215 °C, the yield of LA decreased. Although high temperature could accelerate the rate of conversion of carbohydrates, unwanted side reactions also built up at the same time, which caused the carbonation of MCC, and the produced glucose and LA would further convert into other undesirable byproducts.23 Considering the conversion of MCC (90.9%) and the yield of glucose and LA (38.7% and 33.3%), the optimum reaction temperature was 200 °C. As shown in Figure 1B, the conversion of MCC increased sharply from 28.5% to 90.9% with reaction time ranging from 2 to 5 h under 200 °C. As time extended to 8 h, there was almost no change in conversion compared with that when the reaction time was 5 h, but the yield of glucose and LA decreased drastically, which could be ascribed to the appearance of some

Figure 2. XRD patterns and CrI of (a) MCC and residues of MCC catalyzed by (b) no catalyst, (c) H-resin, (d) Fe-resin, (e) FeCl3, (f) Fe-resin/NaCl, and (g) NaCl under 200 °C for 5 h.

diffraction angles around 14.8°, 16.6°, and 22.6°, and a sharply high peak with a 2θ close to 22.6° (see Figure 2a) which is assigned to the (002) plane of cellulose I.25 Figure 2 also presented the CrI of MCC after catalyzed by different catalysts, which was calculated according to eq 7. Once catalyzed by Feresin/NaCl, the peak intensity at 22.6° greatly decreased, as well as CrI (see Figure 2f), clearly indicating the demolishment of the crystal structure of MCC. For the MCC catalyzed by Fe-resin and FeCl3, the CrI of the MCC catalyzed by the latter (see Figure 2e) was greatly lower than the former (see Figure 2d). It can be explained by the acid sites on solid acid which are not as efficient as those in liquid acid to destroy the crystalline area in MCC. More attention was paid to the CrI of MCC treated in NaCl solution (see Figure 2g). A quite flat diffraction pattern was 6564

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obtained, which indicated an amorphous structure.26 This proved that NaCl can disrupt the hydrogen-bond matrix among cellulose fibers.12 For the difference of the destruction of MCC in FeCl3 solution (see Figure 2e) and NaCl solution (see Figure 2g), the reason may be the smaller radius of sodium ion in sodium chloride compared with that of iron ion in ferric chloride, which is more effective to interact with the hydrogen bonding network of the MCC structure with the assistance of chloride. Comparing the XRD patterns and CrI shown in Figure 2f,g, we came to a conclusion that it was the gradual disruption of the hydrogen-bond matrix among MCC fibers by NaCl and then to the disintegration of MCC in our system, which was proven by the gradual decrease of CrI of MCC treated in the NaCl solution along the extension of time (see Figure 3).

3.2.2. Conversion of Amorphous Cellulose to WSSs. Figure 4A showed the distribution of products of MCC over different catalysts. The conversion of MCC was only 24.4% in the control experiment (see Figure 4A(a)). It was clear that water autoprotolysis27 played a vital role for the conversion of MCC. With H-resin as catalyst (see Figure 4A(b)), the conversion of MCC increased from 24.4% to 44.1%, as well as the yield of glucose and LA, which was attributed to the acid groups on its surface. With Fe-resin as catalyst (see Figure 4A(c)), the yield of WSSs was 8.8% higher compared with the data of MCC catalyzed by H-resin. The amount of surface acid and BET surface areas of H-resin and Fe-resin summarized in Table 2 Table 2. Characteristics of H-Resin and Fe-Resin surface acid amount (mmol/g) catalyst

Brønsted acid amount

Lewis acid amount

BET surface area (m2/g)

H-resin Fe-resin

0.187 0.002

0.018 0.184

17.08 30.69

can explain the difference. The surface acid on the Fe-resin is mainly Lewis acid, while on H-resin, it is Brønsted acid. Lewis acids on Fe-resin are favorable to the depolymerization of MCC to WSSs28 and are inclined to inhibit the degradation of WSSs to WSOCs or water-soluble humins via different pathways. Brønsted acids on H-resin are apt to break β-1,4-glycosidic bonds in cellulose6,18 to produce glucose and then to WSOCs and water-insoluble humins that caused by the combination of acid soluble cellulose and glucose or WSSs.29 That is to say different kinds of acids play different roles during the breakage process of MCC. Meanwhile, the larger BET surface areas in the Fe-resin, which can be attributed to the suitable compromise of FeCl3 between solubility and molecular size30 for the ion-exchange, the larger radius of tervalence iron and the emergence of the steric hindrance31 after the replacement of H ions by Fe ions on −SO3, also have positive effects on the contact of cellulose and surface acid sites on Fe-resin. The

Figure 3. XRD patterns and CrI of the residues of MCC treated in NaCl solution under 200 °C for different time (a) 0 h, (b) 2 h, (c) 3 h, (d) 4 h, and (e) 5 h.

Figure 4. (A) Distribution of products over different catalysts. Reaction conditions: MCC 0.5 g, distilled water 40 mL, 200 °C, 5 h, catalyst (a) no catalyst, (b) H-resin 0.3 g, (c) Fe-resin 0.3 g, (d) FeCl3 0.044 g, and (e) NaCl 2 g. The mass of Fe in Fe-resin and FeCl3 is equivalent. (B) Distribution of products of amorphous cellulose (XRD pattern shown in Figure 2g) catalyzed by (a) H-resin and (b) Fe-resin under 200 °C for 4 h. 6565

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Figure 5. (A) Distribution of products over different catalysts in NaCl solution. Reaction conditions: MCC 0.5 g, 40 mL 5 wt % NaCl solution, 200 °C, 5 h, catalyst (a) no catalyst, (b) H-resin 0.3 g, (c) Fe-resin 0.3 g, and (d) FeCl3 0.031 g. The mass of Fe in FeCl3 is equivalent to the mass difference of Fe on the surface of Fe-resin before and after the reaction in NaCl solution (Table 3). (B) Distribution of products of further hydrolysis of the hydrolysate (products distribution shown in Figure 4B(b)) under 200 °C for 5 h over different catalysts: (a) Fe-resin 0.3 g, NaCl 2 g; (b) FeCl3 0.031 g, and NaCl 2 g.

in the conversion of amorphous cellulose, as shown in Figure 4B(a). The result confirmed that the role of Fe-resin that combined the Lewis acid properties and the advantages of solid phase was to convert amorphous cellulose into WSSs. 3.2.3. Conversion of WSSs to Glucose and LA. It is obvious that the yield of LA increased sharply after the hydrolysis of MCC by H-resin/NaCl, Fe-resin/NaCl, and FeCl3/NaCl which were 25.4%, 33.3%, and 25.4%, respectively (see Figure 5A(a)), compared with that in water (4.2%, 5.5%, and 12.9%). It was consistent with Potvin’s study.32 Comparing the total yield of glucose and LA (72.0% and 38.3%) in Figure 5A(c),(d), it demonstrated that Fe ions on the Fe-resin were gradually released11 rather than blended into NaCl solution, which was preferable to the yield of glucose and LA. The proposal was further confirmed by the following control experiment. Fe-resin and NaCl were added into the hydrolysate mainly containing WSSs (product distribution shown in Figure 4B(b)). Comparing the data in Figure 4B(b) with Figure 5B(a), the yield of LA increased from 2.4% to 20.3%, while the yield of WSSs decreased from 35.8% to 2.3% (see also, Table 3). We also employed FeCl3 instead of Fe-resin to hydrolyze WSSs under the same conditions. Comparing the data in Figure 4B(b) with Figure 5B(b), there was a big difference in the yield of WSSs and LA, but the yield of WSOCs increased by 21.9%. This confirmed that it is more effective to decompose WSSs into glucose and LA without other undesirable byproducts by

above analysis suggested that the yield of WSSs was higher than that in the hydrolysate of MCC catalyzed by H-resin, as well as the selectivity of glucose, LA, and WSSs. It also explain the conversion of MCC catalyzed by Fe-resin, which was a little higher than that of by H-resin, even though the total amount of surface acid on H-resin is a little more than that on Fe-resin, which is consistent with the change of pH value of FeCl3 solution before and after the exchange of ions. We employed FeCl3 to testify the role of resin. The hydrolysis of MCC catalyzed by Fe-resin and FeCl3 differed vastly in conversion, which were 50.5% and 82.5%, respectively, as well as the yield of LA and WSSs (see Figure 4A(c),(d)). However, the selectivity of glucose, LA, and WSSs obtained from MCC catalyzed by Fe-resin was greatly higher than that obtained from MCC by FeCl3, which indicated that resin has an important effect during the depolymerization process of MCC, such as controlling the rate of hydrolysis of MCC into WSSs and then to glucose, inhibiting the formation of WSOCs. Considering the relatively low conversion of MCC catalyzed by H-resin and Fe-resin compared with that by FeCl3 and the increasement of CrI of the residues of MCC (see Figure 2c,d) compared with that of MCC, it can be deduced that the decomposition of MCC took place in amorphous areas during the decomposition process by solid catalyst. On the basis of the analysis of the data in Figure 4A and Table 2, it indicated that Fe-resin is conducive to the conversion of amorphous cellulose to WSSs. Thus, a control experiment was carried out to confirm our proposal. The amorphous cellulose collected from the residue of MCC treated in NaCl solution (XRD pattern shown in Figure 2g) and Feresin was put together to react under 200 °C for 4 h. The conversion of amorphous cellulose and the yield of WSSs were 54.5% and 35.8%, respectively, as shown in Figure 4B(b). However, the distribution of products obtained from amorphous cellulose catalyzed by H-resin was not favorable. The main products were WSOCs, which accounted for 61.0%

Table 3. Atomic Elemental Content of C, O, S, Fe, and Na on the Surface of Fe-Resin and Fe-Resin Used Once in NaCl Solutiona

a

6566

catalyst

C (%)

O (%)

S (%)

Fe (%)

Na (%)

Fe-resin Fe-resin used once in NaCl solution

69.64 69.69

21.96 19.83

5.78 5.50

2.63 0.82

4.16

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selectivity of glucose and LA (80%) under hydrothermal conditions. A three-step degradation procedure is proposed based on the detailed investigation on the role of Fe-resin/ NaCl in the system: (1) the breakage of inter- and intramolecular hydrogen bonds resulting in the destruction of aggregation state of MCC by NaCl; (2) the catalytic cleavage of β-1,4-glucosidic bonds in amorphous cellulose by Fe-resin to generate WSSs; and (3) the decomposition of WSSs into glucose and then to LA by the gradual release of Fe ions on Feresin into NaCl solution.

the progressive release of Fe ions on Fe-resin into NaCl solution, which was proven by the wide scan survey XPS spectrum of Fe-resin and Fe-resin used once in NaCl solution (Figure 6).

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AUTHOR INFORMATION

Corresponding Author

*Tel: 086-592-2188283. Fax: 086-592-2184822. E-mail: jials@ xmu.edu.cn. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research is supported by the general program of National Natural Science Foundation of China (Grant 21176203). The authors are grateful to the Analysis Testing Centre of Xiamen University for the analysis observation work in this study.

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the No. and and

REFERENCES

(1) Mok, W. S.; Antal, M. J., Jr; Varhegyi, G. Productive and Parasitic Pathways in Dilute Acid-Catalyzed Hydrolysis of Cellulose. Ind. Eng. Chem. Res. 1992, 31, 94−100. (2) Morales-delaRosa, S.; Campos-Martin, J. M.; Fierro, J. L. High Glucose Yields from the Hydrolysis of Cellulose Dissolved in Ionic Liquids. Chem. Eng. J. 2012, 181, 538−541. (3) Butera, G.; De Pasquale, C.; Maccotta, A.; Alonzo, G.; Conte, P. Thermal Transformation of Micro-Crystalline Cellulose in Phosphoric Acid. Cellulose 2011, 18, 1499−1507. (4) Bansal, P.; Vowell, B. J.; Hall, M.; Realff, M. J.; Lee, J. H.; Bommarius, A. S. Elucidation of Cellulose Accessibility, Hydrolysability and Reactivity As the Major Limitations in the Enzymatic Hydrolysis of Cellulose. Bioresour. Technol. 2012, 107, 243−250. (5) Kumar, S.; Gupta, R. B. Hydrolysis of Microcrystalline Cellulose in Subcritical and Supercritical Water in a Continuous Flow Reactor. Ind. Eng. Chem. Res. 2008, 47, 9321−9329. (6) Hegner, J.; Pereira, K. C.; DeBoef, B.; Lucht, B. L. Conversion of Cellulose to Glucose and Levulinic Acid via Solid-Supported Acid Catalysis. Tetrahedron Lett. 2010, 51, 2356−2358. (7) Takagaki, A.; Tagusagawa, C.; Domen, K. Glucose Production from Saccharides Using Layered Transition Metal Oxide and Exfoliated Nanosheets As a Water-Tolerant Solid Acid Catalyst. Chem Commun. 2008, 5363−5365. (8) Van de Vyver, S.; Thomas, J.; Geboers, J.; Keyzer, S.; Smet, M.; Dehaen, W.; Jacobs, P. A.; Sels, B. F. Catalytic Production of Levulinic

Figure 6. (A) Wide scan survey XPS spectrum of (a) Fe-resin and (b) Fe-resin used once in NaCl solution. (B) Mechanism for proton release caused by ion-exchange between Na+ in NaCl and Fe3+ at the terminal SO3Fe group on resin.

3.2.4. Relative Content of HMF in WSOCs. GC-MS was applied to analyze the main WSOCs obtained under 200 °C for 5 h with different catalysts, which were shown in Table 4. HMF was the main WSOC in the hydrolysate of blank experiment. After hydrolyzed by different catalysts, LA became the main WSOC and the proportion of HMF turned to be small in the hydrolysate. The proportion of HMF was 21.2% using Fe-resin as the catalyst. However, when Fe-resin was employed in NaCl solution, the proportion was only 5.1%, which meant that the HMF obtained from glucose almost completely converted into LA.

4. CONCLUSIONS The application of Fe-resin combined the Lewis acid properties and the advantages of solid phase in 5 wt % NaCl solution achieves the high conversion of MCC (90.9%) and high

Table 4. GC-MS Analysis Results of the Main Products Obtained during the Process of MCC Degradation with Different Catalysts under 200 °C for 5 ha area (%)

a

no.

name of compound

molecular formula

1 2 3 4 5 total area

formic acid acetic acid furfural LA HMF

CH2O2 C2H4O3 C5H4O2 C5H8O2 C6H6O3

no catalyst

H-resin

Fe-resin

FeCl3

Fe-resin/NaCl

5.0

2.2 1.5 64.6 68.3

21.0 12.4 8.1 38.2 16.9 96.6

20.3 2.3 5.1 57.2 9.6 94.5

7.7 0.4 1.2 79.4 5.1 93.8

5.3 52.7 21.2 84.2

Empty cells indicate no data. 6567

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dx.doi.org/10.1021/ie500318t | Ind. Eng. Chem. Res. 2014, 53, 6562−6568