Conversion of Fructose into Methyl Levulinate
1347
reported the catalytic transformation of fructose, glucose,
and sucrose to ethyl levulinate with different SO3H-ILS. It
was found that ionic liquids based on the [NTf2]– anion
gave a higher yield of ethyl levulinate (77 %). The disac-
charide sucrose was found to form 36 % of ethyl levulinate
along with 33 % of another product, ethyl-D-glucopyran-
oside (EDGP). Glucose was converted into EDGP (63 %)
with a lower yield of ethyl levulinate. Saravanamurugan
and Riisager [19] also investigated various catalysts i.e.
sulfuric acid functionalized SBA-15, sulfated zirconia,
beta, Y, ZSM-5 and mordenite for the dehydration of
sugars to ethyl levulinate in ethanol. They found that the
SO3H-SBA-15 catalyst showed a high catalytic activity for
the selective conversion of fructose to ethyl levulinate
(57 %) and glucose to EDGP (80 %) at 140 °C. Peng et al.
isomerization, dehydration, cracking, alkylation, esterifi-
cation, acylation, etc. [30, 31]. In the present work, we
found that the iron salt of phosphotungstate could effec-
tively catalyze the conversion of fructose into methyl
levulinate. This catalyst could be used repeatedly at least
five times without obvious loss of activity.
2 Experimental
2.1 Materials
Fructose (C98 %), glucose (C98.0 %), sucrose (C98.0 %),
phosphotungstic acid hydrate (C98.5 %), methanol
(C99.5 %) n-butanol (99.0 %) and FeCl3ꢀ6H2O (C99.0 %)
were purchased from Sinopharm Chemical Reagent Co.
Ltd. (Shanghai, China). N2 ([99.99 %) was supplied by the
Xi’an MESSER Gas Company.
[20] investigated a series of solid acid catalysts including
2-
SO42-/ZrO2, SO42-/TiO2, SO42-/ZrO2–TiO2 and SO4
/
ZrO2–Al2O3 for the conversion of glucose in ethanol; they
found that with SO42-/ZrO2 as the catalyst an optimized
ethyl levulinate yield of 30 % was obtained at 200 °C for
3 h. Tominaga et al. [21] presented an efficient catalyst
system for the synthesis of methyl levulinate from cellulose
and glucose by combining two different kinds of acids, a
Lewis acid and a Brønsted acid, where the highest yield of
methyl levulinate reached 75 %. Although the yield of
methyl levulinate is high, the catalytic system of mixed
acids is difficult to separate and recycle.
2.2 Catalysts Preparation and Characterization
Phosphotungstic acid hydrate (H3PW12O40ꢀxH2O) was
dried in an oven at 110 °C for 6 h, and the resultant sample
was denoted HPW. The detailed synthesis procedure of the
other catalysts is as follows: 4 mmol H3PW12O40ꢀxH2O
was dissolved in 10 ml distilled water and then 4 mmol
FeCl3ꢀ6H2O was added into the above solution under vig-
orous stirring at 30 °C for 3 h. Finally, the solution was
cast onto a glass substrate and then transferred into an oven
for evaporation of water at 110 °C for 6 h. The resultant
sample was denoted Fe-HPW-1. A similar procedure was
used for preparing other catalysts with different iron con-
tents. The resultant samples were denoted Fe-HPW-2 and
Fe-HPW-3, respectively.
There have been several reports about the production of
levulinate esters in near-critical alcohols from carbohy-
drates biomass feedstocks, such as cellulose, sucrose, glu-
cose, fructose, etc. [22–24]. Rataboul and Essayem [22]
studied that the conversion of microcrystalline cellulose
using CsxH3-xPW12O40 or sulfated zirconia solid acid cat-
alysts in supercritical MeOH and MeOH-H2O (90/10)
mixtures at 300 °C, 10 MPa, and 1 min. Up to 20 % yield
of methyl levulinate was obtained. Wu et al. [23] investi-
gated the alcoholysis of cellulose in near-critical methanol
using H2SO4 as catalyst. A high yield of up to 55 % methyl
levulinate was achieved at 190 °C for 5 h.
Obviously, the yields of levulinate esters are still
unsatisfied. Moreover, the consumption of alcohols e.g.
methanol, ethanol during reactions was not mentioned in
most studies. Whereas, excessive consumption of alcohols
to diether is one of the substantial obstacles for the
development of the process to synthesize levulinate esters
[25, 26]. Therefore, seeking an efficient and environmental
benign catalyst with high yields of levulinate esters and
low consumption of alcohols is essential for economical
conversion of those biomass feedstocks.
Powder X-ray diffraction (XRD) patterns of the cata-
lysts were recorded with a BRUKER D8 Advance X-ray
diffractometer with a Cu Ka radiation source operated at
40 kV and 40 mA. Data was collected from 5 to 80° with a
step of 0.02° at a scanning speed of 10 °/min. Infrared
spectra were recorded on a Bruker EQUINX55 FTIR
spectrometer using KBr disc technique. The concentration
of the sample in KBr was 1.0 wt%, and 0.2 g of KBr was
used in the preparation of the reference and sample disks.
The relative contents of Fe, P and W in the catalysts were
determined by a Shimadzu XRF-1800 X-ray fluorescence
spectrometer.
2.3 Reaction Test and Product Analysis
Phosphotungstic acid salts as water tolerant acid cata-
lysts with both Brønsted and Lewis acidities have attracted
much attention [27–29]. They can be recycled and sepa-
rated easily and have been broadly applied to catalyze
The experiments were performed in a 35 ml stainless steel
autoclave equipped with a mechanical stirrer. In a typical
experimental, 0.75 g fructose, 24 g methanol, and 0.48 g
catalyst were loaded into the reactor. The autoclave was
123
Liu, Yan
