One-pot catalytic conversion of carbohydrate biomass to lactic acid using an ErCl3 catalyst

Article abstract of DOI:10.1016/j.apcata.2014.05.029

Cellulose was hydrothermally converted into lactic acid in the presence of an ErCl₃ catalyst. Lactic acid yields as high as 91.1% were obtained when reacting 0.1 g cellulose, 0.05 g catalyst and 30 mL water at 240 °C under 2 MPa N₂ for 30 min. Other carbohydrate biomass materials could also be converted into lactic acid effectively under the same reaction conditions. Materials tested included monosaccharides, disaccharides, polysaccharides, and raw biomass such as corn stalks, wheat stems and rice straw. The ErCl₃ catalyst could be reused at least five times without any obvious loss of activity.

Full text of DOI:10.1016/j.apcata.2014.05.029

Accepted Manuscript
Title: One-pot catalytic conversion of carbohydrate biomass to
lactic acid using an ErCl3 catalyst
Author: Xing Lei Fen-Fen Wang Chun-Ling Liu Rong-Zhen
Yang Wen-Sheng Dong
PII:
S0926-860X(14)00363-9
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2014.05.029
APCATA 14849
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
13-1-2014
23-5-2014
26-5-2014
Please cite this article as: X. Lei WangC.-L. LiuR.-Z. YangW.-S. Dong One-pot catalytic
conversion of carbohydrate biomass to lactic acid using an ErCl3 catalyst, Applied
Catalysis A, General (2014), http://dx.doi.org/10.1016/j.apcata.2014.05.029
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

One-pot catalytic conversion of carbohydrate biomass to lactic acid
using an ErCl3 catalyst
Xing Lei, Fen-Fen Wang, Chun-Ling Liu, Rong-Zhen Yang, Wen-Sheng Dong*
Key Laboratory of Applied Surface and Colloid Chemistry (SNNU), MOE, School of Chemistry and
Chemical Engineering, Shaanxi Normal University, Xi’an, 710062, China
*Author to whom correspondence should be addressed.
Phone: +86 (0) 29-81530806
Fax: +86 (0) 29-81530806
E-mail: wsdong@snnu.edu.cn
Highlights
•
•
•
•
Lactic acid was obtained by the conversion of various carbohydrate biomasses.
Erbium chloride is a highly efficient catalyst.
91.1% lactic acid yield was obtained using cellulose feedstock.
This catalyst could be used repeatedly.
1
Page 1 of 24

Abstract
Cellulose was hydrothermally converted into lactic acid in the presence of an ErCl3 catalyst.
Lactic acid yields as high as 91.1% were obtained when reacting 0.1 g cellulose, 0.05 g catalyst
and 30 mL water at 240 °C under 2 MPa N2 for 30 min. Other carbohydrate biomass materials
could also be converted into lactic acid effectively under the same reaction conditions. Materials
tested included monosaccharides, disaccharides, polysaccharides, and raw biomass such as corn
stalks, wheat stems and rice straw. The ErCl3 catalyst could be reused at least five times without
any obvious loss of activity.
Keywords: Cellulose; Lignocellulose; Carbohydrate; Lactic acid; ErCl3 catalyst

3
Page 2 of 24

1. Introduction
Lactic acid is used as a monomer for the production of biodegradable polymers and various
biodegradable, nontoxic solvents and also has applications in the food, cosmetics and
pharmaceutical industries [1]. Lactic acid is considered a top-twelve bio-based platform
molecule and may serve as a precursor for the synthesis of a wide range of useful intermediates,
such as acrylic acid, propylene glycol, 2,3-pentanedione, acetaldehyde, pyruvic acid and lactides
by catalytic routes [2−4]. Currently, lactic acid itself is produced by conventional
biotechnological processes involving the fermentation of carbohydrates, in which glucose and
sucrose are the main raw ingredients [1]. However, low space-time yields and the difficulty in
recovering lactic acid from the fermentation broth have a major impact on the production costs.
Alternative catalytic processes for the production of lactic acid are highly desirable [5]. Many
studies have been performed to investigate the conversion of various biomass resources such as
trioses [6−11], hexoses [12−20] and even cellulose to lactic acid through catalyzed routes
[21−25]. To date, however, the resulting lactic acid yields have been far from satisfactory when
using cellulose or raw lignocellulosic materials, substances that represent the most abundant
sources of inedible biomass on the planet.
Lignocellulosic materials such as agricultural residues (including wheat stalks, rice straw,
corn stalks and peanut shells) and forest products (including poplar and platanus leaves) are
renewable biomass resources that have the potential to serve as sustainable feedstocks to replace
diminishing petrochemical stores in the future synthesis of biofuels and chemicals [26]. These
raw materials have the added advantages of being highly abundant and generate very low net
greenhouse gas emissions.
In a previous study, we found that the Lewis acid erbium triflate was able to efficiently
catalyze the conversion of pure microcrystalline cellulose to lactic acid in an aqueous dispersion
[27]. However, this catalyst is relatively expensive and it would be preferable to use raw
4
Page 3 of 24

lignocellulose as the feedstock for biomass conversion, because this would represent a
significant improvement in the large-scale production of bio-based products. Hence, in the
present work, we employed the less expensive chemical compound ErCl3 as a catalyst when
transforming a variety of carbohydrate biomass materials, such as saccharides, cellulose and raw
lignocellulosic substances, to lactic acid. This catalyst exhibited high catalytic activity, good
recyclability and stability.
2. Experimental
2.1. Materials and characterization
D-Fructose (99%), D-glucose (99%) and sucrose (99%) were purchased from the Tianjin
Chemical Reagents Co. China Microcrystalline cellulose (particles size of 20 µm) was obtained
from Sigma-Aldrich, lactic acid (98%) and inulin were purchased from Alfa Aesar and
D-(+)-cellobiose and mannose were obtained from the Sinopharm Chemical Reagent Co., Ltd.
(Shanghai, China). Starch was obtained from the Beijing Aoboxing Bio-tech Co., Ltd., while
corn stalks, wheat stalks, rice straw, peanut shells, poplar leaves and platanus leaves were
obtained from the ChangAn district of Xi’an. These materials were washed, milled and screened
to capture particle sizes less than 200 mesh, then dried at 120 °C for 24 h before use. All other
reagents were analytical grade and were used without further purification.
The various components of the raw lignocellulosic biomass (water extracts, cellulose,
hemicellulose, lignin and ash) were analyzed according to the Van Soest method [28]. Fourier
transform-infrared spectra were collected on a Bruker EQUINX55 FTIR spectrometer using
KBr discs. The C, H and N contents of the various substrates were determined using a Vario EL
III CHNS analyzer.
5
Page 4 of 24

2.2 Reaction test and product analysis
All reactions were carried out in a 35 mL stainless steel autoclave equipped with a
mechanical stirrer. In a typical experiment, 0.1 g of substrate material, 0.05 g of catalyst and 30
mL of water were added to the reactor, after which the autoclave was purged three times with N2
and then pressurized to 2.0 MPa with N2 at room temperature. The reaction mixture was heated
to 240 °C unless otherwise stated and held at that temperature for 30 min with stirring at 600
rpm. After each reaction the reactor was quickly cooled to room temperature using an ice/water
mixture and then depressurized. The post-reaction sample was diluted with mobile phase
solution prior to analysis.
Sample analyses were performed on a Shimadzu LC-20AT HPLC system equipped with a
RID-10A detector and a Bio-Rad Aminex HPX-87H ion exclusion column (300 × 7.8 mm),
using 0.005 M H2SO4 as the mobile phase at a flow rate of 0.5 mL min−1. The column
temperature was 50 °C and the detector was set to 45 °C. The amount of product was determined
using calibration curves generated with standard solutions.
2.3 The conversion of raw materials and product yield definitions
The conversion of the raw materials and the product yields were defined as follows.
Raw material conversion (wt.%):
⎛
⎞
mass of unconverte d raw materials
mass of in itial raw materials
X = ⎜1−
⎟ ×100%
⎜
⎟
⎝
⎠
Product yield (C%):
moles of carbon in product i
Yi =
×100%
moles of carbon in initial raw materials
6
Page 5 of 24

3. Results and discussion
3.1. The conversion of various biomasses using the ErCl3 catalyst
The hydrothermal conversions of various biomass materials, including monosaccharides
(fructose, glucose and mannose), disaccharides (sucrose and cellobiose) and polysaccharides
(starch, inulin and cellulose), were performed using the ErCl3 catalyst, with the results shown in
Table 1. At 240 °C, the biomass materials (the monosaccharides, disaccharides and
polysaccharides) were completely converted over this catalyst. The main product was lactic acid
with yields greater than 75%, together with lesser amounts of formic acid, acetic acid, levulinic
acid and acetol. An 84.8% yield of lactic acid was obtained when using fructose as the substrate
while glucose and mannose (a C-2 epimer of glucose) gave lactic acid yields of 76.2 and 76.7%,
respectively. The distinct behaviors of these hexoses might stem from the more stable ring
structures of glucose and mannose. The disaccharide sucrose, consisting of one fructose and one
glucose unit, gave a moderate yield of lactic acid (82.9%), while the cellobiose, composed of
two glucose molecules linked by a β(1→4) bond, produced a 75.5% yield, similar to that
obtained with glucose. When using starch as the feed material, a polysaccharide consisting of a
large number of glucose units joined by glycosidic bonds, a 73.7% yield of lactic acid was
obtained. Inulin, a mixture of oligo and polysaccharrides composed of fructose units joined
together by β linkages, gave an 83.2 % yield, which is similar to that obtained when fructose
was used as the feed. Overall, these results suggest that the conversions of fructose and inulin
may follow the same reaction mechanism, such that inulin may initially hydrolyze to form
fructose, followed by the retro-aldol fragmentation of fructose to trioses and the subsequent
conversion of these trioses to lactic acid [1]. When the substrate was cellulose, a polysaccharide
consisting of a linear chain of several hundred to over ten thousand β(1→4) linked D-glucose
units, the highest yield of lactic acid was obtained (91.1%). The above data clearly indicate that
the highest yield of lactic acid is obtained using cellulose as the feedstock, as opposed to the use
7
Page 6 of 24

of the corresponding monosaccharide (glucose) and cellobiose. This suggests that the catalytic
conversion of cellulose may proceed via a different reaction route to that by which glucose and
cellobiose are transformed.
Previously, Wang et al. found that PbCl2 exhibited a remarkable promoting effect during
cellulose depolymerisation [29]. A lactic acid yield of 68% was obtained following the reaction
of 0.1 g ball-milled cellulose (33% crystallinity) in 20 mL water with 0.14 mmol PbCl2 as the
catalyst at 190 °C for 4 h under 3 MPa N2. Wang postulated that the formation of lactic acid was
preceded by a multistep cascade of reactions, including the hydrolysis of cellulose to glucose,
the isomerization of glucose to fructose, the retro-aldol fragmentation of fructose to trioses and
the conversion of these trioses to lactic acid. However, our present results do not fully agree
with this mechanism.
At the elevated temperatures applied in our present study (above 473 K), water will
generate increasing quantities of hydroxonium ions capable of promoting acid-catalyzed
reactions [30,31] and this could be the driving force responsible for the depolymerisation of
cellulose into soluble oligosaccharides. We propose that the Lewis acid centers produced in this
reaction may function together with the hydroxonium ions present in the aqueous medium at
240 °C to convert the soluble oligosaccharides, as shown in Scheme 1 [25].
It has been demonstrated that lanthanide(III) ions can form aquated ions in water solutions.
Ishida et al. stated that, for dehydration of hexoses, the formation of a lanthanide–saccharide
complex between hydrated lanthanide ions and the hexoses is important for the dehydration step
because the lanthanide(III) ions have a high affinity for oxygen-containing functional groups
[32,33].
In the present case, it is very likely that the hydrated erbium ions can coordinate with the
hydroxyl groups at position 2 on the cellulose rings, due to the higher electron density at these
sites [34,35], resulting in easier cleavage of the protonated ether bonds between the two glucosyl
8
Page 7 of 24

units of the soluble oligosaccharide intermediates (Scheme 1, step A) [25]. The second step
could be a dehydroxylation involving C–O bond cleavage following direct coordination with the
Lewis center, as presented in Scheme 1 (steps B and B'). Following this cleavage, a variety of
low molecular weight carboxylic acids and similar products are produced through further C–C
and C–O bonds scissions, including lactic acid, formic acid and acetol. These results suggest
that lactic acid is produced by the direct transformation of the soluble oligosaccharides, without
proceeding through glucose or cellobiose intermediates.
Lignocellulose is primarily composed of cellulose, hemicellulose and lignin, along with
smaller amounts of pectin, protein, extractives (soluble nonstructural materials such as
nonstructural sugars, nitrogenous materials, chlorophyll and waxes) and ash [36]. Among these,
hemicellulose and cellulose are polymers of C5 and C6 sugars that intertwine within the plant
cell walls. In contrast, lignin is an amorphous three-dimensional polymer containing three
primary units (p-coumaryl, coniferyl and sinapyl alcohols) that embeds in and binds to the
former two components. It contains a greater concentration of C–C bonds and provides rigidity
to the structure that protects the lignocellulose against transformations [37]. In the conversion of
lignocellulosic biomass to fuel and chemicals, the biomass generally needs to be treated so that
the cellulose in the plant fibers is exposed. Pretreatment involves the use of various techniques,
including ammonia fiber explosion, chemical treatment, biological treatment and steam
explosion, to alter the structure of the cellulosic biomass with the goal of making the cellulose
more accessible [26,38]. However, these processes are expensive and thus, to some extent, do
not permit the cost effective conversion of lignocellulose. In the present work, the raw
lignocellulosic biomass materials (corn stalks, rice straw, wheat stalks, peanut shells, poplar
leaves and platanus leaves) were hydrothermally converted using the ErCl3 catalyst under
identical conditions, without applying any of the pretreatments noted above. The results of these
trials are also presented in Table 1. The composition of the raw lignocellulosic biomass was
9
Page 8 of 24

analyzed according to the Van Soest method and the results are summarized in Table 2. The data
in Table 1 show again that the ErCl3 catalyst is highly efficient in the conversion of raw
lignocellulosic biomass materials to lactic acid. The highest yield of lactic acid (63.1%) was
obtained when using wheat stalks as the feedstock, while corn stalks were converted to lactic
acid with a yield of 58.6% and using rice straw and peanut shells as feedstocks gave yields of
54.8 and 45.4%, respectively. For poplar leaves and platanus leaves, the yields of lactic acid
were 27.7 and 16.7%, respectively. The yields of lactic acid obtained from the conversion of
these raw lignocellulosic biomass feedstocks roughly increased with increasing cellulose and
hemicellulose content in the feedstocks, with the exception of the wheat stalks. The reason for
this discrepancy is unclear, but it may be attributed to the presence of more soluble
polysaccharides in the wheat stalk extracts.
These results demonstrate that the highest yield of lactic acid (91.1%) was obtained when
using cellulose as the raw material. Hence, in the following trials, cellulose was chosen as the
substrate when investigating the effects of reaction conditions on the performance of the ErCl3
catalyst.
3.2. The optimization of reaction conditions
The temperature dependence of cellulose conversion when using the ErCl3 catalyst was
examined, with the results shown in Fig. 1. When the reaction temperature was increased from
200 to 260 °C, the conversion of cellulose was improved from 12.7 to 100%, the yield of lactic
acid was enhanced from 15.2 to 91.1% and the yields of formic acid and acetol were also
increased. At 240 and 260 °C, the yields of lactic acid were 91.1 and 91.7%, respectively. These
results indicate that no overreaction of lactic acid took place at higher temperatures.
The influence of reaction time is summarized in Fig. 2. When the reaction was carried out at
240 °C for 0 min, the conversion of cellulose was 68.8% and the yield of lactic acid was 55.9%.
10
Page 9 of 24

When prolonging the reaction time to 10 min, the yield of lactic acid was increased to 88.5%
and, when further increasing the reaction to 30 min, the yield was slightly enhanced to 91.1%.
After this point, the yield of lactic acid was essentially constant at ~90%. These results further
confirm that lactic acid is stable at 240 °C in this reaction system and that overreaction of the
lactic acid is negligible.
As shown in Fig. 3, with increasing amounts of cellulose the yield of lactic acid gradually
decreased. When the amount of cellulose was 0.5 g, the yield of lactic acid decreased to ~26%.
Under these conditions, a quantity of dark brown, insoluble matter was found in the autoclave,
which could not be identified. In order to determine whether the insoluble matter was generated
by the polymerization of the formed products, the reaction time was prolonged to 2 h. The
results showed that the yield of lactic acid was 47.2%, while the yields of other products
increased slightly. With further prolonging reaction time to 4 h, the yields of the products
remained almost constant. The data suggests that some soluble oligosaccharides in the reaction
system, derived from the depolymerisation of the cellulose did not convert fully due to a
relatively small amount of the catalyst and a shorter reaction time when the feed of cellulose
was 0.5 g, and the reaction time 30 min. Hence, the dark brown, insoluble matter was not
derived from the polymerization of the formed products; we suppose that the insoluble matter
was probably formed by partial carbonation of the cellulose.
The effects of the catalyst loading on the reaction are presented in Fig. 4. When the reaction
was conducted in the absence of the catalyst, only 6.4% lactic acid and 9.6% HMF
(5-methoxymethylfurfural) yields were obtained, while the conversion of cellulose was 45.9%.
The main product in this case could be soluble oligosaccharide intermediates. In the presence of
0.01 g of the ErCl3 catalyst, the cellulose was converted completely and the yield of lactic acid
reached 82.3% while, with further increases in the catalyst amount, the yields of lactic acid
increased and then decreased slightly. These results indicate that a small amount of the catalyst
11
Page 10 of 24

produces low yields of lactic acid owing to the low concentration of active species available. At
high catalyst concentrations, further reaction of the lactic acid to undesirable products is
promoted, decreasing the yield. The highest lactic acid yield of 91.1% was obtained under the
conditions of 0.1 g cellulose, 30 mL water, 0.05 g catalyst, 240 ºC, 2 MPa N2 and 30 min
reaction time. The corresponding turnover rate of lactic acid formation was 11.7 mol·molEr−1·h−1
and the associated lactic acid productivity was 6.4 g·L−1·h−1, a value that is greater than the
results obtained from the conversion of glucose and sucrose by fermentation (0.3−5 g·L−1·h−1),
heterogeneous catalysis (3.3 g·L−1·h−1) and homogeneous catalysis using a PbCl2 catalyst [1,29].
3.2. Recycling of the catalyst
The stability and reusability of catalysts are extremely important aspects of any industrial
process, since these features reduce production costs, especially in the case of metal chloride
catalysts. It is known that conventional Lewis acids such as AlCl3, SnCl4, CrCl3, TiCl4 and
PbCl2 are decomposed or deactivated in the presence of water [39] and hence these materials
cannot be recovered and reused after the reactions are complete. As an example, Peng et al. [40]
found that chromium chloride was uniquely effective for the catalytic conversion of cellulose to
levulinic acid in water, generating a yield of levulinic acid as high as 67% at 200 °C. The
catalyst, however, decomposed to chromium oxide during the reaction.
The reusability of ErCl3 in the conversion of cellulose to lactic acid was therefore
investigated. After each trial, the water in the solution was removed by evaporation under
vacuum, following which the catalyst was recovered by extracting the liquid products with
diethyl ether. The recycled catalyst was then used for the next run under identical reaction
conditions. Similar yields of lactic acid (~90%) were obtained during as many as five repeated
reaction cycles (see Fig. 5), indicating that the ErCl3 catalyst was not deactivated in the course
of the catalytic runs. Moreover, the fresh catalyst had a very similar UV absorption spectrum to
12
Page 11 of 24

that obtained from the material following its use in the water phase (Fig. S1), providing further
confirmation that the active components of the catalyst were stable.
4. Conclusions
We have demonstrated that ErCl3 can effectively catalyze the conversion of
monosaccharides, disaccharides, polysaccharides and even raw lignocellulosic materials into
lactic acid. The lignocellulosic biomass did not require pretreatment and the reaction medium
was water, and so this system represents a simple, environmentally-friendly means of producing
lactic acid. The almost complete transformation of lignocellulose obtained using this
straightforward method is of great significance with regard to the cost-efficient production of
lactic acid from biomass in large-scale applications.
Acknowledgements
The authors gratefully acknowledge the financial support of the National Natural Science Foundation of
China (Grant no. 20976101), the Program for Key Science and Technology Innovation Team of Shaanxi
Province (2012KCT-21) and the Fundamental Research Funds for the Central Universities (GK201305011).
References
[1] M. Dusselier, P.V. Wouwe, A. Dewaele, E. Makshina, B.F. Sels, Energy Environ. Sci. 6 (2013)
1415−1442.
[2] A. Corma, S. Iborra and A. Velty, Chem. Rev. 107 (2007) 2411–2502.
[3] Y. Fan, C. Zhou and X. Zhu, Catal. Rev. - Sci. Eng. 51 (2009) 293–324.
[4] J.J. Bozell and G.R. Petersen, Green Chem. 12 (2010) 539–554.
[5] L.Z. Kong, G.M. Li, H. Wang, W.Z. He, F. Ling, J. Chem. Technol. Biotechnol. 83 (2008) 383–388.
[6] Y. Hayashi, Y. Sasaki, Chem. Commun. (2005) 2716–2718.
13
Page 12 of 24

[7] C.B. Rasrendra, B.A. Fachri, G.B.N. Makertihartha, S. Adisasmito, H.J. Heeres, ChemSusChem 4 (2011)
768–777.
[8] J.C. Wang, Y. Masui, M. Onaka, Appl. Catal. B: Environ. 107 (2011) 135–139.
[9] F. de Clippel, M. Dusselier, R. Van Rompaey, P. Vanelderen, J. Dijkmans, E. Makshina, L. Giebeler, S.
Oswald, G.V. Baron, J.F.M. Denayer, P.P. Pescarmona, P.A. Jacobs, B.F. Sels, J. Am. Chem. Soc. 134
(2012) 10089–10101.
[10] P. Pescarmona, K.P.F. Janssen, C. Delaet, C. Stroobants, K. Houthoofd, A. Philippaerts, C.D. Jonghe, J.S.
Paul, P.A. Jacobsand, B.F. Sels, Green Chem. 12 (2010) 1083–1089.
[11] R.M. West, M.S. Holm, S. Saravanamurugan, J.M. Xiong, Z. Beversdorf, E. Taarning, C. H. Christensen,
J. Catal. 269 (2010) 122–130.
[12] M.S. Holm, S. Saravanamurugan, E. Taarning, Science 328 (2010) 602–605.
[13] G. Epane, J.C. Laguerre, A. Wadouachi, D. Marek, Green Chem. 12 (2010) 502–506.
[14] M.S. Holm, Y.J. Pagan-Torres, S. Saravanamurugan, A. Riisager, J.A. Dumesic, E. Taarning, Green
Chem. 14 (2012) 702–706.
[15] A. Onda, T. Ochi, K. Kajiyoshi, K. Yanagisawa, Catal. Commun. 9 (2008) 1050–1053.
[16] A. Onda, T. Ochi, K. Kajiyoshi, K. Yanagisawa, Appl. Catal. A-Gen. 343 (2008) 49–54.
[17] W. Zeng, D.G. Cheng, F. Chen, X. Zhan, Catal. Lett. 133 (2009) 221–226.
[18] R.F. Lobo, ChemSusChem 3 (2010) 1237–1240.
[19] C.B. Rasrendra, I.G.B.N. Makertihartha, S. Adisasmito, H.J. Heeres, Top. Catal. 53 (2010) 1241–1247.
[20] Z. Liu, W. Li, C. Pan, P. Chen, H. Lou, X. Zheng, Catal. Commun. 15 (2011) 82–87.
[21] X.Y. Yan, F.M. Jin, K. Tohji, A. Kishita, H. Enomoto, AIChE J. 56 (2010) 2727–2733.
[22] J.B. dos Santos, F.L. da Silva, F.M.R.S. Altino, T. da Silva Moreira, M.R. Meneghetti, S.M.P.
Meneghetti, Catal. Sci. Technol. 3 (2013) 673–678.
[23] S. Zhang, F. Jin, J. Hu, Z. Huo, Bioresour. Technol. 102 (2011) 1998–2003.
[24] C. Sanchez, I. Eguees, A. Garcia, R. Llano-Ponte and J. Labidi, Chem. Eng. J. 181 (2012) 655–660.
[25] F. Chambona, F. Rataboula, C. Pinela, A. Cabiacb, E. Guillonb, N. Essayema, Appl. Catal. B: Environ.
105 (2011) 171–181.
[26] P．Kumar, D.M. Barrett, M.J. Delwiche, P. Stroeve, Ind. Eng. Chem. Res. 48 (2009) 3713–3729.
[27] F.F. Wang, C.L. Liu, W.S. Dong, Green Chem. 15 (2013) 2091–2095.
14
Page 13 of 24

[28] H.K. Goering, P.J.V. Soest, Forage fiber analysis, in USDA-ARS Agriculture Handbook 379,
Government Printing Office, Washington DC, 1970; pp 12–20.
[29] Y. Wang, W. Deng, B. Wang, Q. Zhang, X. Wan, Z. Tang,Y. Wang, C. Zhu, Z. Cao, G. Wang, H. Wan,
Nat. Commun. 4 (2013) 2141–2148.
[30] M. Sasaki, T. Adschiri and K. Arai, AIChE J. 50 (2004) 192–202.
[31] C. Luo, S. Wang and H. Liu, Angew. Chem. 119 (2007) 7780–7783.
[32] K. Seri, Y. Inoue, H. Ishida, Bull. Chem. Soc. Jpn. 74 (2001) 1145–1150.
[33] H. Ishida, K. Seri, J. Mol. Catal. A: Chem. 112 (1996) L163–L165.
[34] Q. Gan, S.J. Allen, G. Taylor, Process Biochem. 38 (2003) 1003–1018.
[35] M.R. Nimlos, X. Qian, M. Davis, M.E. Himmel, D.K. Johnson, J. Phys. Chem. A 110 (2006)
11824–11838.
[36] H. Jorgensen, J.B. Kristensen, C. Felby, Biofuels, Bioprod. Bioref. 1 (2007) 119–134.
[37] C. Li, M. Zheng, A. Wang, T. Zhang, Energy Environ. Sci. 5 (2012) 6383–6390.
[38] T.A. Hsu, M.R. Ladisch, G.T. Tsao, Chem. Technol. 10 (1980) 315–319.
[39] S. Kobayashi, M. Sugiura, H. Kitagawa, W. W. L. Lam, Chem. Rev. 102 (2002) 2227–2302.
[40] L. Peng, L. Lin, J. Zhang, J. Zhuang, B. Zhang, Y. Gong, Molecules 15 (2010) 5258−5272.
15
Page 14 of 24

a
Table 1 The hydrothermal conversion of various substrates catalyzed by ErCl3
Yield (%)
Conversion
Substrates
levulinic
(%)
lactic acid
formic acid
acetic acid
acetol
acid
1.3
0.0
1.0
0.0
4.1
3.4
3.8
3.3
1.0
0.7
1.1
0.3
Fructose
Glucose
Mannose
Sucrose
100
100
100
100
100
100
100
100
91.5
88.5
94.7
79.5
84.8
76.2
76.7
82.9
75.5
73.7
83.2
91.1
58.6
54.8
63.1
45.4
1.2
1.1
2.1
1.1
0.3
0.3
0.4
0.4
0.4
0.3
0.3
0.4
1.0
0.9
1.7
0.9
2.0
3.5
1.5
0.1
4.1
1.8
4.3
2.8
2.6
3.3
4.9
3.2
2.8
3.0
1.5
2.1
2.9
2.8
3.9
2.7
Cellobiose
Starch
Inulin
Cellulose
Corn stalk
Rice straw
Wheat stalk
Peanut shell
Poplar
72.8
63.8
27.7
16.7
0.4
0.4
1.3
1.6
0.3
0.3
2.9
1.1
leaves
Platanus
leaves
a: Reaction conditions: substrate 0.1 g, water 30 mL, catalyst 0.05 g, 240 °C, 2 MPa N2, 30 min.
16
Page 15 of 24

Table 2 The composition of different biomass sourcesa
Extraction
(wt.%)
23.1
Hemicellulose
(wt.%)
27.3
Cellulose
(wt.%)
41.6
Lignin
(wt.%)
7.9
Ash
(wt.%)
0.1
Substrates
Corn stalk
Rice straw
20.8
23.2
41.4
7.8
6.8
Wheat stalk
Peanut shell
Poplar leaves
34.5
30.8
26.9
6.8
1.1
15.4
12.9
40.6
31.0
9.7
0.1
63.4
6.8
18.8
1.4
Platanus
orientalis leaves
53.3
1.3
18.4
26.0
1.0
a: The compositions of biomass were analyzed according to the procedures of the Van Soest method.[32]
17
Page 16 of 24

OH
OH
OH
O
OH
O
HO
HO
O
O
H+
O
O
O
O
O
*
O
water autoprotolysis
HO
OH
HO
OH
OH
OH
n'<n
n
soluble oligosaccharides
Cellulose
H+: Water autoprotolysis
L
: solid Lewis acid site
OH
L
OH
O
OH
OH
HO
O
O
L
OH
step A
O
O
O
+
HO
H+
H+
O
HO
HO
OH
O
H+
HO
OH
+
L
O
OH-
OH
OH
L OH
HO
OH
O
L
OH
n'<n
Step B'
L
OH
L
OH
Step B
OH
..
HO
O
+
( L OH+H+
L +H2O )
O
OH
..
HO
HO
O
..
+
..
OH
OH
L
Scissions
OH
O
OH
Lactic acid
Scheme 1 Proposed mechanism for cellulose transformation catalyzed by ErCl3
18
Page 17 of 24

Figure Captions:
Fig. 1. The effects of reaction temperature on the conversion of cellulose.
(Reaction conditions: cellulose 0.1 g, water 30 mL, catalyst 0.05 g, 2 MPa N2, 30 min.)
Fig. 2. The effects of reaction time on the conversion of cellulose.
(Reaction conditions: cellulose 0.1 g, water 30 mL, catalyst 0.05 g, 240 °C, 2 MPa N2.)
Fig. 3. The effects of initial cellulose amount on the conversion of cellulose.
(Reaction conditions: water 30 mL, catalyst 0.05 g, 240 °C, 2 MPa N2, 30 min.)
Fig. 4. The effects of catalyst amount on the conversion of cellulose.
(Reaction conditions: water 30 mL, cellulose 0.1 g, 240 °C, 2 MPa N2, 30 min.)
Fig. 5. Recycling of ErCl3 during the conversion of cellulose to lactic acid.
(Reaction conditions: cellulose 0.1 g, water 30 mL, catalyst 0.05 g, 240 °C, 2 MPa N2, 30 min.)
19
Page 18 of 24

25
20
15
10
5
100
80
60
40
20
0
Conversion
Lactic acid
Formic acid
Acetic acid
Levulinic acid
Acetol
0
200
220
240
260
Temperature (oC)
Figure 1
20
Page 19 of 24

25
20
15
10
5
100
80
60
40
20
0
Lactic acid
Formic acid
Acetic acid
Levulinate acid
Acetol
0
0
30
60
90
120
Time (min)
Figure 2
21
Page 20 of 24

100
80
60
40
20
0
100
80
60
40
20
0
Lactic acid
Formic acid
Acetic acid
Levulinic acid
Acetol
0.1
0.2
0.3
0.4
0.5
Cellulose amount (g)
Figure 3
22
Page 21 of 24

25
20
15
10
5
100
80
60
40
20
0
Lactic acid
Formic acid
Acetic acid
Levulinate acid
acetol
HMF
0
0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08
Catalyst amount (g)
Figure 4
23
Page 22 of 24

conversion
lactic acid
100
80
60
40
20
0
1
2
3
4
5
Recycling times
Figure 5
24
Page 23 of 24

Graphical abstract
25
Page 24 of 24