Optimization of the solketal production from acetone and
glycerol using CO2 as switchable catalyst
J. A. C. Nascimento a,*, A. L. L. Fortuna a, B. P. Pinto b, C. J. A. Mota a,b
a
Escola de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro, 21941-909, Brazil
Instituto de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro, 21941-909, Brazil
*Corresponding author:[email protected]
b
Keywords: green chemistry, glycerol, biodiesel, carbon dioxide, design of experiments, bioadditives
1. Introduction
Biodiesel is one of the main biofuels used
worldwide and can contribute to the control of the
global heating. The transesterification of vegetal oils
produces biodiesel and 10% wt of glycerol [1].
Glycerol can be used in a large number of
applications such as personal care products,
pharmaceuticals, polymers, food, etc. Nevertheless,
these applications cannot absorb the large amounts
of glycerol being produced. The biodiesel
production growth and the glycerol offer leads to a
growing interest by the scientific community in
looking for glycerol use .
Solketal is produced from the acid-catalyzed
reaction of glycerol and acetone (Figure 1) and can
be used as bioadditives [2]. Usually, solketal
production uses heterogeneously catalysis [3] and
this work reports this production in CO2 presence,
which acts as switchable acid system.
Figure 1. Reaction of glycerol with acetone under CO2 as
acid catalyst.
2. Experimental Part or Theoretical Details
In this work, a design of experiments (DoE) was
used to optimize the solketal production.
Experimental tests were carried out in two steps. The
first one was a fractional factorial design, with 2
levels and 4 parameters (24-1). The factors studied
were temperature, reaction time, glycerol/acetone
ratio and initial pressure of CO2. Analysis of
Variance (ANOVA) was used to determine the
significance and their interactions.
The second step was a Response Surface Method
(RSM) with centered face to optimize the
performance of CO2 in this reaction. It was done a 2³
design of experiments with 6 axial points and 1
center point.
Reactions with doped glycerin were done to
compare the results. The composition of the doped
glycerol is shown in Table 1.
Table 1. Glycerol composition.
Glycerol
Glycerol P.A.+
methanol
Glycerol P.A.+
methanol +
water + NaCl
Methanol
(g Kg-1)
Water
(g Kg-1)
NaCl
(g Kg-1)
50
0
0
10
100
150
3. Results and discussion
The results of the design of 2³ experiments are
shown in Table 2.
Table 2. Results of the fractional factorial analysis.
Run
1
2
3
4
5
6
7
8
CO2
Glycerol
Temperature Time
Molar
pressure
conversion
(ºC)
(h)
ratio
(bar)
(%)
80
110
80
110
80
110
80
110
2
2
4
4
2
2
4
4
20
20
20
20
45
45
45
45
1:2
1:5
1:5
1:2
1:5
1:2
1:2
1:5
32
51
40
55
37
56
52
66
By ANOVA, it can be concluded that the
temperature, time and initial pressure are significant
and the molar ratio is not significant. For the next
step, the glycerol/acetone ratio was fixed in 1:2.
The Pareto’s chart (Figure 2) shows that the
temperature is the most influent factor.
Figure 2. Pareto chart of the fractional factorial analysis.
Figure 4. Surface response with time fixed.
Table 3 shows the results of the RSM and Figure 3
and 4 shows the 3D surface response for the glycerol
conversion with the pressure fixed (Figure 3) and the
time fixed (Figure 4). It shows that the higher the
temperature, the reaction time and the pressure, the
higher the conversion.
Table 3. Results of the response surface method.
CO2
Glycerol
Temperature Time pressure
Run
conversion
(bar)
(ºC)
(h)
(%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
80
110
80
110
80
110
80
110
80
110
95
95
95
95
95
2
2
4
4
2
2
4
4
3
3
3
2
4
3
3
20
20
20
20
45
45
45
45
32,5
32,5
32,5
32,5
20
45
32,5
31,5
45
42,5
51
38
57
56
61
42
52
47,5
54
47
52,5
50,5
Results of the experimental tests with doped glycerol
are shown in Table 4.
Table 4. Results of the analysis with doped glycerol.
Run
1
2
3
4
5
CO2
Glycerol
Temperature Time
pressure conversion
(ºC)
(h)
(bar)
(%)
80
2
20
30
110
2
20
50
80
4
20
32
110
4
20
46
80
2
45
33
Previous works showed that the impurities present in
the doped glycerin have dramatic effects on the
glycerol conversion [4]. In this work, the doped
glycerin showed lower conversion than pure
glycerin, but not as much as reported in the previous
work. It proves that CO2 is viable to catalyze this
type of reaction without the needy of purification.
4. Conclusions
This study proved that it is possible to develop a
greener route to the production of solketal, under
CO2 catalysis. The design of experiments showed
that the best conversion is achieved with 110ºC, 4h
and 45 bar of initial pressure of CO2. Preliminary
results showed that the use of doped glycerin doesn’t
affect the glycerol conversion as much as reported in
reactions using heterogeneous catalysts.
Acknowledgments
Authors thank financial support from CAPES and CNPq.
References
Figure 3. Surface response with pressure fixed.
[1] C. J. A. Mota, C. X. da Silva, V. Gonçalves, Quim Nova
2009, 32, 639-648.
[2] C. X. da Silva, C. J. A. Mota, V, Gonçalves, Green
Chemistry 2008, 11, 38-41.
[3] C. J. A. Mota, C. X. da Silva, N. Rosenbach, J. Costa, F. da
Silva, Energy Fuels 2010, 24, 2733-2736.
[4] C. X. da Silva, C. J. A. Mota, Biomass & Bioenergy 2011, 35,
3547-3551.