Journal of Environmental Protection, 2010, 1, 201-205
doi:10.4236/jep.2010.12024 Published Online June 2010 (http://www.SciRP.org/journal/jep)
1
Catalytic Dehydration of Glycerol under Mild Condition: An
Environmentally Benign Acrolein Production
Ágnes Zsigmond1, Péter Bata1, Mónika Fekete1, Ferenc Notheisz2
1Department of Organic Chemistry, University of Szeged, Szeged, Hungary; 2Organic Catalysis Research Group of the Hungarian
Academy of Sciences, University of Szeged, Szeged, Hungary.
Received February 8th, 2010; revised March 29th, 2010; accepted March 31st, 2010.
ABSTRACT
The increase of biodiesel production results in the accumulation of glycerol, which requires an increasing demand to-
wards the study of chemical application of glycerol. Glycerol has to be transformed to other valuable chemicals, which
can be used as starting materials for organic synthesis. With the final goal to find a reasonable solution for this prob-
lem we have studied the dehydration of glycerol in liquid phase using a supported HPA catalyst and developed an en-
vironmentally benign production of acrolein. Our method does not have any extreme conditions and produces a total
conversion with high (93%) selectivity.
Keywords: Consuming of Excess Glycerol, Production of Acrolein, Heterogeneous Method
1. Introduction
Since people around the world almost exclusively cover
its increasing energy demand with fossil basic materials
(crude oil, natural gas, coal), sooner or later we are going
to run out of these materials. To avoid this situation, the
only possibility is to use biomass as a carbon source for
the synthesis of fuels [1]. However, the use of biomass
industrially in economically relevant chemical synthesis,
new processes have to develop so that crude oil can be
substituted [2]. Crude oil can be substituted by biodiesel
where rape-oil is converted with methanol.
However, there is a problem accompanying the bio-
diesel production, namely the increase of the production
of glycerol as a by-product, which can cause environ-
mental and economical problems, as well. The effective
utilization of this byproduct will be a key issue to pro-
mote the bio-diesel commercialization. Consequently an
increasing demand has been developed towards the study
of chemical application of glycerol to other valuable
chemicals, which can be used as starting materials for
organic synthesis [3].
One of the possibilities is to perform an acid-induced
dehydration of glycerol to acrolein, as it can be seen in
Scheme 1.
CH2
CH
CH2
OH
OH
OH
HPA
CH
CH
CH2
O
+2 H2O
Scheme 1. Heteropolyacid catalyzed dehydration of glycerol to
acrolein
Acrolein is an important chemical intermediate so it is
very important to develop a sustainable and cost-
effective production route via glycerol from biodiesel,
which offers an alternative for the presently dominating
petrochemical process based on propylene.
The dehydration of glycerol to acrolein became a rela-
tively well studied subject recently, when the biodiesel
production started to grow. However, most of these
works applying drastic conditions, e.g. the dehydration of
glycerol in sub- and supercritical water. Bühler et al.
found only low glycerol conversion (31%) and similar
selectivity (37 mol%) meanwhile they used relatively
high pressure (25-45 MPa) and temperature (300-400oC)
[4].
Ramayya et al. have studied the effect of the addition
of sulfuric acid on the dehydration of glycerol and found
that the addition of acid dramatically enhances the ac-
rolein yield [5]. They have also used high temperature
(300-350oC) and pressure (34.5 MPa) and the obtained
acrolein conversion was not too high. The other disad-
vantage of this method was the application of the highly
corrosive sulfuric acid.
Meanwhile it was proven that high reaction tempera-
ture was necessary for the dehydration of glycerol, since
no acrolein formation was detected at 250oC, 34.5 MPa
using sulfuric acid as a catalyst [6].
Some other work can be found dealing with gas phase
dehydration of glycerol on mesoporous ZSM-5 [7], or
Nb2O5 catalyst [8], but either the low selectivity or the
expensive catalyst makes these methods practically un-

Catalytic Dehydration of Glycerol under Mild Condition: An Environmentally Benign Acrolein Production 202
applicable.
H. Atia, et al. have also studied the gas phase dehydra-
tion of glycerol to acrolein using different supported
HPA, as catalysts [9,10]. The influence of selected sup-
port materials, catalyst loading and reaction temperature
on acrolein formation was studied at standardized reac-
tion conditions. Alumina was found to be superior to
silica as support material with regard to catalyst activity
and selectivity.
Some other works were dealing with also the gas
phase dehydration of glycerol using zirconia and silica
supported heteropoly acid catalysts [11-13]. The authors
compared the different catalyst preparation methods and
they found that independently of the preparation history
of ZrO2, the Keggin-anion at the catalyst surface ap-
peared as a key to the selectivity for acrolein production.
Acrolein selectivity as high as 70 mol% was obtained
over the catalysts having the intermediate densities
(0.18-0.65 HPA nm-2).
The dehydration of glycerol to produce acrolein was
performed over several solid acids [14,15]. Supported
heteropoly acids were effective catalysts for the dehydra-
tion of glycerol. The catalytic activity depended on the
types of heteropoly acid and on the size of the mesopores
in the silica support. Silicotungstic acid supported on
silica with mesopores of 10 nm showed the highest cata-
lytic activity with the acrolein selectivity of > 85 mol%
at an ambient pressure and 275°C.
According to our knowledge there is no environmen-
tally benign process for the utilization of the excess
glycerol. With the final goal to develop an environmen-
tally benign production of acrolein, we have prepared a
supported HPA catalyst and studied the dehydration of
glycerol in liquid phase. For our study relatively mild
conditions were selected and a new heterogeneous cata-
lyst, which could replace the very corrosive sulfuric acid
in this process.
2. Experimental
2.1 Catalyst Preparation
7.0 g of Al2O3 was suspended in 30 mL of methanol with
stirring. 1.93 g (0.67 mmol) of phosphotungstic acid hy-
drate (PTA) was dissolved in 25 mL of methanol and this
solution was added dropwise into the alumina suspension
with efficient stirring. The stirring was continued for an
additional hour at room temperature, under an Ar at-
mosphere. The solution was removed from the solid ma-
terial and the solid residue was washed with methanol
several times to remove the weakly adsorbed PTA from
the surface of Al2O3.
The prepared catalyst was characterized by FT-IR
spectroscopy, taking the spectrum of the phosphotungstic
acid hydrate and the anchored PTA/Al2O3, as well. The
FT-IR spectra were recorded on a Bio-Rad FTS–65 A
spectrophotometer, in the range of 400-4000 cm-1, in KBr
pellets.
2.2 Dehydration Experiments
The reaction was carried out in a two neck round-bottom
flask, equipped with a dropping funnel and a column.
The dried catalyst (8.93 g) was suspended in 70 ml high
boiling point solvent (diesel oil) in a round-bottom flask
and was heated gradually to 300oC with efficient stirring.
To keep the high temperature, the flask was covered with
glass wool. The column was connected to a distillation
apparatus and the distilled product was collected in a
flask, cooled by ice. Having reached the suitable tem-
perature 10 mL (0.13 mol) of glycerol was dropped
slowly, meanwhile the product was distilled out. The
two phase product was separated and the organic phase
was dried by MgSO4. The water phase was extracted by
ether and the product distribution of both phases was
determined by HP 5890 GC, using HP1 column and
ethanol inert standard.
3. Results and Discussion
3.1 Catalyst Characterization
With the final goal of developing an environmentally
friendly process for the utilization of glycerol, which was
produced in a large excess in the biodiesel production,
we have anchored the phosphotungstic acid hydrate on
Al2O3 support. The prepared catalyst was characterized
by FT-IR spectroscopy, taking the spectrum of the free
phosphotungstic acid hydrate and the anchored PTA, as
well (Figure 1).
The comparison of the two spectra above shows con-
vincingly that the “free” acid and the heterogenized sam-
ples have several similar bands (1090 and 890 cm-1),
indicating the anchoring of the same acid.
3.2 Dehydration Experiments
The preliminary experiments were done using H3PO4/
Al2O3 catalyst, which was prepared according to a patent
description [16]. For the preparation of acrolein the same
protocol was used as described in the patent and our pre-
liminary experiments showed an increase in acrolein se-
lectivity with increasing temperature. The dehydration
reaction has not started below 240oC, and it seems that a
good acrolein production needs at least 280oC or even
higher temperature. In other words, the most difficult
problem in the laboratory to find a good, neutral solvent
with a high boiling point. We have tried several solvents
e.g. triglykoldimethyl ether, methyldiglykol-tert-butyl
ether and finally a distilled fraction of diesel oil was se-
lected.
Based on data of our preliminary experiments and

Catalytic Dehydration of Glycerol under Mild Condition: An Environmentally Benign Acrolein Production 203
Figure 1. The FT-IR spectra of the “free” and anchored phosphotungstic acid hydrate
Table 1. Comparison of H3PO4/Al2O3 and H3[P(W2O10)4]/Al2O3 catalysts
Catalyst Run Temperature
(
oC)
Conversion
(%)
Yield
(%)
H3PO4/Al2O3 1 260 9.7 17.6
H3PO4/Al2O3 2 260 10.1 18.3
H3[P(W2O10)4]/Al2O3 3 260 31.2 25.5
H3[P(W2O10)4]/Al2O3 4 260 30.9 25.4
former experience, we have selected an other catalyst,
which was the phosphotungstic acid hydrate. Using the
former protocol with a higher boiling point of solvent
and a more active catalyst we have expected a higher
conversion, as well. The comparison of the two catalysts
can be seen in Table 1.
Our expectation was correct as it can be seen in Table
1, with the new catalyst and a higher boiling point of
solvent we obtained about three times higher conversion
and selectivity was also higher. Consequently, studying
the effect of temperature on the dehydration reaction we
have decided to use these conditions (catalyst, solvent).
In the third set of the experiments we have studied the
effect of temperature on the reaction, more precisely we
wanted to determine the optimum temperature for the
formation of acrolein. Having the same reaction condi-
tions we have changed systematically the temperature
and the results can be seen in Table 2.
The systematic increase in temperature has increased
significantly the yield of acrolein, at 300oC we have
reached 97% conversion and also a high 77.5% selectiv-
ity. Another increase in temperature with 20oC could
produce the total conversion and an even higher 92.8%
selectivity.
Applying a good acidic catalyst and a high boiling
point solvent we could determine the optimum conditions
for the dehydration of glycerol. Using the above condi-
tions we could produce total conversion and very high
(93 %) selectivity, which are the best values—according
to our knowledge—so far in the literature. Meanwhile we
could not observe any other dehydration products (e.g.
acetic acid, acetaldehyde).
Table 2. The dehydration of glycerol on H3[P(W2O10)4]/Al2O3
catalysts
Run Temperature
(oC)
Conversion
(%)
Yield
(%)
5 260 31.2 25.5
6 260 30.9 25.4
7 280 52.1 56.4
8 280 53.9 56.6
9 300 97.0 77.5
10 300 98.0 78.0
11 320 100 92.8
12 320 100 92.5
(cm-1)

Catalytic Dehydration of Glycerol under Mild Condition: An Environmentally Benign Acrolein Production 204
The other advantage of this method that it is not ap-
plying drastic conditions- high pressure and temperature-
as the methods described in the literature. So, using the
above conditions we could develop an environmentally
benign method for the utilization of the extra amount of
glycerol produced by the biodiesel formation.
To check the efficiency of our catalyst we have made a
blind experiment, too. During the blind experiment we
have followed the same protocol without catalyst and we
have not observed any acrolein formation. In other words
applying these conditions the thermal dehydration is not
occurring.
3.3 Recycling of the H3[P(W2O10)4]/Al2O3
Catalyst
It is well known that the most important advantage of
heterogeneous catalysts is their recyclability. To check
the reusability of our catalyst, we have applied our cata-
lyst in three subsequent runs and the results can be seen
on Figure 2.
As it can be seen on Figure 2, (light column represents
conversion, dark column selectivity) we could apply
successfully our catalyst in three subsequent runs. Nei-
ther the conversion nor the selectivity has changed dur-
ing the three subsequent experiments, which means that
our catalyst has the advantage of the heterogeneous cata-
lyst.
The material balance is a very important fact from the
point of view the practical application. For the experi-
ments we have used 10 ml (0.13 mol) of glycerol for
each run and the amount of isolated acrolein has in-
creased as a function of temperature.
Table 3 clearly shows that the isolated amount of ac-
rolein has increased with increasing temperature. At the
optimum temperature the material balance is reasonable.
The loss of material is about 10%, which means the
method is still practically useful.
4. Conclusions
With the final goal of the utilization of the extra amount
of glycerol, produced by the biodiesel production, we
Figure 2. The selectivity and conversion in three subsequent
runs at 300oC
Table 3. The material balance as a function of temperature
Temparature
(oC)
Amount of acrolein
(g) (mol)
Yield
(%)
260 0.84 0.02 15.38
280 4.04 0.07 53.84
300 5.80 0.10 76.92
320 6.69 0.12 92.30
have developed a method to prepare valuable starting
material. This starting material is the acrolein, having
two reactive double bonds, which make it possible to
apply in various organic synthesis. The method devel-
oped by us is an environmentally benign method, does
not have any extreme conditions and producing a total
conversion with high (93%) selectivity. According to our
knowledge this is the only environmentally benign
method which produces such a high conversion and se-
lectivity.
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