Research Note pubs.acs.org/IECR
One-Pot Synthesis of 5-(Ethoxymethyl)furfural from Glucose Using Sn-BEA and Amberlyst Catalysts Christopher M. Lew,† Nafiseh Rajabbeigi,† and Michael Tsapatsis* Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States S Supporting Information *
ABSTRACT: 5-(Ethoxymethyl)furfural (EMF) was produced from glucose in ethanol in a single reactor at 90 °C. The reaction proceeds via the isomerization of glucose to fructose with zeolite Sn-Beta, a Lewis acid catalyst. Fructose is converted to 5(hydroxymethyl)furfural, which is then etherified to EMF using a Brønsted acid catalyst, Amberlyst 131. An EMF yield of 31% was achieved.
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INTRODUCTION 5-(Ethoxymethyl)furfural (EMF) has attracted attention as a potential biofuel alternative. Its energy density is 30.3 MJ/L, which is similar to that of gasoline (31.1 MJ/L) and diesel (33.6 MJ/L) and higher than ethanol (23.5 MJ/L).1 Avantium has used EMF as a blend in commercial diesel in engine tests and found that the engines ran smoothly. Furthermore, there is less solid contamination and soot.2,3 EMF may also be hydrogenated over metal catalysts to yield 5-(hydroxyethyl)furfural alcohol, which is much more miscible in diesel and has a similar combustion profile to ethanol.4,5 The synthesis of EMF from both HMF and fructose in ethanol has been reported using Hform zeolites, mesoporous silica, and ion exchange resins, such as Amberlyst.3,6 However, glucose is a more abundant and cheaper feedstock;7 thus, it is of interest to prepare EMF from glucose. Reaction conditions, such as the concentration of the glucose feed, should be chosen carefully, though, as they have recently been found to influence the reaction pathway.8 We explored the possibility of converting glucose to fructose, followed by fructose to HMF, and finally the etherification of HMF to EMF in a single pot (Scheme 1). Previous studies have shown that parts of this reaction sequence can be accomplished using various catalysts. Takagaki et al. performed a one-pot reaction in N,N-dimethylformamide using a base to catalyze the isomerization of glucose to fructose and an acid to catalyze the conversion of fructose to HMF.9 Nikolla et al. used tincontaining zeolite Beta (Sn-BEA) to isomerize glucose to fructose and hydrochloric acid to convert fructose to HMF.10 Their one-pot system utilized an aqueous phase for the reactions and an organic phase to extract HMF and prevent rehydration and other side reactions. We hypothesized that if the glucose-to-fructose-to-HMF sequence could occur in ethanol, then HMF could be further reacted to EMF in onepot. Here, we find that Amberlyst 131 is an efficient and selective catalyst for the formation of EMF from HMF in ethanol. It can also catalyze the formation of EMF from fructose. We also found that Sn-BEA can isomerize glucose to fructose in ethanol. When Amberlyst 131 is combined with the Lewis acid zeolite Sn-BEA, glucose can be converted to EMF with a yield of 31%. As detected by HPLC, EMF does not degrade or react further © 2012 American Chemical Society
to any significant degree under the reaction conditions in the presence of the two catalysts.
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EXPERIMENTAL SECTION Sn-BEA with a Si:Sn ratio of 125 in the synthesis gel was prepared following the procedures developed by Corma et al. and Taarning et al.11,12 ICP-OES analysis (Galbraith Laboratories, Inc.) revealed a Si:Sn ratio of 158 in calcined samples. The synthesis methods, as well as the catalyst characterization, were previously described in detail.13 Catalytic reactions were performed at 90 °C in a 20 mL, thick-walled glass reactor. Glucose (Sigma-Aldrich) was added to ethanol (Decon Laboratories, Inc., 200 proof) at a concentration of 0.159 mol/L. (Glucose solubility tests were performed at 90 °C, and the solubility limit was found to be 0.159 mol/L using high-performance liquid chromatography (HPLC).) Sn-BEA was added at a molar ratio of glucose/Sn 50:1, and the mass of Amberlyst 131 (Sigma-Aldrich) was 10% of the mass of glucose (by weight). The Amberlyst 131 was dried in air at 70 °C beforehand for several days. The reactor was placed in a preheated oil bath with a stir rate of 980 rpm. The reactor was cooled in an ice bath, and samples were taken and filtered for HPLC. HPLC analysis was performed on an Agilent 1200 equipped with a refractive index detector and an autosampler. A Bio-Rad Aminex HPX-87H column was used at 60 °C with 0.005 mol/L sulfuric acid at a flow rate of 0.5 mL/ min as the mobile phase. Saccharin was used as an internal standard. Each reaction was performed a minimum of three times, and differences between runs are reflected in the error bars.
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RESULTS AND DISCUSSION Our results show that a combination of Amberlyst 131 and SnBEA can successfully catalyze the series of reactions in the conversion of glucose to EMF in ethanol. Figure 1 shows the concentrations of glucose and the reaction products versus Received: Revised: Accepted: Published: 5364
November 11, 2011 March 20, 2012 March 27, 2012 March 27, 2012 dx.doi.org/10.1021/ie2025536 | Ind. Eng. Chem. Res. 2012, 51, 5364−5366
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Scheme 1. Scheme Showing the Series of Reactions and the Associated Catalysts
and Amberlyst 131 was added. The concentrations of fructose and mannose decreased, while that of HMF increased. HMF reached a maximum after 480 min and subsequently decreased as it was etherified to EMF. Note that very little HMF or EMF was produced between 0 and 300 min. Sn-BEA, a Lewis acid, was not active in converting fructose to HMF or EMF. Amberlyst 131, however, is active for first producing HMF and subsequently EMF in high yields. Separating the overall reaction into individual components pinpoints why the mass balance is not closed and suggests where further optimization should be considered (see Supporting Information for further information on the carbon balance). After 24 h, the final yield of EMF from glucose was about 31% (Figure 1). However, the yield of EMF from the maximum concentration of fructose produced was nearly 100%, which implies that the isomerization of glucose to fructose is not highly selective in ethanol and limits the overall selectivity to EMF. Indeed, the maximum yield of fructose from glucose was also 31%. When Sn-BEA was added to glucose in ethanol and allowed to run for long times, fructose and mannose concentrations reached steady values after 300 min; however, glucose conversion continued for nearly 24 h. The concentration of a number of byproducts increased as more glucose was consumed. Ethyl lactate was a major constituent of these byproducts, which is similar to previously reported results.14 On the other hand, when starting with fructose and Amberlyst 131 in ethanol, we found that EMF yields were 93% at 70 °C (Supporting Information, Figure S1). Furthermore, when Amberlyst 131 was added to HMF in ethanol, the conversion to EMF was almost 100% (Supporting Information, Figure S2). Thus, the conversion of fructose to EMF over Amberlyst 131 is relatively efficient, and the reduction in the amount of byproducts in the isomerization of glucose to fructose should lead to an increase in the overall yields of EMF. Experiments starting with glucose and Amberlyst 131 in ethanol (without Sn-BEA) resulted in ethyl glucopyranoside and ethyl glucofuranoside (isomers α and β). Similar results have been previously reported with Brønsted acid catalysts in methanol and butanol.14,15 Thus, under these conditions, HMF and EMF cannot be produced from glucose directly and must be made from fructose. All the reactions in this work used 100% ethanol as the solvent, which, combined with previous reports, shows that SnBEA can isomerize glucose to fructose in a number of different solvents. Corma et al. used Sn-BEA for oxidation reactions in organic solvents,11,16,17 while Moliner et al. isomerized glucose to fructose with Sn-BEA under aqueous conditions.18 Using higher temperatures of 160 °C, Holm et al. converted glucose, fructose, and sucrose into methyl lactate in methanol with SnBEA. However, at lower temperatures (100 °C), glucose was isomerized to fructose.14 Moreover, Román-Leshkov et al. found that the mechanism of the isomerization proceeded via an intramolecular hydride shift, which means that the solvent does not directly participate in the reaction.19 Thus, the isomerization could occur in various aqueous and nonaqueous environments. This current study shows that the isomerization
Figure 1. Time versus concentration of glucose and the major products in one-pot. Each reaction was performed a minimum of three times, and differences between runs are reflected in the error bars.
time. Glucose was continuously converted to other products over the course of the reaction. The concentrations of fructose and mannose reached a maximum within 60 min, and these isomers reacted to form HMF and other byproducts. The concentration of HMF reached a maximum after 240 min, while the formation of EMF continued for several more hours. The series of reactions and the role of the two catalysts are more clearly identified when the catalysts are introduced in sequential order (Figure 2). Scheme 1 shows the reaction steps and the associated catalysts. Sn-BEA was added to glucose in ethanol from 0 to 300 min, and it catalyzed the isomerization to fructose and mannose. After 300 min, Sn-BEA was filtered out,
Figure 2. Time versus concentration of glucose and the major products when the catalysts are added in sequential order: Sn-BEA was used from 0 to 300 min, and Amberlyst 131 was used from 300 to 1800 min. Each reaction was performed a minimum of three times, and differences between runs are reflected in the error bars. 5365
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occurs in ethanol at 90 °C, and this result may be useful for other reactions that require anhydrous conditions. While significant build-up of humic acid was not detected, the isomerization of glucose to fructose in ethanol resulted in a slight yellow discoloration. Deactivation of the catalyst was tested by reusing the Sn-BEA for multiple cycles of glucose to fructose isomerization at 90 °C for 300 min (Supporting Information, Table S3). After each run, the Sn-BEA was isolated by centrifugation and washed with pure ethanol. The catalyst was then reused under the same conditions. After the third cycle, the Sn-BEA was also calcined at 550 °C for 6 h at a ramp rate of 2 °C/min. Although the fructose yield increased somewhat during the second cycle, the overall catalytic activity of the Sn-BEA was preserved throughout the tests.
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(8) Srokol, Z. W.; Rothenberg, G. Practical Issues in Catalytic and Hydrothermal Biomass Conversion: Concentration Effects on Reaction Pathways. Top. Catal. 2010, 53, 1258. (9) Takagaki, A.; Ohara, M.; Nishimura, S.; Ebitani, K. A One-Pot Reaction for Biorefinery: Combination of Solid Acid and Base Catalysts for Direct Production of 5-Hydroxymethylfurfural from Saccharides. Chem. Commun. 2009, 6276. (10) Nikolla, E.; Roman-Leshkov, Y.; Moliner, M.; Davis, M. E. “One-Pot” Synthesis of 5-(Hydroxymethyl)furfural from Carbohydrates Using Tin-Beta Zeolite. ACS Catal. 2011, 1, 408. (11) Corma, A.; Nemeth, L. T.; Renz, M.; Valencia, S. Sn-Zeolite Beta as a Heterogeneous Chemoselective Catalyst for Baeyer−Villiger Oxidations. Nature 2001, 412, 423. (12) Taarning, E.; Saravanamurugan, S.; Holm, M. S.; Xiong, J. M.; West, R. M.; Christensen, C. H. Zeolite-Catalyzed Isomerization of Triose Sugars. ChemSusChem 2009, 2, 625. (13) Lew, C. M.; Rajabbeigi, N.; Tsapatsis, M. Tin-Containing Zeolite for the Isomerization of Cellulosic Sugars. Microporous Mesoporous Mater. 2012, 153, 55. (14) Holm, M. S.; Saravanamurugan, S.; Taarning, E. Conversion of Sugars to Lactic Acid Derivatives Using Heterogeneous Zeotype Catalysts. Science 2010, 328, 602. (15) Climent, M. J.; Corma, A.; Iborra, S.; Miquel, S.; Primo, J.; Rey, F. Mesoporous Materials as Catalysts for the Production of Chemicals: Synthesis of Alkyl Glucosides on MCM-41. J. Catal. 1999, 183, 76. (16) Corma, A.; Domine, M. E.; Nemeth, L.; Valencia, S. Al-Free SnBeta Zeolite as a Catalyst for the Selective Reduction of Carbonyl Compounds (Meerwein−Ponndorf−Verley Reaction). J. Am. Chem. Soc. 2002, 124, 3194. (17) Renz, M.; Blasco, T.; Corma, A.; Fornes, V.; Jensen, R.; Nemeth, L. Selective and Shape-Selective Baeyer-Villiger Oxidations of Aromatic Aldehydes and Cyclic Ketones with Sn-Beta Zeolites and H2O2. Chem.Eur. J. 2002, 8, 4708. (18) Moliner, M.; Roman-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. (19) Roman-Leshkov, Y.; Moliner, M.; Labinger, J. A.; Davis, M. E. Mechanism of Glucose Isomerization Using a Solid Lewis Acid Catalyst in Water. Angew. Chem., Int. Ed. 2010, 49, 8954.
ASSOCIATED CONTENT
S Supporting Information *
Reaction and experimental data for (1) carbon balances, (2) catalyst reuse tests, (3) the conversion of fructose to EMF using Amberlyst 131 at 70 °C, and (4) the conversion of HMF to EMF using Amberlyst 131 at 70 °C. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Author Contributions †
These authors contributed equally to this work.
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This material is based upon work supported as part of the Catalysis Center for Energy Innovation, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001004. Parts of this work were carried out in the Characterization Facility, University of Minnesota, a member of the NSF-funded Materials Research Facilities Network (www.mrfn.org) via the MRSEC program.
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REFERENCES
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