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ZrO2–Al2O3 solid catalyst
Bioresource Technology 116 (2012) 302–306
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One-pot synthesis of 5-hydroxymethylfurfural directly from starch over SO24 /ZrO2–Al2O3 solid catalyst Yu Yang a,b, Xi Xiang a, Dongmei Tong a, Changwei Hu a,⇑, Mahdi M. Abu-Omar b,⇑ a b
Key Laboratory of Green Chemistry and Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, Sichuan 610064, PR China Department of Chemistry and the Center for Direct Catalytic Conversion of Biomass to Biofuels (C3Bio), Purdue University, 560 Oval Drive, West Lafayette, IN 47907, USA
a r t i c l e
i n f o
Article history: Received 20 January 2012 Received in revised form 20 March 2012 Accepted 24 March 2012 Available online 30 March 2012 Keywords: Starch 5-Hydromethylfurfural Hydrolysis Dehydration SO24 /ZrO2–Al2O3 catalyst
a b s t r a c t The synthesis of 5-hydroxymethylfurfural (HMF) directly from starch was studied in dimethyl sulfoxide– water. The effects of catalyst variation, reaction time, water content, catalyst loading and temperature on the reaction were investigated. The SO24 /ZrO2–Al2O3 catalyst was found to act as a bifunctional catalyst with high activity for both hydrolysis and dehydration of starch. HMF yield of 55% was obtained after 6 h at 423 K for the reaction of starch (the molar ratio of water to glucose in starch is 44/1) over the SO24 / ZrO2–Al2O3 catalyst, which bears high acidity and moderate basicity with Zr/Al molar ratio of 1:1. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction With declining petroleum resources and rising environmental concerns, the production of energy and chemicals from renewable biomass has become an intense topic of applied and basic research. (Dodds and Gross, 2007; Rostrup-Nielsen, 2005) 5-Hydroxymethylfurfural (HMF), a versatile intermediate between biomass-based carbohydrates and petroleum-based industrial chemicals, has received much attention as an interesting platform molecule in biomass conversion. It can be converted to many value-added chemicals as well as liquid fuels that are compatible with the current infrastructure (Huber et al., 2005; Román-Leshkov et al., 2007; West et al., 2008). Different feedstock such as fructose, glucose, sucrose, inulin, cellulose, and starch, have been reported to give HMF at varying efficiencies (Tong et al., 2010; Zakrzewska et al., 2011). Starch, one of the cheapest and most abundant renewable carbohydrates, can serve as a renewable and sustainable source of carbon for liquid fuels and chemicals (Röper, 2002). Starch is a glucose-based polysaccharide linked mainly by a-(1,6)- and a-(1,4)-glycosidic bonds (Stevnebø et al., 2006). The conversion of starch to HMF can be accomplished in two main steps: (1) hydrolysis of starch into glucose; (2) dehydration of the latter into HMF. Both the hydrolysis and dehydration reactions could be
⇑ Corresponding authors. Tel.: +1 765 494 5302; fax: +1 765 494 0239 (M.M. Abu-Omar). E-mail addresses: [email protected] (C. Hu), [email protected] (M.M. Abu-Omar). 0960-8524/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2012.03.081
catalyzed by acid; as a result many acid catalysts have been used for the conversion of starch to HMF. Chheda et al. (2007) studied the use of HCl, H2SO4 and H3PO4 as Brønsted acid catalysts in a two-phase batch reactor. HMF yield of 36% was obtained. Some Lewis acids such as SnCl4 (Hu et al., 2009b), AlCl3 (Yang et al., 2012) and CrCl3 (Zhao et al., 2007), could divide the dehydration of glucose into two steps: (1) isomerization of glucose to fructose; (2) dehydration of the latter into HMF. The conversion of starch catalyzed by SnCl4 in ionic liquid medium, 1-ethyl-3-methylimidazolium tetrafluoroborate, gives 47% HMF yield (Hu et al., 2009b). Using AlCl3 in H2O–THF system affords 50% HMF yield from starch (Yang et al., 2012). Jae-An Chun (Chun et al., 2010) used HCl–CrCl3 as co-catalysts for the conversion of starch to HMF, and a high yield of HMF (73%) was reported. Base catalysts can also catalyze the isomerization of glucose-to-fructose (James et al., 2010); thus, a mixed catalyst system that contains both an acid catalyst (H3PO4) and a base catalyst (pyridine) has also been used in the conversion of starch to HMF (Mednick, 1962). HMF yield of 44% was obtained in this mixed-acid–base system. The homogeneous Brønsted and Lewis acid catalysts affect both the hydrolysis and dehydration. However, there are some disadvantages of these catalysts including pollution, toxicity, and separation problems. Therefore, a low-toxicity, easy to handle heterogeneous catalyst is more desirable. Solid acid or acid–base catalysts have been used in the hydrolysis of starch (Yamaguchi and Hara, 2010; Matsumoto et al., 2011) and dehydration of glucose into HMF (Watanabe et al., 2005; Yan et al., 2009; Zhang and Zhao, 2011; Yang et al. 2010). Moreover, the basic sites on solid acid–base catalyst could also
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catalyze the isomerization of glucose-to-fructose (Watanabe et al., 2005; Yan et al., 2009), and reasonable HMF yield could be obtained from glucose over a single solid acid–base catalyst. Compared to a mixed solid base, solid acid catalyst (Takagaki et al., 2009), a single bifunctional solid catalyst bears uniform distribution of active sites. These findings inspired us to integrate the hydrolysis and dehydration steps into a one-pot conversion of starch into HMF over a single bifunctional solid catalyst, which can perform two steps consecutively. In this work, we report a one-pot production of HMF from starch over SO24 /ZrO2–Al2O3 catalyst in dimethyl sulfoxide (DMSO)/water solvent. The effects of reaction time, Zr/Al molar ratio, water content, catalyst loading, and reaction temperature were investigated to optimize the process. 2. Material and methods 2.1. Materials Starch, glucose and fructose (99%) were purchased from Kelong Company. HMF (99%) was purchased from Aldrich. The series of SO24 /ZrO2–Al2O3 catalysts (CSZA) were the same as those used in our previous work (Yan et al., 2009). CSZA with Zr:Al molar ratio of 9:1, 7:3, 1:1, 3:7, and 1:9 were labeled as CSZA-1, CSZA-2, CSZA-3, CSZA-4, and CSZA-5, respectively. The data of acidity and basicity of CSZA catalyst were given in the reference (Yan et al., 2009). Sulfonated ion-exchange resin Amberlyst-15 was purchased from Kelong Company (Chengdu, China). H-form zeolite materials, including Hb (Si/Al = 25), HZSM-5 (Si/Al = 25), and HY (Si/Al = 5) were supplied by Nankai University Catalyst Company, Ltd., (Tianjin, China). Al2O3 was purchased from Rihua Company (Taiyuan, China). These five solid catalysts were used in control experiments. All other reagents (analytical grade) were purchased from Kelong Company and used as received. 2.2. General reaction procedure Starch (0.25 mmol based on glucose unit) or glucose (0.25 mmol), catalyst, DMSO (1 ml) and the desired amount of water were loaded into a 5 ml glass flask equipped with a reflux condenser. After the temperature of thermostatic oil bath rose to reaction temperature and kept constant, the reaction vessel was then put into the oil bath. Zero time was taken as soon as the reaction vessel was put into the oil bath. The reaction mixture was stirred magnetically at 400 rpm. At the end of reaction, the reactor was cooled to room temperature, and the solid catalyst was separated from the solution by centrifugation. The solution was diluted by water, then filtered and subjected to total reducing sugars (TRS), glucose, fructose and HMF analysis. All of the data were based on repeated runs and the standard deviation was less than 2%. 2.3. Analytical methods The yield of TRS was determined by DNS method (Miller, 1959). The concentration of TRS was calculated based on a standard curve obtained with glucose. The analytical error in TRS yield was evaluated to be within the range of ±1%. Quantitative analysis of glucose and fructose were analyzed by HPLC using an UltiMate 3000 RS pump, an aminex column HPX-87 column (Agilent), and Shodex Refractive Index 101 detector. H2SO4 (5 mM) was used as the mobile phase at a flow rate of 0.6 mL/min, and the column temperature was maintained at 328 K. All concentrations of carbohydrates were determined by comparison to standards calibration curves. HMF was identified qualitatively by GC–MS (Agilent, 5973 Network 6890N). Quantitative analysis of HMF was performed by
HPLC using a Waters 1525 pump, a SB-C18 reverse phase column (Agilent) and Waters 2487 UV detector (k = 284 nm). A mixture of acetonitrile and water (1:3 v/v, pH = 2) was used as the mobile phase at a flow rate of 1.0 mL/min, and the column temperature was set at 303 K. The concentration of HMF was calculated based on a standard curve obtained using an authentic HMF sample. The analytical error for glucose, fructose and HMF yield was evaluated to be within the range of ±1%. 3. Results and discussion 3.1. The effect of catalyst variation on the conversion of starch CSZA-3 was tested first for the conversion of starch to HMF. As control samples, four solid acid catalysts (Amberlyst-15, Hb, HZSM-5, and HY) and a solid acid–base catalysts (Al2O3) were investigated. The results are summarized in Table 1. Only CSZA-3 showed activity for the conversion of starch to HMF. Within 4 h, HMF yield of 48% was obtained. This value is more than twice of that obtained with H2SO4 as catalyst (21%). Meanwhile, a low TRS yield of 4% with a glucose yield of 1% was observed for CSZA-3 after 4 h. As for the other solid catalysts mentioned above, although some TRS was formed within 4 h, no glucose or HMF was detected. The complex pathway of the hydrolysis of polysaccharides is generically described as follows: polysaccharide ? oligosaccharides ? monosaccharides ? dehydration products (Rinaldi et al., 2008). This means that starch was only hydrolyzed to oligosaccharides over the control solid catalyst within 4 h. A similar phenomenon was observed in the hydrolysis of starch under hydrothermal condition at 473 K (Nagamori and Funazukuri, 2004), where no glucose was detected as the reaction time shortened to 5 min, and glucose yield as high as 630 g/kg on carbon basis could be obtained when the reaction time was prolonged to 30 min. It has been suggested that the degradation of starch to glucose may need prolonged reaction time. Hence, by prolonging the reaction time over those five catalysts to 48 h, glucose and HMF formation was observed, however, the yield was still low. Glucose was used as a starting material to investigate the catalytic performance of CSZA-3. The formation of HMF was observed in the presence of all six solid catalysts, albeit at varying yields. Solid acid catalysts afforded only 8–12% yield of HMF. A higher HMF yield of 37% was obtained over Al2O3. The acidity of Al2O3 is weaker than the solid acid catalysts, which is less than optimal for the dehydration reaction. However, the basic sites on Al2O3 can catalyze the isomerization of glucose-to-fructose (Zeng et al., 2009), which made the conversion of glucose to HMF over Al2O3 more facile than that over the solid acid catalysts. CSZA-3 gave the highest HMF yield from glucose (56%). CSZA-3 bears both basic sites and strong acidic sites (Yan et al., 2009). All the six solid catalysts
Table 1 The yield of HMF, TRS and glucose over solid catalysts tested a. Entry
Catalyst
HMF yield from starch (%)
TRS yield from starch (%)
Glucose yield from starch (%)
HMF yield from glucose (%)
1 2
CSZA-3 Amberlyst15 Hb HZSM-5 HY Al2O3 H2SO4
48 0
4 11
1 0
56 8
0 0 0 0 21
11 8 5 1 5
0 0 0 0 4
9 12 9 37 23
3 4 5 6 7
a Reaction condition: DMSO: 1 mL, H2O: 0.2 mL, starch: 0.25 mmol based on glucose unit (or glucose: 0.25 mmol), catalyst: 2.4 mg, temperature: 423 K, reaction time: 4 h.
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investigated herein showed activity for the hydrolysis of starch to glucose and dehydration of glucose to HMF. However, the formation of HMF from starch was only observed over CSZA-3 within 4 h. CSZA-3 stands out versus the other solid catalysts in its ability to act as a bifunctional catalyst for hydrolysis of starch to glucose and the dehydration of glucose to HMF. Because some TRS was still detected in the product mixture (entry 1, Table 1), the conversion of starch to HMF over CSZA-3 might not be complete within 4 h. Thus, the effect of reaction time was probed. 3.2. The effect of reaction time on the conversion of starch
30
60
25
50
20
40
15
30
TRS yield Glucose yield Fructose yield HMF yield
10
20
5
HMF yield (%)
Yield (%)
A typical time profile for the conversion of starch over CSZA-3 is shown in Fig. 1. In the first 0.5 h, TRS was formed and no glucose or HMF was detectable. This observation led to the conclusion that in the first 0.5 h starch was being degraded to oligosaccharides but not glucose. At longer reaction time, glucose was formed, and a maximum glucose yield of 14% could be obtained after 2 h. Some fructose was also formed as CSZA-3 could catalyze the isomerization of glucose-to-fructose (Yan et al., 2009). Trace amount of HMF was detected at 1 h. After 2 h, TRS yield began to drop but HMF yield continued to rise to a maximum value of 55% after
10
0
0 0
2
4
6
8
10
12
Reaction time (h) Fig. 1. Time profile for the conversion of starch over CSZA-3 catalyst Reaction condition: DMSO: 1 mL, H2O: 0.2 mL, starch: 0.25 mmol based on glucose unit, CSZA-3 catalyst: 2.4 mg, temperature: 423 K.
6 h. This value is close to the maximum HMF yield obtained from glucose over CSZA-3 after 4 h (57%, seen in Fig. 2). After 6 h, only trace amount of TRS was detected, indicating that starch was totally hydrolyzed to glucose, which was subsequently converted to HMF. Further increase in reaction time beyond 6 h results in slow degradation of HMF (Román-Leshkov et al., 2006). Since the conversion of glucose to HMF (Fig. 2) is faster than the conversion of starch to HMF under identical conditions, the hydrolysis step is rate determining in the conversion of starch to HMF over CSZA-3. A similar phenomenon was also observed in another report (Hu et al., 2009b). The conversion of glucose to HMF over SnCl4 reaches 61% yield within 4 h, while from starch only 47% HMF yield is produced after 24 h. The glucose-to-fructose isomerization was more evident when glucose was used as the starting material. A maximum fructose yield of 13% was observed within 0.5 h. 3.3. The effect of the acid–base property of CSAZ on the conversion of starch to HMF CSAZ catalysts with different Zr/Al molar ratios and different acid–base properties were investigated to elucidate the effect of the acid–base property of CSAZ on the conversion of starch to HMF. CSZA-1 with highest Zr/Al molar ratio (9:1) features the highest amount of acid sites and the lowest amount of base sites. As the Zr/Al molar ratio decreases, the amount of acid sites is reduced and the amount of base sites increases (Yan et al., 2009). The hydrolysis of starch to TRS and the dehydration of glucose to HMF were tested individually at first. As only trace amount of HMF is formed within the first hour of reaction, the TRS yield within 1 h was used instead to illustrate the rate of the hydrolysis step. As shown in Fig. 3, the highest TRS yield within 1 h was obtained over CSZA-1, which has the highest amount of acid sites. The yield of TRS correlates linearly with the number of acid sites on the CSZA. The CSZA catalyst with higher acidity displayed higher hydrolysis activity for starch. The results of the dehydration step are given in Table 2. For the dehydration of glucose, the highest HMF yield (56%) was obtained with CSZA-3, which is characterized by high acidity and moderate basicity. This catalyst exhibited the highest catalytic activity for the dehydration of glucose in pure DMSO at 403 K (Yan et al., 2009). Here, with water added and temperature increased, CSZA-3 is still the optimal catalyst for the dehydration of glucose to HMF.
25
CSZA-1
Glucose conversion Fructose yield HMF yield
80
20
CSZA-2 CSZA-3
TRS yield (%)
Conversion and yield (%)
100
60
40
15
CSZA-5
CSZA-4
10
20 5
0 0
0
2
4
6
8
10
12
Reaction time (h) Fig. 2. Time profile for the conversion of glucose over CSZA-3 catalyst Reaction condition: DMSO: 1 mL, H2O: 0.2 mL, glucose: 0.25 mmol, CSZA-3 catalyst: 2.4 mg, temperature: 423 K.
0.8
1.0
1.2
1.4
1.6
1.8
Amount of acid sites (mmol/g) Fig. 3. The effect of the amount of acid sites over CSZA on the TRS yield Reaction condition: DMSO: 1 mL, H2O: 0.2 mL, starch: 0.25 mmol based on glucose unit, CSZA-3 catalyst: 2.4 mg, temperature: 423 K, reaction time: 1 h.
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Y. Yang et al. / Bioresource Technology 116 (2012) 302–306 Table 2 The Effect of the different CSZA catalysts on HMF yield from glucose and starch a. Entry
Catalyst
HMF yield from glucose (%)
HMF yield from starch (%)
1 2 3 4 5
CSZA-1 CSZA-2 CSZA-3 CSZA-4 CSZA-5
40 47 56 52 49
38 46 55 49 45
a Reaction condition: DMSO: 1 mL, H2O: 0.2 mL, glucose: 0.25 mmol (or starch: 0.25 mmol based on glucose unit), catalyst: 2.4 mg, temperature: 423 K, reaction time: 6 h.
The results for starch conversion to HMF are also displayed in Table 2. CSZA-1 with the highest activity for the hydrolysis step, gave the lowest HMF yield (38%). Its low activity towards glucose dehydration led to the low HMF yield from starch. Despite its lower activity towards hydrolysis when compared with CSZA-1 and CSZA-2, CSZA-3 is the best catalyst in the group because it is capable of catalyzing starch hydrolysis and is most effective for the subsequent dehydration of glucose. As for CSZA-4 and CSZA-5, the rate of starch hydrolysis is decreased as the number of acidic sites is lessened, which leads to incomplete hydrolysis of starch within 6 h. The HMF yields for CSZA-4 and CSZA-5 from glucose are also lower than those obtained with CSZA-3. All in all CSZA-3 exhibited the highest activity for HMF formation from starch as it contains the right balance of acidic and basic sites for hydrolysis and subsequent dehydration of glucose. 3.4. The effect of water on the conversion of starch to HMF Water was not only a solvent in this system, but also a reactant for the hydrolysis step as well as a product in the dehydration step. Hence, the amount of water at the offset of the reaction might influence the reaction kinetics or product yields. The effect of water on the hydrolysis of starch to TRS, the dehydration of glucose to HMF and the conversion of starch to HMF were investigated. The results are shown in Fig. 4. For the hydrolysis step, the TRS yield from starch is only 8% for R = 11 (R = molar ratio of water to glucose units). The rate of starch hydrolysis to TRS is slow at low R. For R = 44, the TRS yield is 18%. As R increases to 66, the TRS yield reaches a maximum of 21%.
a
TRS yield HMF yield from glucose HMF yield from starch
60
Additional water leads to faster hydrolysis. However, a slight decrease of TRS yield (17%) was found for R = 88. An optimal amount of water for TRS formation could be attributed to the nature of acid-catalyzed hydrolysis. Water not only shifts the equilibrium to products but also affects the rate of the hydrolysis reaction. The acidity of the catalyst and hence its hydrolysis rate could be markedly decreased as more water is added, due to hydration of the acid sites (Yamaguchi et al., 2009). For the dehydration of glucose to HMF, a decrease in HMF yields was observed as R increased. Up to an R value of 44 the effect is essentially absent, but at higher R values of 66 and 88, a discernable decline in HMF yields was observed. Similar results were reported by Li et al. (2010). They discovered that a small amount of water had little effect on HMF yield. However, at R > 44, the HMF yield decreased significantly. At high water concentration, the rate of catalytic dehydration would also decrease because of hydration of the acid sites (Yamaguchi et al. 2009). Meanwhile, the presence of water would also enhance the rehydration of HMF to levulinic acid and formic acid (Corma et al., 2007), which would result in lowered yields of HMF. For HMF formation from starch, the optimal R was found to be 44. Higher R values follow the trend noted for glucose above. At R < 44 the amount of hydrolysis to TRS is small and hence the HMF yield is also small. Although the hydrolysis of starch is faster for R = 66, the negative effect of water on the HMF yield from glucose leads to lower HMF yield as compared to that obtained for R = 44. Since water plays more than one role in this reaction, reactant for hydrolysis, product from dehydration, and catalyst poison by hydrating acidic sites, a specific amount provides optimal kinetics and yields for HMF formation. Similar phenomena were observed when inulin (a fructose based polysaccharide) was used as raw material (Hu et al., 2009a), and the optimal molar ratio of water to fructose unit in inulin was R = 32. 3.5. The effect of catalyst loading on the conversion of starch to HMF The effect of catalyst loading is presented in Fig. 5. The hydrolysis of starch to TRS and glucose dehydration to HMF over different amount of CSZA-3 were investigated. In the hydrolysis step, an increase of TRS yield was observed as more CSZA-3 is used. TRS yields gradually increased from 13% to 20% as the catalyst loading increased from 0.6 to 9.0 mg. As for the dehydration of glucose, HMF yield was low at low catalyst loading. As the amount of CSZA-3 is increased, HMF yields increased to a maximum of 56% at 2.4 mg catalyst loading. Further increase of CSZA-3 to 9.0 mg
a
50
40
40
30
Yield (%)
Yield (%)
TRS yield HM F yield from glucose HM F yield from starch
60
50
20
30
20
10 10
0 11
22
44
66
88
The mlor ratio of water to glucose unit Fig. 4. The Effect of water on the conversion of starch and glucose Reaction condition: DMSO: 1 mL, starch: 0.25 mmol based on glucose unit (or glucose: 0.25 mmol), CSZA-3 catalyst: 2.4 mg, temperature: 423 K, reaction time: 6 h. a Reaction time: 1 h.
0
0.6
1.2
4.5 2.4 Catalyst amount (mg)
9.0
Fig. 5. The Effect of catalyst loading on the conversion of starch and glucose Reaction condition: DMSO: 1 mL, H2O: 0.2 mL, starch: 0.25 mmol based on glucose unit (or glucose: 0.25 mmol), temperature: 423 K, reaction time: 6 h. a reaction time: 1 h.
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Y. Yang et al. / Bioresource Technology 116 (2012) 302–306 a
TRS yield HMF yield from glucose HMF yield from starch a HMF yield from starch
60
50
Yield (%)
40
30
20
10
0
403
413
423 Temperature (K)
433
443
Fig. 6. The Effect of reaction temperature on the conversion of starch and glucose Reaction condition: DMSO: 1 mL, H2O: 0.2 mL, starch: 0.25 mmol based on glucose unit (or glucose: 0.25 mmol), CSZA-3 catalyst: 2.4 mg, reaction time: 6 h. aReaction time: 1 h.
resulted in a drop in HMF yield (43%). This drop is attributed to additional side-reactions that convert HMF to levulinic acid (catalyzed by acid sites) (Corma et al., 2007) and retro-aldol condensation (catalyzed by basic sites) (Yang and Montgomery, 1996). The HMF yield for the conversion of starch gave a similar trend as the glucose dehydration discussed above. The optimal catalyst loading is 2.4 mg (Fig 5). 3.6. The effect of reaction temperature on the conversion of starch to HMF The reaction was carried out at different temperatures from 403 to 443 K. The results for the conversion of starch and glucose are summarized in Fig. 6. While 403 K is a suitable temperature for glucose conversion, it gives very poor yields for starch because at this low temperature the rate of starch hydrolysis is slow. The optimal temperature for starch conversion is 423 K. On the other hand, the optimal temperature for glucose dehydration is 413 K. Significant decrease in HMF yield is observed at temperatures >423 K. Some 2,5-diformylfuran was detected in the reaction mixture. HMF is oxidized at high temperature. 4. Conclusion Starch was efficiently converted to HMF in the presence of CSZA catalysts, which showed activity for both the hydrolysis of starch to glucose and dehydration of the latter, all in a one-pot reaction. CSZA-3 with high acidity and moderate basicity displayed the best kinetics and selectivity to HMF formation from starch, with 55% yield in 6 h at 423 K. A suitable amount of water (R = 44) was found to promote the hydrolysis of starch into glucose and as a result enhanced the yield of HMF from starch. Acknowledgements This work was financially supported by the National Basic Research Program of China (973 program, No. 2007CB210203), NNSFC 21072136, PCSIRT (No. IRT0846), and the Center for direct Catalytic Conversion of Biomass to Biofuels (C3Bio), an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, and Office of Basic Energy Sciences under Award Number DE-SC0000997. The characterization of the product from Analytical and Testing Center of Sichuan University are greatly appreciated. Y.Y. acknowledges support from China Scholarship Council (Grant 2010624099).
References Chheda, J., Romön-Leshkov, Y., Dumesic, J., 2007. Production of 5hydroxymethylfurfural and furfural by dehydration of biomass-derived monoand poly-saccharides. Green Chem. 9, 342–350. Chun, J., Lee, J., Yi, Y., Hong, S., Chung, C., 2010. Direct conversion of starch to hydroxymethylfurfural in the presence of an ionic liquid with metal chloride. Starch 62, 326–330. Corma, A., Iborra, S., Velty, A., 2007. Chemical routes for the transformation of biomass into chemicals. Chem. Rev. 107, 2411–2502. Dodds, D., Gross, R., 2007. Chemicals from biomass. Science 318, 1250–1251. Huber, G., Chheda, J., Barrett, C., Dumesic, J., 2005. Production of liquid alkanes by aqueous-phase processing of biomass-derived carbohydrates. Science 308, 1446–1450. Hu, S., Zhang, Z., Zhou, Y., Song, J., Fan, H., Han, B., 2009a. Direct conversion of inulin to 5-hydroxymethylfurfural in biorenewable ionic liquids. Green Chem. 11, 873–877. Hu, S., Zhang, Z., Song, J., Zhou, Y., Han, B., 2009b. Efficient conversion of glucose into 5-hydroxymethylfurfural catalyzed by a common Lewis acid SnCl4 in an ionic liquid. Green Chem. 11, 1746–1749. James, O.O., Maity, S., Usman, L.A., Ajanaku, K.O., Ajani, O.O., Siyanbola, T.O., Sahu, S., Chaubey, R., 2010. Towards the conversion of carbohydrate biomass feedstocks to biofuels via hydroxylmethylfurfural. Energy Environ. Sci. 3, 1833–1850. Li, C., Zhao, Z., Wang, A., Zheng, M., Zhang, T., 2010. Production of 5hydroxymethylfurfural in ionic liquids under high fructose concentration conditions. Carbohyd. Res. 345, 1846–1850. Matsumoto, A., Tsubaki, S., Sakamoto, M., Azuma, J., 2011. A novel saccharification method of starch using microwave irradiation with addition of activated carbon. Bioresour. Technol. 102, 3985–3988. Miller, G.L., 1959. Use of dinitrosalicylic acid reagent for determination of reducing sugar. Anal. Chem. 31, 426–428. Mednick, M.L., 1962. The acid-base-catalyzed conversion of aldohexose into 5(hydroxymethyl)-2-furfural. J. Org. Chem. 27, 398–403. Nagamori, M., Funazukuri, T., 2004. Glucose production by hydrolysis of starch under hydrothermal conditions. J. Chem. Technol. Biot. 79, 229–233. Roman-Leshkov, Y., Chheda, J., Dumesic, J., 2006. Phase modifiers promote efficient production of hydroxymethylfurfural from fructose. Science 312, 1933–1937. Rostrup-Nielsen, J., 2005. Chemistry: Making fuels from biomass. Science 308, 1421. West, R., Liu, Z., Peter, M., Gärtner, C., Dumesic, J., 2008. Carbon-carbon bond formation for biomass-derived furfurals and ketones by aldol condensation in a biphasic system. J. Mol. Catal. A: Chem. 296, 18–27. Rinaldi, R., Palkovits, R., Schüth, F., 2008. Depolymerization of cellulose using solid catalysts in ionic liquids. Angew. Chem. Int. Edit. 47, 8047–8050. Román-Leshkov, Y., Barrett, C., Liu, Z., Dumesic, J., 2007. Production of dimethylfuran for liquid fuels from biomass-derived carbohydrates. Nature 447, 982–985. Röper, H., 2002. Renewable raw materials in Europe – Industrial utilization of starch and sugar. Starch 54, 89–99. Stevnebø, A., Sahlström, S., Svihus, B., 2006. Starch structure and degree of starch hydrolysis of small and large starch granules from barley varieties with varying amylose content. Anim. Feed Sci. Technol. 130, 23–38. Takagaki, A., Ohara, M., Nishimura, S., Ebitani, K., 2009. A one-pot reaction for biorefinery: combination of solid acid and base catalysts for direct production of 5-hydroxymethylfurfural from saccharides. Chem. Commun. 41, 6268–6276. Tong, X., Ma, Y., Li, Y., 2010. Biomass into chemicals: conversion of sugars to furan derivatives by catalytic processes. Appl. Catal. A: Gen. 385, 1–13. Watanabe, M., Aizawa, Y., Iida, T., Nishimura, R., Inomata, H., 2005. Catalytic glucose and fructose conversions with TiO2 and ZrO2 in water at 473 K: relationship between reactivity and acid-base property determined by TPD measurement. Appl. Catal. A: Gen. 295, 150–156. Yamaguchi, D., Kitano, M., Suganuma, S., Nakajima, K., Kato, H., Hara, M., 2009. Hydrolysis of cellulose by a solid acid catalyst under optimal reaction conditions. J. Phys. Chem. C 113, 3181–3188. Yamaguchi, D., Hara, M., 2010. Starch saccharification by carbon-based solid acid catalyst. Solid State Sci. 12, 1018–1023. Yan, H., Yang, Y., Tong, D., Xiang, X., Hu, C., 2009. Catalytic conversion of glucose to 5-hydroxymethylfurfural over SO24 /ZrO2 and SO24 /ZrO2–Al2O3 solid acid catalysts. Catal. Commun. 10, 1558–1563. Yang, B., Montgomery, R., 1996. Alkaline degradation of glucose: effect of initial concentration of reactants. Carbohyd. Res. 280, 27–45. Yang, F., Liu, Q., Bai, X., Du, Y., 2010. Conversion of biomass into 5-hydroxymethylfurfural using solid acid catalyst. Bioresour. Technol. 102, 3424–3429. Yang, Y., Hu, C., Abu-Omar, M.M., 2012. Conversion of carbohydrates and lignocellulosic biomass into 5-hydroxymethylfurfural using AlCl36H2O catalyst in a biphasic solvent system. Green Chem. 14, 509–513. Zakrzewska, M.E., Bogel-ukasik, E., Bogel-ukasik, R., 2011. Ionic liquid-mediated formation of 5-hydroxymethylfurfural – a promising biomass-derived building block. Chem. Rev. 111, 397–417. Zeng, W., Cheng, D., Chen, F., Zhan, X., 2009. Catalytic conversion of glucose on Al–Zr mixed oxides in hot compressed water. Catal. Lett. 133, 221–226. Zhang, Z., Zhao, Z., 2011. Production of 5-hydroxymethylfurfural from glucose catalyzed by hydroxyapatite supported chromium chloride. Bioresour. Technol. 102, 3970–3972. Zhao, H., Holladay, J., Brown, H., Zhang, Z., 2007. Metal chlorides in ionic liquid solvents convert sugars to 5-hydroxymethylfurfural. Science 316, 1597–1600.
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One-pot synthesis of 5-hydroxymethylfurfural directly from starch over SO24 /ZrO2–Al2O3 solid catalyst Yu Yang a,b, Xi Xiang a, Dongmei Tong a, Changwei Hu a,⇑, Mahdi M. Abu-Omar b,⇑ a b
Key Laboratory of Green Chemistry and Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, Sichuan 610064, PR China Department of Chemistry and the Center for Direct Catalytic Conversion of Biomass to Biofuels (C3Bio), Purdue University, 560 Oval Drive, West Lafayette, IN 47907, USA
a r t i c l e
i n f o
Article history: Received 20 January 2012 Received in revised form 20 March 2012 Accepted 24 March 2012 Available online 30 March 2012 Keywords: Starch 5-Hydromethylfurfural Hydrolysis Dehydration SO24 /ZrO2–Al2O3 catalyst
a b s t r a c t The synthesis of 5-hydroxymethylfurfural (HMF) directly from starch was studied in dimethyl sulfoxide– water. The effects of catalyst variation, reaction time, water content, catalyst loading and temperature on the reaction were investigated. The SO24 /ZrO2–Al2O3 catalyst was found to act as a bifunctional catalyst with high activity for both hydrolysis and dehydration of starch. HMF yield of 55% was obtained after 6 h at 423 K for the reaction of starch (the molar ratio of water to glucose in starch is 44/1) over the SO24 / ZrO2–Al2O3 catalyst, which bears high acidity and moderate basicity with Zr/Al molar ratio of 1:1. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction With declining petroleum resources and rising environmental concerns, the production of energy and chemicals from renewable biomass has become an intense topic of applied and basic research. (Dodds and Gross, 2007; Rostrup-Nielsen, 2005) 5-Hydroxymethylfurfural (HMF), a versatile intermediate between biomass-based carbohydrates and petroleum-based industrial chemicals, has received much attention as an interesting platform molecule in biomass conversion. It can be converted to many value-added chemicals as well as liquid fuels that are compatible with the current infrastructure (Huber et al., 2005; Román-Leshkov et al., 2007; West et al., 2008). Different feedstock such as fructose, glucose, sucrose, inulin, cellulose, and starch, have been reported to give HMF at varying efficiencies (Tong et al., 2010; Zakrzewska et al., 2011). Starch, one of the cheapest and most abundant renewable carbohydrates, can serve as a renewable and sustainable source of carbon for liquid fuels and chemicals (Röper, 2002). Starch is a glucose-based polysaccharide linked mainly by a-(1,6)- and a-(1,4)-glycosidic bonds (Stevnebø et al., 2006). The conversion of starch to HMF can be accomplished in two main steps: (1) hydrolysis of starch into glucose; (2) dehydration of the latter into HMF. Both the hydrolysis and dehydration reactions could be
⇑ Corresponding authors. Tel.: +1 765 494 5302; fax: +1 765 494 0239 (M.M. Abu-Omar). E-mail addresses: [email protected] (C. Hu), [email protected] (M.M. Abu-Omar). 0960-8524/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2012.03.081
catalyzed by acid; as a result many acid catalysts have been used for the conversion of starch to HMF. Chheda et al. (2007) studied the use of HCl, H2SO4 and H3PO4 as Brønsted acid catalysts in a two-phase batch reactor. HMF yield of 36% was obtained. Some Lewis acids such as SnCl4 (Hu et al., 2009b), AlCl3 (Yang et al., 2012) and CrCl3 (Zhao et al., 2007), could divide the dehydration of glucose into two steps: (1) isomerization of glucose to fructose; (2) dehydration of the latter into HMF. The conversion of starch catalyzed by SnCl4 in ionic liquid medium, 1-ethyl-3-methylimidazolium tetrafluoroborate, gives 47% HMF yield (Hu et al., 2009b). Using AlCl3 in H2O–THF system affords 50% HMF yield from starch (Yang et al., 2012). Jae-An Chun (Chun et al., 2010) used HCl–CrCl3 as co-catalysts for the conversion of starch to HMF, and a high yield of HMF (73%) was reported. Base catalysts can also catalyze the isomerization of glucose-to-fructose (James et al., 2010); thus, a mixed catalyst system that contains both an acid catalyst (H3PO4) and a base catalyst (pyridine) has also been used in the conversion of starch to HMF (Mednick, 1962). HMF yield of 44% was obtained in this mixed-acid–base system. The homogeneous Brønsted and Lewis acid catalysts affect both the hydrolysis and dehydration. However, there are some disadvantages of these catalysts including pollution, toxicity, and separation problems. Therefore, a low-toxicity, easy to handle heterogeneous catalyst is more desirable. Solid acid or acid–base catalysts have been used in the hydrolysis of starch (Yamaguchi and Hara, 2010; Matsumoto et al., 2011) and dehydration of glucose into HMF (Watanabe et al., 2005; Yan et al., 2009; Zhang and Zhao, 2011; Yang et al. 2010). Moreover, the basic sites on solid acid–base catalyst could also
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catalyze the isomerization of glucose-to-fructose (Watanabe et al., 2005; Yan et al., 2009), and reasonable HMF yield could be obtained from glucose over a single solid acid–base catalyst. Compared to a mixed solid base, solid acid catalyst (Takagaki et al., 2009), a single bifunctional solid catalyst bears uniform distribution of active sites. These findings inspired us to integrate the hydrolysis and dehydration steps into a one-pot conversion of starch into HMF over a single bifunctional solid catalyst, which can perform two steps consecutively. In this work, we report a one-pot production of HMF from starch over SO24 /ZrO2–Al2O3 catalyst in dimethyl sulfoxide (DMSO)/water solvent. The effects of reaction time, Zr/Al molar ratio, water content, catalyst loading, and reaction temperature were investigated to optimize the process. 2. Material and methods 2.1. Materials Starch, glucose and fructose (99%) were purchased from Kelong Company. HMF (99%) was purchased from Aldrich. The series of SO24 /ZrO2–Al2O3 catalysts (CSZA) were the same as those used in our previous work (Yan et al., 2009). CSZA with Zr:Al molar ratio of 9:1, 7:3, 1:1, 3:7, and 1:9 were labeled as CSZA-1, CSZA-2, CSZA-3, CSZA-4, and CSZA-5, respectively. The data of acidity and basicity of CSZA catalyst were given in the reference (Yan et al., 2009). Sulfonated ion-exchange resin Amberlyst-15 was purchased from Kelong Company (Chengdu, China). H-form zeolite materials, including Hb (Si/Al = 25), HZSM-5 (Si/Al = 25), and HY (Si/Al = 5) were supplied by Nankai University Catalyst Company, Ltd., (Tianjin, China). Al2O3 was purchased from Rihua Company (Taiyuan, China). These five solid catalysts were used in control experiments. All other reagents (analytical grade) were purchased from Kelong Company and used as received. 2.2. General reaction procedure Starch (0.25 mmol based on glucose unit) or glucose (0.25 mmol), catalyst, DMSO (1 ml) and the desired amount of water were loaded into a 5 ml glass flask equipped with a reflux condenser. After the temperature of thermostatic oil bath rose to reaction temperature and kept constant, the reaction vessel was then put into the oil bath. Zero time was taken as soon as the reaction vessel was put into the oil bath. The reaction mixture was stirred magnetically at 400 rpm. At the end of reaction, the reactor was cooled to room temperature, and the solid catalyst was separated from the solution by centrifugation. The solution was diluted by water, then filtered and subjected to total reducing sugars (TRS), glucose, fructose and HMF analysis. All of the data were based on repeated runs and the standard deviation was less than 2%. 2.3. Analytical methods The yield of TRS was determined by DNS method (Miller, 1959). The concentration of TRS was calculated based on a standard curve obtained with glucose. The analytical error in TRS yield was evaluated to be within the range of ±1%. Quantitative analysis of glucose and fructose were analyzed by HPLC using an UltiMate 3000 RS pump, an aminex column HPX-87 column (Agilent), and Shodex Refractive Index 101 detector. H2SO4 (5 mM) was used as the mobile phase at a flow rate of 0.6 mL/min, and the column temperature was maintained at 328 K. All concentrations of carbohydrates were determined by comparison to standards calibration curves. HMF was identified qualitatively by GC–MS (Agilent, 5973 Network 6890N). Quantitative analysis of HMF was performed by
HPLC using a Waters 1525 pump, a SB-C18 reverse phase column (Agilent) and Waters 2487 UV detector (k = 284 nm). A mixture of acetonitrile and water (1:3 v/v, pH = 2) was used as the mobile phase at a flow rate of 1.0 mL/min, and the column temperature was set at 303 K. The concentration of HMF was calculated based on a standard curve obtained using an authentic HMF sample. The analytical error for glucose, fructose and HMF yield was evaluated to be within the range of ±1%. 3. Results and discussion 3.1. The effect of catalyst variation on the conversion of starch CSZA-3 was tested first for the conversion of starch to HMF. As control samples, four solid acid catalysts (Amberlyst-15, Hb, HZSM-5, and HY) and a solid acid–base catalysts (Al2O3) were investigated. The results are summarized in Table 1. Only CSZA-3 showed activity for the conversion of starch to HMF. Within 4 h, HMF yield of 48% was obtained. This value is more than twice of that obtained with H2SO4 as catalyst (21%). Meanwhile, a low TRS yield of 4% with a glucose yield of 1% was observed for CSZA-3 after 4 h. As for the other solid catalysts mentioned above, although some TRS was formed within 4 h, no glucose or HMF was detected. The complex pathway of the hydrolysis of polysaccharides is generically described as follows: polysaccharide ? oligosaccharides ? monosaccharides ? dehydration products (Rinaldi et al., 2008). This means that starch was only hydrolyzed to oligosaccharides over the control solid catalyst within 4 h. A similar phenomenon was observed in the hydrolysis of starch under hydrothermal condition at 473 K (Nagamori and Funazukuri, 2004), where no glucose was detected as the reaction time shortened to 5 min, and glucose yield as high as 630 g/kg on carbon basis could be obtained when the reaction time was prolonged to 30 min. It has been suggested that the degradation of starch to glucose may need prolonged reaction time. Hence, by prolonging the reaction time over those five catalysts to 48 h, glucose and HMF formation was observed, however, the yield was still low. Glucose was used as a starting material to investigate the catalytic performance of CSZA-3. The formation of HMF was observed in the presence of all six solid catalysts, albeit at varying yields. Solid acid catalysts afforded only 8–12% yield of HMF. A higher HMF yield of 37% was obtained over Al2O3. The acidity of Al2O3 is weaker than the solid acid catalysts, which is less than optimal for the dehydration reaction. However, the basic sites on Al2O3 can catalyze the isomerization of glucose-to-fructose (Zeng et al., 2009), which made the conversion of glucose to HMF over Al2O3 more facile than that over the solid acid catalysts. CSZA-3 gave the highest HMF yield from glucose (56%). CSZA-3 bears both basic sites and strong acidic sites (Yan et al., 2009). All the six solid catalysts
Table 1 The yield of HMF, TRS and glucose over solid catalysts tested a. Entry
Catalyst
HMF yield from starch (%)
TRS yield from starch (%)
Glucose yield from starch (%)
HMF yield from glucose (%)
1 2
CSZA-3 Amberlyst15 Hb HZSM-5 HY Al2O3 H2SO4
48 0
4 11
1 0
56 8
0 0 0 0 21
11 8 5 1 5
0 0 0 0 4
9 12 9 37 23
3 4 5 6 7
a Reaction condition: DMSO: 1 mL, H2O: 0.2 mL, starch: 0.25 mmol based on glucose unit (or glucose: 0.25 mmol), catalyst: 2.4 mg, temperature: 423 K, reaction time: 4 h.
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investigated herein showed activity for the hydrolysis of starch to glucose and dehydration of glucose to HMF. However, the formation of HMF from starch was only observed over CSZA-3 within 4 h. CSZA-3 stands out versus the other solid catalysts in its ability to act as a bifunctional catalyst for hydrolysis of starch to glucose and the dehydration of glucose to HMF. Because some TRS was still detected in the product mixture (entry 1, Table 1), the conversion of starch to HMF over CSZA-3 might not be complete within 4 h. Thus, the effect of reaction time was probed. 3.2. The effect of reaction time on the conversion of starch
30
60
25
50
20
40
15
30
TRS yield Glucose yield Fructose yield HMF yield
10
20
5
HMF yield (%)
Yield (%)
A typical time profile for the conversion of starch over CSZA-3 is shown in Fig. 1. In the first 0.5 h, TRS was formed and no glucose or HMF was detectable. This observation led to the conclusion that in the first 0.5 h starch was being degraded to oligosaccharides but not glucose. At longer reaction time, glucose was formed, and a maximum glucose yield of 14% could be obtained after 2 h. Some fructose was also formed as CSZA-3 could catalyze the isomerization of glucose-to-fructose (Yan et al., 2009). Trace amount of HMF was detected at 1 h. After 2 h, TRS yield began to drop but HMF yield continued to rise to a maximum value of 55% after
10
0
0 0
2
4
6
8
10
12
Reaction time (h) Fig. 1. Time profile for the conversion of starch over CSZA-3 catalyst Reaction condition: DMSO: 1 mL, H2O: 0.2 mL, starch: 0.25 mmol based on glucose unit, CSZA-3 catalyst: 2.4 mg, temperature: 423 K.
6 h. This value is close to the maximum HMF yield obtained from glucose over CSZA-3 after 4 h (57%, seen in Fig. 2). After 6 h, only trace amount of TRS was detected, indicating that starch was totally hydrolyzed to glucose, which was subsequently converted to HMF. Further increase in reaction time beyond 6 h results in slow degradation of HMF (Román-Leshkov et al., 2006). Since the conversion of glucose to HMF (Fig. 2) is faster than the conversion of starch to HMF under identical conditions, the hydrolysis step is rate determining in the conversion of starch to HMF over CSZA-3. A similar phenomenon was also observed in another report (Hu et al., 2009b). The conversion of glucose to HMF over SnCl4 reaches 61% yield within 4 h, while from starch only 47% HMF yield is produced after 24 h. The glucose-to-fructose isomerization was more evident when glucose was used as the starting material. A maximum fructose yield of 13% was observed within 0.5 h. 3.3. The effect of the acid–base property of CSAZ on the conversion of starch to HMF CSAZ catalysts with different Zr/Al molar ratios and different acid–base properties were investigated to elucidate the effect of the acid–base property of CSAZ on the conversion of starch to HMF. CSZA-1 with highest Zr/Al molar ratio (9:1) features the highest amount of acid sites and the lowest amount of base sites. As the Zr/Al molar ratio decreases, the amount of acid sites is reduced and the amount of base sites increases (Yan et al., 2009). The hydrolysis of starch to TRS and the dehydration of glucose to HMF were tested individually at first. As only trace amount of HMF is formed within the first hour of reaction, the TRS yield within 1 h was used instead to illustrate the rate of the hydrolysis step. As shown in Fig. 3, the highest TRS yield within 1 h was obtained over CSZA-1, which has the highest amount of acid sites. The yield of TRS correlates linearly with the number of acid sites on the CSZA. The CSZA catalyst with higher acidity displayed higher hydrolysis activity for starch. The results of the dehydration step are given in Table 2. For the dehydration of glucose, the highest HMF yield (56%) was obtained with CSZA-3, which is characterized by high acidity and moderate basicity. This catalyst exhibited the highest catalytic activity for the dehydration of glucose in pure DMSO at 403 K (Yan et al., 2009). Here, with water added and temperature increased, CSZA-3 is still the optimal catalyst for the dehydration of glucose to HMF.
25
CSZA-1
Glucose conversion Fructose yield HMF yield
80
20
CSZA-2 CSZA-3
TRS yield (%)
Conversion and yield (%)
100
60
40
15
CSZA-5
CSZA-4
10
20 5
0 0
0
2
4
6
8
10
12
Reaction time (h) Fig. 2. Time profile for the conversion of glucose over CSZA-3 catalyst Reaction condition: DMSO: 1 mL, H2O: 0.2 mL, glucose: 0.25 mmol, CSZA-3 catalyst: 2.4 mg, temperature: 423 K.
0.8
1.0
1.2
1.4
1.6
1.8
Amount of acid sites (mmol/g) Fig. 3. The effect of the amount of acid sites over CSZA on the TRS yield Reaction condition: DMSO: 1 mL, H2O: 0.2 mL, starch: 0.25 mmol based on glucose unit, CSZA-3 catalyst: 2.4 mg, temperature: 423 K, reaction time: 1 h.
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Y. Yang et al. / Bioresource Technology 116 (2012) 302–306 Table 2 The Effect of the different CSZA catalysts on HMF yield from glucose and starch a. Entry
Catalyst
HMF yield from glucose (%)
HMF yield from starch (%)
1 2 3 4 5
CSZA-1 CSZA-2 CSZA-3 CSZA-4 CSZA-5
40 47 56 52 49
38 46 55 49 45
a Reaction condition: DMSO: 1 mL, H2O: 0.2 mL, glucose: 0.25 mmol (or starch: 0.25 mmol based on glucose unit), catalyst: 2.4 mg, temperature: 423 K, reaction time: 6 h.
The results for starch conversion to HMF are also displayed in Table 2. CSZA-1 with the highest activity for the hydrolysis step, gave the lowest HMF yield (38%). Its low activity towards glucose dehydration led to the low HMF yield from starch. Despite its lower activity towards hydrolysis when compared with CSZA-1 and CSZA-2, CSZA-3 is the best catalyst in the group because it is capable of catalyzing starch hydrolysis and is most effective for the subsequent dehydration of glucose. As for CSZA-4 and CSZA-5, the rate of starch hydrolysis is decreased as the number of acidic sites is lessened, which leads to incomplete hydrolysis of starch within 6 h. The HMF yields for CSZA-4 and CSZA-5 from glucose are also lower than those obtained with CSZA-3. All in all CSZA-3 exhibited the highest activity for HMF formation from starch as it contains the right balance of acidic and basic sites for hydrolysis and subsequent dehydration of glucose. 3.4. The effect of water on the conversion of starch to HMF Water was not only a solvent in this system, but also a reactant for the hydrolysis step as well as a product in the dehydration step. Hence, the amount of water at the offset of the reaction might influence the reaction kinetics or product yields. The effect of water on the hydrolysis of starch to TRS, the dehydration of glucose to HMF and the conversion of starch to HMF were investigated. The results are shown in Fig. 4. For the hydrolysis step, the TRS yield from starch is only 8% for R = 11 (R = molar ratio of water to glucose units). The rate of starch hydrolysis to TRS is slow at low R. For R = 44, the TRS yield is 18%. As R increases to 66, the TRS yield reaches a maximum of 21%.
a
TRS yield HMF yield from glucose HMF yield from starch
60
Additional water leads to faster hydrolysis. However, a slight decrease of TRS yield (17%) was found for R = 88. An optimal amount of water for TRS formation could be attributed to the nature of acid-catalyzed hydrolysis. Water not only shifts the equilibrium to products but also affects the rate of the hydrolysis reaction. The acidity of the catalyst and hence its hydrolysis rate could be markedly decreased as more water is added, due to hydration of the acid sites (Yamaguchi et al., 2009). For the dehydration of glucose to HMF, a decrease in HMF yields was observed as R increased. Up to an R value of 44 the effect is essentially absent, but at higher R values of 66 and 88, a discernable decline in HMF yields was observed. Similar results were reported by Li et al. (2010). They discovered that a small amount of water had little effect on HMF yield. However, at R > 44, the HMF yield decreased significantly. At high water concentration, the rate of catalytic dehydration would also decrease because of hydration of the acid sites (Yamaguchi et al. 2009). Meanwhile, the presence of water would also enhance the rehydration of HMF to levulinic acid and formic acid (Corma et al., 2007), which would result in lowered yields of HMF. For HMF formation from starch, the optimal R was found to be 44. Higher R values follow the trend noted for glucose above. At R < 44 the amount of hydrolysis to TRS is small and hence the HMF yield is also small. Although the hydrolysis of starch is faster for R = 66, the negative effect of water on the HMF yield from glucose leads to lower HMF yield as compared to that obtained for R = 44. Since water plays more than one role in this reaction, reactant for hydrolysis, product from dehydration, and catalyst poison by hydrating acidic sites, a specific amount provides optimal kinetics and yields for HMF formation. Similar phenomena were observed when inulin (a fructose based polysaccharide) was used as raw material (Hu et al., 2009a), and the optimal molar ratio of water to fructose unit in inulin was R = 32. 3.5. The effect of catalyst loading on the conversion of starch to HMF The effect of catalyst loading is presented in Fig. 5. The hydrolysis of starch to TRS and glucose dehydration to HMF over different amount of CSZA-3 were investigated. In the hydrolysis step, an increase of TRS yield was observed as more CSZA-3 is used. TRS yields gradually increased from 13% to 20% as the catalyst loading increased from 0.6 to 9.0 mg. As for the dehydration of glucose, HMF yield was low at low catalyst loading. As the amount of CSZA-3 is increased, HMF yields increased to a maximum of 56% at 2.4 mg catalyst loading. Further increase of CSZA-3 to 9.0 mg
a
50
40
40
30
Yield (%)
Yield (%)
TRS yield HM F yield from glucose HM F yield from starch
60
50
20
30
20
10 10
0 11
22
44
66
88
The mlor ratio of water to glucose unit Fig. 4. The Effect of water on the conversion of starch and glucose Reaction condition: DMSO: 1 mL, starch: 0.25 mmol based on glucose unit (or glucose: 0.25 mmol), CSZA-3 catalyst: 2.4 mg, temperature: 423 K, reaction time: 6 h. a Reaction time: 1 h.
0
0.6
1.2
4.5 2.4 Catalyst amount (mg)
9.0
Fig. 5. The Effect of catalyst loading on the conversion of starch and glucose Reaction condition: DMSO: 1 mL, H2O: 0.2 mL, starch: 0.25 mmol based on glucose unit (or glucose: 0.25 mmol), temperature: 423 K, reaction time: 6 h. a reaction time: 1 h.
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Y. Yang et al. / Bioresource Technology 116 (2012) 302–306 a
TRS yield HMF yield from glucose HMF yield from starch a HMF yield from starch
60
50
Yield (%)
40
30
20
10
0
403
413
423 Temperature (K)
433
443
Fig. 6. The Effect of reaction temperature on the conversion of starch and glucose Reaction condition: DMSO: 1 mL, H2O: 0.2 mL, starch: 0.25 mmol based on glucose unit (or glucose: 0.25 mmol), CSZA-3 catalyst: 2.4 mg, reaction time: 6 h. aReaction time: 1 h.
resulted in a drop in HMF yield (43%). This drop is attributed to additional side-reactions that convert HMF to levulinic acid (catalyzed by acid sites) (Corma et al., 2007) and retro-aldol condensation (catalyzed by basic sites) (Yang and Montgomery, 1996). The HMF yield for the conversion of starch gave a similar trend as the glucose dehydration discussed above. The optimal catalyst loading is 2.4 mg (Fig 5). 3.6. The effect of reaction temperature on the conversion of starch to HMF The reaction was carried out at different temperatures from 403 to 443 K. The results for the conversion of starch and glucose are summarized in Fig. 6. While 403 K is a suitable temperature for glucose conversion, it gives very poor yields for starch because at this low temperature the rate of starch hydrolysis is slow. The optimal temperature for starch conversion is 423 K. On the other hand, the optimal temperature for glucose dehydration is 413 K. Significant decrease in HMF yield is observed at temperatures >423 K. Some 2,5-diformylfuran was detected in the reaction mixture. HMF is oxidized at high temperature. 4. Conclusion Starch was efficiently converted to HMF in the presence of CSZA catalysts, which showed activity for both the hydrolysis of starch to glucose and dehydration of the latter, all in a one-pot reaction. CSZA-3 with high acidity and moderate basicity displayed the best kinetics and selectivity to HMF formation from starch, with 55% yield in 6 h at 423 K. A suitable amount of water (R = 44) was found to promote the hydrolysis of starch into glucose and as a result enhanced the yield of HMF from starch. Acknowledgements This work was financially supported by the National Basic Research Program of China (973 program, No. 2007CB210203), NNSFC 21072136, PCSIRT (No. IRT0846), and the Center for direct Catalytic Conversion of Biomass to Biofuels (C3Bio), an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, and Office of Basic Energy Sciences under Award Number DE-SC0000997. The characterization of the product from Analytical and Testing Center of Sichuan University are greatly appreciated. Y.Y. acknowledges support from China Scholarship Council (Grant 2010624099).
References Chheda, J., Romön-Leshkov, Y., Dumesic, J., 2007. Production of 5hydroxymethylfurfural and furfural by dehydration of biomass-derived monoand poly-saccharides. Green Chem. 9, 342–350. Chun, J., Lee, J., Yi, Y., Hong, S., Chung, C., 2010. Direct conversion of starch to hydroxymethylfurfural in the presence of an ionic liquid with metal chloride. Starch 62, 326–330. Corma, A., Iborra, S., Velty, A., 2007. Chemical routes for the transformation of biomass into chemicals. Chem. Rev. 107, 2411–2502. Dodds, D., Gross, R., 2007. Chemicals from biomass. Science 318, 1250–1251. Huber, G., Chheda, J., Barrett, C., Dumesic, J., 2005. Production of liquid alkanes by aqueous-phase processing of biomass-derived carbohydrates. Science 308, 1446–1450. Hu, S., Zhang, Z., Zhou, Y., Song, J., Fan, H., Han, B., 2009a. Direct conversion of inulin to 5-hydroxymethylfurfural in biorenewable ionic liquids. Green Chem. 11, 873–877. Hu, S., Zhang, Z., Song, J., Zhou, Y., Han, B., 2009b. Efficient conversion of glucose into 5-hydroxymethylfurfural catalyzed by a common Lewis acid SnCl4 in an ionic liquid. Green Chem. 11, 1746–1749. James, O.O., Maity, S., Usman, L.A., Ajanaku, K.O., Ajani, O.O., Siyanbola, T.O., Sahu, S., Chaubey, R., 2010. Towards the conversion of carbohydrate biomass feedstocks to biofuels via hydroxylmethylfurfural. Energy Environ. Sci. 3, 1833–1850. Li, C., Zhao, Z., Wang, A., Zheng, M., Zhang, T., 2010. Production of 5hydroxymethylfurfural in ionic liquids under high fructose concentration conditions. Carbohyd. Res. 345, 1846–1850. Matsumoto, A., Tsubaki, S., Sakamoto, M., Azuma, J., 2011. A novel saccharification method of starch using microwave irradiation with addition of activated carbon. Bioresour. Technol. 102, 3985–3988. Miller, G.L., 1959. Use of dinitrosalicylic acid reagent for determination of reducing sugar. Anal. Chem. 31, 426–428. Mednick, M.L., 1962. The acid-base-catalyzed conversion of aldohexose into 5(hydroxymethyl)-2-furfural. J. Org. Chem. 27, 398–403. Nagamori, M., Funazukuri, T., 2004. Glucose production by hydrolysis of starch under hydrothermal conditions. J. Chem. Technol. Biot. 79, 229–233. Roman-Leshkov, Y., Chheda, J., Dumesic, J., 2006. Phase modifiers promote efficient production of hydroxymethylfurfural from fructose. Science 312, 1933–1937. Rostrup-Nielsen, J., 2005. Chemistry: Making fuels from biomass. Science 308, 1421. West, R., Liu, Z., Peter, M., Gärtner, C., Dumesic, J., 2008. Carbon-carbon bond formation for biomass-derived furfurals and ketones by aldol condensation in a biphasic system. J. Mol. Catal. A: Chem. 296, 18–27. Rinaldi, R., Palkovits, R., Schüth, F., 2008. Depolymerization of cellulose using solid catalysts in ionic liquids. Angew. Chem. Int. Edit. 47, 8047–8050. Román-Leshkov, Y., Barrett, C., Liu, Z., Dumesic, J., 2007. Production of dimethylfuran for liquid fuels from biomass-derived carbohydrates. Nature 447, 982–985. Röper, H., 2002. Renewable raw materials in Europe – Industrial utilization of starch and sugar. Starch 54, 89–99. Stevnebø, A., Sahlström, S., Svihus, B., 2006. Starch structure and degree of starch hydrolysis of small and large starch granules from barley varieties with varying amylose content. Anim. Feed Sci. Technol. 130, 23–38. Takagaki, A., Ohara, M., Nishimura, S., Ebitani, K., 2009. A one-pot reaction for biorefinery: combination of solid acid and base catalysts for direct production of 5-hydroxymethylfurfural from saccharides. Chem. Commun. 41, 6268–6276. Tong, X., Ma, Y., Li, Y., 2010. Biomass into chemicals: conversion of sugars to furan derivatives by catalytic processes. Appl. Catal. A: Gen. 385, 1–13. Watanabe, M., Aizawa, Y., Iida, T., Nishimura, R., Inomata, H., 2005. Catalytic glucose and fructose conversions with TiO2 and ZrO2 in water at 473 K: relationship between reactivity and acid-base property determined by TPD measurement. Appl. Catal. A: Gen. 295, 150–156. Yamaguchi, D., Kitano, M., Suganuma, S., Nakajima, K., Kato, H., Hara, M., 2009. Hydrolysis of cellulose by a solid acid catalyst under optimal reaction conditions. J. Phys. Chem. C 113, 3181–3188. Yamaguchi, D., Hara, M., 2010. Starch saccharification by carbon-based solid acid catalyst. Solid State Sci. 12, 1018–1023. Yan, H., Yang, Y., Tong, D., Xiang, X., Hu, C., 2009. Catalytic conversion of glucose to 5-hydroxymethylfurfural over SO24 /ZrO2 and SO24 /ZrO2–Al2O3 solid acid catalysts. Catal. Commun. 10, 1558–1563. Yang, B., Montgomery, R., 1996. Alkaline degradation of glucose: effect of initial concentration of reactants. Carbohyd. Res. 280, 27–45. Yang, F., Liu, Q., Bai, X., Du, Y., 2010. Conversion of biomass into 5-hydroxymethylfurfural using solid acid catalyst. Bioresour. Technol. 102, 3424–3429. Yang, Y., Hu, C., Abu-Omar, M.M., 2012. Conversion of carbohydrates and lignocellulosic biomass into 5-hydroxymethylfurfural using AlCl36H2O catalyst in a biphasic solvent system. Green Chem. 14, 509–513. Zakrzewska, M.E., Bogel-ukasik, E., Bogel-ukasik, R., 2011. Ionic liquid-mediated formation of 5-hydroxymethylfurfural – a promising biomass-derived building block. Chem. Rev. 111, 397–417. Zeng, W., Cheng, D., Chen, F., Zhan, X., 2009. Catalytic conversion of glucose on Al–Zr mixed oxides in hot compressed water. Catal. Lett. 133, 221–226. Zhang, Z., Zhao, Z., 2011. Production of 5-hydroxymethylfurfural from glucose catalyzed by hydroxyapatite supported chromium chloride. Bioresour. Technol. 102, 3970–3972. Zhao, H., Holladay, J., Brown, H., Zhang, Z., 2007. Metal chlorides in ionic liquid solvents convert sugars to 5-hydroxymethylfurfural. Science 316, 1597–1600.