High yield production of 5-hydroxymethylfurfural from cellulose by high concentration of sulfates in biphasic system

Article abstract of DOI:10.1039/c3gc40667a

A high 5-hydroxymethylfurfural (HMF) yield of 53 mol% was obtained by direct degradation of cellulose in a biphasic system with concentrated NaHSO₄ and ZnSO₄ as co-catalysts, with 96% of cellulose conversion in 60 min. The high concentration of catalysts in the aqueous solution and the high volume ratio of organic phase to aqueous phase were responsible for the excellent performance. The depolymerization of cellulose is the rate-determine step, and the formed glucose could be efficiently converted by concentrated catalysts in the aqueous solution, leading to low concentration of glucose in the solution and thus suppressing the side reactions such as humin and char formation.

Full text of DOI:10.1039/c3gc40667a

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In a biphase system consisted of tetrahydrofuran (THF) and aqueous solution with high volume
ratio, the cellulose particles and the aqueous solution were highly dispersed into the organic phase
under stirring. For the hydrophilcity of cellulose, its surface was covered by the aqueous solution
to form an aqueous film. The high concentration of NaHSO4 (1.5mol/L) and ZnSO4 (2.3mol/L) in
the aqueous film could efficiently catalyze the degradation of cellulose into
5-hydroxymethylfurfural (HMF), and the formed HMF could efficiently spread into the organic
phase to prevent its further decomposition. High HMF yield of 53mol% was obtained
accompanied with 96% conversion of cellulose in 60mins.

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High Yield Production of 5–Hydroxymethylfurfural from
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Cellulose by High Concentration of Sulfates in Biphasic System
Ning Shia,b, Qiying Liua, Tiejun Wanga, Longlong Maa,*, Qi Zhanga
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aKey Laboratory of Renewable Energy and Gas Hydrate, Guangzhou Institute of Energy
Conversion, Chinese Academy of Sciences, Guangzhou, 510640, P. R. China and
bUniversity of Chinese Academy of Sciences, Beijing, 100049, P. R. China
Abstract: High 5–hydroxymethylfurfural (HMF) yield of 53mol% was obtained by direct
degradation of cellulose in a biphasic system with concentrated NaHSO4 and ZnSO4 as coꢀcatalyst,
accompanied with 96% of cellulose conversion in 60min. The high concentration of catalyst in the
aqueous solution and the high volume ratio of organic phase to aqueous phase were responsible
for the excellent performance. Depolymerization of cellulose presented as the rateꢀdetermine step,
and the formed glucose could be efficiently converted by concentrated catalysts in the aqueous
solution, leading to low concentration of glucose in the solution, thus suppressed the side reactions
such as humins and char formation.
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Keywords: concentrated sulfates, cellulose, 5ꢀhydroxymethyfurfural, biphasic system,
aqueous film
Corresponding author:
Longlong Ma, Tel: +86ꢀ20ꢀ87057673, Fax: +86ꢀ20ꢀ87057673, Eꢀmail: mall@ms.giec.ac.cn.
Tiejun Wang, Tel: +86ꢀ20ꢀ87057751, Fax: +86ꢀ20ꢀ87057737, Eꢀmail: wangtj@ms.giec.ac.cn.
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1. Introduction
With the consumption of fossil fuels and the increasing concern of environmental problem,
production of liquid fuel and fine chemicals from renewable biomass has attracted widespread
attention1. 5ꢀhydroxymethylfurfural (HMF), which can be obtained from lignocellulosic biomass,
is considered to be a key platform chemical for production of a variety of downstream chemicals
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and biofuels1ꢀ2
.
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Recently, great progresses have been approached on HMF production from the cheap and
abundant glucose in ionic liquids, polar aprotic solvents and biphasic systems3.
Chromiumꢀcontained catalysts are employed in most of work for the excellent catalytic activity of
ion Crm+ on isomerization of glucose4, which is generally regarded as a main obstacle for HMF
production from glucose based substrates. Some other metal chlorides, such as ZnCl2, GeCl4,
SnCl4, AlCl3 are also reported to be efficient for isomerization of glucose5. Work of combining
Lewis and Brønsted acid for HMF production from glucose are also reported. AlCl3ꢀHCl,
ZnCl2ꢀHCl, CrCl3ꢀHCl, (SnꢀBeta)ꢀHCl were reported to be efficient on HMF production from
glucose6. High HMF yield of 81% was achieved in BMIM+Clꢀ ionic liquid with the NHC/Cr
catalyst (NHC=Nꢀheterocyclic carbene)7.
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Though high yield of HMF have been approached from glucose and fructose, directly
degradation of wildly existed cellulose into HMF is more feasible for commercial. However, the
recalcitrant of cellulose and the multiple sideꢀreactions8 occurred during the process make the
oneꢀpot synthesis of HMF from cellulose a significant challenge. Under the same condition, the
yield of HMF obtained from glucose was 61mol% but from cellulose was only 37mol%5d.
Systems employing ionic liquid solvents and polar aprotic solvents are reported to be efficient for
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this process, with chromium chloride as catalyst. Binder and his coꢀworker obtained high HMF
yield of 54mol% from cellulose in the DMAꢀLiCl solvent with CrCl3 and HCl as coꢀcatalyst9. Yu
et al. obtained high HMF yield of 62mol% in ionic liquid 1ꢀbutylꢀ3ꢀmethylimidazolium chloride
with CrCl3/LiCl as catalyst4e. Zhang et al. reported the formation of 55mol% HMF from cellulose
using two metal chloride catalysts (CuCl2 and CrCl2) in in 1ꢀethylꢀ3ꢀmethylimidazolium chloride10.
Nevertheless, the high cost of ionic liquids, the high energy consumption in HMF separating
process and the toxic chromiumꢀcontained catalysts all make the process impracticable for
industrialization. On the contrary, waterꢀcontained biphasic systems, which afford the function of
simultaneously producing HMF in aqueous phase and extracting HMF into organic phase to
prevent its further degradation, are proved to be more cost effective11. Recently, some alkylphenol
solvents, which could be obtained from the lignin, are proved to be efficient as extract solvent in
the biphasic system, making the HMF production with biphasic system feasible for
commercial6b,11. However, the HMF yield obtained from cellulose in the biphasic system kept low
compared to that obtained in the ionic liquid and polar aprotic solvents5d.
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Herein, we developed a costꢀeffective method for high yield production of HMF from
microꢀcrystal cellulose in a biphasic system consisted of tetrahydrofuran (THF) and water,
concentrated NaHSO4 and ZnSO4 were employed as coꢀcatalysts.
2. Experimental section
2.1 Chemicals
Glucose (99%), fructose (99%), cellobiose (99%), soluble starch (AR), microꢀcrystalline
cellulose (90 ꢁm) (extra pure graded), 5ꢀhydroxymethylfurfural (HMF) (98%), formic acid (98%)
and levulinic acid (99%) were purchased from Shanghai crystal pure reagent Co., LTD and used
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without further purification. NaHSO4 and ZnSO4 (analytical pure level) were purchased from
Tianjin Fu Chen chemical reagent factory. Tetrahydrofuran (THF) was purchased from Tianjin Fu
Yu fine chemical Co., LTD.
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2.2 Degradation of cellulose to HMF
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Degradation of cellulose was carried out in a 100 ml stainless steel reactor with a teflon inner.
In a typical experiment, 1.0 g cellulose, 4 ml deionized water, 40 ml THF and a certain of catalysts
were loaded into the reactor. High purity N2 was used to remove air inside the reactor and
pressurize the system to 3.0 MPa. Then the reaction system was heated to target temperature with
heating rate of 5K/min and kept at the temperature for a certain period. After reaction, solid
residues were collected by filtration with a 0.45 ꢁm membrane. The liquid products in both
aqueous solution and organic solution were analyzed by GCꢀMS and HPLC instrument. The
collected solid residues were washed with water and dried at 378K with 3 hours for TG analysis,
SEM analysis, elemental analysis and FTꢀIR analysis. For the catalyst reuse process, the aqueous
solution containing catalyst was separated for recycle.
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2.3 Analysis of liquid products
The qualitative analysis of HMF, furfural and levulinic acid were determined by a GCꢀMS
instrument (HP5890; MSD, HP5972A) equipped a DBꢀ5MS capillary column (30 m×0.25
mm×0.25 ꢁm). The oven temperature was retained at 40 °C for 4 min, then ramped to 250 °C at
10 °C/min, and held at this final temperature for 3 min.
The concentration of cellobiose, Dꢀglucose, Dꢀfructose, HMF, furfural and levulinic acid in
the solution were quantified using HPLC equipped with a Hewlett Packard 1050 pump and a
Biorad Aminex HPXꢀ87H organic acid column. A Waters 410 refractive index detector (operated
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at 45 °C) was equipped for detecting of cellobiose, Dꢀglucose, Dꢀfructose and levulinic acid while
a UV detector (with the wavelength of 284 nm) was equipped for detecting of HMF and furfural.
The mobile phase was an aqueous solution of sulfuric acid (5 mM) at the flow rate of 0.55
mL/min and the column was kept at 50 °C. Quantification of products was determined by external
standard method based on the average peak area of each product under three parallel HPLC
measurements of each experiment. All liquid samples obtained after each experiments were
diluted 50 times by pure water before analysis.
The mole yield of the product i was calculated by the following formula, assuming the
molecular weight of the constructed Dꢀglucose unit of cellulose being 162:
ꢃ
ꢀ
ꢁ
ꢀ
ꢁ
ꢀ
ꢁ
ꢀ
ꢁꢒ
ꢄꢅꢆꢇꢈꢆ. ꢅꢉꢊ ꢋ ꢌꢅꢍ ꢅꢉꢊ ꢎ ꢄꢅꢆꢇꢈꢆ. ꢏꢐꢑ ꢋ ꢌꢅꢍ ꢏꢐꢑ /ꢓꢔ
ꢀ
ꢁ
Y mol% ꢂ
ꢕꢉꢏꢖꢗ ꢅꢘ ꢇꢈꢍꢍꢑꢍꢅꢗꢈ ꢍꢅꢏꢙꢈꢙ/162
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ꢓꢔ is the molar mass of each material, its value is 126, 96, 116 for HMF, furfural and
levulinic acid, respectively.
2.4 Characterization of the solid residue
The cellulose conversion was measured by weighting the solid residue and
thermogravimetric (TG) analysis of the solid residue. Thermogravimetric (TG) analysis were
implemented on a NETZSCHꢀSTA 409PC DSCꢀSP thermal analyzer with 5ꢀ10mg of sample by
increasing the temperature from 40 °C to 500 °C at 10 °C/min under an air flow rate of 30
mL/min.
The morphology of cellulose and solid residues (SEM image) were observed using a
scanning electron microscope (HITACHI Sꢀ4800).
Elemental analysis of the solid residue was performed on a Vario EL Z CHN elemental
analyzer under 0.12MPa He and 0.2MPa of O2 at 1145 °C, with a TCD detector.
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The Brunauer–Emmet–Teller (BET) surface area (SBET) of the cellulose was analyzed by
the adsorption and desorption isotherms of nitrogen at ꢀ196oC using a ASIQMO002ꢀ2 analyzer
(Quantachrome, US). The samples were degassed under vacuum at 80oC for 16 h prior to
measurement.
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The structures of the solids were analyzed by FTꢀIR with an IR Prestigeꢀ21 spectrometer
(Shimadzu) with scanning from the wavenumbers of 4000 to 400 cmꢀ1 at 2 cmꢀ1 resolution.
Samples for FTꢀIR analysis were prepared by mixing the sample powders with KBr and
compacting into thin slice.
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3. Results and discussion
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Here we employed high volume ratio of THF solvent to water as 10:1. Because water is
mutually soluble with THF, no aqueous phase was formed with none salt addition. With the
addition of salts, the aqueous solutions were formed with volume of 0.2ꢀ1.5ml, which were much
lower than the volume of water added (Table 1). The strong acidic NaHSO4 was very efficient on
the degradation of cellulose in this system. Little HMF was formed accompanied with great deal
of unreacted cellulose without of NaHSO4 (Table 1, Entry 1ꢀ2), but high HMF yield of 36.7mol%
was obtained by increasing the usage of NaHSO4 to 1.8mmol (Table 1, Entry 4). However,
excessive of H+ significantly decreased HMF yields accompanied with the formation of levulinic
acid (LA), which is a degradation product of HMF (Table 1, Entry 5). The excellent performance
with single NaHSO4 indicated that the H+ offered by NaHSO4 was active for all reactions involved
(hydrolysis of cellulose, isomerization of glucose and dehydration of fructose). Zn2+ is reported to
be efficient for isomerization of glucose to fructose via 1,2ꢀhydride shift12, so here we investigated
the impact of ZnSO4 on HMF production in this reaction system. Addition of ZnSO4 greatly
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increase the HMF yield (Table 1, Entry 6ꢀ12), and the highest yield of 53.2mol% was obtained
with 1.8mmol NaHSO4 and 2.8mmol ZnSO4 as coꢀcatalysts (Table 1, Entry 8). We also noticed
that the volumes of aqueous solutions increased with the addition of ZnSO4, so we propose that
ZnSO4 could also have the function of adjusting the acidity of aqueous solution and increasing its
volume. The HMF yield obtained here was comparable with that of 62mol% obtained in the ionic
liquid with CrCl3 as catalyst4e, and much higher than the 37mol% obtained from biphasic system
with AlCl3 as catalyst5d. Experiment for catalysts recycle was conducted by separating the aqueous
phase, but the HMF yield decreased to 41.3mol%, which could be attributed to the fact that a
certain of catalysts were dissolved in the organic solvent (Table 1, Entry 13).
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Some byproducts were also detected. Furfural (FF) was formed in all the reaction with the
yield of below 5mol%, and the furfural formation mechanism was discussed elsewhere13
(Scheme1). Addition of the transparent organic filtrate into pure water formed a turbid liquid,
indicating that THFꢀsoluble but waterꢀinsoluble polymer existed in the organic solvent.
Comparing the FTꢀIR spectrum of this polymer with that of humins reported by other literature14,
we concluded that the THFꢀsoluble polymer was humins (Figure 1). SEM image showed that this
THFꢀsoluble humins was spherical with the size of 1~3um (Figure 2e). Several work also reported
that humins could be dissolve in some organic solvents14b, 15
.
Brownish black solid residues were detected in all reactions. Effect of reaction time on the
yield of HMF, glucose and solid residue was conducted (Figure 3). The slight decreasing of HMF
yield after 60min indicated that HMF was relatively stable in this system. Only ignorable amounts
of glucose were formed during the process, suggesting that this reaction system was very efficient
for glucose conversion. Lowest residue weight of 8.0wt.% was obtained at 50min, indicating that
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more that 92% of cellulose was converted. The weight of solid residue began to increase after
50min, suggesting the formation of solid humins8d,14b,16. Because humins was formed in the
residue, it’s not precise to determine the conversion of cellulose by simply weighing the collected
solid residue. TG of the solid residues showed two weight losses (Figure 4), the former weight
loss was assigned to the cellulose decomposition, while the latter weight loss was due to
decomposition of humins. Coupling of the TG behaviors and the weight of residues, we concluded
that about 96% of cellulose was converted in 60min. The SEM images showed that the cellulose
was compact while the residue was loose and porous (Figure 2). The elemental analysis showed
that the solid residues contained about 62 wt.% carbon and 30 wt.% oxygen, which was similar
with humins14 (Table 2).
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The water amounts could greatly influence the HMF yield (Table 3). Because the salts are
insoluble in the THF solvent, the salts presented as solid in THF solvent with no water was added.
Insoluble salts were detected with less than 4ml of water addition, indicating that the aqueous
solutions were saturated with these catalysts. Relatively low HMF yield of 37.7mol% was
obtained with 1ml of water addition (Table 3, Entry 14), but the HMF yield increased with
increasing of water addition. Highest yield of HMF was obtained with 4ml of water addition. With
8ml of water addition, only 1.7ml of the aqueous phase was formed accompanied with completely
dissolving of all salts, while the HMF yield decreased to 41.8mol% (Table 3, Entry 17). However,
further increasing the water addition to 16ml, the volume of aqueous solution even decreased to
1.4ml, and HMF yield greatly decreased to 8.2mol% accompanied with more than 80wt.% of
unreacted cellulose (Table 3, Entry 18). The remarkable decreasing of HMF yield with 16ml of
water addition was due to that the solubility of catalyst in the waterꢀTHF mixture increased with
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16ml of water addition, leading to the sharp decreasing of catalyst concentration and poor
performance on cellulose degradation. Here, the salts had functions of catalyzing the degradation
of cellulose and decreasing the miscibility of water with THF.
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As mentioned above, under the conditions of 1ꢀ4ml of water addition, the aqueous solutions
were saturated with catalysts. High concentration of the catalysts in aqueous solution was
responsible for the excellent performance of this reaction system. Adding 4ml of water into the
mixture of 1.8mmol NaHSO4, 2.8mmol ZnSO4 and 40ml THF formed only 1.2ml of aqueous
phase and 43.2ml of organic phase, so the concentration of NaHSO4 and ZnSO4 in the aqueous
phase was 1.5mol/L of and 2.3mol/L, respectively. The high concentration of catalyst was efficient
for hydrolysis of cellulose and decomposition of glucose. Especially, Deng et al. reported that the
concentrated Zn2+ in the aqueous solution could incompletely coordinate with the hydroxyl group
of saccharides to catalyze the converting of saccharides17. Directly degradation of cellulose to
HMF involves the steps of hydrolysis of cellulose to glucose and decomposition of glucose to
HMF. As the active energy of hydrolysis of cellulose (about 180kJ/mol) is much higher than that
of glucose decomposition HMF (about 135kJ/mol)8c,18, hydrolysis of cellulose presents as the
rateꢀdetermining step. In this reaction, when cellulose was hydrolyzed, the formed glucose was
quickly consumed by the abundant H+ and the Zn2+ in the aqueous solution to form HMF, which
reduced the glucose concentration in aqueous solution (Figure 3), thus significantly suppressed the
side reactions of glucose such as condensation with HMF into humins8d,14b , carbonization into
char or reverse into oligosaccharides8c.
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High volume ratio of organic phase to the aqueous phase was another key factor for the
excellent performance of this reaction system. As the volume of organic phase was more than 25
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times of that of aqueous phase, both the catalystꢀcontained aqueous solution and the cellulose
particles were highly dispersed in the organic phase under stirring. Because the surface of
cellulose is abundant of hydroxyl groups, and the polarity of aqueous solvent (10.2) is much
stronger than that of THF solvent (4.2), so the surface of cellulose is likely to be covered by
aqueous solution instead of THF. Assuming that the surface of cellulose is totally covered by the
aqueous solution, we could calculate that the thickness of aqueous film is 1.7um because the
volume of aqueous phase is 1.2ml and the surface of cellulose is 0.7m2/g (determined by the BET
analysis of cellulose). This thin aqueous film containing high concentration of catalysts could
efficiently catalyze the depolymerization of cellulose and dehydration of saccharides, and the
formed HMF molecule could easily spread into the organic phase to prevent it from further
degradation (Figure 5). Here, the organic phase acts not only as HMF protector but also as the
dispersing agent to disperse the cellulose particles and catalystꢀcontained aqueous solution, while
water acts both as the reactant to hydrolyze the cellulose and as the solvent to dissolve the
catalysts. A similar reaction system was reported by Zhao and his coꢀworker, in which the
surfactant in the micellar catalyst Cr[(DS)H2PW12O40]3 could overcome the diffusion problem in
this solidꢀsolid reaction for hydrolysis of cellulose, and the HMF formed on the surface of catalyst
could efficiently spread into the major aqueous solution to avoid its further degradation19. The
system in this work was similar with their system at the following two points: first, the catalyst
could easily contact with the surface of cellulose and efficiently catalyze the depolymerization of
cellulose; second, the formed HMF could easily spread into the major solvent to improve its
stability.
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The performances of the system at temperature from 413K to 453K were studied (Figure 6).
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The low temperature of 413K leaded to low HMF yield of 35.8mol% accompanied with 41.6% of
unreacted cellulose while the high temperature of 453K leaded to the increasing yield of levulinic
acid, which decreased the yield of HMF.
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The reaction system showed excellent performance on synthesis of HMF from cellulose, but
showed relatively poor performance with the soluble sugars (glucose, cellobiose and starch) as the
feedstock. After 45min, the conversion of all these reactants had reached 100%, but less than
40mol% of HMF were obtained accompanied with about 20ꢀ40wt.% of black residue formation
(Table 4, Entry 19ꢀ22). SEM image of the black residue showed that the residue was irregular
particle with size of larger than 10um, which was very different from the stripꢀshaped unreacted
cellulose and the spherical THFꢀsoluble humins (Figure 2). The FTꢀIR spectrums of the black
residue and THFꢀsoluble humins were similar, the absorption peaks at 1604, 1510 and 1395 cmꢀ1
indicated that furan ring existed in both solids14a (Figure 1). However, an obvious difference was
observed. Contrary to humins, the relative intensity of the peak at 1706 cmꢀ1 was stronger than that
at 1672cmꢀ1, indicating fewer C=O bonds were conjugated with the C=C bonds in this black char20.
Compared with literature20, we concluded that this black residue was char instead of humins14.
Generally, char is formed under some extreme conditions, such as high temperature21, high acidic
environment or high concentration of soluble saccharides20,22. Here, the formation of char is
ascribed to the high acidity of aqueous solution and high concentration of soluble saccharides.
Because these substrates (glucose, cellobiose and starch) are hardly dissolve in THF, when 1g
glucose was added into the reaction solution (4ml H2O,1.8mmol NaHSO4, 2.8mmol ZnSO4, 40ml
THF), its concentration in the aqueous solution was as high as 40wt.%. Insoluble saccharides were
detected with 1g cellobiose or starch addition, indicating that the aqueous solutions were saturated
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with them. The high acidity of aqueous solution and the concentrated saccharides could obviously
lead to char formation. Because high concentration of glucose could be favor for the reverse
reaction to form oligosaccharides8c, we proposed that the char was formed by directly dehydration
of oligosaccharides. Relatively higher HMF yields and lower char yields were obtained with lower
glucose dosage, and the HMF yield of 45.2mol% was approached with 0.2g of glucose dosage
(Table 4, Entry 23ꢀ24). This is accord with the former report that ignorable char was detected with
low glucose concentration, but plenty of char was formed with high concentration of glucose22.
High HMF concentration in the solution is desired for its practical applications.23 Herein, we
explored improving HMF concentration by improving the reactant dosage. High HMF yield of
42.5mol% was obtained with 5g of cellulose, indicating that the reaction system was also efficient
with high ratio of cellulose to aqueous solution (Table 5, Entry 25). With the increasing of the
cellulose dosage, the yield of HMF decreased gradually while the weight of solid residue
increased, this is due to that high concentration of HMF is favor for the HMF concentration
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reaction (Table 5). High HMF concentration of 5.9 wt.% was obtained with 15 g cellulose
loading, but the HMF yield decreased to 22.6mol% under this condition (Table 5, Entry 30).
Obtaining high concentration of HMF with high selectivity is the following challenge for
commercial production of HMF.
4 Conclusions
In summary, a biphasic system consisted of THF and concentrated NaHSO4ꢀZnSO4 aqueous
solution was developed for efficiently degradation of cellulose into HMF. High HMF yield of 53%
was obtained accompanied with 96% conversion of cellulose in 60min. High concentration of
catalyst in the aqueous phase and high volume ratio of organic phase to aqueous phase were the
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main factors for the excellent performance. High HMF concentration of 5.9 wt.% in the organic
phase was approached by increasing the cellulose loading. In this system, THF was employed as
the major solvent, which does have some disadvantages, such as the high cost and the
environmental effect. However, we should also notice that the low boiling point of THF could
make the distillation process much less energy consumption. If an abundant, green and
lowꢀboiling point solvent could be developed to replace THF, this system could step much closer
to industrialization.
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Acknowledgements
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The authors gratefully acknowledge the financial support from the National Basic Research
Program of China (2012CB215304), the Natural Science Foundation of China (51161140331) and
the International Coꢀoperation Project of Ministry of Science and Technology of China
(2012DFA61080).
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Green Chemistry
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Page 17 of 21
Green Chemistry
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Table 1 Performance of combined metal sulfates in direct degradation of cellulose to HMF a
Catalyst (mmol)
Product yield (mol%)
Volume of aqueous
solvent (ml)
Entry
NaHSO4
ZnSO4
ꢀ
HMF
<0.5
0.7
FF
<0.5
<0.5
<0.5
1.7
LA
1
2
ꢀ
0
<0.5
<0.5
<0.5
<0.5
10.4
<0.5
<0.5
<0.5
<0.5
0.7
ꢀ
2.8
ꢀ
1.0
0.2
0.3
0.4
0.5
0.8
1.2
1.4
1.5
1.5
1.5
1.2
3
0.9
1.8
2.7
1.8
1.8
1.8
1.8
1.8
2.3
2.7
1.8
29.8
36.7
28.4
45.7
48.7
53.2
48.1
47.8
47.4
45.9
41.3
4
ꢀ
5
ꢀ
1.3
6
0.5
1.0
2.8
3.5
4.2
2.8
2.8
2.8
2.1
7
2.7
8
1.7
9
1.3
10
11
12
13 b
1.5
2.1
6.8
2.0
12.9
<0.5
1.6
2
3
4
5
6
7
a Reaction condition: 1g cellulose; THF 40 ml and H2O 4ml; reaction temperature 433 K; reaction
time 60 min.
b The aqueous phase containing catalyst was separated from Entry 8 with 2.8ml of extra water
addition.
HMF, 5ꢀhydromethylfurfural; FF, furfural; LA, levulinic acid.
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Green Chemistry
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Table 2 Elemental analysis of cellulose and solid residues with different reaction time
Elements percentage (wt.%)
Materials
C
H
O
Cellulose
Residue 60
Residue 120
44.1
61.6
63.6
5.9
6.7
6.5
50.0
31.8
29.9
2
3
4
5
Residue 60 and Residue 120 represented the solid residues collected after 60 min and 120 min of
reaction time, respectively. Reaction condition: 1 g cellulose; 40 ml THF and 4 ml H2O; 1.8mmol
NaHSO4 and 2.8mmol ZnSO4; reaction temperature 433 K.
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Page 19 of 21
Green Chemistry
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Table 3 Impact of water addition on the HMF yield from cellulose a
Volume of solvent (ml)b
Water
Catalyst
HMF
Residue
(wt%)
Entry
Aqueous
solvent
0.2
Organic
solvent
40.8
addition
solution
Yield (wt%)
14
15
16
17
18
1
2
P.D. c
P.D.
37.7
47.6
53.2
41.8
8.2
10.3
9.7
0.5
41.4
4
P.D.
1.2
43.2
8.1
8
C.D. d
C.D.
1.7
46.3
17.2
85.6
16
1.4
55.1
a
2
3
4
5
6
7
8
9
Reaction condition: 1g cellulose; 40 ml THF; 1.8mmol NaHSO4 and 2.8mmol ZnSO4;
temperature, 433 K; reaction time, 60 min.
b The volume of each solvents were measured at 298K;
c P.D. stands for partially dissolved;
d C.D. stands for completely dissolved;
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Green Chemistry
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Table 4 Comparison of direct degradation of glucose, starch and cellobiose to HMF a
Product yield (mol%)
Black Char
(wt.%)
Substrate Time Conversion
Entry Substrate
usage (g) (min)
(%)
HMF
FF
LA
19
20
21
22
23
24
Glucose
Glucose
Starch
1.0
5.0
1.0
1.0
0.5
0.2
30
30
45
45
30
30
98.4
95.5
100
100
99.1
100
35.7
24.1
16.9
17.6
40.9
45.2
0.5 <0.5
0.6 <0.5
0.7 <0.5
1.5 <0.5
0.6 <0.5
<0.5 <0.5
21.7
36.3
24.1
23.8
14.3
10.9
Cellobiose
Glucose
Glucose
2
3
a Reaction condition: 4ml H2O; 40ml THF; 1.8 mmol NaHSO4 and 2.8 mmol ZnSO4; reaction
temperature 433 K,.
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Page 21 of 21
Green Chemistry
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2
Table 5 Effect of cellulose dosage on HMF yield and concentration in direct degradation of
cellulose a
Product yield(mol%)
HMF
concentration
(wt%)
Cellulose
Ratio
Reaction
Residue
Entry
dosage(g) (g/ml) b
time(min)
(wt%)
HMF FF
LA
25
26
27
28
29
30
5
4.2
8.3
60
60
60
60
60
90
42.5
35.0
33.5
31.8
24.9
22.6
1.2
2.1
2.6
1.9
2.2
2.7
<0.5
1.4
1.9
3.3
4.8
5.7
3.3
5.0
5.2
5.4
5.5
5.9
12.2
17.1
19.4
21.2
25.4
30.7
10
11
12
13
15
9.2
10.0
10.8
12.5
3
4
5
a Reaction condition: 4ml H2O; 40ml THF; 1.8mmol NaHSO4 and 2.8mmol ZnSO4; reaction
temperature, 433K.
b Ratio of cellulose to aqueous solution.
6
7
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