Highly efficient production of lactic acid from xylose using Sn-beta catalysts

Article abstract of DOI:10.1039/d0gc02596h

The efficient conversion of xylose into lactic acid, especially with the novel contribution of C2 components, was revealed over the heterogeneous Sn-beta catalyst in water with a very high lactic acid yield of 70.0 wt% at 200 °C for 60 min. The 13C NMR results indicated that glycolaldehyde (C2), the cleavage species of xylose condensate to erythrose (C4), subsequently, erythrose converts to lactic acid (C3) and to formic acid (C1) with the removal of a carbon atom. In this catalytic process, Sn acts as the Lewis acid site in the Si-O-Sn framework, and participates in the coupling and cracking of C-C bonds (C2 → C4 → C3) through the adsorption of α-protons to generate carbonium anions. Thus, more than 10 wt% lactic acid was obtained based on above pathway through the synergy of aldol addition, isomerization and retro-aldol condensation over the Sn-beta catalyst. This journal is

Full text of DOI:10.1039/d0gc02596h

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DOI: 10.1039/D0GC02596H
COMMUNICATION
Highly Efficient Production of Lactic Acid from Xylose Using Sn-
Beta Catalysts
a,b,＆
,Hu Luo a,＆, Lingzhao Kong a,b,*,Xinpeng Zhao a,b, Gai Miao , Lijun Zhu a,b,
a
Yanfei Zhang
Shenggang Li
Received 00th January 20xx,
Accepted 00th January 20xx
a,b,c,
a,b,c,
, Yuhan Sun
*
DOI: 10.1039/x0xx00000x
9
The efficient conversion of the xylose into lactic acid especially for into LA with a yield of 83.0 % . Similar to glucose, as the monomer
the novel contribution of C components were revealed over the of hemicellulose, xylose has abundant reserves in nature, which
heterogeneous Sn-Beta catalyst in water with a very high lactic means xylose is a potential and promising non-toxic renewable
2
acid yield of 70.0 wt% at 200 °C for 60 min. The 1 C NMR results feedstock for LA production . Xu et al. used the Y( Ⅲ ) as the
indicated that the glycolaldehyde (C ) as the cleavage pecies of homogeneous catalyst to convert xylose to LA with the highest yield
xylose condensate into erythrose (C
convert into lactic acid (C ) along with a carbon atom removed as distinct mechanisms: C-C bond cleavage at C2-C3 or C3-C4 position
formic acid (C ). In this catalytic process, Sn acts as a Lewis acid in aldopentose via retro-aldol condensation yielding
site in the framework Si-O-Sn participate the coupling and glyceraldehyde and glycolaldehyde , therefore, it means that the
cracking of C-C bond (C →C →C ) through adsorption of the α- theorical highest yield of LA is 60.0 %. However, we got an excellent
3
10
2
1
1
4
), subsequently, erythrose of 56.4 % at 220 °C for 30 min . In fact, the process involves two
3
1
a
1
2
2
4
3
protons to generate carbonium anions. Thus, more than 10 wt% LA yield of 70.0 % using xylose as feedstock over the Sn-Beta
lactic acid was obtained based on above pathway through synergy catalyst at 200 °C in water. It is conscious that more than 10.0 % LA
of aldol addition, isomerization and retro-aldol condensation over yield cannot provide an appropriate source due to the above two
1
3
the Sn-Beta catalyst.
bond-breaking mechanisms. Thus, in this work, we employed C-
C2/C4-xylose as substrate to reveal the cleavage mechanisms of C-C
As an important platform chemical, lactic acid (LA) and its
derivatives is widely used in food, pharmaceutical, cosmetic and
bond for C
that there was a C3-C4 cleavage in xylose via a retro-aldol
condensation, and the C intermediate were almost ( ～ 100 %)
converted to LA while 10 % yield of LA from C compounds. And,
intermediate into LA was also
5
sugar in the presence of Sn-Beta catalyst. We found
1
, 2
industrial fields . As a biodegradable material from LA, polylactic
acid get more attention because of its environmentally friendly
3
2
3
, 4
characteristic . 70.0 % of the LA in the worldwide is made by
fermentation, which use the sugar-rich biomass such as rice, corn or
sweet potato as the feedstocks, however, biological process still has
some disadvantages of harsh fermentation conditions and low
the novel conversion pathway of C
exploited over Sn-Beta catalyst.
2
Initially, we employed the Sn-Beta catalyst to convert the
monosaccharide (glucose and xylose) and the intermediate
products (GLY, DHA, pyruvaldehyde (PAL) and glycolaldehyde) with
the results showing in Figure 1 and Table S2. At 200 °C and 4 MPa
5
, 6
efficiency . Consequently, the efficient and environmentally
responsible production of LA by chemical catalytic synthesis
received considerable attention (Table S1). Among series of
catalysts, Sn-Beta exhibits excellent performance in the conversion
of sugars to LA. In 2010, Holm et al. used glucose to synthesize
2
N , the xylose and glucose were completely converted over the Sn-
Beta catalyst along with 70.0 and 61.4 % yield of LA was obtained
respectively. The xylitol (2.2 %), sorbitol (7.1 %) and 5-
hydroxymethyl furfural (5-HMF) (3.6 %) were the main by-products
when glucose serves as the feedstock. GLY, DHA and PAL as the
active intermediate products were transformed nearly 100 % and
the yield of LA reached 95.0 %, which illustrates that once C-C bond
cleavage happened in xylose or glucose via retro aldol condensation
7
lactic acid (ester) over the Sn-Beta catalyst with yield of 68.0 % . As
3
the C intermediate of glucose, glyceraldehyde (GLY) and 1,3-
dihydroxyacetone (DHA) can be isomerized to LA with the highest
8
yield of 89.0 % when the SnCl
2
4
and SnCl ·5H
2
O as the catalysts . Zan
et al. developed a formic acid (FA) induced controlled-release
hydrolysis of microalgae (Scenedesmus) over the Sn-Beta catalyst
to form C
to LA with the support of Sn-Beta catalyst. Different from glucose,
the by-products of xylose were sorbitol (C ), erythrose (C ),
3
components, the latter will be converted synchronously
6
4
a. CAS Key Laboratory of Low-Carbon Conversion Science and Engineering, Shanghai
Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210
(
P.R. China). E-mail: konglz@sari.ac.cn, sunyh@sari.ac.cn
b.
c.
University of Chinese Academy of Sciences, Beijing 100049 (P.R. China)
School of Physical Science and Technology, ShanghaiTech University, Shanghai
2
01203（P.R. China）.
＆
. These two authors contribute equally.
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Green Chemistry
Page 2 of 4
COMMUNICATION
Journal Name
results are shown in Figure 2 b. Compared to the results of Figure 2
View Article Online
1
3
DOI: 10.1039/D0GC02596H
a, the NMR spectrum of C-C4-xylose have a few peaks, which
means the C components were converted to different products
2
besides LA. The chemical shift of 178 ppm belongs to C3 position of
LA and 19 ppm can be considered as the chemical shift of LA’s C1
position. In addition, we found that the signal of C2 position of LA
were strengthened compared to LA (Figure S2). The results showed
2
that a part of LA come from the C4-C5 species (C components) of
xylose, which possibly repolymerize into higher carbon number
species, and then, the latter will be decomposed into LA over the
catalyst. The chemical shift for the C2 (78 ppm) position of
glycolaldehyde, and C1 (164 ppm) position of FA, C2 (91 ppm) and
C4 (63 ppm) position of erythrose were verified through NMR
spectrum, which is consistent with experimental results (Figure 1).
Figure 1. Product distributions from different feedstocks over the Sn-Beta catalyst and
conversion rate of feedstocks. Reaction conditions: 200 °C, 1 h, 300.0 mg feedstocks,
a
O
3
0.0 mL deionized water, 4 MPa N
2
, 300.0 mg Sn-Beta catalyst. Pyruvaldehyde (PAL);
OH
1
5
3
2
13C
2
Glyceraldehyde (GLY); 1,3-dihydroxyacetone (DHA); 5-hydroxymethyl furfural (5-HMF)
3
4
1
1
3C
OH
OH
O
OH
Xylose
OH
OH
Lactic acid
glycolaldehyde (C
2 1
) and FA (C ) and the yield of glycolaldehyde was
4
.1 % directly from breaking of xylose C-C bond. When using
glycolaldehyde as the feedstock, the LA, erythrose and FA were
found in aqueous phase with low yields, so there may be a part of
glycolaldehyde repolymerized into erythrose, then erythrose break
the C-C bond into LA and FA. Simultaneously, when erythrose
serves as the feedstock, glycolaldehyde, LA and FA also were found
in the products. To prove this hypothesis, we designed C-labeled-
xylose experiments to track the cleavage and copulation of C-C
bond over Sn-Beta catalyst.
2
00 180 160 140 120 100
ppm
80
60
40
20
0
b
OH
1
3
2
O
13C
1
2
OH
HO
3
OH
O
13C
13C
4
1
OH
3
Glycolaldehyde
OH
1
5
13C
4
Erythrose
2
1
3C
OH
O
O
Formic acid
To obtain LA, the xylose should break the C-C bond between C2-
OH
OH
O
O
1
3
13
Xylose
C3 or C3-C4 position, so we choose the C-C2-xylose and C-C4-
xylose as the reactant with the assistant of Sn-Beta catalyst under
3
2
13C
3
2
1
1
OH
OH
OH
OH
Lactic acid
1
3
Lactic acid
the same atmosphere (Figure S1). C NMR spectra of liquid
products of C-C2-xylose and 13C-C4-xylose in D
1
3
O were shown in
Figure 2. Compared to the C NMR spectrum of LA (Figure S2), the
2
2
00 180 160 140 120 100
ppm
80
60
40
20
0
1
3
1
3
products from C-C2-xylose showed two obviously single peaks at
the chemical shift of 67 ppm and 68 ppm, which belong to the
different optical rotation structure of LA for C2 position. Therefore,
we can conclude that the break of C-C bond is occurred at C3-C4
Figure 2. 13C NMR of liquid products over the Sn-Beta catalyst. (a) 300.0 mg 13C-C2-
xylose, (b) 300.0 mg C-C4-xylose. Reaction conditions: 200 °C, 1 h, 4 MPa N
Sn-Beta catalyst.
1
3
2
, 300.0 mg
position, then the obtained GLY and DHA as the mainly C
intermediate products will be transformed absolutely to LA via the
dehydration, isomerization and hydrolysis over Sn-Beta catalyst.In
3
Based on above findings, we put forward two possible pathways of
xylose to LA (Scheme 1). (a): (1) Xylose isomerization to xylulose. (2)
Xylulose aldol condensation into DHA and GLY. (3) DHA and GLY
dehydration to PAL. (4) PAL hydration to LA. (b): (1) Glycolaldehyde
order to figure out whether the C
we analysed the liquid products of C-C4-xylose and the C NMR
2
components are converted to LA,
1
3
13
Scheme 1. The reaction network for the conversion of xylose into lactic acid in water over the Sn-Beta catalyst.
2
| J. Name., 2020, 00, 1-3
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Journal Name
COMMUNICATION
OH
OH
OH
OH
OH
O H
H
OH
O H
O H
Si
View Article Online
O
+Sn-Beta
1
O
DOI: 10.1039/D0GC02596H
OH
O
O H
H
O
O
2
O
3
4
O
6
OH
H
O
O
5
OH
Sn
O
O
O
Si
Sn
O H
Si
Sn
O
H
Sn
O
Sn
Si
OH Si
OH
O
Sn
OH
O
O
Si
OH
Si
O
OH
O
O
O
H
O
Si
O
O
O
Si
O
O
O
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
OH
OH
H
OH
O H
OH
O H
O H
Sn
O
O H
H O
H
H
O
O
O
O
OH
3
O
O
Si
OH
H
OH
H
O
2
O
H
7
8
Si
9
10
11
O
OH ...
1
OH
O
Sn
O
O
O
Sn
O
O
Sn
O
O
OH
O
H
H
O
Si
O
O
O
Si
O
Si
LA
Si
O
O
Si
Si
Si
Si
Si
Si
Si
Si
Scheme 2. Proposed mechanistic pathway for the C−C coupling and cleavage between glycolaldehyde catalyzed by the framework Lewis acidic Sn sites in Sn-Beta catalyst.
2
0
aldol condensation to erythrose. (2) Erythrose elimination of H
2
O to will be substantial increase (step 1) . Then the Sn-enolate
2
,4-ihydroxy-2-butenal. (3) 2,4-ihydroxy-2-butenal keto-enol intermediate and silanol group is generated by combine the Sn with
tautomerization to FA and PAL. (4) PAL hydration to LA. In the two the basic oxygen atom with the divorce of proton (step 2). And the
pathways (Scheme 1), the isomerization of xylose to xylulose and nucleophilic addition reaction is occurred through the Sn-enolate
cleavage C-C bond of xylulose via retro-aldol condensation are the intermediate and the protonated glycolaldehyde (step 3), and the
1
3
initial but most critical steps . The whole process of conversion is a proton transfer from the silanol of the active site to the oxygen at
multistep reaction by way of xylulose as an intermediate, and each the C3 position (step 4), results in formation of erythrose (step 5).
step requires different types of actives species. The Lewis acid sites The produced erythrose then isomerize into erythrulose through a
services for the isomerization and retro-aldol condensation while 1,2-hydride shift similar to that observed during glucose-fructose
1
4, 15
21
the dehydration steps require Brønsted acids
. Here, Sn-Beta isomerization with Sn-Beta catalyst (step 6-8) . The erythrulose via
catalysts were synthesized by hydrothermal routes with uniform retro-aldol condensation to get DHA (step 9-11), and then the DHA
particle size about 1-2 μm and pore size of 3.9 nm (Figure S4 a, b). transform to LA over Sn-Beta catalyst.
After five times cycles test and regeneration, the catalyst kept a
relatively stable without the loss of Sn (Table S2 and S3). We
Conclusions
conducted several control experiments with Sn-Beta and SnCl
4
as
catalyst to identify the active catalytic species (Figure S5). The
results indicated that Sn-Beta catalyst giving as high as 70.0 % yield to result in an excellent yield of 70.0 % in water. A new conversion
In summary, the xylose over the Sn-Beta catalyst into LA was found
of LA at 200 °C for 1 h, whereas only 12.0 %, 12.0 % and 12.3 % yield route of glycolaldehyde (C ) → erythrose (C ) → LA (C ) was verified
2
4
3
1
3
was obtained from the SnCl
, deAl-Beta and Al-Beta, which by C NMR analysis. The Sn active sites in the framework Sn-O-Si
attributed to the strong Lewis acid of Sn and moderate Brønsted enolization glycolaldehyde by abstract α-proton and then generate
4
1
6
erythrose via aldol condition of glycolaldehyde, following, LA is
produced from erythrose through the isomerization and retro-aldol
condensation. Our research is promising for the highly efficient
acid in molecular skeleton (Figure S4 c) . The diffraction angle of
Sn-Beta was slightly shifted forward compare to Beta zeolite, which
indicated the metal species were introduced into zeolite framework
successfully (Figure S4 d) . The UV-vis (Figure S4 e) showed Sn-Beta
has a characteristic peak in the range of 210-230 nm, which means
Sn as the four-coordinate framework tin in the molecular sieve .
When Sn is inserted into the framework of zeolite, the covalent
bonds of Sn-O cause the formation of Lewis acid site on the Sn atom
because of the differences in electronegativity then generates
carbonium anions by hydride abstraction for cracking or addition
reactions . So, the role of Sn in the conversion of xylose especially
for C components into LA should be further verified.
In here, we employed glycolaldehyde, the C
1
7
5
utilize of C sugars into valued platform chemicals.
1
8
Conflict of interest
The authors declare no conflict of interest.
Acknowledgements
1
9
2
The financial support from the National Natural Science Foundation
of China (21978316) and the Ministry of Science and Technology of
China (2018YFB0604700).
2
intermediate
component for the conversion of xylose to LA, to propose reaction
pathways for the C-C coupling and breaking on Sn active sites
(Scheme 2). We assumed that the enolization process induce aldol
addition step over Sn-Beta catalyst, wherein the combination of Notes and references
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W. Deng, P. Wang, B. Wang, Y. Wang, L. Yan, Y. Li, Q. Zhang,
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framework Si-O-Sn ensemble to deprotonate glycolaldehyde .
Because of the polarization of the carbonyl group of glycolaldehyde
with the Lewis acidic framework Sn atom, the acidity of α-proton
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