Highly efficient conversion of biomass-derived glycolide to ethylene glycol over CuO in water

Article abstract of DOI:10.1039/c3cc49439j

The efficient conversion of biomass-derived glycolide into ethylene glycol over CuO in water was investigated. The reaction of glycolide was carried out with 25 mmol Zn and 6 mmol CuO with 25% water filling at 250 °C for 150 min, which yielded the desired ethylene glycol in 94% yield. the Partner Organisations 2014.

Full text of DOI:10.1039/c3cc49439j

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Highly efficient conversion of biomass-derived
glycolide to ethylene glycol over CuO in water†
Cite this: Chem. Commun., 2014,
0, 6009
5
Lingli Xu, Zhibao Huo,* Jun Fu and Fangming Jin
Received 12th December 2013,
Accepted 15th April 2014
DOI: 10.1039/c3cc49439j
www.rsc.org/chemcomm
The efficient conversion of biomass-derived glycolide into ethylene ethylene glycol by well-defined electron-rich bipyridine-based PNN
glycol over CuO in water was investigated. The reaction of glycolide [2-(di-tert-butyl-phosphinomethyl)-6-(diethylaminomethyl)pyridine]
9
was carried out with 25 mmol Zn and 6 mmol CuO with 25% water Ru(II) pincer complexes under mild conditions. However, these
filling at 250 8C for 150 min, which yielded the desired ethylene reactions still have considerable drawbacks, including the use of
glycol in 94% yield.
high-pressure gaseous hydrogen (10–50 atm), which is not easy to
obtain at a reduced energy cost; organic solvents (THF or
Ethylene glycol (EG) is an important intermediate chemical and 1,4-dioxane); expensive prepared catalysts (PNN-Ru); and longer
solvent that has been widely used in antifreeze, liquid detergents, reaction times (12–48 h). Therefore, the development of a
biodegradable polyester fibers, cosmetic products, pharmaceuticals, suitable reaction process for the production of ethylene glycol
explosives, and plasticisers, among other products and often as a from glycolide is highly desirable.
1
protecting group for carbonyl groups in organic synthesis. Because
Previously, we and other groups reported a series of experiments
10
11
of its industrial importance, the synthesis of ethylene glycol is of investigating the conversion of CO
2
and biomass into value-
considerable interest. The current conventional process involves added chemicals in high-temperature water. In this process, water
industrial production from petroleum-derived ethylene via hydration acts not only as an excellent environmentally benign reaction
2
of the intermediate ethylene oxide. However, over-consumption of medium but also as a source of hydrogen generated by the reduction
12
fossil fuels and their limited supply have necessitated a reduction in of cheap metal reductants. Recently, some research groups have
our dependence on petroleum oil and the development of renewable also reported that ZnO can be converted to Zn through a ZnO/Zn
3
13
and green energy sources. Over the past several decades, biomass as redox process using solar energy. On the basis of these findings, we
a source for producing high value-added chemicals has attracted reasoned that glycolide might produce ethylene glycol in a similar
much attention due to its excellent properties: it is abundant, manner. The results obtained showed that the hypothesis proved
4
renewable, and produces less pollution, among other advantages.
feasible, and the reaction of glycolide proceeded effectively in the
The conversion of biomass-derived carbohydrates into 1,2-diols is presence of CuO to give the desired ethylene glycol in high yield with
5
currently receiving increasing attention.
high selectivity (eqn (1)). The detailed results are reported herein.
The hydrogenation of esters to alcohols is an important reac-
6
tion in organic chemistry. However, the reaction of ester groups,
which have a less electrophilic carbonyl group, is still a great
challenge of both academic and practical importance, especially
for cyclic di-esters. To date, very few studies have reported this
(1)
7
transformation. Glycolides, important biomass-derived compounds,
can be obtained from biomass sources such as sugar cane, sugar-
beet, and immature grape juice. Recently, Milstein et al. reported tiveness of metal or metal oxides in the synthesis of ethylene glycol
Initially, we carried out an experiment to investigate the effec-
8
the hydrogenation of biomass-derived glycolide to the corresponding from glycolide in the presence of 6 mmol Cu and 20 mmol Zn at
2
50 1C for 150 min in water (water filling: 25%). The reaction
proceeded efficiently and produced the desired ethylene glycol in
3% yield, as determined by GC-FID and GC-MS (entry 4). The solid
residue remaining after the reaction was analysed by XRD (see ESI,†
Fig. S1–S3), which showed that Cu is still present in the solid
samples, while Zn was oxidised to ZnO. In this case, Zn acts as a
School of Environmental Science and Engineering, Shanghai Jiao Tong University,
00 Dongchuan Road, Shanghai 200240, China. E-mail: hzb410@sjtu.edu.cn;
Fax: +86-21-54742251; Tel: +86-21-54742251
Electronic supplementary information (ESI) available: Experimental details and
2
8
†
characterization data. See DOI: 10.1039/c3cc49439j
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a
Table 1 Effect of catalysts on the yields of ethylene glycol
The yield decreased as the amount of CuO was further
increased. This may be because more CuO would lead to more
cracking products such as acetic acid, CO and H O (eqn (2)),
b
Entry
Reductant
Catalyst
Yield (%)
2
2
1
2
3
4
5
6
7
8
9
—
Zn
—
—
—
0
9
0
23
0
0
14
10
10
0
0
45
37
15
which might result in a decrease in glycolide selectivity.
Cu
Cu
Fe
Co
Fe
Fe
Ni
TiO
ZrO
CuO
Cu
0
CH OH–CH OH + 5CuO(s) - 5Cu
+ 2CO2(g) + 3H O
2 (g)
2
2
(I)
(s)
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
(2)
2
3
2
O
O
O
3
4
3
Finally, a carbon balance was conducted. The results showed
that the conversion of glycolide for liquid products was approxi-
mately 98%. The main product observed for this transformation
was ethylene glycol, with a yield of 45%, other products included
acetic acid, which had a 5% yield, and unknown compounds, and
10
11
12
13
2
2
2
O
2
CO was the gaseous product observed in the transformation.
a
Reaction conditions: glycolide: 0.5 mmol; catalyst: 6 mmol; water filling:
5%; time: 150 min; temp.: 250 1C. The yield is calculated as the
percentage of ethylene glycol to the initial glycolide on the carbon base.
Experiments were performed using the various active metals,
b
2
such as Zn, Al, Fe, Mn, and Mg, to search for a suitable reductant
for the conversion of glycolide to ethylene glycol. Fig. 1(a) shows
the effect of different reductants on the yields of ethylene glycol.
Among the various metals tested, Zn was highly effective in the
conversion of glycolide and gave the best yield of ethylene glycol
reductant, and Cu acts as a catalyst for the conversion of glycolide.
Next, we screened various catalysts to determine the most suitable
one. The results are summarised in Table 1. The reaction did not
give the desired ethylene glycol at all in the absence of both the
reductant and the catalyst or in the presence of the catalyst only
(45%) compared to Al, Mg, Mn, and Fe. Thus, Zn was chosen for
the following experiments.
Fig. 1(b) shows the effect of the amount of Zn on the yield of
ethylene glycol, using concentrations from 0 to 30 mmol. No
ethylene glycol was observed without the addition of Zn. The
yields of ethylene glycol improved gradually as the amount of Zn
was increased from 0 to 15 mmol, then remarkably increased
from 15 to 25 mmol. The yield of ethylene glycol decreased
somewhat when the amount of Zn exceeded 25 mmol. The
results indicated that the improvement in hydrogen production
with an increased amount of Zn in high temperature water is
favourable for the conversion of glycolide to ethylene glycol.
The optimal amount of Zn was 25 mmol, yielding ethylene
glycol at a maximum value of 94%.
(
entries 1 and 3). The reaction in the presence of 20 mmol Zn,
without the addition of any catalyst, gave the desired ethylene glycol
in 9% yield (entry 2), indicating the importance of the combined
use of both the reductant and the catalyst. Among the various
catalysts we investigated (entries 5–13), Cu O and CuO improved
2
the transformation efficiency and afforded ethylene glycol in good
yield with no glycolide recovery observed by thin layer chromato-
graphy (TLC) (entries 12 and 13); CuO gave much better results.
A low yield was observed using the catalysts Fe
Ni (entries 7, 8 and 9), whereas no reaction occurred when the
catalysts Fe, Co, TiO , or ZrO were used (entries 5, 6, 10 and 11).
2 3 3 4
O , Fe O , and
2 3
O
2
2
The residual solid sample remaining after the reaction in the
presence of CuO and Zn was analysed by XRD. It can be seen that
Cu and ZnO existed in solid samples, as shown in Fig. S3 (ESI†).
Unexpectedly, Cu was observed in the solid sample instead of
CuO. From this result, we reasoned that CuO as a catalyst might
be reduced completely to Cu by in situ-formed hydrogen via the
oxidation of Zn in high-temperature water. We measured the Cu
ion concentration in the solution by ICP and found only a small
amount of Cu ions (o1 ppm) in the liquid sample. This result
suggested that Cu was most likely present in the solid residue.
Thus, we performed the experiment under the same reaction
conditions without the addition of glycolide to investigate the role
of in situ-formed hydrogen. The results suggested that our hypo-
thesis was completely realistic. CuO was reduced completely to Cu
by in situ-formed hydrogen, and Cu and ZnO were found in the
solid samples by XRD analysis after the reaction.
The effect of water filling on the yield of ethylene glycol from
glycolide was investigated at different water filling values from
15% to 45% with the addition of 6 mmol CuO and 25 mmol Zn
at 250 1C for 150 min. The results are shown in Fig. S5 (ESI†).
First, the ethylene glycol yield increased slightly when the water
filling was changed from 15% to 20%. The yield of ethylene glycol
significantly increased as the water filling increased from 15% to
14
25% and then decreased after 25%. The optimum water filling
was 25% obtaining the highest yield of 94% ethylene glycol from
glycolide. The decrease in conversion of glycolide at a higher
Next, we investigated the effect of the amount of CuO on the
yield of ethylene glycol. The reaction was conducted in the
presence of 20 mmol Zn with 25% water filling at 250 1C for
1
(
50 min and 3 to 12 mmol CuO, the results are shown in Fig. S4
ESI†). The yield of ethylene glycol increased significantly at
first as the amount of CuO increased from 0 to 6 mmol, and the
best yield of 45% ethylene glycol was achieved at 6 mmol CuO. 250 1C; water filling: 25%).
Fig. 1 (a) Effect of reductants (glycolide: 0.5 mmol; metal: 20 mmol; CuO:
6
mmol; water filling: 25%; time: 150 min; temp.: 250 1C). (b) The effect of the
amount of Zn (glycolide: 0.5 mmol; CuO: 6 mmol; time: 150 min; temp.:
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then the intermediate acquired one more H from the surface of
Cu/CuO and the desired ethylene glycol was obtained.
Following the success in developing the conversion of
glycolide to ethylene glycol in high temperature water, we next
examined the scope of the reaction with respect to DL-lactide,
and the results are shown in eqn (3). The reaction of DL-lactide
was carried out in the presence of 25 mmol Zn and 6 mmol Cu
with 25% water filling at 250 1C for 150 min and gave the
desired 1,2-propanediol in an 84% yield.
Scheme 1 Proposed mechanism for the formation of ethylene glycol.
(3)
water filling is most likely due to the decreased concentration of
the initial starting materials when water filling increased.
The effect of different temperatures from 100 to 250 1C on the
yields of ethylene glycol was examined. The results are shown in
Fig. S6(A) (ESI†). The reaction did not take place at 100 1C, and no
ethylene glycol was observed. This finding indicated that a lower
reaction temperature was completely ineffective in the conversion of
glycolide. The yield of ethylene glycol improved gradually as the
reaction temperature was increased gradually from 100 1C to 200 1C,
and then remarkably increased as the temperature increased from
In summary, we first developed a highly efficient conversion
for the synthesis of ethylene glycol from biomass-derived
glycolide over CuO in high temperature water. With optimized
conditions in hand, the maximum value of 94% ethylene glycol
was achieved in the presence of 25 mmol Zn and 6 mmol CuO
with 25% water filling at 250 1C for 150 min. The conversion of
DL-lactide also produced 1,2-propanediol in 84% yield under
optimal reaction conditions. This study provided a significant
process for the conversion of biomass-derived cyclic di-esters to
1,2-diols with high selectivity and high yield. Further research is
200 to 250 1C. The maximum value of 94% ethylene glycol was
underway to develop efficient methods for the conversion of
biomass-derived compounds to value-added chemicals in water.
The authors gratefully acknowledge the financial support from
the Program for Professor of Special Appointment (Eastern Scholar)
at Shanghai Institutions of Higher Learning (ZXDF160002). The
Project sponsored by SRF for ROCS, SEM (BG1600002) is also
acknowledged. We thank all reviewers and the editor for reviewing
the manuscript and providing valuable comments.
obtained at 250 1C. However, the temperature was limited to 250 1C
due to the maximum tolerated temperature of the Teflon material.
Experiments were performed by changing the reaction time from
100 to 300 min at 250 1C to examine the effect of reaction time on
the yield of ethylene glycol. Fig. S6(B) (ESI†) indicates that the yield
increased drastically with increasing reaction time for the first
150 min, the maximum yield was obtained at 150 min, with a value
of 94%. However, the yield of ethylene glycol decreased as the time
was further increased. The decreased yield of ethylene glycol after
Notes and references
150 min can be attributed to the decomposition of produced
ethylene glycol. To confirm this assumption, the reaction of ethylene
glycol was performed in the presence of 6 mmol Cu and 25 mmol
ZnO with 25% water filling at 250 1C for 300 min. The GC-FID
results indicated that the initial concentration of ethylene glycol
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