Efficient and selective conversion of glycidol to 1,2-propanediol over Pd/C catalyst

Article abstract of DOI:10.1016/j.catcom.2016.01.026

The present work deals with the catalytic hydrogenolysis of glycidol to 1,2-propanediol. Reactions were carried out in a closed steel reactor using noble metal based heterogeneous catalysts (Pd, Rh, Pt) under hydrogen pressure (1-8 bars) in the temperature range of 25-140°C. Pd/C shows the highest glycidol conversion (96%) under solvent free conditions after 24 h with high selectivity to 1,2-propanediol (93%). The effect of the solvent was also investigated and it was demonstrated that ethanol reduces drastically oligomer production enhancing selectivity up to 99% with a significant reaction time reduction (6 h). The Pd/C catalyst shows high recyclability and could be reused several times (9 cycles) without losses in activity and selectivity.

Full text of DOI:10.1016/j.catcom.2016.01.026

Catalysis Communications 77 (2016) 98–102
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short communication
Efficient and selective conversion of glycidol to 1,2-propanediol over
Pd/C catalyst
a
a
a
a,
b
Raffaele Cucciniello , Concetta Pironti , Carmine Capacchione , Antonio Proto ⁎, Martino Di Serio
a
Dipartimento di Chimica e Biologia, Università degli Studi di Salerno, Via Giovanni Paolo II, 132-84084 Fisciano, SA, Italy
Dipartimento di Chimica, Università di Napoli “Federico II”, Complesso Universitario Monte S. Angelo, Via Cintia 4, 80126 Napoli, Italy
b
a r t i c l e i n f o
a b s t r a c t
Article history:
The present work deals with the catalytic hydrogenolysis of glycidol to 1,2-propanediol. Reactions were carried
out in a closed steel reactor using noble metal based heterogeneous catalysts (Pd, Rh, Pt) under hydrogen
pressure (1–8 bars) in the temperature range of 25–140 °C. Pd/C shows the highest glycidol conversion (96%)
under solvent free conditions after 24 h with high selectivity to 1,2-propanediol (93%). The effect of the solvent
was also investigated and it was demonstrated that ethanol reduces drastically oligomer production enhancing
selectivity up to 99% with a significant reaction time reduction (6 h). The Pd/C catalyst shows high recyclability
and could be reused several times (9 cycles) without losses in activity and selectivity.
Received 19 October 2015
Received in revised form 20 January 2016
Accepted 25 January 2016
Available online 26 January 2016
Keywords:
Glycidol
Diols
© 2016 Published by Elsevier B.V.
Heterogeneous catalysis
Hydrogenolysis
1
. Introduction
The future of humanity is in the sustainable development which is
has been successfully employed in glycerol hydrogenolysis to 1,2-PD
both in the presence and in the absence of added hydrogen [12,13].
Generally, 1,2-PD is derived from propylene oxide [14], moreover,
alternative synthetic routes have been investigated such as vapor
phase catalytic hydrogenation of lactic acid [15]. 1,3-PD is currently pro-
duced from ethylene oxide (Shell route) or acrolein (Degussa–DuPont
route) by catalytic routes.
strictly linked with the reduction of the use of non-renewable re-
sources. This trend is nowadays highlighted by legislative interventions
that favor or impose the use of bio-resources (see for example in
European Directive 2009/28/EC about renewable energy and Horizon
2
020 Program about research investments). In this framework a great
industrial development has been obtained in the biodiesel production
22.5 billion liters were produced worldwide in 2012 [1]). The biodiesel
Both 1,2-PD and 1,3-PD are value added products used in many
applications therefore the synthesis of these chemicals from glycerol
by using less harsh reaction conditions is a highly desirable target. In
this scenario the use of alternative path to obtain the desired diols
from glycerol seems to be a promising strategy. Indeed the hydrogena-
tion of glycidol can give the desired diols in good yield under moderate
reaction conditions. Glycidol can be obtained from glycerol by different
ways (see Scheme 1) by decarboxylation of glycerol carbonate [10] or by
basic treatment of monochlorohydrins [16].
Monochlorohydrins can be obtained by selective hydrochlorination of
glycerol [17] or by hydrolysis of epichlorohydrin [18]. Despite glycerol
carbonate is an interesting product for the industrial chemistry its
practical application is still under development [19], on the contrary
the production of epichlorohydrin from glycerol is now an important in-
dustrial reality [2].
(
is mainly produced by transesterification of triglycerides with metha-
nol. A co-product of biodiesel is glycerol and today around 2 million of
ton of glycerol are on the market. The glycerol glut has produced a
reduction in glycerol price with a strong consequence on the economic
sustainability of biodiesel production. However this situation has
put on the market a new cheap raw material and a great number of
new uses of glycerol has been proposed [2,3]. The production of
propanediols (1,2 propanediol (1,2-PD) and 1,3 propanediol (1,3-PD))
by hydrogenolysis of glycerol has received particular attention [4–9].
The reaction of hydrogenolysis of glycerol is characterized by the
necessity of high hydrogen pressure (1–25 MPa), high reaction temper-
ature (400–500 K), and also by problems related with the selectivity
(
1,2-PD, 1,3-PD, 1 Propanol, 2 Propanol, ethylene glycol, ethanol can
The production of glycidol could be integrated in the epichlorohy-
drin plant also to solve the low reactivity of 2-chloro-1,3-propanediol
in the formation of dichlorohydrins [16]. As a matter of fact the rate of
conversion of this product to dichlorohydrins is very low and to avoid
its accumulation a purge of the recirculation stream is necessary in
the epichlorohydrin industrial plant. The purge stream is rich of
monochlorohydrins that can be recovered by hydrolysis to glycerol or
be formed in the hydrogenolysis reaction) [10,11]. Pd based catalyst
⁎
Corresponding author at: University of Salerno, Via Giovanni Paolo II, 132-84084
Fisciano, SA, Italy.
E-mail address: aproto@unisa.it (A. Proto).
http://dx.doi.org/10.1016/j.catcom.2016.01.026
1566-7367/© 2016 Published by Elsevier B.V.

R. Cucciniello et al. / Catalysis Communications 77 (2016) 98–102
99
Scheme 1. Reaction pathway for glycerol conversion to epichlorohydrin.
in the new proposed process that can be converted to glycidol. It can be
estimated that in an epichlorohydrin industrial plant (from the kinetics
of the hydrochlorination reactions [16]) around 5% of glycidol in respect
to production of epichlorohydrin can be produced by this way. This
means, for example, that an industrial plant of 100,000 tons/y of epi-
chlorohydrin can produce 5000 tons/y of glycidol, and consequently
the same quantity of propanediols.
toluene, tetrahydrofuran, ethanol, methanol, hexane, diethyl ether,
dichloromethane) has been investigated.
2. Material and methods
2.1. Materials
There aren't many data about glycidol hydrogenation, however in a
patent application [20], it has been shown that the hydrogenation of
glycidol can give place to high yield of 1,3 propanediol (50–65%) using
mild reaction conditions 0.8–1.6 MPa, 373 K, metal based catalysts (Ni,
Co, Ru) and solvents. Furthermore, a single reaction is reported by Sajiki
et al. [21] where an efficient selective conversion (89% yield) of glycidol
to 1,2-propanediol (selectivity100%) is obtained using Pd/C-
ethylenediamine complex in methanol for 22 h at a hydrogen pressure
of 1 bar using a glycidol/catalyst weight ratio of 10 (calculated TOF =
The catalysts used in this work were purchased from Sigma-
Aldrich (5% Rh/C, 10% Pt/C, 10% Pd/C, 0.5% Rh/Al
0.5% Pd/Al ). Glycidol 96%, 1,2-propanediol 99.5%, 1,3-propanediol
98%, Al and activated charcoal were purchased from Sigma-Aldrich.
2 3 2 3
O , 0.5% Pt/Al O ,
2 3
O
2 3
O
All the solvents were distilled before reactions and the catalysts were
not pretreated before reaction.
2.2. Catalytic reactions
−
1
2
.9 h ).
Noble metals based heterogeneous catalysts (Pd, Rh, Pt) are
Solvent free hydrogenation of glycidol was carried out in a pressure
reactor (maximum operation pressure 8 bars) of 150 mL capacity
equipped with a pressure gauge, safety valve, valves for gas inlet
and outlet and a thermometer for temperature sensing. Glycidol
(96% of purity, Sigma-Aldrich) was distilled before the experiments.
Reactor was equipped with glass vials containing 5 mL of glycidol, an
appropriate catalyst amount in order to obtain a glycidol/catalyst mass
ratio of 100 and a magnetic stirrer. Experiments were carried out
commonly preferred in hydrogenation reactions and in the reductive
ring-opening of epoxides to the corresponding alcohols [22,23].
In this paper a systematic catalytic screening has been done to
individuate the best catalyst for glycidol hydrogenation under
solvent free conditions. Moreover the effect of reaction conditions
(
temperature, time, hydrogen pressure) and of the solvent (chloroform,
Table 1
Glycidol hydrogenation under solvent free conditions .
a
Experiment
Catalyst/support
Conversion (%)
TOFd (h−1
)
1,2-propanediol (%)
1,3-propanediol (%)
Oligomers (%)
1
2
3
4
5
6
7
8
9
No catalyst
13.8
65.1
59.0
37.8
95.2
96.1
96.7
89.6
95.4
–
b1
b1
b1
b1
b1
1.8
b1
2.7
b1
b1
N99
25.3
19.8
42.8
77.2
6.7
28.4
99.0
99.2
b
Rh/Al
Pd/Al
Pt/Al
2
O
O
2 3
O
2 3
3
4.1
3.9
4.5
6.3
6.6
8.1
–
74.5
79.6
56.9
21
93.1
68.9
b1
b
b
c
Rh/C
c
Pd/C
c
Pt/C
c
C
c
Al
2
O
3
–
b1
a
Reaction conditions.
b
1
.0 g of catalyst, 0.5 mL of glycidol, 8 bars H
.5 g of catalyst, 5 mL of glycidol, 8 bars H , 80 °C, 24 h.
TOF was calculated considering all the metal sites on the surface active in catalysis, in such a way the reported TOF is the lowest possible.
2
, 80 °C, 24 h.
c
0
2
d

100
R. Cucciniello et al. / Catalysis Communications 77 (2016) 98–102
2
Fig. 1. Effect of temperature on glycidol conversion (reaction conditions: 0.5 g of Pd/C, 5 mL of glycidol, 8 bars H , 24 h).
under hydrogen pressure of 8 bars at 80 °C for 24 h. Catalyst was
removed by filtration and the reaction products were purified on celite
before GC-FID analysis.
components. The conversion and selectivity of glycidol were calcu-
lated on the basis of Eqs. (1) and (2):
Glycidol hydrogenation was also carried out using solvents in
order to evaluate their effect on the reaction time and selectivity. In
these experiments 5 mL of distilled solvent and 1 mL of purified
glycidol and substrate were used and catalyst mass ratio was
maintained at 100. Experiments were carried out at 80 °C for 24 h
under magnetic stirrer (300 rpm). Products were purified on celite
and solvent removed using a rotary evaporator before GC analysis.
The samples were prepared for the analysis by diluting 0.1 mL of
product sample to a final volume of 10 mL with ethanol in a glass vial.
Gas chromatographic analysis was carried out using a Thermo
Trace GC equipped with a 30 m × 0.32 mm polar column Famewax.
The initial oven temperature was initially 40 °C then programmed
to 200 °C at 10 °C/min and held at 200 °C for 5 min with He flow
rate of 1.2 mL/min and splitless injection mode was used. FID tem-
perature was 250 °C while 230 °C for the inlet. The integrated areas
were converted to weight percentages for each component present
in the sample using the calibration curves prepared for all the
moles of reacted glycidol
moles of glycidol feed
Glycidol conversion ½%ꢀ ¼
Glycidol selectivity ½%ꢀ ¼
ꢁ 100
ð1Þ
ð2Þ
moles of defined product
moles of reacted glycidol
ꢁ 100:
The relative standard deviation of three replicates was lower than 4%
in all cases.
3. Experimental
3.1. Results and discussion
3.1.1. Catalytic screening and reaction condition optimization
A preliminary catalytic screening in the hydrogenolysis of glycidol is
performed in the presence of heterogeneous catalysts based on noble
metals (Pd, Pt and Rh) commonly used for hydrogenation reactions
2
Fig. 2. Glycidol conversion using Pd/C catalyst (0.5 g Pd/C, 5 mL glycidol, 80 °C, 8 bars H ).

R. Cucciniello et al. / Catalysis Communications 77 (2016) 98–102
101
Table 2
Glycidol hydrogenation using Pd/C .
hydrogenations were carried out also at 1, 5 and 8 bars maintaining
the temperature constant at 80 °C. As expected, the conversion of
glycidol increased from 40% to 96% as the hydrogen pressure increased
from 1 to 8 bars. It is worth noting that both the pressure (8 bars) and
temperature (80 °C) requested for the efficient conversion of glycidol
to 1,2-PD in the presence of 10wt.% Pd/C are decisively milder than
those reported in literature (10–30 bars and 200 °C) for the direct con-
version of glycerol to 1,2-PD. [5,25].
In addition the effect of the reaction time using Pd/C, under the
optimized temperature of 80 °C and hydrogen pressure of 8 bars, was
also studied in the range of 3–24 h. As evidenced in Fig. 2 the conversion
increases up to a value of 96.0% after 24 h while selectivity toward
1,2-PD is retained.
a
Solvent
Conversion 1,2-propanediol 1,3-propanediol Oligomers
(
%)
(%)
(%)
Tetrahydrofuran
Chloroform
Toluene
Ethanol
Diethyl ether
93.2
52.5
99.9
99.2
99.7
95.6
28.7
99.7
99.2
98.9
99.1
98.9
98.0
0.7
0.7
0.2
0.4
0.8
0.7
0.9
0.5
3.7
70.6
b1
0.4
b1
b1
b1
1.5
Dichloromethane 98.3
Methanol
Hexane
97.7
99.4
a
2
Reaction conditions: 0.1 g of catalyst, 1 mL of glycidol, 5 mL solvent, 8 bars H ,
8
0 °C, 24 h.
under solvent free conditions and the results are summarized in Table 1.
Glycidol is conveniently hydrogenolyzed under a hydrogen pressure of
3.1.2. The effect of the solvent using Pd/C
With the aim to reduce the formation of oligomers we also inves-
tigated the glycidol hydrogenolysis using Pd/C at 80 °C and 8 bars
using various solvents as reaction medium. Therefore, the reactions
were carried out in different solvents (chloroform, toluene, tetrahy-
drofuran, ethanol, methanol, hexane, diethyl ether, dichloromethane)
for 24 h. Results of these experiments are reported in Table 2.
In all the used solvents, apart from chloroform where, probably,
HCl impurities promote glycidol oligomerization, the conversion of
glycidol is quantitative and at the same time a drastic reduction of
the oligomer production is observed. Thus, under these conditions,
the selectivity to 1,2-PD increased up to a value of 99%.
As reported in Fig. 2, glycidol oligomers under solvent free condi-
tions, were formed in the first hours of reaction, and consequently
the by-product production reduces the catalytic activity.
From an environmental point of view, based on its green charac-
teristic [26], ethanol was chosen as solvent for a kinetic study.
Besides, as shown in Fig. 3, the use of ethanol considerably shortens
the reaction time (6 h vs. 24 h) to achieve the complete conversion of
glycidol to 1,2-PD. Remarkably, the performances of our catalytic
system are one order of magnitude higher than those reported in lit-
8
bars for 24 h at 80 °C. One can observe that the best results in terms of
conversion and selectivity are obtained in the presence of the palladium
and platinum based catalysts (entries 6 and 7). In particular, using
1
0 wt.% Pd/C the substrate is quantitatively converted, with high selec-
tivity, to 1,2-PD, (93.1%). Notably, at this temperature the main
byproduct is due to the oligomerization via epoxide opening of glycidol
[24]. This reaction is catalyzed by the nucleophilic attack of both acid
(
charcoal) or basic (alumina) substrates (see entries 8 and 9) forming
13
mainly dimers as evidenced by C NMR analysis (see Fig. S3). Under
these conditions, 1,3-PD is obtained only in very small amount with a
maximum observed for the Pt/C catalyst (2.7%).
Owing the good performances in terms of conversion and selectivity
to 1,2 PD of the 10% Pd/C we focus our investigation on this system,
characterized by using XRD, TEM and BET analyses (See also Supporting
information). Indeed, in order to evaluate the effect of temperature
on the conversion and selectivity, the reactions were carried under
solvent-free conditions at 25, 50, 80, 100 and 140 °C, under 8 bars of
hydrogen pressure for 24 h. The effect of temperature on the conver-
sion of glycidol to 1,2-PD is shown in Fig. 1 (See also Supporting
information).
−
1
erature [21] in terms of productivity with a calculated TOF of 27 h
.
On one hand, the temperature has a significant effect on the overall
yield of the 1,2-PD with an increase from 45% to 96% in the conversion
passing from 25°to 80 °C maintaining a good selectivity toward 1,2-PD
this range (around 90%). On the other hand, a further increase results
in a severe loss of selectivity (66% at 100 °C and to 4% at 140 °C) with
glycidol oligomers becoming the main product. In order to study
the effect of the hydrogen pressure on the overall reaction the
3.1.3. Recycling of the catalyst
The 10% Pd/C catalyst is stable and retains high efficiency in the
hydrogenation of glycidol in ethanol during nine consecutive catalytic
cycles maintaining good conversion (99%) and selectivity to 1,2-PD
(96.9%) and resulting in a drop of the catalytic performance only at
tenth cycle (89%) as shown in Fig. 4. The catalyst could be recovered
2
Fig. 3. Glycidol hydrogenation using Pd/C in ethanol (reaction conditions: 1 mL of glycidol, 5 mL of ethanol, 0.1 g of Pd/C, 80 °C, 8 bars H ).

102
R. Cucciniello et al. / Catalysis Communications 77 (2016) 98–102
2
Fig. 4. Stability of the Pd/C catalyst (reaction conditions: 1 mL of glycidol, 5 mL of ethanol, 0.1 g Pd/C, 6 h, 80 °C, 8 bars H ).
almost quantitatively following simple filtration of the catalyst, washing
with EtOH and drying. For all the experiments performed, carbon
balance based on the carbon content in the unconverted glycidol and
in the hydrogenation products is systematically calculated and is in all
cases higher than 95%.
References
[
1] R. Kotrba, Global biodiesel production rises slightly, Biodiesel Mag. 2014 (2012)
http://www.biodieselmagazine.com).
[2] M. Pagliaro, R. Ciriminna, H. Kimura, M. Rossi, C. Della Pina, Angew. Chem. Int. Ed. 46
2007) 434–444.
(
(
[
3] J.J. Bozell, G.R. Petersen, Green Chem. 12 (2010) 539–554.
[
4] Ed de Jong, Bio-based chemicals value added products from biorefineries, IEA
Bioenergy, Task 42 Biorefinery, 2012.
5] Z. Yuan, J. Wang, L. Wang, W. Xie, P. Chen, Z. Hou, X. Zheng, Bioresour. Technol. 101
4
. Conclusions
[
(
2010) 7088–7092.
In this work, a new, promising root to produce 1,2-propanediol
[
6] Y. Nakagawa, M. Tamura, K. Tomishige, J. Mater. Chem. A 2 (2014) 6688–6702.
through glycidol catalytic hydrogenation is reported. This synthetic
strategy could be integrated in the epichlorohydrin plant solving the
problem of low reactivity of 2-chloro-1,3-propanediol. For the first
time, a systematic catalytic screening is conducted, using noble metal
based catalysts, for the hydrogenolysis of glycidol. Results show that
under solvent free conditions at 80 °C Pd/C is highly selective (93%)
for the production of 1,2-propanediol at conversions of glycidol of
[7] A. Bienholz, F. Schwab, P. Claus, Green Chem. 12 (2010) 290–295.
[8] D.G. Lahr, B.H. Shanks, J. Catal. 232 (2005) 386–394.
[
9] Y. Feng, C. Liu, Y. Kang, X. Zhou, L. Liu, J. Deng, H. Xu, Y. Fu, Chem. Eng. J. 281
2015) 96–101.
10] C.-H. Zhou, J.N. Beltramini, Y.-X. Fana, G.Q. Lu, Chem. Soc. Rev. 37 (2008) 527–549.
[11] Y. Nakagawa, K. Tomishige, Catal. Sci. Technol. 1 (2011) 179–190.
(
[
[
12] F. Mauriello, H. Arig, M.G. Musolino, R. Pietropaolo, S. Takakusagi, K. Asakura, Appl.
Catal. B Environ. 166-167 (2015) 121–131.
13] M.G. Musolino, L.A. Scarpino, F. Mauriello, R. Pietropaolo, ChemSusChem 4 (2011)
1143–1150.
14] R. Perrin, J.P. Scharff, Chimie Industrielle, Masson, 1993.
15] R.D. Cortright, M. Sanchez-Castillo, J.A. Dumesic, Appl. Catal. B Environ. 39 (2002)
[
9
6%. The effects of the solvent, temperature, hydrogen pressure and
[
[
the reaction time were also investigated giving useful insights for the re-
action system optimization. As a matter of fact, solvent plays a crucial
role inhibiting glycidol oligomer production with a consequential in-
crease of the selectivity to 1,2-PD up to 99% and reduces the reaction
time. In particular, using ethanol as solvent, glycidol conversion pro-
353–359.
[16] T.H. Rider, A.J. Hill, J. Am. Chem. Soc. 52 (4) (1930) 1521–1527.
[
[
17] E. Santacesaria, R. Tesser, M. Di Serio, L. Casale, D. Verde, Ind. Eng. Chem. Res. 49 (3)
2010) 964–970.
(
18] K. Weissermel, H.-J. Arpe, Industrial Organic Chemistry, Wiley-VCH, Weinheim,
−
1
ceeds in only 6 h with a TOF value (27 h ). Finally, the Pd/C catalyst
shows, under optimized reaction conditions, also high recyclability
being reused several times without losses in activity and selectivity.
Germany, 2003.
[19] J.R. Ochoa-Gomez, O. Gomez-Jiménez-Aberasturi, C. Ramírez-Lopez, M. Belsué, Org.
Process. Res. Dev. 16 (2012) 389–399.
[
20] Y. Kadowaki, M. Kaneda, H. Uchida, Catalyst for Producing Both End-hydroxyl
Group-terminated Diols, Process for Producing the Catalyst, Process for Producing
the Diols by Using the Catalyst, and Both End-hydroxyl Group-terminated Diols
Obtained by the Process, 2007, US7230145.
Acknowledgments
[
[
21] H. Sajiki, K. Hattori, K. Hirota, Chem. Commun. (1999) 1041–1042.
22] A. Proto, R. Cucciniello, A. Genga, C. Capacchione, Catal. Commun. 68 (2015) 41–45.
This work was financially supported by research fund “FARB 2013”,
University of Salerno (ORSA 133584). Authors are indebted with Dr.
Maurizio Celentano and Dr. Patrizia Oliva for technical assistance.
[23] E. Thiery, J. Le Bras, J. Muzart, Green Chem. 9 (2007) 326–327.
[
24] R. Tokar, P. Kubisa, S. Penczec, A. Dworak, Macromolecules 27 (1994) 320–322.
[
25] M.A. Dasari, P. Kiatsimkul, W.R. Sutterlin, G.J. Suppes, Appl. Catal. A Gen. 281 (2005)
225–231.
Appendix A. Supplementary data
[26] C. Capello, U. Fischer, K. Hungerbuhler, Green Chem. 9 (2007) 927–934.
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.catcom.2016.01.026.