Enhancing Energy Efficiency in Saccharide–HMF ... - ACS Publications

Research Article pubs.acs.org/journal/ascecg

Enhancing Energy Efficiency in Saccharide−HMF Conversion with Core/shell Structured Microwave Responsive Catalysts Tuo Ji,† Rui Tu,‡ Liwen Mu,† Xiaohua Lu,‡ and Jiahua Zhu*,† †

Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron, 302 East Buchtel Avenue, Akron, Ohio 44325, United States ‡ State Key Laboratory of Material-Oriented Chemical Engineering, College of Chemistry and Chemical Engineering, Nanjing Tech University, 5 Xinmofan Road, Nanjing, Jiangsu 210009, P. R. China S Supporting Information *

ABSTRACT: Core/shell structured microwave responsive catalysts with carbon nanotube (CNT) core and acidified TiO2 shell were synthesized in this work for catalytic conversion of saccharide to 5-hydroxymethylfurfural (HMF). The microstructures and surface properties of these hybrid composites were carefully characterized. With such a structure of inner microwave absorber and outer catalyst shell, the heat generated at the core area by microwave radiation can be translated to the shell catalyst directly. Such localized heating allows maximum heat utilization in the reaction and enhances the energy efficiency of the catalytic reaction. The energy efficiency of HMF formation reaches up to 4.2 mol·kJ−1·L−1 by using CNT/TiO2 catalyst, which is six-times higher compared to pure TiO2. The reaction can be completed within 30 min. The effects of TiO2 shell thickness, annealing temperature, catalyst concentration, and microwave power on the saccharide conversion and HMF yield were systematically investigated. These catalysts have been demonstrated effective in the hydrolysis conversion of various saccharides, such as fructose, glucose, and sucrose. KEYWORDS: HMF synthesis, Saccharide, Core/shell, Energy efficiency, Microwave

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INTRODUCTION Biomass conversion to platform chemicals is of great interest in facing the challenge of depletion of fossil fuels.1−8 5Hydroxymethylfurfural (HMF), one of the most important biomass-derived platform chemicals, has been well recognized as an important intermediate to produce a broad range of valuable chemicals.9−11 HMF can be synthesized from carbohydrates by Brønsted acidic mineral acids, Lewis acidic metal chlorides, and bifunctional Lewis−Brønsted acidic catalysts.12−15 Homogeneous catalysts are often more efficient, but heterogeneous catalysts such as solid acid catalyst, Niobic acid Amberlyst-15, H3PW12O40, TiO2, ZrO2, WOx, and SnO2 could be more advantageous in terms of easy separation and low risk of corrosion to equipment.16−19 As one kind of solid acid catalyst, acid functionalized TiO2 has been widely used in various heterogeneous reactions due to its tunable acid−base property.20−22 For example, Qi et al. used TiO2/SO42− in the fructose reaction and reached an HMF yield of 38.1% in 5 min.23 Atanda et al. promoted the HMF yield to 81% by using acidic TiO2 catalyst in a water−butanol biphasic reaction system.14 Such a biphasic reaction system would facilitate the HMF transfer from the aqueous reaction phase to the organic phase, drive the reaction equilibrium toward HMF production, and suppress side-reactions. However, the subsequent separa© 2017 American Chemical Society

tion of HMF from the organic phase is absolutely an energy consuming process. Therefore, improving HMF conversion efficiency and yield in aqueous media seems a more promising approach in terms of process simplicity, environmental sustainability, and process economy. Microwave has been demonstrated to have effective energy input to synthesize new nanostructures,24,25 fabricate materials with novel properties,26 and also improve the yield and selectivity of biomass conversion reactions.27 The advantages of microwave heating include uniform temperature field, fast heating rate, and easy reaction control. In carbohydrate reactions, the heating rate has been studied as an important factor that affects the reaction and product distribution. For instance, Qi et al. increased the HMF yield from 12.1% to 27.4% by simply switching sand bath heating to microwave heating, and the accelerated fructose hydration in the microwave was identified as the major reason for the enhanced HMF yield.23 In heterogeneous reactions, microwave energy can be absorbed by both solid catalyst and liquid media, which depends on their dielectric/electric properties and interface Received: February 9, 2017 Revised: March 13, 2017 Published: March 20, 2017 4352

DOI: 10.1021/acssuschemeng.7b00414 ACS Sustainable Chem. Eng. 2017, 5, 4352−4358

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ACS Sustainable Chemistry & Engineering Scheme 1. Schematic Synthetic Procedure of CNTs/TiO2 Nanocomposites

(1.8 mL) was dropwise added to the former Ti(C4H9)4 solution under magnetic stirring. The solution was violently stirred for 2.5 h and then aged for 2 days in the dark at room temperature. Surface Treatment of CNTs. CNTs were initially treated with a H2SO4/APS mixture in order to introduce functional groups, e.g. −OH and −COOH, onto the surface. Briefly, 1.0 g of CNTs was added into 50 mL of a 1.7 M APS and 2.0 M H2SO4 mixture solution and ultrasonicated in a water bath for 3 h to break the agglomerates and better disperse the CNTs. Upon completion, the mixture was kept in an oven at 50 °C for 17 h. Finally, the functionalized CNTs were washed with DI water three times and dried in an oven at 60 °C overnight. Synthesis of CNTs/TiO2 Core−Shell Catalysts. Scheme 1 showed a typical synthesis procedure of CNTs/TiO2 nanocomposite. First, modified CNTs were dispersed into TiO2 sol with a given ratio and then ultrasonicated for 1 h. The mixture suspension was then heated in 50 °C oil bath until dry. The dried samples were heated to 400 °C in a tube furnace with ramping rate of 5 °C/min. Then the CNTs/TiO2 nanocomposites were sulfated following the procedure described as below: 1.0 g CNTs/TiO2 was soaked in 0.8 g 1.0 M H2SO4 aqueous solution for 3 h, and then heated at 80 °C for another 3 h. The resultant powder was calcinated at 400 °C for 4 h. In order to study the optimal ratio of CNTs:TiO2, 4 samples with 20:80, 40:60, 60:40 and 80:20 wt % of CNTs/TiO2 were prepared and designated as CT20, CT40 CT60 and CT80 (20, 40, 60, and 80. represent the weight percentage of CNTs in the CNTs/TiO2 composite. To study the calcination temperature effect, the CT80 samples were heated at 300, 400, and 500 °C and named as CT80−300, CT80−400 and CT80−500, respectively. Catalytic Reaction under Microwave Irradiation. The dehydration reactions of carbohydrates including fructose, glucose, and sucrose were carried out in a 10 mL microwave tube (d = 12.2 mm) under microwave irradiation. Typically, 0.55 mmol of carbohydrate and 50 mg of CNTs/TiO2 catalyst were added into 4.0 g of water and then sonicated for 5 min. A small stirrer bar was used for mixing during microwave reaction. The loaded tube was then placed into the microwave reactor (Discover SP, CEM), presetting at 15 W input power for 40 min. After that, the system temperature was cooled to room temperature. The resulting solution was filtered through a syringe filter (VWR, 0.22 mm PTFE). The filtered liquid was then analyzed by both UV−vis spectrophotometry and HPLC equipped with a RI detector and an HPX-87 column with 0.17 mL/ min of 0.15% H3PO4 at 55 °C. The fructose conversion and HMF yield were calculated by eqs 1 and 2:

structure. To expedite the reaction at the catalyst surface, it is preferred to allocate more microwave energy to the surface of the solid catalyst where the reaction occurs. Although TiO2 has obvious advantages as a catalyst, the intrinsic microwavetransparent property does not make it a good catalyst in microwave reactions.28 Integrating TiO2 and microwaveabsorbing materials could be an effective approach to enable an efficient microwave responsive heterogeneous catalyst. Carbon materials, such as carbon nanotubes (CNTs),29,30 carbon black,31 graphene,32,33 and carbon fibers (CFs),34 are ideal microwave absorbers due to their excellent dielectric polarization properties. The electric energy can be dissipated as heat due to dielectric loss.35,36 Besides, carbon material is also an ideal heat conductor.37 Better heat transfer could be expected due to its high thermal conductivity. To synergistically integrate the advantages of TiO2 and carbon, the catalyst design should align with the following three principles: good transparency of TiO2, that allows maximum transfer of microwave energy to carbon; excellent heat generation capability of carbon once microwave energy is absorbed;38,39 sufficient reactive sites.40,41 Therefore, constructing a core− shell structured hybrid catalyst with a controlled shell thickness seems a realistic approach to satisfy all the desired design principles.42,43 In this work, core−shell structured hybrid catalysts were successfully synthesized with carbon nanotubes (CNTs) as microwave absorber core and with TiO2/SO42− as catalytically active shell. The hollow tube structure of CNTs is expected to promote the microwave reflection inside the tube and improve the overall microwave-absorbing property. The TiO2/SO42− shell thickness was controlled to investigate its effect on microwave heating as well as reaction efficiency. The effects of catalyst composition, concentration, and microwave power on the reaction conversion and yield are investigated. Finally, the optimized catalyst structure has been studied in a series of reactions by using different biomass substrates, including sucrose, glucose, and fructose.

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EXPERIMENTAL SECTION

Materials. CNTs (Pyrograf III PR-24-XT-LHT) were obtained from Pyrograf Products Inc. The diameter of CNTs is in the range 80−120 nm, length of 30−100 μm, and tube wall thickness of about 14 nm. Ammonium persulfate (APS ≥ 98%), titanium butoxide (97%), sucrose (≥99.5%), glucose (≥99%), and fructose (≥99%) were purchased from Sigma-Aldrich. 2,4-Pentanedione (≥99%) was purchased from Acros Organics. Nitric acid (70%) and sulfuric acid (98%) were purchased from Fisher Scientific. Ethanol (200 proof) was purchased from Decon Laboratories, Inc. All reagents were used as received without further purification. Deionized water was purified using a Milli-Q Direct 8 Ultrapure Water system (Millipore, Billerica, MA) with a minimum resistivity of 18.2 MΩ·cm. Preparation of TiO2 Sol. The preparation of TiO2 sol follows a literature reported method.44 Specifically, 17 mL of Ti(C4H9)4 was first added into 50 mL of anhydrous ethanol and stirred for 30 min. Afterward, a mixture of anhydrous ethanol (28.0 mL), acetylacetone (2.57 mL), concentrated nitric acid (0.45 mL), and deionized water

Fructose conversion (%) =

HMF yield (%) =

Fructose consumed (mol) × 100 Initial fructose (mol)

HMF produced (mol) × 100 Initial fructose (mol)

(1)

(2)

Characterization. The catalyst morphology was characterized by scanning electron microscopy (SEM, JEOL-7401) with a sputtercoated silver layer on the sample surface. Energy dispersive X-ray detection (EDX) was conducted to analyze the elemental species on the surface. The shell thickness and crystal lattice structure were further characterized by transmission electron microscopy (FEI Scanning TEM) and high resolution TEM (HRTEM, FEI Tecnai G2 F20 ST TEM/STEM & EDAX energy dispersive X-ray spectrometer). The powder X-ray diffraction analysis was carried out with a Bruker AXS D8 Discover diffractometer with a GADDS 4353

DOI: 10.1021/acssuschemeng.7b00414 ACS Sustainable Chem. Eng. 2017, 5, 4352−4358

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ACS Sustainable Chemistry & Engineering

Figure 1. (a) Modified CNTs, (b) CT80, (c) CT60, (d) HRTEM image of CT80, (e and f) magnified image of (e) CNTs wall and (f) TiO2 shell, and (g−j) EDX elemental mapping of CT80.

Figure 2. (a) Schematic illustration of the working principle of microwave-absorbing catalyst, (b) fructose conversion, and (c) HMF yield as a function of reaction time with TiO2, CNTs/TiO2 (CT60), and CNTs catalysts. Reaction conditions: [fructose] = 0.55 mmol, [catalyst] = 12.5 mg/ mL, input power =15 W. flow rate of 20 mL/min. After that, He gas was purged again to flush out the excess NH3. The NH3 desorption was carried out in the temperature range 423−1073 K at a heating rate of 10 K/min. The amount of desorbed NH3 was continuously monitored in the above temperature range. The 1NMR analysis was performed on INOVA 400. The product solution was extracted with ethyl acetate and concentrated by using a rotary evaporator. The oily organic product was dissolved in CDCl3 for 1H NMR spectroscopy.

(general area detector diffraction system) operating with a Cu Kα radiation source filtered with a graphite monochromator (λ = 1.541 Å). Brunauer−Emmett−Teller (BET) surface area analysis was performed using a TriStar II 3020 surface analyzer (Micromeritics Instrument Corp., USA) by N2 adsorption−desorption isotherms at 77 K. The pore size distribution was calculated by the Barrett−Joyner− Halenda (BJH) method from the adsorption branch. The CNTs loading was determined by thermogravimetric analysis (TGA, TA Instruments Q500) in air atmosphere from 20 to 800 °C with a heating rate of 10 °C/min. For ammonia temperature-programmed desorption (TPD) analysis, the catalyst (100 mg) was loaded into a Ushaped tube glass cell and flushed with He at 723 K for 2 h. After cooling to 423 K, the system was purged with NH3 for 30 min at a

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RESULTS AND DISCUSSION The microstructure of the hybrid catalyst is examined by TEM (Figure 1). The XRD results in Figure S1(a) confirm the crystalline structure of CNTs and TiO2. With CNTs loading 4354

DOI: 10.1021/acssuschemeng.7b00414 ACS Sustainable Chem. Eng. 2017, 5, 4352−4358

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ACS Sustainable Chemistry & Engineering

Figure 3. (a) HMF yield as a function of time by using different catalysts, (a1) equilibrium solution temperatures of pristine CNTs and hybrid catalysts (blank means pure water; in CT20/40/60/80, green bar represents hybrid catalyst, and blue bar is pristine CNTs), (b) HMF yield by using catalyst annealed at different temperatures, (b1−b3) TEM morphology of the core−shell catalyst annealed at 300, 400, and 500 °C, respectively. Reaction conditions: [fructose] = 0.55 mmol, [catalyst] = 12.5 mg/mL, input power = 15 W.

The ratio of CNTs and TiO2 in the hybrid catalyst determines its microwave absorption property as well as the quantity of active sites in the TiO2 shell. More structural information on these hybrid catalyst is provided in the Supporting Information (Section S2). A general trend is that equilibrium temperature increases with increasing CNTs ratio in the composites [Figure S7(a)]. The equilibrium temperature of CT80 reaches its highest value, 162 °C, among all hybrid catalysts due to the largest quantity of microwave absorptive CNTs. To evaluate the effect of TiO2 thickness on the overall microwave absorption property, pristine CNTs and hybrid catalysts containing the same amount of CNTs were comparatively investigated. As seen in Figure 3(a1), the equilibrium temperature of the reaction increases in a similar pattern by using both pristine CNTs and hybrid catalysts. This result could be expected since TiO2 absorbs a negligible amount of microwave irradiation.28 It is worth mentioning that the pure CNTs show similar but slightly higher equilibrium temperature than that of the corresponding hybrid. This could be attributed to the small heat loss during heat transport across the CNTs−TiO2 interface and the TiO2 layer. Benefitting from the better microwave absorption efficiency of CT80, the HMF yield reaches 58 mol % within 20 min. Such a large yield outperforms other reported catalysts, including TiO2 SO42−/ ZrO2, HNb3O8, NbPO-pH2, Ambersty-15, and ion-exchange resin (Table S3). With the reaction proceeding to equilibrium, the yield slightly increases to 62 mol % in 40 min. After 40 min, the fructose conversion reaches 97.6%, together with the formation of side products, including levulinic acid and formic acid [Figure S7(b)]. The effect of the calcination temperature (300, 400, and 500 °C) of CT80 on the catalyst activity is also studied in the fructose dehydration reaction [Figure 3(b)]. For more structural characterization of these catalysts, refer to Supporting Information Section S3. By monitoring the HMF yield, faster reaction occurs with CT80−400 followed by CT80-300 and CT80-500. The microstructural analysis in Figure 3(b1) reveals the incomplete decomposition of TiO2 gel at 300 °C. Such loose aggregates transform into a compact shell when calcination temperature reaches 400 °C [Figure 3(b2)]. Further

below 40 wt %, TiO2 is the continuous phase, with CNTs distributed in the bulk (Figure S3). Increasing CNTs loading to 60 (CT60) and 80 wt % (CT80) leads to the morphology transformation into individual fibrils with TiO2 coated on the CNTs outer surface [Figure 1(b and c)]. The thickness of the TiO2 layer is measured to be 11.1 nm in CT80 and 25.9 nm in CT60. High-resolution TEM (HRTEM) in Figure 1(d) clearly reveals the core−shell structure of CT80. The CNTs wall shows crystalline structure with interplanar spacing of 3.34 Å. The lattice fringe and FFT image clearly indicate the (002) crystal plane of graphite [JCPDS #01-0646, Figure 1(e)]. The clear lattice fringe of 3.46 Å indicates the (101) crystal plane of anatase TiO2 [PDF#15-0806, Figure 1(f)]. Energy-filtered TEM (EFTEM) is conducted to visualize the elemental distribution of CT80. Zero loss image, Ti, O, and C maps are presented in Figure 1(g−j). A brighter area in the elemental map indicates a higher concentration of the corresponding element in that area.45 It is obvious that Ti and O signals cover a wider area than C signal perpendicular to the fiber longitudinal direction, indicating the uniform TiO2 shell surrounding the CNT core. The proposed working mechanism of the core−shell structured hybrid catalyst is illustrated in Figure 2(a). Upon microwave radiation, the internal CNT core would be heated and the radiative heat dissipation across the interface provides localized thermal energy to enable catalytic conversion of saccharide to HMF at the outer TiO2 surface. Figure 2(b and c) shows the fructose conversion and HMF yield as a function of time by using pure TiO2, CNTs, and CNTs/TiO2(CT60) catalysts. Pure TiO2 gives the lowest fructose convention of 40% and HMF yield of 18% due to the lowest equilibrium reaction temperature of 125 °C (Figure S2). Both fructose conversion and HMF yield are significantly improved by using CNTs catalyst. By using the hybrid CT60 catalyst, HMF yield reaches to 59 mol % within 30 min and remained at ∼60% in the next 10 min while fructose conversion still proceeds to form side products such as levulinic acid. Compared with pristine TiO2 and CNTs, the hybrid catalyst shows much higher fructose conversion and HMF yield, that demonstrates the effectiveness of the synergistic combination of CNTs and TiO2. 4355

DOI: 10.1021/acssuschemeng.7b00414 ACS Sustainable Chem. Eng. 2017, 5, 4352−4358

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Figure 4. (a) Effect of catalyst concentration on HMF yield and conversion, [fructose] = 0.55 mmol, input power = 15 W, (b) effect of input power on HMF yield and conversion, [fructose] = 0.55 mmol, [CT80] = 12.5 mg/mL. Temperature−time profile refers to Figure S11.

increasing calcination temperature to 500 °C leads to a corrupted composite structure of both core and shell (BET analysis of these catalysts refers to Table S2 and Figure S9). By monitoring the HMF yield, faster reaction occurs with CT80− 400 catalyst, followed by CT80-300 and CT80-500. Three catalysts achieve a similar HMF yield of 59 mol % after 30 min, which reveals that reaction equilibrium has been achieved. The damaged crystalline structure of CNTs reduces the microwave absorption efficiency as well as the heat transfer and thus lowers the HMF conversion rate. The dehydration of fructose to HMF is also studied at various CT80 loadings. In general, larger catalyst loading leads to higher equilibrium temperature (Figure 4a) and thus higher HMF yield and conversion (Figure 4b). HMF yield increases from 10 to 62 mol % upon increasing the catalyst loading from 10 to 70 mg, Figure 4(b). Higher catalyst loading also enables faster reaction rate. In this system, HMF yield is determined by two factors: microwave absorption ability and the amount of active sites. The increase of catalyst loading positively contributes to both factors, i.e. intensify microwave absorption and enlarge number of reactive acid sites. In general, a lower power input is favorable in terms of energy efficiency.18 The effect of the input power on the equilibrium temperature and HMF yield is systematically studied. Larger power input leads to higher system temperature [Figure 4(c)]. In 10 min, the average system temperature rises from 128 to 169 °C upon increasing the power level from 11 to 19 W. The ramping rate is also higher with larger power (17− 19 W) before the system reaches equilibrium. As a result, the HMF yield increases from 20 mol % at 11 W to 60 mol % at 17

W. A further increase of power to 19 W shows a slight increase of yield to 67 mol %. The HMF yield at different power conditions reveals that the reaction equilibrium could be achieved within 20 min as long as the power input is above 15 W [Figure 4(d)]. Since the dehydration reaction is an endothermic process,46 it is not surprising to see the higher yield of HMF when using larger power in the reaction. However, the larger power does not necessarily increase the overall fructose conversion and HMF yield in terms of unit energy consumption. Therefore, energy efficiency is calculated by using eq 3: Energy efficiency η =

[HMF] P·t ·V

(3)

where P is the input power of microwave, t is elapsed time, and V is the volume of the reaction solution. The energy efficiency of HMF production by using CT80 catalyst is summarized in Table 1. In the first 10 min, 19 W power gives the highest energy efficiency of 5.6 mmol·kJ−1·L−1, but reaction equilibrium has not yet been reached. With reaction time proceeding to 20 min, most reactions reached equilibrium, and the highest energy efficiency is achieved at 4.2 mol·kJ−1L−1 with 15 W power. It is worth mentioning that the energy efficiency of pure TiO2 is only 0.6 mol·kJ−1·L−1 at the same condition (15 W, 10 min). The introduction of CNTs significantly improves the energy efficiency about 6 times. Fructose is the ideal feedstock for HMF, while glucose and sucrose also widely exist as potential resources. In this work, the dehydration reactions of glucose and sucrose are also performed by adopting 15 W microwave power (Figure 5). 4356

DOI: 10.1021/acssuschemeng.7b00414 ACS Sustainable Chem. Eng. 2017, 5, 4352−4358

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ACS Sustainable Chemistry & Engineering Table 1. Energy Efficiency of HMF Production at Different Power Input Conditions by Using TiO2, CNTs, and CT80 Catalysts

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Energy efficiency (mmol·kJ−1·L−1) Catalyst

Time (min)

11 W

13 W

15 W

17 W

19 W

TiO2 CNTs CT80 CT80 CT80

30 30 10 20 30

0.4 0.1 2.3 2.2 1.8

0.5 0.2 3.2 3.9 3.3

0.6 0.8 3.9 4.2 2.9

0.5 1.0 5.2 3.9 2.7

0.6 1.8 5.6 3.8 2.6

Structure and surface property characterization of materials including XRD, TPD, TEM, EDX, SEM, and BET. Temperature profile of microwave reaction. (PDF)

AUTHOR INFORMATION

Corresponding Author

*E-Mail: [email protected]. Tel: 330-972-6859. ORCID

Xiaohua Lu: 0000-0001-9244-6808 Jiahua Zhu: 0000-0002-2238-9147 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Acknowledgement is made to the Donors of the American Chemical Society Petroleum Research Fund (#55570-DNI10) and to the NSF (CBET-1603264). The authors appreciate the instrument support and postdoc assistance provided to Nicholas Callow from Lukwang Ju’s group. HRTEM was performed at the Liquid Crystal Institute, Kent State University, supported by the Ohio Research Scholars Program Research Cluster on Surfaces in Advanced Materials. The authors appreciate the technical support with HRTEM from Min Gao.

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Figure 5. Saccharide conversion (dashed line) and HMF yield (solid line) with time with different saccharide substrates. Reaction conditions: [fructose] = 0.55 mmol, [CT80] = 12.5 mg/mL, input power = 15 W. Temperature−time profile refers to Figure S12.

The glucose conversion and HMF yield are 22.5 and 52%, respectively. The relatively lower glucose conversion and HMF yield can be attributed to the mutarotation and isomerization of glucose before dehydration reaction occurs.47,48 97.3% of sucrose is converted in 20 min, and a maximum HMF yield of 65% is achieved in 30 min. The higher HMF yield with sucrose can be explained by the further hydrolysis of fructose and glucose units, which are concurrently dehydrated to HMF.27

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CONCLUSIONS In conclusion, a microwave responsive core−shell structured CNTs/TiO2 catalyst is synthesized for fast and energy efficient catalytic dehydration of saccharide to HMF. A thinner TiO2 layer is favorable to reach higher reaction temperature as well as reaction conversion and yield. Upon the reaction reaching equilibrium, the highest energy efficiency of 4.2 mol·kJ−1·L−1 is obtained by CT80, which is 6 times higher than pure TiO2 and 4 times higher than CNTs at the same power level of 15 W. An obvious synergistic effect has been realized in these hybrid catalysts. The catalytic activity has also been demonstrated in glucose and sucrose conversion reactions. This study opens up a new opportunity to enhance energy efficiency for saccharide− HMF conversion reactions and promotes the economic feasibility of such reactions in practice.

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REFERENCES

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.7b00414. 4357

DOI: 10.1021/acssuschemeng.7b00414 ACS Sustainable Chem. Eng. 2017, 5, 4352−4358

Research Article

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DOI: 10.1021/acssuschemeng.7b00414 ACS Sustainable Chem. Eng. 2017, 5, 4352−4358