Direct Conversion of Cellulose into Ethyl Lactate in Supercritical Ethanol-Water Solutions

Article abstract of DOI:10.1002/cssc.201500855

Biomass-derived ethyl lactate is a green solvent with a growing market as the replacement for petroleum-derived toxic organic solvents. Here we report, for the first time, the production of ethyl lactate directly from cellulose with the mesoporous Zr-SBA-15 silicate catalyst in a supercritical mixture of ethanol and water. The relatively strong Lewis and weak Br?nsted acid sites on the catalyst, as well as the surface hydrophobicity, were beneficial to the reaction and led to synergy during consecutive reactions, such as depolymerization, retro-aldol condensation, and esterification. Under the optimum reaction conditions, μ33 % yield of ethyl lactate was produced from cellulose with the Zr-SBA-15 catalyst at 260 C in supercritical 95:5 (w/w) ethanol/water.

Full text of DOI:10.1002/cssc.201500855

DOI: 10.1002/cssc.201500855
Communications
Direct Conversion of Cellulose into Ethyl Lactate in
Supercritical Ethanol–Water Solutions
Lisha Yang,[a] Xiaokun Yang,[a] Elli Tian,[b] and Hongfei Lin*[a]
Biomass-derived ethyl lactate is a green solvent with a growing
market as the replacement for petroleum-derived toxic organic
solvents. Here we report, for the first time, the production of
ethyl lactate directly from cellulose with the mesoporous Zr-
SBA-15 silicate catalyst in a supercritical mixture of ethanol and
water. The relatively strong Lewis and weak Brønsted acid sites
on the catalyst, as well as the surface hydrophobicity, were
beneficial to the reaction and led to synergy during consecu-
tive reactions, such as depolymerization, retro-aldol condensa-
tion, and esterification. Under the optimum reaction condi-
tions, ~33% yield of ethyl lactate was produced from cellulose
with the Zr-SBA-15 catalyst at 2608C in supercritical 95:5 (w/w)
ethanol/water.
C6 sugars. Holm and coworkers found that Sn zeolites with
strong Lewis acidity, such as Sn-beta, showed good per-
formance, producing methyl lactate (ML) by reacting mono-
and disaccharides in methanol at 1608C for >16 h.[7] Other Sn-
based catalysts, including SnIV-grafted carbon–silica composite
Sn-MWW zeolite and Sn-MCM-41 were also demonstrated to
be effective for the catalytic conversion of simple sugars to
ML.[8] However, the disadvantages of the tin-zeolite materials
were their poor stability at elevated temperatures and the
narrow channels preventing large biomass molecules from ac-
cessing the active sites.[7a,9]
In contrast, direct use of cellulose to produce LA at high
yields was only seen with homogenous catalysts.[10] Wang et al.
reported 89.6% yield of LA by hydrothermally converting cellu-
lose using the water soluble Er(OTf)3 catalyst.[10a] Ion-exchanged
erbium montmorillonite K10 yielded 67.6% of LA, but it was
believed that the leached Er ions catalyzed the cellulose con-
version reactions.[10b] Wang and coworkers reported a yield of
LA from microcrystalline cellulose reaching >60% at 1908C in
the presence of PbII ions in water.[10c] However, homogenously
catalytic processes face similar separation challenges to the fer-
mentative process. It is worth noting that few reports are avail-
able on the production of LA and its derivatives directly from
cellulose with heterogeneous catalysts. Chambon et al. hy-
pothesized that solid catalysts only acted on the pre-hydro-
lyzed cellulose fragments (soluble oligomers).[11] In their study,
the low LA yields of 13.5% and 9.3% were obtained from cel-
lulose using the tungstated zirconia (ZrW) and tungstated alu-
mina (AlW) catalysts, respectively.
The selective conversion of cellulose, the most abundant and
non-edible biomass, as the renewable carbon resource for the
production of value-added chemicals is of vital importance for
sustainable economy.[1] Among bio-based chemicals, lactates
attract much attention as commodity chemicals.[2] Ethyl lactate
(EL) is derived from lactic acid (LA) and ethanol, which are
both renewable chemical materials currently made from the
fermentation of sugars. As a commercialized green solvent, EL
works in numerous chemical applications especially as a photo-
resist carrier solvent, edge-bead remover, and clean-up solvent
for semiconductor manufacture.[3] Moreover, LA is a platform
molecule leading to multiple chemicals and biodegradable
polymers, and can be produced from EL through a simple hy-
drolysis step.[4]
Fermentation processes suffer from large amounts of waste
products, costly separation, and the inability to utilize cellulose
without expensive pretreatments. Instead, chemo-catalytic pro-
cesses can utilize a variety of cellulosic biomass that are not
competing with food.[5] The conversion of various polyols and
simple sugars (e.g., glycerol, xylose and glucose) to LA and its
ester derivatives with heterogonous catalysts was extensively
studied.[6] It is widely accepted that Lewis acid-catalyzed retro-
aldol condensation is a key step to synthesize LA from C5 and
In our previous work, we demonstrated that ZrO2 was an ef-
fective, stable catalyst for the synthesis of LA from hemicellu-
lose in hydrothermal media.[12] But the LA yields were relatively
low (carbon yields up to 25% and 18% from xylose and xylan,
respectively) as ZrO2 has mixed acid/base and redox properties
that limit the selectivity to LA. Alternatively, incorporating Zr
into charge-neutral silica framework, in which Zr is less coordi-
nated, can significantly enhance Lewis acidity.[13] SBA-15 is
a mesoporous silica material with exclusive properties,[14] such
as thick wall, high surface area, and large pore size (5–30 nm)
which allows large biomass molecules to diffuse in and out. It
is anticipated that Zr containing SBA-15 has stronger Lewis
acidity than ZrO2. However, one of the grand challenges of
solid Lewis acids is their instability in the presence of water.
Contrarily, in alcohol solvents, Lewis acidity of solid catalysts
was retained.[15] Herein, we report our findings on the direct
conversion of cellulose to EL using mesoporous Zr-SBA-15 cat-
alysts in supercritical ethanol–water mixtures.
[a] Dr. L. Yang, X. Yang, Dr. Prof. H. Lin
Department of Chemical and Material Engineering
University of Nevada, Reno
1664 N. Virginia St. M/S388, Reno, NV 89557 (USA)
Fax: (+1)7753275059
E-mail: HongfeiL@unr.edu
[b] E. Tian
Department of Biomedical Engineering
Johns Hopkins University
Baltimore, MD 21205 (USA)
Figure S1 in the Supporting Information illustrates the
curves of ammonia temperature programmed desorption
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.201500855.
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(NH3-TPD) of the Zr-SBA-15 samples with the calculated total
acidity listed in Table S1. The pure SBA-15 silica did not show
nor the pure SBA-15 silica resulted in the high yields of EL
(8.2% and 5.1%, respectively), while the EL yield increased to
~30% over Zr-SBA-15 after reacting with cellulose at 2608C for
6 h in the ethanol–water mixture (95% ethanol and 5% water).
Without adding a catalyst, an EL yield of ~2.1% was obtained.
Note that without catalyst or with the pure SBA-15, noticeable
amounts of HMF and furfural were obtained. The much higher
yields of C4 compounds, including ethyl 2-hydroxybutanoate
(EHB), were obtained over Zr-SBA-15 than over either ZrO2 or
SBA-15. These results suggest that the strong Lewis acidity of
Zr-SBA-15 is crucial for the conversion of cellulose to EL.
any appreciable NH3 adsorption (only 0.02 mmolNH gÀ1) and
3
the ZrO2 sample exhibited less NH3 adsorption of
0.30 mmolNH gÀ1, compared with the Zr-SBA-15 sample pre-
3
senting a 0.72 mmolNH gÀ1 adsorption. Furthermore, the FTIR
3
spectra of pyridine adsorbed on the Zr-SBA-15 distinguished
the Lewis and Brønsted acidic sites, as shown in Figure 1. The
In our one-pot catalytic process, several factors enable the
selective conversion of cellulose to EL. Firstly, water in the su-
percritical ethanol–water mixture (Table 1, entries 1–6) weakens
the intramolecular hydrogen bonds responsible for the robust-
ness of cellulose, and thus decreases the crystallinity of cellu-
lose until dissolution, overcoming the major barrier of cellulose
conversion (i.e., the recalcitrance of cellulose to depolymeriza-
tion).[5a] Secondly, Zr4+ metal centers with empty d orbitals in
the silica framework serve as mildly water-tolerant Lewis acid
sites and the limited hydrophobic property of silica may stabi-
lize the Zr4+ Lewis acidic sites inside the pores of the SBA-15
silica in the presence of 5 wt% water. In contrast, the loss of
Lewis acidity of the Zr-SBA-15 catalyst was observed in the
pure subcritical water: only a trace amount of LA (1.4%) was
produced, whereas HMF (14.6%) and levulinic acid (20.9%)
were the main products (Table 1 entry 7). The transformation
of cellulose to EL was thus completed in the supercritical etha-
nol–water mixture at moderate temperatures and pressures,
which are sufficient for the depolymerization of cellulose but
more compatible for stabilizing the solid Lewis acid sites of the
Zr-SBA-15 catalyst. It is noted that the cellulose loading affect-
ed the yield of EL to a lesser extent. When the cellulose load-
ing was increased from 1 to 10 wt% and the mass ratio of cel-
lulose to catalyst remained constant, the EL yield decreased
from ~30% to ~25%. Under the same conditions, the yield of
solid residue (S.R.) increased from ~8.6% to ~34%. The S.R. in-
cluded unreacted cellulose, and thus longer reaction times
would be needed at higher loadings of cellulose.
Figure 1. FTIR spectra of adsorbed pyridine on Zr-SBA-15. LA: Lewis acid;
BA: Brønsted acid.
prominent adsorption bands at 1446 and 1594 cmÀ1 were as-
signed to the Lewis acid (L) sites, whereas the weak adsorption
band at 1490 cmÀ1 was attributed to a combination of Brønst-
ed and Lewis acid (B+L) sites. A very weak band at 1548 cmÀ1
was observed, which typically corresponds to the Brønsted
acid sites. These results indicated that the Zr-SBA-15 sample
contained predominantly Lewis acid sites. In addition, the mes-
oporous structure of the Zr-SBA-15 silicate was displayed by
the powder XRD and the small-angle X-ray scattering (SAXS,
Figure S2). The TEM images showed that the pore size of the
Zr-SBA-15 was approximately 9 nm (Figure S3).
Table 1 compares the yields of the main products by react-
ing microcrystalline cellulose with different catalysts, solvents,
and feed loadings. The catalytic effect of the Zr-SBA-15 signifi-
cantly increased the yield of EL. Neither the commercial ZrO2
To further understand the role of water in ethanol, anhy-
drous ethanol and ethanol–water mixtures at different water/
ethanol ratios were used under super- and sub- critical condi-
tions. The critical conditions of ethanol–water solutions, adapt-
ed from the literature,[16] are shown in Table S2. We found that
the water content in the ethanol–water solutions has a pro-
found effect on the yield of EL. Water molecules are consumed
in the hydrolytic depolymerization of cellulose.[17] Brønsted
acid (H+) facilitates the cleavage of 1,4’-b-glycosidic linkages in
cellulose, which is considered as the rate determining step.[18]
As shown in Figure 2, in supercritical anhydrous ethanol, the
yield of EL from cellulose was ~17% after reacting for 6 h at
2608C, whereas after the addition of 5% water, the EL yield
almost doubled (~30%) under otherwise identical conditions.
The yield of S.R. decreased significantly from ~20% to ~8%
with the addition of 5% water in the pure ethanol solvent,
suggesting that water facilitates the deconstruction of cellu-
lose. Brand et al. found that faster hydrolytic cleavage was as-
Table 1. The comparison of the main product yields of cellulose conver-
sion with and without catalysts in different solvents.[a]
Entry Catalyst
Solvent
Carbon yield [%]
EL EHB ELE
S.R.
Furfural HMF [%]
1
2
3
4
5[b]
6[c]
7
–
95% ethanol 2.1
95% ethanol 5.1
95% ethanol 8.2
1.0 0.2 0.8
1.8 0.3 2.2
2.3 0.6 0.1
6.6 52.3
5.7 30.8
0.1 21.5
0.1 8.6
0.1 16.1
0.1 33.8
14.6 19.8
SBA-15
ZrO2
Zr-SBA-15 95% ethanol 30.1 13.5 2.2 0.3
Zr-SBA-15 95% ethanol 26.7 10.6 1.2 0.2
Zr-SBA-15 95% ethanol 24.9
Zr-SBA-15 Water
1.4[d]
6.3 0.6 0.4
20.9[e] 0.7
–
[a] Reaction conditions: 2608C, 400 psi initial pressure of N2, 20 g solvent
(95% ethanol and 5% water), 6 h, 0.2 g cellulose, 0.1 g catalyst. EL: ethyl
lactate; EHB: ethyl 2-hydroxybutanoate; ELE: ethyl levulinate; S.R.: solid
residue. [b] 1 g Cellulose, 0.5 g catalyst. [c] 2 g Cellulose, 1 g catalyst.
[d] LA: lactic acid. [e] Levulinic acid.
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mediates enhanced the yields of EL. The synergistic effects of
alcohol and water on biomass liquefaction were also observed
by other groups.[20,21] Yet the EL yield reached the maximum as
the proportion of water was 5 wt%, further increasing the
ratio of water to ethanol decreased the EL yield. Higher water
proportion in the solvent may result in two consequences:
(1) deactivating the Lewis acid sites and (2) increasing the criti-
cal temperatures of the mixed solvent. Water adsorption leads
to the deactivation of Lewis acid sites, which are transformed
to Brønsted-acid sites.[14c,d] When the water proportion is
>20 wt%, the critical temperature of the ethanol–water mix-
ture is above 2608C. We think that the inhibitive effect of
water on the Lewis acid sites, instead of the change of the
sub- or super-critical states of the ethanol–water solvents, is
the primary factor causing the decrease of the yield of EL with
increasing the water content in the ethanol–water mixtures
(from 5 wt% to 25 wt% water in Figure 2). No distinct differ-
ence of product distribution was observed between the super-
critical solvent containing 15 wt% water and the subcritical
solvent with 25 wt% water. However, an effect of the change
of solvent states on cellulose deconstruction cannot be ruled
out completely.
Figure 2. The effect of solvent on the yields of liquid-phase products from
cellulose conversion with Zr-SBA-15. Reaction conditions: 2608C, 6 h, 400 psi
(1 psi=6.89 kPa) initial pressure of N2, 0.2 g cellulose, 0.1 g catalyst. EL: Ethyl
lactate; EHB: ethyl 2-hydroxybutanoate; ELE: ethyl levulinate.
sociated with subcritical water, whereas slower pyrolytic cleav-
age was dominant in supercritical ethanol in the temperature
range of 250–3508C.[19] On the other hand, the repolymeriza-
tion of intermediates was suppressed owing to the reactions
between ethanol and biomass intermediates, such as alde-
hydes, carboxylic acids, ketones, and so on. Therefore, in the
ethanol–water mixtures (up to 15 wt% water), the faster depo-
lymerization of cellulose and slower recombination of inter-
To optimize the yield of EL, cellulose was converted at differ-
ent process conditions (the products identified by GCMS are
shown in Figure S6). As shown in Figures 3c and S4, varying
temperatures have a pronounced effect on the production
Figure 3. Conversion of different feedstocks at different reaction temperatures with Zr-SBA-15. (a) Glucose conversion; (b) fructose conversion; (c) cellulose
conversion; (d) solid residue (S.R.) after the conversion of the different feedstocks. Reaction conditions: 2 h, 400 psi initial pressure of N2, 20 g solvent (95%
ethanol and 5% water), 0.2 g biomass substrate, and 0.15 g catalyst. EL: Ethyl lactate; EHB: ethyl 2-hydroxybutanoate; ELE: ethyl levulinate.
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yield of EL. Below 2008C, cellulose did not show an apprecia-
ble conversion. At 2408C (subcritical condition), the highest
yield of 25.4% was achieved after 10 h. A steadily increasing
amount of EL up to ~30% was produced at 2508C (near-criti-
cal condition) yet it took 6 h to reach the plateau. Whereas
after 2 h at 2608C (supercritical condition), the yield of EL
varied little and reached a maximum yield of 30.3%. Similarly,
the yields of EHB and ethyl levulinate (ELE) consistently in-
creased with extended reaction times. Conversely, the HMF
and furfural yields consistently decreased with increasing reac-
tion time. It is widely accepted that Brønsted acids can hydro-
lyze cellulose to glucose, followed by the dehydration of glu-
cose to HMF;[22,23] thus, the co-existence of furfural, HMF, and
EL in the final products indicates that the Lewis and Brønsted
acid sites co-existed on the Zr-SBA-15 catalyst, which was also
confirmed by the pyridine-FTIR characterization (Figure 1). Of
particular note is the fact that HMF and furfural almost com-
pletely vanished after 4 h at 2608C. Higher temperatures led to
the transformation of HMF and furfural to ELE through Brøn-
sted acid-catalyzed rehydration and transfer hydrogenation
promoted by Lewis acids,[24] respectively. Notably, the S.R. de-
creased steadily with reaction time indicating that the conver-
sion of cellulose increased. The effect of different catalyst load-
ing on the conversion of cellulose was depicted in Figure S5.
The yield of EL showed the steady uptrend as the catalyst
loading increased, reaching ~33% as the catalyst/cellulose
mass ratio reached 1:1. The yield of ELE also increased steadily
with increased catalyst loading, but was much lower than that
of EL. While the EHB increased first with increasing the catalyst
loading and then decreased as the catalyst/cellulose ratio ex-
ceeded 0.5. Contrarily, the yields of HMF and furfural consis-
tently decreased as the catalyst loading increased.
We propose that the reaction pathway of converting cellu-
lose to EL over the Zr-SBA-15 catalyst begins with the hydrolyt-
ic/pyrolytic deconstruction of cellulose, as shown in Scheme 1.
Cellulose decomposed to glucose, which then isomerized to
fructose. The Zr4+ ions as the Lewis acid sites interacted with
the carbonyl group of fructose, breaking it down to glyceralde-
hyde and dihydroxyacetone through retro-aldol condensation.
Glyceraldehyde underwent the dehydration to form 2-hydroxy-
propenal, followed by pyruvaldehyde through keto-enol tauto-
merization, and finally to EL in ethanol as the solvent. Glucose
might also be cleaved to one C4 fragment (aldotetrose) and
another C2 compound (glycolaldehyde). To validate our hy-
pothesis of the reaction pathway, glucose and fructose were
used as the probe reactants (Figure 3a and b). Glucose was
readily converted to EL in a ~30% yield at a lower temperature
of 2008C; however, the yield of EL reached as high as ~40%
from fructose. The position of the CÀC bond cleavage through
retro-aldol condensation of ketohexose and aldohexose led to
the different yields of alkyl lactates, and thus a higher yield of
EL from fructose is a result of preferred disintegration of the
carbon bond between the C3 and C4 position.[7b,c,8a] Figure 3d
shows that at subcritical conditions (ꢀ2408C), the conversion
of cellulose was low, which corresponds to a high S.R. yield of
50%–70%, whereas the S.R. yield decreased sharply at near-
Scheme 1. Proposed reaction mechanism for the conversion of cellulose to EL in ethanol–water with Zr-SBA-15.
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critical (2508C) and supercritical (2608C) conditions. Thus, the
depolymerization of cellulose was likely the rate-limiting step
to convert cellulose to EL with the Zr-SBA-15.
acids and the bands at 1460 and 1360 cmÀ1 belong to the
ÀCH2À and ÀCH3 deformation vibrations.[25–27] Therefore, car-
boxylic acid groups were identified on the spent catalyst sur-
face, which enhanced the Brønsted acidity and led to the
higher yields of HMF and furfural. The organic S.R.s on the
spent catalysts can be easily removed by calcination in air
flow. According to the FTIR characterization, the regenerated
catalyst showed similar spectra to the fresh catalyst. Corre-
spondingly, after the regeneration, the yield of EL was more
steady in the consecutive runs (Figure 4a). The TEM images
(Figure S3) also showed that the structure of the regenerated
catalyst was highly ordered and the average pore size was un-
changed compared to the fresh sample.
The stability of the Zr-SBA-15 catalyst is of importance in the
supercritical ethanol–water solvents. Over three consecutive
runs at 2608C, the yield of EL from cellulose steadily decreased
with the re-used catalyst without regeneration (Figure S7),
which implied that the re-polymerized humins might inhibit
the catalyst activity. The yields of furfural and HMF increased
with increasing catalyst cycles. As only the weak Brønsted acid
sites on the fresh Zr-SBA-15 catalyst were identified, the depo-
sition of the cellulose-derived S.R.s on the spent Zr-SBA-15 cat-
alyst changed the surface properties. As shown in Figure 4b,
The stability of the ethanol solvent itself is also important
from the perspective of process intensification, because the re-
cyclability of the solvent may impact the overall process eco-
nomics. In the presence of the solid Lewis acid catalyst and
under supercritical conditions, ethanol may undergo reactions,
such as gasification, dehydration, and dehydrogenation. How-
ever, in these experiments, ethanol was very stable and no gas-
eous products (e.g., H2, CO, CO2, C2H4) were detected (Fig-
ure S8). The only liquid-phase product obtained was acetalde-
hyde diethyl acetal (ADA) in the control reaction without
adding any biomass feedstock in the supercritical ethanol–
water mixture with Zr-SBA15 (Figure S9). However, the yield of
ADA was negligible, ~0.04% (carbon percent yield from etha-
nol) after 6 h. We assumed that acetaldehyde could be pro-
duced from the dehydrogenation of ethanol,[28] which was the
potential hydrogen donor for transfer hydrogenation reac-
tions.[29] ADA was produced by reacting acetaldehyde with eth-
anol as follows: 2EtOH+CH3CHO!ADA+H2O.[30] The forma-
tion of ADA from ethanol was a reversible reaction as the ADA
yield decreased sharply with increasing the water content in
ethanol, indicating that water inhibited ADA production (Fig-
ure S10). However, a much larger amount of ADA, ~0.69% or
~26.7% carbon yields based on ethanol and cellulose, respec-
tively, was detected during the conversion of cellulose under
the otherwise identical conditions (Figure S6). Thus, ADA could
be one of the main by-products originating from the possible
C2 intermediate glycolaldehyde during the cellulose conver-
sion. We found that approximately 21.8% ADA was produced
with glycolaldehyde as the feedstock; considerable amounts of
EL and EHB were also obtained (Figure S11). Formation of the
C3 and C4 acid esters from the C2 aldehyde indicates that the
CÀC bond-forming aldol condensation occurred on the Lewis
acidic Zr-SBA-15 catalyst and the retro-aldol condensation reac-
tions took place thereafter. However, it is unclear whether or
not the cellulose-derived intermediates and products promot-
ed or inhibited the dehydrogenation of ethanol to form ADA.
In summary, we demonstrated that ethyl lactate (EL) was
produced directly from cellulose in supercritical ethanol–water
mixtures with the mesoporous Zr-SBA-15 catalyst. Under the
tested conditions, the highest EL yield was ~33% at 2608C in
supercritical 95:5 (w/w) ethanol/water. After regeneration, the
Figure 4. a) Effect of re-use of Zr-SBA-15 on the yields of the main products
from the conversion of cellulose in ethanol–water solvent containing 5 wt%
water. The spent catalyst was regenerated by calcination in air at 5508C for
5 h. b) Comparison of the ATR-FTIR spectra of the fresh, spent, and regener-
ated Zr-SBA-15 catalysts. The inset is the full FTIR spectra with the wave-
length in the range of 400–4000 cmÀ1. The spent catalyst was used once
without regeneration. The regenerated Zr-SBA-15 was used three times and
then regenerated by calcination. Reaction conditions: 2608C, 2 h, 400 psi ini-
tial pressure of N2, 0.2 g cellulose, 0.1 g catalyst. EL: Ethyl lactate; EHB: ethyl
2-hydroxybutanoate; ELE: ethyl levulinate.
the attenuated total reflectance (ATR)-FTIR spectra of the spent
Zr-SBA-15 catalyst exhibit a broad peak at ~3380 cmÀ1 that is
attributed to the stretching ÀOH band; the peaks at 2960 to
2840 cmÀ1 are the stretching vibration signal of the CH band in Zr-SBA-15 catalyst exhibited excellent stability after three con-
ÀCH2À or ÀCH3 groups; the peaks located at 1730 cmÀ1 are
secutive catalytic reaction cycles. The addition of an appropri-
ate amount of water (5 wt% in this study) in ethanol, as well
probably the stretching vibrations of C=O bands in carboxylic
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Pagµn-Torres, S. Saravanamurugan, A. Riisager, J. a. Dumesic, E. Taarn-
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as the weak Brønsted acid sites on Zr-SBA-15, facilitated the
hydrolysis of cellulose. The water-tolerant Lewis acidity of the
Zr-SBA-15 catalyst was crucial to produce EL from saccharified
cellulose through a series of isomerization, retro-aldol conden-
sation, Cannizzaro, and esterification reactions. The 95:5 (w/w)
ethanol/water mixture was relatively stable under the test con-
ditions. Overall, this one-pot process is an environmentally-
friendly method to produce EL directly from non-edible cellu-
lose, which has the potential to replace the commercial fer-
mentative process using food-grade corn starch as the raw
material.
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This material is based upon work supported by the National Sci-
ence Foundation under Grant No. CBET 1337017. The authors
thank Dr. Jacob Warner at the University of Minnesota Character-
ization Facility for the SAXS measurements, Prof. Wei Fan at the
University of Massachusetts Amherst for the pyridine-FTIR meas-
urements, Drs. Steven Spain, Mo Ahmadiantehrani and Simon
Poulson at the University of Nevada Reno for the chemical analy-
sis using the facilities in the Shared Instrumentation Laboratory
(SIL), the TEM characterization, and the elemental analysis, re-
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Received: June 24, 2015
Revised: October 27, 2015
Published online on December 18, 2015
ChemSusChem 2016, 9, 36 – 41
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