Efficient One-Pot Production of Biofuel 5-Ethoxymethylfurfural from

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Biofuels and Biomass

Efficient one-pot production of biofuel 5-ethoxymethylfurfural from corn stover: Optimization and kinetics Binglin Chen, Guizhuan Xu, Chun Chang, Zhangbin Zheng, Dongxiang Wang, Shaohao Zhang, Kai Li, and Caihong Zou Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.9b00357 • Publication Date (Web): 17 Apr 2019 Downloaded from http://pubs.acs.org on April 21, 2019

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Energy & Fuels

Efficient one-pot production of biofuel 5-ethoxymethylfurfural from corn stover: Optimization and kinetics Binglin Chen a, Guizhuan Xu a*, Chun Chang

b,c,

Zhangbin Zheng a, Dongxiang Wang a,

Shaohao Zhang a, Kai Li a, Caihong Zou a a

College of Mechanical and Electrical Engineering, Henan Agricultural University, Zhengzhou

450002, China b

School of Chemical Engineering and Energy, Zhengzhou University, Zhengzhou 450001,

China c

Key Laboratory of Biomass Chemical Engineering of Ministry of Education, Zhejiang

University, Hangzhou 310027, China * Corresponding author: [email protected], Tel.: +86 13653860867 Abstract The one-pot production of promising biofuel, 5-ethoxymethylfurfural (EMF) from corn stover with mixed acid as catalyst was investigated and optimized by using the response surface methodology. Catalyzed by the mixed acids comprising of 0.1% H2SO4 and 1.0% zeolite USY, a high EMF yield of 23.9% at 210 °C and 125 min can be obtained from corn stover. Meanwhile, catalytic activity of the zeolite USY was no obvious loss after five recycles. Based on the putative reaction pathway, the kinetics modeling for the EMF production directly from corn stover was developed, which coincided with the first order reaction model. This study provides a

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promising strategy for the EMF preparation from corn stover. Keywords: Corn stover; 5-Ethoxymethylfurfural; Optimization; Kinetics 1. Introduction 5-Ethoxymethylfurfural (EMF) has been considered as a transportation biofuel or fuel additive due to its good fuel property, such as high energy density (8.7 kWh·L–1), fine oxidation stability, good low-temperature fluidity, as well as low soot (fine particles) and SOx emissions .1,2 Besides, it also can be applied as flavor or aroma ingredient in beer and wine.3 So, it has aroused much attention to produce EMF with low cost and sustainable feedstock, high conversion efficiency and environmental friendly reaction system. To synthesis bio-based EMF, biomass or carbohydrates can be firstly transformed to 5-hydroxymethylfurfural (HMF), 5-bromomethylfurfural (BMF) or 5-chloromethylfurfural (CMF), then the separated and purified intermediate can be converted into EMF by etherification.4-6 Generally, the etherification of HMF, BMF or CMF can lead to high EMF yield. Several groups have reported that the EMF yield higher than 90% can be achieved when using HMF as the raw material.7-10 Moreover, Viil got a EMF yield of 88% from BMF and 84% from CMF.11 However, owing to the high cost and complicated production process of HMF, BMF and CMF, the extensive production of EMF is still a barrier. Recently, direct synthesis of EMF from biomass by alcoholysis is regarded as a promising way. In this way, EMF can be produced in situ from biomass without separation of intermidates.12-13


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Different catalysts have been employed in the direct synthesis of EMF from biomass. Mineral acids (H2SO4 and H3PO4) have been first used in the process. However, it has the disadvantages in separation and recovery. In addition, the usage of mineral acids with high concentration may result in the equipment corrosion. To overcome these shortcomings, using extremely low concentrated acid is identified as a promising method due to its minimum environmental impact and equipment corrosion.14 In addition, solid catalysts can provide green alternative to homogeneous catalysts. Different solid acid catalysts, such as Ar-SO3H-SBA-15,2 K-10 clay-HPW,8 Fe3O4@SiO2-HPW,10 mesoporous Al-MCM-41,15 H4SiW12O40/MCM-41,16 H3PW12O40,17 Ag1H2PW,18 [MIMBS]3PW12O40,19 nanosphere PY-PW-1,20 [Cu-BTC][HPM] (NENU-5),21 Cs2STA,22 Fe3O4@SiO2-SHIm-HSO4,23 OMC-SO3H,24 glu-Fe3O4-SO3H,25 etc. have been developed for the EMF synthesis from carbohydrates. Although such solid catalysts showed effective catalytic ability, it may be difficult for most of them to act directly on lignocellulosic biomass. The development of novel catalytic system suitable for catalytic lignocellulosic biomass still needs to be strengthened. Corn stover is a type of abundant, cheap and renewable lignocellulosic biomass, and 2.5×108 tons of corn stover are yielded each year in China. 26 Unfortunately, most of them have been burned without any disposal, which leads to the aggravation of the air pollution and resource waste. The major constituents of corn stover are polymeric carbohydrates and lignin, and the inert structure of cellulose is difficult to be accessed. It will be the challenge to effectively convert corn stover into EMF.27 Therefore, the feasibility of using the sustainable and


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abundant feedstock to produce EMF is worth studying. In this context, we sought to explore a green mixed acids catalytic system with high efficiency for one-pot EMF production. Moreover, the response surface methodology (RSM) was employed for the process optimization. Subsequently, the reaction mechanism and kinetics for the EMF synthesis from corn stover were also investigated. 2.

2.1

Experimental

Materials Corn stover, provided by a local farm (Zhengzhou, China), was grinded, passed through the

100 mesh sieve for experiments after it was dried at 65 ℃ for 24 h. The main composition of the corn stover (cellulose 38.2 ± 0.8%, hemicellulose 22.8 ± 0.5% and lignin 10.8 ± 0.7%) was analysed by the Laboratory Analytical Procedure (LAP) of NREL.28 EMF (CAS 1917-65-3, 97% purity) was obtained from Sigma-Aldrich (Shanghai, China). Ethyl levulinate (EL) (CAS 539-88-8, 99% purity) and HMF (CAS 67-47-0, 98% purity) were purchased from Aladdin Reagent (Shanghai China). The solid catalyst zeolite USY (NKF-7Ⅱ) was purchased from Nankai University Catalyst Co., Ltd (Tianjin, China), with the surface area, Si/Al ratio and Na2O content of USY were 600 m2·g–1, 5.3 and 1.8 % respectively. It was calcined at 500 ℃ for 4 h before reaction. H2SO4 (98% purity) and Ethanol with chemical purity were bought from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China).

2.2

Experimental procedure


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The experimental set-up is illustrated in Fig. 1. All experiments were performed in a cylindrical 100mL pressurized stainless steel reactor with a thermocouple and an electrical heating jacket. In the experiments, ethanol, corn stover and the required catalysts were put into the reactor, and the amount of added catalysts is based on the mass of ethanol. Then the reactor was sealed and heated to the given temperature. In the process, the stirring speed was kept at 500 rpm. At the end of the reaction, the reactor was immersed in the water for ending the reaction. When the temperature decreased to 40 ℃, the reactor was connected with a storage tank contained cold ethanol. Then the gas in the reactor was flowed into the storage tank, and the yield of diethyl ether (DEE) can be determined by the mass change of the tank. After that the liquid samples in reactor were filtered and centrifuged for 30 min at 10000 rpm, upper liquid and solid residues were collected for further analysis respectively.

2.3

Analytical methods The EMF and HMF were separated by a ZORBAX Eclipse XDB-C18 column (250 mm ×

4.6 mm) at 30 oC, and the amounts were determined by HPLC (Agilent Technologies 1260, USA) instrument equipped with an ultraviolet detector (280 nm). The mobile phase was the mixed solution of acetonitrile and acetic acid (0.1%) with a ratio of 30:70 (volume ratio), and the flow rate was 0.6 mL·min–1. Moreover, the EL was separated by a HP-5MS capillary column (30 m × 0.32 mm × 0.50 μm), and analyzed by a GC (Agilent Technologies 6820, USA) with a FID detector and. The starting temperature of column was 60 °C. It was increased to 280 °C with a


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speed of 10 °C·min–1, then kept 280 °C for 2 min. In the process, the flow rate of carrier gas (N2) was maintained at 1.0 mL·min–1, the injector and the detector temperature were 240 °C and 250 °C, respectively. Meanwhile, the liquid products were confirmed by GC-MS (Agilent Technologies 7890B, USA). In addition, the IR spectra of catalyst before and after its use were determined by Fourier Transformed Infrared (Nicolet-IR 200, USA). X-ray diffraction (XRD) patterns were analyzed with an X-ray diffractometer (Bruker D8Advance, Germany). 27 The yields of EMF, HMF and EL were calculated according to the molar amount comparison between EMF (HMF, EL) and the glucose units in the corn stover according to Eq.1-3. The moles of glucose can be determined by using NREL method.

28

In addition, the

recovery rate of catalyst was calculated by Eq. 4. The yield of EMF (mol %) =

moles of EMF formed moles of glucose units in corn stover

× 100 %

(1)

The yield of HMF (mol %) =

moles of HMF formed moles of glucose units in corn stover

× 100 %

(2)

The yield of EL (mol %) = Catalyst recovery (%) =

2.4

moles of EL formed moles of glucose units in corn stover

Mass of reused catalyst Mass of fresh catalyst

× 100 %

× 100 %

(3) (4)

Experimental design The Box-Behnken design (BBD) was applied to select the best combination of four

variables. The levels of the variables determined by the single factor experiments are shown in Table 1, and the variables were coded based on Eq. 5. xi = (Xi ― Xi0)/∆Xi


(5)

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where xi, Xi, are the coded value and the actual value of the independent variables, respectively; Xi0 is the actual value of the center point, ΔXi is value of step change. The yield of EMF was regarded as response Y (dependent variables). The second-order model for the RSM was expressed as the Eq.6. 𝑛=4

𝑛=4

𝑛=4

𝑌 = 𝛼0 + ∑𝑖 = 1 𝛼𝑖𝑥𝑖 + ∑𝑖 = 1 𝛼𝑖𝑖𝑥2𝑖 + ∑𝑖 < 𝑗 = 1𝛼𝑖𝑗𝑥𝑖𝑥𝑖𝑗 ..........................(6) where Y is the value of EMF yield, α0 is the offset term, αi is the linear effect terms, αii is squared effect terms, αij is interaction effect terms.

2.5

Kinetics modeling In this study, a simplified kinetic model of EMF synthesis from corn stover was employed

(Fig. 2). Some assumptions based on our previous study were made as follows (1) The formation of intermediates is negligible, (2) Unknown products are regarded as byproducts, (3) Alcoholysis of corn stover in a parallel reaction mode.

29

Based on these, the following set of differential

equations can be obtained: 𝑑𝐶𝑏 𝑑𝑡

= ― (𝑘1𝐶𝑏 + 𝑘2𝐶𝑏) 𝑑𝐶𝐸𝑀𝐹 𝑑𝑡

= ― 𝑘1𝐶𝑏

k1 + k2 = k

(7) (8) (9)

where Cb is total amount of glucose in corn stover, g·L–1; k1 and k2 are the reaction rate constant of the EMF formation and the byproducts formation, min–1; t is time, min; CEMF is EMF concentration, g·L–1.


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The analytical expression of the EMF concentration and the EMF yield can be expressed as Eq. 10-11 by solving the above Eq. 7-9: 𝑘1

𝐶𝐸𝑀𝐹 = 𝐶𝑏0𝑘1 + 𝑘2{1 ― exp[ ― (𝑘1 + 𝑘2)𝑡]} 𝑘1

𝑌𝐸𝑀𝐹 = 𝑘1 + 𝑘2{1 ― exp[ ― (𝑘1 + 𝑘2)𝑡]}

(10) (11)

where Cb0 is initial total amount of glucose in corn stover, g·L–1; YEMF is yield of EMF, %. The correlation between kinetic coefficients and temperature is as follows: 𝑘𝑖 = 𝐴𝑖𝑒

( ― 𝐸𝑖 𝑅𝑇)

(𝑖 = 1, 2)

(12)

where A1 and A2 are the pre-exponential factors of the main reaction and the side reaction, min– 1,

respectively; E1 and E2 are activation energy values of the main reaction and the side reaction,

kJ·mol–1, respectively; T is temperature, K; R is gas constant, 8.3143 J·mol–1·K–1. 3.

3.1

Results and discussion

Effects of different conditions on EMF production The effects of different reaction conditions on the products yield and the concentration were

investigated firstly. As illustrated in Fig. 3a and Fig.4a, when 0.1% H2SO4 catalyst was used in the reactions, the yield of EMF increased as the reaction time increased. A maximum EMF yield (5.2%) was obtained at 120 min. Then the EMF yield decreased slowly as the reaction time increased. Similarly, the change of products concentration showed the same rule. A maximum EMF concentration (0.35 g·L–1) can be obtained when the reaction time was 120 min. For USY and mixed acid catalyst, same changes can be observed. The maximum yields of EMF were


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9.1% and 13.6% at 150 min, and the corresponding EMF concentrations of 0.61 g·L–1 and 0.92 g·L–1 were achieved. Meanwhile, as the time increased, it was found that the EMF yield and EMF concentration decreased due to the further conversion of EMF.30 It was clear to see that the EMF yield catalyzed by the mixed acid was almost three times higher than that of catalyzed by extremely low acid. The reason may be ascribed to the increased acid concentration of mixed catalyst system. Meanwhile, the combination of B acid and L acid also can enhance the ethanolysis of corn stover, which also can improve the EMF formation.31 In addition, more EL was analyzed in the mixed acid system. This is because that EMF is the precursor of EL, and some EMF was converted into EL in the reaction. Notably, almost no HMF was analyzed in the reaction liquid, indicating the EMF conversed from HMF was easy to occur in the process. Fig. 3b and Fig. 4b illustrate the effect of temperature on the EMF production. Under different catalytic systems, the change of EMF yield showed similar regularity. All the EMF yield and EMF concentration increased first and then decreased. The maximum yield of EMF (13.6%) and maximum EMF concentration (0.92 g·L–1) can be obtained at 190 ℃ with mixed acid as the catalysts. It also can be found that a lower temperature was not conducive to the EMF production from corn stover, and a higher temperature should be required to promote the depolymerization and alcoholysis of biomass.32 However, when the reaction temperature surpassed 190 ℃, both the EMF yield and concentration decreased due to the conversion of EMF into EL, as evidenced by the increase in EL concentration and yield. In comparison, the EMF yield and concentration were much lower at the same temperature when single acid was used as catalyst. These results


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further signified that the mixed acid had better catalytic activity. Effect of substrate concentration on EMF production is shown in Fig. 3c and Fig. 4c. When the concentration of corn stover was 5 g·L–1, more EL can be produced due to excessive acidic sites existed in all the systems. As the concentration of corn stover increased, the yield of EL decreased gradually with the increase of EMF yield, indicating the optimum substrate concentration existed in the process. For the single catalytic system, the optimum substrate concentration was 20 g·L–1, and the maximum yields of EMF from corn stover catalyzed by 0.1% H2SO4 and USY were 5.2% and 10.3%. Meanwhile, the corresponding EMF concentrations (0.35 g·L–1 and 0.69 g·L–1) can be obtained. Similarly, a maximum yield of EMF (16.1%) was obtained at 15 g·L–1 in mixed acid catalytic system, and the EMF concentration reached to 1.09 g·L–1. However, when the concentration of corn stover further increased, the EMF yield decreased. This was because that the catalytic system cannot provide sufficient acidic sites for the EMF synthesis when the substrate concentration exceeded a certain limit. Catalyst dosage is also a key parameter for the production of EMF, and the effect of the catalyst is presented in Fig. 3d and Fig. 4d. As discussed above, the catalytic activity of 0.1% H2SO4 on the formation of EMF from corn stover was not ideal. In comparison, the increase of USY dosage can improve the accumulation of EMF, and the maximum EMF yield (10.3%) and EMF concentration (0.69 g·L–1) can be obtained with 2.0% USY dosage. Nevertheless, as the dosage was over 2.0%, the EMF yield and EMF concentration showed the downward trends, showing that more solid catalyst was negative for HMF conversion to EMF. 31, 33 It was worth noting that


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the combination of 0.1% H2SO4 and 2.0% USY can improve the EMF yield and concentration significantly, and the maximum EMF yield of 16.1 % and EMF concentration of 1.09 g·L–1 can be achieved. These results ascribed that the increase of the acid strength and the suitable L/B ratio in the mixed acids.34

3.2

RSM Optimization The RSM approach with BBD was applied to optimize the EMF production catalyzed by

the mixed acids. All the levels and factors are presented in Table 2. Since the change of EMF yield was consistent with the change of EMF concentration, the results of yield was only used as the response. Thus, the equation (Eq. 13) described the response (EMF yield ) as a function of four variables can be obtained by utilizing RSM. Y = 20.95 + 0.23𝑥1 +5.45𝑥2 +2.83𝑥3 ―2.41𝑥4 ―3.44𝑥1𝑥2 +1.49𝑥1𝑥3 +0.59𝑥1𝑥4 +5.32𝑥2𝑥3 ―8.44𝑥2𝑥4 +3.18𝑋𝑥3𝑥4 ―3.34𝑥21 ―4.41𝑥22 ―6.31𝑥23 ―1.24𝑥24

(13)

The significance of regression coefficient of the equation and the analysis of variance (ANOVA) are presented in Table 3 and Table 4, respectively. It was found that the reaction temperature (x2), the substrate concentration (x3) and the USY dosage (x4) were significant as was proven by their low p-values. Moreover, the quadratic main effect of reaction time (x12), temperature (x22) and the concentration of corn stover (x32) were also significant as well as the interaction effect coefficient (x1x2, x2x3, x3x4, x2x4). It also can be seen that the model was significant (P < 0.0001), and the regression coefficient (R2 = 0.96) indicated a good predictability


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of the model (Fig. 5). Furthermore, a series of three-dimensional response surface plots of the interaction of the four main factors can be obtained from the model equation. Among them, the effects of reaction time (100-200 min) on EMF yield are represented in Fig. 6a-c. It shows that the effects between the reaction time and the reaction temperature were significant, which can be proved by the small ellipse in the plots. Effects of temperature are shown in Fig. 6a, d, e. At 170 ℃, the yield of EMF was not more than 20%. As the temperature elevated gradually, the increase of EMF yield can be observed, suggesting that the EMF formation can be efficiently strengthened by the increase of temperature. 35 Besides this, the interaction effects of corn stover concentration with the other variables (reaction time and USY dosage) are shown in Fig. 6b, d and f. When the corn stover concentration continued to be increased, the EMF yield showed a trend of rising first and then decreasing. This phenomenon suggested that an optimum substrate concentration existed in the process.36 Theoretically, under a higher catalytic dosage can provide more acidic sites for the alcoholysis of corn stover. Nevertheless, the interaction of the catalytic dosage and other factors was complicated. It can be seen from Fig. 6c, e and f that the EMF yield decreased as the amounts of the catalyst increased when the other factors were in a certain range. Applying the methodology of desired function, the optimum reaction conditions can be obtained, and they were reaction time 125 min, reaction temperature 210 ℃, corn stover 20 g·L–1, USY 1.0%. Under the optimum conditions, the predicated yield of EMF was 24.5%. To verify the result, three repeated experiments were conducted, and the EMF yield were 23.2%, 23.8% and 24.7%,


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Energy & Fuels

respectively. Thus, the average EMF yield (23.9%) closed to the predicted value can be obtained, corresponding to a EMF centration of 1.6 g·L–1. As the gaseous by-product, the formation of DEE is inevitable because of the condensation reaction of ethanol by acid catalysts.37-38 To verify the advantage of the optimization results, a comparison study on DEE formation in different acid catalytic systems was further conducted (Fig. 7). It was found that the amount of DEE catalyzed by USY was significantly lower than that of extremely low sulfuric acid, which was in accordance with our previous report.39 In addition, although the amount of DEE in the mixed acid catalytic system was higher than that of USY, the DEE amount was lower than that of extremely low sulfuric acid. The results suggested that the mixed acid catalysts not only has the excellent catalytic activity, but also can reduce the DEE amount to some extent.

3.3

Reusability and characterization of USY Reusability of catalyst is a vital index to evaluate its performance. Accordingly, recycling

experiments of USY were further conducted. As the reaction finished, the solid residue can be collected by filtration and dried at 80 oC to remove the volatile impurity. Then, it was calcined at 500 oC for 4 h before it was reused. As portrayed in Fig. 8, the EMF yield of 23.2% was obtained after the first run. With the increase of recycles to 5 times, the yield of EMF can still be maintained above 20.1%, which clarified that the catalytic activity of reused USY was good. However, after 7 runs, the EMF yield was obviously decreased to 16.5% due to the formed


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humins deposited on the surface of the USY.40 On the other hand, the recovery rate of USY remained stable, and the catalyst recovery rate just dropped from 91.5% for the first recycle to 88.7% in the 7th recycle. Characterizations of fresh and reused USY were determined by FT-IR and XRD. As shown in Fig. 9a, it can be seen that the FT-IR spectra of fresh USY and reused USY showed typical peaks between 3400 and 3450 cm–1, which was attributed to the hydroxyl groups on the surface of the catalyst. In addition, three vibration bands at between 1040-1051 cm–1, 785-795 cm–1 and 450-460 cm–1 can be observed due to the bands of Si–O bonds.41 It also can be seen that the spectra of the reused USY were similar to that of fresh USY. Furthermore, the XRD patterns of the catalysts are shown in Fig. 9b. The typical peaks at around 2θ angles of 6.39°, 10.37°, 12.07°, 15.83°, 18.85°, 20.53°, 23.80°, 27.20° and 31.52° can be observed.42-43 Noticeably, the same typical diffraction peaks of the reused USY can be found after 7 runs, which signified that porous structure of the recycled USY was still maintained well. However, after several reuse, typical diffraction peaks of USY became much weaker presumably due to the changes in catalyst crystal.44-45

3.4

Ethanolysis pathway for EMF production To gain insights into ethanolysis pathway for EMF production, GC-MS was used to identify

the liquid products with different catalysts (Fig. 10). The main products were furan derivatives, glycosides, alkanes, phenols and organic esters, etc. The formation of these products was ascribed to the reactions with degradation, rearrangement, esterification, dehydration.46 It was


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noteworthy that the dominant product was EMF based on the relative peak area. Meanwhile, HMF, EL also can be found. Moreover, ethyl glucoside was identified in the reaction liquid when using extremely low acid and mixed acids as catalysts, while no ethyl glucoside was detected in the single USY catalytic system. The results suggested that glucose was mainly converted to ethyl glucoside when the catalytic system contained more Brønsted acid sites.47 A putative ethanolysis pathway for the production of EMF from corn stover was then given (Fig. 11). Under the action of acidic catalyst, glucose was first obtained through hydrolysis of corn stover, and then glucose was converted into EMF through two possible pathways. In the first pathway, glucose was isomerized to fructose under the action of Lewis acid sites. Subsequently, fructose was dehydrated to form HMF, and HMF was esterified to form EMF. In the second pathway, glucose can be converted into ethyl glucoside under the action of Brønsted acid sites, and then converted into EMF. Moreover, EL was formed due to the further ethanolysis of EMF.48 It should be pointed out that the hexose in the hemicellulose also can be converted into EMF theoretically follow the similar reaction routes. However, since the contents of hexose in hemicellulose were very low (less than 1.0%), the contribution of hexoses in the hemicellulose to EMF production can be ignored in the process. In addition, the composition of collected solid residue after the reaction was analyzed. It was found that the cellulose content decreased from 38.2% to 5.5%. However, the content of lignin increased from 10.8% to 19.1%. These results suggested that the EMF was mainly produced from the cellulose in corn stover.


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3.5

Kinetics of EMF production Base on the above reaction pathways, a pseudo-homogeneous kinetic model was proposed,

and the kinetics of EMF production from corn stover was further investigated. As discussed above, EMF is mainly produced from hexoses in cellulose. Therefore, the EMF yield was calculated according to the molar amount comparison between EMF and the glucose units in the corn stover. The EMF yield evolution over time at different reaction temperatures is shown in Fig. 12. The experimental data were correlated by the Eq. 11, and the results of the kinetic parameters are shown in the Table 5. It can be seen that both the reaction rate constants increased as the temperature increased from 170 ℃ to 210 ℃, indicating that higher temperatures were conducive to the promotion of chemical reactions. Meanwhile, the values of k1/k2 and k1/k increased as the temperature increased. These results suggested that the increasing of temperature was more favorable for the EMF formation compared with the formation of humins. In addition, the value of E1 (131.0 kJ·mol–1) was obviously higher than the value of E2 (39.7 kJ·mol–1), suggesting that high temperature is beneficial to the main reaction and can improve the EMF selectivity. Meanwhile, the values of pre-exponential factor of A1 and A2 were 1.4×1012 min–1 and 618.8 min–1, respectively. As described in Fig. 13, the experimental data were in keeping with the theoretical date from the kinetics model, indicating that the kinetics of EMF formation was appropriately described by the kinetics model. Some related studies about the EMF production and the EL production from HMF and carbohydrates are summarized for further comparison.20, 49-52 As illustrated in Table 6, the activation energy values were different


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because of the diversity of the feedstock. The order of activation energy required for the reaction was as follows: lignocellulose biomass > carbohydrate > HMF. Moreover, the values of activation energy of EMF formation in this study were higher than those of HMF and carbohydrate, indicating high temperature is beneficial to the alcoholysis of corn stover and EMF formation.

3.6

Literature comparison Related literatures about the conversion of biomass into EMF are shown in Table 7.

Bredihhin proposed a two-step method for EMF production, and a high EMF yield (40.0%) was obtained from cellulose.5 However, the intermediate products need to be separated and purified in the reactions. Recently, more researchers focused on EMF production from biomass by using one-pot method, which can effectively simplify the preparation process.53-55 However, most of the reaction processes are time consuming (6~15 h). In this study, a mixed acids system for direct EMF preparation from corn stover was developed, and a higher EMF yield of 23.9% can be obtained under the optimum conditions. Compared to previous studies, the shortening of reaction time to 125 min indicates the reaction efficiency is improved. Meanwhile, the developed catalytic system is very cheap. These merits can make the EMF preparation more economical and practical. 4.

Conclusion Efficient conversion of corn stover into EMF with the mixed acids (0.1% H2SO4 and 1.0%


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

USY) as catalyst was optimized, and a higher EMF yield of 23.9% can be obtained. On the basis, two possible pathways for the EMF production was proposed. Moreover, the reaction kinetics for the synthesis of EMF from corn stover was in coincidence with the first-order reaction model. This study provides a novel strategy for efficient EMF production from corn stover. Acknowledgements The project was financially supported by the Foundation and Frontier Technology Research Project of Henan Province of China (162300410007), the Foundation of Key Laboratory of Biomass Chemical Engineering of Ministry of Education, Zhejiang University (2018BCE001) and the Program of Processing and Efficient Utilization of Biomass Resources of Henan Center for Outstanding Overseas Scientists (GZS2018004). The authors declare no competing financial interest. References (1) Chen, T.; Peng, L.C.; Yu, X.; He, L. Magnetically recyclable cellulose-derived carbonaceous solid acid catalyzed the biofuel 5-ethoxymethylfurfural synthesis from renewable carbohydrates. Fuel 2018, 219, 344-352. (2) Morales, G.; Paniagua, M.; Melero, J. A.; Iglesias, J. Efficient production of 5-ethoxymethylfurfural from fructose by sulfonic mesostructured silica using DMSO as co-solvent. Catal. Today 2017, 279, 305-316. (3) Pereira, V.; Santos, M.; Cacho, J.; Marques, J.C. Assessment of the development of


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Page 19 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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browning, antioxidant activity and volatile organic compounds in thermally processed sugar model wines. LWT-Food Sci. Technol. 2017, 75, 719-726. (4) Jia, X.Q.; Ma, J.P.; Che, P.H.; Lu, F.; Miao, H.; Gao, J.; Xu, J. Direct conversion of fructose-based carbohydrates to 5-ethoxymethylfurfural catalyzed by AlCl3·6H2O/BF3·(Et)2O in ethanol. J. Energy Chem. 2013, 22(1), 93-97. (5) Bredihhin, A.; Maeorg, U.; Vares, L. Evaluation of carbohydrates and lignocellulosic biomass from different wood species as raw material for the synthesis of 5-bromomethyfurfural. Carbohydrate Res. 2013, 375, 63-67. (6) Howard, J.; Rackemann, D.W.; Zhang, Z.; Moghaddam, L.; Bartley, J.P.; Doherty, W.O.S. Effect of pretreatment on the formation of 5-chloromethyl furfural derived from sugarcane bagasse. RSC Adv. 2016, 6, 5240-5248. (7) Yadav, K.K.; Ahmad, S.; Chauhan, S.M.S. Elucidating the role of cobalt phthalocyanine in the dehydration of carbohydrates in ionic liquids. J. Mol. Catal. A Chem. 2014, 394, 170-176. (8) Liu,

A.Q.;

Liu,

B.;

Wang,

Y.M.;

Ren,

R.S.

Efficient

one-pot

synthesis

of

5-ethoxymethylfurfural from fructose catalyzed by heteropolyacid supported on K-10 clay. Fuel 2014, 117, 68-73. (9) Liu, B.; Gou, Z.Z.; Liu, A.Q.; Zhang, Z.H. Synthesis of furan compounds from HMF and fructose catalyzed by aluminum-exchanged K-10 clay. J. Ind. Eng. Chem. 2015, 21, 338-339. (10) Wang, S.G.; Zhang, Z.H.; Liu, B.; Li, J.L. Silica coated magnetic Fe3O4 nanoparticles supported phosphotungstic acid: a novel environmentally friendly catalyst for the synthesis of


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

5-ethoxymethylfurfural from 5-hydroxymethylfurfural and fructose. Catal. Sci. Technol. 2013, 3 (8), 2104-2112. (11) Viil, I.; Bredihhin, A.; Mäeorg, U.; Vares, L. Preparation of potential biofuel 5-ethoxymethylfurfural and other 5-alkoxymethylfurfurals in the presence of oil shale ash. RSC Adv. 2014, 4, 5689-5693. (12) Liu, X.; Li, H.; Pan, H.; Zhang, H.; Huang, S.; Yang, K.; Xue, W.; Yang, S. Efficient catalytic conversion of carbohydrates into 5-ethoxymethylfurfural over MIL-101-based sulfated porous coordination polymers. J. Energy Chem. 2016, 25, 523-530. (13) Jiang, Y.; Chen, W.; Sun, Y.; Li, Z.; Tang, X.; Zeng, X.; Lin, L.; Liu, S. One-pot conversion of biomass-derived carbohydrates into 5-[(formyloxy)methyl]furfural: A novel alternative platform chemical. Ind. Crops Prod. 2016, 83, 408-413. (14) Dai, J.; Peng, L.C.; Li, H. Intensified ethyl levulinate production from cellulose using a combination of low loading H2SO4, and Al(OTf)3. Catal. Commun. 2018, 103, 116-119. (15) Lanzafame, P.; Temi, D. M.; Perathoner, S.; Centi, G.; Macario, A.; Aloise, A.; Giordano, G. Etherification of 5-hydroxymethyl-2-furfural (HMF) with ethanol to biodiesel components using mesoporous solid acidic catalysts. Catal. Today 2011, 175 (1), 435-441. (16) Che, P.H.; Lu, F.; Zhang, J.J.; Huang, Y.Z.; Nie, X.; Gao, J.; X, J. Catalytic selective etherification of hydroxyl groups in 5-hydroxymethylfurfural over H4SiW12O40/MCM-41 nanospheres for liquid fuel production. Bioresour. Technol. 2012, 119, 433-36. (17) Yang, Y.; Abu-Omar, M.M.; Hu, C.W. Heteropolyacid catalyzed conversion of fructose,


Page 20 of 51

Page 21 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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sucrose, and inulin to 5-ethoxymethylfurfural, a liquid biofuel candidate, Appl. Energy 2012, 99, 80-84. (18) Ren, Y.S.; Liu, B.; Zhang, Z.H.; Lin, J.T. Silver-exchanged heteropolyacid catalyst (Ag1H2PW): an efficient heterogeneous catalyst for the synthesis of 5-ethoxymethylfurfural from 5-hydroxymethylfurfural and fructose. J. Ind. Eng. Chem. 2015, 21, 1127-1131. (19) Liu, B.; Zhang, Z.H.; Deng, K.J. Efficient one-pot synthesis of 5-(ethoxymethyl) furfural from fructose catalyzed by a novel solid catalyst. Ind. Eng. Chem. Res. 2012, 51 (47), 15331-15336. (20) Wang, Z.W.; Li, H.; Fang, C.J.; Zhao, W.F.; Yang, T.T.; Yang, S. Simply assembled acidic nanospheres for efficient production of 5-ethoxymethylfurfural from 5-hydromethylfurfural and fructose. Energy Technol. 2017, 5, 2046-2054. (21) Wang,

Z.H.;

Chen,

Q.W.

Conversion

of

5-hydroxymethylfurfural

into

5-ethoxymethylfurfural and ethyl levulinate catalyzed by MOF-based heteropolyacid materials. Green Chem. 2016, 18 (21), 5884-5889. (22) Raveendra, G.; Rajasekhar, A.; Srinivas, M.; Prasad, P.S.S.; Lingaiah, N. Selective etherification of hydroxymethylfurfural to biofuel additivesover Cs containing silicotungstic acid catalysts. Appl. Catal., A 2016, 520, 105-113. (23) Yin, S.S.; Sun, J.; Liu, B.; Zhang, Z.H. Magnetic material grafted cross-linked imidazolium based polyionic liquids: an efficient acid catalyst for the synthesis of promising liquid fuel 5-ethoxymethylfurfural from carbohydrates. J. Mater. Chem. A 2015, 3 (9), 4992-4999.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 51

(24) Wang, J.M.; Zhang, Z.H.; Jin, S.W.; Shen, X.Z. Efficient conversion of carbohydrates into 5-hydroxylmethylfurfan

and

5-ethoxymethylfurfural

over

sufonic

acid-functionalized

mesoporous carbon catalyst. Fuel 2017, 192, 102-107. (25) Thombal, R.S.; Jadhav, V.H. Application of glucose derived magnetic solid acid for etherification of 5-HMF to 5-EMF, dehydration of sorbitol to isosorbide, and esterification of fatty acids. Tetrahedron Lett. 2016, 57 (39), 4398-4400. (26) Fu, P.; Bai, X.Y.; Li, Z.H.; Yi, W.M.; Li, Y.J.; Zhang, Y.C. Fast pyrolysis of corn stovers with ceramic ball heat carriers in a novel dual concentric rotary cylinder reactor. Bioresour. Technol. 2018, 263, 467-474. (27) Chen, B.L.; Xu, G.Z.; Zheng, Z.B.; Wang, D.X.; Z, C.H.; Chang, C. Efficient conversion of corn stover into 5-ethoxymethylfurfural catalyzed by zeolite USY in ethanol/THF medium. Ind. Crops Prod. 2019, 129, 503-511. (28) Sluiter, A., Hames, B., Ruiz, R., Scarlata, C., Sluiter, J., Templeton, D. Determination of Structural Carbohydrates and Lignin in Biomass. NREL, Golden, CO. 2004. (29) Chang, C.; Ma, X.J.; Cen, P.L. Kinetic studies on wheat straw hydrolysis to levulinic acid. Chin. J. Chem. Eng. 2009, 17(5), 835-839. (30) Xu, G.Z.; Chang, C.; Fang, S.Q.; Ma, X.J. Cellulose reactivity in ethanol at elevate temperature and the kinetics of one-pot preparation of ethyl levulinate from cellulose. Renew. Energ. 2015, 78, 583-589. (31) Chang, C.; Xu, G.Z.; Zhu, W.N.; Bai, J.; Fang, S.Q. One-pot production of a liquid biofuel


Page 23 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

candidate-Ethyl levulinate from glucose and furfural residues using a combination of extremely low sulfuric acid and zeolite USY. Fuel 2015, 140, 365-370. (32) Chang, C.; Cen, P.L.; Ma, X.J. Levulinic acid production from wheat straw. Bioresour. Technol. 2007, 98(7), 1448-1453. (33) Wang, H.L.; Deng, T.S.; Wang, Y.X.; Qi, Y.Q.; Hou, X.L.; Zhu, Y.L. Efficient catalytic system for the conversion of fructose into 5-ethoxymethylfurfural. Bioresour. Technol. 2013, 136, 394-400. (34) Deng, L.; Chang, C.; An, R.; Qi, X.G.; Xu, G.Z. Metal sulfates-catalyzed butanolysis of cellulose: butyl levulinate production and optimization. Cellulose 2017, 24, 5403-415. (35) Zhao, S.Q.; Xu, G.Z.; Chang, C.; Fang, S.Q.; Liu, Z.; Du, F.G. Direct conversion of carbohydrates into ethyl levulinate with potassium phosphotungstate as an efficient catalyst. Catalysts 2015, 5, 1897-1910. (36) Zhao, S.Q.; Xu, G.Z.; Chang, J.L.; Chang, C.; Bai, J.; Fang, S.Q.; Liu, Z. Direct production of ethyl levulinate from carbohydrates catalyzed by H-ZSM-5 supported phosphotungstic acid. BioResources 2015, 10, 2223-2234. (37) Mascal, M.; Nikitin, E.B. Comment on processes for the direct conversion of cellulose or cellulosic biomass into levulinate esters. ChemSusChem 2010, 3, 1349-1351. (38) Chang, C.; Li, B.; Xu, G.Z.; Sun, P.Q. Direct conversion of glucose in ethanol and ethanol/water mixed medium. Appl. Mech. Mater. 2013, 291-294, 312-315. (39) Mao, R.L.V.; Zhao, Q.; Dima, G.; Petraccone, D. New process for the acid-catalyzed


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 51

conversion of cellulosic biomass (AC3B) into alkyl levulinates and other esters using a unique one-pot system of reaction and product extraction. Catal. Lett. 2011, 141 (2), 271-276. (40) An, R.; Xu, G.Z.; Chang, C.; Bai, J.; Fang, S.Q. Efficient one-pot synthesis of n-butyl levulinate from carbohydrates catalyzed by Fe2(SO4)3. J. Energy Chem. 2017, 26, 556-563. (41) Niu, L.; Wei, R.P.; Yang, H.; Li, X.; Jiang, F.; Xiao, G.M. Hydrogenolysis of glycerol to propanediols over Cu-MgO/USY catalyst. Chinese J. Catal. 2013, 34, 2230-2235. (42) Li, H.; Govind, K.S.; Kotni, R.; Shunmugavel, S.; Riisager, A.; Yang, S. Direct catalytic transformation of carbohydrates into 5-ethoxymethylfurfural with acid-base bifunctional hybrid nanospheres. Energ. Convers. Manage. 2014, 88, 1245-1251. (43) Li, L.; Quan, K.J.; Xu, J.M.; Liu, F.S.; Liu, S.W.; Yu, S.T.; Xie, C.X.; Zhang, B.Q.; Ge, X.P. Liquid hydrocarbon fuels from catalytic cracking of rubber seed oil using USY as catalyst. Fuel 2014, 123, 189-193. (44) Li, H.; Saravanamurugan, S.; Yang, S.; Riisager, A. Direct transformation of carbohydrates to the biofuel 5-ethoxymethylfurfural by solid acid catalysts. Green Chem. 2016, 18, 726-734. (45) Li, L.; Ding, Z.Y.; Li, K.; Xu, J.M.; Liu, F.S.; Liu, S.W.; Yu, S.T.; Xie, C.X.; Ge, X.P. Liquid hydrocarbon fuels from catalytic cracking of waste cooking oils using ultrastable zeolite USY as catalyst. J. Anal. Appl. Pyrol. 2016, 117, 268-272. (46) Yan,

L.L.;

Liu,

N.A;

Wang,

Y.;

Machida,

H.;

Qi,

X.H.

Production

of

5-hydroxymethylfurfural from corn stalk catalyzed by corn stalk-derived carbonaceous solid acid catalyst. Bioresour. Technol. 2014, 173, 462-466.


Page 25 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(47) Xu, G.Z.; Chen, B.L.; Zheng, Z.B.; Li, K.; Tao, H.G. One-pot ethanolysis of carbohydrates to promising biofuels: 5-ethoxymethylfurfural and ethyl levulinate: one-pot ethanolysis of carbohydrates to biofuels. Asia-Pac. J. Chem. Eng. 2017, 12, 527-535. (48) Chang, C.; Xu, G.Z.; Jiang, X.X. Production of ethyl levulinate by direct conversion of wheat straw in ethanol media. Bioresour. Technol. 2012, 121, 93-99. (49) Hu, L.; Zhao, G.; Tang, X.; Wu, Z.; Xu, J.X.; Lin, L.; Liu, S.J. Catalytic conversion of carbohydrates into 5-hydroxymethylfurfural over cellulose-derived carbonaceous catalyst in ionic liquid. Bioresour. Technol. 2013, 148, 501-507. (50) Hu, L.; Wu, Z.; Xu, J.X.; Sun, Y.; Lin, L.; Liu, S.J. Zeolite-promoted transformation of glucose into 5-hydroxymethylfurfural in ionic liquid. Chem. Eng. J. 2014, 244(10), 137-144. (51) Xu, G.Z.; Chang, C.; Zhu, W.N.; Li, B.; Ma, X.J.; Du, F.G. A comparative study on direct production of ethyl levulinate from glucose in ethanol media catalysed by different acid catalysts. Chem. PAP. 2013, 67, 1355-1363. (52) Zhu, W.N.; Chang, C.; Chen, M.; Du, F.G. Kinetics of glucose ethanolysis catalyzed by extremely low sulfuric acid in ethanol medium. Chin. J. Chem. Eng. 2014, 22 (2), 238-242. (53) De, S.; Dutta, S.; Saha. B. One-pot conversions of lignocellulosic and algal biomass into liquid fuels. ChemSusChem, 2012, 5(9), 1826-1833. (54) Dutta, S.; De, S.; Alam, M.I.; Abu-Omar, M.M.; Saha, B. Direct conversion of cellulose and lignocellulosic biomass into chemicals and biofuel with metal chloride catalysts. J. Catal. 2012, 288, 8-15.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(55) Tan, J.; Liu, Q.Y.; Chen, L.G.; Wang, T.J.; Ma, L.L.; Chen, G.Y. Efficient production of ethyl levulinate from cassava over Al2(SO4)3 catalyst in ethanol-water system. J. Energy Chem. 2017, 26, 115-120.


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Figure Captions Fig. 1

Schematic of the experimental set-up.

Fig. 2

A simplified model of EMF synthesis from corn stover.

Fig. 3

Effect of different factors on yield of products (EMF, HMF and EL) in ethanol medium

(

EMF,

HMF,

EL). Reaction conditions: (a) 20 g·L–1 corn stover, 190 ℃. (b) 20

g·L–1 corn stover, 120 min; 150 min; 150 min. (c) 190 ℃, 120 min; 180 ℃, 150 min; 190 ℃, 150 min. (d) 15 g·L–1 corn stover, 180 ℃, 150 min; 15 g·L–1 corn stover, 190 ℃, 150 min. Fig. 4

Effect of different factors on concentration of products (EMF, HMF and EL) in ethanol

medium (

EMF,

HMF,

EL). Reaction conditions: (a) 20 g·L–1 corn stover,

190 ℃. (b) 20 g·L–1 corn stover, 120 min; 150 min; 150 min. (c) 190 ℃, 120 min; 180 ℃, 150 min; 190 ℃, 150 min. (d) 15 g·L–1 corn stover, 180 ℃, 150 min; 15 g·L–1 corn stover, 190 ℃, 150 min. Fig. 5

Relationship between model predicted values and experimental values.

Fig. 6

3D plots of EMF yield versus different variables.

Fig. 7

Effect of different catalysts on diethyl ether. Reaction conditions: 20 g·L–1 corn stover,

125 min, 210 ℃. Fig. 8

Reusability of catalyst. Reaction conditions: 20 g·L–1 corn stover, 125 min, 210 ℃,

0.1 % H2SO4, 1.0% USY. Fig. 9

FT-IR spectra (a) and XRD patterns (b) of catalyst. Reaction conditions: 20 g·L–1 corn

stover, 125 min, 210 ℃, 0.1 % H2SO4, 1.0% USY.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 10

GC-MS analysis of liquid phase products. Reaction conditions: 20 g·L–1 corn stover,

125 min, 210 ℃. Fig. 11

Routes for the production of EMF from corn stover with mixed acid.

Fig. 12

Reaction process of EMF production. Reaction conditions: 20 g·L–1 corn stover, 0.1 %

H2SO4, 1.0% USY. Fig. 13

Relation between predicted and experimental EMF yields.


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Fig. 1


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 2


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Fig. 3 a

21

0.1% H2SO4 + 2.0% USY

2.0% USY

0.1% H2SO4

18

Yield (%)

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20 15 10 5 0

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d

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20 15 10 5 0

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2

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Fig. 4 1200

Concentration (mg/L)

a

2.0% USY

0.1% H2SO4

0.1% H2SO4 + 2.0% USY

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d

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900

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Fig. 5


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Fig. 6


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Fig. 7 1.5

1.2

DEE (g·L-1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0.9

0.6

0.3

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Energy & Fuels

Fig. 8

25

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80

20 60 15 40 10 20

5

0

0 1

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Number of cycles


7

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Catalyst recovery rate

EMF yield

30

EMF yield (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 51

Page 39 of 51

Fig. 9

a

457

Reused USY

Transmittance (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

795

3436

455

Fresh USY

1049 789

3426 1044

O-H

4000

3500

Si-O

3000

2500

2000

1500 -1

Wavenumber (cm )


1000

500

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 10


Page 40 of 51

Page 41 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Fig. 11


Energy & Fuels

Fig. 12 30

170 ℃ 190 ℃ 210 ℃

25

20

YEMF/%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 42 of 51

15

10

5

0

0

30

60

90

120

150

t/min


180

210

Page 43 of 51

Fig. 13 R2=0.987

20

Predicted value (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

15

10 Equation Plot Weight Intercept Slope Residual Sum of Squares Pearson's r R-Square(COD) Adj. R-Square

5

0

0

5

10

15

Experimental value (%)


20

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table 1.

Page 44 of 51

Independent variable and the corresponding levels Levels

Independent variable

–1

0

1

Reaction time (min)

X1

100

150

200

Reaction temperature (℃)

X2

170

190

210

Substrate concentration (g·L–1)

X3

5

15

25

USY dosage (%)

X4

1

2

3


Page 45 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Table 2.

Experimental design and results

Test

Time(min)

Tmperature(℃)

Substrate concentration(g·L–1)

USY dosage(%)

Yield(%)

1

0

0

–1

1

4.5

2

0

0

0

0

14.8

3

1

0

0

1

12.1

4

1

0

0

–1

15.3

5

0

–1

1

0

3.2

6

0

0

1

1

12.1

7

0

1

0

–1

24.2

8

0

1

1

0

16.8

9

–1

1

0

0

17.6

10

–1

0

0

1

8.3

11

–1

0

0

–1

13.2

12

0

0

0

0

16.5

13

0

1

0

1

7.6

14

–1

0

1

0

9.5

15

1

0

–1

0

4.9

16

0

0

-1

–1

11.6

17

0

–1

0

1

10.6

18

–1

–1

0

0

3.6

19

0

0

0

0

14.8

20

1

–1

0

0

6.2

21

0

0

1

–1

9.8

22

0

0

0

0

14.8

23

0

–1

–1

0

6.5

24

1

0

1

0

12.2

25

-1

0

–1

0

6.5

26

0

–1

0

–1

2.4

27

1

1

0

0

10.1

28

0

1

–1

0

4.4

29

0

0

0

0

15.9


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table 3.

Page 46 of 51

Significance of regression coefficient for EMF yield

Source

Sum of squares

degree of freedom

Mean square

F value

P value prob>F

x1

0.37

1

0.37

0.17

0.6897

x2

193.60

1

193.60

87.53

< 0.0001

**

x3

52.92

1

52.92

23.93

0.0002

*

x4

37.81

1

37.81

17.09

0.0010

*

x1x2

25.50

1

25.50

11.53

0.0044

*

x1x3

4.62

1

4.62

2.09

0.1703

x1x4

0.72

1

0.72

0.33

0.5767

x2x3

61.62

1

61.62

27.86

0.0001

*

x2x4

153.76

1

153.76

69.52

< 0.0001

**

x3x4

22.09

1

22.09

9.99

0.0069

*

x12

39.23

1

39.23

17.74

0.0009

*

x22

68.37

1

68.37

30.91

< 0.0001

**

x32

140.05

1

140.05

63.32

< 0.0001

**

x42

5.66

1

5.66

2.56

0.1320

* is significance, ** is highly significance


Significance

Page 47 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Table 4.

ANOVA of RSM regression analysis

Source

Sum of squares

Degree of Freedom

Mean square

F value

P value prob>F

Model

742.44

14

53.03

23.98

< 0.0001

Residual

30.96

14

2.21

Lack of Fit

28.43

10

2.84

4.49

0.0804

Pure error

2.53

4

0.63

Total

773.41

28

R2

0.96


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table 5.

Page 48 of 51

Rate constants of biomass ethanolysis under different reaction conditions

T/℃

k1/min–1

k2/min–1

k1/k2

k1/k

R2

170

0.0005

0.0146

0.0342

0.0331

0.991

190

0.0024

0.0159

0.1509

0.1311

0.994

210

0.0095

0.0360

0.2639

0.2088

0.994


Page 49 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Table 6. Raw

Activation energy in different kinetic models Kinetic models

Reaction

E1

E2

material

conditions

(kJ·mol–1)

(kJ·mol–1)

HMF

80-120℃

72.0/77.2

-

(20)

Glucose

120-150℃

97.9

-

(49)

Glucose

120-160℃

97.4

-

(50)

Glucose

180-200℃

79.91

145.81

(51)

Glucose

160-200℃

122.6

70.97

(52)

Corn stover

170-210℃

131.0

39.7

This work


Ref.

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table 7.

Page 50 of 51

Comparison of different researches on EMF production from biomass

Raw material

Method

Catalyst

Conditions

Yield (mol %)

Ref.

Cellulose

Two step

CaCO3

1) 65 ℃, 3 h

40.0

(5)

(53)

2) 1h (reflux) Cellulose

One pot

[DMA]+[CH3SO3]+

120 ℃, 15 h

18.9 wt%

Sugarcane bagasse

One pot

[DMA]+[CH3SO3]+

120 ℃, 15 h

25.2 wt%

Sugarcane bagasse

One pot

Zr(O)Cl2/CrCl3

120 ℃, 15 h

21.6 wt%

(54)

Cassava

One pot

NiSO4

200 ℃, 6 h

11.4

(55)

One pot

NaHSO4

200 ℃, 6 h

4.4

One pot

H2SO4(0.1 wt%)/USY

210 ℃, 2.05 h

23.9

Corn stover


This work

Page 51 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Efficient one-pot production of biofuel 5-ethoxymethylfurfural from corn stover: Optimization and kinetics Binglin Chen a, Guizhuan Xu a*, Chun Chang b,c, Zhangbin Zheng a, Dongxiang Wang a, Shaohao Zhang a, Kai Li a, Caihong Zou a


Efficient One-Pot Production of Biofuel 5-Ethoxymethylfurfural from

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